Tuesday, September 26, 2017

CEMS vs PEMS

electric power generating plant where CEMS are used
CEMS, "Continuous Emission Monitoring Systems" monitor the flue gas exiting to the atmosphere from a boiler, a furnace, or oven. Certain installations are subject to compliance with jurisdictional requirements for emissions at the state or federal level. CEMS are designed to comply with specific regulatory requirements for measuring and collecting data about specifically targeted pollutants, and installed by commercial and industrial plants to ensure operating compliance with applicable EPA or other jurisdictional rules and requirements.

In general concept, a CEMS samples flue gas, measures concentration of targeted pollutants, captures the measurements as data records, stores data records and produces reports of the emissions. CEMS may also incorporate other measurements and functions, such as as measuring and reporting fuel flow, its opacity and the gas moisture content.

CEMS usually have the same primary components.
  • Sampling probe 
  • Filter 
  • Sampling line 
  • Sample conditioning 
  • Calibration gas 
  • Gas analyzers for specific monitoring tasks 
Common targeted measurements include:
  • Carbon dioxide 
  • Carbon monoxide 
  • Airborne particulate 
  • Sulfur dioxide 
  • Volatile organics 
  • Mercury 
  • Nitrogen oxides 
  • Hydrogen chloride 
  • Oxygen
  • Liquid or gaseous fuel flow
The US Environmental Protection Agency requires a data acquisition system and handling process to collect and report the data, which CEMS provides. CEMS must operate and provide data continuously in order to assure operational compliance and meet record keeping requirements.

Around the world, air quality standards require various levels of emissions monitoring to assure that excessive levels of harmful chemicals are not spread throughout the environment. The monitoring of emissions involves the application of sensors and processing equipment to provide information regarding the amount of specific pollutants discharged by a plant or process.

A continuous emission monitoring system (CEMS) consists of equipment necessary for determining the emission rate of targeted pollutants, using analyzer measurements and subsequent data processing to provide results in units pertaining to an emission limitation or standard. This type of monitoring system is applicable where required by statute or regulation, but can also be used to provide valuable combustion or process efficiency data to plant operators.

A predictive emissions monitoring system (PEMS) employs an empirical computer model which will relate the inputs of a combustion system (air and fuel) to the emissions produced by the process. Once the model is established for a particular installation, the emissions can be predicted continuously with accuracy in the range of direct measurements used in CEMS. There are instances where this type of system will fulfill governmental compliance requirements, in place of CEMS. PEMS can also be deployed as a complement to a hardware based CEMS. Plant conditions and an engineering evaluation will determine the best implementation of emissions monitoring equipment and systems to meet regulatory requirements and provide the level of risk management needed.

Share your emissions compliance and monitoring requirements with combustion and instrumentation experts. Leverage your own process knowledge and experience with their product application expertise to develop effective solutions.