JP4371098B2 - Waste acid treatment method - Google Patents

Description

  The present invention relates to a method for treating a waste acid solution or the like in a spray-type roasting furnace.

  One of the facilities in steel works is a pickling facility that performs pickling using hydrochloric acid or the like in order to remove oxide scale on the steel surface when steel is produced. Since scales dropped from the steel surface are accumulated in the pickling solution, the pickling solution that reaches a predetermined property is treated as a waste acid in a roasting reaction furnace (hereinafter referred to as “roasting furnace”). Is done.

  A waste acid solution generated at the time of pickling of a steel sheet is treated by spraying it in a roasting furnace. There are two types of spray-type roasting furnaces, one is called the dravo type, and the other is the type called the Rusner type.

  The former method is a method in which the waste acid solution is sprayed directly into the furnace to perform the roasting reaction, and because the furnace volume needs to be large, the equipment is large in size, but the roasting reaction time can be taken long, The chlorine ion concentration of iron oxide can be lowered. For this reason, it is utilized as a hard ferrite raw material.

  In the latter method, the waste acid solution is pretreated and sprayed to the reactor after increasing the hydrochloric acid concentration. The furnace volume is relatively small, but the roasting reaction time is short. The ion concentration is high and the acid resistance of the equipment is necessary. The generated iron oxide is used as a soft ferrite raw material for magnetic tapes and magnetic cards. Moreover, it is said that the lower the chlorine ion concentration in the iron oxide obtained as a product, the more preferable in any of the Dravo type and the Rusner type.

In the roasting furnace, the fine droplets sprayed from the upper spray device concentrate hydrochloric acid and iron chloride due to the evaporation of moisture due to contact with the high-temperature combustion gas to form droplets. Subsequently, the viscosity and surface tension of the waste acid solution increase, and the droplets become more spherical. Concentration of iron chloride due to evaporation of water and hydrogen chloride and formation of a crystal grain film occur. The evaporation of moisture and hydrogen chloride gradually shows a pattern of reduced rate drying as the crystal grain film formed on the surface becomes thicker. Then, the surface temperature rises rapidly, the ferrous chloride melts, and the decomposition reaction proceeds according to the following reaction formula. The iron chloride in the shell becomes a crystal grain film, and there is a space of H ₂ O and HCl gas in the shell. Arise. Furthermore, H ₂ O and HCl gas in the shell are ejected through the outer shell from the temperature rise. After the gas in the shell is ejected, the reaction of FeCl ₂ inside is performed, and the reaction is completed and separated into Fe ₂ O ₃ and HCl gas.
2FeCl ₂ + 2H ₂ O + 1 / 2O ₂ = Fe ₂ O ₃ + 4HCl

In order to operate this roasting furnace efficiently, temperature control in the furnace is an important point.
For example, in Patent Document 1, the iron concentration in an iron chloride aqueous solution as a raw material and the compressed density, average particle size, and chlorine concentration of iron oxide as a product are detected at predetermined intervals, and these detected values are input as input variables. The optimum body temperature and bottom temperature of the furnace are calculated based on the fuzzy theory, and the combustion gas flow rate is cascade controlled so that the body temperature in the roasting furnace matches the calculation result. Using the detected body temperature and bottom temperature in the roasting furnace as input variables, the number of rotations of the valve is calculated based on fuzzy theory, and the number of rotations of the valve is controlled so that the bottom temperature matches the calculation result. Technology is disclosed.
Japanese Patent Laid-Open No. 06-056430

  In the technique of Patent Document 1 described above, the optimum body temperature and bottom temperature are calculated by fuzzy theory, and the combustion gas flow rate is cascade controlled so as to be the target temperature. The target temperature is calculated based on the theory. An error may occur. For this reason, it was impossible to always perform optimum temperature control. For this reason, the chlorine ion concentration in the iron oxide produced in the roasting furnace is not stable, and maintenance work for the roasting furnace is required about once a week. Since this maintenance work requires about 48 hours, loss due to equipment stoppage, labor and cost required for maintenance work cannot be ignored.

