Control method of reducing agent generating device, waste gas purification method, reducing agent generating system and waste gas purification system

Abstract

A control method for a reducing agent generating device 100 is provided. The reducing agent generating device 100 includes: a sprayer 10 capable of spraying a mist reducing agent precursor 50; and a heater 20 including a ceramic substrate 21, which is arranged on the downstream side of the sprayer 10 and capable of heating the reducing agent precursor 50 to generate a reducing agent 60. The control method includes the following steps: a permeation step, in which the mist reducing agent precursor 50 is sprayed from the sprayer 10 when the heater 20 is not heating, so that the reducing agent precursor 50 permeates into the ceramic substrate 21; and a heating step A, in which, after the permeation step, the reducing agent precursor 50 is heated by the heater 20, and the mist reducing agent precursor 50 is sprayed from the sprayer 10 to generate the reducing agent 60.

Description

Technical Field

[0001] The present invention relates to a control method of a reducing agent generating device, an exhaust gas purification method, a reducing agent generating system and an exhaust gas purification system. Background Art

[0002] Reducing agents can reduce other compounds in a redox reaction and are used in various applications. For example, in a urea SCR system, which is known as one of the exhaust gas purification technologies, urea is decomposed by the heat of the exhaust gas to generate ammonia (reducing agent) that reacts with NOx to reduce it to nitrogen and water.

[0003] Conventional urea SCR systems require an exhaust gas temperature of 200°C or higher to generate ammonia from urea. When the exhaust gas temperature is low, ammonia cannot be sufficiently generated from urea. When the exhaust gas temperature is low, the amount of ammonia required for treating NOx may be insufficient.

[0004] Therefore, Patent Document 1 describes the following technology, namely, in a reducing agent injection device, a mist of urea aqueous solution is sprayed into a honeycomb heater that has been electrically heated, thereby enabling sufficient generation of ammonia even when the exhaust gas temperature is low, wherein the reducing agent injection device includes a honeycomb structure (hereinafter referred to as a "honeycomb heater") and a urea spray device that sprays a mist of urea aqueous solution, wherein the honeycomb structure has a honeycomb structure portion and a pair of electrode portions arranged on its side.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent No. 6487990 Summary of the invention

[0008] In the reducing agent injection device of Patent Document 1, after spraying the mist-like urea aqueous solution, the decomposition reaction of urea takes some time, and the generation of ammonia (reducing agent) is delayed. On the other hand, the amount of NOx in the exhaust gas increases immediately after the engine is started, so the delay in the generation of ammonia will lead to a decrease in the purification performance of the exhaust gas.

[0009] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a control method of a reducing agent production device and a reducing agent production system capable of quickly producing a reducing agent.

[0010] Another object of the present invention is to provide an exhaust gas purification method and an exhaust gas purification system that can quickly generate a reducing agent and perform exhaust gas purification immediately after the engine is started.

[0011] The above-mentioned problems are solved by the following present invention, and the present invention is defined as follows.

[0012] That is, the present invention is a control method of a reducing agent generating device, the reducing agent generating device comprising:

[0013] a sprayer capable of spraying a reducing agent precursor in a mist form; and

[0014] a heater including a ceramic substrate, the heater being disposed on the downstream side of the sprayer and capable of heating the reducing agent precursor to generate the reducing agent,

[0015] Characterized in that the control method comprises the following steps:

[0016] a permeation step of spraying the reducing agent precursor in a mist form from the sprayer when the heater is not heating, so that the reducing agent precursor permeates into the ceramic substrate; and

[0017] A heating step A is a step of heating the reducing agent precursor by the heater after the infiltration step, spraying the reducing agent precursor in a mist form from the sprayer, and generating the reducing agent.

[0018] Furthermore, the present invention is an exhaust gas purification method, characterized by comprising a step of bringing the reducing agent generated by the above-mentioned control method into contact with exhaust gas containing NOx.

[0019] In addition, the present invention is a reducing agent generation system, characterized in that it comprises:

[0020] a reducing agent generating device including an atomizer capable of spraying a reducing agent precursor in a mist form, and a heater including a ceramic substrate disposed on a downstream side of the atomizer and capable of heating the reducing agent precursor to generate the reducing agent; and

[0021] a control device including a reducing agent precursor spray control unit for controlling the spraying of the reducing agent precursor in a mist form from the sprayer, and a heater control unit for controlling the heating of the reducing agent precursor by the heater,

[0022] The reducing agent precursor spray control unit performs control to generate a control signal for spraying the reducing agent precursor in a mist form from the sprayer when the heater is not heating, and to allow the reducing agent precursor to permeate into the ceramic substrate.

[0023] In addition, the present invention is an exhaust gas purification system, which includes the above-mentioned reducing agent generation system,

[0024] The exhaust gas purification system is characterized in that:

[0025] The reducing agent generating device is provided in an exhaust pipe through which the exhaust gas containing NOx can flow or in a branch pipe connected to the exhaust pipe.

[0026] Effects of the Invention

[0027] According to the present invention, a control method of a reducing agent production device and a reducing agent production system capable of rapidly producing a reducing agent can be provided.

[0028] Furthermore, according to the present invention, it is possible to provide an exhaust gas purification method and an exhaust gas purification system capable of quickly generating a reducing agent and performing exhaust gas purification immediately after the engine is started. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic cross-sectional view showing a reducing agent generating device used in a reducing agent generating device control method and a reducing agent generating system according to an embodiment of the present invention.

[0030] Figure 2 This is a flowchart for explaining a conventional control method of a reducing agent generating device.

[0031] Figure 3 This is a flowchart for explaining a control method of the reducing agent generator according to the embodiment of the present invention.

[0032] Figure 4 This is a flowchart for explaining a control method of the reducing agent generator according to the embodiment of the present invention.

[0033] Figure 5 This is a graph showing the relationship between time and the amount of ammonia (reducing agent) generated in the control method of the reducing agent generator according to the embodiment of the present invention and a conventional control method of the reducing agent generator.

[0034] Figure 6 It is a schematic cross-sectional view for explaining the reducing agent generation test in the example. DETAILED DESCRIPTION

[0035] The embodiments of the present invention are described in detail below with reference to the accompanying drawings. The present invention is not limited to the following embodiments, and it should be understood that within the scope of the present invention, based on the common knowledge of those skilled in the art, the following embodiments may be appropriately modified, improved, etc. and the resulting solutions also fall within the scope of the present invention.

[0036] Figure 1 It is a schematic cross-sectional view showing a reducing agent generating device used in a reducing agent generating device control method and a reducing agent generating system according to an embodiment of the present invention.

[0037] like Figure 1 As shown, the reducing agent generating device 100 includes: an atomizer 10 that can spray a reducing agent precursor 50 in a mist form; and a heater 20 including a ceramic substrate 21 that is disposed downstream of the atomizer 10 and can heat the reducing agent precursor 50 to generate a reducing agent 60 .

