No. 3, coal series: China imports U.S. technology

Gasification process for low-rank coals, lignite boasts high CO2 capture rate

BY ROSE RAGSDALE FOR GREENING OF OIL

U.S. researchers are working with China to build a 120-megawatt demonstration facility by 2011 that will use an innovative ‘clean coal’ technology developed in the southern United States.

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The scientists and engineers responsible for Transport Integrated Gasification, or TRIG™, technology, a highly efficient method of producing low-emission electricity from low-rank coals, also want to construct a larger, 582-megawatt plant in Kemper County, Miss., with startup proposed for 2014.

TRIG is an advanced integrated gasification, combined-cycle technology first developed in the 1990s. It produces electricity with lower emissions than traditional coal power plants. It is also an outgrowth of technology—the transport gasifier—that has been used successfully for more than 50 years in the petroleum refining industry.

TRIG was developed by Southern Co., an Atlanta-based electric utility company, and KBR Inc. (formerly Kellogg Brown and Root LLC), along with other partners, including the U.S. Department of Energy, at the Power Systems Development Facility in Wilsonville, Ala., which Southern Co. manage and operates.

Technology well-suited to low-rank coals in Asia

In China, the partners, under the terms of their technology licensing arrangements with KBR, will provide Beijing Guoneng Yinghui Clean Energy Engineering Co., Ltd. with licensing, engineering services and proprietary equipment for the implementation of TRIG technology at a power plant operated by Dongguan Tianming Electric Power Co. in Guandong Province, Peoples Republic of China. It will be the world’s first commercial power plant using the TRIG technology.

The new technology will be added to an existing gas turbine combined cycle plant at the Dongguan facility so that it can use clean synthetic gas from coal as its fuel for generating electricity, rather than fuel oil.

Can handle coals with up to 50% ash

Since the TRIG gasifier uses a dry feed and does not melt the ash in the feedstock, it is particularly well-suited for lower-cost fuels such as sub-bituminous coal, lignite coal or other coals with high ash or moisture content. TRIG can economically handle coals with up to 50 percent ash. This is important for India and China where many of the coals contain a large percentage of ash.

“China’s rapid growth vividly demonstrates the global need for advanced technologies to ensure reliable, affordable and cleaner supplies of energy,” said Southern Chairman, President and CEO David Ratcliffe in announcing the project. “This plant will demonstrate that TRIG offers an effective technological solution to these challenges.”

Ratcliffe also noted that Southern Co.’s subsidiary, Mississippi Power, is currently seeking regulatory approval to build the Kemper County plant, a facility that would include 67 percent carbon capture and sequestration. Construction of the proposed integrated gasification combined-cycle power plant would begin this year and be completed in spring 2014. 

Roots in petroleum refining technology

Proponents of clean coal technology using gasification say that it is a promising alternative to meet global energy demand. Information from the Energy Information Administration indicates that since 2004 the use of coal as a global energy source has caught up with the use of natural gas, and is set to surpass it by 2030.

Most existing coal gasification technologies perform best on high rank (bituminous) coal and petroleum refinery waste products, but they are inefficient, less reliable and expensive to operate when processing low-rank coal. These lower-grade coal reserves, including deposits with high ash content, remain underutilized as global energy sources even though they account for half of worldwide coal reserves, proponents say.

TRIG is based on KBR’s fluid catalytic cracking technology, which has been used for decades in petroleum refineries.

KBR started development of the TRIG technology as a bench scale unit at its Houston laboratory with a small 200-pound-per-day coal feed

In the early 1990s, researchers built a 5-ton-per-day unit at the University of North Dakota and then in 1996, scaled up the project to construct a 50 ton-per-day unit at the test facility in Wilsonville, Ala.

The process was refined with each subsequent test facility until today it is considered a commercial process and will have its first commercial demonstration at the China plan. The Mississippi IGCC Project also will be a commercial scale-up of the Wilsonville demonstration plant.

How does TRIG technology work?

Gasification is defined as a method for extracting energy from many different types of materials, even plastics, according to Wikipedia.com. The advantage of gasification is that using synthetic gas, or syngas, is potentially more efficient than directly combusting the original fuel because it combustion can occur at higher temperatures or in fuel cells. This means the thermodynamic upper limit to the efficiency defined by Carnot’s rule is higher or not applicable. (The thermodynamic law known as Carnot’s rule states that you never get something for nothing; that is, there must be a degradation of energy in any machine that outputs free energy.)

Gasification also can begin with materials that are not otherwise useful fuels, such as biomass or organic waste. In addition, the high-temperature combustion refines out corrosive ash elements such as chloride and potassium, allowing clean gas production from otherwise problematic fuels.

Four types of gasifiers are currently available for commercial use: counter-current fixed-bed, co-current fixed bed, fluidized bed and entrained flow.

