When burned by a sugar mill, bagasse, the fibrous material leftover after juice is extracted from sugarcane, usually produces enough electricity to power all of the mill’s operations and then some. For every 10 metric tons of sugarcane crushed, a sugar factory produces nearly 3 metric tons of wet bagasse.
Many mills across the globe that take advantage of bagasse for power are making improvements to their plants to make the whole process more efficient. Mackay Sugar in Australia—the largest producer of sugar on the continent—is currently constructing a $120 million cogeneration power plant at its Racecourse Mill in Queensland that when complete in 2012 will be able to provide about one-third of the Mackay city region’s electricity requirements.
The project, which Mackay has been working on for several years, involves the replacement of traditional boilers that are designed to incinerate bagasse, with a more efficient high-pressure boiler and a new steam turbine generator, capable of generating 36 megawatts (MW). While providing power and steam for the Racecourse Mill and refinery, it will also allow for the export of 27 MW to the grid.
Mackay’s proposed energy model is similar to that of U.S.-based Florida Crystals, which has always used bagasse to power its sugar mills using internal boilers in its mills, says Gus Cepero, company vice president and head of its energy program. “In 1995, [we] took the process a step further when we built the New Hope Power Co. biomass cogeneration plant, which utilizes high-pressure boilers to produce steam for the sugar mill and refinery as well as electricity that the company supplies to the Florida power grid.”
Cepero says that Florida Crystals’s biomass power plant, the largest in North America, uses 800,000 tons of sugarcane bagasse and 700,000 tons of urban wood waste each year. Since the sugarcane milling process does an excellent job of preparing the bagasse for combustion, not much else needs to be done to the bagasse so it is sent directly from the discharge of the milling plant to the boilers by conveyor belt. “Once at the power plant, the necessary volume of bagasse is fed to the boilers and the excess is conveyed to the fuel yard,” Cepero says.
Because the New Hope power plant operates at a high level of thermal efficiency, a significant volume of bagasse is stored at the end of the sugarcane grinding season, typically from mid-October to mid-March, according to Cepero. “The New Hope power plant operates year round, therefore the stored bagasse is used the remainder of the year,” he says.
Utilizing a slightly different business model, a California company is growing sugarcane not for the production of sugar, but for the sole purpose of creating fuel and energy. California Ethanol & Power is growing sugarcane in California’s Imperial Valley that it will harvest and convert into 66 million gallons per year of advanced biofuel, and utilize the bagasse to generate 50 MW of electricity, according to Dave Rubenstein, business development manager.
Each facility will also house an anaerobic digester that will produce 880 million cubic feet of pipeline quality biogas, Rubenstein says. Right now, the company is growing a few hundred acres of sugarcane that will be used for seed purposes. “Those will be harvested and replanted to increase our acreage to have enough for our first plant, for which we’ll need about 60,000 to 70,000 acres,” he says.
Of the 8.8 tons of sugarcane required at each plant per day, about one-third will consist of bagasse that will be converted into power. “It’ll be more of a direct process, but we’ll have some storage available to make sure the plant is running on a continuous basis,” Rubenstein says.
Although initial plans were delayed due to the financial crisis, plans for CE&P’s first plant are now underway. He says the company is currently working with a major national energy company for power off-take agreements, and hopes to have financials closed in 2011.
While CE&P’s plan is to build three or four plants in California, Rubenstein says the company believes the process, technology and engineering could be transferred to other sugarcane growing states in the U.S. and other countries.