Introduction

This topic covers the wool scouring process, presenting the principal objectives and functions of
the modern industry. Wool scouring is the only operation, other than carbonising, which is unique
to the early stage processing of wool fibre. Synthetic fibres are not contaminated to any
significant extent, and therefore are notscoured.
The term ‘scouring’ is generally used to describe a process that removes contaminants fromraw
wool, and includes all steps associated with the process – blending, opening, washing, drying,
packaging – and the steps involved in ‘cleaning up’ the effluent produced. Scouring is a critically
important step in wool processing. It must be carried out using technology that enables the wool
to attain its optimum performance in subsequentprocessing.
During the growth of the wool fibre it becomes coated with grease (more correctly called wool
wax), sweat salts (or suint) and contaminated with dirt, dust, dung and vegetable matter of
various kinds. For wool to be a useful textile fibre it is essential that all of these extraneous
materials be removed, and wool scouring plays an essential part in this. While wool scouring had
very humble origins and was very inefficient and labour intensive up to nearly 50 years ago,
today’s industry is technically advanced and makes wide use of sophisticated technologies to
minimise costs and achieve the level of quality demanded by the customer. Australia and New
Zealand have led the world in innovative scouring developments and the implementation of low
cost, efficient scouring ofwool.

While wool scouring in simple terms is the washing and drying of wool, in reality there are a
considerable number of other operations involved – opening, blending, mechanical cleaning,
baling, sampling and testing. On request, various types of chemical treatments may be carried
out in conjunction with the scouring process.
Given the importance of wool to the economies of Australia and New Zealand, efficient wool
scouring is vital. However, less than 10% of Australian wool is scoured before export while in
New Zealand close to 90% of its wool production is exported in scoured form. The principal
reason for the difference is that many topmakers around the world (who use mostly Australian
fine wool) prefer to control the blending and scouring of their raw material, whereas the majority
of woollen carpet yarn spinners (who use a considerable quantity of New Zealand wool) accept
fully-specified scoured wool blends which are ready for spinning.
Today’s industry is efficient in terms of energy, water and labour resources and is also
environmentally responsible. The days are long gone when scour effluent could be discharged
into a nearby stream, river or at the sea shore. Modern practices ensure that wool scouring
makes minimal impact on theenvironment.
The book by Stewart (1988) provides the most comprehensive coverage of modern wool scouring
practices. Other useful sources of basic information are the book by Teasdale (1995) and the
articles by Stewart and Jamieson (1987) and Christoe (1987). The review paper by Wood (1982)
outlines the major innovations in wool scouring technologies since the 1950s. Robinson (1991)
has authored an IWS Technical Information Letter, “A Basic Guide to Raw Wool Scouring”, which
is quiteinformative.
Significant developments in scouring technology have been achieved in the past 40 years,
especially in Australia and New Zealand. These developments are outlined in the reading
“Innovation in Wool Scouring Technologies”. Another reading relevant to this topic is “An
Historical Overview of Wool Scouring”.

