JP2551173B2 - Denitrification method for internal combustion engine exhaust gas - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to a denitration method for removing nitrogen oxides contained in exhaust gas of an internal combustion engine.

[Prior art]

Since the exhaust gas from such an internal combustion engine of a diesel engine NO _X (nitrogen oxides) that cause environmental pollution are included, subjected to decomposing denitration of NO _X in the exhaust gas prior to release to the atmosphere There is a need. A typical denitration apparatus conventionally used for such denitration processing will be described with reference to FIG. Exhaust gas discharged from the exhaust gas outlet of an internal combustion engine, such as a diesel engine 1, is guided to an exhaust gas silencer 3 and further to a denitration reactor 4 via a flue 2, and finally discharged from a chimney 5 to the atmosphere. A flue bypass 6 is provided in the flue 2, and the exhaust gas emitted from the silencer 3 can be directly guided to the chimney 5 through the bypass 6 by operating the valves 7 and 8 as necessary. A reducing agent injection port 10 of a reducing agent injection device 30 is provided in the flue 2 between the silencer 3 and the denitration reactor 4 and near the denitration reactor 4. The reducing agent injection device 30 is composed of a flow rate measuring device 11, a flow rate control valve 12 and a piping system for these, and passes the reducing agent from the reducing agent generation device 9 through the flow rate measuring device 11 and the flow rate control valve 12 through the flue. It is designed to be injected into flowing exhaust gas. The amount of exhaust gas in the flue and the NO _X concentration in the exhaust gas are determined by the reducing agent injection port 10
Exhaust gas flow rate measuring device 14 with each detecting end upstream
And the NO _X concentration meter 13, and based on these measured values, a control signal is sent from the controller 15 to the reducing agent flow control valve 12
And the amount of reducing agent injected from the reducing agent inlet 10 is controlled. A gaseous reducing agent such as ammonia gas or a liquid reducing agent such as ammonia water or urea water is used as the reducing agent, and the exhaust gas injected with such a reducing agent contacts the catalyst in the denitration reactor 4. Then, NO _X in the exhaust gas is converted into harmless N ₂ and H ₂ O by the reduction reaction, and then released from the chimney 5 to the atmosphere together with the exhaust gas. When a gas reducing agent is used, as shown in FIG. 2, a reducing agent injection device is often provided with a device for premixing the gas reducing agent by the blower 16 to complete mixing with the exhaust gas. In the denitration device shown in FIG. 2, the reducing agent injected from the reducing agent injection device 30 and the exhaust gas need to be uniformly mixed and then sent to the denitration reactor 4. Therefore, the reducing agent injection port 10
It has been proposed to make various improvements in the shape and arrangement of the. Also, as in the denitration device shown in FIG.
10 is provided in the exhaust gas passage 2 between the diesel engine 1 and the exhaust gas silencer 3 to mix the reducing agent and the exhaust gas with the silencer 3
It has also been proposed to do this in-house (Japanese Patent Laid-Open No. 63-
279530). In this case, the detection end of the NO _X concentration meter 13 will be provided upstream of the reducing agent injection port 10.

[Problems to be Solved by the Invention]

As described above, suitability reducing agent injection amount to be injected into the exhaust gas can be determined from the concentration of NO _X measured in the exhaust gas by the exhaust gas flowmeter 14 exhaust gas flow rate and the NO _X concentration meter 13 as measured by . However, in the NO _X concentration meter, (1) the sampling probe is easily contaminated by soot and water in the exhaust gas and the sampling tube is easily clogged, and the measured value tends to be inaccurate.
(2) Therefore, there are problems that the measurement is often stopped and cleaning and maintenance are required, and (3) the mechanism is complicated and expensive. Similarly, in the measurement of the flow rate of exhaust gas, the dust in the exhaust gas has a problem that the pitot tube is easily contaminated or clogged with water, and the measurement tends to be inaccurate. As a solution to the problem of measuring the flow rate of exhaust gas, detecting the amount of exhaust gas from the output of an internal combustion engine is disclosed in, for example, Japanese Patent Laid-Open No. 55-93917. However,
This method does not take into account the case where the fuel composition used by the internal combustion engine changes, and even if the operating conditions change, it is not possible to accurately control the reducing agent injection amount according to the NO _X amount in the exhaust gas. There is. Therefore a first object of this invention is not an instrument of the NO _X concentration meter or exhaust flow meter such as described above used at all in the exhaust gas piping system can respond to changes in the more conventionally proper operating conditions, the exhaust gas (EN) A method for denitrifying exhaust gas of an internal combustion engine capable of injecting an appropriate amount of a reducing agent into the exhaust gas in accordance with the amount of NO _X. A second object of the present invention is not to use the above-mentioned NO _X concentration meter, and instead of the exhaust gas flow rate, which has been the object of measurement in the related art, it is difficult for the instrument to be blocked by soot dust or water in the exhaust gas. In addition, the measurement itself is set so that it can be measured relatively accurately, and it is possible to respond to changes in operating conditions more appropriately than before, and inject an appropriate amount of reducing agent into the exhaust gas according to the amount of NO _X in the exhaust gas. It is intended to provide a denitration method for exhaust gas of an internal combustion engine which can be performed. Then, the present inventors assume that if the NO _X concentration and the amount of exhaust gas in the exhaust gas are calculated from the process data of the internal combustion engine, the above problems associated with the use of the NO _X concentration meter and the exhaust gas flow meter can be solved. Based on this, the present invention has been completed.

