JPH0310876B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for treating exhaust gas generated from a hot metal pretreatment vessel, and in particular, by appropriately controlling the flow rate of combustion exhaust gas, the amount of gas contained in the exhaust gas is reduced. The present invention relates to a method for completely burning combustible gas and recovering valuable components sufficiently. In this specification, "exhaust gas" refers to the gas discharged from the hot metal pretreatment vessel, "combustion gas" refers to the gas obtained by adding combustion air to the above-mentioned exhaust gas, and "combustion exhaust gas" refers to the gas discharged from the hot metal pretreatment vessel. Refers to the gas after combustion gas is combusted.

[Prior Art] Hot metal tapped from a blast furnace is generally received in a ladle, pig iron mixing car, etc. before being charged into a converter, and various preliminary treatments are performed using these as processing vessels. In other words, the preliminary treatment involves adding molten metal in the treatment container to
This is carried out by introducing a dephosphorization and desulfurization agent containing an alkali metal compound as a main component or by blowing in a carrier gas, and the hot metal is subjected to dephosphorization and desulfurization treatment.
By the way, among the scouring agents used in the pretreatment of hot metal, a particularly common alkali metal compound (mainly sodium carbonate, commonly known as soda ash) is mostly emitted as CO ₂ during scouring, but a considerable amount is is emitted as sodium gas or sodium carbonate dust. Therefore, if the exhaust gas generated from the hot metal pretreatment vessel is released to the outside of the system as it is, it will cause environmental pollution. In addition, the above exhaust gas contains a large amount of CO gas, which is a flammable gas, and this exhaust gas also has a large amount of sensible heat, so the effective use of these gases is attracting attention.
Various strategies are being developed. The present applicant has previously proposed a system for recovering dust and valuable components contained in exhaust gas, paying attention to both environmental protection measures and economic efficiency.

FIG. 3 is a conceptual diagram showing the system, in which the exhaust gas generated from the processing container 1 is transferred to the splash cover 2.
After being mixed with the primary air A sucked in through the opening of 8, the air is mixed with the primary air A sucked through the opening of
The inside of b is sucked in the direction of arrow D. In this suction process, the exhaust gas is first mixed with secondary air sucked in through the opening 15 provided in the duct 8, and the CO gas contained in the exhaust gas is completely combusted. The combustion exhaust gas, which has reached a high temperature of 1300℃ or more due to combustion, has radiant heat removed when passing through a flow path with a water-cooled wall 2 provided on the inner surface of the duct (that is, heat is recovered by the water-cooled wall 2). The temperature drops to ~1200℃. Since the combustion exhaust gas temperature is lower than the dust melting temperature due to the above-mentioned temperature drop, the molten dust is solidified, and the phenomenon of dust adhesion to the subsequent wall of the heat recovery device 3 is avoided. The cooled combustion exhaust gas is cooled while passing through a heat recovery device 3 formed by intersecting and arranging water pipes, for example, and sensible heat is recovered. The combustion exhaust gas that has passed through the heat recovery device 3 reaches the duct 8a, is cooled by being supplied with air from the opening 16, and then flows into the electrostatic precipitator 5 to remove dust. Note that when the temperature of the combustion exhaust gas is high, water of about 5% by volume or more may be required to maintain the charged state of the dust, so steam or water is introduced from the opening 16 as necessary. The dust captured by the electric precipitator 5 is transferred to the dust collection device 7
is collected and reused as a processing agent via a recovery route 9. On the other hand, the combustion exhaust gas that has entered the duct 8b is drawn by the suction blower 6 and is dissipated into the atmosphere 10. In the above exhaust gas treatment system, a temperature sensor T is inserted into the water cooling wall 2 of the duct 8, a pressure sensor P is inserted into the duct 8b, and an air introduction path 15a to the opening 15 and the duct 8b are inserted. Dampers 13 and 14 are provided, and detection data from the temperature detector T and pressure detector P is input to the control unit 11, and the damper controller 1 is inputted from the control unit 11 to the damper controller 1.
The exhaust gas treatment, that is, the pressure in the ducts 8, 8a, 8b is controlled by giving commands to the dampers 2, 12a and adjusting the opening degrees of the dampers 13, 14.

