Boiler Water And Boiler Feed Water PDF

Lesson 3 Topic 1 BOILER WATER AND BOILER FEED WATER A. Boiler and its Functions A boiler is the steel pressure vessel in which the water under pressure is converted into steam by the application of combustion. It is simply a heat e...

Lesson 3 Topic 1 BOILER WATER AND BOILER FEED WATER A. Boiler and its Functions A boiler is the steel pressure vessel in which the water under pressure is converted into steam by the application of combustion. It is simply a heat exchanger which radiant heat and the flue gases are liberated for burning fuel, to generate steam, and hot water for heating and process loads. The steam produced by boiler is used onboard ship for various processes like heating applications – Fuel oil heating, Oil tank heating, Cargo heating, Air Conditioning, Galley supply, generating power, running cargo pump turbine, steam driven deck machinery and Fire Fighting, etc. There are two main types of boilers. ▪ Water tube boiler ▪ Fire tube boiler The design and arrangement of both the types is just the opposite. In water tube boilers, the feed water passes through the tubes and the hot gases are made to pass over them, while in fire tube boilers, the hot gases pass through the tubes and the feed water surrounds them. Water tube Boiler A type of boiler where water flows through tubes that are surrounded by hot combustion gases in a shell. It is constructed with small tubes, where the water is contained inside the tubes, with product of combustion passing around the outside of the tubes. A water-tube boiler is a type of boiler in which water circulates in tubes which are heated externally by the fire. Water-tube boilers are used for high-pressure boilers. Fire-tube boiler A type of boiler where hot flow gases flow inside the tubes that are submerged in water within a shell. It is consist of a large tubes where the product of combustion pass through the inside of the tubes, and outside the tube is surrounded by water. A fire tube boiler can be either horizontal or vertical. A fire-tube boiler is sometimes called a "smoke-tube" boiler. Properties of a fire tube boiler Has Pressure up to about 10 bar Can produce up to 14 tons of steam/hr. Can meet wide and sudden load fluctuations because of large water volumes Usually rated in HP (HORSE POWER) Properties of a water tube boiler can produce steam at high pressure and temperature. Is very flexible as regards to changes in steam demand because of their small volume of water. is not liable to explosion. Usually rated in tons of steam. Has high capacity Advantages of Water-tube boilers rapid heat transmission can produce steam at high pressure and temperature they are flexible as regards to changes in steam demand because of their small volume of water. not liable to explosion fast reacting to steam demand since steam pressure can be raised in a relatively short time High efficiency They have small water content, and therefore respond rapidly to load change and heat input. The small diameter tubes and steam drum mean that much higher steam pressures can be tolerated, and up to 160 bar may be used in power stations. Not liable for explosion. Safer than Firetube boilers Disadvantages of the Water Tube Boiler More controls than Firetube boilers they must use pure water they must received constant supervision as regards to steam pressure and temperature to make repairs on tubes, boiler must be emptied. Higher initial cost More complicated to operate Cleaning is more difficult due to the design Advantages of Fire-tube Boilers: Relatively inexpensive (lower initial cost) Easy to clean Compact in size Easy to replace tubes Well suited for space heating and industrial process applications  Can use impure water without serious damaged Few controls Simple operations Disadvantages of Fire-tube Boilers Not suitable for high pressure applications 250 psig and above Limitation for high capacity steam generation drums exposed to heat, increasing the risk of explosion (liable to explosion) limited steam pressure and evaporation Typical efficiency is less than that of a water tube boiler. Three Common Problems of Boiler Water a. corrosion b. carryover c. scale Corrosion Corrosion is partial or complete wearing away, dissolving, or softening of any substance by chemical or electrochemical reaction with its environment. It is the deterioration of a metal or alloy or its properties due to the reaction with its environment. It is the phenomenon that returns metals to their native states