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This article is about metal heat treatments. For ISPM 15 heat treatment of wood, seeISPM 15. For wood heat treatment, see Heat treatment of wood.

This article needs additional citations forverification.Please helpimprove this articleby adding reliable references. Unsourced material may bechallenged andremoved.(July 2008)

Heat treatment is a method used to alter thephysical, and sometimeschemicalproperties of a material. The most common application is metallurgical. Heat treatmentsare also used in the manufacture of many other materials, such as glass. Heat treatmentinvolves the use of heating or chilling, normally to extreme temperatures, to achieve adesired result such as hardening or softening of a material. Heat treatment techniquesinclude annealing, case hardening,precipitation strengthening,temperingandquenching.It is noteworthy that while the term heat treatmentapplies only to processes where theheating and cooling are done for the specific purpose of altering properties intentionally,heating and cooling often occur incidentally during other manufacturing processes suchas hot forming or welding.

Contents

[hide]

1 Processeso 1.1 Annealingo 1.2 Hardening and tempering (quenching and tempering)o 1.3 Precipitation hardeningo 1.4 Selective hardeningo 1.5 Case hardening

2 Specificationo 2.1 Case hardeningo 2.2 Through hardeningo 2.3 Annealing

3 See also 4 References 5 Further reading

6 External links

[edit] Processes

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Heat treating furnace at 1,800 F (980 C)

Metallic materials consist of amicrostructure of smallcrystalscalled "grains" orcrystallites. The nature of the grains (i.e. grain size and composition) is one of the mosteffective factors that can determine the overall mechanical behavior of the metal. Heattreatment provides an efficient way to manipulate the properties of the metal bycontrolling rate ofdiffusion, and the rate of cooling within the microstructure.

Complex heat treating schedules are often devised by metallurgiststo optimize an alloy'smechanical properties. In the aerospace industry, a superalloymay undergo five or moredifferent heat treating operations to develop the desired properties. This can lead toquality problems depending on the accuracy of the furnace's temperature controls andtimer.

[edit] Annealing

Main article: Annealing (metallurgy)

Annealing is a technique used to recovercold workand relax stresses within a metal.Annealing typically results in a soft, ductile metal. When an annealed part is allowed tocool in the furnace, it is called afull annealheat treatment. When an annealed part isremoved from the furnace and allowed to cool in air, it is called a normalizingheattreatment. Astress reliefannealing is when only the first stage of annealing is performed.The second stage of annealing is recrystallization, where new stress-free grains grow.The third stage isgrain growth, which causes the existing grains to grow.

[edit] Hardening and tempering (quenching and tempering)

Main article: Quench

To harden by quenching, a metal (usually steel or cast iron) must be heated into theaustenitic crystal phase and then quickly cooled. Depending on the alloy and otherconsiderations (such as concern for maximum hardness vs. cracking and distortion),cooling may be done with forced airor othergas (such asnitrogen),oil,polymerdissolved in water, orbrine. Upon being rapidly cooled, a portion of austenite (dependenton alloy composition) will transform to martensite, a hard, brittle crystalline structure.The quenched hardness of a metal depends on its chemical composition and quenching

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method. Cooling speeds, from fastest to slowest, go from polymer (i.e.silicon), brine,fresh water, oil, and forced air. However, quenching a certain steel too fast can result incracking, which is why high-tensile steels such as AISI 4140 should be quenched in oil,tool steelssuch as 2767 or H13 hot work tool steel should be quenched in forced air, andlow alloy or medium-tensile steels such as XK1320 or AISI 1040 should be quenched in

brine or water. However, metals such as austenitic stainless steel (304, 316), and copper,produce an opposite effect when these are quenched: they anneal. Austenitic stainlesssteels must be quench-annealed to become fully corrosion resistant, as they work-hardensignificantly.

Untempered martensite, while very hard, is too brittle to be useful for most applications.A method for alleviating this problem is called tempering. Most applications require thatquenched parts be tempered (heat treated at a low temperature, often 300 F or 150 C) toimpart some toughness. Higher tempering temperatures (may be up to 1300 F or 700 C,depending on alloy and application) are sometimes used to impart further ductility,although some yield strength is lost.

[edit] Precipitation hardening

Main article: Precipitation hardening

Some metals are classified asprecipitation hardening metals. When a precipitationhardening alloy is quenched, its alloying elements will be trapped in solution, resulting ina soft metal. Aging a "solutionized" metal will allow the alloying elements to diffusethrough the microstructure and form intermetallic particles. These intermetallic particleswill nucleate and fall out of solution and act as a reinforcing phase, thereby increasing thestrength of the alloy. Alloys may age "naturally" meaning that the precipitates form at

room temperature, or they may age "artificially" when precipitates only form at elevatedtemperatures. In some applications, naturally aging alloys may be stored in a freezer toprevent hardening until after further operations - assembly of rivets, for example, may beeasier with a softer part.

Examples of precipitation hardening alloys include 2000 series, 6000 series, and 7000series aluminium alloy, as well as some superalloys and somestainless steels.

[edit] Selective hardening

Some techniques allow different areas of a single object to receive different heat

treatments. This is called differential hardening. It is common in high qualityknives andswords. The Chinesejianis one of the earliest known examples of this, and the Japanesekatanathe most widely known. The Nepalese Khukuriis another example.

[edit] Case hardening

Main article: Case hardening

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Case hardening is a process in which an alloying element, most commonly carbon ornitrogen, diffuses into the surface of a monolithic metal. The resulting interstitial solidsolution is harder than the base material, which improves wear resistance withoutsacrificing toughness.

Laser surface engineering is a surface treatment with high versatility, selectivity andnovel properties. Since the cooling rate is very high in laser treatment, metastable evenmetallic glass can be obtained by this method.

[edit] Specification

Usually the end condition is specified instead of the process used in heat treatment.[1]

[edit] Case hardening

Case hardening is specified by hardness and case depth. The case depth can be specifiedin two ways: total case depth oreffective case depth. The total case depth is the truedepth of the case. The effective case depth is the depth of the case that has a hardnessequivalent of HRC50; this is checked on a Tukon microhardness tester. This value can beroughly approximated as 65% of the total case depth; however the chemical compositionand hardenability can affect this approximation. If neither type of case depth is specifiedthe total case depth is assumed.[1]

For case hardened parts the specification should have a tolerance of at least 0.005 in(0.13 mm). If the part is to be ground after heat treatment, the case depth is assumed to beafter grinding.[1]

The Rockwell hardness scale used for the specification depends on the depth of the totalcase depth, as shown in the table below. Usually hardness is measured on the Rockwell"C" scale, but the load used on the scale will penetrate through the case if the case is lessthan 0.030 in (0.76 mm). Using Rockwell "C" for a thinner case will result in a falsereading.[1]

Rockwell scale required for various case depths[1]

Total case depth, min. [in] Rockwell scale

0.030 C

0.024 A

0.021 45N

0.018 30N

0.015 15N

Less than 0.015 "File hard"

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For cases that are less than 0.015 in (0.38 mm) thick a Rockwell scale cannot reliably beused, sofile hardis specified instead.[1] File hard is approximately equivalent to 58 HRC.[2]

When specifying the hardness either a range should be given or the minimum hardness

specified. If a range is specified at least 5 points should be given.[1]

[edit] Through hardening

Only hardness is listed for through hardening. It is usually in the form of HRC with atleast a five point range.[1]

[edit] Annealing

The hardness for an annealing process is usually listed on the HRB scale as a maximumvalue.[1]

Water Treatment, Storage and Blowdown for SteamBoilers

A look at the chemistry of water supplies including hardness and pH values.

