Water Treatment Handbook UNITOR

UNITOR

ASA

Mail: P.O. Box 300 Skøyen, N-0212 Oslo, Norway Office: Drammensvn. 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 ORIIGIN: NORWAY

Water Treatment Handbook

C H E M I C A L S

Marine Chemicals

Water Treatment Handbook A PRACTICAL APPLICATION MANUAL

1st Edition

Unitor ASA, P.O. Box 300 Skøyen, N-0212 Oslo, Norway Office: 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

FOREWORD This manual has been edited to specifically apply to Unitor’s Marine Chemical Market. It has been prepared to give the marine engineer basic insight into the chemical water treatment of marine propulsion boilers, low pressure auxiliary and exhaust boilers, diesel engines, evaporators and other associated equipment. The purpose and design of Unitor marine chemical products is to provide the marine engineer with the most environmentally-friendly products and with the most practical and simple applications of their use. Unitor has designed the Spectrapak test kits to accurately determine chemical concentrations of the various products and systems they are being used to check. The Spectrapak tablet system is the most practical and economical testing system available to the marine engineer. Our water treatment programmes are designed to utilize the simplest water testing procedures along with the assistance of our worldwide service personnel and Unitor’s Laboratories which provide the technical expertise required to answer all questions in regard to marine chemical applications. Unitor’s products have been designed to provide the ship operator with a variety of products and systems to cover all requirements for the many different types of boiler systems and crew requirements, which will be detailed in this manual. Unitor has introduced the most up-to-date log review system to utilize today’s technology in communications and computers to provide the operator and marine engineer with a “Rapid Response” to our log review system. Unitor is dedicated to providing the marine operator with the most reliable products available in the marine chemical industry along with the many other areas of expertise and standardisation worldwide. Our products and services are available 7 days a week and we are committed to maintaining this for the marine industry.

INDEX

Page

INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV 1 Water Treatment Philosophy and Overview . . . . . . . . . . . . . . . . . . . . . . .

5

2 Basic Chemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6

3 Problems of Boiler Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 4 Types of Boiler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 5 Boiler Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 6 Unitor Boiler Water Treatment Products . . . . . . . . . . . . . . . . . . . . . . . . . 28 7 Combined Treatment for Low Pressure Boiler Water . . . . . . . . . . . . . . . 29 8 Tests for Boiler Water, Low Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 9 Unitor Coordinated Treatment Products . . . . . . . . . . . . . . . . . . . . . . . . . . 34 10 Tests for Boiler Water, Medium Pressure . . . . . . . . . . . . . . . . . . . . . . . . 38 11 High Pressure Boiler Water Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 12 Boiler Wet Layup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 13 Boiler Blowdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 14 Chemical Cleaning of Boilers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 15 Diesel Engine Cooling Water Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . 60 16 Reporting Analysis Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 17 Water Tests, Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 18 Evaporator Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 19 Marine Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 20 Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

II

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INTRODUCTION This Product Applications Handbook has been designed to provide specific information on the variety of chemical and related products and systems available from Unitor. This handbook will give all the information required to maintain these various 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, Water Treatments: 1. Combitreat (powdered) 2. Liquitreat 3. Condensate Control

1 Water Treatment Philosophy and 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 water is the description of the water to which we have daily access. We can obtain our water from: 1. The ocean 2. Surface sources (e.g. from lakes) 3. Underground sources The water will vary in composition. The natural water cycle may be as below:

Cooling Water Treatments: 1. Dieselguard NB (powder) 2. Rocor NB Liquid Sea Water Cooling Treatment: 1. Bioguard Evaporator Treatment: 1. Vaptreat

While it is evaporating from the surface of a lake or the ocean into the atmosphere, we can designate the water vapour H2O. In the atmosphere, clouds will form, and during suitable humidity and temperature, the clouds will deposit water (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 will dissolve various minerals from the soil.

IV

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2 Basic Chemistry The chemistry of water It is necessary to examine some of the basic theories in order to understand the various problems associated with water treatment. While rain is falling through the air, it absorbs gaseous contaminants, e.g. O2 (Oxygen), which solubility in pure water depends on temperature. At 20 °C, 9 mg/l O2 may dissolve, and at 50 °C approx. 5.5 mg O2/l,

TEMPORARY HARDNESS (Alkaline Hardness) is due to bicarbonates of Calcium and Magnesium which are Alkaline in nature. They are “temporary” because when heated they rapidly break down to form Carbon Dioxide and the corresponding carbonates which deposit as scale. PERMANENT HARDNESS (Non-Alkaline Hardness) is due mainly to Sulphates and Chlorides of Calcium and Magnesium which are acid in nature. They are “permanent” and do not break down, but under certain conditions deposit to form scale of varying hardnesses.

and at 90 °C approx. 1.5 mg O2/l, and

2.1

at 100 °C approx. 0.0. mg O2/l, so, the higher the temperature, the less O2 can dissolve in water. CO2 (Carbon Dioxide) dissolves in water as follows: CO2 + H2O > H2CO3 H2CO3 is a very weak acid. In contact with CaCO3 (ordinary lime), it is reactive and the lime dissolves as follows: CaCO + H CO > Ca++ + 2HCO – 3

2

3

3

Ca(HCO3)2 is called Calcium Bicarbonate. SO2 (Sulphur Dioxide) is an air pollutant which stems from flue gases, so there is usually a high atmospheric content of this gas around industrial areas. 2SO2 + O2 + 2H2O > 2H2SO4 H2SO4 is called Sulphuric Acid, and this acid also dissolves lime (CaCO3) as follows: CaCO3 + H2SO4 > CaSO4 + H2O + CO2. CaSO4 is called Calcium Sulphate (gypsum). In other words, the gases dissolved in the water will increase the leaching of the subsoil’s minerals, so that we may have solutions in water due to: TOTAL HARDNESS

