JP2011179338A - Nox removal system for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a NOx removal system for an internal combustion engine, sufficiently absorbing NOx while employing a method for absorbing and removing NOx in exhaust gas by using NOx absorbing liquid. <P>SOLUTION: This NOx removal system for the internal combustion engine includes a NOx removal device 30 which holds the NOx absorbing liquid absorbing contacted NOx and which absorbs and removes NOx in the exhaust gas by bringing the exhaust gas from the internal combustion engine 10 into contact with the NOx absorbing liquid. A CO<SB>2</SB>removal device 20 removing CO<SB>2</SB>in the exhaust gas is arranged on the upstream side of the NOx removal device 30 in an exhaust pipe 11. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a NOx removal system for an internal combustion engine that absorbs and removes NOx in the exhaust gas by bringing the exhaust gas of the internal combustion engine into contact with a NOx absorbing liquid.

  Conventionally, as an apparatus for removing NOx in exhaust gas, an apparatus using a NOx storage reduction catalyst and an apparatus using a urea selective reduction catalyst are known. The NOx occlusion reduction catalyst is for reducing the occluded NOx by using HC generated by periodically rich combustion of the internal combustion engine as a reducing agent (see Patent Document 1). The urea selective reduction catalyst selectively reduces NOx in exhaust gas using urea as a reducing agent (see Patent Document 2).

  However, these apparatuses have a disadvantage that the reduction function is not exhibited until the temperature rises to a temperature at which the catalyst is activated (for example, 200 ° C.). Moreover, in recent years, since there is a tendency to introduce low-temperature combustion and exhaust heat recovery technology, the above-mentioned disadvantages are particularly noticeable when starting an internal combustion engine.

JP 2008-82315 A JP 2009-281294 A

  Therefore, the present inventors examined the following apparatus, which is a completely different system from the system of reducing with a catalyst as in Patent Documents 1 and 2. That is, it is a device that holds a liquid that can absorb NOx that has come into contact (NOx absorbing liquid), and absorbs and removes NOx in the exhaust gas by bringing the liquid into contact with the exhaust gas. Specific examples of the NOx absorbing liquid include ionic liquid, alkaline aqueous solution, water and the like. Since such a NOx absorbing liquid can absorb NOx even at room temperature, the conventional drawback that NOx cannot be removed until the catalyst activation temperature is reached can be solved.

  However, the present inventors have found that the following problem occurs in the system using the NOx absorbing liquid. That is, the NOx absorbing liquid absorbs not only NOx in the exhaust gas but also CO2. Moreover, while the NOx concentration in the exhaust gas of the internal combustion engine is 0.1% or less, the CO2 concentration is several percent to several tens of percent, so that absorption by the NOx absorbing liquid is dominated by CO2. This causes a problem that NOx cannot be sufficiently absorbed.

  The present invention has been made in order to solve the above-mentioned problems, and its purpose is to absorb NOx sufficiently while adopting a method of absorbing and removing NOx in exhaust gas using a NOx absorbing liquid. An object of the present invention is to provide a NOx removal system for an internal combustion engine.

  Hereinafter, means for solving the above-described problems and the operation and effects thereof will be described.

  According to the first aspect of the present invention, a NOx removing device that holds NOx absorbing liquid that absorbs contacted NOx and that absorbs and removes NOx in the exhaust gas by bringing the exhaust gas of the internal combustion engine into contact with the NOx absorbing liquid; And a CO2 removal device that is disposed on the upstream side of the NOx removal device in the exhaust pipe and removes CO2 in the exhaust gas.

  According to this, since the CO2 removal device is provided on the upstream side of the NOx removal device in the exhaust pipe, the exhaust gas in a state where the CO2 concentration is lowered by the CO2 removal device can be sent to the NOx removal device. Therefore, it is possible to reduce the amount of CO2 that is absorbed by the NOx absorbing liquid held by the NOx removing device, and as a result, the NOx absorbing liquid can absorb a sufficient amount of NOx.

  According to a second aspect of the present invention, the CO2 removing device has a CO2 absorbing liquid that absorbs the contacted CO2, and absorbs CO2 in the exhaust gas by bringing the exhaust gas of the internal combustion engine into contact with the CO2 absorbing liquid. It is characterized by being removed.

  Since such a CO2 absorbing liquid can absorb CO2 even at room temperature, contrary to the above-described invention, for example, when a device that reduces and removes CO2 on a catalyst using a reducing agent is adopted as a CO2 removing device. The problem arises that CO2 cannot be removed until the catalyst reaches the activation temperature. On the other hand, in the above-mentioned invention, a CO2 removing device of a method of adsorbing CO2 with a CO2 absorbing liquid is adopted, and such a CO2 absorbing liquid can absorb CO2 even at room temperature, so that the catalyst activation temperature is reached. The above-mentioned problem that CO2 cannot be removed can be solved. Specific examples of the CO2 absorbing liquid include ionic liquid, alkaline aqueous solution, water, and the like.

  According to a third aspect of the present invention, the CO2 removal device is connected to the circulation path and circulates the CO2 absorption liquid to the circulation path, and is disposed in the exhaust pipe, and the CO2 absorption liquid is used as exhaust gas. And an exhaust gas contactor to be contacted.

  Here, in the case of an internal combustion engine mounted on a vehicle, the exhaust pipe is generally arranged below the floor of the vehicle. When an entire CO2 removal device is to be mounted on such an exhaust pipe, the vehicle floor Below, the mounting space is limited and the degree of freedom of mounting layout is small, so mounting is difficult.

  On the other hand, according to the above invention, the CO2 removal device is configured to connect the exhaust gas contactor to the circulation path through which the CO2 absorption liquid is circulated by the circulation pump. Therefore, for example, a tank that stores the CO2 absorption liquid is connected to the circulation path. In this case, the exhaust gas contactor disposed in the exhaust pipe can be reduced in size. Therefore, it can be easily realized to connect the downsized exhaust gas contactor to the exhaust pipe under the vehicle floor where the mounting space is limited, and the tank and circulation pump are arranged with the exhaust gas contactor under the vehicle floor. Without being limited to this, the degree of freedom of the layout can be improved.

  According to a fourth aspect of the present invention, the CO2 removal device has a circulation control means for controlling a circulation state of the CO2 absorbing liquid, and a NOx emission amount in the exhaust gas is a predetermined amount or more in an operation state of the internal combustion engine. In the case where the operation region that becomes the high NOx operation region and the operation region that becomes less than the predetermined amount is the low NOx operation region, the circulation control means, when the operation region is the low NOx operation region, The circulation of the CO2 absorbing liquid is stopped, or the circulation flow rate to the exhaust gas contactor is reduced as compared with the high NOx operation region.

  Here, the NOx amount in the exhaust gas changes greatly when the operating state of the internal combustion engine changes, such as the engine rotation speed and the operating load, but the NOx removing device is in an operating state in which a large amount of NOx is discharged (high NOx operation). Therefore, it is important to absorb a sufficient amount of NOx, and for this purpose, it is desirable to increase the CO2 removal capability of the CO2 removal device during high NOx operation.

  In the above invention in view of this point, during the low NOx operation, the circulation of the CO2 absorbing liquid to the exhaust gas contactor is stopped or the circulation flow rate is reduced, so the amount of absorbed CO2 with respect to the amount of CO2 absorbing liquid in the entire circulation path is reduced. An increase in the rate (absorption rate) is suppressed. That is, at the time of low NOx operation, it is possible to keep the absorption ratio of the CO2 absorbing liquid in the entire circulation path low in preparation for high NOx operation. Therefore, it is possible to increase the amount of CO2 absorbed during high NOx operation, and as a result, a sufficient amount of NOx can be absorbed by the NOx removal device during high NOx operation.

  Incidentally, specific examples of the “circulation control means” include means for controlling the operation of the circulation pump 23 illustrated in FIG. 1, means for controlling the operation of the valves 22c and 22d illustrated in FIG.

  According to a fifth aspect of the present invention, the CO2 removal device is attached to the exhaust pipe, and an exhaust gas contactor for contacting the CO2 absorbing liquid with the exhaust gas; and a branch from the exhaust pipe to bypass the exhaust gas contactor. NOx in the exhaust gas in the operating state of the internal combustion engine, and a bypass valve that switches the flow of the exhaust gas to any of the bypass passage and the exhaust gas contactor. In the case where the operation region where the emission amount is equal to or greater than the predetermined amount is the high NOx operation region and the operation region where the emission amount is less than the predetermined amount is the low NOx operation region, the exhaust gas is circulated to the exhaust gas contactor in the case of the high NOx operation region. In the low NOx operation region, the operation of the switching valve is controlled so that the exhaust gas flows through the bypass passage.

  As described above, during high NOx operation, it is desirable to increase the CO2 removal capability of the CO2 removal device so that the NOx removal device can absorb a sufficient amount of NOx. In the above invention in view of this point, during low NOx operation, exhaust gas is circulated through the bypass passage to suppress an increase in the absorption ratio of the CO2 absorbing liquid in the entire circulation path, and circulate in preparation for high NOx operation. The absorption rate for the entire route can be kept low. And since exhaust gas is circulated to the exhaust gas contactor during high NOx operation, the amount of CO2 absorbed during high NOx operation can be increased, and a sufficient amount of NOx can be absorbed by the NOx removal device during high NOx operation. .

