Condensing exhaust in engine

[Shandor]

We have a device that needs to water emitted in an exhaust stream of a diesel engine. that is about all I can say about it.

So I am basically looking to route the exhaust through a condenser, collect the water and let the remaining exhaust pass through.

There are some issues with this. First if I do it early enough in the pipe (i.e. before any catalytic converters or anything) the water will be quite acidic.

Second, I want to limit the number of components required to do this. So I am thinking of using the condensed water as the media to remove heat also. Basically, collect water in the bottom of something that would look like a sink trap (but not full, otherwise I add significant pressure drop to the exhaust stream), pump that water at say 10 psi through a radiator, and into a spray nozzle that throws the cooled water into the exhaust stream to collect even more water. The pressure supplied by this pump would supply the water to other areas of the device also.

What do you think of this design? Is there something obivously better? Is it a dumb idea?

so my final questions are: how do I size the radiator and where to I get one? how do I size the flow rate for the cold water spray? I realize its about how much heat I want to remove in order to get the water to condense. but I am unsure of how to get at that.

Im a mechanical engineer who hates engines and thermo. mechatronics is my area.

 

[Shandor]

I dont need to separate them per se. The spray water and the condensed water will end up in the same reservoir. This reservior will be hot water. I will pump out of that reservior to supply water through a radiator to the sprayer. The extra water will be used for what I need and if there is too much it will be dumped.

After a lot of poking around I found out that this method of condensing water is called a "direct contact condenser" and is one of the most efficient methods of condensing water out of a vapor stream. Most applications dont have the cooling fluid being the same as the condensing fluid so this method would be inappropriate. but for my case it will be very effective.

now if someone could help me figure out how big the radiator needs to be, and what the pump rate should be, that would be great.

Or forgetting that method, and lets just say i have a heat pipe with a heat sink on the inside of the vapor stream and a heatsink outside. How big do they have to be?

 

[dcasto]

With a 1000 HP engine burning pure methane, you could circulate 300 gallons/minute of 80F water with a 7.5HP pump (up 50 feet) and recover a net 1 gpm of water. The exhaust and water would be at 96 F, so you would need a huge tank or someway to cool the 96F water to 80 F to start the process over. Now what?

 

[rzrbk]

Install an air conditioner compressor on the engine. Locate the evaporator coil to a wide spot in the exhaust line. Collect drips to a P-trap branch off of the exhaust pipe. This will recover some of the water.

Will also require frequent cleaning and replacing of the coil.

 

[Shandor]

rzrbk,


yes that is something like what I was thinking (for a non-direct contact version), but I am asking about sizing that sort of a system. how much surface area would I need. how big does the AC radiator need to be?

dcasto,

how did you come up with those numbers? I guess I am trying to understand the set of equations that get you there. Obviously if I need 300 gallons to do this, that wont work for me. But I dont need to extract ALL the water, just about 25ml/min (you are saying that all that will only extract 1ml/min, this can not be right, I've seen that rate come out the tailpipe of my car without any heat exchange).

The exhaust stream is about 11% by mole of H2O, it is also between 250 and 700 deg C. I do not know if this exhaust stream is saturated with water as I can not find a calculator or pyschrometric chart that goes that high in temp. It seems that getting the water down to 96F will take out most of the the water out of the stream (I think maximum water content of a 100 degree vapor stream is about 4 or 5% by mole). the water content of the stream is approximately 160 ml/minute (at cruising speed), I dont need that much.

I may be barking up the wrong tree, but it seems this has been done before, I just dont know how.

http://www.popsci.com/popsci/techno...e05a7178706d8010vgnvcm1000004eecbccdrcrd.html

http://edition.cnn.com/2003/TECH/10/01/wow.tech.exhaust.water/index.html

Yes they talk about a refrigerated 'blanket' around the tail pipe, but how big is the refrigeration unit?

They also talk about a shell and tube design. This leads me to beleive that this can be done pretty compactly with the spray method which is more efficient.

 

[MikeHalloran]

Why not just make up a drained jacketed pipe of arbitrary dimensions (e.g. whatever will fit), cool it with _something_, e.g. engine coolant, and measure what comes out of the drain? Most any marine exhaust manufacturer can make you a nice one out of 316L pretty quick.





Mike Halloran
Pembroke Pines, FL, USA

 

[Shandor]

I may end up doing that. I was just hoping to calculate _something_ to get within range of the right amount of water extraction (if I get out 5ml/min or 50 i would be happy). I really dislike going into a design arbitrarily, I find it wastes a lot of time.

 

[Shandor]

here we go!

http://www.google.com/url?sa=t&ct=res&cd=2&url=http://

http://www.ndia-mich.org/events/log...bufHQZSJjAc6RJP7A&sig2=c9-PVYPlMG4IdZS92DNlkQ

That condenser makes way more water than I need and it doesnt look too big.

 

[MikeHalloran]

I can give you one rough data point:

A DDC 16V4000 (~3650BHP, 48l, 2 turbos) typically uses a wye exhaust collector/riser. The branches are 12" diameter, one elbow and 1.5 ft of tube, and the run is 18" diameter about 2 feet long. The total length of interest would be about 4 feet.

When such a riser is jacketed, and the jacket is cooled with winter North Sea water that has gone through the engine's heat exchanger once (maybe 40F at most), I have one report of condensate flow of 5gpm, I'm guessing with the engine running at ~1000HP or so on just one turbo. I estimate that engine's riser had a surface area of 18 square feet condensing at the time.

The gas flow will not cause condensed water to flow uphill away from the engine, so jacketed risers require full time drains at the turbo flanges. You will of course want to slope your pipe so the water runs away from the turbo and cat.



Mike Halloran
Pembroke Pines, FL, USA

 

[Shandor]

Thanks. I'll start with some scale of that!