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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

Assess Environmental Conditions

Consider local factors such as temperature extremes, dust levels, and humidity, which can affect system performance

Regulatory Requirements

Ensure the chosen system meets all CPCB norms and can provide data in the required formats.

Maintenance Capabilities

Evaluate your facility's ability to maintain complex systems.

Cost-Benefit Analysis

Weigh the initial investment against long-term operational costs and benefits.

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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