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 holes 8 mm diameter, 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 R2
R2 = (683)/(π×10) = 12.075m2
R = 3.475 m
Diameter = 6.95 m