Research On Steam Distribution Mode Of Large Steam Turbine In Coal-fired Power Plant

The safe and economic operation of steam turbines is directly related to the way of steam distribution.At present,the power plant 1000 MW ultra-supercritical steam turbine unit is mainly regulated by throttling steam distribution,nozzle steam distribution and composite sliding pressure operation.After the "11th Five-Year Plan",the national economy developed rapidly and the domestic electricity consumption structure changed,the peak-to-valley difference of China's power grid load is getting larger and larger.Many large steam turbines have to participate in the power grid peaking work,and the time for participating in peak shaving is getting longer and longer,which makes the actual operating parameters and design parameters of the unit different.As a result,the economics and safety problems of the entire unit may occur.Therefore,it is necessary to research the steam distribution method of the steam turbine on the premise of ensuring the safe operation of the unit.In this paper,based on the actual operation of large steam turbines in thermal power plants,we analyzes the principles and characteristics of different operating modes of steam turbines,and compares the effects of different steam distribution modes on the thermal economy and safety of the turbines.Based on the principle of steam turbine,the external bypass valve is combined with the steam turbine with throttling steam distribution,and the position of the steam flow mixing point at the outlet of the external bypass valve is comprehensively compared.Taking the 1000MW ultra-supercritical steam turbine produced by Shanghai Steam Turbine Works as an example,the external determination is made.The optimum position of the steam flow mixing point at the outlet of the bypass valve is after the fourth stage of the high pressure cylinder.Then,similar to the design and calculation method of the external bypass valve,the steam turbine of the inner bypass nozzle is matched with the steam turbine for analysis.The 1000MW ultra-supercritical steam turbine produced by Dongfang Steam Turbine Works is taken as an example to determine the outlet flow of the inner bypass valve.The optimum position for the mixing point setting is the third pressure level after the adjustment stage.Finally,the paper also analyzes and calculates the thermal economy of the 1000MW ultra-supercritical steam turbine.In the process of steam turbine distribution,the economic factors are considered,and the influence of the temperature difference of the steam on the safety is considered.Taking THA working conditions as an example,before the steam turbine steam distribution is improved,the steam consumption rate of the SAIC 1000MW steam turbine is reduced by 0.35kg/kW·h,the heat consumption rate is reduced by 58.7kJ/kW·h,and the absolute electric efficiency is increased by 0.39%.The power has increased by 146.7MW.For the Dongqi 1000MW steam turbine,the steam consumption rate has decreased by 0.40kg/kW·h,the heat consumption rate has decreased by 60kJ/kW·h,the absolute electric efficiency has increased by 0.4%,and the power has increased by 171.4MW.In particular,after the improvement of the steam distribution mechanism of the 1000MW ultra-supercritical steam turbine produced by Dongfang Steam Turbine Works,the opening of the control bypass valve can make the pressure in the regulating stage steam chamber almost unchanged when the flow rate is greater than the design value,and the temperature is similar.It does not change,which greatly improves the working conditions of the high pressure part of the cylinder.In general,the bypass valve is opened,and the bypass valve increases the power of the unit,reducing the heat consumption,and the effect is obvious;in terms of safety,the bypass valve can make the pressure in the regulating stage steam chamber larger than the design.The value is almost constant,and its temperature is also approximately constant,which improves the working conditions of the high pressure cylinder of the steam turbine,so that the unit can better perform the peaking work of the power grid.