Comparative Study Of Environmental Sustainability Before And After Ultra Low Emission Reconstruction Of Coal Fired Power Plants

The high environmental emissions of Dust,SO₂ and NOx from exhaust gas of coal-fired thermal power plants become one of the main sources of atmospheric pollution in China,which restricts the sustainable development of China’s industry and national economy.The 13th Five-Year Plan requires that by 2020,all coal-fired power plants in the country that are fit for transformation should strive to achieve ultra-low emissions.However,existing studies only evaluate performance of ultra-low emissions transformation from an economic and technical perspective,and there is still a lack of comparative studies of environmental performance before and after transformation.To explore changes of environmental performance before and after transformation,this paper adopts the emergy based combined methods,which integrate the dilution method and disability adjusted life years（DALY）method,to quantify the impact of pollution emissions.And then a set of performance indictor system suitable for the characteristics of ultra-low emission reconstruction of coal-fired power plants was established,taking the contribution of the environment to the transformation of ultra-low emissions into account,so as to comprehensively evaluate the environmental performance before and after the transformation.This study takes a coal-fired power plant with an installed capacity of2×300 MW in service in Guangdong Province as an example to compare the changes of environmental performance of its flue gas desulfurization system,denitration system,and dust removal system before and after ultra-low-emission transformation.The main conclusions are summarized as follows.（1）The total emergy input of the flue gas desulfurization system before and after the ultra-low emissions transformation is 8.71E+20 sej/yr and 9.60E+20sej/yr;therein,emergy input in the construction phase is 9.79E+18 sej/yr and 1.21E+19 sej/yr,and emergy input in the operation phase is 8.62E+20 sej/yr and 9.48E+20 sej/yr,respectively.Before the transformation,1.12%of the emergy input comes from the construction phase,and 98.88%of the emergy input is derived from the operation phase.After the transformation,1.26%of the emergy input comes from the construction phase and 98.74%of the emergy input is from the operation phase,in which the largest contributor is purchased non-renewable resources.（2）The total emergy input is 1.75E+20 sej/yr and 1.71E+20 sej/yr before and after the ultra-low emission modification of the flue gas denitration system;therein,emergy input in the construction phase is 1.12E+20 sej/yr and 1.13E+20 sej/yr,and emergy input in the operation phase is 6.23E+19 sej/yr and 5.75E+19 sej/yr respectively.Before the transformation,64.39%of the emergy input comes from the construction stage,and35.61%of the emergy input comes from the operation stage.After the transformation,66.33%of the emergy input is derived from the construction stage,and 33.67%of the emergy input comes from the operation stage,to which the largest contributor is purchased non-renewable resources at various stages.（3）The total energy input is 4.03E+19 sej/yr and 5.33E+19 sej/yr before and after the ultra-low emission reconstruction of the flue gas dust removal system;therein,emergy input in the construction phase is 3.95E+18 sej/yr and 7.21E+18 sej/yr,and emergy input in the operation phase is 3.63E+19 sej/yr and 4.61E+19 sej/yr respectively.Before the transformation,9.79%of the emergy input comes from the construction phase,and 90.21%of the emergy input is derived from the operation phase.After the reconstruction,13.51%of the emergy input comes from the construction phase,and 86.49%of the emergy input is from the operation phase,to which the largest contributor is purchased non-renewable resources at various stages.（4）Before and after ultra-low emission transformation of the desulfurization system,the total amount of annual environmental emissions is 1.67E+06 kg and 4.15E+05 kg,the ecological service needed to dilute the environmental emissions is 3.74E+17 sej/yr and9.70E+16 sej/yr,and the emergy loss caused by emissions is 3.77E+18 sej/yr and 1.06E+18sej/yr respectively.Emissions’impact is mainly caused by carbon monoxide,carbon dioxide,phenol in the construction stage,and sulfur dioxide emissions in the operation stage.Before and after the ultra-low emission transformation of the denitration system,the total amount of annual environmental emissions is 1.13E+06 kg and 4.56E+05 kg,the ecological service needed to dilute the emissions is 1.05E+17 sej/yr and 4.59E+16 sej/yr,and the emergy loss caused by emissions is 2.71E+18 sej/yr and 1.32E+18 sej/yr.Emissions’impact is mainly caused by carbon monoxide,carbon dioxide,phenol in the construction stage,and nitrogen oxides emissions in operation stage.Before and after the ultra-low emission transformation of the dust removal system,the annual emissions amount is 1.03E+05 kg and 4.12E+04 kg,the ecological service needed to dilute the emissions is 5.88E+15 sej/yr and 7.86E+15 sej/yr,and the energy loss caused by air emissions is 2.78E+17 sej/yr and 1.12E+17 sej/yr respectively.The main emissions’impact is derived from carbon dioxide,phenol in the construction stage,and dust in the operation stage.（5）After the ultra-low emission transformation,the resource efficiency of the desulfurization system,the denitration system and the dust removal system increases by66.69%,23.63%and 6.42%respectively,the energy efficiency of the three systems ascends by 39.38%,22.31%and 11.02%respectively.After the transformation of ultra-low emissions,the production efficiency of the desulfurization system,the denitration system and the dust removal system climbs by 9.77%,27.49%and 7.77%respectively.After the transformation of ultra-low emissions,the environmental load rate（ELR）of the desulfurization system decreases by 3.66%,and that of the denitration system and the dust removal system increases by 3.07%and 0.51%respectively.After the transformation of ultra-low emissions,the environmental sustainability level（ESI）of the desulfurization system,the denitration system and the dust removal system has risen by 13.71%,23.33%and 6.56%respectively.（6）Even after the ultra-low-emissions transformation,the environmental load rate（EIR）of the three systems is still high due to about 99%of the emergy input coming from the purchased nonrenewable resources,and thus their sustainability level is also low.Finally,this study puts forward the following suggestions,including（1）Formulating and implementing"One Plant,One Policy",（2）Researching and developing low-cost and highly efficient ultra-low emission technologies,（3）Optimizing resources structure,and（4）Strengthening pollution source control.