Reactor for Urea Production and Urea Process Parameters

Low-Pressure Decomposer

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/C_Ao  =  V/f_Ao  =  ΔX_A/ -r_A

From material balance :
f_Ao = 2278.645 Kg mole/hr
C_Ao  = f_Ao /V_o
V_o = (inlet flow of CO₂)/(Density of CO₂) = 100260.42 / 809.29 = 123.886 m³/hr
C_Ao  = 2278.645/123.886 = 18.39 Kg mole/m³

Plotting graph (1/-r_A) Vs C_A :

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× f_Ao/C_Ao
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