Graham - following your lead, I bought a clip-on temperature gauge from RS



However, I wasn't convinced it was telling me the truth so I borrowed a Comark digital thermometer and Cole-Parmer k type surface measuring probe. Sure enough, it proved that the dial gauge consistantly measures 4-6 Centigrade low. This could be an issue as we are reacting only a few degrees below the boiling point of methanol. Now I know, I can allow for it but I thought it might be worth mentioning. Oh and I couldn't find any heat-sink compound so used HMP grease which should ensure a good thermal contact.

Cheers
24/7

After a long gestation, my rig is now up and running.. It is based on Graham's design, with a few modifications.....

I used a direct cylinder so there is no internal heat exchanger coil. This means you have two additional ports to play with and I have used the lower port to provide a sight tube to monitor the fill level - this is visible in the photo. This works really well as it is not connected to the pump plumbing - no need to stop the pump to get an accurate reading during filling. Once the charge has been added, the ball valve at the bottom of the sight tube is closed.

You will see that I've used a braided clear plactic tube from the lower plumbing to the pump - this allows you to see the progress of the reaction and also is very useful to monitor settling of the glyc. All the plumbing on the high pressure side of the pump is copper.

The final modification is an additional T piece, ball valve and pipework that allows me to recirculate the oil in the heated pre-processing tank. This serves two purposes - to prevent scorching of the oil and to help dry the feedstock before pumping into the reactor.

If there's interest, I could post more detailed pics.... and many thanks Graham for the inspiration!

Cheers

24/7

rig.jpg (56 KB, 312 downloads) my-rig

Hi Nick

Nice looking setup! Here's wishing you many, many miles of happy BD motoring!

About the thermometer, I took mine off last night and hooked it onto the CH boiler piping. I checked it against a type T thermocouple and it seemed OK at 55C and at around 18C, within a couple of degrees.

Perhaps you should let RS know about your findings, they may exchange it for you.

Did you give it a tap, in time-honoured analogue dial fashion? Just in case there's any stickiness in the bearing.

Best wishes, and good luck!

Hi Nick, Graham

Very tidy rig - much better than the one I have just finished! Still, it managed its first 'large-scale' batch of 80L at the weekend with no problems....except the time it took to prime the tank!

I turned the heater element off when the temp reached an indicated 55c but kept the oil/methoxide mix circulating for a further hour before quenching/washing with water. After half an hour I noticed that the temp indicated has risen to 60c...is this a quirk of the temp guage or is transesterification exothermic - this is not something I have been able to observe with my old 20L slosh it about in a drum technique!

I used a very second-hand 'indirect' tank and was glad I tested it thoroughly before using it with veg oil - my tank came fitted with the usual ports for indirect heating plus two 'Essex flanges' which leaked profusely. I have used these ports for a level sight tube but have replaced the seals on the flanges with nylon washers and silicone as I was concerned that the biodiesel might corrode the rubber originals.

I notice that diesel is 101.9p per litre on the A1 on my way to work in Leeds at the moment and they reckon it could go higher! Using second-hand bits from ebay and new parts from B&Q amongst others etc.etc. I reckon the total cost of my rig is less than £50. It paid for itself the first time I used it!


Keep up the good work!

Cheers

David

Hi Graham

Thanks for those kind words.... I had a good point to start from

The (pre-heat) tank on the left is rigged standpipe fashion. I heat the oil to about 60*C then let it stand til it's cooled to about 40*C by which time any entrained water has dropped to the bottom - below the standpipe. So, heated, coarse filtered and dry oil goes into the reactor. The rig is compact, clean and tidy but is very much made-to-measure so mods are not so easy. Case in point, the pump - I put it there to keep it out of the glyc settling level but, as you pointed out, with the 5% water prewash, the glyc is nice and runny and should not be such a problem. The pump is way, way higher than the glyc anyway so it could have gone 6" lower or more. Ho-hum! It does prime ok though so I'll leave it there unless I get problems.

I don't yet have arrangements for bulk washing/drying. I need to get this rectified SOON as washing it by hand, 10 litres at a time in a 25l carboy is not so much fun! It has been a useful exercise though as I know how hard I can push it without forming an emulsion - quite hard as it happens - that 5% water pre-wash really helps.

Cheers

Nick

Having now read about this 5% water pre-wash several times....it prompts the question.....Why do we bother to de-water the waste oil if your only gonna bung water back in during the reaction stage?

Matt

Hi Matt

The initial de-watering is to prevent the water interfering with the reaction and producing excess soap.