  In the invention according to claim 6, the CO2 removal device includes a tank that is connected to the circulation path and stores the CO2 absorption liquid, and a circulation control unit that controls a circulation state of the CO2 absorption liquid, The circulation control means discharges the CO2 absorbing liquid in the exhaust gas contactor and absorbs CO2 in the tank when the absorption ratio of CO2 to the CO2 absorbing liquid in the exhaust gas contactor is a predetermined value or more. When the absorption ratio is less than a predetermined value, the CO2 absorption liquid in the exhaust gas contactor is held without being circulated to the circulation path.

  In short, in the above invention, the CO2 absorbing liquid is intermittently circulated, and when the absorption ratio of the CO2 absorbing liquid in the exhaust gas contactor exceeds a predetermined value, the CO2 absorbing liquid in the exhaust gas contactor is discharged to Since it is automatically controlled to replace the CO2 absorbing liquid, it can be automatically avoided that the CO2 absorbing liquid in the exhaust gas contactor becomes in an absorption saturation state where CO2 cannot be absorbed.

  According to a seventh aspect of the present invention, the CO2 removing device includes a circulation speed control means for controlling a circulation speed of the CO2 absorbing liquid to the exhaust gas contactor, and the circulation speed control means is provided to the exhaust gas contactor. When the CO2 absorption liquid is constantly circulated and the absorption ratio of CO2 to the CO2 absorption liquid in the exhaust gas contactor is greater than or equal to a predetermined value, the circulation speed is higher than when the absorption ratio is less than the predetermined value. It is characterized by raising.

  In short, in the above invention, the CO2 absorbing liquid is constantly circulated, and when the absorption ratio of the CO2 absorbing liquid in the exhaust gas contactor exceeds a predetermined value, it is automatically controlled to increase the circulation speed. It can be automatically avoided that the CO2 absorbing liquid of the present invention is in an absorption saturation state where CO2 cannot be absorbed.

  In the invention according to claim 8, the CO2 removal device includes a circulation pump that circulates the CO2 absorption liquid in a circulation path, an exhaust gas contactor that is connected to the circulation path and contacts the CO2 absorption liquid with exhaust gas, and And a separation / release device that is connected to a circulation path and separates and discharges CO2 absorbed by the CO2 absorption liquid from the CO2 absorption liquid.

  According to the above invention, CO2 absorbed in the CO2 absorbing liquid can be separated and released from the CO2 absorbing liquid, so that the absorption ratio of the CO2 absorbing liquid in the entire circulation path can be reduced. Therefore, since it is possible to avoid the CO2 absorbing liquid in the entire circulation path from being saturated, it is possible to eliminate the need for replacement with a new CO2 absorbing liquid. Alternatively, the exchange cycle can be lengthened.

  According to a ninth aspect of the present invention, the CO2 removal device has a separation control means for controlling a separation speed by the separation and discharger, and the NOx emission amount in the exhaust gas in the operating state of the internal combustion engine is a predetermined amount or more. In the case of the high NOx operation region as the operation region and the low NOx operation region as the operation region that is less than the predetermined amount, the separation control means is in the case of the high NOx operation region in the low NOx operation region. Compared to the above, the separation speed is reduced, or the separation operation in the separation discharger is controlled to be stopped.

  As described above, during high NOx operation, it is desirable to increase the CO2 removal capability of the CO2 removal device so that the NOx removal device can absorb a sufficient amount of NOx. In the above-mentioned invention in view of this point, during the low NOx operation, the separation speed in the separation / release device is reduced or the separation operation is stopped, so that an increase in the absorption ratio of the CO2 absorbing liquid in the entire circulation path is suppressed. That is, at the time of low NOx operation, it is possible to keep the absorption ratio of the CO2 absorbing liquid in the entire circulation path low in preparation for high NOx operation. Therefore, it is possible to increase the amount of CO2 absorbed during high NOx operation, and as a result, a sufficient amount of NOx can be absorbed by the NOx removal device during high NOx operation.

  According to a tenth aspect of the present invention, the CO2 removal apparatus has a separation control means for controlling a separation speed by the separation / discharger, and the separation control means has a CO2 absorption ratio with respect to the CO2 absorption liquid of a predetermined value or more. In this case, the separation speed is controlled to be increased as compared with the case where it is less than a predetermined value.

  According to the above invention, when the absorption ratio of the CO2 absorbing liquid reaches a predetermined value or higher, the separation rate is increased, so that it can be automatically avoided that the CO2 absorbing liquid is in an absorption saturation state where CO2 cannot be absorbed. In other words, when the absorption ratio is less than the predetermined value, the separation speed is reduced, so that the driving power consumed by the separation emitter can be suppressed. Therefore, when driving the separation / release device with the electric power generated by the driving force of the internal combustion engine, it is possible to reduce the power generation load by the internal combustion engine. Furthermore, in the case where CO2 is separated from the CO2 absorbing liquid by heating the CO2 absorbing liquid, it is also effective for the following problems.

  That is, depending on the type of the CO2 absorbing liquid, the higher the temperature, the lower the amount that can absorb CO2. Further, when the temperature becomes high, the CO2 absorbing liquid is vaporized, and it becomes a problem that the CO2 absorbing ability cannot be fully exhibited. Therefore, when CO2 is separated by heating the CO2 absorbing liquid, the CO2 absorbing liquid becomes high temperature by heating to separate, and there is a concern about the above problem.

  In order to solve this problem, in the above invention, the separation rate is increased if the absorption ratio is equal to or higher than a predetermined value, while the separation speed is decreased if the absorption ratio is lower than the predetermined value. When the temperature is low, the high temperature of the CO2 absorbing liquid can be suppressed. Therefore, the said problem by CO2 absorption liquid becoming high temperature can be suppressed.

  In the invention according to claim 11, the separation / release device heats the CO2 absorption liquid to separate CO2 from the CO2 absorption liquid, and the temperature of the CO2 absorption liquid in the separation / release device is When the temperature is higher than the upper limit temperature, the degree of heating by the separation discharger is reduced as compared with the case where the temperature is lower than the upper limit temperature.

  According to this, it can avoid that it becomes so high that CO2 absorption liquid evaporates, and it can avoid that CO2 absorption performance falls significantly by evaporating.

  According to a twelfth aspect of the present invention, a heat recovery device attached to the exhaust pipe and recovering the heat of exhaust gas is provided, and the separation / release device uses the heat recovered by the heat recovery device to supply the CO2 absorbing liquid. It is configured to be heated.

  According to this, since the CO2 absorbing liquid is heated using the heat of the exhaust gas, the amount of power consumed by the NOx removal system can be reduced as compared with the case where the heat source such as an electric heater is provided and heated.

  In the invention according to claim 13, the internal combustion engine has a filter (DPF device) that collects particulate matter (PM) in exhaust gas, and removes the collected particulate matter from the filter. And a regeneration process control means for executing a regeneration process for raising the exhaust temperature so as to control the operation of the circulation pump so that the CO2 absorbing liquid flows into the separation / release device at the timing when the regeneration process is performed. It is characterized by doing.

  At the timing of executing the regeneration process, the amount of heat that can be recovered by the heat recovery device is large, and the separation capability of the separation / release device is high. According to this, the heat of the exhaust gas can be used effectively, and CO2 can be separated and released in a short time with respect to the CO2 absorbing liquid that has been sent into the separation / release device.

  The invention according to claim 14 is characterized in that the oxidizing means for oxidizing NO in the exhaust gas to NO2 is arranged in the exhaust pipe upstream of the NOx removal device and downstream of the CO2 removal device. To do.

  Depending on the type of NOx absorbing liquid, NO2 may be used when the ratio of the amount absorbed by the NOx absorbing liquid to the amount that passes through the NOx removal device without being absorbed by the NOx in the exhaust gas is "absorption rate". However, the absorption rate is higher than NO. Therefore, according to the above invention in which the oxidizing means is arranged on the upstream side of the NOx removing device, the NOx absorption rate by the NOx removing device can be improved.

  However, if NO is oxidized to NO2 upstream of the CO2 removal device, there is a concern that the amount of NO2 absorbed by the CO2 absorbing liquid increases depending on the type of the CO2 absorbing liquid. According to the above-mentioned invention in view of this point, since the oxidizing means is arranged on the upstream side of the NOx removing device and the downstream side of the O 2 removing device, the above-mentioned concern can be solved.

  Specific examples of the oxidizing means include an oxidation catalyst and an ozone generator. However, when an oxidation catalyst is employed, in the above invention, the oxidation means (oxidation catalyst) is disposed at a location far from the combustion chamber in the exhaust pipe, so that the oxidation catalyst is heated and activated by the exhaust gas. There is a concern that sufficient heating is not possible. In that case, it is desirable to provide heating means such as a burner or an electric heater in the oxidation catalyst.

  The invention according to claim 15 is characterized in that the CO2 removing device has a cooler for cooling the CO2 absorbing liquid.

