JP2016160881A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine, which causes an absorbent to absorb nitrogen oxides properly over a wider temperature range than that of the prior art.SOLUTION: An exhaust emission control device 10 comprises: a first absorption equipment 22 having water as a first absorbent 26; and a second absorption equipment 24 having an ion liquid different in the temperature characteristics of nitric acid absorption rate from water as a second absorbent 28. In the case where the temperature of water or the first absorbent 26 is lower than a predetermined threshold value, a control part 34 controls a valve 20 so that the exhaust gas from an internal combustion engine 12 flows into the first absorption equipment 22, thereby to cause nitric acid in the exhaust gas to contact with the water. In the case where the temperature of the water or the first absorbent 26 is at or higher than the predetermined threshold value, the control part 34 controls the valve 20 so that the exhaust gas from the internal combustion engine 12 flows into the second absorption equipment 24, thereby to cause the nitric acid in the exhaust gas to contact with the ion liquid.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine for purifying nitrogen oxides contained in the exhaust gas of the internal combustion engine.

Conventionally, techniques for purifying nitrogen oxides (NO _x ) contained in exhaust gas from internal combustion engines such as engines have been proposed.

  For example, Patent Document 1 discloses an absorption device that absorbs nitrogen oxides modified to nitric acid by bringing them into contact with an absorption liquid. Nitrogen oxides contained in the exhaust gas are separated and removed by the absorption device.

JP 2014-62543 A

  Water, alkaline aqueous solution, ionic liquid, etc. are known as what can be utilized as absorption liquid which absorbs nitrogen oxides. These absorption liquids have a feature that the absorption rate of nitrogen oxides (absorption amount with respect to the input amount of nitrogen oxides) varies depending on the temperature. That is, these absorption liquids have temperature characteristics of the absorption rate of nitrogen oxides. Therefore, the absorbing liquid efficiently absorbs nitrogen oxides in a certain temperature range, but may hardly absorb nitrogen oxides in another temperature range. Thereby, no matter which absorption liquid is used, there is a possibility that nitrogen oxides cannot be absorbed properly depending on the temperature of the absorption liquid.

  An object of the present invention is to suitably absorb nitrogen oxides in an absorption liquid in a wider temperature range than before.

  The present invention is an exhaust gas purification apparatus for an internal combustion engine for purifying nitrogen oxides contained in exhaust gas from an internal combustion engine, comprising a first absorbing liquid, and the nitrogen oxides that are circulated as the first exhaust gas. The first absorption device to be absorbed by the absorption liquid, and the second absorption liquid having a temperature characteristic of the absorption rate of nitrogen oxides different from that of the first absorption liquid, and the nitrogen oxide flowing through the second absorption liquid A second absorption device that is absorbed by the liquid, wherein the nitrogen oxide is circulated through at least one of the first absorption device and the second absorption device.

  Desirably, in the first temperature range, the absorption rate of nitrogen oxides in the first absorption liquid is larger than the absorption rate of nitrogen oxides in the second absorption liquid, and is different from the first temperature range. In the above, the absorption rate of nitrogen oxides in the second absorption liquid is larger than the absorption rate of nitrogen oxides in the first absorption liquid.

  Desirably, a flow path switching device that switches a flow path of the nitrogen oxide between the internal combustion engine and the first absorption device and the second absorption device; and at least one of the first absorption liquid and the second absorption liquid Temperature detection means for detecting one temperature, and the flow path switching device selects an absorption device for circulating the nitrogen oxides based on the temperature detected by the temperature detection means, and the selected absorption The flow path is switched so that the nitrogen oxide flows through the apparatus.

  Desirably, a plurality of the second absorption devices are provided, and the exhaust gas purification device of the internal combustion engine detects a concentration of at least one nitrogen oxide in a plurality of second absorption liquids included in the plurality of second absorption devices. And the flow path switching device selects a second absorption device for circulating the nitrogen oxide from a plurality of second absorption devices based on the nitrogen oxide concentration of the second absorption liquid. The flow path is switched so that the nitrogen oxide flows through the selected second absorption device.

  Desirably, one of the first absorbent and the second absorbent is water or an alkaline aqueous solution, and the other is an ionic liquid.

  According to the present invention, nitrogen oxides can be suitably absorbed by the absorbing liquid in a wider temperature range than before.

1 is a schematic configuration diagram of an exhaust emission control device according to a first embodiment. It is a figure which shows the structural example of an absorber. It is a figure which shows the example of the temperature characteristic of the absorption factor of a nitrogen oxide. It is a flowchart which shows the flow of a process of the exhaust gas purification apparatus in 1st Embodiment. It is a figure which shows the other example of the temperature characteristic of the absorption factor of a nitrogen oxide. It is a block schematic diagram of the exhaust emission control device according to the second embodiment. It is a block schematic diagram of the exhaust emission control device according to the third embodiment. It is a flowchart which shows the flow of a process of the exhaust gas purification apparatus in 3rd Embodiment.

