The power producer has been using Mitsubishi Power’s gas turbines in one of its power stations, but wanted to improve the turbines’ efficiency to make more efficient use of scarce natural resources and obtain economic benefit. The power producer decided to perform a review of the turbines’ operation to identify potential areas for improvement.
Fans Running at Full Bore Were Causing Excessive Cooling
The company engineers who inspected the various stages of the generation plant as part of their review noted that the plant’s efficiency fluctuated with the climate and the seasons. The team decided to take a closer look at the relationship between generation plant and temperature. They found that the turbine was being over-cooled, irrespective of the time of year, ambient temperature, or turbine output.
This turbine was cooled by a series of dedicated fans, which provided cooling air to the turbine blades and Gas Turbine hot gas path components. When the engineers dug deeper, they found that the fans’ design meant that their output could not be adjusted, so they were always running at “full bore”.
The team leader recalls:
“Excessive cooling by the nonadjustable fans was causing metal components to expand less than they were supposed to, thereby increasing turbine tip clearance. The resultant gap was impairing the efficiency of the turbine. Of course, zero or insufficient cooling would result in damage to other turbine components, so turning the fans off was not an option either. It was a tricky problem.”
The power producer’s engineering division felt that in the circumstances, optimizing the turbine tip clearance would boost efficiency while ensuring a stable output. However, as they were unable to control the speed of the cooling fans, they felt there was nothing they could do.
- THE PROBLEM
- The output of the turbine’s cooling fans could not be adjusted. This caused the turbine to be excessively cooled.
- The excessive cooling caused metal components to expand less than they were supposed to, resulting in increased tip clearance. This gap was reducing the turbine’s efficiency.