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Good Afternoon,

How can we measure Interface level measurement?

Usually with extreme difficulty.

If you can tell us what the interface is, and some information about each fluid, we might be able to help you.

Interface level measurement is the hardest level measurement application I know of. Help us out and tell us more.

Walt Boyes
Editor in Chief
Control and Controlglobal.com
www.controlglobal.com
Mailto:wboyes@putman.net
Read my blog SoundOFF!! At www.controlglobal.com/soundoff

It is methanol and water.

Dear Sanjib,

Should you need the interface level to control this level in a vessel. let me know the densities and I will redraw a system I designed and installed in a petrochemical plant almost 40 years ago.

No moving parts, no electric or electronic parts (and no need for a level indicator, though I can easily add one)

My email for offlist contacts:
as [at] neda.net

> It is methanol and water.

Another way to do this is to install a tube density meter (Emerson, it is 1 meter long) vertical in a side pipe such that the interface will be somewhere within the height of the density meter.
If the density meter is full of water then the density reported is that of water, if it is full of methanol then the density reported is that of methanol.

If the tube is part filled with methanol and water, the density will be proportionate to the relative amounts of ethanol and water.
This will be true whether the methanol and water are fully mixed or if they are one above the other in the tube.

The density reported is then proportional to the height of the interface whether it is a clean interface or diffuse.

This is an approach adopted for a similar separation in a pharmaceutical plant - they cooled the tank to help separate the methanol and water, and use the signal to regulate the outflow from the bottom of the tank so as to maintain a constant interface level even though this was a continuous separation process.

Dear JMW
Salaam

Seems that very few people read replies to their posts in this forum.
As I have stated before controlling interface level between liquids with different densities DOES NOT need any electronic or even mechanical instrument.No moving parts, no electronics and the interface level(clean or diffuse) will stay where you want it.
Show me you are interested and I can elaborate, or, Drop me a line at as@neda.net for details.

Good morning.

I just joined very recently this forum, so I had not read about this issue before.

I am looking for a good level transmitter for a sump tank in a Wellhead platform (interface level). The sump tank contains crude, water and others. Need transmitters for level indication and Process shutdown.

I am thinking of selecting a GWR transmitter. Is that the best one. If so which manufacturer will you suggest.

Will you be able to advise.

rammohan

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the Interface level are of two different Liquids with Specific Gravity 0.8 & 1.5 Respectively. & we have to Measure it with Water..
Can u tell me that how can we measure..????

Joshi
Mumbai, India

Hi there,

I will tell you what not to use first, in case someone comes up with some bright brain waves again as in this thread.

Do not use ANY type of DP instrument, the explanations why not is to long so just trust me on this.

Do not use a Capacitance probe regardless of how "well" everyone says they work. There are other specific reasons why I do not recommend them. They can also only measure one product, either the level or the I/F but not both.

You best instrument to use for I/F measurements is the Guide Wave Radar but they are difficult to setup and expensive. Very accurate, reliable and not that difficult to work with once you understand the basics of TDR technology and the concept of the dielectric constants of various products. Another advantage is that the GWR can measure the level and interface simultaneously and give out two different 4 to 20 mA outputs.

To see if they will be suited for your application go on the internet and do a search on "di-electric constants" and see what the DC values are for the products you want to use. The bigger this difference between these DC values are the more suitable the GWR will be for your application. Forget about the densities for each product, since the GWR is not density dependent. For example the DC value of water is 80 and the DC value of crude oil is between 1,8 and 4 so they work like a charm on a big product DC difference like this.

My second choice would be to use a displacer and my third choice would be to use a magnetic float type instrument. Both are cheap and easy to setup and reliable enough for most non critical applications. They can also only measure one product and if you have turbulence in the vessel you might have to buy and install stilling wells as well.

Nuclear will also work but the price and rules and regulations involved is a turn off. Also not easy to setup and to work with. This would be my last choice, if nothing else will work.

For critical applications go for the GWR if possible.

