A Review of Urea Pyrolysis to Produce NH₃ Used for NO_x Removal

Table 1

Kinetic reaction scheme of urea decomposition.

	Reaction	γj	A	EA (kJ/mol)
I	CYA(s) ⟶ 3HNCO(g)	0	1.001 × 10^3 mol/s	118.42
II	Biuret(m) ⟶ urea(m) + HNCO(l)	1	1.107 × 10^20 1/s	208.23
III	Urea(m) + HNCO(l) ⟶ biuret(m)	1/1	3.517 × 10^11 ml/mol s	75.45
IV	Urea(m) ⟶ HNCO(l) + NH3(g)	0.3	2.000 × 10^4 mol^0.7/ml^0.7 s	74.00
V	2 biuret(m) ⟶ ammelide(s) + HNCO(l) + NH3(g) + H2O(g)	2	3.637 × 10^26 1/s	257.76
VI	Biuret(m) + HNCO(g) ⟶ CYA(s) + NH3(g)	1/1	9.397 × 10^20 ml/mol s	158.68
VII	Biuret(m) + HNCO(g) ⟶ triuret(s)	1/1	1.091 × 10^15 ml/mol s	116.97
VIII	Triuret(s) ⟶ CYA(s) + NH3(g)	1	1.238 × 10^18 1/s	194.94
IX	Urea(m) + 2HNCO(l) ⟶ ammelide(s) + H2O(g)	1/2	1.274 × 10^20 ml^2/mol^2 s^2	110.40
X	Biuret(m) ⟶ biuret(matrix)	1	8.193 × 10^26 1/s	271.50
XI	Biuret(matrix) ⟶ biuret(m)	1	3.162 × 10^09 1/s	122.00
XII	Biuret(matrix) ⟶ 2HNCO(g) + NH3(g)	1	5.626 × 10^24 1/s	266.38
XIII	Urea(s) ⟶ urea(m)	1	1.000 × 10^15·T^1.5 1/s	160.00
XIV	Ammelide(s) ⟶ ammelide(g)	1	1.000 × 10^14 ml/mol s	201.67
XV	HNCO(l) ⟶ HNCO(g)	Herz–Knudsen equation

Note. States of aggregation: (s): solid, (m): molten, (g): gaseous, (l): liquid/dissolved, (matrix): solid matrix. Triuret: NH₂-CO-NH-CO-NH-CO-NH₂. For reactions with two educts the reaction order γ_j of the second educt is specified as second value.