Synthetic Coal Research Articles

Villages Owned Enterprise Provide Solutions to Leader's Addictionability of Energy Crisis

The Energy Crisis will soon confront at the beginning of the 21st Century and now is the transition period from Fossil Energy to New and Renewable Energy. This century has again seen a transportation revolution as at the beginning of the industrial revolution, everywhere humans are competing to manufacture propulsion sources derived from Solar Cells, Hydrogen Water, Wind Power, Tidal Wave Movement, Geothermal Energy and Synthetic Coal from Botanicals, so that a shift in Fossil Energy is slowly disappearing from the earth's surface. This research was conducted at Village-Owned Enterprises and is expected to be able to provide solutions in the Energy Transition, the Government's Commitment, which is supported by the influence of the Energy Crisis Policy in Indonesia. Energy Crisis Independence Indonesia has 3.6 billion barrels with a constant average of 800,000 barrels per day as future energy reserves, while these reserves will most likely no longer be able to be produced to meet needs in the next 12 years. This imbalance requires the performance policy, competence and commitment of government leaders to create the role of the private sector from rural to urban areas in bonds and EBT shares on stock exchanges by villages enterprise with a level of security and assurance as well as green energy with household waste as a raw material for Home-trash to Green-tech New-energy (MHGNe) Manufacturing technology which is the only closest alternative currently on earth.

Modern Rare Earth Imprinted Membranes for the Recovery of Rare Earth Metal Ions from Coal Fly Ash Extracts.

The need to identify secondary sources of REEs and their recovery has led to the search for new methods and materials. In this study, a novel type of ion-imprinted adsorption membranes based on modified chitosan was synthesized. Their application for the recovery of chosen REEs from synthetic coal fly ash extracts was analyzed. The examined membranes were analyzed in terms of adsorption kinetics, isotherms, selectivity, reuse, and their separation abilities. The experimental data obtained were analyzed with two applications, namely, REE 2.0 and REE_isotherm. It was found that the adsorption of Nd3+ and Y3+ ions in the obtained membranes took place according to the chemisorption mechanism and was significantly controlled by film diffusion. The binding sites on the adsorbent surface were uniformly distributed; the examined ions showed the features of regular monolayer adsorption; and the adsorbents showed a strong affinity to the REE ions. The high values of Kd (900-1472.8 mL/g) demonstrate their high efficiency in the recovery of REEs. After five subsequent adsorption-desorption processes, approximately 85% of the value of one cycle was reached. The synthesized membranes showed a high rejection of the matrix components (Na, Mg, Ca, Al, Fe, and Si) in the extracts of the coal fly ashes, and the retention ratio for these Nd and Y ions was 90.11% and 80.95%, respectively.

Production of Biocoal from Wastewater Sludge and Sugarcane Bagasse: A Review

The rising volume of wastewater sludge and sugarcane bagasse is becoming a prominent concern globally. Furthermore, the growing demand for fuel coupled with the depletion of fossil fuel reserves in South Africa demonstrates the need for alternative energy sources. To minimize the reliance on fossil-based energy sources, a renewable resource such as biomass can be optimized as an energy source. Wastewater sludge and bagasse have the energy potential to produce high-calorific-value biocoal; this will contribute to the supply of energy in South Africa. The synthesis of biocoal from wastewater sludge and bagasse through an artificial synthetic coal production process, i.e., hydrothermal carbonization (HTC), is preferred over other thermal conversion techniques as HTC is capable of handling feed having a high (75–90%) moisture content. This article focuses on the production of biocoal from wastewater sludge and sugarcane bagasse as an alternative to sustainable bioenergy supply and as one of the potential solutions for reducing net CO2 greenhouse gas (GHG) emissions from fossil-fuel power plants, and addresses the use of different thermochemical technologies, previous studies on the composition of wastewater sludge and bagasse, and the benefits of hydrothermal carbonization.

