Minimising energy costs and keeping them low

Commercial laundries probably lead most other UK industrial sectors in terms of productivity improvement, lowering energy consumption and raising water economy. However, there are still opportunities for further reductions in energy costs before significant investment in energy recycling schemes becomes necessary. The potential gains are available to be realised by sound management and modern practices, rather than reaching for the chequebook! This month we summarise the necessary thinking and training needed. The benefits will come from lots of little changes, so that everyone can match the market leaders, moving from a typical average of 1.6 to 1.7 kWh/kg dry textiles sold, down towards 1.0 kWh/kg. Some are now setting even lower targets, with 0.8 kWh/kg now seen as attainable.

Keeping track

Historically, laundries and rental operators have aligned energy (and water) monitoring with monthly accounting periods. A better option now is weekly monitoring, because the number of days in each period is fixed at seven days, so any small change in performance can be picked up precisely and acted on more quickly. You need to monitor kWh/kg and litres water/ kg to two places of decimals, because it is that final digit which you need to see moving remorselessly downwards if the business is to survive.

Gas, electricity and water meters are now far more accurate than they were twenty years ago, so direct digital readings are easy and reliable. Oil is less easy to monitor accurately, because it relies on the accuracy of gauging tank levels and you might want to consider measuring oil energy consumption over say four-week periods and using a moving 4-week average. Converting pieces of linen sold into kgs relies on an accurate average piece weight, which should be recalculated regularly (say every six months) for each classification. This is particularly important if you are planning to target reducing piece weights to reduce your total consumption (and raise productivity), even if your energy/kg figure is not improving by very much.

Steam and compressed air generation

At the centre of every commercial textile rental processing plant twenty years ago, there was usually a large boiler or two and usually more than one powerful air compressor. In the next twenty years, the large boiler can be expected to be phased out, because the loss of 20% of the energy in the fuel in the form of hot flue gas is increasingly unaffordable. All tumble dryers will probably be direct gas fired and the tunnel washers in the washhouse will be washing at 40C or lower, based on recovered heat. There will still be an air compressor, but this could be significantly smaller than at present.

Whilst many plants will still be operating a central boiler for a few more years, the importance of good boiler management to improve boiler efficiency will be even more vital. This should involve the Laundry Engineer and at least one member of the management team in checking the burner service report, the water treatment report and the annual insurance to ensure the following:

1. The air rate to the burner has been minimised throughout the firing range to eliminate excess hot air to the flue. This requires checking the % oxygen or carbon dioxide in the flue gas and comparing this with the target figures for the make and model of burner fitted. Typical avoidable losses from incorrect air rates are usually in the range of 1% to 3% of the fuel being consumed.
2. Once the air rates have been set correctly, the flue gas temperature, throughout the burner range, should be checked against the ‘clean boiler’ figures for your boiler. (These can readily be obtained from the new boiler commissioning report, or if this is not available, from the last burner report after any annual cleaning of the firetubes and smoke tubes.) There is no point in doing this check until the air rate is right, because too high an air rate will give an artificially low flue temperature and false reassurance.
3. The smoke number on an oil burner service report will indicate if any oil is escaping only partially burnt, losing its potential energy and so raising oil consumption unnecessarily.
4. One key figure on the annual insurance report is the thickness of scale formed on the outside of the firetubes. This should be zero; modern water treatment is designed to prevent scale formation. Even slight scaling increases fuel consumption (by up to 20% in extreme cases).
5. The monthly water treatment report should report chemical reserve levels of the treatment with the manufacturer’s target levels for comparison. The actual levels should be checked against the targets, because these control the risk of scale formation and the risk of corrosion, which affect not just the fuel consumption, but also any threat to boiler life.