  Embodiments of the present invention will be described below with reference to the drawings. Note that the present invention is not limited to the embodiments described below.

<First Embodiment>
FIG. 1 is a schematic configuration diagram of an exhaust emission control device 10 according to the first embodiment.

An internal combustion engine (engine) 12 generates power by burning fuel in a cylinder. Here, the internal combustion engine 12 may be a spark ignition engine such as a gasoline engine, or may be a compression ignition engine such as a diesel engine. Exhaust gas after combustion in the internal combustion engine 12 is discharged into the exhaust pipe 14. Exhaust gas discharged from the internal combustion engine 12 into the exhaust pipe 14 contains harmful components such as nitrogen oxides (NO _x ). Examples of nitrogen oxides include NO (nitrogen monoxide), NO ₂ (nitrogen dioxide), N ₂ O (zincated nitrogen), N ₂ O ₅ (dinitrogen pentoxide), and N ₂ O ₃ (dinitrogen trioxide). ), N ₂ O ₄ (dinitrogen tetroxide), HNO ₃ (nitric acid), NO ₃ (nitrate ion), HNO ₂ (nitrous acid), and the like. Nitrogen oxide is separated and removed from the exhaust gas in at least one of the first absorber 22 and the second absorber 24 described later.

Preferably, the exhaust purification device 10 is provided with a reforming device 16. The reformer 16 converts the nitrogen oxides contained in the exhaust gas from the internal combustion engine 12 into nitric acid in order to more efficiently perform the separation and removal process of nitrogen oxides in the first absorber 22 or the second absorber 24. It is a quality. The reformer 16 has a nitric acid generation catalyst for promoting a reaction for converting nitrogen oxides to nitric acid (HNO ₃ ), and the nitrogen oxides contained in the exhaust from the internal combustion engine 12 are converted to nitric acid on the nitric acid generation catalyst. To reform. The nitric acid production catalyst can be constituted by a catalyst having an acid point or a catalyst in which a metal such as silver (Ag), iron (Fe), copper (Cu) is supported on a carrier having an acid point. In order to further promote the oxidation reaction in the reformer 16, it is also preferable to add ozone (O ₃ ) as an oxidant to the exhaust gas from the internal combustion engine 12. Although the 1st absorber 22 and the 2nd absorber 24 can also process nitrogen oxides other than nitric acid, the 1st absorber 22 and the 2nd absorber 24 treat nitric acid as nitrogen oxide after that. This embodiment will be described.

  Exhaust gas from the reformer 16 is discharged to an exhaust pipe 18 connected to the first absorber 22 and the second absorber 24. Hereinafter, the exhaust from the reformer 16 is referred to as “exhaust from the internal combustion engine 12” for convenience.

  A valve 20 is provided in the middle of the exhaust pipe 18. The valve 20 switches the exhaust flow path from the internal combustion engine 12. Specifically, the valve 20 includes an openable / closable valve 20 a provided to prevent the flow of exhaust gas to the exhaust pipe 18 a connected to the first absorption device 22, and an exhaust pipe connected to the second absorption device 24. An openable / closable valve 20b is provided so as to prevent the flow of exhaust gas to 18b. By opening and closing the two valves, the exhaust flow path from the internal combustion engine 12 is switched.

  In the present embodiment, two absorbers, a first absorber 22 and a second absorber 24, are provided as absorbers for separating and removing nitric acid in exhaust gas. Each of the two absorption devices absorbs nitric acid in contact with an absorption liquid that each of the absorption devices has.

The two absorption devices have different absorption liquids. The first absorption device 22 includes a first absorption liquid 26, and the second absorption device 24 has a temperature characteristic of the nitric acid absorption rate (hereinafter simply referred to as “temperature characteristic”) as compared with the first absorption liquid 26. Have different second absorbents 28. Here, the absorption rate of nitric acid is the amount of nitric acid absorbed with respect to the amount of nitric acid input to the absorber, and is specifically defined by the following equation.

{(N _in −N _out ) / N _in } × 100 (Formula 1)

In Equation 1, N _in is the amount of nitric acid input to the absorber, and N _out is the amount of nitric acid discharged from the absorber.

  Examples of the liquid that can be used as the absorbing liquid include water, an alkaline aqueous solution, various ionic liquids, and the like. Of course, other liquids can be used as the absorbing liquid as long as nitric acid can be absorbed. The first absorbing liquid 26 and the second absorbing liquid 28 may be appropriately selected from these liquids as long as the temperature characteristics of the two are different. In the present embodiment, water is used as the first absorbent 26, and 1-butyl-3-methylimidazolium triflate ([BMIM] [OTf], hereinafter simply referred to as “ionic liquid”) is used as the second absorbent. Use. The temperature characteristics of both will be described in detail with reference to FIG.

