Preheated Combustion Research Articles

Experimental and Simulation Study on Ultra-Low NOx Emissions of Anthracite by Preheated Combustion

ABSTRACT In this study, the ultra-low NOx emission of anthracite was achieved by the preheated combustion technology. Meanwhile, the preheated combustion model was established using Aspen Plus. High-temperature preheating (above 950°C) improved the conversion process from fuel-nitrogen to N2 and precursor of NOx, which involved the cracking of N-5 and N-6. The conversion rate from fuel-nitrogen to N2 was 81.88%. In addition, heterogeneous reduction reaction of NOx was the critical conversion path of fuel-nitrogen for the ultra-low NOx emission during the combustion. The conversion rate from NOx to N2 was 0.43%. The average NOx emission of tail flue gas was 40.77 mg/m3 and 46.15 mg/m3 (@6%O2) for Jincheng anthracite and Yangquan anthracite, respectively. The simulation results showed that the preheated combustion model demonstrated precise prediction capabilities for containing-nitrogen gas emission. The maximum error of NOx emission and N2 concentration were 7.71% and 3.37%, respectively. The simulation and experimental results could be mutually verified.

Experimental study on the flexible peak shaving with pulverized coal self-preheating technology under load variability

The integration of renewable energy sources into power grids has led to power fluctuations, necessitating coal-fired power units to provide flexible peak shaving. The pulverized coal self-preheating technology can potentially provide broad-load regulation and rapidly respond to load changes. In this study, the impact of the self-preheating technology on fuel preheating modification, combustion characteristics, and NOx emissions are investigated. Load-stabilization bases are proposed based on preheating temperature, preheated coal gas composition, combustion temperature, and flue gas emissions. Load change rates are calculated using these bases to character the load response. The results demonstrate that the preheated fuel has similar properties as the highly reactive gaseous fuel and exhibits excellent ignition and combustion performances at 25 % load. Preheating treatment improves combustion efficiency, and burnout ratio and reduces NOx emissions. The NOx concentration approaches the ultra-low emission standard at 50 % load. Four load-stabilization bases, covering the preheating and combustion sides, comprehensively characterize the load response performance. The rates based on preheating indicators and combustion indicators maximize to 3.30 %/minute and 2.71 %/minute, respectively. The load change rate in the ramp-up phase is higher than that in the ramp-down phase, which is related to the effective internal heat storage carrier and external thermal insulation conditions. The driving force formed by high load step ranges and the deviation from the full load capacity are conducive to increasing the load change rates.

Numerical study of inlet air conditions on methane flameless combustion characteristics

The current study investigates the influence of inlet air momentum and temperature for flameless characteristics. Three-dimensional computations were implemented by ANSYS FLUENT. A small-scale experimental combustor geometry was used for validation study. Turbulence modelling was performed by RNG k- ε model and the GRI-Eddy Dissipation Concept (GRI-EDC) model was used for the combustion modelling. The influence of inlet air velocity was investigated through using different air jet diameters at constant flow rate. Five different air jet diameters (4,6,8,10 and 12 mm) were studied. It was found that decreasing air jet diameter leads to an increase in the exhaust gas recirculation which reserve in mixture dilution (low O2 content mixture) subsequently, the reaction rate decreases which support the flameless mode creation. Also, this recirculated gas participates in heating up of fresh reactants which make the mixture tends to complete combustion. The influence of combustion air preheating temperature on NO and CO emissions were studied. CO and NO concentration were decreased with reducing the temperature of inlet preheated combustion air.

Experimental study on pulverized coal swirl-opposed combustion preheated by a circulating fluidized bed. Part A. Wide-load operation and low-NOx emission characteristics

In this study, the operating characteristics and NOx emission patterns are explored under a wide load range based on a 2MWth pulverized coal preheated combustion test platform. Preheated char with high physical sensible heat and preheated gas with high calorific value greatly improve the ignition and stability of the combustion characteristics of pulverized coal at low loads. Moreover, performing pre-denitrification during the preheating process helps to lower NOx emissions. Stable operation at a wide load range of 26%–106% was achieved, and ultralow loads of 40% and 26% were achieved when the pre-circulating fluidized bed (PCFB) was operated in double-/single-sided operation mode, respectively. Meanwhile, uniform concentration and temperature fields were achieved when both/one side of the PCFB were/was in operation. When operating on the double side of the PCFB, ultralow NOx emissions (@6% O2) of 39.9 mg/m3 and 43.7 mg/m3 were achieved at 40% and 50% loads, respectively. When operating on a single side, the NOx emission amount was 28.3 mg/m3 at 26% load. Furthermore, when the swirling air and the bottom air are equally distributed, the secondary air equivalent ratio is appropriately increased, and the injection position of the burnout air is properly delayed, NOx emissions are reduced.

