Distillation Column (T-101)Design Criteria:Purpose of distillation column is to separate naphtha from the feed mixture of green diesel and naphtha. As a result, high purity of naphtha can be obtained at the top of the distillation column, whereas green diesel is recovered in as bottom product.

Design Basis:Feed stream into the distillate column T101 consists of a mixture of naphtha and green diesel. The total mass flow rate of feed is 6993.27kg/hr at 230°C and 10 Bar. Distillate is carried out from the top of the column operating at 233°C and 10 Bar, whereas the bottom of column operating at 422°C and 10 Bar.

Type of Column and Materials of Construction:Tray column is usually preferred for initial installations, particularly in this system with

large liquid flow rate. In addition, tray column is used for large column diameter, normally 3ft or more. As for plate contactor, sieve tray will be utilized since it is the most versatile contactor. Furthermore, sieve tray is the least expensive with lowest pressure drop per tray as compared to valve tray and bubble cap tray.

Conventional materials of construction for distillation column are carbon steel, stainless steel of different grades, such as grade 303, 304, 316 and 321. Generally, carbon steel is suitable for noncorrosive environment whereas has better corrosion resistance. Stainless steel is a group of iron-based metal containing at least 10% chromium, nickel, manganese, copper and molybdenum as alloying elements. Since the column is operated at high temperature, and carbon steel will eventually become brittle at high temperature, hence Stainless Steel 304 is chosen to design distillation column.

Design Method:Fenske-Underwood-Gilliland procedure is followed to estimate the number of equilibrium stages. The procedure includes the calculation of minimum reflux ratio, operating reflux ratio and minimum number of equilibrium stages. Actual number of stages and location of feed stage are then obtained. The height and diameter of the distillation column are then calculated with reference from Max S. Peters, Klaus D. Timmerhaus, Ronald E. West, 2003. “Plant Design and Economics for Chemical Engineers”, 5th Edition, McGraw Hill. The design specification of sieve tray is performed with reference from R. K. Sinnott, 1999. “Coulson and Richardson’s Chemical Engineering”, Volume 6, 3rd Edition, Chemical Engineering Design.

1) Determination of Distribution of Light Key and Heavy Key ComponentsDesign Parameters:

i) Average Geometric Relative Volatility, (αLK / HK )av

ii) Minimum Reflux Ratio, Rmin

iii) Operating Reflux Ratio, Riv) Minimum Number of Equilibrium Stages, Nmin

v) Tray Efficiency, Eo

vi) Number of Equilibrium Stages, Neq

vii) Actual Number of Stages, Nact

viii) Location of Feed Stage, NF

2) Determination of Actual Number of Trays, Column Height and DiameterDesign Parameters:

i) Actual Number of Trays, Nii) Tray Spacing, HS

iii) Column Height, HC

iv) Net Vapor Velocity at Flood Condition, Vnf

v) Net Column Area, An

vi) Downcomer Area, Ad

vii) Column Cross-sectional Area, AC

viii) Column Diameter, DC

3) Design of Sieve TrayDesign Parameters:

i) Active Area for Single Pass Plate, Aact

ii) Total Area of All Active Holes, Ah,total

iii) Tray Thicknessiv) Hole Size or Diameterv) Hole Pitch, lp

vi) Area of One Active Hole, Ah

vii) Number of Holes per Trayviii) Weir Height, hw

ix) Weir Liquid Crest, how

x) Weir Length, lw

xi) Vapor Velocity through Holes, uh

xii) Orifice Coefficient, Co

xiii) Fractional Entrainment, ψxiv) Plate Pressure Drop, ΔPT

xv) Column Pressure Drop, ΔPC

Design Calculation:

Product Purity Specifications ~ Distillate and Bottom Composition 99.9% recovery of naphtha to distillate 99.99% recovery of green diesel to bottom

For distillation column, we assumed the feed condition as 230 °C, 10 bar. At this condition, both naphtha (light key component) and green diesel (heavy key component) are in homogeneous liquid mixture. For this condition, we let the recovery of light key and heavy key component as

ξ LK=0 . 999ξ HK=0 . 0001

Hence, the following tables for feed, distillate and bottom product are constructed.

