Water Treatment

Note: The source of the technical material in this volume is the ProfessionalEngineering Development Program (PEDP) of Engineering Services.

Warning: The material contained in this document was developed for SaudiAramco and is intended for the exclusive use of Saudi Aramco’semployees. Any material contained in this document which is notalready in the public domain may not be copied, reproduced, sold, given,or disclosed to third parties, or otherwise used in whole, or in part,without the written permission of the Vice President, EngineeringServices, Saudi Aramco.

Chapter : Process For additional information on this subject, contactFile Reference: CHE10701 R. A. Al-Husseini on 874-2792

Engineering EncyclopediaSaudi Aramco DeskTop Standards

Water Treatment AndDistribution / Sources, Uses And Quality

Engineering Encyclopedia Process

Water Treatment andDistribution / Sources, Uses and Quality

Saudi Aramco DeskTop Standards

CONTENTS PAGE

SOURCES OF WATER 1USES OF WATER 1

Once-Through Cooling Water 2Recirculating Cooling Water 3Boiler Feedwater 3Domestic (Sanitary) Water 4Firefighting Water (See SAES-B-007A) 4Engine Cooling Water 5Chemical Mixing Water 6Hydrostatic Testing Water 6

WATER ANALYSES 7QUALITY OF WATER 9

Scale 9Corrosion 10Solids 11Caustic 11Organics 11Purity Targets for Once-Through Cooling Water 11Purity Targets for Open Recirculating Cooling Water 11Purity Targets for Boiler Steam Water 12Purity Targets for Domestic (Sanitary) Water 13Purity Targets for Firefighting Water 13

CONTENTS PAGE

WORK AID 1: COMMON CHARACTERISTICS ANDIMPURITIES IN WATER 14WORK AID 2: PURITY TARGETS FOR OPENRECIRCULATING COOLING WATER 16WORK AID 3: TYPICAL TREATMENT PURITY TARGETS -MAXIMUM IMPURITIES IN BOILER MAKEUP WATER 17WORK AID 4: TYPICAL TREATMENT PURITY TARGETS -MAXIMUM IMPURITIES IN STEAM DRUM WATER 18GLOSSARY 19REFERENCES

Saudi Aramco Standards 21Saudi Aramco Design Practices 21Exxon Basic Practices 21



Saudi Aramco DeskTop Standards 1

SOURCES OF WATERThe usual sources of water are:

• Purchased or municipal water

• Surface fresh water

• Subsurface ground water

• Sea water

The major concerns with purchased water are the cost, the reliability of supply, and the potential qualityvariations. Saudi Aramco does not purchase water.Surface fresh water can come from rivers, streams, lakes, or ponds. These waters usually contain suspendedmatter, organic matter, dissolved solids, dissolved gases, and other man-made and natural pollutants. Surfacefresh water is rare in Saudi Arabia.Subsurface ground water can originate from springs and shallow or deep wells. These waters are usuallyrelatively free of suspended matter. They can have wide quality variations. Even normally fresh water wellscan have salt water intrusion or limited availability during dry periods. Wells are a common source of waterthroughout Saudi Aramco.Seawater is often used offshore or in arid regions such as Saudi Arabia. This water has a high dissolved solidscontent, frequently over 30,000 ppm. Waste heat or low level heat is used in many cases to evaporate sea wateras a first step in water treatment.

USES OF WATERWater has many uses both in municipalities and in plants. The five main uses of water in Saudi Arabia are:

• Once-through cooling water

• recirculating cooling water (cooling tower) makeup water

• Boiler feedwater

• Domestic (sanitary) water

• Firefighting water




In addition to these five main uses, water is also used for engine cooling, chemical mixing, hydrostatic testing,and for other minor uses.

