Journal of Materials Journal of Materials Journal of Materials Journal of Materials Sciences and ApplicationsSciences and ApplicationsSciences and ApplicationsSciences and Applications

2015; 1(1): 1-10

Published online January 20, 2015 (http://www.aascit.org/journal/jmsa)

Keyword Blast Furnace Hearth,

Wall Shear,

Flow Field,

Slag-Pig

Received: December 05, 2014

Revised: January 09, 2015

Accepted: January 10, 2015

Analysis of flow field of before and after slag-pig form accumulation in blast furnace

Xuewu Feng, Yan Jin, Yang Li, Zhengsheng Chang, Changgui Cheng,

Yelei Jin

Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of Education, Wuhan

University of Science and Technology, Wuhan, China

Email address fengxuewu910102@126.com (Xuewu Feng)

Citation Xuewu Feng, Yan Jin, Yang Li, Zhengsheng Chang, Changgui Cheng, Yelei Jin. Analysis of Flow

Field of before and after Slag-Pig Form Accumulation in Blast Furnace. Journal of Materials

Sciences and Applications. Vol. 1, No. 1, 2015, pp. 1-10.

Abstract The flow of hot metal in blast furnace hearth has the wall shear on the BF hearth and

furnace bottom, which results in erosion. Based on the theory of fluid mechanics, a

three-dimension mathematical model was found for erosion of hot metal in blast furnace

hearth, and model was built after slag-pig form accumulation. Using CFX software

researches in hearth‘s wall shear in different periods and the streamline diagram on

different positions. The results indicate that the largest wall shear presents near the taphole

in hearth; and wall shear increases after slag-pig form accumulation; the hot metal ‘s

velocity decreases slag-pig form accumulation.

1. Introduction

The wear of hearth refractories is widely recognized as the main limitation for a long

campaign of blast furnace life , the flow induced shear stress on the wall of the blast

furnace hearth have important effect upon the erosion in the hearth. Peters et al. and Gauje

et al. have studied the flow pat-tern in the hearth experimentally and numerically,

respectively, without paying much attention to the stress distribution on the wall [1]

.

Although Venturini et al. and Torrkulla et al. have carried out computational fluid

dynamics studies of the blast furnace hearth, they do not discuss the effect of flow induced

stresses on the wall of the furnace [2]

. Vats and Dash have computed the wall shear stress by

solving the flow field and have concluded that there exists an optimum taphole length for

minimum wall shear stress [3]

. The research on the furnace of 1750 m3 in certain factory is

done. The research is based on the related theory of the hydromechanics, and the

three-dimensional mathematical model is established. According to different periods of

the blast furnace hearth’s different situations of erosion, mathematical model of deadman

and different sizes of the hearth are constructed and analyzed.

With the existence of hot metal circuiting flow around deadman, when blast furnace

hearth drainage, the hot metal flow along deadman in circuiting flow. Especially when the

depth of deadman shallows ,the permeability of it deteriorates, and the deadman sits on the

bottom of hearth, the erodent effect will increase ,where is circuiting flow on the sidewall

of hearth , the junction of the hearth sidewall and the hearth bottom. It presents severe

erosion liking the elephant's foot, where are the sidewall lining of hearth and the wall

lining of the junction. After the slag-pig form accumulation, it has influence of blast

furnace hearth wall shear. So the paper compares the wall shear and flow field to two

conditions, which are after and before slag-pig form accumulation.[4-6]

2 Xuewu Feng et al.: Analysis of Flow Field of before and after Slag-Pig Form Accumulation in Blast Furnace

2. Model Description

Fig.1 and fig.2 is the external contour model, those are a blast

furnace hearth before and after formation of slag. The size of

hearth will be certainly changed. The reason is that the erosion

in different degrees and periods is not same. Hot metal flow in

hearth to the steady state method, and in hearth there is a

deadman, the deadman link up the whole hearth and different

periods have different radius, The remaining area in hearth is

the coke free zone. The internal structure of hearth will change

in periods of before and after the formation of slag, and the

degree of clay brick erosion is not same in different time.

Fig. 1. The natural diagram of solid zone and liquid zone in the hearth

Fig. 2. The formation of slag’s diagram of solid zone and liquid zone in the

hearth

3. Assumed Conditions

(1) The speed of inflow of hot metal should vertical the

entrance.

(2) Hot metal in hearth is incompressible fluid.

(3) Ignore the physical and chemical reaction between the

refractory and hot metal.

4. Mathematical Model

The governing equations for fluids flow used in the

three-dimensional mathematical model are based on the

equation (1)–(6).

Continuity Equation:

j

j

x

pu

∂∂ )(

(1)

Where, p is fluid density (kg/m3); ju is mean velocity

represent by tensor (m/s); jx is coordinate value in j direction

(m).