as chemical compounds or minerals. Some metals corrode more rapidly than others in the same environment. Iron ore for example is an oxide of iron that is converted into steels and irons used in engineering. If conditions is correct for corrosion; moisture, acids, salts, etc., the tendency is for the material to revert to oxide of iron by combination with oxygen. Corrosion is one of the greatest enemies of the ship and its machinery. It is also the toughest enemy to fight against for the people working on the ship. Iron is one substance which is used in abundance on the ship. From the main body of the ship to the smallest equipment used in operations, iron makes its presence felt in almost every type of equipment used on board the ship. Causes of Boiler Corrosion Corrosion has several causes, but many relate to the chemistry of the water. Corrosion of metals on board ship usually caused by dissolved gases, dissolved salts, sludge or scale, and high fatty acids for lubrication of machinery. Acidity and dissolved oxygen and solids can contribute to corrosion in a boiler. 1. Oil Lubricating oils may contaminate the feed system and find their way into the boiler, this could be caused due to over lubrication of machinery and inefficient filtering of the feed. Oils such as animal and vegetable oils can decompose in the boiler liberating their fatty acids, these fatty acids can cause corrosion. Hence it is advisable to use pure mineral oil for lubrication of machine parts where contamination of feed can result, but oil of any description should never be allowed to enter the boiler as it can adhere to the heating surfaces causing o0verheating. 2. Caustic Embrittlement The phenomena of caustic embrittlement (or inter crystalline fracture) is believed to be caused by high concentrations of caustic soda (NaOH) and the material under stress. The stress corrosion cracks follow the grain or crystal boundaries of the material and failure of the affected part could result. 3. pH When the boiler water pH drops below about 8.5, a corrosion called acid attack can occur. The effect exhibits rough pitted surfaces. The presence of iron oxide deposits on boiler surfaces can encourage this kind of corrosion. The pH should be maintained between a minimum of 9.5 and a maximum of 11.0 to prevent acidic corrosion of boiler tubes and plates, and to provide for the precipitation of scale forming salts before scale is deposited. 4.Salts Feed water employed for boilers is usually, unevaporated fresh, evaporated fresh or evaporated salt water. Evaporated fresh water is principally employed, along with evaporated salt water for water tube boilers. All these waters can contain salts which could be harmful to the boiler from the point of view of scale formation and corrosion. Obviously, the evaporated fresh water and salt waters should be low in solid content and therefore less harmful. However, feed system can become contaminated with salt water, leaking condenser or an evaporator priming could be the causes. 5. Dissolved Gases Water contains varying amounts of dissolved gases. It can contain up to 9 ppm oxygen at room temperature and atmospheric pressure. As the temperature increase, the solubility of oxygen decreases, but water under pressure can hold higher amounts of dissolved oxygen. Nitrogen, being inert, has little effect on water used in boilers. Water can contain 10 ppm of carbon dioxide, sometimes much more than that due to decaying vegetation and organics in soil. Hydrogen sulfide and methane may be dissolved in water and these gases can be troublesome when they are present in the feed water. 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 (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.  If the water contains carbon dioxide, carbonic acid may be formed, which can cause corrosion. The carbon dioxide may have been absorbed into the feed water due to contact with the atmosphere, it can also be formed due to the breakdown of bicarbonates and carbonates present in the feed. 6. Suspended solids Suspended solids such as muds, sand, and clay settle to form deposits, promoting different Corrosion cells. 