The document summarizes the design and simulation of a divided wall column for separating reformate into benzene, toluene, and p-xylene. It includes the reformate composition, literature review on divided wall columns, material and energy balances, minimum number of trays calculation, Aspen simulation, materials selection, and a cost analysis. The divided wall column consists of a prefractionator with 13 trays separating to a side draw and a main column with 9 + 10 trays achieving high purity products within specifications. The simulation matches the material balances with less than 1% difference. The total capital cost is estimated at $1.67 billion with a payback period of 2.8 years.

1. JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY KAKINADA
UNIVERSITY COLLEGE OF ENGINEERING KAKINADA(A)
Department of Petroleum Engineering and Petrochemical Engineering
Viva Voce Examination on
design and simulation of Divided wall Distillation column for the separation of reformate
By
T. Hari Kiran
(15021A2529)
Under the guidance of
Prof. K. V. Rao
Programme Director
Petroleum Courses

2.  Contents
• Introduction
• Reformate Composition and Uses of Aromatics
• Literature Survey
• Material Balance
• Energy Balance
• Design of DWC
• Simulation using Aspen Plus V 10
• Materials of Construction and Process Control
• Health and Safety Factors of BTX
• Cost Estimation
• References

3.  Introduction
Petlyuk Column and Divided Wall Column
• A Petlyuk column consists of a prefractionator with reflux and boil up from the downstream three- product
column, a setup with only one reboiler and one condenser.
• Dividing wall column (DWC) is a single shell, fully thermally coupled distillation column capable of separating
mixtures of three or more components into high purity products.

4.  Reformate Composition and Uses of Aromatics
Component Wt.%
C5 compounds 3.83
C6 Non-aromatics 5.52
n-Hexane 1.49
Methyl pentanes 2.91
Dimethyl butanes 0.75
C7 Non-aromatics 6.92
C8 Non-aromatics 2.91
Benzene 4.01
Toluene 18.04
Xylene 19.62
o-Xylene 5.72
m-Xylene 9.60
p-Xylene 4.30
Ethyl Benzene 4.05
C9+ 35.10
• Reformates are defined as high octane liquid products.
• These are premium blending stocks for high-octane gasoline.
• Reformate is the main source of aromatic bulk chemicals such as Benzene, Toluene, Xylenes and
EthylBenzene which have diverse uses, most importantly as raw materials for conversion into plastics.

5.  Literature Survey
Divided wall columns can be classified into one of three types, based on the position of the dividing wall: middle divided wall
column (DWCM), lower divided wall column (DWCL), and upper divided wall column (DWCU)
Advantages
• Lower capital investment
• Reduced energy requirements
• High purity for all products
• Less construction volume
Disadvantages
• Higher columns owing to the increased number of theoretical stages.
• Increased pressure drop due to the higher number of theoretical stages.
• Only one operating pressure is available.

6.  Material Balance
The capacity of plant = 0.62 MMTPA
= (0.62*106*103)/ (330*24)
=77916.66 Kg/hr
Feed Conditions
• Temperature: 1350C
• Pressure: 150 KPa
• D2=88.6 kmol/hr; W3 =375.4 kmol/hr
Basis: 801.8 Kmol/hr of feed enters the column
Overall Material Balance: 𝐹 = 𝐷 + 𝑆 + 𝑊
Component Balance:
FZA = D2xA,D2 + SxA,S + W3xA,W3
FZB = D2xB,D2 + SxB,S + W3xB,W3
FZC = D2xC,D2 + SxC,S + W3xC,W3
XC,D2 = 0; XA,W3 = 0
COMPONENT COMPOSITION IN FEED
Benzene 0.1096
Toluene 0.4217
P-xylene 0.4687
Component
Inlet Outlet
Composition
Molar Flow
(Kmol/Hr) Distillate
Side
Product Bottom
Benzene 0.1096 87.87728 86.818 1.02928 0
Toluene 0.4217 338.1190 1.0095 334.587 2.522
P-Xylene 0.4687 375.8036 0 3.558 372.24