[0038] Regarding a preferred embodiment of the reducing agent generating device 100 having the above-described structure, each component will be described in detail.

[0039] (1-1) Sprayer 10

[0040] The type of the sprayer 10 is not particularly limited as long as it can spray the reductant precursor 50 in a mist form, and is preferably an electromagnetic type, an ultrasonic type, a piezoelectric actuator type or an atomizer type. By adopting the above-mentioned sprayer, the reductant precursor 50 in a mist form can be easily sprayed. In addition, if an electromagnetic type, an ultrasonic type or a piezoelectric actuator type is adopted, the reductant precursor 50 in a mist form can be sprayed without using air. Therefore, it is not necessary to heat the air used for spraying the reductant precursor 50, and the heating energy can be reduced. The size (diameter) of the droplets of the reductant precursor 50 in a mist form sprayed from the sprayer 10 is preferably less than 0.3 mm. If the size of the droplets of the reductant precursor 50 is larger than 0.3 mm, it is sometimes difficult to vaporize when heated using the ceramic substrate 21.

[0041] Here, the electromagnetic sprayer 10 is a device that uses electromagnetic vibration or an electromagnetic electric field to move a piston forward and backward to spray out a mist of the reducing agent precursor 50. In addition, the ultrasonic sprayer 10 is a device that uses ultrasonic vibration to spray out a mist of the reducing agent precursor 50. In addition, the piezoelectric actuator sprayer 10 is a device that uses the vibration of a piezoelectric element to spray out a mist of the reducing agent precursor 50. In addition, the atomizer sprayer 10 is a device that, for example, draws out the reducing agent precursor 50 using a tube and blows the reducing agent precursor 50 into a mist from the opening at the front end of the tube using air and sprays it. It should be noted that the atomizer sprayer 10 may be a device that forms a plurality of small openings at the front end of the nozzle and sprays out the mist of the reducing agent precursor 50 from the openings.

[0042] Regarding the nebulizer 10, for example, Figure 1 As shown, when the ceramic substrate 21 is a columnar ceramic honeycomb substrate 22, in order to easily spray the mist-like reducing agent precursor 50 toward the first end face 26a side of the columnar ceramic honeycomb substrate 22, it is preferred that the spray direction of the reducing agent precursor 50 (the direction in which the droplets fly out) is toward the first end face 26a side of the columnar ceramic honeycomb substrate 22.

[0043] (1-2) Heater 20

[0044] The heater 20 is not particularly limited. Figure 1 As shown, it is preferred to include a columnar ceramic honeycomb substrate 22 and a pair of electrode portions 25 disposed on the side of the columnar ceramic honeycomb substrate 22, the columnar ceramic honeycomb substrate 22 having an outer peripheral wall 23 and a partition wall 24, the partition wall 24 being disposed on the inner side of the outer peripheral wall 23 and partitioning a plurality of compartments 27, the plurality of compartments 27 forming a flow path from the first end face 26a to the second end face 26b. By adopting the heater 20 of the above structure, when a voltage is applied to the pair of electrode portions 25, the columnar ceramic honeycomb substrate 22 can be heated by energizing. In addition, the heater 20 of the above structure can increase the surface area, so that the reducing agent precursor 50 can be heated with less energy to generate the reducing agent 60.

[0045] (1-2-1) Columnar ceramic honeycomb substrate 22

[0046] The material of the outer peripheral wall 23 and the partition wall 24 constituting the columnar ceramic honeycomb substrate 22 can be ceramic without any particular limitation, and preferably a silicon-silicon carbide composite material or silicon carbide is used as the main component, and more preferably a silicon-silicon carbide composite material is used as the main component. By adopting the above materials, the resistivity of the columnar ceramic honeycomb substrate 22 can be easily adjusted to an arbitrary value by changing the ratio of silicon carbide to silicon.

[0047] Here, in this specification, "silicon-silicon carbide composite material" refers to a material containing silicon carbide particles as aggregates and metal silicon as a binding material for bonding the silicon carbide particles. The silicon-silicon carbide composite material is preferably a material in which a plurality of silicon carbide particles are bonded by metal silicon. In addition, in this specification, "silicon carbide" refers to a material formed by sintering silicon carbide particles to each other. In addition, in this specification, "main component" refers to a component with a content of 90% by mass or more.

[0048] The resistivity of the columnar ceramic honeycomb substrate 22 is not particularly limited, but is preferably 0.01 to 500 Ωcm, and more preferably 0.1 to 200 Ωcm. By controlling the resistivity to be such, the columnar ceramic honeycomb substrate 22 can be efficiently heated by applying a voltage to the pair of electrode portions 25. In particular, in order to heat the columnar ceramic honeycomb substrate 22 to 160 to 600° C. using a power supply with a voltage of 12 to 200 V, it is preferable to set the resistivity to the above range.

[0049] In addition, the resistivity of the columnar ceramic honeycomb substrate 22 is a value at 25° C. In addition, the resistivity of the columnar ceramic honeycomb substrate 22 is a value measured by a four-probe method.

[0050] The surface area per unit volume of the columnar ceramic honeycomb substrate 22 is not particularly limited, but is preferably 5 cm 2 / cm 3More preferably, 8 to 45 cm 2 / cm 3 , particularly preferably 20 to 40 cm 2 / cm 3 If the surface area is 5cm 2 / cm 3 As described above, it is possible to sufficiently ensure the contact area with the reducing agent precursor 50 and appropriately control the processing speed of the reducing agent precursor 50 , that is, the generation amount (generation speed) of the reducing agent 60 .

[0051] It should be noted that the surface area of ​​the columnar ceramic honeycomb substrate 22 is the area of ​​the surface of the partition walls 24 of the columnar ceramic honeycomb substrate 22 .

[0052] From the viewpoint of infiltrating the reducing agent precursor 50 into the columnar ceramic honeycomb substrate 22 in the infiltration step described later, the total pore volume of the columnar ceramic honeycomb substrate 22 is preferably 0.3cc to 100cc. It should be noted that the required amount of reducing agent varies greatly depending on the size of the internal combustion engine such as the engine using the reducing agent generating device 100, and therefore the total volume of the columnar ceramic honeycomb substrate 22 also varies. The above-mentioned total pore volume increases in accordance with the total volume of the columnar ceramic honeycomb substrate 22.

[0053] The thickness of the partition wall 24 of the columnar ceramic honeycomb substrate 22 is preferably 0.06 to 1.5 mm, and more preferably 0.10 to 0.80 mm. If the thickness of the partition wall 24 is 1.5 mm or less, the pressure loss is reduced, and the processing speed of the reducing agent precursor 50, that is, the generation amount (generation speed) of the reducing agent 60 can be appropriately controlled. If the thickness of the partition wall 24 is 0.06 mm or more, the columnar ceramic honeycomb substrate 22 is suppressed from being destroyed by the thermal shock caused by the electric heating.

