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Distillation (or evaporation) requires lots of energy due to the high boiling points of common liquids.
My idea uses a tall column filled with priming liquid to produce a siphoning effect. This refrigerated tube is connected to the boiler with an airtight seal. While a normally sized condenser
would provide the condensing effect, this design also reduces the boiler pressure. The goal here is to reduce the pressue, which would normally be at atmospheric pressure (open system).
Now, the reduced pressure at the top of the column lowers the vapor pressure and boiling point of the starting liquid. As liquid is distilled, it joins the liquid. Keeping the opening small at the bottom prevents air from bubbling up and removing the siphon effect.
This might be used to liquor, gasoline, maple syrup (concentrating sugars), or anything separated through evaporation.
Flash Distilling Plant
http://images.googl...26rls%3Den%26sa%3DG
Uses boiler steam to create about 24inHg vac and water flashes at about 160-170F I think. [wittyhoosier, Apr 23 2006]
[link]
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I'm sorry, I read it through a few times, but I can't follow completely.
I assume that you want to use a column of liquid, in one side (left side) of an inverted U tube, to draw a partial vacuum in the rest (right side) of the U tube. In the right side is the liquid which will be distilled using a lower temperature than normal.
But I cannot clearly understand your mechanism which will prevent the following problem:
As the heated liquid evaporates, it increases the pressure in the vacuum. The column of liquid in the left side then drops. The vacuum is not so much as before. This continues until the column of liquid in the left side is short, and the vacuum is gone, and the boiling point of the liquid in the right hand side is as normal.
Have I missed anything? A drawing would help.
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Imagine the boiler on the right, tall column descending on the left. As vapor accumulates, it condenses, reducing the pressure. |
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Have you seen the soda-can experiment where water is boiled inside, then the can is inverted and pushed into a bucket of water? The can is crushed by the reduced pressure. Same mechanism here, but continuous. |
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Since any increasing pressure is due to vapor from the boiler, it condenses in the left side and is prevented from growing. |
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OK, so on the left side, the vapour would need to condense *very* quickly. The left side of the inverted U tube could be submerged in a bath of surplus liquid.
When the vapour condenses, it will increase the height of the column of liquid in the left side, and make it flow down a little so that the reservoir grows.
One other problem: the vapour in the right hand side will be a much bigger volume than when the process started. This might be so much that it drives out all the liquid in the left hand side.
For example, if we consider water: it will change volume by approx 1700 times. |
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I had an idea like this, with water being the liquid. So long as the boiler temperature is lower than the normal boiling point, it won't boil enough to drive all the water out of the right hand side, since as it gets close the pressure is increasing to near atmospheric. |
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With the temperature limited like this, the pressure could increase enough to stop or slow boiling if the condenser isn't fast enough. This is not a major problem, just a limit on how fast it works, along with how much heat the boiler can add at lower temperatures. |
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In the version I was thinking of, both sides of the inverted U were connected to pipes to allow a continuous flow. |
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There's one remaining problem I thought of: will dissolved air accumulate at the top of the system, mixed in with the water vapour? |
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Great idea. It could really help people in poor countries get clean water. I have a picture. |
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This is called vacuum distillation, which allows you to distill at lower temperatures. You use a pump to evacuate it though. Using a tall column just to get the air out wouldn’t make sense. |
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Yes it is, you usually do but it would make sense to do otherwise, and yes it would, respectively. Creating a partial vacuum through which fluid moves between a pump and a valve is regularly done, but it takes energy. Oil cheap enough to subsidize through worldwide intervention, (war for oil AND oil for war, so war for oil for war for oil) and thus energy cheap enough to sustain this artificial society, is a thing of the past. Energy is too expensive to do this even now. |
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We're not even using the tall column to get air out, we're using the weight of the water to lower the pressure. The air pump is separate from the boiling action, so the steam would not just all run out the top. Using a tall column would very efficiently recycle the energy used to subject the water to lower pressure. |
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That picture I promised should be ready about now. |
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Thanks for reviving this one, [Agent]. I like it. Also, nice form in working on someone else's idea with your HB debut. |
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I am looking forward to the picture. I understand the start state but it seems like the volume increase once you make steam would ruin your tension column by pushing out the heavy stuff (say ethanol) in your column. If you somehow plug it so it cannot be pushed out, then it is a closed system and the same as a pressure cooker. If you arrange a gas vent to release pressure you will vent your gas phase distillation product. |
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Molecular (or vacuum) distillation. Normally done by pumping down a chamber containing a collector and then heating thin films of fluid in same. It can cut the amount of energy needed to distill to as much as one fortieth. |
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One uses a pump because there is a limit to the vacuum you can produce with water. Your column can't be longer than thirty-three feet or so before you exceed the vapor pressure of water. Same reason that the pump is at the bottom of the well... |
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The steam is condensed on the other side, maintaining the low pressure. Ethanol is not "heavy", but it could be cooled into a liquid so that it will have its own column. It could still be pumped out, yes, but that's just the same thing that would happen anyway. |
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This isn't vacuum distillation, because the pressure isn't low enough. There is a limit to how much vacuum any one liquid can produce, but that is exactly the point. Boiling it is the point. |
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I still can't make out what the original post was proposing. I can't see a link to a picture, either. |
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I have long been kicking around ideas for psuedo-siphon distillation, but never came up with an arrangement that seemed any better than current practices. With water, the heat saved by reducing boiling point is, at best, about one-fifth of the heat needed to convert the liquid to a gas. |
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I looked at ways to capture the heat of condensation and give it back to the boiling side, which is where I got lost. The original idea does not seem to be anywhere near that. |
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[humanbean] you are right about exceeding the vapor pressure of water, but I think that is the whole point. |
