Pumped Condensate Vortex Flowmeter

[Kdolph]

Hi,

I attached a diagram where i sketched the current situation of the installation of a vortex floweter. This flowmeter reads relatively well at max. flow but we have incorrect measuring at lower flows and startups. (The fluid is pumped condensate)
I also drawed a new proposed situation. Will improve the situation if a lower the line to allow complete filling. I also made some modifications in distances.

http://files.engineering.com/getfil...ef5f98d8&file=Pumped_Condensate_Flowmeter.pdf

Thanks in advance.

 

[zdas04]

I think of square-edged orifice meters as "passive" devices. By that I mean that they do not inherently do anything to the flow to correct flow profile deviation from the assumptions. That is why all the straight pipe is needed.

Vortex, and V-Cone meters are "active" devices in that they inherently change the flow profile. Consequently adding straight pipe beyond some (very small) minimum is just a waste of real estate and pipe. It never helps.

Condensate is a difficult thing to measure, because it is not just one thing. You can get wide variation of components from sample to sample on the same stream. There really isn't anything that can be done about that, except to select a meter that is more tolerant of changing conditions. Condensate is a good fluid to run through a Corriolis meter. It can be OK in a mag flow meter if you can keep the line full of liquid. Since the vortex meter has fluid properties as an input, a rapidly changing fluid mixture is not terribly effective.

You will never get great measurement of condensate from a Vortex Meter, regardless of what you do. Adding backpressure and being careful to maximize the possibility of the meter remaining full of single phase liquid can get you to some amount of repeatibility, but you'll never lower your uncertainty much.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[georgeverghese]

Vaguely recall the flow turndown on a vortex meter is approx 10:1 on full range, so are we lower than this at your low flow ? GPSA says upstream flow conditioning should be similar to that for a turbine meter.

Obviously, no meter will read correctly if the line is not completely liquid filled or not liquid primed.

 

[LittleInch]

I think w all assume this is hydrocarbon condensate and not hot water?

The issue remains as before. If you don't maintain an actual preassure at the meter a certain amount greater than the vapour pressure at the temperature you're working at, nothing will work. Difficult to see if your mods will make any real difference as we only have a small piece of the details. What is upstream and downstream of this?. What are the pressures, flows, vapour pressure?

From memory vortex meters require quite a decent amount more pressure than vp to work correctly (at least 10 psi)

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

 

[Kdolph]

zdas04, georgeverghese & LittleInch thanks all of you for your answers.

For better understanding I attached in this link

http://files.engineering.com/getfil...6-9744-cf3e62d3beda&file=Vortex_Flowmeter.pdf

The condensate come from an evaporator. The normal flow is 80 m3/hr of condensate. Next to the condensation is received in a pressure accumulator vessels, when it is pumped to the boiler feed water tank (deareator). After the pump the condensate cross a control valve that regulates the level of the accumulator and after cross a heat exchanger, normally this is by-passed.
The pressure of the steam at the evaporator inlet is 37,7 psi abs. and the pressure of the condensate after the pump and BEFORE the control valve is 50,8 to 58 psi gauge. app. (there is a mistake in the drawing. The temperature of the condensate should be around 129 °C (vapor pressure = 39,7 psia)

As I said we have measurement problems at low flows (40 m3/hr i.e). Could be the pressure reduction at the control valve?? this lower the gap of 10 psi for vapour pressure.

I also review the Memo Calculation of the flowmeter and it is specified at minimun, normal and maximum flows a vapour pressure of 313,2 kPa = 45 psia. For the vortex technology a change in this (lowering) is very sensitive??

 

[bimr]

Turndown is 40:1 so that is not the problem.

Flow metering conditions that would allow cavitation, the release of vapor from a liquid, should be avoided. This flow
condition can be avoided by remaining within the proper flow range of the meter and by following appropriate system design.
For some liquid applications, incorporation of a back pressure valve should be considered.

You need some type of backpressure.

 

[bimr]

Vortex meters can be installed vertically, horizontally, or at any angle, as long as the pipe is kept full. Installing the meter in a vertical line with upward flow will always keep the pipe full. When the flow is horizontal or downward in a vertical line, keep the downstream piping elevated to trap the fluid. Use check valves to keep the piping full of liquid in the no-flow condition. If the replacement of the meter in a particular piping configuration requires stopping the flow, block and bypass valves can be installed around the meter.

http://www.flowcontrolnetwork.com/articles/flowmeter-piping-requirements

 

[bimr]

Not much backpressure is needed. Rosemount's calculation for minimum required pressure:

P = 2.9 * DeltaP + 1.3 *pv or P = 2.9 *DeltaP + pv + 0.5 psia
(use the smaller of the two results)

where:
P = Line pressure five pipe diameters downstream of the meter (psia or kPa abs)
DeltaP = Pressure loss across the meter (psi or kPa)
pv = Liquid vapor pressure at operating conditions (psia or kPa abs)

 

[LittleInch]

Your Ft really needs to be upstream of your Cv and d/s of the pump.

You don't say what the boiler feed water tank pressure is, which is the critical value.

If you fall below the 45psia pressure based on a Vapour pressure of 40,that is a very small margin. I have seen this before with vortex meters and because their operation creates a small area of lower pressure in order for the vortex to form, if this zone creates small bubble, it ruins the vortex and the meter misreads. It is sensitive to this and at your higher flows I'm guessing both the pressure in the pipe is higher due to friction d/s the meter and maybe also the feed water tank pressure is that critical 1 or 2 psi higher.

As said - put it u/s your control valve and all will be good provided you have whatever straight lengths the meter vendor recommends

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

 

[georgeverghese]

As stated by Little Inch , we need the pressure at the BFW tank to be some what higher than that in the evaporator for this vortex meter to work ( when this cross HX is not running) - there is nothing shown on this sketch re how this BFW tank pressure is maintained.

Presume the 45psia sat vap press stated on this datasheet corresponds to the max swing pressure in the upstream evaporator.

So what happens when this cross heat exchanger is running ? - does this meter need to read correctly for this case also ?

You call this BFW tank as " deaerator ", which is usually running at subatmospheric pressure ? In that case, you may have to shift this LCV to downstream of this FT.

 

[Kdolph]

Thank again for your answers,

I review the pressure at the BFW, dearator an it is in a range of 2,0-2,5 barg (29-36 psig).
The heat exchanger is barely used currently. I don't know how it worked on operation
Another information is that the pipeline is 6 inches. There is not much pressure loss (0.5 m at 80 m3/hr, acc to my calcs)