8 replies to this topic

[Reza.R]

Dear friends

I read very useful information about how to size a reflux drum in this forum, but what is less discussed is, what are components of a reflux drum and how can I determine their location in the drum, I mean : a reflux drum contains many parts for example inlet nozzle, outlet nozzle, drain , vent , man hole , .... but I did not see any guildline about how to specify their position in vessel, I need to know what is the position of for example inlet feed nozzle from vessel tangent line , or where must I locate the drain nozzle in vessel layout? or about level controller, what equipment are necessary for installation and where do they install? I mean I need some more details about the designing of reflux drums


Thanks in advance dears, I am eagerly waiting for your kind helps and hints , please help me in this field

[Padmakar Katre]

Hi,

Search for the topics with separator sizing, vessel sizing in this forum and you will find plenty of useful stuff. Please go through and let us know if you have further doubts.

[Reza.R]

Dear Padmakar

thank you very much about your hint, Unfortunately about mechanical design of reflux drum , I could not find my required info,

Please let me know If there is any similar thread to what I cited above

Thanks in advance

Edited by Reza.R, 28 July 2012 - 04:52 AM.

[Reza.R]

In addition to my previous post, I want to add this fact that for total condensers that all of the top distillation column vapor condense in it and no vapor exist beside liquid, How can I size vapor nozzle ?!!

[Art Montemayor]

Reza:

It seems to me that you are getting wrapped up and confused because you are trying to deal with generalities while proposing to design and specify a specific reflux drum. All process equipment are designed and specified to suit one specific application. There is no reflux design specification that suits all applications. That is why you will never find any guideline about how to specify nozzle locations or positions in our Forums. You will find this information on specification (data) sheets and fabrication drawings for the specific vessel.

Now you add that you want to size the overhead vapor nozzle on a distillation column and that although you are condensing all the vapor in a total condenser, you don’t know how to size the nozzle. You are certainly right that you need some more details. You are simply missing the point that it is YOUR JOB to obtain those details. You are supposed to have already made or generated a heat and mass balance around the distillation column – this is a logical pre-requisite before attempting to design the condenser and the related reflux drum. Therefore, you should already know the design flow rates of:

• Feed stream;
• Top vapor overhead stream;
• The bottoms stream;
• The condenser duty;
• The reflux rate;
• The overhead product rate.

What seems to be the problem? I see no problem if you have done your design work in the logical procedure. Can you be more explicit and detailed in defining what you are doing or proposing to do? We can help you – if we knew what you are trying to do, and how you propose to do it.

[Reza.R]

Thank you dear admin for your precious guidance,

Let me explain more about my problem:

I had already simulate a distillation column with a feed stream containing 71% n-butane 27% i-butane (balance C₅+ or propane). The aim is to separate iso and normal butane from the feed stream. The overhead vapor must contain nearly pure i-butane with a rate of 14,317 kg/hr. This amount subsequently condenses in a total condenser. The liquid stream then has a density of 524 kg/hr at T = 50 ^oC and P = 7 bar pressure. This condensed stream must enter a reflux drum (28 m³/hr inlet feed into drum). I designed all dimensions and size of the drum, but in order to instruct the manufacturer to construct this vessel, I must specify many other details as well; and this is just the beginning for me after process designing aspect for this equipment.

I read many documents and spreadsheet about how to size and design a vessel and I got useful info about the designing procedure, but some parts that were absolutely less explained, compared to the others, is mechanical design of the vessel.

Mechanical designing: the questions of this part must be explicitly answered and cleared. I mean all required mechanical components (Inlet nozzles, outlet nozzles, drains, level gauges, vents, steam out, pressure controller necessary equipment, antivortex, deflector and elbow for inlet feed) as well as the sizes and positions of all of mentioned items in vessel.

As you pointed out, I can find similar info in datasheet and fabrication drawing, but the way and procedure that these sizing were obtained is more important and I highly need some guidelines about this project.

Thank you for your patients and grateful for your help.

Edited by Art Montemayor, 29 July 2012 - 11:07 AM.

[Art Montemayor]

Reza:

I know it is difficult for a student to conceptualize the difference between a process design and a mechanical design. A student is at the mercy of his/her instructor to explain and define the normal, expected “deliverables” that a Chemical Engineer owes to his organization after going through the process designing stage. All of us old professionals know this because we’ve been through it or we live it everyday. What we don’t know is what you’ve been taught or told as to what your “battery limits” of the engineering design phase is. But I can accurately tell you: the size and location of nozzles on a process vessel are the responsibility of the Process Design Engineer. That is NOT a mechanical design; it is merely instructions for the mechanical designer to take that information and use it in the design as basic data without the freedom to change it.

