4 replies to this topic

[schc3fling]

My question is regarding sulfur unit operation.

Why there is no relief device on sulfur condenser and the open communication equipments (waste heat exchanger, re-heat train, reactor).

During the design of sulfur condenser and waste heat exchanger why is not tube rupture considered.

Do sulfur seal legs provide path for vapor relief to sulfur pit. How do we do calculations to take credit of sulfur seal legs.

I have one sulfur seal leg on 1st pass and 3 sulfur seal traps on other three passes? Vapor can not pass through sulfur seal traps, how am I suppose to relieve tube rupture or boiler feed water failure rates through 2nd ,3rd and 4th pass of sulfur condenser.

Is there a philosophy or engineering practice to make Tube rupture not applicable ot make the risk acceptable for sulfur condenser.

What is the best book to understand sulfur unit operation and design considerations? Also for what all scenarios we can take credit of sulfur seal legs. Moroever during tube rupture would be a liquid relief (water) of Vapor relief (steam) what is more conservative? Does process stream stop during tube rupture?

[sheiko]

Hi

My question is regarding sulfur unit operation.

Why there is no relief device on sulfur condenser and the open communication equipments (waste heat exchanger, re-heat train, reactor).

During the design of sulfur condenser and waste heat exchanger why is not tube rupture considered.

I believe this is not true. Relief devices are normally required on vessels as per ASME section VIII code. However, it is possible that in your specific case no credible scenario is applicable (or has been found...), what would indeed explain why there is no relief device on the items you mentionned. Another reason could be that the use of High Integrity Pressure Protection Systems (HIPPS) is adequate to protect the plant against overpressure. However, this decision is the responsability of the user and should be thoroughly documented.

What is the best book to understand sulfur unit operation and design considerations?

I believe the best references on the subject can be ordered here: http://www.sulphurex...x/SxLibrary.htm

Edited by sheiko, 12 September 2009 - 05:31 PM.

[schc3fling]

Thanks for your reply.

Sulfur Seal legs have been considered to provide relief protection to sulfur unit process side in history.
Recently sulfur seal traps have been used in various refineries to replace sulfur seal legs. Sulfur seal legs dont allow vapor to pass. So for a relief scenario in pass 2, 3 and 4 or sulfur seal condenser have no where to go due to high pressure drop across the system (for relief loads).

I have seen that tube-rupture scenario has not been considered during design of suflur condenser and also I am not sure if sulfur seal leg provide adequate capacity for vapors to blow by in case of tube-rupture.

Attached is a rough process flow diagram for my system. Thanks for your reply. And I have requested references.

Any more input to understand sulfur recovery unit operation and process safety would be a great help.

Regards

fling...

Attached Files

•  Sulfursketch.pdf   24.76KB   140 downloads

Edited by schc3fling, 14 September 2009 - 04:42 PM.

[schc3fling]

As I am trying to increase my knowledge on Sulfur System and Sulfur condenser operation, during one of my discussion I found that normally Sulfur System new or old have a high pressure shutdown system. Moreover for all other scenarios such as tube -rupture or boiler feedwater failure on condnser they take credit of the normal flow path to the incinerator or the TGTU unit.

Moreover during design of the system they try to make blocked outlet scenario, not applicable by putting adequate controls on the outlet line to TGTU or incinerator or Stack (like multiple paths or high pressure SRU shutdown system or operating procedures).

Though sulfur seal legs are considered to be providing protection to the system for any unacceptable event on the system, plant opearator real dont want the sulfur seal legs to blow-out.

As a safety engineer, I am not sure if the credit for this high pressure shutdown system or operating procedure credit can be taken for this system.

Also for a sulfur system with normal flow through the condenser process side is around 3000-4000 lb/hr and for a tubr-rupture scenario it might be 40000 lb/hr to 100,000 lb/hr (water or steam) if we model the system than there is a huge pressure drop across the system, which does not allow to take credit of normal flow path to incinerator, stack or TGTU unit.

Moreover with sulfur trap configuration where sulfur traps are installed on 2nd, 3rd and 4th pass on sulfur condenser its really hard to figure out if tube-rupture occurs how the system would behave and where would it relieve such high loads.


Regards
fling.....

[schc3fling]

Some more input after discussion with some knowledgable seniors in this field:

Blocked Discharge

Normally SRU train is connected to a paired TGTU train,
and the process gas from the two TGTU trains is routed to a common
incinerator where the process gas is burned and vented to the atmosphere
through an elevated stack. Hand control valves are provided to isolate a
TGTU train from its companion SRU train with a valved branch connection to
vent from the SRU directly to the common incinerator. There are manual
block valves in the absorber off gas lines from each TGTU to the
incinerator that are chain locked open. Provisions to ensure either the
TGTU inlet or bypass hand control valves are the equivalent of being chain
locked open is required to prevent a blocked discharge condition.

Note: There is a high pressure switch at the SRU burner that will shut down
acid gas feed and combustion air to the SRU to avoid blowing the sulfur
seal at the outlet from the First Sulfur Condenser. However this action
does not mitigate the effects of these scenarios for design purposes.

In the event of a waste heat exchanger tube failure, flashing water and
steam will pass from the shell side at 600-700 psig into the process side of
the heat exchanger and flow through the SRU main process lines and
equipment to the connected TGTU and incinerator and will be vented out the
elevated stack to the atmosphere. The hand control valves at the outlet of
the SRU will be lined up either to the incinerator (only at startup when
there is no acid gas feed to the SRU) or to the connected TGTU. The normal
position of the valve to the TGTU is open and there are no automatic
controls to close the valve, allowing for full open credit for venting high
vapor rates in the event of a tube failure. Previous industrial experience indicates
that the pressure increase that occurs during a tube failure does not
exceed the equipment design pressure. The methodology for calculating the
pressure for a tube failure for this project has not been established.

In the event of a sulfur condenser tube failure, the same considerations
apply as indicated for the waste heat exchanger tube failure. The flashing
water and steam rate is significantly less than for the waste heat
exchanger case due to the much lower (50-70 psig) steam side operating
pressure.