Heat transfer characteristics of MSW and its typical components in rotary kiln at different pyrolysis stages

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. ©, 2014, Chemical Industry Press. All right reserved.