Measurements of NOx Emissions From DLE and Non-DLE Gas Turbine Engines Employed in Natural Gas Compressor Stations and Comparison With PEM Models

Abstract

The Environmental Protection Agency (EPA) publishes emissions factors for gas turbines in its Compilation of Air Pollutant Emission Factors, “Volume I Stationary Point and Area Sources, Publication No. AP-42”. This document uses an emissions factor (EF) which is a representative value that attempts to relate the quantity of a pollutant released to the atmosphere with an activity associated with the release of that pollutant. For natural gas-fired gas turbines, EPA NOx (nitrogen oxides) emissions factors are usually expressed as the weight of pollutant per unit fuel volume burned or its equivalent heating value (e.g. kg/m3 or kg/GJ). In most cases, these factors are simply averages of available data, and are generally assumed to be representative of long-term averages for all facilities in the source category. Additionally, AP-42 specifies two EFs depending on the engine load being above or below 80% of rated power. In this paper, NOx emissions tests were conducted on four gas turbines. The first two were non dry low emissions (non-DLE) General Electric engines (LM1600), one in Alberta and the other in Ontario, with significant elevation difference. The other two were Rolls-Royce (R-R) engines; one DLE (RB211-24G) while the other is a non-DLE (RB211-24C), both in Alberta at the same elevation. These tests were conducted at different ambient temperatures varying from −7°C to +28°C using Continuous Emissions Monitoring (CEM) emissions samples based on EPA Method 7E standard. Predictive Emission Monitoring (PEM) systems were also developed based on these and previous testing, and predictions are compared to measured data. The difference between NOx emissions from these four engines at different loads (minimum to maximum) and different ambient conditions are presented and compared. A comparison with AP-42 emissions factors is presented and discussed. It was found that the elevation difference between the two LM1600 engines makes a significant difference in NOx emissions. Additionally, the emissions from the DLE engine when it is operating out of the DLE mode (at low loads) emits higher NOx than a non-DLE engine at the same load and ambient conditions.