Contaminants of greasy wool

Wool is perceived to be a clean, green, natural fibre. However, raw or ‘greasy’ wool is
contaminated with natural impurities, the type and level depending on the breed of sheep, and the
conditions under which the wool is grown. These impurities, which may be up to 40% (or more)
by weight, must be washed off before the wool can be used as a textile fibre.
The main contaminants are wool grease, suint and dirt. Wool grease, which is really a wax, is a
complex mixture of organic compounds called esters. It is produced by the sebaceous glands in
the skin of the sheep and occurs as a stable solid or semi-solid film around the fibre with a
melting point around 43oC. While wool grease is insoluble in water, a solution of water and
detergent forms an emulsion with wool grease to facilitate its removal from the fibre. Wool grease
is soluble in organic solvents such as ethanol anddichloromethane
The amount of wool grease (or wax) present on the wool depends mostly on the sheep breed,
with merinos recording the highest amounts. Crossbred wools, which dominate the NewZealand
clip, have substantially lesswax.
Suint, which is produced by the sudiferous (sweat) glands of the sheep, is dried sweat, consisting
mainly potassium salts of organic acids. In wool scouring liquors, at alkaline pH levels, suint has
detergent properties. The amount of suint also depends on the breed of sheep, with crossbred
wools tending to have higher levels than merinowools.
A third category of contamination acquired by the fleece is termed surface soiling, which includes
dirt, dust, faeces and vegetable matter (VM) such as burrs picked up when the sheepis grazing.
Traces of dipping compounds (for fly strike or lice) and branding compounds may also
bedetected.
If the level of VM contamination is high the wool may have to be carbonised to remove it.Certain
types of VM are more troublesome than other types and must be removed. A major proportion of
the wools requiring carbonising are from Australia and SouthAfrica.
Table 2.1 shows typical contaminant levels in the major Australian and New Zealand sheep
breeds.

Table : Contamination levels in Australian and New Zealand wools.

Source: Hart (1995).

Type of New Zealand Romney Australian Merino

wool
Minimum Average Maximum Minimum Average Maximum
Grease 2 6 9 10 15 25
(%)
Suint 2 8 12 2 6 12
(%)
Dirt (%) 3 8 13 6 20 45

The wide differences in the types and levels of wool contaminants help to explain why different
machinery and processes have proved necessary in wool scouring. For example, the large
amount of fine dirt on some of the fine wools from Western Australia is very difficult to remove
and thus low scouring throughputs are often necessary. On the other hand, high-yielding coarse
wool from New Zealand represents the other extreme in being relatively easy to scour with high
production rates possible.
While as much contamination as possible is removed as wool grease or sludge, a significant
proportion of the contaminants removed from the wool is discharged from the wool scour as an
aqueous effluent. The organic effluent load from a typical wool scour is similar to that of the
sewerage from a town of 30,000 people.
Due to the nature of the wool fibre and its propensity to felt, wool scourers are faced with a
dilemma – they must deliver a product free of scourable contaminants while minimising the level
of fibre entanglement. Generally cleanliness and freedom from entanglement are opposing
outcomes, (i.e. the cleaner the fibres become the more entangled they are likely to be after
scouring). Both characteristics significantly affect the subsequent operations in yarn manufacture.

The objectives of wool scouring

The principal objectives of wool scouring are to remove all wool contaminants at maximum
efficiency, with efficient energy utilisation and with minimum impact on the environment. Quality
control objectives for the scoured product are:
 To produce clean wool of consistently good colour, without causing excessive fibre
entanglement
  Achieving a specified moisture regain by efficientdrying
 Achieving an acceptably low residual grease and dirtcontent
 ToachieveacorrectwoolpHlevel(appropriateforsubsequentdyeing).
Freedom from entanglement was once considered to be the principal quality objective,assuming
that the removal of grease and dirt was satisfactory. Entanglement (or in the extreme case,
felting) results in excessive fibre breakage in subsequent yarn-making processes such as
carding. Fibre breakage has two undesirableeffects:
1. It reduces the mean fibre length in top and yarn, producing products of inferior quality,and
2. The processing yields, as measured by the combing tear in the worsted system, are reduced.
Fibre entanglement is most undesirable in the worsted processing system where it is important to
minimise fibre breakage, but is less critical in woollenprocessing.
More recently, the cleanliness of the scoured product has become more important to the industry,
largely influenced by the development of high speed machinery. Another important consideration
today is concern for the environment, which has changed the attitude of wool scourers in many
countries. This is because the pollution load associated with the conventional aqueous scouring of
greasy wool is extremely high. Today, reduction in pollution has become more important to wool
scouring than freedom from entanglement; adequate dirt removal and subsequent liquor handling
to ensure minimal pollution of the environment are important factors.
The factors that are important in achieving a clean, bright scoured product with a low level of fibre
entanglement are:
 Degree of opening given beforescouring
 Number of bowls in scouringline
 Detergent and buildersused
 Water quality
 Time of immersion in thebowls
 Temperature of scouringbowls
 Amount of mechanical actionused
 Efficiency of the squeezepresses.

