Adsorbed natural gas

Natural gas burns cleanly as a fuel, making it useful in many vehicles. It contains mostly methane and ethane. These light gases have very high vapor pressure at ambient temperatures, and their storage requires either high-pressure compression or an extreme reduction of temperature.

Recently, a process has been introduced to store natural gas called adsorbed natural gas, or ANG. In this process, natural gas adsorbs to a porous sorbent at relatively low pressure (500 to 600 psi) and ambient temperature, solving both the high-pressure and low-temperature problems. If a suitable sorbent is used, it is possible to store more gas in a sorbent-filled vessel than in an empty vessel at the same pressure. The amount of adsorbed gas depends on pressure, temperature and sorbent type. Since this adsorption process is exothermic, an increase of pressure or a decrease of temperature enhances the efficiency of the process. Changing the sorbent also affects efficiency. Activated carbon is a sorbent with high surface area that can be used in ANG storage tanks. Currently, researchers are developing new sorbents with higher adsorption ratio to optimize this process.^[1]

ANG technology companies, such as Cenergy Solutions, has deployed commercially viable ANG tank technology in the USA for CNG vehicles and bio-methane facility storage. Validation ANG tank prototypes have been operational on an 8.1-liter Chevrolet Suburban; and the first ANG system to be used commercially was delivered in December 2015 on an OEM dedicated Dodge Ram 2500 with a 5.3-liter engine.^[2].

ANG technology is a significant step toward solving the “chicken and egg” challenge for broad and rapid adoption of CNG ^[3]. The ANG system creates the low pressure, conformable CNG storage solution for full-scale, affordable NGV-hybrid deployment in the US. Moreover, the lower compression pressures required to “fill” ANG tanks also allows for the more rapid growth of a ubiquitous CNG refueling network. Due to the significantly lower capital investment associated with lower compression requirements, CNG infrastructure will be more easily and cost-effectively added to the network of gas stations and truck stop.

ANG technology also creates a market for compact, affordable, low-pressure CNG Home Refueling Appliances (HRA’s) that will allow consumers to fill their vehicles at home connecting directly to their utility gas line ^[4].

Ford Motor Company’s Fleet Sustainability and Technology Manager is quoted as saying, “The highest cost of a CNG filling station is the compressor, because compressing to 3,600 psi takes a tremendous amount of energy. By reducing that compression to 1,000 psi, or even further to the “Holy Grail” of 500 psi, this is game-changing technology because it enables home refueling, and you have 53 million potential fill points at every residence in the country that has natural gas running into it.” ^[5]

ANG is also being tested for other methane storage applications, including CNG fueling station storage, virtual pipelines, and fugitive/ wellhead methane capture systems. Other significant opportunities for ANG include home heating and cooking applications in developing countries and in Southeast Asia ^[6].

References

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