Spillback Line Return to Tank or Suction of Pump

[MountHorn]

We are adding a spillback line for the chemical injection pump that is on a lower deck (25ft) below the chemical storage tanks. Does it matter whether the spillback is routed to the suction of the pump or to the tank?

 

[bimr]

Don't believe anyone can submit an appropriate answer without knowing the details of what chemical that you are injecting, whether this project is indoors or outdoors, whether the substances are flammable, what effect will the spillback purity have on the system, etc. It would help to have a simple flow diagram.

 

[LittleInch]

Only if the temperature increases in the pump suction.

Too many unknowns.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Heaviside1925]

Yes, it can matter. P&IDs or sketch? pump specifics / information? process description and conditions? spillback type? injection type?

 

[1503-44]

One of these types,

https://www.williamspumps.com/en-us/

or similar low power low volume pumps? can usually be routed to either place.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[mk3223]

IMO, the spillback of the injection pump is typically routed back to the tank without any concern. The return line of the 25ft head shouldn’t be the issue for the pump discharge.

 

[georgeverghese]

Since total injection rate will often be less than pump throughput capacity, pressure spillback should be to source tank, not into pump suction.

 

[1503-44]

If it was full throughput, then it's OK?

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[georgeverghese]

@1503,
If sum total injection rate always matches pump capacity, the pressure spillback line wont be operational at any time, so it wouldnt matter if there were to be a spillback or not, or where it is connected to.
Suspect this is a fixed speed pd pump ?

 

[1503-44]

Only operational when pipeline pressure is greater than max discharge P of pump. Probably not going to occur, unless discharge line is closed while running.

Typical installation is

From

https://www.spxflow.com/assets/pdf/bran-luebbe-1649-us-chemical-injection-for-oil-and-gas.pdf

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[georgeverghese]

If it is going to involve considerable effort to connect this pressure recycle to source tank, it may be possible to return this to pump suction provided :
a)fluid saturated vapor pressure (or bubble point pressure) is much less than minimum suction pressure at say 10degC higher than source tank temp
b)pump is stopped on auto sequence when there is no net forward flow to consumers.

If you dont know bubble point pressure info for the chemical being injected, route pressure recycle to source tank.