Super efficient separation system offers new promise for coal’s future

Valuable hydrogen gas is recovered with membrane technology developed at Oak Ridge, Tennessee

Oak Ridge, Tenn., August 22, 2001 — America’s vast coal resources have long been viewed as a potential hedge against future energy needs. Increased use of this resource, however, is complicated by the emission of pollutants and concerns about global warming.

One promising approach is the deployment of more efficient energy producing plants that rely on cleaner, more efficient coal gasification technology. The DOE Office of Fossil Energy through the National Energy Technology Laboratory (NETL) has sponsored and performed research and development of an advanced system known as the Integrated Gasification Combined Cycle (IGCC).

In concept, ICGG will be 30 to 50 percent more efficient than current coal systems, or in other words, it will provide 30 to 50 percent more energy from the same amount of coal.

The development and demonstration of the IGCC technology, which offers the potential for greater use of coal, has been a collaborative effort between NETL, other national laboratories, universities, and industry. Through this combined effort, the IGCC technology is moving toward commercial acceptance.

Supporting this development is the work of a group of researchers at DOE facilities in Oak Ridge, Tennessee, who are developing novel uses for inorganic membranes à‚– a technology that offers an extremely efficient means of separating a wide variety of compounds. The Oak Ridge team has found a potential solution to a key technical issue with IGCC that may eventually expand the economical uses of coal.

When coal is gasified, a large fraction of the very hot gas produced is hydrogen. Hydrogen itself is a high-value-added fuel. One way to help make the IGCC system economical is to have a unit that can separate and collect a significant portion of the hydrogen for use in more valuable ways, such as fuel for fuel cells or for use in petroleum refinery catalytic crackers. This approach is often termed “fuels decarbonization,” and quite simply refers to the process of converting a hydrocarbon fuel into a fuel, i.e., hydrogen, that does not contain carbon. For such a process to be viable, it must include provisions for separating and capturing carbon dioxide and other oxides of carbon that are produced.

Using inorganic membrane technology, the researchers at the Inorganic Membrane Technology Laboratory (IMTL) in Oak Ridge, Tennessee, have developed a process to manufacture a super-efficient, defect-free separation system that can effectively separate and isolate hydrogen from other gases in coal-derived synthesis gas.

The Oak Ridge-developed gas separation system consists of a porous membrane made of a ceramic material. Molecules of hydrogen are extremely small, as compared to molecules of carbon monoxide, carbon dioxide, and hydrocarbon gases. The difference in size allows the smaller molecules of hydrogen to pass through the porous material and away from the remaining gases.

The high-purity coal-derived hydrogen may then be collected and used as a feedstock for other advanced energy producing technologies, such as hydrogen-fueled turbines or fuel cells or for chemical and petroleum processing, such as hydrotreating.

Development of an inorganic porous membrane for separating hydrogen from very hot gases posed a tremendous technological challenge for the Oak Ridge researchers. A separation device must be able to tolerate both high temperatures and harsh environments associated with coal gasification processes. Laboratory tests have shown that the Oak Ridge-developed process can provide sufficiently high separation factors. Additional tests will be made at NETL as well as at the Oak Ridge National Laboratory to determine their stability under simulated operating conditions.

In a related development, IMTL researchers are developing an economical means of producing a membrane separation system consisting of a carbon membrane on a porous metal support. While being developed primarily for use in petroleum-refining operations to economically recover unused hydrogen from the refinery purge gases. Variants of either of these systems may also be used in existing fossil fuel facilities to remove greenhouse gases. Further development and use of this system promises to help alleviate global warming concerns with increased fossil fuel use.

Prototype testing of these new products will be conducted at the NETL and ORNL later this year. Funding for this research was provided through the DOE’s Office of Fossil Energy through the Advanced Research Materials Program and the Petroleum Technology Program, both of which are administered by NETL.

The IMTL is located at the DOE’s East Tennessee Technology Park, which is operated by Bechtel Jacobs Company LLC.

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