1.
Process design
Design methodology
The approach in designing this reboiler was based on the references from “Chemical Engineering
Design” by Sinnott and Towler (2009), “process Heat Transfer” by Kern (1893). The figure 1 below
shows the algorithm of design the reboiler:
Assumptions and justifications
Some assumptions were made in design the reboiler. They are summarised below:
1- HYSYS data of valve extracting is reliable.
2- Heat Transfer coefficient was found from textbook method.
3- The bottom stream pressure (from HYSYS) is the same as the operating pressure.
4- Boil up stream is vapour.
Basis of design
Before start performing the design, some essential data are required. Therefore, the physical
property and the operational condition of the inlet and outlet stream are tribulated from HYSYS.
Table 1
Therefore, there are three entail type of reboilers used in the industry.
So, to finalise the type of the reboiler, a compression of these types is done to choose the suitable
type. Table 2 below shows the advantages and disadvantages of the reboiler:
Type of Reboiler Advantages Disadvantages
Forced circulation Suitable for handling A pump is required to circulate the fluid
Reboiler viscous and fouling fluids. through the exchanger.
High risk involved. High possibility of hot
Operates at high velocity. fluid leakage.
Can predict the circulation
rate.
Suitable for law
vaporisation.
Thermosyphon Reboiler The lowest price between Not suitable in operating high viscous
the reboilers types. fluid.
Cannot operate at less than a certain
pressure which is commonly 30 Kpa.
Require extra support below the column,
so the cost of construction will be
increased accordingly.
Piping work is quite complex comparing to
other reboilers. Also, more attention is
needed from the operator.
The most reliable and Require more residence time, as it cannot
Kettle Reboiler simple reboiler. withstand fouling fluids.
Has a high duty. Law heat transfer coefficient.
Flexible in implementation.
Good option for vacuum
conditions.
The choice of the suitable reboiler was according to some factors:
1- The nature of the fluid
2- The operating conditions
3- The layout of the equipment.
Therefore, after this analysis, the Kettle reboiler is the most suitable and feasible reboiler
type in this process.
Process design calculation
(a) Make initial specifications.
(i) Fluid placement
There is no choice here; the boiling fluid must be placed in the shell and the heating medium in the
tubes.
(ii) Tubing
One-inch, 14 BWG, U-tubes with a length of 16 ft are specified. A tubing diameter of 3 /4 in. could
also be used.
(iii) Shell and head types
A TEMA K-shell is chosen for a kettle reboiler, and a type B head is chosen since the tube-side fluid
(steam) is clean. Thus, a BKU configuration is specified.
(iv) Tube layout
A square layout with a tube pitch of 1.25 in. is specified to permit mechanical cleaning of the
external tube surfaces. Although this service should be quite clean, contaminants in distillation feed
streams tend to concentrate in the bottoms, and kettle reboilers are very prone to fouling.
(v) Baffles and sealing strips
None are specified for a kettle reboiler. Support plates will be used to provide tube support and
vibration suppression. Four plates are specified to give an unsupported tube length that is safely
below the maximum of 73 in.
(vi) Construction materials
Since neither stream is corrosive, plain carbon steel is specified for all components.
Steps Remarks Results
operating pressure Assumed to be the bottom P=850KPa
stream pressure
bubble point temperature z i=x i ; ∑ K i X i =1 T= 103.11 C
heat load q=c p m ∆T 8256177 KJ/h
Maximum heat load q max =1.1q 9.081.794,7 KJ/h
Heat transfer area qmax
Aext =
U ass ∆ T m
Where, 60 m2
(T s−T i)
∆ T m=
(T −T i )
ln s
(T s−T b )
Assumptions for tube Tube internal diameter:
t ID =¿0.01905 m
Tube outer diameter:
t OD=0.0254 m
Tube length:
Lt =¿4.8768 m
Bundle length:
Lb=¿
Number of tubes A ext 172
Nt=
t OD π Lt
Assumptions for tube Tube counts for 0.0254 m.
arrangements
OD tubes on 0.381 m.
Square Pitch
Heat flux
Initial heat flux qmax 11460.02 KJ/h
q c=
Aext
Actual heat flux Monstinki’s equation 14042.79 KJ/h
Overall heat transfer 1734.95 W/m2C
coefficient
Check Overall heat transfer 1873.74 W/m2C
coefficient
Maximum allowable heat 268437.86 KJ/h
flux
Check maximum allowable 268437.86 KJ/h
heat flux
Shell diameter and freeboard level
1
Bundle diameter N t 2.207 0.5334 m
D b =t OD ( )
K1
Shell diameter Db 1.1 m
0,6
Freeboard L 0.0381 m
N n=
5 Db
Validation of vapour velocity
Surface area of liquid, Als Db
Als =L Liquid 97764,52 Kg/h*m2
2
Vapour velocity at surface mass flow 1 1
V vs =
3600 ρ v A ls 3,50E-06 m/s
Maximum allowable velocity ρl−ρ v 9,906 m/s
V max =
ρv
Tube length A ext L=3.6576 m
L=
π t OD N U −tube
Shell length, weir length and the distance between tube bundle and Weir
Shell length volumetric flow rate Ls =2,4 m
sector area below weir
Height of tube bundle According bibliography (1) 0.5398 m
Weir height Sector Height=Weir Height W h =0.5842 m
Sources:
[1] Serth R., Lestina T. “PROCESS HEAT TRANSFER PRINCIPLES,
APPLICATIONS AND RULES OF THUMB” Elsevier. Pag: 361-394.
Sizing/ specification of peripherals
2. Operational design:
Control design
Control system objective
Description and Justification
Operating procedures
Start-up procedures
Shutdown procedures
HAZID study
3. Mechanical design
Material construction
Pressure vessel design
Pressure vessel calculations
Design pressure
Maximum allowable stress
Wall thickness
Shell outer diameter
Ratio of outer diameter to internal diameter
Ratio of corrosion allowance to internal diameter
Check wall thickness
Pressure Relief valve
Block outlet case
External fire case
Discharge area
Selection of relief valve
Mechanical drawing
4. Summary and critical review
5. Equipment Data sheet
