2. GASEOUS FUEL
Definition
• Burnt in gaseous state in air or oxygen
Usage
• Both domestic and commercial purpose
Advantage
• Mineral impurities are absent
• Consistence in quality
• Effecient in use
• Lowest handling cost on industrial scale
4. General classification:
• Rich gas: if C.V.>4000 kcal/Nm3
• Lean gas: if C.V.<1500 kcal/Nm3
Wobbe Index:
• C.V. is not only satisfactory parameter to classify
• Thermal output depends upon “Wobbe Index”(W.I.)
• Wobbe Index= C.V./√(specific gravity)
• It is a dimensional group
• Its unit depends upon unit of C.V.
CLASSIFICATION
5. TABLE: WOBBE INDEX SCHEDULE
OF FUEL GAS QUALITY
Gas group Wobbe Index(C.V in kcal/Nm3)
1 -
2 -
3 7,650±380
4 6,970±285
5 6,400±285
6 5,870±240
7 5,350±285
Reference:Elements of Fuels, Furnaces & Refractions by O.P. Gupta
6. WEAVER FLAME SPEED FACTOR
Basis of classification for rich fuel gases
Expressed on an arbitary scale
Hydrogen assumed to have 100 arbitrarily
Three groups of gases:
High flame speed gases
Weaver flame speed factor= 32-45
Low flame speed gases
Weaver flame speed factor= 13-25
Intermediate type gases
Weaver flame speed factor= 25-32
7. EFECTS ON W.I. and FLAME
SPPED
Inert gases(N2, CO2) and CO reduce flame
speed and Wobbe Index
Hydrogen increase flame speed and Wobbe
Index
Hydrocarbons-
• Reduce flame speed
• Increase Wobbe Index
8. METHANE FROM COAL BED
• Methane is associated with coal in
mines
• Coal absorbs the methane formed during
coalification
• During coal mining the gas is gradually
desorbed
Origin
• CH4-93-99% •C2H6-0-3%
• CO2-0-4% •N2-2-6%
Composition
• Forms explosive in gas-air mixutre
• So proper ventilation is required for
safety
• Often called “firedump” for explosive
nature
Pre-cautions
9. WOOD GAS
• Carbonisation of wood
• Gasification of wood
Origin
• Has medium C.V. And not much
of commercial interest
• About 50% of wood gas is
consumed in gas produce
• Rest 50% is used elsewhere e.g.
in thermal power plant
Usage
10. GOBAR GAS
• Gobar, Hindi word, means cattle
dung
• Obtained by fermentation of gobar in
absence of air
Origin
• CH4-60% •CO2-30%
• H2S and O2-trace •H2-9.5%
• N2-0.55%
Composition
• Used as domestic cooking fuel in
villages
• Also used for:
• domestic lighting
• small water pump running
• small diesel and petrol engine
running
Usage
12. DETAILS OF PLANT
Digestor:
• Constructed below ground level
• 3-6 meter deep
• 1-6 meter diameter depending on size
• Divided into two compartments by a wall
Gas holder:
• Mild steel drum
• Fits like a cap on the mouth of the wall
• A central pipe guides movement of the drum
13. PROCEDURE
Mixture of
cattle
dung:water=4:5
Sent to
digestor
through inlet
pipe
When digestor fills up,
equal quantity of dung
slurry is discharged
through outlet pipe
Slurry from
outlet used as
fertilizer
Produced
gas to gas
holder
Gas taken using
gas exit
Digest of volatile acids and nitrogen compounds
Temperature:
30-40˚C
•Initial acid forming pH 6
•Rises to pH 8 in 2-3 weeks
14. MAIN PRODUCTS
• 55-60% presence of methane
• Can be used in variuos
purpose
Fuel gas
• Rich in nitrogen
• Used as good fertilizerMannure
15. PRE -REQUISITES TO SET UP
Minimum 45 kg dung needed daily
Should be placed near cowshed and where to
be used(less than 20 meters)
Should not be made within 15 meters of any
well
16. SEWAGE GAS
• CH4 -58.5-76.5% •CO2-30-41%
• H2S -0.1% •N2 -0.55% •O2-0-1.8%
• H2 -0-4.55%
Composition
• Produced during sewage
dosposal by way of aneorobic
decomposition of organic wastes
Origin
• Methane rich gas, can be used as town
gas component
• Higher H2S makes difficulty for engine
use
Usage
17. COAL GAS FROM UNDERGROUND
COAL GASIFICATION
• Coal in underground mines can egasified in situ
even without mining it out of the earth crust
• This is called underground coal gasification
(UCG)
• The gas produced us called coal gas from
underground gasification of coal
Origin
• CO-10.7% •H2-8.4% •CH4-1.8%
• N2-67.4% •O2-0.9% •CO2-10.5%
• CmHn-0.3%
Composition
18. • Electricity generation
• Manufacture of synthesis gas for
ammonia, methanol and liquid fuels
Usage
Suitable coal deposits for gasification using
air/oxygen:
Bituminus
Semi-
bituminus
Mature
brown
coal
COAL GAS FROM UNDERGROUND
GASIFICATION OF COAL(contd.)
20. PRINCIPLE OF UCG(contd.)
Deep vertical channels made parallely where coal
deposits are situated
They are made to supply gasifying medium and take out
product fuel gas
Link is made underground between them
In shaft system parallel galleries are made within coal
bed
Then connected by making horizontal borholes through
confined coal mass
Boreholes are ignited in succession or in small groups
Air is passsed through one borehole and product gas is
taken out from the other