StreamStream

no.

Naphtha Green Diesel Total

m¿

(kg /hr ) Mass fraction, x

Mole fraction, y m

¿

(kg /hr ) Mass fraction, x

Mole fraction, y m

¿

(kg /hr ) Mass fraction, x

Mole fraction, y

Feed 39 170.57 0.024 0.047 6822.7 0.976 0.953 6993.27 1 1Distillate 47 170.40 0.996 0.998 0.68 0.004 0.002 171.08 1 1

Bottom Product 48 0.17 3E-05 5E-05 6822.02 0.99997 0.99995 6822.19 1 1

i. Dew Point and Bubble PointBy using Antoine Equation, the vapor pressure of particular component is determined at corresponding temperature. The Antoine Equation is stated as

log10 p=A+ BT

+C log10 T+DT +ET 2

Where, p = vapor pressure (mm Hg)A, B, C, D and E = regression coefficients for chemical compoundT = temperature (K)

The constants for naphtha (n-C8H18) and green diesel (cetane) are tabulated as below:Components A B C D ENaphtha (n-C8H18) 29.0948 -3.01E+03 -7.2653 -2.27E-11 1.47E-06Green diesel (cetane) 99.1091 -7.53E+03 -32.251 0.010453 1.23E-12

Applying the relation between Raoult’s Law and Dalton’s Law

K i=Pi

sat

PT

and Rachford Rice expressions for determination of dew point and bubble point of a liquid mixture,

Dew point: ∑i

y i

K i

=1 yi = mole fraction in distillate

Bubble point: ∑i

K i x i=1 xi = mole fraction in bottom product

the bubble point and dew point of both distillate and bottom product can be computed, hence estimate the temperature of overhead product and bottom product. Meanwhile, the relative volatility can be estimated by

α LK / HK=PLK

sat

PHKsat

For distillate,

Bubble / Dew point Temperature (K)Pi

sat (bar ) K i α LK /HKNaphtha Green Diesel Naphtha Green Diesel

Dew point determination 506.21 9.98 0.27 0.998 0.027 37.40Bubble point determination 506.44 10.02 0.27 1.002 0.027 37.30

Thus, the temperature of Distillate = 506 K (MUST lower than bubble point of distillate)Overhead vapor = 507 K (MUST greater than dew point of distillate)

For bottom product,

Bubble / Dew point Temperature (K)Pi

sat (bar ) K i α LK /HKNaphtha Green Diesel Naphtha Green Diesel

Dew point determination 694.54 88.36 9.9998 8.84 0.99998 8.84Bubble point determination 694.51 88.33 9.996 8.83 0.9996 8.84

Thus, the temperature of Bottom product = 694 K (MUST lower than bubble point of distillate)Reboiled vapor = 695 K (MUST greater than dew point of distillate)

The dew point and bubble point of overhead product and bottom product can be summarized asDistillate Bottom Product

Dew point (K) 506.21 694.54Bubble Point (K) 506.44 694.51

By considering the dew point of distillate and bubble point of bottom product,Temperature (K) PLK (mmHg) PHK (mmHg) α LK /HK

Distillate 506.21 7486.60 200.16 37.40Bottom Product 694.51 66256.37 7497.43 8.84

Hence, (α LK /HK )ave=√ (α LK / HK )D⋅(α LK / HK )B=18. 18

ii. Minimum Number of Trays

Nmin=

ln [( x D, LK

x D, HK)( x B , HK

x B , LK)]

ln (αLK /HK )ave

=

ln [ ξ LK (1−ξHK )ξHK (1−ξLK ) ]

ln (αLK /HK )ave

From previous assumption, ξ LK=0 . 999 ξ HK=0 .0001

∴N min=5 .56 stages

iii. Reflux Ratio, RSince the gap between the dew point and bubble point of distillate and bottom product is large, therefore average temperature between dew point of distillate and bubble point of bottom product is used instead.

