Clean Coal Combustion Research Articles

Thermal reactivity and gas–solid product evolution during coal catalytic combustion: An experimental study

To achieve efficient and clean coal combustion, catalytic combustion technology has received widespread attention. This paper systematically studied the influence of calcium-based compounds on the thermal reactivity and gas–solid two-phase product evolution behavior of different coal using TG-MS and FTIR analysis, combining kinetics and thermodynamics methods, the catalytic coal mechanism was discussed. Results demonstrated that both catalysts improved the combustion reactivity, the burnout temperatures of lignite, bituminous coal and anthracite were reduced by 30.75 °C, 53 °C and 25.5 °C respectively with CaO, as well as decreased by 24.75 °C, 55.5 °C and 29 °C respectively with CaCl2. Meanwhile, it was worth noting that the activation energy of three coals was also reduced. CaCl2 was more likely to bind with the C = O functional group on the surface of coal, forming CO-Ca2+ complexes, resulting in a decrease in the content of C = O and C-O. While CaO tended to absorb volatile matter, causing local overheating and promoting the breakage of side chains and bridge bonds. Besides, the calcium-based compounds advanced the gas evolution peak of combustion and the emissions of CO2, NO2 and SO2 were effectively controlled. These results aimed at providing a new reference direction for further industrial development of clean coal combustion technology.

Effects of activated fuel and staged secondary air distributions on purification, combustion and NOx emission characteristics of pulverized coal with purification-combustion technology

Under the strategic objectives of carbon peaking and carbon neutrality, clean and efficient coal combustion was important in China. As a novel combustion technology, purification-combustion technology had good research prospects, and high-temperature reduction unit (HTRU) played a crucial role in fuel activation, subsequent combustion and NOx emissions based on the design of this technology. Despite previous research had proved the pivotal role of fuel and combustion air distributions in combustor in influencing the entire thermochemical process, there was the lack of research on their effects in HTRU employing purification-combustion technology. To realize deep NOx emission reduction, this study focused on influences of activated fuel and staged secondary air distributions in HTRU on purification, combustion and NOx emission characteristics in a 30 kW purification-combustion test rig. With the exception of carbon microcrystalline structure, the majority of reductive char properties exhibited superior performance when activated fuel was introduced tangentially, as opposed to axially. Nevertheless, the relationship of carbon microcrystalline structure was regulated by staged secondary air ratio (c12). Properly increasing c12 improved reductive char properties. Additionally, axial introduction of activated fuel more consistently yielded ultra-low levels of NOx emissions; however, this often occurred at the expense of combustion efficiency (η). Properly increasing c12 reduced NOx emissions while increasing η; nevertheless, the benefits derived from c12 were limited. By adjusting introduction direction and c12 (axial, 0.33), minimum NOx emissions decreased to 39.10 mg/m3 (@6 % O2) while maintaining high η of 99.39 %.

Investigation on the chemical structure evolution and action mechanism of coal during catalytic combustion

Catalytic combustion is one of the most promising technologies to realize efficient and clean coal combustion, but its catalytic mechanism is unknown until now. This study selected three types coal to explore the influence of catalysts on the chemical structure, surface morphology, and action mechanism during combustion. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were characterized the surface chemical structure of combustion products. The results showed that the aliphatic hydrogen decreased and then increased, the content of –CO and aromaticity(I) increased, and the aromatic condensation (DOC) and CC content decreased by catalysts. Both FTIR and XPS results demonstrated that the catalysts were easy to promote the dehydrogenation condensation reaction between coal molecules, disrupting the stability of coal aromatic structure, thereby generating many free radicals and improving coal combustion. BET and scanning electron microscopy (SEM) were used to observe the effect of catalysts on the pore structure and surface morphology of combustion products. The results showed that the pore structure of product with catalysts continuously formed from micropores to medium pores and even large pores, which accelerated the oxygen transport and chemical reaction on coal surface. Finally, the mechanism of catalytic coal combustion was summarized.

Gas Particle Partitioning of PAHs Emissions from Typical Solid Fuel Combustions as Well as Their Health Risk Assessment in Rural Guanzhong Plain, China.

