2. Content:-
• Define Gasification.
• Different Gasification Process:-
i. Explaination.
• Types of Gasifiers:-
1)Fixed bed Gasifier
i. Updraft or Counter Current Gasifie
ii. Downdraft or Co Current
Gasifier.
iii. Cross - draft Gasifier.
2)Fluidized Bed Gasifier:-
i. Circulating Fluidized Bed Gasifier.
ii. Bubbling Fluidized Bed Gasifier.
• Application of gasifiers.
FEEDSTOCK
3. Define Gasification?
• Thermochemical process
• Converts carbon based raw material into producer or syngas.
• carbonaceous material = Carbon monoxide,hydrogen and Carbon dioxide.
- Typical composition of producer gas
Slide No.-3
Producer Gas:-
i) Generated at low temperatre(<1000°C)
ii) Mixture of combustible(H2,CO,CH4) non-combustible (N2,CO2)
gases.
Syngas
i) Generated at higher temperatre (above1200°C)
ii) mixture consisting of (H2,CO)
iii)This gas can be produced from producer gas by:-
• Thermal Cracking
• Catalytic reforming
Carbon monoxide 18-22 %
Hydrogen 13-19%
Methane 1-5 %
Heavier hydrocarbons 0.2-0.4%
Carbon dioxide 9-12 %
Nitrogen 45-55 %
Water vapour 4%
4. Slide No.- 4
Different Gasification Process:-
Four Processes:-
i. Combustion
(oxidation).
ii. Reduction.
iii. Pyrolysis.
iv. Drying.
4 Processes in Gasification
not necessarily in order
H2O
biomass* (C H O)
Charcoal and Tar
biomass* (C H O)
This is not necessary that
these processes will be in
the same order in all the
different types of Gasifiers. heat heat no air
Drying Pyrolysis
H2O and CO2
t
tarry gas or charcoal
t
O2/air
Combustion
H2andCO
t
t
CO2 and H2O
Reduction
• Biomass is a combination of C. H, and O (C H, 4O06)
5. Slide No.- 5
Explanation Of different processes:-
BIOMASS
1. DRYING
driving off water with heat
100—15O°C
2. PYROLYSIS
heating without air to make charcoal
3. COMBUSTION 4. CRACKING adding air to
burn and crack tar gases'
5. REDUCTION
converting charcoal to flammable gas
H2O DRY BIOMASS
PRODUCER GAS
H2 and CO with N2 from
combustion air
CHAR-ASH small
pieces of ash-rich
charcoal
* tar cracking is the breakdown of tar into H2, CO, and other flammable gases by exposure to high temperatures.
6. Slide No.- 6
Combustion Process
i)lt is exothermic process.
ii) Combustible gases + 02 —> Heat+water vapour+CO2
1. C + % 02 —> CO (-111MJ/kmol)
2. CO + % O2 -> CO2 (-283MJ/kmol)
3. H2 + % O2 -> H2O (-242MJ/kmol)
Drying Process
i)lt removes the moisture from biomass.
Moist Feedstock + Heat —> Dry Feedstock + H2O
7. Slide No.-7
Pyrolysis Process
• Greek-derived elements pyro "fire"
_____________________lysis "separating".
• occurs at temperatures above 430 °C.
• It is endothermic process.
• Breakdown dry biomass into:-
i) Charcoal
ii) and various tar gasses and liquids.
(Takes place in the absence of air.)
• leaves only carbon as a residue.
BIOMASS LIQUEFACTION via PYROLYSIS
Biomass Catalytic Conversion to
Dry Feedstock —> solid Liquid ♦ Gas
(char or carbon) (tar,heavier hydrocarbons and water ) ( H 2 O, CO 2, CO, CH 4 .aldehydes and acids )
8. Reduction Process
Slide No.- 8
• It direct reverse process of combustion.
• Reduction in a gasifier:-
i) CO2 + H2O passes through charcoal bed
ii) Carbon reactive with 02
iii) Stripping oxygen atoms off combustion
products
i) C02 reduced to two CO molecules
ii) H20 reduced to H2 and CO
iii) H2 and CO are combustable fuel gases
OUTPUT
INPUT
CARBON
MONOXIDE*
HYDROGEN
H2O C CO H2
9. Slide No.- 9
Types Of Gasifiers
Fix Bed Gasifier
1 )Updraft or Counter Current Gasifier.
2)Downdraft or co-current Gasifier.
3)Cross-draft Gasifier.
Fluidized bed Gasifier:-
1 Circulating Fluidized bed Gasifier.
2)Bubbling Fluidized bed Gasifier.
