Energies (Nov 2023)
An Ejector and Flashbox-Integrated Approach to Flue Gas Waste Heat Recovery: A Novel Systematic Study
Abstract
In this study, a comprehensive examination was conducted to explore the technology involved in the recovery of waste heat from flue gas emitted by a 1000 MW unit. Traditional methods are constrained in their ability to harness waste heat from flue gas solely for the purpose of generating medium-temperature water. The system being examined not only recovers waste heat but also utilizes it to generate steam, thereby greatly improving resource efficiency. The process entails utilizing the flue gas to heat water to a certain temperature, followed by subjecting it to flash evaporation. This process leads to the generation of low-pressure waste heat steam. Within the steam ejector, the waste heat steam combines with high-pressure motive steam extracted from the source, resulting in the formation of medium-pressure steam. Within the steam ejector, the waste heat steam blends with high-pressure motive steam drawn from the source, forming medium-pressure steam that eventually feeds into the A8 steam extraction pipe (low-pressure turbine pumping pipe). The present study examines the fluctuation patterns in motive steam flow, suction coefficient, waste heat steam volume, and outlet temperature of the flue water heat exchanger when different motive steam sources are used. Additionally, the research calculates the reduction in CO2 emissions, the coal consumption for power supply, and the cost savings in fuel for the retrofitted system. The findings indicate that maximizing energy utilization can be achieved by operating the retrofitted unit at the lowest feasible waste heat steam pressure. The implementation of the new system has resulted in a substantial decrease in coal consumption for power supply. When employing main steam as the extraction steam source, the consumption of coal for power generation decreases in proportion to the decrease in waste heat steam pressure while maintaining a constant unit load. When the waste heat steam pressure reaches 0.0312 MPa, the recorded coal consumption for power generation varies between 289.43 g/kWh at 100% turbine heat acceptance (THA) and 326.94 g/kWh at 30%THA. When comparing this performance with the initial thermal power plant (TPP) unit, it demonstrates reductions of 2.26 g/kWh and 1.52 g/kWh, respectively. After implementing modifications to this 1000 MW unit, it is projected that the annual CO2 emissions can be effectively reduced by 6333.97 tons, resulting in significant cost savings of approximately USD 0.23 million in fuel expenses. This system exhibits considerable potential in terms of emission reduction and provides valuable insights for thermal power plants aiming to decrease unit energy consumption.
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