Combustion performance of pulverized coal and corresponding kinetics study after adding the additives of Fe_(2)O_(3) and CaO

Combustion performance of pulverized coal(PC)in blast furnace(BF)process is regarded as a criteria parameter to assess the prop-er injection dosage of PC.In this paper,effects of two kinds of additives,Fe_(2)O_(3) and CaO,on PC combustion were studied using the thermo-gravimetric method.The results demonstrate that both the Fe_(2)O_(3) and CaO can promote combustion performance index of PC including igni-tion index(C_(i)),burnout index(D_(b)),as well as comprehensive combustibility index(S_(n)).The S_(n) increases from 1.37×10^(−6) to 2.16×10^(−6)%2·min^(−2)·℃^(−3) as the Fe_(2)O_(3) proportion increases from 0 to 5.0wt%.Additionally,the combustion kinetics of PC was clarified using the Coats-Redfern method.The results show that the activation energy(E)of PC combustion decreases after adding the above additives.For instance,the E decreases from 56.54 to 35.75 kJ/mol when the Fe_(2)O_(3) proportion increases from 0 to 5.0wt%,which supports the improved combustion per-formance.Moreover,it is uneconomic to utilize pure Fe_(2)O_(3) and CaO in production.Based on economy analysis,we selected the iron-bearing dust(IBD)which contains much Fe_(2)O_(3) and CaO component to investigate,and got the same effects.Therefore,the IBD is a potential option for catalytic PC combustion in BF process.

An image segmentation method of pulverized coal for particle size analysis

An important index to evaluate the process efficiency of coal preparation is the mineral liberation degree of pulverized coal,which is greatly influenced by the particle size and shape distribution acquired by image segmentation.However,the agglomeration effect of fine powders and the edge effect of granular images caused by scanning electron microscopy greatly affect the precision of particle image segmentation.In this study,we propose a novel image segmentation method derived from mask regional convolutional neural network based on deep learning for recognizing fine coal powders.Firstly,an atrous convolution is introduced into our network to learn the image feature of multi-sized powders,which can reduce the missing segmentation of small-sized agglomerated particles.Then,a new mask loss function combing focal loss and dice coefficient is used to overcome the false segmentation caused by the edge effect.The final comparative experimental results show that our method achieves the best results of 94.43%and 91.44%on AP50 and AP75 respectively among the comparison algorithms.In addition,in order to provide an effective method for particle size analysis of coal particles,we study the particle size distribution of coal powders based on the proposed image segmentation method and obtain a good curve relationship between cumulative mass fraction and particle size.

Extracting the core indicators of pulverized coal for blast furnace injection based on principal component analysis

An updated approach to refining the core indicators of pulverized coal used for blast furnace injection based on principal component analysis is proposed in view of the disadvantages of the existing performance indicator system of pulverized coal used in blast furnaces. This presented method takes into account all the performance indicators of pulverized coal injection, including calorific value, igniting point, combustibility, reactivity, flowability, grindability, etc. Four core indicators of pulverized coal injection are selected and studied by using principal component analysis, namely, comprehensive combustibility, comprehensive reactivity, comprehensive flowability, and comprehensive grindability. The newly established core index system is not only beneficial to narrowing down current evaluation indices but also effective to avoid previous overlapping problems among indicators by mutually independent index design. Furthermore, a comprehensive property indicator is introduced on the basis of the four core indicators, and the injection properties of pulverized coal can be overall evaluated.

Radiant Image Simulation of Pulverized Coal Combustion in Blast Furnace Raceway

The relationship between two-dimensional radiant image and three-dimensional radiant energy in blast furnace raceway was studied by numerical simulation of combustion process. Taking radiant image as radiant boundary for numerical simulation of combustion process, the uneven radiation parameter can be calculated. A method to examine three-dimensional temperature distribution in blast furnace raceway was put forward by radiant image processing. The numeral temperature field matching the real combustion can be obtained by proposed numeric image processing technique.

Gas-Particle Flow and Combustion Characteristics of Pulverized Coal Injection in Blast Furnace Raceway

The two-dimensional steady-state discrete phase mathematical model is developed to analyze gas-particle flow and combustion characteristics of coal particles, as well as components concentration and temperature distribu- tion of coal gas in the process of pulverized coal injection of blast furnace raceway. The results show that a great deal of coal gas discharges on the top of raceway away from the tuyere, and the residence time of coal particles in the re- gion of blowpipe and tuyere is 20 ms or so and 50 ms when it reaches raceway boundary. The pressure is the highest at the bottom of raceway and the maximal temperature is about 2 423 K. The char combustion is mainly carried out in the raceway and the maximum of char burn-out rate attains 3× 10-4 kg/s.

