Influence of oxygen-rich hot air composite gas medium on sintering performance and function mechanism

Hot air sintering technology is used to improve the quality and production efficiency of sintered ore.However,the current thick layer condition highlights the disadvantage of the low oxygen potential of the hot air sintering layer.Therefore,it is considered to use oxygen enrichment sintering to improve the environment of hot air sintering.Traditional sintering,hot air sintering,and oxygen-rich hot air sintering were compared through sintering cup experiments,and the influence of hot air and oxygen-rich hot air on sintering indexes was clarified.Hot air reduced the vertical sintering velocity,while improved the yield and tumbler index.Oxygen-rich hot air sintering contributed to improving the vertical sintering velocity while ensuring the quality of sintered ore,thus comprehensively improving production efficiency.Under the action of hot air,the highest temperature of the sintering layer increased and the high-temperature holding time was prolonged.After oxygen enrichment,the combustion efficiency of fuels in the upper layer of materials was promoted,which optimized heat distribution in the middle and lower layers of materials and increased the content of calcium ferrite in the sintered ore,thus strengthening the sintering process.

Prediction of suitable water content in granulation of sintering mixture based on Litster's model

Suitable water content plays a decisive role in the granulation of sintering mixtures.Herein,a method was proposed to predict the suitable water content for effective granulation on the basis of Litster's granulation model.The granulation effectiveness of a sintering mixture was predicted by the model,with the allowance error of±10%.The effects of the water absorption properties,particle size composition and content of adhesive particles on the suitable water content were studied.The results showed that the allowable error of prediction was within±0.5%compared to the experimentally determined suitable water content.With an increase in adhesive powder content of mixtures with higher water absorption,the suitable water content increased to achieve similar granulation effectiveness.Moreover,as the amount of concentrates increased,the suitable water content first increased and then remained steady.The influence of the water absorption characteristics of the adhesive particles on the suitable water content was less than that of their particle size composition in the mixture.

Thermodynamic analysis and reaction behaviors of alkali metal elements during iron ore sintering

Reaction thermodynamics and behaviors of alkali metal compounds were studied by FactSage7.1 and sinter pot trials. Main transformation behavior of alkali metal compounds was divided into three parts: part of alkali metal chloride was gasified and emitted into the flue gas, and most of alkali metal chloride turned into sulfate, which was remained in the finished sinter, through reacting with sulfur oxide;KAlSi3O8 and NaAlSi3O8 were transformed into KAlSi2O6, NaAlSi2O6 and alkali metal oxides by reacting with calcium oxide. Moreover, newly formed alkali metal oxides turned into sulfate and silicate, entering finished sinter finally. Only a small amount of KAlSi3O8 and NaAlSi3O8 were reduced into gaseous alkali metals in ambient strong reduction atmosphere and removed into the flue gas. 21.67% of potassium and 14.56% of sodiumentered flue gas. In finished sinter, alkali metal elements existed in the form of alkali metal sulfate, silicate and aluminosilicate. The influences on alkali metal elements distribution, basicity (mass ratio of CaO to SiO2 in sinter), sulfur content, chloride content and coal ratio of raw materials indicated that increasing basicity level, rising coal ratio and adding CaCl2 promoted the removal of alkali metal elements into the flue gas. However, with sulfur content increasing in raw materials, alkali metal elements distribution ratio in the finished sinter rose.

Mineralization characteristics of pellets prepared by ultrafine magnetite concentrate:influence on metallurgical property and improving method

The reducing property of pellets prepared by ultrafine magnetite concentrate(UMC)and improving method were revealed.The results show that the reduction degree of UMC pellets is only about 56%compared with that of pellets prepared from ordinary iron ore concentrate with relatively coarse particle size,which is significantly lower than the general reduction degree of about 70%.When the composite binder composed of bentonite and organic binder was added,the reduction degree was significantly increased to 69.66%.The revealed mechanism shows that the reduced pellets with common bentonite have a concentric structure,the oxidation gap between the inner and outer layers is obvious,and the outer dense oxide layer hinders the oxidation and reduction of the inner layer.After adding the composite binder,the organic components significantly improved the internal porosity of the pellets and the aggregation degree of ultrafine iron ore concentrate particles in the granulation process,forming a porous structure.The non-uniform double-layer structure is eliminated,and the increased pores are conducive to the internal diffusion of CO,and finally the reduction degree of pellets is increased to the level equivalent to that of ordinary magnetite pellets.

