Ore/Coke Descending Melting Behavior - JST

ISIJ International, Vol 31 (1991), No. 5, pp. 505-514

Influence of Ore/CokeDistribution onBurden in Blast Furnace

Descendingand Melting Behavior of

MOrimasaICHIDA, KazuhirO NISHIHARA1),Kenji TAMURA,MasayasuSUGATAand Hajime ONO1)

lronmaking Technology Lab., R&DLaboratories-lll. Nippon Steel Corporation, Edamitsu, Yawatahigashi-ku. Kitakyushu, Fukuoka-ken, 805Japan. 1) YawataWorks, Nippon Steel Corporation, Tobihata-cho. Tobata-ku, Kitakyushu, Fukuoka-ken, 804 Japan.

(Received on October 8, 1990; accepted in the final form on February 25, 1991)

Theinfluence of orelcoke distribution on the descending and melting behaviors of burden wasanalyzed by using a three-

dimensional semicircular warmmodel of the blast furnace under conditions set as similar as possible to the physical

phenomenain the furnace. It is confirmed that the orelcoke largely influences the descending velocity of burden andgas fiow. It is estimated that an increase of +0.1 in the heat-fiow ratio in the wall region of bosh results in adecrease of

about 5'C in the temperature near the reacewayand in the wall temperature of bosh. It corresponds about 80'C in thevalue converted into that of the actual blast furnace based on the Stanton number. In Tobata No. I blast furnace of

Nippon Steel Corp., it is verified that an increase of the orelcoke in wall region results in an increase of the descendingve]ocity in wall region, and the orelcoke and the descending velocity are ones of the main factors which decrease thetemperature in the lower part of the furnace. At the all coke operation, as the wall temperature in the lower part of thefurnace tends to decrease, the orelcoke near the wall should preferably be decreased by the charging of ore closer to thefurnace center. At the operation by injecting a large quantity of pulverized coal, as the melting capacity near the wall is

large, the ore/coke in the wall region should preferably be increased and the ore/coke in the center region should prefera-bly be d~creased by the charging of ore farther from the furnace center.

KEYWORDS:ironmaking process; blast furnace; warmmodel; ore/coke; descending velocity; gas flow; heat-flow ratio;

al[ coke operation; pulverized coal injection operation.

1. Introduction

To stabilize blast furnace operation, it is importantto expand the burden descending region (between thewall and the dead man) in the lower part and securethe smooth descent of burden. In order to do so, it

is necessary to make the radial descending velocitydistribution as uniform as possible and the dead manas small as possible.

On the descending behavior of burden, manystudies conducted using cold modelsl-6) were re-ported. However, a few studies conducted usingquasi-ore warmmodels7~9)on the descending behaviorand melting behavior of burden, were reported, andalmost all of these studies were conducted using sectormodel,7) two-dimensional model8) difiicult to simulatethe descending behavior of burden perfectly.

The authors, therefore, analyzed the influences ofthe ore to coke ratio distribution on the descendingand melting behaviors of burden by charging quasi-

ore of low melting point and coke to a three-dimen-sional semicirclular warmmodel of the blast furnaceunder conditions set as similar as possible to thephysical phenomenain the furnace, especially thedescending and melting behaviors of burden. Simul-taneously with the analysis of the influences of the oreto coke ratio on the descending velocity of burdenestimated along the solid flow lines and the furnacetemperature estimated by infrared radiation thermo-

meter and thermocouples, a theoretical analysis of theinfluence of ore to coke ratio distribution on the gasflow and an analysis of the relation between the tem-peratures in the lower part of the furnace (tempera-ture near the raceway and the wall temperature ofthe bosh) and heat-flow ratio were also conducted.Furthermore, optimumburden distribution in a blast

furnace with normal proflle wasdiscussed.

2. Experimental Method2. 1. Experimental Apparatus

In the experiments using a sector modeland a two-dimensional model, it wasdifiicult to simulate perfect-ly the descending behavior, especially the formationbehavior of dead man, because the descending ve-locity of burden in the center becametoo small dueto the friction force betweenburden and wall.

Fig. I shows the blast furnace three-dimensionalsemicircular modelused for the experiment. Theex-perimental apparatus is a 1/20 scale warmmodelof a4OOOm3class large blast furnace. Aninner wall pro-flle at the time of the blowing-in is as follows; shaft

angle: 81004', bosh angle: 81'07', belly height: 150

mm, bosh height: 200mm, hearth diameter : 690

mm,belly diameter : 756mmand effective heightfrom the tuyere level to the shaft upper end: 1217

mm. Thefront side of the apparatus is madeof heat-resistant glass to permit observation of the descending

C1991 ISII 505

ISIJ International, Vol. 3l (1991), No. 5

and melting behaviors of coke and quasi-ore.

Cokeand quasi-ore (low melting point metal) arecharged layer by layer alternately by the bell andmovablearmors (MA). Air blast heated to 180'C is

blown into the apparatus through 18 tuyeres to melt

and drip the quasi-ore. Molten metal is accumulatedin the hearth and discharged through the taphole.

