bahan kuliah biomass
TRANSCRIPT
Energy from Biomass
Lecture 2
Jeroen van Oijen
Energy from biomass
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Course outline
1. Introduction
• Global warming
• Resources and potential
2. Properties and characterization
3. Conversion processes
4. Modelling reacting flows
5. Conversion of spherical particles
6. Front propagation in a fixed bed
7. Emissions
8. Conversion systems
Course outline
1. Introduction
2. Properties and characterization
• Physical and chemical properties
• Composition of biomass
• Proximate and ultimate analyses
• Heating value
3. Conversion processes
4. Modelling reacting flows
5. Conversion of spherical particles
6. Front propagation in a fixed bed
7. Emissions
8. Conversion systems
Energy from biomass
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Properties and characterization
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Characteristics of biomass fuels
• Wide range of fuel types
• Important for
• Conversion technology
• Plant design
• Homogeneity
• Economy of scales
• Standardization
• CEN, ISO, DIN, ASTM
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Biomass properties
• Internet databases
• ECN www.ecn.nl/phyllis
• DoE Biomass program
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• Wood (untreated, treated)
• Grass
• Manure
• Waste
• Sludge
• Straw
• Husk/shell/pit
• Organic residue
• Algae
• Vegetable oil
Physical properties (1)
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Moisture content Storage, dry-matter losses
Volatile content/
composition
Thermal decomposition,
combustion technology
Ash content Dust emission, ash manipulation
Fixed carbon Combustion technology
Calorific/Heating
Value
Fuel utilization, plant design
Physical properties (2)
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Ash melting Safety, process control
Fungi
Health risks
Bulk density Logistics
Particle density, heat
capacity, conductivity
Thermal decomposition
Dimension, shape,
distribution
Conveying, drying, bridging,
combustion technology
Chemical properties / elements (1)
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Carbon C Heating Value
Hydrogen H Heating Value
Oxygen O Heating Value
Nitrogen N NOx, N2O emissions
Chlorine Cl HCl, PCDD/F emissions, corrosion
Sulphur S SOx emissions, corrosion
Fluor F HF emissions, corrosion
Chemical properties / elements (2)
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Potassium K Corrosion, ash melting
Sodium Na Corrosion, ash melting
Magnesium Mg Ash melting, utilization
Calcium Ca Ash melting, utilization
Phosphor P Ash utilisation
Heavy metals Emission, ash melting
Structure of wood
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Softwood Hardwood
Composition of woody biomass
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Tracheids
Middle
Lamella
Composition of woody biomass
Combination of three CHO components
1. Cellulose
2. Hemicellulose
3. Lignin
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Composition of woody biomass
1. Cellulose (C6H10O5)n
• Structure, fibre walls
• Carbohydrate C6(H2O)5
• Polysaccharide
• Polymer of glucose C6H10O6
• n = ~104
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Composition of woody biomass
2. Hemicellulose (C5H8O4)n
• Encasing of cellulose fibre, cross links
• Carbohydrate, polysaccharide
• Other than glucose: xylose,…
• Branched shorter chain (~103)
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Composition of woody biomass
3. Lignin (C40H44O6)
• Fills the spaces
• Binding agent / strength
• Non-sugar polymer
• Aromatic structure
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Composition of woody biomass
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Cellulose Hemicellulose Lignin
Beech 45.2 32.7 22.1
Birch 44.5 36.6 18.9
Pine 45.0 26.4 28.6
Spruce 48.5 21.4 27.1
Characterization methods
• Proximate analysis
• Moisture content
• Volatile matter
• Fixed carbon
• Ash content
• Ultimate analysis
• C, H, O, N, S, …
• Bomb calorimeter
• Calorific/Heating value
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Proximate analysis
• Place biomass sample on a scale in an oven filled with inert gas
• Heat up to 110˚C → moisture evaporates
• Measure weight loss → moisture content
• Wet basis:
• w = (wet weight-dry weight)/wet weight
• Dry basis:
• u = (wet weight-dry weight)/dry weight
• Conversion:
• w = u/(1+u) u = w/(1-w) u > w
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Moisture content
Moisture content may vary a lot
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Proximate analysis continued
• Sample is heated to 600˚C
• Devolatilization, pyrolysis
• Volatile matter (VM) is released from sample
• Tar: parts/monomers of (hemi)cellulose, lignin
• Gas: CO, H2, CH4, CO2, H2O…
• Weight loss gives VM content
YVM = weight loss / dry weight (wt % d.b.)
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Proximate analysis continued
• Air is allowed to enter the system
• The sample burns and ash remains
• Ash content
YAsh = weight ash / dry weight (wt % d.b.)
• Fixed carbon content determined by difference
YFC = 1 - YVM - YAsh (wt % d.b.)
