Coal Nitrogen Research Articles

Analyzing the combustion characteristics of Thar coal block XI: A comprehensive study

Coal is a key energy resource in the world that is available at low cost and the high energy content in coal makes it a fuel of choice in many developed and developing countries. Regardless of massive reserves, Thar coal of Pakistan is low-rank lignite coal with high moisture contents and has very limited use. The proximate analysis, ultimate analysis and X-ray diffractometry analysis were performed to investigate the combustion characteristics, morphological and mineral characteristics of Thar coal block XI. Thar coal samples in this study are characterized as low-rank lignite coal. The proximate analysis showed a significant difference in moisture content, volatile content, fixed carbon content and ash residue. The ultimate analysis provided the details of elemental contents (Carbon, Hydrogen, Nitrogen and Sulfer) in coal. The combustion characteristics such as combustion performance of lignite at high temperatures (950 °C) was investigated in thermogravimeter and the results showed the variations in the ignition temperature, burnout tempearature, combustion index and burnout index. The marphological characteristic were determined by X-ray diffraction. The mineral congregations, ash yields, major and minor elements (SiO2, Al2O3, CaO,MgO, Fe2O3) varied significantly in the coal. These analyses integrate various results for assessing major monitoring parameters of coal reactivity, its temperature ranges and combustion products.

Study on the Mechanism of Coal Fracturing by Liquid Nitrogen

As a fracturing medium with excellent properties, liquid nitrogen has multiple fracturing effects on coal, and its potential application in coalbed methane mining has become a hot spot in current research. In this paper, the key scientific problems of fracturing and penetration enhancement by liquid nitrogen in low-permeability coals are discussed in depth, and the pore fracturing process and its fracturing mechanism of low-temperature fracturing coal are analyzed. It is found that the ultra-low-temperature fluid fracturing process has the effect of high-energy fluid fracturing to break the rock, and also has the coupled fracturing effect of low-temperature fracturing and phase-change fracturing to increase the energy-driven replacement. It aims to provide theoretical basis and technical support for the efficient and environmentally friendly exploitation of low-permeability oil and gas fields.

The Occurrence and Distribution of Nitrogen in Coal of Different Ranks and Densities

Nitrogen is one of the significant pollutants emitted from coal combustion, and the study of its distribution and occurrence is very important for the efficient and clean utilization of coal resources. Four kinds of coal with different metamorphic ranks from major coal-producing provinces of China were studied. A gravity float-and-sink experiment was applied to obtain coal samples with different densities from Shanxi Province. The microscope optical method, Kjeldahl method, and X-ray photoelectron spectroscopy (XPS) were used to assess the occurrence, form, and distribution of nitrogen in the coal. The results show that the nitrogen content was about 0.47%–1.85%, and the maximum nitrogen content was positively correlated with the rank of coal, but the difference was not obvious. In the low-rank coal, the nitrogen content was mainly related to vitrinite and inertinite, while in the middle–high-rank coal, the nitrogen content was mainly related to inertinite and minerals. Pyrrolic (N-5) and pyridinic (N-6) were the main forms of nitrogen in the low-rank coal. The contents of N-6 and N-5 decreased with increases in the coal density, but the contents of quaternary N-Q1 and quaternary N-Q2 increased. N-Q2 mainly comes from fixed ammonia nitrogen in minerals, and vitrinite and liptinite contain more N-6 and less N-Q1 than inertinite. This research provides valuable evaluation guidance for the efficient utilization of coal.

