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Water conservation in distilleries. D. A. Patil , K. A. Gaikwad and S. V. Patil * Vasantdada Sugar Institute * e-mail: sv.patil@vsisugar.org.in. Indian distillery industry is on fast-track Number of sugar mills: 620 Number of molasses based distillery units: 350
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Water conservation in distilleries D. A. Patil , K. A. Gaikwad and S. V. Patil* Vasantdada Sugar Institute * e-mail: sv.patil@vsisugar.org.in
Indian distillery industry is on fast-track • Number of sugar mills: 620 • Number of molasses based distillery units: 350 • Molasses based installed capacity : 4.29 bln lit. • Gain based distillery units: 100 • Grain based installed capacity : 1.8 bln lit. • Future : Molasses alcohol for Industrial and fuel purpose • Grain alcohol for liquor purpose. • Lignocellulosic ethanol is also expected to come (for fuel purpose).
Demand and Supply of Alcohol (2010-11) • Maharashtra (mln lit.) India • RS for CL : 150-160 400 -500 • ENA for IMFL : 50-60 1000-1100 • Export of ENA : 40-50 -------- • Fuel Ethanol : 140 1050 • Industrial use: 200-350 650-1350 • Ethanol in • neighboring states: 160 ---------- • Total demand : 740 to 920 3100-4000 • Production (Molasses) 550 - 650 2300-2600 • Production (Grain) 60-65 600-700 • Production (Total) 610-715 2900-3300 DRIVER
Three-fourths of earth is water: Rivers, groundwater, snow and ice: 2.5 %, Rest being sea/salt water. Estimates by the Ministry of Water Resources (MoWR) indicate that water used for industry in India is around 7-8 per cent of the total freshwater withdrawal in the country. In the next two decades water consumption will triple current levels.
The industrial sector is the second highest user of water after agriculture. According to CPCB in 2000, India’s annual fresh water withdrawals were about 500 billion cubic meters and the Indian industry consumed about 10 billion cubic meter of water as process water and 30 billion cubic meters as cooling water.
As per the World Bank studies, the water demand for industrial uses and energy production will grow at a rate of 4.2 percent /year, rising from 67 billion cubic meter in 1999 to 228 billion cubic meter by 2025. Therefore, according to World Bank the current industrial water use in India is about 13 per cent of the total fresh water withdrawal in the country.
Cost of water supply varies widely and can be in the range of Rs. 0.09 to 50.0 per cubic meter It can be assumed that at about 2500 million liters of alcohol production per annum in the country, the consumption of fresh water by distilleries alone could be 37,500 million liters per annum or 125.0 million liters per day and spent wash generation could be 25.0 to 30.0 billion liters per annum. This is an alarming situation. Therefore, it is necessary to take immediate steps to minimize the consumption of water in distilleries.This can finally result in reduction in spent wash generation and avoid further complications.
Make-up soft water 96.46 m3/d CO2 Cooling Tower 6.1 m3/d CO2 Scrubber Process Water 493.2 m3/d E – 20.40 m3/d FERMENTATION 410 m3/hr D – 68.87 m3/d Molasses 180 m3/d B/D – 7.2 m3/d (Overflow) Nutrient dil. 0.1 m3/d Spent wash Recycle 39.6 m3/d F.W. 704.62 m3/d Sludge 14.38 m3/d Steam 252 MT/d DISTILLATION ENA 60 KLPD 176 .62 m3/d spent lees for R. S. dil. during ENA production 340 m3 /hr Spent wash 600 m3/d Spent lees recycle 120 m3/d (as a make-up water) Cooling Tower 560.4 m3/d For Biogas E – 92.01 m3/d Composting + OTCLA D – 57.11 m3/d B/D – 2.88 m3/d Typical water consumption in a molasses based distillery (Overflow) Fresh make-up soft water 32 m3/d Total make-up water 152 m3/d (120+32 m3/d)
Table 3: Periodical & fresh water required for starting of distillery
1) Water required for molasses dilution:High alcohol conc., yeast strain used, molasses quality etc.1) Biostil – 1:2.50 to 1:3.00 2) Cascade – 1:3.00 to 1:3.50 3) Fed-batch – 1:3.50 to 1:4.00 4) Batch – 1:4.00 to 1:4.50SW/RO permeate/process condensate recycle Vs FE and alcohol quality • Process water consumption in molasses based • distilleries: (How we can reduce the consumption?)
2) Water required for sludge washing: During alcoholic fermentation some salts can precipitate out of the solution and yeast & suspended solids settle down forming sludge. This sludge can create operational or process problems if carried to distillation columns/reboilers or to biomethanation plant. Sludge has to be properly removed from fermented wash. While removing the sludge, it is necessary to wash it with water to recover alcohol and avoid losses. Sludge content of molasses also varies (8-25 % v/v) depending on sugar processing operations. (Indian molasses is unique and most inferior in the world)
3) Water required for CO2 scrubbing: CO2 evolved during fermentation carries some of the alcohol formed during fermentation. To recover the alcohol, it is necessary to wash CO2 with process water. The CO2 scrubbed water containing alcohol can be easily used for molasses dilution.
4) Water required for Nutrient dilution: For yeast cell growth and yeast fermentation activity, usually nutrients such as urea, DAP, MgSO4 etc. are used. These nutrients are diluted with water to the required concentrations and pumped to the fermenter. It is possible to minimize water consumption for nutrient dilution. 5) DM water for RS dilution during ENA production: To enhance the quality of final product (EQRS or ENA) rectified spirit is diluted with DM water in specific ratio and distilled again. It is possible to recycle spent lees generated during distillation process to some extent for RS dilution in place of fresh DM water depending on the final alcohol quality required.