A number of other key functions are performed in a wool scour:

 Blending auction lots together on instructions from the owner of thewool
 Using mechanical means to remove as much dust and dirt as possible prior to, and after,
scouring
 Carrying out optional chemical treatments as requested by the client, eg, peroxide bleaching
to improve the woolcolour
 Sampling the scoured wool fortesting
 Extraction of wool grease from the scoureffluent.

Fibre damage in wool scouring

Wool is a relatively weak fibre, compared to other staple fibres. During scouring, wool
experiences various adverse conditions which can lead to fibre damage and loss of strength.
Three possible sources of fibre damage in wool scouring are mechanical damage, pH and
temperature.
Mechanical damage will be fairly minimal since the actions of the moving parts in scouring tend to
be relatively gentle. Since wool is a protein fibre, wool suffers a loss of tensile strength when it is
wet. The nature of the protein chains in wool mean that the hydrogen bonds are dissociated in
aqueous conditions causing strength loss. Disulphide bonds can also be reduced in some
conditions, causing a further wet strength loss which is generallyreversible.
Wool can also become more susceptible to chemical damage in an aqueous medium since the
protein chains can be ionised and are attractive to small, charged molecules such as acids and
alkalis. Alkaline conditions are far more damaging to the fibre, and at pH>9.5 will cause yellowing
and damage to thefibre.
Thermal degradation of wool will occur with prolonged exposure to even relatively mild conditions,
such as those experienced during scouring. This degradation is also manifested asa strength loss
and yellowing. The appropriate conditions and controls within in wool scour should ensure that
the types of wool damage outlined here areminimised.

Aqueous scouring usingdetergents

Detergents are cleansing agents and they contain surfactants. The term surfactant is the
abbreviated form of surface active agent. A surfactant is a substance that reduces the interfacial
tension between water and other liquids. Surfactants are used widely in textile processing in
many forms, including wetting agents, emulsifiers, and detergents.
In wool scouring, water alone cannot remove the lubricant and dirt because water molecules
cannot penetrate the greasy layer to detach it from the fibre surface. To remove the fibre
impurities, such as the film of grease with dirt attached, it is necessary to transfer the greasyfilm
from the fibre into the liquor. To do this, the liquor must first wet the fibres. The presence of a
surfactant in a detergent enables water to coat (i.e. wet) a non-wettable (ie, hydrophobic) surface.
The wetting reduces the interfacial tension between the grease and the water, so that the grease
droplet detaches and floats away from thefibre.
A molecule is the smallest chemical unit of a substance that is capable of a stable, independent
existence. It is a group of atoms held together by chemical bonds. Molecules are attracted to one
another. For example, each individual molecule of water is attracted to others and they coalesce
to form a liquid. However, where the water molecules meet another substance such as grease, a
lower attractive force is present between the water and that substance. This lower attraction
means that the water molecules pull away from the contact surface of the other substance, and
so the water will not penetrate a greasyfilm.

Removing grease from wool

For effective grease and dirt removal the aim is to spread the water over the complete surfaceof
the fibres, loosen and remove the grease and dirt, and then suspend the molecules of grease and
dirt in the liquor so that they can be rinsed away. The detergent, with the required surfactant
properties, doesthis.
While there are various types of detergents (anionic, cationic, non-ionic), in general, a detergent
molecule has
a. a hydrophilic ‘head’ (which has an affinity for water and is repelled by oil and grease)and
b. a hydrophobic ‘tail’ (which has an affinity for oil and grease and is repelled bywater).
A simplified diagram of an anionic detergent molecule, and the way in which these surround a
blob of grease to form a tiny globule called a micelle, is shown in Figure 2.1.
 Figure2.1 Micelle formation by detergent molecules. Source: Wood,2011.

