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An employee publication of the Texas Department of Criminal Justice
March/April 2010

Unit kitchens' waste cooking oil recycled as biodiesel fuel


Garry Kent standing in front of old gas pump with jars of cooking oil sitting on top.

Agribusiness, Land and Minerals manager Garry Kent shows bottles containing biodiesel at various stages of refinement. The process begins with waste vegetable oil, far left, and ends with pure biodiesel, far right. Glycerin, second from left, is drained off, before water is added to the biodiesel, second from right, to wash it of impurities.
Photos by David Nunnelee

The same tractors used to raise food cooked in TDCJ kitchens now run on biodiesel recycled from unit kitchens' waste oil.

A program to turn plant-based oils into biodiesel got underway at the Eastham Unit near Lovelady last February under the direction of the Agribusiness, Land and Minerals Department. By September, more than 1,000 gallons of the fuel had been refined and burned in two farm tractors at the unit. Four other unit tractors are powered by black diesel, a fuel fashioned separately from recycled motor oils and lubricants. (See Black Diesel, May/June 2009 Connections)

The making of biodiesel at Eastham starts with the collection of waste vegetable oils from TDCJ unit kitchens in the Huntsville area. Garry Kent, who oversees the project, said the kitchen wastes are filtered at the contributing units to remove as many solids as possible and then trucked to Eastham in 4-gallon plastic jugs.

"The cleaner the grease, the better," Kent said. "If you use waste oils with a lot of solids in it, you're going to have problems."

At Eastham, waste oil is poured into an 80-gallon plastic tank and heated at 120 degrees for two hours. Meanwhile, in a second 20-gallon tank, 12 to 15 pounds of powdery potassium hydroxide is mixed with approximately 16 gallons of methanol and allowed to dissolve. The mixture is then pumped into the waste oil tank where, over a number of hours, it reacts to form a thick layer of amber-colored biodiesel atop a thinner layer of black, biodegradable glycerin. Once cooled, the glycerin, which still contains traces of methanol, is drained off and used at the unit as an accelerant in the burning of brush piles and for controlling weeds along fence lines.

Terry Price pointing to drum full of biodiesel fuel.
Eastham Unit maintenance supervisor Terry Price points out a layer of biodiesel atop a darker layer of glycerin.

Once the layer of glycerin has been siphoned off, fresh water is pumped into the top of the tank, where it washes the biodiesel clean of impurities as it settles to the bottom. After two or three more washings, the water is drained, leaving behind pure biodiesel that can be pumped directly into a fuel tank and burned in any diesel engine. Kent said biodiesel is clean enough to burn on the highway whereas the black diesel produced at Eastham is strictly for use in off-road vehicles.

Kent said that depending on its purity, the 80 gallons of kitchen waste oil poured in the tank at the outset combines with the chemicals to make between 60 and 72 gallons of pure biodiesel. The greater the reaction between the ingredients, the greater the fuel yield, he said.

"If everything goes right, we're looking at a 90 percent reaction rate," he said. "But every batch is different."

Because the biodiesel is now made in relatively small amounts, TDCJ gets as much mileage as possible from each batch by mixing every gallon with a gallon of regular diesel. Last September, when regular diesel was selling for about $2.20 a gallon, Kent calculated that the agency's 50-50 biodiesel mixture was costing just $1.55 a gallon to produce. The biodiesel itself cost less than 90 cents a gallon, he said.

"There's a cost avoidance of between 60 and 70 cents a gallon," Kent said.

Kent said mixing in regular diesel with the biodiesel also diminishes its odor, which is reminiscent of the foods cooked in the waste vegetable oils.

"Pure biodiesel does have an odor of food when you burn it," he said. "The first time we ran it in a tractor, it smelled like fried chicken."

Kent said processing of biodiesel could be expanded on a regional basis, provided the making the fuel remains economically attractive.

"As long as it's cheaper than regular diesel, it's worth doing," he said. "From a dollar standpoint, it makes sense for us to continually improve our agricultural operations."


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