Air pollutants from the incomplete combustion of rural solid fuels are seriously harmful to both air quality and human health. To quantify the health effects of different fuel-stove combinations, gas and particle partitioning of twenty-nine species of polycyclic aromatic hydrocarbons (PAHs) emitted from seven fuel-stove combinations were examined in this study, and the benzo (a) pyrene toxicity equivalent (BaPeq) and cancer risks were estimated accordingly. The results showed that the gas phase PAHs (accounting for 68-78% of the total PAHs) had higher emission factors (EFs) than particulate ones. For all combustion combinations, pPAHs accounted for the highest proportion (84.5% to 99.3%) in both the gas and particulate phases, followed by aPAHs (0.63-14.7%), while the proportions of nPAHs and oPAHs were much lower (2-4 orders of magnitude) than pPAHs. For BaPeq, particulate phase PAHs dominated the BaPeq rather than gas ones, which may be due to the greater abundance of 5-ring particle PAHs. Gas and particle pPAHs were both predominant in the BaPeq, with proportions of 95.2-98.6% for all combustion combinations. Cancer risk results showed a descending order of bituminous coal combustion (0.003-0.05), biomass burning (0.002-0.01), and clean briquette coal combustion (10-5-0.001), indicating that local residents caused a severe health threat by solid fuel combustion (the threshold: 10-4). The results also highlighted that clean briquette coal could reduce cancer risks by 1-2 orders of magnitude compared to bulk coal and biomass. For oPAH, BcdPQ (6H-benzo(c,d)pyrene-6-one) had the highest cancer risk, ranging from 4.83 × 10-5 to 2.45 × 10-4, which were even higher than the total of aPAHs and nPAHs. The dramatically high toxicity and cancer risk of PAHs from solid fuel combustion strengthened the necessity and urgency of clean heating innovation in Guanzhong Plain and in similar places.

Modelling of multiphase reactive flows in a full-loop coal-direct chemical looping combustor

The coal-direct chemical looping (CDCL) process is a promising clean coal combustion technology, yet the internal multiphase reactive flows in the full-loop system are not clear. In this paper, for the first time, a multi-fluid CFD model of gas–solid-powder reactive flow is developed to describe the gas-oxygen carrier-coal reactive flow in a full-loop CDCL unit, based on Eulerian-Eulerian-Lagrangian framework. The model is validated by comparing with experimental data in terms of flow and reaction behaviours. The model predicts the unique gas-oxygen carrier-coal flow in the full-loop moving-bed CDCL unit, including multiple fluidisations, mixing and separation between the oxygen carrier and coal. The mean residence time of coal particles is around 13 s ∼ 20 s through statistics of discrete particles at the reducer outlet. The high temperature in the CDCL system is observed in the AR riser, cyclone and the top section of the fuel reactor (FR); whereas the low temperature is observed at the bottom of the FR and the l-valve, as a collected result of endothermic and exothermic reactions. A less than 5 mol%, leaks of O2 from the combustor to the reducer can be captured, which is caused by the unbalanced pressure distribution. Overall, over 90 vol% CO2 concentration and 100 % coal carbon conversion are achieved at the FR outlet, which indicates a high CO2 separation efficiency and coal carbon conversion of this CDCL system. This work provides a useful tool for designing and optimising CLC processes.

A Review on the Application of Circulating Fluidized Bed Fly Ash in Building Materials

Circulating fluidized bed (CFB)-based coal burning technology is a type of clean coal combustion technology. Owing to its characteristics of low temperature combustion and desulfurization in furnace, the CFB fly ash is quite different from ordinary fly ash. Based on the comprehensive understanding of physical and chemical characteristics of CFB fly ash, this review summarizes the research progress of the application of CFB fly ash in Portland cement, magnesium oxysulfate (MOS) cement, solid-waste–based cementitious material (SWCM), concrete, geopolymer, artificial aggregate, and other building materials. The study shows that CFB fly ash can improve the early physical and mechanical properties and reduce the drying shrinkage properties for cementitious materials. Its unique chemical composition endows it with good application performance in the MOS cement, geopolymer, and SWCM. However, unfavorable characteristics of CFB fly ash, such as loose and porous structure, self-hardening behavior, and expansibility greatly hinder its practical applications in building materials. Therefore, some measures, such as addition of rational water-reducing agent, ultrafine grinding, mixing of ordinary fly ash, controlling the dosage of CFB fly ash, and water-cement ratio, must be taken to improve the negative influence of CFB fly ash on the building materials, in order to expand its application range. This article summarizes the application and research status of CFB fly ash in building materials, aiming at further promoting the research studies on CFB fly ash resource utilization in building materials and improving the efficiency of CFB fly ash resource utilization.