Coke is transferred into the lower hopper by the six

rotary feeders installed just under the raceway and is

further discharged in to the enclosed container by the

tubular conveyor.Table I showsan outline of the probes for this ex-

perimental apparatus. The temperature, gas pres-

sure, burden pressure and gas flow velocity in the

furnace were measured by thermocouples, pressure

gauges, burden pressure gauges and hot wire anemo-meter, respectively. The temperature distribution in

the furnace (glass surface temperature), scarecely

Movab[e_ Belt ~~ArmorQuas I - ore~~~~~

Shaft ~~~~

Bclly//~:\~~or'~:~rvl:~:ezS'vel ----

DiSdlar9e~'

Ta:~inM:~~j:)e ~osll /ace. Zt~1Tuyere

~iMetal :Coke

Rotary feeder t ~

measureduntil now, wasmeasuredby infrared radia-tion thermometer.

2.2. Experimental Conditions Basedon Modeling Rules

Experimental conditions were determined by intro-

ducing the mechanical modeling rulesro) which candetermine both the descending behavior of burdenand the forming behavior of the raceway and energymodeling ruleslo) which can determine the formingbehavior of the cohesive zone, as shownin Table 2.

Blast volumewasdetermined by Eq. (8) derived fromthe Froude numberin Eq. (3) which determines theforming behavior of the raceway which has an im-portant influence particularly on the descending be-havior and melting behavior of burden in the lowerpart of the furnace.

Table 3shows the values) calculated based on thescale factor, of principal variables of a model at ageometric scale ratio (1'/1) of l/20 and those of anactual blast furnace. Table 4 shows the actual fur-

nace operation conditions adopted to determine theexperimental conditions and also the correspondingstandard experimental conditions.

2. 3. Experimental Samples

Cokeand quasi-ore were used as the experimentalsarnples. The grain size of the coke is 2-4 mm,andthat of the quasi-ore is 1-5 mm. The quasi-ore is amixture of a granular fusible alloy and stearic acid,

and it shrinks in a temperature range of 90-lOO'C,undergoes a large pressure loss in a temperature rangeof 100-1 lO'C, and melts and drips in a temperature

Table l. Outhne of measuring items.

Measuring items Probes Measuring points

(1)

~)

CC@

TemperatureWall

Burden attuyere level

Top gasBurden

Tehrmocouples

Thermocouples

ThermocouplesInfrared radiation

thermometer

8HeightCircumference 14

Radius 7

Radius 7

Tubular Conveyorq~~

(2) Gas pressure HeightPressure gauges(3) Burden pressure Burden pressure Height

at wall gaugesFig. 1. Schematic illustration of three dimenslonal senu (4) Gas velocity at Hot wire anemo- Radius

circular model. top level meter

Table 2. Main dimensionless numbers and scale factors which dominate the physical phenomenainthe lower part of the blast furnace. (Dash (/) indicates the model.)

86

Dimensionless number (1r) Scale factors Remarks

Fi Pf' V~~ F ~ ps'g'l

gFf

_lr2 - F ~ Peg

.(1)

.(2)

= ~-F1't

1r3 Fg

Q-

h7r4 -~ Qc ~

Q,i

= Pfutpc'g'l

h. AO(~

ps' cs ' Vs 'AOi

In" Pln

.(3)

IT5 = Qc Ps ' cs ' AOt

.

(4)

.(5)

_=P__,1_;pj•~-

Vf'

Vf

pe = pc

_=:pf llut

ut 7T'T

.(6)

.(7)

.(8)

lri : Froudep~=ps

IT3 :ut :

IT4 :

number

A0~ h' cg. V~' A0~

AOdA0~

hl'cs' Vs'AOtIns' cs

Aei 11~ 'c!

.

(9)

.(lO)

Froude numberBlast velocity

Stanton numberV~/ Vs= V;/ VfA9i =tm~ to

AO~=Tf ~ tc

506


Table 3. Comparison of principal variables betweenl/20 scale model and actual blast furnace.

BlastRemarksfurnace

4

Variables Scale model

c w

3Superficial gas velocity

Blast velocity at atuyere

Flame temperatureCoke temperature at

a tuyereMelting point of ore

Vf =O.29 m/s

u; =43 m/s

Tf =180'C

t~ = 145'C

t,~* =120'C

Vf = I .39 m/s

ut =174 m/s

Tf =2350'C

tc =1550'C

t~ =1450'C

lrl

It3

7r4

IT5

I

J"2\J.

1

Table 4. Standard experimental conditions.o

Charging patternO: (CoOo)e : (C0020)A : (CzoOo) /A\

// \I J

//--l.~r'~/'

\\

\ \ \1. Bla~t

(1)

(2)

(3)

furnace operation conditions

Productivity coef~icient

Fuel rate

Racewaydepth

2. 5t/(d. m8)480 kg/tp

l.3m

Fig. 2.

O IOO50 150 200 250Distance from center (mm)

Radial distribution of orefcoke layer thickness ratio

(L./L* ).

2. Standard experimental conditions(1) Blast volume(2) Blast temperature(3) Amountof coke discharge(4) Charging number(5) Amountof coke charge(6) Amountof quasi-ore charge

l30 Nm3/hl80'C91 kg/h26 chlh

3. 5kg/ch

l I . 7kg/ch

Table 5, Properties of quasi-ore and coke.