Dear Sam
We have different application, organic layer is heavier than water & difference in density is about 0.15 only, we understand displacer requires minimum 0.2 specific gravity difference.

We would appreciate your feedback

Jari
iconcnl@yahoo.com

Hi there,

In a situation like this you have various options that will work but since I cannot know what the vessel looks like I can only give you some basic info.

In my previous post I said that capacitance probes should not be used and the reason for that is that it is very difficult to setup and in some cases virtually imposable.

It is a long story to explain but in your case the capacitance probe could be the best option since they do work well once you get them setup properly.

The way to do it is simple and not a problem.
The problem is if you will be able to do it in your application.

Set all the generic parameters on the meter then fill the vessel, or standpipe next to the vessel, with the lightest product (water in your case) to the 100% mark on your vessel or standpipe. At this point you set the LRV based on what pf the probe reads. You then need to drain all the water and fill the vessel up with bottom heavy product also to the 100% mark and set the URV based on the pf that the meter display. The principle of calibration is based on the concept of 100% of top product is 0% of bottom product and 100% of bottom product is 0% of the top product. The principle stays the same, even if you work with flooded vessels and two outputs.
If you have a sight glass on the vessel that will be a big help or if the vessel is accessible and you can actually see inside the vessel that will also be helpful.

Like I said the capacitance probe work well if you have all these extra features on the vessel to help during initial setup. In a closed online pressurized vessel it becomes virtually imposable to do without any other reference instrument to work from.

The other option is to use a magnetic float type instrument.You will use the one float to measure the interface and a different float instrument to measure the top product level. You obviously need to make sure the density of the bottom float instrument is 1,5 more than the density of the water float (sg=1) so that the I/F float will sink through the water and only float on the heavier bottom product. The calibration is as simple as moving the floats by hand to the position on the guide rod where zero and span should be and set the values. In your case with both floats at the bottom of the rods will be zero and with both floats at the 100% mark on the rods will be the span settings.

To stabilize the readings in a turbulent application, you can install the floats in stilling wells and play with the damping.

Dear Jari
Salaam

If the ultimate aim is to control interface level and separate the two liquids give me the exact sg of your heavier than water liquid and I will redraw a system I designed and implemented 40 years ago to separate water (sg=1) and DDB (sg=.865) without any instrumentation whatsoever.

Abdollah Sadjadian
as@neda.net

I need to measure the interface level of glycol and gasoline. The vessel is under 300 psi. I would be interested in your idea.

Thank you

Will GWR work in a continuously density changing environment where there is no clear interface?

Define "work"! If you mean, will it read something, sure. If you mean, will it accurately detect an interface level even though there is a very large rag layer, no.

The fact is that if there is not a defined interface, there is no way to detect an accurate interface level. Sounds simple, right?

What a lot of measurements are trying to do is to create an inferred measurement from the best signal they can get from their level device. For example, a vortexing fluid doesn't really HAVE a level, but we need to measure a custom engineering unit called "what the level would be if the mixer was turned off and there was one."

There are three ways I can think of to attempt to get a reasonable (and I am defining reasonable loosely here) measurement in your situation. One is to use a gamma level gauge configured as a densitometer to give you continuous density compensation for your GWR probe. That's tricky and expensive.

The other is to talk to J. M. Canty Co (www.jmcanty.com) about their camera-based interface detection and control systems. These are also tricky and expensive.

You could use a dual GWR system. One GWR transmitter would measure top level and the other would be calibrated to track the highest interface point it can see. This is tricky, less expensive, and likely not to work very well.

This is a very difficult measurement because, like the example of a vortexing level, you want to measure an engineering unit called "what the interface would be if the darn density wasn't changing all the time." That is a difficult measurement.

Walt

Walt Boyes, FInstMC, Chartered Measurement and Control Technologist
Life Fellow, International Society of Automation
Editor in Chief, Control and ControlGlobal.com
wboyes@putman.net

Dear Soovo Sen
Salaam.

