uneven distribution of burden materials at blast furnace

2177 © 2012 ISIJ

ISIJ International, Vol. 52 (2012), No. 12, pp. 2177–2185

Uneven Distribution of Burden Materials at Blast Furnace Top in Bell-less Top with Parallel Bunkers

Huatao ZHAO,1)* Minghua ZHU,1) Ping DU,1) Seiji TAGUCHI1) and Hongchao WEI2)

1) Ironmaking & Environment Research Group, Institute of Research of Iron & Steel, Shasteel, Jinfeng, Zhangjiagang, Jiangsu,215625 P. R. China. 2) Hongfa Ironmaking plant, Shasteel, Jinfeng, Zhangjiagang, Jiangsu, 215625 P. R. China.

(Received on May 30, 2012; accepted on August 21, 2012)

In the blast furnace operation equipped with parallel bunker-type bell-less top, the uneven charging ofmaterials in circumferential direction is an important issue to be avoided. This unexpected circumferentialimbalance is caused by dynamics of burden materials in charging system. Full analysis is necessary forovercoming this problem.

In this paper, on-site measurements such as charging rates of coke at different flow control gate open-ings, burden falling trajectories in the air, height distribution of burden stock surface at furnace peripheraland at orthogonal two diameter directions, were done during the filling-up stage. Dislocation of centerpoint was found in this measurement.

Mechanical equations of burden materials flow are derived for three successive regions such as bunker-to-chute colliding point, materials motion on the chute and free falling in the air. Influence of operationalfactors such as flow control gate opening, rotating speed and tilting angle of chute, and stock line on cir-cumferential weight and falling point distribution was investigated. By making use of the mathematicalmodel, H value and K value are introduced to quantitatively evaluate the circumferential height and ore/cokedistribution in several charges. Measured results and simulation results matched well. Observeddislocation of center point was explained well by the mathematical simulation.

It is concluded that change of rotation direction is thought to be much effective in correcting theunevenness of circumferential height distribution. On the other hand, application of bunker change in turnat coke and ore charging is effective to realize circumferential even distribution of ore/coke.

KEY WORDS: uneven burden charging; circumferential distribution; parallel bunker-type bell-less top.

1. Introduction

Based on extensive dissection surveys after blow-out ofblast furnace operation, it has been well recognized that theradial distributions of the coke and ore layer are basicallymaintained until the ore layer melts down in the lower partof the furnace. And the control of ore/coke ratio distributionin the radial direction is significant in forming the gaspassage and resultant gas permeability in the furnaceoperation. Since then, many efforts such as operationalexperiments and analyses on site, small-scale laboratoryexperiments, 1-to-1-scale cold model experiments, andmathematical model simulations and so on, were done onradial distribution control of burden materials throughoutthe world. BF engineers realized that the radial distributionchange of burden materials at the blast furnace top couldresult in a big difference in operation. Consequently, blastfurnace performance was greatly improved both in stabilityand in a lower fuel operation.

On the other hand, there were some reports on the unevencharging of materials in circumferential direction in the blastfurnace equipped with parallel bunker-type bell-less top.

That unexpected circumferential imbalance is caused bydynamics of burden materials in charging system, but notfully analyzed and overcome yet. Due to the parallel config-uration of two bunkers at the blast furnace top, the burdenflow from a bunker deviate from the center line in verticalchute and the flow path is tend to peculiar one for eachbunker if the flow rate remains constant. During one revo-lution of the chute, the deviation results in different velocityand collision point on the chute and leads to unevencharging of materials at stock surface, for example, unevenore/coke ratio, in circumferential direction. The change inore/coke ratio in circumferential direction causes thedifference in silicon content and hot metal temperature alongthe direction which draws much attention of BF operators.But during the normal operation, the operators can hardlyget the imbalance signals. So, it is essential to construct amathematical model to inform blast furnace operators quan-titatively how much unevenness occurs in the circumferen-tial distributions of both burden height and ore/coke ratio.

