WTP Basic Question

7/30/2019 WTP Basic Question

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1. What are the Physical Properties of Water?2. What is the Chemical Composition of Water?3. At Temperatures Does Water Boil?4. Why is Steam Ideal for "Carrying" Heat Energy?5. Why is Water Not Always Satisfactory for Boiler Use?6. What General Type of Impurities Does Water Contain?7. What Dissolved Minerals Do Natural Waters Contain?8. What is Water Hardness?9. What Gases are Dissolved in Natural Waters?10.What Types of Other Impurities May Water Contain?11.What is the Difference between Sea Water and Fresh Water?12.What are the Sources of Fresh Water and How do they Vary in Composition?13.How Does Water Composition Vary from Geographical Standpoint?14.What is Boiler Feed Water?15.Is there any Relationship between Good water for drinking use and for Boiler Feed?16.How Pure Must Feed Water be?

17.How does Operating Pressure Influence Boiler Water Composition requirements?18.What is Meant by 'External' and 'Internal' Feed water Treatment?19.What Causes Boiler Deposits?20.Which are some Common Types of Boiler Deposits?21.What are the Characteristics of a carbonate deposit?22.What are the Characteristics of a Sulphate Deposit?23.What are the Characteristics of a Silica Deposit?24.What are the Characteristics of an Iron Deposit?25.What Problems do Deposits Cause?26.What is Corrosion?27.Where is Corrosion Usually Experienced?28.What is Corrosion Fatigue?29.What is Caustic Cracking?30.What Problems does Corrosion Cause?31.What Measures are taken to Prevent Boiler System Corrosion?32.What is Boiler Water Carry-over?33.What Causes Foaming?34.What Causes Priming?35.How Does Oil Affect Carry-over?36.How Do Suspended Solids Affect Carry-over?37.What is Selective Silica Carry-over?38.What Problems are Caused by Carry-over?39.What Measures are Usually Taken to Prevent Carry-over?

40.What is Clarification?41.What is Coagulation?42.What Various Types of Coagulants are Used?43.What is Chemical Precipitation?44.How Does Lime React in the softening Process ?45.How Does soda Ash React in the Softening Process?46.What are the Various Methods of Lime Soda Softening?47.Why are Coagulants Used in the Lime Soda Process?


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48.Under What Conditions Are Phosphate Softeners Use?49.What are the Disadvantages of Lime Soda Softening?50.What are the Advantages of Lime Soda Softening?51.What is Ion Exchange?52.What are the Various Types of Ion Exchange Materials?53.What is Boiler Water Carry-over?54.What are the Disadvantages of Ion Exchange?55.What are the Advantages of Ion Exchange?56.How Does Oil Affect Carry-over?57.How Do Suspended Solids Affect Carry-over?58.What is Selective Silica Carry-over?59.What Problems are Caused by Carry-over?60.What Measures are Usually Taken to Prevent Carry-over?61.What is Clarification?62.What is Coagulation?63.What Various Types of Coagulants are Used?

64.What is Chemical Precipitation?65.What is the Purpose of Deaeration?66.How are Evaporators Employed?67.What Combinations of External Treatment Methods are Generally Used?68.When is Internal Treatment of Boiler Feed water Necessary?69.What Should a Good Internal Water Treatment Programme Accomplish?70.What chemicals are Used in Internal Treatment?71.How are Carbonates Reacted on by Internal Treatment?72.How are Sulphates Reacted on by Internal Treatment?73.How is Silica Reacted upon by Internal Treatment?74.How is Sludge Conditioned in Internal Treatment?75.What Difficulties are Encountered in Internal Treatment?

76.What are the Advantages of Internal Treatment?77.How are Internal Treatment Chemicals Fed?78.How are Chemical Dosages Controlled?79.What Boiler Water Tests are Used for Treatment Control?80.What Tests are Usually Made as a Check for Contaminants?81.What Units are Used in Expressing Water Analysis Results?82.Why are some Analysis Results Express As CaCO2 E83.What is Blow-down?84.How much Blow-down is Needed?85.What Tests are Made in Regulating Blow-down?86.What is the Difference between Continuous and Puff Blow-down?

87.What Causes Corrosion in Steam Condensate Systems?88.How is Steam Condensate Corrosion Prevented?89.How do Chemical Oxygen Scavengers Help Control Condensate System Corrosion?90.What is the Basis for Choice between Neutralizing and Filming Inhibitors?91.What Characteristics Should a Good Condensate Corrosion Inhibitor Have?92.How are Deposits and Corrosion Prevented in Feed water Systems?93.What is the Wet Method of Boiler Lay-Up?


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94.What is the Dry Method of Boiler Lay-Up?

Answer to :backWhat are the Physical Properties of Water?Water is a tasteless, odorless, colourless liquid in its pure state. It is the only inorganic material which occurs in three forms(ice, water, steam) within the natural temperature range on earth. Because water can be converted to steam at a convenietemperature.

Answer to :backWhat is the Chemical Composition of Water?

Pure water is a simple combination of hydrogen and oxygen. The common formula is H2O. As a matter of general intereshowever, there are several 'hybrid' forms of water which are present in all supplies. Water contains about 300 ppm of

deuterium oxide (D.,O) or "heavy water". This doesn't quench thirst or make plants grow but in a pure form it has found umoderating nuclear reactors. Another form of water, tritium oxide (T2O), is made radioactive by cosmic rays. Although onminute fraction of water exists in this form, its radioactivity serves as a means of measuring the age of a water supply. Fo

practical purposes, though, only ordinary water (H2O) is considered for use in boilers.

Answer to :backAt Temperature Does Water Boil?

The boiling point of water depends on the pressure to which the water is subjected. At atmospheric pressure water boilsabout 100C. As pressure increases the boiling point also increases. At the critical pressure near 22.000kPa (where water be converted to steam without a change in volume) the boiling point is lowered. Under extreme vacuum conditions, water

boil at temperatures as low as 2C.

Answer to :backWhy is Steam Ideal for "Carrying" Heat Energy?

The Traditional formula was : 1 Btu raises 1 pound of water 1F. This can be converted to 4.2 kJ to raise 1 kg. of water 1takes an additional 2256 kJ/kg. to change 1 kg. of water (at the boiling point) to steam. This amount of heat (the heat o

vaporization) is then "stored" in the steam. When steam condenses, this heat energy is given off. Consider, for example, t

amount of heat which can be "carried" by 1 kg. of water. If the water temperature is originally 38C (100F) it takes 260 kJto heat it to 100C and 2256 kJ/kg. to convert it to steam. A total of 2516 kJ/kg. has been added and will be released as

water is condensed and cooled back to 38C. Since this transfer is never 100 percent efficient, some of the heat energy wi

dissipated in the process. But much of the heat from burning fuel can be absorbed by boiler water, transported with the steand released at the desired points.

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Why is Water Not Always Satisfactory for Boiler use?Completely pure water is nonexistent. All natural waters contain various types and amounts of impurities. Since water

impurities cause boiler problems, careful consideration must be given to the quality of the water used for generating stea


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What General Types of Impurities Does Water Contain?Impurities picked up by natural waters may be classed as : (a) dissolved solids, (b) dissolved gases, and (c) suspended ma

Water is a good solvent; it dissolves the rocks and soil it contacts. It dissolves gases from the air and gases given off fro

organics is the soil. It picks up suspended matter from the earth. It is also subject to contamination with trade wastes, oilsprocess materials. In general, the type of impurities water contains depends on what it contacts; the amount of impuritie

deepens on the contact times.

Answer to :backWhat Dissolved Minerals Do Natural Waters Contain?

The minerals which water picks up from rocks consist chiefly of calcium carbonate (limestone); magnesium carbonate(dolomite); calcium Sulphate (gypsum), magnesium Sulphate (Epsom salts); silica (sand); sodium chloride (common salt

sodium Sulphate (Glaubers salts); and small quantities of iron, manganese, fluorides, aluminum, and other substances. Wa

from mines and certain industrial processes make some surface waters very acin, while minerals in the earth make somground waters very alkaline. Sometimes Nitrates are found in water and in many cases, this is associate with sewage

contamination.

