A fibre‐mat catalytic burner for the heating system of PVC tiles

This study aims to develop the low‐temperature catalytic burner using Al₂O₃ fibre and Pt catalyst as a substrate and an active material, respectively, and then to apply it to the heating system of PVC tiles. Three types of fibre‐mat catalytic burners—natural diffusion catalytic burner, forced diffusion catalytic burner and premixed catalytic burner—were tested. For the natural diffusion catalytic burner, the combustion efficiency was significantly affected by the installation method. Its combustion efficiency was above 99.5% when it was placed vertically and upward, whereas the combustion efficiency rapidly deteriorated to less than 80% when it was installed in downward position. When the forced diffusion combustion mode was employed, the combustion efficiency of the fibre‐mat catalytic burner was successively improved over 99.5%. The optimal operation condition of the premixed fibre‐mat catalytic burner was obtained when the excess air ratio is 4.3 and the heat load is 3.0 kcal h^?1 cm^?2. The heat load of the premixed catalytic burner was found to be twice as much as those of the natural and forced diffusion catalytic burner, meaning that the size of the catalytic burner can be reduced to its half if the premixed catalytic burner is used. We also performed the field test of the fibre‐mat catalytic burner in the heating system of the PVC tiles. The combustion efficiency of the catalytic burners appeared to be satisfactory, above 99.5%, and the energy saving by replacing the existing electrical heaters with the fibre‐mat catalytic burners were shown to be 27.7%. Copyright © 2002 John Wiley & Sons, Ltd.     

Frontiers in combustion techniques and burner designs for emissions control and CO2 capture: A review

The use of fossil fuel is expected to increase significantly by midcentury because of the large rise in the world energy demand despite the effective integration of renewable energies in the energy production sector. This increase, alongside with the development of stricter emission regulations, forced the manufacturers of combustion systems, especially gas turbines, to develop novel combustion techniques for the control of NO_x and CO₂ emissions, the latter being a greenhouse gas responsible for more than 60% to the global warming problem. The present review addresses different burner designs and combustion techniques for clean power production in gas turbines. Combustion and emission characteristics, flame instabilities, and solution techniques are presented, such as lean premixed air‐fuel (LPM) and premixed oxy‐fuel combustion techniques, and the combustor performance is compared for both cases. The fuel flexibility approach is also reviewed, as one of the combustion techniques for controlling emissions and reducing flame instabilities, focusing on the hydrogen‐enrichment and the integrated fuel‐flexible premixed oxy‐combustion approaches. State‐of‐the‐art burner designs for gas turbine combustion applications are reviewed in this study, including stagnation point reverse flow (SPRF) burner, dry low NO_x (DLN) and dry low‐emission (DLE) burners, EnVironmental burners (including EV, AEV, and SEV burners), perforated plate (PP) burner, and micromixer (MM) burner. Special emphasis is made on the MM combustor technology, as one of the most recent advances in gas turbines for stable premixed flame operation with wide turndown and effective control of NO_x emissions. Since the generation of pure oxygen is prerequisite to oxy‐combustion, oxygen‐separation membranes became of immense importance either for air separation for clean oxy‐combustion applications or for conversion/splitting of the effluent CO₂ into useful chemical and energy products. The different carbon‐capture technologies, along with the most recent carbon‐utilization approaches towards CO₂ emissions control, are also reviewed.     

Development and characterization of a low-NOx partially premixed hydrogen burner using numerical simulation and flame diagnostics

The utilization of hydrogen as a fuel in free jet burners faces particular challenges due to its special combustion properties. The high laminar and turbulent flame velocities may lead to issues in flame stability and operational safety in premixed and partially premixed burners. Additionally, a high adiabatic combustion temperature favors the formation of thermal nitric oxides (NO). This study presents the development and optimization of a partially premixed hydrogen burner with low emissions of nitric oxides. The single-nozzle burner features a very short premixing duct and a simple geometric design. In a first development step, the design of the burner is optimized by numerical investigation (Star CCM+) of mixture formation, which is improved by geometric changes of the nozzle. The impact of geometric optimization and of humidification of the combustion air on NO_x emissions is then investigated experimentally. The hydrogen flame is detected with an infrared camera to evaluate the flame stability for different burner configurations. The improved mixture formation by geometric optimization avoids temperature peaks and leads to a noticeable reduction in NO_x emissions for equivalence ratios below 0.85. The experimental investigations also show that NO_x emissions decrease with increasing relative humidity of combustion air. This single-nozzle forms the basis for multi-nozzle burners, where the desired output power can flexibly be adjusted by the number of single nozzles.     

