Value chain models for sweet sorghum for ethonol

Sweet sorghum is a new generation bioenergy crop that has potential to accumulate sugars (10-15%) in its stalks similar to sugarcane apart from producing grains. The crop has ability to adapt to various agro-climatic conditions and reasonably tolerate drought, and saline-alkaline conditions. Water requirement of this crop is one third of sugarcane on a comparable time scale. Also, sweet sorghum requires about 22% less water than maize. With this advantages, sweet sorghum is a good bioenergy crop and can complement the available feed stocks for biofuel production.

For use as a biofuel feedstock, it is important to choose appropriate cultivars of sweet sorghum and follow improved crop management practices for achieving higher yields. The distillery/industry should develop a command area for supply of raw material. Sweet sorghum commercial cultivation is yet to pick up in India and other countries.

The uncertainty of the fossil fuel supplies, sharp escalation of international crude oil prices, and the need to protect the environment has forced several countries to look for renewable energy, especially for transportation fuels. Ethanol is the most popular biofuel used either directly or blended with gasoline for fueling automobile engines. Use of sugarcane, corn, sugar beet, and cassava for large-scale ethanol production is a common practice.  There are, however, concerns about the future of biofuel program since it is apprehended that these feedstock intensive programs will reduce the availability of grains for human consumption or take up land that could be used for food production in the face of policy induced demand for biofuels, leading to food and feed insecurity. Additionally, this would also remove crop residues that sustain soil productivity and structure. Sweet sorghum is a crop of great potential that can overcome some of the above concerns related to food, fuel and fodder security and rising grain prices since it produces sugar-rich stalks for ethanol production without sacrificing the grain production. Sweet sorghum produces food/feed, fodder and fuel, without significant tradeoffs in any of these uses in the production cycle. 

Value chain models

Centralized model

While centralized distilleries crush the stalks in bulk quantities and produce ethanol, the decentralized units crush the stalks at the village level and convert the sweet juice into syrup. The syrup can be stored for up to 2 years at room temperature there by increasing the period availability of raw material (syrup for ethanol production) to the industry. Decentralized crushing reduces the legwork inherent in dealing with high volumes of stalk and the costs of transportation under the centralized model (Fig 1).

In the centralized model, a typical 40 kilo litres per day (KLPD) ethanol distillery requires feedstock from 8000 ha of crop area per year spread over two seasons – 3500 ha in the rainy season (rainfed) and 4500 ha in the postrainy season (irrigated). As farmers supply stalks directly to the distillery, it requires mobilization of farmers in villages within 50 km radius of a distillery so that the time for and cost of transportation of stalks is kept at minimum.  However, the centralized model has some limitations:

• Farmers located more than 50 km from the distillery will be burdened by high transportation costs owing to the bulk of stalks. 

• Delay in crushing stalks beyond 24 hours of harvest causes a 6% reduction in juice yield.

• Delay in transportation of stalks to distilleries by 24 hr. after harvest leads to reduction in stalk weight up to 20%, depending on climatic conditions causing a financial loss to the grower.

• Finding 4500 ha with irrigation facilities within the stipulated radius during the postrainy season is a daunting task in SAT areas. Organizing such a large number of farmers to undertake sweet sorghum cultivation is also difficult. 

• Growing other crops like soybean, maize, rice, and wheat may be more economical than sweet sorghum under irrigated conditions.

The decentralized model overcomes some of these difficulties.

Issues in centralized model

• Fixing stalk procuring price by the distillery
• Timely harvesting and transportation of stalks to distillery
• Quality of stalk based on sugar content, (Brix %)
• Staggered planting for continuous stalks supply
• Availability of cultivars of varying maturity period (early-< 90 days; medium-90 to 120 days; late > 120 days) for widening harvesting window
• Availability of cultivars for post rainy season cultivation
• Stability of fermentable sugars in juice and syrup

Decentralized Crushing Unit Model

The purpose of setting up decentralized crushing unit (DCU) at the village level is to crush sweet sorghum stalks and extract and boil the juice to produce syrup.  It aids supply chain management particularly by reducing the volume of feedstock that would otherwise have to be supplied to centralized crushing units and increasing the period of feedstock (supply of syrup) availability to industry to make sweet sorghum ethanol a commercial reality. The by-product, bagasse (crushed stalk) is left in the village to be used as animal feed or as organic matter to enrich the soil. This paves the way for a more efficient whole-plant utilization of sweet sorghum. Also the DCU serves as a model for farmer-centric, farmer-driven rural industry for improving the livelihoods of small-scale sorghum farmers (Fig 2).

Issues in decentralized crushing units:

• Initial high investment for establishment of DCU
• Assurance by distillery for small quantities of syrup procurement from DCU
• Criteria for price fixation for syrup for industry and payment schedule
• Basis for payment to farmers (stalk weight, syrup (Brix %) or any other)
• Procedure for giving back bagasse to farmers or use of bagasse by the DCU.
  

   

  Fig. 1: Value chain models for Sweet Sorghum for ethonol