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What is Hardness?Waters which contain large amounts of calcium and magnesium minerals are "hard to wash with". The calcium and magne

compounds react with soap to form a curb in the water. These compounds are therefore referred to as water hardness. Tamount of hardness in a natural water may vary from several parts per million to over 500 parts per million. Since calcium

magnesium compounds are relatively insoluble in water, they tend to precipitate out to cause scale and deposit problem

Water hardness, therefore, is an important consideration in determining suitability of a water or use in generating steam

Answer to :backWhat Gases are Dissolved in Natural Waters?

Water dissolves varying amounts of air which is composed of 21% oxygen, 78% nitrogen, 1% other gases (including 0.0

0.06% carbon dioxide). Oxygen is soluble in water at room temperature and atmospheric pressure to the extent of abou9ppm. The solubility of oxygen decreases as the temperature of the water goes up, but water under pressure can hold lar

quantities of dissolved oxygen. Although nitrogen is dissolved in natural water it is inert gas and has little effect on thecharacter of water used in boilers. Water doesn't usually pick up more than 10 ppm of carbon dioxide from the air. Carbo

dioxide may be dissolved in water to a much greater extent, though, through the decay of vegetation and organics in the sHydrogen Sulphate and methane may be dissolved in some waters, but this is not a general occurrence. These gases, how

can be important when they occur as contaminants.

Answer to :backWhat Types of Other Impurities May Water Contain?

Natural waters may contain turbidity, colour, soil, and precipitated minerals, as well as oil and other trade wastes. Coloucomes from decaying vegetable matter. Turbidity may consist of very finely divided organic material and microorganisms,

well as suspended clay and silt. Oils, fats, greases, sewage and other wastes may contaminate water supplies.

Answer to :backWhat is the Difference between Sea Water and Fresh Water?

The main difference is in the amount of dissolved minerals. Sea water contains about 30 kg. of minerals per 1000 liters (mo


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salt). The mineral content of fresh water supplies is much lower and generally ranges form 5 g. to 1 kg. per 10001. While wis now in progress on methods of purifying sea and brackish water at the present time only fresh water supplies are gener

used for boiler feed purposes.

Answer to :backWhat are the Sources of Fresh Water and How do they Vary in Composition?

Fresh water supplies may be either surface water (rivers, streams, reservoirs, etc.) or ground water (shallow or deep wewaters). In general, ground water supplies are more consistent in composition and contain less suspended matter and turbthan surface supplies which are affected directly by rainfall, soil erosion, and trade wastes. On the other hand, ground waare usually harder than surface waters. For example, an average surface supply will contain about 95 ppm total hardnessopposed to an average of about 200 ppm total hardness for ground supplies. In some instances where the ground water

normally encountered in surface supplies.

Answer to :backHow Does Water Composition Vary from Geographical Standpoint?

Water composition varies throughout the states depending upon the type and strata of the earth formations. In the limest

areas the waters contain large quantities of calcium carbonate. In parts of the country where there is more of the granite tof rock formation, much less mineral matter is dissolved and the water will not contain much hardness. Throughout some sthere are deposits of alkali which the water will pick up. These are the general geographic variations, but local conditions in

area may greatly influence the composition of the water.

Answer to :backWhat is Boiler Feed Water?

The water added to a boiler to repave evaporation and blow-down losses is termed 'feed water'. In may cases, steam iscondensed and returned to the boiler as part of the feed water. Whatever water is needed to supplement the condensatreturned is termed 'make-up water'. The make-up water is usually natural water either in its raw state, or treated by som

process before use. Feed-water composition therefore depends on the quality of the make-up water and the amount ocondensate returned to the boiler.

Answer to :backIs there any Relationship between Good water for drinking use and for Boiler Feed?

Except that sewage pollution is harmful to both, there is not a great deal of similarity between the requirements for drinkawater and the requirements for boiler feed-water. The minerals in drinking water, while they might affect the taste, are

absorbed by the body and many so called 'health waters' are high in minerals. On the other hand, water impurities cannot

handled as well by boilers. Although a boiler is a mass of steel, it is generally more sensitive about what it consumes than ihuman stomach. For this reason, much care is needed in selecting water treatment.

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How Pure Must Feed Water be?Feed-water purity is a matter both of quantity of impurities and nature of impurities... some impurities such as hardness, and silica are of more concern, for example, than sodium salts, The purity requirements for any feed-water depend on homuch feed water is used as well as what the particular boiler design (pressure, heat transfer rate, etc.) can tolerate. Feewater purity requirements therefore can vary widely. A low pressure fire-tube boiler can usually tolerate high feed-wate

hardness with proper treatment while virtually all impurities must be removed from water used in some modern, high presboilers.


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Answer to :backHow does Operating Pressure Influence Boiler Water Composition requirements?

The Boiler and affiliated Industries Manufacturers' Association has established limits for boiler water composition with respto operating pressure to assure good quality steam. Pending the evolving of new, round figure ratios in S.I. units, we liter

convert the p.s.i.g. column below :BOILER PRESSURE TOTAL SOLIDSALKALINITY SUSPENDED

(kPa) (psig) (ppm) (ppm) solids silica*0-2070 0-300 3500 700 300 125

2070-3100 301-450 3000 600 250 903100-4135 451-600 2500 500 150 504135-5170 601-750 2000 400 100 355170-6200 751-900 150 300 60 206200-6890 901-1000 1250 25 40 86890-10335 1001-1500 1000 20 20 2.510335-13780 1501-2000 750 50 10 1.5over 13780 over 2000 500 100 5 0.5

(*) Silica limits based on limiting silica in steam to 0.02-0.03 ppm.Answer to :back

What is Meant by 'External' and 'Internal' Feed water Treatment?External treatment is the reduction or removal of impurities from water outside the boiler. In general, external treatment

used when the amount of one or more of the feed=water impurities is too high to be tolerated by the boiler system inquestion. There are many types of external treatment (softening, evaporation, deaerarion, etc.) which can be used to taimake feed-water for a particular system. Internal treatment is the conditioning of impurities within the boiler system. Th

reactions occur either in the feed lines or in the boiler proper. Internal treatment may be used alone or in conjunction wiexternal treatment. Its purpose is to properly react with feed water hardness, condition sludge, scavenge oxygen and prev

boiler water foaming.

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What Causes Boiler Deposits?Boiler scale is caused by impurities being precipitated out of the water directly on heat transfer surfaces or by suspendematter in water settling out on the metal and becoming hard and adherent. Evaporation in a boiler causes impurities to

concentrate. The high temperatures break down some minerals, cause others to become less soluble. In general, water contact with hot metal will tend to deposit out impurities as it evaporates.

Answer to :backWhich are some Common Types of Boiler Deposits?

In untreated boiler water, the formation of deposits is like a back to nature movement. That is as minerals are deposited from water they form many types of crystalline and rock like structures such as are encountered in the earth's strata. Depoare seldom composed of one constituent alone but are generally a mixture of various types of minerals, corrosion products

other water contaminants. The most common types of boiler deposits may contain : Calcium carbonate, Sulphate or silica


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magnesium hydroxide or silicate, iron oxide, and silica, sludge deposits form boiler water which has been treated may alcontain calcium and magnesium phosphates.

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What are the Characteristics of a carbonate deposit?A carbonate deposit is usually granular and sometimes of a very porous nature. The crystals of calcium carbonate are largeusually are matted together with finely divided particles of other materials so that the scale looks dense and uniform. A

carbonate deposit can be easily identified by dropping it in a solution of acid. Bubbles of carbon dioxide will effervesce fromscale.

Answer to :backWhat are the Characteristics of a Sulphate Deposit?

