Low-concentration Coal Mine Methane Research Articles

Applying high efficiency internal reforming catalyst for direct low concentration coal mine methane solid oxide fuel cells

Solid oxide fuel cells (SOFCs) are green and efficient power generation devices, which can efficiently utilize the abundant low concentration coal mine methane (LC-CMM), and play an important role in energy saving and emission reduction. However, there are still challenges need to be addressed, such as low conversion efficiency and deposit carbon. In this work, a Sr2Fe1.4Ni0.1Mo0.5O6-δ-Gd0.1Ce0.9O2-δ (SFNM-GDC) internal reforming catalyst is prepared, generating abundant oxygen vacancies with in situ precipitates Fe–Ni alloys in the reducing atmosphere, leading to improved methane reforming efficiency and carbon deposition resistance. The results show that the cell exhibits excellent electrochemical performance with the internal reforming catalyst, with the maximum power density (Pmax) of 1212 mW cm−2 and 980 mW cm−2 at 800 °C with H2 and LC-CMM, respectively, corresponding to polarization impedances of 0.16 Ω cm2 and 0.47 Ω cm2. More importantly, the single cell combining SFNM-GDC reformed layer can maintain stable performance for 100 h at 700 °C under the atmosphere of LC-CMM. These results highlight that the reformed layer enhances CH4 reforming, optimizes electrochemistry and increases resistance to carbon deposition.

Power generation via solid oxide fuel cell using ex-reformed oxygen-containing low-concentration methane

Solid oxide fuel cells (SOFCs) using oxygen-containing low concentration coal mine methane (O-LCM, CH4<30 %) for power generation are an attractive way to cleanly and efficiently convert abundant O-LCM resources into clean energy. However, direct use of O-LCM for power generation leads to low internal reforming performance and anode coking problems. Therefore, in this study, simulated O-LCM (30 vol% CH4-70 vol% air) was used as fuel and Ni–BaO–CeO2 (NBC) and Ni–BaO-(Ce,Zr)O2 (NBCZ) catalysts were prepared to improve the electrochemical performance and carbon deposition resistance of SOFCs. The composite catalyst containing nanoscale Ni and (Ce,Zr)O2 solid solution with abundant oxygen vacancies are favorable for the enhancement of CH4 reforming and the elimination of carbon deposit. The results show that the NBCZ-modified SOFCs using O-LCM exhibits the much better electrochemical performance, resistance to carbon deposits and discharging stability than the NBC-modified SOFCs. The research provides a strategy for the utilization of O-LCM for power generation via SOFCs.

Efficient conversion of low-concentration coal mine methane by solid oxide fuel cell with in-situ formed nanocomposite catalyst

Solid oxide fuel cell is promising to efficiently convert the low-concentration coal mine methane (methane concentration c(CH4) <30%) from pollutant to clean energy. However, the low internal reforming performance and the coking at anode become the big challenges of SOFC using LC-CMM. Therefore, the Mo-doped NiTiO3 catalyst layer is fabricated over SOFC anode in this work. The catalyst can be in-situ reduced to nanoscale Ni and Mo-doped TiO2-δ composite catalyst with plentiful oxygen vacancies, thus adsorbing oxygen species to enhance CH4 internal reforming and remove carbon. It is demonstrated that the catalyst-modified SOFC using LC-CMM exhibits the much better electrochemical performance, anti-carbon effect and discharging stability than the un-modified SOFC. The modified SOFC also shows the good electrochemical and internal reforming performances under different LC-CMM with various methane concentration c(CH4) and oxygen concentration c(O2). The distribution of relaxation time (DRT) indicates that the catalyst can remove carbon and facilitates the adsorption, dissociation and transport of surface species through the enhanced oxygen-species mediated surface reactions. Besides, a 2D multi-physics coupling model is built to study the reforming-enhancing and anti-carbon mechanisms of the catalyst layer.

Combustion characteristics of a self-preheating burner with gradually-varied porous media

ABSTRACT Porous media combustion technology provides an excellent alternative scheme for the efficient utilization of low concentration coal mine methane and the effective control of emissions. A self-preheating combustion system was built and combined with gradually varied porous media. And the spiral, tubular, and finned heat exchangers were designed to compare the combustion characteristics at different working conditions. Results indicated that the combustion temperature was increased effectively and the emission of pollutants was reduced under the addition of preheater. Moreover, the spiral heat exchanger increased the average temperature of preheating zone by 21%. And the starting time of the burners mainly depended on the pore density of the ceramic foam at the burner exit. With the increasing of velocity and equivalence ratio, the combustion temperatures were significantly increased. Meanwhile, the 3 mm-10-30 PPI burner combined the advantages of large and small pore density to realize the reduction of CO emissions below 20 ppm.

