title: SNCR De-NOx within a moderate temperature range using urea-spiked hydrazine hydrate as reductant.
abstract: In this research, urea-spiked hydrazine hydrate solutions are used as reductants for the Selective Non-Catalytic Reduction (SNCR) De-NOx process below 650 °C. The urea concentration in the urea/hydrazine hydrate solutions is chosen through experimental and theoretical studies. To determine the mechanism of the De-NOx process, thermogravimetric analysis (TGA) of the urea/hydrazine hydrate solutions and their thermal decomposition in air and nitrogen atmospheres were studied to understand their decomposition behaviours and redox characteristics. Then a plug flow reactor (PFR) model was adopted to simulate the De-NOx processes in a pilot scale tubular reactor, and the calculated De-NOx efficiency vs. temperature profiles were compared with experimental results to support the mechanism and choose the proper reductant and its reaction temperature. Both the experimental and calculated results show that when the urea is spiked into hydrazine hydrate solution to make the urea-N content approximately 16.7%-25% of the total N content in the solution, better De-NOx efficiencies can be obtained in the temperature range of 550-650 °C, under which NH3 is inactive in reducing NOx. And it is also proved that for these urea-spiked hydrazine hydrate solutions, the hydrazine decomposition through the pathway N2H4 + M = N2H3 + H + M is enhanced to provide radical H, which is active to reduce NO. Finally, the reaction routes for SNCR De-NOx process based on urea-spiked hydrazine hydrate at the proper temperature are proposed.
authors.affiliation: Thermal and Environmental Engineering Institute, Tongji University, 200092, Shanghai, China.
authors.forename: H
authors.initials: H
authors.lastname: Chen
authors.affiliation: Thermal and Environmental Engineering Institute, Tongji University, 200092, Shanghai, China. Electronic address: chendezhen@tongji.edu.cn.
authors.forename: D Z
authors.initials: DZ
authors.lastname: Chen
authors.affiliation: Thermal and Environmental Engineering Institute, Tongji University, 200092, Shanghai, China.
authors.forename: S
authors.initials: S
authors.lastname: Fan
authors.affiliation: Thermal and Environmental Engineering Institute, Tongji University, 200092, Shanghai, China.
authors.forename: L
authors.initials: L
authors.lastname: Hong
authors.affiliation: Thermal and Environmental Engineering Institute, Tongji University, 200092, Shanghai, China; Institute of Energy and Environment Engineering, Shanghai University of Electric Power, 200090, China.
authors.forename: D
authors.initials: D
authors.lastname: Wang
mesh_terms: D002384:Catalysis; D006834:Hydrazines / Q000737:chemistry*; D008962:Models, Theoretical; D009589:Nitrogen Oxides / Q000737:chemistry*; D010084:Oxidation-Reduction; D019163:Reducing Agents / Q000737:chemistry*; D013696:Temperature; D014508:Urea / Q000737:chemistry*
chemical_list: D006834:Hydrazines; D009589:Nitrogen Oxides; D019163:Reducing Agents; C029424:hydrazine; D014508:Urea
keywords: Concentration; Hydrazine hydrate; SNCR De-NO(x); Temperature window; Urea-spiked