The Adsorptive Storage Reservoir

In the design of an adsorptive storage reservoir, several factors should be taken into account. The more relevant ones are:

• Reduction of storage pressure

• Efficient use of the available storage space in the vehicle, a well as ease of installation

• Lightness in order not to penalize the energetic consumption

• Ease of construction

• Safety and certifiability as any commercial tank for compression storage.

The wall of a reservoir for compression storage must withstand the charge pressure during the expected operating life of the vehicle. As a safety precaution, the reservoir is always over-dimensioned to withstand a burst pressure of 2.5 times its normal charge pressure. In compressed gas storage, the high storage pressure forces the use of cylindrical reservoirs. But this geometry is not the most efficient one from the point of view of profiting from the available space in the vehicle.

Traditionally, steel has been the more commonly used material in the manufacture of pressurized tanks. With the emergence of composite materials, the weight of the reservoirs has substantially decreased. The most economic solution in terms of weight is a body with walls of reduced thickness made of aluminium reinforced by a fibrous composite high tensile strength, such as glass fiber. The use of these composite materials can reduce the weight of the tank by as much as 40%.

One advantage of adsorption storage is that its charge pressure is sufficiently low that does not restrict the shape of the reservoir to be cylindrical. This degree of freedom can be profitably used to maximize the storage space onboard the vehicle.

The proposed solution is the manufacture of small storage cells that can be easily packed to profit from the available space in the vehicle. The storage cell has a triangular cross section. This geometric shape is sufficiently flexible that it can efficiently fill any volume (Figure 10).

Figure 10. Multicellular reservoir for onboard NG storage by adsorption. The shape of the storage cell allows for an efficient filling of the available space inside the vehicle for fuel storage. The inlet/outlet fuel port which is common to all cells, is located at one of the extremes of the reservoir. Each cell is easily filled with contiguous carbon monolith disks with a geometrical shape identical to the cross section of the cell.

Figure 10. Multicellular reservoir for onboard NG storage by adsorption. The shape of the storage cell allows for an efficient filling of the available space inside the vehicle for fuel storage. The inlet/outlet fuel port which is common to all cells, is located at one of the extremes of the reservoir. Each cell is easily filled with contiguous carbon monolith disks with a geometrical shape identical to the cross section of the cell.

It should be noted that the design, manufacture and certification of a specific storage reservoir for a given vehicle model increases significantly the production costs of the vehicle. This will hardly be accepted by the automotive industry where the low-cost, automated manufacture is a determining factor of competitiveness. The manufacture of small storage cells with a fixed geometry that allows for a flexible design of the final storage tank eliminates that sort of difficulties.

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