Adsorbed Renewable Energy Gas Storage
Gases are a main renewable energy resource. Biogas, as a mixture of mainly methane and carbon dioxide, may be produced from a multitude of sources. With Power-to-gas electrical power is converted to hydrogen or even methane, which may be mixed with other gas (e.g. biogas, gasgrid).
For storing, the gas is compressed and transferred to pressure vessels Due to the high pressures required this process is expensive in terms of equipment and energy consumption. A sustainable and effective alternative is the adsorption of the gas by porous media. The adsorbents used are mostly activated carbons and metal-organic frameworks. Adsorbed gas storage is of particular relevance for vehicles, where the fuel storage volume is limited.
For methane and hydrogen the performance of adsorption tanks have already been investigated and road tests in vehicles were performed. The data for biogas mixtures is significantly scarcer.
The storage performance of activated carbon beds for methane, carbon dioxide, hydrogen and their mixtures is investigated. A lumped parameter model is used to describe composition, pressure, mean temperature and flow rate.
The Dubinin-Astakhov isotherm is used to describe the adsorbed amount at different temperatures and pressures. The heat flux which depends on shape, size and heat removal is prescribed. The resulting set of transient differential equations is solved numerically.
The charging process with regard to filling time and temperature is examined. The discharge process with regard to discharge rate, concentration and temperature is investigated. The charge and discharge time are significantly influenced by the heat of adsorption. For the outlet flow the composition of the gas mixture changes over time.