Folko Flehmig, Rüdiger von Watzdorf, Wolfgang Marquardt:
Dynamic MSF plant modeling and simulation: brine flow hydraulics
In: Encyclopedia of Desalination and Water Resources (DESWARE), EOLSS Publishers Co. Ltd., Oxford, UK, EOLSS Publishers Co. Ltd., Oxford, UK, 2000
This article tackles the problem of modeling the interstage brine flow for MSF desalination plants. Particular attention is paid to the application of the brine flow model within a dynamic model for the whole plant. Measured brine levels obtained from large-scale experiments on a 20-stage industrial size MSF plant serve to evaluate several brine flow models under steady-state as well as under dynamic plant operating conditions. Two alternative models to describe the submerged jet flow are discussed in this article. One of the various differing contraction coefficient correlations published in the literature is studied as a representative example for those correlations preferably applied for plant design. In addition, a new correlation tailored to the requirements of dynamic simulation is presented here. It was identified from the experimental data available for this particular industrial size plant. In comparison, the newly derived correlations outperforms the contraction coefficient correlation in predicting measured steady-state brine levels accurately. Dynamic simulation studies involving the contraction coefficient correlation failed almost immediately due to unrealistic brine levels. Hence, this approach seems inapplicable for dynamic problems. Apparently, blow through occurs on some stages during plant operation. Justified by the fact that the brine levels are close to the orifice height under blow through conditions, a very simple model for the blow through case is suggested. However, due to the simplicity of the postulated blow through model, switching between the two flow regimes, blow through and submerged jet, cannot be captured in the lumped brine flow model. The experimental data illustrate that this phenomenon can lead to suddenly and strongly increasing brine levels which poses the danger of stage flooding. Consequently, the suggested brine flow model is not capable to describe an important physical phenomenon although it otherwise gives rise to reasonable and accurate brine level predictions.