How Does Continuous Emissions Monitoring Work
Continuous emission monitoring systems (CEMS) are used as a tool to monitor the effluent gas streams resulting from combustion in industrial processes. CEMS can measure flue gas for oxygen, carbon monoxide and carbon dioxide to provide information for combustion control in industrial settings. They are also used as a means to comply with air emission standards such as the Central Pollution Control Board (CPCB), SPCBs (State Pollution Control Boards) and PCCs (Pollution Control Committees) permitted emission standards.
How Does CEMS Work
CEMS typically consist of analyzers to measure gas concentrations within the stream, equipment to direct a sample of that gas stream to the analyzers if they are remote, equipment to condition the sample gas by removing water and other components that could interfere with the reading, pneumatic plumbing with valves that can be controlled by a PLC to route the sample gas to and away from the analyzers, a calibration and maintenance system that allows for the injection of calibration gases into the sample line, and a Data Acquisition and Handling System (DAHS) that collects and stores each data point and can perform necessary calculations required to get total mass emissions. A CEMS operates at all times even if the process it measures is not on. They can continuously collect, record and report emissions data for process monitoring and/or for compliance purposes.
Importance Of CEMS
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 CPCB regulations for either continual compliance determinations or determination of exceedances of the standards. The individual subparts of the CPCB rules specify the reference methods that are used to substantiate the accuracy and precision of the CEMS.
Performance Specifications are used for evaluating the acceptability of the CEMS at the time of or soon after installation and whenever specified in the regulations.
A predictive emission monitoring system (PEMS) is the total equipment necessary for the determination of a gas concentration or emission rate using process or control device operating parameter measurements and a conversion equation, a graph, or computer program to produce results in units of the applicable emission limitation or standard. The CPCB is studying the applicability of PEMS for NOx compliance determinations for various sources. A draft protocol for assessing the accuracy and precision of PEMS has been developed and is expected to be proposed sometime in the near future.
GENESIS OF PROBLEM
The highly polluting industries such as Power, Cement, Iron & Steel, Chloralkali, Pharmaceuticals, Fertilizers, Refineries, Pesticides, Distilleries, Sugar, Pulp & Paper, Textile, Tanneries, and other categories of industries emit particulate matter and other gaseous pollutant into atmosphere. These industries also release pollutants through effluent discharge.
The SPCBs (State Pollution Control Boards) and PCCs ( Pollution Control Committees) have prescribed standards for various pollutants emitted/ discharged by the industries as notified under the Environment (Protection) Act, 1986.
The compliance monitoring needs to be strengthened to ensure that emissions/ effluent complying with the stipulated norms are only discharged by the industries. With rapid industrialization, it is becoming a need and necessity to regulate compliance by industries with minimal inspection of industries. Therefore, efforts need to be made to bring discipline in the industries to exercise self-monitoring & compliance and transmit effluent and emission quality data to SPCBs/PCCs and CPCB on continuous basis.
For strengthening the monitoring and compliance through self-regulatory mechanism, online emission and effluent monitoring systems need to be installed and operated by the developers and the industries on, 'Polluter Pays Principle'.
Various technologies are available for monitoring the particulate matter and gaseous emission from the stack of industries and common treatment facilities in terms of the parameters specified in the directions issued by CPCB.
Analyzer Systems
Optimum solutions to the measurement and monitoring of various pollutants like SO2,NOx, CO, CO2, NH3, HCI, HF, THC, Mercury, etc. solutions on technology platforms are Dilution Extractive, Hot Extractive, or In-situ measurement.
Dilution System
Dilution extractive CEM systems are the most effective way to monitoring flue gas emissions as these utilize built in modules based on NDIR technology for CO, Chemiluminescence technology for Nox & UV Fluoroscent Technology for SO2. Minimizes time spent on site performing maintenance through superior remote instrument control, diagnostic viewing and calibration through dilution technique.
In this technique the sample is extracted and diluted with zero air in the probe. Since, dilution takes place within the probe, there is no need for a heat-traced sample transportation line.
Hot - Wet Extraction System
Hot Extractive CEM Systems are most popular to meet your gas analysis needs-for environmental monitoring, with Simultaneous and Continuous Measurement of the Concentration of up to 5 Gas Components in single Analyzer assembly. Built-in NDIR Module for each gas is placed in a single enclosure's Systems Provided with Two Range Selection with Automatic, Manual & Remote Calibration
In this technique sample is extracted from stack / duct through a heated filter. Blow back arrangement provided for cases where there is high dust load. Extracted sample is transported using heat-traced line to the sampling system.
In-Situ Instruments
An in-situ gas analyzer sits directly at the measurement point on the stack / duct. Both, cross duct and probe measurement techniques are available. Measures corrosive components like HCL, NH3, H2S, HF and also O2, CO+CO2, CH4 with ease. This method has Negligible interference by other gas components and high-speed response.
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