US EPA Method 2G—Determination of Stack Gas Velocity and Volumetric Flow Rate With Two- Dimensional Probes

Note: This method does not include all of the specifications (e.g., equipment and supplies) and procedures (e.g., sampling) essential to its performance. Some material has been incorporated from other methods in this part. Therefore, to obtain reliable results, those using this method should have a thorough knowledge of at least the following additional test methods: Methods 1, 2, 3or 3A, and 4.

 

 1.0 Scope and Application

 

1.1 This method is applicable for the determination of yaw angle, near-axial velocity, and the volumetric flow rate of a gas stream in a stack or duct using a two-dimensional (2-D) probe.

 

2.0 Summary of Method

 

2.1 A 2–D probe is used to measure the velocity pressure and the yaw angle of the flow velocity vector in a stack or duct.  Alternatively, these measurements may be made by operating one of the three-dimensional (3-D) probes described in Method 2F, in yaw determination mode only. From these measurements and a determination of the stack gas density, the average near-axial velocity of the stack gas is calculated. The near-axial velocity accounts for the yaw, but not the pitch, component of flow. The average gas volumetric flow rate in the stack or duct is then determined from the average near-axial velocity.

 

3.0 Definitions

 

3.1. Angle-measuring Device Rotational Offset (R _ADO).

The rotational position of an angle-measuring device relative to the reference scribe line, as determined during the pre-test rotational position check described in section 8.3.

 

3.2 Calibration Pitot Tube.

  The standard (Prandtl type) pitot tube used as a reference when calibrating a probe under this method.

 

3.3 Field Test.

  A set of measurements conducted at a specific unit or exhaust stack/ duct to satisfy the applicable regulation (e.g., a three-run boiler performance test, a single or multiple-load nine-run relative accuracy test).

 

3.4 Full Scale of Pressure-measuring Device.

Full scale refers to the upper limit of the measurement range displayed by the device. For bi-directional pressure gauges, full scale includes the entire pressure range from the lowest negative value to the highest positive value on the pressure scale.

 

3.5 Main probe.

Refers to the probe head and that section of probe sheath directly attached to the probe head. The main probe sheath is distinguished from probe extensions, which are sections of sheath added onto the main probe to extend its reach.

 

3.6 May,’’ “Must,’’ “Shall,’’ “Should,’’and the imperative form of verbs for method provisions

 

3.6.1 “May’’ is used to indicate that a provision of this method is optional.

 

3.6.2 “Must,’’ “Shall,’’ and the imperative form of verbs (such as “record’’ or “enter’’) are used to indicate that a provision of this method is mandatory.

 

3.6.3 “Should’’ is used to indicate that a provision of this method is not mandatory, but is highly recommended as good practice.

 

3.7 Method 1.

  Refers to 40 CFR part 60, appendix A, “ Method 1- Sample and velocity traverses for stationary sources.’’

 

3.8 Method 2.

  Refers to 40 CFR part 60, appendix A, ‘ ‘Method 2- Determination of stack gas velocity and volumetric flow rate (Type S pitot tube).’’

 

3.9 Method 2F.

Refers to 40 CFR part 60, appendix A, “ Method 2F- Determination of stack gas velocity and volumetric flow rate with three-dimensional probes.’’

 

3.10 Near-axial Velocity.

The velocity vector parallel to the axis of the stack or duct that accounts for the yaw angle component of gas flow. The term “near-axial’’ is used herein to indicate that the velocity and volumetric flow rate results account for the measured yaw angle component of flow at each measurement point.

 

3.11 Nominal Velocity.

  Refers to a wind tunnel velocity setting that approximates the actual wind tunnel velocity to within 1.5 m/ sec (5 ft/sec).

 

3.12 Pitch Angle.

The angle between the axis of the stack or duct and the pitch component of flow, i.e., the component of the total velocity vector in a plane defined by the traverse line and the axis of the stack or duct. ( Figure 2G-1illustrates the “pitch plane.’’) From the standpoint of a tester facing a test port in a vertical stack, the pitch component of flow is the vector of flow moving from the center of the stack toward or away from that test port. The pitch angle is the angle described by this pitch component of flow and the vertical axis of the stack.

 

3.13 Readability.

  For the purposes of this method, readability for an analog measurement device is one half of the smallest scale division. For a digital measurement device, it is the number of decimals displayed by the device.

 

3.14 Reference Scribe Line.

  A line permanently inscribed on the main probe sheath (in accordance with section 6.1.5.1) to serve as a reference mark for determining yaw angles.

 

3.15 Reference Scribe Line Rotational Offset (R _SLO).

The rotational position of a probe’s reference scribe line relative to the probe’s yaw-null position, as determined during the yaw angle calibration described in section 10.5.

 

3.16 Response Time.

The time required for the measurement system to fully respond to a change from zero differential pressure and ambient temperature to the stable stack or duct pressure and temperature readings at a traverse point.

 

3.17 Tested Probe.

  A probe that is being calibrated.

 

3.18 Three-dimensional (3-D) Probe.

  A directional probe used to determine the velocity pressure and the yaw and pitch angles in a flowing gas stream.

 

3.19 Two-dimensional (2-D) Probe.

A directional probe used to measure velocity pressure and yaw angle in a flowing gas stream.

 

3.20 Traverse Line.

  A diameter or axis extending across a stack or duct on which measurements of velocity pressure and flow angles are made.

 

3.21 Wind Tunnel Calibration Location.

  A point, line, area, or volume within the wind tunnel test section at, along, or within which probes are calibrated. At a particular wind tunnel velocity setting, the average velocity pressures at specified points at, along, or within the calibration location shall vary by no more than 2 percent or 0.3 mm H20 (0.01 in. H2O), whichever is less restrictive, from the average velocity pressure at the calibration pitot tube location. Airflow at this location shall be axial, i.e., yaw and pitch angles within 3 of 0. Compliance with these flow criteria shall be demonstrated by performing the procedures prescribed in sections 10.1.1and 10.1.2. For circular tunnels, no part of the calibration location may be closer to the tunnel wall than 10.2 cm (4 in.) or 25 percent of the tunnel diameter, whichever is farther from the wall. For elliptical or rectangular tunnels, no part of the calibration location may be closer to the tunnel wall than 10.2 cm (4 in.) or 25 percent of the applicable cross-sectional axis, whichever is farther from the wall.

 

3.22 Wind Tunnel with Documented Axial Flow.

A wind tunnel facility documented as meeting the provisions of sections 10.1.1 (velocity pressure crosscheck) and 10.1.2 (axial flow verification) using the procedures described in these sections or alternative procedures determined to be technically equivalent.

 

3.23 Yaw Angle.

The angle between the axis of the stack or duct and the yaw component of flow, i.e., the component of the total velocity vector in a plane perpendicular to the traverse line at a particular traverse point. (Figure 2G-1 illustrates the “yaw plane.’’) From the standpoint of a tester facing a test port in a vertical stack, the yaw component of flow is the vector of flow moving to the left or right from the center of the stack as viewed by the tester. (This is sometimes referred to as “vortex flow,’’ i.e., flow around the centerline of a stack or duct.) The yaw angle is the angle described by this yaw component of flow and the vertical axis of the stack. The algebraic sign convention is illustrated in Figure 2G-2.

 

3.24 Yaw Nulling.

A procedure in which a Type-S pitot tube or a 3-D probe is rotated about its axis in a stack or duct until a zero differential pressure reading (“yaw null’’) is obtained. When a Type S probe is yaw-nulled, the rotational position of its impact port is 90° from the direction of flow in the stack or duct and the Delta P reading is zero. When a 3-D probe is yaw-nulled, its impact pressure port (P1) faces directly into the direction of flow in the stack or duct and the differential pressure between pressure ports P2 and P3 is zero.

 

4.0 Interferences. [Reserved]

 

5.0 Safety

 

5.1 This test method may involve hazardous operations and the use of hazardous materials or equipment. This method does not purport to address all of the safety problems associated with its use. It is the responsibility of the user to establish and implement appropriate safety and health practices and to determine the applicability of regulatory limitations before using this test method.

 

6.0 Equipment and Supplies

 

6.1 Two-dimensional Probes.

Probes that provide both the velocity pressure and the yaw angle of the flow vector in a stack or duct, as listed in sections 6.1.1 and 6.1.2, qualify for use based on comprehensive wind tunnel and field studies involving both inter- and intra-probe comparisons by multiple test teams. Each 2-D probe shall have a unique identification number or code permanently marked on the main probe sheath. Each probe shall be calibrated prior to use according to the procedures in section 10. Manufacturer-supplied calibration data shall be used as example information only, except when the manufacturer calibrates the probe as specified in section 10 and provides complete documentation.

 

6.1.1 Type S (Stausscheibe or reverse type) pitot tube.

This is the same as specified in Method 2, section 2.1, except for the following additional specifications that enable the pitot tube to accurately determine the yaw component of flow. For the purposes of this method, the external diameter of the tubing used to construct the Type S pitot tube (dimension Dt in Figure 2-2 of Method 2) shall be no less than 9.5 mm (3/8 in.). The pitot tube shall also meet the following alignment specifications. The angles a1, a2, b1, and b2, as shown in Method 2, Figure 2-3, shall not exceed 2°. The dimensions w and z , shown in Method 2, Figure 2-3 shall not exceed 0.5 mm (0.02 in.).

 

6.1.1.1 Manual Type S probe.

This refers to a Type S probe that is positioned at individual traverse points and yaw-nulled manually by an operator.

 

6.1.1.2 Automated Type S probe. This refers to a system that uses a computer-controlled motorized mechanism to position the Type S pitot head at individual traverse points and perform yaw angle determinations.

 

6.1.2 Three-dimensional probes used in 2-D mode.

A 3-D probe, as specified in sections 6.1.1through 6.1.3 of Method 2F, may, for the purposes of this method, be used in a two-dimensional mode (i.e., measuring yaw angle, but not pitch angle). When the 3-D probe is used as a 2-D probe, only the velocity pressure and yaw-null pressure are obtained using the pressure taps referred to as P1, P2, and P3. The differential pressure P1-P2 is a function of total velocity and corresponds to the Delta P obtained using the Type S probe. The differential pressure P2-P3 is used to yaw-null the probe and determine the yaw angle. The differential pressure P4-P5, which is a function of pitch angle, is not measured when the 3-D probe is used in 2-D mode.

 

6.1.3 Other probes. [Reserved]

 

6.1.4 Probe sheath.

The probe shaft shall include an outer sheath to: (1) provide a surface for inscribing a permanent reference scribe line, (2) accommodate attachment of an angle-measuring device to the probe shaft, and (3) facilitate precise rotational movement of the probe for determining yaw angles. The sheath shall be rigidly attached to the probe assembly and shall enclose all pressure lines from the probe head to the farthest position away from the probe head where an angle-measuring device may be attached during use in the field. The sheath of the fully assembled probe shall be sufficiently rigid and straight at all rotational positions such that, when one end of the probe shaft is held in a horizontal position, the fully extended probe meets the horizontal straightness specifications indicated in section 8.2below.

 

6.1.5 Scribe lines.

 

6.1.5.1 Reference scribe line. A permanent line, no greater than 1.6 mm (1/16 in.) in width, shall be inscribed on each manual probe that will be used to determine yaw angles of flow. This line shall be placed on the main probe sheath in accordance with the procedures described in section 10.4 and is used as a reference position for installation of the yaw angle-measuring device on the probe. At the discretion of the tester, the scribe line may be a single line segment placed at a particular position on the probe sheath (e.g., near the probe head), multiple line segments placed at various locations along the length of the probe sheath (e.g., at every position where a yaw angle-measuring device may be mounted), or a single continuous line extending along the full length of the probe sheath.

 

6.1.5.2 Scribe line on probe extensions. A permanent line may also be inscribed on any probe extension that will be attached to the main probe in performing field testing. This allows a yaw angle-measuring device mounted on the extension to be readily aligned with the reference scribe line on the main probe sheath.

 

6.1.5.3 Alignment specifications. This specification shall be met separately, using the procedures in section 10.4.1, on the main probe and on each probe extension. The rotational position of the scribe line or scribe line segments on the main probe or any probe extension must not vary by more than 2°. That is, the difference between the minimum and maximum of all of the rotational angles that are measured along the full length of the main probe or the probe extension must not exceed 2°.

