Engineering Chemistry S Datta

402 ENGINEERING CHEMISTRY
This gas burns with a blue flame owing to high carbon monoxide content and hence
known as blue water gas. The bed of coke in the reactor is at 1400°C to 1000°C. As the reaction
is endothermic temperature gradually falls and when it comes to 1000°C the blast of steam is
stopped and air blast is passed and the following exothermic reactions occur.
C + O 2
⎯⎯→ CO 2
+ 97 kcal
2C + O 2
⎯⎯→ CO + 59 kcal
The reaction again rises and these cycles alternately take place to maintain the
temperature. After the production, ash is removed and the generator recharged. The water
gas passing through the superheater is cooled and then purified.
The average composition is H 2
: 51%, CO: 41%; N 2
: 4%, CO 2
: 4%
Blue water gas is used as a source of hydrogen, as a fuel gas.
The calorific value of water gas can be enhanced by adding gaseous hydrocarbons
(obtained from cracking crude oils) to get carburetted water gas (Calorific value 4500 kcal;
CO 2
→ 3%(m 3 )); composition of carburetted water gas is 35% H 2
, 25% CO, 35% saturated and
unsaturated hydrocarbons and 5% N 2
+ CO 2
.
Steam
Purge
steam
Oil
spray
Products of
combustion
Blast
of air
Tar separator
Cooler
Purifier
Fig. 18.14 Manufacture of carburetted water gas.
Biogas Production
Aquatic plants, organic wastes from domestic, agricultural and industrial sectors with
high B.O.D. value (Feed stock) are digested anaerobically to produce biogas. The biogas is
totally used as fuel. The chief constituent of biogas is methane, so the process is also called
biomethanation. Composition of biogas is given below:
Component
Volume%
CH 4
52-95
CO 2
9-45
H 2
S 0.001-2
H 2
0.01-2
N 2
0.1-4
O 2
0.02-6.5
CO 0.001
NH 3
Small