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.

A novel model for cost performance evaluation of pulverized coal injected into blast furnace based on effective calorific value

The combustion process of pulverized coal injected into blast furnace involves a lot of physical and chemical reactions. Based on the combustion behaviors of pulverized coal, the conception of coal effective calorific value representing the actual thermal energy provided for blast furnace was proposed. A cost performance evaluation model of coal injection was built up for the optimal selection of various kinds of coal based on effective calorific value. The model contains two indicators: coal effective calorific value which has eight sub-indicators and coal injection cost which includes four sub-indicators. In addition, the calculation principle and application of cost performance evaluation model in a Chinese large-scale iron and steel company were comprehensively introduced. The evaluation results finally confirm that this novel model is of great significance to the optimal selection of blast furnace pulverized coal.

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.

Flame radiant image numeralization for pulverized coal combustion in BF raceway

In order to establish correlativity between pulverized coal combustion in a blast furnace raceway and its radiant image, we investigated the relationships between two dimensional radiant images and three dimensional radiant energy in a blast furnace raceway, focusing on the correlativity of the numerical simulation of combustion processes with the connection of radiant images information and space temperature distribution. We calculated the uneven radiate characteristic parameterby taking radiant images as a kind of radiative boundary for numerical simulation of combustion processes, and put fonward a method to examine three-dimensional temperatures distribution in blast furnace raceway by radiant image processing. The numeral temperature fields matching the real combustion can be got by the numeric image processing technique.

Two-stage numerical simulation for temperature profile in furnace of tangentially fired pulverized coal boiler

Considering the fact that the temperature distribution in furnace of a tangential fired pulverized coal boiler is difficult to be measured and monitored, two-stage numerical simulation method was put forward. First, multi-field coupling simulation in typical work conditions was carried out off-line with the software CFX-4.3, and then the expression of temperature profile varying with operating parameter was obtained. According to real-time operating parameters, the temperature at arbitrary point of the furnace can be calculated by using this expression. Thus the temperature profile can be shown on-line and monitoring for combustion state in the furnace is realized. The simul-(ation) model was checked by the parameters measured in an operating boiler, (DG130-9.8/540.) The maximum of relative error is less than 12% and the absolute error is less than 120℃, which shows that the proposed two-stage simulation method is reliable and able to satisfy the requirement of industrial application.

Analysis of NO_X Emission Characteristics of Pulverized Coal Combustion in Different Atmosphere

Researches on the NOx emission characteristics of HT （Huangtai coal）, LC（Laicheng） coal are carried out in different atmosphere. The results show that the NOx emission time is postponed in O2/N2 atmosphere mixed with CO. The releasing times of volatile nitrogen and char nitrogen approach, the amount of NOx reduces. In high 02 concentration atmosphere mixed with CO2, the nitrogen releasing times cane ahead of time, NOx congregate in the beginning of the combustion. On the contrary, nitrogen releases separately, and the amount of NOx reduces greatly.

Influence of constricted air distribution on NO_x emissions in pulverized coal combustion boiler

This paper reports a field testing of full scale PCC (Pulverized Coal Combustion) boiler study into the influence of constricted air distribution on NO x emissions at unit 3 (125 MW power units, 420 t/h boiler) of Guixi power station, Jiangxi and puts forward the methods to decrease NO x emissions and the principle of boiler operation and regulation through analyzing NO x emissions state under real running condition. Based on boiler constricted air distribution, the experiment mainly tested the influence of primary air, excessive air, boiler load and milling sets (tertiary air) on NO x emissions and found its influence characteristics. A degraded bituminous coal is simply adopted to avoid the test results from other factors.

Discussion on Selection of Pulverizer and Moisture of Pulverized Coal for Lignite Boilers

In China,the abrasion index and the free moisture are regarded as the criteria for determining whether the medium-speed pulverizer or the fan pulverizer could be selected.Based on comprehensive studies on foreign methods for choosing the pulverizing system for lignite boilers,it is suggested that the particle size of coal,the drying time,the drying temperature and the humidity should be taken into account when measuring the free moisture of lignite,and the total moisture could also be the principle for type selection of pulverizer for lignite boilers.Furthermore,the determination of pulverized-coal moisture has great influence on the running of pulverizing systems.The actual moisture of certain pulverized coals is compared with that calculated with different methods and a feasible method for determining the moisture of the pulverized coal is suggested.

Numerical simulation of the effect of coaxial and cross-axis injection modes on pulverized coal combustion in the raceway of blast furnace tuyere

The aim of this study is to investigate the influence of the angle of the pulverized coal (PC) injection lance on the combustion characteristics of fuel in the raceway of blast furnace tuyeres. Using FLUENT software, a Euler-Lagrange three-dimensional numerical model was constructed to analyze the influence of different positions of blast furnace tuyere coal powder injection lance (coaxial and cross-axis) on key parameters such as temperature distribution, gas flow, and combustion efficiency. The results demonstrate that adjusting the angle of the injection lance significantly modifies the average and peak temperatures in the raceway, while the composition of gas components remains relatively stable. When the injection lance angle is 10°, the average temperature and peak temperature in the raceway are 2294 K and 2747 K, respectively. When the injection lance angle is 12°, the combustion efficiency of the PC reaches 80.8%. This study reveals the significant impact of the injection lance angle on the combustion process. Especially at an angle of 12°, the combustion efficiency of the blast furnace significantly improves. With coaxial injection, the combustion rate increases as the distance between the injection lance tip and the tuyere increases. This paper is instructive for the optimization of the blast furnace combustion system, which improve fuel utilization efficiency and reduce environmental emissions. This paper provides practical recommendations for adjusting blast furnace operational parameters, offering insights for achieving more efficient and environmentally friendly industrial production.

