Conclusions Spreadsheet methods/models have been presented for estimating the time-dependent profiles of mass discharge rates, pressures, and temperatures for LNG feed gas adia- batic depressurisation cases. The results have been com - pared to those calculated from a commercial simulator using PR and SRK. For the adiabatic cases, the spreadsheet model is based on isentropic expansion and is fairly simple, and the results are in good agreement with those from a commercial sim - ulator. However, for the LNG feed gas examples, transient compressibility factors ( Z s) generated by the simulator vary depending on the property package selected to simulate the depressurisation. For non-adiabatic (or fire) depressurisation case, the spreadsheet model, without accounting for heat transfer rates, requires good estimates of transient Z values as a function of P and T for a given composition to predict the transient P profile in reasonable agreement with those from a simulator. C p or C v values at the applicable ranges of P and T are required in the spreadsheet to predict T profile closely matching those from the simulator. However, the assumption of constant C p or C v in the spreadsheet results in T profiles with trends consistent with those from the simulator. References 1 Cengel Y A, Boles M A, Thermodynamics, An Engineering Approach , McGraw Hill, 2nd Edition, 1994.
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Figure 8 Comparison of non-adiabatic temperature profiles
2 Salater P, Overaa S J, Kjensjord E, Size Depressurization and Relief devices for Pressurized Segments Exposed to Fire, Chemical Engineering Progress , 98(9), 2002. 3 Beggs D H U, Brill J P U, A study of two phase flow in inclined pipes, J. Pet. Technol. 25: 607-617, 1973. Dr Tek Sutikno is a Process Engineering Manager with Fluor and a Professional Engineer registered in 11 US states with more than 30 years of experience in the process industries. He holds BSc, MSc, and DEngr degrees in chemical engineering and a MBA degree, all from the University of Kansas. Email: tek.sutikno@fluor.com
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