Sweet Sorghum, Other Sugar Crops Show Promise

Obstacles to scaling up production are surmountable
By Rafael A. Nieves | June 12, 2012

Up to three years ago, there was substantial excitement in the U.S. for the use of sweet sorghum as an alternative feedstock for fuel ethanol production. The noted advantages of sweet sorghum were, and continue to be, the drivers for touting its benefits: 1) yield potential and composition, 2) water-use efficiency and drought tolerance, 3) established production systems and, 4) the potential for genetic improvement using both traditional and genomic approaches. Public and private entities continue to perform research to maximize sugar content, increase or diminish its grain production capacity and increase production yields. A typical composition of sweet sorghum is shown in the accompanying table.

Even with these positive attributes, the use of sweet sorghum in the U.S. has been slow to develop. Some of the impediments to its commercialization are the same ones facing all new technologies. Even though sweet sorghum harvesting and processing is similar to sugarcane, it is considered a “new” technology by many. That’s because it’s never been produced in large commercial scale in the U.S.  To produce the crop in large scale, several issues need to be addressed which are important but not insurmountable.

Agronomic Best Practices
Optimal growth of sweet sorghum for fuel ethanol production depends on numerous growing conditions and considerations. Since sweet sorghum hybrids produce both grain and sugars, harvesting must be timed appropriately to maximize the sugar yields that can be obtained. Optimum sugars are attained just prior to physiological maturity of the grain. Plant density is also important. Densities that are too high will result in thin stalks and reduced juice and sugar yields. Weed control is also of concern, so appropriate herbicides should be used.

Continuous cropping of sorghum will result in systematic reductions in biomass yields over years. Therefore, it is critical that any sweet sorghum production system include a crop rotation system that maximizes land use and maintains the productivity of all crops. As with any large agricultural operation, diseases and insects can be a problem. Field trials can be performed to determine which chemicals or insecticides are most beneficial for growth.  Rotation of crops not only provides soil benefits but it also mitigates damage from insects and diseases.

Sweet sorghum has reportedly been a good rotational crop for soybean and cotton. Sugar beets (energy beets) are also an ideal feedstock for ethanol production. Recent trials by international seed company Betaseed using new varieties indicate that energy beets can be grown in the Southeast. Sugar beets could be a possible rotation crop providing a second complementary feedstock. Plant modifications and additional unit operations would be required, however, for multifeedstock processing. A pilot program proving the integration of sweet sorghum and sugar beets was completed by the company BioDimensions Delta BioRenewables LLC of Tennessee in 2010.  That year the company produced and sold nearly 100,000 pounds of sugar juice at up to 14.8 brix (One degree brix is 1 gram of sucrose in 100 grams of liquid solution). It also tested harvesting and extracting beets produced in a 20-acre field trial. Plans are to plant 960 acres of sweet sorghum by 2016—still considered a small effort by commercial standards.

Economic Requirements
Questions were initially asked about the economic viability of sweet sorghum ethanol facilities. Several studies that we have performed, which include power-production units, have shown these projects can be economically viable, as have other studies. Small sweet sorghum trials in the U.S. have been performed mostly by universities and a few private sector organizations and seed companies. A large cultivation effort is required, however, for any significantly sized ethanol plant. For a large plant to be financed, the lender needs to be assured that the feedstock will be available at a price that makes the plant economically viable. Similarly, the growers need to have assurance that there will be a physical plant in place to accept the crop once they harvest it. As a result, you have the obvious chicken and egg scenario faced by many of the second- and third-generation biofuels technologies.

One approach used by various groups is to involve farmer cooperatives, such as the Delta Sweet Sorghum Ethanol Producers LLC in Lake Village, Ark. Other scenarios address the issue of feedstock availability by growing sweet sorghum as a complementary crop to existing sugarcane operations. One such group is Highlands Envirofuels LLC in Riverview, Fla., near Tampa. The company is on its way to constructing a 30 MMgy sugarcane and sweet sorghum ethanol facility. The planned groundbreaking for the facility is mid-2012. Similarly, the Louisiana Green Fuels Group in Lacassine, La., has used its sugarcane processing facilities and infrastructure for processing sweet sorghum syrup for ethanol production. Since sweet sorghum can be harvested within 120 days of planting, its growth can be staggered with the harvesting of sugarcane, either before or after sugarcane harvesting, thereby extending the yearly ethanol production operations.     

Internationally, sweet sorghum projects are proceeding slowly. The most active countries have strong biofuels programs including Brazil and the Philippines. As in the U.S., projects are still in precommercial scale, usually incorporating sweet sorghum into existing sugarcane operations. In some cases, the projects are performed in conjunction with agriculture departments in universities and the private sector. Sugarcane harvest last year was lower than expected in Brazil. The lower harvest numbers stimulated the use of sweet sorghum to make up some of the difference. Monsanto and Ceres deployed their sweet sorghum varieties in the country in last year, however some of these plantings were affected by drought.  Monsanto expected to sell enough sweet sorghum for about 20,000 hectares (49,000 acres) in Brazil this year. That’s enough to produce about 80 million liters per year of ethanol (21.1 million gallons).  The company is working with 20 sugarcane mills.

Various projects continue to be developed in the Philippines. Recently, San Carlos Bioenergy Inc., a sugar and ethanol production company in the city of San Carlos, announced that it will be incorporating sweet sorghum syrup as a supplement for ethanol production. Supported by the Philippine National Oil Co.’s Alternative Fuels Corp., a pilot trial of 1,000 hectares is planned for conversion to syrup. The trial plantation would supply feedstock for 2.5 million liters annually and the bagasse will be consumed by the onsite biomass power facility. 

In San Mariano, Philippines, Isabela Green Future Innovation Inc. will use sweet sorghum as complementary feedstock when it begins running a primarily sugarcane-based plant in the first half this year. Green Future Innovation Inc. is a joint venture between Itochu Corp. of Japan, JGC Corp.-Japan, Philippine Bioethanol and Energy Investment Corp. and Taiwanese holding firm GCO. The Isabela plant has a production capacity of 52,840 gallons of bioethanol per day. A total planting of 400 hectares of sweet sorghum is planned by June this year.

Although efforts to commercialize sweet sorghum are slowly developing, opportunities to integrate this crop’s unique qualities into the nation’s and the world’s biofuels industry are real. As efforts to integrate sweet sorghum into new and existing processes continue, establishment of large commercial plantations will require investment capital from well-informed investors, experienced agricultural specialists and diligent planning.  

Author:  Rafael A. Nieves, PhD
Managing Director, BBI Consulting Services
(303) 895-8180
[email protected]


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