  Accordingly, the present invention stabilizes the roasting reaction in the furnace so that the roasting reaction temperature falls within a predetermined temperature range, and performs optimal roasting reaction temperature control, thereby extending the maintenance cycle and the roasting furnace. It is an object of the present invention to provide a waste acid solution treatment method capable of suppressing the chlorine ion concentration in iron oxide produced by the above method.

In order to solve the above problems, the present inventors have conducted various experiments paying attention to the temperature in the roasting furnace, and have obtained the following knowledge.
(1) In the roasting furnace, pay attention to the temperature immediately before the roasting reaction occurs (temperature range from the temperature immediately below the roasting reaction temperature to a temperature lower by 150 ° C, 550 to 695 ° C when the acid solution is hydrochloric acid). When a stable roasting reaction is in progress in the furnace, the furnace area that is the "temperature immediately before the roasting reaction occurs" is specified, and the temperature in this area is controlled within a predetermined temperature range. This will stabilize the furnace temperature distribution.
(2) If the furnace temperature is controlled by changing the fuel flow rate, not the waste acid solution flow rate, the furnace temperature distribution is stabilized.

  The present invention has been completed based on such findings. Thus, according to the first aspect of the present invention, the temperature range of (T-150) ° C. to (T-5) ° C. is specified in the furnace when the roasting reaction temperature is T ° C. in a normal furnace state. In this waste acid solution treatment method, the temperature of the roasting reaction in the furnace is controlled such that the temperature at the position of at least one point in this region is in the range of (T-150) ° C. to (T-30) ° C. .

  Here, the “normal furnace state” refers to a state in which the furnace pressure changes in a range of −980 to −1960 Pa (negative pressure). The “roasting reaction temperature T” means a temperature of usually 700 ° C. when the acid solution is hydrochloric acid. Therefore, the temperature at the position to be specified in the furnace is 550 to 695 ° C.

  In the waste acid solution treatment method, it is preferable to control the temperature of the roasting reaction in the furnace by the flow rate of the fuel.

  According to the present invention, it is possible to stably control the temperature of the spray-type roasting furnace, and automatic operation that has been impossible in the past is also possible. Furthermore, the maintenance cycle which has been conventionally performed at intervals of about one week can be extended to about one month. That is, long-term stable operation exceeding one month is possible by continuous operation, and unmanned operation can also be realized, which has an excellent effect in labor saving. Moreover, the chlorine ion concentration in the iron oxide produced | generated can be restrained low.

(Example)
FIG. 1 is a schematic view schematically showing an example of roasting equipment used in the waste acid solution treatment method of the present invention. In the illustrated roasting facility 100, the waste acid solution 2 discharged from the pickling facility (not shown) in the ironworks is supplied from the furnace top 10 of the roasting furnace 1. In the furnace top portion 10, a waste acid solution 2 is guided by a pipe 11 from a buffer tank (not shown) that temporarily stores the waste acid solution 2, and a spray nozzle 3 is disposed at the tip of the pipe 11. ing. Usually, a plurality of spray nozzles 3 are provided at the top 10 of the roasting furnace 1.

In this example, the type of the acid solution used for pickling was hydrochloric acid, and typical properties of the waste acid solution were as follows.
HCl: 2.0 to 6.0% by mass
FeCl: 23.0-33.0 mass%
Specific gravity: 1.28 to 1.33
In addition, a small amount of scales such as F, As, P, S, Si, C, SS, etc. are included.

  From the hot stove inlet 12 of the roasting furnace 1, a mixture of C gas (generated from a coke plant or the like) 5 that is a heat source for promoting the roasting reaction in the roasting furnace 1 and the combustion air 15. I am guided. The hydrogen chloride gas 6 which is a product of the roasting reaction generated in the furnace is discharged from the furnace top 10, and the iron oxide 4 is settled and accumulated in the furnace bottom 13 and taken out from the furnace as appropriate.

