Porous Burner Research Articles

The enhanced strength and radiation efficiency of alumina reticulated porous ceramics via coal gangue addition

Al2O3 reticulated porous ceramics (ARPC) are widely selected for high-temperature porous media burners due to their excellent thermal stability. However, the relatively low mechanical property and infrared emissivity of ARPC led to a low lifespan and radiation efficiency of the burner, limiting its application in high-temperature porous burners. In this work, a novel strategy was proposed to synergistically improve mechanical and radiation properties of ARPC and recycle of coal gangue. ARPC with three-layered struts, including microporous alumina-mullite coating, alumina skeleton and filling layer, were prepared by polymer replica technique and vacuum infiltration method. The addition of coal gangue could obviously strengthen ARPC, because coal gangue was attributed to form mullite, as well as the generation of residual compressive stress in the coating of three-layered struts. The decomposition of organic compounds within coal gangue enhanced the degree of microporosity on the coating, thereby increasing infrared emissivity by 21.8%, which increased the surface temperature of porous burner from 857.4°C to 905.7°C.

Combustion of Raw Biogas/Hot Air in a Porous Radiant Burner and Performance Prediction Using a Machine Learning Algorithm

Abstract Combustion of raw biogas/hot air was performed in a porous radiant burner associated with a solar heater, and performance was predicted by a linear regression model using a machine learning algorithm. The test was conducted for the combustion of three different compositions of raw biogas mixtures having CO2 percentages of 25%, 30%, and 35% at the thermal load of 200–400 kW/m2. The hot air was supplied at an average temperature of 50 °C from the solar heater air supply system for proper combustion in lean mixture conditions. The porous radiant burner associated with a solar heater has offered radiation efficiency of 15.34–47.93%, NOX of 1–3.1 ppm, and CO of 25–87 ppm for three different compositions of raw biogas mixtures at the thermal load of 200–400 kW/m2 and equivalence ratio of 0.70–0.91. The increased radiation efficiency has indicated that the porous radiant burner can be an alternative for low-calorie fuel like raw biogas. Data analysis and processing have been performed using the machine learning algorithm, and the linear regression model has been developed using the python programming language. The error between predicted and experimentally calculated radiation efficiency is 1.67%.

Stable lean co-combustion of ammonia/methane with air in a porous burner

Ammonia is being considered as a promising zero carbon fuel due to its unique properties, while its combustion still poses challenges in term of instability and higher nitrogen oxides (NOx) emissions. In this study, the co-combustion stability of ammonia/methane with air under lean burn condition is experimentally investigated using a silicon carbide (SiC) ceramic foam burner with a two-layer structure stabilizing the flame. The influences of different operating parameters (methane fraction ω, equivalence ratio φ, and flow velocity V) on the co-combustion flame temperature and emissions are analyzed. The results indicate that the lean stable co-combustion of ammonia/methane with air can be achieved in two-layer ceramic foam burner, with its lower limit extending to φ = 0.5, even for the pure ammonia at specific operating conditions. Notably, the nitric oxide (NO) emissions decrease significantly as the equivalence ratio increases, particularly with a rise in methane fraction. The reduction can reach as low as 843 ppm with φ increasing to 0.9, further reducing to an ultra-low level of less than 150 ppm at φ = 1.3, significantly lower than those of traditional free flame burners. Carbon monoxide (CO) emissions remain at ultra-low levels, indicating the excellent co-combustion efficiency of ammonia/methane-air in the porous burner. An optimal co-combustion region with lower NO and CO emissions were conclusively identified. These findings demonstrate the effectiveness of porous media combustion in improving the co-combustion stability of ammonia/methane and reducing NO emissions, thereby helping to develop the porous burners of ammonia-based fuel and promoting its clean utilization for realizing carbon neutrality.

