Lesson 2 Topic 1: Cooling Water Properties (PDF)

Topic 1 Lesson 2. Physical and Chemical Properties of Cooling Water 1.1 Introduction Water chemistry analyses are carried out to identify and quantify the chemical components and properties of water samples. The type and sensitivity of the analysis depends on the purpose of the analysis and t...

Topic 1 Lesson 2. Physical and Chemical Properties of Cooling Water 1.1 Introduction Water chemistry analyses are carried out to identify and quantify the chemical components and properties of water samples. The type and sensitivity of the analysis depends on the purpose of the analysis and the anticipated use of the water. Pure water is a clear, colorless liquid made up of oxygen and hydrogen. It is the most common substance on the earth’s surface. In either liquid or solid form (ice) it covers more than 70 percent of the planet. It is also present in the atmosphere as a gas (water vapor or steam). Water is essential to life on earth and constitutes a large part of most living things. Human beings for example, are about two-thirds water. The exact chemical formula of the water molecule is H20 (two atoms of hydrogen and one atom of oxygen. Water is an organic substance whose formula may be written either H20 or HOH ; it exists in three forms or phases: (a) a crystalline solid at or below 0 0C (ice) ; (b) as a colorless liquid from 0 to 1000 C ; and as a vapor at above 1000C. It Is a powerful solvent and acts as a catalyst for many reactions. Water has a boiling point of 1000C (212 0F) and freezing point 00C (320 F). Difference of Fresh Water and Sea Water Freshwater is water that contains less than 1% salt and thus has little to no taste, odor, or color. Some definitions put this percentage even lower at a maximum of 0.5% salt. Freshwater is found in lakes, streams, rivers, groundwater, ice, and glaciers. Salt Water is defined as the water present in the oceans and seas with a greater percentage of salt, minerals in them. Because of the high levels of salinity, it is not safe for drinking or any other purposes for humans. Saltwater is considered to have much more density. Some examples of fishes living in saltwater are – sharks, tuna, yellowtail, bluefish, albacore, common dolphins. Saltwater is water that is composed of at least 3% salt and minerals. Saltwater makes up marine ecosystems like oceans and seas. Marine organisms have adaptations to deal with the salty conditions, such as specialized cells in their gills that filter out salt. Seawater contains most all elements found on earth. ANALYSIS OF SEA WATER Salt Chemical App. % of total PPM Symbol dissolved solids Sodium chloride NaCl 79 25,000 Magnesium Chloride MgCl2 10 3, 000 Magnesium sulfate MgSO4 6 2,000 Calcium sulfate CaSO4 4 1,200 Calcium bicarbonate Ca(HCO3 ) 2 less than 1 200 Amount of salts in one kilogram of seawater Sodium chloride - 27.21 gm magnesium chloride - 3.81 gm Magnesium sulfate – 1.66 gm calcium sulfate - 1.26 gm Potassium sulfate - 0.8gm calcium carbonate - 0.12 gm Magnesium bromide - 0.08 gm ANALYSIS OF A FRESH WATER SAMPLE Salt Symbol PPM Sodium Chloride NaCl 50 Sodium Nitrate NaNO3 35 Magnesium Sulfate MgSO4 30 Calcium sulfate CaSO4 90 Calcium carbonate CaCO3 200 6 Ions Present in Most Solids Present in Sea Water Chloride (Cl-) 55.03% Sodium (Na+) 30.59% Sulfate (SO4-2) 7.68% Magnesium (Mg+2) 3.68% Calcium (Ca+2) 1.18% Potassium (K+) 1.11% 1.2 Marine Engine Cooling Water The Cooling Water System One of the most critical systems on ships is the cooling system. Large vessels need a way to safely remove unusable heat from their main engine, auxiliary engines, generators, and other machinery. Cooling of engines is achieved by circulating a cooling liquid around internal passages within the engine. The cooling liquid is thus heated up and is in turn cooled by a sea water circulated cooler. Without adequate cooling certain parts of the engine which are exposed to very high temperatures, as a result of burning fuel, would soon fail. Cooling enables the engine metals to retain their mechanical properties.  Cooling water is used in industrial processes to dissipate large amounts of heat. The water has to meet specific requirements which is why it is analyzed on a regular basis. When it comes to cooling for ships, efficiency is crucial. The good news is that modern cooling systems provide excellent performance while running as efficiently as possible. The machinery systems fitted on board ships are designed to work with maximum efficiency and run for long hours. The most common and maximum energy loss from machinery is in the form of heat energy. This loss of heat energy has to be reduced or carried away by a cooling media, such as central cooling water system, to avoid malfunctioning or breakdown of the machinery. There are two cooling systems used onboard for the cooling purpose: 1. Sea Water cooling system: Seawater is directly used in the machinery systems as a cooling media for heat exchangers. 