L6 Flashcards
1
Q
Biomass pyrolysis
A
- Thermal devolatilization of biomass organic components in the absence of oxygen
- Classified by residence time, heating rate and pyrolysis temperature
Carbonation
- Method for charcoal production
Conventional pyrolysis or slow pyrolysis
Fast pyrolysis
- High yield of liquid or gases
2
Q
Fast pyrolysis
A
- Produces liquid product that can be used to produce bio-liquid fuel and bio-chemicals
- Liquid is called pyrolysis oil
- Residence time a few seconds
- Needs finely ground biomass for high heating rates
- Biomass feed moisture content less than 10%
- 450 - 650 Celsius
- Rapid cooling of vapours to produce liquid
3
Q
Undesirable properties of pyrolysis liquid
A
- High viscosity
- Miscibility: miscible with polar solvents but immiscible with petroleum-derived fuels
- Distillation: cannot be completely vaporised
- Unstable: increasing storage time increases viscosity and decreases volatility. Phase separation and solid decomposition occurs
4
Q
Physical methods for upgrading pyrolysis liquid
A
- Hot-gas filtration to reduce ash and alkali content. Increases burning rate and decreases ignition delay
- Addition of surfactants will produce stable micro-emulsions
- Polar solvents can added to reduce viscosity
5
Q
Chemical upgrading of pyrolysis oil basics
A
- Upgraded by high temperature cracking
- Zeolites used as catalysts to reduce oxygen content and improve stability
- 350 - 500 Celsius and atmospheric pressure
- Integrated system can be connected to pyrolysis reactor so hot vapor fed directly into upgrading system
6
Q
Methods for chemical upgrading
A
Acetalization
- Reaction between alcohols (added) and aldehydes to for acetate and water
Esterification
- Reaction between alcohols (added) and acid anhydrides to form esters and water.
- Acidity and oxygen content of bio-oil reduced
Both upgrading methods
- Decrease viscosity
- Decrease aging rate and acidity
- Improve volatility
- Improve heating value
- Improve miscibility with diesel fuels
7
Q
Hydrotreating
A
- Key process in oil refining
- Removes sulphur, nitrogen and olefins using hydrogen
- Hydrogen addition also improves the distilled fuels
8
Q
Hydro-cracking
A
- Upgrades heavy oil feed into lighter hydrocarbons, higher values and low sulphur products
9
Q
Hydrodeoxygenation (HDO)
A
- Method for upgrading bio-oil.
- Under hydrogen pressure, converted oxygenated compounds to hydrocarbons
10
Q
Non-condensable gas from pyrolysis
A
- Pyrolysis of biomass can produce up to 70% non-condensable gases depending on temperature used
11
Q
Pyrolysis system requirements
A
Pyrolysis systems need
- high heating rate
- well controlled reaction temperature
- Rapid cooling or quench rate of vapours to liquid product
12
Q
Types of reactors
A
- Bubbling fluidised bed
- Circulating fluidised bed
- Entrained flow
- Rotating cone
- Vacuum
13
Q
Bubbling fluidised bed system
A
- Pilot scale
- Simple construction and operation
- Silica sand used as bed material
- Good temperature control
- Reaction rate limited by rate of heat transfer through a biomass particle
- Good and consistent performance
- High liquid yield (70-75% mass) from wood.
14
Q
Circulating fluidised bed
A
- Commercial unit available
- Silica sand used as bed material
- Integrated char combustion
- Good temperature control
- Reaction rate limited by rate of heat transfer through a biomass particle
- Liquid yield (60-70% mass) from wood.