[Problems to be Solved by the Invention] However, in the above exhaust gas treatment method, the basics of pressure control and temperature control vary depending on the type of pretreatment (dephosphorization, desulfurization, or desiliconization), the amount of pretreatment, and the pretreatment time. This method has the disadvantage that it is necessary to change the target setting value each time, and the operation is complicated. In addition, since the temperature control and pressure control are simple, they have poor ability to follow pressure fluctuations within the processing system, and the amount of intake air cannot be properly adjusted.
It was not possible to completely burn the CO gas.
In particular, since the pressure on the inlet side of the suction blower 6 is controlled, the pressure on the inlet side of the heat recovery device cannot be said to be properly controlled. Combustion exhaust gas may flow backward through the introduction passage 15a etc. and be ejected, and since combustion air is not introduced into the duct 8, unburned gas remains and is not effectively utilized.
It may be discharged to the outside of the system via 8b. On the other hand, if the above pressure becomes significantly negative, excessive low-temperature air flows into the duct 8, which lowers the combustion exhaust gas temperature and deteriorates the heat recovery efficiency in the heat recovery device 3, making it impossible to recover waste heat sufficiently. become unable.

The present invention has been made in view of these circumstances, and provides a treatment method that can completely burn CO gas in exhaust gas, and in particular a method that achieves complete combustion of CO gas by controlling the flow rate. By providing this, it is possible to prevent the outflow of unburned gas and explosive combustion of the outflowed unburned gas, avoid backflow jetting of combustion exhaust gas, and perform efficient heat recovery.

[Means for Solving the Problems] The method of the present invention, which achieves the above object, calculates the predicted combustion exhaust gas amount based on the time function pattern of the exhaust gas amount coefficient determined for each type of pretreatment, the supply rate of the scouring agent, and the blown oxygen flow rate. The gist of this method is to calculate the predicted amount of combustion exhaust gas, correct the estimated amount of combustion exhaust gas based on O ₂ concentration detection data at a stage after combustion, and control the flow rate of combustion exhaust gas using the obtained correction value.

[Function] The amount of exhaust gas generated from the hot metal pretreatment vessel and the amount of combustion exhaust gas when the exhaust gas is completely combusted depend on the type of pretreatment, the rate of supply of the scouring agent to the pretreatment furnace, the amount of oxygen supplied for oxygen blowing, etc. determined by. Therefore, by knowing the time-function pattern of the amount of exhaust gas, especially the amount of combustion exhaust gas generated,
By comparing the amount of combustion exhaust gas actually generated, it can be determined whether the combustion conditions at that time, especially the amount of combustion air supplied, are appropriate. If the combustion exhaust gas flow rate is increased or decreased based on this judgment, complete combustion of the combustible gas can be achieved as a control effect. Therefore, in the present invention, the predicted combustion exhaust gas amount is calculated from the time function pattern of the exhaust gas amount coefficient determined for each type of pretreatment, the supply rate of the scouring agent, and the blown oxygen flow rate, and the combustion exhaust gas flow rate is controlled based on this. It consists of The flow rate of the combustion exhaust gas can be controlled, for example, by adjusting the opening degree of a damper provided in the flow path of the combustion exhaust gas, and by increasing or decreasing the amount of suction gas by a suction blower provided downstream.

