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[JohnO]

This has been slowly evolving for a couple years. Only last weekend did it finally come together this way, and with the motor.
Basic description: two piston/cylinders on a common lever arm, worked together by a 30rpm gear motor. The larger cylinder pumps about 50cc Oil per stroke, the smaller just 16% as much Methoxide. They are essentially "metering" pumps, pushing exactly the right proportions of oil and methoxide toghether through a series of static mixers.

How it works: The large hose is flopped into the dry, warm oil barrel. The small hose is stuck into the premixed methoxide carboy. One valve is opened to prime that liquid, closed, then the other is opened. When both liquids are sucked up to the valves, both are opened and it's off and running.

Initially it was "upright", which looks simpler and cleaner, but the check valves are on the bottom, so air bubbles don't get flushed out, making the actual pumping volume unpredictable. Turning it "upside down" fixed that problem. The initial single static mixer was increased to a line of 3, which is like stirring 2 to the 33 power times (8,589,934,592 times). I find it hard to believe that's the same as a couple hours mixing, but it seems to work.

Process speed is 1/3 gallon per minute, or 3 minutes per gallon, 20 gallons per hour, 480 gallons per day. You get the idea. I have it running on a 60-minute bathroom timer, so it will use about 3.2 gallons methoxide before shutting off. Rather than having to carefully measure out both the methanol and oil, only the methanol needs careful measurement, as long as there's an excess supply of oil. It's supposed to stop jsut before it runs out of methoxide (methoxide doesn't keep easily, but oil does).

I've made 3 "batches" so far. The first one got screwed up, running out of oil before finishing the methoxide (air bubble trapped in the methoxide cylinder), so I ran it through a second time to use the last of the methoxide. It settled and seperated just fine. I turned it upside down and ran the 2nd and 3rd batches, which worked just like theory said they should. Next weekend I'll try a 3/27 test on them to see how well they converted. This oil was nasty, but titrated less than 4.5 as I recall.
Cheers,
JohnO

[Rick]

This is really a slick way to mix. BTW If run 24hrs a day This thing will do almost 180K gallons a year.

John please let us know how the 3/27 fairs.

Rick

[JohnO]

The 3/27 test of the first two "batches" (Can I still use the term?) passed with slight cloudiness and nothing dropping out. I used 11.4 gm KOH and 12.1, respectively. This weekend I processed another 33 gallons using 12.4 with apparent good results, but haven't tried the 3/27 test. I DID try re-reacting a little sample with 1 gm KOH and it clouded and got a little viscous!!. I've never seen that with KOH, only NaOH. I've obviously found the upper limit.

For yucks I tried a shakeumup test of one of the first two batches and measured the water pH, surprised that it was just 6.5. I expected 8.2 or thereabouts. That used to indicate to me that it was under-reacted, back in the days when I used NaOH. Any reason it wouldn't also work with KOH? (BTW, the water turned cloudy, but the BD cleared nicely in a couple hours).
Cheers,
JohnO

[JohnO]

I mounted the double-pumper on the wall above the settling tank, within hose reach of the svo tank and (new) methoxide tank. The check valves work better when vertical. This has now made two more batches - one with an in-line oil heater, the other without heat. I'm waiting for them to finish settling to compare, but initial results look like the heated batch has a higher yield.

The in-line heater was an automotive coolant "tank" heater, powered by an autotransformer set to 70%, which would be roughly 750 watts. This kept the oil at about 150F. I think I'll make a dedicated oil preheater, using a thermostatically controlled water heater element in a length of pipe, running at reduced voltage (maybe using the same auto-transformer). It needs to be wired to the same switch that controls the pump, so it's only on when the pump is running.

The methoxide mixer is a 5-gallon propane bottle with a mag-drive pump, siteglass, pump hose quick disconnect, and a big 1-inch ball valve on top to add KOH through. I premix the methoxide according to the titration of the oil, but use the methanol volume for my calculations, rather than the oil volume (multiply by 6.25 to determine how much oil a quantity of methanol will convert, at 16% for instance).

I can be reached for questions at jouster@red.gd-ots.com

[morris1524]

JohnO,

Nice set up!

Which static mixer are you using? What is the total length, diam. and # of elements? From where?

You are a true pioneer.

Andrew

[JohnO]

"Which static mixer are you using? What is the total length, diam. and # of elements? From where?"