  Exhaust gas from the first absorption device 22 and the second absorption device 24 is discharged through the exhaust pipe 30 to the exhaust outlet.

  The temperature sensor 32 detects the temperature of the water that is the first absorbing liquid 26. As the temperature sensor 32, a thermocouple, a thermistor, an infrared temperature sensor, or the like is used. Data indicating the temperature of the first absorbing liquid 26 detected by the temperature sensor 32 is sent to the control unit 34 or read by the control unit 34.

  The control unit 34 is composed of, for example, a microcomputer, and controls the valve 20. Specifically, the control unit 34 controls the valve based on data indicating the temperature of the first absorbent 26 detected by the temperature sensor 32 and a threshold value stored in a predetermined storage unit (not shown in FIG. 1). An instruction signal is transmitted to 20. The valve 20 switches the flow path of the exhaust gas from the internal combustion engine 12 by opening and closing the valves 20a and 20b based on the instruction signal. Details of the flow path switching procedure by the controller 34 will be described later with reference to the flowchart of FIG.

  FIG. 2 is a schematic view showing a structural example of the first absorption device 22.

  The first absorption device 22 includes a storage unit 40 that stores the first absorption liquid 26, a gas-liquid contact unit 42, and a pump 44 that pumps the first absorption liquid 26 stored in the storage unit 40 to the gas-liquid contact unit 42. It consists of

  The gas-liquid contact part 42 is configured to cause the exhaust gas from the internal combustion engine 12 to come into contact with the first absorption liquid 26 and to absorb the nitric acid in the exhaust gas into the first absorption liquid 26. As a contact method between the exhaust gas and the first absorbing liquid 26, a known technique such as bubbling, scrubber, gas-liquid contact film, or the like can be used. In the present embodiment, the exhaust passage and the absorbing liquid are separated by the porous film in the gas-liquid contact portion 42, and the nitric acid contained in the exhaust contacts the first absorbing liquid 26 from the exhaust passage through the porous film. Let As the porous membrane, a porous PTFE (polytetrafluoroethylene) membrane or the like can be used.

  The first absorption liquid 26 that has absorbed nitric acid in the gas-liquid contact part 42 is returned to the storage part 40. Then, the pump 44 is pumped up again from the storage unit 40 to the gas-liquid contact unit 42. Thus, the 1st absorption liquid 26 circulates between the storage part 40 and the gas-liquid contact part 42. FIG. Due to the circulation, the nitric acid concentration of the first absorbing liquid 26 increases, so when the nitric acid concentration of the first absorbing liquid 26 increases to some extent, it is discarded and a new first absorbing liquid 26 is replenished.

  Note that the contact amount of the first absorbing liquid 26 with respect to the exhaust gas in the gas-liquid contact portion 42 may be set as appropriate. Moreover, in the 1st absorption device 22, the structure of the gas-liquid contact part 42 or the pumping force of the pump 44, etc. can be adjusted, and it may be made possible to adjust the quantity of the 1st absorption liquid 26 which contacts exhaust_gas | exhaustion.

  The first absorbing liquid 26 in the gas-liquid contact portion 42 is brought into contact with the exhaust gas from the internal combustion engine 12, so that the temperature rises due to the heat of the exhaust gas. The temperature rise of the first absorbent 26 varies depending on the temperature of the exhaust from the internal combustion engine 12 or the amount of exhaust. That is, the temperature of the first absorbing liquid 26 in the gas-liquid contact portion 42 is varied depending on the exhaust conditions of the internal combustion engine 12. The temperature of the first absorbing liquid 26 is also influenced by the outside air temperature and the like, but the temperature fluctuation factor is mainly exhaust conditions. The temperature sensor 32 is provided in or near the gas-liquid contact portion 42, and the temperature of the first absorption liquid 26 in the gas-liquid contact portion 42, that is, the contact position between the first absorption liquid 26 and the exhaust from the internal combustion engine 12. Is detected.

  Since the second absorption device 24 has the same structure as the first absorption device 22 described above, the description thereof is omitted.

  FIG. 3 is a graph showing temperature characteristics of water and ionic liquid. In FIG. 3, the horizontal axis represents the temperature of the absorbing solution, and the vertical axis represents the nitric acid absorption rate of the absorbing solution or the weight of the absorbing solution. In the graph shown in FIG. 3, the white square indicates the nitric acid absorption rate of water, and the black square indicates the nitric acid absorption rate of the ionic liquid. As is clear from FIG. 3, water and ionic liquid have different nitric acid absorption rates depending on the temperature, that is, have temperature characteristics. Moreover, the changes in the nitric acid absorption rates of water and ionic liquid with respect to temperature fluctuation are different from each other, that is, the temperature characteristics of water and ionic liquid are different from each other.

