Screw Pump Flow Control

Dear all, is it good (will it work well) to perform flow regulation of screw pump with pressure control at the outlet (with recirculation valve) and flow control valves at loading arms measuring lines downstream of the pump . The pump is transfer vacuum residue to the 8 loading arms for rail truck loading. Every loading arms has his own measuring line with flow control valve. Pump capacity is 800 m3/h. The problem for other type of regulation (VFD) is that at start of the loading, flow control valves reduced capacity from normal (100 m3/h; every loading arms-flow control valves) to 40 m3/h and loading must be performed when only one loading arms is in function but also all eight. Every advice will be helpful. Thanks in advance

Edited by suljaga, 15 February 2020 - 03:33 PM.

Why must all 8 be filled at the same time??

Due to the fact that the train composition contains 24 wagons which should be filled in the shortest possible time (max 5-6h).

Hi ,

Why the recycling line is at the discharge of the pump ? It should be at the outlet of header feeding the 8 lines .

my 2 cents 

Breizh 

Edited by breizh, 16 February 2020 - 04:04 AM.

Dear Breizh, I'm not sure I understood the question. Since this is a PD pump, it sends a constant flow (800m3 / h) regardless of the downstream pressure. My idea is to keep a constant pressure on the pump discharge near the pump. For normal flow, when all 8 loading arms are operating, the pump disharge pressure is cc 15 barg (for 800 m3 / h) and recirculation valve is closed. For example, when one loading arm completes the filling and starts to closing the control valve, the pressure on the pump discharge will increase, which will cause the recirculation valve to open. Distance from pump to the loading arms is cc 2000m.

I have a slightly more radical suggestion..

Is it possible to have that PD pump to pump to a tank near the train wagons at an elevated position, then from that tank, have 8 overflow pipes that go into the eight train wagons.

The PD pumps that are 2000m away just need to keep the tank filled and the tank will just flow into the train wagons by overflow in a constant overflow.

That flow valve above the train wagon can still be flow control if still desired with no risk of damaging the pump that is 2000m away.

Of course, this idea is only workable if you have space to build a tank near the train area. But this method effectively decouples the pump and the filling so that it is easier and safer to control.

Mr.Thorium90, thank you for your suggestion but it is not possibe because the train wagons are at the high point area and elevated tank is not possible to be installed. I am thinking two days but I can not get a solution which could be satisfying from my point of view. My another idea is to install Flow transmitter, just before loading colector, which will get flow set point from number of loading arms which are in filling mode ( 3 arms in filling mode set point 3X loading rate, 4 arms in filling mode set point 4X loading rate). From that flow transmitter I will send signal to the set point for the pump (I will put VFD regulator on the pump). For safety reason I will leave recirculation valve at the pump discharge.

Your controls as shown on your sketch look to be what is required for a PD pump.

Bobby

Thanks Bobby. I am worry about acting of flow control valves/recirculating valve because pressure will rise very quickly when (for example) one loading arm stop filling. I am not sure will it be enough time to open recirculation valve before prassure rise to the PSV set point. I  do not want to have PSV opening at normal operating conditions. Also I will  pu design pressure for all equipment to PSV set pressure .

Best regards

https://www.chemical...ntrol-pd-pumps/

Hi,

To support your work.

Breizh