Experimental investigation on dynamic characteristics of methane/air combustion in double‐layer pellets porous media

AbstractThe double‐layer porous media burner is considered as an effective way to realize stable lean‐burn. In order to quickly achieve a stable combustion state in a double‐layer porous media burner, this work investigated the dynamic characteristics of methane/air premixed combustion in a bench‐scale double‐layer porous media burnspanning from ignition to stable combustion and ultimately flameout. The experimental results indicate that regulating the equivalence ratio and the inlet velocity enables the establishment of a stable flame front and the φ = 0.75 and the Vin = 0.20 m/s are the appropriate start‐up conditions. The average propagation velocity of the combustion wave variation along the axial direction and ranged approximately from −0.022 to −0.078 mm/s. Moreover, the transition time to a stable combustion state is reduced by nearly 47.14% as the equivalence ratio increases from 0.60 to 0.70. During start‐up stage, there are significant fluctuations in CO and NOx concentrations, but both emissions remain low during steady combustion state, with the maximum concentrations of 37.5 and 40.2 mg/m3, respectively. Furthermore, the porous media combustion exhibits a pronounced re‐ignition capacity. At higher equivalence ratios, longer interruptions of premixed gas are allowed.

Numerical investigation of premixed methane-ammonia combustion in a mesoscale porous combustor

The present study focuses on the numerical modeling of the premixed methane-ammonia combustion in a mesoscale porous combustor. The primary objective is to reduce carbon dioxide emissions by using ammonia as a carbon-free fuel while maintaining constant the combustor wall temperature compared to pure methane. Ammonia addition in the mixture increases nitrogen oxide compared to pure methane-oxygen combustion, which is undesirable. On the other hand, porous material improves fuel and air mixing and leads to more appropriate fuel distribution which could lower the combustion temperature and as well NOx emission. So, simultaneous using ammonia and porous media in the combustion is the effective combination to reduce the consumption of hydrocarbon fuels. In the current study, porosity of porous media is changed within the range of 50 %–90 %, molar fraction of ammonia is varied from 0.1 to 0.9, and equivalence ratios ranging from 0.8 to 1. Also, to find the optimal combustion parameters, the response surface methodology has been employed. The results indicated that to achieve satisfactory conditions for methane-ammonia-oxygen combustion in contrast to the combustion of pure methane-oxygen, it is the best condition to employ a porosity of 63 %, an ammonia mole fraction of 0.9, and a stoichiometric equivalence ratio. Because of the utilization of porous media, the mean wall temperature reached to 1543 K, indicating a 3.5 % reduction compared to pure methane combustion. Simultaneously, nitrogen oxide emission drops to 2270 ppm, showcasing a 10 % reduction compared to the non-porous media ammonia-methane combustion. Additionally, the use of the 0.9 M fraction of ammonia leads to a noteworthy 75 % decrease in the mass fraction of carbon dioxide emissions compared to pure methane combustion. These findings accelerate the optimal use of carbon-free fuels such as ammonia as alternatives to hydrocarbon fuels.

Lean Biogas-Air Mixture Combustion on Porous Burner with a Flamethrower Ignition System

ABSTRACT Combustion in a porous medium burner is an effective technology that deals with low heat capacity fuels, producing low emissions of pollutant gases. Experimental investigations of filtration combustion were carried out on a laboratory-scale prototype developed by our research group. This prototype is outfitted with a novel spark ignition system attached in the middle of the reactor, which does not change the porous medium properties because it works as a flamethrower. The ignition system produces a flame front into the porous matrix that quickly reaches the operational combustion temperature of 1200 K. By applying pure methane and biogas with different CO2 contents (15% − 40%) for combustion processes, the influence of equivalence ratio, gas flow velocity, energy extraction efficiency and NOx emissions was evaluated. Experimental results such as temperature profiles, reaction stability and flammability limits also have been evaluated. According to the operational parameters tested in this study, this prototype setup presented a low time-consuming process to reach the temperature of combustion, almost ten times faster than those with electrical resistance. Furthermore, the prototype was capable of operating at an equivalence ratio of 0.4 and gas flow velocity of 0.2 m/s, maintaining high CO2 content in the fuel, to reach NOx emission values lower than 1.0 ppm.

