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Reducing the energy costs of steam

03 July 2012

Steam is used in many industries and can account for as much as 40% of a company’s fuel bill which means that steam traps and steam systems can represent a large proportion of a plants total operating cost. Grant Bailey, sales & marketing director at Thermal Energy International, says that finding ways to reduce these costs is now of major importance to energy, and plant managers.

In addition to being used to heat raw material and semi-finished products, steam is also used to evaporate, distil, boil, brew, react, agitate, clean and sterilise for a wide range of equipment in many processes. As fuel costs increase, so does the cost of producing steam. Ensuring that a steam system is working at maximum capacity and efficiency is, therefore becoming an increasingly important consideration.

It is essential to determine how efficiently your steam generation is operating, based on steam output versus fuel input. It is also important to determine how much steam is being used and how much it is costing to generate this steam and to determine the effectiveness of your steam traps and whether they are working efficiently.

For a steam system to operate effectively it requires the efficient use of steam traps. The job of a steam trap is to get rid of condensate, air and non-condensables as quickly as they accumulate. The use of substandard steam traps will reduce the efficiency of the system and increase costs. A steam trap is the most important link in the condensate loop, because it connects steam usage with the condensate return.

Malfunctioning steam traps represent a significant source of wasted energy and condensate losses in addition to replacement and maintenance costs. Depending on the individual maintenance routine, around 15% to 25% of steam traps can be leaking within any factory or site at any one time. This represents a major cost for lost steam and results in additional expenditure in maintaining, stocking, checking and replacing mechanical steam traps.
Why do steam traps fail?

Anything that is mechanical is liable to malfunction at some point and mechanical steam traps are no exception. Pressure surges, due to sudden steam valve openings and improper piping or trap misapplication, which in addition to malfunction can result in water hammer, are some of the main reasons for failure, resulting in either leakage or the trap failing closed. Additionally, when such steam traps fail open, and discharge into condensate return systems, they cause pressurisation of the condensate lines, which inhibits trap drainage and often reduces heat output and production.

Steam traps also need to be working at optimum efficiency so that they minimise the impact on the environment. For example, for each litre of heavy fuel oil burned unnecessarily to compensate for a steam leak, approximately 3kg of CO2 is emitted to the atmosphere.
The venturi orifice design

According to research carried out at Queen’s University in Belfast, venturi orifice designed steam traps have been proven to be the most efficiently designed steam traps, providing an average reduction of 11.5% in the portion of the boiler fuel bill that is used to generate trapped steam.

While the venturi orifice design retains its initial efficiency indefinitely, the mechanical trap, with its moving parts, begins to gradually deteriorate. With mechanical steam traps, when heat from steam is lost, vapour condenses to the bottom of the pipe and finally makes its way to the mechanical trap. With the venturi orifice trap, the difference in density between steam and condensate and the continuous flow preferentially discharges the higher density condensate, resulting in significantly less condensed water on the heat transfer side of the equipment. This also maintains the steam on the heat transferring side of the equipment, resulting in better thermal efficiency.

Unlike a mechanical trap, because the venturi orifice steam trap enables continuous condensate discharge, the trap is equipped with an orifice, sized to the application. The live steam loss through a venturi orifice trap is, therefore, significantly lower than the loss through a conventional mechanical trap, even when new.

Through the correct application of venturi throat design and orifice size, the capacity of the venturi orifice design can be self-regulated, dependant on load, and operated from the maximum running conditions to zero. This provides greatly increased capacity during start up.

The venturi orifice steam trap effectively drains condensate from the steam system. As it has no moving parts to wedge open or fail, it is more reliable, requiring only minimal maintenance and requiring no spares, testing or monitoring equipment. Since the trap can handle variable loads and can accommodate wide load changes, it is suitable for use in a wide variety of applications.
 
Many companies carry out a steam trap inspection just once or twice a year, by which time at least 10% of their steam traps will have failed open, shut or partly open. Losses will include wasted energy as well as the cost of replacing damaged equipment and misuse of man-hours.

Confirmed savings for Italcables
Metered tests carried out on Thermal Energy International’s GEM steam traps by Italcables, an Italian producer of wire strands for pre-stressed concrete and post-tensioned structures, for example, demonstrated steam savings of up to 30% compared to mechanical traps. The company has since fitted GEM traps to its steam baths and kettle boiler used for ‘pickling’ and treating iron wire strands within production process.

Mr Rizzinelli, energy manager at the Italcables facility, conducting a metered trial to validate the potential energy savings that the venturi steam traps could offer. The original mechanical traps fitted to the steam baths and kettle boiler were replaced by the GEM venturi design and steam meters to test their performance. The results showed that the new traps were reducing steam consumption by between 20 and 30%.

“I decided to carry out monitored tests to quantify the amount of steam that could be saved with the GEM traps and whether there would be a reduction in condensate,” said Rizzinelli. “The test results, together with the steam meter readings, have proved that the GEM traps save energy and operate well over a wide range of condensate loads”.

“The fact that such a small device can obtain such important savings and provide a fast payback is really good news. Thermal Energy International supported us throughout the project and we hope to continue this collaboration at other sites and with other projects”.


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