JPH0776713A - Operation of shifting layer type scrap melting furnace - Google Patents

Abstract

PURPOSE:To use fine grain coke for blast furnace having lower cost than coke for foundry and to reduce a coke ratio be adjusting the suitable factor in operational variable and executing the melting operation. CONSTITUTION:Scrap is charged into the central part and the intermediate part in the furnace and the fine grain coke is charged into the peripheral part of a furnace wall, and only the coke is used as fuel, or pulverized solid fuel, gas fuel or liquid fuel is blown from tuyeres as auxiliary fuel to melt the scrap. One or more factors in the operational variable E decided with number of the tuyeres, diameter of the tuyere, average grain diameter of the charged coke and blasting quantity, blasting temp., oxygen enriched ratio and apparent density, blasting temp. and blasting pressure of the charging coke, are adjusted so as to satisfy the expression I. By this method, not only the fine grain coke for blast furnace can be used, but also further lower cost of the pulverized coal can be used in a large quantity as the auxiliary fuel. Further, the reduction of the coke ratio can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a raceway forming method and an auxiliary fuel blowing method in a hot metal manufacturing operation using a moving bed type scrap melting furnace.

[0002]

2. Description of the Related Art A cupola as shown in FIG. 2 has been used for a long time as a moving bed type melting furnace for producing hot metal from scraps such as steel scraps and pig iron scraps and iron sources such as mold pig iron and ferrosilicon as main raw materials. Came. Compared to the blast furnace method that produces hot metal from iron ore as the main raw material, the cupola method does not require the energy required for reducing iron ore, so the amount of coke used as fuel, that is, the coke ratio is about 1/3. . For example, the coke ratio in the blast furnace is 450-500 kg
/ T (hot metal), the steel compounding ratio is 40-6
It has been reported that the coke ratio in the cupola method using 0% scrap is 140 to 160 kg / t (hot metal) (Toru Ishino: "Cupola", (1985), p.
83, (New Japan Cast & Forging Association)). Therefore, the cupola method is an energy-saving hot metal manufacturing method, and considering that the amount of scrap generated will increase in the future, it is expected that the importance of the scrap melting and recycling process including the cupola method will further increase in the future. The features and problems of the cupola method as a conventional technique will be briefly described below with reference to FIG.

The first feature is that in the cupola, the coke bed 16 is formed up to a level of about 1 m above the tuyere 6a. _{C + O 2 = CO 2 +} 8080kcal / kg (C) ...... (3) C + CO 2 = 2CO-3180kcal / kg (C) ...... (4) C + 1 / 2O 2 = CO + 2450kcal / kg (C) ...... (5) CO + 1 / 2O ₂ = CO ₂ +3020 kcal / Nm ³ (CO) (6)

The second characteristic and problem is that the surface area per unit mass of coke is reduced as much as possible to delay the exothermic reaction of the formula (3) in the coke bed as much as possible and suppress the endothermic reaction of the formula (4). In order to increase the temperature in the coke bed and to expand the high temperature region, it is that a coke for casting a large lump of low reactivity is used.
The proper average particle size of coke is 1 / the diameter of the cupola hearth.
It is reported that it is 6 to 1/12 (Japan Foundry Association: "Foundry Handbook", (1992), P.242, (Maruzen)). For example, the appropriate average particle size of coke in a cupola with a hearth diameter of 1.5 m is 1 according to the above numerical value.
25 mm to 250 mm with an average particle size of 250 mm
The foundry coke is actually manufactured and used.
By the way, the average particle size of blast furnace coke is 45 to 60 m.
m. However, the reaction of the formula (4) is 1000
Since it actively progresses in the high temperature range of ℃ or more, most of the CO ₂ generated by the reaction of the equation (3) is converted to CO by the reaction of the equation (4), and eventually, in the coke bed, (5) It is presumed that the exothermic reaction of the equation is predominantly performed. In a cupola, it is not necessary to reduce iron ore as in a blast furnace, so it is desirable to convert CO gas into CO ₂ gas as much as possible. Therefore, in the cupola, the secondary tuyere 6b is installed in the vicinity of the upper end surface of the coke bed, and the divided air is blown to accelerate the reaction of the equation (6), and the generated heat is used for heating the filling in the upper part of the furnace. Some methods have been adopted.

As is clear from comparison between the equations (3) and (5), the amount of heat generated by the reaction of the equation (5) per 1 kg of carbon (C) is equal to the amount of heat generated by the reaction of the equation (3). If the amount of oxygen (O ₂ ) blown from the tuyere is the same, the amount of C consumed by the reaction of the equation (5) is consumed by the reaction of the equation (3). It is twice the amount of C. Therefore, the problem of cupola is that the consumption of coke is large and the calorific value in the coke bed is small, so that the combustion gas temperature (hereinafter, theoretical The combustion temperature) is low. By the way, in the blast furnace method,
The total amount of C in the coke on the front of the tuyere is consumed by the reaction of the formula (5), but rather it plays an important function of producing a reducing gas (CO), and the combustion gas is generated by the high temperature air blow of 1000 ° C or more. The temperature (theoretical combustion temperature) is also 2200 ° C or higher, and the function of melting iron ore is sufficiently fulfilled.

