Tu1:3 - 1 Tu1 – Efficient blast furnace operation: High productivity, low coke rate - 3 LKAB'S EXPERIMENTAL BLAST FURNACE - THE LEARNING CURVE Lawrence Hooey, LKAB, Box 952, Luleå, Sweden (Currently: Rautaruukki Oyj, Ruukki Production, P.O. Box 93, 92101 Raahe, Finland) Bror-Erik Sköld, MEFOS, Box 812, 97125 Luleå, Sweden Lena Sundqvist Ökvist, SSAB Tunnplåt AB, 97188 Luleå, Sweden. Matti Seppänen, Rautaruukki Oyj, Ruukki Production, P.O. Box 93, 92101 Raahe, Finland Guangqing Zuo, LKAB, Box 952, 97128 Luleå, Sweden, [email protected]Abstract Since 1997 LKAB has run 14 campaigns of 6-12 weeks each in the experimental blast furnace (EBF) located at MEFOS in Luleå, Sweden. The plan at that time was 5 campaigns with testing of new pellet grades aimed at both 100% pellet operations typical in the Nordic region, and at mixed burdens of pellets and sinter typical in middle Europe. A great deal of information has been gathered, a new pellet developed and the use of the EBF has been extended to include much more research than was originally planned. In addition, the furnace has been used extensively for applied research by LKAB, by LKAB's customers and various research organisations and other companies. Such testing includes, for example, testing of injection techniques with coal-flux co- injection, high oxygen/oil injection, blast conditions testing with high moisture, investigations of scaffolding, evaluation of equipment and measurement devices such as a new type of bell-less top. The furnace is providing an excellent springboard to both the next generation of blast furnace pellets and blast furnace operations in the years to come. The EBF will be modified for testing of full oxygen blast furnace concepts for reduction of CO 2 emissions within the scope of the ULCOS project. Introduction LKAB's experimental blast furnace, Figure 1, was commissioned in 1997 after study of the world's previous experimental furnaces. The EBF was planned for 5 campaigns of about 6 weeks each for development and testing of LKAB's experimental pellets. The furnace was built to overcome the gap between laboratory behaviour of pellets and that of industrial application as it has been LKAB's experience that laboratory testing is not sufficient for the development of new pellet types. 1,2,3,4 Within the first few campaigns it became clear that the EBF was a very valuable tool not only for development of pellets but for other research and development of the blast furnace process. To date 14 campaigns have been run. From campaign 3 and on, the EBF has been used in various external research projects such as ECSC, Jerkontoret, and also by individual companies.
LKAB'S EXPERIMENTAL BLAST FURNACE - THE LEARNING CURVE Lawrence Hooey, LKAB, Box 952, Luleå, Sweden (Currently: Rautaruukki Oyj, Ruukki Production, P.O. Box 93, 92101 Raahe, Finland) Bror-Erik Sköld, MEFOS, Box 812, 97125 Luleå, Sweden Lena Sundqvist Ökvist, SSAB Tunnplåt AB, 97188 Luleå, Sweden. Matti Seppänen, Rautaruukki Oyj, Ruukki Production, P.O. Box 93, 92101 Raahe, Finland Guangqing Zuo, LKAB, Box 952, 97128 Luleå, Sweden, [email protected] Abstract Since 1997 LKAB has run 14 campaigns of 6-12 weeks each in the experimental blast furnace (EBF) located at MEFOS in Luleå, Sweden. The plan at that time was 5 campaigns with testing of new pellet grades aimed at both 100% pellet operations typical in the Nordic region, and at mixed burdens of pellets and sinter typical in middle Europe. A great deal of information has been gathered, a new pellet developed and the use of the EBF has been extended to include much more research than was originally planned. In addition, the furnace has been used extensively for applied research by LKAB, by LKAB's customers and various research organisations and other companies. Such testing includes, for example, testing of injection techniques with coal-flux co-injection, high oxygen/oil injection, blast conditions testing with high moisture, investigations of scaffolding, evaluation of equipment and measurement devices such as a new type of bell-less top. The furnace is providing an excellent springboard to both the next generation of blast furnace pellets and blast furnace operations in the years to come. The EBF will be modified for testing of full oxygen blast furnace concepts for reduction of CO2 emissions within the scope of the ULCOS project. Introduction LKAB's experimental blast furnace, Figure 1, was commissioned in 1997 after study of the world's previous experimental furnaces. The EBF was planned for 5 campaigns of about 6 weeks each for development and testing of LKAB's experimental pellets. The furnace was built to overcome the gap between laboratory behaviour of pellets and that of industrial application as it has been LKAB's experience that laboratory testing is not sufficient for the development of new pellet types.1,2,3,4 Within the first few campaigns it became clear that the EBF was a very valuable tool not only for development of pellets but for other research and development of the blast furnace process. To date 14 campaigns have been run. From campaign 3 and on, the EBF has been used in various external research projects such as ECSC, Jerkontoret, and also by individual companies.
