Field Qualification of an Improved DLE Gas Turbine Control Algorithm to Reduce Part Load Emissions

Abstract

The importance of expanded operating flexibility with reduced emissions on dry low emissions (DLE) gas turbines to lower loads has grown in importance for operators in many applications including natural gas transmission. Solar Turbines has developed an improved emissions control algorithm for Solar’s SoloNOx DLE gas turbines being offered as Enhanced Emissions Control. The new algorithm reduces carbon monoxide (CO) and unburned hydrocarbons (UHC) emissions from idle to 50% load. The corresponding startup and shut down emissions are reduced so that operators can obtain permits for operation over longer periods outside of low emissions mode. The algorithm has been evaluated in field trials at two different compressor stations using different gas turbine engine models. Solar’s Taurus™ 60 was tested at a field site in West Virginia and a Mars® 100 was tested near Houston, Texas in the United States. The new control scheme reduces emissions from part load down to idle. The new controls extend the bleed valve or variable guide vanes’ operating range where they modulate to control combustor temperature from idle to full load. The pilot fuel schedule is also changed to work more directly with the combustor temperature control. Two field trials were completed to measure emissions continuously for more than 10 months at each site to validate the effectiveness of the new algorithm. Operation of the test units was largely at loads over 50% and the continuous data served to validate that the new algorithm with the modifications to pilot control did not change the emissions signature in the ‘low emissions mode.” In addition, multiple site visits were completed to map emissions from idle to 50% load over a range of engine settings. This mapping fully documented the complete emissions performance of the test units from idle to 100% load over a range of ambient temperatures from below freezing to 38°C. The field trials validate that the improved controls reduce CO and UHC emissions from idle to 50% load when compared to the current production algorithm. The testing also validated that the emissions above 50% load were unchanged compared to the current control algorithm. Specifically, CO and UHC emissions were reduced by 35 to 99% over the idle to 50% load operating range. By optimizing the pilot fuel controls the NOx emissions were also reduced 20 to 75% from idle to 50% load. The algorithm makes it possible to offer 15 ppm NOx warranties for the subject engine models in gas transmission applications down to 40% load that have been restricted to 50% load and higher. Over the wide ambient temperature range experienced during the field trial periods, emissions were consistent and no clear trends were documented with ambient temperature or engine speed (load).