Evaluation of washing Methods:

WET WASHING:
A wet wash, using water, is commonly used to remove production residues and impurities from the fuel. A fine water mist is spayed over the fuel and as the water settles to the base of the wash container, the impurities are collectively removed. Once the effluent waste has been drained off, the water (one of the most harmful contaminants) then needs to be effectively removed from the fuel to below 500 ppm in order to meet international industry standards. This is usually a very expensive and time-consuming process.

However, wet washing has become less popular in recent times. Poor quality methyl esters are troublesome to wash using this method.

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Additional disadvantages include:
Inadequate water supply
Geographical location; authority restrictions
May require pretreatment, e.g. hard water

High soap levels can produce emulsions -“Gloop”
Poor separation and long separation time
Potential loss of product

Time and cost of drying your BD

Effluent treatment - disposal costs

DRY WASHING:
Dry washing is becoming increasingly popular in biodiesel production. Dry washing methods allow for a strong affinity for polar compounds eg.methanol, glycerine, glycerides, metals, soap.
Dry washing is a simple process that eliminates the need for wet washing. This reduces fresh water usage, disposal costs and significantly reduces your overall operating costs.

What are the main Advantages of “Dry Washing” over “Wet Washing”?

Time:
The common denominator that links all producers of biodiesel is that the demand for the product is always greater their ability to supply. With biodiesel now becoming increasingly attractive to end users due to the environmental and cost saving advantages, producers are looking at streamlining production to cope with the spiralling demand of biodiesel.
Bio-diesel that is “dry washed” can be ready for use in a few hours and is significantly quicker to produce than “wet wash” fuel. As water is not used in a dry wash, producers can at last keep up with demand and eliminate production bottle-necks so common with wet washing.

Cost:
In addition to the ever-increasing cost of water and the significant expense of water-removal machinery, disposal of effluent water is often the largest single cost during this stage of production. Environmental agencies are vigorously discouraging illegal disposal of effluent waste. Imminent closure and hefty fines have been known to be imposed on those in breach of this.

Space:
Settling is the key to effective water removal. Numerous large wet wash and additional settling tanks are usually required for this. These tanks can occupy a large surface area. With Dry washing, space can be used more effectively and smaller, higher out-put production facilities are now a reality.

Fuel Quality:
As water is not added in the dry wash, achieving <500ppm water content in accordance with the industry standard EN14214 is now possible. By “wet washing” water is used to remove the impurities from the fuel. Once the impurities have been removed the water content is usually >1000ppm, making it expensive, difficult and time consuming to remove effectively.