T ave=600 . 36 K

At Tave, the corresponding saturation pressure and relative volatility of naphtha and green diesel are determined.

Component Psat (mmHg) α i=Pi

sat

PHKsat

Mole fraction,xF ,i

Mole fraction,xD ,i

Naphtha 2.64E+04 15.55 0.047 0.998Green diesel 1.70E+03 1 0.953 0.002

In order to determine the minimum reflux ratio, the value of θ in equation below is to be determined by trial and error.

∑i=1

n αi xF, i

α i−ϴ=1−q

At feed condition (230 °C, 10 bar), the feed is exist as saturated liquid. Hence, q=1.αLK xF , LK

αLK−θ+

αHK x F , HK

αHK−θ=0

∴θ=9 . 218By using the value of θ, minimum reflux ratio (Rmin) can be determined by equation

Rmin+1=∑i

αi x D , i

αi−θ →Rmin=1. 45

By rule of thumb, R=1.2 Rmin ∴R=1. 74

Hence, we approximate the reflux ratio, R as 2.

iv. Tray EfficiencyThe efficiency of tray column could be determined by

E0=0. 492

[ (αLK /HK )aveμF ]0. 245

where Viscosity of feed mixture, μF can be estimated by using Kern’s equation

1μF

=∑x i

μi with xi = mass fraction of individual component

Component

Mass flow (kg/hr)

Mass fraction

Viscosity (mNs/m2)

x/μ

Naphtha 170.57 0.024 0.07501 0.3252GD 6822.7 0.976 0.2315 4.2143

∴μm=0.2203

Previously,(α LK /HK )ave=18.18

E0=0 . 35

v. No. of Equilibrium StageBy using Gilliland Correlation,

N−N min

N+1=0. 75(1−

R−Rmin

R+1 )0.566

Since Nmin = 5.56; Rmin = 1.45; R = 2

No . of equilibrium stage , N eq∨N=11.21

Actual no . of trays , N act=NE0

=32.003=33 trays

No . of trays , N tray=Nact−1=32 trays

vi. Feed Point LocationApplying Kirkbride Equation, the location of feed point calculated from bottom or top of trays can be determined.

LogN D

N B

=0. 206 log { BD ( x HK

x LK)F [ (xLK )B

(x HK )D ]2

}From previous calculation,B = 6822.7 kg/hr xHK,F = 0.976 xHK,D = 0.004D = 170.57 kg/hr xLK,F = 0.024 xLK,B = 3E-05

Meanwhile, N D+NB=Nact

By using the two relations,N B=21 stages N D=11 stages

Hence, the feed is entered at 21st stages calculated from the bottom of column.

vii. Height of ColumnSince tray spacing of 0.3 – 0.6m are normally employed in industry, henceTray spacing, Hs = 24 in = 0.61 m

Column height is calculated with tray spacing and the additional space for vapor-liquid disengagement at column top and for liquid sump at column bottom. An approximation of 15% allowance for the additional space for phase disengagement and required internal hardware.

Column Height , H c=1.15 N t ray H s=22.45 m

viii. Diameter of ColumnTo determine the diameter of a column, the surface tension (σ) of liquid-vapor interaction is prerequisite. According to [Ref 1], Sugden (1924) had developed a method to estimate the surface tension of pure component as well as mixture of components.

For pure component:σ=[ Pch (ρL− ρv )

M ]4

×10−12

where σ = surface tension (mJ/m2)Pch = Sudgen’s parachor (Refer Table 8.7)ρL = Liquid density (kg/m3)ρv = Density of saturated vapor (kg/m3)M = molecular mass

For mixture of liquid: σ m=σ1 x1+σ2 x2+. ..

Where x1, x2 = component mole fractions

To determine the density of vapor at particular pressure, the ideal gas behavior can be assumed for pure component and non-ideality for mixture to account for the molecular interaction of individual component.

