9 replies to this topic

[ayan_dg]

My atmospheric water storage tank in having high level alarm & an emergency shut down system to close tank inlet valve at very high level. The time required to fill the tank from NLL to HLL (high level) is 6 min & from HLL (high level) to HHLL (very high level) is also 6 min at maximum inflow. Considering I have put two safety systems (alarm & trip) & consideable time for manual action , should I need to provide an overflow line.

[Art Montemayor]

You certainly should provide an overflow. Why haven't you considered this prior to incorporating an alarm as well? It would seem that this is common sense.

[ayan_dg]

Thanks for the reply.
The problem in providing an overflow line is it is getting too big. The inlet line is 32 inch as such the overflow nozzle will be atleast 34 inch (850 mm ). The inlet lines enters through the top (roof) of the tank while the overflow line should be at the side wall of the tank. That means I have to leave 850 mm at the top for providing overflow nozzle. This would provide a large amount of dead volume.

[Art Montemayor]

Ayan:

Allow me to "paint" a scenario for you:

Imagine that the high level alarm detection switch failed on your large water storage tank and that your local newspaper ran a front page new story on this event in the following manner:

"Today, the large water storage tank on Capitalistic Enterprises Corporation property collapsed and caused the death of several work persons in the area while also destroying considerable structures and other equipment in the immediate area surrounding the installation of the tank. The responsible design engineer on this project, Engineer Ayan_dg was questioned on the cause of this disaster and he replied, 'I apologize for all the inconvenience this has caused everybody. Although I normally would have provided an emergency overflow to the tank, I had a problem because it was too big and it would have required a large amount of dead volume and a lot of extra investment costs.'"

How do you think your society – which you ethically are bound to protect – and your fellow engineers would feel about this type of decision on your part?

[JoeWong]

Mr. Montemayor,
I like your scenario...

Ayan,
Pressure relief device is ultimate safeguard on lost of high PRESSURE trip function whilst Overflow is ultimate safeguard on lost of LEVEL trip function.

[ayan_dg]

Thanks for the eye opener !

If a tank have a nitrogen blanket then how to provide an overflow line (because the nitrogen will escape through it !)

[JoeWong]

Thanks for the eye opener !

If a tank have a nitrogen blanket then how to provide an overflow line (because the nitrogen will escape through it !)

Ayan,
Your first post stated "...atmospheric water storage tank..."

What type of water is that ?
Why you blanket the storage tank ?
When you said "atmospheric", does it imply open to atmosphere ? If not, why you said "atmospheric" ?
Is the tank blanketed with storage tank ?
Even though the tank is blanketed, do you know that an overflow still can be provided without losing N2 ?

You last post seem to prove that we are foolish...where we have provided responses without getting sufficient information and completely understanding the situation...

[Art Montemayor]

Ayan:

Correct me if I am interpreting your question wrong. I believe that you mean to ask: how are other tanks (that happen to have nitrogen blanketing) protected against over-pressurization due to a an over-fill of liquid? Is an over-flow line provided? If so, how does one contain the nitrogen blanket so that it doesn't leak out through the overflow line during normal operation?

If the above is what you meant, then the answer is: Sometimes an overflow line can be provided very easily on a blanketed tank. All that is done is to create a Seal Pot on the overflow line - something very similar to what is used on a flare header line or on a flame arrestor.

On some toxic or hazardous fluids, one can use a seal pot. You are left with employing redundent instrumentation and or HIPPS technology.

Allow me to stray back to the original theme of your first question: SAFETY. What Joe Wong has tried to do is what I have also tried: to instill in young Chemical Engineering Students that while it is important to get the right mathematical and logical engineering answer, it is FAR MORE IMPORTANT to DO THE RIGHT THING. You started your thread off great; you employed the word "Safety" as the first word in your title. However, you seemed to forget all about what the scope of your thread is, when you started to worry about how large the overflow line would be and how much space it would take. You seemed to forget the one thing that you started off to do: Protect the Human Beings and the product you are dealing with. That's why I "painted" the hypothetical scenario, trying to show you what can happen to you and your projects when you lose sight of the main scope of work. Don't feel bad it happens to the best of engineers. We have to be reminded of our priorities constantly. I think that Joe Wong knows all too well what I was trying to put across to you in my hypothetical response. He's a professional and has obvious experience in knowing the responsibility and accountability that the profession carries. That is what he is trying to make you and other students focus on: ACCOUNTABILITY. When you become a professinal you will be held accountable (legally and financially) for your actions and the results of your decisions. That's why Joe is also pointing out that as a student you are accountable for giving detailed and accurate information so as to generate a worthy answer.

[ayan_dg]

I am really sorry Joe if I have hurt your feeling. I tried to ask exactly the question which Mr. Montemayor stated above that is " what for other tanks which have nitrogen cover / having toxic fluid "

[Qalander (Chem)]

Ayan:

Correct me if I am interpreting your question wrong. I believe that you mean to ask: how are other tanks (that happen to have nitrogen blanketing) protected against over-pressurization due to a an over-fill of liquid? Is an over-flow line provided? If so, how does one contain the nitrogen blanket so that it doesn't leak out through the overflow line during normal operation?

If the above is what you meant, then the answer is: Sometimes an overflow line can be provided very easily on a blanketed tank. All that is done is to create a Seal Pot on the overflow line - something very similar to what is used on a flare header line or on a flame arrestor.

On some toxic or hazardous fluids, one can use a seal pot. You are left with employing redundent instrumentation and or HIPPS technology.

Allow me to stray back to the original theme of your first question: SAFETY. What Joe Wong has tried to do is what I have also tried: to instill in young Chemical Engineering Students that while it is important to get the right mathematical and logical engineering answer, it is FAR MORE IMPORTANT to DO THE RIGHT THING. You started your thread off great; you employed the word "Safety" as the first word in your title. However, you seemed to forget all about what the scope of your thread is, when you started to worry about how large the overflow line would be and how much space it would take. You seemed to forget the one thing that you started off to do: Protect the Human Beings and the product you are dealing with. That's why I "painted" the hypothetical scenario, trying to show you what can happen to you and your projects when you lose sight of the main scope of work. Don't feel bad it happens to the best of engineers. We have to be reminded of our priorities constantly. I think that Joe Wong knows all too well what I was trying to put across to you in my hypothetical response. He's a professional and has obvious experience in knowing the responsibility and accountability that the profession carries. That is what he is trying to make you and other students focus on: ACCOUNTABILITY. When you become a professinal you will be held accountable (legally and financially) for your actions and the results of your decisions. That's why Joe is also pointing out that as a student you are accountable for giving detailed and accurate information so as to generate a worthy answer.

I am really sorry Joe if I have hurt your feeling. I tried to ask exactly the question which Mr. Montemayor stated above that is " what for other tanks which have nitrogen cover / having toxic fluid "

May be I humbally tip in with the possibilty that the student could not consolidate thoughts while/during posting.
Probably He or She have API 650 Design Near-Atmospheric Tanks case containing Contaminated/Toxic Water having harmful effects mitigated through Nitrogen Blanketting.
I may suggest additionally that effective Overflow area be managed through multiple smaller diameter pipelines alongwith hydraulic seals as mentioned by Art.
Best Regards to everyone and keep it up student(s) with keen interest.
Qalander