Gas-turbine inlet-air cooling: you can almost pick your payback

Selecting the right inlet-air cooling technology is not an engineering problem--it`s an economic one. This article helps the design engineer understand the options, and some economic rules of thumb, then pick the payback that best serves each project. Gas turbines in cogeneration service work worst when they`re needed most--at least in many areas of the country. Power output decreases during the hot summer months, just when electricity demand is at its highest and capacity is most valuable. Reason for the performance drop is that hot air entering the turbine is less dense than cool air, so mass flow through the machine is reduced. Lower mass flow through the gas turbine also means there`s less exhaust energy supplied to the heat-recovery steam generator (HRSG), so steam production is reduced as well. One way to avoid the performance degradation is by installing an inlet-air cooling system--an old technology that`s becoming increasingly popular in light of electric industry restructuring. Indications are that when electric wheeling becomes a reality, the price of energy sales will be relatively low, but the price of capacity will rise. In such a market, the ability to consistently maintain capacity can give a cogenerator a competitive edge. The keymore » is to design and size the inlet-air cooling system based on specific project economics and the incremental buyback rates for each time-of-use period. In most cases, sizing the system based on a maximum cooling day is not going to be the most cost-effective option.« less