biomass resources, characterisation and technologies(ag)
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Biomass Resources, Characterisation and Technologies
Prof. Anuradda Ganesh
Energy Systems Engineering, IIT Bombay
21st September 2006
Biomass - a natural solar cell
• What is Biomass?• Why Biomass?• Limitations?• Effective Utilisation of Biomass!
Any organic matter formed, directly or indirectly,
by virtue of photosynthesis, is called biomass
• Crop residues• Forest residues• Agro-industrial residues• Animal waste• Aquatic plants• Purpose grown trees
• Others like MSW and synthetic organics.
Why Biomass?
• Fossil fuels are fast depleting
• Gap between supply & demand increasing
• Green house gas emissions steadily increasing and causing concernBiomass is a renewable source and available in abundance
[ Annual emissions of greenhouse gases from fossil fuel combustion and land use change (deforestation) ~ 6.7 and 1.6 Pg C respectively]
[ Earth’s natural biomass replacement represents an energy supply of around 3x1021J a year, of which just under 2% is currently used as a fuel]
LimitationsCrop residues generated in country side—Low in bulk density
High transportation costs
Seasonal availability
High moisture content, high bio-degradability
Therefore,
Decentralised utilisation preferred
Dedicated system for single biomass is questionable due toseasonal availability, R & D on multi-fuel flexibility
Should be called “feedstock” for fuels rather than “fuel”
Consequences of Limitations
•Limitation on scale
•Upgradation required for wider use
•Dedicated system for single biomass is questionable due to seasonal availability
•High transportation costs
Therefore,
• Decentralised utilisation preferred
• Upgradation to better fuel taken up
• R & D on multi-fuel flexibility
Effective Utilisation of BiomassBiomass
Improved solid fuels(Pellet, Char pellet) Gaseous Fuels
Thermo-chemical Gasification
(Producer Gas)
Bio-chemical Biomethanation
(Bio gas)
Liquid Fuels
Thermo-chemical (Pyrolysis Oil)
Bio-chemical (Ethanol)
Extraction –Trans-esterificationSeed based crop
(Biodiesel)
Biomass and CoalProperties Coal Biomass
Volatile matter(dry basis)
<20 - ~50% 60 – 90%
Fixed Carbon(dry basis)
~ 40 – ~80% <5 - ~25%
Ash(dry basis)
<10 - ~45% <1 - ~25%
C (d.m.m.f) ~ 80% ~ 50%
H (d.m.m.f) ~ 5- ~10% ~10%
O (d.m.m.f) ~10- ~20% ~ 40%
Calorific value (MJ/kg) 16 - 34 16 - 19
Flame intensity…If = (dω/dt) h
Where… I - flame or reaction intensity(dω/dt) - weight loss with respect to time
& h - heat content
Therefore, the rapid weight loss of bio-fuels, when compared to any coal compensates for lower calorific values
“Co-firing in spreader-stoker boilers is easily adaptable”
Surface combustion
CharHeatAir
CO2
Flaming combustion
Biomass
Air Heat
Volatiles
CO2
Heat
In biomass combustion process,Biomass is having 70% volatiles
Typically 50% Carbon, 10% Hydrogen, 40% Oxygen
Most oxygen is released in ‘combined’ form with
volatiles
About 50% energy is contributed by gas phase
combustion through ‘volatiles’
Rate of release of volatiles is high and different for
different biomass
Therefore, provision of air, mixing are critical
TGA of Biomass 1 and Biomass 2
Biomass Volatiles Ash Ash deformation temp. range (0 C)
Ash fusion temp. range (0 C)
Arhar stalk 83.47 1.77 1250-1300 1460-1500
Bagasse 75.10 8.03 1300-1350 1420-1450
Bamboo dust 75.32 9.09 1300-1350 1400-1450
Cotton stalk 70.89 6.68 1320-1380 1400-1450
Coconut coir 70.30 2.93 1100-1150 1150-1200
Corn cob 80.20 3.60 800-900 950-1050
Dhaincha stalk 80.32 2.67 < 800 800-900
Groundnut shell 68.12 6.91 1180-1200 1220-1250
Jute stick 75.33 5.67 1300-1350 1400-1450
Kikar (Acacia) 77.01 0.64 1300-1350 1380-1400
Mustard shell 70.09 15.43 1350-1400 1400-1450
Pine needle 72.38 1.50 1250-1300 1350-1400
Rice husk 60.64 19.48 1430-1500 1650
Sal seed leaves 60.03 19.75 1200-1250 1350-1400
Sal seed husk 62.54 9.40 1450-1500 1500-1550
Characteristics of biomass
Conclusions
Every biomass has a characteristic behaviour depending on its
basic composition and morphology of its components.
