KR100820395B1 - Nox reduction method and apparatus of exhaust gas - Google Patents

Abstract

An apparatus and a method for reducing NOx of exhaust gas are provided to reduce time and cost for additionally mounting a sensor and to simplify the manufacturing process. A method for reducing NOx of exhaust gas comprises steps of injecting urea through an injector by a preset amount Qi such that the NOx(200) is reduced, and determining if the amount of nitrogen detected by an integration sensor is greater than a reference value H(210). When the amount of nitrogen is greater than the reference value, the amount of the urea injected through the injector is reduced at a predetermined ratio(220). After the injected amount of the urea is reduced, the amount of the urea injected through the injector varies depending on the amount of nitrogen detected by the integration sensors(240,250).

Description

NOx reduction method and apparatus of exhaust gas

1 is a flow chart of a nitrogen oxide reduction apparatus of the conventional exhaust gas,

2 is a flowchart of a method for reducing nitrogen oxides in exhaust gas according to the present invention;

3 is an ammonia slip start diagram of the method for reducing nitrogen oxides of the exhaust gas according to the present invention;

4 is a nitrogen oxide slip start diagram of the method for reducing nitrogen oxides of the exhaust gas according to the present invention;

5 is a flow chart of the nitrogen oxide reduction device of the exhaust gas according to the present invention.

<Description of the symbols for the main parts of the drawings>

200: first step 210: second step

220: third step 240: ammonia control step

250: nitrogen oxide control step 260: return step

The present invention relates to a method and apparatus for reducing nitrogen oxides in exhaust gases, and in particular, nitrogen oxides in exhaust gases, which reduce the installation cost and process time of the sensor by installing an integrated sensor that detects the amount of nitrogen by uniting the ammonia sensor and the nitrogen oxide sensor. It relates to a reduction method and apparatus.

In general, the exhaust gas discharged from the engine through the exhaust manifold is guided to a catalytic converter formed in the middle of the exhaust pipe and purified, and the noise is attenuated while passing through the muffler and then released into the atmosphere through the tail exhaust pipe. .

The catalytic converter is a type of diesel particulate filter (DPF) that serves to treat contaminants contained in the exhaust gas.

In addition, a catalyst carrier for trapping particulate matter (PM) included in the exhaust gas is formed inside the catalytic converter to purify various exhaust gases discharged from the engine through a chemical conversion process.

One of the types of catalysts applied to the catalytic converter which plays such a role is Selective Catalytic Reduction (SCR).

Selective Catalytic Reduction Devices (SCRs) are termed 'selective' catalytic reduction in the sense that reducing agents such as CO react better with NOx in oxygen and NOx.

Among the selective reduction catalysts, ammonia-SCR uses ammonia as a reductant to purify NOx. It has excellent selectivity for NOx and has the advantage of promoting the reaction between NO and ammonia in the presence of oxygen. It is known to be advantageous for application to diesel exhaust gases.

In fact, ammonia-SCR has been proven in its performance in thermal power plants, which are large fixed pollution sources, and Urea-SCR (Urea-SCR) is intended to selectively remove NOx by applying such ammonia-SCR to automobiles.

The urea-SCR may be regarded as ammonia-SCR based on the SCR catalyst because the urea-SCR is injected into the urea aqueous solution upstream of the SCR catalyst to selectively reduce NOx using ammonia generated as the urea decomposes.

In addition, in order to cope with tougher future EURO-V emission regulations, it is necessary to install an efficient NOx removal after-treatment device for diesel vehicles. Such post-treatment methods include ammonia (Ammonia, NH3) in high-temperature fossil fuel products (exhaust). Injecting additives (reducing agents) such as Urea: NH2CONH2, or high temperature exhaust (170 ~ 600 ℃) and additives in the catalytic bed, the mixture is reacted with each other. Selective Catalytic Reduction of NOx (SCR of NOx) and higher temperature exhaust (800 ~ 1100 ℃) without additives and additives to reduce NOx to nitrogen There is a selective non-catalytic reduction of NOx.

Many studies applying the aftertreatment device report the possibility of high efficiency NOx removal, which is considered as a potential alternative as a NOx reduction device for future diesel vehicles.

1 is a flow chart of a conventional nitrogen oxide reduction device.

