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This work presents a computational investigation of hydrodynamics, coal combustion and NOx emissions in a tangentially fired pulverized coal boiler at different loads (630, 440 and 300 MW; relative loads of 100%, 70% and 48%) to clarify the effect of load change on the furnace processes. A computational fluids dynamics model was established; the flow field, temperature profile, species concentration and NOx emissions were predicted numerically; and the influence of burner tilt angles was evaluated. Simulation results indicate that a decrease in boiler load decreases the gas velocity, attenuates the airflow rotations, and increases the tangent circle size. The high-temperature zone and flame moved toward the side walls. Such behaviors impair air–fuel mixing, heat transfer and steady combustion in the furnace. In terms of species concentrations, a decrease in boiler load increased the O2 content, decreased the CO content, and decreased the char burnout rates only slightly. A change in boiler load from 630 to 440 and 300 MW increased the NOx emissions from 202 to 234 and 247 mg/m3, respectively. Burner tilt angles are important in coal combustion and NOx emissions. A burner angle of –15° favors heat transfer and low NOx emissions (

Publisher Summary This chapter attempts to provide sufficient knowledge to specify burners, critically assess a burner design and optimize furnace performance and heat transfer. The performance of the burners has a huge effect on furnace operation and efficiency, yet it is relatively rarely that burner design is fully integrated with the furnace heat transfer requirements; little wonder then that poor performance is often the result. A burner is a transducer since it transforms one form of energy into another form of energy. In the case of the burner, it transforms the chemical energy in the fuel into heat energy within the furnace using the chemical reactions in a flame. The effectiveness with which this is achieved is a measure of its performance. Gas burners are generally classified as premixed or turbulent jet diffusion burners, such as premixed burners, where the fuel and most of the air are mixed together prior to passing through the nozzle and turbulent jet diffusion burners, where the fuel and most of the air are introduced separately and are mixed within the furnace. Burners and furnaces are also classified by the air delivery system as natural draught, forced draught, induced draught and balanced draught. Oil burners have the added complexity of two-phase flow resulting from the spray of fuel. Pulverized coal firing has many advantages over other forms of coal firing and makes burning coal similar to oil firing from a process viewpoint. Pulverized coal burners are similar to oil burners but the atomizer is replaced with a coal nozzle. The fine coal is air conveyed to the nozzle. Burners are often specified and selected from a catalogue based on little more than the estimated heat liberation required for the furnace, the number of burners needed and the price of the burner.

The utilization of hydrogen is gaining increasing attention due to its high heating value and environmentally friendly combustion product. The supercritical water circulating fluidized bed reactor is a promising and potentially clean technology that can generate hydrogen from coal gasification. Cyclone is a vital part of the reactor which can separate incomplete decomposition of pulverized coal particles from mixed working fluid. This paper aims to gain in-depth understanding of the cyclone separation mechanisms under supercritical fluid by computational fluid dynamics (CFD). Although the amount of supercritical carbon dioxide in mixed working fluid is minor, it obviously influences the flow fields and separation efficiency of a cyclone. The simulation results suggest that both the decreasing content of supercritical carbon dioxide and adding the extra dipleg cause the promoting performance of cyclones. Research findings could refine the design of supercritical fluid–solid cyclones.

Inert powders played an important role in the explosion inhibition of dust removal equipment and coal gasification process. In this paper, SiO2, dry water, carrageenan dry water, and NaHCO3 were adopted to explore the influences of inert powders on the deflagration flame propagation characteristics of mixed pulverized coal by a vertical pipeline. The results showed that the flame brightness of the mixed pulverized coal decreased with the irregularly discrete of flame front after the addition of inert powders. As the increasing of pulverized coal mesh number, the peak flame temperature first increased and then decreased, while the drop value of peak flame velocity and temperature increased with the increasing of mass concentration. In addition, the inerting rate affected the propagation of pulverized coal composite flame. When the inerting rate exceeded 1.0, the peak temperature drop increased rapidly and dry water exhibited the best inhibition performance.

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.