For pure component:ρv=

PMRT

For mixture:ρv , m=

Pr' M r , mix

zRT r'

wherePr

'

= Pseudoreduced pressure =

P

Pc'

Mr,mix = Molecular weight of mixture

T r'

= Pseudoreduced temperature =

T

Tc'

z = Compressibility factorP = Pressure of system

Pc' = Preudocritical pressure = y A PcA+ y B PcB+.. .

T c' = Pseudocritical temperature = y A T cA+ yB TcB+. ..

yA, yB = component mole fractionPcA, PcB = component critical pressureTcA, TcB = component critical temperature

Therefore the following table is constructed for purpose of calculation.Physical properties of pure component in distillate and bottom product:

Pure components Naphtha GD

ρv (kg/m3)Distillate 27.04 53.62Bottom 19.73 39.11

ρL (kg/m3)Distillate 490.1 616.5Bottom 282.7 380.4

Pch 346.2 658.2

σ (mJ/m2)Distillate 3.91 7.22

Bottom 0.407 0.976Mole

fractionDistillate 0.998 0.002Bottom 5E-05 0.99995

Pc (bar) 24.86 14.19Tc (K) 568.83 720.6

For mixture in distillate and bottom product:

PropertiesMixture

Distillate Bottom

Pc' 24.84 14.19Pr' 0.403 0.705Tc' 569.14 720.59Tr' 0.891 0.964z 0.798 0.645

Take note: z is obtained by interpolation from Figure 5.4-4 based on the value of P r’ and Tr’ in [Ref 3].

For mixture in both liquid and vapor in overhead and bottom product, the methods used to estimate the physical properties (ρv, ρL and Mr) are stated as below:-

Molecular weight, Mr:

1M r

=x A

M A

+xB

M B

+.. .

where xA, xB = component mass fractionMA, MB = component molecular weight

Liquid density, ρL:

1ρL

=x A

ρA

+xB

ρB

+.. .

On top of that, the mass balances for distillation column after considering reflux are as below:

StreamStream

No.Mass flow

(kg/hr)T(K)

Mass fractionNaphtha GD

Feed 39 6993.27 503 0.0244 0.9756Overhead 41 513.25 507 0.996 0.004Distillate 47 171.08 506 0.996 0.004Reflux 42 342.16 506 0.996 0.004

Reboiled 43 513.25 695 0.996 0.004Bottom 44 6822.19 694 2.5E-05 0.999975

Take note: m42=R × m47 ; m41=m42+m47 ; m43=m41

Hence, the following table is generated.

Mixture Overhead Bottomρv (kg/m3) 33.96 60.64ρL (kg/m3) 490.50 380.40σ (J/m2) 0.00392 0.000976

L (kmol/hr) 2.996 34.68V (kmol/hr) 4.493 4.493

Mr 114.23 225.99

In order to find out diameter of column based on both top and bottom section, the methods of approach are sequenced as below:

→ Determine

FLV=( LV )( ρV

ρL)0 .5

→ Based on the value of FLV and tray spacing, Hs of 0.61 m, determine the value of Csb

from Figure 14.4 in [Ref 2].→ Using the value of Csb and physical properties above to compute the net vapor

velocity at flooding condition,

V nf =C sb( σ20 )

0.2( ρL−ρV

ρV)0 .5

→ Assume 80% flooding, compute actual vapor velocity by V n=0 . 8 V nf

→ Next, find out the volumetric flowrate of vapor by

V=V (kmol /hr )×M r (kg /kmol )

ρv( kg /m3 )×3600 s

hr

→ The net column area, An=

VV n

→ Assume 12% of total downcomer area, Column cross-sectional area, AC=

An

1−0. 12

→ Downcomer area, Ad=AC−An

→ Diameter of column, DC=( 4 AC

π )0. 5

Therefore, the following table is generated

Basis Top Section Bottom SectionFLV 0.1754 3.0816Csb (m/s) 0.09144 0.01219Vnf (m/s) 0.06079 0.003844Assume 80% flooding,Vn (m/s) 0.04863 0.003075V (m3/ s) 0.004198 0.004652An (m2) 0.08634 1.5126Assume 12% total downcomer areaAc (m2) 0.09811 1.7188Ad (m2) 0.01177 0.2063Dc (m) 0.35 1.48