ItemsQuasi-ore

Fusible alloy Stearic acidCoke

(1) Weight composition(2) Melting points(3) True density(4) Bulk density(5) Diameter

92.6 o/o

120- 123'C9. I glcm82.0-2. I glcm33-5 mm

7.4 o/o

65-70'C0.85 glcm30.43 glcm3

1-4 mm

1.09 g/cms0.54 glcm32-4 mm

range around 120'C.10) Table 5shows the composi-tion of the quasi-ore and the properties of the mixedcomponents. The weight ratio of fusible alloy tostearic acid wasdetermined so that the flow rate ratio

of solid to liquid and the bulk density of the packedmaterials approximate the conditions of the actualblast furnace.

2. 4. Experimental Method

The charging and discharging of coke alone werestarted first, and after about 5hwhenthe raising ofthe temperature of the coke and furnace body wascompleted, quasi-ore and coke were charged alter-

nately. Then, temperature and pressure were mea-sured during the time of about I to 2h after start-ing the charging of quasi-ore, whenthe descendingconditions of burden and the furnace temperaturedistribution were judged to have reached almostthe stationary state. The I h meanvalues of themeasuredvalues of temperature and pressure wereadopted as experimental values.

3. Experimental Results andDiscussion

3. 1. Influences of OrelCoke Distribution on the DescendingBehavior and Melting Behavior of Burden

For the charging conditions were selected three

charging patterns (MAnot yet used (CoOo), chargingof ore closer to the furnace center (C0020) and charg-ing ofcoke closer to the furnace center (CaoOo): hereincalled the " charging of ore farther from the furnacecenter "). The suffix used in each pattern is theangle of the plate of the MAwith the vertical plane.As shownin Fig. 2, whenthe MAwas not yet used,the layer thickness ratio of quasi-ore to coke (LOILC'

herein called the " ore/coke ") in the radial directionis distributed nearly uniformly. In the case of thecharging of ore closer to the furnace center, the ore/

coke in the intermediate region is at its maximum,while in the case of the charging of ore farther fromthe center, the ore/coke in the wall region is at its

maximum.Figs. 3and 4 show the influences of ore/coke dis-

tribution on the packed conditions of burden and theretention time (time line). In the case of the nonuseof the MA, the descending velocity distribution ofburden in the shaft was nearly uniform in the radialdirection, but the descending velocity in the centerregion decreased from the upper end of the belly, anddead manwas formed in the region from the middlestage to lower end of the belly. The descending ve-locity near the wall decreased from the lower part ofthe shaft. Themain flow of burden in the lower partof the furnace descendedtoward the raceway throughthe region between the wall and the dead man. Asa result, an inverted V-shaped cohesive zone wasformed. In the case of the charging of ore closer tothe furnace center, the descending velocity from the

center region to the intermediate region, where theore/coke washigh, washigh and the dead mancon-tracted. As a result, a W-shapedcohesive zone wasformed, and unmolten cohesive layers were built onthe deadmansurface. In the case of the charging of

ore farther from the furnace center, the descendingvelocity in the wall region, where the ore/coke washigh, washigh and the dead manexpandedupward.As a result, an inverted U-shapedcohesive zone wasformed, and its root wasenlarged. At the sametime,unmolten materials flowed into the raceway.

507


(1) Charging pattern (2) Charging pattern(CoOo) (C0020)

(3) Ch~r9ing pattern(C200Q)

Fig. 3.

Influence of Lo/Lc distribution on cohe-sive zone profile and dead manprofile.

o' o'

10' Io'

20'20+

30'

40' ' 30'

50'40'

,B 50'

o BTuye_re70' A Tuyere 70' A -

Dead' man Dead'man(1) Charging pattern (2) chargjn9 pattern

(CoOo) (Co020)3.2. Influences of OrelCoke Distribution on Temperature

Distribution in the Furnace

Fig. 5showsthe relation between the ore/coke dis-

tribution and the temperature distribution in the10wer part of the furnace measuredby infrared radia-tion thermometer. Figs. 6and 7showthe influencesof ore/coke distribution on the radial distribution ofthe temperatute of burden at the tuyere level andvertical distribution of wall temperature.

In the case of the nonuse of the MA, the regionsurrounded by the inverted V-shaped cohesive zoneand the dead manwith the tuyere as its center wasthe high-temperature region. The temperature ofpackedbedwasnearly uniform in the radial direction

at the tuyere level and was lower in the center regionof the furnace. The wall temperature sharply in-

creased from the lower part of the shaft.

In the case of the charging of ore closer to the fur-

nace center, the temperature of the wall region, wherethe ore/coke was low, was 10 to 20'C higher through-out the furnace height than that in the case of the

nonuseof the MAand the temperature of packedbedat the tuyere level wasalso high in the wall region.

In the case of the charging of ore farther from thefurnace center, the temperature of the wall region,

where the ore/coke was high, was 20 to 30'C Iowerthroughout the furnace height than that in the caseof the nonuseof the MAand particularly in the bosh,

and the temperature ofpacked bed at the tuyere level

wasalso low in the wall region.

