| Considering the cluster effect of industrial park,it is expectable that could improve energy efficiency of the entire park by recovering the waste heat in each single plant via inter-plant medium fluids which absorb heat in some plants and release heat into other plants.In the past years,with the development of industrial parks,researchers have conducted a lot of research around the optimization methods of inter-plant heat integration,such as inter-plant connection,inter-plant heat transfer,intermediate fluid properties and optimization algorithms.Obviously,the selection of heat exchange medium and the setting of medium heat recovery loop will highly affect the optimal design of the waste heat recovery system and the energy-saving effect.However,in the actual industrial park,due to the large number of plants in the park,the number and types of process streams in the plant are large.The inter-exchange heat transfer method using only one intermediate fluid may not optimize the inter-plant heat integration problems,therefore,we consider a variety of intermediate fluid loops at the same time for inter-plant heat integration to improve the heat transfer efficiency of the park and reduce the total annual cost.In order to utilize the waste heat in each plant,this paper conducts single-period and multiperiod inter-plant waste heat integration research via two mediums,and establishes a mixedinteger non-linear programing(MINLP)model to optimize the heat exchanger network.It can be promoted for more mediums and more loops.The content of this paper is divided into the following three aspects:(1)In order to make full use of the process heat in each temperature zone in the industrial park,other than single medium integration strategy,this work uses both hot water and thermal oil as mediums to implement the inter-plant waste heat integration.A heat exchanger network(HEN)superstructure coupling the matches between medium fluids and inner-plant process streams and the allocation of medium streams across plants is proposed.Accordingly,a MINLP model is formulated for network optimization aiming at the target of minimum total annual cost.At last,an example involving three plants is studied in three synthesis cases(single mediumsingle loop,single medium-dual loops,dual mediums-dual loops),and the comparation of results shows the effectiveness of the method proposed in this study.(2)Considering the dynamic characteristics of the industrial park during its operation and development,this paper further develops multi-period inter-plant heat integration research based on the single-period inter-plant waste heat integration research.The inter-plant heat integration method using two intermediate fluid is combined with the multi-period design requirements.Considering the coupling relationship between the period,propose the coupling strategy,and the logical constraints representing the interaction between the periods are constructed.The mathematical model is used to optimize and balance the various periods.The heat exchanger configuration and piping design ultimately results in a heat exchanger network structure and inter-period adjustment scheme that meets all periods requirements.In this paper,the method is applied to a two-period and a three-period case.The results prove the effectiveness of the method.(3)In order to further reduce the cost of the heat exchanger network in the industrial park,the automatic identification and switching strategy of the intermediate fluids between the periods is introduced in the multi-period design,and the medium selection constraints of each period are relaxed,so that the medium configuration can be considered separately in each period of the park;three different heat exchanger time sharing strategies are used to realize the sharing of heat exchangers among different periods,which provides the possibility of obtaining a heat exchanger network with lower annual total cost. |