Exploring influence of MgO/CaO on crystallization characteristics to understand fluidity of synthetic coal slags

The crystallization has significant influence on fluidity of slag and slag discharge of entrained-flow-bed (EFB) gasifier. The crystallization characteristics and fluidity of five synthetic slags with different MgO/CaO ratios prepared on the basis of the range of oxide contents of Zhundong coal ash were investigated in this study. The results show that with the MgO/CaO ratio increase, the initial crystallization temperature increases, and the main temperature range of crystallization ratio growth moves to higher temperature range gradually which causes Tp25 (Tp25 is the temperature corresponding to the viscosity of 25 Pa·s) to increase. Mg-rich crystals are formed preferentially than Ca-rich crystals when adding the same amount of MgO and CaO during cooling. The effective slagging operating temperature range decrease from 217 °C for the slag with a 0:4 MgO/CaO ratio to 44 °C for the slag with a 4:0 MgO/CaO ratio with the MgO/CaO ratio increase. The slags with 2:2 and 1:3 MgO/CaO ratios show similar effective slagging operating temperature range, Tp25 and the temperature corresponding to the viscosity of 2 Pa·s. However, compared with the slag with a 1:3 MgO/CaO ratio, the crystallization ratio and rate of slag with a 2:2 MgO/CaO ratio are lower within lower temperature range (1300–1200 °C), causing its lower critical viscosity temperature and wider actual operating temperature range. Of the five slags, the widest effective slagging operating temperature range and the lowest Tp25 of the slag with a 0:4 MgO/CaO ratio due to its low crystallization ratio, and wider actual operating temperature range of the slag with a 2:2 MgO/CaO ratio make the two slags suitable for slag discharge of EFB gasifier.

Production of biocoal from wastewater sludge and sugarcane bagasse using hydrothermal carbonization

AbstractThe growing demand for fuel in South Africa coupled with the depletion of fossil fuel reserves demonstrates the need for alternative energy sources. A renewable resource such as biomass can be optimized as an energy source. Wastewater sludge and bagasse have the energy potential to produce high calorific value biocoal; this will contribute to the supply of energy in South Africa. The synthesis of biocoal from wastewater sludge and bagasse through an artificial synthetic coal production process, i.e. hydrothermal carbonization, is preferred over other thermal conversion techniques as hydrothermal carbonization is capable of handling feed having a high (75–90%) moisture content. In this study, wastewater sludge and sugarcane bagasse were subjected to hydrothermal carbonization, and the effect of temperature was explored at 180, 210, 240 and 260°C. Variation of the ratio of dry sludge to bagasse of 100:0, 80:20, 60:40, 40:60, 20:80 and 0:100 and the composition of solid to liquid (solid loading wt%) of 1:10, 2:10, 3:10 and 4:10 (SB:H2O) corresponding to 9.09, 16.67, 23.08 and 28.57 wt% loading was investigated. The results obtained in this study reveal that solid loading, temperature, biomass type and ratio variation had a substantial impact on the yield and calorific value of the biocoal produced. The highest biocoal yield of 23.36 wt% was achieved at 210°C and derived from sludge/bagasse with a sludge content of 20%. Across all of the runs, the highest calorific value of 20.21 MJ kg−1 was achieved at 260°C when pure bagasse was employed (0% sludge content). © 2022 The Authors. Biofuels, Bioproducts and Biorefining published by Society of Industrial Chemistry and John Wiley & Sons Ltd.