  Specifically, water exhibits a relatively high absorption rate at a temperature of less than about 70 ° C., but the absorption rate rapidly decreases when the temperature reaches about 70 ° C. or higher. On the other hand, the ionic liquid shows a value lower than the water absorptivity at a temperature below about 70 ° C., but the absorptance does not decrease much even at a temperature of about 70 ° C. or higher. As a result, in a temperature range of less than about 70 ° C., water absorbs nitric acid more than ionic liquid, and in a temperature range of about 70 ° C. and higher, ionic liquid absorbs nitric acid more than water. Is high.

  The nitric acid absorption rate also varies depending on the contact amount of the absorbing solution with nitric acid. For example, if the contact amount of the ionic liquid with nitric acid is increased, the black square graph shown in FIG. In this embodiment, the nitric acid contact amount of the ionic liquid is about 70% of the contact amount of water, and FIG. 3 shows the temperature characteristics in that case.

FIG. 3 shows the remaining weight ratio of water and ionic liquid. The remaining weight ratio is a ratio of the weight of the absorbing liquid after a lapse of a predetermined time to the weight before the lapse of a predetermined time when maintained at a certain temperature, and is specifically defined by the following equation.

(Q _after / Q _before ) × 100 (Expression 2)

In Equation 2, Q _after is the weight of the absorbing solution after a predetermined time has elapsed, and Q _before is the weight of the absorbing solution _before the predetermined time has elapsed. The weight of the absorbent varies (decreases) due to evaporation of the absorbent. In other words, it means that the smaller the remaining weight ratio, the easier the absorbing liquid evaporates.

  In the graph shown in FIG. 3, the white triangle indicates the remaining weight ratio of water, and the black triangle indicates the remaining weight ratio of the ionic liquid. The remaining weight percentage of water decreases as the temperature increases. That is, water is more likely to evaporate as the temperature increases. In particular, in a temperature range exceeding 70 ° C., it is very easy to evaporate, and as a result, nitric acid can hardly be absorbed. On the other hand, the remaining weight ratio of the ionic liquid is maintained almost 100% in the range shown in the graph of FIG. That is, the ionic liquid hardly evaporates at least up to around 120 ° C.

  FIG. 4 is a flowchart showing the flow of processing of the exhaust emission control device 10 in the first embodiment. Specifically, the control procedure of the valve 20 by the control unit 34 is shown. Hereinafter, each step of the flowchart of FIG. 4 will be described with reference to FIG.

  When the internal combustion engine 12 is started, the exhaust purification device 10 starts controlling the exhaust gas passage. In step S10, the control unit 34 compares data indicating the temperature of the first absorbent 26 detected by the temperature sensor 32 with a threshold value that is set in advance and stored in a storage unit (not shown in FIG. 1).

  The threshold value is a value that serves as a criterion for determining whether the exhaust gas from the internal combustion engine 12 is circulated through the first absorber 22 or the second absorber 24. The threshold is set based on the temperature characteristics of the absorbing liquid or the contact amount of the absorbing liquid with the exhaust gas in the absorbing device. Specifically, based on the temperature characteristics in consideration of the contact amount of the first absorbent 26 and the second absorbent 28 with nitric acid, the temperature at which the superiority or inferiority of the nitric acid absorption rate of both may be set as the threshold value. As shown in FIG. 3, the superiority or inferiority of the nitric acid absorption rate of water and ionic liquid is switched at about 70 ° C., and therefore, in this embodiment, 70 ° C. is set as the threshold value.

  When it is determined in step S10 that the temperature of the first absorbent liquid 26 is equal to or higher than the threshold value, in step S12, the control unit 34 transmits an instruction to close the valve 20a and open the valve 20b to the valve 20. The valve 20 opens and closes the valve according to the instruction. Thereby, the exhaust from the internal combustion engine 12 is not circulated to the first absorber 22 but is circulated to the second absorber 24 via the exhaust pipe 18b.

  When it is determined in step S10 that the temperature of the first absorbent liquid 26 is lower than the threshold value, in step S14, the control unit 34 transmits an instruction to open the valve 20a and close the valve 20b to the valve 20, The valve 20 opens and closes the valve according to the instruction. Thereby, the exhaust from the internal combustion engine 12 is not circulated to the second absorber 24 but is circulated to the first absorber 22 via the exhaust pipe 18a.

  In step S16, the control unit 34 determines whether or not the internal combustion engine 12 has stopped. When the internal combustion engine 12 is stopped, the control of the exhaust passage is finished. If the internal combustion engine 12 is operating, the process returns to step 10 again. That is, while the internal combustion engine 12 is operating, the control unit 34 continues to control the exhaust passage.

