liquid butane flow control 1

[rika kose]

We have a liquid butane tank 6 barg pressurized by N2.
We want to have constant flow injecting into a reactor, e.g. 0.05 kg/s. At this moment, there is only one flow control valve in the injecting line. Butane flashes in the valve. downstream the valve, icing. flow is very unstable. a mass flow meter is near the storage tank, around 30 m before the control valve.

What is the right setup? how to improve the system?

 

[georgeverghese]

If you cannot add an internal heating bundle, then install an external kettle type (TEMA AKU or BKU ) heat exchanger with LP steam or similar as heating medium on tubeside. Draw off vapor only from vapor side of kettle to user. Operate the kettle on constant level control with LCV upstream. And modulate steam feed on vapor space pressure control - say 4.5-5.0barg. PIC cascade on steam flow control would be better.

 

[rika kose]

Typically the Cv listed on the valve body and datasheet will be the 100% open Cv. A Cv of 0.4 does not sound oversized to me - an equal % CV will get down to 0.1 Cv around 60-70%, while a linear CV will likely be near 30% open to get a Cv of 0.11. In either case, the valve seems sized appropriately.

Further questions:
What is your flowmeter type?
What is the CV doing when operating? By this, I mean two things. First, you need to physically look at the valve during operating and see how much the stem is moving. Second, can you tell us what the output value is during normal operation. Does the output to the CV jump around when the flowmeter reading goes from 0.005 to 0.5?

Putting a restriction orifice downstream of the control valve will help the flow instability due to flashing in the valve, but it won't help an improperly designed flowmeter, a control valve that is sticking or needs other maintenance, or bad control loop tuning parameters.

Then something strange is happening with your flow meter as that size valve simply cannot be flowing the flows you're quoting at changes of 100 times.

Again that flow meter needs to be very small and what type is it? Maybe its cycle time is too high and its reading are not smooth enough to count enough pulses or whatever it is doing. If its a turbine then maybe it is jumping or just not enough pulses per second to make it accurate.

Or your valve is actually pulsing open and close rapidly to try and react to this very strange flow input (too high, too low, too high....) and the whole thing is having a heart attack....

Get your data and control system understood before you start messing around with things like orifices and manual valves.

Thanks for the ideas and advices.

The flowmeter is a coriolis flowmeter. I don't have the specificiations. It is quite small. I can read the MV from the system which is jumpping hard.
I think we should replace the control valve with a hand globe valve, as we only want to control the total amount at this moment. The dosing flow is 0.05 kg/s, total 100kg. when the total amount 100 kg is reached, on/off valve closed. dosing flow doesn't need to be adjusted for temperature.

 

[LittleInch]

Not sure if it's been mentioned, but your control valve could simply be worn away by the flashing of the liquid. It would be very interesting to take it apart when you get a replacement.

Be warned though that controlling a flashing liquid across a control valve is not standard and hence any standard sizing and types of valve will very quickly get worn away.

See e,g, https://www.imi-critical.com/wp-con...B01023.01-22en_EroSolve-Flashing_Brochure.pdf for an idea and please talk to the vendors otyherwise you will get the same issue even with a manual valve which will quickly wear away and become uncontrollable after a short period of time.

You're doing a strange and difficult thing here so will need almost certainly a high cost valve designed for flashing liquid.

See e.g. https://www.emerson.com/en-gb/automation/valves/controlvalves/control-valve-flashing#:~:text=Control Valves for Flashing Applications,-Selecting a valve&text=Sliding-stem angle valves are,offer straight-through flow paths.

Basically this is a very small choke valve where you want the flow path to go from outside to inside with some sort of plug and cage arrangement by the looks of it.

 

[hacksaw]

Improper valve sizing, inappropriate flow meter, sound like the problem is higher up.

 

[hacksaw]

improper valve selection and sizing, improper flow measurement, sounds like the problem is at the management level.