Experimental study of deep and flexible load adjustment on pulverized coal combustion preheated by a circulating fluidized bed

Peak shaving of coal-fired power plants is a key to promoting renewable energy generation in a grid system. In this study, the deep and flexible load regulation characteristics of pulverized coal preheating combustion are explored. The determination criteria of the variable load related to the preheating temperature, preheated coal gas, combustion temperature and main flue gas (NO, N2O, CO and O2) emission concentrations are established, and the temperature hysteresis coefficient is introduced to characterize the hysteresis of the combustion process. The results show that this system has a deep load regulation capability and can operate stably over a wide load range from 25% to 113%. The chemical reactivity of the pulverized coal is enhanced with thermal modification, which ensures stable combustion in the combustion chamber at ultralow loads. Moreover, the optimal rate of variable load is achieved when the load step is 25%, and the maximum rates of variable load for the preheating process and combustion process are 4.17%/min and 3.13%/min, respectively. Furthermore, an excessively high load step will trigger a large amount of combustion hysteresis, which negatively affects the variable load process.

Low-NOx study of a 600 MW tangentially fired boiler based on pulverized coal preheating method

Boiler emissions are the primary sources of atmospheric nitrogen oxide (NOx) emissions. Exceeding the NOx emission limit can shut down the boiler, causing financial losses. Herein, a new preheated combustion method is proposed to prevent coal-fired boilers from exceeding the NOx emission limit at low loads. This is a simulation study of internal combustion burners and a 600 MW tangentially fired boiler using a pulverized coal preheating method that explores syngas production patterns after pulverized coal is preheated, the effects of flow characteristics, and variations in NOx and unburned carbon content under different preheating ratios. Our results indicated that the internal combustion burner had a stable preheating effect. The volume fractions of CH4, CO, and H2 at the burner outlet were 0.95%, 12.7%, and 0.8%, respectively. The fuel nitrogen precipitated during the preheating process was converted into N2. High-temperature char and syngas entered the furnace chamber and were mixed with air to accelerate combustion, which enhanced the jet flow intensity and improved the combustion stability at 50% load. The top burner exhibited a more significant nitrogen reduction than the bottom burner. The NO reduction from retrofitting Layers D and E accounted for 53% after retrofitting all five layers. When the preheating ratio was increased from 0 to 100%, NOx concentration was reduced by 63.6% at 6% O2, while unburned carbon content was reduced by 41%, which improved combustion efficiency. By discussing the advantages of internal combustion burners for retrofitting a 600 MW tangentially fired boiler, this study provides theoretical guidance for the application of preheating methods in peaking conditions.

Preheating and combustion characteristics of anthracite under O2/N2, O2/CO2 and O2/CO2/H2O atmospheres

In this study, the anthracite was preheated by a circulating fluidized bed under O2/N2, O2/CO2 and O2/CO2/H2O atmospheres. And the preheating and combustion characteristics of anthracite were studied. Compared with the O2/N2 atmosphere, the structural characteristics of preheated char was improved more obviously under the O2/CO2 and O2/CO2/H2O atmospheres when the oxygen concentration was 31%, which mainly reflected in the increase of BET surface and the increase of small aromatic rings. HCN was mainly NOx precursor during the preheating under different atmospheres. In addition, a novel comprehensive evaluation of ignition and stable combustion characteristics for preheated fuel was proposed. And the minimum thermal power required for preheated char combustion and the combustion heat of preheated coal gas were main factors affecting on the ignition and stable combustion characteristics. The highest combustion efficiency of anthracite was 98.85% under the O2/N2 atmosphere (the oxygen concentrations of primary gas, secondary gas and tertiary gas were 31.0%, 36.0% and 35.0%), and the lowest NO emission in tail flue gas was 24.24 mg/MJ under the air atmosphere.

