Numerical simulations are carried out on a 125 MW coal-fired power unit to study the feasibility of application of urea direct injection pyrolysis technology in flue duct at inlet of the selective catalytic reduction(SCR) denitration system. The results show that

under the SCR inlet flue gas condition

the products of urea pyrolysis are NH_3 and HNCO. When the temperature varies from 300 ℃ to 400 ℃

the urea pyrolysis efficiency can reach over 95% when the residence time of urea is longer than 0.5 s. By setting up 12 injectors at inlet flue duct of the SCR denitration system

the average atomization particle size of urea solution can reach 35 μm. Using proper mixer at downstream of the urea solution injectors can achieve an optimum uniform distribution of NH_3 mole fraction on inlet plane of the first catalyst layer

with a root mean square deviation of 4.8%. For engineering application of the urea direct injection pyrolysis technology

dual-fluid injectors used in the SCR denitration system should have thermal insulation structure and cooling air device

and the injectors should be divided into several zones to achieve optimum NH_3 distribution.