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2 / BASIC CHEMISTRY

Temporary hardness

Permanent hardness

Calcium Bicarbonate Ca (HCO3)2 Magnesium Bicarbonate Mg (HCO3)2

Calcium Sulphate CaSO4 Magnesium Chloride MgCl2

BOILER WATER TREATMENT FUNDAMENTALS

The concept of employing water, fresh or distilled, as a power generating source and heat exchange medium originated and was realised with the inception of the steam generator or boiler, and has been applied most successfully and beneficially in this manner ever since. Water has the ability to transfer heat from one surface to another, thereby maintaining the system within the correct operational temperature range while generating steam to carry out work. However, water can adversely affect metal components under the operational conditions normally found in steam boilers and other heat exchange devices. The extent of deterioration depends on the specific characteristics of the water and the system in which it is being used. In order to counteract the detrimental properties normally attributed to water and its contaminants (dissolved and suspended solids and dissolved gases), special chemical treatment programmes have been devised. Accepted water treatment processes and procedures are constantly being upgraded and modernised, and new methods are being developed to complement and/or replace older ones. Unitor utilizes the most modern, practical programmes for the marine operator. Although water from marine evaporators and boiler condensate return systems is essentially “pure”, minute quantities of potentially harmful salts and minerals can be carried by this composition and feedwater into the boiler, where they will accrue, ultimately resulting in serious problems in the steam generating unit. In addition, the water can also contain dissolved gases, i.e. CO2 and Oxygen, which can result in corrosion of the system. Using unprocessed fresh water (e.g. shore water) as a makeup source can present some of the same problems experienced with distilled water, but in addition, certain contaminants which are naturally present in fresh water can be extremely destructive in boiler systems if not dealt with promptly and effectively. Soluble salts such as Chloride, Sulphate and Carbonate are present

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as electrolytes in the untreated water, leading to galvanic and other types of corrosion, depending on the conditions in the system. In addition, Sulphates and Carbonates have the potential to form insoluble, adherent, insulating “hard water” scale deposits on heat exchanger surfaces.

2.2

CONTRIBUTING ELEMENTS WHICH AFFECT BOILER WATER TREATMENT

Most dissolved mineral impurities in water are present in the form of ions. These ions contain an electrical charge which is either positive (cation) or negative (anion). These ions can join together to form chemical compounds. To know which ions will combine, we need to know their electrical charge. Ions of concern to us include the following: Positive ions

Chemical symbol

Negative ions

Chemical symbol

Sodium Calcium Magnesium Hydrogen

Na+ Ca++ Mg++ H+

Chloride Bicarbonate Carbonate Hydroxide

Cl – HCO3 CO3– – OH –

Cations will combine only with anions. An example of this combining of ions is the action between Calcium and Carbonate. The chemical compound which forms is Calcium Carbonate. Other impurities which will affect the boiler water treatment control include Copper, Iron Oxides, oil and dissolved gases. 2.2.1 Copper Copper is introduced into a system by corrosion of Copper piping and Copper alloys. In boilers, the source of this corrosion could be dissolved gases in the boiler water or the excessive use of Hydrazine which will corrode Copper and Copper alloys, allowing Copper to be carried back to the boiler. Copper in the boiler displaces metal from the tube surfaces and plates out on the tubes. This condition often occurs under existing scale and sludge deposits, which is known as under deposit Copper corrosion. Copper deposits are a serious problem in high pressure boilers. Waterside deposits may be submitted to Unitor for complete analysis and determination of the correct procedures to follow for cleaning. 2.2.2 Oil To prevent oil from entering condensate and feedwater systems, certain safety equipment is generally incorporated to detect, remove, and arrest such contamination.

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2 / BASIC CHEMISTRY

Oil contamination may occur through mechanical failure, for example, faulty oil deflectors at turbine glands passing lubrication oil to gland seal condensers and main condensers, etc., or undetected leaks at tank heating coils. Any oil film on internal heating surfaces is dangerous, drastically impairing heat transfer. Oil films therefore cause overheating of tube metal, resulting in possible tube blistering and failure. If oil contamination is suspected, immediate action must be undertaken for its removal. The first corrective measure in cleaning up oil leakage is to find and stop the point of oil ingress into the system. Then, by using a Unitor degreaser, a cleaning solution can be circulated throughout the boiler system to remove the existing oil contamination. Complete details on this cleaning operation are covered later in the handbook. Boiler Coagulant can assist in removing trace amounts of oil contamination. Consult your Unitor representative for more specific recommendations. 2.2.3 Iron Oxides Iron may enter the boiler as a result of corrosion in the pre-boiler section or may be redeposited as a result of corrosion in the boiler or condensate system. Often, Iron Oxide will be deposited and retard heat transfer within a boiler tube, at times resulting in tube failure. This usually occurs in high heat transfer areas, i.e. screening tubes nearest to the flame. When iron is not present in the raw feedwater, its presence in the boiler indicates active corrosion within the boiler system itself. Rust, the reddish form, is fully oxidized. More often, in a boiler with limited Oxygen, it is in the reduced or black form as Magnetite (Fe3O4). Fe3O4 is magnetic and can be readily detected with a magnet. It is a passivated form of corrosion and its presence shows that proper control of the system is being maintained. 2.2.4 Magnesium Carbonate (MgCO3) Magnesium hardness in fresh water usually accounts for about onethird of the total hardness. The remaining two thirds can normally be attributed to calcium. Since Magnesium Carbonate is appreciably more soluble in water than Calcium Carbonate, it is seldom a major component in scale deposits. This is due to the preferential precipitation of the Carbonate ion by Calcium as opposed to Magnesium which remains in solution until all soluble Calcium is exhausted. Once this point is reached, any free Carbonate remaining in solution will combine with the Magnesium and begin precipitating out as