Once-Through Cooling WaterAlmost any type of water can be used for once-through cooling water. This includes sea water containing highdissolved solids. Typical sources of once-through cooling water are rivers, lakes, and the sea.Storage of this water is usually not required since once-through systems are limited to locations where thesource is essentially unlimited. Discharge rates of the heated water are very high. Care must be taken tosegregate water intake from water discharge to prevent recirculation of impurities and heat that would raise thetemperature of the intake.Filtering of once-through cooling water is usually required; however, this can be accomplished only by coarsescreening in may cases. At some locations, this filtering or screening is the only treatment required.There can be environmental restrictions on once-through cooling water discharge. The most frequent concern isthe temperature of the discharge water.The main problems that can be encountered in once-through cooling water systems are fouling, microbiologicalgrowth, corrosion, and scale.Screening or filtering and shock treatment by chlorine addition are the most common ways to control foulingand microbiological growth. In some cases, other chemicals may be substituted for chlorine formicrobiological control. These include sodium pentachlorophenate, acrolein, and some vendor proprietarycompounds of zinc, copper, mercury, tin, silver, and cadmium.Biodispersants and antifouling materials can help to disperse fouling materials and sludge. They includepolyacrylates, natural organic materials, and other organic polymers. Maintaining water velocities in thesystems, and particularly in heat exchanger tubes, greater than 3 ft/sec will keep the suspended solids movingthrough the system. In spite of the best efforts to control fouling and sludge, the heat exchanger usually needsperiodic cleaning.Calcium carbonate, the most common scale in once-through systems, can be inhibited by applying one or acombination of deposit-control materials such as polyphosphates, phosphonates, and polyacrylates.The first step in corrosion control in a once-through system is proper selection of the materials of construction.Aluminum, brass, cupro-nickel, and titanium are typical corrosion-resistant materials. Fiberglass-reinforcedplastic, and cement-lined and plastic-lined pipe are also used for distribution. Maintaining tube metaltemperatures below 150°F will also help to limit corrosion.




Recirculating Cooling WaterWater used in recirculating systems can come from any water source. It is normally filtered before use. In arecirculating system, the hot water is returned to a cooling device such as a cooling tower, heat exchanger, or airfin. In a cooling tower, water mixes with air. Evaporation cools the water. The exhaust air becomes saturatedwith water. Some of the water is drawn off as blowdown to dissolved solids in the water. Some of the water isdrawn off as blowdown to remove concentrated contaminants and is replaced with makeup water. Disposalrates and makeup rates are much lower than those with once-through systems.Storage of water is usually required, often in a cooling tower basin or sump. The quantity stored depends uponthe reliability of the water source and whether the services being cooled are critical.

Boiler FeedwaterBoiler feedwater must be treated in nearly all cases. Makeup water is frequently a low percentage of totalfeedwater, often less than 10%, because most of the condensate is returned. Water quality required depends onthe use of the water. For example, higher pressure boilers require a better quality of water. Returnedcondensate can also require treatment, particularly to remove oil and control pH.Boiler feedwater treatment will be discussed in detail in the module on Water Treatment Systems.Storage of the treated boiler feedwater is required if steam is used in critical services. Typically, a supply equalto 4 to 8 hours of treated water consumption is maintained.




Domestic (Sanitary) WaterTypical usages of raw water, potable water (drinking water), and irrigation water are given in SADP-S-040.Domestic or sanitary water is usually fresh water that is either potable or can be made potable by biocideinjection. However, this is not always the case. In some areas or at some plants, sanitary water and potablewater systems are completely separate.Potable water systems, in particular, are normally isolated from potentially contaminated water systems by anatmospheric break or by physical separation with free fall of water to prevent contamination of the potablewater system. At least one standby well is required at Saudi Aramco when domestic water is supplied fromwells. Where pumping is required for domestic water, at least one standby pump is required. For additionalpumping requirements, see SAES-S-040.Storage of domestic water is essential if the water source is not extremely reliable. Saudi Aramco requires 14hours of drinking water storage. For a community, storage must provide 50% of peak daily raw waterconsumption plus four hours of maximum firewater requirements. For a plant, storage must provide 50% ofplant building average daily consumption plus 100% of processing water daily requirements plus eight hours ofmaximum fire water requirements. (See SAES-B-007A and SAES-S-040.)The mineral content of domestic water is usually low, below 500 ppm; however, Saudi Aramco permits amaximum of 1,500 ppm. Other Saudi Aramco limits on domestic water impurities are listed in SAES-A-110.Design water pressures for Saudi Aramco domestic water systems are 40 psig minimum, 65 psig normalmaximum, and 85 psig absolute maximum. The minimum pipeline diameter allowed is 2 inches.