In addition to the above-mentioned flow rate control, the present invention detects the O ₂ concentration at a stage after combustion in order to more reliably and stably completely burn the combustible gas in the exhaust gas, and controls the combustion exhaust gas flow rate based on this data. . In other words, the O ₂ concentration in a complete combustion state should show a predetermined value based on various processing conditions, and this has been confirmed experimentally.
It has been found that when the detected O ₂ concentration deviates from the specified value, the following drawbacks occur. In other words, if the detected O ₂ concentration is higher than the specified value, it means that the amount of exhaust gas combustion air supplied is excessive, and since excess combustion air (low temperature) is mixed with the exhaust gas, the combustion exhaust gas temperature decreases. As a result, the heat recovery rate in the heat recovery device deteriorates. On the other hand, if the detected O ₂ concentration is lower than the specified value, the amount of combustion air supplied is insufficient, and complete combustion cannot be achieved. Detected like this O ₂
If the concentration deviates from the specified value, it will lead to the occurrence of corresponding problems, so in order to solve this problem, correction control based on the O ₂ concentration detection data is added to the combustion exhaust gas flow rate control.

As described above, by combining the combustion exhaust gas flow rate control based on the predicted combustion exhaust gas amount and the combustion exhaust gas flow rate control based on the O ₂ concentration detection data, highly accurate flow rate control can be achieved, and the combustible gas in the exhaust gas can be completely eliminated. Combustion can be measured.

[Example] FIG. 1 is a conceptual diagram showing an embodiment of the method of the present invention,
FIG. 2 is an explanatory diagram showing the detailed structure of the control section in FIG. While passing through, it burns and becomes combustion exhaust gas, which is emitted from the dispersion tower 31 to the atmosphere 10. That is, first, the CO gas in the exhaust gas is sucked in through the opening of the splash cover 28.
The secondary air A and the secondary air B taken in from the opening 15 of the duct 8 are mixed and combusted, and the generated combustion exhaust gas is cooled in the heat recovery device 3 and the heat retained in the combustion exhaust gas is recovered. Next, the combustion exhaust gas reaches the duct 8a, receives tertiary air from the opening 16, and the temperature of the combustion exhaust gas further decreases (below 350°C), and reaches the electrostatic precipitator 5, where dust is removed and purified. The converted combustion exhaust gas is discharged into the atmosphere 10 through a suction blower 6.

In this embodiment, during such an exhaust gas combustion process, the flow rate of the combustion exhaust gas is adjusted by a control mechanism as shown in FIG. That is, signals emitted from the exhaust gas amount coefficient pattern setter 18 and the scouring agent blowing speed setter 17, which are determined according to the type of preliminary treatment, are added, subtracted, multiplied, and divided by a calculator (hereinafter simply referred to as a calculator) 20.
The data obtained by inputting the data into the above pattern setting device 1
The data obtained by inputting the signals from 8 and the oxygen injection amount setting device 19 to the computing unit 20a are respectively input to the computing unit 20b to calculate the predicted combustion exhaust gas flow rate, and input to the computing unit 20c. Meanwhile, heat recovery device 3
The O 2 concentration data detected by the O ₂ detector _{30 inserted in the duct 8a space on the outlet side of the duct 8a until the combustion exhaust gas is mixed with the tertiary air C is input to the O 2 concentration} regulator 22. After converting the signal into a numerical signal, the signal is multiplied by a predetermined ratio value (for example, 200%) set in the setting device 29 via the computing device 20d, and then inputted to the computing device 20c to obtain the predicted combustion exhaust gas flow rate data. Correct. The correction data thus obtained is input to the computing unit 20e, and corrected using the signal from the tertiary air conditioner 32. That is, the correction is performed by inputting a signal corresponding to the output of the tertiary air conditioner 32 to the tertiary air amount detection calculator 24, and providing this signal in the duct 8a space through which the combustion exhaust gas mixed with the tertiary air flows. This is performed by correcting using the detected data from the pressure detector _P2 and further inputting this corrected data to the calculator 20e. That is, the correction data is the predicted combustion exhaust gas amount data (corrected by O ₂ concentration data) sent from the calculator 20c.
will be added to. Then, input the addition/correction data to the flow rate regulator 27 via the high selector 25,
The numerical value is compared with the detection data from the flow rate detector V inserted in the inlet side duct 8b of the suction blower 6, and the opening degree setting data of the damper controller 12a is determined based on the difference. The opening degree is adjusted.

Through the above-described control, the combustion exhaust gas flow rate is controlled such that the combustible gas in the exhaust gas is completely combusted.

