CEMS: An Overview

by | Aug 20, 2014 | CEMs

We’ve written an introductory overview to explain where Continuous Emissions Monitoring Systems (CEMS) are required, types of site that require CEMS and future requirements.

What are CEMS?

A CEM is a collection of products which are integrated into a system with the purpose of monitoring emissions to air within process applications.

Standard CEMS consist of a sample probe, a filter, sample line, gas conditioning system, calibration gas system, a series of gas analysers which reflect the parameters being monitored and Data Acquisition Software.

What is the Purpose of a CEM System?

CEMS are used as a means for a site permit to comply with stringent emission limits as regulated by the Environment Agency (EA).

CEMS are used to continuously collect, process and report data from industrial process operators that produce emissions to air.

Who Regulates the CEMS Market?

Environment Agency

Under the Environmental Permitting Regulations, the EA or local council will refer to European Legislation, the Industrial Emissions Directive (IED 2010/75/EU).

Sites are required to continually measure emission parameters from their chimney-stacks to ensure that they are compliant, as defined in their site permit.


In 1998, the EA introduced the MCERTS scheme to provide tighter controls for emissions to air including a technical specification that CEMS had to meet.

The criteria of the scheme included: detection limits, response time, linearity, zero and span drift etc.

A requirement of the MCERTS scheme enforces that any CEMS equipment used to monitor emissions must also be approved and certified.

Any new installation seeking a permit will need to comply with the Industrial Emissions Directive (IED).

The IED supersedes seven directives under one directive, creating a more simplified legislative framework:

  • Integrated Pollution Prevention & Control (IPPC)
  • Large Combustion Plant Directive (LCPD)
  • Waste Incineration Directive (WID)
  • Solvent Emissions Directive
  • And three Titanium Dioxide Directives

Under the new changes set by the IED, large combustion plants will be affected by the new emission limit values (ELVs).

This will be particularly significant to the future of coal fired power stations.

Where are CEMS Installed?

Most CEMS installations are utilised in applications where power is generated or where waste is burnt.

Fuel consisting of fossil fuels, gas or waste is burnt or heated at very hot temperatures to produce heat or power or both to generate electricity.

Which Emissions do CEMS Monitor?

Typical monitored emissions include: sulphur dioxide, nitrogen oxides, carbon monoxide, carbon dioxide, ammonia, hydrogen chloride, total organic compounds, particulates, and oxygen.

CEM systems can also measure temperature, air flow, flue gas opacity and moisture.

CEMS Processes:

  • Mass Burn Incinerators
  • Thermal Treatment – Gasification or Pyrolosis
  • Boilers
  • Turbines