The tunnel washer evolution

The tunnel washer concept was first introduced in the 1960s, a time when the laundry industry was undergoing great changes.

In the UK, the idea of continuous wash production was explored by Michael Ross, of Watford Steam Laundry, who installed the Baker Perkins Streamline in 1969.

This was effectively a hollow tube with an Archimedian screw welded down the inside to form a scroll. Its speed was controlled by jacking up the height at the loading end and cycle times varied.

Over the following years a number of manufacturers entered the tunnel washer market and each brought a raft of ideas to improve efficiency and productivity and to reduce total operating costs.

There is now a full list of options that can be incorporated in machine design: single or double skin construction or a mixture of both; top or bottom transfer of the work and fully adjustable water levels in each compartment as well as almost infinite control of the water usage and flow direction.

Most models offer the option of energy recovery and split rinsing is reducing water requirements still further. The market leaders are using detergent systems that require less than 2litres of water per kg of textiles.

The first mainstream tunnel washers were manufactured to take loads of ±35kg and had 13 compartments. This gave them an average output of 910kg (2,000pieces) per hour based on a total 30minutes cycle time.

Slowly the size of the tunnels began to increase from the 35kg unit through 50, 60 and 75kg to the 100kg units now available. The number of compartments rose and machines with up to 18 and even 23 compartments were made and installed.

Cycle times were gradually reduced to 24 – 25minutes as mechanical action increased with large-lifter designs and greater diameters. Machines with output levels now approaching 4,500kg (10,000pieces) per hour are becoming the mainstay of the larger laundries in the textile rental industry.

However, these larger machines began to encounter complications further along the production line. An 18 compartment machine operating on a 24minute cycle time will discharge 100kg of wet, clean work every 80seconds but the extraction units at the end of the washer often required 90seconds or more to achieve the optimum pressure to give the 45% moisture retention levels required.

This is essential not only for efficient use of water but also for efficient drying, especially of terry towels, as drying is the most thermally inefficient stage in the whole laundry line.

Even on a 30minute cycle time, the 18 compartment batch washer discharged a load every 100seconds and therefore membrane presses needed to be improved. They had to be able to achieve pressures of up to 58bar and to do so in a short time – certainly less than the 45seconds often required on the older style membrane presses, which only achieved 27bar.

The increased speed required to achieve optimum pressures in the membrane press also brought its own problems – especially when processing linen with a very high thread count or fabric that retained a lot of the fabric dressing (or warp sizing) that is applied during manufacture.

Such materials are often not very porous and air or water only passes through the material with difficulty. As a result the steep ramp up to high pressure in the membrane press caused larger items, such as sheets, to develop a pattern of small holes. This was caused by the air and water being rapidly forced through the fabric causing it to burst. Slugs of water proved to be a particular problem because water cannot be compressed so pressure on the slug tends to rupture the textile.

Recent developments in tunnel-washer rinsing and in de-watering technology are already starting to solve these problems.

Garment washing tunnels havefor some time used two hydro-extractors instead of one membrane press to solve both creasing and de-watering problems.

The Kannegeisser Jet machine brings the extraction stage into the body of the machine and carries out rinsing here rather than in a separate compartment.

The focus for development is also changing. In the early days, the tunnel washer was seen as the machine for the larger laundry and so research and development aimed to increase output and improve efficiency. A side effect of this has been a dramatic improvement in reliability.

A number of manufacturers have now produced compact tunnel washers to cater for the needs of the smaller laundries.

A five-stage tunnel washer that is double skinned so process parameters can be adjusted for different classifications and that works working on a 5 – 6minute wash cycle transfer time will produce 10 – 12 loads per hour.

If the machine handles a load size of 45kg it will produce 450 – 540kg (1,000 – 1,200 pieces) of work per hour so it is suitable for laundries processing 40,000 pieces per week.

A five-stage tunnel handling 35kg batches is economic even for laundries handling smaller volumes but probably needs to be worked for more than 40hours per week to give an acceptable payback.

I believe that the Girbau tunnel washer, which is available as a five-stage machine, is particularly interesting because the design greatly reduces the risk of blockage.

This is achieved by making the compartments, including the first one, identical and by controlling the water levels in each. This means that the machine will not attempt to transfer its load if the water level in any compartment is low. The company, which has around 1,000 tunnels in service worldwide, claims that this design virtually eliminates blockages.

An annual check on the Textile Services Associations’ cost index shows clearly how the global economy affects the laundry industry.

Comparing water consumption in a laundry in the 1960s with that in laundries today illustrates the large savings that have been achieved. The early tunnel washers used around 8litres per kg. Modern machines can reduce that figure to less than 2litres per kg by using advanced wash chemistry. Energy and chemicals use has been similarly reduced.

The focus on energy and water saving has clearly influenced the designer of a tunnel produced by German company Black and White (distributed in the UK by Broadbent Laundry Systems).

This uses two large beaters to re-create the “lift and drop” action of the washer extractor and has external weirs to improve the rinse efficiency (bringing the rinse requirement down from 4.7 to 3.5litres/kg).

The same “blue-skies” thinking has resulted in greatly reduced electric motor sizes for the membrane press and for the tumble dryers, just one symptom of a total re-design using the latest technology from other sectors.

The improvements in the speed of membrane press action and the detailed re-design of drainage of extracted water from the press basket that have been introduced by all the main suppliers means that it is now possible to justify replacing a press that is just five years old.

The same is true of tumble dryers, with broader burners and modulating air flow available from Kannegeisser and with Black and White, through a combination of airflow control, cage diameter and speed, claiming drying times below 14minutes for a 60kg load of 450gsm terry towels (including load, cooldown and unload).

The industry now has a variety of options for achieving energy savings and reducing its carbon footprint. The tunnel washer cuts water, energy and chemicals use as well as exceeding all the industry demands for meeting carbon reduction levels. Laundries that already use tunnel washers for most of their work will find that the improvements in tumble dryers and the membrane press offer further significant reductions.

However, I believe there is still room for further developments. Over the past 50 years we have reduced water consumption by over 90%, wash house labour by around 80%, detergent use by 75% and overall energy consumption by 40%. Surely our goal must be an industry that is carbon neutral, with little or no requirement for mains water.