JPS6361367B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention forms a stable softened cohesive zone even when conditions inside the furnace change due to fluctuations in the quality and production volume of pig iron produced in a blast furnace. The present invention also relates to a method for controlling the position of the cohesive zone for smooth blast furnace operation.

(Prior art) Generally, iron ore charged in a blast furnace reaches a high temperature while undergoing reduction, begins to soften and shrink, then further descends and melts when it enters a high temperature region. A series of semi-molten ore layers is defined as a cohesive zone.

Since this cohesive zone has very high gas flow resistance, the part of the blast furnace where the cohesive zone is located is considered to be a part that resists gas flow. Therefore, how to control the shape of the cohesive zone viewed from the radial direction has a large effect on the stability and productivity of the blast furnace.

In order to control the shape of the cohesive zone in this way,
Its shape must be known, but it is impossible to observe it directly. Therefore, in recent years, attempts have been made to insert a sonde into a blast furnace and estimate the shape of the cohesive zone using various measurement data obtained. For example, "Tetsu to Hagane" 67 (1981) S69 or "Tetsu to Hagane" 69 (1983) S5 includes the TDR method or
Voltage pulses are sent to a flexible conductive cable inserted into the blast furnace called the TDR molten zone sensor, and the position of the molten material is determined by the length of the cable until the reflected wave that is generated when the cable melts in the molten zone returns. A method for measuring is shown. Another method is to simultaneously insert several flexible vertical probes with thermocouples in the radial direction of the furnace and track the temperature pattern to determine the shape of the cohesive zone.

However, inside the blast furnace, the descending speed of the charge differs between the upper and lower parts due to the slope of the shaft. For example, the descending speed is 7 m/hour in the upper part of the furnace, but it decreases to 4 m/hour in the lower part of the furnace. Therefore, in the above case where a flexible cable is used, the cable is bitten by the charge at the top of the furnace and descends with the same particles, but since the falling speed is different between the tip and the biting position, the sonde This causes a problem with the accuracy of the tip position.

In addition, "Tetsu to Hagane" 66 (1980) S685 is a system that estimates the shape of the cohesive zone using information on the gas temperature and gas composition of two sondes, the upper and lower ones installed horizontally on the shaft of a blast furnace. is disclosed. This method estimates the shape of the molten zone by defining the line where the solid temperature is 1050°C and the CO ₂ in the gas is 0 as the upper shape of the cohesive zone while maintaining consistency between the measured values and calculated values.
However, with this method, since the position of the horizontal sonde is located in a low-temperature region well above the actual cohesive zone, there is a possibility that a considerable error may occur in estimating the shape of the cohesive zone at the bottom, which is far away from that position. be.

Furthermore, a common problem with the methods using these sensors is that although it is possible to estimate the upper shape of the cohesive zone, it is impossible or impossible to estimate the lower shape.

(Problems to be Solved by the Invention) The present invention solves the above-mentioned problem, that is, it is impossible or inaccurate to estimate the position of the cohesive zone, especially the lower shape.

(Means for solving the problem) By the way, the cohesive zone is an ore layer between the softening start temperature Tms and the melting temperature Tmd,
Tms and Tmd are not constant and vary depending on the type of ore and the reduction rate of the ore until reaching it.
In other words, it has become clear that when the reduction rate is low, the material softens at low temperatures and melts off at low temperatures. Therefore, the position of the cohesive zone cannot be determined solely from the temperature information obtained by the sonde, and an estimation system is required that also takes into consideration information on the gas concentration representing the reduction situation. Furthermore, if the sonde penetrates both the upper and lower sides of the cohesive zone at the same time, the position of the cohesive zone can be determined accurately, but in other cases, the temperature distribution and reduction rate distribution in the vicinity must be estimated using some method. There is a need to.

The present invention allows estimation of the position of the cohesive zone and control of the cohesive zone based on the estimation to suit the operating conditions of the blast furnace.

