5 replies to this topic

[Gin]

Hello,

I am a final year student in the university of Nottingham. I've recently stumbled upon this site and saw the great information and help that it provided. I believe I was reading a thread on the kettle reboiler design before I found out great answers from mr. montemayor here.

Currently, I am designing a heat exchanger with the following specification:
Cold stream:
main component (benzene, hydrogen, cyclohexane (lower))
vapor phase: 0.9831 to 1
supply temp: 57.51 C
target temp: 115 C
Pressure: 4000 kPa
Pressure drop allowance: 50 kPa
Mass flow: 4.85 x 10^4 kg/h
Molar entropy: 99.84 to 106.7 kJ/kgmole C
Molecular W. :6.35
Mass density: 9.276 to 7.693 kg/m3
Mass heat capacity: 5.223 to 5.295 kJ/kg C
Cp/Cv: 1.348 to 1.346
Cv (semi-ideal): 3.914 to 3.986 kJ/kg C
Viscosity: 1.128 x 10^-2 cP
Kinematic viscosity: 1.466 cSt
Thermal conductivity: 0.1631 W/m K

Hot stream:
main component (benzene, hydrogen, cyclohexane (higher))
vapor phase: 1
supply temp: 184.2 C
target temp: 116.9 C
Pressure: 3250 kPa
Pressure drop allowance: 50 kPa
Mass flow: 6.238 x 10^4 kg/h
Molar entropy: 110.2 to 104.1 kJ/kgmole C
Molecular W. :8.916
Mass density: 7.565 to 8.753 kg/m3
Mass heat capacity: 4.461 to 4.225 kJ/kg C
Cp/Cv: 1.276 to 1.302
Cv (semi-ideal): 3.529 to 3.246 kJ/kg C
Viscosity: 1.31 x 10^-2 cP
Kinematic viscosity: 1.6225 cSt
Thermal conductivity: 0.1689 W/m K

(continued)

[Gin]

Additional notes of my design:
1. All of the data is iterated in HYSYS
2. Cold stream is a mixture of benzene, recycle cylohexane, and hydrogen. This stream need to be heated up to a certain degree (115 C in here) before it enters the 1st reactor.
3. There are 3 catalytic reactor in series, reactor operated at the total vapor phase to give the fixed bed reactor the best efficiency.
4. The outlet from the 3rd/ final reactor is used the hot stream.
5. Benzene in the cold stream came from the first benzene supply. There's additional benzene that will enter the 2nd and the 3rd reactor's feed.
6. The design utilized the heat integration technology.

Things that I have done prior visiting this site:
1. Calculated area of transfer (using a basic guidelines from Coulson and Richardson vol 6 and Applied Process Design by ernest e. ludwig), and all of the preliminaries data.
2. Tried to determine the pipe for the tube side, at 1.6 m3/s... (a single U tube is impossible to achieve, a fixed tube have to have a 2" o.d with 1.843" i.d with 560 tubes at a 2.44 m tube)
3. Tried to determine the pt for the tube and to avoid a vapor blanket 1.5 x tube o.d was used.
4. Realized the drawback of a fixed tube HE (we have to make sure there's no vapor entrained in the pipe, so a fixed tube is impossible) in the reactor design.
5. Then tried to look at thermosyphon and kettle reboiler design. With a specific design for a fixed tube.
6. Redraw the 1st detailed heat exchanger networks with cascade control included.
7. Stumbled upon the site, and read a few articles on reboiler for a large amount of volumetric flowrate.

Things that I have done after visiting this site:
1. Redraw the 2nd detailed heat exchanger networks (with a flash drum in the middle of 2 heat exchanger). I am also conviced that a single fixed tube can handle the works.
2. Recalculate the number of tubes, outer diameter and inner diameter for 2 heat exchanger

(continued)

[Gin]

Things that occured when I was doing calculation for the process steam generation:
1. The nozzle on the shell side should be 10 m/s for the outlet, but does that also hold true for the inlet?
2. When I reexamine the design, I found that I am designing a vertical heat exchanger on the process, which would certainly mean the Uo will be different for the submerged part and the non submerged part. In turn, this would not give us an accurate value of our estimated area. How can I tackle this problem? I've read books from Collier and Thome about Convective boiling. Should I see on the nucleate boiling case for this particular design and just taking the average value of the U?
3. I noticed the trade off of this method, a high liquid residence time will reduce the area of HE, yet at the same time this will give a big safety issues (benzene, hydrogen and cyclohexane in quite a big tank)

PS: I'll be grateful if anyone can help me with my design. I have wasted the last 3 weeks to figure out the operatable design.
PPS: The original plant setup in HYSYS is provided in the following word file (it's a picture)

Attached Files

•  Pic.doc   165KB   72 downloads

[Gin]

Hi, it's Gin again here... I figured out I should also include the plant after the integration. Of course, feel free to ask any additional data. I'll try to provide them as soon as possible.

PS: I will try to include the rough sketches of the heat exchanger with the process control integrated as well tonight. (added)

Attached Files

•  final_with_T_and_P.JPG   160.84KB   53 downloads
•  Pic.JPG   26.93KB   59 downloads

[Gin]

Thank you for all your help and the advice for the previous month. I have finished and submitted my final design towards the school office. If it is possible, I would like anyone to comment on my final report (particularly the heat exchanger design) to improve my knowledge on designing the equipment for the future designs. I am also keen and interested in answering any question or the assumption that I made during my final report (I considered that this a practice and challenge before my final presentation in front of my lecturers).

PS: report and extended summary as attached inside

Attached Files

•  Extended_Summary.doc   26KB   51 downloads

[Gin]

(edit) Since the file is too big (even after being compressed into zip folder, it is still a staggering 5 MB file) to be posted in this thread. Therefore, I have taken the liberty on uploading it in sendspace. The link is as follow

http://www.sendspace.com/file/jtzv4i