Experimental study on the premixed lean-burn in alumina particles based porous burner

Coal mine methane (CMM) emissions from underground coal mines is becoming a global problem since it produces greenhouse gas contributing to global warming. It is critical to reduce low-concentration CMM(LCM) and ventilation air methane (VAM) emissions, which has become the focus to be solved urgently. One of the methods is utilizing this VAM as a fuel by mixing of CMM with the help of the porous burning system. In order to optimize the performance of a porous burning system composed of alumina particles, a series of complex porous media burners composed of two layers of alumina particles were proposed, after which a laboratory experimental system based on these burners was built. The lean-burn limits, lean-burn stabilization temperature and lean-burn fluctuation patterns of the burners built in this study were tested and reported in this paper. Results show that cylindrical burner with equal segment length of 3 mm diameter alumina particles at the upstream and 6 mm diameter alumina particles at the downstream is suitable for lean-burn with low flow rate, and cone burner with equal segment length of 3 mm diameter alumina particles at the upstream and 6 mm diameter alumina particles at the downstream is more suitable for lean-burn with high flow rate and low methane concentration, and the lean-burn limits for cone burner with volume methane concentration of 1.5% is obtained, which is the lowest lean-burn limit have reported at present.

Solar-energy-driven conversion of oxygen-bearing low-concentration coal mine methane into methanol on full-spectrum-responsive WO3−x catalysts

Sunlight-driven photocatalysis is regarded as a promising strategy for direct conversion of methane in low concentration coal mine methane (LC-CMM) to value-added methanol, yet remains a grand challenge to efficiently activate and convert methane. Herein, WO3−x nanosheets with gradient concentration of oxygen vacancy were synthesized and firstly served as full-spectrum responsive catalysts for transformation of LC-CMM to methanol at ambient conditions. Defect-rich WO3−x-N2.0 shows a methanol yield of 1475 μmol·g−1, roughly 4.5 times higher than WO3-A2.0 under simulated solar light irradiation. The selectivity of CH3OH on the optimal WO3−x-N2.0 is up to 76%. More importantly, WO3−x-N2.0 exhibits a methanol yield of 396 μmol·g−1 with the selectivity of 82% even under near infrared light irradiation while almost no CH3OH is detected over WO3-A2.0. Based on the results of energy-band structure, photoelectrochemical characterization, PLs and EPR tests, the significantly enhanced photocatalytic performance over WO3−x-N2.0 is ascribed to the synergistic effect caused by the formation of oxygen vacancies, including extending light absorption into NIR region, improving separation of photoinduced electron-hole pairs and boosting production of hydroxyl radicals (key active species that drive CH3OH production). This work will offer a sustainable pathway to broaden the utilization of LC-CMM via efficient coupling of solar energy.

Overview and Outlook on Utilization Technologies of Low-Concentration Coal Mine Methane

Coal mine methane (CMM) with the worldwide reserves of 2.6 × 1014 m3 is one of the important unconventional natural gases. However, most of the low-concentration coal mine methane (LC-CMM, cCH4 < 30 vol %) is not utilized and directly emitted to the atmosphere, producing up to about 28 billion m3 CH4 emissions annually and causing a serious greenhouse effect and energy loss. Evidently, resource utilization of LC-CMM is of vital significance to achieve energy transition and carbon neutrality. Herein, we review the recent advances of LC-CMM utilization technologies in terms of low-concentration drainage gas (1 vol % < cCH4 < 30 vol %) and ventilation air methane (VAM, cCH4 < 0.75 vol %). Especially, the great progresses of LC-CMM utilization in China are extensively introduced. A large amount of the low-concentration drainage gas with cCH4 > 6 vol % has been utilized in China due to the wide application of specially designed internal combustion engines (ICEs) and safe pipeline transport technologies. To avoid the shortages of low efficiency and high pollution of ICEs, solid oxide fuel cells (SOFCs) fueled by LC-CMM were recently proposed and modified for improving safety, efficiency, and stability. Also, methane enrichment such as pressure swing adsorption (PSA) and direct burning are key technologies to improve the utilization ratio of the drainage gas with cCH4 < 6 vol %. The modifications to improve the safety and efficiency of the PSA process and the new metal fiber combustion have been developed and applied in China. Furthermore, the recent advances of VAM utilization technologies are introduced. A thermal flow reverse reactor (TFRR) for VAM utilization has been applied in some coal mines. VAM enrichment and a catalytic flow reverse reactor (CFRR) create opportunities to efficiently use VAM with much lower CH4 concentration. Finally, the technical and economic challenges as well as the coping strategies of LC-CMM utilization are described. It is believed that LC-CMM with all various CH4 concentrations can be effectively and cleanly utilized in the near future, contributing to the new energy structure establishment and environment protection.

