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Is Your Steam Quality Worse Than You Think?

Most steam users are probably familiar with the terms ‘dry steam’ and ‘wet steam.’ The question is, just how dry is the steam being used in steam processes? It isn't uncommon to have wet steam, i.e. steam containing condensate droplets, even in piping that is in continuous in use.

When steam is wet, there is a greater tendency to encounter problems due to scale and other foreign matter. This is because water has a higher mass than steam, and entrained droplets are more likely to break off hard pieces of foreign matter such as dirt from the pipe walls to be carried downstream. Condensate also has high concentrations of solidified conditioning agents used in boiler feed water.

How to Improve Steam Quality

An effective improvement measure against the various issues that arise from wet steam is the installation of pressure reducing valves with built-in separators and steam traps (COSPECT® series) or cyclone separators (DC series separators and SF1 separator filter).

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Fig. 1 Condensate droplets and foreign matter flowing within the piping can severely affect equipment service life and the quality of the product being heated.

What Causes Wet Steam?

There are 2 main reasons why steam may contain moisture:

  • Firstly, the initial dryness level of the steam is set by the boiler. This dryness can often decrease as a result of sudden fluctuations in load, causing some of the boiler water to get caught up and transported with the steam. Unless additional superheating is performed, it is uncommon for perfectly dry steam to be supplied from the boiler.
  • Secondly, a decrease in steam dryness occurs when the condensate is not completely removed from the steam in the transport piping. Condensate continuously forms in the steam transport piping as heat radiates from the piping. If the condensate is not all removed by steam traps, some of it is picked up and becomes entrained in the steam flow. Even with properly spaced and trapped drip legs, a certain amount of moisture entrainment is inevitable.

The Effects of Wet Steam

The effects of steam with entrained moisture are particularly devastating for heating processes where steam comes into direct contact with the product, such as those in food, rubber and textile applications. The condensate in the steam adheres to the surface of the product and can result in product defects. Even in a heat exchanger, which is a typical example of indirect use of steam, wet steam can lower the heat transfer efficiency, which can result in a drop in productivity.

Condensate and scale entrained in steam can wear out strainers, isolation valves, elbows, and other piping elements. Wet steam can often lead to failure due to trim erosion in devices such as pressure reducing valves, control valves, and flowmeters, as well as the shortenend service life of heat exchanger tube bundles.

Wet steam can be detrimental in terms of flare stack pilot and flame control, and when delivered to turbines, can lead to critical failures resulting in expensive maintenance and unscheduled downtime for large sections of a steam using facility.

 

COSPECT® Series Pressure Reducing Valves with Built-in Separator and Steam Trap

COSPECT®, with its built-in Super Cyclonical Effects Separator and built-in free float steam trap, is a pressure reducing valve that uses centrifugal force to first remove approximately 98% of the entrained condensate. The steam is then further dried as it undergoes pressure reduction through the valve to provide almost 100% dry process steam. The built-in steam trap discharges all separated condensate before it has a chance to reenter the steam flow.

In addition to ensuring the supply of high-quality dry steam, the built-in separator and steam trap also ensure the long service life of the PRV itself.

 

Main Features of COSPECT® PRVs

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SF1 Separator Filter

A built-in cyclone separator eliminates condensate, dirt and scale before filtering. This extends the filter maintenance cycle. Compared to a filter without a built-in cyclone separator, the time between required maintenance is improved nearly three times.

The cyclone separator also supplies dry steam, eliminating water spots.

 

Main Features of the SF1 Separator Filter

SF1 cut view

DC Cyclone Separator

A separator that forcibly separates out the condensate generated and entrained in pipelines of steam or air, etc. All models are equipped with a cyclone separator that demonstrates a remarkably high 98% separation efficiency.

 

Main Features of DC Cyclone Separators

SF1 cut view