wilhemsen water treatment handbook

8/12/2019 Wilhemsen Water Treatment Handbook

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Water

Treatment

Handbook

C H E M I C A L S

U N I T O R A S A

Mail: P.O.Box 300Skyen,N-0212 Oslo, NorwayOffice: Drammensvn. 211, N-0277 Oslo, Norway

Tel: +47 22 13 14 15. Fax: +47 22 13 45 00Tlx: 76004UNTORN

ID.NO.08173REV.NO.00LOBO

09.975K

COUNTRYOFORIIGIN:NORWAY


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Marine Chemicals

Water TreatmentHandbookA PRACTICAL APPLICATION MANUAL

1st Edition

Unitor ASA, P.O. Box 300 Skyen, N-0212 Oslo, NorwayOffice: Drammensveien 211, N-0277 Oslo, Norway

Tel: +47 22 13 14 15. Fax: +47 22 13 45 00

Tlx: 76004UNTOR N

ID. NO. 08 173 REV. NO. 00 LOBO 09.97 5K COUNTRY OF ORIGIN: NORWAY


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1 Water Treatment Philosophyand Overview

1.1 TYPES OF WATER

General

Water could generally be described as the most important of all chemical

substances. Its chemical designation is H2O; the water molecule is composedof 2 Hydrogen atoms and 1 Oxygen atom.

Natural water

Raw water is the description of the water to which we have daily access.

We can obtain our water from:

1. The ocean2. Surface sources (e.g. from lakes)

3. Underground sources

The water will vary in composition.

The natural water cycle may be as below:

While it is evaporating from the surface of a lake or the ocean into the atmo-sphere, we can designate the water vapour H2O. In the atmosphere, cloudswill form, and during suitable humidity and temperature, the clouds will

deposit water (rain). While the rain is falling towards the earth, it absorbsgases which are in the air, e.g. CO2 (Carbon Dioxide), SO2 (Sulphur Dioxide)and O2 (Oxygen).

When the water hits the earth, it absorbs additional Carbon Dioxide (from

biological degradation). The rainwater which is now slightly acid will dissolvevarious minerals from the soil.

INTRODUCTIONThis Product Applications Handbook has been designed to provide specificinformation on the variety of chemical and related products and systems

available from Unitor.This handbook will give all the information required to maintain these vari-

ous products, including the application of individual chemical products toproperly maintain Low Pressure, Medium Pressure and High Pressure Boilers,Diesel Engine Cooling Systems and Evaporators.

Single Function Treatment Products:

1. Hardness Control

2. Alkalinity Control

3. Oxygen Control (Hydrazine)4. Catalysed Sodium Sulphite (Powdered & Liquid)5. Condensate Control6. Boiler Coagulant

Low Pressure Boilers, Water Treatments:

1. Combitreat (powdered)

2. Liquitreat3. Condensate Control

Cooling Water Treatments:

1. Dieselguard NB (powder)

2. Rocor NB Liquid

Sea Water Cooling Treatment:

1. Bioguard

Evaporator Treatment:

1. Vaptreat

IV WATER TREATMENT HANDBOOK 5WATER TREATMENT HANDBOOK


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3.1.1 Pitting Corrosion

Pitting is the most serious form of waterside corrosion and is theresult of the formation of irregular pits in the metal surface as shown inthe figure below. Evidence of pitting is usually found in the boiler shellaround the water level and is most likely caused by poor storage proce-

dures when the boiler is shut down for lengthy periods, and by inade-quate Oxygen scavenging.

Pitting corrosion.

3.1.2 Stress Corrosion

Stress corrosion cracking is the process caused by the combinedaction of heavy stress and a corrosive environment.The stages of fail-

ure of the metal due to stress corrosion are shown below. Corrosion isinitiated by breakdown of the surface film followed by the formation of a

corrosion pit which becomes the site for stress corrosion cracking,eventually leading to mechanical failure due to overloading of themechanical strength of the metal. This form of attack is often found

around the ogee ring in vertical auxiliary boilers, when undue stressingis set up by poor steam-raising procedures.

