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NEW proposed methanol recovery system
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quote:
Originally posted by jdoughy:
noooooooo!!!! not that i'm opposed, but that i've been wanting to build a flash evaporator and can't for awhile. so, wanted to live vicariously through someone else's spectacular results. i think fe is a far more elegant solution.


haha.. the problem with flash is that you might not get your methanol content as low as you want with one pass. Unless you have mega heat+vacuum. From what i see commercial plants use FE for quick and dirty separations. Eg before a resin bed to knock the majority of methanol out but leave enough for the ion exchange to work, then demeth thoroughly again afterwards. Every setup is different though.

Like you said, a spray nozzle for the fluid entering the tank would probably be a good idea to maximise surface area. There are other evaporators like falling film, or plate etc, all work on same principle of increasing surface area..
 
Registered: March 02, 2009Reply With QuoteReport This Post
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quote:
Originally posted by dkenny:
my question would be what's the goal?
faster recovery times?
higher purity?
lower energy input to get the methanol out?
a combination of the above?
-dkenny


Hi Dkenny, thanks again for replying to another one of my vacuum, demeth biodiesel threads..its a working progress..almost there though.

My goal is to get rid of enough methanol out of my biodiesel so that it can meet 130 deg C flash point (astm). Im going to move across to dry wash right away (have the resin and tanks),but want to finalize a full proof method to demeth to 1% methanol before the resin beds, and then as close to 0% after the resin beds. I know it sounds tedious, but its important for me to get that astm spec (as some of the bd is sold to retailer). For lots of people who use the BD soley for their own use I understand how a little methanol in the fuel isnt much of a problem. Despite the fact methanol is not friendly on some components of engine.

Methanol purity is not my highest priority. Im happy with the amount I get back from the glycerine which is 98.5% pure atleast. At the starts its right up at 99.5%. If my purity isn't great I would blend it with fresh stuff.

Yes lower energy to get methanol out, and quickness as time is something we all have little of. A flash evaporator just seems really neat too..
 
Registered: March 02, 2009Reply With QuoteReport This Post
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the problem with flash is that you might not get your methanol content as low as you want with one pass. Unless you have mega heat+vacuum.

It seems most people run their reaction around 140. I'm now running up in the 175-180 range with pressure, which puts it right in line to get to 1% or better in a single pass. Commercial recommendations for running the acid step are in excess of 210, which would push 0.5%. Your assertion is why I recommended the low flow avenue first, then scaling up. It's fairly simple to add heat, nozzles & other mechanical equipment on the pressure side. Scaling & tuning vacuum is a bit trickier and mostly costly.
quote:
There are other evaporators like falling film, or plate etc, all work on same principle of increasing surface area..

Remember they can be combined in the same chamber.

The FE equipment I've seen is multi-stage, but I'm not sure it's really necessary for our purposes. I'm still working through mental designs myself, but it's been in conjunction with other equipment. One of the current iterations involves the bio/byproduct mixture to a 2 or 3 phase separator to FEs, or vice versa. One problem being that separation is more efficient after demeth, but could result in back reaction depending on some variables which might be solved.

Rather than the industrial standard of separating processes into distinct functions & beating the product out with brute force by scaling up, I'm a fan of marrying equipment & process requirements into systems to reduce costs and increase efficiency - i.e. continuous flow w/o equipment multiplication, only redundancy if needed.
 
Registered: June 03, 2008Reply With QuoteReport This Post
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If you have any brain waves or good process design ideas make sure you sketch them up and post..I would be very interested to see other ideas out there. The problem then is I can never be happy with my setup. This one of mine was a starting point. Already thinking scrap recirc, pull the vacuum off a separate tank and isolate the pump.

I was also thinking about de-mething the whole batch after reaction 2, but neutrolizing the catalyst with a little acid to prevent back reaction. Of course titrating the solution with HCL to find how much to add. I wonder if this method is 100% at avoiding back reactions? I know of a commercial producer who does flash evaporation on the whole batch so that the time for a reverse is absolutely minimal. I doubt they were completely 100% demething in that step, rather knocking out enough methanol to increase settling/separation time. Then after separation do something more thorough. This might be another idea aswell.. instead of cooking the guts out of the whole batch for 2 hours and letting it back react, just do it quick enough to get methanol down to a point it separates quickly and lets soaps drop out in little time.
 
Registered: March 02, 2009Reply With QuoteReport This Post
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Always have loads of ideas, it just takes time to let'em marinate before figuring out most are junk, a few are half decent, and none are great.
I don't like the tank isolation idea b/c the restrictions imposed on head space/pipe volumes, that a lot of heat must be added to compensate for vapor losses, and with large volumes you'd have to stop to re-up on vacuum or compensate w/ a larger tank, it is purely a batch solution. I don't like equipment that can't perform work a large percentage of the time so I'm trying to move away from this.
What dkenny proposes is a heat pump. I've thought of this, but never pursued so don't have anything to add currently. Anyone?

