13 replies to this topic

[ogpprocessing]

Dear All,

I need some infomration about ventilation nozzle including:

1. What process engineer should know about ventilation nozzle when specifying process data sheets of vessels and tanks?
2. When and for which services ventilation nozzle to be considered?
3. Recommended size and number of nozzles?

[Zauberberg]

Ventilation nozzles are normally specified for Fixed Roof Tanks with internal floaters, to assure free ventilation between outside air and vapor space bounded by the fixed roof and the floating roof.

One of the process manuals I have, sets the requirement for 0.2 ft^2 ventilation area for each ft of tank diameter.

[ogpprocessing]

Ventilation nozzles are normally specified for Fixed Roof Tanks with internal floaters, to assure free ventilation between outside air and vapor space bounded by the fixed roof and the floating roof.

I have seen at one project that for all of the pressure vessels and storage tanks 6" ventilation nozzle has been considered regardless of service fluid nature.

[Zauberberg]

Oggprocessing,

Ventilation nozzle for what? Between the refrigerated LNG and atmosphere? Between pressurized Propane and atmosphere? Between the Amine and atmosphere? I will chew up my ChE degree if you show me such storage tanks!

[SSWBoy]

Oggprocessing,

Ventilation nozzle for what? Between the refrigerated LNG and atmosphere? Between pressurized Propane and atmosphere? Between the Amine and atmosphere? I will chew up my ChE degree if you show me such storage tanks!

I think what oggprocessing is getting at is another nozzle (in addition to manway) for allowing ventilation of air through the vessel when it is being inspected, cleaned etc. Whereas I think you're talking about atmospheric vents on say a raw water tank where the conents are non-flammable etc... I think?

[ogpprocessing]

For the project that I have mntioned all of the vessels and storage tanks are equipped with one 6" ventilation nozzle such as fuel gas scrubber, instrument air receiver, plant air receiver, nitrogen receiver, hydrocarbon condensate (sour) flash drum and etc.

[Zauberberg]

Can you please upload the vessel sketch/datasheet? Normally all vessels have vent lines and an isolation valves installed at the top head, and the size may vary depending on vessel size. Vent connection is provided to ensure sufficient inflow of vapor/air during steam-out conditions, to avoid creation of vacuum inside the vessel. Some also practice venting the steam itself through this connection during the steaming process.

Everything would be so much easier if you can just upload the sketch showing position and arrangement of such "ventilation" nozzle. As Art Montemayor keeps repeating (for everyone's sake), we should be communicating as engineers and provide all the input data when looking for assistance, instead of chatting as housewives on a coffee break, and speculating without any data supplied.

[ogpprocessing]

Dear,

Check the attached extract from process data sheet of one of the drums of mentioned project.

Attached Files

•  Sketch for Ventilation Nozzle.bmp   1.27MB   100 downloads

[Art Montemayor]

Ogpprocessing:

I am going to respond as if I were writing and communicating with a professional process engineer that is working on a real-life process application – exactly as I communicate daily with other process and project engineers working under me. I do this because I consider the question presented as a serious one and I also know from personal experience that I (as well as other member contributors – such as Zauberberg, Ankur,and SSWBoy) all know that our comments and advice is often taken seriously and applied in the the field. This naturally raises a deep concern on our part that our advice must be defined as specific and detailed to the point that it is perfectly understood and applicable to the problem at hand. We cannot afford to be generalized, speculative, guessing, or experimenting with the O.P.’s (original poster’s) problem. A dreadful or tragic mistake can easily take place if our advice and comments are mis-interpreted or mis-applied. As professional engineers bound and ruled by ethics and morals, we cannot allow this possibility to take place. This is the reason we strongly request that all posters supply ALL the basic data and scope of work information that they have available at the very outset of the original post. We cannot generate quality responses using bad quality input and basic data.

