Grain Receiving, Storage and Milling
Grain unloaded, is initially received by grain receiving hopper. From receiving hopper, grain is shifted to storage silo through screw conveyor and bucket elevator. The silo is well equipped with aeration facility so as to keep proper air circulation inside the silo. Some part of the dust that is carried along with the incoming grains is removed in this section. Pre-cleaned Grains are fed in controlled rate to the hammer mill. In this unit operation, Grain is broken down into small particles (flour) of required size distribution. Oversized particles are segregated with the help of vibratory screen. They are then recycled back to the hammer mill through the coarse bin. Flour from Vibratory screen is collected in the Hopper and then fed to the Slurry Mixing tank at a controlled rate.
Liquefaction
The starch from the slurry is liquefied for sugar production. This is done in three steps liquefaction, continuous jet cooking and post-liquefaction. Heat stable enzymes are used for the process. The cooking process is done at high temperature to sterilize the slurry and to get high yields of sugar. This process is designed to maximize product yields using minimum process water and is based on classical concept of Simultaneous Saccharification and Fermentation. Hot Process water and recycled thin slop is added to Pre-masher to make slurry. The mixed slurry is taken to the Initial Liquefaction Tank where additional quantity of water is added as per requirement. Viscosity reduction Enzyme and stabilizing chemicals and a portion of liquefying enzyme are also added at this stage. This slurry is then "cooked" in the jet cooker. The slurry is continuously pumped to a steam jet cooker where high-pressure steam at 3.5 bar (g) / 147 °C rapidly raises the slurry temperature. The mixture of slurry and steam is then passed through the Retention vessel for desired retention time at a given flow rate. The cooked mash is discharged to a Flash Tank. The cooking process, accomplished in the above manner, converts the slurry into a hydrated, sterilized suspension (as starch molecule is solubilized) and is therefore susceptible to enzyme attack for liquefaction. The gelatinized mash from the Flash Tank is liquefied in the Final Liquefaction Tank where liquefying enzyme is added. The liquefied mash is cooled in Mash Coolers and transferred to Fermentation section for further action.
Fermentation
During the fermentation, yeast strains of the species Saccharomyces Cerevisiae, a living microorganism belonging to class fungi converts sugar (Glucose, Fructose, Sucrose, Maltose or Maltotrioes) present in the Cane Syrup or sugar cane juice to alcohol. However, Saccharomyces Cerevisiae cannot use starch as such. To produce alcohol from starch containing raw materials such as grains or cassava etc. by fermentation, the starch has to first hydrolyze to glucose. Industrially, this conversion is accomplished by the cooking of starch slurry and use of enzymes to breakdown the polymers of glucose (Amylose and Amylopectin), Transformation of starch to glucose consists of Gelatinization (Cooking), Liquefaction and Saccharification.
Multi-Pressure Distillation for Wash to Rectified Spirit
Multi – pressure distillation scheme has three distillation columns. These columns operate under different pressure conditions. Energy from column operating under high pressure is re utilized by column operating under low pressure to conserve energy. The columns in order of flow are: Mash/Stripping Column, Rectification Column, and Aldehyde cum Recover Column. Fermented wash is preheated in the Fermented Wash Pre heater and fed at the top of the Mash/Stripping column. This column is provided with Re-boilers. Top vapors of Mash/Stripping column containing all the alcohol in the wash are sent to Rectification column. Rest of the fermented wash flows down the Mash/Stripping column and is taken out as spent wash from column bottom. In Rectification column, higher volatile ethanol component is separated from ethanol plus water binary mixture. Rectified Spirit draw is taken from the top of Rectification column, which is sent to Molecular Sieve Dehydration Fuel Ethanol Plant.
Molecular Sieve Dehydration (Fuel Ethanol Plant)
Molecular sieve technology works on the principle of pressure swing adsorption. Here water is removed by adsorbing on surface of `molecular sieves' and then cyclically removing it under different conditions (steaming). Molecular sieves are nothing but synthetic zeolites typically 3Ao zeolites. Zeolites are synthetic crystalline Alumino silicates. This material has strong affinity for water. They adsorb water in cold condition and desorb water when heated. This principle is used to dehydrate ethanol. The crystalline structure of zeolites is complex and gives this material the ability to adsorb or reject material based on molecular sizes. Water molecule can enter the sieve and be adsorbed, but larger alcohol molecule will not be retained and will go through the bed.
Decantation Section
Decantation section comprises of a Centrifuge Decanter for separation of suspended solids from Spent Wash coming out of Grain Distillation Plant. Wet cake is removed from bottom of Decanter. Spent wash/Thick Slops from Mash Column is pumped to Thick Slops Tank. Thick Slops is then fed to Decanter Centrifuge through Decanter Feed Pump. In Decanter suspended solids from Thick Slop are separated and removed as Wet Cake while Thin Slops is collected in Thin Slops Tank. Thin slops from this tank are then fed to Evaporator for further concentration.
Thin Slop Evaporation
Thin slop evaporation plant is designed to concentrate thin slop coming out of decantation unit from 5% to 30% w/w solid concentration. This evaporation plant is multi-effect and combination of falling film & forced circulation type. Evaporation is integrated to distillation and DDGS dryer for energy conservation. The product at the desired concentration of 40% w/w total solid is obtained at the outlet of the final effect. Each effect is provided with recirculation cum transfer pumps. The condensate from surface condensers is collected in a common condensate pot.
DDGS Dryer
Wet cake with 30% w/w solids concentration from decantation section and Concentrated Syrup with 30% w/w solids concentration produced in evaporation section are mixed together & fed into the dryer housing at controlled rate through a suitable feeding system. The Rotary Tube Bundle is enclosed in an insulated dryer housing and on its outer flights are fixed. Dry, saturated steam is to be supplied to the tube bundle through rotary joint at one end & the condensate is discharged through rotary joint mounted of another end. The heat transfer is primarily by conduction. The water vapours are exhausted through an Exhaust Blower & passed through a cyclone separator for separating fines.
