I think of autothermal processes as involving an exothermic chemical reaction with the material being processed in the reactor whereas allothermal involves heat transfer to the material in the reactor but no reaction of the material. 

I will illustrate the difference between allothermal and autothermal by the following examples:

1) In coal gasification, coal is heated by external heat sources the process is called "allothermal."

2) When steam in a reaction with methane to form syngas (CO + H2), the process is called "autothermal reforming" or ATR.

Hope this helps answer your question.

Professor Yehia Khalil

Yale University

USA

I agree with Prof. Baxter. In autothermal processes, part of the energy content of the fuel is used to keep an endothermal process running. When this heat is provided from external sources (e.g. from combustion within another reactor, as in the example), it is allothermal.

Allothermal originates from the Greek word allos meaning other. Basically allothermal means heating from an external source for instance ceramic band heaters or heating elements. However, autothermal means heating from using heat from exothermic process within the reactor usually with a highly combustible material. In oil palm waste valorization, palm kernel shell is typically used for autothermal heating.  

Your process as have described is allothermal. Because heat requirement for pyrolysis was supplied from external source. If there is partial combustion in the pyrolyser to supply the heat necessary for pyrolysis of the remaining material than it would be auto thermal.