Abstract: Heat transfer characteristics of typical components of municipal solid wastes (MSWs), including paper, fabric and biomass and MSW without inert components during the pyrolysis process were experimentally studied in an externally heated rotary-kiln pyrolyser at different heating rates and different rotational speeds. According to the data of thermogravimetric analysis at similar heating rate, the pyrolysis process could be divided into four stages: moisture evaporation stage, pre-pyrolysis stage, violent pyrolysis stage and ending stage. In the moisture evaporation stage, apparent heat transfer coefficients of typical MSWs components and MSW without inert components were the highest but decreased rapidly till reaching a minimum. In the pre-pyrolysis stage, apparent heat transfer coefficients of typical MSWs components and MSW without inert components changed little, having the characteristics of lowest steady heat transfer coefficient. Then in the violent pyrolysis stage, apparent heat transfer coefficients of typical MSWs components and MSW without inert components increased gradually as temperature rose. When the pyrolysis proceeded to the ending stage, the above mentioned apparent heat transfer coefficients decreased again. Apparent heat transfer coefficients also varied with rotational speed and heating rate of the rotary kiln and the effects of rotational speed and heating rate on different materials were different. In general, under the condition of low heating rate (22±2)℃·min^-1, higher rotational speeds of the rotary kiln had inhibitory effects on heat transfer at the end of moisture evaporation stage and in the pre-pyrolysis stage; while under the condition of high heating rate (32±2)℃·min^-1, higher apparent heat transfer coefficients were obtained, and the total pyrolysis time was shortened. Except for biomass, the higher the rotational speed, the higher the apparent heat transfer coefficients in the corresponding pyrolysis stage and the pre-pyrolysis stage would disappear when rotational speed was up to 3 r·min^-1. Those results could provide useful guides for the design and use of rotary kiln pyrolysis reactors.

Key words: municipal solid wastes, rotary kiln, pyrolysis, apparent heat transfer coefficient, four stages

摘要： 采用外热式回转窑,对生活垃圾主要组分[纸类、织物、生物质类(含厨余)]及除去惰性成分的垃圾在不同的升温速率和不同转速下热解过程中的传热特性进行研究,获得物料和内壁面之间的表观传热系数.根据相近升温速率下热重分析结果将热解过程分为干燥阶段、热解预备阶段、剧烈热解阶段以及热解完成阶段4个阶段.研究结果表明:在干燥阶段的表观传热系数最大,并随着温度升高而迅速减小,到水分蒸发完、进入热解预备阶段时降至最低.在热解预备阶段的升温过程中,各物料表观传热系数随温度升高基本不变,具备最低稳定传热系数特征;在剧烈热解阶段,表观传热系数随温度升高而逐渐增大;在热解完成阶段,表观传热系数再次减小.回转窑转速和升温速率对表观传热系数的影响复杂,对不同物料的影响也不相同.总体上在较低的加热速率(22±2)℃·min^-1条件下,更高的回转窑转速(3 r·min^-1)对干燥末段和热解预备阶段的传热有抑制效果;当升温速率增加到(32±2)℃·min^-1时,各种物料在对应热解段的表观传热系数均有增大的趋势,且热解总时间缩短;除生物质外,转速越高,在热解的不同阶段表观传热系数越大,在3 r·min^-1条件下热解预备阶段消失.本研究为回转窑热解反应器的针对性设计提供参考.

关键词: 生活垃圾, 回转窑, 热解, 表观传热系数, 四阶段