In the past decades, a few mathematical models wereestablished to simulate the uneven burden distribution in thecircumferential direction. Kondoh et al.1) presented amathematical simulation model to clarify the materialscharging rate distribution in circumferential direction and

* Corresponding author: E-mail: [email protected]: http://dx.doi.org/10.2355/isijinternational.52.2177

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ISIJ International, Vol. 52 (2012), No. 12

showed numerically that burden flow deviation in verticaltube caused unevenness of material charging on the stocksurface in the blast furnace. Nomura et al.2) calculated thelocal coke rates distribution in circumferential directions atthe furnace top by detecting the top gas composition, fromeach quadrant region. They showed that it could be changedby selecting charging pattern of bell-less top to achieve itsuniform distribution as well as that of hot metal temperaturein the actual operation. Ren et al.3) calculated charging ratedistributions in circumferential direction at different bun-ker-material combinations and chute rotating directions. Xuet al.4) investigated the mechanism of circumferentialdistribution more precisely. They pointed out that both thefalling point distribution and the mass flow rate distributionof burden materials in the circumferential direction haverespectively a maximum and a minimum values on thedefinite horizontal directions, and that the respectivedirections in both falling point and mass flow rate differ by90 degree with each other.

In this study, the movement of charging materials fromtwo parallel bunker-type bell-less top was investigated in theview point of both the change in falling trajectory and themass flow rate distribution of burden materials in circum-ferential direction. Firstly, mass flow rates of coke weremeasured at actual blast furnace and correlated with theopenings of flow control gate at west bunker, and the resul-tant equation was used as one of input data for circumfer-ential imbalance model. Burden trajectories in the blastfurnace were also measured by laser detection system at thepiling process of burden materials before blowing-in andwere used to verify the simulation results of the trajectoriesby a mathematical model. The circumferential distributionsof both burden falling point on stock surface and of burdenlayer thickness were investigated by making use of themathematical simulation model. Circumferential imbalanceof burden height and volume-metric ore/coke distributionswas investigated under the conditions of variouscombinations of bunker usage and burden materials, andchute rotating direction in different overall ore/coke ratios.A plant experiment of surface height measurement on topburden surface was also done before the blowing-inoperation of an actual blast furnace. Burden surface heightdistributions were measured not only in circumferentialdirection at wall-side but also on two rectangular crossdiameters. The results measured at wall side were in goodcoincidence with simulated one. The radial dislocation ofactual center point, minimum height point of the burden inthe experiment could be explained by the simulation modeltoo.

2. Mathematical Model Construction

2.1. Description of Overall Burden Flow at Charging inBell-less Top

As shown in Fig. 1, burden material flows down from theflow control gate of a bunker in bell-less top, and passesthrough the vertical tube, then collides with the surface ofrotating chute, and moves to the lower tip end of the chute.After falling from the chute tip end into the air, it finallylands on the stock surface at the furnace throat. In thismathematical model, equations of burden flow are given by

dividing the investigating region into three parts, above-chute, on-chute and bellow-chute. The part “above-chute”covers the area from the flow control gate to the collisionpoint on rotating chute surface, “on-chute” from collisionpoint to the chute lower tip end and “bellow-chute” fromchute tip end to the stock surface, respectively. In treatingthe burden materials movement of particles flow, it wasassumed that shape of flow was represented as continuousmedium, but that equation of motion was represented by themovement of a particle which had the same dimension ofactual one and was located just in the centroid of the flow.The particle would not collide with other particles andbehaves as a single particle in motion.1,3,4) The dimensionsof the bell-less top charging system in our investigation,used as input in the simulation model, are listed in Table 1.

2.2. Burden Movement in the Region above the ChuteThe correction factor Kf in equation of motion, Eq. (1), is

introduced to get the burden velocity vin when it gets to thesurface of rotating chute,5) where v0 is an initial burdenvelocity at the flow control gate(here, = 0), H is an effectiveheight from the flow control gate to the surface of rotatingchute, Kf is employed for correcting both the inter-particlescollision and the friction between particles and wall of theflow path. Kf is 0.28 and 0.26 respectively for coke and orein this calculation.

vin = [v02 + 2gH]0.5·Kf ........................ (1)

Fig. 1. The overall burden flow at charging in bell-less top.

Table 1. Dimensions of the bell-less top charging equipment.

