The brine enters stage three evaporator then goes to stage 2 and then stage three in a continuous flow. As the brine concentrates certain salts such as sodium chloride begin to crystallize and salt out of the solution. There is a pipeline that comes off of the first and second evaporators that go to a device called a drainer. The drainer screens out the salt crystals and the liquid is returned to the evaporators. The brine is then sent to a tank called a thickener where the soda ash starts falling out of solution settling to the bottom and the brine containing borax and potash overflow off the top.
The steam from the boilers goes to the turbines first where it is used to generate power. The steam leaving the turbines is still at 25 psi and is feed into the heat exchanger for the stage one evaporator.
The vapors (steam) from stage one are feed into the heat exchanger for the stage two evaporator. The vapors (steam) from stage two are feed into the heat exchanger for the stage three evaporator.
The vapors from stage one condense in the stage two heat exchanger. This causes the pressure to drop in stage one.
The vapors from stage two condense in the stage three heat exchanger. This causes the pressure to drop in stage two.
The vapors from stage three are cooled by sprayers. This causes the vapors from stage three to condense and resulting in a pressure drop in stage three.
Stage 3 is operated at 24.5 inches of vacuum at temperature of 122-131 degrees F.
Stage 2 is operated at 21 inches of vacuum at temperature of 158-167 degrees F.
Stage 1 is operated at 12.5 inches of vacuum at temperature of 194-203 degrees F.
The vacuum lowers the boiling point of the brine and allows the evaporators to operate at lower temperatures. By doing this it is possible for heat that is leaving the first stage in the water vapor to be reused to heat the second stage and the heat is reused again as the vapor from stage 2 heats stage three.
Vacuum is measured in inches of mercury, meaning that using a “U” tube a 24.5 inch vacuum would pull the mercury up the vacuum up the tube 24.5 inches. More exactly, atmospheric pressure would push the mercury up the tube 24.5 inches. An absolute vacuum is 29.92 inches of mercury. If you substitute water for mercury, atmospheric pressure can push water up a pipe about 34 feet.
If you were to look at the barometric condenser I am sure you would find that the pipe extending into it was about 34 foot long or longer. This prevents condensate from being sucked back into the evaporator.