Hearth diameter 1.2 m Working height 6.0 m Tuyeres 3 Tuyere diameter 54 mm Top pressure (max) 1.5 bar guage Injectants Coal/oil/propane Oxygen enrichment up to 40% Blast temperature c. 1200oC Production 30 - 40 t/d Reducing agents 500 - 580 kg/thm
Figure 1. Experimental blast furnace showing in-burden probe positions. Upper and lower shaft probes are either material or gas/temperature. Inclined and tuyere probes are material probes only. Development of the EBF as a tool for BF research In order to broaden the use of the furnace to other research areas and increase its reliability in burden testing, the furnace has undergone many improvements since commissioning. The availability of the EBF is over 99% of planned operation time. Basic design of the Experimental BF The EBF is equipped with all systems typical for a full-scale blast furnace operation (Figure 2 shows general layout). Starting with material handling system, the material is screened to 6 mm - 50 mm and then transported to bins and from there weighed on precision scales before charged to the furnace via a single skip and a bell-less type top. The coal injection system is a dense phase type system with a capacity of more than 300 kg/THM. The coal flow is individually controlled for each tuyere. Furthermore the furnace is equipped with injection systems for oil and gas that can be co-injected with oxygen. The injection and raceway are constantly monitored by video cameras at each tuyere that are viewed from the control room. The hot blast is produced in propane-fired pebble bed type hot stoves, supplied by ATZ in Germany. The stoves are very efficient and can produce hot blast up to 1300 oC. The stoves can be brought up to operational temperature from room temperature in two days and be cooled down in three days. The hot blast valves and the vent valve is water cooled. The furnace is insulated in order to reduce heat losses and the cooling of the bosh is more as a back up in case of severe wear of the refectory. Beside the bosh cooling it is only the tuyere and
jumbo coolers that are cooled by water. The cooling system is a closed system with heat exchanger and a basin with cooling tower for the primary system. The furnace was originally equipped with a bell type top in combination with movable armours. The furnace operates today with a new type of bell less top with extremely flexible charging possibilities designed and supplied by Zimmermann & Jansen. The top gas is cleaned by a dust catcher for the cursed grain size and the finer part of the dust is cached by a venturi scrubber in combination with a wet ESP. The top pressure (max 2,5 bar (a)) is controlled by two control valves after the dust cleaning system and then flared over the roof of the BF building. The tapping of the furnace is made by conventional tapping machines. A pneumatic drilling hammer and a hydraulic mud gun are used. The metal and slag is tapped into a movable sand bed and cooled, weight and stored for sale. The EBF is equipped with two gas analyzers, one for the top gas and one for the shaft gas probes. The pressure drop over the furnace is monitored by pressure gages in five levels at two positions per level. The vertical temperature profile can be monitored by a device that allows a thermocouple to be inserted anywhere over the radius of the furnace top. The thermocouple will follow the burden down to a temperature where it burns off. The furnace is equipped with two shaft probes and one that penetrates the cohesive zone (Figure 1). The inclined probe for the cohesive zone sample solids and the other two samples both solids and gas/temperature.
