Developing a long-term plan for energy management

The laundering and textile rental sector is committed to reducing its carbon footprint by some 35% over the next five years. This calls for some long term strategic planning, which will impinge on purchase decisions for new plant and equipment.
This month's article takes an overview of some of the factors that need to be considered when drawing up the strategic plan.
There is no point in contemplating any investment at all until the basics of energy management have been implemented. This vital point is often overlooked in many plants. The payback on getting the basics right is often a very short time indeed but it does require thought and effort. Once the basics are under control, there is a bewildering array of options for the future design and operation of a low-carbon plant. These need to be considered carefully individually, but they also need to be linked together in the optimum way. Some plans realise short-term savings, only to find that the route chosen then blocks access to further savings down the line.
The most common example of this is the incorrect use of the heat in the flash steam from the condensate main. If the plan uses this to raise the temperature of the fresh water to the tunnel washer, it may preclude future heat recovery schemes from hot effluent and makes achievement of the 35% current target more difficult to achieve.

Getting the basics right
Before embarking on any plan for energy saving investment, it is vital to go through the basics and ensure that everything that can be done for free has been done.
This involves much management and engineer time but it cannot be skimped. For a laundry which has not yet taken these basic steps, the results of doing so can be startling; even just getting washer and tumble dryer load factors up to design capacities is still paying large dividends on those plants which are only now doing this.
The following are the key areas:
Insulation and losses: As a rule of thumb, at least 50mm of resin impregnated fibreglass with aluminium backing foil is needed on all steam pipes and fittings (but excluding thermostatic and thermodynamic steam traps, as these rely on cooling of the caps to function correctly). At least 25mm of insulation is needed on condensate pipe and fittings including the flash steam separation vessel, right back to the boiler feed tank. The latter requires 75mm on all four sides plus top and bottom. Typical distribution losses are around 10% of the fuel account and this can be reduced down to 1% to 3% with the right degree of care, taking insulation right down to the inlet valve for each machine. Other losses, such as leaks, are now down to a very low level on most plants, with the exception of leaks through steam traps.
Plants monitoring these in-house (the meter costs less than £750) on a two-weekly or four-weekly frequency will generally fare better than those that rely solely on an external assessment every six months.
Condensate losses: Many condensate systems have seriously corroded pipework and they leak hot condensate to drain. This is usually because of the alkalinity in the local water supply, which makes the condensate acidic. Condensate can contain up to 17% of the heat in the fuel purchased and you cannot afford to waste this. The flash steam should be separated out from the condensate main by using a small flash vessel and then put to profitable use.
It will then be found that all of the remaining heat in the liquid condensate is needed to keep the boiler feed tank above 80C, to maintain thermal economy at the boiler and to minimise thermal shock when the boiler is topped up with fresh water. The best use of flash steam is usually to replace mains pressure steam for direct injection into the tunnel washers by using slightly larger injectors so that these can be run on "free" steam. The typical saving is 10% of the fuel account.
Dips: There is no point in investing in heat recovery from hot effluent if even more can be saved with no investment by adjusting washer-extractor pre-wash and main-wash dips to the correct levels.
The best guidance for dip levels is still that given several years ago by the British Launderers Research Association (BLRA) and summarised in the BLRA Pocketbook. By getting these right you do not make more hot water than is needed, quality generally improves, water supply and effluent discharge volumes decrease and fill times and drain times are less, so that productivity increases.
Now to examine the five-year plan.

Combined heat and power
Generation of electricity on a laundry site was always bedevilled by the difficulty of getting the power and the waste heat into balance with the demands of the laundry.
This changed when the UK government arranged for power supply companies to purchase automatically all of the surplus power generated, as part of its commitment to reduce carbon emissions. Now all that a laundry needs to do is to select the size of the combined heat and power (CHP) plant to be installed, knowing that the power output will be taken care of.
This leaves the question of the waste heat. For the plant to deliver a good financial return there must be sufficient "free" heat to substitute for prime energy in the laundry and this heat must be in a form in which the laundry can use it directly. Most laundries rely on steam at 8, 10 or 12bar pressure.
The temperature of saturated steam at these pressures is 175, 184 and 192C respectively, which means that the flue gas from the generator exhaust must be appreciably above these temperatures in order to obtain heat transfer via small waste heat boiler.
If the flue gas exhaust temperature is say 235C, then generating 8 bar steam at 175C would cool this down to say 185C and recover a substantial portion of the heat available.
If the laundry uses steam at 12 bar pressure, then the flue gases can only be cooled to about 202C and much less heat will be recovered. This will make a significant difference to the pay-back on the investment.
Many suppliers of CHP equipment believe that the laundry has an insatiable demand for hot water at say 80C, which would in theory give a much greater heat recovery rate.
Unfortunately, the laundry demand for hot water is limited and likely to be reduced even further, so these savings are rarely available.
A mid-way solution is to generate low pressure steam at say 2 bar (134C) and take out enough heat to bring the flue gas temperature down to 144C.
This would probably be enough to power a couple of tunnel washers, fitted with enlarged injectors.
However, before embarking on this route, it would be wise to explore the economics of powering the washers on flash steam at 2 bar (from the condensate main), with a capital cost much lower than that for a CHP unit.
The first step when considering CHP is to draw up a schematic diagram showing the heat requirements of the laundry in each area in kilowatts.
These requirements are the essential flow-rates of energy into the equipment when the laundry is working normally.
On the same chart, the laundry engineer should mark the temperature at which the energy is needed and the present form of the energy stream (such as direct gas firing, low pressure steam, high pressure steam and hot water).
This is the information needed by the CHP engineers in order to work out the maximum amount of energy they can recover in a usable form and the cost of the equipment needed to do this. CHP suppliers are expert in this area, once they know the parameters, which they have to satisfy.

Latest process systems
There are two innovative systems, now fully developed, which are making useful contributions to carbon reduction.
The first makes use of "split rinsing" and takes this further than before.
An extra pipe and pump are used to draw relatively clean water from the press tank of the tunnel washer and inject this into the centre of the rinse zone. The effect is to raise significantly the rinse efficiency so that relatively little fresh water is needed into the last pocket of the rinse section.
The same principle is being used around the pre-wash, so that some of the liquor from the pre-wash drain is re-circulated back into the wetting out chute and first compartment.
The advantage of this is that some of the pre-wash make-up can be cold soft water, which enables temperatures below 40C in all pre-wash compartments. This allows protein staining and soiling on hospitality and healthcare textiles to be fully softened so that it is easily removed in the hot wash zone. It also solves the main problem with heat recovery on tunnel washers, which is setting of protein stains in too hot a pre-wash, resulting in staining of the entire circulating stock over a short time.
The second innovation in detergent technology is the maturity of low temperature washing systems which deliver the same performance at 40C as was previously attainable only at 75C. This is a major step forward, delivering both quality and economy with a step reduction in carbon emissions.
Two key developments have accompanied this innovation.
The first is the ability of these modern low temperature systems to deliver disinfection to healthcare standards (the UK's National Health Service usually demands a log 5 reduction in all viable micro-organisms).
Testing is generally undertaken by the Robert Koch Institute in Germany, who issue appropriate certificates.]
The second development is the recent acceptance by most UK healthcare customers of a disinfection regime which has the assurance of the system set out in the European Standard EN14065 and which may not rely necessarily on implied thermal disinfection conditions (such as 71C for three minutes plus mixing time). EN14065 relies on good practices and in-house and external monitoring to ensure that disinfection is achieved (which was overlooked in most systems based on implied thermal disinfection).
The ideas set out are not exhaustive. The opportunities described this month are just a few of those now available.