Modeling Simulation And System Optimization Of Ultra-supercritical Units Under Wide Load Operation

Large-capacity thermal power units have gradually developed into the main body of the task of energy storage and peak regulation.which means that it is necessary to improve the economy and flexibility of its wide load operation.In this paper,an ultra supercritical 1050 MW steam turbine unit is taken as the research object,a model based on the APROS simulation platform is established,and the optimization research of wide load operation is carried out.Firstly,the reason for the low economical efficiency of the throttling steam distribution unit in wide load operation was analysed.Based on a new configuration method of high pressure cylinder arrangement,the model and simulation of the new unit were carried out based on APROS platform,and the strategy of the optimized unit adapting to wide load operation was studied.Compared with the reference unit,the heat consumption rate is reduced by 151 k J/k Wh in the cylinder cutting condition,and the energy saving is obvious.From the thermal analysis method and the exergy analysis method,the optimized system was analyzed economically,and the heat consumption rate calculation model was established.Through the relationship between the valve opening with the comprehensive valve throttling efficiency,and the relationship between the main steam pressure with the cycle efficiency,the heat consumption rate corresponding to the working condition can be directly obtained according to the above-mentioned relational model.An exergy analysis of the optimized unit found that the overall exergy loss is 35 MW smaller than that of the reference unit,and the parts where the exergy efficiency is improved are in the boiler,heater,and condenser.Secondly,from the perspectives of shafting safety,high-pressure cylinder performance changes,temperature changes,the safety performance of the optimized unit was analyzed.The axial thrust of the unit can be partially offset due to the opposing arrangement of the large and small cylinders during the operation of the unit,it is smaller than the original design.The axial thrust value under the load of 68.8%THA(the small cylinder is completely cut off)is the largest,but it is still lower than the axial thrust under the maximum load,which is within a safe range.The pressure prediction model after valve was established to study the effect of throttle loss on the cylinder efficiency of the high-pressure cylinder,and the flow efficiency model of the high-pressure cylinder was constructed using the relationship between speed ratio and efficiency.When the load is reduced,the speed ratio of the large cylinder will drop slightly,and the efficiency will be reduced,but it will still be maintained at a high level.The speed ratio of the small cylinder changes greatly,which will greatly deviate from the optimal speed ratio value,and the efficiency of the small cylinder decreases more significantly than that of the large cylinder.Aiming at the situation of extraction steam recirculation and large temperature difference of the first stage extraction port of the large and small cylinders during the operation of the unit after configuration optimization,small cylinder without one extraction model was designed to compare the performance differences of the two systems.Finally,a dynamic simulation model of the ultra-supercritical 1050 MW unit was established,and the accuracy of the dynamic model was verified by experimental data.The load response characteristics of the regenerative system when participating in wide-load operation were studied,including condensate throttling adjustment and heater extraction throttling adjustment.The load response capability and dynamic characteristics of the unit under different load adjustment modes were studied.The condensate throttling flow rate,the extraction steam flow rate and the maximum load change have a linear relationship,and the load regulation ability of under high load is stronger.The influence of heat supplying on the output power and economy of the unit under different loads is analyzed.Under low load,heat supplying has a greater influence on the output of the unit,and the relationship between the load variation and the steam extraction quantity is linear.The heat supplying realizes the cascade utilization of energy,the cascade energy utilization efficiency is improved,the comprehensive heat consumption rate is reduced,and the lower the extraction steam parameter,the more economical.Under the same condensate throttling ratio,the load change ratio of the unit decreases with the increase of the heating extraction steam flow.The impact of different adjustment methods on unit economy was discussed.During the extraction and throttling process,the temperature at the feedwater outlet decreases.The load increases,while the heat consumption first decreases and then increases.The temperature at the outlet of the feedwater regulated by the condensate throttling is basically unchanged,and the trend of heat consumption rate is opposite to the trend of load.