5 Tips to Maintain CEMS

The Continuous Emission Monitoring System (CEMS) is not only a legal requirement for industrial plants but also a critical system that reflects the efficiency of your production process and pollution control system. Investing in preventive maintenance is a smart decision that ensures CEMS operates with accuracy, stability, and longevity. This article presents 5 detailed best practices your facility should adopt:

1. Scheduled Calibration: The Heart of Accuracy

Objective: Ensure analyzers provide accurate and precise readings compared to standard values. Calibration is not just verification—it’s the process of adjusting the equipment to restore its accuracy, forming both a legal requirement and a foundation of system reliability.
Key Actions:

• Quarterly Calibration (Zero & Span Check):
   -  Zero Check: Use a reference gas without the target pollutant to correctly set the "zero point."
   -  Span Check: Use standard gas with known concentrations to verify and adjust the analyzer's readings.
• Relative Accuracy Test Audit (RATA):
   -   A major verification conducted annually by an external third party registered with the Department of Industrial Works.
   -   Method: The auditor installs a reference measurement setup in parallel with the plant’s CEMS, simultaneously collects gas samples, and compares the data to determine relative accuracy.
   -   Frequency: Typically, every 6 months or at least once per year, as legally required.
  
  Recommendations:
       Create a calibration calendar, maintain certificates for all standard gas cylinders, and log all calibration records systematically for audit and performance analysis.

2. Sample Handling System Maintenance: The “Lifeline” of CEMS

Objective: Deliver representative gas samples from the stack to the analyzer without altering their properties or concentrations. Over 80% of CEMS issues stem from sample handling system failures rather than the analyzer itself.

Key Inspection Areas:

• Probe & Primary Filter at the Stack:
   -   Clean filters every 1–2 months using compressed air.
   -   Replace filters every 3–6 months due to dust and ash buildup.
   -   Clean the probe monthly using instrument air and a brass wire brush to remove blockages.
• Heated Sample Line:
   -   Maintain temperature (~120°C) to prevent condensation that could dissolve SO₂ and NOx gases.
   -   Check heater performance and clean the line using instrument air (4–6 bar). If severely clogged, clean with pure water and dry thoroughly.
• Moisture Removal System (Cooler/Dryer):
   -   Ensure cooler maintains set temperature (e.g., 3–5°C).
   -   Check dryer for cracks or wear; replace squeeze hoses every 6–12 months.
   -   Condensate Drain System must be free of blockages.
• Sample Pump:
   -   Inspect diaphragms and check valves for blockages that may cause unusual noises or damage.
   -   Replace diaphragms and valves every 6–12 months.
  

Recommendations : Implement a daily visual inspection checklist and schedule monthly/quarterly replacement of consumables like filters and O-rings.

3. Data Acquisition System (DAS) Management: The "Brain" That Must Not Fail

Objective: Ensure the “brain” of the CEMS accurately records and processes data in compliance with regulatory requirements.

Key Actions:

• Data Backup: Regularly back up monitoring data and configuration files at least weekly to avoid data loss from power outages or hardware failure.
• System Clock Check: Ensure DAS time and date are accurate to avoid timestamp errors.
• Log File Monitoring: Check system log files for warnings or errors regularly.
• Software Updates: Consult the vendor to keep the software up-to-date for bug fixes and enhanced security.

4. Proactive Spare Parts and Consumables Management: Aim for Zero Downtime

Objective: Minimize system downtime when failures occur. Waiting to order spare parts after a failure can lead to days of missing data, impacting legal reporting.

Recommended Minimum Stock:

• Consumables: Filters (all sizes), O-rings, seals, and moisture removal chemicals (if applicable).
• Critical Spares: Consult your vendor, but generally include spare pumps, certain electronic circuit boards, oxygen sensors, and spare probes.

Recommendations: 

• Prepare a complete inventory list of required parts and define Re-order Points to maintain availability at all times.

5. Staff Development and SOP Creation: The Most Valuable Investment

Objective: Ensure operators are capable of maintaining and troubleshooting the system. Even the best equipment is ineffective without proper understanding.
Key Actions:

• Training: Conduct annual refresher training for responsible personnel—through both vendors and experienced supervisors.
• SOP (Standard Operating Procedures):
   -  Develop user-friendly Thai SOPs with illustrations for daily tasks and alarm responses.
   - Create a Troubleshooting Guide for common issues.
• Maintenance Logbook: Foster a culture of documenting all maintenance, repairs, and unusual events. These records are invaluable for long-term issue analysis.

ASE Tips:

• Maintaining your CEMS is not just about compliance—it’s about ensuring production reliability and building long-term plant credibility.
• Don’t wait for a breakdown—proactive maintenance always outperforms reactive solutions.

• Email: sales@ase-thai.com
• LINE: @ase-thai
• Phone: 083-298-9222