Transformation of organic to inorganic nitrogen in NH4+-illite-bearing and Ga-Al-REE-rich bituminous coals: Evidence from nitrogen isotopes and functionalities

Nitrogen is one of the most important elements and mainly occurs as organic forms in coal, and in a few cases, in an inorganic form. Organic nitrogen in coal is mainly derived from the proteins of plants and micro-organisms but sources of inorganic nitrogen remain controversial. One hypothesis for the source of inorganic nitrogen is the organic matter of coal, but this lacks strong evidence. In the Daqingshan Coalfield of Inner Mongolia, northern China, an igneous intrusion in the east of the coalfield led to a coal rank increase from the Hailiushu through the Datanhao mines to the Adaohai mine from the west to east, with NH4+-illite being detected in the coals from the Datanhao and Adaohai mines. These coals are highly enriched in Ga, Al, and rare earth elements (REE). This study aims to explore the transformation of organic to inorganic nitrogen in these coals by means of nitrogen isotopes, element distribution in NH4+-illite, and nitrogen functional groups.The analysis of NH4+-illite by Electron Probe Microanalysis (EPMA) indicates partial substitution of nitrogen during the transition from kaolinite to NH4+-illite. Thermal metamorphism has resulted in the organic nitrogen isotope (δ15No) values in coals from the Adaohai Mine being more positive than those in the Datanhao and Hailiushu mines. 15N is more enriched in NH4+-illite than in the associated organic matter. The distribution of nitrogen functional forms showed a decrease in pyrrolic nitrogen (N-5) and an increase in pyridinic nitrogen (N-6) from coals in the Hailiushu to Datanhao and Adaohai mines. Ammonium quaternary nitrogen (N-Q) was detected in the NH4+-illite-bearing samples. This study provides significant evidence for the conversion of organic nitrogen to inorganic nitrogen in coals as a result of thermal metamorphism.

3D modeling of cryogenic cracking by liquid nitrogen in coal under true triaxial stresses

Coalbed methane (CBM) plays an indispensable role in total natural gas production and consumption, and for the bottlenecks encountered in stimulating CBM reservoirs by conventional fracturing methods, studying more environment-friendly and efficient stimulation methods is imperative. Cryogenic fracturing using liquid nitrogen has been trialed for the development of coalbed methane, demonstrating great significance as more and more research corroborated. This study extended our previous coupled thermo-mechanical-damage (TMD) numerical procedure to investigate the cryogenic fracturing or damage process in 3D coal cubes. The cryogenic fractures on concrete cubes along with analytical solutions of temperature and first principle stress distributions for the borehole cooling process were first employed to verify the correctness and feasibility of this method, which incorporates the boundary conditions affected by the Leidenfrost effect at the initial stage. Then sensitivity analyses of cryogenic fracture generation including the maximum fracture cross-sectional area and the fractured volume were carried out. Results show that the coal rock with a high modulus of elasticity and coefficient of thermal expansion is more prone to be damaged in terms of the cross-sectional area and volume than other parameters within the parameter range analyzed. Damage cross-sectional area and damage volume expand with both the increasing coefficient of thermal expansion and the increasing modulus of elasticity, while they shrink with increasing heat capacity and coal density. Cryogenic fractures are relatively less sensitive to the thermal conductivity, density, and heat capacity of coal. This 3D modeling study provides a technical route and a panorama of the cryogenic fracturing process under varied conditions in opaque coal rocks.

Study on the Influence of Coal Structure and Oxidation Performance by Endogenous Bacterium

In order to solve the defects of traditional coal spontaneous combustion prevention technology in a closed goaf, a strain of aerobic endogenous bacteria was isolated from coal and used as a blocking raw material. Based on the metabolic and reproductive characteristics of microorganisms, the experimental study on the inhibition of coal spontaneous combustion by microorganisms was carried out. The colonies were isolated and purified by the dilution concentration plate method and the scribing plate method. The growth morphology of microorganisms was analyzed, and the growth curve was determined. The strains were identified by seamless cloning technology for high-throughput sequencing. The surface morphology of coal was analyzed by SEM, the differences of oxidation characteristic temperature points were analyzed by TG–DTG–DSC images, a programmed heating experiment was used to analyze the concentration of the indicator gas CO, and the changes in microscopic groups before and after microbial action were analyzed by FTIR and XPS spectra. Therefore, the inhibition of coal oxidation by endogenous bacteria was verified from macroscopic and microscopic perspectives. The results show that the coal bacteria isolated from the coal is Lysinibacilus sp. After the culture of Lysinibacilus sp., the surface of the coal demonstrated less detritus, and was relatively smooth. In the early stage of low temperature oxidation of coal spontaneous combustion, the characteristic temperature point of coal oxidation and the reaction between coal and O2 could be delayed by Lysinibacilus sp., and the total heat release was reduced in the combustion process. Not only that, Lysinibacilus sp. could also reduce the CO concentration during coal heating. After the coal was decomposed by Lysinibacilus sp., the C=C thick ring skeleton structure had little effect; however, the aromatic substitution pattern changed. This bacterium had an effect on the C-O bond, reducing the percentage of -CH2- and increasing the percentage of -CH3. It might also use the crystalline water in coal for life activities. The carboxyl carbon in coal changed the most, with a decrease of 12.03%, so it might become the carbon source required for microbial growth. The reproductive metabolism of microorganisms also affected the form of nitrogen, and the percentage of pyridine nitrogen in coal was reduced. The ratio of single-bond carbon to double-bond carbon in raw coal was about 3:2, but after this bacterial action, the ratio of the two was about 1:1. The analytical conclusions of XPS and FTIR spectra were consistent, and the results supported each other.