Comparison of conventional and metal fiber burners in a compact methane reformer using CFD modeling

Compact reformers can be used to produce hydrogen for fuel-cell automobiles. The heat of the mehane seam reforming reaction is provided by methane burning. Generally, conventional burners have been used in combustion chambers. The Computational Fluid Dynamic (CFD) approach was used for the comparison of conventional burners with metal fiber burners and their locations for the first time. The rate of steam reforming reactions and methane combustion reactions were introduced to the CFD model and the Finite Rate/Eddy Dissipation model was used for reactions on the reforming and combustion sections. After validation of the compact reformer results by available experimental data, metal fiber was modeled using the porous-jump interior boundary condition. The results show that the best burner position for the metal fiber is the Bottom (near the catalyst) and for the conventional burner is the Top (far from the catalyst). The results show that the conventional burner in both the Middle and Bottom positions leads to an increase in the reaction zone temperature above 1200 K, which is higher than the catalyst tolerance, but placing a simple burner on the Top of the reactor does not have an out-of-range temperature problem. The hydrogen mass yield for a conventional burner at the Top position is 27.75% relative to methane. Due to the thermal uniformity in the metal fiber burner, the temperature does not exceed the catalyst limitation in the three positions (Top, Middle, and Bottom). The metal fiber burner at the Bottom of the combustion chamber shows the best performance with a hydrogen mass yield of 40.82%. The results indicate that metal fiber burners can distribute the flame more uniformly than conventional burners and increase the available heat for the reformer side.     

多孔介质稳焰器对旋流火焰振荡燃烧特性影响的试验研究

为研究多孔介质稳焰器孔密度变化对贫预混旋流火焰振荡燃烧特性的影响,通过光电倍增管测量全局火焰热释放率,采用双麦克风方法测量旋流器入口速度脉动,获得不同孔密度多孔介质稳焰器火焰传递函数;并通过高速相机测量不同孔密度多孔介质稳焰器振荡火焰结构的变化。试验结果表明：多孔介质能够改变燃烧室声模态,有效抑制燃烧振荡,但孔密度对受迫燃烧火焰热释放率和压力脉动影响具有非线性;高频入口扰动对火焰响应特性影响较弱,火焰受迫响应呈现低通滤波特性;火焰传递函数增益峰值对应入口激励频率存在差异,但相位分布斜率基本一致;多孔介质导致火焰向稳焰器中心轴线聚拢,相干结构更加明显;宽频扰动范围内的火焰张角分布趋势与火焰传递函数增益曲线的分布趋势相反。     

Fuel‐lean VOCs combustion in a porous burner stacked with alumina balls: A case for ethylene combustion

A porous burner stacked in turn with 3‐ and 9‐mm alumina pellets was established to perform C₂H₄ combustion experiments by acquiring the flammable limits, temperature variation characteristics, combustion wave velocity, pollutant emissions, and treatment efficiency. The burner operated well at equivalence ratios within 0.3 to 0.7. Larger alumina pellets widened the burner's lower flammable limit. As the flame propagated downstream, the higher premixed gas flow velocity and larger alumina pellets, the higher combustion wave velocity, whereas the circumstances were opposite as the flame spread upstream. The combustion temperature increased with the equivalence ratio and premixed gas flow velocity. In response to the effect of the alumina pellet dimension, 3‐mm alumina pellets corresponded to higher combustion temperatures, lower CO emissions, and higher treatment efficiency than those less than 9‐mm conditions.     

Rich methane premixed laminar flames doped by light unsaturated hydrocarbons: III. Cyclopentene

In line with the studies presented in Parts I (methane flame seeded with allene and propyne) and II (methane flame seeded with 1,3-butadiene) of this paper, the structure of a laminar rich premixed methane flame doped with cyclopentene has been investigated. The gases of this flame contain 15.3% (molar) of methane, 26.7% of oxygen, and 2.4% cyclopentene, corresponding to an overall equivalence ratio of 1.79 and a C₅H₈/CH₄ ratio of 15.7%. The flame has been stabilized on a burner at a pressure of 6.7 kPa using argon as dilutant, with a gas velocity at the burner of 36 cm/s at 333 K. The measured temperature ranged from 627 K close to the burner up to 2027 K. Species quantified by gas chromatography included the usual methane C₀–C₂ combustion products, but also propyne, allene, propene, propane, 1-butene, 1,3-butadiene, 1,2-butadiene, vinylacetylene, diacetylene, cyclopentadiene, 1,3-pentadiene, benzene, and toluene. A new mechanism for the oxidation of cyclopentene has been developed and added to the former model for the oxidation of small unsaturated hydrocarbons, benzene, and toluene described in Parts I and II. The whole mechanism involved 175 species in 1134 reactions. The main reaction pathways of consumption of cyclopentene and of formation of benzene and toluene are presented and discussed from flow rate analyses.     