2. Freshwater or central cooling system: Freshwater is used in a closed circuit to cool down the engine room machinery. The freshwater returning from the heat exchanger after cooling the machinery is further cooled by seawater in a sea-water cooler. Water carried in pipes is used to cool machinery. The main engine is cooled by two separate but linked systems: an open system (sea-to-sea) in which water is taken from and returned to the sea (seawater cooling), and a closed system where freshwater is circulated around an engine casing (freshwater cooling). Freshwater is used to cool machinery directly, whereas seawater is used to cool freshwater passing through a heat exchanger. The particular feature of an engine cooling system is continuous fluid flow. Fluid in motion causes abrasive corrosion and erosion. To reduce the effects of turbulent flows, seawater systems incorporate large diameter mild steel pipes, the ends of which open to the sea through sea chests where gate valves are fitted. Why is it necessary to have water cooling in marine engines? When combustion takes place inside an engine there are mainly three byproducts: Exhaust Gases(30%) Work Done(40%) Heat(30%)  We must control the amount of heat generated from the engine so that the temperature of the engine does not get too high and cause thermal stress to arise in each component. Why is freshwater used instead of seawater for cooling the engine? Seawater cannot be used for cooling the engine because it is highly corrosive and the replacement of these parts can be very costly. Therefore fresh water is stored in a tank and circulated to these parts and after the water absorbs all the excess heat it is passed through a plate type heat exchanger, which helps to remove the excess heat from the water with the help of seawater before returning to the tank. Some of the heated water from the water jacket is also sent to the freshwater generator so that the heat inside it can be utilized to make fresh water more efficient. Physical Properties of Engine Cooling Water Low-temperature circuit The low-temperature circuit is used for low-temperature zone machinery and this circuit is directly connected to the main seawater central cooler; hence its temperature is lower than that of high temperature (H.T circuit). The L.T circuit comprises all auxiliary systems. The L.T circuit comprises all auxiliary systems.  The total quantity of low-temperature or L.T fresh water in the system is maintained in balance with the H.T. freshwater cooling system by an expansion tank which is common to both systems. The expansion tank used for these circuits is filled and makeup from the hydrophore system or from the distilled water tank using the Feed Water (F.W) refilling pump. High-temperature circuit (H.T) The H.T circuit in the central cooling system mainly comprises of the jacket water system of the main engine where the temperature is quite high. The H.T water temperature is maintained by low-temperature fresh water and the system normally comprises of the jacket water system of the main engine, FW generator, DG (Diesel Generator) during standby condition, Lube oil filter for stuffing box drain tank. The HT cooling water system is circulated by electrical cooling water pumps, one in service and one on standby. Chemical Properties of Engine Cooling Water Chemicals are periodically added into the freshwater tank in the cooling system so that the quality of the water is maintained and it does not turn corrosive. Critical Parameters to be Monitored. Depending on the type of the facility) This is the only way of ensuring flawless and cost-effective operation. pH Hardness Conductivity Turbidity Phosphates Sulfates Ammonium Chlorides Calcium Magnesium Aluminum Iron Zinc  Silicate Nitrate Nitrite Chemical Oxygen demand Total Organic Carbon Quality of Cooling Water The cooling water of the engine should be only demineralized (distilled) water with proper treatment, which is necessary for keeping effective cooling and preventing corrosion of the system. Though the distilled water matches best to the requirements for cooling water, it is necessary to add corrosion inhibitor. Because untreated distilled water absorbs carbon dioxide from the air and then becomes corrosive. Rainwater is heavily contaminated and highly corrosive in general, which is also not recommended as cooling water. Tap water (drinking water) is not recommended as cooling water due to risk of chalk deposit formation inside the cooling system. However, if the distilled water, for example from fresh water generator, is not available, tap water may be used as cooling water after softening and some other treatments according to the ingredients. Sea water or fresh water contaminated by sea water even in small amount is not allowed to be used as cooling water of the engine due to high risk of severe corrosion and deposits formation in the system. Problems Encountered by Cooling Water Systems on the Quality of Cooling Water and Feed Water. 