JPS6157059B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for controlling the mixing ratio of two reaction gases, more specifically, a method for controlling the mixing ratio when two gases are reacted and the remaining amount of each gas is lower than a reference value. Regarding.

The exhaust gas from gas turbines used as prime movers in power plants, etc. usually contains 50 to 100 ppm of nitrogen oxides (hereinafter referred to as NOx), and the high-temperature exhaust gas is led to a waste heat boiler, where the waste heat is recovered and released into the atmosphere. released. However, since NOx in this exhaust gas is a substance that causes air pollution, the national and local governments have established emission standard values for it. NOx and NH ₃ are injected into the waste heat boiler, and NOx and NH ₃ are reacted in a catalytic reaction device installed in the waste heat boiler, converting them into the harmless substances nitrogen and water. This reaction increases the mixing ratio (molar ratio) of NOx and NH ₃ to approximately 1:1.
When maintained at
Can be lowered to 10. Increasing the ratio of the amount of NH ₃ injected can further reduce the amount of residual NOx, but this will increase the amount of unreacted residual NH ₃ ; conversely, decreasing the ratio of the amount of NH ₃ injected will reduce the amount of residual NOx. NOx amount increases. Also, NOx and _NH3
The reaction rate is greatly affected by the reaction temperature, and the reaction rate ((inlet NOx amount - residual NOx amount) / inlet NOx amount) can be maintained at approximately 90% at the normal exhaust gas temperature range of 350 to 400°C. The reaction rate decreases in the low temperature range of around 300°C, such as immediately after the gas turbine starts up or under low load. _NH3 at the catalytic reactor inlet
and NOx mixing ratio (NH ₃ /NOx (molar ratio)), residual NOx amount (Nm ³ /h), and residual NH ₃ amount (Nm ³ /
h) is shown in Figure 1, where curves A and B represent the residual temperature in the normal temperature range of 350 to 400°C.
Curves C and D represent the NOx amount and residual _NH3 amount.
It shows the amount of residual NOx and the amount of residual _NH3 in the low temperature range of 250 to 330°C. Also, Po
is the emission standard value for NOx and _NH3 (e.g. 5N
m ³ /h). R ₁₁ and R ₁₂ each have a residual NOx amount at the standard value Po in the normal temperature range.
Indicates the mixing ratio when it becomes equal to and the mixing ratio when the amount of residual _NH3 becomes equal to the reference value Po,
MR ₁ is the average value of these mixing ratios R ₁₁ and R ₁₂ (R ₁₁
+R ₁₂ /2) (hereinafter referred to as average mixing ratio). Furthermore, R ₂₁ and R ₂₂ indicate the mixing ratio when the amount of residual NOx becomes equal to the reference value Po and the mixing ratio when the amount of residual NH ₃ becomes equal to the reference value Po in _the low temperature range, respectively. Average mixing ratio of R ₂₁ and R ₂₂ (R ₂₁ + R ₂₂ /2)
It shows. Conventionally, when injecting _NH3 into the exhaust gas of a gas turbine, the amount of NOx emissions at the outlet of the waste heat boiler is measured, and if this measured value is larger than a set standard value, the amount of _NH3 injected is increased and the measured value is increased. If it is smaller than the set standard value, the amount of NH ₃ injected is reduced. However, in order to minimize the emissions of NOx and NH ₃ and to equalize the adjustment margins a and b in the direction of increasing and decreasing NH ₃ , the mixing ratio of NOx and NH ₃ must be adjusted to the average mixing ratio MR. ₁ ,
It is preferable to control the amount of NH ₃ injected so that MR ₂ is achieved. Also, the average mixing ratio when the exhaust gas temperature is in the normal temperature range and when it is in the low temperature range.
MR ₁ and MR ₂ change, for example, even though it is in the low temperature range, the average mixing ratio MR ₁ in the normal temperature range
When controlled using MR, the residual NH ₃ amount P ₁ becomes larger than the residual NH ₃ amount P ₂ when controlled using the average mixing ratio MR ₂ in the low temperature range, which is not preferable.

An object of the present invention is to provide a method for controlling the mixing ratio of two reaction gases, which can minimize the remaining amount of both gases even if the gas temperature fluctuates when the two gases are reacted. be.

In order to achieve the above object, the control method according to the present invention causes a first gas and a second gas to react,
And when reducing the residual amount of each gas to below the standard value,
The average mixing ratio is the average of the mixing ratio of the two gases when the remaining amount of the first gas becomes equal to the reference value and the mixing ratio of the two gases when the remaining amount of the second gas becomes equal to the reference value. The relationship between the residual amount of the first gas and the average mixing ratio in a certain temperature range and the relationship between the average mixing ratio and the gas temperature with respect to the reference value are determined, and the gas temperature and the amount of the first gas before the reaction are determined. The remaining amount of the first gas after the reaction is measured, the average mixing ratio is determined with respect to the set reference value, and this average mixing ratio is corrected based on the measured value of the gas temperature to determine the target value of the average mixing ratio. , find the measured value of the average mixing ratio from the measured value of the residual amount of the first gas, find the set value of the average mixing ratio from the measured value of this average mixing ratio and the target value of the average mixing ratio, and react with this set value. The method is characterized in that the supply amount of the second gas is controlled based on the previously measured value of the amount of the first gas.

