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Old 09-27-2011, 02:19 PM   #1
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Question Engineering Help: Water from Propane?

Hi, All.

Burning one gallon of propane produces almost a gallon of water(see below).
Any ideas as to how this water could be "captured" for use rather than lost to the atmosphere?
In my case specifically, I'd like to capture the water produced in my trailer interior by my catalytic heater.

Thanks!

Francesca

The Below is from:
nswers.yahoo.com/question/index?qid=20081226062215AA5J1xM
Propane is C3H8. Molar mass is about 44g. Water is H2O, at 18g. So, 4 * 18 / 44 = 1.6x.
Thus, about 1.6lb of water per lb of propane. Density of liquid is 0.507, vs. 1 for water. 1.6*.507 = 0.81 gal water per gallon of propane.


See also:
Google Answers: Combustion of natural gas
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Old 09-27-2011, 06:57 PM   #2
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Francesca,

Are you sure you're not a closet scientist or engineer? You certainly ask a lot of questions that get the resident bucks banging their heads on their keyboards!
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Old 09-27-2011, 06:59 PM   #3
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The thing is that it's vapor, not liquid - at least until it condenses on something cold.

This is one reason why catalytic heaters, ovens, and stoves and other such things that burn propane without outside exhaust need proper ventilation. It can get dank in a hurry (not to mention other combustion byproducts that can cause severe health risks).

You can see this on a cold day with your car -- the water drips out of the exhaust as it has condensed on the still cold exhaust pipes. The army has looked at trapping this to reduce water transport costs. For an RV, the most common solution is a dehumidifier.

Thanks for posting the calculation. I've always considered this from a gas point of view. The conversion to liquid is something I need to check and think about.
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Old 09-27-2011, 07:13 PM   #4
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Try using a de-humidifier, the bigger the better.
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Old 09-27-2011, 07:22 PM   #5
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The equation for the combustion of propane is:
C3H8 + 5 O2 → 3 CO2 + 4 H2O + energy
for Complete Combustion...

However, you do not get complete combustion
2 C3H8 + 7 O2 → 2CO + 8 H2O + 2CO2 + energy

So burning 2 moles of propane will produce 8 moles of water.

1 mole of propane is 44 grams and 1 mole of water is 18 grams.

44 grams = 0.0970024 pounds
18 grams = 0.0396828 Pounds X 4 = 0.158731 pounds

0.09070024 / 0.1587312 = 1/x

x= 1.75 pounds of water for each pound of propane

For water, 1 gallon = 8.33#

For liquid propane, it varies according to temperature. At 77 degF, it is 1 gallon per 4.11#

1 pound of propane contains 21591 BTU of heat, so 1 gallon will contain 86,364 BTU (at 77 deg F)

My calculator battery just died and you can do the rest of the math. These are based on regular combustion. A catalytic heater has a catalyst to react with to get the heat or energy.

I would not capture the water for potable use. The catalyst used can contaminate the water and it will not be pure.

Additionally, read the following paper:
http://www.cpsc.gov/library/foia/foia05/os/co03.pdf
Paying attention to page 15 concerning CO emissions and O2 depletion.

The paper is fairly informative.

Ken
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Old 09-27-2011, 07:43 PM   #6
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Ken,
Good post. Thanks for the link!
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Old 09-27-2011, 07:56 PM   #7
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Quote:
Originally Posted by Full.Monte View Post
Francesca,

Are you sure you're not a closet scientist or engineer? You certainly ask a lot of questions that get the resident bucks banging their heads on their keyboards!

I'm much worse than that-
I'm an undereducated 'satiable curiousity machine ...
But who needs an education when I've got all of you?????

Thanks for your kind attention to my problem!

First let me say to Bryant that the fact of the vapor condensing in the trailer was my initial and only problem associated with the heater, which is by the way more than adequately supplied with combustion air.
My first efforts involved simply preventing its "wetting" of interior surfaces...
But I've gotten greedy.
Capturing that water would increase my supply by a gallon a day in winter.
That's no small amount to a seasoned drycamper!

I see by Rjay's suggestion that I left out an important parameter in the experiment:
Recovery must be achieved without consuming any more energy than that already being used.
That means no electricity, which lets out the dehumidifier.

Plus- Where's the Earhshaking New Camping Discovery in that?

And, Ken:
Your figures pretty much duplicate those I referenced in the opener, I think, but: Per contamination by the catalyst:
I'm after the water vapor- is there something that burns off the platinum catalyst that contaminates it???

