13 replies to this topic

[ziba]

Hi all :

 

I attached an excel file, will appreciate if you could send me some feed back regarding  the best control option :

 

summary: two water wells with VFD hooked up pumps, water runs from each well to one common tank , client did not want any level control valve in between(tank and pumps)

 

.

saying that it is  client's preference, I believe that we need a level control valve for  tank water level control however client did not like it, at the end we had to add a pressure control valve between tank and pumps to closeup  in case of high pressure based on ABSA REQUIREMENTS or VFD fault .

 

 

how can i optimize the system now?tx 

 

what do you do normally in these situations when client want something that does not look normal.

 

tx in advance

Attached Files

•  control- schematic.xlsx   15.66KB   49 downloads

[prengr]

Dear ziba,

 

Based on my experienced oil sand project, there is two control system.

1. Flow control with pressure compensation by pump VSD

2. Level or Pressure control with a selector

 

I hope that this reply helps you.

 

Thanks.

[TS1979]

You did not mention if the water tank is a pressure tank or atmospheric pressure tank. If the tank is an atmospheric pressure tank, using level to control the VFD is okay. The tank should have an overflow line to protect the tank.

 

If the tank is a pressure tank, you need a PSV to protect the tank.

 

The pump discharge pressure is determined by the water flow rate and pump speed. There is no need for the pressure control valve.

[fallah]

Dear Ziba,

 

Actually client has selected the VFD pumps in order to ignore the LCV between the pump and tank. The configuration with LIC triggering directly the VFD pumps seems to be OK and no need to PV inbetween. Of course adequate protection should be considered for LIC failure...

 

In such situations if there would be an alternative solution we have to follow client query...

[sukanta87]

Hi Ziba,

 

* What was the purpose of the water? The discharge from the tank is continuous?
* Normally what we see the water tanks are atmospheric. What you have? If it's atm tank, then no need of pressre controlling/ PSV/ PCV.
* You can consider the level switch (LS) for the operation rather than LCV and VFD ( see the attached schem.). VFD is not reliable more for pump operation and not frequently used if the process isn't sensitive more.
* If you think your control system is better and simple than the client wanted then try to convince the client and acknowledge the advantages.

Attached Files

•  Water pump.pdf   390.88KB   37 downloads

[ziba]

You did not mention if the water tank is a pressure tank or atmospheric pressure tank. If the tank is an atmospheric pressure tank, using level to control the VFD is okay. The tank should have an overflow line to protect the tank.

 

If the tank is a pressure tank, you need a PSV to protect the tank.

 

The pump discharge pressure is determined by the water flow rate and pump speed. There is no need for the pressure control valve.

Hi:

 

Thanks for reply, 

 

Tank is an atmospheric vessel

Client doesnot want overflow line from tank as it contains water with some natural gas.

 

LIC is controlling pump VFD speed, thats the way client wanted no LCV between but ABSA in alberta requires a valve. either LCV or PCV to protect tank.

 

now how to optimize it should I make it cascade now

Edited by ziba, 03 April 2014 - 11:33 AM.

[ziba]

Dear Ziba,

 

Actually client has selected the VFD pumps in order to ignore the LCV between the pump and tank. The configuration with LIC triggering directly the VFD pumps seems to be OK and no need to PV inbetween. Of course adequate protection should be considered for LIC failure...

 

In such situations if there would be an alternative solution we have to follow client query...

Hi Mr Fallah:

 

Thanks for your reply.

 

having a valve between an atmospheric tank and a well is ABSA requirement, they reject registration if the control system between a tank and well is just based on one level transmitter on tank controlling pump speed , they need double protection.the question is in case of LIT failure and VFD failure, what should we do?

 

now if you can sketch what is actually best way to do it , that would be very much appreciated,  

 

being said that there is also an ESDV upstream of PV valve. I edited my excel drawing, it is two sheets.

 

tx

[fallah]

Dear ziba,

 

Nothing attached as edited EXCEL drawing...

 

Seems the tank has been blanketed with natural gas, am i right?

 

Anyway, an additional protection layer to protect the tank against overflow in the case of LIC failure can be: considering a level switch triggers the ESDV to be closed and at the same time the pumps to be tripped in HH position...

 

Hope above helps you out...

[ziba]

Dear ziba,

 

Nothing attached as edited EXCEL drawing...

 

Seems the tank has been blanketed with natural gas, am i right?

 

Anyway, an additional protection layer to protect the tank against overflow in the case of LIC failure can be: considering a level switch triggers the ESDV to be closed and at the same time the pumps to be tripped in HH position...

 

Hope above helps you out...

Hi:

 

I forgot to attach the edited file,Sorry  here you are.

 

Yes tank is blanketed and produced gases are connected to VRU suction manifold.

