Prices:
Gas = R24 per GJ (GigaJoule)
Electricity = R0,18 per kW/h
Capacity 220 000 kg/month = 1,111 kg/hour
Steam = R45 per ton
Capacity of new equipment = 1,375 kg/h
Personnel = R14 400 per year
The capital cost of the proposed
equipment has been excluded but the capital costs would be recovered from the
savings within 3 years.
Side loading machines with no
built-in hydro extraction
The washing is taken out (usually manually) dripping wet from the machine, placed
into trollies and hand loaded into hydro extractors. From there the washing is loaded
into hydro extractors. From there the washing is loaded into trollies and either
tumbled dried or transported to the flatbed ironers or laundry presses. The machines
are reliable, unsophisticated and can take a lot of abuse. Few of these machines
are used for Third World situations. They are referred to, affectionately by some,
as the "donkeys" of the industry and by others as antiquated. They are
the most labour, energy, water and space consuming machines when compared to washer-extractors
and CBW machines but require the minimum of skilled maintenance. They are generally
used in medium sized laundries. They are available in models ranging from 2-140
kg dry weight per machine. These machines are manufactured in the RSA, USA and Far
East and heated by steam or electricity. See Figure 1 for an isometric sketch of
a side-loading machine.
Figure 1
Isometric sketch of side loading washing machine.
Washer extractor machines
There are many models available which differ greatly in sophistication from rigidly
mounted machines to others mounted on "hydro cushions" to obviate vibration.
For the non cushion type machines, vibration can be a problem if these machines
are mounted on floors above ground level. The various models take from 10-300kg
dry weight of washing per machine. As the name implies most of the washing
from these machines does not require further hydro extracting. Flat work can generally
be taken directly to drying ironers - uniforms, shirts, etc. would normally be tumble
dried prior to pressing and towels, etc. would be tumble dried ready for folding.
For convenience in this report washer-extractors have
been divided into four basic types:
- normal spin producing 80-90G
- medium spin producing 135-150G
- high spin producing 200-250G
- super high spin producing ±350G
The spin referred to above is the final spin of the
machines and the breakdown is fairly arbitrary.
The efficiency of hydro extraction is most effective
from 100-200G. Above 200G the amount of water extracted is more gradual. Figure
2 illustrates the extract efficiency of the G Force on the percentage of water retention
for cotton, poly-cottons and terry towels. From this it can be seen that water retention
in cotton goods decreases from 100% to 62% at 200G and to about 53% at 400G.
The normal, medium and high speed spin machines are
used most frequently in South Africa. The trend in Europe and the Far East is for
super high spin washer-extractors that are free standing and can be installed above
ground level, which gives total flexibility in positioning them. Further, these
machines can be installed with water re-use tanks, for greater water and effluent
efficiency. These machines are available locally but cost considerably more than
fixed machines.
Figure 2: Extract efficiency of "G" Force on the percentage of water retention
in various textiles.
Most washer-extractor machines are available with
or without water recovery mechanisms. For example, a washer-extractor with no water
recovery would use 20 - 25l water/kg work whereas one with a single water recovery
would use 15 - 20l water/kg work and one with a double water recovery would use
only 12 - 17l water/kg work. The most cost-effective schemes for water economy normally
involve integration of heat and water recovery.
Machines are available that are pre-programmed for
specific laundry types such as hotels, motels, health care institutions, shirt laundries,
commercial laundries, restaurants, etc. In addition machines are also available
with large variety of built-in programmes that can be chosen with the press of a
button.
Washer-extractors are used in small coin operated
laundrettes up to medium to fairly large laundries. They are the most popular and
generally the only choice for small to medium sized laundries in all First World
countries. They consume less labour, energy, water and space than side loading machines
but require more sophisticated maintenance skills than side loaders.
In the USA, as in South Africa, many institutions,
especially hotels and motels with in-house laundries, use poly-cottons for sheets
and pillow cases. These are the "wash and wear" type. The items are tumble
dried, folded and placed directly on the bed. Washer-extractors are used for the
laundering process. Some of these machines are programmed with a cool-down facility
for poly-cottons and care must be taken in the choice of machines for 100% cotton,
which is a popular choice for local hospitals. Aspects to look at are the gradual
temperature changes necessary for poly-cottons from the hot wash to the cold rinse
and the lower spin speeds - especially in some of the larger machines that take
30kg dry weight or more. Machines that allow for re-programming do not constitute
a problem.
