The Use of Torrefaction in Superheated Steam Medium to Obtain Biochar from Potato Peel

The article presents the results of studying the wet torrefaction (or accelerated hydrothermal carbonization) process in a fluidized bed in superheated steam medium. The aim of such experiment is to obtain charcoal from biomass the characteristics of which are at least as good as those of biochar obtained using the classic hydrothermal carbonization method, but with a drastically reduced the process duration and abandoning the use of reactors operating at high pressure. Previously, the processes of torrefaction in superheated steam medium of a mixture of chicken manure and wood sawdust, wastewater settlement, hazelnut shell, already used tea leaves, and sunflower husk were studied. Samples of biochar that can be used as biofuel, sorbents, or soil improvers were obtained. The duration of the wet torrefaction process in a fluidized bed was not more than 30 min instead of 5–12 h in the case of using the classic hydrothermal carbonization, and the steam gage pressure was not higher than 0.07 MPa. In the framework of the project that is being implemented jointly with the universities of the BRICS member states, the thermochemical reprocessing of potato peel into biofuel with the process temperature varied from 200 to 300°С and duration from 10 to 30 min was studied. As a result of potato peel torrefaction, the biomass heating value (in ash-free dry state) increases by a factor of 1.35 (from 20.68 to 28.0 MJ/kg). It has also been found that an increase in the torrefaction process temperature and duration facilitates an increase in the potato peel heating value with the activation energy ranging from 16.8 to 23.9 MJ/kg.