TVA’s Clean Diesel Test Sets World Record

At 1 p.m. Wednesday, Oct. 23, combustion turbine foreman Tim Goss clicked a mouse on a computer in the control room at Tennessee Valley Authority’s Johnsonville Combustion Turbine Plant in Humphreys County, Tennessee.

About 100 yards to the north, Unit 18 roared to life.

Goss guided the General Electric 7EA turbine up to 44 megawatts. Then 65 megawatts. Then the full capacity given that day’s weather conditions – 76 megawatts.

“There were lots of high-fives and smiles,” plant manager Steven Trull said.

For the first time in the nation, a utility-scale gas combustion turbine was running on renewable diesel fuel.

After more than a year of preparations, TVA’s renewable diesel test – conducted in partnership with EPRI – became a resounding success. It's expected to help open the door to greater adoption of a cleaner fuel that reduces overall carbon emissions by up to 75% compared to conventional petroleum-based diesel.

“This has been tested in Europe, but never in the United States,” Trull said. “So that was a big win and an initiative in the right direction for cleaner energy.”

Kevin Collins, TVA’s senior program manager for innovation and research, said the Johnsonville test also set a second record: With 76 megawatts of electrical output, it was the largest renewable diesel test anywhere in the world.

The blue temporary storage tank at left holds renewable diesel piped into Unit 18 at TVA’s Johnsonville Combustion Turbine Plant in Humphreys County, Tennessee.

A True ‘Drop-In’ Fuel

Johnsonville Unit 18 is a simple cycle combustion turbine. TVA dispatches it to meet peaks in electricity demand because it can start up in just 12 minutes.

It can run on natural gas or conventional diesel.

And the test proved it can also run on renewable diesel, a low-carbon equivalent to petroleum-based diesel that’s made from renewable sources like vegetable oil and used cooking oil.

“When you compare the life cycle of the two products, renewable diesel produces far less greenhouse gases than petroleum diesel,” Collins said.

The Johnsonville test, which burned four truckloads of renewable diesel – almost 30,000 gallons – demonstrated that it can be used as a direct 1-to-1 replacement for conventional diesel.

Robert Steele, technical executive with EPRI’s Low-Carbon Resources Initiative, which evaluates alternative fuels, said renewable diesel has numerous advantages, right down to its molecular structure. But practically speaking, the biggest benefit is that it’s a true “drop-in” fuel – no operational changes are required to burn it.

“You don’t have to drain the tank or clean the tank,” Steele said. And unlike other liquid replacement fuels, such as aviation fuel, there are no restrictions on blending.

“You can run a 0% to 100% blend with conventional diesel,” Steele said.

The Johnsonville test proved the unit could start on renewable diesel and run at varying loads, without affecting the equipment.

The experiment also included extensive emissions testing.

“We did two days of testing on the petroleum diesel to get baseline results, and then we did two days on the renewable diesel,” Collins said.

“Preliminary results all look very favorable across the board. This is being further evaluated, but it all looks very good.”

Renewable diesel, made from vegetable oil and used cooking oil, is dyed red to distinguish it from other fuels.

Challenge Accepted

With 13 simple cycle combustion turbines contributing a generating capacity of 708 megawatts – and as one of the larger peaking plants in TVA’s portfolio – the Johnsonville facility served as an excellent test bed for renewable diesel.

Johnsonville is also at the forefront of TVA’s shift to cleaner energy. TVA closed a coal plant at the site in 2017. And it is now installing 10 state-of-the-art aeroderivative combustion turbines, which will support TVA’s expanded use of solar.

Plant manager Trull said the Johnsonville team embraced the renewable diesel project.

“It's a very busy site with a lot of new units going in,” Trull said. “I was a little concerned about the extra workload on my folks here, but once we explained the importance of this test and the fact that it had never been completed in the United States, that was a challenge for them, and they accepted that challenge.”

Preparations were rigorous.

“I did have a lot of challenging questions because of the protection of my asset,” Trull said. “The as-found, as-left condition of the unit was extremely important. We did all the necessary testing and inspections to ensure that we were not going to have any negative effects to the unit.”

For the actual testing, the team ran piping and valves to a temporary fuel tank that held the red-dyed renewable diesel.

Trull addressed a common question: With the renewable diesel being derived from used cooking oil, would it smell like egg rolls or French fries?

“We did discuss that early on, but it was a very mild-smelling diesel, much milder than standard diesel. No, it didn’t smell like we were cooking fish.”

From left, TVA senior program manager Steve Halcomb, EPRI technical executive Robert Steele and TVA combustion turbine foreman Tim Goss keep watch on the renewable diesel test from the control room at the Johnsonville plant.

Next Steps and Ripples

The successful test created excitement about next steps.

“We're exploring alternatives to reduce the amount of carbon that's being added to the environment to make the world a cleaner place,” Collins said. “Through this testing, we successfully proved that here is another option, another tool in our toolkit. And this is just the beginning of additional fuels we would like to explore that could push the ball even further toward reducing carbon emissions.”

The test is also expected to generate ripples far beyond TVA.

“We're already in conversations with some of the utilities that are considering doing similar testing to prove it out as an alternative for themselves,” Collins said.

Hospitals and other facilities that burn petroleum diesel in backup generators may also be able to substitute renewable diesel, said Steve Halcomb, TVA’s senior program manager for generation research and development.

“The next step is a transition study,” Halcomb said. “How can we apply this across TVA and to other sectors?”

For plant manager Trull, the test gave TVA a great opportunity to put its mission of service into action.

“We strongly believe in providing a cleaner and safer environment for everyone, and the willingness to test not only for TVA but other entities and other power companies,” Trull said. “From the TVA Act in 1933, we’ve always been trailblazers, doing what’s right for the people of the United States and Tennessee Valley. This shows we continue that mission.”

As for Goss, the foreman who operated the unit, the testing triumph was a good story to share with his family.

“I was just glad to be able to help out,” he said. “It was kind of a privilege and kind of just doing your job all at the same time.”

Photo Gallery

The test burned four truckloads of renewable diesel fuel.

Johnsonville plant manager Steven Trull stands near key equipment, such as this green liquid fuel supply pressure regulator.

Johnsonville gas operations manager Brian Fazekas, center, with TVA senior project managers Billy Sabin, left, and Kevin Collins, inspects temporary piping installed to carry renewable diesel fuel.

In a building alongside Unit 18, instruments track gas emissions data.

PHOTO AT TOP OF PAGE: Johnsonville Unit 18 hosted the world’s largest-ever test of renewable diesel fuel, generating 76 megawatts of electricity.