The mixers are Simpson Emn 22 Construction Epoxy nozzles, trimmed to fit inside ¾ inch reinforced vinyl hose. They have 16 elements each, roughly ½ inch diameter, by roughly 10 inches long (I haven’t measured the length, so might be wrong by a few inches either way). At just $4 each they’re a bargain, compared to other static mixers. I found them at the local building contractor’s supply (lumber yard). I also did a web search and found them at http://www.simpsonanchors.com/catalog/adhesives/accs/nozzles.html

The pump moves about 50cc per stroke, 30 strokes per minute. There’s a fair amount of back pressure, seemingly from the small outlet nozzle on each mixer, so I trimmed them back a bit, too, which helped. I’ve tried comparing a sample taken directly from the static mixers to a sample that was subsequently shaken violently, then both left to settle side-by side. Both settled in similar time, both showed identical levels of glycerin, both were identical in appearance. This crude quality comparison indicates there seems to be adequate mixing taking place. It still seems a bit spooky – I’m used to running a pump mixer for at least 20 minutes to 2 hours to guarantee thorough mixing, but in any kind of tank mixing system the proportions of methoxide to oil vary widely from region to region, thus the need for long mix times, to homogenize the chemistry. With two metering pumps, the oil and methoxide streams are parallel and correctly proportioned upon entry to the static mixers, so they only need to mix “sideways”, not top to bottom. It’s a theory anyway.

I just started bubble washing a mix (the 6th?) from the double-pumper, made using NaOH, low titration, single stage. It seems to be washing easily. I was nervous because the small sample I pulled in the middle of the "mix" gelled! The batch seemed to have settled just fine though, so I assume the difference is heat - the small uninsulated sample cooled off quickly, while the large insulated batch stayed hot long enough to settle. If true, then the batch must be right at the upper limit of NaOH.

[jlkunka]

johno-

Love your concept - could you provide a picture or some description on the type of piston and seal you used inside the plungers? Also, are you using swing check valves or spring-type at the four locations around the pumps (looks like spring type to me).

Keep up the good work!

[JohnO]

The Pistons were turned from mild steel bar-stock. I cheated when making the larger one by using 1.00-inch diameter bar (it was what I had on hand), even though it was a little under-sized for the cylinder. I wanted about a 0.015 clearance, and it worked out to something like 0.045, but the Viton o-rings are 0.094 or 0.125 diameter (I’m not at home to measure them). The grooves for the o-rings are as close to the Parker recommended dimensions as I could conveniently make, providing 15% squish on their diameter.

Making the pistons under-sized concentrates the wear on the cylinder wall. The piston bears against the cylinder wall as it rocks back and forth. With a large contact area, wear is reduced, but a small contact area may wear the cylinder wall enough to leak, eventually. The simple solution is to start with slightly larger bar-stock (1-1/16 is available at the supplier).

The Viton o-rings are from the local hydraulic supply shop. I don’t know the compound used, except that it’s intended for agricultural chemicals. They’ve now been in use for a couple months without indication of deterioration.

Check valves are indeed spring-loaded swing gate style. They were the last of the stock at the store. The replacement ones are gravity-swing gate style, without springs. I’m waiting for a response from another source to see if I can get spring-loaded poppet-style steel valves.

[jlkunka]

Thanks, JohnO.

...when in doubt, McMaster has bezillions of check valves... http://www.mcmaster.com/

I doubt your cylinder will wear - the O-ring should center the piston and keep the piston from touching the cylinder walls. It doesn't look like your linkage will put much side load into the piston, either.

[JohnO]

The o-ring only keeps the bottom of the piston centered. The top part bears against the cylinder wall. I think it'll last a long time as-is, but I also know that it wouldn't hold up to continuous use for long.

McMaster-Carr does have a great selection of check-valves.

[JohnO]

I tested a bunch of checkvalves from McMaster-Carr, and concluded that ball check valves are the only ones worth considering. McMaster part number for my favorites are: 1371T78 (nylon pipe-to-hose barb, for outlet connections), and 47715K23 (1/2 inch bronze, with teflon ball and stainless steel spring). It has rather low opening pressure, so it works well for suction. So far, the bronze appears unaffected by sitting for the winter with oil and methoxide on/in it.

My next project is to rebuild it beginning with smooth-bore pipe. Schedule-40 has a weld seem that is difficult to remove smoothly. I'll need to turn new pistons to fit the new pipe, and relocate the linkage attachment points. This means rebuilding most of the major components. I'm seriously considering trying stainless steel pipe fittings, but they're quite expensive. OTOH, they're a LOT cheaper than buying a commercial metering pump or two. I calculated that a large version capable of 600 gallons/hour would need about $1000 in parts and assembly labor, using an air cylinder instead of a motor. That's a serious small production processor, in theory.

[JohnO]

I'm well along with machining a new double-pumper. The oil cylinder is turned from 3/4 inch pipe, and the methoxide cylinder is turned from 1/2 inch pipe. The cylinders screw into 3/4 and 1/2 inch tees, respectively. Each tee is machined to pivot inside bearing rings. The pistons will extend past the ends of the cylinders, nearly to the bottoms of the Tees, to eliminate trapped air bubbles.

This one is being made to pump slower, just able to keep up with the Bird Waterer. The idea is to use the freshly dried oil while it's still warm. There's no actual storage container for the oil - it dribbles from the Bird Waterer outlet into a cup directly connected to the oil cylinder. A float switch inside the cup turns on the pump motor when there's oil present, processing it almost immediately into biodiesel.

The 10rpm motor only draws a tiny amount of power (about 10 watts). The BirdWaterer draws nearly 1000 watts, but is only "on" about 50% of the time, so the average current draw is about 4.25 amps.