[0006] The third feature is that since cupola uses large coke in the cupola, a raceway is formed in front of the tuyere, that is,
That is, the coke does not turn around to form a combustion space having a central space. The present inventors have reported equation (7) as an equation for estimating the raceway depth D _R formed in the front of the tuyere of the blast furnace (Japanese Patent Publication No. 1-353623).

D _R = 5D _t · u _t · [(P _b +1) / {ρ _C · d _p · (T _b +273)}] ^1/2 (7) Where, D _R : Raceway depth (m), D _t: blade diameter (m), u _t: tuyere wind _{(m / s), P b} : blast pressure (kgf / cm ^2; gage), [rho _C: charging coke apparent density (kg / Nm ³ ), d _p : average particle diameter (m) of charging coke, T _b : blast temperature (° C.).

Since the raceway depth D _R of a general blast furnace calculated by the equation (7) is 0.8 m <D _R <1.5 m, even if d _p = 0.06 m, (D _R / d _p )> 13
This creates a raceway space where the coke can freely turn. However, in the conventional cupola, according to the equation (7), it is estimated that D _R <0.3 m, and usually,
Since d _p > 0.10 m, (D _R / d _p ) <3, it is estimated that the raceway space where the coke can freely turn is not formed. In fact, there is no report that the raceway was formed in Cupola.

The fourth feature and problem is that even in cupolas, injection of auxiliary fuel such as anthracite or coke dust has been attempted for the purpose of reducing the coke ratio and promoting carburization of hot metal. The amount of inclusion is small, and it is about 15 kg / t at most (Toru Ishino: “Cupola”,
(1985), P. 138, (New Japan Cast & Forging Association).
As described above, the reason why the injection amount of the auxiliary fuel is small in the conventional cupola is that there is no sufficient combustion space because the raceway is not formed, and
It is presumed that the amount of heat generated before the tuyere is small and the theoretical combustion temperature is low because the reaction of equation (5) is mainly performed.

Kamei et al. Used the blast furnace coke instead of the large lump foundry coke described in the above-mentioned second feature and problem of cupola, and rather aimed at increasing the calorie of the furnace top gas. Then, the total amount of C in the coke is consumed in the reaction of the formula (5), and the increase in the coke ratio due to this is increased by a large amount of pulverized coal (PCR / V _Ox = 0.8 kg / Nm ³ ; however, PC
R: pulverized coal ratio (kg / t), V _Ox : amount of oxygen blown from tuyere (Nm ³ / t)) to further reduce the decrease in theoretical combustion temperature due to large amount of pulverized coal blow We have proposed a method of maintaining the theoretical combustion temperature at 2000 ° C to 3000 ° C by compensating by oxygen enrichment (oxygen enrichment rate> 40%) (Yasuo Kamei et al., "Iron and Steel", 79 (1993)). , N
o. 2, P.I. 139). However, in the method of Kamei et al., Even if a large amount of pulverized coal is blown (PCR ≧ 115 kg / t),
A coke ratio of 125 kg / t is reportedly required, increasing the fuel ratio rather than the conventional cupola. Furthermore, the PCR / V _Ox = 0.8 in the method of Kamei et al.
The condition of kg / Nm ^{3 is} as follows:
Is 0.76, and it is estimated that a large amount of unburned pulverized coal, so-called unburned char, was generated even under the condition of high oxygen enrichment.

Ito et al., Instead of directly blowing pulverized coal into a cupola, blow it into a pre-combustion furnace as shown in FIG. 3 and oxygen, air, and steam under a low air ratio (0.5) condition. The pulverized coal is gasified by 60% to 70% (CO
And it proposes a method of blowing seen complete combustion of pre-combustion reducing gas scrap melting furnace containing H ₂₎ (JP 1-
195225). However, in the method of Ito et al., In addition to the problem of increasing the heat loss of the furnace body by installing the pre-combustion furnace, a large amount of unburned char is generated due to gasification under low air ratio (0.5) conditions. And the problem that a large amount of oxygen enrichment is required to suppress the generation of unburned char. Ito et al. Also reported that 10% or more of unburned char was generated in the pre-combustion furnace.

The inventors of the present invention conducted a combustion experiment of pulverized coal using a combustion furnace simulating the tuyere portion and raceway portion of an actual blast furnace at a scale of 1/2, and the raceway depth was 0.5.
When blowing pulverized coal with a particle size of 0.1 mm or less into the tuyere under conditions of m or less and theoretical combustion temperature of 2000 ° C. or less,
It has been clarified that the lower limit of the air ratio μ that can burn all pulverized coal in the raceway is 0.1 (theoretical value is 0.84) (Kenji Tamura et al .: "Iron and Steel", 77 (199).
1), No. 6, P. 775). Therefore, even in the cupola, in order to completely burn the pulverized coal blown from the tuyere and prevent the generation of unburned char, the air ratio is set to 1.0 or more, and the race as a combustion space is also set. It is judged necessary to form a way. Here, the air ratio μ is expressed by equation (8).