There are two limitations on the design conditions of distillation column, which are the column height and height-to-diameter ratio. The general guidelines are column height, HC <

54 m and height-to-diameter ratio,

HC

DC

<30 (James M. Douglas, 1988. “Conceptual

Design of Chemical Processes”, McGraw Hill, pg 457)

By considering the diameter of column bottom, H c

Dc

=22 . 451. 48

=15 .17

Since Hc : Dc < 30 for our column at this condition, hence the design conditions are acceptable.

ix. Plate DesignConsider the preliminary specification of column T-101 on basis of bottom section,Dc = 1.48 mAc = 1.7188 m2

An = 1.5126 m2

Ad = 0.2063 m2

→ Active area of single plate

Aact=AC−2 Ad=1. 3063 m2

→ Total area of all active holesAssume all active holes take 10% of active area respectively,

Ah , total=0 .1×Aact=0 .1306 m2

→Tray thickness

Stainless steel 304 is employed as material of construction due to high thermal stability.

Plate thickness = 3 mm (typical value for stainless steel)

→Weir length

When

Ad

Ac

=0 .12

,

lw

Dc

=0 .7386

(Interpolated from Figure 11.31 in[Ref 1])

Weir length, lw = 1.093 m

→Hole size

For stainless steel, minimum hole size that can be punched is twice the plate thickness.

Furthermore, due to handling of heavy hydrocarbons in the column, large-sized hole

will not susceptible to fouling.

Hole size or diameter = 6 mm

→Hole pitch, lp

The normal range of hole pitch-to-diameter ratio will be 2.5 to 4. Taking average value of the range, assume hole pitch is 3.25 times of hole diameter.

lp=3 . 25×hole size=0. 0195 m

→Area of one active hole, Ah

Ah=π ( Dh

2 )2

=2.827×10−5 m2

→Number of holes per unit tray

Number of Holes per Tray=Ah , total

Ah

=4620 holes

→ Weir Height, hw

For column operating above atmospheric pressure,weir height of 40 to 50 mm is

recommended. Thus, assume weir height equals 50 mm. hw=0 .0500 m

x. Plate Pressure Drop

At 70% turndown,

Maximum vapor flowrate,

V B=0 .004652m3 /s

Maximum vapor velocity through holes,

u h=V B

Ah , total

=0 .03561m / s

From Figure 11.34 (Ref 1),

When Plate thicknessHole diameter

=0.5∧%Ah, total

Aact

=10 ,

Orifice coefficient, C0=0 .7315

hdry=51[ uh

Co]2

( ρV

ρL)B

=0 . 008367 mm liquid

From Figure 11.29 [Ref 1], for FLV,Top = 0.1754 and 80% flooding, ψ = 0.28

hdry , corrected=hdry(1+ ψ1−ψ )=0 . 01162

mm liquid

Weir liquid crest,

how=750[ Lbottom( kmolhr )×M r ,bottom( kg

kmol )× hr3600 s

ρL,bottom lw]2

3

=22 .62 mm liquid

Residual head,

hr=12500ρL,bottom

=32 .86 mm liquid

Total plate pressure drop,

hT=hdry ( corrected )+(hw+how )+hr=105 .49 mm liquid

Total column pressure drop,

ΔPT=ρL,bottom ghT

1000=393 . 67 Pa=0 .003937 bar

Column pressure drop,

ΔPC=N×ΔPT=0 .1260 bar

Mechanical Design

i. Design Pressure

The operating pressure of the column is 10 bar. However since there is quite a lot of number of plates, there is significant pressure drop. It is predicted that pressure at bottom of the column will be higher. Therefore, an extra 10% of pressure will be considered in mechanical design.Design Pressure, Pi = 11 bar

ii. Design Temperature

The feed is entered at 230 °C. However, the maximum temperature is observed at the bottom

of the column, i.e. 422 °C. As we are using Stainless Steel 304 as the material of

construction, and SS304 can withstand temperature up to 600 °C, thus the design temperature

we will consider will be the nearest upper temperature limit, i.e. 500 °C.

