Comparative Studies of the Biochar Production Process Using Hydrothermal Carbonization and Superheated Steam Torrefaction

• Published in: Thermal engineering 2022-12, Vol.69 (12), p.981-988
• Main Authors: Is’emin, R. L., Kuz’min, S. N., Konyakhin, V. V., Milovanov, O. Yu, Mikhalev, A. V., Muratova, N. S., Nebyvaev, A. V., Kokh-Tatarenko, V. S.
• Format: Article
• Language: English
• Subjects: Aqueous solutions; Biofuels; Biomass; Boiler Auxiliary Equipment; Burners; Calorific value; Carbon content; Carbonization; Chickens; Combustion; Comparative studies; Drying; Engineering; Engineering Thermodynamics; Expenditures; Fluidized bed furnaces; Fluidized bed reactors; Fluidized beds; Heat and Mass Transfer; Hydroxymethylfurfural; Litter; Manures; Mixtures; Poultry; Poultry farming; Power Plant Fuels; Pyrolysis; Reagents; Sawdust; Steam Boilers; Volatile compounds
• ISSN: 0040-6015; 1555-6301
• DOI: 10.1134/S0040601522120035

— Accumulation of chicken manure with litter (sawdust or fragmented straw) that is produced in large quantities at poultry farms (in producing 1 kg of poultry, 1–3 kg of manure with litter is obtained) poses a serious problem for the environment. Poultry farms are among the largest consumers of electricity, which can be generated by combusting manure with litter, also jointly with coal, in bubbling or circulating fluidized bed furnaces. For making the combustion more efficient and environmentally friendly (reducing carbon oxide emissions) the manure wetness and the content of volatiles in it should be decreased, and its heating value should be increased. To this end, manure with litter can be subjected, prior to its combustion, to pretreatment using the hydrothermal carbonization or torrefaction method. The article presents a comparison of the results obtained from studies of methods for processing a mixture of chicken manure and sawdust into biofuel in superheated steam. Chicken manure and its mixture with sawdust in the ratios 1 : 1, 1 : 2, and 2 : 1 were subjected to thermochemical treatment. Hydrothermal carbonization was carried out in a batch laboratory autoclave at a temperature of 220°С for 1 and 4 h. Biomass torrefaction was carried out in a fluidized bed reactor with the bed formed by biochar particles that were preliminarily obtained in superheated steam at temperatures of 300 and 350°С. It has been found that by applying the hydrothermal carbonization method, the carbon content in manure with litter can be increased from 42 to 63%, and the higher heating value from 16.7 to 17.8 MJ/kg. In turn, by applying the method of fluidized bed torrefaction in superheated steam, these indicators can be increased to 75% and 18.8 MJ/kg, respectively. The hydrothermal carbonization and torrefaction processes require significant energy expenditures. For making both processes more economically efficient, the possibility of extracting, from the spent water (or condensate), 5-hydroxymethylfurfural, which is regarded as a key reagent, a so-called platform chemical, for producing various practically important substances, including polymers, pharmaceutical drugs, solvents, and fuels, is being researched. It has been determined that the content of 5-hydroxymethylfurfural in these aqueous media makes 0.02–0.80 g/dm 3 and depends on the biomass thermochemical treatment method and temperature at which the process was performed.