There has been much talk of warm rinsing as a way of reducing energy costs. By using a heat exchanger the effluent can be cooled and at the same time used to increase the temperature of the rinse water. Moving on from the energy savings of warm rinsing Christeyns, the European detergent manufacturer, has taken the process one step further by introducing a totally new washing process, the Sanoxy system, which not only offers improved bleaching and energy savings but also significantly lower water consumption with the added possibility of shortening the cycle time.

Conceived and tested in Holland in 1997 the Sanoxy system, at first look, defies all basic washroom chemistry. The bulk of the fresh water is put into the first compartment instead of the last-but-one. The entire press water is put back into the penultimate compartment with a small addition (0.5 cubic meters/h) of fresh water and the rinse drain is plumbed back into the wash zone.

By adding very little fresh water the temperature in the rinse zone remains relatively high. A heat exchanger is still recommended but whilst this is used to increase the temperature of the fresh water it is predominantly for use in the prewash area thus achieving the optimum temperature of around 35-38 degrees C in compartment 1.

Wash chemistry

The wash chemistry is also different, the majority of the detergent is now put into the first compartment rather than the middle of the tunnel. The bleach, in form of Sanoxy Liquid, is no longer added in the main wash zone but in the last compartment. By adding at this point, three advantages are gained.

• The acidic nature of Sanoxy Liquid neutralises the wash alkalinity without the need for an extra product (sour).

• The bleach contact time is significantly increased with both the wash and rinse zones being used (at 55-85 degrees C.) enabling better bleaching but with lower levels of chemical addition.

• The presence of Sanoxy Liquid in the press water automatically disinfects the press thus removing an often difficult recontamination hazard.

The additional savings in energy required for drying come, firstly from the more effective press extraction (the surface tension of the water is lower thus allowing more water to be extruded), and secondly from the fact that heat is often no longer required in the tumble dryers. These are only used to break up the cake as the residual humidity is already low enough for the ironers.

No negatives

oncerns regarding possible negative aspects of the process (chemical damage, high ash content or skin allergies) have proved unfounded. Whilst there are obviously relatively high residues of the Sanoxy Liquid in the linen these are relatively pH-neutral having buffered the residual alkalinity brought forward from the wash zone.

Test pieces have shown not only normal ash and silicate levels but also very low levels of chemical damage indicating further savings in textile life against typical chlorine bleach processes. Furthermore the Sanoxy process has been in use in several Dutch hospital laundries for more than two years without any skin complaints, either from laundry personnel or user.

Changes that are necessary to the continuous batch washer are limited to re-plumbing the water flows via the heat exchanger. A site survey can determine the exact time required but as a general guide modifications can normally be carried out overnight.

Savings achieved on a typical flatwork process represent 25% on water consumption and 35-40% on steam consumption (batch washer only).

Further energy savings in tumble drying and textile life will also offer significant money savings and by effectively combining the wash and rinse zones and giving the chemistry more room to work it is often possible to decrease the cycle times thus offering increased capacity.

The system has been extensively trialled in Holland for two years and further large-scale trials have been launched in both the UK and Belgium. Results so far confirm the experience gained in Holland and the trials will be expanded over the next few months. Assuming these are equally successful Christeyns expect to launch the system across Europe towards the end of this year.