Embodiments of the present invention will be described below with reference to the drawings.

Figure 2 shows an air pollution prevention device at a power plant, etc. This device includes a gas turbine 1 exhaust gas flow meter and NOx analyzer 2, an NH 3 injection device that injects NH ₃ into the exhaust gas and sends it to a waste heat boiler ₃ . A device 4, an NH ₃ mixing dilution chamber 6 and a dilution fan 7, which dilute NH ₃ supplied from the NH ₃ supply pipe 5 and send it to the injection device 4, an NH ₃ flow meter 8 provided in the NH 3 supply pipe 5, and an NH _{3 3} Flow control valve 9 is installed in the waste heat boiler 3 to control the flow rate in the exhaust gas.
A catalytic reaction device 10 that generates nitrogen and water by reacting NOx and NH ₃ , a thermometer 11 installed at the inlet of the catalytic reaction device 10 , and a gas discharge pipe 12 of the waste heat boiler 3
control for controlling the opening degree of the NH ₃ flow rate control valve 9 based on the outputs of the residual NOx analyzer 13 provided in the NH ₃ flow meter 13, the exhaust gas flow meter, the NOx analyzers 2, 13, the NH 3 flow meter 8, and the thermometer 11; It is composed of a device 14.

The configuration of the control device 14 is shown in FIG.
Next, with reference to this, the operation of the control device 14, that is, one example of the control method of the present invention will be explained.

The output (Nm ³ /h) of the flow meter 15 of the exhaust gas of the gas turbine 1 and the output (ppm) of the NOx analyzer 13 at the outlet of the waste gas boiler 3 are sent to the multiplier 16, and thereby the flow rate of NOx at the outlet of the waste gas boiler 3 is In other words, the residual NOx amount Q ₁ (Nm ³ /
h) is required. This measured value of residual NOx amount Q ₁
is sent to the central control unit and flow rate indicators 19, 20 of discharge standard value setters 17, 18 installed at the site, respectively. The two setting devices 17 and 18 have
The NOx emission standard values can be set separately, and one of these set values is selected by the switch 21 and sent to the calculator 22. This calculator 22 stores the relationship between the amount of residual NOx and the average mixing ratio in the normal temperature range as shown in FIG. Assuming that, the reference value MRr of the average mixture ratio is calculated. As is clear from the graph in Figure 1, there is a certain relationship between the amount of residual NOx and the average mixing ratio in the normal temperature range.
By changing the amount of NOx and plotting the average mixing ratio against it, the curve shown in FIG. 4 is obtained. Note that the relationship between the amount of residual NOx and the average mixing ratio shown in FIG. 4 changes slightly due to deterioration of the denitrification catalyst in the catalytic reaction device 10, so these relationships are corrected as appropriate in consideration of changes over time. The reference value MRr of the average mixing ratio obtained in this way and the output (°C) of the thermometer 11 at the inlet of the catalytic reaction device 10 are sent to the temperature compensation calculator 23, and based on these, the average mixing ratio is calculated. The target value MRo is calculated. This calculator 23 stores the target value MRo and reference value of the average mixing ratio for the reaction temperature as shown in FIG.
The relationship between the ratio of MRr (hereinafter referred to as temperature compensation coefficient) is stored, and the target value MRo of the average mixing ratio is obtained by multiplying the input reference value MRr and the measured reaction temperature value by the temperature compensation coefficient. As mentioned above, in Fig. 1, when the reaction temperature changes, curves A and C representing the amount of residual NOx and curves B and D representing the amount of residual NH ₃ change, and the average mixing ratio for a fixed emission standard value also changes. It changes according to.
Then, for a fixed emission standard value (for example, P ₀ ), the average mixing ratio at each reaction temperature is determined and the ratio of this to the average mixing ratio in the normal temperature range (for example, MR ₁ ) is plotted as shown in Figure 5. A graph of is obtained. The relationship between the reaction temperature and the temperature compensation coefficient obtained in this way is almost constant even if the emission standard value changes, and the coefficient is a constant value close to 1 in the normal temperature range of about 330°C or higher. ,
It becomes slightly smaller as the reaction temperature decreases between 330 and 250°C, and becomes 0 below 250°C. Furthermore, since these relationships change slightly over time, they are corrected as appropriate, as in the case of the arithmetic unit 22. On the other hand, the measured value Q ₁ of the amount of residual NOx is also sent to the computing unit 24 which is the same as the computing unit 22, and the output thereof is further sent to the computing unit 25 which is the same as the computing unit 23 for temperature compensation. The output of the thermometer 11 is input to this calculator 25, and from these, the measured value MRc of the average mixing ratio is determined. The target value MRo and the measured value MRc of the average mixing ratio are sent to the average mixing ratio controller 26, and this controller 26
The set value MRm of the average mixing ratio is output so that the measured value MRc approaches the target value MRo. This setting value
For example, when the measured value MRc is larger than the target value MRo, MRm is set to a smaller value than the target value MRo according to the difference, and when the measured value MRc is smaller than the target value MRo, the target value MRo is set to a smaller value according to the difference. can be set to a larger value. Average mixing ratio setting value
MRm is suppressed within a certain range by a limiter 27 and sent to a multiplier 28. On the other hand, the output of the exhaust gas NOx analyzer 2 is sent to this multiplier 28, and the set value Q ₂ of the amount of NH ₃ to be injected is determined by these outputs.
(Nm ³ /h) is determined and the NH ₃ flow rate indicator controller 2
Sent to 9th. The output (Nm ³ /h) of the flow meter 8 of the NH ₃ supply pipe 5 is sent to this controller 29, and the controller 29 is configured so that the measured value by the flow meter 8 is equal to the set value Q ₂ . The opening of the flow control valve 9 of the NH ₃ supply pipe 5 is controlled and the flow rate is instructed. Further, the NH ₃ supply pipe 5 is provided with an emergency shutoff valve 30 that is normally open and an emergency release valve 31 that is normally closed, and normally flows NH ₃ to the NH ₃ injection device 4, but for example, In an emergency such as when the reaction temperature falls below 250° C., the emergency shutoff valve 30 is closed and the emergency release valve 31 is opened to prevent NH ₃ from flowing into the NH ₃ injection device 4.

