GE powers turbines with ethanol in Brazil

By Kris Bevill | September 23, 2010
Posted Oct. 7, 2010

General Electric Co. announced Oct. 7 that it has been contracted by Petrobras to convert the second of two units at a power plant near Rio de Janiero to burn ethanol. The Juiz de Fora power plant is an 87 megawatt, simple-cycle, natural gas plant that serves approximately 300,000 homes. Two of GE's 43.5 megawatt, LM6000 model gas-fired turbines are used to power the plant, and soon both will be capable of burning ethanol as well. The plant is believed to be the first power plant in the world to be powered by ethanol.

The combustor on the first unit was converted to become ethanol-capable one year ago and endured 1,000 hours of testing using 100 percent hydrous ethanol. John Ingham, GE's aeroproducts manager for Latin America, said various tests were conducted, mostly to determine what effects ethanol may have on the wear and tear of the machine when operating at baseload capacity. "The results were very satisfactory and very equivalent to that of any other liquid fuel," he said.

The LM6000 model turbine, as well as several other turbine models produced by GE, is known as an aeroderivative and is a modification of aviation turbine designs. "This particular model is derived from the turbine that is used on wide-body jets like the 747," Ingham said. "It's originally designed to work with liquid fuels. The aeroderivatives version of it is normally operated with gas. The model that was installed at this power plant was a gas-only turbine and we've converted it to be dual fuel." Ingham said the turbine can now burn any liquid fuel, including gasoline, diesel, biodiesel or kerosene, but it has only been tested using ethanol. The unit can be switched from fuel to fuel during operation, with no downtime required.

A massive amount of ethanol is required to fuel the 43.5 megawatt turbine. Ingham said one turbine burns 18,000 liters (approximately 4,700 gallons) per hour. If operated continuously, the two turbines at the Petrobras plant would require about 6.7 million gallons of ethanol every 30 days. Petrobras is heavily invested in many ethanol production projects, but Ingham said most of the ethanol used for testing at the power plant came from ethanol mills not owned by Petrobras because they were located in closer proximity to the power plant. The strategic move for Petrobras to convert to dual-fuel turbines was more of a hedge against future fossil fuel issues than to create a use for Brazilian ethanol, he said. "They are investing in having alternative fuel sources for their power plants in case of any problem in the supply of natural gas," he said. "They will also have a secondary fuel to be able to use and continue generating power."

The renewable aspect of ethanol is also a motivator to convert turbines at power plants, Ingham said. After five-months of testing sugarcane ethanol at the Petrobras plant, the companies found that nitrous oxide (NOx) emissions and water requirements had been greatly reduced, while efficiency and power levels remained the same. "We were quite surprised about the low levels of water and NOx emissions," he said. "We expected them to be lower, but they were even lower than what we hoped for."

GE has not tested corn-based ethanol in its turbines, but Ingham doesn't foresee any problems with using that as a fuel. "Our main rule is that the fuel does have to follow GE's liquid fuel specs, as does any fuel," he said. "We're not making special exceptions for ethanol." The company currently has no plans to expand its technology to the continental U.S., but it is exploring possibilities in Hawaii. "In the U.S., you have some difficulties because of the local price of ethanol and also the tariff to import ethanol into the U.S.," he said. "One of the problems with ethanol becomes the logistics18,000 liters an hour is a lot of ethanol. If you were to double that and go for 100 megawatts, you'd have to have a substantial logistics system to do that." Hawaii poses an intriguing opportunity because it already imports fossil fuels to burn at its power plants. "The appeal of having a renewable fuel source that could be used for generating power is pretty interesting and it actually makes economic sense to use ethanol instead of diesel or kerosene," he said, adding that GE is also exploring dual-fuel turbine unit possibilities in Japan and Southeast Asia.

The cost of an ethanol compatible dual-fuel turbine is comparable to other gasoline-diesel turbines, Ingham said. Upgrading a gas-only turbine to become dual-fuel compatible, such as what is being done at the Petrobras plant, requires an additional cost to install liquid fuel systems to the gas turbine. Ingham said a converted turbine costs between 5 and 10 percent more than a gas-only turbine.

The first turbine at the Petrobras plant has been burning natural gas since testing was completed in May, but it could be switched back to ethanol at any time, Ingham said. "Since the test, the unit has resumed normal operations without being stopped for maintenance or taken out for repairs or anything like that," he said, adding that prior to testing, the unit already had undergone 10,000 hours of run time. Conversions to the second turbine are estimated to be complete in January, exactly one year after the start-up of the first unit.