quote:

Originally posted by GrahamLaming:
If your batch is X gallons, use a circulation pump rated at least X/2 gallons per minute.

Use another circulation pump, rated the same as your main circulation pump, to flow the vacuum liquid through the venturi, as in the diagram.

I feel like there are diminishing returns with that equivalency, whereas a 100gpm pump on the main reactor would seemingly be overkill pushing fluid through a 3/4" venturi... Also, isn't the vacuum generated by the venturi related to the gpm that passes through it? In that case, wouldn't an excessive amount of flow suck a rediculous amount of vacuum.

I would imagine that the amount of vacuum generated by a 20gpm pump would pull the same vacuum regardless of the main batch size...

I could be totally off here, it's just that a pump like Murphy's or a Goulds pump doesn't come cheap! So if something smaller would work on the rapeseed tank, like that Wilo Gold, that would be much better for the wallet.

JB

Hi JB

The bigger the batch size, the more methanol in the batch which needs to be removed.

You can move that larger amount of methanol to the condenser with a smaller pump, but it will take longer.

More work to do, means more power needed to do it, if it is to be done in the same time as a smaller task requiring less work.

The venturi would need to be sized accordingly, too.

Look at it this way -

We want to limit our max temperature, so we'll set our controller to 40C, for example. We switch on the vacuum pump, and there will be no boiling until we get the pressure down to a certain level.

As soon as boiling occurs, the pressure in the tank will rise, and will be limited by the rate at which the venturi can empty that vapour out.

If the venturi empties the vapour slowly, the pressure will rise and boiling would stop, until pressure can be dropped again to below the pressure at which methanol boils at 40C.

So, a bigger batch will need a bigger pump, and bigger pumps do cost more, but bigger batches are more economical to run in the long term.

Plus, a faster bigger batch is more economical to run than a slower one, if "man-hours in attendance" or "output per working day" are being added to the costings and profit/loss calculations. So again, a bigger pump could easily make good economic sense.

I think that using a smaller pump, whilst cheaper initially, is likely to be false economy for every batch it is run in.

But I know what you mean, it would sure be nice to be able to use small pumps on big batches!

Hi Graham

if you're pulling a vacuum at present of 10 psia then your methanol boiling point will be 55*C - correct? So the solution is to keep the temperature up while recovering methanol this way?

Do you have a part number for the Wilo pump?

Paul

Hi Paul

40C would be a nice target - my 10psia is dreadful - no-one should try to emulate that !!

For 40C as your upper target, you'd be looking for around 5psia, bearing in mind the boiling point of methanol in a mixture is higher than that of pure methanol, for a given pressure.

The pump is a Wilo Gold RS60.

Cheers

Graham

Hi Graham,

Thanks for the info on the pump sizing (x/2 method). One more question though:

If my tank size is 60 gallons I will need 2 30 gpm pumps or can I use a single 60 gpm pump and fabricate a manifold and split the flow like 2 pumps would operate but use only one pump.

Cheers.

Darren

Darren: for a 60 gallon batch you only need one 30 gpm pump.
If you want to either use 2 or use a single 60 gpm pump, I would go for the 2 pump setup, mostly because if one of them breaks while processing, you can still finish the BD with the other one. Just make sure to run the outlets individually to the tank, to avoid the liquid backing up through the pump if one of them breaks.

bernyjb,
how did that last batch of b/d that you made turn out?

Don't know. I'll tell you when I make one.

Berny

Thanks for the quick response but your answer confused me.

Graham's design shows 2 pumps operating simultaneously. I gather that the second one is primarily to operate the venturi. If this is not so then how would you operate the venturi? Would you pipe the venturi as shown on Graham's design but just w/o the 2nd pump?

quote:

Thanks for the quick response but your answer confused me.

Graham's design shows 2 pumps operating simultaneously. I gather that the second one is primarily to operate the venturi. If this is not so then how would you operate the venturi? Would you pipe the venturi as shown on Graham's design but just w/o the 2nd pump?

Sorry. I think I'm the one who got confused. When I read your post about using 2 pumps, I thought you were talking about using the 2 pumps for the reactor.
You're right. You do need the second pump for the venturi, which is the one that provides the vacuum.
Sorry I messed up.

Okay back to the methanol condensing topic....has anyone experimented with using an old car radiator and using an electric fan blowing across it to get the methanol to condense OR using an old discarded condensing unit (AC unit for a home or apartment) and circulating the methanol through the condensor section and running the condensor fan. I have a back ground in the refrigeration field and really like the idea of using an old condensing unit. Thoughts??????

If you like the idea then try it but you will be hard pressed to beat the efficiency of the plumbers delight condensor that is cheap and easy to make.

quote:

I added a 3" section of the clear braided hose

You can get an inline glass windowed view port from refrigeration places. Screws into the pipework.

quote:

We want the pump to be between the processor and the condenser - a refrigeration pump would have a short life there.

Would an air powere diagphram pump work?

You can use an air operated diaphragm pump.

Figured i'd post this as we're back on processor design.

This is what i'm going to the welder with and hopefully it works. The oil flow certainly will work, but i'm a little skeptical about the foam trap at the top (2" black iron fittings) and whether or not i'll be able to observe a color change through 1 1/4" clear tubing.

There are more pictures at the bottom here and if anyone wants a better shot of anything there for clarification, please PM me: http://biodieselpictures.com/viewtopic.php?p=1086#1086

Thanks for doing such amazing graphics!!!

Hi JB,

I agree, your graphics are great!!!! Quick question, have you figured out an elegant way to insulate your tanks?
I am also building a system (much smaller though) and want to do a good job of insulation.

Bob

Great graphics!!! Do happen to have a parts list that we could all look over? I'm interested in seeing what is what. Thanks!

--Tony

Okay Gents....couple of more dumb questions:

1. In the graphic above the smaller tank to the right of the reactor...what should be the capacity of this tank assuming your reactor is 50 gallons?

2. The reactor tank that I am going to use (appleseed design) does not have as many ports as the one shown. Mine has two on the top and two on the side BUT NOT one on the bottom. Was this added after the fact? Mine has a drain but it is on the side (it is one of the two connections on the side of the tank). Should I add another drain at the bottom?

Thank you in advance.