What are you guys doing for controlling the heater element? There was quite a discussion about this in the St Louis Biofuels Club, and they're using a variety of methods (Maud's got an old variac to turn down the wattage of her heating element).

Mark

Hi Mark,

I am looking into this now. The standard heater thermostats just dont cut it due to the cycle lag between on and off. Both Graham and I have found that when the thermostat cuts off on reaching temp, the recovery stops and does not start again until the stat has cooled by several degrees.

What we need to achieve is a method of holding the stock liquid at a desired temperature with very little variation and a much shorter on/off cycle.

I am hoping to achieve this with a couple of cheap thermocouple switches linked to a contactor to switch the heating element. One thermocouple will monitor the stock liquid temp and the other the head temp on the condenser as this fluctuates far more in my experience than the liquid temp.

The important element that I have found is to have a LOT of circulation of liquid, otherwise, the only recovery you will get is from the meth boiling off when in contact with the heater.

Yeah, that's exactly what I found.

You need to keep adding BTU's to the pot (meaning the heating element can't turn off as a thermostat would do), but not so many BTU that you raise the temp higher than you want. One way to do that is to use a low-wattage heating element and leave it on all the time in an uninsulated reactor, but I havne't figured out a good combination, plus the outside temperature variations from winter to summer would mess this plan up.

I'm wondering about dimmer switches- my amateur electronics advisor boyfriend claims they're the right thing for this job- anyone else know? I'd be running a 120V low-watt heating element through one.

Mark

Hi, and welcome back GM!

Matt Stevens designed a continuously adjustable heater controller at http://biodiesel.infopop.cc/eve/forums/a/tpc/f/449605551/m/5481062151

You can also buy a power control module if you're not into homebrew electronics.

A good example of an affordable one is at http://rswww.com

Type 655-644 into the search box. I'm sure these are distributed worldwide.

You can always go the PID route if you're really concerned about precision. Many PID controllers also offer a ramping setpoint which would seem useful, if you know the approx. thermal timeconstant of your system. Just keep ramping the temp in line with BP forecast.

Hope that helps.

Thanks, I tried to find that on Mouser Electronics last night and wasnt familiar with this type of part, so I asked the boyfriend to translate it to stuff found in American catalogs, and here's what he dug up:

quote:

Heh, it's essentially a high-power dimmer switch, but with a nifty new name for high-power applications
http://home.howstuffworks.com/dimmer-switch.htm

Those wily brits!

You can find triacs (the important bit of the dimmer) on mouser, but they don't carry assemblies like this, that's more of an industrial automation thing.

Going to rs-electronics.com, I found out that Allied Electronics is their North American dealer. However, Allied doesn't carry these exact items though: the closest they have is this:
http://www.alliedelec.com/Search/ProductDetail.asp?SKU=...sid=45381180271CE17F
.. and you have to supply your own potentiometer.
Maybe there's a regulatory reason they can't be sold here assembled, I looked around on google and didn't find much (but didn't look too long, either).

watlow programmable controller
relay
type "T" theromcouple

you can adjust the ramping to any value you wish

Welcome back GM.

I've done a fair bit of methanol recover so I thought I might chime in on this one.

I think one of the most important part of a good methanol recovery system is to match the element with the size of the batch. I have a 27 gallon still in which I put 20 gallons of glycerin. I have a 5500 watt element that I start out on 220 volts. When the methanol starts coming out of the condenser I switch to 115 volts and let it run. My still is insulated with the foil looking bubble wrap.
I also have a recalculating pump and a spray bar in the top of the still. I have found that if you aerate the glycerin you also aerate the water and the purity of the methanol drops considerably.
Any time the heat is stopped the methanol stops running. The trick is to have an element that raises the temp at a rate that gets the methanol out before the temp is too high.

A variac is a great way to adjust the Btu output of your element without having "off" time.

Here is something new that really worked well.

