10 replies to this topic

[CHSO4]

Hello Members,

 

I am dealing with centrifugal compressor for natural gas compression for one of our clients. I came across compressor capacity control valve (560FV-230405), parallel to compressor anti-surge valve (560XV-230426), while going through P&IDs (refer attached screenshot). Can someone explain function of this capacity control valve & it's working principle please?

 

 

Attached Files

•  Capacity Control Valve.JPG   24.49KB   1 downloads

Edited by Ghanshyam Gabani, 22 July 2024 - 11:32 PM.

[breizh]

Hi,

No attachment.

Use the full editor button, next to save changes button then choose file and attach this file.

Breizh

[fallah]

Hello Members,

 

I am dealing with centrifugal compressor for natural gas compression for one of our clients. I came across compressor capacity control valve (560FV-230405), parallel to compressor anti-surge valve (560XV-230426), while going through P&IDs (refer attached screenshot). Can someone explain function of this capacity control valve & it's working principle please?

 

Hi,

 

My be the line including FV-230405 is the minimum flow line which can be activated before Anti Surge Valve and following to a process upset leading to discharge flow rate reduction less than a pre specified value upper than that of the surge point. Anyway, to get a proper response try to attach the P&ID as Breizh explained for you.

[CHSO4]

 

Hello Members,

 

I am dealing with centrifugal compressor for natural gas compression for one of our clients. I came across compressor capacity control valve (560FV-230405), parallel to compressor anti-surge valve (560XV-230426), while going through P&IDs (refer attached screenshot). Can someone explain function of this capacity control valve & it's working principle please?

 

Hi,

 

My be the line including FV-230405 is the minimum flow line which can be activated before Anti Surge Valve and following to a process upset leading to discharge flow rate reduction less than a pre specified value upper than that of the surge point. Anyway, to get a proper response try to attach the P&ID as Breizh explained for you.

 

 

My apologies, Now the snap of P&ID is attached, please refer updated post. Would appreciate your views on this.

[breizh]

Hi,

Share the PId to understand the philosophy.

Breizh

Attached Files

•  anti surge valve.pdf   5.44MB   35 downloads
•  anti surge system.pdf   261.86KB   28 downloads

[fallah]

 

 

 

Hi,

 

My be the line including FV-230405 is the minimum flow line which can be activated before Anti Surge Valve and following to a process upset leading to discharge flow rate reduction less than a pre specified value upper than that of the surge point. Anyway, to get a proper response try to attach the P&ID as Breizh explained for you.

 

 

My apologies, Now the snap of P&ID is attached, please refer updated post. Would appreciate your views on this.

 

 

Hi,

 

Please let's have the whole P&ID or, at least, the notes of 1 and 4.

 

Anyway, please pay attention to my guess about the function of two mentioned valves.

[CHSO4]

Hi

 

Please see attached P&IDs, would appreciate any clarification on this.

 

 

 

 

 

Hi,

 

My be the line including FV-230405 is the minimum flow line which can be activated before Anti Surge Valve and following to a process upset leading to discharge flow rate reduction less than a pre specified value upper than that of the surge point. Anyway, to get a proper response try to attach the P&ID as Breizh explained for you.

 

 

My apologies, Now the snap of P&ID is attached, please refer updated post. Would appreciate your views on this.

 

 

Hi,

 

Please let's have the whole P&ID or, at least, the notes of 1 and 4.

 

Anyway, please pay attention to my guess about the function of two mentioned valves.

 

 

Attached Files

•  P&ID.pdf   325.87KB   18 downloads

[fallah]

 

Hi

 

Please see attached P&IDs, would appreciate any clarification on this.

 

 

Hi,

 

Please let's have the whole P&ID or, at least, the notes of 1 and 4.

 

Anyway, please pay attention to my guess about the function of two mentioned valves.

