Design and Testing of an Independently Controlled Urea SCR Retrofit System for the Reduction of NOx Emissions from Marine Diesels

详细信息    查看全文

• 作者：Derek R. Johnson ; Clinton R. Bedick ; Nigel N. Clark ; David L. McKain
• 刊名：Environmental Science & Technology
• 出版年：2009
• 出版时间：May 15, 2009
• 年：2009
• 卷：43
• 期：10
• 页码：3959-3963
• 全文大小：349K
• 年卷期：v.43,no.10(May 15, 2009)
• ISSN：1520-5851

文摘

Diesel engine emissions for on-road, stationary and marine applications are regulated in the United States via standards set by the Environmental Protection Agency (EPA). A major component of diesel exhaust that is difficult to reduce is nitrogen oxides (NO_x). Selective catalytic reduction (SCR) has been in use for many years for stationary applications, including external combustion boilers, and is promising for NO_x abatement as a retrofit for mobile applications where diesel compression ignition engines are used. The research presented in this paper is the first phase of a program focused on the reduction of NO_x by use of a stand-alone urea injection system, applicable to marine diesel engines typical of work boats (e.g., tugs). Most current urea SCR systems communicate with engine controls to predict NO_x emissions based on signals such as torque and engine speed, however many marine engines in use still employ mechanical injection technology and lack electronic communication abilities. The system developed and discussed in this paper controls NO_x emissions independent of engine operating parameters and measures NO_x and exhaust flow using the following exhaust sensor inputs: absolute pressure, differential pressure, temperature, and NO_x concentration. These sensor inputs were integrated into an independent controller and open loop architecture to estimate the necessary amount of urea needed, and the controller uses pulse width modulation (PWM) to power an automotive fuel injector for airless urea delivery. The system was tested in a transient test cell on a 350 hp engine certified at 4 g/bhp-hr of NO_x, with a goal of reducing the engine out NO_x levels by 50%. NO_x reduction capabilities of 41−67% were shown on the non road transient cycle (NRTC) and ICOMIA E5 steady state cycles with system optimization during testing to minimize the dilute ammonia slip to cycle averages of 5−7 ppm. The goal of 50% reduction of NO_x can be achieved dependent upon cycle. Further research with control optimization, urea distribution and possible use of oxidation catalysts is recommended to improve the NO_x reduction capabilities while minimizing ammonia slip.