科研之友
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摘要
A sequential three-step programming method is proposed for determining the minimum flowrate of fresh water and corresponding regenerated water in water-using system of single contaminant with regeneration reuse. In step 1, a programming with the objective of min f(ws) is used to determine the minimum flowrate of fresh water, in which the mathematical representation is a mixed integer nonlinear programming (MINLP1). Then under the same constraints with step 1, a programming with the objective of min f(reg) in step 2 and a programming with the objective of min C-r in step 3 are subsequently used to determine the minimum flowrate of regenerated water and the minimum inlet concentration to regeneration process corresponding to the minimum flowrate of fresh water based on step 1. The method is easy to apply because we only need to change the objective function but keep the constraints constant to go along the following steps after step 1. In addition, the relationship between the fresh water flowrate required, f(ws), and inlet concentration to regeneration process, C-r, is investigated. It is found that there exist three relationships between f(ws) and C-r, which indicate three possibilities for C-b: below the pinch, above the pinch or at the pinch. Therefore, a new conclusion is drawn, which differs from that "regeneration of water at pinch minimizes fresh water flowrate" derived in literature and indicates that in some cases, regeneration at other point also minimizes fresh water flowrate.
