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Down flow tube reactor was used for the pyrolysis of biomass and proved to be effective. The mechanism of heat exchange within the down flow tube reactor,however,was not fully understood at present.Because of the high temperature in the reactor,biomass powders are turn into chars instantly as it enters the tube.Therefore,it made great practical sense to study the heat exchange between ceramic balls and biomass chars.An experiment apparatus was used to simulate the industry device,and the heat exchange mechanism was studied in this paper.The study included the following aspects.Firstly,the down flow tube heat exchange apparatus was designed and fabricated for simulating the pyrolysis of biomass at various conditions such as feeding,mixing,heat exchanging and separating.The mechanism of heat exchange at high temperature could be generalized from lower temperature experimental condition by similarity theory.Secondly,experiments on heat exchange between ceramics balls and air have been performed at different initial temperature of ceramic balls.Temperatures at different positions in the vertical tube were measured and the temperature change of ceramic balls was studied.The heat exchange between ceramic balls and biomass chars at different feeding ratios were also tested and the optimal ratio was then determined.From the experiments at different initial heat carrier temperatures(50℃,60℃,70℃)and different feed ratio(10:1,13:1,16:1),the following conclusions can be drawn:1,under the conditions of heat convection only between ceramic balls and air,temperature inside the tube decreases with the increase of the distance from the inlet,but when biomass chars are fed in,the temperature increases;2,the best heat exchange effect can be achieved at the feeding ratio of 13:1;3,the heat convection coefficient between ceramic balls and air is 600W/(m~2 k)at the aforementioned conditions through the heat exchange analysis;4,heat convection is the dominate way in a mixed heat exchange condition in vertical down flow tube.
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