10'

20*

Deadman:Region defined by the isochronal line

B at the time of 70 min

Tuye_r~ 70' Az Deadzone A+sluggishly descending

~ zone BDeadman Fig. 4.

(3) Charq_in9 pattern Influence of L~/L, distribution on bur-

(C20Oo) den descending.

3.3. Influences of OrelCoke on the Descending Velocity ofBurden and the Temperature of the Loz()er Part of the

Furnace

3.3. I .DescendingVelocity Calculation Method

To calculate the descending velocity of burden,solid flow lines were assumedas shown in Fig. 8.

Burdenwasassumedto descendas follows:(1) In the shaft, burden descends along the flow

lines which have as their point of origin, the vertexof the imaginary cone defined by the wall.11)

(2) In the belly, burden descends along the flowlines which are parallel to the wall.

(3) In the bosh, burden descends along the flowlines which connect the points of the intersection offlow lines on the lower end of the belly or on the sur-face of the deadmanto the tip of tuyere nose.

Thedescending velocity Vwascalculated by divid-ing the descending distance of burden along the aboveflow lines by the descending time and the relative

descending velocity V/V..., wascalculated as the ratio

of the descending velocity Vto the average descendingvelocity V*.... The descending velocity V(0-30) inthe shaft is the descending velocity calculated from thetime lines at the times of Oand 30 min, and the de-scending velocity V(30-60) in the lower part of thefurnace is the descending velocity calculated from thetime lines at the times of 30 and 60 min.

3.3.2. Influence of Ore/Coke Distribution on De-scending Velocity Distribution

Fig. 9 shows the relation between the ore/coke

508

ISIJ International, Vol. 31 (1991), No. 5

lOO.OOac

90 .OOoC

80 .OOoC

70 . OO'C60 .

OOoc50 . OOoc40,. OO'C

Fig.

(1) Charging pattern (2) Chargin9 pattern (3) Charging pattern(Co020)(CoOo) (C2000)

5. Relation between L~/L* distribution and temperature distribution in the lower part of blast furnace model.

Fig. 6.

c W200

p l'-4('L

150 / ''

.

:,

~ ~~~,o

Lo'2 100ECharging pattern(,

~ O : (CoOo)ccu 50 e : (C0020)E

A : (C2000 )1~,o(D

Q O 3002001OOODistance from center (mm)

Influence ofLo/Le distribution on radial distribution

of deadmantemperature at tuyere level.

EE- 10001)

Lo~vEoL

oo'10

~v'

S

1000

500

O

Char9in9 pattern' \ O : (CoOo)\ e : (C0020)

IL~ A : (C2000)

~. \\

150100O 50Wall temperature (~C)

~lL\lt1L\

o'

lDeadman

30'

60'

Tuyere

Fig. 7. Influence of Lo/Lc distribution on wall temperaturedistribution.

distribution and the relative descending velocity VlV^**. distribution of burden in the shaft and the lowerpart of the furnace and Fig. 10 showsthe influence ofrelative ore/coke near wall calculated as the ratio ofthe ore/coke near wall to the average ore/coke (herein

called the " relative ore/coke in the wall region ") onthe relative descending velocity of burden near wall(herein called the " relative descending velocity in

the wall region ").

In both the shaft and the lower part of the furnace,

there is a positive correlation between the relative

descending velocity and the relative ore/coke, and in

regions where the relative ore/coke is high, the rela-

tive descending velocity is high, and the influence is

large particularly in the lower part of the furnace.

Fig. 8. Assumedsolid flow lines

As shownin Eq. (11) in the shaft and in Eq. (12)

in the lower part of the furnace, as the relative orel

coke in wall region increases, the relative descendingvelocity in wall region increases.

In the shaft,

V~/V.... =O918+0070((L./L.)~/(L./L ) )' "~"' '

r = 0.926....

.........(1 1)

In the lower part of furnace,

V~/V.~.. = l, I II+0 125((L jL.)~j(L~/L ) )' "~*' ,

r=0.989 .............(12)

It is suggested as one of the reasons that in the highore/coke region the descending velocity increases dueto the high velocity of the softening, contracting andmelting of quasi-ore layers. It is supported by theexperimental facts in Fig. 9 that the descending ve-locity distribution in the case of the alternate chargingof quasi-ore and coke shows a larger radial changethan that in the case of the single charging of coke.

3.3.3. Influence of DescendingVelocity Distribution

on the Temperature of the Lower Part of the

FurnaceFigs. II and 12 show the influence of relative

509

ISrJ International, Vol. 3l (1991), No. 5

;~

c'el~~la'~ *~O' .sta)

'H >1:'c~'

~fl\

,L)\0.8

c"f\(a' ~~ 0.61:'

e'O:)\J'~ :>~Jcl~

*~~

1.6

1.4

1.2

10 ~(

0.8 -ipCharging pattern

0.6 o: (CoOo)0.4 e: (Co020)

A: (C2000)02 x : Cokealone

oo 50 100 150 200 250

Distanoe from center

c W l~ n.~ 25~

'~~~:'~ 200e)c!)GeL1 150

hcee.$::1 100,a.

