- Q: What is gasification?
Gasification is the first step in many processes that are used to convert coal into plastic, fertilizer, gasoline, diesel fuel, hydrogen, chemicals, and electricity. Specifically, gasification is a technological process that uses heat, pressure, steam, and often oxygen or air to convert any carbonaceous (carbon-based) raw material into synthesis gas (syngas for short). Syngas is composed primarily of the colorless, odorless, and highly flammable gases of carbon monoxide (CO) and hydrogen (H2
), with only a minor amount of the carbon completely oxidized to carbon dioxide (CO2
) and water. Gasification is different than the more familiar process of combustion (i.e., burning or complete oxidation) because it typically uses only 25 to 40 percent of the theoretical oxidant (either pure oxygen or air) to generate enough heat to gasify the remaining unoxidized fuel, producing syngas as the desired product. For further information, see:
- Gasification Introduction
- Q: Why is DOE performing coal gasification research & development?
Coal gasification research and development (R&D) will improve the fuel and product versatility, efficiency, and environmental performance (including capture and storage of carbon dioxide), while also improving the economics of gasification processes. This all leads to savings in capital and operating costs for a wide array of gasification-based applications, such as electricity generation, chemical processing, and gas and liquid fuel synthesis. Ultimately, a key benefit of ongoing coal gasification R&D is advancement in technology to ensure continued, secure electricity production, liquid fuels, and chemicals production from the extensive U.S. coal resource. For further information, see:
- DOE Gasification Systems Program and Benefits
- Q: Can biomass be gasified?
Similarly to coal, biomass can be converted into synthesis gas (syngas for short) by applying heat and pressure in the presence of air, oxygen, and/or steam to produce syngas. But while the principles are the same, biomass does not gasify as easily as coal, and is usually quite different physically and chemically from coal, leading to differences in feeding systems, the gasifiers utilized, syngas cleanup, etc. The key benefit of biomass utilization is that it is carbon-neutral, causing no net increase of atmospheric carbon dioxide (CO2
) through its utilization life cycle. The U.S. Department of Energy Gasification Research Program is interested in the co-utilization of biomass with coal, especially for the benefit of helping to reduce overall CO2
emissions from gasification. For further information, see:
- Alternatives/Supplements to Coal - Feedstock Flexibility: Biomass
- Q: I never heard of it; is gasification a new technology?
GASIFICATION AND THE ENVIRONMENT
- Q: How can gasification make coal clean?
Gasification-based processes result in much lower emissions of pollutants compared to conventional coal combustion. This is mainly because pollutant capture can be performed efficiently on a concentrated pressurized stream of synthesis gas (syngas for short), instead of inefficiently on a large dilute volume of combustion exhaust gas. In particular, this benefit results in very low air pollutant emissions and allows relatively inexpensive carbon capture, which are the key aspects of making coal clean. In addition, gasification has the benefit of producing solid wastes that are relatively non-toxic, useful materials for further use. For further information, see:
- Emissions Advantages of Gasification
- Major Gasification Solid Byproducts
- Q: What impacts does gasification have on ground water and rivers?
Gasification requires water as an essential source of hydrogen to convert the carbon-rich composition of coal to a slate of products having increased hydrogen content, such as fertilizer or liquid transportation fuels. Also, gasification-based power production requires water for steam cycles and cycle cooling. However, electricity produced from gasification plants (due to the combined cycle) tends to use less water than conventional electricity produced from coal combustion. Existing and new gasification plants are models of water resource conservation and careful use. Also, the problems of ash ponds contaminating rivers are not an issue with inert slag-producing coal gasification processes. For further information, see:
- Water Usage in Coal to Power Application
- Gasification Process Aqueous Effluents/Wastewater
- Solid Waste/Byproducts of Gasification: Background
- Q: Does coal gasification cause global warming?
Although coal gasification (like other coal-based technologies) is operated in configurations that result in anthropogenic carbon dioxide (CO2
) emissions, gasification-based processes are unique among other fossil fueled technologies in their ability to efficiently and cost-effectively capture large amounts of those CO2
emissions. The Kemper County integrated gasification combined cycle (IGCC) plant is a prime example. Two-thirds of the plant’s CO2
emissions will be captured and used in enhanced oil recovery (EOR) operations, effectively storing the CO2
and preventing it from contributing to potential global warming. As a result, the Kemper County IGCC plant would have less impact on potential global warming than an equivalently sized conventional natural-gas fired power plant. For further information, see:
- Increasing Importance of Carbon Dioxide Emissions Control
- Kemper County IGCC Project
- Q: Is gasification a renewable energy technology?
Combining biomass with the coal in gasification processes brings elements of renewable energy benefits to the technology. This is why the U.S. Department of Energy/National Energy Technology Laboratory’s Research and Development (R&D) Program places emphasis on combined coal and biomass utilization. For further information, see:
- Coal and Coal-Biomass to Liquids
- Q: Will coal gasification make acid rain?
Answer: Acid rain is caused by uncontrolled emissions of nitrogen oxides (NOx) and sulfur oxides (SOx), mostly from conventional coal combustion. The latest regulations to control the emissions of these pollutants demand increasing stringency in order to greatly reduce acid rain. In particular, coal gasification facilitates extremely low emissions of acid rain-causing pollutants, and therefore has negligible impact on the formation of acid rain. For further information, see:
- Nitrogen Oxides (NOx) Emissions From Coal
- Sulfur Oxides (SOx) Emissions from Coal
- Q: Can coal gasification really be used to turn coal into plastic and fertilizer?
Yes, synthesis gas (syngas for short) produced from coal gasification is a feedstock for plastics synthesis, and the hydrogen in syngas is essential for making ammonia, the backbone of fertilizer manufacturing across the world. The Great Plains Synfuels Plant has recently expanded its slate of products into fertilizer, and coal gasification is used on a very large-scale, particularly in China, for the synthesis of ammonia, fertilizers, and derivative plastics precursors such as olefins. For further information, see:
- Great Plains Synfuels Plant
- Commercial Examples of Gasification-Based Chemicals Production
- Commercial Technologies
- Q: Is China gasifying coal?
Yes, China is gasifying coal on a very large scale (and with new capacity currently being added) for many products, including electricity, synthetic fuels, chemicals, and fertilizer. For further information, see the China Gasification Database
- Q: Are there new U.S. gasification plants?
- Q: Can gasification compete with inexpensive natural gas and petroleum?
With today’s natural gas prices below $5/MMBtu it would be cheaper to use it directly for power production, or make synthetic liquid fuels from it, than using coal gasification to make either synthetic natural gas or synthetic liquid fuels (assuming one needs to build new plants to do either). Likewise, with abundant cheap crude oil available, coal-gasification based synthetic liquid fuels cannot compete. This said, historically, prices of natural gas have fluctuated wildly and have repeatedly exceeded the $7-8/MMBtu price point at which coal gasification starts to become attractive. Similarly, petroleum prices have also continuously fluctuated and periodically been so high that gasification projects have been considered as a cost-competitive alternative. For example, expensive oil has resulted in China opting to gasify coal to synthesize fuels and chemicals instead of exclusively importing oil to satisfy their fuel and petrochemical demands. Sasol’s large paid-for investment in coal-to-liquids infrastructure means that their profitability extends even further, making it profitable to use coal as feedstock even in the face of inexpensive natural gas and petroleum. For further information, see:
- Challenges for Gasification
- U.S. Economic Competitiveness
For additional information:
Gasifipedia is a gasification resource that includes history, state-of-the art technologies, DOE R&D, etc., all via a pictorial index showing major gasification processes and products.