System for low temperature plasma pre-oxidizing NOx of auxiliary NH3-SCR fine purification diesel engine

Abstract

The invention relates to a system for using NH3-SCR to purify NOx in a diesel engine by the assistance of pre-oxidization of a low-temperature plasma, and belongs to the control technical field of the exhaust pollutants of the tail gas of the diesel engine; the invention adopts the combining use of a DBD reactor and an SCR reactor in the working condition of low temperature, wherein, the DBD reactor adopts coaxial medium to block a discharging reactor, which has good safety performance, simple structure and stable, uniform and dispersing discharging and can effectively reduce the energy consumption which is needed by the medium for blocking the discharging; the process of the low-temperature plasma replaces the process of noble metal catalytic oxidization to carry out the pre-oxidization to NO, thus realizing that NOx is reduced in the wide temperature window at the temperature of 100 DEG C to 550 DEG C, avoiding the use of the noble metal catalyst and solving the problem of sulfur poisoning of the catalyst simultaneously and effectively. The system of the invention is applicable to the diesel with high sulfur in China and can improve the NOx conversion efficiency of NH3-SCR when the diesel engine carries out cold starting or is in idle speed in the low temperature.

Description

Technical field: [0001] The present invention relates to NH 3 -SCR (Ammonia-Selective Catalytic Reduction) to purify diesel engine NO x System, especially a low-temperature plasma pre-oxidation auxiliary NH with diesel engine exhaust temperature in the low temperature range 3 -SCR purification diesel engine NO x The system belongs to the technical field of diesel engine exhaust pollutant control. Background technique: [0002] Particulate (PM) and nitrogen oxides (NO) in diesel engine emissions x ) There is an inherent "trade-off" effect. In view of the current level of diesel engine technology, it is difficult to significantly reduce NO at the same time by relying only on the front and internal measures of the diesel engine. x And PM emissions. Internationally, it is generally believed that the NO x To meet the emission standards of Euro IV and above at the same time as PM emissions, a combination of internal and external control must be adopted. At present, optimized in-cylind...

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Problems solved by technology

However, SCR technology still has many deficiencies in many aspects, such as NH 3 -SCR can only treat NO in the high temperature zone (250℃~550℃) x It has a large catalytic conversion efficiency, and the activity of the catalyst is quite low in the low temperature region (100 ° C ~ 250 ° C), and the catalytic conversion effect on NOx is very poor, resulting in low exhaust gas temperature during cold start or idling of diesel vehicles. NO and NH 3 Reduction of NO x The efficiency is very low, therefore, in urban road conditions, NO x Emissions are difficult to achieve the expected goal. In recent years, foreign research has found that the diesel engine pre-oxidation catalytic device (DOC) is added in front of the SCR reactor to partially oxidize the NO in the exhaust gas of the diesel engine. x NO in the exhaust gas of diesel vehicles accounts for the vast majority, so that NO and NO 2 The molar ratio is close to 1:1, which realizes the fast SCR method and makes NO x The problem of low low-temperature reduction efficiency has been alleviated, although the fast SCR technology is to solve the NO x The fundamental way of low reduction efficiency, foreign pre-oxidation devices generally use P t and other precious metal catalysts, but it is only suitable for low-sulfur fuel oil with a sulfur content of less than 15ppm restricted by foreign emission regulations, while in my country, the current diesel sulfur content reaches or exceeds 500ppm, such a high sulfur content will poison the diesel pre-oxidation catalyst , so that a fast SCR process is difficult to achieve reliably

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