6.5   Bled-steam inlet

 

Attention must also be given to ensuring that local high velocities are not present at the steam inlet to the heater.

There must be ample area to allow the steam into the desuperheating section and also to flow across and along the tube bundle without causing excessive local velocities. The escape area should be at least equal to the steam inlet area.

ТЕМА 1978 [12] specifies the maximum permissible velocity at the exit from the steam inlet branch into the heater shell without provision of an impingement plate or baffle to protect the tubes in terms of the limiting values of e(vns)2 where ρ is the steam density (kg/m3) and vns is the velocity of dry steam (m/s), as

If a velocity greater than this value is to be encountered, even for short periods of operation (e.g., previous heater by-passed), the provision of a larger branch or some form of impingement plate is needed.

 

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