  With the above treatment, if the temperature of the water as the first absorbent 26 is less than 70 ° C., the nitric acid in the exhaust gas is absorbed by water having a higher nitric acid absorption rate than the ionic liquid in the temperature region, and the temperature of the water is 70. When the temperature is higher than or equal to ° C, nitric acid in the exhaust gas can be absorbed by an ionic liquid having a higher nitric acid absorption rate than water in the temperature range. That is, according to the present embodiment, the nitric acid in the exhaust can be brought into contact with the absorbing liquid having the highest nitric acid absorption rate at the time of the nitric acid absorption treatment among the plurality of absorbing liquids to be absorbed. Thereby, it is possible to absorb nitric acid in the exhaust gas from the internal combustion engine 12 more suitably in a wider temperature range as compared with an exhaust gas purification device provided with only one absorber having only one type of absorbent.

  Since a plurality of absorption devices are provided, in order to absorb nitric acid in the exhaust gas in a wider temperature range, a plurality of absorption devices are connected in series to a plurality of absorption devices having absorption liquids having different temperature characteristics. There is also an idea that the nitric acid in the exhaust gas is always circulated, and such a form can also be adopted in practice. However, the absorption liquid that has absorbed nitric acid needs to be discarded, and when water and ionic liquid are used as the absorption liquid as in this embodiment, water is less expensive than ionic liquid, There is a request to prioritize the use of water as an absorbent. That is, it is preferable to use the ionic liquid only when the nitric acid absorption rate of water is lowered. Therefore, in this embodiment, when the temperature of water is 70 degrees C or less, exhaust is not made to contact an ionic liquid.

  Further, in the present embodiment, when the water as the first absorbing liquid 26 is 70 ° C. or higher, the exhaust from the internal combustion engine 12 is not brought into contact with the water, so that the temperature of the water further increases. Can be prevented. As shown in FIG. 3, the higher the temperature, the easier the water evaporates. By preventing the water from reaching 70 ° C. or higher, the amount of water evaporation can be reduced. By reducing the evaporation amount of water, it is possible to suppress a decrease in the weight of water as the first absorption liquid 26 and, in turn, the replenishment frequency of the first absorption liquid 26 can be reduced. On the other hand, when the temperature of the water is 70 ° C. or higher, it is considered that the temperature of the exhaust from the internal combustion engine 12 is high or the amount is large. It is considered that the temperature of the ionic liquid becomes 70 ° C. or higher when it is brought into contact with. However, as shown in FIG. 3, the ionic liquid has a feature that it is difficult to evaporate even at a high temperature.

  In the present embodiment, the control unit 34 switches the flow path of the exhaust gas from the internal combustion engine 12 based on a predetermined threshold and the temperature detected by the temperature sensor 32, but at least as shown in the graph shown in FIG. The temperature characteristic (that is, the correspondence between the amount of water absorbed in nitric acid and the temperature) in consideration of the amount of contact of the first absorbent 26 with the nitric acid is stored in the storage unit. Based on the temperature data from the temperature sensor 32, an instruction signal for switching the exhaust flow path may be transmitted to the valve 20. In this case, based on the temperature of the first absorption liquid and the temperature characteristics of the first absorption liquid, for example, when the nitric acid absorption rate of the first absorption liquid 26 becomes 60% or less, control is performed to send an instruction signal to the valve 20. .

  In the present embodiment, two absorption devices are provided. However, a larger number of absorption devices may be provided. Also in this case, it is preferable that the plurality of absorbing liquids included in the plurality of absorbing devices have different temperature characteristics. For example, when three absorption devices are provided, the first absorption liquid having the graph 46a shown in FIG. 5 as the temperature characteristic, the second absorption liquid having the graph 46b as the temperature characteristic, and the third having the graph 46c as the temperature characteristic. It is preferable to provide each of the absorbing devices with the absorbing liquid. And the temperature sensor which detects the temperature of each absorption liquid is provided, and if the temperature of the 1st absorption liquid is the range of T1 shown in FIG. 5, exhaust_gas | exhaustion will be contacted with the 1st absorption liquid and the 2nd absorption liquid's If the temperature is in the range of T2, it is brought into contact with the second absorbent, and if the temperature of the third absorbent is in the range of T3, it is brought into contact with the third absorbent.

Second Embodiment
FIG. 6 is a schematic configuration diagram of an exhaust emission control device 50 according to the second embodiment. In FIG. 6, illustration of the internal combustion engine and the reformer is omitted. Since the exhaust purification device 50 has the same components as those of the exhaust purification device 10 according to the first embodiment, individual descriptions are omitted. Also in the second embodiment, the first absorbing liquid 26 is water and the second absorbing liquid 28 is an ionic liquid.