Firefighting Water (See SAES-B-007A)Reliability of the firewater source is critical. A river, lake, or even seawater are good sources. Generally, thequality of firewater is not a concern except potential from salt water. If firewater must be taken from a tank,storage requirements for various facilities are given in SAES-B-007A, paragraph 7.3.A firewater system must provide the required flow rate to the protected area, assuming only one major fireoccurrence at any one time. System design should include ways to isolate critical components that might failfor reasons such as loss of power. The system must be able to deliver a minimum of 50% of the required flowto the protected area at all times.




The firewater system should have a minimum of two electrically driven normal pumps with a total capacity ableto supply the maximum design rate. Spare diesel-driven pumps are required to supply at least 50% of thedesign rate if there is a total power failure.The firewater distribution system should be kept under pressure at all times. Within Saudi Aramco, theminimum pressure allowed at a hydrant is 100 psig in process areas and 80 psig in offsite and other areas. Tokeep the system under pressure, a small jockey pump (300 to 500 gpm capacity) can be used. For systemsrequiring 500 gpm maximum or less, no jockey pump is required. System pressure can be maintained byrunning a regular pump. For systems requiring 500 to 1,000 gpm, one jockey pump is required. For systemsrequiring more than 1,000 gpm, two jockey pumps are required.If a motor-driven firewater pump is used, the motor should be automatically started when firewater systempressure is low. It should also be provided with remote start capability.Firewater piping should be installed below ground in areas where the risk of fire is high. The piping shouldarranged in loops with adequate valving so that any section of broken pipe can be isolated. Pipes must be largeenough to provide the required pressures at hydrants at 50% of maximum flow to any fire risk area with anyone section of pipe out of service.The entire system should be tested frequently to make certain it is all in working order. Frequency of testing isestablished based upon the experience with a specific system.

Engine Cooling WaterEngine cooling water often has its own self-contained, closed, recirculating system. However, it can also bepart of a larger cooling water system such as a plant cooling tower recirculating water system.A closed system must be separately treated to control corrosion and scaling. Makeup water to a closed systemshould be of very good quality. Condensate is often a good source. Domestic water or boiler feedwater is alsoacceptable.Additional storage of engine cooling water is usually not required.




Chemical Mixing WaterThe quality of water used for mixing chemicals depends upon the chemical used and the chemicalmanufacturer's recommendations. It is usually best to use the highest quality water available. Condensate,boiler feedwater, or domestic water may be acceptable.

Hydrostatic Testing WaterFresh water is preferred for hydrostatic testing because it is less corrosive than brackish or salt water. Almostany source of fresh water is acceptable. Protection from corrosion must be considered.If chemical additives are used for corrosion protection, disposal of the water must be planned andenvironmental requirements considered.