KBR researchers say TRIG is a true circulating bed gasifier, which differentiates it from previously developed/demonstrated technologies as almost all other coal gasifiers have either a fixed or fluidized bed, which have very different performance characteristics.

The TRIG system uses transport gasification, an advanced circulating fluidized bed gasifier that is designed to operate at high solids circulation rates and gas velocities, resulting in higher throughput, carbon conversion and efficiency.

TRIG takes advantage of the reactivity of low-rank coals to form raw synthesis gas in a very short period in the riser portion of the TRIG unit. The synthesis gas laden with un-reacted solids passes through a series of cyclones where the solids are removed. Un-reacted components in the coal, such as ash, are re-circulated through the riser to transport the fresh coal into the reaction zone of the riser. As un-reacted components accumulate in the down comer, they are discharged from the unit.

The large circulating bed of solids provides for exceptional heat and mass transfer and for very controlled process conditions. This allows for a very high-quality synthesis gas product, while using a minimum amount of steam and air or oxygen.

The TRIG technology produces high-quality, tar-free syngas at high gasification efficiencies.

As a gasifier that does not produce slag, TRIG operates at moderate temperatures and below the melting point of ash. This provides more reliable operation, while using less oxidant and energy. In particular, the KBR gasifier’s proprietary ash removal system eliminates the technical difficulties associated with slag handling faced by conventional slagging gasifiers. Unlike other commercial gasifiers, which operate at much higher severity and therefore require costly spare equipment, or the maintaining of multiple gasifiers (trains), to ensure that when one breaks, another can take its place and reliability targets are achieved, TRIG requires no spares.

The TRIG system also incorporates high-temperature syngas cooling and uses a downstream particulate filter. These elements will result in high-process efficiencies, while eliminating water scrubbing and significantly reducing plant water consumption and effluent discharge. Other unique aspects of the TRIG process can be found in KBR’s proprietary heat integration and optimized syngas processing schemes, which directly result in reduced auxiliary energy consumption.

What makes TRIG technology special?

Rather than burning coal directly to make electricity, TRIG breaks coal down into chemical components. Gases that result from this chemical breakdown can fuel IGCC plants, which are more efficient and therefore cleaner than current coal-fired plants. Moreover, impurities can be removed from the coal before it is fired, avoiding some emissions.

TRIG also uses air rather than pure oxygen along with lower grade coals and lignite, the cost of which is both lower and less volatile than that of natural gas and higher-ranked coals. The result is the most efficient coal-fired electricity generation technology in the world, according to Southern Co.

The technology also produces more power and offers lower capital, operating and maintenance costs than other systems.

With TRIG, the IGCC facility in Kemper County, Miss. will turn Mississippi lignite mined on adjacent properties by North American Coal Corp. into syngas, while scrubbing out emissions of sulfur dioxide, nitrogen oxides and mercury to near natural-gas levels. It also will produce 65 percent less carbon dioxide emissions than current pulverized coal-fired power plants.

The Mississippi project also will be the only IGCC plant in the United States planned to provide carbon capture and sequestration from Day 1 of its operation, its proponents say. The proposed plant would capture up to about 67 percent of its CO2 emissions, which would be sold for use and geologic storage in enhanced oil recovery projects.

TRIG’s success would be important milestone

Though researchers at DOE’s National Energy Technology Laboratory decline to speculate on how clean the technology can get, they say that if the Kemper County IGCC Project successfully demonstrates the TRIG air-blown gasification technology using Mississippi’s lignite reserves, while its syngas cleanup system achieves 67 percent CO2 capture, then the technology will be an important advancement in the use of the nation’s abundant lower-grade coal deposits.

The project “would meet the purpose and need of the DOE’s mandate from Congress to demonstrate advanced coal-based technologies that can generate clean, reliable, and affordable electricity in the United States. Further, by demonstrating this technology at a commercial and economical scale, the project would meet DOE’s purpose and need under the loan guarantee program to encourage early commercial use in the United States of new or significantly improved energy technologies and reduce or eliminate emissions of greenhouse gases and other air pollutants,” NETL said.

The project also would generate technical, environmental, and financial data from the design, construction, and operation of the facility to confirm that the technology can be implemented at a commercial scale, according to an environmental impact statement prepared for the project by the DOE in cooperation with the U.S. Army Corps of Engineers.

For the longer term, NETL said it aims to continue developing technologies that will enable

future coal power systems to achieve unprecedented levels of efficiency and environmental performance. Numerous test and demonstration projects currently underway across the country are guided by DOE’s goal of developing a cost-competitive central power plant capable of 60 percent efficiency with near-zero emissions by 2020.

Links of interest

Southern Co.

KBR Inc.

Transport Gasifier animation

NETL

Gasification

EarthCents

DOE’s National Carbon Capture Center

Contact Rose Ragsdale at editor@miningnewsnorth.com