Influence mechanism of Na2O on the network structure depolymerization of ZD coal ash silicate under high temperature

Na2O is the basic alkali metal oxide in Zhundong (ZD) coal, the content of Na2O directly affects the ash fusion temperatures (AFTs) of coal ash. Fourier transform infrared (FTIR) spectroscopy and molecular dynamics (MD) simulation were used to study the structural characteristics of synthetic coal ash under Na2O concentration of 1–13 mol%. Both FTIR experiments and MD simulation show that Na+ attacks the tri-coordinate oxygen (Ot) and the bridge oxygen (Ob) formed by [SiO4]4− and [AlO4]5− tetrahedron structure, generates more non-bridge oxygen (Onb), the shelf-like network structure(Q4) in fused coal ash is depolymerized to form layered silicate structure (Q3), chain or cyclic silicate structure (Q2, Q1). O(Al, Al, Si) and O(Al, Al, Al) in Ot decreased their trend by 3% each, Si–O–Si was reduced from 12% to 7%. Al–O–Si was reduced from 36% to 29%. The intricate structures are gradually depolymerized into plain structures, which leads to the decrease of AFTs.

High temperature erosion of T22 steel coated by Cr–Ni electroplating, HVOF sprayed stellite–6 and WC–12Co

In present study, erosion behavior of ASTM–A213–T22 steel (T22 steel) coated by different coating processes was evaluated at high temperature. Cr–Ni electroplating and high–velocity oxy–fuel (HVOF) spraying using Stellite–6 and WC–12Co powders were chose as coating processes. Average coating thicknesses of the Cr–Ni electroplated coating and the HVOF sprayed Stellite–6 and WC–12Co coatings were 40 µm, 226 µm and 200 µm respectively. Oxide scale formation on an uncoated T22 steel specimen and coated specimens was done by covered the specimens with a synthetic coal ash and then annealed under a synthetic flue gas at temperatures of 700 °C with annealing times of 24 h 72 h and 123 h. After oxide scale formation process, the specimens were eroded in erosion tester at temperature of 700 °C using SiC erodent particle with average particle size of 60 µm at impingement velocity of 40 m s−1 and impingement angles of 30° and 90°. The experimental results showed that erosion rate of the specimens dramatically increased with increasing of exposure time at 700 °C. Erodent impingement angle was unaffected to erosion rate of the uncoated T22 steel, the Cr–Ni electroplated and the HVOF sprayed Stellite–6 and WC–12Co coatings. Microcracks, debonding of coating as well as deep cavities were observed on eroded surface of the uncoated T22 steel, the Cr–Ni electroplated and the HVOF sprayed Stellite–6 and WC–12Co coatings. Erosion resistance of the HVOF sprayed Stellite–6 coating was highest compared with that of the Cr–Ni electroplated and the HVOF sprayed WC–12Co coating. The superior erosion resistance of the HVOF sprayed Stellite–6 coating was due to high hardness, more thickness and low porosity of the deposited coating.

Effect of iron valence distribution on ash fusion behavior under Ar atmosphere by a metallic iron addition in the synthetic coal ash

The impurities in coal can cause serious ash-related problems at high temperature, threatening the stable operation of the coal gasifier. The effect of iron on the ash fusion properties is still unclear due to its multiple valences (Fe3+, Fe2+ and Fe0). In this study, we investigated the effect of iron valence on the fusion behavior of synthetic coal ash by the metallic iron addition. The ash fusibility was characterized by the ash fusion temperature (AFT) analyzer and thermomechanical analysis (TMA), and the corresponding ash fusion mechanism was revealed from the crystallized phase evolution, heat change, and the thermodynamic modelling. Results demonstrated that the initial deformation temperature of coal ash fails to reflect the initial ash shrinkage/melting event. The addition of metallic iron leads to the formation of Fe2+-containing minerals which facilitates the low-temperature eutectic reaction, decreasing the initial melting temperature of ash. However, the initial shrinkage temperature depends on the liquid content and is influenced by the CaO content. For the low-calcium ash, the metallic iron addition results in the formation of Fe2+ which advantages the eutectic reaction of Si-Fe-O system. The initial shrinkage temperature of low-calcium ash decreases for the massive formation of liquid. In contrast, the abundant calcium of high-calcium ash prevents the transition of Fe3+ to Fe2+, and combined with Fe2+ to form hedenbergite, retarding the eutectic reaction of both Si-Al-Ca-O system and Si-Fe-O system. Therefore, the initial shrinkage temperature of high-calcium ash increases with the metallic iron addition. Finally, the initial melting temperature can be correlated with the initial liquid temperature which is obtained by thermodynamic modelling, potentially acting as the guide to predict the initial ash melting event.

