12 replies to this topic

[Qalander (Chem)]

Dear all, We have revamped our Crude through put.Original Desalter Vessels(2XHorizotal 10 ft ID and 13 ft Tangential Length each)Rate 16000BPD
original design had Normal spring loaded Pressure relieving valve one on each delivering to flare system;that is now undersized.
Now reviewed route is propsed at the inlet pipeline of our preflash tower upstream and the revised scheme shows back pressure on the Relif Valves at the extent of >24% and
Balanced bellow type Relief valves are proposed at theis pipeline,closed to preflash inlet.
My quetion is that is this type suitable?
As the pre-flash Relief Valves open to atmos, the proposed scenario is increasing danger;true or not?
The crude water mix max. flow (i.e. 36000 BPD plus 5% wash water) will have upsetting scenario for preflash internals;true or not?
I have these reservations plus not very much satisfied if Conventional relief valves at least two should be used,instead of bellow type suggested.,The flare system upsizing is needed;I understand.Or the Pre-flash PSV's to be routed to Flare System,Not very sure!
Please help as soon as possible
Best Regards
qalander

[Zauberberg]

I've never heard before, anywhere, that desalter RVs are discharging vessel inventory to the flare system! Are you sure about this? More than 95% of desalter inventory is liquid at flare conditions!
Discharge of RVs is commonly routed directly to the main tower flash zone (bypassing heat exchangers and process furnace).

Pre-flash drum RVs should be routed to the flare system, as this vessel operates at lower temperatures and higher pressures than ADU main tower, and so the gas inventory is much smaller than, for example, ADU overhead stream which is discharged straight to atmosphere.

[Qalander (Chem)]

I've never heard before, anywhere, that desalter RVs are discharging vessel inventory to the flare system! Are you sure about this? More than 95% of desalter inventory is liquid at flare conditions!
Discharge of RVs is commonly routed directly to the main tower flash zone (bypassing heat exchangers and process furnace).

Pre-flash drum RVs should be routed to the flare system, as this vessel operates at lower temperatures and higher pressures than ADU main tower, and so the gas inventory is much smaller than, for example, ADU overhead stream which is discharged straight to atmosphere.

True,but what existed as legacy;was indicated.
Now if "Preflash flash zone entry is recommedable as per customary/practices,then existing open to atmosphere Pre-flash relif valves are to be routed through flare system,as described.
This will put additional load and will mandatorily need up-sizing of flare system accordingly.
Regards
Qalander

[Zauberberg]

Yes, I agree. You can't have both at the same time - if estimated gas load is too high for existing flare system, you need to re-evaluate and resize it, if required. But, believe me, it's much simpler and more safe if you re-route desalter PSV outlet to the main column flash zone: relief consequences cannot be so dramatic as in the existing layout. Actually, I cannot remember one single bad outcome, except for temporary losing distillate yield due to quenching effects of desalter inventory entering column flash zone. I still cannot believe someone has designed desalter PSV discharging to the flare.

Where this pre-flash drum vapor is going in regular conditions? It is usually routed somewhere up in the main ADU tower as separate vapor feed; if the worst case scenario is such that it assumes ADU overhead condensers in operation, then it can be possible to direct flash drum PSV outlet to the same place. It depends on overall gas load, condensing capacity of overhead coolers, and flare system capacity - you have to check it in your calculations. Maybe you will find out that flare will not be overloaded in such case.

Best regards,

[Qalander (Chem)]

QUOTE (Zauberberg @ Apr 17 2008, 08:27 AM) Yes, I agree. You can't have both at the same time - if estimated gas load is too high for existing flare system, you need to re-evaluate and resize it, if required. But, believe me, it's much simpler and more safe if you re-route desalter PSV outlet to the main column flash zone: relief consequences cannot be so dramatic as in the existing layout. Actually, I cannot remember one single bad outcome, except for temporary losing distillate yield due to quenching effects of desalter inventory entering column flash zone. I still cannot believe someone has designed desalter PSV discharging to the flare.

Where this pre-flash drum vapor is going in regular conditions? It is usually routed somewhere up in the main ADU tower as separate vapor feed; if the worst case scenario is such that it assumes ADU overhead condensers in operation, then it can be possible to direct flash drum PSV outlet to the same place. It depends on overall gas load, condensing capacity of overhead coolers, and flare system capacity - you have to check it in your calculations. Maybe you will find out that flare will not be overloaded in such case.

Best regards,
Thanks Zauberberg, It seems as if "Blocked Outlet Scenario" is not considerable for Pre-flash case having multiple cooling/condensing loops,thus your explanation indicates as a much reduced Pre-flash overhead relief valve could be or should be routed to existing flare system without affecting much of the loading.
Now any comments on the relief valve types on the desalters;A) 1 or 2 varied or same set pressures? B)Conventional spring type or balanced bellow type preferred?
Best regards
Qalander

Edited by Qalander (Chem), 10 October 2010 - 11:41 AM.

