Two measures for coke saving and increase in blast furnace efficiency related to coke characteristics -reactivity and size -are discussed in this paper. Modern blast furnace operation with low coke rate and high injection rate causes a change in coke quality requirements. A discussion has arisen recently about highly reactive coke. Here, a theoretical analysis of influence of coke reactivity on the thermal reserve zone, direct reduction and carbon consumption in the blast furnace has been undertaken. Experiments have been performed using non-standard test scenarios that simulate coke behaviour under real blast furnace operating conditions. Coke reactivity and microstructure have also been investigated under the impact of alkali and pulverised coal ash and char. Operation of many blast furnaces has proved the possibility of coke saving and increase in productivity when using small-sized coke (so-called nut coke) mixed with the burden, but the reasons for this phenomenon, and consequently the limit for nut coke consumption, are still not very clear. An analytical method and cold model simulations have been used to quantify the change in shaft permeability and furnace productivity when using nut coke.

Nowadays the use of charcoal in metallurgy is intimately linked to small blast furnaces in Brazil. Due to the challenge for CO 2 mitigation, interest for charcoal use as a renewable energy source is rising. In the scope of European efforts to mitigate carbon dioxide emissions in the steel industry in the post-Kyoto period, the use of charcoal in cokemaking and ironmaking has been investigated. This paper presents results of an experimental study on charcoal behaviour under the blast furnace simulating conditions performed at the Department of Ferrous Metallurgy, RWTH Aachen University and at the National Centre for Metallurgical Investigations, Madrid. Conditions in the raceway and in the furnace shaft were simulated using thermo-analytical, laboratory and pilot facilities. Charcoal samples were produced in two furnaces for pyrolysis from different wood types at various carbonisation conditions. Furthermore technological and ecological assessment of blast furnace process when injecting different types of charcoal was performed using a mathematical model. All the experiments and calculations were also performed with reference mineral coals for injection. Conversion efficiency of all the tested charcoals is better or comparable with coals. Change in coke rate, furnace productivity and further operation parameters when replacing pulverised coal with charcoal depends on charcoal ash content and composition.KEY WORDS: blast furnace; charcoal injection; CO 2 emission; raceway simulation; secondary consumption. 81© 2010 ISIJ coal Brazilian furnaces not only in terms of larger dimensions and higher operational parameters but also in terms of in-furnace reaction conditions: the chemical reactivity of coke is significantly lower compared with charcoal and Boudouard reaction occurs in the coke blast furnace at higher temperatures. Therefore the degree of indirect reduction in the furnace shaft is higher and consequently carbon monoxide content in top gas and its calorific value are lower. Effect of charcoal injection on large blast furnaces and at high injection rates was studied up to now mainly by mathematical modelling. 7) There are also studies on waste wood use for producing metallurgical coke and for BF injection, 8,9) but the raw wood is difficult to be grinded, because it is composed of rigid structure of cellulose and lignin.10) In Ref. 10) a study was done on biomass injection. In this work, firstly technological and ecological assessment of BF operation when injecting charcoal was conducted using a mathematical model. Afterwards, laboratory and pilot injection trials, microscopic study as well as tests using thermal analysis were carried out to investigate the charcoal behaviour under the blast furnace raceway simulating conditions. Furthermore solution loss reaction of charcoal in the furnace shaft was investigated to evaluate the possibilities of secondary utilisation of charcoal outside the raceway. Effect of charcoal on coke reactivity was studied as well. Injection of PC used in the industrial blast furnace...

Sinters were produced in the pilot plant using four different ore mixtures with varying proportions of iron ores, fluxes and coke. All the resulting sinters were characterised by chemical and granulometric analysis, degradation testing during reduction in the blast furnace (RDI test), cold resistance testing (Tumbler test), reducibility testing, determination of softening and melting temperatures, and determination of the sinter structure by electron microscopy. The obtained result allow for the establishment of better operation conditions to manufacture sinters.KEY WORDS: sintering; quality of sinter; ore mixtures; iron ores; blast furnace. 1089© 2010 ISIJ line with the ores present, but is three percentage points lower in mixtures 3 and 4 due to the inclusion of 'Goa Silicioso' ore with its lower total iron content. The ferrous content between 3.1 and 4.8 % can be considered as low as correspond to the hematitic nature of the iron ores that make up part of the mixtures. The alkalis content is low. Granulometric AnalysisGranulometric analysis has been performed using a ROT-TAP unit, which combines reciprocating eccentric rotary screening with a percussion system on the screen column. Figure 1 displays the granulometric curve for ore mixture 1, with an average particle size of 1.69 mm. Table 5 lists these values for the four different mixes. Granulation FitnessThe ore mixtures are subjected to granulation treatment prior to sintering in order to increase the average size of the very fine grained ores, with the aim of improving their dynamic behaviour during sintering.The granulation treatment is of basic importance in iron ore sintering, because good sinter bed permeability to a large extent determines the sintering rate and thus the plant's productivity.Granulation fitness testing of each iron ore and each ore mixture has been carried out following the SAFE (Size Analysis on Frozen Elements) standard procedure established by Centro Sviluppo Materiali (CSM) of Italy. Figure 2 shows the granulometry curve of ore mixture 1 before and after the SAFE test. Table 5 indicates the average particle size of the ore mix- ISIJ International, Vol. 50 (2010), No. 8 4) 1090© 2010 ISIJ Table 1. Chemical analysis of iron ores (wt%). Table 2. Chemical analysis of fluxes (wt%). Table 3. Composition of ore mixtures (wt%). Table 4. Chemical analysis of ore mixtures (wt%). tures after undergoing the SAFE test. All the mixtures present good granulation fitness. ReducibilityA reducibility test has been performed at 900°C following the ISO standard for sinters, adapted for ore mixtures of the 3.3-2.0 mm fraction.5) The results are displayed in Table 5. The R 60 value ranges between 50-56 % and may be considered good. Softening and Melting TemperaturesThe test to determine softening and melting temperatures of the ore mixtures has been carried out using a LECO AF-600 unit, with an oven that reaches a maximum temperature of 1 650°C, in which the following parameters have been fixed with the help of a computer: ASTM standard with inert ...

Blast furnace (BF) coal injection became a routine practice among European BFs; roughly, 40% of total energy required for the process is covered by auxiliary reducing agents. Pulverized coal (PC) remains the most commonly used auxiliary reductant. The key trend is increasing PC injection rates; over 200 kg tHM À1 PC on an annual basis is no rarity any more. Despite numerous measures for intensifying the coal conversion in the raceway, [1] it is hardly possible to combust such a high amount of coal within a very short residence time of few tens of milliseconds. Recent computational fluid dynamics calculations showed that at PC injection rate of 240 kg tHM À1 , about 50% of the coal amount entering the raceway may leave it as so-called char. [2] Another theoretical study from 2011 calculated a maximum PC injection rate of 190-210 kg tHM À1 for some BFs, considering that no ash deposition nor change in the gas flow distribution due to unburnt coal fines trapped in the coke bed takes place. [3] The following types of coal residues appear depending on different conditions and stages of its formation (Figure 1): 1) devolatilized coal particles (after light gases and tar have been released); 2) pyrolyzed (partly or completely) particles (caused by the thermal decomposition of the organic matter); and 3) not completely gasified particles (residues). Char formation, transportation, and behavior outside the raceway may significantly affect the BF process both negatively with respect to process stability and positively by increasing the combustion efficiency by possible consumption of char. The knowledge on these phenomena was limited because the main efforts over the last few decades were focused on the complete conversion of PC within the raceway. A char morphology system was introduced for the characterization of char types. [4] However, few studies are devoted to the