混合生物质燃料循环流化床锅炉受热面结焦机理研究

Study on slagging mechanism of multiple biomass co-combustion on heatingsurface in a circulating fluidized bed boiler

某75 t/h生物质循环流化床锅炉长期燃用混合燃料(桉树皮、木尾、木板、竹子和工业合成板),在实际运行过程中高温过热器和低温过热器区域结焦严重。考虑到不同生物质燃料特性的差异性,了解混合生物质燃料燃烧中壁面的结焦机理尤为迫切。研究了5种生物质燃料的灰成分和灰熔点特性,并对该循环流化床锅炉结焦严重的高温和低温过热器受热面区域的结焦和积灰样品进行物理和化学特性表征。研究结果表明:该锅炉所燃用的生物质燃料中,竹、木尾和木板的钙和钾含量高,灰中CaO含量在30%左右,K_(2)O含量在10%以上;桉树皮硅和铝含量高,灰中SiO_(2)含量高达62.4%;工业合成板与木尾含有较多的氯元素,灰中氯含量分别为0.670%和0.865%。5种生物质除竹和工业合成板灰熔融温度较低外,其余生物质灰熔融温度高,软化温度在1200℃以上。过热器区域的结焦呈分层结构:高温过热器焦样的外层较硬,中层包含白色的KCl晶体和飞灰颗粒,外层以及飞灰颗粒均以Ca_(2)Al_(2)SiO_(7)、SiO_(2)、KCl、Ca_(2)MgSi_(2)O_(7)等为主;低温过热器焦样外层的灰成分与高温过热器侧焦样的组分相同,但白色中层的KCl晶体含量更高,其同烟气中KCl蒸气的冷凝析出密切相关。

A 75 t/h biomass circulating fluidized bed(CFB)boiler burns mixed fuels for long time,including eucalyptus bark,wood tail,wood board,bamboo,and industrial composite board.On the high-temperature superheater and low-temperature superheater,a severe slagging phenomenon was observed during actual operation.As a result,it's critical to investigate the slagging mechanism of mixed biomass fuels while considering the characteristics of various biomass fuels.The slagging samples from a biomass CFB boiler's high-temperature superheater and low-temperature superheater were collected firstly.Following that,the physical and chemical properties of the collected samples were investigated by analyzing the ash composition and ash fusion temperatures.The results show that among the biomass used in the boiler,bamboo,wood tail and wood board have high calcium and potassium content,with approximately 30% CaO content and more than 10% K_(2)O content.Eucalyptus bark contains high silicon and aluminum,with an ash content of SiO_(2) as high as 62.4%.Industrial composite board and wood tails have high levels of chlorine,and the chlorine content in the ash is 0.67% and 0.865%,respectively.In addition to bamboo and Industrial composite board,others have high ash fusion temperatures with a soften temperature above 1200℃.The slagging samples from high-temperature superheater area have a layered structure:the outer layer of the slagging sample is hard,the middle layer contains white KCl crystals and fine particles,and the outer layer of slagging and ash particles are made of Ca_(2)Al_(2)SiO_(7),SiO_(2),KCl,Ca_(2)MgSi_(2)O_(7).The low-temperature superheater's outer slagging samples have the same composition as the high-temperature superheater's.However,white KCl crystal content in the middle layer is higher,which is related to the condensation and precipitation of KCl vapor in the flue gas.