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What can turn animal waste, offal, old tyres, junked computers and any old waste into oil. What can turn 100lb of sewage into 26lb of oil, 9lb of gas, 8lb of minerals and carbon and 57lb of water. The thermal depolymerisation process (TDP) can. That's what!

An experimental recycling plant in Philadelphia is turning waste from a nearby turkey factory into gas and oil. It could, in theory, convert any old kind of rubbish into fuel. Jerome Burne reports.
The Guardian
Thursday May 22, 2003
Original here

How about this for a ridiculous modern myth. There is a machine somewhere in America that can take virtually any sort of waste - offal from an abattoir, old tyres, junked computers - and turn it into high quality oil, plus pure minerals and clean water, all in a few hours. It is an invention that could change the world. Not only might it end the west's, and in particular America's, dependence on imported oil, but it has also the potential simultaneously to solve the increasingly pressing problem of waste disposal.

A fantasy along with the everlasting light bulb, the car that runs on water and the perpetual motion machine, right? Well, no.

An experimental unit that uses a technique known as the "thermal depolymerisation process" (TDP) that can recycle seven tonnes of waste a day into gas and oil has been running for three years in Philadelphia. A scaled up version is due to open in Carthage, Missouri next month. It is designed to transform 200 tonnes of guts, beaks, blood and bones a day from a nearby turkey processing plant into 10 tonnes of gas and 600 barrels of oil.

This is not being funded by some eccentric billionaire. The impressive results from the Philadelphia plant convinced the US environmental protection agency to put up $14.5m (£9m) to fund four more plants, while private investors are backing the Missouri plant to the tune of $40m (£25m). The company, Changing World Technologies, has also acquired such powerful friends as James Woolsey, former CIA director, and Alf Andreassen, former science adviser to George Bush. It's worth mentioning such well-connected backers because, says chief executive officer Brian Appel: "When people first hear about us they always say they don't believe it."

Trials at the Philadelphia pilot project have given the engineers a good idea of what different feedstocks would produce.

For instance, a 175lb (79kg) man could, theoretically, yield 38lb of oil, 7lb of gas, 7lb of minerals and carbon and 123lb of sterilised water. More practically, 100lb (45kg) of sewage becomes 26lb (11kg) of oil, 9lb of gas, 8lb of minerals and carbon and 57lb of water. Medical waste, generally regard as tricky to dispose of, is particularly valuable - its equivalent yields are 65, 10, 5 and 20.

Philadelphia council is planning to give this value-added treatment to its sewage and there are also plans to handle chicken offal and manure in Alabama and pork and cheese waste in Italy.

The company envisions a large chunk of the world's agricultural, industrial and municipal waste going through TDP recycling plants all over the globe. "You are not only cleaning up waste: you are talking about the distributed generation of oil all over the world" says Michael Roberts, an engineer with the Gas Technology Institute.

Changing World say that converting all of the US agricultural waste into oil and gas would yield the energy equivalent of 4bn barrels of oil, roughly equal to the volume of US oil imports in 2001. So oil tankers might soon go the way of tea clippers.

Transforming waste into energy is an old vision and there have been many attempts at it but only a few minor successes, such as the production of ethanol from cornstarch. All suffer from two big flaws.

They can only handle a few different types of "feedstock" and they usually generate only a little more energy than they use. "The only thing this process can't handle is nuclear waste," says Appel. "If it contains carbon we can do it."

TDP is said to be 85% efficient - that is, only 15% of the energy it produces goes to fuelling the process.

The initial estimate of the cost of the oil from the Missouri plant is $15 (£9) a barrel. The "lifting" price - how much it costs to get oil out of the ground - is very cheap in the Persian Gulf, around a dollar a barrel, while from Gulf of Mexico, North Sea or Alaska the "lifting" price is $8-12.

So a price of $15 a barrel for this technology is high but Appel predicts his prices will come down to $10 in a few years, making them comparable with a medium-size oil exploration and production company.

"The oil that comes out is very light," says Appel. "It is essentially the same mix as half fuel oil, half gasoline."

Environmental legislation seems to be running in TDP's favour. Last month, tougher emissions standards were set for diesel in the US, prompting a switch to the type of low-sulphur fuel that Changing World produces. The US is expected to ban recycling of abattoir waste into animal feed soon. That could well launch TDP big-time.

Making the switch is going to take a long time, but experts reckon it can make the oil industry cleaner and more profitable. The process can handle heavy crude, shale and tar sands - generally considered not to be cost-effective - as well as heavy solid waste left over from normal refining. A modified version could also be used to pre-treat coal, extracting a range of minerals and leaving the residue to burn hotter and more cleanly.

Although trial results have been impressive, the technology has to prove itself at the new Missouri plant. There are a few sceptical voices. "Once they are producing something as valuable as they say they are," says Professor Robert Brown of the Center for Sustainable Environmental Technologies at Iowa State University, "people aren't going to give dead chickens to them any more."

Where there's muck there's the recycler works

Turning organic waste into oil is a trick the earth perfected long ago. Applying pressure and heat to the decaying remains of plants and animals transforms their long chains of hydrogen, oxygen and carbon into the short-chain hydrocarbons that make up oil. But while the earth takes millions of years, TDP takes a few hours.

The principles remain the same, however, and no fancy new technologies are involved. In fact most of the pressure tanks and reactor vessels the system uses are available off the shelf.

What allows TDP to succeed where others fail is the way it handles the volumes of water found in most organic waste.

Feedstock is first ground into slurry and heated under pressure, which breaks down some of the long carbon chains. Then it flows into a "flash vessel" where a dramatic drop in pressure removes much of the water far more efficiently than boiling it off. Minerals settle out at this stage and the remaining organic soup is then heated in "coke ovens" to break any remaining chains before the end products - oil, gas, water and carbon - are drawn off from a distillation column.

The "coke oven" heats the organic soup to about 900F (480C) turning it into a vapour. What happens next is just the same as what goes on in an oil refinery, or indeed in a whiskey still. The vapour flows into tall containers, known as distillation columns, where the various molecules separate out - the lightest molecules rising to the top and the heaviest sinking to the bottom. So the gas is drawn off from the top, the oils are removed from the middle and the powdered carbon is taken out from the bottom.

The gas, expensive to transport, is used to power the process, while the oil, minerals and carbon are sold off. The calcium and magnesium produced from the turkey waste, for instance, make a perfect fertilizer.

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