As I have mentioned in my previous posts, effective interface level control based on density does not (repeat NOT) need any electronic instruments. Your case,the way you have stated, is a special one, having "no interface!!" Still,let me have the specifics of your system and what you want to do,off the list if this would be a long post, and I will send you my 40 years old simple solution that is still working perfectly.

Abdollah Sadjadian as@neda.net

Hi Sam,

I have some questions with regards to using a DP transmitter for Interface level control. I read through some of the feeds and it seems you are the right guy to ask. Would you mind contacting me on my email address (brett.allan@sasol.com) so that I can ask you a few things?

I would really appreciate it.

Thanks,
Brett

You could use the VDM250.2 portable density/viscosity meter.
Since you have a good density difference the density only version is quite suitable. This is manufactured by LEMIS
See http://www.viscoanalyser.com or http://www.lemis-process.com

Dear Joshi
Salaam

Please can you explain what you mean by:

"..... & we have to Measure it with Water.."

AND, what do you need the interface level measurement for??

I will appreciate more details, maybe offlist if you prefer.
as [at] neda.net

Dear Joshi
Salaam
Would you kindly explain what you mean by .. measure it with water.

And if you need interface level to control it look at my reply to Sanjib in this thread or drop me a line offlist at as@neda.net


Abdollah Sadjadian

According to me, interface level measurement is for the tank containing two different media, having two different densities. eg. drum level with steam and water, crude/bitumen etc...

G.Vivegan
Coimbatore,TN
INDIA.

first you can do simple equation that will give you the required calibration the equation is as follows say for instance oil which is 0.8 and water is 1. and other liquid is as you say 1.5
and you are using water as calibration the maths is simple
1.5 DIVIDED BY 0.8 DIVIDED BY 1.00 X WHATEVER RANGE YOU REQUIRE I.E IF IT WAS 50% IT WOULD BE 0.8 DIVIDED BY 1.5 DIVIDED BY 1.00 X 50 =0.26.
this would be 50% of your level if calibrating with water so for 100% output if calibrating waith water the level it the torque tube should be 0.52% or 50% of the measurement between tapping points i hope this helps you.

regards tom holland

Radar, Bubble tubes, Displacer, Magnetorestrictive, DP cell, Conductivity, Capacitance, Nuclear, need I go on. But you need to tell us what the two fluids are.

Roy

Thanks for your reply. It is liquid level, is water and methanol.

Sanjib,

You will not get an interface between methanol and water. The methanol will dissolve in water.

Roy

Sorry, it is petrol and diesel. How do we calculate this level in DP type methol?

Are you talking about interface detection or interface level detection? The first refers to product detection within a hydrocarbon pipeline; the second refers to product detection inside a storage vessel.

Regards,

Tomy Zacharia

>Are you talking about interface detection or interface level detection? The first refers to product detection within a hydrocarbon pipeline; the second refers to product detection inside a storage vessel.>

Please explain briefly with some examples. I need this for academic purpose.

Are you teaching or trying to get us to do your homework for you?

Walt Boyes
Editor in Chief
Control and Controlglobal.com
www.controlglobal.com
Mailto:wboyes@putman.net
Read my blog SoundOFF!! At www.controlglobal.com/soundoff

You can measure the interface between two fluids using a DP cell with High and Low connections or using two bubble tubes. First of all you need to establish the density of the fluids at the working temperature.

Diesel seems to have a wide range: 820-950 kg/m3
Petrol (Natural) 711.22 kg/m3 or vehicle 737.22 kg/m3
For example, if you have two bubble tubes 1,000 mm apart in petrol you will get a DP of 737 mm WC - this is your Zero. In Diesel you will get 820 mm WC - this is your 100%. For a DP mounted on tank taps 1,000 mm apart, assuming the top connection is filled with petrol,
when the interface is at bottom connection the DP would be zero because the HP and LP connection are both subject to the same column of petrol (assuming the temperature is equal), so your Zero is 0 mm WC. When the interface is at the top tap, the HP connection will see 108 mm more pressure than the LP.

I would have thought Petrol and Diesel would mix since they are both hydrocarbons, in which case the DP would indicate the mixture ratio.

