Coal Gasification, A New Way Of Looking At Coal?
By Andy McAllister, Watershed Coordinator
More than half of the electricity produced in the United States currently comes from coal. With the demand for electricity expected to double by 2050, environmental concerns growing ever stronger, and renewable resources still years away from offsetting the increased energy demand, industry and government have been looking for ways to keep up with our energy demands while utilizing currently available energy sources and technologies. One fairly recent technological innovation getting more press lately is the process of coal gasification.
The gasification process was originally developed in the 1800s to produce gas for lighting and cooking. Electricity and natural gas later replaced town gas for these applications, but the gasification process has been used for the production of synthetic chemicals and fuels since the 1920s.
Just What is Coal Gasification?
Simply put, gasification itself is a process that converts carbonaceous materials, such as coal, petroleum, or even wood, into carbon monoxide and hydrogen by reacting the raw material at high temperatures with a controlled amount of oxygen and/or steam. The resulting gas mixture is called synthesis gas or “syngas” (containing mostly Hydrogen with some Carbon monoxide and small amounts of other constituents) and is itself a fuel. This syngas is potentially more efficient than direct combustion of the original fuel because it can be combusted at higher temperatures or even in fuel cells. The hydrogen obtained from gasification can be used for various purposes such as powering a hydrogen economy, making ammonia, or upgrading fossil fuels. Additionally, liquid fuels such as a low sulfur diesel fuel, can be created from the products of gasification.
Gasification can also be used with materials that are not seen as traditionally useful fuels, such as plastic or organic waste. Practically any type of organic material can be used as the raw material for the gasification process. In a traditional coal combustion plant, heat from burning coal is used to boil water to make steam that drives a steam turbine-generator. According to reports, only a third of the energy value of coal is actually converted into electricity by most old-fashioned combustion plants, the rest is lost as waste heat.
In a coal gasification power plant, everything revolves around the “gasifier.” This is basically a big compartment where feedstock (coal, in this case) is fed in and is then converted into syngas by applying heat and steam in a high pressure environment. The amount of oxygen allowed into the gasifier is very carefully controlled so that only a small amount of the feedstock burns completely. This partial oxidation process provides the heat necessary to break the feedstock down chemically into syngas (source: U.S. Dept. of Energy).
Co-Generation, More Bang For The Buck
The gasification plant typically gets double duty from the gases it produces. First, the coal gases, cleaned of their impurities, are fired in a gas turbine much like natural gas, to generate one source of electricity. The hot exhaust of the gas turbine is then used to generate steam for a more conventional steam turbine-generator. This dual source of electric power, called a “Combined cycle” or “Co-generation” (Co-gen for short) converts much more of coal’s inherent energy value into useable electricity.
While Coal Gasification plants are “Co-gen” plants, not all “Co-gen” plants are Coal Gasification plants. For example, non-traditional power plants using a different process called “Circulating Fluidized Bed” technology, known as CFB plants, may also be Co-generation plants. For more information on CFB plants, click here to view WPCAMR’s CFB educational brochure.
Waste coal piles, a bane of life in the coal regions, can be used to fuel Coal Gasification plants just as they can fuel CFB plants. This use for waste piles helps remove an eyesore and pollution source while at the same time making use of a resource long considered unprofitable for more conventional uses.
Greenhouse gas production is still an issue with coal gasification as it is with traditional coal combustion. However, some contend that the gasification process lends itself better to carbon sequestration but we’re not aware of any practical application of that at this point.
The US. Department of Energy’s Office of Fossil Energy says there are currently two commercial gasification plants currently operating in the U.S., one in Florida and one in the State of Indiana. A $400 million coal gasification plant is currently proposed for the Good Spring area of Schuylkill County, PA where, once permits are secured, construction is slated to begin in 2010.
Click here to read an additional article about the future of coal gasification plants.
March 3rd, 2009 at 5:23 am
Technology which can convert coal into a clean pumpable liquid with low burnoff emissions. Both are now readily available at competitive costs.