7 replies to this topic

[LoaiSowwan]

i/ve posted a topic looks the same as this one buth the previuos one i wanted to get the diameter i got it, and now i want to calculate the cost for the whole design.

 

so i have this project which is designing a distillation column. the design is theoritical so nothing is exactly 100% right and alot of errors is expected, but again it is theoritical and there is values are based on assumptions. i got most of the values i need but i don't know how to calcuate the total cost of the column.

 

the distillation tower is an deethanizer and iam using it to separate ethane and propane (ignoring water and CO2).

assuming my column temperature is 72 Fehrenheit and my column pessure is 270 psia.

i got the relative volatility by getting the K values of my componenets and divided K of ethane on the K of propane and the relative volatility is 3.2

 

iam using sieve trays in the column with an efficiency of 0.75

 

i got the number of trays by using McCabe Thiele diagram, the number of trays i got is 11 trays after removing the condenser and the reboiler trays.

 

i also got the reflux ratio from the same diagram which is 0.438

 

i calculated the tower height by assuming i have a 0.6 m space between the trays, so  0.6 *11 = 6.6 m

 

What iam stuck on is how to calculate the total cost for the colum ,what should i do ? what equations should i use? what should i calculate first? what about trays, reboiler , condenser, maintenance and other important costs.

 

Thank you

[LoaiSowwan]

i also forgot to mention that i calculated the diameter of the column which is 2 meter.

[Art Montemayor]

Where have you been taught how to design a distillation column?  You've done it wrong because you have failed to take into consideration the efficiency of the number of trays you have calculated - which is only a theoretical value.

 

Agreeably, you're only after an "estimated" size of column - but the most important part of studying Chemical Engineering is NOT applying equations or calculations.  It is knowing and understanding what is the basis of the principles you are applying.  The McCabe-Thiele method is a great way to understand and calculate the workings and sizing of a distillation column.  But you must understand that it is a THEORETICAL calculation and fully understand how to convert the theoretical results into practical, working results by taking into consideration the principles of how a distillation column works.  Your professor or instructor should have taught you that every mass transfer device has an inherent efficiency.  You have to apply that efficiency if you are to be believed that you know what you are doing.

[LoaiSowwan]

@Art Montemayor

 

I am a petroleum engineering student.  My instructor told us to not worry about the efficiency as he will explain it in details in the next course.  But for now I need to know how to do the cost calculations for the tower and is it done, i'll appreciate your help.

[Pilesar]

Your column is way too short. Deethanizers typically have minimum 25 trays and 65-75% overall efficiency. Tray count may be up to 65 trays. There is more space required in a column than just between trays. You will have a large sump at the bottom to hold a liquid level and introduce the reboiler return to the column. You will have space over the top tray to introduce the reflux stream and disengage liquid from the vapor. The feed area also will need extra space. The deethanizer may be 30 or 40 meters tall. You should probably learn a bit more about distillation column design before costing the equipment so you can get close to the right dimensions.

 

Cost can be estimated but you need some economic data to begin. A good textbook is a start. I used Plant Design and Economics for Chemical Engineers by Peters and Timmerhaus in school many years ago but there may be better references now. Plant estimating costs in literature are referenced to a particular year. There is a plant costing index that lets you scale the estimated cost based on data from a previous year to the current year.

[shantanuk100]

Hi Loaisowwan,

 

I understand that you are trying to figure out how to design a column.

But before that, let us try to understand more of how the design is done.

Even though your design is preliminary as your professor had said, I would suggest you try and take time and do it in detail for your own understanding.

Once you get the detailed design, your understanding of your professor's lectures will also be better.

 

For a preliminary design check out the documents attached below. One has basic cost estimation too.

 

http://www.che.utah....tion design.pdf

 

http://kolmetz.com/p... Rev 04 web.pdf

 

For detailed design, I would recommend using "Distillation Design" by Henry Kister which is a great resource. He has done a lot of in-depth work on Distillation. Also, I agree with Pilesar. Timmerhaus is a great book for Plant design and economics concepts.

You should take some time and do these thoroughly so that'll save much more time in understanding, late on.

 

Regards,

Shantanu

Edited by shantanuk100, 12 April 2016 - 11:58 PM.

[Padmakar Katre]

 

i/ve posted a topic looks the same as this one buth the previuos one i wanted to get the diameter i got it, and now i want to calculate the cost for the whole design.

 

so i have this project which is designing a distillation column. the design is theoritical so nothing is exactly 100% right and alot of errors is expected, but again it is theoritical and there is values are based on assumptions. i got most of the values i need but i don't know how to calcuate the total cost of the column.

 

the distillation tower is an deethanizer and iam using it to separate ethane and propane (ignoring water and CO2).

assuming my column temperature is 72 Fehrenheit and my column pessure is 270 psia.

i got the relative volatility by getting the K values of my componenets and divided K of ethane on the K of propane and the relative volatility is 3.2

 

iam using sieve trays in the column with an efficiency of 0.75

 

i got the number of trays by using McCabe Thiele diagram, the number of trays i got is 11 trays after removing the condenser and the reboiler trays.

 

i also got the reflux ratio from the same diagram which is 0.438

 

i calculated the tower height by assuming i have a 0.6 m space between the trays, so  0.6 *11 = 6.6 m

 

What iam stuck on is how to calculate the total cost for the colum ,what should i do ? what equations should i use? what should i calculate first? what about trays, reboiler , condenser, maintenance and other important costs.

 

Thank you

 

 

Hi,

When you talk about costing of a distillation column there are various steps involved ahead of costing. Your approach should be,

1. Generate VLE data and arrive at theoretical tray count - you have thru

2. Generate the vap-liq traffic to estimate diameter - 2 meter is what you estimated

3. Use a conservative effieciency of say 65% and get the actual tray count - 11 / 0.65 = 17 use 20 trays (theoretical tray count looks low ? just check once agian)

4. Tray spacing is 600 mm so total 19 spaces so trayed section height = 600 * 19 = 11.4 meter

5. Feed locations, manholes after every 10 trays, top vapor space, bottom sump arrangements, reboiler return vapor distribution etc. you may need around 9 meter

6. total column height is ~ 21 meter

7. Design P, T and material to arrive at thickness and total weight of shell and metal and fabrication cost basis $/ton

8. Tower attachment costs to accomodate trays, feed pipes etc

9. add some cost for internals like trays, feed pipes

10. foundation cost, skirt support cost

 

These are typical cost components which you should be accounting as a minimum. All the best

[Jamal Khan]

Hi Loaisowwan,

For my project in my final year I had to do the sizing and costing of the ditillation columns for which I referred Biegler (Systematic Methods Of Chemical Process Design). The procedure is far more simpler then you would expect. Judging by the way you posted your question I think this would solve your problem.