JP2003232216A - Nox removal system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve problems with a complicated control circuit and increase in an initial cost caused by a feedback control using a NOX meter, for controlling NOX removal in exhaust gas. <P>SOLUTION: This NOX removal system comprises a cooling water injection start determination part to start preparation for water injection when a temperature of a NOX removal reactor is compared with a set temperature of cooling water injected into a vaporizer and the temperature of the reactor is higher than the set temperature, a cooling water injection starting part to execute/stop cooling water injection when the temperature of the vaporizer is compared with the reaction set temperature of the vaporizer and the temperature of the vaporizer is higher/lower than the reaction set temperature, an injection starting part to inject a reducing agent when the temperature of the NOX removal reactor is compared with a reducing agent injection set temperature and the temperature of the reactor is higher than the set temperature, and a stop control part to stop cooling water injection when the temperature of the reactor is low as a result of the comparison. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a denitration apparatus for removing NO _X from the nitrogen oxides such as flue gas of an internal combustion engine (NO _X) containing gas.

[0002]

2. Description of the Related Art A selective catalytic reduction method, which is one of dry methods, has attracted attention as a processing technology of NO _x generated from a diesel engine, and a processing method thereof has been proposed. This selective catalytic reduction method can treat NO _x with a simple system, and can decompose NO _x into harmless nitrogen gas and water with a high denitration rate, so that waste liquid treatment is unnecessary. There are advantages. Although ammonia gas or ammonia water is used as the reducing agent in this method,
Recently, urea water is used from the viewpoint of cost.

[0003]

In the selective catalytic reduction method, it is necessary to control the injection of the reducing agent such as urea water so that the denitration reaction occurs at a ratio close to the theoretical reaction. When the amount is too small, the denitration rate is lowered, and when the amount is too large, there is a fear of giving off a bad odor. As one method of controlling the injection quantity being usually carried out, the concentration of NO _X in the exhaust gas discharged from the internal combustion engine measured by the measuring instrument, the error amount is zero with respect to a set value by feeding back the measured value Controlled to be.

However, a diesel internal combustion engine, since the exhaust gas amount and NO _X concentration that varies greatly depending on ambient conditions, complicates the feedback control circuit or, in the honeycomb formed in the shape denitration catalyst that is inserted into the denitration reactor The amount is increased to maintain a denitration rate of 90% or more. For this reason, the denitration reactor becomes large and the space for installation becomes large. Further, the feedback control circuit is also complicated and the initial cost is high.

The present invention has been made in view of the above points, and an object thereof is to provide a relatively small and simple control means.

[0006]

The first aspect of the present invention is to send exhaust gas from an internal combustion engine connected to a generator to a vaporizer to which a reducing agent is added, and through this vaporizer, a denitration reactor. Introduced into and contacting with a denitration catalyst, a temperature detector is installed in the vaporizer and the denitration reactor, and the reducing agent is injected and cooling water without referring to the temperature signal detected by each temperature detector. In which NO _X in the exhaust gas is removed while controlling the injection of the internal combustion engine, the internal combustion engine starts operation, and the reducing agent is stored in the tank. The detected temperature signal TC1 is compared with the cooling water injection start set temperature signal TS1 to the vaporizer, and a cooling water injection start determination unit that starts preparation of water injection into the vaporizer when TC1 ≧ TS1 and this determination signal are used as conditions. Temperature detected by the vaporizer No. TC2 and the reaction set temperature TS3 of the vaporizer are compared, and when TC2 ≧ TS3, the cooling water injection is executed, and when TC2 <TS3, the cooling water injection start portion that stops the injection cooling water and the detection from the denitration reactor Temperature signal T
C1 is compared with the set temperature signal TS2 for reducing agent injection, and when TC1 ≧ TS2, the reducing agent injection start portion that starts the reducing agent injection and the detected temperature signal TC1 and the set temperature signal TS2 are TC1 <TS2. And a stop control unit for stopping the injection of the reducing agent and the injection of the cooling water when the operation of the internal combustion engine is stopped.

A second aspect of the present invention is characterized in that the TS1, TS2 and TS3 are set to 300 ° C., 320 ° C. and 95 ° C., respectively.

A third aspect of the present invention is characterized in that each of the TS2 and TS3 is provided with a temperature range of a dead zone region.

A fourth aspect of the present invention is characterized in that the reducing agent is urea water.

A fifth aspect of the present invention is characterized in that the control of the reducing agent supply amount to the vaporizer is carried out based on the output electric power amount of the generator.

In a sixth aspect of the present invention, in the stop control section,
The present invention is characterized in that cleaning means for injecting cleaning water into the vaporizer for a predetermined time after the cooling water injection is stopped is provided.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention, showing a case where a denitration device is applied to a diesel engine of a diesel engine generator as an internal combustion engine. . 1 is a diesel generator, and the electric power generated by the generator is a power converter 1
Control panel 2 after being detected by 1 and its value converted
It is output to the internal control unit 21. The control unit 21 is composed of a program controller and controls as described later. Further, the exhaust gas generated from the diesel engine of the diesel power generator 1 is supplied to the denitration reactor 5 via the conduit 3 and the vaporizer 4.

