RU2576758C1 - System for selective catalytic reduction of nitrogen oxides in exhaust gases of diesel engines - Google Patents

Abstract

FIELD: treatment plant.

SUBSTANCE: invention relates to cleaning of exhaust gases of diesel engine. System comprises neutraliser 1 for exhaust gas, catalyst 2, device 3 to store and feed urea, tube 4 for urea supply through nozzle 5 into pipeline 6 for exhaust gas. Tube 4 is made of non-magnetic material and represents zigzag with two elbows, between which there is magnetic ring 7.

EFFECT: technical result is increased rate of thermal decomposition of urea solution, higher efficiency of NO_x reduction, wider temperature range of efficient interaction between nitrogen oxides and ammonia, and reducing emissions of unreacted ammonia.

1 cl, 2 dwg

Description

The technical solution relates to internal combustion engines, namely to diesel engines. It concerns the purification of exhaust gases of a diesel engine from harmful substances, namely, the reduction of emissions with exhaust gases (OG) of harmful substances CO, HC, NO _x .

The most common technical solution to reduce nitrogen oxide emissions is the catalytic reduction of nitrogen oxides by the decomposition products of urea fed to the heated exhaust gas stream before a selective catalyst (see, for example, patents issued in the USA, Nos. 6833272, 6996975, 7498010, 7264785, 8479497 Application No. 2614231 published by EP, Applications WO 2012031536, WO 2008122460, Applications No. 20110146237, 20130115150, 20110146241, published in the USA).

The method of reducing nitrogen oxides with ammonia over the past 10-15 years has been widely developed as the basic method for the neutralization of NO _x in diesel exhaust gases, including on heavy vehicles. As selective catalysts, the most widely used are catalysts based on titanium and vanadium oxides doped with promoters in the form of transition metal oxides. This provides a sufficiently reliable recovery of up to 70% of nitrogen oxides. A 32.5% aqueous solution of urea NHCO (urea), which is injected into the exhaust gas stream in the form of an emulsion with the participation of air, is used as a reducing reagent. Urea is highly soluble in water, the main properties are extremely weak. In aqueous solutions, urea attaches a water molecule. The urea solution (called AdBlue in international practice) is non-toxic and easy to use. The nominal operating temperature range of the reagent is - 11 ° C to 60 ° C.

As a prototype, a system of selective catalytic reduction of nitrogen oxides in the exhaust gases of diesel engines was adopted, containing an exhaust gas neutralizer, a catalyst, a urea storage and supply device, a urea supply pipe through an injector into the exhaust gas pipe. This system, presented in application No. 2013/0255233, published in the USA, provides an accurate dosage of urea depending on the mass content of NO _x in the exhaust gas and allows the selective reduction of nitrogen oxides to free nitrogen at moderate temperatures (300-400 ° C) ) The process (SCR-NO _x + NH ₃ -process) proceeds continuously for a long time. The reduction of NO _x in the exhaust gas with an excess of oxygen is carried out only in the presence of a catalyst and a reducing agent at optimal temperatures and the stoichiometric ratio of NO _x and NH ₃ .

However, in this system, a relatively slow decomposition of urea occurs in the exhaust gas temperature range of 200-300 ° C, which leads to the need to increase the length of the zone between the urea feed nozzle and the selective catalyst or to find other methods for intensifying this process, for example, by installing special catalysts for urea hydrolysis in the presence of acids and alkalis, as well as under the action of the enzyme uraza.

The task is to increase the rate of thermal decomposition of the urea solution to increase the efficiency of NO _x reduction, expand the temperature range of the effective interaction of nitrogen oxides and ammonia, and reduce emissions of unreacted ammonia.

The solution to this problem is provided by the fact that in the system of selective catalytic reduction of nitrogen oxides in the exhaust gases of diesel engines containing an exhaust gas neutralizer, a catalyst, a urea storage and supply device, a urea supply pipe through an nozzle to the exhaust gas pipe, according to the problem to be solved, the supply pipe urea is made of non-magnetic material and is made zigzag with two elbows, between which there is a magnetic ring.

When the urea feed tube is zigzag with two elbows between which there is a magnetic ring, conditions are created for accelerating hydrolysis even at temperatures of 100-150 ° C and thereby earlier release of ammonia NH ₃ due to significant activation of urea by intensive exposure to magnetic fields changing their direction.

The figure 1 presents a system of selective catalytic reduction of nitrogen oxides in the exhaust gases of diesel engines.

Figure 2 shows a magnetic ring and a urea feed tube.

The system for selective catalytic reduction of nitrogen oxides in diesel engine exhaust gases shown in FIG. 1 comprises an exhaust gas catalyst 1, a catalyst 2, a urea storage and supply device 3, a tube 4 of non-magnetic urea supply material through an injector 5 to the exhaust gas discharge pipe 6. The urea supply tube 4 is located in the magnetic ring 7. The urea storage and supply device 3 consists of a urea tank 8, a solution supply unit 9, an air supply unit 10, and a metering device 11. In addition, the system includes a CAN bus 12, an electronic unit 13 control, sensors 14 and 15 exhaust gas temperature sensor 16, the nitrogen oxides (NO _x) in exhaust gas of the diesel engine 17.

When the diesel engine 17 is operating, the exhaust gases pass through the exhaust gas pipe 6 through the catalyst 1 and catalyst 2. In the pipe 6 of the exhaust gas discharge in the area between the catalyst 1 and the catalyst 2, urea is fed through a pipe 4 of non-magnetic material through the nozzle 5. When urea is fed to the nozzle 5, it passes through the magnetic field created by the magnetic ring 7 (figure 2). Due to the execution of the tube 4 zigzag with two elbows and the location of the magnetic ring between the two elbows, the magnetic flux acting on the urea changes its direction several times, increasing the activation of urea.

By mixing with the hot exhaust gas, urea decomposes into water and ammonia, which then enters catalyst 2. In the catalyst, ammonia NH ₃ reacts with nitrous oxide NO _x to form nitrogen and water, which are released into the atmosphere.

Due to the intense influence of urea on magnetic fields that change their direction, the rate of thermal decomposition of the urea solution is increased, as a result of which the efficiency of NO _x reduction is increased, the temperature range of the effective interaction of nitrogen oxides and ammonia is expanded, and thereby emissions of unreacted ammonia are reduced.

Claims (1)

A system for the selective catalytic reduction of nitrogen oxides in diesel engine exhaust gases, comprising an exhaust gas catalyst, a catalyst, a urea storage and supply device, a urea supply pipe through an nozzle to an exhaust gas pipe, characterized in that the urea supply pipe is made of non-magnetic material and is made zigzag with two bends between which the magnetic ring is located.

Images