The Design And Development Of Ammonia Supply Device For Solid Ammonium SCR

With the increase of retaining automobile, it is more and more important to reduce car engine pollutant to satisfy stricter emission standard. For diesel engines, its main emissions are NOx and particulates. Current solutions are Combustion Optimize +SCR and Exhaust Gas Recirculation+. On account of its good fuel economy and high NOx reduction rate, Combustion Optimize +SCR solution is commonly used in heavy-duty diesel engines. However,there are some drawbacks of traditional Urea_SCR that are difficult to overcome, such as poor ammonia carrying capacity of urea solution, condensation of urea solution at temperature below-11℃ and decomposition incompletely problems when exhaust gas temperature is low and so on. The solid ammonium SCR system uses solid ammonium salts as ammonia storage material, which works to generate ammonia gas when heated, then ammonia gas will be injected directly into exhaust pipe to provide reducing agents for reducing NOx. Compared with traditional Urea_SCR, solid ammonium SCR can overcome the drawbacks of the Urea_SCR effectively, and has the following advantages: 1) the ammonia storage capacity of solid ammonium is much better, the ammonia amount of ammonium salt per unit volume or unit mass can be three times of the urea solution; 2) the ammonia is injected directly into the exhaust pipe, and unable to form depositions on the catalyst surface which may reduce catalyst activity; 3) there exists no hydrolysis and pyrolysis during the process, can further broaden the operating temperature range of SCR, and reduce NOx emissions.Several foreign institutions researched the ammonia supply device in theoretical and practical application, and applied small-scale and non-commercial. The domestic research about the supply of solid ammonium ammonia of SCR is late and behindhand, the research on the pyrolysis of ammonium forward and reverse reaction characteristic is unclear. And it’s not easy to solve the problem that the ammonia crystallizes in pipeline and regulator.In view of the advantages of solid ammonium SCR system mentioned above, under the support of Youth Natural Science Foundation projects, this research focused on the forward and reverse reactions characteristic of salt pyrolysis and reduction characteristics of different SCR catalyst at low temperatures.The main contents of this article are: 1) design the ammonia supply device which uses solid salts as SCR reducing agent, and requires the ability of quantitative and stable supply of ammonia gas according to SCR controller commands; 2) design programs to monitor and control the ammonia supply process, make diagnosis and appropriate response measures to malfunctions potential in its use. The main works and conclusions of the article list as follows:1) the structural design of solid ammonia SCR supply device mainly includes four aspects: in the selection of ammonium salt, evaluated the pyrolysis and amount of ammonia restore of different salts, and choosed ammonium carbamate as reductant of solid ammonia SCR system; in ammonia pressure building and regulating process, the ammonia gas generator, electric heater and regulator were designed; in ammonia injection metering aspect, the supply ability of ammonia nozzle is 0~7.8L/min; in terms of anti-crystallization, compared the characteristics of Circulating Water Heating and Electric Heating methods, ultimately adopted Circulating Water Heating as insulation means of the device, and temperature is 95~98℃.2) the work of software side lists as follows: in ammonia pressure building and regulating process, Simulink models of pressure and temperature changes over time in ammonium pyrolysis process were established, the relationship of temperature-time and pressure-time within the ammonia generator at different heating power were studied, and the pressure control program based on the results of theoretical calculations was designed; in ammonia injection metering aspect, the control program was designed for ammonia gas metering device to adjust pulse width of nozzle and spray specified amount of ammonia into the exhaust pipe according to demand changes; in anti-crystallization aspect, process were designed to control circulating water temperature, and make sure the temperature of circulating water is higher than crystallization temperature corresponding to the pressure toensure the smooth of ammonia gas supplying process; in terms of system reliability, the program was designed to test various failures of sensors and actuators.3) Finally, experiments were conducted to test the hardware and software of solid ammonium SCR system ammonia supply means, and verify of ammonia supply capacity on engine bench.