JPS5824688B2 - Flow rate control method in exhaust gas treatment equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a flow rate control method in an exhaust gas treatment device provided with an exhaust gas treatment device.

Normally, when installing an exhaust gas treatment device for treating exhaust gas, a branch flow path is provided in the duct 2 leading from the exhaust gas generation source 1 to the chimney T, with both ends communicating with each other, as shown in Fig. 1. An exhaust gas treatment device 4 is provided.

In this system, if the exhaust gas treatment device 4 only needs to treat a constant amount of exhaust gas at all times, it is sufficient to simply control the inlet gas amount of the exhaust gas treatment device 4 to be constant. Difficulties arise in control when the amount of exhaust gas from the exhaust gas source changes.

In order for the exhaust gas treatment device 4 to treat the entire amount of exhaust gas emitted from the exhaust gas generation source 1, the gas flow rate in the duct 2 must be zero or at least must not flow toward the chimney.

To this end, the following methods can be easily devised.

That is, either the pressure at the point in the figure and the zero point are kept exactly the same, or the pressure at the zero point is kept extremely slightly higher than the point (■) to allow a small amount of gas to flow backwards.

As another method, the above conditions can be satisfied by providing a valve in the duct 2 and keeping it closed at all times, and opening it when the device malfunctions.

However, these are difficult to realize due to the following points.

In the former case, if there is a pressure difference of several m1H20 between point 2 and point 0, an extremely large amount of gas will flow, so it is necessary to detect the pressure at the two points with extremely high accuracy.

Furthermore, the pressures at the two points vary depending on the load of the exhaust gas source and are not constant.

In the latter case, it is expensive to manufacture leak-free valves in large-diameter ducts, and if the exhaust gas source is a power generation boiler, the exhaust gas source must be shut down even in an emergency such as a failure of the exhaust gas treatment equipment. Since it is not possible to do so, it is necessary to discharge the exhaust gas from the chimney through the duct 2, and if the valve malfunctions, it is necessary to provide a spare duct, which is not practical.

Therefore, the present inventors have proposed a method that does not have these drawbacks.

(Refer to Japanese Unexamined Patent Publication No. 49-134563) According to this, an exhaust gas flow rate detector 8 detects the flow rate of the cape gas coming out from the exhaust gas source and a flow rate detector 9 detects the exhaust gas flow rate in the branch flow rate leading to the exhaust gas treatment device. Both flow rates are detected, and if the latter is smaller than the former, the exhaust gas flow rate in the branch flow path is controlled.

In this case, the detection signal of the exhaust gas flow rate detector 8 becomes the setting signal of the throughput controller 10, and the flow rate in the branch flow path is controlled by the control damper 5 of the blower 6 so that the flow rate detected by the detector 9 does not become smaller than this. It is supposed to be done.

In the figure, 11 is a counter when exhaust gas is recirculated in the duct 2 with some backflow from the mouth point to the point A.

In this case, even if there is an error in the exhaust gas flow rate detector 8 or the exhaust gas flow rate detector 9 in the branch flow path or in an excessive state during load fluctuation, the exhaust gas treatment device 4 can completely process all of the exhaust gas from the exhaust gas generation source 1. In other words, in order to keep the S02 concentration and/or NOx concentration of the gas released into the atmosphere below the regulation value, in order to keep the S02 concentration and/or NOx concentration of the gas released into the atmosphere below the regulatory value, approximately 5 to 10% of the air flow from the chimney 7 to the exhaust gas treatment device 4 in the duct 2 takes into account the safety factor. The reality is that many vehicles are operated with a backflow of exhaust gas.

In other words, the exhaust gas treatment device 4 is operated to process 5 to 10 times more exhaust gas than the exhaust gas from the exhaust gas generation source 1 (operation to recirculate the exhaust gas), and the power to drive the exhaust blower 6 is In addition, in the case of a wet flue gas desulfurization system, the flue gas is heated in a reheating furnace to raise its temperature after desulfurization, which increases the consumption of heavy oil for heating, etc. The disadvantage was that it was uneconomical.

The present invention eliminates the drawbacks of the above-mentioned proposed invention, and provides a control method that maintains the concentration of gas SO2 and/or NOx below the regulation value before being released into the atmosphere, and further reduces the amount of recirculated exhaust gas, allowing for economical operation. This was proposed for the purpose of exhaust gas generation.