An investigation of pore structure of blended coal coke produced by pyrolysis of three kinds of coal

ABSTRACT Blended coal combustion technology is being adopted by more and more power plants as a clean coal combustion technology, while the combustion of coal coke accounts for more than 85% of the total combustion process of pulverized coal. In order to investigate the effects of different factors on the pore structure and fractal properties of the blended coal coke, a low-temperature nitrogen adsorption method and scanning electron microscopy are used to study the coal coke consisting of three types of coal after pyrolysis. The adsorption isotherm analysis indicates that the pore structure in blended coal coke consisted mainly of semi-open pores with semi-cates. Petroleum coke can severely inhibit microporosity when the content of petroleum coke in the blended coal sample exceeds 10%. The microporosity distribution of blended coal coke with different blending ratios is more concentrated than that of mesopores. In addition, it is found that the trend of D1 is consistent with the trend of the ratio of the microporous specific surface area to the total specific surface area in the blended coal coke. Bituminous coal will make the blended coal coke have a complex structure and petroleum coke will make it have a smooth surface.

Experimental study on graded capture performance of fine particles with electrostatic-fabric integrated precipitator

As the national environmental protection emission standards become increasingly stringent, achieving ultralow emission for thermal power plants has become an urgent requirement. In this study, a 4000 m3/h electrostatic–fabric integrated precipitator was installed to optimize the technical parameters of the process, including the inlet air volume, cathode type, inlet dust concentration, and voltage. Some significant conclusions were reached. The charging effect of a needle wire cathode was slightly better than that of a barbed wire cathode under identical working conditions. As the voltage increased, the graded dust removal efficiency of the electric zone of the integrated precipitator increased remarkably, but the total dust removal efficiency did not change much. Furthermore, the inlet air volume has a great impact on the precipitator outlet concentration, but inlet dust concentration had a relatively smaller effect. After optimization, the total dust removal efficiency was greater than 99.9%. Thus, the proposed optimization strategy can serve as a useful reference for the application of clean coal combustion technology.

The energy demand and environmental impacts of oxy-fuel combustion vs. post-combustion capture in China

Oxy-fuel combustion is one of the clean coal combustion technologies for CO2 capture. However, post-combustion capture is studied as a challenged technology against oxy-fuel combustion. This paper presented the life cycle assessment (LCA) of these two CO2 capture technologies used in the 300 MW coal fired power plant. The purpose was to identify and quantify the energy demand and the environmental impacts of oxy-fuel combustion throughout its whole life cycle and compared the results with post-combustion capture by an amine (MEA) absorbent. The results showed an increase in cumulative energy demand in oxy-fuel combustion compared with post-combustion capture. Total life cycle energy consumption of oxy-fuel combustion system was more 0.065 MJ than post-combustion capture system. However, oxy-fuel combustion can reduce 0.00047 mPET2000 of global warming, 0.04084 mPET2000 of acidification, 0.04486 mPET2000 of eutrophication, 0.001 mPET2000 of photochemical ozone formation and 0.35082 mPET2000 of slag and ashes compared with post-combustion capture. The total environmental impact loading (EIL) of oxy-fuel combustion to produce 1 kWh of electric energy was 9.06382 mPET2000, which was less than that of post-combustion capture (9.50181 mPET2000), indicating that the oxy-fuel combustion can play a relatively important role in reducing environmental impacts.

Effect of iron on ZrO2-based catalysts for direct synthesis of isobutanol from syngas

Direct conversion of syngas (H2/CO) to isobutanol is a promising route for clean coal combustion. However, there are still many challenges in the catalyst system of isobutanol synthesis, such as low CO conversion and alcohol yield. In this paper, we introduce Fe component with strong chain increasing ability into CuZrO2-based catalyst to modify it, which significantly improved the CO conversion and total alcohol space–time yield (STY). The results of the characterization showed that the introduction of Fe increased the specific surface area of the catalyst, promoted the dispersion of components, and enhanced the interaction between Cu and ZrO2. The KFe0.013CuZrO2 catalyst surface possessed the most amount of weakly adsorbed CO and basic sites, which were conductive for C2 intermediate formation and aldol-condensation reaction respectively. Thus, it exhibited a CO conversion of 48.6%, a selectivity of 21.8(wt)% and a space time yield (STY) of 202 g·Lcat−1·h−1 total alcohols.