Oxy-fuel combustion with low NOx emission has been received more attention in recent years. In this work, a series of oxygen-staged experimental investigations of Shenmu bituminous coal with the preheated combustion technology was carried out under O2/CO2 atmosphere to obtain the effect of oxygen-staged on combustion and NOx emission. The results showed that the increase of excess oxygen coefficient of the primary air(λPr) decreased the temperature difference at each measuring point in the circulating fluidized bed, promoted the production of coal gas, facilitated the release of elements, and improved the mass conversion ratio of volatile matter up to 92.3%. Besides, the increase of λPr inhibited the conversion process of N-5 to N-6. At the same time, the release of nitrogen-containing volatile matter during the partial gasification process was also reduced. As the λPr increases, reducing the excess oxygen coefficient of the secondary air(λSe) or increasing the oxygen partial pressure of primary air were beneficial to reduce the emissions of NOx to a certain extent.

Preheating of pulverized coal (PC) has previously been verified as an effective method for reducing NO emission during coal combustion. However, studies on NO formation and destruction characteristics related to the combustion of high-temperature preheated PC are rare. In this study, two drop tube furnaces were connected in series to model the preheating-combustion process, and the effect of combustion temperature on NO emission during the oxidation of high-temperature preheated PC was studied in detail through experiment and kinetic modeling. Results confirmed the effectiveness of preheating on NO reduction with a maximum efficiency as high as 71.73%. Results also indicated that increasing the combustion temperature promoted both the formation and destruction of NO, while the increase in the NO formation rate was steeper than its destruction. This led to an increase in NO from 223 to 273 mg·m−3 as the combustion temperature increasing from 1273 K to 1473 K at preheating temperature of 1673 K. In addition, the rate of production (ROP) of NO formation increased from 8.54E-9 to 3.49E-7 mol·cm−3·s−1 with an elevated temperature from 1073 K to 1873 K, whereas the rate of NO destruction increased only from 1.40E-9 to 7.45E-8 mol·cm−3·s−1. Finally, the ROP analysis also indicated that the presence of background NO posed heavy impact on conversion of char-N and significantly improved the NO destruction rate.

Aiming to solve the difficult treatment for Enteromorpha found on beaches as well as the requirements for new types of environment-friendly dust suppressants, an Enteromorpha-based environment-friendly dust suppressant was prepared by graft polymerization. The optimal reaction conditions were determined based on the viscosity of the dust suppressant solution as follows: the mass ratios of Enteromorpha, acrylic acid, and polyacrylamide were 2:5:0.3; the reaction temperature was 70 °C; the solids content was 5%; and a mass concentration of 0.2% lauryl sodium sulfate was added to enhance the wettability performance. Fourier transform infrared spectroscopy (FTIR) and thermogravimetry (TG)-derivative analysis (dTG) were used to characterize the chemical structure and thermal stability of the dust suppressant, respectively. Scanning electron microscopy (SEM) was used to analyze and evaluate the film structure formed on the coal samples after it was sprayed with the dust suppressant. The dust suppression performance of dust suppressant was studied through a series of experiments, and the results showed that the dust suppressant had a good wetting ability for coal dust. The contact angle of the dust suppressant solution with the coal dust was reduced by 77% compared to water, and the improved infiltration of the suppressant into the dust improved the dust suppression range. After it was sprayed on the surface of the coal dust, the dust suppressant formed a solidified layer, and the compressive strength of the layer reached 122.6 kPa. The pulverized coal loss rate was only 2.94% at a wind speed of 10 m/s. The water retention time of the coal samples after they were treated with the dust suppressant reached 12 h at 60 °C. The degradation of the dust suppressant in soil reached 40% after the 12th cycle, which suggested the newly synthesized materials would not be a secondary pollutant in the environment. This work provides a new approach for Enteromorpha treatment and a basis for the preparation of new types of environmentally friendly and highly efficient dust suppressants.

