Samenvatting
Production of biogas from biomass waste is a viable strategy to reduce greenhouse gas emissions and consequently manage greenhouse warming. Greenhouse warming could lead to permanent and irreversible changes in the ecosystem and the human systems. Biomass, if untreated, can naturally emit methane (20 times more potent than CO2 in terms of global warming potential) and other greenhouse gases. On the other hand, usage of biomass to produce biogas, as an energy source, reduces the need for fossil fuels. Biomass waste conversion to biogas, a mixture of mainly CH4:CO2:N2, through anaerobic decomposition of waste, can be done in anaerobic digesters. Among different sources for biogas production, organic waste is the most environmentally friendly feedstock.
Biogas upgrading, i.e., the removal of unwanted components to achieve high methane purity, allows for the reduction of methane and CO2-emissions through simultaneous production of separate biomethane and CO2 streams. Biogas upgrading is imperative to meet the stringent specifications for pipeline transportation and renewable fuel applications.
In this work, with the focus on biogas upgrading via vacuum pressure swing adsorption (VPSA), different configurations for enhancing the upgrading process are proposed. First,
simultaneous removal of N2 and CO2 from biogas was the objective of upgrading. Second, a techno-economic model is developed and applied to analyze the possibility of usage of a simple VPSA configuration for CO2 removal from biogas. Third, a novel hybrid membrane and VPSA configuration is developed for simultaneous production of separate streams of grid quality biomethane and high purity CO2 through biogas upgrading.
To achieve these targets, a new VPSA configuration was designed, modeled, and numerically simulated in Aspen Adsorption for upgrading a biogas containing CH4:CO2:N2 (50/40/10 mol%). The goal was to achieve CH4 purity of 98% and with N2 content less than 2 mol%. Aspen Adsorption was used for conducting simulations. In the proposed process, carbon molecular sieves (CMS) and Sr-ETS-4 were chosen as the selective adsorbents for removal of CO2 and N2, respectively. Exergy analysis was used for comparison of the developed configurations with configurations proposed in literature. For the proposed configuration, 15% improvement in CH4 recovery in comparison to the basic configuration was obtained. Additionally, energy consumption of the developed configuration was ~ 4 kJ/mol CH4 less than the basic one. Exergy-based efficiency calculations revealed an increase in simple efficiency from 64% to 74%, further demonstrating the superiority of the developed configuration.
Next, an integrated techno-economic model was developed based on discount cash flow. The model takes into account different steps of the entire biogas production and upgrading process, namely: waste transport to the plant; biogas production in an anaerobic reactor; biogas dehydration; biogas desulfurization; VPSA separation of methane and carbon dioxide, and grid injection. For this part of the work, it was assumed that N2 concentration in biogas is negligible. Net present value (NPV), discounted payback time (DPBT), and upgrading cost were used as the economic indices for profitability analysis. Two VPSA configurations were examined and compared with literature. The impact of gas price and the role of feed processing revenues on the profitability of the model was investigated via sensitivity analysis. The configuration of VPSA integrated with a combined heat and power (CHP) engine, emerged as a promising approach requiring less economic support than the VPSA cascade design. The integrated process showed positive NPV for biogas plant with production capacity ≥ 5,000 Nm3/h. The sensitivity analysis revealed the critical impact of gas price, electricity price, and feedstock processing revenues on the economic feasibility of the hybrid VPSA plant. The results suggest that specific levels of governmental incentives and revenues are necessary to support biomethane production at different plant sizes.
Finally, a hybrid membrane VPSA configuration for CH4:CO2 separation, which benefits from the advantages of both technologies while having a lower upgrading cost, was developed. Aspen Adsorption and Aspen custom modeler were integrated to model this hybrid configuration. For this section, it was assumed that N2 has been already removed in a pretreatment unit. To automate the Aspen model, visual basic application in Microsoft Excel was used to connect Aspen Adsorption to MATLAB. Then MATLAB optimization functions were used for optimization of the process. Main objectives of the optimization were to achieve high methane purity, high methane recovery, and low energy consumption. The hybrid configuration delivers a methane purity > 96% and methane recovery > 99% by consuming 14.78 kJ/mol of feed biogas. To compare the hybrid configuration with the current technologies, upgrading cost was used. The new hybrid process showed ~ 15% reduction in upgrading cost in the most probable cases. The hybrid biogas upgrading configuration is robust and less complex compared to benchmark technology. It achieves high efficiency and could enable a new generation of upgrading technology for simultaneous biomethane production and CO2 capture.
