Reducing agent suitable for double-SCR aftertreatment system and preparation method of reducing agent

Abstract

The invention discloses a reducing agent suitable for a double-SCR aftertreatment system and a preparation method of the reducing agent, and belongs to the field of tail gas emission of diesel vehicles. The reducing agent comprises the following components in percentage by mass: 0.01-0.2% of a surfactant, 15-30% of high-purity urea particles, 3-15% of carbonate, 0.001-0.2% of a defoaming agent, 0.001-0.05% of a buffering agent and the balance of high-purity water. The preparation method comprises the following steps: adding carbonate and high-purity urea particles into high-purity water, adding a surfactant diluted with pure water, adding a defoaming agent, and dropwise adding a buffering agent to adjust the pH value to 7.5-8.0, thereby obtaining the reducing agent. According to the reducing agent suitable for the double-SCR aftertreatment system and the preparation method of the reducing agent, the effect of reducing consumption of the reducing agent in the operation process of the double-SCR aftertreatment system can be achieved.

Description

Technical Field

[0001] The invention relates to tail gas emission of diesel vehicles, in particular to a reducing agent suitable for a dual SCR post-processing system and a preparation method thereof. Background Art

[0002] The harmful substances in diesel vehicle exhaust are mainly nitrogen oxide particles. Technical means can be used to reduce particle emissions inside the engine. Urea can be used to reduce the emission of nitrogen oxide particles in the exhaust after-treatment device. Urea decomposes into ammonia at high temperature, and reacts with nitrogen oxides under the action of a catalyst to generate harmless nitrogen and water, thereby achieving exhaust emissions from the diesel engine.

[0003] The automotive urea standard solution (AUS32) is suitable for trucks, buses, non-road heavy-duty vehicles and other vehicles with diesel engines that have a selective catalytic reduction (SCR) system. With the continuous upgrading and improvement of laws and regulations, exhaust emission requirements are becoming more and more stringent. At present, the Euro VII emission rule proposal has further restricted harmful exhaust emissions such as nitrogen oxides. In order to meet the stringent exhaust emission requirements, it is planned to use an engine after-treatment system equipped with dual SCR to replace the existing engine after-treatment solution. Its specific composition is SCR1+ASC1+DOC+DPF+SCR2+ASC2. The modified engine after-treatment system is more efficient in reducing nitrogen oxides, but relatively speaking, the consumption of automotive urea aqueous solution is much higher than that of the existing engine after-treatment system. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a reducing agent suitable for a dual SCR after-treatment system to reduce the consumption of the reducing agent during the operation of the dual SCR after-treatment system.

[0005] Another object of the present invention is to provide a method for preparing a reducing agent suitable for a dual SCR after-treatment system, so as to reduce the consumption of the reducing agent during the operation of the dual SCR after-treatment system.

[0006] Technical solution: The reducing agent suitable for the dual SCR post-treatment system of the present invention includes, by mass fraction, 0.01-0.2% of surfactant, 15-30% of high-purity urea granules, 3-15% of carbonate, 0.001-0.2% of defoaming agent, 0.001-0.05% of buffer, and the rest is high-purity water.

[0007] Preferably, the surfactant is a water-soluble substance.

[0008] Preferably, the surfactant is one or more of fatty alcohol polyoxyethylene ether, polysorbate, and alkylphenol polyoxyethylene ether.

[0009] Preferably, the carbonate is one or more of ammonium carbonate and ammonium bicarbonate.

[0010] Preferably, the mass fraction ratio of the carbonate is 12-15%.

[0011] Preferably, the defoamer is a silicone defoamer.

[0012] Preferably, the buffer is one or more of citric acid-ammonium citrate buffer and acetic acid-ammonium acetate buffer.

[0013] The method for preparing a reducing agent suitable for a dual SCR post-treatment system of the present invention comprises the following steps:

[0014] (1) adding carbonate and high-purity urea granules into high-purity water and stirring until dissolved to obtain a reducing agent stock solution;

[0015] (2) diluting the surfactant with pure water and adding it to the reducing agent stock solution described in step (1), stirring and dissolving; adding a defoaming agent, stirring and dissolving, to obtain a urea solution;

[0016] (3) Using a pH meter to measure the pH value of the urea solution in step (2), adding a buffer to adjust the pH to 7.5-8.0, thereby obtaining a reducing agent.

[0017] Preferably, the carbonate in step (1) is one or more of ammonium carbonate and ammonium bicarbonate, preferably ammonium carbonate.

[0018] Preferably, the surfactant in step (2) is one or more of fatty alcohol polyoxyethylene ether, polysorbate, and alkylphenol polyoxyethylene ether, preferably fatty alcohol polyoxyethylene ether.

