Workwear rental energy challenge

So far there has been much advice published concerning flatwork rental and the ways in which the impact of the Climate Change Levy can be neutralised by better technical management.

Garments generally have a higher price per piece so theoretically the garment rental sector ought to be better placed to absorb what should be a smaller percentage cost increase. In practice, margins in garment rental have been pared to the bone so dealing with a new tax is every bit as important in this sector as in flatwork.

Washhouse economy

Most food industry contracts need a two-wash process because the garments tend to be heavily soiled, the staining is quite difficult to remove and most customers call for near complete removal. However, there are still lightly soiled contracts around, or contracts in which the bulk of the work is lightly soiled, and for these it is often possible, with expert help from the soap supplier, to devise a two-stage wash without an intermediate drain, avoiding the need for a second fill and reheating. This requires superb suspension power from the detergent and it may work better with cotton goods than polyester cotton but it has to be investigated, contract by contract.

Of even more importance is the accuracy of the wash dips because modern dip gauges on washer-extractors are generally crude devices. Only the latest machines have microprocessors that accurately measure the number of litres of water for each stage, modifying this automatically if the batch is underweight. Controls of this type have now become a necessity for new equipment purchase.

Rinse dip

They are equally valuable in controlling the rinse dip, where the worst excesses of water wastage occur, although removing these will not affect the climate change levy. Water companies are becoming increasingly awkward about accepting high alkalinity wash liquors (and about accepting very hot wash liquors for that matter). The latest washing technology means that most detergent suppliers can now offer very effective processes at slightly lower alkalinity and slightly lower temperature, both of which need to be explored classification by classification. Not only will there be a saving at the washing stage but the amount of rinsing required will also reduce and quality ought to improve.

At present, most UK launderers work to Department of Health guidelines for disinfection, based on hospital recommendations that call for a wash stage involving a minimum of three minutes at 710C or more.

Across continental Europe, more and more launderers are using a combination of thermal and chemical disinfection, enabling wash temperatures to be reduced to around 600C. Most UK detergent suppliers have systems of this type available and now may be the time to investigate them. They need to go hand-in-hand with routine monitoring for any residual micro-organisms on the finished work, but advances in dip slide technology mean that this is an inexpensive routine that ought to be implemented anyway.

Lowest consumption

Organisations achieving the lowest water consumption generally make careful use of interspins, selecting the correct speed and spin time to extract as much rinse water as possible without inducing excessive creasing. The interspin after the first rinse is more critical than that after the second and if the engineer has an invertor drive on the motor it is possible to fine tune the second interspin with considerable benefit. It is usually possible, at the very least, to reduce the dip level of any third rinse.

The same degree of care is needed for the final extract. For some contracts, a short, fast spin will cause far less creasing than a longer slower one.

Of course the initial wetness of the garment influences not only the amount of energy needed in tunnel finishing (and also the productivity of the tunnel finisher in garments per hour) but it also has a significant effect on crease removal. The wetter the garment the better the crease removal (but the greater the risk of yellowing if the rinses have been incorrectly designed).

The drying temperature and the air rate then determine the speed of drying and generally, the higher the temperature the better, as far as productivity is concerned. The reverse applies to the cost of energy consumed which is usually minimised by slow steady drying with a good residence time within the tunnel.

So provided air can get down between each garment, loading on every peg will give the best residence time and it ought to give optimum drying. To achieve the maximum capacity of the tunnel this means that the fan has to be turning in the right direction (it’s amazing how often this is not so, especially after maintenance work), the air ducts and louvres need to be clear of lint and the screens need to be properly delinted on the upstream side, with removal of softener and any other wash chemical from the downstream side. It is the latter which often gets missed.

Tunnel drying is not a very energy efficient operation but it is improved dramatically by using the correct air recycle ratio. Reducing the recycle so as to lower the humidity in the drying zone might increase productivity marginally but this improvement is more than offset by the cost of the increased energy needed.

The most energy efficient tunnels in the industry are those that work steadily and continuously throughout the working day. Work which goes through in short sharp batches followed by long idle periods always involves much more energy consumption per garment, sometimes twice as much.

Direct gas-fired tunnels are generally easier to control and maintain at uniform temperature than those heated by steam. With steam-heated units it is vital to have dry steam at the correct pressure because even a drop of a few psi will reduce the metal temperature in the heater battery. To work efficiently the batteries need to be well trapped so that they drain completely and the traps need to be fitted with proper air vents to eliminate air blanketing. The best systems have adjustable air vents and steam traps positioned well below the battery they are draining.

  Energy economy

During the 1980s research trials were carried out using heat recovery systems fitted in tunnel exhausts to generate a stream of warm air that could either be ducted back into the tunnel or used for space heating. These systems require appreciable maintenance and do not save a great deal of energy so they have not acquired any popularity.

They really have been overtaken by much better air flow designs that ensure the air going to the stack is quite humid. This means that the heat transfer areas on plate heat exchangers would tend to get fouled up quite rapidly with oil and water and lint, producing maintenance costs out of proportion to the energy saving.

Rather more attractive is the concept of recycling last rinse liquor to create a reservoir of recovered water for wetting out, first wash and main wash. If this is heated by flash steam from the tunnel finisher it is possible to achieve a very respectable payback (typically twelve months) because a water saving of around 25% can be added to an energy saving of around 10%.

Benefits

Those organisations now using tunnel washing for garment processing have all the benefits of internal heat and water recycling but they can usually use the flash steam available (which still goes to waste in most plants) for direct injection into the tunnel washer, provided the washer has been designed for this (with injectors the correct size).

  Although, gearing up to cope with the Climate Change Levy in a garment washhouse will be a problem for the laundry engineer, much can still be achieved and the goal of neutralising the levy by careful design and management is still achievable.

Good hunting!