Forums
Blogs
Articles
File Library
FAQ
Search
FB
I have a gas line ( 24 " and 65 bara) going to the separator . On this INLET line there is 2 " bypass line with the Valve and Restriction orifice.
Valve , restriction orifice assembly is used during the start up.
How to specify flow for this orifice?
Sunny
|
|
Restriction Orifice Sizing
Started by Guest_Sunny_*, Sep 06 2005 09:44 AM
4 replies to this topic
Share this topic:
#2
mbeychok
-
- ChE Plus Subscriber
-
- 364 posts
Gold Member
Posted 06 September 2005 - 01:06 PM
Sunny:
As long as the pressure upstream of the orifice and downstream of the valve is more than twice the pressure downstream of the orifice, the gas flow through the orifice is "choked". For the choked flow of a gas through an orifice, the flow is directly proportional to the upstream pressure.
If you know the molecular weight of the gas, the Cp/Cv of the gas, the diameter of the orifice, the pressure downstream of the orifice, and you have a pressure gauge between the bypass valve and the orifice, you can calculate the choked flow rate of the gas.
The equation for calculating the choked flow of a gas is available by visiting:
<a href="http://www.air-dispe...#Gas Discharge" target="_blank">http://www.air-dispe...s Discharge</a>
which is in metric units. If you want the customary units used in the USA, visit:
<a href="http://www.air-dispe...#Gas Discharge" target="_blank">http://www.air-dispe...s Discharge</a>
The equations you will find at the above web sites assume that the downstream pressure (PA) is atmospheric pressure. If that is not so in your case, simply use your downstream pressure as PA.
As long as the pressure upstream of the orifice and downstream of the valve is more than twice the pressure downstream of the orifice, the gas flow through the orifice is "choked". For the choked flow of a gas through an orifice, the flow is directly proportional to the upstream pressure.
If you know the molecular weight of the gas, the Cp/Cv of the gas, the diameter of the orifice, the pressure downstream of the orifice, and you have a pressure gauge between the bypass valve and the orifice, you can calculate the choked flow rate of the gas.
The equation for calculating the choked flow of a gas is available by visiting:
<a href="http://www.air-dispe...#Gas Discharge" target="_blank">http://www.air-dispe...s Discharge</a>
which is in metric units. If you want the customary units used in the USA, visit:
<a href="http://www.air-dispe...#Gas Discharge" target="_blank">http://www.air-dispe...s Discharge</a>
The equations you will find at the above web sites assume that the downstream pressure (PA) is atmospheric pressure. If that is not so in your case, simply use your downstream pressure as PA.
#3
Guest_Sunny_*
Guest_Sunny_*
-
- guestGuests
Posted 07 September 2005 - 03:34 AM
OK.
I have all the properties needed, mol wt, cp/cv.
But the bypass line size (2") which i was talking about was the crude assumption while developing the P&ID initially and now needs to be checked.
The gas flowing in main line is 1.8 * 10 e005 kg/hr at 65 bara presssure.
The concern is I need to size this bypass line with orifice ,which is to be used in for start up purpose. The equation is talking about requirment of discharge hole area.This hole area is not available.
how to go about this ?
#4
mbeychok
-
- ChE Plus Subscriber
-
- 364 posts
Gold Member
Posted 07 September 2005 - 11:24 AM
Sunny, I don't quite know how to answer your question. It seems to me that you must somehow determine how much gas flow you will need for your startup condition. Then you must size your bypass line and orifice hole.
#5
djack77494
-
- ChE Plus Subscriber
-
- 1,282 posts
Gold Member
Posted 07 September 2005 - 04:22 PM
I would suggest that this is an equalizing line and is used to equalize pressure (approximately) on both sides of your 24" valve so that it may operate with very little pressure differential across the valve. This will do wonders to save the valve as well as make for a much smaller valve actuator.
So now, to address your question, it's a matter of sizing the orifice so that the time required to achieve the desired degree of equalization is not excessive. I can't really help you by suggesting a time - it's really totally arbitrary and a matter of plant and project preference. I also cannot help you with the target differential pressure. Talk to the valve manufacturer about that. Once you have the criteria, you have an unsteady state mass balance as you flow gas from the constant upstream pressure to a continuously changing downstream pressure. I don't recall the appropriate equation, but I'm sure it's easily found (or perhaps another reader can supply it).
Doug
So now, to address your question, it's a matter of sizing the orifice so that the time required to achieve the desired degree of equalization is not excessive. I can't really help you by suggesting a time - it's really totally arbitrary and a matter of plant and project preference. I also cannot help you with the target differential pressure. Talk to the valve manufacturer about that. Once you have the criteria, you have an unsteady state mass balance as you flow gas from the constant upstream pressure to a continuously changing downstream pressure. I don't recall the appropriate equation, but I'm sure it's easily found (or perhaps another reader can supply it).
Doug
Similar Topics
Two Phase Reverse Flow -Psv Sizing For Check Valve Failure CaseStarted by Guest_namita.modak1_* , 01 Apr 2026 |
|
|
||
 Answered
Free Pump Sizing Calculator For Preliminary Engineering ChecksStarted by Guest_Gonoklab_* , 16 Mar 2026 |
|
|
||
Conceptual Sizing Of Adsorber ColumnStarted by Guest_JJvdM_* , 24 Oct 2019 |
|
|
||
Free Pump Sizing Calculator For Preliminary Engineering ChecksStarted by Guest_Gonoklab_* , 16 Mar 2026 |
|
|
||
Separator SizingStarted by Guest_HOTTEST_* , 12 Mar 2026 |
|
|
