| In view of the situation of coal as the main primary energy resource in China,the coalfired power generation in electricity industry has always been in a dominant position.While coal-fired power generation not only consumes a lot of coal,but also brings serious pollution to the environment,so it is of great significance to save energy and reduce emissions.The ultra-super-critical coal-fired power unit is prospective because of its high steam parameters,high thermal efficiemcy and good economy.Compared with the traditional pulverized coal boiler,the circulating fluidized bed(CFB)combustion boiler has the advantages of high combustion efficiency,wide fuel adaptability,low pollutant emission and wide load regulation range.Therefore,the development of ultra-supercritical circulating fluidized bed boiler technology has important practical significance.In this work,a fictitious 660 MW ultra-super-critical CFB boiler power station was taken as an actual physical model to study its thermal system optimization and thermal efficiency improvement by using of the simulation method.In order to explore the feasibility and validity of the simulation method,a 75 t/h CFB boiler system was tested insitu in measurement,and a schematic simulation software of Aspen Plus was used to build the models of the 75 t/h CFB boiler system.The correctness and feasibility of the model were verified between the model prediction results and the measurement data through the power plant performance test and the boiler anti-balance test.The results showed that the simulated results of the flue gas components at exit of the 75 t/h CFB boiler were very close to the measured data,with an error of 0.08%-0.26%.The simulation results of the heat efficiency and heat losses of the boiler system were also similar to those by the boiler anti-balance method with an error of 0.25% ～ 1.27%.The simulated value of boiler thermal efficiency is 88.66% with an error of 1.41%.Based on the above-mentioned results,a new method of Aspen Plus modelling program was proposed to predict the heat losses and heat efficiency of a large scale CFB boiler unit,which laid a foundation for simulation and optimization of a ultra-super-critical high-parameter CFB boiler power plants.Secondly,the design blueprint of a contracted 660 MW ultra-supercritical CFB boiler was used as the modeling object.,the Aspen Plus software was used to model and analyze its coal combustion subsystem,steam water subsystem and steam turbine electric generator subsystem respectively,which results were compared with the cited research data of a600 MW supercritical CFB boiler unit.The results showed that the models of each subsystem had good accuracy and simulation precision.It provided the base to use this models to carry out the technical and economic analysis and parameter optimization of the whole process thermodynamic system of a 660 MW ultra-super-critical CFB boiler power plant unit.Then,the coal combustion subsystem and the steam-water subsystem of the virtual660 MW ultra-supercritical CFB boiler power station were coupled to establish the model of the main boiler system.The relationships among the operational parameters such as air flow rate,cold air temperature,excess air coefficient,feed water temperature and flue gas exhausted temperature were studied.The influences of various operational parameters on the thermal system of the power station were obtained,and the optimal operation parameters of the boiler are required.The research results were helpful to better understand the change and adjustment of the combustion conditions in the boiler,and to guide the reasonable operation of the ultra-super-critical CFB boiler coal-fired power station.Finally,the Aspen Plus software was used to couple the boiler combustion subsystem and the steam turbine electric generator subsystem,and the whole process models of the660 MW ultra-super-critical CFB boiler power plant were established.The effects of different main/reheat steam parameters and the way of steam turbine regeneration on the energy efficiency and thermal economy of the unit were investigated,and the thermodynamic system of the unit was optimized.The optimal parameters and operation mode of the unit under various operating conditions were obtained.The results showed that the thermal efficiency of the unit increased with the increase of the main/reheat steam temperature,and the increment of the main steam temperature had a greater effect on the thermal efficiency of the unit than the increase of the main steam pressure and reheat steam temperature.When the main steam pressure elevated to 33 MPa,the thermal efficiency of the unit remains almost constant.Under the full load operation,the optimal steam parameter was 35 MPa/620 ℃ / 620 ℃,and the thermal efficiency of the unit reached the highest value of 46.37%,which was 2.12% higher than the designed working condition.From the consideration of economy and manufacturing technique,the optimum steam pressure parameter was 31 MPa/620 ℃/620 ℃,the corresponding steam efficiency was45.21%.When the main steam temperature is increased by 10 ℃,the thermal efficiency of the unit is increased by 0.161% ～ 0.201%.When the temperature of reheated steam is increased by 10 ℃,the thermal efficiency of the unit is increased by 0.05% ～ 0.066%.The thermal efficiency of the unit increases by 0.012%～0.063% for every increase of main steam pressure by 1 MPa.The unit heat economy added with increment of the reheat series.In contrast to the thermal efficiency,the ten-level recuperation scheme > nine-level recuperation scheme> the original eight-level recuperation scheme.The thermal efficiency of the ten-level recuperation system scheme was increased by 3.28% compared with the original scheme,the heat consumption rate was reduced by 25.3 k J/(k W·h),and the standard coal consumption rate was reduced by 0.927 g/(k W·h).The regenerative power level of the 660 MW ultra-super-critical CFB boiler power station was recommended to be ten stages,that was,the regenerative system was "four high temperature regenerators,five low temperature regenerators and one deaerator". |
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