## Sunday, 10 April 2011

### 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+CpL*(Tb-Tf) / 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
NB= 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
NB=5 / 0.42=    12
ND=15 / 0 .42=35
Maximum liquid flow rate in rectifying section = Ln = D Rm= 0.304598x0.113196
= 0.0345479kmole/sec
Maximum vapor flow rate in rectifying section = Vn  = Ln + D
= 0.0345479+0.1131962
= 0.147744 kmole/sec
Maximum liquid flow rate in stripping section = Lm = Ln+qF
0.034479+(1.157)(0.1254)=0.17958 kmole/sec
Maximum vapor flow rate in stripping section = Vm = Lm – W
= 0.17958 - 0.012216=0.167364 kmole/sec

COLUMN DIAMETER
The plate diameter is calculated based on the flooding considerations
FLG  = Lm / Vm {r g/ r l}0.5
Now for,FLG = 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*FLG^0.842)

FLOODING PARAMETER
Csb, flood = 0.093m/s.
Now,        (V/ 20) ^ Unf = Csb, flood × (σ0..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 = Lm / 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 Ac                          Ac= 10.42m2
Net area An                                        =         Ac – Ad  =       8.857m2
Active area Aa              =         Ac – 2Ad  =     7.294 m2
Hole area Ah take 10% Aa as first trial    =   0.7294 m2
WEIR LENGTH
Ad / Ac = 1.563 / 10.42 = 0.15     Lw / d= 0.81         Lw =2.95 m
Take weir height , hw                 = 40 mm
Hole diameter, dh                      = 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
how                   = weir crust       Maximum = 38.7 mm liquid
Minimum  = 30.5 mm liquid at minimum hw + how = 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
lo = 0.84
= 69.67mm liquid

mm liquid
TOTAL PRESSURE DROP
ht = hd + (hw + how) + hr
Total pressure drop = 69.67+(40+38.7)+13.24
ht = 161.6 mm liquid

# Down comer Liquid Backup

Take hap = hw – 10 = 30 mm  Area under apron
Aap        =0.0885m2
As this is less than Ad use Aap

= 8.564 mm liq.

BACKUP IN DOWN COMER
hb         = (hw + how) + ht + hdc
hb         = 0.249 liq. m
0.249 < ½ (Tray spacing + weir height)      So tray spacing is acceptable

CHECK RESIDENCE TIME
t r = (Ad x hbc x ℓL)/Lwd
= 19 sec       >3 sec. so, result is satisfactory

# CHECK ENTRAINMENT

Uv       = Maximum Volumetric Flow Rate of vapors/Net Area
UV          =         27.56 / 8.86     =          3.11 m/s
Percent flooding            =          3.11/3.886       =          0.8 = 80 %
FLV = 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.
Lw/Dc    =         0.81     θc          =         106o
Angle subtended at plate edge by imperforated strip = 180 – 106 = 74o
Mean length, imperforated edge strip:
Area of imperforated edge strip Ap/ m2
Mean length of calming zone  m
Area of calming zone Acal m2
Total area of perforations, Ap = Aa – Ap/ - Acal
= 7.29 – 0.4572 – 0.566 = 6.2668 m2

lp/dh = 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