19 replies to this topic

[dhns]

Dear sir,

Could you anyone Explain about the following my issue !

In level alarms settings (like LALL,LAL,LAH,LAHH) in the vessels ,the percentage (like 30 %,60%,..80%..90%) is what ?.

Is it based on the Vessel Diameter percentage ?

or Liquid actual percentage bases ?

or Spam (level sensor) length based ?



Please Explain with an example the content behind of my dismay !

Thanks,
Regards,
Dhns

[Qalander (Chem)]

Dear

This is not a very simple and straight forward thing since many process safety related issues are to be considered

Bare minimum Might include but can not be limited to

Any Applicable Code(s)/Standards compliance(s) Mandatory and/or Compulsory etc.

Streams inflow rate(s) Min. and Max. and usual

Streams outflow rate(s) Min. and Max. and usual

Operator(Human Beings) reaction time/intervention protocol or

Automatic Process Logical Control intervention protocol

and etc. etc.

Hope this helps

[micdmaloney]

I'm afraid I don't have an example, but I believe that when levels are expressed as a percentage it refers to a percentage of the vessel working volume, rather than to any "elevation" measured in terms of metres. I hope I have understood your question correctly and that my answer helps.

[smalawi]

Hi,

LALL is low low level alarm, at times may also mean same as LZA LL which is low low level trip (safety driven action)


LAL is low level alarm to alert the operator


LAH is high level alarm to alert the operator


LAHH is high level alarm to alert the operator, may also mean same as LZA HH which is high high level trip (safety driven action)

the % is not out of the total vessel for alarms, its usually for the LC range. for safety trips, the LC range is the total vessel dia range so its the same

actually when the vessel is designed, its the level height in inches / mm that is specified not % level, then its converted to % level once the level taps location / length are decided

the residence time in the vessel (for the fluid) is a design criteria for sizing the vessel not the % level, it plays a major part if the vessel capacity is revamped to higher feed, the & level might need to be increased.

the vessel level elevations for LAHH LL (LZA) heights are related to the residence time and response time for the operator to respond from the process high or low alarms (LA H/L)

hope this helps,

cheers,

sm

[Andrei]

These levels are set in the design phase and have different basis throughout the project development, and also they are influenced by the type of the level sensor used. I had to set up these levels in numerous occasions.
In all situations encountered the settings are expressed in percentage referenced to length on not to volume. Although there were clients that specifically asked for a volume based calibration in some places; if level was used to control something usually the primary (controlling) measurement was length calibrated, and they were getting a second measurement, read-only, volume calibrated.
Before having a safety role these levels should have strict operating meanings. For instance in a gas-liquid-liquid separator the levels are determining minimum/maximum retention times required for a certain separation performance to be achieved and they are set when the separator/vessel is designed.
A different example, levels in the bottom of a tower are set to account for the delayed response of the temperature control present there.
A different one, the levels in a tank may be set to ensure a certain response time of combined equipment and operators, to avoid downtimes, or to allow a safe plant shutdown in case of raw materials shortages.
Of course, like any other instrumentation, these levels have a safety component. In some parts of the world the levels may be regulated; for instance in the area I work it is illegal to operate a tank above 80% of it’s capacity.

In all the cases these levels have to be reported on the P&ID's, programmed in the DCS/PLC, and described in the plant shut-down key document (the relevant ones) and operating manuals.

In the initial design phases the levels are measured from the lower tangent line of the vessel; later, when the level measurement sensor is specified, the level values are corrected to be consistent with instrument measurement span. A level sensor specification have to be started by a process engineer, and he/she should ensure that the set levels are consistent with the process requirements for the specific equipment.

If for example a radar type level sensor is installed, the level calibration reference remains at the lower tangent line of the vessel. But if a Differential Pressure or a floating device type sensor is installed, the reference is changed to the lower tap point of the sensor. There may be some liquid level values that are not measured because they are out of sensor range; process engineers have to take into account these values.

