Manufacturing Process of Distillery

Molasses is the chief raw material used for production of alcohol. Molasses contains about 50% of total sugars, of which 30% to 33% are cane sugars and the rest are reducing sugars. During the fermentation yeast strains, such as the species of Saccharomyces cerevisiae(belonging to fungi class), convert sugar present in the molasses such as sucrose or glucose to alcohol.

Sucrose is present as non-reducing fermentable sugar in all sugary raw material e.g. sugarcane and sugar beet juice, syrup and molasses. Before fermentation, yeast enzymatically converts sucrose in to glucose and fructose. Glucose and fructose are reducing monosaccharide and get converted in to ethanol and CO2 within yeast cell Conversion of glucose to ethanol takes place through a series of biochemical reactions called as Embden Mayer Hoff (EMP) pathway.

Chemically, this transformation of sucrose to alcohol can be approximated by the following equation.

I) C12H22O11 + H2O 2 C6H12O6 Cane Sugar Inversion Glucose

II) C6H12O6 C2H5OH + 2CO2 Glucose Fermentation Ethyl Alcohol Carbon dioxide

180 2 X 46 + 2 X 44

100 kg of sugar would theoretically yield 51.11 kg of ethanol and 48.89 kg CO2. Part of glucose is used for yeast growth and by-product formation.

Fermentation Process

Normally, molasses is made up of water or moisture and solids. Solids are further categorized as organic and inorganic. The organic solids can be classified as fermentable sugars, non-fermentable sugars, volatile acids, nitrogenous matter, caramel, gum and waxes as well as other concentrated components which had been added during sugar processing like polyelectrolyte’s, biocides etc.

The volatile acid content has profound effect on yeast performance. The term volatile acids present in molasses are acetic acid, propionic acid, butyric acid, valeric acid and isovaleric acid. The volatile acidity is expressed in terms of acetic acid. Acetic acid affects cell multiplication. As ethanol fermentation is growth-associated product, due to less growth of yeast, alcohol formation rate is decreased. This affects fermentation efficiency and capacity. Butyric acid is more potent to yeast than acetic acid for the same concentration. Saccharomyces is versatile in nature and most preferred yeast to carry out fermentation at industrial scale because of its fast growing and fast fermenting characteristics. Raw material is diluted to appropriate sugar concentration. Yeast is inoculated and fermentation is carried out at optimum temperature, pH, aeration, agitation and supplementary nutrients. The plant has been designed to produce fermented wash for producing 60,000 liters per day of total alcohol based on cane molasses as the feedstock.

Fermentation section is based on HIFERM-FERMENTATION continuous / semi continuous fermentation process. The fermentation plant is four-fermenter system. The individual fermenter is equipped with molasses dilution system, aeration for mixing in fermenter, safety system etc. The process utilizes special culture yeast fast fermenting property.

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In continuous mode of operation, molasses and process water are added proportionately to maintain desired alcohol concentration in individual fermenter. Fermented wash from last fermenter is passed to Clarified wash tank through Wash settling tank from which it is fed to distillation.

In semi continuous mode of operation, molasses and process water are added along with yeast to maintain desired alcohol concentration in individual fermenter. After reaction completion, individual fermenter is harvested. Dedicated molasses weighing system is provided to determine molasses consumption. In spent wash recycle section, spent wash cooler and distribution system is provided. A part of spent wash from distillation section is cooled and recycled to fermentation and used as diluent by replacing process water.

CO2 scrubber recovers alcohol from carbon dioxide. Alcohol scrubbed water from scrubber is further sent to clarified wash tank. Air is sparged in yeast culture vessels, activation Vessel and fermenter. Systems for dosing nutrients, sulfuric acid and de foaming agent are provided with appropriate tanks and pumps.

Distillation Operation

The Multi-pressure distillation system is designed to produce Rectified Spirit, Extra Neutral Alcohol and Ethanol from fermented wash. Mainly, following columns play important role in the distillation operation.

