Booster pump discharge - check valve or isolation valve? 1

[rutherford703]

Please see attached doument for your information.
The purpose for the check valve or automatic isolation valve is to prevent reverse flow through the pump during pump trip

Check valve:
Advantages
1). Immediately stop reverse flow during pump trip

Disadvantages
1). check valve not reliable for slurry service
2). will the slam close of the check valve create a pressure spike due to the 70m static slurry head to damage the check valve?

Isolation valve:
Advantages
1). Isolation valve is more reliable

Disadvantages
1). Automatic close the isolation valve will create a dead head for the pump
2). Quick close the isolation will create a pressure surge upstream of the booster pump.

Waht do you think? I appreciate your input!

 

[BigInch]

What's wrong with both?

The vfd may not do much good with that static head. It depends on what your pump curve looks like. VFD (or any low rpm device) produces low torque at low speeds and you have 70 meters of static head. You will get reverse flow as soon as the block valve opens, if you don't have a check, and your pump is not up to speed to overcome that 70 m static head. You probably won't be able to start flow at low speed. Depends on at what speed your pump can generate the 70 m of head to initiate forward flow. If that takes a long time, you may need a discharge to suction recycle line.

Put a check valve in there downstream of a block valve. USE BOTH. Have the block valve auto close on overpressure and a PSV in the suction, in case the check valve breaks and puts 40 bars on your HDPE piping.

Use a soft close check.

What would you be doing, if you knew that you could not fail?

 

[BigInch]

post the pump curves and the slurry density for more help.

What would you be doing, if you knew that you could not fail?

 

[rutherford703]

BigInch, good comments.

In slurry service, normally people do not use check valve because people think that check valve is not reliable in slurry service and there is no indication when the check valve is failed.

Your comments about the VFD control for the booster pumps are especially true for this system because the slurry system behaves as a Bingham type fluids - Non-Newtonian flow. The pump head required to move the fluid is almost constant regardless the fluid velocity inside the pipe.

Do you think there will be a pressure surge on the check valve due to reverse flow during pump trip? I don't think there will be a pressure surge resulted by the check valve stopping the reverse flow.

Just curious, how did you get the 40bar pressure upstream the booster pump? The total elevation difference is 100m.

The specific gravity for the slurry is 1.3

 

[BigInch]

Oh sorry. You're right about the pressure, I looked at the 400 m elevation and didn't subtract the pump elevation. I was writing faster than I was thinking. Happens sometimes. But anyway, you could have pump discharge head making its way towards suction piping with a trip and reverse flow. Maybe a pressure still higher than the HDPE allowable pressure. Be careful. Rough conservative estimate might be as high as 50% higher than normal discharge pressure. I normally analyze a trip assuming a broken check. I would think that a pressure spike and reverse flow is definitely possible probable.

With slurries flow will increase once initiated. If it doesn't take too long to do that, the motor has spare torque at speed it can use to start flow. Then as flow picks up, pressure will drop and get to normal power and normal discharge pressure, or are the two pumps in series to overcome the startup resistance, then you shut down one when it gets going. Optionally can, or do you change configuration to parallel flow and start moving twice the volume at what was 1/2 start up pressure? I've done that with extra heavy crudes.

What would you be doing, if you knew that you could not fail?

 

[stanier]

Rotherford 703,

What is the slurry in terms of size distribution, top size, sharpness of solids, density solids, temperature, Cw%, CV%. Are the large particles carried in a carrier fluid made up of a slurry of fine particles?

I would consider a Red duckbill check valve with a Wey knife gate valve for isolation.

For transient analysis Ellis provides a great insight into the behaviour of the Red check valve in Pressure Transients in Water Engineering.

When it comes to PE pressure capability in surge conditions there has been a major rethink on its capabilities. Pressures up to 2.5 times design rating are now used. I like to be more conservative and use 1.5 times the derated capability ( temperature, fatigue factors taken into account). I have used such factors on long pipelines on mine sites where the PE is up to DN1200 PN20 where the operating temperature is 28C.

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

http://waterhammer.hopout.com.au/

 

[rutherford703]

Stanier,

Thanks for your response. The fluid inside the piping is Bingham plastic flow - pseudo-homogeneous flow. The maximum operating temperautre is about 20°C. The particle size is fine particles (90% <44 micron). The density of the solid is about 2,650 kg/m3 and the solid content is about 35 wt%.

The HDPE piping rating pressure is 200 psig. It seems OK for the system.

The operation do not want check valve. "A check valve will not operate for more than a couple of days in this service, the fluids solids contents will plug / gum up the moving parts" that's what they said.

Thanks again BigInch for your response.