석탄가스 모델 가스터빈의 연소실 형상 변화에 따른 연소불안정 특성

Combustion instability of a synthetic coal gas flame in a partially-premixed gas turbine combustor has been numerically studied by utilizing a lumped network code, OSCILOS. Both H₂ percentage of the coal gas consisting H₂ and CH₄ and the length of the combustor were varied in this study. A companion experimental data were borrowed and used for validating the numerical results. The predicted results reasonably agree well with the afore-mentioned experimental ones. It was found that the mode of the instability shifted to the higher mode when H₂ content of the gas became larger, and that the dominant frequency of the instability was reduced as the combustor was getting longer.

Concentrating rare earth elements to phosphate in molten coal ash by a temperature gradient approach

Synthetic coal ash bearing 560 ppm europium oxide, blended with aluminum phosphate, was heat treated above its melting temperature and crystal evolutions with respect to europium concentration under controlled cooling were studied. The sample in a boat crucible was subjected to a temperature gradient of 100 °C across it to cause zone refining effects on crystallization behaviors in the melt (slag). Post analysis found six mineral phases formed from the melt while europium was only present in calcium phosphate, implying the majority of europium was segregated to the calcium phosphate. Europium concentrations in the calcium phosphate phase tended to be higher at zones with higher temperatures: as high as 7200 ppm, a 13-fold increase from the initial concentration.

Separation of rare earth elements from mixed-metal feedstocks by micelle enhanced ultrafiltration with sodium dodecyl sulfate

ABSTRACT Micelle enhanced ultrafiltration (MEUF) is a surfactant-based membrane separation process that may be used to separate target ions from mixed metal aqueous solutions, such as leachates of coal ash and other geological wastewaters. The ability of MEUF to separate rare earth elements (REEs) was evaluated using sodium dodecyl sulfate (SDS) as the sorbent in surfactant micelle phase, which was subsequently separated using ultrafiltration, acidification, and ferricyanide precipitation. Separation experiments were performed with a synthetic coal ash leachate feedstock as an example mixed-metal feedstock. Experiments tested the influence of surfactant concentration, pH, and co-existing competitive ions on REE recoveries, and also tested methods for SDS recovery and reuse. Membrane rejection efficiencies of REEs were 97% and 71% respectively for synthetic and real leachate under optimized operating conditions. A two-step process of precipitation with CaCl2 and Na2CO3 following membrane separation was the best for recovering SDS with a yield of 99.7%.

Understanding the influence of iron on fluidity and crystallization characteristics of synthetic coal slags

Iron was an important component in coal ash slag and had a significant influence on the gasification reactivity and slag discharge in industrial gasification process. In this study, five synthetic slags with different iron contents (Fe2O3 ratios: 0%, 5%, 10%, 15%, 20%) were prepared to investigate the effect of iron on fluidity and crystallization characteristics of synthetic slag. The results showed that the fusion temperatures of synthetic slags decreased with the increase of iron content, which was mainly resulted from the neutralization between iron and high-melting-temperature lime and the formation of lower-melting-temperature srebrodolskite during fusion process of synthetic slag. At high temperatures, slag viscosity decreased with the increase of iron content. But as the temperature further decreased, the viscosity changes of coal ash diverged without following the simple monotonous trend. Viscosity transformation after crystallization was affected by multi-factors such as interfacial crystallization, temperature and atmosphere. The sudden viscosity changes of synthetic slags showed close relationship with the formation of gehlenite and anorthite, which was mainly owing to the position replacement and polymerization degree decrease of Al3+, Si2+ and Ca2+ in melt network by iron as an amphoteric substance.