Increasing the efficiency of radiant burners by using polymer membranes

Gas-fired radiant burners are used to convert fuel chemical energy into radiation energy for various applications. The radiation output of a radiant burner largely depends on the temperature of the combustion flame. In fact, the radiation output and, thus, the radiant efficiency increase to a great extent with flame temperature. Oxygen-enriched combustion can increase the flame temperature without increasing fuel cost. However, it has not been widely applied because of the high cost of oxygen production. In the present work, oxygen-enriched combustion of natural gas in porous radiant burners was studied. The oxygen-enriched air was produced passively, using polymer membranes. The membranes were shown to be an effective means of obtaining an oxygen-enriched environment for gas combustion in the radiant burners. Two different porous radiant burners were used in this study. One is a reticulated ceramic burner and the other is a ceramic fibre burner. The experimental results showed that the radiation output and the radiant efficiency of these burners increased markedly with rising oxygen concentrations in the combustion air. Also investigated were the effects of oxygen enrichment on combustion mode, and flame stability on the porous media.     

Catalytic combustion of hydrogen for residential heat supply application

Hydrogen can be converted to thermal energy by combustion or to electricity energy by fuel cells. Considering the stringent requirements for safety from fire hazards and elimination of pollutants, the flameless catalytic combustion of hydrogen is favorable over conventional flame combustion for residential heat supply application. This paper reported an industrial‐scale heat acquisition system based on hydrogen catalytic combustion. The 1 wt% Pt‐loaded glass fiber felts prepared by an impregnation process were used as the combustion catalyst, and a catalytic combustion burner with a capacity of 1 kW was designed. It was found that 100% hydrogen conversion rate could be obtained during the stable combustion stage, and the stable combustion could be achieved by adjusting hydrogen flow rate. The change in H₂/air ratio would influence the initial combustion stage but has little impact on the stable combustion stage. A heat efficiency of 80% for hot water supply was obtained based on the present catalytic hydrogen combustion burner. Copyright © 2016 John Wiley & Sons, Ltd.     

Investigation of the structural and reactants properties on the thermal characteristics of a premixed porous burner

Porous burners offer attractive features such as competitive combustion efficiency, high power ranges, and lower pollutant emissions. In the present study, the thermal characteristics of a porous burner are numerically investigated for a range of operating conditions and design specifications within a practical range. The premixed flame propagation of a methane/air mixture in a ceramic porous medium is simulated through an unsteady, one-dimensional model. The combustion process is modeled using a suitable single-step chemical kinetics. The reaction location is not predetermined, thus the flame is allowed to float within the solid matrix or to run off from either side of the porous medium. The numerical results indicate that flame stability and thermal characteristics of the burner are strongly dependent on the inlet mixture specifications and the solid matrix structural properties. For a fixed value of the inlet firing rate, the combustion products temperature will increase by an increase in the inlet gas temperature, an increase in the matrix porosity, or by a decrease of the matrix pore density. Among the geometrical properties, the burner length has virtually no effect on the burner performance. An increase in the solid matrix porosity or burner firing rate will increase the efficiency of the preheating zone, while increasing the inlet gas temperature or matrix pore density will cause a reduction in this efficiency. Simulation results also suggest that in order to prevent flame blow-out or flash-back, critical values of the burner settings and design parameters must be avoided.     

Catalytic combustion of hydrogen—II. An experimental investigation of fundamental conditions for burner design

The performance of catalysts in different forms was investigated for the design of a catalytic combustor with hydrogen fuel. The catalysts tested had dimensions of 150 × 150 mm, and consisted of a ceramic honeycomb impregnated with Pt, two Ni metal foams coated with Pd powder which differed from each other in pore size, and a ceramic foam coated with Co-Mn-Ag oxide powder. In the diffusive mode of operation, the Pd-coated Ni foam with larger pores exhibited the highest combustion efficiency. The ceramic foam with the oxide coating also provided smooth hydrogen combustion in the range 0.2–1.0 kcal cm^?2 h^?1. Combustion efficiency was improved by increasing the amount of premixed air and totally supplied air. Spot measurements of surface temperature and gas composition were carried out over the catalyst surface and the characteristic features of each catalyst were compared and discussed.     