[Means for solving problems]

That is, the invention of claim 1 is a denitration method in which a reducing agent is injected into the exhaust gas of an internal combustion engine and then sent to a denitration reactor to perform denitration treatment. A method for denitration of exhaust gas from an internal combustion engine is characterized in that the reducing agent injection amount is controlled based on the data of the fuel composition and the fuel usage amount. According to the invention of claim 2, in a denitration method in which a reducing agent is injected into exhaust gas of an internal combustion engine and then sent to a denitration reactor to perform denitration treatment, relative humidity of intake air, intake air temperature, and fuel composition of the internal combustion engine are set. Based on the data of the fuel usage and the residual oxygen concentration in the exhaust gas, or based on the data of the intake air relative humidity, the intake air temperature, the intake air amount and the fuel composition of the internal combustion engine, and the residual oxygen concentration in the exhaust gas, A method for denitrifying exhaust gas from an internal combustion engine, which is characterized by controlling the injection amount of a reducing agent.

[Work]

The NO _X concentration of exhaust gas is correlated with the relative humidity of intake air and the temperature of intake air of the internal combustion engine. Therefore, the NO _X concentration in the exhaust gas can be calculated from the data of the relative humidity of intake air and the temperature of intake air if the correlation between them is actually measured in advance for an actually used internal combustion engine. On the other hand, the exhaust gas amount is obtained from the correlation between the fuel composition of the internal combustion engine and its usage amount and the intake air amount, or from the correlation between the fuel composition of the internal combustion engine and its usage amount and the residual oxygen concentration in the exhaust gas, or It can be calculated from the correlation between the fuel composition of the engine, the intake air amount, and the residual oxygen concentration of the exhaust gas. Therefore, the appropriate reducing agent injection amount can be obtained based on the data of the intake air relative humidity of the internal combustion engine, the intake air temperature, the intake air amount, the fuel composition, and the fuel usage amount thereof. It is necessary to use a NO _X concentration meter that is easily affected by soot and dust, and a measuring instrument such as an exhaust gas flow rate measuring instrument that is also easily affected by soot and dust in exhaust gas for the exhaust gas piping system. Therefore, it is possible to respond more appropriately to changes in operating conditions such as fuel changes. Further, based on the data of the intake air relative humidity of the internal combustion engine, the intake air temperature, the fuel composition, the amount of fuel used, and the residual oxygen concentration of the exhaust gas, or the intake air relative humidity of the internal combustion engine, the intake air temperature, and the intake air amount. It is necessary to use an NO _X concentration meter that is expensive and easily affected by soot and dust in the exhaust gas, because it is possible to obtain the appropriate amount of reducing agent injection based on the data of the fuel composition and the residual oxygen concentration in the exhaust gas. In addition, there is no pulsation, and the measurement itself is difficult because the exhaust gas flow rate, which is also easily affected by soot and dust in the exhaust gas, is not measured, and a sensor is simply put in the exhaust gas, such as a zirconia oxygen concentration meter. It is only necessary to set the oxygen concentration as the measurement target, which is unlikely to cause instrument clogging due to dust and water in the exhaust gas, and the measurement itself is relatively easy to measure. Therefore, it is possible to more appropriately respond to changes in operating conditions such as fuel changes.