Momentum conservation equation:

m

i

j

j

i

jij

jiS

x

v

x

vu

xxp

p

x

vv+

∂∂

+∂∂

∂∂+

∂∂−=

∂

∂ )( (2)

Where, iv , jv is speed in i , j direction (m/s); ix , jx is

coordinate value in i , j direction(m); u is effective viscosity

coefficient; mS is resistance of hot metal flow though

dead-man.

( )( ) i

pp

im uv

dp

d

uvS

εε

εεε −+−= 1

75.11

15023

2

(3)

Where,ε is porosity; pd is the average particle diameter of

the iron ore(m);

The loss coefficient of the viscous and inertial resistance in

each direction is:

2

32

)1(150 εε

α−

= pd (4)

( )32

15.3

εε

pdC

−= (5)

( )( )

( )d

pv

d

vu

H

p AA

φωε

φωω 2

323

21

75.11

150−+

′−=∆ (6)

Where, p∆ is pressure difference between tuyere level and

the bottom of hearth; H is distance between tuyere level and

the bottom of hearth; Av is The flow rate of the fluid is

calculated in accordance with the cross-sectional area; d is

particle diameter; u ′ is fluid viscosity;φ is the shape factor

of the particles.[7-10]

5. Boundary Conditions

The entrance velocity is the reducing rate of the liquid

level, the velocity is calculated daily production and time of

hot metal. Taphole angle is 10 degrees, the two tapholes are

symmetrical distribution. Therefore, only need to simulate a

taphole tapping position. The application of numerical

simulation is ANSYS-CFX fluid simulation tool, it provides

Navier-Stokes equation based on finite element method, the

computational domain is marked off three-dimensional

tetrahedral mesh, and mesh number is about 200 thousand.

deadman in hearth is set in the porous medium, considering

the flow of molten iron in the simulation process, and the

temperature of molten metal is constant. Taphole has only

hot metal and not coke. The temperature of hot metal is set at

1450℃, all walls are set to no slip. Calculation of fluid near

the wall in the viscous sublayer uses wall function method,

the viscosity coefficient is 0.00715 Pa •s. The porosity is

0.45, the heat capacity is 850J/kg-K. The heat conduction

coefficient is 33W/m-K.

Journal of Materials Sciences and Applications 2015; 1(1): 1-10 3

6. Results and Discussion

6.1. Analysis Simulation of Normal Blast

Furnace Hearth

From fig.3 to fig.6 we can know, when the invasion depth of

hearth brick is changed, the velocity vector in the level of

taphole will change in different degree, and the circulation

phenomenon can be seen. When depth of erosion changes in

hearth, the size of deadman will change. The reason of

circulation phenomenon is that coke porosity distribution is

not uniform , hot metal tends to flow into the larger porosity of

the region, and then flow into the taphole, resulting in hot

metal circulation phenomenon. As shown in Fig.4 and Fig.5,

the circulation phenomenon of hot metal tends to a side. The

reason is that the change with the invasion depth, it has

influence on the middle deadman , resulting in hot metal ‘s

side of circulation .

Fig. 3. The velocity distribution of horizontal section through the center line

of taphole

Fig. 4. The velocity distribution of horizontal section through the center line

of the first layer of clay brick invasion taphole

Fig. 5. The velocity distribution of horizontal section through the center line

of the second layer of clay brick invasion taphole

Fig. 6. The velocity distribution of horizontal section through the center line

of the third layer of clay brick invasion taphole

Fig. 7. The velocity distribution in vertical plane

4 Xuewu Feng et al.: Analysis of Flow Field of before and after Slag-Pig Form Accumulation in Blast Furnace

Fig. 8. The velocity distribution in vertical plane of the first layer of clay brick

invasion

Fig. 9. The velocity distribution in vertical plane of the second layer of clay

brick invasion

Fig. 10. The velocity distribution in vertical plane of the third layer of clay

brick invasion

From fig.7 to fig.10 we can know, flowing to the taphole in

hearth do not have obviously mixed flow phenomenon. When

the erosion of clay brick degree unceasingly changes, central

position of hot metal flow appears arched streamline.

Fig. 11. The level streamline chart of hearth

From fig.11 to fig.14 we can know, the depth of clay brick

invasion in hearth is different , hearth streamline chart also

shows the circulation phenomenon in different degree, more

invasion and more fuzzy circulation phenomenon. In the

central deadman position also appears flow of hot metal ,the

reason is that the upper deadman has big porosity ,so the

retention effect is not strong for the hot metal .

