Freshly Squeezed Ethanol Feedstock
Seventy-five percent of U.S. oranges are grown in Florida. The sunshine state's citrus processing industry produces nearly all of the orange juice consumed in the country, resulting in up to five million tons of citrus waste each year. Options for turning that waste into something useful are limited, so the possibility of using citrus waste as a feedstock for ethanol plants is being closely monitored.
Bill Widmer is a research chemist at the USDA Agricultural Research Service's Citrus and Subtropical Products Laboratory in Winter Haven, Fla., and has been working on the conversion of citrus peels to ethanol for the past four years. His work is a continuation of research first conducted in the 1990s by Dr. Karel Grohmann, who developed the conversion process. At the time of Grohmann's research, gas prices were relatively low and enzyme costs were high. When Widmer took on the project four years ago, gas prices were substantially higher and enzyme costs had come down enough to make it possible to further explore citrus-peel-to-ethanol technology. Widmer set out to modify the process into something that would be economically feasible and that could be a continuous process for commercialization purposes.
His research was a success. Four years ago it took $12 to $15 worth of enzymes to produce one gallon of ethanol. Widmer was able to lower the enzyme cost to approximately 80 cents per gallon and create a pretreatment process capable of running on a continuous basis. The process consists of using the raw waste citrus peels and treating them to remove the peel oil present in the waste stream before liquefying the peels to begin the conversion to ethanol.
The peel oil removed in the pretreatment process is called d-limonene and is considered to be a valuable byproduct of citrus peel conversion. Widmer has developed a way to remove the oil and recover it for use in solvents and as a fragrance in cleaning products. "D-limonene has a value of 50 cents to $1 per pound," Widmer says. "If we were to convert citrus peel to ethanol and only get ethanol it wouldn't be feasible, but for every gallon of ethanol we produce, we also get one pound of d-limonene." Widmer says it costs approximately $2 to produce one gallon of ethanol and producers can expect to receive $1.50 to $2 per gallon of ethanol sold. Add to that approximately 75 cents per pound of d-limonene recovered, and the additional revenue of pelletized animal feed that can be produced from leftover waste and the citrus peel conversion process is a money maker.
Widmer says there are three patents pending concerning his research. The USDA and Southeast Biofuels LLC have rights to all three patents. Southeast Biofuels will be able to negotiate for exclusive rights to the technology with the USDA. The company, a subsidiary of Xethanol Corp. received a $500,000 grant through Florida's Farm to Fuel initiative in January and plans to construct a $6 million pilot plant in Auburndale. The plant will be colocated on property owned by Cutrale Citrus Juices USA Inc. After initial testing, Xethanol plans to expand the plant to produce up to 8 MMgy ethanol from about 800,000 tons of citrus waste annually supplied by Cutrale.
Jay Levenstein, Florida's deputy commissioner of agriculture and consumer services, says his department supports the continued development of citrus waste to ethanol. "The quicker we have a local ethanol supply, the better," he says. According to Levenstein, the ethanol market in Florida is growing. The department will continue to support citrus-waste-to-ethanol projects through grant programs such as the Farm to Fuel initiative. He says the department would ultimately like to see citrus growers benefit economically from these projects via cooperative agreements with processors, somewhat like the ethanol co-ops in parts of the Midwest.
In order for citrus-peel-to-ethanol facilities to be successful, it is vital those plants be collocated with citrus processors. Because the waste product is 80 percent water, the product needs to be converted within 10 hours of its production, Widmer says. "Even though the d-limonene is a stabilizer, it is localized so there are parts (of the waste) that will ferment and rot in a very short time," he says.
David Stewart, president of Citrus Energy LLC in Boca Raton, Fla., also feels that colocating is the key to a successful ethanol plant. "We've got a little niche feedstock and we've got to play to the strengths of that feedstock," he says. "We basically just get the material delivered to us via conveyor and we've got a continuous supply of feedstock for seven or eight months of the year. By colocating, having a continuous supply and by piggybacking on top of the citrus processors permits, the project becomes a lot more economically attractive." Stewart formed his technology company two years ago to focus on converting citrus waste to ethanol and received a $250,000 grant from the Farm to Fuel program for that purpose last year. Citrus Energy and FPL Energy have teamed up to start a commercial scale citrus-peel-to-ethanol plant. FPL is the nation's leader in wind energy and operates the two largest solar fields in the world. The company is branching out into citrus-peel-to-ethanol production as part of its strategy to become a clean energy company, according to project manager Cindy Tindell.
