Calibrating Continuous Emissions Monitoring (CEM) gas analyzers is crucial for ensuring the reliable measurement of emissions from industrial smokestacks and maintaining compliance with environmental regulations. Using a CEM calibration system can create precise and dependable emission measurements. Read our guide to understand the key steps and requirements for calibrating CEM gas analyzers with a CEM calibration system.

CEM Calibration Systems

CEM calibration systems are computerized gas dilution devices that allow for the dilution of a single high-concentration cylinder of span gas to the low levels required for calibrating the analyzers. These systems precisely dilute certified gas cylinders to generate an infinitely variable range of concentrations.

Benefits of CEM Calibration Systems

  • Cost Savings: Significant cost savings can be obtained through CEM calibration systems. They can cut gas cylinder usage and rental costs by up to 60%. Fewer cylinders also means a lighter truck or van.
  • Repeatability: CEM calibration systems have a repeatability of ±0.05% of full scale.
  • Accuracy: They use NIST-traceable calibrated precise thermal mass flow controllers, with the most accurate equipment providing a flow accuracy of better than +/-1% of setpoint. This is critical in that it provides all calibration points the same high level of accuracy.

Calibration Process

Pre-Calibration Requirements

Before calibration, several preliminary steps must be completed:

  1. Calibration Certification: Ensure the gas analyzers have a calibration certificate verifying their function, drift, linearity, detection limit, output, operating temperature, and other parameters. This certificate should be obtained before and during installation.
  2. Span Gas Concentration: The span gas concentration should be approximately 80% of the selected measurement range. This facilitates accurate calibration by closely matching the operational conditions.
  3. Initial Multi-Level Calibration: Perform an initial calibration at multiple levels. This will be ideally a minimum of five, including zero and span points. The multi-point calibration compares the CEMS output with actual gas concentrations. These concentrations are determined by the reference method or injection of known calibration gases.

CEM Calibration Procedure

CEM calibration involves several systematic steps to ensure the accuracy of the CEMS readings:

  1. Introduction of Calibration Gases: For extractive systems, introduce calibration gases upstream of all filters and sample conditioning systems. These must be as close to the probe tip as possible.
  2. Daily Zero and Span Checks: Conduct daily zero and span checks using procedures recommended by the manufacturer. This ensures the system remains accurate. Record daily zero drift, and make adjustments if the drift exceeds 10% of the calibration gas value.
  3. Weekly and Monthly Checks: Perform more comprehensive checks on a weekly and monthly basis. This includes checking zero and span drift, linearity, and system stability. Regular maintenance tasks should also be scheduled monthly.
  4. Quarterly Data Comparison and CEM Calibration Verification: Every three months, compare the CEMS data with standard reference materials to verify CEM calibration accuracy.

Post-Calibration Requirements

After CEM calibration, ongoing verification and maintenance are crucial:

  1. Health and Data Accuracy Checks: Six months post-installation, reassess the system’s health, data accuracy, and reliability through multi-point calibration.
  2. Recalibration Triggers: Recalibrate the system under several conditions, such as after major repairs, lamp changes, alignment adjustments, or significant changes in fuel quality. Use standard methods and certified reference materials for these recalibrations.
  3. Daily and Weekly Verification: Check the zero drift daily and span drift weekly at a fixed time. For differential optical absorption spectroscopy (DOAS) and non-dispersive ultraviolet (NDUV) or non-dispersive infrared (NDIR) systems, revalidate the calibration every three months and after lamp replacements.

Calibration Error and Performance Specifications

  1. Calibration Error: The calibration error is defined as the difference between the instrument’s response to a known standard and the actual value without adjustment. Keeping this error within acceptable limits is crucial for data integrity.
  2. Performance Specifications: Maintain the following performance specifications:
  • Zero Drift: ≤ ±2% of span over 24 hours
  • Span Drift: ≤ ±4% of span over 24 hours
  • Analyzer Linearity: ≤ ±2% of span from the calibration curve
  • Performance Accuracy: ≤ ±10% compared to reference measurements.

Quality Assurance and Control

A robust Quality Assurance Plan (QAP) must be in place to ensure data integrity:

  1. Operational Checks: Daily checks should include zero and span checks, visual inspection of system indicators, and recording adjustments. These checks ensure the system functions correctly and accurately records emissions data.
  2. Routine Maintenance: Monthly maintenance should involve replacing filters, bearings, and cleaning pumps. Quarterly tasks include leak checks and linearity tests.
  3. Performance Tests: Regular performance tests, including calibration drift and relative accuracy tests, should be conducted periodically or after significant changes in plant operations.

Elevate The Results of your CEM Gas Analyzer With Our Calibration Products

The proper calibration of CEM gas analyzers is essential for ensuring accurate emissions monitoring, maintaining regulatory compliance, and preventing the release of dangerous chemicals into the air. Acting as gas detectors, these devices are extremely useful for calculating and observing gas concentrations emitted from refineries, incinerators, and power plants. Therefore, it is crucial they are calibrated properly. We, Environics, have advanced calibration systems, like the Series 4040, that provide unparalleled precision, flexibility, and cost savings. With our CEM calibration instruments, you can trust that your emissions data will be accurate, reliable, and compliant with all regulatory standards.For more guidelines and industry-specific calibration requirements, refer to the manual by the Central Pollution Control Board (CPCB). You can also explore our website for more information on CEM gas analyzers, gas calibration, or other topics, including the use of gas flow systems and multi-gas calibration. Utilize our detailed insights to discover the perfect equipment for calibration and achieve the best outcome.

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