Divriği A kafası manyetit cevherlerindeki alkalilerin klorlayıcı buharlaştırma yöntemi ile giderilmesi

Abstract

ÖZET Bu çalışmada Divriği A kafası manyetit cevherlerin de mevcut alkalilerin (K, Na), cevher yüksek fırına şarj edilmeden önce, klorlayıcı buharlaştırma yöntemi ile giderilme koşullarının incelenmesi amaçlanmış ve cevher ve konsantreye değişen miktarlarda CaCl ilave edilerek alka lilerin uçucu klorür bileşikleri şelclinde sistemden uzak laştırılması sağlanmıştır. Bu amaçla yapılan deneylerle; farklı boyut aralıkla rındaki cevherlerde, sinter harmanında ve pelet üretim koşullarında alkalilerin giderilmesi incelenmiştir. Deneyler büyük oranda pelet üretim koşullarında gerçekleştirilmiş ve bu gruptaki deneylerde çapı yüksekliğine eşit özel briket peletler kullanılmıştır. Sinter harmanında ve pelet üretim koşullarında ger çekleştirilen deneylerde toplam alkali (K^O+Na^O) giderme veriminin sırasıyla % 73 ve 87.5 olduğu ve pelet üretim koşullarında alkalilerin daha yüksek bir verimle giderildiği görülmüştür. Pelet üretimi ve bazik pelet üretim koşullarında CaCl` ilavesi ile gerçekleştirilen deneyler sonucunda, gerek alkali gideriminde elde edilen yüksek verim gerekse silindirik peletlerin sahip olduğu fiziksel özellikler nedeniyle, CaCl`'ün pelet üretiminde kullanılabileceği gö rülmüştür. Divriği A kafası konsantresinden hazırlanmış örneklerde optimum CaCl` ilavesi olan % 5 CaCl` (stokio- metrik miktarın 4.0 katı) miktarında ve 1230 C reaksiyon sıcaklığında peletlerde mevcut K`0 miktarı % 90.4 giderme verimi ile % 0.072'ye Na~0 miktarı ise % 61.3 giderme ve rimi ile % 0.058'e düşmüştür. Bazik pelet üretim koşullarında CaC0` ilavesi ile sağlanan baziklik oranı artışı ile peletlere ilave edilecek CaCl` miktarının azaltılabileceği görülmüştür. Bazik peletlerde optimum sonuçların elde edildiği % 3 CaCl2 içeren ve baziklik oranı `1` olan peletlerde 1230°C reaksiyon sıcaklığında K?0 % 92 giderme verimi ile % 0.062'ye Na`0 ise % 74.6 giderme verimi ile % 0.038'e düşmüştür. Demir cevherlerinde mevcut kükürt de % 99'un üzerin de bir giderme verimi ile eser miktara inmiştir. Alkalilerin ve kükürdün yanısıra demir cevherinde mevcut Cu ve Zn'nun da giderildiği görülmüştür. CaCl` ilavesi ile hazırlanan örneklerin indirgenme deneylerin indirgenme hızının sadece bentonit içeren örneklere göre çok az düştüğü ve indirgenme sırasında ör neklerde kabul edilebilir sınırın çok altında şişmenin meydana geldiği görülmüştür. - v -

