How Does It Work ?
OVERVIEWA continuous emission monitoring system (CEMS) is the total equipment necessary for the determination of a gas or particulate matter concentration or emission rate using pollutant analyzer measurements and a conversion equation, graph, or computer program to produce results in units of the applicable emission limitation or standard. CEMS are required under some of the EPA regulations for either continual compliance determinations or determination of exceedance of the standards.
Why Emission Monitoring?
- Compliance with environmental legislation
- Collecting data for environmental impact assessments
- Collecting data to assess process efficiency and process control
- Assessing the performance of a pollution control device / scrubber
- In situ – analyzers located directly in the stack or duct.
- Extractive CEMS capture a sample from the duct or stack, condition the sample by removing impurities and water, and transport the sample to an analyzer in a remote, environmentally protected area.
Category Of Industries Covered
- Iron and Steel, Zinc, Copper
- Power Plants
- Chemical Industry
- Oil refinery and petrochemicals
- Food and beverage
- Distillery, Brewery, Malting
- Cement Manufacturing and grinding
- The Tribo-flow principle is an impact principle where a Sensor is placed in the path of the emissions, which are to be monitored.
- As the emission particles come in contact with the Sensor, a Tribo-flow signal is generated which is proportional to the emissions. This principle works only for Solid particles
- Since this principle is not affected by Liquid or Gas particles, it is particularly suitable for emission or stack monitoring.
- The Sensor of the Tribo Flow Stack Monitor/ Dust Monitor is mounted on the stack / duct and the existing S.P.M. level is determined using Thimble / Iso-Kinetic Process. The CEMS / Stack Monitor.
- Dust Monitor is then calibrated to continuously display the S.P.M. or Emission level in terms of mg/nm3 in an on-line manner. A 4 to 20 mA DC Analog Output is also provided for recording or control purposes & integration with the Central Control Room.
PartsThe CEMS is highly accurate and reliable.
- It consists of a Sensor with shielded cable and a remote Electronic Control Unit.
- The Sensor is a 316 stainless steel rod with Teflon Insulator.
- The Sensor is installed in the duct / stack where the emission particles are to be monitored / measured, as shown. As the particles flow in the duct / stack and strike the Sensor, a Tribo-electric current and a Tribo-electric voltage is generated. These signals are then conditioned, amplified & processed through sophisticated electronic circuitry and micro-processors and an Output Signal is generated which is directly proportional to the emissions flowing in the duct / stack.
- In this system the amount of light scattered by the particles in a specific direction is measured.
- These systems are available as Forward, side or backscatters are a function of the angle of scattered light that is measured by the detector
- Light scattering techniques (especially forward scatter) are capable of measuring dust concentrations several magnitudes smaller than that measured by transmissometers.
- When light is directed toward a particle, the particle may both absorb and scatter the light, deflecting it from its incident path.
Light Scattering Dust Monitoring depends on:
- The intensity of the scattered light which depends on .
- The angle of observation
- Its refractive index and shape
- The wavelength of the incident light.
Both in-situ and extractive analyzers of this type have been developed.
A light beam is passed through the Particulate Matter (PM) laden flue gas. Absorption and scatter attenuate the light. Light scatter analyzers measure the intensity of the scattered light at a predetermined angle to the beam direction.
The amount of light scattered in any direction is dependent on the size distribution and shape of the dust particles. Variations in the intensity of the light source and sensitivity of the detector are compensated for by the use of a reference beam, in the opposite phase to the measuring beam, onto the photoelectric detector.
- Scatter light measurement is a more sensitive measurement method for low dust loading.
- Scatter light analyzers measure only the scattered light and do not have to deal with the small variation in a large amount of transmitted light.
- Instruments can be based on the forward scatter, side scatter or back scatter principles, and can be in-situ, point in-situ or extractive.
- These type of analyzers can claimed to be more accurate for measure low PM concentrations of upto 1mg/m3.
Opacity meters measure the opacity, where the amount of light absorbed by particles crossing a light beam is measured and correlated to dust concentration.
In Opacity/Extinction instruments the amount of light reduction is measured directly, whereas in Ratiometric Opacity systems the ratio of the amount of light variation (flicker) to the transmitted light is measured.
Opacity meters are in – situ systems for PM measurement in stack. As with in-situ path systems for monitoring gaseous pollutants, transmissometers may be :
- Single-Pass Dust Monitor– single-pass designs use two identical senders and receivers on each side of the stack to alternatively transmit and receive light in order to increase sensitivity and reduce the effects of fouling of the optical surfaces.
- Double-pass Design – Double-pass types use a reflector on the opposite side of the stack or duct so that the light is transmitted twice through the flue gas.
Sophisticated analyzers that are equipped with on-line zero and span adjustment can be programmed to produce an output proportional to 1mg/m3based on the results of calibration measurements.
Transmissometers are usually of the cross duct design with a sender and receiver on opposite sides of the stack, or with a reflector to pass the light through the flue gas twice. Point in-situ analyzers have been developed in which the light source and detector are carried at opposite ends of a rigid tube. The tube contains a series of slots which allows the passage of PM-laden flue gas through the tube and hence between the light source and detector.
This arrangement overcomes some of the problems associated with the cross duct systems with regard to alignment of sender and receiver and differential expansion caused by temperature variations, and stack vibrations.
PartsThe light sources use includes..
- Filament bulbs
- Light emitting diodes and lasers
Adoption of opacity monitors for particulate matter monitoring in stacks is less universal due to their inapplicability to the lower levels of particulate now found in industrial processes. Industries where
Opacity monitors are well accepted for:
- Steel industries