Properties and Structural Optimization of Pulverized Coal for Blast Furnace Injection

The properties of mixed coals were studied on the basis of known various properties of the injecting coals in the treatise.The structure of the injecting coals was optimized and put into practical application.It was found that the ignition point was lowered with mixed coals,however,both combustibility and grindability were improved,and explosibility of the mixed coals were decreased as well.Hence,mixed coals injection not only can improve the amount of the injecting coals greatly,but also improve the economical and technical indexes of the blast furnace.

Evaluation of Four Coals for Blast Furnace Pulverized Coal Injection

One of the effective methods of reducing coke consumption is pulverized coal injection. The most important problems encountered in this method are reduced permeability, unburned and high ash content. To select the best coal for injection, suitable tests can be used. Therefore, experiments such as proximate and ultimate analysis, Rock- Eval and combustion tests were performed on four kinds of coals from different mines, including Sarakhs, Sangrood, Karmozd, and Tabas. The results of proximate and ultimate analysis indicated that although the sulfur content and ash content of selected coals were a little high, they were suitable for coal injection. The results of combustion experiments and Rock-Eval tests showed that Karmozd coal was the best one to be injected into blast furnace. The result indicated that the mixing of coals could improve the combustion properties of pulverized coals.

Investigation on Pulverized Coal Combustion Behavior by Non-Isothermic Integral Thermogravimetry Method

The combustion process of pulverized coal was investigated by non-isothermic integral thermogravimetry. The thermogravimetry curves were fitted by the Coats-Redferm approximation function, and kinetic parameters and characteristic temperatures were obtained. The optimal mixing ratio and particle size can be ascertained. The characteristic temperature of pulverized coal can be obtained from the thermogravimetry curve, and the combustion of coal can be divided into homogeneous and heterogeneous combustion according to the differential thermal analysis curve. The activation energy of a single type of coal ranking from low to high is as follows： bituminous coal, meager-lean coal, and anthracite. In the first mixing method, with more low-price meager-lean coal B replacing high price anthracite A, the activation energy slightly decreases; with more bituminous coal replacing meager-lean coal, total tendency makes a declining of activation. In the later mixing method, with an increase in particle size, a declining activation energy can be seen in total tendency.

Thermodynamic analysis of improvement of converter gas by injecting pulverized coal into vaporization cooling flue

In order to improve the calorific value and the recovery yield of converter gas during the steelmaking process, a novel and thermodynamically admissible process was proposed. This method involved injecting pulverized coal into the vaporization cooling flue of a converter, and the approach was developed based on an industrial 30 t converter. The effects of temperature, O2 content, and the volumetric ratio of CO to CO2 on the conversion of the mixed components of gas were analyzed using thermodynamic calculations. Furthermore, the effect of the injection rate on the quality and quantity of gas was investigated. The results show that the O2 and CO2 components of flue gas decrease as the injection rate increases, whereas the CO and H2 components synchronously increase. With the injection rate of 30 kg min-1, the 02 and CO2 components of the gas decreased by 64.12 and 41.19%, respectively, while the CO and H2 increased by 20.09 and 236.84%, respectively, and the recovery time of gas increased by 11.61%, compared to non-injection.

Pulverized Coal Combustion of Nitrogen Free Blast Furnace

The efficiency of coal combustion is an important factor for the blast furnace process.The influence of low xO/xC on coal combustion performance under nitrogen free blast furnace condition was researched through the self-developed pulverized coal burning device.The results show that the coal combustion rate reduces with xO/xC decreasing,and the combustion rate of bituminous coal is higher than that of anthracite.The coal combustion rate ascends with the rise of volatile matter,but when volatile matter of pulverized coal is more than 18%,the combustion rates will not increase correspondingly.Small amount of CaCO3 and CO2 additions can promote coal combustion,and the effect of CaCO3 is more apparent,which can increase the pulverized coal combustion rate by 15%-18% or so.

