JP2010038034A - Control method of exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To avoid a risk of separating a large quantity of ammonia from a selective reduction type catalyst, in combustion of a burner. <P>SOLUTION: A control method of an exhaust emission control device is provided for reducing and removing NOx by adding urea water to the inlet side of the selective reduction type catalyst 15 provided in the middle of an exhaust pipe 11, collecting particulates in exhaust gas 9 by a particulate filter 12 provided upstream, and regenerating the particulate filter 12 by incinerating the collected particulates by burning the burner 13 on its inlet side. When requiring to regenerate the particulate filter 12, adsorption ammonia in the selective reduction type catalyst 15 is used for the reduction-removing reaction of NOx by reducing an adding quantity of the urea water, to thereby start combustion of the burner 13 when an adsorption quantity of the ammonia in the selective reduction type catalyst 15 is reduced to an allowable value or less by consuming the adsorption ammonia. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for controlling an exhaust emission control device.

  Conventionally, a diesel engine is equipped with a selective reduction catalyst having a property of selectively reacting NOx with a reducing agent even in the presence of oxygen in the middle of an exhaust pipe through which exhaust gas flows, and the selective reduction catalyst A required amount of a reducing agent is added to the upstream side of the catalyst so that the reducing agent undergoes a reduction reaction with NOx (nitrogen oxide) in the exhaust gas on the selective catalytic reduction catalyst, thereby reducing the NOx emission concentration. There is what I did.

In addition, in the field of industrial flue gas denitration treatment in plants and the like, the effectiveness of a method for reducing and purifying NOx using ammonia (NH ₃ ) as a reducing agent is already widely known. In recent years, it has been difficult to ensure the safety of traveling with ammonia itself, and in recent years, the use of non-toxic urea water as a reducing agent has been studied.

  That is, if urea water is added to the exhaust gas upstream of the selective catalytic reduction catalyst, the urea water is thermally decomposed into ammonia and carbon dioxide gas in the exhaust gas, and NOx in the exhaust gas is converted into the selective catalytic reduction catalyst. It will be reduced and purified well by ammonia.

  On the other hand, when purifying exhaust gas from a diesel engine, it is not enough to remove NOx in the exhaust gas, and particulates contained in the exhaust gas are also collected through the particulate filter. Although it is necessary, there are few opportunities to obtain exhaust temperatures that are high enough for particulates to self-combust under normal diesel engine operating conditions, so an oxidation catalyst with Pt, Pd, etc. as the active species is used as the particulate filter. It is made to carry integrally.

  That is, if such a particulate filter carrying an oxidation catalyst is employed, the oxidation reaction of the collected particulates is promoted to lower the ignition temperature, and the particulates are burned and removed even at a lower exhaust temperature than in the past. It becomes possible.

  However, even when such a particulate filter is adopted, the trapped amount exceeds the processing amount of particulates in the operation region where the exhaust temperature is low, so operation at such a low exhaust temperature is required. If the state continues, there is a possibility that the particulate filter will fall into an over trapped state without the regeneration of the particulate filter proceeding well.

  Therefore, a flow-through type oxidation catalyst is attached to the upstream of the particulate filter, and when the amount of particulate accumulation increases, fuel is added to the exhaust gas upstream of the oxidation catalyst to force the particulate filter. It is considered to play.

  In other words, if fuel is added to the exhaust gas upstream of the oxidation catalyst, the added fuel (HC) undergoes an oxidation reaction while passing through the preceding oxidation catalyst. The catalyst bed temperature of the particulate filter immediately after that is raised, the particulates are burned out, and the particulate filter is regenerated.

  However, the catalyst bed in which the oxidation catalyst in the previous stage can exhibit sufficient catalytic activity in a vehicle with an operation state in which the operation state with a low exhaust temperature continues for a long time such as an urban route bus traveling only on a congested road There is a problem that the particulate filter cannot be efficiently regenerated within a short time because it is difficult to raise the temperature to the temperature and the oxidation reaction of the added fuel in the oxidation catalyst is not activated.

