Molecular Distillation Modeling and Simulation to Split Heavy Petroleum Fractions

Modeling and simulation of molecular distillation to split of heavy petroleum residues (400°C + AET) are proposed. A theoretical study of this problem is illustrated for a heavy petroleum cut (372°C-811°C AET) divided into six pseudo-components.

In the process simulation, a falling film, a heater and an extremely low pressure evaporator are considered.

The mathematical model comprises equations for the evaluation of the physico-chemical properties, in order to characterize the distilled mixture. Physico-chemical properties are formulated through the adjustment of experimental parameters such as molecular mass, specific heat, viscosity, and density.

Heat and material balances on the liquid film are numerically solved by using a central finite-difference method. Specifically, the Crank-Nicolson method is adopted.

The simulation is carried out at the steady-state conditions, where the relevant process variables, such as film thickness, surface evaporation rate, liquid interface temperature, concentration profiles, and amount of distillate flow rate are computed.

In molecular distillation, the concentration of the most volatile components shrinks in both axial and radial directions, especially due to the fast increase of the temperature in the falling film. As a consequence, the less volatile component of the liquid mixture undergoes a fast increase on the liquid interface, by clearly showing the potentialities of the molecular distillation process in separating heavy petroleum residues.

As the results show, the inlet variables such as the temperature and the feed flow rate largely influence the final composition of the condensate flow.

Keywords: Molecular distillation; Simulation; Heavy petroleum residues; Physico-chemical properties.