Use the quick links below to take you to the main sections of this tutorial:

The printable version of this page has now been replaced byThe Steam and Condensate Loop Book

Try answering the Questionsfor this tutorial View the complete collection ofSteam Engineering Tutorials Contact Us

Before boiler blowdown can be discussed and understood it is necessary to establish adefinition of water along with its impurities and associated terms such as hardness, pHetc.

Water is the most important raw material on earth. It is essential to life, it is used fortransportation, and it stores energy. It is also called the 'universal solvent'.

Pure water (H20) is tasteless, odourless, and colourless in its pure state; however, purewater is very uncommon. All natural waters contain various types and amounts ofimpurities.

Good drinking water does not necessarily make good boiler feedwater. The minerals indrinking water are readily absorbed by the human body, and essential to our well being.Boilers, however, are less able to cope, and these same minerals will cause damage in asteam boiler if allowed to remain.

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Of the world's water stock, 97% is found in the oceans, and a significant part of that istrapped in the polar glaciers - only 0.65% is available for domestic and industrial use.

This small proportion would soon be consumed if it were not for the water cycle (see

Figure 3.9.1). After evaporation, the water turns into clouds, which are partly condensedduring their journey and then fall to earth as rain. However, it is wrong to assume thatrainwater is pure; during its fall to earth it will pick up impurities such as carbonic acid,nitrogen and, in industrial areas, sulphur dioxide.

Charged with these ingredients, the water percolates through the upper layers of the earthto the water table, or flows over the surface of the earth dissolving and collectingadditional impurities.

These impurities may form deposits on heat transfer surfaces that may:

Cause metal corrosion. Reduce heat transfer rates, leading to overheating and loss of mechanical strength.

Table 3.9.1 shows the technical and commonly used names of the impurities, theirchemical symbols, and their effects.

Fig.3.9.1

Typical water cycle

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Table 3.9.1Impurities in water

Top

Raw water quality and regional variations

Water quality can vary tremendously from one region to another depending on thesources of water, local minerals (see Figure 3.9.2). Table 3.9.2 gives some typical figuresfor different areas in a relatively small country like the UK.

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Fig. 3.9.2Regional variations in water quality

Table 3.9.2Water variation within the UK

All impurities expressed in mg/l calcium carbonate equivalents

The common impurities in raw water can be classified as follows:

Dissolved solids - These are substances that will dissolve in water.

The principal ones are the carbonates and sulphates of calcium and magnesium,which are scale-forming when heated.

There are other dissolved solids, which are non-scale forming.

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In practice, any salts forming scale within the boiler should be chemically alteredso that they produce suspended solids, or sludge rather than scale.

Suspended solids - These are substances that exist in water as suspendedparticles.

They are usually mineral, or organic in origin.These substances are not generally a problem as they can be filtered out.

Dissolved gases - Oxygen and carbon dioxide can be readily dissolved by water.

These gases are aggressive instigators of corrosion. Scum forming substances - These are mineral impurities that foam or scum.

One example is soda in the form of a carbonate, chloride, or sulphate.

The amount of impurities present is extremely small and they are usually expressed in

any water analysis in the form of parts per million (ppm), by weight or alternatively inmilligrams per litre (mg/l).

The following sections within this Tutorial describe the characteristics of water.

Top

Hardness

Water is referred to as being either 'hard' or 'soft'. Hard water contains scale-formingimpurities while soft water contains little or none. The difference can easily be

recognised by the effect of water on soap. Much more soap is required to make a latherwith hard water than with soft water.

Hardness is caused by the presence of the mineral salts of calcium and magnesium and itis these same minerals that encourage the formation of scale.

There are two common classifications of hardness:

Alkaline hardness (also known as temporary hardness) - Calcium andmagnesium bicarbonates are responsible for alkaline hardness. The salts dissolvein water to form an alkaline solution. When heat is applied, they decompose to

release carbon dioxide and soft scale or sludge.

The term 'temporary hardness' is sometimes used, because the hardness isremoved by boiling. This effect can often be seen as scale on the inside of anelectric kettle.

See Figures 3.9.3 and 3.9.4 - the latter representing the situation within the boiler.

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Fig. 3.9.3Alkaline or temporary hardness

Fig. 3.9.4Non-alkaline or permanent hardness (scale + carbonic acid)

Non-alkaline hardness and carbonates (also known as permanent hardness) -This is also due to the presence of the salts of calcium and magnesium but in the

form of sulphates and chlorides. These precipitate out of solution, due to theirreduced solubility as the temperature rises, and form hard scale, which is difficultto remove.

In addition, the presence of silica in boiler water can also lead to hard scale,which can react with calcium and magnesium salts to form silicates which canseverely inhibit heat transfer across the fire tubes and cause them to overheat.

Top

Total hardness

Total hardness is not to be classified as a type of hardness, but as the sum ofconcentrations of calcium and magnesium ions present when these are both expressed asCaCO3. If the water is alkaline, a proportion of this hardness, equal in magnitude to thetotal alkalinity and also expressed as CaCO3, is considered as alkaline hardness, and theremainder as non-alkaline hardness. (See Figure 3.9.5)

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Fig. 3.9.5Total hardness

Top

Non-scale forming salts

Non-hardness salts, such as sodium salts are also present, and are far more soluble thanthe salts of calcium or magnesium and will not generally form scale on the surfaces of aboiler, as shown in Figure 3.9.6.

Fig. 3.9.6The effects of heat

Comparative units

When salts dissolve in water they form electrically charged particles called ions.

The metallic parts (calcium, sodium, magnesium) can be identified as cations becausethey are attracted to the cathode and carry positive electrical charges.

Anions are non-metallic and carry negative charges - bicarbonates, carbonate, chloride,sulphate, are attracted to the anode.

Each impurity is generally expressed as a chemically equivalent amount of calciumcarbonate, which has a molecular weight of 100.

Top

pH value

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Another term to be considered is the pH value; this is not an impurity or constituent butmerely a numerical value representing the potential hydrogen content of water - which isa measure of the acidic or alkaline nature of the water. Water, H2O, has two types of ions- hydrogen ions (H+) and hydroxyl ions (OH-).

If the hydrogen ions are predominant, the solution will be acidic with a pH value between0 and 6. If the hydroxyl ions are predominant, the solution will be alkaline, with a pHvalue between 8 and 14. If there are an equal number of both hydroxyl and hydrogenions, then the solution will be neutral, with a pH value of 7.

