煤粉燃烧产生的飞灰导致炉膛和烟道内出现结渣沾污现象,飞灰的黏附特性受煤中碱金属/碱土金属(Alkali and Alkaline Earth Metals,AAEM)的影响,为减少飞灰在换热面上的沉积,分析其燃烧过程中AAEM的赋存形态和迁移机理,论述了AAEM蒸汽冷...煤粉燃烧产生的飞灰导致炉膛和烟道内出现结渣沾污现象,飞灰的黏附特性受煤中碱金属/碱土金属(Alkali and Alkaline Earth Metals,AAEM)的影响,为减少飞灰在换热面上的沉积,分析其燃烧过程中AAEM的赋存形态和迁移机理,论述了AAEM蒸汽冷凝对飞灰特性产生的影响,同时分析了飞灰在换热面上的沉积机理。结果表明,燃烧温度和AAEM赋存形态的差异导致其析出过程和析出量不同。温度升高会促进AAEM的释放,随着AAEM在萃取液中的溶解性降低,在燃烧时释放更困难;释放到气相中的AAEM在换热面或飞灰表面异相冷凝形成黏性层,增大了换热面对飞灰的捕集效率;在气相中均相冷凝形成气溶胶,气溶胶作为前驱体在后续聚并过程中形成亚微米飞灰;飞灰的沉积受分子扩散、布朗运动、涡流碰撞、热泳、重力沉降、惯性碰撞等多种因素影响,重力沉降、惯性碰撞主要影响大粒径飞灰颗粒的运动轨迹,其他因素则主要影响小颗粒的运动;在换热面上形成的沉积层会出现分层结构,沉积内层的生成主要由无机蒸汽冷凝和小粒径飞灰沉积造成,外层沉积层主要由大颗粒飞灰沉积形成。黏附在换热面上的飞灰影响锅炉热效率、高温下腐蚀金属壁面,对锅炉的安全稳定运行埋下隐患。因此部分学者提出煤粉的水洗、掺烧、吹灰、换热面涂层、结构改进等方案来减缓沉积层的形成。但由于煤中成分多变,难以准确预测对燃料结渣沾污行为,应加强不同赋存形态元素的研究、不同形态飞灰的沉积及飞灰形成过程中复杂的物理化学,为结渣沾污的防治提供理论支持。展开更多
Using age adjusted effective modulus(AAEM)method,creep of concrete filled steel tube(CFST)member was formulated considering of creep coefficient and aging coefficient.Ten CFST specimens were tested including eight for...Using age adjusted effective modulus(AAEM)method,creep of concrete filled steel tube(CFST)member was formulated considering of creep coefficient and aging coefficient.Ten CFST specimens were tested including eight for creep and two for shrinkage.The experimental result was compared with the computed result using AAEM in which the creep coefficient was taken from calibration of ACI model based on experimental result on sealed concrete,and aging coefficient was supplied from relaxation test on sealed concrete specimen.Furthermore,the creep of CFST member was analyzed using author's own subroutine to input concrete properties through user programmable feature(UPF)in ANSYS software.Comparison was made on authors' own experimental database,some existing experimental results,and results from AAEM and numerical analysis.Finally,the conditions of applicability of AAEM method are put forward,and numerical approach to compute creep of CFST specimen is delineated.展开更多
文摘煤粉燃烧产生的飞灰导致炉膛和烟道内出现结渣沾污现象,飞灰的黏附特性受煤中碱金属/碱土金属(Alkali and Alkaline Earth Metals,AAEM)的影响,为减少飞灰在换热面上的沉积,分析其燃烧过程中AAEM的赋存形态和迁移机理,论述了AAEM蒸汽冷凝对飞灰特性产生的影响,同时分析了飞灰在换热面上的沉积机理。结果表明,燃烧温度和AAEM赋存形态的差异导致其析出过程和析出量不同。温度升高会促进AAEM的释放,随着AAEM在萃取液中的溶解性降低,在燃烧时释放更困难;释放到气相中的AAEM在换热面或飞灰表面异相冷凝形成黏性层,增大了换热面对飞灰的捕集效率;在气相中均相冷凝形成气溶胶,气溶胶作为前驱体在后续聚并过程中形成亚微米飞灰;飞灰的沉积受分子扩散、布朗运动、涡流碰撞、热泳、重力沉降、惯性碰撞等多种因素影响,重力沉降、惯性碰撞主要影响大粒径飞灰颗粒的运动轨迹,其他因素则主要影响小颗粒的运动;在换热面上形成的沉积层会出现分层结构,沉积内层的生成主要由无机蒸汽冷凝和小粒径飞灰沉积造成,外层沉积层主要由大颗粒飞灰沉积形成。黏附在换热面上的飞灰影响锅炉热效率、高温下腐蚀金属壁面,对锅炉的安全稳定运行埋下隐患。因此部分学者提出煤粉的水洗、掺烧、吹灰、换热面涂层、结构改进等方案来减缓沉积层的形成。但由于煤中成分多变,难以准确预测对燃料结渣沾污行为,应加强不同赋存形态元素的研究、不同形态飞灰的沉积及飞灰形成过程中复杂的物理化学,为结渣沾污的防治提供理论支持。
文摘Using age adjusted effective modulus(AAEM)method,creep of concrete filled steel tube(CFST)member was formulated considering of creep coefficient and aging coefficient.Ten CFST specimens were tested including eight for creep and two for shrinkage.The experimental result was compared with the computed result using AAEM in which the creep coefficient was taken from calibration of ACI model based on experimental result on sealed concrete,and aging coefficient was supplied from relaxation test on sealed concrete specimen.Furthermore,the creep of CFST member was analyzed using author's own subroutine to input concrete properties through user programmable feature(UPF)in ANSYS software.Comparison was made on authors' own experimental database,some existing experimental results,and results from AAEM and numerical analysis.Finally,the conditions of applicability of AAEM method are put forward,and numerical approach to compute creep of CFST specimen is delineated.
