which of the following fuels is expected to leave a residue on burning?
a). coal
b). petrol
c). LPG
d). CNG
Answers
Answer:
(a): coal
Explanation :Depending upon the efficiency of burning, the residue after coal combustion which is called "ash", may vary in composition. Real ash will contain oxides of silica, aluminium, iron, calcium. Etc. However, as told before, it may have varying amount of unburnt carbon.
The oxides of minerals might be further processed to recover trace elements like garmenium, zircon, etc. The unburnt carbon after enrichment may be used as domestic fuel, and also as activated carbon for water purification and absorpt.ion o.fbpolluting gas .
Now a days the fine ash particles which fly as fine particules from the top of chimnies, may be used in conjunction with portland cement as building materials. Some small quarz bubbles are also produced during high temp combustion in large pulverised fuel thermal power plants. They are very costly and highly demanded as the are light weight (like sp.gr. <0.6), germs free,and suitable for making floting bridges and causeways for military purposes.
in the olden days, before advent of portland cement, this "gensh" was mixed with fresh lime and used as morter for construction of standard building materials.
Thus, unburnt coal particles and purer mineral oxides are tried to be separated and used judiciously. India produces about 200 million tonne fly ash about 50% of which are used for making fly ash bricks, roads and road side embankments and filling up of low lying areas.
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