Research On System Modeling And Consumption Reduction Optimization Of 600MW Circulating Fluidized Bed Boiler Power Plant

The energy resources of"rich coal,poor oil and less gas"dominate that the fossil fuel energy will be for a very long period for China’s primary energy supply.For purpose of utilizing the lean coal in high efficiency and requiring the ever increasing stringent air pollutant emission standards,the circulating fluidized bed combustion technology is developing toward to the super-high and ultra super-critical steam parameters and super-low emissions.Therefore,it is imperative and meaningful to analyze thermodynamically the whole process system of the supercritical circulating fluidized bed boiler coal-fired power plant,investigate the energy consumption distribution of the main and auxiliary systems,and obtain the reasonable energy effective utilizationl in order to make the supercritical circulating fluidized bed coal-fired power plant run in low consumption and high efficiency.Firstly,taking a 600MW supercritical circulating fluidized bed boiler power plant as the actual physical model and using the modular method,three sub-system modules were established of the circulating fluidized bed boiler power plant,which was divided into the modules of boiler coal combustion sub-system,steam turbine power cycle sub-system,and pollutant ultra-low emission sub-system.Based on the Aspen Plus,a large-scale commercial process simulation software,three subsystem modelling were built respectively.They were compared with the actual 600MW supercritical circulating fluidized bed boiler power plant model,and the prediction errors was acceptable so that the validity and accuracy of the Aspen Plus model was verified.Secondly,based on the exergy analysis theory,the exergy analyses of the subsystems of the boiler island,steam turbine thermal system,and SCR,ESP and WFGD were calculated and the energy consumption distribution of the above-mentioned subsystems were obtained along with the evaluation indexes.The results showed that the boiler had the largest exergy loss by reaching 12606.15 k J/kg and accounting for 85.4%.The steam turbine system followed by accounting for about 12%.Of the steam turbine system,the steam turbine body occupied the largest proportion of the exergy loss close to 46%,followed by the condenser,accounting for22.5%,and then the feeding water regenerative heating system,accounting for 16%.Of the air pollution control system,WFGD had the biggest exergy loss indicating the weak energy utilization compared to SCR.Under different boiler loads,ESP and SCR exergy efficiency was not sensitive to the load change,whose exergy efficiency was stable at 98%and 95%,while WFGD exergy efficiency varied from 89%to 93%.The exergy efficiency of the air pollutant control system ranked in the order of ESP>SCR>WFGD.Next,the whole process system model of the coal-fired power plant of supercritical circulating fluidized bed boiler was established by coupling the subsystems.The influences of different operational parameters on the energy consumption distribution of the boiler subsystem,turbine subsystem and pollutant treatment subsystem were explored,and the regenerative heating system of steam turbine and the technical route of pollutant emission technical route were optimized.Finally,the effects of coal slime blending ratio on bed temperature,exhaust gas temperature,fan power consumption and boiler thermal efficiency were further investigated,and the economical analysis of coal slime blending was discussed.The results showed that the heat consumption rate reduced by 23.1 k J/(k W·h)by adding a low-pressure heater and optimizing the regenerative heating system.The recovered flue gas heat was up to 37.8 MW,and the heat consumption rate was reduced by 48.3 k J/(k W·h),by adding two stage low-temperature economizer.As the proportion of coal slime blending increases,the bed temperature showed a slow downward trend.When the proportion of coal blending reached30%,the temperature of the bed fell approximately by 30 ~oC;At the same time,the exhaust gas temperature and fan power consumption both showed a relatively small upward trend.The exhaust heat loss q2 and the incomplete combustion heat loss q4 both showed an upward trend.The boiler efficiency tended to decline slowly.When the proportion of coal slime blending was40%,the boiler efficiency dropped by about 2.5 percentage points.