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 reversion of a metal to its ore form. Iron, for example, reverts to iron oxide as the result of corrosion. Corrosion is one of the serious problems on board ships. Several forms of corrosion normally occur on cooling water system are, general wastage, pitting, crevice corrosion, galvanic corrosion, stress corrosion, and erosion corrosion. The product of corrosion can form an insulating scale interfering with the heat transfer, while pitting corrosion, crevice corrosion, can lead to complete failure of that part of the cooling system where the attack occurs. Scale Scale is hard mineral coatings and corrosion deposits made up of solids and sediments that collect on or in distribution system piping, storage reservoirs and household plumbing. Scaling, which is the deposition of mineral solids on the interior surfaces of water lines and containers, most often occurs when water containing the carbonates or bicarbonates of calcium and magnesium is heated. Scale formation can be reduced by applying proper water softening methods. In Diesel engine cooling water system, scale is usually formed by the breakdown of calcium and magnesium bicarbonate in the water used to fill the cooling system and to replace losses due to evaporation or leakage. Scale can also be produced as a result of the interaction of an alkaline corrosion inhibitor and the calcium and magnesium salts present in water, the precipitated sludge giving rise to a scale which ca impair engine performance by the formation of hard deposits on the heat transfer surfaces.  On board ship, the water used for make-up to the diesel cooling water system will normally be: a. evaporated sea water or occasionally evaporated fresh water b. fresh water or shore water. How Scale Forms The potential for scale formation on hot metal cooling system surfaces is affected by a number of dynamic conditions. Some of the mechanisms and parameters that affect the formation of these deposits: Water hardness – the harder the water being used in an engine coolant, the greater the amount of scale formation. Temperature – as coolant temperatures increase, hardness salts (calcium and magnesium) in solution become less soluble and increase their propensity to plate out on hot metal cooling system surfaces Flow characteristics – scale generally forms on the hot side of a cooling system and in areas of low or turbulent flow. Entrapped air – any air bubble formation in a coolant area (bubbling around a hot source) increases the tendency for scale to form in that area. pH – increases in pH will increase the potential for scale deposits. Damage to water pump seals. Calcium and magnesium have the tendency to combine with the phosphates found in old-fashioned antifreeze and some additive packages. They form calcium and magnesium phosphate scale on heat transfer surfaces, especially on water pump seal faces. These deposits can destroy the flatness of a seal face, preventing the water pump seal from sealing. The result can be destruction of the water pump bearings. Engine Coolants Marine Antifreeze Coolant (or antifreeze) protects your engine from freezing while defending components against corrosion. It plays a critical role in sustaining engine heat balance by removing heat. In a heavy-duty diesel engine, only one-third of the total energy produced works to propel the vehicle forward. An additional one-third is removed as heat energy by the exhaust system. The remaining one-third of heat energy produced is taken away by the engine coolant. This heat removed by the coolant provides a balance in the removal of engine heat that is critical in ensuring that the engine operates properly. Overheating could result in accelerated deterioration of the oil and the engine itself. While water provides the best heat transfer, glycol is also used in engine coolants to provide freeze protection. The addition of glycol slightly reduces the heat transfer of the water, but in most climates and applications, freeze protection is critical. A marine antifreeze contains propylene glycol that raises water’s freezing point. The non-toxic formula inhibits the freezing of liquids, which minimizes the chances that the engine will crack or burst, even as temperatures begin to drop. It also has anti-rust and corrosion benefits, helping maintain the boat engine’s peak condition and performance. Aside from protecting the engines, antifreeze is also often used in a boat’s potable water system.  