Continuous Emission Monitoring System (CEMS)

GAS ANALYZERS

WORKING PROCESS

How Does It Work ?

OVERVIEW

A 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 determination(s) 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 India together CPCB, NGT & MoEF have collaborated and framed a certain set of guidelines and parameters for monitoring emission from industries.

Gas Analyzers and Monitoring Technologies

A continuous emission monitoring system(s) (CEMS) is an integrated system that demonstrates source compliance by collecting samples directly from the duct or stack discharging pollutants to the atmosphere. A CEMS consists of all the equipment necessary for the determination of a gas or particulate matter concentration or emission rate. This includes three basic components:
  • Sampling and conditioning system
  • Gas analyzers and/or monitors, and
  • Data acquisition system (DAS) and controller system.
A CEMS can be designed to monitor a single pollutant or multiple pollutants and waste gas stream parameters. Gaseous compounds, particulate matter, opacity, and volumetric flow rate are typically monitored by CEMS. CEMS are divided into two major categories, extractive and in situ.
  • 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.

Anodyne Services

At Anodyne, we offer Emission Monitoring System for process, boilers, coke ovens, furnaces (both coal and electricity based), Cement Kilns and other applications.
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

Available Technologies

We offer tailor-made and customized solutions for analysis of gases, dust measurement.
Our gas Analyzers employ:
  • Cold dry extractive principle, coupled with
  • Particulate filters (Sintered and Pleated Filter)
  • Sample dryers (Dehumidifiers and Dessicant Dryers)
  • Peltier Cooling System at Probe
Our Gas Analyzers employ various technologies for gas specific measurements, multi-gas measurement. Years of proven research, constant endeavor in Analytics has catered us to provide industry specific Gas Monitoring and Detection Solutions. The technologies available are:

Chemiluminiscence

What Is It?

Chemiluminescence is the production of light from a chemical reaction. Two chemicals react to form an excited (high-energy) intermediate, which breaks down releasing some of its energy as photons of light to reach its ground state.

A + B ->AB* ->Products + Light
Excited Intermediate

For Gases

This light emitting detection principle is suitable for Gases:
  • Nitrogen Oxides (NOx, NO, NO2)
  • Ammonia (NH3)

Technological Description

The chemiluminescence method offers the best results whenever the difficult analysis of the tiny molecule NO in gases is required.
Chemiluminescence method allows detection of extremely low concentrations of NO, being not only fast but also very sensitive and NO specific.
The reaction scheme of NO and O3 by chemiluminescence is as follows:

NO + O3 NO2+ O2 [ 1 ]
NO + O3NO2* + O2 [ 2 ]
NO2*  NO2 + hv[ 3 ]
NO2* + M  NO2+ M [ 4 ]

The radiation emission is in the wavelength between 600 and 3000 nm with an intensity maximum at approximately 1200nm. This chemiluminescence signal is detected photo-electrically.

Advantageous Factors:
  • Band- Pass filters for passage of only those wavelengths, which are emitted by NOx and NH3 molecules separately.
  • Signal is proportional to the NO concentration of the sample gas.
  • Sensor doesn’t come in contact with gas
  • Inbuilt Ozone generator using fresh air from atmosphere
  • Inbuilt NO2 – NO converter
  • Excess Ozone Removal
  • Dust removal
  • Water vapour removal

NDIR

What Is It?

Infrared Spectroscopy, is a multi-gas measurement technology, that works as:

    • NDIR (Non-Dispersive Infrared) measurement that allows all light to pass through sample.

  • Dispersive Infrared measurement for passage of selected wavelengths to pass through sample.Dispersive IR detectors are usually used in benchtop analytic instruments for their ability to scan a broad wavelength range.

For Gases

NDIR is a versatile and highly recommended monitoring technique, considering range of gases that can be detected, the accuracy, life of the sensor, non-interaction of sensor with gas make this technique a satisfactory monitoring technique.
Non Dispersive Infra-Red technique is highly specific as it chooses gas specific infrared absorption wave length of the target gas by cutting off all other wave lengths. This technique is cost effective and reliable for measurement of gas concentration in parts per million range.

