JP3243643B2 - Exhaust gas denitration method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a denitration apparatus for removing nitrogen oxides from exhaust gas of an internal combustion engine, and more particularly to an exhaust gas denitration apparatus suitable for a diesel engine.

[0002]

2. Description of the Related Art Conventionally, ammonia injection control of an exhaust gas denitration system is performed by receiving a start signal of an engine from a start / stop signal transmitter, opening a valve, starting injection of ammonia, receiving a stop signal, closing the valve and injecting the ammonia. To end.

In Japanese Patent Application Laid-Open No. 1-168318, a bypass duct is provided for bypassing a denitration device provided in an exhaust gas duct of a diesel engine, and a thermometer for measuring exhaust gas temperature is provided in the exhaust gas duct downstream of the bypass duct. A device for controlling the opening and closing of an ammonia valve by comparing a gas temperature signal of the thermometer, an engine operation signal, and a denitration device operation temperature setting temperature signal is disclosed.

Further, Japanese Patent Application Laid-Open No. 223623/1990 discloses a NOx device for exhaust gas of a diesel engine for power generation in which a sequencer is used to previously learn an amount of supplied ammonia and supplies a necessary amount of ammonia based on the learned amount.

[0005]

However, in the case of supplying ammonia by opening and closing only the above-mentioned conventional valve,
Since it is not possible to finely control the flow rate of ammonia corresponding to the amount of generated nitrogen oxides, it is not possible to control the amount of discharged nitrogen oxides, thereby increasing the amount of leaked ammonia.

Conventionally, control for adjusting the flow rate of ammonia in response to a change in the amount of generated nitrogen oxides has been performed. In this method, however, the concentration of nitrogen oxides, the amount of exhaust gas, and the like are constantly measured. There is a problem that it is necessary to calculate the ammonia supply amount, and maintenance costs such as adjustment of the NOx meter and cleaning of the gas sampling pipe are increased.

In Japanese Patent Application Laid-Open No. 223623/1990, the supply amount of ammonia is learned by a sequencer in advance and the required amount of ammonia is supplied based on the learned amount. There is a problem that adjustment is difficult. The present invention has been made in view of the above points, and eliminates the above-mentioned problems, has a simple structure, and can supply an appropriate flow rate of ammonia to exhaust gas according to a change in load of an internal combustion engine. It is to provide a device.

[0008]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a method for injecting ammonia into exhaust gas of an internal combustion engine,
In the exhaust gas denitration method of removing the nitrogen oxides in the exhaust gas by passing the exhaust gas into which the ammonia is injected through a nitrogen oxide catalytic reaction tower, the exhaust gas is converted into a nitrogen oxide amount and a constant oxygen concentration with respect to the load of the internal combustion engine. The allowable nitrogen oxide amount at the regulated concentration in the case of performing the above is obtained as a linear function of the load, and the ammonia supply amount until the nitrogen oxide concentration in the exhaust gas becomes equal to or less than the regulated concentration is obtained from the difference between the nitrogen oxide amount and the allowable nitrogen oxide amount. Is calculated by a linear function equation with respect to the load,
The calculated amount of ammonia is supplied according to a change in load.

A nitrogen oxide catalyst reaction tower is connected to an exhaust gas duct for discharging exhaust gas from an internal combustion engine, and ammonia is used as a nitrogen oxide reducing agent in an exhaust gas duct between the internal combustion engine and the nitrogen oxide catalyst reaction tower. In an exhaust gas denitration device connected to an ammonia supply device that supplies nitrogen, the amount of nitrogen oxides discharged with respect to the load of the internal combustion engine and the allowable amount of nitrogen oxides at the regulated concentration when converted to a constant oxygen concentration are linear functions of the load, respectively. The coefficient of a linear function formula for calculating the load of ammonia as a linear function to make the nitrogen oxide concentration in the exhaust gas equal to or less than the regulated concentration from the difference between this nitrogen oxide amount and the allowable nitrogen oxide amount is stored, Calculating means for calculating the ammonia supply amount in accordance with a change in load using a coefficient value; Characterized by a control nitrogen oxide concentration of ammonia supply from the charging device provided with a control means for the following regulation value.