The exhaust gas flow rate from the exhaust gas generation source of the exhaust gas treatment device and the exhaust gas flow rate in the branched flow path are detected, and the exhaust gas flow rate in the branched flow path is detected. Flow rate control in an exhaust gas treatment device that controls the flow rate of exhaust gas in the same branch flow path using a detected value of the flow rate of exhaust gas emitted from the exhaust gas generation source as a set value so that the flow rate of exhaust gas flowing through the branch flow path does not become smaller than the flow rate of exhaust gas emitted from the exhaust gas generation source. A method for controlling a flow rate in an exhaust gas treatment device, characterized in that the method detects the concentration of SO□ and/or NOx in the exhaust gas before the atmosphere discharge side of the duct, and changes the set value according to the detected value. It is.

The present invention will be specifically explained below with reference to an embodiment shown in FIG.

In the figure, 1 is an exhaust gas generation source, 2 is a duct, 4 is an exhaust gas treatment device, 5 is a damper, 6 is an exhaust blower, T is a chimney,
8 is an exhaust gas flow rate detector, 9 is a flow rate detector that detects the exhaust gas flow rate in the branch flow path leading to the exhaust gas treatment device 4, 10 is a throughput controller, 11 is a coefficient unit, and 12 is an exhaust gas at the inlet of the exhaust gas source 1. In the quantity detector, the configuration, operation and mutual relationship structure of the components are substantially similar to those of the device implementing the proposed method.

(Equivalent parts are given the same reference numerals.

), 13 is a gas concentration detector that detects the SO□ or NOx concentration of the gas before it is released into the atmosphere, 14 is a ratio coefficient unit or function unit that calculates a set value slight increase correction signal for the exhaust gas amount control system, and 15 is a function unit Adder, 16 is limiter, 17 is slight increase correction signal, 18 is S0 of outlet gas of exhaust gas treatment device
2 or a gas concentration detector for detecting NOx concentration, respectively.

An example of a device for carrying out the present invention is configured as described above.

In this case, we will discuss the case where S02 in the gas is removed by the exhaust treatment device.

According to the configuration shown in FIG. 2, the gas S02 concentration before being released into the atmosphere (chimney murky gas S02 concentration) is detected by the gas S02 concentration detector 13, and the gas S02 concentration is detected by the ratio coefficient unit or function unit 14.
02 A set value slight increase signal of the exhaust gas amount control system according to the output signal of the concentration detector 13 is calculated.

(If the output of the gas S02 concentration detector 13 increases, the output of the ratio coefficient unit or function unit 14 is increased.) Therefore, for example, in a transient state due to load fluctuation, the exhaust gas source 1 is connected to the chimney 7 in the duct. When untreated gas flows in the direction of the population and the output signal of the gas SO2 concentration detector 13 before being released into the atmosphere increases and is about to deviate from the regulation value, the output of the ratio coefficient unit or function unit 14 also increases. The output of the exhaust gas flow rate detector 8 is somewhat larger than the output of the exhaust gas flow rate detector 8.

Therefore, the output of the limiter 16, that is, the set value of the processing controller 10 also increases, and the output of the exhaust gas flow rate detector 9 in the branch flow path increases.

(Because the set value and the output of the exhaust gas flow rate detector 9 become equal due to the action of the throughput controller 10.) Therefore, there is no untreated gas flowing in the duct 2 from the exhaust gas source 1 to the chimney T side, and conversely, 7, the exhaust gas begins to flow back toward the exhaust gas source 1.

In this way, the gas SO2 concentration detector 13 before being released into the atmosphere
This prevents the output from deviating from the regulated value.

(A guarantee is given to keep the value below the regulation value.) FIG. 3 illustrates a specific example of the present invention.

For example, if the regulation value is 90-, the outlet gas SO2 concentration of the exhaust gas treatment device 4 (according to the detector 18 in FIG.
The system operates at about 100 pm, and the amount of exhaust gas recirculated through the duct 2 is set to be as small as possible, about 2 to 5 coefficients, which is lower than the conventional 5 to 10 coefficients.

At this time, it is assumed that the function unit 14 is set as shown in FIG. 3A.

In such a state, the amount of exhaust gas recirculated in the duct 2 is minimized, and there is almost no margin in control to reduce the amount of untreated gas to zero in any case.