When the detergent molecules meet the layer of grease on wool fibres, the tails are drawn into the
grease but the heads remain immersed in the water. The attractive forces between the head
groups and the water are so strong that the grease is lifted away from the surface. The micelleis
now completely surrounded by detergent molecules and is washed away by the water. The
sequence of grease removal is shown in Figure2.2.

Figure2.2 Removal of grease coating from a fibre by detergent action, Source: Wood,
2011.

The stages of grease removal in the scouring bowl are:

1. Water is heated to above the melting point of wool grease, which is about 40°C. Theheated
wool grease forms a stable film over the surface of the fibre. The wool grease is more
attracted to the fibre than to itself, and this is why it forms a film over thefibre.
2. The scouring liquor wets thefibre.
3. Surfactant molecules from the detergent cover the film of grease. The grease-seeking tails
are attracted to the grease, with the heads in theliquor.
4. Surfactant molecules on the wetted fibre reduce the attraction of the grease to the fibre. The
grease rolls up intodroplets.
5. The water-seeking heads of the surfactant molecules on the fibre and on the greasedroplet
attract water to themselves. The water attracted to these molecules pushes between the
 fibre and the grease droplet. This helps to detach the greasedroplet.
6. Agitation by the harrows and the high-speed liquor flow at the squeeze rollers transport the
grease droplets away from thefibre.
7. Particles of dirt are removed from the fibreby:
- agitation of theliquor
- being washed away with the grease droplets,and
- mutual repulsion between fibre anddirt.
Emulsion stability is maintained when there is sufficient detergent in the liquor to completely
disperse in the water and surround the surfaces of all the fibres and grease droplets.
If the amount of detergent in the liquor falls below the required minimum level:
 There is a quick drop in the amount of wool grease removed from thefibre
 Droplets of emulsified grease may redeposit on the fibre because fewer surfactant molecules
surround thedroplet
 Droplets of emulsified wool grease may combine to form larger masses. This will, in turn,
break down the emulsion and form a layer of grease on the surface of the liquor. Again, the
reason is that fewer surfactant molecules surround each droplet ofgrease.

Removing dirt from wool

Dirt is harder to remove than wool grease and sufficient mechanical action by the harrows is
essential for good dirt removal. The squeeze rollers play a key part in dirt removal too. Pressure
on the squeeze rollers must be sufficient to ensure that:
 As much dirt and grease as possible is removed from the wool,and
 As little dirty liquor as possible is carried to the next bowl so that less dirt is re-deposited on
thewool.
It is important to remove as much dirt as possible during scouring to avoid problems in later
processing. For example, dirt in yarn can cause variable light fastness and inferior colours in
dyeing. Most dirt and impurities are removed in the first bowl, with the rest being removed in
subsequent bowls. After the last (rinse) bowl, almost all impurities have been removed, except for
about 0.1 - 0.4% of wool grease (in New Zealand), or 0.3 – 0.8% in Australia.
Research has shown that all the contaminants, not only the grease, can be divided into two
fractions – an easy-to-remove fraction and a hard-to-remove fraction (Christoe and Bateup 1987).
The former fraction comprises the unoxidised grease, most of the oxidised grease, readily soluble
suint and loosely held mineral organic and proteinaceous dirt (i.e. wool fragments). The latter
fraction comprises a small fraction of the oxidised grease, slowly-soluble suint, submicron mineral
dirt and flakes of proteinaceous contaminants adhering to the fibre surface
The current picture of contaminant removal from raw wool is as follows:
 Penetration of the grease by water and surfactant, followed by rapid swelling of bothgrease
and proteinaceous contaminants (ie, woolfragments);
 Formation of grease globules (unoxidised grease in particular) within the swollen matrix of
thecontaminants;
 Mechanical action causes most of this matrix to be displaced from the wool into the
surroundingliquor;
 The remaining contaminants, which still adhere to the fibre, are removed more slowly to give
a cleanfibre.