7.  Energy Balance
Equations used
Cp = A + BT + CT2 + DT-2
𝐶 𝑃 𝑚𝑖𝑥
𝑖𝑔
= 𝑦𝑖 𝐶 𝑃
𝑖𝑔
Energy balance for feed , 𝑄 𝐹 = 𝐹𝐶 𝑃∆𝑇 = 801.8 × 130.4219(135 − 25) = 11502950.74Kj/hr
Energy balance for distillate, 𝑄 𝐷 = 𝐷𝐶 𝑃∆𝑇 = 88.6 × 91.3883(85 − 25) = 485819.6712Kj/hr
Energy balance for bottom, 𝑄 𝐵 = 𝐵𝐶 𝑃∆𝑇 = 375.5 × 172.1533(141.99 − 25) = 6451729.822 Kj/hr
Energy balance for side stream, 𝑄 𝑆 = 𝑆𝐶 𝑃∆𝑇 = 337.8 × 139.1413(117.98 − 25) = 3790540.623 Kj/hr
𝑄𝑐𝑜𝑛𝑑𝑒𝑛𝑠𝑒𝑟 = 𝑉𝐻 𝑉 − 𝐷𝐻 𝐷 − 𝐿𝐻𝐿
= 81756476.39 – 485819.6712 – 11173854.48
= 70096802.24 KJ/hr
𝑄 𝑟𝑒𝑏𝑜𝑖𝑙𝑒𝑟 = 𝑄𝑐 + 𝐷𝐻 𝐷 + 𝐵𝐻 𝐵 + 𝑆𝐻𝑆 − 𝐹𝐻 𝐹
= 70096802.24 + 485819.6712 + 6451729.822 + 3790540.623 – 11502950.74
= 69321941.71 KJ/hr
Total energy into the column = 𝑄 𝑓 + 𝑄 𝑟𝑒𝑏𝑜𝑖𝑙𝑒𝑟 = 11502950.74 + 6321941.71 = 80824892.45 KJ/hr
Total energy coming out from the column = 𝑄 𝐷 + 𝑄 𝐵 + 𝑄 𝑆 + 𝑄 𝑐𝑜𝑛𝑑𝑒𝑛𝑠𝑒𝑟 = 80824892.3562 KJ/hr
Therefore, Energy into the system= Energy out of the system

8.  Design of DWC
Step 1: Calculate Vmin for every section.
Step 2: Calculate Rmin and R
Step 3: Calculate Nmin
Step 4: Calculate N
Step 5 : Calculate Liquid split
Step 6 : Calculate Vapour split
Under Wood Equation
1-q = Σ αi*zi / (αi-θ) , q=1 for saturated feed
Minimum vapor flow calculation
Vmin,i = Σ αi*xi,Di *Di/ (αi-θ)
Fenske Equation
Nmin = ln ((zlk/zhk)D *(zhk/zlk)B)
ln αavg
• 𝑅1 = 2𝑅 𝑚𝑖𝑛,1 = 2 1.289 = 2.578
• 𝑅2 = 2𝑅 𝑚𝑖𝑛,2 = 2 4.5499 = 9.0998
• 𝑅3_1 = 2𝑅 𝑚𝑖𝑛,3_1 = 2 1.8752 = 3.7504
• 𝑅3_2 = 2𝑅 𝑚𝑖𝑛,3_2 = 2 3.6122 = 7.224
• 𝑅4 = 2𝑅 𝑚𝑖𝑛,4 = 2 15.037 = 30.074

9.  Calculation on Number of Trays
Gilliland correlation
𝑁 − 𝑁 𝑚𝑖𝑛
𝑁 + 1
= 0.75 1 −
𝑅 − 𝑅 𝑚𝑖𝑛
𝑅 + 1
0.5688
N1= 12.844 ≅ 13
N2= 8.5582 ≅ 9
N3_1 = 7.36671 ≅ 7
N3_2 = 3.70329 ≅ 4
N4 = 10.1638 ≅ 10
The number of trays in prefractionation column is 13 trays
The total number of trays in main column is 9+13+10 = 32 trays
• 𝐿𝑖𝑞𝑢𝑖𝑑 𝑆𝑝𝑙𝑖𝑡 𝑆𝐿 =
𝐿1
𝐿2
=
587
1387.2
= 0.42315
• 𝑉𝑎𝑝𝑜𝑢𝑟 𝑆𝑝𝑙𝑖𝑡 (𝑉𝐿) =
𝑉1
𝑉4
=
348.2
1049.23
= 0.3317
9
13 13
10

10.  Simulation using Aspen Plus V 10
• For rigorous simulation, MultiFrac model of ASPEN PLUSTM has been used. Different columns can be interconnected by using
connecting streams. The simulation is done using NRTL model.
Flow rate kmol/hr Calculated values (Kmol/hr) Aspen plus results (Kmol/hr)
Distillate flow rate 87.8773 85.9882
Side flow rate 338.119 336.399
Bottom flow rate 375.804 373.411
Comparison of Material Balances

11.  Plots

12.  Materials of Construction and Process Control
Important materials available
 Carbon Steel
 Stainless Steel
Properties of S.S-304:
• Have high corrosion resistance
• They are shock resistant.
• Strength about 750 MN/m2.
• Yield strength about 270 MN/m2.
• Elongation varies between 30-75% depending upon carbon constant.
 Nickle and its alloy
Process Control Objectives
• Safer Plant Operation
• To keep the process variables within known safe operating limits
• To detect dangerous situations and to provide alarms & automatic shut-down systems
• To provide inter locks and alarms to prevent dangerous operating procedures
• Production rate: To achieve the design product output
• Product Quality: To maintain the product composition within specific quality standards
• Cost: To operate at the lowest production cost, commensurate with the other objectives

