JP7707935B2 - Method for producing dried or burned material using a rotary kiln, and method for producing crude zinc oxide - Google Patents

Description

The present invention relates to a method for producing a dried or calcined material using a rotary kiln, and a method for producing crude zinc oxide using this method. More specifically, the present invention relates to a method for producing a dried or calcined material that can improve the economic efficiency of producing a dried or calcined material by optimizing the amount of fuel input to a burner in a rotary kiln equipped with a heating burner that uses heavy oil or the like as fuel and a rotary heating furnace body that is driven by electricity, and a method for producing crude zinc oxide using this method.

For example, rotary kilns, which are cylindrical furnaces with a total length of about 30 m and equipped with an electrically powered rotary heating furnace body and burners that use heavy oil or the like as fuel, are widely used as industrial heating furnaces for drying, calcining, or both (collectively referred to as "calcining processes" in this specification) of raw materials and intermediate products during the smelting process of various non-ferrous metals (see Patent Document 1).

When using the rotary kiln to perform the "calcination process" of the input materials, in order to ensure sufficient drying or calcination in the furnace, it is necessary to supply a sufficient amount of fuel to maintain the specified temperature inside the furnace. However, at the same time, there is a demand to reduce the cost of fuel such as heavy oil fed into the heating burner to a bare minimum to improve the economic efficiency of the "calcination process" using the rotary kiln. In order to meet such demands, in the past, the amount of fuel fed was adjusted by checking the "quality of the dried and calcined materials obtained" and responding to any changes in these qualities.

As a technique for adjusting the amount of fuel fed to the burner of a rotary kiln, an operating method is known in which the amount of heavy oil and air fed to the burner is controlled in order to maintain the CO concentration in the exhaust gas and the temperature inside the rotary kiln within a specified range (see Patent Document 2). However, this technique does not pay special attention to improving the efficiency of fuel use. In the process of performing calcination treatment using a rotary kiln, the above-mentioned measures (measures that respond to changes in the quality of the resulting dried and calcined products) are still insufficient to improve the economics of operation by limiting the amount of fuel fed to a minimum amount that is necessary and sufficient while maintaining the production volume of the product, and there has been a demand for further improving the efficiency of fuel use and improving the economics of operation.

JP 2017-48411 A JP 2001-280849 A

The present invention aims to make it possible to manufacture dried or sintered materials more economically than ever before by optimizing the amount of fuel fed to the burner while maintaining the production volume of dried or sintered materials in a process carried out using a rotary kiln equipped with a heating burner that uses heavy oil or the like as fuel and a rotary heating furnace body that is driven by electricity.

The inventors came up with the idea that the above problem could be solved by replacing the real-time "production volume per unit time" that should be used as an index for adjusting the amount of fuel fed to the burners of the rotary kiln with the "estimated production volume per unit time" calculated from a regression equation between the driving power of the rotary kiln and the production volume per unit time, and thus completed the present invention. Specifically, the present invention provides the following.

(1) A method for producing a dried or sintered product using a rotary kiln equipped with a burner and a rotary heating furnace body driven by electricity, comprising: an estimated production volume per unit time calculation process for calculating the estimated production volume per unit time of the rotary kiln from a regression equation between the driving power of the rotary kiln and the production volume per unit time; and a fuel input adjustment process for adjusting the amount of fuel input to the burner to approximate the product of the estimated production volume per unit time and the fuel consumption rate.

According to the manufacturing method of the dried or calcined material in (1), in the process using a rotary kiln equipped with a heating burner using heavy oil or the like as fuel and a rotary heating furnace body driven by electricity, the amount of fuel fed to the burner is optimized while maintaining the production volume of the dried or calcined material, making it possible to manufacture the dried or calcined material more economically than before.

(2) The method for producing a dried or burned material described in (1), wherein the regression equation is an equation obtained by stratifying the relationship between the driving power of the rotary kiln and the production amount per unit time according to the rotation speed of the rotary kiln.

According to the manufacturing method of the dried or calcined material in (2), the amount of fuel input to the burner in the manufacturing method in (1) can be optimized with higher precision, further improving the economic efficiency of manufacturing the dried or calcined material.

(3) A method for producing crude zinc oxide, in which a drying and heating step for obtaining crude zinc oxide cinder by calcining a crude zinc oxide cake is carried out by the method for producing a dried or calcined product described in (1) or (2).

