Absorption Refrigeration Cycle Turbine Inlet Conditioning

Abstract

Ambient temperature markedly impacts combustion turbine performance. A typical aeroderivative turbine loses 25% of ISO capacity at 38°C ambient. There are two traditional options to mitigate that degradation: evaporative cooling and mechanical chilling. They boost turbine performance, but consume significant water and/or electric load. Also, the turbine requires separate anti-icing equipment for low ambient temperature operation (less than 4.4°C). This paper describes the Absorption Refrigeration Cycle Turbine Inlet Conditioning (ARCTIC) system that chills or heats the inlet air of a combustion turbine to maintain maximum turbine performance at all ambient temperatures. The ARCTIC unit is an ammonia–water absorption cycle that is powered by turbine exhaust heat. The design and performance of a 7034 kW (2000-ton) ARCTIC unit is presented. This ARCTIC achieved a new record for net power and heat rate from this model aeroderivative gas turbine in hot weather. It provides reliable and dispatchable hot day power at about half the cost of new plant. On a typical summer day (38°C dry bulb, 26°C wet bulb), ammonia refrigerant from the ARCTIC chills the inlet air to 8.9°C. The gas turbine power is increased from 40 to 51 MW. After allowing for the 230 kW electric parasitic load, the resulting net power is 2 MW more than the output of a comparable mechanically chilled gas turbine. As a result, the heat rate is also improved. On cold days the ARCTIC automatically switches to heating mode. The inlet air is heated by 11°C to eliminate inlet icing potential. Additional benefits include a lower exhaust temperature which is better for the Selective Catalytic Reduction (SCR) catalyst. The condensate recovered from the inlet-air chilling (up to 25 gallons per minute) can also be a valuable by-product. The ARCTIC system has a small cost premium relative to a mechanical chiller. However, when all the auxiliary functions are credited (anti-icing, tempering air, less switchgear, no 4160 volt service), the overall installed cost is comparable. The standout advantages are the increased hot weather power output, improved operating efficiency, and reduced maintenance, all obtained at minimal additional cost. Combined cycle and cogeneration configurations (both frame and aeroderivative) benefit even more from the ARCTIC due to the increased value of improved heat rate.