KR20070003322A - Selective catalytic reduction apparatus of nox - Google Patents

Abstract

A selective catalytic reduction apparatus of NOx is provided to permit NOx in exhaust gas to be reacted to NH3 and HNCO at an optimum condition, by sensing the state of exhaust gas varying during travel and controlling the amount and pressure of NH3 and HNCO supplied from a solid urea sublimation device on the basis of the sensed state of exhaust gas. A selective catalytic reduction apparatus of NOx, comprises a reactor(40), a front NOx sensor(31), an exhaust pressure sensor(32), a rear NOx sensor(36), and an ECU(50). The reactor is arranged in an exhaust pipe such that NH3 and HNCO flow into the reactor and react to exhaust gas. The reactor has a catalytic unit(43) for promoting reaction. The front NOx sensor is arranged in a front exhaust pipe(20) of the reactor, and measures NOx content in the exhaust gas introduced from an engine(10). The exhaust pressure sensor is arranged in the front exhaust pipe of the reactor, and measures pressure of the exhaust gas introduced from the engine. The rear NOx sensor is arranged in a rear exhaust pipe(21) of the reactor, and measures NOx content in the exhaust gas passed through the reactor. The ECU takes, as an input, signals from the front and rear NOx sensors and the exhaust pressure sensor, and controls the amount and inflow pressure of solid urea sublimated in a solid sublimation unit(6) by determining the amount and inflow pressure of NH3 and HNCO required in the reactor.

Description

Selective catalytic reduction apparatus of NOx by solid urea sublimation

1 is a graph showing the relationship between the temperature and the amount of ammonia and cyanic acid generated when subliming a solid element;

2 shows a solid element sublimation apparatus;

3 schematically shows a nitrogen oxide reduction apparatus according to the present invention; And

4 is a view showing the configuration of a nitrogen oxide reduction device according to the present invention.

<Explanation of symbols for main parts of the drawings>

6: solid element sublimation device 10: engine

20, 21: front and rear exhaust pipe 31, 36: nitrogen oxide detection sensor

32: exhaust pressure sensor 33: exhaust temperature sensor

34: auxiliary heater 35: catalyst temperature sensor

40 reactor 43 catalyst part

44: reaction space 62: heater

67b: discharge tube 68: pressure regulator

69: blower

The present invention relates to a nitrogen oxide reduction device for removing NOx which is nitrogen oxide in exhaust gas of automobiles. More specifically, the solid urea is sublimated and reacted with the exhaust gas as an additive to remove nitrogen oxides (NOx) in the exhaust gas, but sublimates by sensing the state of the exhaust gas and the amount of nitrogen oxide contained. The present invention relates to a device for reducing nitrogen oxides, in which the reaction of the solid urea and nitrogen oxides in an optimum state occurs.

In diesel vehicles, in order to efficiently remove nitrogen oxides, it is necessary to install a nitrogen oxide reduction device. As a method for reducing nitrogen oxides, NOx in the exhaust gas is allowed to mix and react with the exhaust gas and the additive in a catalyst section prepared by injecting an additive such as ammonia (NH ₃ ) or urea (Urea, NH ₂ CONH ₂ ) into a high temperature exhaust gas. Selective Catalytic Reduction of NOx is used to reduce nitrogen to N ₂ .

In selective catalytic nitrogen oxide abatement apparatus using urea as an additive, the optimal injection amount of urea additive to maintain maximum NOx removal efficiency is half of the volume of NOx present in the exhaust gas (i.e. [urea] / [NOx as volume ratio). ] = 0.5). NOx occupies only about 100 ppm of the total volume of exhaust gas on the average of the exhaust gas of engines or vehicles using actual diesel fuel. Should be supplied. Therefore, there is a need for a nitrogen oxide reduction device capable of precisely controlling the amount of urea.

Most nitrogen oxide reduction devices proposed to date use liquid urea solution as an additive. The urea solution supply device for supplying urea solution includes a supply pump, a compressor, and an atomizer or an injector. Therefore, the entire equipment / device is complicated and expensive, and there is a problem that solids generated by evaporation at the moment of supplying the urea solution with the high temperature exhaust prevent the spray / injector, thereby preventing normal operation.

In order to solve the problems associated with using such a urea solution, the present applicant has proposed a solid urea sublimation apparatus capable of subliming a solid urea to a high temperature in order to sublimate the solid urea as an additive instead of the urea solution. Patent Application No. 10-2004-0107514).

