Experimental And Simulation Study On Coal-fired Power Generation With Biomass Fluidized Bed Positive Pressure Gasification

In the biomass gasification coupled coal-fired power generation system,the gasification furnace mostly adopts the fluidized bed.It generally operates at a slight negative pressure or balance.By the heat exchanger,the combustible gas generated by gasification is either cooled to normal temperature and sent into the boiler by a normaltemperature booster fan,or cooled to 400～500°C and sent into the boiler through a medium-high temperature booster fan.When the combustible gas is cooled to normal temperature,the tar in the combustible gas will condense on the pipeline,and in severe cases,the system may not operate normally.When the combustible gas is cooled to 400～500℃,it can effectively solve the problem of tar condensation,so the existing biomass gasification coupled power generation projects mostly adopt this method.However,considering the high equipment cost of medium-high temperature booster fans and its long-term operation at high temperature,it’s not conducive to the safe operation of the system.When the gasification furnace is operated under positive pressure,the gasification pressure can be used as the power for the combustible gas to enter boiler.It reduces the equipment cost by avoiding the use of medium-high temperature booster fan.What’s more,it can effectively improve the economics and safety of system operation,and is in line with the needs of current technological development.However,there are few studies on the impact of positive pressure gasification on coupled power generation,and no public reports have been reported.This paper explores the effect of positive pressure conditions on the gasification process through experiments.Based on the 600 MW burner pulverized coal powder boiler,the Aspen Plus software is used to compare the technical and economical analysis of the coupled power generation modes of gasifier operating in balance and positive pressure.First,a biomass fluidized bed gasification stand has been built to study the effects of temperature,air equivalent ratio-ER,and positive pressure(1700 Pa～6300 Pa)on the gasification process.During gasification under positive pressure conditions,the fluidized bed can run stably.With the change of gasification pressure,the composition of syngas and the gasification index doesn’t change significantly.The impact of positive pressure is not obvious.Then,Aspen Plus software is used to establish two coupled coal-fired power generation system models for gasifier operation in balance and positive pressure.As the proportion of co-firing increases,the boiler flue gas volume increases,the furnace temperature decreases,the exhaust gas temperature increases,and the boiler thermal efficiency decreases.Under the same proportion of co-firing,compared with the gasifier operating in balance,the operation of the gasifier in positive pressure mainly provides power for the combustible gas to enter the boiler,and it’s operation index of the boiler does not change significantly under different positive pressure(4000 Pa～8000 Pa).Finally,the economic analysis of the traditional coal-fired power plant and the two gasification coupled power generation methods are carried out,and the impact of key parameters in the gasification coupled power generation system such as biomass fuel prices and by-product prices on the system power generation cost is explored.For the two coupled power generation methods that the gasifier operates in balance and positive pressure,as the proportion of co-firing increases,the power generation cost of both power generation modes increase.Based on the power generation cost of traditional coal-fired power plants of 0.3088 CNY/k W·h,when the co-firing ratio is 20%,the system power generation costs of the gasifier operating in balance and positive pressure are 0.3552 CNY/k W·h and 0.3545 CNY/k W·h,respectively.The power generation cost of the system operating the gasifier under positive pressure is lower and the economic benefit is better.In this paper,based on the safety and economy of biomass gasification coupled power generation system,the two gasification coupled power generation methods are compared and studied.Compared with the operation of the gasification furnace in balance,the operation of the gasification furnace under positive pressure has no obvious effect on the operation of the system,but it can improve the safety and economy of the system operation.This conclusion will help promote the advancement of biomass gasification coupled coal-fired power generation technology.