Figure 2. Basic layout of the EBF. Moving from left to right are the material storage bins, coal injection pressurised chambers, skip system, pebble heaters, furnace, tapping equipment and top-gas cleaning system.
Improvements in EBF after commissioning Many improvements have been made since commissioning in order to facilitate an increasing variety of testing as well as to extend the lifetime. Some milestones are shown in Figure 3. To name a few improvements: the control systems have been improved to accommodate an increasing number of measurements; the number of materials bins has been increased to accommodate two more feed materials; the injection systems have been modified to allow for co-injection of slag formers, high rates of oil injection, and combined oxygen injection; new ventilation and dedusting systems; new XRF hot metal and slag analyzer; new Zimmerman & Jansen bell-less top. Testing began with ferrous burden quality, but has extended much further to include injection techniques, blast conditions, coke quality and so on.
CommissioningFirst tests: with sinter; with flux injection; oil injection; first customer trial
First test with lump ore
Blast O2 40% + oil 200 kg/thm; coke rate kg/thm; first tuyere coke probingIntroduction of Z&M bell-less top
First use of propane injectionTesting of ilmenite injection
Testing of coke qualityInstallation of EBF’s own hot metal/slag analyzer
Figure 3. Milestones in the development and use of the EBF Comparison of the EBF to commercial furnaces One important factor to consider was how the EBF compares to the behaviour of commercial furnaces. Tables 1, 2 and 3 show the comparison of several industrial furnaces to the EBF with various ferrous burden structures. The general result was that the EBF had a reductant rate about 50-70 kg/thm higher that of industrial furnaces. This is attributed to higher heat losses in the EBF and hot metal silicon about 1% higher than in industrial furnaces. Table 1. EBF test vs. SSAB Tunnplåt No. 3 furnace. EBF SSAB Luleå No. 3 (2004) Burden Pellets 100% Pellets 100% Injection Coal Coal Coke rate 439 326 Injection rate 100 139 Total Fuel rate 539 464 Table 2. EBF compared to Bremen furnace no. 2. EBF Bremen no. 2 Burden Pellets 46%, Sinter 54% Pellets 49, sinter 44%, lump ore 7%
(2 week test period) Injection Oil Oil/plastic Coke rate 474 406 Injection rate 54 48/21 Total fuel rate 528 475
Table 3. EBF compared to Duferco Furnace EBF Duferco Clabeq no.6 (2000) Burden Pellets 73%, Lump ore 27% Pellets 80%, Lump ore 20% Injection Coal Coal Coke rate 477 391 Injection rate 100 118 Total Fuel rate 577 509 It was first thought the EBF's small hearth and tapping conditions with tapping times of 5 minutes with a tap to tap time of 1 hour and hot metal silicon values over 1% would make comparison of hot metal quality and slag behaviour to commercial operations difficult. However, as can be seen in section 2.1, hot metal and slag behaviour with respect to sulphur and alkalis is similar to commercial furnaces. BF Research and Development Areas LKAB Product development LKAB introduced the Olivine-fluxed pellet in the early 1980's replacing acid pellets. The Olivine pellets have been the mainstay of LKAB's blast furnace pellet production up to the development of the KPBA high iron content acid pellet, commercialised since 2000. The advantage of the KPBA pellet has been found to be in stability of softening/melting properties in the mixed burden with basic sinter.5 Figure 4 shows a comparison of the resistance to gas flow for a condition whereby the furnace is going from colder to warmer conditions. The KPBA pellets show a consistent permeability for a given heat level as measured by Si in hot metal.
