Question and Answers

    Question
    marinetales June 28, 2021
    Following preventive actions shall be taken against the Boiler Uptake fire - Soot Blowers : Soot blowing should be carried out on regular basis to ensure soot and ash deposits do not build up on tubes. It should be carried out more frequently when the engine is operating at low loads or when fuel has high ash content. It should be carried out after water washing of main engine turbocharger (water side). Water Washing of Exhaust gas Boiler : The combustion of residual fuel results in formation of slag. These slag gradually build up on the boiler tubes. Soot blowing keeps these deposits at low levels, however it does not reach all areas of boiler. These slag are soluble in water and can be removed by hot water washing. • Regularly inspect boiler flame to ensure correct air fuel ratio is maintained. This makes complete combustion with clean flue gas. • Carry out boiler burner maintenances as per PMS. • Use proper grade of fuel oil for boiler. • Fuel oil used for boiler to be treated well. • Avoid low load operation of boiler for long period. • Running boiler near full load periodically, helps in expelling out carbon deposits adhered in uptake passages and reduces chances of boiler uptake fire considerably.
    marinetales June 28, 2021
    Actions in case of Boiler uptake fire - • Inform bridge and C/E. • If fire does occur the engine should be stopped immediately and the turbocharger air intake covered to starve the fire off air. • Ensure full water circulation is maintained for cooling purposes. • Arrange boundary cooling. • A small fire may burn itself out as the heat will be conducted away by the circulating water. • If water washing system is fitted, it can be used to extinguish the fire.
    marinetales June 28, 2021
    Indication of boiler uptake fire: 1) Spark emission from funnel. 2) High steam generating rate. 3) Increase the flue gas temperature and fire alarm
    marinetales June 28, 2021
    Engine exhaust gas contains partially burnt fuel and lubricating oil and ash. These particulates can form deposits on boiler Tubes. Especially during prolonged low load operation, which reduces exhaust gas velocity, it may lead to higher soot deposition. It may be due to burning poor quality fuel, poor combustion due to defective injector or inefficient fuel purification. These deposits on the tubes may get heated and rise above self ignition temperature. Soot deposits may be ignited by glowing carbon particulates in the exhaust gases. The ignition temperature of the soot is usually less than 400 C, however if the deposits stick, it could fall below 200 C. Soot fires can occur after the engine has shut down, therefore it is important to maintain water circulation after shut down.
    marinetales June 26, 2021
    • It is a filter element fitted at the oily water separator system made of steel wire mesh or nylon fibers • They are generally incorporated in the 2nd stage for bilge separation towards the 15 ppm equipment • When small droplets of oil come into contact with coalescer surface they coagulate and form large oil droplets. They remain in coalescer surface until they grow large enough to achieve buoyancy forces required to float away.
    marinetales June 21, 2021
    Advantages of plate type cooler - 1. Simple and compact in size. 2. Heat transfer efficiency is more. 3. Can be easily dismantled for cleaning. 4. No extra space is required for dismantling. 5. Capacity can be increased by introducing plates in pairs. 6. Leaking plates can be removed in pairs, if necessary without replacement. 7. Maintenance – cleaning is easier as surface is visible. 8. Turbulent flow helps to reduce deposits which would interfere with heat transfer. Disadvantages of plate type cooler - 1. Initial cost is high since Titanium plates are expensive. 2. Finding leakage is difficult since pressure test is not as easy as tube coolers. 3. Bonding material between plates limits operating temperature of the cooler. 4. Pressure drop caused by plate cooler is higher than tube cooler. 5. Careful dismantling and assembling to be done. 6. Over tightening of the clamping bolts result in increased pressure drop across the cooler. 7. Joints may be deteriorated according to the operating conditions. 8. Since Titanium is a noble metal, other parts of the cooling system are prone to corrosion
    marinetales June 21, 2021
    Advantages of tube type cooler - 1. Less expensive as compared to Plate type coolers 2. Can be used in systems with higher operating temperatures and pressures 3. Pressure drop across a tube cooler is less 4. Tube leaks are easily located and plugged since pressure test is comparatively easy 5. Tubular coolers in refrigeration system can act as receiver also. 6. Using sacrificial anodes protects the whole cooling system against corrosion 7. Tube coolers may be preferred for lubricating oil cooling because of the less pressure differential Disadvantages of tube type cooler - 1. Heat transfer efficiency is less compared to plate type cooler. 2. Cleaning and maintenance is difficult because cleaning surface isn’t visible. 3. Capacity of tube cooler cannot be increased. 4. Requires more space in comparison to plate coolers.
