(216b) Detailed 3-D Dynamic Analysis of Depressurizing Vessels

The detailed dynamic modeling and simulation of the rapid depressurization (?blowdown?) of high-pressure vessels is a key element of the safety analysis of oil & gas production plant and other high-pressure installations. This depressurization not only determines the load imposed on the pressure relief system (e.g. flare network) but, more importantly, may result in significantly reduced temperatures of the vessel walls, which may lead to embrittlement and high thermal stresses.

Models for blowdown have been proposed by several authors over the past two decades, such as Haque, Richardon and Saville (1992), Mahgerefteh and Wong (1999) and Speranza and Terenzi (2005). Some of this work has been applied extensively in industrial applications.

This paper presents a next-generation model for blowdown calculations. In contrast to earlier models in the literature, the model incorporates a 3-dimensional model of the metal walls taking account of the transfer of heat between regions of the wall in contact with different phases. This allows a more accurate estimation of the wall temperatures, and the direct computation of thermal stresses. The model also incorporates a more accurate description of the non-equilibrium interactions among the various phases which does not rely on the use of adjustable parameters.

Implemented in gPROMS, the model has been validated against the set of experimental data obtained from a full-scale vessel, as reported by Haque et al. (1992) and Szczepanski (1994).

References

M.A. Haque, S.M. Richardson, G. Saville, ?Blowdown of Pressure Vessels. I ? Computer Model?, Transactions of the Institute of Chemical Engineers Part B: Process Safety Environmental Protection, 70(BI), 1 (1992).

H. Mafgerefteh, S.M.A. Wong, ?A numerical blowdown simulation incorporating cubic equations of state?, Comput. chem. Engng., 23, 1309 (1999).

A. Speranza, A. Terenzi, ?Blowdown of Hydrocarbons pressure vessel with partial phase separation?, Series of Advances in Mathematics, available from http://www.i2t3.unifi.it/upload/file/Articoli/animp_2004.pdf (2005).

R. Szczepanski, ?Simulation programs for blowdown of pressure vessels.? IChemE SONG Meeting (1994).