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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.

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.

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.

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.

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.

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.

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 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.

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.

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.

Because ammonia is one of the most promising candidates for energy carrier in the future, various applications of ammonia as a fuel are currently considered. One medium for utilizing ammonia is by introducing it to coal-fired boilers. To the best of our knowledge, this paper is the first to report the fundamental mechanism of the flame propagation phenomenon for pulverized coal/ammonia co-combustion. The effects of the equivalence ratio of the ammonia-oxidizer mixture on the flame propagation velocity of pulverized coal/ammonia co-combustion in turbulent fields were clarified by the experiments employing a unique fan-stirred constant volume chamber. The flame propagation velocities of pulverized coal/ammonia co-combustion, pure ammonia combustion, and pure pulverized coal combustion were compared. As expected, the flame propagation velocity of pulverized coal/ammonia was higher than that of the pure pulverized coal combustion for all conditions. However, the comparison of the flame propagation velocities of pulverized coal/ammonia co-combustion and that of the pure ammonia combustion, revealed that whether the flame propagation of the pulverized coal/ammonia was higher than that of the pure ammonia combustion was dependent on the equivalence ratio of the ammonia-oxidizer. This unique feature was explained by a mechanism including three competing effects proposed by the authors. In the ammonia lean condition, the positive effects, which are the strong radiation from the luminous flame and the increment of local equivalence ratio by the addition of volatile matter, are larger than the negative effect, which is the heat absorption by coal particles in preheat zone. In the ammonia rich condition, the effect of an increment of the local equivalence ratio by the addition of volatile matter turns into a negative effect. Consequently, the negative effects overcome the positive effect in the ammonia rich condition resulting in a lower flame propagation velocity of pulverized coal/ammonia co-combustion.

To better understand Moderate or intense low-oxygen dilution (MILD) combustion, numerical simulations of pulverized coal MILD combustion with different inlet velocities and oxygen concentrations are presented in this work. The flow and chemical reaction characteristics are analyzed and the MILD performance is determined by the Damkohler number, Da, and the circulation coefficient, K υ , with different oxygen concentrations and inlet velocities. Results show that the oxygen concentration has a more pronounced impact on the chemical reaction, and the inlet velocity has a more pronounced impact on the flow time scale. The K υ values are found increasing with the oxygen concentrations, which is caused by the decreased total amount of flue gas. Modified schematic diagram of combustion regimes is presented based on the analysis. The Da number increases with the increase of oxygen concentration. This is because, on the one hand, the increase in oxygen concentration leads to the decrease in the inlet velocity. On the other hand, the oxygen concentration intensifies the chemical reaction. This indicates that, with the increasing oxygen concentration, the larger K υ or the smaller Da is required to establish the MILD combustion. If the burner structure is not changed, increasing the oxygen concentration will reduce flue gas entrainment and aggravate chemical reactions, which is not conducive to the MILD coal combustion.

Vanadium–titanium magnetite is one kind of important strategic resources. However, there exist some common problems in the current smelting process of vanadium–titanium magnetite. In the present paper, we propose the rotary kiln pre-reduction and bath smelting process reasonably for smelting vanadium–titanium magnetite. The smelting reduction test of vanadium–titanium magnetite carbon-bearing pellet in the bath was conducted under laboratory condition, and the effect of end slag basicity, the smelting temperature, the smelting time and the amount of pulverized coal on the separation of slag–iron and the quality of hot metal were mainly investigated. The results showed that the reasonable smelting parameters for vanadium–titanium magnetite smelting of the process introduced in the paper were above 1450 °C of smelting temperature, above 0.8 of basicity of slag, 30–40 min of smelting time and 20–22% of coal addition. Nevertheless, the sulfur content of the iron particle was higher than the demand of steelmaking and it needed further desulfurization. The process is economically feasible for smelting vanadium–titanium magnetite, which can recover the vanadium and titanium resources effectively.

Aiming to reduce coal dust pollution and spontaneous coal combustion during coal mining, storage, and transportation, a kind of DOPO-nano-SiO2 modified polyacrylic acid-based polymer flame retardant dust suppressant for coal was fabricated using 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), γ-aminopropyl triethoxysilane (KH550), nano-SiO2, sodium alginate (SA), and acrylic acid (AA) as raw materials, potassium persulfate (K2S2O8) and sodium bisulfite (NaHSO3) as initiator, and N,N′-methylenebisacrylamide (MBA) as a cross-linking agent by the aqueous solution polymerization method. The product was characterized and analyzed by FT-IR, XPS, XRD, GPC, TG, and DSC techniques. Its flame retardant property, thermal stability, and dust suppression performance were tested, and the activation energy of the pyrolysis reaction was calculated using Flynn–Wall–Ozawa (FWO) method. Compared with the coal sample sprayed with water, the CO mass concentration of the coal sample sprayed with flame retardant dust suppressant was decreased by 80.6%, inhibition rate reached 82.8%, LOI value was 26.1%, and the UL-94 rating was V-0. Moreover, the initial degradation temperature and pyrolysis activation energy were increased by 10.6% and 108%, respectively. After spraying the flame retardant dust suppressant, the pulverized coal particles were tightly bonded together to form a flexible consolidation layer, thereby inhibiting coal dust pollution and loss. The water loss rate, wind erosion loss rate, and oscillation loss rate were decreased by 56.9%, 98.7%, and 97.5%, respectively. These results revealed that the pulverized coal sprayed with the flame retardant dust suppressant exhibited better flame retardant property, thermal stability, and dust suppression performance than that sprayed with water. In summary, the flame retardant dust suppressant prepared in this work could play a key role in inhibiting coal dust pollution and spontaneous coal combustion.

