A study on the efficiency of the steam module of a high power combined-cycle plant with a different number of heaters
The newest developments of the Siemens Company in the area of combined cycle plants (CCP) [1, 2] make it possible to use different schemes of low pressure heater (LPH) systems for turbine plants (TP), due to which the economy and reliability of the steam module of CCPs are improved. Currently, there are various heater schemes that depend on the type of turbine plant. Our study considered CCPs with LMZk600-166 turbines (OJSC Power Machines). Calculations were made for the following heater schemes [3–8]: – Scheme 0: no heaters; – Scheme 1: gas heater (GH) + low-pressure heater 1 (LPH1); – Scheme 2: GH + LPH1 + LPH2; – Scheme 3: GH + LPH1 + LPH2 + deaerator; – Scheme 4: GH + deaerator.
The technical parameters of the low pressure heaters were selected according to the recommendations for the LMZk600-166 turbines. The technical parameters of the gas heater are considered on the basis of the input parameters of the LPH1 (Schemes 1 – 3) or the deaerator (Scheme 4); the technical parameters of the deaerator are based on the parameters of the heat recovery steam generator.
The calculation results showed that when the heaters are not used, the efficiency of the turbine plant is 36.6%. As the number of the heaters increases, the efficiency of the turbine plant grows, thereby increasing the total efficiency of the CCP. But if the feed water is heated to the maximum possible temperature (as in Scheme 3), the heater system could not compensate the heat loss of the exhaust gas and the efficiency of the turbine plant drops sharply. But in Scheme 4, when the GH performs the role of LPH1, 2 and 3, using the heat of the exhaust gas, which would be released into the atmosphere in Scheme 3, the efficiency of the turbine plant reaches the highest value (37.3%). It is important to note that in other world’s CCP versions, the heater system is not currently used for its steam plant due to the limitation of the technical parameters of the gas circuit and the heat recovery steam generator. Compared with the most efficient CCP in the world at the moment, the calculated net efficiency of CCPs using a heater system of Scheme 4 for its steam turbine is higher by 1.6% (63.8% versus 62.2%).
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Siemens SGT-9000HL CCP efficiency steam module gas heater (GH) turbine plant (TP) low-pressure heater (LPH) high pressure drum-separator (HPDS) medium pressure drum-separator (MPDS) low pressure drum-separator (LPDS) high pressure cylinder (HPC) medium pressure cylinder (MPC) low pressure cylinder (LPC) feed water (FW) feedwater pump (FWP) deaerator (D) condensate path (CP)