It is the Process designer who knows what is expected of the vessel as far as operational characteristics and flexibility. He/she are the only ones who know the process limitations and hazards involved in what is being designed and built. The SIZE of the nozzles are dependent on the results of stream calculations (i.e., a simulation output) or the process scope of work (future capacity). The LOCATION of the nozzles is also a major concern and specification item in the hands of the process designer. This information is carefully specified in a process Data Sheet that the process designer originates and passes on to the mechanical designer to complete. The alloy is another specification that many times falls into the process responsibility. You should already have received instructions and examples of Data Sheets, clearly outlining all the items for identification by a process designer. This Data Sheet always includes a detailed sketch of the subject vessel and a table of all the nozzles with their size and ratings.

You are obviously a student and you haven’t given us all the basic data until now. This always causes a delay and confusion when trying to help students. You should always communicate all the basic data, scope of work, and detailed explanations at the very first posting of a thread. We cannot read your mind. You now state that you have “read many documents and spreadsheet about how to size and design a vessel”, but you lack the help. We know nothing about you from your personal data – such as: university attended, year of study, age, country, etc. Therefore, what I can advise you is that the information for designing the details you seek is to be found in your university instructor’s lecture and the text book you have been assigned. This is normal procedure.

We on the Forum can help you with these details (we don’t “teach”; your university is supposed to do that), and advise you how to handle these details – if you choose to follow that advice. But it is important that you cease labeling those details that you lack in a general manner. You MUST BE SPECIFIC to receive specific help and assistance. Start by identifying ALL the nozzles in a spreadsheet table, together with the proposed rating and size. If you are unable to identify the size and rating (as you indicate), then at the very least you should furnish a detailed description of your scope of work and design basis. Your input of the nozzle schedule (as we call it in industry) is best done in a workbook and you should include a Data Sheet (or Specification Sheet) also, with a detailed sketch of the vessel. You should already have started on the Data Sheet and have it ready with only those details that you now identify missing in size and location (and also ratings). Tell us if you don't have a Data Sheet (which you can download from our Forum) - and I will submit one.

That is how a professional process engineer works in industry and how you will be expected to work when you graduate. The faster and the more details you give the Forum, the faster and the more accurate will be the advice.

Await your positive, detailed response.

[Reza.R]

Thank you again dear admin,I want to deeply appreciate your help and time, I taught that designing a vessel has a general procedure. So you helped me to change my

Let me add more about the project. The inlet feed which is obtained from the condensation of top vapor has the following info:

T=50 'C

P= 7 bar

m= 7158.5 kg/hr , M.W=57.97 ( close to pure i-butane)

n=123 kmol/hr

density= 524 kg/hr

vap. fraction= 0.0

volumetric flowrate= 14 m3/hr

the reflux drum was sized using the attached article:

D= 1.219 m , L=3.6 m , Vessel Weight: 1280.38 , Vessel Volume: 4.709 m3, Feed: 14 m3/hr (vap fraction=0)

I begin sizing inlet nozzles, first feed nozzle , from the website below , some criteria indicate that vent and drain line size must be 2 inches, and also it stipulate a condition for inlet nozzle , vapor nozzle and liquid nozzle.

http://www.red-bag.c...sel-sizing.html

My project indeed is increasing the capacity of an existing plant two times. ( the above figures is based on the current capacity) so the flowrates must become 2 times greater.

I want to start with current capacity , the designers obtained the inlet feed pipe size= 4 inches, This is not consistent with my knowledge since the minimum liquid velocity in pipe must be 1-3 m/s and with considering the minimum number which gives the maximum pipe diameter , it gives us a pipe with inside diameter = 2.8 inches while the existing pipe is 4 inches !! this really confused me because I don't know it is due to oversizing for probable future scale up or not !?!

the same nozzle size may be expect for the liquid outlet from vessel

for vapor we can just use only from the data of top vapor of the distillation column :

vapor density: 17 kg/m3

so the question is here: with no incoming vapor, how can we size the vapor outlet nozzle?? (Only with knowing minimum vapor velocity and nozzle criteria ??)

The man hole size in existing plant is 18 inches but the above website recommend 24 inches, so which one may be chosen?