Emission factors, characteristics, and gas-particle partitioning of polycyclic aromatic hydrocarbons in PM2.5 emitted for the typical solid fuel combustions in rural Guanzhong Plain, China

Solid fuel is a the most dominant energy source for household usages in developing countries. In this study, emission characteristics on organic carbon (OC), elemental carbon (EC) and fifty-two polycyclic aromatic hydrocarbons (PAHs) in gaseous and particulate phases from seven fuel-stove combinations were studied in a typical rural village in northwest China. For the PAHs, the highest gaseous and particulate phase emission factors (EFs) were both observed for bituminous coal with one-stage stoves, ranging from 459 ± 154 to 1.09 ± 0.36 × 103 mg kg−1. In contrast, the PAHs EFs for the clean briquette coal with two-stage stoves were two orders of magnitude lower than those of the bituminous coals. For parent PAHs (pPAHs) and total quantified PAHs (∑PAHs), they mainly contributed in gaseous phases with compositions of 69–79% and 64–70%, respectively. The gas-to-particle partitioning was mostly governed by the absorption. Moreover, the correlation coefficient (r) between EC and ∑PAHs, OC and parent PAHs (pPAHs), OC and nitro PAHs (nPAHs) were 0.81, 0.67 and 0.85, respectively, supporting that the PAHs species were potential precursors to the EC formation during the solid fuel combustion. The correlation analyses in this study further deduced that the formations of pPAHs and nPAHs were more closely related to that of OC than alkylated PAHs (aPAHs) and oxygenated PAHs (oPAHs). Diagnostic ratios of selective PAHs were calculated and evaluated as well. Among those, the ratio of retene (RET)/[RET + chyrene (CHR)] was found to be an efficient tool to distinguish coal combustion and biomass burning. In general, it was found that the amounts of pollutant emissions from clean briquette coal combustion were definitely lower than those from bituminous coal and biomass combustions. It is thus necessary to introduce and recommend the use of cleaner briquette coal as energy source.

Effect of mineral extraction on the evolution of nitrogen functionalities during coal pyrolysis

The mineral composition of coal has a significant effect on the pyrolysis of coal and the evolution of the nitrogen-containing functional groups. Thermogravimetry-differential thermal analysis-Fourier transform infrared-mass spectrometry (TG-DTA-FTIR-MS), X-ray photoelectron spectroscopy (XPS), and pyrolysis–gas chromatography-mass spectrometry (Py-GC-MS) were used to study the effects of extraction pretreatment (water-washing, NH4Ac-washing, and HCl-washing) on the pyrolysis characteristics and the three-phase nitrogen transformation mechanism in Xinjiang Hongshaquan coal. The results show that the minerals in each extraction stage can inhibit the transformation of char-N to tar-N/gas-N. The presence of H2O-soluble and HCl-soluble minerals makes the tar-N content of the raw coal (R-coal) 25.5% lower than that of the water-washed coal (W-coal), and the tar-N content of the NH4Ac-washed coal (N-coal) 18.7% lower than that of the HCl-washed coal (H-coal). By contrast, NH4Ac-soluble minerals make the tar-N content of the W-coal 86.3% higher than that of the N-coal. The gas-N was increased by the extraction. The HCl-soluble minerals were the most important factor affecting the gas-N yield, which results in a large amount of char-N being converted into gas-N, while the NH4Ac-soluble minerals inhibit the process. The results of this study will provide data support and theoretical basis for clean coal combustion and improving the quality of coal tar.

Microstructure analysis of fluidized preheating pulverized coal under O2/CO2 atmospheres

The high efficient and clean coal combustion with fundamental deep low pollution emission was extensively explored worldwide. In this work, the Shenmu bituminous coal was preheated in a circulating fluidized bed (CFB) and this modified fuel including the preheated fuel and the coal gas was burned in a down-fired combustor (DFC) under the O2/CO2 atmospheres. The microstructure change of fuel was analyzed to reveal the reaction process and particle change behavior during high temperature coke combustion. Analysis at the micro scale was important for understanding macro phenomena and achieving deep low pollution emission. The results showed that the main forms of N, C, and O elements in coal were pyrrole, hydrocarbon (aromatics or aromatic substituted alkanes), and carbon-oxygen single bond (including ether and hydroxyl) respectively. During the preheating process, pyrrole converted to pyridine, the coal char reached a state of deep oxidation on the surface, and the stable structure between carbon and oxygen was destroyed. Besides, the number of reacting sites increased after preheating process, which was beneficial to the further combustion.