Hot Metal Si wt%
7,5
0,0 0,5 1,0 1,5 2,0 2,5
PV-Bosh
PV-bosh = (Blast Pressure2-Top Pressure2)/(bosh gas volume)1,7* constant
Figure 4. EBF data showing improved stability of pressure drop for LKAB acid pellets (KPBA) in a mixed burden compared to KPBO in a mixed burden. Arrow shows increased pressure drop when going from cold to hot conditions, as for example during start-up after a stop. 5 Further development example: Coating of blast furnace pellets The Olivine pellets have been highly successful in 100% pellet operations, however LKAB has been working towards improving both the properties of the olivine pellets and trying new concepts for 100% pellet burdens. A high iron content fluxed pellet is one possible pellet that was tested at the EBF and in full-scale.6 Operation with the fluxed pellet was acceptable. However, slag formation appeared to give less favourable alkali output versus desulphurisation capacity, Figure 5. After careful examination of various material samples from EBF testing, it
appeared likely that applying a coating to the surface of the fluxed pellet could improve the slag formation and pellet descent. This treatment appears to be successful in the EBF, Figure 6, and development of the concept is continuing.
0
25
50
75
100
0,2 0,4 0,6 0,8 1,0 1,2K2O Content of Slag
(S)/[S]
MPBO (>80%) MPB1 (>60%)
MPBO
MPB1
0
25
50
75
100
0,1 0,3 0,5 0,7 0,9(K2O) wt%
(S)/[S]
MPB1
MPB1 - olivine coated
Figure 5. S and K2O behaviour in slag in commercial furnace6; Figure 6. EBF testing of olivine coating of MPB1 MPBO = standard LKAB olivine pellets showing improved relationship between sulphur MPB1 = experimental fluxed pellets and alkali distribution. 6 General applied research As well as being used directly for product development, the overall blast furnace process is being investigated with several examples given below. Testing of various conditions in the EBF involves no risk to industrial production and is ideal for this type of research. Blast conditions - high moisture In two separate campaigns, the effect of blast moisture at varying flame temperatures where tested.7 Table 4 shows the general conditions in each campaign and test. The experiments were undertaken to establish at which point the blast moisture and/or flame temperature become critical factors in the BF operation in furnaces running with little or no oxygen enrichment. In the first test, Test A, an increase of blast moisture from 17 g/nm3 to 36g/nm3 had little impact on fuel rate, but stabilised the burden descent, Figure 7. In a second test, B, even higher moisture contents were used, and a clear limit was reached between 35g/nm3 and 52 g/nm3, Figure 8. The total fuel rate about the same up to 35 g, but it was necessary to increase the fuel rate dramatically between 35 and 52g (or at flame temperature between 2110 and 2000oC). Table 4. Testing conditions for effect of increased blast moisture
TEST PERIODS
Test A. Oil injection
Injection rate
kg/thm
Blast moisture
g/nm3
Blast temperature
oC
Flame Temperature
oC
Test time hours
1 42 17 1198 2260 48 2 44 36 1198 2135 40 Test B. Propane Injection 1a* 29 16 1198 2220 70 1b* 31 16 1199 2220 33 2 30 35 1199 2110 42 3 30 52 1199 2000 78 Period 1 a and b: Period 1a the furnace was underfueled and becoming colder; period 1b was after a charging disruption and the furnace was overfueled and becoming warmer (see Figure 8).
Figure 7. Burden descent and gas utilisation with increased blast moisture up to 35g/nm3.
