Internal Recirculation Zone Research Articles

A novel swirl burner with coal co-firing ammonia: Effect of extension length of the dual-channel ammonia pipe on combustion and NOx formation

The coal/ammonia co-firing technology for thermal power generation is a feasible method to effectively reduce CO2 emissions. However, the easy formation of NOx is one of the challenges faced by this technology owing to the high nitrogen content in ammonia. This study proposes a novel swirl burner with a scalable dual-channel ammonia pipe, and evaluates the combustion and NOx formation under different extension lengths of the dual-channel ammonia pipe (i.e., 0 m, 0.4 m, 0.8 m, 1.0 m, 1.2 m). The results show that the extension length of the dual-channel ammonia pipe significantly affects the flow, combustion, and NOx formation. When the extension length of the dual-channel ammonia pipe is above 0.8 m, the ammonia stream can completely penetrate the internal recirculation zone into the high CO environment, which contributes to promoting the ammonia pyrolysis and inhibiting the ammonia oxidation to form NOx. NOx emissions significantly decrease from 846 ppm to 146 ppm as the extension length of the dual-channel ammonia pipe from 0 m to 0.8 m, but change slightly as further increases from 0.8 m to 1.2 m. The carbon content in fly ash decreases from 4.53% to 3.40% as the extension length of the dual-channel ammonia pipe increases from 0 m to 1.0 m. Still, it increases from 3.40% to 3.70% as the extension length of the dual-channel ammonia pipe rises to 1.2 m. Overall, it is reasonable to set the extension length of the dual-channel ammonia pipe at 1.0 m in this studied condition, which can obtain low NOx and low carbon content in fly ash.

Natural draft direct dry cooling system performance at various application scales under windless and windy conditions

The natural draft direct dry cooling system (NDDDCS) presents a promising alternative to conventional forced draft air-cooled condensers (ACCs) and indirect natural draft dry cooling systems, overcoming their limitations by efficiently condensing process steam directly and passively. The NDDDCS achieves superior thermal efficiencies while reducing system complexities, operational costs, and auxiliary power consumption. Potential reductions in operational expenses for the system may offset initial capital investments, resulting in lower lifetime costs. While research to date has focused on large-scale NDDDCS performance under varying wind conditions, this work addresses a critical gap by investigating the system’s scalability for various applications, including a large-scale coal-fired power plant (900 MWt, 165 m total height), a medium-scale concentrated solar power plant (CSP) (100 MWt, 65 m total height), and a small-scale water desalination plant (1 MWt, 11.5 m total height) under both windless and windy conditions. To achieve this, a steady-state 3-D computational fluid dynamics (CFD) model is developed, validated and scaled, incorporating innovative features such as an atmospheric pressure gradient and the ability to capture reversed flows through the system’s heat exchangers. Additionally, the model assesses inlet air temperature data at a per-cell resolution, enabling the ability to predict non-uniform temperature distributions in the heat exchangers, including hot-spots caused by airflow recirculation. Analysis of velocity and temperature fields across all scales reveals that recirculation effects negatively impact NDDDCS performance, particularly at the middle circumferential heat exchanger sector. The hyperbolic shape of the tower shell induces internal recirculation zones and reduces the effective flow volume. Under windy conditions, performance losses of 44%, 40%, and 40% are observed at crosswind speeds of 3 m/s, 6 m/s, and 9 m/s for small, medium, and large-scale towers, respectively. Beyond these speeds, the relationship between system performance and draft driving potential becomes non-linear due to crosswind effects dominating. Furthermore, a novel effect is identified at wind speeds of 9 m/s, 15 m/s, and 18 m/s for small, medium, and large-scale systems, respectively, where an inflection point allows for system performance recovery. This study underscores the NDDDCS’s potential as a cooling solution for modern power cycles across various scales, while highlighting the implications of scaling the system for medium- and small-scale thermal applications.

