Area-based retrofit and operational optimization of existing crude oil heat exchanger networks

Retrofit and operational optimization projects are frequently implemented in crude oil heat exchanger networks (HENs) to reduce operating costs. However, it is a challenge to optimize these HENs because of their complexity and the many practical constraints to be considered (e.g. plant layout, installed area, limited budget, pressure drop limitations). This work presents an optimization approach for industrial crude oil preheat HENs. The approach identifies the retrofit modifications and/or operating conditions that minimize operating and retrofit capital costs. Retrofit modifications considered include adding, deleting and relocating an exchanger, and adding and deleting a stream splitter. Operational optimization variables include stream split fractions and heat transfer area. The main feature of this practical approach is the specification of heat exchangers in terms of heat transfer area. With area-based models, it is easier to monitor and constrain the heat transfer area of individual exchangers during optimization, compared to duty-based models. Furthermore, this consideration significantly simplifies the optimization, while capturing the details of the existing HEN. Temperature-dependent heat capacities are also considered. Practical constraints are implemented to ensure that industrially-relevant solutions can be achieved. These constraints include existing heat transfer area, maximum number of modifications, and forbidden relocations and matches. A case study on an industrial HEN demonstrates how the approach identifies opportunities to reduce energy consumption with minimal structural modifications.