[0010]

The exhaust gas discharged from the internal combustion engine is mixed with the supplied ammonia and flows into the nitrogen oxide catalytic reaction tower, where nitrogen oxides are removed, that is, denitration is performed by the action of the catalyst.

The supply amount of ammonia to be injected into the exhaust gas is determined by the difference between the amount of nitrogen oxide discharged to the load of the internal combustion engine and the amount of nitrogen oxide at the regulated concentration when converted to a constant oxygen concentration. Is calculated as a linear function of the load, and ammonia is injected into the exhaust gas based on the calculation result. Therefore, an appropriate amount of ammonia is always supplied in accordance with the amount of nitrogen oxides in the exhaust gas. Good and stable denitration will be performed.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration example of an exhaust gas denitration apparatus of the present invention. The exhaust gas denitration device of FIG. 1 shows the configuration of the exhaust gas denitration device of the diesel engine 1 that drives the generator 11.

An exhaust port of the diesel engine 1 is connected to a nitrogen oxide catalytic reaction tower, that is, a denitration tower 2 by an exhaust gas duct 9. An ammonia injector 8 is installed in the exhaust gas duct 9 and upstream of the denitration tower. The load signal line 6 of the generator 11 directly connected to the diesel engine 1 is connected to the ammonia supply amount calculator 5, and the ammonia supply amount calculator is connected to the ammonia flow control valve controller 4.

The ammonia injector 8 is connected to the ammonia storage cylinder 3 through the ammonia flow control valve 7. The ammonia flow control valve 7 is connected to the ammonia flow control valve controller 4.

The outlet of the denitration tower 2 is an exhaust gas discharge duct 1
The exhaust gas denitrated by the denitration tower 2 is connected to a chimney or the like (not shown) through 0 and discharged to the atmosphere. Hereinafter, the operation of the exhaust gas denitration apparatus having the above configuration will be described.

As described above, in an apparatus in which ammonia is injected and mixed into the exhaust gas of an internal combustion engine (diesel engine 1) as a reducing agent for reducing nitrogen oxides and denitration is performed by a nitrogen oxide catalytic reaction tower. FIGS. 2 and 3 show the results of measuring the values of various items of the internal combustion engine provided with the device with respect to the load of the internal combustion engine.

FIG. 2A is a diagram showing the nitrogen oxide concentration NOx with respect to the load, and FIG. 2B is a diagram showing the exhaust gas flow rate with respect to the load. The amount of nitrogen oxide is calculated by the following equation (1). (Nitrogen oxide) = (Nitrogen oxide concentration) × (Exhaust gas flow rate) (1) Accordingly, as shown in FIG. 2C, the amount of nitrogen oxide is represented by a substantially linear function.

The allowable nitrogen oxide amount when the regulation value (reduction target value) is expressed by the nitrogen oxide concentration converted to a specific oxygen concentration is expressed by the following equation (2). (Allowable nitrogen oxide amount) = (Allowable oxide concentration) × (Exhaust gas flow amount) × (21−O ₂ ) / (21−O ₂ O) (2) where O ₂ O is A specific oxygen concentration [%] is shown, O ₂ is an arbitrary oxygen concentration, and 21 is an oxygen concentration in the air. The emission standard for nitrogen oxides in exhaust gas from diesel engines is set at 13% in terms of oxygen concentration (O ₂ O).

FIG. 3A shows the oxygen concentration with respect to the load, and FIG. 3B shows the (allowable oxide concentration, that is, the regulated value) × (21-O ₂ ) / (21-O ₂ ) with respect to the load. FIG.

FIG. 3 (c) is a view showing a calculation result of an allowable nitrogen oxide amount with respect to a load. As shown in FIG. 3C, the nitrogen oxide amount with respect to the regulated value of the nitrogen oxide concentration converted to the specific oxide concentration is represented by a linear function with respect to the load.

