| Due to the limitation of resources and the deterioration of environment,more attention is paid to the tracking of material flow and energy flow,especially carbon,which is closely related to global warming.Since 2000,global steel production and demand have increased sharply,and carbonaceous materials as a carrier of energy and emissions burn fiercely.Fe-C interaction has always been a focus of interest,which occurs in different iron metallurgical processes,such as the dissolution of coke in blast furnace(BF)molten iron,and the erosion of carbon bricks by molten iron.A thorough understanding of the dissolution behavior of various carbonaceous materials in molten iron is of great significance for optimizing the ironmaking process.It is also the key to improving resource utilization and reducing environmental load.This thesis uses laboratory simulation experiments and internal sampling methods in BFs to study the factors affecting the dissolution of coke in molten iron and the multiphase behavior of slag-iron-coke in the middle and lower BFs in detail.Firstly,the physical and chemical behavior of coke in the tuyere area was analyzed through the method of tuyere core drilling and BF dissection,as well as the slag-iron-coke sample near the edge of the deadman.The graphitization degree of 25～20 mm tuyere coke is higher,but its pore size is much larger.The porosity of the 5～1 mm tuyere coke is obviously low,and it contains a considerable amount of Fe2O3,which will play a positive role in the gasification reaction.In the cohesive zone,complex reactions occur inside the coke to produce SiC,which also speeds up the gasification reaction.The pores inside the coke are filled with molten slag and a small amount of molten iron.The iron-carbon interface is covered by a slag layer.The coke still has a large number of micropores with a volume less than 1 mm3.There is still coke larger than 60 mm(more than 1%)in deadman,indicating that the reaction of coke is very uneven.The d002 and Lc of the coke in the hearth after demineralization are 3.368 A and 587 A,respectively.Through the diffraction pattern of the transmission electron microscope,the interlayer graphite flakes can be observed.Secondly,the dissolution behavior of graphite into molten iron was analyzed with the help of static drop method and iron covering method.At the same time,the impact of coke pores,carbon structure,and ash were compared by studying the dissolution behavior of four different carbon materials in molten iron.The dissolution of carbon significantly reduces the melting point of the iron alloy.After the carburizing is completed,the C dissolved in the graphite will form an irregular lamellar structure with a smaller size,which will interact with the original C in the ferroalloy,and then aggregate to form dendrites with a larger size.Due to the greater repulsive force between the Fe-Fe bonds,it is more difficult for the Fe atoms to move into the graphitic carbon,and finally a Fe-C interface layer is formed between the Fe and C.At 1500℃,the thickness of the interface layer between graphite and iron alloy is about 200 μm,which does not change with the initial carbon content.The mineral layer formed at the interface can reduce the iron-carbon contact and hinder the further carburizing reaction.Although the carbon structure of coke has a high degree of disorder and high ash content,the existence of pores not only avoids the accumulation of interfacial minerals,but also provides an effective contact area for the iron-carbon reaction,resulting in the promotion of carburizing reaction.Thirdly,a new coke analogue was prepared to replace metallurgical coke to replace in the laboratory.At the same time,isothermal and non-isothermal monitoring of the carbon dissolution process was carried out using a high temperature tube furnace and high temperature confocal.And the dissolution rate and carbon dissolution limit of different carbon materials was compared.The coke analogue prepared from deash metallurgical coke powder are more simulating.The main advantage is the relatively simple and disordered structure obtained from coal,which is also conducive to the addition of minerals and metals.The non-isothermal experiments show that graphite starts to carburize into solid iron at around 920℃.And the occurrence of carburization accelerates the phase transformation and melting of iron.After carbon reaches saturation,there is no obvious carburization.The C activity in molten iron a[c]and the activity of carbonaceous materials ac are the main reasons for the difference in the carbon dissolution limit.The carbon structure of graphite is highly ordered,resulting the lower dissociation energy of carbon atoms;the existence of minerals causes the increase of impurity elements in the interface layer,and the influence of other elements on ac is aggravated;The pores reduce the mineral content at the interface,and increase the effective contact area between iron and carbon,which weakens the influence of impurity elements.Finally,in order to clarify the effect of carburizing reaction on iron ore reduction in different regions of BF,the effect of pure FeO on the dissolution rate of graphitic carbon and the complex multiphase reaction between FeO-containing slag-molten iron-coke were analyzed.And the influence mechanism of FeO exists on the coke degradation in molten iron and slag was also analyzed.The main conclusions are as follows:the rate of coke participating in the dissolution reaction is faster than that of direct reduction of FeO in the slag.The degree of dissolution degradation of coke at the slag-iron interface is significantly stronger than that of the slag leaching layer and iron leaching layer,and the increase of FeO content also accelerates the degradation.The change of FeO content in the slag composition has little effect on the dissolution of C.The severe deterioration of coke at the slag-iron interface is mainly the combined effect of C dissolution reaction,reduction reaction and gasification reaction.Improving the dissolution rate of coke into molten iron and avoiding the accumulation of undissolved carbon particles at the interface are the key to iron oxide reduction and slag phase formation.Reasonable control of coke dissolution behavior is very important to control the position and thickness of the cohesive zone.Coke degradation in the middle and lower part of BF is the severe liquid-solid solution loss reaction by molten slag-iron.Therefore,the carburization of coke should be controlled in a reasonable range,not only to ensure a certain carburizing,but also to ensure the strength after the liquid-solid solution loss reaction,which is very important to ensure the gas and liquid permeability in BF and the stability of the furnace condition. |
PDF Full Text Request