Types of Continuous Emissions Monitoring Systems (CEMS) Analysers

Introduction

CEMS Analysers use a variety of technologies to measure emissions data such as lasers, infrared, ultra violet, electrochemical cells and light. These technologies allow emissions data to be accurately measured even when opeating in hostile environments. Once measured, the data can be sent to a Data Acquisition and Handling System (DAHS) where it can be processed, stored and reported on.

Types of CEMS Analysers are as follows:-

Fourier-transform infrared (FTIR)

Equipment built on FTIR technology is commonly used in the emissions monitoring industry. FTIR gas analysers are built to identify and quantify gaseous compounds by their absorbance of infrared radiation. When exposed to infrared light, the gaseous compound will produce a unique infrared spectrum. The infrared spectrum of a gas is similar to a fingerprint in that each component has its own unique molecular structure or combination of atoms. This enables each gas to be identified and measured

Ultraviolet Visible Spectroscopy (UV VIS) CEMS Analysers

Ultraviolet spectroscopy is used by UV CEMS analysers to measure and calculate gas emissions. UV absorption spectroscopy is the technique used to examine the full UV spectrum and calculate gas emissions concentrations. UV light is directed into the gas and the analyser's spectrometer measures the amount of light absorbed by the gas allowing the accurate reporting of each gas concentration.

Tuneable Diode Laser (TDL) Gas Analysers

Tuneable Diode Laser Gas Analysers use tuneable diode laser absorption spectrometer (TDLAS) technology to measure the amount of a laser’s light that gets absorbed when it travels through a gas. By measuring the dilution due to the infrared absorption (as defined by Lambert Beers' Law), gases such as carbon monoxide, methane, ammonia, moisture, carbon dioxide can be accurately measured in seconds. Not only is this technology fast but maintenance is low because the sensor does not come into contact with any gases. As a result, it is ideal for use under extreme conditions including high dust, temperature, pressure and highly corrosive environments.

Non-Dispersive Infrared Sensors (NDIR)

NDIR is the abbreviation for Non-Dispersive Infrared which is used in the CEMS Industry to detect the composition and concentration of various gases. No prism or optical elements are present which is why this sensor is called non-dispersive (i.e. defration is not used). Individual gases have their own levels in which they absorb specific frequencies of infrared light. The NDIR sensor measures the concentration and composition by analysing the frequencies and extent of light absorbed.

Electrochemical CEMS

An analyser incorporating electrochemical cells uses chemical reactions to generate electrical currents (energy). The electrical current generated is analysed and is directly proportional to the gas concentration being measured. Electrochemical CEMS analysers are well suited when measuring explosive or volatile gases such as hydrocarbons and VOC’s. Over time, the chemical stimulus in the electrochemical cells is consumed and the make-up of the cells change. Therefore, recalibrations can be used ensure the accuracy of the measurements is maintained.

Forward scatter laser dust monitors

Forward scatter laser dust monitors incorporate a laser light source and measures the scattering light levels when dust is in the lasers path. The intensity of the forward scattering of light is measured and proportional to the dust concentration.

Backward scatter laser dust monitors

Backward scatter laser monitors are housed in a single unit where a laser beam is sent into the dust particles. The intensity of the scattering light returned backwards provides an accurate measure of the dust concentrations

Optical Dust Monitors

Optical Dust Monitors use a visible light source which passes between a transmitter and receiver. The levels of light which hit the receiver will be analysed to measure the opacity and dust within the location being monitored. Where vapour or liquid droplets are present, inaccurate readings can be encountered because light beams can refract or reflect when moister is present.

Extractive Dust Monitors

Extractive Dust monitors extract wet samples and expose them to high temperatures to prevent moisture influencing the accuracy of the measurements. Once the sample is dry, a light beam is used and the scattering affect will accurately measure the dust concentrations.