~:s~'c:' 50

y(L,

,~e)~ O~

O:

e:

\ \e\\~.~

\\e\

Shaft zone(between Omin andBelty and bosh zones(between 30 min and

30 min)

60 min)

V(0-30)/Vave.

;~ 16

~)/~ 14o '

-1_''l)

:) 12

~e)~':)

1.01:~>~:~ 0.8e'c:)':"" nl:t1:' I u'u,:'~:~*~ 0.4~;>ee

0.2I~c~':

O

c

(1)

(mm)Relative descending velocitybetween Omin and 30 uiln

Shaft zone

W_-I~

Fig.

~-~~/

lxll// '

x--/-x /'::~/

:~~~'4

Charging patternO: (CoOo)e : (C0020)

A : (C2000)x :Coke alone

O 50 1OO 150 OO 250Distance from center (mm)

V(30 60)/Vave. : Relative descending velocitybetween Omin and 30 min

(2) Belly and bosh zonesRelation betweenLo/Lc distribution and radia] dis-

tribution of relative burden descending velocity (VlV*+e.)'

0,5 1.0 1.5

Relative descending VeIOCity in Wall regionVW/Vave. (-)

11.Influence of relative burden descending velocity

in wall region on temperature near raceway.

/~250

Q~\J

200

Fig. 9.

~ 150c!'h

e),:~,:,Ei 100

~'

- 50c~'

~:

O

O:elA:

>.~

1.5~'cL)

or~*-1aL)~J

+Jc~ 'e)(L' O'!) >

1,

elc:s(:')>~'\>cL)

>~Jce O,5-~(L)c~:

Shaft zoneBetly zoneBosh zoneTuyere zone \\:'\.

~~t \1'~' '\' ~~l~

oe

~Eq

l'leCf Eq

-CrShaft zone(between Ou]in and 30 R]in)

Oel ly and bosll zones(between 30 min and 60 mim)

.(12)

.(11)

Fig. 10.

O 1 2 3Relative ore/coke layerthicklleSS ratio(Lo/Lc)/(Lo/Lc)ave. (-)

Influence of relative L~/L, in wall region on rela-

tive burden descending velocity in wall region.

descending velocity of burden in the wall region onthe temperature of the lower part of the furnace (tem-

perature near the raceway and the wall temperatureof bosh, respectively), which is an important processvariable for the stable operation of the blast furnace.

The relative descending velocity in the wall regionlargely influences the temperature near the racewayand the wall temperature of bosh. An increase of+0.1 in the relative descending velocity in the wallregion of the belly and the bosh results in a decrease

Fig.

0,5 1.0 1.5

RelatiVe deScending VeIOCity in Wall regionVW/VaVe. (-)

12, Influence of relative burden descending velocity in

wall region on wall temperature.

of about 15'C in the temperature near the racewayand in wall temperature of bosh. This experimentalvalue of the temperature difference of about 15'C,whenconverted into the value of the actual blast fur-

nace by the conversion Eq. (13) shownbelow based

on the Stanton numbershownas Eq. (4) in Table2, corresponds to a temperature difference of about200'C. In Eq. (13), the term of the numerator is the

temperature difference Aea between the flame tem-perature at the tuyere nose of the actual blast furnaceand the melting point of burden, and the term of thedenominator is the temperature difference betweenthe blast temperature of the model and the meltingpoint of quasi-ore.

2350- 1450 Ae(~

180-120 ~ 15 '""""'(13)

Figs. 13 and 14 show the influence of ore/coke in

the wall region on the furnace temperature in the10wer part of the furnace. The ore/coke in the wallregion influences largely the temperature near the

racewayand the wall temperature of each zone.

3.4. Influence of OrelCoke Distribution on the GasFlowSince it is difficult to accurately measure the gas

flows in the packed bed in the blast furnace three-dimensional semicircular model, the gas flow velocity

510


in the model was estimated by theoretical analysis,

and the influence of the ore/coke on the gas flow wasanalyzed.

For the gas flow mathematical model, the gas flowlines were obtained by numerically integrating a par-tial differential equation of second order expressedby the flow function ip, based on tne model by Sugi-

yamaand Sugatal2) which was obtained by makingsimultaneous a continuous equation as shownin Eq.(14) and Ergun's two-dimensionally expandedequa-tion for pressure drop as shownin Eqs. (15) to (17).

r~(G.)+~(rG.)= O .....

........(14)

-grad P= (fl+f2 1GDG...............(15)

~p 250~;htl'

~e)ocT~

~~c:'

a,f::2

'l)

~cey(LJ

C~~a)

~Fig. 13.

200

150

100

50

o

o\

r~o(:)

\J

aJ~;:,+-ce~cL)

~LF~(:J

+-

ce~

O 1 2 3Lo/Lc in Wall region (-)

Influence of Lo/Lc in wall region on temperaturenear raceway.