Preliminary Study of Preheated Decarburized Activated Coal Gangue-Based Cemented Paste Backfill Material

This study proposes a novel idea of the use of coal gangue (CG) activation and preheated decarburized activated coal CG-based cemented paste backfill material (PCCPB) to realize green mining. PCCPB was prepared with preheated decarburized coal CG (PCG), FA, activator, low-dose cement, and water. This idea realized scale disposal and resource utilization of coal CG solid waste. Decarbonization and activation of CG crushed the material to less than 8 mm by preheated combustion technology at a combustion temperature of 900 °C and a decarbonization activation time of 4 min. The mechanism of the effect of different Na2SO4 dosages on the performance of PCCPB was investigated using comprehensive tests (including mechanical property tests, microscopic tests, and leaching toxicity tests). The results show that the uniaxial compressive strength (UCS) of C-S2, C-S3, and C-S4 can meet the requirements of backfill mining, among which the UCS of C-S3 with a curing time of 3 d and 28 d were 0.545 MPa and 4.312 MPa, respectively. Na2SO4 excites PCCPB at different curing time, and the UCS of PCCPB increases and then decreases with the increase in Na2SO4 dosage, and 3% of Na2SO4 had the best excitation effect on the late strength (28 d) of PCCPB. All groups' (control and CS1-CS4 groups) leachate heavy metal ions met the requirements of groundwater class III standard, and PCCPB had a positive effect on the stabilization/coagulation of heavy metal ions (Mn, Zn, As, Cd, Hg, Pb, Cr, Ba, Se, Mo, and Co). Finally, the microstructure of PCCPB was analyzed using FTIR, TG/DTG, XRD, and SEM. The research is of great significance to promote the resource utilization of coal CG residual carbon and realize the sustainable consumption of coal CG activation on a large scale.

Preheated combustion characteristics and fuel-nitrogen conversion paths for bituminous coal and anthracite in wide-range preheating temperature

In this study, the characteristics of preheated combustion and fuel-nitrogen (fuel-N) conversion paths in wide-range preheating temperature (700 °C −900 °C) for bituminous coal and anthracite were revealed during the preheated combustion. The conversion of fuel-N mainly underwent three procedures, including the conversion from fuel-N to char-nitrogen (char-N), tar-nitrogen (tar-N) and gas-nitrogen (gas-N) in the PCFB, the reduction from preheated fuel-N to N2 in the reduction region of combustor and the release of NOx from the char-N in the oxidation region of combustor. During the preheating, the highest conversion ratio from fuel-N to tar-N was 9.94% at the preheating temperature of 700 °C for bituminous coal. However, the conversion ratio from fuel-N to tar-N was below 2% for anthracite from 700 °C to 900 °C. Most of fuel-N was transformed into char-N and N2 during the preheating. Although higher preheating temperature promoted the conversion of fuel-N during the preheating, the reduction of char-N was inhibited due to the lower temperature of reduction region in the combustor for anthracite. The lowest concentration of NOx emission was 226.01 mg/m3(@ 6% O2) at the preheating temperature of 850 °C for anthracite.

Flame and emission characteristics of preheated ammonia combustion based on chemical reaction network

Ammonia (NH3) is an ideal fuel for achieving decarbonisation in energy production and industrial combustion, but suffers from low flammability and high nitrogen oxides (NOx) emissions in combustion. Preheating of NH3 can lead to stable combustion of NH3 and reduce nitric oxide (NO) emissions. In this study, the special combustion characteristics of the fuel preheated flame were investigated. Combustion, optical temperature measurement and gas measurement systems were set up. The flame images were captured and the flame temperature distribution was reconstructed by experiment. The temperature field in the longitudinal profile at the flame centre was divided into 11 temperature regions. Computational fluid dynamics (CFD) was carried out on the preheated NH3 combustion to analyse the distributions of components and velocity vectors. Then, a chemical reaction network (CRN) with 10 perfectly stirred reactors (PSR) was constructed based on the temperature field reconstructed by experiment and the distributions of components and velocity vector by CFD simulation. The temperature, the concentration of products and reactants, intermediate product components and reaction pathways were analysed by the CRN method to investigate the jet combustion characteristics of preheated NH3 combustion. Experimental and CFD simulation results showed that differently coloured regions appeared in the upstream of the pure NH3 flame, and the high-temperature region was widely distributed in the temperature field. CRN simulation results showed that the formation of special flame characteristics was associated with the generation of large amounts of hydrogen (H2) and water (H2O), and the reactions of NH2 with NH2 were the most dominant generating pathway of H2. Reaction pathway analysis of NH3 showed that H and OH radicals were most relevant to the production of NO, while NH2 radicals were most relevant to the consumption of NO in preheated NH3 combustion.

