500:1 Liquid Flow Control Turndown Needed
500:1 Liquid Flow Control Turndown Needed
(OP)
Currently modifying catalyst control system.
Current flow rates vary quite a bit by grade.
.5lbs/hr to 150lbs/hr liquid (0.88 S.G.) is the most striking flow range seen. I am estimating a controllability turndown required of about 300:1 to 500:1.
Current pump set up is a single stage diaphram pump, pulsation dampener, pressure regulator recycle after dampener, Coriolis meter after recycle, then flow control valve. In order to obtain these relatively large turndown ratios and bring the flow control valve OP into a controllable range, operations adjust the pressure regulator setpoint, pump micrometer (and subsequently the pulsation dampener), and tuning of regulator and control valve. This amount of adjustment results in a lot of inconsistency based on the knowledge and experience levels of the people on shift, which in turn may affect our quality due to flow variations. I should mention that the pressure varies downstream of our flow control valves from 60 psig to 140 psig depending on campaign. Maximum regulator pressure upstream of flow control valve is limited to 350 psig.
After speaking to pump vendor as to best course of action they recommended running the pump/recycle loop at a constant high pressure (300-350 psig) and flow while tackling the turndown issue at the control valve level. (An actuated micrometer is not an acceptable option due to limited turndown according to vendor).
Is it possible to get adequate control with a single valve? Is it possible to obtain this level of controllability turndown without resulting to 2 valves ran in split range?
Thanks
Current flow rates vary quite a bit by grade.
.5lbs/hr to 150lbs/hr liquid (0.88 S.G.) is the most striking flow range seen. I am estimating a controllability turndown required of about 300:1 to 500:1.
Current pump set up is a single stage diaphram pump, pulsation dampener, pressure regulator recycle after dampener, Coriolis meter after recycle, then flow control valve. In order to obtain these relatively large turndown ratios and bring the flow control valve OP into a controllable range, operations adjust the pressure regulator setpoint, pump micrometer (and subsequently the pulsation dampener), and tuning of regulator and control valve. This amount of adjustment results in a lot of inconsistency based on the knowledge and experience levels of the people on shift, which in turn may affect our quality due to flow variations. I should mention that the pressure varies downstream of our flow control valves from 60 psig to 140 psig depending on campaign. Maximum regulator pressure upstream of flow control valve is limited to 350 psig.
After speaking to pump vendor as to best course of action they recommended running the pump/recycle loop at a constant high pressure (300-350 psig) and flow while tackling the turndown issue at the control valve level. (An actuated micrometer is not an acceptable option due to limited turndown according to vendor).
Is it possible to get adequate control with a single valve? Is it possible to obtain this level of controllability turndown without resulting to 2 valves ran in split range?
Thanks





RE: 500:1 Liquid Flow Control Turndown Needed
I was going to suggest you include a much bigger accumulator and cycle the pump on and off at low flows, but the pump suppliers suggestion is probably as good.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: 500:1 Liquid Flow Control Turndown Needed
I was going through some control forums and one person suggested a course and fine valve operation and trying to avoid split range control. In other words, set the OP% of the course valve and perform fine flow control with the fine valve such that the fine valve is averaging 20-80% OP during control. Once reactors are lined out, we operate at fairly steady rate so I wonder if something like this would be an option. Does anyone have experience with this type of control scheme?
Thanks
RE: 500:1 Liquid Flow Control Turndown Needed
This is still a hell of a variance in flow though you might get away with two valves in parralel if you can somehow convince the control system to play ball...
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: 500:1 Liquid Flow Control Turndown Needed
RE: 500:1 Liquid Flow Control Turndown Needed
You can also do 100:1 with a pump, between stroke rate and stroke length adjustment- but because of check valve efficiency, you still need the flowmeter.
So you need either two pumps or two 30:1 fine control valves.
A coriolis meter can do 1000:1 turndown- but you shouldn't count on that unless the top flow is absolutely at the top flow end of the meter model selected and the lowest flow is well above the zero stability. Two coriolis meters would be a safer bet due to both pressure drop and practical approach to the zero stability.
I too vote for using a single pump as a pulseless pressure source with pulse dampening and spillback through an adjustable back pressure regulator or better still, a back pressure control valve loop so you can remotely adjust the pressure. Do the whole flow control with the valves. With a 3:1 range on upstream pressure, two control valves with positioners in parallel each with a coriolis meter, you should be able to achieve this.
RE: 500:1 Liquid Flow Control Turndown Needed
RE: 500:1 Liquid Flow Control Turndown Needed
RE: 500:1 Liquid Flow Control Turndown Needed
Barb
www.Exlar.com
Best alternative to hydraulic and pneumatic actuation
RE: 500:1 Liquid Flow Control Turndown Needed
RE: 500:1 Liquid Flow Control Turndown Needed
Who manufactures the kind of digital control valves, with multiple orifices you mention?
I googles but cannot find the kind of design you refere to.