 

6.1.6 Probe and system characteristics to ensure horizontal stability.

 

6.1.6.1 For manual probes, it is recommended that the effective length of the probe (coupled with a probe extension, if necessary) be at least 0.9 m (3 ft.) longer than the farthest traverse point mark on the probe shaft away from the probe head. The operator should maintain the probe’s horizontal stability when it is fully inserted into the stack or duct. If a shorter probe is used, the probe should be inserted through a bushing sleeve, similar to the one shown in Figure 2G-3, that is installed on the test port; such a bushing shall fit snugly around the probe and be secured to the stack or duct entry port in such a manner as to maintain the probe’s horizontal stability when fully inserted into the stack or duct.

 

6.1.6.2 An automated system that includes an external probe casing with a transport system shall have a mechanism for maintaining horizontal stability comparable to that obtained by manual probes following the provisions of this method. The automated probe assembly shall also be constructed to maintain the alignment and position of the pressure ports during sampling at each traverse point. The design of the probe casing and transport system shall allow the probe to be removed from the stack or duct and checked through direct physical measurement for angular position and insertion depth.

 

6.1.7 Tube Connect Diameter

The tubing that is used to connect the probe and the pressure-measuring device should have an inside diameter of at least 3.2 mm (1⁄8 in.), to reduce the time required for pressure equilibration, and should be as short as practicable.

 

6.1.8 Detachable Probe Head

If a detachable probe head without a sheath [e.g., a pitot tube, typically 15.2 to 30.5 cm (6 to 12 in.) in length] is coupled with a probe sheath and calibrated in a wind tunnel in accordance with the yaw angle calibration procedure in section 10.5, the probe head shall remain attached to the probe sheath during field testing in the same configuration and orientation as calibrated. Once the detachable probe head is uncoupled or re-oriented, the yaw angle calibration of the probe is no longer valid and must be repeated before using the probe in subsequent field tests.

 

6.2 Yaw Angle-measuring Device.

One of the following devices shall be used for measurement of the yaw angle of flow.

 

6.2.1 Digital inclinometer.

This refers to a digital device capable of measuring and displaying the rotational position of the probe to within 1°. The device shall be able to be locked into position on the probe sheath or probe extension, so that it indicates the probe’s rotational position throughout the test. A rotational position collar block that can be attached to the probe sheath (similar to the collar shown in Figure 2G-4) may be required to lock the digital inclinometer into position on the probe sheath.

 

6.2.2 Protractor wheel and pointer assembly.

This apparatus, similar to that shown in Figure 2G-5, consists of the following components.

 

6.2.2.1 A protractor wheel that can be attached to a port opening and set in a fixed rotational position to indicate the yaw angle position of the probe’s scribe line relative to the longitudinal axis of the stack or duct. The protractor wheel must have a measurement ring on its face that is no less than 17.8 cm (7 in.) in diameter, shall be able to be rotated to any angle and then locked into position on the stack or duct test port, and shall indicate angles to a resolution of 1°.

 

6.2.2.2 A pointer assembly that includes an indicator needle mounted on a collar that can slide over the probe sheath and be locked into a fixed rotational position on the probe sheath. The pointer needle shall be of sufficient length, rigidity, and sharpness to allow the tester to determine the probe’s angular position to within 1° from the markings on the protractor wheel. Corresponding to the position of the pointer, the collar must have a scribe line to be used in aligning the pointer with the scribe line on the probe sheath.

 

6.2.3 Other yaw angle-measuring devices.

Other angle-measuring devices with a manufacturer’s specified precision of 1° or better may be used, if approved by the Administrator.

 

6.3 Probe Supports and Stabilization Devices.

When probes are used for determining flow angles, the probe head should be kept in a stable horizontal position. For probes longer than 3.0 m (10 ft.), the section of the probe that extends outside the test port shall be secured. Three alternative devices are suggested for maintaining the horizontal position and stability of the probe shaft during flow angle determinations and velocity pressure measurements: (1) monorails installed above each port, (2) probe stands on which the probe shaft may be rested, or (3) bushing sleeves of sufficient length secured to the test ports to maintain probes in a horizontal position. Comparable provisions shall be made to ensure that automated systems maintain the horizontal position of the probe in the stack or duct. The physical characteristics of each test platform may dictate the most suitable type of stabilization device. Thus, the choice of a specific stabilization device is left to the judgment of the testers.

 

6.4 Differential Pressure Gauges.

The velocity pressure (Delta P) measuring devices used during wind tunnel calibrations and field testing shall be either electronic manometers (e.g., pressure transducers), fluid manometers, or mechanical pressure gauges (e.g., Magnehelic® gauges). Use of electronic manometers is recommended. Under low velocity conditions, use of electronic manometers may be necessary to obtain acceptable measurements.

 

6.4.1 Differential pressure-measuring device.

This refers to a device capable of measuring pressure differentials and having a readability of 1 percent of full scale. The device shall be capable of accurately measuring the maximum expected pressure differential. Such devices are used to determine the following pressure measurements: velocity pressure, static pressure, and yaw-null pressure. For an inclined-vertical manometer, the readability specification of 1 percent shall be met separately using the respective full-scale upper limits of the inclined and vertical portions of the scales. To the extent practicable, the device shall be selected such that most of the pressure readings are between 10 and 90 percent of the device’s full-scale measurement range (as defined in section 3.4). In addition, pressure-measuring devices should be selected such that the zero does not drift by more than 5 percent of the average expected pressure readings to be encountered during the field test. This is particularly important under low pressure conditions.

 

6.4.2 Gauge used for yaw nulling.

The differential pressure-measuring device chosen for yaw nulling the probe during the wind tunnel calibrations and field testing shall be bi-directional, i.e., capable of reading both positive and negative differential pressures. If a mechanical, bi-directional pressure gauge is chosen, it shall have a full-scale range no greater than 2.6 cm (i.e., -1.3 to +1.3 cm) [1 in. H2O (i.e., -0.5 in. to +0.5 in.)].

 

6.4.3 Devices for calibrating differential pressure-measuring devices.

A precision manometer (e.g., a U-tube, inclined, or inclined-vertical manometer, or micromanometer) or NIST (National Institute of Standards and Technology) traceable pressure source shall be used for calibrating differential pressure-measuring devices. The device shall be maintained under laboratory conditions or in a similar protected environment (e.g., a climate-controlled trailer). It shall not be used in field tests. The precision manometer shall have a scale gradation of 0.3 mm H2O (0.01 in. H2O), or less, in the range of 0 to 5.1 cm H2O (0 to 2 in. H2O) and 2.5 mm H2O (0.1 in. H2O), or less, in the range of 5.1 to 25.4 cm H2O (2 to 10 in. H2O). The manometer shall have manufacturer’s documentation that it meets an accuracy specification of at least 0.5 percent of full scale. The NIST-traceable pressure source shall be recertified annually.

 

6.4.4 Devices used for post-test calibration check.

A precision manometer meeting the specifications in section 6.4.3, a pressure-measuring device or pressure source with a documented calibration traceable to NIST, or an equivalent device approved by the Administrator shall be used for the post-test calibration check. The pressure-measuring device shall have a readability equivalent to or greater than the tested device. The pressure source shall be capable of generating pressures between 50 and 90 percent of the range of the tested device and known to within 1 percent of the full scale of the tested device. The pressure source shall be recertified annually.

 

6.5 Data Display and Capture Devices.

Electronic manometers (if used) shall be coupled with a data display device (such as a digital panel meter, personal computer display, or strip chart) that allows the tester to observe and validate the pressure measurements taken during testing. They shall also be connected to a data recorder (such as a data logger or a personal computer with data capture software) that has the ability to compute and retain the appropriate average value at each traverse point, identified by collection time and traverse point.

 

6.6 Temperature Gauges.

For field tests, a thermocouple or resistance temperature detector (RTD) capable of measuring temperature to within 3°Cdeg;C (5°F) of the stack or duct temperature shall be used. The thermocouple shall be attached to the probe such that the sensor tip does not touch any metal. The position of the thermocouple relative to the pressure port face openings shall be in the same configuration as used for the probe calibrations in the wind tunnel. Temperature gauges used for wind tunnel calibrations shall be capable of measuring temperature to within 0.6°Cdeg;C (1°F) of the temperature of the flowing gas stream in the wind tunnel.

 

6.7 Stack or Duct Static Pressure Measurement.

The pressure-measuring device used with the probe shall be as specified in section 6.4 of this method. The static tap of a standard (Prandtl type) pitot tube or one leg of a Type S pitot tube with the face opening planes positioned parallel to the gas flow may be used for this measurement. Also acceptable is the pressure differential reading of P1-Pbar from a five-hole prism-shaped 3-D probe, as specified in section 6.1.1 of Method 2F (such as the Type DA or DAT probe), with the P1 pressure port face opening positioned parallel to the gas flow in the same manner as the Type S probe. However, the 3-D spherical probe, as specified in section 6.1.2 of Method 2F, is unable to provide this measurement and shall not be used to take static pressure measurements. Static pressure measurement is further described in section 8.11.

 

6.8 Barometer. Same as Method 2, section 2.5.

 

6.9 Gas Density Determination Equipment.

Method 3or 3Ashall be used to determine the dry molecular weight of the stack or duct gas. Method 4shall be used for moisture content determination and computation of stack or duct gas wet molecular weight. Other methods may be used, if approved by the Administrator.

 

6.10 Calibration Pitot Tube.

Same as Method 2, section 2.7.

 

6.11 Wind Tunnel for Probe Calibration.

Wind tunnels used to calibrate velocity probes must meet the following design specifications.

 

6.11.1 Test section cross-sectional area.

The flowing gas stream shall be confined within a circular, rectangular, or elliptical duct. The cross-sectional area of the tunnel must be large enough to ensure fully developed flow in the presence of both the calibration pitot tube and the tested probe. The calibration site, or “test section,’’ of the wind tunnel shall have a minimum diameter of 30.5 cm (12 in.) for circular or elliptical duct cross-sections or a minimum width of 30.5 cm (12 in.) on the shorter side for rectangular cross-sections. Wind tunnels shall meet the probe blockage provisions of this section and the qualification requirements prescribed in section 10.1. The projected area of the portion of the probe head, shaft, and attached devices inside the wind tunnel during calibration shall represent no more than 4 percent of the cross-sectional area of the tunnel. The projected area shall include the combined area of the calibration pitot tube and the tested probe if both probes are placed simultaneously in the same cross-sectional plane in the wind tunnel, or the larger projected area of the two probes if they are placed alternately in the wind tunnel.

 

6.11.2 Velocity range and stability.

The wind tunnel should be capable of maintaining velocities between 6.1 m/sec and 30.5 m/sec (20 ft/sec and 100 ft/sec). The wind tunnel shall produce fully developed flow patterns that are stable and parallel to the axis of the duct in the test section.

 

6.11.3 Flow profile at the calibration location.

The wind tunnel shall provide axial flow within the test section calibration location (as defined in section 3.21). Yaw and pitch angles in the calibration location shall be within 3° of 0°. The procedure for determining that this requirement has been met is described in section 10.1.2.

 

6.11.4 Entry ports in the wind tunnel test section.

 

6.11.4.1 Port for tested probe. A port shall be constructed for the tested probe. This port shall be located to allow the head of the tested probe to be positioned within the wind tunnel calibration location (as defined in section 3.21). The tested probe shall be able to be locked into the 0° pitch angle position. To facilitate alignment of the probe during calibration, the test section should include a window constructed of a transparent material to allow the tested probe to be viewed.

 

6.11.4.2 Port for verification of axial flow. Depending on the equipment selected to conduct the axial flow verification prescribed in section 10.1.2,a second port, located 90° from the entry port for the tested probe, may be needed to allow verification that the gas flow is parallel to the central axis of the test section. This port should be located and constructed so as to allow one of the probes described in section 10.1.2.2 to access the same test point(s) that are accessible from the port described in section 6.11.4.1.