[Qalander (Chem)]

Yes, I agree. You can't have both at the same time - if estimated gas load is too high for existing flare system, you need to re-evaluate and resize it, if required. But, believe me, it's much simpler and more safe if you re-route desalter PSV outlet to the main column flash zone: relief consequences cannot be so dramatic as in the existing layout. Actually, I cannot remember one single bad outcome, except for temporary losing distillate yield due to quenching effects of desalter inventory entering column flash zone. I still cannot believe someone has designed desalter PSV discharging to the flare.

Where this pre-flash drum vapor is going in regular conditions? It is usually routed somewhere up in the main ADU tower as separate vapor feed; if the worst case scenario is such that it assumes ADU overhead condensers in operation, then it can be possible to direct flash drum PSV outlet to the same place. It depends on overall gas load, condensing capacity of overhead coolers, and flare system capacity - you have to check it in your calculations. Maybe you will find out that flare will not be overloaded in such case.

Best regards,

Thanks Zauberberg, It seems as if "Blocked Outlet Scenario" is not considerable for Pre-flash case having multiple cooling/condensing loops,thus your explaination indictes as a much reduced Pre-flash overhead relief valve could be or should be routed to existing flare system without affecting much of the loading.
Now any comments on the relief valve types on the desalters;A) 1 or 2 varied or same set pressures? B)Conventional spring type or balanced bellow type preferred?
Best regards
Qalander

Dear Zauerberg, Furthermore;Somehow I still feel that with slight variation the Pre-flash resembels to 'Raffinate Splitter of BP Texas Refinery ISOM unit', except that no Fired Heater in loop.
The Raff. Splitter over there was hooked up with open Atmos. Vent,our Preflash has Relif Valves venting to atmos; the resemblence. Refer attachment for PSRM's sake
Best regards
Qalander

[Qalander (Chem)]

Yes, I agree. You can't have both at the same time - if estimated gas load is too high for existing flare system, you need to re-evaluate and resize it, if required. But, believe me, it's much simpler and more safe if you re-route desalter PSV outlet to the main column flash zone: relief consequences cannot be so dramatic as in the existing layout. Actually, I cannot remember one single bad outcome, except for temporary losing distillate yield due to quenching effects of desalter inventory entering column flash zone. I still cannot believe someone has designed desalter PSV discharging to the flare.

Where this pre-flash drum vapor is going in regular conditions? It is usually routed somewhere up in the main ADU tower as separate vapor feed; if the worst case scenario is such that it assumes ADU overhead condensers in operation, then it can be possible to direct flash drum PSV outlet to the same place. It depends on overall gas load, condensing capacity of overhead coolers, and flare system capacity - you have to check it in your calculations. Maybe you will find out that flare will not be overloaded in such case.

Best regards,

Thanks Zauberberg, It seems as if "Blocked Outlet Scenario" is not considerable for Pre-flash case having multiple cooling/condensing loops,thus your explaination indictes as a much reduced Pre-flash overhead relief valve could be or should be routed to existing flare system without affecting much of the loading.
Now any comments on the relief valve types on the desalters;A) 1 or 2 varied or same set pressures? B)Conventional spring type or balanced bellow type preferred?
Best regards
Qalander

Dear Zauerberg, Furthermore;Somehow I still feel that with slight variation the Pre-flash resembels to 'Raffinate Splitter of BP Texas Refinery ISOM unit', except that no Fired Heater in loop.
The Raff. Splitter over there was hooked up with open Atmos. Vent,our Preflash has Relif Valves venting to atmos; the resemblence. Refer attachment for PSRM's sake
Best regards
Qalander

Dear Art and Phil Hello and Good Afternoon, may I invite your kind attention to throw some light on this or should I pst again in the Industrial Professional's Forum.
Hoping an early positive/professional response covring any aspects might have been missed out,un-identified by me please!
Best Regards

[binzee]

The relief valves of pre flash may be routed to flare keeping in view the governing case.

Normally but not necessarily Intermediate Power failure is the governing case for flare.If the governing cases for flare design and relief valves are same then your flare would be undersized but if the governing cases are different, the new load can be easily routed to flare ( provided it doesnt exceed the design load of flare)

As far as desalter is concerned, the PRV's must be routed to flash zone not the flare. Normally desalter PRV's have different relief scenario as compared to that for the flare design. If the existing PRV's are routed to flash zone (not to flare) then you may get some space to cater for the Pre flash PSV's in existing flare with out redisgning. This all rounds upto calculations.

Hope this helps

Thanks

[Qalander (Chem)]

The relief valves of pre flash may be routed to flare keeping in view the governing case.

Normally but not necessarily Intermediate Power failure is the governing case for flare.If the governing cases for flare design and relief valves are same then your flare would be undersized but if the governing cases are different, the new load can be easily routed to flare ( provided it doesnt exceed the design load of flare)

As far as desalter is concerned, the PRV's must be routed to flash zone not the flare. Normally desalter PRV's have different relief scenario as compared to that for the flare design. If the existing PRV's are routed to flash zone (not to flare) then you may get some space to cater for the Pre flash PSV's in existing flare with out redesigning. This all rounds upto calculations.