0
1
2
3
4
2003
-09-
29
2003
-09-
30
2003
-10-
01
2003
-10-
02
2003
-10-
03
2003
-10-
04
2003
-10-
05
2003
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06
2003
-10-
07
2003
-10-
08
2003
-10-
09
2003
-10-
10
2003
-10-
11
2003
-10-
12
2003
-10-
13
[Si] wt%
325
375
425
475
525
Coke ratekg/thm
HM Si % Coke rate kg/thm
Charging disruption
1a (16 g/nm3) 1b (16 g/nm3)
2 (35 g/nm3)
3 (53 g/nm3)
Figure 8. Second test of blast moisture with blast moisture up to 53 g/nm3. Raceway dissections The EBF offers the possibility to inject different materials into each tuyere. The effect of different injectants on raceway conditions have been examined by operating the furnace.8 For example, in one test each tuyere was injected with different conditions for 8 hours prior to nitrogen quenching. Condition of each raceway was then evaluated. In this example, Figure 9, the tuyeres had 1) no injection; 2) coal; and 3) coal + BOF slag. Clear differences were visible in raceway condition with tuyeres 1 and 3 showing porous end of raceway, whereas tuyere 2 showed a clear development of a hard dense bird’s nest composed of acidic components of coke ash. Further testing has been conducted using propane, oil and coal injection. 9
Figure 9. Coal rate corresponding to equivalent 98 kg/thm (if same level for all three tuyeres) for tuyeres 2 and 3, and tuyere 3 containing equivalent 37 kg/thm BOF slag mixed with the coal. Blast furnace chemistry and mineralogy Using both the in-burden probes and samples taken from dissections after nitrogen quenching of the furnace, it is possible to examine in detail the reactions occurring in different materials and various positions in the furnace. For example, alkalis are known to affect burden materials significantly. Figure 10 shows the process of potassium absorption into relic olivine grains found in olivine pellets. 10
Carburisation phenomena have also been examined, which is difficult to due in industrial furnaces as sampling is virtually impossible. However, the meltdown of burden and flow characteristics in the melting and dripping zones are critical to furnace performance. Figure 11 shows examples of iron slightly carburised by CO gas.11 Due to difficulties to analyse carbon in microprobe, the carbon content has been estimated by the pearlite, cementite, ledeburite and ferrite contents. Combining controlled laboratory meltdown tests with examination of the same materials removed from the EBF using the in-burden probes is also proving information about the reliability and application of laboratory experiments in the evaluation of high temperature properties.12 The details of the ferrous burden morphology evaluated by microscopic examination as well as chemical data for selected excavations is being placed in a visual database developed by Sintef that allows for easy handling of large quantities of information.13 Several excavations have been systematically mapped and recorded into the database.
a) b) Figure 10. Reaction of olivine in olivine pellets taken from the EBF inclined probe 10
a) Image of olivine grain under transmission light with crossed polarisation b) Backscattered scanning electron image of the same grain.
Point 27: enstatite (Mg2Si2O6); Point 28, 29: complex pyroxene (Fe,Mg,Ca)2SiO6 with 3-5% K2O dissolved; point 30: high FeO content silicate glass.
a) b) Figure 11. Reflected light images of two pellets removed from the inclined probe of the EBF. 11 Carbon content can be estimated from the quantity of pearlite found. Sample a) contains circa 0.3% C (40% pearlite); sample b contains circa 0.6% carbon (80% pearlite). Scale bar is 20 micron.
