Publication: Methane purification from biogas using compact plate pressure swing adsorption under non-isothermal and non-adiabatic conditions
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Date
2023-05-02
Authors
Ammar Ali Abd
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Abstract
Upgrading biogas is a promising way to reduce greenhouse gas emissions from landfill sites on a global scale. This approach can also provide a sustainable and renewable source of energy, supporting the United Nations' SDG13 and SDG7. Technologies to upgrade biogas are critical for achieving the mitigation goals. Pressure swing adsorption (PSA) is a well-established industrial technology that can be used to abate anthropogenic greenhouse gas emissions and meet increasingly stringent environmental regulations. However, there is a concern related to the heat dissipation in PSA and power consumption during its operation and this thesis addresses the issue critically. The objectives of the thesis are, to analyse the measured properties of raw spent coffee (RSC) and zirconium MOF (UiO-66) adsorbents for carbon dioxide (CO2) capture and biogas upgrading, to investigate the effect of operating conditions on compact plate PSA performance from breakthrough study and 4 steps PSA operations under non-isothermal and non-adiabatic conditions, to develop empirical correlations to predict the total heat dissipation through the compact plates from adsorption bed to desorption bed, and finally to evaluate the effects of various bed configurations on products’ purity and recovery under different operating conditions, while also comparing the bio-CH4 properties for both single and double adsorption plates.
The surface area of the RSC sample was found to be 5.88 m2/g, while the UiO-66 sample exhibited a significantly higher surface area of 313 m²/g. The mesoporous RSC material showed promising indications of having a lamellar structure, potentially consisting of three intercalated microlayers. This inference was drawn from the detection of a small diffraction peak at around 16 degrees in the XRD analysis. In contrast to the amorphous nature of RSC, the UiO-66 adsorbent displayed a highly crystalline composition. The crystals of UiO-66 formed distinctive aggregate particles with a specific geometric shape, suggesting a well-defined structure. Despite having a lower surface area and larger pore size compared to the crystalline UiO-66, the RSC exhibited remarkable methane purity and recovery rates of 97.9% and 68.12%, respectively. The optimal conditions for achieving the highest methane purity were observed at a 4-minute adsorption time, a pressure of 3 bar, and a methane to carbon dioxide feed ratio of 70% to 30%, respectively. The validated empirical correlations show that about 18.92 kJ/mol of heat was released during adsorption at 2.5 min or 0.5 cm of the bed height and continued downward as time elapsed for more than 60 min. The performance of a two-cell, four-adsorption bed PSA system using RSC adsorbent was investigated in both parallel and serial configurations. In the parallel configuration, a biomethane (bio-CH4) purity of 95.05% with a recovery of 66.15% was achieved. In the serial and layered configurations, a bio-CH4 purity of 99.99% with a recovery of 69.60% was obtained. According to the evaluation of physical gas characteristics, phase envelope, and critical properties conducted in this study, the PSA products obtained from the compact PSA system met the standard fuel quality requirements with a methane content of ≥ 97%.