F9 Biomass Gasification Flashcards
It is not likely that all transportation can be run by electricity, what can biofuels be a role for?
Aviation
Heavy duty trucking
Sea shipping
What is biomass?
It refers to living and recently dead biloogical material that can be used as fuel or for industrial production.
Examples of biomass
• Examples of biomass:
– Wood from the forest
– Fast growing trees: popplar, willow (energy crops)
– Grass: hemp, Lucerne, Miscanthus (energy crops)
– Wood form bushes, brushwood
– Forest residue: stubs, branches, bark
– Refuse derived fuel
– Agricultural residues: straw
- Black liquor?
What are the most important properties in case of gasification?
Describe the drying step in biomass gasification (temp. and what gases leave)?
Describe the pyrolysis step in biomass gasification (temp. and what gases leave)?
Describe the heterogeneous reactions (char combustion and char gasification)
What is gasification?
The overall reaction scheme for gasification (primary reactions and secondary reaction)
What is tar?
Different pretreatments for biomass
- Drying: with steam or flue gas (rökgas)
- Size: chipping, pyrolysis slurry
- Fractioning: separating hemicellulose and ligning
Gasification is an endothermic process → needs to add heat.
There is autothermal gasification (direct heating) and allothermal gasification (indirect heating) - describe them.
Name the three different types of gasifiers (and their subtypes)
Moving or fixed bed gasifier - updraft gsaifier
- Fuel is fed at the top
- Gasifying medium (air or oxygen and/or steam) is introduced at the bottom
- Size, shape and moisture content of biomass particles are not critical
- The quality of the syngas is generally quite low - high tar
- In most cases autothermal
- Small-scale, <10 MWthermal
- T = 300 - 1000˚C, P = Atmospheric
Moving or fixed bed gasifier - downdraft gsaifier
- Fuel is fed at the top
- Gasifying medium is introduced into a downward flowing packed bed
- Only dense and solid feedstock with low water content can be gasified
- The produced gas is generally of relatively good quality and has low level of tars
- Small-scale, <1-2 MWthermal
- T = 300 - 1000˚C, P = Atmospheric
Bubbling Fluidised Bed (BFB) gasifier
Circulating Fluidised Bed (CFB) gasifiers
Entrained Flow Gasifiers
- Fuel, as gas, solid powder or slurry, is mixed with a steam/oxygen stream and converted in a turbulent powderized flame at high temperatures (above 1200ºC) in a very short time (a few seconds).
- An almost tar-free and methane-free syngas, and a leach-resistant molten slag are produced (good fuel capacity)!
- The syngas passes a radiant gas cooler and then over the surface of a pool of water and exits the vessel.
- The slag drops into the water pool and is through a lock hopper.
- Requiring integration with steam user industry
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High fuel flexibility but also high efforts for fuel pretreatment (pyrolysis, torrefaction , etc). Difficult to pulverize biomass since grinded particles tend to stick together. Requires pre-treatment:
- Pyrolysis
- Torrefaction?
- T > 1200˚C P = 20 – 50 bar
What does the route of gas cleaning and gas conditioning depend on?
What do we want from a fuel used for ex FT, DME and Methanation (three aspects)
What are the main challenges of biomass gasification?
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The formation of tars is the Achilles heel of biomass gasification as tars are the major technical obstacle in the implementation of this technology
- Blocking of downstream pipes and process equipment
- Coking of catalysts in downstream gas upgrading processes
- Energy efficient particulate removal
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Removal of impurities such as H2S, CS2, COS, AsH3, PH3, HCl, NH3, HCN, and alkali salts
- Catalyst poisons
- Deposit formation of alkali salts
What determines the quality of the produced gas?
What are the effects of different gasifying agents?
H2/CO ratios depending on gasifying agent and requirements for end-user (methane, FT and methanol)
Study a walkthrough of a process! F9
Slide 60 - 88 :))))))
