[Objective

]

This paper aims to solve many practical problems of urea pyrolysis system in SCR flue gas denitrification technology of gas-steam combined cycle units. [Methods

]

The SCR flue gas denitration system of a 9F gas-steam combined cycle unit is taken as an example to study the application of urea direct injection pyrolysis technology under the flue gas condition of gas turbine outlet by numerical simulation method. Based on theoretical research

the technology is extended to engineering design and practical application. [Results

]

The results show that the main products of urea pyrolysis are ammonia and isocyanic acid under the flue gas condition of gas turbine outlet. The urea pyrolysis efficiency increases rapidly with the flue gas temperature and the extension of residence time: when the flue gas temperature i

s 300 ℃

the residence time is 0.5 s

the flue gas temperature is 650 ℃

and the residence time is 0.1 s

the urea pyrolysis efficiency exceeds 95%. The urea pyrolysis efficiency increases with the distance from the injection point: when the distance from the injection point is 31 m

the urea pyrolysis efficiency reaches 99%. When the injection points of urea solution are arranged with 12 and 29 injectors according to the equal area method

the root mean square deviation of pyrolysis product distribution on the catalyst inlet section is less than 5%. In practical engineering design and application

considering the uniformity of urea pyrolysis product distribution on the catalyst inlet cross-section and investment costs

12 injectors are arranged inside the circular flue according to the principle of equal area. The atomized particle size of urea solution sprayed from each injector is selected to be D

V

0.5

=52.0 μm. The metering dilution system with dilution water can keep the atomized particle parameters of each injector in the optimum working condition under different loads

and the injector with heat insulation structure and cooling air can avoid water evaporation of urea solution. [Conclusion

]

After the actual operation of the project

the technology can stably provide reducing agent for the SCR flue gas denitrification system. The NO

x

mass concentration reduces from 35 mg/m

3

to 5 mg/m

3

the ammonia escape is less than 3 μL/L

and the root mean square deviation of pyrolysis product distribution on the catalyst inlet section is less than 5% under the high and low load conditions of the unit

indicating that the uniformity of the ammonia concentration distribution at the inlet of the catalyst is good

and the technology realizes the energy saving

low consumption

low pollution and economic operation of the denitration environmental protection system of the gas-steam combined cycle unit.