As shown in FIG. 1, a urea injection injector is installed at a rear end of a Catalyzed Particulate Filter (CPF) to reduce NOx in exhaust gas components of engine combustion, and the injected urea is mixed well in a mixer. Reaction with NOx is reduced to N2 and H2O in the catalyst section.

In addition, the amount of slipped NOx and the amount of ammonia are sensed by the NOx sensor and the ammonia sensor installed at the rear of the catalyst unit.

Here, the more urea is injected, the more NOx emission is reduced, but when excessively sprayed over a certain level, an unpleasant odor is emitted due to slipped ammonia, which minimizes NOx by chemical reaction with NOx. Skill is needed.

Accordingly, the amount of slipped ammonia is sensed by the ammonia sensor and fed back to the ECU, and the ECU instructs the urea injection injector to appropriately adjust the amount of urea injected.

Here, the SCR system is a new technology introduced in order to cope with future exhaust regulations, but there is a problem that the production cost increases due to the addition of the after-treatment device and the Nox sensor and the ammonia sensor.

Therefore, the present invention has been invented to solve the above-mentioned problems, and the amount of urea is injected by the injector by the injector so that the nitrogen oxides are reduced, and after determining whether the amount of nitrogen detected by the integrated sensor is greater than or equal to the reference value, the amount of nitrogen Above this threshold, the urea injection volume of the injector decreases at a constant rate, and when the amount of nitrogen detected by the integrated sensor increases for a certain time after the decrease of the urea volume, the urea injection volume of the injector is reset to a value that is increased from the preset value by a predetermined amount. It is an object of the present invention to provide a method and apparatus for reducing nitrogen oxides in exhaust gas, in which a sensor and a nitrogen oxide sensor are united so that a nitrogen oxide reduction device equipped with an integrated sensor for detecting nitrogen amount is efficiently operated to reduce installation costs and process time.

In order to achieve the above object, the present invention provides a method for reducing nitrogen oxides in an exhaust gas, comprising: a first step of urea spraying by a preset value Qi by an injector to reduce nitrogen oxides; A second step of determining whether the amount of nitrogen detected by the integrated sensor is greater than or equal to the reference value H; A third step of reducing the urea injection amount of the injector by a predetermined ratio ΔQ1 / Δt1 when the amount of nitrogen is greater than or equal to the reference value H in the second step; After reducing the amount of urea in the third step, characterized in that it comprises a fourth step of changing the amount of urea injection of the injector according to the amount of nitrogen detected by the integrated sensor.

In a preferred embodiment, in the fourth step, when the amount of nitrogen detected by the integrated sensor decreases, the urea injection amount of the injector continues to decrease at a constant ratio (ΔQ1 / Δt1) until the nitrogen amount reaches the reference value (H). Ammonia control step;

When the amount of nitrogen detected by the integrated sensor increases for a certain time (Δt2), the nitrogen oxide is set to a value that increases the amount of urea injection from the injector to the constant amount (ΔQ2) until the nitrogen reaches the reference value (H). Characterized in that the adjustment step.

In another preferred embodiment, the ammonia control step and the nitrogen oxide control step further includes a return step of returning the urea injection amount of the injector to the preset value Qi when the amount of nitrogen detected by the integrated sensor reaches the reference value H. Characterized in that.

In another preferred embodiment, when the ammonia control step is repeated three or more times consecutively, the urea injection amount preset value (Qi) of the injector is reset to a predetermined value (ΔQ3) reduced value, the nitrogen oxide control step is When repeated three or more times in succession, the urea injection amount preset value Qi of the injector is further characterized in that it further comprises an adjustment step of resetting to a value increased by a constant value ΔQ4.

In another preferred embodiment, an apparatus for reducing nitrogen oxides in exhaust gas, comprising: an exhaust pipe through which exhaust gas containing nitrogen oxide passes; An injector through which urea is injected to purge nitrogen oxides on one side of the exhaust pipe; A mixer in which urea injected from the injector and nitrogen oxide are mixed; A catalytic part for promoting a reaction between the urea and the nitrogen oxide mixed in the mixer; Characterized in that it consists of an integrated sensor for measuring the amount of nitrogen at the rear end of the exhaust pipe.

As a result, the integrated sensor detects the amount of nitrogen, and the nitrogen oxide sensor and the ammonia sensor are united, thereby satisfying the enhanced exhaust regulation and reducing the time, cost, and process for mounting the sensor.

