Simulation of a forward feed multiple effect desalination plant with vertical tube evaporators

In recent years, vertical tube falling film evaporators have been widely used in desalination industries. In this paper mathematical modeling of a multiple effect evaporators (MEE) system has been carried out for brackish water desalination. The system includes a set of forward feed vertical tube evaporators with thermal vapor compression (TVC) and a condenser. Modeling has led to calculation of several parameters such as overall heat transfer coefficients, entrainment ratio and recovery of the process which is restricted by scale formation. A scaling prediction chemical model has been employed to calculate the allowable rate of recovery for prevention of scale formation. Physical properties of streams have been assumed as functions of temperature and salinity. A code has been developed for simulation of the process based on mass and energy balance equations. Results showed maximum allowable recovery of 74% for the treated brackish water sample with total dissolved solid (TDS) of 14,761 ppm is achievable. Dealing with mentioned sample under specified set of conditions, it was concluded that changing the number of effects from 3 to 8, enhances gained output ratio (GOR) value from 3.8 to 7.5. However, specific heat transfer surface is increased from 215 to 1052.