Distillation Column Design

Topics: Distillation, Theoretical plate, Chemical engineering Pages: 58 (13752 words) Published: February 10, 2014
EXECUTIVE SUMMARY:
The main objective of this project was to carry out a design on the Propane distillation column for a process that produces 1,3 Butadiene. The raw materials used are Butane, Oxygen and Water and the process capacity is 100 000 tonnes per annum nominal. In the previous work it was stated that the plant is located in China. The main location of the plant is in the capital city of the Gansu Provence, Lanzhou. This was decided as the location over other provinces due to the excellent transport links and the availability of raw materials and cheap labour. The close proximity to suppliers, customers and skilled labour all make Lanzhou the ideal location for the plant to be located.  The design of the distillation column consists of the packed type. The distillation is a multi-component distillation involving separation of Propane from the other components at very high pressure. The number of theoretical stages chosen was 16 stages based on a reflux ratio of 0.608. The column diameter calculated was 0.61 at maximum pressure gradient possible for distillation columns and 0.66m for minimum pressure gradient, which was then scaled up to 0.65m. This was a reasonable decision as it may be helpful when the plant capacity increases. The column has a height of 8m. Feed location for the arrangement of packing is at stage 3 from the top of the column. Pall rings constructed out of stainless steel with a size of 25mm is used for packing. The vessel thickness of the column is around 5mm, constructed out of stainless steel also to avoid corrosion.   A preliminary design on the condenser for this distillation column was also carried out. The type of condenser is a fixed plate with a 1 shell and 1 tube pass. The tubes are stainless steel, 119 in number, 2.44m in length, and with a square pitch arrangement. The overall heat transfer coefficient was also calculated as 486.026W/m2C.  The pressure drop on the tube side was 7.306 N/m2 (almost negligible) as only one tube pass is used with a very short length. The pressure drop on the shell side was 46.64 N/m2 The next section details on the Piping and Instrumentation over the column. The control system used for better efficiency of the units is also featured in the same P and ID.. The control mainly used for this, is the cascade control for the temperature and product composition, also in the varying of the bottom product flow rate to control the level at the bottom of the column. The variables controlled are the top and bottom temperatures including product composition and the reflux drum and also the level at the base of the column.  There were two group tasks performed in this term along with the individual design. The first group task performed was the HAZOP on the feed line of the propane distillation column. The aim of the HAZOP was to evaluate the selected process line and identify the possible deviations which could result into a hazard; the possible causes to the deviations, consequences and actions needed to avoid the consequences were also discussed. An improvised P and ID was then produced after Hazop was done. The Hazop was done with Dr. Titiloye as the Study Leader. The deviations discussed include no flow, less flow, less temperature due to weather conditions, more temperature likely to occur as a result of external fire and extra phase in an event of poor separation, presence of heat transfer fluids, presence of off gases, corrosion inside the pipe catalyst pellets in the pipe and excess residue due which leads ultimately to contamination. The second group work is the economic appraisal, which was useful in concluding that if this project were to be operational; the payback period would be two years which would leave 13 years of net profit. So, from a financial aspect, the project was found to be very viable and attractive. Both the group works are attached in the Appendix VI and VII

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References: [11]: Coulson J.M & Richardson J.F ‘’Chemical Engineering Design’’, 4th ed., vol. 6, Pergamon, Oxford, 2005 page 579
[12]: Coulson J.M & Richardson J.F ‘’Chemical Engineering Design’’, 4th ed., vol
[13]: Coulson J.M & Richardson J.F ‘’Chemical Engineering Design’’, 4th ed., vol. 6, Pergamon, Oxford, 2005 page 526
[14] : Coulson J.M & Richardson J.F ‘’Chemical Engineering Design’’, 4th ed., vol
[15]: Coulson J.M & Richardson J.F ‘’Chemical Engineering Design’’, 4th ed., vol. 6, Pergamon, Oxford, 2005 page 592
[16]: Dr
[19]: Coulson J.M & Richardson J.F ‘’Chemical Engineering Design’’, 4th ed., vol. 6, Pergamon, Oxford, 2005 page 812
[20]: Coulson J.M & Richardson J.F ‘’Chemical Engineering Design’’, 4th ed., vol
[23]: Coulson J.M & Richardson J.F ‘’Chemical Engineering Design’’, 4th ed., vol. 6, Pergamon, Oxford, 2005 page 709
[24]: http://www.alibaba.com/showroom/condenser-tube.html; assessed on 26/02/10
[27]: Coulson J.M & Richardson J.F ‘’Chemical Engineering Design’’, 4th ed., vol. 6, Pergamon, Oxford, 2005 page 711
[28]: Coulson J.M & Richardson J.F ‘’Chemical Engineering Design’’, 4th ed., vol
[29]: Coulson J.M & Richardson J.F ‘’Chemical Engineering Design’’, 4th ed., vol. 6, Pergamon, Oxford, 2005 page 195-199
[30]: http://www.azom.com/Details.asp?ArticleID=863; accessed date 09/03/10
Graph 1 : Coulson J.M & Richardson J.F ‘’Chemical Engineering Design’’, 4th ed., vol. 6, Pergamon, Oxford, 2005 page 524
Grapgh 2: Coulson J.M & Richardson J.F ‘’Chemical Engineering Design’’, 4th ed., vol
Graph 5: Coulson J.M & Richardson J.F ‘’Chemical Engineering Design’’, 4th ed., vol. 6, Pergamon, Oxford, 2005 page 646
Graph 6: Coulson J.M & Richardson J.F ‘’Chemical Engineering Design’’, 4th ed., vol
Graph 7: Coulson J.M & Richardson J.F ‘’Chemical Engineering Design’’, 4th ed., vol. 6, Pergamon, Oxford, 2005 page 668
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