Hope this helps

Thanks

The Hydraulic calculation were done/ verified and thereafter the decisions were taken to rout desalter relief load into pre-flash flash zone inlet.;
the redesigned/ revamped load capacity relief valves are on-order and will be installed in near future.

Although As per various constraints the plant is still to be operated at revamped capacity thus all the needed safeguards will be ensured in-place prior to regular sustainable revamp capacity operation.

Edited by Qalander (Chem), 10 October 2010 - 11:55 AM.

[binzee]

The relief valves of pre flash may be routed to flare keeping in view the governing case.

Normally but not necessarily Intermediate Power failure is the governing case for flare.If the governing cases for flare design and relief valves are same then your flare would be undersized but if the governing cases are different, the new load can be easily routed to flare ( provided it doesnt exceed the design load of flare)

As far as desalter is concerned, the PRV's must be routed to flash zone not the flare. Normally desalter PRV's have different relief scenario as compared to that for the flare design. If the existing PRV's are routed to flash zone (not to flare) then you may get some space to cater for the Pre flash PSV's in existing flare with out redesigning. This all rounds upto calculations.

Hope this helps

Thanks

The Hydraulic calculation were done/ verified and thereafter the decisions were taken to rout desalter relief load into pre-flash flash zone inlet.;
the redesigned/ revamped load capacity relief valves are on-order and will be installed in near future.

Although As per various constraints the plant is still to be operated at revamped capacity thus all the needed safeguards will be ensured in-place prior to regular sustainable revamp capacity operation.

Thanks for the update...

However, what happend to the pre-flash PSV's

[Padmakar Katre]

Dear All,
Nice thread to be discussed and tempted me to be in. As Zauberberg suggested not to route the Desalter PSV discharge to flare and rather route it to ADU column Flash Zone.Here I anticipate one possibility to route the Desalter PSV(I consider the PSV Sizing basis as either Blocked outlet or fire case)discharge to pre-flash drum, since the Desalter liquid is at lower temperature (less than 150-160 Deg C), which will cause to upset the main fractionator operation. If we route the discharge to pre-flash drum where the bottom liquid will be pumped by bottom crude booster pumps and sent to crude heater via the preheat network. The PSV(here I consider fire case as PSV sizing basis) discharge on the pre-flash drum should be routed to ADU column as the additional lighters will be sent through the ovhd vapor line of pre-flash drum on pressure control and net vaporization at the crude heater discharge will remain same. So the net vapor in the main fractionator will not alter much. Please correct me if my comments don't make any sense.Ignore if not helpful.

Edited by Padmakar S Katre, 11 October 2010 - 10:38 AM.

[Qalander (Chem)]

The relief valves of pre flash may be routed to flare keeping in view the governing case.

Normally but not necessarily Intermediate Power failure is the governing case for flare.If the governing cases for flare design and relief valves are same then your flare would be undersized but if the governing cases are different, the new load can be easily routed to flare ( provided it doesnt exceed the design load of flare)

As far as desalter is concerned, the PRV's must be routed to flash zone not the flare. Normally desalter PRV's have different relief scenario as compared to that for the flare design. If the existing PRV's are routed to flash zone (not to flare) then you may get some space to cater for the Pre flash PSV's in existing flare with out redesigning. This all rounds upto calculations.

Hope this helps

Thanks

The Hydraulic calculation were done/ verified and thereafter the decisions were taken to rout desalter relief load into pre-flash flash zone inlet.;
the redesigned/ revamped load capacity relief valves are on-order and will be installed in near future.

Although As per various constraints the plant is still to be operated at revamped capacity thus all the needed safeguards will be ensured in-place prior to regular sustainable revamp capacity operation.

Thanks for the update...

However, what happend to the pre-flash PSV's

Dear
I'll come back with whole scenario soon

[Qalander (Chem)]

Dear All,
Nice thread to be discussed and tempted me to be in. As Zauberberg suggested not to route the Desalter PSV discharge to flare and rather route it to ADU column Flash Zone.Here I anticipate one possibility to route the Desalter PSV(I consider the PSV Sizing basis as either Blocked outlet or fire case)discharge to pre-flash drum, since the Desalter liquid is at lower temperature (less than 150-160 Deg C), which will cause to upset the main fractionator operation. If we route the discharge to pre-flash drum where the bottom liquid will be pumped by bottom crude booster pumps and sent to crude heater via the preheat network. The PSV(here I consider fire case as PSV sizing basis) discharge on the pre-flash drum should be routed to ADU column as the additional lighters will be sent through the ovhd vapor line of pre-flash drum on pressure control and net vaporization at the crude heater discharge will remain same. So the net vapor in the main fractionator will not alter much. Please correct me if my comments don't make any sense.Ignore if not helpful.

Dear Padmakar,
The Governing Scenario is as If recalled correctly now? Most Probably was "Blocked Discharge Case"& not 'Fire Case' indeed!
However let me re-confirm after checking whole present scheme once again to eliminate any doubts and update everything as far as possible.