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THERMOCHEMICAL CONVERSION OF BIOMASS I - Coggle Diagram
THERMOCHEMICAL CONVERSION OF BIOMASS I
COMBUSTION
Exothermic
release energy in the form of heat or light
Biomass component that react with O2
C, H, O, S, N
Direct Combustion
biomass is burned in open air or in the presence of excess air.
Wood chips, grasses, waste burnt
Boilers
5 Types of Combustion
https://www.aci-controls.com/blog/back-to-the-basics-5-important-classifications-of-combustion/
Complete Combustion
Require fuel & Oxygen ----> CO2 + H2O, very little by-product
Incomplete combustion
Not enough O2 for fuel to react ----> CO + soot , less effiecient
Rapid Combustion
Require external heat energy ---> heat & light energy at rapid pace
Spontaneous Combustion
No outside energy is required. Work by internal reaction increase temperature, thermal runaway & sufficient oxygen.
Eg. phosphorus self-ignite w/o heat
Explosive Combustion
Occur at extremely rapid pace. Force ---> ignite the fuel, heat, light and sound energy are produced instantly.
Eg. Fireworks
Combustion Method
Fixed bed
combustion air is first supplied through the grate from below, and initial combustion of solid fuel takes place on the grate and some gasification occurs.
Moving Bed
Fluidized bed
http://www.esru.strath.ac.uk/EandE/Web_sites/06-07/Biomass/HTML/combustion_technology.htm#:~:text=Fixed%20Bed%20Combustion,-There%20are%20two&text=With%20these%20methods%20of%20combustion,where%20secondary%20air%20is%20added
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Bubbling Fluidised Bed (BFB)
Circulating Fluidised Bed (CFB)
Rotary hearth furnace
Burner
Application
Obtain heat which can be used as energy for power generation. For eg. heat release from steam and hot water is recovered and reuse for electrical & mechanical purpose (Waste heat : higher temperature = higher quality)
https://www.sciencedirect.com/science/article/pii/S2451904918300015
Combined Heat & Power (CHP)
Produce electricity & captures the heat waste at the same time
Energy from biomass ---> kinetic energy
Eg. Steam from combustion of biomass & steam turbine ---> electricity
Combustible gas from pyrolysis ---> electricity
TORREFACTION
Conditions :
Slow heating,
inert atmosphere,
Temperature = 200 - 300 °C,
No presence of O2,
Particle size = < 4cm thickness,
Residence time = 30 - 90 min
Products : Coal-like properties, pellets/briquettes
Easy to pack and transport in the form of pellets/briquettes
Benefits : Products are low in moisture - low transport cost, fuel quality is high
Dry Torrefaction (Mild Pyrolysis)
Conditions : Inert gas environment, temperature 200-300 °C
Lignin = 180 - 600°C
Hemicellulose = 200 - 400°C
Cellulose = 300 - 400°C
Products : torrefaction char
By-products : solid and gas
Principle : remove oxygen and increase carbon content in solid product, biomass has lower O/C ratio (O2 is reduced, C is increased
Depolymerization of hemicellulose ---> Low energy volatiles
Obtain 60 -80% mass, 70-90% energy value
Wet Torrefaction (Hydrothermal Carbonization, HTC)
Conditions: use hot water at 200 - 260°C
Lignin = 180 - 220°C
Hemicellulose = 180 - 200°C
Cellulose 220°C
Products:
Solid = HTC char (high energy value, high energy density)
Liquid = Acetic acid, sugar (high amount)
Gas
Obtain 55-90% mass yield, 80-95% energy yield
Torrefied biomass blend with coal/ co-fired in coal boiler
Improve gasifier operation - stable
substitute coal (homogeneity)
exothermic reactions
GASIFICATION
High temperature/pressure vessel where oxygen/steam directly contacted with biomass raw material ---> fuel gas (syngas) + ash (mineral residues)
Temperature : 450 - 900°C
Controlled amount of oxygen & steam
CO-FIRING
Firing biomass with coal, natural gas, oil ---> electricity
Low emission of CO2 , SO2, Nitrogen Oxides emissions
Cheaper, environmental friendly
Biomass combustion --> electricity close to 33 - 37 % when co-fire with coal
https://www.nrel.gov/docs/fy00osti/28009.pdf
Feedstock used : Woody biomass because it has less fuel nitrogen, reduce emission of Nitrogen Oxides
PYROLYSIS
Condition : absence of air
Temperature : 300 - 500°C
Product : char, bio-oil (volatiles)
Liquefaction is similar to pyrolysis but at low temperature, high pressure
Products : Bio-oil (main product) + biochar + gases
Conditions : 250–400 °C under pressures of 5–25 MPa.
https://link.springer.com/chapter/10.1007/978-3-319-49595-8_11#:~:text=Liquefaction%20is%20a%20promising%20thermochemical,pressures%20of%205%E2%80%9325%20MPa
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Types of pyrolysis
Slow pyrolysis
500°C, Residence time : >5 seconds
Fast pyrolysis
650 to 1000 °C, char accumulated removed frequently
Microwave pyrolysis
200-300 °C, produce bio-oil with higher value chemicals, replace crude oil as feedstock for chemical processes