[0054] It should be noted that when the shape of the compartment 27 (the shape of the cross section orthogonal to the direction in which the compartment 27 extends) is circular, the thickness of the partition wall 24 refers to the thickness of the partition wall 24 at "the portion where the distance between the compartments 27 is the shortest (the portion where the thickness of the partition wall 24 is smaller)".

[0055] The density of the cells 27 is preferably 7 to 140 cells / cm 2 , more preferably 15 to 120 cells / cm 2 If the density of compartment 27 is 7 compartments / cm 2 The above can ensure sufficient contact area with the reducing agent precursor 50, and the processing speed of the reducing agent precursor 50, that is, the amount (generation speed) of the reducing agent 60, can be appropriately controlled. If the density of the cells 27 is 140 cells / cm 2Below this value, the pressure loss is reduced, and the processing speed of the reducing agent precursor 50, that is, the generation amount (generation speed) of the reducing agent 60 can be appropriately controlled.

[0056] In the columnar ceramic honeycomb substrate 22, a plugging portion may be provided at the end portion on the first end surface 26a side for a part of the cells 27. The material of the plugging portion is preferably the same as that of the partition walls 24, but may be another material.

[0057] The shapes of the first end face 26a and the second end face 26b are not particularly limited, and may be various shapes such as square, rectangle, other polygons, circle, ellipse, etc. In addition, the shape of the first end face 26a is the same as the shape of the second end face 26b, preferably the same as the shape of the cross section orthogonal to the direction in which the compartment 27 extends.

[0058] Regarding the size of the columnar ceramic honeycomb substrate 22, the areas of the first end surface 26a and the second end surface 26b are preferably 50 to 10000 mm 2 , more preferably 100 to 8000 mm 2 .

[0059] The shape of the cell 27 in the cross section perpendicular to the direction in which the cell 27 extends is not particularly limited, and is preferably circular, elliptical, quadrilateral, hexagonal, octagonal, or a combination thereof. By adopting such a shape, the pressure loss of the exhaust gas when flowing through the columnar ceramic honeycomb substrate 22 is reduced, and the reducing agent precursor 50 can be efficiently decomposed.

[0060] The columnar ceramic honeycomb substrate 22 may include a catalyst (eg, a urea hydrolysis catalyst) for hydrolyzing the reducing agent precursor 50. By using such a catalyst, the reducing agent 60 can be efficiently generated from the reducing agent precursor 50. Examples of such a catalyst include titanium oxide and the like.

[0061] (1-2-2) Electrode Section 25

[0062] The pair of electrode portions 25 is configured such that, in a cross section of the columnar ceramic honeycomb substrate 22 orthogonal to the direction in which the cells 27 extend, the other electrode portion 25 is disposed on the opposite side of one electrode portion 25, sandwiching the central axis of the columnar ceramic honeycomb substrate 22. In addition, the pair of electrode portions 25 are preferably formed in a strip shape along the direction in which the cells 27 extend. By adopting such a configuration, when a voltage is applied between the pair of electrode portions 25, it is possible to suppress the current flowing through the columnar ceramic honeycomb substrate 22 from being biased, thereby suppressing the biased heating of the columnar ceramic honeycomb substrate 22.

[0063] It should be noted that the electrode portion 25 may be a pair, but may be a plurality of pairs from the viewpoint of improving the heat generation efficiency of the columnar ceramic honeycomb substrate 22 .

[0064] In addition, it is preferable that the voltage is applied to the pair of electrode portions 25 in such a way that the temperature at the first end face 26a is 900°C or less to heat the columnar ceramic honeycomb substrate 22. By directly providing a temperature measuring mechanism on the columnar ceramic honeycomb substrate 22, the temperature at the first end face 26a can be measured. Alternatively, the temperature at the first end face 26a can be estimated based on the exhaust gas temperature, the exhaust gas flow rate, and the spray amount of the reducing agent precursor 50. In addition, if the operating conditions of the engine are mapped, the measurement of the exhaust gas temperature and the exhaust gas flow rate can also be substituted.

[0065] The material of the electrode portion 25 is not particularly limited, but is preferably the same as the main component of the partition walls 24 of the columnar ceramic honeycomb substrate 22 .

[0066] The resistivity of the electrode portion 25 is preferably 0.0001 to 100 Ωcm, and more preferably 0.001 to 50 Ωcm. By setting the resistivity of the electrode portion 25 to such a range, the pair of electrode portions 25 can effectively play the role of electrodes in the exhaust pipe where the high-temperature exhaust gas flows. The resistivity of the electrode portion 25 is preferably lower than the resistivity of the columnar ceramic honeycomb substrate 22.

[0067] In addition, the resistivity of the electrode portion 25 is a value at 25° C. In addition, the resistivity of the electrode portion 25 is a value measured by a four-terminal method.

[0068] (1-3) Cylindrical Member 30 and Insulation Holding Portion 40

[0069] like Figure 1 As shown, the reducing agent generating device 100 may further include a cylindrical member 30 and an insulating holding portion 40. In this case, the heater 20 is accommodated in the cylindrical member 30, and preferably the heater 20 and the cylindrical member 30 are fixed by the insulating holding portion 40. By adopting such a configuration, the insulation between the columnar ceramic honeycomb substrate 22 provided with a pair of electrode portions 25 and the cylindrical member 30 is ensured.

[0070] The material of the tubular member 30 is not particularly limited, but stainless steel or the like is preferred.

[0071] Regarding the shape of the cylindrical member 30, in order to fit it with the columnar ceramic honeycomb substrate 22, it is preferred that the shape of the cylindrical member 30 is the same as that of the columnar ceramic honeycomb substrate 22 in the cross section perpendicular to the direction in which the cells 27 extend. Here, in this specification, "the same shape" means that when the shape of the cylindrical member 30 is square, the shape of the columnar ceramic honeycomb substrate 22 is also square; when the shape of the cylindrical member 30 is rectangular, the shape of the columnar ceramic honeycomb substrate 22 is also rectangular. It should be noted that, for example, when the shape of the cylindrical member 30 and the shape of the columnar ceramic honeycomb substrate 22 are the same shape and the shape is rectangular, the length ratio of the length to the width does not need to be the same.

[0072] A connector 29 for connecting an external electric wiring 28 to the electrode portion 25 may be disposed on the outer surface of the tubular member 30 .

[0073] The insulating holding portion 40 is disposed between the columnar ceramic honeycomb substrate 22 provided with a pair of electrode portions 25 and the cylindrical member 30. The insulating holding portion 40 may be provided between the columnar ceramic honeycomb substrate 22 provided with a pair of electrode portions 25 and the cylindrical member 30, and even if there is a portion (space) where the insulating holding portion 40 is not provided between them, the insulating holding portion 40 may be provided throughout the entire space between them.

