Chemical Engineering and Processing, Vol.130, 67-75, 2018
Modelling and improvement of heat transfer coefficient in auger type reactors for fast pyrolysis application
Simulations of auger type reactors are conducted with the aim of assessing the rate of heat transfer between heat carrier and biomass particles to achieve fast pyrolysis conditions. It is shown that the heat transfer coefficient can be comparably high as in fluidized bed reactors due to the dense packing of particles that is kept by mechanical agitation under certain conditions. This holds specifically true if the system is designed such that heat dissipation through the packed bed is avoided. An auger reactor design featuring twin screws that is under operation in pilot scale since several years at KIT has been investigated in more detail. Inefficiencies in the initial mixing section have been identified that lead to the fact that most of the heat is transferred under suboptimal conditions. By investigating three design changes by simulation some of these inefficiencies could be removed and the relevant initial mean heat transfer coefficient increased significantly as compared to the original design. Additionally, this changed design has further potential for process intensification due to a decrease in the mean residence time of biomass particles in the reactor by 50%.