Flowserve Desuperheaters - Manual (Page 13)

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Desuperheaters FCD VLENIM0115-00 – 09/11
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c WARNING: Operating nozzles below the minimum ΔP creates undeveloped water spray
patterns with large droplet sizes which could impinge on equipment causing thermal
shock resulting in equipment damage.
4. The maximum pressure drop between the steam and the water should be approximately 30.0 bar
(435 psi) for the MaxCool MCX nozzle. The optimum maximum pressure drop for the VaporCool
nozzle is 10 Bar (145 psi), but pressure drops up to 20 Bar (290 psi) are acceptable. The maximum
pressure drop for the VaporCool MicroNozzle is 40 Bar (580 psi).
5. Higher cooling water temperatures will provide for more efficient atomization and evaporation.
6. Condensate is most likely to build up in lines during system startup and shutdown. The effects of
corrosion and thermal shock on steam pipes can be reduced by minimizing process deviations.
7. The cooling water control valve should have a “fail close" actuator.
8. To enhance proper cooling water evaporation there should be a minimum of 10 feet (3 meters)
of straight downstream pipe from the desuperheater location with a slight downward gradient.
Factors such as velocity, how close the steam temperature is to saturation temperature, percent
of cooling water being injected, pipe diameter, etc. can require longer straight pipe lengths. The
minimum required straight pipe length for the actual application is provided on the desuperheater
sizing sheet.
c WARNING: Inadequate straight pipe length does not allow sufficient time for the cooling
water to evaporate allowing cooling water impingement on the piping system, especially
the downstream elbow, causing thermal fatigue and premature failure.
9. To allow for accurate temperature feedback, the temperature sensor(s) should be located a
minimum distance of 12 ft downstream of the desuperheater. Factors such as velocity, how close
the steam temperature is to saturation temperature, percent of cooling water being injected, pipe
diameter, etc. can require longer distances to the temperature sensor. The minimum required
distance to the temperature sensor for the actual application is provided on the desuperheater
sizing sheet. Multiple shielded temperature sensors will provide more accurate average feedback.
c WARNING: Inadequate distance from the desuperheater to the temperature sensor can
cause inaccurate temperature measurement resulting in poor process control.
10. A pipe drain and/or steam trap should be placed at least 6 pipe diameters downstream of the
desuperheater.
11. When cooling water flows over 50 gpm are required, for optimum performance, consider using
multiple nozzles and/or multiple injection sites. This allows smaller water droplet sizes, better
cooling water evaporation, and lower risk of cooling water impingement on the piping system.
MAINTENANCE (LANCE MOUNTED)
Maintenance of lance mounted desuperheater nozzles may be required if:
• A degradation in cooling efficiency is noted while maintaining constant steam process conditions.
This may be an indication that the nozzle is partially plugged.
• The steam process conditions change. If the steam load increases, the nozzle may need to be
upsized to keep the downstream steam at the required temperature.