Abstract: Direct air-cooled power generation units can supply heat adopting the high back pressure heating scheme or the extraction heating scheme. In this paper, the analysis model is established to compare the thermal economic performance of the two schemes. Through calculation, the energy utilization efficiencies of the two heating schemes for a 330 MW unit are compared under constant main steam flow rate or constant power output with the back pressure of 34 kPa for high back pressure heating and that of 10 kPa for extraction heating at various water supply temperatures and heating loads. The results indicate that the high back pressure heating scheme shows higher energy utilization efficiency than the extraction heating scheme with the heating loads increasing at the water supply temperatures not higher than 70 ℃. With the water supply temperature rising, part of steam has to be extracted from the intermediate pressure cylinder outlet for the high back pressure heating scheme, which lowers the economic performance. The higher the water supply temperature, the fewer advantages in energy saving are shown in the high back pressure heating scheme. When the heating loads are low, part of the electrical loads can be shifted from the high back pressure heating unit to another unit if permitted.

Key words: direct air-cooled power generation unit, high back pressure heating, extraction heating, thermal economic performance, energy utilization efficiency