    marinetales June 21, 2021
    Preferential trips are designed to disconnect the non-essential circuits (breakers controlling air conditioning, ventilation fans, galley equipment’s) in the event of overload or partial failure of power supply, with the aim of preventing operation of the main breaker trip and loss of power on essential trip. The relays will disconnect the non-essential circuit at 5(galley exhaust fan, vent fans, air conditioning etc.) and 10 seconds (refrigerating panel) time delay and if the overload persists will trip the main circuit breaker at 15 seconds interval.
    marinetales June 17, 2021
    As per SOLAS chapter II- 1, Regulation 44 1. All passenger and cargo vessels shall be provided with emergency sources of electrical power, for essential services under emergency conditions. 2. Emergency generator and emergency switchboard of the ship should be located above the uppermost continuous deck, away from machinery space, behind the collision bulkhead. 3. The main switchboard of the ship should not interface with supply, control, and distribution of emergency power. 4. Emergency generator should come on load automatically within 45s after the failure of main power supply. 5. Emergency source of power should be capable of operating with a list of up to 22 ½ ° and a trim of up to 10 ° 6. The generator should have independent fuel supply having flash point not less than 43°C. 7. Emergency generator should be capable of giving power for the period of 18 hours for the cargo ship and 36 hours for the passenger ship. 8. Emergency generator should start at or below 0°C and if temperature fall below this then there should be heating arrangement. 9. If the emergency generator fails to come on load the indication should be given to ECR. 10. Emergency generator should have two different starting arrangement - • Primary may be the battery, should be fully charged at all time and capable of providing 3 consecutive Start. • Secondary may be pneumatic or hydraulic, capable of providing 3 consecutive starts within 30 minutes, and 1st start within 12 minutes
    seawizard June 13, 2021
    1. Make sure the piston is on TDC. i. From the marking on the flywheel. ii. From the fuel cam. iii. Push rod should be free. (both the valve should be close at this stage ie at the end of compression stroke) 2. Make sure the engine has cooled down. 3. Loosen the lock nut of the rocker arm. 4. Now adjust the tappet clearance between the rocker arm and valve stem by tightening or loosing the nut below the lock nut. 5. Use feeler gauge to adjust the suction valve clearance as .35mm an exhaust valve clearance as .45mm
    seawizard June 13, 2021
    Tappet clearance is the clearance between the top of the valve stem and the rocker arm. Its purpose is to allow for some mechanical expansion and lengthening of the valve stem and push rods as the engine warms up.
    seawizard June 13, 2021
    1. Blow down frequently. 2. Reduce the boiler load to minimum. 3. If high contaminate shut down completely and wash out. 4. Trace and find out the fault
    seawizard June 13, 2021
    It is an inter crystalline fracture. High concentration of caustic soda NaOH and the material under stress cause it. The stress corrosion cracks follow the grain or crystal boundaries of the material land failure of the affected part could result. • Sodium sulphate or sodium nitrate is used for the prevention of caustic embrittlement. It can be found in high stress area in boiler tube and tube plate connection, riveted head, seam and boiler mountings.
    seawizard June 13, 2021
    Easing gear is fitted to allow for manual operation of safety valve in case of failure to open when the boiler has been over pressurized. The easing gear also allows for regular testing of safety valves at sea to ensure correct operation.