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Magnesium Carbonate when the solubility of this salt is exceeded. Because of this latter phenomenon, where “soft” water is used for boiler structure, any Magnesium present must be removed along with the Calcium. 2.2.5 Magnesium Sulphate (MgSO4) Magnesium Sulphate is an extremely soluble salt, having a solubility of 20 % in cold water and 42 % in boiling water. It exists as the Sulphate only in water with a low pH. Because of its high solubility, it will not normally precipitate. The Sulphate ion, however, will be precipitated by the Calcium hardness present if no free Carbonate exists. 2.2.6 Magnesium Chloride (MgCl2) Magnesium Chloride, like Magnesium Sulphate, is soluble in fresh water. In the high temperature and alkaline conditions normally maintained in a boiler, any soluble Magnesium ions in the boiler water become extremely reactive with Hydroxyl ions, which may be present in high concentrations in this type of environment. This can result in the formation of Magnesium Hydroxide precipitates which form insulating scale on the boiler tube surfaces. If Chloride ions are also available, they react with the Hydrogen ions previously associated with the precipitated Hydroxyl ions, to form Hydrochloric acid, thereby lowering the alkalinity of the water. If this situation is allowed to continue, the pH of the boiler water will decrease until acid conditions result in corrosion of the metal surfaces. Unlike Carbonate and Sulphate ions, the Chloride ion does not precipitate in the presence of soluble Calcium. 2.2.7 Silica (SiO2) Silica scale is not normally found in boiler systems except in minute quantities. It can be admitted to the system when severe carryover occurs in evaporators processing water with a high Silica content. Other sources of such feedwater may be high Silica river or raw fresh water as well as distilled/deionized or unprocessed fresh water which has been stored and taken from cement-washed or silicatecoated tanks. Once formed, pure Silica scale is extremely difficult to remove. It forms a tight adherent glass-like film on metal surfaces, thereby preventing proper heat transfer. In addition, in steam-generating devices it can carry over with the steam coating the after-boiler sections, particularly the superheater. If a turbine forms part of the system, the Silica can deposit on the blades as well as cause erosion of the finned surfaces of the blading, resulting in imbalance of the turbine, which in turn may result in turbine failure.

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2 / BASIC CHEMISTRY

Besides the pure form of Silica (i.e. Silicon Dioxide), possible Silicate deposits can form in combination with Calcium and Magnesium, which are extremely insoluble in water and very difficult to dissolve and remove. Besides being an extremely difficult process, the chemical removal of Silica and silicate deposits can also be very hazardous, since it involves the use of Hydrofluoric Acid or Ammonium Bifluoride, both of which are severely destructive to human tissue by inhalation, ingestion and physical contact. In some instances, alternate acid and alkaline washings have been used to successfully combat this problem. The only alternative to chemical cleaning is mechanical removal. 2.2.8 Calcium Carbonate (CaCO3) Calcium Bicarbonate alkalinity exists in almost all unprocessed fresh water under normal conditions. Its solubility is about 300–400 ppm at 25 °C. If heat is applied or a sharp increase in pH occurs, the Calcium Bicarbonate breaks down to form Carbon Dioxide and Calcium Carbonate. While the bicarbonate salt has been shown to be moderately soluble in water, the solubility of Calcium Carbonate at 25 °C is only about 14 ppm. This value continues to decrease as the temperature increases, becoming the least where the temperature is greatest. In a boiler, this would be on the surface of the furnace tubes where contact is made with the water. The resulting insoluble Calcium Carbonate precipitate forms “building block-like” crystals which adhere not only to one another, but also to the hot metal surfaces, resulting in a continuous, insulating scale deposit over the entire heat exchange area.This deposit will continue to grow, building upon itself to form a thick coating until all the Calcium Carbonate produced is exhausted. If suspended matter is also present in the water, it can become entrained within the crystal structure, creating a larger volume of deposit than that formed by the Carbonate precipitation alone. If this condition is allowed to continue, heat exchange efficiency at the water/tube interface falls rapidly, resulting in an increase in fuel consumption necessary to compensate for the decline in thermal transfer and to regain design temperature as well as steam production requirements. This increase in the furnace-side temperature needed to run the system at optimum conditions exposes the metal surfaces to overheating which, in turn, can cause blistering fatigue, fracture, and failure of boiler tubes. In addition, if pockets of water become trapped beneath the scale deposits and are in contact with the hot metal surfaces, concentration of acid or alkaline materials may occur and lead to the formation of local electrolytic cells (underdeposit corrosion).

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2.2.9 Calcium Sulphate (CaSO4) Although Calcium Sulphate is more soluble in water than Calcium Carbonate, it can be just as troublesome when present in boiler and cooling water systems. Calcium Sulphate, like Calcium Carbonate, but unlike most salts, has an inverse temperature/solubility relationship in water. As gypsum, the hydrated form in which Calcium Sulphate is normally present in fresh water, its solubility increases until a temperature of about 40 °C is achieved. At 40 °C, its solubility is 1,551 ppm; at 100 °C, which is the normal boiling point of water, its solubility decreases to 1,246 ppm, and at 220 °C it falls to 40 ppm. Calcium Sulphate reacts at high-temperature surfaces essentially in the same manner as Calcium Carbonate and with the same effects and consequences. However, whereas Calcium Carbonate deposits are relatively easy to remove using a comprehensive acid cleaning procedure, Calcium Sulphate is essentially impervious to the effects of normal acid descaling methods and usually must be removed by mechanical means.

D. ALKALINITY RELATIONSHIP TABLE

2.2.10 Dissolved Gases Gases such as Oxygen and Carbon Dioxide that are dissolved in distilled or fresh water, will further contribute to the deterioration of the boiler system. Dependent upon conditions in the system (e.g. temperature, pressure and materials of construction), dissolved Oxygen can cause pitting corrosion of steel surfaces, while Carbon Dioxide lowers the pH, leading to acid and galvanic corrosion. Carbon Dioxide has the added disadvantage of forming insoluble carbonate scale deposits in an alkaline environment when Calcium and Magnesium are present.

*This is the correct alkalinity relationship for boiler water

2.2.11 Acidity, Neutrality and Alkalinity All water can be classified into one of these categories. Acidity, Neutrality and Alkalinity are only very general terms. We require more accurate methods of testing to know the degree of each condition. When testing boiler water, it is important to understand what you are testing for.

