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The concept and analysis of integrating membrane distillations (MD) with reversal once-through Multistage Flash (RV-MSF) desalination is presented. The analysis is based on numerical simulation. The MD vessels are integrated into the terminal ends of the RV-MSF system to leverage the thermal energy associated with these terminal streams. Hybridisation at the last MSF stage, i.e. by replacing the brine cooler, contributes marginally to the overall production rate which amounts to 2%. However, it is found that hybridisation at stage one, i.e. utilising the energy of the MSF reject brine can increase the overall production rate by 65%. For seawater feed temperature of 80 oC and 24 MSF stages, 5 MD vessels in series can be integrated with the RV-MSF process. This ultimate hybridisation helped improve the recovery ratio from 7 to 23%, decreasing the specific cooling water requirement from 23 to 12 kg/kg and reducing the specific energy consumption from 129 to 41 kWh/m3 with respect to the stand-alone RV-MSF system. However, this achievement incurs an additional specific area for heat transfer which increased from 29 to 65 m2/(kg/s). This is because a large number of MD modules are incorporated into the hybridisation. [ABSTRACT FROM AUTHOR]

A pilot plant comprising membrane distillation is tested for coordinated inlet temperature for the feed and cold streams with a fixed difference. Selected inlet temperature differences of 30, 40, and 50 °C were examined. It is found that water production increases with both temperature difference and inlet feed temperature. Specifically, the water production at a temperature difference of 50 °C can be 13%, and 30% higher than that at a temperature difference of 40, and 30 °C, respectively. The measurements of the mass flux were used to validate the internal mass and heat transfer equations which proved to provide an excellent prediction of the water production with up to 3.7% average error. The measurements of the exit temperature of the brine and permeate streams were used to confirm the macroscale heat balance equations. They revealed a considerable discrepancy between the heat supplied by the feed stream and the heat transferred between the two channels as well as between the heat gained by the cold stream and the heat supplied. The first discrepancy is ascribed to the existence of environmental heat loss at the feed side. The second discrepancy is attributed to the existence of environmental heat loss and the contribution of the heat of condensation to additionally warm up the cold stream. [ABSTRACT FROM AUTHOR]

An improved model for multistage flash (MSF) structures is developed and used to assess the performance of a novel MSF configuration, termed as MSF reversal (RV‐MSF) and consisting of reversing the brine circulation stream. The improved model determines the temperature distribution within the stages using heat balance equations while the simplified one, which is commonly used, is based on pre‐specified, constant, and equal temperature distribution throughout the stages. The performance of the RV‐MSF is investigated and compared with conventional MSF once‐through (OT‐MSF) with and without brine mixing using simplified and full models. It is found that the simplified model overestimates the required heat transfer specific area for both MSF configurations. Moreover, it underestimates the cooling water and energy requirements for the reversal configuration. Hence, the simplified model may be good for quick analysis but leads to inaccurate design specifications and economic analysis. When brine mixing is utilized, the simplified model still provides erroneous estimates of the heat transfer area for both MSF configurations. Nevertheless, for OT‐MSF structure, the simple model can provide comparable predictions with that of the improved model in terms of recovery ratio, performance ratio, and specific energy consumption. For the RV‐MSF structure, a mismatch in the two model predictions of surface area, cooling water, and energy requirements is observed. Furthermore, the temperature drop in the cooling system for RV‐MSF has a significant influence on the specific surface area and cooling water requirements especially at low values. The different behaviour of the simplified model between the OT‐MSF and RV‐MSF configurations is attributed to the fact that brine recycling does not affect the feed temperature or the temperature distribution in the system. [ABSTRACT FROM AUTHOR]