Direct customer-Oriented tests Co-injection of additives with PC The effects of injection of BOF slag and BF flue dust together with coal have been tested in the EBF.14 Each additive was transferred into the coal fluidisation chamber using a volumetric screw feeder (Figure 12). The mixture of PC and additive was then injected into the three tuyeres of the EBF. The goal of BOF slag injection was to modify the meltdown behaviour of the burden, lessening the extremes of slag chemistry in the cohesive zone, and also to add basic components into the raceway to help prevent acid bird’s nest formation with high levels of coal injection. Flue dust injection provides a method to recycle the dust and utilise the carbon content as a fuel. Injection of hematite containing BF flue dust results in higher FeO content of the tuyere slag.15 The increase of FeO and the slightly increased basicity improves the melting properties of tuyere slag a bird’s nest is less easily formed. Figure 12. Injection of fluxes with PC
As can be seen from Table 5, the Si content of hot metal and the consumption of reducing agents significantly decreased when BOF slag or BF flue dust are co-injected with coal. Decreased Si content of hot metal reduced the consumption of coal and coke but this great effect cannot be expected at a large BF. However, the decreased slag amount and reuse of C in BF flue dust can be expected to be similar in an industrial furnace. Full-scale test at SSAB Tunnplåt in Luleå indicates that carbon contained in the BF flue dust can be efficiently used and replace some coal. Table 5. Summary of tests with co-injection of additive with coal BOF slag injection BF flue dust injection Co-injectant kg/tHM 0 25 36 0 23.4 PCI kg/tHM 98 93 98 101 103 Coke kg/tHM 439 440 428 444 412 Pellet A % 70 70 0 100 100 Pellet B % 30 30 100 0 0 %Si in HM % 1.28 1.04 1.00 2.18 1.78 HM Temp °C 1416 1426 1423 1461 1448 Slag vol. kg/tHM 136 110 101 144 145 Cold-bonded pellets (CBP) trial Since 1978, when the sinter plant was closed down, the blast furnaces at SSAB in Luleå have operated with 100% pellet burden together with a cold bonded briquette produced from recyclable by-products. Amounts of 40-85 kg/tHM of cold-bonded briquettes have been charged to the blast furnaces at SSAB Tunnplåt in Luleå since 1993. The effect from charging high amounts of cold bonded agglomerates on the BF process is evaluated in the EBF by producing a cold-bonded pellet (CBP) with almost the same raw materials as normally are used to produce the briquettes.14 The pellet contains approximately 40% Fe and 12% C and has a basicity B2 = 2.1. With a high level of cold-bonded pellets, the addition of fluxes (limestone and LD-slag) becomes unnecessary. Charging of CBP results in decreased consumption of reducing agents, see Table 6 mainly due to their content of C and metallic Fe. However, the amount of flue dust also increased. Table 6. Raw materials used during the test of cold-bonded pellets made from by-products.
The effect of size distribution of pellets on the BF behaviour Decreased filling levels in pellet bins at BF No 2 at SSAB Luleå have resulted in severe process disturbances on a number of occasions. These disturbances are shown by changes in burden permeability and gas utilisation followed by slips and changed heat level of hot metal. Practical studies carried out at SSAB Tunnplåt in Luleå showed, contrary to what was expected, no increase in the amount of fines charged to the blast furnace but an accumulation of coarse
material at low bunker levels. The EBF was used to test the behaviour by charging pellets with varying size fractions.14 The experiments confirmed that a high ratio of pellets greater than 12.5 mm caused production disturbances.
Table 7 summarise the results from the tests with different particle size distribution of pellets. The gas utilisation of the first period of testing, when pellets of the reference fraction are charged, varies as a result of some process disturbances, including a chilled hearth that was remedied just before the start of the test. The blast furnace performance deteriorates gradually, when the particle size distribution of charged pellets includes increased ratios of pellets of fraction 12.5-16mm and +16mm. The gas utilisation decreases and starts to vary more when pellets of particle size distribution 66% 9.5-12.5 mm/ 22% 12.5-16 mm/ 12% +16mm is charged. The burden descendent also becomes irregular. Some small slips occur at the same time as EtaCO reaches minimum values of approximately 44. After the start of charging pellets of particle size distribution 33/37/30, the gas utilisation decreases further and starts to vary even more. The blast furnace performance improves rapidly when pellets of particle size distribution 100/0/0 are charged into the EBF with the gas utilisation increasing to an average of 50%. When charging the pellets of particle size distribution 33/37/30 a couple of small slips occurred, as well as some periods with quite long intervals between the dumps. The behaviour of the EBF correlates well with what was experienced in the industrial furnace. Table 7. Average of process data related to particle size distribution of charged pellets.
