control loop and flow meter totalizer question 1

[hswang2]

I have a control loop and two flow meters(totalizer flow meter type).(Pls see attached file)

My question is follwing

N1. Refer from control loop naritive, this loop FIC-030 is to assure a correct feeding quality
of nonyl phenol into reactor, in order to reach this goal, it is
required to provided a flow controller combined with totallizers.(?? why the engineer put
two totallizer on the same process line instead of putting one totallizer on the other DEG
feed process line-although it will close when nonyl phenol feed in)

N2.Which type totallizer is better?Vortex, positive displacement, turbine, coriolis-
although we use coriolis


N3. How the engineer to determine this coriolis type mass flow meter
should be used in this process from purpose of measurement point of view?
Actually I don't understand why they use totallizer instead of using common
type flow meter. (some books totallizer always used in ratio control
and it can verify the overall correctness of total blended product and
it has memory of the amount of past error but my case seems not ratio control)


Thank you very much your kindly help.

 

[Chance17]

N2. Whatout question the Coriolis meter is the best. But some models are no better than the vortex, PD or turbine. From my experience, the "elite" model is outstanding.

I did have one major issue with the "elite".
Any gas in a liquid stream causes significant errors.
This is true especially in beginning a batch reactor charge.
To solve this problem, you have to purchase the non-standard electronics to ignore noise from gases.
With this modification, you can make pin-point accuracy charges.
You'll only need one meter.

The vendor makes more money by selling larger units.
This seems to be OK due to the coriolis high turn down ration.
I have had to replace previously purchased large units (not elite)with smaller units.
The lesson - don't oversize the corilois.

 

[jmw]

Emerson, E&H and Foxboro have all spent a lot of time and money to develop their coriolis meters so that they can accurately measure mass flow of aerated liquids.
The probable target market was/is well head metering but they are all making a great play for thee marine fuels market.
It could be worth asking about these variants for industrial applications.
The alternative is to use a volumetric (PD) meter and an entrained gas densitometer. This will also give you the true mass flow and thee EGA density meter will cover from 0-100% aeration.

Not sure that this answers the original post though.

The coriolis meter gives flow rate and flow total data and you should also get the density.


JMW

http://www.ViscoAnalyser.com

 

[JackR]

A Micro Motion Elite meter will solve the problem just as Chance17 says. The addition would be to clarify the offering for entrained gas applications. Micro Motion recognized some time ago that low frequency Coriolis meters (around 140-200 Hz) had a large advantage in entrained gas applications because they didn’t accelerate the gas bubbles and run into speed of sound effects like high frequency meters (around 300Hz to 1,200 z). They first put in what they call “special mode” in their Core Processor which can be used to make a standard meter perform much better in entrained gas applications. Then they introduced what they call “Enhanced Core Processors” which is an advance model offering not only great operation under entrained gas conditions, but also the ability to check the integrity of the Coriolis meter and electronics at the touch of the button – eliminating any uncertainty about the measurement. They now offer both, since not everyone has entrained gas applications.

Also, one way of thinking about the problem with high frequency meters is to visualize the effect of a volume of gas moving faster that a volume of liquid in a pipe that you are trying to vibrate at its natural frequency. It would be like sticking your finger on a tuning fork – it causes all sorts of havoc. There is no solution for high frequency meters, but they often try to put in smaller meters which increases back pressure in the line, keeping the bubbles from breaking out of solution to some degree.

 

[jmw]

JackR,
The Emerson 7835/45EGA variants of the tube density meters solve the problem of entrained air by operating in a different harmonic mode where the VOS effects are considered much less.
The trouble with going to low frequencies is interference; i.e. sensitivity to pipe born noise and to crosscoupling with other mass meters.
Originally operating at low frequencies, coriolis meters needed to be detuned if there were to be operated within close proximity.
In general the ideal is to operate at higher frequencies because most high frequency pipe borne noise is very quickly attenuated close to the source and doesn't propagate to the sensor with any significant amplitude.
So dealing with entrained air means balancing conflicting requirements if the only approach is to operate at low frequencies.
The standard tube density meters operating at 800-1200Hz and could operate next to each other and not interfere with each other.
It also takes very high amplitude noise to interfere with them or unsettle them.

Air creates a number of problems.
Problems of lost lock and having to hunt again for the resonant frequency have been largely overcome by better amplifiers, PLL drive and more power. Some design changes also have helped the 7835 and 7845 be better sensors than the 7830 and 7840 sensors (as a part of the development of these into the MassMaster series of single straight tube coriolis meters (now discontinued, wrongly in my view).

One mechanism is where the air bubbles migrate to the tube walls so when the tube walls vibrate the tube moves and the air flows around the liquid column so the liquid doesn't get displaced.

But to what extent can they manage entrained air and not suffer serious loss of accuracy?
How "organised" or chaotic can the entrained air be?
Is it the mass flow that is least affected or the density?

What about air pockets?

Hswang2 mentions start and end conditions.
It is common to run dry to dry where the lines may be charged with air initially and they flooded with liquid. Most usually, with low viscosity fluids, one can use air eliminators to void most of this before a meter. Or you can detect the air and inhibit registration on meters where false registration can occur.

The question I have about twin tube coriolis is if you have high volume air pockets, is there a risk of unbalancing the tubes if the air preferentially flows through one tube stalling liquid in the other tube?

