Sound Wave-Driven Refrigerator May Offer New Way to Bring Unused Natural Gas to Market

Liquefier will Operate on Novel Concept that Burns Natural Gas to Generate Sound Waves

A portable refrigerator that uses sound waves to cool natural gas to the point it liquefies could help producers market gas that is often wasted or left behind in today's oil fields.

The U.S. Department of Energy will co-fund the construction and testing of a prototype of such a device. The department will provide $350,000 to Cryenco, Inc., a Denver-based company that specializes in cryogenic vessels, to develop a small-scale liquified natural gas (LNG) production device. Cryenco will contribute $200,000 to the effort.

The natural gas liquefier will operate on a novel concept that burns natural gas to generate sound waves that, in turn, drive natural gas refrigerators.

Natural gas is a widely used, abundant and clean fuel that is typically transported directly from producing gas wells through pipelines to the eventual user. But not all gas deposits are accessible to pipelines. In locations where there is no pipeline, gas is sometimes injected into a non-producing formation. As a result, much of the gas is wasted.

Converting this gas to LNG provides a method for getting it to market. LNG's density - 600 times greater than natural gas - reduces storage and transport volumes. But to make LNG, a conventional producer must compress the gas and cool it to minus 250 degrees Fahrenheit. This has typically required sophisticated large-scale refrigeration machinery to be cost-effective. A modern natural gas liquefaction plant can cost a billion dollars or more. Economies of scale often dictate that such a plant liquefy upwards of a billion cubic feet of gas per day with substantial operating and maintenance costs.

Currently, no commercially available, economical, small-scale LNG production technology exists for remote gas fields.

Cryenco's new LNG process, at commercial scales, is expected to be economical at rates of one to four million cubic feet per day and cost significantly less than traditional refrigeration processes of similar scale.

If the technology proves to be a success, offshore producers will benefit from the ability to produce LNG by installing the technology on remote offshore oil platforms. Producers operating smaller oil wells that are not connected to natural gas pipelines will also have the ability to produce LNG and eliminate the costly reinjection process. In addition, coal producing regions that lack pipeline access could produce LNG from the natural gas (methane) released from their coal mines.

The technology could have other applications as well. For example, it may make portable refueling stations possible for compressed natural gas vehicles, or create a way for hospitals to store natural gas for emergency use. Power companies might also have a new option for making LNG for storage near the gas turbine generators they use to meet peak electricity demands.

Although the technology has the name "ThermoAcoustic Stirling Heat Engine and Refrigeration" or TASHER, its basic process is relatively simple. There are no moving parts and only minimal electric power requirements. The device is expected to be maintenance-free, environmentally benign and boast operation efficiencies approaching conventional large-scale LNG plants.

With the Energy Department's funding, Cryenco will build a 500 gallon per day prototype model of a TASHER unit at its principal cryogenic manufacturing plant in Denver.

The liquefier will have three steps. First, some of the natural gas will be burned to provide a power source. Second, a "thermoacoustic Stirling heat engine" will convert the thermal power into acoustic power (soundwaves) by alternately compressing and decompressing helium. Third, refrigerators will convert the acoustic power to draw off heat from a second supply of natural gas. The prototype model will use three refrigerators in series, each taking the gas down to a cooler level until it liquefies. About 70 percent of the initial gas feed is converted to LNG while 30 percent will be burned to generate the acoustic power.

DOE's Los Alamos National Laboratory (LANL) will provide technical assistance in scaling up a laboratory model. LANL first developed the novel cryogenic concept in early laboratory work with Cryenco and others, in part with the support of DOE's Office of Fossil Energy program.

This cooperative agreement with Cryenco, including LANL's support work, will be managed by DOE's Federal Energy Technology Center which implements the Office of Fossil Energy's gas processing research and development efforts. Cryenco is a division of Chart Industries, Inc., a Cleveland, Ohio-based manufacturer of industrial process equipment.

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For more information contact:

Hattie C. Wolfe, U.S. Department of Energy Office of Fossil Energy, 202/586-6503, E-mail hattie.wolfe@hq.doe.gov.

Technical Contact: Brad Tomer, U.S. Department of Energy Federal Energy Technology Center, 304/285-4692, E-mail: brad.tomer@fetc.doe.gov.