Stress corrosion

15WATER TREATMENT HANDBOOK

3 Problems of Boiler Water

Feedwater produced by distillation for use in a boiler is not pure, even with a

good distillation method. Worse still is ordinary water taken from ashore to beused as feedwater. The water will contain some of the elements (impurities)

mentioned in Chapter 5.Problems will then arise when the water is used in the boiler. The types

of problem will depend on the type of impurities and in which quantities theyare present.

The most common problems are:

CORROSION

SCALING CARRYOVER

3.1 CORROSION

The corrosion processes can affect boilers in the following ways:

General wastage is the overall reduction of metal thickness and is common

in heating surface areas, such as boiler tube walls. This thinning of boilertubes is often found in boilers having open feed systems (mostly auxiliary

boilers) without any protective treatment. An example of wastage is given inthe figure below.

14 3 / PROBLEMS OF BOILER WATER

General w astage of a boiler tube.


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3.3 CARRYOVER

Carryover is any contaminant that leaves the boiler with the steam.

Carryover can be:

Solid Liquid Vapour

Effects of carryover:

Deposits in non-return valve Deposits in superheaters Deposits in control valves Deposits on turbine

Carryover in superheaters can promote failure due to overheating.

Turbines are prone to damage by carryover, as solid particles in steam can

erode turbine parts. When large slugs of water carry over with steam, thethermal and mechanical shock can cause severe damage.

Causes of carryover:Mechanical:

Priming Sudden load changes Boiler design Soot blowing High water level

Chemical:

Foaming due to: High Chlorides High TDS High alkalinity Suspended solids Oil Silica

The most common form of encrustation in a steam system stems fromcarryover.The boiler manufacturers stipulate a maximum allowed salinity of

the boiler water (as a rule at 0.4 Be =4000 mg salts dissolved per litre). If thisvalue is exceeded, there is a risk of normal bubble size being prevented;

larger bubbles will be produced and the turbulence in the water surface willincrease and cause foaming.The foam may be carried over with the steam,particularly when the generation of steam is at maximum, which causes boiler

water (containing Sodium Hydroxide and salt) to pass out into the steampipes.

The content of Silicic Acid is important for boilers with high pressures.

Silicic Acid in its volatile form may be carried away with the steam and bedeposited on turbine blades, for instance, on which it will form a very hard,

porcelaine-like scale.However, not only the chemical composition may cause carryover. Circum-

stances such as periodic overloads, periods of a too high a water level (or more

correctly: too small a steam volume) are two of the most common causes.

Finally, impurities from the condensate, such as oil from the preheaterscoils if they are leaking are very common causes of priming.

19WATER TREATMENT HANDBOOK18 3 / PROBLEMS OF BOILER WATER

Illustration ofTypical Conditions With

a Clean Boiler Tube

Change in Conditions Whena Layer of Scale of just 3 mm

Thickness Exists

The scale causes the fuel consumption to increase by approx.18 percent.

Stress will arise in the steel as a result of the insulating effect of the scale.

Excess Fuel Consumption in %,depending on Thickness of ScaleCurve of middle values.The differenc es in the test results can be

explained by differences in the composition of scale (poroushard).


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Typical packaged boiler. Packaged boilers include a pressure vessel, burner, all the controls, airfans, and insulation. The boiler is tested at the manufacturers plant and shipped to the customer,ready for use, when the fuel lines and piping and electrical connections have been installed.

Typical Scotch Marine firetube boiler (courtesy of Orr & Sembower, Inc.).


4 Types of Boiler

What is a boiler?

A boiler is a steel pressure vessel in which water under pressure is con-verted into steam by the application of combustion. In other words, it is

simply a heat exchanger which uses radiant heat and hot flue gases, liberatedfrom burning fuel, to generate steam and hot water for heating and

processing loads.There are two types: Fire tube boilers and water tube boilers.