  According to this, the above-mentioned problem that the CO2 absorbing liquid becomes high temperature and the CO2 absorbing ability is lowered or vaporizes can be solved. In particular, when a separation / release device that separates CO2 from the CO2 absorbing liquid by heating is provided, the above invention of cooling the CO2 absorbing liquid by a cooler is effective.

  In the invention of claim 16, the CO2 absorbing liquid is a solution in which a solute that absorbs contacted CO2 is dissolved in a solvent, and the CO2 removing device is a concentration control means for controlling the solute concentration of the CO2 absorbing liquid. It is characterized by providing.

  Here, the solvent (for example, water) may be vaporized to increase the solute concentration of the CO2 absorbing liquid, or the water component in the exhaust gas may be mixed into the CO2 absorbing liquid to decrease the solute concentration. On the other hand, according to the said invention, since it can control automatically so that a solute density | concentration may become an optimal density | concentration, it can suppress that the absorption capacity of CO2 absorption liquid falls by a density | concentration change.

The figure which shows the NOx removal system concerning 1st Embodiment of this invention. The figure explaining the CO2 absorption capability by CO2 absorption liquid (NaOH aqueous solution). The flowchart which shows the procedure controlled to circulate a CO2 absorption liquid intermittently in 1st Embodiment. The figure which shows the NOx removal system for internal combustion engines concerning 2nd Embodiment of this invention. The figure which shows the liquid recovery device in FIG. The figure which shows the modification of the liquid recovery device in FIG. The flowchart which shows the procedure which controls the density | concentration of an absorption liquid in 2nd Embodiment. In 2nd Embodiment, the flowchart which shows the procedure controlled to circulate a CO2 absorption liquid intermittently. The figure which shows the NOx removal system concerning 3rd Embodiment of this invention. The figure which shows the relationship between the driving | running state of an internal combustion engine, NOx emission amount, and CO2 emission amount. The flowchart which shows the procedure which controls operation | movement of a bypass valve etc. in 3rd Embodiment. The figure which shows the NOx removal system concerning 4th Embodiment of this invention. The flowchart which shows the procedure controlled to circulate CO2 absorption liquid continuously in 5th Embodiment of this invention.

  Hereinafter, embodiments embodying the present invention will be described with reference to the drawings. In the following embodiments, parts that are the same or equivalent to each other are denoted by the same reference numerals in the drawings, and the description of the same reference numerals is used. The internal combustion engine to which the NOx removal system according to each embodiment is applied is mounted on a vehicle and functions as a travel drive source, and assumes a compression self-ignition type diesel engine.

(First embodiment)
FIG. 1 is a diagram showing a NOx removal system and an internal combustion engine 10 according to the present embodiment. First, exhaust gas discharged from the combustion chamber 10a of the internal combustion engine 10 is discharged from a predetermined location behind the vehicle through an exhaust pipe 11 disposed under the vehicle floor. An oxidation catalyst (DOC12) that oxidizes NOx contained in the exhaust gas is attached to the exhaust pipe 11. By this DOC12, NO in the exhaust gas is oxidized to NO2.

  Further, a filter (DPF 13) for collecting particulate matter (PM) in the exhaust is attached to the exhaust pipe 11 downstream of the DOC 12. Then, in order to burn the PM collected by the DPF 13, the injection amount and injection timing from the fuel injection valve 14 are controlled (regeneration processing control) so as to raise the exhaust gas temperature. The control device (ECU 15) when the operation of the fuel injection valve 14 is controlled so as to control the regeneration process corresponds to “regeneration process control means” described in the claims.

  A CO2 removal device 20 that removes CO2 in the exhaust gas is provided on the downstream side of the DPF 13 in the exhaust pipe 11, and NOx in the exhaust gas is removed on the downstream side of the CO2 removal device 20 in the exhaust pipe 11. A NOx removing device 30 is provided. Hereinafter, the configuration of each of the devices 20 and 30 will be described in detail.

<About the CO2 removal device 20>
The CO 2 removal device 20 is mainly configured to include a tank 21, an exhaust gas contactor 22, a circulation pump 23, and a separation / release device 24, which are connected by a circulation pipe 25. A CO 2 absorbing liquid (described in detail later) is stored in the tank 21. This CO 2 absorbing liquid circulates in the circulation path formed by the circulation pipe 25 by the operation of the circulation pump 23. The exhaust gas contactor 22 is attached to the exhaust pipe 11 and functions to bring the circulating CO 2 absorbing liquid into contact with the exhaust gas.

The CO2 absorbing liquid is a liquid that absorbs CO2 by coming into contact with CO2 in the exhaust gas. Specific examples include ionic liquids, alkaline solutions, water (for example, engine cooling water) described in JP-A-2008-296211, and the like. The liquid that selectively absorbs CO2 with little absorption of NOx in the exhaust gas _{(e.g., NaOH, KOH, Na 2 CO} 3, K 2 CO 3, Ca (OH) 2, ethanolamine, etc.) by using the This is preferable because the amount of CO2 absorption can be increased. The CO2 absorbing liquid may be a substance that absorbs CO2 (chemical adsorption) with a chemical change, or a substance that absorbs CO2 (physical adsorption) without a chemical change. The CO2 absorbing liquid may be a gel substance or a slurry substance.

  FIG. 2 is a test result showing the effect of removing CO2 when an aqueous NaOH solution is used as the CO2 absorbing liquid. When exhaust gas having a CO2 concentration of about 6% is caused to flow into the exhaust gas contactor 22, the exhaust gas contactor 22 It was confirmed that the CO2 concentration of the exhaust gas flowing out was reduced to about 1%.

  The exhaust gas contactor 22 includes a holding body 22a that soaks and holds the CO2 absorbing liquid, and a case 22b that houses the holding body 22a therein. The case 22b is connected to the exhaust pipe 11, and exhaust gas circulates in the case 22b. The case 22b is connected to the circulation pipe 25, and the CO2 absorbing liquid that has flowed into the case 22b through the circulation pipe 25 from the inlet of the case 22b is held by the holding body 22a. The holding body 22a is disposed so as to be exposed to the exhaust gas flowing through the case 22b. Therefore, the CO2 absorbing liquid held by the holding body 22a comes into contact with the exhaust gas.

  An inlet valve 22c and an outlet valve 22d are provided at the inlet and outlet of the case 22b. These valves 22c and 22d are electromagnetically driven valves, and their opening and closing operations are controlled by the ECU 15. Therefore, if the ECU 15 opens the outflow valve 22d, the CO2 absorbing liquid in the case 22b can be discharged, and if the ECU15 opens the inflow valve 22c, the CO2 absorbing liquid can flow into the case 22b. it can.

  The inlet is formed in the upper part of the case 22b, and the outlet is formed in the lower part of the case 22b. Therefore, when the outflow valve 22d is operated to open, the discharge can be performed by its own weight even if the circulation pump 23 is not driven. In addition, when the inflow valve 22c is opened while the CO2 absorbing liquid in the case 22b is discharged, the inflow valve 22c can flow by its own weight even if the circulation pump 23 is not driven.

  The separation / release device 24 includes a tank 24a for storing the CO2 absorbing liquid discharged from the exhaust gas contactor 22, and a heater 24b (heating means) provided in the tank 24a. When the CO2 absorbing liquid discharged from the exhaust gas contactor 22 and flowing into the tank 24a is heated by the heater 24b, CO2 absorbed in the CO2 absorbing liquid is separated from the CO2 absorbing liquid.

  The operation of the heater 24b is controlled by the ECU 15. Therefore, if the ECU 15 controls the heater 24b to operate, CO2 separation is promoted, and if the heater 24b is controlled to stop operating, the CO2 separation speed decreases. That is, the ECU 15 functions as a separation control unit that controls the separation speed by controlling the operation of the heater 24b (controlling the degree of heating).

  Here, there is a limit to the amount of CO2 that can be absorbed by the CO2 absorbing liquid per unit amount. In this specification, the state of the CO2 absorbing liquid that has absorbed such a limit amount is referred to as an absorption saturation state. Further, the ratio of the CO2 absorption amount to the amount that the CO2 absorption liquid can absorb CO2 (maximum absorption amount) in a state where the CO2 absorption amount is zero is referred to as an absorption ratio. That is, the absorption ratio in the absorption saturation state is 100%. Then, when CO2 is separated from the CO2 absorbing liquid by the separation / release device 24, the absorption ratio decreases, and the absorbing capacity of the CO2 absorbing liquid increases and returns. The separated CO2 is released to the atmosphere from the discharge port 24c. Then, the CO 2 absorbing liquid in a state where CO 2 is separated and removed by the separation / release device 24 circulates in the order of the tank 21, the CO 2 removal device 20, and the separation / release device 24.

  The operation of the circulation pump 23 is controlled by the ECU 15. In this embodiment, the circulation pump 23 is operated not intermittently but intermittently. That is, the CO2 absorbing liquid is not circulated constantly but is circulated intermittently. The contents of control of the circulation pump 23, the heater 24b, etc. will be described in detail later.

<About the NOx removing device 30>
Next, the configuration of the NOx removing device 30 will be described. The NOx removing device 30 mainly includes a tank 31, an exhaust gas contactor 32, and a circulation pump 33, which are connected by a circulation pipe 35.

