Estudo dos parâmetros cinéticos da combustão de resíduos provenientes da indústria cervejeira

Abstract

Brazil stands out as one of the world’s largest beer producers and consumers; however, this production chain generates lignocellulosic by-products, such as spent malt grains and hop residues, which are often improperly discarded, contributing to greenhouse gas emissions. In parallel, low-cost regional biomasses, such as mesquite wood, remain widely used as solid fuels in boilers of breweries, despite their efficiency limitations. In this context, the energy recovery of these lignocellulosic by-products through thermochemical conversion routes for bioenergy production aligns with the principles of the circular bioeconomy. The objective of this study is to investigate the energy potential of malt bagasse (MB), hop bagasse (BL), and mesquite wood (MA) through physicochemical characterization, multicomponent kinetic modeling, and estimation of the thermodynamic parameters of the combustion process, aiming to improve their use as solid fuels for bioenergy production. The physicochemical characterization of the biomasses was performed through elemental analysis, proximate analysis, calorific value determination, evaluation of bulk and energy densities, as well as analysis of the chemical composition of the ashes. The lignocellulosic by-products presented acceptable ash contents (5.6 – 12.18%), high volatile matter contents (71.29 – 79.06%), and moderate fixed carbon levels between 8.76 and 18.91%, indicating behavior compatible with solid fuels of good thermal reactivity. The calorific value ranged from 18.18 to 22.35 MJ kg⁻¹, levels comparable to or higher than those of other biomasses used in combustion systems. The bulk density ranged from 222.67 to 358.67 kg m⁻³, reflecting good conditions for logistics and storage. The inorganic composition of the ashes indicated the predominance of Si, K, Ca, Mg, and P, with relative variations among the biomasses. The multicomponent kinetic analysis identified five pseudocomponents in all lignocellulosic by-products, enabling the determination of the kinetic triplet through isoconversional methods, kinetic compensation effects, and integral master plots. The activation energy estimated by the Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose, Starink, and Friedman isoconversional methods ranged from 90.33 to 177.40 kJ mol⁻¹, reflecting the intrinsic differences in the thermal decomposition reactions of pseudo-extractives, pseudo-hemicellulose, pseudo-cellulose, pseudo-lignin, and pseudo-biochar. The kinetic compensation method allowed the estimation of high-magnitude pre-exponential factors, between 10¹³ and 10²⁰ s⁻¹. Reaction model definition through integral master plots indicated the predominance of n-order mechanisms and volumetric contraction models. The thermodynamic activation parameters (ΔH≠, ΔS≠, and ΔG≠) confirmed that the three biomasses exhibit energy profiles favorable for bioenergy production, with energy barriers compatible with industrial operation in combustion systems. In conclusion, the results demonstrate that the investigated lignocellulosic by-products exhibit suitable performance for use as solid fuels, reinforcing the feasibility of bioenergy production and contributing to the diversification of the renewable energy matrix, in line with the principles of circular economy and the mitigation of environmental impacts from brewery activities.