A shift from coal to liquefied natural gas for electricity generation can mitigate CO2 emissions and respond to the intermittent and variable characteristics of renewable energy. With this objective, numerical simulation was performed in this study to determine the optimal position of the methane injector and evaluate the achievable reduction in NO x emissions before applying methane cofiring to an existing 550 MW tangentially fired pulverized-coal boiler (Boryeong Unit 3). The combustion and NO x reduction in the furnace were intensively analyzed based on the methane cofiring rate (up to 40%). The optimal position of the methane injector was found to be inside the oil port based on the spatial distribution of NO x and the stoichiometric ratio along the furnace height. The NO x reduction rate was logarithmically proportional to the methane cofiring rate, and compared to the base case, a 69.8% reduction was achieved at the 40% cofiring rate. In addition, the fraction of unburned char at the boiler outlet was equivalent to that of the existing boiler as the increase in the flow rates of the close-coupled and separated overfire air improved fuel and air mixing. Simultaneously, methane cofiring led to a reduction in the total fuel loss and CO emissions. Finally, this study showed that the recommended optimum cofiring rate was 20% based on the furnace exit gas temperature. Under the 20% methane cofiring condition, the boiler achieved a 57.3% reduction in NO x emissions and a 7.4% improvement in fuel loss.

Circulating fluidized bed fly ash (CFBFA), the solid waste discharged from thermal power plants using circulating fluidized bed boilers, has significantly different properties to the fly ash produced in pulverized coal boiler (PCFA) units because of the relatively low combustion temperature used. Thus, CFBFA cannot be used as a direct replacement for PCFAs. Nevertheless, the use of CFBFA in construction materials is the most promising method for the large-scale waste-to-resource transformation and disposal of CFBFA. In this review, the CFBFA is classified according to the desulfurization process used in the CFB boiler, and we also summarize the physicochemical properties and hazards of CFBFA, and discuss its potential applications in the construction industry, In particular, we focus on the preparation of aerated or roller-compacted concrete and zero-cement binders, which are ideal methods for recycling CFBFA. Finally, suggestions for future research and the prospects of recycling CFBFA in the construction industry are proposed.

Fully utilizing the energy generated by the explosion of pulverized coal will contribute to realize the clean and efficient exploitation of coal resources. The pulverized coal explosion characteristics will be a far-reaching and important task to explore. In this paper, ten kinds of low-quality coals such as high sulfur, high ash, and low metamorphic degree coals were investigated and the minimum ignition energy (MIE), lower explosion limit (LEL), and explosion intensity (EI) parameters under different particle sizes and coal powder concentration conditions were also analyzed combined with a 1.2-L Hartmann tube and a 20-L explosion sphere experimental system. Finally, the morphological characteristics of the exploded coal powder surface were evaluated by scanning electron microscopy (SEM). The results show that the particle size is positively correlated with MIE. LEL shows an inverted “U”-shaped trend with the increasing degree of coal deterioration. The low-rank coal is more flammable and explosive. The maximum pressure PMax at the LEL concentration and maximum pressure rise rate (dP/dt)Max overall value is small. Here, optimum pulverized coal particle size (75μm) for explosive utilization of low-quality coal was determined. Within 50–225 g/m3 of pulverized coal concentration range, the explosion intensity increases with increasing concentration. The smaller the particle size of pulverized coal, the greater the possibility of agglomeration of pulverized coal particles. The surface of the exploded coal particles produces more developed pores. They are irregularly shaped and have more rounded edges than the original coal.

Pulverized coal injection is widely used for the sustainability of ironmaking blast furnace process. However, the quantification of unburnt pulverized coal in the blast furnace is not well understood. The gas-powder flow in a packed bed in the raceway presence is studied using a two-dimensional cold model to understand the static and dynamic holdups of powder. Due to the lack of clarity in the existing literature about the procedures for estimating the powder holdups, it is proposed in the present work that the steady state and dynamic holdup can be quantified based on the mass balance concept and elutriation velocity, respectively, to get reproducible results. The application of these concepts across both rectangular and cylindrical geometries helped to validate and reproduce the results. The different parameters, such as powder flux, powder size, and gas flowrate, helped to evaluate the powder holdups in the blast furnace’s cold model with the raceway presence.

The outlet velocity field of the pulverized coal burner is one of the important factors affecting its operating characteristics. In this article, cold tests were carried out for a new swirl burner ...