【Example】

There are various formulas for calculating the NO _X concentration in the exhaust gas from the correlation between the intake air relative humidity of the internal combustion engine and the intake air temperature. For example, the formula can be obtained by the following formula. NO _X = N ・ NO _X (0) (A) N = a ・ T.H + b ・ T + c (B) where NO _X : NO _X concentration in exhaust gas (ppm [13% O ₂ concentration conversion]) NO _X (0): A reference concentration appropriately selected in consideration of the NO _X concentration range emitted by the internal combustion engine, which is provided merely for convenience of calculation. (Ppm [13% O ₂ concentration conversion]) N: Concentration multiplication variable of reference concentration NO _X (0) with respect to NO _X concentration in exhaust gas, which is a function of temperature and relative humidity. T: Intake air temperature (° C) H: Intake air relative humidity (%) a to c: Constants specific to the internal combustion engine NO _x (0) and constants a to c in the above formulas (A) and (B)
The process of determining the temperature will be explained by taking a diesel engine as an example.First, the diesel engine is operated by changing the relative humidity and temperature of the air supplied to the diesel engine, and the NO _X concentration in the exhaust gas at each relative humidity and temperature. (Ppm [13%
Measure O ₂ concentration]). Obtaining the relative humidity, such as FIG. 1 from the measured data, the temperature, the correlation data of the NO _X concentration in the exhaust gas. This can be easily obtained by, for example, searching the inside or outside of the actually measured data to find the NO _X concentration at a given relative humidity at a given temperature, and plotting this. Figure 1 calculates the concentration of NO _X when the actual relative humidity at the predetermined temperature by the outer Investigation or inner Sagasuru the temperature reference from the measured data, further external search-based relative humidity from the obtained data or 40% relative humidity at each predetermined temperature by the inner Sagasuru, 60%, in which to determine the 80% of the NO _X concentration. As is clear from FIG. 1, the exhaust gas in the exhaust gas has almost no relation to the load of the internal combustion engine within the normally used range.
The NO _X concentration is almost a function of the air temperature and the air relative humidity, and if the temperature is constant, the NO _X concentration is proportional to the relative humidity, and if the relative humidity is the same, the lower the temperature, the higher the NO _X concentration tends to be. Recognize. That is, it is understood that the concentration multiplication variable N of a certain reference concentration NO _X (0) (1000 ppm in FIG. 1) with respect to the NO _X concentration in the exhaust gas is a function of temperature and relative humidity. The constants a, b, and c in the equation (B) can be calculated by, for example, reading the data from FIG. 1 and establishing at least three simultaneous equations relating to the equation (B). The relational expression for obtaining the density multiplying variable N should originally use the following equation (C) instead of the above equation (B), and its constant should be obtained mathematically as described above, but in practice it is a simple equation. The above formula (B) may also be used. N = d · T · H + e · T + f · H + g (C) (d to g: constant) In the above formulas (B) and (C), the above constant a depending on the data value adopted to obtain the constant. Since the values of ~ g are slightly different, it is preferable to obtain a plurality of constant values from as much data as possible and use each constant value obtained by averaging them. Further, as is clear from FIG. 1, since the relative humidity at each temperature and the NO _X concentration in the exhaust gas are in a proportional relationship, the relational expression between the relative humidity at each temperature and the NO _X concentration in the exhaust gas is obtained, and the computer The relevant temperature relational expression may be used each time. In any case, there are various formulas for estimating the NO _X concentration in the exhaust gas from the correlation between the relative humidity of intake air of the internal combustion engine and the intake air temperature. The amount of exhaust gas from the internal combustion engine is obtained, for example, stoichiometrically without using an exhaust gas flow path measuring device. That is, from the fuel composition of the internal combustion engine and its usage amount and intake air amount,
The stoichiometric amount of exhaust gas is calculated from the fuel composition of the internal combustion engine and its usage amount and the residual oxygen concentration in the exhaust gas, or from the fuel composition of the internal combustion engine, the intake air amount and the residual oxygen concentration in the exhaust gas by the following formulas. can do. From the fuel composition of the internal combustion engine pipe and its usage and intake air amount, From the fuel composition of the internal combustion engine and its usage and the residual oxygen concentration in the exhaust gas, From the fuel composition of the internal combustion engine, the intake air amount, and the residual oxygen concentration in the exhaust gas, However, G: Exhaust gas amount (Nm ³ / H) A: Intake air amount [Nm ³ / H] Q: Fuel usage amount [Kg / H] A ₀₂ : Oxygen concentration in intake air [Volume fraction] ₂ : Exhaust gas Residual oxygen concentration [Volume fraction] V ₀ : Gas standard molecular capacity [/ mol] c: Carbon concentration in fuel [Weight fraction] h: Hydrogen concentration in fuel [Weight fraction] o: In fuel Oxygen concentration [weight fraction] s: Sulfur concentration in fuel [weight fraction] n: Nitrogen concentration in fuel [weight fraction] M _C : Atomic weight of carbon _MH : Atomic weight of hydrogen M _O : Atomic weight of oxygen M _S : Sulfur atomic weight M _N : Nitrogen atomic weight [Effect of the invention] As described above, in the exhaust gas denitration method of the invention of claim 1, the NO _X amount in the internal gas is compared with the intake air relative humidity of the internal combustion engine. to control the reducing agent injection amount is calculated as an intake air temperature of intake air quantity and the fuel composition as the process data of the fuel consumption, soot expensive NO _X densitometer and the exhaust gas The instrument susceptible flue gas flow rate meter, such as the effect need not be used at all in the exhaust gas pipe system by. Therefore, NO
_The problem with the use of the _X concentration meter, that is, the sampling probe of the NO _X concentration meter due to the dust and water in the exhaust gas, tends to contaminate or block the pitot tube of the exhaust gas flow rate measuring instrument, which makes the measured value inaccurate. It is possible to solve the problem that the measurement is often stopped and cleaning and maintenance are required. Further, in this method, since the fuel composition is also a data object, it is possible to obtain the appropriate reducing agent injection amount in response to changes in the operating conditions such as fuel changes. Further, in the exhaust gas denitration method of the invention of claim 2,
The amount of NO _X in the exhaust gas can be determined by the process data of the intake air relative humidity of the internal combustion engine, the intake air temperature, the fuel composition, the amount of the fuel used, and the residual oxygen concentration in the exhaust gas, or the intake air relative humidity and the intake air of the internal combustion engine. because calculated by the process data of the temperature and the residual oxygen concentration in the intake air amount and the fuel composition and in the exhaust gas controls the reducing agent injection amount, susceptible exhaust gas flow rate affected by dust or the like of expensive NO _X densitometer and the exhaust gas Avoid using a measuring instrument. Therefore, it is possible to eliminate the above-mentioned problems associated with the use of the NO _X concentration meter, and the oxygen concentration is measured instead of the exhaust gas flow rate measurement, so that a sensor in the exhaust gas such as a zirconia oxygen concentration meter is simply put out. It only needs to be placed, and the instrument is unlikely to be blocked by soot and water in the exhaust gas. In addition, since the fuel composition is also a data target, it is possible to determine the appropriate reducing agent injection amount in response to changes in operating conditions such as fuel changes.