The basis for subliming the solid element can be found in the contents described in "Caton and Siebers 1989, Combust. Sci. And Tech. Vol. 65, pp. 277-293". According to the paper, the same amount of ammonia (Ammonia: NH ₃ ) and cyanuric acid (HNCO) are generated when subliming solid urea. Specifically, referring to the graph shown in FIG. 1, when subliming an initial solid element equivalent to 3700 ppm relative to the total volume, about 1500 ppm of NH ₃ and HNCO gases are generated at a temperature of about 427 K (= 150 ° C.), and the sublimation temperature. It can be seen that the higher the amount of NH 3 and HNCO gas is increased to the same, and the initial volume of 3700 ppm of solid urea is sublimated to 3700 ppm of NH ₃ and HNCO gas, respectively, at about 727 K (= 450 ° C.). If this is expressed as a chemical formula,

NH ₂ CONH ₂ (solid) → NH ₃ + HNCO (1)

One mole of urea is sublimed into one mole of NH ₃ gas and one mole of HNCO gas.

On the other hand, when heating the urea solution,

NH ₂ CONH ₂ + H ₂ O → 2NH ₃ + CO ₂ (2)

2 moles of ammonia gas can be obtained from 1 mole of urea solution. In this case, ammonia acts as a main additive to remove NOx, which is a nitrogen oxide. However, both types of gases NH ₃ and HNCO generated by sublimation of solid urea have the ability to remove NOx, which is nitrogen oxides (US Pat. No. 3,900,554 and US Pat. No. 4,731,231).

Therefore, the use of NH ₃ and HNCO as an additive by sublimating the solid urea solves the above-mentioned problems in using the urea solution and can remove NOx, which is nitrogen oxide, with the same efficiency. The present applicant has proposed a solid element sublimation apparatus that can remove NOx, which is a nitrogen oxide, by sublimating a solid element in a patent application No. 10-2004-0107514 and supplying it to a catalytic reactor provided in an exhaust pipe of a vehicle.

The solid element sublimation device proposed by the applicant is attached to one end of the receptor 60, which contains the solid urea crystal 61 therein, and one end of the receptor 60, as shown in FIG. A heater 62 for heating the solid urea crystal 61, an inner cap 63 installed at the other end of the container 60 and movable in the axial direction, and the inner cap 64 and the elastic member 65; It is installed as an intermediary and consists of an outer cap 66 surrounding the receptor. In addition, one side of the receiver 60 in which the heater 62 is installed is provided with an inlet tube 67a through which air is introduced from the outside and a discharge tube 67b for discharging the sublimed NH ₃ and HNCO from the inside.

When it is necessary to sublimate the solid element, the ECU of the vehicle signals the heater 62, whereby one end of the receiver 60 is heated to a predetermined temperature required for sublimation by the heater 62. When the solid urea 61 stored at one end of the receptor 60 is heated to sublimate, the urea is changed to NH ₃ and HNCO gas. At this time, if the air is blown to the blower (not shown) connected to the inlet pipe (67a), the sublimed NH ₃ and HNCO enters the reactor (not shown) through which the exhaust gas passes through the discharge pipe (67b) together with the air. . When the solid element 61 is sublimed at one end of the receptor 60, the other solid element 61 fills the space occupied by the sublimed solid element 61, which is the elastic member 65 located at the other end of the inner cap ( By pressing 63). In addition, a sensor 64 for detecting the position of the inner cap 63 that moves according to the amount of the solid element 61 accommodated is installed at the side of the receiver 60 to detect whether the solid element 61 is exhausted.

However, as described above, since the nitrogen oxide contained in the exhaust gas occupies a small volume, the amount of NH ₃ and HNCO reacted with the nitrogen oxide is also small, so that it can be accurately controlled in order to supply the required amount accurately. Is needed. In particular, since the amount of nitrogen oxide changes depending on the driving conditions, a device capable of accurately detecting and supplying the required amount of NH ₃ and HNCO according to the change of nitrogen oxide during driving is required.

The present invention has been proposed by this demand, and it detects the state and composition of the exhaust gas from the engine, and detects the state and composition of the exhaust gas passing through the catalytic reactor, the amount of NH ₃ and HNCO required by the solid element It is an object of the present invention to provide a nitrogen oxide reduction apparatus capable of reducing the nitrogen oxides (NOx) in the exhaust gas at an optimum state by forming an appropriate reaction state by introducing the catalyst reactor into a catalyst sublimation apparatus.