That is, the present invention involves inserting one or more sondes into the blast furnace from the belly or lower part of the blast furnace, and determining the upper side of the cohesive zone from the actual measured values of gas/solid temperature and gas composition obtained from the sondes. and the lower position of the cohesive zone, and the distribution of the ratio of the ore layer thickness and coke layer thickness in the radial direction of the blast furnace is controlled so that the position of the cohesive zone occupies an optimal position for blast furnace operation. It is something to do. The method of the present invention will be explained in detail below with reference to the drawings.

FIG. 1 is an explanatory diagram of the present invention, in which 1 is a blast furnace, 2 is a blast furnace, and 3 is a sonde inserted into the furnace from the furnace belly, which is connected to a gas concentration measuring mechanism 10 and a gas/solid temperature measuring mechanism 11. . 4 is a cohesive zone, 5 is an upper side thereof, and 6 is a lower side thereof. 7 is a coke layer 7 charged from the top of the furnace, 8 is an ore layer, and 9 is a tuyere. 1
2 is an arithmetic device for estimating the cohesive zone shape from the measured values from the gas concentration measuring mechanism 10 and the gas/solid temperature measuring mechanism 11; 13 is the arithmetic device 12;
a setting mechanism (hereinafter referred to as O/C distribution setting mechanism) that sets the distribution of ore and coke ratio according to the output from the
14 is a raw material charging control device whose operation is controlled by the setting mechanism 13.

In order to control the position of the cohesive zone according to the method of the present invention, one or more probes 3 are inserted into the blast furnace 1 horizontally or inclined at any height below the belly 2 of the blast furnace 1 . This sonde can measure the gas/solid temperature and the concentration of gases such as CO, CO ₂ , H ₂ , H ₂ O, N _2, etc. at any position on the inserted trajectory, so these measurement results can be obtained from the gas concentration measurement mechanism. 10, it is sent to a calculation device 12 for estimating the cohesive zone shape via the gas/solid temperature measuring mechanism 11, and the cohesive zone shape is estimated by the device, which will be described later. Further, based on the results, the O/C distribution setting mechanism 13 determines the mode of analysis of the charge amount of ore and coke, and as a result, the raw material charging control device operates, and the radial direction of the charge at the top of the furnace is controlled. Layer thickness distribution is controlled. Therefore, it is possible to create an efficient cohesive zone shape that best suits the current operating conditions and realize smooth blast furnace operation.

Next, a method for estimating the cohesive zone position in the present invention will be explained. First, a method for estimating the temperature distribution and reduction rate distribution near the cohesive zone will be explained.

First, the height direction and radial direction inside the blast furnace are
Divide into a square lattice with a minute length of DL. On each grid point, the gas flow rate u, the reaction amount kc due to chemical reaction,
It has a mechanism for calculating the reduction rate RR, solid descent rate Us, gas concentration F, gas temperature Tg, and solid temperature Ts.

The gas temperature Tg and solid temperature Ts can be expressed from the heat balance as follows.

Heat storage rate = due to bulk flow (heat input - heat output)
It can be expressed as speed + heat transfer rate based on temperature gradient + exothermic (or endothermic) rate due to reaction heat + heat transfer rate from (and to) other phases + heat loss. From now on, assuming that the model is in a steady state, and using the basic equations (1) and (2) of heat transfer obtained with heat storage rate = 0, we will use the basic equations of gas temperature - {(Cg + TgdCg / dTg) (Ggr∂Tg / ∂r + Ggz∂T
g/∂z)}+[kg(∂ ² Tg/∂r ² +∂ ² Tg/∂Z ² +1/r ∂Tg/∂r)+∂kg/∂T
g{(∂Tg/∂r) ² + (∂Tg/∂z) ² }] −Qr(1−η)−ha(Tg−Ts)=0 ……(1) Basic equation of solid temperature −{( Cs＋TsdCs／dTs）(Gsr∂Ts／∂r＋Gsz∂T
s/∂Z)}+{ker(∂ ² Ts/∂r ² +1/r ∂Ts/∂r)
＋∂ker／∂Ts(∂Ts／∂r) ² ＋kez∂ ² Ts／∂Z ²
+∂kez/∂Ts(∂Ts/∂Z) ² } −Qr〓+ha(Tg−Ts)=0 ……(2) T: Temperature (℃), C: Specific heat (Kcal/Kg℃),
G: mass velocity (Kg/ ^m2・s), k: thermal conductivity,
ke: Effective thermal conductivity (kcal/m・s・℃) r: Radial distance m, Z: Height distance (m), ha: Heat transfer coefficient (kcal/m ²・s・℃) Subscript “g ”: gas “s”: solid “r”: radial direction “Z”: height direction The basic equation regarding the gas concentration distribution F is expressed as a function of position as shown in equations (3) to (7) from the mass balance.