250

200

150

1OO

50

o

O: Sl]aft zonee : Bel ly zoneI : Bosh zone

~L A : Tuyere zonc~"-L~__-{II_

-- J'_ J]1 -~ _

~ ~~1L__~e----_ ~\

_J)- - - -*

-1___'~

~~~o~\\~~

Fig. 14.

O 1 2 3LO/Lc in Wall region (-)

Influence of L~/L, in wall region on wall tempera-ture.

Fig. 15.

Influence of LolLcflow.

distribution on gas

Shart middle-

Shaft bottonl'- !BeIIy

Bel IyBosh bottom-

(1 -e)2fl = 150

g.(cdp)2e3pf P ••••••••••(16)

1-sf2 = I.57g*(ipdp)e3pf " "" "

'(17)

In calculating the gas flow lines, experimentalvalues were used for the shapes of the coke layer, orelayer, cohesive zone and the dead man. The voidfractions of the coke layer and ore layer were set at0.51 and 0.45 basedon the experimental results. Thevoid fraction of the raceway was set at 1.4 timesl3)

that of the coke layer and the void fraction of thecohesive zone was set at 0.7 timei4) that of the orelayer. The void fraction of the dead manwas as-sumedat 0.9 time that of the coke layer based on theknowledgel5) that more than 10 o/o flne coke exists inthe deadman.

Fig. 15 shows the resu].ts of the calculation of gasflow lines. In any case of charging conditions, the

gas flow lines in the lump zone were spaced equallyapart, and the gas flow velocity was nearly uniformin the radial direction. The influence of the ore/cokedistribution on the gas flow velocity was large in thecohesive zone and the regions underneath it (dripping

zone and dead man). In the case of the nonuse ofthe MA,in which an inverted V-shapedcohesive zonewasformed, as the permeability resistance of this zonewaslarge, the gas from the tuyere went around its rootand flowed out into the lump zone through the cokeslit. In the case of charging ore closer to the furnacecenter, in which a W-shaped cohesive zone wasformed, a part of the gas from the tuyere flowed outalong the wall into the lump zone. In the case ofthe charging of ore farther from the furnace center,in which an inverted U-shaped cohesive zone wasformed, the gas from the tuyere went around the cohe-sive zone and toward the center region of the furnaceand flowed out into the lump zone through the cokeslit.

Fig. 16 obtained based on the calculations shownin Fig. 15 shows the influence of the ore/coke in thewall region on the gas flow velocity in the wall regionof bosh. The influence of the ore/coke in the wallregion on the gas flow velocity in the wall region of

~r=0. 9963W=0.9688W=0.9182

i W=0.8299W5:o. 7188 1

{ W=0.5799•:,

(. ~~ ,f

l\\i,

~Cohe~i\

liddle-

ottonl'-

e

i,.

~ Cobesive ~ Cohesiv ey top- zone one i l

~ }~:~~T'

;'! ~

=};',t~

*

:"b~ad '~an

*~j '~ ?~~*;1~;:~~'~,!!~:"!':

bottOnl- : ' '~"!

t t: tl *i:

f.'~

It.'

ottom ~~~ ,Racewayi aTuye re- ' D~ad man Raeeway

~~..,~' .{. 1~~')i' l

;~

(1) Charging pattern (2)

(CoOo)Charging pattern (3)

(C002o)

Cohesive

{-

Reiceway

Charging pattern(C2000)

511


e:1

O~0/~'a'C'!~\~J~~:

'-1~.FI

~,a.~'F:I'-1 OC'~'lO•-1/::'l)e">0~,C"CE'tH

CJ:CD

0.5

o.4

O.3

0.2

O.1

o

e(c o )o 2o

e(c o )oo

(c200o )

o 1 2 3Relative ore/coke layer thickneSSratio in wall region

(Lo/Lc)w/(Lo/Lc)ave. (-)

Influence of L~/L* in wall region on gas velocity in

wall region of bosh zone.

180

~)

150

1'

5+~aEh 100 O:

e:

(c o )O o 2Q

(c o )o oO

\\ .'

\(co 02o) \\e \\

(c o ) \Q o \ \ \Temperature near racewayWa[1 temperature at bosh

\

(c o )20 o

\ \(c2000 )

Fig. 16.

both was large, and the gas flow velocity in the wallregion of bosh decreased with increasing the ore/cokein the wall region.

3.5. Relation betweenHeat-flow Ratio and Temperature in

the LowerPart of the Furnace

As described in Secs. 3.3 and 3.4, the temperaturedistribution in the furnace is influenced by not onlythe descending velocity distribution of burden but also

the gas velocity distribution. Therefore, the relation

between the heat-flow ratio expressed by Eq. (18) andthe temperature in the lower part of the furnace wasalso analyzed.

Heat flow ratio =c*•G* c*'p*' V*

..(18)cf ' Gf cf ' pf ' Vf

In the analysis, for the descending velocity wasusedthe experimental value obtained in Sec. 3.3, and for

the gas flow velocity was used the value calculatedfrom the mathematical model obtained in Sec. 3.4.

For the physical property values of burden and gaswere used the values at 90'C.

Theheat-flow ratio largely influences the tempera-ture near the raceway and the wall temperature atbosh as shown in Fig. 17. An increase of +0.1 inthe heat-flow ratio in the wall region of bosh results

in a decrease of about 5'C in the temperature nearthe raceway and in the wall temperature at bosh.

The experimental value of temperature difference ofabout 5'C, whenconverted into the value of the ac-tual blast furnace basedon the Stanton numbershownas Eq. (4) in Table 2, is about 80'C. In actual blast

furnace operation, the heat-flow ratio in the wall re-gion is also considered to be an important meansofcontrol for the temperature near the racewayand thewall temperature in the lower part of the furnace.

