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The EERC is pursuing development of petroleum-alternative fuels from domestic resources as a means of ensuring long-term energy supply security for military and, eventually, commercial civilian use. These fuels must be “drop-in-compatible” and cost-competitive with their counterparts but also have a reduced carbon footprint. Producing alternative fuels uses a process called gasification to convert solid carbon-rich fuel—coal, biomass, and biomass–coal blends—to primarily CO, H2, CO2, CH4, and H2O; all of which exit the conversion system as synthesis gas (syngas). The syngas can then be converted using catalytic processes to distillate fuels like methanol, gasoline, or diesel.

The EERC has on its property six high-bay (three- to seven-story) technology demonstration facilities dedicated to providing near-commercial-scale testing for the energy and environmental industries. The facilities feature a wide variety of combustion, gasification, liquefaction, carbon capture, and emission control technologies.

The EERC is currently gasifying coal–biomass blends in two pilot-scale gasifier systems: a (~400-lb/hr fuel throughput) Transport Reactor Integrated Gasifier (the TRIG™, developed by KBR and Southern Company) and a smaller fuel throughput (~10-lb/hr) EFG. The seven-story-high TRIG can produce about 400 scfm of syngas, and the three-story-high EFG can produce about 20 scfm. Both systems can be operated in air-blown or oxygen-blown mode. These well-instrumented gasifiers are the primary tools being used to evaluate the gasification of biomass and biomass–coal blends for EERC gasification work.

“Dozens of fuels have been tested in these gasification systems over the past two decades,” said EERC Senior Research Manager Mike Swanson, who leads the TRIG testing. “For example, since its commissioning in 1990, our TRIG gasifier has proven to be an excellent system for evaluating the operational performance of all ranks of coal, coal–biomass blends, and 100% biomass. The TRIG system is seven stories high and enables the gasification reactions to be self-sustaining, but it is still small enough that several different operating conditions can be evaluated in a single day. TRIG testing has been done on an Australian brown coal, three coals from India, a Bulgarian lignite, four coals from China, and several Powder River Basin coals as well as lignites from North Dakota, Texas, and Mississippi.”

“Each of the technologies—EFG and TRIG—has different attributes and functionalities, different benefits, and different challenges,” said Josh Stanislowski, EERC Research Manager and lead for the EFG testing. “Many of the studies undertaken are to evaluate how well each of these systems works with a variety of fuels.”

Most gasification systems are designed for uniformly sized coal particles. Introducing biomass by itself as a fuel or in a blend with coal can create challenges due to the different size, density, and physical attributes of the biomass. The EFG has to be fed very fine feedstock material—almost a powder—whereas the TRIG can take coarser material. Coal is relatively easy to grind to a powder because it is hard. Biomass (such as corn stover and straw) is not easily ground to a powder. Preparing the fuel is more energy-intensive than coal, even if it is possible to do. EFGs operate at a higher temperature than does the TRIG, so EFGs are less energy-efficient. However, because EFGs operate at higher temperatures, they can destroy almost all of the tar species formed during biomass gasification. The TRIG can produce a fair amount of tars when converting biomass feedstocks. Biomass is generally high in potassium, which forms a sticky ash that can plug gasification systems. This presents more of a problem for the TRIG than the EFG because the ash must remain as a solid for proper operation. The ash must be turned into a liquid in the EFG, and potassium beneficially lowers the melting temperature of the ash.

“Many developers out there are providing commercially available full-scale EFG systems, but these systems are not necessarily guaranteed for biomass,” said Stanislowski. “They are typically focused on high-rank bituminous coal, and developers can’t guarantee how they will perform using biomass. We’ve worked with  multitudes of fuels in the EERC’s EFG, which has been operational since 2008. This system is intended to mimic the designs of several commercial systems.”

Stanislowski added that there are a few commercial EFG systems operating in the United States with bituminous coal, but none uses low-rank coal. There are hundreds operating worldwide, where the systems  burn coal and even petroleum coke or residue.

“The TRIG is a versatile system that can run bituminous coal, subbituminous coal—even petcoke and biomass, but it is really geared for low-rank coals found in the middle of the country, like Powder River Basin coal,” said Swanson. “Our work until about 2007 involved optimizing the gasifier with a wide range of different fuels. Now most work involves commercial entities that come to us and want a particular fuel tested.”

The TRIG technology is currently being installed commercially as part of the Kemper County Energy Facility, a 582-MW integrated gasification combined-cycle facility in Mississippi.

“The EERC has been able to successfully gasify coal–biomass blends. We have also taken it all the way to liquid fuels production. We’ve shown that we can gasify coal–biomass, clean up the syngas, use a catalyst to make liquid fuels, and upgrade those liquids to drop-in-compatible jet fuel,” said Stanislowski.