Study On The Optimization Design Of Water-Using Network

Water pollution and scarcity of water is a life-and-death problem that human being is facing, it is worthy of investigation evolving water-using processes to reduce both fresh water consumption and wastewater production. This paper will focus on the optimization design of water-using networks, in which the design of a set of water-using processes requiring water of a certain temperature is approached preliminarily. The key ideas in the paper are extracted and listed below:1. A new method is addressed for determining minimum flowrate of fresh and regenerated water in water-using processes. This paper approaches reuse, regeneration reuse, regeneration recycling process for single contaminant respectively, the mathematical formulation of these synthesis problems leading to a linear programming, of which the two-step linear programming are presented respectively for regeneration reuse and regeneration recycling. For regeneration reuse, in step 1, the linear programming 1(LP1) is established, which targets the minimum flowrate of fresh water and corresponding regenerated water. In step 2, based on the minimum flowrate of fresh water and corresponding regenerated water along with the interval in which C'b exists, the linear programming (LP2) with the same constraints with LP1 is established, which can be easily solved to yield the value of the Cb.2. In addition, two different relationships between the fresh water flowrate required and inlet concentration to regeneration are found out, which indicate two possibilities with Cb : at pinch or above pinch, therefore a new conclusion is drawn, which differs from "Regeneration of water at pinch minimizes fresh water flowrate" derived by some papers and points out that in some cases, regeneration at pinch point can't always minimizes fresh water flowrate. One example is solved to demonstrate the advantage and validity of the new method.3. This paper approaches the optimized design of water-using systems of multiple contaminants, i.e. wastewater minimization. Stem from the step-by-step linear programming method, a modified method is addressed, which we name step-by-step non-linear programming method. From the beginning, the processes are collated according to the limiting operating data of each contaminant, and then the matchingbetween the rich streams and lean steams (water sources) is optimized step by step in accordance to the collated processes for each process sequence, ultimately the design of water-using network which minimizes the fresh water usage is selected by comparison. Two examples are solved to demonstrate the effectiveness and convenience of the new method.4. Water and energy are among the most highly used commodities for water-using system requiring water of a certain quality and temperature, however, the influence of heat integration on the solution of water-using systems has been ignored for a long time. This paper approaches the design of single contaminant water-using system requiring water of a certain quality and temperature, and introduces a two-stage reduced design approach for the design of water-using networks targeting minimum freshwater usage and minimum energy consumption in process plants by water reuse and energy integration. This paper focuses on the research of the design method in stage 1, and the design method in stage 2 will be researched later on. In stage 1, the step-by-step optimization matching method is presented to design the water-using network, which targets minimum freshwater usage and minimum exergy loss and resolves the water network design into two layers. The first layer is the water-using unit, in which, the sequential two-step linear programming is used to determine each water source flowrate, the corresponding original temperature and target temperature for each water-using unit, which targets minimum freshwater usage and minimum exergy loss of the water-using unit. The second layer is the overall water-using system, in which, the step-by-step optimization matching meth...