ISSN 0967�0912, Steel in Translation, 2013, Vol. 43, No. 11, pp. 732–739. © Allerton Press, Inc., 2013.Original Russian Text © A.N. Dmitriev, Yu.A. Chesnokov, K. Chen, O.Yu. Ivanov, M.O. Zolotykh, 2013, published in “Stal’,” 2013, No. 11, pp. 8–14.

732

A blast furnace is a metallurgical system of shafttype. Its internal working space is bounded by a refrac�tory lining, which is intended to protect the furnace’smetal structures from high temperatures and to main�tain the initial geometric configuration of the workingspace for a long time. Numerous factors break downthe lining: impacts (when the charge is introduced inthe furnace); abrasion (as the batch descends in theshaft); wear by the hot metal and slag; and the penetra�tion of soot, zinc, and alkalis into the lining seams.The destructive effect is greatest in the lower part of thefurnace: the lining of the well and the hearth. There�fore, appropriate measures are taken in the design ofthe refractory lining and the cooling systems in thewell and the hearth, so as to minimize the need formajor repairs and ensure reliable furnace operation for15–20 years.

Considerable losses of production occur whenlarge�capacity blast furnaces are shut down for liningrepair, which may take 2–3 months. The factorsresponsible for wear and measures for its limitationwere considered in [1]. The selection of the coolingsystem and the refractories and the furnace design areof primary importance here. The hot�metal fluxesassociated with the hearth design and the quality of thecoke employed also have some influence on hearthand hence furnace life. The influence of the produc�tivity on furnace life was discussed in [1].

At present, Russian and non�Russian researchersare interested in the analysis of hearth operation and

prediction of its wear, so as to prevent penetration ofthe hot metal through the lining, which would be cat�astrophic. The creation of adequate systems for suchanalysis and prediction calls for complex mathemati�cal software, information regarding the latest achieve�ments in blast�furnace technology, thermal calcula�tions, and computer simulation.

At present, the lining thickness may be monitoredby measuring the flow rate and temperature differenceof the water entering and leaving the cooled furnacesection and by means of thermosensors in the lowerfurnace lining. Other methods are based on ultra�sound, radioactive isotopes, elastic shock waves, mea�surements of the resistance of electrofurnaces, and soon [2–13].

The most promising approach is measurement ofthe lining temperature and corresponding calculationof the remaining lining thickness on the basis of math�ematical models.

Existing diagnostic methods based on direct andindirect measurements involve solving nonsteadyheat�conduction problems and the analysis of hugequantities of data—for example, in formulating a setof possible characteristic states of metallurgical sys�tems or their components. The agreement between themodels and the actual blast�furnace processes dependson the stability of the thermal and geometric charac�teristics on which the mathematical models of therefractory lining are based.

Monitoring the Wear of the Refractory Lining in the Blast�Furnace Hearth

A. N. Dmitrieva, c, Yu. A. Chesnokova, K. Chenb, O. Yu. Ivanovc, and M. O. Zolotykha, c

aInstitute of Metallurgy, Ural Branch, Russian Academy of Sciences, Yekaterinburg, RussiabBeijing Liberty International Engineering Technology Co., China

cYeltsin Ural Federal University, Yekaterinburg, Russia

Abstract—The Razgar Gorna computer program is developed for calculating two�dimensional temperaturefields in any vertical and horizontal cross section of the blast�furnace hearth. In the calculations, the heat�conduction equations are solved by means of readings from many temperature sensors (up to 1000, dependingon the volume) installed within the furnace lining between the refractory modules. Continuous temperaturemonitoring at each point permits the determination of the remaining lining thickness and prediction of theonset of lining wear, as necessary. A mathematical model is employed in continuous temperature monitoringof the lining. The database of the Razgar Gorna program relies on the collection, analysis, and transmissionof information from the temperature or heat�flux sensors. The program is in use at blast furnaces in Chinesesteelworks at Jinan (two furnaces), Jiyuan, and Liuzhou.

Keywords: monitoring system, mathematical simulation, blast furnace, refractory lining, lining wear

DOI: 10.3103/S0967091213110041

STEEL IN TRANSLATION Vol. 43 No. 11 2013

MONITORING THE WEAR OF THE REFRACTORY LINING 733

The efficiency of existing automatic diagnostic sys�tems for refractory linings may be increased by includ�ing a module detecting structural changes in the mon�itored signals in real time. As a rule, such changes indi�cate changes in state of the system being monitored. Itis expedient to use the corresponding information inpredicting the dynamics of the signals. Continuousoperation of such a module permits timely detectionof significant discrepancies.

