Analysis And Design Of Water-Using Network With Single-Contaminant Involving Regeneration Reuse/Recycle

Being an effective technology for saving freshwater and reducing wastewater, water-using network integration has become the research focus recently. When regeneration is introduced in a water-using network, both freshwater consumption and wastewater discharge can be reduced significantly. However, the targeting and design of the networks involving regeneration is often complicated. In this work, based on the contaminant mass-load balance and pinch analysis, a new method of process analysis is proposed for the water-using networks with single-contaminant involving regeneration reuse/recycle. The main contents are listed as follows:Firstly, a new analyzing and designing method is proposed. When the source streams are used to satisfy the demand streams below the regeneration pinch, the contaminant mass-load and flowrate of the source streams should be equal to that of the demand streams. On this base, if the regenerated amount is enough, a relationship between the regenerated stream target and the regeneration pinch-source stream consumption is obtained. By using the relationship developed, with known targets at a regenerated concentration, the targets at other regenerated concentrations can be obtained easily if the pinch points are not changed.In addition, the relationship between the freshwater target and the freshwater pinch-source stream consumption is also developed based on the fixed contaminant mass-load and flowrate. If the consumption of the freshwater and that of the freshwater pinch-source stream at an un-sufficient amount of the regenerated stream are known, the freshwater targets and the freshwater pinch-source stream consumptions at other un-sufficient amounts can be obtained easily if the freshwater pinch is not changed. A few case studies show that the results obtained in this work are the same as that obtained by the literature methods. The calculation procedure proposed in this work is simple and accurate.Secondly, a variation of the pinches and the targets at different regenerated concentrations and flowrates is analyzed. If the regeneration pinch remains unchanged with the increment of the regenerated concentration, the freshwater target remains unchanged, the consumption and contaminant mass-load of the regenerated stream increase and that of the regeneration pinch-source stream reduce gradually. When the amount of the regenerated stream is un-sufficient, with the increasing amount of the regenerated stream, the freshwater target reduces gradually. The target will reach the lowest value until the amount is sufficient. The variation revealed in this paper is important for the water-using network design.Then,the relationship between the regenerated concentration and regeneration pinch is proposed by analyzing the shifted composite curves. The contaminant mass-load supplied by the source streams remains unchanged at the critical point when the regeneration pinch just changed. The regenerated concentration which causes the changing of the regeneration pinch can be obtained by using a simple mathematical operation, the variation scope of regenerated concentration will be obtained in water network design.Finally, a new idea is applied to design the hydrogen network. We consider that there are some similarity between water-using network involving regeneration and the hydrogen network with fresh hydrogen source. In this work, the design methodology of the iterative method for water-using network with single-contaminant is applied to design the hydrogen network. The initial concentration of the fresh hydrogen source is calculated by the concentrations and flowrates of the hydrogen source streams. The final design will be obtained after several iterations. In conclusion, the design method is simple and effective.