High-concentration H2S formed in the reduction zone of pulverized coal air-staged combustion can result into the high temperature corrosion of water wall tube of boiler, so it is of great importance to accurately predict H2S concentration for the safe operation of boilers and burners. H2S formation and evolution depends on two steps: the sulfur release from coal conversion and gas-phase reactions of sulfur species. In this study, the sulfur release characteristics from the pyrolysis of 17 coals, including 5 lignite, 9 bituminous coals and 3 anthracites, are investigated in a drop tube furnace (DTF). Sulfur release model is developed to describe the relationship between sulfur release and coal types. A global gas-phase reaction mechanism of sulfur species composed of ten reactions is used to calculate and predict the formation and evolution of H2S, COS and SO2 in the reduction zone of pulverized coal air-staged combustion. A wide range of air-staged combustion experiments of 17 coals are conducted in the DTF at different temperatures and stoichiometric ratios to validate the developed model. The results show that the prediction errors of sulfur species, including SO2, H2S and COS, are within ± 30%, which indicates that the developed prediction model of sulfur species is of great assistance for CFD modeling of actual engineering application.

The ignition and combustion of coal particle groups are investigated numerically in a laminar flow reactor. The Flamelet Generated Manifold method is extended to account for the complex mixture of gases being released during devolatilization, which is calculated with a competing two-step model. A second mixture fraction is introduced to include the mixing with the second methane fuel stream. The interactions of the gas phase with particles are modeled within a fully coupled Euler-Lagrange framework. To investigate the influence of particle groups on ignition and combustion, successively increasing densities of particle streams have been analyzed. The ignition delay time is increased significantly by higher particle densities. This delay is validated successfully with the available measurements. Moreover, the shape of the volatile flame was found to be strongly influenced by the particle number density inside the flame. A transition from spherical flames around single particles to a conical flame around the particle cloud could be found in numerical results as well as in experiments. As the primary mechanism for the substantial ignition delay and the formation of the flame, the increased heat transfer from the gas-phase to the particle group, resulting in lower gas-phase temperatures, was identified.

Biomass co-firing within the existing pulverized coal boiler is thought as a practical near-term way of biomass utilization, while its detailed combustion characteristics and pollutant formation have not yet been fully understood. In the present study, we report a Carrier-phase Direct Numerical Simulation study coupled with detailed mechanism to provide a deep insight into the coal/biomass co-firing (CBCF) jet flames under different blending ratios. It is found that compared with the pure coal flame, the CBCF could (i) prompt the volatiles ignition, produce higher H2O and similar CO2 mass fractions at blending ratios of 20% and 40%, and obviously reduce the gas temperature and CO2 mass fraction at the blending ratio of 50%; (ii) prompt the coal devolatilization and char burnout at blending ratios of 20% and 40%, while the char burnout is reduced when blending ratio is 50% due to the local enrichment of large particles and lack of oxygen; (iii) reduce the thermal, prompt, NNH and N2O-intermediate routes of NO formation, but show limited effect on the NO-reburning route of NO destruction, therefore, resulting in an obvious NO reduction.

Influence of coal micronization on air-blown conversion of pulverized coal fuel is under study. On the basis of these experiments, computational fluid dynamics methods are used to perform simulation determining the conditions of the process under study. Conversion of coarse coal in a medium of combustion products of fine coal with the following parameters: a flow rate ratio of primary and secondary coal is 0.82; a corresponding air flow rate is 0.35; the stoichiometric coefficient of primary, secondary, and total air are 0.8, 1.87, and 1.39; temperatures in the active zone are higher than 1200°C. According to the computational results for this regime, the carbon conversion rate for the primary and secondary coal is 100% and 60%, respectively, and its total value is $$\approx$$ 80%. The results obtained suggest that it is possible to increase the efficiency of coal combustion due to micronization technologies as applied to oil-free ignition and torch illumination systems on steam pulverized coal boilers at TPPs.

