Cylindrical Burner Research Articles

Combustion of rich hydrogen–air mixture stabilised near a cylindrical porous burner

In this paper, the effect of geometry on the dynamics of the hydrogen–air flame stabilised on the surface of a burner is investigated numerically. Two main regimes of combustion front stabilisation near the cylindrical burner: attached and detached flames are investigated and compared to the planar case. The neutral stability boundary for diffusive-thermal instability is studied in detail. The attached flame regime is characterised by the fact that for rich mixture compositions the flame becomes less stable in comparison to the combustion front stabilised near a planar burner. The detached flame regime is influenced by the divergent outflow, which significantly perturbs the flow field in the product regions of the flame. In contrast to the detached regime in the attached regime curvature stabilises the flame front. The flame properties investigated in this study are extremely sensitive to chemical kinetic models. The results and observations made can be used to support experimental design to set-up experiments for additional validation of detailed mechanisms of chemical reactions.

Lung injury caused by exposure to the gaseous fraction of exhaust from biomass combustion (cashew nut shells): a mice model.

Currently, to reduce the use of nonrenewable energy sources in energy matrices, some industries have already incorporated biomass as a source of energy for their processes. Additionally, filters are used in an attempt to retain the particulate matter present in exhaust gases. In this work, the emission gases of a cashew nut shell (CNS) combustion reactor and the deleterious effects on the respiratory system of mice exposed to gaseous fraction present in CNS emissions (GF-CNS) are analyzed. The system for CNS combustion is composed of a cylindrical stainless steel burner, and exhaust gases generated by CNS combustion were directed through a chimney to a system containing two glass fiber filters to retain all the PM present in the CNS exhaust and, posteriorly, were directed to a mice exposure chamber. The results show changes in the variables of respiratory system mechanics (G, H, CST, IC, and PV loop area) in oxidative stress (SOD, CAT, and NO2-), as well as in the histopathological analysis and lung morphometry (alveolar collapse, PMN cells, mean alveolar diameter, and BCI). Through our results, it has been demonstrated that even with the use of filters by industries for particulate material retention, special attention should still be given to the gaseous fraction that is released into the environment.

Numerical research of thermal stress in a gas burner with a cylindrical mantle in relation to its construction

Over the last few years there has been a great interest in research into the improvement of gas condensing boilers with pre-mixing. Many researchers are concerned with the improvement of the construction of these boilers, whose individual parts directly affect some parameters such as combustion efficiency, burning intensity, flame stability and NOx emissions. The outer mantle of a cylindrical burner stands out among the parts of the structure as the said parameters depend on it This paper analyses the outer cylinder of the premixed burner in relation to thermal stress. Numerical FEM analysis was performed based on experimental measurements and CFD input data. The tests were carried out in different gas and different materials. The results obtained show different thermal stresses which are dependent on the different gas and materials on the outer cylindrical mantle. This indicates the necessity to optimize materials and patterns applied to the outer cylindrical mantle of the burner, which will be the subject of further research.

A simple model with detailed chemistry for estimation of NOx and CO emission of porous burners

A simple model with detailed chemistry for predictions of NO and CO emission from cylindrical porous burners is proposed on the basis of chemical reactor network concept. Combustion in the inner hollow of the burner is modelled by laminar premixed flame while the processes inside the porous shell are described by zero-dimensional constant pressure perfect stirred reactor. Numerical results on NO and CO concentrations in combustion products are compared with experimental data obtained for combustible mixtures of different compositions including natural gas/air blended with hydrogen or oxygen. It is found that CO concentration is highly sensitive to the conditions in an exhaust pipe and processes in this pipe have to be modelled to achieve accurate enough prediction of carbon oxide emission. Numerical results are in a good qualitative agreement with experimental data and provide an estimate of pollutant emission concentration. Both computational and experimental results coincide in conclusion that hydrogen additives slightly reduce pollutant emission while usage of oxygen-enriched oxidiser noticeably increase NO concentration. The proposed model is also applied to predict the effect of water vapour injection on NO and CO emission of porous media burners. In this case, numerical results allow to expect more prominent emission reduction compared with Hl addition. The model assumptions, limits of applicability, possible ways of further improvement and expansion of the model are also discussed in the paper.

