MODELING AND SIMULATION OF BIOMASS PYROLYSIS AND GASIFICATION PROCESSES
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For many years, oil derivatives, natural coal, and natural gas were used and still are, as primary energy supply due to their calorific potential, and their great availability on the planet. However, the utilization of these feedstocks causes greenhouse effects and helped in global warming, creating a general concern about this issue, and leading to the creation of urgent measures to overcome these problems. Hence, guidelines and public policies were granted to guarantee the reduction of emissions and increase the portion of renewable sources in the energy system production, namely the use of biofuels produced from waste biomass such as straw, stover, husks, and shells. Thermochemical processes can convert biomass sources into energy and/or fuels with a high heating value through high-temperature treatments. It comprises combustion, pyrolysis and gasification, which can be employed together or separated, depending on the need. The product of gasification is Synthesis Gas, comprehended mainly by hydrogen gas and carbon monoxide, which can be used posteriorly to produce electric energy. In this process, many parameters as temperature, pressure, gasifying agent, biomass composition, gasifier configuration, etc, influence the final composition of the gas. A challenge to show the feasibility of Syngas production is trying to know the conversion yields and its composition to evaluate the efficiency of the process. Simulating Software helps in this task, bringing real processes closer to virtual ones. Through UniSim Design software, this work main objective is the creation and implementation of a hybrid model (Kinetic and Equilibrium approaches) able to predict the lignocellulosic biomass gasification products for Downdraft and Updraft gasifiers, using different sources such as olive and corn agricultural wastes, and grape bagasse residue from wine culture.
In computer simulation, the processes and equipment operate following the sequence of input data, data processing, and return output data. Typically, these data are mass flows, temperatures,
compositions, and pressures. Specifically, modeling and simulation of gasification systems aid in predicting the outlet gas composition when operating conditions and scale size alter. This assists in
planning the construction or retrofitting of existing equipment. UniSim Design is a chemical process modeling software, similar to Aspen Plus and Aspen Hysys. It is used in engineering to create
dynamic and steady-state models for plant design, monitoring, troubleshooting, planning, and management [1]. However, regardless of the software used for modeling and simulation of the
gasification process, there is a pattern of steps that must be followed in order to successfully perform the simulation. Therefore, this process is divided into 4 main steps: Drying or removal of
moisture present in the biomass until 5% w/w; followed by Pyrolysis, which was split into Devolatilization, and Char cracking, both calculated with the help of Microsoft Excel; Combustion, where
oxidation equilibrium reactions are added; and finally the Reduction step, which is divided in the heterogeneous and homogeneous stages, where equilibrium reactions are also inserted