Fig. 12. The level streamline chart of the first layer of clay brick invasion

hearth

Fig. 13. The level streamline chart of the second layer of clay brick invasion

hearth

Journal of Materials Sciences and Applications 2015; 1(1): 1-10 5

Fig. 14. The level streamline chart of the third layer of clay brick invasion

hearth

Fig. 15. The distribution of hearth wall shear

Fig. 16. The distribution of hearth wall shear of the first layer of clay brick

invasion

Fig. 17. The distribution of hearth wall shear of the second layer of clay brick

invasion

Fig. 18. The distribution of hearth wall shear of the third layer of clay brick

invasion

From fig.15 to fig.18 we can know, in the case of different

erosion, hearth wall shear gradually decreases, because there

is a certain influence erosion clay bricks for hot metal flow

and flow velocity, more invasion and hot metal sidewall

erosion is small, so the hearth erosion degree is reducing

continuously.

Fig. 19. The distribution of bottom wall shear

Fig. 20. The distribution of bottom wall shear of the first layer of clay brick

invasion

6 Xuewu Feng et al.: Analysis of Flow Field of before and after Slag-Pig Form Accumulation in Blast Furnace

Fig. 21. The distribution of bottom wall shear of the second layer of clay brick

invasion

From fig.19 to fig.22 we can know, before the third layer of

clay brick invasion ,the bottom wall shear increases gradually

near taphole position , because of existence of central hearth

deadman the hearth is far from the taphole iron down along a

small gap of deadman and furnace wall and deadman between

the narrow space flow , and flow to the bottom then bypass the

porosity smaller deadman to taphole , the distal bottom which

is far from taphole has small erosion .At the proximal bottom

of blast furnace ,hot metal from upper deadman ,which it goes

through deadman porosity and then the taphole ,increases the

erosion of hearth .After the invasion of the third layer of clay

brick ,the most severe wall shear appears to the distal bottom

sides .

Fig. 22. The distribution of bottom wall shear of the third layer of clay brick

invasion

6.2. Analysis Simulation of Formation of Slag

Blast Furnace Hearth

From fig.23 to fig.26 we can know, formation of slag has

influence on flow of hot metal in the blast furnace, circulation

phenomenon appears on condition of no clay brick

erosion .After the invasion of clay brick, hot metal tends to

flow one side, and more depth of invasion ,more obvious.

Fig. 23. The velocity distribution of horizontal section through the center line

of formation of slag taphole

Fig. 24. The velocity distribution of horizontal section through the center line

of the first layer of clay brick invasion of formation of slag taphole

Fig. 25. The velocity distribution of horizontal section through the center line

of the second layer of clay brick invasion of formation of slag taphole

Journal of Materials Sciences and Applications 2015; 1(1): 1-10 7

Fig. 26. The velocity distribution of horizontal section through the center line

of the third layer of clay brick invasion of formation of slag taphole

Fig. 27. The velocity distribution in vertical plane of formation of slag

Fig. 28. The velocity distribution in vertical plane of formation of slag and the

first layer of clay brick invasion

From fig.27 to fig.30 we can know, hot metal flows directly

to outlet near the taphole, while the distal hot metal flows to

taphole near the hearth wall region, and bottom corner exists

of mixed flow. This is because the center of deadman’s edge

loose ，the porosity is large , however the center is dense ,the

porosity is small, hot metal bypass the poor areas of

permeability ,so as to form the edge of circulation .And

deadman is in a sink condition, the distal bottom’s hot metal

tends to upward flow. It can increase erosion of hearth, what is

the mixed flow of hot metal flow area to "panning" effect on

the furnace bottom corner.

Fig. 29. The velocity distribution in vertical plane of formation of slag and the

second layer of clay brick invasion

Fig. 30. The velocity distribution in vertical plane of formation of slag and the

third layer of clay brick invasion

Fig. 31. The level streamline chart of formation of slag hearth

8 Xuewu Feng et al.: Analysis of Flow Field of before and after Slag-Pig Form Accumulation in Blast Furnace

From fig.31 to fig.34 we can know, the level streamline of

generating slagging hearth changes with the invasion depth of

clay brick, it tends to be very chaotic phenomena, more deep

of invasion, more chaos of erosion degree, those will result in

progressively larger of hearth.

Fig. 32. The level streamline chart of the first layer of clay brick and

formation of slag hearth

Fig. 33. The level streamline chart of the second layer of clay brick and

formation of slag hearth

Fig. 34. The level streamline chart of the third layer of clay brick and

formation of slag hearth

Fig. 35. The distribution of wall shear of formation of slag hearth

Fig. 36. The distribution of wall shear of the first layer of clay brick invasion

and formation of slag hearth

Fig. 37. The distribution of wall shear of the second layer of clay brick

invasion and formation of slag hearth

Journal of Materials Sciences and Applications 2015; 1(1): 1-10 9

Fig. 38. The distribution of wall shear of the third layer of clay brick invasion

and formation of slag hearth

From fig.35 to fig.38 we can know, the invasion depth is

gradually deepening in formation of slag hearth wall, the wall

shear will increase near the taphole , other partial hearth’s wall

shear do not obviously changes.