Acids and alkalis have the effect of increasing the conductivity of water above that of aneutral sample. For example, a sample of water with a pH value of 12 will have a higherconductivity than a sample that has a pH value of 7.

Table 3.9.3 shows the pH chart and Figure 3.9.7 illustrates the pH values alreadymentioned both numerically and in relation to everyday substances.

Table 3.9.3The pH scale

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Fig. 3.9.7pH chart

Boiler water treatmentThe treatment and conditioning ofboiler feed watermust satisfy three main objectives:

Continuous heat exchange Corrosionprotection

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Production of high quality steam

External treatmentis the reduction or removal of impurities from water outside the boiler.In general, external treatment is used when the amount of one or more of the feed waterimpurities is too high to be tolerated by the boiler system in question. There are many

types of external treatment (softening,evaporation, deaeration, membrane contractorsetc.) which can be used to tailor make feed-water for a particular system.Internaltreatmentis the conditioning of impurities within the boiler system. The reactions occureither in the feed lines or in the boiler proper. Internal treatment may be used alone or inconjunction with external treatment. Its purpose is to properly react with feed waterhardness, condition sludge, scavenge oxygen and prevent boiler water foaming.

External treatment

The water treatment facilities purify and deaerate make-up water or feed water. Water is sometimes pretreated by

evaporation to produce relatively pure vapor, which isthen condensed and used for boiler feed purposes.Evaporators are of several different types, the simplestbeing a tank of water through which steam coils arepassed to heat the water to the boiling point. Sometimesto increase the efficiency the vapor from the first tank ispassed through coils in a second tank of water to produceadditional heating and evaporation. Evaporators aresuitable where steam as a source of heat is readilyavailable. They have particular advantages overdemineralization, for example, when the dissolved solids

in the raw water are very high.Certain natural and synthetic materials have the ability to remove mineral ions from waterin exchange for others. For example, in passing water through a simple cation exchangesoftener all ofcalciumandmagnesium ions are removed and replaced with sodium ions.Since simple cation exchange does not reduce the total solids of the water supply, it issometimes used in conjunction with precipitation type softening. One of the mostcommon and efficient combination treatments is the hot lime-zeolite process. Thisinvolves pretreatment of the water with lime to reduce hardness, alkalinity and in somecases silica, and subsequent treatment with a cation exchange softener. This system oftreatment accomplishes several functions: softening, alkalinity and silica reduction, someoxygen reduction, and removal of suspended matter and turbidity.

Chemical treatment of water inside the boiler is usually essential and complementsexternal treatment by taking care of any impurities entering the boiler with the feed water(hardness,oxygen, silica, etc.). In many cases external treatment of the water supply is notnecessary and the water can be treated only by internal methods.

Internal treatment

Internal treatment can constitute the unique treatment when boilers operate at low or

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moderate pressure, when large amounts of condensed steam are used for feed water, orwhen good quality raw water is available. The purpose of an internal treatment is to

1) react with any feed-water hardness and prevent it from precipitating on the boiler metal

as scale;

2) condition any suspended matter such as hardness sludge or iron oxide in the boiler andmake it non-adherent to the boiler metal;

3) provide anti-foam protection to allow a reasonable concentration of dissolved andsuspended solids in the boiler water without foam carry-over;

4) eliminate oxygen from the water and provide enough alkalinity to prevent boilercorrosion.

In addition, as supplementary measures an internal treatment should preventcorrosion andscaling of the feed-water system and protect against corrosion in the steam condensatesystems.

During the conditioning process, which is an essential complement to the water treatmentprogram, specific doses of conditioning products are added to the water. The commonlyused products include:

Phosphates-dispersants, polyphosphates-dispersants (softening chemicals):reacting with the alkalinity of boiler water, these products neutralize the hardnessof water by forming tricalcium phosphate, and insoluble compound that can be

disposed and blow down on a continuous basis or periodically through the bottomof the boiler. Natural and synthetic dispersants(Anti-scaling agents): increase the dispersive

properties of the conditioning products. They can be:o Natural polymers: lignosulphonates, tanninso Synthetic polymers: polyacrilates, maleic acrylate copolymer, maleic

styrene copolymer, polystyrene sulphonates etc. Sequestering agents: such as inorganic phosphates, which act as inhibitors and

implement a threshold effect. Oxygen scavengers: sodium sulphite, tannis, hydrazine, hydroquinone/progallol-

based derivatives, hydroxylamine derivatives, hydroxylamine derivatives, ascorbic

acid derivatives, etc. These scavengers, catalyzed or not, reduce the oxides anddissolved oxygen. Most also passivate metal surfaces. The choice of product andthe dose required will depend on whether a deaerating heater is used.

Anti-foaming or anti-priming agents: mixture of surface-active agents thatmodify the surface tension of a liquid, remove foam and prevent the carry over offine water particles in the steam.

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The softening chemicals used include soda ash, caustic and various types of sodiumphosphates. These chemicals react with calcium and magnesium compounds in the feedwater. Sodium silicate is used to react selectively with magnesium hardness. Calciumbicarbonate entering with the feed water is broken down at boiler temperatures or reactswith caustic soda to form calcium carbonate. Since calcium carbonate is relativelyinsoluble it tends to come out of solution. Sodium carbonate partially breaks down at hightemperature to sodium hydroxide (caustic) and carbon dioxide. High temperatures in theboiler water reduce the solubility of calcium sulphate and tend to make it precipitate outdirectly on the boiler metal as scale. Consequently calcium sulphate must be reacted uponchemically to cause a precipitate to form in the water where it can be conditioned andremoved by blow-down. Calcium sulphate is reacted on either by sodium carbonate,sodium phosphate or sodium silicate to form insoluble calcium carbonate, phosphate orsilicate. Magnesium sulphate is reacted upon by caustic soda to form a precipitate ofmagnesium hydroxide. Some magnesium may react with silica to form magnesiumsilicate. Sodium sulphate is highly soluble and remains in solution unless the water isevaporated almost to dryness.

There are two general approaches to conditioning sludge inside a boiler: by coagulation ordispersion. When the total amount of sludge is high (as the result of high feed-waterhardness) it is better to coagulate the sludge to form large flocculent particles. This can beremoved by blow-down. The coagulation can be obtained by careful adjustment of theamounts of alkalis, phosphates and organics used for treatment, based on the fee-wateranalysis. When the amount of sludge is not high (low feed water hardness) it is preferableto use a higher percentage of phosphates in the treatment. Phosphates form separatedsludge particles. A higher percentage of organic sludge dispersants is used in thetreatment to keep the sludge particles dispersed throughout the boiler water.The materials used for conditioning sludge include various organic materials of the tannin,lignin or alginate classes. It is important that these organics are selected and processed, sothat they are both effective and stand stable at the boiler operating pressure. Certainsynthetic organic materials are used as anti-foam agents. The chemicals used to scavengeoxygen include sodium sulphite and hydrazine. Various combinations of polyphosphatesand organics are used for preventing scale and corrosion in feed-water systems. Volatileneutralizing amines and filming inhibitors are used for preventing condensate corrosion.