Analysis Study of Thermal and Exergy Efficiency in Double-Layers Porous Media Combustion Using Different Sizes of Burner: A Comparison

Experimental investigations are currently exploring the impact of adding porous layers within burner housing on thermal and exergy efficiency. Specifically, the focus is on understanding the significance of double layers on porous media combustion and how it can improve fuel mixing and flame stability. Premixed butane-air combustion in rich conditions was examined using three different sizes of burners (i.e., 23 mm, 31 mm, and 44 mm) porous media with equivalence ratios ranging from ф = 1.3 to 2.0. The experimental findings revealed a substantial improvement in performance efficiency (thermal and exergy) as the equivalence ratio increased. This study reveals that smaller burner diameters (ID, inner diameter = 23 mm) provide greater efficiency than larger ones (ID = 31 mm and 44 mm). The maximum flame temperature and porous wall temperature are found to decrease as the equivalence ratio increases. The highest temperature measured was 924.82°C for 23 mm, 910.23°C for 31 mm, and 850.76°C for 44 mm at ф = 1.3. Lastly, the thermal and exergy efficiency in a 23 mm porous media burner (PMB) is higher at ф = 2.0 at 84.30% and 83.47%, respectively. It can be concluded that the diameter size of the burner and equivalence ratio for double-layer porous material influence the performance (efficiency) of PMB.

60 Years of Open‐Celled Ceramics Based on Replica Technique: Applications, Obstacles, and Opportunities

Open‐celled ceramics look back on a remarkable history of development and innovation spanning around 60 years. Starting with the first patents to produce ceramic foams in the 1960s, the Schwartzwalder process became established industrially for manufacturing molten metal filters. Since then, a wide range of potential applications for these specific structured materials has been identified and discussed in the literature, such as porous burners, direct heaters, structured catalyst supports, filters, bone substitute materials, energy absorbers, preforms, and lightweight or acoustic construction components. For such high‐performance applications, ceramic foams require high quality in terms of purity, mechanical strength, high temperature, and chemical resistance or structural design. On this account, production technologies and material variety of ceramic foams have developed rapidly over the past few decades, and there are numerous applications in the industrial sector. This article gives an overview of the current state of development of open‐celled ceramic foams for various applications. Based on selected examples, it is demonstrated for which applications an industrial implementation is successfully realized and why some applications will never get beyond the proof‐of‐concept stage in research.

Optimization of performance and emission characteristics of liquid fuel fired porous medium burner using RSM and desirability approach

ABSTRACT The porous medium combustion (PMC) is an emerging area in liquid fuel combustion, which has the ability to reduce emission and increase the fuel economy. Various operational parameters will affect the performance of liquid fuel-fired Porous Medium Burner (PMB). So, this present work focuses on finding the effect of operational parameters on the performance of PMB and to optimize it. This study was conducted in a double-layered porous burner with self-aspirated pressurized stove. Three input factors were selected, namely, fuel pressure (bar), throttle angle (°), and type of burner (Conventional burner (CB), PMB). The three output responses selected are thermal efficiency (ηth), CO (ppm), and NOX (ppm) emissions. The inscribed central composite design (ICCD) was used to design the experimental run. The response surface methodology (RSM) with desirability approach was used to optimize the multi-objective responses. The statistical analysis with ANOVA confirmed the significance of all the three input variables on the output responses. The regression model was developed with quadratic fit and it well predicts the burner performance and emission with R2 value close to 1. The multi-objective optimum input settings are found by desirability approach, i.e. fuel pressure = 1.60 bar, throttle angle = 161.3°, and burner type = PMB. The corresponding optimized responses are found as ηth = 58.39%, CO = 201. 49 ppm, and NOX = 6.43 ppm. The above optimum settings and responses are confirmed with experimental confirmation test, which is in the satisfactory level.