Corrosion Inhibitors Corrosion destroys various metals such as iron, steel, and copper. Various techniques and substances are used to inhibit or prevent the process of corrosion. Coolant corrosion inhibitors help decrease the corrosion rate of metals within your equipment and help maintain other coolant properties. Corrosion inhibitors are designed to minimize metal loss, which can reduce the useful life of heat exchangers, recirculating water piping, and process cooling equipment. Some examples are chromates, nitrates, molybdates, and tungstate. These inhibitors slows down the cathodic reaction to limit the diffusion of reducing species to the metal surface. Before deciding on the corrosion inhibitors to be used, it is essential to consider the following factors: Presence of aluminum and copper alloys. The full range of metals and alloys in the system. Example the choice of corrosion inhibitors is simplified if there is no aluminum in the engine. Aluminum Alloys with copper are considered in the same way as copper. But the corrosion of Aluminum can be increased by copper components in contact with the aluminum or where copper is deposited from the soluble copper on to the aluminum. Presence of Zinc Whether or not any of the metal components or pipework in the system has been galvanized. Zinc (galvanizing) is used to protect mild steel since it has a low resistance to corrosion and will act as sacrificial metal. Temperature increase is the main cause of corrosion of zinc due to reverse polarity effect. This is at its maximum temperature between 600C to 900C. Galvanized piping is therefore not recommended as a means of preventing corrosion of iron in a diesel cooling system, but should only be considered for protecting the mild steel piping during construction. Before applying corrosion inhibitors in the system it is advisable to remove the zinc galvanizing by acid treatment.  Composition of Cooling Water. Water testing should be conducted to decide the concentration of inhibitor required. The higher the chloride or sulfate concentration, the higher the level of corrosion inhibitor necessary. Engine Cooling Water Treatment The treatment used to prevent corrosion in a diesel cooling water system differs from the type of treatment employed to protect steaming boilers or boiler feed systems. The following are the Chemicals Used in Cooling Water Treatment Aboard Ship: Sodium Nitrite (NaNO2) - A corrosion inhibitor used for diesel cooling water Treatment - protective to cast iron, steel and aluminum. - dosage 1000 to 3000 ppm. Sodium Benzoate (C8H5CO2Na) - A corrosion inhibitor used for diesel cooling water treatment - protective to steel and solder - dosage 10,000 to 15,000 ppm Sodium borate (Na2B4O7) – In conjunction with other corrosion inhibitors for treatment of diesel cooling water systems. - protective to copper and copper alloys. - provide some alkalinity in that it buffers at pH of 8.9 - it is also useful as a fungicide. - dosage 1000 to 3000 ppm when used with other inhibitors Sodium Chromate (Na2CrO4) - A corrosion inhibitor for treatment of diesel cooling water systems. - protective to cast iron, steel, copper and copper Alloys - dosage 1000 to 3000 ppm. Disodium hydrogen phosphate (Na2HPO4) - A corrosion inhibitor for treatment of diesel cooling water systems. Sodium Silicate (Na2SiO3) - A corrosion inhibitor for treatment of diesel cooling water systems when aluminum alloys, and solders are present - dosage 1000 to 2000 ppm  Triethanol ammonium (C6H5O3N) - A corrosion inhibitor for treatment diesel cooling water systems when aluminum alloys are present - dosage 1000 to 2000 ppm Benzoitriazole (C6H5N3) - A corrosion inhibitor for protection of copper and copper alloys in a diesel cooling water systems. Sodium mercaptobenzothiazole (C7H4NS2Na) - A corrosion inhibitor for protection of copper and copper alloys in a diesel cooling water systems. - dosage 300 to 500 ppm Soluble Oil - A corrosion inhibitor for treatment of diesel cooling water systems - protective to steels, cast iron and solder. - dosage variable. Polyphosphate and polyelectrolytes – In diesel cooling water systems to prevent scale where hard water is used as make – up water. Correct cooling water treatment and follow-up of the cooling water condition are of utmost importance for keeping the cooling water systems of the engines in good condition. The corrosion processes that could occur due to a bad cooling water quality may under certain circumstances be local and by their nature proceed very rapidly. This may cause unexpected operating problems or engine failures even within relatively short periods of time, for example in the cylinder head exhaust valve seat pockets and other areas prone to corrosion in the cooling water systems of the engines. Cooling water