JPH05222923A - Nox-in-engine-exhaust-gas reducing device by means of catalyst - Google Patents

Abstract

PURPOSE:To supply a proper quantity of reducing agents in accordance the operating condition of an engine, even if a hydrocarbon reducing agent having a low invert ratio of NOx to N2 in respect of component constitution is used, by reforming it so as to efficiently reduce NOx. CONSTITUTION:The exhaust pipe 12 of an engine 10 is provided with a NOx catalyst 14 and an injection nozzle 18 arranged upstream thereof. A reducing agent supply means 20 for supplying a hydrocarbon reducing agent to the injection nozzle 18 is provided with a storage tank 22 for storing liquid hydrocarbon 21, a force-feeding pump 24 for forcibly feeding the hydrocarbon 21 stored in this tank 22 through a liquid feeding pipe 23, a reactor 26 for reforming the forcibly fed hydrocarbon 21 so as to reduce the number of carbons thereof, a hydrocarbon separating chamber 27 for separating the reformed hydrocarbon from the unreformed hydrocarbon, and a compressor 29 for forcibly feeding the reformed hydrocarbon to the injection nozzle 18 through a pneumatic tube 28.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for reducing nitrogen oxides (hereinafter referred to as NOx) contained in exhaust gas of an engine by a catalyst. More specifically, it relates to a device for reducing NOx in exhaust gas of a vehicle engine.

[0002]

2. Description of the Related Art As a NOx reducing device of this type, a catalyst chamber for accommodating a NOx catalyst is provided in an exhaust pipe of an engine, and a NOx reducing agent is injected from an exhaust gas upstream side of the NOx catalyst by an injection nozzle so that the catalyst is used. Devices for converting NOx to harmless N ₂ are known. Conventionally, ammonia has been used as the reducing agent.

[0003]

However, ammonia is unsuitable as a NOx reducing agent for vehicle engines because of its poor vehicle mountability and the problem of odor when it leaks. When light oil is used as the reducing agent, the light oil has 16 carbon atoms.
However, in this respect, NOx could not be efficiently converted to N ₂ , and the proportion of NOx that was directly released to the atmosphere was high. The object of the present invention is to efficiently reform a hydrocarbon-based reducing agent that has a low NOx conversion rate to N _{2 in} terms of composition.
NOx by catalyst of engine exhaust gas that can reduce Ox
It is to provide a reduction device. Another object of the present invention is to
An object of the present invention is to provide a NOx reduction device that can supply an appropriate amount of reducing agent according to the operating state of the engine.

[0004]

A structure of the present invention for achieving the above object will be described with reference to FIG. 1 corresponding to an embodiment. The present invention includes a catalyst chamber 16 provided in an exhaust pipe 12 of an engine 10 for accommodating a NOx catalyst 14, and a NOx catalyst 1.
4, an injection nozzle 18 provided upstream of the exhaust gas and capable of injecting a hydrocarbon-based reducing agent toward the NOx catalyst 14, and a reducing agent supply means 2 for supplying the reducing agent to the injection nozzle 18.
Is an improvement of the NOx reduction device by the catalyst of the engine exhaust gas provided with 0. The characteristic configuration is that the reducing agent supply means 20 has a storage tank 22 for storing a liquid hydrocarbon 21,
Hydrocarbon 21 stored in this tank 22
And a reactor 26 for reforming the pumped hydrocarbon 21 so as to reduce its carbon number, and a reformed hydrocarbon and a non-reformed hydrocarbon are separated from each other. That is, it is provided with a hydrocarbon separation chamber 27 that operates and a compressor 29 that pressure-feeds the reformed hydrocarbons to the injection nozzle 18 through the air delivery pipe 28. In this NOx reduction device, a temperature sensor 46 provided on the exhaust gas upstream side of the NOx catalyst 14, a load sensor 44 for detecting the load of the engine 10, a rotation sensor 42 for detecting the rotation speed of the engine 10, and a liquid sensor A first flow rate adjusting valve 31 provided in the delivery pipe 23, a second flow rate adjusting valve 32 provided in the air delivery pipe 28, and a pressure feed pump based on detection outputs of the temperature sensor 46, the load sensor 44, and the rotation sensor 42. 24, a compressor 29, and a controller 40 for controlling the first and second flow rate adjusting valves 31, 32 are preferably provided. Further, a recovery tank 33 for recovering unreformed liquid hydrocarbons is provided at the bottom of the hydrocarbon separation chamber 27 of the NOx reduction device, and a recovery pump for returning the liquid hydrocarbons in the recovery tank 33 to the storage tank 22. It is preferable to provide 36.

