Keeping fuel costs in check

With oil prices peaking above US$30 per barrel, the industry can expect substantial increases in heavy and medium fuel oil and even natural gas prices this winter. Contract price increases of up to 50% are being reported.

However, a recent whistle-stop tour round several laundries shows that the industry can contain its fuel costs by good technical management, even before it considers a substantial investment in heat recovery.

Boilerhouse

The amount of heat lost each morning as boiler blow-down varies tremendously from site to site. Such variation often has little to do with removal of contamination from the boiler water down to an acceptable level. Most modern, shell-type laundry boilers are designed to operate with total dissolved solids (TDS) of 3500ppm. Operating above this level, increases the risk of foaming leading to priming and carryover of large quantities of droplets and froth into the steam main. This wets all the heat-transfer surfaces in the calenders and tumble dryers and sprays dirty water onto white coats in the tunnel finisher with fairly disastrous results.

Blowing dirty water out of the boiler reduces the level of dissolved solids, but there is no point in operating much below 3500ppm because the cost of the heat lost in the boiler blow-down escalates rapidly. In a typical boiler plant heat loss through blow-down might represent 2% of the fuel account. Trying to operate at 2500ppm or even 1500ppm can increase this loss to 6 or 7% of the fuel account. The lesson is obvious.

However, operating a continuous blow-down through a small needle valve mounted on the side of the boiler will generally produce around half the loss associated with opening the main blow-down valve full bore for a couple of minutes twice daily. Such reductions can be achieved even without an expensive automatic monitor. You should discuss this with your boiler water treatment supplier.

Insulation

Many laundries still have a surprising amount of bare pipe or bare metal at steam temperature. Investing in 25-50mm of resin impregnated fibreglass insulation, with an aluminium backing foil to prevent it getting wet and to keep it smart, will bring high financial returns in terms of the energy saved. Payback time is generally less than six months and the total saving will usually approach 10% of the fuel account. Repairing leaks at the same time as you sort out the insulation is a sensible move. If leaks are audible or visible they could cost as much as £100-200 per year for each one.

Overnight pressure

If you close the crown valve on top of the boiler each evening and if it seats properly, you should maintain a reasonable pressure on the boiler overnight, provided the boilerhouse itself is well insulated. If you prevent convection cooling through the fire tube in the boiler by using a flue damper or similar device, a boiler operating at 8bar could well display a pressure of 4bar when next fired up, even on a chilly winter morning.

Burner maintenance

The company which services your burner will usually produce a Burner Service Report which includes flue-gas analysis figures. You can use these figures to verify complete combustion. For an oil-fired unit the carbon dioxide in the flue gas should be above 13% and ideally will approach 14%. For a gas-fired boiler, the service engineer will usually measure oxygen in the flue gas. This figure should be around 9%. You will want to bring it down towards 8% without incurring the risk of carbon monoxide formation.

If you have a smoky flue, especially from an oil-fired boiler, it is time to check the efficiency of atomisation and the condition of the shaped quarls. (The brickwork around the burner inlet which promotes good air/fuel mixing.) You need uniformly fine droplet formation and smooth vigorous swirling of the air into this to eliminate smoke and smuts.

The efficiency of an oil-fired burner relies on good combustion together with effective heat transfer on the second and subsequent passes.

This means adopting a regular cleaning schedule for the fire tubes and sticking to it. A flue-gas temperature indicator will quickly show whether the fire tubes are sooting. When the boiler is absolutely clean and firing correctly, the flue-gas temperature at high-fire will be at a minimum. If you have a suitable temperature gauge available you can mark this minimum temperature on the gauge and then monitor sooting up. The greater the insulation provided by the soot, the more the flue-gas temperature will rise as waste heat goes out of the stack instead of being transferred to the boiling water. As a rule of thumb a rise of 15ºC in flue-gas temperature represents a 1% increase in oil requirement to meet the laundry’s steam demand.

Feed water temperature

A modern multi-stage Grundfoss feed-pump requires a head of at least 2m but at this temperature it will pump feed water at around 80degC (depending on the length of the pipe run and the number of valves and fittings) without risk of cavitation. Cavitation must be avoided to minimise bearing wear. At a head of 5m, most good feed pumps of this type will pump water virtually up to boiling point. Every 5degC reduction in feed temperature below the optimum represents a further 1% increase in fuel consumption, so it makes sound sense to optimise the feed temperature.

Simply mixing in the entire contents of the condensate main, including flash steam, will tend to give a boiler feed tank temperature of over 90degC, possibly as much as 100degC, so this is rarely the best solution. It is generally better to separate out the flash steam and then to ensure that the contents of the boiler feed tank are well mixed. It may be best to raise the temperature to the optimum by reintroducing a little of the flash, via a sparge pipe, into the base of the feed tank. Alternatively, it may be possible to use the flash elsewhere and raise the feed tank temperature by recovering the blow-down heat. Either technique will produce immediate and worthwhile returns for relatively little outlay.

Washer-extractors

A recent survey of washer-extractors across the laundry industry shows many opportunities for substantial savings, both in water and in steam. Water, effluent and fuel are now so expensive that managing these costs needs to be given much higher priority than in the past. This winter every profitable laundry is going to need its own improvement programme.

Even the best of the modern washer-extractor designs still have rudimentary dip controls which take scant recognition of the fact that the cage reverses regularly.

Monitoring the average running dip requires rather more than a probe or a pressure transducer. Dip measurement is best taken off the centre of the sump. The output, whether measured as a liquid level in a tube or as a pressure level in an air-line, needs smoothing and averaging. If a change of rotation results in a momentary drop in dip level that opens the inlet water valve for a few seconds, then the average dip will simply increase throughout the wash, requiring more steam and more chemicals to maintain the correct concentrations. With modern microprocessor controls it should be possible to calculate a running average dip rather than an instantaneous dip and to use this for control purposes.

Hydro-extraction

Every washer-extractor has an optimum spin-speed and spin-time. Extracting as much moisture as possible out of cotton towels is critical. The original work by the British Launderers’ Research Association during the 1950’s called for spin-times of around 8minutes. Some modern machines may need slightly more, others slightly less, but to try and save time by cutting the spin-cycle to 3minutes is a false economy. You will increase the tumble drying time disproportionally, reducing both the energy efficiency of the operation and its productivity

Interspins

The big advantage of a washer-extractor is that by programming an interspin between rinses it is possible to reduce either the total number of rinses or the dip level for rinsing or even both. Few operators appear to have used this feature to its best advantage and rely very much on the soap supplier to provide a water-efficient process.

That would be fine if the soap supplier was paying for the water, but this is not usually the case. There is nothing glamorous about optimising total washing costs in a washer-extractor system. This may be why the majority of the industry still sees the cost of washing as the cost of the chemicals and fails to grasp the real nettle.

Fuel prices will continue to rise, water costs will rise with them and the pace of increases in effluent charges will outstrip them both. We are in for a grim winter and the only brightness on the horizon is the significant potential for saving which most laundries offer. Good hunting!