In addition to these checks, every laundry should by now be utilising every kWh of energy in the condensate returned to the boiler. This is still the Achilles heel in many laundries. For every 5kWh of steam energy supplied to heat a calender, for example, there is another 1kWh sent back in the condensate main. Just putting this back into the boiler feed tank only recovers about half of this energy. A system is needed for recovering the rest (which is often represented by the flash steam venting from the vent on the boiler feed tank). This loss is frequently doubled by the additional leakage of live steam passing through faulty steam traps, resulting in fuel wastage totalling some 20%. It pays to get this right.

The air compressor is a sturdy workhorse, which will run satisfactorily for years provided the maintenance is correct (with oil changes at the right intervals). However, if the output of the compressor fails to meet demand and the system pressure falls, the immediate reaction of many engineering and management teams is to call in the supplier. The outcome of this meeting is usually a quote for a larger compressor, followed by a purchase order. This is often not the correct solution. The reason that a compressor fails to meet demand is rarely because it is too small (unless significant equipment additions have been made). It is often because the system leakages from piping joints and around worn seals means the compressor can no longer cope. It needs the leaks to be located (they are usually audible) and corrected. This can save not only the cost of a new compressor, but it will also cure the wastage of air (and associated energy), which has may have been increasing for some time. The long-term cumulative saving in electric power can be very considerable.

Textile selection

Modern textile rental demands a common pool of circulating stock, to maximise the economies of scale and eliminate marking and sorting of finished goods, customer by customer. However, there are more opportunities here. Energy consumption in laundering is heavily dependent on fibre mix and piece weight. At present energy costs, the initial purchase price of new stock could be less important than the first cost plus the lifetime processing cost.

100% cotton generally requires more energy for tumble drying and finishing, because a membrane press or high-speed spin leaves more moisture in the fabric than for polyester cotton blends. Dryng off moisture in an ironer consumes some five times more energy than membrane pressing or high-speed hydro-extraction. Tumble drying consumes up to fifteen times more (depending on the thermal efficiency of the dryer)! 50:50 polyester cotton should carry over 20% less moisture than cotton after dewatering, which translates into proportionate savings in drying and finishing energy, but the finished product does not match the 100% cotton equivalent in perceived quality, based on appearance, handle and breathability. The volume hotel rental market in the UK has reached a very successful compromise with cottonrich textiles for sheeting products, with both 70% and 80% cotton-rich products in use. However, 70% cotton-rich has captured the majority of the UK highvolume market, because its perceived quality, appearance and performance are sufficiently close to that of 100% cotton to be widely acceptable and it offers the greater energy saving.

The textile finish put onto the fabric by the cloth finisher is important. Historically, finishes on the warp yarns (put on to speed weaving and thus lower manufacturing cost) were not always removed adequately by the cloth finisher, resulting in fine irremovable creasing surviving multiple laundering for the first twenty washes or so (until the finish had worn away), significantly increasing rewash and refinishing costs. Most suppliers have now corrected this, by removing the finish before heat setting, but it can still occur, if the purchase specification is inadequate.

Towels are still predominantly 100% cotton, although there are several examples of makers strengthening the ground weave by blending polyester into these yarns to extend towel life. This should theoretically give a towel which is slightly quicker to tumble dry, raising productivity and reducing energy costs. There is also a slightly increased risk of greying in drying, but this has not been reported as significant, possibly because most greying of towels is the result of over-drying, alongside which the presence of a little polyester has only a minor effect.

By far the greatest improvements in energy requirement for ironing and tumble drying have occurred in those laundries which have carefully increased water extraction, with optimised spin times, or maximised time at pressure in the membrane press. These improvements have been followed in the best plants by fitting automatic cycle terminators in their dryers (based on infra-red detection of moisture in the drying textiles, careful setting up of these and regular maintenance to keep the sensors clean). Not only have they benefited from reduced energy and improved productivity, but the whiteness of the towelling is also maintained for much longer.

Conclusion

So far, we have only looked at modern energy management practices as regards boiler and compressed air management and textile purchase, which we believe will give rise to some significant savings in the majority of laundries. In a future article we look at washing, drying and finishing to complete the picture. In the meantime, we hope we have given you some food for thought and a demanding agenda, from which permanent benefits will flow.