Optimization of heat exchanger design taking corrosion into account

The design of shell-and-tube heat exchangers is typically done based on standards, best practices and experience. This is however a time consuming process that does not necessarily yield the optimal design. Recently, several methods have been proposed to optimize this process to minimize the combined investment and pumping costs. While most publications use only a fixed fouling factor, some studies apply a more elaborate fouling model and take cleaning or maintenance into account. Besides fouling, also corrosion of the heat transfer surface is possible. This causes the wall thickness to change, which is typically not considered in heat exchanger design models. Therefore, this paper proposes a method where the total cost of ownership of a shell-and-tube heat exchanger is evaluated in case the heat transfer surface is subject to uniform corrosion and corrosion fouling. The novelty of this model lies in the fact that the wall thickness reduction and possible heat exchanger replacements are considered, while typically the performance of the device is assumed constant. Both tube- and shell-side performance are determined, a corrosion model is implemented, and investment, cleaning and pumping costs are calculated. The presented methodology is demonstrated with the design of a heat exchanger for a geothermal power plant, where the cost of using an expensive, non-corroding material for the construction of a heat exchanger is compared to the cost of using a more economic, but corroding metal. The results indicate that a lower cost is possible by using a corroding material, as long as the corrosion rate does exceed a certain threshold.