1. CO2 stripper2. Stripping3. Pre-rectifier column4. Extraction5. Rectification6. Refining7. Fusel oil concentration8. Evaporator column

The fusel oil column concentrates the heads and fusel oil and recovers alcohol. In CO2 column non-condensable gasses remove from the top. The plant is operated from control room through PLC system. The CO2 stripper, extraction and refining columns work at the pressure below the atmospheric whereas the rectifier and fusel oil columns work above atm. pressure. The rectifier column, fusel column & pre-rectifier columns are indirectly heated by steam. The pressurized vapours from the top of rectifier column supply thermal energy to the re-boiler of stripper column. The top vapours of pre-rectifier column supply the thermal energy to the re-boiler of extraction column and also to the re boiler of the refining column. The stripper column top and middle vapours supply direct heat to CO2 column.

1. CO2 Stripper Column

The fermented wash after clarification and yeast separation is pumped to the column through the Beer heater & plate heat exchanger by adjusting wash flow through flow meter. The fermented wash fed to the top of column and the vapours coming from the stripper column heat the wash. The hot wash is fed to stripper column. The non condensable gasses escapes from the top of the column and condensed in the condenser. The condensate get recycled back to the column. The non condensable gasses are connected to vacuum pump.

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2. Stripper Column

Hot fermented wash from CO2 column is fed to stripper column. Spent wash at the bottom of the column is circulated by axial flow pump and passed through re-boiler and is taken out from bottom by pump. The heat recovered from outgoing spentwash through is used to heat incoming fermented wash. The alcohol vapors coming out from top of this column and fed to the pre-rectifier column under ENA mode. Otherwise, they are fed to the extraction column for operations under RS mode through pump. The spent lees from the bottom of the column are free from alcohol and are used for heating by passing through. The bottom liquid is pumped and partly fed to extraction column.

3. Pre Rectifier Column

The steam flow control valve is adjusted to get required reflux and temperature to the column. Subsequently, the bottom level of the column is checked and adjusted up to 50% and thereafter the level control valve is set on auto mode. Also, the level of reflux tank is checked. During the operation, the concentration of reflux, product and fusel oil draw is checked periodically. Then the RS draw valve is gradually opened.

4. Extraction Column

The column is designed to separate all low boiling impurities; aldehydes, esters and sulfur compounds from the feed alcohol. Addition of process water or spent less or chemicals dosing increases volatility of low boiling compound with respect to ethanol in solution containing of water. In this process the impurities of ethanol water mixture get removed at the bottom of the column. Then the impurities go on the top portion of the column. The dilution water/spent lees get heated by passing through PHEs. The top vapour from the column is condensed in main condenser and vent condenser and reflux is sent to the column through glass tube rotameter. Partly the fusel oil and other impurities are fed to FOC and the vent is connected to vacuum system. The bottom liquid containing alcohol water mixture is fed to rectifier column.

5. Rectifier Column

Rectification column is provided to accommodate the alcohol. It takes some time to build up the required alcohol profile in the column. Here, it is extremely essential to observe the temperature difference of alcohol draw plate and fusel oil draw plate which are required to be near the designed temperature. From this column, the alcohol is fed to refining column by opening the product control valve.

6. Refining Column

The refining column is mainly designed for polishing the product by removing traces of volatile impurities and maintaining aroma and flavors to meet the premium quality norms. The pure alcohol is removed from bottom of the column & after cooling it is pumped to ENA day storage section.

7. Fusel Oil Column

The impurities from rectifier column &pre-rectifier column are concentrated in this column. The concentrated heads are taken out from top of the column. Spent lees from the bottom of column are passed through PHE to recover the heat. Concentrated fusel oil is drawn from middle portion of the column and sent for decantation. Subsequently, the fusel oil is sent to the FO storage tank.

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8. Fusel Oil Decanter

The fusel oil comes from fusel oil column, cooled in cooler and fed to fusel oil decanter. In decanter, fusel oil is washed to remove traces of alcohol by adding process water. The fusel oil layer is taken out as by-product and the bottom liquid is recycled back to fusel oil column for further recovery.

A question was asked during PH about spentwash. Consultant answered to this question as spent means waste and wash is a term used in distillery for discharges from fermentation, distillation section, etc. Thus, spent wash indicates nothing but waste discharge from a distillery, which is generated after recovery of alcohol through distillation of fermented wash. This spent wash is having dark brown colour when in fresh condition and contains considerable organic matter due to which it is good for bio-methenation.

A query was raised during public hearing about type of process used for alcohol production. It was replied by consultant that continuous fermentation followed by multi-pressure vacuum distillation process is adopted in existing distillery and same shall be followed under expansion project

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