  In the tank 31, a supply tank unit 31a that stores unused NOx absorbing liquid (described in detail later) supplied to the exhaust gas contactor 32, and a recovery tank unit 31b that stores the recovered used NOx absorbing liquid. It is divided into and. Thereby, it is avoided that the used NOx absorbing liquid is mixed into the unused NOx absorbing liquid. The NOx absorbing liquid in the supply tank 31 a is supplied to the exhaust gas contactor 32. The NOx absorbing liquid used in the exhaust gas contactor 32 is recovered to the recovery tank portion 31b by operating the circulation pump 33.

  The exhaust gas contactor 32 is attached to the downstream side of the exhaust gas contactor 32 of the CO2 removal device 20 in the exhaust pipe 11 and functions to bring the NOx absorbing liquid into contact with the exhaust gas.

The NOx absorbing liquid is a liquid that absorbs NOx by contacting with NOx in the exhaust gas. Specific examples include ionic liquids, alkaline solutions, water (for example, engine cooling water) described in JP-A-2008-296211, and the like. Further, if a liquid that selectively absorbs NOx without substantially absorbing CO2 in the exhaust gas (for example, FeSO ₄ , Ca (OH) ₂ , H ₂ SO ₄ , K ₂ Cr ₂ O _7, etc.), NOx is used. This is preferable because the amount of absorption can be increased. The NOx absorbing liquid may be a substance that absorbs NOx (chemical adsorption) with a chemical change, or may be a substance that absorbs NOx (physical adsorption) without a chemical change. The NOx absorbing liquid may be a gel substance or a slurry substance.

  The exhaust gas contactor 32 includes a holding body 32a that holds the NOx absorbing liquid, and a case 32b that houses the holding body 32a therein. The case 32b is connected to the exhaust pipe 11, and exhaust gas circulates in the case 32b. Further, the case 32b is connected to the circulation pipe 35, and the NOx absorbing liquid that has flowed into the case 32b through the circulation pipe 35 from the inlet of the case 32b is held by the holding body 32a. The holding body 32a is disposed so as to be exposed to the exhaust gas flowing through the case 32b. Therefore, the NOx absorbing liquid held in the holding body 32a comes into contact with the exhaust gas.

  An inlet valve 32c and an outlet valve 32d are provided at the inlet and outlet of the case 32b. These valves 32c and 32d are electromagnetically driven valves, and their opening and closing operations are controlled by the ECU 15. Therefore, if the outflow valve 32d is opened by the ECU 15, the NOx absorbing liquid in the case 32b can be discharged, and if the inflow valve 32c is opened by the ECU 15, the CO2 absorbing liquid can be flowed into the case 32b. it can.

  The inlet is formed in the upper part of the case 32b, and the outlet is formed in the lower part of the case 32b. Therefore, when the outflow valve 32d is opened, it can be discharged by its own weight even if the circulation pump 33 is not driven. In addition, when the inflow valve 32c is opened while the NOx absorbing liquid in the case 32b is discharged, the inflow valve 32c can flow by its own weight even if the circulation pump 33 is not driven.

  Here, there is a limit to the amount of NOx that can be absorbed by the NOx absorbing liquid per unit amount. In this specification, the state of the NOx absorbing liquid that has absorbed such a limit amount is referred to as an absorption saturated state. Further, the ratio of the NOx absorption amount to the amount (maximum absorption amount) that the NOx absorbing liquid can absorb NOx in a state where the NOx absorption amount is zero is referred to as an absorption ratio. That is, the absorption ratio in the absorption saturation state is 100%, and the absorption ratio of the unused NOx absorption liquid stored in the supply tank portion 31a is 0%.

  In short, the NOx absorbing liquid in the supply tank unit 31 a has an absorption ratio of zero and is supplied to the exhaust gas contactor 32. And the NOx absorption liquid in which the absorption rate became higher than the predetermined value in the exhaust gas contactor 32 is recovered by the circulation pump 33 to the recovery tank portion 31b. The used NOx absorbing liquid recovered in the recovery tank unit 31b is extracted from the tank 31 and discharged at a processing facility outside the vehicle. The supply of the new NOx absorbing liquid to the supply tank unit 31a is performed as needed by the vehicle user or the maintenance worker.

  The operation of the circulation pump 33 is controlled by the ECU 15. In this embodiment, the circulation pump 33 is operated not intermittently but intermittently. That is, the NOx absorbing liquid is not circulated constantly but is circulated intermittently.

  More specifically, the NOx removing device 30 has a sensor that detects a physical quantity correlated with the absorption ratio of the NOx absorbing liquid. In the present embodiment, a ph sensor 32e is used as the sensor, and the ph sensor 32e is attached to the exhaust gas contactor 32. If the ph detected by the ph sensor 32e is equal to or less than a predetermined value (if the acidity is high), the ECU 15 considers that the absorption ratio of the NOx absorbing liquid in the exhaust gas contactor 32 is equal to or greater than the predetermined value. The replacement control described below is performed.

  In the replacement control, first, the outflow valve 32d is opened to discharge the NOx absorbing liquid in the exhaust gas contactor 32. At this time, by driving the circulation pump 33, the discharged NOx absorbing liquid is recovered to the recovery tank portion 31b. When the outflow valve 32d is opened for a predetermined time, it is considered that the discharge of the NOx absorbing liquid is completed, and the outflow valve 32d is closed and the inflow valve 32c is opened. As a result, the NOx absorbing liquid in the supply tank 31 a flows into the exhaust gas contactor 32. When the inflow valve 32c is opened for a predetermined time, it is considered that the supply replacement of the NOx absorbing liquid is completed, and the inflow valve 32c is closed.

<About circulation control of CO2 absorption liquid>
Next, the procedure of the circulation control of the CO2 absorbing liquid by controlling the operation of the circulation pump 23 and the separation speed control by the separation / release device 24 by controlling the operation of the heater 24b will be described.

  FIG. 3 is a flowchart showing the procedure of the control, and is repeatedly executed by the microcomputer of the ECU 15 at a predetermined cycle (for example, every calculation cycle of the microcomputer or every predetermined crank angle).

  First, in step S10 shown in FIG. 3, it is determined whether or not the absorption ratio of the CO2 absorbing liquid in the exhaust gas contactor 22 is equal to or higher than a predetermined value. More specifically, the CO 2 removal device 20 has a sensor that detects a physical quantity correlated with the absorption ratio of the CO 2 absorbing liquid. In this embodiment, a ph sensor 22e is used as the sensor, and the ph sensor 22e is attached to the exhaust gas contactor 22. In step S10, if ph detected by the ph sensor 22e is equal to or less than a predetermined value (if the degree of acidity is high), it is considered that the absorption ratio of the CO2 absorbing liquid in the exhaust gas contactor 22 is equal to or greater than a predetermined value. The process proceeds to the next step S11.

  In step S11 (circulation control means), the operation of the circulation pump 23 is started. At this time, both the inflow valve 22c and the outflow valve 22d may be opened, or only the outflow valve 22d may be opened. Or it is good also as a structure which abolished both valves 22c and 22d. Thereby, the discharge of the CO2 absorbing liquid from the exhaust gas contactor 22 is started. In the subsequent step S12 (separation control means), energization to the heater 24b is started. Thereby, separation of CO2 by the separation discharger 24 is started.

  In the subsequent step S13, it is determined whether or not a predetermined operation time has elapsed since the operation of the circulation pump 23 was started in step S11. If it is determined that the predetermined operation time has elapsed (S13: YES), it is considered that the amount of the CO2 absorbing liquid that can be held by the exhaust gas contactor 22 has been discharged, and the circulation pump 23 of the circulation pump 23 is determined in subsequent step S14 (circulation control means). Stop operation. When both valves 22c and 22d have been opened since the start of operation of the circulation pump 23, both valves 22c and 22d are closed when the operation of the circulation pump 23 is stopped.

  On the other hand, when only the outflow valve 22d is opened when the operation of the circulation pump 23 is started, the outflow valve 22d is closed and the inflow valve 22c is opened when the circulation pump 23 is stopped. . According to this, it is possible to suppress mixing of the used CO2 absorbing liquid whose absorption ratio has increased to a predetermined value or more and the unused CO2 absorbing liquid supplied from the tank 21.

  In the subsequent step S15, it is determined whether or not the CO2 has been sufficiently separated and released so that the absorption ratio of the CO2 absorbing liquid in the separation and discharger 24 is reduced to below a predetermined value. Specifically, when the operation time of the heater 24b is equal to or higher than a predetermined temperature and a predetermined time has elapsed (S15: YES), it is considered that CO2 is sufficiently separated and released, and the subsequent step S16 (separation control means). The operation of the heater 24b is stopped.

  According to the embodiment described in detail above, the following effects can be obtained.

  (1) Since the exhaust gas contactor 22 of the CO2 removal device 20 is provided upstream of the exhaust gas contactor 32 of the NOx removal device 30 in the exhaust pipe 11, the exhaust gas in a state where the CO2 concentration is lowered by the CO2 removal device 20. Can be fed into the NOx removal device 30. Therefore, the amount of CO2 absorbed by the NOx absorbing liquid can be reduced, and as a result, a sufficient amount of NOx can be absorbed by the NOx absorbing liquid.

