Making the boiler fit for inspection

Around half the improvement notices issued by factory inspectors in England and Wales related to boilers, according to a recent summary.

A large number of these stemmed simply from the failure of the launderer to be able to produce a current insurance certificate. However, other defects were more serious. The law has tightened recently and operators who fail to meet legal requirements cannot expect much leniency from the inspector.

Boiler lifespan

The question "how long should a boiler last?" is best answered by the boiler surveyor from your insurance company. By law the surveyor must inspect the boiler at least every 14 months. He will indicate items for immediate repair, points to improve over the next 12 months and the likely time for boiler replacement.

You can greatly extend boiler life by attention to a few key details. First, every boiler needs feed water treatment to prevent oxygen pitting and corrosion of the heat transfer surfaces. This is essential, even in soft water areas, otherwise tube failure will occur in under two years leading to expensive tube replacement and unplanned downtime.

There has been a general move from washer-extractors to continuous batch washers throughout the laundry sector and this has reduced the number of stress surges imposed by two or three washer-extractors calling for steam simultaneously.

If the boiler is undersized or the wash house steam main is not reduced to a reasonably low pressure (below 4bar), then a surge in steam demand will be accompanied by a reduction in boiler pressure, because the boiler cannot cope. This produces rapid change in stress and also in temperature.

Rental plants operating very large boilers will also suffer the stress cycles produced by regular injections of cold feed water. These can be minimised by delivering feed water to the pump at the maximum temperature it can handle (generally around 80°C, but sometimes up to 95°C).  Organisations with the foresight to fit a modulating feed pump that injects a small quantity of water continuously to maintain the level in the boiler will find stress problems reduced quite markedly.

Safety routines

By law, a boiler must be fitted with proper level controls which initiate feed water make-up whenever the boiler needs it. There must also be separate sight glasses for a visual check on boiler level. The level controls and the sight glasses must be blown out daily to remove solids and contamination and they must be thoroughly cleaned annually. The latter is particularly important with annular boilers (such as the designs from Fulton) where the stub pipes through the shell need careful clearing, especially in very hard water areas.

During the mandatory daily blowdown of the level controls you should be able to hear the very low water level alarm which, in an unattended boiler house, represents the final level of safety.

Historically, many boiler explosions occurred because of failure of the level controllers and failure of the very low warning bell. A laundry operator should be able to produce a signed record of these daily safety checks for an unattended boiler house.

A boiler produces three or four different impacts on the environment. Laundries that do not use the flash steam in the condensate main but allow this to blow from the top of the boiler feed tank can be recognised by the unsightly plume of steam visible from afar as the inspector approaches. This plume represents 10% of the fuel account, so to be cost efficient, a rental laundry should use this flash steam effectively.

Another way in which boilers can affect the environment, is the intermittent discharge of steam from the blowdown receiver when dirty boiler water is blown to drain in order to control the build up of solids within the boiler shell. 

It is now a legal requirement to have a proper blowdown receiver or effective blowdown arrangement (for which planning permission may well be needed).

Shrewd operators

Shrewd operators have installed continuous blowdown to halve the total quantity of liquor blown to drain and to reduce significantly the associated steam emission and the quantity of hot water that has to be cooled prior to discharge to sewer.  Dropping it quietly into the local stream is no longer an environmentally acceptable option. Unfortunately, there is no way of eliminating the occasional surge of liquor to the blowdown receiver because it is necessary to move every valve on the boiler every day including the bottom drain valve.

The wisp of steam from the pipe on the top of the boiler usually points to a weeping safety valve which, if not corrected, will gouge out a path through the seat and call for a new valve at the next inspection.  Delay here is false economy as well as being environmentally unsightly.

What else will the inspector want to see? For some years it has been a legal requirement that all boiler plant and steam systems at laundry pressures have a written scheme of inspection and examination prepared by a competent engineer, and this must be accompanied by evidence that annual examination has been carried out and everything found to be in order.

This is in addition to the annual survey of the boiler itself and the associated insurance certificate. When the inspector visits he may well ask to see the written scheme, together with documentary evidence that this has been followed, in addition to having sight of the insurance certificate.

Signed records

Most laundry boilers do not have permanent staff in the boiler house so the inspector will also want to see signed records of the daily checks as satisfactory evidence that these were actually carried out. Although the laundry industry has not got a reputation for good, systematic documentation procedures, it does have a remarkably good record as far as boiler explosions are concerned. Where accidents have occurred it is usually through scalds from unlagged pipework or steam leaks.

Environmentally, however, the record is not so good. Most laundry boilers display strong evidence of their position with plenty of plumes of steam rising skywards. This problem is even worse where safety valves downstream of pressure reducing sets are lifting regularly, sending wasteful quantities of steam to atmosphere. The routines and procedures now demanded by law have benefited the industry.

Combustion efficiency has improved greatly over the last 20 years, partly because of the change to gas as a fuel and partly due to the greater attention paid to annual burner maintenance.

Air rates

As a result, air rates to burners have been controlled to near the minimum, reducing the volume of hot air going to the stack and eliminating almost entirely smoke and smuts. This has made possible reduced frequency of tube cleaning and produced thermal efficiencies 10% or 20% higher than they used to be. In parallel with this, much laundry equipment is now designed for direct gas firing, eliminating much flue heat loss from the boiler chimney, therby using energy more efficiently.

There is now little doubt that direct gas- fired laundry equipment for tumble drying and tunnel finishing is firmly established throughout the rental sector as the most cost effective and productive technique for producing drying energy.

The additional capital cost for the gas burner and gas installation is usually recouped over the first couple of years but the ongoing savings in higher machine productivity and improved machine flexibility lasts throughout the life of the plant. Direct gas-fired ironers are available but they do not have the uniformity and reliability of their steam-heated counterparts and have never achieved success in the high volume rental plant where three and four roll steam-heated units are the norm.

Steam heated

The latest ironer developments have all concentrated on steam heating and the resulting uniformity of heat transfer. This trend seems unlikely to change.

The same is true of washing equipment where the convenience of steam injection is preferred to any other technique. Modern tunnel washers are being designed to operate just on the flash steam from the condensate main, allowing the rental wash house to operate solely on recovered heat. This has become essential because margins on rental prices are wafer thin and shrewd energy design makes the difference between profit and loss.

A well-engineered steam/energy system is vital for a modern cost-effective rental laundry. As well as reviewing the increasingly stringent legal requirements, I have indicated where these can be turned to advantage. Complying with regulations is not all doom and gloom!