Common Water Impurities

The following factors indicate the problems that poor-quality water may cause to the engineering plant and to human health:

• Metal corrosion

• Scale formation on the heat transfer surface

• Dezincification

• Plumbosolvency

• Biological health hazards

Water supplies should never be assumed to be chemically pure. Groundwater from wells and springs contains dissolved impurities. Its properties depend

TABLE 4.13 Common Water Impurities

Constituent	Formula	Problems caused	Methods of treatment
Alkalinity	Bicarbonates (HCOj) Carbonates (CO-j) Hydroxyl (OH) as CaCO,,	Steam systems: foaming and solid carry over Steel embrittlement (HC03) and (CO,) Corrosion	Distillation Demmeralization lime and lime soda Dealkalization (ion exchange) Acid treatment hydrogen zeolite
Ammonia	NH,	Corrosion of copper He zinc alloys	Cation exchanger (hydrogen zeolite) Chlorinating Deaeration
Carbon Dioxide	CO,	Severe corrosion in condensate lines	Aeration Deaeration Alkalies (neutralization! Filming and neutralization amines
Chloride	Cl	Increases solid contents Produces a corrosive solution	Distillation Demmeralization
Color		Boiler foaming Presents problems with iron removal Discoloration of Manufactured product	Adsorption (activated carbon) Coagulation Filtration Chlorination
Conductance	US	Due to ionizing solids in solution; an increase in conductivity occurs resulting in corrosive water	Reduce dissolved solids by lime softening or demineralization
Dissolved solids		Caused by evaporation, in steam generation resulting in blockage and foaming Frequent blow down Loss of treated water L, oss of heat	Lime softening Distillation Cation exchange. (hydrogen zeolite) Demineralization
Fluoride	F	Few major industrial water problems Reduces dental decay	Alum coagulation Magnesium Hydroxide reaction Anion exchange Membrane separation
Free mineral acids	HC1 H2so4	Corrosion	Any process using alkalines to neutralize
Hydrogen sulphide	H2S	Corrosion (rotten egg smell)	Aeration Chlorination Ozone
Iron	Fe(II) (ferrous) Fe(III) (ferric)	Discolored water Deposits formed will foul surfaces	Coagulation and filtration Catalytic filtration Lime softening Aera tion

continues)

Constituent	Formula	Problems caused	Methods of treatment
Manganese	Mn(Il)	See iron	See iron
Nitrate	NO,	Increased solid content assists in the reduction of metal embrittlement Health problems with infants if used in foods	Distillation Demineralization
Oil		Scale Sludge Foaming Fouling of pipe work and heat exchangers	Baffle separators Strainers Coagulation Diatomaceous earth
Oxygen	0,	Severe metallic corrosion	Addition of corrosion inhibitors, sodium sulfite Automatic air vents, deaeration
PH	PH = log-^ H+	Graded into acidic or alkaline water Scale 0-14: 0 = highly acidic 7 = neutral 14 = highly alkaline	Increased by alkaline addition Decreased by The addition of acid
Silica	Si 0,	Scale buildup on Surrounding surfaces, reducing flow and heat transfer	Removed by applying hot magnesium salts Demmeralization Processes
Sulphate	So4	Increased solid content Combines with Ca to form calcium sulfate salt	Distillation Demineralization
Suspended Solids		Clogs pipelines Fouls heat exchanger Surfaces	Settling Filtration
Total solids		Sum of dissolved and suspended solids	See dissolved and suspended solids

On the nature of the ground over which it flows or passes through. Surface water from lakes and rivers contains silt, dissolved impurities, and organic matter; its quality varies widely depending on flow rate.

Table 4.13 lists and briefly describes some of the impurities found in typical water supplies. As can be seen, a wide range of problems have been considered, and no one method of treatment is suitable for all cases. The

Pharmaceutical industry and silicon chip manufacturers require the greatest purity in the water used.

Posted in INDUSTRIAL VENTILATION DESIGN GUIDEBOOK

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Common Water Impurities

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