Design Temperature = 500 °C

iii. Material of Construction and Corrosion Allowance

As justified earlier, SS304 is chosen as the material of construction.

At 500 °C,

Design stress, f = 90 N/mm2

Since the process fluid is absent in corrosive material, thus severe corrosion will be expected

to absent. Therefore

Corrosion allowance = 2 mm

iv. Welded Joint Factor

The typical joint efficiency, J = 0.85

v. Wall Thickness

Cylindrical Section

Internal diameter, Di or Dc = 1.48 m

Minimumwall thickness , tmin=DesignPressure × Di

(2× DesignStress × J )−D esign Pressure¿10.72mmConsider corrosion allowance of 2mm, Effective thickness = tmin + Corrosion allowance = 12.72 mmTherefore, for fabrication purpose, Wall thickness = 13 mm

Head and ClosuresFlat heads are inefficient, thus dome heads are employed. Since the design pressure is less than the upper pressure limit (15 bar) of torispherical head, so torispherical head is employed.

As crown radius (Rc) must not greater than internal diameter of column, so we will consider Crown radius, Rc = 1.2 mLet the ratio of Knuckle radius (Rk) : Rc = 0.06Ratio smaller than 0.06 will lead to buckling.

Stress concentration factor, C s=0 .25 (3+√ Rc

Rk)=1. 77

Thickness, e=

Pi RcC s

2Jf +Pi (C s−0 . 2 )=15 .11 mm

Since the thickness of head is comparable with wall thickness of cylindrical section, thus torispherical head is suitable as the closure head at this operating condition.

A much thicker wall will be needed at the column base to withstand the wind and dead weight loads. Thus, we divide the column into 5 sections with each section increases 2mm in thickness one after another. The first section is counted from top of column.Hence,

Section 1 15 mmSection 2 17 mmSection 3 19 mmSection 4 21 mmSection 5 23 mm

Average thickness: 19 mm

vi. Stress AnalysisPreliminary specifications:

Design stress, f 90 N/mm2

Density of material (SS304), ρm 8000 kg/m3

Design Pressure, Pi 11 barCorrosion allowance 2 mmInner column diameter, Di 1.48 mHeight of column, Hc 22.5 mJoint factor, J 0.85No. of trays, Ntray 32Tray spacing, Hs 0.61 mMax wind velocity, uw 1280 N/m2

Insulation, tI 75 mmInsulation (wool) density, ρI 130 kg/m3

Dead Weight of VesselFor vessel,Mean diameter, Dm = Di +Average thickness = 1.499 m

Shell weight, W v=Cv πρm Dm g (H v+0 .8 Dm ) t×10−3

where Cv = 1.15 for distillation columnHv = height of column (22.5 m)t = average wall thickness (19 mm)ρm = density of vessel material (SS304)Dm = mean diameter of vessel

Hence, Shell weight, Wv = 191.38 kN

For plates,

Plate area= π4

Di2=1.72 m2

Total weight of plate , W p=ρm g ( Plate area × Plate thickness ) × N tray=12.96 kN

For insulation layer,

Volumeof insulation ,V I=π Di t I H c=7.846 m3

Weight of insulation=ρ I V I g=10006 N

The weight of insulation is doubled to account for fittings,Total weight of insulation, WI = 2 ρI V I g=20.01 kN

Total dead weight , W Total=W v+W p+W I=224.35 kN

Wind LoadingTake dynamic wind pressure as 1280 N/m2.

Mean diameter of vessel (including insulation), Dm' =Di+2 (twall , ave+t I )=1.668 m

Loading per unit length , Fw=uw

Dm' =2135.04 N /m

Bendingmoment , M x=Fw

2× H c

2=540432 N /m

Analysis of Stress

Pressure stress:

Longitudinal stress , σ h=Pi D i

2twall ,ave

=42.84 N /mm2

Circumferential stress , σL=Pi Di

4 twall , ave

=21.42 N /mm2

Stress due to dead weight: σ w=

W total

π ( Di+twall ,ave ) twall ,ave

=2.507 N /mm2

Since the vessel is above the support, so stress is applied from top of support, thus it is comprehensive (-ve).