A Sulphate deposit is much harder and more dense than a carbonate deposit because the crystals are smaller and cemetogether tighter. A Sulphate deposit is brittle, does not pulverize easily, and does not effervesce when dropped into acid

Answer to :backWhat are the Characteristics of a Silica Deposit?

A high silica deposit is very hard, resembling porcelain. The crystal of silica are extremely small, forming a very dense animpervious scale. This scale is extremely brittle and very difficult to pulverize. It is not soluble in hydrochloric acid and is us

very light coloured.

Answer to :backWhat are the Characteristics of an Iron Deposit?

Iron deposits, due either to corrosion or iron contamination in the water, are very dark coloured. Iron deposits in boilers amost often magnetic. They are soluble in hot acid giving a dark brown coloured solution.

Answer to :backWhat Problems do Deposits Cause?

The biggest problem that deposits cause is overheating and failure of boiler tubes. A deposit acts as an insulator and excesdeposits prevent an efficient transfer of heat through the tubes to the circulating water. This causes the metal itself to bec

over heated. When the overheating is severe enough the metal fails. Boiler deposits can also cause plugging or partial

obstruction of corrosive attack underneath the deposits may occur. In general, boiler deposits can cut operating efficiencproduce boiler damage, cause unscheduled boiler outages, and increase cleaning expense.

Answer to :backWhat is Corrosion?

Stated simply, general corrosion is the reversion of a metal to it 's form. Iron, for example, reverts to iron oxide as the resu

corrosion. The process of corrosion, however is a complex electro chemical reaction and it takes many forms. Corrosion mproduce general attach over a large metal surface or it may result in pinpoint penetration of metal. While basic corrosion

boilers may be primarily due to reaction of the metal with oxygen, other factors such as stresses, acid conditions, and spechemical corrodents may have an important influence and produce different forms of attack.

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Where is Corrosion Usually Experienced?


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Corrosion may occur in the feed-water system as a result of low pH water and the presence of dissolved oxygen and carbdioxide. Corrosion in the boiler proper generally occurs when the boiler water alkalinity is low or when the metal is expose

oxygen bearing water either during operation or idle periods. High temperatures and stresses in the boiler metal tend to

accelerate the corrosive mechanisms. In the boiler metal tend to accelerate the corrosive mechanisms. In the steam ancondensate system corrosion is generally the result of c contamination with carbon dioxide and oxygen. Specific contamina

such as ammonia or sulphur bearing gases may increase attack on copper alloys in the system.

Answer to :backWhat is Corrosion Fatigue?

This type of cracking in boiler metal may occur by two different mechanisms. In the first mechanism, cyclic stresses such ascreated by rapid heating and cooling are concentrated at points where corrosion has roughened or pitted the metal surfaThis is usually associated with improper corrosion prevention. The second type of corrosion fatigue cracking occurs in boilwith properly treated water. In these cases corrosion fatigue is probably a misnomer. These cracks often originate where

metal surfaces are covered by a dense protective oxide film and cracking occurs from the action of applied cyclic stresse

Corrosion fatigue cracks are usually thick, blunt and cross the metal grains. They usually start at internal tube surfaces andmost often circumferential on the tube.

Answer to :backWhat is Caustic Cracking?

Caustic cracking (caustic embrittlement) is a serious type of boiler metal failure characterized by continuous, mostly integranular cracks. The following conditions appear to be necessary for this type of cracking to occur :

1. The metal must be stressed,2. the boiler-water must contain caustic,

3. at least a trace of silica must be present in the boiler-water, and4. some mechanisms, such as a slight leak, must be present to allow the boiler water to concentrate on

the stressed metal.

Answer to :backWhat Problems does Corrosion Cause?

Corrosion, in general, causes difficulty from two standpoints. The first is deterioration of the metal itself, and the seconddeposition of the corrosion products to form deposits. Generally, uniform corrosion of boiler surfaces is seldom of real concCorrosion, however, takes many insidious forms and deep pits resulting in only a minimum of iron loss may cause penetraand leaking of boiler tubes. Corrosion underneath certain types of boiler deposits can so weaken the metal that failure of tu

occurs. In steam condensate system, replacement of lines and equipment due to corrosion can be a costly problem.

Answer to :backWhat Measures are taken to Prevent Boiler System Corrosion?

Corrosion, in general, causes difficulty from two standpoints. The first is deterioration of the metal itself, and the seconddeposition of the corrosion products to form deposits. Generally, uniform corrosion of boiler surfaces is seldom of real concCorrosion, however, takes many insidious forms and deep pits resulting in only a minimum of iron loss may cause penetraand leaking of boiler tubes. Corrosion underneath certain types of boiler deposits can so weaken the metal that failure of tu

occurs. In steam condensate system, replacement of lines and equipment due to corrosion can be a costly problem.Why Water Treatment is Needed :

As feed-water enters a boiler the heat causes hardness (calcium and magnesium salts) to come out of solution. Untreatedhardness deposits on the hot boiler metal to from scale. As water evaporates in the boiler the feed-water impurities

concentrate. Even small amounts to iron, copper, and silica can accumulate in the boiler-water and cause serious depos


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problems in higher pressure boilers. Since scale can cause overheating and failure of boiler metal, preventive water treatmis needed. The corrosion of boiler system metal is a complex process and takes many forms: general attack, localized pitti

and various types of cracking in stressed metal. In general, the main factors causing corrosion are dissolved gases in the w

(primarily oxygen) and acid conditions. High temperatures speed up the corrosion process. Corrosion is damaging from sevstandpoints: it causes weakening and failure of metal and produces corrosion products which can cause boiler deposits. H

concentrations of dissolved and suspended matter in boiler-water can cause foaming of the water at the steam release surfThis produces carry-over of the water and its impurities into the steam. Carry-over results in deposits and other problemsturbines, engines and other processes using steam. While mechanical and operational factors also cause carry-over, prop

control of water conditions is important in producing pure steam.

Answer to :backWhat is Boiler Water Carryover?

Boiler water carry-over is the contamination of the steam with boiler-water solids. There are four common types of boiler-wcarry-over. In one bubbles or froth actually build up on the surface of the boiler-water and pass out with the steam. This

called foaming and can be compared to the stable foam found on beer. In the second type small droplets of water in the fof spray or mist are thrown up into the steam space by the bursting of the rising steam bubbles at the steam release surfaThis is sometimes called aquaglobejection Eand is like ginger ale or champagne where no stable foam is formed but dropof liquid are ejected from the liquid surface. The third condition of carry-over, called priming, is a sudden surge of boiler-wthat carries over with the steam, similar to the effects produced in uncapping a bottle of charged water. stem contaminat

may also occur from leakage of water through improperly designed or installed steam separating equipment in a boiler dru

Answer to :backWhat Causes Foaming?

Very high concentrations of any solids in boiler-water cause foaming. It is generally believed, however, that specific substa

such as alkalis, oils, fats, greases, certain types of organic matter and suspended solids are particularly conducive to foam

Answer to :backWhat Causes Priming?

Priming may be caused by improper construction of boiler, excessive ratings, or sudden fluctuations in steam demand. prim

is sometimes aggravated by impurities in the boiler-water

Answer to :backHow Does Oil Affect Carryover?

Oil contamination in boiler feed-water, usually form reciprocating engines, pumps, etc., can cause serious foaming. This

generally attributed to the formation of soaps in the boiler-water due to specification of the oil by boiler-water alkalis.

Answer to :backHow Do Suspended Solids Affect Carryover?

The theory advanced is that suspended solids collect in the surface film surrounding a steam bubble and make it tougher. steam bubble therefore resists breaking and builds up a foam. It is believed that the finer the suspended particles the gre

their collection in the bubble. Experience indicates, however, that many boilers operate with exceedingly high suspended swithout carry-over while others have carry-over with only a trace of suspended solids. This would seem to indicate that t

type as well as the quantity of suspended solids has much to do with carry-over.