This paper studied the effect of high temperature (up to 1873K) and separated combustion mode (volatile combustion and char combustion are separated) on SO2 release characteristics during pulverized coal combustion under O2/CO2 atmosphere. Coal combustion experiments were conducted at different combustion environment temperatures utilizing a high temperature fixed-bed setup. The results show that as temperature rises, the SO2 release curve is transformed from a single-peak process to a double-peak process. In separated combustion, temperature has little effect on the volatile-SO2 (SO2 released during volatile combustion) but brings about a significant effect on char-SO2 (SO2 released during char combustion). Char-SO2 release amount and the ratio of it to fuel-SO2 release amount (total SO2 released during coal combustion) increase with temperature rising. The increase of temperature leads to a dramatic decreasing of sulphur mass fixed in the ash and causes SO2 release amount to rise when temperature is lower than 1573 K. Separated combustion causes a higher SO2 release amount than coupled combustion (the same as conventional combustion, volatile combustion and char combustion are simultaneous). Thermochemistry equilibrium composition calculation results show that alkali metals and alkaline-earth metals are significant in sulphur retention. CaSO4 and Na2SO4 are the main sulphates at high temperatures.

The complex of research works carried out by the NTMK team and the leading research teams of UIM, IMET UB RAS and Ural Federal University expanded the theoretical foundations of processing vanadium-containing titanomagnetites. The blast furnaces have achieved a specific productivity of over 3.0 t/m3, which is the best indicator in Russia. Specific fuel and carbon consumption is the best in Russia. The conditions for the operation of blast furnaces, in which the development of carbide formation processes is significantly reduced, have been established. Measures have been implemented that ensure the smelting of cast iron with a low content of silicon and titanium. The main measures are: maximum forcing of the furnace; increased pressure under the mouth; oxygen enrichment of the blast; as well as increasing the rate of filtration through the coke packing by optimizing the properties of the slag and increasing the hot strength of the coke. The introduction of blast-furnace smelting technology with the use of staflux and the injection of pulverized coal has made it possible to reduce the consumption of total carbon in the fuel to 418 kg/t of cast iron.

During coal and coal gangue combustion, many heavy metal pollutants are emitted and cause serious environmental problems. In this paper, the environmental effect values of As and Pb emission during coal gangue and coal combustion in the 330 MW pulverized coal boiler, 50 kW circulated fluidized bed boiler and laboratory were calculated by ReCiPe2016. The results show that when coal combustion in 330 MW pulverized coal boiler, the environment effect values of as for bottom slag, fly ash and flue gas are 3.28×10−6, 2.68×10−5 and 3.89×10−3 respectively; while the environment effect value of Pb for bottom slag, fly ash and flue gas are 8.57×10−6, 6.00×10−5 and 4.83×10−2, respectively. The environmental effects of As and Pb in bottom slag are lower than those in the fly ash; and the environmental effects of As and Pb on air are higher than those on soil. Moreover, when coal combustion in the 50 kW circulated fluidized boiler, the effect values of As and Pb in fly ash on environment are 3.26×10−5 and 1.28×10−4; and the effect values of As and Pb in bottom slag are 1.16×10−6 and 1.43×10−5 respectively. The results also show that when coal gangue combustion in the laboratory, the effect values of As and Pb emission increase with increasing of the temperature; and the proportions of total environmental effects of As and Pb on air are higher than those on soil. Besides that, this study also indicates that the effect of Pb emitted into environment is higher than that of As at the same conditions during coal combustion both in circulated fluidized boiler and pulverized coal boiler. The results may provide basic data for predicting the environmental effects of As and Pb during coal gangue combustion in circulating fluidized bed for life cycle impact assessment.

Increasing the share of hydrogen in reduction of iron oxide in the blast furnace iron making will directly reduce the share of blast furnace greenhouse gas emissions. In the present study, injection of H2-rich biomass and plastic materials was studied in terms of its devolatilization, gasification and combustion characteristics. The released gases were identified using mass spectroscopy attached to a thermogravimetric analyzer and the corresponding kinetics parameters were estimated. The devolatilization was found to occur through two or more steps. The first step is always associated with the release of CO2, CO, H2, H2O and hydrocarbons while only CO and H2 were detected during the later steps. Combustion and gasification starting temperatures of char of H2-rich carbonaceous materials were lower than that of pulverized coal char by ≥ 100 °C. The estimated activation energies suggested that, under the present conditions, devolatilization, gasification and combustion were chemically controlled. Carbon reactivity of the char of the studied H2-rich carbonaceous materials were higher than that of pulverized coal. Moreover, increased H2–H2O content in the blast furnace gas, due to injected H2-rich carbonaceous materials, was found to improve the iron ore pellets reduction kinetics.

Due to its low volatile characteristics of lean coal, it is difficult to catch fire and burn out. Therefore, high temperature is needed to maintain combustion efficiency, while, this leads to high nitrogen oxide emission. For power plant boilers burning lean coal, stable combustion with lower nitrogen oxide emission is a challenging task. This study applied the 3D numerical simulation on the analysis of a novel de-coupling burner for low-volatile coal and its structure and operation parameters optimization. Results indicate that although it was more difficult for lean coal decoupling burner to ignite lean coal than high volatile coal, the burner formed a stepwise ignition trend, which promoted the rapid ignition of lean coal. Comparison of three central partition plate structure shows that in terms of characteristics of the flow field distribution, rich and lean separation and combustion, the structure with an inclination of 0 ° showed good performance, with its rich-lean air ratio being 0.85 and concentration ratio being 22.94, and there was an apparent decoupling combustion characteristic. Finally, the structure of the selected burner was optimized for its operational conditions. The optimal operating parameters was determined as the primary air velocity of 24.9 m/s and the mass flow rate of pulverized coal of 2.5 kg/s, in which the pyrolysis products were utilized as reductive agent more fully. Eventually, the nitrogen oxide was efficiently reduced to nitrogen, which emission concentration was 61.88% lower than that in the design condition.

