Trends for portable emission analyzers
Nitrogen oxide (NOX) and carbon monoxide (CO) are produced as a result of common combustion processes. NOX is a precursor of ground level ozone, or smog, and is the only criteria pollutant that has increased in the United States since the Clean Air Act was established (U.S. EPA National Air Quality and Trends Report, 1997, Dec. 1998). Consequently, NOX has received more than its share of attention from the state and federal environmental regulatory agencies that are making a concerted effort to monitor, control and, hopefully, reduce it.
When it comes to knowing what is coming out of industrial stacks, we all have our own dilemmas. Maybe you are faced with a complicated or widely varying combustion process. Or, you have a stack that consumes more fuel and resources than it should. Perhaps you are spending an increasing amount of time on maintenance, and it has now become a "problem child" in your overall emissions inventory.
You are searching for a monitoring compromise, but one that contains the required degree of accuracy, is cost-effective and provides the added benefit of reducing operating costs. Do you schedule a session with a monitoring company and its "emissions trailer" to generate the emissions data you need? Although the data is usually very accurate, it does not always provide you with on-the-spot data when you need it.
Current technology for portable emission analyzers can embody all of these requirements. Portable electrochemical (EC) analyzers provide cost-effective and accurate measurements of NOX, CO, oxygen (O2) and sulfur dioxide (SO2). This means they provide valuable process knowledge that can affect product quality assurance and plant operating efficiency. Portable EC analyzers can also provide critical defensible emissions data that fulfills many state and federal record-keeping objectives.
Industry needs to find ways to sharpen its competitive edge to stay viable in the new global economy. With rules like credible evidence (40 Code of Federal Regulations (CFR) Sections 51.212, 52.12, 52.33, 60.11 and 60.12) now a reality, regulations target smaller and smaller combustion sources (Title V Periodic Monitoring, 40 CFR Sections 70.6 (a) (3), 71.6 (a)(3)). So how does a facility manager gain confidence in the monitoring and reporting of his or her process or total facility emissions? In many cases, portable EC analyzers provide an uncomplicated alternative to continuous emission monitoring systems (CEMs) or frequent third-party stack testing.
Portable emission analyzers also have the added benefit of being cross-utilized between maintenance and regulatory applications. Process engineers and maintenance personnel use the analyzer as an evaluation tool to better monitor process control. Many federal and state authorities recognize their use for facility compliance determinations.
Electrochemical technology
At the heart of portable emission analyzers are electrochemical (EC) cells. They are available to measure many different gases, including O2, CO, nitric oxide (NO), nitrogen dioxide (NO2), SO2 and hydrogen sulfide (H2S). These sensors are similar to a fuel cell in that they consist of at least two electrodes placed within an electrolytic solution. Sample pumps typically draw a sample from a source. Gases permeate through a membrane and diffuse into the cell. The gas reacts to the electrolyte through an oxidation or reduction reaction and generates an electrical current that is proportional to the concentration. This signal is then processed to display a readout in milliamps (mA), parts per million (ppm), percentage or as an emission standard (i.e., pounds per hour).
EC cells are inherently linear over their entire measurement range. They require little to no power to operate, making them ideal for portable applications. EC cells are robust, unaffected by most vibration and can operate over wide temperature ranges. One of the strongest attributes of an EC cell is its stability. New EC cells can last two to three years, depending on quality, and drift less than 5 percent in a year. Most importantly, they are inexpensive to purchase and maintain. Even NASA relies on EC cells in critical applications.
Unlike CEMS, which use chemiluminescence, EC-based portables measure NO2 directly. This eliminates NO2 underreporting attributed to NO/NO2 converter losses. The NO2 component of NOX can be substantial in low-NOX applications (the next generation of low-NOX turbines is expected to have a total NOX emission containing 50 percent to 70 percent NO2, ASME Report, No. 98554 1/11/99). When using proper testing procedures, well-designed portable analyzers can be more accurate than their reference testing counterparts (College of Engineering - Center for Environmental Research and Technology, Evaluation of Portable NOX Analyzer, Testo 350, June 18, 1997).
