Consequences of High-Pressure Tube Ruptures in Low-Pressure Liquid-Filled Shell Heat Exchangers

摘要

Shell-tube type heat exchangers are often used to exchange heat between a highpressurefluid and a low-pressure fluid. The pressure difference between these two fluidscould be significantly high. In the event of a partial or full rupture of a tube, a problem mayarise in that a transient pressure rise phenomenon could occur due to the flashing of the highpressure sub-cooled fluid in the tube into the low-pressure shell, which may cause the shell torupture with subsequent damage to equipment. This paper presents a dynamic model todescribe the transient phenomenon occurring on the shell-side following various scenarios oftube rupture.The spatial and temporal aspects of the flow transients along the pressure safety valve riserare accounted for by solving the one-dimensional continuity and momentum hyperbolic partialdifferential equations as applied to the liquid-filled riser. The dynamics of the attached pipingsystem are also accounted for via two mechanistic models; the first is based on an inertialresistiveassumption of the fluids in this system, while the other is based on the assumption ofanechoic perturbations passing through a long section of the attached piping. The latter isjustified in cases where the attached piping is long enough such that reflections from thedownstream end do not interfere with transients occurring in the shell during the initial phaseof fluid flashing into the shell-side following rupture. The various phases of this phenomenonare described, however the paper focuses on the initial phase of the phenomenon duringwhich shell overpressure may be encountered. The model is applied to two ethylene heatersin tandem; the first uses propylene on the shell-side to heat the ethylene on the tube side,while the second uses methanol, also on the shell-side. The ratio between the shell designpressure to the tube design pressure in these two heaters are 0.169 and 0.154, respectively,hence the motivation to accurately model the transients involved in this phenomenon. Thepractical aspects and discussion around the dynamic response of PSVs, rupture disks andattached piping systems are emphasized throughout the paper.