Μ = {1+ (0.224 / 32) · (O) _PC · (PCR / V _Ox )} / [0.2 24 (PCR / V _Ox ) · {(C) _PC / 12 + (H) _{PC /4}+0.01(NGR / V Ox) · G} ] ...... (8) _{However, G = 2 (CH 4)} NG +3.5 (C 2 H 6) NG +5 (C 3 H 8) NG +6 .5 (C ₄ H ₁₀ ) _NG +0.5 (CO) _NG +0.5 (H ₂ ) _NG (9) where PCR: fine powder solid fuel ratio or liquid fuel ratio (kg / t), V _Ox : Amount of oxygen blown from tuyere (Nm ³
/ T), NGR: gas fuel ratio (Nm ³ / t),
(O) _PC , (C) _PC , (H) _PC : Mass percentage (%) of oxygen, carbon, and hydrogen in fine powder solid fuel or liquid fuel,
(C _i H _j ) _NG : Volume percentage (%) of the gas component C _i H _{j in} the gas fuel.

[0014]

The first problem to be solved by the present invention is to reduce the formation of coke beds as much as possible and to remove C in the coke and / or auxiliary fuel by the reaction of the formula (3). Complete combustion is performed to suppress the reaction of the equation (4) using the combustion gas as a raw material and reduce the coke ratio. A second problem to be solved by the present invention is to further reduce the coke ratio under the condition of low oxygen enrichment rate. A third problem to be solved by the present invention is to use an inexpensive and fine-grained blast furnace coke in place of the expensive and low-reactivity large-scale foundry coke.

[0015]

In order to solve such a problem, the present invention is to charge scrap into the center and middle of the furnace and charge fine grain coke into the peripheral area of the furnace wall to obtain coke as fuel. In order to satisfy the formula (1) in the operating method of the moving-bed-type scrap melting furnace, only one is used, or one or more of fine powder solid fuel, gas fuel and liquid fuel is directly blown into the tuyere as an auxiliary fuel. , The number of tuyere N _t , and the tuyere diameter D
_t , mean particle size d _p of charged coke and air flow rate, air humidity, oxygen enrichment rate, apparent density of charged coke, air temperature, adjusted one or more factors among operation variables E determined by air pressure. This is a method for operating a moving bed type scrap melting furnace. _{N t · D t · d p} 1/2 ≦ E ...... (1) provided that _{E = (V b / 772)} · {804 / (804-M b) + X O2 / (79- X O2)} · [( T _b +273) / {ρ _C · (P _b +1)}] ^1/2 (2) where N _t : number of tuyere (−), D _t : tuyere diameter (m), d
_p: average particle diameter of the charging coke (m), V _b: blast volume ^{(Nm 3 (dry) / min} ), M b: blowing Humidity (g /
Nm ³ (wet)), X _O2 : oxygen enrichment rate (%), ρ _C :
Apparent density of charging coke (kg / Nm ³ ), T _b : blast temperature (° C.), P _b : blast pressure (kgf / cm ² ; gauge) Further, here, upstream of the fine powder solid fuel injection position. One or more types of gas fuel and liquid fuel are injected as auxiliary fuel.

[0016]

The present invention will be described in detail below. Figure 1
FIG. 1 is an example of a schematic view of a moving bed type scrap melting furnace according to the method of the present invention used in an experiment. Here, 1 is a furnace body of a melting furnace, which is lined with a refractory 2. The outline specifications of the furnace are as follows: furnace diameter 1.2 m, hearth diameter 1.32 m, effective height from tuyere to charging line 3.5 m, hearth height from tuyere to furnace bottom 1.0 m, The shaft angle is 89 °. 3 is a pel type charging device, 4 is a movable armor, and scrap 13 is charged from the center part of the furnace to the middle part by the swinging operation of the moveable armor, and the coke 14 is blown by the swinging operation. Charge and deposit in the vicinity. 6a is a primary tuyere for blowing air and has a tuyere diameter of 0.05 m, 7 is a blow pipe, 8 is an annular pipe, 9 is a blowing pipe, and 10 is a burner for blowing pulverized coal, which is inserted through the blow pipe 7. However, the tip of the burner is installed inside the primary tuyere 6a. 11
Is a burner for blowing gas fuel, and is installed upstream of the burner 10 for blowing pulverized coal. 12 is a taphole, 15 is a raceway, and 16 is a coke bed. Needless to say, at the beginning of the experiment, the coke bed was formed by fully charging coke into the lower part of the furnace to increase the temperature of the furnace body. Lower the top surface to the tuyere level surface.

In the method of the present invention, by loading the fine grain coke for the blast furnace in the peripheral portion of the furnace wall, the load of the charge on the front surface of the tuyere can be greatly reduced and the fine grain coke can be used. By a synergistic action, a raceway 15 having a depth of 0.3 m or more can be formed based on the principle of the above formula (7) as described later, and by utilizing the raceway as a combustion space, coke and pulverized coal can be obtained. Can be completely combusted by the reaction of the above formula (3). The main flow of the combustion gas containing CO ₂ generated in the raceway 15 and rising in the furnace avoids the coke layer 14 around the furnace wall where the ventilation resistance is large due to the fine particles, and the ventilation resistance due to the coarse particles is generated. Since the small scrap layer 13 rises, it is rarely converted to CO by the reaction of the equation (4). Further, since the supply of coke to the raceway 15 is performed from just above the tip of the tuyere, not only is a large raceway required as a combustion space formed, but also a fine grain is formed in order to form a stable raceway. It is necessary to charge the coke around the furnace wall, which is an important constituent feature of the present invention.

