JP2000325754A - Exhaust gas denitration system for cogeneration - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inject a reducing agent corresponding to the amount of NOx generation at all times regardless of the fluctuation of power generation output by utilizing the power generation output of a gas engine as a variable and approximating an NOx content in exhaust gas by a function of correlation having the gradient increasing continuously or discontinuously. SOLUTION: A generator driven by a gas engine 1 and a waste heat boiler 2 is heated and utilized as a heat source for air conditioning, heating and the like. A high temperature catalyst reactor 4 is interposed in a high temperature air exhaust oven 3 set all through from the engine 1 to the waste heat recovering boiler 2. Also an NOx decomposition catalyst 7 is filled in the catalyst reactor 4, and a reducing agent injection inlet 9 is provided on an exhaust line 3 on the upstream side of the catalyst reactor 4, and urea water is fed quantitatively from an electromagnetic diaphragm pump 6 into the reducing agent injection inlet and jetted into the exhaust line 3. The reducing agent injection amount is controlled by utilizing the power generating output of the engine 1 as a variable and approximating an NOx content in the exhaust gas by the function of correlation having the gradient increasing continuously or discontinuously.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a denitration system for removing NOx in exhaust gas in a cogeneration system.

[0002]

2. Description of the Related Art In general, in a cogeneration system, a NOx reducing agent such as ammonia, ammonium bicarbonate or urea water is injected into the exhaust gas of a gas engine, and the reducing agent reacts with NOx in the exhaust gas on a catalyst. NOx is decomposed into nitrogen and water,
x emission is prevented. FIG. 1 shows an example of an exhaust gas denitration system, in which a catalytic reactor 4 filled with a NOx decomposition catalyst is interposed in an exhaust passage 3 from a gas engine 1 to an exhaust heat recovery boiler 2. A reducing agent injection port 5 for spraying and injecting a reducing agent is provided on the upstream side of the vessel 4, and a control panel 18 for controlling the amount of the reducing agent supplied, as shown in FIG. In addition to an inverter 19 for detecting and converting this to a frequency, the output of the inverter 19 provides a motor 20 for driving the reducing agent supply pump.
By controlling the speed, the supply amount of the reducing agent is made proportional to the exhaust gas amount. As described above, the reason that the amount of the reducing agent injected must be controlled by using an expensive control device such as the inverter 19 is that if the amount of the reducing agent is too small, the NOx remaining without being reduced in the exhaust gas is converted into the air. If the amount of the reducing agent is too much larger than the reaction amount with NOx, harmful and odorous ammonia gas leaks into the air together with the exhaust gas.

[0003]

However, the conventional configuration shown in FIG. 5 has the following problems. That is, the curve A shown in FIG. 2B shows the relationship between the power generation output and the urea water injection amount in the configuration of FIG. 2, and thus the urea water injection amount is made proportional to the power generation output. This is because the exhaust gas flow rate was considered to be proportional to the power generation output, and the NOx generation amount was proportional to the exhaust gas amount. However, in actuality, the amount of generated NOx is not proportional to the amount of exhaust gas,
As shown by the curve B in the figure, it has been confirmed that when the power generation output is reduced, the NOx generation amount increases. The reason is that, for example, in lean-burn gas engines, which are currently widely used in cogeneration, combustion becomes unstable when the power generation output is reduced, so a high air ratio (1.3 or more) near the rated output is required. However, it is considered that when the output is low, the air ratio is lowered because the combustion becomes unstable when the fuel is thin, and as a result, the NOx content increases as the exhaust gas flow rate decreases. Therefore, an object of the present invention is to provide a cogeneration denitration system of this type that can always inject a reducing agent in an amount corresponding to the amount of generated NOx irrespective of fluctuations in power generation output.

[0004]

An exhaust gas denitration system according to the present invention is, as shown in FIGS.
A catalyst reactor 4 for reacting and decomposing NOx with a reducing agent is interposed in an exhaust passage 3 from the exhaust gas to the exhaust heat recovery boiler 2, and a reducing agent injection port 5 is provided upstream of the catalyst reactor 4. NOx in exhaust gas in generation system
The reduction agent injection amount is controlled by approximating the content with a correlation function in which the gradient increases continuously or discontinuously with the power generation output of the gas engine as a variable,
Focusing on the fact that the amount of Ox generation is not proportional to the power generation output, it is characterized in that NOx can be efficiently reduced regardless of fluctuations in the power generation output.

The second aspect of the present invention employs a quadratic function as shown in FIG. 2 (b) as the above-described correlation function. In addition, for example, the function form can be easily set by inputting three measured values to the sequencer, and the invention according to claim 3 has a constant power generation output as shown in FIG. When the power generation output is less than a certain value, the reducing agent injection amount is proportional to the power generation output, and when the power generation output is less than a certain value, the reduction agent injection amount is controlled to be constant regardless of the change in the power generation output. Although it is inferior in accuracy, it is characterized in that it can provide extremely simple and sufficiently practical control means. Further, the invention according to claim 4 is characterized in that NO
By using urea water as the x reducing agent and using an electromagnetic diaphragm type metering pump 6 as shown in FIG. 3 as the injection amount control means, the control means based on the above calculation output can be realized with a very simple configuration. It is characterized by points.

