5 replies to this topic

[satendra.deshmukh]

Dear,

I am want to analys PSV on MP Boiler blowdon flash drum..

I have to check existing PSV on flash drum is adequeate or not ..

Source to that flash drum are continuous blowdown from various steam drum..

my question is do i need to consider normal flowrate through blowdon valve or shoud i consider max flow from that blowdwon valve..

can anybody guide me on this..??

 

Regards,

Satendra

 

My PSV size is 3 K 4

Steam drum Presure is 1110 psig

flash drum PSV set at 95 psig

[kkala]

Note/ experience: In boiler duty spec we have required such "continuous blow down drum" with flash steam directed to deaerator.

Flash drum has to be protected against overpressure even at max input flow. More flash steam will be produced at max input flow and PSV should have adequate capacity for that.

I think max flow rate through continuous blow down valve should be considered for PSV sizing. Existing PSV has to be checked for this case.

Well, all flash steam has to pass from PSV in case of blocked steam outlet. Ingoing boiler water has temperature about 292 oC. You do not want a vapor pressure higher than 95 psig in the flash drum, corresponding to ~168 oC. Flash steam through PSV will provide the necessary cooling (if outlet gets blocked).

Blocked steam outlet is assumed as credible contingency in this case, with water content of the drum being under level control and reacting relatively slow. I think it not safe to assume that the level control valve will prevent overpressure.

Edited by kkala, 13 March 2013 - 06:56 AM.

[fallah]

satendra,

 

You have various blowdown lines from various steam drums. So, at first you should determine maximum flow through each blowdown valve and then specify highest flow among them. Finally, in order to existing PSV evaluation you should consider this highest flow plus normal flows through all remain blowdown valves because it is supposed at a moment just one valve can be in a position with maximum flow throughput...

[satendra.deshmukh]

Dear fallah, kkala

Thanks for your guidance..

i was thniking k max flow in case fash drum PSv analysis is considered in case of inadvernt opening of intermitent blowdown valve & normal flow to be considerd for continuous blowdwon valve..

by considering max flow through continuous blowdwon valve existing PSV seems to be inadequate..

System sketch is attached below

 

 

Thanks & regards,

Satendra

 

 

 

Attached Files

•  PD-16600.xlsx   34KB   46 downloads

Edited by satendra, 14 March 2013 - 01:53 AM.

[MI_Sidd]

Dear Satendra,

 

As already explained by Fallah,

 

at first you should determine maximum flow through each blowdown valve and then specify highest flow among them. Finally, in order to existing PSV evaluation you should consider this highest flow plus normal flows through all remain blowdown valves because it is supposed at a moment just one valve can be in a position with maximum flow throughput...

 

This is the flow u need to consider for safety valve sizing. Now since the existing safety valve seems to be inadequate, u can consider a mechanical stopping device on valves which will limit the opening of control valve and thus reducing relief load.

Edited by MI_Sidd, 14 March 2013 - 04:19 AM.

[S.AHMAD]

You may consider steam breakthrough as one credible case.