  Therefore, in recent years, a burner is provided on the entrance side of the particulate filter, and the collected particulates are incinerated by combustion of the burner regardless of the operation state of the vehicle, and the particulate filter can be efficiently removed in a short time. Regeneration is being considered.

Prior art document information relating to a technique for heating this type of exhaust purification catalyst or exhaust gas using a burner includes the following Patent Document 1 and Patent Document 2.
JP-A-5-86845 JP-A-6-167212

  However, since the excess ammonia in the NOx reduction and purification reaction is adsorbed and stored in a large amount in the selective catalytic reduction catalyst, if the exhaust gas temperature is suddenly raised by combustion of the burner, the selective catalytic reduction catalyst The catalyst bed temperature also suddenly increased, and a large amount of ammonia was desorbed at a time and could be discharged together with the exhaust gas as a high concentration ammonia gas.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to avoid the possibility that a large amount of ammonia is desorbed from the selective catalytic reduction catalyst during combustion of the burner.

  The present invention reduces and purifies NOx by adding urea water to the inlet side of the selective catalytic reduction catalyst provided in the middle of the exhaust pipe, and uses a particulate filter provided on the upstream side of the selective catalytic reduction catalyst in the exhaust gas. A control method for an exhaust emission control device that collects particulates, burns a burner on the inlet side of the particulate filter, and incinerates the collected particulates to regenerate the particulate filter. When regeneration of the particulate filter becomes necessary, the amount of urea water added is reduced and the ammonia adsorbed on the selective catalytic reduction catalyst is used for the NOx reduction and purification reaction. Combustion of the burner is started when the amount of adsorption of ammonia in the type catalyst falls below the allowable value. .

  Thus, even if it is necessary to regenerate the particulate filter, as long as the ammonia adsorption amount in the selective reduction catalyst exceeds a predetermined value, the burner combustion is not started, and the selective reduction is not performed. Is the selective reduction type in which the temperature of the burner burns up suddenly because the adsorbed ammonia in the type catalyst is consumed in the NOx reduction purification reaction and the ammonia adsorption amount falls below the allowable value, so that the burner combustion starts. A situation in which a large amount of ammonia is desorbed from the catalyst does not occur.

  According to the control method of the exhaust purification apparatus of the present invention described above, when the regeneration of the particulate filter becomes necessary, the amount of urea water added is reduced without immediately burning the burner, and the adsorbed ammonia in the selective catalytic reduction catalyst Is used for the NOx reduction and purification reaction, and combustion of the burner is started when the ammonia adsorption amount falls below the allowable value. It is possible to obtain an excellent effect that it is possible to avoid the possibility that the ammonia is desorbed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows an example of an embodiment of the present invention. Reference numeral 1 in FIG. 1 denotes a diesel engine equipped with a turbocharger 2, and intake air 4 introduced from an air cleaner 3 passes through an intake pipe 5. The intake air 4 sent to the compressor 2 a of the turbocharger 2 and pressurized by the compressor 2 a is sent to the intercooler 6 to be cooled, and the intake air 4 is further guided from the intercooler 6 to the intake manifold 7. The exhaust gas 9 is distributed to each cylinder 8 of the diesel engine 1 (the case of in-line 6 cylinders is illustrated in FIG. 1), and the exhaust gas 9 discharged from each cylinder 8 of the diesel engine 1 Is sent to the turbine 2b of the turbocharger 2 through the exhaust manifold 10, and sent to the exhaust pipe 11 after driving the turbine 2b. Going on.

  Further, a particulate filter 12 that integrally carries an oxidation catalyst is provided in the middle of the exhaust pipe 11, and a burner that injects an appropriate amount of fuel and ignites and burns it before the particulate filter 12. The burner 13 includes a fuel injection nozzle that injects an appropriate amount of fuel from a fuel tank (not shown), and an ignition plug for igniting the fuel injected from the injection port. It has become so.

