Modelling and simulations of MSF desalination plant: the effect of venting system design for non-condensabe gases

Abstract

The presence of non-condensable gases )NCGs( such as carbon dioxide, nitrogen, oxygen, and argon caused by air leakages to stages and the release of dissolved gases in brine have, even small proportions, great effect on the heat transfer rate at the vapour side of the stage condensers. Due to the low conductivity of these gases, they work as insulation material and decrease the heat transfer rate and in turn they affect the plant performance. In this work, a dynamic mathematical model is developed and implemented to analyse the effect of NCGs in MSF desalination process using gPROMS software. The model is based on coupling the mass balance, energy balance and heat transfer equations with supporting correlations for physical properties calculations. The effect of NCGs on heat transfer rate and the variation of the amount of NCGs from stage to stage are studied. The present model is validated against actual plant data collected from literature. The results showed a good agreement with actual data. The results showed that the concentration of NCGs in the vapour space depends on the location of venting points and the rate release of the NCGs. Also the results revealed that the overall heat transfer coefficient (OHTC) is affected by high concentration of NCGs. The optimum location of the venting system can be obtained by variation of the venting stages.