Andreassen and others anticipate that a large chunk of the world's agricultural, industrial, and municipal waste may someday go into thermal depolymerization machines scattered all over the globe. If the process works as well as its creators claim, not only would most toxic waste problems become history, so would imported oil. Just converting all the U.S. agricultural waste into oil and gas would yield the energy equivalent of 4 billion barrels of oil annually. In 2001 the United States imported 4.2 billion barrels of oil. Referring to U.S. dependence on oil from the volatile Middle East, R. James Woolsey, former CIA director and an adviser to Changing World Technologies, says, "This technology offers a beginning of a way away from this."
But first things first. Today, here at the plant at Philadelphia's Naval Business Center, the experimental feedstock is turkey processing-plant waste: feathers, bones, skin, blood, fat, guts. A forklift dumps 1,400 pounds of the nasty stuff into the machine's first stage, a 350-horsepower grinder that masticates it into gray brown slurry. From there it flows into a series of tanks and pipes, which hum and hiss as they heat, digest, and break down the mixture. Two hours later, a white-jacketed technician turns a spigot. Out pours a honey-colored fluid, steaming a bit in the cold warehouse as it fills a glass beaker.
It really is a lovely oil.
"The longest carbon chains are C-18 or so," says Appel, admiring the liquid. "That's a very light oil. It is essentially the same as a mix of half fuel oil, half gasoline."
Private investors, who have chipped in $40 million to develop the process, aren't the only ones who are impressed. The federal government has granted more than $12 million to push the work along. "We will be able to make oil for $8 to $12 a barrel," says Paul Baskis, the inventor of the process. "We are going to be able to switch to a carbohydrate economy."
Making oil and gas from hydrocarbon-based waste is a trick that Earth mastered long ago. Most crude oil comes from one-celled plants and animals that die, settle to ocean floors, decompose, and are mashed by sliding tectonic plates, a process geologists call subduction. Under pressure and heat, the dead creatures' long chains of hydrogen, oxygen, and carbon-bearing molecules, known as polymers, decompose into short-chain petroleum hydrocarbons. However, Earth takes its own sweet time doing this—generally thousands or millions of years—because subterranean heat and pressure changes are chaotic. Thermal depolymerization machines turbocharge the process by precisely raising heat and pressure to levels that break the feedstock's long molecular bonds.
Many scientists have tried to convert organic solids to liquid fuel using waste products before, but their efforts have been notoriously inefficient. "The problem with most of these methods was that they tried to do the transformation in one step—superheat the material to drive off the water and simultaneously break down the molecules," says Appel. That leads to profligate energy use and makes it possible for hazardous substances to pollute the finished product. Very wet waste—and much of the world's waste is wet—is particularly difficult to process efficiently because driving off the water requires so much energy. Usually, the Btu content in the resulting oil or gas barely exceeds the amount needed to make the stuff.
That's the challenge that Baskis, a microbiologist and inventor who lives in Rantoul, Illinois, confronted in the late 1980s. He says he "had a flash" of insight about how to improve the basic ideas behind another inventor's waste-reforming process. "The prototype I saw produced a heavy, burned oil," recalls Baskis. "I drew up an improvement and filed the first patents." He spent the early 1990s wooing investors and, in 1996, met Appel, a former commodities trader. "I saw what this could be and took over the patents," says Appel, who formed a partnership with the Gas Technology Institute and had a demonstration plant up and running by 1999.
Thermal depolymerization, Appel says, has proved to be 85 percent energy efficient for complex feedstocks, such as turkey offal: "That means for every 100 Btus in the feedstock, we use only 15 Btus to run the process." He contends the efficiency is even better for relatively dry raw materials, such as plastics.
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."