  Here, a combustion air supply pipe 14 branched from the downstream of the compressor 2a of the turbocharger 2 is connected to the burner 13, and the combustion air supply pipe 14 was supercharged by the compressor 2a. A part of the intake air 4 can be extracted and guided as combustion air.

  In addition, the exhaust pipe 11 downstream of the particulate filter 12 is equipped with a selective reduction catalyst 15 having the property of selectively reacting NOx with ammonia even in the presence of oxygen, and this selective reduction catalyst. 15 is provided with a urea water injection nozzle 16 so that urea water guided from a urea water tank (not shown) can be added to the exhaust gas 9, and the urea water addition position by the urea water injection nozzle 16 and the above-mentioned A gas mixer 17 is provided between the selective reduction catalyst 15 so as to promote the mixing of urea water and the exhaust gas 9.

Between the urea water addition position by the urea water injection nozzle 16 and the particulate filter 12, unburned HC in the exhaust gas 9 is oxidized and oxidation of NO in the exhaust gas 9 to NO ₂ is performed. An oxidation catalyst 18 that promotes the reaction is interposed.

  Further, an accelerator sensor 19 (load sensor) that detects an accelerator opening as a load of the diesel engine 1 is provided in an accelerator of a driver's seat (not shown), and a rotation sensor 20 that detects the engine speed of the diesel engine 1 includes The diesel engine 1 is installed at an appropriate position, and the load signal 19 a from the accelerator sensor 19 and the rotation speed signal 20 a from the rotation sensor 20 are input to the control device 21.

  The control device 21 determines the fuel injection amount in each cylinder 8 of the diesel engine 1 on the basis of the load signal 19a and the rotation speed signal 20a from the accelerator sensor 19 and the rotation sensor 20, and instructs the combustion injection system. The basic particulate generation amount based on the current operating state of the diesel engine 1 is estimated from the particulate generation map based on the fuel injection amount and the rotational speed of the diesel engine 1. The final generation amount is obtained by multiplying the basic generation amount by a correction coefficient considering various conditions related to the generation of particulates, and subtracting the processing amount of the particulates in the current operation state. The amount of particulates accumulated is estimated by momentarily integrating the generated amount.

  However, there are various ways of estimating the amount of particulate deposition, and it is of course possible to estimate the amount of particulate deposition using a method other than the estimation method exemplified here. It is also possible to estimate the accumulated amount of particulates based on the differential pressure before and after the curate filter 12, or to estimate the accumulated amount of particulates based on the operation time and travel distance.

  Further, the control device 21 estimates the amount of NOx generated based on the rotational speed of the diesel engine 1, the amount of fuel injection, etc., and determines the basic urea water addition amount that matches the amount of NOx generated. However, in the present embodiment, ammonia adsorption control that positively utilizes the ammonia adsorption characteristics of the selective reduction catalyst 15 to increase the NOx reduction efficiency is employed. The amount of urea water added is appropriately corrected according to the amount of ammonia adsorbed.

  That is, as shown in FIG. 2, a saturated adsorption amount curve representing the relationship between the catalyst bed temperature of the selective catalytic reduction catalyst 15 and the saturated adsorption amount of ammonia on the selective catalytic reduction catalyst 15 is shown on the low temperature side (for example, about 20 ° C. lower side). ) Is set in the control device 21, the target adsorption amount of ammonia corresponding to the catalyst bed temperature of the selective catalytic reduction catalyst 15 is calculated, and the actual amount of ammonia on the selective catalytic reduction catalyst 15 is calculated. The adsorption amount is obtained, and the urea water addition amount is controlled to decrease when the actual adsorption amount of ammonia reaches the target adsorption amount, and to increase when the ammonia adsorption amount falls below the target adsorption amount.