Computer simulation of CH4–G222–H2 behaviour in a non-premixed combustion chamber

This paper presents the numerical results of the study of a turbulent flame of methane enriched with hydrogen/air generated by a cylindrical burner. Computational Fluid Dynamics (CFD) code “FLUENT” and “Gambit” were used to perform the numerical simulation of the networking process. The Navier-Stokes equations, which estimate flow using a limited size method, have been resolved. The modeling of the disturbance/chemistry interaction has been used to associate the LES/PDF models with the state of system transfer equations. The calculations were analyzed for axial velocity, temperature, and carbon monoxide emissions. The results of the numerical calculations have been compared and checked for accuracy by returning to experimental data. The combustion behavior of CH4, G222 and H2 was employed by using the aforementioned parameters. The G222 is a mixture consists of 77% of methane and 23% of hydrogen. The obtained results confirm the fact of considering hydrogen as a clean non-polluting fuel compared to methane since it has no carbon monoxide emissions in combustion products. In addition, the velocity of hydrogen gas in the flame was significantly higher than the methane gas velocity.

Development of an Industrial Burner Accommodating Methane-Air Triple Flames

ABSTRACT Concentric fuel-rich and fuel-lean mixtures of methane and air were fed in the form of multiple pairs of circumferentially oriented opposing jets that are normal to an air cross flow inside a cylindrical burner to achieve the maximum firing capacity. As two premixed flames developed per each set of concentric jets (while the excess fuel and air diffused into a non-premixed flame wing), combustion via triple flames was thus sustained by a duplicated stagnation impact and a vortical flow field with intense heat recirculation. Setting equivalence ratios of 1.35 and 0.80 for six pairs of opposing jets increased the firing intensity to 100.4 MW/m3 which corresponded to jet flow velocities of 74.5 m/s. While the maximum blow-out velocity corresponded to a combined equivalence ratio of one, the minimum flame length and the peak combustion efficiency were reached at a combined equivalence ratio of 0.6. Switching from normal to inverse triple flames increased the blowout velocity limit from 74.5 to 82.2 m/s but increased the maximum value of the visible flame length/burner diameter ratio from 1.52 to 1.64.

Chemiluminescence usage in finding optimum operating range of multi-hole burners

In the present study, chemiluminescence analysis is used to determine the optimum range for equivalence ratio (Φ) in a multi-hole cylindrical burner. The premixed burner which uses natural gas is widely applied in gas condensing boilers and is examined here by Flame Emission Spectroscopy (FES). A spectrometry setup was implemented to capture emission of the burner, in order to detect OH*, CH*, C2*, and CO2* species by their chemiluminescence. The emission of OH* and CO2* was investigated for different equivalence ratios and burner power showing a peak in the lean ranges of Φ = 0.77–0.85 and 0.78–0.85 respectively, that corresponds to the maximum heat release rate. In addition, the OH*/CH* intensity ratio was investigated for range of Φ = 0.6–1.2 for all burner power, resulting in a power independent relation for OH*/CH*. It can be used as a tool to derive equivalence ratio from the OH*/CH* ratio. Moreover, the maximum surface temperature of the burner in power range occurred at Φ = 0.82 in a promising agreement with chemiluminescence peaks of OH* and CO2*. The main contribution is to find the optimum range of equivalence ratio corresponding to the maximum heat release rate.

Environmental and radiative characteristics of cylindrical Ni-Al burners for LPG combustion

This paper presents experimentally studied environmental and radiation parameters of hollow cylindrical burners during operation with LPG-air fuel mixture. Two combustion modes have been examined – an external combustion mode where the flame anchored near the outer surface of the burner, and an internal combustion mode when the combustion takes place in the inner cavity of the burner. The dependences of CO/NOx emissions and radiation efficiency on a firing rate in the range of 160-420 kW/m2, air-fuel equivalence ratio in the range of 1.0 - 1.4, as well as the porous structure of a burner have been analyzed. An influence of a flow deflector installed in front of the burner inlet in order to distribute the flow over the inner cavity of the cylindrical burner on environmental characteristics of the burner is discussed. The necessary condition that ensures CO emission below 50 ppm, NOx emission below 20 ppm and radiation efficiency in the range of 45-55 % is described in the paper.