Catalytic Internal Reforming, Electrochemical Performance and Thermal Effect of Large-Scale SOFC Single Cell Using Oxygen-Bearing Low-Concentration Coal Mine Methane

Coal mine methane is one kind of clean fuel with the global resource quantity of 260×1012 m3, however more than 230×108 m3 low concentration coal mine methane (LC-CMM) is directly emitted to the atmosphere annually in China, causing the severe energy loss and global warming effect. We proposed to utilize the LC-CMM through SOFC for realizing the efficient and clean conversion of LC-CMM. In this paper, the catalytic internal reforming efficiency, electrochemical performance and thermal effect of the large-scale 10cm × 10cm single cell were investigated using the oxygen-bearing LC-CMM as fuel. The results show that the peak power density and open circuit voltage can respectively reach 1.13 V and 100 mW cm-2 using the simulated LC-CMM (12.2 % CH4-4% O2) under 780 oC. Importantly, the stable discharging for nearly 400h using the oxygen-bearing LC-CMM were also be achived based on the large-scale single cell. The CH4 conversion and CO selectivity can also respectively reach 68.5% and 97.9%. The anodic temperature distribution of the large-scale single cell were tested, which implied that the exothermic oxidation reaction happen in the inlet side of anode, causing the higher tempeature of the area. However, the largest temperature gap in the whole large anode is smaller than 5oC, which cannot lead to the thermal distress. Therefore, above experimental results demonstrated the feasibility of efficient oxygen-bearing LC-CMM utilization through SOFC, which might create the opportunity to greatly improve the utilization ratio of LC-CMM and prevent the fuel waste and greenhouse effect by LC-CMM direct emission.

Efficient and stable conversion of oxygen-bearing low-concentration coal mine methane by the electrochemical catalysis of SOFC anode: From pollutant to clean energy

Large quantity of low-concentration coal mine methane (LC-CMM) has been directly emitted to the air, causing severe greenhouse effect and energy loss. We propose to convert the pollutant gas to clean energy by the anodic electrochemical catalysis of solid oxide fuel cells. In the electrochemical conversion of oxygen-bearing LC-CMM, the Ni-based anode shows high catalytic activity and good stability without severe carbon deposition, Ni oxidation or thermal runaway. High electrochemical performance and good discharging stability were achieved with very flexible O2/CH4 ratio and low CH4 concentration. The high electric efficiency of 38.2 % with the fuel utilization of 72 % and the stable discharging for 400 h can be realized by the stacks using the LC-CMM. Accordingly, a heterogeneous kinetics and electrochemical charge-transfer model was established to study the elementary reaction mechanism of O2 in CH4 conversion and carbon removing, also showing the theoretical thresholds of coking and Ni oxidation.

Application research of low concentration methane oxidation heat supply for underground refrigeration

In order to solve the problem of low concentration coal mine methane (CMM) emission and low utilization rate in coal mine and the underground refrigeration demand of coal mine, this paper puts forward a technology of regenerative thermal oxidation (RTO) to provide waste heat vapor for lithium bromide refrigeration unit, which can effectively solve the problem of low concentration CMM utilization and provide stable heat source output for the refrigeration unit. The integrated process of oxidizing heat supplying to refrigerating unit includes low concentration CMM transportation security system, CMM RTO system and waste heat utilization system. The designed methane concentration is 1.2%, with flow rate 100, 000 Nm3/h, and steam heat of 7537kW. The expected effect of project operation is analyzed, and the economy of the project is demonstrated. The technology of CMM RTO supplying steam for underground refrigeration, through the destruction of methane, and the output of heat for underground refrigeration, has multiple meanings of energy saving and emission reduction, improving the utilization efficiency of coal bed gas in coal mine area, and promoting the safe production of coal mine.

