Questions
What is the need for “desalination of water” programme? #
Rise in population→water sources insufficient→desalination programme is required
Causes of Corrosion of boilers #
- Oxygen corrosion if boiler water is not properly deaerated.
- Electrochemical corrosion, also known as out of service corrosion, when boiler is shut down.
Disadvantages of scale formation in a boiler #
- Scales and sludges are bad conductors of heat, as a result fuel consumption increases.
- Tubes and plates are clogged as a result the efficiency of the boiler is decreased.
- Tubes of the boiler are corroded by the scales deposited and they may crack and lead to boiler failure.
Why is demineralisation preferred to zeolite softening? #
Free from all the ions whereas the zeolite softened water contains sodium salts which are sources of caustic embrittlement.
Why is chloramine preferred to Cl2 for sterilization of drinnking water? #
Chloramine does not impart any repulsive odour to the treated water
Criteria for drinking water #
Should be devoid of any suspending matter, and harmful dissolved matter of organic or inorganim matter and pathogenic organisms.
UV radiation superior to other methods of sterilization of water #
It does not impart any unpleasant taste or odour to the water and the process is simple
Pitting #
It is the corrosion of the boiler. Dissolved gases corrode the iron surface of the boiler near the rivet, bends and leads to leak or boiler failure.
Boiler compounds #
Chemicals are added to the boiler water to make scale loose and easily removable. These are called boiler compounds: flour, kerosene, tannin, agar-agar
Sludge vs Scale #
Sludge is soft, loose, slimy deposit formed inside the boiler (easier to remove) while scale is hard, sticky, adherent deposit on the inner surface of the boiler which is difficult to remove.
Harmful effects of silica present in water #
Presence of silica in the water leads to the formation of calcium and magnesium silicates and these silicates form sticky scales in the boiler which are very difficult to remove.
Alkalinity of water cannot be due to the simultaneous presence of OH⁻, CO₃²⁻ and HCO₃⁻ #
OH⁻ and HCO₃⁻ ions react to form CO₃²⁻ ions: OH⁻+HCO₃⁻=CO₃²⁻+H₂O