Mega Factories: Ethanol Project
I. INDIAN ETHANOL BLENDING PROGRAMME (EBP)
The government of India (GOI) is implementing the Ethanol Blending Programme (EBP), in which fuel grade ethanol of 99.6 % purity is blended with petrol as a motor fuel. In the year 2018-19, 5.0% and in the year 2019-20, 4.5% blending has been achieved. This is against 10% EBP stipulated by GOI.
Considering GOI policy of 20% EBP, the requirement of fuel grade ethanol by the year 2022-23 is 6.9 billion liters. So far the total procurement in Ethanol Supply Year (ESY 2019-20) by the Oil Marketing Companies (OMCs) is 1.73 billion liters. In (ESY 20120-21) it is expected to be around 2.85 billion liters. Therefore, there is a shortage of 4.05 billion liters of fuel-grade ethanol. This gap can be covered with the establishment of new molasses, Sugarcane Syrup, and grain-based distilleries.
The Government has 10% blending target for mixing ethanol with petrol by 2022 & 20% blending target by 2025.
The GOI has made 10% EBP mandatory from the coming crushing season 2019-20.
The requirement of ethanol at 10% blending will be around 3.6 billion liters.
For the years 2019-20, the OMC’s floated a tender for procurement of Ethanol to the tune of 5.11 billion liters. So far the total procurement orders finalized by the OMCs are 1.70 billion liters’ against the offer of 1.92 billion liters. Therefore, there is a shortage of 1.92 billion liters of Fuel Grade Ethanol. This gap for 10% EBP can be covered with the establishment of new dual-feed distilleries i.e. molasses and grain-based. As of date around 150 distilleries are going to be established or modernized/ increasing their capacities. At the most, it is required for the modernization of molasses distilleries into dual-feed distilleries.
● To encourage EBP GOI also decided to move away from the Tender process to a revised fixed price of Ethanol tenders.
● To encourage EBP GOI has a revised price of Ethanol from:
Sugarcane juice/Syrup – 62.65 Rs. /Lit.
C-heavy molasses – 45.69 Rs /Lit.
B-heavy molasses – 57.61 Rs /Lit.
Grain – 52.95 Rs /Lit.
FCI Rice – 56.87 Rs /Lit.
The allocation of Ethanol supplies from distilleries will be made by the Oil Marketing Companies by Yearly/Quarterly allotments.
II. PROCESS FLOW DIAGRAM
III. PROCESS DESCRIPTION
1. MANUFACTURING PROCESS DETAILS
The Distillery will use grains as raw material in the production of Fuel Grade Ethanol. The process description of alcohol production in using grain as raw materials is as follows:
1.1 MILLING AND FLOUR HANDLING
The incoming grain is first cleaned with the help of a de-stoner and magnetic separators to remove stones and other material which may damage the hammers during milling. The grain is fed to the hammer mill in a controlled manner. In milling, grains are crushed to flour of uniform size. Oversized screening rejects are segregated with the help of a vibratory screen. These are taken to the coarse bin before sending it to the mill again. An intermediate hopper is provided for buffer capacity for flour storage. The flour gets transferred to the mixing tank for the slurry preparation process.
1.2 SLURRY PREPARATION/LIQUEFACTION
1.3 SACCHARIFICATION AND FERMENTATION
A. Yeast Propagation
Yeast seed material is prepared in water-cooled vessels by inoculating sterilized mash with dry yeast / cultured yeast. Optimum temperature is maintained by cooling water. The contents of the yeast vessel are then transferred to pre-fermenters. The pre-fermenters are filled with mash and loaded with the contents of the yeast. The pre-fermenter contents are transferred to the main fermenters.