Common internal chemical feeding methods include the use of chemical solution tanks

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and proportioning pumps or special ball briquette chemical feeders. In general, softeningchemicals (phosphates, soda ash, caustic, etc.) are added directly to the fee-water at apoint near the entrance to the boiler drum. They may also be fed through a separate linedischarging in the feed-water drum of the boiler. The chemicals should discharge in the

fee-water section of the boiler so that reactions occur in the water before it enters thesteam generating area. Softening chemicals may be added continuously or intermittentlydepending on feed-water hardiness and other factors. Chemicals added to react withdissolved oxygen (sulphate, hydrazine, etc.) and chemicals used to prevent scale andcorrosion in the feed-water system (polyphosphates, organics, etc.) should be fed in thefeed-water system as continuously as possible. Chemicals used to prevent condensatesystem corrosion may be fed directly to the steam or into the feed-water system,depending on the specific chemical used. Continuous feeding is preferred but intermittentapplication will suffice in some cases.

Check also our web page about the production of high pure water through

Electrodeionization (EDI).Click here for more details about deaeration (deaerating heaters ormembranecontractors).Find information about the main problems occurring in boilers:scaling,foaming andpriming, and corrosion.For a description of thecharacteristics of the perfect boiler water click here.

Read more: http://www.lenntech.com/applications/process/boiler/boiler-water-treatment.htm#ixzz11qVcJomZ

Non-Cng ngh ha hc Quy m v kim sot cngTechnology for improving energy efficiency through the removal or prevention of scale.Cng ngh nng cao hiu qu nng lng thng qua vic loi b hoc phng c quym.

Abstract Tm tt

The magnetic technology has been cited in the literature and investigated since the turn ofthe 19 th century, when lodestones and naturally occurring magnetic mineral formationswere used to decrease the formation of scale in cooking and laundry applications. Cng

ngh t tnh c trch dn trong cc ti liu v iu tra k t th k th 19, khilodestones v khong sn t nhin hnh thnh t c s dng lm gim s hnh thnhcc quy m v git ng dng nu n. Today, advances in magnetic and electrostatic scalecontrol technologies have led to their becoming reliable energy savers in certainapplications. Ngy nay, nhng tin b trong cng ngh kim sot quy m in v t tnh dn ti tit kim nng lng tr nn ng tin cy ca h trong cc ng dng nht nh.

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Manufacturers | Who is Using the TechnologyCc nh sn xut | Ai S dng Cng nghFor Further Information | Appendixes | ContactsThng tin thm |Ph lc | Lin h

To top of page u trang

About the Technology Gii thiu v Cng ngh

The technology addressed in this FTA uses a magnetic or electrostatic field to alter thereaction between scale-forming ions in hard water. Cc cng ngh c cp trongFTA ny s dng mt hoc in t trng thay i cc phn ng gia cc ion hnh thnhquy m trong nc cng. Hard water contains high levels of calcium, magnesium, andother divalent cations. Nc cng c cha hm lng cao canxi, magi, v cation hoa trhai khc. When subjected to heating, the divalent ions form insoluble compounds withanions such as carbonate. Khi b nung nng, cc ion hoa tr hai dng hp cht khng hatan vi cc anion nh cacbonat. These insoluble compounds have a much lower heattransfer capability than heat transfer surfaces such as metal. Cc hp cht ny khng hatan c kh nng chuyn nhng thp hn nhit nhiu hn so vi b mt truyn nhit nhkim loi. They are insulators. H l nhng cht cch in. Thus additional fuelconsumption would be required to transfer an equivalent amount of energy. Nh vy tiuth nhin liu b sung s c yu cu chuyn mt s tin tng ng vi nng lng.

The magnetic technology has been cited in the literature and investigated since the turn ofthe 19 th century, when lodestones or naturally occurring magnetic mineral formationswere used to decrease the formation of scale in cooking and laundry applications. Cngngh t tnh c trch dn trong cc ti liu v iu tra k t th k th 19, khilodestones hoc t nhin hnh thnh t khong sn c s dng lm gim s hnh

thnh cc quy m v git ng dng nu n. However, the availability of high-power, rare-earth element magnets has advanced the magnetic technology to the point where it ismore reliable. Tuy nhin, s sn c ca quyn lc cao, yu t t him c nam chm,nng cao cng ngh t tnh ti thi im m n l ng tin cy hn. Similar advances inmaterials science, such as the availability of ceramic electrodes and other durabledielectric materials, have allowed the electrostatic technology to also become morereliable. nhng tin b tng t trong cc ti liu khoa hc, chng hn nh s sn c cain cc v in mi bng gm bn vt liu khc, cho php cc cng ngh in cngtr nn ng tin cy.

The general operating principle for the magnetic technology is a result of the physics of

interaction between a magnetic field and a moving electric charge, in this case in the formof an ion. Nguyn tc iu hnh chung cho cng ngh t tnh l kt qu ca vt l ca stng tc gia t trng v in ph di chuyn, trong trng hp ny di hnh thc mtion. When ions pass through the magnetic field, a force is exerted on each ion. Khi ccion i qua t trng, lc lng c tc trn mi ion. The forces on ions of oppositecharges are in opposite directions. Cc lc lng trn cc ion ph i din l cc hngngc li. The redirection of the particles tends to increase the frequency with which ionsof opposite charge collide and combine to form a mineral precipitate, or insoluble

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compound. Vic chuyn hng ca cc ht c xu hng tng tn sut m cc ion ca vachm ph i din v kt hp to thnh kt ta khong sn, hoc hp cht khng hatan. Since this reaction takes place in a low-temperature region of a heat exchangesystem, the scale formed is non-adherent. T phn ng ny din ra trong mt khu vcnhit thp ca mt h thng trao i nhit, quy m c hnh thnh l khng dnh. At

the prevailing temperature conditions, this form is preferred over the adherent form,which attaches to heat exchange surfaces. iu kin nhit hin hnh, hnh thc nyl u tin hn cc dng dnh, c gn vo b mt trao i nhit.

The operating principles for the electrostatic units are much different. Instead of causingthe dissolved ions to come together and form non-adherent scale, a surface charge isimposed on the ions so that they repel instead of attract each other. Cc nguyn tc hotng cho cc n v in ang c nhiu khc nhau. Thay vo gy ra cc ion gii th n vi nhau v hnh thc, quy m khng dnh, b mt l mt khon ph i vi cc ion h y li thay v thu ht ln nhau. Thus the two ions (positive and negative, orcations and anions, respectively) of a kind needed to form scale are never able to come

close enough together to initiate the scale-forming reaction. Do , hai ion (tch cc vtiu cc, hoc cc cation v anion, tng ng) ca mt loi hnh quy m cn thit khng bao gi c th n gn vi nhau bt u hnh thnh phn ng quy m. Theend result for a user is the same with either technology; scale formation on heat exchangesurfaces is greatly reduced or eliminated. Kt qu cui cng cho mt ngi s dng cngging vi cng ngh hoc; quy m hnh thnh trn cc b mt trao i nhit s gim ngk hoc loi b.

