Turbine inlet cooling evaporative

The work required to drive the turbine eompressor is reduced by lowering the compressor inlet temperature thus increasing the output work of the turbine. Figure 2-35 is a schematic of the evaporative gas turbine and its effect on the Brayton cycle. The volumetric flow of most turbines is constant and therefore by increasing the mass flow, power increases in an inverse proportion to the temperature of the inlet air. The psychometric chart shown shows that the cooling is limited especially in high humid conditions. It is a very low cost option and can be installed very easily. This technique does not however increase the efficiency of the turbine. The turbine inlet temperature is lowered by about 18 °F (10 °C), if the outside temperature is around 90 °F (32 °C). The cost of an evaporative cooling system runs around 50/kw. 

Where hot ambient temperatures are expected, overall turbine efficiency and horsepower output can be increased by installing an evaporative cooler in the inlet. Inlet air flows through a spray of cold water. The temperature of the water and the cooling effect caused by the inlet air evaporating some of the water cools the inlet air. In desert areas where the inlet air is dry and thus able to evaporate more water before becoming saturated with water vapor, this process is particularly effective at increasing turbine efficiency. 

The gas turbine is a high-volume air machine. The compressor air power required is usually between 50-70 percent of the total power produced by the turbine. Thus, the ambient temperature affects the output of the gas turbine. On hot days, the gas turbine produces less output than on cold days. In dry climates, the use of evaporative cooling in the gas turbine decreases the effective inlet temperature and increases the power output of the unit. 

The cooling of the inlet air using an evaporative cycle, the simplest of the cycles, and which can be put into operation with the least outlay in capital is not very useful in operation in high humidity areas. The system would cost between 300,000- 500,000 per turbine thus amounting to a cost of 135 per KW. 

The injection of steam in the compressor discharge has been utilized over the years and has been found to be very effective. The amount of steam to be injected can vary from 5-15%. The injection of steam created from properly treated water does not affect the life of the hot section of the turbines. This is based on a large number of units where steam injection has been used. Steam injection, with an evaporative cooling inlet system would be best suited for hot humid areas this application based on the efficiency and cost as shown in Figure 2-45. 

Determine the COP, horsepower required, and cooling load of a Carnot vapor refrigeration cycle using R-12 as the working fluid and in which the condenser temperature is 100°F and the evaporation temperature is 20°F. The circulation rate of fluid is O.llbm/sec. Determine the compressor power required, turbine power produced, net power required, cooling load, quality at the inlet of the evaporator, quality at the inlet of the compressor, and COP of the refrigerator. 

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