These findings have had important implications in the design of modern scouring lines. The result
is that optimal systems for scouring Australian merino wools are quite different to the standard
scouring lines designed for handling New Zealand crossbred wools. The major differences in the
properties of these wools that are relevant to scouring mean that rather more sophisticated
scouring lines are required for the gentler, thorough scouring required for Merino wools (see the
comparison of these properties in Table 2.1).

Table 2.1 Properties of New Zealand and Australian wools relevant to scouring
performance. Source: Wood, 2006.

Property New Zealand crossbred wool Australian merino wool

Fineness coarse fine

Staple length longer shorter

Fleece density open densely packed

Crimp/bulk low high

Entangling propensity lower higher

Grease content lower higher

Proportion of oxidised grease higher lower

Dust and dirt content lower higher

Suint content higher lower

Steps in the wool scouringprocess

Figure 2.3 shows the layout of a typical scouring plant for crossbred wools, which generally
require more extensive blending machinery.

Figure 2.3 Scouring plant layout. Source: Wood, 2006.

Blending, opening and cleaning

A consignment of scoured wool may comprise a large number of farm lots. Furthermore, the
components of a scoured wool blend may vary widely in their characteristics, especially for wool
destined for the woollen system. Therefore it is important that blending be undertaken to
amalgamate the components into a reasonably homogeneous batch, keeping in mind that further
blending will occur in the topmaking and spinningplants.
Figure 2.4 shows a blending line in a modern scouring plant. The system is computer controlled,
and each component has its own dedicated hopper, feeding to a common conveyor (at right of
photo).
 Figure 2.4 Blending system in a wool scour. Source: Andar Holdings Ltd.

Mechanical opening is carried out before scouring to:

1. enable dirt and dust to fall from the fibrous mass,and
2. deliver the wool in a more open form to the scouring bowls so that the liquor can penetrate
moreeffectively.
A range of machines is used for opening and cleaning. The early removal of dust and dirt in a dry
form contributes to more efficient and effective scouring. If fleeces are cotted, a decottermay be
required to be used as a preparatory opening machine to separate the felted fleecesinto
smallerclumps.
Because of the relative homogeneity of fine wools entering the worsted processing route, and the
huge amount of blending that occurs in this route, these wools require less blending before (and
after) scouring than coarser wools that are mostly processed on the woollen processing route.

Scouring
The open, blended wool is scoured in a series of bowls containing hot scouring liquor, followed by
cold and hot water rinses. The scouring water is normally around 60-65 oC, which is hot enough to
melt the wool wax (or grease). Detergent is added to help remove the dirt from the fibres and to
emulsify the wax so that it does not re-deposit on the wool.
Figure 2.5 shows the parts of a typical scouring ‘mini-bowl’, which is the basis of most modern
scouring lines.

Figure 2.5 Scouring bowl Source: Andar HoldingsLtd.

As the wool enters each bowl, it is pushed under the surface to wet it thoroughly with the liquor in
that bowl. A set of metal teeth (rakes or harrows) gently drags the wool through the liquor, as
shown in Figure 2.6. When the wool reaches the other end of the bowl it is lifted up into a pair of
rollers that squeeze the liquor out of it. The wool is then dropped into the next bowl where the
process isrepeated.

Figure 2.6 Immersed wool being moved by the rakes in a scouring bowl.
(Photo supplied by E J Wood)

The suint dissolves quickly in the first bowl while the wax and dirt particles are steadily removed
by a combination of detergent action, mechanical agitation and gravity, and by the pressure
applied by the squeeze rollers. As the wool moves through the bowls it becomes cleaner, and
moves into cleaner liquor.
The liquor flows in the reverse direction to the wool movement and is discharged from the first
bowl for treatment. Wool grease is extracted from this effluent and refined for a variety of uses.
Finally, the wool is rinsed to remove the detergent and to eliminate the remaining solids. The first
rinse is normally done with copious quantities of cold water, followed by a final rinse in hot water
beforedrying.