The quantity of NOx emission from cement production is second only to thermal power generation and vehicle exhaust. In this paper, a phenomenon found by Taniguchi is used to achieve NOx reduction in the cement precalciner. Based on his results, it is proposed to reduce NOx that ammonia is injected in the high-temperature and lean-oxygen zone (HT-DeNOx) during pulverized coal combustion. For a large cement precalciner (3200 t/d), numerical simulation is used to evaluate the technology of HT-DeNOx combined with the traditional selective non-catalytic reduction (SNCR) method. The results indicate that NH3 and HCN in HT-DeNOx can reduce NO during the reaction process. With very little ammonia injection (normalized stoichiometric ratio NSR=0.1, the normalized stoichiometric ratio), the efficiency of NO reduction by HT-DeNOx is 27.72%. Combining SNCR (NSR=1.1) and HT-DeNOx (NSR=0.1), the reduction efficiency will be improved to 60.05%, compared with 50.83% efficiency when using only SNCR at NSR=1.2.

NOx emission is a serious problem during fossil fuel combustion. Novel reburning fuels, namely, nitrogen-containing tar compounds, including pyridine and pyrrole were taken into consideration for NO reduction and investigated by quantum chemical method. Theoretical calculation results show that pyridine could first decompose into small species, such as CN and hydrocarbon radicals, then reduce NO to N2. The decomposition of pyridine should overcome quite high energy barrier and adsorb a large amount of heat. This pathway may occur at high temperature zone, such as core flame zone of pulverized coal fired boiler. As soon as pyridine decomposes, the active intermediates (CN radical, etc.) could reduce NO very quickly. The direct reduction of NO by pyridine molecule should overcome lower energy barrier, which could occur at wider temperature range. Pyrrole is less thermostable than pyridine; the energy barriers of pyrrole cracking and direct reduction of NO stay at same level. Therefore, the reburning efficiency of pyrrole may be better at lower temperature than pyridine. Theoretical calculations indicate that nitrogen-containing tar compounds produced during biomass pyrolysis/gasification could have good performance for NO reduction in pulverized coal fired boiler as well as biomass or MSW furnace.

Circulating fluidized bed combustion (CFBC) is a newer type of burner that employ a circulating process to burn fuel effectively. CFBC burning process is gaining more popularity due to its compact size, high efficiency and lower burning temperature compared to the pulverized coal combustion (PCC) burner. The CFBC burner produces fly ash with different physical properties compared to the PCC burner, i.e. the fly ash is not rounded, and required higher water content for comparable workability. The CFBC fly ash also has a high sulfur content that is detrimental for hardened concrete. Due to its drawbacks, the CFBC hardly used as cementitious material and geopolymer precursor. This study focuses on comparing variations in the concentration of NaOH solution and variations in the ratio of alkaline activators to the setting time and compressive strength of geopolymer mortars on a new class of CFBC fly ash, which have low sulfur content. The concentrations of NaOH solution were 6M, 8M, 10M, and 12M, while the alkaline activator ratios used were 3.0, 2.5, 2.0, 1.0, and 0.5. It was concluded that the low sulfur CFBC fly ash has a potential to be utilized as geopolymer precursor, however, with a shortcoming in its high water demand. The CFBC fly ash used in this study resulted in a geopolymer matrix with good compressive strength and stability. The water demand varies with the fly ash sampling time shows the challenges in the utilization of the fly ash. The highest mortar’s compressive strength, 33.4 MPa at 90 days was achieved at NaOH concentration of 8M and ratio of sodium silicate solution to sodium hydroxide solution of 2.5 with excellent stability.

The preparation of functional material titanium carbide by the carbothermal reduction of Ti-bearing blast furnace slag with microwave heating is an effective method for valuable metals recovery; it can alleviate the environmental pressure caused by slag stocking. The dynamic dielectric parameters of Ti-bearing blast furnace slag/pulverized coal mixture under high-temperature heating are measured by the cylindrical resonant cavity perturbation method. Combining the transient dipole and large n bond delocalization polarization phenomena, the interaction mechanism of the microwave macroscopic non-thermal effect on the titanium carbide synthesis reaction was revealed. The material thickness range during microwave heating was optimized by the joint analysis of penetration depth and reflection loss, which is of great significance to the design of the microwave reactor for the carbothermal reduction of Ti-bearing blast furnace slag.

