EG REFINER DESIGN

Bottom product from Light end column contains Monoethylene glycol and higher glycols DEG and TEG and also a negligible amount of water .MEG is separated from higher glycols and impurities. For polyester grade MEG 99.9% pure MEG is required. For this purpose we selected tray column. Selection criteria has been discussed with light end column

NUMBER OF PLATES

Fenske equation

=6.71 plates with reboiler

q =1+Cp_L*(T_b-T_f) / λ=1+0.44*(157-95) / 214.77= 1.157        

By hit and Trial      Θ = 1.0675          Rm = 0.2538

R = 1.2xRm       R = 0.3046       N= 20

ED PLATE LOCATION

By, using kirkbridge Equation

N_B= 5

So feed is entering at 5th plate from bottom.

 

Column efficiency

using O’connell method

Molar avg. liquid viscosity  =0.3899mNs/m²                                                                                                                                                                                                                                                                             Average relative volatility of the light key =5.179

So, Actual no. of plates = 20 / 0.42 = 47 plates

N_B=5 / 0.42=    12

N_D=15 / 0 .42=35

Maximum liquid flow rate in rectifying section = L_n = D R_m= 0.304598x0.113196

                                                                        = 0.0345479kmole/sec

Maximum vapor flow rate in rectifying section = V_n  = L_n + D

                                                                              = 0.0345479+0.1131962                         

                                                                         = 0.147744 kmole/sec

Maximum liquid flow rate in stripping section = L_m = Ln+qF

0.034479+(1.157)(0.1254)=0.17958 kmole/sec

 Maximum vapor flow rate in stripping section = V_m = L_m – W

= 0.17958 - 0.012216=0.167364 kmole/sec

COLUMN DIAMETER

The plate diameter is calculated based on the flooding considerations

F_LG  = L_m / V_m {r g/ r l}^0.5

Now for,F_LG = 0.17958 /0.167364  { 0.6414/ 944.23}^0.5    = 0.028

and for a tray spacing of Ts=500 mm.

Csb=0.0105+(8.127/10000)*(Ts^^0.755)*EXP(-1.463*F_LG^^0.842)

FLOODING PARAMETER

Csb, flood = 0.093m/s.

Now,        (V/ 20) ^ Unf = Csb, flood × (σ^0..2 [(r l - r g) / r g] ^0.5                    

where       

Unf = gas velocity through the net area at flood, m/s  

Csb, flood = capacity parameter, m/s

                   = liquid surface tension, mN/m σ

                   r l = liquid density, kg/m3

Unf = Csb, flood × (σ / 20) ^^0..2 [(r l - r g) / r g] ^0.5                    

 Unf=0.093×(27.714)^0.2[(944.23 - 0.64159)/0.64159] ^0.5 

      = 3.886m/sec                                                                               

Let  Actual velocity, Un= 0.8×Unf  i.e., Un = 3.11 m/s

Net area available for gas flow (An)

Net area = (Column cross sectional area) - (Down comer area.)                                                                    

An = Ac – Ad     An = (0.1674*105.62 / (0.64159))/3.11  = 8.86 m2

Let    Ad = 15 % of the Ac (cross sectional area)

Ac=  An / 0.85   Ac = 8.86/0.85    Ac = 10.42m²

DIAMETER OF THE COLUMN                                     

D = {(4 xAc/p)}^0.5 = {(4 x 10.42x7/22)}^0.5= 3.64 m

Maximum volumetric flow rate = L_m / ℓ

Top=    0.17958 × 105.62 / (944.23)   =           0.02m³/sec 

Our required flow pattern is single pass

PROVISIONAL PLATE DESIGN

Column diameter  (base)  =  3.64m 

Column Area A_c                          A_c= 10.42m²

Down comer area A_d                 =1.563m²

Net area A_n                                        =         A_c – A_d  =       8.857m²

Active area A_a              =         A_c – 2A_d  =     7.294 m²

Hole area A_h take 10% A_a as first trial    =   0.7294 m²

WEIR LENGTH

A_d / A_c = 1.563 / 10.42 = 0.15     L_w / d_c  = 0.81         L_w =2.95 m

Take weir height , h_w                 = 40 mm

Hole diameter, d_h                      = 5mm

Plate thickness             =5mm                                                                              

CHECK WEEPING                 

Maximum liquid rate                 = 0.17958 × 105.62   

                                                =  18.98 kg/sec

Minimum liquid rate at 70% turn down       = 13.28kg/sec

h_ow                   = weir crust       Maximum = 38.7 mm liquid

Minimum  = 30.5 mm liquid at minimum h_w + h_ow = 40+30.5= 75.5 mm liquid

K₂ = 30.7

= 15.36m/s

Actual minimum vapour velocity                                

                                                                                                                      =26.29m/s         So minimum vapor rate will be well above the weep point.

 

Plate Pressure Drop

Dry Plate Drop

Max. Vapour velocity through holes

 = Volumetric Flow Rate / Hole Area     =37.56 m/s 

For plate thickness/hole dia =  5/5 = 1    and 

l_o = 0.84

                                                                  = 69.67mm liquid  

Residual Head

 mm liquid

TOTAL PRESSURE DROP

h_t = h_d + (h_w + h_ow) + h_r

Total pressure drop = 69.67+(40+38.7)+13.24

h_t = 161.6 mm liquid

 

Down comer Liquid Backup

Take h_ap = h_w – 10 = 30 mm  Area under apron 

A_ap        =0.0885m²

As this is less than A_d use A_ap

                           

= 8.564 mm liq.

BACKUP IN DOWN COMER

h_b         = (h_w + h_ow) + h_t + h_dc

h_b         = 0.249 liq. m

0.249 < ½ (Tray spacing + weir height)      So tray spacing is acceptable   

CHECK RESIDENCE TIME

t _r = (Ad x h_bc x ℓL)/Lwd

= 19 sec       >3 sec. so, result is satisfactory    

 

CHECK ENTRAINMENT   

Uv       = Maximum Volumetric Flow Rate of vapors/Net Area

U_V          =         27.56 / 8.86     =          3.11 m/s

Percent flooding            =          3.11/3.886       =          0.8 = 80 %

F_LV = 0.028

Fractional entrainment y = 0.09  which is below 0.1  so result is satisfactory

 

Trial Lay Out

Use cartridge type construction. Allow 100 mm imperforated strip round plate edge; 100 mm wide calming zone.

L_w/D_c    =         0.81     θc          =         106^o

Angle subtended at plate edge by imperforated strip = 180 – 106 = 74^o

Mean length, imperforated edge strip:        

Area of imperforated edge strip Ap^/ m²

Mean length of calming zone  m

Area of calming zone A_cal m²

Total area of perforations, A_p = A_a – A_p/ - Acal

                                                = 7.29 – 0.4572 – 0.566 = 6.2668 m²

l_p/d_h = 2.7                   Satisfactory within 2.6 - 4.0

 No of Holes

Area of one hole

Number of Holes = Hole Area / Area of one hole

No. of holes

                        = 37138

 HEIGHT OF COLUMN:            

Number Of plates = 47

Spacing between each plate = 0.5 m

Space for disengagement of vapor and liquid on top = .5 m

Space for disengagement of vapor and liquid in bottom = 0.5 m

Height of column = (#of plates × space between each plate) + (space for

disengagement on top and bottom)

= (47×0.5) + (0.5+0.5) = 24.5 m     

So

Height of column  = 24.5 m