Design and economic evaluation of low concentration methane (CMM) regenerative thermal oxidation heating system

Based on the pursuit of coal mine methane (CMM) emission reduction, CMM utilization and the tendency of heating system in the coal mine sites, a design of the low concentration CMM regenerative oxidation technology (RTO) specified in a coal mine was introduced. The design method of the technology was carried out in detail, and the low concentration CMM regenerative oxidation heating system replacing traditional heating by coal-fired boiler in coal mines was compared technically and economically, including method of “Incremental return on investment” and corrected-cost method. In addition, the application of low concentration technology was prospected. And it would give a great contribution to the design and project promotion in this area.

Influence of temperature on adsorption selectivity: Coal-based activated carbon for CH4 enrichment from coal mine methane

In order to study the effect of temperature on the adsorption separation characteristics of CH4/N2 mixtures, activated carbons (AC) were prepared from low-rank bituminous coal by KOH activation method, marked as DF-AC and SM-AC. The adsorption isotherms of pure CH4 and N2 on AC were described by Langmuir-Freundlich model based on the high-pressure adsorption experiments. The adsorption selectivity calculated by ideal adsorption solution theory (IAST) method was used to evaluate the adsorption and separation characteristics of CH4/N2 binary mixtures. The influence of temperature on adsorption selectivity from 273 K to 373 K (20 K interval) were systematically analyzed. Results show that the adsorption equilibrium states of pure CH4 and N2 on activated carbons are significantly different, and the CH4 is more sensitive to the variation of temperatures. The isosteric heat of adsorption of CH4 is always larger than that of N2 under experimental pressure condition. This indicates that the interaction between the CH4 molecules with activated carbons is stronger than that of N2 molecules. With the temperature increasing from 273 K to 373 K, the separation factors first increase rapidly and then decrease slowly after arriving at the maximum value, while the adsorption selectivity decrease sharply at low pressure and subsequently tended to slowly decrease. When the experimental temperature is higher than 313 K, the adsorption selectivity is increasing monotonically with the increase of adsorption pressure. Under present experimental condition, for CH4:N2 = 50:50 mixture, the maximum adsorption selectivity of DF-AC (S = 7.06) can be obtained at 273 K and low pressure, while the minimum adsorption selectivity of DF-AC (S = 2.82) is obtained at 373 K and low pressure. The influences of temperature on adsorption selectivity of CH4/N2 binary mixture on coal-based activated carbons indicate that the lower adsorption temperature is contributed to the CH4 enrichment from low-concentration coal mine methane. And the effect of temperature on adsorption selectivity is greater than that of pressure, which provides a certain guiding significance for the efficient separation of low concentration gas combined with PSA and TSA technologies.

Premixed combustion of low-concentration coal mine methane with water vapor addition in a two-section porous media burner

During the transport of low-concentration coal mine methane (CMM), water mist spraying into the pipeline is used to eliminate the risk of explosion, but it leaves abundant vapor in the methane. This study was aimed to explore the effects of water vapor addition on the low-concentration CMM combustion in porous media. Thereby, a 2D numerical model based on a two-section ceramic foam burner setup with high flame stability was established and multi-step kinetics mechanisms were imported to the model. In this paper, the effects of vapor concentrations on the temperature distribution, flame stability limit, and chemical reaction during low-concentration CMM combustion in ceramic foam were investigated. Results indicate that with the increase of vapor mole fraction in the inlet methane, the overall temperatures in the downstream section of the burner gradually decreased, while the vapor mole fractions were linearly and negatively correlated with the peak temperatures in the burner. A small amount of vapor was involved in the chemical reactions of combustion, and with the increase of vapor mole fraction, more vapor took part in the reactions when the vapor addition into the inlet methane was unchanged. As the vapor mole fraction in the low-concentration CMM increased, the velocity range of flame stability limit was gradually narrowed down. In addition, the lower limit of velocity changed very slightly and maintained at 0.13–0.20 m/s, while the upper limit dropped obviously. The key elementary reactions underlying the effect of vapor on combustion reactions were determined by defining the changing rate of peak reaction rate. Addition of vapor into methane affected the peak rate of each elementary reaction, and altered the area of axial region where elementary reactions occurred.

A review of oxygen removal from oxygen-bearing coal-mine methane.

