As equipment within natural gas generation plants ages, challenges can arise in maintaining continued compliance with environmental regulations. To reduce these challenges and keep systems operating optimally, upgrades to existing continuous emission monitoring systems (CEMS) are often planned. However, a great deal of planning and evaluation is required upfront to deliver a long-lasting system.

Embarking On a Complete System Overhaul

Older CEMS within plants can prove troublesome as replacement parts become scarce or even unavailable due to obsolescence. Rather than attempting to locate these components to maintain the existing system, it is more cost-effective for utilities to upgrade the entire CEMS with new equipment. In addition to alleviating maintenance issues, a new system can help see that the plant remains in compliance with current reporting and certification requirements as governed by the U.S. Environmental Protection Agency (EPA).

Complete system upgrades are complicated to execute in an active plant, though. Extended downtime can prove detrimental from a fiscal perspective, so a thorough engineering design and detailed project milestone schedule are vital to minimize outage duration and optimize system functionality during the transition to in-service operation. This preparation begins by fully understanding what the existing system has to offer and determining if that system should be augmented with new capabilities.

For example, if an existing system has a stack monitoring component to the CEMS, the utility may want to install turbine exhaust monitoring. This means there are now two different components — the stack and the turbine exhaust — that need CEMS monitoring equipment. Also, evaluation of available space inside the existing shelter is critical to be certain there is room for any additional equipment to be installed.

Best Practices for Coordination and Installation

To identify these potential scenarios before the project impacts plant operation, a comprehensive walkthrough of the CEMS shelter, stack and turbine exhaust locations of interest is needed, as well as a full review of existing CEMS design drawings. During this process, shelter dimensions, new design components under consideration, data communication preferences and power requirements are verified.

This review approach involves considerations, including:

  • Developing an accurate and detailed equipment specification package, both from a hardware and software perspective. This includes the provision of required analog and digital signals for process conditions such as temperature, pressure and flow.
  • Investigating the existing stack and turbine exhaust flange orientations. If existing orientations differ from the newly furnished probe boxes, new flange adapters or welding modifications to the existing flanges will be required.
  • Verifying the current condition of the existing stack and turbine exhaust ports. If screw threads exist, but are not satisfactory, the threads will need to be restored.
  • Verifying the new sample line lengths, new cable tray design (as required) and specifying the proper sample line fastening materials, which will prove to be resilient in outdoor conditions.
  • Confirming the new sample line insulation removal is minimized for the termination of the polytetrafluoroethylene (PTFE) tubing and electrical conductors to the sample conditioning plate inside the CEMS shelter. This will minimize the chance of condensation forming within the new sample line.
  • Performing a load calculation for the existing CEMS shelter power panel, transformer and motor control center (MCC) cubicle. Additionally, the full run of existing cable will require a sizing calculation to be verified as sufficiently large enough for the new, possibly increased, CEMS load ampacity.
  • Taking adequate measures to secure nitrogen oxide exhaust pumps to limit vibration and possible risk of damage to nearby equipment.
  • Determining requirements for the existing CEMS shelter bulkhead such as if the existing bulkhead can be reused or if new bulkhead needs to be furnished and installed. During the design phase, verification of the existing bulkhead dimensions and penetration diameters is essential to confirm that any new vent, sample line, gas tubing or instrument cable can be routed through the bulkhead.
  • Determining if the utility prefers a specific calibration gas bottle configuration layout such as requiring an individual solenoid for each bottle or routing and directing multiple quarterly (linearity) gases to a single solenoid. This determination can minimize required maintenance activities performed by plant personnel. Additionally, gas bottles need to be protected from direct sunlight, potentially requiring the fabrication and installation of a new sunshade.
  • Confirming that plant IT personnel coordinate the timely configuration of ethernet switch ports and communication protocols, in advance of commissioning, to facilitate the transmission of reporting data between multiple control systems.
  • Creating comprehensive supporting documentation such as a control narrative, alarm responses and a CEMS system description. This documentation will prove critical in support of possible future CEMS maintenance and troubleshooting activities required of plant personnel.

Through successful execution of each of these design elements and deliverable documents, installation and commissioning of the new CEMS can begin. By following best practices for design upfront in the project development process, utilities will benefit from a long-lasting, safe and efficient CEMS with accurate emission data reporting for environmental compliance.


Modernized control systems are the gateway to optimum performance, safety and reliability. Reap the benefits while mitigating risks during these upgrades.

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Michael Lee is an electrical engineer-in-training at Burns & McDonnell specializing in conventional extractive CEMS upgrades for natural gas-fired simple- and combined-cycle plants for utility clients.