Engineering Chemistry S Datta

FUELS AND COMBUSTION 411
Q. 25. What is white gasoline?
Ans. It is unleaded gasoline used for motor boats.
Q. 26. Why is calorific value of coal gas higher than that of producer gas?
Ans. Coal gas contains all the combustible gases like CH 4
, C 2
H 4
, C 2
H 2
, CO and H 2
,
whereas producer gas contains CO, H 2
and N 2
. N 2
acts as inert diluent.
So calorific value of coal gas is higher than that of producer gas.
Q. 27. Producer gas is made by passing air and steam through a thick bed of
coal. Why?
Ans. The primary purpose of steam is to use up the heat developed during exothermic
reaction of coal and O 2
of air to maintain the temperature of producer.
Q. 28. Why is NCV greater than GCV?
Ans. Gross calorific value GCV includes the latent heat steam during combustion of a
fuel, but Net calorific value NCV excludes the latent heat of steam.
Q. 29. Why a good solid fuel must have low ash content?
fuel.
Ans. Ash is inorganic in nature. So high ash content decreases the calorific value of a
Q. 30. What is CNG?
Ans. CNG is compressed natural gas used in motor engines now-a-days instead of gasoline
fuel causing less pollution.
Q. 31. What is synthesis gas or syn gas?
Ans. Modern processes produce a mixture of CO and H 2
from coal and steam more
efficiently than the old water gas and producer gas plants. Two varieties of gas are obtained:
(i) Low heat gas (ii) Medium heat gas. Low heat gas contains 50% N 2
. These gases are known
as synthesis or syn gas. The gasification is done in fixed bed: (i) Fluidised bed.(ii) Entrained
bed.
Reactions:
(i) C + H 2
O = CO + H 2
(ii) CO + H 2
O = CO 2
+ H 2
(iii) C + CO 2
= 2CO
Q. 32. What is SNG (Substitute Natural Gas)?
Ans. (i) During the production of syn gas, at sufficiently high pressure i.e., during
hydrogasification H 2
liberated converts carbon to CH 4
.
cat
C + 2H 2
= CH 4
, CO + 3H 2
⎯⎯→
CH 4
+ H 2
O
The gas produced was known as synthetic natural gas. But the synthetic product cannot
be known as natural; so now it is called substitute natural gas (SNG). The operating pressure
may be atmospheric to 7 MPA and temperature 800°C-1650°C for gasification. The higher
pressure and lower temperature result in the formation of larger amount of SNG.