    seawizard June 13, 2021
    ▪ Sodium phosphate (Na3PO4) – to prevent scale formation ▪ Calcium hydroxide / sodium carbonate (Ca(OH)2, Na2CO3) – to give alkalinity and minimize acidic corrosion ▪ Sodium sulphite / hydrazine (Na2SO3 / N2H4) – to remove oxygen ▪ Antifoam – to reduce foaming ▪ Sodium aluminate – to conditioning sludge
    seawizard June 13, 2021
    Following precautions shall be taken to prevent Boiler furnace blow back - • Allow sufficient time for pre purging the furnace with dampers full open to ensure all the accumulated vapors are expelled out. • Purging to be carried out 5-6 times the furnace volume for effective expelling. • Never try to reduce purging time or bypass it. • Carry out boiler burner and swirler routine as per planned maintenance system. • Do not fire boiler with heavy fuel oil or sludge if it is not designed for the same. • Air fuel ratio of oil compound regulator to be adjusted correctly to maintain proper and complete combustion. • Pilot burner to be maintained in good condition so that flame failure while starting does not occur. • Igniter or ignition transformer, its leads, etc. to be properly insulated and tightened. • Fuel oil fed to the boiler to be properly treated as per manufacturer’s recommendations. • If an economizer or pre heater is fitted in the boiler exhaust, same to be water washed and inspected regularly to avoid back pressure of gases. • Conduct furnace inspections periodically to inspect conditions inside. • When a flame failure is experienced find and rectify the root cause. Do not try to fire again and again.
    seawizard June 13, 2021
    Main cause of boiler furnace blow back is accumulation of hydrocarbons inside the furnace. Hydrocarbons may exist as vapours or liquid form inside the boiler furnace. Accumulated fuel vapors inside furnace catches fire and develops high pressure inside the furnace thereby resulting in dangerous explosion. It is a usual practice that when there is frequent flame failure, operator try to fire the boiler in manual mode. In manual mode pre purging is not automatically controlled. Hence an attempt is made to fire boiler with insufficient pre purging time and eventuality may be catastrophic explosion.
    seawizard June 13, 2021
    Priming is the rapid carryover of large amount of water in steam as it leaves the boiler. It occurs due to - 1. Excessive foaming 2. Improper amount of steam space 3. By a sudden rush of steam such as is produced when steam stop valve is suddenly opened. To prevent priming, water level should not be kept too high. Steam stop valve should be opened slowly.
    seawizard June 13, 2021
    Foaming is the thick layer of steam bubbles on top of water surface inside boiler. It occurs due to - 1. High concentration of impurities. 2. By the animal or vegetable fats in feed water carry over from the oil heaters. 3. Increase in level of dissolved and suspended solid TDS level. 4. Increase in water level. To prevent foaming, surface or scum blow down should done frequently to expel any floating impurities for the boiler and no lube oil should be allowed to enter the boiler.
    seawizard June 13, 2021
    Maintenance of rotary cup burner - ▪ Clean the rotating cup ▪ Check and adjust the belt tension between the motor and rotating shaft ▪ Clean carbon deposited on the electrode ignite and adjusts the gap ▪ Clean pilot burner nozzle and filter ▪ Check the fuel valve and air register ( leakage in joints ) ▪ Check and clean the flame eye glass cover ▪ Check and clean inspection peep hole glass cover ▪ Adjust the fuel and air ratio, clean the fuel oil filter ▪ Check the fuel oil pressure
    seawizard June 13, 2021
    A boiler burner which atomizes and swirls the fuel by throwing it from the edge of a rotating tapered cup is called a Rotary cup burner. Advantages of rotary cup burner ▪ Turn down ratio high ▪ Can deal with viscous liquid ▪ Ensure good combustion of fuel
    seawizard June 13, 2021
    There are three types of Burners in Boilers - ▪ Steam jet burner ▪ Ultrasonic burner / pressure jet burner ▪ Rotary cup burner
    seawizard June 13, 2021
    Tests carried out in Boliers - ▪ PH test ▪ p alkalinity ▪ T alkalinity ▪ chloride test ▪ phosphate test ▪ hydrazine test ▪ dissolved solid test
    seawizard June 13, 2021
    Following can be the reasons for the Boiler water level to be low - ▪ Evaporation and consumption rate high than feed rate ▪ Cascade tank empty ▪ Defective feed pump ▪ Feed water regulator not functioning properly ▪ Safety valve blowing ▪ Blow down valve leaking ▪ Boiler tubes leaking ▪ One of the gauge glass is defective
    seawizard June 13, 2021
    Following could be the reasons due to which the boiler is not firing - ▪ Flame failure ▪ Carbon deposit on photocell ▪ Electrode clearance too high ▪ Carbon deposit on electrode ▪ Pilot burner not firing ▪ DO tank empty ▪ Water contamination with FO ▪ FO low temperature ▪ Low FO pressure ▪ Incorrect fuel and air ratio ▪ FD fan failure ▪ Filter choked ▪ Defective burner ▪ Nozzle choked