E. Dick

Technological and economical analysis of water recovery in steam injected gas turbines.

Steam injected gas turbines are an interesting technology for co-generation applications. In these gas turbines the heat of the exhaust gases is used to produce steam. This steam is injected in the combustion chamber, resulting in a high specific power and a high thermal efficiency. A major disadvantage of steam injected gas turbines is the large water consumption. Placing a condenser in the cycle makes it possible to recover all the injected steam. An analysis is made of different types of condensers. Condensers based on finned tubes and direct-contact-condensers are considered. The dimensions of the condensers are determined for existing steam injected gas turbines. Furthermore, the investment costs and the exploitation costs for each type are compared.

Cycle improvements to steam injected gas turbines.

The efficiency and specific power of the steam injected gas turbine is analysed by modelling the thermodynamic cycle. In this model special attention is paid to the blade cooling. The basic cycle as well as cycles with improvements such as intercooling, heat recovery by regenerator and blade cooling using steam are studied. The different cycles are compared with the combined cycle and the intercooled regenerative cycle. The conclusion is that the steam injected cycles have high efficiency and specific power. Adding heat exchangers to the cycle is not beneficial. Using steam as coolant for the blades offers interesting perspectives. Copyright

Analysis of Efficiency and Water Recovery in Steam Injected Gas Turbines

The study presented in this paper has two objectives. The first objective is to analyse the efficiency of the steam injected gas turbine by modelling the thermodynamic cycle. This is done by adapting a calculation model for turbine blade cooling proposed by El Masri (1986). The expansion path is divided into small subintervals, to take into account the changing gas properties during the expansion. This model is then verified for four different industrial machines.The basic cycle as well as cycles with thermodynamic improvements as intercooling, heat recuperation by heat exchanger and blade cooling using steam are studied. The calculations are done for a range of pressure ratios (PR) and turbine inlet temperatures (TIT), with methane (CH4) as fuel being representative of natural gas. A comparison is made with a simple cycle gas turbine and with a combined cycle system. The maximum efficiency of the basic cycle is found to be around 49 % with current gas turbine technology. Steam blade cooling is extremely simple to implement in a steam injected gas turbine and is found to be thermodynamically very attractive, bringing the maximum efficiency to about 52 %.Secondly the water recuperation in the condenser is analysed. Due to the combustion of the fuel, water is formed. As a result, the dew point temperature of the combustion gas without steam injection can be rather high, i.e. around 45 °C. As a consequence, the amount of water corresponding to the injected steam can be recuperated by cooling the gas mixture to the original dew point temperature. Closing the cycle for water is in this case thermodynamically possible. The practical recuperation of water in the condenser is studied on a test rig with a simulated gas turbine augmented with a condenser and steam injection. This proves that complete recuperation of the injected water is technically possible.The conclusion of the study is that a steam injected gas turbine with complete water recuperation is possible and has a high efficiency.Copyright