should be treated properly and corrosion inhibitor should be added. The analysis and treatment of cooling water are recommended to be carried out by a famous and familiar specialist. Otherwise, keep the treatment procedures strictly according to the instructions from the supplier. The cooling water before adding corrosion inhibitor should be checked and treated to satisfy following requirements: pH 7 to 9 Total hardness as CaCOз max. 75 ppm(mg/l) Chloride max. 50 ppm(mg/l) Sulphate max. 100 ppm(mg/l) Silicate max. 150 ppm(mg/l) Residue after evaporation max. 400 ppm(mg/l) Note: Chloride and Sulphate are corrosive even in the presence of an inhibitor. Some recommended products are listed as follows: Note: Oily inhibitors adhere to cooling surface and influence cooling efficiency, which are not recommended for cooling water. Only nitriteborate based inhibitors are recommended. Note: Do not mix the inhibitors of different types or properties. Specific Example of Recommended Product, Checking Cooling Water and the System The property of the cooling water may be changed during service due to contamination or evaporation. Therefore, the cooling water itself and the system should be checked periodically during service, preferably once a week. These tests may be done by means of test kits from inhibitor maker with sample water from the circulating system. However, laboratory test of the sample water by specialist is also recommended regularly at least every three month. All checking results should be recorded and kept for trend evaluation, which contribute to reliable engine operation with right cooling water treatment. If test result shows that the contents of cooling water changes suddenly or gradually, the cooling water system should be checked to trace the cause. Some of the changes may indicate the cause as follows: Chloride content increasing: ▪ Check possibility of seawater penetrating into cooling water. ▪ Check the system which includes sea water, for example fresh water cooler cooled by sea water. pH value decreasing or sulphate content increasing: ▪ Check if cooling water is contaminated by exhaust gas. ▪ Check cylinder head by hydraulic pressure test. Note: If the quality of the cooling water after checking exceeds control limit by water treatment, the cooling water should be replaced completely by newly treated water. Cleaning of Cooling Water System If any deposit or rust is abnormally detected in the cooling water system, the system should be cleaned thoroughly and then the cooling water also should be refilled up completely by newly treated water. The cleaning of the cooling system includes degreasing and descaling procedures which need special chemicals. As the chemicals may be hazardous, the cleaning of the cooling water system is recommended to be carried out by reliable specialist firm. Otherwise it should be done strictly in accordance with instructions from the supplier of cleaning chemicals. References https://marineengineeringonline.com/cooling-water-treatment-for-diesel-engines-on- ships/ https://sea.hach.com/coolingwater- boilerfeedwater#:~:text=Cooling%20water%20is%20used%20in,analyzed%20on%20a%20 regular%20basis. https://www.marineinsight.com/guidelines/general-overview-of-central-cooling-system- on-ships/ https://www.merchantnavydecoded.com/cooling-water-system-of-the-marine-engine/ Video References https://www.youtube.com/watch?v=uX-ultgtYYI Marine Engineering - Introduction | Study Call with Chief MAKOi 001 https://www.youtube.com/watch?v=IHYNYXN2w7c&t=170s Ship's Fresh Water Cooling System | Study Call Ep 003 Chief MAKOi https://www.youtube.com/watch?v=ii11V201oFI Ship's Sea Water Cooling System/ Study Call with Chief MAKOi episode 002 https://www.youtube.com/watch?v=X62P2rLTAKY Marine Diesel Engine Cooling Water System https://www.youtube.com/watch?v=4DxmEKnbC-c Central Cooling Water System https://www.youtube.com/watch?v=fh1JoNPRk4Y Main Engine Jacket cooling water analysis on board a vessel (Nitrite Test) https://www.youtube.com/watch?v=keCej9LOAtU&t=1s WATER TEST Engine Cooling Water Nitrite, Chloride, ph https://www.youtube.com/watch?v=IHYNYXN2w7c Ship's Fresh Water Cooling System | Study Call Ep 003 Chief MAKOi https://www.youtube.com/watch?v=1jsIRBI_clE&t=8s Maintenance and Treatment of Diesel Engine Cooling Water Systems https://www.youtube.com/watch?v=5QwTpiramY4 Marine Water Treatment for Engine Cooling Systems https://www.youtube.com/watch?v=1jsIRBI_clE Maintenance and Treatment of Diesel Engine Cooling Water Systems https://www.youtube.com/watch?v=X62P2rLTAKY&t=27s Marine Diesel Engine Cooling Water System https://www.youtube.com/watch?v=- gkJBzHlB0A&list=PLXNEJpAaCDcxBijMyluhZpXuXydxBMVmJ Diesel Engine Cooling System https://www.youtube.com/watch?v=1jNRN81ezSE Sea Water Cooling System | Seachest - Stainer – Pump