Hydrogen storage tank system based on gas adsorption on high-surface materials comprising an integrated heat exchanger

A gas storage system that stores a gas by cryo-adsorption on high surface materials. The gas storage system includes an outer container having insulated walls and a plurality of pressure vessels disposed therein. Each of the pressure vessels includes a high surface material. A manifold assembly distributes the gas under pressure to the pressure vessels where the gas is adsorbed by cryo-adsorption using the high surface materials. A cooling fluid is provided within voids between the pressure vessels to remove heat as the pressure vessels are being filled with the gas.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a gas storage system and, more particularly, to a hydrogen gas storage system for storing hydrogen gas by cryo-adsorption on high surface materials.

2. Discussion of the Related Art

A hydrogen vehicle is generally defined as a vehicle that employs hydrogen as its primary source of power for locomotion. A primary benefit of using hydrogen as a power source is that it uses oxygen from the air to produce only water vapor as exhaust. The most efficient use of hydrogen involves the use of fuel cells and electric motors instead of a traditional engine. Hydrogen reacts with oxygen inside the fuel cells, which produces electricity to power the motors.

One primary area of research of hydrogen vehicles involves hydrogen storage to increase the range of hydrogen vehicles while reducing the weight, energy consumption, and complexity of the storage systems. Thus, the efficient storage of hydrogen is a necessary prerequisite for the mass introduction and consumer acceptance of hydrogen-propelled vehicles. Current storage technologies, such as compressed gaseous hydrogen (CGH2) or liquid hydrogen (LH2), pose a limitation on the driving range of such vehicles. Solid-state storage systems, such as classical or complex metal hydrides, for example, FeTi2, NaAlH4and/or the like, might be a viable alternative, but present heat management challenges for fundamental thermodynamic reasons. In terms of storage capacity, these compounds typically deliver lower system hydrogen capacities than conventional technologies, such as CGH2and LH2.

Accordingly, there exists a need for a new and improved hydrogen storage system for use with hydrogen-powered vehicles, where the hydrogen storage tank system is operable to efficiently store increased amounts of hydrogen.

SUMMARY OF THE INVENTION

In accordance with the teachings of the present invention, a gas storage system is disclosed that stores a gas by cryo-adsorption on high surface materials. The gas storage system includes an outer container having insulated walls and a plurality of pressure vessels disposed therein. Each of the pressure vessels includes a high surface material. A manifold assembly distributes the gas under pressure to the pressure vessels where the gas is adsorbed by cryo-adsorption using the high surface materials. A cooling fluid is provided within voids between the pressure vessels to remove heat as the pressure vessels are being filled with the gas.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following discussion of the embodiments of the invention directed to a gas storage system is merely exemplary in nature, and is in no way intended to limit the invention or its applications or uses. For example, the gas storage system of the invention has particular application for storing hydrogen for a fuel cell system. However, as will be appreciated by those skilled in the art, the gas storage system of the invention may have application for storing other gases for other systems.

In accordance with one aspect of the present invention, an alternative gas storage mechanism is provided by the so-called physisorption or cryo-adsorption, i.e., physical adsorption of hydrogen molecules on high-surface materials, such as, but not limited to, activated carbons, zeoliths, metal-organic frameworks (MOFs), polymers of intrinsic microporosity (PIMs) and/or the like.

FIG. 1is an illustration of hydrogen gas molecules being absorbed by a metal hydride surface on the right and by cryo-adsorption on a high-surface material on the left. As is well understood in the art, metal hydride absorption has a high binding energy (typically ranging from 10 to 40 MJ/kg hydrogen) as a result of the hydrogen being strongly bound to the metal hydride in an atomic phase, where the absorption can occur at relatively high temperatures (ranging from ambient temperature to elevated temperatures of 200° C. and higher). As the hydrogen absorbs in the metal hydride, a significant amount of heat is generated by the chemical absorption process, which needs to be removed so that the structural integrity and/or the capacity of the storage system is not affected. Cryo-adsorption adsorbs hydrogen in the molecular phase, where the molecules adhere to the high-surface material by weak bonds, such as Van der Waals forces. Because the surface bonding is weak, it is necessary to reduce the kinetic energy of the hydrogen by reducing its temperature to cryogenic temperatures. As the hydrogen adheres to the high-surface material, heat is generated (order of magnitude of 2.5 MJ/kg), but at a much lower rate than for the metal hydride absorption.

It is necessary to fill a hydrogen tank for a fuel cell vehicle with 5 kilograms of hydrogen in under 5 minutes to meet industry demands. In order to store that amount of hydrogen in that amount of time using a conventional metal hydride storage system, heat has to be removed from the system at a rate of about 25 MJ/kg times 5 kg/300 s, which equals 420 kW for a typical metal hydride. However, in order to maintain the temperature of the hydrogen at cryogenic temperatures for the low binding temperature necessary for cryo-adsorption, the temperature removal rate is about 2.5 MJ/kg of hydrogen times 5 kg/300 s, which equals 42 kW. Therefore, the use of cryo-adsorption to store hydrogen may provide a viable alternative.