  A furnace top gas outlet thermometer TI-0 is installed at the gas outlet 14 containing HCl at the furnace top 10. Moreover, five thermometers TI-1, TI-2, TI-3, TI-4, and TI-5 are provided in the furnace side part in order from the top in the furnace height direction. It is placed in the furnace. Of these thermometers, only TI-3 is actually required during steady operation, and the other thermometers are used to know the temperature conditions in the furnace. In the roasting furnace 1, when the temperature in the furnace in a steady state was investigated using each thermometer, the TI-3 thermometer showed a temperature range of 550 to 670 ° C. In the present invention, the temperature of at least one point in the temperature range is controlled to a temperature range of 550 to 670 ° C. Temperature information obtained by the in-furnace thermometer TI-3 is transmitted to a later-described in-furnace temperature indicating controller TIC-1.

  In addition, the magnitude | size of the roasting furnace used for the present Example, and the arrangement position of each thermometer are shown in FIG.

熱風炉床を基準値（０）とした場合の寸法。炉の内径は７３６０ｍｍである。

Dimension when the hot-blast hearth is the reference value (0). The inner diameter of the furnace is 7360 mm.

  A furnace pressure gauge PI-1 for detecting the pressure in the roasting furnace is provided in the vicinity of the center of the furnace height on the side of the furnace.

  The pipe 11 for introducing the waste acid solution 2 into the roasting furnace 1 is provided with a waste acid solution flow indicator FI-1, and based on the information from now on, the waste acid solution flow indicator controller FIC-1 The flow rate of the waste acid solution 2 into the roasting furnace 1 is controlled by adjusting the opening degree of the waste acid solution flow valve FV-1.

  The temperature information obtained by the roasting furnace thermometer TI-3 is sent to the furnace temperature indicating controller TIC-1. The in-furnace temperature indicating controller TIC-1 transmits the optimum flow rate information of the C gas 5 at that time to the C gas flow rate indicating controller FIC-2 based on this temperature information. The C gas flow rate indicating controller FIC-2 adjusts the opening of the C gas flow rate valve FV-2 based on information from the C gas flow rate indicator FI-2 and the furnace temperature indicating controller TIC-1, The flow rate of the gas 5 is determined.

  On the other hand, the combustion air flow rate indicating controller FIC-3 disposed in the supply line of the combustion air 15 receives the information from the C gas flow rate indicator FI-2, and also receives the information from the combustion air flow rate indicator FI-3. In consideration, the optimum air amount is calculated to determine the opening degree of the combustion air flow valve FV-3. Thus, the mixture of the optimum amount of C gas 5 and combustion air 15 such that the temperature at the position of the in-furnace thermometer TI-3 is 550 to 670 ° C. is supplied from the hot stove inlet 12 to the roasting furnace 1. Supplied in.

  Moreover, the pressure information in the roasting furnace 1 obtained by the furnace pressure gauge PI-1 is transmitted to the furnace pressure indicating controller PIC-1. The in-furnace pressure indicating controller PIC-1 controls the opening degree of the in-furnace pressure adjustment valve HV-1 based on this information, and discharges an appropriate amount of outlet gas from the inside of the furnace to the outside. Thus, the furnace pressure is adjusted to a predetermined range.

In the waste acid solution treatment method of the present invention, in order to find a control temperature point at which the furnace temperature can be stably controlled, each thermometer TI-0 to TI-5 provided in the height direction of the roasting furnace 1 is used. A test operation was performed while measuring the temperature over time. As a result, it was confirmed that operation by temperature control in the in-furnace thermometer TI-3, which is slightly above the center in the height direction of the roasting furnace 1, has the most stable iron oxide chloride ion concentration and stable furnace temperature distribution. did. When this reason was considered, it turned out that the temperature range of the thermometer TI-3 in a furnace is 550-670 degreeC, and this temperature is a temperature just before a roasting reaction occurs. The most important point of the present invention is to specify a region showing the temperature immediately before the so-called HCl or H ₂ O evaporates and the roasting reaction occurs, and to control the temperature in this region. That is, control by the thermometer (TI-4, TI-5) in the region indicating the temperature at which the roasting reaction occurs, or the thermometer (TI-0 to TI-0 in the region indicating the temperature before the roasting reaction occurs) It was found that the temperature in the furnace becomes unstable in the control by TI-2). In addition, in one embodiment of the present invention shown in FIG. 1, the in-furnace thermometer TI-3 is represented in the vicinity of the central portion of the total height of the roasting furnace 1, but the present invention is not limited to this, The part whose temperature is to be controlled is the part in the furnace that indicates the temperature immediately before the roasting reaction occurs.