Fig. 39. The wall shear distribution of formation of slag bottom

Fig. 40. The wall shear distribution of the first layer of clay brick invasion

and formation of slag bottom

Fig. 41. The wall shear distribution of the second layer of clay brick invasion

and formation of slag bottom

From fig.39 to fig.42 we can know, the wall shear increases

gradually as invasion depth, but the time is the third layer of

clay brick invasion, the wall shear distribution is different

from the other cases, the maximum of wall shear appears to

both sides of the bottom in the longitudinal section of the

taphole parallel bits.

Fig. 42. The wall shear distribution of the third layer of clay brick invasion

and formation of slag bottom

7. Comparison of before and after

Formation of Slag Blast Furnace

Hearth

(1) Comparison of the level velocity vector of before and

after formation of slag taphole center line: Two cases of

velocity distribution difference is the invasion of the first layer

of clay brick, the normal hearth has normal circulation.

Another case tends to flow to one side, after flows to outlet.

(2) Comparison of the vertical section velocity vector of

before and after formation of slag taphole center line: The

velocity vector is compared in different periods, there is

circulation phenomenon and the path changed in the formation

10 Xuewu Feng et al.: Analysis of Flow Field of before and after Slag-Pig Form Accumulation in Blast Furnace

of slag hearth, the other is not.

(3) Comparison of the level streamline of before and after

formation of slag hearth: The normal hearths appear obviously

circulation phenomenon ,and a part of hot metal flows in the

center .But the formation of slag hearths do not appear

obviously circulation phenomenon ,and the path of hot metal

is confusion.

(4) Comparison of wall shear stress of before and after

formation of slag hearth: The two cases of wall shear are

increased with the depth of invasion. Formation of slag

hearth’s wall shear is lager then normal hearth.

(5) Comparison of bottom wall shear of before and after

formation of slag hearth: the side of taphole’s wall shear

increases with the increasing of invasion depth, before bottom

hearth is eroded the third layer of clay brick. But after it, two

different bottom wall shears’ maximum appears in two sides

of bottom hearth.

8. Conclusion

(1) Before and after formation of slag the furnace bottom

and hearth’s wall shear increases with the increasing depth of

erosion.

(2) The level velocity vector’s circulation phenomenon in

the before and after formation of slag center hearth with the

increasing depth of erosion is not obvious.

(3) The vertical velocity vector has mixed flow

phenomenon in the before and after formation of slag hearth,

the path of hot metal changes.

(4) The slag adhering to hearth has buffer effect on hot

metal’s erosion of hearth sidewall, and reduces erosion on the

heath of hot metal.

References

[1] K. H. Peters, H. W. Gudenau and G. Still: Steel Res, 1985(54): 547-551.

[2] P. Gauje, R. Nicalle, J. M. Steiler, M. J. Venturini and J. M. Libra-lesso: Proc. 2nd Euro. Conf.on Ironmaking, IOM, London, 1994:328-334.

[3] A. K. Vats and S. K. Dash. Optimisation of taphole angle to minimise flow induced wall shear stress on the hearth [J] . Ironmaking Steelmaking, 2004, 31(3):207-215.

[4] Hui Ding, Yan Jin, Chang Gui Cheng, Yang Li, Zhi bin Tian. The inflence of wall shear in the BF hearth after add the dam [J]. Metalurgia international

[5] H.W. Gudenau, J.P. Mulanza, D.G.R. Sharma, Carburization of hot metal by industrial and special cokes, Steel Research 61(1990)97-104.

[6] A.Preuer, J.Winter, H.Hiebler, Computation of the erosion in the hearth of a blast Furnace, Steel Research 63(1992) 139-146.

[7] C.E.Huang, S.W.Du, W.T.Chang, Numerical investigation on the hot metal flow in blast furnace hearth through CFD, ISIJ International 48 (2008) 1182-1187.

[8] K. Shibata, Y. Kimura, M.Shimizu, S.-i.Inaba, Dynamics of dead-man coke and hot metal flow in a blast furnace hearth, ISIJ International 30 (1990) 208-215.

[9] Iida.M, Maeda. E. Okamoto.T: Evaluation of apparent thermal conductivity of green taphole mix, Proceedings of the Unified International Technical Conference on Refractiories: UNITECR ‘05 Worldwide Congress, pp 470-475, 2006.

[10] Kumar: Heat tranfer analysis and estimation of refractory wear in an iron blast furnace hearth using finite element method, ISIJ International. Vol. 45, no.8, pp.1122-1128.2005.