Hydroxide Alkalinity

Carbonate Alkalinity

Bicarbonate Alkalinity

P Alkalinity =0

0

0

Equal to total

P Alkalinity less than 1/2 M Alkalinity

0

2 times P Alkalinity

M Alkalinity minus 2 times P Alkalinity

P Alkalinity equal to 1/2 M Alkalinity

0

2 times P Alkalinity

0

*P Alkalinity greater than 1/2 M Alkalinity

2 times P Alkalinity minus M Alkalinity

2 times the difference between M and P Alkalinity

0

P Alkalinity equal to M Alkalinity

Equal to M Alkalinity

0

0

pH The pH of a solution is a measurement of the concentration of active acid or base (alkaline constituent) in a solution. To give a precise definition, pH is the negative logarithm of the Hydrogen ion concentration. A simpler explanation of pH is that it is a measure of relative acidity or alkalinity of water. In other words, it reflects how acidic or alkaline the water is. pH is the number between 0 and 14 which denotes the degree of acidity or alkalinity. A pH value of 7 indicates neutral. Below 7 indicates increasing acidity. Above 7 up to 14 indicates increasing alkalinity.

Acidic

Neutral

Alkaline

A. ALKALINITY. The presence of Alkalinity in a water sample may be due to many different substances. For the sake of simplicity, the presence of Bicarbonate, Carbonate and Hydroxide contributes to the alkalinity of water.

1

B. P ALKALINITY. Phenolphtalein (P) Alkalinity (pH values greater than 8.3) measures all the Hydroxide and one half of the Carbonate Alkalinity which is sufficient for our purpose of control. Bicarbonates do not show in this test as they have a pH of less than 8.4.

pH is a very important factor for determining whether a water has a corrosive or scale-forming tendency. Water with a low pH will give rise to corrosion of equipment.

2

3

4

5

6

7

8

9

10

11

12

13

14

C. M ALKALINITY. Total Alkalinity or M Alkalinity (pH values greater than 4.3) measures the sum of Bicarbonate, Carbonate and Hydroxide Alkalinity.

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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 be used 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.

3.1.1 Pitting Corrosion “Pitting” is the most serious form of waterside corrosion and is the result 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 procedures when the boiler is shut down for lengthy periods, and by inadequate Oxygen scavenging.

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 boiler tubes is often found in boilers having open feed systems (mostly auxiliary boilers) without any protective treatment. An example of wastage is given in the figure below.

General wastage of a boiler tube.

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3 / PROBLEMS OF BOILER WATER

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 failure of the metal due to stress corrosion are shown below. Corrosion is initiated 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 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

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3.1.3 Other Related Problems “Corrosion fatigue” occurs when a sufficiently high alternative stress level causes failure of the subjected material. It is the joint action of a corrosive environment and cyclic stressing and results in a series of fine cracks in the metal. This is found in water tube boilers where irregular circulation through tubes in high temperature zones induce these cycling stresses. ”Caustic cracking” results from the contact of water of concentrated caustic alkalinity and steel which has not been stress relieved, e.g. in riveted seams. This form of cracking follows the grain boundaries. This is rarely observed nowadays, as both high and low pressure boilers are usually of all welded construction and are stress relieved. Caustic corrosion takes place only in high pressure boilers (above 60 bar) when excessively high concentrations of Sodium Hydroxide (Caustic Soda) cause breakdown of the magnetite layer and localised corrosion. This form of attack is often controlled by the coordinated PO4 Treatment Programme. ”Hydrogen attack” is another form of corrosion damage that can take place in ultra high pressure boilers. Whichever form of corrosive attack occurs, the risk of tube failure or serious structural damage is very apparent, both often leading to considerable expense in the shape of repair costs.

3.2

SCALING

Causes and Effects If the inside of a boiler is scaled, there is a great risk that the boiler material will overheat, leading to tube failure. The efficiency of operation will also be adversely affected. Hardness in the feedwater will usually present problems in relation to the operation of boilers. Hardness of more than 5dH° (90 ppm as CaCO3) in the feedwater will, as the temperature rises, cause an increase in the formation of sludge in the feedwater tank. If scale-preventing chemicals are put into the feedwater tank, this problem will be aggravated, as nearly all precipitation of sludge will take place in the feedwater tank. The suction pipe stub of the feed water line will usually be placed 5–10 cm above the bottom. However, if the feed water is not very clean, sludge will after a time be sucked into the piping and choking may occur. In a modern centrifugal pump, the very narrow vanes may be blocked, which will cause the pump to stop. Finally, there is a risk of the valves sticking and becoming blocked. In spite of the fact that a boiler plant may be equipped with a water treatment system of some sort, there will always be a risk of hardness or other type of pollution in the feedwater, because: 1. The capacity of the water treatment system is insufficient. 2. There are defects in the water treatment system.

3.1.4 Factors Affecting Corrosion

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1) pH

Metal oxides are more soluble as pH decreases. Corrosion is increased.

2) Dissolved solids

Chloride and Sulphate can penetrate passive metal oxide film which protects the base metal from corrosion.

3) Dissolved gases

Carbon Dioxide and H2S reduces pH and promotes acid attack. Oxygen promotes pitting corrosion.

4) Suspended solids

Mud, sand, clay, etc. settle to form deposits, promoting different corrosion cells.

5) Micro organisms

Promote different corrosion cells.

6) Temperature

High temperature increases corrosion.

7) Velocity

High velocity promotes erosion/cavitation.

8) Copper

Copper ions plate out on steel surfaces and promote pitting corrosion.

3 / PROBLEMS OF BOILER WATER

3. The condensate is polluted: a. By heat exchanger leaks b. By lubrication oil Daily analysis of the quality of the feedwater will ensure that action can be taken in time to prevent irregularities. Hardness in the boiler water will inevitably lead to the formation of scale and the rate of this formation will depend on the composition and quantity of the hardness, on the temperature conditions in the boiler and on the circulation in the boiler. Increased surface heating effect means increased production of steam bubbles, which again will make more boiler water “pass” the spot on the heating surface (where the steam bubbles are formed) and this spot will thus also be “passed” by the hardness-producing and corroding salts in the boiler water. In addition, the most common hardness salts are less soluble at increasing temperatures. This explains why the largest amount of encrustation will always be found where the temperature of the heating surface is the highest. Scale formed just at this point means that the critical temperature of the boiler material will be reached quickly and that damage to the boiler will be inevitable.