A Comparative Investigation of the Adsorption Characteristics of CO2, O2 and N2 in Different Ranks of Coal

The adsorption mechanism of carbon dioxide, oxygen and nitrogen in coal is important for preventing and controlling coal spontaneous combustion and for understanding the technology of CO2 storage in goaf. Adsorption amount and adsorption heat are key adsorption parameters that are required to understand the material and energy conversions during adsorption in coal. In this study, we studied the factors that influence the adsorption amounts and adsorption heat values of carbon dioxide, oxygen and nitrogen in coal by testing four different coal samples using conventional coal quality analysis, low-pressure nitrogen and carbon dioxide adsorption, Fourier transform infrared spectroscopy and three gas adsorption experiments at different temperatures. Then, we analyzed the relationships between the structural parameters of the coal samples and the adsorption amounts and the adsorption heat values of carbon dioxide, oxygen and nitrogen. The results show that the adsorption isotherms of carbon dioxide conform to the Langmuir equation, and the adsorption isotherms of oxygen and nitrogen conform to Henry’s law between 0 and 110 kPa. The adsorption amounts of carbon dioxide, oxygen and nitrogen decreased with an increase in temperature, and the change in the rate of the adsorption amount with temperature was determined by the adsorption heat. The results of the pore structure show that the pores of the coal samples are composed of mesopores and micropores; the micropores contribute to the main specific surface area. The micropore and mesopore structures are the main determinants of the adsorption amounts of carbon dioxide, oxygen and nitrogen in coal. The gas adsorption heat is affected by the pore structure and the chemical composition of coal. The adsorption heat of nitrogen correlates positively with the pore structure of the coal. The adsorption heat of oxygen correlates positively with the ash, elemental nitrogen, elemental sulfur and mineral contents of the coal. The adsorption heat of carbon dioxide correlates positively with the elemental sulfur content of the coal.

Causal analysis of nitrogen oxides emissions process in coal-fired power plant with LiNGAM

Coal has been an important energy source worldwide; however, it is the largest source of nitrogen oxide (NOx) emissions because the amount of nitrogen in coal is larger than that of other fossil fuels. Precise control of NOx emissions is required in operations of coal-fired power plants from the viewpoint of air pollution control. Although theoretical analyses of NOx generation from a coal-fired power plant have been conducted, it is difficult to precisely predict NOx generation in an actual plant. NOx generation is affected by various factors, such as furnace design and operating conditions, and there are complicated relationships among them. Thus, it is necessary to identify important operating factors that affect NOx generation in actual coal-fired power plants. A linear non-Gaussian acyclic model (LiNGAM) is an exploratory causal analysis method that identifies a causal ordering of variables and their connection strengths without any prior knowledge of causal relationships among variables. In this study, we analyzed real operation data collected from a coal-fired power plant using LiNGAM to identify factors of NOx generation. The causal relationship between process variables and NOx generation was estimated by means of LiNGAM, and the connectional strengths of the variables on NOx generation were derived. The analysis results agreed with previous reports on NOx generation mechanisms, such as combustion air temperature, steam temperature on a specific side of the furnace, and air flow rate of forced draft fans. In addition, we found the steam flow rate and the furnace pressure as new candidate factors of NOx generation through causal analysis using LiNGAM, which heretofore has not been suggested. Our analysis result should contribute to reducing NOx emissions from coal-fired power plants in the future.