Distance from FCG to vertical tube bottom end in height 4.1 m

Diameter of vertical tube 750 mm

Distance from hook point of chute to semi-circle chute bottom 1.194 m

Distance from hook point to stock line level 0 4.76 m

Chute length 3.7 m

Diameter of semi-circle chute 800 mm

Angle of repose of coke 35°

Angle of repose of ore 33°

Throat diameter of BF 8.3 m

Throat height of BF 1.8 m


2179 © 2012 ISIJ

The volumetric flow rate of burden material, V, in the ver-tical tube is the function of flow control gate opening(fcg)as shown in Eq. (2). The function is got from the onsitemeasurement of Hongfa No.1 2 500 m3 BF in Shasteel, asshown later in Fig. 7. Assuming that the cross-section of theburden flow forms a crescent shape in the vertical tube asdepicted in Fig. 2 and the burden flow velocity is uniformin it, the burden flow centroid G can be given by making useof Eqs. (1), (2) and bulk density of the burden. The symbolT represents the angle of crescent of the burden flow fromthe center axis of the tube.

V = f(fcg) .................................. (2)

2.3. Burden Movement on the ChuteBy decomposing the particle velocity vin and coordinates

of burden centroid G into the chute longitudinal direction ,namely paralell to the center line of the chute and the tangen-tial direction of the chute bottom surface in rectangular crosssection to the center line , we can get those components ofinitial values such as particle location z0, velocity u0 = (dz/dt)0,deviation angle θ0 and angular velocity β0 = (dθ/dt)0. Andvk is always zero during this motion. Here is the directionrectangular to the chute bottom surface (See Fig. 3).

A particle motion in the 3-dimensional equation on thechute can be expressed as Eq. (3).6)

........ (3)

By decomposing these vectors in Eq. (3) into three direc-tions, we can get equations of motion in 3-components, i, jand k as shown in Fig. 3. As the result, equations of particlemotion can be given by Eqs. (4), (5), (6) and (7) as shownbelow. The variables used in Eqs. (3)–(7) are listed in Table 2.

.......................................... (4)

.......................................... (5)

.......................................... (6)

..................... (7)

Here, N is the normal force from the particle to the chutewall, v is absolute value of particle velocity on the chute.The fourth order Runge-Kutta method is applied to solvethese ordinary differential equations and get the final loca-tion zn, velocity un, rising angle θn and angular velocity βn

at the chute tip end. Finally, the total travelling time of theparticle on the chute, tc is calculated by the increment of thetime in motion.

2.4. Burden Movement in the Section Below the ChuteThe effect of gas flow on particle motion is ignored

because a drag effect of gas flow is small enough. Equations

Fig. 2. The overview of the vertical tube and rotating chute.

i

j

k

ma F m r m v Fg fr= − × × − × −[ ( )] ( )ω ω ω2

d z

dtg z R R

Rd

dt

2

22

2

= + − +

−

cos ( sin cos cos cos )sin

sin cos

α ω α θ α α α

ω α θθ−− ⋅η

dz

dt

N

mv

Rd

dtg z R

R

2

22 2

2 2

θα θ ω α α α θ

α θ ω

= − + +

+ +

sin sin ( sin cos sin cos

cos )sin siin cosα θ ηθdz

dt

Rd

dt

N

mv− ⋅

Fig. 3. Three dimensional expression of the particle movement onthe chute.

Table 2. Variables in the Eqs. (3)–(7).

m mass of the particle

acceleration vector of the particle

gravity forcce working on the particle

angular velocity vector of the chute rotation

radial position vector of the particle from a cross point ofrotation axis and chute bottom surface

velocity vector of the particle

friction force vector working on the chute wall

R radius of the cross-section of chute

t particle motion time on chute

θ rising angle of the particle position in rectangular cross-sectionalsemi-circle of the chute from chute bottom direction

η friction coeffecient between particle and chute surface

particle velocity in i component

particle velocity in j component

a

Fg

ω

r

V

Ffr

dzdt

R ddtθ

N m g R R

R z

= + − +⎡⎣−

sin cos cos cos cos

sin sin sin

α θ ω α ω θ α

ω α θ ω α

2 2 2 2

2 2 2 2 ccos cos

cos sin sin

α θ

ω αθ

ω α θ

+

+ ⎤⎦⎥

2 2Rd

dt

dz

dt

vdz

dtRd

dt= ⎛

⎝⎜

⎞⎠⎟ + ⎛

⎝⎜

⎞⎠⎟

⎡

⎣⎢⎢

⎤

⎦⎥⎥

2 21

2θ

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of free fall motion of a particle in three rectangularcoordinates system, shown in Fig. 4, are solved to get theparticle trajectory. In the figure variables are; γ = α + α ′,α ′ = tan–1{R(1-cosθn)/zn}, rn = {zn

2 + 2R2(1-cosθn)}1/2,respectively.