An experimental study of a cylindrical multi-hole premixed burner for the development of a condensing gas boiler

This study experimentally examined a cylindrical multi-hole premixed burner for its potential use for a condensing gas boiler, which produces less NO_x emissions and performs better. In this study, the hole diameters and the arrangement of a multi-hole burner were investigated using a flat burner model. The combustion characteristics for the flame stability as well as the NO_x and CO emissions were examined using a cylindrical burner. For an optimal operating condition, the equivalence ratio for the cylindrical burner was between 0.70 and 0.75. For this condition, the turn-down ratio was 3:1 or higher, which was suitable for appropriate control of the boiler operation. The NO_x and CO emissions were less than 40 ppm and less than 30 ppm, respectively, for a 0% O₂ basis. The LPG and LNG were able to be used in this type of burner because there was no phenomenal difference in the stable combustion region between them.     

How “flat” is the rich premixed flame produced by your McKenna burner?

McKenna burners are widely used in the combustion community for producing “flat” premixed flames. These flames are considered as standards for the development and calibration of optical techniques. Rich premixed flames produced by McKenna burners are frequently investigated in order to understand soot formation processes both by optical and by sampling techniques. Measurements are normally performed along the axis of the flames, with a uniform distribution of temperature and species concentration assumed in the radial direction. In this work it is shown that the soot radial profiles of rich premixed ethylene–air flames produced by a McKenna burner with a stainless steel porous plug may be far from being “flat.” Soot is mainly distributed in an annular region and nonsoot fluorescing species are present in the core of the flames. This surprising result was verified under several working conditions. Furthermore, flames cannot be considered axial-symmetric but present a skewed soot distribution. Another McKenna burner with a bronze porous disk was used to produce flames of the same equivalence ratio and flows. These flames show a completely different soot radial profile, closer to the claimed flat distribution. These results cast doubts about the conclusions drawn in several studies on soot formation performed with a stainless steel McKenna burner.     

Optimization of producer gas fired premixed burner

Much work is reported in the literature pertaining to premixed burners using hydrocarbon fuels. However, very little work is available on similar burners using producer gas as a fuel. The present work aims at testing and optimization of a premixed burner with producer gas as a fuel.A burner of 150 kW capacity is used in the experimental investigations. The burner is of concentric tube type fully premixed in which air is supplied through central pipe and gas is supplied through annular passage. Swirl vane is provided to air and gas for thorough mixing. The bluff body is provided for flame stabilization. The premixed burner was tested on open core throat-less down draft gasifier for flame quality. A stable and uniform flame was observed with this premixed burner. Thereafter, an instrumented test set up to evaluate burner performance was installed on an open core gasifier. The burner was experimentally optimized for size and location of bluff body and flammability limits. The burner was optimized by using bluff bodies of 46, 61, 73, 80, 85, 98, 110 and 122 mm diameters. The burner was operated in batch operation of 6–8 h for optimization of various parameters. The experiment reveled that the uniform and high-temperature premixed flame was observed at conventional bluff body having blockage ratio of 0.65. The flammability limits for producer gas fired burner was established in the range of 40–55.     

Helmholtz behavior and transfer function of an industrial fuel swirl burner used in heating systems

Combustion instabilities, due to dynamical phenomena in the combustion system, may lead to strong noise emissions in modern industrial and domestic heating devices. Lean premixed burners are often used in these systems helping to respect the pollutant legislations. On the other hand, these kind of burners are more sensitive to dynamical phenomena, and acoustical coupling with other system compounds may occur. In order to predict the acoustical response of a given combination of burner, boiler and chimney system, the acoustical transfer function of the burner is necessary. In this study we present the experimental determination of the transfer function of a 22 kW commercial fuel swirl burner, mounted in a corresponding boiler, for different operational conditions.     

Limits for hydrogen leaks that can support stable flames

Quenching and blowoff limits of hydrogen diffusion flames on small burners were observed. Four burner types, with diameters as small as 8 μm, were considered: pinhole burners, curved-wall burners, tube burners, and leaky fittings. In terms of mass flow rate, hydrogen had a lower quenching limit and a higher blowoff limit than either methane or propane. Hydrogen flames at their quenching limits were the weakest flames recorded to date, with mass flow rates and heat release rates as low as 3.9 μg/s and 0.46 W. The quenching limit for a hydrogen flame at a 6 mm leaky compression fitting was found to be 28 μg/s. This limit was independent of supply pressure (up to 131 bar) and about an order of magnitude lower than the corresponding limits for methane and propane.     