WATER ANALYSESWater analysis must be performed in order to determine if impurities are within acceptable limits for therequired use. Water analyses are conventionally expressed, for both cations and anions, in parts per million byweight (ppw) except for hardness and alkalinity, which are usually expressed in ppmw of calcium carbonate(CaCO3). These ppmw values can be converted to a common basis (such as milli-equivalents/liter). Thispermits the summation of oppositely charged ions such that total cations will then equal total anions. Cationand anion concentrations in milli-equivalents/liter can be converted to ppmw CaCO3.The calculations for water at a specific gravity of 1:

Molecular Weight

Valence = Equivalent Weight

Water AnalysisIon ppmw MW

EquivalentWeight

Calcium (Ca+2) 100.1 40.08

40

Magnesium (Mg+2) 20.4 24.32

24

Sodium (Na+1) 12.0 23.00

23

Bicarbonate (HCO3-1) 366.0 61.02

61

Sulfate (SO4-2) 48.1 96.06

96

Chloride (C1-1) 7.1 35.46

35




Parts Per Million by WeightEquivalent Weight = Milli − Equivalents / Liter

Milli-equivalents/liter x molecular weight of CaCO3 = ppmw of CaCO3

Cations

Ion Milli-Equivalents/Liter (Sp Gr = 1.0) ppmw CaCO3

Ca+2Mg+2Na+1

100.1/20.04 = 5.0020.4/12.16 = 1.68

12.0/23 = 0.52

(5.0)(50.05) = 250(1.68)(50.05) = 84(0.52)(50.05) = 26

Totals 7.20 360

Anions

Ion Milli-Equivalents/Liter (Sp Gr = 1.0) ppmw CaCO3

HCO3-1SO4-2Cl-1

366/61.02 = 6.0048.1/48.03 = 1.68

7.1/35.46 = 0.20

(6)(50.05) = 300(1.0)(50.05) = 50

(0.20)(50.05) = 10

Totals 7.20 360

Total hardness is the sum of calcium and magnesium and is therefore equal to 334 ppmw as CaCO3 (250 + 84).Correspondingly, alkalinity is the sum of CO3-2, HCO3-1, and OH-1 ions and is equal to 300 ppmw asCaCO3.The values obtained by these calculations can be compared with the Purity Target Tables (Work Aids 2, 3, and4) to determine if additional treatment is required.




QUALITY OF WATERFive types of impurities found in water are a concern in cooling or steam generation applications. For asummary of water impurities, difficulties and treatment methods, see Work Aid 1. The five impurity types are:

• Scale-forming and deposit-forming insoluble solids

• Soluble salts and dissolved gases that can enhance or cause corrosion

• Dissolved solids, oil, and silica than can carry over into the steam from a boiler

• Caustic (sodium hydroxide - NaOH), which can cause embrittlement

• Organics, which can foul anion exchangers

ScaleScale and deposits result when insoluble salts deposit on heat transfer surfaces. This reduces heat transfer andcan cause equipment failure. Scale is caused primarily by the hardness salts, metals, and silica.Among the significant scale- and deposit-forming impurities are:

• Calcium

• Magnesium

• Silica

• Phosphates

• Oil

• Iron, copper

• Other suspended solids and turbidity




CorrosionCorrosion affects distribution piping, feedwater piping, boiler internals, and condensate piping. The maincauses are oxygen, carbon dioxide, chlorine, and excess alkalinity.Corrosives act in different ways. Oxygen causes pitting or formation of small pits in distribution piping,feedwater systems, and boilers. It also aggravates corrosion in condensate systems. It can be removedexternally in a deaerator, and it can be scavenged internally by adding sulfite or hydrazine.Carbon dioxide also causes condensate system corrosion. It can be removed in a deaerator, degasifier ordecarbonator.Ammonia attacks copper alloys. It is sometimes added for feedwater or condensate pH control. It can also beformed by hydrazine decomposition. A deaerator will remove ammonia.Abnormal alkalinity produces caustic embrittlement, film corrosion, and turbine fouling.Excessive chelates or dispersants can cause corrosion in steam piping and throughout the steam system.Impurities that enhance corrosion include:

• Oxygen

• Carbon dioxide

• Ammonia

• Alkalinity

• Chlorides

• Sulfites

• Hydrazine

• Chelates

• Organics




SolidsCarryover of solids from boiler water into the steam is caused by inadequate separation in a boiler drum, byvolatilizing of silica, and by foaming resulting from oil contamination of boiler water. Solids carryover canresult in superheater failure, steam turbine blade fouling, and process catalyst fouling. The main causes of suchproblems are high total dissolved solids (TDS), alkalinity, oil, and silica in the boiler drum.

