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原文传递 Study on mixing, modelling and control of an SCR system

论文题名：	Study on mixing, modelling and control of an SCR system
关键词：	船用柴油机;氮氧化物;排放控制;选择性催化还原;SCR催化剂
摘要：	In recent years, more and more research attention has been paid to the NOx emissions caused by marine diesel engines. Selective catalytic reduction (SCR) system has been proven to be an effective technology for the removal of NOx emitted from marine diesel engines.In order to comply with stringent International Maritime Organization(IMO)Tier III NOx emission regulations,a number of engine manufacturers have developed their own SCR systems with an option of installing SCR reactors before or after the turbines of engine turbochargers.This thesis focuses onmodelling of evaporation and decomposition of urea-water-solution(UWS) droplets, design and optimisation of static mixers,modelling of an SCR reactor and developing model-based urea dosing control strategy. 　　The amount of ammoniaconverted from UWS has a significant effect on the NOx removal efficiency of SCR systems. Due to a limited installation space for SCR systems on board,choosingthe location of urea injection nozzle appropriately has become a critical issue for SCR systemdesign. An evaporation and decomposition model of UWS droplets has been developed in this researchin orderto determine the total depletion time of a UWS droplet, which is helpful to calculate the proper length between the urea nozzle and reactor of an SCR system. 　　In order to achieve a high NOx removal rate andreduce the quantity of NH3 slip, static mixers arecommonly used before SCR reactors to improve the mixing between ammonia and exhaust gases. 4 novel static mixershave beendesigned and the performance of the mixersis comparedin the study.An experiment has been conducted to validate the mixing performance and pressure loss of the static mixers developed. It shows that there is a satisfied agreement between the simulationand experiment results. 　　A mathematical model of SCR reactorshas been established. The unknown parameters of the model are identified by minimising the error between the model predicted and measured values of both the temperature and the species concentration after the SCR reactor.The SCR reactor model is further used in a simulation for the purpose of developing model-basedurea dosing control strategies. 　　A state observer is used to determine the actual states in the reactor which supplies the mandatory information for developing model-based urea dosing control strategies. The NH3 cross-sensitivity of NOx sensors can be described by a lineare quation. The simulation results of the observer show that the NH3 cross-sensitivity of NOx sensors can be neglected when estimating the actual states of the reactor if NH3 is of a low concentration in the exhaust.
作者：	Xinna Tian
专业：	Ocean and Marine Engineering
导师：	Youhong Xiao
授予学位：	博士
授予学位单位：	哈尔滨工程大学
学位年度：	2016
正文语种：	中文