[Art Montemayor]

Dhns:

Values of percentages (without a basis as to volume, distance, mass, etc.), parts per million (without indication as to parts of volume, mass, moles, etc.) , & concentrations (without indication as to mass, volume, moles, etc.) are clearly flawed and ignorant information simply thrown out at a reader or client for the mere sake of doing a minimum of mental work. Engineers who do this type of disservice and inaccurate communications and advice should be kicked out of the engineering profession. The information they pass on (as illustrated by your query) is essentially useless.

One cannot simply "assume" (make an ass out of u and me) that the values obviously mean something if a specific definition is not given. In such circumstances I have simple thrown back the useless information in the face of the originating engineer and demanded a fair compensation for my paymentts in the form of accurate, detailed, and concse information. That's what engineers are paid to do, and that is what we must do.

A serious and possibly dangerous situation may be in the waiting when we "ASSUME" that we know what was in the mind (or fantasy) of some incompetent engineer who wrote such useless information. There is no logical reason or justification for thinking that there exists a universal engineering standard (or "code") that clearly establishes the units of such things as percentages, ppms, concentrations, etc. I know of none, and further have seen and been with other engineers in many countries who swear by their units - which are totally different from each other.

I would not assume anything until I proved what the percentage units are - and spelled out clearly. Your example is just another reason why I am so insistant on engineers giving ALL of the facts and not assuming anything.

[mishra.anand72@gmail.com]

Dear Art,

Why u r so negetive?? Everybody did their best to help that person who is confused about level measurement and their explaination is very good.

If somebody asks u hw much water left in the bottle, what u reply is 30%, 40% 50% etc. Now this percentage is what?? Ok u can not assume but at least u can imagine.

ur friends do not need further explaination because they like u.
ur enemies do not deserve explaination because they will never accept it.

I don't need ur payment if I don't hv to feed myself and family to feed. Rest everything is same. we all strive to improve our quality of life. We all like to share what we have.

What is wrong in their explaination?? They have stated just facts. When u do not find that relative, what can be done??

Never Mind

I take this opportunity to thank u for providing me vessel partial volume calculation excel sheet.

Bye

Have a great day

[ARAZA]

Hi There,

I agree what the others has to say, there is no simple answer to this question since it depends on many variables such as process upset, pump protection, gas blow thru', overfilling the vapor line with liquid etc etc... There could be at least 50 reasons why you want to have a level alarms.

In really simple terms, the way I would approach this problem for a specific system.

Say for a vessel which acts as vapor / liquid separator, liquid line from botom goes to a pump and vapor line from top goes to a compressor. Now, let's say, you want protect the pump under low level scenario and protect the compressor on high liquid level.

Low level alarm = 10" from bottom tan line
low low level alarm with pump shutdown or some supervisory action = 6" from bottom tan line.

Similarly high level alarm = 12" below the feed inlet
high high level alarm with some high level action = 8" below the feed inlet.

These guidelines might change due to the type of level switch employes and nozzle sizes.

Please note that, these are only guidelines to be followed in one particular scenario ONLY, this does not necessarily apply to all systems. You have to analyse the system in detail and set the alarms accordingly.

Hope this helps.

ARAZA

[Dacs]

I may have been posting lately but I've lurked this forum for quite a while and I think I can say my 2 cents regarding Mr. Art's intention.

I've had my share of hiccups in my line of work as a design engineer such as not being concise with the basis of my calculations. Let me put it this way, the argument with my lead engineer did not end very well and for the most part I got the receiving end of all his frustrations.

I never felt humiliated and embarrassed to the point that I want to pass my 30-day notice the next day (which I did not since we ended up in a dinner later, good times ). Looking at hindsight however, my lead is just trying to make a point: there's no room for error and glaring assumptions in our field. I've experienced that "standards" aren't really set in stone. Case in point is the "standard" and "normal" volume flow. One must look at the basis of it before doing any flow calculation and not just assume a specific basis since it's been labeled as "standard" and "normal" that it's indeed universal.

