Modeling And Optimal Design Of Circulating Cooling Water System

With the problems of energy shortage and environmental pollution becoming increasingly serious,saving energy and reducing consumption have become inevitable choices to realize sustainable development.Moreover,as one of the most important living resource for human beings,water is suffering from the same problems.Therefore,improving the utilization efficiency of energy and water can be employed as a key solution for above problems.In the industrial production process,lots of waste heat is generated and the waste heat has bad effects on the operating efficiency and service life for production equipment.Furthermore,the waste heat may lead to poor quality of products.As one of the most important systems in many industrial enterprises,circulating cooling water system plays a significant role in guaranteeing the security of production process by supplying cooling water to absorb the waste heat.In general,the existing cooling water systems can meet the demand of cooling,but there is still room for further improvemnent by optimizing.Therefore,on the basis of keeping normal production,improving the utilization efficiency of energy and water,and reducing the investment costs and operating costs of circulating cooling water system have become serious problems that need to be solved urgently.Optimal design for circulating cooling water system using mathematical programming approach is the foundation to solve these problems.To save energy and cooling water by optimizing the circulating cooling water system,modeling the key devices of system is carried out according to the actual operating conditions and characteristics of cooling water system.Based on the established models,optimization of individual devices and whole system are studied,respectively.Finally,a set of software is developed for the optimal design of circulating cooling water system.The main results are summarized as follows:1.Circulating cooling water system is a complex system with multiple key devices such as pumps,plate heat exchanger and mechanical draft cooling tower.In the cooling process,exchanging heat and circulating water are conducted at the same time.Thus,for plate heat exchanger and cooling tower,the thermodynamic model and the dynamical model are established,respectively.In addition,data-driven model is developed for pumps to describe the relationships between flow rate and head of delivery.The established models lay an important foundation for the optimal design of individual devices and whole system.2.To aim at the requirement of design and renovation for circulatingg cooling water system,optimal design of individual devices in the system is performed.To give more reasonable combination of pumps,the variable frequency pumps are added to compose the pump set with the fixed frequency pump.Moreover,operating of pumps in different working conditions is considered in designing process,which reduces the composite cost of pumps by making them work efficiently in various operating conditions.For the cooling tower,changes of working conditions caused by variations of heat loads and weather conditions are considered when the cooling tower is designed,which saves the investment cost and the operating cost.3.To obtain more reasonable structure of circulating cooling water system,a more general superstructure is developed in this study.The superstructure includes pump set composed of fixed frequency pumps and variable prequency pumps,multiple cooling towers and heat exchanger network comprised of heat exchangers connected with various forms.Based on the developed superstructure,optimization model of circulating cooling water system is established,where the operating conditions are considered.4.Optimization model of circulating cooling water system is a large,complex,and non-convex mixed integer nonlinear programming model and finding a better solution of this model has become a challenging task.This study explores the use of collaborative optimization(CO)approach to solve this model.According to the CO approach,the optimization model of circulating cooling water system is transformed into a system-level optimizer and three parallel subsystem-level optimizers.Since each subsystem-level optimizer operates without considering the effects from other optimizers,the system-level optimizer is used to coordinate the discordances of optimization results from different subsystem-level optimizers.The developed solution method not only reduces the computation time but also finds a better configuration of circulating cooling water system.5.Based on the developed models of circulating cooling water system and the optimization algorithm,a software for the optimal design of circulating cooling water system is developed by using the technologies of MySQL database,interface in Delphi and programming in Matlab.This software has good interface and can be used easily.The developed software can perform the optimal design of whole circulating cooling water system efficiently,which has great significance for saving energy and cooling water by reducing the computation time and finding the better configuration and parameters for the cooling water system.