The problems of using pulverized coal to save coke during iron smelting in the NLMK blast furnaces are considered. The iron smelting technology was implemented in two stages: (i) commissioning of the pulverized-coal preparation and charging system and (ii) selection of charging system and blast conditions that ensure the maximum utilization of pulverized coal and required output. An analysis of the dynamics in the consumption of coke and fuel additives showed that the total fuel carbon consumption has decreased, despite the difference in the amount of carbon charged with natural gas and pulverized coal. The calculations based on a mathematical model showed that with increase in the consumption of pulverized coal and decrease in the consumption of natural gas, the gas-to-coke replacement ratio increases by 0.09 kg of coke per 1 m3 of natural gas on average.

As the development of coal gasification technology expands in China, the resulting solid by-products can become environmental and economic concerns. Evaluation of carbon forms and elemental composition in coal gasification solid residues from three advanced commercial-scale entrained-flow gasification plants in China related to feedstock coal properties are studied and their potential utilization is discussed in the present study. The properties of the residues of the three entrained-flow gasification processes differed as a result of the type of process applied, even though the properties of their feedstocks are similar. Eight types of carbon forms were identified. The high-inertinite feedstock resulted in a fusinite-like carbon being the primary carbon form of the residues, except for the General Electric fine residue (GE-FR) sample. The carbon contents of the coarse residues (CRs) produced from the Opposed Multi-Burner (OMB) coal-water slurry gasifier and the Gaskombiant Schwarze Pumpe (GSP) pulverized coal gasifier are comparable, lower than 2% (Cd), but a high content of carbon present as "black particles" (79.90%, Cd) was concentrated from the OMB-CR sample. Fourier transform infrared spectroscopy (FTIR) analyses indicate that the main functional group of the fusinite-like material in OMB-CR is methyl (CH3-). From the chemical composition point of view, the high proportions of F2O3 and CaO in the GE residues make them potential sources of high-Fe or high-Ca material. The relatively high concentrations of In, Ga, Sb, Cs, Cr, Ba, and rare earth elements in the residues make them potential raw materials for extracting critical trace elements, especially the OMB-FR and GSP-FR samples for extracting Ga.

As an emerging clean coal combustion technology, Moderate or Intense Low-Oxygen Dilution (MILD) combustion or oxy-fuel combustion, compared with traditional coal combustion, has many advantages. However, compared with MILD combustion and oxy-fuel combustion, MILD-oxy combustion is believed more attractive. In this work, MILD-oxy combustion characteristics with oxygen concentrations from 10% to 50% are studied numerically. The results show that within a certain range, increasing the oxygen concentration is in favor of MILD-oxy combustion performance close to that of MILD-air combustion. When the oxygen concentration is higher enough, the momentum reduced by the increase of oxygen concentration has a great influence on the furnace temperature. With the increase of oxygen concentration, the radiation heat transfer is enhanced and the convective heat transfer is weakened. The increase of oxygen concentration can promote the occurrence of char gasification reaction with CO2. In addition, MILD-oxy combustion has a large impact on CO emission.

The mercury emission was obtained by measuring the mercury contents in flue gas and solid samples in pulverized coal (PC) and circulating fluidized bed (CFB) utility boilers. The relationship was obtained between the mercury emission and adsorption characteristics of fly ash. The parameters included unburned carbon content, particle size, and pore structure of fly ash. The results showed that the majority of mercury released to the atmosphere with the flue gas in PC boiler, while the mercury was enriched in fly ash and captured by the precipitator in CFB boiler. The coal factor was proposed to characterize the impact of coal property on mercury emissions in this paper. As the coal factor increased, the mercury emission to the atmosphere decreased. It was also found that the mercury content of fly ash in the CFB boiler was ten times higher than that in the PC boiler. As the unburned carbon content increased, the mercury adsorbed increased. The capacity of adsorbing mercury by fly ash was directly related to the particle size. The particle size corresponding to the highest content of mercury, which was about 560 ng/g, appeared in the range from 77.5 to 106 µm. The content of mesoporous (4–6 nm) of the fly ash in the particle size of 77.5–106 µm was the highest, which was beneficial to adsorbing the mercury. The specific surface area played a more significant role than specific pore volume in the mercury adsorption process.

Considering that the utilization of fly ash in the removal of flue gas pollutants not only provide a way of high value-added utilization of fly ash, but also greatly reduce the cost of removing flue gas pollutant, the synthesis of silica sulfuric acid catalyst from fly ash and its application in simultaneous removal of NOx and SO2 with H2O2 were investigated in this work. Circulating fluidized bed boiler (CFB) fly ash and pulverized coal boiler (PC) fly ash were selected as raw material to prepare silica sulfuric acid catalyst by H2SO4 activation. PC fly ash was difficult to be activated by H2SO4 due to its dense structure, while CFB fly ash could be treated with H2SO4 to promote dealumination, thereby increasing the silica content. Moreover, the -SO3H withdrawing groups were detected on the silica surface by XPS and Py-FTIR technologies, indicating the formation of silica sulfuric acid. Silica sulfuric acid showed higher activity in catalyzing the NO oxidation by H2O2, and a possible reaction mechanism was proposed. Combined with alkali absorption, 99% SO2 and 92% NOx removal efficiencies can be achieved. The effects of activation conditions such as activation temperature, activation time and calcination temperature and removal experimental parameters such as H2O2 concentration, SO2 concentration and simulated flue gas temperature on the catalytic performance were studied. Finally, the catalyst was not found to be deactivated for ten hours in the stability test.

