Studying the Sunflower Husk Ash Properties after Husk Treatment Using Various Torrefaction Methods

• Published in: Thermal engineering 2023-04, Vol.70 (4), p.290-298
• Main Authors: Nebyvaev, A. V., Milovanov, O. Yu, Klimov, D. V., Kuz’min, S. N., Ryzhenkov, A. V., Dubina, V. A., Zavizhenets, R. V.
• Format: Article
• Language: English
• Subjects: Agglomerates; Ashes; Biomass; Boiler Auxiliary Equipment; Boilers; Burner Units; Calorific value; Chemical composition; Criteria; Drying; Energy consumption; Engineering; Engineering Thermodynamics; Fluidized bed combustion; Fluidized beds; Fuels; Greenhouse gases; Heat and Mass Transfer; Melt temperature; Melting; Moisture effects; Power Plant Fuel; Power plants; Pyrolysis; Slagging; Steam Boilers; Sunflowers
• ISSN: 0040-6015; 1555-6301
• DOI: 10.1134/S0040601523040043

— Plant cultivation waste (straw and husk of sunflower, rice, miller, and other cereal crops) feature low moisture and ash content, and their heating value is close to or even higher than that of many power plant coals. The utilization of such waste for energy-generation purposes could help solve environmental problems connected with decreasing greenhouse gas emissions. At the same time, the chemical composition of the ash from this waste results in its having a low melting temperature, which causes the furnace slagging to occur and a rapid growth of ash deposits on the boiler convective heating surfaces. The well-known methods for waste pretreatment before combustion (water flushing and hydrothermal carbonization) feature excessive energy consumption and low yield. Therefore, it is proposed to estimate the effect on ash-melting properties of such a treatment method as torrefaction. Two biomass torrefaction methods were used: in the medium of gaseous torrefaction products in a plate reactor with a mechanically stirred biomass bed and fluidized bed torrefaction in a superheated steam medium. The chemical composition of the ash from biochars obtained using both methods is studied. Based on the known data, prediction criteria were calculated using which it is possible to estimate the possibility of biochar ash to melt, slag agglomerates to emerge, ash deposits to form on the boiler convective heating surfaces, and agglomerates to form during sunflower husk fluidized bed combustion. As is known, the use of prediction criteria often yields contradictory results. In view of this circumstance, for estimating the melting properties of ash from biochars and similar biomass, a 3D diagram was used, with the concentrations of various oxides contained in the ash marked on its axis. By using this diagram, the melting properties of the obtained biochars can be compared with those of other biomass kinds. This allows the following conclusion to be drawn: biochar produced as a result of torrefaction performed in a superheated steam medium is close in its fuel characteristics to wood waste; i.e., it can be combusted alone without additions or mixtures with other kinds of fuel having a refractory ash.