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Reactor for Urea Production and Urea Process Parameters

diagram of low pressure decomposer used in continuous production of urea in large scale
Low-Pressure Decomposer
line diagram of urea production at low pressure section
Diagram of Low Pressure
Urea Section


A complete urea process description with flow sheet

Brief equipment design of a reactor for producing 2100 MTPD of Urea:

Internal trays :

 

Sieve trays           :
480  hot trays: equispaced triangular pitch
Number of trays : 15 equispaced , 666.67 cm diameter

 

Feed distribution nozzle : 

 

CO2 inlet 265 holes of 8 mm diameter
NH3 inlet 440 holes of 8 mm diameter
Operating/ Design temperature 188/210oC
Operating/ Design pressure 155/170 Kg/cm2 g
Design pressure 170 Kg/cm2 g
Joint efficiency = j 0.85
Allowable stress = f 22.5 Kg/cm2 g
Capacity 2100 MTPD
Density of NH3/CO2 at 188oC 881.5387/809.29 Kg/m3

 

Concentration Vs Rate of reaction data for carbon dioxide:

Concentration
CA, Kgmole/m3

18.39

16.55

14.71

12.87

11.03

9.19

7.35

5.51
Rate of reaction, -rA
Kgmole/hr m3

27.05

21.92

17.31

13.25

9.74

6.76

4.33

2.43


Calculation:                                                                                       

 τ/CAo  =  V/fAo  =  ΔXA/ -rA

From material balance :
fAo = 2278.645 Kg mole/hr
CAo  = fAo /Vo
Vo = (inlet flow of CO2)/(Density of CO2) = 100260.42 / 809.29 = 123.886 m3/hr
CAo  = 2278.645/123.886 = 18.39 Kg mole/m3


Plotting graph (1/-rA) Vs CA :
Concentration
CA Kgmole/m3
18.39 16.55 14.71 12.87 11.03 9.19 7.35 5.51
Rate of reaction  -rA
Kgmole/hr m3
27.05 21.92 17.31 13.25 9.74 6.76 4.33 2.43
        1/-rA 0.037 0.046 0.058 0.075 0.102 0.148 0.231 0.411


From graph :

Area = 137.8×2×0.02 = 5.512 hr
Area = τ = 5.512 hr
Now V = τ× fAo/CAo
V = (5.512×2278.65)/18.39 = 682.974 m3
Assuming height to be 18 meters
V = pi R2H
R2 = (683)/(π×10) = 12.075m2
R = 3.475 m
Diameter = 6.95 m