JPS581355B2 - Shaft kiln furnace condition control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of controlling the furnace condition of a shaft kiln by setting and managing an appropriate amount of ore feed during operation of the shaft kiln.

In recent years, due to the poor mineralization of raw materials for steel manufacturing, preliminary treatment of raw materials has become popular, and one method for this is pelletizing.

This pelletized raw material is fired at high temperature to improve its properties and then put into use, and a rotary kiln or a shaft kiln is used as the firing furnace.

One type of shaft kiln is shown in FIG.

In this kiln, pellets are charged into an annular space 3 surrounded by double cylindrical furnace walls of an inner cylinder 1 and an outer cylinder 2, and the pellets charged by a feeder 4 are charged into the space. (inside the furnace) and is supported from below by a circular hearth 5.

The hearth 5 is provided with a discharge port 6, but since its diameter is smaller than the diameter of the cylinder, the pellets form an angle of repose slope from the edge of the discharge port to the lower end of the inner cylinder wall (inner wall). Forms an inverted conical pellet firing surface.

The discharge port 6 is eccentric to the axis of the inner and outer cylinders, and as the hearth 5 rotates at low speed, the pellets are discharged from the bottom, and the fired pellets are removed from the furnace by the amount discharged (until the angle of repose is reached). flows out, and in this way the pellets are sequentially and continuously discharged.

Combustion gas for pellet firing is produced by a burner (not shown) installed below the hearth, rises against the falling of the fired pellets, enters the furnace, and burns the pellets. After rising inside the furnace, it is guided out of the furnace through an exhaust hood (not shown).

The pellets of the shaft kiln with the above-mentioned mechanism are subject to compressive loads and are susceptible to pulverization and shelf-hanging phenomena;
Also, there are drawbacks such as uneven firing of pellets due to uneven gas flow, so it is necessary to control the furnace conditions to avoid these problems.

In order to obtain high-quality pellets, it is necessary to bring the pellets into contact with combustion gas at a sufficiently high temperature during calcination, but if the calcination is overheated, the pellets will turn into sludge (sintering phenomenon).
Forms a bridge within the furnace, making further operations impossible.

In addition, if the amount of heat received is small, the pellets will fall to the bottom of the kiln in a weak state, and will not be able to withstand the compressive load at the bottom, causing cracks, which will obstruct the flow of gas and deteriorate the furnace condition. make worse.

Furthermore, if excess heat is given to raise the high temperature region to the top of the furnace,
The drying speed in that area becomes faster, and the rapid release of moisture within the pellet causes a bursting phenomenon, causing the pellet to become powder.

Therefore, in order to maintain stable furnace conditions and obtain high-quality beresoto, it is necessary to adjust the heat flow ratio (
solid-gas heat capacity ratio), stable drying,
It is important to preheat and form a firing zone.

In conventional shaft kiln furnace condition control, even though the above concept is well understood, it is not possible to find an index that directly indicates the furnace condition, so the temperature at the outlet of the exhaust hood,
Pressure drop in the kiln and rate of occurrence of discharged pellets below 5mm sieve (
The condition of the furnace was determined and controlled by taking into account factors such as powder rate).

However, these indicators include: (1) changes in hood outlet temperature and pressure drop are small and the response is slow; (2) powder ratio can often be used as an indicator to judge furnace conditions; It is measured by sieving after cooling, and there is a long loss time when passing through a cooler etc. during the discharge process, so there are disadvantages such as the lack of effectiveness even if you take action after seeing the results. .

For this reason, operational management often relies on the operator's intuition and tricks, and it has been desired to control the furnace condition using appropriate indicators that can more quickly determine the furnace condition.

As a result of various studies carried out by the present inventors to solve the above-mentioned problem, it has been found that the temperature measured at a specific position on the outer cylinder wall (outer wall) of a shaft kiln is directly linked to the furnace condition.
It was discovered that this is a suitable indicator for furnace condition control.

Temperature measurement of shaft kilns has conventionally been carried out simply for the purpose of lining management, but the purpose of temperature measurement in the present invention is clearly different from that and has a more advanced purpose.

In the present invention, the temperature inside the outer wall of the kiln (hereinafter referred to as T-A) between 0.4 and 0.7 of the material charging height from the top of the charged material in the kiln is clearly and Based on the fact discovered by the present inventors that the response speed is fast and it responds to the situation inside the furnace, the furnace condition can be optimized by setting the amount of ore feeding according to this temperature and its amount of change. It is something to control.

The results of the above research that formed the basis of the present invention will be explained below.

The present inventors have developed an outer cylinder with a diameter of 7. OOOm
m, width of annular space 700mm, height of outer cylinder 3,700mm
Six thermocouples were inserted into the pellet packed bed of a shaft kiln, and the temperature was continuously measured using a current collecting ring and trolley duct method, and the relationship between individual temperature changes and operation was studied.

(In the figure, 1 is the inner cylinder of the shaft kiln, 2 is the outer cylinder, and 5 is the inner cylinder of the shaft kiln.
indicates the hearth, I indicates the temperature recorder, A-F indicates the measurement points, and 0.4H and 0.7H indicate the height H of the charge layer from the top of the charge material, respectively. Shows the 7x position.

) As a result of this research, as shown in Figures 3 and 4, it was discovered that the temperature at point A, that is, T-A, and the powder ratio and kiln internal pressure drop, which have traditionally been indicators of operational management, have a relationship with strength. Ta.

In other words, both the powder ratio and the kiln internal pressure drop in Figures 3 and 4 show similar trends with respect to T-A, and by appropriately managing T-A, it is possible to control both of them so that they are in good condition. This shows that it is possible.

However, there was almost no correlation between the temperature at other measurement positions and the powder ratio and kiln internal pressure drop.