[0074] The material of the insulating holding portion 40 is not particularly limited as long as it has excellent insulating properties, but is preferably alumina.

[0075] The reducing agent generating device 100 having the above-described structure can be manufactured by a method known in the relevant technical field. Specifically, the reducing agent generating device 100 can be manufactured as follows.

[0076] First, the sprayer 10, the heater 20, the cylindrical member 30 provided with the connector 29 on the outer surface, the insulating holding portion 40, and the electrical wiring 28 are prepared. Next, the heater 20 is inserted into the cylindrical member 30, the heater 20 is fixed by the insulating holding portion 40, and the sprayer 10 is arranged at one end of the cylindrical member 30. Then, the connector 29 of the cylindrical member 30 and the pair of electrode portions 25 of the heater 20 are connected by the electrical wiring 28.

[0077] Next, a typical method of manufacturing the heater 20 will be described.

[0078] First, the molding raw material is extruded and molded to produce a honeycomb molded body having the same structure as the columnar ceramic honeycomb substrate 22. The molding raw material preferably includes a ceramic raw material and an organic binder. In addition to the ceramic raw material and the organic binder, the molding raw material may further contain a surfactant, a sintering aid, a pore-forming material, water, etc. By mixing these raw materials, a molding raw material can be obtained.

[0079] The ceramic raw material in the molding raw material is "ceramic" or "raw material that becomes ceramic by firing". Ceramic raw materials all become ceramics after firing. The ceramic raw material in the molding raw material preferably contains metal silicon and silicon carbide particles (silicon carbide powder) as the main components, or contains silicon carbide particles (silicon carbide powder) as the main components. Accordingly, the obtained columnar ceramic honeycomb substrate 22 has conductivity. Preferably, the metal silicon is also metal silicon particles (metal silicon powder). It should be noted that "containing metal silicon and silicon carbide particles as the main components" means that the total mass of metal silicon and silicon carbide particles is more than 90% by mass of the whole (ceramic raw material). In addition, as components other than the main component contained in the ceramic raw material, SiO2, SrCO3, Al2O3, MgCO3, cordierite, etc. can be cited.

[0080] When silicon carbide is used as the main component of the ceramic raw material, the silicon carbide is sintered by firing. In addition, when metal silicon and silicon carbide particles are used as the main components of the ceramic raw material, the silicon carbide as aggregate is bonded to each other by firing using the metal silicon as a bonding material.

[0081] When silicon carbide particles (silicon carbide powder) and metal silicon particles (metal silicon powder) are used as ceramic raw materials, the mass of the metal silicon particles is preferably 10 to 40 mass % based on the total mass of the silicon carbide particles and the mass of the metal silicon particles.

[0082] Examples of the organic binder include methylcellulose, glycerol, and hydroxypropylmethylcellulose. One or more organic binders may be used. When the total mass of the ceramic raw materials is 100 parts by mass, the amount of the organic binder is preferably 5 to 10 parts by mass.

[0083] As the surfactant, ethylene glycol, dextrin, etc. can be used. As the surfactant, one surfactant can be used, or multiple surfactants can be used. When the total mass of the ceramic raw material is set to 100 parts by mass, the amount of the surfactant is preferably 0.1 to 2.0 parts by mass.

[0084] As the sintering aid, SiO2, SrCO3, Al2O3, MgCO3, cordierite, etc. can be used. As the sintering aid, one sintering aid can be used, or multiple sintering aids can be used. When the total mass of the ceramic raw materials is set to 100 parts by mass, the amount of the sintering aid is preferably 0.1 to 3 parts by mass.

[0085] As a pore-forming material, it is sufficient to form pores after firing, and there is no particular limitation, and examples thereof include: graphite, starch, foamed resin, water-absorbent resin, silica gel, etc. As a pore-forming material, one pore-forming material can be used, or multiple pore-forming materials can be used. When the total mass of the ceramic raw materials is set to 100 parts by mass, the amount of the pore-forming material is preferably 0.5 to 10 parts by mass.

[0086] When the total mass of the ceramic raw materials is 100 parts by mass, the amount of water added is preferably 20 to 60 parts by mass.

[0087] When the molding raw material is extruded, first, the molding raw material is kneaded to make a blank. Next, the blank is extruded to obtain a honeycomb molded body. The honeycomb molded body has an outer peripheral wall 23 and a porous partition wall 24, which is arranged on the inner side of the outer peripheral wall 23 and partitions a plurality of compartments 27 extending from a first end face 26a to a second end face 26b. The partition wall 24 of the honeycomb molded body is: an undried, unfired partition wall 24.

[0088] Next, the obtained honeycomb formed body is dried to produce a honeycomb dried body. The drying conditions are not particularly limited, and known conditions can be used. For example, it is preferably dried at 80 to 120° C. for 0.5 to 5 hours.

[0089] Next, an electrode forming slurry containing a ceramic raw material and water is applied to the side surface of the dried honeycomb body, and then the electrode forming slurry is dried to form a pair of unfired electrode portions, thereby manufacturing a honeycomb body with unfired electrode portions.

[0090] Regarding the honeycomb body with the unfired electrode part, it is preferred that the honeycomb dried body is provided with a rectangular unfired electrode part having a large width and extending in a strip shape along the direction in which the cells 27 extend and also extending in the circumferential direction. The circumferential direction refers to the direction along the side surface of the honeycomb dried body in a cross section perpendicular to the direction in which the cells 27 extend.

[0091] The electrode forming slurry used in the step of manufacturing the honeycomb body with the unfired electrode portion contains a ceramic raw material and water. The electrode forming slurry may contain a surfactant, a pore forming material, water, and the like.

[0092] As the ceramic raw material used in the electrode forming slurry, the ceramic raw material used in the production of the honeycomb formed body is preferably used. For example, when the main components of the ceramic raw material used in the production of the honeycomb formed body are silicon carbide particles and metallic silicon, the ceramic raw materials of the electrode forming slurry can also be silicon carbide particles and metallic silicon.

[0093] The method of applying the electrode forming slurry to the side surface of the honeycomb dried body is not particularly limited. For example, the electrode forming slurry may be applied using a brush or by a printing method.

[0094] After the electrode forming slurry is applied to the dried honeycomb body, the electrode forming slurry is dried to obtain an unfired electrode portion (a honeycomb body with an unfired electrode portion). The drying temperature is preferably 80 to 120° C. The drying time is preferably 0.1 to 5 hours.

[0095] Next, the honeycomb body with the unfired electrode portion is fired to produce a honeycomb structure (columnar ceramic honeycomb substrate 22).

[0096] The firing conditions may be appropriately determined according to the types of the ceramic raw material for producing the honeycomb formed body and the ceramic raw material for the electrode forming slurry.