The method for producing crude zinc oxide (3) provides the above-mentioned effects of the method for producing (1) or (2), and contributes to reducing the production costs of crude zinc oxide ore.

According to the present invention, in a process using a rotary kiln equipped with a heating burner that uses heavy oil or the like as fuel and a rotary heating furnace body that is driven by electricity, the amount of fuel fed to the burner can be optimized while maintaining the production volume of the dried or calcined material, making it possible to manufacture the dried or calcined material more economically than in the past.

1 is a schematic cross-sectional view showing the overall configuration of a rotary kiln in which the manufacturing method of the present invention can be suitably carried out. 1 is a flow chart showing an example of a process for producing zinc oxide ore that can be carried out using the production method of the present invention. FIG. 1 is a graph showing the correlation between the driving power of a rotary kiln and the production amount per unit time. FIG. 1 is a graph showing the correlation between the driving power of a rotary kiln and the production amount per unit time, stratified by the rotation speed of the rotary kiln. FIG. 1 is an X-Rs control chart of heavy oil consumption unit in an embodiment. FIG. 1 is an X-Rs control chart of heavy oil consumption unit of a comparative example.

A preferred embodiment of the method for producing a dried or baked product of the present invention will be described below. However, the present invention is not limited to the following embodiment.

<Method for producing fired product>
The manufacturing method of the present invention, i.e., "a manufacturing method for a dried or calcined product using a rotary kiln equipped with a burner and an electrically powered rotary heating furnace body (also referred to as a "manufacturing method for a calcined product" in this specification)" is, as an example, a manufacturing method that can be preferably used as a method for carrying out a drying and heating step (FIG. 2: S30) in which intermediate products such as crude zinc oxide and secondary raw materials are calcined using a rotary kiln in a manufacturing process for crude zinc oxide ore (also referred to as "crude zinc oxide ore" in this specification) performed in the flow shown in FIG. 2.

Here, in order to improve the economic efficiency of operations by limiting the amount of fuel input to the minimum necessary and sufficient in the dry heating process, i.e., the process of "calcination treatment" using a rotary kiln, the ideal adjustment in terms of economy is to match the amount of fuel input to the rotary kiln to the theoretically necessary and optimal fuel input, which is the product of the "fuel unit consumption," which is the amount of fuel input required per unit production volume and can be estimated in advance for each plant where operations are carried out, and the real-time "production volume per unit time" of the rotary kiln in that plant.

However, in a rotary kiln, where the materials fed into the kiln progress through a cylindrical furnace with a total length of around 30m over a period of around one to three hours, it is practically impossible to directly measure and grasp the "production volume per unit time" in real time, which is one of the quantities mentioned above that can serve as indicators for adjusting the amount of fuel fed into the kiln.

Therefore, in the "manufacturing method for fired products" of the present invention, instead of calculating the real-time "production volume per unit time" which is extremely difficult to grasp as described above, two new processes, namely, a "calculation process of estimated production volume per unit time" that calculates the "estimated production volume per unit time" of the rotary kiln from the "regression equation between the driving power of the rotary kiln and the production volume per unit time" and a "fuel input adjustment process" that sets the product of the "estimated production volume per unit time" and the "fuel consumption rate" as a management target value and adjusts the actual fuel input amount to approach this management target value, are performed as essential processes.

[Rotary kiln]
Fig. 1 is a schematic cross-sectional view showing the overall configuration of a rotary kiln that can produce dried or fired products using the "production method for fired products" of the present invention. The "production method for fired products" of the present invention is a technology that can be widely applied to various processes carried out using a rotary kiln 1, such as the rotary kiln 1 shown in the figure, that is equipped with a burner 30 that burns fuel such as heavy oil to heat the inside of the furnace and a rotary heating furnace body 10 that is driven by electricity.

As shown in FIG. 1, the rotary kiln 1 is a rotary furnace that includes a rotary furnace body 10, which is a hollow cylindrical furnace, a kiln body support (not shown) that supports the rotary furnace body 10 so that it can rotate (for example, in the direction R in the figure), a fixed hood 20 that covers one end of the rotary furnace body 10, a burner 30 that burns fuel such as heavy oil supplied from a fuel supply pipe 31 and emits a flame 32 to heat the inside of the rotary furnace body 10, and a drive gear 40 that drives and rotates the rotary furnace body 10 using electricity.