Therefore, due to errors in the instruments such as the detectors 8 and 9, or in transient conditions when the load of the exhaust gas source changes, the untreated gas may flow through the duct 2 in the opposite direction to the circulation direction, and the outlet gas SO2 concentration may exceed 60 ppm. The output of this time counter 14 begins to increase slightly.

Therefore, the output of the adder 15 also increases slightly, and the output of the set value bilimiter 16 of the throughput control system of the exhaust gas treatment device begins to increase slightly.

. At this time, if the atmospheric release gas SO□ concentration is 80 ppm
Then, the output of the function unit 14 will be corrected by increasing by four.

By the above-mentioned slight increase correction processing of the exhaust gas treatment gas amount control system settings, the atmospheric release gas S02 concentration is again reduced to .

If the value becomes 60 PPI or less, the slight increase correction amount will be removed.

The reason why the characteristic A in FIG. 3 is provided with a limit characteristic is to prevent a state in which the processing amount exceeds the maximum processing amount due to a large increase in the correction signal.

(If the amount of circulating gas becomes excessive, it should be considered that the cause is somewhere other than the control system! Also, if it becomes excessive, there is a risk that the exhaust gas source and exhaust gas treatment device will trip.

) The setting of the characteristic A in FIG. 3 is only an example, and the starting point of the slight increase signal, the slope, and the limit value can be changed arbitrarily.

In addition, A in Fig. 3 shows an example in which the correction signal is changed continuously, but it is also possible to provide a multi-stage (two-stage in this example) switching characteristic, as shown in Fig. 3, for example. You can also do it.

In this case, the signal of the atmospheric emission gas S02 concentration detector 13 and the regulation value etc. are compared with the reference value determined from 4 (in this case, 60pp).
m), and the output signal of the comparator drives a relay that switches the signal from the constant voltage generator (in this case, the signals from the 4th to 8th ratios) to obtain the slight increase in Figure 2. A correction signal 11 is obtained.

In addition, Fig. 3A and mouth characteristics both describe a method of slightly increasing the set value of the processing gas amount, but in addition to this method, there is a method to obtain an equivalent effect using the ratio coefficient
The same result as shown in FIG. 3 can also be obtained by changing the ratio according to the SO2 concentration of the atmospherically released gas (having a characteristic that the ratio slightly decreases as the atmospherically released gas S02 concentration increases).

In the process gas flow rate control device of the exhaust gas treatment device 4 shown in FIG.
Assume that the exhaust gas flow rate from the exhaust gas generation source 1 increases in a stepwise manner.

Accordingly, the set value of the processing gas flow rate control system (output of the bilimiter 16) is increased via the exhaust gas flow rate detector 8, adder 15, and bilimiter 16 (provided to prevent the amount of processing gas from exceeding the maximum processing gas amount). .

The processing gas flow rate controller (processing amount controller) 10 operates and outputs a correction signal so that this set value and the detection signal calculated by the ratio coefficient unit 11 via the exhaust gas treatment equipment inlet gas flow rate detector 9 become equal. .

According to this correction signal, the opening degree of the damper 5, that is, the inlet gas flow rate increases, and finally the inlet gas flow rate (
(processing gas flow rate).

However, before the final balance is reached, the damper 5 temporarily becomes insufficiently opened, the treated gas flow rate becomes lower than the set value, and the untreated gas flows through the duct 2 toward the chimney 7, and the atmospheric release gas SO2 concentration ( The smoke inlet gas SO2 concentration) becomes equal to or higher than a predetermined value.

Conventionally, in order to cope with this transient increase in the SO2 concentration of the atmospheric gas released, the value of the ratio counter 11 is set to a small value with a margin, and the amount of exhaust gas to be recirculated is set to a large amount (about 5 to 10 L:l). However, according to the present invention, the amount of exhaust gas recirculated in the duct 2 can be reduced compared to the conventional method since the operation described below is added.

That is, the atmospheric release gas SO2 concentration detector 13 detects an increase in the atmospheric release gas S02 concentration, and the function unit 14 provides a set value slight increase signal to the adder 15.

Therefore, the treatment gas flow rate setting value is increased by approximately the correction amount, and the treatment gas flow rate is increased to balance the new setting value, so that the untreated gas that was flowing through the duct 2 toward the chimney is no longer flowing into the atmosphere. The released gas SO2 concentration automatically decreases.

Thereafter, the set value slight increase correction signal is further removed as the atmospheric emission gas SO2 concentration decreases.

