Porous Burner Research Articles

Visual investigation on optimizing combustion characteristic of porous media burner combined with bluff body

ABSTRACT Coalbed methane as an unconventional natural gas is suitable for the utilization in thermal photovoltaic systems through optimized burners. In order to improve the radiation and utilization efficiency of coalbed methane, a combination of bluff body and porous media was proposed. Moreover, the bluff body spacing and porous media structure were changed to analyze the influence on flame characteristics. The results showed that the maximum temperature and radiation efficiency increased with decreasing of bluff body spacing. When the bluff body spacing was 30 mm, the maximum temperature of 933 K was obtained, and the radiation efficiency increased by 68%. The increase of the equivalence ratio also improved the radiation efficiency, and the maximum radiation efficiency was 14.5% at φ = 0.90. In addition, the increase of inlet velocity and bluff body spacing was beneficial to downstream flame propagation, but had a negative effect on upstream propagation. At v in = 40 cm/s, the maximum downstream propagation velocity was 0.267 mm/s. Due to the difference in thermal conductivity, flame fragmentation occurred in the 8 mm pellets, but the flame propagation was gradually stable with the increase of bluff body temperature.

Experimental and numerical investigation on ultra-high intensity premixed LPG- air combustion in a novel porous stack burner

Experimental and numerical investigation on ultra-high intensity premixed LPG- air combustion in a novel porous stack burner

Toward pore-scale simulation of combustion in porous media using a low-Mach hybrid lattice Boltzmann/finite-difference solver

A hybrid numerical model previously developed for combustion simulations is extended in this article to describe flame propagation and stabilization in porous media. The model, with a special focus on flame/wall interaction processes, is validated via corresponding benchmarks involving flame propagation in channels with both adiabatic and constant-temperature walls. Simulations with different channel widths show that the model can correctly capture the changes in flame shape and propagation speed as well as the dead zone and quenching limit, as found in channels with cold walls. The model is further assessed considering a pseudo two-dimensional porous burner involving an array of cylindrical obstacles at constant temperature, investigated in a companion experimental study. Furthermore, the model is used to simulate pore-scale flame dynamics in a randomly generated three-dimensional porous media. Results are promising, opening the door for future simulations of flame propagation in realistic porous media.

On the drastic improvement of porous burner efficiency

On the drastic improvement of porous burner efficiency

Correction: Experimental investigation and heat transfer analysis of a natural gas fueled porous burner in domestic application

Correction: Experimental investigation and heat transfer analysis of a natural gas fueled porous burner in domestic application

Experimental studies on the role of thermoelectric module structure in developing a powerful miniature power generator with a meso-scale opposed flow porous combustor

At present, the rapid development of miniaturized electronic devices relies on energy sources with long endurance and high power density, leading to the demand for the comprehensive performance of combustion based micro-thermoelectric systems such as high power supply and high power density. In this study, a meso-scale opposed flow porous combustor was designed and an experimental platform for thermoelectric systems with observable flames was built with different thermoelectric modules. The influence of the thermoelectric module structure on the characteristics of the thermoelectric system is studied, which is based on experiments. An evaluation method based on λ is proposed to analyze the matching of thermoelectric modules with different system performance. The results show that the λ has a different non-linear relationship with the optimal load, output voltage and output current. The maximum output power (9.8 W), system efficiency (4.13 %), power density (0.17 W/cm3), and the conversion efficiency of thermoelectric module (6.12 %) are obtained by experiments. Compared with previous studies, the thermoelectric system in this study has outstanding comprehensive performance, which provides a guidance for the optimization of the thermoelectric system. At the same time, the results provide that the evaluation method has the ability to quickly identify the thermoelectric module and the suitable solution for the cold and heat source.

Combustion Performance of the Premixed Ammonia-Hydrogen-Air Flame in Porous Burner

ABSTRACT Flame stability and pollutant emission performances of a porous burner fueled with ammonia/hydrogen blend were investigated numerically in this study. In this regard, a 2D solver based on finite volume method was developed in order to simulate reacting flow and heat transfer modes through a porous medium. Combustion characteristics in terms of porous structure, equivalence ratio and fuel component were studied and the pollutant emission trends were discussed. Flame stability limit was observed to be extended with increasing equivalence ratio regardless to ammonia fraction. Results proved that addition of ammonia in the fuel blend reduced the flame stability limits and thermal flame thickness but led to the enhanced NO emission. Increasing equivalence ratio led to a decrease in thermal flame thickness under fuel-lean conditions while it caused that the thickness of flame zone to be increased slightly under fuel-rich conditions. It was found that flame stability limits were extended as the mean pore diameter of the porous medium increased. The maximum amounts of NO concentration were achieved at stoichiometric conditions while, NO emission increased as equivalence ratio increased at fuel-lean conditions and it decreased as equivalence ratio increased at rich combustion regimes.