[0097] After the honeycomb formed body with the unfired electrode portion is dried, it is preferably pre-fired before firing to remove a binder etc. The pre-fired is preferably performed at 400 to 500° C. for 0.5 to 20 hours in an air atmosphere.

[0098] <Control method of reducing agent generating device>

[0099] The control method of the reducing agent generating device involved in the embodiment of the present invention is a control method of the reducing agent generating device 100 having the above-mentioned structure, which includes the following steps: an infiltration step, in which a mist reducing agent precursor 50 is sprayed from the sprayer 10 when the heater 20 is not heating, so that the reducing agent precursor 50 penetrates into the ceramic substrate 21; and a heating step A, in which the reducing agent precursor 50 is heated by the heater 20 after the infiltration step, and the mist reducing agent precursor 50 is sprayed from the sprayer 10 to generate the reducing agent 60.

[0100] Here, first, we use Figure 2 A conventional control method of the reducing agent generating device 100 will be described with reference to a flowchart of FIG.

[0101] like Figure 2 As shown, in the conventional control method, when the reducing agent generating device 100 is started, the heater 20 is heated to a predetermined temperature, and then the atomized reducing agent precursor 50 is sprayed from the sprayer 10. When the reducing agent generating device 100 is stopped, the spraying of the reducing agent precursor 50 is stopped, and then the heating of the heater 20 is stopped. Each time the reducing agent generating device 100 is used, the above-mentioned start-stop process is repeated.

[0102] In the previous start-stop process, when the reducing agent generating device 100 is stopped, in order to suppress the deposition of the reducing agent precursor 50 (e.g., urea) remaining in the ceramic substrate 21 of the heater 20, the heating of the heater 20 is stopped after the spraying of the reducing agent precursor 50 is stopped. Therefore, when the reducing agent generating device 100 is stopped, the reducing agent precursor 50 is usually not left in the ceramic substrate 21 of the heater 20.

[0103] Therefore, in this start-stop process, when the reducing agent generating device 100 is started, when the heater 20 is heated to a predetermined temperature and then the mist reducing agent precursor 50 is sprayed from the sprayer 10, the sprayed mist reducing agent precursor 50 first penetrates into the ceramic substrate 21, so the temperature of the heater 20 temporarily decreases. Thereafter, when the heater 20 is heated to a predetermined temperature again, the reducing agent precursor 50 is thermally decomposed to generate the reducing agent 60. As described above, the conventional control method of the reducing agent generating device 100 has the following problem, that is, after the mist reducing agent precursor 50 is sprayed from the sprayer 10, it takes a long time for the reducing agent precursor 50 to thermally decompose and generate the reducing agent 60, and it is difficult to quickly generate the reducing agent 60.

[0104] In contrast, in the control method of the reducing agent generating device 100 according to the embodiment of the present invention, when the heater 20 is not heating, the reducing agent precursor 50 in the form of mist is sprayed from the sprayer 10, and after the reducing agent precursor 50 is infiltrated into the ceramic substrate 21, the reducing agent precursor 50 is heated by the heater 20, so that the reducing agent 60 can be generated more quickly than in the conventional control method. In addition, since the reducing agent precursor 50 in the form of mist is subsequently sprayed from the sprayer 10, the reducing agent 60 can be continuously generated.

[0105] Here, we use Figure 3 and Figure 4 A typical example of the control method of the reducing agent generator 100 according to the embodiment of the present invention will be described with reference to the flowchart of FIG.

[0106] Figure 3 This is a method for controlling the reducing agent generating device 100 including a heating step A after the infiltration step.

[0107] The infiltration step includes a preliminary spraying step of the reducing agent precursor 50. Specifically, the infiltration step is a step of spraying the reducing agent precursor 50 in a mist form from the sprayer 10 in advance when the heater 20 is not heating, so that the reducing agent precursor 50 is infiltrated into the ceramic substrate 21.

[0108] The heating process A includes a heating start step of the heater 20 and a spray start step of the reducing agent precursor 50. Specifically, the heating process A is a process of heating the reducing agent precursor 50 by the heater 20, spraying the reducing agent precursor 50 in a mist form from the sprayer 10, and generating the reducing agent 60. In addition, the heating process A may further include a spray stop step of the reducing agent precursor 50 and a heating stop step of the heater 20, so as to stop the reducing agent generating device 100. It should be noted that Figure 3 2 shows an example in which the heating stop step of the heater 20 is performed after the spray stop step of the reducing agent precursor 50, but the spray stop step of the reducing agent precursor 50 may be performed after the heating stop step of the heater 20. In addition, the spray start step of the reducing agent precursor 50 and the heating start step of the heater 20 may be performed substantially at the same time. Each time the reducing agent generating device 100 is used, such an infiltration step and heating step A are repeatedly performed.

[0109] Figure 4 This is a control method of the reducing agent generating device 100 that further includes a heating step B before the infiltration step. That is, in this control method, the heating step B, the infiltration step, and the heating step A are performed in this order.

[0110] The heating process B includes a heating start step of the heater 20 and a spray start step of the reducing agent precursor 50. Specifically, the heating process B is a process of heating the reducing agent precursor 50 by the heater 20, spraying the reducing agent precursor 50 in a mist form from the sprayer 10, and generating the reducing agent 60. In addition, the heating process B may further include a spray stop step of the reducing agent precursor 50 and a heating stop step of the heater 20, so as to stop the reducing agent generating device 100. It should be noted that Figure 4 , an example is shown in which the heating stop step of the heater 20 is performed after the spray stop step of the reducing agent precursor 50, however, the spray stop step of the reducing agent precursor 50 may be performed after the heating stop step of the heater 20. In addition, in the heating step B, the heating start step of the heater 20 and the spray start step of the reducing agent precursor 50 may be performed substantially simultaneously.

[0111] Here, it will be indicated according to Figure 3 The control method of the reducing agent generating device 100 according to the embodiment of the present invention is shown in the flowchart of Figure 2 A graph showing the relationship between time and the amount of ammonia (reducing agent 60) generated in a conventional control method of a reducing agent generator 100 is shown in FIG. Figure 5 .like Figure 5As shown, the control method of the reducing agent generator 100 according to the embodiment of the present invention can generate ammonia more quickly than the conventional control method of the reducing agent generator 100 .

[0112] In the infiltration step, the permeability of the reducing agent precursor 50 in the ceramic substrate 21 is preferably 5 to 75% relative to the total pore volume of the ceramic substrate 21. By setting the permeability of the reducing agent precursor 50 to 5% or more, it is easy to stably ensure rapid generation of the reducing agent 60. In addition, by setting the permeability of the reducing agent precursor 50 to 75% or less, the reducing agent precursor 50 that has infiltrated the ceramic substrate 21 can be suppressed from being deposited. In addition, it is also possible to suppress a portion of the reducing agent precursor 50 from being released directly without being thermally decomposed.

[0113] Here, the permeability of the reducing agent precursor 50 can be obtained by the following equation (1).