The process disturbances were mainly attributed to
• decreased indirect reduction rate and increased direct reduction of the coarse pellets • fines generation in the shaft caused by disintegration of the coarse pellets during
reduction • increased softening and melting temperature interval caused by residual FeO in the
pellet core of the coarse pellets High oxygen and oil rate testing Typical oil and oxygen rates in Rautaruukki furnaces are 100 kg/thm oil and 27% O2 in blast. The oil price compared to coke price makes the use of oil economic. In order to test the limits and effect of high oxygen/oil operation, and EBF trial was carried out. The aims of testing very high oil and oxygen rates in the EBF were to:
• clarify and get experimental data on production increase with high oil and O2 rates • define reducing agents dependency on high oil and O2 rates • gain knowledge about BF process at high oil and O2 rates, and test where maximum
points lie due to heat balance effects • provide values for production cost estimates based on experimental data
A BF mass/heat balance model developed by Åbo Akademi was used to evaluate the EBF data. The EBF operation was quite close to target process values and little correction was necessary to estimate outcome of the target values. Table 8 shows the results of the test periods. Results showed that even at high oxygen and oil rates, the productivity increase was circa 1% for every 1% increase in blast oxygen rate at constant bosh gas rate. With an increased bosh gas rate at constant oil rate, periods 3 and 4, the production rate increase was 1.5% for 1% increase in blast O2. The relation between oil injection and coke rate showed that the replacement ratio remained close to 1:1, Figure 13, indicating that increasing the hydrogen content continued to lower the direct reduction rate and kept the total reductant rate constant. Table 8. Summary of testing of high oxygen and oil rates in the EBF for Rautaruukki. Period 1 Period 2 Period 3 Period 4 Period 5 Length (stable operation) hours 32 45 40 34 27 Blast O2 % 28 34 37 39 39 Oil rate kg/thm 100 142 168 169 203 Coke rate kg/thm 404 362 333 335 302 Total reductant rate kg/thm 504 504 501 504 505 Bosh gas volume nm3/h 2165 2172 2312 2297 2375 Productivity t/m2/d 29,2 30,8 31,5 32,5 30,8 Specific blast consumption Nm3/thm 1081 916 858 799 814
275
300
325
350
375
400
425
90 120 150 180 210Oil rate kg/thm
Coke rate kg/thm
Figure 13. Coke rate versus oil rate in the EBF Collaborative industrial research programs Starting from the dissection of campaign 3 in 1998, the furnace has been used extensively in support of various European (ECSC, RFCS) and Nordic (Jernkontoret, MiMer) research projects. Examples of several projects are found below, with these and other projects described recently in MEFOS News. 16 Accretion formation An ECSC project of which MEFOS is a partner, is the study of formation of accretions (scaffolds) in the blast furnace. Evaluation of the scaffold formation process has been done by tracking heat losses on the furnace walls and comparing to scaffolds mapped and sampled from the EBF during dissection. Detailed chemical and mineralogical study, example in Figure 14,
provides information on the processes leading to the formation that provides information for strategies to minimise the problem. A statistical model has been developed that is being tested industrially. Hearth protection by Ti injection MEFOS is a partner in a project to study the protection of the furnace hearth by formation of titanium carbo-nitrides that deposit on the hearth walls. The goal of this is to test the protection of the hearth for longer furnace campaign life. The type of material, position of injection and volume of injection are being considered. Evaluation is made by injection of Ti-compounds, Figure 15, in two campaigns just prior to quenching, and study of the distribution of titanium carbo-nitrides in the hearth of the EBF.
Figure 15. Injection of Ti-compounds in a separate lance at EBF tuyere. 16
Figure 14. Analyses of a scaffold from an EBF dissection16
Changes in microstructure of coke while passing the blast furnace The behaviour of coke in the blast furnace is being investigated in an ongoing ECSC project in which MEFOS is a partner.16 This has involved evaluation of BF operation using different grades of coke as measured by tradition laboratory quality tests (CSR, CRI). The coke is also sampled during EBF operation, and excavated coke with evaluation using chemical and mineralogical techniques. Status of EBF as a tool in Blast Furnace Research From the 14 campaigns to date, the EBF has undergone extensive modifications to equipment. There have been a wide range of research and testing done with the EBF, with only a part of research discussed in this paper. Extensive evaluation of EBF tests and comparison to industrial furnaces has lead to a deeper understanding of how the EBF can be used for blast furnace research and development.