Ash composition and fusion temperature also influence the
adaptability and suitability.
Physical properties of biomass also play an important role
particularly in sizing of the reactor/hopper and extent of co-firing.
For all thermo-chemical conversion processes pyrolysis plays a key role.
Contd..
Biomass is not a low grade fuel as the rate of weight loss
compensates for the lower calorific values when compared with coal.
The design and operation however, has to consider the large
flaming combustion/amount of gases and vapours to be handled.
Interchangeability of biomass in a reactor is subject to both the
physical and chemical properties.
Co-firing…
Co-firing – practice of supplementing a primary or a base fuel with a dissimilar fuel
Recently, in US & Europe, there has been a considerable emphasis
on co-firing biomass fuels with coal in PULVERISED COAL and
CYCLONE BOILERS owned and operated by utilities – to address
issues like CO2 reduction, generation of green power etc.
Co-firing technology comprises of…
Blending the biomass and coal in fuel handling system and feeding that blend to the boiler
Preparing the biomass fuel separately from coal, and injecting it into the boiler without imparting the conventional coal deliverysystem
Gasifying biomass with subsequent combustion of producer gasin either a boiler or a combined cycle combustion turbine generating plant
Gasifying biomass to partially substitute the furnace oil used ina furnace
Co-firing with natural gas for performance enhancement in biomassand coal-fired boilers
Lets take a re-look at the properties of biomass…
• Modest heat content : 15-22 MJ/kg• Sulphur : Low• Nitrogen : Low• Volatile / fixed carbon ratio : 3.5 – 5
• Typically fuels co-fired at 10-25% ( mass basis)~ 4 – 10% co-firing on a heat input basis
Also, say we take straw which has very low bulk density of 80 kg/m3
as against coal – 880 kg/m3
A 5% straw/95% coal on mass basis ~ 1m3 straw/1.7 m3 coal blend
i.e., 37% straw on a volumetric basis
There are three main types
Fixed bed type – typically Grate fired
- Traditional technology developed for coal combustion and combustion of municipal solid waste
- Used for biomass fuels with high moisture content, different particle sizes and high ash content
- Capacities upto 20 MWth
Fluidised bed combustion
- A fairly recent innovation entering into the second generation design
- Sized particles, large scale applications
Dust combustion- suitable for fuels which are dry and small such as saw dust
Technologies for biomass combustion
Gaseous Fuels from Biomass
Biomethanation/Anaerobic Digestion
Anaerobic decomposition of biomassthrough bacterial action
CO2 + CH4 ( called BIOGAS)(40%) (60%) (C.V- 20MJ/Nm3)+ Nutrient rich organic manure
Biomass: Less lignin and more moisture content
Biomass Clean, combustible gas mixture PRODUCER GAS
Average composition:
CO 19±3H2, 18 ±2 CH4 3 ±1CO2 10 ±2N2 balance
The reactor is called GASIFIER• Calorific value (C.V) of Gas~ 4-5 MJ/Nm3, Acceptable limit : Tar < 100mg/ Nm3
P<50mg/ Nm3
GasificationPartial Combustion
Liquid Fuels---Concept & Introduction
Ethanol Bio-diesel Pyrolysis oil
Petrol substitute Diesel substitute
Starch/sugar based biomass
Straight Vegetable oil (triglycerides of fatty acids) from oil seeds
Any Bio fuel
Fuel oil substitute (later for diesel)
Biomass
Charcoal
Producer Gas
Air
Cooling & Condensing
Air
Air
Heat
Tar Removal
Tar Cracking
Heat ??