In pulverized coal particle combustion, part of the ash forms the ash film and exerts an inhibitory influence on combustion by impeding the diffusion of oxygen to the encapsulated char core, while part of the ash diffuses toward the char core. Despite the considerable ash effects on combustion, the fraction of ash film still remains unclear. However, the research of the properties of cenospheres can be an appropriate choice for the fraction determination, being aware that the formation of cenospheres is based on the model of coal particles with the visco-plastic ash film and a solid core. The fraction of ash film X is the ratio of the measuring mass of ash film and the total ash in coal particle. In this paper, the Huangling bituminous coal with different sizes was burnt in a drop-tube furnace at 1273, 1473, and 1673 K with air as oxidizer. A scanning electron microscope (SEM) and cross-section analysis have been used to study the geometry of the collected cenospheres and the effects of combustion parameters on the fraction of ash film. The results show that the ash film fraction increases with increasing temperature and carbon conversion ratio but decreases with larger sizes of coal particles. The high fraction of ash film provides a reasonable explanation for the extinction event at the late burnout stage. The varied values of ash film fractions under different conditions during the dynamic combustion process are necessary for further development of kinetic models.

Pulverized coal cloud deflagration in a methane–oxygen atmosphere is a fairly intricate process owing to transient turbulent combustion accompanied by gas–particle premix flow. We developed a comprehensive computational fluid dynamics model that considers gas–solid two-phase flow, interaction between gaseous and discrete coal particles, and homogeneous–heterogeneous reactions. Numerical results revealed nonconforming and random particle temperature at different instants. The temperature threshold and distribution of high-temperature particles were quantitatively and qualitatively analyzed using the simulation results. Particle accumulation and agglomeration reported for previous experiments was verified and interpreted using turbulence theory. In addition, we analyzed the coupling and heat-mass transfer between coal particles and gas. This investigation has yielded the detailed mechanism of heat transfer for a dust explosion and provided valuable information for prediction, precaution, and control of an explosion involving discrete particles.

In this study, the flash reduction process of hematite particles with six hydrogen-rich gases of purified COREX (PCOREX), dry pulverized coal gasification (DPCG), water-coal slurry gasification (WCSG), Midrex, HYL-III, and reformed coke oven gas (RCOG) was investigated. The homogeneous and heterogeneous reactions occurring in the reduction temperature range were determined by thermodynamic analysis. On this basis, a three-dimensional computational fluid dynamics model was established to demonstrate the flash reduction process in a drop tube furnace and describe hematite particle characteristics during the in-flight reduction process. Results showed that a higher hydrogen content led to a faster reduction rate and a higher reduction degree. Hence, the reduction degree increased according to the following trend of PCOREX 90%.

The catalytic behavior of alkali vapor on unburned pulverized coal (UPC) prepared from bituminous coal, anthracite, semi coke and coke have been investigated. Experiment results show that the alkali metal vapor has catalytic effect on the gasification reaction of UPC. The catalytic effect of coke UPC is the most obvious, followed by anthracite UPC and bituminous coal UPC. Semi coke UPC is the least catalyzed by alkali metals but its gasification reactivity is the best. As the concentration of alkali metal vapor increases, the alkali metal content adsorbed by UPC increases, and there may be a phenomenon of saturated adsorption. The amount of alkali metal adsorbed is between 2% and 6%. AUPC has the highest ability to adsorb alkali metals, and SUPC is the weakest, which may be related to the minerals (CaO, Al2O3) in the coal ash. Changes in stomatal parameters are not the main factors affecting the catalytic effect. The results of X-ray diffraction experiments show that alkali metal aluminosilicate exists in the ash of coal after adsorption of alkali metal, and the average stack height of carbon atoms decreases significantly. The alkali metal catalytic gasification reaction is mainly achieved by destroying the carbon basic structural unit. The alkali metal nepheline and the interlayer compound may be the main catalytic substances, and the destructive ability of alkali intercalation is obviously stronger than that of alkali nepheline. The catalytic mechanism of alkali metals on unburned coal and the destruction mechanism of alkali metals on carbon crystals were discussed. It can provide reference for reducing alkali metal corrosion on coke and improving pulverized coal utilization rate.