I have an Appleseed with a condenser on the side. After I process, settle, and drain the glycerin I turn the heating element back on and recover the methanol from the BD. I wasn't concerned about purity I just wanted to get the job done quickly so I turned on the pump and circulated while distilling. I let it run until the methanol completely stopped coming out and shut down the system. It reached 230f when I stopped and I think I damaged the seal in my pump. Anyway, when I pumped the BD into a settling tank and there was still a strong aroma of methanol. I was a little disappointed so I tried something different.

On my next run, once the glycerin was drained I started the heat. While it was heating up I hooked an air compressor to the glycerin drain on my Appleseed. As soon as the temp of the BD reached 150F I turned the regulator way down on the air compressor and started letting the air into the bottom of the Appleseed. Not a lot of air, probably similar to what a good aquarium pump might put out or perhaps a smidge more. Right away I could see that the flow of methanol was much stronger than normal. I let the temp get up to 200F (bd in the tank not the head temp) and I turned off the heating element. I continued letting the air in and much to my surprise the methanol kept on running. Even though I was pumping cool air into the tank the temp was not dropping. The methanol ran for a while and then I noticed it slowed. At just about that time I saw the temp drop 1 F. Shortly after that the methanol completely stopped and the temp started dropping much more quickly.
The amount of methanol recovered was about 30% more than I had been getting and the BD was absolutely methanol free.

This particular batch was an acid/base batch so it had quite a bit of water in it. The purity of the methanol was 94.5 % which is lower than I usually get.

I collect my less pure methanol until I have 20 gallons and then redistill it.

Note: You don't want to put too much air into the tank otherwise you could raise the pressure inside the tank and cause the methanol to stop boiling and this will stop it distilling.

-mcguyver

Hi mcguyver

Why do you think the temperature only started dropping after you ceased vapourising the methanol?

I can't understand why you would have more heat loss after the vapourisation process than during it.

What was your circulation rate, and were you spraying the return into the vapour space?

Looking at the outlet pipe of your condenser during the air injection phase, can you describe exactly what you saw coming out? Was the flow steady, a dribble, and were there any puffs of methanol cloud dropping out?

I'd like to try this, because I presently can't get enough heat into my batch to remove as much methanol as I'd like.

I haven't used it before in a full batch, because I'd been concerned about the injected air causing the dewpoint to drop, meaning I'd need to chill the condenser jacket more to capture the same amount of methanol, or lose it to the airstream.

I guess if the air stream is minimal, the dewpoint will be dropped only slightly. So you'd want to be sure you don't drop the dewpoint to a temperature approaching that of your condenser coolant inlet temp, or you'll just get puffy white clouds of methanol wafting away in the breeze.

I had tried this on a small test batch before with an overkill air pump and obviously overdid it - didn't think to cut back on the flow, so dismissed the idea - duh.

Nice idea - thanks.

quote:

the closest they have is this:
http://www.alliedelec.com/Search/ProductDetail.asp?SKU=...sid=45381180271CE17F

That is a solid state relay or SSR. They come up cheaply on ebay all the time.

You would need a control circuit to drive it.

I use them to turn my heaters on and off in response to a simple honeywell controller running with a K type thermocouple.

Not the best arrangement but it works well enough.

quote:

Originally posted by mcguyver:
As soon as the temp of the BD reached 150F I turned the regulator way down on the air compressor and started letting the air into the bottom of the Appleseed. Not a lot of air, probably similar to what a good aquarium pump might put out or perhaps a smidge more. Right away I could see that the flow of methanol was much stronger than normal. I let the temp get up to 200F (bd in the tank not the head temp) and I turned off the heating element. I continued letting the air in and much to my surprise the methanol kept on running. Even though I was pumping cool air into the tank the temp was not dropping. The methanol ran for a while and then I noticed it slowed. At just about that time I saw the temp drop 1 F. Shortly after that the methanol completely stopped and the temp started dropping much more quickly.
The amount of methanol recovered was about 30% more than I had been getting and the BD was absolutely methanol free.

How long does it take from first turning on the compressor until the flow of methanol stops?

Cheers

Nick

quote:

Why do you think the temperature only started dropping after you ceased vapourising the methanol?

I can't understand why you would have more heat loss after the vapourisation process than during it.

What was your circulation rate, and were you spraying the return into the vapour space?