 

6.11.4.3 Port for calibration pitot tube. The calibration pitot tube shall be used in the port for the tested probe or in a separate entry port. In either case, all measurements with the calibration pitot tube shall be made at the same point within the wind tunnel over the course of a probe calibration. The measurement point for the calibration pitot tube shall meet the same specifications for distance from the wall and for axial flow as described in section 3.21for the wind tunnel calibration location.

 

7.0 Reagents and Standards. [Reserved]

 

8.0 Sample Collection and Analysis

 

8.1 Equipment Inspection and Set Up

 

8.1.1 All 2-D and 3-D probes, differential pressure-measuring devices, yaw angle measuring devices, thermocouples, and barometers shall have a current, valid calibration before being used in a field test. (See sections 10.3.3, 10.3.4, and 10.5 through 10.10 for the applicable calibration requirements.)

 

8.1.2 Before each field use of a Type S probe, perform a visual inspection to verify the physical condition of the pitot tube. Record the results of the inspection. If the face openings are noticeably misaligned or there is visible damage to the face openings, the probe shall not be used until repaired, the dimensional specifications verified (according to the procedures in section 10.2.1), and the probe recalibrated.

 

8.1.3 Before each field use of a 3-D probe, perform a visual inspection to verify the physical condition of the probe head according to the procedures in section 10.2 of Method 2F. Record the inspection results on a form similar to Table 2F-1presented in Method 2F. If there is visible damage to the 3-D probe, the probe shall not be used until it is recalibrated.

 

8.1.4 After verifying that the physical condition of the probe head is acceptable, set up the apparatus using lengths of flexible tubing that are as short as practicable. Surge tanks installed between the probe and pressure-measuring device may be used to dampen pressure fluctuations provided that an adequate measurement system response time (see section 8.8) is maintained.

 

8.2 Horizontal Straightness Check.

 

A horizontal straightness check shall be performed before the start of each field test, except as otherwise specified in this section. Secure the fully assembled probe (including the probe head and all probe shaft extensions) in a horizontal position using a stationary support at a point along the probe shaft approximating the location of the stack or duct entry port when the probe is sampling at the farthest traverse point from the stack or duct wall. The probe shall be rotated to detect bends. Use an angle-measuring device or trigonometry to determine the bend or sag between the probe head and the secured end. (See Figure 2G-6.) Probes that are bent or sag by more than 5° shall not be used. Although this check does not apply when the probe is used for a vertical traverse, care should be taken to avoid the use of bent probes when conducting vertical traverses. If the probe is constructed of a rigid steel material and consists of a main probe without probe extensions, this check need only be performed before the initial field use of the probe, when the probe is recalibrated, when a change is made to the design or material of the probe assembly, and when the probe becomes bent. With such probes, a visual inspection shall be made of the fully assembled probe before each field test to determine if a bend is visible. The probe shall be rotated to detect bends. The inspection results shall be documented in the field test report. If a bend in the probe is visible, the horizontal straightness check shall be performed before the probe is used.

 

8.3 Rotational Position Check.

 

Before each field test, and each time an extension is added to the probe during a field test, a rotational position check shall be performed on all manually operated probes (except as noted in section 8.3.5 below) to ensure that, throughout testing, the angle-measuring device is either: aligned to within 1° of the rotational position of the reference scribe line; or is affixed to the probe such that the rotational offset of the device from the reference scribe line is known to within 1°. This check shall consist of direct measurements of the rotational positions of the reference scribe line and angle-measuring device sufficient to verify that these specifications are met. Annex Ain section 18 of this method gives recommended procedures for performing the rotational position check, and Table 2G-2gives an example data form. Procedures other than those recommended in Annex A in section 18 may be used, provided they demonstrate whether the alignment specification is met and are explained in detail in the field test report.

 

8.3.1 Angle-measuring device rotational offset.

The tester shall maintain a record of the angle-measuring device rotational offset, R _ADO, as defined in section 3.1. Note that R _ADOis assigned a value of 0° when the angle-measuring device is aligned to within 1° of the rotational position of the reference scribe line. The R _ADOshall be used to determine the yaw angle of flow in accordance with section 8.9.4.

 

8.3.2 Sign of angle-measuring device rotational offset.

The sign of R _ADOis positive when the angle-measuring device (as viewed from the “tail’’ end of the probe) is positioned in a clockwise direction from the reference scribe line and negative when the device is positioned in a counterclockwise direction from the reference scribe line.

 

8.3.3 Angle-measuring devices that can be independently adjusted

Angle-measuring devices that can be independently adjusted (e.g., by means of a set screw), after being locked into position on the probe sheath, may be used. However, the R _ADOmust also take into account this adjustment.

 

8.3.4 Post-test check.

If probe extensions remain attached to the main probe throughout the field test, the rotational position check shall be repeated, at a minimum, at the completion of the field test to ensure that the angle-measuring device has remained within 2° of its rotational position established prior to testing. At the discretion of the tester, additional checks may be conducted after completion of testing at any sample port or after any test run. If the 2° specification is not met, all measurements made since the last successful rotational position check must be repeated. Section 18.1.1.3 of Annex A provides an example procedure for performing the post-test check.

 

8.3.5 Exceptions.

 

8.3.5.1 A rotational position check need not be performed if, for measurements taken at all velocity traverse points, the yaw angle-measuring device is mounted and aligned directly on the reference scribe line specified in sections 6.1.5.1 and 6.1.5.3 and no independent adjustments, as described in section 8.3.3, are made to device’s rotational position.

 

8.3.5.2 If extensions are detached and reattached to the probe during a field test, a rotational position check need only be performed the first time an extension is added to the probe, rather than each time the extension is re-attached, if the probe extension is designed to be locked into a mechanically fixed rotational position (e.g., through the use of interlocking grooves), that can re-establish the initial rotational position to within 1°.

 

8.4 Leak Checks.

 

A pre-test leak check shall be conducted before each field test. A post-test check shall be performed at the end of the field test, but additional leak checks may be conducted after any test run or group of test runs. The post-test check may also serve as the pre-test check for the next group of test runs. If any leak check is failed, all runs since the last passed leak check are invalid. While performing the leak check procedures, also check each pressure device’s responsiveness to changes in pressure.

 

8.4.1 To perform the leak check on a Type S pitot tube, pressurize the pitot impact opening until at least 7.6 cm H2O (3 in. H2O) velocity pressure, or a pressure corresponding to approximately 75 percent of the pressure device’s measurement scale, whichever is less, registers on the pressure device; then, close off the impact opening. The pressure shall remain stable (2.5 mm H2O, 0.10 in. H2O) for at least 15 seconds. Repeat this procedure for the static pressure side, except use suction to obtain the required pressure. Other leak-check procedures may be used, if approved by the Administrator.

 

8.4.2 To perform the leak check on a 3-D probe, pressurize the probe’s impact (P1) opening until at least 7.6 cm H2O (3 in. H2O) velocity pressure, or a pressure corresponding to approximately 75 percent of the pressure device’s measurement scale, whichever is less, registers on the pressure device; then, close off the impact opening. The pressure shall remain stable (2.5 mm H2O, 0.10 in. H2O) for at least 15 seconds. Check the P2 and P3 pressure ports in the same fashion. Other leak-check procedures may be used, if approved by the Administrator.

 

8.5 Zeroing the Differential Pressure-measuring Device.

 

Zero each differential pressure-measuring device, including the device used for yaw nulling, before each field test. At a minimum, check the zero after each field test. A zero check may also be performed after any test run or group of test runs. For fluid manometers and mechanical pressure gauges (e.g., Magnehelic® gauges), the zero reading shall not deviate from zero by more than 0.8 mm H2O (0.03 in. H2O) or one minor scale division, whichever is greater, between checks. For electronic manometers, the zero reading shall not deviate from zero between checks by more than: 0.3 mm H2O (0.01 in. H2O), for full scales less than or equal to 5.1 cm H2O (2.0 in. H2O); or 0.8 mm H2O (0.03 in. H2O), for full scales greater than 5.1 cm H2O (2.0 in. H2O). ( Note: If negative zero drift is not directly readable, estimate the reading based on the position of the gauge oil in the manometer or of the needle on the pressure gauge.) In addition, for all pressure-measuring devices except those used exclusively for yaw nulling, the zero reading shall not deviate from zero by more than 5 percent of the average measured differential pressure at any distinct process condition or load level. If any zero check is failed at a specific process condition or load level, all runs conducted at that process condition or load level since the last passed zero check are invalid.

 

8.6 Traverse Point Verification.

 

The number and location of the traverse points shall be selected based on Method 1guidelines. The stack or duct diameter and port nipple lengths, including any extension of the port nipples into the stack or duct, shall be verified the first time the test is performed; retain and use this information for subsequent field tests, updating it as required. Physically measure the stack or duct dimensions or use a calibrated laser device; do not use engineering drawings of the stack or duct. The probe length necessary to reach each traverse point shall be recorded to within 6.4 mm (¼ in.) and, for manual probes, marked on the probe sheath. In determining these lengths, the tester shall take into account both the distance that the port flange projects outside of the stack and the depth that any port nipple extends into the gas stream. The resulting point positions shall reflect the true distances from the inside wall of the stack or duct, so that when the tester aligns any of the markings with the outside face of the stack port, the probe’s impact port shall be located at the appropriate distance from the inside wall for the respective Method 1 traverse point. Before beginning testing at a particular location, an out-of-stack or duct verification shall be performed on each probe that will be used to ensure that these position markings are correct. The distances measured during the verification must agree with the previously calculated distances to within ¼ in. For manual probes, the traverse point positions shall be verified by measuring the distance of each mark from the probe’s impact pressure port (the P1 port for a 3-D probe). A comparable out-of-stack test shall be performed on automated probe systems. The probe shall be extended to each of the prescribed traverse point positions. Then, the accuracy of the positioning for each traverse point shall be verified by measuring the distance between the port flange and the probe’s impact pressure port.

 

8.7 Probe Installation.

 

Insert the probe into the test port. A solid material shall be used to seal the port.

 

8.8 System Response Time.

 

Determine the response time of the probe measurement system. Insert and position the “cold’’ probe (at ambient temperature and pressure) at any Method 1 traverse point. Read and record the probe differential pressure, temperature, and elapsed time at 15-second intervals until stable readings for both pressure and temperature are achieved. The response time is the longer of these two elapsed times. Record the response time.

 

8.9 Sampling.

 

8.9.1 Yaw angle measurement protocol.

With manual probes, yaw angle measurements may be obtained in two alternative ways during the field test, either by using a yaw angle-measuring device (e.g., digital inclinometer) affixed to the probe, or using a protractor wheel and pointer assembly. For horizontal traversing, either approach may be used. For vertical traversing, i.e., when measuring from on top or into the bottom of a horizontal duct, only the protractor wheel and pointer assembly may be used. With automated probes, curve-fitting protocols may be used to obtain yaw angle measurements.

 

8.9.1.1 If a yaw angle-measuring device affixed to the probe is to be used, lock the device on the probe sheath, aligning it either on the reference scribe line or in the rotational offset position established under section 8.3.1.

 

8.9.1.2 If a protractor wheel and pointer assembly is to be used, follow the procedures in Annex Bof this method.

 

8.9.1.3 Curve-fitting procedures. Curve-fitting routines sweep through a range of yaw angles to create curves correlating pressure to yaw position. To find the zero yaw position and the yaw angle of flow, the curve found in the stack is computationally compared to a similar curve that was previously generated under controlled conditions in a wind tunnel. A probe system that uses a curve-fitting routine for determining the yaw-null position of the probe head may be used, provided that it is verified in a wind tunnel to be able to determine the yaw angle of flow to within 1°.

 

8.9.1.4 Other yaw angle determination procedures. If approved by the Administrator, other procedures for determining yaw angle may be used, provided that they are verified in a wind tunnel to be able to perform the yaw angle calibration procedure as described in section 10.5.

