JPH0752001B2 - NOx decomposition reduction method by reburning - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a NOx decomposition reduction method for decomposing and reducing NOx (nitrogen oxide) contained in exhaust gas of an internal combustion engine by recombustion.

[Prior Art] Exhaust gas emitted from an internal combustion engine such as a diesel engine contains NOx, which is a harmful component, and can be released to the atmosphere only after removing this NOx to render it harmless. Can not. However, when the internal combustion engine is a diesel engine, since the exhaust gas contains oxygen and a medium, it is not possible to use the catalytic method for reducing NOx.

As a NOx reduction method that does not rely on such a catalyst system,
Conventionally, exhaust gas recirculation method and reduction combustion method using multiple burners are known, but all of them have the disadvantage that the device becomes large and the cost is high, and simple method is effective for NOx It is hoped that a reduction method capable of reducing the above will appear.

As a method that can be effectively used to reduce such NOx, there is a combustion denitration method as disclosed in JP-A-54-84628. This combustion denitration method utilizes a staged combustion mechanism and an exhaust gas circulation combustion mechanism to remove the above-mentioned nitrogen oxides in the exhaust gas containing a large amount of nitrogen oxides. The experiments and researches conducted in this study confirmed that NOx can be reduced extremely effectively by selecting the fuel for combustion when exhaust gas is recirculated and reductively combusted in the combustion chamber by a similar method.

[Problems to be Solved by the Invention] The present invention is based on such findings, and its technical problem is to reduce the exhaust gas exhausted from an internal combustion engine by recirculating it in the combustion chamber for reduction combustion. It is an object of the present invention to provide a method for effectively reducing NOx in exhaust gas in the entire air-fuel ratio region by selecting a fuel for combustion.

[Means for Solving the Problem] A method for decomposing NOx of the present invention for solving the above problem is to take in exhaust gas discharged from an internal combustion engine into a combustion chamber through an intake port, and take the taken-in exhaust gas into the combustion chamber. NO, which causes combustion gas to be re-circulated by a recirculator in the combustion chamber and is reduced and burned.
In the x decomposition reduction method, ethanol is used as a fuel for burning the exhaust gas in the combustion chamber.

[Operation] The exhaust gas taken into the combustion chamber through the intake port is burned by the supply of fuel in this combustion chamber, and the combustion gas is recirculated by the recirculator and partially reduced and burned in front of the recirculator. To do. This reducing combustion produces reducing substances such as hydrogen (H ₂ ), carbon monoxide (CO) and total hydrocarbon (THC), and these reducing substances reduce and decompose NOx in the exhaust gas.

In this case, ethanol is used as the fuel,
As a result, effective decomposition of NOx is obtained in the entire range of the air-fuel ratio, as will be made clear in the examples described later. The reason is considered to be that THC is produced at a considerably high concentration over the entire region, and this THC plays a complete role.

Example FIG. 1 shows the structure of a recombustor for carrying out the method of the present invention.

In the figure, 1 is a casing of a combustor, 2 is a combustion chamber formed inside the casing 1, and one side of this combustion chamber 2 is exhaust gas discharged from an internal combustion engine such as a diesel engine. Is provided with an intake port 3 for taking in the combustion chamber 2
An exhaust port 4 for exhausting combustion gas is provided on the other side.

A conduit 5 for guiding exhaust gas to the combustion chamber 2 and an injection nozzle 6 for injecting fuel are arranged in a portion of the intake port 3 outside the combustion chamber 2, and the conduit 5 has exhaust gas. A rectifying plate 7 and a swirling plate 8 (see FIG. 2) formed in a tapered shape for narrowing down the gas are attached, and the exhaust gas is narrowed down by the rectifying plate 7 and the swirling plate 8 to reduce fuel and exhaust gas. In addition to improving the mixing state with the exhaust gas, the flow rate of exhaust gas is increased.

A recirculator 9 for recirculating the combustion gas burned in the combustion chamber 2 is attached to the opening of the intake port 3 inside the combustion chamber 2. As is clear from FIGS. 2 and 3, this recirculator 9 is composed of a cylindrical portion 10 having a uniform diameter and a tapered portion 11 that is tapered, and a plurality of swivel plates 12 are provided on the inner wall surface of the swirl plate 12. The taper portion 11 is attached in a state of being inclined with respect to the inlet port 3 side, and a plurality of mounting members 14 are provided with a suction gap 13 maintained between the tapered portion 11 and the inlet port 3. It is fixed by.