Effects of volatile matter and oxygen concentration on combustion characteristics of coal in an oxygen-enriched fluidized bed

Oxygen-enriched combustion in fluidized bed is a promising clean coal combustion technology which can efficiently control the emission of coal-fired pollutants, especially CO2. In this paper, by using several judging methods, the combustion characteristics of five kinds of coal under four different oxygen concentrations (20.9%, 27.8%, 40.7% and 52.7%, CO2 as equilibrium gas) were measured in the small-scale fluidized bed reactor with electric heating in detail. The oxygen consumption and volatile release characteristics were explored online. The influence of coal types, volatile matter and oxygen concentration on coal combustion characteristics was analysed. It’s found that the higher the bed temperature was, the faster the reaction rate was and the more oxygen consumption was. At a certain oxygen concentration and proper bed temperature, the separated combustion of volatile and char were observed. When the oxygen concentration was high, the separation phenomenon was more obvious. High-volatile, a certain bed temperature and oxygen concentration were the basic factors for the formation of separated combustion. The total volatile matter is not comprehensive as the index of reaction combustion characteristics and the effect of combustible components should be specifically considered. It’s found that for the coal with high combustible components, the separated combustion is more obvious. Volatile matter plays a dual role in the ignition and combustion of coal. The volatile matter (lower volatile matter) of some coals has a great promoting effect on coal combustion at higher temperature, while that (higher volatile matter) of other coals is not, which is closely related to the properties of char and the diffusion of volatile matter in pores.

Comparison of metallic oxide, natural ore and synthetic oxygen carrier in chemical looping combustion process

As one of clean coal combustion ways, chemical looping combustion (CLC) showed high CO2 capture efficiency with lower energy penalty. But these processes were limited by the low reaction rate between oxygen carriers (OCs) with coal char. This study evaluated the performances of Cu-based OCs with coal in in-situ gasification chemical-looping combustion (iG-CLC) and chemical-looping with oxygen uncoupling (CLOU) process. CuO modified by iron ore and chrysotile were employed as OCs which the addition of chrysolite improved the char gasification and iron ore enhanced the stability of CuO at high temperature. Results showed that CuO supported by ores (chrysolite and iron ore) had better H2 and CO conversion under H2O atmosphere than CuO and iron ore. Chrysolite decorated CuO can convert almost all H2 to H2O at 850 °C. Synthetic OCs showed better stability and high temperature tolerance during 10 redox cycles.

Application Research on deep recovery and utilization technology of flue gas waste heat of coal water slurry boiler

Coal water slurry boiler has attracted great attention in the field of urban heat system because of its efficient and clean coal combustion. The coal water slurry contains 35% moisture, which makes the waste heat recovery potential of flue gas greater. After the combustion of coal water slurry, the 100°Cunsaturated flue gas becomes 50°C saturated wet flue gas after Wet Desulfurization Process. The Direct Contact Thermal Storage System and Heat Pump technology are used to realize the deep recovery of low-temperature flue gas. The technology has been successfully applied in the 6×70MW coal water slurry boiler of La Shan Heat Source Company. After 120 days of operation, 393000 GJ of flue gas waste heat is recovered, about 23000 tons of coal water slurry is replaced, and 84000 tons of flue gas condensate is recovered. It has good economic and social utility. It is an effective way to recover and utilize waste heat from flue gas of coal-fired boiler, and has a broad application prospect.