Looking at the outlet pipe of your condenser during the air injection phase, can you describe exactly what you saw coming out? Was the flow steady, a dribble, and were there any puffs of methanol cloud dropping out?

Hey Graham,

I'm not sure why the heat loss occurred after the vapors stopped. I have a pid hooked up to a thermocouple inside the tank about a foot off the bottom. Every time I drain the tank while it is hot, the temp goes up during the draining. I thought perhaps I had equipment malfunctions first time but it does this ever time. I think it is related to "Berelli's theorem" (I know I didn't spell his name right) but it states something about expansion creating heat. Somehow the methanol vapors leaving the BD create heat. Just guessing at it, I'm not a scientist.

I wasn't circulating the BD because I was concerned about damaging the seal in my HF pump. The last time I circulated at high temps the pump slung some black oil, not Bd, out of the area between the pump and the motor. I figure it's just a matter of time before it dies.

As far as the output, it was a steady flow for most of the time and then to a steady dribble for the last 10-15 minutes. When it stopped it was abrupt. The dribble was followed by a few drops (maybe 30 or 40 seconds worth) then nothing. There was never any problem condensing the methanol vapor. I can tell if the methanol isn't being condensed because I've experienced it a couple times when I forgot to turn on the water to the condenser. I could feel the bottom of the condenser and it was very cool. The whole time the methanol was coming out the top of the condenser was quite warm, even after I turned off the heat and it was just the air carrying the methanol out.


I use city water to run the condenser and I don't know the temp but it not unusually cold.


Twenty4seven,
Unfortunately I didn't time the process. It was shorter than usual. I was changing the front brakes and wheel bearings on my crane while I was doing this. The only time I stayed with the processor was when the temp hit 200F and I turned off the heat. I wanted to see what was going to happen. From that time on it was less than an hour from turning off the heat to the methanol stopped. It was probably in the neighborhood of 3 hours or less before I turned off the heat. One note I wanted to mention, when the bd reached 150F and I first turned the air comp on I had a real slow rate of air and I don't think it made much difference. When the temp of the BD reached around 180F (I think) I turned the air up a little and then I could see a difference in the flow of methanol. I left the high air flow on for the rest of the time.


In my mind's eye I can imagine the compressed air entering the hot Bd at the bottom of the tank and dispersing into a lot of smaller bubbles each with a considerable surface area and collecting methanol vapors on the way to the top. Since there is a steady flow of air it has to exit through the condenser carrying the methanol with it. BTW, I couldn't see anything different looking at the discharge of the condenser as far as seeing extra air coming out. Although the air being put in made a lot of noise inside the tank it easily expelled out the condenser without "blowing".

Here is a picture of my appleseed. I'm using a small 3" pvc pipe condenser.


-mcguyver

Hi mcguyver

I just ran an 80 litre batch and tried air injection when the condenser stopped producing - it works!

I injected air into the vapour space above the BD liquid level.

quote:

I injected air into the vapour space above the BD liquid level.

Well that shoots my theory in the buttocks.

Graham,
It's interesting that you didn't have to have the air pass through the BD but just across the top. I thought the air was collecting the methanol from with in the BD.

The only test I did to see if there was any residual methanol was the handy dandy fry pan test. After I finished recovering my methanol after air injection, there wasn't so much as a peep of a sputter from in the fry pan. Every last bit of methanol (and water) was gone. Do you feel you got a good complete removal of the methanol?

BTW, were you recirculating the BD through the same head space as the air was being injected?

Finally, did you get any appreciable difference in the amount of recovered methanol than you usually get?


-mcguyver

I was circulating all the time, so this probably explains why I didn't need to bubble thru the BD - there was a constant refresh of methanol carrying liquid being sprayed into the vapour zone.

I got more out than I could have by traditional distillation -

Traditional distillation to 90C gave me 1.8 litres and I got around 280ml more after that with the air. I suspect the last bit was quite watery - it behaved differently when it hit the sides of the collecting flask, not free running, but sticking in droplets on the side.

I didn't get all the methanol out, but I recon there was very little left. I stopped really only because of the water suspicions.