Your vessel data sheet reveals 22 nozzles and the fact that this is nothing more than a horizontal, Flare Knockout drum. Fortunately we know the basic scope of work for a HP Flare Knockout drum (or, I hope we all do) because you haven’t furnished it (it is noted here that the Data Sheet you furnish is INCOMPLETE - there is information missing). The function of the drum is one of its being a separator and surge vessel prior to issuing inlet gas to the HP flare for disposal as a flame. This is a basic pressure vessel and, as such, is not designed for continuous atmospheric venting. So why the need for a venting nozzle(s)? The venting nozzles in question are two (while you only mention one:

N5 – a 3” vent nozzle
N7 – a 6” venting nozzle (reference to a note 7)

Where is the referenced Note 7? This is a key portion of the basic data if you want to discuss the need for N7. You have failed to supply the complete Data Sheet for this vessel and, as such, we can only “guess” at what the scope of work for the vessel is regarding its application. This may be a land-based installation or one on an offshore platform – either way, the application dictates what the scope of work is as related to its operation. Hence, we can only speculate that the intended duty of N7 is a blow down procedure in the event of a process upset or an emergency. The vessel is directly connected to the almost perfect disposal (and de-pressuring) method: a flare. However, if there is a block valve or shutdown valve in the outlet line, another means must be available to depressurize it. You have not furnished the detailed, as-built, P&ID so that we can’t tell if that is the case.

I now address your specific questions:

1. What process engineer should know about ventilation nozzle when specifying process data sheets of vessels and tanks?
Obviously, a process engineer should be the ONE discipline engineer that dominates ALL of the process in question and be ready to address all process needs and potential hazards. I personally hold process engineers totally responsible for the proper design and safety of the entire process – including all Data Sheets for vessels (which includes ALL nozzle requirements). I demand –and fully expect – my process engineers to be fully capable and expert in leading and responding to all HAZOP questions and problems arising from the same. If they cannot do this, they do not deserve to be on the Process Design Team – period.
2. When and for which services ventilation nozzle to be considered?
This is a subject to be addressed and resolved by the Process Engineer in charge of that part of the process design. This is totally dependent on the process requirements and the scope of work involved with the process.
3. Recommended size and number of nozzles?
This is a resultant action of the action taken in Step 2 by the responsible Process Engineer. Process Engineers are the ones that “own” the process and its design and, therefore, carry the weight and responsibilty of ensuring a proper, safe, and continuous process operation devoid of any potential hazard to humans and equipment – in that order.

[ogpprocessing]

Dear Mr.Montemayor,

Thank you so much for your great help. Please find my clarification and more information as follows:

Your vessel data sheet reveals 22 nozzles and the fact that this is nothing more than a horizontal, Flare Knockout drum. Fortunately we know the basic scope of work for a HP Flare Knockout drum (or, I hope we all do) because you haven’t furnished it (it is noted here that the Data Sheet you furnish is INCOMPLETE - there is information missing). The function of the drum is one of its being a separator and surge vessel prior to issuing inlet gas to the HP flare for disposal as a flame. This is a basic pressure vessel and, as such, is not designed for continuous atmospheric venting. So why the need for a venting nozzle(s)? The venting nozzles in question are two (while you only mention one:

N5 – a 3” vent nozzle
N7 – a 6” venting nozzle (reference to a note 7)

Where is the referenced Note 7? This is a key portion of the basic data if you want to discuss the need for N7. You have failed to supply the complete Data Sheet for this vessel and, as such, we can only “guess” at what the scope of work for the vessel is regarding its application. This may be a land-based installation or one on an offshore platform – either way, the application dictates what the scope of work is as related to its operation. Hence, we can only speculate that the intended duty of N7 is a blow down procedure in the event of a process upset or an emergency. The vessel is directly connected to the almost perfect disposal (and de-pressuring) method: a flare. However, if there is a block valve or shutdown valve in the outlet line, another means must be available to depressurize it. You have not furnished the detailed, as-built, P&ID so that we can’t tell if that is the case.