In order to achieve the above object, the present invention is to heat the heater of the solid urea sublimation device to react the NH ₃ and HNCO generated by sublimation of the solid urea contained in the receptor with the nitrogen oxide in the exhaust gas in the exhaust pipe to the nitrogen oxide in the exhaust gas An apparatus for reducing nitrogen oxides, the apparatus comprising: a reactor installed at a predetermined position in an exhaust pipe, the reactor including a catalyst unit for introducing NH ₃ and HNCO sublimated by the solid element, reacting with the exhaust gas, and promoting a reaction; A front nitrogen oxide sensor installed at the front exhaust pipe of the reactor to measure nitrogen oxide content in the exhaust gas flowing from the engine; An exhaust pressure sensor installed at a front exhaust pipe of the reactor to measure a pressure of exhaust gas flowing from the engine; A rear nitrogen oxide sensor installed at a rear exhaust pipe of the reactor to measure nitrogen oxide content in the exhaust gas passing through the reactor; ECU which controls the amount and inlet pressure of the solid element sublimated in the solid sublimation device by determining the NH ₃ and HNCO amount and inlet pressure required by the reactor by receiving signals from the front and rear nitrogen oxide sensor and exhaust pressure sensor It includes, it can be supplied by adjusting the amount and pressure of the NH ₃ and HNCO to react with the nitrogen oxide in the exhaust gas by detecting the state of the exhaust gas changes during driving.

In addition, in the present invention, an exhaust temperature sensor for measuring the temperature of the exhaust gas is installed in the front exhaust pipe of the reactor, the reactor is provided with an auxiliary heater for adjusting the reaction temperature and a catalyst temperature sensor for measuring the reaction temperature The ECU receives the exhaust gas temperature and the reaction temperature from the temperature sensor and the catalyst temperature sensor and controls the auxiliary heater to adjust the reaction temperature of the exhaust gas so that the nitrogen oxides of the exhaust gas and NH ₃ and HNCO are activated at the temperature at which the catalyst is activated. To react.

In addition, the solid element sublimation apparatus of the present invention supplies the NH ₃ and HNCO to the reactor through a discharge pipe end is inserted into the reactor, the discharge pipe is provided with a non-return valve in the middle, the end of the reactor The discharge hole is formed in the direction facing the exhaust gas to prevent the sublimed NH ₃ and HNCO from flowing back to the solid element sublimation apparatus, and the discharged NH ₃ and HNCO flows backward while being mixed with the exhaust gas. It is possible to increase the reaction efficiency.

Hereinafter, with reference to the accompanying drawings will be described a preferred embodiment according to the nitrogen oxide reduction device according to the present invention. 3 is a view schematically showing a nitrogen oxide reduction device according to the present invention, Figure 4 is a view showing the configuration of the nitrogen oxide reduction device according to the present invention.

Referring to FIG. 3, the nitrogen oxide reduction device according to the present invention uses a conventional solid urea sublimation device 6 to introduce NH ₃ and HNCO sublimed in the solid urea sublimation device 6 into the reactor 40. To react with the nitrogen oxide contained in the exhaust gas. Since the solid element sublimation apparatus 6 has already been described in the related art, a detailed description thereof will be omitted. The solid element sublimation device 6 receives a heater 62 for heating one end of the receiver 60 to sublimate the solid, and air of a predetermined pressure to introduce sublimated NH ₃ and HNCO into the reactor 40. The blower 69 which blows into the sublimation apparatus 6, and the pressure regulator 68 for adjusting a blowing pressure are provided. The blower 69 may be connected to the engine 10 to operate dependently on the engine 10 or may be operated by a separate power supply.

The reactor 40 is located at a predetermined position of the exhaust pipe 20 connected to the engine 10 and has a reaction space 44 in which NH ₃ and HNCO react with nitrogen oxide, and a reaction catalyst for promoting the reaction. A catalyst portion 43 having a 41 and an oxidation catalyst 42 is included. The reaction catalyst 41 is for activating the reaction of NH ₃ and HNCO with nitrogen oxide, and metal oxides such as titanium oxide (TiO ₂ ), vanadium oxide (V ₂ O ₅ ), and the like are used. To activate the reaction at ˜600 ° C., a zeolite-based catalyst is used, and to activate the reaction at a relatively low temperature (170-300 ° C.), precious metals of platinum (Platinum, Palladium, etc.) are used. The oxidation catalyst 42 is a catalyst for oxidizing or reducing NH ₃ or HNCO remaining or not reacted after the reaction is performed by the reaction catalyst 41.