  (2) In the NOx removal system according to this embodiment, NOx is absorbed by bringing the NOx absorbing liquid into contact with the exhaust gas, and CO2 is absorbed by bringing the CO2 absorbing liquid into contact with the exhaust gas. Therefore, since the removal function by the CO2 removal device 20 and the NOx removal device 30 can be exhibited even at room temperature, even in the cold start of the internal combustion engine 10, NOx can be removed.

  (3) Here, the CO2 removal device 20 according to the present embodiment circulates the exhaust gas contactor 22 attached to the exhaust pipe 11 and the tank 21 separately, but the capacity of the exhaust gas contactor 22 If the heater 24b is provided in the exhaust gas contactor 22, the separation / release device 24 and the tank 21 can be integrated with the exhaust gas contactor 22, and the above-described circulation can be eliminated. However, when integrated in this way, the exhaust gas contactor 22 becomes large, and it becomes extremely difficult to install the exhaust gas contactor 22 under the floor of the vehicle.

  On the other hand, in this embodiment, since the exhaust gas contactor 22, the tank 21 and the separation / release device 24 are separately configured and circulated, the exhaust gas required to be connected to the exhaust pipe 11 located below the floor. The contactor 22 can be reduced in size. Therefore, it is possible to easily implement the exhaust gas contactor 22 below the floor, and to improve the degree of freedom of the mounting layout when the CO2 removal device 20 is mounted on the vehicle.

  Furthermore, according to the present embodiment in which the exhaust gas contactor 22, the tank 21 and the separation / release device 24 are separately configured and circulated, the capacity of the tank 21 is increased for the internal combustion engine 10 having a large displacement. While dealing with increasing the frequency of supplying the CO2 absorbing liquid to the exhaust gas contactor 22, the exhaust gas contactor 22 can be shared by the internal combustion engines 10 having different displacements.

  (4) When the absorption ratio of the CO2 absorbing liquid in the exhaust gas contactor 22 exceeds a predetermined value, the control is automatically performed so that the CO2 absorbing liquid in the exhaust gas contactor 22 is discharged and replaced with the CO2 absorbing liquid in the tank 21. It is possible to automatically avoid that the CO2 absorbing liquid in the exhaust gas contactor 22 is in an absorption saturation state where CO2 cannot be absorbed.

  Here, in determining whether or not to execute the control (replacement control) for replacing the CO2 absorbing liquid in the exhaust gas contactor 22, the determination is made based on the operation time of the internal combustion engine 10 or the travel distance of the vehicle. The ph sensor 22e can be eliminated and the cost can be reduced. However, according to the present embodiment in which the execution timing of the replacement control is determined by detecting the ph of the CO2 absorbing liquid using the ph sensor 22e, the absorption ratio can be accurately managed so as not to exceed a predetermined value. In addition, it is possible to solve the problem of being replaced at an early stage although it is less than the predetermined value.

  (5) Here, when NOx in the exhaust gas is absorbed by the exhaust gas contactor 32, the absorption rate of NO2 can be higher than that of NO. Therefore, in the present embodiment, since the DOC 12 that oxidizes NO to NO 2 is disposed on the upstream side of the exhaust gas contactor 32, the NOx absorption rate in the exhaust gas contactor 32 can be improved. Moreover, since DPF is arrange | positioned upstream of the exhaust gas contactors 22 and 32, it can suppress that PM in exhaust gas adheres inside the exhaust gas contactors 22 and 32, and clogging arises.

(Second Embodiment)
In the present embodiment shown in FIG. 4, functions such as a heat recovery device 24 d, a cooler 26, a liquid recovery device 27, and a solution tank 28 described below are added to the CO 2 removal device 20 according to the first embodiment, The functions of the liquid recovery device 37 and the solution tank 38 are also added to the NOx removal device 30. Hereinafter, the system configuration of FIG. 4 will be described focusing on differences from FIG. In FIG. 4, the same reference numerals as those in FIG.

  The heat recovery unit 24d is attached to the exhaust pipe 11 and recovers the heat of the exhaust gas. For example, engine cooling water is used as a heat medium. The engine cooling water is connected to the tank 24a of the separation / release device 24 through the pipe 24e, and is heated by exchanging heat with the CO2 absorbing liquid in the tank 24a. In short, the heater 24b shown in FIG. 1 is eliminated, and the CO2 absorption liquid is heated by the heat recovery device 24d to separate CO2.

  A pump 24f controlled by the ECU 15 is attached to the piping 24e through which the engine cooling water flows, and the degree of heating (that is, the separation speed) is controlled by controlling the operation of the pump 24f. For example, the temperature sensor 24g is attached to the tank 24a of the separation / discharger 24, the temperature of the CO2 absorbing liquid in the tank 24a is detected, and the on / off control of the pump 24f is switched according to the detected temperature, thereby controlling the degree of heating. Control.

  The cooler 26 is disposed in the separation / release device 24 and the tank 21 in the circulation pipe 25, and cools the CO 2 absorbing liquid immediately after being heated and separated by the separation / release device 24. The cooler 26 may be an air-cooling type that exchanges heat with the surrounding air, or may be a type that takes in a refrigerant that circulates through an evaporator included in the vehicle interior air conditioner and exchanges heat between the refrigerant and the CO2 absorbing liquid.

  The amount of CO2 absorbing liquid that can absorb CO2 decreases as the temperature rises. In particular, when the temperature rises above a predetermined temperature, the amount of CO2 that can be absorbed decreases rapidly. Therefore, the CO 2 absorbing liquid heated by the separation / release device 24 is cooled by the cooler 26.

  The liquid recovery unit 27 is disposed in the exhaust pipe 11 on the downstream side of the exhaust gas contactor 22 and on the upstream side of the NOx removing device 30. There is a concern that a part of the CO2 absorbing liquid that has been contacted by the exhaust gas contactor 22 is taken away into the exhaust pipe 11 together with the exhaust gas. The liquid recovery device 27 recovers the CO2 absorption liquid that has been taken away and has flowed out of the case 22b. Moreover, while removing CO2 from the collect | recovered CO2 absorption liquid and reducing an absorption rate, it functions so that the CO2 absorption liquid processed in this way may be returned to the circulation piping 25 through the piping 27a.

  FIG. 5 is a diagram illustrating the configuration of the liquid recovery device 27, and the liquid recovery device 27 includes an electrode 27 b disposed in the exhaust pipe 11 and an electric cell 27 c attached to the inner wall surface of the exhaust pipe 11. When a DC high voltage is applied to the electrode 27b, electrons adhere to the CO2 absorbing liquid that has flowed into the exhaust gas and are ionized. When the ionized CO2 absorbing liquid adheres to the electric cell 27c, only the CO2 ions absorbed by the CO2 absorbing liquid pass through the electric cell 27c and move to the storage unit 27d to be deposited. Since the reservoir 27d is electrically grounded, the CO2 ion electrons that have moved to the reservoir 27d flow into the ground. In other words, the CO2 absorbing liquid remaining without being able to pass through the electric cell 27c is in a state in which CO2 is removed, and the absorption ratio is reduced.

  In short, the CO2 absorbing liquid in the exhaust is charged at a high voltage to be deposited on the electric cell 27c and collected. Thereafter, CO2 is removed from the CO2 absorbing liquid recovered using the electric cell 27c, and the CO2 absorbing liquid having a reduced absorption rate is returned to the circulation pipe 25 through the pipe 27a. Note that the CO 2 accumulated in the reservoir 27d may be released to the atmosphere.

  FIG. 6 is a view showing a modification of the liquid recovery device 27 shown in FIG. 5, and the electric cell 27c is omitted. The CO2 absorbing liquid in the exhaust gas charged at a high voltage by the electrode 27b is collected in the storage tank 27e. In the storage tank 27e, the CO2 absorbing liquid having a high absorption rate and absorbing a large amount of CO2 is deposited at the bottom of the storage tank 27e. Therefore, in the storage tank 27e, the CO2 absorbing liquid (CO2 diluted liquid) having a low absorption rate and the CO2 concentrated liquid having a high absorption rate are separated. Then, the upper CO2 diluted liquid of the CO2 absorbing liquid stored in the storage tank 27e is returned to the circulation pipe 25 through the pipe 27a. The CO2 concentrated liquid collected in the lower layer of the storage tank 27e may be collected and discarded at a vehicle repair shop or the like.

  Here, the CO2 absorbing liquid according to the present embodiment uses a solution in which a solute (for example, ion or alkali) is dissolved in a solvent (for example, water), such as an ionic liquid or an alkaline solution. In this case, maintaining the solute concentration at a predetermined concentration is important for exhibiting a predetermined CO2 absorption function. However, the concentration increases as the solvent evaporates, and the concentration decreases as water components in the exhaust gas are mixed into the CO2 absorbing liquid by the exhaust gas contactor 22.

  Therefore, in the present embodiment, a solute such as ions and alkalis and a solvent such as water are stored in the solution tank 28, and the solute and the solvent are replenished to the tank 21 according to the concentration detected by the concentration sensor 28a. . The concentration sensor 28a is attached in the vicinity of the downstream side of the tank 21 in the circulation pipe 25. For example, a sensor that detects a viscosity having a high correlation with the concentration of the liquid is employed as the concentration sensor 28a.