The purpose of fermentation is to convert the fermentable substrate into alcohol. To prepare the mash for fermentation, it may have to be diluted with water. The pH of the mash is adjusted to about 5.0 accomplished primarily by recycled slops (which also provides nutrients). Yeast is available in sufficient quantity to initiate fermentation rapidly and gets completed within 72 hours. Significant heat release takes place during fermentation. This is removed by forced circulation cooling in external heat exchangers to maintain an optimum temperature of 30°C. The re-circulating pumps also serve to empty the fermenters into the beer well. After the fermenters are emptied, they are cleaned with water and caustic solutions and sterilized for the next batch. The carbon dioxide evolved during the process is scrubbed to prevent ethanol emissions by process water, which is taken to beer well
⮚ Fermented wash to Rectified Spirit:
Multi-pressure vacuum distillation system for the production of Rectified Spirit consists of distillation columns namely-
1. Degasifying-cum-analyzer column- Operation under vaccum
2. Rectifier-cum- Exhaust column- Operated under pressure
3. Recovery/Fusel Oil Column- Operated atmospheric
Pre-heated fermented wash is fed at the top of the Degasifier column. Analyzer Column is provided with reboiler. Top vapors of Analyzer column containing all the alcohol in the wash are sent to Rectifier column and are taken out as spent wash from Analyzer column bottom. Low-strength alcohol is concentrated in the Recovery column and Fusel Oil is separated. The vapor from Analyser is sent to Rectifier-cum-Exhaust column. The Rectifier/Exhaust Column concentrates the alcohol to 96 % v/v. The high-grade spirit is drawn from the upper trays of the rectification column. Fusel oil build up is avoided in the Rectifier-cum exhaust column by withdrawing side stream (Fusel Oil). Degasifier condensates and Fusel Oil drawn from Rectifier/Exhaust column are sent to Recovery column where this fusel oil is concentrated and then sent to Fusel Oil decanter where Alcohol and Fusel Oil mix are diluted with water to separate fusel oil. Washings are sent back to the column to recover alcohol. The high spirit drawn from the Rectifier column is sent to the MSDH Plant to produce Fuel Grade Ethanol.
⮚ Benefits of pressure vacuum distillation:
Following are the advantages of pressure vacuum distillation
1. Since the analyzer column operates under vacuum, the formation of by-products such as acetal may minimize thereby improving in the quality of alcohol.
2. The chances of scaling due to inverting solubility of certain precipitating inorganic salts are minimized in vacuum distillation.
3. Vacuum distillation requires low steam consumption with Reboiler i.e. 1.8 Kg/lit. of Rectified Spirit.
1.5 MOLECULAR SIEVE DEHYDRATION (MSDH)
As by simple distillation, only 96.48 % v/v alcohol strength is achievable, so for Ethanol production, either Azeotropic distillation (using Benzene or Cyclohexane) or Molecular Sieve Dehydration is being used. However, at present, Molecular Sieve Dehydration is the Industry standard and by adopting this technology a better quality and strength of product i.e. Ethanol is maintained with comfort and confidence. It requires very little operator interface and can tolerate reasonable variations in feed
rate or quality.
In this process, the Rectified spirit feed from the Rectifier column through a bed of desiccant beds. Twin beds are provided to allow for bed regeneration in a continuous operation. One bed is in dehydration mode, while the other is regenerating. The regeneration is accomplished by applying vacuum to the bed undergoing regeneration followed by recharging of the bed to its original condition. Depending on feed and product specifications, “Dehydration Regeneration” exchange takes place at a
certain interval with PLC controlled system.
As the regeneration process releases absorbed water with ethanol, it is recycled back to the vaporizing column for reprocessing. The feed is pumped to the vaporizing column. The overhead vapour is superheated to the required operating temperature and is passed through the sieve bed 1. After passing through the desiccant, the enriched alcohol vapour is condensed, cooled and sent to product storage.
A small portion of the product vapour is sent under a high vacuum, through bed 2 which is in regeneration mode to regenerate the desiccant. The regeneration operation in a vacuum expedites the release of moisture from the desiccant, making bed 2 readies for the next cycle. The recovered low concentration vapours during regeneration are condensed and recycled back to the vaporizing column.