The high concentration of CO2 and low concentration of O2 at relatively low temperatures of 1123-1223 K are typical reactive atmospheres in the fuel reactor of a chemical looping with oxygen uncoupling (CLOU) unit. Char within this environment can be converted via lean-O2 oxidation and/or rich-CO2 gasification. Conventional models, which either considered the oxidation only or considered the oxidation and gasification contributions independently by simply adding the two individual conversion rates together, seem arbitrary. Therefore, it is necessary to quantitatively explore the contributions of the oxidation and the gasification reactions as well as their interactions in CLOU conditions through more detailed particle-resolved simulations. In this work, a single particle model which described a spherical reacting porous particle with its reacting boundary layer was developed to investigate the conversion characteristics of pulverized coal char in lean-O2 and/or rich-CO2 conditions (analogous CLOU conditions). The heterogeneous reaction kinetics developed by Tilghman and Mitchell [35] and the simplified GRI-Mech 3.0 gas-phase reaction kinetics were adopted. It was found that the char conversion rate in CLOU conditions could be basically modeled as the sum of the full oxidation consumption rate and the partial gasification consumption rate, i.e. rmix=φ1rgasi+roxid. The interactions between the oxidation and gasification reactions were elaborated in two aspects: on the one side, the oxidation of coal char in CLOU conditions is within the weak zone II burning region, where the oxidation reaction only happens peripherally and is nearly unaffected by the high concentration of CO2; on the other side, the gasification reaction within the external layer of the coal char particle is inhibited by the oxidation reaction, consequently the gasification reaction only happens inside the coal char particle where O2 cannot penetrate into. Based on these understandings, a correlation between the coefficient, φ1, and the effectiveness factor of the oxidation reaction, η, was proposed to describe the overall char conversion rate in CLOU conditions. Through fitting the simulation results under typical CLOU conditions, the quantitative relationship between φ1 and η was finally attained.

This study aims to explore the mechanism under which ash deposition propensity is improved by coal blending in a real modern boiler situation. In this paper, Zhundong coal (ZD), from northwestern China, known to have a heavy ash deposition problem in boilers, was blended with Jincheng anthracite (JC), which has a high ash fusion temperature (AFT). The density composition of the coal blend, which reflects the mineral distribution in pulverized coals, was found to change during the intergrinding process. The higher rank coal JC was found to be more concentrated in its lower and highest density fractions. The variances in the chemical composition among density fractions in the pulverized coal blend were found greatly narrowed as compared with the parent coals. AFT results indicate that the ash melting behavior in the coal blend (ZD/JC = 50:50) varies with density, which is confirmed by corresponding slag contents calculated with FactSage 7.1. Particle size distributions of the density fractions in ZD, JC, and the coal blend were determined with a laser particle analyzer. The size distribution of ash particles in each density fraction was estimated according to the char morphology, which is deduced from the ash content and coal particle size distribution. Minerals in the lowest density fractions will form ash with a particle size of around 2 μm. Included minerals in the medium density fractions will form ash particles with size related to its ash content, and excluded minerals will undergo slight fragmentation and have a ash particle size similar to the corresponding coal particles. A comprehensive comparison between ash volume, ash particle size, and softening temperature indicates that ash deposition propensity of the coal blend is improved not only because of an apparent increase in AFT but also because of an apparent decrease in the total volume of ash particles possibly arriving on the deposition surface.

The paper discusses the experience gathered at the Yenakievo metallurgical plant and Dnepr metallurgical complex with respect to using manganese-containing materials in the blast-furnace charge, which results in one of the greatest scrubbing effects when rationally formed in the feed charging cycle and contributes to maintaining the stability of the blast furnace operation at low and unstable quality of the charge material and pulverized coal injection (PCI). As an alternative to manganese-containing scrubbing materials, it is proposed to use the roller-pressed briquettes of ferroalloy production waste characterized by high quality parameters consistent with the iron source requirements.

This study was aimed at investigating the effects of 0%, 20%, 40%, 60%, 80% and 100% load of powdered Khaya ivorensis [heartwood] on proximate analysis, elemental analysis and calorific value of coal briquette and the results were compared with that of blank samples. Ignition and combustion properties were determined using standard methods. The results for pulverized coal and powdered Khaya ivorensis showed moisture content (%) 6.8 and 12.3: ash content (%) 16.8 and 1.73: volatile matter (%) 54.70 and 82.12: fixed carbon (%) 21.7 and 3.85: calorific value (kJ/kg) 19765.55 and 16084.44 and bulk density (g/cm2) 0.83 and 0.20 respectively. The results showed the presence of SiO2, SO3, K2O, CaO, TiO2, Cr2 O3, Fe2O3 in the coal and Khaya ivorensis. The results of briquette analyses showed that porosity index, moisture content(%), volatile matter(%) increased with increase in mass load. The density (g/cm3), ash content (%), sulphur content(%) and ignition time (sec)decreased with increase in mass load while there is variation in compressive strength (N/mm2), calorific value, burning rate (kg/s) and thermal efficiency (%) as mass load increases. It was observed from the results that powdered Khaya ivorensis [heartwood] enhanced the properties of coal briquette.