Application Domain ng dng Domain

These technologies can be used as a replacement for most water-softening equipment.

Nhng cng ngh ny c th c s dng nh l mt thay th cho cc thit b nc lmmm nht. Specifically, chemical softening (lime or lime-soda softening), ion exchange,and reverse osmosis (RO), when used for the control of hardness, can be replaced by thenon-chemical water conditioning technology. C th, ha cht lm mm (vi hoc soda-vi lm mm), trao i ion, v thm thu ngc (RO), khi c s dng kim sot cng, c th c thay th bng cc cht ha hc cng ngh nc iu khng. Thiswould include applications both to cooling water treatment and boiler water treatment, inonce-through and recirculating systems. iu ny s bao gm cc ng dng c hai lmmt x l nc v x l nc ni hi, trong mt ln, thng qua v tun hon h thng.Other applications mentioned by the manufacturers include use on petroleum pipelines asa means of decreasing fouling caused by wax build-up, and the ability to inhibit

biofouling and corrosion. Cc ng dng khc c cp bi nhng nh sn xut baogm s dng trn cc ng ng du m nh mt phng tin gim nhim gy ra bisp xy dng, kh nng v c ch biofouling v n mn.

The magnetic technology is generally not applicable in situations where the hard watercontains "appreciable" concentrations of iron. Cng ngh t tnh thng khng p dngtrong cc tnh hung m cc nc kh c "ng" nng cc cht st. In this FTA,appreciable means a concentration requiring iron treatment or removal prior to use, on the

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order of parts per million or mg/L. Trong FTA ny, ng c ngha l mt s tp trung cniu tr bng st hoc loi b trc khi s dng, v trnh t ca cc phn triu hoc mg /L. The reason for this precaution is that the action of the magnetic field on the hardness-causing ions is very weak. L do ca s phng nga ny l cc hnh ng ca t trngtrn gy ion cng l rt yu. Conversely, the action of the magnetic field on the iron

ions is very strong, which interferes with the water conditioning action. Ngc li, cchnh ng ca t trng v cc ion st l rt mnh, m can thip vo hnh ng iu hanc.

A search of the Thomas RegisterTM in conjunction with manufacturer contact yieldedeleven manufacturers of magnetic, electromagnetic or electrostatic water conditioningequipment that fell within the scope of this investigation. Mt tm kim ca Thomasng k TM kt hp vi h vi nh sn xut mang li cc nh sn xut mi mt, inhoc in nc, thit b iu t gim trong phm vi ca iu tra ny. The definedscope includes commercial- or industrial-type magnetic, electromagnetic or electrostaticdevices marketed for scale control. Phm vi c xc nh bao gm thng mi, hoc

loi cng nghip, in hoc thit b in t th trng kim sot quy m. Devicesintended for home use, as well as other non-chemical means for scale control, such asreverse osmosis, are not within the extended scope of this FTA. Thit b dnh cho sdng nh, cng nh cc phng tin khc khng c ha cht kim sot quy m, chnghn nh thm thu ngc, khng phi trong phm vi m rng ca FTA ny.

Figure 1.Hnh 1.Diagram of General Magnetic Device ConstructionS t thitb xy dng Tng

Exact numbers of units deployed by these manufacturers are virtually impossible tocompile, as some of the manufacturers had been selling the technology for up to 40 years.con s chnh xc ca cc n v trin khai bi cc nh sn xut hu nh khng th bin dch, nh mt s cc nh sn xut c bn cng ngh cho n 40 nm. One

manufacturer claims as many as 1,000,000 units (estimated total of all manufacturersrepresented here) are installed in the field. Mt nh sn xut tuyn b c n 1.000.000n v (c tnh tng tt c cc nh sn xut hin ti y) c ci t trong lnh vc ny.Where not withheld by the manufacturer because of business sensitivity reasons,customer lists included both Federal and non-Federal installations. Nu khng gi li bicc nh sn xut v l do nhy cm kinh doanh, danh sch khch hng bao gm c Linbang v lin bang khng phi ci t. Those manufacturers who did withhold thecustomer list indicated a willingness to disclose customer contacts to legitimate

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prospective customers. Nhng nh sn xut, nhng ngi gi li trong danh schkhch hng cho bit sn sng tit l a ch lin lc ca khch hng khch hng timnng hp php.

Literature provided by and discussions with manufacturers described a typical installation

for a boiler water treatment scheme as including the device installed upstream of theboiler. Vn hc cung cp v tho lun vi cc nh sn xut m t mt ci t in hnhcho chng trnh x l nc l hi mt lc bao gm c cc thit b c ci t thngngun ca l hi. Manufacturers vary in their preference of whether the device should beinstalled close to the water inlet or close to the boiler. Cc nh sn xut khc nhau v sthch ca h v vic liu thit b ny nn c ci t gn u nc hoc gn vi l hi.Both locations have been documented as providing adequate performance. Generally, thepreferred installation location for use with cooling towers or heat exchangers is upstreamof the heat exchange location and upstream of the cooling tower. C hai a im cghi nhn nh cung cp thc hin y ,. Thng thng cc v tr ci t a thch sdng vi thp lm lnh hoc trao i nhit l thng ngun ca a im trao i nhit v

thng ngun ca thp lm mt. Downstream of the cooling tower but upstream of theheat source was also mentioned as a possible installation location, primarily for the usewith chillers or other cooling equipment. on sau ca thp lm mt nhng ngc dngca cc ngun nhit cng c nhc n nh l mt v tr ci t c th, ch yu cho vics dng vi thit b lm lnh hoc thit b lm mt khc.

The primary caveaton installation of the magnetic technology is that high voltage (230V,3-phase or above) power lines interfere with operation by imposing a second magneticfield on the water. Thngbo trc chnh trn ci t ca cc cng ngh t tnh crng in p cao (230V, 3 pha hoc trn) ng dy in cn tr hot ng bng cchp t mt t trng th hai trn mt nc. (This is most noticeable when these electric

power sources are installed within three feet of a magnetic device.) This second magneticfield most likely will not be aligned with the magnetic field of the device, thusintroducing interference and reducing the effectiveness of the treatment. (iu ny lng ch nht khi cc ngun nng lng in c ci t trong vng ba chn ca mtthit b t tnh.) Ny t trng th hai rt c th s khng ph hp vi t trng ca thitb, do gii thiu nhiu v lm gim hiu qu iu tr. Installations near high voltagepower lines are to be avoided if possible. Lp t gn ng dy in cao th l trnhc nu c th. Where avoidance is not possible, the installation of shielded equipmentis recommended to achieve optimum operation. Trnh trng hp l khng th, lp tthit b bo v c khuyn khch t c hot ng ti u. Some manufacturers alsohave limitations on direction of installation--vertical or horizontal--because of internalmechanical construction Mt s nh sn xut cng c nhng hn ch v hng ci t -theo chiu dc hoc chiu ngang - v c kh xy dng ni b

