Filtering and Dewatering

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Water in WVO

Implications of Water in WVO

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Standards releated to water in WVO

See Also: Fuel Standards

Dewatering Overview

Settling

Example of insulated settling barrel. Shown here is insulated barrel with gear pump, sock filter, heating element (note electrical cord & plug) and drain valve at bottom.

Most popular seems to be the settling method. The oil is prefiltered to 10 microns or less and the water is allowed to drop out of the oil by keeping the oil completely liquid but avoiding strong convection currents. It is always difficult to add heat and not create currents. A good way to do this is to add outer insulation to the barrel, such as fiberglass home insulation wrapped around it.

Settling out water also has the advantage of removing water soluble contaminants. Typical settling time is about 24 hours in a well-designed unit. Settling CAN take a long time, several weeks, if the WVO is not prefiltered or is too viscous/not heated sufficiently.

Benefits:

• Low cost.
• Simple to set up.

Drawbacks:

• Settling CAN take a long time (see above.)
• Can be difficult to keep oil hot without creating convection currents. In cold climates where the temperature dips below 65*F, outer barrel insulation is required to hold heat in.

Vacuum Dewatering

Vacuum dewatering uses a combination of vacuum and heat to cause water to "boil off" as vapor. Unfortunately this leaves behind most water soluble contaminates. If the WVO is not washed prior to dewatering this method will condense any water soluable contaminants (sugars/salts/acids) to the point that the water they ARE dissolved in will not boil off. Deep Vacuum (50-250 microns) of pressure is required to boil water at room temperature.

Links:

• Pressure Corrected Boiling Temperature Of Water Calculator.

Benefits:

• Fast dewatering

Drawbacks:

• Must pre-filter and/or wash oil.
• More equipment needed:
  • Source of heat
  • Source of vacuum
  • Container structurally sound enough to hold the WVO and vacuum without imploding or crumpling.

Centrifuge Dewatering

The best but most expensive method is using a centrifuge. Traditionally too expensive for most to consider, although cheaper centrifuge products introduced to the market lately have started to change this.

For a full discussion of centrifuges, see Centrifuges.

Benefits:

• Filters and dewaters at the same time.
• Very fast - hours instead of days/weeks/months.

Drawbacks:

• Expensive relative to other options