Analysis And Research On Energy Saving System Of Zero Energy Plant Based On Waste Heat Utilization Of CFB Boiler

In the environment of accelerating the adjustment of energy structure,the circulating fluidized bed boiler plays an irreplaceable role as a kind of efficient clean coal technology.In recent years,with the soaring installed capacity of new energy,the main task of thermal power has gradually changed from power supply to heat supply and peak regulation.Compared with traditional coal-fired units,circulating fluidized bed boiler units not only have the conditions of pumping steam for heat supply,but also have good load peak regulation performance.Therefore,the circulating fluidized bed boiler unit plays an important role in the thermal power transformation process.On the other hand,the fuel fluidized combustion form of circulating fluidized bed boiler determines its characteristics of large slag discharge and high plant electricity rate,which reduces its market competitiveness.Therefore,it is of great practical significance to study how to effectively utilize a large amount of waste heat such as slag of circulating fluidized bed boiler,improve the thermal efficiency of unit,reduce the power consumption rate of plant,and even realize zero energy consumption of plant power.In this thesis,145 MW circulating fluidized bed boiler unit is taken as the research object,and EBSILON simulation software is used to establish a complete thermodynamic system model of the unit.As the reference system,the unit thermodynamic test is carried out on site,and the accuracy of the simulation model is verified.The flue gas,slag and waste heat of the boiler are recovered and used to heat the condensate water of the unit,the backwater of the heating network or the hot air at the outlet of the boiler air preheater.The secondary hot air system of the waste heat heating of the furnace,the steam pump system of the waste heat of the furnace and the waste heat of the waste heat drying into the furnace coal system are constructed,and the simulation models of each waste heat utilization system are loaded.Among them,the steam dynamic pump system of slag waste heat adopts the small back pressure steam turbine,aiming at four different connection modes of small steam turbine exhaust pipe and condensate system,the exhaust steam utilization economy of small steam turbine is compared and analyzed.The simulation results show that when the exhaust heat exchanger is parallel with 6# and the exhaust steam condensate and drain reinjection into 5# and the low inlet pipe,the energy saving benefit is the largest,and the average annual replacement plant power is 6005 kW.The comparison and analysis of the economy of three kinds of boiler waste heat utilization modes show that the standard coal consumption rates of the three power supply systems of slag waste heat heating secondary air,steam pump,dry coal into the furnace are reduced by 11.5g/(kW·h),12.54g/(kW·h)and 12.88g/(kW·h)respectively.The substituted plant power accounts for 61.43%,67.26% and69.52% of the total plant power,respectively.None of the three methods can achieve the effect of zero energy consumption plant power,among which the coal-fired drying system replaces the largest plant power.In order to realize zero energy consumption of circulating fluidized bed unit,the drying system of coal in the furnace is optimized,the deaerator of the unit is used to pump steam and further dry the coal in the furnace.The influencing factors and the reduction of power consumption of the plant are analyzed.On this basis,the zero energy consumption plant power system of circulating fluidized bed unit is established.The results show that the power of steam compressor increases with the increase of coal dryness.The power of boiler blower and induced draft fan decreases gradually.The power of circulating pump and condensate pump increases first and then decreases.The power of steam turbine increases first and then decreases.Power of auxiliary plant increases;Power reduction of the unit plant increases.When the heat source steam of the dry coal in the furnace needs to be filled by the steam extraction of the turbine,the increase trend of the power consumption of the replacement unit plant slows down,and the difference of energy saving between non-heating and heating season increases with the increase of the dryness of the coal in the furnace.The economic change of coal drying system under variable load condition and zero energy plant power system is compared and studied.The variable condition analysis of coal drying system shows that,under 100%THA,75%THA and 50%THA,the power substitution rate of the drying system before optimization is 69.52%,58.19% and 51.33%,respectively.The standard coal consumption rates of power supply were respectively reduced by 12.88g/(kW·h),12.35g/(kW·h)and 13.82g/(kW·h).For zero energy plant power system,the reduction of power supply standard coal consumption is 18.18g/(kW·h),20.53g/(kW·h),25.96g/(kW·h),indicating that the lower the load,the greater the reduction of power supply standard coal consumption of zero energy plant power system.