Blowdown of hydrocarbons pressure vessel with partial phase separation

TL;DR

This paper develops a non-equilibrium two-phase hydrocarbon vessel blowdown model considering partial phase separation, heat transfer, and phase temperature differences, improving accuracy over equilibrium assumptions.

Contribution

It introduces a compositional, non-equilibrium model for vessel blowdown that accounts for phase temperature differences and heat transfer, enhancing simulation fidelity.

Findings

Model shows good agreement with experimental data.

Non-equilibrium effects significantly impact temperature distribution.

Design implications for vessel temperature considerations.

Abstract

We propose a model for the simulation of the blowdown of vessels containing two-phase (gas-liquid) hydrocarbon fluids, considering non equilibrium between phases. Two phases may be present either already at the beginning of the blowdown process (for instance in gas-liquid separators) or as the liquid is formed from flashing of the vapor due to the cooling induced by pressure decrease. There is experimental evidence that the assumption of thermodynamic equilibrium is not appropriate, since the two phases show an independent temperature evolution. Thus, due to the greater heat transfer between the liquid phase with the wall, the wall in contact with the liquid experiences a stronger cooling than the wall in contact with the gas, during the blowdown. As a consequence, the vessel should be designed for a lower temperature than if it was supposed to contain vapor only. Our model is based on a compositional approach, and it takes into account internal heat and mass transfer processes, as well as heat transfer with the vessel wall and the external environment. Numerical simulations show a generally good agreement with experimental measurements.