[Brief description of drawings]

FIG. 1 is a graph showing the correlation between the relative humidity and temperature of intake air of an internal combustion engine and the NO _X concentration in exhaust gas, FIG. 2 is an explanatory view showing an example of a conventional exhaust gas denitration device, and FIG. It is explanatory drawing which shows another example of an exhaust gas denitration apparatus. 1 ... Internal combustion engine, 2 ... Flue, 3 ... Exhaust gas silencer, 4 ... Denitration reactor, 5 ... Chimney, 10 ... Reductant inlet, 13 ... NO _X concentration meter, 14 ... Exhaust gas flow rate measuring device.

 ─────────────────────────────────────────────────── --- Continuation of the front page (56) Reference JP-A-2-204614 (JP, A) JP-A-3-36409 (JP, A) JP-A-2-259223 (JP, A) JP-A-55- 93917 (JP, A)

Claims (2)

(57) [Claims] 1. A denitrification method in which a reducing agent is injected into exhaust gas of an internal combustion engine and then sent to a denitrification reactor to perform denitrification treatment. In the denitrification method, the relative humidity of intake air, the temperature of intake air, the amount of intake air, and the fuel composition. And a denitrification method for exhaust gas from an internal combustion engine, characterized in that the reducing agent injection amount is controlled based on the fuel consumption data. 2. A denitrification method in which a reducing agent is injected into exhaust gas of an internal combustion engine and then sent to a denitrification reactor to perform denitrification treatment. In the denitrification method, a relative humidity of intake air of an internal combustion engine, an intake air temperature, a fuel composition and use of the fuel. Of the reducing agent based on the amount and the data of the residual oxygen concentration in the exhaust gas, or based on the data of the relative humidity of the intake air of the internal combustion engine, the intake air temperature, the intake air amount, the fuel composition, and the residual oxygen concentration of the exhaust gas. A method for denitrifying exhaust gas from an internal combustion engine, which comprises controlling the amount of the exhaust gas.