Study On Water Allocation Network Design And Retrofit

The shortage of freshwater causes more and more people's attention. The opinionthat the war occurred in the tWenty-first century wi1l mostly caused by freshwater resourceis accepted by most peop1e. Faced with such situation, it is an urgent taSk to minimize ourusage of freshwater without blocking the improvement of our living standard. Por processindustry it is required to minimize the requirement for freshwater by carrying on tWo kindsof work. The first one is to improve the production method to reduce water usage, forexampIe, to install air cooler instead of water cooler or change the rinse process to dry-clean process. The second one is to increase the reuse ratio by water reuse or recycle reuseor regenerate reuse or regener8te recycle. Obviously, these tWo options both are importantto reduce the water usage. ln reality the first one has priority. The paper will fOcus on thedesign and retrofit of the water allocation network in process industry for wastewaterminimization. At the first part of this paPer, we study the design method and firstdecompose the water allocation network into two parts, one is water-using network, theother is wastewater treatment netWork. We study the design method of each pall separateIy.As for the water-using netWork, we systemize the optimality conditions of water utilianionsystems in process plant with single contaminant or multiple contaminants and make somecomplements. AdditionalIy, we attempt to develop a design algorithm based on theoptimality conditions of water utilitalion systems with multiple contaminants. As forwastewater treatment netWork, we develop a new design method based on ourunderstanding to the problem's nature. The new design method can overcome the defectsof present methods and find better solution easily as far as the same problem is concerned.Then the design method for water allocation network is studied, a new solution strategy isproposed. At the second part of this paPer, we deal with the retrofit of water allocationnetwork. The mass integration strategy is applied to the water allocation network retrofitand a hybrid method is developed. The key ideas in this paper are extracted and listedbelowt1. A new method for wastewater treatment network design is put forward. In themethod, a primary distributed network without mixed streams is first obtained byguaranteeing that every unit contaminant mass is removed at the lowest cost wheneach step is taken during the design procedure; then, we evolve the primarynetwork according to four ruIes. When the design objective is to minimize the totaItreated flowrate, those evolutions can reduce the number of treatment processes,. when the design objective is to minimize the total costs, that is, the costfunction(such as AQ'+BQ) of each available treatment process is specified, thoseevolutions can not only reduce the number of treatment processes, but also reducethe total costs. As for multiple contaminants system, the primary distributedsubnetwork considering only one contaminant is designed first. Then, the primarydistributed network considering all contarninants is obtained by merging thosesubnetworks based on each stream. Finally, we evoIve the distributed networkaccording to rules.2. Four rules are proposed and proved to guide the design and evoIution ofwastewater treatment network. The first ruIe is, if two effiuent streams are treatedseparately by the same type of treatment process and have to be mixed immediateIyafter the treatment, the same effect after the treatment can be got by treating themixed effiuent stream. The second rule points oUt, if the costS of a treatmentprocess can be stated as AQ'+BQ(in which A and B are constantS, Q is theflowrate treated by the process, AQ' represents the capitaI costS and BQ representsthe operating costs), then we shouId decide whether to adopt distributed treatmentor centralized treatment according to the interval of index a. The third ruIe...