Experimental investigation on the NO formation of pulverized coal combustion under high-temperature and low-oxygen environments simulating MILD oxy-fuel combustion conditions

The NO formation experiments simulating moderate and intense low-oxygen dilution(MILD)oxy-coal combustion conditions were conducted on a laminar diffusion flame burner with the coflow temperatures of 1473-1873 K and the oxygen volume fractions of 5%-20%in O_(2)/CO_(2),O_(2)/Ar and O_(2)/N_(2)atmospheres.The flame images of pulverized coal combustion were captured to obtain the ignition delay distances,and the axial species concentrations were measured to obtain the variation of NO formation and reduction.The NO yield in O_(2)/Ar atmosphere decreased by nearly 0.2 when the oxygen volume fraction decreased from 20%to 5%and by about 0.05 when the coflow temperature decreased from 1873 K to 1473 K.The NO yield in O_(2)/CO_(2)atmosphere was 0.1-0.15 lower than that in O_(2)/Ar atmosphere.The optimal kinetic parameters of thermal NO and fuel NO formation rate were obtained by a nonlinear fit of nth-order Arrhenius expression.Finally,the relative contribution rates of thermal NO to total NO(Rth)and NO reduction to fuel NO(Rre)were quantitatively separated.Rth decreases with the increase of oxygen volume fraction,below 6%at 1800 K,25%at 2000 K.Rre is almost unaffected by the coflow temperature and affected by the oxygen volume fraction,reaching 30%at 5%O_(2).

Factors Influencing Conversion of Pyritic Sulfur in Coal by Microwave Irradiation

The high sulfur coal from southwest of China was used to examine the influence of different factors such as irradiation time, particle size of coal, and leachant (Na2CO3, NaOH and CuCl22H2O)on the conversion rate of pyrite to pyrrhotite by microwave irradiation. Single factor experiment was performed firstly, then orthogonal test method was used to explore these factors. The result shows that the optimal treating conditions for the conversion are a treatment time of 3 min, a particle size from 0.086 mm to 0.102 mm, and a favorable leachant of sodium hydroxide. Under these conditions the conversion rate of pyrite can reach 45.7 %.

Combustion characteristics of semicokes derived from pyrolysis of low rank bituminous coal

Various semicokes were obtained from medium-low temperature pyrolysis of Dongrong long flame coal.The proximate analysis,calorific value and Hardgrove grindability index(HGI) of semicokes were determined,and the ignition temperature,burnout temperature,ignition index,burnout index,burnout ratio,combustion characteristic index of semicokes were measured and analyzed using thermogravimetry analysis(TGA).The effects of pyrolysis temperature,heating rate,and pyrolysis time on yield,composition and calorific value of long flame coal derived semicokes were investigated,especially the influence of pyrolysis temperature on combustion characteristics and grindability of the semicokes was studied combined with X-ray diffraction(XRD) analysis of semicokes.The results show that the volatile content,ash content and calorific value of semicokes pyrolyzed at all process parameters studied meet the technical specifications of the pulverized coal-fired furnaces(PCFF) referring to China Standards GB/T 7562-1998.The pyrolysis temperature is the most influential factor among pyrolysis process parameters.As pyrolysis temperature increases,the yield,ignition index,combustion reactivity and burnout index of semicokes show a decreasing tend,but the ash content increases.In the range of 400 and 450 °C,the grindability of semicokes is rational,especially the grindability of semicokes pyrolyzed at 450 °C is suitable.Except for the decrease of volatile content and increase of ash content,the decrease of combustion performance of semicokes pyrolyzed at higher temperature should be attributed to the improvement of the degree of structural ordering and the increase of aromaticity and average crystallite size of char.It is concluded that the semicokes pyrolyzed at the temperature of 450 °C is the proper fuel for PCFF.

3D model study of coal/coke combustion in a blast furnace effects of coal properties

A three-dimensional mathematical model of the combustion of pulverized coal and coke has been developed.The model is applied to the blowpipe-tuyere-raceway-coke bed region in an ironmaking blast furnace in one computational domain,which includes two parts:pulverized coal combustion model in the blowpipe-tuyere-raceway cavity and the coal/coke combustion model in the surrounding coke bed.The effects of coal properties are examined comprehensively,in terms of coal burnout and gas species distributions.The results indicate that using a coal of fine particle size or high VM content could improve burnout and would affect the gas composition considerably.The burnout is examined in two ways:compared with burnout along tuyere axis,burnout over the raceway surface is a more sensitive and sensible parameter to describe the amount of unburnt char entering the coke bed.The model is useful for examining the flow-thermo-chemical characteristics of the pulverized coal injection (PCI) process under various conditions in a blast furnace.

