4 replies to this topic

[deltaChe]

I tried to do the condenser vacuum hydraulic check, but I don't how to start it.

It seems very dumb cause I know this similar topic has discuss a lot in the forum.

Please bear with me.

My goal is to (1.) calculate the min. elevation of the reactor condenser?

(2) calculate the height of flooding

I know the difference in elevation between the Condenser and the hot well must be exceed the static head of the water in the barometric leg, and also confessor must be

Placed at a height that is sufficient to prevent flooding



The head from vaccum pressure is P1~-1 barg

P1*10.2/SG = (-10 m) . so the min elevation of condenser may be -10 m ?

Please give me some suggestion and guide.



Thank you very much for your kindly help

Attached Files

•  Book1.xlsx   20.52KB   68 downloads

[deltaChe]

I make a simple calculation for this hydraulic question, but not sure that is correct or not.
(pls see the attachemnt )

Thank you so much.

Attached Files

•  test1.pdf   113.42KB   61 downloads

[Art Montemayor]

hhyy7788:

First and foremost, I want to commend you for your attempt to resolve this problem using a spreadsheet. This is the basic, practical, engineering method to employ in all engineering problems requiring a graphic as well as a calculation tool. I wish all chemical engineering students would use common sense and arrive at the simple conclusion that they have a perfect tool at their disposal for attacking practically all of their university problems by the use of a spreadsheet.

However, in my opinion, you ruined what you initially started out doing by not continuing within the same workbook and using the basic number-crunching ability of a spread sheet to do your work for you. Instead, you use what appears to be a word processor and a scanner to communicate your calculations when you could have done everything in a compact, rational, easily calculated spreadsheet within the same workbook where you drew your original schematic drawing.

I don’t have access to the original description or write-up of your textbook problem, but I can immediately see that you have made several basic student errors in depicting your problem. This is a bad situation because it immediately can lead you to the wrong answer or conclusion. In order to solve a problem correctly, you must first be able to understand WHAT the problem is and communicate it correctly. This is always the first step in attacking any engineering problem. If you cannot explain the problem to another person, you will never be able to resolve it. Therefore, a clear, concise and accurate graphical description of the problem gives you a definite advantage in being able to resolve it. So let’s start with your sketch first:

• Even though you fail to state what the process involves, I can guess what it is that you are confronting. I believe that you are given a reactor operating under a vacuum and the vacuum is developed and maintained by a series of steam jet ejectors. The fact that you show multiple ejectors in series tells me that the vacuum you are pulling on the reactor is a very deep vacuum (very low absolute pressure). If I am correct, then the pressure you indicate as P1 = 1.0 barg for the reactor products in the reactor condenser IS WRONG. You cannot have 2 x 760 = 1,560 mm Hg absolute pressure in your reactor. I know this because if you did, then you wouldn’t have any vacuum! You must have a vacuum in your reactor condenser in order to justify the use of 3 vacuum jet ejectors.
• If your first jet ejector is discharging at 83 mm Hg absolute pressure, then the pressure in the reactor condenser must be LOWER than this. Otherwise, the jet ejector is acting as a vacuum ejector IN REVERSE! This simply cannot be.
• You show the reactor vapors entering the condenser in the tubeside. And then you show the vacuum being pulled on the shellside of the condenser. This also cannot be. It doesn’t make sense.
• You fail to show where the condensed vapor liquids from the condenser are going to. I believe they should be going to a condensate drum. Is that correct? You should finish the total schematic and show this.
• What is the hot well that you write about? How is it connected to the jet ejectors? If you have different stages of vacuum in your series of ejectors you probably have different hot wells. Is this correct? You should show the entire vacuum system complete with all lines.
• You state you want to calculate the min. elevation of the reactor condenser but then you mention the hot well. Again, which is which? The reactor condenser is condensing vapors which go to a condensate drum. The excess vapors from the reactor condenser are going to the jet ejectors that will produce an aqueous mixture of excess condensed vapors and steam condensate. You must distinguish between these different streams because you are now getting confused and your calculations will show this.
• Do you want to find out the height of liquid that is in the condensate outlet pipe on the reactor condenser? I don’t think so; but you are not specific in your description – written or sketched. I believe you want to calculate the height of condensate in the outlets of one of the jet ejectors – but which one is anybody’s guess since you don’t even sketch the hot wells on your drawing. Please be specific and detailed.
• If indeed you want to find the height of condensate on the tail pipe of one of the jet ejectors, then you don’t need the Bernoulli equation as such. You need to know the density of the condensate and the partial vacuum above its surface as well as the pressure in the hotwell (I assume it is atmospheric – right?)

In any event, you started out OK, but you need to perfect your communications skills – both written and graphic. I await your response to these comments.