7. Temperature High temperature increases corrosion. Usually, a temperature or pressure increase directly leads to a higher corrosion rate because electrochemical reactions generally occur faster at higher temperatures. Temperature increases add energy to the reactions, which increases the corrosion rate. High temperature corrosion – this formed of attack can occur when loss of circulation causes the metal to over heat in a steam atmosphere. Forms of Corrosion that Attack the Boiler Boiler corrosion is the destruction of boiler metal. It occurs when the oxygen within the boiler dissolves into the water. The dissolved oxygen then causes a reaction with iron- rich (ferrous) boiler metal in a process known as oxidation. General Wastage 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. Pitting Corrosion or “oxygen corrosion” Pitting Corrosion 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. It happens when there is dissolved oxygen in boiler water. 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. Galvanic Corrosion Galvanic corrosion, also known as bimetallic corrosion, is an electrochemical process whereby one metal corrodes in preference to another metal that it is in contact with through an electrolyte. Galvanic corrosion occurs when two dissimilar metals are immersed in a conductive solution and are electrically connected. One metal (the cathode) is protected, whilst the other (the anode) is corroded. The rate of attack on the anode is accelerated, compared to the rate when the metal is uncoupled. We all know it needs two dissimilar materials to create a galvanic cell.  Boiler condenser tubes are made of copper and boiler tube material is made of steel. Copper may react with oxygen and may be carried as copper oxides inside the boiler. This two dissimilar materials are mainly responsible for galvanic corrosion. The table below is an extract from the galvanic series of materials at sea water. The metals at the bottom are more susceptible to corrosion like Magnesium and Zinc. Noble end of Table Titanium Graphite Monel metal Stainless Steel Nickel 170/30 Cupro Nickel Gunmetal Aluminum Bronze Copper Admiralty Brass Manganese Steel Cast Iron Mild Steel Zinc Aluminum Magnesium Base end of Table Similarly to protect important metals from galvanic corrosion Zinc, Aluminum, and Magnesium are used as sacrificial anodes. Cathode and Anodes An anode is an electrode through which the conventional current enters into a polarized electrical device. This contrasts with a cathode, an electrode through which conventional current leaves an electrical device. When two metals are connected, determination of which will be the cathode and anode is made by looking at the relative galvanic potentials of each material. Of the two materials, the metal with the lowest potential will be the anode. Sacrificial anodes are sometimes used deliberately to give cathodic protection to more expensive material, e.g., iron anodes give protection to the brass tubes and plates in condensers, magnesium anodes give protection to steel plates in tanks. Sacrificial Anode Sacrificial Anodes are highly active metals that are used to prevent a less active material surface from corroding. Sacrificial Anodes are created from a metal alloy with a more negative electrochemical potential than the other metal it will be used to protect. The sacrificial anode will be consumed in place of the metal it is protecting, which is why it is referred to as a "sacrificial" anode. Sacrificial anodes are sometimes used deliberately to give cathodic protection to more expensive material, e.g., iron anodes give protection to the brass tubes and plates in condensers, magnesium anodes give protection to steel plates in tanks. How Sacrificial Anodes Work? Sacrificial anodes work on the principle similar to electrolysis, according to which, if an anode and a metallic strip are dipped in an electrolytic solution, anode electron will dissolve and deposit over the metallic strip and make it a cathode. The materials used for sacrificial anodes are either relatively pure active metals, such as zinc or magnesium, or are magnesium or aluminum alloys that have been specifically developed for use as sacrificial anodes. Zinc Anodes are usually used for seawater. Aluminum Anodes are usually used for Brackish, salt or fresh water. Magnesium Anodes are usually used for fresh water. Since the sacrificial anode works by introducing another metal surface with a more negative electronegative and much more anodic surface. The current will flow from the newly introduced anode and the protected metal becomes cathodic creating a galvanic cell. The oxidation reactions are transferred from the metal surface to the galvanic anode and will be sacrificed in favor of the protected metal structure.  1. 2. 3. 4. 5. 6. 