Experimental investigation on the partial oxidation of methane with the effect of shrunk structure

Hydrogen energy is an ideal clean energy to solve the expanding energy demand and environmental problems caused by fossil fuels. In order to produce hydrogen, a double-layer porous media burner with shrunk structure was designed to explore the partial oxidation (POX) of methane. And the combustion temperature, species concentration and reforming efficiency were studied under different shrunk parameters and operating conditions. The results indicated that the shrunk structure greatly influenced the flame position and temperature distribution. The flame moved to the downstream section with the decreasing of the inner shrunk diameter and the increasing of the shrunk height. When the diameter of the filled Al2O3 pellets was 8 mm, the hydrogen yield reached the highest value of 43.8%. With the increasing of equivalence ratio, the reforming efficiency increased first and then decreased, and the maximum value of 53.0% was reached at φ = 1.5. However, the reforming efficiency and axial temperature kept increasing when the inlet velocity increased from 10 to 18 cm/s. The corresponding results provided theoretical reference for the control of flame position and species production by the design of shrunk structure in porous media burner.

Numerical investigation of an innovative furnace concept for industrial coil coating lines

In this work, the engineering performance of an innovative furnace concept developed for continuous drying and curing of paint-coated metal sheets (coil coating process) is investigated through advanced modeling and numerical simulation techniques. Unlike the traditional and wide-spread coil coating furnaces – which operate according to the so-called convective air-drying technology –, the present furnace concept relies on infrared radiative heating to drive solvent evaporation and curing reactions. Radiative heat is provided by the operation of radiant porous burners which are fed with evaporated solvents. The current furnace concept consists of two main chambers (the radiant burner section and the curing oven section) with different gas compositions (atmospheres) that are separated by a semi-transparent window. The window allows energy transfer and prevents gas mixing between the two sections. To utilize the solvent-loaded atmosphere available in the curing oven section as fuel – and to prevent the development of explosive conditions therein –, a novel inertization concept shielding the curing oven section from the external environment is considered. The current furnace concept aims at improving process intensification and promoting energy efficiency. For the current furnace concept, numerical simulation results support a suitable and competitive performance for drying the applied coatings in comparison with the traditional approach. Simultaneously, a safe operation is predicted, without (i) solvent leakage from the furnace and (ii) oxygen entrainment from the surrounding ambient into the furnace. These conditions are satisfied demonstrating a safe operation and a complete evaporation of solvents from applied liquid film coatings.

La-Ce-hexaaluminate doped by multivalent metal ion as the oxygen carrier for the optimization of hydrogen production

The efficiency of porous media combustion was greatly improved by combining the high-temperature catalyst of hexaaluminate. In this paper, a double-layer porous media burner filled with cylinders was built with the loading of La0.8Ce0.2MAl11O19 (M = Fe, Co, Cu). The effects of hexaaluminate and cylinders parameters on the products concentration and temperature distribution were studied at different working conditions. Results indicated that the La0.8Ce0.2CuAl11O19 obtained the excellent catalytic performance with the most adsorbed oxygen and oxygen channels, so that the maximum hydrogen mole fraction was achieved. With the increasing of the 13 mm cylinders volume ratio from 0 to 1, the hydrogen and carbon monoxide yield increased by 53.3 % and 50.9 %, respectively. Meanwhile, the increased heat releasing of the higher velocity contributed to improving the combustion temperature and syngas production. These results provided theoretical guidance for the catalytic porous media reactor in energy utilization and environmental protection.