The travelling time of the particle in the air, ta iscalculated by using vertical component of the particlevelocity as shown in Eqs. (8) and (9). Here, symbol vv isvertical component of initial particle velocity at chute tipend. h; the height from chute tip end to the stock surface andin Fig. 5; ϕ = tan–1(Rsinθn/zn).

.................... (8)

.... (9)

2.5. Calculation of Unevenness of Burden ChargingRate in Circumferential Direction and of FallingPoint Deviation in Radial Direction during aRotation of the Chute

At first, definition of circumferential direction isimportant in this analysis. As depicted in Fig. 5, two bunkersof bell-less top are located in a horizontal plane and on aline, which crosses with center axis of the furnace. Here, thedirection of the east side bunker is assumed as 0 degree andthe chute direction is defined as 0 degree if the chute tip end

faces to the east. If the rotation of the chute is clock-wise asshown in the figure, the chute direction shifts from 0 to π/2,and then π, (3/2)π and 2π, and angular velocity vector, ,points to the downward perpendicular to the paper plane isdefined as positive in this case. For a calculation of burdencharging rate on stock surface in circumferential direction,we assume a definite amount of burden materials which fallsdown on the chute between the chute angles of ξ and ξ +dξ. Then we can calculate and identify the directions ofdistribution of falling points of burden materials between λand λ + dλ by making use of burden movement simulation.If the calculation results of dξ and dλ are not the same,burden distribution rate per unit circumferencial lengthdiffers from the average value during one rotation of thechute because that burden amounts of falling down on thechute and of distributing on stock surface shoud be thesame. If dξ > dλ, the distribution rate of the circumferencialpart is more than average, and if dξ < dλ, the distributionrate of the part is lower than average. The calculation of dξand dλ are actually put into practice as followings. When thechute rotation angle is ξ, the burden collides with the surfaceof the rotating chute, when the chute direction moves to ξ +ωtc, the burden leaves from chute tip end, and after the freefalling time ta from Eq. (8) when the particle positon isrotation angle of λ, the burden materials loads on the stocksurface. λ is given by Eqs. (10) and (11).

λ = ξ + ω tc – ϕ + δ ........................ (10)

δ = tan–1{vwta/(vrta + rn sinγ)} .................(11)

where, vw is a velocity component of the particle in rotatingdirection of the chute when it leaves the chute tip end.Symbol rn denotes the length from center axis of the furnaceto particle position at lower tip end of the chute. γ is theangle between rn and the vertical line.

In the next step, when the circumference angle is ξ + dξ,the burden collides with the surface of the rotating chute,and a series of calculations are the same likewise justmentioned above. In this case, tc′ and ta′ are also given byburden travelling time on the chute and in the air respective-ly. Resultant equation for the case of angle, λ + dλ, is givenby Eqs. (12) and (13). Symbol Ψ is a normalised flow ratedistribution ratio at the circumferential angle λ.

λ + dλ = ξ + dξ + ω tc′–ϕ ′ + δ ′ ............... (12)

δ ′ = tan–1{vw′ta′/(vr′ta′ + rn′sinγ ′)}............. (13)

.... (14)

In addition to the burden charging rate distribution incircumferential direction, radial distribution of burdenfalling point, FP, during a rotation of the chute at definitechute tilting angles can be calculted at the same time. FPvalue denotes the distance from the furnace center axis toimpact point of falling material on stock surface. When weget λ or λ + dλ, falling trajectory of a burden particle is alsogot in the same calculation process.

Fig. 4. Calculation of burden trajectory in the air.

