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Buyer's Guide | OCEMS | Emission Monitoring
Extractive vs. In-Situ OCEMS (Online Continuous Emission Monitoring Systems)
by Rutvij Shah on 01/04/24
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Understanding the distinctions between extractive and in-situ CEMS is crucial for selecting the right system for your emission monitoring needs. Below is a detailed comparison presented in a tabular format for your convenience.
Generic Differences
| Aspect | Extractive CEMS | In-situ CEMS | |
| Sampling Method | Gas samples are extracted from the emission source and transported to an external analyzer. | Measurements are conducted directly within the stack or duct without extracting the gas sample. | |
| Measurement Location | Analyzers are located outside the stack, often in a controlled environment like an analyzer shelter. | Sensors or analyzers are installed directly into or across the stack, measuring emissions in real-time | |
| Space Requirements | Needs additional space for external equipment like shelters and conditioning units. | Minimal external space needed as equipment is mounted on or within the stack. | |
| Environmental Conditions | Analyzer panel is kept controlled environments hence NO impact of harsh environmental conditions. | Materials must be compatible with local environmental factors like monsoons and high humidity to withstand the harsh stack conditions. | |
| Applicability in Indian Context | Suitable for all industries in India as there is NO impact of different harsh environmental conditions. | Check required to ensure equipment must withstand local stack conditions. |
Technical Capabilities
| Aspect | Extractive CEMS | In-situ CEMS | |
| Suitability for Different Gases | Capable of measuring a wide range of gases, including those sensitive to temperature and pressure changes. | Best suited for gases that can be measured directly; may face challenges with sticky or corrosive gases. | |
| Response Time | Comparatively slower response but does not have any major impact as data sent to server is real-time. | Faster response with real-time or near real-time measurements. | |
| Influence of Stack Conditions | Less influenced by variations in stack conditions due to sample conditioning prior to analysis. | Measurements can be affected by temperature, pressure, and particulate levels within the stack. | |
| Compliance with Regulations | Widely accepted and proven technology that meets international and Indian regulatory standards. | Accepted by regulatory bodies but may require demonstration of equivalency and adherence to specific guidelines. |
Ease of Use
| Aspect | Extractive CEMS | In-situ CEMS | |
| Installation Costs | Simple probe installation but needs connection between the probe and shelter. | Specialized equipment required to mount OCEMS properly on the stack. | |
| Longevity | As analyzer is in shelter area, the equipment can easily run for 10+ years. | It is made to be durable but Harsh stack conditions can impact equipment longevity. | |
| Ease of Calibration | Easier calibration performed on external analyzers in controlled conditions. | Calibration can be more challenging; may require on-site calibration gases or built-in reference cells. | |
| Ease of Maintenance | Regular cleaning of filters from analyzer placed in shelter. | Optical surfaces of analyzer mounted on the chimney may require periodic cleaning. | |
| Ease of Spares Replacement | Very simple as the analyzers and sampling system are in shelter and can be easily replaced. | Complex and may require permissions from EHS team as person will have to climb on stack |
Recommendations for Indian Clients
By understanding these differences, you can make an informed decision that best suits your operational needs and compliance obligations in the Indian industrial context.
References:
Guidelines for Continuous Emission Monitoring Systems (CEMS) byCentral Pollution Control Board (CPCB), India
Performance Specifications for Continuous Emission Monitoring Systems byU.S. Environmental Protection Agency (EPA)
Stationary source emissions — Determination of the mass concentration of carbon monoxide, carbon dioxide, and oxygen byInternational Organization for Standardization (ISO)
Air quality — Certification of automated measuring systems — Part 3: Performance specifications and test procedures for automated measuring systems for monitoring emissions from stationary sources byEuropean Committee for Standardization (CEN)
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