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SLOP / VINASSE CONCENTRATION AND INCINERATION
PRESENT STATUS OF TECHNOLOGY
AVANT-GARDE
Vinasse
• Fermented Wash from which the Ethanol and other Volatile
Hydro Carbons have been removed in the Stripper Column
• Dark Brown acidic liquid with the pH of 3.5 to 4.5
• Contains all Inorganic substance that were present in the
Molasses
• BOD and COD Levels at 55,000 and 130,000 respectively
results in Eutrophication if let into water bodies
• Solids concentration is expected to be around 14 to 15%
• The Quantity of Vinasse depends on the alcohol percentage tolerable in the fermented wash, osmatic pressure tolerance of yeast and Vinasse recycling (used instead of water for molasses dilution in fermentation)
• With about 8% v/v alcohol content and no vinasse recycling the quantity is expected to be 10 litres/litre of alcohol
• This Quantity could come down to 7.5 to 8 litres per litre of alcohol if recycling is resorted to
• Most of the distillery suppliers today go with vinasse recycling anywhere between 15 to 25%
Vinasse Contd..
Vinasse Disposal
• Considered as one of the worst Polluting agent, because of its colour and high BOD and COD content, various disposal methods have been attempted
• Some of the disposal methods are: Fert-irrigation Composting the raw spent wash with filter mud and bagasse ash Anaerobic digestion with Bio-Gas Generation and Composting Incineration
• Out of the above, Incineration is a clean way of disposal provided there are no technical issues in the process
• If the Incineration results in some useful heat it will be an added advantage
• The raw Vinasse with 17.5% w/w solids concentration will have about 6.7% Carbon, 0.645% Hydrogen and has approximate Gross Calorific Value (GCV) of 525 Kcals/Kg (2195 Kj/Kg)
• The low GCV of Vinasse cannot support combustion and even with a support fuel the Heat Energy in Vinasse could be just used to evaporate the water in the Vinasse
• The Vinasse needs to be concentrated to a higher solids content so that the combustion could be sustained and some useful heat energy is derived
• It has been found that the Vinasse could be concentrated to 60% w/w solids without much of difficulty in terms of viscosity and severe scaling
Vinasse Disposal Contd..
Vinasse Concentration
• The concentration process needs heat energy for removing the moisture. A Multiple effect Evaporation system provides steam economy
• Various Evaporator designs have been tried and the one found to be suitable and economical is a combination of falling film and forced circulation and flash Evaporation system
• The Vinasse could be concentrated to about 30 to 35% solids concentration in a falling film evaporator and further concentration could be done in a forced circulation evaporator system
Vinasse Concentration Contd..
• The forced circulation Evaporator, at the cost of additional electrical power consumption eliminates severe scaling in the heat exchanger tubes. It employs forced circulation heat exchanger and flash vessel for Evaporation
• In the concentration process the energy economy is very important as the incineration should yield a net benefit in terms of energy recovery and expenditure
• Today’s Distilleries adopt multi pressure distillation principle in which the various columns operate at different pressures. Some of the columns operate at vacuum some at higher pressure and some at atmospheric pressure
• This affords the advantage of using the vapours from one column in the other for the supply of energy. This principle has also offered the advantage of using the vapours from the stripper column to be used for concentrating the vinasse in the first stage
• The above called as Integrated Evaporator system uses the stripper vapours to concentrate the vinasse from a solid concentration of about 17.5% w/w to 25% w/w
Vinasse Concentration Contd..