  In addition, although it is preferable to control the temperature in a furnace to the temperature range of 550-670 degreeC, More preferably, it is 570-630 degreeC, Most preferably, it is the range of 600-620 degreeC.

  Furthermore, in order to stabilize the roasting reaction, it is necessary to use the fuel flow rate that is not affected by the waste acid solution concentration or the waste acid solution flow rate as a medium to stabilize the roasting reaction and stabilize the chloride ion concentration of iron oxide. It is preferable for conversion. Here, the “fuel” is not particularly limited, such as a gas such as C gas or a fluid such as heavy oil, and may be any fuel.

  The ratio of the combustion air may be either constant or changed, but this ratio may be changed when it is desired to control the particle size of the ferric oxide that is the product.

(Comparative example)
FIG. 2 is a schematic view schematically showing a conventional waste acid solution treatment facility 200. In addition, when the same member as the member demonstrated in FIG. 1 is used, the same referential mark as the case in FIG. 1 may be attached | subjected and the description may be abbreviate | omitted.

  In the roasting facility 200 of the comparative example, the waste acid solution 2 is sent to the spray nozzle 3 by controlling the opening degree of the flow valve FV-1 according to an instruction from the flow indicator FI-1.

  Further, fuel (C gas 5) and combustion air 15 are sent from the lower portion of the roasting furnace 1 and burned. The in-furnace pressure gauge PI-1 only measures the in-furnace pressure independently, and the measurement result is not used for the in-furnace pressure management. The inside of the furnace is instructed by the pressure indicator HM-1 so as to be about −980 to −1960 Pa, and the opening degree of the in-furnace pressure adjustment valve HV-1 is controlled.

  In the conventional roasting equipment 200, the temperature control in the furnace is performed based on the actual value of the thermometer of the furnace top gas outlet thermometer TI-0. That is, the outlet gas temperature obtained by the furnace top gas outlet thermometer TI-0 is monitored, and the waste acid liquid flow indicator FI-1 and the waste acid liquid flow valve FV-1 are manually opened and closed. We have controlled the firing reaction. However, since the fluctuation of the chlorine ion concentration of iron oxide, which is a product due to the roasting reaction, is large and the temperature distribution in the furnace is not stable, continuous stable operation cannot be performed. Furthermore, in the conventional outlet gas temperature control, the flow rate of waste acid solution was used as the control medium. However, because the concentration of waste acid solution discharged from the factory was unstable, the reaction heat fluctuated due to the roasting reaction inside the reactor. Was big.

  The reactor pressure in the reactor is always adjusted to a target value that is -980 to -1960 Pa, but the pressure is changed in concentration of the waste acid solution, the flow rate of the spray, and the C gas of the fuel. Since it changes due to pressure fluctuations and misalignment can lead to misfires and explosions, extreme caution is required.

(Evaluation methods)
In the example of the present invention, the waste acid solution was treated by the waste acid solution treatment facility shown in FIG. In the comparative example, the waste acid solution was treated by the waste acid solution treatment facility shown in FIG.

  The waste acid solution discharged from the pickling factory in the ironworks was sent into the roasting furnace of the waste acid solution treatment facility of the present invention example and the comparative example, respectively, to treat the waste acid solution.

FIG. 3 shows the measured values of the temperature of each part in the height direction of the inner wall of the roasting furnace and the transition of the C gas flow rate over time according to the present invention. In FIG. 3, the left scale represents temperature (° C.) and C gas flow rate (Nm ³ / H). In addition, in FIG. 3, although the temperature transition of TI-2 is not represented, this is because TI-2 is not always measured. The temperature of TI-2 is usually about 480 to 530 ° C, and is in a temperature range of less than (T-150) ° C.
FIG. 4 shows measured values of changes in the furnace pressure, waste acid spray amount, waste acid spray pressure, and combustion air pressure, respectively. In FIG. 4, the left scale represents combustion air pressure (kPa), furnace pressure (kPa), waste acid spray pressure (MPa), and waste acid spray flow rate (m ³ / H).

