Making sure it's full steam ahead

Many steam systems have the scope to achieve higher efficiency through improved control, closer monitoring and more regular maintenance.Paul Mayoh, technical manager at Spirax Sarco, offers tips on how best to maintain the boiler house to ensure it is running to its full capabili

Steam is an established energy source for the efficient, reliable production of hot water and humidification control for buildings and processes. However, its inherent reliability can lead to neglect, hiding the need for regular servicing. The Carbon Trust estimates that poor operation and maintenance of industrial boilers wastes up to 10% of the energy input from fuel, while up to 25% of energy is lost through heat distribution systems and waste at the point of use.

You can improve boiler house efficiency by taking time to assess how your system is operating. By ensuring daily maintenance checks are being carried out and that proper testing is being done and recorded, you will improve safety, and may find that savings in energy, water and treatment chemicals are there for the taking.

Health check Check that all statutory daily and weekly tests of boiler water level alarms are being performed and recorded properly. Safety is the first priority here, but routine checks can often highlight inefficiencies worth tackling.

Regular monitoring of water treatment records and visible indication in gauge glasses can often help identify ways of improving the use of water treatment chemicals and lead to cost savings. Look particularly for hardness slippage through the water softener, contamination of the condensate return, and correct chemical dosing.

Feedtank conditions You can improve boiler efficiency by increasing the temperature of the feedwater, as less fuel is needed to produce steam from hot feedwater. For example, using returned condensate to raise the feedwater temperature by 6°C gives a fuel saving of 1%. Ideally, feedwater should be maintained at 90°C.

Adding hot condensate to the boiler feedtank can reduce the need for preheating, but simply feeding condensate into the top of the tank can be inefficient. As condensate falls through the space above the water, vapour and energy can be lost and air will be admitted. A deaerator head can solve the problem by mixing returned condensate, flash steam and cold make-up water as they enter the feedwater tank.

Condensate recovery Returning condensate to the boiler is a straightforward measure that can save thousands of pounds per year. Condensate can contain up to 20% of the energy in the steam from which it came. Returning water to the boiler feedtank typically recovers about half this energy, with the remainder coming from the flash steam produced as the condensate pressure drops. Virtually all this flash steam energy can be recovered by installing a flash steam vessel or pressurised condensate return system.

As well as saving energy, condensate return saves water and treatment chemical costs. Effluent charges may also be reduced because less water is discharged to drain.

Automatic blowdown Using returned condensate as a higher proportion of the boiler feed means that the level of contamination in the boiler is generally lower. However, all boilers need to be periodically purged by blowdown.

The key to doing this efficiently is to remove only enough water to maintain contamination at an acceptable level.

Manually controlled blowdown can be inefficient, often purging more water than is necessary to reduce contamination in the boiler. An automatic TDS (Total Dissolved Solids) blowdown controller may be a better option. Continuously monitoring TDS build-up in the boiler, the controller opens the blowdown valve only as required to reduce contamination, therefore minimising energy losses. Greater efficiency is achieved by recovering the heat from the TDS blowdown water as it flashes to steam. Flash steam can be separated in a flash vessel and injected into the boiler feedtank saving both energy and water.

Good practice Steam and water meters play an important role in energy monitoring and targeting (M&T) schemes. This is especially true across large sites that include several different buildings. M&T systems enable plant managers to break down their sites into separate cost centres and monitor the performance of each one separately.

According to a report prepared for the Carbon Trust last year, M&T schemes can yield savings of 10% across many premises, with 5% considered to be a conservative average.Many of these measures won't incur any cost, but even those that require some investment should pay for themselves in a matter of months. After that, the ongoing benefits will be reflected directly in your company's bottom line.