At present, the world is committed to the development of environmentally friendly, sustainable and industrial safety. The effective treatment of industrial solid waste can be applied in the field of industrial safety. It is one of the ways to apply industrial solid waste to industrial safety to modify industrial solid waste and combine active powder to prepare industrial solid waste-based composite powder explosion inhibitors and apply it to underground coal dust explosion. This paper introduces the modification and preparation methods of industrial solid waste, and analyzes the good explosion suppression effect and good economic benefit of industrial solid waste-based composite powder explosion inhibitors on coal dust explosion. In this paper, four kinds of industrial solid wastes (red mud, slag, fly ash and sludge) were modified, and the modified solid waste materials with good carrier characteristics were obtained. Combined with a variety of active powders (NaHCO3, KH2PO4 and Al(OH)3), the industrial solid waste-based composite powder explosion inhibitors were obtained by solvent-crystallization (WCSC) and dry coating by ball milling (DCBM). Those kinds of explosion inhibitors can suppress the explosion of pulverized coal in 40–50% of cases. Compared with the powder explosion inhibitor commonly used in industry, it has a lower production cost and better explosion suppression effect. Those kinds of explosion inhibitors have a good industrial application prospect.

Large-eddy simulation (LES) is applied to a multi-burner pulverized coal combustion furnace in which three advanced low- NO x burners, each with a coal combustion capacity of approximately 100 kg/h, are vertically installed. The effects of an in-furnace blending method, in which different types of coal (high-fuel-ratio coal and low-fuel-ratio coal) are injected at each burner stage, on NO emission and unburned carbon fraction in fly ash are investigated. Pulverized Newlands coal and Tanito Harum coal that are classified as high-fuel-ratio coal and low-fuel-ratio coal, respectively, are used as fuels. The results indicate that oxygen is consumed rapidly and NO decreases near the burner from which the high-fuel-ratio coal is injected because the reducing atmosphere becomes dominant owing to the lack of oxygen. Further, the unburned carbon fraction decreases when low-fuel-ratio coal is injected from the upper burner because the residence time is longer for the combustion of high-fuel-ratio coal than when low-fuel-ratio coal is injected from the lower burner.

In order to achieve highly efficient utilization of three valuable elements Fe, Ti and V simultaneously from vanadium-bearing titanomagnetite ore sands, an improved carbothermic reduction method was proposed and verified in both laboratory scale and industrial test-bed scale. The method combined the process of direct reduction and the process of further reduction and separation. Particularly, pulverized coal injection was introduced. In experimental tests, the effects of parameters such as carbon content in briquette, reduction duration and reduction temperature on the contents of metallic Fe and FeO as well as Fe metallization rate were analyzed. Experimental results indicated that Fe metallization rate in the carbon-containing briquette could reach 75.83%. In the industrial test-bed tests, the effects of carbon content in briquette, reduction duration and reduction temperature were also investigated, respectively. In addition, processes with and without pulverized coal injection were tested. The comparative analysis indicated that the content of TiO2 in titaniferous slag was increased by applying pulverized coal injection, and it can reach 82.5 wt.%. Meanwhile, the energy performance analysis showed that the equivalent electricity consumption of the test-bed dropped significantly to 2071 kWh per ton of slag, about 26.0% less than that of traditional method. Moreover, the investment payback of the test-bed is 3.4 years. Both experiments and industrial test-bed tests demonstrated that the proposed method has the advantages of highly efficient utilization, high energy efficiency as well as good economic performance.

Coal-fired power plants (CFPPs) are an important anthropogenic emission source of atmospheric mercury (Hg). Understanding the co-benefits of conventional air pollution control devices (APCDs) on Hg reduction is crucial for reducing Hg emission from this source. In this study, atmospheric Hg emission from a pulverized coal (PC) utility boiler in North China was investigated along the emission control stage of selective catalytic reduction (SCR), electrostatic precipitator (ESP) and fabric filter (FF) and lime stone-gypsum wet flue gas desulfurization (WFGD). Historical atmospheric Hg emission from this CFPP with total 1550 MW capacity since its operation in 1976 was estimated based on the implementation of different configurations of APCDs. The results showed that a combination of SCR + ESP-FF + WFGD leads to a co-beneficial Hg control of 96%, with the in-stack Hg concentration (0.87 μg m−3) much lower than the Chinese national standard for CFPPs (30 μg m−3), and the stack Hg speciation (Hg0:Hg2+:Hgp) was in 86%:13%:1%. Mass balance analysis indicates that Hg from the input of feed coal and limestone was mainly ended up in fly ash (89%), followed by gypsum (5%), stack gas (5%) and bottom ash (1%), respectively. During the past 42 years of operation (1976–2017), the total air Hg emission from this CFPP summed to 17.62 tonnes, in which Hg0 make up 14.02 tonnes (79.5%), Hg2+ make up 3.15 tonnes (17.9%) and Hgp 0.45 tonne (2.6%). Although the speciation of emitted Hg into the atmosphere changed with respect to the configuration of APCDs, Hg0 was the most dominated emission species (64–98%) for all time. Nearly 90% of total Hg emissions occurred in the first three decades when venturi scrubber (VS) and ESP were the primary APCDs. The installation of WFGD and SCR substantially decreased the Hg emission factors by 17 times compared to the peak values during 1998–2004. This study demonstrates the combination of SCR + ESP-FF + WFGD as a best available technology (BAT) for Hg control in CFPPs in China.