Fine wool scouring systems

The Andar Topmaster range of scouring lines exemplifies the most modern systems available for
scouring fine wools (Figure 2.7). The scouring line includes a suint bowl where dirt and suint are
removed while protecting the fibres from damage or entanglement. This is achieved by operating
the bowl at a temperature lower than the emulsification point of woolgrease.

Figure 2.7 A scouring line forcombingwools. Source: Andar HoldingsLtd.

Three different bowl configurations are available in the range, as shown in Figure 2.8. These
configurations, all based on rake bowls, are designed for high yielding, medium yield and low
yield wools. In each case the first bowl can be a suint bowl.
 Figure 2.8 Topmaster and Topmaster LE configurations for fine wool scouring.
Source: Andar Holdings Ltd. (b).

Also shown in Figure 2.8 are the configurations for the Andar Topmaster LE (LowEntanglement)
range of scouring lines. Using the most advanced scouring technologies and processes
(incorporating suction bowls in which a set of suction drums gently transport the wool), the fibre
entanglement of fine wools (which is of major concern to topmakers) is minimised.
Two versions of Topmaster LE scouring lines are available:
(a) High yield – designed as a specialist system for topmaking, to provide the highest levelsof
performance for all fine and superfine types. The six bowl line can include one suint bowl if
required
(b) Medium yield – this is a seven bowl system, with two rake action bowls to remove most of
the heavy contaminants before entering the suctionbowls.
The suction bowl design is shown in Figure 2.9.

Figure 2.9 Suction bowl. Source: Andar Holdings Ltd. (b).

Accompanying these fine wool scouring lines are sophisticated systems for the removal and
treatment of the various components of the effluent – water, woolgrease and heavy solids. These
systems are designed to minimise waste and the impact of scouring on theenvironment.

Coarse wool scouring systems

The WRONZ Comprehensive Scouring System with mini-bowls revolutionised the scouring of
coarse wools in the 1960s. Modern scours for carpet wools are based on this system and fine
wool scouring systems developed since then have been adaptations of the WRONZ approach.
Features of the WRONZ system were:
 small-volume mini-bowls minimise water and energyuse,
 The integration of the contaminant removal systems into the operation of the scour so that all
heavy effluent (i.e. that originating from the hot scouring bowls rather than from the rinsing
bowls) received treatment before discharge. Such treatment included the removal of fibre
and heavy solids and the recovery ofwoolgrease.
 Batchwise operation, where the scour bowls were ‘dumped’ to drain periodically, was
replaced by a fully continuousprocess.
 Liquor management also became better controlled, with the avoidance of bowl overflows and
the use of bowl-to-bowl flowback running in the opposite direction to the woolflow
 The ‘flowdown’ of heavy liquor to the drain was at a controlled rate that could be set
manually or automatically by measuring the clarity of theliquor
 Heat was recovered from the flowdown and used to pre-heat fresh water being fed to the
scour.

The entire system is computer-controlled. Figure 2.10 shows the WRONZ Comprehensive
System with seven mini-bowls.

Figure 2.10 WRONZ Comprehensive Scouring System. Source: Wood, 2006.