Thermal performance of cocoa pod cook stove

Indonesia produces approximately 550.000 ton/year of cocoa pod waste from chocolate indus-try. The waste has a good potential to be used as a biomass feedstock of a cook stove. How-ever, thermal performance of the conventional cook stove is low when using a high moisture content feedstock, such as a cocoa pod waste. In addition, conventional cook stove generates high pollutant when high moisture content feedstock is used. In other to encounter the prob-lems, the present work develops gasifier based cocoa pod cook stove and investigates thermal performance of the stove at various equivalence ratios. The data collection is performed by varying equivalence ratio at 0.4, 0.5, and 0.6. Temperature of the stove, flame image, flame temperature, and water temperature are collected and used to analyze the thermal perfor-mance (i.e. useful heat and thermal efficiency) of the stove. The results reveal that a waste of cocoa pod can be used as a feedstock of gasifier based cook stove. Maximum useful heat of 1337.6 kJ and maximum thermal efficiency of 3.5% are obtained at optimum equivalence ratio of 0.5. To improve performance of the stove, the cocoa pod waste should be sun dried to reduce its moisture content and the porous burner may be applied as a burner of the gasifier based cook stove in the future work.

Impact of porous materials on the performance of a biogas porous burner

Impact of porous materials on the performance of a biogas porous burner

Temperature control of porous media burner based on advanced reduced instruction machine: PID algorithm and embedded processor

Against the backdrop of the rapid development of metal smelting processes, the requirements for reaction temperature control are gradually increasing, and the temperature control system for porous media burners based on advanced simplified instruction embedded processors has been developed. In this burner, the fuel is heated using a porous medium for conduction, which generates various complex data during operation and can overload conventional algorithms. To reduce the difficulty of algorithm operation, this study introduced an adaptive database into the proportional integral differential algorithm to classify data and establish a load balancer in the advanced reduced instruction algorithm, which is convenient for embedded processing of large amounts of data. To avoid the algorithm falling into local optima, this study merged the digital output module with it during temperature control to generate a fusion system. Finally, this study conducted experiments on the Porbu dataset and compared it with three systems such as generalized predictive control to verify the superiority of the fusion system. The temperature control accuracy of the four systems was 99.7%, 97.2%, 96.1%, and 93.5%, respectively, indicating that the efficiency of the fusion system performs the best among the four systems. The energy consumption of this system was 0.038 kWh, which performs best among the four systems. The experimental results indicate that the fusion system proposed in this study has the strongest performance and is suit-able for precise temperature control of porous media burners.

Stabilization of methane–hydrogen flames inside a divergent porous media reactor

The energy transition process triggered by the threat of climate change has created the need for cleaner heat generating systems. Using blends of hydrocarbons with increasing presence of green fuels, such as green hydrogen, has been proposed as an initial step of this process. The present study aims to investigate methane–hydrogen flames stabilized inside a divergent inert porous media burner. Experimentally, four stable operating points were found for the considered burner with a hydrogen presence between 0% and 30% in the fuel mixture at a constant thermal output of 2 kW. Temperatures are presented for each condition, noticing a decreasing trend as hydrogen presence was increased, since the equivalence ratio was gradually reduced to achieve stabilization. CO and NOx emissions were below 15 ppm for all studied cases. A 2-dimensional numerical model incorporating the GRI-Mech 3.0 mechanism was developed and validated against experimental data.The model revealed that the stabilized flame front is observed as a straight line that runs parallel to the radial coordinate. This line exhibits a slight curvature close to the burner wall, which is caused by heat losses and the influence of the divergent geometry. Solid surface temperature was not constant due to the reduced convective heat exchange with flue gases in the periphery of the burner. To reduce this issue a lower expansion angle is proposed as an alternative. In addition, changes in the chemical kinetics due to H2 addition were also evaluated. As results, a general trend towards reaction shifting was found with a 56% of the reactions being strongly promoted by H2 presence, which is associated with an increase in radical concentration in the flame front due to H2 decomposition.

