Abstract:
In modern steam turbine installations, steam is superheated in an isobaric process. As is known from technical thermodynamics, when the working fluid is heated from a given state to the same temperature, the heat in the isobaric process is greater than the heat of the isochoric one. In addition, the expansion of the working fluid during the isobaric process of heat supply is harmful, since in this case no external work is performed, that is, the main property of the working fluid is lost – its physical expansion in order to obtain external mechanical work. In an isochoric process, steam, like a mechanical spring, accumulates more mechanical energy at a lower cost of heat. Therefore, it is proposed in steam turbine plants that both primary superheating and subsequent steam superheating processes be carried out isochorically. Comparative calculations of the characteristics of steam turbine installation, operating according to the Rankine cycle with primary superheated steam up to a pressure of 6.0 MPa and a temperature of 600 °C, at a steam pressure in the condenser of 0.004 MPa, with the characteristics of an installation with an isochoric steam superheating process with the same initial data, showed significant energy and economic advantages of the latter in comparison with basic. So, with a lower fuel consumption in the modified installation (by 10.1 %), its specific work increased by 3.9 %, and thermal efficiency – by 11.2 %. Even more significant energy and economic advantages have a modified STP with one additional reheat of steam: with a lower fuel consumption by 15.9 %, the specific work increased by 6.8 %, and the thermal efficiency increased by 18.8 %. Due to the smaller volumes of steam at the end of the expansion, the weight and size parameters of the turbines and the condenser of the modified unit are reduced by 5.2 % compared to the base unit. Considering the above conclusions and the scale of use of STP at modern power plants, where up to ten intermediate steam reheats are used, the proposed modernization of their thermodynamic cycles guarantees even greater energy and economic effects.