Experimental investigation of the influence of pulsating hydraulic fracturing on pre-existing fractures propagation in coal

This study aims to investigate the propagation behavior of pre-existing fractures in a coalbed methane (CBM) reservoir during pulsating hydraulic fracturing (PHF). An innovative test system capable of true triaxial loading and multi-mode PHF was developed to conduct PHF on pre-existing fracture specimens of synthetic coal. The fluid pressure, strain around the pre-existing fracture, and propagation morphology of the pre-existing fractures were measured to analyze the influences of the coupling action between the pulsating parameters and the confining stress on pre-existing fracture propagation and fatigue damage of the coal. The results show that the evolution of fluid pressure under PHF can be divided into four periods: slow growth, rapid rise, steady drop, and decline. In the steady drop period, the intermittent fluid injection causes alternating pressure pulsation in the pre-existing fractures and cyclical strain fluctuation around the pre-existing fractures, leading to an abrupt propagation. With the increase in confining stress, the propagation morphology changes from single to cross direction exhibiting a “T” shape. Under flow-control injection mode, the frequency and amplitude of the pulsating pressure significantly influence the fatigue damage of coal, stimulating fracture propagation. With the increase in pulsating frequency, the pulsating amplitude decreases gradually, and the pre-existing fracture propagation rate and the pressure drop rate both increase first and then decrease; thus, an optimal pulsating frequency can be chosen to accelerate fracture propagation. Furthermore, the pulsating pressure has weakening effects on the coal around the pre-existing fractures, thus enriching the seepage channels around the primary fracture. Based on this work, a PHF method integrated with multi-mode injection is proposed to achieve the control of hydraulic fractures and perform efficient fracturing of CBM reservoirs.

Analysis of sorbing method of water treatment from oil

The efficiency of simple and accessible methods of cleaning of oil-contaminated water is investigated. The maximum absorption capacity of cotton as a natural material is identified, that quickly absorbs oil components and does not require the use of additional resources to combat water contamination. It is found that natural charcoal absorbent is inefficient in comparison with other methods of water purification from oil and requires a long time and additional pollution catchers, which is economically unprofitable. Synthetic polymer foam and white coal absorb oil in a short time, but in the latter case, nevertheless, small spots remain on the surface of the water. According to the efficiency of oil absorption by natural and synthetic materials, we can distinguish the following series of investigated materials: black coal → foam → white coal → cotton.

A quantitative evaluation of uranium mobility and potential environment risk in coal ash with SiO2-Al2O3-Fe2O3-CaO system

Uranium-enriched coal ash (CA) receives a significant attention as a supplementary nuclear resource also due to its potential environmental risk. Combining with CA, the changing trend of uranium occurrence in synthetic coal ash (SCA) was described at CaO-Al2O3-Fe2O3 ternary phase diagrams with a fixed SiO2 (wt. %, 30%, 50% and 70%) and Na2O (2%) content. This study reveals that the mode of uranium occurrence proposes a three-stage changing process during coal combustion including uranium oxidation, combination and encapsulation. Furthermore, a high frequency of encapsulated uranium resulted from the complicated interactions among major components with a medium SiO2 content, whereas the degree was higher at a higher SiO2, resulting in the decrease of uranium mobility. Uranium was encapsulated by Si-Al matrix and Fe-Si depletion if provided the high Al2O3 and Fe2O3 but low CaO contents. However, with the development of calcium looping and biomass co-firing process, the change of element mobility should be considered in industry owing to the extra-added alkaline metals. As the activation of Ca2+ induces a significant susceptibility of acid attack, cautions must be paid in CA with a higher Ca/Si ratio to avoid its utilization as constructive materials for the potential environmental risk.

