Air Pollution Control Innovations

Three Things to Do Before a Stack Compliance Test

Posted by Andy Olds on Mon, Nov 02, 2015 @ 05:00 AM

Find me on:

Compliance testing often brings anxiety to environmental managers.  Testing is expensive and can comprise a significant fraction of the environmental operating budget.  Planning takes several months, often culminating in a tight testing window with long days and unforeseen delays.  And always looming is a dreaded phone call of a failed test.  What three things should environmental managers do to ensure a successful compliance test?


  1. Calibrate your control instruments

Manufacturers use complex instruments to ensure that their equipment meets its performance objectives.  These instruments must remain calibrated for the control equipment to perform properly. pH sensors, ORP probes, flow transmitters and conductivity sensors ensure optimal acid gas removal.  RTDs and thermocouples are vital to reliable operation for thermal oxidizers, condensers and reheaters.  Pressure transmitters provide important information for the performance of Venturis, and the condition of baghouse, carbon beds and packed beds.

The most common deficiency reported in our service call database is an out-of-calibration instrument.  Make sure that your instruments calibration is up to date, and check its performance a month prior to compliance testing to ensure you have the time to order a replacement instrument if required.

  1. Inspect and clean your equipment

Environmental control equipment typically faces an array of upset conditions.  Waste streams change or cycle through daily, weekly or seasonal disruptions.  Auxiliary equipment fails leading to changes in the quality of makeup water, instrument air, or power.  Repeated startups and shutdowns lead to transient states of substandard performance.  The struggle to keep environmental compliance equipment operational at all times leads to an "emergency-only" attitude towards preventive maintenance.  All of these factors lead to degradation of equipment and instruments.

Ahead of compliance testing, it is important to challenge the operations staff to inspect and clean the equipment.  Ensure instruments do not have buildup that dampens response time.  Confirm pressure drops across filters, strainers, spray nozzles are at design conditions; high pressures may be indicative of fouling.  Make sure consumables such as pH probes and filter bags are new and up to date.  Check for air ingress; most compliance tests measure the oxygen content of the gas to ensure that emissions are not artificially lowered by dilution air.  Clean sumps, separators and nozzles during regular shutdowns.  Ensure that your emissions are limited to that which occurs during steady state operation, and not from old emissions that have built up on the internal surfaces of your equipment.

  1. Interview your stack tester

The EPA has well-developed procedures for every type of emission test.  However, with ever lowering standards, stack testers are forced to push their instruments and apparatuses to their technological limit in order to accurately measure emissions.  Stack testers have found ways to extend these limits, but the difference between emissions and noise is narrowing.  Minimizing the noise, and understanding the methodology of the stack test, will ensure you and your equipment are well-prepared.

For all stack tests, ask the following:

  • What EPA procedures will you be using?
  • Are there any known interferences for the procedures?
  • What is the experience level of the stack test operators with each procedure?
  • Are you prepared for lower than expected gas flow rates, greater than expected dilution, or other flue gas variances?

For initial testing:

  • What is your expectation of the non-detectable limit with the procedure provided?
  • Is the expected non-detectable limit sufficiently low to provide accuracy below my emission limit?
  • How do you intend to reliably rig and stabilize your instruments?
  • What can I do to give the stack testers the best opportunity to provide reliable data?

If your permit has changed since your last stack compliance test:

  • Have you accounted for my new permit requirements, and how has that changed your testing protocol?

Getting ready to perform a stack compliance test?  Contact Envitech Service for a site visit to calibrate your instruments and inspect your equipment.

Contact Envitech Service

Topics: Stack Testing