Pure Green Power

As the first utility company in the United States to use B100 in a stationary power generation application, McMinnville Electric in Tennessee has experienced trials, tribulations and, by most measures, good success in its progressive experiment to produce green electricity from a clean and renewable domestic fuel.
By Nicholas Zeman | April 01, 2006
Diesel-fueled generators are a mainstay of back-up power for public and private buildings such as hospitals, police departments, fires stations, public shelters, schools and office buildings. They have also provided standby power and assistance during peak electrical usage-the hottest and coldest days of the year-for utility companies.
Unfortunately, these power machines, however essential, are known to emit harmful air pollutants like NOx, sulfur and carbon monoxide. It makes sense, then, that biodiesel is gaining acceptance among those who maintain and rely on stationary power generation.

In central Tennessee, McMinnville Electric has been testing B100 in a 2 megawatt power generator to produce clean energy. The objective of the project is as simple as it is green, says Rodney Boyd, CEO of the utility. "Our objective [is] to generate power, and for that generation to occur as cleanly and efficiently as possible using biodiesel," he says.

McMinnville Electric System was founded in 1939 and generates power for the Tennesse Valley Authority. It is thought to be the first municipal electric utility to generate electricity for the grid using B100. So far, the company has logged hundreds of testing hours on its biodiesel-powered generator and continues to tweak the process.
The machine being used in the project is a Caterpillar D3516 B electric generator-similar in size to a locomotive engine-a model that's been in production since 1998. However, unlike earlier versions of the model, this generator is equipped with an electronic fuel system that presented some challenges in transitioning from petroleum diesel to B100. Because of the reduced heating value per gallon of pure biodiesel compared to diesel, Caterpillar had to calibrate the machine to consume more fuel than it would originally need so that it would crank out 1,640 kilowatts of power. "We had to turn it up," says Tom Stanzione of Thompson Caterpillar in Tennessee, who is working closely with McMinnville Electric on the project.

Project coordinators say they required the machine to achieve 1,640 kilowatts because they wanted the generator to operate at the height of its horsepower range in real conditions. Before the machine was tweaked for the renewable fuel, it struggled significantly. "It is similar to a tractor-trailer trying to pull an 80,000 pound load up a 75 degree slope," Boyd says. "It's pulling hard the whole time it's running. Since the biodiesel does not quite have the Btu value of the petroleum diesel, we were having problems with the engine shutting down initially. It was thinking it was starving for fuel." That problem was overcome after an adjustment to the throttle sensory indicator was made. In fact, Boyd says, "I have no hard numbers to prove it, but everyone of my linemen out there in the substation around this project will tell you the engine runs quieter and smoother with the biodiesel than it did with the petrol-diesel."

Caterpillar has also been pleased with how the testing has progressed. Once the ASTM provisional specification (PS-121) for B100 came out, the company became more comfortable with the use of the alternative fuel in its engines. "Caterpillar has supported evaluating the potential impacts of the use of various biodiesel [blends]," Stanzione says. But, because fuel-related failures are not covered in the warranties from engine manufacturers like Caterpillar, Cummins and Detroit Diesel, these and other companies have not officially endorsed the use of biodiesel in their engines. After a few conversations with Boyd, however, Stanzione was convinced of the project's relevance, even though the experimental nature of the endeavor contained certain elements of risk.

"I am not sure everyone would participate in a test like this," says Stanzione, explaining that the primary concern of most major engine manufacturers is to make sure their products perform with the fuel they are made for. In other words, getting into biodiesel-especially B100-opens up a whole new can of worms. "We need to test the fuel against the metallurgy, against the rubber components and sealants used in an engine to secure it [internally]," says Brian Muncher of Stowers Caterpillar in Tennessee. "In the use of biodiesel, you have to keep an eye on seals and hoses and anything that is rubber, silicone or a non-metal surface to see how it reacts to the particular fuel that you are using."

Cracking molecules, cleaning exhaust
Aside from Caterpillar, there have been several other partners in the biodiesel testing project at McMinnville Electric. EmeraChem, a chemical engineering firm based in Knoxville, Tenn., built the catalyst that is essential to reducing the harmful pollutants emitted in the exhaust from the diesel generator.