THE REMOVAL OF ALKALIS FROM `DİVRİ?İ A BLOCK` IRON ORES BY THE CHLORIDE VOLATILIZATION PROCESS SUMMARY The presence of alkalis in the blast furnace has long been recognized as a source of trouble to the smooth functioning of the blast furnace. Severe operating problems may arise when higher alkali pellets are used. The alkali metals, sodium and potasium enter the blast furnace as complex silicates with the charge which consist of ore, pellets, sinter, flux and coke. Some of the alkalis entering the furnace goes into the slag, some of them go out as dust with the gases, some of them are absorbed by refractory lining and the rest is recirculat ed. The concentration of sodium and potasium in the furnace is concequently much higher than that would be expected from the amounts introduced since recirculating part of alkali metals accumulate over a period of time. The disadvantages of alkali accumulation can be listed as follows: a) Alkali compounds cause erratic performance of the blast furnace resulting in hanging and slipping and causing scaffolds on the walls of the furnace, b) The presence of alkali increases the coke con sumption due to the transfer of heat to higher levels in the blast furnace, c) Alkalis causing catastrophic swelling and dis integration of pellets and coke, d) The formation of alkali cynanides which contribute to the recirculation of the alkali within the furnace and cause environmental problems, e) The damaging effect of alkali on the blast furnace refractories. - vi -The problems caused by alkalis can be eliminated in two ways: - The first is minimising the alkali input. Alkali input to the furnace can be minimized by blending of ores, upgrading of alkali containing ores, reduction of the coke rate by chemical removal of alkalis from the ore before charging, - The second is increasing the alkali content of the slag by controlling the slag volume and basicity ratio. Consequently the alkali output can be maximized. The alkali problem in principle can be controlled by both lowering their contents in the raw materials and by avoiding certain combinations of operating para meters. The constraints imposed on the operation con ditions often have adverse effects on the performance of a blast furnace. Therefore, the fundamental solution is the removal of alkalis from raw materials before charging into the furnace. Economical removal of alkalis from iron ore, con centrates and ore pellets necessitates high reaction rates. Therefore the only opportinuty is to carry out this separation process during the high temperature period of iron ore preparation i.e. sintering or induration of iron ore pellets. The only phase which should be used as the sink for the removal of alkalis is the gaseous phase. Under the conditions of iron ore agglomeration, the vapour phases such as metal vapours and cynanides are not stable. Vapour pressures of alkali chlorides under induration conditions are high enough for their removal by volatilization. A source of chlorine must be provided. The chloride with much lower vapour pressure than that of alkali chlorides should be used, so that it will remain in situ until the gasification of alkalis takes place. Calcium chloride which has low vapour pressure even at high temperature satisfies this requirement. In the present work the removal of alkalis (Na, K) which exist in the `Divriği A block` iron ores were investigated. The chloride volatilization process were chosen for removal of alkalis. The average chemical com position of the ores used were: 56.8% Fe, 9.2% SiO-, 1.16% - VXl -K20, 0.20% Na20, 0.57% S, 0.03% Cu, 0.033% Zn. Chloride was added to iron ore and concentrate as calcium chloride. Experiments were carried out in three main groups in order to investigate the removal of alkalis. The first group of experiments were carried out to determine the effect of the size distribution of the ore on the removal of alkali during pelletizing and sintering. The second group of experiments were carried out to investigate the removal of alkalis in a sinter mix with 10% moisture, 5% coke dust and enough CaC0` with a basicity ratio of `l`. The third group of experiments were carried out to investigate the removal of the alkalis during pelletizing. In these experiments cylindirical test pellets whose dia meters were equal to their heights with equal physical properties were used. Experiments were carried out by using tubular furnace with alumina reaction tube (about 26 mm I.D). The temperature of the experiments was measured by Pt-PtRh thermocouple which was placed right above the ceramic boats. During the whole experiments air flow rate of 5 liters per minute was maintained through the tube. The experiments were started when the temperature profile had reached the desired state and ceramic boat was placed in the cold region which is close to the end of the reaction tube. Then the ceramic boat was immediately pushed into the hot zone of the furnace. All samples hold in the desired temperature for 30 minutes. The samples were taken out. Later they analysed by means of atomic- absorbstion spectrophotometre Perkin Elmer 3030 and a C- S analyser of Leybold-Heraus. The variables of the present investigation are ore size, amount of CaCl` used, amount of the alkalis in the ore, temperature, basicity of sample (Ca0/Si0`) and reaction time. - vm -The results were obtained from experiments as follows: Efficiency of the alkali removal is 73% and 87.5% in the sinter mix and pelletizing operations respectively, therefore it was concluded that the removal of alkalis are much more effective under pelletizing conditions. In the light of the experiments carried out with the addition of calcium chloride it was concluded that calcium chloride addition could be used during normal pelletizing and basic pelletizing because of the high efficiency of alkali removal and physical properties of the cylindirical pellets. It was observed from the results of the experiments that it is necessary to add more calcium chloride than what it is expected from the stockiometry to remove the alkalis present in iron ore and concentrates. For iron ore and sinter mix the optimum calcium chloride addition was found to be 6.0% whereas for iron ore concentrates 5.0%. These values are 3.6 and 4.0 times of the stockiometric values respectively and the efficiency remain unchanged above these values. Experiments showed that in order to obtain pellets with low alkali content and physical properties which are suitable for the blast furnace, induration temperature should be around 1230°C. At 1230°C residual K20 was found to be 0.072% with a 90.4% removal efficiency and Na20 0.058% with a 61.3% removal efficiency for the pellets which were prepared with 5.0% calcium chloride addition from iron ore concentrate. The increase in basicity by addition of calcium carbonate has a positive effect on the removal efficiency. The removal efficiency was higher for the pellets which were prepared with only 3.0% calcium chloride addition but a basicity ratio of one than the pellets which were prepared with 5.0% calcium chloride addition. - xx -For these pellets residual K`0 was found to be 0.062% with an removal efficiency of 92.0% and Na~0 0.038% with an removal efficiency of 74.6%. These pellets have also good physical properties to be used in the blast furnace. - It was also observed that more than 99.0% of the sulphur present in the ore was eliminated at 1230°C. Copper and zinc were also eliminated during this process. - It was established that the samples whose alkalis removed by the calcium chloride is suitable for charging the blast furnace in con sideration of the rate of reduction and behaviours under the reduction conditions from reduction experiments. - x -