Biogas is one of the most widespread renewable fuels, obtained from diverse biomasses and processes. Its composition strongly varies depending on the process adopted and on the chemical properties of the digested feedstock; it consists of a mixture of mostly methane and carbon dioxide with minor quantities of nitrogen, oxygen, hydrogen sulphide, halogenated and aromatic compounds [1]. Even though biogas is nowadays mostly used to produce heat and electricity through power turbines and internal combustion engines, in some cases this could result in low electrical conversions, high levels of noise, strict maintenance requirements and pollutant emissions [2]. Among the different routes for biogas valorization, the transformation of biogas in products with a higher added value is one of the most interesting [3]. In this work, a direct conversion of syngas to methanol has been proposed as alternative of the conventional process that requires WGS and PSA clean-up steps for syngas upgrading A comparative thermodynamic equilibrium analysis of biogas reforming processes (dry reforming, steam reforming and oxy-steam reforming) was studied by Gibbs free energy minimization method to highlight the effects of process variables such as temperature and inlet composition on the reforming performances in term of CH4 and CO2 conversion, H2/CO and H2/CO2 ratios, coke deposition and energy consumption. The calculations were carried out by PRO II® software varying biogas composition (CH4/CO2=1-2.3), temperature (400-900°C), H2O/CH4 (0.0-3.0) and O2/CH4 (0.0-0.2) molar ratios. The methanol synthesis step was simulated by PRO II® software in order to identify the optimal composition range for methanol production in term of H2/CO and H2/CO2 ratios curves (Figure 2). The simulations were carried out varying temperature (230-300°C), pressure (50-150 bar) and (H2-CO2)/(CO+CO2) ratio (2-5). Coupling the thermodynamic results of biogas reforming processes with the feasibility curve of methanol synthesis it was possible to identify the optimal operating conditions (temperature, inlet composition) to guarantee the following conditions: (i) syngas with suitable composition in term of H2/CO and H2/CO2, with simultaneously high methane conversion (>80%); (ii) no carbon formation in order to avoid the catalyst deactivation; (iii) energy consumption as lower as possible to reduce maintaining costs. The results indicated that the SR process of biogas with high methane content can be used to produce syngas suitable for the proposed process, characterised by an optimal composition in absence of carbon formation, employing the minimum quantity of energy.
From biogas to methanol through reforming processes: a thermodynamic and energetic analysis
A Vita;C Italiano;A Palella;L Pino;C Fabiano;
2017
Abstract
Biogas is one of the most widespread renewable fuels, obtained from diverse biomasses and processes. Its composition strongly varies depending on the process adopted and on the chemical properties of the digested feedstock; it consists of a mixture of mostly methane and carbon dioxide with minor quantities of nitrogen, oxygen, hydrogen sulphide, halogenated and aromatic compounds [1]. Even though biogas is nowadays mostly used to produce heat and electricity through power turbines and internal combustion engines, in some cases this could result in low electrical conversions, high levels of noise, strict maintenance requirements and pollutant emissions [2]. Among the different routes for biogas valorization, the transformation of biogas in products with a higher added value is one of the most interesting [3]. In this work, a direct conversion of syngas to methanol has been proposed as alternative of the conventional process that requires WGS and PSA clean-up steps for syngas upgrading A comparative thermodynamic equilibrium analysis of biogas reforming processes (dry reforming, steam reforming and oxy-steam reforming) was studied by Gibbs free energy minimization method to highlight the effects of process variables such as temperature and inlet composition on the reforming performances in term of CH4 and CO2 conversion, H2/CO and H2/CO2 ratios, coke deposition and energy consumption. The calculations were carried out by PRO II® software varying biogas composition (CH4/CO2=1-2.3), temperature (400-900°C), H2O/CH4 (0.0-3.0) and O2/CH4 (0.0-0.2) molar ratios. The methanol synthesis step was simulated by PRO II® software in order to identify the optimal composition range for methanol production in term of H2/CO and H2/CO2 ratios curves (Figure 2). The simulations were carried out varying temperature (230-300°C), pressure (50-150 bar) and (H2-CO2)/(CO+CO2) ratio (2-5). Coupling the thermodynamic results of biogas reforming processes with the feasibility curve of methanol synthesis it was possible to identify the optimal operating conditions (temperature, inlet composition) to guarantee the following conditions: (i) syngas with suitable composition in term of H2/CO and H2/CO2, with simultaneously high methane conversion (>80%); (ii) no carbon formation in order to avoid the catalyst deactivation; (iii) energy consumption as lower as possible to reduce maintaining costs. The results indicated that the SR process of biogas with high methane content can be used to produce syngas suitable for the proposed process, characterised by an optimal composition in absence of carbon formation, employing the minimum quantity of energy.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