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3.3 Illustration of Typical Conditions With a Clean Boiler Tube

Change in Conditions When a Layer of Scale of just 3 mm Thickness Exists

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 control valves

• Deposits in superheaters • 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, the thermal and mechanical shock can cause severe damage.

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 Scale

Causes of carryover: Mechanical: • Priming • Soot blowing

• Sudden load changes • High water level

Chemical: Foaming due to: • High Chlorides • Suspended solids

• High TDS • Oil

• Boiler design

• High alkalinity • Silica

Curve of middle values. The differences in the test results can be explained by differences in the composition of scale (porous–hard).

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 0.4° Be = 4000 mg salts dissolved per litre). 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 will increase 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 steam pipes. 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 be deposited 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. Circumstances 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 preheater’s coils if they are leaking are very common causes of priming.

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4 Types of Boiler What is a boiler? A boiler is a steel pressure vessel in which water under pressure is converted 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 because of large water volumes • Usually rated in HP

4.2

WATER TUBE BOILER

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

Water flows through tubes that are surrounded by hot combustion gases in a shell. • Usually rated in tons of steam/hr • Used for H.P. steam • High capacity BOILERS HAVE SIX BASIC PARTS 1) 2) 3) 4) 5) 6)

Burner Combustion space Convection section Stack Air fans Controls and accessories

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

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4.3

FIRETUBE BOILERS

Wet back designs Have a water wall at the back of the boiler in the area where combustion gases reverse direction to enter tubes. Dry back designs Refractory is used at the back, instead of a water 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.

4.5

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. By increasing the temperature and pressure of the hot water and increasing the size of the generators, some advantages are gained over the low pressure steam 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 direct contact heater. This is referred to as a cascade system.

WATERSYSTEM AND STEAMSYSTEM

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 treatment programme are mandatory. The most common problem is Oxygen pitting on the inside portion of the coil near the fire. The two most common name brands are Vapor-Clarkson and Clayton.

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4 / TYPES OF BOILER

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

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5 Boiler Systems 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

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 water treatment. The steam plant consists of the following:

Disadvantages: • More control than firetube boilers • Higher initial cost • More complicated to operate

Storage tank This tank will 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 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 treatments. This is where all the water collects 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 from that tank may contain oil, or if cargo heating has been used, some of

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the cargo product may be returned with the steam. That is why this tank is sometimes called the observation tank – steam returns can be inspected for contamination here. There is a series of plates and filters in the hot well which allows the contaminating oil, etc., to be removed. Any sort of contamination is definitely not wanted in the water entering the boiler, as it would cause damage. Dosage of the combined product boiler water treatment is normally carried out into the hot well.

The system described provides the more common, modern system. There are many systems where the exhaust gas boiler and the oil-fired boiler are combined (composite boiler). A diagram of one is shown below. One section of the tube is used for the oil-fired boiler and the other section for the exhaust gases to pass through. This unit must be situated in the funnel area because the exhaust trunking passes that way and it is placed at a convenient point.

The boiler: The water is drawn from the hot well by the feed pump and pumped into the upper drum of the boiler (this is normally called the steam drum). From here it circulates in the boiler, is heated and turns into steam. There are normally two different ways in which it is heated.

5.1.2 The Steam Lines The steam comes from the steam drum of the boiler and is distributed to the areas where it is required. That is for heating tanks, fuel, hot water, etc. No testing is required in this area under normal circumstances. Once the useful heat has been taken out of the steam, it enters the steam return lines and comes back to the drains cooler.

1. When the main diesel engine is running, the water is pumped from the lower drum (called the water drum) and circulated through a heat exchanger in the exhaust trunking which takes the exhaust gases away from the engine to the atmosphere. The remaining heat in these exhaust gases is used to generate the steam. 2. The auxiliary boiler has a burner (one or more) which uses either heavy oil or diesel oil to provide the heat to produce steam. If the heat available from the exhaust gases is insufficient, the oil fired burner(s) can be used to make the steam required by the vessel.

5.1.3 Drains Cooler This unit is another heat exchanger and it is there to ensure that all the returning steam is turned to water. The returns would be a mixture of hot water and steam before this cooler, and the cooler ensures that any return steam is condensed to water. The drains cooler normally uses sea water to cool the steam returns, and this can be a source of contamination if there is a leak. This will show up as a high chloride level in the feedwater if it occurs. Sunrod Exhaust Gas Economiser.

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6 Unitor Boiler Water Treatment Products

7 Combined Treatment for Low Pressure Boiler Water

6.1

THE MAIN PURPOSE OF BOILER WATER TREATMENT IS

7.1

A. To eliminate the total hardness of the boiler water.

Liquitreat is a combined chemical treatment product suitable for use in small, low pressure boilers. It precipitates hardness, provides the boiler water with the necessary alkalinity, and scavenges dissolved Oxygen. Liquitreat should be added when deemed necessary as shown by water analysis results. If the boiler is open and not being fired, Liquitreat can be poured through a manhole, but when the boiler is in operation, the treatment must be applied through a special dosing line. When a dosing arrangement is utilized, the chemical must be flushed to remove any residual left in the dosage lines and equipment. If dosing lines are not fitted, the chemical can be added directly to a feed tank as required. Ensure proper circulation through the feed tank to allow the chemical to enter the boiler being treated. Under low load conditions, complete changeover in the feed tank can take some time. It is necessary to know the details of the flow pattern in the boiler for proper testing and dosing of the chemical treatment to take place. When several boilers have a common feed tank, dosing should be carried out through independent dosing lines to ensure the proper treatment of each boiler. Re-test within 2 hours of when the boiler water chemical treatment was dosed to the boiler water. For further recommendations on product dosage and control limits, refer to the product data sheet in the Marine Chemical’s Manual.

