Numerical simulation of the direct reduction of pellets in a rotary hearth furnace for zinc-containing metallurgical dust treatment

A mathematical model was established to describe the direct reduction of pellets in a rotary hearth furnace （RHF）. In the model, heat transfer, mass transfer, and gas-solid chemical reactions were taken into account. The behaviors of iron metallization and dezincification were analyzed by the numerical method, which was validated by experimental data of the direct reduction of pellets in a Si-Mo furnace. The simulation results show that if the production targets of iron metallization and dezincification are up to 80% and 90%, respectively, the furnace temperature for high-temperature sections must be set higher than 1300~ C. Moreover, an undersupply of secondary air by 20% will lead to a decline in iron metallization rate of discharged pellets by 10% and a decrease in dezincing rate by 13%. In addition, if the residence time of pellets in the furnace is over 20 min, its further extension will hardly lead to an obvious increase in production indexes under the same furnace temperature curve.

Preparation of ZnO Nanoparticles from Zn-containing Rotary Hearth Furnace Dust

To solve the problem of the low added value Zn-containing rotary hearth furnace(RHF)dust,two deep eutectic solvents(DESs)were employed,such as choline chloride-urea(ChCl-urea)and choline chloride-oxalic acid dihydrate(CC-OA)solvent and Zn-containing RHF dust(water-washed)as the research target.Then,we prepared ZnO nanoparticles using two DESs or their combination,namely,ChCl-urea(Method A),CC-OA(Method B),first CC-OA and then ChCl-urea(Method B-A)and first ChCl-urea and then CCOA(Method A-B),respectively.The effects of these methods on the properties of as-obtained precursors and ZnO nanoparticles were investigated in detail.The results indicated that the precursor obtained by Method A was Zn_(4)CO_(3)(OH)_(6)·H_(2)O,and those by Methods B,B-A,and A-B were all ZnC_(2)O_(4)·2H_(2)O.Moreover,the decomposition steps of the last three methods were similar.The ZnO contents of 95.486%,99.768%,99.733%,and 99.76%were obtained by Methods A,B,B-A,and A-B,respectively.Methods A,B,and B-A led to the formation of spherical and agglomerated ZnO nanoparticles with normal size distributions,where Method B showed the best distribution with an average diameter 25 nm.The ZnO nanoparticles obtained by the Method A-B did not possess good properties.

Influence of furnace temperature and non-uniform heat flux density on direct reduction process of newly designed carbon containing pellet

In this study,innovative ellipsoid pellet with craters on its surface was designed,and the direct reduction process was compared with ellipsoid(without craters)and sphere pellets.In addition,furnace temperature and uneven heat flux density effects on the pellet direct reduction process were also studied.The results show that ellipsoid pellet is better than that of spherical pellet on metallization ratio.However,under the condition of non-uniform heat flow,the ellipsoid pellet final metallization rate and zinc removal rate were lower.Although the heat transfer effect of ellipsoid pellet with craters was not improved significantly,the metallization rate and zinc removal rate were found improved,which will have a cumulative effect on the pellets direct reduction process in rotary hearth furnace.Under varying furnace temperature conditions,the pellet temperature was higher than that of the constant furnace temperature.After 1200 s,pellet Fe concentration increased to 123.6%,metallization rate and zinc removal rate increased to 113.7%and 102.2%,respectively.These results can provide references for the carbon-containing pellet design used in rotary hearth furnace.

Mathematical model of the direct reduction of dust composite pellets containing zinc and iron

Direct reduction of dust composite pellets containing zinc and iron was examined by simulating the conditions of actual production process of a rotary hearth furnace （RHF） in laboratory. A mathematical model was constructed to study the reduction kinetics of iron oxides and ZnO in the dust composite pellets. It was validated by comparing the calculated values with experimental results. The effects of furnace temperature, pellet radius, and pellet porosity on the reduction were investigated by the model. It is shown that furnace temperature has obvious influence on both of the reduction of iron oxides and ZnO, but the influence of pellet radius and porosity is much smaller. Model calculations suggest that both of the reduction of iron oxides and ZnO are under mixed control with interface reactions and Boudouard reaction in the early stage, but only with interface reactions in the later stage.

Comprehensive Utilization of Complex Titania Ore

To fully utilize Panzhihua titanium resources, a new process was proposed. In the process, Panzhihua ilmenite concentrate was first reduced in a rotary hearth furnace （RHF） to produce a titanium-rich material and iron. The titanium-rich material was then used in a new chlorination process to produce TiCl4. The comparison of different groups of experimental results or calculation results showed that the utilization ratio of material was improved by using the titanium-rich material after pretreatment other than low level titanic ilmenite directly and the combined fluidized beds （FTF） were more likely to reduce bed height and reaction time than the single fluidized beds （Single F or Single T） under the condition of the same chlorination conversion ratio. Finally, the influence of reduction temperature and the anti-agglomeration capacity of the combined fluidized bed was analyzed.