 

8.9.2 Sampling strategy.

At each traverse point, first yaw-null the probe, as described in section 8.9.3, below. Then, with the probe oriented into the direction of flow, measure and record the yaw angle, the differential pressure and the temperature at the traverse point, after stable readings are achieved, in accordance with sections 8.9.4 and 8.9.5. At the start of testing in each port (i.e., after a probe has been inserted into the flue gas stream), allow at least the response time to elapse before beginning to take measurements at the first traverse point accessed from that port. Provided that the probe is not removed from the flue gas stream, measurements may be taken at subsequent traverse points accessed from the same test port without waiting again for the response time to elapse.

 

8.9.3 Yaw-nulling procedure.

In preparation for yaw angle determination, the probe must first be yaw nulled. After positioning the probe at the appropriate traverse point, perform the following procedures.

 

8.9.3.1 For Type S probes, rotate the probe until a null differential pressure reading is obtained. The direction of the probe rotation shall be such that the thermocouple is located downstream of the probe pressure ports at the yaw-null position. Rotate the probe 90° back from the yaw-null position to orient the impact pressure port into the direction of flow. Read and record the angle displayed by the angle-measuring device.

 

8.9.3.2 For 3-D probes, rotate the probe until a null differential pressure reading (the difference in pressures across the P2 and P3 pressure ports is zero, i.e., P2 = P3) is indicated by the yaw angle pressure gauge. Read and record the angle displayed by the angle-measuring device.

 

8.9.3.3 Sign of the measured angle. The angle displayed on the angle-measuring device is considered positive when the probe’s impact pressure port (as viewed from the “tail’’ end of the probe) is oriented in a clockwise rotational position relative to the stack or duct axis and is considered negative when the probe’s impact pressure port is oriented in a counterclockwise rotational position (see Figure 2G-7).

 

8.9.4 Yaw angle determination.

After performing the applicable yaw-nulling procedure in section 8.9.3, determine the yaw angle of flow according to one of the following procedures. Special care must be observed to take into account the signs of the recorded angle reading and all offsets.

 

8.9.4.1 Direct-reading. If all rotational offsets are zero or if the angle-measuring device rotational offset (R _ADO) determined in section 8.3 exactly compensates for the scribe line rotational offset (R _SLO) determined in section 10.5, then the magnitude of the yaw angle is equal to the displayed angle-measuring device reading from section 8.9.3.1 or 8.9.3.2. The algebraic sign of the yaw angle is determined in accordance with section 8.9.3.3. [ Note: Under certain circumstances (e.g., testing of horizontal ducts) a 90° adjustment to the angle-measuring device readings may be necessary to obtain the correct yaw angles.]

 

8.9.4.2 Compensation for rotational offsets during data reduction. When the angle-measuring device rotational offset does not compensate for reference scribe line rotational offset, the following procedure shall be used to determine the yaw angle:

 

(a) Enter the reading indicated by the angle-measuring device from section 8.9.3.1 or 8.9.3.2.

(b) Associate the proper algebraic sign from section 8.9.3.3 with the reading in step (a).

(c) Subtract the reference scribe line rotational offset, R _SLO, from the reading in step (b).

(d) Subtract the angle-measuring device rotational offset, R _ADO, if any, from the result obtained in step (c).

(e) The final result obtained in step (d) is the yaw angle of flow.

 

[ Note: It may be necessary to first apply a 90° adjustment to the reading in step (a), in order to obtain the correct yaw angle.]

 

8.9.4.3 Record the yaw angle measurements on a form similar to Table 2G-3.

 

8.9.5 Impact velocity determination.

Maintain the probe rotational position established during the yaw angle determination. Then, begin recording the pressure-measuring device readings. These pressure measurements shall be taken over a sampling period of sufficiently long duration to ensure representative readings at each traverse point. If the pressure measurements are determined from visual readings of the pressure device or display, allow sufficient time to observe the pulsation in the readings to obtain a sight-weighted average, which is then recorded manually. If an automated data acquisition system (e.g., data logger, computer-based data recorder, strip chart recorder) is used to record the pressure measurements, obtain an integrated average of all pressure readings at the traverse point. Stack or duct gas temperature measurements shall be recorded, at a minimum, once at each traverse point. Record all necessary data as shown in the example field data form (Table 2G-3).

 

8.9.6 Alignment check.

For manually operated probes, after the required yaw angle and differential pressure and temperature measurements have been made at each traverse point, verify (e.g., by visual inspection) that the yaw angle-measuring device has remained in proper alignment with the reference scribe line or with the rotational offset position established in section 8.3. If, for a particular traverse point, the angle-measuring device is found to be in proper alignment, proceed to the next traverse point; otherwise, re-align the device and repeat the angle and differential pressure measurements at the traverse point. In the course of a traverse, if a mark used to properly align the angle-measuring device (e.g., as described in section 18.1.1.1) cannot be located, re-establish the alignment mark before proceeding with the traverse.

 

8.10 Probe Plugging.

 

Periodically check for plugging of the pressure ports by observing the responses on the pressure differential readouts. Plugging causes erratic results or sluggish responses. Rotate the probe to determine whether the readouts respond in the expected direction. If plugging is detected, correct the problem and repeat the affected measurements.

 

8.11 Static Pressure.

 

Measure the static pressure in the stack or duct using the equipment described in section 6.7.

 

8.11.1 If a Type S probe is used for this measurement, position the probe at or between any traverse point(s) and rotate the probe until a null differential pressure reading is obtained. Disconnect the tubing from one of the pressure ports; read and record the Delta P. For pressure devices with one-directional scales, if a deflection in the positive direction is noted with the negative side disconnected, then the static pressure is positive. Likewise, if a deflection in the positive direction is noted with the positive side disconnected, then the static pressure is negative.

 

8.11.2 If a 3-D probe is used for this measurement, position the probe at or between any traverse point(s) and rotate the probe until a null differential pressure reading is obtained at P2-P3. Rotate the probe 90°. Disconnect the P2 pressure side of the probe and read the pressure P1-Pbar and record as the static pressure. ( Note: The spherical probe, specified in section 6.1.2 of Method 2F, is unable to provide this measurement and shall not be used to take static pressure measurements.)

 

8.12 Atmospheric Pressure.

 

Determine the atmospheric pressure at the sampling elevation during each test run following the procedure described in section 2.5 of Method 2.

 

8.13 Molecular Weight.

 

Determine the stack or duct gas dry molecular weight. For combustion processes or processes that emit essentially CO2, O2, CO, and N2, use Method 3 or 3A. For processes emitting essentially air, an analysis need not be conducted; use a dry molecular weight of 29.0. Other methods may be used, if approved by the Administrator.

 

8.14 Moisture.

 

Determine the moisture content of the stack gas using Method 4 or equivalent.

 

8.15 Data Recording and Calculations.

 

Record all required data on a form similar to Table 2G-3.

 

8.15.1 2-D probe calibration coefficient. When a Type S pitot tube is used in the field, the appropriate calibration coefficient as determined in section 10.6 shall be used to perform velocity calculations. For calibrated Type S pitot tubes, the A-side coefficient shall be used when the A-side of the tube faces the flow, and the B-side coefficient shall be used when the B-side faces the flow.

 

8.15.2 3-D calibration coefficient. When a 3-D probe is used to collect data with this method, follow the provisions for the calibration of 3-D probes in section 10.6 of Method 2Fto obtain the appropriate velocity calibration coefficient (F2 as derived using Equation 2F-2in Method 2F) corresponding to a pitch angle position of 0°.

 

8.15.3 Calculations. Calculate the yaw-adjusted velocity at each traverse point using the equations presented in section 12.2. Calculate the test run average stack gas velocity by finding the arithmetic average of the point velocity results in accordance with sections 12.3 and 12.4, and calculate the stack gas volumetric flow rate in accordance with section 12.5 or 12.6, as applicable.

 

9.0 Quality Control

 

9.1 Quality Control Activities.

 

In conjunction with the yaw angle determination and the pressure and temperature measurements specified in section 8.9, the following quality control checks should be performed.

 

9.1.1 Range of the differential pressure gauge.

In accordance with the specifications in section 6.4, ensure that the proper differential pressure gauge is being used for the range of Delta P values encountered. If it is necessary to change to a more sensitive gauge, replace the gauge with a gauge calibrated according to section 10.3.3, perform the leak check described in section 8.4and the zero check described in section 8.5, and repeat the differential pressure and temperature readings at each traverse point.

 

9.1.2 Horizontal stability check.

For horizontal traverses of a stack or duct, visually check that the probe shaft is maintained in a horizontal position prior to taking a pressure reading. Periodically, during a test run, the probe’s horizontal stability should be verified by placing a carpenter’s level, a digital inclinometer, or other angle-measuring device on the portion of the probe sheath that extends outside of the test port. A comparable check should be performed by automated systems.

 

10.0 Calibration

 

10.1 Wind Tunnel Qualification Checks.

 

To qualify for use in calibrating probes, a wind tunnel shall have the design features specified in section 6.11and satisfy the following qualification criteria. The velocity pressure cross-check in section 10.1.1 and axial flow verification in section 10.1.2 shall be performed before the initial use of the wind tunnel and repeated immediately after any alteration occurs in the wind tunnel’s configuration, fans, interior surfaces, straightening vanes, controls, or other properties that could reasonably be expected to alter the flow pattern or velocity stability in the tunnel. The owner or operator of a wind tunnel used to calibrate probes according to this method shall maintain records documenting that the wind tunnel meets the requirements of sections 10.1.1 and 10.1.2 and shall provide these records to the Administrator upon request.

 

10.1.1 Velocity pressure cross-check.

 

To verify that the wind tunnel produces the same velocity at the tested probe head as at the calibration pitot tube impact port, perform the following cross-check. Take three differential pressure measurements at the fixed calibration pitot tube location, using the calibration pitot tube specified in section 6.10, and take three measurements with the calibration pitot tube at the wind tunnel calibration location, as defined in section 3.21. Alternate the measurements between the two positions. Perform this procedure at the lowest and highest velocity settings at which the probes will be calibrated. Record the values on a form similar to Table 2G-4. At each velocity setting, the average velocity pressure obtained at the wind tunnel calibration location shall be within 2 percent or 2.5 mm H2O (0.01 in. H2O), whichever is less restrictive, of the average velocity pressure obtained at the fixed calibration pitot tube location. This comparative check shall be performed at 2.5-cm (1-in.), or smaller, intervals across the full length, width, and depth (if applicable) of the wind tunnel calibration location. If the criteria are not met at every tested point, the wind tunnel calibration location must be redefined, so that acceptable results are obtained at every point. Include the results of the velocity pressure cross-check in the calibration data section of the field test report. (See section 16.1.4.)

 

10.1.2 Axial flow verification.

 

The following procedures shall be performed to demonstrate that there is fully developed axial flow within the wind tunnel calibration location and at the calibration pitot tube location. Two options are available to conduct this check.

 

10.1.2.1 Using a calibrated 3-D probe. A probe that has been previously calibrated in a wind tunnel with documented axial flow (as defined in section 3.22) may be used to conduct this check. Insert the calibrated 3-D probe into the wind tunnel test section using the tested probe port. Following the procedures in sections 8.9and 12.2of Method 2F, determine the yaw and pitch angles at all the point(s) in the test section where the velocity pressure cross-check, as specified in section 10.1.1, is performed. This includes all the points in the calibration location and the point where the calibration pitot tube will be located. Determine the yaw and pitch angles at each point. Repeat these measurements at the highest and lowest velocities at which the probes will be calibrated. Record the values on a form similar to Table 2G-5. Each measured yaw and pitch angle shall be within 3@ of 0@. Exceeding the limits indicates unacceptable flow in the test section. Until the problem is corrected and acceptable flow is verified by repetition of this procedure, the wind tunnel shall not be used for calibration of probes. Include the results of the axial flow verification in the calibration data section of the field test report. (See section 16.1.4.)