I was running the push-pull setup, so have played plenty with neutralization. It works well, but my personal take is that it's not worth it due to the greater return & less work using the byproduct for pretreat, then demething it later. Across the pond they're claiming that whole batch demething w/o neutralization works by only approaching the stoichiometric limit. It's my thought that it works to mitigate risks by not explicitly crossing the line, but assumes that there isn't enough energy present to push the back reaction while removing free methanol, which requires more energy to do with glycerol than bio. So, while imparting more energy to the batch in order to remove meth from the glycerol, it's simultaneously going to work on the bio, which has already given up its smaller share of suspended/free meth. My conjecture is that if it were lab tested, one would see an exponential increase in back reaction wile approaching the limit, creating mg & dg then tg close to/at the end point. Mg & dg won't show up in 3/27 while tg will. Anecdotally this might be borne out by their reports of failing 3/27 & shake test (can't remember if it's one or both) if taking it to the limit, but passing 3/27 stopping short of it. However, take my thoughts for what they're worth, conjecture. Either way, I think the byproduct has more value with excess chemicals left in it, which also leads me to think that, within reason, methanol & caustic reduction is for naught. This one I'll test.
quote:
I know of a commercial producer who does flash evaporation on the whole batch so that the time for a reverse is absolutely minimal. ... instead of cooking the guts out of the whole batch for 2 hours and letting it back react, just do it quick enough to get methanol down to a point it separates quickly and lets soaps drop out in little time.

This is part of what I need to figure out regarding reverse reaction. If I can move 3-5 gpm through a FE & PS, reducing risk of significant back reaction, then I believe it's a viable solution. I'm still slowly working out the prototypical design for the phase sep.
 
Registered: June 03, 2008Reply With QuoteReport This Post
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Back when textbook torent site was up I downloaded a bunch of process engineering and equipment design handbooks. Got some great information regarding phase separator designs, how they work and some stuff you might not have thought of.. a real good one is rules of thumb for chemical engineers. Has a litle bit of everything..would email to you but its about 25mb so Im not sure of an efficient way to transfer that.

So with your fridge set up do you have your vacuum pump running during the whole duration of your biodiesel demeth process?
For my original design I posted I wanted the process to be a little more continuous than batch. So just pump from the crude biodrum thru the FE then to the finished BD drum (thats after i scrapped recirc idea). While giving a residence time in the FE of not much. I really like the nozzle spray idea. If you check out the flash evap on good old wiki, you will see that on the tank inlet they have a 'diffuser' similar im guessing to a misting device to maximize evaporation.

I think its a matter of time before someone really smart starts to quantify 3/27 a little more..Something Im sure every home brewer is waiting for.
 
Registered: March 02, 2009Reply With QuoteReport This Post



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Always down with learning more. I like using Dropbox. Lemme know.

Yes, re: vac pump. I also have a paper on nozzle design. More than you really want to know but good stuff. Smile

Let us know what else you work out.

Oh, and FE is just a heat pump...
 
Registered: June 03, 2008Reply With QuoteReport This Post
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Reece123,

ah.good. know that we know the goal..get the methanol out! purity doesn't matter.
what about temperature? can you heat the mix under pressure? I ask because the biggest problem I see using a vacuum is what kind of pump? pump flow rate? so how might we bypass these questions..

food for thought..
if you can heat the mix between the pump and spray nozzle( think something a diesel injector here, very high pressure low..low volume)..ok maybe not that high a pressure but say 100-200psi and couple of hundred F..then a small nozzle to create a vapor into a large pot..methanol ideally would stay vapor anything else..turn to liquid. if it was already liquid...no vacuum pump..maybe a small air pump to force vapors out. add a reflux column to dump back into the pot( the starting mix not the other collection liquid)..you might be high purity methanol and very low methanol/biodiesel out.

just thinking out load here..never tried these ideas..so use at your own risk.


my other idea. is how propane is moved from a large tank into a small tank..seen it done..use to have the compressor for this setup up..the compressor didn't work a vacuum pump for methanol and self destructed on day..I think it was because I didn't pressurize the collection tank. Frown
fyi I use the condenser coils from this setup in the current methanol recovery setup..its air cooled. and works..

-dkenny


'84 bluebird school bus, DD8.2L turbo( 4/2011, the bus tranny has died..Frown 8.23.11 bus driven to scrap yard Frown )
2006 Jeep Liberty CRD Smile - the wife's
99 dodge 2500 5.9l 24v..-mine Smile
everything run B100 when its warm enough Smile
 
Location: RTP, North Carolina | Registered: December 15, 2004Reply With QuoteReport This Post
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Hi Dkenny,
I haven't really considered a high pressure system..Good suggestion.. my mind has always been in the mode of pull the biggest vacuum you can and clean it up. Might be worth some more investigation.

Your condenser sounds neat.. Ive seen around in the biodiesel world how many people use air cooled condensers.. I think its an auxiliary heat for the cab of a car. Basically a fluid runs thru a radiator kind of set up with a fan blowing it. Is this similar to your set up?
At the moment my condenser is pretty much identical to the one on Legal Eagles website. 4inch pvc with copper spiraling. Then pumping cooling water thru it.
Do you know if air cooled is as good??
Seems a little easier just to plug it in and your condensing..rather than messing around with cooling water which gets warm from the pump and of course taking the heat of condensation from the methanol
 
Registered: March 02, 2009Reply With QuoteReport This Post
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actually mines from a fridge system. but its the same idea. one to be sure it working is to check the input and output temp. I can barely touch the top of the condenser but have no problems on the bottom. almost feels cold.