13.  Health and Safety Factors of BTX
FIRE AND EXPLOSION DATA FOR BENZENE
Flash points CLOSED CUP: -11.10C (120F)
Products of combustion Carbon oxides such as CO and CO2
Auto-Ignition temperature 497.880C
Flammability limits Lower flammability limit: 1.2%
Upper flammability limit: 7.8%
POTENTIAL HEALTH EFFECTS OF TOLUENE
Eye contact Causes eye irritation
Skin contact Causes moderate skin irritation, may
cause cyanosis of extremities
Ingestion Aspiration hazard. May cause irritation of
the digestive tract. May cause effects
similar to those of inhalation exposure
Inhalation May cause central nervous system effects
characterized by nausea, headache
Chronic exposure May cause dermatitis, cardiac
sensitization
FIRST AID MEASURES FOR TOLUENE
Eye contact Flush eyes with plenty of water
Skin contact Wash with water and get medical aid if
irritation develops
Ingestion Do not induce vomiting. Possible
aspiration hazard
Inhalation Remove from exposure to fresh air. If not
breathing, give artificial respiration. If
breathing is difficult, give oxygen
FIRE EXPLOSION DATA FOR P-XYLENE
Flammability of the product Flammable
Flash point CLOSED CUP: 250C (120F)
Products of combustion Carbon oxides such as CO and CO2
Auto-Ignition temperature 5270C
Flammability limits Lower flammability limit: 1.1%
Upper flammability limit: 7%

14.  Cost Estimation
Type of cost Amount (in US $ )
Purchased Cost 515,000,000
Installation Cost 128,750,000
Instrumentation and Controls Cost 61,800,000
Piping Installation Cost 92,700,000
Electrical Cost 77,250,000
Building process and auxiliaries Cost 103,000,000
Service Facilities 154,500,000
Yard Improvement 51,500,000
Land 25,750,000
Total Direct Costs 1,210,250,000
Type of cost Amount (US $)
Engineering supervision 121,025,000
Construction expenses 181,537,500
Contractor fee 60,512,500
Contingency costs 96,820,000
Total indirect costs 459,895,000
Total Indirect CostsTotal Direct Costs
Fixed capital investments = Direct + Indirect costs = US $ 1,670,145,000
Total capital investment = total fixed capital + working capital = US $ 1,920,666,750
Total product cost (T) = Direct production cost + fixed costs + plant overhead costs + general expenses = US $ 1,597,076,156.25
Total selling price per annum = US $ 2,568,560,800
Gross earnings = Total selling price -Total Product costs = US $ 971,484,643.75
Income Tax = 30% Gross earnings = US $ 291,445,393.125
Net profit = Gross earnings – Tax = US $ 680,039,250.625
Pay-out Time = TCI/Net Profit = 2.8243 years

15.  References
• [1] Asprion, N., Kaibel, G. (2010). Dividing wall columns: Fundamentals and recent advances. Chemical Engineering and
Processing: Process Intensidication.
• [2] A Method for the Design of Divided Wall Columns by Nouroddin Sotoudeh Chafi, S15ptember 2007
• [3] Consider Dividing Wall Columns , by John G. Pendergast, David Vickery, Patrick Au-Yeung and Joe Anderson, The Dow
Chemical Company, Dec 19, 2008
• [4] Chu, K. T., Cadoret, L., Yu, C. C., & Ward, J. D. (2011). A new shortcut design method and economic analysis of divided
wall columns. Industrial & Engineering Chemistry Research, 50(15), 9221-9235. Bumbac, G., El
• [4] Dejanović, I., Matijašević, L., & Olujić, Ž. (2010). Dividing wall column—a breakthrough towards sustainable distilling.
Chemical Engineering and Processing: Process Intensification.
• [5] DIVIDED WALL DISTILLATION COLUMN: DYNAMIC MODELING AND CONTROL, Alexandru Woinaroschy,
Raluca Isopescu
• [6] Energy efficient control of a BTX dividing-wall column, panel Anton A.KissaRohit R.Rewagadab
• [7] J M Smith, H C Van Ness, Introduction to chemical engineering Thermodynamics, Mc Graw Hill education 7th edition
• [8] Plant design and economics for chemical engineers/Max S Peters Klaus D. Timmerhaus.4th ed.
• [9] Process Heat Transfer by Donald. Q. Kern
• [10] Robert E Treybal, Mass transfer operations, Mc Graw Hill Education 3rd Edition
• [11] Separation of Mixture by Divided Wall Column using ASPEN PLUS Kishore Khushalani1, Akanksha Maheshwari2, Nikita
Jain3
Web links:
• https://en.wikipedia.org/wiki/Catalytic_reforming
• https://www.researchgate.net/publication/243803667_A_Method_for_the_Design_of_Divided_Wall_Columns
• https://www.chemicals-technology.com/projects/jurongaromatics/

16. THANKYOU