SimTec conducted a Computational Fluid Dynamics (CFD) project for the heavy oil flow inside a submarine pipe, during the fuel feeding of a power generation station on a Greek island from a tanker ship. The pipe consists of a flexible rubber part, which is attached on the tanker and a permanent steel part with a cement coating of 1 [cm]. Both parts have neither insulation nor heating system. The flexible pipe is assumed to have a perpendicular position, whereas the steel pipe of 650 [m] length lies on the sea bottom and has a small inclination towards the island shore. The junction of the two pipes takes place at a sea depth of 10 [m].

The heavy oil enters the pipe at an elevated temperature of 50 [oC], whereas the sea temperature is assumed at [oC] (wintertime). The purpose of the study was to detect possible solidification of the heavy oil (solidification temperature is 30 [oC]).

The simulation was performed by the CFD package FLUENT. Initially at time=0 [s] the pipe was assumed to be filled with sea water. The solution confirmed that the combination of the flow rate (600 [m3/h]) and the feeding temperature prohibit the large-scale solidification of the heavy oil, hence the obstruction of the pipe.

The CFD study included:

  • Creation of the geometric model and computational mesh in the pre-processor GAMBIT.
  • Solution of the fluid flow inside the pipe along using simultaneously multiphase model (sea water – heavy oil), heat transfer and phase change (solidification – melting).

The results showed that the sea water – heavy oil interface is changing with time as the heavy oil flows into the pipe (1st animation) creating small pockets of solidified heavy oil, which at a later time melt again due to the hot stream that comes from the tanker. This can be associated with the 2nd animation that shows the corresponding temperature field in the pipe. The evolution of the temperature of the various parts of the system is presented in the 2nd figure. The 1st figure shows the time history of the total pressure drop inside the pipe, therefore representing the pumping demand for the feeding system of the tanker.