Probability Density Function Modeling of Turbulence/Chemistry Interactions in Methane Flame Enrichment by Hydrogen

The present investigation illustrates a computational study of the turbulent diffusion flame in a cylindrical burner that is confined by two coaxial jets (methane/hydrogen and air). This is to improve the reactive mixture, the reactants combustion and to reduce the concentration of carbon monoxide as pollutant chemical species. The coupled models LES/PDF are, hereby, used to surmount the turbulence/chemistry interaction in the transport equations of chemical species. The predicted mixture fraction, the progress variable, and the carbon monoxide mass fraction are selected to validate the coupled models with respect to the experimental references data. Furthermore, the same scalar parameters which are considered in the previous numerical validation are evaluated from different fuel compositions of the hydrogen and the methane percentage to supply the combustion chamber. The computed results are carried out by FLUENT-CFD; where, they prove that hydrogen addition reduces the carbon monoxide concentration in the combustion products and improves the reactants combustion caused by the rich mixture.

Influence of heat conductivity and pore size of porous materials on the efficiency of cylindrical radiative burners with filtrational gas combustion

The problem of filtrational gas combustion wave stabilization in a porous cylindrical burner with different pore sizes and heat conductivities of porous carcass is numerically investigated. Simulation is carried out within the framework of the conventional one-dimensional diffusion-thermal model of filtrational gas combustion with allowance for radiative heat losses from the external surface of the burner. The data on influence ofthe carcass pore size and the thermal conductivity ofporous material on the radiative efficiency is investigated.

Effects of tangential inlet shape and orientation angle on the fluid dynamics characteristics in a biomass burner

The perennial crops are potentially used as renewable fuels in the boiler furnace. Due to its specific characteristics, the burner design for this biomass needs to be properly developed. The burner design proposed here is a cylindrical burner having an axial inlet and a pair of tangential injection. This study is aimed to investigate the effect of tangential inlet geometry on the burner performance, through numerical evaluation of fluid dynamics characteristics. The numerical evaluations are conducted using k-ε turbulence model under Ansys-Fluent software. The simulation results showed that, at certain orientation angles of tangential inlet, there are back flows from furnace to the internal burner. This phenomenon is responsible to the flame stability in the burner. The turbulence intensity and convective heat transfer coefficient are also influenced by the tangential inlet orientation angle. For same cross sectional area, the rectangular tangential inlet shape generated deeper backflow penetration and higher turbulence intensity than that was done by the circular ones. One of the rectangular shape shortcomings to the circular ones is to produce the higher static pressure, which correlate to the higher burner operating cost. This investigation study concluded that the burner with rectangular tangential inlet shape and orientation angle of 200 potentially produces the best burner performance.

A study on the effects of porous structure on the environmental and radiative characteristics of cylindrical Ni-Al burners

A promising type of radiation burners are hollow cylindrical burners made of materials with high thermal conductivity. In such burners, an internal combustion mode is possible when the combustion takes place in the cavity space of the burner, which allows obtaining radiation efficiency of up to 60%. The aim of the present work is to experimentally define the impact of the cylindrical burner porous structure on NOX/CO emission values and radiation efficiency with respect to equivalence ratio and firing rate. It has been found that NOx emission is <15 ppm if the equivalence ratio is <0.7. The findings indicate that the lower the firing rate and the smaller the size of the structural elements of the burner, the higher the radiation efficiency and emission of CO is. To gain a further understanding of the combustion conditions influence on the radiation efficiency, the analysis of possible efficiency with the assumption of equality the temperatures of flue gases and the burner surface has been carried out. The results suggest that effective heat exchange processes between combustion products and emitter are realized in cylindrical burners, which allows to achieve radiation efficiency close to the maximum possible in all considering operating conditions.

Flame transition velocities at various intercylinder spacing for side-by-side dual blowing cylindrical burners

Flame transition velocities at various intercylinder spacing for side-by-side dual blowing cylindrical burners

Combustion of a hydrogen jet normal to multiple pairs of opposing methane–air mixtures