CausticCaustic embrittlement is the cracking of metal along grain boundaries. It can result from too much caustic inboiler water particularly in poorly controlled caustic-pH programs where caustic is added for pH control.

OrganicsOrganics in the makeup water can also foul water-treating exchangers.Organics are complex acids resulting from decaying plants and other forms of pollution. If they exist inmakeup water in large quantities, they can foul anion exchanges, affect the quality of treated water, anddrastically reduce anion exchanger run lengths. They can be detected by a permanganate test or a total organiccarbon (TOC) test.Organics can be removed by coagulation and filtration, by chlorination and by preceding a strong anionexchanger by a weak anion exchanger. Exchangers can be regenerated by periodic rinsing with salt water.

Purity Targets for Once-Through Cooling WaterOnce-through cooling water may be obtained from any source. As impurities are flushed out of the systemimmediately, quality of the water is not a consideration.

Purity Targets for Open Recirculating Cooling WaterWork Aid 2 lists recommendations for the maximum concentration of impurities in open recirculating coolingwater systems.




Purity Targets for Boiler Steam WaterBoiler water is treated to protect equipment on both the water side and the steam side of a steam generationsystem. The steam quality can be affected in several ways.Steam drums are designed with internals to improve the separation of water droplets from steam. Vendors whobuild steam generators in accordance with American Boiler Makers Association (ABMA) standards guaranteeless than 1 ppm of solids carryover into steam with 2,000 ppm of total dissolved solids (TDS) in the drumwater. Non-ABMA vendors have various other standards. Most process steam generators are special designsand can have widely varying standards.In addition to solids carryover, silica is volatile at higher temperatures and can carry over as a vapor. Othersolids also have some solubility in superheated steam.Alkalinity, high TDS, and the presence of oil in drum water can affect foaming, which results in carryover.Antifoaming agents can be added to drum water to help reduce foaming. Another method of minimizingfoaming is to keep alkalinity and TDS below ABMA maximum limits. Many plants operate at 50% of ABMAlimits or below.Auxiliary devices also help to improve steam quality. Steam washers are feasible but are seldom used becausethey are difficult to control. External dry drum separators are very effective. In-line axial and T-type separatorsalso help reduce solids that have been carried over.Another factor that can affect steam quality is the quality of desuperheating or attemperating water which isinjected into steam to reduce and control the steam temperature. Condensate or very high-quality treated boilerfeedwater is recommended for this use to minimize the quantity of solids injected into the steam.Impure steam can cause superheater tube ruptures, steam turbine blade fouling and corrosion, and catalystcontamination.To minimize superheater fouling and tube ruptures, limiting solids carryover to 0.5 ppm instead of the ABMAlimit of 1 ppm will make a significant improvement. This is particularly true for process steam generators.To minimize turbine blade fouling, silica should be limited to one half of ABMA limits and the caustic to TDSratio should be controlled.




Caustic and sulfur gases must be controlled to reduce steam turbine blade corrosion and stress corrosioncracking.To protect catalysts, the following limits should be met for impurities in steam:

• Sulfur < 0.1 ppm

• Chlorides < 0.05 ppm

• Silica < 0.02 ppm

• Sodium < 1.0 ppm

• Organics < 0.2 ppm

Work Aid 3 lists the maximum quantities of various impurities permitted in boiler makeup water based on theconditions listed in the notes.Work Aid 4 lists the maximum quantities of various impurities allowed to accumulate in steam generator drumwater.If impurity concentrations do not exceed these targets, most of the difficulties associated with impurities inboiler water and steam can be avoided.

Purity Targets for Domestic (Sanitary) WaterSpecifications for domestic water are covered in SAES-A-110.

