Meth mixer ideas

Pump too much meth, too fast, into the oil in your pipework and you get all sorts of quality variances which will give disappointing results. Feed it in nice and slow, and results seem repeatably good.

Why?

Very rough approximations...
The normal ratio of methanol to oil is around 20%
The normal ratio of NaOH to oil is around 6g/l


Now, if you introduce the methoxide fast, you may get a much higher concentration of NaOH to oil - let's say 10g/litre, 50g/litre - just depends how fast you introduce the meth.

So it can mean your mixing ratios are WAY out, for the liquid in the pipes and tank.

What happens if you overdose on NaOH? You make a thick jelly of soap, especially if the oil is slightly damp. There is such an excess of sodium ions, they hook up with the FFA to form a lot of sodium soap.

This jelly can jam up your pipework and block your pump.

It can leave blobs of jelly floating around in your tank, unable to mix well.

This is why it can be good to limit the mixing ratio.

All we need is a way to limit that concentration, without having to carefully adjust valve openings each time. I want to be able to open a valve fully and know that I'm feeding in at the right rate. That way I'm going to be reasonably confident that my batches will be consistent, all other factors being consistent too.



Here's how I do it ...

I use 20mm inner diameter (22mm o.d.) copper pipe for oil feed and recirculation.

I figured if I feed meth in thru a tube with around 20% cross sectional area of the oil pipe, I should be somewhere around the right mix ratio.

Cross sectional area of pipe = Pi x r2 and I'm making a really rough guesstimate to the flow relationship!

So, I use 8mm inner diameter copper pipe for the meth feed, which is around 15% of the area of the oil pipe, but I have the meth pipe poke into the stream of oil by around 8mm, and that seems to give around 20% mix ratio.

I've ended up with the meth pipe being cut at a 45 degree angle and this seems to help give consistent flow rate, and probably helps add turbulence to improve the local mixing before it hits the pump.

The open face of the 45 degree cut faces downstream to help the oil 'drag thru' the meth.

Here are the parts I use...

From top to bottom...

  • 22mm/15mm/22mm Tee
  • 6cm of 15mm copper pipe
  • A copper push-fit 15mm insert
  • 7cm of 10mm o.d. (8mm i.d.) pipe, with a 45 degree cut one end
  • A 15mm gas rated ball valve (yellow handle)

These are the 15mm push fits I used...




Slide the pushfit onto the pipe with 45 degree cut.. Have the collar of the pushfit come right up to the edge of the 45 degree cut. Gently crimp the pushfit with a pair of pliers so it stays put.




Now solder the pair together for permanent security.

Slide the 15mm pipe onto the assembly, and solder the collar in place. Try not to get solder on the outside of the 15mm tube, or you'll have trouble sliding on the compression fitting.

A simple way to avoid solder on the outside is to wrap masking tape all round the outside of the tube while you solder, then unwrap it when done.

Next fit the assembly into the tee piece and tighten up. Add ball valve, and you're ready to roll.






A closer look into the feed, from the downstream side...




Good luck, hope it helps you as much as it's helped me.

I've used parts easily available in UK, but I'm sure you can adapt the idea to suit whatever you've got available in your part of the world.



Graham


You can email me at grahamlaming at hotmail dot com


Posted Dec 29 2005

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