  An electromagnetic valve 28 b that is controlled by the ECU 15 is provided at a connection point between the solution tank 28 and the tank 21. The ECU 15 controls the replenishment amount of the solute and the solvent by controlling the opening and closing of the valve 28b according to the detection value of the concentration sensor 28a so that the concentration of the CO2 absorbing liquid in the tank 21 is within the optimum concentration range. To do.

  The NOx removal device 30 includes a liquid recovery device 37 having the same configuration as the liquid recovery device 27 included in the CO 2 removal device 20. The liquid recovery device 37 is disposed on the downstream side of the exhaust gas contactor 32 in the exhaust pipe 11. There is a concern that a part of the NOx absorbing liquid contacted by the exhaust gas contactor 32 is taken away into the exhaust pipe 11 together with the exhaust gas. The liquid recovery device 37 recovers the NOx absorption liquid that has been taken away and has flowed out of the case 32b. Further, the NOx is removed from the collected NOx absorbing liquid to reduce the absorption ratio, and the NOx absorbing liquid thus treated functions to return to the circulation pipe 35 through the pipe 37a.

  The NOx removing device 30 includes a solution tank 38, a concentration sensor 38a, and an electromagnetic valve 38b having the same configuration as the solution tank 28, the concentration sensor 28a, and the electromagnetic valve 28b that the CO2 removing device 20 has. The ECU 15 controls opening and closing of the valve 38b according to the detection value of the concentration sensor 38a, thereby controlling the amount of solute and solvent supplied in the NOx absorbing liquid, so that the concentration of the NOx absorbing liquid in the tank 31 is within the optimum concentration range. Control to be

  It should be noted that the degree to which the concentration is lowered due to the mixing of moisture in the exhaust gas is lower than the degree to which the concentration is increased by vaporization of the solute. Therefore, storing and replenishing the solvent in the solution tanks 28 and 38 may be abolished.

  FIG. 7 is a flowchart showing a procedure for controlling the concentrations of the CO2 absorbing liquid and the NOx absorbing liquid by controlling the replenishment amount of the solute in order to eliminate the increase in concentration due to vaporization of the solute. It is repeatedly executed by a computer at a predetermined cycle (for example, a calculation cycle of a microcomputer or every predetermined crank angle).

  First, in step S20 (concentration control means) shown in FIG. 7, it is determined whether or not the liquid viscosity (concentration) detected by the concentration sensors 28a and 38a is equal to or greater than a predetermined value. If it is equal to or greater than the predetermined value, the electromagnetic valves 28b and 38b are opened in a subsequent step S21 (concentration control means) in order to replenish the tanks 21 and 31 with a solvent (for example, water). On the other hand, if the detected viscosity (concentration) is less than the predetermined value, the electromagnetic valves 28b and 38b are closed to replenish and stop.

  FIG. 8 is a flowchart showing a procedure for controlling the operation of the pump 24f of the heat recovery unit 24d and the circulation pump 23 of the circulation pipe 25. The microcomputer of the ECU 15 has a predetermined cycle (for example, a calculation cycle of the microcomputer or a predetermined cycle). Repeatedly at every crank angle).

  First, in step S30 shown in FIG. 8, it is determined whether or not the regeneration process of the DPF 13 is being executed. The regeneration process is a process of temporarily raising the exhaust gas temperature by retarding the timing of injecting fuel from the fuel injection valve 14 or increasing the fuel injection amount. Thereby, PM collected by the DPF 13 can be burned and removed, and the DPF 13 can be regenerated.

  If it is determined that the DPF 13 is being regenerated, the pump 24f of the heat recovery unit 24d is driven in a subsequent step S31. As a result, the heat medium of the heat recovery device 24d is circulated to the separation / release device 24, and the CO2 absorption liquid in the separation / release device 24 is heated by the heat of the exhaust gas whose temperature has increased with the execution of the regeneration process. Separation is promoted. In the subsequent step S32, the discharge port 24c is opened and CO2 is released from the separation / release device 24.

  In a succeeding step S33, it is determined whether or not all of the separated CO2 is released. Specifically, it is determined that the discharge has ended when a predetermined time has elapsed since the discharge port 24c was opened. Alternatively, it is determined that the discharge is completed when a predetermined time has elapsed after the temperature of the CO2 absorbing liquid in the separation / release device 24 has risen to the predetermined temperature. When it is determined that the release is completed, the pump 24f is stopped to terminate the separation of CO2 by heating. When the CO2 absorbing liquid in the separation / release device 24 rises to the upper limit temperature, the operation of the pump 24f is stopped even if the CO2 release is not completed. Thereby, it avoids that the temperature of the CO2 absorption liquid supplied to the exhaust gas contactor 22 rises excessively and the absorption capacity decreases.

  When it is determined that the discharge has been completed, the operation of the circulation pump 23 of the circulation pipe 25 is driven to supply the CO2 absorbing liquid in the tank 21 to the exhaust gas contactor 22 in the subsequent step S34. In this case, even if the above-described replacement control (control for opening the outflow valve 32d to complete the liquid discharge from the exhaust gas contactor 22 and then opening the inflow valve 32c to supply the liquid) is performed. Alternatively, the operation of the circulation pump 23 may be started while the valves 22c and 22d are opened.

  In a succeeding step S35, it is determined whether or not a volume of liquid that can be held by the holding body 22a is supplied from the tank 21 to the holding body 22a. Specifically, when the drive operation time of the circulation pump 23 has elapsed for a predetermined time, it is determined that the replacement has been completed by supplying a volume of liquid (S35: YES), and in step S36, the circulation pump 23 is turned on. Stop operation to stop the circulation of the liquid.

  According to the embodiment described in detail above, the effects (1) to (4) are obtained, and the following effects are also obtained.

  (5) Since the heat recovery device 24d is provided to recover the heat of the exhaust gas and heat the liquid in the separation / release device 24, the heater 24b in FIG. 1 can be eliminated and the power consumption can be reduced.

  (6) Since the heat recovery is performed by driving the pump 24f at the timing of executing the regeneration process of the DPF 13, it is possible to secure a sufficient amount of heat for heating and separating the liquid.

  (7) By providing the cooler 26, the liquid whose temperature has increased as it is heated and separated is cooled, so that the CO2 absorption capacity can be restored to the liquid whose CO2 absorption capacity has decreased as the temperature has increased. it can.

  (8) By providing the liquid recovery devices 27 and 37, it is possible to suppress a part of the absorbing liquid flowing out from the exhaust gas contactors 22 and 32 into the exhaust pipe 11 from being discharged together with the exhaust gas. Moreover, since CO2 and NOx are separated from the collected absorption liquid and the absorption ratio is lowered and the absorption liquid is returned to the circulation pipes 25 and 35, the absorption ratio of the absorption liquid in the circulation pipes 25 and 35 increases. Can be suppressed.

  (9) Since the solution tanks 28 and 38 and the concentration sensors 28a and 38a are provided, the concentration of the absorbing liquid is maintained at a predetermined concentration, so that it is possible to avoid a decrease in absorption capacity due to a change in concentration.

(Third embodiment)
In this embodiment shown in FIG. 9, the NOx removal system according to the first embodiment is provided with a bypass pipe 40 and a bypass valve 41 (switching valve). In the following, the system configuration of FIG. 9 will be described focusing on the differences from FIG. In FIG. 9, the same reference numerals as those in FIG.

  The bypass pipe 40 is a pipe that forms a bypass passage 40 a that bypasses the exhaust gas contactors 22 and 32 and distributes the exhaust gas, and is located upstream of the exhaust gas contactor 22 and downstream of the exhaust gas contactor 32 in the exhaust pipe 11. It is connected to the. The inlet of the bypass passage 40a is opened and closed by a bypass valve 41. The bypass valve 41 is driven by an electric motor, and the operation of the motor is controlled by the ECU 15.

  In the case where the bypass pipe 40 is provided in a system including the heat recovery unit 24d as shown in FIG. 4, the inlet of the bypass pipe 40 may be connected to the downstream side of the heat recovery unit 24d and the upstream side of the exhaust gas contactor 22. desirable. Thereby, regardless of the operating state of the bypass valve 41, the waste heat can be recovered and the liquid in the separation / release device 24 can be heated. In addition, when the bypass pipe 40 is provided in the system including the liquid recovery device 37 as shown in FIG. 4, the outlet of the bypass piping 40 may be connected to the downstream side of the exhaust gas contactor 32 and the upstream side of the liquid recovery device 37. desirable. Thereby, the leaked NOx absorbing liquid can be recovered regardless of the operating state of the bypass valve 41.

  Here, as shown in FIGS. 10A and 10B, the NOx emission amount and the CO2 emission amount in the exhaust gas depend on the operating state of the internal combustion engine 10 (for example, the rotational speed NE of the engine output shaft and the engine load). Change greatly. For example, FIG. 10 shows that the NOx emission amount and the CO2 emission amount increase as the engine load increases. Further, FIG. 10A shows that the NOx emission amount decreases when the engine rotational speed NE is in the vicinity of 2000 rpm even at a medium load.

