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Biomass can be considered an alternative to coal in the production of heat and electricity. Many types of biomass are waste from agriculture and the food industry. This waste is cheap, readily available, and replenished annually. However, most agricultural and food industry wastes (sugar cane pulp, olive and sunflower oil production wastes, straw, etc.) have ash with a low melting point. This leads to a rapid growth of ash deposits on the heating surfaces of boilers; as a result, the actual efficiency of boilers in which waste from agriculture and the food industry is burned is 45–50%. Known biomass pre-treatment technologies that allow for the fuel characteristics of biowaste. For example, leaching of biowaste in water at a temperature of 80–240 °C makes it possible to drastically reduce the content of alkali metal compounds in the ash, the presence of which reduces the melting point of the ash. However, this biomass pre-treatment technology is complex and requires additional costs for drying the treated biomass. We proposed to use torrefaction for pre-treatment of biomass, which makes it possible to increase the heat of combustion of biomass, increase the hydrophobicity of biomass, and reduce the cost of grinding it. However, we are not aware of studies that have studied the effect of torrefaction on the chemical composition of ash from the point of view of solving the problem of preventing the formation of agglomerates and reducing the growth rate of ash deposits on the convective heating surfaces of boilers. In this paper, the characteristics of sunflower husk subjected to torrefaction in an environment of superheated steam at a temperature of 300 °C and in an environment of gaseous products at a temperature of 250 °C are studied. All experiments were conducted using fluidized bed technology. The resulting biochar has a calorific value of 14.8–23% higher than the initial husk. To assess the behavior of sunflower husk ash, predictive coefficients were calculated. Torrefaction of sunflower husks does not exclude the possibility of slagging of the furnace but reduces the likelihood of slagging by 2.31–7.27 times. According to calculations, the torrefaction of sunflower husks reduces the likelihood of ash deposits on the convective heating surfaces of the boiler by 2.1–12.2 times. According to its fuel characteristics, the husk, after torrefaction in an environment of superheated steam, approaches wood waste, i.e., can be burned separately without additives or mixtures with other fuels with refractory ash.

The process of wet torrefaction (WT) in a fluidized bed powered by superheated steam is applied to produce biochar, which can be subsequently processed into activated carbon, as an interesting bioproduct with high specific surface area. In this study, WT process was carried out at a temperature of 300-350 °C using mixtures of chicken manure and pine sawdust. Both the composition of the initial biomass, and the temperature of WT process had a considerable effect on the contents of non-condensable gaseous torrefaction products. Increasing the proportion of chicken manure in the mixture increased processing time from 30 to 46 minutes. Hence, in this work, it is hypothesized that two processes may have taken place concomitantly in the reactor: wet torrefaction of chicken manure and wet gasification of sawdust. Biochar obtained after WT of chicken manure as sole feedstock, and in mixture with sawdust was further activated using potassium hydroxide at a temperature of 750 °C. The activated carbon had following characteristics: specific pore surface area according to BET: 2031-3392 m2/g, and specific volume of pores with a size of less than 2 nm (micropores): 0.592-0.841 cm3/g. Furthermore, the quality of activated carbon in terms of porosity decreased with higher shares of sawdust in the mixture.

Torrefaction is a technology for the preliminary thermochemical treatment of biomass in order to improve its fuel characteristics. The aim of this work is to conduct comparative studies and select the optimal operating conditions of fluidized bed torrefaction for the processing of poultry litter (PL) into an environmentally friendly fuel. PL torrefaction was evaluated according to three different process configurations: (1) torrefaction of PL pellets in a fixed bed in a nitrogen medium at temperatures of 250 °C, 300 °C and 350 °C (NT1, NT2 and NT3); (2) torrefaction of PL pellets in a fluidized bed of quartz sand in a nitrogen medium at temperatures of 250 °C, 300 °C and 350 °C (NT4, NT5 and NT6); and (3) torrefaction of PL pellets in a fluidized bed of quartz sand in an environment of superheated steam at temperatures of 250 °C, 300 °C and 350 °C (ST1, ST2 and ST3). The duration of the torrefaction process in all experiments was determined by the time required for completion of CO2, CO, H2, and CH4 release from the treated biomass samples. The gas analyzer (Vario Plus Syngaz) was used to measure the concentration of these gases. The torrefaction process began from the moment of loading the PL sample into the reactor, which was heated to the required temperature. After the start of the torrefaction process, the concentration of CO2, CO, H2, and CH4 in the gases leaving the reactor initially increased and, subsequently, dropped sharply, indicating the completion of the torrefaction process. The chemical composition of the obtained biochar was studied, and it was found that the biochar contained approximately equal amounts of oxygen, carbon, nitrogen, hydrogen and ash, regardless of the torrefaction method. Furthermore, the biogas yield of the liquid condensate, obtained from the cooling of superheated steam used in the torrefaction process, was evaluated. The results highlight the efficiency of fluidized bed torrefaction, as well as the performance of superheated steam as a fluidization medium.

This work analyzes the heat transfer and fluid flow within a batch reactor for hydrothermal carbonization (HTC) of raw olive pomace (ROP). The autoclave is partially filled with a mixture of ROP and distilled water and hence it is considered as a dispersed medium. The reactor is heated through its lateral surface, whereas the bottom wall and the upper surface of the mixture are thermally insulated. Under the effect of heat and pressure, the fluid moves inside the reactor, while particles are subject to other forces. Additionally, the biomass (ROP) is decomposed into very fine particles to produce a solid product (hydrochar). COMSOL Multiphysics software is used for the analysis of heat transfer and fluid dynamics. Chemical kinetics of the reactions are modeled by a basic kinetics model. Numerical results are validated using experimental data carried out in similar operating conditions. They are in good agreement since the deviation between them does not exceed 6%. Isotherms, velocity fields, and isobars are evaluated within the reactor as well as velocity and distribution of particles. These amounts are influenced by the imposed heat flux at the lateral wall (q0). Also, it has been shown that the temperature and pressure values reached are above those required by the HTC process and, consequently, a HTC reactor could be designed with optimal operating conditions.

This paper aims at investigating the production of high quality briquettes from olive mill solid waste (OMSW) mixed with corn starch as a binder for energy production. For this purpose, different mass percentages of OMSW and binder were considered; 100%-0%, 90%-10%, 85%-15%, and 70%-30%, respectively. The briquetting process of the raw mixtures was carried out based on high pressures. Physico-chemical and mechanical characterizations were performed in order to select the best conditions for the briquettes production. It was observed that during the densification process, the optimal applied pressure increases notably the unit density, the bulk density, and the compressive strength. Mechanical characterization shows that the prepared sample with 15% of corn starch shows the best mechanical properties. Moreover, the corn starch binder affects quietly the high heating value (HHV) which increases from 16.36 MJ/Kg for the 100%-0% sample to 16.92 MJ/Kg for the 85%-15% sample. In addition, the kinetic study shows that the binder agent does not affect negatively the thermal degradation of the briquettes. Finally, the briquettes characterization shows that the studied samples with particles size less than 100 μm and blended with 15% of corn starch binder are promising biofuels either for household or industrial plants use.