Wasted steam is a major issue

Published:  07 May, 2007

gem
The huge savings made possible by fully functioning steam traps are illustrated by the replacement of 200 steam traps at Aesica, a supplier of ingredients to the pharmaceutical industry at its Ponders End site — with energy savings of 28%. The new steam traps were GEM venturi-orifice types — immediately meeting an energy-reduction target of 25% over three years set by its American headquarters.

Steam systems with leaking steam traps could easily waste a third of their energy input — and more. TIM GARDNER explains the vital role of steam traps in curbing this huge waste of energy.

Steam has been a popular mode of conveying energy since the industrial revolution. It is used in hospitals and extensively in process industries. As a heat transfer medium, steam has an advantage over fluids such as hot water and oil as it can store very large quantities of heat, which can be given up at constant temperature as the steam condenses. Unfortunately, more energy is lost in industry through steam wastage than through any other medium. Research studies by industry experts in early 2000 suggested that losses from steam systems make up about 35% of all identified potential energy savings.

Important functions

The purpose of installing steam traps is to obtain fast heating by keeping the steam lines and equipment free from condensate, air and non-condensable gases. A steam trap discharges condensate and air from the line or piece of equipment without discharging the steam. Steam traps have three important functions.

• Discharging condensate as soon as it is formed.
• Not allowing steam to escape.
• Being capable of discharging air and other condensable gases.

However, around 10% of mechanical steam traps will fail each year. Traps that fail open result in a loss of steam and its energy. Where condensate is not returned, the water is lost as well. The result is significant economic loss — directly via increased boiler plant costs and potentially indirectly via decreased steam heat capacity. Steam leakage is a visible indicator of waste and accounts for up to 11% of steam consumption in a small- or medium-scale and rising to an astonishing 55% in high-usage applications.

Steam traps need to be working at optimum efficiency to minimise impact on the environment. For example, each litre of heavy fuel oil burned unnecessarily to compensate for a steam leak leads to about 3 kg being emitted to the atmosphere.

Steam traps can have different sized orifices to suit different conditions. If a trap leaks steam, the amount wasted will depend on the size of the trap and the steam pressure. The cost of waste will also depend on the number of traps and the operating time. For example an installation with 200 traps based on an average trap size of DN20 and a steam pressure of 14 bar gauge with 10% failing annually will waste 8900 t of steam a year. If the overall cost of steam for this plant were £10 per tonne, the direct cost of ignoring these leaking steam traps would be £178 000 each year — equivalent to well over a million litres of fuel oil. The cost to the environment would be 3000 t of carbon dioxide dumped into the atmosphere.

Options

UK companies are looking for ways of reducing overheads, and many are cutting maintenance budgets and staff. The consequence is a spiral of ever-increasing steam loss and escalating fuel bills as mechanical steam traps fail open. This has left management with two options.

• Minimal maintenance and watch the steam plume from the condensate receiver rise — along with the fuel, water and chemical treatment costs.
• Regularly test, repair and replace faulty mechanical traps at considerable ongoing cost.
Those options indicate what to look for in a steam trap. To be efficient and economical, a steam trap has to meet the following requirements.
• Minimise the loss of steam.
• Provide long lasting and dependable service by minimising trap testing, repair, cleaning, downtime and other associated losses.
• Be corrosion resistance to prevent the damaging effects of acidic or oxygen-laden condensate.
• Ventilate air for efficient heat transfer and also to prevent the system binding.
• Remove carbon dioxide to prevent the formation of carbonic acid. This means that the steam trap must function at or near steam temperature since carbon dioxide dissolves in condensate that has cooled below steam temperature.
• Operate against the actual back-pressure build-up in the return lines.
• Be free of the dirt collected by the condensate as it travels through the distribution piping and on to the boiler. Even particles passing through strainer screens are erosive, so the steam trap must be able to function in the presence of dirt.

Numerous steam traps are available and selecting the correct type is an important element of any steam system. Whilst thermostatic, thermodynamic and mechanical traps are extensively used, the fixed-orifice condense-discharge trap is now becoming the steam trap of choice.

Instead of using a valve mechanism to close off steam for maximum energy and water conservation, the venturi orifice design effectively drains condensate from the steam system. As these steam traps have no moving parts to wedge open or fail, they provide the ultimate in reliability and require only minimal maintenance and no spares, testing or monitoring equipment. They are available in a range of options for specific applications, manufactured from corrosion resistant stainless steel and are performance guaranteed for 10 years, obviating the need for repair or replacement.

Complacency

Unfortunately people often ignore steam traps, and this complacency costs much more than they realise. Just maintaining boiler plant and forgetting about the rest of the steam system can be a horribly wasteful proposition. Losses can include not only wasted energy but also replacement of damaged equipment and misuse of man-hours. Fortunately, installing low maintenance venturi orifice steam traps can avert much of these potential losses.

Tim Gardner is managing director of Gardner Energy Management.



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