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Thread: Creating partial vacuum without a vacuum pump to aid the drying of biodiesel

  1. #1
    Join Date
    Oct 2005
    Western Australia

    Creating partial vacuum without a vacuum pump to aid the drying of biodiesel

    I am planning to use partial vacuum in two parts of the processing WVO into biodiesel to remove unwanted water more quickly.
    Before adding to the Reactor, the WVO is cleansed and purified as much as possible to remove contamination that will hinder the transestification process. So the WVO is filtered to remove particulate materials, it is left to stand to let any free water gravitate to the bottom of the container so that it can be decanted, but any water held in suspension is not removed. So we can heat the WVO to drive off the water by "boiling", but this takes time and energy and heats the WVO to a temprature that then requires it to be cooled before adding the Acid/Methoxide, particulaly the Methoxide.
    So having a partial vacuum over the filtered and heated WVO during its drying phase allows a much lower temperature to be utilized to drive off any water held in suspension. The net result of this is that (1) the WVO does not need to be cooled before further processing, which means that (2) time is not wasted on unnecessary heating and cooling so that the processing takes place in less time and (3) money is not wasted on unnecessary heating costs.
    Again, after the washing of the biodiesel to remove any residual hydroxide, soap or methanol the biodiesel needs to have any excess water in it removed. Settling and decantation removes the free water that will gravitate to the bottom of the tank, but the suspended water needs to be "boiled off". This can be done by spraying the biodeisel to enhance the evaporation of the water, but this produces some oxidation of the biodeisel, an unwanted reaction.
    So heat is usually used with the attendant issues listed above and again using a partial vacuum allows a lower temperature to be used with the attendant benefits.
    So, using partial vacuum has real benefits.
    However, producing it is usually considered expensive - think vacuum pumps.
    A cheaper and equally efficient method to produce partial vacuum is to use an Aspirator, a device usually associated with laboratories. It uses Bernoulli's Principle better know as the Venturi Effect in a fitting that is attached to a tap and uses the flow of water through a venturi with the vacuum produced via the suction produced by the low pressure within the venturi.
    Look up "Aspirator" in Google and you will find info and pictures
    There is an added advantage in using a Aspirator. When drying either the WVO or the biodeisel, one may not wish to vent any fumes to atmosphere, in which case a condensor and associated condenate capture container would be used in-line before the vacuum pump or the Aspirator. Condensors need to have a flow of cooling water run through them for maximum efficiency, and so a happy win-win solution can be found for both needs of running water.
    To conserve water use within the condesor and operate the aspirator at the same time as the condenser so as to extract unwanted water from either WVO or washed biodiesel, a tank of 100-200 litres of water could be used to provide the fluid required by both devices: The water could be pumped from the storage tank through the condenser for cooling purposes, but then be used to produce the partial vacuum in the Aspirator - being discharged through air to the storage tank for settling before re-use. This discharge through the air back into the storage tank would provide partial cooling of the water through evaporative losses which would aid the effectiveness of the condenser. The partial vacuum produced by the Aspirator would allow any suspended water to boil out at close to 60o C thus “drying” the WVO or the washed biodiesel fairly rapidly. It would entail the use of a small water pump to circulate the water, but this is more sustainable than just wasting water for hours on end to work both devices.
    Sorry to be so wordy, but I think there is some merit in thinking about the whole process in terms of efficiency.
    I await any thoughts

  2. #2
    Join Date
    Sep 2005
    South West Sydney

    Re: Creating partial vacuum without a vacuum pump to aid the drying of biodiesel

    I've read that some people use vacuum pumps out of old fridges.
    Here's another simple method that uses a static head of water:

    I've got a venturi type device that works off compressed air, but so far I havn't had to use it. To dewater WVO I've had good success in just heating the oil to about 60C and let the water settle out. The oil is then the right temp for processing. I dry my washed BD by just bubbling air through the oil with an aquarium pump for about 24 hours, together with a small 12V computer fan blowing air across the BD surface in the open washing tank.