The mechanism for the oxidation of benzoquinoline: A theoretical study

The relationship between the coal nitrogen chemistry and the emission of NOx is a topic attracting wide-ranging interest due to its adverse impact on the environment. In this work, a comprehensive reaction network is proposed based on the DFT calculations to show the possible oxidation mechanisms of benzoquinoline that may result in the generation of NOx and/or other nitrogen-containing species. The kinetics of the reaction network is evaluated by Chemkin using the rate parameters computed from the transition state theory (TST). The first important contribution is the consideration of the role of O2 in the oxidation reaction, with the indication that the addition of O2 to N atom and neighboring CN bond that can activate the C(N) species will be more competitive than the addition of O2 to neighboring CC towards the benzoquinoline oxidation. Furthermore, benzoquinoline will be directly oxidated to NO and indirectly to HCN with the help of H radical. The H radical will promote the rupture of the CN bond, and thus accelerate the generation of HCN. The second important contribution is the obtained transition of the reaction mechanism over the temperature range of 1173–1273 K. The increase of the temperature will shift back the low-temperature formed NO to some important intermediates that can lead to the release of HCN. The mechanisms reported are capable of reproducing some general observations that previously did not have a fundamental explanation, and will be important for the future design of the low-NOx combustion technology.

Molecular structure characterization analysis and molecular model construction of anthracite.

Coal is the largest non-renewable energy as well as an important basic energy and industrial raw material. Thus, correctly understanding the molecular structure characteristics of coal has important theoretical value for realizing carbon neutralization. In this work, we clarified the molecular structure characteristics of anthracite, where the organic matter in anthracite was characterized and analyzed by industrial/elemental analysis, FTIR, XPS, XRD and solid 13C NMR. The ratio of bridge carbon to the perimeter carbon of anthracite was 0.38, and the degree of condensation in the aromatic structure was high. Nitrogen in coal primarily exists in the form of pyridine and pyrrole. Based on the information on functional group composition, the carbon skeleton structure, and surface element composition, a molecular structure model of Yangquan anthracite could be constructed, where the molecular formula was C208H162O12N4. This study may serve as a reference for researchers in this field to consult and refer to the construction ideas and methods of molecular structure models of different coal samples.

Effects of contact metamorphism on δ13C, δ15N, and XPS nitrogen functional forms of inertinite-rich Witbank coals (South Africa): Indications for possible alteration by hydrothermal fluids

In this study, δ13C, δ15N, and nitrogen functional forms were used to evaluate the effects of contact metamorphism on inertinite-rich Main Karoo Basin coals (South Africa). Eighteen samples were collected at 0.25 m intervals from the western and eastern sides of a ∼ 2.6 m thick dolerite dyke emplaced into the No. 2 Seam; an unaltered coal from the same seam was included as a control (Witbank Coalfield). Inertinite (semifusinite and inertodetrinite) dominated the organic composition of the samples. δ13C and δ15N for the unaltered coal were − 21.1‰ VPDB and 1.5‰ Air, respectively. For the intruded coals from the western side, δ13C ranged between −22.4 and −21.4‰ VPDB, and δ15N between 1.2 and 2.6‰ Air. The δ13C for samples from the eastern side ranged between −21.8 and −20.7‰ VPDB, and between 1.8 and 3.0‰ Air for δ15N. Differences in δ15N between the unaltered and the intruded coals were generally more significant than in δ13C, especially for samples from the eastern side. The positive shifts in δ15N may reflect reactions between organic nitrogen in coal and mobile nitrogen transported by hydrothermal fluids. The absence of a relationship between δ15N and distance from the dyke, may reflect secondary, localized contact metamorphism due to hydrothermal fluid migration within the intruded seam. The circulation of a fluid transporting 15N-rich moieties, apparently more active on the eastern side, was supported by the higher ash yields, δ15N, and Ntotal/Corganic ratios. The correlation between Ntotal/Corganic and ash yields suggests deposition of NH4+ − bearing inorganic components preferentially into the eastern side. Similar to the unaltered coal (N-5 = 47.24 at.%), N-pyrrolic was the dominant nitrogen functional form of the intruded coals, reflecting the developmental pathways for the inertinite macerals as opposed to the contact metamorphism. The low proportion of graphitic (quaternary) nitrogen, irrespective of sample distance from the dyke, suggests metamorphic temperatures lower than 900 °C.

