(Updated with new research 1-29-08)
Plasma Arc Gasification is a new waste disposal technology that turns garbage into usable byproducts without burning it. The heart of the PAG “plasma converter” is its “electrical arc gasifier,” which passes very high voltage electrical current through two electrodes, creating an arc in the space between them.
Inert gas under pressure is passed through the arc into a sealed container of waste material [garbage]. Temperatures as high as 13,871°C (25,000°F) are reached in the arc column. The temperature one meter from the arc can reach ~4000°C (~7,200°F). At these temperatures most types of waste are broken into basic elemental components in a gaseous form, and complex molecules are atomized – separated into individual atoms.
25,000ºF is hotter than the surface of the sun.
The byproducts of PAG are:
1. Syngas, a mixture of hydrogen and carbon monoxide. The plant scrubs the syngas and uses two-thirds of it to generate the electricity that powers the plant. The remaining one-third is sold to utility companies. Syngas can be produced from just about any organic material, and PAG is only one method of producing it.
2. Heat. The uses of this byproduct aren’t addressed in lay sources, but presumably it could be used to power a steam turbine in the plant, generating more electricity.
3. Slag, a solid residue resembling obsidian. Once it’s cleaned of contaminents, slag can be processed into bricks, synthetic gravel or asphalt, and other materials that we currently mine out of the ground.
What is the potential of PAG to reduce the stream of trash landfilled each year? Tremendous–if the gas and slag can be cleaned up–because PAG doesn’t burn trash; it gasifies it in a closed-loop system. Burying garbage in the ground is primitive technology with numerous harmful effects that aren’t taken into consideration when figuring cost per ton. No matter how miraculous the liner material in today’s modern landfills, they all eventually leak and dump a nasty toxic stew into the groundwater below.
Currently there are no large-scale PAG plants processing municipal waste in the U.S.–the ones in Tallahassee and St. Lucie County, FL, are the closest to coming online and according to this article they’re still in the permitting phase. I believe there are some very small U.S. operations being used to process medical waste, which the process is ideal for, as it obliterates every possible contaminent.
This Slate article does a nice job of summing up the pros and cons of the process:
So, why doesn’t every hamlet in America do away with its landfills and build one of these wondrous plants? The plasma gasification industry claims it’s mostly a matter of economics: Burying garbage has long been a lot cheaper than zapping it, even if you factor in the money to be made selling electricity. Landfills charge municipalities an average of $35 per ton of trash; according to a recent study in Hamilton, Ont., dropping off a ton of garbage at a plasma gasification plant would run $172 per ton.
Plasma gasification companies dispute this figure, contending that their method has become more affordable because of increasing efficiency in electricity generation: Canada’s Plasco Energy Group, for example, says that 46 percent of zapped waste now becomes energy, compared with 18 percent with earlier plant designs.
This is the cost/benefit issue that led Honolulu to reject its plant initially as mentioned in the Wikipedia piece linked above. I’m not impressed with the 46 percent efficiency figure–it needs to improve, and it probably will, because this technology is still in its infancy. I also think the cost/benefit ratio will pull even with and then surpass landfilling once the demand for electricity goes up because of the switch from gasoline to electric transportation.
This USA Today article lists some of the environmental questions surrounding PAG. It says that the facilities already processing garbage in Japan are doing so on a much smaller scale than the Florida plants would. Japan’s air quality standards are slightly stricter than those in the United States. If the plants are passing inspection over there, then critics can’t very well say the process is unavoidably dirty. The Slate article has some limited material on cleaning up the gas and slag byproduct. Proponents claim that burning Syngas produces CO2 emission on par with a natural gas power plant–pretty low, in other words.
One criticism of PAG worth consideration is that it provides an excuse for people to keep pumping out trash. The biggest opponent is the Global Alliance for Incinerator Alternatives, (GAIA) a very vocal and well organized nonprofit with an international presence. They’re quoted in the USA Today article:
We’ve found projects similar to this being misrepresented all over the country,” said Monica Wilson of the Global Alliance for Incinerator Alternatives. Wilson said there aren’t enough studies yet to prove the company’s claims that emissions will likely be less than from a standard natural-gas power plant. She also said other companies have tried to produce such results and failed.
GAIA was formed to fight traditional trash-burning incinerators being dumped into third-world countries, which is a legitimate form of NIMBYism. It raised red flags with me that a plant is being proposed for New Orleans (which has become a third world country of its own)–but then there has to be tons and tons of flood trash to get rid of down there, some of it hazardous waste. Why not process it with PAG and get some use out of it, as long as the people of New Orleans benefit from the money saved?
GAIA has said that PAG plants in Australia and Europe were “closed” because they couldn’t meet emission standards. This quote is all over the internet, but in two days of exhaustive searching I haven’t come up with anything resembling a primary source.
Here’s my quarrel with GAIA: it’s immoral to block a developing but basically sound technology because you want to modify the public’s behavior. Humans will always produce trash. I’m about as far from advocating Friedman free market economics as a blogger can get, but trash disposal one area where the marketplace will modify our behavior effectively, because the oil crisis is about to make wastefulness very expensive.
I do suggest that communities hold back on offering public funds to PAG companies that want to locate in their area until PAG has proven itself. The glut of ethanol plants is a caution against committing public money to an economically volatile technology, no matter how promising it might look.
Did you know that a natural latex pillow is 100% biodegradable?
Over at Blogging for Michigan, AikoAdam has written a nice post on PAG.