Design Research And Calculation Of Supercritical Heat Recovery Steam Generator Of Gas-steam Combined Cycle

With rapid development of the gas-steam combined cycle power generation technology and continuous improvement of the gas turbine exhaust gas temperature,in order to further improve waste heat utilization of gas turbine exhaust gas and efficiency of combined cycle,the bottom cycle of gas-steam combined cycle using three-pressure reheat supercritical steam system is put forward,its high pressure system adopts supercritical steam conditions,its middle pressure system and low pressure system use subcritical natural circulation steam conditions.Taking the 397 MW gas turbine as the top cycle of the gas-steam combined cycle,and taking supercritical steam conditions of 27MPa/585? and subcritical steam conditions of 13.5MPa/585? as the high pressure conditions of the bottom of the combined cycle.The bottom cycle efficiency and combined cycle efficiency are calculated,the results show: when the middle and low pressure steam conditions are different,the bottom circulation efficiency of supercritical steam is 4.52 percentage points higher than that of subcritical natural circulation,the percentage of the bottom circulation output power accounting for the combined cycle output power is increased from 30.4% to 32.91%,and combined cycle net efficiency is improved by 2.34 percentage points;When the middle and low pressure steam conditions are the same,the bottom circulation efficiency of supercritical steam is 2.93 percentage points higher than that of subcritical natural circulation,the percentage of the bottom circulation output power accounting for the combined cycle output power is increased from 31.42% to 32.91%,and combined cycle net efficiency is improved by 1.46 percentage points.Based on the supercritical steam conditions of gas-steam combined cycle,for the first time,the supercritical heat recovery steam generator(HRSG)adopting double-layer flue horizontal structure is put forward,in which the high pressure evaporator adopting vertical convection evaporating tube bundles through the flue separator across the upper and lower flue,the fluid is from bottom to top,the lower is the hot water section,the upper is the overheating section and the middle is the flue separator,the diameter of the same heat pipe of the upper and lower layers is different,the lower pipe diameter is less than the upper pipe diameter,the connection of the middle uses variable diameter.By the calculation and analysis of the high pressure direct evaporation tube bundles,the results show: the height of the upper layer of the high pressure direct evaporation tube bundles is 23 m and the height of the lower layer is 21 m,which not only ensures a reasonable flow rate of fluid quality and ensures a reasonable flue gas flow rate.Using heat transfer and hydrodynamic calculation model calculates temperature,pressure drop and flow of the high pressure once-through evaporation bundles.When fluid pressure reached 27 MPa,the fluid enthalpy far away from the pseudo-critical enthalpy zone,the wall temperature increases with the increase of enthalpy,in the quasi-critical enthalpy zone,the heat transfer enhancement exists and the wall temperature changes gently with enthalpy.The fluid specific volume of the hot water section of the high pressure once-through evaporation bundles is less than the upper superheat section.The lower fluid mass flow rate is high and the flow resistance is large causing the pressure drop in the lower tubes higher than that in the upper layer.The high pressure once-through evaporation bundles fluid flow shows a positive flow response characteristics,the strongest heating and the maximum mass flow rate is in the middle position.Thermal calculation and flue gas resistance calculation of the supercritical HRSG are carried out by thermodynamic model.According to exothermic coefficient,flue gas resistance,steel consumption and occupied area,the number of the annular finned tubes and the fin structure of the heated surface of the supercritical HRSG are determined.The relative errors of the supercritical HRSG is less than 2% and the flue gas resistance of the supercritical HRSG is 3110.1Pa,which met the design standards of HRSG.