Effect of CO_2 and H_2O on gasification dissolution and deep reaction of coke

To more comprehensively analyze the effect of CO_2 and H_2O on the gasification dissolution reaction and deep reaction of coke, the reactions of coke with CO_2 and H_2O using high temperature gas–solid reaction apparatus over the range of 950–1250°C were studied, and the thermodynamic and kinetic analyses were also performed. The results show that the average reaction rate of coke with H_2O is about 1.3–6.5 times that with CO_2 in the experimental temperature range. At the same temperature, the endothermic effect of coke with H_2O is less than that with CO_2. As the pressure increases, the gasification dissolution reaction of coke shifts to the high-temperature zone. The use of hydrogen-rich fuels is conducive to decreasing the energy consumed inside the blast furnace, and a corresponding high-pressure operation will help to suppress the gasification dissolution reaction of coke and reduce its deterioration. The interfacial chemical reaction is the main rate-limiting step over the experimental temperature range. The activation energies of the reaction of coke with CO_2 and H_2O are 169.23 kJ ·mol-1 and 87.13 kJ·mol^(-1), respectively. Additionally, water vapor is more likely to diffuse into the coke interior at a lower temperature and thus aggravates the deterioration of coke in the middle upper part of blast furnace.

Formation mechanism of the protective layer in a blast furnace hearth

A variety of techniques, such as chemical analysis, scanning electron microscopy-energy dispersive spectroscopy, and X-ray diffraction, were applied to characterize the adhesion protective layer formed below the blast furnace taphole level when a certain amount of titanium-bearing burden was used. Samples of the protective layer were extracted to identify the chemical composition, phase assemblage, andistribution. Furthermore, the formation mechanism of the protective layer was determined after clarifying the source of each componenFinally, a technical strategy was proposed for achieving a stable protective layer in the hearth. The results show that the protective layemainly exists in a bilayer form in the sidewall, namely, a titanium-bearing layer and a graphite layer. Both the layers contain the slag phaswhose major crystalline phase is magnesium melilite（Ca2Mg Si2O7） and the main source of the slag phase is coke ash. It is clearly determinethat solid particles such as graphite, Ti（C,N） and Mg Al2O4play an important role in the formation of the protective layer, and the key factofor promoting the formation of a stable protective layer is reasonable control of the evolution behavior of coke.

Reduction kinetics of iron oxide pellets with H_2 and CO mixtures

Reduction of hematite pellets using H2-CO mixtures with a wide range of H2/CO by molar （1：0, 3：1, 1：1, 1：3, and 0：1） at different reducing temperatures （1073, 1173, and 1273 K） was conducted in a program reducing furnace. Based on an unreacted core model, the effective diffusion coefficient and reaction rate constant in several cases were determined, and then the rate-control step and transition were analyzed. In the results, the effective diffusion coefficient and reaction rate constant increase with the rise in temperature or hydrogen content. Reduction of iron oxide pellets using an H2-CO mixture is a compound control system; the reaction rate is dominated by chemical reaction at the very beginning, competition during the reduction process subsequently, and internal gas diffusion at the end. At low hydrogen content, increasing temperature takes the transition point of the rate-control step to a high reduction degree, but at high hydrogen content, the effect of temperature on the transition point weakens.

Reduction mechanisms of pyrite cinder-carbon composite pellets

The non-isothermal reduction mechanisms of pyrite cinder-carbon composite pellets were studied at laboratory scale under argon （Ar） atmosphere. The composite pellets as well as the specimens of separate layers containing pyrite cinder and coal were tested. The degree of reduction was measured by mass loss. The microstmctures of the reduced composite pellets were characterized by scanning electron mi- croscopy （SEM）. It is found that the reduction processes of the composite pellets may be divided into four stages： reduction via CO and H2 from volatiles in coal at 673-973 K, reduction via H2 and C produced by cracking of hydrocarbon at 973-1123 K, direct reduction by carbon via gaseous intermediates at 1123-1323 K, and direct reduction by carbon at above 1323 K. Corresponding to the four stages, the apparent activation energies （E） for the reduction of the composite pellets are 86.26, 78.54, 72.01, and 203.65 kJ.mol-1, respectively.