Modelling a Turbulent Non-Premixed Combustion in a Full-Scale Rotary Cement Kiln Using reactingFoam

No alternatives are currently available to operate industrial furnaces, except for hydrocarbon fuels. Plant managers, therefore, face at least two challenges. First, environmental legislation demands emission reduction. Second, changes in the origin of the fuel might cause unforeseen changes in the heat release. This paper develops the hypothesis for the detailed control of the combustion process using computational fluid dynamic models. A full-scale mock-up of a rotary cement kiln is selected as a case study. The kiln is fired by the non-premixed combustion of Dutch natural gas. The gas is injected at Mach 0.6 via a multi-nozzle burner located at the outlet of an axially mounted fuel pipe. The preheated combustion air is fed in (co-flow) through a rectangular inlet situated above the attachment of the fuel pipe. The multi-jet nozzle burner enhances the entrainment of the air in the fuel jet. A diffusion flame is formed by thin reaction zones where the fuel and oxidizer meet. The heat formed is transported through the freeboard, mainly via radiation in a participating medium. This turbulent combustion process is modeled using unsteady Favre-averaged compressible Navier–Stokes equations. The standard k-ϵ equations and standard wall functions close the turbulent flow description. The eddy dissipation concept model is used to describe the combustion process. Here, only the presence of methane in the composition of the fuel is accounted for. Furthermore, the single-step reaction mechanism is chosen. The heat released radiates throughout the freeboard space. This process is described using a P1-radiation model with a constant thermal absorption coefficient. The flow, combustion, and radiative heat transfer are solved numerically using the OpenFoam simulation software. The equations for flow, combustion, and radiant heat transfer are discretized on a mesh locally refined near the burner outlet and solved numerically using the OpenFoam simulation software. The main results are as follows. The meticulously crafted mesh combined with the outlet condition that avoids pressure reflections cause the solver to converge in a stable manner. Predictions for velocity, pressure, temperature, and species distribution are now closer to manufacturing conditions. Computed temperate and species values are key to deducing the flame length and shape. The radiative heat flux to the wall peaks at the tip of the flame. This should allow us to measure the flame length indirectly from exterior wall temperature values. The amount of thermal nitric oxide formed in the flame is quantified. The main implication of this study is that the numerical model developed in this paper reveals valuable information on the combustion process in the kiln that otherwise would not be available. This information can be used to increase fuel efficiency, reduce spurious peak temperatures, and reduce pollutant emissions. The impact of the unsteady nature of the flow on the chemical species concentration and temperature distribution is illustrated in an accompanying video.

Investigation of Heat Recovery Potential According to Flue Gas Field Measurements in Solid Fuel-Fired Buildings with District and Central Heating Systems

In this study, flue gas heat recovery potential was determined by using the flue gas measurements from boilers of buildings with solid fuel-fired district and central heating systems in Balikesir, Turkey. Potential flue gas heat recovery potential in terms of energy savings were examined. The potential of heating the preheated water and combustion air supplied to the boiler was analyzed. Thus, the efficiency of the heating system was increased, and energy savings were achieved by providing fuel savings. In order to reduce the flue gas temperature in solid fuel-fired boilers, the acidification temperature, fuel properties and excess air coefficient should be known. Below the acidification temperature, corrosion and other adverse effects may occur in the flue and in the heat exchanger. In this study, acidification temperature and fuel and combustion characteristics of coal were taken into account. Generally, seven types of coal are used for heating purposes in Balikesir province. Thus, flue gas heat recovery potential was determined for these seven types of coal. In terms of energy savings, the recovery potential in Balikesir province was calculated to be between 287,706 and 152,780 kW.

