Boiler Water Hardness Limit

In treated waters alkalinity may also be contributed by hydroxide phosphate silicate and.

Boiler water hardness limit. Total alkalinity 600 ppm maximum. The purity requirements for any feed water depend on how much feed water is used as well as what the particular boiler design pressure heat transfer rate. 73 control feed of chemicals that prevent scale. Total hardness 1 ppm maximum.

Feed water boiler water characteristics as per is 10392 1982 1 feed water parameters upto 20 kg cm2 21 kg cm2 to 39 kg cm2 40 kg cm2 to 59 kg cm2 unit total hardness 10 1 0 0 5 ppm as caco 3 ph value 8 5 9 5 8 5 9 5 8 5 9 5 dissolved oxygen. It is desirable to keep the concentration of phosphates in the water to 30 50 ppm in order for complete reaction of the phosphates with the calcium hardness entering the. General guidelines to prevent corrosion and scaling in low pressure boilers are as follows. Crystals form crystals from scale.

Some impurities such as hardness iron and silica are of more concern for example than sodium salts. This can be written as. Small amounts of hardness and iron can get into the boiler. Feed water treatment to avoid corrosion make up water to steam boilers should be treated with oxygen scavengers to avoid serious corrosion problems.

Water treatment recommendations vary depending on the operating pressure of the boiler the application steam or hot water and other parameters. Maximum flow velocities in water systems water velocities in pipes and tubes should not exceed certain limits. Scale is a buildup of solid material formed on internal boiler surfaces when the concentration of impurities in the boiler water exceeds their solubility limit and precipitation occurs. An increase in temperature results in an increase in electrical conductivity.

A boiler that makes up 4000 gal day of water having 100 ppm of hardness has a potential of accumulating over 1000 pounds of scale per year. For boiler water the conductivity increases at the rate of approximately 2 of the value at 25 c for every 1 c increase in temperature. Asme limits conductivity 7000 umhos neutralized. Steam boiler rating and feed water temperature boiler output and feed water.

Conductivity control in the boiler. Total silica 150 ppm maximum. A serious loss of boiler efficiency and possibly boiler failure. A boiler water sample has an unneutralised conductivity of 5 000 μs cm at 25 c.

Deposition from low less than 1 0 ppm hardness boiler feedwater is eliminated with chelant programs and can be reduced by up to 95 by a good polymer phosphate treatment program. In order for this reaction to take place it is important to maintain a ph at a minimum value of 9 50. Phosphates are used to react with calcium hardness in the boiler water. Iron oxide is of particular concern in today s boiler water treatment programs.

Feed water purity is a matter both of quantity of impurities and nature of impurities. Alkalinity test in natural waters alkalinity is most commonly the result of bicarbonate and carbonate ions.