Theoretical and Experimental Evaluation of a Plate Heat Exchanger Aftercooler in an Evaporative Gas Turbine Cycle Available to Purchase

The evaporative gas turbine pilot plant (EvGT) has been in operation at Lund Institute of Technology in Sweden since 1997. This article presents the experimental and theoretical results of the latest process modifications made, i.e. the effect of the installation of an aftercooler. The purpose of the aftercooler is to increase the performance of the cycle by utilizing more low-level heat in the humidification tower. The chosen aftercooler is of plate heat exchanger type, which is very compact, has high thermal efficiency and low pressure drop. The installation of an aftercooler lowers the temperature of the air entering the humidification tower. This also lowers the temperature of the circulating humidification water, which facilitates the extraction of more low-level heat from the economizer. This low-level heat can be utilized to evaporate more water in the humidification tower and thus increase the gas flow in the expander. The pilot plant has been operated at different loads and the measured results has been evaluated and compared with theoretical models. The performance of a plate heat exchanger in power plant applications has also been evaluated. Experience from the measurements has then been used for the potential cycle calculations. It has been shown that the aftercooler lowers the flue gas temperature in the pilot plant to 93°C, the rate of humidification was increased from 13 wt% to 14.5 wt%, and the pressure drop on the airside in the aftercooler is 1.6%. The electrical efficiency for the pilot plant was increased by 0.4%. The increase in electrical efficiency for a more advanced EvGT cycle with an intercooler, aftercooler and economizer will be around 3.5 percentage units in comparison with a cycle without an aftercooler. The plate heat exchanger showed very good performance in terms of cost, size, pressure drop and thermal efficiency. An alternative to the chosen heat exchanger is the tubular one, but it is 10 times heavier, has a higher pressure drop and is more expensive. The aftercooler increases the electrical efficiency significantly by lowering the flue gas temperature and increasing the expander work.