 

10.1.2.2 Using alternative probes. Axial flow verification may be performed using an uncalibrated prism-shaped 3-D probe (e.g., DA or DAT probe) or an uncalibrated wedge probe. ( Figure 2G-8illustrates a typical wedge probe.) This approach requires use of two ports: the tested probe port and a second port located 90° from the tested probe port. Each port shall provide access to all the points within the wind tunnel test section where the velocity pressure cross-check, as specified in section 10.1.1, is conducted. The probe setup shall include establishing a reference yaw-null position on the probe sheath to serve as the location for installing the angle-measuring device. Physical design features of the DA, DAT, and wedge probes are relied on to determine the reference position. For the DA or DAT probe, this reference position can be determined by setting a digital inclinometer on the flat facet where the P1 pressure port is located and then identifying the rotational position on the probe sheath where a second angle-measuring device would give the same angle reading. The reference position on a wedge probe shaft can be determined either geometrically or by placing a digital inclinometer on each side of the wedge and rotating the probe until equivalent readings are obtained. With the latter approach, the reference position is the rotational position on the probe sheath where an angle-measuring device would give a reading of 0°. After installation of the angle-measuring device in the reference yaw-null position on the probe sheath, determine the yaw angle from the tested port. Repeat this measurement using the 90° offset port, which provides the pitch angle of flow. Determine the yaw and pitch angles at all the point(s) in the test section where the velocity pressure cross-check, as specified in section 10.1.1, is performed. This includes all the points in the wind tunnel calibration location and the point where the calibration pitot tube will be located. Perform this check at the highest and lowest velocities at which the probes will be calibrated. Record the values on a form similar to Table 2G-5. Each measured yaw and pitch angle shall be within 3° of 0°. Exceeding the limits indicates unacceptable flow in the test section. Until the problem is corrected and acceptable flow is verified by repetition of this procedure, the wind tunnel shall not be used for calibration of probes. Include the results in the probe calibration report.

 

10.1.3 Wind tunnel audits.

 

10.1.3.1 Procedure. Upon the request of the Administrator, the owner or operator of a wind tunnel shall calibrate a 2-D audit probe in accordance with the procedures described in sections 10.3 through 10.6. The calibration shall be performed at two velocities that encompass the velocities typically used for this method at the facility. The resulting calibration data shall be submitted to the Agency in an audit test report. These results shall be compared by the Agency to reference calibrations of the audit probe at the same velocity settings obtained at two different wind tunnels.

 

10.1.3.2 Acceptance criterion. The audited tunnel’s calibration coefficient is acceptable if it is within 3 percent of the reference calibrations obtained at each velocity setting by one (or both) of the wind tunnels. If the acceptance criterion is not met at each calibration velocity setting, the audited wind tunnel shall not be used to calibrate probes for use under this method until the problems are resolved and acceptable results are obtained upon completion of a subsequent audit.

 

10.2 Probe Inspection.

 

10.2.1 Type S probe.

Before each calibration of a Type S probe, verify that one leg of the tube is permanently marked A, and the other, B. Carefully examine the pitot tube from the top, side, and ends. Measure the angles (a1, a2, b1, and b2) and the dimensions (w and z) illustrated in Figures 2-2and 2-3 in Method 2. Also measure the dimension A, as shown in the diagram in Table 2G-1, and the external tubing diameter (dimension Dt, Figure 2-2b in Method 2). For the purposes of this method, Dt shall be no less than 9.5 mm (3⁄8 in.). The base-to-opening plane distances PA and PB in Figure 2-3 of Method 2 shall be equal, and the dimension A in Table 2G-1 should be between 2.10Dt and 3.00Dt. Record the inspection findings and probe measurements on a form similar to Table CD2-1 of the “Quality Assurance Handbook for Air Pollution Measurement Systems: Volume III, Stationary Source- Specific Methods’ (EPA/600/R-94/038c, September 1994). For reference, this form is reproduced herein as Table 2G-1. The pitot tube shall not be used under this method if it fails to meet the specifications in this section and the alignment specifications in section 6.1.1. All Type S probes used to collect data with this method shall be calibrated according to the procedures outlined in sections 10.3 through 10.6 below. During calibration, each Type S pitot tube shall be configured in the same manner as used, or planned to be used, during the field test, including all components in the probe assembly (e.g., thermocouple, probe sheath, sampling nozzle). Probe shaft extensions that do not affect flow around the probe head need not be attached during calibration.

 

10.2.2 3-D probe.

If a 3-D probe is used to collect data with this method, perform the pre-calibration inspection according to procedures in Method 2F, section 10.2.

 

10.3 Pre-Calibration Procedures.

 

Prior to calibration, a scribe line shall have been placed on the probe in accordance with section 10.4. The yaw angle and velocity calibration procedures shall not begin until the pre-test requirements in sections 10.3.1 through 10.3.4 have been met.

 

10.3.1 Perform the horizontal straightness check described in section 8.2 on the probe assembly that will be calibrated in the wind tunnel.

 

10.3.2 Perform a leak check in accordance with section 8.4.

 

10.3.3 Except as noted in section 10.3.3.3, calibrate all differential pressure-measuring devices to be used in the probe calibrations, using the following procedures. At a minimum, calibrate these devices on each day that probe calibrations are performed.

 

10.3.3.1 Procedure. Before each wind tunnel use, all differential pressure-measuring devices shall be calibrated against the reference device specified in section 6.4.3 using a common pressure source. Perform the calibration at three reference pressures representing 30, 60, and 90 percent of the full-scale range of the pressure-measuring device being calibrated. For an inclined vertical manometer, perform separate calibrations on the inclined and vertical portions of the measurement scale, considering each portion of the scale to be a separate full-scale range. [For example, for a manometer with a 0-to 2.5-cm H2O (0-to 1- in. H2O) inclined scale and a 2.5-to 12.7-cm H2O (1-to 5-in. H2O) vertical scale, calibrate the inclined portion at 7.6, 15.2, and 22.9 mm H2O (0.3, 0.6, and 0.9 in. H2O), and calibrate the vertical portion at 3.8, 7.6, and 11.4 cm H2O (1.5, 3.0, and 4.5 in. H2O).] Alternatively, for the vertical portion of the scale, use three evenly spaced reference pressures, one of which is equal to or higher than the highest differential pressure expected in field applications.

 

10.3.3.2 Acceptance criteria. At each pressure setting, the two pressure readings made using the reference device and the pressure-measuring device being calibrated shall agree to within #2 percent of full scale of the device being calibrated or 0.5 mm H2O (0.02 in. H2O), whichever is less restrictive. For an inclined-vertical manometer, these requirements shall be met separately using the respective full-scale upper limits of the inclined and vertical portions of the scale. Differential pressure-measuring devices not meeting the #2 percent of full scale or 0.5 mm H2O (0.02 in. H2O) calibration requirement shall not be used.

 

10.3.3.3 Exceptions. Any precision manometer that meets the specifications for a reference device in section 6.4.3 and that is not used for field testing does not require calibration, but must be leveled and zeroed before each wind tunnel use. Any pressure device used exclusively for yaw nulling does not require calibration, but shall be checked for responsiveness to rotation of the probe prior to each wind tunnel use.

 

10.3.4 Calibrate digital inclinometers on each day of wind tunnel or field testing (prior to beginning testing) using the following procedures. Calibrate the inclinometer according to the manufacturer’s calibration procedures. In addition, use a triangular block (illustrated in Figure 2G-9) with a known angle, ’’, independently determined using a protractor or equivalent device, between two adjacent sides to verify the inclinometer readings. ( Note: If other angle-measuring devices meeting the provisions of section 6.2.3 are used in place of a digital inclinometer, comparable calibration procedures shall be performed on such devices.) Secure the triangular block in a fixed position. Place the inclinometer on one side of the block (side A) to measure the angle of inclination (R1). Repeat this measurement on the adjacent side of the block (side B) using the inclinometer to obtain a second angle reading (R2). The difference of the sum of the two readings from 180° (i.e., 180R1R2) shall be within #2 of the known angle, “.

 

10.4 Placement of Reference Scribe Line.

 

Prior to the first calibration of a probe, a line shall be permanently inscribed on the main probe sheath to serve as a reference mark for determining yaw angles. Annex C in section 18 of this method gives a guideline for placement of the reference scribe line.

 

10.4.1 This reference scribe line shall meet the specifications in sections 6.1.5.1 and 6.1.5.3 of this method. To verify that the alignment specification in section 6.1.5.3 is met, secure the probe in a horizontal position and measure the rotational angle of each scribe line and scribe line segment using an angle-measuring device that meets the specifications in section 6.2.1 or 6.2.3. For any scribe line that is longer than 30.5 cm (12 in.), check the line’s rotational position at 30.5-cm (12-in.) intervals. For each line segment that is 12 in. or less in length, check the rotational position at the two endpoints of the segment. To meet the alignment specification in section 6.1.5.3, the minimum and maximum of all of the rotational angles that are measured along the full length of main probe must not differ by more than 2°. ( Note: A short reference scribe line segment [e.g., 15.2 cm (6 in.) or less in length] meeting the alignment specifications in section 6.1.5.3 is fully acceptable under this method. See section 18.1.1.1 of Annex Afor an example of a probe marking procedure, suitable for use with a short reference scribe line.)

 

10.4.2 The scribe line should be placed on the probe first and then its offset from the yaw-null position established (as specified in section 10.5). The rotational position of the reference scribe line relative to the yaw-null position of the probe, as determined by the yaw angle calibration procedure in section 10.5, is the reference scribe line rotational offset, R _SLO. The reference scribe line rotational offset shall be recorded and retained as part of the probe’s calibration record.

 

10.4.3 Scribe line for automated probes. A scribe line may not be necessary for an automated probe system if a reference rotational position of the probe is built into the probe system design. For such systems, a “flat’’ (or comparable, clearly identifiable physical characteristic) should be provided on the probe casing or flange plate to ensure that the reference position of the probe assembly remains in a vertical or horizontal position. The rotational offset of the flat (or comparable, clearly identifiable physical characteristic) needed to orient the reference position of the probe assembly shall be recorded and maintained as part of the automated probe system’s specifications.

 

10.5 Yaw Angle Calibration Procedure.

 

For each probe used to measure yaw angles with this method, a calibration procedure shall be performed in a wind tunnel meeting the specifications in section 10.1 to determine the rotational position of the reference scribe line relative to the probe’s yaw-null position. This procedure shall be performed on the main probe with all devices that will be attached to the main probe in the field [such as thermocouples, resistance temperature detectors (RTDs), or sampling nozzles] that may affect the flow around the probe head. Probe shaft extensions that do not affect flow around the probe head need not be attached during calibration. At a minimum, this procedure shall include the following steps.

 

10.5.1 Align and lock the angle-measuring device on the reference scribe line. If a marking procedure (such as described in section 18.1.1.1) is used, align the angle-measuring device on a mark within 1° of the rotational position of the reference scribe line. Lock the angle-measuring device onto the probe sheath at this position.

 

10.5.2 Zero the pressure-measuring device used for yaw nulling.

 

10.5.3 Insert the probe assembly into the wind tunnel through the entry port, positioning the probe’s impact port at the calibration location. Check the responsiveness of the pressure-measurement device to probe rotation, taking corrective action if the response is unacceptable.

 

10.5.4 Ensure that the probe is in a horizontal position, using a carpenter’s level.

 

10.5.5 Rotate the probe either clockwise or counterclockwise until a yaw null [zero Delta P for a Type S probe or zero (P2-P3) for a 3-D probe] is obtained. If using a Type S probe with an attached thermocouple, the direction of the probe rotation shall be such that the thermocouple is located downstream of the probe pressure ports at the yaw-null position.

 

10.5.6 Use the reading displayed by the angle-measuring device at the yaw-null position to determine the magnitude of the reference scribe line rotational offset, R _SLO, as defined in section 3.15. Annex Din section 18 of this method gives a recommended procedure for determining the magnitude of R _SLOwith a digital inclinometer and a second procedure for determining the magnitude of R _SLOwith a protractor wheel and pointer device. Table 2G-6 gives an example data form and Table 2G-7is a look-up table with the recommended procedure. Procedures other than those recommended in Annex D in section 18 may be used, if they can determine R _SLOto within 1° and are explained in detail in the field test report. The algebraic sign of R _SLOwill either be positive if the rotational position of the reference scribe line (as viewed from the “tail’’ end of the probe) is clockwise, or negative, if counterclockwise with respect to the probe’s yaw-null position. (This is illustrated in Figure 2G-10.)

 

10.5.7 The steps in sections 10.5.3 through 10.5.6 shall be performed twice at each of the velocities at which the probe will be calibrated (in accordance with section 10.6). Record the values of R _SLO.