The effect of the dielectric barrier discharge plasma actuator in the control of non-reactive flow in a non-premixed bluff body burner

Active flow control methods based on dielectric barrier discharge plasma actuators can be used to increase the efficiency of combustion systems. In this study, the influence of the location of plasma actuators on the bluff body in a non-premixed burner on the non-reactive flow field of fuel and oxidizer is investigated numerically. Flow field properties and spatial mixing deficiency (SMD) are calculated to evaluate the plasma actuator's influence on the reactants' mixing inside the burner. The results show that the plasma actuator can influence the recirculation areas and are effective in mixing fuel and oxidizer. The presence of the plasma actuator results in the formation of a vortex, which slows down the movement of the flow and improves the mixing between the fuel and airflow streams resulting in more favorable combustion. The results show that at a higher air velocity (4 m/s), the formation of a plasma zone near the air duct strengthens the external circulation zone (ERZ) in such a way that it surrounds the internal recirculation zone and reduces the value of SMD by an average of 7.89%. While activating the actuator also strengthens the ERZ for a lower air velocity (0.3 m/s), this affects the air inflow, and the flow field becomes dominated by the fuel jet flow. When the diameter of the bluff body is increased, both when the plasma actuator is active or inactive, the ERZ is greatly strengthened, and the flow field is more dominated by the airflow.

Influence of pilot H[formula omitted] injection on methane-air swirled flame stabilization and acoustic response

Large Eddy Simulation is used to investigate the effect of localized pilot H2 injection on the Flame Transfer Function (FTF) of a premixed CH4-air swirled flame. The response of a perfectly premixed methane-air flame is compared to the one with an additional pilot hydrogen injection that supplies 10% of the original power. Numerical simulations are validated against experiments in terms of global FTF values at selected forcing frequencies, acoustic pressure and velocity signals, CH* flame images and flame root position dynamics. The unforced cases are first considered showing that, when H2 is injected in the center, the flame becomes slightly lifted with a localized diffusion front above the pilot injection. As in the experiments, LES retrieves that hydrogen pilot injection leads to a global redistribution of the heat release rate towards the flame root due to higher burning rates which translates to an overall FTF gain reduction over the entire frequency range explored. Then, the flame acoustic response for the two injection strategies is scrutinized at two distinct forcing frequencies: 240 Hz where the FTF gain difference is maximum, and 590 Hz where the FTF phase shift is maximum. LES reveals that, despite H2 pilot injection does not modify the dynamics of the large vortical structures shed in the external shear layer of the swiling jet which are synchronized by the acoustic forcing, the redistribution of the heat release rate towards the flame base weakens their interaction with the flame tip, explaining partly the FTF gain reduction at the two selected frequencies. In addition to that, a marked axial movement of the internal recirculation zone is observed at 240 Hz during the forcing cycle. For the pilot injection, it leads to an oscillation of the lifted flame root while, for the CH4-air case, the flame anchoring point is not affected. This additional oscillation leads for the pilot case to heat release rate fluctuations acting in phase opposition with respect to those observed at the flame tip, generating a further drop of the FTF gain at this specific frequency. The increased burning rate at the flame root and the flame length reduction of the pilot hydrogen flame also affect the characteristic time lag of the flame response. For both frequencies f = 240 Hz and 590 Hz, the phase shift between the two injection strategies is proportional to the flame length reduction caused by hydrogen injection. These simulations confirm that pilot hydrogen injection is an efficient way to reduce the acoustic response of swirled flames over a large frequency bandwidth.

Characterizing Swirl Strength and Recirculation Zone Formation in Tangentially Injected Isothermal Flows

This paper presents a computational study characterizing the swirl intensity distribution and Internal Recirculation Zone (IRZ) formed in a cylindrical domain with tangential injections and isothermal flow. The range of inlet boundary conditions investigated is 5o to 25o for the injection angle and 7190 to 100711 for the bulk flow Reynolds number. The evolution of swirl intensity is presented with and without incorporating effects of the accompanying pressure variations. The Shear Stress Transport (SST) k-ω is used to model turbulence. Results show that the Swirl strength created by such tangential injections strongly depends on the injection angle but does not vary with bulk flow Reynolds number (Re), except for low Re values. The swirling flow is shown to result in IRZ formation at injection angles 6o and above or when asymptotic value of the maximum Swirl Number in the domain exceeds approximately 0.6, same as the transition value of inlet Swirl Number in swirling flows with axial injections. The IRZ length increases with injection angle and varies with Re for lower values of Re at a given injection angle but asymptotes for higher values above 40000. The conventional Swirl Number rises rapidly downstream of the injection plane followed by a slow decline. On the other hand, an alternative Swirl Number, which incorporates the gauge pressure variation, shows slow and consistent decay all the way downstream of the injection plane. The Swirl Number incorporated with gauge pressure term subsumes interconversions between the axial momentum and pressure in the regions of vortex breakdown and IRZ formation, thereby presenting an alternative picture of swirl intensity evolution in swirling flows.