A discharge tube 67b for introducing NH ₃ and HNCO from the solid element sublimation device 6 is inserted into the reaction space 44 of the reactor 40. The discharge pipe 67b is provided with a non-return valve 670 to prevent the reverse flow of NH ₃ and HNCO flowing out of the solid element sublimation device (6). If the pressure of the exhaust gas is higher than the outlet pressure of the NH ₃ and HNCO, the there is flow in the reverse NH ₃ and HNCO wherein the non-return valve 670 is blocking the reverse flow of the NH ₃ and HNCO. In addition, the end 671 of the discharge tube 67b has a spherical shape as shown in FIG. ₃ and has a hole 672 formed to allow NH ₃ and HNCO to flow out in a direction opposite to the direction in which the exhaust gas flows. NH ₃ and HNCO are emitted via 672. Therefore, NH ₃ and HNCO discharged through the hole 672 are mixed to face the exhaust gas and flows to the catalyst unit 43 located at the rear with the exhaust gas, thereby increasing the reaction efficiency during the reaction in the catalyst unit. You can.

Inside the reactor 40, an auxiliary heater 34 is provided in front of the spherical end 671 of the discharge tube 67b. The auxiliary heater 34 is controlled by the ECU 50 to be described later to function to heat the exhaust gas to match the catalyst activation temperature of the catalyst unit 43. That is, when the temperature of the exhaust gas is lower than the activation temperature of the catalyst, the ECU 50 of the vehicle to be described later detects this and operates the auxiliary heater 34 to raise the temperature of the exhaust gas to the catalyst activation temperature.

Front and rear exhaust pipes 20 and 21 of the reactor 40 are provided with a front nitrogen oxide sensor 31 and a rear nitrogen oxide sensor 36 for measuring the content of nitrogen oxides in the exhaust gas. The front and rear nitrogen oxide sensor (31, 36) measures the amount of nitrogen oxide contained in the exhaust gas before and after the reactor 40 and sends it to the ECU 50, the ECU based on this the reactor ( In 40), it is determined whether the nitrogen oxide is sufficiently reduced, and thus the required amount of NH ₃ and HNCO, and based on this, the amount of NH ₃ and HNCO supplied from the solid element sublimation device 6 is adjusted.

In addition, in order to measure the pressure and temperature of the exhaust gas, the exhaust pressure sensor 32 and the exhaust temperature sensor 33 are provided in the front exhaust pipe 20 of the reactor 40. The pressure and temperature of the exhaust gas measured by the exhaust pressure and temperature sensors 32 and 33 are transmitted to the ECU 50 of the vehicle.

In addition, the nitrogen oxide reduction device according to the present invention is provided with a catalyst temperature sensor 35 for sensing the temperature of the reaction catalyst inside the reactor 40, the catalyst temperature sensor 35 measures the temperature of the reaction catalyst and It transmits to ECU50.

Referring to FIG. 4, the ECU 50 used in the nitrogen oxide reduction device according to the present invention includes information on the engine speed from the engine 10, and the nitrogen oxide from the front and rear nitrogen oxide detection sensors 31 and 36. Information on the degree of reduction, information on the pressure and temperature of the exhaust gas from the exhaust pressure sensor 32 and the exhaust temperature sensor 33, and information on the temperature of the exhaust gas during the catalyst reaction from the catalyst temperature sensor 35 are inputted. The pressure regulator 68 and the heater 62 of the solid element sublimation apparatus 6 to adjust the supply pressure and the supply amount of NH ₃ and HNCO flowing into the reactor 40 from the solid element sublimation apparatus 6. In addition, the auxiliary heater 34 is adjusted to adjust the exhaust gas to the reaction temperature, that is, the catalyst activation temperature.

Hereinafter, the operation of the nitrogen oxide reduction device according to the present invention.

When the heater 62 of the solid element sublimation device 6 operated by the vehicle power source heats the solid element in the receiver 60, the solid element is sublimed to generate NH ₃ and HNCO. The heater 62 is preferably heated and controlled by the ECU in the range of 150 to 450 ° C. where urea sublimation occurs efficiently.

Thereafter, when air is introduced into the solid element sublimation device 6 by the blower 69 of the solid element sublimation device 6, NH ₃ and HNCO are discharged together with the air through the discharge tube 67b to react the reactor 40. Flows into. At this time, the pressure regulator 68 is controlled by the ECU 50 is adjusted so that the NH ₃ , HNCO and air is introduced into the reactor 40 at a pressure greater than the pressure of the exhaust gas in the reactor (40). At this time, the ECU 50 receives the information on the exhaust gas through the exhaust pressure sensor 32 and the exhaust temperature sensor 33, and also the nitrogen in the front and rear of the reactor 40 from the front and rear nitrogen oxide detection sensors 31 and 36. It receives information on the amount of oxide and controls the exact amount of NH ₃ and HNCO and the supply pressure.

