Techno-economic viability of using twisted tubes in shell-and-tube heat exchangers for the petrochemical industry

Abstract

The petrochemical industry of South Africa is constantly developing and improving the necessary heat exchanger designs. Heat exchangers play a crucial role within the petrochemical industry. This equipment is necessary for heating or cooling fluids from one process before it can be used for the following process. Twisted tubes within shell-and-tube heat exchangers have been proven, within experimental studies, to provide significant benefits to the potential of the heat exchanger's design. While twisted tubes do not only provide a self-reinforcing design, they also provide a change in tube side & shell side flow. This mentioned change in flow increases the ability of the heat exchanger to provide better heat exchange to occur during an operating process. While this study is only focused on shell-and-tube heat exchangers (STHE's) and fixed tube sheets within the heat exchangers, the study outcomes for the selected heat exchanger designs, presented to be significant. Comparing the change in a single heat exchanger output, while only changing the tube design from plain straight tubes to twisted tubes, provided significant information for the petrochemical industry of South Africa. This thesis has been completed using mathematical and thermal physics solutions for each heat exchanger design. The calculations for the completion of the thesis have been done using Engineering Equation Solver (EES). EES was also used to generate the graphed outputs used for the validating comparisons and the comparisons between the two heat exchanger designs.The EES calculation setups used within this study was validated using the data of other completed studies. The validations done on each aspect of interest, presented to all be below a maximum percentage error of 8%, which certifies that the EES calculation setups are accurately setup compared to the outputs reached within the other completed studies. Comparing the different outcomes found within this study, it was found that the twisted tube heat exchanger generated a much higher tube side heat transfer coefficient than that of the plain tube heat exchanger, however it was also concluded that the twisted tube heat exchanger generated a higher tube side & shell side pressure drop than the plain tube heat exchanger. Another conclusion found during the study analysis was that the twisted tube heat exchanger generated a higher operating effectiveness. It was also clearly concluded by means of using the data of a fully operational petrochemical plant in Mpumalanga, South Africa, that the twisted tube is roughly 350 million rand more beneficial than the plain tube heat exchanger over a yearly operational period, based on its generated effectiveness and heat transfer capabilities. The findings of this thesis provide insightful outcomes and reasoning perspectives for engineers and plant managers regarding the best selection of heat exchanger design for each petrochemical process within Mpumalanga, South Africa. The thesis clearly stated the findings of performance between the two heat exchanger designs, and the thesis motivates the viability for implementation in petrochemical plants located in Mpumalanga, South Africa.