Numerical investigation of extracted position characteristics in porous media with lean methane and air premixtures combustion

Hydrogen production through steam generated from low-grade fuel recovery is considered a prospective method. To maximize the energy recovery, the influence of the heat exchanger position on the heat extraction stability of lean methane-air premixtures combustion in a porous burner has been numerically explored. The extracted position coefficient (EPC) is defined and a heat extraction model is validated through the experimental findings. It is shown that extracted position has a significant influence on the temperature profile, heat transfer capacity, heat loss as well as heat recovery rate. When the EPC is lower than 0.18, the filtration burner shows worse stability with great heat loss, the heat transfer behavior of the heat exchange tubes is severely weakened and heat recovery efficiency is merely about 13%. The optimal heat recovery position is recommended in the EPC range of 0.36–0.55, which has shown excellent heat extraction performance and accelerated the process of acquiring a quasi-steady state. Within this EPC range, the fluctuation of outlet temperature difference can be stabilized within 0.2 K, which maximizes the heat flux of heat exchangers, and heat recovery efficiency of about 70%–89% recovered with a concentration of 0.4%–0.8%.

Experimental investigation on flame stability and emissions of lean premixed methane–air combustion in a developed divergent porous burner

Flame stability and pollutant emissions are issues of the greatest concern for low-calorific-value gas combustion. Although the conventional straight porous burner is conducive to improving the flame stability, it still cannot meet the industrial demand. To improve the flame stability and reduce the pollutant emissions during fuel-lean combustion, a divergent double-layer porous burner was creatively proposed in this study. The influences of the inlet velocity and equivalence ratio on the flame stability, temperature distributions, the emissions were experimentally investigated in detail. The results showed that the flame front gradually moved downstream, the preheating zone length increased as the inlet velocity increased. Compared with the traditional straight porous burner, the divergent porous burner extended the blowout limit by 300%. Since the burner was operated under fuel-lean conditions (the equivalence ratio range was 0.45–0.6), the CO emissions were relatively high when the inlet velocity was less than 0.4 m/s. When the inlet speed was equal to or greater than 0.4 m/s, the maximum CO emissions concentration was 132 ppm. The burner showed superior performances in terms of NO emissions, with emissions concentrations of less than 20 ppm under all test conditions. In summary, the great advantage of the divergent porous burner lies in extending the flame stability limit. For clean combustion it is recommended that the burner be operated at a higher velocity (greater than or equal to 0.4 m/s) to obtain lower CO and NO emission levels.

Transition to unstable oscillatory flames in porous media combustion

The flames inside porous burners with low filtration velocity are prone to oscillatory behavior similar to unstable combustion in narrow channels but accompanied by complicated dynamics due to the irregularity of porous structure, flow field, and thermal gradient formed as a result of heat recuperation. This work is a numerical study within the framework of the pore-scale simulation approach devoted to investigating the flame oscillation mechanisms and characteristics in a two-dimensional pseudo-irregular packed bed of particles generated using the Voronoi tessellation algorithm with constant pore size. The results demonstrate that unstable flame oscillations like flames with repetitive extinction and ignition (FREI) lead to the velocity pulsation in adjacent pore channels, where the stable flame fragments are exposed to the hydrodynamically-driven fluctuations. In the case of the flow rate close to the stability threshold, the flow pulses can reach a magnitude enough to shift the stable flame in the upstream quenching zone, promoting its oscillations with repetitive extinction and ignition. Results of parametric simulation with a variation of the particle diameter and flow velocity were summarized in the regime diagram revealing the transition between stable normal flame, FREI, and stable weak flame with the velocity reduction. The pulsating transitional regime was detected between the stable normal flame and the FREI. The amplitude and intensity of such pulsations increase monotonically with the flow rate reduction in a narrow range. Oscillations of the unstable flame and hydrodynamically-driven flame pulsations are similar in dynamics but different in their physical mechanisms. However, in irregularly packed beds of particles, both these phenomena unavoidably coexist and interfere significantly with each other due to the connectivity of the pore channels.

