6 replies to this topic

[arvind]

Dear all,

I am working for the modification job for the refinery unit.

I am going to size the PSV (curently it is 6Q8 which was under design)on Deaerator which having inlet from number of streams (BFW and condensate). Downstream to this deaerator there are 5 centrifugal pump (BFW) working on level control on deaerator with the rated capacity of 120 m3/hr.

governing case define by the client is blocked outlet. Also client is suggesting for blocked outlet consider only 2 pumps gets blocked and that rate to be relieve (i.e 240 m3/hr).

I am wondering how can one knows only 2 pumps are not working for this case, for blocked outlet case we are supposed to go for total blocked outlet conditions including vents (which are normally open) and drain. and then I have to go for summation of all the pressurising streams having design pressure more than the design pressure of deaerator. and that rate to be relieve.

This question is come in my mind because the calculated ( considering clients requirement of blocking only 2 pumps) orifice area is come (4P6) lower than that of the present.

Please clear my understanding.....


Thanks in advance

[fallah]

Dear all,

I am working for the modification job for the refinery unit.

I am going to size the PSV (curently it is 6Q8 which was under design)on Deaerator which having inlet from number of streams (BFW and condensate). Downstream to this deaerator there are 5 centrifugal pump (BFW) working on level control on deaerator with the rated capacity of 120 m3/hr.

governing case define by the client is blocked outlet. Also client is suggesting for blocked outlet consider only 2 pumps gets blocked and that rate to be relieve (i.e 240 m3/hr).

I am wondering how can one knows only 2 pumps are not working for this case, for blocked outlet case we are supposed to go for total blocked outlet conditions including vents (which are normally open) and drain. and then I have to go for summation of all the pressurising streams having design pressure more than the design pressure of deaerator. and that rate to be relieve.

This question is come in my mind because the calculated ( considering clients requirement of blocking only 2 pumps) orifice area is come (4P6) lower than that of the present.

Please clear my understanding.....


Thanks in advance

Blocked outlet doesn't mean all outlet of a vessel to be blocked.

It should be investigated that the relieving fluid would be liquid or two phase.

Your calculated orifice area (4P6) may obtained based on not considering two phase flow (due to flashing) passing PSV during relief,while present one (6Q8) may consider this subject.If so,and if there is two phase flow relieving, recalculate your sizing with considering two phase relief.

[sheiko]

governing case define by the client is blocked outlet.

You should check that. What about other scenarii like fire, steam control valve fully open, etc.?
Also, remember that blocked outlet (and upstream steam control valve fully open scenario) is a credible scenario only if the upstream design pressure is higher than the deaerator relieving pressure (or design pressure, depending on the client).

for blocked outlet case we are supposed to go for total blocked outlet conditions including vents (which are normally open) and drain.

As far as i remember, one should consider each outlet separately. Check with API STD 521 or client spec.

[arvind]

Dear all,

I am working for the modification job for the refinery unit.

I am going to size the PSV (curently it is 6Q8 which was under design)on Deaerator which having inlet from number of streams (BFW and condensate). Downstream to this deaerator there are 5 centrifugal pump (BFW) working on level control on deaerator with the rated capacity of 120 m3/hr.

governing case define by the client is blocked outlet. Also client is suggesting for blocked outlet consider only 2 pumps gets blocked and that rate to be relieve (i.e 240 m3/hr).

I am wondering how can one knows only 2 pumps are not working for this case, for blocked outlet case we are supposed to go for total blocked outlet conditions including vents (which are normally open) and drain. and then I have to go for summation of all the pressurising streams having design pressure more than the design pressure of deaerator. and that rate to be relieve.

This question is come in my mind because the calculated ( considering clients requirement of blocking only 2 pumps) orifice area is come (4P6) lower than that of the present.

Please clear my understanding.....


Thanks in advance

Blocked outlet doesn't mean all outlet of a vessel to be blocked.

It should be investigated that the relieving fluid would be liquid or two phase.

Your calculated orifice area (4P6) may obtained based on not considering two phase flow (due to flashing) passing PSV during relief,while present one (6Q8) may consider this subject.If so,and if there is two phase flow relieving, recalculate your sizing with considering two phase relief.

Fallah thanks,

Earlier calculation is done by one of my coligue and he has connnnsidered the relieving temperature is the same as that of the operating i.e 140°C.( operating conditions press 2.6 barg, temp.140°C)
But what I unserstand from the system is, accumilated liquid can go upto the relieving pressure of 6.623 bar a ( PSV set press 5.1 barg and 10% accumilation+ 1 atm), hence the relieving temperature should be the coresponding temperature i.e 162.76°C instead of 140°C ( which initially used)
So for revised temp. of 162.76°C we are getting the higher orifice area (8T10) as compare to the instaaled.

Please correct my understanding.........

[fallah]

Fallah thanks,

Earlier calculation is done by one of my coligue and he has connnnsidered the relieving temperature is the same as that of the operating i.e 140°C.( operating conditions press 2.6 barg, temp.140°C)
But what I unserstand from the system is, accumilated liquid can go upto the relieving pressure of 6.623 bar a ( PSV set press 5.1 barg and 10% accumilation+ 1 atm), hence the relieving temperature should be the coresponding temperature i.e 162.76°C instead of 140°C ( which initially used)
So for revised temp. of 162.76°C we are getting the higher orifice area (8T10) as compare to the instaaled.

Please correct my understanding.........

Arvind,

I need more detail information and assumptions can submit better assistance....

Did you consider the deaerator as a liquid filled vessel?

Regards

[arvind]

Fallah thanks,

Earlier calculation is done by one of my coligue and he has connnnsidered the relieving temperature is the same as that of the operating i.e 140°C.( operating conditions press 2.6 barg, temp.140°C)
But what I unserstand from the system is, accumilated liquid can go upto the relieving pressure of 6.623 bar a ( PSV set press 5.1 barg and 10% accumilation+ 1 atm), hence the relieving temperature should be the coresponding temperature i.e 162.76°C instead of 140°C ( which initially used)
So for revised temp. of 162.76°C we are getting the higher orifice area (8T10) as compare to the instaaled.

Please correct my understanding.........

Arvind,

I need more detail information and assumptions can submit better assistance....

Did you consider the deaerator as a liquid filled vessel?



Thanks for your quick response fallah,

Our calculations are based on the liquid filled systm.
In the operation there are various stream are entering in the deaerator
LP steam: 3.5 barg and 175°C, HP condensate: 8 barg and 163°C, BFW: 3.2 barg and 115°C.

My basic question is In the normal opearting condition my deaerator is working at 2.6 abrg and at saturation temp. at 140°C.
But because of block outlet condition deaerator pressure will rise upto the relieving pressure. in this case what will be the maximum tempearture of fluid inside the dearerator can go upto the?
will it reach upto the saturation temperature with respect to the relieving pressure ( 6.623 bara) i.e 162.7°C.

Please clear my understanding...............



Regards

[fallah]

But because of block outlet condition deaerator pressure will rise upto the relieving pressure. in this case what will be the maximum tempearture of fluid inside the dearerator can go upto the?
will it reach upto the saturation temperature with respect to the relieving pressure ( 6.623 bara) i.e 162.7°C.

I think considering liquid filled situation,you can consider operating temperature as relieving temperature in the case of block outlet.