 

 

 

Hi,

 

Almost in all centrifugal compressors a surge control system is designed for surge prevention and its function should cover three basically different scenarios as follows:
• Process control, such as handling the range between maximum required flow to turndown
• Surge protection, such as in emergency shutdown case
• Surge protection during start up
Despite of the first scenario in which the system just plays the role of a classical control system, in other two scenarios (especially in the second one) there is no particular control function and it's just needed opening of the anti-surge valve as fast as possible such that sometimes dual solenoids fitted with quick exhausts are installed to ensure that the valve opens quickly when the operating point approaches the surge point.
In many cases, all above mentioned scenarios can be covered by a single valve, say by applying a three-way solenoid valve into the positioner’s output of the anti-surge valve, hence the valve can be made such that to open with either a proportional (4-20 mA) signal for modulating process control, or a discrete (24 VDC) signal for total fast opening.
But in some cases, say, it's required the forward flow to be less on low demand case, and in one hand the control system should open the anti-surge valve to recycle some of the gas back to the suction and, on the other hand, having the significant difference between the turndown flow requirement and required anti-surge flow; the result yields a large anti-surge valve size which in turn means longer modulation time between fully open and fully closed positions plus the poor controllability leading to the valve behavior in oppose to the anti-surge prevention response. In these cases, considering separate valves, one for surge protection at emergency shutdown and start up and the other for modulating control handling the process upsets and turndown condition is more reasonable than considering a single valve.

[astro]

Note 4 of the posted P&ID states:

 

Capacity control valve requirement to be confirmed by compressor vendor and shall be part of vendor scope of supply and control. This shall be mutual agreed with company during compressor bidding phase.

For a compressor driven by a gas turbine (GT), the most effective way (generally) to control capacity is by using the GT's capability for variable speed.

 

Using a recycle valve for routine capacity control wastes energy and should only be used for startup/shut down/upset conditions that are relatively short lived events. The anti-surge is a must have but this valve should normally be closed.

 

My first thought when I looked at the 2 valves in parallel, was that it would be for split range control. However the anti-surge is marked as an XV (inferring to me on/off not modulating behaviour) with note 4 indicating that the FV is for "capacity control". The inlet line to these valves is marked as 20" with the outlet at 24", so it wouldn't surprise me that it's a tough ask to find a single valve to service the entire operating envelope.

 

For smaller systems, I'm used to seeing a single modulating control valve providing anti-surge and low flow recycle (in cases where the variable speed driver - of whatever type - can't slow down the machine enough without reducing the head beyond process needs) service combined.

 

Even so, I'd be pushing the design to work with one valve. Looks to me that this is indeed the plan and the FV is a contingency with a view to trimming the scope in consultation with the machine supplier. Speaking from experience, dynamic simulation is a sensible scope item to plan in to confirm that the design is robust once sufficient detail is available, so it might take a while before the final design decision can be made.

[Robert Montoya]

Hi,

Share the PId to understand the philosophy.

Breizh

Hi Breizh; 

1. Capacity Control Valve (640FV-230005):

   • If the flow into the compressor is high and approaches the upper operational limits, the capacity control valve (640FV-230005) typically acts first. Its role is to adjust the gas flow into the compressor to maintain operation within the desired parameters, preventing an overload of the compressor.

2. Antisurge Valve (640XV-230426):

   • If the flow remains too high despite the adjustment by the capacity control valve and there is a risk of surge, the antisurge valve will activate. This valve recirculates the gas from the compressor discharge back to the inlet, reducing the discharge pressure and preventing damage to the compressor.

Low Flow Condition:

1. Antisurge Valve (640XV-230426):

   • In the case of dangerously low flow, the antisurge valve is typically the first to operate. Its purpose is to prevent surge (a condition where the flow through the compressor is insufficient, potentially causing flow reversal and mechanical damage). The valve opens to allow the gas to recirculate from the compressor's discharge back to the inlet, keeping the flow through the compressor at a safe level.

2. Capacity Control Valve (640FV-230005):

   • If the control system detects that the flow is too low but not yet in the surge zone, it may attempt to open the capacity control valve to increase the flow into the compressor, if possible. However, if the flow continues to decrease, the primary concern is the operation of the antisurge valve.

Summary:

• High Flow: The 640FV-230005 valve operates first to control the flow, followed by the antisurge valve if necessary.
• Low Flow: The antisurge valve (640XV-230426) operates first to prevent surge, while the capacity control valve may be adjusted if the system allows and it is necessary. 

BR

[breizh]

Hi,

Consider reading this paper.

Breizh

Attached Files

•  process control.pdf   2.57MB   11 downloads