Topping with a Natural Gas-Fired Combined Cycle Unit of a Coal-Fired Cogeneration Power Plant with Cross Connections

Abstract

Thermal power plants (TPP) with cross connections and having a minimum reference fuel rate of 321 g/(kW h) prevail in the structure of the generating capacities in Russia. In practice, this characteristic is often above 500 g/(kW h). Application of parallel-type, dual-fuel combined-cycle units (CCUs) using coal as the main fuel, for improving the efficiency of power plants with cross connections is considered. Such CCUs have high efficiency and are suitable for modernization of operating subcritical power plants with cross connections. The power of CCUs with gas turbines manufactured in Russia or having a high degree of production localization in Russia can be as high as 200–250 MW. In all the cases, a new heat-recovery steam generator (HRSG) and a new steam turbine for a live-steam pressure of 12.8 and 8.8 MPa must be developed. The paper considers the process features of such dual-fuel cogeneration CCUs based on a 6FA gas turbine. A CCU thermal scheme is developed. Bled steam conditions under different operating conditions are determined considering the bypass of the main condensate and feedwater lines. GCU performance indices as a function of ambient air temperature are determined. In addition, an option was considered for modernizing the existing cogeneration power plant (TETs) in the town of Seversk by implementation of a dual-fuel CCU based on an 82 MW 6FA gas turbine and a T-96/122-8.8 steam turbine while maintaining the coal-fired power steam boilers in operation. It is demonstrated that the proposed modernization option makes it possible to reduce the fuel cost by approximately 240 million rubles per year while increasing the electricity delivery under cogeneration conditions by 1.7 times.