Through the above control, for example, if the emission standard value is set to Po in Figure 1, the average mixing ratio will be MR ₁ in the normal temperature range represented by curves A and B.
, the residual NOx amount becomes P ₃ , and in the low temperature range represented by curves C and D, the average mixing ratio becomes MR ₂ ,
The amount of remaining NOx becomes P ₄ , and the amount of remaining NH ₃ becomes P ₂ . In either case, equal adjustment margins a and b are provided both in the direction of increasing and in the direction of decreasing the amount of injected NH ₃ .

As described above, according to the control method of the present invention,
The average mixing ratio is the average of the mixing ratio of the two gases when the remaining amount of the first gas becomes equal to the reference value and the mixing ratio of the two gases when the remaining amount of the second gas becomes equal to the reference value. Since the mixing ratio of the two gases is controlled to be the average mixing ratio, the remaining amounts of both the two gases can be minimized as much as possible. In addition, the relationship between the residual amount of the first gas and the average mixing ratio in a certain temperature range and the relationship between the average mixing ratio and the gas temperature with respect to the reference value are determined, and the relationship between the gas temperature and the first gas before the reaction is determined. The remaining amount of the first gas after the reaction is measured, the average mixing ratio is determined with respect to the set reference value, and this average mixing ratio is corrected based on the measured value of the gas temperature to determine the target value of the average mixing ratio. , find the measured value of the average mixing ratio from the measured value of the residual amount of the first gas, find the set value of the average mixing ratio from the measured value of this average mixing ratio and the target value of the average mixing ratio, and react with this set value. Since the supply amount of the second gas is controlled based on the previously measured value of the amount of the first gas,
Even if the gas temperature changes, the remaining amount of both gases can always be kept as small as possible.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the mixing ratio of two reaction gases and the residual amount of these gases, Figure 2 is a block diagram of an air pollution prevention device for carrying out this invention, and Figure 3 is its control. FIG. 4 is a graph showing the relationship between the average mixing ratio and the amount of residual NOx, and FIG. 5 is a graph showing the relationship between the reaction temperature and the temperature compensation coefficient. 1...Gas turbine, 2,13...NOx analyzer,
3... Waste heat boiler, 4... NH ₃ injection device, 8... NH ₃ flow meter, 9... NH ₃ flow control valve, 10... Catalyst reaction device, 11... Thermometer, 14... Control device, 17, 18
...Emission standard value setter, 22, 23, 24, 25...
Arithmetic unit, 26...average mixing ratio controller.

Claims (1)

[Claims] 1. When reacting the first gas and the second gas and reducing the remaining amount of each gas to below the reference value, the mixing ratio of the two gases when the remaining amount of the first gas becomes equal to the reference value. The average mixing ratio of the two gases when the remaining amount of the second gas becomes equal to the reference value is defined as the average mixing ratio, and the relationship between the remaining amount of the first gas and the average mixing ratio in a certain temperature range. Determine the relationship between the average mixing ratio and gas temperature with respect to the reference value, measure the gas temperature, the amount of the first gas before the reaction, and the residual amount of the first gas after the reaction,
Find the average mixing ratio for the set standard value,
Correct this average mixing ratio based on the measured value of the gas temperature to obtain a target value of the average mixing ratio, obtain a measured value of the average mixing ratio from the measured value of the residual amount of the first gas, and calculate the measured value of this average mixing ratio. A set value of the average mixing ratio is determined from the target value of the average mixing ratio, and the supply amount of the second gas is controlled based on this set value and the measured value of the amount of the first gas before the reaction. A method for controlling the mixing ratio of two reaction gases.