My clarifications:
1. Note 7 describes that: "Ventilation nozzle to be opposite side of man hole"
2. I have attached the HP flare drum P&ID from this you can see the location and configuration of the ventilation nozzle. The Note 4 of P&ID besides the N7 just describes that N7 is ventilation nozzle.
3. Please kindly be informed that as I mentioned before for this project the Engineer has been considered 6" ventilation nozzle for all of the drums such as HP flare drum, LP flare drum, Utility air receiver, instrument air receiver, nitrogen receiver, fuel gas scrubber, sour hydrocarbon condensate flash drum, condensate stabiliser tower nd etc.

I now address your specific questions:


1. What process engineer should know about ventilation nozzle when specifying process data sheets of vessels and tanks?
Obviously, a process engineer should be the ONE discipline engineer that dominates ALL of the process in question and be ready to address all process needs and potential hazards. I personally hold process engineers totally responsible for the proper design and safety of the entire process – including all Data Sheets for vessels (which includes ALL nozzle requirements). I demand –and fully expect – my process engineers to be fully capable and expert in leading and responding to all HAZOP questions and problems arising from the same. If they cannot do this, they do not deserve to be on the Process Design Team – period.
2. When and for which services ventilation nozzle to be considered?
This is a subject to be addressed and resolved by the Process Engineer in charge of that part of the process design. This is totally dependent on the process requirements and the scope of work involved with the process.
3. Recommended size and number of nozzles?
This is a resultant action of the action taken in Step 2 by the responsible Process Engineer. Process Engineers are the ones that “own” the process and its design and, therefore, carry the weight and responsibilty of ensuring a proper, safe, and continuous process operation devoid of any potential hazard to humans and equipment – in that order.[/font][/size]

According to attached P&ID it seems that ventilation nozzle is not intended to be used for applications which are described by you such as blowdown.
And unfortunately I could not find the clear answers to my questions after reading your reply. I want to know what are the applications of ventilation nozzle? recommended size?

Thanks again for your help.

Attached Files

•  P&ID.pdf   482.22KB   79 downloads

[Art Montemayor]

Ogpprocessing:

Thank you for submitting your P&ID. We finally have a clear description of what you were describing.

Both Nozzles N5 and N7 are clearly blinded on the P&ID and are not used. Consequently, they serve no purpose for your scope of work as per the P&ID. As I stated previously, “This is a basic pressure vessel and, as such, is not designed for continuous atmospheric venting. So why the need for a venting nozzle(s)?” And, as suspected, there is no venting taking place with this HP flare drum.

I am presently working with a flare drum on the project I am on and it is similar in size to yours in dimensions. It is sized for 4.2 MM Nm3/day of flaring and it has no venting nozzles on it. We vent directly through the HP flare. Your P&ID indicates the same operating scope of work.

To answer your question, “what are the applications of ventilation nozzle? recommended size?”, I can only repeat what I wrote previously. Additionally, the recommended size depends directly on the gas flow rate expected to be vented – if and when there is a vent requirement (which your application obviously does not have).

Your concern with regards to the N5 and N7 nozzles is seen on the P&ID as one that is not justified since these nozzles are clearly simply there because of a whim or for some unknown reason – perhaps a change in scope of work after the detailed engineering. Since their presence is not explained or indicated on the P&ID, I would not worry about them. Simply leave them blinded as they are indicated. They serve no purpose.

[ogpprocessing]

Dear Art,

As you know maintenance activities for pressure vessels is something related to confined space entery activities that needs special permit to work system. Usually one of the requiremnets of confined space entery permit to work is to ensure that inside of the pressure vessel is safe for the operator before he enters into the confined space. As far as I know this is done by fan and diluting the inside of the pressure vessel.

By chance is this ventilation nozzle the one which is to be used for above mentioned application?

