Requirement of Water for Steam Boiler

Fig.1: Water Tank of Steam Boiler
Water is only medium for generation of steam. In a steam boiler system, water is continuously fed as feedwater that is converted into steam and delivered constantly to main steam header. The quality of water is obviously an important factor to make steam boiler has maximum combustion & heat transfer efficiency, safe operation, minimum maintenance, and long working life. Good quality of water is a necessity for economic and efficient operation of a steam boiler.

There are various types of water processed and used in the steam boiler system:

§         Raw Water : raw water is available from nature. An unlimited quantity of raw water is available form ponds, lakes, rivers, and oceans.
§         Make up water: Make water is the water supplied from municipal water system, wells, and other sources, for addition of new water to the boiler required to replace the water converted to steam.
§         Steam condensate: When steam has performed its work, it transfers heat and reverts to liquid state called steam condensate.
§         Feedwater: Feedwater is the treated water that is stored in a water tank after necessary treatment.
§         Steam Boiler water: This is the water that circulates within the steam boiler system. Chemicals are injected into the steam boiler water, making it suitable for use under pressure in the system

Requirement of feed water before be supplied to steam boiler should be follow the following criteria:
§         Freedom from scale
Raw water contains hardness like dissolved salt, mainly calcium and magnesium compound, silica scale, iron deposit that is formed as iron oxide and accumulate on steam boiler surface. If hardness is present in the feedwater and not controlled chemically, then scaling of the heat transfer surfaces occur, reducing heat transfer and efficiency making frequent cleaning necessary. In extreme cases, local hot spots can occur, leading to mechanical damage or even tube failure.

§         Freedom from oxygen
Oxygen make the water corrosive, causing localized pitting of the steam boiler metal.

§         Freedom from acid attack
If the PH is too low, the acidic solution will attack metal surfaces of the steam boiler.

§         Freedom from caustic embrittlement
If the PH value is too high and the water is contain high alkaline solution that work itself into the crack may cause caustic embrittlemnet.

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