  The ECU 15 opens the bypass valve 41 when the engine is operating such that the NOx emission amount is less than the predetermined threshold value TH, and closes the bypass valve 41 when the NOx emission amount exceeds the threshold value TH. The operation of the circulation pumps 23 and 33 is stopped when the bypass valve 41 is opened, and the circulation pumps 23 and 33 are operated when the bypass valve 41 is closed.

  FIG. 11 is a flowchart showing a procedure for controlling the operation of the bypass valve 41, which is repeatedly executed by the microcomputer of the ECU 15 at a predetermined cycle (for example, every calculation cycle of the microcomputer or every predetermined crank angle).

  First, in step S40 shown in FIG. 11, it is determined whether or not the engine load and the rotational speed NE are within a predetermined range (low NOx operation region) in a map prepared in advance. The map is created by testing in advance the relationship between the engine load and the rotational speed NE and the NOx emission amount. The region where the engine load and the rotational speed NE are in the region where the NOx emission amount is less than the threshold value TH is set as the low NOx operation region.

  When it is determined that the low NOx operation region is set (S40: YES), the bypass valve 41 is opened in the following step S41. As a result, the exhaust gas flows through the bypass passage 40a and bypasses the exhaust gas contactors 22 and 32. In the subsequent step S42 (circulation control means), the operation of the circulation pumps 23, 33 is turned off to stop the circulation of the liquid in the circulation pipes 25, 35. In the subsequent step S43 (separation control means), the operation of the heater 24b is turned off. To stop the separation of CO2.

  On the other hand, when it is determined that the engine load and the rotational speed NE are in the high NOx operation region that is not the low NOx operation region in the map (S40: NO), in the subsequent step S44 (separation control means), the heater 24b Turn on and start CO2 separation. In the subsequent step S45 (circulation control means), the operation of the circulation pumps 23, 33 is turned on to circulate the liquid in the circulation pipes 25, 35. In the subsequent step S46, the bypass valve 41 is closed. As a result, the exhaust gas flows through the exhaust gas contactors 22 and 32.

  According to the embodiment described in detail above, the effects (1) to (4) are obtained, and the following effects are also obtained.

  (10) During high NOx operation, it is desirable to increase the CO2 removal capability of the CO2 removal device 20 so that the NOx removal device 30 can absorb a sufficient amount of NOx. Therefore, in the present embodiment, during low NOx operation, the exhaust gas is circulated through the bypass passage 40a, thereby suppressing an increase in the absorption ratio of the entire CO2 absorbing liquid circulated through the circulation pipe 25, and absorbing in preparation for high NOx operation. The ratio can be kept low. In addition, since the exhaust gas is circulated to the exhaust gas contactors 22 and 32 at the time of high NOx operation, the amount of CO2 absorption at the time of high NOx operation can be increased, and as a result, a sufficient amount of NOx is absorbed by the NOx removal device 30 at the time of high NOx operation. Can be made.

  Similarly, at the time of low NOx operation, an increase in the absorption rate of the entire NOx absorbing liquid circulated through the circulation pipe 35 can be suppressed, and the absorption rate can be kept low in preparation for high NOx operation.

  In the internal combustion engine 10 for a vehicle, the engine load and the rotational speed NE change rapidly in a short time. On the other hand, in this embodiment, since the absorption ratio of the CO2 absorbing liquid and the NOx absorbing liquid is kept low during the low NOx operation, even if a large amount of NOx is discharged in a short time, the NOx is sufficiently reduced. Can be absorbed.

  (11) Since the operation of the heater 24b is stopped during the low NOx operation, power consumption in the heater 24b can be suppressed. Therefore, battery consumption can be suppressed, and as a result, the amount of power generated by the internal combustion engine 10 can be suppressed and fuel consumption can be improved.

(Fourth embodiment)
In the first embodiment, as shown in FIG. 1, the DOC 12 (oxidation means) that oxidizes NO in the exhaust gas to NO 2 is arranged on the upstream side of the exhaust gas contactor 22. This is advantageous in that the temperature rise of the DOC 12 can be realized in a short time by high-temperature exhaust by disposing the DOC 12 as close as possible to the exhaust port of the internal combustion engine 10 in order to activate the oxidation catalyst. However, when NO is oxidized to NO2, the NOx absorption rate in the exhaust gas contactor 32 can be improved, and at the same time, NOx is easily absorbed by the CO2 absorbing liquid in the exhaust gas contactor 22.

  In this embodiment in view of this point, as shown in FIG. 12, in the exhaust pipe 11, downstream of the exhaust gas contactor 22 of the CO 2 removal device 20 and upstream of the exhaust gas contactor 32 of the NOx removal device 30. The oxidizing means 12a is disposed on the surface. According to this, it can suppress that a CO2 absorption liquid absorbs NOx, and can improve that a NOx absorption liquid absorbs NOx.

  However, if the oxidizing means 12a is disposed at such a position, the position becomes far from the exhaust port, so that it becomes difficult to activate the oxidation catalyst in a short time by high-temperature exhaust. Therefore, it is desirable to employ an ozone generator or a radical generator in place of the DOC using the oxidation catalyst for the oxidation means 12a according to the present embodiment. Or when an oxidation catalyst (DOC) is used, it is desirable to provide an electric heater or a burner for heating the DOC.

(Fifth embodiment)
In the said 1st Embodiment, the circulation pump 23 of the CO2 removal apparatus 20 is operated intermittently, and the CO2 absorption liquid in the circulation piping 25 is circulated intermittently. On the other hand, in this embodiment, the circulation pump 23 of the CO2 removal apparatus 20 is always operated, and the CO2 absorbing liquid in the circulation pipe 25 is constantly circulated. However, when the operation of the circulation pump 23 is controlled, the ECU 15 variably controls the circulation speed according to the absorption ratio of the CO2 absorbing liquid. In this embodiment, the inflow valve 22c and the outflow valve 22d shown in FIG. 1 are omitted.

  FIG. 13 is a flowchart showing the above control procedure, and is repeatedly executed by the microcomputer of the ECU 15 at a predetermined cycle (for example, every calculation cycle of the microcomputer or every predetermined crank angle).

  First, in step S50 shown in FIG. 13, it is determined whether or not the absorption ratio of the CO2 absorbing liquid in the exhaust gas contactor 22 is within a predetermined range. If determined to be within the predetermined range (S50: OK), the output of the heater 24b of the separator / discharger 24 and the output of the circulation pump 23 are maintained at the current output. Thereby, the separation speed in the separation / release device 24 and the circulation speed of the CO2 absorbing liquid are maintained. Note that the absorption ratio may be detected by the ph sensor 22e in the same manner as in the first embodiment.

  If it is determined that the ph value by the ph sensor 22e is within a predetermined range (S50: below), it is considered that the absorption ratio of the CO2 absorbing liquid is above the predetermined range, and the following step S51 (circulation speed control means), In S52 (separation control means), the outputs of the heater 24b and the circulation pump 23 are increased. As a result, the separation rate in the separation / release device 24 and the circulation rate of the CO2 absorbing liquid increase, so that the amount of CO2 that can be absorbed per unit time by the exhaust gas contactor 22 increases.

  On the other hand, if it is determined that the ph value by the ph sensor 22e is within the predetermined range (S50: or more), the absorption ratio of the CO2 absorbing liquid is regarded as being below the predetermined range, and the subsequent step S53 (circulation speed control means) ), In S54 (separation control means), the outputs of the heater 24b and the circulation pump 23 are reduced. As a result, the separation rate in the separation / release device 24 and the circulation rate of the CO2 absorbing liquid are reduced, so that the amount of CO2 that can be absorbed per unit time by the exhaust gas contactor 22 is reduced.

  In a succeeding step S55, it is determined whether or not the temperature of the CO2 absorbing liquid in the separation / release device 24 is equal to or higher than a predetermined upper limit temperature. If it is determined that the temperature is equal to or higher than the upper limit temperature (S55: YES), the operation of the heater 24b of the separation / release device 24 is turned off regardless of the determination result of step S50.

  As described above, according to the present embodiment, the amount of the NOx removal device that passes through the NOx removal device without being absorbed by the processing of steps S50 to S54 can be kept constant. Moreover, it can avoid by the process of step S55, S56 that the temperature of CO2 absorption liquid exceeds upper limit temperature and CO2 absorption performance falls remarkably.

(Other embodiments)
The present invention is not limited to the description of the above embodiment, and may be modified as follows. Moreover, you may make it combine the characteristic structure of each embodiment arbitrarily, respectively.

  ・ CO2 absorption liquid and NOx absorption liquid may absorb CO2 and NOx (physical absorption) without changing molecular structure, or absorb CO2 and NOx (chemical absorption) while changing molecular structure. )

  In each of the above embodiments, the tanks 21 and 31 and the exhaust gas contactors 22 and 32 are configured separately, and the exhaust liquid contactors 22 and 32 are reduced in size by circulating the absorption liquid with the circulation pumps 23 and 33. However, the exhaust gas contactors 22 and 32 may be enlarged and the tanks 21 and 31 may be eliminated. In this case, the circulation pumps 23 and 33 may be abolished so as not to circulate, or the absorption liquid may be circulated using the pump inside the exhaust gas contactors 22 and 32.