The combustion performance of a cylindrical burner accommodating up to six multiple pairs of opposing methane–air mixtures with a cross-flow of hydrogen was addressed. The cross-flow initially duplicated the stagnation impact and enriched the vortical structures. Aided by the resulting flow strain, the transport of heat and active species from the hydrogen oxidation zone to the methane reaction zones accelerated the combustion across the opposing premixed flames and reduced the peak temperature across the outer diffusion flame. Increasing the cross-flow/opposing jets’ velocity ratio to 0.89 merged the two stagnation centers and maximized the shearing stress. By the slight increase in the velocity ratio to 1.07, the H and OH pools provided for methane combustion became closer to the ports such that a hydrogen/methane mass percent of 10.3% extended the stoichiometric blowout velocity from 28.3 to 35.7 m/s. Since the turbulent kinetic energy thus increased to 8.4 m2/s2, the firing intensity reached values as high as 48.2 MW/m3. Not only was there a reduction in the residence time for NOx formation, but also the blowout velocity relative gain overrode the relative increase in the NOx formation rates such that the NOx emission index decreased to 17 g/MWhr. By the excessive increase in velocity ratio, the vortical structures shrank such that the NOx exponential increase became dominant above 21 ppm. With fuel-lean mixtures, the hydrogen was partially combusted by the excess air from the opposing flames but the blowout velocity decreased to 13.1 m/s at Φ = 0.50. The hydrogen flame NOx emissions decreased by providing the excess air at larger jets’ diameter/separation ratios, thus reducing the residence times for thermal NOx formation and simultaneously interrupting the prompt NOx formation. At the lean operational limit, tripling the number of opposing jets decreased the hydrogen flame length by 54% such that the NOx emissions decreased by 38.4%.

A Study of Methane Hydrate Combustion Phenomenon Using a Cylindrical Porous Burner

ABSTRACTDirect hydrate combustion usually leads to unstable flame and flame extinction due to the “self-preservation” phenomenon. A novel cylindrical porous burner to maintain a stable methane hydrate flame for further experimental investigation is proposed and developed in this study. The characteristic flame patterns, flame structure, and reaction pathway of methane hydrate flame are studied using experimental and numerical methods. The proposed burner can effectively solve the burning issues and sustain a stable flame. The methane hydrate flame is characterized as a methane flame with a high percentage of water vapor addition in the stream. Furthermore, the chemical effects of high percentage of water vapor addition on the reaction pathway of premixed CH4/air flame are numerically investigated and the results show that the enhanced OH radical production through water decomposition (R86) promotes progressive dehydrogenations of CH4 to CH3, CH3 to CH2(s), and CH2O to HCO, and finally oxidation of CO to CO2, providing additional pathways for methane oxidation reaction.

Combustion via multiple pairs of opposing premixed flames with a cross-flow

A cylindrical burner accommodating stoichiometric fuel–air mixture combustion via multiple pairs of opposing jets and a cross-flow provided heat intensification and duplication of the stagnation impact for extending the firing limits and maximizing the power density. Six pairs of circumferentially opposing stoichiometric mixture jets sustained bulk injection velocities as high as 21.8 m/s and were associated with NOx emissions of 22 ppm, while emissions of 10 ppm were recorded upon reaching a lean limit equivalence ratio of 0.59. A stoichiometric mixture jet issuing perpendicular to the opposing jets at a momentum flux ratio of 0.3 increased the turbulence production rates to the extent that increased the maximum bulk injection velocity to 28.3 m/s and reduced the NOx emissions to 17 ppm. Since the recirculation zones between the two stagnation centers got compressed by increasing the momentum flux ratio to 0.8, the corresponding residence time reduction decreased the NOx emissions to 12 ppm. As the cross-flow mixture was made fuel–lean, dilution of the stoichiometric mixture by the fuel–lean mixture combustion products made it possible to get NOx emissions of single digit ppm. Emissions of 9 ppm resulted from using the cross-flow fuel–lean mixture jet due to compromising the flame stability limit extension and the temperature reduction in the post flame region. Such emissions, in turn, decreased to 4 ppm as the momentum flux ratio increased to 1.7 at which the stoichiometric mixture flames shrank into their ports. A minimum NOx emission index of 0.27 g/kg fuel was thus obtained at a volumetric heat release of 50.4 MW/m3. The momentum flux ratio corresponding to merging the two stagnation zones was correlated with Reynolds and Froude numbers, the jets’ separation as well as the density and viscosity values pertaining to the lean and stoichiometric mixtures’ flame temperatures.

Numerical Study of Combustion Regimes and Heat Radiation of Cylindrical Porous Burner

Temperature and radiative characteristics of different regimes of premixed gas combustion in porous cylindrical burner are investigated numerically. Two-temperature thermal diffusion model with radiative heat transfer and external radiative heat losses described in the framework of Eddington model is applied. It is found that two different combustion regimes can be realized under the same mixture equivalence ratio and flow rate depends on ignition conditions. It is shown that total radiative heat flux from the external surface of the burner and burner’s radiative efficiency strongly depend on the combustion regime.

