I can't see your immage.
Your going to make me break out the steam tables. My first thought is that it is possible, but your going to reach a maximum limit on the TDS in the resulting brine before you need to flush it out.
lowers the vapor pressure of the solution it's in. IIRC, it lowers the vapor pressure by a molar relationship. If the vapor pressure of water
is 5 psi at 150F, and you start with 3.4% NaCl salt
by weight, it should lower the vapor pressure of that water by about 2.2%. The more water you evaporate from the solution, the higher the salt content, and the lower the resulting vapor pressure. IIRC, about the maximum for a salt solution is a 30% brine, above that the salt starts to fall out of solution. A 30% brine would lower the vapor pressure of the solution by about 21%. So at 150F, the vapor pressure of water is around 3.7 psi. If you start droping the vapor pressure with salt, you can easily see that you'll need to be around 3 psi abolute pressure to get the water to boil.
Depending on the constraints in your design, your going to have a minimum pressure. This minimum pressure for the unit is going to basicly be set to how fast your condensor can remove heat from the unit. The lower the pressure of the water vapor goes, the more surface area is required to remove a given quantity of heat. Also the lower the pressure is the less tempreture diffrental there is over that heat exchanger
, slowing the rate of transfer of the heat. Since there is a maximum possible size to your condensor, and a maximum temperture for heat sink that your going to dump the heat into, there is a minimum pressure for the design.
This minimum pressure will then be used with the concentration of the brine to tell you when you have to dump the brine, and get more sea water. Dumping that hot brine will remove heat from the system, which will lower it's production of water. I belive that most units use the water dumped here in a sort of feed water heater, that is used to preheat the freash sea water that is being used to replace the brine. This is to concerve the heat, and minimize the loss of water production.
Another thing is that you can't use the exaust gas to directly heat the sea water. The exaust gas is too hot, and will cause the first part of the heat exchanger
to heat up above the scaling tempreture. This will cause scale to form direct on the heat exchanger, lowering the efficency of the unit, and pushing the part the area that gets above the scaling limit to a larger part of the heat exchanger. It's hard for me to describe this effect, but it's basicly like trying to melt chocolate in a pan. The part of the pan directly under the fire gets too hot, and burns it. The solution is to use a liquid medium that you can control the tempreture of to make sure that the heat exchanger's surface never goes over the scaling tempreture. Basicly, you have to make a "double boiler" of some sort.
Again, all of this can be solved
, but it typicly takes a unit that is rather large to make the economics of scale work out for the unit. As you can see, it will likly need several control units for the air removal
system, the brine removal
system, level controls in the unit, freashwater removal, and tempreture control. All of these issues have been solved
, but they are why there are no mass produced, small size waste heat vacuum distilation units on the market. Instead everyone uses RO systems that don't have the size problems of the vacuum units, but instead work more efficently on a small scale with minimul control.