Sea Water Desalination

The single effect thermal vapor compression seawater desalination process is illustrated schematically in Fig. 2. This process uses low-temperature heat source such as waste heat from an industrial process or solar energy to generate fresh water. This system has two distinct advantages: First, it can utilize the low-temperature heat source in the range of 50 °C to 80 °C, which leads to lower grade energy is used. Second, seawater doesn’t need to be heated to a high temperature, which saves energy and reduces scale. The main components of the system are the primary evaporator, the secondary evaporator, the steam ejector and the condenser. The performance of the steam ejector directly affects the amount of fresh water produced by the single effect

A known mass of seawater (Mcw + Mf1 + Mf2) at temperature Tcw, and salt concentration Sf, is pumped into the condenser to condense the steam into liquid, where its temperature increases to Tf. The cooling water, Mcw, is discharged into the sea. The feed seawater 1, Mf1, and the feed seawater 2, Mf2, are chemically treated and de-aerated before being pumped to the primary evaporator and secondary evaporator, respectively. In the primary evaporator, the feed seawater 1 was heated up by the low-temperature heat source, where its temperature is raised from Tf to the evaporating temperature, Tp. In the secondary evaporator, the feed seawater 2 was heated up by the mixed steam from the steam ejector, where its temperature is raised from Tf to the evaporating temperature, Ts. The secondary steam from the secondary evaporator splits into two portions: the first part is condensed in the condenser, while the rest is entrained by the steam ejector, where it is compressed by primary steam to raise the pressure and temperature and then it is introduced into the secondary evaporator as the heat source and is completely condensed into liquid. A known mass of fresh water (Mp + Ms) is