Water Network Optimization For Typical Steel Industry In China

With the increasingly scarcity of water source and ever-tightening environmental regulations in our country,water conservation and emission reduction for steel manufacture brooks no delay,due to the water-consuming and high-pollution features of steel manufacture which has driven more and more attention in recent years.Water network optimization method,based on process system engineering theory,via optimal allocation of water resource and exploiting potentials of water conservation and emission reduction,is efficient for water resource utilization and water pollution control.In this work,typical long process steel manufacture is used as the subject for the study of water network optimization of industrial park,expecting for data and method support for water conservation and emission reduction in steel industrial park.Main research contents and results are listed below:(1)Multiple outlets unit model in typical long process steel industrial park.According to the practical features of units,unit models for the typical water systems in the water network of steel industrial park(indirect closed circulating cooling water system,indirect open circulating cooling water system,direct open circulating cooling water system,once though water process system,water source system,water demand system,wastewater treatment system,desalination system)are developed,which lays a foundation for fully consideration of reuse of multiple outlet streams.(2)Superstructure design of plant-scale water network.Based on the unit models,integrating the features of water use and discharge in plants,the plant-scale superstructure is established via water reuse,water recycle,regeneration reuse and regeneration recycle water management strategy.(3)Superstructure design of the water network of steel industrial park.Using the plant-scale water network superstructure as the base,integrating the water pretreatment system,centralized wastewater treatment system and desalination system,the park-scale water network superstructure is established,in which centralized wastewater treatment system and multiple outlets desalination system perform as utility hub,and both direct and indirect integration strategies are proposed.(4)Development of multi-scale water network optimization mathematical model for typical steel industrial park.Based on the efforts presented above,the mathematical model framework containing unit-,plant-and park-scale models is established.By the primary recycle of streams at unit-scale,secondary recycle at plant-scale,and tertiary recycle at park-scale,as well as the coordination between different scale water systems,the model is used to explore the optimization schemes of water conservation and emission reduction in steel industrial park.An industrial example is carried out,and the results show that,when only considering indirect integration strategy between plants,the total annualized cost is reduced by 21%compared with practical values,and when considering both direct and indirect integration strategies,the total annualized cost can be reduced by 23%.Further,the analysis of how the change of operating parameters influence optimal solutions show that salt balance is significant for water network operation in steel industrial park,and the salinity in freshwater,the salinity regulations on inlet streams to water systems,as well as the performance of desalination all have significant effects on the water network optimization solutions.(5)Propose of wastewater zero liquid discharge scheme for steel industrial park.Due to that brine is the main block for steel industry to achieve wastewater zero liquid discharge,in this paper,two zero liquid discharge systems for brine are presented and compared.By developing unit model for the brine zero liquid discharge system firstly,and then integrating with the park-scale water network superstructure proposed above,the model for brine zero liquid discharge is developed.The industrial example results show that the developed superstructure and mathematical can achieve zero liquid discharge,and two stage reverse osmosis based brine zero liquid discharge system shows cost advantage over the other system.(6)Optimization of the water network in steel industrial park under uncertainty.Inside the water network of steel industrial park,the water systems are closely related,thus to improve the robustness of the water network,the two stage stochastic programming method is used to optimize the water network under uncertainty.The fluctuation of water quality of freshwater and the overflow of coking wastewater are considered as the uncertainties in the case study,and the results show that the maximum allowable flowrate in desalination,centralized wastewater treatment systems and brine-to-salt system increased under uncertainty,which means the water network cannot operate optimally by only adjusting the flowrates between units when uncertainty occurs,and also needs to increase the capacity of those water treatment units.