Improving heat recovery in China
Power generation in China
depends highly on coal-fired power plants, which contribute around 70% of the
total installed power capacity (1.25 billion kW at the end of 2013) and
approximately 78% of the total electricity generation (5.25 trillion kWh
In this paper, an improved
system to efficiently utilize the low-temperature waste heat from the flue gas
of coal-fired power plants is proposed based on heat cascade theory. The essence
of the proposed system is that the waste heat of exhausted flue gas is not only
used to preheat air for assisting coal combustion as usual but also to heat up
feedwater and for low-pressure steam extraction. Air preheating is performed by
both the exhaust flue gas in the boiler island and the low-pressure steam
extraction in the turbine island; thereby part of the flue gas heat originally
exchanged in the air preheater can be saved and introduced to heat the feedwater
and the high-temperature condensed water. Consequently, part of the
high-pressure steam is saved for further expansion in the steam turbine, which
results in additional net power output. Based on the design data of a typical
1000 MW ultra-supercritical coal-fired power plant in China, an in-depth
analysis of the energy-saving characteristics of the improved waste heat
utilization system (WHUS) and the conventional WHUS is conducted. When the
improved WHUS is adopted in a typical 1000 MW unit, net power output increases
by 19.51 MW, exergy efficiency improves to 45.46%, and net annual revenue
reaches USD 4.741 million while for the conventional WHUS, these performance
parameters are 5.83 MW, 44.80% and USD 1.244 million, respectively. The research
described in this paper provides a feasible energy-saving option for coal-fired
power plants