June 15, 2007

Kimberlina: A zero-emissions demonstration plant

Keith Pronske, Clean Energy Systems Inc.

Clean Energy Systems Inc. (CES) has developed a zero-emissions power generation technology by integrating a component proven in the aerospace industry with conventional power plant equipment. Figure 1 is a simplified schematic of the CES process. Its most distinctive element (the third box from the left) is an oxy-combustor, similar to one used in rocket engines, that generates steam by burning a clean, gaseous fuel in the presence of gaseous oxygen and water. The clean fuel is prepared by processing a conventional fossil fuel such as coal-derived syngas, refinery residues, biomass or biodigester gas, or natural or landfill gas.

 

Combustion takes place at near-stoichiometric conditions to produce a mixture of steam and CO₂ at high temperature and pressure. The steam conditions are suitable for driving a conventional or advanced steam turbine-generator, or a gas turbine modified to be driven by high-temperature steam or to do work as an expansion unit at intermediate pressures. After passing through the turbine(s), the steam/CO₂ mixture is condensed, cooled, and separated into water and CO₂. The CO₂ can be sequestered and/or purified and sold for commercial use. Most of the water, which is purified separately, is recycled to the combustion chamber of the steam generator. Any excess can be sold.

Every component in the CES process, except for the oxy-fuel combustor, has been commercially proven in the power generation industry. Combustors similar to the one in Figure 1 have been a mainstay of rocket engines for decades. CES's innovation has been to adapt them to power generation, in much the same way that aircraft jet engine prime movers were turned into aero-derivative gas turbine-generators.

 

 

Three rounds of initial funding

In 1999, the California Energy Commission (CEC) awarded CES an Energy Innovation Small Grant to help pay for the construction of a laboratory-scale oxy-combustor. With the money, CES built a test bench and a lab-scale combustor and operated the latter at temperatures up to 2,700F and pressures up to 300 psia. The combustor ran reliably and stably on O₂, methane (CH₄), and water for up to 48 minutes following more than 75 starts. The successful demonstrations provided the "proof of principle" for producing clean, high-energy drive gases suitable for generating electricity. The experimental work was completed in January 2001; for more details, see the final CEC program report at www.energy.ca.gov/pier/final_project_reports/CEC-500-2006-074.html.

In September 2000, the U.S. Department of Energy's National Energy Technology Laboratory (NETL), under its Vision 21 program, began funding a CES effort to design, fabricate, and test a larger (20-MW_t) combustor, fueled again by O₂, CH₄, and water. That unit (Figure 2) was tested during late 2002 and early 2003. The tests successfully demonstrated operation at temperatures ranging from as high as 3,000F to as low as 600F at pressures from 1,100 to 1,540 psia. The combustor operated successfully from 20% to 100% of its rated output during more than 95 tests.

 

In early 2002, the CEC gave CES a much larger grant of $2 million to fabricate and demonstrate a natural gas–fired zero-emissions power plant based on CES's oxy-combustor. The goals of this project were to evaluate the durability of the combustor and to identify desirable design refinements. In August 2003, CES acquired the idled, 5-MW Kimberlina biomass power plant near Bakersfield, Calif., from AES Corp. The CEC approved the use of this facility for the evaluation project in November 2003 and provided $2 million in supplemental funding in March 2004. After acquiring the Kimberlina plant, CES designed a complete control system for the 20-MW_t combustor and integrated it into the unit.

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