Removal Mechanism of Zn,Pb and Alkalis from Metallurgical Dusts in Direct Reduction Process

The high-temperature tube furnace was applied to simulate the rotary hearth furnace （RHF） for the direct reduction of zinc-bearing dusts from steel plants. The removal mechanism of Zn, Pb and alkalis from cold bonded briquettes made by mixing metallurgical wastes, such as dust from bag house filter, OG sludge, fine converter ash and dust from the third electric field precipitator of the sinter strand, in various proportions was investigated. More than 70% of metallization rate, more than 95% of zinc removal rate, 80% of lead removal, as well as more than 80M of K and Na removal rates were achieved for the briquettes kept at 1473-1603 K for 15 min during the direct reduction process respectively. The soot generated in the direct reduction process was studied by chromatography, X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The results suggested that the main phases of the soot were ZnO, KC1, NaC1 and 4ZnO · ZnC12 · 5H20. Furthermore, the content of Zn reached 64.2 %, which could be used as secondary resources for zinc making. It was concluded that KC1 and NaC1 in secondary dust resulted from the volatilization from the briquettes, whilst ZnO and PbO were produced by the oxidation of Zn or lead vapour from briquettes by direct reduction.

Effect of quaternary basicity on reduction behavior of iron-bearing dust pellets

The treatment of iron-bearing dusts and sludges by the rotary hearth furnace process has the advantage of sufficient utilization of valuable metals and a high impurity removal rate,but the lower strength of the metallized product needs to be addressed.The effects of quaternary basicity R4(w(CaO+MgO)/w(SiO_(2)+Al_(2)O_(3)))on the reduction behavior and physical and chemical properties of metallized pellets,including phase composition,compressive strength,microstructure and soft melting area,were investigated with FactSage thermodynamic software and experiments.The strength of metallized pellets depended on the gangue composition,such as CaO,MgO,Al_(2)O_(3) and SiO_(2),due to the altered chemical composition,physical phase composition,microscopic morphology and stability of the slag phase.The reduction of carbon-bearing pellets was significantly promoted by suitable basicity.The lower basicity(R_(4)<1.4)facilitated the formation of low melting point iron-containing compounds from SiO_(2) and Al_(2)O_(3) with FeO,resulting in increased liquid phase generation,but lower metallization rate,due to the hindered precipitation and growth of iron grains.Interestingly,the higher basicity(R_(4)>1.8)also increased the amount of liquid phase and improved the strength of the pellets,due to the granular iron crystals bonded into sheets.Notably,the main component of the liquid phase in high-basicity conditions was calcium ferrite.Although the additional amount of liquid phase was beneficial to the strength of the metallized pellets,calcium disilicate was formed at R_(4)=1.6,resulting in a reduction in the compressive strength of the pellets to 1521.9 N/pellet.

Experimental study and industrial demonstration on utilization of Fe,Ti and V from vanadium-bearing titanomagnetite ore sands

In order to achieve highly efficient utilization of three valuable elements Fe,Ti and V simultaneously from vanadium-bearing titanomagnetite ore sands,an improved carbothermic reduction method was proposed and verified in both laboratory scale and industrial test-bed scale.The method combined the process of direct reduction and the process of further reduction and separation.Particularly,pulverized coal injection was introduced.In experimental tests,the effects of parameters such as carbon content in briquette,reduction duration and reduction temperature on the contents of metallic Fe and FeO as well as Fe metallization rate were analyzed.Experimental results indicated that Fe metallization rate in the carbon-containing briquette could reach 75.83%.In the industrial test-bed tests,the effects of carbon content in briquette,reduction duration and reduction temperature were also investigated,respectively.In addition,processes with and without pulverized coal injection were tested.The comparative analysis indicated that the content of TiO2 in titaniferous slag was increased by applying pulverized coal injection,and it can reach 82.5 wt.%.Meanwhile,the energy performance analysis showed that the equivalent electricity consumption of the test-bed dropped significantly to 2071 kWh per ton of slag,about 26.0%less than that of traditional method.Moreover,the investment payback of the test-bed is 3.4 years.Both experiments and industrial test-bed tests demonstrated that the proposed method has the advantages of highly efficient utilization,high energy efficiency as well as good economic performance.