7. Rusting or Wearing Rusting or Wearing is a fairly even wearing away of the boiler metal in its cause by oxygen dissolve in boiler water. Oxygen does not exist in the water in a free state but is combined with nitrogen. The nitrogen, however, is inert and causes no damage. Water has the property of absorbing large quantities of air, and oxygen present in the absorbed air is the cause of rusting.  Hydrogen Attack Hydrogen irons are generated by concentration of acid under a hard dense deposit. It can penetrate the grain boundary of tube metal and react with carbon and produces methane gas. This carbon loss weakens the tube metal and methane gas exerts a pressure which separates the grains of tube. Hydrogen damage is a specialized form of under-deposit corrosion sometimes found in boiler tubes. During operation, deposit builds up on the tube surface, and when the tube metal corrodes, hydrogen is produced. Hydrogen evolves from the corrosion reaction and, when trapped between heavy deposit and the tube wall, diffuses more easily into the tube metal than through the Deposit. Hydrogen attack can also occur when hydrogen is released by caustic corrosion. Grooving Whenever any section of the boiler is subjected to a localized stressing action, such as when holes are drilled in boiler plate or riveting, the metal in the immediate vicinity develops very tiny cracks, which are not visible to the naked eye but can be seen with a microscope. When excessive amounts of alkaline compound are fed into the boiler water, the alkali will settle out in these small fissures. The result is to make the metal around the cracks very brittle. Hence, such condition is referred to as caustic embrittlement. When the boiler is cut in on the line, the metal expands, and when the boiler is removed from the line, the metal contracts. Caustic Cracking This is a form of intercrystalline cracking caused by water with a high level of caustic alkalinity coming into contact with steel has not been stress relieved. It is very rare in marine boilers but may occasionally occur in w ay of leaking riveted joints or bolted fittings.  This form of cracking differs from that of corrosion fatigue in that the cracks follow the grain boundaries of the metal, whereas the fatigue cracks pass across these boundaries. Carryover These are contaminants that leave the boiler with the steam. Foaming and carryover are those bubbles and other solid particles on the surface of the water in the boiler. When foaming is excessive, these leave the boiler with the steam and accumulate in the control valves, non-return valves, heat exchangers, and turbine blades as hard deposits. Most common cause of turbine damage is due to carry over on the steam. Carryover also damages protective coating of the metal oxide which lead to corrosion. Carryover in super heaters 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. Scale It is a hard adherent coating that collects on the waterside of any heating surface. Scale formation or deposits in the boilers results from hardness contamination of feed water.The primary minerals in the water that make the feed water “hard” are Calcium (Ca++) and Magnesium (Mg++). These minerals form a scale over the surface of piping, water heaters, and on everything it comes in contact with. Hardness contamination of the feed water may also result from either deficient softener systems or raw water in leakage of the condensate.  This kind of scale/ deposits act as insulators and lower the heat transfer rate. The insulating effect of deposits also causes the boiler metal temperature to rise and lead to tube-failure by overheating. Large amounts of such deposits throughout the boiler would reduce the heat transfer enough to drop the overall boiler efficiency. Boiler Water and Feed Water Testing and Treatment Water is a necessity in boiler operation. Yet, water can have some impurities that can result in rust, scale, corrosion and, eventually, boiler failure. It is an integral factor to the boiler’s ability to produce the steam to be converted into heat, therefore it is imperative that the water must be treated properly to remove the impurities present. Feed Water Composition In order to generate steam on a constant basis, boiler should be continuously supplied with water, called as feed water. Feed water consists of condensate, which gets collected after the steam gets condensed by losing heat to the process or radiation losses, flash steam and make up water. Quantity of makeup water depends upon the quantity of the condensate and flash steam collected. Condensate and flash steam