  The exhaust purification device 50 is different from the exhaust purification device 10 in the arrangement relationship of the valve 20, the first absorption device 22, and the second absorption device 24. Specifically, the second absorption device 24 is disposed immediately after the reforming device 16, and the exhaust gas from the internal combustion engine 12 is always circulated to the second absorption device 24. Then, the exhaust from the second absorber 24 is discharged to the exhaust pipe 52. The valve 20 is provided in the middle of the exhaust pipe 52, and the exhaust flow path from the second absorption device 24, the flow path to the exhaust pipe 52 a connected to the first absorption device 22, and the exhaust pipe 30 to the exhaust outlet. It switches between the flow path to the exhaust pipe 52b connected directly to.

  As in the first embodiment, the control unit 34 controls the valve 20 when the temperature of the water is lower than 70 ° C. based on the temperature data from the temperature sensor 32 that detects the temperature of the water that is the first absorbent 26. Then, an instruction to open the valve 20a and close the valve 20b is transmitted. When the water temperature is 70 ° C. or higher, an instruction to close the valve 20a and open the valve 20b is transmitted to the valve 20. The valve 20 opens and closes the valves 20a and 20b according to the instruction.

  According to the present embodiment, nitric acid in the exhaust from the internal combustion engine is always brought into contact with the ionic liquid that is the second absorbing liquid 28, and nitric acid in the exhaust is changed according to the temperature of the water that is the first absorbing liquid 26. It is possible to select whether to contact with water. When the temperature of the water which is the 1st absorption liquid 26 is less than 70 degreeC, the nitric acid in exhaust_gas | exhaustion is made to contact both the ionic liquid which is the 2nd absorption liquid 28, and water. Thereby, nitric acid can be separated and removed from the exhaust gas more than in the case of using one absorber. In addition, the temperature of water being less than 70 ° C. means that the temperature of the exhaust gas from the internal combustion engine 12 is low, and the exhaust gas comes into contact with the ionic liquid in this state, so that the ionic liquid becomes 70 ° C. or less. Conceivable. However, as is apparent from FIG. 3, the nitric acid absorption rate of the ionic liquid is relatively high although it does not reach water even in the temperature range of 70 ° C. or lower, and a certain amount of nitric acid absorption is expected. it can.

  When the temperature of the water which is the 1st absorption liquid 26 is 70 degreeC or more, the exhaust_gas | exhaustion from the 2nd absorption device 24 bypasses the 1st absorption device 22, and is discharged | emitted as it is to an exhaust outlet. As a result, the exhaust from the internal combustion engine 12 can be circulated only through the second absorber 24. When the temperature of the water is 70 ° C. or higher, the nitric acid absorption rate of water is low, so there is not much significance in contacting nitric acid with water, and evaporation is promoted if the water is kept at a high temperature. Therefore, the exhaust gas purification device 50 does not allow the exhaust gas to flow through the first absorption device 22 when the water is 70 ° C. or higher, so that the nitric acid absorption rate of the exhaust gas purification device 50 as a whole is not significantly reduced. The evaporation of water as the liquid 26 is prevented.

<Third Embodiment>
FIG. 7 is a schematic configuration diagram of an exhaust emission control device 70 according to the third embodiment. Also in FIG. 7, illustration of the internal combustion engine and the reformer is omitted. The description of the same components of the exhaust purification device 70 as those of the exhaust purification device 10 according to the first embodiment will be omitted. Also in the third embodiment, the first absorption liquid 26 is water, and the second absorption liquids 28a and 28b are ionic liquids.

  As compared with the first embodiment, the exhaust gas purification device 70 is further added with one absorption device. Specifically, the exhaust purification device 70 includes a first absorption device 22, a second absorption device 24, and a third absorption device 72.

  The third absorption device 72 is the same device as the second absorption device 24, and the second absorption liquid 28b included in the third absorption device 72 is the same type as the second absorption liquid 28a included in the second absorption device 24. is there. That is, the second absorbing liquid 28b included in the third absorbing device is also an ionic liquid.

  In the exhaust purification device 70, the exhaust from the internal combustion engine 12 is exhausted to the exhaust pipe 74. A valve 20-1 and a valve 20-2 are provided in the middle of the exhaust pipe 74, and the exhaust flow path is switched by these two valves. Specifically, the valve 20-1 and the valve 20-2 are connected to the exhaust pipe 74 a connected to the first absorber 22, the exhaust pipe 74 b connected to the second absorber 24, and the third absorber 72. The exhaust passage is switched so that the exhaust from the internal combustion engine flows through any of the exhaust pipes 74c.

  The exhaust purification device 70 is further provided with concentration sensors 76a and 76b. The concentration sensor 76a is a sensor that measures the concentration of nitric acid in the second absorbing liquid 28a of the second absorbing device 24. The concentration sensor 76b is a sensor that measures the concentration of nitric acid in the second absorbing liquid 28b of the third absorbing device 72.