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What is Selective Silica Carryover?Silica can carry over into the steam in two ways. It can be present in the steam as the result of general boiler-water carry-or it can go into steam in a volatile form. In the latter case silica acts much like a gas and is considered to be selectively ca

over. As Pressures increase above 2760 kPa (400 p.s.i), there is an increased tendency for silica to be selectively carried ithe steam in amounts proportionate to the amount of silica in the boiler-water.

Answer to :backWhat Problems are Caused by Carry-over?

The disadvantages of wet steam include a general decrease in operating efficiency and erosion of turbines and engines. addition any dissolved or suspended solids in the boiler-water tend to deposit out in the steam and condensate system,. w

the solids deposit in super heaters and turbine, overheating and failure of superheated tubes and reduction in turbine efficican result. Impurities carried over with the can cause difficulties in many processes for which the steam is used.

Answer to :backWhat Measures are Usually Taken to Prevent Carryover?

The most common measure is to maintain the concentration of solids in the boiler water at reasonably low levels. Avoiding

water levels, excessive boiler loads, and sudden load changes also helps. Very often contaminated condensate returned toboiler system causes carry-over problems. In these cases the condensate should be temporarily wasted until the source

contamination is found and eliminated. The use of chemical anti-foam agents can be very effective in preventing carry-over

to high concentrations of impurities in the boiler-water.Removing Impurities from Water :

Coagulants are chemicals to enmesh fine particles of suspended matter in a water supply to form a flock which settles or be filtered out. Adding softening chemicals (lime, soda, ash, etc.) to a water causes some dissolved hardness salts to

precipitate and the suspended matter can then be coagulated and filtered out. Precipitation processes such as lime sod

softening can effectively remove suspended matter, hardness and alkalinity and in some cases reduce the silica content ofwater. When a salt dissolves in water it forms positive ions (cations) and negative ions (anions). For example, calcium

carbonate (CaCO3) forms a calcium cation (Ca++) and a carbonate anion (CO3=). The most common form of ion exchan

involves passing water through material which substitutes sodium for calcium and magnesium cations. This is a typicalsoftening treatment. Anions can also be removed from water by the use of special ion exchange resins. Demineralization

complete removal of dissolved minerals involves the use of both cation and anion exchange materials. In removing impurifrom water there are many possible combinations of coagulation, precipitation and ion exchange methods. Other methods

treatment include: deaerarion (heating the water and venting the gases) for reduction of oxygen and carbon dioxide; anevaporation to produce distilled water.

Answer to :backWhat is Clarification?

Clarification is the removal of suspended matter and/or colour from water supplies. The suspended matter may consist of lparticles which settle out readily. In these cases clarification equipment merely involves the use of settling basins and/or fil

Most often, however, suspended matter in water consists of particles so small that they do not settle out and even passthrough filters. The removal of these finely divided or colloidal substances therefore requires the use of coagulants.

Answer to :backWhat is Coagulation?

Coagulation is the clumping together of finely divided and colloidal impurities in water into masses which will settle rapidand/or can be filtered out of the water. Colloidal particles have large surface areas which keep them in suspension and i

addition the particles have negative electrical charges which cause them to repel each other and resist adhering togetheCoagulation, therefore, involves neutralizing the negative charges and providing a nucleus for the suspended particles t


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adhere to.

Answer to :backWhat Various Types of Coagulants are Used?

The most common coagulants are iron and aluminum salts such as ferric Sulphate, ferric chloride, aluminum Sulphate (aluand sodium acuminate. Ferric and alumina ions each have three positive charges and therefore their effectiveness is relat

their ability to react with the negatively charged colloidal particles. With proper use these coagulants form a flock in the wwhich serves as a kind of net for collecting suspended matter. In recent years synthetic materials called polyelectrolyte ha

been developed for coagulation purposes. these consist of long chain like molecules with positive charges. In some caseorganic polymers and special types of clay are used in the coagulation in making the flock heavier, causing it to settle out m

rapidly.

Answer to :backWhat is Chemical Precipitation?

In precipitating processes the chemicals added react with dissolved minerals in the water to produce a relatively insolubreaction product. Precipitation methods are used in reducing dissolved hardness, alkalinity and in some silica. The most

common example of chemical precipitation in water treatment is lime soda softening.

Answer to :backHow Does Lime React in the softening Process ?

Hydrated lime (calcium hydroxide) reacts with soluble calcium and magnesium bicarbonates to form insoluble precipitates.

is shown by the following equations:Ca(OH)2 + Ca(HCO3)2 ======> 2CaCO3 + 2H2OLime Calcium Calcium Water

Bicarbonate Carbonate

Ca(OH)2 + Mg(HCO3)2 ======> Mg(OH)2 + 2CaCO3 + 2H2OLime Magnesium Magnesium Calcium Water

Bicarbonate Hydroxide Carbonate Most of the calcium carbonate and magnesium hydroxide come out of solution as a sludge and can be removed by settlingfiltration. Lime, therefore, can be used to reduce hardness present in the bicarbonate form (temporary hardness) as well decrease the amount of bicarbonate alkalinity in a water. Lime reacts with magnesium Sulphate and chloride and precipitamagnesium hydroxides but in this process soluble calcium Sulphate and chloride are formed. Lime is not effective in remov

calcium Sulphate and chlorides.

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How Does soda Ash React in the Softening Process?Soda ash is used primarily to reduce non-bicarbonate hardness (also called Sulphate hardness or permanent hardness).

reacts as follows:Na2CO3 + CaSO4 ======> CaCO3 + Na2SO4Soda Ash Calcium Calcium Sodium

Sulphate Carbonate SulphateNa2CO3 + CaC12 ======> CaCO2 + 2NaCl

Calcium Calcium SodiumChloride Carbonate Chloride

The calcium carbonate formed by the reaction tends to come out of solution as a sludge. The sodium Sulphate and chlorformed are highly soluble and non-scale forming.

Answer to :backWhat are the Various Methods of Lime Soda Softening?

The two general types are intermittent (batch type) and continuous. The older method of intermittent softening consists mixing the chemicals with the water in a tank, allowing time for reaction and settling of the sludge, and drawing off the c

water. The more modern method of continuous lime soda softening involves the use of specially compartmented tanks wprovisions for

1. proportioning chemicals continuously to the incoming water2. retention time for chemical reactions and settling of sludge, and

3. continuous draw-off of softened water. Lime soda softening may also be classified as hot or cold,

depending on the temperature of the water. Hot process softeners increase the rate of chemicalreactions and give better quality water.

Answer to :backWhy are Coagulants Used in the Lime-Soda Process?

Just as coagulants are used for removing suspended matter in clarification processes, they serve to clump together precipitin the softening process. Coagulants can speed up settling of sludge as much as 25 - 50 per cent. Sodium acuminate has

special advantage as a coagulant in lime soda softening since unlike most other coagulants it is alkaline and also contributethe softening redactions, particularly in reducing magnesium. Effective use of coagulants helps remove silica in the soften

process. Silica tends to be absorbed in the flock produced by coagulation of sludge.

Answer to :backUnder What Conditions Are Phosphate Softeners Use?

Sodium phosphates react readily with calcium and magnesium salts. Phosphate softeners are generally used only on natur

soft or pre softened waters, however, because relatively high amounts of magnesium in the water cause a very stickyprecipitate in reacting with phosphate. Properly used, phosphate softeners can effectively reduce hardness to very low lev


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Improved ion exchange softening methods have largely supplanted phosphate softeners in new installations.

Answer to :backWhat are the Disadvantages of Lime Soda Softening?

The main disadvantage is that while hardness is reduced it is not completely removed. Wide variations in raw watercomposition and flow rate also make control of this method difficult since this involves adjusting the amounts of lime and s

ash being fed.

Answer to :backWhat are the Advantages of Lime Soda Softening?

The main advantage is that in reducing hardness, alkalinity and silica can also be reduced. In addition, prior clarification ofwater is not usually necessary since suspended matter and turbidity are also removed in the process. Another advantage is

with continuous hot process softening some removal of oxygen and carbon dioxide can be achieved.