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I have a number of problems with this idea - primarily related to the title; Distillation already is, almost by definition, gravity assisted. Imagine trying to run a still in zero-G. How would you go about doing that? |
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Secondly, we already have gravity (or rather acceleration) assisted distillation in the form of those things that wizz round in science labs settling out all the platelets from the plasma in blood samples, or enriching uranium by increasing the acceleration of gaseous U235 and U238 in order to try and separate the two. |
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The whole point of distillation is to extract a pure product from a less pure one. |
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Hungrily sucking stuff off the top is going to result in a much less pure distillate. |
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As with all good things, one must either wait, or spin it round at a high rate of knots. |
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After rereading the original several times, let me try this: |
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Apparatus described is a distillation column with a boiler (heat source) at the bottom, and a tube attached at some point to the distillation column. This tube is at a lesser temperature than distillate at the point where it enters the column. the tube is also vertical, and long enough to create a lowered pressure within itself and the distillation column by filling with an initial charge of the end product. Product is removed gradually from the tube in order to maintain the lowered pressure. |
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If I have this correct, then I believe what you are looking at is called a gooseneck still. Used mainly in aqueous binary separations, such as making whiskey. |
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[baconbrain] - you could capture heat of condensation by using a countercurrent mechanism. Imagine that only a small amount of boiling solution is in your vessel. It is slowly replenished from a reservoir. The tube from the reservoir wraps around (or is contained within) the tube containing the condensate. The condensate gives up heat to the cool fluid on its way to the vessel. |
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Column distallation is common. The heat source is at the bottom and there is a continuum of temperatures from the hottest at the bottom to the coolest at the top. The desired finished product is drawn off at the precise position in the column where the temperature is exactly right. |
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[Baconbrain]: The picture is not on the site because the proprietor cares about the look and feel of the site. The original post proposed putting the distillation machine at the top of two columns of water, one with impure water going up and the second one with pure water going down. This is not simply to remove water from a condenser. This is not simply to reduce the heat involved, but to reduce the temperature. With less temperature change, the heat exchanger would have to do less to stop the heat from all flowing out and need replacement. With a pressure type distillation device at the top, the pressure reduction would be far easier to create. In fact, I thought of a simple way to get heat from one side to another. The impure water column goes through a sealed port in a larger container, into a large tray with heat sinks in the bottom. The tray has a sealed roof, so there is no splash. There is also a filter or centrifuge to get the spray out of the vapor. The level of the pure water is lower, because of less solute to “want” the water, but also because of a longer column or pump. This should allow enough of an energy level difference to get impure water to evaporate and condense into pure water, but the centrifuge to keep out the spray also works as a gas pump to make the water vapor move. |
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[zen_tom]: The gravity assistance is just to remove product from a condenser and to keep the beer at the bottom of the pot, not to reduce pressure. Traditional distillation does not seal the condenser, nor does it have enough length to lower the pressure enough to get it to cold boil. Since water and the impurities are both liquids, then no amount or spinning will make much difference. Neither blood nor uranium centrifuges qualify as distillation. Uranium centrifuges need lots of energy. I don’t quite understand what you mean by “
Hungrily sucking stuff off the top is going to result in a much less pure distillate”, but there is a pipe to remove the impure water that refuses to evaporate. |
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[humanbean]: I looked it up on Images: Google, and gooseneck stills do not look anything like what we’re describing here. Also, if the impure water were at such a different level than the pure water, then it would be a batch process, and an unnecessarily energy intensive one to lift up the water like that. |
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[bungston]: That’s not necessary. Just hold the impure water with a tray with heat sinks in the bottom. There is a pump at the top to pump out the vapor. The water will condense on the underside. |
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[bristolz]: This is not straightforwardly column distillation. Column distillation alone has to go through all the same problems of working at ordinary pressure, but also goes through the same problems again and again. Column distillation is basically lots of stills packed together. In fact, it’s even more energy intensive because it uses “reflux”, meaning the condensate leaks right back down into the lower chambers that it just came from. In gravity assisted distillation, a column is not just a shape to compact many normal pressure stills into, but is used to lower the pressure to get more energy efficiency. But surely they could be combined. The more volatile parts would boil off at the bottom, where the heat would come from condensing the vapor in the way that I described to [baconbrain], but there would be many such stages for what would not boil at that pressure, but at lower pressure, all the way up the column. |
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Is everyone OK? It's getting to be a long time. |
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The heat source could be human body heat. I wonder if you could purify enough water to survive that way. |
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It's tricky to get heat from the pure side to the impure side, since the impure side has to be either hotter or at a lower pressure to boil while the pure side is condensing. |
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Using a heat pump reduces the simpicity advantage of the device compared to pumped vacuum distillation. |
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Having a pressure difference between the boiling and condensing surfaces based on height takes a lot of height, because there's light gas in between, instead of the heavy liquid that makes the pressure difference between the atmosphere and the boiling surface. |
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I'd originally thought of using solar heating for the water, the advantage of doing this at a lower temperature is not needing to concentrate it or insulate much. |
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[baconbrain] No, you're not saving much heat, but the heat can be cheaper or easier to get at lower temperatures. |
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[Agent Nguyen] If you can put the picture on the web somewhere you can link to it. It's only pictures that go directly on this site that I've seen being restricted to fit the style. |
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[caspian]: just have the impure water in a sealed tray with heat sinks on the bottom and a gas pump to make the vapor condense onto the bottom. |
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