Modulation of Heat Transfer in a Porous Burner Based on Triply Periodic Minimal Surface

Abstract The list of reacting flows in porous media applications is quite long, including porous media combustion, syngas production, and fuel cells. Porous media combustion is recognized as a cutting-edge combustion technique for increasing flammability. In this process, heat is transferred from the exothermic reaction zone to the incoming reactants through porous media. This role of porous media distinguishes reacting flows in porous media from free combustion processes. Local heat transfer, such as solid conduction, solid–solid radiation, and solid–gas convection, as well as the response behavior, are affected by the topology of the porous material. Theoretical studies indicate that continuously graded porous materials can significantly enhance the performance benefits of heat transfer. However, topology design is challenging for smooth graded porous media, and thus investigations of combustion within graded porous media are still required. In this study, we constructed a porous structure of type W/P/D/G (porosity ε = 0.3–0.5, hydraulic diameter dh = 1.33–3.86 mm) using a triply periodic minimal surface (TPMS), and a computational model of the combustion reaction in porous media was established to compare the range of flame stability within different pore types. In addition, topology gradation was achieved via TPMS to modulate the heat transfer to ensure the dependable functioning of premixed flames and improved heat recirculation. Heat transfer in the graded TPMS-based porous structure was analyzed numerically. The conclusions obtained from this study can effectively address the aforementioned challenges related to porous media burner design.

Modelling challenges of volume-averaged combustion in inert porous media

In porous burners, the flame thickness can be smaller than the pore size, resulting in sharp and locally-anchored flame fronts. The presence of such steep gradients at the pore level is a major hurdle for the derivation of volume-averaged models, particularly for the highly non-linear reaction rates. With the intent to address the difficulties associated with volume-averaging for porous media combustion, this work makes use of 3D Pore-Level Direct Numerical Simulations including conjugate heat transfer and complex chemistry in burners of finite length. These detailed 3D simulations are compared to their 1D volume-averaged counterpart, with effective properties estimated directly on the computational domains and of identical thermo-chemical scheme. Discrepancies in terms of burning rate, profiles, and a priori analysis on the reaction rates are discussed. Various pore sizes and geometries are considered. At the pore level, it is shown that preheating, wrinkling and wall quenching are the three main factors driving the global burning rate. Importantly, hydrodynamic dispersion is shown to have an indirect role on combustion processes. From the observations of combustion at pore scale, a new closure for reaction rates based on a flamelet assumption is proposed. It accounts for flame wrinkling and eliminates the unwanted effect of hydrodynamic dispersion on burning rate.

Modelling of Catalytic Combustion in a Deformable Porous Burner Using a Fluid–Solid Interaction (FSI) Framework

The various concepts involved in the mathematical modeling of the fluid-solid interactions (FSIs) of catalytic combustion processes occurring within a porous burner are presented and discussed in this paper. The following aspects of them are addressed: (a) the relevant physical and chemical phenomena appearing at the interface between the gas and the catalytic surface; (b) a comparison of mathematical models; (c) a proposal of a hybrid two/three-field model, (d) an estimation of the interphase transfer coefficients; (e) a discussion of the proper constitutive equations and the closure relations; and (f) a generalization of the Terzaghi concept of stresses. Selected examples of application of the models are then presented and described. Finally, a numerical verification example is presented and discussed to demonstrate the application of the proposed model.

Second stage porous media burner for syngas enrichment

The syngas production from hydrocarbons by porous media combustion (or conventional gasification) processes has been intensively and extensively studied due its calorific value and its applications in the energy sector. However, the syngas produced in a first stage gasifier can still have concentrations of light hydrocarbons (e.g., methane) which can be post-processing for further enrichment of hydrogen and carbon monoxide. The present work numerically investigates the performance of a second stage porous media burner to enrich the syngas content, mainly hydrogen and carbon monoxide. A one-dimensional model based on a two-temperature approximation is implemented, based on the PREMIX code, and supported by CHEMKIN and GRI-MECH 3.0 database and routines. From hybrid porous bed reactor experiments, five types of mixtures in the equivalence ratio range between 0.4 and 2.4 are tested: pure methane as baseline, pure Eucalyptus nitens syngas, pure Pinus radiata syngas, and two mixtures of methane with each of the biomass syngas in equal volume quantities, as transition points. The results obtained show that in the enriched syngas, in comparison to the first content after the first stage reactor, the concentrations of hydrogen and carbon monoxide increase, due to the partial oxidation of methane, however part of the hydrogen is consumed in the process. The intermediate species present in methane processing for pure syngas mixtures have broader reaction zones and in lower concentrations compared to the use of pure methane. For equivalence ratios greater than 1.9, pure syngas mixtures show higher conversion efficiencies compared to the baseline. At the equivalence ratio of 2.4, the pure syngas from Eucalyptus nitens and Pinus radiata has an energy return over energy invested (EROI) of 58.27% and 53.95%, respectively, and a maximum hydrogen and carbon monoxide yields of 31.66% and 48.40%, respectively. In the case of the Pinus radiata, the outlet syngas concentrations of the hydrogen and carbon monoxide on dry basis expose an increment about two times in comparison to the initial concentrations.