Slagging characteristics of molten coal ash on silicon-aluminum combustion liners of boiler

In order to study the slagging characteristics of boiler combustion liners during pulverized coal stream combustion, the slag samples on the surface of combustion liner were investigated by X-ray diffractometry, scan electron microscopy and energy dispersive X-ray analysis, and the transformation characteristics of the compositions and crystal phases were studied. The results show that the size of slag granules decreases as the slagging temperature increases; the crystallinity of coal ash I reduces to about 48.6% when the temperature is increased up to 1 350 ℃, and that of the coal ash II reduces to about 65% when the temperature is increased up to 1 500 ℃; the encroachment of molten coal ash to the combustion liner is strengthened. At the same time, the diffusion and the segregation of the compositions in combustion liners have selectivity, which is in favor of enhancing the content of crystal phases, weakening the conglutination among molten slag compositions and combustion liner, and avoiding yielding big clinkers. But the diffusion of the compositions in combustion liners increases the porosity and decreases the mechanical intensity of combustion liner, and makes the slag encroachment to the liner become more serious.

Research and Development of Hot Primary Air Heater for Coal-Fired Boilers in Power Plant

The reasons of introducing cold air into pulverizer are analyzed for boilers with large capacity and high parameters. The temperature rises of the exhaust gas are calculated when varying the amount of the cold air. The hot primary air heater, a new technology, is developed to eliminate the cold air from the pulverized coal system. The applications, advantages and disadvantages are introduced in detail for the new device and system. It is concluded that introducing cold air into pulverizer is one of the major factors that causes the exhaust gas temperature of boilers with large capacity to be high. The amount of the cold air could be reduced signif icantly, even to zero in some cases by adopting the hot primary air heater, which drops the exhaust gas temperature of the boiler effectively. The hot primary air heater, which could play part roles of the steam-air heater or the hot air recirculation system, could also be used to adjust the exhaust gas temperature within the range of 20 ℃ by controlling the flow rate of the cooling medium. Moreover, the startup period of the steam-air heater or the hot air recirculation system will be shortened, which is a unique advantage of the hot primary air heater among the measures to drop the exhaust gas temperature.

Four Years of Operating Experience with DryFiningTM Fuel Enhancement Process at Coal Creek Generating Station

Lignite and sub-bituminous coals from western U.S. contain high amounts of moisture （sub-bituminous： 15%-30%, lignites： 25%-40%）. German and Australian lignites （brown coals） have even higher moisture content, 50% and 60%, respectively. The high moisture content causes a reduction in plant performance and higher emissions, compared to the bituminous （hard） coals. Despite their high-moisture content, lignite and sub-bituminous coals from the western U.S. and worldwide are attractive due to their abundance, low cost, low NOx and SOx emissions, and high reactivity. A novel low-temperature coal drying process employing a fluidized bed dryer and waste heat was developed in the U.S. by a team led by GRE （Great River Energy）. Demonstration of the technology was conducted with the U.S. Department of Energy and GRE funding at Coal Creek Station Unit 1. Following the successful demonstration, the low-temperature coal drying technology was commercialized by GRE under the trade name DryFiningTM fuel enhancement process and implemented at both units at Coal Creek Station. The coal drying system at Coal Creek has been in a continuous commercial operation since December 2009. By implementing DryFining at Coal Creek, GRE avoided $366 million in capital expenditures, which would otherwise be needed to comply with emission regulations. Four years of operating experience is described in this paper.

Influence of Recirculated Flue Gas Distribution on Combustion and NOx Formation Characteristics in S-CO_(2) Coal-fired Boiler

Supercritical carbon dioxide(S-CO_(2))Brayton power cycle power generation technology,has attracted more and more scholars'attention in recent years because of its advantages of high efficiency and flexibility.Compared with conventional steam boilers,S-CO_(2) has different heat transfer characteristics,it is easy to cause the temperature of the cooling wall of the boiler to rise,which leads to higher combustion gas temperature in the furnace,higher NOX generation concentration.The adoption of flue gas recirculation has a significance impact on the combustion process of pulverized coal in the boiler,and it is the most effective ways to reduce the emission of NOX and the combustion temperature in the boiler.This paper takes 1000MW S-CO_(2) T-type coal-fired boiler as the research target to investigate the combustion and NOX generation characteristics of S-CO_(2) coal-fired boilers under flue gas recirculation condition,the influence of recirculated flue gas distribution along the furnace height on the characteristics of NOX formation and the combustion of pulverized coal.The results show that the recirculated flue gas distribution has the great impact on the concentration of NOX at the boiler outlet.When the bottom recirculation flue gas rate is gradually increased,the average temperature of the lower boiler decreases and the average temperature of the upper boiler increases slightly;The concentration of NOx at the furnace outlet increases.