Requirement 2 – Steam consumption required to raise the temperature of fuel oil in tanks

Not only is steam required to compensate for the heat losses from fuel oil tanks, but steam is also used to heat the fuel oil to the required temperature before being used in the engine.

For this, the time (t) in hours, required to heat up the oil in each type of tank is generally considered as follows:

                                                                                    ∆T/t

• For Storage Tank – 0.2 DEG C/HR RISE IN TEMP.
• Service and Settling tank – 4 DEG C/HR RISE IN TEMP.
• All other Tanks – 1 DEG C/HR RISE IN TEMP.

This calculation includes two steps:

• Calculation of heat (Q in watts) required to heat contents of each tank, and summation of all the individual heat requirements to obtain total heat transfer required to raise the temperature of fuel oil in tanks (Q2)
• Utilising the above-obtained heat requirement to find the required mass flow rate of steam for this purpose.

A sample of this calculation is shown below:

The amount of heat required to raise the temperature of fuel oil tanks can be expressed as:

Q2 = m C_p dT / t  

Where Q2 = mean heat transfer rate (kW)

m = mass of fuel oil in the tank (kg)

C_p = specific heat capacity of the fuel oil (kJ/kg ^oC)

dT = Change in temperature of the fuel oil (^oC)

t = total time over which the heating process occurs (hours)

As we know the heat transfer rate, the mass flow rate of steam can be calculated using the following formula :

m_s = Q2 / ∆h    

Where m_s = mass flow rate of steam (kg/hr)

Q2 = calculated heat required to raise the temperature (kW)

∆h = enthalpy drop of the steam (kJ/kg)