I add 5% water once the reaction is complete to remove a good proportion of the soap produced in the reaction due to the presence of F.F.A's. This speeds up the later washing stages as the glycerol (and residual heat) in the mix helps the water/soap mix to separate from the methyl ester.

I run un-washed fuel except for the initial 5% water/glycerol wash as it makes the fuel much easier to use and has significantly reduced filter blocking.

Hope this helps

David

hello all, i've only just registered but have been reading this thread recently, amongst others 8)

i am about to start building my plant, can i ask a few questions please?

please could you advise on the pre wash methods?

i was planning to just filter it through a sheet in an oil drums as per grahams design (btw, top design :beer: saved me from having to work out how to do the appleseed with uk parts)....

what's the latest ideas on washing/drying please?

i am planning to have one reactor, but maybe 6 wash/dry drums, and a transferrable was/dry 'rig'...washing assembly at top, air bubbler suspended below on a frame so it can be lifted from drum to drum.......please can i have your thoughts on this?

thanks in advance

pabs

Hi everyone,
can someone please explain the 5%prewash step by step?
VINO

Hi Vino,

When your reaction is complete, say after 90 minutes or so, you add around 5% water.

So if you had 60 litres of oil in your reaction, you'd add around 3 litres water right at the end.

Keep mixing for around 15 minutes, then leave to settle for an hour or so.

You can now drain off the dark glycerine.

I then recirculate the pump for 5 minutes just so the BD picks up any of the little remaining water / glycerol in the piping and tank, so that the reactor will be sufficiently clean and dry for the next run.

The BD may now be drained off, washed and dried using your preferred method.

Hi Graham

thanks for the info. will try with the next batch.
vino

quote:

Originally posted by GrahamLaming:

When your reaction is complete, say after 90 minutes or so, you add around 5% water.

Keep mixing for around 15 minutes, then leave to settle for an hour or so.

You can now drain off the dark glycerine.

Sorry, I'm still not clear on this.

You mix for 90 mins or so, THEN add 5% water whilst still mixing for another 15mins?

Surely this would cause an emulsion to form?

What happens to the water - do you drain it with the glyc and does it sit above or below it?

Tripi.

Hi Tripi

I know it seems to go against intuition, and I know I cringed the first time I added water and mixed, but it works very well, and no emulsion forms.

Adding water at the END is OK, because your reaction has been completed, the Free Fatty Acids are now methyl esters.

If you added water at the beginning, you would indeed form lots of soap and an emulsion.

So, adding water at the end is fine.

Most of the water ends up in the glycerol/methanol/Caustic residue which drops out. A little gets dispersed in the BD itself.

So, why do we need to mist wash bio then if we can just stick water in it and flush it aggressively through a pump?

Once I have gathered an end-to-end picture, I'm going to have a stab at writing a newbie guide I think.

Hi Tripi

What stops the emulsion forming in the prewash stage is all the glycerine. It is a very effective de-emulsifier.

After settling and draining off all the residue, ready to go to the wash stage, your BD will have a much lower concentration of glycerine.

This will make it more prone to developing an emulsion with agitation in water, with some soap present.

Especially if the temperature is low, say 10-35C

After the 1st few washes, the soap level will be much reduced and you can start to wash more aggressively.

Hope that helps, and all power to you - a good intro guide covering all the stuff which looks to be counter-intuitive would be well received by many, I'm sure.

Actually I think it's the glycerin that stops the emulsion from happening. I haven't tried it with glycerin that has had its methanol removed yet, but there are many reasons why it makes sense to me that it specifically the glycerin (and water added to the glycerin to make it absorb more polar material) that causes this.

you can test this by making a prewash in a 2-liter test batch and varying the amount of water (too much water= emulsion) and adding some methanol (which should prevent the same degree of emulsion if you're correct). But it's kind of irrelevant- this is a technique that works really well the way that people normally do it , who cares how...

Mark

Great info folks,
I also will try the pre-wash thing on my next batch.
Rembo.

quote:

Originally posted by Tripitaka:
So, why do we need to mist wash bio then if we can just stick water in it and flush it aggressively through a pump?

Once I have gathered an end-to-end picture, I'm going to have a stab at writing a newbie guide I think.

5% water is apparently not enough to make an emulsion. If you add lots more, like in a regular wash step, the pump impeller will generate a wonderful emulsion. Like the water will eventually overwhelm the glycerol.

GM

You're right - it is glycerine - I've modified my post. Thanks for spotting the error.