has abstract
| - 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 flue gas for oxygen, carbon monoxide and carbon dioxide to provide information for combustion control in industrial settings. They are also used as a means to comply with air emission standards such as the United States Environmental Protection Agency's (EPA) Acid Rain Program, other US federal emission programs, or state permitted emission standards.CEMS typically consist of analyzers to measure gas concentrations within the stream, equipment to direct a sample of that gas stream to the analyzers if they are remote, equipment to condition the sample gas by removing water and other components that could interfere with the reading, pneumatic plumbing with valves that can be controlled by a PLC to route the sample gas to and away from the analyzers, a calibration and maintenance system that allows for the injection of calibration gases into the sample line, and a Data Acquisition and Handling System (DAHS) that collects and stores each data point and can perform necessary calculations required to get total mass emissions. A CEMS operates at all times even if the process it measures is not on. They can continuously collect, record and report emissions data for process monitoring and/or for compliance purposes. The standard CEM system consists of a sample probe, filter, sample line (umbilical), gas conditioning system, calibration gas system, and a series of gas analyzers which reflect the parameters being monitored. Typical monitored emissions include: sulfur dioxide, nitrogen oxides, carbon monoxide, carbon dioxide, hydrogen chloride, airborne particulate matter, mercury, volatile organic compounds, and oxygen. CEM systems can also measure air flow, flue gas opacity and moisture. A monitoring system that measures particulate matter is referred to as a PEMS. 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. SO2 emissions are measured in pounds per hour using both an SO2 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. (en)
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