Adsorbent storage of natural gas

The natural-gas vehicle represents a cost-competitive, lower-emission alternative to the gasoline-fueled vehicle. The immediate challenge that confronts the natural-gas vehicle is extension of its driving range. This paper addresses the question of driving range by reviewing the storage technologies for natural gas. Technical comparisons are made between storage systems for adsorbent, liquefied and compressed natural gas, and estimates are made of the costs associated with refueling with compressed and adsorbent natural gas. We discuss carbon adsorbents, vehicle emissions, designs of storage tanks, cost and safety. For storage-tank system design, we advance the concept that carbon adsorbents, when used with conformable-shaped tanks offer a means of increasing onboard fuel storage and, thereby, the driving range of the vehicle. The cost envelope being assigned to this technology is US$2000 or less per vehicle for 10 gallon gasoline-equivalent storage. For adsorbent natural-gas (ANG), this cost is based on 200 lbs of adsorbent at a purchase price of US$5 lb-1, a US$600 conformable tank and US$400 for miscellaneous hardware. Because the volumetric storage density of ANG is similar to that of compressed natural-gas (CNG), the benefit of the former is its lower operating pressure. Lower pressures have the advantages of small refueling costs, the availability of conformable tanks and safety. Our suggested solution to the driving-range problem of a natural-gas vehicle is the use of improved adsorbents in a low pressure (500 psi) conformable-shaped storage tank.