Comparison of semi-coke with traditional pulverized coal injection and iron ore sintering fuels based on chemical structure and combustion behavior

Substantial semi-coke has been produced through the industrialized low-temperature pyrolysis process,which has great potential as an alternative fuel for pulverized coal injection(PCI)and iron ore sintering.X-ray diffraction,Raman spectroscope,and thermal analysis were used to compare the carbon chemical structure and combustion reactivity of semi-coke,pulverized coal,and coke breeze.The results show that the average volatile matter content in 46 types of semi-cokes is 8.94 wt.%.The fluctuation range of the characteristic parameters of the semi-coke chemical structure is d_(002)=(0.352–0.379)nm and A_(D1)/A_(G)=(2.51–7.92),while the fluctuation range of the characteristic parameters of pulverized coal is d_(002)=(0.348–0.373)nm and A_(D1)/A_(G)=(1.71–9.03)(where d_(002)means the interlayer spacing between the aromatic planes,and A_(D1)/A_(G)is an index that characterizes the degree of disorder of the char structure through the area ratio of the defect peak band D1 to the perfect graphite peak band G);the overlap between these ranges is relatively high.Contrarily,the fluctuation range of the characteristic parameters of coke breeze is d_(002)=(0.343–0.350)nm and A_(D1)/A_(G)=(0.75–2.51),which is markedly different from that of semi-coke.Semi-coke combustion reactivity is close to that of pulverized coal,but considerably better than that of coke breeze.In terms of chemical structure and combustion reactivity,semi-coke can be used as an alternative fuel for PCI;however,when used for sintering alternative fuel,matching of the heat supply and demand in the later sintering stage must be scrupulously analyzed.

Mechanism of Effect of Microwave Modification on Pulverized Coal Combustion Properties

The mechanism of microwave modification or： facilitating the combustion properties of pulverized coal （PC） was investigated. Experimental researches on granularity and functional group as well as combustion properties of PC before and after modification were carried out. Micromorphology observation indicated that the size of PC par- ticles was relatively small, which was in accordance with the results of granularity analysis of PC. FT-IR （Fourier- transform infrared） spectra of two PCs indicated that the proportion of the functional groups with high activity in- creased after microwave irradiation. Furthermore, no valid effect of microwave was found on carbon matrix except small variations in PC particle size, which only led to subtle improvement in combustion of residual coke. Activation energies of Yungang and Yangquan PCs in temperature zone between 450--650 ℃ were reduced by 12.00% and 10.13%, respectively, which meant that microwave modification might effectively facilitate the combustion proper- ties of PC. Nevertheless, decrease in activation energies of residual cokes was 3.560% and 3.67% respectively, which was subtle and can be regarded as the result of smaller particle size produced by microwave irradiation.

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.

Combustion Property and Kinetic Modeling of Pulverized Coal Based on Non-isothermal Thermogravimetric Analysis

Non-isothermal combustion kinetics of two kinds of low volatile pulverized coals （HL coal and RU coal） were investigated by thermogravimetrie analysis. The results show that the combustibility of HL coal was better than that of RU coal, and with increasing heating rate, ignition and burnout characteristics of pulverized coal were improved. The volume model （VM）, the random pore model （RPM）, and the new model （NEWM） in which the whole combustion process is considered to be the overlapping process of volatile combustion and coal char combustion, were used to fit with the experimental data. The comparison of these three fitted results indicated that the combustion process of coal could be simulated by the NEWM with highest precision. When calculated by the NEWM, the activation energies of volatile combustion and coal char combustion are 130.5 and 95.7 kJ · mol^-1 for HL coal, respectively, while they are 114.5 and 147.6 kJ ·mol^-1 for RU coal, respectively.

Multi-scale analysis on the pulverized coal flow behaviors under high,pressure dense-phase pneumatic conveying

To deeply knowledge of the flow behaviors of pulverized coal particles in dense gas-solid two-phase flow,a multi-scale analysis method based on electrostatic sensor array is applied for the multi-scale characterization of flow behaviors of dense gas-solid flow.The experimental results indicate that:for steady flow,with the increment of conveying pressure difference,the individual particles increase and the particle clusters decrease,the individual particle distribution is always inhomogeneous but the particle cluster distribution tends to be more homogeneous over the cross-section of pipe,while the average flow behavior of pulverized coal particles is always in the relatively static state.For unsteady flow,the average flow behavior of pulverized coal particles is dynamic,and the flow behaviors of the multi-scale flow structures over the cross-section of pipe are all significantly inhomogeneous.Moreover,the effect of particle size on flow behavior of pulverized coal is also investigated and validated.