What about low viscosity fluids?
Bent tube designs will cause a degree of conglomeration of the bubbles together on the inside of the bends...
Air bubbles are much more manageable in high viscosity fluids because they tend not to be so mobile.

It was my supposition that the entrained gas coriolis were initially developed for crude oil well head metering and have only subsequently been marketed for heavy fuel oils.
This is latter something I don't fully understand (marketing wise) as I don't see this as the best solution.

Entrained gas in well head metering is an unavoidable integral part of the fluid stream and so some form of multi-phase metering is essential, especially as you will want to totalise both phases.

In HFO the vapour phase flow is air which does not need to be accounted for but it is not an integral or desirable part of the flow stream.

Any sensor that responds dramatically to entrained air can be used to detect and inhibit flow when excessive air is present.
If suppliers can't supply fuel when it has excessive air they will stop trying and revert to supplying fuel which is air free.

HFO from the refinery or terminal is usually bubble free. The reason air entrainment is an issue is because the industry persists with old fashioned methods such as tank dipping with tapes.
Thus it is an easy fraud to blow air into the fuel which, because it is black and viscous, is not often evident as having large volumes of entrained air pumped into the fuel and the air will tend to stay in the fuel for a very long time.
The operator then converts the volume (determined from tank tables) to mass using the density the original fuel supplier quotes.

In these applications the cost of mass flow meters is significant because the meters have to be oversized because of their headloss and the pumps have to be upgraded simply to stand to be able to deliver the same rates as without mass meters.
However, the industry requires higher lifts, larger stems and faster turnarounds, all of which imposes even greater headloss burden and there is a move to even more viscous fuels. This all makes the Coriolis meters even less suitable.

The pressing need to minimise headloss will, I think, see coriolis as a short lived solution and the other solutions will come to the fore.




JMW

http://www.ViscoAnalyser.com

 

[JackR]

JMW,
I finally went to your website so I now understand why you steer and twist the conversation towards bunkering and HFO. And you seem to have a quite few things wrong so I will keep my reply short with just two points…
(1) Read AP Moller - Maersk articles on bunkering – the biggest marine transport company in the world has chosen Coriolis as the best solution for its ability to work on entrained gas, and deal with starting and stopping with partially full or empty pipes. Their success in real-world applications should answer any doubts you have…. and others seem to be enjoying similar success on fuel efficiency and similar applications where vibration is present. If I am not mistaken these are low frequency Coriolis meters they are using.
(2) Engine efficiency seems like it is also using more and more Coriolis meters because of their multivariable information. Well designed meters operate in high vibration environments whether they are high or low frequency. (simple principle of harmonics means vibration affects at multiple levels throughout 5-2,000 Hz in a plant environment so high frequency meters are affects the same way).
… good luck with your solution. It may be an uphill battle though.

 

[jmw]

JackR,

No one disputes that coriolis meters are excellent meters and no one disputes that a lot of money and effort has been spent solving problems including the problem of noise in low frequency operation sensors and high vibration environments.

BUT:
Do not let us confuse marketing issues and successes with Technical issues and successes.

Many more coriolis meters have been sold as density meters than density meters of equivalent or better performance.
The reasons are simple and nothing to do with technical suitability.

In the marine market there is nothing wrong with coriolis meters and the will certainly do the measurement.
But as a final solution?
I will say again I do not think it is the best solution and I think that as the various Port Authorities address the issue, then we may see some complications.

I don't want to take this thread up with the arguments but simply put the main reason for choosing coriolis and evolving it to suit fuel oils is entrained air.
The trouble is that entrained air is deliberately introduced as part of the many bunker frauds that take place where there is no instrumentation.

Once these frauds no longer work, and that includes where using Coriolis meters, then the entrained air problem will go away and that will leave air blowing. Same problem and same cure.

Once you take away entrained air handling as a must have (and there are many other ways to solve the problem) then you are forced to compare coriolis with other technologies.

Long term my money is on multi-chord ultrasonic meters.

It happens I presented a paper on instrumentation at a marine industry syposium along with Dr Manus Henry (Invensys/BP) and alongside the AP Moeller manager (whose name I forget for the moment) and many others all looking the the problems of instrumentation.

It is a shame I was not able to be in Singapore for the big coriolis initiative because I understand there was a lot of heat generated and not least as a result of a range of criticisms put forward by CBI Engineering.

At the conference I was at there was not unanimous acceptance of the view that Coriolis is the future.

Many people would like to see coriolis as the panacea for all things but it just isn't true.

So don't be surprised if, once you have coriolis meters on both the supply barges and the receiving vessels then I suspect the headloss issues will dominate.

Compared to US meters I think once we take out the little bubbles, there is every incentive for the US guys to solve the high viscosity problems because for weight, footprint, headloss and collateral costs, US meters could have coriolis meters in a corner.

It makes more sense to solve high viscosity issues with US meters than entrained air problems with coriolis because the high viscosity is a problem that will be with us while the bubbles will disappear.

By the way, what is the multi-variable advantage of mass meters at the engine?

You could answer these questions:
How is density measurement affected in entrained gas coriolis meters?
How is flow affected by gas pockets?
Can the flow tubes become unbalanced by air pockets preferentially flowing through one tube rather than another?
How does headloss for coriolis meters compare to US meters at 500cst?






JMW

http://www.ViscoAnalyser.com

 

[jmw]

PS by "along with" I mean we all presented in the same session on instrumentation, no other interpretation intended.



JMW

http://www.ViscoAnalyser.com