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Sweet sorghum to ethanol

A cold, October rain did not slow the harvesting and roller milling of about 8,000 pounds of sweet sorghum during a development trial conducted in rural west Tennessee by BioDimensions, a Memphis-based firm that is coordinating efforts to build a bioeconomy in the Mid-South. Juice extracted from sweet sorghum can be converted to ethanol for use as a biofuel.

The 7-acre sweet sorghum field is owned by west Tennessee farmer Willie German, who planted the crop the second week of June. German also provided a covered facility in Whiteville, Tenn., for crushing operations.

German is a member of the 25Farmer Network, a new business network of entrepreneurial farmers in 21 west Tennessee counties. The goal of the group is to form new ventures supplying renewable, farm-grown products to local industries.

The sweet sorghum harvest operation consisted of a 195-horsepower tractor, a New Holland pull-type forage harvester and a silage wagon.

The 12-foot to 14-foot tall sweet sorghum was harvested at 14 percent sugar.

The forage harvester produces 32-millimeter pieces of sorghum, but ultimately, the ideal size should be closer to 2 to 3 inches.

Hillary Spain, who runs the 25Farmer Network for BioDimensions, noted, “We had been told that if we shredded the stalks, we would get some juice loss, but so far that hasn’t happened.”

Chopping the sorghum increases its bulk density, which can reduce per pound transportation costs, allowing the product to be moved greater distances. On this day, the sorghum is transported to a roller mill a half-mile down the road, situated in the unloading bay of an idle gin in Whiteville.

The objective of the harvest and roller mill demonstration is not to showcase modern technology — the mill is far from a polished process — rather, it’s to demonstrate that a biorefinery can be a feasible venture for entrepreneurial farmers and investors in the rural Mid-South.

Missouri farmer Boyd Vancil, hired on a temporary basis to handle the logistics of the trial, was the lead operator at the control panel.

Steve Smith, with BioDimensions, fed shredded sorghum from the silage wagon onto a conveyor belt which dropped the material into the top of a commercial-scale roller mill, loaned by Fulton Iron Works. The mill sits on a flat-bed trailer.

“The roller mill was originally designed to crush sugar cane,” said Randy Powell, a consultant for BioDimensions. “Some of the data we’re collecting will help Fulton Iron customize a roller mill for sweet sorghum.”

The cellulosic material left over after the juice is extracted, called bagasse, is caught in a hopper, and conveyed to a waiting truck. In the future, Spain says, bagasse can be used to help fuel a biorefinery. Currently, it’s being used successfully as livestock feed. “It still has some sugar in it and the cows like the taste.”

The bagasse contains about 8 percent to 9 percent protein.

The extracted sorghum juice drips into a catch pan underneath the roller. On top of the pan is a screen to prevent plant material that escapes the process from falling into the juice pan.

Powell’s job in the demonstration is to occasionally dump the contents of the screen. In the future, this will likely be an automated process.

The extracted juice flows down a flexible pipe and empties into a 250-gallon tank, where Michael Gong with BioDimensions runs tests and adds distillers yeast.

The juice will be fermented in the tanks. The fermentation process has to take place quickly, Powell noted. “Sweet sorghum juice contains simple sugars, which decompose. So you have to stabilize it by concentrating it or fermenting it to alcohol. Once the sweet sorghum is fermented to alcohol, it’s stable.”

The end product for this demonstration is hydrous alcohol, which contains approximately 75 percent alcohol. It’s still a step away from the final distillation process, which removes the remaining water to create a 99 percent solution. This process will likely occur at a downstream facility.

The 8,000 pounds or so of sweet sorghum harvested that day produced between 450 gallons and 500 gallons of raw juice. Some of the raw juice will be sent to a local farmer in exchange for use of his equipment, seed and other services. The farmer plans to convert the product to syrup.

The sweet sorghum experiment impressed German, who farms corn, cotton and soybeans in west Tennessee. “It amazed me how many gallons of juice can come off an acre, plus all that biomass.”

The trial will also examine production costs for sweet sorghum versus other energy crops.

“One of the things we like about sweet sorghum is that it’s a low input crop,” Powell said. “It uses around 60 pounds per acre of nitrogen. It’s also a drought-tolerant crop. We think it’s a good rotational crop for our farmers. Some of the other energy crops are perennials. With a perennial, a farmer has to make a decision on whether or not he wants to take three years to establish a stand.”

Currently, Mid-South producers don’t capture much value from corn’s conversion to ethanol — other than a higher commodity price — because of a lack of interest in building refineries south of the Mason-Dixon line.

The technology to convert biomass to ethanol could attract local biorefineries, but the technology — which requires the use of special enzymes — is at least five years away. That’s why sweet sorghum is considered “low-hanging fruit” for Mid-South entrepreneurs. No enzymes are needed, so the only thing holding it back is a well-designed factory and some entrepreneurial spirit.

Powell says the experiment in Whiteville “is to demonstrate the mechanized models, the high-volume commercial factories. There are people working on smaller models, mounting mills on old cotton pickers, but we’re trying to work this out on a true commercial scale, where you’d produce fuel to sell to the major oil companies.”

With a fully operational biorefinery, Powell figures the harvest and processing season will run about 120 days out of the year. The sweet sorghum has to be harvested prior to a hard freeze. “Once the ground freezes, you kill the plant and lose the sugar. When we do design a rural ethanol biorefinery, we’re going to need to run really hard during harvest season. Weather will be a factor.”

Spain says another experimental field of sweet sorghum was planted in west Tennessee behind winter wheat.

Sweet sorghum varieties being evaluated at the Whiteville operation include M81E, Topper 76 and Keller, noted Gong.

Another issue with on-farm fermentation is that the distillers yeast operates in a fairly narrow temperature range, Powell noted. “A factory is going to have to have the capability to adjust the juice temperature.”


TAGS: Corn
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