Evaluation, Experience and Potential of Gas Turbine Based Cycles with Humidification

University dissertation from Department of Heat and Power Engineering, Lund university

Abstract: Gas turbines, in simple and combined cycle, are common and economically profitable on the power generating market today. Several new cycles have been proposed as future competing technologies, but all studies about these cycles have, so far, been paperwork. The requirements for these new cycles are better efficiency than those of today, provide better flexibility, offer short start up times, less harmful to the environment, offer lower specific investment costs, the operation can be fully automised, offer lower operating and maintenance costs and the technology can be applicable to a gas turbine of any size. One of these cycles is known as the evaporative gas turbine cycle, which is intercooled, aftercooled, recuperated and the air is humidified. This cycle has been proposed as one of the candidates, that matches most of the previously mentioned requirements. In this work; a theoretical model has been established in order to evaluate the thermodynamic performance of the evaporative gas turbine cycle; a 600 kWe pilot plant, based upon the evaporative gas turbine technology, has been built for the first time ever; the developed theoretical model has been validated with measurements from the evaporative gas turbine pilot plant; the validated theoretical model has been applied in a comparative study, where the performance of the evaporative gas turbine cycle is compared with competing technologies; the capability of the evaporative gas turbine technology to meet the demand of the market in terms of performance, operation and maintenance, emissions, space requirements and economy has been analysed and discussed. It has been shown that the thermodynamic and component sizing models predict the performance and size of the evaporative gas turbine cycle well. The pilot plant can be started, shut down, deliver full power output and can follow load-changes almost as fast as the simple cycle. The part-load performance is better than for the combined cycle. It has been shown that the emissions from combustion with humid air in a diffusion flame combustor are very low. It has been shown that the evaporative gas turbine cycle can be self-sufficient of make up water, if the flue gases are chilled in a flue gas condenser. The quality of the condensed water is very good, and can easily be treated with a CO2 stripper and a mixed-bed ion exchanger to be reused as demineralised make up water. It has been shown that the efficiency of a mid-size evaporative gas turbine cycle is slightly better than the combined cycle and much better than the steam injected gas turbine cycle. It has been shown that trigeneration and inlet compressor air humidification can increase the fuel utilisation, even well above 100\%, when applied to gas turbine based cycles with humidification. It has been shown that external low level heat from any source can be utilized to enhance the performance of the combined cycle and evaporative gas turbine cycles by means of air humidification. In a preliminary study, it has been shown that the footprint of a evaporative gas turbine cycle is smaller than for a corresponding combined cycle. The humidification tower is less than 10 m high, and all heat exchangers, intercooler, aftercooler and recuperator, can be made of welded plate heat exchanger technology, which are associated with low pressure drops, high thermal performance and are inexpensive.

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