[breizh]

HI ,
Hope this helps
http://www.graham-mf...bVacuum/217.PDF

Breizh

[deltaChe]

hhyy7788:

First and foremost, I want to commend you for your attempt to resolve this problem using a spreadsheet. This is the basic, practical, engineering method to employ in all engineering problems requiring a graphic as well as a calculation tool. I wish all chemical engineering students would use common sense and arrive at the simple conclusion that they have a perfect tool at their disposal for attacking practically all of their university problems by the use of a spreadsheet.

However, in my opinion, you ruined what you initially started out doing by not continuing within the same workbook and using the basic number-crunching ability of a spread sheet to do your work for you. Instead, you use what appears to be a word processor and a scanner to communicate your calculations when you could have done everything in a compact, rational, easily calculated spreadsheet within the same workbook where you drew your original schematic drawing.

I don't have access to the original description or write-up of your textbook problem, but I can immediately see that you have made several basic student errors in depicting your problem. This is a bad situation because it immediately can lead you to the wrong answer or conclusion. In order to solve a problem correctly, you must first be able to understand WHAT the problem is and communicate it correctly. This is always the first step in attacking any engineering problem. If you cannot explain the problem to another person, you will never be able to resolve it. Therefore, a clear, concise and accurate graphical description of the problem gives you a definite advantage in being able to resolve it. So let's start with your sketch first:

• Even though you fail to state what the process involves, I can guess what it is that you are confronting. I believe that you are given a reactor operating under a vacuum and the vacuum is developed and maintained by a series of steam jet ejectors. The fact that you show multiple ejectors in series tells me that the vacuum you are pulling on the reactor is a very deep vacuum (very low absolute pressure). If I am correct, then the pressure you indicate as P1 = 1.0 barg for the reactor products in the reactor condenser IS WRONG. You cannot have 2 x 760 = 1,560 mm Hg absolute pressure in your reactor. I know this because if you did, then you wouldn't have any vacuum! You must have a vacuum in your reactor condenser in order to justify the use of 3 vacuum jet ejectors.
  P1=-1 barg @ outlet from precondensor to 1st ejector

• If your first jet ejector is discharging at 83 mm Hg absolute pressure, then the pressure in the reactor condenser must be LOWER than this. Otherwise, the jet ejector is acting as a vacuum ejector IN REVERSE! This simply cannot be.
  Yes Sir, you are right. P1=-1 barg is much lower than 83 mm Hg absolute pressure

• You show the reactor vapors entering the condenser in the tubeside. And then you show the vacuum being pulled on the shellside of the condenser. This also cannot be. It doesn't make sense.

I made a mistake. It should come from the tube side of the condenser.

• You fail to show where the condensed vapor liquids from the condenser are going to. I believe they should be going to a condensate drum. Is that correct? You should finish the total schematic and show this.

• The vapor liquid will return to the cooling water return side(from the precondeser shell side) which I didn't show that on the drawing.
• What is the hot well that you write about? How is it connected to the jet ejectors? If you have different stages of vacuum in your series of ejectors you probably have different hot wells. Is this correct? You should show the entire vacuum system complete with all lines.

• Each drain line from different condenser will go to the same hot well with different location separte by the 4 baffle in the hotwell.
  
• You state you want to calculate the min. elevation of the reactor condenser but then you mention the hot well. Again, which is which? The reactor condenser is condensing vapors which go to a condensate drum. The excess vapors from the reactor condenser are going to the jet ejectors that will produce an aqueous mixture of excess condensed vapors and steam condensate. You must distinguish between these different streams because you are now getting confused and your calculations will show this.

• Sorry to make you misunderstand, the flooding height which I want to
  calculate is from the hotwell to the precondenser.
• Do you want to find out the height of liquid that is in the condensate outlet pipe on the reactor condenser? I don't think so; but you are not specific in your description – written or sketched. I believe you want to calculate the height of condensate in the outlets of one of the jet ejectors – but which one is anybody's guess since you don't even sketch the hot wells on your drawing. Please be specific and detailed.
• If indeed you want to find the height of condensate on the tail pipe of one of the jet ejectors, then you don't need the Bernoulli equation as such. You need to know the density of the condensate and the partial vacuum above its surface as well as the pressure in the hotwell (I assume it is atmospheric – right?)

Dear Mr. Montemayor and Breizh, I really appreciate and thank you so much for your patient and comment. Your comment is very knowledgeable and wisdom.

To calculate the flooding height, just like you said that the Bernoulli equation
is not necessary for this calcuation.
I guess the reason for this is that the fluid velocity beteween the
hotwell and 1'st condenser tail pipe is very small.
Or the velocity is zero when the fluid climb up the condensers reach at
equilbrium so the pressure loss is neglibible?


In any event, you started out OK, but you need to perfect your communications skills – both written and graphic. I await your response to these comments.

• Thank you again. Your generous help for other people are my example.

Attached Files

•  Book1.xls   120KB   52 downloads

Edited by hhyy7788, 29 September 2010 - 05:41 PM.