Hereinafter, a control process of the present invention will be described in detail with reference to the accompanying drawings.

2 is a flowchart illustrating a method for reducing nitrogen oxides in exhaust gas according to the present invention.

As shown in Figure 2, when the engine is running, urea is injected from the injector to reduce the amount of nitrogen oxides, nitrogen (N) component is detected by the integrated sensor to determine whether or not the proper injection of urea, the amount of nitrogen If the reference value is higher than the urea injection amount is increased, and the injection amount of urea is controlled according to the change of the nitrogen amount after the injection.

First, in the first step 200, the urea of the preset value Qi is injected from the injector located at the rear of the smoke reduction device so that the amount of nitrogen oxide is reduced, and the integrated sensor at the rear of the catalytic part detects the nitrogen component.

Here, the integrated sensor is a nitrogen oxide sensor and ammonia sensor is integrated into one, and the nitrogen oxide (NOx) and ammonia (NH3) is due to the common nitrogen content.

Next, the second step 210 determines whether the amount of nitrogen detected by the integrated sensor at the rear end of the catalyst unit is greater than or equal to the reference value (H).

Here, the determination of whether or not the nitrogen amount is more than the reference value is to determine the excessive increase of nitrogen oxide or ammonia.

Next, in the third step 220, when the amount of nitrogen detected by the integrated sensor is equal to or greater than the reference value H, the ECU transmits a reduction signal to the injector, and the urea injection amount of the injector decreases at a constant ratio (ΔQ1 / Δt1). .

Here, the increase in the amount of nitrogen above the reference value may be determined to increase the slip amount of the nitrogen oxide or the slip amount of ammonia, but once the slip amount of ammonia is determined to increase, the injection amount of urea is reduced.

Next, in the fourth step, the ammonia control step 240, when the amount of nitrogen detected by the integrated sensor decreases with a negative slope, the urea injection amount is continuously increased until the nitrogen amount reaches the reference value (H). / Δt1).

Here, when the amount of urea injection decreases, it is recognized that the nitrogen content decreases because the amount of nitrogen detected by the amount of ammonia slip increases because the amount of ammonia is greater than the amount of nitrogen oxides. Urea injection volume decreases in succession

In addition, in the fourth step, the nitrogen oxide control step 250, when the amount of nitrogen detected by the integrated sensor increases by a predetermined time (Δt2) plus the slope, the urea injection amount is established until the nitrogen amount reaches the reference value (H). In stationary Qi, a certain amount ΔQ2 is increased as added.

Here, although the amount of urea injection decreases, it is recognized that the amount of nitrogen increases because ammonia is less than nitrogen oxide and the amount of nitrogen increases due to the slip amount of nitrogen oxides. The amount of urea injection increases significantly for the reduction.

Next, when the nitrogen amount of the integrated sensor reaches the reference value H in the ammonia and nitrogen oxide control step, the return step 260 returns the urea injection amounts in both steps to the preset value Qi.

This is because there is no need to change the injection amount of urea when the nitrogen amount is normally detected.

Next, when the amount of nitrogen of the integrated sensor does not reach the reference value and the ammonia control step 240 is repeated three or more times in succession, the preset value Qi of the urea injection amount is reset to a predetermined value (ΔQ3). When the oxide control step 250 is repeated three times or more consecutively, the preset value Qi of the urea injection amount is reset to a value increased by a constant value ΔQ4.

Here, the ammonia control step 240 is repeated three times or more due to the increase in the amount of ammonia slip which does not react with nitrogen oxides because the amount of urea's predetermined value injection is greater than the appropriate amount.

In addition, repeating the nitrogen oxide control step 250 three or more times is due to the increase in the amount of nitrogen oxide slip which cannot be combined with ammonia because the predetermined amount of urea injection is less than an appropriate amount, and thus an increase setting of the installation is necessary.

FIG. 3 is an ammonia slip start diagram of a method for reducing nitrogen oxides of exhaust gas according to the present invention, and FIG. 4 is a start diagram of nitrogen oxide slip of a method for reducing nitrogen oxides of exhaust gas according to the present invention.