Release of nitrogen during thermochemical conversion of Shenhua bituminous coal under Ar, CO2, and air atmospheres

AbstractCoal thermochemical conversion processes unavoidably generate gaseous pollutants, endangering the environment or influencing synthetic processes downstream. In order to display the differences in release behaviours of nitrogen among different coal thermochemical conversion stages, the nitrogen release characteristics of Shenhua bituminous coal under Ar, CO2, and air atmospheres were investigated using X‐ray photoelectron spectrum (XPS) and thermogravimetry‐mass spectrometry (TG‐MS). Results indicate that the reaction atmosphere has an important influence on nitrogen release. The total released mass of nitrogen when using 100 g raw coal in the whole experiment under Ar, CO2, and air atmospheres is 0.54, 0.64, and 0.75 g, respectively. The organic forms of nitrogen in raw coal and coal char are pyridine nitrogen (N‐6), pyrrole nitrogen (N‐5), quaternary nitrogen (N‐Q), and nitrogen oxide (N‐X). While in the coal ash, the sub‐peaks of N‐Q and N‐X disappear entirely, leaving only N‐5 and N‐6 sub‐peaks. The released nitrogen‐containing gas consists of NH3, HCN, NO, and NO2 during experiments in CO2 and air atmospheres. However, only NH3 and HCN are detected during experiments in the Ar atmosphere. The revolution characteristics of NH3 and HCN under Ar and CO2 atmospheres are similar.

Characterization of nitrogen and sulfur migration during pressurized coal pyrolysis and oxy-fuel combustion

In the present work, pressurized coal pyrolysis and oxy-fuel combustion experiments were carried out in a pressurized drop tube furnace to investigate the migration and transformation characteristics of nitrogen and sulfur. The pyrolysis experiments showed that high pyrolysis pressure inhibited the release of nitrogen and sulfur. The content of oxidized nitrogen (N-X), pyrite, sulfide, sulfoxide and sulfate in char decreased, while the content of pyridine nitrogen (N-6), pyrrole nitrogen (N-5), quaternary nitrogen (N-Q), thiophene and sulfone in char increased with the increase of pyrolysis pressure. The elevated pyrolysis temperature was conducive to the decomposition of nitrogen and sulfur-containing functional groups, and it also promoted the conversion of nitrogen and sulfur to functional groups with high stability such as N-Q and thiophene. The release of volatiles and the decomposition of nitrogen and sulfur-containing functional groups in coal were promoted by CO2 gasification. The increase of the total CO2 gasification pressure led to more nitrogen and sulfur remaining in char. During pressurized oxy-fuel combustion in O2/CO2 atmosphere, the emissions of NO, NO2 and SO2 were lower than those in air combustion. The emissions of NO, NO2 and SO2 gradually decreased with the increase of pressure at air and oxy-fuel atmospheres. The increase of temperature increased the emissions of NO and SO2 at different pressures, but the NO2 emission decreased at elevated temperature. In addition, the emissions of NO and NO2 increased, but the emission of SO2 decreased with the increase of oxygen concentration.

The characterization of organic nitrogen and sulfur functional groups in coals after biomethane production.