To address the emissions and formation of fine particulate matter (PM2.5) from co-firing of algal biomass (Chlorella (Ch), Sargassum (Sa), and Enteromarpha (En)) and pulverized coal (Huating coal), the emission characteristics were experimentally investigated using a one-dimensional tubular furnace. The results indicate that algae species, the mixing ratio, and the reaction temperature have complex impacts on PM2.5 emissions. Its emission characteristics present either single- or double-peak distribution. The higher temperature and higher biomass fraction accelerate the formation of PM2.5 during co-firing. Different from the reduction in NOx and SO2 emissions, the PM2.5 emission from algal biomass-based co-firing is higher than that of coal alone on the whole, particularly for Sa and En. For En, the maximum PM2.5 concentration occurred at 900 °C with 91.73 mg/m3 when 20% En was co-fired with 80% coal. Meanwhile, the PM2.5 emission yield reached the peak of 553.64 ( × 10−2) mg/g. For Sa, the highest PM2.5 concentration and PM2.5 emission yield appeared when 20% Sa and 80% coal were co-fired at 1000 °C, were 125.30 mg/m3 and 354.41 ( × 10−2) mg/g, respectively. For Ch, the highest PM2.5 concentration appeared when 20% Ch and 80% coal were co-fired at 1000 °C and reached 1.11 mg/m3, but the largest PM2.5 emission yield was 3.21 ( × 10−2) mg/g when 20% Ch and 80% coal were co-fired at 1100 °C. PM2.5 generated from co-firing are mainly formed by vaporization and homogeneous/heterogeneous condensation, as well as fragmentation of internal/external minerals and char particles. In addition, it also depends upon a series of reactions between the alkali metal salt and other incombustible particles. The morphological characteristics of ash residues from Ch co-fired with coal were irregular and fragmented, and the structure was relatively compact, and those for Sa and En co-fired with coal are similar, both of which are irregular massive structures with white crystal particles attached.

Background: Pulverized coal detection is an indispensable detection measure in the coal industry. The current detection devices can be divided into two types: invasive and non-invasive. The coal dust detection methods and devices based on acoustics, optics, and electricity have been extensively studied. In order to achieve a high-efficiency online detection scheme, improving the accuracy and stability of the detection means is the primary goal of the research. Objective: The general problems and characteristics of coal dust detection device design are summarized, as well as recent technological developments and the need for online testing to predict future research trends. Methods: The current typical detection devices are classified according to the detection principle and whether they invade the target, analyzing its advantages and disadvantages according to the device performance and application scenarios. Results: It has a beneficial effect on the design of the pulverized coal concentration detection device. Conclusion: The paper summarizes and analyzes several representative coal concentration detection device patents in recent years. Then it points out advantages and main problems. On this basis, the main development direction of the coal dust concentration detection device in the future is discussed.

Medium oxygen-enriched blast furnaces that utilize reducing gas injections are a feasible new ironmaking process that can significantly reduce the coke ratio and carbon dioxide emissions. To better inject the reducing gas into the blast furnace, two injection methods were designed in this study, and the effects of the reducing gas on the combustion of pulverized coal in three types of medium oxygen-enriched processes were studied using a three-dimensional lance-blowpipe-tuyere-raceway model. The reducing gas was injected into the blowpipe from a sleeve spray lance, which was suitable for injecting a small amount of reducing gas. The optimal coal burnout was 6% higher than that of a traditional blast furnace (TBF). The reducing gas was also directly injected into the raceway from a spray lance, which was suitable for injecting a large amount of reducing gas. The optimal coal burnout was 13% higher than that of a TBF using this system.

In this study, two connected drop tube furnaces (DTFs) were used to clarify the NO emission characteristics during the high-temperature preheating-combustion process. The most important factors, including preheating temperatures, residence times, and excess air ratios (EAR), were studied systematically. Experimental results showed that both increasing the preheating temperature and prolonging the residence time in the preheating zone promoted the release of coal-N as volatile-N, the reduction of volatile-N, and the interaction between char-N and nitrogen-containing gases, and therefore enhanced NO reduction. With the EAR increased in the preheating zone, the NO emission first decreased and then increased. There was an optimal EAR for NO reduction, which was 0.4 in this work. Meanwhile, the lowest NO emission was 223 mg·m−3, corresponding conversion ratio of coal-N to NO was 12.6% and NO removal efficiency was 60.38%. Moreover, kinetic modeling confirmed the experimental results, and rate of production (ROP) analysis indicated that the main radicals for NO destruction were NH2, hydrocarbon (CiHj), HCCO, NCO and HCO. In addition, the NO reduction by CiHj was stronger than other nitrogen-containing compounds, except NH2, which contributed nearly 30% of overall NO destruction.

