1. The heart of gasification lies in (shocker) the gasifier, which takes coal, water and air and applies heat under high pressure to make "syngas"-a mixture of carbon monoxide and hydrogen. Minerals in the fuel (i.e., the rocks, dirt and other non-carbon-based material) separate, leaving the bottom of the gasifier either literally in ashes or as an inert, glass-like slag-materials that can be reused for materials such as concrete and road fill.
2. The crude syngas leaves the gasifier piping hot and full of contaminants (hydrogen sulfide, ammonia, mercury and nasty particulates, to name a few). A combination of heat exchangers, particulate filters and quench chambers cool the syngas to room temperature and remove most of the solids.
3. Syngas then passes through a small bed of charcoal to capture mercury, removing over 90 percent of this toxic metal (click here to learn more). Used charcoal containing captured mercury leftover is sent to a hazardous landfill for disposal.
4. The final step for cleaning in gasification is the removal of sulfur impurities in acid gas removal units, where the impurities are converted into sulfuric acid or elemental sulfur-both valuable byproducts.
5. A combustion turbine then reheats the clean syngas, dilutes it with nitrogen for control of NOx (the greenhouse gas that makes smog) and burns it, driving a generator to make electricity.
6. Leftover heat from combustion is recovered in a Heat Recovery Steam Generator (HRSG), which generates steam to power the internal turbine. Some of that air is compressed and can be channeled back to the air separation unit for oxygen, which is then reused within the gasifier.
7. The steam generated in the HRSG and the steam made in Step 1 combine to drive a steam turbine for even more power production. The steam then cools and condenses into water, which pumps back into the steam generation cycle. In an IGCC plant, two-thirds of the total electricity produced comes from the gas turbine and one-third from the steam turbine.
The great thing is, once coal is converted to a gas, it's fairly straightforward to remove pollutants. Mercury, sulfur, and particulates can be stripped out and sold commercially. This "clean" gas can then be used for a variety of fuels such as oil for heating homes or fuel for cars. "The gas can also sub for natural gas, fueling "integrated gasification combined-cycle" (IGCC) power plants to create electricity. Pennsylvania hopes to replace many of its filthy coal-fired power plants with IGCC plants."
""You could put a million scrubbers on an old coal-fired power plant and never even approach the environmental performance of a coal gasification plant," says Kathleen McGinty, secretary of Pennsylvania's Department of Environmental Protection."
So the benefits work out as a reduction of air pollutants, a solution to the waste-coal problem, and a boost to economy.
So what are the drawbacks?
"There are three drawbacks, and they are substantial:
- If gasification takes off, there isn't enough waste coal in the country to feed the beast. Thus, you're back to coal mining, which is a nightmare.
- Gasification is largely untested and unproven, at least in the U.S. And IGCC plants are more expensive than old-fashioned dirty coal-fired plants. Thus, gasification relies heavily on subsidies. State and U.S. Dept. of Energy tax incentives for the Penn. plant, for instance, add up to over $140 million. More big industries getting chummy with gov't; more semi-permanent corporate welfare recipients.
- Carbon dioxide. Global warming. That whole thing. IGCC plants are certainly an improvement over dirty coal-fired plants -- they use less coal to create more energy -- but they still produce plenty of CO2. They do make the CO2 fairly easy to capture, which is nice, but the question is what to do with it once it's captured. The big idea is to sequester it: pump it underground or into plant tissues and soil. However:
5 comments:
You might want to take a look at www.hybridpwr.com. CO2 from gasification can be dramatically reduced in a completely unexpected way.
Yes (in response to above comment and the link they posted), and then where do we put the nuclear waste? Do we stick it on Indigenous Land and let them develop diseases disproportionate to the "profits" they actually will never see... ?
this is only bad things about coal... and since when is coal the 'left handed red head step child'? :(
Alternative energy refers to energy sources which are not based on the burning of fossil fuels or the splitting of atoms. λεβητες πέλλετ
"Gasification is untested and unproven":
And yet there are massive industrial plants such as Sasol's plants which have been running successfully since the 1970s on coal. How is this technology not tested or proven?
I have even done some work on their plants previously. It is very impressive technology indeed and quite well established.
http://en.wikipedia.org/wiki/Sasol
Post a Comment