Energy-Savings Mechanism C ch tit kim nng lng

The primary energy savings result from a decrease in energy consumption in heating orcooling applications. Tit kim nng lng chnh l kt qu ca s suy gim tiu thnng lng si m hoc lm mt trong cc ng dng. This savings is associated with the

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prevention or removal of scale build-up on a heat exchange surface where even a thinfilm (1/32" or 0.8 mm) can increase energy consumption by nearly 10%. Examplesavings resulting from the removal of calcium-magnesium scales are shown in Table 1. Asecondary energy savings can be attributed to reducing the pump load, or systempressure, required to move the water through a scale-free, unrestricted piping system. tit

kim ny c kt hp vi cc phng hoc loi b cc quy m xy dng trn mt b mttrao i nhit m ngay c mt mng mng (1 / 32 "hoc 0,8 mm) c th tng tiu thnng lng ca gn 10%. V d tit kim thu c t vic loi b cc canxi -magi quym c th hin trong Bng 1. Mt tit kim nng lng th cp c th c quy chogim ti my bm, hoc h thng p lc, yu cu phi di chuyn nc qua mt min ph,khng hn ch, h thng ng ng quy m.

Table 1.Bng 1.Example Increases in Energy ConsumptionV d trong tiu thnng lng tng

as a Function of Scale Thicknessnh l mt chc nng ca m dy

Scale ThicknessQuy m dy(inches)(Inch)

Increased EnergyTng cng nng lngConsumption (%)Tiu th (%)

1/32 1 / 32 8.5 8.5

1/16 1 / 16 12.4 12.4

1/8 1 / 8 25.0 25.0

1/4 1 / 4 40.0 40.0

As was discussed above, magnetic and electric fields interact with a resultant forcegenerated in a direction perpendicular to the plane formed by the magnetic and electricfield vectors. Nh ni trn, v in t trng tng tc vi mt lc lng kt quto ra theo mt hng vung gc vi mt phng hnh thnh bi cc vect in trng vt trng. (See Figure 2 for an illustration.) This force acts on the current carrying entity,the ion. (Xem hnh 2 minh ha mt.) Lc lng ny hot ng trn cc thc th thchin, cc ion. Positively charged particles will move in a direction in accord with theRight-hand Rule, where the electric and magnetic fields are represented by the fingersand the force by the thumb. Tch cc cc ht tch in s di chuyn theo hng ph hpvi Quy tc bn tay phi, ni m in trng v t trng c i din bng cc ngntay v buc bng ngn tay ci. Negatively charged particles will move in the oppositedirection. Cc ht mang in tch m s di chuyn theo hng ngc li. This force is inaddition to any mixing in the fluid due to turbulence. lc lng ny l b sung bt ktrn trong cht lng do nhiu lon khng kh.

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Figure 2.Hnh 2.Diagram Showing Positioning of Fields and ForceHin th s nh v ca Trng v Lc lng

The result of these forces on the ions is that, in general, positive charged ions (calciumand magnesium, primarily) and negative charged ions (carbonate and sulfate, primarily)are directed toward each other with increased velocity. Kt qu ca cc lc lng trn ccion l, ni chung, tnh ion dng (canxi v magi, ch yu) v cc ion m tnh (cacbonat

v sulfate, ch yu) c hng v nhau vi vn tc tng ln. The increased velocityshould result in an increase in the number of collisions between the particles, with theresult being formation of insoluble particulate matter. Tc tng nn dn n s giatng s lng cc v va chm gia cc ht, c hnh thnh vi kt qu ca ht khngha tan. Once a precipitate is formed, it serves as a foundation for further growth of thescale crystal. Sau khi kt ta c hnh thnh, n phc v nh mt nn tng cho s phttrin hn na ca cc tinh th quy m. The treatment efficiency increases with increasinghardness since more ions are present in solution; thus each ion will need to travel ashorter distance before encountering an ion of opposite charge. Vic iu tr lm tnghiu qu vi s gia tng cng t nhiu ion c mt trong dung dch, do mi ion scn phi i mt khong cch ngn trc khi gp phi mt ion ph i din.

A similar reaction occurs at a heat exchange surface but the force on the ions results fromthe heat input to the water. Mt phn ng tng t xy ra ti mt b mt trao i nhit,nhng lc lng v kt qu cc ion t u vo nhit vo nc. Heat increases the motionof the water molecules, which in turn increases the motion of the ions, which then collide.Nhit lm tng s chuyn ng ca cc phn t nc, m trong tng ln lt chuynng ca cc ion, sau va chm. In addition, scale exhibits an inverse solubilityrelationship with temperature, meaning that the solubility of the material decreases astemperature increases. Ngoi ra, quy m trng by mt mi quan h nghch o vi nhit ha tan, c ngha l ha tan ca vt liu gim khi nhit tng. Therefore, at thehottest point in a heat exchanger, the heat exchange surface, the scale is least soluble,

and, furthermore due to thermally induced currents, the ions are most likely to collidenearest the surface. Do , ti im nng nht trong mt trao i nhit, cc b mt traoi nhit, quy m t nht l ha tan, v, hn na do gy ra dng nhit, cc ion c nhiukh nng va chm gn nht trn b mt. As above, the precipitate formed acts as afoundation for further crystal growth. Nh trn, cc kt ta thnh lp hot ng nh mtnn tng cho s tng trng tinh th hn na.

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When the scale-forming reaction takes place within a heat exchanger, the mineral form ofthe most common scale is called calcite. Khi hnh thnh phn ng quy m din ra trongmt trao i nhit, cc mu khong sn quy m ph bin nht c gi l canxit. Calciteis an adherent mineral that causes the build-up of scale on the heat exchange surface.Canxit l mt khong cht dnh gy ra xy dng c quy m trn b mt trao i nhit.

When the reaction between positively charged and negatively charged ions occurs at lowtemperature, relative to a heat exchange surface, the mineral form is usually aragonite.Khi cc phn ng gia tnh ph v tiu cc ion tch cc xy ra nhit thp, so vi mtb mt trao i nhit, cc mu khong sn thng aragonit. Aragonite is much lessadherent to heat exchange surfaces, and tends to form smaller-grained or softer-scaledeposits, as opposed to the monolithic sheets of scale common on heat exchangesurfaces. Aragonit l t dnh vo cc b mt trao i nhit, v c xu hng hnh thnh hthoc nh nhng hn tin gi c quy m nh hn, nh tri ngc vi nhng tm nguyn khi c quy m ph bin trn cc b mt trao i nhit.