are pure in form without any impurities. This is not the case with the makeup water as it is raw water which can have many impurities depending upon the composition of natural water at that particular location. Both condensate and makeup water are mixed in feed tank from where they are fed to the boiler. The quality of feed water depends solely on the quality of makeup water. If feed water is not treated properly, it can result in multiple problems like scale formation or corrosion. It can also increase the amount of blow down required and hence can result in wastage of fuel. In order to avoid all these later problems related to feed water, the wise decision is to treat makeup water and ensure that different impurities are under their allowed limits.  The different impurities in the feed water can be grossly classified into three classes, namely dissolved gases, dissolved solids and suspended solids. Each of these impurities affects the boiler system in a different way. Feed water is to be treated for each of these types of impurities. Boiler Water Tests Boiler water should be regularly tested, and the treatment of the boiler water should be conducted according to the results obtained from the tests. 1. pH Test - 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. For boiler water it is very important to monitor the pH value to prevent corrosion and scale. Usually, boiler water is maintained at high pH (9.5 -11.5) to suppress corrosion. 2. Alkalinity Test - water is considered to contain alkalinity when some alkaline substance is present. The presence of bicarbonate, carbonate and hydroxide ions is commonly considered as alkalinity. Boiler and the feed system must be treated to inhibit corrosion and scale formation and all possible contaminants in the form of metal salt, gas, oil and suspended particles. Boiler and feed water are tested regularly for alkalinity, as successive alkalinity of the boiler water can cause caustic embrittlement and scale formation. 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. M ALKALINITY. Total Alkalinity or M Alkalinity (pH values greater than 4.3) measures the sum of Bicarbonate, Carbonate and Hydroxide Alkalinity. 3. Phosphate test - for the precipitation of scale forming salts into sludge and to give alkalinity, phosphates are used. Phosphate will combine with the calcium in the boiler water forming tricalcium phosphate [Ca3(PO4)2], which will precipitate as its solubility is low in the form of a sludge or porous scale. Phosphate will also combine with the magnesium compounds forming magnesium phosphate [Mg3(PO4)2] which also precipitates into the form of sludge. Frequent used of phosphates instead of sodium carbonate for conditioning high concentration of caustic soda are avoided, since at high temperatures sodium carbonate can break down into sodium hydroxide and carbon dioxide and the caustic soda content of the boiler water would increase. Thus, phosphate test is conducted. 4. Chloride Test - Chloride is a major constituent of sea water and is extremely corrosive in acidic environments. It requires close monitoring in applications such as marine boiler systems that are prone to seawater contamination. Chlorides may be present in the boiler water sample and it is essential that it may be measured as they would be an indication of salt water leakage into the feed system, either a leaky condenser, or a primed evaporator. Sodium chloride could react with magnesium sulphate to produce magnesium chloride and sodium sulphate. Magnesium chloride on the other hand could react with water to form magnesium hydroxide and hydrochloric acid which can cause corrosion to the boiler metal. 5. Sulfite Test - sodium sulfite is added to the feed water to remove the oxygen content of water and produces sodium sulphate which remains as solution in the boiler water under normal conditions. Reaction of sulfites with alkaline solution could produce hydrogen sulfide and possibly sulfur dioxide which can attack steel, brass, and copper. 6. Hardness Test - Can be carried out by means of conductivity meter or we can use standard soap solution. Take boiler water in a beaker. Add soap solution and stir it for some time. More foam/bubbles formed, the lesser is the hardness in boiler water. 