Answer to :back

What is Ion Exchange?When minerals dissolve in water they form electrically charge particles called ions. Calcium carbonate, for example, formscalcium ion with plus charges (a cation) and a carbonate ion with negative charges (an anion). Certain natural and synthematerials have the ability to remove mineral ions from water in exchange for others. For example, in passing water througsimple cation exchange softener all of calcium and magnesium ions are removed and replaced with sodium ions. Ion exchamaterials usually are provided in the form of small beads or crystals which compose a bed several feet deep through which

water is passed.

Answer to :backWhat are the Various Types of Ion Exchange Materials?

Ion exchange materials are basically of two types: cation and anion exchangers. Cation exchange materials react only wi

positively charged ions such as Ca++ and Mh++. Anion exchanger materials react only with the negatively charged ions sas carbonate (CO3) and Sulphate (SO4). Zeolite materials are cation exchangers composed chiefly of sodium, aluminum a

silica. There are several other types of cation exchange materials of an organic or resinous nature. The anion materials ausually organic in nature and are of two basic types: weak base and strong base types. Weak base exchangers dont take

carbon dioxide or silica (actually carbonic acid and silica acid) but remove strong acid anions by a process that is more lik

adsorption than ion exchange. Strong base anion exchangers on the other hand can reduce silica and carbon dioxide to vlow values. Cation exchangers usually opals which settle out readily. In these cases clarification equipment merely involvesuse of settling basins and/irate on either a sodium or hydrogen cycle E That is, they may be designed to replace all cationthe water with either sodium or hydrogen. Strong base anion exchangers are generally operated on a hydroxide weak base

a carbonate cycle. Chloride anion exchange is also used in some processes.Why Water Treatment is Needed :

As feed-water enters a boiler the heat causes hardness (calcium and magnesium salts) to come out of solution. Untreatedhardness deposits on the hot boiler metal to from scale. As water evaporates in the boiler the feed-water impurities

concentrate. Even small amounts to iron, copper, and silica can accumulate in the boiler-water and cause serious deposproblems in higher pressure boilers. Since scale can cause overheating and failure of boiler metal, preventive water treatmis needed. The corrosion of boiler system metal is a complex process and takes many forms: general attack, localized pitti

and various types of cracking in stressed metal. In general, the main factors causing corrosion are dissolved gases in the w(primarily oxygen) and acid conditions. High temperatures speed up the corrosion process. Corrosion is damaging from sevstandpoints: it causes weakening and failure of metal and produces corrosion products which can cause boiler deposits. H

concentrations of dissolved and suspended matter in boiler-water can cause foaming of the water at the steam release surfThis produces carry-over of the water and its impurities into the steam. Carry-over results in deposits and other problems


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turbines, engines and other processes using steam. While mechanical and operational factors also cause carry-over, propcontrol of water conditions is important in producing pure steam.

Answer to :back

What is Boiler Water Carryover?Boiler water carry-over is the contamination of the steam with boiler-water solids. There are four common types of boiler-wcarry-over. In one bubbles or froth actually build up on the surface of the boiler-water and pass out with the steam. This

called foaming and can be compared to the stable foam found on beer. In the second type small droplets of water in the fof spray or mist are thrown up into the steam space by the bursting of the rising steam bubbles at the steam release surfaThis is sometimes called aquaglobejection Eand is like ginger ale or champagne where no stable foam is formed but dropof liquid are ejected from the liquid surface. The third condition of carry-over, called priming, is a sudden surge of boiler-wthat carries over with the steam, similar to the effects produced in uncapping a bottle of charged water. stem contaminatmay also occur from leakage of water through improperly designed or installed steam separating equipment in a boiler dru

Answer to :backWhat are the Disadvantages of Ion Exchange?

The main disadvantage with sodium cycle ion exchange softening is that the total solids, alkalinity and silica contents of traw water are not reduce. A problem encountered with cation exchange on the hydrogen cycle is corrosion from acidity of

effluent. With demineralization the chief difficulties are with cost particularly on high solids raw waters, and the corrosiv

nature of the effluent water. In general, fouling of the ion exchange material with suspended or colloidal matter in the rawater can produce difficulties and some water impurities cause degradation of the material. In many cases, therefore, io

exchange processes require pretreatment of the water supply.

Answer to :backWhat are the Advantages of Ion Exchange?

The main advantage of zeolite softening is ease of control. Ordinary variations of hardness in the raw water or in flow rate

not affect completeness of softening. Also the system generally takes up less space than the lime-soda system and in mocases gives a softer water. The use of acid exchangers has advantages when a low alkalinity soft water is required. The madvantage of ion exchange demineralization is its ability to produce better quality water than can be obtained by any oth

method.

Answer to :backHow Does Oil Affect Carry-over?

Oil contamination in boiler feed-water, usually form reciprocating engines, pumps, etc., can cause serious foaming. This

generally attributed to the formation of soaps in the boiler-water due to specification of the oil by boiler-water alkalis.

Answer to :backHow Do Suspended Solids Affect Carry-over?

The theory advanced is that suspended solids collect in the surface film surrounding a steam bubble and make it tougher. steam bubble therefore resists breaking and builds up a foam. It is believed that the finer the suspended particles the gre

their collection in the bubble. Experience indicates, however, that many boilers operate with exceedingly high suspended swithout carry-over while others have carry-over with only a trace of suspended solids. This would seem to indicate that t

type as well as the quantity of suspended solids has much to do with carry-over.

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What is Selective Silica Carry-over?Silica can carry over into the steam in two ways. It can be present in the steam as the result of general boiler-water carry-or it can go into steam in a volatile form. In the latter case silica acts much like a gas and is considered to be selectively ca

over. As Pressures increase above 2760 kPa (400 p.s.i), there is an increased tendency for silica to be selectively carried ithe steam in amounts proportionate to the amount of silica in the boiler-water.

Answer to :backWhat Problems are Caused by Carry-over?

The disadvantages of wet steam include a general decrease in operating efficiency and erosion of turbines and engines. addition any dissolved or suspended solids in the boiler-water tend to deposit out in the steam and condensate system,. w

the solids deposit in super heaters and turbine, overheating and failure of superheated tubes and reduction in turbine efficican result. Impurities carried over with the can cause difficulties in many processes for which the steam is used.

Answer to :backWhat Measures are Usually Taken to Prevent Carry-over?

The most common measure is to maintain the concentration of solids in the boiler water at reasonably low levels. Avoiding

water levels, excessive boiler loads, and sudden load changes also helps. Very often contaminated condensate returned toboiler system causes carry-over problems. In these cases the condensate should be temporarily wasted until the source

contamination is found and eliminated. The use of chemical anti-foam agents can be very effective in preventing carry-over

to high concentrations of impurities in the boiler-water.Removing Impurities from Water :

Coagulants are chemicals to enmesh fine particles of suspended matter in a water supply to form a flock which settles or be filtered out. Adding softening chemicals (lime, soda, ash, etc.) to a water causes some dissolved hardness salts to

precipitate and the suspended matter can then be coagulated and filtered out. Precipitation processes such as lime sod

softening can effectively remove suspended matter, hardness and alkalinity and in some cases reduce the silica content ofwater. When a salt dissolves in water it forms positive ions (cations) and negative ions (anions). For example, calcium

carbonate (CaCO3) forms a calcium cation (Ca++) and a carbonate anion (CO3). The most common form of ion exchang

involves passing water through material which substitutes sodium for calcium and magnesium cations. This is a typicalsoftening treatment. Anions can also be removed from water by the use of special ion exchange resins. Demineralization

complete removal of dissolved minerals involves the use of both cation and anion exchange materials. In removing impurifrom water there are many possible combinations of coagulation, precipitation and ion exchange methods. Other methods

treatment include: deaerarion (heating the water and venting the gases) for reduction of oxygen and carbon dioxide; anevaporation to produce distilled water.