The cooled regenerate liquid is weak in ethanol concentration, as it contains all the water desorbed from the Molecular Sieve Beds. This low-strength liquid is recycled back to the Stripper/Rectifier Column for recovering the ethanol. The water leaves from the bottom of the column and contains only traces of alcohol.
2 EFFLUENT TREATMENT PLANT (ETP)
Various technologies with the different combinations are available for effluent treatment in distilleries, however, for grain-based distilleries, the recovery of DDGS and Condensate Polishing will be the main effluent handling procedures taken to achieve ZLD.
In the proposed grain-based distillery, the spent wash will be subjected to decantation to separate wet cake and thin slop (5% w/w solids) and that will be fed to the evaporator. The thick syrup (@ 20-25%) solids after the evaporation would then be fed to DWGS dryer to produce DDGS (with 88-90% w/w solids) which will be sold as cattle feed.
2.1 DECANTATION SECTION
The decantation of DWGS is a physical solid-liquid separation technique. After the distillation of alcohol, the whole stillage (Spent Wash) is coming to the decantation section from the Analyzer column bottom.
Spent wash from Analyzer column is fed to Decanter centrifuge. The wet cake from the decanter will be sent for further treatment. The thin slop from the decanter is collected in a tank. Part of it is pumped back to the Liquefaction tank for dilution and the balance is concentrated in an evaporator
2.2 MULTIPLE EFFECT EVAPORATOR
Part of the thin stillage is evaporated to an appropriate concentration of TDS by evaporation plant integrated and standalone five effects (1 falling + 4 rising film) evaporator. This evaporator will have a surface condenser and vacuum pump system. The condensate is used as cooling tower feed water makeup and/or for diluent water in the fermentation section after due treatment discussed in ETP section.
2.3 DRYING SECTION: -
The DWGS from the decantation section and Thick Syrup from the Evaporation section will mix and be fed into a feed conditioner where around 30% of pre-dried DDGS will mix for pre-conditioning of feed. This pre-conditioned feed will be fed into the “tube bundle dryer” where steam will be applied inside the tubes and the pre-mixed feed will be showered outside the tube bundle. The dryer will be equipped with internal mixing and re-lifting of feed mixtures onto the rotating tubes in such a way, that the whole feed will be getting mixed and dried and flow onward. The vapors with a little amount of water will be regularly sucked and pass through the collection cyclone. The feed mixed from the other end of the dryer will be fed to a multi-cyclone pneumatically so that the temperature of the product will be cooled to 40°C from 95°C temperature. Then the product will be collected and sold.
2.4 CONDENSATE POLISHING UNIT (CPU)
⮚ Treatment Approach
With the conservation of resources approach, it is essential to recycle the maximum possible sources back in the process. Spent wash and Spent Lees generated in the process offer an ideal opportunity for recycling after treatment in the distillery; where there are major water-consuming activities, and which can effectively minimize the freshwater intake.
⮚ Process Description
The Boiler blows down, spent lees, DM plant, and softener re-generation water will be treated in a CPU plant (neutralization tank). After the treatment, it will be used as a cooling tower makeup water. Process condensate from the evaporation section will be partially recycled and balance will be treated in the process condensate treatment plant. The treated water will be used for dilution in slurry preparation and as cooling water makeup. The steam condensate will be recycled back to the Boiler.
This is an anaerobic process of treatment that will be having the capacity for the treatment of condensate and spent lees of the plant quantity as are below.
After adjusting the pH is neutral, the condensate and spent lees will be collected in an equalization tank. Then this will be sent to an RCC/ MS bio-reactor of suitable capacity for treatment. The effluent of the bio-reactor will pass through the activated sludge process for further reduction of organic matter. The selected micro-organisms will carry out the bio-degradation process in the control environment. Finally, this treated effluent will be passed through the activated carbon filter before using for cooling towers.
This treated water will be clear and re-used in the process of achieving Zero Discharge norms.