6 replies to this topic

[process705]

HI:
Can any one explain me that why Flow control valve is used after solution pump in amine system.
The solution pumps are provided with VFD. Using this VFD one can maintain flow rate of lean amine to the amine contactor. So why Flow valve is provided?
Thank you very much in advance.

[Zauberberg]

It is the other way round: flow control valve is there to control the flow, while the purpose of VFD is to adjust the power consumption based on actual flow rate of pumped fluid. VFD itself cannot control the flow. Without VFD (assuming constant-speed motor), any excess energy delivered to the fluid would be wasted across the control valve.

It's not possible for any pump to operate properly without a control valve on the discharge line (if we want to control the flow), since its purpose is to allow the pump to ride on its curve by adjusting the system resistance, for any given flowrate.

[Tajammal Hussain]

If the Flow Control Valve will not be there then pump will deliver its design flow to the system which is usually not required in process systems. Also it is difficult to interlink VFD with flow rate, there will be variation in flow and pump motor may be overload and heat up. Now days in industry usually pump speed is kept constant and a FVC is provided at discharge to control the flow.There is only one limitation for using the control valve that while and before runnig the pump control valve should be 5% open, its a rule of thumb to protect the pump seals or inshort the minimum opening while pump is running should not less than 5% inorder to provide safety to pumps parts.
Tajammal
OMV GmbH

[fallah]

As per what included in attached (from the book of NORMAN P. LIBERMAN) regarding the possibility of not considering control valve in discharge line of the pumps with variable speed driver:

Don't you think with an orifice plate and sending the flow signal through relevant flow transmitter to variable speed driver,eliminating of FCV could be possible?

Attached Files

•  Pages from Working Guide to Process Equipment 3rd Ed - McGrawHill (2008) - 0071496742.pdf   67.38KB   27 downloads

[Zauberberg]

Norm's scheme will work (no reason to have doubts in the wisdom of our guru), and it also appears to be quite logical from control point of view: coupling steam flow to the turbine directly to the controlled variable (level in the tower). And that is the main advantage of a VFD in his example: direct control. But honestly, I've never seen such scheme implemented anywhere so far.

The question from this particular thread is somewhat different in nature and it is related to control of the amine flow in AGR units. I believe that - without having a dedicated FC - controlling actual amine flow just by a means of an VFD into the absorber would be impractical - how would one do it? We don't know from where the VFD receives the control signal in this case (regenerator bottom level, amine surge tank level, flow controller...?) so it's quite difficult to give a complete answer. I do however agree with what you have said in your post.

[Art Montemayor]

All:

I am attaching a file I believed I downloaded from our Forums sometime in the past.

I have applied variable speed drive to high pressure, multi-stage centrifugal pumps - in downhole water injection applications.

The attached file describes the two types of applications:

• One where friction head loss predominates; and,
• One where a high static head exists.

I think you will find the descriptions ample for understanding how a VSD is applied.

Attached Files

•  Variable Speed Pumping Executive Summary.pdf   1.54MB   44 downloads

[Padmakar Katre]

Dear Art,

Thanks, a very nice information on the topic.