In normal multi-stage flash distillation desalination, after the feedwater has been heated, it sprays through a nozzle into a gas/liquid separator; the liquid (now slightly more concentrated) then passes through another nozzle into a slightly lower pressure gas/liquid separator, etc.

For this idea, imagine there are three stages of gas/liquid separator, called A, B, and C. A is the lowest pressure and temperature, C is the hottest and highest pressure.

Instead of having liquid simply move through a nozzle from C to B, it moves from C, through an eductor pump, to a nozzle in B, pulling some of the steam from A into B.

If there are more than three stages, this can be done for every adjacent trio of stages.

What does this accomplish, you ask? Because we are, in effect, compressing the steam that we are pulling from A to B, we are raising the temperature of that flow of steam.

Since a greater mass of steam condenses at a higher temperature than a lower temperature, the temperature of the coolant moving from B to C is higher... since the coolant is our feedwater, this means that our boiler will need to add less heat than it otherwise would.
-- goldbb, Aug 08 2011

On recycling heat energy Vacuum_20Desalting
Your Idea mentions some stuff that this one seems to describe, also. [Vernon, Aug 09 2011]

I thought it said "Educator assisted multi-stage distillation"
-- sqeaketh the wheel, Aug 10 2011


me too.

//Since a greater mass of steam condenses at a higher temperature than a lower temperature// eh ?
-- FlyingToaster, Aug 10 2011


Vernon, your vacuum desalting idea is basically a form of mechanical vapor compression distillation. It works, but one the mechanical power that's used to run the vacuum pump can be considered "high grade" power, which is more valuable than the "low grade" thermal power that's being used in my idea.

Basically, one BTU of electricity (to run a vacuum pump in your idea) costs more money than one BTU of heat (to supply the seawater boiler in my idea).

FT, let's imagine that in normal Multi Stage Distillation, we have stages A, B, and C, as I described in the main idea; suppose that in each stage, 10 pounds of water evaporate per minute, and 10 pounds of steam condense per minute.

Now, with the ejector pump added, 10 pounds of water per minute evaporates in each section, but the saltwater moving from C to B through the ejector sucks 1 pound of steam per minute from A into B... so 9 pounds of steam per minute condenses in A (the lowest temperature section), and 11 pounds of steam per minute condenses in B (the middle temperature section).

Those 11 pounds of steam are warmer than those 9 pounds of steam.

The water that's being used as coolant to cause that condensation, and which will eventually go to the boiler, will absorb more high temperature heat in B (from that extra 1 pound of steam) than it would have gotten if the ejector hadn't been there.
-- goldbb, Aug 14 2011



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