We all know that air quality regulations are designed to reduce the amount and/or types of air pollutants released into the atmosphere. But what’s less well-known is how the emitted air pollutants are measured.
There are two ways to go about this. The first is by taking a “point in time” sample and extrapolating long-term figures. The second method is what we’ll focus on in the rest of this post: continuous measurement.
While violations are a facility manager’s biggest bugbear, a close second is a CEMS (pronounced sems), or continuous emission monitoring system. “Continuous” is the reason for the headaches: Anytime any process occurs on a continuous basis, there’s bound to be gremlins that muck up the works. In next week’s post, we’ll review some of these gremlins in more detail. But for now, here’s a quick CEMS overview.
What Is a CEMS?
A CEMS is a system designed to measure and record emissions from a piece of equipment. Components of a CEMS can include sample conditioners, sample probes, pumps, sample lines, emissions analyzers, calibration gases, etc.
In practice, a complete CEMS is purchased from a systems integrator that designs and assembles a system specific to your needs. Because of this custom-made nature, there’s a near limitless number of CEMS combinations that can exist.
Each CEMS is built to meet certain EPA-defined criteria, called “performance specifications.” Air districts, including the AQMD, will often add requirements of their own, so the CEMS needs to comply with both agencies’ regulations.
Although there are several types of CEMS, the most common is a non-dilution extractive-type system — which is just a fancy term for a system in which a non-diluted part of the exhaust gas is extracted from the stack via a sample pump, then sent through a conditioning system before being analyzed by an emissions analyzer.
Do I Need a CEMS?
In all our years of environmental consulting, we’ve rarely had a client who voluntarily installed a CEMS unit. In almost every single case, the installation was done specifically to comply with air-quality regulations.
Some of the more common AQMD rules that require a CEMS are:
- Rule 1110.2, for internal combustion engines
- Rule 431.1, for combustion equipment using a fuel other than natural gas
- Rules 2011 and 2012, for “major source units” within the RECLAIM program
There are the rare cases where folks install a CEMS in order to collect data about their process, such as part of a control system to monitor or control a process — which is really just a sort of self-regulation.
Does a CEMS Need a Permit?
Per Rule 201, a CEMS does not require permit, as it isn’t creating emissions, only measuring them. However, a CEMS does need to be certified — a process that is far less onerous than getting a permit.
The purpose of the certification process is to ensure that the system collects the most accurate data possible, thus ensuring that your process is in compliance. In the AQMD, Form ST-220 is used to apply for CEMS certification — but don’t let the name fool you. Although it’s “just a form,” it still requires a good deal of information, which could be anything from drawings of the exhaust stack, make/model of the equipment, measurement ranges, etc.
Once the completed Form ST-220 is submitted, an AQMD engineer will review the material and then issue an initial certification. At that point, you can install the CEMS and start a series of tests to ensure that the system is accurate and operating properly. Of these, the most important is the relative accuracy test audit (RATA), in which a facility’s CEMS is compared to a third-party testing company’s reference system.
In next week’s newsletter, we’ll talk about some of the common problems associated with operating a CEMS — and what you can do to prevent or minimize them.