Tindell says that although the FPL-Citrus Energy project has a long way to go, their planned 4 MMgy plant could be operational in two years. Cost of feedstock, capital and technical factors are all factors that have to be considered in developing this project. "The technology is there at a price," Tindell says.
Stewart says they are negotiating with citrus processors and, as soon as a lease is signed, construction on a plant can begin. The technology is ready to be used, Stewart says. "We're using enzymatic hydrolysis," he says. "There are various technologies out there on biomass conversion to ethanol, from gasification to acid hydrolysis or some combination thereof. Ours is relatively straightforward, but actually building a commercial plant is a challenge. It's the same challenge that people using wood waste are facing. There are a lot of pilot plants and small-scale facilities but actually building a commercial facility is yet to be done."
Southern Gardens Citrus is the third-largest grower of oranges in Florida and produces 120 million gallons of not-from-concentrate orange juice each year. President Rick Kress is cautiously optimistic about converting citrus waste into ethanol. "Technology-wise, it's doable," he says. "Commercially it's yet to be determined. It's very expensive. Questions are still to be answered, but we always have to look at the opportunity. We have to take the steps to utilize every ounce of whatever we purchase." Southern Gardens Citrus will process 850,000 tons of oranges this year, half of which will become waste material.
Current Waste Uses
From the citrus processor's viewpoint, it may be less profitable to process waste into ethanol today than it would have been a year ago. It is illegal for processors to dump citrus waste into landfills, so they must dry the waste product and turn it into pelletized animal feed. Feed prices have increased dramatically over the past year, which means what was once a break-even citrus waste solution at best for processors has become slightly more lucrative. According to Widmer, the price of pellets has fluctuated from $40 to $80 per ton and cost producers $50 to $90 per ton to produce for almost two decades. However, at one time last summer pellet prices hit $180 a ton. Widmer says the stability of pellet prices is unsure. In the meantime, fuel costs are certain to increase which should keep ethanol an attractive option for producers.
Kress says that while processors have benefited from the rise in feed prices their production costs have also gone up, cutting into profits. "The making of animal feed is very expensive because it takes a lot of energy to dry the feed material to a suitable moisture level," he says.
So while ethanol may prove to be cost effective, Kress says he still has concerns about how to deal with the waste after ethanol production. Fifty pounds of waste material used to produce ethanol will leave behind 45 pounds of waste. It may be possible to turn that remainder into animal feed, but the nutritional value of the product is debatable because carbohydrates are lost in the ethanol production process. Southern Gardens and Citrus Energy are currently conducting nutritional analysis of the waste. Stewart says it is a mistake to think that there is no food value in the byproduct. "If you look at corn to ethanol, a very significant part of the revenue is distillers grains and we are the same," he says. "We would have something called distillers peels that is very palatable to cows and has a significant feed value."
According to Widmer, "The (citrus) industry has a lot of interest in value-added coproducts from citrus processing waste because they feel they're not making much on cattle feed. With fruit and juice price fluctuations the juice industry is up and down and many producers find it hard to make a profit some years," he says. If all the citrus waste in Florida were to be used in ethanol facilities, the state could produce 30 MMgy to 50 MMgy. That amount would satisfy a local demand and would keep more money in the local economy.
However, Widmer will be exploring even more potential uses for waste in the next few years. While a lot of progress has been made, there is still a lot more research to be done. He hopes that by 2014 there will be multiple uses for citrus waste. His group is researching citrus waste as a cement additive, paper product additive and material for removing heavy metals from waste waters. He says that because citrus waste has good ion exchange capacity and water holding capacity, these uses are real possibilities. "We will not have a commercial product ready in 2009," he says. "We hope that in the next five years we'll have some of these materials ready and hopefully people will be interested in them. It's all a matter of industry interest."
Kris Bevill is a Biomass Magazine staff writer. Reach her at firstname.lastname@example.org or (701) 373-0636.