Abstract
To address the large temperature difference in the air heater (AH) inlet of a traditional exhaust heat utilization system and energy grade mismatch problems during the heat and mass transfer processes, this study proposed a new multi-level waste heat cascade utilization system. Based on a principle of “temperature-to-port and cascade utilization”, this system uses the boiler side high-temperature flue gas and low-temperature air, and the turbine side high-temperature feed water and low-temperature condensate water, to conduct cross heat exchange according to the energy grade matching principle. Combined with a typical 1000 MW coal-fired unit, the heat transfer characteristics and energy-saving benefits of the new system were analyzed. The results showed that the new system has excellent performance: the heat rate decreased by 91 kJ/kWh, coal consumption decreased by 3.3 g/kWh, and power generation efficiency increased to 49.39%.
Highlights
In line with its economic development increasing energy consumption demands, China faces enormous environmental and energy pressures
In order to further reduce coal consumption and improve the energy saving efficiency of a double reheat unit, this study proposes a new type of boiler-turbine deep-coupled multi-level cascade utilization system for an ultra-supercritical power plant
air heater (AH) flueto gasthe and the AH bypass andcomes the flow ratio condensate water system, exchanges heat with the flue gas in the second low-temperature bypass, In the new system, the main flue gas AH system is connected in series with the I low-temperature economizer (LE), precipitators, and returns to the deaerator; and one path comes from the inlet, passes the a draft fan, the II LE, and a desulfurization tower
Summary
In line with its economic development increasing energy consumption demands, China faces enormous environmental and energy pressures. In order to further reduce coal consumption and improve the energy saving efficiency of a double reheat unit, this study proposes a new type of boiler-turbine deep-coupled multi-level cascade utilization system for an ultra-supercritical power plant. In this system, a front air preheater is added that makes use of the cross heat transfer of the condensate and bypass flue gas to increase the first low-temperature economizer (I LE) inlet temperature and strengthen heat transfer on the turbine and boiler side. This study further analyzes the thermal performance and economy of one 1000 MW double reheat unit in China and compares it with a conventional waste heat saving system
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