In this article, a comparison will be made concerning the advantages and disadvantages of five kinds of coal mine methane (CMM) deoxygenation method, including pressure swing adsorption, combustion, membrane separation, non-metallic reduction, and cryogenic distillation. Pressure swing adsorption has a wide range of application and strong production capacity. To achieve this goal, adsorbent must have high selectivity, adsorption capacity, and adequate adsorption/desorption kinetics, remain stable after several adsorption/desorption cycles, and possess good thermal and mechanical stabilities. Catalytic combustion deoxygenation is a high-temperature exothermic redox chemical reaction, which releases large amounts of thermal energy. So, the stable and accurate control of the temperature is not easy. Meanwhile partial methane is lost. The key of catalytic combustion deoxygenation lies in the development of high-efficiency catalyst. Membrane separation has advantages of high separation efficiency and low energy consumption. However, there are many obstacles, including higher costs. Membrane materials have the requirements of both high permeability and high selectivity. The development of new membrane materials is a key for membrane separation. Cryogenic distillation has many excellence advantages, such as high purity production and high recovery. However, the energy consumption increases with decreasing CH4 concentrations in feed gas. Moreover, there are many types of operational security problems. And that several kinds of deoxygenation techniques mentioned above have an economic value just for oxygen-bearing CMM with methane content above 30%. Moreover, all the above methods are not applicable to deoxygenation of low concentration CMM. Non-metallic reduction method cannot only realize cyclic utilization of deoxidizer but also have no impurity gases generation. It also has a relatively low cost and low loss rate of methane, and the oxygen is removed thoroughly. In particular, the non-metallic reduction method has good development prospects for low concentration oxygen-bearing CMM. This article also points out the direction of future development of coal mine methane deoxygenation.

Molecular simulation study of metal organic frameworks for methane capture from low-concentration coal mine methane gas

Methane and nitrogen are the main components in the coal mine drainage gases. However, it is the most difficult to separate methane from CH4 to N2 mixtures due to the completely nonpolar molecule for these two components. Research on the adsorption and separation properties of CH4 and N2 may have great significance for methane purification from coal mine methane. In the present work, adsorption and separation performance of 22 different metal–organic frameworks (MOFs) for CH4, N2 and their binary mixtures at room temperature have been investigated using molecular simulation method. Results show that the adsorption capacity is mainly dominated by the occupied sites and small pore spaces for pure CH4 or N2 adsorption. Compared with N2, CH4 would be preferentially adsorbed in all MOFs, which is consistent with the rules of adsorption heat, especially at low pressure ranges. Methane uptake with low gas adsorption loadings is mainly controlled by the interactions between adsorbate and frameworks caused by small pore spaces. And, there is a linear rule between methane uptakes and surface areas or pore volumes. The adsorption isotherms of CH4/N2 binary mixtures could be well predicted based on single-component isotherms using IAST method. Analyses on CH4/N2 mixture adsorption selectivity show that MOFs are the promising candidate for methane capture from CH4/N2 mixtures. Among all the selected MOFs, ZIF-7 is the most promising porous material for CH4/N2 mixture separation. The parameter of adsorbility is showing well correlations with the selectivity of CH4/N2 mixture, which can be served as a general criterion for the preliminary screening of MOFs for methane separation applications.

Two-Dimensional Experimental Study of Superadiabatic Combustion in a Packed Bed Burner

High-efficiency use of low-concentration coal mine methane is favorable for energy savings and the reduction of greenhouse gas emissions. During the porous media combustion, abundant methane at extremely low concentrations will be used not through stable combustion, but through superadiabatic combustion, which transmits flames to the downstream. To study the superadiabatic combustion of low-concentration methane intuitively, we set two-dimensional (2D) temperature measuring points in the burners, extended the temperature measurements via a radial basis function (RBF) to the entire burner, and plotted a 2D temperature distribution. The effects of working conditions, pellet diameter, and burner length on the superadiabatic combustion of low-concentration methane then were investigated. The results show that unstable phenomena such as flame rupture and inclining occurred during the combustion wave propagation in the porous medium. The effects of the heat dissipation through burner walls and the heat dissipat...