Bending stress:

Outer diameter, Do = Di + 2twall,ave = 1518 mm

Second moment of vessel area , I v=π

64(D o

4−Di4 )

¿25135536116 mm4

Bending stress ,σ b=±M x

I v( Di

2+ twall , ave)=16.32 N /mm2

Resultant stress: Resultant longitudinal stress , σ z=σ L+σw ± σb

Since σw is comprehensive, thus it is less than zero.

σ z (upwind )=σ L−σ w+σb=35.23 N /mm2

σ z (downwind )=σ L−σ w−σ b=2.59 N /mm2

The greatest difference between the principal stresses will be on the down-wind side.Stressdiffrence=σh−σ z ( downwind )=40.25 N /mm2

vii. Elastic Stability

Critical buckling stress , σc=20000twall , ave

Do

=250.33 N /mm2

Maximum compressive stress occurs when vessel is not under pressure. Hence,

Maximum compressive stress=σw+σb=18.83 N /mm2Since the maximum compressive stress is well below the critical buckling stress, so the material of construction suits well with the operating condition.

viii. Vessel SupportConnical Skirt will be employed due to greater gravitational stability.AssumeSkirt diameter, ds = 5 mSkirt height, hs = 3 m

tanθ s=ds

0.5 (d s−Di )∴θ s=70.61 °

For Stainless Steel 304 at 500 °C,Design stress = 90 N/mm2

Young’s Modulus, E = 2 ×105 N/mm2

Maximum dead weight load occur when vessel is fully filled with water,

Approximate weight= π4

Di2 H c ρw g=379.72 kN

Previously, Vessel weight = 224.35 kNTotal weight = Approximate weight + Vessel weight = 604.07 kNWind loading, Fw = 2.135 kN/mBending moment at base of skirt

¿ 12

Fw ( H c+Skirt height )2=694.15 kN /m

Consider skirt thickness = Average thickness of vessel = 19 mm

Bending stress∈skirt , σbs=4 × Bendingmoment at base of skirt

π Di twall , ave ( Di+twall ,ave )¿20.97 N /mm2

Dead weight stress∈skirt , σ ws ( test )= Totalweightπ tw all ,ave ( Di+twall, ave )

=6.75 N /mm2

Dead weight stress∈skirt , σ ws (operating )= Vessel weightπ twall ,ave ( Di+ twall, ave )

¿2.51 N /mm2

Maximum compressive stress , σ s ,c=σbs+σws (test )=27.72 N /mm2

Maximum tensile stress , σ s ,t=σ bs−σws ( operating )=18.46 N /mm2

For joint factor = 0.85Criteria for design:

σ s ,t=J f i sin θs=72.16 N /mm2

σ s ,c=0.125 E ( twall , ave

Di)sin θ s=302.74 N /mm2

Since both the maximum tensile (σ s ,t) and compressive (σ s ,c) stress are below the design criteria, thus the design is satisfied.Hence, design thickness = Average thickness, twall,ave + Corrosion allowance = 21mm

ix. Base Ring And Anchor BoltsLet approximate pitch diameter = 5.5mCircumference of bolt circle = π × pitch diameter=17278.76 mmSince the pitch must not less than 600 mm, henceNumber of bolts required, at minimum recommended bolt spacing

¿ Circumference600

=28.8

∴Closest multiple of 4=32 bolts

From above calculations and assumptions,Bolt design stress = 90 N/mm2

Bending moment, Ms = 694.15 kNmW eight at operating value, Wopt = 224.35 kN

Bolt area , Ab=1

Nbolts f i[ 4 M s

pitch diameter−Vesselweight ]=97.39 mm2

Bolt root diameter=√ 4 Ab

π=11.14 mm

Total compressive on basering per unit length , Fb=4 M s

π Di

+W opt

π Di

=451752.13 N /m

Consider the nearest average bearing pressure ranged 3.5 – 7 N/mm2 = 5 N/mm2

Minimumwidth of base ring, Lb=Fb

Averagebearing pressure=90.35 mm

We will use M24 bolts whose root area = 353 mm2

From Figure 13.30 [Ref 1], for M24 bolts, Lr = 76 mm

Actual widthrequired=Lr+Designthicknness+50=147 mm2

Actual bearing pressure at concrete foundation , f c' =

Fb

Actual width

¿3.073 N /mm2

Minimumthickness , tb=Actual width×√ 3 f c'