Purity Targets for Firefighting WaterFirefighting water can be drawn from any source, regardless of quality.




WORK AID 1: COMMON CHARACTERISTICS AND IMPURITIES IN WATER

Common Characteristics and Impurities in Water

Constituent Chemical Formula Difficulties Caused Means of Treatment

Turbidity None usually expressed inJackson Turbidity Units

Imparts unsightly appearance to waterdeposits in water lines process equip-ment,boilers, etc.; interferes with most processuses

Coagulation, settling and filtration

Color None Decaying organic material and metallicions causing color may cause foaming inboilers; hinders precipitation methodssuch as iron removal, hot phosphatesoftening; can stain product in process use

Coagulation, filtration, chlorination,adsorption by activated carbon

Hardness Calcium, magnesium, bariumand strontium salts expressed asCaCO3

Chief source of scale in heat exchangeequipment, boilers, pipelines, etc.; formscurds with soap; interferes with dyeing,etc.

Softening, distillation, internal boilerwater treatment, surface active agents,reverse osmosis, electrodialysis

Alkalinity Bicarbonate (HCO3-1), carbo-

nate (CO3-2), and hydroxyl (OH-

1), expressed as CaCO3

Foaming and carryover of solids withsteam embrittlement of boiler steel;bicarbonate and carbonate produce CO2in steam; a source of corrosion

Lime and lime-soda softening, acidtreatment, hydrogen zeolite softening,demineralization, dealkalization by anionexchange, distillation, degasi-fying

Free Mineral Acid H2SO4, HCl, etc. expressed asCaCO3, titrated to methylorange end-point

Corrosion Neutralization with alkalies

Carbon Dioxide CO2 Corrosion in water lines and particu-larlysteam and condensate lines

Aeration, deaeration, neutralization withalkalies filming and neutralizing amines

pH Hydrogen ion concentrationdefined as

pH

pH varies according to acidic or alka-linesolids in water; most natural waters have apH of 6.0 - 8.0

pH can be increased by alkalies anddecreased by acids

Sulfate (SO4)-2 Adds to solids content of water, but, initself is not usually significant; combineswith calcium to form calcium sulfate scale

Demineralization, distillation, reverseosmosis, electrodialysis

Chloride Cl-1 Adds to solids content and increasescorrosive character of water


Nitrate (NO3)-1 Adds to solids content, but is not usu-allysignificant industrially; useful for controlof boiler metal embrittlement


Fluoride F-1 Not usually significant industrially Adsorption with magnesium hydro-xide,calcium phosphate, or bone black; Alumcoagulation; reverse osmosis;electrodialysis

Silica SiO2 Scale in boilers and cooling water systems;insoluble turbine blade deposits due tosilica vaporization

Hot process removal with magnesiumsalts; adsorption by highly basic anionexchange resins, in conjunction withdemineralization, distillation




WORK AID 1 (Cont’d)

Common Characteristics and Impurities in Water (Cont'd)

Constituent Chemical Formula Difficulties Caused Means of Treatment

Iron Fe+2 (ferrous)

Fe+3 (ferric)

Discolors water on precipitation; source ofdeposits in water lines, etc.; inter-feres withdyeing, tanning, paper mfr., etc.

Aeration, coagulation and filtration, limesoftening, cation exchange, contactfiltration, surface active agents for ironretention

Manganese Mn+2 Same as iron Same as iron

Oil Expressed as oil or chloroformextractable matter, ppmw

Scale, sludge and foaming in boilers,impedes heat exchange, undesirable inmost processes

Baffle separators, strainers, coagula-tionand filtration, diatomaceous earthfiltration

Oxygen O2 Corrosion of water lines, heat exchangeequipment, boilers, return lines, etc.