 

10.5.8 The average of all of the R _SLOvalues shall be documented as the reference scribe line rotational offset for the probe.

 

10.5.9 Use of reference scribe line offset. The reference scribe line rotational offset shall be used to determine the yaw angle of flow in accordance with section 8.9.4.

 

10.6 Velocity Calibration Procedure.

 

When a 3-D probe is used under this method, follow the provisions for the calibration of 3-D probes in section 10.6 of Method 2F to obtain the necessary velocity calibration coefficients (F2 as derived using Equation 2F-2 in Method 2F) corresponding to a pitch angle position of 0°. The following procedure applies to Type S probes. This procedure shall be performed on the main probe and all devices that will be attached to the main probe in the field (e.g., thermocouples, RTDs, sampling nozzles) that may affect the flow around the probe head. Probe shaft extensions that do not affect flow around the probe head need not be attached during calibration. (Note: If a sampling nozzle is part of the assembly, two additional requirements must be satisfied before proceeding. The distance between the nozzle and the pitot tube shall meet the minimum spacing requirement prescribed in Method 2, and a wind tunnel demonstration shall be performed that shows the probe’s ability to yaw null is not impaired when the nozzle is drawing sample.) To obtain velocity calibration coefficient(s) for the tested probe, proceed as follows.

 

10.6.1 Calibration velocities. The tester may calibrate the probe at two nominal wind tunnel velocity settings of 18.3 m/sec and 27.4 m/sec (60 ft/sec and 90 ft/sec) and average the results of these calibrations, as described in sections 10.6.12 through 10.6.14, in order to generate the calibration coefficient, Cp. If this option is selected, this calibration coefficient may be used for all field applications where the velocities are 9.1 m/sec (30 ft/sec) or greater. Alternatively, the tester may customize the probe calibration for a particular field test application (or for a series of applications), based on the expected average velocity(ies) at the test site(s). If this option is selected, generate the calibration coefficients by calibrating the probe at two nominal wind tunnel velocity settings, one of which is less than or equal to and the other greater than or equal to the expected average velocity(ies) for the field application(s), and average the results as described in sections 10.6.12 through 10.6.14. Whichever calibration option is selected, the probe calibration coefficient(s) obtained at the two nominal calibration velocities shall meet the conditions specified in sections 10.6.12 through 10.6.14.

 

10.6.2 Connect the tested probe and calibration pitot tube to their respective pressure-measuring devices. Zero the pressure-measuring devices. Inspect and leak-check all pitot lines; repair or replace them, if necessary. Turn on the fan, and allow the wind tunnel air flow to stabilize at the first of the selected nominal velocity settings.

 

10.6.3 Position the calibration pitot tube at its measurement location (determined as outlined in section 6.11.4.3), and align the tube so that its tip is pointed directly into the flow. Ensure that the entry port surrounding the tube is properly sealed. The calibration pitot tube may either remain in the wind tunnel throughout the calibration, or be removed from the wind tunnel while measurements are taken with the probe being calibrated.

 

10.6.4 Check the zero setting of each pressure-measuring device.

 

10.6.5 Insert the tested probe into the wind tunnel and align it so that the designated pressure port (e.g., either the A-side or B-side of a Type S probe) is pointed directly into the flow and is positioned within the wind tunnel calibration location (as defined in section 3.21). Secure the probe at the 0° pitch angle position. Ensure that the entry port surrounding the probe is properly sealed.

 

10.6.6 Read the differential pressure from the calibration pitot tube (Delta Pstd ), and record its value. Read the barometric pressure to within 2.5 mm Hg (0.1 in. Hg) and the temperature in the wind tunnel to within 0.6°Cdeg;C (1°F). Record these values on a data form similar to Table 2G-8.

 

10.6.7 After the tested probe’s differential pressure gauges have had sufficient time to stabilize, yaw null the probe (and then rotate it back 90° for Type S probes), then obtain the differential pressure reading (Delta P). Record the yaw angle and differential pressure readings.

 

10.6.8 Take paired differential pressure measurements with the calibration pitot tube and tested probe (according to sections 10.6.6 and 10.6.7). The paired measurements in each replicate can be made either simultaneously (i.e., with both probes in the wind tunnel) or by alternating the measurements of the two probes (i.e., with only one probe at a time in the wind tunnel).

 

10.6.9 Repeat the steps in sections 10.6.6 through 10.6.8 at the same nominal velocity setting until three pairs of Delta P readings have been obtained from the calibration pitot tube and the tested probe.

 

10.6.10 Repeat the steps in sections 10.6.6 through 10.6.9 above for the A-side and B-side of the Type S pitot tube. For a probe assembly constructed such that its pitot tube is always used in the same orientation, only one side of the pitot tube need be calibrated (the side that will face the flow). However, the pitot tube must still meet the alignment and dimension specifications in section 6.1.1 and must have an average deviation (s) value of 0.01 or less as provided in section 10.6.12.4.

 

10.6.11 Repeat the calibration procedures in sections 10.6.6 through 10.6.10 at the second selected nominal wind tunnel velocity setting.

 

10.6.12 Perform the following calculations separately on the A-side and B-side values.

 

10.6.12.1 Calculate a Cp value for each of the three replicates performed at the lower velocity setting where the calibrations were performed using Equation 2-2 in section 4.1.4 of Method 2.

 

10.6.12.2 Calculate the arithmetic average, Cp(avg-low), of the three Cp values.

 

10.6.12.3 Calculate the deviation of each of the three individual values of Cp from the A-side average Cp(avg-low) value using Equation 2-3 in Method 2.

 

10.6.12.4 Calculate the average deviation(s) of the three individual Cp values from Cp(avg-low) using Equation 2-4 in Method 2. Use the Type S pitot tube only if the values of s (side A) and s (side B) are less than or equal to 0.01. If both A-side and B-side calibration coefficients are calculated, the absolute value of the difference between Cp(avg-low) (side A) and Cp(avg-low) (side B) must not exceed 0.01.

 

10.6.13 Repeat the calculations in section 10.6.12 using the data obtained at the higher velocity setting to derive the arithmetic Cp values at the higher velocity setting, Cp(avg-high), and to determine whether the conditions in 10.6.12.4 are met by both the A-side and B-side calibrations at this velocity setting.

 

10.6.14 Use Equation 2G-1 to calculate the percent difference of the averaged Cp values at the two calibration velocities.

 

 

The percent difference between the averaged Cp values shall not exceed 3 percent. If the specification is met, average the A-side values of Cp(avg-low) and Cp(avg-high) to produce a single A-side calibration coefficient, Cp. Repeat for the B-side values if calibrations were performed on that side of the pitot. If the specification is not met, make necessary adjustments in the selected velocity settings and repeat the calibration procedure until acceptable results are obtained.

 

10.6.15 If the two nominal velocities used in the calibration were 18.3 and 27.4 m/sec (60 and 90 ft/sec), the average Cp from section 10.6.14 is applicable to all velocities 9.1 m/sec (30 ft/sec) or greater. If two other nominal velocities were used in the calibration, the resulting average Cp value shall be applicable only in situations where the velocity calculated using the calibration coefficient is neither less than the lower nominal velocity nor greater than the higher nominal velocity.

 

10.7 Recalibration.

 

Recalibrate the probe using the procedures in section 10 either within 12 months of its first field use after its most recent calibration or after 10 field tests (as defined in section 3.3), whichever occurs later. In addition, whenever there is visible damage to the probe head, the probe shall be recalibrated before it is used again.

 

10.8 Calibration of pressure-measuring devices used in the field.

 

Before its initial use in a field test, calibrate each pressure-measuring device (except those used exclusively for yaw nulling) using the three-point calibration procedure described in section 10.3.3. The device shall be recalibrated according to the procedure in section 10.3.3 no later than 90 days after its first field use following its most recent calibration. At the discretion of the tester, more frequent calibrations (e.g., after a field test) may be performed. No adjustments, other than adjustments to the zero setting, shall be made to the device between calibrations.

 

10.8.1 Post-test calibration check.

A single-point calibration check shall be performed on each pressure-measuring device after completion of each field test. At the discretion of the tester, more frequent single-point calibration checks (e.g., after one or more field test runs) may be performed. It is recommended that the post-test check be performed before leaving the field test site. The check shall be performed at a pressure between 50 and 90 percent of full scale by taking a common pressure reading with the tested probe and a reference pressure-measuring device (as described in section 6.4.4) or by challenging the tested device with a reference pressure source (as described in section 6.4.4) or by performing an equivalent check using a reference device approved by the Administrator.

 

10.8.2 Acceptance criterion.

At the selected pressure setting, the pressure readings made using the reference device and the tested device shall agree to within 3 percent of full scale of the tested device or 0.8 mm H2O (0.03 in. H2O), whichever is less restrictive. If this specification is met, the test data collected during the field test are valid. If the specification is not met, all test data collected since the last successful calibration or calibration check are invalid and shall be repeated using a pressure-measuring device with a current, valid calibration. Any device that fails the calibration check shall not be used in a field test until a successful recalibration is performed according to the procedures in section 10.3.3.

 

10.9 Temperature Gauges.

 

Same as Method 2, section 4.3. The alternative thermocouple calibration procedures outlined in Emission Measurement Center (EMC) Approved Alternative Method (ALT-011) “Alternative Method 2 Thermocouple Calibration Procedure’’ may be performed. Temperature gauges shall be calibrated no more than 30 days prior to the start of a field test or series of field tests and recalibrated no more than 30 days after completion of a field test or series of field tests.

 

10.10 Barometer.

 

Same as Method 2,section 4.4. The barometer shall be calibrated no more than 30 days prior to the start of a field test or series of field tests.

 

11.0 Analytical Procedure

 

Sample collection and analysis are concurrent for this method (see section 8.0).

 

12.0 Data Analysis and Calculations

 

These calculations use the measured yaw angle and the differential pressure and temperature measurements at individual traverse points to derive the near-axial flue gas velocity (a(ii)) at each of those points. The near-axial velocity values at all traverse points that comprise a full stack or duct traverse are then averaged to obtain the average near-axial stack or duct gas velocity a(avg).

 

12.1 Nomenclature

 

A = Cross-sectional area of stack or duct at the test port location, m2 (ft2).

Bws = Water vapor in the gas stream (from Method 4 or alternative), proportion by

volume.

Cp = Pitot tube calibration coefficient, dimensionless.

F2(i) = 3-D probe velocity coefficient at 0 pitch, applicable at traverse point i.

Kp = Pitot tube constant,

 

 

for the metric system, and

 

 

for the English system.

 

Md = Molecular weight of stack or duct gas, dry basis (see section 8.13), g/g-mole (lb/

lb-mole).

Ms = Molecular weight of stack or duct gas, wet basis, g/g-mole (lb/lb-mole).

 

 

Pbar = Barometric pressure at velocity measurement site, mm Hg (in. Hg).

Pg = Stack or duct static pressure, mm H2O (in. H2O).

Ps = Absolute stack or duct pressure, mm Hg (in. Hg),

 

 

 

Pstd = Standard absolute pressure, 760 mm Hg (29.92 in. Hg).

13.6 = Conversion from mm H2O (in. H2O) to mm Hg (in. Hg).

Qsd = Average dry-basis volumetric stack or duct gas flow rate corrected to standard conditions, dscm/hr (dscf/hr).

Qsw = Average wet-basis volumetric stack or duct gas flow rate corrected to standard conditions, wscm/hr (wscf/hr).

ts(i) = Stack or duct temperature, °Cdeg;C (°F), at traverse point i.

Ts(i) = Absolute stack or duct temperature, °K (°R), at traverse point i.

 

 

for the metric system, and

 

 

for the English system.

 

Ts(avg)=Average absolute stack or duct gas temperature across all traverse points.

Tstd=Standard absolute temperature, 293°K (528°R).

va(i)=Measured stack or duct gas impact velocity, m/sec (ft/sec), at traverse point i.

va(avg)=Average near-axial stack or duct gas velocity, m/sec (ft/sec) across all traverse points.

Delta Pi=Velocity head (differential pressure) of stack or duct gas, mm H2O (in. H2O), applicable at traverse point i.

