23/05/2017

Less steam = lower energy costs

The steam used in production at Rütgers plant in Castrop-Rauxel, Germany makes up a large percentage of the total energy expenditure. The condensate produced during the distillation process is discharged from the steam system via mechanical steam traps. To reduce costs, Delta Steam Systems, through their distributor for Germany, was commissioned to supply 10-year guaranteed Delta venturi steam traps in a distillation plant in the Aromatic Chemicals division. Significant improvements were evident after a very short period of operation.

 

Thanks to the use of the venturi steam traps, the steam consumption for the distillation cycle under consideration could be reduced by more than 20%, according to Thomas Reisensauer, sales manager and project manager at Rütgers.

Steam traps are used to remove condensed steam from steam systems, improving the efficiency thereof. There are several types, depending on the application. They all contain a mechanism which automatically opens the trap in the presence of condensate and closes it again as soon as steam escapes. The steam traps installed have a venturi opening and have zero moving parts. As a result, it is particularly reliable because the venturi opening allows condensate to freely pass, but not steam, through the laws of physics. It is the flash steam that is forming as the condensate moves from a high pressure to a low-pressure zone that stops the costly live steam from escaping and this regulates the amount of condensate discharged as the load changes.

 

Typical losses with mechanical steam traps and old orifice plate steam traps

Various mechanisms are used to ensure timely opening and closing of mechanical steam traps. For this purpose, internal floats, inverted buckets, bimetallic expansion valves and thermostatic cylinders are all used. During operation, steam traps must open and close several times per minute, hundreds of times per hour. This results in wear and leakage. According to the manufacturer, these mechanical steam traps must therefore be replaced every one to two years.

 

Often confused with advanced venturi type steam traps, a simple orifice plate type steam trap has only a limited application range with varying loads. It will only work if the load is relatively constant. With the venturi type steam trap, varying condensate loads are easily and effectively discharged without losing steam or backing up condensate. The orifice steam trap is also susceptible to ‘wire draw’ or wear of the orifice edges, which is eliminated with the venturi nozzle.

 

The condensate that is present before the opening of the venturi is under pressure and at temperature, and thus contains a lot of energy passing through the elongated nozzle, it opens up into the mouth of the diffuser and a pressure drop occurs; i.e. energy. Since this energy cannot simply disappear, it converts a part of the condensate in the opening back into steam at lower pressure, called flash steam.

 

The greater the pressure difference across the steam trap, the more flash steam is generated in the venturi opening. However, this also creates a counter-pressure, since this steam consumes a thousand times as much volume as the condensate from which it originated.

Due to this sudden expansion, the steam generated in the orifice is accelerated and generates pressure both forwardly and equally to the rear. This limits the flow of steam through the steam trap.

 

Since the amount of steam generated in the venturi opening changes according to the operating conditions, the flow of the condensate regulates itself through the steam trap and therefore is able to self regulate condensate loads without the need for any moving parts.