4.1 FIRE TUBE BOILER

Hot flue gases flow inside tubes that are submerged in water within a shell. Pressures up to about 10 bar

Produce up to 14 tonnes of steam/hr

Can meet wide and sudden load fluctuations becauseof large water volumes

Usually rated in HP

4.2 WATER TUBE BOILER

Water flows through tubes that are surrounded by hot combustion gasesin a shell.

Usually rated in tons of steam/hr

Used for H.P. steam

High capacity

BOILERS HAVE SIX BASIC PARTS

1) Burner2) Combustion space

3) Convection section

4) Stack

5) Air fans

6) Controls and accessories

20 4 / TYPES OF BOILER


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4.5 HIGH TEMPERATURE WATER (HTW) HEATING SYSTEMS

In recent years, interest has been revived in high temperature hot water

heating systems for institutional, industrial and commercial plants. Byincreasing the temperature and pressure of the hot water and increasing the

size of the generators, some advantages are gained over the low pressuresteam heating systems previously used. In other cases, special forcedcirculation boilers have been designed, which consist of many rows of tubeswithout a steam drum. In another type, heat is supplied by steam from

a standard type of boiler which heats the water in a direct contact heater.This is referred to as a cascade system.


4.3 FIRETUBE BOILERS

Wet back designs

Have a water wall at the back of the boiler in the area where combustiongases reverse direction to enter tubes.

Dry back designs

Refractory is used at the back, instead of a water wall. Internal maintenanceis simplified, but refractory replacement is expensive and overheating,

gauging and cracking of tube ends at the entrance to return gas passagesoften cause problems.

4.4 CLAYTON STEAM GENERATOR

The coil type generator is a vertical coil with fuel combustion taking place

inside the coil. High quality feedwater and a closely monitored chemical treat-ment programme are mandatory. The most common problem is Oxygen

pitting on the inside portion of the coil near the fire. The two most commonname brands are Vapor-Clarkson and Clayton.

22 4/ TYPES OF BOILER

Medium-sized watertube boilers may be classified according to three basic tube arrangements.

WATERSYSTEM AND STEAMSYSTEM


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WATER TREATMENT HANDBOOK

5.1 TYPICALBOILERSETUPONAMOTORSHIP

5.1.1 The Boiler System

This does not just consist of a boiler. As indicated by the figure above, itis a complete plant. Most motor ship boilers operate at low pressure,that is, not more than 20 bar pressure. This makes it suitable for the

single treatment: the combined boiler water treatment.

The steam plant consists of the following:

Storage tank

This tank will hold the make-up water to be supplied to the varioussystems as they lose water through leaks and through evaporation.Normally, this water is made by alow pressure evaporator (this will

be described later on).The water produced in this way is normally ofgood quality if the evaporator is set up correctly. When it is introduced

to the boiler, it will require the minimum amount of treatment. However,at some stage the vessel will very likely take water from ashore, andthe quality can vary considerably.This water would probably require

more treatment to correctly condition it for use.

Hot well, observation tank or cascade tank

This has a very important function for the dosing of chemical treat-ments.This is where all the water collects on returning from the various

areas where steam has been used. It is also where water enters thesystem from the storage tank(s) to make up the quantity required in the

system. If the steam has been used for heating fuel, the returns fromthat tank may contain oil, or if cargo heating has been used, some of

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4.6 FIRETUBE BOILERS

Advantages:

Lower initial cost

Few controls

Simple operation

Disadvantages:

Drums exposed to heat, increasing the risk of explosion

Large water volume, resulting in poor circulation

Limited steam pressure and evaporation

WATERTUBE BOILERS

Advantages:

Rapid heat transmission

Fast reaction to steam demand

High efficiency

Safer than firetube boilers

Disadvantages:

More control than firetube boilers

Higher initial cost

More complicated to operate

24 4 / TYPES OF BOILER

5 Boiler Systems


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11.7.3Recommended Sampling Points

Point (A) Condensate pH, Ammonia, Chlorides.Point (B) Feed Water Dissolved Oxygen, pH, TDS, Chlorides.

