Results from the comparative analysis of the energy and economic efficiencies of the torrefaction reactors (or low-temperature pyrolysis reactors) with the heat of the heating gas supplied directly to the processed biomass are presented. Upright reactors of two types are considered, viz., reactors with a bed of dense biomass moving by gravity towards the heating gas flow and fluidized-bed reactors. Advantages and drawbacks of the different types of torrefaction reactors are discussed. Criteria for the evaluation of the torrefaction reactors' energy efficiency have been defined based on the data of experimental research conducted on a pilot power-engineering plant at the Joint Institute for High Temperatures, Russian Academy of Sciences, equipped with a moving-bed reactor and the results of numerical modeling of a fluidized-bed reactor. The conditions for creating the thermal effect of the hemicellulose decomposition reaction and the mechanism that restricts the increase in the biomass temperature during the self-heating by the exothermic reaction heat are considered. The analysis performed has shown that a moving-bed reactor with a controlled exothermic biomass destruction reaction has the highest energy efficiency and the best criteria for estimating the financial and commercial efficiency of the investments. Conclusions have been made that moving-bed reactors are preferable for small-scale production for which granulated biomass (biomass pellets) is the optimal feedstock, while fluidized-bed reactors and fine-dispersed feedstock materials are more suitable for large-scale production.

Raw biomass presents challenges for energy use due to its high moisture content, low bulk density, and susceptibility to biological degradation, which hinder storage, transport, and utilization. An experimental setup was developed to investigate exothermic behavior during torrefaction of agricultural and food industry wastes. Exothermic reactions were observed between 190 °C and 450 °C, with more prominent effects in corn waste, sugarcane bagasse, and straw compared to sunflower husks, palm residues, and coffee skin. A series of tests performed on a torrefaction reactor with a core-type wall heating system showed that the heat generated by exothermic reactions makes it possible to reduce the torrefaction time by a factor of 1.5 (from 120 to 80 min) to obtain biochar of the required quality, with only a slight process temperature increase (15%, from 200 to 230 °C). These findings offer practical pathways for transforming waste into valuable biochar, fostering environmental resilience and socio-economic benefits in communities reliant on biomass resources.

This paper analyzes the features of the implementation of the torrefaction process according to the technology developed at the Joint Institute for High Temperatures of the Russian Academy of Sciences using the internal energy of a controlled exothermic reaction. This technology allows reducing energy consumption by several factors for the torrefaction process. In experiments on the installation and in the numerical simulation of the process, an oscillatory change in the temperature of the processed biomass is revealed. A mechanism is presented for controlling the mode parameters of the torrefaction process using the effect of exothermic heat release, which ensures the smoothing of temperature oscillations of the process in a highly energy-efficient manner.

The installation for studying the processes of low-temperature pyrolysis of biomass was created in JIHT RAS. A feature of the installation is heated biomass through the exhaust gas of the internal combustion engine (mini-power stations) through the solid granules, the dried biomass (pellets). A series of experiments was conducted to study the effect of oxygen on the process of torrefaction on the installation. The oxygen content in the combustion products varied from 0.8 to 2% in the course of the experiments. Studies have shown that a slight increase in oxygen content increases the rate of heating of the processed raw materials.