We assume a one�dimensional steady flux Q at thewell and hearth walls. It may be described by thefamiliar formula for the flux through a multilayerplane wall [14]

(1)

where Tin and Tex are the internal and external surfacetemperatures of the walls; ΔS1,…, n is the thickness ofthe wall layer; k1,…, n is the thermal conductivity of thewall layer.

We now consider two possible approaches to calcu�lating the remaining lining thickness for three layers(for example, the lateral wall of a furnace), with twothermosensors.

1. With growth of the slag coating (Fig. 1), when anew layer (thickness ΔSx) with thermal conductivity kxis formed, we write

(2)

where ΔSx = r0 – rx is the coating thickness; ΔS1 = r1 – r0

is the thickness of the third layer; ΔS2 = r2 – r1 is thethickness of the second layer; ΔS3 = r3 – r2 is the thick�ness of the first layer; ΔS4 = r4 – r3 is the thickness ofthe layer between the sensors; T1 is the temperature atthe first sensor; T2 is the temperature at the secondsensor; Tx is the temperature at the coating boundary(specified as 1150°C); k1, k2, k3, and kx are the heat�transfer coefficients of the corresponding layers.

Hence, we may write the formula for the boundary Sxof the lining with coating formation

(3)

QTin Tex–

1k1

����ΔS1 …1kn

����ΔSn+ +����������������������������������������,=

Tx T1–1kx

����ΔSx1k1

����ΔS11k2

����ΔS21k3

����ΔS3+ + +����������������������������������������������������������������

= Tx T2–

1kx

����ΔSx1k1

����ΔS11k2

����ΔS21k3

���� ΔS3 ΔS4+( )+ + +���������������������������������������������������������������������������������,

Sx r0

kx

T1 r4 r2–( ) T2 r2 r3–( )+

+ Txk2 r3 r4–( ) k3 T1 T2–( )–

× k1 r1 r2–( ) k2 r2 r0–( )–( )

k1k2k3 T1 T2–( )�����������������������������������������������������������������+ .=

2. In the case of lining wear (Fig. 2), the layer thick�ness ΔS3 is reduced. Then the formula for the residuallining thickness Sx takes the form

(4)

In this calculation, we need to verify that the calcu�lated Sx value satisfies the condition |Sx –S3| < 0.001,since the thickness of third layer may become criticallysmall. Verification is based on the formula

(5)

The same formula may be used when the third layerhas completely burned away (Sx < S3). When readingsfrom three or more sensors at the same level areobtained, the equations remain the same, but specifiedpair coefficients must be employed. In other words,the confidence level of the sensor readings must betaken into account. Analogous formulas may beobtained to calculate the thickness of the well lining;in that case, there are usually more than five layers.

From the given equations for a one�dimensionalsteady heat flux through a multilayer wall, if we calcu�late the boundary radius of the internal wall by linearinterpolation (or any other method) when Tx =1150°C and the sensor readings T1 and T2 are known,

Sx S3k1ΔS2ΔS3

k3ΔS2 k2ΔS3+�����������������������������

T2 Tx–( )

T1 T2–( )������������������ .+=

Sx S2k1ΔS2

k2ΔS2

������������Tx T2–T2 T1–��������������.+=

1.02.03.05.06.07.0 4.0

T2 T1 Tx

r4r3r0rxr1

r2

L = 225° (16)

270

180

Fig. 1. Formulation of the problem with coating growth.

734

STEEL IN TRANSLATION Vol. 43 No. 11 2013

DMITRIEV et al.

it is relatively simple to find the temperature distribu�tion over the lining thickness in the region of the sen�sor positions. It is more difficult to establish the distri�bution of the temperature curves over the radius,between the groups of the sensors, in the well or thelateral walls of the blast furnace. The use of variousnumerical methods for difference schemes wouldrequire significant computer resources and machinetime. Therefore, at this stage, we calculate the temper�atures between the sensors (groups of sensors) bycubic�spline approximation [15]. We should also notehere that the consistency of numerical methodsbecomes problematic at junctions where the gridswitches from horizontal to vertical (or vice versa).The proposed approach offers speed (which is impor�tant in making timely decisions) but also adequateaccuracy of the calculations.