Fig. 5. The definition of unevenness of burden charging rate.

tg

v gh va v v= + −⎡⎣⎢

⎤⎦⎥

122( )

v u R rv n n n n= + +cos sin cos sin sinα β θ α ω γ ϕ

ω

ψξλ

ξ

ξ ω δ δ ϕ ϕ= =

+ ′ − ⋅ + ′ − − ′ −

d

d

d

d t tc c( ) ( )


2181 © 2012 ISIJ

3. Methods and Data of Preliminary Experiments inActual Blast Furnace

3.1. The Relationship between the Flow Control GateOpening and Flow Rate at Different Bunker-material Combinations

It is easily thought that the flow control gate opening willaffect the centroid of burden flow in the vetical tube asdepicted like in Fig. 2 and that it results in change of thecharging rate distribution on stock surface in the circumfer-ential direction. A ball-type flow control gate is equiped inbell-less top charging system in Hongfa No.1 BF of Shasteelas shown in Fig. 6. During the material filling for blow-inoperation, the weight and discharging time were recordedfor coke and ore under different flow control gate openings.From the results, linear fitting method was used to getcorrelation function in Eq. (2) between flow control gateopening and burden flow rate from a bunker as shown inFig. 7. This equation is applied as input to the simulationmodel to investigate the influence of flow control gate open-ing in west bunker on coke charging rate distirbution on thestock surface in the circumferential direction.

3.2. Burden Trajectory Measurement in the Freeboardof Furnace Top at Various Tilting Angles of theChute

While the burden height near the wall in circumferentialdirection is considered to be affected not only by the cir-cumferential burden charging rate distribution but also bythe distance between the burden impact point and the wall,the calculation of burden falling trajectory from the rotating

chute is needed to determine both the circumferential flowrate distribution and the impact point at the stock surface.The calculation procedure is shown later in section 3. Here,burden trajectory measurment data in actual blast furnaceare mentioned. Figure 8 represents the results of centerposition of burden flow measured by crossed laser beammethod7) during the material filling for blow-in, which is incomparison with the simulation result as shown in the fig-ure. The computed and measured results agreed well witheach other in a constant inlet velocity at chute surface andconstant friction factors for coke and ore with the chuteexcept for the small tilting angle, which is the same with thatreported by Yamamoto et al.8) That means the burden fallingtrajectory can be simulated by the mathematical modelexcept small tilting angle.

3.3. The Burden Height Measurement at the Top StockSurface

During the material-filling-up, the burden stock surface isassumed to be flat before the last 4 charges due to the largekinetic energy of falling materials at deep stock line level.As shown in Fig. 9, the last 4 charges consist of one coke(with flux) charge and 3 alternative coke and ore charges.The composition and physical property of the last 4 chargesof burden are listed in Table 3 and the charging pattern set-ting is listed in Table 4.

For verification of the mathematical simulation model,the circumferential burden height distribution at wall sideand radial burden height distribution were measured afterfilling-up of Hongfa No. 1 BF. The measurement methodsare sketched in Fig. 10. Cross-circle denotes the measure-

Fig. 6. The geometry of the flow control gate.

Fig. 7. The relationship between charging rate and flow controlgate opening. (a) Coke from west bunker, (b) Ore from eastbunker.

Fig. 8. Comparison of measured falling trajectories and simulationresults in Hongfa No.1 BF of Shasteel. (a) Burden trajec-tory of coke, (b) Burden trajectory of ore.

Fig. 9. The Burden structure of the last 4 charges.

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ment point of the distribution.As results of the measurements, measured burden profiles

in radial direction at the top of Hongfa No.1 BF of Shasteelare shown in Fig. 11. Small deviation to south and to westdirections was observed in this measurement. For measure-ment results of circumferential direction, data are discussedin section 3.

4. Simulation Analysis and Discussion

4.1. The Influence of Operational Parameters on Dis-tritbution of Variables in a Single Layer

Ψ value as expressed in Eq. (14) denotes the normalizedcharging rate distribution of coke or ore in circumferentialdirection. The influence of such items, flow control gateopening, chute rotating speed and height of stock level onthe distribution ratio and radial distance of falling point(FP)of coke under the condition of charging from west bunkeris inverstigated under counter-clock wise rotation of thechute as follows.

Distribution of ψ value with a rotation of chute has amaximum and minimum value as pointed out by Kondohet al.1) and Xu et al.4) And FP value changes in the same ten-dency with Xu et al.4) Here, rotating direction of the chutein counter-clock wise proceeds from 360° to 0° (right handside to left hand side) on horizontal axsis in Fig. 12. Thedifference between maximum and minimum value of bothψ value and FP significantly changes with the flow controlgate opening. When the flow control gate opening is larger,angle γ of the crescent of burden flow dipicted in Fig. 2,becomes bigger, which means the centroid of burden flowin vertical tube comes closer to the center of vertical tube,and both ψ value and FP distribution becomes more uni-form. When the chute rotates from east→north→west, Ψvalue decreases gradually but increses rapidly duringrotation from west→south→east. This asymmetric changeof Ψ value is due to synthesizing both transfer speeds ofspecific motion of centroid,4) G point, and of burdenmaterials flow down on the chute.