CO；∂FCO／∂rGr＋∂FCO／∂zGz−G(FRCO−FCO・TFR
) / (TVML + dTVML) = 0... (3) CO ₂ ; ∂FCO ₂ / ∂rGr + ∂FCO ₂ / ∂zGz−G(FRCO ₂ −FCO ₂
・TFR) / (TVML + dTVML) = 0... (4) H ₂ ; ∂FH ₂ / ∂rGr + ∂FH ₂ / ∂zGz−G (FRH ₂ −FH ₂・TFR
)/(TVML+dTVML)=0……(5) H ₂ O; ∂FH ₂ O/∂rGr+∂FH ₂ O/∂zGz−G(FRH ₂ O−FH ₂ O
・TFR）／(TVML＋dTVML)＝0……(6) N ₂ ；∂FN ₂ ／∂rGr＋∂FN ₂ ／∂zGz−G(FRN ₂ −FN ₂・TFR
)/(TVML+dTVML)=0...(7) Gr, Gz, G are the calculated gas mass velocity r
The direction, z-direction component and absolute value, FCO~FN ₂ are
It is the gas concentration expressed in MOL fraction.

FRCO~FRN2: Increment in gas amount per unit volume due to reaction (mol/m ³ bed・s) TFR: Total amount per unit volume due to reaction
Increment in gas volume (mol/m ³ bed・s) TVML; Total MOL flow rate of gas (mol/m ²・s) dTVML; Increment in total MOL flow rate of gas (mol/m 2・s)
^m2・s) Next, the reduction rate at each position is the solid flow rate.
It is related to Usr, Usz and the flow direction. The reduction of iron ore changes from hematite to magnetite (RR1), from magnetite to wustite (RR2), and at each reduction stage.
As the reduction rate of iron (RR3) from wustite (8) ~
It is expressed by equation (10).

∂RR ₁ /∂rUsr＋∂RR ₁ /∂zUsz −V ₁ /W ₀・d ₀₁ =0 ……(8) ∂RR ₂ /∂rUsr＋∂RR ₂ /∂zUsz −V ₂ /W ₀・d ₀₂ = 0 ... (9) ∂RR ₃ / ∂rUsr + ∂RR ₃ / ∂zUsz −V ₃ /W ₀・d ₀₃ = 0 ... (10) Usr and Usz are the velocity components of the solid at each position found from the solid flow model (m/s). V ₁ to _{V 4} are the reaction rates (mol CO/s・
, mol H ₂ /s·ko).

W ₀ is the weight of one particle (g/co), and d ₀₁ to _{d 04} are the amount of oxygen to be reduced in the ore at each reduction stage (gmolO ₂ /g). The total reduction rate (RR) of ore is expressed by equation (11).

RR=0.111RR1+0.1871RR2 +0.7017RR3...(11) The reduction rate at each position is calculated by integrating equations (8) to (11) along the direction of solid flow from the top of the furnace.

For example, since the gas/solid temperature at a certain point on a grid point is affected by u, RR, Us, kc, F, etc., these are calculated simultaneously.