10. Slide No. 10
Updraft Or
Counter Current Gasifier
• Simplest and most common types of gasifier
• Biomass feed moves downwards
• Gasifying agents move upwards to biomass
• Ash is removed at bottom
i) dry ash or slag
• hot gases pass through:-
i) Combustion at the bottom,
ii) reduction, iii) pyrolysis, iv) and drying zones of the
bed.
• Product exist from top at lower temperature.
Updraft Gasifier
11. Slide No. 11
Downdraft Or
Co-Current Gasifier.
• Biomass feedstock is fed from the top
• air is passed downwards
• producer gas leaves from the bottom
• Biomass passes through:-
i) Drying Zone ii) Pyrolysis Zone
iii) Combustion Zone iv) Reduction Zone
• Advantage:-
i) Producer gas = low tar content
ii) Suitable for gas engines.
• Disadvantage:-
Solid fuel
Gasification agent
(ail or oxygen) C
Drying zone
Pyrolysis zone
Combustion zone
Reduction zone
_____) Producer gas
• Oxidation zone position is critical (design).
12. Slide NO. 12
Cross-draft Gasifier.
• Biomassfeed moves downwards
• Air is introduced from the side
• Producer gas leaves from the opposite side
• start-up time - relatively short
• High temperature can be attained.
• ash bin, fire and reduction zone separated
• Doesn’t handle fuel - high tar content.
• C02 reduction is poor.
* Disadvantage:-
i) Gives lower efficiency
( no provision internal exchange) ii) product has low
calorific value.
Crossdraft Gasifier
Drying Zone
Gas
Reduction
Zone
Combustion
Zone
13. Slide No 13
Fluidized bed Gasifier
• solid fuel is broken into small pieces
• introduced over a gas distributor plate
through which oxidant flows upward.
• Undergo:-
i) turbulent movement-promtes uniform
temperature.
ii) back-mixing.
• bed temperature must be below the ash
melting
• 900 and 1050 °C range
• Pyrolysis -> raw syngas cyclotron reduction
zone.
Ash
14. Slide NO. 14
Circulating Fluidized Bed Gasifier
• Handle high capacity of material
• Circulation of bed material & charcoal takes
place:-
Reaction vessel cyclone returning leg reaction
vessel
• Cyclone seperater removes ash
• Operated at high pressure -^Compression
of gas takes place
• Used for gas turbine
• Gas velocity decreases
• decrease the char loss.
feeding
solid fuel
particles
circulating
fluidized
bed
cyclone
returning
leg
exiting gas ■'7.1 and
particles
not capturer
by cyclone
Air or other gases
larger particles
bubbling
fluidization
15. Slide No. 15
Bubbling Fluidized Bed Gasifier
• Most popular designs for biomass gasification.
• Gasifing agent introduced in two zones:-
i) First zone within the fludized bed (to maintain
temperature)
ii) second zone is located above the bed (convert
entrained unconverted volatiles and char
particles into fuel gas)
• Biomass is fed from the side into the hot bed
• Gasifying agent is introduced upward
• Velocity fast enough (0.5-1.0 m/s)
• Agitation of bed material takes place.
• Ash is separated from the syngas in gas-solid
separation units downstream.
Biomass
Gasifying
agent
Ash
Bed
material
16. The advantages of the bubbling fluidized-bed gasifier are
(1) It yields a uniform product gas.
(2) It exhibits a nearly uniform temperature distribution throughout the
reactor.
(3) It is able to accept a wide range of fuel particle sizes, including fines.
(4) It provides high rates of heat transfer between inert material, fuel, and
gas.
(5) A high conversion is possible with low tar and unconverted carbon.
The disadvantages of bubbling fluidized-bed gasification are that a large
bubble size may result in gas bypass through the bed.
17. Slide No. 16
Application Of Gasifierss-
• Syngas -> methanol+ethanol+
chemical and liquid fuels.
• Methanol can be further
refined into biofuels
(ex=gasoline,jet fuel etc.)with
addition of vegetable oils or
animal fats
• It can fed into a natural gas
distribution system
• Syngas or producer gas can be
burnt to create heat, steam or
electricity.
( FEEDSTOCKS
O
< O
LU
CO
STEAM
TRANSPORTATION
FUELS
FERTILIZERS
POWER
0
SYNGAS
HYDROGEN FOR
OIL REFINING
CONSUMER
PRODUCTS
SUBSTITUTE
NATURAL GAS
CHEMICALS