Effects of minerals containing sodium, calcium, and iron on oxy-fuel combustion reactivity and kinetics of Zhundong coal via synthetic coal

The greatly high contents of alkali and alkali earth metals in Zhundong coal have a negative impact on the combustion and utilization of the coal, which results in serious fouling and slagging problems. In the present study, the influences of different minerals on the oxy-fuel combustion of Zhundong coal via synthetic coal were investigated by thermal analysis, and two isoconversional methods were applied to conduct the kinetic analysis. Additive minerals with single metallic elements including sodium (NaCl, NaCO3, NaAlSi3O8), calcium (CaCl2, CaCO3, CaSO4), and iron (Fe2O3, Fe3O4 and FeS2) rather than complex mixtures were added into synthetic coal to avoid the combined catalysis among various minerals. The experimental results show that the thermogravimetric and derivative thermogravimetric curves of synthetic coals under oxy-fuel conditions are similar to those of Zhundong coals. Most of selected additive minerals affect the ignition temperature slightly (less than 10 °C) but tend to lower the burnout temperature (5–25 °C), which narrows the main combustion temperature zone. The addition of CaCl2 raises the burnout temperature from 645.4 to 689.5 °C and drives down the average combustion rate from 4.44 to 3.83% min−1, while other minerals exhibit negative correlation with the maximum and average combustion rates in most cases. The reaction kinetics analysis indicates that the apparent activation energy of coal combustion depends heavily on the category of additive minerals, which varies from 21.31 to 39.05 kJ mol−1 (average values calculated by KAS method). Besides, the apparent activation energy declines with an increase in the conversion rate of samples.

Improved prediction of critical-viscosity temperature by fusion behavior of coal ash

Coal ash slag viscosity is critical for slag tapping in entrained-flow coal gasifiers, so the accurate prediction of slag viscosity and the critical temperature of viscosity (Tcv) will help the coal selection, flux addition and gasifier operation. Many empirical correlation models based on ash fusion temperature have been proposed to calculate Tcv. In order to correlate the viscosity with the fusion behavior and then improve the prediction of Tcv, we measured the viscosity of several synthetic coal ash slags with a high-temperature rotary viscometer and studied their ash fusion behavior through thermomechanical analysis. X-ray diffraction was used to compare the mineral transformation before and after Tcv combined with the FactSage calculation. The viscosity measurement shows that the viscosity above Tcv of glassy slags is higher than that of the crystalline type. The mineral transformation from FactSage also demonstrates that the precipitation rate of solid phase is lower for glassy slags. The fusion behavior for the glassy and the crystalline slag is also distinctly different.The fusion range from deformation temperature (DT) to flow temperature (FT) of the ash for the glassy slag was larger than that of the crystalline one, and the shrinkage above FT in TMA trace slopes gently. The correlation between the fusion behavior and viscosity-temperature behavior for the glassy slag is reasonable, because the large temperature range from DT to FT and the low shrinking rate of the stage III indicate the high viscosity of the liquid phase formed and the slow melting of the remained solid phase respectively, which are also the correlative condition prefer for the formation of glass as mentioned above. For the crystalline slag, the small fusion range from DT to FT means the rapid melting of the solid phase and the high flowability of the liquid phase which are indicative for the rapid precipitation during cooling. The slow rate of the stage III indicates the slow melting of the remained solid which can be the crystal nucleus. When the viscosity of the liquid phase is low, it also benefit for the formation of crystalline slags. The characteristic in fusion behavior for different type of slag also suggested that the predicting Tcv by applying one method to all the crystalline slags and non-crystalline slags is not appropriate.