[0006]

1 to 3 show an embodiment of the system according to the present invention. In the gas cogeneration system, a generator is driven by a gas engine 1 to generate electric power, and the exhaust heat thereof is used to heat a boiler 2 to use as a heat source for cooling and heating. The catalyst reacts with the reducing agent and NOx to remove NOx contained in the exhaust gas. Since this catalytic reaction is effective at a high temperature, the catalytic reactor 4 extends from the engine 1 to the exhaust heat recovery boiler 2. It is interposed in the high-temperature exhaust passage 3. The catalytic reactor 4 is filled with a NOx decomposition catalyst 7, and a reducing agent inlet 5 is provided in the exhaust passage 3 upstream of the catalytic reactor 4. The urea water is supplied in a fixed amount by the diaphragm pump 6 and is injected into the exhaust passage 3. In the figure, reference numeral 8 denotes a compressor for injecting urea water with compressed air, and reference numeral 9 denotes a cooling blower for protecting the reducing agent injection nozzle from high temperatures.

FIG. 2A is a control block diagram of the system of the present invention. An arithmetic circuit for obtaining the NOx content in the exhaust passage 3 as a quadratic function of the power output of the gas engine 1 is constituted by a sequencer 10. Then, a pulse signal having a frequency proportional to a quadratic function is output from the sequencer 10 to control the electromagnetic diaphragm type metering pump 6, thereby controlling the injection amount of the urea water. FIG. 3 shows a principle diagram of the electromagnetic diaphragm pump 6, in which a diaphragm 12 is adsorbed and vibrated by an iron core 11 of an electromagnet driven by a frequency-variable pulse current, and the vibration of the diaphragm 12 causes the pump chamber 13 to vibrate. The volume is changed to control the amount of liquid sent, and a check valve 14 is provided in the liquid passage on the input side and the output side of the pump chamber 13. Reference numeral 15 denotes an electromagnet coil, reference numeral 16 denotes a movable iron piece, and reference numeral 17 denotes a dial for changing a gap between the iron core 11 and the diaphragm 12 to adjust a discharge amount per pulse.

In FIG. 2B, a curve A shows the correlation between the power generation output of the gas engine and the amount of the reducing agent injected by the control method according to the present invention. In addition, the injection amount can follow the NOx generation amount with extremely high accuracy. The arithmetic circuit can be configured with little increase in cost only by adding a small program to the sequencer 10 conventionally used for controlling the cogeneration system. Also, the initial setting of the function type is
The measurement values at three points can be easily obtained simply by inputting the measured values to zero.

FIG. 4 shows another embodiment of the present invention. When the power generation output is equal to or more than a predetermined value, the injection amount of the reducing agent is made proportional to the power generation output. The injection amount is controlled to be constant irrespective of a change in the power generation output, and is a simplified form of the function shown in FIG. According to this configuration, it is possible to provide an extremely simple and sufficiently practical control means, although the accuracy is slightly inferior to the embodiment of FIG.

[0010]

According to the present invention, as described above, NOx in exhaust gas
Since the content of the reducing agent is controlled by approximating the content with a correlation function such that the gradient increases continuously or discontinuously with the power generation output of the gas engine as a variable, the power generation output has a wide fluctuation range. In this case, there is an advantage that the injection amount of the reducing agent can accurately follow the actual generation amount of NOx over the range.

[Brief description of the drawings]

FIG. 1 is a schematic system diagram showing a system of the present invention.

FIG. 2 is a block diagram and a graph showing a control method according to the first embodiment;

FIG. 3 is a principle diagram of an electromagnetic diaphragm type metering pump used in the above.

FIG. 4 is a graph showing another embodiment of the present invention.

FIG. 5 is a block diagram and a graph showing a conventional control method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Gas engine 2 Exhaust heat recovery boiler 3 Exhaust path 4 Catalytic reactor 5 Reducing agent inlet 6 Electromagnetic diaphragm type quantitative pump 7 NOx decomposition catalyst 8 Compressor 9 Cooling blower 10 Sequencer 11 Iron core 12 Diaphragm 13 Pump room 14 Check valve 15 Electromagnetic coil 16 Movable iron piece 17 Dial 18 Control panel 19 Inverter 20 Motor

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (reference) F23J 15/00 ZABH

Claims (4)

[Claims] 1. An exhaust passage from a gas engine to an exhaust heat recovery boiler is provided with a catalytic reactor for reacting and decomposing NOx with a reducing agent, and a reducing agent inlet is provided upstream of the catalytic reactor. In the cogeneration system provided, the amount of NOx in the exhaust gas was controlled by approximating the NOx content in the exhaust gas with the correlation function in which the gradient increases continuously or discontinuously with the power output of the gas engine as a variable. Exhaust gas denitration system of cogeneration characterized by the following. 2. The exhaust gas denitration system according to claim 1, wherein the NOx content is approximated by a quadratic function using the power output of the gas engine as a variable. 3. When the power output of the gas engine is equal to or higher than a certain value, the injection amount of the reducing agent is made to be proportional to the output power. The exhaust gas denitration system for cogeneration according to claim 1, wherein the system is controlled as follows. 4. The exhaust gas denitration system for cogeneration according to claim 1, wherein urea water is used as said reducing agent, and an electromagnetic diaphragm type metering pump is used as injection amount control means of urea water.