Cytotoxicity and Potential Pathway to Vascular Smooth Muscle Cells Induced by PM2.5 Emitted from Raw Coal Chunks and Clean Coal Combustion

Coal combustion emits a large amount of PM2.5 (particulate matters with aerodynamic diameters less than 2.5 μm) and causes adverse damages to the cardiovascular system. In this study, emissions from anthracite and bitumite were examined. Red mud (RM) acts as an additive and is mixed in coal briquettes with a content of 0-10% as a single variable to demonstrate the reduction in the PM2.5 emissions. Burnt in a regulated combustion chamber, the 10% RM-containing bitumite and anthracite briquettes showed 52.3 and 18.6% reduction in PM2.5, respectively, compared with their chunk coals. Lower cytotoxicity (in terms of oxidative stresses and inflammation factors) was observed for PM2.5 emitted from the RM-containing briquettes than those from non-RM briquettes, especially for the bitumite groups. Besides, the results of western blotting illustrated that the inhibition of NF-κB and MAPK was the potential pathway for the reduction of cytokine levels by the RM addition. The regression analyses further demonstrated that the reduction was attributed to the lower emissions of transition metals (i.e., Mn) and PAHs (i.e., acenaphthene). This pilot study provides solid evidence for the cytotoxicity to vascular smooth muscle cells induced by PM2.5 from coal combustion and potential solutions for reducing the emission of toxic pollutants from human health perspectives.

Effects of oxygen partial pressure on physical and chemical characteristics of fuel and deep low NOx emission

The high efficient and clean coal combustion with fundamental deep low pollution emission is extensively explored worldwide. In this work, the Shenmu bituminous coal was preheated in a circulating fluidized bed (CFB) and this modified fuel including the preheated fuel and the coal gas was burned in a down-fired combustor (DFC) under the O2/CO2 atmospheres. The coal char and coal gas produced by preheating raw coal were measured and analyzed to obtain the changes of physical and chemical characteristics and the reduction of NOx original emissions. The results showed that both G band FWHM and IG/IALL of the preheated fuel were lower than those of raw coal, respectively, while both ID1/IG and ID3+D4/IG were significantly higher than those of raw coal, and the intensity of quartz, the anhydrite peaks and the fuel particle size were significantly reduced after preheating process. During the oxygen partial pressure of primary air increasing from 28.6% to 36.0%, and the increase of NH3/HCN from 0.61 to 1.26, NOx emissions decreased from 39.6 mg/MJ to 37.3 mg/MJ (@6%O2). The increased oxygen partial pressure of primary air improved the conversion ratio of fuel-N to coal gas-N. In the period of pulverized bituminous coal preheating, it destroyed and reconstructed the stability of carbon molecular micro-structure and the regularity of crystal structure for modified fuel microphysical morphology.

Technology of Thermal Preparation of Coal for Ecologically Pure Combustion of Fuel in Small Boilers

The problems of ecologically clean coal combustion are connected with the need to reduce the formation of pollutants to the environment during thermal transformation of fuel. Currently, about 180-190 million tons of coal are burned in Russia to produce heat and electricity, with more than 60% in the eastern regions of the country. Most of the coal (about 80%) is consumed by large thermal stations, which are equipped with pollutant trapping systems. The remaining part is burned in numerous boiler houses that operate in both urban and rural areas to provide heat to social facilities and the population. The analysis shows that the role of boiler houses increases significantly in the territories with a low population or in remote and decentralized areas. In this regard, the coal pretreatment technology before burning including the thermal preparation of coal is important. The use of thermally prepared fuel (semi-coke) will significantly reduce emissions of NOx and SOx, as well as improve the “culture” of thermal energy production at small boilers by switching to fully automated technologies, as well as significantly reducing the financial burden of utilities by reducing the wage fund and emission fees.

The ultra-low NOx emission characteristics of pulverized coal combustion after high temperature preheating

Preheating combustion is a promising low-nitrogen combustion technology. The article mainly describes the ultra-low NOx emission characteristics during preheating combustion, including preheating characteristics, combustion characteristics, and fuel nitrogen migration and transformation characteristics. Under the condition of fluidized bed equivalence ratio of 0.63 and preheating temperature of 980 °C, the calorific value of high-temperature coal gas is about 1.75 MJ/Nm3. Compared with raw coal, preheated char is modified and upgraded with a smaller particle size, larger specific surface area, and more pore structure. The combustion temperature is about 1045 °C, and the main form of NOx (NO2 or NO) along the DFC changes with the intensity of combustion. During the preheating process, 76.1% of the fuel nitrogen is converted to N2. Only 5.9% of the fuel nitrogen is converted to NH3, and NH3 is the only precursor of NOx. The average NOx emission is 31 mg/m3 (@6% O2), and corresponding conversion ratio of fuel nitrogen to NOx is 0.85%. This experimental results will play a vital role in the development of efficient and clean coal combustion technology.