Distritbuions of the circumferential charging ratio ψ val-ue and of the falling point FP are also thought to beinfluenced by the chute rotating speed. The differencebetween maximum and minimum value of ψ significantlychanges with chute rotation speed and the distributioncurves in circumferential direction moves to the counter-clcokwise direction with the increase of chute rotating speedas shown in Fig. 13. With respect to FP value, the value itselfincreased as a whole with the increase in rotating speed.

When stock line changes from 0 to 2 meter which was inthe range of normal operation in actual blast furnace, thereis little change in the distribution curve of ψ value as shownin Fig. 14, but FP value becomes larger significantly withdeeper stock line level as imagined naturally.

When tilting angle changes from 25° to 45°, thedifference between maximum and minimum point values ofψ value becomes a little bit smaller and the distributioncurve shifted to counter-clockwise direction (See Fig. 15).The reason why the difference between maximum andminimum values becomes smaller may be attributed to thevelocity of burden materials on the chute becomes smaller

Table 3. The burden composition of last 4 charges.

Burden composition

Coke(with flux) Coke+Ore

Coke Dolomite Silica CokeOre

Dolomite Silica Sinter Pellet Lump Manganese

Weight (ton) 14.5 2.7 0.6 14.5 2.8 1.1 18 3.5 5.5 1

Bulk density (ton/m3) 0.50 1.55 1.5 0.50 1.55 1.5 1.85 2.3 2.2 1.8

Table 4. The charging pattern setting for last 4 charges.

Tilting position 11 10 9 8 7 6 5 3 2 1

Angle setting 50° 47° 45.5° 43° 40.5° 37° 34° 27° 23° 12°

Revolutionnumber Coke 2 2 2 4

Revolutionnumber Ore 2 5

Note; Rotating speed: 48°/s, Rotating direction: Counter-clockwise

Fig. 10. The outline of plant measurement, (a) The circumferentialmeasurement, (b) The radial distribution measurement.

Fig. 11. The Measured burden profiles in radius direction at thethroat part of Hongfa No.1 BF of Shasteel. (a) Radialheight distribution in North-South direction, (b) Radialheight distribution in West-East direction.


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with increased tilting angle. The distribution curve of FPvalue shifts a little to counter-clcokwise direction shown inFig. 15 when tilting angle increases.

It is found from Figs. 12 and 14 that the respectiveminimum directions both in falling point and in mass charg-ing rate differ with each other by almost 90 degree which isthe same with Xu’ s simulation result.4) This 90-degree shift

can be explained by the difference of mechanisms betweenmass charging rate and falling point of particles, namelyacceleration and deceleration motion of particles on therotating chute and the change in effective length of thechute. On the other hand respective maximum directions,however, both angular positions look like almost the samein Fig. 12 and in Fig. 14. Factors forming the maximumdirection may somewhat change in the case of falling pointdistribution.

4.2. Control of Stock Height and Ore/Coke Ratio Dis-tribution in Circumferential Direction

Based on Ψ value distributions of coke and ore layers forone charge, H and K values are introduced, which denote

Fig. 12. Circumferential charging ratio and falling point distritbu-tions of coke in circumferential direction at different flowcontrol gate openings in west bunker. (a) Circumferentialflow ratio distritbuion, (b) Circumferential falling pointdistribution, (c) Crescent angle of the burden flow in ver-tical tube.

Fig. 13. Circumferential charging ratio distritbutions of coke fromwest bunker at different chute rotating speeds.

Fig. 14. Circumferential charging rate distritbuion and radialdistance of falling point on stock suface when chargingfrom west bunker at different stcok lines. (a) Circumfer-ential charging distritbuion, (b) Circumferential fallingpoint distribution.

Fig. 15. Circumferential charging rate distritbuion and radialdistance of falling point on stock suface when chargingfrom west bunker at different tilting angles. (a) Circum-ferential charging distritbuion, (b) Circumferential fallingpoint distribution.

