Drying wet biodiesel

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Spray bar in operation drying Biodiesel. Source: jgs600

Introduction

After washing your biodiesel, it will usually have a slightly hazy or cloudy appearance to it. This is because there are micro droplets of water still in suspension in your just washed fuel - biodiesel has an ability to keep this water in suspension. Up to 500 parts per million is allowable by international quality specifications, but even at these levels your biodiesel should look clear.

There are several ways to remove the excess water which causes this cloudiness, but the main objective of them all is to expose the biodiesel to as much air as possible to allow evaporation of the water. This can be achieved by just leaving the biodiesel in a container with its top open to air exposure, but depending on the temperature of the air and how much it is circulating over the container, it can take from days to weeks to evaporate the water off and for the biodiesel to lose it's haze. Biodiesel dries more quickly or more slowly depending on how well washed it is (IE less soap = quicker drying).


Contents


Speeding up the drying process

There are several ways to do this:

  • Increase the amount of air contact with the biodiesel - use a larger open topped container.
  • Increase the movement of air around the container - use a fan to move the air.
  • Increase the temp of the air - warm air can hold more water vapour than cold air.
  • Bubble air through the biodiesel.

So far these options have concentrated on methods of getting air to the biodiesel, all of which are easy to implement, however there is another way, but it does involve a little more work to set up. It is the opposite of getting air to your biodiesel, instead to get the biodiesel to the air. This can be done by spraying biodiesel through the air in a fan pattern to achieve maximum air contact and evaporation. Experiments so far have shown that this seems to be one of the quickest methods of drying biodiesel. So long as the relative humidity is not too high, just spraying through the air should dry your biodiesel very quickly, however if the relative humidity is too high it will help to warm the biodiesel as well.

What you need to do

First it's best to have some way to warm your biodiesel up, possibly by using your biodiesel processor's heater, or by adding a heating element to your washing tank.

Secondly you need some way of pumping/circulating your biodiesel to get the biodiesel moving through the air; the outlet pipe from your pump needs to be fitted with a spay type nozzle or just crimped flat to give as much of a fanned out spray pattern to the biodiesel as possible, increasing the surface area of biodiesel in contact with the air.

Once you have the means to achieve these two things you are ready to dry your biodiesel quickly. Start by warming your biodiesel to 50°C (122°F), then turn on your pump to get the biodiesel circulating. Direct the spray of the pump outlet onto the inside wall of the tank; the more surface/air contact you can create the better the evaporation of the water will be, and the quicker the biodiesel will be dried.

Some notes

Higher temperatures will speed things up, although there is no need to go much higher than the boiling point of water. Heating the biodiesel to 110°C (230°F), turning off the heat and circulating/spraying for an hour should clear all but the wettest biodiesel. But as always remember that higher temperatures require extra care!

If you cannot work out a means of heating your biodiesel then good results have been achieved by using a hot air fan blowing across the spraying biodiesel.

Good results have also been achieved using an upturned dustbin lid in the top of the tank with some small holes drilled into it. This will allow the biodiesel to run across its large surface area, then down through the holes and back into the tank - again a hot air fan blowing across the dustbin lid could be used instead of heating the biodiesel.

See also