Advanced Exergoenvironmental Analyse And Evaluation For Coal-fired And Natural Gas-fired Power Plants Based On Life Cycle Assessment

Coal-fired power plants of near-zero air pollutant emissions and gas-steam combined cycle power plants are prominent parts to ensure that electricity generation is friendly to the environment in the increasingly severe environmental situation.Advanced exergoenvironmental evaluation combines thermodynamics with environmental analyses based on life cycle assessment(LCA),states the formation process of environmental cost,and therefore determines environmental impact saving potential of the system and environmental relations of the components,which provides useful suggestions for the design and operation of the cost-effective system.In this paper,complex 600 MW coal-fired power plants with and without dust,SO2 and NOx mitigation controls and a typical 9FA single shaft gas-steam combined cycle power plant are investigated based on LCA,advanced exergy and exergoenvironmental analyses.First,the environmental impact assessment methods of power plants are summarized and development processes of exergy analyses and different approaches that combine an exergy analysis with an environmental assessment environment analysis are clarified.Exergy destruction within a system component is further split:the avoidable and unavoidable parts,the endogenous and exogenous parts,and their combinations,and the same splittings are applied to the environmental impacts related to exergy destruction and pollutant formation.Then,the structure of the exergoenvironmental method and evaluating indicator and calculation method are introduced.An exergoenvironmental analysis consists of an exergy analysis,an LC A of the environmental impact and an exergoenvironmental evaluation conducted in analogy with the exergoeconomic one.On these foundations,thermal models for coal-fired power plants of direct emissions and ultra-low emission are established and the exergy analysis is conducted.Whole life-cycle environmental impacts of components are obtained through comprehensive collections of weight and material information.A calculation method for endogenous exergy destruction of heat exchangers is improved and PM2.5 environmental impact is taken into consideration.The specific environmental impact of electricity produced by the system drops from 282.06 to 10.77 mPts/MJ after adopting purification units.The environmental impacts of components are mainly caused by exergy destruction and the relations between the components are weak.Avoidable environmental impacts within most components are endogenous while environmental impact related to pollutant formation is avoidable and endogenous.At last,the exergoenvironmental performance of the gas-steam combined cycle power plant is compared with the coal-fired power plant of near-zero air pollutant emissions.It was found that the environmental impact ot pollutant tormation is negative and the specitic environmental impact of electricity generation is 5.80mPts/MJ.According to the results obtained,directions for minimizing environmental impacts of components in the coal-fired and natural gas-fired power plants are given.