Use testing to control costs
Increasing efficiency and reducing the stack temperature by only a few percent on a 180 million Btu-per-hour boiler can mean fuel savings of more than $200,000 per year. The industry trend is toward reducing NOX emissions by installing low-NOX burners and selective catalytic reduction (SCR) converters. EC analyzers provide inexpensive insurance, as well as a more accurate and flexible means to verify performance of these expensive upgrades.
Compliance trends
Many states, including California, Pennsylvania, New York, New Jersey, Texas, Arizona, New Mexico, Colorado, Wyoming and Louisiana, have approved, or are in the process of approving, portable analyzers to solve some of their source testing dilemmas. Federal authorities are treating periodic monitoring with portable emission analyzers as a serious alternative to infrequent stack tests. Recent changes in the Title V guidance require periodic monitoring of smaller and smaller sources for documenting facility compliance. Collected monitoring information can provide a defendable or credible base of data. In many instances, performing periodic emission testing can defend and support parametric or predictive emission monitoring systems (PEMS) verification.
Economic globalization and ISO 14000 requirements drive industry to demand environmentally friendly processes. The World Bank has strict environmental requirements for funding corporate expansion abroad. The use of an affordable monitoring device is an absolute necessity for many developing nations. Portable EC analyzers operated according to approved test protocols are a cost-effective alternative to CEMS.
Questions of industry and regulators
Can portable emission analyzers be used to satisfy state or federal emission standards? In 1998, the U.S. Environmental Protection Agency (EPA) approved the use of portable EC analyzers for determinations of NOX, CO and O2 using Conditional Test Method CTM-30, which can be found at www.epa.gov/ttn/emc/ctm. CTM-30 was developed by the Gas Research Institute (GRI-96/0008), to provide a cost-effective reference-level method for its thousands of customers and service professionals. Many states are using this procedure, or a variation of it, to meet their districts' needs.
For more frequent testing, procedural requirements have been streamlined with minimal data quality compromise, in a new method proposed to EPA by the Institute of Clean Air Companies (ICAC). A consensus of industry and analyzer manufacturers developed this method to fill the gap between infrequent third-party stack testing and CEMS. This allows plant personnel to establish their own facility compliance through periodic testing. The ICAC method is under EPA review for a guidance document under periodic monitoring, and could be listed mid-year.
How often should a facility perform monitoring? If monitoring frequency is strictly for process or quality control reasons, it is guided by market factors. Fuel costs dictate how frequently combustion efficiency determinations are performed, and when adjustments are made. The return on investment (ROI) for an analyzer strictly based on fuel costs can be as short as a few weeks.
If monitoring is required for compliance with state or federal regulation it will vary greatly. EPA is currently working on a guideline to define frequency, based on factors such as location in a compliance or non-compliance area, permit level, compliance history and process variability. Many sites will be required to perform quarterly tests.
Emission analyzers certified by official agencies
Specs-manship is a game played around the world. Putting the best spin on the performance of products allows a company to sell more competitively.
When compliance is the issue, however, performance is everything. State and federal governments recognize this. Government-sanctioned verification programs level the playing field by performing independent analysis and evaluation of critical technologies.
California's South Coast Air Quality Management District (SCAQMD) pioneered the concept of equipment verification for the RECLAIM - NOX trading - program. Canadian and U.S. Environmental Technology Verification (ETV) programs quickly followed. The U.S. EPA ETV Advanced Monitoring Program is on track to present its recent evaluation of portable emission analyzers.
The testing program, performed by Battelle in Columbus, Ohio, verifies the operational accuracy of analyzers as approved by EPA ETV procedures. This verification program has been the most comprehensive and thorough to date. The performance results of verified analyzers will be posted on EPA's ETV Web site in June 1999 at wwww.epa.gov/etv/07/07_main.htm.
Gaining broad-based acceptance
Today's generation of portable EC analyzers satisfies today's needs of industry, state and federal regulators. The ruggedness, ease of use and low operating costs of EC analyzers is greatly appreciated by industry. They are an affordable energy management and compliance tool. Confidence in the analyzers' ability to provide accurate and reproducible data has been verified through EPA's ETV program. New testing methods for portables, such as ICAC's proposed method for periodic monitoring and CTM-30, provide a method to collect compliance data from a portable. Finally, regulators and industry have access to more accurate and more affordable emissions monitoring of NOX and other criteria pollutants.
This article originally appeared in the 05/01/1999 issue of Environmental Protection.