In summary, this work has proposed promising novel biogas upgrading configurations with high potential to be implemented in industry
Biogas upgrading, i.e., the removal of unwanted components to achieve high methane purity, allows for the reduction of methane and CO2-emissions through simultaneous production of separate biomethane and CO2 streams. Biogas upgrading is imperative to meet the stringent specifications for pipeline transportation and renewable fuel applications.
In this work, with the focus on biogas upgrading via vacuum pressure swing adsorption (VPSA), different configurations for enhancing the upgrading process are proposed. First,
simultaneous removal of N2 and CO2 from biogas was the objective of upgrading. Second, a techno-economic model is developed and applied to analyze the possibility of usage of a simple VPSA configuration for CO2 removal from biogas. Third, a novel hybrid membrane and VPSA configuration is developed for simultaneous production of separate streams of grid quality biomethane and high purity CO2 through biogas upgrading.
To achieve these targets, a new VPSA configuration was designed, modeled, and numerically simulated in Aspen Adsorption for upgrading a biogas containing CH4:CO2:N2 (50/40/10 mol%). The goal was to achieve CH4 purity of 98% and with N2 content less than 2 mol%. Aspen Adsorption was used for conducting simulations. In the proposed process, carbon molecular sieves (CMS) and Sr-ETS-4 were chosen as the selective adsorbents for removal of CO2 and N2, respectively. Exergy analysis was used for comparison of the developed configurations with configurations proposed in literature. For the proposed configuration, 15% improvement in CH4 recovery in comparison to the basic configuration was obtained. Additionally, energy consumption of the developed configuration was ~ 4 kJ/mol CH4 less than the basic one. Exergy-based efficiency calculations revealed an increase in simple efficiency from 64% to 74%, further demonstrating the superiority of the developed configuration.
Next, an integrated techno-economic model was developed based on discount cash flow. The model takes into account different steps of the entire biogas production and upgrading process, namely: waste transport to the plant; biogas production in an anaerobic reactor; biogas dehydration; biogas desulfurization; VPSA separation of methane and carbon dioxide, and grid injection. For this part of the work, it was assumed that N2 concentration in biogas is negligible. Net present value (NPV), discounted payback time (DPBT), and upgrading cost were used as the economic indices for profitability analysis. Two VPSA configurations were examined and compared with literature. The impact of gas price and the role of feed processing revenues on the profitability of the model was investigated via sensitivity analysis. The configuration of VPSA integrated with a combined heat and power (CHP) engine, emerged as a promising approach requiring less economic support than the VPSA cascade design. The integrated process showed positive NPV for biogas plant with production capacity ≥ 5,000 Nm3/h. The sensitivity analysis revealed the critical impact of gas price, electricity price, and feedstock processing revenues on the economic feasibility of the hybrid VPSA plant. The results suggest that specific levels of governmental incentives and revenues are necessary to support biomethane production at different plant sizes.
Finally, a hybrid membrane VPSA configuration for CH4:CO2 separation, which benefits from the advantages of both technologies while having a lower upgrading cost, was developed. Aspen Adsorption and Aspen custom modeler were integrated to model this hybrid configuration. For this section, it was assumed that N2 has been already removed in a pretreatment unit. To automate the Aspen model, visual basic application in Microsoft Excel was used to connect Aspen Adsorption to MATLAB. Then MATLAB optimization functions were used for optimization of the process. Main objectives of the optimization were to achieve high methane purity, high methane recovery, and low energy consumption. The hybrid configuration delivers a methane purity > 96% and methane recovery > 99% by consuming 14.78 kJ/mol of feed biogas. To compare the hybrid configuration with the current technologies, upgrading cost was used. The new hybrid process showed ~ 15% reduction in upgrading cost in the most probable cases. The hybrid biogas upgrading configuration is robust and less complex compared to benchmark technology. It achieves high efficiency and could enable a new generation of upgrading technology for simultaneous biomethane production and CO2 capture.
In summary, this work has proposed promising novel biogas upgrading configurations with high potential to be implemented in industry
| Originele taal-2 | English |
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| Datum van toekenning | 8 mei 2025 |
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| Status | Published - 2025 |