This study, that followed on from initial experimental work and process overview (Phase I), investigated the feasibility of using sweet sorghum as raw material for the production of an ethanol solution (wine), to be supplied to an existing still producing potable alcohol for only part of the year. This was possible since the still was not operating during the time sorghum juice would be available.

The second phase involved the development of detailed models covering mass and energy flows and balances as well as full raw material, processing and product costs. A sorghum production cost model was devised, and validated against local true production costs. Models were developed for a number of process options. These included the use of conventional sugar cane processing technology based on diffusion, mills or proprietary technology, followed by yeast fermentation of the juice, with bagasse used as fuel for steam and power generation, and wastes treated by anaerobic digestion.

Other models were developed for cases in which flash pyrolysis was used to make bio-oil from bagasse, used in an internal combustion engine to produce power with cooling water used to generate process steam in a small boiler. Further models considered systems in which the juice was converted to biogas and used in a gas-engine turbine to produce electricity and/or the fibre was hydrolysed (acid or enzyme) and either both hexose and pentose fermented, or only hexose fermented with pentose digested. The model provided mass balance, energy balance and economic balance figures where raw material price and composition, as well as various process parameters and efficiencies, were varied within process flow sheets covering both low technology and high technology options. Break-even points were established for sorghum of various sugar content, bought at various prices (based on varying biomass yields), generating various amounts of ethanol and or electricity, using various integrated process streams. The content of the report included:

Materials and energy balance
Model description
Raw material costs
Results from model

Conventional sugar process

Pyrolysis option

Biogas/pyrolysis option

Hydrolysis option

Raw material costs

Product values

Optimisation of income

Recommendations

Factory gate price for sorghum

Sugar recovery

Anaerobic digestion

Solid-state fermentation