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Proximate analyses
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VM FC Ash VM FC Ash
Thermo-Gravimetric Analysis (TGA)
• Put sample in inert atmosphere
• Pure nitrogen N2
• Slowly heat up sample
• Heating rate ~20 °C/min
• Measure weight loss as function of time
• Typical result…
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TGA of pine bark
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10.47% moisture(0.5128mg)
49.41% Volatiles(2.419mg)
37.96% F.C.(1.858mg)
Residue:2.037% Ash(0.09972mg)
0
200
400
600
Te
mp
era
ture
(°C
)
0
20
40
60
80
100
120
We
igh
t (%
)
0 20 40 60 80 100 120
Time (min)
Sample: Bark 90 micronSize: 4.8961 mgMethod: BiomassComment: first test
DSC-TGAFile: C:\TA\Data\TGA\Bark90micron.002Operator: AdrianRun Date: 5-Nov-03 13:58
Universal V3.0G TA Instruments
Results of pine bark
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% Wet % Dry % DAF
Moisture 10.5 - -
Ash 2.1 2.3 -
Volatile Matter 49.4 55.2 56.5
Fixed Carbon 38.0 42.4 43.4
Low
Derivative TGA curve
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Cellulose
Hemicellulose
Lignin
TGA and DTG for softwood biomass
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TGA and DTG for hardwood
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A devolatilization model
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Exam question
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Sample is put in N2 filled
furnace. After 45 min. the
temperature is increased to
110 ℃. After 30 min. it is
slowly increased to 600 ℃.
Finally, air is supplied.
a) Explain the curve.
b) Determine composition
on wet basis, and dry-
and-ash-free basis.
Answer
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Ultimate analysis
• Sample is burned in O2 atmosphere with He as carrier gas
• Combustion gases are CO2, H2O, NO, NO2, SO2, SO3 and N2
• SO3, NO and NO2 are reduced at copper contact to SO2 and N2
• H2O, SO2 and CO2 are captured in different adsorption columns
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Ultimate analysis continued
• N2 is not captured and is detected by a thermal conductivity detector (TCD)
• N2 → N
• Consecutively, H2O, SO2 and CO2 will be sent to TCD
• H2O → H
• SO2 → S
• CO2 → C
• Mass percentage is determined integrally
• O is found by difference
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Ultimate analyses
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Coalification (Van Krevelen) diagram
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Gross calorific / Higher heating value
• Empirical relation for biomass
GCV = 34.91 YC + 117.83 YH + 10.05 YS
– 1.51 YN – 10.34 YO – 2.11 Yash [MJ/kg d.b.]
Yi is content in wt% d.b.
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Calculation exercise for CH1.0O0.4375
Bomb calorimeter
Device to measure
heating value
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Effect of moisture on heating value
• Gross Calorific Value (GCV) Higher Heating Value (HHV)
• Heat released during combustion per mass unit fuel
• Final temperature same as initial temperature
• Water is formed in liquid phase
• Net Calorific Value (NCV) Lower Heating Value (LHV)
• Water is formed in gaseous phase
• Latent heat + sensible heat (100-25℃)
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Lower heating value
Derived from HHV
Dry basis:
Wet basis:
YH = hydrogen wt% d.b. (~6%)
w = moisture content wt% w.b.
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18
2.442
db
HLHV HHV Y
Calculation exercise for dry CH1.0O0.4375
(1 ) 2.44wb dbLHV LHV w w
Ash
• Inherent ash versus entrained ash
• Bottom ash versus fly ash
• Constituents
• Plant nutrients: CaO, MgO, K2O,
P2O5, Na2O
• Other oxides: SiO, Al2O3, Fe2O3
• Heavy metals: Cu, Zn, Cr
• Organic contaminants: PCDD/F
and PAH
• Ash utilization: manufacturing
cement and concrete, road
construction, soil improver,…
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Ash melting behavior
• Sintering: agglutination of particles
• Softening temperature: change of surface, rounding,
shrinking.
• Hemisphere temperature: spherically shaped
• Melting temperature: size reduced to 1/3
• Ca and Mg increase
• K and Na decrease
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Improving biomass quality
• Growing phase
• Harvesting date (moisture)
• Fertiliser (Cl in straw)
• Rainfall during storage on the field
• Supply phase: Upgrading
• Increase energy density
• More homogeneous
− Chunking, chipping, grinding
− Drying
− Compressing (pellets and briquettes)
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Leaching of barley straw by rainfall
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Conversion processes
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Biomass conversion routes
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Thermochemical conversion
• Advantage: High throughput, second generation
biomass
• Three main processes
• Pyrolysis Air ratio = 0
• Gasification Air ratio = 0.25 – 0.50
• Combustion Air ratio = 1 – inf.
• Difference: the amount of oxidizer (air) available
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Air ratio = Actual air fuel ratio
Air fuel ratio for stoichiometric combustion
Questions
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