Stack testing is an important tool used to determine a facility’s compliance with emission limits or capture or control efficiencies established pursuant to the Clean Air Act (CAA). A stack test:
- measures the amount of a specific regulated pollutant or pollutants being emitted;
- demonstrates the capture efficiency of a capture system; or,
- ascertains the destruction or removal efficiency of a control device used to reduce emissions at facilities subject to the requirements of the CAA.
A stack test does not include visible emission observation testing.
Stack tests provide a means to determine the concentration of emissions of an air pollutant at the point of release. These tests are conducted according to established procedures. Stack tests provide a snapshot of emissions during the period of the test. Samples are collected using probes inserted into the stack. Pollutants are collected in or on various media and sent to a laboratory for analysis. Pollutant concentrations are obtained by dividing the amount of pollutant collected during the test by the volume of the air sampled. The most accurate way of determining a source’s emissions is directly measuring the concentration of air pollutants in the stack gas.
The specific measures arrived at during detailed stack emissions tests are used to correlate emissions with the operating parameters of a facility. These parameters include feed rate, temperature, flow rate, voltage, and fan speed. The operating parameters recorded during a test become the required continuous operating parameters for the facility.
What the Numbers Mean
The stack gas leaving an incinerator contains certain levels of air pollutants which can be made to appear smaller if the total stack gas quantity is increased by adding non-pollutant gas to the stream. The volume fraction of any gas present in the stack gas can be reduced by adding air. That is why combustion equipment concentration emission standards are written with a specified amount of excess air, such as 7% oxygen (O2). These excess air corrections are important when comparing stack test results to the emission standards.
The emission standards are expressed as pollutant concentrations in gaseous emissions and include the reference conditions (such as temperature and pressure) that apply to these limits. These limits are expressed using different units of measurement, depending on whether the pollutant is in a solid or gas state. For example, a permit might limit the concentration of a gas such as nitrogen oxide (NOx) to 250 ppmdv (parts per million dry volume) corrected to 7% volume percent O2, the specified amount of excess air. The same permit could limit the concentration of particle pollutants such as dioxin or lead, using nanograms (ng) or milograms (mg) per dry standard cubic meter (dscm) of gas.
| Pollutant | Test / Frequency (years) | Test Date | Results | Limit |
|---|---|---|---|---|
| PM mg/dscm | 3 | 11/11/2009 11/08/2012 1/25/2013 | 2 25 20 | 34 34 34 |
| CO ppmdv | 3 | 11/11/2009 11/08/2012 1/25/2013 4/10/2013 | 20 2 5 3 | 40 40 40 40 |
| HCL ppmdv | 3 | 11/11/2009 11/08/2012 1/25/2013 4/10/2013 | 6 0.03 143 5 | 100 100 100 100 |
| Dioxin/furan ng/dscm | 5 | 10/18/2006 12/28/2011 2/15/2012 1/25/2013 | 2 616 2 6 | 125 125 125 125 |
| Dioxin/furan (TEQ) ng/dscm | 5 | 10/18/2006 12/28/2011 2/15/2012 1/25/2013 | 0.1 11.7 0.1 0.3 | 2.3 2.3 2.3 2.3 |
| SO2 ppmdv | 5 | 10/18/2006 12/28/2011 1/25/2013 | 6 1 10 | 55 55 55 |
| NOx ppmdv | 5 | 10/18/2006 12/28/2011 9/13/2012 1/25/2013 4/10/2013 | 250 336 438 122 177 | 250 250 250 250 250 |
| pb mg/dscm | 5 | 10/18/2006 12/28/2011 1/25/2013 | 0.004 0.001 0.02 | 1.2 1.2 1.2 |
| Cd mg/dscm | 5 | 10/18/2006 12/28/2011 1/25/2013 | 0.001 0.001 0.003 | 0.16 0.16 0.16 |
| Hg mg/dscm | 5 | 10/18/2006 12/28/2011 1/25/2013 | 0.004 0.04 0.005 | 0.55 0.55 0.55 |
Contacts
- Air Quality Compliance History: Jay Morris ([email protected]) (801) 536-4079
- Air Quality Permit: Jon Black ([email protected]) (801) 536-4047
- Health Related Concerns: Steve Packham ([email protected]), Toxicologist (801) 536-4036
- Solid Waste Permit and Compliance History: Roy Van Os ([email protected]) (801) 536-0245
Sources include the Environmental Protection Agency and the Michigan Department of Environmental Quality.