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Filtering waste oils to power off-road diesel equipment proves successful

It looks something like an old-time still, but it’s far from being a backwoods operation.

It’s a no frills three-tank filtering system that turns waste oils into a sooty solvent which, when blended with regular diesel fuel, can be burned in unmodified diesel engines. The filtered fuel is called “black diesel,” an economically attractive and environmentally friendly product which backers contend has the potential to become black gold if used on a grand scale during times of high pump prices. TDCJ successfully tested the filtering system at the Eastham Unit near Lovelady last year and plans on installing it at five additional prison facilities this year.

Velicia Burns and husband stand in front of demolished home
Black diesel is pumped into a motor grader at the Eastham Unit near Lovelady in December. The fuel is filtered through tanks seen in the background.

Photo by David Nunnelee

“I’m comfortable enough now to burn as much of it as we can wherever we can,” said Garry Kent, who led the testing of the fuel at Eastham for TDCJ’s Agriculture, Land and Minerals Department. “What I’d like to see happen is that we take all the waste oils we generate and burn it as fuel.”

Like the system itself, the steps in making black diesel aren’t complicated. Into one large cone-shaped tank go all of the used motor, hydraulic, gear and transmission oils taken from vehicles during routine maintenance. Allowed to settle for a couple of days so any solids or water can be drained off, the oils are pulled out of the first tank by an electric motor and pushed through two tightly woven filters to remove most of the remaining impurities before draining into a second tank. From the second tank it passes through an even finer filter and finally into a third, smaller tank containing regular diesel. And that’s pretty much it. After an additive is added, the mixture is aerated and then pumped straight into vehicles.

Kent, who oversees the agency’s farm equipment, cannery and crop production, said he proposed the pilot project at Eastham after becoming frustrated with the high price he was paying at the pump for diesel last summer. He, along with Eastham Farm Manager Mack Currie and Maintenance Supervisor Glenn Smith, used some salvaged parts to piece together the system and began burning black diesel in three tractors and a motor grader in late July. Just over 1,400 gallons of waste oil had been filtered through early December and approximately 1,300 gallons of the fuel mixture had been burned. The testers started with a 60-40 blend of filtered waste oil and regular diesel but switched to a 50-50 mixture in September. Kent said none of the equipment used in the six-month pilot project experienced mechanical problems while burning the fuel and that there was no discernable difference in mileage or performance. In fact, since black diesel burns hotter than regular diesel, he said the blend actually boosted horsepower in the equipment.

Building on its success at Eastham, Kent’s department plans to expand the waste oil filtering system to the Ramsey, Darrington, Ellis, Coffield and Hilltop units during the first six months of this year. The department is also exploring the feasibility of taking yellow grease waste from unit kitchens and turning it into pure bio-diesel. Initial study shows that TDCJ units produce approximately 300,000 gallons of yellow grease annually, enough to replace about one third of the regular diesel now consumed by unit farm shops each year.

Cost avoidance realized

Kent said putting in the pipes, pumps and tanks necessary to filter waste oils costs about $2,000 per installation. He added, however, that those one-time costs can be quickly recouped through lower fuel prices. In December, for example, a gallon of regular diesel was still about a dollar above the $1.20 it cost to produce a gallon of black diesel at Eastham.

“We’re having a cost avoidance of about 99 cents a gallon at today’s prices,” Kent said in December.

Kent said the average cost of filtering the waste oil itself was actually just 12 cents a gallon. The fuel additives and regular diesel contained in the mixture brought its final cost to about $1.20.

“The bottom line is how much does it cost you to filter a gallon of waste oil?” Kent asked in discussing the economics behind black diesel. “It’s costing us 12 cents, so diesel would have to fall to 12 cents a gallon before this wouldn’t be economical. Diesel going to 12 cents a gallon would be a good thing, I guess, but I doubt that will happen.”

Kent said environmentalists also like black diesel because the filtering system allows for the recycling of motor oils used in state-owned vehicles and farm equipment a second time.

“We’re doubling the recycling process,” he said. “We’re mandated by the legislature to buy recycled oil for our vehicles, so the oil we use has already been recycled once. Then by filtering it and burning it as fuel, we’re virtually taking it out of the waste stream.”

Kent said that TDCJ’s farm shops normally produce between 40,000 and 50,000 gallons of waste oil annually and that hundreds of thousands of gallons more are generated by departments throughout the agency. He said that while the concept of burning waste oils as fuel is not new, there wasn’t much of an incentive to produce it until the cost of conventional fuels skyrocketed last summer.

“Up until the recent spike in oil and gas prices, nobody really cared about recycling and the filtering of fuel to burn in their vehicles,” he said in December. “Even with the drastic fall in the price of oil over the past month or two, it’s still economical to do.”


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