  In the present embodiment, a pH meter that measures the hydrogen ion index (pH (pH)) of the absorbing solution is used as the concentration sensor. The more nitric acid is absorbed by the absorbent, the higher the acidity of the absorbent. Therefore, the concentration of nitric acid in the absorbing solution can be grasped by a pH meter that measures the degree of acidity.

  FIG. 8 is a flowchart showing a processing flow of the exhaust purification device 70 in the third embodiment. Specifically, the control procedure of the valves 20-1 and 20-2 by the control unit 34 is shown. Hereinafter, each step of the flowchart of FIG. 8 will be described with reference to FIG.

  The exhaust gas purification device 70 starts control of the exhaust gas flow path when the internal combustion engine 12 is started. In step S20, the control unit 34 compares the temperature data of the first absorbent 26 detected by the temperature sensor 32 with a threshold value that is set in advance and stored in a storage unit (not shown in FIG. 7). Also in the present embodiment, 70 ° C. is set as the threshold value.

  When it is determined in step S20 that the temperature of the first absorbent liquid 26 is lower than the threshold value, in step S22, the control unit 34 opens the valve 20-1a and opens the valve 20-1b with respect to the valve 20-1. A close instruction is transmitted, and the valve 20 opens and closes the valve according to the instruction. Thereby, the exhaust from the internal combustion engine 12 is circulated only to the first absorber 22 via the exhaust pipe 74a.

  When it is determined in step S20 that the temperature of the first absorbing liquid 26 is equal to or higher than the threshold value, in step S24, the control unit 34 refers to the two concentration data detected by the concentration sensor 76a and the concentration sensor 76b, The nitric acid concentrations of the absorbing liquid 28a and the second absorbing liquid 28b are compared.

  When the nitric acid concentration of the second absorption liquid 28a is equal to or higher than the nitric acid concentration of the second absorption liquid 28b, in step S26, the control unit 34 closes the valve 20-1a with respect to the valve 20-1, and closes the valve 20-1b. Is transmitted, and further, an instruction to close the valve 20-2a and open the valve 20-2b is transmitted to the valve 20-2. The valves 20-1 and 20-2b open and close the valves according to the instructions. As a result, the exhaust from the internal combustion engine 12 is circulated only to the third absorber 72 via the exhaust pipe 74c.

  When the nitric acid concentration of the second absorbing liquid 28a is less than the nitric acid concentration of the second absorbing liquid 28b, in step S28, the control unit 34 closes the valve 20-1a with respect to the valve 20-1, and closes the valve 20-1b. Is transmitted, and further, an instruction to open the valve 20-2a and close the valve 20-2b is transmitted to the valve 20-2. The valves 20-1 and 20-2b open and close the valves according to the instructions. Thereby, the exhaust from the internal combustion engine 12 is circulated only to the second absorber 24 through the exhaust pipe 74b.

  In step S30, the control unit 34 determines whether or not the internal combustion engine 12 has stopped. When the internal combustion engine 12 is stopped, the control of the exhaust passage is finished. If the internal combustion engine 12 is operating, the process returns to step 10 again. That is, while the internal combustion engine 12 is operating, the control unit 34 always executes control of the exhaust passage.

  In the present embodiment, when the temperature of the water that is the first absorbing liquid 26 is less than 70 ° C., the nitric acid in the exhaust is brought into contact with water, and when the temperature of the water is 70 ° C. or more, This is the same as the first embodiment in that nitric acid is brought into contact with the ionic liquid. Since the exhaust gas purification device 70 according to the third embodiment is provided with two absorption devices having an ionic liquid as the absorption liquid, when the temperature of the water becomes 70 ° C. or higher, the second purification device 24 and the second absorption device The question is which of the three absorbers 72 the nitric acid in the exhaust is circulated.

  From the viewpoint that the nitric acid absorption rate decreases as the concentration of nitric acid in the absorption liquid increases, the exhaust gas purification device 70 compares the concentration of nitric acid in a plurality of absorption liquids of the same type possessed by the plurality of absorption apparatuses. Circulate the nitric acid in the exhaust through the lower absorption liquid. Thereby, the nitric acid in exhaust_gas | exhaustion can be distribute | circulated by selecting an absorber with a higher nitric acid absorption rate from the some absorber which has the same kind of absorption liquid. Note that the fluctuation of the nitric acid absorption rate is dominated by the effect of the temperature of the absorbing solution, and the influence of the nitric acid concentration is smaller than the effect of the temperature.

