The experimental use of wood chips in a coal-fired power plant operated by Nevada’s main utility was a bit of a flop. But utility and state officials are hoping it will wind up being the first step toward using waste wood that is stacking up in Nevada.
NV Energy had hoped that burning waste wood at its Reid Gardner Station coal plant in Moapa, outside Las Vegas, would provide a cheap way to fulfill part of a state-mandated renewable energy standard.
The test, which began late last year, found that wood could be burned to generate electricity. But the fuel needs more processing first, and it might require expensive and time-consuming changes in plant design.
By the end of this year, 12 percent of the state’s electricity is expected to come from renewable sources, and utilities will be required by 2025 to produce 25 percent of the state’s electricity from renewable energy resources and conservation efforts.
Legislators and environmentalists at the time of the tests said they would prefer to see a plant specifically designed to use only biomass fuel rather than wood-coal blends. But they said using the blend was better for the environment than either mining and burning coal or disposing of the wood by burning it in the open. At the plant, the emissions from the blend were scrubbed before coming out of the smokestacks.
Prescorched wood, known as wood char, has been used in the fuel mix for U.S. coal plants for several years. But feeding raw wood into boilers is relatively new, and tests involving feeding raw wood chips of various sizes into the boilers along with coal provided important information.
Early attempts with larger wood chips clogged the plant’s pulverizers, so operators switched to a more finely ground wood. That, too, caused clogging problems, said David Sims, NV Energy renewable energy project development director.
The results were dramatic decreases in plant efficiency, Sims said. The plant produced 20 to 25 percent less electricity during the wood chip tests than when it burns pure coal.
That’s because the pulverizers, designed to crush coal, smashed the comparatively wet wood into giant pancakes. That led to less fuel being pushed into the boilers and periodic shutdowns to clean out the pulp. Because the plant couldn’t run constantly, less electricity was generated.
NV Energy was also underwhelmed by results of emissions monitoring from the plant during the test. Plant operators substituted enough wood for coal to make up about 5 percent of the fuel mix. But changes in emissions from the plant were negligible, spokesman Mark Severts said.
“We were hoping that the emissions might improve slightly,” Severts said. “They did not worsen, but also did not significantly improve.”
Although the last batch of wood was from Arizona, Nevada has plenty of waste wood.
The Nevada Division of Forestry needs to thin certain forest areas to reduce the threat of wildfires and to maintain sagebrush habitat for endangered and sensitive species, said Eric Roussel, head of the NDF biomass program.
“With thinning, waste products are developed that are currently rendered unusable and burned on site or sent to landfills due to the limited need in Nevada,” Roussel said. “This wood waste would be a good source of renewable fuel for energy generation.”
Officials say there are about 9 million acres of waste wood and encroaching forest removed to prevent wildfires and preserve sagebrush habitat. Treeclearing in the Lake Tahoe area and tree removal in other parts of the state will continue, the division recently announced.
There have been a few proposals and tests of biomass fueled generators in northern Nevada, including one at a rural elementary school and another near a prison. Both were aimed at reducing the facilities’ utility bills. But the $8.8 million plant at the prison could not cover its expenses, and the equipment is for sale.
NV Energy is interested in biomass technology and may invest in a biomass plant or sign a power-purchase agreement if the right project comes up, Severts said.
That’s one reason NV Energy plant operators haven’t given up on the idea of burning wood in the coal plant.
They’re considering future tests with wood chips ground to sawdust, and building a secondary input system that could feed sawdust directly into the boilers.
Plant managers are also looking more closely at torrefaction, which is basically a fancy type of charcoal. Other coal plants are testing the use of this wood material with mixed results, Sims said.
“The idea is that you could use it in the existing fuel system, because it would theoretically be a crushable material, so you wouldn’t need to build the additional input equipment,” Sims said.
“But we’re hearing mixed reviews on torrefaction,” the NV Energy official said. “Sometimes the material doesn’t dry all the way through, so when it goes through the feed system, it might still have some of the same problems as wood.”
Distributed by The Associated Press