Moreover, the measured value of the transition of the temperature of each part of the roasting furnace inner wall portion in the height direction and the C gas flow rate over time in the comparative example is shown in FIG. In FIG. 5, the left scale represents temperature (° C.) and C gas flow rate (Nm ³ / H). FIG. 6 shows measured values of changes in the furnace pressure, the waste acid solution spray amount, the waste acid solution spray pressure, and the combustion air pressure, each representing the inside of the furnace. In FIG. 6, the left scale represents combustion air pressure (kPa), furnace pressure (kPa), waste acid spray pressure (MPa), and waste acid spray flow rate (m ³ / H).

  Of these results, the main parts are summarized in Table 2. The variation is indicated by (maximum value-minimum value).

  Thus, according to the waste acid solution processing method of the present invention example, there was little variation in the furnace state and products, and the chlorine concentration of ferric oxide was reduced. Further, since the operation state in the furnace is extremely stable, the pressure control valve HV-1 in the furnace is automatically set from the pressure indicating controller PIC-1 based on the value of the pressure gauge PI-1 in FIG. It became possible to control. On the other hand, in the comparative example, since the fluctuation of the furnace pressure was large, automation was impossible.

  While the present invention has been described in connection with embodiments that are presently the most practical and preferred, the present invention is not limited to the embodiments disclosed herein. However, it can be appropriately changed without departing from the spirit or idea of the invention that can be read from the claims and the entire specification, and a waste acid solution treatment method involving such a change is also included in the technical scope of the present invention. Must be understood.

It is the schematic which shows one Embodiment of the waste acid liquid processing equipment used for the waste acid liquid processing method concerning this invention. It is the schematic which shows one Embodiment of the waste acid liquid processing equipment used for the waste acid liquid processing method concerning a prior art. It is a figure which shows transition by the time passage of the temperature of each site | part of a roasting furnace inner wall part height direction by the example of this invention, and C gas flow rate. It is a figure which shows transition of the furnace internal pressure, waste acid liquid spray flow volume, waste acid liquid spray pressure, and combustion air pressure showing the condition in a furnace by the example of this invention. It is a figure which shows the transition by the time passage of the temperature of each part of a roasting furnace exit in a comparative example, a roastering furnace inner wall part height direction, and C gas flow rate. It is a figure which shows transition of the furnace pressure in a comparative example, waste acid liquid spray flow volume, waste acid liquid spray pressure, and combustion air pressure, respectively. It is a figure which shows the magnitude | size of the roasting furnace used for the present Example, and the arrangement position of each thermometer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Roasting furnace 2 Waste acid liquid 3 Spray nozzle 4 Iron oxide 5 C gas 6 HCl gas 10 Furnace top part 11 Piping 12 Hot-blast furnace inlet 13 Furnace bottom part 14 Furnace top gas outlet 15 Combustion air 100, 200 Waste acid solution processing equipment FI-1 Waste acid liquid flow indicator FI-2 C gas flow indicator FI-3 Combustion air flow indicator FV-1 Waste acid liquid flow valve FV-2 C gas flow valve FV-3 Combustion air flow valve HV-1 Furnace pressure regulating valve HM-1 Furnace pressure indicator FIC-1 Waste acid liquid flow rate indicating controller FIC-2 C Gas flow rate indicating controller FIC-3 Combustion air flow rate indicating controller PIC-1 Furnace pressure indicating controller TIC-1 Furnace temperature indicating controller PI-1 Furnace pressure gauge TI-0 Furnace top gas outlet thermometer TI-1, TI-2, TI-3, TI-4, TI-5 Roasting furnace thermometer

Claims (2)

In the state where the pressure in the furnace has changed in the range of −980 to −1960 Pa , a temperature range of 550 ° C. to 695 ° C. is specified in the furnace, and the temperature at the position of at least one point in this range is 550 ° C. A hydrochloric acid waste liquid treatment method for controlling the temperature of a roasting reaction in a furnace so as to be in a range of ˜670 ° C. 2. The hydrochloric acid waste liquid treatment method according to claim 1, wherein the temperature of the roasting reaction in the furnace is controlled by the flow rate of the fuel.

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