Furthermore, even if an error occurs in the gas flow rate detectors 8 and 9 and untreated exhaust gas flows through the duct 2 toward the chimney 7, the function unit 14 operates and a set value slight increase correction signal is given to the adder 15, and the atmospheric release gas is The SO2 concentration will automatically decrease and be kept below the regulatory value.

Although the above explanation has been made regarding the case where SO2 in gas is removed by a flue gas desulfurization device, the pond water invention can be used in a denitrification device and a simultaneous desulfurization and denitration device.

In the case of a denitrification device, use the gas SO2 concentration detector 13 in Figure 2.
Instead, gas NOx (NO and NO2) concentration detectors are used, and other control equipment 8, 9, 10, 14, 1
By using the same elements 5, 16, and 5, the NOx concentration of the gas released into the atmosphere can be maintained at a predetermined value.

In this case, the set value of the processing gas amount may be changed depending on the NOx concentration of the gas released into the atmosphere.

An example of application to a simultaneous desulfurization and denitrification equipment is shown in Fig. 4.

In the figure, 20 is a NOx concentration detector for detecting the NOx concentration of gas released into the atmosphere, 21 is a function unit, and 22 is a biselector.

21, a set value slight increase correction signal is output in response to the detection signal of the gas NOx concentration detector 20.

(It has a characteristic that the set value slight increase correction signal increases as the NOx concentration of the atmospheric gas discharged increases.) 22 is the function unit 14 and 2
Adder 1 selects the larger value of the two output signals of 1.
It functions to output to 5.

In Figure 4, if untreated gas flows toward the chimney through duct 2, the SO2 concentration or NO
When the x concentrations exceed a predetermined value, the increase in these concentrations is detected in step 13.20, and the function generator 14.
At step 21, set value slight increase signals 23 and 24 are obtained.

The selector 22 selects the larger value of the signals 23 and 24 and supplies the adder 15 with a signal to slightly increase the processing gas amount set value.

Therefore, the processing gas flow rate increases, and the SO2 and NOx concentrations of the gas released into the atmosphere are automatically reduced and maintained at predetermined values.

In FIG. 4, the member 22 is a biselector, but there is also a method in which a coefficient adder is used instead and the signals 23 and 24 are added in proportion to obtain the signal 17.

As explained above, according to the present invention, the atmospheric release gas S02 is
It is possible to automatically prevent the concentration and NO2 concentration from deviating from the regulation values, and it is possible to operate the exhaust gas treatment equipment with a smaller amount of gas than before, making it more economical and stable. I can drive well.

It goes without saying that the present invention can also be used to control various harmful gases without departing from the spirit of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of a further exhaust gas treatment device for explaining the flow rate control method proposed above, and FIG. 2 is a system diagram of another exhaust gas treatment device for explaining the flow rate control method according to the present invention.
FIG. 3 is a graph showing a function between the atmospheric emission gas S02 concentration and the output of the function generator 14, and FIG. 4 is another system diagram of the exhaust gas treatment device using the control method according to the present invention. Exhaust gas generation source, 2: Duct, 4: Exhaust gas desulfurization equipment, 5
: Control damper, 6 Ni blower, T: Chimney, 8: Exhaust gas flow rate detector from exhaust gas generation source, 10: Processing amount controller, 11
: Coefficient unit, 13: Exit gas treatment equipment outlet gas S02 or NOx concentration detector, 14: Function unit, 15: Adder, 1
6: Bi-limiter, 17: Slight increase correction signal, 18 Exit gas S02 or NOx concentration before being released into the atmosphere.

Claims (1)

[Claims] 1. Detect the flow rate of exhaust gas coming out of the exhaust gas generation source and the flow rate of exhaust gas in the branch flow path of an exhaust gas treatment device in which the exhaust gas treatment device is installed in a branch flow path that communicates both ends with a duct leading from the exhaust gas generation source to the chimney. In an exhaust gas treatment device that controls the flow rate of exhaust gas in the branch flow path using a detected value of the flow rate of exhaust gas emitted from the exhaust gas generation source as a set value so that the flow rate of exhaust gas flowing in the branch flow path does not become smaller than the flow rate of exhaust gas flowing out from the exhaust gas generation source. A flow rate control method in an exhaust gas treatment device, comprising detecting the exhaust gas S02 and NOx concentration in the duct before being released into the atmosphere, and changing the set value according to the detected values.