Formation mechanism of the graphite-rich protective layer in blast furnace hearths

A long campaign life of blast furnaces is heavily linked to the existence of a protective layer in their hearths. In this work, we conducted dissection studies and investigated damage in blast furnace hearths to estimate the formation mechanism of the protective layer. The results illustrate that a significant amount of graphite phase was trapped within the hearth protective layer. Furthermore, on the basis of the thermodynamic and kinetic calculations of the graphite precipitation process, a precipitation potential index related to the formation of the graphite-rich protective layer was proposed to characterize the formation ability of this layer. We determined that, under normal operating conditions, the precipitation of graphite phase ~om hot metal was thermodynamically possible. Among elements that exist in hot metal, C, Si, and P favor graphite precipitation, whereas Mn and Cr inhibit this process. Moreover, at the same hot-face temperature, an increase of carbon concentration in hot metal can shorten the precipitation time. Finally, the results suggest that measures such as reducing the hot-face tem- perature and increasing the degree of carbon saturation in hot metal are critically important to improve the precipitation potential index.

Reduction behavior and kinetics of vanadium–titanium sinters under high potential oxygen enriched pulverized coal injection

In this work, the reduction behavior of vanadium–titanium sinters was studied under five different sets of conditions of pulverized coal injection with oxygen enrichment. The modified random pore model was established to analyze the reduction kinetics. The results show that the reduction rate of sinters was accelerated by an increase of CO and H2contents. Meanwhile, with the increase in CO and H2contents, the increasing range of the medium reduction index (MRE) of sinters decreased. The increasing oxygen enrichment ratio played a diminishing role in improving the reduction behavior of the sinters. The reducing process kinetic parameters were solved using the modified random role model. The results indicated that, with increasing oxygen enrichment, the contents of CO and H2in the reducing gas increased. The reduction activation energy of the sinters decreased to between 20.4 and 23.2 kJ/mol. ? 2017, The Author(s).

Combustion characteristics and kinetics of anthracite with added chlorine

The combustion process of Yangquan anthracite（YQ） with the addition of 0.045wt%, 0.211wt%, 1.026wt%, and 2.982wt% chlorine was investigated using a thermogravimetric method from an ambient temperature to 1173 K in an air atmosphere. Results show that the YQ combustion characteristics are not significantly affected by an increase in chlorine content. Data acquired for combustion conversion are then further processed for kinetic analysis. Average apparent activation energies determined using the model-free method（specifically the KAS method） are 103.025, 110.250, 99.906, and 110.641 k J/mol, respectively, and the optimal kinetic model for describing the combustion process of chlorine-containing YQ is the nucleation kinetic model, as determined by the z（α） master plot method. The mechanism function of the nucleation kinetic model is then employed to estimate the pre-exponential factor, by making use of the compensation effect. The kinetic models to describe chlorine-containing YQ combustion are thus obtained through advanced determination of the optimal mechanism function, average apparent activation energy, and the pre-exponential factor.

Effect of Al2O3 on the viscosity of CaO-SiO2-Al2O3-MgO-Cr2O3 slags

We investigated the effect of Al2O3 content on the viscosity of CaO-SiO2-Al2O3-8wt%MgO-1wt%Cr2O3(mass ratio of CaO/SiO2 is 1.0,and Al2O3 content is 17wt%-29wt%)slags.The results show that the viscosity of the slag increases gradually with increases in the Al2O3 content in the range of 17wt%to 29wt%due to the role of Al2O3 as a network former in the polymerization of the aluminosilicate structure of the slag.With increases in the Al2O3 content from 17wt%to 29wt%,the apparent activation energy of the slags also increases from 180.85 to 210.23 kJ/mol,which is consistent with the variation in the critical temperature.The Fourier-transform infrared spectra indicate that the degree of polymerization of this slag is increased by the addition of Al2O3.The application of Iida’s model for predicting the slag viscosity in the presence of Cr2O3 indicates that the calculated viscosity values fit well with the measured values when both the temperature and Al2O3 content are at relatively low levels,i.e.,the temperature range of 1673 to 1803 K and the Al2O3 content range of 17wt%-29wt%in CaO-SiO2-Al2O3-8wt%MgO-1wt%Cr2O3 slag.

