Exergy and economic optimization of heat-integrated water regeneration networks

Implementing optimization strategies enhance resource conservation and pollution prevention of chemical processes. The above is a key factor to gear chemical process industry toward sustainability. Considering the above, this work presents, for the first-time, exergy loss as a decision-making objective into a process integration problem to reduce utility consumption (energy and water) of chemical processes. The methodology combines mathematical programming, superstructure formulation, and a 2-dimensional approach by integrating heat and water streams. A case study based on a magnetite nanoparticles production is presented to test the methodology. Different scenarios illustrated perspectives of including exergy loss as optimization objective; scenario 1 for cost optimization, scenario 2 for exergy optimization, and Scenario 3 for a combined 2-dimensional-optimization. Scenario 1 delivered the lowest total annualized cost (436,734.50 $USD/y) with an exergy loss of 2,519.76 MJ/h. Scenario 3 presented a more balanced performance with a total cost of 481,007.50 $USD/y and an exergy loss of 2,519.76 MJ/h. Scenario 2 showed the lowest exergy loss but with a poorer economic performance. The exergy variable provides a new way of optimizing chemical process at conceptual design level to reduce water and energy consumption.