Further, by charging the fine grain coke to the peripheral portion of the furnace wall, it is useful for preventing damage to the side wall bricks of the furnace floor composed of carbon and silicon carbide bricks. This is because when carbon-unsaturated hot metal generated intensively near the raceway drips along the side wall of the hearth and stores it in the hearth, carbon in the bricks on the side wall of the hearth elutes into the hot metal. Therefore, the side wall bricks are easily damaged. However, according to the method of the present invention, since the coke that descends to the raceway and descends to the hearth while remaining unburned, and the coke that descends to the middle of the adjacent raceways act as a carburizing material, the sidewall This is because it helps prevent brick damage. Needless to say, the coke dropped to the hearth in this manner is used as supplementary coke for forming a coke bed.

Here, the central portion is defined as an area within 1/3 of the radius of the furnace, and the peripheral portion of the furnace wall is the horizontal distance R from the furnace wall of the coke layer 14 calculated by the equation (11) described later. _It is defined as a region within _C , and the middle part is defined as a region sandwiched between the central part and the peripheral part of the furnace wall. In addition, fine coke is defined as coke having an average particle diameter of 0.060 m or less.

Next, the relationship between the horizontal distance R _C (m) of the coke layer 14 charged in the peripheral portion of the furnace wall, the furnace opening radius R _T (m) and the coke ratio C _R (kg / t) will be described. The radius of the scrap layer 13 charged into the furnace is ( _{RT- RC} )
(M), the scrap layer 13 and the coke layer 14
When the ratio of the cross-sectional areas of B is set to B (-), the equation (10) is established, and when rearranged, the equation (11) is obtained.

B = π (R _T −R _C ) ² / π {R _T ² − (R _T −R _C ) ² } ... (10) R _C / R _T = 1− {B / (B + 1)} ^1/2 (11) where the scrap ratio is S _R (kg / t) and the bulk densities of scrap and coke are ρ _S and ρ _K (kg / m), respectively.
³⁾ Distant, assuming equal bed height of scrap and coke SoIrigoto, the volume ratio of the scrap and coke becomes equal to the cross-sectional area ratio B is (12) holds. B = (S _R / ρ _S ) / (C _R / ρ _K ) ... (12) Using the equations (11) and (12), S _R = 1000 kg
/ T, ρ _S = 3000 kg / m ³ , ρ _K = 500 kg /
R _C (m) and R _T (m) and C when m ³
Table 1 shows the result of calculating the relationship of _R.

[0022]

[Table 1]

As is clear from Table 1, the coke ratio C _R
Since the horizontal distance R _C of the reduction and furnace opening radius R _T decreases with furnace wall periphery coke layer of the decreases, depending on the conditions of the furnace opening radius R _T and coke ratio C _R of scrap melting furnace, ( It is important to calculate the horizontal distance R _C of the coke layer based on the equations (11) and (12), and use the calculation result as a guide to load the fine grain coke into the peripheral portion of the furnace wall. Here, when R _C ≧ 0.3 m, it is desirable to set the R _C as the target value of the raceway depth D _R. On the other hand, R _C <
In the case of 0.3 m, the position where the coke flows into the raceway is directly above the tuyere tip, so the distance between the tuyere tip and the furnace wall, that is, the in-furnace protrusion length of the tuyere tip, is determined by the coke layer above. It is important to set the horizontal distance R _C or less.
However, the secondary tuyere 6b is located at the bottom of the shaft due to the split air flow
In the case of installing the above, contrary to the case of the tuyere of the hearth, the distance between the tip of the secondary tuyere and the furnace wall is set to the horizontal distance R _C or more of the coke layer, and the secondary It is important that the air or oxygen gas blown from the tuyere 6b does not react with the fine coke near the furnace wall.

Next, the raceway depth D _R is 0.3 m
As described above, the method of adjusting the operating conditions determined by the tuyere number N _t , the tuyere diameter D _t , the average particle diameter d _p of the charging coke, and the blowing condition will be described. Here, Raceway depth D _R
The lower limit of 0.3 m is set to 0.3 m because the blast furnace coke having an average particle diameter d _p of 0.060 m is used as the charging coke and the coke can move within the raceway without causing a crosslinking phenomenon. It is calculated from the condition (D _R / d _p ≧ 5), and further, the air ratio ≧ 1.0 at the low raceway depth (≦ 0.5 m) performed by the present inventors.
It goes without saying that the above results of the large-scale combustion experiment of pulverized coal were referred to. The upper limit value of the raceway depth D _R is estimated to be about 0.54 m from the trial calculation results of Tables 3 and 4 described later.

