Laundry engineering for flatwork - Part 2

This month we continue our examination of the role of the laundry engineer and what they need to know to reap the benefit of the opportunities now available to streamline rental processing in particular, so as to maximise productivity while minimising operating cost. It is equally important to build in the changes which the laundry engineer is going to have to incorporate to accommodate the phasing out of fossil fuels (particularly natural gas). This will involve major changes in laundry design and needs to be thought out now.

Assembly of soiled textiles at customer premises

A major problem for the engineer is the continuing use of plastic bags, for collecting healthcare work, in particular. Although these facilitate colour coding, they introduce several additional problems, including safe sorting of foul bags, safe recycling of contaminated plastic, blockage of laundry pipework and fittings and molten plastic blocking perforations in the tumbler cages (leading to progressive deterioration in drying performance). The task now confronting engineers, in many laundries, centres on how to eliminate plastic completely before or during sorting. There may well be slightly different solutions for every plant, but they will have to be found by the individual laundry engineers and leading equipment suppliers. The key may well lie in a combination of automation including vacuum, robotics and pneumatics, with which every engineer will need to become familiar.

RFID identification involves the labelling of every rental item with a readable tag (capable of withstanding multiple laundering), so that rental operators can recognise changes in textile life, the emergence of regular theft issues, automatic handling through the production process, automatic assembly of deliveries and so on. The latest technology enables tag readers to scan an entire bag in a few seconds, reliably and with consistent accuracy (currently with an error rate of less than one in a thousand). If the contents are distributed automatically along the conveyor belt, then a suitable pneumatic system can blow each item into its proper classification for processing, eliminating the human operative from the hazards of the sorting area entirely. This would of course have to be combined with automatic elimination of metal and other solid objects, and automatic weighing, which are generally possible. Some suppliers of automated sorting systems claim they can separate a metal object from the textile with which it is entangled.

One important possibility for healthcare launderers is the possibility of automatic sorting of foul and infective work. This would require RFID or similar labelling of every item, or at the very least every coloured item. It then offers the possibility of eliminating colour contamination of white textiles mixed in with coloured items, especially in red bags (which are traditionally processed unsorted). This would create a step improvement in quality of white healthcare fabrics, by elimination of the progressive greying which at present characterises this market sector. The way is now open for the laundry engineer to achieve automatic handling of infective textiles.

Washing

Most volume laundries are processing all textiles through a tunnel washer, which will give high productivity whilst still maintaining good wash quality, with good whiteness retention and stain removal. The not so obvious points for the engineer to check regularly are the accuracy of chemical dosages and water flows (both of which could become incorrectly adjusted quite easily).

Ideally every volume laundry should have at least two tunnel washers, so that whites and coloureds can be separated. For maximum economy, healthcare launderers may be processing foul and infective work in a separate CBTW, which must be capable of being cleared (in the event of a blockage) in line with TSA guidance. It is important that the engineer knows the correct procedure for this. It is even more important that the Laundry engineer checks regularly for the fault symptoms that indicate high risk of blockage and eliminates these. They include calibration checks on automatic weighing equipment, tanks occasionally running dry, pump failures that do not automatically stop the washer and so on. These should be essentials on even the simplest of any Planned Preventative Maintenance schedule.

Minimum energy consumption is becoming more reliant on low temperature washing, which still requires accurate temperature measurement and control, so the engineer should be able to ensure accurate thermostat functioning and chemical dosage (with the correct low temperature chemistry,) to ensure good solubilisation of fats, oils and greases as well as successful stain removal. This means of course that disinfection must also be achieved at low temperature, because using implied thermal disinfection may not economic, especially with the high energy costs currently being seen across the globe. The Laundry engineer may well be best placed to monitor disinfection on a daily or weekly basis, preferably as part of an assurance system which meets the requirements of BS EN 14065:2016 (see LCN April 2023 issue).

Mysterious black marks (including ‘snakebite’ marks) frequently come from chemical and physical breakdown of compartment seals, gaskets, rubber hoses, rubber weir box seals and connectors. The trained engineer is well-placed to recognise and track these down very quickly (and save spoilage of the stock of circulating textiles). The best will ensure that items which display breakdown most frequently (such as the final intercompartmental seal on a tunnel washer and the membrane press rubber) are always in stock on-site. Some ‘black mark’ faults are the result of interaction between wash chemistry (particularly sour) and the flexible component, so they vary with equipment and process chemistry. It is always urgent to track down the source of black marks, because some laundries have ruined large quantities of the circulating stock, with very expensive replacement costs.