The following calculation method uses the temperature information and gas concentration information measured by the sonde as input conditions to obtain the optimal temperature distribution and gas concentration distribution in the vicinity of the actual measured values (minimizes the error). be.

1 First, select the target sonde. This is one or more sondes installed below the belly of the reactor.

2 Determine the grid point closest to the in-furnace measurement point of each sonde.

3 The temperature at each grid point is determined by converting the differential equation developed from the local heat balance that takes into account heat conduction, convective heat transfer between particle fluids, reaction heat, sensible heat changes, etc. into differences, and using the relaxation method. It is solved by repeated convergence calculations, but when the grid points coincide with the measurement points, actual measured values are given instead of calculations using a system of differential equations. Since the heat balance is calculated at other grid points, the influence of the measured temperature gradually spreads to the surrounding area each time it is repeated, and in the end, the heat balance is taken into account near the actual measurement point, and the actual value is the most It is possible to converge to a suitable gas/solid temperature distribution.

Next, a method for estimating the position of the cohesive zone from the estimated gas/solid temperature distribution and reduction rate distribution will be explained. As explained at the beginning, the cohesive zone is defined as the area where the ore softens and contracts. The conditions under which the ore undergoes softening and shrinkage are determined by the solid temperature, layer reduction rate, and type of ore, as shown in Figure 5. The softening start temperature Tms and the melting temperature Tmd are determined by the layer reduction rate and the type of ore. When the temperature on a grid point near the cohesive zone is given, it is determined whether the temperature is between the two, and if it is between the two, it can be defined as a cohesive zone.

The softening start temperature Tms for sintered ore is the reduction rate RR
can be expressed as a function of (12).

Tms=1140−153.6RR+244.7RR ² ...(12) Also, the burn-through temperature Tmd of sintered ore is expressed by equations (13) and (14).

Tmd=129RR+1291 (0<RR<0.7) ...(13) Tmd=230×(RR−0.7)+1381 (RR>0.7) ...(14) If it is a cohesive zone, the temperature on the lattice point and the softening The shrinkage rate of the cohesive zone is calculated from the difference in starting temperatures. The shrinkage rate S _R of sintered ore is the solid temperature of the lattice point (I, J)
Ts, softening start temperature Tms and reference temperature T ₀ (=1000℃)
It is expressed as a function of the dimensionless temperature T expressed by .

The dimensionless temperature T is T = (Ts - Tms) / T ₀ ...... (15) The shrinkage rate S _R is S _R = 0.02 - 0.251T + 26.7T ² -12.1T ³ ... (16) In this way, welding Since the cohesive zone is determined, the temperature, and the shrinkage rate are calculated at all grid points near the zone, it is possible to estimate the current distribution of the cohesive zone.

In fact, it goes without saying that the accuracy of estimating the shape of the cohesive zone improves as the actual measurement point approaches the cohesive zone.

Next, a method of controlling the O/C distribution to control the shape of the cohesive zone will be explained. The reason why the O/C distribution influences the cohesive zone shape is explained by the gas permeability, the transferability of gas sensible heat, the degree of progress of the reaction, and the radial distribution of the amount of oxygen to be reduced.

The particle size and void ratio of the ore layer are smaller than that of the coke layer, so the gas permeability is poor in the radial direction of the blast furnace where the ore layer is relatively thick, so the gas flow rate through that area is low. Gas flow rate decreases. A decrease in gas flow rate affects various aspects. Regarding heat transfer, this results in a decrease in the amount of sensible heat of the gas flowing through a unit cross-sectional area, and a deterioration in heat transfer to solids. Regarding the reaction, since a sufficient amount of gas is not supplied to reduce the ore, the concentration of the reducing gas decreases, and the driving force for reduction weakens, resulting in a relative decrease in the reduction rate.

From the above, a portion with high O/C in the radial direction brings about a decrease in the reduction rate and a decrease in gas/solid temperature.