Mr Art may be uptight and harsh with his statements, but I'd really rather have that than making an error in my design that may cause life, property and trust from our clients.

I think the bottom line here is we must be concise with every information that we give to our colleagues so that we won't be working on assumptions when interpreting other people's work.

And to be honest, if you're sensitive with every criticisms that you receive, I don't think it'll be very productive on your part since at one point, we need to collaborate with other people and it's most likely that disagreements will go in our way. And when that happens, you need to set aside your emotion and ego and be objective (as an engineer should).

On topic: In my experience designing level gauges, usually the percentages are related to the level itself. During the design phase however, those readings are based on holdup and surge times, which depend primarily on a number of things, such as (but not limited) inventory and operator response time.

[Qalander (Chem)]

Dear All,

Please do not superficially misunderstand Mr. Art. Comments.

He is a thorough gentleman trying to help and discipline (as Admin.) & very Considerate indeed!

Occasionally the comments seem harsh/bitter; which they are not really.

Sometimes he might be busy/overworked as contributing in other capacities; then a PM (with your specific help needs) might prove useful, followed by a tickler if at all necessary!

All above is opinion gathered during stay at these forums. Nothing to do with any of the Admins./Mr.Art.

[Dacs]

I sincerely apologize if my past reply imply to even remotely judge Mr. Art's response on this thread and certainly it's not an attempt on even claiming on what Mr. Art thinks on the time he made the response. If that's the case, then I really am sorry

That said, I just addressed mishra.anand72's reply and his apparent frustration on Mr. Art's reply on this thread.

This is going to be way off topic but I think it's noteworthy of mention that among all of us, we collaborated with people from different parts of the world and in as much as engineers tend to speak the same language (technically that is), we cannot avoid dealing with cultural differences among us.

I for myself came from Asia and I've had the chance to work with American, European and Asian engineers before. Western people tend to be frank and straight to the point (which I would surmise what Mr. Art's post may show for some people) and generally (well, some) people from Asia tend to take it in a different way.

My previous company recognizes this and they made a program specifically to address the cultural boundaries.

I normally would be taken aback (and I'm not really surprised with mishra.anand72's reaction) if I were at Mr. Art's receiving end of his post but I've learned well enough that we must be accommodating enough to adjust to other people's attitude (this is not race specific but in general) and not to be carried away by our emotions and ego.

And in fact (cultural biases aside) Mr. Art's post really does make a very important point, especially for younger engineers (like me).

Hope this clears things up

[Andrei]

I am extremely glad that there are others thinking like me.
I see that an innocent question sparked an off topic discussion.
I do not want to judge anybody, and I strongly advise everybody to do the same. There is only one authority entitled to judge on this world, and His judgments are final.
There is only one thing that I cannot excuse in my relations with others: dirty and offending words. .
It was very sad for me to read dirty words in one of the administrator of this forum posting.
Even if the general ideea was right, even the words were not directly addressed to me, what I have done wrong to hear dirty words around me?

[Art Montemayor]

Andrei:

Please indicate to me where you have spotted or identified a dirty and offending word in our Forums. As an Administrator I try to look for this type of offense and have tried to do my best to keep such language out of our forums.

[Qalander (Chem)]

Dear Andrei/Dacs Hello/Good Evening,

One thing I am astonished to hear someone using "Dirty Words" for 'any one on the forum'.
This is really shocking thing .

I don't know whom do you pretended as administrator and what were the dirty words if any.

I humbly suggest an update, on this.

Whatever I, in my personal capacity requested was as a third person for Shear Decency and Gratitude to Elder's sake

Best regards
Qalander

[Andrei]

Art,

I am just quoting from your first post on this topic.

One cannot simply "assume" (make an ass out of u and me)

My interpretation is only through whatever the books are teaching us, readers with English as a second language. This is what I mean:
http://dictionary.re....com/browse/ass
This is what books are teaching us, non-native English speakers.
I am sorry, I made a mistake, the dictionary was giving a vulgar meaning to the word not a dirty one as I said.