B. To maintain the correct pH and alkalinity values in feedwater and boiler water. C. To prevent corrosion, especially corrosion caused by Oxygen. D. To prevent the formation of scale, among other things by conditioning the sludge. E. To avoid foaming.

6.2

UNITOR PRODUCTS

Combined Treatment 1. Liquitreat 2. Combitreat Single Function Treatment 1. Alkalinity Control

LIQUITREAT

2. Hardness Control

7.2

3. Oxygen Control

Combitreat is a combined product chemical treatment similar to Liquitreat but in powder form without Oxygen scavenger, which precipitates hardness and provides the boiler water with the necessary alkalinity. Combitreat should be applied as a solution and added when deemed necessary as shown by water analysis results. The recommended dosage must be dissolved in warm water, 30–60 °C in a suitable steel or plastic container, not exceeding the solubility limit of 180 grams per litre. Combitreat must be added slowly to the water (not vice versa) and the solution being prepared must be constantly stirred. Combitreat is best dosed by means of a bypass potfeeder directly in the boiler water feed line. It can also be dosed into the hot well after premixing with hot water at a ratio of 1 kg per 9 litres of water.

4. Catalysed Sodium Sulphite 5. Cat. Sulphite L 6. Boiler Coagulant 7. Condensate Control

COMBITREAT

NOTE: In addition to our combined product chemicals, Condensate Control should be used in all boiler systems to keep the Condensate pH level between 8.3–9.0. Also, the hot well temperature is of great importance when it comes to Oxygen scavenging (ref. basic chemistry at the beginning of the book). We recommend that you maintain a hot well temperature of between 70 °C and 90 °C. For further recommendations on product dosage and control limits, refer to the product data sheet in the Marine Chemicals Manual.

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8 Tests for Boiler Water, Low Pressure 8.1

UNITOR’S LOW PRESSURE COMBINED BOILER WATER TREATMENT PROGRAMME

The tests recommended in order to maintain boiler water within the desired level of quality when treating with Unitor Liquitreat/Combitreat are as follows: A. P-Alkalinity – Recommended Limits: 100–300 ppm as CaCO3. B. Chlorides – 200 ppm maximum as Cl. C. Condensate pH – 8.3–9.0. Dosage level of Liquitreat/Combitreat is based on the P-Alkalinity value of the boiler water. However, Chlorides and condensate pH must also be controlled and maintained as recommended. Knowledge of all relevant parameters is desirable to enable better interpretation and correct application of treatment. To increase the condensate pH, use Unitor’s Condensate Control in conjunction with your combined product boiler water treatment. It is recommended that you dose Condensate Control on a continuous basis, to maintain the condensate pH within the recommended range of 8.3–9.0 at all times.

8.2

CONTROLLING ALKALINITY

The alkalinity is a more accurate indicator of the boiler water condition than is the pH. The Phenolphtalein (P) alkalinity is measured to determine whether the correct conditions of alkalinity exist in the boiler to:

8.4

pH

Recommended limits of 9.5–11.0. An additional test to determine the pH of the boiler water can be carried out to give a better overall understanding of the boiler water quality. This test is optional. The pH of the boiler water should be maintained within the range of 9.5–11.0 to prevent any corrosion attack on the boiler metal. pH values below 9.5 indicate, a greater possibility of corrosion and in such a situation, treatment levels should be increased accordingly to restore boiler water to optimum quality.

8.5

CONDENSATE pH

To control corrosion in after boiler, condensate and feedwater sections, the condensate pH should be kept between 8.3 and 9.0. Monitoring the pH of this water is very important in being able to maintain a complete Boiler Water Treatment Management Programme.

8.6

TESTING REQUIREMENTS 8.6.1 Low Pressure Boiler Water Treatments: A. Unitor Combined Treatment Products a. Combitreat – For systems up to 17.5 bar. b. Liquitreat – For systems up to 30 bar. B. Test Equipment – Unitor Spectrapak 310 Test Kit.

A. Provide a suitable environment for the precipitation of hardness salts as desirable sludge materials. B. To help the formation of Magnetite (Fe3O4) in the presence of Oxygen scavengers (i.e. Hydrazine/Sulphite). C. Maintain Silica in solution to prevent Silica scale formation.

8.3

CONTROLLING CHLORIDES

The Chloride value will reveal any presence of dissolved salts in the boiler. An increase, gradual or sudden, in the level of Chlorides is an indication of contamination by sea water, and Chlorides are often used as a reference point when controlling rate of blowdown. Too high a Chloride level indicates that undesirable amounts of salts are present, leading to possible foaming and/or scale and deposit formation.

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8 / TESTS FOR BOILER WATER/LOW PRESSURE

C. Specification Control Limits. a. P-Alkalinity: 100–300 ppm (as CaCO3). b. Chloride: 200 ppm maximum. c. Boiler Water pH: 9.5–11.0 (optional). d. Condensate pH: 8.3–9.0. D. Testing preparations and equipment. a. Boiler Water Sample preparation: – Cool sample to 20–25 °C. – Filter as required. b. Sample Analysis: – Spectrapak 310 Test Kit Reagents: – P-Alkalinity tablets – Chloride tablets. – pH strips with ranges 6.5–10.0 and 7.5–14.0. – Equipment – 200 ml sample bottles. – Test procedures.

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8.6.2 P-Alkalinity test A. Take a 200 ml water sample in the stoppered bottle provided. B. Add one P-Alkalinity tablet and shake to disintegrate. If P-Alkalinity is present, the sample will turn blue.

It is essential that the condensate pH is maintained within 8.3–9.0. Test this with Unitor’s pH paper and use Condensate Control to adjust pH upwards if necessary. 8.6.5 Instructions Sulphite Test Kit (optional test for low pressure single product treatment)

C. Repeat tablet addition until the blue colour changes to permanent yellow. Calculation: P-Alkalinity ppm (CaCO3) = (No. of tablets used x 20) –10 For example: If 8 tablets are used, then P-Alkalinity = (8 x 20) –10 = 150 ppm.

