What it is
The Thermo-Depolymerization Process (TDP) is a proprietary technology developed by Changing World Technologies in conjunction with about a dozen other companies, primarily ConAgra (makers of just about every pre-packaged food product not owned by Philip Morris. Yes, even Big Momma Sausage), to convert biological waste into water, minerals, natural gas, and fuel oil. That's right, light, sweet crude that's chemically indistinguishable from No. 2 fuel oil and can be further refined into things like gasoline and kerosene. Essentially, it works like Mr. Fusion from Back to the Future. Take absolutely anything with carbon in it, like milk jugs, medical waste, turkey guts, banana peels, or Sprite and throw it into the TDP machine. Hell, throw the Sprite can in too. It won't make any oil, but it certainly won't hurt. Then, wait a half hour, and oil comes out the other end.
How it works
Nearly every previous attempt to convert waste into energy has failed due to the same nagging problem: water. It takes so much energy to remove the water from virtually anything that the energy recovered by burning the dried refuse almost never makes up for it. However, TDP achieves a remarkable 85% energy efficiency through the clever realization that water is a actually a good thing.
In the first step, the waste product is thrown into a
grinder and mechanically broken down into small pieces (or
goo, depending on what was thrown in). These pieces are then dumped into the first
reactor, which is essentially a giant
pressure cooker. The ground waste is mixed with additional water, and then super-heated to somewhere in the neighborhood of 500 degrees
Fahrenheit and 600
PSI of pressure. In this phase, long chemical chains (
polymers) begin to break down into shorter, simpler
molecules. This has the added benefit of killing just about anything that was living in the waste (and survived the grinder, of course), even
Bacillus Stearothermophilus spores (which are notably durable) and
bovine spongiform enchephilitis (mad cow disease). Unlike other waste disposal techniques, the water is advantageous here because it transfers heat and generates pressure very efficiently, lowering the total energy required to
cook (depolymerize) the waste
After this slurry cooks for about 15 minutes, it is rapidly dumped into a decompression chamber. The 500-degree water, now at standard pressure, realizes that it should have boiled off almost 300 degrees ago and proceeds to do so very rapidly. The resulting super-heated steam is used to help heat the next batch of waste, and then can either be reclaimed and used later, or safely dumped like the distilled water that it is. At this point, most of the dissolved minerals fall out as well. In the case of biological products, these are almost always useful as fertilizers. In non-biologicals, they tend to be safe, industrially useful things like metal salts.
The waste, now pre-digested and 90% dry, is transferred into a standard coke oven and is refined using age-old, tried-and-true, oil refining techniques, which include heating it to nearly 900 degrees and waiting for everything to evaporate up the separating column. Natural gas is skimmed off the top and used on-site to heat the reaction chambers. Light oils, heavy oils, and water come from the middle, and industrial-grade graphite comes out the bottom.
The Results
Overall, the process is about 85% efficient, thanks to clever reuse of water and natural gas. Changing World has also compiled a list of interesting statistics for what comes out after putting 100 pounds of waste in:
Plastic Bottles: 70 lbs oil, 16 lbs gas, 8 lbs water, 6 lbs graphite
Municipal Sewage: 26 lbs oil, 9 lbs gas, 8 lbs solids, 57 lbs water
Tires: 44 lbs oil, 10 lbs gas, 42 lbs carbon and metal, 4 lbs water
Used Heavy Oil: 74 lbs oil, 17 lbs gas, 9 lbs graphite
Medical Waste: 65 lbs oil, 10 lbs gas, 5 lbs metal and graphite, 20 lbs water
Is this for Real?
Almost unbelievably, yes. There was a proof-of-concept plant constructed in Philadelphia, PA, and ConAgra constructed a full-sized production plant right across the street from its Butterball Turkey processing plant in Carthage, MO that currently processes 200 tons of turkey-related waste each day. I'll omit the company line about saving the world while eliminating terrorism because hype is still hype, but this process is very real and apparently works as advertised.
What about the Big Oil? You know, the guys that oppress all of the USENET cranks?
Turns out the Oil Industry is thrilled with this technology and is providing millions of dollars in funding for research and development. It turns out that you can take most of the waste from the oil production process (tar sands, used motor oil, grease, and the crud they scrape off the bottoms of oil tankers), dump it into a TDP facility and squeeze just a bit more oil out of it for $10 per barrel, approximately the same price as they would pay a medium exploration company, while giving the finger to the EPA the whole time. Additionally, the oil still needs to be refined, transported, marketed, and sold. Most companies see it as drilling the Alaskan Oil Reserves without all of the messy pipes or environmentalists.
What about Environmentalists?
Changing World estimates that a 175 pound person would result in 38 lbs of oil, 7 lbs of gas, 7 lbs of minerals (mostly rust and chalk), and 123 lbs pure water. Seriously, the process is so clean that the EPA does not even consider the TDP plants to be waste handlers, instead classing them as production.
References
The Changing World website, for a more sucinct overview, focusing on favorable compairisons and advantages:
http://www.changingworldtech.com
Discover Magazine appears to have the definitive coverage of the topic, along with their usual heady optimism
http://www.discover.com/may_03/featoil.html