  In each of the above embodiments, the exhaust gas and the absorbing liquid are brought into contact with each other by exposing the holding bodies 22a and 32a soaked and holding the absorbing liquid to the exhaust gas. For example, the absorbing liquid is atomized into the exhaust gas. You may comprise so that it may contact by injecting. Alternatively, the absorbing liquid and the exhaust gas may be brought into contact with each other by blowing the exhaust gas into a tank that stores the absorbing liquid.

  In the separation / release device 24 according to the first embodiment, CO2 is separated by the heater 24b (heating means) for heating the CO2 absorption liquid, but a decompression means for reducing the CO2 absorption liquid is provided instead of the heater 24b. The CO2 absorbing liquid may be configured to separate CO2 by reducing the pressure.

  In the first embodiment, the absorption ratio of the absorbing liquid is detected using the ph sensors 22e and 32e, but the viscosity, translucency, electrical conductivity, and specific gravity of the liquid are also highly correlated with the absorption ratio. The sensors for detecting these physical quantities may be used in place of the ph sensors 22e and 32e. When the absorbing liquid is an ionic liquid, the absorption ratio can be detected using a sensor that detects the ratio of cations (plus ions) and anions (minus ions) in the absorbing liquid.

  In the first embodiment, the circulation pump 33 of the NOx removing device 30 is intermittently operated to circulate the NOx absorbing liquid in the circulation pipe 35 intermittently. On the other hand, the NOx removal liquid in the circulation pipe 35 may be constantly circulated by always operating the circulation pump 33 of the NOx removal device 30. In this case, when controlling the operation of the circulation pump 33, the ECU 15 may variably control the circulation speed in accordance with the absorption ratio of the NOx absorbing liquid in the same manner as steps S50, S51, and S53 in FIG. In this case, it is desirable to eliminate the inflow valve 32c and the outflow valve 32d shown in FIG. In this case, it is necessary to eliminate the partition plate that partitions the inside of the tank 31 into the supply tank portion 31a and the recovery tank portion 31b.

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 11 ... Exhaust pipe, 12, 12a ... DOC (oxidation means), 13 ... DPF (filter), 15 ... ECU (regeneration processing control means), 20 ... CO2 removal device, 22 ... Exhaust gas of CO2 removal device Contactor, 23 ... circulation pump of CO2 removal device, 24 ... separation discharger, 24d ... heat recovery device, 26 ... cooler, 30 ... NOx removal device, 40a ... bypass passage, 41 ... bypass valve (switching valve), S11, S14, S42, S45 ... circulation control means, S12, S16, S43, S44, S52, S54 ... separation control means, S20, S21 ... concentration control means, S51, S53 ... circulation speed control means.

Claims (16)

A NOx removal device that holds NOx absorption liquid that absorbs NOx that has come into contact, and absorbs and removes NOx in the exhaust gas by bringing the exhaust gas of the internal combustion engine into contact with the NOx absorption liquid;
A CO2 removal device that is disposed upstream of the NOx removal device in the exhaust pipe and removes CO2 in the exhaust gas;
An NOx removal system for an internal combustion engine, comprising:   The CO2 removing device has a CO2 absorbing liquid that absorbs the contacted CO2 and absorbs and removes CO2 in the exhaust gas by bringing the exhaust gas of the internal combustion engine into contact with the CO2 absorbing liquid. The NOx removal system for an internal combustion engine according to claim 1, wherein The CO2 removal device
A circulation pump for circulating the CO2 absorbing liquid in a circulation path;
An exhaust gas contactor connected to the circulation path and disposed in the exhaust pipe for contacting the CO2 absorbing liquid with exhaust gas;
The NOx removal system for an internal combustion engine according to claim 2, comprising: The CO2 removal device has a circulation control means for controlling the circulation state of the CO2 absorbing liquid,
Among the operating states of the internal combustion engine, when the operating region where the NOx emission amount in the exhaust gas is equal to or greater than a predetermined amount is the high NOx operating region, and the operating region where it is less than the predetermined amount is the low NOx operating region,
The circulation control means stops the circulation of the CO2 absorbing liquid to the exhaust gas contactor in the low NOx operation region, or circulates to the exhaust gas contactor compared to the high NOx operation region. The NOx removal system for an internal combustion engine according to claim 3, wherein the flow rate is reduced. The CO2 removal device
An exhaust gas contactor attached to the exhaust pipe for contacting the CO2 absorbing liquid with exhaust gas;
A bypass passage branched from the exhaust pipe and bypassing the exhaust gas contactor to distribute the exhaust gas;
A switching valve for switching the flow of exhaust gas to either the bypass passage or the exhaust gas contactor;
Comprising
Among the operating states of the internal combustion engine, when the operation region where the NOx emission amount in the exhaust gas is equal to or greater than a predetermined amount is the high NOx operation region, and the operation region where the NOx emission amount is less than the predetermined amount is the low NOx operation region,
The operation of the switching valve is controlled so that the exhaust gas is circulated to the exhaust gas contactor in the high NOx operation region and the exhaust gas is circulated to the bypass passage in the low NOx operation region. The NOx removal system for an internal combustion engine according to claim 2 or 3. The CO2 removal device
A tank connected to the circulation path and storing the CO2 absorbing liquid;
Circulation control means for controlling the circulation state of the CO2 absorbing liquid;
Have
The circulation control means includes
When the absorption ratio of CO2 with respect to the CO2 absorbing liquid in the exhaust gas contactor is a predetermined value or more, the CO2 absorbing liquid in the exhaust gas contactor is discharged and replaced with the CO2 absorbing liquid in the tank,
5. The internal combustion engine NOx according to claim 3, wherein when the absorption ratio is less than a predetermined value, the CO 2 absorbing liquid in the exhaust gas contactor is held without being circulated to the circulation path. Removal system. The CO2 removal device comprises a circulation speed control means for controlling the circulation speed of the CO2 absorbing liquid to the exhaust gas contactor,
The circulation speed control means constantly circulates the CO2 absorbing liquid to the exhaust gas contactor, and when the absorption ratio of CO2 to the CO2 absorbing liquid in the exhaust gas contactor is equal to or greater than a predetermined value, the absorption ratio 5. The NOx removal system for an internal combustion engine according to claim 3, wherein the circulation speed is increased as compared with a case where is less than a predetermined value. The CO2 removal device
A circulation pump for circulating the CO2 absorbing liquid in a circulation path;
An exhaust gas contactor connected to the circulation path for contacting the CO2 absorbing liquid with exhaust gas;
A separation / discharger connected to the circulation path and separating and releasing CO2 absorbed by the CO2 absorption liquid from the CO2 absorption liquid;
The NOx removal system for an internal combustion engine according to any one of claims 2 to 7, wherein the NOx removal system for an internal combustion engine is provided. The CO2 removal apparatus has a separation control means for controlling a separation speed by the separation and discharger,
Among the operating states of the internal combustion engine, when the operating region where the NOx emission amount in the exhaust gas is equal to or greater than a predetermined amount is the high NOx operating region, and the operating region where it is less than the predetermined amount is the low NOx operating region,
The separation control means controls to lower the separation speed in the low NOx operation region or to stop the separation operation in the separation discharger compared to the high NOx operation region. The NOx removal system for an internal combustion engine according to claim 8. The CO2 removal apparatus has a separation control means for controlling a separation speed by the separation and discharger,
The said separation control means is controlled to raise the said separation speed when the absorption ratio of CO2 with respect to the said CO2 absorption liquid is more than a predetermined value compared with the case where it is less than a predetermined value. The NOx removal system for internal combustion engines according to 8 or 9. The separation and discharger separates CO2 from the CO2 absorbing liquid by heating the CO2 absorbing liquid,
When the temperature of the CO2 absorbing liquid in the separation discharger is higher than the upper limit temperature, the degree of heating by the separation discharger is reduced as compared with the case where the temperature is lower than the upper limit temperature. The NOx removal system for internal combustion engines according to any one of claims 8 to 10. A heat recovery device attached to the exhaust pipe for recovering heat of the exhaust gas;
The NOx removal system for an internal combustion engine according to claim 11, wherein the separation / discharger is configured to heat the CO2 absorbing liquid using heat recovered by the heat recovery unit. The internal combustion engine has a filter that collects particulate matter in the exhaust gas, and also has a regeneration process control means that executes a regeneration process that raises the exhaust temperature so as to remove the collected particulate matter from the filter. And
13. The NOx removal system for an internal combustion engine according to claim 12, wherein the operation of the circulation pump is controlled so that a CO 2 absorbing liquid flows into the separation / release device at a timing of executing the regeneration process.   The oxidation means for oxidizing NO in exhaust gas to NO2 is arranged in the exhaust pipe upstream of the NOx removal device and downstream of the CO2 removal device. The NOx removal system for internal combustion engines as described in any one.   The NOx removal system for an internal combustion engine according to any one of claims 2 to 14, wherein the CO2 removal device includes a cooler that cools the CO2 absorption liquid. The CO2 absorbing liquid is a solution in which a solute that absorbs contacted CO2 is dissolved in a solvent,
The internal combustion engine NOx removal system according to any one of claims 2 to 15, wherein the CO2 removal device includes a concentration control means for controlling a solute concentration of the CO2 absorption liquid.

Images