Now, the blast humidity is changed to M _b (g / Nm ³ (we
t)), and the air flow rate is V _b (Nm ³ (dry) / min),
The amount of steam injected corresponding to the blast humidity is V _H2O (Nm ³
/ Min), the equation (13) is established, and by rearranging V _H2O , the equation (14) is obtained. V _H2O = (22.4 / 18000) · M _b · (V _b + V _H2O ) …… (13) V _H2O = M _b · V _b / (804−M _b ) …… (14)

When the oxygen enrichment ratio is X _O2 (%) and the oxygen enrichment amount is V _O2 (Nm ³ (dry) / min), V _O2
Is expressed by equation (15). _{V O2 = X O2 · V b} / (79-X O2) ...... (15) Further, when placing the tuyere wind speed _{u t (m / s),} u t is expressed by equation (16). _{u t = (V b + V} O2 + V H2O) · (T b +273) / {(60 × 273/4) · π · N t · D t 2 · (P b +1)} ...... (16) However, T _b : blast temperature (° C), P _b : blast pressure (kg
f / cm ² ; gauge), π = circular ratio (−), N _t : number of tuyere (−), D _t : tuyere diameter (m).

Therefore, by substituting equations (14) and (15) into equation (16) and rearranging, equation (17) is obtained. _{u t = C / (N t} · D t 2) ...... (17) _{However, C = (V b / 12865} ) · (T b +273) · {804 / (804-M b) + X O2 / (79- X _O2 )} / (P _b +1) ...... (18)

From equation (17), equation (19) is obtained. D _t · u _t = C / (N _t · D _t ) (19) On the other hand, if the formula (7) for estimating the raceway depth D _R is modified, formula (20) is obtained. D _t · u _t = D · D _R · d _p ^1/2 (20) However, D = 0.2 {ρ _C · (T _b +273) / (P _b +1)} ^1/2 …… ( 21) where d _p : average particle size (m) of charged coke, ρ
_C : Apparent density of charged coke (kg / Nm ³ ). Therefore, equation (22) is obtained by arranging equations (19) and (20) equally. D _R = (C / D) / (N _t · D _t · d _p ^1/2 ) ... (22)

In equation (22), setting D _R ≧ 0.3 and substituting equations (18) and (21) into equation (22) and rearranging yields equations (1) and (2). . _{N t · D t · d p} 1/2 ≦ E ...... (1) provided that _{E = (V b / 772)} · {804 / (804-M b) + X O2 / (79-X O2)} · [( T _b +273) / {ρ _C · (P _b +1)}] ^1/2 (2) By the way, since the relationship of C / D = 0.3E holds,
Expression (22) is expressed by Expression (23). D _R = 0.3E / (N _t · D _t · d _p ^1/2 ) ... (23)

Below, D _R ≧ 0.
A method of adjusting the number of tuyeres N _t , the tuyere diameter D _t , the average particle diameter d _p of the charging coke, and the operation variable E determined by the blowing condition will be described. Here, the tapping ability 41t /
As operating conditions of the moving bed type scrap melting furnace of h, air flow rate V _b = 350 (Nm ³ (dry) / min), air flow humidity M _b = 20 (g / Nm ³ (wet)), oxygen enrichment rate X
_O2 = 6 (%), blast temperature T _b = 25 (℃), charging coke apparent density _{ρ C = 1000 (kg / Nm} 3), blowing pressure _{P b = 0.2 (kgf / cm} 2; gage) Assuming that the number of tuyere N _t and the average particle diameter d _p of the charging coke are changed, the upper limit of the tuyere diameter D _t for setting the raceway depth D _R to 0.3 m or more is (1). Table 2 shows the results calculated based on the formula. The upper limit of the tuyere diameter D _t is
It may be adjusted according to the number of tuyere N _t and the average particle diameter d _p of the charging coke, and the tuyere diameter D _t in the conventional cupola
Taking ≦ 0.200 m as a reference, for example, d _p = 0.0
In the case of 45 m, (N _t = 6, D _t ≦ 0.197
m) or (N _t = 7, D _t ≦ 0.169 m) is desirable. Therefore, d _p = 0.0
45 m, N _t = 6, D _t ≦ 0.197 m
Raceway depth D _R (m) and tuyere wind speed u _t when _t is changed from 0.110 m to 0.190 m
Table 3 shows the results of calculating (m / s) based on the equations (23) and (17), respectively.

[0031]

[Table 2]

[0032]

[Table 3]

[0033]

[Table 4]

The raceway depth D _R can be increased by decreasing the tuyere diameter D _t . Since increasing the raceway depth means expanding the combustion space, it is a desirable direction for injecting a large amount of pulverized coal, but as shown in Table 3, the tuyere wind speed u _t decreases as the tuyere diameter D _t decreases. increases, since the blowing pressure is estimated to increase, u _t is about 100 m / s is the upper limit of a conventional cupola of u _t
It is desirable to determine the tuyere diameter D _t so that Therefore, in the case of Table 3, the lower limit of D _t is 0.110 m and the upper limit of the raceway depth D _R is 0.5.
It is estimated to be 4 m. By the way, as is clear from comparing equations (17) and (2), the tuyere wind speed u _t and the operating variable E
The direction of the change is the same, and the tuyere wind speed u _t or the operation variable E is mainly adjusted by the air flow rate V _b .

