Synthesis And Optimization Of Heat Integrated Water Network

Water and energy are essential resources in the process industry.Today the world is facing an energy crisis,and energy conservation in the process industry is urgent.The design of heat integrated water network has always been the research focus of the process system engineering community.There are two methods of water and energy integration,namely conceptual design method and mathematical planning method.Mathematical planning method mainly solves problems by constructing mathematical models and using appropriate solvers to obtain the optimal or near-optimal network structures.The advantage is that it can solve large-scale optimization problems,and can optimize multiple objectives at the same time.The conceptual design method mainly uses pinch technology as the core,and uses graphic tools to explore the design goals,and therefore the operation is concise.Aiming at the problem of integration of water and energy in the process industry,this thesis uses mathematical planning and conceptual design methods to explore the optimal design of heat integrated water network,aiming to obtain the most water-saving and energy-saving network structure,reduce resource consumption,improve economic efficiency.The main contents of this thesis are as follows:1、A mathematical programming method of sequential design is constructed for a single-impurity heat integrated water network.The non-linear programming(NLP)model and the mixed integer non-linear programming(MINLP)model were constructed respectively,and the minimum energy target and heat exchange area target were obtained,and the water network structure with the largest energy recovery and the smallest total heat exchange area was obtained.This article proves the feasibility of the method through two calculation examples.2、On the basis of the water network obtained by the mathematical programming method,the heat exchange network is designed by the conceptual design method,and new evolution steps and rules of the combined curve of the separation system are proposed.By evolving the combination curve of the stream to reduce the number of heat exchange matching,thereby simplifying the heat exchange network.During the evolution of the combination curve,the five steps and five rules for constructing heat transfer matching were clarified,making the graphical method more operability and reproducibility.The calculation example shows that the method in this paper can further reduce the number of heat exchangers and the total heat exchange area while minimizing the amount of public works.3、From the perspective of a given number of heat exchangers,a super-structured NLP mathematical model that simultaneously optimizes the water network and heat exchange network is constructed,and a heat integrated water network structure with a lower total annual cost is obtained.The number of variables of the superstructure model is greatly reduced,and a better solution can be obtained within the effective time.