Compressor Water Wash Performance
26 February 2008
Gas Turbine Compressors consume approximately 60% of the overall cycle energy during operation. Consequently, the efficiency of the compressor is very important to maintain to achieve optimum performance of the gas turbine power plant. The gas turbine cycle consumes very large quantities of air. Although this air is filtered, small quantities of dust, aerosols and water pass through the filters and deposit on the blades. These deposits decrease the air flow of the compressor and the overall performance of the gas turbine.
Compressor cleanliness can be maintained using a routine program of water washing. There are two water wash procedures performed on gas turbines. An off-line wash is conducted with the gas turbine in a cooled state using cranking speed. This operation can effectively clean the entire gas turbine core with a highly atomized wash spray that is positioned to enter the compressor core at 30% to 50% of blade span. Detergent is frequently used in this operation to dissolve blade deposits, and is followed by a rinse.
The second water wash procedure used to maintain compressor performance is an On-Line wash only. This operation is conducted with the machine at operating temperature and uses water only. The operation is able to address the first three to five compressor stages due to working compressor temperatures. However, these stages are important to maintain air flow. This operation is most effective using a highly atomized wash spray positioned similarly to the off-line procedure, such that the wash spray strikes the compressor core at 30 to 50% of blade span.
GTE Water Wash Systems operate by injecting atomized water into the compressor inlet such that the spray enters the compressor throat to wet blades and remove fouling. The design of the washing fluid is controlled by selecting a nozzle and a supply pressure to deliver water flow at less than 1% of mass flow and a mean droplet size of approximately 150 microns. GTE off-line washing is typically conducted using detergent for an initial cycle of six minutes followed by a soak and than followed by two six-minute rinse cycles. GTE On-Line washing is typically conducted daily to maintain compressor output and heat rate between off-line washes.
Off-line washing is needed to initially clean the compressor and to fully wash the entire compressor core. Before and after blade conditions are shown by Figure 2. These pictures show the effective cleaning of the full compressor core. This is necessary to achieve full gas turbine performance and is needed at the start of any wash program.
Comparison of this performance to a typical low pressure system using output and heat rate as indicators shows an average additional recovery of a full percent of output and .34 percent of heat rate with the GTE design. At these rates a typical operator would enjoy a US$400,000 benefit per 100MW of base load operation in a year.
The use of a well atomized water wash process that directs water in optimum position for off-line and on-line washing is an important operation for mantaining turbine performance. GTE has developed designs for most models of gas turbines using these principles and has validated the design in field operation.
