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.