Development of energy efficient porous medium burners on surface and submerged combustion modes

Two compact premixed LPG burners based on submerged and surface combustion modes in porous medium (abbreviated as MSB and SSB respectively) are developed and their combustion and emission characteristics are compared to those of the CB (conventional burner). The preheating and reaction zones of MSB are made from porcelain form and Alumina spheres of 30 mm size, respectively, and the corresponding zones in SSB are made from Alumina (Al₂O₃) foams of pore densities 26 ppcm and 8 ppcm. NO_x emission is reduced by 76% and 75% by the use of MSB and SSB, respectively, compared with the CB, with acceptable CO and SO₂ emissions. For a thermal load of 0.62 kW, the thermal efficiencies of CB, MSB and SSB are estimated to be 47%, 59% and 71%, respectively.     

Characterization of confined hydrogen-air jet flame in a crossflow configuration using design of experiments

Hydrogen combustion has many industrial applications and development of new hydrogen burners is required to fulfil new demands. A novel configuration of hydrogen burner utilizing crossflow injection of fuel jets into swirling combustion air is characterized empirically in this work. It is intended as a first step in the development of new burner technologies having reduced emission levels and improved efficiency. Experiments were designed using the full factorial design method. Operating parameters were varied simultaneously and the NO_X emissions from the flame stabilized on the burner were measured. Statistical analysis of the experimental data showed that overall equivalence ratio is the dominant factor and lower NO_X emissions are observed at low equivalence ratios, irrespective of the burner power level. The analysis yielded an empirical relationship among NO_X emission, overall equivalence ratio, and power level that is useful in the design activity for a future combustion system based on the proposed configuration.     

Performance and analysis by particle image velocimetry (PIV) of cooker-top burners in Thailand

Cooker-top burners are used extensively in Thailand because of the rapid combustion and high heating-rates created by an impinging flame, which is characteristic of these types of burners. High thermal efficiency with low level of CO emissions is the most important performance criteria for these burners. The wide variation in reported performances of the burners appears to be due to the ad hoc knowledge gained through trial and error of the local manufacturers rather than sound scientific principles. This is extremely undesirable in view of safety, energy conservation and environmental protection. In the present work, a nationwide cooker-top burner performance survey and an implementation of a PIV technique to analyze the burner performance as well as advising local manufacturers were carried out. Experimental data were reported for the base line value of thermal efficiency of all the burners. The thermal performance parameters and dynamic properties of the flow field at a flame impingement area, i.e. velocity magnitude, turbulent intensity, vorticity and strain rate were also reported as a function of burner type, which was categorized into four types based on the configuration of the burner head: radial flow burners, swirling flow burners, vertical flow burners and porous radiant burners.     

Interactions for flames in a coaxial flow with a stagnation point

The possible burning structures existing in two co-flowing combustible mixtures with different compositions, and their implications to the field of turbulent combustion are examined in this study. A coaxial burner with a quartz plate was used to experimentally investigate the flames of methane/air and propane/air mixtures propagating in a coaxial flow impinging onto a stagnation surface. The possible burning structures were observed to be: (1) a single-flame (a lean or rich premixed flame); (2) a double-flame (two lean or rich premixed flames, or a rich premixed flame and a diffusion flame); and (3) a triple-flame (a rich premixed flame, a diffusion flame and a lean premixed flame). An inner (or outer) mixture, far beyond the flammability limit, can still burn if a stronger outer (or inner) flame supports it. The extinction limit of the top part of the inner hat-shaped premixed flame is nearly independent of the burning intensity of the outer flame. It was found that the inner flame has a wider flammable region than the outer flame, and that the latter has a narrower flashback region than the former. Both propane and methane flames may exhibit flame-front instability, although the former displays much more clearly than the latter. Cellular and polyhedral instabilities can exist individually or appear simultaneously in the inner flame. However, only polyhedral (stripped-pattern) instability was observed in the outer flame. Finally, the experiments were analyzed theoretically using a simple geometrical model incorporated with the numerical simulations. The predicted shapes and locations of the flames are in good agreement with the experimental observations qualitatively.