A nonlinear dynamic model considering the effect of heat transfer on outlet pulverized coal mass flow is established based on the principles of conservation laws. Raw coal moisture estimation which is connected to coal mass and internal energy in coal mills is included in the model. The model has proved to have good predictions and reflects the dynamics of the coal mill by verifications on historical data and dynamic simulation tests. Results show that the mean absolute error of mill differential pressure, mill electric current and outlet primary air temperature are 3.08%, 3.05% and 0.05% on validation operation data, respectively. The predictions fit the curves of the measured data that cover the whole operation of coal mill from starting up to shutting down.

A combined species transport and reaction-discrete phase model was established to numerically study pulverized coal gasification using waste heat from high temperature slag particles. The effects of slag particles temperature, coal/gasification agent mass ratio and water content in gasification agent on the gasification characteristics were discussed. The results indicate that higher particle temperature leads to better gasification reaction efficiency. Compared to the maximum syngas productivity (67.9%) and carbon conversion efficiency (91.7%) at 1500 K, they are respectively reduced to about 45% and 60% when temperature drops to 1000 K. Excessive or insufficient pulverized coal would have a negative effect on the syngas production for a specific flow rate of gasification agent, and the appropriate proportion range is 0.8–0.84. The CO yield declines with the increase of particles diameter, while H2 firstly increases and then declines attributing to the lower gasification agent temperature and higher flow velocity gained at larger diameter. The raise of water content in gasification agent is beneficial to H2 production, but CO yield continues to decline after the water content exceeds 5% for the reason that the incomplete combustion of volatiles and the gasification reaction of coke are inhibited. The diameter of slag particles and the water content suitable for coal gasification reaction are 2.0–2.5 mm and 5%–10%, respectively.

The paper considers a staged conversion process of pulverized coal fuel in the MHPS-type gasifier, which uses mixtures of oxygen and carbon dioxide as a gasifying agent instead of air. Similar conversion processes can be applied in the process diagrams with the capture and disposal of carbon dioxide. The research tool is a reduced-order mathematical model of coal particles' conversion in a reacting gas flow. Replacement of nitrogen with carbon dioxide leads to significant changes in the gasification process characteristics: the average reaction temperature decreases, but this decrease is partially compensated by an increase in the concentration of gaseous reactants. Thus, the gasification process efficiency and the fuel conversion degree increase. Calculations make it possible to identify a range of parameters with the highest cold gas efficiency values. The influence of oxygen concentration is estimated, the dependence of the fuel conversion degree on the reaction temperature is analyzed.

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 SiO2 with C in the coke, can improve the interface wettability by reducing the interface wetting angle and increase the basicity of slag by consuming SiO2, thus improving the fluidity of the liquid and reducing the static holdup rate.

This article discusses the improvement methods of blast furnace energy efficiency by combined injection of preheated pulverized coal fuel and iron oxides (concentrates of advanced beneficiation, flue dust, and others) into its tuyeres. The reasonability of the aforementioned measures is substantiated. Based on the overall energy balance, their influence on heat energy parameters of blast furnace smelting has been established including its exergy, environmental, and technoeconomic performances. It has been determined that injection of preheated pulverized coal fuel into blast furnace well together with constant temperature of the tuyere area allows to increase the furnace output by at least 0.3% per each 100°C increase in the temperature of pulverized coal fuel, to decrease coke consumption by about 3%, and to increase exergy efficiency by up to 0.2%. Favorable influence of injection of pulverized iron oxides into blast furnace well of blast furnace on heat and gas dynamic operation of the furnace are demonstrated.