In the hotel /motel industry, where poly-cottons are used, sheets, etc are sometimes
ironed to ensure a good appearance. This defeats the whole concept of the use of
poly-cottons and indicates poor washing and drying processes. (See also para 1.6)
The industrial machines use either steam or electricity for heating. See figure
3 for an isometric sketch of a washer-extractor.
Figure 3 Isometric
sketch of washer extractor washing machine.
Continuous
batch washing machines (CBW) (See also Appendix C)
These machines are only considered for large laundries (600 kg dry weight washing
per hour or more.) As the name implies, the washing can
be separated by textile compatibility into batches with a continuous throughput
of washing producing clean dry washing from the soiled state to the dry clean product
at pre-determined batch intervals. A tunnel washer does not just replace a line
of batch washers, it must be regarded as the core of a wash system. The installation
of a tunnel washer should dictate the end of 'ad hoc' planning of production through
the laundry.
The main differences between a CBW machine and a washer-extractor are as follows:
-
In a CBW machine the linen moves through the unit from one separate compartment
to the next. It spends the same times in each compartment, undergoing a succession
of specific treatments, which together make up the total laundering process.
-
The water and detergent/ chemical (liquor) movement is mainly contra-flow to that
of the work, flowing from compartment to compartment.
-
It is possible to control accurately the temperature, chemicals concentration and
dip level in most compartments. The design of the wash process for an existing CBW
machine thus requires a detailed knowledge of the machine being used.
The forerunner of these machines is the Archimedean Screw type. This type has small
washing compartments with a bottom transfer of water and at the time of writing
this was the type generally in use locally - mostly at Provincial central laundries.
In general terms the interior of a tunnel cage is designed as an Archimedean Screw,
each section holding a batch of work. Normal wash movement of the screw retains
the work in its position but a 360° forward turn of the screw moves the work forward
to the next stage of processing.
The tube or tunnel cage is therefore divided into processing sections which conform
to pre-wash, hot-wash and rinse zones, the work moving from pre-wash through the
machine and out after rinsing.
Movement of work is from the load end of the machine to the discharge point.
Water flow is from the discharge point to the load end of the machine.
A competitor on the market is the batch washer with larger compartments with a top
transfer of water. This type of machine has sealed water compartments which allows
modules to be added to increase capacity.
There are a number of different modules available. They are sophisticated with fully
automated washing transport systems and programmable chemical, water and timing
control systems. They are capital intensive but
if properly maintained and managed are the most economical in terms of labour,
space, energy and water. Regarding economical use of water, for example, a CBW machine
will use 7-10 l water/kg of work compared to a washer-extractor with a double water
recovery system which would use 12-17 l water/kg of work. To assist in a better
understanding of these machines see Appendix C.
These machines only operate with steam and as with the side loaders and washer-extractors
that use steam, the cost of steam generation (either existing or new) has to be
added to total cost. Steam is generally the best energy source for the large laundry
that uses either washer extractors or CBW machines. The smaller on-site laundries
generally use electrical water heating unless there is a steam generating plant
on the site, such as a hospital, using steam for other purposes. (see also para
15.3).
Productive output per hour is the key to most purchasing decisions in the laundry.
It is perhaps more critical in the case of a CBW machine because of its high capital
cost. This capital investment must enable the launderer to achieve a considerable
increase in output, together with other savings in running costs. How does one determine
the number of compartments? Brown states that two exercises need to be carried out:
The first part is obvious but the second, according to Brown, is not as simple as
the systems must be planned and designed to process the most difficult or most heavily
soiled work. If this is a small portion of the linen to be laundered, then a dedicated
washer-extractor(s) could be used for this work.
The problem of determining the wash process required
within the machine is briefly addressed in Appendix C. At the
early briefing stage clients and designers should consult with experienced
laundry consultants in this regard. Brown states: "Get the process specification
correct first, then look at comparative steam, water and chemical usage and don't
over-complicate requirements. Then look for the simplest, easiest way of meeting
your demands. The more complex the system, the
more problems you will get."
See Figure 4 for an isometric layout for a CBW system.
As stated in para 3.3, it is strongly recommended that "infected" work
is not processed through a CBW machine. This work should be processed through a
dedicated washer-extractor.
This information courtesy of Division
of Building Technology, CSIR.
