13 replies to this topic

[T_bag]

Hello everyone,

 

I am currently working on  blowdown line & RO sizing for a gaseous system. The estimated RO size for depressurization to 100 psig is around 0.12 inch (3mm). The upstream and downstream line sizes are 1.5 & 2 inches. I am concerned that RO size of 0.12 is too small. is there any guideline on what minimum RO size to be used.

 

I am also concerned with the temperature drop due to increased RO size with increase of depressurization rate.

 

looking for some suggestions.   

[breizh]

Hi,

You may want to use the documents attached .

Breizh

Attached Files

•  depressurization rev1.xlsx   61.09KB   29 downloads
•  depressurization Mike beychock.doc   126.5KB   22 downloads

[T_bag]

Hi Breizh,

 

so I am using Unisim for depressurization calculation and reached to a orifice size of 3mm. The doubt I am having, is it acceptable to install a 3mm orifice in a line size of 1.5 inch (38mm).

[breizh]

Hi,

How long to depressurize your system? 

What is the temperature at the outlet?

Note: I've no clue about Unisim.

Breizh 

[T_bag]

Hi, 

 

1. 

Case 1:-

Currently I have assumed 10 minute of depressurization to 100 psig. the Beta ratio for the estimated RO is 0.1 (API recommends >0.2).

(Line size :- 40mm (1.5 inch), RO size :- 4mm (0.16 inch)

 

The downstream RO temperature for current condition is -60 oC.

 

2.

Case 2:- To main beta ratio of 0.2,

Depressurization time decreased to 3 minutes (RO size :- 0.3 inch (8mm)

Down stream RO temperature :- -84 oC

 

which case is practically possible.

[fallah]

 

 

Hello everyone,

 

I am currently working on  blowdown line & RO sizing for a gaseous system. The estimated RO size for depressurization to 100 psig is around 0.12 inch (3mm). The upstream and downstream line sizes are 1.5 & 2 inches. I am concerned that RO size of 0.12 is too small. is there any guideline on what minimum RO size to be used.

 

I am also concerned with the temperature drop due to increased RO size with increase of depressurization rate.

 

looking for some suggestions.   

 

Hi,

 

API recommends a beta ratio of 0.2 or higher...

Edited by fallah, 28 December 2023 - 04:08 AM.

[fallah]

Hi, 

 

1. 

Case 1:-

Currently I have assumed 10 minute of depressurization to 100 psig. the Beta ratio for the estimated RO is 0.1 (API recommends >0.2).

(Line size :- 40mm (1.5 inch), RO size :- 4mm (0.16 inch)

 

The downstream RO temperature for current condition is -60 oC.

 

2.

Case 2:- To main beta ratio of 0.2,

Depressurization time decreased to 3 minutes (RO size :- 0.3 inch (8mm)

Down stream RO temperature :- -84 oC

 

which case is practically possible.

 

Hi,

 

Considering low temperature in downstream of RO for both cases, case 2 is highly preferred; because if it's intended the material of downstream RO would be selected based on the reported low temperatures, for both cases the stainless steel pipe should be selected while at least in case 2 the criteria for minimum beta ratio has been met.

[breizh]

Hi,

https://bssa.org.uk/...temperatures-2/

 

To me the depressurization time should be about 15' .

 

Breizh 

[breizh]

Hi,
Did you check with multiple orifices?
Should be easy with your simulator.
Breizh

[snickster]

Seems like the temperature drop will be the same in any case and not depedent upon the rate of depressurization but only on the ratio of downstream to upstream pressures during depressurization.  The flow will be choked at the orifice throughout the depressurization if downstream pressure is atmospheric or low enough which I believe it is in your case.  The cholked flow critical pressure and temperature will be same throughout regardless of orifice diameter, only thing that changes is the flowrate and therefore time to depressurize.  The flow at orifice pressure and temperature and upstream will vary same but at different rate in my opinion.

[T_bag]

Hi,
Did you check with multiple orifices?
Should be easy with your simulator.
Breizh

Hi Breizh,

I did Check. 

Increased RO Size leads to lower temperature with lower depressurization rate (around 5 minutes for double RO size to maintain beta ratio of 0.2). 

I also consulted with our seniors and I have received the suggestion that lower depressurization time should not be a concern as API suggested time of 15 minutes is the maximum limit. 

FYI our system volume is low (35 ft3) .   

Edited by T_bag, 29 December 2023 - 01:25 AM.

[T_bag]

Seems like the temperature drop will be the same in any case and not depedent upon the rate of depressurization but only on the ratio of downstream to upstream pressures during depressurization.  The flow will be choked at the orifice throughout the depressurization if downstream pressure is atmospheric or low enough which I believe it is in your case.  The cholked flow critical pressure and temperature will be same throughout regardless of orifice diameter, only thing that changes is the flowrate and therefore time to depressurize.  The flow at orifice pressure and temperature and upstream will vary same but at different rate in my opinion.

Hi Snickster,

I am surely seeing a lower temperature with higher depressurization rate.

[breizh]

Hi,

Yes, the volume is small, less than 1 m3.  

Next time supply all the process data, nature of the fluid, P discharge, volume of the system.

Good luck

Breizh 

[katmar]

The reason API recommend 0.2 as the minimum beta ratio is because the uncertainty in the coefficient of discharge increases for smaller beta values.  If the accuracy of your discharge time is not critical then you can use lower values.  Remember that with a high pressure drop across the orifice the thickness of the plate should be enough to keep the plate from dishing.