In the rotary kiln 1, the rotary heating furnace body 10 is, for example, a cylindrical furnace with a total length of several meters to 100 meters, and is installed so that when in use, it has a 3 to 4% inclination with respect to the horizontal in the direction in which the treated material moves from the loading opening 11 to the discharge opening 12. The rotary kiln 1 may also be provided with a dam 13 on the inner periphery near the discharge opening 12, the dam 13 having a height of 2% or more of the inner diameter of the rotary kiln. The dam 13 is provided primarily for the purpose of extending the residence time of the treated material.

In the rotary kiln 1 configured as above, as shown in FIG. 1, the inside of the rotary heating furnace body 10 is heated to a high temperature by the burner 30, and the rotary heating furnace body 10 is rotated in the R direction by the drive gear 40 while the material to be treated is carried in the direction a from the loading port 11. The material to be treated moves toward the discharge port 12 while being stirred along the inclination inside the rotary heating furnace body 10, which is heated to a high temperature, and the high-temperature fired material is discharged from the discharge port 12 in the direction b.

The "method of producing a fired product" of the present invention has a particularly significant effect in improving economy when used in large rotary kilns, particularly those with a total length of the rotary heating furnace body of 20 m or more, preferably 30 m or more, among the above-mentioned rotary kilns.

[Estimated production volume per unit time calculation process]
Hereinafter, the "estimated production amount per unit time calculation step", which is the first essential step in the "production method for a fired product" of the present invention, will be described in detail.

In this specification, the "estimated production volume per unit time" is an estimated production volume per unit time in a rotary kiln, used as an alternative indicator of the "production volume per unit time" in the rotary kiln. In the "production method for fired products" of the present invention, in the estimated production volume per unit time calculation process, the real-time "estimated production volume per unit time" is calculated from a regression equation between the driving power of the rotary kiln and the production volume per unit time. Since the driving power of the rotary kiln can be continuously measured in real time, the "estimated production volume per unit time", which changes from moment to moment, can be constantly grasped in real time while the rotary kiln is operating.

(Regression equation between rotary kiln driving power and production volume per unit time)
The regression equation between the driving power of the rotary kiln and the production volume per unit time (also referred to simply as the "regression equation" in this specification) can be obtained from a scatter diagram of the driving power for rotating the rotary heating furnace body 10 of the rotary kiln 1 and the production volume per unit time. FIG. 3 is an example of such a scatter diagram. The production volume shown in the figure is a value indexed with a reference value of 100, and the driving power is a value indexed with a reference value of 10. The values of the production volume and the driving power are all similar in FIG. 4. Note that, as a sample of the combination of power and production volume required to create such a scatter diagram, the power value at a given time and the production volume value at that given time collected in the control room of the rotary kiln can be used.

In addition, regarding the correlation between the driving power for rotating the rotary heating furnace body 10 of the rotary kiln 1 and the production volume per unit time, it is generally known that in a rotary kiln that dries and fires dehydrated cakes of metal oxides, when the daily production capacity per unit volume within the rotary heating furnace body of the rotary kiln is 0.5 to 1.3 tons, there is a strong correlation between the driving power of the rotary kiln and the production volume per unit time. Therefore, under such operating conditions, the "estimated production volume per unit time" can be calculated with particularly high accuracy from the above-mentioned "regression equation."

More preferably, the above-mentioned "regression equation" is an equation obtained by stratifying the relationship between the driving power of the rotary kiln and the production volume per unit time according to the rotation speed of the rotary kiln. By creating a scatter diagram (see Figure 4) stratified by the rotation speed of the rotary kiln, which affects the driving power, and using the "regression equation" obtained from the stratified scatter diagram, the "estimated production volume per unit time" can be calculated with higher accuracy.

In addition, in the scatter diagram of Figure 4, when the rotary kiln's rotation speed is in the range of 0.4 rpm or more and less than 0.6 rpm (the normal rotation speed range of the rotary kiln), there is a strong correlation between the driving power of the rotary kiln and the production volume per unit time. Therefore, when the rotary kiln is operated at a rotation speed within this range, the "estimated production volume per unit time" can be calculated with high accuracy from the "regression equation."

