7 replies to this topic

[wan]

Hai.

Im new here. I need a help as I have to design a column that work at 0.3 bar with 30 stages. I used total condenser to get all liquid product. Now I need to design the vacuum system. I reckon that liquid ring pump or steam ejector would be among the best choices. But im not sure about those devices, how it works and how to install it to my distillation column. May u guide me on this.

p.s Column to separate diethyl maleate and monoethyl maleate and very small amount of water. 99% of DEM goes to the bottom while MEM and water will be recycled.

Many thanks!

[Art Montemayor]

Wan:

Welcome to our Forums. We are here for the purpose of helping engineering students get a better understanding of what they are involved in and what they should be doing to succeed in their chosen career.

In order to lend a helping hand, we need for the student to make life easy for us with regards to describing their concerns and problems in clear, concise, and accurate writing. We can only be effective in helping if we receive all of the basic data and scope of work involved in the query. Let me give you some examples:

1) What specific type of “design” are you supposed to do – a process design or a mechanical design? It would seem like you already have the process design since you identify the pressure and the number of stages in your distillation column. What does your “design” entail?

2) We are all engineers here. We’re all pretty smart. However, we can’t read minds when it comes to identifying the correct pressure units. Specifically, what do you mean when you state your column will operate at “0.3 bar”? Is this in barG or is it barA? As you and everyone else should know, it makes a big, big difference. Please be specific and accurate in your submittal of basic data.

3) Have you researched our Forums on the key word, “vacuum”? If you did, you would find not only answers to how a vacuum distillation works, but you would find a lot of illustrations, drawings, sketches, and calculations of how a vacuum system is designed and how it is assembled and controlled. I know this is so because I produced a lot of that information --- which I have repeated over and over to a lot of students who come to our Forums. Please try to do some research on prior threads related to your specific problem. It could easily save you a lot of trouble and time.

4) You tell us what you plan to separate, but you don’t furnish a sketch, flowrates, temperatures, pressures, heat and mass balances, and compositions. You also state that the “MEM and water will be recycled”. Do you mean “refluxed” instead of recycled? There are no recycle streams in a distillation column if you design it correctly. A simple schematic sketch of your system should illustrate exactly what you are proposing as a system.

You say you want guidance on the vacuum system and I think I just gave you some idea on where you can find specific answers. Can you be specific in what you need guidance on? Please furnish us with specific questions – not general ones. Tell us what it is that you don’t understand in detail. That way we can form an idea just where and how to best show or teach you what you don’t know.

I’ll wait for your reply.

[wan]

Hai. Thanks and sorry for the lacking of msg

I need to send my report in few days time and im still struggle with this vacuum system

Actually I already set up a process design to my distillation column

My column works at 0.3 Bar absolute, with 30 stages ( 28 trays as I used total condenser and a kettle reboiler )

I would say that I prefer to use LRP to set up vacuum distillation. I believe the LRP should be installed before my total condenser as I got total liquid distillate. ( I used bubble point for my condenser )

For (1 stage) condenser MW = 140.996
liquid rates =26118 kg/h

For the top tray (2 stage) - MW (vapour)= 140.996
Vapour rates = 31906 kg/h
MW (liquid) = 145.255
liquid rates = 32709 kg/h

Now I need to explain on how I set up and maintain my column to be at 0.3 BarA, what item I used and design the item mechanically hence find the cost for the item ( LRP ). Thats the thing I need to do

I do my simulation using Pro II. If any information u need I havent supplied, hope u will let me know.

I hope u can guide me through as I only get few days left. Many thanks!

[wan]

oh before I forgot, the 0.3 barA is the first tray pressure, i.e the condenser, the goes up down the column, about 0.55 barA at the final stage, reboiler. thanks!

[Art Montemayor]

Wan:

If you have waited all this time until you only have a few days to put together a vacuum system for your project, you have practically run out of time. There is more to a reasonable and practical vacuum maintenance system than what you suppose.

You want to use a Liquid Ring Piston (LRP) vacuum pump, but you don’t tell us the operating temperature and fluid that you have selected for the pump. Have you had prior study or analysis of how an LRP works and what it depends on?

Please read my comments on: http://www.cheresour...amp;#entry27410

As well as my long, detailed posts to Sara on the referenced June 2007 thread titled “"Vacuum Distillation Column: Design And Control" in the Student Forum.

You have a bunch or reading and research to do in order to properly design and plan your vacuum system. In the meantime, you will find a lot of solutions to your problem in the above two threads.

[djack77494]

I believe the LRP should be installed before my total condenser as I got total liquid distillate.

wan, Just one small comment. If you try to draw vacuum upstream of your condenser, you will be "sucking" your overhead product vapors out of your system and into the vacuum pump exhaust. I believe you really want the vacuum pump (i.e. compressor) downstream of the condenser and accumulator. If you post again, tell us what you expect to be downstream of your "total condenser".

[wan]

hai.

Yes, im not so sure actually, we never learn in detail about the vacuum system, and now seem i need a column to work at 0.3 bar. i have to do some extra study on the system. I got a total condenser where the product/downstream of the condenser are the distillate and reflux, all liquid. Im not really sure when should i set up my vacuum pump. Is it before or after the condenser? thanks!

[Art Montemayor]

Wan:

Some things in life are pretty obvious.

First, you come to this Forum with "need to send my report in few days time" and no knowledge of how a vacuum system works. That's why I responded with a lengthy and detailed thread, telling you how and where the answers to your dilemma are located.

More than "a few days" have come and gone and you still have obviously not read and studied the material I recommended. It is also obvious that it probably is too late by now - if what you first stated is true.

Your lack of understanding of how a vacuum system works and what it takes to develop and maintain a vacuum is all too obvious when you propose to install a vacuum device UPSTREAM of a condenser. In that location, the required vacuum device would be tremendously huge and impractical. My detailed explanations in the recommended materials details it all out, but I have the impression that you are unwilling to invest the time and effort in doing the work.

I hope there is still time for you to dedicate the required time in order to learn how to design and operate a vacuum Unit Operation.

Good Luck.