Design And Exergy Analysis Of 1000-MW Double-reheat Double-turbine Regeneration System

At present,China’s large-capacity,high-parameter double reheat thermal power units have made remarkable achievements.The development of ultra-supercritical double-reheat technology is a practical choice to further improve the power generation efficiency,reduce coal consumption,reduce carbon emissions,and save resources.There are some problems in the double reheat units,such as prodigious superheat degree of extraction steam in the regenerative heaters.This problem hinders the further improvement of the power generation efficiency of the unit.It is of great significance to study the underlying causes and solutions of excessive superheat of extraction steam to promote the development of double-reheat technology.In this paper,a domestic 1000MW ultra-supercritical double reheat unit is taken as an example and the Ebsilon software is used to simulate the unit.The units are divided into three schemes:original unit,outer-steam cooler unit and double-turbine regeneration unit.At present,outer-steam cooler system in double reheat units has been commonly adopted to solve the problem of prodigious superheat degree of extraction steam.More and more researches show that double-turbine regeneration system has shown a better economy and practicability in resolving prodigious superheat degree of extraction steam for double reheat.A improved concept and scheme of double reheat double-turbine regeneration system are proposed,and compared with the original unit and outer-steam cooler unit,the main features and performance of the double reheat double-turbine regeneration system are discussed and analyzed.Firstly,the thermal equilibrium analysis method and the exergy analysis method are used to calculate the power generation efficiency and coal consumption of different units under the design conditions.The exergy parameters of boiler,steam turbines,condenser,regenerative heaters,etc.are obtained.The superheat degree of the regenerative heaters of different units is calculated and analyzed.The results show that under the design conditions,the superheat degree of every regenerative heater of the double-turbine regeneration system is reduced,and the energy-saving performance is better than that of the outer-steam cooler system.Secondly,the performance of the three units under off-design conditions is studied.The power generation efficiency and coal consumption are calculated and compared.The exergy loss and exergy efficiency of the two key equipments of steam turbine and regenerative heater are further analyzed.The results show that the energy-saving performance of the double-turbine regeneration system gradually decreases as the load decreases.At low loads,the performance of the regenerative turbine is significantly reduced,and the energy-saving effect of the double-turbine regeneration system is not as good as that of an outer steam cooler system.Finally,the reheat pressure of the three units is optimized by the enumeration method,which improve the cycle efficiency of the units.The results show that:since the additional effect of the reheat cycle is impaired,the optimum reheat pressure of the outer-steam cooler and the double-turbine regeneration system is lower than that of the original unit.The research of double reheat double-turbine regeneration system has better solved the key problems of the existing double reheat technology,further promote the innovation and development of double reheat technology.It provides a feasible direction for the practical application of double reheat technology,and has important practical significance for China to achieve energy conservation and green development.