Development of a cylindrical burner comprising multiple pairs of opposing partially premixed or inverse diffusion flames

A cylindrical burner was developed to combine extensive firing limits, high combustion efficiencies, and low NOx emissions from partially premixed or inverse diffusion flames by setting multiple pairs of circumferentially opposing jets (of concentric fuel and air streams). Normal strain rates as high as 1600 s−1 in addition to transverse strain rates of 640 s−1 were combined with a cross-flow impact and elliptical jet dispersion such that a turbulent kinetic energy peak of 15.4 m2/s2 was produced. The fuel/air mixing was enhanced and the peak temperature was reduced due to the stimulation of cross-flow wake zones and the axis switching of the elliptical jets. Partially premixed methane/air combustion of 12 opposing mixtures at Φ=1.5 led to NOx reduction to 0.36 g/kg fuel via controlling the flow residence time and adjusting the separation between the premixing and diffusion zones of each flame. As elliptical ports are used, the NOx concentrations decreased to 4 ppm with an aspect ratio of 3.0. Increasing the ratio between the diameter of the jets and their axial separation decreased the CO and HC emissions respectively to 489 ppm and 0.019%. Upon having opposing inverse diffusion flames, the blowout stability limit reached a maximum value of 53.2 m/s. With a separation of 4.0 cm, the NOx emissions reached a minimum level of 25 ppm by increasing the momentum flux ratio between the cross-flow air jet and the opposing jets to 1.5. By optimizing the cross-flow/primary air velocity ratio and the primary air/fuel jet diameter ratio, the CO and HC emissions were respectively minimized to 721 ppm and 0.039%. The velocity fluctuations indicated that increasing the opposing jets increases the turbulent kinetic energy and decreases the smallest scales of turbulence.

Results of the Field Operation of a Distributed-Flux Burner in a Heater Treater in a Northern Canada Heavy Oil Field: Thermal Performance and Firetube Life

Summary Horizontal heater treaters are commonly used to separate oil/water emulsions from enhanced oil recovery in heavy oil reservoirs. Conventional burners used in these heaters can cause hot spots that result in coking of the viscous emulsion on the outer surface of the firetube. This coking layer acts as an insulator and results in high tube-wall temperatures, leading to an early failure of the firetube. The problem may be exacerbated when polymer injection is used in the recovery fluid because of the increased viscosity of the fluid and the thermal breakdown of the polymer, which create a thicker insulating layer along the firetube. To reduce the coking and the resulting firetube failures, a conventional burner can be replaced with a radiant distributed-flux burner that spreads the heat over a much larger area, with a very uniform flame shape. The distributed-flux burner consists of a porous-ceramic cylindrical surface that provides surface-stabilized premixed combustion, such that combustion characteristics at every point along the cylindrical burner surface are nearly identical. This reduces the peak heat flux within the combustion zone significantly, reducing the likelihood of hot spots and the potential for coking compared with conventional burners. At the same time, more heat is distributed farther down the length of the firetube, increasing heat transfer in the rear section of the heater and improving its overall efficiency and heater throughput. Firetube life is increased because of the lower peak temperatures of the tube wall, and because less heat may be needed to achieve the required process throughput and water cut. This paper presents data from both pilot tests and field tests of a recent burner retrofit of a horizontal heater treater at an oil sands field in northern Canada. The retrofit was completed in a 2-day effort. On the basis of recent field data, thermal analysis, and measurements made in laboratory tests, the distributed-flux burner is compared with a conventional burner with respect to thermal efficiency and tube-wall temperatures.

Optimization of a premixed cylindrical burner for low pollutant emission

A premixed cylindrical burner is numerically and experimentally investigated to realize low pollutant emission. The geometrical parameters of nozzle exit position and nozzle diameter are optimized by using a validated Computational Fluid Dynamics model. The natural gas-air mixing in the mix chamber indicates that the uniformity of methane concentration increases with the increase of distance from ejector outlet. It is found that the nozzle exit position at −3.0mm improves the overall performance of premixed cylindrical burner, when nozzle diameter is not less than 1.6mm. The emission characteristics of nitrogen oxides and carbon monoxide are also examined by experimental approach. It is found that load factor has a great influence on nitrogen oxides and carbon monoxide emissions, but the effect is gradually disappeared when air coefficient is not less than 1.4. When nozzle exit position is −3.0mm, nozzle diameter is not less than 1.6mm and air coefficient is not less than 1.4, the emissions of nitrogen oxides and carbon monoxide are less than 20ppm and 50ppm, respectively.