[0114] Permeability of the reducing agent precursor 50 [%] = mass of the reducing agent precursor 50 permeated into the ceramic substrate 21 [g] / (total pore volume of the ceramic substrate 21 [cc] × density of the reducing agent precursor 50 [g / cc]) ... (1)

[0115] For example, when AdBlue (32.5 mass % urea aqueous solution, a registered trademark of the German Association of the Automotive Industry (VDA)) is used as the reducing agent precursor 50, the density of the urea aqueous solution can be obtained by the following formula (2).

[0116] Density of urea aqueous solution [g / cc] = density of urea × 0.325 + density of water × 0.675 (2)

[0117] The total pore volume is a value measured by mercury porosimetry. Examples of the mercury porosimeter include Autopore 9500, a product of Micromeritics.

[0118] The reducing agent precursor 50 used in the control method of the reducing agent production device 100 is not particularly limited, and may be appropriately selected according to the type of the reducing agent 60 to be produced.

[0119] For example, when the reducing agent 60 is ammonia, a urea aqueous solution may be selected as the reducing agent precursor 50 .

[0120] The reducing agent 60 obtained by the above-described control method of the reducing agent generating device 100 can be used in various applications requiring the reducing agent 60 .

[0121] For example, when the reducing agent 60 is ammonia, it can be used to treat exhaust gas containing NOx (nitrogen oxides).

[0122] When a urea aqueous solution is used as the reducing agent precursor 50, in the heating step, the reducing agent precursor 50 is sprayed from the sprayer 10 in a mist state, and the reducing agent precursor 50 is heated by the heater 20. Specifically, when the reducing agent precursor 50 is sprayed from the sprayer 10 toward the first end surface 26a of the columnar ceramic honeycomb substrate 22, the reducing agent precursor 50 is supplied to the cells 27 of the columnar ceramic honeycomb substrate 22. Urea in the urea aqueous solution supplied to the cells 27 is decomposed by the temperature of the heated columnar ceramic honeycomb substrate 22 to generate ammonia (reducing agent 60), which is discharged from the second end surface 26b of the columnar ceramic honeycomb substrate 22.

[0123] When the generated ammonia is used to treat exhaust gas containing NOx, the amount of urea aqueous solution supplied in the heating process is preferably 1.0 to 2.0 in terms of an equivalence ratio relative to the amount of NOx contained in the exhaust gas. When the equivalence ratio is less than 1.0, the amount of NOx discharged without being purified sometimes increases. However, if the SCR catalyst is given a NOx storage function, it is possible to have a period in which the equivalence ratio is less than 1.0. If the equivalence ratio exceeds 2.0, there is a possibility that the exhaust gas is discharged in a state where ammonia is mixed in the exhaust gas.

[0124] The urea aqueous solution is not particularly limited, but is preferably an aqueous solution containing 10 to 40% by mass of urea. If the urea content is less than 10% by mass, a large amount of misty urea aqueous solution needs to be sprayed for NOx reduction, and the amount of electricity required for the electrical heating of the columnar ceramic honeycomb substrate 22 sometimes increases. If the urea content exceeds 40% by mass, coagulation of the urea aqueous solution may occur in cold regions. As a preferred example of a urea aqueous solution, the above-mentioned AdBlue (32.5% by mass urea aqueous solution, a registered trademark of the German Association of the Automotive Industry (VDA)) can be cited.

[0125] The heating temperature of the columnar ceramic honeycomb substrate 22 is not particularly limited, but is preferably 160° C. or higher, more preferably 160 to 600° C., and even more preferably 250 to 400° C. If the heating temperature is 160° C. or higher, urea is easily and efficiently decomposed. If the heating temperature is 600° C. or lower, it is possible to suppress ammonia from being burned and causing ammonia supply shortage.

[0126] The maximum voltage applied to the columnar ceramic honeycomb substrate 22 is preferably 12 to 200 V, more preferably 12 to 100 V, and even more preferably 12 to 48 V. If the maximum voltage is 12 V or more, it is easy to increase the temperature of the columnar ceramic honeycomb substrate 22. If the maximum voltage is 200 V or less, the device for increasing the voltage becomes expensive and is suppressed.

[0127] <Reducing agent generation system>

[0128] The reducing agent generation system according to the embodiment of the present invention includes the reducing agent generation device 100 having the above-mentioned structure and a control device, wherein the control device includes: a reducing agent precursor spray control unit that controls the spraying of the mist reducing agent precursor 50 from the sprayer 10; and a heater control unit that controls the heating of the reducing agent precursor 50 by the heater 20. The reducing agent precursor spray control unit performs control such that a control signal for spraying the mist reducing agent precursor 50 from the sprayer 10 is generated when the heater 20 is not heated, and the reducing agent precursor 50 is infiltrated into the ceramic substrate 21. By performing such control, the reducing agent 60 can be quickly generated.

[0129] It should be noted that the permeation step is the same as that described in the control method of the reducing agent generating device 100 , and therefore the description thereof will be omitted.

[0130] The control device is not particularly limited, and is a computer. For example, when the reducing agent generation system is used in an exhaust gas purification treatment system, the control device may be an ECU (engine control unit). The ECU is composed of, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), an input port, and an output port. The various functions of the ECU described later are implemented by, for example, the CPU referring to the control program and various data stored in the ROM, RAM, etc. However, this function is not limited to software processing, and can also be implemented by a dedicated hardware circuit. By communicating with the sprayer 10, the heater 20, etc., the ECU can control these mechanisms or obtain status information of these mechanisms.

[0131] The reducing agent precursor spray control unit generates a control signal for controlling the amount of the misted urea aqueous solution (reducing agent precursor 50) sprayed from the sprayer 10, the presence or absence of spraying (timing, etc.), the spraying time, etc. The reducing agent precursor spray control unit can control the spray amount of the reducing agent precursor so that the permeability of the urea aqueous solution in the ceramic substrate 21 is 5 to 75% relative to the total pore volume of the ceramic substrate.

[0132] The heater control unit generates a control signal for controlling the power applied to the heater 20 so as to control the heating temperature of the heater 20 , the presence or absence of heating (timing, etc.), the heating time, and the like.

[0133] <Waste gas purification treatment method>

[0134] The exhaust gas purification method according to the embodiment of the present invention includes bringing the reducing agent 60 generated by the control method of the reducing agent generating device 100 described above into contact with the exhaust gas containing NOx.

[0135] The control method of the reducing agent generating device 100 described above can quickly generate the reducing agent 60 . Therefore, according to the exhaust gas purification method, the reducing agent 60 can be quickly generated immediately after the engine is started to perform the exhaust gas purification.

[0136] In the exhaust gas purification method according to the embodiment of the present invention, the reducing agent 60 can be brought into contact with the exhaust gas and then subjected to reduction treatment using the SCR catalyst. This can efficiently remove NOx in the exhaust gas.