[0005]

The gas discharged from the engine 10 is discharged to the exhaust pipe 12
Through the injection nozzle 18 and the reducing agent supplied to the catalyst chamber 16, where NOx in the exhaust gas is converted to NOx.
After being reduced by the catalyst 14 and converted into harmless N ₂ , it is released into the atmosphere. The reducing agent supplied from the injection nozzle 18 is qualitatively cracked in the reactor 26,
Since it is a low molecular weight hydrocarbon having a reduced number of carbons, which has been purified and separated in the separation chamber 27, NOx is converted to N ₂ with high efficiency. In terms of quantity, the controller 40 supplies an appropriate amount of reducing agent corresponding to the NOx content in the exhaust gas stored according to the operating state from the injection nozzle 18 by controlling the flow rate adjusting valves 31, 32 and the like.

[0006]

An embodiment of the present invention will be described in detail with reference to the drawings. As shown in FIG. 1, a diesel engine 1
An exhaust pipe 12 is connected to the exhaust manifold 11 of 0.
A reducing agent injection chamber 13, a catalyst chamber 16 accommodating the NOx catalyst 14, and a muffler 17 are provided in this order from the engine side in the middle of the exhaust pipe 12. In this example, the NOx catalyst 14 is a copper ion exchanged zeolite (Cu-ZSM-5).
It is composed of This copper ion-exchanged zeolite is a substance in which sodium ions contained in zeolite are replaced with copper ions, and has a property of reducing NOx with hydrocarbons. An injection nozzle 18 is provided in the reducing agent injection chamber 13 toward the NOx catalyst 14.

A reducing agent supply means 20 for supplying a hydrocarbon reducing agent to the injection nozzle 18 includes a storage tank 22 for storing light oil 21, a pressure pump 24 for pressure-transmitting the light oil 21 via a liquid-feeding pipe 23, and a pressure-feeding device. The reactor 26 for reforming the reformed light oil so as to reduce the carbon number thereof, the hydrocarbon separation chamber 27 for separating the reformed hydrocarbons from the unreformed hydrocarbons, and the reformed hydrocarbons. It is configured by a compressor 29 that pressure-feeds to the injection nozzle 18 via an air feeding pipe 28. In this example, the compressor 29 is driven by the motor 30. The liquid delivery pipe 23 on the discharge side of the pump 24 is provided with a first flow rate adjusting valve 31, and the air delivery pipe 28 on the discharge side of the compressor 29 is provided with a second flow rate adjusting valve 32. The adjusting valves 31 and 32 are electromagnetic valves, and the adjusting valves 31 and 32 are connected to a return pipe 31a to the tank 22 and a returning pipe 32a to the hydrocarbon separation chamber 27, respectively.

The reactor 26 cracks the light oil containing a hydrocarbon having 16 carbon atoms as a main component, which is pumped from the pump 24, and reforms it mainly into a component having 3 to 10 carbon atoms. In this example, the reactor 26 includes a column 26a filled with granular zeolite and a heater 2 for heating the column 26a.
6b. The hydrocarbon separation chamber 27 has 3 to 10 carbon atoms.
A separator 27a for separating the light oil that has been reformed into light oil and the other light oil, and a heater 27b are provided around the separator 27a. The inlet of the column 26a is connected to the liquid delivery pipe 23, and the outlet thereof is directed to the separator 27a of the hydrocarbon separation chamber 27.
A recovery tank 33 for recovering unreformed liquid hydrocarbons is provided at the bottom of the separation chamber 27.
The aforesaid air feeding pipe 28 for sucking the reformed and vaporized hydrocarbons and the return pipe 32a are connected to the top of the. A recovery pipe 34 is connected between the recovery tank 33 and the storage tank 22, and a recovery pump 36 is provided in the recovery pipe 34.

The control output of the controller 40 is connected to the first and second flow rate adjusting valves 31 and 32, the pressure feed pump 24, the compressor driving motor 30, the heaters 26a and 27b, and the recovery pump 36. This controller 40
The control inputs of the rotation sensor 42 for detecting the rotation speed of the engine 10 and the injection pump 4 for detecting the load of the engine.
Load lever position sensor 44 of No. 3 and NO of the catalyst chamber 16
x Temperature sensor 4 for detecting the temperature of exhaust gas flowing into the catalyst 14.
6 and 6 are connected. The controller 40 includes a memory (not shown). This memory stores the NOx catalyst 1 from the injection nozzle 18 according to the engine speed, load and exhaust temperature.
4, the amount of hydrocarbons to be supplied is stored in advance, and the controller 40 adjusts the control valves 31 and 32 based on this supply amount.
It controls the pressure pump 24, the compressor driving motor 30, and the like.

The operation of the NOx reducing device having such a configuration will be described. First, the gas discharged from the engine 10 passes through the exhaust pipe 12 and enters the reducing agent injection chamber 13, where the injection nozzle 18 receives the supply of the hydrocarbon-based reducing agent. The exhaust gas supplied with this reducing agent enters the catalyst chamber 16,
The NOx in the exhaust gas is reduced by the Ox catalyst 14 to be converted into harmless N ₂ and then released to the atmosphere. Here, the quality of the reducing agent injected from the injection nozzle 18 is improved by the following method. First, light oil is sent from the storage tank 22 to the column 26a of the reactor 26 by the pressure pump 24,
The zeolite catalyst is decomposed and vaporized at a temperature of 400 to 500 ° C. By cracking the light oil, the light oil is mainly reformed into a low molecular weight hydrocarbon having 3 to 10 carbon atoms. The high molecular weight hydrocarbons that have not been reformed in the reactor 26 are separated from the reformed hydrocarbons in the separator 27a of the hydrocarbon separation chamber 27. The refined and reduced reforming reducing agent is compressed by the compressor 29 and injected from the injection nozzle 18. This hydrocarbon-based reducing agent having a reduced carbon number converts NOx to N ₂ in the NOx catalyst 14 with high efficiency.