Note: Testing can be done at the discharge from the feed pump. However, if highdissolved Oxygen residuals are found, water in the storage area of the de-aeratorshould be checked to ensure no air is leaking into the feed pump.

53WATER TREATMENT HANDBOOK52 11 / HIGH PRESSURE BOILER WATER CONTROL

12Boiler Wet Layup

Boilers are likely to suffer more from corrosion during periods when not in use

or laid up.They must be protected. Proper layup procedures are essential.Corrosion will occur if :A. Low pH conditions occur.

B. Oxygen is present in the boiler water.

The procedure starts 23 days before the layup date

1 Test the boiler treatment levels and blow down the boiler at regular inter-

vals to reduce potential sludge. The boiler should not be laid up dirty.2 Raise the treatment levels for alkalinity to the maximum allowable level for

that boiler pressure.3 The boiler should then be treated with a high level of Oxygen Control after

it has been isolated from the main steam line. Gentle firing of the boiler

should be used to fully circulate the treatment with the boiler vented.150200 ppm Hydrazine is dosed into the boiler. (This works out at1.25 litres/tonne of water.)

NB!Full watercapacity must be used to calculate this no t working capacity.

4 The vent cock on top of the boiler should be opened and the boiler filledwith feedwater that is as hot as possible (90C).

5 The boiler should be given aheadof water to ensure that the boiler is keptfull of water.This is achieved by connecting a hose of a drum of treated

water to the boiler vent cock to make up for any losses due to leaks.6 Where super heaters are in place, the manufacturers instructions must

be followed.

7 This principle of wet layup can be used for exhaust gas economisers, etc.8 Wet layup of boilers is for the short term. A different procedure should

be used for a long term layup .

Returning to ServiceDrain the boiler of excess Hydrazine, refill with water and warm through in thenormal way.


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3) Calculate the amount of cleaner required for a solution strength of 2% i.e.20 litres per 1000 litres cooling water. Drain of similar amount of cooling

water from engine if necessary. Add Tankleen Plus to the expansion tankor return tank.

4) Circulate the solution through the system and heat until the water reachesa temperature of about 60C.

5) Continue circulation of the solution through the system for a minimum

of 5 hours.

6) Take a sample of cleaning solution from the system after a minimum

of 5 hours.7) When cleaning is completed, drain off the cooling water system, and

thoroughly flush with clean water prior to refilling and adding an anti-

corrosion treatment such as Dieselguard NB or Rocor NB Liquid.

71WATER TREATMENT HANDBOOK70 15 / DIESEL ENGINE COOLING WATER TREATMENT

16Reporting Analysis Results

One important aspect of a good water treatment management system is toensure that analysis results and any action taken are recorded as the eventstake place and the reports are properly maintained for future reference.

As mentioned earlier, special log forms are supplied separately for bothboiler water treatment and diesel engine cooling water treatment. These

should be completed by the water treatment officer responsible. Attentionshould be paid not only to recording the results of various water analyses,but to reporting any changes in circumstances that may have a direct or an

indirect influence on the results, including any major cleaning or repairs tothe system.

In order that Unitor may keep a watchful eye on water treatment pro-

grammes onboard individual vessels, it is essential that the instructions forour Rapid Response programme are followed and logs sent promptly to our

Rapid Response Centre for review and comment.Unitor will monitor the progress and performance of the onboard water

treatment programme and liaise with the vessels head office and ship

accordingly.Examples of how to complete the report logs are given overleaf. Make sure

you use the correct log form in conjunction with your treatment programme.

Picture page 72, 73, 74, 75, and 76, shows log examples.


