Abstract
Global warming is predominantly caused by methane (CH4) and carbon dioxide (CO2) emissions. CH4 is estimated to have a global warming potential (GWP) of 28–36 over 100 years. Its impact on the greenhouse effect cannot be overstated. In this report, a dual-bed eight-step pressure swing adsorption (PSA) process was used to simulate the separation of high-purity CH4 as renewable energy from biogas (36% CO2, 64% CH4, and 100 ppm H2S) in order to meet Taiwan’s natural gas pipeline standards (>95% CH4 with H2S content < 4 ppm). Three selectivity parameters were used to compare the performance of the adsorbents. In the simulation program, the extended Langmuir–Freundlich isotherm was used for calculating the equilibrium adsorption capacity, and the linear driving force model was used to describe the gas adsorption kinetics. After the basic case simulation and design of experiments (DOE) for the laboratory-scale PSA, we obtained a top product CH4 purity of 99.28% with 91.44% recovery and 0.015 ppm H2S purity, and the mechanical energy consumption was estimated to be 0.86 GJ/ton-CH4. Lastly, a full scale PSA process simulation was conducted for the commercial applications with 500 m3/h biogas feed, and the final CH4 product with a purity of 96.1%, a recovery of 91.39%, and a H2S content of 1.14 ppm could be obtained, which can meet the standards of natural gas pipelines in Taiwan.
Highlights
Methane (CH4 ) is a valuable renewable energy source and one of the leading gases responsible for the greenhouse effect
A single-bed three-step pressure swing adsorption (PSA) process was used for simulation verification
The results showed that the COSMO’s zeolite 13X has the highest values of equilibrium selectivity, working capacity selectivity ratio, and selection parameter at 298 K and 333 K
Summary
Methane (CH4 ) is a valuable renewable energy source and one of the leading gases responsible for the greenhouse effect. CO2 has a global warming potential (GWP) of 1 regardless of the time period used, whereas CH4 is estimated to have a GWP of 28–36 over 100 years [1]. After CO2 , CH4 is the second most abundant anthropogenic greenhouse gas, accounting for approximately 20 percent of global emissions [2]. The main components of biogas are 60–70% CH4 , 30–40% CO2 , and other trace gas compounds, such as 0–4000 ppm hydrogen sulfide (H2 S) produced by anaerobic decomposition [3]. In order to mitigate global warming, biogas upgrading technologies have been promoted in various countries worldwide in recent years. Gas separation technologies can recover CH4 and capture CO2 in order to reduce greenhouse gas emissions, but can produce high-purity natural gas for use in industrial applications, such as heating and power generation, or as biofuel for vehicles
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