7. Conductivity Test – The conductivity test provides an accurate measurement of steam purity as well as a simple control for boiler water solids. The higher the conductivity, the higher the hardness. Onboard boiler water tests are carried out by professional water test kits provided by recognized companies such as Unitor and Drew Marine. Procedure in Taking Boiler Water Sample 1.Allow to drain the water from the sample cock before taking the sample for testing to ensure the line is clear of sediment. 2. Cool down the sample for about 250C. 3. Put the sample in clean container and make sure no contamination of other substances. 4. Boiler water should be taken from the steam drum through the salinometer valve. 5. Feed water sample should be taken from the suction or discharge of feed water pump or after the condenser.  Table 1- Desired Results (UNITOR Kit) Test Limits Phosphate Test 20 - 50 ppm PO4 P- Alkalinity 100 - 150 ppm CaCO3 M-Alkalinity (Total ) Below 2x P-Alkalinity Chloride Test Below 100 ppm Cl Sulfite Test 20 - 50 ppm Na2SO4 pH Test 9.5 -11.5 Table 2 -Testing Program Water Sample Mode of Testing Tests Boiler water Daily P-Alkalinity, pH, Chloride M-Alkalinity, Phosphate, Conductivity, Hydrazine Feed water As required Chloride, conductivity Make up water As required Chloride, hardness Condensate return Weekly Chloride, pH, ammonia Engine cooling water Every 4 days Nitrates, chlorides, pH Table 3 Water Treatment Recommendation Purpose Chemical Type of Boiler a. To prevent scale Na3PO4 all Up to 84 bar wp b. To give alkalinity and NaOH or all minimize corrosion Up to 84 bar wp Na2CO3 all Up to 60 bar wp c. to condition sludge Polyelectrolyte or All, Up to 84 bar wp Starch or All, Up to 84 bar wp Tannins or All, Up to 84 bar wp Al3AlO3 All, Up to 31.5 bar wp d. to remove traces of oxygen Na2SO3 or All, Up to 32 bar wp hydrazine From 31.5 - 84 bar e. to reduce risk of Caustic Na2SO4 or All, up to 31.5 bar Cracking NaNO3 All, up to 31.5 bar  f. reduce risk of carryover of Anti-foam All, Up to 84 bar foam g. To protect feed & Filming amines or All, Up to 60 bar condensate systems from corrosion Neutralizing From 17.5 – 84 bar amines Note: 1 bar= 1 atm 1 bar= 1 kg/ cm2 1 bar=100 KN/m3 wp = working pressure Summary of the boiler water tests, the purpose of the test results, and actions to be taken: Phosphate Reserve Purpose of test: To test the presence of phosphate compounds Test Result Action to be taken Low Add Phosphates No action, Important to maintain the phosphate levels to a High minimum of 10ppm Alkalinity Purpose of test: To measure acidity or alkalinity of the boiler water Test Result Action to be taken High Partial blow down or add sodium sulphite Low Add NaOH to get desired result Dissolved solids Purpose of test: To test the presence of ferrous ions and metal contents Test Result Action to be taken High Partial blow down and take fresh feed Low Good, No action required Chlorides Purpose of test: To test the presence of chloride compounds Test Result Action to be taken Trace sources of leak and rectify. blow down High and increase completely and take fresh feed Can be reduced by phosphate treatment and Steady but high partial blow down Low Good, No action required Hydrazine Purpose of test: To test the hydrazine reserve Action to be taken Trace sources of leak and rectify. blow down completely and take fresh feed Feed water hardness Purpose of test: To test the presence of carbonate compounds Test Result Action to be taken High Add Phosphates Good, Low No action required Boiler Water treatment Boiler water treatment is crucial to ensure that the steam boiler is properly operating. As the impurities enter the boiler water, it fouls the steam boiler and leads to damaging the boiler system, reducing its lifespan and efficiency. It results in excessive bills for the same operation. Dissolved salts in the boiler water causes scaling, while the other contaminants in the boiler water impact the machinery if not removed by external or internal boiler treatment. Ideally only distilled water should be used, all dissolved solids and gases being exclude from the feed system and boiler. Economically this is not practicable at sea and some form of treatment must be provided. This can be divided into external and internal forms of treatment. The treatment and conditioning of boiler feed water must satisfy three main objectives: Continuous heat exchange Corrosion protection and prevention in the boiler and feed system. Prevention of scale formation in the boiler and feed system by using distilled water or precipitating all scale forming salts into the form of a non-adherent sludge Production of high quality steam Control of sludge formation and prevention of carry over with the system Boiler-water