On non-premixed flames of dual porous cylinders in tandem

A porous burner is one of the most efficient combustion devices nowadays due to its recycling features of heat and burning performance. To exploit its advantages for a wide range of external fields, we propose a novel arrangement in terms of tandem porous cylindrical burners and investigate the applicability, specifically on the extension of extinction limits under forced convection. A key parameter is the separation distance (L), presented as a ratio to the cylinder diameter (D). The results of paired cylinders in terms of various experimental and simulation techniques demonstrate superior features of flow pattern, specifically on its stabilization, and thermal interaction achieved by using the tandem array, which led to widened extinction limits at the same total fueling rate. It was found that the extension of the extinction limit reached the maximum near L/D = 1.4. A smaller L/D may discourage entrainment of air into the gap between the cylinders due to inhibition of large vortices, causing the reaction zone to move outward from the gap where the flow is relatively stable. For a larger L/D, the performance degraded due to degeneration of favorable thermal interactions behind the cylinders and excess cold air drawn into the gap by strong vortices.

Experimental analysis and performance of refinery fuel gas on lean and rich fuel–air premixed combustion

Refinery fuel gas (RFG) is a blend of gas streams produced as by-products in various refinery processes. Large amounts of RFG are burning around the clock in the air with thermal energy waste and adverse effects on the environment. The present work investigates experimentally the performance of different compositions of RFG from lean to rich fuel–air premixed combustion, with focus on an efficient and low-emission combustion for its heat recovery. Radiant and porous media burners are the combustion technologies used. For the radiant burner, fuel compositions are propane and ethane with an average ethane ratio of 5%, 10%, and 15% (E05, E10, E15 respectively), which are contrasted with pure propane and liquefied petroleum gas (LPG). The pure gases fluxes are fixed as 1 and 2 m3/h for low and high flame configurations, respectively. The lean fuel–air flames investigated are stable for all ethane ratios with low carbon monoxide (CO) and nitrate oxides (NOx) emissions. Maximum temperature is given by pure propane flame (besides LPG), followed by E05, E10 and E15, for both flame configurations. Then, the radiation heat flux of ethane mixtures exhibits a reduction in comparison with LPG. For the porous media burner, lean and rich fuel–air mixture composed by natural gas (NG, 97% methane) and representative flue samples of 55% (C1) and 70% (C2) methane concentration are tested. The C1 and C2 flue samples present high combustion temperatures, showing a positive swap from NG. The NG rich-fuel combustion exposes high hydrogen conversion (27%) at high equivalence ratio (ϕ=1.8). Finally, for both burners lean fuel–air premixed combustion shows high combustion efficiencies, 74.8% with E05 and 80.7% with C1 flue sample.

Experimental and numerical investigation of flame stabilization and pollutant formation in matrix stabilized ammonia-hydrogen combustion

Ammonia (NH3) is a carbon-free fuel that offers an attractive alternative for reducing greenhouse gas emissions. However, the slow flame speed, low heating value, and emissions of nitrogen-containing pollutants present significant issues for practical combustion applications. To address these issues, we investigate the use of matrix stabilized combustion. In this type of burner, combustion is performed within an inert porous ceramic foam, heat is recirculated by solid conduction and radiation, which enhances flame speed and combustion stabilization, thereby permitting combustion over a wide range of equivalence ratio conditions. We present a new porous media burner (PMB) capable of stabilizing NH3/air flames at ambient conditions. An extensive experimental characterization of the stability of this burner is conducted with up to 30% by volume of hydrogen (H2) in the fuel stream. A 15:1 turndown ratio is demonstrated, with a high thermal power density of 62MWm−3. Concentrations of NO, unburnt NH3, and H2 in the exhaust stream are measured. Two regimes are identified for low NO operation: rich and very lean. For rich conditions, NO emissions decrease with increasing equivalence ratio and decreasing H2 blending. Unburnt NH3 emissions follow opposite trends. These measurements are complemented by simulations in which the burner is represented by a coupled solid-gas reactor network. This model captures the burner’s pollutant emissions to good accuracy and is used to analyze the mechanisms of pollutant formation.