The operation of the main engine, various types of auxiliary machinery, and handling of fuel oil results into the production of sludge on board ships. This sludge is stored in various engine room tanks and is discharged to shore facility or incinerated onboard. Also, various leakages from seawater and freshwater pumps, leakages from coolers, etc. generate bilges.
Sludge Production On Ship
Sludge on board ships comes from various sources:
- Fuel Oil Purifiers
The fuel oil purifiers have a designated discharge interval depending on the quality of the fuel oil. After every set interval the bowl of the purifier discharges the sludge accumulated, into the sludge tank or designated fuel oil purifier sludge tank. This sludge contains oily water and impurities which have been separated from the fuel oil by the purifiers.
- Lube Oil Purifiers
The lube oil purifiers have a designated discharge interval depending on the quality of lube oil and the running hours of the Main engine and Auxiliary generators. After every set interval the bowl of the purifier discharges the sludge accumulated, into the sludge tank or designated lube oil purifier sludge tank. This sludge contains oily water and impurities which have been separated from the lube oil by the purifiers.
- Main Engine Scavenge Drains
When the main engine is running, oil residue in scavenging spaces is collected from the cylinder lubrication being scrapped down from the liners. This oil is drained through scavenge drains of each unit of the main engine and collected into the sludge tank or designated scavenge drain tank.
- Main engine stuffing box
When the main engine is running, oil residue is collected from the stuffing box scraping oil on the piston rod. This oil comes from the stuffing box drains of each unit of the main engine and is collected into the sludge tank or designated Stuffing Box drain tank.
- Save all tray drains of oil machinery
All fuel oil machinery i.e. pumps, filters, purifiers, etc. have a tray under them to collect any leakage if occurs. The drain of the tray goes into sludge tanks.
- Miscellaneous
Other drains are going into the sludge tank, for example, air bottle drains, fuel oil settling and service tank drains, etc. All these drains are oily water and are collected in sludge tanks.
Sludge Tanks
The number of sludge tanks varies from ship to ship, it depends on from which shipyard the ship is built and also depends on the machinery in the engine room. Some ships have one common sludge tank and some have individual sludge tanks.
A sludge pump is used to make internal transfers and transfer to a shore reception facility. All sludge tanks have to comply with the flag state oil record book and every transfer has to be recorded in the oil record book. All designated sludge tanks and bilge tanks have to be mentioned in the International Oil Pollution Prevention (IOPP) certificate. Any transfer from or into IOPP tanks has to be recorded in the Oil Record Book for the Engine room by the Chief Engineer.
Sludge Incineration And Oily Water Evaporation
The sludge generated has some water content in them coming from HFO & LO purifiers, from HFO settling and service tank drains, Air bottle drains. This water can be evaporated in the waste oil tank. Sludge is transferred from various sludge tanks into waste oil tank for incineration. Before incineration, all the water has to be evaporated so that sludge can be burned efficiently in the incinerator.
Sludge is transferred from the HFO purifier sludge tank, LO purifier sludge tank and Oily bilge sludge tank into the Waste oil tank and steam valves (inlet and return) are kept open for water evaporation. The tank temperature reaches 100 degrees Celsius and the water starts evaporating, when the temperature goes above 100 degrees Celsius it indicates that the water has been evaporated and oil has started to heat up. Now the sludge is ready for incineration. The quantity of water evaporated has to be recorded in the oil record book.
If there is a common sludge tank, then water is allowed to settle for a few days in the common sludge tank at the bottom. After the water has been settled at the bottom, suction from the bottom is taken and transferred to a waste oil tank for water evaporation.
Before transferring any sludge into the waste oil tank, the temperature of the waste oil tank should be less than 90 degrees Celsius to prevent boil-off in the tank. Boil-off will result into an instant tremendous pressure rise in the tank.
After the water has been evaporated and the sludge is heated up, it is ready for incineration. For incineration, follow these steps:
- Drain and check if any water from waste oil (sludge) in the tank before burning.
- Agitate the sludge in the waste oil tank if an agitator is present. This will help in emulsifying the oil into an even mixture for fine atomization.
- Warm up the incinerator with diesel oil. The incinerator should be operated by a qualified person with all necessary safety precautions.
- After warming up, open the feed valve for waste oil from the waste oil tank. Ensure steam tracing is proper for the waste oil line and strainers are not choked. Adjust the damper and temperature according to the manual.
- The waste oil pump will take suction from the waste oil tank. Continue burning waste oil and maintain incinerator parameters. Depending on the capacity of the waste oil pump, compare and check how much waste oil is burning in the incinerator. The final amount of sludge incinerated has to be recorded in an oil record book.
Engine Room Bilge Water Generation
Leakages from fresh water and seawater pumps, and coolers are collected in bilge wells in the engine room. Bilge wells are located at the forwarding of the bottom platform at the tank top port and starboard. Other bilge wells are at the aft of engine room, recess bilge well under the flywheel, and shaft tunnel bilge well if separate space for shaft tunnel is present.
All the leakages in the engine room bottom platform are collected in these bilge wells and can be transferred to the bilge holding tank via the oily bilge pump. The oily bilge pump may also pump these spaces to the sludge tank (via the sludge pump bypass line) and the deck connections for discharge to shore or barge.
The oily bilge pump transfers bilges to the bilge holding tank via bilge primary tank. The bilge primary tank is of smaller capacity present to separate oil from bilges. The bilge primary tank is overflowed to the bilge holding tank. Any oil layer formed on top of the bilge primary tank can be removed.
The bilge tanks in the engine room are:
Bilge Holding Tank
Bilges from the bilge well are transferred here and stored to be discharged overboard via oily water separator and PPM monitor or to be discharged ashore.
Bilge Primary Tank
Bilge is transferred here to separate oil by gravity. Any oil layer formed on the top can be removed
Bilge Evaporation Tank
Present on some ships in which bilge can be transferred and evaporated by heating.
Air cooler drain tank
All the moisture from the Main Engine scavenge air coolers and generator scavenge air cooler is drained in this tank. They might have some oil as engine room air may contain oil vapor. Hence they are discharged overboard via PPM monitor.
Cargo Hold Bildge Water Production
Cargo holds, generally of container vessels, have bilge wells located at the bottom on each side, port, and starboard. The hold bilges are normally pumped overboard through the bilge eductor from the Fire & GS pump as they contain only water. However, before pumping hold bilge wells, a visual inspection has to be carried out of the bilge wells. If any traces of oil is found, then they have to be pumped to the hold bilge collecting tank or other designated engine room tank, from where they would be processed in the OWS. Before any bilges are pumped directly overboard, it must be ensured that no local or international anti-pollution regulations will be contravened. The educator should only be used when at sea.
The hold bilge line additionally takes suction from bow thruster room bilge wells, pipe duct bilge wells, chain locker bilge wells, and forepeak void space. All the bilge wells valves can be operated remotely from the ship’s office or engine control room.
Sludge and bilge management on board are critical. MARPOL rules are very stringent and have to be followed properly to prevent pollution at sea. Any violation of MARPOL can lead to imprisonment and huge fines.
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Source: MarineInsight
