Heating of Fuel Oil Storage Tank - Guideline for Cargo Ships
Ships fuel oil bunker tanks and waste oil tanks must have some form of tank heating. Normally
the heating is by way of steam produced by an oil-fired boiler and passed through coils
inside the oil tank. Other ways to heat the fuel tanks are by using thermal oil. It also
utilizes an oil fired boiler that heats the thermal oil, which is circulated through coils
inside the tank by a pump. Temperature regulation and monitoring can be automatic and
self-adjusting but are commonly effected by checking the tank temperature and manually
adjusting the heating accordingly.
Heating coil integrity in the case of using steam as the
heating should be monitored by checking the steam condensate returns in the engine room
observation tank. If the oil is observed, the source must be traced. An increase in steam
consumption should be checked out as this may indicate a steam coil failure. In the case
of thermal oil heating, oil analysis should be regularly taken and results checked for any
HFO contamination. The monitoring of the thermal oil header tank level should also be strictly
monitored. Onboard viscosity checks may be useful in determining any thermal oil viscosity
change caused by HFO contamination.
The fuel oil ( FO ) storage tanks should be heated taking the following matters into consideration:
Proper heating temperature :
Based on the correlation drawing between temperature and viscosity of heavy oil, easy pumping range and depending on the type, FO shall be heated as per HFO analyzing report.
For FO storage tanks, only one tank in use shall be heated in principle, and the next tank shall be heated gradually from the preceding day of the changeover.
If steam heating coils are separated into several layers, the tank capacity corresponding to each section of coils shall be grasped beforehand so that the coils in use may always be under the FO level in the tank.
The tank heating steam valve shall be secured properly for the valve not to open by itself by vibration or other reasons.
If cargo is loaded on the tank top, care shall be given for the heating, not affect the cargo.
Use of heating coils or deck heaters to more quickly increase the cargo temperature
The cargo could also be heated using the cargo heating system or portable heaters brought on board for the purpose. To the operation in the worst expected conditions, the heating medium supply piping requires to be provided with efficient thermal insulation in order to provide the high temperature at the heater inlet. Condensate lines should be provided with heat tracing / suitably insulated as should all valves in the system.
Deck heat exchangers :
Steam in the heat exchangers is introduced at around 130 deg C. The flow rate of cargo must be carefully controlled to avoid freezing of the heating medium. It will damage the heat exchanger. A critical safety aspect when heating by heat exchangers occurs when the cargo has a low boiling point introducing the risk of explosion. The temperature of the heated cargo in heaters must be kept below the cargo boiling point, preferably 10 deg C below the boiling point.
Heaters must be kept in permanent operation or drained and isolated after each use so that they are not rendered inoperative due to ice build-up or thermal oil gelation.
Portable heat exchanger heating cargo at the manifold during loading.
Should the facility be available at the loading port, then this is the preferred solution
Heating coils:
In general, heating coils are preferable over deck heaters. The heating ability should be re-calculated to establish sufficient heating availability. All coils must be completely free from the water before loading the cargo; otherwise, the collected water will immediately freeze in the coil resulting in damaged heating coils. All steam traps should be cleaned so that the flow will not be impeded by condensation or freezing. Therefore, heating coils and all associated isolation valves essentially to be in perfect condition, leak-free, and tight. Consideration should be given to blanking off coils that will not be utilized both on the supply and condensate sides.
The minimum number of coils should be used to ensure proper flow through the coil and maintenance of condensate temperatures above freezing. When starting steam delivery to the coil, the steam should be returned quickly to the condensate return drain to heat the coil before bringing the steam trap into operation. Care must be taken to avoid all condensate collecting and freezing on working decks. If the heating system fails the heating coils and all lines must be cleared of water immediately before the water freezes and causes damage to the coils and supply and condensate deck lines.
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