The primary goals of the information system devel�oped for monitoring the wear of the refractory lining inthe blast�furnace hearth are to extend its working lifeand to prevent accidents in the blast furnace. Algo�rithms and programs have been developed for calcu�lating the remaining lining thickness in the furnacehearth and the temperature distribution vertically andhorizontally within the lining. On that basis, blast�fur�nace operation may be analyzed and controlled.

The program employs three windows: a windowmapping the vertical cross section of the furnace; a

window mapping its horizontal cross section; and awindow showing the parameter variation over time.

In the vertical cross section, most of the screen isdevoted to two radial cross sections (Fig. 3). The draw�ing of the furnace predominates; its scale may bejudged from the coordinate grid. The coordinates(height and radius) are expressed in m. Above theradial cross sections, a sketch of the horizontal crosssection is shown, with information regarding the posi�tions of the left and right cross sections. Short boldlines at the circumference indicate these positions,and appropriate text is provided. For example, L(18)means that the furnace cross section for sector 18 isshown on the left side, while (6)R means that the righthalf shows the cross section for sector 6. The sameinformation may be provided in headline form: Verti�cal Cross Section of Blast Furnace with AzimuthalAngles of 270° and 90°. Dashed lines show the bound�aries of the sectors in containing the tap holes (four inFig. 3), while long bold lines show their positions.Numerical values may be shown on the isotherms.Finally, the furnace may be colored in accordance withthe local temperatures.

In Fig. 4, we show the horizontal cross section. Asin the vertical case, we may observe the position of thethermocouples, the wear lines, isotherms, and colora�tion of the cross section in accordance with the localtemperatures. Where necessary, numerical values maybe shown on the isotherms. The inner section of thecross section is not colored, because this is a diagramof the hearth.

In Fig. 5, we show a screen displaying the variationin the remaining lining thickness. In Sensor Readingmode, we may track the change in the thermosensorreadings over time. As an example, in Fig. 6, we showthe variation in thermocouple readings within the

1.02.03.05.06.07.0 4.0

T2 T1 Tx

r2

r3

rx

r1

r0

Fig. 2. Formulation of the problem with lining wear.

L (18)8.0

7.0

6.0

5.0

4.0

2.0

1.0

4.05.07.0 6.0 3.0 2.0 1.0 4.03.01.0 2.0 5.0 6.0 7.0

0 300 600 900 1200

180

270 90(6) R

0

9.0

3.0

Temperature, °C

Fig. 3. Vertical cross section of blast furnace.

L = 225° (16)

270

180

STEEL IN TRANSLATION Vol. 43 No. 11 2013

MONITORING THE WEAR OF THE REFRACTORY LINING 735

same horizontal cross section but in different groups,over the course of a week.

The Razgar Gorna computer program was installedat blast furnace 4 (volume 3200 m3) operated by JinanIron and Steel Co. (Jinan, China) at the end of 2010.Information is collected by 683 thermosensors.RS�232 controllers receive and send analog signalswith a response frequency no less than 10 Hz; themeasuring precision is no less than 0.1%.

Besides the Razgar Gorna computer program, KhAor NN thermal�conversion cables are used to measurethe temperature in the hearth and well lining at speci�fied points; gas�tight modules permit transfer of thecables outside the furnace and are soldered to the fur�nace housing; cross�connectors are placed around thefurnace in accordance with the configuration of the gas�tight modules; and communication lines transfer thesignals to the control panel. The monitors and otherancillary computer equipment employed are connectedthrough a local network to the controllers of the primarycomputer in the control board.

The thermal�conversion cables are assumed to bestandard devices for temperature measurements ingases, solids, or liquids, with two thermoelectrodes ofKhA or NN type. The protective casing (diameter3 mm) is made of special alloy. The cables are pro�duced in accordance with international standards andcomply with State Standard GOST R 8.585–2001.They are shown in Fig. 7.

The gas�tight modules permit passage of the ther�mal�conversion cables outside the blast furnace. Theyconsist of a metallic tube, within which the cables pass.The interior of the tube is sealed with special temper�

ature�resistant material so as to ensure gas�tightness at1000°C and 16 MPa. The modules are shown in Fig. 8.

Prolonged operational experience shows that thesystem is highly reliable. However, the algorithm mustbe improved so as to take account of the complex profilein the lower part of the blast furnace. In particular, wewant to construct a curve passing through points A, B,C, and D in Fig. 9a. (These points are obtained byanalysis of thermosensor readings.)