Hope this helps,

Roy

Thank u roy. I need this for academic purpose. What is other method? Is there any DP type measurment?

Roy,
If the fluids are to be crude oil and water could you advise me about using DP to measure the interface level? Which method is more common in industry in accordance to new technology?

Thank you,
Vahid

Vahid,
I don't work with crude but do so with other hydrocarbons. We use bubble tubes in glass lined vessels and also DP cells on the side of tanks. I suspect displacer type transmitters are still very popular for the high pressure applications. Guided wave radar is another applicable method because the crude dielectric will be significantly different from water. The radar signal would penetrate the crude and reflect off the water.

Nuclear is another good method because water has a very high absorbtion rate for gamma rays.

I have been advocating electrodeless conductivity for short range interface, so far I have been unable to convince anyone to try it. One of the larger donuts should work over one or two inches.
I would need to know a lot more about your application before I would recommend the exact method.

The problem with using nuclear for a oil-water interface level measurement is the distance between the source and the detector. If the vessel is larger than 12 inches or so in diameter, it may not be possible with a conventional nuclear level gauge. This measurement is often done with a standpipe so that the gamma source (a strip source) can be mounted closely enough to the detector so that radiation will penetrate the steel-water-steel to reach the detector (a strip detector). This is a very expensive measurement.

I really am starting to recommend using guided wave radar for this
application.

Walt Boyes
Editor in Chief
Control and Controlglobal.com
www.controlglobal.com
wboyes@putman.net

Most "strip sources" are really a series of small Cs-137 point sources equally spaced along a strip. If you use a Co-60 rod source (radioactive metal wire wrapped around a steel spindle), you can generally make a good interface measurement on vessels that are much larger in diameter than 12" (6 ft or more). The gamma radiation from Co-60 is much more energetic than from Cs-137, so there is more penetrating power.

From a cost standpoint, it would certainly make sense to do the measurement with guided-wave radar if it is possible. In my personal experience, I have found that capacitance probes are another good low-cost, reliable method. But if there are other application considerations that make a non-contact solution attractive, then nuclear will work well.

Jon Buchanan
Berthold Technologies USA
865-483-1488
http://www.berthold-us.com

two phase flow measurement.

I thought methanol was 100%, fully miscible in water (completely soluble).

Is that not the case?

Please educate me. I don't understand why a two phase interface level measurement would apply to methanol/water.

David

Use GWR or Capacitance type level measurement. These are preferred one.

I agree. but some notes about GWR:

I experienced some problems last days with a reflex radar interface level. We changed the process and now, aquous phase is lighter than organic phase,(and is on top of the organic phase) and then, radar waves can't penetrate the aquous phase and the interface detection isn't possible. Reflex radar requires the liquid with the highest permitivity between the emission point and the other liquid.
I solved the problem with a capacitive device.It works very well under all conditions

Yes, that's why there are many types of level and flow measurement
methods... one of the darn things will always more or less work.

Walt Boyes
Editor in Chief
Control and Controlglobal.com
www.controlglobal.com
Mailto:wboyes@putman.net
Read my blog SoundOFF!! At www.controlglobal.com/soundoff

Possibly an application for ABB DP Transmitter Model 264DL which is specifically designed for Liquid Level Interface and Density measurement.

D-PS-264DL_5 Data Sheet (pdf, 313 KB)
http://www.tagteam.com/TagTeam/link.asp?id=511C2754

Ken Frisbie
ABB Inc.

How we take high and low pressure impulse line? How do we calibrate the DP with respect to Level?

Sanjib,
It's difficult to answer without knowing some more details, do you have a sketch you could send me or send your e-mail address and I will send you some typical details

roy_matson at yahoo dot ca

Roy

I have previously used a single straight tube density meter e.g.Solartron/Micromotion 7845.

This is a useful 1 meter long and arranged vertically in a manometer style arrangement it has been very effective at determining the interface (even if diffuse) in methanol and water separation system in a pharmaceutical plant.

