Study On Operation Performance And Combustion Products Of Straw Gasification Coupled With Coal-fired Boiler

Based on the design parameters of a 330MW coal-fired boiler,the model of biomass gasification coupled with coal-fired boiler system was established by Aspen Plus simulation software in this paper,in which straw was selected as biomass.The influences of air to biomass ratio and straw moisture content on straw syngas compositions and gasification performance,and straw syngas co-firing,excess air coefficient and boiler load on coupled system operation and combustion product emissions were discussed.The main research contents are as follows:?1?The model of biomass gasification process was established.The influences of air to biomass ratio and straw moisture content on straw syngas compositions and gasification performance were analyzed.The optimal air to biomass ratio under different straw moisture content was determined.The straw syngas was obtained under optimal gasification conditions.With the increase of straw moisture content,the volume fraction of H₂ in straw syngas first increases and then decreases,the volume fraction of CO,NO and SO₂ decrease,the volume fraction of CH₄ increases,the lower heating value of straw syngas,gasification temperature,gasification efficiency and gasification heat efficiency decrease,while the sensible heat of straw syngas increases.?2?The model of bio-syngas coupled coal-fired boiler system was established.The influences of straw syngas co-firing ratio and straw moisture content on coupled system operation performance and pollutant emissions were studied.Under the condition of theoretical combustion air volume,with the increase of co-firing ratio,furnace combustion temperature and flue gases volume under standard conditions decrease,flue gases density increases.When straw moisture content is 10%,flue gases temperature first decreases and then increases,boiler efficiency and system efficiency increase slightly with the increase of co-firing ratio.The flue gases temperature increases,boiler efficiency and system efficiency decrease with the increase of straw moisture content.The emission reduction rates of NO and SO₂ increase with the increase of co-firing ratio,and with the increase of straw moisture content,those reduction rates increase.?3?Under the condition that the capacity of the gasifier is constant and the rated load of the boiler,the influences of excess air coefficient and straw moisture content on the operating performance and combustion products of coupled system were studied.With the increase of excess air coefficient,furnace combustion temperature decreases,NO and SO₂ emission reduction rates decrease.When the excess air ratio is constant,with the increase of straw moisture content,the mass flow rate of standard coal savings and co-firing ratio decrease,furnace combustion temperature decreases,flue gases temperature increases,flue volume under standard conditions decreases,boiler efficiency and coupled system efficiency decrease,NO emission reduction rate increases,SO₂ emission reduction rate decreases,and the moisture content in the flue gases does not change much.?4?Under the condition that the capacity of the gasifier is constant,the influences of straw syngas co-firing on operation performance and combustion products at variable boiler loads of coupled system were studied.With the decrease of boiler load,straw syngas co-firing ratio and optimal excess air coefficient increase,the furnace combustion temperature,H₂O,CO₂,NO,N₂O and SO₂ volume fraction in flue gases decrease,NO₂ and SO₃ volume fraction increase,flue gases temperature and flue gases volume under standard conditions decrease,boiler efficiency and coupled system efficiency first increase and then decrease when syngas and coal co-firing at the optimal excess air coefficient.Meanwhile,the coupled system efficiencies are higher than 84%at variable boiler loads when the optimal air to biomass ratio of gasification process and optimal excess air coefficient of co-firing process were guaranteed.