Optimal Design Of Heat-integrated Water Allocation Network For Chemical Industrial Parks

Industrial parks can achieve the cooperative utilization and rational distribution of resource among multiple enterprises,and have become a major trend of chemical industry.To promote the resource conservation and enhance the symbiotic relationship in the park,it's crucial to establish the coupling system of water and energy in industrial parks.So far,most of the works on water and energy integration are carried out either separately or within a single plant,which limits the potential of resource conservation.Concerning the combined consumption issue of water and energy in industrial parks,this thesis presents a methodology for the optimal design of inter-plant heat-integrated water allocation network(HIWAN),to explore the potential of water and energy conservation in industrial parks.Based on superstructure,sequential design approach and simultaneous design approach are respectively employed to solve the problem,and a comparison between the two approaches is performed.The main research content is as follows:(1)Sequential approach is adopted for the design of HIWAN in industrial park by optimizing the water allocation and heat integration subsystems of the overall network in sequence.A “plant-based” water allocation network(WAN)superstructure for industrial park is established,taking both direct and indirect mode of cross-plant water reuse into consideration,and the optimal WAN is synthesized under economic objective.On the basis of the economically optimal WAN,suitable strategies for heat integration specific to industrial parks are selected to determine the participant streams and regional boundary of heat integration.The strategies ensure that all the water streams are involved in heat integration while making the heat exchanger network(HEN)structure relatively less intricate,meanwhile making the most of direct heat exchange to lower utility consumption.Based on stage-wise superstructure and transshipment model of HEN,the HEN subsystem with minimum total annual cost(TAC)is obtained,and the overall HIWAN for the industrial park via sequential optimization is obtained by incorporating the two subsystems.Two case studies are introduced to illustrate the feasibility of the proposed methodology.The mathematical models are implemented in GAMS and the optimal HIWANs via sequential approach are obtained.(2)On the basis of sequential design,simultaneous design is studied to further explore the overall optimum of water and energy consumption.Based on the water allocation scheme and heat integration strategies in sequential design,an inter-plant HIWAN superstructure and corresponding nonlinear programming(NLP)model are established and optimized under the single objective of minimum TAC of the overall HIWAN.The NLP model includes all the possibilities of water reuse and heat integration,as well as the interconnections of parameters and the identification of potential hot/cold streams in HEN subsystem.Regarding the problem that simultaneous model features greater complexity and heavier computation load,a couple of measures are taken to simplify the model and enhance the solution process.The aforementioned case studies are re-designed via simultaneous approach and the optimized networks feature lower TAC,which agrees with the mechanism of simultaneous optimization.(3)Based on the result of case studies,also taking the characteristics of industrial parks into account,the two design routes are compared from various angles and the pros and cons of each route are analyzed.The result of stand-alone integration for each plant is introduced as the base case for comparison.Compared with simultaneous design,sequential design provides inferior results due to its inability in fully exploring the interactions between the two subsystems.However,sequential approach features lower complexity in modelling and solution,as well as more flexibility in objective targeting,which makes it more suitable for the circumstances where the sub-problems follow rigid optimization sequence or the inner-correlation is relatively weaker.As for the spacial scale of integration,compared with stand-alone integration,it is indicated that inter-plant integration of the park via simultaneous design presents preferable result,which validates the effectiveness of inter-plant integration on resource conservation.