Dear reza Behrami The ...

Dear reza Behrami

The process is relatively simple to operate and once set up, is stable in operation. Because of the thermal inertia of the plant and vacuum considerations, the process is best suited for continuous operation. As seawater is corrosive to carbon steel, there is an increasing tendency to construct plants, particularly small ones, using stainless steels and copper nickel alloys. The following is the description of process operation:

1. The feed is pumped through a large duct, which contains the coarse screens. The screens remove large suspended solids. This is necessary to prevent fouling and blockage of the pumping units and the condenser tubes.
2. The feed is deaerated to remove dissolved gases, i.e., oxygen, nitrogen, and carbon dioxide. If these gases are not removed, it is released in the flashing stages due to heating and reduction in pressure.
3. The deaerator may have vertical or horizontal configuration, which is equipped with spray nozzles or trays. Deaeration is accomplished by heating steam, which results in increase in the feed temperature and as a result reduces the gas solubility in the feed water. Also, the heating steam contains no dissolved gases, this generates a gradient for desorption of the dissolved gases into the steam in order to achieve equilibrium.
4. Other treatment chemicals are then added to the feed water. The chemicals include antiscalent, chlorine, and antifoaming. The antiscalent/antifoaming agents have to be added at the proper dosage otherwise scaling or excessive foaming may occur in the high temperature stage. The chlorine is added to the feed water to prevent biofouling inside the condenser tubes.
5. The deaerated feed water flows through the condenser tubes starting from the cold end or the last stage. The feed seawater temperature increases as it recovers the latent heat of the flashed off vapor. The feed seawater is heat to the desired top brine temperature in the brine heater.
6. The feed seawater flows on the tube side of the brine heater. This is necessary to simplify cleaning and removal of fouling and scaling material. This is achieved through use of on-line ball cleaning as well as acid cleaning.
7. The heating steam flows on the shell side; where more than one inlet is used to achieve uniform temperature distribution within the heater. The steam condensate is collected in a small well at the bottom of the heater. The well generates sufficient hydraulic heat to prevent vapour flushing within the condenser pump.
8. The hot feed seawater then flows through the stages, where vapor flashing takes place.
9. The distillate product flows in the distillate trays across the flashing stages.
10. In the last stage the brine blow down and distillate are collected, where the brine blow down is rejected back to the sea and the distillate is treated further through chlorination and adjustment of its pH value.                                                                          Regards                                                                                                                                             Prem Baboo