NH ₃ , HNCO and air are introduced into the reactor 40 through holes 672 formed at the end 671 of the discharge tube 67b, mixed with the exhaust gas, and flow into the catalyst unit 43. In the catalyst unit 43, the following reaction occurs.

4NH ₃ + 4NO + O ₂ → 4N ₂ + 6H ₂ O (3)

4NH ₃ + 2NO ₂ + O ₂ → 3N ₂ + 6H ₂ O (4)

2NH ₃ + NO + NO ₂ → 2N ₂ + 3H ₂ O (5)

8NH ₃ + 6NO → 7N ₂ + 12H ₂ O (6)

6HNCO + 9NO → 7.5N ₂ + 6CO ₂ + 3H ₂ O (7)

That is, the nitrogen oxide reacts with NH ₃ and HNCO to change to nitrogen, water or carbon dioxide. When the exhaust temperature does not reach the catalyst activation temperature, the ECU 50 operates the auxiliary heater 34 to heat the exhaust gas to adjust the temperature of the exhaust gas. In addition, since the activation temperature varies depending on the type of the reaction catalyst 41 of the catalyst unit 43, the exhaust gas temperature of the catalyst in which the reaction takes place is measured through the catalyst temperature sensor 35 to adjust the heating degree of the auxiliary heater 34. It can be adjusted precisely.

The exhaust gas passing through the reaction catalyst 41 passes through the oxidation catalyst 42. At this time, the remaining NH ₃ and HNCO remaining after the nitrogen oxide reduction reaction is subjected to the redox reaction as follows.

4NH ₃ + 5O ₂ → 4NO + 6H ₂ O (8)

_{6HNCO + 6.5O 2 → N 2 +} 6CO 2 + 3H 2 O + 4NO (9)

The rear nitrogen oxide sensor 36 then measures the amount of nitrogen oxide in the exhaust gas and sends it to the ECU 50.

As described above, the present invention senses the state of the exhaust gas that changes during the driving of the vehicle and adjusts the amount and pressure of NH ₃ and HNCO supplied from the solid element sublimation apparatus based on this, so that the nitrogen oxide in the exhaust gas is in an optimal state. Allow to react with NH ₃ and HNCO at

As a result, the present invention requires an unnecessarily large amount of NH ₃ And by preventing the supply of HNCO it is possible to reduce the cost by preventing the waste of solid elements.

Claims (3)

Nitrogen oxide abatement system for reducing nitrogen oxides in exhaust gas by heating NH ₃ and HNCO generated by sublimation of solid urea contained in the receiver by heating the heater of the solid urea sublimation device. A reactor installed at a predetermined position in the exhaust pipe, the reactor having a catalyst unit for introducing NH ₃ and HNCO sublimated by the solid element, reacting with the exhaust gas, and promoting a reaction; A front nitrogen oxide sensor installed at the front exhaust pipe of the reactor to measure nitrogen oxide content in the exhaust gas flowing from the engine; An exhaust pressure sensor installed at a front exhaust pipe of the reactor to measure a pressure of exhaust gas flowing from the engine; A rear nitrogen oxide sensor installed at a rear exhaust pipe of the reactor to measure nitrogen oxide content in the exhaust gas passing through the reactor; ECU which controls the amount and inlet pressure of the solid element sublimated in the solid sublimation device by determining the NH ₃ and HNCO amount and inlet pressure required by the reactor by receiving signals from the front and rear nitrogen oxide sensor and exhaust pressure sensor Nitrogen oxide reduction device comprising a. The method of claim 1, An exhaust temperature sensor for measuring the temperature of the exhaust gas is installed in the front exhaust pipe of the reactor, and the reactor is provided with an auxiliary heater for adjusting the reaction temperature and a catalyst temperature sensor for measuring the reaction temperature, The ECU is a nitrogen oxide reduction device, characterized in that for adjusting the reaction temperature of the exhaust gas by controlling the auxiliary heater receives the exhaust gas temperature and reaction temperature from the temperature sensor and the catalyst temperature sensor. The method of claim 1, The solid element sublimation apparatus supplies NH ₃ and HNCO to the reactor through a discharge tube having an end inserted into the reactor, and the discharge tube is provided with a non-return valve in the middle, and the end of the reactor faces the exhaust gas. A nitrogen oxide reduction device, characterized in that the discharge hole is formed in the viewing direction.

Images