Multiple effect evaporator(Evaporation)

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Operation
 In the beginning, the equipment is at room temperature and atmospheric pressure. The liquid feed is introduced to all the three evaporator up to the level of the upper sheets. The following operations are attempted to achieve the effects as specified below.
 1. The vent valves V1, V2 and V3 are kept open and all other valves are closed.
 2. Now high vacuum is created in liquid chamber of evaporator.
 3.The steam valve S1 and condensate valve C1 are opened. Steam is supplied. Steam first replaces cold air in the steam space of 1st evaporator. When all the cold air is removed, the valve, V1 is closed.
 4. The supply of steam is continued until the desired pressure Po is created in the steam space of 1st evaporator. At this pressure, the temperature of the is t0.
 5. Steam gives its temperature to the liquid feed in the 1st evaporator and gets condensed. Condensate is removed through the valve C1.
 6. Due to heat transfer, the liquid temperature increases and reaches the boiling point. During this process, vapor will be generated from the liquid feed.
 7. So formed vapor displaces air in the upper part of 1st evaporator. Moreover, the vapor also displaces the air in the steam space of the 2nd evaporator.
 8. After complete displacement off air by vapor in the steam compartment of 2nd evaporator, the valve V2 is closed.
 9. The vapor of 1st evaporator transmits its heat to the liquid of 2nd evaporator and gets condensed. Condensate is removed through the valve C2. These steps continue in the 3rd evaporator also.
 As the liquid in the 1st evaporator gains temperature, the difference in temperature between the liquids and steam decreases hence, the rate of condensation decreases..
 A similar changes takes place in the 2nd evaporator and the liquid reaches the boiling point. Similarly, the process will be repeated in 3rd evaporator. Finally three evaporators comes to a steady state with the liquid boiling in all three bodies.
 As boiling proceeds, liquid level in evaporator comes down. Feed is introduced through the feed valve F1, F2 and F3 are used for 1st, 2nd and 3rd evaporators, respectively, to maintain the liquid level constant.
 Thus in this evaporator, there is a continuous supply of feed, steam and continuous withdrawal of liquid from all the three evaporators. Hence, evaporator works continuously with all the temperature and pressure in balance.
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