The flow characteristic of high pressure dense-phase pneumatic conveying of pulverized coal is essential to the safe and stable operation of the gasifier. In this paper, the effects of coal moisture content on conveying behavior and resistance characteristics of dense-phase pneumatic conveying were explored. Meanwhile, a model of the additional pressure drop of particles was proposed and compared with the experimental data. The results show that though the resistance and cohesiveness increase with increasing moisture content, its influence is different in dense and dilute phase. In the dense-phase region, the coal with lower moisture content shows a larger solid mass flow rate and solid concentration; while in the dilute-phase region, the moisture content has minor effect on conveying characteristics. For the coal with lower moisture content in dense-phase region, the solid mass flow rate and solid concentration are larger, and the gas velocity has a small effect on solid friction factor, due to its smaller cohesiveness and resistance, which is showed in our experiments and inferred from our model. The additional pressure drop model was proposed for straight pipes and bends, whose parameters are probably effective than the existing parameters in this kind of model, as the deviation in the vertical rise pipe, horizontal pipe and bend pipe is controlled within ±30%, and the corresponding vertical down pipe are controlled within ±40%.

Coal and gas outburst is still a major safety problem in the process of coal production in China. Correctly understanding of the migration law of outburst high gas and pulverized coal is an important basis for accurately predicting the occurrence time and possible scope of outburst. To reveal the airflow disturbance characteristics and coal-gas flow rule in coal and gas outburst process, outburst coal-gas migration simulations under different gas pressures were conducted using a self-developed visual outburst dynamic effect test device. The results showed that coal-gas flow state at the outburst port is divided into subcritical flow, critical flow, and supercritical flow state. The pulverized coal-gas flow migration in the roadway space can be divided into coal gas two-phase flow area, air compression area, and undisturbed area. Under the experimental conditions, the maximum propagation velocities of wave are 342.22~359.21 m/s, and the coal gas two-phase flow is far less than the propagation velocities of outburst wave, just 3.68~33.33 m/s. When the outburst energy is large, multiple compression waves can superimpose to form shock waves. The peak value of the wave does not necessarily appear in the first boosting range. The presence of pulverized coal leads to a faster attenuation of shock wave, but it makes a greater dynamic destructive force at the same speed.

The evolution of pore structure and functional groups of coal char in different stages of Shenhua coal combustion process in O2/CO2 atmosphere was studied by the low temperature nitrogen adsorption method, the scanning electron microscopy and the FTIR method. The relationship between the pore structure, oxygen-containing functional groups and NO generation characteristics of coal char under different inlet oxygen concentrations was analyzed. The result shows that the overall pore structure and shape of pulverized coal particles change continuously with the combustion; and the oxygen-containing functional groups on the surface of coal char indicate multi-peak changes and are related to NO generation. The oxygen concentration poses a larger impact on the change in coal particle size, oxygen-containing functional groups and NO generation; and there is an oxygen concentration that optimizes the reduction effect of the oxygen-containing functional group on NO.

The state of and development prospects for the technology of selective noncatalytic reduction (SNCR) of nitrogen oxides in the combustion products of organic fuels are considered. Its advantages and disadvantages and factors influencing the efficiency of its application for gas purification of technological furnaces for natural gas conversion at power and waste incineration boilers are analyzed. The results of experimental studies into the process of reducing nitrogen oxides by products of thermal decomposition of carbamide are presented, depending on the temperature, flow rate, and the method of introducing the reagent into the flue gases. The results of pilot tests and industrial implementation of the technology are shown. The possibility of increasing the technical and economic indicators of SNCR plants by organizing a multizone injection of the reducing mixture into the gases to be cleaned with a flow rate less than the stoichiometric one is substantiated, which makes it possible to achieve high technology efficiency with a minimum ammonia slip. Relatively low capital costs for the construction of SNCR plants and the manufacture of main equipment at domestic enterprises and the small area required for equipment placement can significantly reduce emissions of nitrogen oxides into the atmosphere, even at operating boilers in a short time. It is advisable to widely introduce SNCR technologies at pulverized coal TPPs and enterprises for thermal waste disposal as one of the best available technologies.

In order to obtain similar materials with specific physical and mechanical parameters and adsorption and desorption indexes used in coal and gas outburst simulation tests, pulverized coal was selected as aggregate, sodium humate as cementing agent and river sand as auxiliary materials. Based on this, an orthogonal test with 6 factors and 5 levels was designed, and the tests of weighing, uniaxial compression, firmness and adsorption and desorption were carried out. The parameters such as density, uniaxial compressive strength, elastic modulus, firmness coefficient and adsorption-desorption index of similar materials with different ratios were obtained, and the sensitivity of each factor was analyzed by range analysis. The influence law of various factors on the parameters of similar materials was studied, the ratio model of similar materials was obtained and the reliability of the model was verified, and a complete method for determining the ratio model of similar materials of outburst coal was put forward. The results show that the density of similar materials increases with the increase of river sand content, the uniaxial compressive strength and elastic modulus increase significantly with the increase of pulverized coal ratio and sodium humate content, and the firmness coefficient increases linearly with the increase of pulverized coal ratio. The adsorption constant an increases linearly with the increase of sodium humate content, while the adsorption constant b decreases linearly with the increase of sodium humate content. The initial elution rate △p of similar materials increases at first and then decreases with the increase of sodium humate content.