On the other hand, when the rotation speed of the rotary kiln is in the range of 0.6 rpm or more, which is outside the range of normal rotation speeds, the variation becomes large and the correlation between the drive power and the production volume per unit time becomes weak. This is thought to be because when the rotation speed is above a certain level, the state inside the furnace is such that factors other than the rotation speed, such as scumming of the molten material, have a relatively large effect on the drive power. For this reason, when it is expected that the correlation will be weakened, such as when the rotation speed of the rotary kiln is 0.6 rpm or more, it is preferable to use the present invention in combination with the conventional method, i.e., the adjustment method of determining the amount of fuel used in proportion to the amount of raw material charged or while checking the quality of the resulting dried or fired product, or to temporarily switch to the conventional method as necessary.

[Fuel input amount adjustment process]
Next, the details of the "fuel input amount adjustment step", which is the second essential step in the "production method of the burned product" of the present invention, will be described. In this step, the product of the "estimated production amount per unit time" and the "fuel consumption rate" (estimated production amount per unit time x fuel consumption rate) calculated in the above-mentioned "estimated production amount per unit time calculation step" is set as a management target value, and the amount of fuel input to the burner 30 is adjusted to approach this value, or preferably to match this value.

Here, "fuel unit consumption" is a value that is determined in advance based on the basic performance and operating conditions of the rotary kiln actually used. For example, when the fuel is heavy oil, it is calculated based on the operating performance of the rotary kiln, using the formula (heavy oil unit consumption = heavy oil consumption / production amount), that is, the amount of heavy oil actually required per unit production amount.

As mentioned above, in the "estimated production volume per unit time calculation process," the "estimated production volume per unit time," which fluctuates from moment to moment while the rotary kiln is in operation, can be constantly grasped in real time. Therefore, the optimal management target value for the real-time fuel input amount can be set from the grasped "estimated production volume per unit time" and the given basic data, "fuel consumption rate."

<Method of manufacturing crude zinc oxide cinder>
The "method for producing a dried or calcined product" of the present invention described in detail above can be preferably used as a method for carrying out the drying and heating step S30 in the "method for producing crude zinc oxide cinder" carried out in a crude zinc oxide cinder production plant using the Weltz process, in which a dehydrated cake of crude zinc oxide (also referred to as "crude zinc oxide cake" in this specification) and secondary raw materials are dried and heated to obtain crude zinc oxide cinder.

As shown in Figure 2, the above-mentioned "method for producing crude zinc oxide cinder" sequentially includes a reduction roasting process S10 in which primary raw materials such as steel dust are reduced and roasted to obtain crude zinc oxide, a wet process S20 in which chlorine, fluorine, etc. are separated and removed from the crude zinc oxide dust obtained in the reduction roasting process S10 to obtain a crude zinc oxide cake, and a dry heating process S30. In the above overall process, primary raw materials containing zinc, such as steel dust, are charged into the reduction roasting process S10, which is an upstream process. Separately, secondary raw materials containing zinc may be directly charged into the dry heating process S30, which is a downstream process.

[Reduction roasting process]
The reduction roasting step S10 is a step of obtaining crude zinc oxide dust by reduction roasting primary raw materials containing zinc. The reduction roasting process is performed by a reduction roasting rotary kiln (RRK). The steel dust is reduction roasted in the RRK body, and the metallic zinc reduced and volatilized is reoxidized in the exhaust gas to become powdered zinc oxide.

[Wet process]
The wet process S20 is a process for removing water-soluble impurities from the crude zinc oxide dust containing zinc oxide recovered in the reduction roasting process S10 by wet treatment to obtain a crude zinc oxide cake. In the wet process S20, the slurry from which the impurities have been sufficiently removed is dehydrated by a vacuum suction type dehydrator or the like to obtain a crude zinc oxide cake containing zinc oxide.

[Drying and heating process]
The dry heating step S30 is a step that can enjoy the effect of improving economic efficiency by performing the "manufacturing method for dried or calcined material" of the present invention. This step is a step in which the crude zinc oxide cake obtained in the wet step S20 is calcined to obtain crude zinc oxide cinder. The calcination treatment is performed by a dry heating rotary kiln (DRK) as shown in FIG. 1. In the dry heating step S30, the crude zinc oxide cake is charged into the DRK and calcined to further reduce the concentrations of chlorine, fluorine, etc., to obtain crude zinc oxide cinder. It is preferable to maintain the heating temperature in the dry heating step S30 so that the temperature of the calcined ore when discharged from the DRK is 800°C or higher and 1150°C or lower.