Direct pore-level simulation of hydrogen flame anchoring mechanisms in an inert porous media

This work addresses the stabilization of hydrogen flames inside porous media. Hydrogen is a peculiar fuel with a large molecular diffusivity, triggering preferential diffusion and other effects related to non-unity Lewis numbers. Consequently, the macro-scale behavior of hydrogen flames is highly influenced by the flame-wall interactions at the pore-scale. In this study, direct pore-level simulations are used for the investigation of anchoring mechanisms and burning-rate enhancement for lean hydrogen flames embedded in inert porous media. It is observed that preferential diffusion greatly enhances flame anchoring, in the wake of the struts, leading to a high increase in flame surface. Also, the local heat release rate is enhanced not only by the higher gas temperature resulting from the heat recirculation but also by the higher local equivalence ratio resulting from preferential diffusion. Furthermore, most of the heat produced by a hydrogen flame is released by the hydroperoxyl reactions, effective at low temperatures but necessitating radicals, mostly H. These radicals are produced by the shuffle reactions, effective at higher gas temperatures. The coupling between those two reaction groups is very dependent on the transport of radicals, which can be impacted by the pore scale velocity gradient, leading to hydrodynamic dispersion and flame wrinkling. Consequently, it is shown that the burning-rate enhancement observed within porous burners fueled with hydrogen is not only due to heat recirculation but also to increased transports of radicals and preferential diffusion effects, which should be accounted for in macroscopic models.

Experimental and computational (Chemical Kinetic + CFD) analyses of Self-Recuperative annular tubular porous burner for NH3/CH4 -air Non-Premixed combustion

Ammonia is now being explored as a potential gas turbine fuel because of its renewable and carbon-free nature. Ammonia combustion possesses various limitations, such as high NO emissions, low burning velocity, and high auto-ignition temperature. Moreover, dual-fuel combustion approaches can be used to mitigate these drawbacks. However, the limitations of available information about the resulting emissions are insufficient to encourage widespread adoption. In this work, an NH3/CH4-air fueled self-recuperative high aspect ratio annular tubular porous burner is developed for gas turbine power applications. In this burner, an annular zone surrounds the combustion chamber to preheat the incoming air, while two perforated discs are mounted between the combustor and annular zone for uniform distribution of air. Eight Zirconia foams (4 of 10 PPI and 4 of 20 PPI) are stacked at the upstream side of the combustor. Experimentally, air preheat temperature, combustor exit temperature, NO, and CO emissions are analyzed and measured for various ammonia addition (0–41 % by weight) percentages, equivalence ratio of 1.0, and heat inputs of 17 & 21 kW for 10 PPI and a combination of 10 and 20 PPI porous foams. A preheated air stream coming from the annular zone speeds up fuel dissociation and helps in stabilizing the flame on the upstream side of the combustor. Combustor exit temperatures are lower in sandwich cases of 10 + 20 PPI than the porous foams of 10 PPI. However, with porous foams of 10 PPI, the air preheat temperature is higher. The insertion of porous foams shows better recirculation of heat and stable combustion is observed for higher percentages of ammonia and higher thermal inputs. The OH radicals are distributed for larger areas inside the dumb combustor, while for porous combustion, it is distributed near the porous foams. The porous sandwich cases of 10 + 20 PPI shows higher combustion efficiency compared to 10 PPI and without porous cases. The chemical kinetic analysis shows that the HNO and HCO radicals act as the main intermediate channel for NO and CO production.

A novel Fe2O3/Al2O3 porous media catalyst prepared by ultrasonic-assisted impregnation for low-concentration methane catalytic combustion

Porous media (PM) catalytic combustion offers a potential strategy for stable and efficient combustion of low-concentration methane (LCM). Herein, a porous media catalyst loaded with Fe2O3 as the active component (Fe2O3/Al2O3) was developed by ultrasonic-assisted impregnation for LCM catalytic combustion in a four-layer porous media burner. The influences of the gas flows, velocities, equivalence ratios, and PM arrangement patterns on the temperature distribution, combustion stability, methane conversion, and emissions were investigated in detail. The results indicated that the Fe2O3/Al2O3 catalyst possessed exceptional catalytic activity and thermal stability at medium-to-high temperatures, which broadened the limiting equivalence ratio for CH4 stationary combustion to 0.43 with the CH4 conversion exceeding 99 %. LCM enabled higher combustion stability in the PM burner with a gradually varied configuration, achieving steady combustion for more than 120 min under the lean combustion condition (0.43 equivalence ratio and 50 L/min). The high-quality flue gas from LCM catalytic combustion with an average temperature over 600 ℃, lower CO (< 150 ppm) and NOx emissions (< 10 ppm) could serve for the comprehensive utilization of power generation, heating, and cooling. The catalytic oxidation of LCM on the Fe2O3 surface was primarily divided into four steps with the second-step CH4 dehydrogenation in CH4 dissociation being the dominant rate-limiting step. This work proves that the catalyst fabricated by ultrasonic-assisted impregnation can effectively break through the lean combustion threshold, which provides a valiant reference for the clean and efficient utilization of LCM.