f r

The typical allowable design stress in ring material, fr = 140 N/mm2

Hence, t b=19.50 20 mm

x. NozzlesFor feed, Mass flow rate of fluid, W = 6993.27 kg/hr

Density of feed, ρf can be computed by

1ρf

=∑ x i

ρi

∴ ρf =769.79 kg /m3

For feed opening,

Dopt=8 . 41W 0. 45

ρf0 .31

=57 . 56 mm=2. 27 in

xi. ReinforcementReinforcement area, Ar=( Dopt+2×Corrosion allowance ) × Designthickness

∴ A r=85.87 mm2

Based on the method used to calculate Dopt and Ar above, it used to calculate other openings within the distillation column which are the feed, overhead vapor, reflux, bottom product and reboiled vapor. Hence, the following table is constructed:

Stream W (kg/hr) ρ (kg/m3) Dopt (mm) D (in) Ar (mm2)Feed inlet 6993.27 769.79 57.56 2.27 85.87Top outlet 513.25 33.96 46.76 1.84 85.52

Reflux 342.16 490.50 17.03 0.67 84.55Bottom 7335.43 371.45 73.72 2.90 86.40

Reboiled 513.25 60.64 39.07 1.54 85.27

Distillation ColumnIdentification: Item: Distillation column Date: 23/10/2010

Item no.: T-102 By: Teng Wai LunNo. required:

1

Function: To separate naphtha and green diesel from their liquid mixtureOperation: Continuous

Operating DataMaterials Handled: Feed Distillate BottomsQuantity (kg/hr) 6993.27 171.08 6822.19Composition (kg/hr)Naphtha 170.57 170.40 0.17Green Diesel 6822.70 0.68 6822.02

Temperature (°C) 230 233 421Design Data:No. of trays: 32 Reflux ratio: 2Feed stage (from bottom): 21 Tray Spacing (m): 0.61

Pressure (bar): 10Material of construction (MOC):

Stainless steel 304

Functional height: 22.5Liquid density (kg/m3): 769.79Vapor density (kg.m3) 60.64Maximum vapor flowrate (m3/s) 0.0047Recommended inside diameter (m): 1.48Utility: Low pressure superheated stem (LPSS), molten salt (High-Tech molten salt)

Plate SpecificationPlate I.D. (m): 1.48 Plate material: Stainless Steel 304Hole size (mm): 6 Turndown (%): 70Hole pitch (mm): 19.5 Plate thickness (mm): 3Active holes: 4620 Plate pressure drop (mm liquid): 105.49

Mechanical Design DataOutside diameter (m): 1.518 Feed inlet connection (mm): 58Design Pressure (bar): 11 Vapor discharge outlet connection (mm): 47Wall thickness (mm): 13 Reflux inlet connection (mm): 17Type of Ends: Torispherical Reboiled vapor inlet connection (mm): 39End thickness (mm): 16 Liquid bottoms outlet connection (mm): 74Vessel support: Conical skirtInsulation: Mineral woolInsulation thickness (mm): 75Radiograph (%): 85Corrosion allowance (mm): 2

References1. SINNOTT, R. K. 2003. Coulson & Richardson's Chemical Engineering, Butterworth-

Heinemann.2. SEIDER, W. D., SEADER, J. D. & LEWIN, D. R. Product and Process Design Principles:

Synthesis, Analysis and Evaluation, John Wiley and Sons, Inc.3. FELDER, R. M. & ROUSSEAU, R. W. Elementary Principles of Chemical Processes, John

Wiley & Sons, Inc.