Cogeneration System Design And Research Of Small Capacity Coal-fired Units With Advanced Steam Condition

In order to meet the demand of using high-efficiency clean coal-fired units to realize central heating in county and township cities,the technical proposal of using small capacity and advanced steam condition units for heating was put forward.Based on the enthalpy-entropy diagram of steam,the main steam conditions of the 50MWe unit in service were increased from 8.82MPa,535?to 12MPa,625?under the condition of ensuring the high-pressure stage blade height and the final stage exhaust steam humidity are reasonable and no reheating is needed,and the rated boiler evaporation was still220t/h.The combined power of heat and power supply in heating period is 40MWe,while in non-heating period it can be operated in pure coagulation mode,with a power of64MWe Since the unit has no reheating and is a natural circulation drum boiler,its investment,floor space and maintenance costs are greatly reduced.The use of efficient flue gas purification technologies such as dust removal,desulfurization and denitration can meet the standard of ultra-low emission of atmospheric pollutants.Taking a county seat with a heating area of 2.5 million m~2 in North China as an example,this paper analyzes and compares the economy of short-distance heating of40MWe advanced-condition back-pressure units and long-distance heating of 1000MW units.The results show that the standard coal consumption rate for heating of 40MWe back pressure units is 39.208kg/GJ,which is 5%higher than 1000MW units.Considering such factors as standard coal consumption for heating,heat dissipation loss of heating pipelines and pipeline laying cost,the economy of using 40MWe advanced-condition units for heating is better than 1000MW units.The 220t/h advanced condition boiler body is designed and calculated.The feed water temperature 270?,boiler efficiency is 93.2%and coal consumption is 26089kg/h when bituminous coal is used.The furnace and convection heating surfaces are designed and checked.Compared with the 220t/h boiler with conventional conditions,the low temperature superheater is increased in horizontal section,the heating surface area of feed water preheating and evaporation decreases,while that of superheated heating surface increases.The steam turbine system of 64MWe advanced condition units during pure condensing operation is designed and calculated,and the thermal economy indexes are calculated and compared.The results show that the pure condensing power of the unit is64MWe,the high-pressure stage is increased by two stages and the low-pressure stage by one stage on the basis of the original 50MWe steam turbine,and the steam dryness of the steam turbine is 89.7%,within a reasonable range.The volume flow of high-pressure stage steam is reduced by 1.5%compared with the original 50MWe steam turbine,high pressure stage blade height and the increase of blade height loss and impeller friction loss are all within a reasonable range,and the design of small capacity and advanced condition steam turbine is feasible The power supply coal consumption rate of the unit is309.8g/(kW·h),the heat consumption rate is 7832kJ/(kW·h),and the net efficiency of the power plant is 39.7%.Compared with 50MWe units,the coal consumption rate of power supply is 62g/(kW·h)lower,the heat consumption rate is 16%lower,and the net efficiency of the power plant is 6.6 percentage points higher.The thermal economic indexes are equal to those of subcritical 600MW units and higher than those of ultra supercritical 1000MW units at 50%load.The exergy analysis of the unit shows that each equipment efficiency index of 64MWe unit has reached the level of 600MW unit.