Opportunity to cut costs

Energy prices are still rising despite assurances from major UK energy producers that there is no reason to panic because available reserves still have thirty or more years to run.

Prices in the USA and the UK are more vulnerable to the new dependence on import reliability than global capacity.

The UK laundering and textile rental industries are big energy users and energy management now makes an important contribution to an operation’s profit – or loss.

Most UK laundries still have significant opportunities to cut their energy use and the ratio of best to worst is still close to three to one in terms of energy consumed per kilogram of work produced. Let’s look at some of the basic principles which are now driving the market leaders steadily ahead.

Steam generation

Most laundries rely on a shell boiler for steam raising with a steam space above the boiling water which gives sufficient surge capacity for those times when two or three washer-extractors call for steam simultaneously.

Some laundries still experience problems either with wet steam (containing water droplets) which insulates the heat transfer surfaces and slows everything down, or priming when a sudden surge in demand causes an abrupt drop in boiler pressure and the entire contents of the boiler become a foam. This rises and flows out into the steam main and can bring the entire plant to a halt for half an hour.

The solution to wet steam and priming is the same. Some form of throttle is needed in the supply to the washer-extractors so that however many calls for steam, for however long, the demand felt at the boiler is constrained. Most plants use a pressure-reducing valve and reducing the setting on this by half a bar will often cure the problem instantly. Others use a regulating valve and some use a section of narrow bore pipe, which is the cheapest but least manageable solution.

Most plants have now completed their steam pipe insulation and sealed up the leaks at flanges and valve stems in the process.

However, not all laundries have checked all of the steam inlet valves to the washer-extractors which usually leak a little steam steadily across the seat. These leaks are hidden from view which is why they frequently go unnoticed.

Even fewer plants have started work on their dip controls to reduce these to the minimum possible consistent with good washing and rinsing.

The old British Launderers’ Research Association advice that prescribed a 5inch pre-wash, a 3inch main wash and a 15inch rinse dip is now out of date in the present era of expensive water and even more expensive effluent and both costs are set to rise by around 5% above inflation every year for the foreseeable future.

Excessively high wash dips waste energy and high rinse dips waste water and incur unnecessary effluent charges. Optimising both will lead to improvements in wash quality and reductions in chemical consumption.

Energy consumption is directly proportional to load factor but this point is not reflected in load management in many plants, with under-used machines the norm at many times of the day. Where this is genuinely essential, a half-load program for the washer-extractor will work wonders.

Tunnel washers also suffer from an endemic tendency to operate below capacity, often because of a history of blockages or washover problems. Both of these can usually be solved by attention to the controls or water flows or weir settings, to produce major gains in machine productivity and reduced unit energy costs.

The first key to management of tumble drying energy is optimisation of moisture extraction during the high-speed spin in the washer-extractor or during membrane pressing at the end of the tunnel washer.

The target for terry towelling must be below 50% moisture, based on bone dry weight. This is because tumble drying is the least energy efficient process in the laundry with only 30% of the drying energy actually evaporating water to dry the goods, and the rest lost to the exhaust as hot air.

Achieving minimum moisture retention in the washer-extractor will need a final spin time of around 8min. It is generally false economy to settle for less because it is fifteen times more expensive to tumble dry the moisture than it is to spin it or press it out.

Tuning a membrane press, especially for a tunnel washer with a short cycle time, means maximising the time at full pressure so that work is squeezed ideally for a minimum of 1min with a 24bar press or 30sec with a 45bar unit.

Once the initial moisture content is correct, each dryer’s performance should be checked against its as-new performance and the slow ones serviced to bring the full dry time for terry towelling down to a typical 17min. A multi-roll ironer acts a bit like a large radiator, keeping the laundry warm in winter and making it unbearable in summer. This is the standing heat loss representing the energy consumed when it is idle or under-used.

In order to make this loss negligible, it is essential to keep the ironer running at full capacity all day. This can be assessed by looking at the bed coverage.

If the bed is as fully covered as possible, with edge-to-edge feeding and all lanes in use then all of its heat transfer potential is being used.

The size of the gaps indicates the magnitude of the waste. Linear speed is less important than coverage. If fully covering the bed gives rise to problems of damp clothing or poor entry into the in-running nips, then first take a look at the vacuum system, and second at the bed heating.

Condensate collection

Liquid condensate is removed from dryers and ironers via steam traps. A well-maintained trap will let the condensate out but hold back the live steam. A leaky trap will pass both through and in a typical laundry increase the fuel account by at least 10%. Every modern laundry needs one of the several proprietary techniques now available for trap monitoring, run fortnightly with prompt repair of every fault found.

Condensate produced by 8bar steam contains over 17% of the energy put into the original steam by the burning gas or oil in the boiler. This has to be recovered and used carefully.

There is too much to be absorbed into the boiler feed tank, which is why these have a steaming vent in most laundries. Efficient plants separate out the low-pressure steam produced in the condensate main by the high-pressure condensate. This ‘flash’ steam can be used to heat a tunnel washer (designed for this pressure), to produce a supply of hot water for the washer-extractors or to power a boiler feed pre-heater to raise boiler output. Laundries which do not use their flash generally need 10% more primary fuel than those which do.

To sum up, the laundering and rental sector in the UK is going into this winter with an energy bill which, on average, is at least 10% higher than it need be. Some smaller plants are still using double what they really require. But, almost every plant could reduce their energy use by 10% without making any capital investment. It can be achieved simply by disciplined application of the principles of sound energy management outlined here. It is an opportunity which is still available.