  For example, as shown in FIG. 3, when the optimum equivalent amount of urea water is as shown by a solid line curve A, if the actual adsorption amount of ammonia is zero, the addition exceeds the optimum equivalent value as shown by a dashed line curve B. If the actual adsorption amount of ammonia is sufficient, the addition amount is reduced to less than the optimum equivalent amount as shown by a dashed line curve C.

  Here, the catalyst bed temperature of the selective catalytic reduction catalyst 15 is grasped based on detection signals 22a and 23a from temperature sensors 22 and 23 disposed before and after the selective catalytic reduction catalyst 15, and The actual adsorption amount of ammonia is calculated by calculating the NOx reduction concentration from the difference in the NOx concentration based on the detection signals 24a and 25a from the NOx sensors 24 and 25 arranged upstream of the urea water injection nozzle 16 and downstream of the selective reduction catalyst 15; The reduced NOx flow rate is obtained from the NOx reduced concentration based on the exhaust flow rate, the urea water consumption amount is calculated based on this, the consumption amount is subtracted from the actual addition amount, and the value is converted into ammonia and integrated. Thus, the actual adsorption amount of ammonia is set.

  In this embodiment, when it is necessary to regenerate the particulate filter 12, the amount of urea water determined by the ammonia adsorption control as described above is reduced to reduce the adsorbed ammonia in the selective reduction catalyst 15 to NOx. When the adsorbed ammonia is consumed as a result of this, and the amount of adsorbed ammonia in the selective catalytic reduction catalyst 15 has fallen below an allowable value (the amount that does not cause desorption of ammonia during combustion of the burner 13). A combustion command signal 13a is output from the control device 21 to the burner 13, and combustion of the burner 13 is started.

  That is, as shown in the flowchart of FIG. 4, the engine control, the urea SCR system, and the burner system are controlled in cooperation. First, in the engine control, the accumulated amount of particulates in step S1. After the counting, it is determined in step S2 whether or not the particulate accumulation amount is greater than or equal to the reference value A. If YES, the process proceeds to step S3 to reduce the ammonia adsorption amount to the urea SCR system (step S11). On the other hand, if NO, the process returns to step S1.

  Further, in the next step S4, it is determined whether or not the estimated value of the particulates is not less than a reference value B greater than the reference value A, and whether the ammonia adsorption amount in the selective catalytic reduction catalyst 15 is not more than an allowable value. In this case, the process proceeds to step S5, where the regeneration instruction of the particulate filter 12 is issued to the burner system (step S19), and the return instruction to the control in consideration of the ammonia adsorption amount is issued toward the urea SCR system (step S17). On the other hand, in the case of NO, the process returns to step S1.

  In the next step S6, the regeneration temperature in the particulate filter 12 is measured by a temperature sensor (not shown), and the processing amount (combustion amount) of the collected particulates is estimated from the duration at the regeneration temperature. In step S7, the amount is subtracted from the particulate accumulation amount, and when the accumulation amount becomes zero, the regeneration completion is determined. In the next step S8, the regeneration completion instruction of the particulate filter 12 is sent to the burner system. It has come out.

  Note that while the regeneration completion determination is not reached in step S7, estimation of the amount of collected particulates in step S6 and subtraction from the accumulation amount are repeated, and in step S8, the burner is repeated. After a reproduction completion instruction is issued to the system (step S21), the process returns to step S1.

  On the other hand, in the urea SCR system, ammonia adsorption control is performed in step S9, and the ammonia adsorption amount (actual adsorption amount) in the selective catalytic reduction catalyst 15 is counted in the next step S10.

  Then, in the next step S11, it is determined whether or not an instruction to reduce the amount of adsorption of ammonia has been issued from step S3 of the engine control described above. If YES, the process proceeds to step S12 and the urea water addition amount (injection amount) is determined. In the case of NO, the process returns to step S9.

