water treatment handbook unitor
TRANSCRIPT
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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 300 Skyen, N-0212 Oslo, Norw ayOffice: Drammensvn. 211, N-0277 Oslo, Norway
Tel: +47 22 13 14 15. Fax: +47 22 13 45 00Tlx: 76004 UNTOR N
ID.
NO.
08173
REV.
NO.
00
LOBO
09.9
7
5K
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: 76004 UNTOR 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 composed
of 2 Hydrogen atoms and 1 Oxygen atom.
Natural water
Raw w ater is the description of the water to w hich we have daily access.
We can obtain our water from:
1. The ocean
2. Surface sources (e.g. from lakes)
3. Underground sourc es
The water will vary in composition.
The natural water c ycle may be as below:
While it is evaporating from the surface of a lake or the oc ean into the atmo-
sphere, we can designate the water vapour H2O. In the atmosphere, c louds
will form, and during suitable humidity and temperature, the clouds will
deposit w ater (rain). While the rain is falling towards the earth, it absorbs
gases 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 wi ll dissolvevarious minerals from the soil.
INTRODUCTIONThis Product Applications Handbook has been designed to provide specific
information on the variety of chemical and related products and systemsavailable from Unitor.
This handbook will give all the information required to maintain these vari-
ous products, including the application of individual chemical products to
properly 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 Control
6. Boiler Coagulant
Low Pressure Boilers, Wate r Treatments:
1. Combitreat (powdered)
2. Liquitreat
3. Condensate Control
Cooling Water Treatments:
1. Dieselguard NB (powder)
2. Rocor NB Liquid
Sea W ater Cooling Treatment:
1. Bioguard
Evaporator Treatment:
1. Vaptreat
IV WATERTREATMENT HANDBOOK 5WATERTREATMENT 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 in
the figure below. Evidence of pitting is usually found in the boiler shell
around 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 combined
action of heavy stress and a corrosive environment. The stages of fail-
ure of the metal due to stress corrosion are shown below. Corrosion is
initiated by breakdown of the surface film follow ed by the formation of a
corrosion pit whic h becomes the site for stress corrosion cracking,
eventually leading to mechanical failure due to overloading of the
mechanical strength of the metal. This form of attack is often found
around the ogee ring in vertical auxiliary boilers, when undue stressing
is set up by poor steam-raising procedures.
Stress corrosion
15WATERTREATMENT HANDBOOK
3 Problems of Boiler Water
Feedwater produced by distillation for use in a boiler is not pure, even w ith 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 they
are 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 w alls. This thinning of boiler
tubes 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 wastage 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 c arry over wi th steam, the
thermal 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 from
carryover. The boiler manufacturers stipulate a maximum allowed salinity of
the boiler water (as a rule at 0.4Be = 4000 mg salts dissolved per l itre). If this
value is exceeded, there is a risk of normal bubble size being prevented;
larger bubbles will be produced and the turbulence in the water surface w ill
increase and cause foaming.The foam may be carried over w ith the steam,
particularly when the generation of steam is at maximum, which c auses boiler
water (containing Sodium Hydroxide and salt) to pass out into the steam
pipes.
The content of Silicic Acid is important for boilers wi th high pressures.
Silicic Acid in its volatile form may be carried away with the steam and be
deposited on turbine blades, for instance, on whic h it w ill 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.
19WATERTREATMENT HANDBOOK18 3 / PROBLEMS OF BOILER WATER
Ill ustration 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 w ill 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 differences in the test results c an be
explained by differences in the composition of scale (poroushard).
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Typical pac kaged boiler. Packaged boilers inc lude a pressure vessel, burner, all the controls, airfans, and insulation. The boiler is tested at the manufacturers plant and shipped to t he customer,ready for use, when the fuel lines and piping and electrical connections have been installed.
Typical Scotc h Marine f iretube boiler (courtesy of Orr & Sembower, Inc.).
21WATERTREATMENT HANDBOOK
4 Types of Boiler
What is a boiler?
A boiler is a steel pressure vessel in which water under pressure is c on-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, liberated
from 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 w ater 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 TEM PERATURE WATER (HTW) HEATING SYSTEM S
In recent years, interest has been revived in high temperature hot water
heating systems for institutional, industrial and commercial plants. By
increasing the temperature and pressure of the hot w ater and increasing the
size of the generators, some advantages are gained over the low pressuresteam heating systems previously used. In other cases, special forced
circulation boilers have been designed, which consist of many rows of tubes
without a steam drum. In another type, heat is supplied by steam from
a standard type of boiler which heats the water in a direc t contact heater.
This is referred to as a cascade system.
23WATERTREATMENT HANDBOOK
4.3 FIRETUBE BOILERS
Wet back designs
Have a water wall at the back of the boiler in the area where c ombustion
gases reverse direction to enter tubes.