It is most expedient to use polar coordinates. InFig. 9a, the origin of the polar coordinates is on thefurnace axis, at the top of the hearth. The polar axisruns downward; the angle is measured clockwise.

0° 15°30°

45°

60°

75°

90°

105°

120°

135°

150°

165°180°185°210°

225°

240°

255°

270°

285°

300°

315°

330°

345°

1.0 2.0 3.0 4.0 5.0

1502503504505506507508509501050

Temperature, °C

Fig. 4. Horizontal cross section of blast furnace.

2500

2400

2300

2200

2100

2000

1800

1700July 27July 25July 23

1900

Rem

ain

ing

wal

l th

ickn

ess,

mm

Date (2010)

Fig. 5. Graphs of the remaining lining thickness.

9.0

8.0

7.0

5.0

4.0

3.0

2.0

1.0

7.06.02.01.0 5.04.03.01.02.06.07.0 3.04.05.0

6.0

400

300

200

100 July 27July 23 July 25

0

0 300 600 900 1200

Temperature, °C

Vertical cross section of furnace hearth (azimuthal angles 270° and 90°

Sen

sor

tem

pera

ture

, °C

Date (2010)

Fig. 6. Operation in Sensor Reading mode.

736

STEEL IN TRANSLATION Vol. 43 No. 11 2013

DMITRIEV et al.

Thus, the furnace profile may be represented by afunction r = F(α) where α = 0°–90° and r is the radius.For the furnace geometry in Fig. 9a, F(α) takes theform in Fig. 9b. For the sake of clarity, we presenthighly simplified furnace geometry. However, thecomplexity of the profile has practically no influenceon the interpolation method employed. As we see,F(α) has a smoothly varying section and a section witha large gradient. Correspondingly, its spectrum is rela�tively broad.

According to the Nyquist–Shannon theorem, thisfunction must be established by selecting the distancebetween the readings Td (the discretization interval) inthe form [16, 17]

(6)

where fc is the upper frequency bound on the spec�trum. This interval is not available in the diagnosticsystem considered here for the wear of a refractoryblast�furnace lining. Therefore, to plot the curve, werequire additional information—for example, the ini�tial blast�furnace geometry (profile), which is knownin advance.

Td 1/2fc,<

(a)

(b)

Fig. 7. Thermal�conversion cables.

(a)

(b)

Fig. 8. Gas�tight modules.

Fig. 9. Geometric relations (a), graph of F(α) (b), and lin�ing thickness according to sensor readings (c).

9.08.07.05.03.01.01.0

7500

6000

5000

400090807040300

6.04.02.0

E0

D0

C0

B = B0

D

C

A

αBαC

αD

60502010

4500

5500

7000

8000

6500

(a)

(b)

(c)

6.0

3.0

1.0

9.0

2.0

5.0

7.0

4.0

7.0 5.0 3.0 1.0 1.0 3.0 5.0 7.0 9.0

90°

A

D

BC

α

r

0°

A0

STEEL IN TRANSLATION Vol. 43 No. 11 2013

MONITORING THE WEAR OF THE REFRACTORY LINING 737

We now consider the interpolation method for theexample in Fig. 9c. In furnace operation, the geometrychanges (wear or coating application). Informationregarding the current profile is provided by ther�mosensors in the lining. On the basis of temperaturereadings at the sensors, the remaining lining thicknessin the hearth and well at specific points is determined.Points A, B, C, and D correspond to the calculated lin�ing thickness. Subscript 0 denotes the initial points ofthe function F(α) (the initial furnace profile) at thecorresponding angular coordinate. To obtain the cur�rent profile, we need to determine F '(α), by interpola�tion of the values at points A–D on the basis of F(α).

Interpolation will be undertaken on individual seg�ments. On segment αA–αB, the values of F '(α) aremainly determined by the thermosensor readings atpoint αA and αB. The influence of the other ther�mosensors is negligible, and therefore they will beignored. To form the last segment of the functionF '(α), we introduce the point E0 at the top of thehearth (αE = 90°). The lining thickness at this point isalways the same, since the probability of lining wear atthat point is negligible.

In interpolation, we must take account of two fac�tors.