E-POD investigations of turbulent premixed flame dynamics approaching lean blow-out conditions

Thanks to the continuous computational power increase, the use of high-fidelity computational fluid dynamics (CFD) simulations is nowadays customary, especially in the gas turbines design process. The extraordinary temporal and spatial detail of such analyses generate large datasets, which must be carefully studied to correlate different quantities and gain information to characterize the behavior of combustor designs. Several advanced post-processing tools have been proposed; however, the Extended-POD (E-POD) holds the greatest potential for turbulent combustion applications when the mutual influence of different quantities is the main goal of the investigation. The present work investigates the application of the E-POD to an LES model of a perfectly-premixed, swirl-stabilized, methane-air flame approaching Lean-Blow-Out. Leveraging the validation against the experimental data at two different operating conditions on a laboratory test case, the numerical model has been used to collect several quantities of interest for shedding light on the flow-flame interaction near the blow-out. The post-processing algorithm has been used to highlight the differences between two conditions approaching the extinction at distinct air-flow velocities. It has been found that, when the burner is operated with a higher velocity, the flame is subjected to a cyclic low-frequency breakdown around the internal recirculation zone, leading to an ingestion of cold products from the external parts of the combustor toward the center. Although other local effects acting on the flame brush have been found in both conditions, they are related mainly to higher order coherent structures with a lower energy content. As a result, their impact onto flame stability is found to be of secondary importance since their limited interaction with flame stabilization. The work shows that E-POD represents a powerful tool for investigating the key features of flame dynamics even at near-blow-out conditions, constituting a valid algorithm for interpreting the results of CFD analyses on gas turbines combustors.

Flamelet LES of a 40 kW[formula omitted] pulverized torrefied biomass furnace in air and oxy-fuel atmospheres

For the first time, large-eddy simulations are conducted for a 40 kWth self-sustained pulverized torrefied biomass furnace in air and oxy-fuel atmospheres using an extended flamelet model. A recently developed chemical reaction mechanism specifically for oxy-fuel combustion (117 species and 840 elementary reactions) is employed. The simulation results are compared to the experimental data, including the axial and tangential velocities and selected species mass fractions. In addition to this, certain characteristics are investigated: the flame structure, thermo-chemical variable distributions and the NOx emissions in different atmospheres. The flame in the oxy-fuel atmosphere is predicted to be longer and broader than that in the air atmosphere. The main reason for this is the significantly different flow dynamics in different atmospheres that are specifically designed to achieve the same oxidizer-to-fuel ratio near the burner. Two external recirculation zones (ERZs) and a central internal recirculation zone (IRZ) exist in the air atmosphere due to the designed boundary condition with a strongly swirled flow. In contrast, only a single ERZ and a weak IRZ can be observed in the oxy-fuel atmosphere. These different flow dynamics significantly influence the torrefied biomass combustion characteristics for the two atmospheres. Overall, the combustion characteristics in the air atmosphere exhibit features which are expected for a strongly swirling flow, while the thermo-chemical variable distributions in the oxy-fuel atmosphere are similar to those of a jet flame. It is also found that the atmospheres have significant effects on the NOx emissions, particularly for the furnace studied, which features staged oxidizer combustion.

Flame characterisation of gas-assisted pulverised coal combustion using FPV-LES

A multiphase flamelet/progress variable (FPV) model for the large eddy simulation (LES) of gas-assisted pulverised coal combustion (PCC) is developed. The target of the simulation is the Darmstadt turbulent gas-assisted swirling solid fuel combustion chamber. The coal particles are treated as Lagrangian point particles, the position, momentum and energy of which are tracked. The gas phase is described by the low-Mach Navier-Stokes equations alongside the Eulerian transport equations of the governing variables for the FPV model. The set of chemical states of the PCC flame is pre-tabulated in a six-dimensional flamelet table and determined by the mixing of the primary fuel stream, volatiles and char off-gases with the oxidising air, the progress of chemical reactions, the interphase heat transfer, as well as sub-grid scale variations. A presumed β-PDF approach for the total mixture fraction is applied to capture sub-grid scale effects. The discrete ordinate method (DOM) with the weighted sum of grey gases model (WSGGM) is employed to model radiation. The FPV-LES results are validated against the experimental evidence and a good agreement of the predicted mean and RMS velocities, as well as the mean gas temperature between experiments and simulations is obtained. The contributions of the pilot, volatile and char off-gas fuel streams to the coal flame are analysed. It is found that most regions of the furnace are dominated by either pilot or volatile combustion, while char conversion only occurs in the far downstream and outer furnace regions. The pilot gas dominates the near-wall region inside the quarl, whereas the volatile gas mainly released from small particles dominates a first volatile combustion zone in the interior of the internal recirculation zone. Larger particles heat up more slowly and release their volatile content further downstream, leading to a secondary volatile combustion zone.

Study Of Soot Aggregate Formation And Oxidation In A Swirled Stratified Premixed Ethylene/Air Flame

Soot particles are one of the main causes of today's pollution because of their negative contribution to global warming and human health. Aviation is one of the domains dealing with soot reduction as the new engine concepts are developed to reduce fuel consumption and global emissions. Despite the fact that most combustion devices used for air transportation operate at high pressure (e.g., aircraft gas turbines up to 40 bar), our understanding of soot formation and oxidation in such conditions is not yet at an appropriate level, as there is still a fundamental lack of experimental data and corresponding predictive models in the literature. Thus, the objective of the current study is to evaluate soot formation and oxidation processes in stratified, swirled, premixed ethylene/air flames examined with a variety of laser diagnostics designed to simultaneously measure soot particle and soot precursor 2D-distributions, as well as the flame structure and the aerodynamic field. For that, the SIRIUS burner was selected because of its ability to produce flames with topologies similar to those encountered in aircraft combustors. Soot particle distributions are measured by Planar Laser-induced incandescence (PLII) diagnostic. The flame structure is obtained by detecting the hydroxyl radicals (OH) with Planar laser-induced fluorescence (PLIF). A second PLIF diagnostic is also used to investigate the production of polycyclic aromatic hydrocarbons (PAH) with the detection of two benzene rings molecules which are recognized as good precursors of soot nucleation and growth. Finally, the particle Image Velocimetry (PIV) diagnostic is used for measuring the velocity distributions. These laser diagnostics are coupled together in order to obtain cross-correlations between several scalar parameters playing a determining role in the soot formation/consumption processes. The experimental results collected at atmospheric pressure are reviewed and critically assessed. A scenario describing the link between the soot inception, growth, aggregation and oxidation processes is proposed by analyzing velocity, OH, PAHs and soot distributions. In particular, the data reveal the presence of distinct regions for these processes. Incipient soot production zone is strongly function of specific local conditions of velocity, PAH concentration, and strain rate encountered at the interface of the internal recirculation zone and the fuel/air jet. The central part of the inner recirculation zone in which large structures move at low velocities provides suitable conditions for the aggregation of nascent soot particles while an oxidation region located in the upper zone of the internal recirculation zone favors the consumption of soot.

Household slow sand filters operating in continuous and intermittent flows: Computational fluid dynamics simulation and validation by tracer experiments

This paper analysed geometries and flows in household slow sand filters (HSSFs) through computational fluid dynamics (CFD) to evaluate the hydrodynamics of filters. Four HSSFs in full scale were studied with a capacity to produce 48 L.d-1 each with diameters of 190 mm and 250 mm and with a filter medium depth of 0.5 m. The hydrodynamics of the four mathematical models of the HSSFs was validated using the experimental residence time distribution (RTD). The Kruskal Wallis non-parametric test indicates that the results of the experimental RTDs and the simulated RTDs did not show significant differences, therefore the mathematical models represent the physical models, which requires a detailed 3D analysis of the flow in the filters. The results showed that the HSSFs have a flow close to plug flow reactor. Internal recirculation zones were not found, nor short-circuit ones; however, dead zones were verified at the base of the filter with volumes below 3% when compared to the total volume of the filtering and draining layers, not necessary to make changes in geometry. The results of the computational simulation showed that the continuous filters had a smaller velocity variation and the filters with smaller diameter presented a reduction in dead zones when compared to the filters with larger diameters operated in the same flow regime. The study focused on the hydraulic aspects of HSSFs, but it is noteworthy that the choice of the type of operation to be adopted by families that use this type of treatment depends on studies that assess the efficiency of water treatment filters that were not considered in this work.

Effects of nozzle inlet size and curvature on the flow development in a bidirectional vortex chamber

A finite-volume solver is used to describe the cyclonic motion in a cylindrical vortex chamber comprising eight tangential injectors and a variable nozzle size. The simulations are performed under steady, incompressible, and inviscid flow conditions with air as the working fluid. First, we apply a fine tetrahedral mesh to minimize cell skewness, particularly near injectors. Second, this mesh is converted into a polyhedral grid to improve convergence characteristics and precision. After achieving convergence, the velocity components are evaluated and compared to existing analytical solutions. We find that well-resolved numerical simulations can accurately predict the expected forced vortex behavior in the core region as well as the free vortex tail in the outer region. We also confirm that the swirl velocity remains axially invariant irrespective of the outlet radius. Similarly, we are able to ascertain that the axial and radial velocities embody the bidirectional nature of the motion. As for the computed pressure distribution, it is found to agree quite well with both theoretical formulations and experimental measurements of cyclone separators. Then using a parametric trade study, the effect of nozzle variations on the internal flow character, mantle structure, and recirculation zones is systematically investigated. Apart from the exit diameter, we find that the nozzle length and inlet curvature can substantially affect the internal flow development including the formation of backflow regions, recirculation zones, and mantle excursions. Finally, an empirical relation is constructed for the nozzle radius of curvature and shown to effectively suppress the emergence of recirculation and backflow regions.

Combustion Instability of Swirl Premixed Flame with Dielectric Barrier Discharge Plasma

The effects of plasma on the combustion instability of a methane swirling premixed flame under acoustic excitation were investigated. The flame image of OH planar laser-induced fluorescence and the fluctuation of flame transfer function showed the mechanism of plasma in combustion instability. The results show that when the acoustic frequency is less than 100 Hz, the gain in flame transfer function gradually increases with the frequency; when the acoustic frequency is 100~220 Hz, the flame transfer function shows a trend of first decreasing and then increasing with acoustic frequency. When the acoustic frequency is greater than 220 Hz, the flame transfer function gradually decreases with acoustic frequency. When the voltage exceeds the critical discharge value of 5.3 kV, the premixed gas is ionized and the heat release rate increases significantly, thereby reducing the gain in flame transfer function and enhancing flame stability. Plasma causes changes in the internal recirculation zone, compression, and curling degree of the flame, and thereby accelerates the rate of chemical reaction and leads to an increase in flame heat release rate. Eventually, the concentration of OH radicals changes, and the heat release rate changes accordingly, which ultimately changes the combustion instability of the swirling flame.

Numerical modelling of oxy-coal combustion to access the influence of swirl strength, combustion environment and gasification reactions on the flow and combustion behaviour

A simplified 2D axisymmetric computational fluid dynamics simulation of oxy-coal combustion is performed to address the influence of swirl strength and the combustion environment on the flow field and combustion characteristics. A quantitative analysis of the internal recirculation zone length and flame length under various operating conditions is studied by employing developed numerical models. The influence of char-CO2 and char-H2O gasification reactions on the species consumption and temperature profile is also studied through numerical modelling. The swirl strength considerably influences both the flow field and temperature profile inside the furnace. At higher swirl strength, radially dispersed shorter flames are obtained due to spreading of the secondary stream. Results showed that the flame shifted towards the burner at higher oxygen content due to rapid devolatilisation at higher flame temperature. The ignition of pulverised coal particles is enhanced at higher oxygen concentration due to increased stoichiometry near the burner. Oxy-35% O2 has 300 K higher flame temperature than oxy-21% O2. Endothermic gasification reactions significantly influence the temperature profile in the furnace. CO2-char gasification reaction has a more pronounced influence than the H2O-char gasification reaction. The consideration of gasification reactions has resulted in an approximately 5% reduction in peak temperature.

Large-Eddy Simulation of Flame Dynamics During the Ignition of a Swirling Injector Unit and Comparison With Experiments

Abstract During the ignition of a swirled single-injector combustor, two phases have been identified experimentally. In the first, the flame penetrates the injection unit, while in the second, the flame lifts off after a substantial delay before stabilizing at a distance from the injector. This transient phenomenon is investigated using Large Eddy Simulations based on an Euler–Lagrange description of the liquid spray, an energy deposition model to mimic ignition, and the thickened flame combustion model. It is shown that the initial penetration of the flame in the injector unit is linked with the positive pressure excursion induced by the rapid volumetric expansion of burnt gases. This sudden expansion is itself due to the fast increase in heat release rate that occurs during the initiation of the process. The corresponding positive and negative pressure disturbances induce a rapid reduction of the mass flow rate through the injector, followed by an acceleration of the flow and a return to the nominal value. It is also shown that the flame root disappears after another delay, which results in the flame edge lifting and stabilization at a distance from the injector exhaust corresponding to steady operation of the device. The relatively long delay time before this liftoff takes place is found to correspond to the residence time of the cooled burnt gases in the vicinity of the chamber walls, which are ultimately entrained by the internal recirculation zone and quench the lower flame foot.

Computational Study of 16 kWth Furnace Cofired Using Pulverized Bituminous Coal and Liquified Petroleum Gas Operated in Un-Staged and Air-Staged Conditions

Abstract This paper presents a computational study on air-fuel combustion of bituminous coal and liquified petroleum gas (LPG) in a 16 kWth test facility with a coflow-swirl burner. The performance of three turbulence models is investigated for the furnace operated under both air-staged and un-staged conditions by comparing their predictions with the reported measurements of temperature and species concentrations. This comparison shows that the shear stress transport (SST) k–ω model and SST k–ω model with low-Re correction predict the profiles of temperature and species concentrations reasonably well, but significantly underpredict the temperature in the furnace core at axial locations away from the burner. On the other hand, the transition SST k–ω model provides better overall congruency with the measured temperature and species concentrations when compared with the other turbulence models used, as indicated by relatively higher values of the Pearson correlation coefficient at locations away from the burner. The present high-fidelity computational model developed is also capable of accurately simulating the effect of coal particle size on the furnace environment, which is verified by the match between the computational predictions and the experimental results for two different sized coal samples. The model is also used to investigate the effect of coal particle size on the internal recirculation zone (IRZ) and the reattachment length (LR) for the same inlet swirl number (SN). A decrease of nearly 50% in the coal sample size results in the increase of LR and IRZ length by 20% and 82.6%, respectively.

Numerical study of inlet air swirl intensity effect of a Methane-Air Diffusion Flame on its combustion characteristics

In this paper, the effect of inlet air swirl number of a Methane-Air Diffusion Flame on dynamic flow behavior, temperature, and radiation heat flux distribution was investigated using ANSYS-Fluent CFD code. Based on the swirling effect on dynamic flow behavior, a specific equation in terms of axial and tangential velocity components was used to reach the swirl number. The modeling of the chemical reaction was carried out by applying the Eddy Dissipation Model (EDM). Furthermore, radiation heat flux and turbulent flow characteristics were performed by using P-1 and standard k-ϵ models.The results showed that the elevating swirl number of the inlet air from 0.0 to 0.6 develops the furnace internal recirculation zone which leads to producing the combustion products in the internal recirculation zone. Consequently, fuel and air are mixed more efficiently, which results in the enhancement of combustion efficiency by removing the high-temperature zones as the leading cause of producing nitrogen oxides (NOx). Moreover, as the swirl number increases, the radial flow distribution improves, and the flame heat exchange area enhances regardless of the maximum flame temperature reduction, which will increase the flux radiation efficiency by 36.5% and reduces the pollutant NOx by 58.6%.

Numerical investigation on ammonia co-firing in a pulverized coal combustion facility: Effect of ammonia co-firing ratio

Recently, the co-firing ammonia (NH3) with coal in boiler has been paid more and more attention. A computational Fluid Dynamics (CFD) simulation approach was built to investigate the NH3 co-firing in a pulverized coal combustion facility with a single swirling burner. The simulation accuracy was evaluated with the experimental data. The differences between coal firing and NH3 co-firing can be well reproduced with simulation. Then, the effects of NH3 co-firing ratio (CR) on the combustion characteristic and NOx emission were investigated. The flame shape is significantly affected by NH3 CR, due to the changes of momentum of NH3 jet from center of burner. When the NH3 CR exceeds 40 cal.%, the internal recirculation zone is completely penetrated by high velocity NH3 flow, which leads to a long flame and much unreacted NH3 in downstream. As the increase of NH3 CR, the overall trend is that the total heat absorbed slightly decreases due to the decrease of particle radiation, and unburnt carbon in fly ash obviously increases due to decrease of flame temperature. In the case with NH3 CR of 10 cal.%, the NO concentration at exit increases due to the more intense combustion and more fuel-NOx, compared with the case of coal-firing. When the NH3 co-firing ratio exceeds 10 cal.%, the NO concentration at exit decreases monotonously due to the DeNOx effect of unreacted NH3. However, once the NH3 co-firing ratio exceeds 40 cal.%, the unreacted NH3 concentration at exit increases rapidly, which requires careful designs of burner and furnace.

Computational study of non-reactive swirling flow in tangentially-fired configuration gasifier

This paper presents a computational study of swirling flow in a tangentially-fired air blown entrained flow Mitsubishi Heavy Industries gasifier in a non-reactive environment. Flow fields are obtained by using the Reynolds-averaged Navier Stokes turbulence model. Shear-stress transport k-ω model is used for the modelling the effect of turbulence. Variation in length of the internal recirculation zone with the swirl number for tangentially injected flow is reported. It is observed that for the MHI gasifier the length of the internal recirculation zone in a non-reactive environment increases upon increasing the swirl number at the inlet of the gasifier.

Stability and structure of inverse swirl diffusion flames with weak to strong swirl

Flame stabilization in many practical devices is achieved primarily through swirl; however, the application of swirl to an inverse diffusion flame and its effect on both flame stability and structure have not yet been reported. Therefore in this work, flame stability and structure of inverse diffusion swirling flames are investigated. The most stable flame is achievable at a critical swirl intensity, Scr. Lifted swirl jet-like flames at swirl intensity <Scr, and compact flames at swirl intensity >Scr are observed. Simultaneous PIV/OH-PLIF measurements are conducted to investigate the flame-flow interaction for three flames. The flame at Scr is stabilized due to the mutual dependence of two flame zones, the conical flame, and the flame root. The conical flame zone is located along with the inner shear layer (ISL) between the internal recirculation zone and the jet flow, while the flame root is positioned close to the burner nozzle. The ISL is favorable for flame stabilization due to the enhancement of the mixing of burned gas and fresh-fuel/air associated with the frequently-formed vortices. The flame root is stabilized due to the instantaneous opposed flow between the hot burned gas and the fresh reactants. The flame root essentially requires the upstream flow of hot exhaust gases associated with the IRZ. It is inherently unstable at high swirl intensities due to the high strain rate coupled with the strong IRZ. At low swirl intensities, the flame root is extinguished by the high momentum of the central jet, and a lifted flame is anchored in low-velocity regions of the jet, with the flame adjusting axially and radially to meet this criterion. These results emphasize the crucial role of the flame root in stabilizing the flame and suggest that well-aimed modifications of the flow field to further enhance mixing in this region may increase the stability of lifted jet-like swirling flames.

Modeling and Simulation in Engineering Modeling of the Electrocoagulation Processes in Nonisothermal Conditions

The paper suggests an approach to modeling the electrocoagulation process that is based on the generalization of the equations of incompressible fluid flow in nonisothermal conditions. In the model was taking into account the ratio between the values of the parameters which characterize the domination of convective and mass-exchange components of the process over diffusion. An asymptotic approximation of solutions of corresponding boundary value problems is constructed. Based on the received solutions, we conducted a computer simulation of the process of distribution of iron concentration inside the reactor that allows predicting various hydrodynamic phenomena such as internal recirculation and dead zones that affect the formation of a coagulant. The influence of current strength on the concentration of the target component at the exit from the reactor was investigated using the developed mathematical model. In addition, our findings also show the effect of the rate of heat formation from the electrodes on the efficiency of obtaining of coagulant.