Authors: L. Gunnewiek, U.Shah
6th International Conference on CFD in Oil & Gas, Metallurgical and Process Industries, SINTEF/NTNU, Trondheim, Norway,
June 2008
Abstract
The flash vessel is commonly used equipment in an autoclavecircuit to let down the pressure of the autoclave discharge slurry stream. The high-pressure slurry (normally at >10 bar) enters the flash vessel where the pressure reduction and subsequent slurry flashing operation is generally contained inside the flashtube, a conical frustum shaped tube usually mounted at the top of the flash vessel. The slurry-vapor mixture exits the flashtube as a high velocity jet and expands into the larger region where slurry and vapor phases are separated. The process model of the flash vessel operation is very useful for designing and optimising the vessel and its operating performance. The objective of this paper is to outline the flash vessel process modeling effort.
To make process modeling of the flash vessel tractable, it is divided into two parts: 1) The flashtube model, and 2) the vessel model. The flashtube operation is modeled using the process simulator, AspenPlus. The output of the flashtube model then provided the boundary conditions needed for the vessel model which is simulated using CFD with the volume of fluid (VOF) approach. The model predicted the jet travel and its penetration into the hold-up pool. It also predicted the splashing height on the walls of the vessel. Overall, this combined approach to the process modeling of flash vessels has proven very useful for reliably predicting the overall performance of the flash vessel, plus optimising design parameters such as pool depth, splash height and slurry carryover.