Dripping and evolution behavior of primary slag bearing TiO2 through the coke packed bed in a blast-furnace hearth

To investigate the flow of primary slag bearing TiO2 in the cohesive zone of blast furnaces, experiments were carded out based on the laboratory-scale packed bed systems. It is concluded that the initial temperature of slag dripping increases with decreasing FeO content and increasing TiO2 content. The slag holdup decreases when the FeO content is in the range of 5wt%-10wt%, whereas it increases when the FeO content exceeds 10wt% . Meanwhile, the slag holdup decreases when the TiO2 content increases from 5wt% to 10wt% but increases when the TiO2 content exceeds 10wt%. Moreover, slag/coke interface analysis shows that the reaction between FeO and TiO2 occurs be- tween the slag and the coke. The slag/coke interface is divided into three layers： slag layer, iron-rich layer, and coke layer. TiO2 in the slag is reduced by carbon, and the generated Ti diffuses into iron.

Reduction of Pyrite Cinder Pellets Mixed with Coal Powder

Direct reduction of pyrite cinder in a rotary hearth furnace （RHF） was studied under the condition of labo ratory simulation. Effects of reduction temperature, reduction time, molar ratio of carbon to oxygen, .and CaO addition on metallization rate as well as compressive strength of the pellets after reduction were discussed. The results showed that the metallization rate and compressive strength were 93.9% and 2 160 N per pellet respectively under the conditions of the reduction temperature of 1 200 ℃, the reduction time of 16 min, and the molar ratio of carbon to oxygen （xc/xo） of 1. 0; adding 2.5% CaO was beneficial to sulfur enrichment in slag phase of pellet, and metal- lization rate increased slightly while compressive strength decreased.

Mechanisms of Swelling of Iron Ore Oxidized Pellets in High Reduction Potential Atmosphere

The influences of the time, temperature and atmosphere on the reduction swelling of oxidized pellets were investigated by single factor experiments. The mechanisms of reduction swelling of oxidized pellets were analyzed and investigated by SEM （scanning electron microscopy） and XRD （X-ray diffractometer） analysis. The results show that the change rules of reduction swelling index of oxidized pellets in different reduction atmospheres are very similar. With the increase of reduction time, the reduction swelling index moves up firstly and then down. When the reduction temperature is above 900 ℃, α-quartz turns into α-tridymite, and the transition generates additional volume expansion effect. The reduction swelling index changes faster in H2 atmosphere than in CO atmosphere. Increasing Ha content in the reduction atmosphere is useful to decrease the reduction swelling index, but it is also easy to cause oxidized pellets cracking.

A new technology for treating waste incineration fly ash by shaft furnace

At present,lots of municipal solid wastes(MSWs)are treated by incineration technology,which produces a large amount of fly ash that needs to be treated innocuously.A new method of using metallurgical shaft furnace to treat the MSW fly ash was thus proposed,and some research was done for this method.Firstly,the basic physical properties of MSW fly ash were analyzed,and then,the briquetting experiment and melting treatment of MSW fly ash were explored.In the process of briquet-ting,the influence of different factors(water content,cement content,forming pressure and curing time)on the compressive strength of the briquettes was studied.The results showed that with the increase in water content,cement content,forming pressure and curing time,the compressive strength of the briquettes increased correspondingly.However,the compressive strength of the briquettes showed a downward trend when these values exceeded a specific range.In the melting experiment,it was found that some heavy metals(such as Cr,Be and Ba)could be solidified in the slag when the fly ash was treated at 1450℃ for 50 min,and the leaching toxicity of heavy metals was lower than the landfill standard of waste in China.At the same time,the decomposition rate of dioxins in fly ash reached 99.66%after melting treatment.