That is, at measurement points D, E, and F on the inner wall of the kiln, gas resistance is small, so ventilation is constantly ensured, and the measurement points D-F are not related to the overall furnace condition. There is almost no change in the temperature.

In addition, in the area of the measurement points of the lower ends B and C of the outer wall, the fifth
As shown in the figure, the powder ratio is unevenly high and a kind of dead space is formed, resulting in poor gas flow, resulting in small temperature changes and slow response speed.

(In Fig. 5, 1 indicates the inner wall, 2 indicates the outer wall, 5 indicates the hearth, and the numerical value in the box indicates the powder percentage.

) Therefore, the temperature at the measurement point B-F is inappropriate for use in furnace condition control.

On the other hand, the thermocouple at measurement point A in Figure 2 shows a rise in temperature to point F on the inner wall when the furnace condition is good, but on the other hand, when the furnace condition deteriorates, the temperature rapidly decreases, and the temperature changes. was large, and the response was also large compared to other measurement points.

The present invention is based on the above research results, and is based on the above-mentioned T-
This is a furnace condition control method that maintains the kiln at a constant temperature by increasing or decreasing the feed amount of raw material pellets in response to A and its variation, thereby making it possible to obtain high-quality fired pellets.

(The amount of fed pellets and the amount of fired pellets discharged are automatically controlled to maintain a constant surface level of the contents in the furnace and are correlated, so adjusting the amount of fed ore is equivalent to adjusting the discharge amount. It also means that.

) When controlling the furnace condition by adjusting the amount of ore feed based on the temperature T-A, manual operation can be effective, but automatic control is appropriate for fine-grained control.

Next, an example of the method of the present invention using automatic control will be shown.

FIG. 6 is a flow chart thereof. In the figure, k is the shaft kiln, ta is the thermocouple installed at the temperature measurement point according to the present invention, tr is the converter, r is the recording controller, C is the ore feed amount control device, and 0 is the constant supply adjustment operation unit. , f is a quantitative ore feeder, l is a level detector, and m is a hearth rotation motor for discharging pellets.

The material charging height from the top of the material to the outer wall of the shaft kiln is 0.
．． The thermoelectromotive force and electromotive force change generated by the thermocouple ta, which is attached within the range of 4 to 0.7, are converted into voltage by the converter tr, and the pellets corresponding to the voltage are converted by the converter tr. The furnace condition was controlled by setting the amount of ore to be fed, instructing the quantitative feed adjustment operation unit 0 to operate the quantitative ore feeder f, and feeding the amount of pellets corresponding to the measured furnace temperature.

The level detector l detects the charge level in the furnace, instructs the hearth rotating motor m to maintain this level constant, rotates the hearth, and adjusts the discharge amount.

The following table shows a comparison of the operational results when the furnace conditions were controlled by the automatic control method of the present invention as described above, by manual control, and by the conventional method.

Next, the relationship between TA and the amount of ore feed in the method of the present invention will be explained.

As can be understood from the relationships shown in Figures 3 and 4 and the data obtained from the operations in the table above, the content of the product under 5mm is 4.
In the case of ~5%, a relationship as shown in Fig. 7 is recognized between T-A and the amount of ore supplied.

In other words, even if the amount of ore fed is increased as the T-A is higher, the content below 5 mm of the product is lower in T-A and is the same as when the amount of ore fed is lowered.

Based on this fact, T-A is continuously measured, and the feedback is to detect the temperature difference ΔT from the previous time T1 in hourly units, and if ΔT>50°C or more, (T, Gradually increase or decrease the amount of ore supplied to ±1) T/Hr.

Further, in the case of ΔT-20 to 49°C, the ore supply amount is gradually increased or decreased so that the ore supply amount becomes (T1 ore supply amount ±0.5) T/Hr in 30 minutes.

Further, if ΔT<19°C, the supply amount is not increased or decreased and continues for 1 hour.

Originally, T-A does not change greatly on an hourly basis (ΔTmax = 50℃), so the increase or decrease in the amount of ore feed is actually small, and by gently adjusting it, the furnace The situation will remain stable.

As shown in the table above, if the charging amount is automatically controlled by the method of the present invention, productivity will be significantly improved compared to manual control and conventional methods, and the characteristics of the product pellets will also be significantly improved. It can be seen that the method of the present invention is extremely effective for operational management of shaft kilns.

[Brief explanation of drawings]

Figure 1 shows the general configuration of a shaft kiln, Figure 2
The figure shows the various positions of temperature measurement in the shaft kiln,
Fig. 3 is a diagram showing the relationship between the temperature TA at the measurement point according to the present invention and the powder ratio, Fig. 4 is a diagram also showing the relationship with the kiln internal pressure drop, and Fig. 5 is a diagram showing the powder ratio in the lower end region of the shaft kiln. The diagram showing the distribution, FIG. 6, is a flowchart showing the method of the invention. FIG. 7 is a graph showing the relationship between the TA temperature and the amount of ore supplied. 1; Inner cylinder, 2; Outer cylinder, 5; Hearth, 6; Outlet, A-F;
Temperature measurement position, k: kiln, ta: thermocouple, tr: converter, C: feed amount control device, 0: constant supply adjustment operation unit,
f: Quantitative ore feeder, l: Level detector.

Claims (1)

[Claims] 1 In a shaft kiln having an annular raw material charging section cross section, the height of the raw material charging from the top of the charged raw material is 0.4 to 0.
A shaft kiln characterized in that the temperature inside the outer cylinder of the furnace is continuously measured between 7 and 7, and the amount of ore to be fed is automatically set by a control device according to the temperature and the amount of change thereof, and the ore is fed. Furnace condition control method.