Slop Boiler (Spent wash)
SLOP BOILER
Slop, also known as Vinasse, is an Acidic Effluent from Fermentation of Sugar Cane Molasses in Distillery unit . It is a Hazardous Waste and not suitable for Direct Disposal.
Various methods of Slop disposal
Disposal methods:
- Biomethanation.
- Composting.
- Incineration Technology.
Benefits.
These do not result in “Zero Liquid
Discharge”. Zero liquid discharge can be achieved through Eco –friendly
Incineration Technology which is also energy efficient.
Concentrated Slop/ Spent Wash is
directly fired in the Boiler to meet Zero Liquid Discharge.
A. To
Meet the Statutory Norm of Zero Discharge:
· By Firing Concentrated Distillery Effluent spent wash (Slop) in a boiler.
· Steam Generation to meet the process requirement of Distillery.
·
Power Generation to
meet captive requirement.
· Ash generated is of potash rich ash is
saleable, generates good revenue and also eliminates disposal problem.
·
Reduction in overall
production cost per liter of alcohol.
·
In depth study of Slop
and its Ash characteristics.
·
Ash deformation and
Fusion temperature.
·
Selection of
appropriate steam parameters (Pressure / Temperature Cycle).
·
Option of Support
Fuel(s)
·
Efficient combustion
system.
·
Effective Air Pollution
Control equipment.
Characteristics of raw slop
|
Colour |
Drak Brown |
|
Odour |
Pungent |
|
pH |
4.0 – 4.5 (Acidic) |
|
Solids Content |
9 – 12 % (Weight) |
|
Biological Oxygen Demand |
45000 – 60000 PPM |
|
Chemical Oxygen Demand |
110000 – 135000 PPM |
The various supporting fuels used in Incineration Boilers are.
1. Spent
wash + Coal (Indian/Imported).
2. Spent
wash + Rice husk.
3. Spent
wash + Bagasse
Type of Boilers are used in Incineration
Technologies
· 1) Travelling grate
Boiler: Rice husk & Bagasse.
· 2) AFBC Boiler: Indian
& Imported coal
·
Analysis of Slop and Comparison with
Bagasse
Constituent (% Weight) |
Slop (60 Brix) |
Bagasse |
|
Carbon |
22.22 |
23.50 |
|
Hydrogen |
2.15 |
3.25 |
|
Nitrogen |
1.85 |
- |
|
Oxygen |
14.50 |
21.75 |
|
Moisture |
40.00 |
50.00 |
|
Sulphur |
0.62 |
- |
|
Ash |
18.62 |
1.50 |
|
Gross Calorific Value (Kcals / Kg) (MJ / Kg) |
1800 7.5 |
2270 9.5 |
Combustor & fuel feeding system in AFBC boilers.
Combustor is located in pass-1 & Super heater, Evaporator; Economiser & Super heaters are located in Pass-3, fabricated with high temperature refractory material, enclosed by steel casing and supporting structure. Combustor is divided into various compartments & for all compartments ash drain system is provided.Coal feeding system: Consists of
coal bunker, VFD screw feeders to feed the coal. Coal is distributed inside the
combustor by pneumatic spreading system.
Spent wash feeding system: Concentrated and pre-heated Spent wash from the storage tank is conveyed to boiler through variable speed pump. Spent wash is sprayed over the fluidising bed at first pass through spray guns.
Around 8 to 10 kg of steam is generated
per square meter of heating surface in Spent wash AFBC boilers.
Around 10 to 12 kg of steam is generated
per square meter of heating surface in Spent wash Bagasse or rice husk Boilers.
VARIATION IN CALORIFIC VALUE OF SLOP
WITH CONCENTRATION
|
Solids
Concentration (Brix) (%) |
Gross
Calorific Value (Kcals/Kg) |
|
40 |
850 |
|
45 |
1200 |
|
50 |
1400 |
|
60 |
1800 |
TYPICAL ANALYSIS OF SLOP ASH VS BAGASSE
ASH
|
Constituent
(% Weight) |
Slop
Ash |
Bagasse
Ash |
|
Silica, SiO2 |
2.50 |
69.88 |
|
Iron Oxide, Fe2O3 |
2.00 |
6.49 |
|
Calcium Oxide,CaO |
14.00 |
4.75 |
|
Magnesium Oxide, MgO |
6.50 |
2.83 |
|
Sulphate, SO3 |
16.50 |
0.08 |
|
Phosphate,P2O5 |
10.00 |
2.01 |
|
Potassium Oxide, K2O |
47.00 |
2.79 |
|
Sodium Oxide, Na2O3 |
0.50 |
1.22 |
|
22 Aluminium Oxide, Al2O3 |
- |
9.10 |
|
Chlorides, Cl |
1.00 |
- |
Constituents which cause problems in
Boiler are Alkalis (Na2O3+K2O), Chlorides, Calcium Oxide & Sulphates.
COMBUSTION
·
Low
Calorific Value of Slop even at 60 Brix (1800Kcals/Kg). However it fluctuates between
45 to 60 Brix.
·
Low
Ash fusion temperature due to high Alkali constituents in ash (K2O + Na2O).
·
High
Chlorides (>1%), Calcium Oxide and sulphate in ash.
·
Low
Silica in ash.
· Ensuring Continuous operation.
For Pressure parts online cleaning mechanisms are:
·
Mechanical rapping
systems
·
Steam Soot blowers .
·
Sonic soot blowers.
Spent
wash Boilers have taller furnaces because to maintain higher residence time in
furnace up to 8 seconds. And to maintain optimum flue gas temperature at super
heater inlet to avoid coils fouling due to alkali ash property and to avoid
corrosion of super heater coils due to chlorides (1%) in ash.
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