Answer to :back

Answer to :back

What is Coagulation?Coagulation is the clumping together of finely divided and colloidal impurities in water into masses which will settle rapidand/or can be filtered out of the water. Colloidal particles have large surface areas which keep them in suspension and i

addition the particles have negative electrical charges which cause them to repel each other and resist adhering togetheCoagulation, therefore, involves neutralizing the negative charges and providing a nucleus for the suspended particles t

adhere to.


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Answer to :backWhat Various Types of Coagulants are Used?

The most common coagulants are iron and aluminum salts such as ferric Sulphate, ferric chloride, aluminum Sulphate (alu

and sodium acuminate. Ferric and alumina ions each have three positive charges and therefore their effectiveness is relattheir ability to react with the negatively charged colloidal particles. With proper use these coagulants form a flock in the w

which serves as a kind of net for collecting suspended matter. In recent years synthetic materials called polyelectrolyte habeen developed for coagulation purposes. these consist of long chain like molecules with positive charges. In some case

organic polymers and special types of clay are used in the coagulation in making the flock heavier, causing it to settle out mrapidly.

Answer to :backWhat is Chemical Precipitation?

In precipitating processes the chemicals added react with dissolved minerals in the water to produce a relatively insolubreaction product. Precipitation methods are used in reducing dissolved hardness, alkalinity and in some silica. The most

common example of chemical precipitation in water treatment is lime-soda softening.

Answer to :backWhat is the Purpose of Deaeration?

Since dissolved oxygen in water is a big factor in corrosion in boiler systems it is desirable that this be removed before th

water is put into a boiler. Feed-water deaerarion is accomplished by intimately mixing the water and steam in a deaeratiheater. Part of the steam is vented, arraying with it the bulk of the dissolved oxygen from the water. There are two basic t

of steam deaerators: the spray type and the tray type. In the spray deaerator a jet of steam mixes intimately with the fewater being sprayed into the unit. In the tray type the incoming water is allowed to fall over a series of trays causing the w

to be broken up into small droplets to permit intimate contact with incoming steam.

Answer to :back

How are Evaporators Employed?Water is sometimes pretreated by evaporation to produce relatively pure vapor which is then condensed and used for boifeed purposes. Evaporators are of several different types, the simplest being a tank of water through which steam coils a

passed to heat the water to the boiling point. Sometimes to increase the efficiency the vapor from the first tank is passethrough coils in a second tank of water to produce additional heating and evaporation. Other types of evaporation includeflash type which operates under a partial vacuum causing a lowering of the boiling point of water and evaporation at lowtemperatures. Evaporators have advantages where steam as a sources of heat is readily available. They also have particu

advantages over demineralization, for example, when the dissolved solids in the raw water are very high.

Answer to :backWhat Combinations of External Treatment Methods are Generally Used?

As mentioned previously, water containing suspended solids, organics, and/or turbidity usually requires clarifications prior texchange methods. Also, since simple cation exchange does not reduce the total solids of the water supply, it is sometim

used in conjunction with precipitation type softening. One of the most common and efficient combination treatments is thelime-zeolite process. This involves pretreatment of the water with lime to reduce hardness, alkalinity and in some cases si

and subsequent treatment with a cation exchange softener. This system of treatment accomplishes several functions:softening, alkalinity and silica reduction, some oxygen reduction, and removal of suspended matter and turbidity.

Answer to :backWhen is Internal Treatment of Boiler Feed-water Necessary?


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Chemical treatment of water inside the boiler is usually essential whether or not the water has been pretreated. Internatreatment, therefore, complements external treatment by taking care of any impurities entering the boiler with the feed w(hardness, oxygen, silica, etc.) regardless of whether the quantity is large or small. In many cases external treatment of t

water supply is not necessary and the water can be treated by internal methods alone. Internal treatment can constitute sole treatment when boilers operate at low or moderate pressure, when large amounts of condensed steam are used for f

water, or when the raw water available is of good quality.

Answer to :backWhat Should a Good Internal Water Treatment Programme Accomplish?

The purpose of an internal treatment programme is fourfold: (1) react with any feed-water hardness and prevent it fromprecipitating on the boiler metal as scale, (2) condition any suspended matter such as hardness sludge or iron oxide in th

boiler and make it non-adherent to the boiler metal, (3) provide anti-foam protection to permit a reasonable concentrationdissolved and suspended solids in the boiler water without foam carry-over, and (4) eliminate oxygen from the water anprovide enough alkalinity to prevent boiler corrosion. In addition, as supplementary measures an internal treatment shou

prevent corrosion and scaling of the feed-water system and protect against corrosion in the steam condensate systems

Answer to :backWhat chemicals are Used in Internal Treatment?

The softening chemicals used include soda ash, caustic and various types of sodium phosphates. These chemicals react w

calcium and magnesium compounds in the feed water. At times sodium silicate is used to contributed alkalinity as well as rselectively with magnesium hardness. The materials used for conditioning sludge include various organic materials of th

tannin, lignin or alginate classes. It is important that these organics are so selected and processed that they are both effecand stand stable at the boiler operating pressure. Certain synthetic organic materials are used as anti-foam agents. Thechemicals used to scavenge oxygen include sodium sulphite and hydrazine. Various combinations of polyphosphates an

organics are used for preventing scale and corrosion in feed-water systems. Volatile neutralizing amines and filming inhibitare used for preventing condensate corrosion.

Answer to :backHow are Carbonates Reacted on by Internal Treatment?

Calcium bicarbonate entering with the feed water is broken down at boiler temperatures or reacts with caustic soda to focalcium carbonate. Since calcium carbonate is relatively insoluble it tends to come out of solution. Sodium carbonate partibreaks down at high temperature to sodium hydroxide (caustic) and carbon dioxide. When phosphates are used in intern

treatment they react with calcium carbonate to form calcium phosphate and sodium carbonate (soda ash). In the presencsufficient hydroxides (caustic) alkalinity, magnesium bicarbonate will precipitate as magnesium hydroxide or will react with

silica present to form magnesium silicate. The minerals precipitated from solution (calcium carbonate, calcium phosphatmagnesium hydroxide, magnesium silicate, etc..) form sludge in the water which must be conditioned to prevent its stickin

the metal. The conditioned sludge is removed from the boiler by blow-down.

Answer to :back

How are Sulphates Reacted on by Internal Treatment?High temperatures in the boiler water reduce the solubility of calcium Sulphate and tend to make it precipitate out directlythe boiler metal as scale. Consequently calcium Sulphate must be reacted upon chemically to cause a precipitate to form in

water where it can be conditioned and removed by blow-down. Calcium Sulphate is reacted on either by sodium carbonasodium phosphate or sodium silicate to form insoluble calcium carbonate, phosphate or silicate. Magnesium Sulphate is reaupon by caustic soda to form a precipitate of magnesium hydroxide. some magnesium may react with silica to form magne

silicate. Sodium Sulphate is highly soluble and remains in solution unless the water is evaporated almost to dryness.


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Answer to :backHow is Silica Reacted upon by Internal Treatment?

In untreated waters silica tends to precipitate out directly as scale at hot spots on the boiler metal or it may combine witcalcium to produce a hard calcium silicate scale. Treatment for silica involves keeping the boiler-water alkalinity high enoug

hold silica in solution. Usually there is enough magnesium in the water to precipitate some of the silica as sludge. At timproper treatment with magnesium can tie up silica when it is a special problem. Some organic materials such as starches t

to prevent the adherence of silica to the boiler metal probably by a physical action.

Answer to :backHow is Sludge Conditioned in Internal Treatment?