In the selective denitration by ammonia, the reaction between ammonia and nitrogen oxides is performed at a molar ratio of 1: 1. Therefore, the amount of ammonia necessary to satisfy the nitrogen oxide concentration is represented by the following equation (3). (Required ammonia) = (nitrogen oxide)-(allowable nitrogen oxide) · (3)

Equation (3) for calculating the amount of ammonia
Since both the (nitrogen oxide amount) and the (allowable nitrogen oxide amount) on the right side of are approximated by a linear expression, the result of the subtraction can also be approximated by a linear expression. In other words, the amount of ammonia supply necessary to make the nitrogen oxide concentration in the exhaust gas equal to or less than the regulation value can be approximated by a linear expression with respect to the load.

As described above, with respect to the load of the internal combustion engine,
It can be seen that the amount of nitrogen oxides discharged and the amount of nitrogen oxides at the regulated (target) concentration when converted to a specific oxygen concentration are each represented by a substantially linear function. For this reason, the ammonia supply amount required for denitration may be set and supplied as a linear function of the load of the internal combustion engine.

In the exhaust gas denitration apparatus having the structure shown in FIG. 1, the NOx concentration with respect to the load of the diesel engine 1 in which the exhaust gas denitration apparatus is installed {see FIG. 2 (a)} and the exhaust gas flow rate with respect to the load {see FIG. 2 (b). Measure 実 and find it. From the NOx concentration and the exhaust gas flow rate with respect to the load, the amount of nitrogen oxide expressed as a linear function with respect to the load is calculated using Equation (1) (see FIG. 2C).

Further, the oxygen concentration with respect to the load of the diesel engine 1 is actually measured (see FIG. 3A). From the oxygen concentration for this load, (allowable oxide concentration) × (21−O ₂ ) / (21−) for a load as shown in FIG.
O ₂ O). Then, the allowable nitrogen oxide amount expressed as a linear function with respect to the load is obtained by using the equation (2) (see FIG. 3C).

From the difference between the nitrogen oxide amount and the allowable nitrogen oxide amount, the amount of supplied ammonia is determined as shown in equation (3). In this case, since both the nitrogen oxide amount and the nitrogen oxide amount are expressed as linear functions of the load as described above, the equation for calculating the amount of supplied ammonia from the difference between the two is a linear function equation for the load. The coefficient of the linear function formula for calculating the supply ammonia amount from this load is stored in the internal memory of the ammonia supply amount calculator 5.

As described above, the coefficient of the formula for calculating the amount of supplied ammonia is stored in the internal memory of the ammonia supply amount calculator 5 so that the load value can be transmitted from the load signal line 6 to the ammonia supply amount calculator 5. When input, the amount of ammonia supply required for this load value is calculated, and the result is output to the ammonia flow control valve controller 4.

The ammonia flow control valve controller 4 adjusts the opening of the ammonia flow control valve 7, and supplies an ammonia supply amount calculator from the ammonia storage cylinder 3 into the exhaust gas duct 9 via the ammonia flow control valve 7 and the ammonia injector 8. The amount of supplied ammonia calculated in step 5 is injected.

As a result, the ammonia injected into the exhaust gas duct 9 is mixed with the exhaust gas and flows into the denitration tower 2. The nitrogen oxides in the exhaust gas react with ammonia by the catalyst in the denitration tower 2 and are decomposed into water and nitrogen, that is, denitrated. The denitrated exhaust gas is released into the atmosphere via a chimney tower.

In the above embodiment, an example is shown in which the load of the internal combustion engine (diesel engine) is used. However, instead of this load, the fuel consumption or the load of the machine connected to the internal combustion engine, that is, the generated power It is possible to use an amount, an electric current and the like, and a torque and the like in a machine such as a pump.

The supply of ammonia is preferably performed when the internal temperature of the catalyst of the denitration tower is within a preset temperature range.

Although the above embodiment has been described with reference to a diesel engine, the present invention is not limited to this, and can be used for all internal combustion engines.

[0033]

As described above, according to the present invention, the following excellent effects can be obtained. (1) Since an appropriate amount of ammonia is always supplied to the exhaust gas in accordance with the amount of nitrogen oxides in the exhaust gas, efficient and stable denitration can be performed, and the risk of ammonia leak can be reduced. (2) Since the ammonia flow rate is controlled only by the load signal, NO for detecting nitrogen oxides in the exhaust gas for control is used.
The x-meter is not required, and the apparatus is simplified. (3) Since the ammonia supply amount is expressed as a linear function, it is easy to change the coefficient set in the arithmetic unit, the configuration of the arithmetic unit is easy, and the control is reliable.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a denitration apparatus of the present invention.

