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Weird Science

What kind of fuel am I?

In the film "Back to the Future," Doc popped the hood of his time-traveling DeLorean and tossed kitchen scraps and beer cans into his gigawatt fusion converter thingamajig. It functioned much like a food processor/trash compactor, but converting waste into automotive fuel. Turns out that this cinematic solution to contemporary problems of both excess litter and fuel shortages isn't that far off the mark.

Petroleum-based fuels have always been a politically charged issue, especially now with Middle East turmoil and gas prices topping $2 a gallon in the U.S. There's a lot of information available on alternative sources of energy, but perhaps the most interesting, and weirdest, is the conversion of turkey parts, used restaurant grease and pig manure into usable fuel. Like the futuristic DeLorean, these fuel sources might solve multiple problems.

Biodiesel

Biodiesel isn't a new concept. The Massachusetts Port Authority runs biodiesel in its Logan Airport shuttle buses and the USDA's Agricultural Research Center is heated with it. Made from soybeans or waste cooking oil, biodiesel can be used straight or mixed with petroleum-based diesel fuel, and emits a distinctive French fry odor rather than the traditional diesel odor. Bus conversion includes the simple and fairly inexpensive addition of a catalytic converter to the exhaust system, but costs roughly one and a half times the cost of petroleum-based diesel.

The use of plants with higher oil content than soybeans or waste cooking oils would bring that cost down. A pair of Gustavus Adolphus College grads took the biodiesel theory literally. Last year, Aaron Crowell and Phil Graeve converted a 1981 VW Rabbit diesel pickup, named the Crisco Kid, to run on used restaurant grease with plans to take the Kid on a postgraduate road trip.

The conversion cost $250, and the Kid gets about 35 mpg, the same as diesel. The pickup starts on regular diesel fuel. Once the radiator heats up, warming the oil, the driver flips a switch to change the fuel source to its grease tank. Canola oil, one of the most common commercial deep fat fryer oils, is chemically similar to diesel fuel in the energy produced and burning characteristics, but it's more viscous and has to be heated before it runs through an engine.

Crowell and Graeve aren't the first to see America in a grease-fueled VW. Justin Craven made a cross-country trip in 2000 in a converted diesel and now sells conversion kits for around $800.

Grease is the Word

When tooling around Duluth, Minnesota, Crowell and Graeve pull up to "grease only" vats in the back of restaurants to refuel their Rabbit. Restaurant owners have to pay to have the waste removed, so they're more than happy to ladle it over to the grads.

Grease generates the same horsepower as diesel and promises a longer engine life. The only downside is the need to change grease filters regularly to keep errant fries or food tidbits out of the engine, along with storage issues such as congealed grease caused by cold temperatures. While the MPA buses smell like French fries, the Crisco Kid emits the odor of whatever foodstuffs its fuel source was initially used to cook (Chinese reportedly has the best aroma and performance).

On a much larger scale, ConAgra and Changing World Technologies teamed up to convert turkey waste from Butterball turkey processing into crude oil. The plant in Carthage, Missouri is designed to handle 200 tons of inedible turkey bits a day. The thermal conversion process simulates the natural, eons-long geothermal activity that produces petroleum, but cuts the time down to a matter of minutes.

Basically, the organic waste is mixed with water, placed under pressure and heated, and then rapidly cooled to separate the desired products. The only waste in the process is the water, which is recycled. CWT equates the cost of production to that of a small exploration and production company's finding costs. The bio-derived oil can be refined in existing facilities, so the infrastructure, which is a problem with other alternative fuels, is already in place.

Going to an even cruder source (in every sense of the expression), Yanhui Zhang, a researcher at the University of Illinois, is using similar technology to convert pig manure into a form of crude oil. It can be refined to heat homes, run electrical plants or make plastics, ink or asphalt.

Existing oil refineries aren't currently set up to process pig manure-derived oil, however. Zhang has successfully produced pig crude in small batches, but additional research is needed to make the system economically viable. (And we can just imagine the challenges involved in marketing a swine-derived fuel source to consumers.) Zhang predicts that a reactor the size of a home furnace could eventually process 2,000 pigs' worth of manure at a cost of about $10 per barrel.

One of the catch phrases of the 21st century is renewal resources. We will never be at a loss for waste products, so converting these wastes into fuels is tantamount to killing two birds, or rather turkeys, with one stone.