[0019] Preferably, the defoaming agent in step (2) is a silicone defoaming agent.

[0020] Preferably, the buffer in step (3) is one or more of citric acid-ammonium citrate buffer and acetic acid-ammonium acetate buffer, preferably citric acid-ammonium citrate buffer.

[0021] Principle of the invention: Since the urea hydrolysis reaction starts at above 60°C but the reaction speed is extremely slow, the reaction speed gradually increases above 80°C, and the reaction speed increases sharply above 145°C; while ammonium carbonate or ammonium bicarbonate can begin to decompose at room temperature, and the decomposition speed is faster at 60°C, producing a large amount of ammonia and carbon dioxide. The composition of the exhaust gas entering the primary SCR system is changed, so that the hydrocarbons therein are partially incompletely burned, and carbon monoxide is generated. Under the joint action of ammonia and carbon monoxide, the nitrogen oxides in the exhaust gas are reduced, and the reduction performance of the reducing agent is improved. Under the joint action of the change in the surface tension of the surfactant and the release of carbon monoxide, the consumption of the reducing agent during the operation of the diesel engine equipped with a dual SCR after-treatment system is reduced.

[0022] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) By adding carbonate to the urea aqueous solution, the nitrogen oxides in the exhaust gas are reduced under the combined action of ammonia and carbon monoxide, so that the reducing performance of the reducing agent is improved; (2) Under the combined action of the change in the surface tension of the surfactant and the release of carbon monoxide, the consumption of the reducing agent during the operation of a diesel engine equipped with a dual SCR after-treatment system is reduced. DETAILED DESCRIPTION

[0023] The technical solution of the present invention is further described below in conjunction with embodiments.

[0024] Example 1

[0025] The reducing agent applicable to the dual SCR post-treatment system of the present invention comprises, by mass fraction, 0.05% of fatty alcohol polyoxyethylene ether, 23% of high-purity urea particles, 10% of ammonium carbonate, 0.002% of organosilicon defoamer, 0.005% of citric acid-ammonium citrate buffer, and the rest is high-purity water.

[0026] The method for preparing a reducing agent suitable for a dual SCR post-treatment system of the present invention comprises the following steps:

[0027] (1) adding 10% ammonium carbonate and 23% high-purity urea granules in a mass fraction ratio to 66% high-purity water, stirring until dissolved, to obtain a reducing agent stock solution;

[0028] (2) diluting 0.05% fatty alcohol polyoxyethylene ether by 100-1000 times with pure water and adding the mixture to the reducing agent solution described in step (1), stirring and dissolving; adding 0.002% organosilicon defoaming agent, stirring and dissolving, and obtaining a urea solution;

[0029] (3) Using a pH meter to measure the pH value of the urea solution in step (2), adding citric acid-ammonium citrate buffer dropwise to adjust the pH to 7.5-8.0, thereby preparing a reducing agent.

[0030] Example 2

[0031] The reducing agent applicable to the dual SCR post-treatment system of the present invention comprises, by mass fraction, 0.05% of fatty alcohol polyoxyethylene ether, 18% of high-purity urea particles, 15% of ammonium carbonate, 0.002% of organosilicon defoamer, 0.005% of citric acid-ammonium citrate buffer, and the rest is high-purity water.

[0032] The method for preparing a reducing agent suitable for a dual SCR post-treatment system of the present invention comprises the following steps:

[0033] (1) adding 15% ammonium carbonate and 18% high-purity urea granules in a mass fraction ratio to 66% high-purity water, stirring until dissolved, to obtain a reducing agent stock solution;

[0034] (2) diluting 0.05% fatty alcohol polyoxyethylene ether by 100-1000 times with pure water and adding the mixture to the reducing agent solution described in step (1), stirring and dissolving; adding 0.002% organosilicon defoaming agent, stirring and dissolving, and obtaining a urea solution;

[0035] (3) Using a pH meter to measure the pH value of the urea solution in step (2), adding citric acid-ammonium citrate buffer dropwise to adjust the pH to 7.5-8.0, thereby preparing a reducing agent.

[0036] Example 3

[0037] The reducing agent applicable to the dual SCR post-treatment system of the present invention comprises, by mass fraction, 0.05% of fatty alcohol polyoxyethylene ether, 30% of high-purity urea particles, 3% of ammonium carbonate, 0.002% of organosilicon defoamer, 0.005% of citric acid-ammonium citrate buffer, and the rest is high-purity water.