B) Non-process water consumption in molasses based distilleries: 1) Water requirement for cooling towers: (2nd major use)Fermentation is an exothermic reaction and normally, fermentation temperatures are maintained at 32-330C. During distillation the enriched alcohol vapours are also required to be condensed using cooling water. Cooling towers are necessary in distillery plants. To avoid scaling in condensers, cooling towers are run using soft water. Because of losses of water due to evaporation and drift losses, the hardness of soft water goes on increasing and it becomes necessary to take water blow-down. After blow-down, it is necessary to make-up the lost water by adding fresh soft water.
… Contd. In a distillery unit, two to three cooling towers may be required depending on final products to be produced. Proper check on hardness built-up and minimizing leakages & losses can result in minimizing make-up soft water requirement. 2) Water requirement for laboratory use, floor washing, rinsing & washing of softener/DM plant, domestic use etc.: For maintaining cleanliness and hygienic conditions in day to day process operations, floor washing is necessary. For routine analysis and for washing of various equipments in laboratory, fresh water is required. Similarly, fresh water is also required for periodic rinsing & washing of softener/DM water plant as well as for domestic purpose. Use of water for such applications can be rationed and minimized.
3) PRDS de-superheating, Air & CO2 blowers, vacuum pump and pumps gland cooling water etc.:Fresh water is also required for uses such as PRDS de-superheating, Air & CO2 (water ring type) blowers, vacuum pumps and pumps gland cooling etc. Use of water for such applications should be minimized by employing recycle/reuse principle. Mechanical seal for pumps can be used to minimize contamination of water streams.4) Periodical fresh water requirement: Fresh water is also required periodically for cleaning of Plate Heat Exchangers (PHEs), distillation plant, yeast separators. RO plant rinsing and evaporation calendria cleaning also requires fresh water periodically. Use of water for such applications should be minimized by employing recycle/reuse principle.
Capacities and configurations • Distillery A: 80 KLPD, Batch fermentation system (9-Fermenters) & conventional atmospheric distillation without reboilers. • Distillery B: 30 KLPD, Cascade continuous fermentation system (4-Fermenters) without yeast and spent wash recycle & MPR distillation with reboilers. • Distillery C: 60 KLPD, Cascade Continuous Fermentation system with spent wash recycle & 60 KLPD RS atmospheric distillation without reboilers and 55 KLPD RS to ENA atmospheric distillation system without reboilers. www.vsisugar.com
4) Distillery D: 425 KLPD, Batch fermentation system (285 KLPD, 14 batch Fermenters) with 205 KLPD conventional atmospheric distillation system with reboilers to produce R.S. and 80 KLPD MPR distillation system to produce ENA and Cascade continuous fermentation system (6-Fermenters, 140 KLPD) with spent wash recycle system, atmospheric distillation (140 KLPD) and reboilers. 5) Distillery E: 120 KLPD, Biostill Continuous Fermentation system (2-Fermenters) with MPR distillation, reboilers & integrated evaporation system. 6) Distillery F: 25 KLPD, Batch Fermentation System (6 Fermenters) & conventional atmospheric distillation without reboilers. www.vsisugar.com
Results and Discussion www.vsisugar.com
(SW+SL) www.vsisugar.com
Table 7: Average fresh water requirement in molasses based distilleries for different fermentation technologies. * Other than cooling tower www.vsisugar.com
Table 8: Average waste water generation in molasses based distilleries for different fermentation technologies. www.vsisugar.com
Water requirement of a modern grain based distillery:1. Grain Cleaning & storage section consisting of grain silos. 2. Grain handling & milling section consisting of pre-cleaner, de- stoner, magnetic separator, hammer mills, bag filters etc.3. Flour handling, slurry preparation & pre-liquefaction.4. Jet cooking, post liquefaction & pre-saccharification. 5. Simultaneous saccharification & fermentation.6. Distillation to produce Rectified Spirit or Extra Neutral Alcohol or Dehydration section to produce fuel ethanol.7. Decantation section to separate whole stillage into wet cake & thin stillage.
8. Multiple-effect evaporators for concentration of thin stillage to syrup. 9. Mingler section for mixing of wet cake & syrup to produce distiller’s wet grains with solubles (DWGS).10. Drying of DWGS in a dryer to produce distiller’s dried grains with soluble (DDGS).11. Segregation of various non-process waste water streams for reuse.12. Effluent treatment system for treatment of non-process final combined effluent. … Contd.
Conclusion In the last few years, “spent wash recycle” has emerged as one of the measures to reduce fresh water consumption. Existing distilleries & new coming distilleries should consider the spent wash recycling system.(FE & Spirit Quality) Instead of direct steam sparging, where ever possible, reboilers should be fitted to distillation columns, to reduce the quantity of spent wash generation. Spent lees can be recycled in process or non-process after correcting the pH. Higher alcohol concentration in fermented wash can substantially reduces the fresh water requirement in the process as well as steam requirement for distillation. However, this would depend on the quality of molasses available with the distillery. www.vsisugar.com
5. The CO2 scrubbing water can be used for molasses dilution. 6. The non-process wastewater generated from pump glands, air and CO2 blowers and vacuum pumps can be recycled back to the fermentation process. For avoiding scaling in condensers and coolers and for proper maintenance of the plant, it is advisable to use soft water as make up water for cooling tower. 8. The evaporation plant steam condensate can be recycled back as boiler feed water and evaporation plant process condensate can be recycled back as process water after pH correction and polishing treatment. www.vsisugar.com
9. To reduce leakages from process pumps it is advisable to install mechanical seal. 10. The fresh water requirement in molasses and grain based distilleries is found out to be average 15.0 and 16.0 liters per liter of alcohol produced, respectively.
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