Steam Mass Flow Transducer 1

[ilan7]

For all the Experts
I need to recommand the best economical way to measure Saturated Steam Mass flow at a 36” (!!!) pipe. According to the contract, Accuracy must be 2% (Mass Flow).
The Only Option I know is the Rosemount Mass Probar Flow Transmitter with integral Temperature and Abs. pressure.
Does any one have another suggestion? can Orifice, DP, Abs. Pressure Temp. transmitter and flow computer can give 2% accuracy? Thanks to all

 

[hacksaw]

there are a half-dozen suppliers of that sort of hardware.

the averaging pitot technology is one of the more economical

 

[ilan7]

My Question is: Do you think I get the 2% Mass flow accuracy with Orifice, DP Abs. pressure and Temp. calculations?

 

[CARF]

To measure mass flow in steam (or any other gas) you need to know the volumetric flow (m3/sec), temperature and absolute pressure. These are the three inputs you need to calculate the mass flow (kg/sec). Or you can measure mass flow directly with an expensive Coriolis massflow meter.

Volumetric flow in steam can also be measured with a Vortex flowmeter, these a quite cheap and very reliable.

See:

http://www.flowresearch.com/articles/Plant_Engineering_0498.PDF

See also (bottom of page):

http://home.hccnet.nl/m.dijk/pressure_drop_calculator/calcs/calcs.html

Good luck,
MVD

 

[xeno]

Re the measurement of sat steam in a 36" pipe. The averaging Pitot is one option and note that it doesn't need to be a Mass Probar, there are other very good Pitot tubes, pressure transmitters and flow computer combinations which would be less expensive.

Since the Mass probar only uses a single 0.075% fsd pressure transmitter then for a 2% accuracy then turn down = sq rt of 2/0.075 = five to one, assuming that to be the only uncertainty.

The accuracy will also be largly dependent on the steam flow velocity, condition of the pipe and how long and straight it is. Re the velocity, unless the full scale velocity is high i.e. 20 to 30 mtrs per second, then the DP at the lower flows will be out of the accurate measurement range.

The better alternatives are a meterrun with an orifice, nozzle, or venturi. Wet calibrated you could expect accuracies of better than 0.5% when used with two DP transmitters and a good flow computer, what's more you would get a far better turndown and the measurement would be according to the ISO5167 standard. However, the orifice shouldn't be used unless the steam has some superheat. Sat steam is too wet and abrasive to give a good life to the sharp edge.

 

[ilan7]

Thanks Xeon

 

[jsummerfield]

Forget about a Coriolis massflow over six-inch. The mass-probar sounds OK. If the requirement is 2% mass data, I would include the temperature and pressure compensation of the multivariable transmitter and purchase calibration certificate for the element with the required data.


John

 

[gunasekar]

hai ilan,

for me orifice with temperature and pressure compensation is the best idea for this application.but if you install the orifice in the vertical line then you can avoid the dam effect problems which will afect the accuracy.

 

[cornejoi]

The problem with using Orifice plate to do ANY mass flow is the straight pipe requirements needed in order to ENSURE that you have your accuracy within the required limits (Read AGA Report # 3). Moreover, even when installed correctly and configured (You properly sized your orifice plate, the straight pipe requirements are as required, the impulse tubing is installed correctly, ect - in other words you've made a calibrated meter run) you can only garuntee an accuracy of ± 2 % to ± 4 % of full scale.

You said that you needed 2% accuracy. 2% in terms of what? Full Scale Flow? Calibrated Span? Rate? You'll need to ask yourself accuracy in terms of these values because 2% accuracy in Full Scale Flow is not the same as 2% accuracy in calibrated span.

Let's assume that your accuracy requirements are 2% of full scale. For a 36" line, with an orifice plate, I'll almost garuntee that you won't get anything close to that.

I know other people in this forum are big on Orifice plates. Yes they work, they are reapeatable, and are easy to calibrate (at least the dP transmitter). However, if you need good accuracy you shouldn't be looking at using an orifice plate unless you can garuntee the straight pipe requirements required for accuracy.

