Simulation of the Cyclic Adsorption-Desorption Processes in an Adsorbed Natural Gas Storage System Loaded by a Peat-Derived Nanoporous Carbon Adsorbent

Practical vehicular application of the adsorbed natural gas (ANG) storage technique depends on the selection of an accessible adsorbent with required properties and the development of optimal charge-discharge conditions that ensure the maximum efficiency and vehicle tank mileage. In the present study, we carried out the simulation of the charge-discharge of a full-size ANG vessel with a volume of 65 and 150 L employing a carbon adsorbent under conditions with and without using forced thermal control (TC) for different gas flow rates of charge ranging from 5 to 5000 L min(-1). A lumped-parameter model of the charge-discharge of the ANG system used the experimental methane adsorption data, including adsorption-induced deformation and heat effects on the commercial peat-derived carbon adsorbent PAC-3 measured over a temperature range of 213 to 393 K. According to the X-ray diffraction and scanning electron microscopy data, PAC-3 possessed the heterogeneous morphology and diverse chemical composition inherited from the precursor and activation conditions. The analysis of low-temperature nitrogen adsorption revealed its predominantly microporous structure with a small proportion of mesopores. The dilatometric measurements observed the methane adsorption-induced changes in the linear and volumetric dimensions of PAC-3 granules with a maximum magnitude of 0.62 and 1.85%, respectively, which should be taken into account in order to maintain the integrity of the ANG vessel as well as to accurately assess the temperature fluctuations arising during the charge-discharge processes. The simulations revealed that the use of TC facilities in the ANG system prevented the strong heating of the adsorbent, improved the deliverable capacity, and increased the vehicle tank mileage. The advantages of using TC in the ANG systems are most obvious at low gas flow rates (5 to 80 L min(-1)), high pressures, and large volumes of the vessel.