On the other hand, a plate 15 for discharging the combustion gas in a detoured state is provided in the portion of the combustion chamber 2 on the exhaust port 4 side, and the pressure in the combustion chamber 2 is increased by this plate 15.

Reference numeral 16 in the figure is a spark plug for ignition.

In the re-combustor having the above-mentioned configuration, ethanol is used as the fuel supplied from the nozzle 6, and the exhaust gas taken into the combustion chamber 2 through the straightening plate 7 of the conduit 5 from the intake port 3 becomes the exhaust gas inside the combustion chamber 2. In, the fuel is burned by the supply of ethanol from the nozzle 6. The burned combustion gas diffuses into the combustion chamber 2, and then a part of the combustion gas bypasses the plate 15 and flows out to the outside from the discharge port 4, but the remaining combustion gas is
Flow around the recirculator 9 toward the inlet 3,
Exhaust gas flowing into the combustion chamber 2 at a high speed from the inlet 3 is sucked through the gap 13, recirculated in front of the recirculator 9 and partially reduced and burned.

At this time, since the combustion gas is prevented from being discharged straight by the plate 15 provided at the discharge port 4, the pressure in the combustion chamber 2 increases and the circulation efficiency of the combustion gas increases. Thus, this reducing combustion produces reducing substances such as hydrogen (H ₂ ), carbon monoxide (CO), and total hydrocarbon (THC), and these reducing substances cause a reduction in the exhaust gas.
NOx is reductively decomposed at high temperature.

When the above ethanol is used for combustion of exhaust gas, effective decomposition of NOx is obtained in the entire range of the air-fuel ratio, as will be made clear in the examples described below. The reason is considered to be that THC is produced at a considerably high concentration over the entire region and this THC plays a role of reduction.

Figures 4 and 5 were made using the reburner described above.
The results of the NOx reduction experiment are shown. Fig. 4 shows a comparative example using white kerosene as a fuel, and Fig. 5 shows an example using ethanol as a fuel. These experiments
NO and NOx when air with a certain mixture of NO is supplied to the reburner and white kerosene or ethanol is burned as fuel
And the temperature of the combustion chamber are investigated with respect to the air-fuel ratio.

In the case of the comparative example of FIG. 4, when the air-fuel ratio is around 8, the supply NO
For concentration 640ppm, NO concentration of exhaust gas 270ppm, NOx concentration 290ppm and decomposed to less than 1/2, and in the vicinity of the equivalent of air-fuel ratio 14, supplied NO concentration 430ppm, NO concentration of exhaust gas 280ppm, The NOx concentration is 300ppm, which is reduced by about 1/3, but when the air-fuel ratio exceeds 20, the NO and NOx concentrations in the exhaust gas are reduced by only about 10% of the supplied NO concentration, and the air-fuel ratio NOx cannot be effectively decomposed in all regions. This is because recirculation combustion is efficiently performed up to an air-fuel ratio of around 18, and NO is decomposed by reducing substances such as CO, but when the air-fuel ratio is high, the oxygen concentration increases and NO
It is presumed that the reduction effect is small because the decomposition of is suppressed.

On the other hand, in the case of the embodiment in which ethanol is used as the fuel of FIG. 5, efficient decomposition of NOx is observed in all regions. The reason seems to be that in the case of ethanol, THC is produced at a considerably high concentration over the entire region, and this THC plays a role of reduction. This is also understood from the fact that the reduction of NOx is suppressed in the vicinity of the equivalence ratio where the production of THC is small.

[Effects of the Invention] As described in detail above, according to the method of the present invention, by using ethanol as a fuel for recirculating exhaust gas discharged from the internal combustion engine in the combustion chamber to perform reductive combustion, Hydrogen and carbon monoxide produced by reducing combustion,
It is possible to effectively reduce the reduction decomposition of NOx in the exhaust gas by the reducing substance such as total hydrocarbon in the entire range of the air-fuel ratio.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a recombustor according to the present invention, FIG. 2 is an enlarged sectional view of an essential part thereof, FIG. 3 is a side view thereof, and FIGS. 4 and 5 show experimental results. It is a diagram showing. 2 ... Combustion chamber, 3 ... Intake port, 9 ... Recirculator.

Claims (1)

[Claims] 1. An exhaust gas discharged from an internal combustion engine is taken into a combustion chamber through an intake port, the taken-in exhaust gas is burned in the combustion chamber, and the combustion gas is recirculated by a recirculator in the combustion chamber. A method for reducing NOx decomposition by reburning, wherein ethanol is used as a fuel for burning the exhaust gas in the combustion chamber in the method for reducing NOx decomposition by reducing combustion.