3 replies to this topic

[Subramaniam K]

Hi,
I am doing depressuring calcualtions for gas oil sepration, I want reference for calculating depressuring rates, and any reference regarding HYSYS simulation for dynamic depressurization kindly also post if any body have chapter 14 of HYSYS operation guide.

[sheiko]

Hi,
I am doing depressuring calcualtions for gas oil sepration, I want reference for calculating depressuring rates, and any reference regarding HYSYS simulation for dynamic depressurization kindly also post if any body have chapter 14 of HYSYS operation guide.

Go to this blog: http://webwormcpt.blogspot.com/ and use the search feature. There are plenty of very good info. about depressurization and Hysys namely.

[Joyy]

Hi,

See attached Dynamic Depressuring Utility User's Guide: "Depressurisation: A Practical Guide" for using the Hysys dynamic depressuring utility.

For more discussion on this topic we need to know system you intend to depressurise like equipment or pipeline since both have different depressuring philosophy.

The equipment requires depressuring for both fire case and during a process requirement like equipment shutdown.
Criteria applied is based on API 521 recommendations, which states to reduce the equipment pressure from initial conditions to 50%of the vessel design pressure within 15 mins. This generally applies to carbon steel vessels with thickness greater than 1". For smaller thickness vessels 15 mins. criteria is not applicable and will require faster depressuring.
Emergency depressuring during fire case is generally applied to vessels operating at higher than 250 psi pressure. In such cases depressuring to 690 kPa is done.

Depressuring a pipeline or a section of pipeline is done for process reasons / maintenance requirements. Due to large inventories of long pipeline, depressuring is achieved over several hours.

Apart from the requirement of final pressure and depressuring time, there are other areas which a designer should look into while sizing a RO on the downstream of a blowdown valve such as
- negative temperature as the gas cools by expansion
- peak depressuring rate is less than or equal to the flare capacity
- An equipment like compressor can have multiple blowdown valves at the downstream of each stage.

Best Regards,
Joyy

Attached Files

•  Depressuring___A_Practical_Guide.doc   402.5KB   753 downloads

[Subramaniam K]

Thanks for ur replies and useful references.
Can u provide me a detailed calculations steps for depressuring rates like formula to calculate initial depressuring rates as the rate is maximum during first few seconds of depressurization.