Other technologies that you could consider:

Ultrasonic (You may be able to get away with a clamp on style rather than asking a vendor to manufacture a 36" spool piece. However, I can almost bet you that a 36" ultrasonic meter will still cost you less than using an orifice plate once you factor in installation costs of a calibrated meter run - which it seems you'd require based on your accuracy.)

Insertion type turbine meter

Anubar / Pitot tube - Go with your gut feeling about the Rosemount / Dietrich mass pro bar. I'm not sure what accuracy you can achieve, but I believe it is a high order of accuracy. It also gives you a flow average which is probably more benificial to you. Moreover, look for a multivariable transmitter (If you're DCS supports Hart or any bus technology)and you will save yourself a couple of DCS points.

--Igor

 

[Sierra]

Have a look at this solution:

http://www.sierrainstruments.com/products/240_241.html

The insertion version (241-VT) should do the job if you have enough straight length on you piping.

Paul

 

[xeno]

ilan,

Please please be careful with any velocity device which is inserted into the flow stream in an existing pipe. There is no doubt that an averaging pitot can provide good measurement and that it's use with a multivariable transmitter provides a cost effective solution. But I repeat the measurement will only be as good as the pipe it is installed in. Far too many manufacturers are 'economical' in their information regarding the uncertainty due to pipe condition.

The same argument applies to orifices and venturis. However if the orifice or venturi is manufactured with a precision made meter-run strictly in accordance with the AGA 3 or ISO 5167. Then the uncertainty of the primary element will be within the standard which in the case of an orifice is 0.6%. Yes you can use a multivariable transmitter but my own preference would be to use two high quality transmitters in stacked format and a separate flow computer.

If you really want to tighten up the accuracy then wet calibrate the primary element in it's meterrun, wet calibrate the transmitters, program the flow computer to linearise from the calibration data and then it's conceivable that the uncertainty will be well under 1% of reading over a 20 to 1 turndown.

Differential pressure metering has got a new lease of life with the advent of increasingly accurate and stable transmitters. The ability to internally machine with high precision any pipe roughness and irregularities such as weld distortion such that not only can the standard be met, it can be improved on. Further more, today's fiscal steam flow computers are cleverer, and considerably less expensive than even just a couple of years ago.

Last years text books are already out of date. Those of ten years ago are simply no longer relevent.

Finally. it's steam. If it's saturated there almost certainly be some wetness which can and will reek accuracy havoc unless the meter is designed to take the punishment. The ISA nozzle is designed to take the punishment of steam and will retain it's design performance without question where as an orifice would lose it's edge. Standard high accuracy (non multivariable) transmitters are very easy to prove and to calibrate at any number of calibration houses or on site without specialist knowledge.

And the arguement between a multivariable or a flow computer ? Personally, give me an instrument which allows me to look at the inputs and outputs, to observe the pressure, the flow, the density and entathalpy any time I wish without the need for some hooked on communicator. An instrument which will totalise, store and log data just in case I need look back historically or in the event that the energy management falls over.

 

[jsummerfield]

We are applying V-Cones for many velocity type flow meter applications. They can work well with only three diameters upstream and one diameter downstream. However, I would require the supplier to provide supporting data bevore buying a McCrometer V-cone in a 36-inch steam application.

John

 

[ilan7]

XEON
Thanks for all the explanations, and appriceate the time you spend on writing the long message.

jsummerfield
I assume Vicon flow meters are good instruments, but to get the accuracy we need the instrument pressure drop is much higher then we allow.

 

[JoeHalliday]

Simple, use an insertion Multi-parameter Mass Vortex flowmeter from Sierra Instruments.
This unit will deliver 2% Reading accuracy for steam mass flow. It incorporates velocity, temperarature and pressure sensors integral to the sensing head and can fit pipe sizes from a 2" up to a 72"...

check out the website

http://www.sierrainstruments.com

Here's a direct link to the product spec

http://www.sierrainstruments.com/products/pdf/240.pdf

enjoy!

 

[jsummerfield]

When you mentioned steam I did not ask about your steam pressure or superheat. Your mention of pressure drop regarding the V-cone may bring more application specifics into play.

