Abstract

Coal-based electric power generation remains the basic source of obtaining energy. With increasing pressure to reduce CO₂ emissions, improving power unit efficiency has become an issue of utmost significance. Surely, one of the possibilities to improve the efficiency of new power units is raising the steam parameters. With improved power plant efficiency, there is a lower demand for power of almost all auxiliary equipment except the boiler feed pump. The reason for this is that the power needed to drive the feed pump is an almost linear function of the steam pressure. This means that, even though the steam mass flow (and, consequently, the feed water mass flow) is reduced and the efficiency of feed pumps is improved, their power increases. For this reason, it is very important to find the optimum drive of the boiler feed pump. The main aim of the conducted analysis was to compare various drive options of the boiler feed pump for a conceptual ultra-supercritical 900-MW steam power unit. The following drive configurations of the boiler feed pump were presented and compared:

· A frequency-controlled electric motor

· A condensing turbine fed with steam extraction from the immediate-pressure turbine

· An extraction-backpressure turbine fed with steam from a cold reheat steam line with bleeds shifted from the low-pressure turbine

· A backpressure turbine fed with steam from a hot reheat steam line operating in parallel with the intermediate-pressure turbine

· An extraction-backpressure turbine fed with steam from a cold reheat steam line with bleeds shifted from the intermediate-pressure turbine (the master cycle idea).

The analysis of the operation of the 900-MW unit with various configurations of the feed pump drive was carried out for three load levels: for the nominal mass flow of live steam and for the partial mass flow of 75% and 50%.

Keywords:

Ultra-supercritical coal-fired power units; Boiler feed pump drive; Master cycle; Net efficiency of electric power generation