8.6.6 Testing procedure: A. Take a 20 ml sample in the shaker tube supplied. B. Add one Sulphite No. 1 tablet; shake to dissolve. C. Add Sulphite No. 2 L.R. tablets one at a time until the sample turns blue. Note the number of tablets used.

D. Mark the result obtained on the log sheets provided, against the date at which the test was taken.

D. Calculate as follows: Sulphite content = Number of Sulphite No. 2 L.R. tablets x 10.

8.6.3 Chloride test A. For boilers under 30 bar, take a 50 ml sample in the stoppered bottle provided.

E. After use, thoroughly rinse out the shaker tube before storage. PLEASE NOTE! The Sulphite No. 1 tablet is used only to condition the sample. Do not count this tablet when calculating the Sulphite level.

B. Add one Chloride tablet and shake to disintegrate; sample will turn yellow if chlorides are present. C. Repeat tablet addition until the yellow colour changes to orange/brown. Calculation: Chloride ppm = (No. of tablets used x 20) –20 For example: If 4 tablets are used then Chloride ppm = (4 x 20) –20 = 60 ppm. D. Mark this result on the Spectrapak 310 log sheet, against the date at which the test was taken. 8.6.4 pH test: For boiler water pH test, 7.5–14.0. For Condensate water, 6.5–10.0. A. Take a 50 ml sample of water to be tested in the plastic sample container provided. B. Using the white 0.6 grm scoop provided, add one measure of the pH reagent to the water sample, allow to dissolve – stir if required. C. Select the correct range of pH test strip and dip it into the water sample for approximately 10 seconds. D. Withdraw strip from sample and compare the colour obtained with the colour scale on the pH indicator strips container. E. Record the pH value obtained on the log sheet provided, against the date at which the test was taken.

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8.7

TEST RESULTS – COMBINED TREATMENT A. Recording – Always use Unitor’s Rapid Response log forms to record all readings and to keep track of all results. 1. Log form – Combined Boiler Water Treatment Log, no. 310. 2. Frequency – Samples should be drawn, tested and results logged at least every three days. B. Reporting – The completed log sheet for the month should be distributed as shown at the bottom of the form, at the end of each month: 1. White copy – to Unitor’s Rapid Response Centre in Norway (address labels at back of log pad) 2. Pink copy – Vessel owner 3. Yellow copy – to be kept onboard C. Evaluation 1. Logs will be reviewed at the Unitor Rapid Response Centre for adherence to recommended specifications, with the aid of Unitor’s Rapid Response staff. 2. A report letter indicating the status of the ship’s system, any problems and relevant recommendations will be issued to the ship’s operator.

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9 Unitor Coordinated Treatment Products The use of combined product treatment for medium and high pressure boilers, is not recommended. Because higher pressures and temperatures increase the tendency of scaling and corrosion, which makes it necessary to have the possibility of changing the chemical conditions and test parametres individually. The Unitor Coordinated Treatment Programme includes single function chemicals which are dosed and monitored separately. This programme may of course also be applied to low pressure boilers as an alternative to combined product treatment.

9.3

OXYGEN CONTROL (HYDRAZINE, N2H4)

Hardness Control is a Phosphate powder product used in boiler water treatment to precipitate dissolved calcium hardness salts and to convert these salts to non-adherent Calcium Phosphate sludge, which can be easily removed by blowdown. Hardness Control is highly effective in achieving this function; minimum dosages are required. Reduced dosage of chemicals minimises dissolved and suspended solids in the boiler water. Hardness Control provides neutral reaction products in the boiler. A high level of dissolved and suspended solids are the principal causes of carryover and priming. Note here the term “phosphate hide-out”; as the temperature of the boiler increases, less Phosphate can be held in solution in the boiler water. Therefore, testing and dosage of Phosphate to control hardness salts deposits should be done when the boiler is under full load conditions. If the Phosphate residual increases under low load conditions, this is an indication of a dirty boiler, and increased bottom blows should be carried out to remove the sludge. The sludge holds excess Phosphate and re-dissolves when the boiler water temperature is reduced. For further recommendations on product dosage and control limits, refer to the Marine Chemicals Manual.

Hydrazine is a colourless liquid at ambient temperatures, being completely miscible with water. Its solution has an odour resembling Ammonia, but is less pungent. It is used to efficiently scavenge and remove Oxygen from condensate, feedwater and boiler water. Hydrazine reacts with Oxygen, acting as a scavenger. The reaction results in Nitrogen and water, no solids being added to the boiler system. Some of the Hydrazine will carry over with the steam, helping to maintain the condensate pH in an alkaline range, which thereby helps combat acid formation. Hydrazine will also form Magnetite which will act as a protective layer against further corrosion. Hydrazine should be added to the system using a separate dosing tank. The tank should be filled daily with Hydrazine diluted with condensate or distilled water. This solution should be dosed continuously to the storage section of the de-aerator. Alternatively, Hydrazine can be fed continuously to the feed pump suction or atmospheric drain tank over a 24-hour period. It is important that Hydrazine should not be overdosed. At temperatures above 270 °C, Hydrazine starts to break down, creating free Ammonia. Excessive free Ammonia and Oxygen, when combined, form a corrosive condition on non-ferrous metals. This corrosive action can cause Copper to deposit in the watersides of boilers, causing additional boiler problems, as discussed earlier.

9.2

The reaction of Hydrazine in boilers is therefore threefold:

9.1

HARDNESS CONTROL

ALKALINITY CONTROL

Alkalinity Control is used to obtain the correct pH level necessary for the Phosphate treatment to react with Calcium salts. In addition, Alkalinity Control is used to maintain the required alkalinity in the boiler water to prevent acid corrosion. By adopting simple testing procedures to determine the Phenolphthalein alkalinity (P-Alkalinity) and the total alkalinity (M-Alkalinity), we can determine the amount of free caustic present in the boiler water by using the formula 2(P) – M = OH. If a positive number is obtained, free caustic (OH-Alkalinity) is present in the boiler water.

