Continuous emissions monitoring system
Continuous emission monitoring systems (CEMS) are used as a tool to monitor the effluent gas streams resulting from combustion in industrial processes. CEMS can measure
The standard CEM system consists of a sample probe,
In the U.S., the EPA requires a data acquisition and handling system to collect and report the data. Measurements of concentration can be converted to mass/hour by including flow rate measurements. The types of gases being measured and the calculations required are dependent upon the source type and each source type has its own subpart under 40 CFR part 60 and part 75.[4] SO
2 emissions are measured in pounds per hour using both an SO
2 pollutant concentration monitor and a volumetric flow monitor. For NOx, both a NOx pollutant concentration monitor and a diluent gas monitor are used to determine the emissions rate in weight per volume or weight per heat value (for example lbs/million Btu, lbs/ft3, kg/kWh or kg/m3). Opacity measurements are sometimes required, depending on the source type. CO2 measuring is sometimes a requirement, however if monitored, a CO2 or oxygen monitor plus a flow monitor should be used. The DAHS must be able to collect, record and store data, usually at 1-minute intervals. For compliance purposes, a DAHS must be in continuous operation 24/7/365 even when no process is on. For a valid measurement, the DAHS must record at least one reading every 15 minutes for 3 out of 4 quarters. The readings are then averaged hourly.[5]
Operation
A small sample of flue gas is extracted, by means of a
Another sample extraction method used in industrial sources and utility sources with low emission rates, is commonly referred to as a "dry extractive", "hot dry" extractive, or "direct" CEMS. The sample is not diluted, but is carried along a heated sample line at high temperature into a sample conditioning unit. The sample is filtered to remove particulate matter and dried, usually with a chiller, to remove moisture. Once conditioned, the sample enters a sampling manifold and is measured by various gas analyzers, typically NOx and O2 (and sometimes CO) for combustion turbines and engines running natural gas or diesel. NOx analyzers typically work using chemiluminescence. O2 analyzers a magnetic field which attracts O2 to measure the concentration. The O2 causes movement of a suspended mirror within the analyzer which then changes the amount of light being reflected by that mirror onto a photocell. The amount of current required to move the mirror back to center is proportional to the O2 concentration. The ability to measure % oxygen in the sample is required to perform the required calculations.
Quality assurance
Accuracy of the system is demonstrated in several ways. An internal
The EPA also allows for the use of Continuous Emissions Monitoring Calibration Systems which dilute gases to generate calibration standards.
In the U.S., periodic evaluations of the equipment must be reported and recorded.[5] This includes daily calibration error tests, daily interference tests for flow monitors, and semi-annual (or annual) RATA and bias tests.[8] CEMS equipment is expensive and not always affordable for a facility. In such cases, a facility will install non-EPA compliant analysis equipment at the emissions point. Once yearly, for the equipment evaluation, a mobile CEMS company measures emissions with compliant equipment. The results are then compared to the non-compliant analyzer system.[9]
References
- ISBN 0-9634570-1-2.
- ISBN 978-0471292272.
- United States Code of Federal Regulations, Title 40, Part 60, 63, 72, and 75
- ^ "Federal Register :: Request Access".
- ^ a b "Continuous Emissions Monitoring Fact Sheet". US EPA. Archived from the original on February 11, 2009.
- ^ "Tier 2 Generation Capital Projects". www.pnm.com. Retrieved 23 February 2016.
- ^ "EPA Traceability Protocol for Assay and Certification of Gaseous Calibration Standards, "EPA-600/R93/224. Revised September 1993.
- ^ "Specifications and Test Procedures for Total Hydrocarbon Continuous Monitoring Systems in Stationary Sources" (PDF). www3.epa.gov. Retrieved 23 February 2016.
- ^ "Flue Gas & Emissions Analyzers | Nova Gas". Nova Gas. Retrieved 2016-02-23.