The vaporizer 4 is for adding a reducing agent to the exhaust gas, and ammonia or the like may be used as the additive, but here, urea water is added and generated by heating and evaporating the urea water. A method of adding ammonia to exhaust gas is adopted. Therefore, a temperature detector is attached to the vaporizer 4, and the detected temperature signal is converted into an electric signal by the temperature converter 22 and output to the control unit 2.

A denitration catalyst formed in a honeycomb shape is laminated inside the denitration reactor 5. Zeolite is used as a main raw material of this catalyst, and the catalyst is formed in a honeycomb shape and then fired. To produce a catalyst carrier. Further, a catalyst carrier on which cobalt is carried by ion exchange is used. In addition, inside the denitration reactor 5,
A temperature detector such as a thermocouple is provided to detect the temperature of the denitration catalyst (reactor outlet side temperature), and the measured temperature signal is converted to an electric signal by the temperature converter 23 and output to the control unit 2. To be done.

Reference numeral 6 is a urea water tank for storing urea water which is a reducing agent, and this tank is connected to the carburetor 4 by a pipe line 7 via an injection pump 24 installed in the control unit 2. That is, the urea water is injected into the vaporizer 4 by driving the injection pump 24. Reference numeral 8 is a pipe for supplying cooling water, which supplies cooling water from a water source (not shown) to the carburetor 4 via the electromagnetic valve 25.

FIG. 2 shows a control flow of the denitration device by the function of the control unit 2. By the way, when urea water is heated and evaporated as a reducing agent, depending on the decomposition conditions, it does not decompose into ammonia and changes to other high melting point substances such as melamine and cyanuric acid, which not only lowers the decomposition efficiency but also is harmful. There is a fear that various substances will occur. Therefore, when the decomposition characteristics of urea were investigated, urea started to evaporate at 136 ° C,
Refractory substances are formed at temperatures above 162 ° C,
It was confirmed that the decomposition of the high-melting point substance started around ℃. In the control unit 2, control is executed with reference to these temperatures.

In FIG. 2, it is determined in step S1 whether or not the generator is in an operating state. In the diesel power generator 1, a diesel engine, which is a prime mover, is started, and accordingly, the generator also rotates to generate power, but the detection signal thereof is introduced into the control unit 2 via the power converter 11, and the operation signal is also transmitted. be introduced. In step S1, the presence or absence of this operation signal is determined, and if there is, a step S
Move to 2. In S2, it is judged whether or not there is urea water in the urea water tank 6, and a water level detector such as a float switch is installed in this urea water tank 6 and the stored urea is detected depending on the presence or absence of the limit signal. Water is judged.

In step S3, the temperature TC1 of the denitration reactor 5 installed in the denitration reactor 5 and detected through the temperature converter 23 is compared with a preset temperature TS1 for starting the cooling water injection, When TC1 ≧ TS1, injection of cooling water into the carburetor 4 is started in step S4, but if not, the process returns to the start point as in S1 and S2. The set temperature TS1 is determined in consideration of the decomposition temperature of the high melting point substance during the above-mentioned urea evaporation, and is set to, for example, 300.
Set to ° C.

The cooling water injection in step 4 is started according to the routine shown in FIG. That is, in S40, the temperature TC2 of the vaporizer 4 input via the temperature converter 22 is compared with the set determination temperature TS3, and when TC2 ≧ TS3, the process proceeds to step 41. T
S3 is set to 95 ° C., for example, and cooling water injection is on standby until the detected temperature signal TC2 becomes 95 ° C. or higher, and when the temperature reaches the temperature, the solenoid valve 25 is opened (S41 ) And inject cooling water into the vaporizer.

In step 42, the carburetor 4 is cooled by the injected cooling water, and it is judged whether or not the temperature becomes TC2 <TS3. When the temperature becomes 95 ° C. or lower, the electromagnetic valve 25 is closed to cool it. Stop water injection. At the time of this determination, a dead zone region is provided in order to prevent the hunting phenomenon, and for example, the temperature rise is set to ON at 95 ° C and the temperature fall is set to OFF at 93 ° C.

In step 5 after the injection of the cooling water is started, the temperature TC1 of the denitration reactor and the set temperature T of the urea water injection are set.
A comparison judgment with S2 is made. Similar to TS1, this TS2 is determined in consideration of the decomposition temperature of the high melting point substance during the evaporation of urea, and as a result, when TC1 ≧ TS2, the injection pump 24 is driven to drive the urea water in the urea water tank 6. Is injected into the vaporizer 4 to continue the operation (step S
6).

In the comparison judgment of S5, when it is judged that the temperature of the NOx removal reactor does not rise, it is confirmed in step S7 whether or not the generator is operating. As a result, if the generator is stopped for some reason, the electromagnetic valve 25 is closed (S8) to stop the injection of cooling water, and the process proceeds to S1 to wait for the generator operation.