Efficient dewatering after rinsing is key to minimising tumble-drying time, and maximising both ironer productivity and the life of calender clothing, so it pays to get this right! Failure to extract the maximum amount of moisture in dewatering means that there is excess alkalinity going forward and this will create areas of degradation on the outer layer of calender clothing very rapidly, creating a ‘map of the world’ appearance. For a washer extractor, maximum extraction means spinning at the maximum speed possible for each classification, with a spin time such that spinning for another 30 seconds makes no difference to the moisture retention. A membrane press cycle should be adjusted to maintain the maximum pressure for a least 30 seconds (which might need to be increased to 60 seconds for an old press operating below 30bar). In any case, the longer the better, because evaporating an extra one litre of moisture in an ironer requires five times the energy of spinning it out. A tumble dryer requires fifteen times the energy! If a plant is suffering from ‘tumbler holds’, with the CBTW idling whilst waiting for a tumbler to become free, then the shrewd engineer will start the investigation at the membrane press! With high thread count fabrics (which might be prone to press bursts), it is often better to tamp a few times to get rid of the majority of the loose water, so that the pressure can then be ramped up rapidly with much reduced risk.

The Laundry engineer may well be the best choice to manage the level of bacteria and viruses in the rinse zone and press tank. Forward thinking launderers who have checked infection levels in the press tank have frequently been horrified at the concentration and composition of the microbes found, particularly in healthcare plants. All leading detergent suppliers can supply cleaning chemicals and advice on cleaning for this, to remove biofilm.

Any laundry processing polyester or nylon blended fabric will be contributing many millions of tiny plastic particles to its effluent on a daily basis. Tests have shown that the tiniest particles are not removed in sewage treatment and are discharged into rivers and ultimately the world’s oceans (where they can take up to 500 years to decompose). This is unsustainable and it is already leading to contamination of bottled water and the human bloodstream worldwide. It is only political inertia which is delaying legislation to ban this contaminated discharge and leading suppliers are already offering filtration units capable of reducing this to manageable levels. Implementation is not expected to be that expensive if planning is started now, so as to minimise disruption and capital cost.

Tumble drying

This is the ‘Cinderella’ of the laundering and rental sector, with major untapped opportunities in most plants. Energy efficiencies vary from 30 to 55%, with leading tumbler suppliers still striving for over 60%. Astute laundry engineers have long recognised the importance of membrane press tuning (and washer extractor spin cycles) on minimising energy wastage cost, but few have yet persuaded their production teams to eliminate conditioning of flatwork to be ironed. The ironer can offer thermal efficiencies of around 95%, so it makes sound sense to keep the tumbler time down to 30 sec or so on a tunnel washer line, and to eliminate tumbling entirely for sheets, pillowcases and table linen from washer extractors.

Direct gas-fired dryers have long been preferred by textile rental plants, because they offer much higher productivity than steam heated units operating at 8bar pressure. They also have enormous energy saving benefits over steam dryers, because they eliminate losses from boiler flue gas, steam system distribution and condensate/flash steam. Many healthcare laundries still opt for steam dryers because they cope with plastic bags slightly better than gas-fired ones (simply because the dryer temperature is limited by the steam pressure, so they do not run as hot). The solution is not to buy steam heated dryers for this reason – they are seriously wasteful – but to limit specify drums resistant to plastic adhesion, and drum panels that can be easily and quickly replaced for removal of plastic. This should be followed by a serious attempt to eliminate plastic bag contamination at source, so that you can get the full productivity and energy economy benefit of gas fired dryers without blocking up your tumblers.

Maximising tumble dryer performance

Dryer performance depends heavily on the correct airflow. On many plants this is only achieved immediately after the lint screens have been cleared, after which it slowly declines until the screens are cleared again. Automatic systems for continuous removal of lint are now available and it makes sound sense to instal these and optimise their working. Clearing lint screens is an outdated manual job best delegated to a machine, freeing operatives and engineers for much more advanced work.

Automatic drying cycle termination has been available for many years. In plants with correctly tuned and maintained terminators, it has proved to be a game changer. Although many such systems are sold on the basis of the saving in energy (with a payback of well under 12 months at current prices) they offer two other major advantages. The first is increased dryer productivity, with reduced drying times over the working day (coupled in turn with increased tunnel output from eliminating ‘tumbler holds’). The second is significantly reduced greying of towels by elimination of over-tumbling.