[0038] The method for preparing a reducing agent suitable for a dual SCR post-treatment system of the present invention comprises the following steps:

[0039] (1) adding 3% ammonium carbonate and 30% high-purity urea granules in a mass fraction ratio to 66% high-purity water, stirring until dissolved, to obtain a reducing agent stock solution;

[0040] (2) diluting 0.05% fatty alcohol polyoxyethylene ether by 100-1000 times with pure water and adding the mixture to the reducing agent solution described in step (1), stirring and dissolving; adding 0.002% organosilicon defoaming agent, stirring and dissolving, and obtaining a urea solution;

[0041] (3) Using a pH meter to measure the pH value of the urea solution in step (2), adding citric acid-ammonium citrate buffer dropwise to adjust the pH to 7.5-8.0, thereby preparing a reducing agent.

[0042] Comparative Example 1

[0043] The reducing agent applicable to the dual SCR post-treatment system of the present invention comprises, by mass fraction, 0.05% of fatty alcohol polyoxyethylene ether, 15% of high-purity urea particles, 18% of ammonium carbonate, 0.002% of organosilicon defoamer, 0.005% of citric acid-ammonium citrate buffer, and the rest is high-purity water.

[0044] The method for preparing a reducing agent suitable for a dual SCR post-treatment system of the present invention comprises the following steps:

[0045] (1) adding 18% ammonium carbonate and 15% high-purity urea granules in a mass fraction ratio to 66% high-purity water, stirring until dissolved, to obtain a reducing agent stock solution;

[0046] (2) diluting 0.05% fatty alcohol polyoxyethylene ether by 100-1000 times with pure water and adding the mixture to the reducing agent solution described in step (1), stirring and dissolving; adding 0.002% organosilicon defoaming agent, stirring and dissolving, and obtaining a urea solution;

[0047] (3) Using a pH meter to measure the pH value of the urea solution in step (2), adding citric acid-ammonium citrate buffer dropwise to adjust the pH to 7.5-8.0, thereby preparing a reducing agent.

[0048] The reducing agents prepared in Examples 1-3 and Comparative Example 1 and common automotive urea aqueous solution were tested for exhaust emissions and reducing agent consumption using an engine bench equipped with a close-coupled dual SCR post-treatment system. Table 1 shows the test results.

[0049] Table 1 Test results of close-coupled dual SCR aftertreatment bench

[0050]

[0051] According to the test results, the introduction of carbonate can reduce the consumption of reducing agent to a certain extent and improve the reducing performance of the reducing agent, but too much carbonate replacing urea will lead to insufficient release of ammonia and reduce its reducing performance.

Claims

1. A reducing agent suitable for a dual SCR post-treatment system, characterized in that: The composition includes, by mass fraction, 0.01-0.2% of surfactant, 15-30% of high-purity urea granules, 3-15% of carbonate, 0.001-0.2% of defoaming agent, 0.001-0.05% of buffer, and the rest is high-purity water.

2. The reducing agent suitable for a dual SCR post-treatment system according to claim 1, characterized in that: The surfactant is one or more of fatty alcohol polyoxyethylene ether, polysorbate, and alkylphenol polyoxyethylene ether.

3. The reducing agent suitable for a dual SCR post-treatment system according to claim 1, characterized in that: The carbonate is one or more of ammonium carbonate and ammonium bicarbonate.

4. The reducing agent suitable for a dual SCR post-treatment system according to claim 1, characterized in that: The mass fraction ratio of the carbonate is 12-15%.

5. The reducing agent suitable for a dual SCR post-treatment system according to claim 1, characterized in that: The buffer is one or more of citric acid-ammonium citrate buffer and acetic acid-ammonium acetate buffer.

6. A method for preparing a reducing agent suitable for a dual SCR post-treatment system according to claim 1, characterized in that: The following steps are involved: (1) adding carbonate and high-purity urea granules into high-purity water and stirring until dissolved to obtain a reducing agent stock solution; (2) diluting the surfactant with pure water and adding it to the reducing agent stock solution described in step (1), stirring and dissolving; adding a defoaming agent, stirring and dissolving, to obtain a urea solution; (3) Using a pH meter to measure the pH value of the urea solution in step (2), adding a buffer to adjust the pH to 7.5-8.0, thereby obtaining a reducing agent.

7. The preparation method according to claim 6, characterized in that: The carbonate in step (1) is one or more of ammonium carbonate and ammonium bicarbonate.

8. The preparation method according to claim 6, characterized in that: In step (2), the surfactant is one or more of fatty alcohol polyoxyethylene ether, polysorbate, and alkylphenol polyoxyethylene ether.

9. The preparation method according to claim 6, characterized in that: The defoaming agent in step (2) is an organosilicon defoaming agent.

10. The preparation method according to claim 6, characterized in that: The buffer in step (3) is one or more of citric acid-ammonium citrate buffer and acetic acid-ammonium acetate buffer.

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