6 replies to this topic

[Bryanlee]

Hi everyone, I am a Year 1 chemical engineering student. I have to do the corsework for equipment design. I choose distillation system. The distillation system here is too extract around 15% ethanol by mass from the fermented mash( containing crushed corn, extracted starch, unreacted glucose, enzymes and water). I am not sure whether this should be considered as multicomponent distillation or just binary( ethanol + mash).  

 

I choose tray distillation column because tray is suitable for feed which contains solids. Theoretical mash flow rate calculated is 121 tonnes per hour.

 

I just want to ask is that should I consider my distillation as multicomponent or binary? Because there are different ways for these two types of distillation to calculate for the tray position and plates needed. Besides, I want to ask whether the mash flow rate is realistically feasible or not. 

 

I am sorry if I sound ignorant here but I would be grateful if I can get some advice.

 

Thanks in advance.

[PingPong]

I just want to ask is that should I consider my distillation as multicomponent or binary?

It is basically a binary mixture of water and ethanol, with some solids present that do not vaporize.

 

Note however that dissolved sugars and salt do have an impact on the vapor pressure of the watery liquid. Or in other words: they increase the boiling point of the watery liquid. http://en.wikipedia....point_elevation

 

Besides, I want to ask whether the mash flow rate is realistically feasible or not.

It is feasible.

[Bryanlee]

I assume that the distillation column has 20 trays, a height of 19.6m with area of tower is 1.824 m2 . Do you think the dimension of this column is appropriate to support 121 tonnes per hour of flow rate?

 

How to determine the viscosity of the mash?

 

Thank you for your help.

[PingPong]

I assume that the distillation column has 20 trays, a height of 19.6m with area of tower is 1.824 m2 .

Assume?

You are supposed to calculate the dimensions of the column. They depend not only on the mash feed flow but also on the feed temperature, the water concentration in the distillate and the ethanol concentration in the bottoms product you intend to produce.

 

Viscosity of the mash depends on the amount and particle size of the solids in the mash. I don't think this can be calculated but has to be measured, so you need to google to find actual data for such service.

Edited by PingPong, 28 October 2013 - 11:58 AM.

[Bryanlee]

I am sorry if I annoy you in the first place. I have not undergone any modules related to separation processes. I take values from a published source to calculate a standard simple distillation tank. I might sound intolerable here but I would just need some experience from others to tell me a typical distillation column dimensions so that I can start drawing. The dimensions calculated by me seems ridiculous to me so I am asking around to see if it can support my mash flow rate or not.

 

Thank you very much and sorry once again.

[Art Montemayor]

Alexandre:

 

I am not trying (nor could I) to speak for PingPong, but I can advise you that in this Student Forum our professional engineers take a very serious and dedicated attitude to help and assist students – especially those they know are going down the wrong path with regards to Chemical Engineering.  They have been there before and know the hardships and pitfalls that a student has to overcome to succeed as a graduate.  I am sure PingPong is not "annoyed" but concerned in giving you the help he knows you need.  Allow me to try to help you by pointing out some basic engineering criteria:

 

Never take a criticism or correction as a negative or personal response.  Engineers are asked to make some very serious and expensive decisions in the course of their professional career and a mistake, error, or mis-communication could result in serious consequences.  That is the nature of our profession and most of us take it seriously and would hate to see a student fail to understand the importance of a good, constructive attitude when it comes to dealing with other engineers.  Any words or actions taken by our colleagues in correcting, checking, and seeing to it that our work is safe, proper, and correct is to our benefit and that of our project(s).  If they didn't care about us, they would never give us their advice and corrections.  That would be the worse treatment we could receive from our colleagues.

 

Chemical engineers develop and produce Process design – not Mechanical design.  Therefore, we don’t generate any drawings other than Process Flow Diagrams (PFDs) and Piping and Instrumentation Diagrams (P&IDs).  We generate sketches of some details in our design – in order to communicate and explain how we need for certain details to be constructed or fabricated (such as nozzles, tower internals, etc.).  But we don’t make drawings of a distillation column.  There is no such thing as a “typical distillation column dimension” and no need to draw it.

 

Calculating a distillation process design requires you to have the knowledge obtained in a Unit Operations distillation course.  There, you will understand the basics of applying heat and mass balances as well as the theory volatility and the application of various methods to determine the required number of separations stages as well as calculating the diameter and height of the required distillation column.  You will also determine the reboiler and overheads condenser duties as well as the required reflux ratio to maintain the overhead purity.  As PingPong infers, there are no assumptions here – just pure, hard calculations based on given Basic Data.

 

You state you made calculations on the dimensions.  Why haven’t you submitted them here so that you can have them checked (for free!) and receive experienced comments from them.

 

I know our Forum members can help you.  But you have to make an effort to help them as well.  Without your Basic Data and detailed explanations, they are powerless to help you out.

 

I hope you can see the logic and facts of my reasoning and that you will make an effort to work with our members.  We are all doing it for you.

[Pilesar]

I never made ethanol, but my grandfather did and my father helped hide it from government agents. If I were to design a process to separate ethanol from a mash containing solids, I would not feed the mash into the trays of a distillation column as you propose. I would first boil the water and ethanol out of the mash and feed only the vapor stream to the distillation column. At that point, you can assume a binary system and can feed the dregs to the hogs. For practical details, there are many examples in published literature for ethanol/water distillation as it has worldwide, historical applications.