[Art Montemayor]

Ogpprocessing:

I always design for eventual confined space entry into a pressure vessel. This is part of a normal, conventional Scope of Work during the detail design of the vessel. I fully expect serious operating companies to implement this type of philosophy into their process projects. However, I have seen companies evade this type of design in order to economize on capital costs. That is why I continue to respond to your question stating that it depends on your Scope of Work for this specific vessel. If you work for the company that owns the P&ID, then you should be aware of that Scope of Work. You have not shared it with us and I can’t comment on any specifics because I am ignorant of the design Scope of Work for the specific vessel. I don’t how many times I have to mention this important point.

There are no magical formulas or so-called “codes”, “standards”, or “rules of thumb” for determining how many nozzles (or their sizes) go on a vessel. Every pressure vessel is designed according to its specific Scope of Work and the wishes of the owner. I seriously doubt there is a law in your country that states that you must have a 6” nozzle on every pressure vessel. Why you got them on your project is anybody’s guess. If it were me and I needed to know why, I would contact the engineering contractor of the vessels and ask them directly what these nozzles were intended for since it is obvious that they are not meant for operational needs being that they are blinded.

Long before a person enters a confined pressure vessel space I always demand that the vessel be thoroughly purged, cleaned, rinsed, dried, monitored for residual chemicals, and ventilated using atmospheric air. The ventilation is done by having two (not one) manways – directly opposite each other. This allows the air to travel through the entire length of the vessel and not just one short section. Your nozzles (even the 6” size) are too small for ventilation and simply in the wrong position to be effective as positive ventilation. However, I agree with your speculation that it could be that they were intended for that purpose – but this is pure guess work at this point. All process design being done is not necessarily the correct, safe, and proper process design. There are always mistakes and bad designs being done. Process design is not devoid of bad or inexperienced and sloppy engineers. I know because I have fired some of them from projects I have led.

Summarizing, the nozzles in question could be there because of sloppy scope of work that was changed after detailed design, or they could be for ventilation, or they could simply be contingency items or “spares” for some undefined duty in the future. Who can tell if we don’t have the original Scope of Work? I regret that I can't give a specific, positive answer to your query, but I would be lying if I gave you a specific response meant to please you rather than to confront the truth.

[ogpprocessing]

[size="4"][font="Times New Roman"]
Ogpprocessing:

That is why I continue to respond to your question stating that it depends on your Scope of Work for this specific vessel. If you work for the company that owns the P&ID, then you should be aware of that Scope of Work. You have not shared it with us and I can’t comment on any specifics because I am ignorant of the design Scope of Work for the specific vessel. I don’t how many times I have to mention this important point.

I am not working for the company that owns or has been developed the P&ID. I only have used this engineering documents package for self training and because of this fact that this package has been developed by a very good and reputable company within the world (Technip)this made this question in my mind that why for all of the pressure vessels of a plant 6" nozzle is considered for ventilation.

There are no magical formulas or so-called “codes”, “standards”, or “rules of thumb” for determining how many nozzles (or their sizes) go on a vessel. Every pressure vessel is designed according to its specific Scope of Work and the wishes of the owner.

I fully agree with you and that is why this made a doubt for me that why for all of the pressure vessels of a project one 6" ventilation nozzle is considered regardless of the scope of work of the pressure vessel.

I seriously doubt there is a law in your country that states that you must have a 6” nozzle on every pressure vessel.

There is not such a rule in my country.

Long before a person enters a confined pressure vessel space I always demand that the vessel be thoroughly purged, cleaned, rinsed, dried, monitored for residual chemicals, and ventilated using atmospheric air. The ventilation is done by having two (not one) manways – directly opposite each other. This allows the air to travel through the entire length of the vessel and not just one short section. Your nozzles (even the 6” size) are too small for ventilation and simply in the wrong position to be effective as positive ventilation.

As I did upload the data sheet the engineer has been considered the combination of ventilation nozzle and manway together and not only one manway. They are considered at opposite side as mentioned at data sheet.

Thank you so much for your great help and kind attention.