Comparison of oxy-fuel preheated combustion characteristics of high- and low- volatility carbon-based fuels

A comparative evaluation and analysis study of combustion characteristics, main pollutant emission behaviors, and fuel-N conversion paths of high- and low- volatility carbon-based fuels are conducted under O2/CO2 atmospheres in a preheating combustion reactor, i.e., CFB. Compared with conventional air combustion, the oxy combustion with high oxygen concentrations from 21% to 27.3% is studied. The studies show that the net calorific value of the preheated coal gas of semi-coke in O2/CO2 is up to 2 times that in air, and the net calorific value of the preheated coal gas of bituminous coal in O2/CO2 is up to 1.3 times that in air. During the preheating process of semi-coke, CH4 and HCN occupy a discreet proportions of preheating coal gas. Fuel characteristics and preheating atmosphere have no effect on the particle size of preheated coal char. Under an O2/CO2 atmosphere, the highest BET surface area of preheated coal char of bituminous coal is up to 30 times that of raw coal and that of semi-coke is up to 40 times that of raw coal. The carbon structure modification ratio of preheated coal char during the preheating process of bituminous coal is larger than that during the preheating process of semi-coke. With the increase in the concentration of oxygen in the primary stream, the NO emission decreased during the bituminous coal combustion process but increased during the semi-coke combustion process. In addition, the main generation path of NO in the reduction zone in O2/CO2 is NH3-NH2-NH-HNO-NO. In O2/CO2, the total promotion effect of reactions on NO formation in the combustion process of semi-coke preheated fuel is larger than that of bituminous coal.

Nonlinear Dynamic Analysis of the Transition from MILD Regime to Thermoacoustic Instability in a Reverse Flow Combustor

ABSTRACT In the present study, the stability limit of the MILD regime of combustion has been studied in a reverse flow combustor using syngas (20% H2, 20% CO, 60% N2) as fuel. Pressure oscillations obtained from the combustor are analyzed using regular approaches from the dynamical systems theory as the oxidizer preheat temperature varies from 772 K to 424 K. Stable MILD combustion is obtained at preheat temperatures ≥724 K; at lower preheat temperatures combustion becomes unstable, leading to high amplitude periodic oscillations. Permutation spectrum test and recurrence plot of the MILD condition unravels the deterministic nature of the pressure oscillations. The correlation dimension confirms that the system has high-dimensional chaotic characteristics. At temperatures <724 K, the correlation dimension becomes close to 1 as the system transitions to combustion instability. In these conditions, the permutation spectrum test shows close to zero standard deviation in all ordinal indices, the phase-space shows doughnut-shaped structures, and recurrence plot consists of long diagonal lines, all confirming the periodic nature of the system. The dominating frequency during combustion instability is attributed to the second axisymmetric mode of the combustor. Finally, three recurrence quantification criteria, namely, Recurrence Rate, Determinism, and Laminarity, and K-value obtained from 0 to 1 test, are tested as indicators for the onset of combustion instability. Determinism and K-value are recommended for capturing the transition in the underlying dynamics.

Comparison of detailed nitrogen-containing mechanisms in preheating combustion technology under O2/CO2 atmosphere

ABSTRACT Comprehension of the nitrogen-containing mechanism in oxy-fuel combustion is beneficial for understanding the migration path of NO x under an O2/CO2 atmosphere and controlling the emissions of NO x . In this study, the Chemkin code was used, and the various nitrogen-containing detailed mechanisms and experimental results were compared and analyzed to explore the adaptability of the existing detailed nitrogen-containing mechanism in oxy-fuel combustion and the influencing factors of NO x in the down-fired combustor (DFC) of the novel preheating combustion technology. A Perfectly Stirred Reactor (PSR) was chosen to simulate the combustion process of the DFC. Multiple detailed nitrogen-containing mechanisms were compared and analyzed. The results showed that the results for the simulation tendency using these mechanisms in the PSR reactor model were consistent with the experimental results. The mechanisms for the smaller NO concentration error between the predicted results and the experimental results of the oxy-fuel preheated combustion technology were USC-Mech 2.11 NO x , GRI-Mech 2.11, konnov0.6, and PG2009. Moreover, in the main combustion zone, the reaction with the highest NO production rate in all detailed nitrogen-containing mechanisms was HNO+H≤>NO+H2.

