Laundry engineering for flatwork – Part 3

26 March 2024



Richard Neale of LTC Worldwide looks at drying and ironing, with special emphasis on fire prevention, which he says is the biggest risk to a laundry


This month we conclude our miniseries on the laundry engineer’s role in the continued productivity and profitability of a modern laundry. The articles in the November 2023 and January 2024 international issues, and in this current issue, together comprise a comprehensive overview of what your laundry engineer needs to know in order to maximise your laundry’s potential. You may want to keep these as a training syllabus for your team, because technology has moved very fast in the UK industry over the last ten years, and this should help to keep you up to date.

The next generation of tumble dryer?

Energy recycling from the hot humid exhaust air into the cold air intake has had a very mixed success rate over many years, but the practice of recycling a portion of the exhaust air seems still to offer the best chance of a worthwhile return, coupled with only a small increase in initial cost. The industry is still waiting for an intelligent recycling system, with a continuously varying proportion of recycle depending either on the exhaust humidity or temperature. Clearly the recycled amount has to be very low early in the cycle when the exhaust is well saturated with evaporated moisture, but this can safely be increased to near 100% recycle when the batch is almost dry, saving significant amounts of energy, without extending drying time by much, if anything.

Ironing

In order to achieve the savings at the dryers, by essentially eliminating conditioning, it is necessary to optimise ironer performance to maintain its previous quality and productivity. This means that the laundry engineer has to know how to tune an ironer to achieve its full potential. Each individual step in tuning is straight forward enough and easy to implement, but the sum total of these small steps can be very significant. Correct waxing, with a proper waxing cloth and the correct amount of wax applied at the correct intervals is a vital first step. Over-waxing or waxing with the vacuum fans switch on will result in blinding of the clothing surface, blockage of the vacuum ducts and increased risk of fire in the vacuum system. We have seen this type of fire occur!

The beds must offer a uniform temperature with no cold spots which means checking the traps regularly and the vacuum to the rolls must give the correct uniform suction across each roll to remove the evaporated water. The suction to each roll will need to be tuned separately, with the highest suction going to the first roll. The roll to bed fit must be adequate to give maximum roll to bed contact at uniform pressure and the roller speed differential must be geared to give the correct rollto- roll stretch. Adding a cover on the top of the ironer, if there isn’t one, can also help. Don’t forget to ensure the steam line feeding a steam heated ironer is fully lagged, including any flanges etc, to ensure the maximum steam pressure and therefore temperature is retained. Operate the ironer at the correct speed to optimise bed coverage. Ensure the ironer surface is cleaned with a scouring cloth regularly and check the leading edge of the first bed for a build-up of wax, lint and possibly starch, which will adversely affect the leading edge of items being ironed causing creasing. Only when all this has been achieved will the predicted quality, productivity and savings from eliminating conditioning in the dryers be delivered.

Steam-heated ironers rely heavily for energy economy on the selection and maintenance of their steam traps. These are designed to release liquid condensate into the condensate main, without leaking any live steam. The best choice of trap is one which releases condensate at the same rate as it is being produced, which calls for designs such as the float trap or the inverted bucket. There are several systems available for monitoring for leakage, some manual and at least one continuous and automatic. Energy efficiency is now such an important component of laundry costs that it is absolutely imperative that every Laundry Engineer is trained in monitoring steam trap efficiency, with regular reporting to management.

Longer term, the laundry engineer may need to address clothing life and reclothing. Developments in clothing design and performance now make possible better air permeability with fewer turns of thicker clothing. Clothing life in hard water areas also depends on maximum dewatering in the membrane press, because hard water is more alkaline, even after softening. A decline in membrane press performance can often be accompanied by degradation of the surface of ironer clothing, caused by alkaline hydrolysis of the outermost layer at high temperature, especially on the first roll.

An ironer depends on the resilience of its springs and the life of these can vary considerably. If a duvet cover goes forward with an undiscovered pillowcase trapped inside it, the resulting localised increase in pressure when this goes through the ironer can cause permanent deformation to some springs, which will then need replacement – a skilled task with unwanted downtime. Acid corrosion of springs is an equally prevalent problem, especially where a tunnel is being dosed with acidic chemistry at the end of the rinse zone. The high temperature in the ironer accelerates chemical damage, even from very dilute acidity.