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73WATER TREATMENT HANDBOOK72 16 / REPORTING ANALYSIS RESULTS

Unitor ASAChemical Business UnitP.O. Box 300 SkyenN-0212 OsloNorway

C H E M I C A L S


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Unitor ASAChemical Business UnitP.O. Box 300 SkyenN-0212 OsloNorway

C H E M I C A L S

Unitor ASAChemical Business UnitP.O. Box 300 SkyenN-0212 Oslo

Norway

C H E M I C A L S

17W t T t S


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17Water Tests, Summary

17.1 SPECTRAPAK TEST KITS

309 Test Kit: Nitrite pH

Cl

310 Test Kit: P-Alkalinity

Cl pH

311 Test Kit: P-Alkalinity M-Alkalinity

PO4

Cl pH

312 Test Kit: Hydrazine/Sulphite

PC 22 Test Kit: P-Alkalinity M-Alkalinity PO4 Cl pH

Conductivity

Hardness Ammonia

Hydrazine Silica

Samples to be tested: Boiler water Feed water Condensate return

Make up water Engine cooling water

17.2 TESTING

Boiler water: P-Alkalinity

M-Alkalinity Cl PO4 pH Hydrazine/Sulphite Conductivity

Silica

Appearance

UnitorASA

ChemicalBusinessUnit

P.O.Box300

S

kyen

N-0212

Oslo

Norway

C

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M

IC

A

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Feedwater: Cl Otheractionsinconjunctionwithpreviouslymentioned:


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79WATER TREATMENT HANDBOOK78 17 / WATER TESTS, SUMMARY

Feed water: Cl Conductivity

Make up water: Cl Hardness

SilicaCondensate return: Cl

pH Ammonia

Engine cooling water: Nitrites Chlorides

pH Appearance

Testing is mandatory to make sure the water treatment programmes areeffective.

BOILER WATER TEST DAILY

FEED WATER AS REQUIREDCONDENSATE TEST WEEKLY

ENGINE COOLING WATER EVERY FOUR DAYS

MAKE-UP WATER AS REQUIRED

Record all chemic al tests on the Rapid Response logs.

17.3 TROUBLESHOOTING

17.3.1Boiler water tests

Fault Action

P-Alkalinity Too high BlowdownToo low Dose Alkalinity Control to the boiler

M-Alkalinity Too high Blowdown

Chlorides Too high Blowdown

pH Too low Dose Alkalinity Control to boilerToo high Blowdown

Phosphate Too high Blowdown

Too low Dose Hardness Control

Hydrazine/Sulphite Too high Blowdown

Too low Check for source of Oxygen leakageIncrease chemical dosage

Conductivity Too high Blowdown

Other actions in conjunction with previously mentioned:

Alkalinity

If P-Alkalinity test results are above limits even after notdosing chemicals,check the P-Alkalinity of the make-up water.

ChloridesIf high Chloride readings exist after blowdown, check for sources of saltwater leaks:

A) Drain cooler B) Condenser C) Heat exchangers

Always check the Chlorides of the feedwater, condensate return and make-up

water when Chloride readings in the boiler continue to be above maximumlimits. If you have steam on deck, check the return lines.

pHCheck pH of condensate. If too low, increase dosage of Condensate Control.If too high, decrease dosage of Condensate Control.

Phosphate

If unable to maintain a Phosphate reading after dosing Hardness Control,check the make-up water for Chlorides.

Hydrazine/Sulphite

Check temperature of feedwater. In most cases, the higher the temperature

of the feedwater, the lower the dosage of Oxygen Control or Sulphite.

Conductivity

If conductivity readings remain high after blowdown, check for:

A) Chloride levels/leaks B) Condensate return C) Phosphate level

17.3.2Cooling water tests

Fault Action

Nitrites Too low Dose Dieselguard NBor Rocor NB Liquid.

Too high Stop dosing of chemical until theNitrite level is back down below the

max. limit.

pH Too low Check for salt water leaks andcombustion gas leakage.

Chlorides Too high Check for leaks. Increase thechemical dosage to bring the Nitrite

level close to the upper limit (2400 ppm).

