Water Networks Synthesis Study For Chemical Industrial Parks Involving Inter-plant Allocation

Water has been one of the most significant resources strategically. However, current water shortage and pollution have seriously restricted the development of human beings. Thus, it is an extremely important issue for the chemical industry to convert water utilization patterns from the extensive form of wasting and pollution to the intensive form which requires saving and high-efficiently usage. Based on the overall water networks of chemical industrial parks, the author constructs a network superstructure involving both indirect integration with intra-plant pretreatment and multi-period planning. The optimization synthesis is realized through a mixed integer non-linear programming (MINLP) mathematical model. The main contents of this study are listed as follows:(1) The current existing indirect integration does not include the constraints of upper limit of central regenerator's inlet concentration, which might bring about over-treatment of waste water. Meanwhile, the selection of regenerators'regenerating rate cannot is not included. To solve these problems, the author proposes a new indirect integration with intra-plant preprocessors set in each single plant and introduces logic constraints reflecting the selection of regenerators'regenerating rate. The study selects a minimum freshwater consumption as well as a minimum total annualized cost as the objective function, then considers the constraints on material balance, mass load limit of sinks and the upper limit of preprocessors' outlet concentration etc. The study also investigates the influence of central regenerator's upper inlet concentration limit on fresh water consumption, total annualized cost as well as water network structure. An example involving five cases is finally analyzed, the result of which shows the feasibility of the proposed method.(2) Individual-period optimization could not satisfy the global optimal goals for some problems including capacity change of plants and the establishment of new plants in the industrial park. To address these issues, the study combines indirect integration, which considers intra-plant preprocessors, with multi-period planning. The author also classifies the multi-period water network synthesis into two types of problems:predictable problem and unpredictable problem. Predictable problem aims at designing water network under the condition of construction plan, while unpredictable problem is a plant production control analysis on the operational issues, such as reduction and expansion of capacity of plants. During each period, the study utilizes the mathematical formulation of proposed indirect integration. The mathematical model is solved and the water network with minimum fresh water consumption and minimum total annualized cost are obtained respectively. Setting scheme of preprocessors and controlling scheme under different cases are also presented.