To study the change characteristics of nitrogen and sulfur functional types in the raw coal and coal residues after anaerobic fermentation, three different rank coals from Baiyinhua mine (BY coal), Qianqiu mine (QQ coal), and Malan mine (ML coal) in China were collected and treated with methanogenic microorganisms, then X-ray photoelectron spectroscopy (XPS) was used to test the nitrogen and sulfur functional types in raw coals and coal residues. The results show that the pyrrolic nitrogen (N-5) and aromatic sulfur are the main nitrogen type and sulfur type in three coals. The N-5 increases by 17.42% in BY coal residue and decreases by 2.37% and 8.51% in QQ and ML coal residues, respectively. The pyridinic nitrogen (N-6) in BY, QQ, and ML coal residues decreases by 2.18%, 5.44%, and 2.75%, respectively. The aromatic sulfur increases by 2.13%, 3.14%, and 4.02% in BY, QQ, and ML coal residues, respectively. The aliphatic sulfur has obvious changes in BY and QQ coal residues with the increment of 9.17% and decrement of 11.64%, respectively. The results reveal that the nitrogen and sulfur types have changed in the coal residues after the biomethane production, and the instable types such as N-5 and aliphatic sulfur have obvious changes in the low-rank BY and QQ coals. The research provides a sight to the changes about nitrogen and sulfur types after biomethane yield and more deep thoughts about the clean and effective utilization of coals.

Structural characterization of high fidelity for bituminous and semi-anthracite: Insights from spectral analysis and modeling

Although molecular structure evolution in response to coalification process has been reported to be prevalent recently, their characterization accuracy for coals of different ranks still needs to be enhanced. In this paper, the occurrence information of the carbon skeleton structure, functional groups, and nitrogen and sulfur heteroatoms in coals of different ranks (Ro, max = 0.99% for XZ-02, 1.39% for YT-09, 1.63% for YT-11, 2.29% for ZC-15) were extracted via ultimate and spectrum analysis. Then four molecular structure models were created using computer-aided molecular design (CAMD). Results show that the oxygen atoms in coal primarily exhibit phenolic hydroxyl groups, ether groups, and carbonyl groups. The nitrogen heteroatoms are present as pyrrole and protonated pyridine, and the sulfur heteroatoms mainly served as thiophene. The content of aliphatic structures gradually decreased as coalification continued. Their length first decreased (Ro, max ≤ 1.9%) and subsequently increased (Ro, max > 1.9%). The content of aromatic structures gradually increased accompanied by the gradually cleaving of oxygen functional groups and alkyl side chain from the aromatic clusters. Hence, the degree of aromatization gradually increased, and condensation reactions dominated in the late stage of coalification. The initial molecular formulas and structural models were determined for the four coals. Also, the bonding modes among the aromatic clusters, aliphatic side chains, and oxygen functional groups within the molecular structure were adjusted based on the comparison between experiment and calculation spectra, finally creating the following molecular representations: C174H128O8N2 (XZ-02), C167H114O5N2S2 (YT-09), C151H96O7N2 (YT-11), and C146H80O4N2 (ZC-15). The fitting carbon spectra of these molecular representations were consistent with the experimental carbon spectra whose error is within the allowable range (relative error < 15%), verifying the applicability of the molecular structure model and the above method. Furthermore, the mechanism of coalification was discussed based on the variations of the side chains and chemical bonds. The above research can provide a theoretical reference for the molecular structural evolution for coals of different ranks and a high fidelity method to create molecular structure representation.

A Review on Self-Preheating Combustion Technology for Reducing NOx Emission in the Process of Carbon-Based Fuel Combustion

Energy and environment are the two major themes of today's social development. Self-preheating combustion technology has opened a new path for the directional transformation of coal nitrogen, achieved the inhibition of NO_x generation in the combustion in-situ reaction, better realized the organic integration of efficient combustion of pulverized coal and low NO_x emission, and showed stronger advantages in the denitration efficiency, environmental compatibility and investment and operation cost. This study first introduces the basic principle of self-preheating combustion technology, including the principles of self-preheating, the principles of preheated fuel combustion and the NO_xformation mechanism. Subsequently, the research progress in reducing NO_x emission by self-preheating combustion technology in 30 kW bench scale text rigs and MW grade pilot-scale text rigs, and the industrial application of self-preheating combustion technology are respectively illustrated. Finally, the corresponding conclusions are given, and the future development direction of self-preheating combustion technology is prospected.