FIG. 2 is a diagram showing various values with respect to a load of an internal combustion engine;
2A shows the NOx concentration with respect to the load, FIG. 2B shows the exhaust gas flow rate with respect to the load, and FIG.
The relationship between the quantities is shown.

FIG. 3 is a diagram showing various values with respect to a load of an internal combustion engine;
3A shows the relationship between the O ₂ concentration with respect to the load, FIG. 3B shows the relationship between the regulated value with respect to the load × (21−O ₂ ) / (21-13), and the allowable nitrogen oxide amount and the load NOx amount with respect to the load. .

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Diesel 2 Denitration tower 3 Ammonia storage cylinder 4 Ammonia flow control valve controller 5 Ammonia supply amount calculator 6 Load signal line 7 Ammonia flow control valve 8 Ammonia injector 9 Exhaust gas duct 10 Exhaust gas exhaust duct 11 Generator

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-210017 (JP, A) JP-A-2-259223 (JP, A) JP-A-1-180220 (JP, A) JP-A-60-1985 90029 (JP, A) JP-A-63-302120 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01D 53/94 B01D 53/74 F01N 3/08

Claims (6)

(57) [Claims] An exhaust gas denitration method for injecting ammonia into exhaust gas of an internal combustion engine and passing the ammonia-injected exhaust gas through a nitrogen oxide catalytic reaction tower to remove nitrogen oxides in the exhaust gas. The amount of nitrogen oxides discharged for the load and the allowable amount of nitrogen oxides at the regulated concentration when converted to a constant oxygen concentration are obtained as linear functions of the load, and the difference between this amount of nitrogen oxides and the amount of allowable nitrogen oxides is determined. An exhaust gas denitration method comprising: calculating an ammonia supply amount that makes the nitrogen oxide concentration in exhaust gas equal to or less than a regulated concentration as a linear function of a load; and supplying the calculated ammonia amount according to a change in load. 2. An exhaust gas duct for discharging exhaust gas from an internal combustion engine is connected to a nitrogen oxide catalyst reaction tower, and an ammonia gas as a reducing agent for nitrogen oxide is supplied to an exhaust gas duct between the internal combustion engine and the nitrogen oxide catalyst reaction tower. In an exhaust gas denitration device connected to an ammonia supply device for supplying nitrogen gas, the amount of nitrogen oxides discharged to the load of the internal combustion engine and the allowable amount of nitrogen oxides at a regulated concentration when converted to a constant oxygen concentration are respectively determined as primary loads. Obtained as a function, the coefficient of the equation for calculating the ammonia supply amount to make the nitrogen oxide concentration in the exhaust gas equal to or less than the regulated concentration from the difference between this nitrogen oxide amount and the allowable nitrogen oxide amount as a linear function of load is stored, Calculating means for calculating the ammonia supply amount in accordance with a change in the load used; and an output from the ammonia supply device based on a calculated output of the calculating means. Exhaust gas denitration apparatus characterized by providing a control means for controlling the pneumoniae supply amount or less regulation value of nitrogen oxide concentration. 3. The exhaust gas denitration apparatus according to claim 2, wherein the fuel consumption of the internal combustion engine is used instead of the load of the internal combustion engine. 4. The exhaust gas denitration apparatus according to claim 2, wherein a load of a device connected to the internal combustion engine is used instead of the load of the internal combustion engine. 5. The ammonia supply amount calculating means according to claim 2, 3, or 4 arbitrarily sets the proportionality constant between the fuel consumption amount or the load and the ammonia amount according to the type of the internal combustion engine, the nitrogen oxide reduction target value, and the like. An exhaust gas denitration apparatus characterized in that: 6. The method according to claim 2 or 3 or 4 or 5,
The exhaust gas denitration apparatus according to claim 1, wherein the supply of the ammonia is performed when the temperature of the catalyst in the nitrogen oxide catalytic reaction tower is within a set temperature range.