(P1-P2)=Velocity head (differential pressure) of stack or duct gas measured by a 3-D probe, mm H2O (in. H2O), applicable at traverse point i.

3,600=Conversion factor, sec/hr.

18.0=Molecular weight of water, g/g-mole (lb/lb-mole).

0y(i)=Yaw angle of the flow velocity vector, at traverse point i.

n=Number of traverse points.

 

12.2 Traverse Point Velocity Calculations.

Perform the following calculations from the measurements obtained at each traverse point.

 

12.2.1 Selection of calibration coefficient.

Select the calibration coefficient as described in section 10.6.1.

 

12.2.2 Near-axial traverse point velocity.

When using a Type S probe, use the following equation to calculate the traverse point near-axial velocity (va(i)) from the differential pressure (Delta Pi), yaw angle ( 0y(i)), absolute stack or duct standard temperature (Ts(i)) measured at traverse point i, the absolute stack or duct pressure (Ps), and molecular weight (Ms).

 

Use the following equation when using a 3-D probe.

 

 

12.2.3 Handling multiple measurements at a traverse point.

For pressure or temperature devices that take multiple measurements at a traverse point, the multiple measurements (or where applicable, their square roots) may first be averaged and the resulting average values used in the equations above. Alternatively, the individual measurements may be used in the equations above and the resulting calculated values may then be averaged to obtain a single traverse point value. With either approach, all of the individual measurements recorded at a traverse point must be used in calculating the applicable traverse point value.

 

12.3 Average Near-Axial Velocity in Stack or Duct.

 

Use the reported traverse point near-axial velocity in the following equation.

 

 

12.4 Acceptability of Results.

 

The acceptability provisions in section 12.4 of Method 2F apply to 3-D probes used under Method 2G. The following provisions apply to Type S probes. For Type S probes, the test results are acceptable and the calculated value of va(avg) may be reported as the average near-axial velocity for the test run if the conditions in either section 12.4.1 or 12.4.2 are met.

 

12.4.1 The average calibration coefficient Cp used in Equation 2G-6 was generated at nominal velocities of 18.3 and 27.4 m/sec (60 and 90 ft/sec) and the value of va(avg) calculated using Equation 2G-8 is greater than or equal to 9.1 m/sec (30 ft/sec).

 

12.4.2 The average calibration coefficient Cp used in Equation 2G-6 was generated at nominal velocities other than 18.3 or 27.4 m/ sec (60 or 90 ft/sec) and the value of va(avg) calculated using Equation 2G-8 is greater than or equal to the lower nominal velocity and less than or equal to the higher nominal velocity used to derive the average Cp.

 

12.4.3 If the conditions in neither section 12.4.1 nor section 12.4.2 are met, the test results obtained from Equation 2G-8 are not acceptable, and the steps in sections 12.2 and 12.3 must be repeated using an average calibration coefficient Cp that satisfies the conditions in section 12.4.1 or 12.4.2.

 

12.5 Average Gas Volumetric Flow Rate in Stack or Duct (Wet Basis).

 

Use the following equation to compute the average volumetric flow rate on a wet basis.

 

 

12.6 Average Gas Volumetric Flow Rate in Stack or Duct (Dry Basis).

 

Use the following equation to compute the average volumetric flow rate on a dry basis.

 

 

 

13.0 Method Performance. [Reserved]

 

14.0 Pollution Prevention. [Reserved]

 

15.0 Waste Management. [Reserved]

 

16.0 Reporting.

 

16.1 Field Test Reports.

 

Field test reports shall be submitted to the Agency according to applicable regulatory requirements. Field test reports should, at a minimum, include the following elements.

 

16.1.1 Description of the source.

This should include the name and location of the test site, descriptions of the process tested, a description of the combustion source, an accurate diagram of stack or duct cross-sectional area at the test site showing the dimensions of the stack or duct, the location of the test ports, and traverse point locations and identification numbers or codes. It should also include a description and diagram of the stack or duct layout, showing the distance of the test location from the nearest upstream and downstream disturbances and all structural elements (including breachings, baffles, fans, straighteners, etc.) affecting the flow pattern. If the source and test location descriptions have been previously submitted to the Agency in a document (e.g., a monitoring plan or test plan), referencing the document in lieu of including this information in the field test report is acceptable.

 

16.1.2 Field test procedures.

These should include a description of test equipment and test procedures. Testing conventions, such as traverse point numbering and measurement sequence (e.g., sampling from center to wall, or wall to center), should be clearly stated. Test port identification and directional reference for each test port should be included on the appropriate field test data sheets.

 

16.1.3 Field test data.

 

16.1.3.1 Summary of results. This summary should include the dates and times of testing, and the average near-axial gas velocity and the average flue gas volumetric flow results for each run and tested condition.

 

16.1.3.2 Test data. The following values for each traverse point should be recorded and reported:

 

(a) Differential pressure at traverse point i (Delta Pi)

(b) Stack or duct temperature at traverse point i (ts(i))

(c) Absolute stack or duct temperature at traverse point i (Ts(i))

(d) Yaw angle at traverse point i ( 0y(i))

(e) Stack gas near-axial velocity at traverse point i (va(i))

 

16.1.3.3 The following values should be reported once per run:

 

(a) Water vapor in the gas stream (from Method 4 or alternative), proportion by volume (Bws), measured at the frequency specified in the applicable regulation

(b) Molecular weight of stack or duct gas, dry basis (Md)

(c) Molecular weight of stack or duct gas, wet basis (Ms)

(d) Stack or duct static pressure (Pg)

(e) Absolute stack or duct pressure (Ps)

(f) Carbon dioxide concentration in the flue gas, dry basis (%d CO2)

(g) Oxygen concentration in the flue gas, dry basis (%d O2)

(h) Average near-axial stack or duct gas velocity (va(avg)) across all traverse points

(i) Gas volumetric flow rate corrected to standard conditions, dry or wet basis as required by the applicable regulation (Qsd or Qsw)

 

16.1.3.4 The following should be reported once per complete set of test runs:

 

(a) Cross-sectional area of stack or duct at the test location (A)

(b) Pitot tube calibration coefficient (Cp)

(c) Measurement system response time (sec)

(d) Barometric pressure at measurement site (Pbar)

 

16.1.4 Calibration data.

The field test report should include calibration data for all probes and test equipment used in the field test. At a minimum, the probe calibration data reported to the Agency should include the following:

 

(a) Date of calibration

(b) Probe type

(c) Probe identification number(s) or code(s)

(d) Probe inspection sheets

(e) Pressure measurements and calculations used to obtain calibration coefficients in accordance with section 10.6 of this method

(f) Description and diagram of wind tunnel used for the calibration, including dimensions of cross-sectional area and position and size of the test section

(g) Documentation of wind tunnel qualification tests performed in accordance with section 10.1 of this method

 

16.1.5 Quality assurance.

Specific quality assurance and quality control procedures used during the test should be described.

 

17.0 Bibliography.

 

(1) 40 CFR Part 60, Appendix A, Method 1 - Sample and velocity traverses for stationary sources.

(2) 40 CFR Part 60, Appendix A, Method 2 - Determination of stack gas velocity and volumetric flow rate (Type S pitot tube) .

(3) 40 CFR Part 60, Appendix A, Method 2F - Determination of stack gas velocity and volumetric flow rate with three-dimensional probes.

(4) 40 CFR Part 60, Appendix A, Method 2H - Determination of stack gas velocity taking into account velocity decay near the stack wall.

(5) 40 CFR Part 60, Appendix A, Method 3 - Gas analysis for carbon dioxide, oxygen, excess air, and dry molecular weight.

(6) 40 CFR Part 60, Appendix A, Method 3A - Determination of oxygen and carbon dioxide concentrations in emissions from stationary sources (instrumental analyzer procedure).

(7) 40 CFR Part 60, Appendix A, Method 4 - Determination of moisture content in stack gases.

(8) Emission Measurement Center (EMC) Approved Alternative Method (ALT-011)  “Alternative Method 2 Thermocouple Calibration Procedure.’’

(9) Electric Power Research Institute, Interim Report EPRI TR-106698, “Flue Gas Flow Rate Measurement Errors,’’ June 1996.

(10) Electric Power Research Institute, Final Report EPRI TR-108110, “Evaluation of Heat Rate Discrepancy from Continuous Emission Monitoring Systems,’’ August 1997.

(11) Fossil Energy Research Corporation, Final Report, “Velocity Probe Tests in Nonaxial Flow Fields,’’ November 1998, Prepared for the U.S. Environmental Protection Agency.

(12) Fossil Energy Research Corporation, “Additional Swirl Tunnel Tests: E-DAT and T-DAT Probes,’’ February 24, 1999, Technical Memorandum Prepared for U.S. Environmental Protection Agency, P.O. No. 7W-1193-NALX.

(13) Massachusetts Institute of Technology, Report WBWT-TR-1317, “Calibration of Eight Wind Speed Probes Over a Reynolds Number Range of 46,000 to 725,000 Per Foot, Text and Summary Plots,’’ Plus appendices, October 15, 1998, Prepared for The Cadmus Group, Inc.

(14) National Institute of Standards and Technology, Special Publication 250, “NIST Calibration Services Users Guide 1991,’’ Revised October 1991, U.S. Department of Commerce, p. 2.

(15) National Institute of Standards and Technology, 1998, “Report of Special Test of Air Speed Instrumentation, Four Prandtl Probes, Four S-Type Probes, Four French Probes, Four Modified Kiel Probes,’’ Prepared for the U.S. Environmental Protection Agency under IAG #DW13938432-01-0.

(16) National Institute of Standards and Technology, 1998, “Report of Special Test of Air Speed Instrumentation, Five Autoprobes,’’ Prepared for the U.S. Environmental Protection Agency under IAG #DW13938432-01-0.

(17) National Institute of Standards and Technology, 1998, “Report of Special Test of Air Speed Instrumentation, Eight Spherical Probes,’’ Prepared for the U.S. Environmental Protection Agency under IAG #DW13938432-01-0.

(18) National Institute of Standards and Technology, 1998, “Report of Special Test of Air Speed Instrumentation, Four DAT Probes, “ Prepared for the U.S. Environmental Protection Agency under IAG #DW13938432-01-0.

(19) Norfleet, S.K., “An Evaluation of Wall Effects on Stack Flow Velocities and Related Overestimation Bias in EPA’s Stack Flow Reference Methods,’’ EPRI CEMS User’s Group Meeting, New Orleans, Louisiana, May 13-15, 1998.

(20) Page, J.J., E.A. Potts, and R.T. Shigehara, “3-D Pitot Tube Calibration Study,’’ EPA Contract No. 68D10009, Work Assignment No. I-121, March 11, 1993.

(21) Shigehara, R.T., W.F. Todd, and W.S. Smith, “Significance of Errors in Stack Sampling Measurements,’’ Presented at the Annual Meeting of the Air Pollution Control Association, St. Louis, Missouri, June 1419, 1970.

(22) The Cadmus Group, Inc., May 1999, “EPA Flow Reference Method Testing and Analysis: Findings Report,’’ EPA/430-R-99-009.

(23) The Cadmus Group, Inc., 1998, “EPA Flow Reference Method Testing and Analysis: Data Report, Texas Utilities, DeCordova Steam Electric Station, Volume I: Test Description and Appendix A (Data Distribution Package),’’ EPA/430-R-98-015a.

(24) The Cadmus Group, Inc., 1998, “EPA Flow Reference Method Testing and Analysis: Data Report, Texas Utilities, Lake Hubbard Steam Electric Station, Volume I: Test Description and Appendix A (Data Distribution Package),’’ EPA/430-R-98-017a.

(25) The Cadmus Group, Inc., 1998, “EPA Flow Reference Method Testing and Analysis: Data Report, Pennsylvania Electric Co., G.P.U. Genco Homer City Station: Unit 1, Volume I: Test Description and Appendix A (Data Distribution Package),’’ EPA/430-R-98-018a.

(26) The Cadmus Group, Inc., 1997, “EPA Flow Reference Method Testing and Analysis: Wind Tunnel Experimental Results,’’ EPA/430-R-97-013.