  Further, in the next step S13, it is counted how much the ammonia adsorption amount in the selective catalytic reduction catalyst 15 has been reduced by the decrease in the urea water addition amount in the previous step S12, and in the next step S14. It is determined whether or not the ammonia adsorption amount has fallen below the allowable value. If YES, the process proceeds to step S15, and information indicating that the ammonia adsorption amount has fallen below the allowable value is sent to step S4 of engine control. In this case, the process returns to step S12.

  Note that when counting the amount of adsorbed ammonia, the amount of urea water added after being reduced and the amount of urea water consumed determined from the NOx reduction results measured by the NOx sensors 24 and 25 are known. Therefore, the amount of ammonia adsorbed on the selective catalytic reduction catalyst 15 can be counted by calculating the amount of ammonia that would have been compensated from the adsorbed ammonia due to the insufficient amount of urea water added.

  Next, in step S16, the control is switched to the basic control instructing the addition amount of urea water corresponding to the NOx generation amount without considering the ammonia adsorption amount, and in the next step S17, an instruction to return to ammonia adsorption control is issued. The basic control is continued until it is confirmed that the engine control step S5 has been issued. On the other hand, when the return instruction to the ammonia adsorption control from the engine control step S5 is confirmed, the process returns to step S9. It returns to ammonia adsorption control.

  In the burner system, the standby state of step S18 is continued until it is confirmed in step S19 that the regeneration instruction of the particulate filter 12 is issued from step S5 of engine control. When the regeneration instruction of the particulate filter 12 from step S5 is confirmed, the process proceeds to step S20, where regeneration of the particulate filter 12 by combustion of the burner 13 is started.

  The combustion of the burner 13 is continued until it is confirmed in step S21 that the regeneration completion instruction has been issued from engine control step S8, while the regeneration completion instruction from engine control step S8 is confirmed. In this case, the process returns to step S18 to return to the standby state.

  Therefore, according to the above embodiment, when regeneration of the particulate filter 12 becomes necessary, the amount of urea water added is reduced without immediately burning the burner 13, and the adsorbed ammonia in the selective catalytic reduction catalyst 15 is reduced to NOx. Since the combustion of the burner 13 is started when the amount of adsorbed ammonia is reduced below the allowable value due to the consumption of the reduction purification reaction, a large amount of the selective reduction catalyst 15 is burned when the burner 13 burns. The risk of desorption of ammonia can be avoided in advance

  It should be noted that the method for controlling the exhaust purification apparatus of the present invention is not limited to the above-described embodiment, and it is needless to say that various changes can be made without departing from the scope of the present invention.

It is the schematic which shows an example of the form which implements this invention. It is a diagram explaining the target adsorption amount of ammonia. It is a diagram explaining the relationship between ammonia adsorption amount and urea water addition amount. It is a flowchart which shows the control procedure performed with the control apparatus of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 9 Exhaust gas 11 Exhaust pipe 12 Particulate filter 13 Burner 15 Selective reduction type | mold catalyst 16 Urea water injection nozzle 21 Control apparatus

Claims (1)

  Urea water is added to the inlet side of the selective catalytic reduction catalyst provided in the middle of the exhaust pipe to reduce and purify NOx, and the particulate filter provided upstream of the selective catalytic reduction catalyst captures particulates in the exhaust gas. A method for controlling an exhaust gas purification apparatus, wherein the particulate filter is regenerated by burning a burner on the inlet side of the particulate filter and incinerating the collected particulates, When the regeneration of the catalyst becomes necessary, the amount of urea water added is reduced and the adsorbed ammonia in the selective catalytic reduction catalyst is used for the NOx reduction purification reaction. As a result, the adsorbed ammonia is consumed and ammonia in the selective catalytic reduction catalyst Control of an exhaust emission control device characterized in that combustion of a burner is started when the amount of adsorbed gas falls below an allowable value Law.

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