Effect of chemical composition on the fusion behaviour of synthetic high-iron coal ash

High-iron coal is widely distributed throughout China and could be used as the feedstock for slagging gasifiers. To enable cleaner, efficient, large-scale use of high-iron coal by the slagging gasifier, a solid understanding of coal ash fusion behaviour is required. In this study, we investigated the fusion behaviour of synthetic high-iron coal ash (SiO2-Al2O3-Fe2O3-CaO) using an ash fusion temperature (AFT) analyser, X-ray diffractometer (XRD), differential scanning calorimeter (DSC) and thermodynamic modelling. We found that AFTs decreased with increasing α values (CaO/(SiO2 + Al2O3), mass ratio) due to the formation of low-melting-point minerals. AFTs also decreased with increasing S/A (SiO2/Al2O3, mass ratio), attributed to massive generation of the amorphous phase. The ash fusion process is described with three stages, namely, the mineral transformation, formation of the initial liquid phase, and melting of the residual solid phase. In the first stage, the mineral species was considered as the key parameter, and the increase in α and S/A favoured the formation of mineral with a low melting point. S/A also significantly influenced the second stage, with greater S/A ratios correlating with lower temperature and higher content of the initial liquid phase. In contrast, the third stage was accelerated by intense mass transfer, as the viscosity of the liquid phase dropped dramatically with increasing α value. The fusion heat corresponding to the melting of minerals at high temperature showed a negatively linear correlation with the flow temperature of synthetic coal ash, which may provide an alternative method of predicting the flow temperature of real coal ash.

Depolymerization mechanism of CaO on network structure of synthetic coal slags

In entrained flow gasifier, slag properties such as melting and viscosity of molten slag are critical for continuous operation. Molten coal slag belongs to silicate-containing melts and slag behaviors are intrinsically determined by the microstructure transformation. Calcium is believed as an effective ingredient to decrease viscosity as well as reduce the polymerization degree. The structure of coal slags with different calcium ranging from 10% to 25% is investigated by solid-state nuclear magnetic resonance (SS-NMR) and molecular dynamics (MD). 29Si, 27Al spectra were obtained through quenching slags under 1873 K and the distributions of Qn species are analyzed. For simulation part, the radial distribution function, the proportion of bridge oxygen (Ob) and non-bridge oxygen (Onb) as well as the distributions of Qn species were calculated. Both NMR experiment and MD simulation show that increase of CaO can lead to a reduced degree of polymerization. The Ca ions enter into the network formed by Si and Al tetrahedral and bond with oxygen ions, which weakens the network stability. Consequently, the proportion of non-bridge oxygen increases and complex network unit-Q4 breaks into smaller units such as Q3, Q2, Q1, reducing the polymeric network. The depolymerization effect of CaO can explain the change of slag properties such as viscosity or melting temperature.

Experimental Study on NOx Reduction in Oxy-fuel Combustion Using Synthetic Coals with Pyridinic or Pyrrolic Nitrogen

Oxy-fuel combustion technology can capture carbon dioxide (CO2) in the large-scale and greatly lower nitrogen oxides (NOx) emission in coal-fired power plants. However, the influence of inherent minerals on NOx reduction still remains unclear and the impact of oxy-fuel combustion on the transformation of different nitrogen functional groups has yet to be fully understood. The present work aims to obtain a further understanding of the NOx reduction during oxy-fuel combustion using synthetic coals with pyrrolic or pyridinic nitrogen. Compared to pyridinic nitrogen, more of the pyrrolic nitrogen in synthetic coal was converted to NOx. The conversion ratio of nitric oxide (NO) first increased significantly with the rising oxygen content and then trended to an asymptotically constant as the oxygen (O2) content varied between 10–50%. The nitrogen dioxide (NO2) formation was roughly proportional to the oxygen content. The NO2 conversion was increased with particle size but the case of NO showed a non-monotonic variation. The catalytic effects of sodium carbonate (Na2CO3), calcium carbonate (CaCO3), and ferric oxide (Fe2O3) on the transformation of pyridinic nitrogen to NO were independent of the combustion atmosphere, while the alteration from air to the oxy-fuel combustion led to a change of mineral catalytic effect on the oxidation of pyrrolic nitrogen within the coal matrix.