The 1/2 inch pipe bored cleanly to 0.660 inches. The 3/4 inch pipe bored to 0.880. The pistons are machined with viton o-ring grooves far enough from the end to stay inside the bored pipe even when the ends are touching the bottoms of the Tees. There's a certain amount of break-in period that results in worn-out o-rings until the bore gets polished.

The o-ring grooves can be made without a lathe, by chucking in a drill-press and using a file or hack-saw and patience. The cylinders can be reamed with a big drill bit, then honed with carborundum wet/dry sand paper. All the pivots are 1/4 inch bolts, fitting drilled holes and tapped holes, with a lock-nut. The steel bars are simply 1/2 x 1 inch plain structural steel. The methoxide cylinder connection point is at 3.5 inches from the pivot, the oil cylinder is at 10 inches, and the motor connects at the 12 inch point. This gives almost exactly 20% methanol ratio.

The rings that the Tees pivot in are 1-1/4 inch pipe, and 1-inch pipe, bored to fit the Tees. The original double-pumper used simple U-bolts to do the same thing, and that would be my recommendation for anyone who didn't have a lathe and welder. The two cylinders only tilt a couple degrees. They'll be connected with a short length of braided vinyl hose that will have the 3 static mixers inside.

The pitman arm on the motor has a 1-1/4 inch throw, giving a 2-1/2 inch stroke at the end of the walking beam. That gives the oil cylinder a stroke of 2.08 inches, and the methoxide cylinder a stroke of 0.73 inches.

The ball-check valves work well with methoxide and dirty oil as long as they're blow the supply levels. Otherwise they can trap air bubbles that change the displacement volume, changing the chemistry ratio with bad results.

[Mango Boy]

JohnO, I like where your head is at with this clever, original design. I noticed that you have also posted photos of your centrifuge - have you thought about linking it all together for a continous system ?

I'm assuming from the materials and tolerances that your pumper can generate a decent pressure. If you raise the oil feed temp to 70-75 celcius, regulate the pressure in the output to 80+ PSI (to stop the meth boiling), then you could discharge the output through a spray nozzle into a flash tank to recover the meth in realtime. Plumb the drain from the flash tank into your centrifuge, output to a continous ion exchange dry wash (amberlite, lewatit, etc.), and you could have the whole process down to a few minutes !


Quote - "It seems to be washing easily. I was nervous because the small sample I pulled in the middle of the "mix" gelled! The batch seemed to have settled just fine though, so I assume the difference is heat - the small uninsulated sample cooled off quickly, while the large insulated batch stayed hot long enough to settle."


Maybe you need a longer residence time in the mixers ? As well as being insulated, the large batch is effectively being agitated with every "squirt" from your pumper, and with the meth still present, it's possible that some of the reaction is taking place in the output drum, rather than the mixers. Increasing the heat and pressure can improve this (you may need to replace the flexible output hose and plastic mixers with steel to handle the pressure, and possibly lengthen it to increase the residence time).

just thinking out aloud now . . . What if you replaced the pumper with 2 small positve displacement pumps ? Second hand gear pumps are pretty cheap - if you got 2 identical models you could run them from the same motor and set the feedstock:methoxide ratio by the drive pulley sizes. Would make maintaining the pressure easier and could increase the throughput dramatically . . .

Congrats again for thinking "outside the drum"

[JohnO]

Mango: I've considered gear pumps, but they have rather high internal leak rates that are enough to alter the pumping ratios of the oil and methoxide. With oil, a good pump will have an internal leak rate of 2 or 3%, meaning 98 or 97% volumetric efficiency, operating at its design speed. Higher pressures or slower speeds result in higher internal leak rates. On methanol though, the leak rate might be as high as 20%, and gets worse as speed slows down. Trying to compensate for those inefficiencies isn't practical for my purposes. Piston pumps with tight o-ring seals and well sealing check valves are nearly 100% volumetrically efficient at all speeds, so they work well for my purposes.

[JohnO]

I finished installing the float-switch actuated motor relay and set the DP (Double Pumper) under the Birdwaterer outlet. When the BirdWaterer pump is running continuously, it nearly keeps up with the Double Pumper (DP). Since the warm oil flow is usually a little less than continuous (it only pumps continuously if the oil is already quite dry) it usually runs for a minute then stops and waits for about 10-15 seconds. I'm quite pleased with the speed match, assuming nothing goes wrong with the DP pump. If it hangs-up for any reason, the oil will quickly overflow the inlet cup. I'd better think of a solution, such as an overflow pipe.

The methoxide cylinder has a problem though. Despite my best effort, the weld seam is still evident and ate a divot in the piston o-ring, causing an air leak. I need to use seamess tubing to avoid this. McMaster-Carr has some (9220K341 for 3/8, 9220k411 for 3/4, and 89975K351 for 1.5 inch). I'll try that next.

I forgot to mention above that this is a good feed rate for the centrifuge.