In step 6, the supply to the carburetor 4 is performed by the urea pump operation, and the supply amount is controlled as follows. The amount of exhaust gas generated by the internal combustion engine is roughly proportional to the load factor of the generator, although it varies. In the control unit 21, the urea amount to be supplied is experimentally obtained in advance based on the relationship between the exhaust gas amount and the generator load factor and stored as a table. Therefore,
The control unit 21 introduces the output power of the generator detected and converted by the power converter 11 to determine the current load factor, estimates the exhaust gas amount at that time, and determines the urea amount supplied to the carburetor 4. The determination is made, and the operation of the urea pump 24 corresponding to the amount is executed.

Although the above is the operation mode, FIG. 2B shows the stop mode. In the figure, in step S11, it is determined whether or not the generator is in a stopped state,
In the case of the stopped state, in step S12, the operation of the pump 24 is stopped to stop the injection of the urea water, and in step S14, a valve for supplying wash water (not shown) is opened to wash the inside of the carburetor. This cleaning is executed for an arbitrary time of, for example, about 5 minutes (S15), and the cleaning valve is closed in step S16 when the time has elapsed.

On the other hand, if it is determined NO in S11, it is determined in step S17 whether TC1 <TS2. If the determination condition is satisfied, the process proceeds to S12.
If not, it is determined in S18 whether or not the urea water tank 6 is out of urea water. In the case of running out of urea water, the processing from S12 is performed, and in the case of no, the processing moves to S11.

[0026]

As described above, according to the present invention, the supply amount of the reducing agent is controlled by the proportional control based on the output power amount of the generator, and the control is performed without using the NO _X meter. Therefore, the control is simple and the cost is advantageous. In addition, and that the NO _X meter is not required,
By making it a relatively simple device corresponding to the control means,
It is possible to reduce the amount of the honeycomb catalyst incorporated in the denitration reactor, so that the space for the denitration reactor can be saved. According to the experiment, a denitration rate of about 90% to a denitration rate of 50
And when about%, dimensions, can confirm that it is possible to close reduction rate of 80% in mass both by the whole device is small, in particular, adapted to loose areas with relatively NO _X standard value The device can be provided.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a control flow diagram showing an embodiment of the present invention,
(A) is a start mode, (b) is a stop mode, (c) is a cooling water injection mode,

[Explanation of symbols]

1 ... Diesel generator 2 ... Control panel 3, 7, 8 ... Pipeline 4 ... Vaporizer 5 ... Denitration reactor 6 ... Urea water (reducing agent) tank 11 ... Power converter 21 ... Control unit 22, 23 ... Temperature converter 24 ... Infusion pump 25 ... Solenoid valve

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F01N 3/02 B01D 53/34 129E 3/04 ZAB 3/28 301 F term (reference) 3G091 AA06 AA18 AA28 AB05 BA04 BA05 BA14 BA36 CA17 DA01 DA02 DA07 DB10 DC01 EA00 EA17 EA26 FB10 FC04 GA06 HA36 HA37 HA42 4D002 AA12 AC10 BA06 CA01 CA04 DA57 DA70 GA03 GB06 4D048 AA06 AB02 AC03 BA11X BA37X BB02 DA01 DA02 DA13

Claims (6)

[Claims] 1. Exhaust gas from an internal combustion engine to which a generator is connected is sent to a vaporizer to which a reducing agent is added, introduced into a denitration reactor through this vaporizer and brought into contact with a denitration catalyst, and A temperature detector is installed in the vaporizer and the denitration reactor,
In the one in which NO _X in the exhaust gas is removed while controlling the injection of the reducing agent and the injection of the cooling water while referring to the temperature signal detected by each temperature detector, the internal combustion engine operates Starting, and under the condition that the reducing agent is stored in the tank, the detected temperature signal TC1 from the denitration reactor is compared with the cooling water injection start set temperature signal TS1 to the vaporizer, and TC1 ≧ TS1 Sometimes a cooling water injection start determination unit that starts preparation for water injection into the vaporizer is compared with the detected temperature signal TC2 from the vaporizer and the reaction set temperature TS3 of the vaporizer under the condition of this determination signal, and TC2 ≧ TS3
At the time of TC2 <TS3, the cooling water injection is performed, and the cooling water injection start portion that stops the injection cooling water is compared with the detected temperature signal TC1 from the denitration reactor and the set temperature signal TS2 for reducing agent injection. , TC1 ≧ TS2, the reducing agent injection start portion for starting the reducing agent injection, and the detected temperature signal TC1 and the set temperature signal TS2 are TC1 <TS2 and the reducing agent injection and the cooling water injection when the operation of the internal combustion engine is stopped. A denitration device having a stop control unit for stopping the operation. 2. The denitration apparatus according to claim 1, wherein the TS1, TS2 and TS3 are set to 300 ° C., 320 ° C. and 95 ° C., respectively. 3. The temperature range of the dead zone region is provided in each of TS2 and TS3.
The denitration device described. 4. The denitration apparatus according to claim 1, wherein the reducing agent is urea water. 5. The control of the reducing agent supply amount to the vaporizer is
The denitration device according to claim 1, wherein the denitration device is implemented based on the output power amount of the generator. 6. The denitration device according to claim 1, wherein the stop control unit is provided with cleaning means for injecting cleaning water into the vaporizer for a predetermined time after the cooling water injection is stopped.