| Efficient energy utilization and pollutant removal in cold end of boiler were great way to improve energy saving and pollutant emission reduction performance of coal-fired power generation system.Clean and efficient coal-fired power generation system was the main content of the research.Firstly,thermodynamic optimization of boiler cold end was conducted,which could achieve energy efficient utilization.Secondly,breaking the independent pattern of energy utilization and pollutant emission reduction processes was proposed,and the promotion mechanism as well as collaborative optimization of them were investigated,which could achieve both clean and high efficiency.Next,the research area of conventional coal-fired power generation system was further broken.Based on solar added power generation systems,the coupling mechanism and collaborative optimization of solar energy and SCR de-NOx were investigated.Last,the key equipment for energy saving and environment protection in cold end of boiler were investigated,and coordinated arrangement of low temperature economizer(LTE)and clean gas heater was achieved.In the thermodynamic optimization of energy utilization in boiler cold end,the performance of LTE system and bypass flue system was analyzed firstly.The energy saving mechanism of bypass flue system was revealed based on the first law and second law of thermodynamics.Next,the variation of graphical exergy analysis with flue gas bypass portion is investigated.It revealed that in the aspect of both first law and second law of thermodynamics,the energy saving mechanism and optimization direction of boiler cold end were same.Based on the trend of graphical exergy analysis,the thermodynamic optimization principles were obtained.Breaking the heat and mass transfer pattern between boiler and turbine was proposed,and the flue gas,air,extraction steam as well as condensed water were regarded as the unified working fluid of heat and mass transfer process in the system,which could achieve deep coupling between boiler and turbine.The research results indicated that,based on a typical 1000 MW unit,the integration system based on deep coupling between boiler and turbine could increase by 0.51%of thermal efficiency and 10.96 MWe of net power output,with 3.16 g/kWh of standard coal consumption reduction and 9.5 MWth of exergy loss decrease in air preheating process.Besides,the integration system brought 13.573 million CNY of net annual revenues,which were significantly higher than those of the current energy utilization systems in boiler cold end.Based on the proposed advanced energy utilization pattern(i.e.,deep coupling between boiler and turbine),the energy level matching as well as coupling mechanism between bypass flue gas and SCR de-NOx were revealed by energy level analysis.Combined with the coupling mechanism as well as low-low temperature electrostatic precipitator and low water consumption desulfurization,the collaborative optimization principles of energy utilization and pollutant emission reduction processes in cold end of boiler were obtained.The bypass flue gas with high temperature was used to heat feed water before economizer,which could increase both SCR de-NOx efficiency and energy saving effect.Besides,the waste heat of flue gas was recovered by the cold air and the exhaust flue gas temperature was reduced,which could increase the dust removal efficiency and decrease the water consumption of desulfurization.Thus,the clean and efficient coal-fired power generation system was achieved.The research results indicated that,based on an advanced 1000 MW unit,the proposed clean and efficient system could decrease the standard coal consumption by 3.30 g/kWh,3.02 g/kWh and 2.73 g/kWh for high,medium and low loads,respectively,and increase SCR de-NOx temperature from 15 ? to 18 ?,with 0.9%,2.6%and 4.5%of SCR de-NOx efficiency increase,respectively.For high,medium and low loads,the water consumption reduction of desulfurization was 30.2,16.4 and 7.8 t/h,respectively.The proposed system could decrease the fly ash resistivity and flue gas volume velocity of electrostatic precipitator,which could improve the performance of dust removal.The increase of SO3 removal efficiency varies from 27.1%to 29.8%in different loads.Besides,the proposed clean and efficient system could reduce CO2 production over 50 thousand tons and bring 12.417 million CNY of net annual revenues.Based on the main development direction of coal-fired power generation system,i.e.solar added power generation system,the energy level matching as well as coupling mechanism between solar energy and SCR de-NOx were revealed by energy level analysis.The collaborative optimization principles of solar energy utilization and SCR de-NOx in cold end of boiler were obtained,and the concept of improving SCR de-NOx performance by solar energy was proposed.The research results indicated that,based on an advanced 1000 MW ultra-supercritical unit,the standard coal consumption rate of the proposed system could decrease by 2.68 g/kWh,4.05 g/kWh and 6.31 g/kWh for high,medium and low loads,respectively.The SCR de-NOx temperature could be kept in the optimal range in all loads,and the SCR de-NOx efficiency could increase by 3.1%and 7.9%under medium load and low load conditions,respectively.Besides,the influence of solar fluctuations on the proposed system significantly decreased because of the flexible solar energy distribution.The cost of solar generated electricity was low.In the aspect of key equipment for energy saving and environment protection in boiler cold end,coordinated arrangement of LTE and clean gas heater was investigated.Based on fluoroplastic heat exchanger and flue gas waste heat deep recovery,coordinated arrangement of LTE and media gas-gas heater(MGGH)was proposed,which could collaboratively optimize waste heat recovery as well as dilution and purification of pollutants.Based on heat transfer curve analysis,allocation optimization of heat transfer area in boiler cold end was conducted to match the energy level of heat source and cold source better.The results revealed that based on a typical 1000 MW ultra-supercritical unit,coordinated arrangement of LTE and MGGH with heat transfer area allocation optimization could decrease the standard coal consumption rate by 1.05 g/kWh.The clean flue gas was heated up to 80 ?,which could significantly increase the performance of pollutants dilution and purification.The net annual revenues were 0.936 million CNY.Besides,the proposed system could decrease the desulfurization water consumption significantly and achieve low-low temperature electrostatic precipitator.Recovering both sensible heat and latent heat of flue gas by coupling coal drying technology was proposed.Based on coal drying technology,the latent heat of flue gas could be extracted and transfer into exhaust dryer gas.Thus,the total recovered waste heat was enlarged and coordinated arrangement of LTE and dryer gas-flue gas heater could be achieved,which could collaboratively optimize waste heat recovery as well as dilution and purification of pollutants in cold end of boiler.The results revealed that based on a typical 1000 MW ultra-supercritical unit,coordinated arrangement of LTE and dryer gas-flue gas heater could decrease the standard coal consumption rate by 3.83 g/kWh.The clean flue gas was heated up to 82.5 ?,which could significantly increase the performance of pollutants dilution and purification.The recoverd water was 13.9 kg/s and the net annual revenues were 24.998 million CNY.Besides,the arrangement of dryer gas-flue gas heater could solve the ash blocking problem in the conventional gas-gas heater. |
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