Gasification
The term “gasification,” as used in this blog, describes the process which enables Integrated Gasification Combined Cycle systems (IGCC) with Carbon Capture and Storage to achieve high power efficiencies while cutting greenhouse gas emissions. Gasification power systems are able to achieve high power efficiencies because they use both a combustion and steam turbine in what is known as a "combined cycle." "Higher efficiencies mean that less fuel is used to generate the rated power, resulting in better economics (which can mean lower costs to ratepayers) and the formation of fewer greenhouse gases (a 60%-efficient gasification power plant can cut the formation of carbon dioxide by 40% compared to a typical coal combustion plant)" (U.S. Department of Energy, 2008).
Schematic depicting processes of an IGCC system. Image source U.S. Department of Energy. http://fossil.energy.gov/programs/powersystems/gasification/howgasificationworks.html
THE SCIENCE BEHIND THE SYSTEM
An Integrated Gasification Combined-Cycle (IGCC) system uses the heat and pressure of a gasifier to partially oxidize carbon-containing feedstock (fuel) (U.S. Department of Energy, 2008). This process produces a concentrated gas stream of carbon dioxide (which is then captured and sequestered to prevent the gas from escaping into the environment) and syngas, a primarily hydrogen and carbon monoxide substance (U.S. Department of Energy, 2008). The syngas gets cleaned of its hydrogen sulfide, ammonia and particulate matter and burned as fuel in a combustion turbine. The best technologies can remove around 98%, 90% and 99% of sulfur dioxide and NOx (nitrogen oxides) (Bergerson & Lave, 2007). The exhaust heat from the combustion turbine is then used to boil water, creating steam for a steam turbine-generator.
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THE ECONOMICS OF IGCC SYSTEM IMPLEMENTATION
Incentives:
- Through tax credits and loan guarantees the U.S. Energy Policy Act of 2005 incentivizes companies to build Integrated Gasification Combined-Cycle (IGCC) systems (Bergerson & Lave, 2007, p. 3431)
- The U.S. has large coal deposits and, in our current economy, the argument that domestic coal extraction offers mining and transportation jobs to American workers is gaining more traction in the media.
- IGCC plants are dependent on cheap, abundant supplies of domestic coal
Disincentives:
- Environmental regulations would have to be two-times more stringent than current standards to justify the additional expense of building and IGCC plant with Carbon Capture and Storage (CCS) instead of a Pulverized Coal (PC) plant.
- For instance, only a carbon tax of $29 or more per ton of carbon, would incentivize companies looking for the cheapest plant to favor an IGCC system with CCS over a PC plant. (Bergerson & Lave, 2007, p. 3433)
- By nature of its newness, there is uncertainty concerning the performance and reliability of IGCC technology.
- IGCC plants minimize costs (defined as the “sum of capital costs, operations, maintenance and the cost of pollution emissions) at the expense of efficiency (Bergerson & Lave, 2007)
- Higher quality coal can increase efficiency (from 34% efficiency using Illinois coal no. 6 to 37% using Pittsburgh no. 8), but higher quality coal is more expensive than lower quality (Bergerson & Lave, 2007, p. 3433)