[djack77494]

I think I join with others in being somewhat shocked over the direction this thread has moved. Perhaps it is a cultural thing, but I did not find anything even a bit offensive in previous comments. I really don't even feel previous comments were harsh.

The importance of clear, unambiguous communication regarding technical topics cannot be overstated. I find it distressful to constantly see queries that are poorly defined and reflect an extreme lack of thought on the part of the OP. Queries are requests to the other forum members to volunteer their time and efforts to resolve a problem(s) facing the person issuing the query. If you can make such a request, shouldn't it be expected that you would expend a rather minimum effort to properly formulate the query? I don't think it too much to expect, and I do think it reasonable to experience some exasperation when such minimal efforts are not made.

The original posting reflects the extremely poor practice for which one would (or at least should) be severely chastised in the professional engineering field. There are so many widely disparate interpretations that could be applied to the question. One couldn't begin a useful response without some serious upfront assumptions. They could be totally erroneous leading to poor or even dangerous recommendations. Yet all this is absolutely unnecessary if a minimum preparation effort is endured by the requestor.

If anything, it was harsh of the requestor to not grace us with this minimal effort. Those who selflessly attempt to answer the anonymous pleadings of those in need deserve only praise-even if the response involves a bit of well deserved chastisement.

[Art Montemayor]

Andrei:

Your e-dictionary states that the word "ass" is:

A noun.
1. a long-eared, slow, patient, sure-footed domesticated mammal, Equus asinus, related to the horse, used chiefly as a beast of burden.
2. any wild species of the genus Equus, as the onager.
3. a stupid, foolish, or stubborn person.

It fails to state that this word is a formal, correct name for what others call a "donkey" - a foolish and dumb beast of burden. The description I used is an old, well-documented and used American engineering description of why engineers should not "assume" anything. The reason being is that the word is composed of ass, u, and me. This an American engineer's way to remind himself and everyone involved that making assumptions without a good justification can lead to gross and sometimes dangerous mistakes that leave one looking like a donkey (an ass). It's kind of like what has happened in this thread to some people who write before engaging their brain into gear.

I see nothing wrong, questionable, or "vulgar" in the use of this term - be it in English or in its Latin genus as used in the Spanish (asno) and Italian (asino). All these words mean the same: a donkey (onager).

I am answering your concerns because just like mishra.anand72 (who, somehow has conveniently made himself/herself scarce), you also have "ASSUMED" certain aspects about me and my post which did nothing else than offer my engineering opinion on why I consider it important to always be explicit in your engineering communications. I never mentioned anybody, never pointed to anybody, and never reprimanded anybody. I wrote my opinion – which everyone is free to do on our Forums. In fact, I explicitly agreed with the OP's concern and confusion with the obvious lack of identity of what kind of percentage he was being given.

If this example of totally wrong and false translations of one of the world's most read and practiced languages isn't proof of what I stated, I don't know what is.

And yes, mishra.anand72, I WILL have a very good day – especially since it is my birthday and my use of the English language was obviously correct in keeping with the topic at hand. I cannot explain why some people can't understand correct, formal English. I am not responsible for their knowledge in it or their lack of it. All I can do is to keep trying to help them by expounding the importance of correct and accurate engineering communications.

[gvdlans]

Congratulations Art, and thanks (again) for sharing your wisdom and experience with us!

Guido

[Qalander (Chem)]

Dear All

We should rather bury this thread

Allowing latitude of forgiveness to All of Us 'Humans' never in-fallable

At times misconceptions get generated from exposure to slang

It is better to avoid its usage.

[smalawi]

Art,

thanks for always sharing without asking for anything in return, happy birthday (for the second time !)


Gents (short for gentlemen, as opposed to alternative name for the toilet!)

This misunderstanding is simply that, no place for hard feelings. We are all professionals

Please remember the effort that Art puts into these forums, I'm for one only visit these forum because he is such an inspiration to me.

keep that in mind because next time you need advice and have to pay for it, you will know the real value that Art brings to these forums.

cheers,

sm