-dkenny


'84 bluebird school bus, DD8.2L turbo( 4/2011, the bus tranny has died..Frown 8.23.11 bus driven to scrap yard Frown )
2006 Jeep Liberty CRD Smile - the wife's
99 dodge 2500 5.9l 24v..-mine Smile
everything run B100 when its warm enough Smile
 
Location: RTP, North Carolina | Registered: December 15, 2004Reply With QuoteReport This Post
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Hello Dkenny and all. Would a methanol recovery work like this? Heated biodiesel/pressure tank, 24" reflux column coming off top of tank, attach a plate heat exchanger to side outlet of reflux column, pipe it to a vacuum/pressure collection tank. Pulling vacuum on the collection tank.
I have done this using a plumbers delight, but without pressure tanks, with success. My question is would it work much better or any faster to blow some air into the heated tank and pull vacuum through the exchanger/condenser? Would a larger exchanger, having more surface area help it work
faster. My 9 foot x 1/2"copper plumbers delight is works, but very slow. I have a small Thomas
vacuum pump pulling slight vacuum on a collection drum, with vacuum relief valve as not to callapse drum. Thanks Carl Tel. 815-790-9637
 
Location: Dayton OH & Wilmington, IL | Registered: August 16, 2007Reply With QuoteReport This Post
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a little off topic to the original post..but I can say that if you just inject air into the pot you increase the rate of recovery..with or without vacuum.

vacuum just change the temperature that things happen not the rate.

a 24" reflux column is small. mine's 2" diameter and 60" tall..now if I had 3 or more of these in parallel I could increase the heat input. be sure condenser must handle this extra heat load on the output.

-dkenny


'84 bluebird school bus, DD8.2L turbo( 4/2011, the bus tranny has died..Frown 8.23.11 bus driven to scrap yard Frown )
2006 Jeep Liberty CRD Smile - the wife's
99 dodge 2500 5.9l 24v..-mine Smile
everything run B100 when its warm enough Smile
 
Location: RTP, North Carolina | Registered: December 15, 2004Reply With QuoteReport This Post



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Does the 60" height of your the reflux column help to pack more vapor pressure to outlet?
I have an Alfa Laval, Stainless Steel Plate Heat Exchanger with a 4" Flange/inlet reducing to 2" going into plate style exchanger. I got this thing for a scrap price on e-bay. I want to attach it to a former propane tank to condense methanol from glycerol and biodiesel. I'm a homebrewer
and don't have the engineering skills to know the best way to construct this. Could the propane tank be horizontal, with 60" reflux coming off top? My overall height limits are 110", being inside
a semi trailer. Thanks Carl
 
Location: Dayton OH & Wilmington, IL | Registered: August 16, 2007Reply With QuoteReport This Post
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As dkenny said, it'll work faster, not necessarily better if the condenser/heat exchanger can't handle the heat load from increased flow.

Vapor doesn't like to travel horizontally. If you place the propane tank on its side, you'll be creating a lot of vapor that will continually condense & fall back into the liquid. If you're set on using reflux w/ height constraints, tilt the tank so that when it's filled, the head space will be at one end where the cylinder transitions into the dome end.
 
Registered: June 03, 2008Reply With QuoteReport This Post
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Originally posted by jdoughy:
Across the pond they're claiming that whole batch demething w/o neutralization works by only approaching the stoichiometric limit. It's my thought that it works to mitigate risks by not explicitly crossing the line, but assumes that there isn't enough energy present to push the back reaction while removing free methanol, which requires more energy to do with glycerol than bio. So, while imparting more energy to the batch in order to remove meth from the glycerol, it's simultaneously going to work on the bio, which has already given up its smaller share of suspended/free meth. My conjecture is that if it were lab tested, one would see an exponential increase in back reaction wile approaching the limit, creating mg & dg then tg close to/at the end point. Mg & dg won't show up in 3/27 while tg will. Anecdotally this might be borne out by their reports of failing 3/27 & shake test (can't remember if it's one or both) if taking it to the limit, but passing 3/27 stopping short of it. However, take my thoughts for what they're worth, conjecture.


I'm just a poor English tinker and cannot afford lab tests and I've been trying to get some of those rich guys in the UK and some of you guys across the pond who have done WBD and have PHlip or gc access to have their bio tested to confirm either way, but so far no takers, I'm not saying their is definitely no reversal but my whole batch demethed bio passes both 3/27 and shake em up soap test no problem, so if there is any reversal is minimal enough for me personally not to worry about, I've used bio with slight fallout without issue so getting no fallout is even better in my book.

Most stuff I've researched on 3/27 against GC testing indicates that a quick clear bright 3/27 pass will usually pass ASTM/EN standard and even just a cloudy 3/27 fail with no fallout will not.


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Location: S.E. England | Registered: September 05, 2004Reply With QuoteReport This Post
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