This paper presents detailed measurements of gaseous species during the reburning process with high CO2 concentration in a bench-scale furnace. Superfine pulverized coal, with the average particle size below or around 20 μm, is used as the reburning fuel. The data of flue gas concentration (NOx, HCN, NH3, CH4, O2, CO, CO2 etc.) is obtained in order to reveal the intrinsic connection between NOx emissions and other influential gaseous species at different positions of the furnace. The finding concludes that the advantage of superfine pulverized coal with regard to NO reduction is more efficient in homogeneous stage rather than heterogeneous stage. Meanwhile, the evolution of HCN and CH4 agrees well with each stage of NO reduction, which indicates that these gaseous species are favorable for NO abatement. Eventually, oxygen consumption rate for superfine pulverized coal is relatively faster, conducive to strengthen both homogeneous and heterogeneous NO reduction under CO2 reburning condition.

Reverse-swirl (RS) burner which has been industrialized couples reverses jet and swirl flow for the stabilization of flame. Using Dantec multichannel constant-temperature anemometer, experiments on airflow characteristics were implemented on a 1:2 scaled burner model with different values in terms of reverse primary air (RPA) ratio and swirl inner secondary air (SISA) ratio. It was found that the shape of annular coupled recirculation zone (ACRZ) had stayed symmetrical all the time. The RPA ratio was the main factor that had an impact on the values of axial and RMS velocity as well as the radial velocity direction of ACRZ. Both RPA ratio and SISA ratio had a great impact on the area of ACRZ, relative reverse flow rate, mixing between SISA and outer secondary air (OSA) as well as swirling ability of the airflow. The area of ACRZ reached its peak when the RPA ratio was 11.92% or SISA ratio was 17.03%; however, when the RPA ratio and SISA ratio reached 14.86% and 28.41% respectively, the combination of RPA and SISA became relatively favorable; besides, ACRZ area, relative reverse flow and swirling ability became suitable and the mixing between SISA and OSA was relatively delayed. The research was of great practical and theoretical importance to the design and operation of RS burner.

This article presents the statistical data of power steam boilers installed at combined heat and power plants in Russia. This work also summarizes the experience of creating Russian boilers, starting from the first Ramzin straight-through boiler and ending with powerful boilers for a 1200-MW gas/oil unit and 800-MW pulverized coal unit. Notably, following the main global tendencies, Russian boiler plants are ready to create modern boilers for both ultra-supercritical parameters and circulating fluidized bed units and boilers for burning nonconventional fuels.

To analyze the secondary oxidation of the active structures of pulverized coal and reduce risks of coal spontaneous combustion, free radical theory and functional group analysis were combined to study the effects of particle size and oxidation temperature on the active structure of coal molecules. This process was based on electron paramagnetic resonance (EPR) and Fourier-transform infrared (FTIR) technology. The results show that the reduction in pulverized coal particle size can enhance the secondary oxidation activity of coal and that the reactivity is the strongest when the particle size is 0.074−0 mm. The smaller the coal particle size is, the shorter the aliphatic side chain is after secondary oxidation. The reaction in which the side chain breaks to form a stable chain structure is also more intense. A smaller coal particle size also makes it easier to produce −OH after secondary oxidation, resulting in a large increase in the Average A (−OH) in the Coal 1# and Coal 3# at the minimum particle size range of 0.074−0 mm. The −C=O and −C−O− in Coal 1# with a lower metamorphic grade are greatly affected by temperature and particle size, and the consumption of −C=O during oxidation plays a dominant role in the secondary oxidation process. The −C=O and −C−O− in Coal 2# and Coal 3# are less affected by temperature and more affected by particle size, and −C−O− is the main group driving the secondary oxidation reaction.