1. With slight wear (buildup), F '(α) must maintainthe initial furnace geometry.

2. With greater wear, the form of the cross sectionchanges, on account of lining disintegration.

These two factors impose opposite requirements onthe interpolation algorithm. To obtain a compromise,we need an adaptive interpolation procedure. Anexample is as follows

(7)

F ' α( ) F1' α( ) P d α( )– /P F2' α( )+=

× 1 P d α( )– /P–( ) when d α( ) P,<

F ' α( ) F2' α( ) when d α( ) P.≥=

Here d(α) is the auxiliary function, which character�izes the deviation of the calculated value from the ini�tial profile. For segment αA–αB

(8)

Also in Eq. (7), P is the threshold value of F '(α);(α) is the interpolation function for large changes in

furnace geometry. In the simplest case of linear inter�polation

(9)

The interpolation of the other segments (αB–αC,αC–αD, and αD–αE) is analogous. In Fig. 10, we showthe result of interpolation for this example.

This method of interpolation is not intended tofind local lining defects between the groups of temper�ature sensors. Therefore, the sensors must be placed atthe most likely defect sites. It is very important to placebackup sensors at the center of the furnace, since fail�ure of the sensors at that location renders interpolationimpossible.

In Fig. 11, we show the vertical cross section of thehearth in 3200�m3 blast furnace 4 at Jinan Iron andSteel Co. (Jinan, China) for azimuthal angles of 240°and 60°. The position of the thermocouples is evidentin Fig. 11. Information regarding the wear at pointswithout sensors may be obtained on the basis of theproposed algorithm, by taking account of the readingsof several thermocouples in a row.

This system has also been installed in 1080�m3 blastfurnace 2 at Henan Jiyuan Iron and Steel Co. and in2500�m3 blast furnace 4 at Guangxi Liuzhou Iron andSteel (Liuzhou, China), with 212 and 383 thermocou�ples, respectively.

d α( ) A[ 0 A– B0 B–( )(+=

– A0 A–( ) ) ]/ αB αA–( ) α αA–( )[ ].

F2'

F2' α( ) A B A–( )/ αB αA–( ) α αA–( ).+=

Fig. 10. Result of interpolating the furnace profile.

8.0

7.0

5.0

4.0

3.0

2.0

1.0

7.06.02.01.0 5.04.03.0

6.0

0 300 600 900 1200Temperature, °C

9.0

270

180L = 240° (17)

R = 60° (5)90

0

8.03.04.08.09.0 5.06.07.0 1.02.0

9.0

Fig. 11. Vertical cross section of the hearth in 3200�m3

blast furnace 4 at Jinan Iron and Steel Co. for azimuthalangles of 240° and 60°.

9.08.07.05.03.01.01.0 6.04.02.0

E0

D0

C0

B = B0

D

C

A

A0

αBαC

αD

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STEEL IN TRANSLATION Vol. 43 No. 11 2013

DMITRIEV et al.

In March 2013, during major repairs, the proposedsystem was also installed in 1750�m3 blast furnace 3 atJinan Iron and Steel Co., with 524 thermocouples(Fig. 12). This system was used to monitor the furnaceas it was restarted, beginning on May 15, 2013. InFig. 13, we show the temperature variation at the ther�mocouples for a single vertical cross section in the fur�nace hearth.

CONCLUSIONS

A new system for monitoring the lining wear in theblast�furnace hearth has been introduced at severalsteel plants in China. The system includes a programfor calculating two�dimensional temperature fields inany vertical and horizontal cross section of the hearthlining on the basis of thermosensor readings.

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8.0

7.0

5.0

4.0

3.0

2.0

1.0

7.06.02.01.0 5.04.03.01.02.07.08.0 3.04.05.0

6.0

0 300 600 900 1200Temperature, °C

8.06.0

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180

L = 173° (12)

R = 353° (24)

90

0

Jinan blast furnace 3, vertical cross section, azimuthal angles 173° and 353° (July 8, 2013, 8:57:47)

Fig. 12. Vertical cross section of the hearth in 1750�m3 blast furnace 3 at Jinan Iron and Steel Co.

180

180525

425

325

225175

25April 17

180

475

375

275

12575

April 27 May 7 May 17 May 27 June 6 June 16 June 26 July 6

April 22 May 2 May 12 May 22 June 1 June 11 June 21 July 1

Sen

sor

tem

pera

ture

, °C

Temperature variation (April 17 to July 16, 2013)Azimuthal angle: 353°

Date (2013)

Fig. 13. Temperature variation at the thermocouple locations in a vertical cross section of the hearth in 1750�m3 blast furnace 3at Jinan Iron and Steel Co.

STEEL IN TRANSLATION Vol. 43 No. 11 2013

MONITORING THE WEAR OF THE REFRACTORY LINING 739

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Translated by Bernard Gilbert