[0137] <Exhaust gas purification system>

[0138] The exhaust gas purification system according to the embodiment of the present invention includes the reducing agent generation system described above. The reducing agent generation device 100 of the reducing agent generation system is provided in an exhaust pipe through which the exhaust gas containing NOx can flow or in a branch pipe connected to the exhaust pipe.

[0139] The reducing agent production system can quickly produce ammonia (reducing agent 60 ). Therefore, according to the exhaust gas purification treatment system, ammonia can be quickly produced immediately after the engine is started to perform exhaust gas purification treatment.

[0140] The amount of ammonia released from the reducing agent generating device 100 to the exhaust pipe is not particularly limited, but is preferably 1.0 to 2.0 in terms of equivalence ratio relative to the amount of NOx contained in the exhaust gas. When the equivalence ratio is less than 1.0, the amount of NOx discharged without being purified may increase. If the equivalence ratio exceeds 2.0, there is a possibility that the exhaust gas may be discharged in a state where ammonia is mixed in the exhaust gas.

[0141] Example

[0142] Hereinafter, the present invention will be described in more detail with reference to Examples; however, the present invention is not limited to these Examples.

[0143] <Production of reducing agent generation device>

[0144] Production Figure 1 The reducing agent generating device shown in the figure has a specific manufacturing method as follows.

[0145] Silicon carbide (SiC) powder and metal silicon (Si) powder are mixed in a mass ratio of 70:30 to prepare a ceramic raw material. Then, hydroxypropyl methylcellulose as a binder, a water-absorbent resin as a pore-forming material, and water are added to the ceramic raw material to prepare a molding raw material. Then, the molding raw material is kneaded using a vacuum clay extruder to obtain a blank. The content of the binder is 7 parts by mass when the ceramic raw material is set to 100 parts by mass. The content of the pore-forming material is 3 parts by mass when the ceramic raw material is set to 100 parts by mass. The content of water is 42 parts by mass when the ceramic raw material is set to 100 parts by mass. The average particle size of silicon carbide powder is 20μm, and the average particle size of metal silicon powder is 6μm. In addition, the average particle size of the pore-forming material is 20μm. The average particle sizes of silicon carbide, metal silicon and pore-forming material are values ​​measured using a laser diffraction method.

[0146] Next, the obtained billet is formed using an extruder to obtain a cylindrical (a cross section perpendicular to the direction in which the cells extend is circular) honeycomb formed body. The obtained honeycomb formed body is dried by high-frequency dielectric heating, and then dried at 120° C. for 2 hours using a hot air dryer, and both end faces are cut off by a predetermined amount to obtain a honeycomb dried body.

[0147] Next, silicon carbide (SiC) powder and metal silicon (Si) powder are mixed in a mass ratio of 60:40 to produce a ceramic raw material for an electrode. Then, hydroxypropyl methylcellulose as a binder, glycerin as a humectant, and a surfactant as a dispersant are added to the ceramic raw material for an electrode, and water is added and mixed. The mixture is kneaded to form a slurry for electrode formation. The content of the binder is 0.5 parts by mass when the ceramic raw material for an electrode is set to 100 parts by mass. The content of glycerin is 10 parts by mass when the ceramic raw material for an electrode is set to 100 parts by mass. The content of the surfactant is 0.3 parts by mass when the ceramic raw material for an electrode is set to 100 parts by mass. The content of water is 42 parts by mass when the ceramic raw material for an electrode is set to 100 parts by mass. The average particle size of the silicon carbide powder is 52 μm, and the average particle size of the metal silicon powder is 6 μm. The average particle sizes of silicon carbide and metal silicon are values ​​measured using a laser diffraction method. Kneading is performed using a vertical mixer.

[0148] Next, the electrode forming slurry was applied in a stripe shape on the side of the dried honeycomb body and then dried to form a pair of unfired electrode portions, thereby obtaining a honeycomb body with unfired electrode portions. The drying temperature of the electrode forming slurry was 70°C.

[0149] Next, the honeycomb body with the unfired electrode portion was degreased, fired, and then oxidized to obtain a heater. The degreasing conditions were: 550°C for 3 hours. The firing conditions were: 1450°C for 2 hours in an argon atmosphere. The oxidation treatment conditions were: 1300°C for 1 hour.

[0150] In the obtained heater, the thickness of the partition wall of the columnar ceramic honeycomb substrate was 0.152 mm, and the cell spacing was 1.11 mm. In addition, the surface area per unit volume of the columnar ceramic honeycomb substrate was 31.1 cm 2 / cm 3 In addition, the shape of the columnar ceramic honeycomb substrate is: the two end faces are square with a side length of 30 mm, and the length in the cell extension direction is 25 mm. In addition, the resistivity of the electrode part is 0.1Ωcm, and the resistivity of the columnar ceramic honeycomb substrate is 1.4Ωcm.

[0151] Next, a cylindrical component is made of stainless steel, and two connectors are assembled on its outer surface. A heater is inserted into the cylindrical component, and the heater is fixed by means of an insulating retaining portion made of aluminum oxide, and an electromagnetic sprayer is arranged at one end of the cylindrical component. In addition, the connector of the cylindrical component and a pair of electrode portions of the heater are connected by electrical wiring.

[0152] <Reducing agent generation test>

[0153] The reducing agent generation device obtained above was installed in the exhaust pipe, and a reducing agent generation test was carried out. In this test, AdBlue (32.5% by mass urea aqueous solution, a registered trademark of the German Association of the Automotive Industry (VDA)) was used as a reducing agent precursor, and the time required for the generation of a predetermined amount of ammonia (reducing agent) was measured for evaluation. In addition, the shedding of the urea aqueous solution (reducing agent precursor) (the urea aqueous solution was directly discharged from the reducing agent generation device) was also evaluated. The specific test method is as follows.

[0154] First, if Figure 6 As shown, the reducing agent generating device 100 is installed in the exhaust pipe 200. The reducing agent generating device 100 is installed in a branch pipe branched and connected at an angle θ of 45° with respect to the exhaust pipe 200. In addition, the distance L1 between the midpoint A of the branch portion where the reducing agent generating device 100 is installed and the reducing agent generating device 100 is set to 10 mm.

[0155] Next, in the reducing agent generating device 100, before heating by the heater, a mist of urea aqueous solution was sprayed from the sprayer at a permeation rate shown in Table 1 to permeate into the columnar ceramic honeycomb substrate (permeation step). However, in Test No. 1, this permeation step was not performed.

[0156] The permeability of the urea aqueous solution is calculated according to the above formula (1). It should be noted that the mass of the columnar ceramic honeycomb substrate after the spraying of the urea aqueous solution is subtracted from the mass of the columnar ceramic honeycomb substrate before the spraying of the urea aqueous solution to calculate: the mass of the urea aqueous solution that permeates the columnar ceramic honeycomb substrate (permeation amount). The columnar ceramic honeycomb substrate is removed from the reducing agent generating device 100, and the permeation amount of the urea aqueous solution is calculated. In addition, the density of the urea aqueous solution is calculated according to the above formula (2).

