1 reply to this topic

[ayan_dg]

In my present project we have a Waste heat boiler to generate MP steam. On tube side we have hot process gas. BFW is used as feed water , flow of BFW in shell side is controlled by level control valve.
The system us designed as per ASME section 1.
Now is there a credible liquid overfill case if the inlet BFW valve open losing control. I was thinking that there should not be as the steam side is open and hence the water will go to steam piping after filling the boiler.
Does anyone have any experience on this.
Also if there is a credible case is it eliminated by sizing the boiler PSV for this case or a shutdown valve is provided on BFW line which closes on high liquid level.

[ashwanikaul]

Dear Ayan,

 

In case Boiler overfills with BFW, the disengagement space for vapour and steam will not be effective and BFW will be carried over with steam. Steam shall continue to be generated as Process gas will continue to flow in tube side.

 

This will create two phase flow, significant turbulence (and noise) in downstream equipment. This shall also lead to vibration in supports of pipes and equipment.

 

Besides water carryover may affect equipment performance eg heat exchanger flooding with water etc. If steam does not get condensed because of flooding of HE, steam pressure shall rise upto saturation teparature equiv to hot process gas inlet temperature.

 

Shutdown valve on BFW inlet line shall be a better idea. Valve to be activated by Level HH trip signal.

regards,

Hope this was useful