Evaporative gas turbine cycle - A description of a pilot plant and operating experience

In recent years the interest for new advanced thermodynamical gas turbine cycles has increased. One of the new designs is the evaporative gas turbine cycle. A lot of effort worldwide has been put into predicting the possible efficiency, pollutants, and dynamic behaviour of the evaporative gas turbine cycle, but all results so far have been affected by uncertain assumptions. Until now this cycle has not been demonstrated in a pilot plant. The purpose of this work has been to identify the potential of this cycle, by erecting a pilot plant at the Lund Institute of Technology. The project was financed on a 50/50 basis from the Swedish National Energy Administration and the industrial partners. Three different thermodynamical cycles have been tested in the pilot plant: the simple, the recuperative, and the evaporative cycle. The final pilot plant roughly consists of a 600 kW gas turbine, a hydraulic brake, a recuperator, a humidification tower, an economiser, and a flue gas condenser. All layout and functional analysis were made within the project. The pilot plant is, however, optimized neither for best efficiency nor for best emissions, due to the choice of standard components out of economical reasons. It has only been built for demonstration purpose. Maximum simplicity, flexibility and safety have been the main emphasis in the design of the EvGT cycle. The flow mismatch that occurs between the compressor and the expander in evaporative cycles makes it hard to use a standard gas turbine unit. To be able to use a standard unit, an air bleed off system has been introduced. The water circuit can, at any time, be connected or disconnected from the humidification tower, thereby creating a possibility of controlling when humidification takes place or not by means of a water bypass past the humidification tower. Two starting sequences have been developed, one with the humidification process fully integrated from the beginning and one without. It has been shown that it is possible to reach full power output from the evaporative gas turbine cycle almost as fast as for the simple cycle. It has also been shown that the process is very stable when operated at various loads and during load transients. Furthermore, it is possible to start the power plant quickly from a remote place.