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Grease Recovery and Dirt Removal in Wool Scouring

 

GH Michell & Sons, Salisbury, South Australia

Industry contact:

Dr. Vincent O'Brien   (vincent.obrien@michell.com.au)

Moderators:

Dr. Steven Barry  ADFA    (s.barry@adfa.edu.au)

Assoc. Prof. Tim Marchant U of Wollongong (tim@uow.edu.au)

Company Background:

G. H. Michell and Sons now a family owned company was formed as a one man business in 1870 by George Henry Michell. Today it is the largest exporter and processor of Australian wool employing more than 800 people and servicing clients in 50 countries around the world including Asia, the United States, South Africa, and the European Community. While buying and processing wool remain the core business interests the company has also grown to become the largest processor and exporter of Australian hides and leather. Growing grain, raising sheep and cattle and developing property are also part of Michell's diverse interests. Today the Michell wool enterprise is run from an Adelaide base utilising excellent trading relations and long standing marketing structures around the world  as a basis for international business dealings.

Aim

To maximise grease recovery and dirt removal in the scouring operation through understanding the inherent flows involved in these separations processes and the influence of various parameters available to manipulation.

Background

Wool scouring is the process of washing dirty greasy wool once it has been removed from the sheep’s back.  It forms the first step in the processing of wool into a fibre and yarn and can impact on the effectiveness of all subsequent operations.

Impurities present on the wool can be classified into three groups, natural, acquired and applied. The natural impurities consist of wool grease and suint or sweat from the sheep. Acquired impurities include minerals and vegetable matter. Applied impurities include branding fluids, sheep dipping material and other pasture dressings.

 


The scouring process attempts to remove all these impurities from the wool with as little fibre damage as possible. Fibre damage occurs through the wool opening process prior to scouring, through chemical attach in highly acidic or alkaline conditions and through fibre entanglement through excessive agitation.

The scour bowls can be split into two sections separated by the horizontal grid shown in Figure 1. Section 1 contains the wool mat as it moves through the bowl. Section 2 houses the residual liquor and allows separation of the dirt and grease. The wool mat is moved through section 1 through the action of harrows. The harrows gently provide agitation to the wool through dunking it below the liquor surface and pushing it along the scour bowl. Section 2 contains four inverted tetrahedral shaped hoppers. Liquor is sampled from under the grid at the exit to the scour bowl for subsequent processing, (sample point 1).

Scouring is done on a continuous basis minimising chemical additions and water usage. This requires cleaning and regeneration of the scour liquors to stop the build up of contaminants. Scour liquors taken from sample point 1 are centrifuged to remove suspended dirt and to recover emulsified wool grease for sale before it is returned back to the bowl for reuse. Dirt is also removed from the scour liquor within the hopper through gravity separation. Periodic flushing from the base of the scour bowl purges the built up material.

In an effort to improve processing quality and production quality the scour performance is being addressed. Pertinent issues include cleanliness of the wool, entanglement of the wool, dirtiness of scour liquors and grease recovery. Information about scour bowl flows and their effect on these parameters can be generated through

  • Knowing the bowl concentration profiles for dirt and grease under standard processing conditions;

  • Knowing the variation of these with varying inflow and outflow rates;

  • The effect of wool processing rate, wool yield and grease removal rate on concentration profileles;

  • The potential of vortex formation and methods for avoiding them and

  • Optimum sampling point position to maximise grease removal and minimising dirt concentrations.

Work Required by GH Michell

        A complete description of an average scour bowl including dimensions and flow rates needs to be formulated including the typical range of these values;

       A basic model of the grease removal section;

       Collaboration about information most desired and assumptions necessary to get them;

       Experimental evidence to compare with simulation predictions

 

Results

        A complete description of scour bowl flows and the resulting distribution of grease and dirt concentrations;

        Optimum positions for sample point 1 to maximise grease recovery and dirt removal;

        The effect of wool processing rate, wool yield and grease removal rate on concentration profiles;

        The potential of vortex formation and methods for avoiding them.'

Benefits

The potential benefits for improving grease recovery and liquor cleanliness could be huge especially if we have stable vortexes or significant concentration gradients in the scour bowl. The information obtained will provide foundations upon which to make changes.