The present invention proposes a tank design for storing hydrogen using the afore-mentioned cryo-adsorption mechanism. The cryo-adsorption tank system of the present invention is operated at pressures between 10 and 50 bar and at temperatures from 25K to 200K. Although primary reference will be made to the storage of hydrogen, it should be appreciated that the system of the present invention is capable of storing other gases besides hydrogen.

FIG. 2is a lengthwise cross-sectional view andFIG. 3is a cross-sectional view of a gas storage system10for storing hydrogen gas, according to an embodiment of the present invention. The storage system10includes a cylindrical outer container12having a sidewall14and end covers24and26. A plurality of pressure vessels18are positioned within the outer container12in a predetermined configuration, as shown. In this non-limiting embodiment, there are seven pressure vessels18, where six of the pressure vessels18surround a center pressure vessel18. This configuration of the pressure vessels18creates voids20between the vessels18, as shown. The outer container12provides thermal insulation for the pressure vessels18for reasons that will become apparent from the discussion below. The outer wall14and the covers24and26can include any suitable thermal insulation for the purposes discussed herein, such as a multi-layer vacuum super insulation (MLVSI)16or a powder-based vacuum insulation. The outer container12also protects the inner components from any potential mechanical damage. The pressure vessels18can be made of a suitable high-pressure material, such as stainless steel.

The pressure vessels18are filled with a high-surface material28, such as activated carbons, zeolites, metal-organic frameworks, polymers of intrinsic micro-porosity, etc, suitable for cryo-adsorption. The high-surface material28can take on any suitable configuration, such as powders or pellets. It is desirable that the high-surface material28includes a high surface area, and that the hydrogen can be adsorbed on the surface area. Therefore, gas distribution lines (not shown) may be required within the pressure vessels18to adequately distribute the hydrogen within the vessels18depending on the configuration of the high-surface material28.

The gas storage system10also includes a manifold assembly30proximate the end cover24and a manifold assembly32proximate the end cover26within the container12. The manifold assembly30includes a hydrogen gas inlet nozzle34, gas distribution lines36and couplers38. Likewise, the manifold assembly32includes a gas outlet nozzle40, gas distribution lines42and couplers44. Hydrogen gas is introduced into the pressure vessels18through the inlet nozzle34, through the distribution lines36, through the couplers38and into the pressure vessels18. Hydrogen gas is removed from the pressure vessels18through the couplers44, the gas distribution lines42and the outlet nozzle40. In one embodiment, the hydrogen gas is stored in the pressure vessels18at a pressure between 10 and 50 bar. In an alternate embodiment, the manifold32can be eliminated, and the manifold assembly30can be used to introduce hydrogen into the pressure vessels18and remove hydrogen from the pressure vessels18.FIG. 4is a close-up, cut-away view of a portion of the manifold assembly32and the pressure vessels18.

If the pressure vessels18store hydrogen under pressure, then this pressure can be used to remove the hydrogen from the vessels18to operate the fuel cell system. Once the pressure within the vessels18is reduced to the pressure of the fuel cell system, any hydrogen remaining within the pressure vessels18needs to be removed from the high-surface material28by heat, which breaks the weak bonds of the hydrogen molecules to the high surface material28.

The gas storage system10also includes a coolant inlet nozzle50and a coolant outlet nozzle52in fluid communication with the voids20. When the pressure vessels18are being filled with hydrogen, the voids20are typically filled with a cryogenic coolant through the nozzle50to cool the pressure tanks18and remove the heat generated by the cryo-adsorption process. Suitable coolants include, but are not limited to, liquid nitrogen, liquid argon, hydrogen, etc. As the coolant is warmed by the adsorption reaction, it evaporates, and reduces its ability to remove heat (contingently to limit the pressure, some coolant has to be vented). The container12maintains the coolant in the cryogenic state for as long as possible. Once the pressure vessels18are filled, then it may be necessary to remove the coolant through the outlet nozzle52, and replace it with a warm fluid, such as gaseous nitrogen, to facilitate the desorption of hydrogen from the pressure vessels18during system operation. In an alternate embodiment, the coolant outlet nozzle52can be removed, and the coolant can be introduced and removed from the voids20through the nozzle50.

It should be appreciated that other auxiliary components can be included in the gas storage system10, including but not limited to, conduits, gauges, valves, electrical heaters to facilitate desorption and/or the like, as are known in the art, but have not be shown here for purposes of clarity.