Predictive Emission Monitoring Systems: Innovation in Measurement Technology
Authors: Sadois Claude , Suliono Andi , Julien Philippe , Raja Mohsin , Al-Sulaiti Ahmed 
Published: May 2016

Per State of Qatar environmental regulations, Continuous Emission Monitoring Systems (CEMS) are required to be installed on combustion units with a heat input capacity of greater than 25 megawatts (MW). CEMS are well regulated in US and European jurisdictions to monitor air emissions compliance. However, CEMS entail extensive calibration requirements and are difficult to maintain and operate in the harsh climate of the Arabian Gulf.

Based on the challenges noted above, Qatargas Operating Company Limited (Qatargas) and TOTAL E&P Qatar (TOTAL) collaborated on a study to assess the viability of Predictive Emissions Monitoring Systems (PEMS) as a reliable and sustainable emissions monitoring technique. The first part of the study focused on the development of PEMS algorithms and comprised a blind benchmarking evaluation of the three main types of PEMS technologies (first principles, statistical and neural networks) using data collected from an operating Qatargas gas turbine. The second part of the study assessed the operational, maintenance and cost aspects of PEMS installation with reference to international guidelines.

This paper summarizes results of the first part of the above study which includes the results of the technical, blind benchmarking comparison of PEMS technologies on the pilot gas turbines. These results suggest that PEMS measurements can be as accurate as that of CEMS. One of the advantages of PEMS, being a software based-solution, is the reduced requirement for installation of additional physical monitoring instrumentation, which translates into substantially lower capital and operational costs as well as reduced calibration and maintenance requirements. The findings of the second part of the study with regard to installation and operation of PEMS installations will be discussed in a future paper.

PEMS have been successfully regulated in several worldwide jurisdictions, including by the USEPA. This paper aims to demonstrate that PEMS can be a viable emission monitoring tool as both an alternative and complementary capacity to CEMS.

Introduction

Many current regulations require traditional direct emission monitoring of fired units using Continuous Emission Monitoring Systems (CEMS). This is normally intended to monitor compliance against operating permits and/or regulatory limits. CEMS is an extractive sampling device installed on the exhaust stack of a fired unit to extract flue gas samples for emissions measurement. This direct monitoring system requires frequent maintenance and calibration. Over a period of direct exposure to the flue gas, the CEMS analyzers drift and require periodic adjustments in the form of calibrations using reference calibration gas standards. On the other hand, software-based monitoring systems such as Predictive Emission Monitoring Systems (PEMS) predict or estimate emissions from fired units using the units' operating parameters as a basis. This predictive approach therefore does not require physical emissions measurement and hence significantly minimizes associated maintenance and calibration requirements.