Fig. 16. The stock height and ore/coke distribution in circumferen-tial direction under equal V(O) and V(C). (a) Circumferen-tial stock height distribution, (b) Circumferential ore/cokedistribution.

Fig. 17. Comparison of falling point lines of coke and ore at thelargest tilting angle.

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the total dimensionless stock height distribution of the cokeplus ore layer and ore/coke height ratio distribution in acharge respectively in circumferential direction. H and Kvalues are given by Eqs. (15) and (16).

........................................ (15)

............ (16)

Where, N is the total number of the circumferential sec-tions. V(C) and V(O) are the average volumetric chargingrate of coke and ore respectively.

Four patterns of burden charging sequence are definedconcerning the bunker-material combination and chuterotating direction as shown in Table 5.

From Fig. 16(a), it is found that unevenness ofcircimferential burden heght distributions remains even ifcoke and ore are charged from different bunkers in a chargewith an equal volume and when bunker-material combina-tion is changed in turn, such as from charging pattern (1) to(3) or from (2) to (4), the distribution does not change, andwhen the chute rotating direction is changed in turn, fromcharging pattern (1) to (2) or from (3) to (4), distributionsof H value will not become fully uniform by adding bothcurves. In K value, volumetric ore/coke distributions incircumferential direction are different in all of four cases buthave some regularity. When bunker-material combination ischanged, such as from (1) to (3) or from (2) to (4), bothdistributions in before and after change are almost reverseduring a rotation. When the chute rotating direction ischanged, such as from (1) to (2) or from (3) to (4), bothdistributions are somewhat different but not so big during arotation. This behaviour mentioned above was basically inthe same tendency when V(O)/V(C) is changed from 0.5 to1.5.

Therefore, two important things are concluded in thissection as follows;i) As for the unevenness in circimferential surface height

distribution of burden materials, the uneven heightdistribution occurs in the ordinary operation of paralell-type bell-less top and the distribution can not be madefully uniform by making sequential use of these fourpatterns, (1)–(4). However, change of rotation directionis thought to be much effective in correcting theunevenness.

ii) In case of the circumferential unevenness of volumetricore/coke distribution, application of bunker-materialcombination change in turn, (1) to (3), or, (2) to (4), isan effective method to realize circumferential evendistribution of ore/coke.

4.3. Analysis and Discussion on Experimental Datafrom Actual Blast Furnace

From Fig. 11, it is observed that the burden surface profileis typical “V” shape, which means the charged material atthe largest tilting angle comes near to the wall side,9) leadingto the largest height in the wall side. From Table 4, the max-imum tilting angle was 40.5° for coke and 37° for ore. Theestimated falling point lines of coke and ore during a chute

rotation calculated from simulation model are shown in Fig.17. The distance from falling point of coke to wall is around0.45–0.9 m, but 0.9–1.35 m for ore. Therefore, burden dis-tribution of V shape was thought to be attained in case ofcoke charging.

For the comparison of measured plant data with comput-ed result, the plant data are converted to dimensionless formfirstly as shown below.

The H(4)i value for the last 4 charges are adopted as sum

of each circumferential section value and represented by Eq.(17), Vj is the average volume flow rate of charging materialat charging in jth stock line. This equation is used to calcu-late the dimensionless circumferential height distribution ofthe stock surface at wall side after filling-up.

...... (17)

There are two cases in assumption, one is ore-ignoredcase that means charged ore at maximum tilting angle didn’tcontribute to the burden height at wall side, which is plottedin Fig. 18(a), and the other is ore-considered case thatmeans charged ore at maximum tilting angle contributes tothe burden height at wall side, which is plotted in Fig. 18(b).The dots represent the measured data and are approximatedby the dashed lines in fourth-order polynomial in both Figs.18(a) and 18(b). The simulated results given in solid linesrepresent a case ore-ignored and ore-considered respectivelyin Figs. 18(a) and 18(b). It is clearly observed that the ore-ignored case is in good accordance with the plant measure-ment results. The reason why the contribution of charged

H V C C V O O V C V Oi i i= ⋅ + ⋅ +[ ( ) ( ) ( ) ( )] / [ ( ) ( )]ψ ψ

K V C O V O Ci i i= ⋅ ⋅[ ( ) ( )] / [ ( ) ( )]ψ ψ

i N= 1, ,

Table 5. Patterns of burden charging sequence.