Vinasse Concentration Experience
• There are a few plants in India concentrating vinasse. The Integrated Evaporator concept has just come in and a few plants have Independent Evaporators for concentration from about 14% to 60% w/w
• Some of the early designs had faced scaling problems and are normally cleaned with regular CIP. The new designs with forced circulation have very slight scaling. The experience is that the evaporators other than the last body could operate with out cleaning even for 30 days. The last body needs CIP once in 8 to 10 days
• Chinese have also used the forced circulation evaporators successfully
• Adopting forced circulation system has ensured that there is no severe problem on account of scaling. Adopting lower temperature regime has immensely helped
Concentrated Vinasse Analysis
• The following gives the Ultimate Analysis of the Vinasse with a solids concentration of 60% w/w, and the Ash Analysis
Constituent % by Weight
Carbon 22.93%
Hydrogen 2.21%
Oxygen 15.22%
Nitrogen 1.91%
Sulphur 0.63%
Moisture 40%
Mineral Matter 17.11%
Gross Calorific Value 7780 kJ/Kg
Ash Analysis Percent
Silica as SiO2 Nil
Iron oxide as FeO3 2.0
Calcium Oxide as CaO 14.0
Magnesium Oxide as MgO 6.50
Sulphate as SO3 20.0
Phosphate as P2O5 10.0
Potassium oxide as K2O 47.0
Sodium Oxide as Na2O 0.50
Chlorides 6.00 [email protected]
Vinasse Incineration – Concerns
• There is no issue in Incinerating the Vinasse in a refractory furnace and letting the gases out after tempering
• The concern is only when the Vinasse is to be fired in a Boiler for Steam Generation
Highly fouling nature of ash due to high alkali (Sodium & Potassium) presence
Severe corrosion potential specifically on Superheaters due to the presence of Alkalies Chloride and Sulphur
Alkalies, specifically potassium with chlorine forms potassium chloride and corrodes the Superheater Tubes
Low temperature corrosion due to presence of Chlorine and Sulphur
Vinasse Incineration Boiler Salient Points
• Adequate furnace volume to ensure complete combustion of Vinasse
• Adequate furnace heat transfer area to absorb the heat released in the furnace so as to cool the gases to a lower temperature of about 500°C at Superheater entry
• Proper spacing of tubes for heat absorbing areas to eliminate bridging of slag
• Higher flue gas temperature leaving the boiler to eliminate low temperature corrosion
• Higher economizer inlet feed water temperature to eliminate low temperature corrosion in economizer
• Limit Superheater outlet steam temperature to around 400°C, to eliminate high temperature corrosion
• Use Steam Air Heater
• Appropriate spray gun selection for Vinasse feeding to the boiler
• Adequate soot blowers and wall blowers both in numbers and in locations
• Preferably Travelling Grate design for the Boiler
• Support fuel for drying and combustion of Vinasse, could be coal or bagasse or wood chips
Vinasse Incineration Boiler Salient Points Contd..
Vinasse Incineration Advantages
• Foremost is the disposal of Vinasse
• The steam generation from Vinasse itself will meet with about 65% of the Process Plant’s Energy requirements
• Typically for a 60 KLPD plant the Vinasse could generate 13.5
TPH of 42 bar (a) 400°C Steam and using that Steam the Power Generation could be about 1200 kW
• In Indian scenario, the variable cost of steam at 42 bar(a) with coal firing will be Rs.750 per MT. The Steam generated from Vinasse will save Rs.7.3 Crores in fuel cost
• The Ash from Vinasse firing is rich in potash and could be
sold as a fertilizer. One of the Indian company has already
started granulating this ash and selling it as a fertilizer. The
Ash Generation will be about 25 to 30 MT per day
• A Boiler designed with Vinasse and other supplementary fuel
firing could meet with all the Steam and Power requirements
of the distillery
Vinasse Incineration Advantages Contd..
Vinasse Incineration Boiler - Technology and Experience
• Eventhough Vinasse is an obnoxious Pollutant, Parallel can be drawn with the black liquor in paper plants
• Numerous black liquor fired boilers are in operation for ages world wide
• The ill effects of firing the Vinasse in a conventionally designed boiler not understood hitherto have now been understood. Even the concentration technology with low temperature and forced circulation have eliminated the severe scaling faced earlier
• China and India have been using this technology for a few years now and they have used both FBC and Travelling Grate technology both technologies work
• Coal, Bagasse or Wood Chips could be used as supplementary fuel along with Vinasse
• Some of the boilers commissioned earlier had faced fouling of the heat transfer surfaces. This was due to lack of understanding of the behavior of Vinasse as a fuel
• This called for the frequent shut down and cleaning
• Recently commissioned boilers do not face this problem and the experience has been good
• With good grasp of the Vinasse combustion technology, there are other Indian boiler manufacturers who are capable of and ready to supply these boilers
Vinasse Incineration Boiler - Technology and Experience
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AVANT-GARDE
AVANT-GARDE
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