Fate of fuel‑nitrogen during in situ gasification chemical looping combustion of coal

In situ gasification chemical looping combustion (iG-CLC) was a promising way to inherently sequestrate CO2. Due to the nitrogen in coal, the NOx emission was a key issue in iG-CLC. In this study, we aimed to identify the nitrogen conversion and distribution characteristics in two elementary stages of coal conversion (pyrolysis and subsequent char gasification) during the iG-CLC process in a tailor-made two-stage fluidized bed reactor. HCN was the dominant precursor of NOx in iG-CLC, almost all the NOx precursors were rapidly released during the coal pyrolysis stage, and no gaseous nitrogen pollutant was detected within the subsequent CO2-char gasification process. The generated HCN could be completely converted by the Fe-based oxygen carrier (OC) to either NO or N2. The high CO2 concentration and reducing reaction atmosphere in the fuel reactor were found to exert certain inhibitory effects on the formation of NO. Meanwhile, the operating conditions, that is, the O/fuel ratio and temperature, exhibited insignificant effects on the fate of fuel-N. Finally, the fate of nitrogen in volatiles, char, and tar of coal during iG-CLC and the potential homogeneous nitrogen conversion in the iG-CLC of coal were proposed based on the results obtained from both experiments and thermodynamic simulations.

Efecto de la descomposición de gas de amoniaco (NH3) sobre el hinchamiento de óxidos de hierro durante reducción

Con el objeto de estudiar la relación y efecto del gas nitrógeno en los gases reductores utilizados en los ensayos de reducibilidad de óxidos de hierro, en condiciones isotérmicas, se ejecutó un esquema de ensayos utilizando gas amoniaco, tal que la descomposición del gas en el reactor produjera un gas de H2 y N2. Además, se planifico la adición de 6% de NH3 en una corriente de gas 28% H2 y 68% N2 para obtener una composición de gas de 70% N2 y 30% H2. Esto permitiría la reinterpretación de los datos de laboratorio para comparar las curvas d reducibilidad entre ambas condiciones, asumiendo que la posible diferencia entre ambas condiciones a comparar los cambios de volumen de las muestras reducidas. La diferencia a estudiar se basará en la estimación y comparación de la velocidad de formación de hierro metálico en las etapas de reducción de hematita/magnetita/wustita (FeO), así como los efectos del nitrógeno absorbido por el hierro metálico fresco producido, partir de la mezcla de gas reductor, sobre el cambio de volumen de las muestras. Así mismo se comparan empíricamente los cambios catastróficos de volumen causados por el nitrógeno comparando fuentes de este gas en reductores carbonosos sólidos.&#x0D; Palabras clave: reducción gaseosa, hierro de reducción directa (HRD), catálisis, catalizador de hierro, amoniaco, hinchamiento, absorción, nitruración. ensayos isotérmicos, nitrógeno en carbón.&#x0D; Referencias&#x0D; [1]O.G. Dam . The Influence of Nitrogen on the Swelling Mechanism of Iron Oxides During Reduction. Univ. of London. PhD Thesis 1983.&#x0D; [2]J.D Bogde.- Thermoelectric Power Measurements in Wustite. Univ. of Michigan. 1976.&#x0D; [3]O.G. Dam y J. Jeffes. Model for the Assessment of Chemical Composition of reduced iron ores from single measurements. Ironmaking and Steelmaking. 1987. Vol. 14, N`5.&#x0D; [4]M. Yang. Nitriding-Fundamentals, modelling and process optimization. Tesis PhD. Worcester PolytechInstitute. 2012.&#x0D; [5]T. EL Kasabgy y W-K. LU. (1980). The Influence of Calcia and Magnesia in Wustite on the Kinetics of Metallization and Iron Whisker Formation. Metallurgical 1980 American Society for Metals and the Metallurgical Society of AIME Volume 11b, September 1980, pp. 410-414.&#x0D; [6]Srikar Potnuru Studies nn the Physical Properties and Reduction Swelling Behavior of Fired Haematite Iton ore Pellets. MSc Thesis. Department of Metallurgical and Materials Engineering National Institute Of Technology, Rourkela May 2012.&#x0D; [7]R.S Agarwal y S.S. Hembram. To Study the Reduction and Swelling Behavior Iron Ore Pellets. BSc. Department of Metallurgical and Materials Engineering National Institute Of Technology, Rourkela May 2013.&#x0D; [8]C.E. Seaton y J.S. Foster. and Velasco. Structural Changes Occurring during Reduction of Hematite and Magnetite Pellets Containing Coal Char. Transactions ISIJ, Vol. 23, 1983, pp.&#x0D; [10]C. Bozco. et.al. Interaction of Nitrogen with Iron Surfaces. Journal of Catalysis 49. 1977.&#x0D; [11]L.S. Darken y R.W. Gurry, Physical Chemistry of Metals. Mc Graw hIll . 1953.&#x0D; [12]H. A. Weirdt, y Z .Zwell. Trans. AIME. 229. 142. 1969.&#x0D; [13]J.J.S.Schulten. et al. Trans. Soc. Faraday. 53, 1363, 1957.&#x0D; [14]E.G.Barret y C.F. Wood. Bureau of Mines R-I 3229. 1934.