    Vacuum is a very efficient means to remove water and reclaim methanol, but remember that all containers will need to be rated as pressure vessels to sustain even a partial vacuum. IMHO, unless there a large volumes to be processed the I don't think it's worth the extra work and expense for small scale home brewers.

  3. #3
    Join Date
    Nov 2005
    Blue Mountains (West Of Sydney)

    Re: Creating partial vacuum without a vacuum pump to aid the drying of biodiesel

    I am going to be using an old 4 stroke lawn mower engine.

    Remove the engine from the mover chassis
    remove the carby and anything else thats not needed
    add a pully to the bottom of the crankshaft where the blade rotor is attached
    add an small electric motor and a drive belt

    you'll have to build a chassis of some sort to mount it all on and there you have it, either a compressor or a vaccum pump, take your pick !!

    Keep it simple, the old engine doesn't have to be spinning very fast to get a vaccum

    If you want to reclaim the methanol plumb it via an old beer keg, there stainless steel pressure vessels

    Fat Man
    Last edited by Fat Man; 14th December 2005 at 10:32 AM.

  4. #4
    Join Date
    Feb 2006

    Re: Cheap Vacuum

    Hi I created a mega-vacuum for another experiment using a 12V electric car tyre pump.

    Put the pump in a sealed cylinder or box, install a tyre valve pumping out to the outside world.

    My theory was that the pump should be able to pump ot the outside world until the vacuum inside is negative 60 PSI (below atmosphere)
    In reality
    What happened was the pump burned out because there was no air inside to take away the heat.
    And the mechanical pumping mechanism stops functioning efficiently when the air becomes too scarce.
    But it still achieves enough vacuum to boil water at room temperature.

    My suggestions
    1. Put the 12v tyre pump inside a steel or aluminium pipe.

    2. Ensure good heat conduction between the pump and the pipe so heat from the pump can escape.

    3 Install a 10 PSI blowoff valve or similiar pointing INTO the pipe (vacuum)
    (could obtain a ~20 PSI from a plastic garden sprayer).

    Now you have a regulated mega vacuum.


  5. #5
    Join Date
    Feb 2006
    Corio, Vic'.

    Re: Creating partial vacuum without a vacuum pump to aid the drying of biodiesel

    G'day Quentin,

    I'm only getting started with BD but you may find this Canadian site to be of interest to you, Joe the site owner is using vacuum: There are some good pictures of the full set-up.


    Who says you can't teach old dogs new tricks?
    This old dog has been learning new tricks for years and...
    I hope I can continue to do so!:cool:

  6. #6
    Join Date
    Nov 2005
    Hervey Bay, Qld

    Re: Creating partial vacuum without a vacuum pump to aid the drying of biodiesel

    Hi folks,

    I hear references to vacuum pumps for assistance in processing. I am again in the process of making one from an old freezer/fridge compressor. I have used these before but only with rubber tubing. This time it will be a bit more elaborate. This time its to pump out the oil from my hotel restaruarant source. To pump 120 Lts of qaulity oil once or twice a week with a 44 gll hand pump (60 pumps to fill 25 lt carboy) it aint a joke buddy? So once again the el cheapo vacuum will once again come to the rescue. I intend to pressure my drums with needle valves or scheader valvesand a cap with hose and a ball valve terminated with a clear PVC to watch for crud picup. No burnt out motors as the fill leave little left vacuum, so you dont have to be as attentive as a motor. I thought of using a 44Gll drum wit about 20' of pvc tube with a ball valve. On return to base reverse the process and use the other end put posivtive pressure in the drum and it will pump it out for you, saves a lot of grunts. Anyone like the schematic I will attach as a PDF file. This is sketch I saw recently with an extra bit than mine usually -- it has a relief valve.


    Last edited by dillyman; 12th March 2006 at 01:14 PM.

  7. #7
    Join Date
    Nov 2005
    Hervey Bay, Qld

    Re: Creating partial vacuum without a vacuum pump to aid the drying of biodiesel

    Sorry folks!!! I should have used the spell checker, I think I'd better have a bit of a rest on the bed. One of those days today!*%$^#^&


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