Subadiabatic combustion of premixed gas in ceramic foam burner

During the combustion of low-concentration coal mine methane in a porous medium, subadiabatic combustion will occur with the upstream propagation of combustion waves. The lower concentration limit of methane combustion can be broadened, when the porous medium skeleton is preheated by the upstream propagation of combustion waves. In this study, an experimental apparatus of porous medium combustion was built and used to validate a numerical model. Then numerical tests were conducted to characterize the upstream propagation of combustion waves, and investigate the effects of many factors (e.g. methane working conditions, heat loss through walls, and dispersion effect) on the propagation. Results show that the upstream propagation of combustion waves is kept at an even velocity. During the propagation, the combustion products temperature at the burner outlet gradually decreases, while the peak temperature is unchanged. With the increase of methane concentration, the upstream propagation velocity of combustion waves and the peak temperature both increase. As the inlet gas velocity is increased, the upstream propagation velocity decreases but the peak temperature raises. As the heat loss through walls is increased, the upstream propagation velocity and the peak temperature both decrease. The CO emission quantity gradually decreases during the upstream propagation of combustion waves. With the increase of inlet velocity and heat loss through walls, the CO emission quantity within the same propagation period gradually increases. The NO emission quantity first increases slowly and then stabilizes during the upstream propagation of combustion waves. Moreover, with the increase of inlet velocity and decrease of heat loss through walls, the NO emission quantity within the same propagation period increases.

Combustion characteristics of low-concentration coal mine methane in ceramic foam burner with embedded alumina pellets

Ceramic foam as a rigid matrix is difficult to be embedded with various shapes of heat exchange tubes. In this paper, a ceramic foam burner with embedded alumina pellets was designed, which can set different shapes of tubes by taking advantage of the discrete pellets. An experimental system was built to study the effects of the pellet diameter and pellet location on the combustion of low-concentration coal mine methane (LCM). Results indicate that the heat transfer features of 13-mm pellets are more similar to those of 10-PPI ceramic foam compared with 6-mm pellets and 9-mm pellets. When arranged in upper section of the burner, the 13-mm pellets preserve the combustion heat, which helps to move the flame stabilization position to the upstream of the burner. In addition, the start-up time in the burner with the upper 13-mm pellets is longer than that with the intermediate 13-mm pellets. The total NOx emissions of the studied burners are improved with the increasing inlet velocity, while the CO emissions first decrease and then increase. The HC emissions of the ceramic foam burner with embedded pellets are between those of the pellet burner and the ceramic foam burner.

Performance evaluation of methane separation from coal mine gas by gas hydrate formation in a stirred reactor and in a fixed bed of silica sand

Coal mine methane (CMM) gas is a sort of unconventional natural gas that can be used as a clean supplementary energy resource when methane is purified. In this work, methane separation from a low-concentration CMM gas (30mol% CH4, 60mol%N2, and 10mol% O2) was investigated using gas hydrate formation in a stirred reactor and in a fixed bed of silica sand with the presence of tetrahydrofuran (THF) and sodium dodecyl sulfate (SDS). The concentration of THF and SDS was fixed at 1.0mol% and 500ppm, respectively. The experiments were carried out in batch operation with the initial pressure fixed at 3.6MPa, and the temperature was set at 277.15K. The results indicated that gas hydrate formation in the stirred reactor and in the fixed bed of silica sand were both promoted by adding SDS in THF solutions. It was found that the hydrate-based separation process for CH4 recovery from the CMM gas mixture performed better in the stirred reactor as compared to the fixed bed of silica sand employed in this work. The CH4 recovery obtained at 1.0mol% THF and 500ppm SDS in the stirred reactor was about 40.5%, which was much higher than those obtained in TBAB solutions (26.2%) and cyclopentane/SDS solutions (33.3%).

Scale Effect of Ceramic Foam Burner on the Combustion Characteristics of Low-Concentration Coal Mine Methane

The apparatus of low-concentration coal mine methane (LCM) combustion, from experimental scale to industrial scale, is necessary for the large volume of LCM. In this paper, an experimental system has been set up for the LCM combustion to validate the corresponding numerical model. Following this, the revised burner, with increased inlet diameter and burner length, was used to study the combustion characteristics numerically based on the reliable model. Results indicated that the temperature distribution exhibits a one-dimensional nature evidently and the temperature discrepancy among different inlet diameters is negligible with the adiabatic wall. However, the temperature discrepancy is apparent when the heat loss of the wall is considered, which shows the importance of heat preservation outside the burner wall. As the burner diameter increases, the total temperature increases and appears to be more homogeneous with the heat loss wall. In addition, NO emissions decrease gradually and CO emissions increase...