What is priming, foaming and carrying over

What is priming, foaming and carrying over ? What are their disadvantages ? 

Priming, foaming and carryover all these phenomena occurs inside the boilers due to the improper composition of the boiler feed water. 

When the steam is produced rapidly inside the boiler at this time some small droplets of water are also carried along with the steam.

The steam which carries the water droplets along with them is known as wet steam which creates problems inside the boiler.

1. Priming :- 

priming is the process of formation of wet steam inside the boiler the phenomena occurs inside the boiler due to the rising of water in the boiler due to foaming. 

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Causes of priming :- this phenomenon inside the boiler occurs due to the certain reasons such as presence of large amount of dissolved solids in the water, very high level of water inside the boiler, high steam velocity, improper designing of boiler, and due to sudden increment in the production rate of steam which leads to the sudden boiling.  

Steps required for the prevention of priming :- 

-> by the use of mechanical steam purifier 

-> by keeping the water level lower 

-> by controlling rapid changes in the rates of steam

-> by using a proper boiler design

-> by using efficient softening and filtration of boiler feed water 

-> by blowing off sludge or scales from time to time

2. Foaming :- 

The phenomenon of formation of foam and bubble on the surface of water inside the boiler is called as foaming which becomes rigid by the time and did not break easily 

Causes :-

The process of foaming in the boiler feed water generally happens due to the presence of oil, grease, and alkalis in water and these substance reduces the surface tension of the boiler and causes foaming 

it may also cause due to the presence of finely divided sludge particles in the boiler feed water. 

Prevention method of foaming :- 

It can be prevented by adding coagulants like ferrous sulphate, sodium aluminate etc. because it removes oil,grease and finely sludge particles from boiler feed water. 

Another prevention method is by adding anti-foaming agents like caster oil spreads on the surface of water and neutralises the surface tension of the boiler feed water. 

Disadvantages of priming and foaming :- 

Priming and foaming often affects the efficiency of the boiler we have seen some of its disadvantages above now we will see some other disadvantages of priming and foaming 

-> due to the presence of water droplet in the steam may lead to the corrosion in the steam inlet ends of super heater it appears as a serious problem in the biollers because the replacement cost of the tube is huge  

-> height of the water column cannot be judged properly due to the foaming making also it affects the maintenance process of the boiler 

-> a part of dry salts may be carried along with the steam farther and deposits on the engine valves thereby decreasing their life 

3. Carry over :- 

The phenomenon of carrying water along with impurities by steam is called “carry over” ; this phenomenon mainly occurs due to priming and foaming.

the phenomena of priming and foaming usually occurs together and the  are objectionable because

• Dissolved solids or suspended solids in water carried by the wet steam to superheated and to the turbine blades and they get deposited over the blades of the turbines which decreases the efficiency of the boiler.

• Dissolved salts may enter to the parts of other machinery and then decrease their life. 

• The maintenance of the boiler pressure becomes difficult because of improper judgement of actual height of water. 

I hope the above mentioned information helped to gather knowledge about the phenomenon which occurs inside the boilers 

Thankyou

BY :- ADARSH GUPTA