Next, N _t = 6 and D _t = 0.170
Under the condition of m, u _t = 43.2 m / s, the raceway depth D _R (m) when d _p is changed from 0.020 m assumed in actual operation to 0.060 m is given by the formula (23). Table 4 shows the results calculated based on the above. The raceway depth D _R can be increased to 0.52 m by reducing the charging coke average particle diameter d _p to 0.020 m. Here, since the reduction of the average particle diameter d _p of the charged coke increases the ventilation resistance of the coke layer, the amount of gas rising in the coke layer around the furnace wall is decreased, and conversely, it rises in the scrap layer. Since the amount of gas is increased, the preheating effect of scrap is enhanced, and the effect of reducing the heat loss of the furnace body due to the decrease in the gas flow around the furnace wall can also be expected, which is a desirable direction, contrary to the common sense of the conventional cupola, It is clear that fine grain coke works better in the scrap melting furnace according to the method of the present invention.

The method for forming the raceway in the moving bed type scrap melting furnace has been described above. Next, the method for injecting the auxiliary fuel mainly for injecting the pulverized coal will be briefly described. FIG. 4 shows an example of the method of the present invention in which the auxiliary fuel is blown into the tuyere. When only the fine solid fuel is blown, the method proposed by the present inventors by the blast furnace method (Japanese Patent Publication No. No. 2642). That is, the tip of the fine powder solid fuel injection burner 10 is inserted into the tuyere 6a through the blow pipe 7. Fine powder solid fuel injection burner 1 when only fine powder solid fuel is injected
The tip position of 0 may be installed in the blow pipe 7 or in the raceway 15 formed on the front surface of the tuyere,
When it is inserted into the blow pipe 7 on the upper end side, there arises a problem that the fine solid fuel is attached near the boundary between the tuyere and the blow pipe or to the inner wall surface of the blow pipe, while it is inserted into the raceway 15. In this case, the heat resistance of the burner becomes a problem, so the method of inserting the burner into the tuyere 6a is optimal.

In order to further improve the combustibility of the pulverized solid fuel, hot air blowing, which is used in the conventional cupola, may be used, but it is normal temperature blowing and has a low oxygen enrichment rate of about several percent. Under the conditions, by blowing the gas fuel or the liquid fuel upstream from the blowing position of the fine solid fuel, the blowing temperature at the blowing position of the fine solid fuel is 60
The method of preheating to 0 ° C. or higher is simple and practical. This is because, in the method of the present invention, as shown in Examples described later, since the CO combustion rate η _CO of the furnace top gas is large, the calorific value of the furnace top gas is low, and there is a high possibility that hot air blowing cannot be performed. Because. As shown in FIG. 4 (a), the method of blowing the gas fuel or the liquid fuel is the same as the method of blowing the fine powder solid combustion. It may be inserted through or inserted into the tuyere, as shown in FIG. 4 (b).

Here, the reason for setting the blast temperature at the blowing position of the pulverized solid fuel to be 600 ° C. or higher is based on the assumption that pulverized coal is used as the pulverized solid fuel and the combustion of volatile matter of the pulverized coal is promoted. In this case, the temperature of pulverized coal is 600 ° C which is the ignition point of coal gas or tar which is a volatile component of pulverized coal.
This is because it is necessary to preheat above. Here, at the injection position of the gas fuel or the liquid fuel in the case of FIG. 4A, the combustibility of the fuel is high and the injection amount is small,
Moreover, considering that the combustion temperature is as low as about 600 ° C,
Either in the tuyere or in the blow pipe. Also, the blast temperature at the blowing position of the fine solid fuel is 6
Whether or not the temperature is 00 ° C or higher is determined directly by installing a thermocouple thermometer at the tip of a fine powder solid fuel injection burner, or by measuring the mass balance of gas fuel or liquid fuel injection and blast. And the theoretical combustion temperature may be estimated based on the heat balance. If the blast temperature at the blowing position of the pulverized solid fuel is less than 600 ° C, the temperature will be 600 ° C.
Adjust (increase) the injection amount of gas fuel or liquid fuel so that the temperature becomes ℃ or higher.

Next, regarding the injection amount of the auxiliary fuel,
The method of blowing under the condition of air ratio ≧ 1.0 is a desirable method because it is possible to completely burn the pulverized coal in the raceway as described above. However, even if a large amount of auxiliary fuel is blown under the condition that the air ratio is less than 1.0, unburned char is expected to be generated considerably, but most of the unburned char is discharged from the top of the furnace, so the air permeability deteriorates. It is presumed that the problem will not occur. Rather, some unburned char may be used as a carburizing material in the hot metal to reduce the coke ratio. Therefore, the lower limit of the air ratio is set to 1.0 based only on the flammability. It is not always necessary to limit the injection amount of the auxiliary fuel.

[0040]

EXAMPLES Examples according to the method of the present invention will be described below. For the experiment, the moving bed type scrap melting furnace (with 6 tuyeres) shown in FIG. 1 was used. The particle size and chemical composition of the raw fuel used are as follows. The scrap used as the iron raw material is processed steel scrap with a maximum dimension of 0.100 m (C: 0.
5%, Si: 0.2%, Fe: 98.0%) Coke is a fine coke (C: 8) having an average particle diameter d _p of 0.013 m.
8.0%, H: 0.2%, ash content: 11.0%), and the fine powder solid fuel used as an auxiliary fuel has a particle size of 0.074 m.
80% pulverized coal with m or less (C: 75.0%, H: 5.0
%, Ash content: 11.0%), natural gas (CH _4: 88.
_{0%, C 2 H 6:} 6.0%, C 3 H 8: 4.0%, C 4
H _10: it was 2.0%). Table 5 shows the main experimental conditions and experimental operation indexes.

