An efficient optimization algorithm for waste Heat Integration using a heat recovery loop between two plants

• Convex reformulation and piecewise wise relaxation are used to reduce the computational efforts.
• Connection cost and pump related cost are involved.
• Industrial scale problem can be solved efficiently.
• Lower total cost can be obtained.

Heat recovery loop (HRL) is an indirect approach for waste Heat Integration between plants. The mathematical model for HRL design is a complex and nonlinear problem, which results in a non-convex Mixed Integer Nonlinear Programming (MINLP) model. Solving the problem without any strategy is difficult since computational results can easily be trapped in the local optimum solutions. This is mainly due to the reasons that operation cost, capital cost of heat exchanger networks, piping and pumping cost are considered simultaneously. To overcome this limitation, an efficient optimization algorithm is proposed for the complex problem. With application of convex reformulation and piecewise wise relaxation, the problem can be reformulated as a convex MINLP model, in which the objective function is convex and all constraints are linear. The computational efforts are reduced largely and better solutions can be obtained for the HRL design. As this work concentrates on low grade heat recovery, hot water is selected as the intermediate fluid to achieve waste Heat Integration between plants. An industrial case is demonstrated to illustrate the effectiveness of the proposed algorithm.