Cooling phenomena in blast furnace hearth

Cooling water provides the best protection for refractory in the blast furnace hearth. Stable and suitable water quality and abundant cooling water are the basis for long service life of the hearth. Some phenomena about cooling system in the commercial blast furnaces were described, and reasonable explanations of these phenomena were analyzed. The results show that increasing the amount of cooling water and reducing the inlet temperature of cooling water can increase the cooling effect significantly in the case of water scaling. Heat flux in the blast furnace hearth is the average heat flux of cooling stave, and the erosion of carbon brick is uneven. There is no direct connection between the actual erosion condition and the heat flux in the hearth. The change trend of thermocouple temperature and heat flux in the hearth can reflect whether the gaps exist among the bricks or not, providing an effective guidance for industrial production and the evaluation of safety state in the hearth. And, the film boiling will not occur in the normal cooling system in the blast furnace hearth.

Behavior of liquid passing through deadman:influence of slag/iron ratio and unburned pulverized coal

The ability of a blast furnace hearth liquid(iron and slag)passing through deadman characterizes the activity of the blast furnace hearth.To explore the influence of various factors on the static holdup rate of liquid in the process of passing through the deadman,a physical transport model of liquid passing through the deadman was firstly established.Then,a self-designed experimental device was used to simulate the process,and the influences of slag/iron ratios(250–450 kg/t)and unburned coal content(0%–9%)on the static holdup rate were studied.The experimental results indicate that with the slag/iron ratio increasing,the behavior of liquid passing through the coke packed bed gets much more difficult,and the static holdup rate increases.As the content of unburned pulverized coal(UPC)increases,the static holdup rate decreases first and then rises.This is caused by the dual effects of UPC.On the one hand,UPC can promote the carburizing reaction of unsaturated molten iron,thereby improving the fluidity of molten iron and reducing the static holdup rate.On the other hand,when the content of UPC rises to a certain level,it will be regarded as a kind of solid particle which will increase the liquid viscosity,causing an increase in the static holdup rate.Moreover,the liquid and coke will present interfacial chemical reactions when the liquid flows through the coke packed bed.And the Si-containing iron droplets at the slag–coke interface,generated by the reaction of SiO_(2)with C in the coke,can improve the interface wettability by reducing the interface wetting angle and increase the basicity of slag by consuming SiO_(2),thus improving the fluidity of the liquid and reducing the static holdup rate.

Smelting practice of scrap addition in blast furnace and theoretical analysis of cost saving

The recycling of scrap has attracted more attention in recent years,and scrap can be used as iron-bearing material to smelt hot metal.The smelting practice of blast furnace(BF)with scrap addition in China was investigated,with the types of scrap being small pieces of scrap,such as crushed materials,light and thin materials,and small compacts which were easy to be added into BFs.The higher productivity of BFs with scrap addition was observed compared with that of BFs without scrap addition at the same volume,and the positive correlation between production increase rate and addition amount of scrap was found.The reducing agent rate of most BFs with scrap addition was lower than the average reducing agent rate at the same volume,while the gas utilization of BFs with scrap addition would not be reduced significantly.The theoretical analysis of cost saving was carried out as well,and the results indicated that the cost could be saved by scrap addition.The melting and carburizing were the two main processes of scrap in BF,in which three steps were involved in the melting process of scrap.The amount of carburization depended on the carbon content of hot metal in hearth and the original carbon content in scrap.The calculation showed that the coke rate could be reduced by 27 kg with 100 kg scrap addition per ton of hot metal,and the saving cost was decided by the amount of scrap and the actual situation of BF.