The amount of reducing agent injected from the injection nozzle 18 is controlled by the following method. The controller 40 reads out an appropriate amount of reducing agent corresponding to the NOx content in the exhaust gas stored in the memory according to the operating states by the detection outputs of the sensors 42, 44, 46, and according to the amount of the reducing agent, the flow rate adjusting valve. An appropriate amount of reducing agent is supplied from the injection nozzle 18 by controlling 31, 32, the pressure feed pump 24, the compressor driving motor 30, and the like. Specifically, the controller 40 controls so that the injection amount is reduced when the engine 10 has a light load in the low speed rotation range, and increases when the engine 10 has a medium and high load in the medium and high speed rotation range. Further, the high-boiling-point hydrocarbon-based reducing agent that has not been reformed in the hydrocarbon separation chamber 27 is recovered in the recovery tank 33 and returned to the storage tank 22 by the recovery pump 36. In the above example, copper ion-exchanged zeolite is used as the NOx catalyst, but other zeolite-based or oxide-based catalysts may be used. Although an example of catalytic cracking of light oil using a zeolite catalyst in the reactor is shown, other catalysts such as titanium oxide and silica-alumina catalyst may be used.

[0012]

As described above, according to the present invention, the hydrocarbon-based reducing agent is a gas oil or the like containing a high-boiling hydrocarbon having a low NOx conversion to N _{2 in} terms of component composition. Also, since it is reformed in the reactor, refined and separated in the hydrocarbon separation chamber, and the effective hydrocarbon-based reducing agent is selectively taken out and injected from the injection nozzle, NOx in the exhaust gas is efficiently converted to N ₂ on the NOx catalyst. Convert to. Further, the injection amount of the reducing agent is controlled according to the operating state of the engine, and as a result, NO in the exhaust gas is reduced.
Since an appropriate amount of reducing agent is supplied according to x, NOx contained in the exhaust gas can be effectively reduced.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a NOx reduction device according to an embodiment of the present invention.

[Explanation of symbols]

 10 engine 12 exhaust pipe 13 reducing agent injection chamber 14 NOx catalyst 16 catalyst chamber 18 injection nozzle 20 reducing agent supply means 21 light oil (hydrocarbon-based reducing agent) 22 storage tank 23 liquid feed pipe 24 pressure feed pump 26 reactor 27 hydrocarbon separation chamber 28 Pneumatic tube 29 Compressor 31 First flow rate adjusting valve 32 Second flow rate adjusting valve 33 Recovery tank 36 Recovery pump 40 Controller 42 Rotation sensor 44 Load sensor 46 Temperature sensor

Claims (2)

[Claims] 1. An N provided in an exhaust pipe (12) of an engine (10)
A catalyst chamber (16) for accommodating the Ox catalyst (14) and the NOx catalyst (14) provided on the exhaust gas upstream side of the NOx catalyst (14).
x Engine exhaust gas provided with an injection nozzle (18) capable of injecting a hydrocarbon-based reducing agent toward the catalyst (14) and a reducing agent supply means (20) for supplying the reducing agent to the injection nozzle (18) NOx by catalyst
In the reducing device, the reducing agent supply means (20) stores a liquid hydrocarbon (21) in a storage tank (22) and a liquid feed pipe for the hydrocarbon (21) stored in the storage tank (22).
(23) a pressure-fed pump (24) for pressure-fed, a reactor (26) for reforming the pressure-fed hydrocarbon (21) so as to reduce the carbon number thereof, and the reformed hydrocarbon A hydrocarbon separation chamber (27) for separating unreformed hydrocarbons, and a compressor (29) for pressure-feeding the reformed hydrocarbons to the injection nozzle (18) via a pneumatic pipe (28). An NOx reduction device using a catalyst for engine exhaust gas, comprising: 2. A temperature sensor (46) provided on the exhaust gas upstream side of the NOx catalyst (14), a load sensor (44) for detecting the load of the engine (10), and a rotational speed of the engine (10). Rotation sensor (42), the first flow rate adjusting valve (31) provided in the liquid delivery pipe (23), the second flow rate adjusting valve (32) provided in the air delivery pipe (28), and the temperature Sensor (46), load sensor (44) and rotation sensor (4
Compressed pump (24), compressor based on the detection output of 2)
The NOx reduction device according to claim 1, further comprising: (29) a controller (40) for controlling the first and second flow rate adjusting valves (31, 32).