[0041]

[Table 5]

Here, Example 1 is an example in which only coke is used, and Example 2 is a case where a large amount of pulverized coal is injected as an auxiliary fuel (1
04 kg / t; air ratio 1.0), Example 3 is a composite fuel of pulverized coal and natural gas as auxiliary fuel (pulverized coal 77
This is an example in which kg / t, natural gas 15 Nm ³ / t; In all the experiments, the scrap ratio was 954 kg / t, the die / pig ratio was 0, that is, the entire amount of steel scrap was used, the blast temperature was room temperature (25 ° C.), and the blast humidity was atmospheric humidity (20 g / Nm ³ ). In the experiment using only the coke of Example 1, the air flow rate V _{b was} 51.9 Nm ³ / min (air flow rate basic unit 679 Nm ³ / t), and the oxygen enrichment rate X _O2 2.0.
%, The amount of tapping was 4.58 t / h, the coke ratio was 129 kg / t, and the CO burning rate of the furnace top gas was η.
_CO {η _CO = CO ₂ / (CO ₂ + CO) × 100}
A good result of 60% was obtained. In the operation of the conventional cupola, as described above, the coke ratio is 140 to 160 kg / t under the condition of the steel material mixture ratio of 40 to 60%, whereas in the case of Example 1, the steel material mixture ratio is 100. Even under the condition of%, a coke ratio of 130 kg / t or less was achieved. Incidentally, as shown in Table 5, the tuyere wind speed u in the case of Example 1
_t is 73.3 m / s, raceway depth D _R is 0.31
6 m (> 0.3 m), the theoretical combustion temperature was 2610 ° C, and the hot metal temperature was 1530 ° C.

In the experiment in which a large amount of pulverized coal (104 kg / t) was injected as the auxiliary fuel of Example 2, the air flow rate V _b 49.
8 Nm ³ / min (air flow rate basic unit 598 Nm ³ / t),
Oxygen enrichment ratio X _O2 was carried out under 4.0% blowing conditions, and good results were obtained with a tapping rate of 5.00 t / h, a coke ratio of 33 kg / t, and a CO burning rate η _{CO of} 75% of the furnace top gas. In particular, the coke ratio was significantly reduced as compared with the experiment using only the coke shown in Example 1, and a low coke ratio corresponding to the amount of carburized hot metal (C: 3.7%) was obtained. Further, in the case of the second embodiment, the tuyere wind velocity u _t is 72.1 m / s, the raceway depth D _R is 0.311 m (> 0.3 m), and the theoretical combustion temperature is 2.
The temperature was 527 ° C and the hot metal temperature was 1510 ° C. As described above, the theoretical combustion temperature was slightly lowered by the large amount of pulverized coal injection, but the theoretical combustion temperature was 250 even under the condition of the low oxygen enrichment ratio X _O2 (4.0%).
A high temperature of 0 ° C. or higher was obtained.

In the experiment in which pulverized coal and natural gas were injected as the auxiliary fuel of Example 3, the blast rate V _{b was} 47.8 Nm ³
/ Min (air flow rate basic unit 579 Nm ³ / t), oxygen enrichment rate X _O2 5.0% air flow conditions, and natural gas 15 N
The blowing temperature is 735 ° C (> 60 by blowing m ³ / t).
It was carried out by blowing 77 kg / t of pulverized coal into the tuyere preheated to 0 ° C. As a result, the amount of tapped iron was 4.95 t / h, the coke ratio was 35 kg / t, and the CO burning rate η _CO 90 of the furnace top gas
%, A high thermal efficiency was achieved due to high η _CO . Further, the tuyere wind velocity u _{t in} the case of the third embodiment is 7
0.2m / s, raceway depth D _R is 0.302m
(> 0.3 m), the theoretical combustion temperature was 2621 ° C, and the hot metal temperature was 1520 ° C.

[0045]

Industrial Applicability As described above, the present invention is an epoch-making method for melting and treating scrap, which is less expensive than coke for casting and can be reduced in coke ratio by using fine coke. By forming a raceway in front of the tuyere, it is possible to greatly reduce the coke ratio by burning a large amount of pulverized coal, which is cheaper than coke, under conditions of low oxygen enrichment ratio of several percent or less. However, the effect of the invention is extremely large.

[Brief description of drawings]

FIG. 1 is a schematic view of a moving-bed-type scrap melting furnace experimental apparatus for carrying out the present invention.

FIG. 2 is a schematic diagram of a conventional cupola.

FIG. 3 is a schematic view of a conventional scrap melting furnace equipped with a pulverized coal pre-combustion furnace.

FIG. 4 is a schematic view of an auxiliary fuel injection method according to the method of the present invention.