Identifying the optimum operating conditions for the integration of a solar loop to power an industrial flash dryer: Combining an exergy analysis with genetic algorithm optimization

With the objective to reduce fossil fuels consumption and greenhouse gas emissions, the integration of solar thermal energy into energy-intensive processes represents the most effective solution. This paper investigates the best solar integration scenarios to an industrial dryer unit through an exergy analysis. The exergetic balance for each subsystem is conducted, and a sensitivity parametric analysis was carried out. The optimization using the Genetic Algorithm was then conducted to define the optimum solar operating conditions. The exergetic evaluation showed an important exergy destruction at the dryer and combustion chamber, accounting for 58% and 42% of the inlet exergy flow, respectively. The sensitivity analysis outcomes showed that the exergy efficiency is clearly increased by increasing both drying temperature, decreasing the inlet moisture content, with preheating the combustion air temperature. Considering these variables, the optimization problem enabled enhancing the exergy efficiency by 40% and 30% for the overall process and flash dryer, respectively, when increasing drying temperature to 850 °C, an inlet moisture content of 14.9% and a preheated air combustion of 150 °C. Finally, the solar field could be integrated to the industrial dryer to preheat the ambient air for the combustion chamber to the setpoint temperature of 150 °C.

TP 78 An Interactive Genetic Algorithm and Machine Learning approach for validating the effect of preheated air combustion on fuel consumption of oil-fired industrial furnace

This paper presents an interactive approach of Genetic Algorithm and Machine Learning being used as tool for optimizing the Fuel Consumption of oil-fired rotary furnace operating with 20% preheated excess air. The author has attempted to solve a crucial problem of optimizing fuel consumption in ferrous foundries. Based on experiments carried on a self-designed and developed 200 kg rotary furnace in a foundry, it was found that crucial operating parameters like preheated excess air not only affects the flame temperature and melting rate but also significantly the fuel consumption An attempt has been made to establish a correlation between fuel consumption as output parameter and all others as input parameters It is expected that this model may prove practically beneficial for industry by estimating the effect of input process parameters for predicting the fuel consumption The results of Genetic Algorithm and Machine approach correlates with the experimental results

Sustainability potentials of an innovative technology and plant system in non-ferrous foundries

The planetary boundaries of our earth, the increasing economic importance of resource efficiency as well as the responsibility for the livelihoods of future generations require, today more than ever, the development of sustainable production solutions in which the necessary resources are used efficiently instead of being consumed. The energy-intensive industrial sectors, such as the foundry industry, are particularly committed to the set goals of sustainability and resource efficiency. In this context, an innovative technology and plant system for a flexible and automatable melt supply in non-ferrous foundries was developed and presented. This system enables closed-loop process control, which completely eliminates the previously mandatory ladling processes and reveals considerable potential for saving energy costs and CO2 emissions. As a consequent continuation, the presented paper focuses on a closer examination of the central innovative burner technology, which for the first time enables the safe and efficient processing of preheated combustion air with a control quality previously only known from electrical heating solutions. The effects that can be achieved with the new system in terms of energy demand and CO2 emissions, logistical flexibility, reduced production costs and the elimination of the previously required measures for melt cleaning (chemical and mechanical) are presented. Finally, the potentials for further sustainability improvements are discussed.

Experimental investigation on combustion and emission characteristics for heavy fuel and used motor oils blends in a free-flames burner

The main objective of this experimental investigation is to evaluate the feasibility of heavy fuel (HFO) and used motor (UMO) oils blends combustion in a free-flames burner installed in an isothermal oven. Temperature and chemical products of the combustion process are reported for mass percentages blends from 25% to 100% UMO (UMO25, UMO50, UMO75, and UMO100). For these tests, a burner with preheated oil blends and a primary and secondary air injection system are considered. Firstly, pure heavy fuel oil (HFO100) combustion is tested on its thermal effect as a baseline, recording emission factors for gaseous and solid emissions. Then, fuel blends are tested using secondary air injection regulated for minimal CO emissions. Overall results show that: i) flames radiation heat transfer for fuel blends are higher than for HFO100, ii) combustion efficiencies increase in the range of 48.8% to 63.5% for UMO25 and UMO100, respectively, and iii) exergy balance with a preheated air combustion shows the highest value for UMO100. Finally, this study suggests that used motor oils as fuel have a potential application in free-flames combustion process.

Effect of oxygen-staging on fluidized preheating combustion of pulverized coal under O2/CO2 atmosphere

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