Deaeration, sodium sulfite, corrosioninhibitors, hydrazine or suitablesubstitute

Hydrogen Sulfide H2S Cause of "rotten egg odor;" corrosion Aeration, chlorination, highly basic anionexchange

Ammonia NH3 Corrosion of copper and zinc alloys byformation of complex soluble ion

Cation exchange with hydrogen zeo-lite,chlorination deaeration, mixed-beddemineralization

Conductivity Expressed as micromhos, spe-cific conductance

Conductivity is the result of ionizable solidsin solution; high conductivity can increasethe corrosive characteris-tics of a water

Any process which decreases dis-solvedsolids content will decrease conductivityexamples are deminerali-zation, limesoftening

Dissolved Solids None "Dissolved solids" is measure of totalamount of dissolved matter determined byevaporation; high concentrations ofdissolved solids are objectionable becauseof process interference and as a cause offoaming in boilers

Various softening process such as limesoftening and cation exchange by hy-drogen zeolite, will reduce dissolvedsolids; demineralization; distillation;reverse osmosis; electrodialysis

Suspended Solids None "Suspended solids" is the measure ofundissolved matter, determined gravi-metrically suspended solids plug lines,cause deposits in heat exchange equip-ment, boilers, etc.

Subsidence filtration usually preced-ed bycoagulation and settling

Total Solids None "Total solids" is the sum of dissolved andsuspended solids, determinedgravimetrically

See Dissolved Solids and SuspendedSolids

Source: GPSA Engineering Data Book




WORK AID 2: PURITY TARGETS FOR OPEN RECIRCULATING COOLINGWATER

IMPURITY MAXIMUM CONCENTRATION

Calcium (Ca ++) 800 mg/L as CaCO3

Inhibitor with phosphate 400 mg/L as CaCO3

Sulfate (SO4 - -) AS CaCO3 5 x 105 divided by calcium mg/L

Silica (SiO2) 150 mg/L as SiO2

Magnesium (mg ++) AS CaCO3 3.5 x 104 divided by silica mg/L

*Chlorides (Cl -) 1,000 mg/L as Cl-

Ammonia (NH3) 10 mg/L as Cl-

**Phosphate (PO4 - -) 5 mg/L with Ca++ at 400 mg/L

*Total dissolved salts 3,000 mg/L as is

Suspended solids (< 0.45 microns) 200 mg/L

Oil and grease 10 mg/L

Biological Oxygen Demand 60 mg/L

pH 6.0 to 7.5

*For carbon steel tubes**Depends on tricalcium phosphate solubility




WORK AID 3: TYPICAL TREATMENT PURITY TARGETS - MAXIMUMIMPURITIES IN BOILER MAKEUP WATER

BOILER OPERATINGPRESSURE

(psig) (barg)

TOTAL DISSOLVEDSOLIDS (TDS)

(ppm)

SILICA

(ppm)

TOTALHARDNESS

(ppm)

TOTALALKALINITY

(ppm)

TURBIDITY

(ppm)

150 10 220 15 2 45 1

300 20 200 11 2 40 1

450 30 155 6 1 30 1

600 40 125 4 1 25 0.5

750 50 100 2 1 20 0.5

900 60 80 0.8 1 15 0.5

1200 80 6 0.03 1 0.1

1500 100 5 0.01 1 0.1

2000 140 3 0.005 0.5 0.1

NOTE: This table is based on the following criteria:• Makeup water temperature of 10°C (40°F)

• 20% dilution from condensed heating steam in the deaerator or hot lime softener

• Boiler blowdown rate of 10% for operating pressure up to 60 barg (900 psig)

• Silica can be less than 0.1 ppm from a demineralizer




WORK AID 4: TYPICAL TREATMENT PURITY TARGETS - MAXIMUMIMPURITIES IN STEAM DRUM WATER

BOILER OPERATINGPRESSURE

HYDRATE(psig) (barg)

TOTAL DISSOLVEDSOLIDS

(ppm)

SILICA

(ppm)

ALKALINITYTOTAL

(ppm) (ppm)

