Browsing by Author "Maldonado, Pedro"
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- Biomass gasification processes - modeling and simulationPublication . Maldonado, Pedro; Brito, Paulo; Gomes, Helder; Lenzi, Giane GonçalvesThermochemical processes prove to be a sustainable way of using residual biomass, replacing non-renewable sources such as coal and petroleum derivatives, and serving as a means for the creation of Synthesis Gas, or Syngas, mostly consisting of hydrogen gas and carbon monoxide, which is the basis for the chemical industry and power generation. The modeling and simulation of this process is feasible, as it portrays real gasifiers, such as Downdraft type gasifiers, in order to test variables and verify the system's behaviors when changing them. However, there is still some difficulty in modeling Pyrolysis, due to the complexity of this process, as well as predicting the tar generated during the process. Thus, the present study aims to model and simulate using the UniSim Design software, the gasification of three biomass residues from Portuguese agriculture: grape marc, olive trees, and corn straw residues, in an attempt to predict Syngas production under different process conditions and validate the method proposed comparing with data from the literature. Pyrolysis modeling was performed using a second-order model based on the process temperature, providing the yields of gases: CO2, CO, H2, and CH4, residual coal, and tar, which is composed of benzene, toluene, and naphthalene. Regarding the results obtained, both Pyrolysis and the general model, even at different conditions of mass flow of air and steam inlet, were compatible with results obtained in the literature, quantitatively and qualitatively. The rise in equivalence ratio (ER) from 0.23 to 0.54 caused an increase in the process temperature, as well as in the molar fraction of H2 and CO while reducing the other components, thus consuming the tar, for the biomasses in the ER range 0.36-0.37. The increase in the steam-to-biomass ratio (S/B) from 0 to 0.95 had a positive effect on the H2 and CO2 components, while it decreased the others, having no effect on the tar fraction. For both analyses, corn straw residue was converted into the richest gas in hydrogen, with the peak of the fraction of the component in Syngas, free of water and nitrogen, being 0.48 and 0.52, for ER and S/B ratio, respectively.
- Modeling and simulation of biomass pyrolysis and gasification processesPublication . Maldonado, Pedro; Lenzi, Giane G.; Gomes, Helder; Brito, PauloIn 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
- Modeling and simulation of biomass pyrolysis and gasification processesPublication . Maldonado, Pedro; Lenzi, Giane G.; Gomes, Helder; Brito, PauloFor 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.
- Modeling and simulation of biomass pyrolysis processesPublication . Maldonado, Pedro; Lenzi, Giane G.; Gomes, Helder; Brito, PauloPyrolysis is a thermochemical process where organic matter is decomposed into gaseous products, oils constituted by tars, and non-volatilized residual char, through the elevation of the system temperature (400-800°C), in the absence of oxygen. This process can be modeled and simulated for deeper analysis and optimization. However, since the process is clearly influenced by a high number of operational parameters such as temperature, pressure and dozens of simultaneous parallel reactions, its simulation becomes significantly complex. Thus, the aim of this work is the modeling of a more robust pyrolysis process, considering more components present in tar composition, as well as the evaluation of pyrolysis products distribution under different pyrolysis temperatures: 400, 500 and 600°C. Hence, a model was developed based on second-order equations [1], using pyrolysis temperature as the main variable, achieving as result the yield of three macro components: gases, tar and residual char. The gas fraction is composed by: carbon monoxide (CO), carbon dioxide (CO2), methane (CH4) and hydrogen (H2); tar fraction is constituted by: benzene (C6H6), toluene (C7H8) and naphthalene (C10H8), and the residual char is accompanied by ash in its composition. Simulation was implemented using biomass data based on the composition of olive residues applying the chemical process simulation software UniSim Design. The modeling first step is biomass decomposition in a conversion reactor, applying the yields obtained using the previous equations, while the second step is the decomposition of residual char in a yield reactor, resulting in the elemental constituents: carbon (C(s)), hydrogen gas (H2), oxygen gas (O2), nitrogen gas (N2), solid sulfur (S(s)), and ash. It is possible to note that the pyrolysis model results (see Table 1), implemented with the Software UniSim Design, show, in general, compatibility with the results available in the literature [2, 3]. The model reveals low sensitivity for the yield results, when using different sources of biomass with similar compositions, possibly due to the use of the temperature as the main variable