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.

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.

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.

Effect of H_2O(g)Content in Circulating Flue Gas on Iron Ore Sintering with Flue Gas Recirculation

The influence of H2O （g） content in circulating flue gas on sintering was studied by simulating the flue gas circulating sintering. The results show that the burning speed of solid fuel and the heat transfer rate during sintering process are improved when the H2O （g） content increases from 0 to 6%, which accelerates the sintering speed. However, when the H2O （g） content exceeds 6 %, the over-wet zone in sinter bed is thickened, which deteriorates the permeability of sintering bed. In addition, the magnetite content in sinter increases, while the acicular calcium ferrite content decreases. Accordingly, the sinter yield and tumble index decrease with excessive H2O （g） content. To guarantee the yield and quality of sinter, the favourable H2O （g） content in circulating flue gas should be controlled to be less than 6%.

Effect of Ca-Fe oxides additives on NOx reduction in iron ore sintering

As the emission control regulations get stricter,the NO;reduction in the sintering process becomes an important environmental concern owing to its role in the formation of photochemical smog and acid rain.The NOxemissions from the sintering machine account for 48% of total amount from the iron and steel industry.Thus,it is essential to reduce NO;emissions from the sintering machine,for the achievement of clean production of sinter.Ca-Fe oxides,serving as the main binding phase in the sinter,are therefore used as additives into the sintering mixture to reduce NOxemissions.The results show that the NO;reduction ratio achieves 27.76% with 8% Ca-Fe oxides additives since the Ca-Fe oxides can advance the ignition and inhibit the nitrogen oxidation compared with the conventional condition.Meanwhile,the existence of Ca-Fe oxides was beneficial to the sinter quality since they were typical low melting point compounds.The optimal mass fraction of Ca-Fe oxides additives should be less than 8%since the permeability of sintering bed was significantly decreased with a further increase of the Ca-Fe oxides fines,inhibiting the mineralization reaction of sintering mixture.Additionally,the appropriate particle size can be obtained when mixing an equal amount of Ca-Fe oxides additives of-0.5 mm and 0.5-3.0 mm in size.

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.

Optimization of Cooling Process of Iron Ore Pellets Based on Mathematical Model and Data Mining

Cooling process of iron ore pellets in a circular cooler has great impacts on the pellet quality and systematic energy exploitation. However, multi-variables and non-visualization of this gray system is unfavorable to efficient production. Thus, the cooling process of iron ore pellets was optimized using mathematical model and data mining techniques. A mathematical model was established and validated by steady-state production data, and the results show that the calculated values coincide very well with the measured values. Based on the proposed model, effects of important process parameters on gas-pellet temperature profiles within the circular cooler were analyzed to better understand the entire cooling process. Two data mining techniques—Association Rules Induction and Clustering were also applied on the steady-state production data to obtain expertise operating rules and optimized targets. Finally, an optimized control strategy for the circular cooler was proposed and an operation guidance system was developed. The system could realize the visualization of thermal process at steady state and provide operation guidance to optimize the circular cooler.

Intelligent Control of Grate-kiln-cooler Process of Iron Ore Pellets Using a Combination of Expert System Approach and Takagi-Sugeno Fuzzy Model

Grate-kiln-cooler has become a major process of producing iron ore pellets in China. Due to the diversity of the raw materials used and the multi-device multi-variable characteristics,this process still encounters with control problem. An attempt was proposed to deal with this issue. The three-device-integrated feature of the process was firstly analyzed to obtain control strategy,and then an intelligent control system using a combination of expert system approach and Takagi-Sugeno（ T-S） fuzzy model was developed. Expert system approach was used to diagnose and remedy the abnormal conditions,while T-S fuzzy model was used to stabilize the thermal state. In the construction of T-S fuzzy rules,antecedents were identified by fuzzy c-mean clustering algorithm incorporated with subtractive clustering algorithm,and consequent parameters were identified by recursive least square algorithm. The control system was applied in a Chinese pelletizing plant and the application results demonstrated its effectiveness of stabilizing the thermal states within three devices.