Volatiles
Heat
Ash
Condensing
Oil & Chemicals
Vol. Cracking
Useful Carbon
Pyrolysis as we understand today
Why not (!) Straight Vegetable Oils (SVO) ???
Basic constituent of SVO is ‘Triglycerides’
Small amounts of mono and diglycerides
Substantial amounts of oxygenates
Free fatty acid
OCH2 – O - C- R1
CH – O – C – R2
CH2 – O – C – R3
O
O
A typical triglyceride molecule
High Viscosity – poor injection characteristics, poor atomisation,
inefficient mixing with air, incomplete combustion
Oxidative and thermal polymerisation, deposition on injectors
Therefore, engine must be more or less modified or use derivatives
Making of Bio-Diesel (from oil of low fatty acid)
O
O
Triglycerides
O
O
CH2 – O - C- R1
CH – O – C – R2
CH2 – O – C – R3
O
CH3OH
NaOH
CH2 – OH
CH - OH
CH2 - OH
R1 - C- O – CH3
R2 – C –O - CH3
R3 – C – O - CH3
ONa
Na
Na
(Na salt of HFA soap)
Bio-diesel(methyl ester of HFA)
(Heating & stirring) Glycerol
+
I f p e r c e n t a g e o f F r e e F a t ty A c i d s ( F F A ) a r e m o r e , t h e n i t w o u ld f o r m s o a p
R - C - O – H
ON a O H
C H 3 O HR - C - O – N a +
OH 2 O
( S o a p )F F AA c id
c a ta ly s tC H 3 O H
R - C - O – C H 3
O
( E s te r )
Recent advancement…
Two step process using co-solvent (e.g. THF)
High conversion efficiency
Reaction time 30-35 mins.(lower than 6-7 hrs. for one stage process)
Comparison of SVO and Biodiesel with Diesel
0.200.20(B100)(B100)
0.620.62(B100)(B100)
9911110.050.05Moisture Moisture Content(wt.%)Content(wt.%)(Karl(Karl--Fischer Fischer titrat ion)titrat ion)
162162(B100)(B100)
160160(B100)(B100)
2802802252256666Flash Point(0C)Flash Point(0C)ASTM D93ASTM D93
41.1241.1240.9340.9338.1438.1437.9937.994242Calorif ic Value Calorif ic Value (MJ/kg) (MJ/kg) ASTM D240ASTM D240
878878861861917917969969844844Density (kg/m3)Density (kg/m3)ASTM D4052ASTM D4052--8686
99775858505044Viscos ity at Viscos ity at 404000C (C (cStcSt) ) ASTM D445ASTM D445
Kusum Kusum BiodieselBiodieselB20B20
Karanj Karanj BiodieselBiodieselB20B20
KusumKusumKaranjKaranjDieselDieselOil propertiesOil properties
Biorefinery
Conclusion
• Biomass is a source of carbon and hydrogen (with external alterations)
• It is time for an integrated approach at all levels—small, medium and large scale—for fuels and chemicals from biomass
Thank You
Properties of Bio-diesel prepared at IIT Bombay:
S.No. Properties Bio-diesel1. Kinematic viscosity (cm2/s) 6.51
2. Specific gravity @ 300C kg/lit 0.88
3. Density @ 300C 0.875
4. Moisture content (%) 0.4
5. Carbon residue 0.04
6. Flash point (0C) 190
7. Calorific value (kcal/kg) 8880
8. Acid number mgKOH/g 0.836
9. Iodine number 101
10. Copper strip corrosion No.2
11. Carbon (wt %)Hydrogen (wt %)Oxygen (wt %)
771211
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