treatment generally involves the dose of chemicals into the boiler water. These chemicals must be dosed at highly accurate rates and speeds so that they themselves do not interfere with the quality of the water and the operation of the boiler. This means that the operator must identify and employ the right type of chemical-injection technology. External Treatment External treatment is the reduction or removal of impurities from water outside the boiler. In general, external treatment is used when the amount of one or more of the feed water impurities is too high to be tolerated by the boiler system in question. There are many types of external treatment (softening, evaporation, deaeration, membrane contractors etc.) which can be used to tailor make feedwater for a particular system. The water treatment facilities purify and deaerate make-up water or feed water. Water is sometimes pretreated by evaporation to produce relatively pure vapor, which is then condensed and used for boiler feed purposes. Certain natural and synthetic materials have the ability to remove mineral ions from water in exchange for others. For example, in passing water through a simple cation exchange softener all of calcium and magnesium ions are removed and replaced with sodium ions. Since simple cation exchange does not reduce the total solids of the water supply, it is sometimes used in conjunction with precipitation type softening.  One of the most common and efficient combination treatments is the hot lime-zeolite process. This involves pretreatment of the water with lime to reduce hardness, alkalinity and in some cases silica, and subsequent treatment with a cation exchange softener. This system of treatment accomplishes several functions: softening, alkalinity and silica reduction, some oxygen reduction, and removal of suspended matter and turbidity. Internal Treatment Internal treatment is the conditioning of impurities within the boiler system. The reactions occur either in the feed lines or in the boiler proper. Internal treatment may be used alone or in conjunction with external treatment. Its purpose is to properly react with feed water hardness, condition sludge, scavenge oxygen and prevent boiler water foaming. Internal treatment can constitute the unique treatment when boilers operate at low or moderate pressure, when large amounts of condensed steam are used for feed water, or when good quality raw water is available. The purpose of an internal treatment is to: react with any feed-water hardness and prevent it from precipitating on the boiler metal as scale condition any suspended matter such as hardness sludge or iron oxide in the boiler and make it non- adherent to the boiler metal provide anti-foam protection to allow a reasonable concentration of dissolved and suspended solids in the boiler water without foam carry-over eliminate oxygen from the water and provide enough alkalinity to prevent boiler corrosion. In addition, as supplementary measures an internal treatment should prevent corrosion and scaling of the feed-water system and protect against corrosion in the steam condensate systems. During the conditioning process, which is an essential complement to the water treatment program, specific doses of conditioning products are added to the water. Lime and Soda Treatment Lime (calcium hydroxide, Ca(OH)2 and soda ash (sodium carbonate, Na2CO3) are used to deal with the calcium and magnesium compounds in the boiler water. Calcium hydroxide (lime, Ca(OH)2 react with temporary hardness salts and magnesium compounds. Sodium carbonate (soda ash, Na2CO3) reacts with the calcium compounds originally in the water and those found through using calcium hydroxide. Calcium hydroxide is used to react with magnesium compounds and alkaline hardness salts. Sodium carbonate is used to react with calcium compounds in the boiler feed including those formed through employing calcium hydroxide. This combination of lime and soda gives zero hardness and alkaline feed water. The following are chemical equations that represent the Lime’s reaction with temporary hardness salts and magnesium Calcium bicarbonate + Calcium Hydroxide Calcium carbonate + water Ca(HCO3)2 + Ca(OH)2 2 CaCO3 + H2O Magnesium + Calcium Magnesium + Calcium + water bicarbonate Hydroxide hydroxide carbonate Mg(HCO3)2 + 2Ca(OH)2 Mg(OH)2 + 2CaCO3 + H2O Magnesium sulfate + Calcium hydroxide Magnesium hydroxide + Calcium sulfate MgSO4 + Ca(OH)2 Mg(OH)2 + CaSO4 Magnesium nitrate + Calcium hydroxide Magnesium hydroxide + Calcium nitrate Mg(NO3)2 + Ca(OH)2 Mg(OH)2 Ca(NO3)2 Magnesium Chloride + Calcium Hydroxide Magnesium Hydroxide + Calcium Chloride MgCl2 + Ca(OH)2 Mg(OH)2 + CaCl2 Calcium sulfate + Sodium carbonate Calcium carbonate + Sodium sulfate MgSO4 + Na2 CO3 CaCO3 + Na2SO4 Calcium Chloride + Sodium carbonate Calcium carbonate + Sodium Chloride CaCl2 + Na2 CO3 CaCO3 + NaCl Calcium Nitrate + Sodium carbonate Calcium carbonate + Sodium Nitrate Ca(NO3)2 + Na2 CO3 CaCO3 + NaNO3 Caustic Soda Treatment Calcium + Sodium Calcium + Sodium + water Bicarbonate Hydroxide carbonate Carbonate Ca(HCO3)2 + NaOH CaCO3 + Na2CO3 + 2H2O Magnesium + Sodium Magnesium + Sodium + water Bicarbonate Hydroxide hydroxide carbonate Mg(HCO3)2 + 4 NaOH Mg(OH)2 + 2Na2CO3 + 2H2O Magnesium + Sodium Magnesium + Sodium sulfate Sulfate hydroxide hydroxide MgSO4 + 2 NaOH Mg(OH)2 + Na2SO4 Magnesium nitrate + Sodium hydroxide Magnesium hydroxide + Sodium nitrate Mg(NO3)2 + 2 NaOH Mg(OH)2 + 2 NaNO3 Magnesium + Sodium Magnesium + Sodium Chloride Hydroxide Hydroxide Chloride MgCl2 + 2NaOH Mg(OH)2 + 2NaCl Phosphate Treatment Calcium Carbonate + Sodium Phosphate Calcium phosphate + Sodium carbonate CaCO3 + Na3PO4 Ca3 (PO4)2 + Na2CO3 Calcium sulfate + Sodium Phosphate calcium phosphate + sodium sulfate CaSO4 + Na3PO4 Ca3(PO4)2 + Na2SO4 Calcium Chloride + Sodium Phosphate Calcium Phosphate + Sodium Chloride CaCl2 + Na3PO4 Ca3 (PO4)2 + NaCl Magnesium Sulfate + Sodium Phosphate Magnesium Phosphate + Sodium Sulfate MgSO4 + Na3PO4 Mg3 (PO4)2 + Na2SO4 The commonly used products include: Phosphates-dispersants, polyphosphates-dispersants (softening chemicals): reacting with the alkalinity of boiler water, these products neutralize the hardness of water by forming tricalcium phosphate, and insoluble compound that can be disposed and blow down on a continuous basis or periodically through the bottom of the boiler. Oxygen scavengers: sodium sulphite, tannis, hydrazine, hydroquinone/progallol- based derivatives, hydroxylamine derivatives, hydroxylamine derivatives, ascorbic acid derivatives, etc. These scavengers, catalyzed or not, reduce the oxides and dissolved oxygen. Most also passivate metal surfaces. The choice of product and the dose required will depend on whether a deaerating heater is used. Natural and synthetic dispersants (Anti-scaling agents): increase the dispersive properties of the conditioning products. They can be: Natural polymers: lignosulphonates, tannins Synthetic polymers: polyacrilates, maleic acrylate copolymer, maleic styrene copolymer, polystyrene sulphonates etc. Anti-foaming or anti-priming agents: mixture of surface-active agents that modify the surface tension of a liquid, remove foam and prevent the carry over of fine water particles in the steam. The softening chemicals used include soda ash, caustic and various types of sodium phosphates. These chemicals react with calcium and magnesium compounds in the feed water. Sodium silicate is used to react selectively with magnesium hardness. Calcium bicarbonate entering with the feed water is broken down at boiler temperatures or reacts with caustic soda to form calcium carbonate. Since calcium carbonate is relatively insoluble it tends to come out of solution. Sodium carbonate partially breaks down at high temperature to sodium hydroxide (caustic) and carbon dioxide. High temperatures in the boiler water reduce the solubility of calcium sulphate and tend to make it precipitate out directly on the boiler metal as scale. Consequently calcium sulphate must be reacted upon chemically to cause a precipitate to form in the water where it can be conditioned and removed by blow-down.  Calcium sulphate is reacted on either by sodium carbonate, sodium phosphate or sodium silicate to form insoluble calcium carbonate, phosphate or silicate. Magnesium sulphate is reacted upon by caustic soda to form a precipitate of magnesium hydroxide. Some magnesium may react with silica to form magnesium silicate. Sodium sulphate is highly soluble and remains in solution unless the water is evaporated almost to dryness. References: https://www.youtube.com/watch?v=fRh6QnFRC54 Common Boiler Problems – SteamWorks https://www.youtube.com/watch?v=ZRCjC9OiX5o&t=436s Marine Steam Boiler https://www.youtube.com/watch?v=Nqxi_qtf8ik&t=56s BOILERS - Steam System on ships (Overview and Operation) https://www.youtube.com/watch?v=is5wdVgPOkI&t=15s Explanation of Boiler Feed Water & Its Treatment | Engineering Chemistry https://marineengineeringonline.com/internal-corrosion-in-boilers/