Conventionally, the amount of fuel (heavy oil) fed to the rotary kiln in this drying and heating process was generally adjusted in accordance with the amount of raw materials fed to the process, as described above. However, as shown in FIG. 2, in addition to the crude zinc oxide cake obtained in the upstream wet process, secondary raw materials of various properties are also fed to the drying and heating process S30. The total amount and composition ratio of these feed materials fluctuate in complex ways due to various factors, so it was difficult to supply the optimal amount of heavy oil based on these values. In contrast, according to the "manufacturing method for dried or fired materials" of the present invention, the amount of heavy oil fed can be adjusted to the optimal amount with high precision.

In the production of crude zinc oxide according to the flow shown in Figure 2, a test operation was carried out as follows to verify the effect of improving the economy by carrying out the drying and heating step according to the "production method for a dried or burned product" of the present invention. The rotary kiln used for the drying and heating step was a rotary kiln for drying and heating, which was equipped with a burner and a rotary heating furnace body driven by electricity, with the total length of the rotary heating furnace body being 31 m and the furnace volume being 191 ^m3 .

[Example]
In the above-mentioned production of crude zinc oxide, the drying and heating step was changed to be performed according to the "production method of dried or calcined material" of the present invention, and the test operation was continued for about one month. Specifically, for the regression equation between the driving power of the rotary kiln and the production amount per unit time, a regression equation stratified according to the rotation speed of the rotary kiln, i.e., for every 0.1 rpm of the rotation speed, was used. The driving power of the rotary kiln measured in real time was applied to this regression equation to calculate the estimated production amount per unit time, and the operation was continued in a mode in which the amount of heavy oil input was adjusted with the heavy oil amount calculated from this value and the heavy oil consumption unit as the target control value. The X-Rs control chart of the heavy oil consumption unit for the test operation period of about one month (N=26) is shown in FIG. 5. It can be confirmed from FIG. 5 that both the X control chart and the Rs control chart are within the control limits during the period of about one month. The heavy oil consumption unit shown in FIG. 3 shows a value indexed with a reference value of 50. The same applies to the values of the heavy oil consumption unit in the following figures.

[Comparative Example]
In the production of crude zinc oxide under the same conditions as in the Examples, the amount of heavy oil fed to the rotary kiln in the drying and heating step was adjusted for one year by a conventional method in which the amount of heavy oil fed to the rotary kiln was adjusted in proportion to the amount of oil fed, not by the method of the present invention. FIG. 6 shows an X-Rs control chart of the heavy oil consumption rate.

Comparing the heavy oil consumption rate between the working example and the comparative example, the variation in heavy oil consumption rate was smaller, and by implementing the present invention, a reduction in heavy oil consumption rate of -6.9% was achieved. From the above results, it can be seen that the "manufacturing method for dried or calcined materials" of the present invention is a manufacturing method that can economically manufacture dried or calcined materials while optimizing the amount of fuel input to the burner in a rotary kiln equipped with a heating burner that uses heavy oil or the like as fuel and a rotary heating furnace body that is driven by electricity.

Reference Signs List 1 Rotary kiln 10 Rotary heating furnace body 11 Charging inlet 12 Discharge outlet 13 Dam 20 Fixed hood 30 Burner 31 Fuel supply pipe 32 Flame 40 Drive gear S10 Reduction roasting process S20 Wet process S30 Dry heating process

Claims (3)

A method for producing a dried or fired product using a rotary kiln equipped with a burner and a rotary heating furnace body driven by electricity,
An estimated production amount per unit time calculation step of calculating an estimated production amount per unit time of the rotary kiln from a regression equation between the driving power of the rotary kiln and the production amount per unit time;
a fuel input amount adjusting step of adjusting the amount of fuel input to the burner so as to approach the product of the estimated production amount per unit time and the fuel consumption rate;
Equipped with
A method for producing a dried or fired product. The regression equation is an equation obtained by stratifying the relationship between the driving power of the rotary kiln and the production amount per unit time according to the rotation speed of the rotary kiln.
A method for producing the dried or fired product according to claim 1. The drying and heating step of calcining the crude zinc oxide cake to obtain crude zinc oxide cinder is carried out by the method for producing a dried or calcined product according to claim 1 or 2.
Method for producing crude zinc oxide.