Is the Predictive Emission Monitoring System a Better Alternative than CEMS?

 A predictive emission monitoring system is the total equipment necessary to determine gas concentration or emission rate using a processor control device operating parameter measurements and a conversion equation, graph or computer program that would be able to produce results in units of the applicable emission limitation or standard. The predictive emission monitoring system (PEMS) is being proposed recently as an alternative to hardware continuous emissions monitors (CEMS) due to lower costs of installation and maintain and the ability to provide information on emissions under various conditions. PEMS can be configured, delivered and installed within 30 to 45 days. All that it requires is the installation of a single computer with the DAS/PEMS software installed and interfaced to a boiler control system.

Differences between CEMS and PEMS

  • Aside from the lower capital costs of predictive emission monitoring system, it has lower startup costs, typically 1 day using DAS. CEMS is more complex since it requires various skill trades (electrical, mechanical, computer) for the installation of probes, ports, umbilical trays CEMS rack, gas cylinders, cylinder racks, gas tubing runs, drain and exhaust lines including all interconnecting wirings. Actually the installation of CEMS might tend to cost more than the equipment.
  • PEMS has higher data availability of at least 100% and it does not rely on any one process input to maintain system uptime or accuracy of emissions quality. PEMS technology uses numerous inputs on a robust database and even PEMS failure the data from DCS input for the prediction are still available within the DCS and can easily be retrieved and calculated once PEMS is brought back online. With the CEMS analyzer, once a critical component fails, the system has no capability for retrieval which will require data substitution when required.
  • PEMS do not require EPA protocol calibration gases, piping, wiring, gas regulators or software to operate the auto calibration system. On the other hand, CEMS require calibration systems. The cylinders of calibration gases also require safe storage and supplier documentation.
  • PEMS do not have requirements for preventive maintenance except for a periodic cleaning of the computer. However, the process instruments that provide data to predictive emission monitoring system must be calibrated and regularly maintained. CEMS require consumable and spare part inventories to maintain uptime. Only trained staff can provide maintenance to the CEMS equipment.
  • PEMS does not require duel range analyzers since it can measure the full dynamic range of emission from a source, including start-up to shutdown. CEMS may require dual ranges to cover the entire range of operations. The system may require additional calibration gases, hardware and software.

Advantages of predictive emission monitoring system

  • Lower costs of regulatory compliance
  • Local and remote access since PEMS can be installed wherever access is required
  • Improved operational planning for daily, weekly, monthly and annual planning
  • Potential enabler for emission credit trading
  • Tailored notifications that provide specific recommended actions and guidance
  • Enhanced condition monitoring
  • 24/7/365 emission prediction to account for engine performance, degradations, variations in ambient conditions and changes in operating conditions. 

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