Tagged: economiser, EGB, EGE, exhaust gas
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03/08/2020 at 19:44 #13410
It is the responsibility of the Chief Engineer to ensure that all members of the Engine room Staff are familiar with the procedures for the safe operation and maintenance of the exhaust gas boiler/economizers. Principles of safe operation, such as ensuring that valves and mountings are operational and correctly set and the necessity to warm through and cool down in a gradual manner are similar to those detailed previously for oil fired boilers. Maker’s recommendations concerning operations must always be followed.
Boiler circulating pump should always be in use when EGE/economiser is being warmed up, in service and during cool down period. The actual manufacturer’s instructions coupled with practical on-board experience will determine the actual sequence to be followed.Start Up From Cold:
• Ensure drain valves are shut.
• Open air vent.
• Ensure circulating pump valves are open. Start circulating pump and ensure stand-by unit on auto mode.
• Crack open inlet valve and close air vents when dry steam is vented out.
• Check valves, flanges etc. for leakage
• Allow unit to warm through.
• Check pump pressures, motor load etc.
• Check that the gas side differential pressure manometer is operational.Start Up From Hot:
• If the system has been temporarily stopped, ensure that full circulation of water is established before gas is allowed through boiler. It is the responsibility of the Chief Engineer, or the Second Engineer in his absence, to ensure that a Circulating Pump is running and operating correctly before starting the Main Engine.
• On vessels with an exhaust economizer by pass valve, water temperature is a critical factor in preventing condensation and acid formation on the gas side. The minimum temperature of 140oC should be kept, when running with the exhaust gas bypassing the economizerOperation:
• Exhaust gas boiler circulation must be maintained at all times. This is to maintain tube temperature and prevent “cold end” corrosion of tube and fins & prevent economiser fire.
• Soot blowing to be carried out at least three times daily. Frequency is to increase if the pressure drop of exhaust gas across EGE/Economiser exceeds 120mm water column.
• If soot release chemical & injection arrangements is available then inject as per the manufacturer’s instructions at least twice daily at 12 hrs interval.
• If it is necessary to stop circulation for any reason, the unit should be soot-blown prior to shut down, office need to be informed immediately. Follow maker’s instructions. Exhaust gas bypass valve to be opened on the vessels fitted with exhaust bypass arrangements.
• It is essential to take care that when slow steaming or running the main engine in a condition where the exhaust produced is likely to foul the gas side surfaces (auxiliary blower running), if fitted, the gas by-pass should be used.
• Monitor the differential pressure across the gas side and high exhaust gas outlet temperature alarm if fitted.
• Flue gas temperature before and after the economizer must be checked regularly. If the temperature of flue gas after the boiler is higher than inlet this indicates possibility of soot fire.
• Pressure drop before and after the economizer must be monitored regularly in order to know the fouling of the economizer gas side.CAUTION:
When main engine speed is increased after a period of slow steaming, soot blowing should be increased and engine power increased very slowly whilst monitoring the economizer parameters.Normal Shutdown:
• Immediately prior to the end of sea passage operate the soot blowers.
• Maintain circulation for a minimum of 12 hours after engine shutdown.
• Shut down circulating pumps.
• NOTE: Vessels with short periods of Port time should not stop the circulating pump either at anchorage or in port.
• Shut boiler isolating valves.
• Open drains and vent valve.
• During the port stay monitor the economizer unit casing for signs of high temperature, especially within 2 hour of shut down and 2 hour of start-up.Emergency Shutdown in case of tube failure:
In emergency follow below procedure and inform the office ASAP.
• Operate soot blowers thoroughly.
• Stop the circulation pump and isolate the unit.
• Depressurise the economiser by manually venting boiler thru safety valve. If possible open the air vent valve.
• Bypass economiser where bypass arrangements are provided.
• Open the drain valves, drain all the water. Keep the drain valves open at all times.
• Open valves of EGE drain wash line/s.
• Depending upon circumstances stop the main engine, open turbocharger drain.
• Monitor the temperature of EGE before and after the tube bank and also monitor the funnel for signs of smoke.Water Washing:
Soot blowing will remove dry deposits from the tube banks but for removal of heavier accumulations water washing is necessary. Experience and inspection will determine the frequency necessary however it is recommended to carry out water washing every 500 hours of operation or once a month.
Prior to commencement of water washing ensure all drains etc. are clear and that precautions have been taken to avoid water entering turbochargers and the main engine. It is important to use maximum possible flow of water to wash away soot. Small quantity of water is not to be used as it can lead to soot fire.
• Shutdown boiler and allow unit to cool.
• Water wash using a hand held hose or lance. Salt water may be used for initial washing although fresh water is preferable, usual quantity in the region of 15 – 20 tons. To aid the removal of acidic soot deposits, a mildly neutralizing detergent may be added to the water wash.
• If fouling is severe and deposits are difficult to remove, it may be necessary to apply chemical detergent solutions directly to the tube surfaces prior to washing. Allow time to soak before hosing down.
• Final rinsing of tubes should be at least 30 minutes with fresh water to remove all salt water if used and/or cleaning chemicals
• It is important that all the wash water is cleared from the gas side of the economizer as the wash water tends to be acidic. If all the water traces are not removed from the crevices, acidic corrosion will start leading to erosion of the economizer tubes, finally resulting in failure of the economizer tubes.
• Water arising from the gas side cleaning should be managed with proper planning. The wash water should not be pumped out at port or in restricted water. Also the wash water should be pumped out only in day so as to check if any oil sleek goes out with the water. This is because if there is any unburnt fuel from main engine carried over to economizer; this may cause oil sheen in the wash water.Upon completion of water washing, it is essential that the economizer tube bank be closely examined for any remaining soot deposits. Close up examination from within the economizer casing is required.
Caution: The possibility of soot fire increases after washing due to any remaining cold wet soot deposits, and also sparks being emitted from the funnel. Exh gas temp is to be closely monitored during start-up of ME after water washing. Soot blow may be required. Small amount of sparks may be emitted from the exhaust at funnel during full away. Precautions are to be taken like protecting mooring ropes etc. and firefighting appliances are to be in a state of readiness.Dry Running:
The practice of operating an exhaust gas boiler without circulation through the tubes should be avoided except in emergency situations. The following normal dry running procedures must be adhered to:
• The engine exhaust gas temperature must be no higher than 320 degC.
• The tube bank must be drained and vented and all drain & vent valves to be in open condition
• The period of dry running must be as short as possible.
• Prior to dry running the tube banks must be cleaned to remove all traces of soot and other accumulations.
• Cleaning by soot blowing must continue throughout the dry running period with at least the same frequency as for normal operation.
• Monitoring of inlet and outlet gas temperatures is important to ensure no sudden rise occurs. Sudden rise in temp indicates presence of a soot fire. -
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