As shown in FIG. 3, when the nitrogen detection amount is higher than the reference value H due to the ammonia slip, the urea injection amount decreases from the preset value Qi to a predetermined ratio (ΔQ1 / Δt1), and the nitrogen detection amount is reduced due to the injection amount decrease. When lowering below H), the urea injection amount returns to the preset value Qi.

As shown in FIG. 4, when the nitrogen detection amount is greater than the reference value H due to the nitrogen oxide slip, the urea injection amount is once reduced from the preset value Qi to a predetermined ratio ΔQ1 / Δt1.

Thus, even though the amount of urea injection decreases, when the nitrogen detection amount is increased by a certain time (Δt2), the amount of urea injection is increased from the preset value Qi to a value added by the constant value (ΔQ2), and thus the nitrogen detection amount is a reference value (H). When it is lower than), the urea injection amount returns to the preset value Qi.

5 is a flowchart of a nitrogen oxide reduction apparatus for exhaust gas according to the present invention.

As shown in FIG. 5, the exhaust gas moves along the exhaust pipe, and the nitrogen oxide contained in the exhaust gas is mixed with urea injected from the injector by the mixer, and the reaction is promoted by the catalyst part.

In addition, the integrated sensor is a nitrogen oxide sensor and ammonia sensor united, serves to measure the amount of nitrogen, the amount of urea injected from the injector according to the measured amount of nitrogen is controlled by the method for reducing the nitrogen oxides of the exhaust gas.

As described above, the nitrogen oxide reduction method of the exhaust gas according to the present invention provides the following effects.

First, the integrated sensor detects the amount of nitrogen atoms, so the nitrogen oxide sensor and the ammonia sensor are united.

Second, the nitrogen oxide reduction device that is conventionally operated by two sensors is operated by one sensor, reducing the purchase cost of the sensor,

Third, the time and cost for additional mounting of the sensor is reduced, the process is simplified.

Claims (5)

In the nitrogen oxide reduction method of the exhaust gas, A first step of injecting urea by a preset value Qi by the injector to reduce nitrogen oxides; A second step of determining whether the amount of nitrogen detected by the integrated sensor is greater than or equal to the reference value H; A third step of reducing the urea injection amount of the injector by a predetermined ratio ΔQ1 / Δt1 when the amount of nitrogen is greater than or equal to the reference value H in the second step; And a fourth step of changing the amount of urea injection of the injector according to the amount of nitrogen detected by the integrated sensor after the reduction of the amount of urea in the third step. The method of claim 1, wherein in the fourth step, when the amount of nitrogen detected by the integrated sensor decreases, the urea injection amount of the injector continues to decrease at a constant ratio (ΔQ1 / Δt1) until the nitrogen amount reaches the reference value (H). Ammonia control step; When the amount of nitrogen detected by the integrated sensor increases for a certain time (Δt2), the nitrogen oxide is set to a value that increases the amount of urea injection of the injector from the stun set point (Qi) to a certain amount (ΔQ2) until the nitrogen reaches the reference value (H). Nitrogen oxide reduction method of the exhaust gas, characterized in that consisting of a control step. The method of claim 2, wherein the ammonia control step and the nitrogen oxide control step further comprises a return step of returning the urea injection amount of the injector to the preset value Qi when the amount of nitrogen detected by the integrated sensor is equal to or less than the reference value H. A method for reducing nitrogen oxides in exhaust gas. The method according to claim 3, wherein the ammonia control step is repeated three or more times in succession, the urea injection amount preset value (Qi) of the injector is reset to a reduced value (ΔQ3), the nitrogen oxide control step is three or more times If continuously repeated, the urea injection amount preset value (Qi) of the injector further comprises an adjustment step of resetting to a value increased by a constant value (ΔQ4) further comprises the step of reducing nitrogen oxides of the exhaust gas. In the nitrogen oxide reduction device of the exhaust gas, An exhaust pipe through which exhaust gas containing nitrogen oxide passes; An injector through which urea is injected to purify nitrogen oxide on one side of the exhaust pipe; A mixer in which urea injected from the injector and nitrogen oxide are mixed; A catalytic part for promoting a reaction between the urea and the nitrogen oxide mixed in the mixer; An apparatus for reducing nitrogen oxides in exhaust gases, characterized in that it comprises an integrated sensor for measuring the amount of nitrogen at the rear end of the exhaust pipe.

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