Energy Forum / Alternative Energy

So how does it work? In the cold Philadelphia warehouse, Appel waves a long arm at the apparatus, which looks surprisingly low tech: a tangle of pressure vessels, pipes, valves, and heat exchangers terminating in storage tanks. It resembles the oil refineries that stretch to the horizon on either side of the New Jersey Turnpike, and in part, that's exactly what it is.

Appel strides to a silver gray pressure tank that is 20 feet long, three feet wide, heavily insulated, and wrapped with electric heating coils. He raps on its side. "The chief difference in our process is that we make water a friend rather than an enemy," he says. "The other processes all tried to drive out water. We drive it in, inside this tank, with heat and pressure. We super-hydrate the material." Thus temperatures and pressures need only be modest, because water helps to convey heat into the feedstock. "We're talking about temperatures of 500 degrees Fahrenheit and pressures of about 600 pounds for most organic material—not at all extreme or energy intensive. And the cooking times are pretty short, usually about 15 minutes."

Once the organic soup is heated and partially depolymerized in the reactor vessel, phase two begins. "We quickly drop the slurry to a lower pressure," says Appel, pointing at a branching series of pipes. The rapid depressurization releases about 90 percent of the slurry's free water. Dehydration via depressurization is far cheaper in terms of energy consumed than is heating and boiling off the water, particularly because no heat is wasted. "We send the flashed-off water back up there," Appel says, pointing to a pipe that leads to the beginning of the process, "to heat the incoming stream."

At this stage, the minerals—in turkey waste, they come mostly from bones—settle out and are shunted to storage tanks. Rich in calcium and magnesium, the dried brown powder "is a perfect balanced fertilizer," Appel says.

The remaining concentrated organic soup gushes into a second-stage reactor similar to the coke ovens used to refine oil into gasoline. "This technology is as old as the hills," says Appel, grinning broadly. The reactor heats the soup to about 900 degrees Fahrenheit to further break apart long molecular chains. Next, in vertical distillation columns, hot vapor flows up, condenses, and flows out from different levels: gases from the top of the column, light oils from the upper middle, heavier oils from the middle, water from the lower middle, and powdered carbon—used to manufacture tires, filters, and printer toners—from the bottom. "Gas is expensive to transport, so we use it on-site in the plant to heat the process," Appel says. The oil, minerals, and carbon are sold to the highest bidders.

Depending on the feedstock and the cooking and coking times, the process can be tweaked to make other specialty chemicals that may be even more profitable than oil. Turkey offal, for example, can be used to produce fatty acids for soap, tires, paints, and lubricants. Polyvinyl chloride, or PVC—the stuff of house siding, wallpapers, and plastic pipes—yields hydrochloric acid, a relatively benign and industrially valuable chemical used to make cleaners and solvents. "That's what's so great about making water a friend," says Appel. "The hydrogen in water combines with the chlorine in PVC to make it safe. If you burn PVC [in a municipal-waste incinerator], you get dioxin—very toxic."

The technicians here have spent three years feeding different kinds of waste into their machinery to formulate recipes. In a little trailer next to the plant, Appel picks up a handful of one-gallon plastic bags sent by a potential customer in Japan. The first is full of ground-up appliances, each piece no larger than a pea. "Put a computer and a refrigerator into a grinder, and that's what you get," he says, shaking the bag. "It's PVC, wood, fiberglass, metal, just a mess of different things. This process handles mixed waste beautifully." Next to the ground-up appliances is a plastic bucket of municipal sewage. Appel pops the lid and instantly regrets it. "Whew," he says. "That is nasty."

Experimentation revealed that different waste streams require different cooking and coking times and yield different finished products. "It's a two-step process, and you do more in step one or step two depending on what you are processing," Terry Adams says. "With the turkey guts, you do the lion's share in the first stage. With mixed plastics, most of the breakdown happens in the second stage." The oil-to-mineral ratios vary too. Plastic bottles, for example, yield copious amounts of oil, while tires yield more minerals and other solids. So far, says Adams, "nothing hazardous comes out from any feedstock we try."

"The only thing this process can't handle is nuclear waste," Appel says. "If it contains carbon, we can do it."

This Philadelphia pilot plant can handle only seven tons of waste a day, but 1,054 miles to the west, in Carthage, Missouri, about 100 yards from one of ConAgra Foods' massive Butterball Turkey plants, sits the company's first commercial-scale thermal depolymerization plant. The $20 million facility, scheduled to go online any day, is expected to digest more than 200 tons of turkey-processing waste every 24 hours.