(108b) One-Dimensional Transient Model of a Heat Exchanger Tube Rupture Using Thermophysical Data: Discharging a High-Pressure Liquid into a Low-Pressure Liquid-Filled Shell

The process industries require heat or cool High-pressure (HP) liquid. The most common method used has been shell and tube heat exchanges. The Low-pressure side (LP) of exchanger which contains a utility fluid is therefore at risk in the event of any leakage from High-pressure (HP) side of heat exchanger. Such exchangers need to be designed concerning maximum pressure generated under the tube rupture event. The heat exchanger designers have to consider the peak pressure value of the shell in the event of tube rupture to select suitable materials for the shell. It has become common practice for the LP side to be designed to withstand a pressure above the operating pressure of the utility fluid. The risk of tube failure could lead to failure of the LP pressure shell and release of large quantities of flammable gas. The LP side, therefore, should be protected against tube failure by fitting relief devices. The consequences of such a failure can cause a catastrophic rupture of the LP side with considerable financial loss and risk to personnel.

API Std 521 (Clause 4.4.14.2.2) recommends that dynamic analysis be performed to determine the overpressure and the required relief flow rate within the protection devices. Dynamic analysis using an appropriate simulation program allows calculation of the transient pressures in the LP side of the heat exchanger following a tube rupture. Dynamic analysis is required to ascertain that the maximum surge pressure that could be reached does not compromise the integrity of the LP side of the exchanger.

The use of one-dimensional models is preferred as their accuracy is fit-for-purpose. The alternative approach is 3D/2D Computational Fluid Dynamics (CFD) which requires significant computing time and higher cost, especially if the model intends to include the upstream and downstream piping of the shell.

Several one-dimensional dynamic models have been developed in the literature (Ennis et al. (2011), K. K. Botros (2015), and A. Harhara and M. F. Hasan, (2020)). However, these models ignored the effects of temperature on their transient pressure calculation. If the released liquid in the shell being in contact with hot shell liquid reaches its superheat limit, the increased heating and vaporization contributes to pressure buildup in the event of tube rupture. Hence, the exclusion of temperature effect seems to underpredict the peak pressure.

This study aims to investigate the suitability of a heat exchanger design for a flashing liquid-liquid system under the case where one tube ruptures and the release of process liquid inside the shell occurs. In the proposed system, the subcooled liquid will flash once entering the low-pressure shell-side. A 1D dynamic model will be developed using Python to perform the transient overpressure analysis which can predict the excessive pressure of the shell in the tube rupture event of the heat exchanger. In this paper, the thermophysical data is a key input and needs to be provided before the 1D simulation. This research explains how thermophysical properties data is generated and employed in the 1D model. In the current work, the effect of temperature and vaporization will also be included.