I see that most V-Cone models are available to 24-inch and larger sizes available. The annubar should likely drop less than the V-Cone. I would not overly praise the V-Cone but can share sizing data for a disimilar gas application. At about 6.2 million SCFH and 1200 psi and 7 pound/ft3 density sour-gas, a 10-inch V-Cone drops 155 in-water. This meter has a beta over 0.72. I do not know the permanent loss. In 1200 psi gas I do not regard 155 in-H2O to be excessive loss. I also do not know the drop for your steam application. If this seams like a reasonable drop, find McCrometer at

http://www.mccrometer.com/

John

 

[xeno]

JoeHalliday,

2% accuracy on the Sierra Multi-parameter insertion vortex?
Is this regardless of the pipe condition?

Ilan,

Your best bet may be to speak to an independant specialist for some unbiased advice, try

http://www.flowquip.co.uk

 

[JoeHalliday]

Xeno,

You are correct in that most, if not all, manufactureres are "economical" regarding the information of pipe conditions. I used to be in the Clamp on ultrasonic industry and that is one which is totally contingent upon the pipe conditions. Regarding the insertion mass vortex, there is simply no "easy" way to simulate customers pipe conditions. It is a point velocity device, in which the vortex sensor measures the fluid velocity in feet per second. The electronics will multiply this Feet Per Second by the square foot area of the pipe ID. (Pipe ID is entered by the user, the meter calcuates the area), resulting in cubic feet per second.
The meter actively measures real time temperature and pressure at the same point the velocity is measured and uses equations to calculate the density of the fluid. In the case of steam, it is not a simple steam table look up, but an true calculation, using the same equations that the steam table uses, but here it has real time data rather than assumed table values.

I read your earlier post, mentioning staked transmitters and flow computers. This is an accepted procedure, however depending on the actual applicaiton, can be very expensive, resulting in double the equipment to make a measurement.
The single biggest issue that the insertion mass vortex meter faces today is the pipe sizes are typically larger than necessary, in order to reduce as much pressure loss as possible. This results in somewhat lower velocities during steam usage cycles.

In the intial post, a 36" saturated steam line, assuming 125 PSIG steam will allow an insertion mass vortex meter a measurable range of 65,000 to 2.1 Million pounds per hour. Should the pressure be 200 PSIG, the range becomes 80,000 to 3.28 Million pounds per hour.
These are wide turndown ranges, but if the actual application is only running at 1 Million pounds per hour, then your are subject to the max application flow compared to the minimum meter measurable flow....

This unit allows the user to read, disply and transmitt compensated steam flow, temperature, & pressure simultaneously. Additionally, it will totalize the flow and transmitt a pulse for a remote counter as well...

I know by now, this post seems extremely biased, but there simply is no other product on the market that accomplishes all these feats. In order to get all this flow information, as you have mentioned, will require 4 devices, flow, temp, pressure and the flow computer to calcualte the compensated flow rate...you must account for the inaccuracy of each of these devices when looking at overall steam flow accuracy as well.

Insertion Annubars are fine, but they plug up.
V-Cones are an excellent choice when straight run is limited, however, this is still a DP measurement and subject to the turndown of that technology, not to mention it's still a volumetric measurement and requires additonal instrumentation for T & P conpenstation.
Calibrated meter runs / orifice runs are also an excellent device, but they are also limited to turndown and as was mentioned here, the technology has been overdone...you said it yourself, "Last years text books are already out of date. Those of ten years ago are simply no longer relevent"

The downside of vortex is the low flow issues, since the fluid must be traveling at a velocity sufficient enough to generate vortices....

Regards

 

[dcasto]

Either use a clamp on ultra sonic with a temperature and pressure transmitter or an orifice plate. Don't let anyone tell you you cannot get 2% accurracy. About 90% of the very expensive ethylene commodity in the US is measured by orifice. The biggest error in measurement is the error associated with the density. If you have the best Vortex shedder or ultra sonic in place and the desity measurement is off by 2%, then the whole thing is off by the 2%. On the otherhand, if your density is off the same on an orifice meter, then the whole measurement is off by 1/2 the 2% or just 1%.

 

[Sierra]

Have a look at this solution:

http://www.sierrainstruments.com/products/240_241.html

The insertion version (241-VT) should do the job if you have enough straight length on you piping.

Paul