There is a very good density difference between methanol and water which makes this particularly effective for controlling the underflow pump out.

It didn't matter if the interface was diffuse because in the operation the methanol water separator, as the two fluids separated the density in the bottom of the tank increased as the water content increased. Above a certain level it was virtually all water.
In the pilot installation a sight glass was installed in parallel to confirm the operation.

The interface height is simply a function of the density. 1000kgm/3 and the interface is above the top of the tube, 791kg/m3 and the interface is below the bottom of the tube. 895kg/m3 and it is halfway up the tube.... a useful sensor in that it would accurately report the mean density even if not homogenous...not sure how other sensors would respond under similar circumstances.

For pipeline applications e.g. common pipeline supply to tank farm the straight tube density meter (e.g. 7835 or equivalent accuracy coriolis meter etc) is used to detect the interface between different refined fuels including between diesel and green diesel etc.

There are two methods one of which uses a single density meter and a knowledge of the product density to control the divert and the second uses two density meters in series.

In this case it doesn't matter what the actual densities are so long as they are different and so long as the operator knows, from the denisty or from a knowledge of which products have been put into the pipeline which products he will see at the density meter.

In the two sensor installation the first sensor provides a first alert of the arrival of an interface so the operator can correctly set up the diverts.

All the while the pipe is full of a single product they density meters will read the same value, as the interface reaches the first density meter its reading will change and a density difference is detected by comparing the two density meters. When the interface reaches the second density meters they will again agree.
This method has been used by the UK Pipeline Operator. In some installations the upstream density meter may be a cheaper or less accurate sensor since it only provides a first alert.

Density software includes zoning which is simply a set of density alarms that can be programed to look for interfaces. (visit www.mobrey.com and download the manual for the liquid density single converter software version 7950/1).

Check this transmitter that can measure density and interface level:

http://www.smar.com/products/dt300series.asp

Good Afternoon,

Displacer type of level transmitter if used for the measurement of Interface level at Water/Crude Oil Separation tanks, how long normally would it take to give stable / representative reading after flushing/calibration (where the lower tapping is from about 5 ft of Tank height(having almost 100% water) and higher tapping of chamber is from about 9 ft of 40ft high Tank (having about 10% oil-90% water)?
What is the best procedure of commissioning the LT chamber?

Try this company. In the past they made a great RF level meter.

Atis Inc, Automatic Terminal Information Systems Inc, Atis
7110 Satsuma Drive
Houston, TX 77041-1812

(713) 937-4993

You can measure interface level with a guided wave radar level transmitter
http://www.processonline.com.au/articles/34104-New-EDDL-is-guiding- radar-interface-level-made-easy-

long URL, copy from http:// all the way to easy- in a single line into your browser address bar if clicking doesn't work

Commissioning is demonstrated in this video:
http://www.youtube.com/watch?v=luFBxjnX974

Cheers,
Jonas

> What is the best procedure of commissioning the LT chamber?

please try to allow and open lower tapping of LT and check the observe the LT reading and reading shall be 100%and after that open the LT top tapping v/v and observe the LT reading shall be 0%and after that commissioned it the settling time around 3 minutes.

Hello,

To use a differential pressure transmitter to measure interface, search the internet using ISA Multivariable approach to Level Measurement.
This site will explain the theory and provid a picture and a formula. Follow the formula and picture and this should help you with your problem.

Try this site. We use it successfully to measure interface in black liquor and soap. Very a lot more difficult application than what you are doing. This would suite your application well. It can handle applications with high solids, fouling and interfaces of two very tight liquid densities.

see: www.sms2000.ca

Hey... Can anyone tell me the difference between the Capacitance type and displacer type

> Hey... Can anyone tell me the difference between the Capacitance type
> and displacer type

Capacitance meter has fixed area electrodes and the capacitance varies according to the dielectric constant of your process fluid so varying level or interface will vary the capacitance measured in proportion to your level. The displacer works on the principle of Archimedes where the displacers apparent weight changes according to the process fluid level or interface level.