These smaller-grained or softer-scale deposits are stable upon heating and can be carried

throughout a heating or cooling system while causing little or no apparent damage.Nhng ht hoc nh nhng hn quy m nh hn tin gi n nh khi lm nng v c thc thc hin trong sut mt h thng si m hoc lm mt trong khi gy thit hi thoc khng r rng. This transport property allows the mineral to be moved through asystem to a place where it is convenient to collect and remove the solid precipitate. iuny cho php vn chuyn ti sn khong sn c chuyn qua h thng mt n mt nim n l thun tin thu thp v loi b cc kt ta rn. This may include removal withthe wastewater in a once-through system, with the blowdown in a recirculating system, orfrom a device such as a filter, water/solids separator, sump or other device specificallyintroduced into the system to capture the precipitate. iu ny c th bao gm vic loib vi l nc thi trong mt ln qua h thng, vi x y trong mt h thng tun hon,

hoc t mt thit b nh l mt nc, lc /, cht rn h cha phn cch hoc cc thit bc bit a vo h thng, nm bt c kt ta.

Water savings are also possible in recirculating systems through the reduction inblowdown necessary. Tit kim nc cng c th trong tun hon h thng thng quavic gim x y cn thit. Blowdown is used to reduce or balance out the minerals andchemical concentrations within the system. X y c s dng lm gim hoc cnbng cc cht khong v nng ha cht trong h thng. If the chemical consumptionfor scale control is reduced, it may be possible to reduce blowdown also. Nu tiu th hacht kim sot quy m l gim, c th l c th gim cng x y. However, themanagement of corrosion inhibitor and/or biocide build-up, and/or residual products ordegradation by-products, may become the controlling factor in determining blowdownfrequency and volume. Tuy nhin, cht c ch n mn qun l v / hoc cht dit khunxy dng, v / hoc cc sn phm cn st li, suy thoi cc sn phm, c th tr thnhyu t kim sot trong vic xc nh tn s v khi lng x y.

Other Benefits Li ch khc

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Aside from the energy savings, other potential areas for savings exist. Ngoi vic titkim nng lng, cc khu vc khc c tim nng tit kim tn ti. The first is eliminationor significant reduction in the need for scale and hardness control chemicals. u tin lloi b hoc gim ng k s cn thit phi kim sot cng ha cht v quy m. In atypical plant, this savings could be on the order of thousands of dollars each year when

the cost of chemicals, labor and equipment is factored in. Second, periodic descaling ofthe heat exchange equipment is virtually eliminated. Trong mt nh my in hnh, titkim ny c th l vo th t ca hng ngn la mi nm khi chi ph lao ng, ha chtv thit b l yu t nhp Th hai, nh k ty cn ca cc thit b trao i nhit l gnnh loi b. Thus process downtime, chemical usage, and labor requirements areeliminated. Nh vy qu trnh thi gian cht, ha cht s dng, v cc yu cu lao ngc loi b. A third potential savings is from reductions in heat exchanger tubereplacement due to failure. Mt tit kim tim nng th ba l t thay th gim trong ngtrao i nhit do s tht bi. Failure of tubes due to scale build-up, and the resultanttemperature rise across the heat exchange surface, will be eliminated or greatly reducedin proportion to the reduction in scale formation. Tht bi ca ng do quy m xy dng,

v kt qu tng nhit trn b mt trao i nhit, s c loi b hoc gim ng k tl vi vic gim s hnh thnh quy m.

Variations Bin th

Devices are available in two installation variations and three operational variations. Thitb c sn trong hai bin th ci t v ba bin th hot ng. First to be discussed are thetwo installation variations: invasive and non-invasive. u tin s c tho lun l haici t cc bin th: xm ln v khng xm ln. Invasive devices are those which havepart or all of the operating equipment within the flow field. thit b xm hi l nhng cmt phn hoc tt c cc thit b hot ng trong lnh vc dng chy. Therefore, these

devices require the removal of a section of the pipe for insertion of the device. Do ,nhng thit b ny i hi vic g b mt phn ca ng ng a vo thit b. This,of course, necessitates an amount of time for the pipe to be out of service. iu ny, ttnhin, i hi mt lng thi gian cho cc ng ng c ra khi dch v. Non-invasive devices are completely external to the pipe, and thus can be installed while thepipe is in operation. Xm nhp cc thit b khng hon ton bn ngoi ng, v do c th c ci t trong khi ng ng ang hot ng. Figure 3 illustrates the twoinstallation variations. Hnh 3 minh ha cc bin th ci t hai.

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Figure 3.Hnh 3.Illustration of Classes of Magnetic Devices by InstallationLocationTc gi ca lp hc ca thit b t bi V tr lp t

The operational variations have been mentioned above; illustrations of the latter twotypes are shown Figure 4: Cc bin th hot ng c cp trn, minh ha trongcc loi sau hai c th hin Hnh 4:

Magnetic, more correctly a permanent magnet T tnh, ng hn l mt namchm vnh cu

Electromagnetic, where the magnetic field is generated via electromagnets in,ni m t trng c to ra thng qua cc in t

Electrostatic, where an electric field is imposed on the water flow, which serves toattract or repel the ions and, in addition, generates a magnetic field. Tnh in,trong mt in trng l i vi dng nc, phc v thu ht hoc y li

cc ion v, ngoi ra, to ra mt t trng.

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Figure 4.Hnh 4.Illustration of Classes of Non-Permanent Magnet DevicesTc gica lp hc ca cc thit b nam chm vnh cu, khng

Electrostatic units are always invasive. in cc n v lun lun xm ln. The other twotypes can be either invasive or non-invasive. Hai loi c th l xm hi hoc xm lnkhng. The devices illustrated in Figure 3 are examples of permanent magnet devices.Cc thit b c minh ha trong hnh 3 l nhng v d ca cc thit b nam chm vnhcu.

Installation Ci t

Most of the devices are in-line--some invasive, some non-invasive--as opposed to side-stream. Hu ht cc thit b nm trong dng - mt s xm hi, mt s khng xm ln -nh tri ngc vi dng pha. The invasive devices require a section of pipe to be

removed and replaced with the device. Cc thit b xm hi yu cu mt phn ca ngng phi c loi b v thay th bng thit b. Most of the invasive devices are larger indiameter than the section of pipe they replace. Hu ht cc thit b xm hi cng ln hnng knh hn so vi cc phn ca ng ng m n thay th. The increased diameter ispartially a function of the magnetic or electromagnetic elements, and also a function ofthe cross sectional flow area. ng knh tng mt phn l mt chc nng ca cc phnt hoc in t trng, v cng l mt chc nng ca khu vc ct ngang dng chy. Theflow area through the devices is generally equivalent to the flow area of the section of

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pipe removed. Din tch lu lng thng qua cc thit b ni chung l tng ng vidin tch dng chy ca cc phn ca ng ng loi b.

The non-invasive in-line devices are designed to be wrapped around the pipe. Thusdowntime, or line out-of-service time, is minimized or eliminated. Cc khng xm ln

trong dng thit b c thit k c bao bc xung quanh ng thi gian cht. Do ,hoc ng out-of-dch v thi gian, c gim thiu hoc loi b.