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The term “excess chemicals” or “reserve of chemicals” ensures that chemicals are always readily available to perform their necessary functions. For further recommendations on product dosage and control limits, refer to the Marine Chemicals Manual.

9 / UNITOR COORDINATED TREATMENT PRODUCTS

1. It scavenges any free or dissolved Oxygen. 2. It reduces red Iron Oxide to a metal-protective black oxide coating (Magnetite). 3. It raises the pH of the condensate reducing acid corrosion of the condensate and re-boiler sections of the system. For further recommendations on product dosage and control limits, refer to the Marine Chemicals Manual.

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9.4

CATALYSED SODIUM SULPHITE (POWDER) AND CAT. SULPHITE L (LIQUID)

Unitor’s Catalysed Sulphite products are used as scavengers in place of Hydrazine where economy is of importance, or used in low pressure boilers with open feed systems where feed inlet temperatures are low. Sulphite combined with Oxygen forms Sulphate, which adds solids to the boiler water. It should subsequently not be used in boilers at pressures above 30 bars where the TDS level is critical. Sulphite is also used as a substitute for Hydrazine when rust and scale deposits are present in boiler systems on ships being returned to service. Hydrazine tends to remove Iron Oxide deposits present throughout the boiler system. An amine (Condensate Control) should be used in conjunction with Oxygen scavengers to maintain the condensate pH within the desirable ranges throughout the entire condensate and feedwater system. For further recommendations on product dosage and control limits, refer to the Marine Chemicals Manual.

9.5

CONDENSATE CONTROL

Condensate Control is a neutralising volatile amine recommended for use in all boiler systems to raise the pH of condensate and steam to a non-corrosive level (pH 8.3–9.0). The dosage is determined by the results of a daily condensate pH test. Condensate Control should be dosed using a continuous feed system. It can be introduced, using a flowmeter or metering pump, to the condensate pump discharge, the hot well, the condensate return tank, or to the de-aerator storage tank. Condensate Control can be dosed together with Oxygen scavengers. However, optimum control of condensate pH is achieved by dosing separately from the Hydrazine dosage system. For further recommendations on product dosage and control limits, refer to the Marine Chemicals Manual.

9.6

9.7

CHEMICAL INJECTION POINTS FOR LOW PRESSURE Boiler systems

The following diagram depicts a typical Low Pressure Boiler System. Note injection point for chemicals; when dosing chemicals, the recommendation to achieve the best possible results is to always dose all chemicals in the diluted form on a continuous basis. 1 Dosage to hot well or feed tank. All chemicals can be dosed at these points. However, the recommended dosage of Alkalinity Control and Hardness Control is either no. 2 feed line or no. 3 chemical feed injection directly to the boiler. Oxygen Control and Sulphite should preferably be dosed to the feed tank on a continuous basis. All combined products can be dosed into the hot well. 2 Dose to injection no. 2 is required to the feed line by means of a pressure injector or dosage pump. Dosage should be continuous, however water can be shock treated. 3 Dosage direct to boiler no. 3. All chemicals can be dosed to this point by means of pressure pot injector or dosage pump. Alkalinity Control or Hardness Control is best controlled at this location and and the use of Hydrazine, Sulphite or Condensate Control is recommended on a continuous basis in the condensate system.

BOILER COAGULANT

Boiler Coagulant is a polymeric compound used in boilers contaminated with small quantities of oil, or as a sludge conditioner in conjunction with the use of Hardness Control when high levels of solids are experienced. Boiler Coagulant should be dosed at 250cc per day. No testing is necessary if used regularly. Daily flash blowdown is recommended to remove precipitated solids or coagulated oil. For further recommendations on product dosage and control limits, refer to the Marine Chemicals Manual.

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10 Tests for Boiler Water, Medium Pressure (31–60 BAR) In dosing medium pressure boilers, utilise Unitor’s Coordinated Boiler Water Treatment Management Programme. This includes Alkalinity Control, Hardness Control, Oxygen Control, Condensate Control and Boiler Coagulant. The following tests are recommended to maintain medium pressure boiler water within the desired level of quality when utilising Unitor’s Coordinated BWT Programme are as follows:

10.3.1 Phosphate (ppm) PO4 A. Take the comparator with the 10 ml cells provided. B. Slide the Phosphate disc into the comparator. C. Filter the water sample into both cells up to the 10 ml mark.

10.1 UNITOR TESTS REQUIRED CONTROL LIMITS

D. Place one cell in the left-hand compartment.

1. 2. 3. 4. 5. 6. 7.

E. To the other cell add one Phosphate tablet, crush and mix until completely dissolved.

P-Alkalinity: . . . 100–130 ppm CaCO3 M-Alkalinity: . . Below 2 x P-Alkalinity Phosphate: . . . . 20–40 ppm as PO4 Hydrazine: . . . . 0.03–0.15 ppm as N2H4 Chlorides: . . . . . 30 bar • Babcox & Wilcox • Combustion Engineering • Foster Wheeler • IHI 19.1.2 Low Pressure Boilers < 30 bar • Sunrod • Aalborg • Cochran • Osaka • Kawasaki • MHI 19.1.3 Slow Speed Diesel Enginees < 120 rpm • Mitsubishi • Sulzer • MAN B & W • Gøtaværken • Fiat GMT 19.1.4 Medium Speed Diesel Engines 120–900 rpm • Wartsila • Sulzer • Pielstick • Enterprise • MAN B & W • MaK • Deutz • Bergen Diesel • Daihatsu 19.1.5 High Speed Diesel Engines > 900 rpm • Hitachi • Yanmar • EMD • Cummins • Caterpillar 19.1.6 Evaporators • Alfa-Laval Desalt • Atlas (bought by Alfa-Laval) • Nirex • Maxim • Weir

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Notes:

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Notes:

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Notes:

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