The WRONZ system with mini-bowls have been found to give the following benefits compared
with the traditional coarse wool scouring systems:
1. An increase in wool grease recovery of about50%
2. Recovery of about 80% heat from the effluent by using heatexchangers
3. Effective effluent treatment before discharge,including:
(a) maximum removal of heavy solids, fibres, and wool grease,and
(b) less discharge to about 2 litres/kg of scoured greasywool
4. Less water used through positive control. A set, regulated amountof:
(a) fresh water enters the bowls,and
 (b) scouring liquor leaves thesystem
5. Less energy or power is used. With less effluent discharge, less steam is needed to heat
the water. Heat recovered from the effluent also savesenergy
6. The scouring runs before bowl cleaning are longer. The liquor has a higher detergency with
a more effective contaminant removal, and so the bowls need washing out onlyabout once
a week. In the old system, the bowls were washed moreoften
7. Longer runs mean increasedproduction
8. Efficiency is improved and scouring iseasier.
The Cardmaster scouring system, manufactured by Andar, is the latest version of the WRONZ
Comprehensive Scouring System, with enhancements. This system is designed to handle the
rigorous demands and high volume processing associated with coarser carding and carpet wools.
This system is capable of processing in excess of 5 tonnes of wool per hour.
Figure 2.11 shows a typical configuration, with the three scouring bowls and three rinsing bowls.

Figure 2.11 Cardmaster scouring line. Source: Andar Holdings Ltd. (b).

Longer bowls are available for scouring low-yielding wools to provide a longer residence time and
maximise dirt removal at high throughput rates. Figure 2.12 shows a ‘quad’ bowl with four
hoppers, supplied by Andar.

Figure 2.12 Four hopper rake action scouring bowl. Source: Andar Holdings Ltd. (b).

The amount of wool that a single scour train can process depends on the width of the train – the
typical range is from 0.6 – 5 tonnes per hour. The wool passes through the entire plant (scouring,
drying and baling) in about 20-30minutes.
Dealing with scouring waste
Wool scouring produces a highly polluting effluent stream which is very difficult to degrade by
biological microorganisms, especially the grease component. Other components of the effluent
include pesticides, which are applied to wool to control various sheep parasites, and potassium, a
nutrient which is contained in the suint. All pose significant problems in effluent treatment and
disposal. A typical scour produces an organic load in its effluent that is equivalent to a town of
around 30,000 people.
Dealing with the effluent provides one of the biggest challenges in a wool scouring business,
which is often faced with increasingly stringent regulations. These demand an environmentally
responsible performance in all aspects of wool scouring operations and sophisticated systems
are now used to ensure that scouring wastes are dealt with efficiently and responsibly. The
principles of waste minimisation involve (Figure 2.13):
1. Reducing the generation of waste through the recovery of wool grease (woolwax);
2. Reusing any waste where possible. While the waste cannot be used directly, the reuse of
process liquors by passing them through contaminant recovery loops maximises the reuse
of water andchemicals;
3. Reclaiming waste that cannot be reused. Ideally, all scouring wastes should bereclaimed;
4. Recycling as much unused reclaimed material as possible. If all the available water in the
effluent was recycled, then there would be no liquid effluent discharges to the environment.

energy
INPUTS rawwool water
chemicals PRODUCTS

scoured wool
Recovery
Scouring loops
loops
reuse
reus recovered
e wool wax

recycle
recycle
fertiliser

Sludge
Sludge
treatment
treated sludge

WASTES
effluent

Figure 2.13 Waste minimisation in wool scouring. Source: IWS

 Primary treatments
Basic (ie, primary) treatment systems involve combining the various aqueous discharges and
after centrifuging these are discharged from the plant with or without further treatment. Only a
proportion of the wool grease and dirt (around 30%) is removed from the recovery loops that
continuously treat the scouring liquors before returning them to the scour. The remaining
contaminants are discharged from the scour as waste water.
Modern scouring effluent treatment systems:
1. Reduce the amount and variability of thedischarge,
2. Remove settlable solids and fibre,and
3. Recover as much wool grease and heat aspossible.

Figure 2.14 shows one such system as developed by WRONZ (Wool Research Organisation of
New Zealand).