There are two general approaches to conditioning sludge inside a boiler: by coagulation or dispersion. When the total amoof sludge is great (as the result of high feed-water hardness) it is practical to coagulate the sludge to form large flocculeparticles. This flow readily with the boiler water and can be removed by blow-down. This can be accomplished by carefu

adjustment of the amounts of alkalis, phosphates and organics used for treatment, based on the fee-water analysis. Whenamount of sludge is not great (low hardness feed-waters) it is more practical to use a higher percentage of phosphates in treatment. Phosphates form finely divided sludge particles. A higher percentage of organic sludge dispersants is used in t

treatment to keep the sludge particles dispersed throughout the boiler water.

Answer to :backWhat Difficulties are Encountered in Internal Treatment?

The main difficulty is the presence of a large amount of sludge formed when feed-water hardness is high. This may increathe amount of blow-down required. When internal treatment is used alone (without pretreatment of the water by extern

means) there is more possibility for scale in the pre-boiler system and fee-water lines. it is important that someone experiein the technology helps to set up an internal treatment programme which will minimize these difficulties.

Answer to :backWhat are the Advantages of Internal Treatment?

The prime advantage is that in many instances internal treatment can eliminate the need for extensive external treatmeequipment. This gives a definite economic advantage. In addition, the simplicity of an internal treatment programme offerdecided savings in manpower for feeding and control. A qualified consultant can help decide what water quality is required

a specific boiler system, and choose the most economical means of obtaining the required quality.

Answer to :backHow are Internal Treatment Chemicals Fed?

Common feeding methods include the use of chemical solution tanks and proportioning pumps or special ball briquettechemical feeders. In general, softening chemical (phosphates, soda ash, caustic, etc.) are added directly to the fee-water

point near the entrance to the boiler drum. They may also be fed through a separate line discharging in the feed-water druthe boiler. The chemicals should discharge in the fee-water section of the boiler so that reactions occur in the water befor

enters the steam generating areas. Softening chemicals may be added continuously or intermittently depending on feed-whardiness and other factors. Chemicals added to react with dissolved oxygen (Sulphate, hydrazine, etc.) preferably shouldfed continuously as far back in the feed-water system as possible. Similarly, chemicals used to prevent scale and corrosion

the feed-water system (polyphosphates, organics, etc.) should be fed continuously. Chemicals used to prevent condensasystem corrosion may be fed directly to the steam or into the feed-water system, depending on the specific chemical use

continuous feeding is preferred but intermittent application will suffice in some cases.


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Answer to :backHow are Chemical Dosages Controlled?

Chemical dosages are based primarily on the amount of impurities in the feed-water. For example, the amount of softeni

chemicals needed depends on fee-water hardness; the amount of sodium Sulphate needed depends on the amount ofdissolved oxygen in the feed-water. In addition, however, a set amount of extra chemical treatment is added to provide

residual is alkies of insurance and serves as the basis for treatment control.

Answer to :backWhat Boiler Water Tests are Used for Treatment Control?

Routine control test of the boiler water vary according to the type of chemical treatment used but they may include tests alkalinity M phosphate, Sulphate and organic color. Boiler water hardness tests are not often made because it is general

assumed that if there is enough alkalinity and/or phosphate present in the boiler-water, the hardness has reacted completIn testing for Sulphate it is assumed that if an adequate residual is present, the feed-water oxygen has been removed; th

may not always be true, especially if the Sulphate feed is not continuous and if ordinary unanalyzed sodium Sulphate is us

Generally antifoams are incorporated in organic treatments so testing for organic color gives an indication both of sludgconditioner present as well as level of antifoam treatment.

Answer to :backWhat Tests are Usually Made as a Check for Contaminants?

Here, again, the specific tests made vary with the type of contamination suspected. Some checks made fairly often, howevinclude test for: iron, oil and silica. Usually the iron test serves as a check on corrosion products brought back with the

condensate but may also be used when appreciable iron is present in the make up water. Oil tests usually require laboratfacilities but visual inspection of samples can show up gross contamination. While silica is usually present to some extent

boiler waters, periodic checks are sometimes made to detect unusual contamination or to indicate when additional blow-do

is needed to keep silica concentrations below a preset limit.

Answer to :backWhat Units are Used in Expressing Water Analysis Results?

The most common unit is parts per million. One p.p.m. of a substance in a water sample represents one unit mass of th

substance in each million unit mass of the water. For example, one p.p.m of salt (NaCl) means one kg of salt per million kwater. There is still some diehard use of the classic unit grains per gallon (g.p.g.) but this expected to disappear due to

universal S.I. usage as will the unit equivalents per million (e.p.m). This mention is therefore made merely as a matter orecord.

Answer to :backWhy are some Analysis Results Express As CaCO2 E

Water treatment reactions are based on the combining mass of the reacting substances. For example, 106 kilograms of soash (molecular mass 106) reacts with 136 kilograms of calcium Sulphate (molecular weight 136). The molecular mass ocalcium carbonate (CaCO3) is the round number 100. In order to simplify chemical dosage calculations all hardness and

alkalinity results are usually based on the molecular mass of calcium carbonate and are expressed as CaCO3 E For examusing this system, one p.p.m of calcium Sulphate (expressed as CaCO3). This is the same as converting English poundsGerman marks, or fresh francs into a 100 cent dollar.

Answer to :backWhat is Blow-down?

Blow-down is the removal from the boiler of water containing concentrated dissolved and suspended solids. As the blow-d


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water is replaced with lower solids feed water the boiler water is essentially being diluted. By regulating the amount of blodown, therefore, the amount of solids in the boiler-water can be controlled.

Answer to :back

How much Blow-down is Needed?This depends on how many concentrations of the various feed-water impurities a given boiler can tolerate; the moreconcentrations possible the less blow-down needed. For example, with 10 feedwater concentrations in a boiler, blow-dowequal to 10 per cent of the feed-water flow rate is needed; with 20 concentrations only 5 per cent blow-down is needed.

illustrate how blow-down requirements are calculated let us assume that the maximum amount of suspended solids (sludgthe boiler water that a particular boiler can tolerate is 500 p.p.m. If the fee-water contains 50 p.p.m. of hardness it can bconcentrated only about 10 times (since feed water hardness is precipitated as suspended solids in the boiler water). Th

means that for every 50 kg of water fed to the boiler about 5 kh of boiler water must be blown down to keep the suspendsolids from exceeding 500 p.p.m. Suspended solids, however, may not be the limiting factor in all cases; other factors wh

may limit feed-water concentrations include dissolved solids, alkalinity, silica or iron.

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What Tests are Made in Regulating Blow-down?Since there are no simple test for routinely checking the amount of suspended solids in boiler-water, blow-down is usualcontrolled through use of a simple instrument which measures the electrical conductivity of the water. This test gives an

estimate of the dissolved solids present in the boiler-water. Chloride tests are also used for blow-down control since chloriare not reacted on by chemical treatment. By checking both the fee-water and boiler-water chlorides the number of feed-w

concentrations can be calculated. In some higher pressure boilers, silica or iron tests may also be made to control blow-do

Answer to :backWhat is the Difference between Continuous and Puff EBlow-down?

All boilers have blow-down connections located at low points where sludge is likely to collect. Opening these blow-down va

periodically for shot intervals gives a puff Eor intermittent removal of sludge and solids. Many boilers also have blow-doconnections consisting of an overtake located just below the water level in the steam release area. A small amount of wate

continuously removed through these connections. The use of continuous blow-down in addition to puff Eor bottom blowdown keys it possible to maintain the solids and chemical residuals at more consistent levels in the boiler water. Continuo

blow-down also minimizes the amount of blow-down required with resultant savings in heat and chemicals. Continuous blodown also causes less upset in boiler water circulation and operation.

Answer to :back

What Causes Corrosion in Steam Condensate Systems?Most condensate system corrosion is caused by carbon dioxide and oxygen, arrived into the system with the steam. Carbdioxide, dissolved in the pure condensed steam, form corrosive carbonic acid. if oxygen is present with carbon dioxide, th

corrosion rate is much higher, and is likely to produce localized pitting. Ammonia, in combination with carbon dioxide ooxygen, attacks copper alloys.