Techno-economic assessment of pulverized coal boilers and IGCC power plants with CO_(2) capture

The current studies on power plant technologies suggest that Integrated Gasification Combined Cycle(IGCC)systems are an effective and economic CO_(2) capture technology pathway.In addition,the system in conventional configuration has the advantage of being more“CO_(2) capture ready”than other technologies.Pulverized coal boilers(PC)have,however,proven high technical performance attributes and are economically often most practical technologies.To highlight the pros and cons of both technologies in connection with an integrated CO_(2) capture,a comparative analysis of ultrasupercritical PC and IGCC is carried out in this paper.The technical design,the mass and energy balance and the system optimizations are implemented by using the ECLIPSE chemical plant simulation software package.Built upon these technologies,the CO_(2) capture facilities are incorporated within the system.The most appropriate CO_(2) capture systems for the PC system selected for this work are the oxy-fuel system and the postcombustion scheme using Monoethanolamine solvent scrubber column(MEA).The IGCC systems are designed in two configurations:Water gas shift reactor and Selexol-based separation.Both options generate CO_(2)-rich and hydrogen rich-gas streams.Following the comparative analysis of the technical performance attributes of the above cycles,the economic assessment is carried out using the economic toolbox of ECLIPSE is seamlessly connected to the results of the mass and energy balance as well as the utility usages.The total cost assessment is implemented according to the stepcount exponential costing method using the dominant factors and/or a combination of parameters.Subsequently,based on a set of assumptions,the net present value estimation is implemented to calculate the breakeven electricity selling prices and the CO_(2) avoidance cost.

Influence of mass air flow ratio on gas-particle flow characteristics of a swirl burner in a 29 MW pulverized coal boiler

In a gas/particle two-phase test facility, a three-component particle-dynamics anemometer was used to measure the characteristics of gas/particle two-phase flows in a 29 megawatt (MW) pulverized coal industrial boiler equipped with a new type of swirling pulverized coal burner. The distributions of three-dimensional gas/particle velocity, particle volume flux, and particle size distribution were measured under different working conditions. The mean axial velocity and the particle volume flux in the central region of the burner outlet were found to be negative. This indicated that a central recirculation zone was formed in the center of the burner. In the central recirculation zone, the absolute value of the mean axial velocity and the particle volume flux increased when the external secondary air volume increased. The size of the central reflux zone remained stable when the air volume ratio changed. Along the direction of the jet, the peak value formed by the tertiary air gradually moved toward the center of the burner. This tertiary air was mixed with the peak value formed by the air in the adiabatic combustion chamber after the cross-section of x/d = 0.7. Large particles were concentrated near the wall area, and the particle size in the recirculation zone was small.

Effects of microstructural evolutions of pyrolysis char and pulverized coal on kinetic parameters during combustion

Pyrolysis chars have potential as fuels for pulverized coal injection(PCI);however,their proper and efficient utilization requires evaluation of char combustion kinetics.The combustion characteristics of two chars(F-char and M-char)and two pulverized coals(H-PCI and P-PCI)were analyzed herein using thermogravimetric analysis–mass spectrometry.The apparent activation energy(Ea)of the sample under non-isothermal combustion conditions was obtained using the Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose methods,and the reaction mechanism for the fuels was established using the Malek method.Additionally,changes in the microscopic pore structure and carbon chemical structure of the fuels at different stages of combustion were characterized using N2 adsorption and X-ray diffraction to analyze the relationship between microstructural evolution and Ea.The results suggested that Ea of the sample first rapidly decreased and then became stabilized during combustion.Compared with pulverized coals,the two chars presented more developed micro-scopic pore structure,less-ordered carbon chemical structure and lower Ea during reaction.During combustion,the stacking height of the aromatic layer first decreased and then increased,whereas the specific surface area first increased and then decreased.The volatile content significantly influenced Ea only during the initial stage of combustion.During the middle stage,Ea was controlled more by the microscopic pore structure and the carbon chemical structure,and those influences disappeared in the later stage.The transition point of the structures affecting Ea occurred at a combustion rate between 52.9%and 72.0%.In general,the microscopic pore structure and the carbon chemical structure influenced kinetic parameters more than the volatile content.

Thermal analysis and kinetic modeling of pulverized coal combustion accompanied with coke breeze

Pulverized coal injection technique has been widely used as a means of reducing coke consumption during ironmaking process.Owing to the increasing shortage of fossil fuels,other substitutes such as biomass,plastic,and waste tires have been studied in recent years.Coke breeze as one of the by-products of coking industries has been investigated as a substitute for partial pulverized coals.The combustion characteristics of blended fuels were estimated based on the flammability index C and the combustion characteristic index S.For different coke breeze additions,the combustion was divided into two stages,and the apparent kinetic parameters of the two stages were estimated by fitting the experimental data to the shrinkage reaction model and shrinkage diffusion model,respectively.Results showed that with the increase in coke breeze addition from 15% to 60%,the indexes C and S decrease,and the activation energy of the first stage remains almost constant,while that of the last stage increases from 16.89 up to 67.18 kJ mol^(-1),which indicates that adding coke breeze decreases the combustion efficiency of pulverized coal.Comparing the combustion and kinetic parameters under different coke breeze addition conditions,the optimal addition amount is suggested to be within 15%.