Briquettes of acai seeds: characterization of the biomass and influence of the parameters of production temperature and pressure in the physical-mechanical and energy quality

Abstract

Agro-industries, leveraged by the high demand of acai products, promote environmental impact through the generation of wastes in several locals in Amazon. The use with bioenergetic purposes has capacity to mitigate these scenario. Thus, the aim of the study was to characterize the biomass of acai seeds and establish the technical parameters of temperature and pressure of work to the production of briquettes of physical, mechanical and thermal quality. Temperatures of 120, 140 and 160 °C; and pressures of 15, 20 and 25 MPa were studied. We analyzed the briquettes mechanical compressive strength, rate of water absorption, rate of volumetric expansion and energy and apparent density. To the characterization of in natura seeds, the proximate analysis, chemical composition (extractives, holocellulose and lignin contents), higher, lower and useful heating value were determined. The proximate analysis indicated biomass thermal resistance, potential to direct burning and conversion by thermochemical processes. The lignin content may increase briquettes compressive strength produced in high temperatures. It was observed that the temperature had more influence in the evaluated briquettes characteristics than the pressure. The compressive strength was greater in 160 °C and 15 MPa briquettes, indicating that the lignin works as binder in this temperature, however, with pressure improvement the resistance is not favored due to the limit of resistance to compaction. The rate of water absorption decreased with the pressure increase and the temperature statistically affected in 140 °C briquettes. We observed volumetric expansion values in consonance to other found in dense biofuels of the literature. Further, the apparent density and energy density were favored by pressure improvement and the temperature helped in the increase of the apparent density. Moreover, the produced briquettes presented gain in the apparent density regarding the in natura biomass and had energy density comparable to coal and adequate to co-firing in boilers.