Answer to :backHow is Steam Condensate Corrosion Prevented?

The general approach may involve removing oxygen from the feed-water mechanically and chemically, and providingpretreatment of the make-up water to minimize potential carbon dioxide formation in the boiler. In addition, an effectiv

chemical treatment programme is required. This may consist of using volatile amines to neutralize carbon dioxide and/orvolatile filming inhibitor to form a barrier between the metal and the corrosive condensate. Mechanical conditions such as p


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trapping and draining of lines, and air in-leakage may need to be correct-ed.

Answer to :backHow do Chemical Oxygen Scavengers Help Control Condensate System Corrosion?

As previously mentioned mechanical equipment (de-aerator) is often used to reduce feed-water oxygen. The best designedoperated de-aerators can reduce oxygen to as low as 0.007 parts per million or less. Most de-aerators or feed-water heat

are less effective. Since very small amounts of oxygen, however, can cause boiler corrosion and corrosion in steam condensystem, chemical treatment is therefore, needed to assure complete oxygen removal. Sodium Sulphate is the chemical mcommonly used for this purpose. Greatly improved oxygen removal is obtained, however, when the Sulphate is catalyzed

Catalyzed sodium Sulphate can reduce oxygen content of water (at room temperature) from the saturation point to zero inthan 30 seconds. Without a catalyst it takes up to 10 minutes under the same conditions to reduce the oxygen content by about 30 per cent. Fast reactions are important since oxygen should be removed before the water enters the boiler. Otherw

some oxygen will escape form the boiling water into the steam lines and corrosion in the condensate system.

Answer to :backWhat is the Basis for Choice between Neutralizing and Filming Inhibitors?

The proper choice of inhibitor depends on the boiler system, plant lay-out operating conditions and fee-water compositiongeneral, volatile amines are better with low make-up, low feed-water alkalinity, and good oxygen control. Filming inhibitousually give more economical protection with high make-up, air in-leakage high feed-water alkalinity or where the system

operated internally. In some cases a combination of treatments is needed.

Answer to :backWhat Characteristics Should a Good Condensate Corrosion Inhibitor Have?

A good volatile neutralizing amine should have a favorable distribution ratio in steam and condensate so that it protects tentire steam-condensate system. It should have no insoluble reaction products and should be stable at high temperatures pressures. A good filming inhibitor should be easy to disperse in water so that it can be fed uniformly. It should be stale un

usage conditions and form a thin protective film without causing deposits in either the boiler or the steam-condensate syst

Answer to :backHow are Deposits and Corrosion Prevented in Feed-water Systems?

Deposits in feed-water systems are most frequently caused by hardness coming out of solution as the water goes throug

feed- water heaters or as the feed lines enter the boiler. Deposits also can occur from premature reaction of treatmentchemicals with hardness in the feed-water. Prevention involves the use of stabilizing chemicals fed continuously to retarhardens precipitation. Proper design of the chemical feed system can minimize premature chemical reactions. Corrosion

feed-water system generally results from low alkalinity or dissolved oxygen in the water. Raising the pH of the water and continuous feed of catalyzed sodium Sulphate will minimize this problem.

Answer to :back

What is the Wet Method of Boiler Lay-Up?This is a method of storing boilers full of water so that they can be readily returned to service. it involves adding extrachemicals (usually caustic, organics, and sodium sulphite to the boiler-water.) The water level is raised in the idle boiler eliminate air spaces and the boiler is kept completely full of treated water. Special considerations are needed for protecti

super heaters.

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What is the Dry Method of Boiler Lay-Up?This method of lay-up is usually for longer boiler outages. It involves draining, cleaning and drying out the boiler. a mater

which absorbs moisture such as hydrated lime or silica gel is placed in trays inside the boiler. The boiler is then sealed care

to prevent in leakage of air. Periodic inspection and replacement of the drying chemical is required during long storage per

DATA USED IN WATER CHEMISTRY

The chemicals listed in this section include those found as impurities in water and also those used as treatments. The chemformulas, ion forms, and molecular and equivalent weights are given for each substance. Abbreviations and symbols are uextensively to simplify water analysis reports and calculations. This section explains the meanings of some common symband what they represent in water analyses. Very often the units used in water chemistry need to be converted back and fo

for practical application. For example, parts per million may be converted to grams per 1000 liters and vice versa. Theconversion factors in this section simplify this type of calculation.

CATIONS IonFormula IonicWeight EquivalentWeight

Aluminum A1+++ 27.0 9.0Ammonium NH4+ 18.0 18.0Calcium CA++ 40.1 20.0Hydrogen H+ 1.0 1.0Ferrous Iron Fe++ 55.8 27.9Magnesium Mg++ 24.3 12.2Manganese Mn++ 54.9 27.5Potassium K+ 39.1 39.1Sodium Na+ 23.0 23.0

ANIONSBicarbonate NCO3- 61.0 61.0Chloride CO3- 60.0 60.0Fluoride F- 19.0 19.0Nitrate NO3- 62.0 62.0Hydroxide

OH-

17.0

17.0

Phosphate ( PO4-- 95.0 31.7Phosphate (dibasic) HPO4-- 96.0 48.0Phosphate (monobasic) H2PO4- 97.0 97.0Sulphate SO4-- 96.1 48.0Sulphite SO3-- 80.1 40.0


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COMPOUNDS Formula MolecularWeight EquivalentWeight

Aluminum hydroxide Al(OH)3 78.0 26.0Aluminum Sulphate Al2(SO4)3 342.0 57.0Alumina Al2O3 102.0 17.0Calcium bicarbonate Ca(HCO3)2 162.1 81.1Calcium carbonate CaCO3 100.1 50.1Calcium chloride CaCl2 111.0 55.5Calcium hydroxide (pure) Ca(OH)2 74.1 37.1Calcium hydroxide (90%) Ca(OH)2 -- 41.1Calcium Sulphate

(anhydrous) CaSO4 136.2 68.1Calcium Sulphate (gypsum) CaSO4.2H2O 172.2 86.1Calcium phosphate Ca3(PO4)2 310.3 51.7Disodium phosphate Na2HPO4.12H2O 358.2 119.4Disodium phosphate(anhydrous) NaHPO4 142.0 47.3Ferric oxide Fe2O3 159.6 26.6Iron oxide (magnetic) Fe3O4 321.4 -Ferrous Sulphate (copperas) FeSO4.7H2O 278.0 139.0Magnesium oxide MgO 40.3 20.2Magnesium bicarbonate Mg(HCO3)2 146.3 73.2Magnesium carbonate MgCO3 84.3 42.2Magnesium chloride MgCl2 95.2 47.6Magnesium Mg(OH)2 58.3 29.2Magnesium phosphate Mg3(PO4)2 263.0 43.8Magnesium Sulphate MgSO4 120.4 60.2Monosodium phosphate NaH2PO4.H2O 138.1 46.0Monosodium phosphate

(anhydrous) NaH2PO4 120.1 40.0Metaphosphate NaPO3 102.0 34.0Sodium acuminate Na2Al2O4 164.0 27.3Sodium bicarbonate NaHCO3 84.0 84.0Sodium carbonate Na2CO3 106.0 53.0


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Sodium chloride NaCl 58.5 58.5Sodium hydroxide NaOH 40.0 40.0Sodium nitrate NaNO3 85.0 85.0Sodium Sulphate Na2SO4 142.0 71.0Sodium sulphite Na2SO3 126.1 63.0Trisodium phosphate Na3PO4.l2H2O 380.2 126.7Trisodium phosphate(anhydrous) Na3PO4 164.0 54.7

GASESAmmonia NH3 17 --Carbon Dioxide CO2 44 --Hydrogen H2 2 --Oxygen O2 32 --

ACIDSCarbonic H2CO3 62.0 31.0Hydrochloric HCl 36.5 36.5Phosphoric H3PO4 98.0 32.7Sulphuric H2SO4 98.1 49.1

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