150 10 1750 125 350 175

300 20 1500 90 300 150

450 30 1250 50 250 125

600 40 1000 35 200 100

750 50 750 20 150 75

900 60 625 8 125 60

1200 80 500 2.5 100 0

1500 100 350 1.0 75 0

2000 140 250 0.5 50 0




GLOSSARYalkalinity The total carbonate, bicarbonate, and hydroxide ion concentration in the

water expressed as ppm calcium carbonate equivalent. These ions reactwith acid.

anions Negatively charged ions in the water, for example, sulfates, chlorides,nitrates, and bicarbonates.

anion exchanger A vessel containing insoluble resin that is capable of exchanging oneanion, usually hydroxide ions, for other undesirable anions in the water,for example, sulfates, chlorides, and nitrates.

attemperating Spraying water on steam coming out of a boiler to lower the temperatureof the steam.

biochemical oxygen demand(BOD)

A measure of the oxygen consumed in the oxidationof organic and oxidizable inorganic materials in wastewater (expressed inppm).

biocide A poisonous chemical substance that can kill living organisms.blowdown The removal of a portion of water from a system or boiler drum to control

the concentration of dissolved and suspended impurities in the system orboiler water.

calcium and magnesiumhardness

The concentration of calcium and magnesium ions in the water, expressedas ppm calcium carbonate equivalent.

cations Positively charged ions in the water, for example, calcium, magnesium,and sodium.

caustic or caustic soda Sodium hydroxide (NaOH).caustic embrittlement A type of boiler corrosion characterized by cracking of the metal along the

grain boundaries. It may occur when highly stressed metal is exposed toconcentrated boiler water. It is usually associated with high concentrationof sodium hydroxide.

coagulation A process whereby suspended and colloidal particles, which causeturbidity and color in water, are combined by physical means into masseslarge enough to settle.

desuperheating Spraying water on steam in the system to reduce the temperature of thesteam.

dissolved solids See Total Dissolved Solids.filtration The process of passing water containing suspended matter through a

porous material to remove the suspended matter. The suspended matter isnormally reduced to less than one NTU of turbidity.

hardness Same as calcium and magnesium hardness.ion Electrically charged particle formed when a molecule dissociates into

positive and negative particles, for example, salt into positive sodium andnegative chloride ions.

jockey pump A small pump used to maintain pressure on a firewater system when thereis little or no demand on the system.

makeup water Water added to a system to make up for losses or blowdownnephelometric turbidity unit(NTU)

A measurement of the turbidity of a sample of water, determined by lightreflection.

organics Complex acids resulting from decaying plants and other forms ofpollution.

pH A measurement of the acidity or alkalinity of a system. The referencetemperature for pH is 25°C (77°F) and the pH scale runs from 0 (highlyacidic) to 14 (highly basic), with pH = 7.0 being neutral.

potable water Drinkable water.raw water Water that has not yet been processed by a water treating plant.




suspended solids Finely divided insoluble matter present in water. The suspended solidsare normally inorganic material, such as clay, rock, silt, etc.

total hardness Calcium plus magnesium hardness.turbidity Lack of clarity due to the presence of suspended or colloidal matter,

expressed in Nephelometric Turbidity Units (NTU).




REFERENCES

Saudi Aramco Standards• SAES-A-103 Marine Wastewater Discharge

• SAES-A-104 Water Reuse and Land Disposal

• SAES-A-110 Drinking Water Supply

• SAES-B-007A Firewater System Design

• SAES-S-040 Saudi Aramco Water Systems

Saudi Aramco Design Practices• SADP-S-040 Saudi Aramco Water Systems

• SADP-Section IV Firefighting Facilities

Exxon Basic Practices• BP11-1-1 Filters for Water Treating Systems

• BP11-2-1 Fixed-Bed Ion Exchange Water Treating Units

• BP11-4-1 Hot Process Water Treaters

• BP11-4-2 Cold Process Water Treaters

• BP11-5-1 Water Deaerators and Degasifiers (Decarbonators)

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