Thanks again, guys!

Francesca
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Old 09-27-2011, 08:21 PM   #8
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Someone posting in this thread is just a little bit nuts! Maybe it's me, but if not, take a look to your left and right. If you are certain it's not them then it must be you!
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Old 09-27-2011, 08:43 PM   #9
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Hi, Bill

If you're talking about me...
I'm dead serious!
But possibly also a little nuts.

The water's there- I just want to figure out a way to collect it.

Do you think mine is an impossible dream???

Francesca
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Old 09-27-2011, 11:00 PM   #10
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Quote:
Originally Posted by Francesca View Post
Hi, Bill

If you're talking about me...
I'm dead serious!
But possibly also a little nuts.

The water's there- I just want to figure out a way to collect it.

Do you think mine is an impossible dream???

Francesca
I think you have a built in humidifier ...Go with it!! Some people have to buy one.....
Richard
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Old 09-28-2011, 10:39 AM   #11
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Quote:
Originally Posted by Francesca View Post

I'm much worse than that-
I'm an undereducated 'satiable curiousity machine ...
But who needs an education when I've got all of you?????

Thanks for your kind attention to my problem!

First let me say to Bryant that the fact of the vapor condensing in the trailer was my initial and only problem associated with the heater, which is by the way more than adequately supplied with combustion air.
My first efforts involved simply preventing its "wetting" of interior surfaces...
But I've gotten greedy.
Capturing that water would increase my supply by a gallon a day in winter.
That's no small amount to a seasoned drycamper!

I see by Rjay's suggestion that I left out an important parameter in the experiment:
Recovery must be achieved without consuming any more energy than that already being used.
That means no electricity, which lets out the dehumidifier.

Plus- Where's the Earhshaking New Camping Discovery in that?

And, Ken:
Your figures pretty much duplicate those I referenced in the opener, I think, but: Per contamination by the catalyst:
I'm after the water vapor- is there something that burns off the platinum catalyst that contaminates it???

Thanks again, guys!

Francesca
Francesca,

Are you trying to collect water from the combustion side of the heater, which should exhaust outside, or from the humid atmosphere inside the MH? They should be completely separate. I don't see how a heater would increase moisture inside the MH, since you are heating it. When air cools, that's when you will see condensation happening on walls and mirrors or anything metal.
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Old 09-28-2011, 10:49 AM   #12
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If you have a gallon of water after you use it, your probably going to die in your sleep anyway. Vent it before it's too late
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Old 09-28-2011, 10:59 AM   #13
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How to collect water vapor is easy... You use a STILL, (distillery) Same as a moonshiner

Basically run the exhaust through something that can radiate the heat out and the water will condense out of the exhaust.. the problem is I don't know what will condense out with it, if there are any impurities, they will condense out, as will other stuff, Pure propane is very likely not what is in your tank.
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Old 09-28-2011, 01:29 PM   #14
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Before we go on, let me say that I'm very well informed about the safety concerns connected with propane combustion, take measures to address them all, and have been using this system for five years without any problems.
Unlike gasoline/diesel burning, propane produces only trace amounts if any of carbon monoxide. The primary safety concern is of course oxygen depletion, and I assure you all that ample combustion/replacement air is supplied.

I guess a picture's in order! See below...

The whole combustion surface is exposed to the interior.
Some water vapor escapes via the (AMPLE) venting, some stays suspended as vapor, and some condenses on colder surfaces, most notably the windows of course.
Mopping up that water is what got me to thinking about this.

Wayne's "still" suggestion is the sort of thing I have (hazily) in mind, but before going further with it, I'd appreciate some clarification on the point of contaminants in the water vapor.
It's my understanding that propane doesn't actually "contain" water- it's the hydrogen therein combining with the oxygen in the air that produces H2O.
(see Google Answers: Combustion of natural gas)
Is that a fact, and if so, what contaminants if any might also be produced?
I'm specifically asking about this information from you, Ken:
Quote:
Originally Posted by TXiceman View Post
A catalytic heater has a catalyst to react with to get the heat or energy.
I would not capture the water for potable use. The catalyst used can contaminate the water and it will not be pure.
Ken
The catalyst in this case is platinum (I think)- what's given off that could get into the water???
Or the air, for that matter!
I can't find anything in the literature about this...

Thanks, all!

...
Francesca
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