With the goal of elimination of fossil fuel combustion in the UK and the potential demise of the central laundry boiler, the options for a direct gas fired ironer (to heat thermal oil to the beds) are likely to be a blend of natural gas and hydrogen (for a few years), or (ultimately) hydrogen alone. Firing with a blend of natural gas and hydrogen will probably be available for at least 10 years, but this is still subject to trials now in progress and will almost certainly be more expensive. Long term, the price of green electricity, from hydro, wind, solar, tidal and wave generation, might bring the cost of this down to below the current gas price, but that is well into the future. Decarbonising and upgrading the capacity of the National Grid in the UK, and investment in renewable generation will cost billions of £, so meeting this will keep prices high well into the medium term (beyond 2050). The design problems of embedding electric heating in the ironer beds have not yet been solved at an industrial laundry level (to avoid cool spots) although widely used in OPL laundries and smaller plants, so it may be that initially at least, electrically heated ironers may rely on an internal/external thermal oil heater.

Fire prevention

Fire is the biggest risk in a laundry. Laundry fires are generally foreseeable and preventable, if the laundry engineer knows how to foresee and prevent them. Fires that occur during the working day are often the easiest to deal with, because there are staff on-site who can check for tell-tale symptoms and respond appropriately. For example, fires in a tunnel finisher caused by an exploding lighter which was missed in the pocket check can often be extinguished very rapidly, provided there are adequate extinguishers of the right type readily to hand and staff are trained in their use. It may be possible to retrofit an automatic quench triggered by a fusible link, (some tumble driers have an inbuilt fire suppression system currently) but it is essential for engineers to check that when the link melts, the quench valve does actually open. In many checks, this is found to have seized up and a six-monthly test is needed. Its also important to be aware of any legionella risk with these systems.

However, quench and sprinkler systems do not prevent fires, they only help to ensure that when one breaks out in an empty laundry this does not result in total loss. The fact that the most serious laundry fires occur in the middle of the night means that better systems of prevention are needed. The most common cause of laundry fires is spontaneous combustion, usually around the dryers or in the finished goods area. The cause of spontaneous combustion is generally poor removal of oily contamination from textiles, followed by drying, folding and stacking. If residual oils are left on warm textiles, they can start to oxidise by chemical reaction with the oxygen in the air. This reaction is exothermic – that is it gives off heat. If this heat is prevented from dissipating because it happens in the middle of a warm pile, then this will accelerate the oxidation reaction. After a time (usually several hours) the reaction will produce so much heat that it reaches the autoignition temperature of the contaminated textile and the entire pile will ignite, and the fire will spread rapidly if lint levels are not well controlled. Fires of this type are unusual, but they occur on average one to three times a year in total in the UK’s large laundries, with many more occurring in small OPL and medium sized laundries. They nearly always result in total loss of the laundry, the buildings and the contents.

Spontaneous combustion is avoided by good washing, with special provision for incoming textiles contaminated with oily material. For example, spa towels and spa sheets are known to be very susceptible to spontaneous combustion and the first preventative step is always to wash these with an emulsifier geared to the removal of highly refined essential oils (with an HLB (hydrophilic lipophilic balance) value down towards 7 . The second check is to regularly sniff the dried towels as they are discharged from the dryer. If they still have an odour of essential oils, or (even worse) a rancid odour of degraded oils, then they must be immediately sent for a recovery wash. In practice, if the correct emulsifier is used, the recovery wash is rarely needed.

Conclusion

The role of the laundry engineer is changing out of all recognition. As laundering and textile rental enter the new age of zero carbon emissions and modern efficiency, productivity and profitability. The best launderers have recognised this, and it is central to their ongoing success.

Tuning the membrane press cycle is vital to energy economy and high productivity at the ironer and tumbler
Key points to check when tuning the ironer
FIRE RISK: Poor removal of oily soil from chef’s trousers is a sure way of creating a pile of warm finished goods which are liable to spontaneous combustion, especially if you adopt low temperature washing with the wrong emulsifier
MIDNIGHT PERIL: Poor washing of oily soiling, leading to spontaneous combustion in the middle of the night, is still believed to be behind most laundry fires


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