Cost-effective reconstruction of existing two-stream heat exchanger systems

This paper proposes a method for optimizing a two-stream heat exchange system, taking into account the technical limitations imposed by the heat exchange equipment and cost-effectiveness of the reconstruction project. Optimization of the heat exchanger network is performed taking into account the need for industrial safety expertise in case the design temperatures for the heat exchangers are exceeded by the process flows. This method was applied to optimize energy consumption at a real hydrocracking unit. Two types of heat exchangers were considered - shell-and-tube and plate heat exchangers for possible increase of heat exchange surface area in the existing heat recovery system. For shell-and-tube heat exchangers, the minimum present value of the reconstruction project is observed when the heat exchange surface is increased by 500 m2, which corresponds to the installation of a two-section heat exchanger. It allows to reduce specific consumption of hot utilities by 51%, and cold utilities - by 31%. However, the simple payback period of such a project is ~ 1.5 years. At the same time for plate heat exchangers the minimum annual costs are observed when the heat exchange surface is increased by 400 m2. The cost of such a modernization project is 18% less than for shell-and-tube heat exchangers, and the reduction of specific consumption of hot and cold utilities is 66% and 40%, respectively.