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10/01/10

"Sweet Sorghum as an Ideal Near-term, Advanced Ethanol Bio-fuel Feedstock"


Category: news
Posted by: jeff_admin

By Jeff Turner

January 2010

In 2010, the United States will have the capacity to produce approximately 13 billion gallons of ethanol annually. Revisions to the Renewable Fuels Standard as part of the Energy Independence and Security Act of 2007, requires a total U.S. biofuel production capacity of 36 billion gallons per annum by 2022. The majority percentage of this production will be ethanol manufactured from cellulosic feedstock and others sources that meet the advanced biofuel requirements. The likely candidates must have a low carbon footprint, sustainable cultivation, provide appropriate energy return on energy input and not compete with food crops. Sweet sorghum meets these criteria. As a drought tolerant grass that requires limited fertilizer and insecticides, it is an ideal choice for arid and marginal locations that are not optimum for growing food.

Sweet sorghum is not new to North America. It was introduced in the mid 1800's and for well over 100 years was a staple in many agricultural communities. It was grown from Louisiana to Minnesota. Farmers planted it primarily for the sweet syrup extracted from the stalk and animal feed from the remaining foliage and grain buds. As the business of farming consolidated and grew beyond regional borders, competition from corn and higher value food crops pushed sweet sorghum cultivation to the extreme margins. This trend can and should be reversed. Research and academic institutions across the globe are defining the unique value that sweet sorghum brings to the production of ethanol. While it remains undesirable to replace food crops with energy crops, creative people are finding ample opportunity to grow sweet sorghum on marginal, abandoned and/or contaminated lands.

Sweet sorghum's advantages are not limited to cultivation opportunities. There are several reasons that make it an attractive choice. Unlike grain and cellulosic feedstocks, sweet sorghum juice does not need to be processed in order to release the sugars. It is simply filtered for impurities and then added to the fermentation process. This eliminates the energy intensive starch breakdown requirement and potentially offers low cost capacity to an existing grain ethanol plant. Likewise, sweet sorghum is an efficient producer of biomass. The grain and foliage can provide energy rich animal feed while the remaining biomass can be used for multiple purposes.

Typically sweet sorghum juice extraction methods follow traditional sugar cane processing. The stalks are crushed in a rotating mill, forcing the liquid to collect in a hopper. The juice is filtered and sent to the next stage while the "bagasse" is used for biomass combustion, feed or potentially paper pulp. A more contemporary approach is to separate the juice in a controlled process retaining specific plant materials and creating the opportunity for additional value added products. An example of this separation technology is the KTC Tilby separation system. Designed for both sugar cane and sorghum, the KTC Tilby system slices the stalk as opposed to crushing it. The controlled separation process limits the need for wash water and reduces overall connected horse power. The net result is clean sugar juice, wax, fiber, woody strands and minimal waste. This substantially increases the opportunities for by-product utilization and resale.

Sweet sorghum has a substantial role to play in the rapid expansion of ethanol biofuel. It does not need to compete with food crops, it is sustainable, it has a low carbon footprint, it has an outstanding net energy return and depending on the processing technology, it can provide additional value through co-product sales. Sweet sorghum is an ideal near term, advanced ethanol biofuel feedstock choice.

 


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