Q. Write short notes on priming and foaming.

Ans. Priming and foaming: When a boiler produces steam rapidly, some particles of the liquid water are carried along with the steam. This process of "Water-steam" formation is called priming. Priming is caused by the following reasons:

(1)         The presence of large amount of dissolved solids.

(2)         High steam velocities.

(3)         Sudden boiling.

(4)         Improper boiling design and

(5)         Sudden increase in steam production rate.

Foaming is the production foam or bubbles in boilers, which do not break easily. Foaming is due to presence of substances like oil.

Priming and foaming usually occur together. They are objectionable because

(1)         Dissolved salts in boiler water are carried by the wet steam to super-heater and turbine blades, where they get deposited as water evaporates. This water reduces their efficiency.

(2)         Dissolved salts may enter the parts of other machinery, where steam is being used, thereby decreasing the life of the machinery.

(3)         Actual height of the water column is judged properly; thereby making the maintenance of the boiler pressure becomes difficult.