The EMx NOx trap system has two chambers that treat exhaust intermittently in four-minute intervals. The exhaust passes through the platinum-coated trap where the NOx is absorbed, and carbon monoxide and unburned hydrocarbons are absorbed. When one chamber is fully loaded with NOx, the mechanism switches to a second chamber.
A plasma reformer produces the hydrogen gas needed to regenerate the catalyst by cracking the biodiesel molecules. The regeneration gas flows out of the plasma reformer and into the chamber of the catalyst undergoing regeneration. "EMx is a continuous process designed to achieve the required emissions reduction at the maximum NOx flow-rate," says Lisa Mitchell, project engineer for EmeraChem and the manager of the McMinnville project. "We have successfully installed the NOx trap in large natural gas turbines [and in] on-road diesel engines, but this is our first foray into stationary diesel applications with this product." Earlier installations of the NOx trap have regenerated the catalyst using natural gas to produce hydrogen. McMinnville Electric, however, was adamant about using the engine's native fuel to regenerate the catalyst and resisting the introduction of another fuel into the process.

This experimental procedure caused concerns for Boyd and company. "Since this was something new-reforming biodiesel and creating 21 percent hydrogen out of the bottom of that plasma reformer-we are actually cracking the [biodiesel] molecules and producing hydrogen, and we ran into some issues," Boyd says. "Anytime you start cracking an element at that high a temperature- 1,100 to 1,200 degrees Celsius range-you find out things that you didn't know, one being that the biodiesel was creating carbon in there, and that was simply because we had been operating in the 850 to 950 degrees Celsius range."

After temperature adjustments were made, problems with the purity of the water supply were addressed. This issue caused "plugging simply because when you heat normal tap water to that temperature, you have a lot of mineral impurities that drop out of it as well," Boyd says. McMinnville solved this problem by beginning to use de-ionized water and was able to run the generator for 36 hours straight with only some minor tweaking. The EMx catalyst reportedly achieved the cleanest diesel generator emissions ever reported (based on generator size and type). NOx, carbon monoxide and unburned hydrocarbons were extremely low. "It got to be so boring out at the substation that we were going to go out and get something to eat and grab a shower and come back," Boyd says. "Well, during that time, a little $2 fuel filter that was not the correct filter plugged, starved the system for fuel, and it burned a hole in the side of that plasma reformer. So we are in the process of rebuilding that piece of equipment right now."

Like many experiments, the McMinnville biodiesel project has required a certain amount of trial and error in order to bring the Caterpillar generator to its peak performance in the use of an alternative fuel source. But as these bugs have been worked out, McMinnville is producing some very clean electricity in central Tennessee.

Energy crops
McMinnville Electric had been purchasing its fuel from Biodiesel of Mississippi, but received its first load of fuel from a Tennessee producer, AgriEnergy LLC in Lewisburg, this month. Boyd says he hopes McMinnville will be a leader in developing new markets for Tennessee-grown soybeans.

Using biodiesel to generate power benefits farmers in several ways other than simply providing a potential new market for soybean oil. John Dodson, a Tennessee soybean producer and an officer of the American Soybean Association, is happy to see McMinnville Electric moving ahead with the project. "I am excited that they chose to use biodiesel instead of natural gas," Dodson says. "The more biodiesel we use to generate electricity, the less natural gas we have to use, and that means that there is more available to make fertilizer-and that keeps the price down."

Parks Wells, spokesman for the Tennessee Soybean Promotion Council, says that biodiesel will not have an immediate impact on the Tennessee farmer, but increasing demand for the fuel will likely have a big effect over time. "Our biggest issue in soybean production right now is the need for increased acreage for the crop, and biodiesel could help, but this is going to happen over an extended period of time, and it will not be anything sudden," Wells says. Although Wells was hesitant to hail biodiesel as the savior of the Tennessee farmer, he did express excitement in regard to the biodiesel experiment at McMinnville and said he felt Boyd was a visionary in the use of alternative fuels to generate power. "He understands electricity like no one else," Wells says.

McMinnville Electric, as the first utility company in the United States to generate power using B100, is a leader in the application of biodiesel. "I see the future of biodiesel as one of the saving products of a good energy portfolio, and I don't think we need to rely on any one single energy source," Boyd says. "I have never seen an Army man guarding a soybean field in Tennessee, so we need to learn how to be independent of foreign sources; I certainly see Tennessee moving in that direction, especially when you talk about being able to put Tennessee farmers back to work growing energy crops."

Nicholas Zeman is a Biodiesel Magazine staff writer. Reach him at nzeman@bbibiofuels.com or (701) 746-8385.
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