4. Relation amongOrelCoke, Descending Ve-Iocity, and Temperature in the Lower Partof Actual Blast Furnace

Fig. 1816) shows the relation between the relative

Fig.

O 0.5 1,0 1.5

Heat flow ratio (- )17, Influence of heat flow ratio in wall region of bosh

zone on temperature near raceway and wall tem-perature at bosh.

1.15~ l~,

Eq.(19)

'F4 I~)o I l

r-1.1- ~~rJl- I

q) I;) l l

\J Ieec~ l I1.

05 I l1:' ~ei lF:: I l I,aDsl> ~. I ll I

~oc:sC,e "H P\CLD eGr1:; (:J\ 1 ,II I

y~ IcL) ;>>'~

ll

',~ r~~'cece ~: O(J5 ,,

I I : Monthly data-~CL)F:~ 1986. 1-1990. 7p:~ •~4

0.9r;

Fig. 18.

(19)

O,Jr 1 1.5 2 2.5

Relative ore/coke in Wall region(.O/Ow/(O/Oave_ (-)

Relation between relative ore/coke and relative

descending velocity in wall region of Tobata No. 1blast furnace.

ore/coke and the relative descending velocity in thewall region (between wall and less than I mfrom wallat top) of Tobata No. I blast furnace. Both thevalues were measured by the profilemeter installed

in the top of the furnace. Betweenboth the values,

as shown in Eq, (19), there is a positive correlation,

and an increase of +0.1 in the relative ore/coke in thewall results in an increase of +0.008 in the relative

descending velocity in the wall. This result is almostthe sameas the experimental result in Fig. lO.

Vw/V..e. = 0.954+0.082 ((O/C)~/(O/C)..e.)'

r=0.749......

.........(19)

In actual blast furnaces, the temperature of AB2,which is the difference between the temperature in

stave at bosh and the temperature of water supplied

to the stave at bosh, is influenced not only by theore/coke and the descending velocity in the wall re-gion but also by another operation factors. Then,Eq. (20) was obtained by the multiple regressionanalysis (stepwise), where the blast furnace operationfactors are independent variables and the descending

512


velocity in the wall region is included by the ore/cokein the wall region (O/C)~.

ABZ= 0.9 1(HFR)- 32.38(OIC)~+ I . 121(OilR)

+0.775(pCR)-3 13.7,

5. OptimumBurden Distribution Based onKnowledgeObtained from the Blast FurnaceThree-dimensional Semicircular Model Ex-perlment

Based on the knowledge obtained from the blast

furnace three-dimensional semicircular model experi-

mentdescribed in Chap. 3, optimumburden distribu-

tion in a blast furnace with normal profile was con-sidered.

In the case of the charging of ore closer to the fur-

nace center, the temperature in the wall region in-

creases due to the decrease in the orelcoke and theheat-flow ratio in the wall region. Therefore, thecharging of ore closer to the furnace center is effective

in preventing the lowering of temperature in the wallregion at the all coke operation. However, ifthe orel

coke in the intermediate region is raised too high,

manycohesive layers are accumulated on the dead

mansurface and the dead manbecomesprobably in-

active because its temperature decreases due to theabsorption of heat by the direct reduction reaction ofthe cohesive layers and also due to the poor per-meability of the deadman.

In the case of the charging of ore farther from thefurnace center, the descending velocity in the wallregion increases due to the increase in the ore/coke in

the wall region and at the sametime a solid root ofthe cohesive zone becomes large. Therefore, thecharging of ore farther from the furnace center is ap-plicable at the time of operation by injecting a largequantity of pulverized coal, in which the melting ca-pacity near the wall is large.

Although optimumburden distribution varies ac-cording to the blast furnace operation conditions, asdescribed above, a local increase in the ore/coke is notdesirable in any burden distribution because it brings

a local increase in the descending velocity and heat-flow ratio and decreases the temperature of the lowerpart of the furnace. In the case of the radially uni-form ore/coke distribution, on the other hand, theradial descending velocity distribution and tempera-ture distribution do not decrease locally. Therefore,although the optimumvalue of the ore/coke in thewall region varies according to the injection quantityof pulverized coal and other auxiliary fuels, the radial

ore/coke distribution controlled as uniformly as pos-sible is basically important for the stabilization of blast

furnace operation without lowering the temperaturein the lower part of the furnace.

6. Conclusion

The influences of the ore/coke distribution on thedescending and melting behaviors of burden were

analyzed by using a three-dimensional semicircularmodel of the blast furnace under conditions set assimilar as possible to the physical phenomenain thefurnace, and the following knowledgewasobtained.

(1) In the case of the radially uniform ore/cokedistribution, the descending velocity distribution inthe shaft is nearly uniform in the radial direction, andan inverted V-shapedcohesive zone is formed.