[Explanation of symbols]

 1 Scrap melting furnace body 2 Refractory 3 Bell-type charging device 4 Movable armor 5 Gas rising pipe 6 Tuyere (a: primary, b: secondary) 7 Blow pipe 8 Annular pipe 9 Blast pipe 10 Pulverized coal injection Burner 11 Gas-fuel injection burner 12 Tap hole 13 Scrap (layer) 14 Coke (layer) 15 Raceway 16 Coke bed 17 Pre-combustion furnace

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] November 17, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction content]

The inventors of the present invention conducted a combustion experiment of pulverized coal using a combustion furnace simulating the tuyere portion and raceway portion of an actual blast furnace at a scale of 1/2, and the raceway depth was 0.5.
When blowing pulverized coal with a particle size of 0.1 mm or less into the tuyere under conditions of m or less and theoretical combustion temperature of 2000 ° C. or less,
It has been clarified that the lower limit of the air ratio μ that can burn the entire amount of pulverized coal in the raceway is 1.0 (theoretical value is 0.84) (Kenji Tamura et al .: "Iron and Steel", 77 (199).
1), No. 6, P. 775). Therefore, even in the cupola, in order to completely burn the pulverized coal blown from the tuyere and prevent the generation of unburned char, the air ratio is set to 1.0 or more, and the race as a combustion space is also set. It is judged necessary to form a way. Here, the air ratio μ is expressed by equation (8).

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction content]

[0016]

The present invention will be described in detail below. Figure 1
FIG. 1 is an example of a schematic view of a moving bed type scrap melting furnace according to the method of the present invention used in an experiment. Here, 1 is a furnace body of a melting furnace, which is lined with a refractory 2. The outline specifications of the furnace are as follows: furnace diameter 1.2 m, hearth diameter 1.32 m, effective height from tuyere to charging line 3.5 m, hearth height from tuyere to furnace bottom 1.0 m, The shaft angle is 89 °. 3 bell-type charging device, 4 is a removable armor, deposited was charged to the intermediate portion of the scrap 13 by the inner swing operation of the removable armor from the center of the furnace, furnace coke 14 by the outer swing operation Charge near the wall and deposit. 6a is a primary tuyere for blowing air and has a tuyere diameter of 0.05 m, 7 is a blow pipe, 8 is an annular pipe, 9 is a blowing pipe, and 10 is a burner for blowing pulverized coal, which is inserted through the blow pipe 7. However, the tip of the burner is installed inside the primary tuyere 6a. 11
Is a burner for blowing gas fuel, and is installed upstream of the burner 10 for blowing pulverized coal. 12 is a taphole, 15 is a raceway, and 16 is a coke bed. Needless to say, at the beginning of the experiment, the coke bed was formed by fully charging coke into the lower part of the furnace to increase the temperature of the furnace body. Lower the top surface to the tuyere level surface.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0036

[Correction method] Change

[Correction content]

The method for forming the raceway in the moving bed type scrap melting furnace has been described above. Next, the method for injecting the auxiliary fuel mainly for injecting the pulverized coal will be briefly described. FIG. 4 shows an example of the method of the present invention in which the auxiliary fuel is blown into the tuyere. When only the fine solid fuel is blown, the method proposed by the present inventors by the blast furnace method (Japanese Patent Publication No. No. 2642). That is, the tip of the fine powder solid fuel injection burner 10 is inserted into the tuyere 6a through the blow pipe 7. Fine powder solid fuel injection burner 1 when only fine powder solid fuel is injected
The tip position of 0 may be installed in the blow pipe 7 or in the raceway 15 formed on the front surface of the tuyere,
When inserted into the upper stream side of the blowpipe 7, the problem of adhesion of finely divided solid fuel to the tuyere and the inner wall surface of the boundary around or blow pipe blowpipe occurs while inserted into the raceway 15 In that case, the heat resistance of the burner becomes a problem, so the method of inserting the burner into the tuyere 6a is optimal.

[Procedure amendment 4]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 1

[Correction method] Change

[Correction content]

[Figure 1]

Claims (2)

[Claims] 1. Scrap is charged into the central part and intermediate part of the furnace, fine coke is charged into the peripheral part of the furnace wall, and only coke is used as fuel, or fine solid fuel and gas are used as auxiliary fuel. In the operating method of the moving bed type scrap melting furnace in which at least one of fuel and liquid fuel is directly blown into the tuyere, the number of tuyere N _t and the tuyere diameter D are set so as to satisfy the equation (1).
_t , mean particle size d _p of charged coke and air flow rate, air humidity, oxygen enrichment rate, apparent density of charged coke, air temperature, adjusted one or more factors among operation variables E determined by air pressure. A method for operating a moving bed type scrap melting furnace, which is characterized by: _{N t · D t · d p} 1/2 ≦ E ...... (1) provided that _{E = (V b / 772)} · {804 / (804-M b) + X O2 / (79- X O2)} · [( T _b +273) / {ρ _C · (P _b +1)}] ^1/2 (2) where N _t : number of tuyere (−), D _t : tuyere diameter (m), d
_p: average particle diameter of the charging coke (m), V _b: blast volume ^{(Nm 3 (dry) / min} ), M b: blowing Humidity (g /
Nm ³ (wet)), X _O2 : oxygen enrichment rate (%), ρ _C :
Charging coke apparent density ^{(kg / Nm 3), T} b: blast temperature (℃), P _b: blast pressure (kgf / cm ^2; gage) 2. The operating method for a moving bed type scrap melting furnace according to claim 1, wherein at least one of gas fuel and liquid fuel is blown as an auxiliary fuel upstream of the fine powder solid fuel blowing position.