On the other hand, in this embodiment, a pressure detector _P1 is inserted into the inlet duct 8 of the heat recovery device 3, and the amount of secondary air is controlled based on pressure detection data. That is, the detection data from the pressure detector _P1 is input to the pressure regulator 21, where the opening setting data of the damper 13 is determined, and the data is input to the pressure regulator 21.
Control data is transmitted to.

Furthermore, if the configuration is configured so that the secondary air amount control is performed using the pressure detector _P1 , even if the processing vessel 1
Even if the space between the splash cover 28 and the dust collection hood is blocked by slag or hot metal blowing out from the
P ₁ detects the pressure drop in duct 8 and immediately
Since the amount of air is increased, exhaust gas combustion is not affected. In addition, if some abnormality occurs and the pressure detection data from the pressure detector _P1 exceeds the upper limit, the pressure regulator 21 is activated and an O ₂ concentration control release command is issued, and the switch S is O ₂ concentration control is switched from constant control to position. That is, when there is an abnormality in the pressure detected by the pressure detector _P1 , it is desired to quickly return to the normal state, but if O ₂ concentration control is continued, the recovery will be delayed. Therefore, by switching the correction control from O ₂ concentration control to constant control (this constant is set to a normal value) using a constant (for example, 50%) set in the setting device 23, it is possible to quickly Recovery can be achieved.

In addition, if an abnormality occurs in one or more of the calculation of the predicted combustion exhaust gas amount, the O ₂ concentration control, and the calculation of the tertiary air amount, and the calculated value of the calculator 20e becomes abnormally small, the high selector 25 operates to cut off the signal from the computing unit 20e and transmit the signal from the minimum gas amount setting device 26 to the flow rate regulator 27. As a result, combustion exhaust gas flow rate control is performed based on the minimum necessary flow rate prediction.

[Effects of the Invention] The present invention is configured as described above, and the flow rate of the combustion exhaust gas can be controlled with high precision, and the combustible gas in the exhaust gas can be completely combusted. In this way, valuable components in the exhaust gas can be effectively recovered.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram showing an embodiment of the present invention,
FIG. 2 is an explanatory diagram showing the detailed structure of the control section in FIG. 1, and FIG. 3 is a schematic explanatory diagram showing a conventional exhaust gas treatment method. 1... Processing container, 3... Heat recovery device, 5... Electric precipitator, 6... Suction blower, 8, 8a, 8b...
...Duct, 9...Recovery route, 11...Control unit, 1
2, 12a... damper controller, 13, 14...
Damper, 15a... Secondary air flow path, 16a...
Tertiary air flow path, 17... Scouring agent supply speed setting device,
18... Time function pattern setter for exhaust gas amount coefficient, 19... Oxygen flow rate setter, 20... Addition/subtraction multiplication/division calculator, 21... Pressure regulator, 22... O ₂ concentration regulator, 23... Setting device , 24... Tertiary air amount detection calculator, 25... High selector, 26... Minimum combustion exhaust gas amount setter, 27... Flow rate regulator, 28
... Splash cover, 29 ... Setting device, 30
……O ₂ detector, P ₁ , P ₂ ……Pressure detector, V……
Flow rate detector, A...Primary air, B...Secondary air,
C...Tertiary air.

Claims (1)

[Claims] 1 After mixing air with the exhaust gas generated from the hot metal pretreatment container and combusting it, the combustion exhaust gas is cooled by a heat recovery device, and then the dust in the combustion exhaust gas is removed by a dust collector and sent out of the system. When discharging,
The predicted combustion exhaust gas amount is calculated from the time function pattern of the exhaust gas amount coefficient determined for each type of pretreatment, the supply rate of the scouring agent, and the blown oxygen flow rate, and the predicted combustion exhaust gas amount is used as O ₂ concentration detection data at the stage after combustion. An exhaust gas treatment method comprising: correcting the flow rate of combustion exhaust gas based on the correction value obtained by controlling the flow rate of the combustion exhaust gas.