Dry back designs
Refractory is used at the back, instead of a w ater wall. Internal maintenance
is simplified, but refractory replacement is expensive and overheating,
gauging and cracking of tube ends at the entrance to return gas passages
often 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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WATERTREATMENT HANDBOOK
5.1 TYPICAL BOILER SETUP ON A MOTOR SHIP
5.1.1 The Boiler System
This does not just consist of a boiler. As indicated by the figure above, it
is 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 w ater treatment.
The steam plant consists of the following:
Storage tank
This tank wil l hold the make-up water to be supplied to the various
systems as they lose water through leaks and through evaporation.
Normally, this water is made by a low pressure evaporator (this will
be described later on). The water produced in this way is normally of
good 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, and
the quality can vary considerably. This water w ould probably require
more treatment to correctly c ondition it for use.
Hot w ell, observation tank or cascade tank
This has a very important function for the dosing of chemical treat-
ments. This is where all the water c ollects on returning from the various
areas where steam has been used. It is also where water enters the
system 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
25
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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11.7.3 Recommended Sampling Points
Point (A) Condensate pH, Ammonia, Chlorides.Point (B) Feed Water Dissolved Oxygen, pH, TDS, Chlorides.
Note: Testing can be done at the disc harge 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 i s leaking into the feed pump.
53WATERTREATMENT HANDBOOK52 11 / HIGH PRESSURE BOILER WATER CONTROL
12 Boiler 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 occ ur 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 w ith the boiler vented.
150200 ppm Hydrazine is dosed into the boiler. (This works out at
1.25 litres/ tonne of water.)
NB! Full water capacity must be used to calculate this not working capacity.
4 The vent cock on top of the boiler should be opened and the boiler filled
wi th feedwater that is as hot as possible (90 C).
5 The boiler should be given a head of water to ensure that the boiler is kept
full of w ater. 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 the
normal 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 tank
or return tank.
4) Circulate the solution through the system and heat until the water reaches
a temperature of about 60 C.
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.
71WATERTREATMENT HANDBOOK70 15 / DIESEL ENGINE COOLING WATER TREATMENT
16 Reporting Analysis Results
One important aspect of a good water treatment management system is to
ensure that analysis results and any action taken are recorded as the events
take place and the reports are properly maintained for future reference.
As mentioned earlier, special log forms are supplied separately for both
boiler water treatment and diesel engine cooling w ater treatment. These
should be completed by the w ater treatment officer responsible. Attention
should be paid not only to recording the results of various water analyses,
but to reporting any changes in circ umstances that may have a direct or an
indirect influence on the r esults, including any major cleaning or repairs to
the system.
In order that Unitor may keep a watc hful 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 w ith your treatment programme.
Picture page 72, 73, 74, 75, and 76, shows log examples.
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73WATERTREATMENT 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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75WATERTREATMENT HANDBOOK74 16 / REPORTING ANALYSIS RESULTS
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
17 W T S
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77WATERTREATMENT HANDBOOK76 16 / REPORTING ANALYSIS RESULTS
17 Water 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
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18 Evaporator Treatment
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83WATERTREATMENT HANDBOOK82 18 / EVAPORATOR TREATMENT
18 Evaporator Treatment
THE FRESH WATER EVAPORATOR (OR GENERATOR)
There are two main types:THE VACUUM or FLASH EVAPORATOR
and
THE 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 the
heating water. Sea water is pumped into the vertical tubes from below to be
heated by the jacket water. The water vapour produced rises to the top of the
evaporator w here it comes into c ontact w ith cooling tubes and condenses.
The condensate is then taken off for storage. The system is very efficient
when c orrectly 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 pull
the 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 periods
of time. It works in the following w ays:
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-foaming
agents.
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.
19 M arine Equipment
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85WATERTREATMENT HANDBOOK84 18 / EVAPORATOR TREATMENT
FRESH WATER GENERATORType AFGU 1-E-10/1-E-15
19 M arine Equipment
19.1 SOM E COM M ON M ARINE EQUIPM ENT
19.1.1 High Pressure Boilers > 30 bar Babcox & Wilcox Combustion Engineering
Foster Wheeler IHI
19.1.2 Low Pressure Boilers < 30 bar
Sunrod Aalborg Coc hran Osaka Kaw asaki M HI
19.1.3 Slow Speed Diesel Enginees < 120 rpm
M itsubishi Sulzer MAN B & W Gtavrken Fiat GMT
19.1.4 M edium Speed Diesel Engines 120900 rpm War tsila Sulzer Pielstic k Enter pr ise MAN B & W
MaK Deutz Ber gen Diesel Daihatsu
19.1.5 High Speed Diesel Engines > 900 rpm
Hitac hi Yanmar EMD Cummins Cater pillar
19.1.6 Evaporators
Alfa-Laval Desalt Atlas (bought by Alfa-Laval) Nirex
M axim Weir
Notes: Notes:
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87WATERTREATMENT HANDBOOK
Notes:
86 20 / NOTES
Notes:
Notes:
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88 20 / NOTES
Notes: