Propagation Of Combustion Front Research Articles

Propagation of glowing combustion front in a packed bed of activated carbon particles and the role of CO oxidation

The propagation of a glowing combustion front in a packed bed of activated carbon (AC) particles was investigated with particular attention to the role of gas phase oxidation of carbon monoxide (CO). The AC particles were loosely packed in a cylindrical quartz column. A N2/O2 mixture of varying O2 concentration flowed through the bed from the bottom. Following ignition at the top of the bed, a glowing combustion front was formed and propagated downwards. Experiments were conducted at different oxygen mass fluxes with varying oxygen concentration and total flow rate. The bed mass loss rate, propagation velocity and temperature of the glowing front, were measured. A transient two-dimensional axisymmetric numerical model considering surface and gas phase reactions and transport properties were developed to describe the combustion phenomena. By comparing with the experiments, the validity of the proposed numerical model was confirmed. The results demonstrated that both the CO2 and CCO2 surface reactions contribute to carbon consumption and a constant mass loss rate is attained at a given oxygen flux. The gas phase oxidation of CO acted as a major heat source to sustain the propagation of combustion front through the bed. Suppressing CO oxidation would reduce the propagation velocity but may increase the combustion front temperature because of the prolonged residence time per unit of bed mass.

Experimental and numerical analysis of using thermochemical injection for preheating to improve in-situ combustion of bitumen

High production cost, inefficient energy utilization, high water requirement, and environmental pollution are the major challenges to heavy oil production through the conventional steam injection method. Thermochemical fluid injection is a novel and environmentally benign technology for in-situ generation of heat and nitrogen from the exothermic reaction of certain chemicals. Thermochemical stimulation offers several advantages including minimal heat loss and reduced emission of CO2 compared with steam injection. This study aims at harnessing the potential of injecting thermochemical fluids (TCF) to preheat the reservoir for improved in-situ combustion of bitumen (TCF-ISC). Bitumen sample was preheated using TCF (ratio: 10 ml TCF: 5 g bitumen) or steam. Thermogravimetric Analysis (TGA) was conducted to compare the combustion characteristics of original bitumen sample (B0), those pre-treated using steam (B1) and TCF (B2). In addition, numerical simulation studies were performed to evaluate the performance of the proposed process. The thermochemical reaction produced temperature and pressure of 67 °C and 1600 psi, respectively, and ΔH = 370 KJmol−1. The SEM-EDX analysis show that TCF treatment created open cavities on the matrix of the bitumen sample (B2) which strongly supports potential to increase thermal communication during the ISC process. The thermogravimetric analysis (TGA) show that the TCF treatment of bitumen sample improve combustion performance with higher exothermicity and reactivity. These results revealed higher combustion reactivity and higher potential for combustion front propagation with TCF. Moreover, numerical simulation confirms higher cumulative oil production (m3), oil recovery factor (%), and lower heat loss (GJ/m3) using TCF preheating before the ISC.

Effect of the Fluid–Vapor Phase Transition in the Combustion of Calcium with Iron Trifluoride

Combustion of a Ca–FeF3–Fe model system is under study. It is shown that the combustion front propagation in the Ca–FeF3–Fe system is a hot-spot propagation. The hot spots of ignition of calcium particles arise ahead of the front, followed by the expansion of the reaction zone until the hot spots completely merge with each other and with the formation of new centers of ignition in the heating zone. The dependences of the temperature and the burning rate on the degree of dilution with iron and pressure in the system are presented. Thermodynamic calculations are performed, and the calculated and experimental data are compared. Under the general tendency of an increase in the burning rate with increasing pressure, its decrease was found to be associated with the vapor–calcium metal liquid phase transition.

Simulation study on the effect of reservoir bottom water on the performance of the THAI in-situ combustion technology for heavy oil/tar sand upgrading and recovery

Some of the bitumen/tar sand/heavy oil reservoirs are underlain by bottom water (BW) layer, which often severely affects the performance of thermal EOR (enhanced oil recovery) processes. The effect of bottom water on the performance of the toe-to-heel air injection (THAI) in-situ combustion (ISC) process is investigated through reservoir simulation using CMG STARS simulator. The current study has shown that there is a limit to BW thickness above which the performance of the THAI process is affected even though the combustion front propagated stably. It is found that the thickness of the ‘‘basal gas layer’’ (BGL) depends on how further down into the BW zone the horizontal producer (HP) well is located. From this study, it is found that the critical BW thickness, when the THAI process is implemented in any heavy oil BW reservoir with the wells arranged in an SLD (staggered line drive) pattern, should lie in the range of 50% OL (oil layer) < BW (bottom water) < 100% OL (oil layer). A comparative study between the active and non-active aquifers models shows that the same cumulative volume of water is produced and that over the 715 days of the process, only negligible amount of oil is produced from BWN (i.e. static aquifer model). It is found that in neither of the models does oxygen bypass the combustion front and as in the previous studies, both fronts are restricted to the upper part of the reservoir, within the oil zone. Therefore, it follows that even in the presence of active aquifer (i.e. BWA model), the THAI process still operates stably in terms of combustion front propagation and sustenance. For the combustion initiated at the oil–water (O–W) interface, it is found that controlled gravity override resulted in a high rate of advancement of combustion front at the top of the reservoir. The combustion is observed to not propagate along the BGL, rather, it propagates as though it is initiated at the top of the reservoir. It is shown that the BGL is only formed during the early period of air injection as the combustion gases could not reach the HP well without displacing the water to create initial gas flow pathway into the HP well. It is also observed that initiating the combustion at the oil–water interface results in a massively improved oil recovery rates, most especially when implemented in the DLD (direct line drive) pattern.

Oxygen Index of Magnesium Powder

The combustion regimes were studied and the oxygen index for the bulk-density magnesium powder with a particle size of ~80 μm placed in a paper cup was determined in nitrogen–oxygen and argon–oxygen mixtures at pressures from 0.3 to 1 atm. It was shown that at a constant pressure of the mixture, there was a minimum concentration of oxygen at which sustained propagation of the combustion front was possible. The boundaries of the region of stable combustion of such a system in the pressure–oxygen concentration coordinates were determined. It was shown that, depending on the oxygen concentration, two combustion modes were possible: one-step mode far from the combustion limit and spin mode at the combustion limit. As the pressure or oxygen concentration in the mixture increased, the characteristic spin rotation time decreased and the propagation of the combustion front over the sample passed into a layer-by-layer mode. The dependence of the combustion front propagation velocity on the sample near the combustion limit on the mixture pressure and the oxygen concentration in its composition was determined.

Critical Conditions of Spark Ignition of a Bidisperse Aluminum Powder in Air

This paper presents a physicomathematical model and the results of numerical solution of the spark ignition problem for a suspension of a bidisperse aluminum powder in air. The critical ignition conditions of the aluminum-air suspension were determined numerically as a function of the particle size and mass concentration and the content of large and small particles in the suspension. The study has shown the effect of the fine particle fraction in the bidisperse aluminum powder on the critical spark ignition conditions of the aluminum-air suspension with the subsequent establishment of a steady regime of combustion front propagation.

The burning rate of coal-dust-air suspension

The paper provides the numerical investigation on the propagation of the coal dust-air combustion front. We determined the apparent and normal burning rate of the coal dust-air suspension depending on the size and mass concentration of coal dust and on the percentage of volatile components in coal dust particles. We also made an analysis on the influence of the percentage content of volatile components on the burning rate of the suspension with small and large particle radiuses.

A comparative study of heavy oil oxidation thermal behavior in the presence of Cu-Mn tallates

Heavy oil in-situ combustion process has many benefits among other thermal enhancing oil recovery methods. However, its application is still a complex task due to the irregular propagation of combustion front in the reservoir and its early breaking down. Recent finding regarding in-situ combustion development have led to use catalysts based on transition metals in order to stabilize and enhance combustion front flow. Transition metals was chosen rather than other types of catalysts because of their practical, feasible and economic impact in a wide range of industrial processes.Current solutions to catalytic in-situ combustion are inconsistent with their application in real fields due the problems associated to the injection of catalysts in the reservoir from one side and to the high cost that can be generated from the use of certain type of catalysts. In this context, we studied the effect of copper and manganese tallates in different metal ratios on the oxidation of heavy oil by applying various physical and physical-chemical methods. As a result, we have obtained accurate results demonstrating the potential effect of Cu-Mn tallates in stabilizing combustion front during high temperature oxidation reactions.

Effect of Heat Loss on Propagation Limits of Combustion Fronts in Heterogeneous Mixtures

ABSTRACTThe effect of heat loss on the propagation limits of combustion front is studied by considering one-dimensional chain of discrete point sources using two systems, namely (i) periodic and (ii) disordered. Each point source in the system is characterized by heat loss parameter (β). Unstable modes of combustion front propagation in periodic system have been detected with the manifestation of bifurcation patterns for different value of heat loss. Combustion front rate, quenching of combustion front for periodic and several disordered systems are investigated theoretically at different value of heat loss. It has been found that the heat loss in the nonadiabatic system does not affect the burn rate, although it plays a vital role in deciding the combustion limit. Theoretical results of combustion limit and burn rate have been compared with available experimental data.

Phase Formation in the Ti–Al–C System during SHS

The phase formation of Ti–Al–C powder mixtures with compositions close to MAX phases during self-propagating high-temperature synthesis (SHS) is investigated using time-resolved X-ray diffraction. It is found that the formation of the material during combustion in air under low heat-removal rates is a staged process. At the first stage, the dominant reaction is titanium carbide formation, providing major heat release and combustion front propagation. This reaction leads to the formation of TiC crystals surrounded by the Ti–Al melt. Titanium carbide is dissolved in the surrounding melt behind the combustion front with the subsequent crystallization of the Ti2AlC ternary compound. No TiC formation is observed during synthesis in helium, which provides rapid heat removal. The first phase appearing in the diffraction field is Ti2AlC. The TiC life cycle of 5–10 s for the mixtures synthesized in air substantially decreases when performing the process in helium and does not exceed 1 s. SHS leads to the formation of the composite material based on Ti2AlC phase containing less than 20 wt % TiAl and 2 wt % TiC. The material structure is characterized by lamellar Ti2AlC grains surrounded by the TiAl matrix. The microhardness of synthesized materials is 4.0–4.5 GPa and corresponds to the microhardness of the Ti2AlC phase. The dispersity of Ti2AlC grains during the synthesis in helium is lower than during the synthesis in air. Lamellar MAX-phase grains grow to 8–15 μm in length and 2–5 μm in width during slow cooling in air. The dispersity of Ti2AlC grains grown in helium is lower, being no larger than 8 and 1 μm, respectively.

Combustion Rate of Solid Fuels in the Superadiabatic Mode

Theoretical and experimental dependences of the combustion front propagation velocity in a layer of a solid carbon fuel on various external factors and conditions were examined in the case of filtration of the gaseous oxidizing agent. Particular attention was given to the superadiabatic modes with heat accumulation. It was shown that, in the case of a superadiabatic filtration combustion mode, the combustion velocity is primarily determined by the supply rate of the oxidizing agent and by the stoichiometric process ratio for particular conditions.

Diffusion mechanism of fingering in smolder combustion of thin solid fuel

ABSTRACTThe frontal propagation of smolder combustion of thin solid fuel in airflow in a narrow channel is considered. It is shown that the governing process that determines the propagation of the smolder combustion front is the diffusion of oxygen in flow and its absorption by the front. A two-dimensional thermodiffusion model of propagation of the smolder combustion front is considered and the equations describing the front propagation have been obtained. The solution of the equations was obtained in general form that allows constructing an algorithm for the numerical simulation. The stability of the planar smolder combustion front is investigated. It is shown that diffusion of oxygen and thermal conductivity in airflow are competing processes and can play either a stabilizing or destabilizing role depending on the mutual direction of airflow and the propagation of the smoldering front. So, if airflow occurs against the propagating smoldering front, the diffusion of oxygen in airflow plays a destabilizing role while the thermal conductivity is a stabilizing factor. If, however, airflow and the propagation of the smoldering front occur in the same direction, the phenomenon will be reversed. The diffusion of oxygen in airflow is a stabilizing factor while the thermal conductivity plays a destabilizing role.

Pore-scale modelling of the coupled thermal and reactive flow at the combustion front during crude oil in-situ combustion

A stable combustion front is important to achieve a successful in-situ combustion process for the crude oil recovery. The understanding of the multiple physicochemical and thermal processes at the combustion front is fundamental to reduce the potential risks, such as high burning temperature and low oxygen utilization. In the present study, a pore-scale modelling of the combustion front was employed based on the Lattice Boltzmann method to couple the fluid flow, heat and mass transfer and chemical reactions with the geometrical evolution. A thermal counter-slip algorithm was developed to solve the coupled interface conditions between conjugated heat transfer and heterogeneous reactions. The accuracy of the coupled lattice Boltzmann numerical models was validated by the finite element method. Pore-scale simulation was then performed to model the thermal and reacting flows through a two-dimensional model porous medium. The numerical simulation distinguished four characteristic regimes corresponding to different control mechanisms for the reacting flow. The study showed that the diffusion-limited mechanism is most desirable for the stable combustion in terms of the ideal burning temperature and full oxygen utilization. The control regime diagram was mapped on the Péclet-Damköhler plane for the specified computational domain. The effects of the Péclet and Damköhler numbers on the burning temperature, combustion front propagation velocity and oxygen utilization were then analyzed to obtain some insights about the control of the combustion front in the ISC process.

Front velocity in the combustion of blends of poultry litter with straw

The paper presents experimental studies on the burning characteristics of poultry litter and its blends with straw in the context of their potential usage in small-scale heat and power generation. For comparison purposes classic fuel such as wooden pellets was also investigated. The samples were analyzed in terms of water content, chemical composition and devolatilization, heating values, ash composition and ignition temperatures. An experimental analysis was performed of the combustion process of various sample beds in a small laboratory reactor that covered the temperature measurements and visual observations. This resulted in estimation of the speeds of ignition front propagation in the studied fixed beds, which is of general importance in the design of grate-fired furnaces. The combustion dynamics was discussed in terms of the physical properties of the bed, such as bulk density and porosity. The authors concluded that the main issue regarding the efficiency of poultry litter combustion was closely connected to a low bulk density of the fuel bed, which led to faster combustion front propagation but lower temperatures compared to a more dense fuel bed such as a wood pellet bed.

Micro-heterogeneous regimes for gasless combustion of composite materials

ABSTRACTReactive Ni/Al composite particles with different internal microstructures were fabricated by ball milling (BM). The propagation of gasless combustion waves through the compacted composite particle media was investigated using high-speed microscope video recording (HSMVR), with a resolution of 10 μm/pixel and 21.25 μs/frame. The microstructural combustion-wave characteristics, including hesitation time, propagation step size, instantaneous velocity, intraparticle reaction time, and average combustion-wave velocity, were studied as functions of measured internal microstructural parameters. The micro-heterogeneous relay-race combustion mechanism prevails across the investigated conditions. Decreasing the metal layer thicknesses in the composite particles leads to significant decrease in hesitation time, while only weakly affecting the instantaneous velocity. Characteristic times of hesitation and thermal relaxation defined two combustion front propagation regimes limited by interparticle heat transfer and by chemical reaction kinetics. Understanding the existence of these two discrete regimes allows us to effectively control the combustion parameters in this high-energy-density system.

Investigation of the combustion characteristics of Bati Raman oil with sand

In situ combustion (ISC) is one of the thermal oil recovery processes that has been applied in a variety of reservoirs. The energy is generated within the reservoir by a series of multi-step reactions that provide energy to heat the reservoir and reduce oil viscosity. Also, the oil is upgraded in situ by burning heaviest fractions.In this study, combustion characteristics of Bati Raman crude are investigated. The Bati Raman oil field is the largest known oil field in Turkey. Ramped temperature oxidation (RTO) experiments with effluent gas analysis (EGA) are performed with oil-sand mixtures having different sand particle size. The results are analyzed using isoconversional kinetic approach, which is a model-free method, based on effluent gas analysis and temperature measurements. Effective activation energy values are estimated for the sample with two different sand particle size. Besides, for the same samples, laboratory combustion tube experiments are conducted to evaluate ignition and combustion front propagation characteristics. Asphaltene content and API gravity of the oil sample prior to experiments and produced oil are measured and compared. Results indicate that the oil is upgraded through a reduction in asphaltene content.A complete set of kinetics and combustion experiments are provided for Bati Raman oil. There are only limited number of studies in the literature to link kinetic experiments to proposed reaction models of ISC. This work presents a way to link a reaction model to isoconversional fingerprint obtained through kinetic experiments. In addition, it is shown that Bati Raman oil exhibits good combustion characteristics and it is associated with its isoconversional fingerprint.

Effect of local rearrangements in the particle bed on the stability of filtration combustion of solid fuel

The effect of local rearrangements in the particles bed during filtration combustion is studied experimentally and numerically. It is shown that for upward gas filtration and propagation of combustion front, there exists a stabilizing mechanism. It is due to filling of caverns formed as the result of burning-out of solid fuel by the fuel mixture from overlying layers. This mechanism prevents deformations and decay of the combustion front. The stabilization effect has a threshold for the gas flow rate that corresponds to the minimal fluidization gas velocity in combustion zone. In case of downward gas flow and combustion front propagation, this stabilizing mechanism does not occur.

PHASE FORMATION IN TI–AL–C SYSTEM DURING SHS

The phase formation of Ti–Al–C powder mixtures with compositions close to the composition of the MAX phases in self-propagating high-temperature synthesis (SHS) was investigated using time resolved X-ray diffraction. It is found that material formation during combustion in air under low heat removal rates is a staged process. At the first stage, the dominant is the reaction of titanium carbide formation providing major heat release and combustion front propagation. As a result, TiC crystals surrounded by the Ti–Al melt are formed. Behind the combustion front titanium carbide dissolves in the surrounding melt and then the Ti 2 AlC ternary compound is crystallized. TiC formation is not observed with the synthesis in helium providing high heat removal rates. The first phase emerging on the diffraction field is Ti 2 AlC. The TiC life cycle of 5–10 s for air-synthesized mixtures is significantly reduced for helium processes and does not exceed 1 s. SHS reaction in helium yielded a Ti 2 AlC-based composite containing less than 20 wt.% of TiAl, and 2 wt.% of TiC. The material structure is characterized by laminated Ti 2 AlC grains surrounded by the TiAl matrix. The microhardness of synthesized materials was 4,0–4,5 GPa that corresponds to that of the Ti2AlC phase. Ti 2 AlC grains synthesized in helium are smaller than in air. Laminated MAX-phase grain sizes grow up to 8–15 μm in length and 2–5 μm in width at slow air cooling. The Ti 2 AlC grain size in helium is lower – up to 8 μm in length and 1 μm in width.

Effect of thermo-hydrodynamic instability on structure and characteristics of filtration combustion wave of solid fuel

Numerical modelling of flame front stability for the inverse wave (with trailing combustion front) of filtration combustion of solid fuel is performed. The problem is treated in terms of dimensionless variables and parameters. It is found that propagation of a plane combustion front becomes unstable under certain conditions. In this case the front spontaneously inclines. The thermo-hydrodynamic mechanism is supposed to be responsible for instability developing. Anisotropic effective mass diffusivity (dispersion) is also taken into account. It turns out that anisotropic diffusivity affects structure and conversion distribution of the inclined combustion front. It is shown that the key parameters determining stability of combustion wave are dimensionless gas flow rate and width of reactor. The range of these parameters corresponding to the stable plane front is determined. It is shown that stability occurs either for small reactor widths (dimensionless values <1), or low gas flow rate (below 0.2). The optimised values of considered dimensionless parameters for maximal productivity are determined.

Effects of disordered microstructure and heat release on propagation of combustion front

AbstractNumerical experiments for diagnosis of combustion of actual heterogeneous systems are performed on a one-dimensional chain. The internal microstructure of actual heterogeneous systems is apriori unknown, various distributions like uniform, beta, and normal have been considered for distributing neighboring reaction cells. Two cases, for the nature of distribution of heat release of reaction cells are taken into account, one with identical heat release and the other with disordered heat release. Role of different random distributions in describing heterogeneous combustion process is established in present paper. Particularly, the normal distribution of arranging neighboring reaction cells has been found to be powerful methodology in explaining the combustion process of an actual heterogeneous system at higher ignition temperatures for both cases of distributing heat release. Validation of the developed model with the experimental data of combustion of the CMDB propellants, gasless Ti + xSi system, a...