Blowdown Simulation Incorporating Cubic Equations of State

Photograph of a pressure vessel

The rapid depressurisation or blowdown of process vessels or sections containing high-pressure hydrocarbons is contemplated when emergencies arise, particularly in offshore operations where there is a fire or escape of flammable gases.

In this work, we have developed a robust computer programme, BLOWSIM for predicting the associated temperature drops as a result of rapid expansion of inventory during blowdown thereby evaluating the risk of brittle vessel wall fracture. Taking full account of all the important processes taking place during blowdown, the main emphasis of the study has been investigation of the effect of the choice of three types of equations of state (EOS) on BLOWSIM's performance.

In general, we find that BLOWSIM is capable of predicting fluid and vessel wall temperatures with an accuracy of c.a. ±5 K when compared to published experimental data. The choice of the type of EOS has little effect on BLOWSIM's performance as shown by the diagram below.

Figure 1 - click on image for further details
Click on image for details

References

Mahgerefteh, H. and S.M.A. Wong, 'A numerical blowdown simulation incorporating cubic equations of state', Computers in Chemical Engineering, 23(9), 1309 - 1317 (1999).
Mahgerefteh, H., S.M.A.Wong and N.Giri, 'Standing blowdown on its head', The Chemical Engineer, 548, 12 (1993).
Mahgerefteh, H., S.M. A.Wong and N.Giri, 'High pressure phase equilibrium calculations for blowdown of vessels containing two-phase multi-component hydrocarbon mixtures', High Temperatures-High Pressures, 25, 475-479 (1993).
Mahgerefteh, H. and S.M.A. Wong, 'An evaluation of the performance of Twu-Cunningham cubic equation of state', High Temperatures - High Pressures, 31(5), 473 - 486 (1999).