  In this embodiment, two absorption devices having an ionic liquid as an absorption liquid are provided, but three or more absorption devices having an ionic liquid as an absorption liquid may be provided. In this case as well, it is only necessary to detect the nitric acid concentration of the ionic liquid included in each absorption device and determine the absorption device that distributes the nitric acid in the exhaust gas based on the nitric acid concentration. Specifically, the nitric acid in the exhaust gas is circulated through the absorption device having the absorption liquid having the lowest nitric acid concentration.

  In the present embodiment, the concentration of nitric acid in both the second absorption liquid 28a and the second absorption liquid 28b is detected, and the absorption device that circulates the exhaust gas from the internal combustion engine 12 is selected by comparing the concentrations thereof. It is also possible to adopt a mode in which it is determined whether to distribute the nitric acid in the exhaust gas to either the second absorber 24 or the third absorber 72 based on only one nitric acid concentration. In this case, for example, when the temperature of the water that is the first absorption liquid 26 becomes 70 ° C. or higher, it is predetermined that the exhaust gas is preferentially circulated through the second absorption device 24, and the second absorption liquid 28 a Only detect nitric acid concentration. Then, the nitric acid in the exhaust gas is caused to flow through the third absorption device 72 when the nitric acid concentration of the second absorption liquid 28a becomes equal to or higher than a predetermined value near the absorption saturation.

  In the present embodiment, two absorption devices having ionic liquid as an absorption liquid are provided. However, a plurality of absorption devices having water as an absorption liquid may be provided. Also in this case, a plurality of concentration sensors that detect the concentration of nitric acid in water that each absorption device has may be provided, and the absorption device that distributes the nitric acid in the exhaust gas may be determined by comparing the concentration of nitric acid in the water that each absorption device has. . Further, in this case, in place of the concentration sensor, a plurality of temperature sensors that detect the temperature of the water that each absorption device has are provided, and the absorption device that distributes nitric acid in the exhaust gas based on the temperature of the water that each absorption device has May be determined. Specifically, the exhaust gas is circulated through an absorption device in which the temperature of water as an absorption liquid is a predetermined value (for example, 70 ° C.) or less. This means that the water that is the absorbing liquid is heated by the heat of the exhaust gas, but the exhaust gas has not been circulated so far, that is, the nitric acid in the exhaust gas is circulated through the absorbing liquid that has not been heated and has a low temperature.

  10, 50, 70 Exhaust purification device, 12 Internal combustion engine, 16 Reformer, 20, 20-1, 20-2 Valve, 22 First absorber, 24 Second absorber, 32 Temperature sensor, 34 Control unit, 72 3rd absorber, 76a, 76b Concentration sensor.

Claims (5)

An exhaust purification device for an internal combustion engine for purifying nitrogen oxides contained in exhaust from the internal combustion engine,
A first absorption device that has a first absorption liquid and causes the first absorption liquid to absorb the nitrogen oxide that is distributed;
A second absorption device having a second absorption liquid having a temperature characteristic of an absorption rate of nitrogen oxides different from that of the first absorption liquid, and absorbing the nitrogen oxide flowing through the second absorption liquid;
With
The nitrogen oxide is circulated through at least one of the first absorption device and the second absorption device.
An exhaust emission control device for an internal combustion engine, characterized in that: In the first temperature range, the absorption rate of nitrogen oxides in the first absorption liquid is larger than the absorption rate of nitrogen oxides in the second absorption liquid,
In a second temperature range different from the first temperature range, the absorption rate of nitrogen oxides in the second absorption liquid is larger than the absorption rate of nitrogen oxides in the first absorption liquid.
The exhaust emission control device for an internal combustion engine according to claim 1, wherein: A flow path switching device for switching the flow path of the nitrogen oxides between the internal combustion engine and the first absorption device and the second absorption device;
Temperature detecting means for detecting the temperature of at least one of the first absorbent and the second absorbent;
Further comprising
The flow path switching device selects an absorption device that circulates the nitrogen oxides based on the temperature detected by the temperature detection means, and the flow channel switching device is configured so that the nitrogen oxides are circulated through the selected absorption device. Switch,
The exhaust emission control device for an internal combustion engine according to claim 1 or 2, characterized by the above. A plurality of the second absorption devices are provided,
The exhaust gas purification device for the internal combustion engine includes:
Concentration detecting means for detecting the concentration of at least one nitrogen oxide in the plurality of second absorbing liquids of the plurality of second absorbing devices;
Further comprising
The flow path switching device selects a second absorption device for circulating the nitrogen oxide from a plurality of second absorption devices based on the nitrogen oxide concentration of the second absorption liquid, and selects the second selected Switching the flow path so that the nitrogen oxide is circulated through the absorber;
The exhaust emission control device for an internal combustion engine according to claim 3, wherein: Either one of the first absorption liquid and the second absorption liquid is water or an alkaline aqueous solution, and the other is an ionic liquid.
The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 4, wherein the exhaust gas purification device is an internal combustion engine.

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