I also don not know anything about level gauges and its necessary equipment to set it up in the vessel

steam out is another my concern , why this connection must be installed and how can I size it ?

And another question is after all of these, what options are available for me to specify the right location and position of these nozzles and connections to the vessel, the distance of these nozzles with respect to each others

the picture of the reflux drum is also attached




Dear admin , about datasheet I have no datasheet. It would be better to search deeply for it in the forum ( Reflux drum sizing datasheet ? )

Thank you again dear admin ,

Attached Files

•  Design_Two_Phase_Seperators.pdf   4.23MB   146 downloads
•  New Bitmap Image.bmp   720.05KB   40 downloads

Edited by Reza.R, 29 July 2012 - 02:11 PM.

[Art Montemayor]

Reza:

You continue to confuse the issue and, I believe, yourself.

This thread's topic is about nozzle sizes and locations on a Reflux Drum. That is how I have responded to your queries. Instead of responding to my requests, you offer what you want to give us as "information". We are not interested in the process design conditions of the drum. The drum, according to you, is already sized. Therefore, we should not be discussing temperatures, pressures, fluids, etc.

That you are confused is obvious. You said you read our threads on separators and decided to size your drum according to the CEP article by Svrcek & Monnery. That's fine; except that you are not designing according to the Scope of Work you have described (which is sparse). You are faced with designing a Reflux Drum - NOT A 2-PHASE SEPARATOR. Your fluid may be saturated, but it is still SINGLE PHASE. Therefore, you simply need a vessel to give you simple, common-sense capacity in the form of residence time to carry out the refluxing and overhead product pumping that you obviously will need. In not preparing (nor furnishing) a scope of work, you have designed the wrong vessel using the wrong methods. You have over-worked the problem to the point where you have reason for confusion: you have designed a right-handed glove when you were asked for a left-handed glove.

I continue to repeat what I say to so many students: We are willing and happy to help you in resolving your problems and queries. However, a student has no right to demand help with conditions tied to his/her request. We will help you - but not under your terms. You must heed this common sense request. Otherwise, you will never get any help. For example, you have not paid any attention to my requests for specific information. We are not asking for your telephone number, ID of personal bank account, family information, etc. All we ask is for the information that leads us to best assist and help you out in this dilemma. When I asked you for a spreadsheet format of your nozzle schedule it was done for a specific and logical reason. I did not request a hand-scrawled sketch of a separator with dimensions. I requested a Data Sheet - which you should be able to easily download and prepare. In fact, you (and everyone else reading this) know perfectly well that you should already have a Data Sheet at least started - if not finished. You said you are to prepare information to a vessel fabricator; therefore, you HAVE TO PREPARE A PRESSURE VESSEL DATA SHEET. But you have not responded. I am attaching a Data Sheet Form.

Your confusion continues with respect to the quantity and type of nozzles needed. As I stated, you should have received these instructions from your teachers in university - whereever that is. You must apply common sense to the fact that you have to use visual liquid level detection in order to operate and calibrate other level instruments - such as level alarms.

Manways are there for a purpose: to allow safe ingress and egress of personnel doing any required inspection and maintenance of internals. If you have no internals (as it seems to be), then you need no manway! If you do need a manway, then make it a size that allows for safe ingress and egress - such as 24" (minimum). This is discussed many times in our Forums and is common, safety sense.

Why are you worrying about "steam out"? Do you believe that you will have sludge, tars, or heavy hydrocarbons in this overheads vessel. I certainly do not believe that you can make a case out of that. Process knowledge and in-depth understanding of the operation is a requirement before even attempting to design process equipment. You don't design merely relying on "equations" and "formulas". You require common sense - which is what engineering is all about.

The most ridiculous problem is one that isn't a problem: how can you be concerned about a vapor line mounted on a reflux drum meant to store and handle liquid? There is no need for such a notion - at least not according to what you have described. But you have not furnished a scope of work and an explanation of what you are encharged with doing - nor for what purpose. Therefore, all I can comment on a vapor nozzle on the reflux drum is that it is not needed in the basic scope; get rid of it.

I don't want this thread to continue to wander and meander through a lot of useless information and lack of direction because it will only confuse you even more. I strongly advise you to follow the recommendations and requests I have made - not because I like it like that, but because I do know better how to resolve this since I have gone through what you are going through countless times in the past - and with success.

Attached Files

•  Art's Process Vessel Data Sheet.xls   83KB   217 downloads