During the last decade intensive research and development have been carried out to increase the efficiency of the multi stage flash (MSF) desalination system. Although a great number of reviews have been published on this topic, no relevant improvements on the flow pattern distribution have been achieved to improve the efficiency and/or the economy of the process. A different configuration for the MSF evaporator is presented in this paper. This configuration was obtained by considering a superstructure for the evaporator where, the flow pattern of the streams and the number of stages are variables of the problem. The resulting configuration is characterized by distillate extraction from stages, improving the efficiency of the evaporator. The distillate extraction not only decreases the heat area transfer (investment), but also the seawater feed (pre-treatment costs). In this paper, the influence of the main parameters such as maximum admissible temperature, number of stages, heat consumption, heat transfer area, different modes of recycles (MSF-OT and MSF-M) and the desaltor distillate extraction efficiency are discussed. Finally, the solution obtained in this paper is compared to the solution reported previously in [1].