The Ethanol Production Process

The ethanol production process begins with the receipt of molasses from the sugar manufacturing factories which is weighed and stored in storage tanks. The molasses is then pumped into fermentation tanks, into which yeast, water and other nutrients are added. 
This mixture goes through a fermentation process that produces carbon-dioxide (CO2) and ethanol in a mixture called beer. Some of the CO2 is recovered to produce liquid CO2. The beer is fed to a distillation process which produces the low and high grade ethanol called feints and potable ethanol respectively.  Some of the ethanol is passed through a dehydration process to remove as much water as possible to produce anhydrous grade ethanol at 99.9% absolute alcohol by volume. 
The distillation process also produces a byproduct called vinasse which is passed through an evaporation process to remove as much of the water as possible to produce Concentrated Molasses Stillage (CMS). The stillage is then blended with other chemicals to produce fertilizer that is used in the cane growing process.

Molasses as feedstock

In the production of ethanol various feedstock can be used in different production processes. Such feedstock material includes molasses, corn, sweet sorghum, cassava etc. At RES the feedstock for the distillery is cane molasses. Molasses produced from both Mhlume and Simunye mills is transported and stored in tanks and dams that feed the distillery.

Fermentation

Fermentation is the process by which the sugar in the molasses, in the form of sucrose, glucose and fructose, is converted to ethanol by the use of yeast. The molasses is diluted with water and yeast and diamonium phosphate are added in the mixture. Fermentation then takes place for 40+ hours to produce 7-9%+ beer.

Distillation

This is the final stage in the ethanol production process in which the ethanol is purified by removing all impurities and concentrating the product. The impurities removed results in two products called feints and fuel oil. This alcohol, at 96.4% absolute alcohol by volume, is the final product in the ethanol production process and the product is then used downstream to make a wide range of other products.

Evaporation

After the distillation process a byproduct called vinasse is produced. The vinasse is then passed through an evaporation process to remove as much water as possible. The resulting product is called concentrated molasses stillage (CMS) which is then applied to the cane growing fields as a fertilizer.

Anhydrous Ethanol

Ethanol, when highly concentrated to 99.9%+, can be blended with petrol and used in motor vehicles. The ethanol from the distillery is passed through an anhydrous plant that removes most of the remaining water to concentrate the ethanol to 99.9%+, now called anhydrous ethanol. This product is then preserved in nitrogen covered to flow with the subsequent word tank to prevent the ingress of water, and finally blended with petrol, at various ratios, to produce bio-fuel.