Nitrite The diagramonthe previouspage shows the typical dosage layout


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81WATER TREATMENT HANDBOOK80 17 / WATER TESTS, SUMMARY

Nitrite

If Nitrite readings remain low after dosing Dieselguard NB or Rocor NBLiquid, you may have a bacteriological problem. The cooling water

should then be analysed with appropriate test dip slides which can beordered from Unitor.Unitor also has available an effective biocide called

MAR-71, which is specially developed for bacteriological problems.

pH

Increase chemical dosage. If Nitrite level is within recommended limits,dose Alkalinity Control to increase the pH.

17.3.3Sea water cooling treatment

To avoid fouling in sea water systems, Unitor has developed a very

effective Amine-based dispersant of marine growth such as ShellfishAlgae and micro-organisms in order to prevent the a.m. problem.

Because of its filming properties, the product also acts as a corrosioninhibitor.

Bioguard can be used in both static and flowing systems such as

ballast tanks and looped cooling systems.

The diagram on the previous page shows the typical dosage layout.This can be modified to suit a particular situation. Although the

product will gradually clean fouled systems, treatment should

preferably be started on a clean system.

Dosage for sea water cooling systems:Dose 0.6 ltr Bioguard for every 100 m3 of seawater flowing through thesystem per hour. The system throughput is to be determined either from

the rating of the pump(s) or from the system specifications. Treatment isnecessary in coastal waters and should commence three days before

entering these waters and continue for three days after leaving coastalwaters. The calculated dose should be given over a one-hour periodand repeated every 48 hours.

Dosage for static ballast tanks:

Dose one litre of Bioguard per 100 m

3

of water prior to ballasting,followed by a monthly dose of 2 litre per 100 m3.

NB! Bioguard should only be diluted with fresh w ater prior to dosing

if necessary.

18EvaporatorTreatment


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83WATER TREATMENT HANDBOOK82 18 / EVAPORATOR TREATMENT

18Evaporator Treatment

THE FRESH WATER EVAPORATOR (OR GENERATOR)

There are two main types:THE VACUUM or FLASH EVAPORATOR

andTHE STEAM HEATED EVAPORATOR

18.1 THE VACUUM EVAPORATOR

Vacuum is maintained in the evaporator, considerably reducing the boiling

point of the water.The heat source used is the engine jacket water. The jacket water is

circulated through the lower section of the evaporator where the heating

section is. This heating section is a series of vertical tubes surrounded by theheating water. Sea water is pumped into the vertical tubes from below to beheated by the jacket water. The water vapour produced rises to the top of the

evaporator where it comes into contact with cooling tubes and condenses.The condensate is then taken off for storage. The system is very efficient

when correctly set up, but there are several points to consider:

A. 3 percent of seawater is dissolved minerals.

B. Evaporators of this type have a tendency to allow the seawater to foamand so salt is carried over with the distilled water.

The treatment is to be fed continuously. The evaporator vacuum will pullthe treatment in and it will enter the evaporator with the seawater.

Sufficient treatment should be mixed for 24 hours operation. Treatment is

essential to keep the evaporator operating efficiently for longer periodsof time. It works in the following ways:

a. Some of the dissolved solids may form scale and the treatment

will help prevent the solids from adhering to the heating surfaces andkeep these scale formers in solution.

b. The sludge will be conditioned to make extraction of the concentrated

sea water (brine) easier.

c. The foaming tendency of the brine will be suppressed by anti-foamingagents.

Unitor treatment is: Vaptreat.

Average dosage: 0.3 l/10 tonnes of distillate produced.

This is calculated on a standard brine density of 1.038 kg/l.

19MarineEquipment


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85WATER TREATMENT HANDBOOK84 18 / EVAPORATOR TREATMENT

FRESH WATER GENERATORType AFGU 1-E-10/1-E-15

19Marine Equipment

19.1 SOME COMMON MARINE EQUIPMENT

19.1.1High Pressure Boilers >30 bar Babcox & Wilcox Combustion Engineering Foster Wheeler IHI

19.1.2Low Pressure Boilers


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Notes:

86 20 / NOTES

Notes:

Notes:


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88 20 / NOTES

Notes:

wilhemsen water treatment handbook

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