Therefore, for example, in order to achieve a high cohesive zone in the center, it is necessary to supply sufficient heat to the center of the lower part of the furnace. For this purpose, it is necessary to increase the supply of gas to the center of the furnace, that is, to reduce the O/C in the center. Furthermore, in order to realize a high cohesive zone in the peripheral area, the O/C in the peripheral area may be reduced for the same reason.

(Example) Examples of this invention will be shown below.

Figure 2B shows a direct observation of the conditions inside the blast furnace at each position using a fiberscope mounted on a blast furnace probe that can be inserted up to 4 m into the blast furnace at an angle of 25 degrees. The tunnel portion in the figure corresponds to the cohesive zone. In this case, the cohesive zone has been penetrated.

FIG. 2A shows a comparison between the cohesive zone shape estimated by calculation with the given O/C distribution and the position of the tunnel portion. Direct observation using a fiberscope and the estimation results show good agreement.

FIG. 3 is an example of estimating the temperature in the vicinity using the temperature of each part obtained by the furnace belly sonde as an input condition. In this figure, information on the sonde installed above the reactor belly is also entered at the same time. Black positions indicate actual measured values. The shape of the cohesive zone shown in FIG. 2A is based on this temperature distribution, and it can be seen that the surrounding temperature also converges to an approximately appropriate value based on this measured value.

Figure 4 a shows the melting temperature estimated based on the actually measured O/C distribution (layer thickness distribution) during operation under low O/C and the solid temperature information measured from the furnace belly sonde. It is in the shape of a belt. In this case, as the ore layer is thinner in the center, it is thicker at the periphery, and as a result, the periphery of the cohesive zone enters the combustion zone, presenting a bad situation. The temperature measured in the belly of the reactor was also relatively low and the reactor conditions were unstable.

On the other hand, in Figure 4b, where the O/C layer thickness distribution in the radial direction is made relatively uniform by appropriate control of the O/C distribution, a furnace condition with a uniform gas flow distribution is achieved, and the actual measurement of the furnace belly sonde The solid temperature also increased, and we were able to achieve the desired cohesive zone shape.

(Effects of the Invention) The effect of stabilizing the shape of the cohesive zone appears in the reduction of Si in the hot metal and in the variation in Si concentration. With this invention,
This showed a decrease of 0.1% in Si in the molten pig iron, and the effect of stabilizing the furnace conditions led to a decrease in the blast furnace fuel ratio of 3Kg/tpig.

Furthermore, by managing the stable cohesive zone shape through fine-grained O/C distribution control, it was possible to maintain stable blast furnace operation even in the unstable situation of increasing or decreasing production.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing the overall configuration of the present invention, including signal processing flow and control method, Fig. 2 shows an embodiment of the present invention, and Fig. 2A shows the structure installed in the belly of the blast furnace in which the present invention was implemented. A diagram showing the position of the sonde, the position of the cohesive zone observed by the fiberscope, and the shape of the cohesive zone estimated by the present invention. Figure 2B shows the furnace charge observed by the fiberscope. Explanatory diagram showing the comparison between the distribution state and observation position, Part 3
The figure is a graph showing the gas temperature at each position in the furnace calculated by the present invention and the gas temperature measured at the actual value. A diagram showing a comparison of two types of cohesive zone shapes estimated using measurement information of the installed sonde, and FIG. 5 is an explanatory diagram showing a cohesive zone shape estimation method in the present invention.

Claims (1)

[Claims] 1. Insert one or more sondes into the blast furnace from the belly or lower part of the furnace, and use the measured values of gas/solid temperature and gas composition obtained from the sondes to determine the upper and lower sides of the cohesive zone. The method is characterized by determining the position and controlling the distribution of the ratio of the ore layer thickness to the coke layer thickness in the radial direction of the blast furnace and the particle size distribution so that the position of the cohesive zone occupies an optimal position for blast furnace operation. A method for controlling the position of the cohesive zone in a blast furnace.