The EBF has clearly proven its usefulness as a research tool both for LKAB’s original purpose of effective pellet development but also general blast furnace research and development. The EBF will continue to provide opportunities of advanced research and development in the future. One of the major projects requiring significant modification and multi-national involvement is the modification of the EBF to a full-oxygen blast furnace in support of the ULCOS project. References 1. M. Tottie, 'LKAB's Experimental Blast Furnace at Mefos/Luleå', 57th Ironmaking Conference,
Toronto March 22-25, 1998, ISS, pp. 1587-1590. 2. A. Dahlstedt, M. Hallin and M. Tottie, 'LKAB's Experimental Blast Furnace for Evaluation of
Iron Ore Products', Scanmet I, Luleå, Sweden, MEFOS, pp. 235-245. 3. L. Hooey and B. Sundelin, 'Evaluation of High Temperature Properties of High Iron Content
Fluxed Pellets', 57th Ironmaking Conference, Toronto March 22-25, 1998, ISS, pp. 1609-1614.
4. L. Hooey, J. Sterneland and M. Hallin, 'Evaluation of High Temperature properties of blast furnace burden', 1st International Meeting on Ironmaking, Belo Horizonte, Brazil, September 24-26, 2001, pp205-220.
5. L. Hooey, J. Sterneland and M. Hallin, 'Evaluation of Operational Data from the LKAB Experimental Blast Furnace', 60th Ironmaking Conference, Baltimore, March 22-25, 2001, ISS, pp. 197-208.
6. L. Hooey, M. Hallin and K. Raipala, ' Development of fluxed blast furnace pellets with application of coatings', METEC Congress 2003, 3rd International Conference on Science and Technology of Ironmaking', Düsseldorf, VDEh, June 16-20, 2003, pp. 256-261.
7. J. Riesbeck, Effekter av blästerfukt på LKAB:s experimentmasugn, Master's thesis, Luleå University of Technology, 2004.
8. J-O Wikström, Peter Sikström, L. Sundqvist and G. Zuo, ‘Improved Slag Formation in the Blast Furnace by Co-injection of Basic Fluxes, Together with Pulverised Coal, Through the Tuyeres’, International BF Lower Zone Symposium, Wollongong, Australia, November 2002, paper no. 18.
9. P. Sikström and B. Lindblom, 'Different reductant injectants influence on BF raceway', Scanmet II, 6-9 June, 2004, Luleå, Sweden, MEFOS, pp. 417-427.
10. E. Eliasson, Formation of Potassium Slag in Blast Furnace Pellets, Master's thesis, Uppsala University, 2004.
11. K. Raipala, On hearth phenomena and hot metal carbon content in blast furnace, Doctoral thesis, Helsinki University of Technology, 2003.
12. N. Eklund, 'Trials with mixed burden in the LKAB Experimental Blast Furnace', Scanmet II, 6-9 June, 2004, Luleå, Sweden, MEFOS, pp. 353-364.
13. G. Tranell, T. Hagelien, L. Kolbeinsen, A. Dahlstedt and M. Hallin, 'Results and Visualisation from the First Campaign in LKAB's Experimental Blast Furnace in Luleå, Sweden', 59th Ironmaking Conference, Pittsburgh, March 26-29, 2000, pp 125-136.
14. L. Sundqvist-Ökvist, Co-injection of Basic Fluxes or BF Flue Dust with PC into a BF Charged With 100% Pellets- Effects on Slag Formation and Coal Combustion, Doctoral thesis, Luleå University of Technology, 2004.
15. K. Kushima, M. Naito, K. Shibata, H. Sato, H. Yoshida and M. Ichida, ’Iron ore injection into blast furnace raceway’, ISS Ironmaking Conf. Proc. 1988, pp 457-466.
16. MEFOS News, April 2004, ed. K. Edfast, MEFOS, Luleå, Sweden.
