Development of a Novel Vacuum Pyrolysis Reactor with Improved Heat Transfer Potential

Abstract

A novel reactor has been developed in our laboratory which addresses the heat transfer limitations usually encountered in vacuum pyrolysis technology. Conventional pyrolysis reactors such as multiple hearth furnaces, rotary kilns and screw type reactors exhibit overall heat transfer coefficients ranging from 10 to 60 W·m^‒2K^‒1, depending primarily on the type of feedstock treated. The new reactor design includes a novel feedstock transport and agitation system which produces a forced exchange between the feedstock particles heated at the surface of the heating plate and the colder particles located at the core of the packed particle bed. Thus, the heat transfer between the reactor and the pyrolyzed material is dramatically increased. The other novelty of this reactor is the use of an indirect heating system involving commercial molten salts (Hitec®). Experimental and theoretical studies have been undertaken in order to tentatively correlate the reactor design parameters and the heat transfer coefficient. A new heat transfer model, based on Schlunder’s heat transfer model, has been developed to model the heat transfer in the bed of particles as a function of the mechanical movement of particles created by the agitation. This model is validated by comparing theoretically calculated overall heat transfer coefficients in a batch reactor with experimentally measured values for gravel feedstock in the same reactor. The model is then used to predict overall heat transfer coefficients for various feedstocks in the novel continuous reactor. Coefficients ranging from 70 to 250 W·m^‒2K^‒1 are obtained with this new system.

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