(2) In the case of the charging of ore closer to thefurnace center, the dead mancontracts, a W-shapedcohesive zone is formed and the temperature in thewa]1 region increases.

(3) In the case of the charging of ore farther fromthe furnace center, the dead manexpands, an in-

verted U-shapedcohesive zone is formed and the tem-perature in the wall region decreases.

(4) As the ore/coke is locally increased, the de-scending velocity of burden in that region increases,

and the gas flow velocity in the lower part of the fur-

nace decreases. Anincrease of +0. I in the heat-flowratio in the wall region of bosh results in a decrease ofabout 5'C in the temperature near the raceway andin the wall temperature of bosh. (It corresponds toabout 80'C in the value converted into that of the ac-tual blast furnace basedon the Stanton number.

(5) In Tobata No. I blast furnace, it is verifiedthat an increase of the ore/coke in the wall region re-sults in an increase of the descending velocity in thewall region, and the ore/coke and the descending ve-10city are ones of the main factors which lower the

temperature of AB2, which is the difference betweenthe temperature in stave at bosh and temperature of

water supplied to the stave at bosh.(6) Optimumburden distribution differs to blast

furnace operation conditions.(i) Although the optimumvalue of the ore/coke

in the wall region varies according to the injection

quantity of pulverized coal and other auxiliary fuels,

control of the radial ore/coke distribution as uniformas possible is basically important for the stabilization

of blast furnace operation without lowering the tem-perature in the lower part of the furnace.

(ii) At the all coke operation, as the wall tem-perature in the lower part of the furnace tends to de-

crease, the ore/coke near the wall should preferablybe decreased by the charging of ore closer to the fur-

nace center.(iii) At the operation by injecting a large quantity

of pulverized coal, as the melting capacity near thewall is large, the ore/coke in the wall region shouldpreferably be increased and the ore/coke in the cen-ter region should preferably be decreased to improvepermeability by the charging of ore farther from thefurnace center.

Nomenclaturecf: Speciflc heat ofgas (J/(kg'K))c*: Specific heat of packed materials (coke) (J/

(kg ' K))dp: Average diameter ofpacked materials (m)Ff: Frictional force ofpacked materials (N)Fg: Gravitational force (N)

513


Fi:Fit:

Gf :Gg:

G.:

Gz:

g:

g. :HFR:

h:

l:

02:OilR :

P:PCR:

Q, :Qg:

QA:

Tf:t* :t~ :to :ut:Vf:V,:

VBG:z:

AOd:

Aei :1~:

ke:

p*:

Inertial force ofgas (N)Inertial force ofblast (N)

massvelocity of gas (kg/(m2.s))

massvelocity of packedmaterials (kg/ (m2. s))

mass velocity of gas in horizontal direction(kg/ (m2.

s) )massvelocity of gas in vertical direction (kg/

(m2.s) )

Gravitational acceleration (m/s2)

Conversion factor (kg'm/(s2.N))Fuel rate corrected by b]ast temperature,blast moisture, auxiliary fuel rate, ash in cokeand slag volume (kg/t)

Heat transfer coeflicient between particles

and fluid (W/(m2.K))Representative length (m)Oxygenvolume (Nm8/h)Oil rate (kg/t)

Gaspressure (Pa)Pulverized coal rate (kg/t)

Heat accumulated in packedmaterials (J)

Heat transferred from gas to packed materials

(J)

Heat offusion of cohesive materials (J)

Distance in horizontal direction (m)Flametemperature ('C)

Coketemperature at tuyere level ('C)Melting point of ore ('C)Softening temperature of ore ('C)Blast velocity at tuyere level (m/s)

Gasvelocity (superficial gas velocity) (m/s)

Velocity of packedmaterials (m/s)

Boshgas volume (Nm3/min)Distance in vertical direction (m)Void fraction (-)Temperature difference between gas andpackedmaterials ('C)

Temperature rise of packedmaterials ('C)

Heat of fusion of cohesive materials (J/kg)Viscosity of gas (Pa '

s)

Coefficient ofinternal friction (-)

ITi: Dimensionless numberPe' Pf' P,n' Ps: Density of coke, gas, cohesive mate-

rials and packedmaterials (kg/m8)ip : Shapefactor (-)

c(~r) : Flow function (kg/s)

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Tetsu-to-Hagand, 67 (1981), S23; Trans. Iron Steel Inst. Jpn,,

21 (1981), B423.2) M. Shimizu, A. Yamaguchi, S. Inaba and K. Narita:

Tetsu-to-Hagan~, 68 (1982), 936.

3) H. Sato, T. Sugiyama.M. NakamuraandY. Hara: Tetsu-

to-Hagand, 66 (1980), S634; Trans. Iron Steel Inst. Jpn., 21(1981 ). B50.

4) T. Miyazaki. Y. Kajiwara and T. Jinbo : Tetsu-to-Haganl,

66 (1980), S91; Trans. Iron Steel Inst. Jpn., 20 (1980), B495.5) M. Shimizu, Y. Kimura, M. Isobe, C. Cheand S. Inaba:

Tetsu-to-Hagani, 73 (1987), 1996.

6) K. Mio, H. Nakanishi, M. Kuwabara and I. Muchi:Tetsu-to-Hagan~, 69 (1983). S6.

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8) M. Ichida. K. Tamuraand Y. Hayashi and M. Sugata:

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Ore/Coke Descending Melting Behavior - JST

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