Considering these advantages, NDIR is available for:
  • Sulphur Dioxide (SO2)
  • Nitrogen Oxides (NO, NO2)
  • Carbon Dioxide (CO2)
  • Carbon monoxide (CO)
  • Water vapor (H2O)

Technological Description


NDIR is based on absorption of infrared radiation, for specific wavelengths when a sample of gas is exposed to IR radiation.
The basic components that form a part of this technology and instrument are:

  • Two identical tubes, namely sample gas flow cell and reference tube.
  • IR radiation source or lamp
  • IR detector
  • Gas filter

Continuous emission of IR radiation to the gas flow cell (with gas sample) and reference cell (with reference gas generally N2) generates two separate signals, which are detected by the IR detector.

The difference of the two signals, is directly proportional to amount of absorbing gas, resulting in ppm levels/concentration of gas.

Electrochemical

Electrochemical Description

Electrochemical gas sensors date way back to the 50’s. These sensors have been used for gas detection for flammable and toxic gases, and have been in application for portable and fixed gas detection.

With wide range of applications for gas detection, lower cost and ease of operation, electrochemical gas sensors have gained popularity in the field of Continuous Emission Monitoring. Analyzers based on electrochemical principle, are significantly cost efficient, and support ease of maintenance, however the life of the sensor for continuous measurement is around 1 year, which is significantly very less as compared to NDIR sensor life of 3 – 5 years and UV sensor (life > 5 years).

However, with respect to current economical instability and plunge, this technology has become widely applicable for low cost options.

What Is It ?

An electrochemical gas sensor is a chemical base sensor, which consists of a membrane, sensing and reference electrodes, electrolyte and maybe a filter to prevent unwanted gases to enter.

In this type of sensing mechanism, the sensor comes in contact with the type of gas to be sensed / monitored or detected, thus not so advantageous over NDIR and UV based sensing technology.

Please refer to the next tab for the gases that can be monitored.

For Gases

The low cost of sensor, flexibility in application, wide range in detection makes an EC sensor adept to detect various gases, like:

  • Sulphur dioxide (SO2)
  • Nitrogen Oxides (NOx)
  • Carbon Monoxide (CO)
  • Oxygen (Zirconia based and amperometric)
  • Hydrogen Chloride gas (HCl)
  • Hydrogen fluoride (HF)
  • Hydrogen Sulphide (H2S)
  • Ammonia (NH3)
  • Chlorine (Cl2)
  • Hydrogen (H2)

TDLAS (Tunable Diode Laser Absorption Spectroscopy)

Technological Description

TDLAS (Tunable Diode Laser Absorption Spectroscopy) fibre coupled monitor measures gas concentration over an open path. The monitoring system consists of a rack mounted integrated transmitter/receiver known as the Central Control Unit (CCU), an open path transceiver head or duct probe, and a remote, passive retroreflector array.

The laser signal from the Multi-Channel System is sent through a fibre optic cable to the remote head or duct probe where it is emitted and propagates through the atmosphere to the retroreflector. It then returns to the cell where it is focused on to a photo diode detector. The detector converts it to an electrical signal which travels through a coaxial cable to the electronics in the Multi-Channel System.

A portion of the laser beam is passed through an on board reference cell to provide a continuous calibration check. These two optical signals are converted into electrical waveforms which the computer processes to determine the actual concentration of gas along the optical path. The computed gas concentration is then displayed on the rear panel of the instrument, and can be transmitted to a computer where the data can be collected, stored, and graphically displayed.

For industrial applications a 4-20mA, serial, MODBUS, TCP/IP, and dry-contact relay outputs are also available.

For Gases

TDLAS in-situ measurement is available for various gases, as mentioned below:

  • Methane
  • Carbon Monoxide
  • Carbon Dioxide
  • Hydrogen Sulphide
  • Hydrogen fluoride
  • Hydrogen cyanide
  • Hydrogen chloride
  • Nitrous Oxide
  • Water vapour
  • Ammonia
  • Acetylene
  • Ethylene