Stack Testing:
Stericycle Inc.

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

Sources include the Environmental Protection Agency and the Michigan Department of Environmental Quality.