Effect of the Cross-Section of a Porous Burner on the Combustion Stability Limit of Premixed Oxy-Methane Flames.

This study presents the idea of using a porous media burner to improve the oxy-methane combustion reaction rate and broaden the stability limit. Numerical studies on the premixed combustion of CH4/O2/CO2 in a two-layer porous medium burner using a two-dimensional symmetrical volume-average model with the skeleton mechanism based on OpenFOAM. The combustion characteristics of burners with variable cross-sectional (VC) and straight cylindrical (SC) structures were compared, including stable range, temperature field, thermal cycle efficiency, and CO emissions. It is confirmed that the cross-sectional structure is effective for broadening the stable range, and the broadening rate is more than 4 times. As more heat is lost from the outlet due to the increased cross-section, the solid-phase temperature of VC is lower than that of SC. As a result, the flame temperature of VC will be about 200 K lower than that of SC under the condition of insulated walls. It also leads to a reduction of about 2% in thermal cycle efficiency compared with SC. Meanwhile, it is shown that the VC structure slightly increases CO emissions at low thermal power but is smaller than that of SC at high power. When the wall heat loss of the burner is considered, the VC structure is still effective for improving the stable range. In addition, the VC structure slightly affects flame tilt and temperature uniformity at the burner outlet when the thermal power is large. It is confirmed that the VC structure is effective for increasing the power adjustment range and reducing pollutant emissions at high power.

Thermal Radiation Characteristics of Cylindrical Porous Burner with Axial Supply of Combustible Mixture

Thermal Radiation Characteristics of Cylindrical Porous Burner with Axial Supply of Combustible Mixture

Syngas production by ultrarich oxy-natural gas combustion in a pilot-scale porous burner

A mixture of H2 and CO called syngas is a strategically important intermediate synthetic gas in chemical industries. A common production method of the syngas is catalytic steam reforming of natural gas which is limited due to the environmental and energy consumption subjects. In the current work, as a proper alternative, the ultra-rich thermal partial oxidation (non-catalytic) of natural gas was experimentally investigated to produce syngas with H2/CO ratio near two in a zirconia inert porous burner. High equivalence ratio aiming to extend ultra-rich fuel with pure oxygen (oxy-natural gas combustion) was considered at higher thermal loads by modifying the previous facility. The experimental tests were obtained at high thermal powers of 12–20 kW with equivalence ratios of 2.7 up to 3.1 where only pure oxygen was used as the oxidizer. Analyzing the product samples captured from the reactor output showed that a syngas with H2/CO of about 1.8 was produced at the equivalence ratio of 3.1 at 20 kW. The more thermal power was applied, the more H2/CO was produced with a greater conversion of natural gas within the reactor.

Thermal and structural performance of additively manufactured ceramic porous media burners

This study examines the effect of porosity, topology and material composition on the performance of additively manufactured ceramic porous media burners. Thermal-structural simulations of triply periodic minimal surfaces (TPMS) were performed to investigate thermal-stress magnitude and distribution. Alumina and mullite TPMS structures were 3D-printed and tested in a methane-air combustion experiment, where the mullite structures showed superior durability compared to alumina. X-ray imaging revealed notable correlation between predicted high tensile stress regions and experimental crack formation. At equivalent porosity and cell size, TPMS structures with higher specific surface area and tortuosity were found to have lower thermal strain and propensity for structural failure. Structures with these features, namely diamond and I-WP, demonstrated favorable thermal and structural behavior under identical thermal conditions. These findings can guide the design and manufacturing of high-temperature applications with embedded porous structures, such as heat exchangers, catalytic converters, and thermal management systems.