1. Field of the Invention
This invention relates broadly to cooling inlet air to a gas turbine.
2. Description of Related Art.
A conventional gas turbine system includes: an air compressor for compressing the turbine inlet air; a combustion chamber for mixing the compressed air with fuel and combusting the mixture, thereby producing a combustion gas; and a power turbine that is driven by the combustion gas, thereby producing an exhaust gas and useful power.
Over the years, various technologies have been employed to increase the amount of useful power that the power turbine is able to produce. One way of increasing the power output of a gas turbine is to cool the turbine inlet air prior to compressing it in the compressor. Cooling causes the air to have a higher density, thereby creating a higher mass flow rate through the turbine. The higher the mass flow rate through the turbine, the more power the turbine produces. Cooling the turbine inlet air temperature also increases the turbine's efficiency.
Various systems have been devised for chilling the inlet air to the compressor. One such system uses evaporative cooling, wherein ambient temperature water is run over plates or over a cellular media inside of a chamber, thereby creating thin films of water on each plate, or on the media. The turbine inlet air is then drawn through the chamber, and through evaporative cooling, the air is cooled to near the wet bulb temperature. This system is limited to cooling the air to the wet bulb temperature, which is dependent upon the atmospheric conditions at any given time. Another system uses a chiller to chill water that is then run through a coil. The inlet air is then drawn through the coil to cool the air. This system requires parasitic power or steam to drive the chilling system which has the further drawback that when inlet air cooling is needed the most, i.e. during the day when the temperature is the highest, is also the time when power demand from the turbine is the highest, i.e. during the day when power users are in operation. In order to run the chiller, power from the turbine is required, but this power is needed by the users of the turbines power. On the other hand, when cooling is needed the least, i.e. at night when the temperatures are the lowest, surplus power from the turbine is available because the consumers of the turbine's power are largely not in operation. Accordingly, a continuing need exists for a turbine inlet air cooling system which: would efficiently cool turbine inlet air; would take advantage of surplus power available during times of low consumer power demand; and would not drain the system of power during times of high consumer power demand.