Research on NH3-SCR reductant technology progress for diesel vehicles

Abstract

This paper describes the technical principle, research status and application status of four reducing agents (aqueous urea solution, solid ammonium salt, solid ammonia compound and liquid ammonia) which supply NH₃ for SCR of diesel vehicles, introduces the replacement methods of solid ammonia, and analyzes the application feasibility of liquid ammonia. A comprehensive comparative study of the four reducing agents is carried out in terms of storage and validity requirements, low temperature performance, ammonia storage capacity, replacement mode, replacement frequency, safety, cost and future application prospect. It is found that the ammonia storage density of solid ammonia and liquid ammonia is 2.5 ~ 3.5 times of that of aqueous urea solution. And there is no significant difference in the theoretical use cost of several reducing agents, however, the actual use cost of aqueous urea solution is higher than the theoretical value on account of its actual decomposition rate less than 100%. The analysis shows that the requirements for NH₃-SCR reductant technology in the future are excellent low temperature supply capacity, small space occupation, convenient use, low cost and guaranteed quality, and etc. As a traditional technology, aqueous urea solution is easy to crystallize at low temperature and can not meet the requirements of low temperature performance. Solid ammonium salt also has the problem of crystallization at low temperature. Solid ammonia compounds meet the above requirements, and the market application is gradually mature. If liquid ammonia wants to be applied in large-scale engineering, its safety problem of storage tank should be solved.