Control of nitrogen oxides emission by selective non-catalytic reduction in preheating section during iron ore pellets production

Reducing the NO_(x) emission from pelletizing process is of great importance to the green development of iron and steel industry.The flue gas temperature of preheating(PH)section during grate-kiln iron ore pelletizing process typically ranges within 850–1050℃,which meets the temperature requirements of selective non-catalytic reduction(SNCR)for NO_(x).The in-bed SNCR behavior of NO_(x) in the PH section was investigated,and the influence of relevant parameters was revealed.Results show that with the flue gas temperature rising,the denitration rate reached a peak value and then declined,where the appropriate temperature range was 950–1000℃.Increasing the NH_(3)/NO ratio(NSR)contributed to improving the denitration rate,and the appropriate NSR was 1.0.Oxygen content in the flue gas also showed an important influence on denitration rate,which reached a peak value and then dropped with the oxygen content rising.Under the condition of 18 vol.%oxygen content,the denitration reaction mainly occurred in the form of 4NO+4NH_(3)+O_(2)=4N_(2)+6H_(2)O.For restricting the competitive reaction of NH_(3) oxidation,the oxygen content in flue gas of PH section should be kept at an appropriate range.In general,the denitration rate reached about 25%in the PH section through spraying ammonia.

Migration behavior of solid fuel particles during granulation process and its influence on combustion property

Iron ore sintering process is the main CO_(2) emission source throughout the integrate steelworks,which primarily comes from the combustion of solid fuels.Improving the combustion efficiency and reducing the solid fuel consumption are important ways to reduce the CO_(2) emission in the sintering process.Around the efficient combustion of fuel,the migration behavior and combustion characteristics of solid fuel in the granulation process were investigated.The results indicated that during the granulation process,fuel particles with size less than 0.5 mm mainly migrated into the granules with grain size of 1-3,3-5 and 5-8 mm;fuel particles with size of 0.5^(-1)mm mainly migrated into granules of 1-3 mm;fuel particles with size of 1-3,3-5 and 5-8 mm mainly entered the granules with the same grain size.With the increase in fuel particles grain size from-0.5 to+8 mm,the combustion efficiency exhibited a firstly-increasing and then decreasing tendency,while the NO_(x) exhibited a decreasing tendency.Potential reason can be described that finer fuel particles(-1 mm)easily distributed in the outer layer of the granules,which combusted fiercely due to its larger specific surface area,leading to the development of incomplete combustion and the conversion of fuel nitrogen;the combustion efficiency of larger fuel particles was restricted by the inner diffusion of O_(2),which then contributed to the reduction of NO_(x) under the inadequate combustion atmosphere.

Production of ultrafine iron powder by low-temperature hydrogen reduction: properties change with temperature

Ultrafine iron powder is widely used due to its excellent performance. Hydrogen reduction of fine-grained high-purity iron concentrate to prepare ultrafine iron powder has the advantages of low energy consumption, pollution-free, and low cost. The hydrogen reduction of high-purity iron concentrates, characterized by the maximum particle size of 6.43 μm when the cumulative distribution is 50% and the maximum particle size of 11.85 μm when the cumulative distribution is 90% while the total iron content of 72.10%, was performed. The hydrogen reduction could be completed at 425 ℃, and the purity of ultrafine iron powders was more than 99 wt.% in the range of 425–650 ℃. Subsequently, the effect of reduction temperature on various properties of ultrafine iron powder was investigated, including particle morphology, particle size, specific surface area, lattice parameters, bulk density, and reaction activity. It was found that the reaction activity of the iron powders prepared by hydrogen reduction was much higher than that of the products of carbonyl and liquid phase synthesis. Below 500 ℃, the reduced iron powders were nearly unbound, with a small particle size and a low bulk density. The particles had a porous surface, with a specific surface area as high as 11.31 m^(2) g^(−1). The crystallization of reduced iron powders was imperfect at this time, the amorphization degree was prominent, and the interior contained a high mechanical storage energy, which had shown high reaction reactivity. It was suitable for catalysts, metal fuels, and other functionalized applications.

Emission characteristics and control technology of heavy metals during collaborative treatment of municipal solid waste incineration fly ash in iron ore sintering process

The municipal solid waste incineration fly ash (MSWI-FA) contains a large amount of heavy metals, and the process of iron ore sintering and treating fly ash needs to pay attention to the migration characteristics of heavy metals. The impact of the application of MSWI-FA in the sintering process on the emission law of heavy metals in the collaborative treatment process was studied, and corresponding control technologies were proposed. The results showed that the direct addition of water washing fly ash (WM-FA) powder resulted in varying degrees of increase in heavy metal elements in the sinter. As the amount of WM-FA added increases, the content of heavy metal elements correspondingly increases, and an appropriate amount of WM-FA added is 0.5%–1.0%. The migration mechanism of heavy metals during the sintering treatment of WM-FA was clarified. Heavy metals are mainly removed through direct and indirect chlorination reactions, and Cu and Cr can react with SiO_(2) and Fe_(2)O_(3) in the sintered material to solidify in the sinter. Corresponding control techniques have been proposed to reduce the heavy metal elements in WM-FA through the pre-treatment of WM-FA. When the WM-FA was fed in the middle and lower layers of the sintered material, the high temperature of the lower layer was utilized to promote the removal of heavy metals. The Ni element content has decreased from 130 to 90 mg kg^(−1), and the Cd removal rate has increased by 23%. The removal rates of Cd and Cr elements increase by 2.4 and 5.5 times, respectively. There is no significant change in sintering indexes.