Dust resistivity is determined as a function of temperature in accordance with IEEE Standard 548. This test is conducted in an air environment containing a specified moisture concentration. The test is run as a function of both ascending and descending temperature. Data are acquired using an average ash layer electric field of 4 kV/cm. Since relatively low applied voltage is used and no sulfuric acid vapor is present in the environment, the values obtained indicate the maximum ash resistivity.
Between the two test modes, the sample is thermally equilibrated in dry air at 850°F for about 14 hours. This temperature is believed to anneal the ash and restore the particle surfaces to pre-collection condition. It can remove the effect of unburned combustibles, the residual effect of a conditioning agent other than sulfuric acid vapor, or the effect of some other agent that inhibits the reaction of the ash with water vapor. This can result in ascending and descending temperature resistivity curves that show a hysteresis related to the presence and removal of some effect such as a significant level of combustibles as shown in the image below.
The image below shows resistivity determined in accordance with IEEE Standard 548-1984, Ascending and Descending Temperature Modes.
Not really a compound-specific analysis. This algorithm determines the electrical properties of a dust. These properties can be used to determine the effectiveness of:
Coal-switching studies that evaluate the resistivity of select coals and blends to predict precipitator collection performance;
Flue gas conditioning used to improve precipitator collection performance; and
Precipitator design and optimization studies.
A bulk sample (about ten grams) is required for this analysis. Optimally, samples should be pulled from every precipitator hopper and blended into a representative inlet sample. This is simple across the rows, a little more involved from inlet to outlet. The Deutsch-Anderson equation is used along with hopper mapping to blend samples in a row from inlet to outlet fields.
Isokinetic samples can also be used for this analysis. One major inconvenience is the bulk quantity required for the measurements.
Flyash samples are generally non-hazardous for shipping purposes.
Samples should be shipped in airtight containers.
Modeled resistivity is well-suited for predictions of how well a candidate coal will work. It can also predict:
How well sulfuric acid conditioning might help a given situation;
How well temperature changes might affect a given situation;