 

So my undersatnding is that " you mean that having the valve is not necessary? and it is redundant" but what about ABSA rules for PROTECTION OF LOW MOP side of system ,

 

I have attached a sheet from ABSA for pipeline pressure control and over-pressure protection, high pressure pipeline is connected to the water tank , pipeline design  pressure = 300 ANSI rating , it is connected to an atmospheric tank with design pressure of only 3.45 Kpag.

 

 pipeline is designed based on CSA and the  inlet header from pipeline designed based on ASME.

 

Based on ABSA regulations ,all sources of over-pressure including operator error and those involving fire , start up and shutdowns and upset scenarios should be accounted (including instrumentation malfunctions.)

 

Please let me know if there are other options than" level switches on tank to close inlet ESDV"?

 

How can I improve the control with added  valve  . There are two files attached, appreciate if you take a look at ABSA file, many thanks again 

 

Thanks   control- schematic 2.xlsx   16.97KB   17 downloads  20140403144913.pdf   254.28KB   23 downloads

Edited by ziba, 04 April 2014 - 09:59 AM.

[TS1979]

Ziba,

 

Your pressure control valve does nothing to protect the tank. Further, control valve is not acceptable as a protection layer because control valve can fail. Your ESDV is strange too. What signal will close the ESDV?

 

The simplest way to protect your tank is to install another level transmitter. When the level is HH, trip the pump or close the ESDV if you prefer to install one. Once again, no pressure control valve is required in your indicated case.

 

Hope this help 

[yazdanpanahimehrdad]

Dear ziba;

you need double protection for tank against probable failures. 

1-Tank level is controlled using LCV and VFD pump. this action is normally defined in PLC or DCS system.

2- You can use another protection layer for protection of tank against pump or LCV failure. As Mr.Fallah said you can use a mechanical LSHH. in case of reaching level to high high it will close ESDV located before LCV and simultaneously it will shut down the pump. please note that this is different from LCV action. for more protection you can define this action in your ESD system not DCS system. because ESD system is more reliable.

3- for protection of tanks aganise over pressure you have to equip the tank with PCV and also vacuum breaker. also necessary PSV and emergency vents according to API 2000 shall be foreseen for the tank.  

[fallah]

  

Yes tank is blanketed and produced gases are connected to VRU suction manifold.

 

So my undersatnding is that ? you mean that having the valve is not necessary? and it is redundant" but what about ABSA rules for PROTECTION OF LOW MOP side of system ,

 

I have attached a sheet from ABSA for pipeline pressure control and over-pressure protection, high pressure pipeline is connected to the water tank , pipeline design  pressure = 300 ANSI rating , it is connected to an atmospheric tank with design pressure of only 3.45 Kpag.

 

 pipeline is designed based on CSA and the  inlet header from pipeline designed based on ASME.

 

Based on ABSA regulations ,all sources of over-pressure including operator error and those involving fire , start up and shutdowns and upset scenarios should be accounted (including instrumentation malfunctions.)

 

Please let me know if there are other options than" level switches on tank to close inlet ESDV"?

 

How can I improve the control with added  valve  . There are two files attached, appreciate if you take a look at ABSA file, many thanks again 

 

Thanks control- schematic 2.xlsx20140403144913.pdf

 

 

Dear ziba,

 

Thanks a lot for the info provided...

 

As per the ABSA file you attached, and if you should follow the guideline included i suggest using following configuration among suitable cases submitted there with keeping present situation in your attached EXCEL file (sheet 1) as much as possible:

 

Moving from higher MOP toward lower, an ESDV as a pressure limiting device would be activated by high pressure (max of higher of 10% and 35 kPa than lower MOP) signal, followed by a pressure relieving device with the set pressure same as the value of ESDV pressure signal...

 

In fact, in your configuration just a pressure control device (PV) has been substitued by a pressure relieving device and the second configuration among suitable cases has been selected.

Edited by fallah, 03 April 2014 - 11:55 PM.

[ziba]

Dear ziba;

you need double protection for tank against probable failures. 

1-Tank level is controlled using LCV and VFD pump. this action is normally defined in PLC or DCS system.

2- You can use another protection layer for protection of tank against pump or LCV failure. As Mr.Fallah said you can use a mechanical LSHH. in case of reaching level to high high it will close ESDV located before LCV and simultaneously it will shut down the pump. please note that this is different from LCV action. for more protection you can define this action in your ESD system not DCS system. because ESD system is more reliable.

3- for protection of tanks aganise over pressure you have to equip the tank with PCV and also vacuum breaker. also necessary PSV and emergency vents according to API 2000 shall be foreseen for the tank.  

Thanks Mr Yazdan:

 

I have enough tank protection including  PVRV, EPRV and TH.

 

I also added a LSHH to close inlet ESDV. the purpose is to get ABSA approval in next step.

[yazdanpanahimehrdad]

Dear ziba;

Thanks for reply

please note if LSHH only closes ESDV, pump may damage because it works with closed discharge. So LSHH should also shut down the pump..