Charging pattern (1) (2) (3) (4)

West bunker Coke Coke Ore Ore

East bunker Ore Ore Coke Coke

Chute rotatingdirection Clockwise Counter-

clockwise Clockwise Counter-clockwise

Fig. 18. The comparison of computed burden height at wall side inthe circumferential direction with the measured one inHongfa No.1 BF of Shasteel. Case(a) Ore contribution tothe burden height at wall side is ignored, Case(b) Ore con-tribution considered.

H

C V C O V O

V C V Oi

i j i jj

j jj

( )

( ) ( ) ( ) ( )

( ) ( )

4 1

4

1

4=

⋅ + ⋅⎡⎣ ⎤⎦

+⎡⎣ ⎤⎦

=

=

∑

∑

ψ ψ

ii N= 1, ,


2185 © 2012 ISIJ

ore to burden height could be ignored at wall-side is becausethe layer thickness of coke charge at wall was thought to besuperior to that of ore charge after the mechanism mentionedabove. We are now going to develop a cylindricallysymmetric burden distribution model of BF and will makethe point more clear in the future.

From Fig. 18, materials charged in the South-West direc-tion are minimum in the circumferential direction, and it isthought that it leads to a dislocation of minimum heightposition at top surface to South-West side. This can explainthe dislocation of center point to South-West side as mea-sured in Fig. 11.

5. Conclusion

In Hongfa No.1 blast furnace, 2 500 m3 in capacity, ofSha-steel, measurements on circumferential imbalance atthe furnace top were done in burden materials filling processbefore the blow-in. A mathematical simulation model wasbuilt to make clear the obtained results quantitatively. Theresults obtained are as follows:

(1) The relationships between the flow rate and the flowcontrol gate opening were measured under different bunker-material combinations, and they are used as input for math-ematical model on circumferential imbalance at the blastfurnace top. It is found that smaller flow control gate open-ing leads to eccentric burden centroid in vertical tube, as aconsequence the circumferential imbalance of both distribu-tions in charging rate and falling point on the stock surfaceoccurs.

(2) The burden trajectory was measured in the blastfurnace during the filling-up of burden before blow-in byusing cross laser beam method and compared with simula-tion results. They are in good agreement with each otherexcept small tilting angle of the chute.

(3) From simulation results, influence of such factors as

flow control gate opening, chute rotating speed, the heightof stock line and tilting angle was quantitatively investigat-ed on the distributions of materials charging rate and fallingpoint.

(4) As for the unevenness in circimferential surfaceheight distribution of burden materials, the uneven heightdistribution occurs in the ordinary operation of paralell-typebell-less top, and the distribution can not be made fully uni-form by making sequential use of bunker change for cokeand ore charge or change in chute rotation direction. How-ever, change of rotation direction is thought to be mucheffective in correcting the unevenness.

(5) In case of the circumferential unevenness of volu-metric ore/coke distribution, application of bunker change inturn at coke and ore charging is an effective method torealize circumferential even distribution of ore/coke.

(6) The distributions of burden heights both at wall sidein circumferential direction and in radial direction at the fur-nace top were measured after the filling-up for blow-in. Theresults coincide well with the simulation results and dislo-cation of the center point at the burden surface wasexplained by simulation results of circumferential heightdistribution.

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3) T. Z. Ren, X. Jin, H. Y. Ben and C. Z. Yu: J. Iron Steel Res Int., 13(2006), No.2, 14.

4) J. Xu and S. L. Wu: Appl. Math. Model, 35 (2011), 1439.5) V. R. Radhakrishnan: J. Process. Contr., 11 (2001), 565.6) M. Kondoh, K. Okabe, J. Kurihara, K. Okumura and S. Tomita: Tetsu-

to-Hagané, 63 (1977), No.11, S441.7) Y. F. Zhao, J. C. Capo and S. J. MaKnight: Proc. of Iron and Steel

Technology Conf., Vol. 1, AIST, Warrendale, PA, (2010).8) R. Yamamoto: NKK Tech. Rep., (1985), No. 106.9) M. Hattori, B. Iino, A. Shimomura, H. Tsukiji and T. Ariyama: Tetsu-

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uneven distribution of burden materials at blast furnace

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