In view of the problems faced by a conventional moving bed coal pyrolysis process, such as the inability to deal with pulverized coal, low light tar yield, poor tar quality, etc., a moving bed pyrolysis process with baffled internals was developed to control heat and mass transfer of the gas-solid two-phase and the pyrolysis reaction process. The multi-stage gas gathering system can collect the oil and gas products released in different pyrolysis stages of coal in time. The pyrolysis behavior and product quality of Naomaohu coal at different temperatures and residence times were investigated. The results show that the baffle internals enhance heat and volatile matter transfer among particles, enabling it to process 0.4–6.0 mm pulverized coal. When pyrolysis temperature is 550°C and residence time is 3.0h, the pyrolysis tar yield reaches the highest 11.38%, which is 86.87% of the Gray-King assay yield, and the mass fraction of light components below 360°C in the tar fraction is 85.0%. With the extension of the residence time, the H2 volume fraction in the pyrolysis gas increases from 22.1% to 35.1%, and the CO volume fraction increases from 8.0% to 9.5%. Tar yield in the first and second layer reactors increases with increasing residence time, and the tar yield in the third and fourth layer reactors isobtained when the residence time is 2.0 h. As the number of beds increases, content of light components in the tar simulated distillation fraction increases; content of tar aliphatic hydrocarbon compounds decreases, and that of monocyclic aromatic hydrocarbons and bicyclic aromatic hydrocarbons gradually increases. Based on the above results, it provides technical support for large-scale industrial processing of small particle size pulverized coal, and preparation of higher yield and quality tar.

Adaptation of a mathematical model of gas diffusion combustion for different flow rates of CO–H2 and a constant coal flow rate is carried out. It is shown that the results of calculating the main characteristics of the flame are in satisfactory agreement with experimental data and can be used to determine the structure of pulverized coal–gas flow, gas composition, particle and gas temperature, carbon combustion efficiency, etc. The proposed model is suitable for analyzing the stability of coal–gas flame and the transient processes accompanying changes in the mode of supply of the fuel-oxidizer medium.

Pulverized coal and biomass co-firing in the 150MWe unit of Tuncbilek power plant is computationally investigated, within the scope of a preliminary feasibility study. The considered furnace, burning Turkish lignite, has totally eighteen burners, positioned at three different levels. First, the pulverized coal combustion in the furnace is calculated and the predicted temperatures in the boiler first pass are compared with the previous measurements. Subsequently, a co-firing scenario is computationally analyzed, where the burners of the lowest level that supply 43% of the total fuel mass are fed by biomass, instead of coal. Turkish red pine is assumed to be the source of the biomass. In replacing the coal by biomass, the mass flow rates of the biomass and the corresponding air are adjusted in such a way that the thermal load and the equivalence ratio remain unaltered. Due to the lack of more accurate data for the biomass, the rate constants for the pyrolysis and chemical conversion of biomass are assumed to be the same as those of coal, along with the assumption of the same particle size distribution for both fuels. It is observed that the resulting flame structure for the case of co-firing is very similar to that of coal combustion. This result is encouraging for the application of biomass co-firing in the considered furnace.

A three-dimensional numerical simulation was performed to investigate the physics and combustion characteristics of a two-phase reacting turbulent flow in a pilot-scale pulverized coal combustion furnace. This included an elementary reaction mechanism using an extended flamelet/progress variable (EFPV) method. The simulation was validated via comparison with an experiment in terms of the gaseous temperature and distribution of the gas mole fraction. The EFPV method predicted the flame structure and combustion characteristics of the pulverized coal. In the main reaction zone where the released gas combustion was dominant, two separate combustion regions were observed, and they were attributed to hydrocarbons and CO combustion. Gas flow characteristics such as mixing of low temperature gas and hot burnt gas were well described in the inner recirculation zone. The CO2 conversion reaction to CO occurred slowly and decreased the gaseous temperature beyond the main reaction zone in the low and zero oxygen environments. The simulation predicted the unburned CO combustion correctly beyond the flame when staged air was injected; however, the combustion rate was overestimated due to the fundamental assumption of the EFPV method, attributable to the limitations of the steady state flamelet approach.