Gasification plants can capture carbon dioxide, the leading greenhouse gas, much more easily and efficiently than coal-fired power plants. In many instances, this carbon dioxide can be sold for Enhanced Oil Recovery (EOR) and other uses, creating additional value from the gasification process. The Dakota Gasification Plant in Beulah, North Dakota captures its carbon dioxide while making substitute natural gas and sells it for EOR. Since 2000 this plant has captured and sent the carbon dioxide via a 205 mile pipeline to EnCana’s Weyburn oil fields in Saskatchewan, Canada, where it is used to help recover additional oil. (See www.dakotagas.com)
In a gasification system, carbon dioxide can be captured using commercially available technologies before it would otherwise be vented to the atmosphere. One process, called the water-gas shift reaction, is illustrated below:
Converting the carbon monoxide to carbon dioxide and capturing it prior to combustion is more economical than removing carbon dioxide after combustion, effectively “de-carbonizing” or, at least, reducing the carbon in the syngas.
Gasification plants manufacturing ammonia, hydrogen, fuels, or chemical products routinely capture carbon dioxide as part of the manufacturing process.
According to the Environmental Protection Agency, the higher thermodynamic efficiency of the Integrated Gasification Combined Cycle (IGCC) plant cycle minimizes carbon dioxide emissions relative to other technologies. IGCC plants offer today’s least-cost alternative for capturing carbon dioxide from a coal-based power plant. In addition, IGCC will experience a lower energy penalty than other technologies if carbon dioxide capture is required. While carbon dioxide capture and sequestration will increase the cost of all forms of power generation, an IGCC plant can capture and compress carbon dioxide at one-half the cost of a traditional pulverized coal plant. Other gasification-based options, including the production of motor fuels, chemicals, fertilizers or hydrogen, have even lower carbon dioxide capture and compression costs.
During gasification, virtually all of the carbon in the feedstock is converted to syngas. The mineral material in the feedstock separates from the gaseous products, and the ash and other inert materials melt and fall to the bottom of the gasifier as a non-leachable, glass-like solid or other marketable material. This material can be used for many construction and building applications.
Gasification Slag, Courtesy of Westinghouse Plasma Corporation (WPC), a division of Alter NRG Corp.
In addition, more than 99% of the sulfur can be removed using commercially proven technologies and converted into marketable elemental sulfur or sulfuric acid.
Gasification uses approximately 14–24% less water to produce electric power from coal compared to other coal-based technologies, and water losses during operation are about 32–36% less than other coal-based technologies. This is a major issue in many countries — including the United States — where water supplies have already reached critical levels in certain regions.
Converting Waste to Energy
Each year the bulk of the world’s municipal waste is disposed of in landfills. Gasification can convert this waste into electricity and other useful products—reducing the need for landfill space, decreasing methane emissions from the decomposition of organic materials in the landfill, and reducing the risk of groundwater contamination for landfills.