Graham,

That’s quite impressive; you got an additional 15.5% after you stared air injection. I agree; you probably had a high percentage of water in that last bit.

I did another test using my still this time.

I let me still run for 6.5 hours with a batch of 18 gallons (68 liters of glycerin). Some of the glycerin was from a re-processed batch so it was fairly heavily laden with methanol. I do have a circulation circuit on my still (with a spray bar in the top) but I don't use it very often. My still is a tall slender cylinder and the convection currents seem to do a good job of keeping it stirred up.

I let it run until it was a fairly steady drip (you could count the drips). This yielded 4.2 gallons (15.9 liters) of 95% pure methanol.

Usually I swap collection containers after around 3.5 hours so that I have higher purity on the first methanol and then what I collect after I swap contains goes into the "re-distill" container to be further purified. I've been doing a lot of acid/base processes lately and the purity of my recovered methanol has dropped a little.

Anyway, back to the subject;
After the 6.5 hours and the recovery slowed to a steady drip I started injecting the air. The only place I can inject air on my still is at the very bottom through the drain. Instantly I got a very vigorous stream of methanol/water. In 10 minutes it again slowed to a steady drip and I stopped the process.

Much to my surprise, in only 10 minutes air injection of glycerin that was considered to be "distilled" I got an additional 745 mls. For those of you that don't do much distilling, I know that doesn't sound like much but consider this; for an average over the previous 6.5 hours I was only getting 41 ml/minute and that was from glycerin with an abundance of methanol so 745 ml in only 10 minutes is somewhat of an accomplishment.

As for the purity, not so impressive. The last 745 mls recovered was only 66% pure

I didn’t do quite as well as you as far as additional percentage recovered after air injection. You got an additional 15.5% where I only got an additional 4.65%. Do you have any idea of the purity of your methanol before and after air injection?

(That was a lot of “as s” in the previous paragraph)

I'm going to have to do some tests to see if air injection during the whole process would speed things up. I suspect it will considerably speed up the process of distillation however the purity will most likely suffer. I have to have at least 15 gallons in my still to run it so I plan to collect 30 gallons of glycerin, mix it well, and try a run with and without air injection.

I think air injection would be a good addition to the process if your more concerned about getting the job done quickly or if getting a complete removal of the methanol is more important than purity (such as a soap maker or someone feeding the glycerin). The resultant methanol would not be suitable for immediate reuse but would be fine if it was run though a "normal" distillation process at a later time.


I'm always a little disheartened when I get a whiff of methanol from a batch of bd/glycerin that I have already distilled. It good to know that I have a way of getting "all" of the methanol out. I will probably go back to running without air injection for the first half of any methanol recovery to keep the first methanol recovered relatively pure. Then swap collection containers and start air injection for the final recovery. This will work well for me since I already do some re-distilling and I'll have the satisfaction of knowing I got nearly all of the methanol out of the product.

Seems the air injection approach may be suitable for treating the bio portion, as it sounds like it may also take with it moisture content.
The smaller amount of lower purity methanol could be saved, and distilled further if it was deemed worth it.

quote:

but it states something about expansion creating heat.

As I recall you create heat when you compress a material, you lose heat when you expand a gas, kinda like how a/c works.

I am not quite clear on one thing though, when recovering methanol from the "BD" isn't there a possibility of running the reaction backwards. I had mentioned doing just that and was warned rather pointedly of that fact.
Seems a lot more elgante' to do it that way, recover from the BD/glycerin mix or am I missing something?
I am using vacuum recovery and have injected air at the bottom drain to relive vacuum and it does seem to give the recovery a "bump"

Again, is there a consensus in terms of a backwards reaction as to whether or not to recover methanol from the BD/glycrin mix or to just recover from the glycerin? If anyone would care to unconfuse me I would appreciate it. Thanks

just a thought, but instead of using 1/4 inch copper 3/8ths would give much more surface area for cooling?

quote:

Originally posted by gigem75:

I am not quite clear on one thing though, when recovering methanol from the "BD" isn't there a possibility of running the reaction backwards.

Not if the glycerol has settled and been removed from the biodiesel before methanol recovery.