Capacity and Thermodynamic Nomograph for an Adsorption Methane Storage System

Abstract

General equations for calculation of the capacity and thermodynamic properties of adsorption methane storage systems were written. Experimental results for methane adsorption on AU-1 adsorbent were analyzed and plotted in the nomograph of capacity and thermodynamic properties of the adsorbentadsorbate-gas adsorption system. Methods for graphical calculation of the processes occurring in the system were presented.Adsorption storage systems for natural gas (methane) are very promising not only for storage but also for transportation. An adsorption storage system comprises a container fi lled with a microporous adsorbent. A gas volume of 150-193 m 3 per m 3 of the best carbon adsorbents, e.g., carbon fi ber [1] and active carbons [2], and, according to calculations, 230-284 m 3 per m 3 of metal-organic adsorbents [3], is achieved at pressures of 3.5-7.0 MPa. This is comparable to the corresponding values for compressed natural gas at 20 MPa. Industrial adsorbents (active carbons and zeolites) were developed for different problems so that their capacity is usually lower at 90-110 m 3 /m 3 at 3.5 MPa and 20-25°C.Adsorption storage systems are considered to be safer than traditional compressed and liquid storage systems because the stored gas is bound, which prevents detonation within a tank and rapid loss of gas through a breach. Highly hazardous acetylene is commonly stored in active-carbon adsorption storage systems [4]. An adsorption storage system can conserve energy because of the lower loading pressure and other features.The high heat of adsorption of methane is the principal drawback of natural-gas adsorption storage systems. Considering the signifi cant amount of stored gas, the temperature changes considerably during adsorption and desorption. The adsorbent temperature during loading increases by 30-60 K [5] although the adsorbent dynamic capacity decreases as a result [6]. The reverse effects arise during desorption, i.e., the temperature decreases whereas the adsorption capacity and the amount of residual gas in the empty tank increase. The heat of desorption has a smaller negative effect because of the low residual gas pressures [7].Methods for dissipating heat of adsorption (during loading) or adding heat (during gas release) were developed because the thermal effects were signifi cant. They usually involved placing a heat exchanger within the adsorbent or purging with natural gas.The majority of the research was either experimental or simulated by computer. Both approaches were expensive or labor-intensive and poorly suited for practical calculations of the many processes occurring in adsorption storage systems. Graphs of the properties of various compounds are convenient to use in practice to calculate the processes occurring in them.

Thermodynamic Behaviors of Adsorbed Methane Storage Systems Based on Nanoporous Carbon Adsorbents Prepared from Coconut Shells

“…Since only the changes in the enthalpy are relevant, its reference value can be chosen arbitrarily and separately for each element of the ANG system. Thus, the enthalpy of the adsorbent–adsorbate system H a for isothermal equilibrium adsorption is calculated as follows [ 38 , 39 ]: where c c and c b are the specific heat capacities of regenerated carbon adsorbent without methane and a polymer binder, respectively; x is the mass content of a binder in the monolithic adsorbent; T is the temperature of the adsorption system; T 0 is the arbitrary reference temperature, for example, 273.15 K; a is the adsorption value reduced to a “pure” adsorbent without the binder, i.e., it corresponds to the plot in Figure 7 ; ρ p is the packing density of adsorbent on the volume of the system; V tank is the internal volume of the ANG tank.…”

“…Recently, the authors developed a mathematical model of the circuit charging process of a flow-type ANG storage system [ 33 ]. Therefore, a practical engineering solution for the ANG facilities must consider the thermal effects of adsorption/desorption [ 34 , 35 , 36 , 37 , 38 , 39 ]. In this context, thermodynamic functions of adsorption systems, operating under conditions of high pore filling with adsorbate at high pressures, i.e., the HEAS conditions are of particular interest [ 40 , 41 ].…”

Investigation of the processes of adsorbent regeneration by compression heat in an adsorption dryer of compressed air

“…During the technology under consideration heat and mass transfer processes within the drying and regeneration cycle are purely dynamic nature, due to the A and B columns switching. The dynamic problem, according to many authors, has no analytical solution and can be solved only by numerical methods [5], [6], [7]…”

Heat and Mass Transfer in an Adsorbed Natural Gas Storage System Filled with Monolithic Carbon Adsorbent during Circulating Gas Charging

“…The main dependencies for calculating the characteristics of ANG storage systems are presented in [24]. Charging without the removal of adsorption heat is the fastest charging method, but at the same time the least efficient in the amount of accumulated gas.…”

“…The main correlations for simulating the characteristics of an ANG storage system are presented in [24,25].…”