 

18.0 Annexes

 

Annex A, C, and D describe recommended procedures for meeting certain provisions in sections 8.3, 10.4, and 10.5 of this method.

Annex B describes procedures to be followed when using the protractor wheel and pointer assembly to measure yaw angles, as provided under section 8.9.1.

 

18.1 Annex A - Rotational Position Check.

 

The following are recommended procedures that may be used to satisfy the rotational position check requirements of section 8.3 of this method and to determine the angle-measuring device rotational offset (R _ADO).

 

18.1.1 Rotational position check with probe outside stack.

Where physical constraints at the sampling location allow full assembly of the probe outside the stack and insertion into the test port, the following procedures should be performed before the start of testing. Two angle-measuring devices that meet the specifications in section 6.2.1 or 6.2.3 are required for the rotational position check. An angle-measuring device whose position can be independently adjusted (e.g., by means of a set screw) after being locked into position on the probe sheath shall not be used for this check unless the independent adjustment is set so that the device performs exactly like a device without the capability for independent adjustment. That is, when aligned on the probe such a device must give the same reading as a device that does not have the capability of being independently adjusted. With the fully assembled probe (including probe shaft extensions, if any) secured in a horizontal position, affix one yaw angle-measuring device to the probe sheath and lock it into position on the reference scribe line specified in section 6.1.5.1. Position the second angle-measuring device using the procedure in section 18.1.1.1 or 18.1.1.2.

 

18.1.1.1 Marking procedure. The procedures in this section should be performed at each location on the fully assembled probe where the yaw angle-measuring device will be mounted during the velocity traverse. Place the second yaw angle-measuring device on the main probe sheath (or extension) at the position where a yaw angle will be measured during the velocity traverse. Adjust the position of the second angle-measuring device until it indicates the same angle (1°) as the reference device, and affix the second device to the probe sheath (or extension). Record the angles indicated by the two angle-measuring devices on a form similar to Table 2G-2. In this position, the second angle-measuring device is considered to be properly positioned for yaw angle measurement. Make a mark, no wider than 1.6 mm (1⁄16 in.), on the probe sheath (or extension), such that the yaw angle-measuring device can be re-affixed at this same properly aligned position during the velocity traverse.

 

18.1.1.2 Procedure for probe extensions with scribe lines. If, during a velocity traverse the angle-measuring device will be affixed to a probe extension having a scribe line as specified in section 6.1.5.2, the following procedure may be used to align the extension’s scribe line with the reference scribe line instead of marking the extension as described in section 18.1.1.1. Attach the probe extension to the main probe. Align and lock the second angle-measuring device on the probe extension’s scribe line. Then, rotate the extension until both measuring devices indicate the same angle (1°). Lock the extension at this rotational position. Record the angles indicated by the two angle-measuring devices on a form similar to Table 2G-2. An angle-measuring device may be aligned at any position on this scribe line during the velocity traverse, if the scribe line meets the alignment specification in section 6.1.5.3.

 

18.1.1.3 Post-test rotational position check. If the fully assembled probe includes one or more extensions, the following check should be performed immediately after the completion of a velocity traverse. At the discretion of the tester, additional checks may be conducted after completion of testing at any sample port. Without altering the alignment of any of the components of the probe assembly used in the velocity traverse, secure the fully assembled probe in a horizontal position. Affix an angle-measuring device at the reference scribe line specified in section 6.1.5.1. Use the other angle-measuring device to check the angle at each location where the device was checked prior to testing. Record the readings from the two angle-measuring devices.

 

18.1.2 Rotational position check with probe in stack.

This section applies only to probes that, due to physical constraints, cannot be inserted into the test port as fully assembled with all necessary extensions needed to reach the inner-most traverse point(s).

 

18.1.2.1 Perform the out-of-stack procedure in section 18.1.1 on the main probe and any attached extensions that will be initially inserted into the test port.

 

18.1.2.2 Use the following procedures to perform additional rotational position check(s) with the probe in the stack, each time a probe extension is added. Two angle-measuring devices are required. The first of these is the device that was used to measure yaw angles at the preceding traverse point, left in its properly aligned measurement position. The second angle-measuring device is positioned on the added probe extension. Use the applicable procedures in section 18.1.1.1 or 18.1.1.2 to align, adjust, lock, and mark (if necessary) the position of the second angle-measuring device to within 1° of the first device. Record the readings of the two devices on a form similar to Table 2G-2.

 

18.1.2.3 The procedure in section 18.1.2.2 should be performed at the first port where measurements are taken. The procedure should be repeated each time a probe extension is re-attached at a subsequent port, unless the probe extensions are designed to be locked into a mechanically fixed rotational position (e.g., through use of interlocking grooves), which can be reproduced from port to port as specified in section 8.3.5.2.

 

18.2 Annex B - Angle Measurement Protocol for Protractor Wheel and Pointer Device.

 

The following procedure shall be used when a protractor wheel and pointer assembly, such as the one described in section 6.2.2 and illustrated in Figure 2G-5 is used to measure the yaw angle of flow. With each move to a new traverse point, unlock, re-align, and re-lock the probe, angle-pointer collar, and protractor wheel to each other. At each such move, particular attention is required to ensure that the scribe line on the angle pointer collar is either aligned with the reference scribe line on the main probe sheath or is at the rotational offset position established under section 8.3.1. The procedure consists of the following steps:

 

18.2.1 Affix a protractor wheel to the entry port for the test probe in the stack or duct.

 

18.2.2 Orient the protractor wheel so that the 0° mark corresponds to the longitudinal axis of the stack or duct. For stacks, vertical ducts, or ports on the side of horizontal ducts, use a digital inclinometer meeting the specifications in section 6.2.1 to locate the 0° orientation. For ports on the top or bottom of horizontal ducts, identify the longitudinal axis at each test port and permanently mark the duct to indicate the 0° orientation. Once the protractor wheel is properly aligned, lock it into position on the test port.

 

18.2.3 Move the pointer assembly along the probe sheath to the position needed to take measurements at the first traverse point. Align the scribe line on the pointer collar with the reference scribe line or at the rotational offset position established under section 8.3.1. Maintaining this rotational alignment, lock the pointer device onto the probe sheath. Insert the probe into the entry port to the depth needed to take measurements at the first traverse point.

 

18.2.4 Perform the yaw angle determination as specified in sections 8.9.3 and 8.9.4 and record the angle as shown by the pointer on the protractor wheel. Then, take velocity pressure and temperature measurements in accordance with the procedure in section 8.9.5. Perform the alignment check described in section 8.9.6.

 

18.2.5 After taking velocity pressure measurements at that traverse point, unlock the probe from the collar and slide the probe through the collar to the depth needed to reach the next traverse point.

 

18.2.6 Align the scribe line on the pointer collar with the reference scribe line on the main probe or at the rotational offset position established under section 8.3.1. Lock the collar onto the probe.

 

18.2.7 Repeat the steps in sections 18.2.4 through 18.2.6 at the remaining traverse points accessed from the current stack or duct entry port.

 

18.2.8 After completing the measurement at the last traverse point accessed from a port, verify that the orientation of the protractor wheel on the test port has not changed over the course of the traverse at that port. For stacks, vertical ducts, or ports on the side of horizontal ducts, use a digital inclinometer meeting the specifications in section 6.2.1 to check the rotational position of the 0° mark on the protractor wheel. For ports on the top or bottom of horizontal ducts, observe the alignment of the angle wheel 0° mark relative to the permanent 0° mark on the duct at that test port. If these observed comparisons exceed 2° of 0°, all angle and pressure measurements taken at that port since the protractor wheel was last locked into position on the port shall be repeated.

 

18.2.9 Move to the next stack or duct entry port and repeat the steps in sections 18.2.1 through 18.2.8.

 

18.3 Annex C - Guideline for Reference Scribe Line Placement.

 

Use of the following guideline is recommended to satisfy the requirements of section 10.4 of this method. The rotational position of the reference scribe line should be either 90° or 180° from the probe’s impact pressure port. For Type-S probes, place separate scribe lines, on opposite sides of the probe sheath, if both the A and B sides of the pitot tube are to be used for yaw angle measurements.

 

18.4 Annex D - Determination of Reference Scribe Line Rotational Offset.

 

The following procedures are recommended for determining the magnitude and sign of a probe’s reference scribe line rotational offset, R _SLO. Separate procedures are provided for

two types of angle-measuring devices: digital inclinometers and protractor wheel and pointer assemblies.

 

18.4.1 Perform the following procedures on the main probe with all devices that will be attached to the main probe in the field [such as thermocouples, resistance temperature detectors (RTDs), or sampling nozzles] that may affect the flow around the probe head. Probe shaft extensions that do not affect flow around the probe head need not be attached during calibration.

 

18.4.2 The procedures below assume that the wind tunnel duct used for probe calibration is horizontal and that the flow in the calibration wind tunnel is axial as determined by the axial flow verification check described in section 10.1.2. Angle-measuring devices are assumed to display angles in alternating 0° to 90° and 90° to 0° intervals. If angle-measuring devices with other readout conventions are used or if other calibration wind tunnel duct configurations are used, make the appropriate calculational corrections. For Type-S probes, calibrate the A-side and B-sides separately, using the appropriate scribe line (see section 18.3, above), if both the A and B sides of the pitot tube are to be used for yaw angle determinations.

 

18.4.2.1 Position the angle-measuring device in accordance with one of the following procedures.

 

18.4.2.1.1 If using a digital inclinometer, affix the calibrated digital inclinometer to the probe. If the digital inclinometer can be independently adjusted after being locked into position on the probe sheath (e.g., by means of a set screw), the independent adjustment must be set so that the device performs exactly like a device without the capability for independent adjustment. That is, when aligned on the probe the device must give the same readings as a device that does not have the capability of being independently adjusted. Either align it directly on the reference scribe line or on a mark aligned with the scribe line determined according to the procedures in section 18.1.1.1. Maintaining this rotational alignment, lock the digital inclinometer onto the probe sheath.

 

18.4.2.1.2 If using a protractor wheel and pointer device, orient the protractor wheel on the test port so that the ° mark is aligned with the longitudinal axis of the wind tunnel duct. Maintaining this alignment, lock the wheel into place on the wind tunnel test port. Align the scribe line on the pointer collar with the reference scribe line or with a mark aligned with the reference scribe line, as determined under section 18.1.1.1. Maintaining this rotational alignment, lock the pointer device onto the probe sheath.

 

18.4.2.2 Zero the pressure-measuring device used for yaw nulling.

 

18.4.2.3 Insert the probe assembly into the wind tunnel through the entry port, positioning the probe’s impact port at the calibration location. Check the responsiveness of the pressure-measuring device to probe rotation, taking corrective action if the response is unacceptable.

 

18.4.2.4 Ensure that the probe is in a horizontal position using a carpenter’s level.

 

18.4.2.5 Rotate the probe either clockwise or counterclockwise until a yaw null [zero Delta P for a Type S probe or zero (P2-P3) for a 3-D probe] is obtained. If using a Type S probe with an attached thermocouple, the direction of the probe rotation shall be such that the thermocouple is located downstream of the probe pressure ports at the yaw-null position.

 

18.4.2.6 Read and record the value of 0null, the angle indicated by the angle-measuring device at the yaw-null position. Record the angle reading on a form similar to Table 2G-6. Do not associate an algebraic sign with this reading.

 

18.4.2.7 Determine the magnitude and algebraic sign of the reference scribe line rotational offset, R _SLO. The magnitude of R _SLOwill be equal to either 0null or (90°– 0null), depending on the type of probe being calibrated and the type of angle-measuring device used. (See Table 2G-7 for a summary.) The algebraic sign of R _SLOwill either be positive if the rotational position of the reference scribe line is clockwise or negative if counterclockwise with respect to the probe’s yaw-null position. Figure 2G-10 illustrates how the magnitude and sign of R _SLOare determined.

 

18.4.2.8 Perform the steps in sections 18.3.2.3 through 18.3.2.7 twice at each of the two calibration velocities selected for the probe under section 10.6. Record the values of R _SLOin a form similar to Table 2G-6.

 

18.4.2.9 The average of all RSLO values is the reference scribe line rotational offset for the probe.