To top of page u trang

Federal Sector Potential Lin bang khu vc tim nng

The potential cost-effective savings achievable by this technology were estimated as partof the technology assessment process of the New Technology Demonstration Program(NTDP). Cc tim nng tit kim chi ph-hiu qu t c ca cng ngh ny c ctnh l mt phn ca qu trnh nh gi cng ngh ca Chng trnh trnh din cng nghmi (NTDP).

Technology Screening Process Quy trnh cng ngh

New technologies were solicited for NTDP participation through advertisements in theCommerce Business Daily and trade journals, and, primarily, through directcorrespondence. Responses were obtained from manufacturers, utilities, tradeassociations, research institutes, Federal sites and other interested parties. Based on theseresponses, the technologies were evaluated in terms of potential Federal-sector energysavings and procurement, installation, and maintenance costs. They were also categorizedas either just coming to market ("unproven" technologies) or as technologies for whichfield data already exist ("proven" technologies).

The energy savings and market potentials of each candidate technology were evaluatedusing a modified version of the Facility Energy Decisions Screening (FEDS) softwaretool (a) (Dirks and Wrench, 1993).

Non-chemical water treatment technologies were judged life-cycle cost-effective (at oneor more Federal sites) in terms of installation cost, net present value, and energy savings.In addition, significant environmental savings from the use of many of these technologiesare likely through reductions in CO 2 , NO x , and SO x emissions.

Estimated Savings and Market Potential

As part of the NTDP selection process, an initial technology screening activity wasperformed to estimate the potential market impact in the Federal sector. L mt phn caqu trnh la chn NTDP, mt cng ngh ban u hot ng kim tra c thc hin c tnh nh hng th trng tim nng trong lnh vc lin bang. Two technologies were

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run through the assessment methodology. Hai cng ngh c chy qua cc phngphp nh gi. The first technology was assessed assuming the technology was applied tothe treatment of boiler make-up water. Cng ngh u tin c nh gi gi nh cngngh ny c p dng iu tr lm cho nc ln l hi. The second technologywas assessed assuming the technology was applied to both the treatment of boiler make-

up water and cooling tower water treatment. Cng ngh th hai c nh gi gi nhcng ngh ny c p dng iu tr cho c hai nc ln l hi v nc thp giinhit, cha bnh. The technology screenings used the economic basis required by 10CFR 436. Cc chiu cng ngh s dng c s kinh t theo yu cu ca 10 CFR 436. Thecosts of the two technologies were different based on information provided by themanufacturers, thus leading to different results. Cc chi ph ca hai cng ngh l khcnhau da trn thng tin cung cp bi cc nh sn xut, dn n kt qu khc nhau.

The technologies were ranked on a total of ten criteria. Cc cng ngh c xp hngtrn tng s mi tiu ch. Three of these were financial, including net present value(NPV), installed cost, and present value of savings. Ba trong s c ti chnh, bao

gm c gi tr hin ti rng (NPV), chi ph ci t, v gi tr hin ti ca tin tit kim.One criterion was energy-related, annual site energy savings. Mt tiu ch c lin quann nng lng, hng nm trang web tit kim nng lng. The remaining criteria wereenvironmental and dealt with reductions in air emissions due to fuel or energy savingsand included SO 2 , NO x , CO, CO 2 , particulate matter and hydrocarbon emissions. Cctiu ch cn li c x l mi trng v gim pht thi kh do nng lng tit kimnhin liu v bao gm 2 SO, NO x, CO, CO 2, ht vt cht v du kh pht thi.

The ranking results from the screening process for this technology are shown in Table 2.Kt qu xp hng t qu trnh sng lc cho cng ngh ny c th hin trong Bng 2.These values represent the maximum benefit achieved by implementation of the

technology in every Federal application where it is considered life-cycle cost-effective.Nhng gi tr ny i din cho li ch ti a t c bng cch thc hin cc cng nghtrong mi ng dng lin bang, ni n c xem l chu k cuc sng c hiu qu. Theactual benefit will be lower because full market penetration is unlikely to ever beachieved. Cc li ch thc t s thp bi v thm nhp th trng y l th s khngt c.

Table 2.Bng 2.Screening Criteria ResultsKt qu sng lc tiu chun

Screen CriteriaTiu chun mn hnh

ResultsKt qu

First ScreenMn

hnh u tin

Second ScreenMn

hnh th haiNet Present Value ($) Gi tr hin ti rng($)Installed Cost ($) Chi ph lp t ($)Present Value of Savings ($) Gi tr hinti ca tit kim ($)Annual Site Energy Savings (Mbtu) Trang

147,518,000.147.518.000.

52,819,000.52.819.000.200,336,000.200.336.000.

158,228,000.158.228.000.

35,299,000.35.299.000.193,527,000.193.527.000.

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web hng nm tit kim nng lng(Mbtu)SO 2 Emissions Reduction (lb/yr) Gimpht thi SO 2 (lb / nm)NO x Emissions Reduction (lb/yr) Pht thi

NO x gim (lb / nm)CO Emissions Reduction (lb/yr) Gimpht thi CO (lb / nm)CO 2 Emissions Reduction (lb/yr) CO 2pht thi gim (lb / nm)Particulate Emissions Reduction (lb/yr)Gim pht thi ht (lb / nm)Hydrocarbon Emissions Reduction (lb/yr)Gim pht thi kh hydrocarbon (lb / nm)

4,166,000.4.166.000.3,292,000.3.292.000.1,028,000.

1.028.000.304,000. 304.000.303,000. 303.000.

60,000. 60.000.7,000. 7.000.

3,761,000. 3.761.000.427,000. 427.000.550,000. 550.000.128,000. 128.000.234,000. 234.000.

29,000. 29.000.3,000. 3.000.

Note : First Screen: Boiler make-up water treatment. Lu : Trc mn hnh: Ni hi

make-up x l nc.Second Screen: Cooling tower water treatment and boiler make-up water treatment. Mnhnh th hai: Thp gii nhit nc thi v l hi ln lm cho nc thi.

Laboratory Perspective Phng th nghim nhn thc

The primary question to be answered is "Does the technology work as advertised?" Cccu hi chnh cn tr li l "C cng vic cng ngh nh qung co?" The history of thetechnologies, as illustrated through primarily qualitative--but some quantitative--assessment in many case studies, has shown that when properly installed, a decrease in orelimination of scale formation will be found. Lch s ca cc cng ngh, nh c minhha qua ch yu l nh tnh - nhng mt s nh lng - nh gi trong cc nghin cunhiu trng hp, ch ra rng khi ci t ng cch, gim hoc loi b cn s c tmthy. While the evidence supporting the technologies may be thought of as mainlyanecdotal, the fact remains that upon visual inspection after installation of these devicesthe formation of new scale deposits has been inhibited. Trong khi cc bng chng h trcc cng ngh c th c dng nh ch yu l giai thoi, s tht vn l khi kim trabng mt sau khi ci t ca cc thit b ny hnh thnh cc m