Figure 2.14 WRONZ effluent treatment system. Source: IWS

A counter-flow system is used, with the liquor flowing from the first bowl passing through a
primary dirt removal stage and then to a grease centrifuge. A proportion of the partially degreased
water is returned to the first main scouring bowl.
Different techniques are used to remove the various types of pollutants in the scour effluent:
 Fibre removal is carried out on hot liquors using screens, which must be cleaned at regular
intervals to remove grease andgrit.
 Suspended solids removal is carried out in a settling tank where the particles of dirt fall to
the bottom of the tank to be removed as asludge.
 Grease removal is the major pollutant and about 45 - 50% of grease can be removed by
centrifuging.
 Heat removal by heat exchangers reduces the heat content of the primary effluent before it
isdischarged.
More complex (secondary and tertiary) treatment systems enable more wool grease to be
removed from the effluent stream, and reduce the amount of water and solids discharged to the
environment through the recovery of various components for use as fertilisers etc.

Other treatments
Wool scouring, as a wet process, also provides an opportunity for various chemical treatments
that may be undertaken in the scouring or rinse bowls. For example:
 Hydrogen peroxide is often used as a bleach to further brighten good colour wools
 Sodium metabisulphite is sometimes used as a bleach to reduce the yellowness of average
and poor colourwools
 Insect resistant (i.e. mothproofing) chemicals may beadded
 Organic acids such as acetic or formic acid can be added to adjust the pH of thewool
 A bacteriostat may be added to sanitise wool destined for beddingproducts
 Various ‘fibre differentiation’ treatments that modify the lustre, dyeability and other wool
characteristics are conveniently carried out as wet processes in a wool scour.

Drying
Drying is a crucial part of wool scouring. Once the wool has been squeezed for the final time it
may still hold 50% water (by weight), while the scourer’s clients will require the wool dried to a
precise level at around 16 or 17%. The wool is dried by hot air in a chamber, with the drying
process being monitored by a computer-controlled sensing system that ensures that the required
moisture level (or regain) is maintained. Figure 2.15 shows the three main types of dryers used in
wool scouring: suction drum, conveyor dryer andUnidryer.

Figure 2.15 Types of dryers using in wool scouring. Source: Andar Holdings Ltd.

Scoured wool handling

Dried, scoured wool may be further processed, mainly to remove any dust remaining and to
provide further opening and blending. A widely used cleaning machine is the stepped opener
blender, as shown in Figure 2.16. As the wool is moved up the ‘steps’ by the spiked rollers, the
dust falls through perforated screens and is removed by a vacuum duct.
 Figure 2.16 Stepped opener blender. Source: Andar Holdings Ltd.

Finally, the fibre must be either packaged for shipping to a mill, or presented to the next stage of
production. If the scoured wool is to be moved within a plant, conveyors or pneumatic ducting are
used. Alternatively, wool may be pressed into farm bales (around 130 kg) or into high density
bales (300-450kg).
Packaging scoured wool in high density bales, restrained by steel bands, minimises the volume
that each bale occupies in a shipping container and hence reduces transportation costs. The bale
wrapper, which is a nylon or polypropylene fabric, protects the wool from soiling and
contamination until the bale is opened for subsequent processing.
It is usually required to regularly take samples of scouring production for quality control purposes
(ie, in-house testing) or testing by a test house (for certification purposes). A set of narrow tubes
with sharp ends are driven into each bale to extract a representative core sample of wool for both
testingpurposes.
Figure 2.17 shows a high density bale at the core sampling station.

Figure 2.17 Core sampling of a high density bale. Photograph supplied by E J Wood
Conclusion
In simple terms wool scouring is the high production washing and drying of wool. However, there
are a considerable number of other operations involved including opening, blending, mechanical
cleaning, baling, sampling and testing. While the principles are the same for scouring fine wools
and coarse (carpet) wools, there are significant differences in the scouring systems used for them.
Wool scouring also provides the opportunity for other chemical processes to be undertaken. The
treatment and disposal of effluent to recover heat and wool grease is an important aspect of wool
scour operations.