[0157] Next, a mist of urea aqueous solution is sprayed from the sprayer at a rate of 1.0 g / min, and a voltage of about 39 V is applied to the columnar ceramic honeycomb substrate to heat the heater, thereby generating ammonia (heating process). It should be noted that the maximum voltage that can be applied from the power supply to the columnar ceramic honeycomb substrate is set to 48 V. Then, 650 mL / min of air is circulated in the exhaust pipe 200, and the time required to detect 20 ppm and 100 ppm of ammonia is measured. The measurement is performed at a measuring point B in the exhaust pipe 200 at a distance L2 of 600 mm from the center of the exhaust pipe 200 corresponding to the midpoint A of the branch portion where the reducing agent generating device 100 is provided.

[0158] Regarding the falling of the urea aqueous solution, the exhaust pipe 200 was visually observed, and if no urea was precipitated in the exhaust pipe 200, it was evaluated as no falling of the urea aqueous solution (A). On the contrary, if urea was precipitated in the exhaust pipe 200, it was evaluated as falling of the urea aqueous solution (B).

[0159] Table 1 shows the above evaluation results.

[0160] [Table 1]

[0161]

[0162] As shown in Table 1, it was confirmed that the control method of test No. 2 to 5 (examples of the present invention) that performed the penetration process took a shorter time to detect 20 ppm and 100 ppm of ammonia than the control method of test No. 1 (comparative example) that did not perform the penetration process, and ammonia could be generated quickly.

[0163] From the above results, it can be seen that according to the present invention, a control method for a reducing agent generating device and a reducing agent generating system that can quickly generate reducing agent can be provided. In addition, according to the present invention, an exhaust gas purification method and an exhaust gas purification system that can quickly generate reducing agent and perform exhaust gas purification treatment just after the engine is started can be provided.

[0164] Explanation of symbols

[0165] 10. Sprayer

[0166] 20 Heater

[0167] 21 Ceramic substrate

[0168] 22 Columnar ceramic honeycomb substrate

[0169] 23 Outer wall

[0170] 24 Next Door

[0171] 25 Electrode

[0172] 26a First end face

[0173] 26b Second end face

[0174] 27 compartments

[0175] 28 Electrical wiring

[0176] 29 Connectors

[0177] 30 Cylindrical parts

[0178] 40 Insulation holding part

[0179] 50 Reducing agent precursor

[0180] 60 Reducing agent

[0181] 100 Reducing agent generation device

[0182] 200 Exhaust pipe

Claims

1. A method for controlling a reducing agent generating device, the reducing agent generating device comprising: a sprayer capable of spraying a reducing agent precursor in a mist form; and a heater including a ceramic substrate, the heater being disposed on the downstream side of the sprayer and capable of heating the reducing agent precursor to generate the reducing agent, It is characterized in that The control method comprises the following steps: a permeation step in which, when the heater is not heating, the reducing agent precursor is sprayed from the sprayer in a mist form to allow the reducing agent precursor to permeate into the ceramic substrate; as well as A heating step A is a step of heating the reducing agent precursor by the heater after the infiltration step, spraying the reducing agent precursor in a mist form from the sprayer, and generating the reducing agent.

2. The control method according to claim 1, characterized in that: In the infiltration step, the permeability of the reducing agent precursor in the ceramic substrate is 5 to 75% relative to the total pore volume of the ceramic substrate.

3. The control method according to claim 1 or 2, characterized in that: The control method further includes a heating step B, in which the reducing agent precursor is heated by the heater, and the reducing agent precursor is sprayed from the sprayer in a mist form to generate the reducing agent. The heating step B, the infiltration step, and the heating step A are performed in the order of the heating step B, the infiltration step, and the heating step A.

4. The control method according to claim 1 or 2, characterized in that: The reducing agent precursor is a urea aqueous solution, and the reducing agent is ammonia.

5. The control method according to claim 1 or 2, characterized in that: The heater comprises: a columnar ceramic honeycomb substrate, and a pair of electrode portions arranged on the side of the columnar ceramic honeycomb substrate, the columnar ceramic honeycomb substrate having an outer peripheral wall and a partition wall, the partition wall being arranged on the inner side of the outer peripheral wall and partitioning a plurality of compartments, the plurality of compartments forming a flow path from a first end face to a second end face, The columnar ceramic honeycomb substrate generates heat when electricity is applied.

6. The control method according to claim 1 or 2, characterized in that: The heater is accommodated in a cylindrical member, and the heater and the cylindrical member are fixed via an insulating holding portion.

7. A method for purifying waste gas, characterized in that: include: The reducing agent produced by the control method according to any one of claims 1 to 6 is brought into contact with exhaust gas containing NOx.

8. A reducing agent generation system, characterized in that: include: a reducing agent generating device including an atomizer capable of spraying a reducing agent precursor in a mist form, and a heater including a ceramic substrate disposed on a downstream side of the atomizer and capable of heating the reducing agent precursor to generate the reducing agent; and a control device including a reducing agent precursor spray control unit for controlling the spray of the reducing agent precursor in a mist form from the sprayer, and a heater control unit for controlling the heating of the reducing agent precursor by the heater, The reducing agent precursor spray control unit performs control to generate a control signal for spraying the reducing agent precursor in a mist form from the sprayer when the heater is not heating, and to allow the reducing agent precursor to permeate into the ceramic substrate.

9. The reducing agent generation system according to claim 8, characterized in that: The reducing agent precursor spray control unit controls the spray amount of the reducing agent precursor so that the permeability of the reducing agent precursor in the ceramic substrate is 5 to 75% of the total pore volume of the ceramic substrate.

10. The reducing agent generation system according to claim 8 or 9, characterized in that: The heater comprises: a columnar ceramic honeycomb substrate, and a pair of electrode portions arranged on the side of the columnar ceramic honeycomb substrate, the columnar ceramic honeycomb substrate having an outer peripheral wall and a partition wall, the partition wall being arranged on the inner side of the outer peripheral wall and partitioning a plurality of compartments, the plurality of compartments forming a flow path from a first end face to a second end face, The columnar ceramic honeycomb substrate generates heat when electricity is applied.

11. The reducing agent generation system according to claim 8 or 9, characterized in that: The heater is accommodated in a cylindrical member, and the heater and the cylindrical member are fixed via an insulating holding portion.

12. An exhaust gas purification system, comprising the reducing agent generation system according to any one of claims 8 to 11, The exhaust gas purification system is characterized in that: The reducing agent generating device is provided in an exhaust pipe through which the exhaust gas containing NOx can flow or in a branch pipe connected to the exhaust pipe.

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