Effect of sodium on three-phase nitrogen transformation during coal pyrolysis: A qualitative and semi-quantitative investigation

Alkali metals have a significant effect on the transformation of three-phase nitrogen during coal pyrolysis, but there is a lack of understanding about this mechanism of action. In this work, the effects of inorganic sodium (NaCl) and organic sodium (CH3COONa) on the mutual transformation of three-phase nitrogen in coal pyrolysis were studied by TGA-MS/FTIR, XPS and Py-GC/MS. Results shown that more nitrogen remained in char, the conversion of heterocyclic nitrogen in coal to tar-N was inhibited with most of CH3COONa and lower addition NaCl, including the transformations of N-5 to pyrrole-N and amine-N, and the transformations of N-6 to pyridine-N and nitrile-N. While higher NaCl addition promotes the transformations of char-N to volatile-N. Sodium decreases the yield of tar, especially amine-N and nitrile-N through promoting the transformation of nitrile-N and pyridine-N in tar to HCN and the transformation of amine-N and pyrrole-N in tar to NH3. Both of promotion of NaCl on HCN release and inhibition on tar-N yield are stronger than CH3COONa. The HCN release of NaCl-added samples is higher 2.69%–4.29% than CH3COONa-added samples, while the content of char-N in NaCl-added samples is lower 2.6%–18.6% than CH3COONa-added samples.

Experimental and kinetic study on the transformation of coal nitrogen in the preheating stage of preheating-combustion coupling process

Preheating-combustion of pulverized coal has been demonstrated as an effective low NOx combustion technology. This method preheats a coal stream to high temperatures before the coal stream is injected into a utility boiler for combustion. Considering the complex mechanisms during the preheating, the effects of the preheating parameters, including temperature, residence time and excess air ratio are studied in a drop-tube furnace in detail. Meanwhile, a kinetics analysis on the transformation of coal-N in gas phase is also performed by means of Chemkin-Pro coupled with mature NOx reduction mechanisms. The experimental results show that the yield of coal-N converted to NO decreases at first and then increases with increasing excess air ratio. The lowest NO yield after preheating is achieved at excess air ratio of 0.1. To reduce NOx formation effectively, the preheating zone should be under high temperature and long residence time. Kinetic modeling indicates that NO was reduced into N2 by both hydrocarbon radical and HCN. Also, the modeling results show that the increasing excess air ratio weakens the effect of hydrocarbon radical reduction, and the mole ratio of NOHCN/NOHCN+CiHj decreases from 1.99 to 1.17 with the increasing excess air ratio from 0.1 to 0.6.