|Operation • Hazardous Cargoes • Dangers • Handling • Cleaning • Gas Blanketing • Heating • Miscellaneous • Fault Finding|
the steam supply
Examples of Reefer Components
|Tanks equipped for steam
heating have a series of steam channels on the outside of the lower half
of the tank, and on some designs, around the tank circumference. These channels
provide up to ten square metres of heating area with a heat input roughly
equivalent to 100 kW at a pressure of 2 bar (31 psi). Steam heating is the
most efficient means of heating the tank cargo.
The steam channels terminate at the rear of the tank and are closed by threaded dustcaps.
The inlet and outlet can be fitted with a valve and the outlet should be fitted with a steam condensate trap.
The maximum working pressure of the system is indicated on the data plate.
|Two different methods are used:
• Immersion Tubes which have the highest efficiency
• External Shell heating which provides even cargo heating and a high degree of control.
The immersion system consists of two 17 foot (5.2m) heating elements fitted within fully welded, pressure tested, stainless steel tubes running inside and parallel to the base of the tank shell. This system operates on either 200-280 V 3-phase or 340-480 3 phase. Power output at 440 V is 12kW.
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Do not exceed the maximum steam working pressure. This is marked on the
tank data plate. The use of excessive pressure may damage the tank shell.
2. Do not overheat the cargo. Excess heat can degrade sensitive cargoes, so it is important that the heat input is directly related to steam pressure. To avoid damage to the tank shell or cargo through excess steam pressure, it is recommended that a variable relief valve and gauge be fitted to the steam supply line.
3. Prevent pressure build-up. The pressure build-up caused by cargo expansion must be relieved. If the cargo is non toxic, open the air inlet. If toxic, vent back to a storage tank.
Note: With some solidified products such as maleic anhydride the pressure increase in the lower melted portion of the cargo may not find a leakage path through the solid portion, and the pressure build-up may exceed the working pressure of the tank. In such a case it is necessary to fit steam traces on the dip tube to provide a path for the molten product through the still solid product to the top of the tank.
Do not discharge during heating. Continue to apply heat until ALL the cargo
is melted and has reached the correct temperature. Do not commence discharge
until the correct temperature has been reached. This will assist the melting
of solidified material, and prevent overheating and consequent damage to
the cargo or tank shell.
Cargoes with low heat-transference properties may require a long time to melt.
5. Do not attempt to force open valves blocked with solid cargo. Continue to apply heat until all the cargo has melted. A steam trace at the valve outlet might be necessary.
6. Heat small quantities of cargo with extreme care, overheating may damage the cargo and tank shell.
7. Ensure that the carrier is aware of the maximum temperature to which the cargo may be heated.
8. Ensure that neither personnel nor cargo are endangered by escaping steam.