Burner Outlet Research Articles

Influence of over fire air system on NOx emissions: An experimental case study

In this work, various combinations of the NO emission influencing factors and their x combined effects in air staging combustion on level of furnace, using over fire air, were investigated in an experimental lab-scale furnace. At this, process temperature were varied in the range from 950?C to 1450?C, excess air ratio in primary zone in the range ? = 0.9 - 1.2, while distance of over fire air nozzles from the burner outlet varied until a 1 given distance of 2/5 of total length of furnace. Basic fuel is brown coal from Middle Bosnia coal basin, mixed in two coal blends and one coal-woody biomass blend, to combine an effect of fuel characteristics variation on NO emission. Results shows that x an average reduction of NO emission over tested temperature range, when using over x fire air against conventional air supply with over fire air switched off, is 26.5%. At this, much more NO emission reduction for two coal blends were occurred at higher x temperatures ? at 1350?C and above, where an average NO emission reduction is x 32.5%. Furthermore, it was found that the NO emission decreased with an increase in x distance of over fire air nozzles from the outlet level of burner until a distance of 1/3 of total furnace length; with further increase of the distance, NOx emission is stabilised and no further effect to NOx emission reduction was observed, while CO emission and unburnt increased.

Effects of secondary air distribution in primary combustion zone on combustion and NOx emissions of a large-scale down-fired boiler with air staging

A new air-staged and low-NOx emission combustion technology has been applied to a 300 MWe anthracite- and down-fired boiler with swirl burners. To achieve the optimum air distribution in the primary combustion zone and further reduce NOx emissions, full-scale industrial experiments varying the ratios between burner secondary air ratio (Rbsa) and staged air ratio (Rsa) (i.e., Rbsa/Rsa ratios of 42.9/17.8, 47.1/13.5 and 51.5/9.3), on the premise that the overfire air (OFA) ratio was approximately 20%, were performed to evaluate the overall performance of retrofitted boiler. The improved ignition of coal/air flow was at a distance of 0.8–1.4 m to the burner outlet with increased Rbsa/Rsa ratio. Compared with the boiler before retrofit, under Rbsa/Rsa ratios of 47.1/13.5 and 51.5/9.3, the flue gas temperature in the primary combustion zone of the retrofitted boiler increased slightly. Oxygen and carbon monoxide concentrations in the near-sidewall region revealed the furnace flame fullness varied under different Rbsa/Rsa ratios. With increased the air staged level in the lower furnace, NOx emissions decreased continually and the carbon content in fly ash did not necessarily increased. Under the optimum Rbsa/Rsa ratio of 47.1/13.5, the NOx reduction efficiency was approximately 46% with increasing boiler thermal efficiency slightly.

Studying the Aerodynamics of the TPP-210A Boiler Furnace When It Is Shifted to Operate with Dry-Ash Removal and Vortex Fuel Combustion

To reduce the amount of nitrogen oxide emissions and achieve more reliable operation of the TPP-210A boiler, a process arrangement for firing Grade TR Kuznetsk coal that involves using straight-flow burners and shifting the boiler from slag-tap to dry-ash removal is developed. Owing to a large burner downward slope angle and special arrangement of burners and nozzles, four large vertical vortices rotating in opposite directions are produced in the furnace lower part, as a result of which the combustion products dwell for a longer period of time in the burning zone and more complete fuel combustion is achieved. For verifying the operability and efficiency of the proposed combustion arrangement, investigations on a boiler furnace physical model were carried out using a technique for visualizing fuel jets and secondary and tertiary overfire air jets. The fuel jet temperature boundaries in the course of jet propagation in the furnace model are also determined. The study results have shown that staged fuel combustion will be set up with using the proposed arrangement of burners and nozzles. In addition, large vertical vortices produced in the furnace lower part will help to achieve more efficient use of the dry bottom hopper heating surfaces, due to which lower coal combustion product temperature in the furnace upper part and smaller content of combustible products in fly ash will be obtained. Owing to low values of air excess factor at the pulverized coal burner outlet and gradual admission of air into the vortex zone through a few nozzles with intense inner recirculation of combustion products to the jet initial section, staged combustion of pulverized coal and low nitrogen oxide emissions will be secured. Owing to expansion of fuel jets, a rapid growth of mass in the fuel jet is achieved, which is obtained both due to ejection of the jet itself and due to forced admission of hot fuel gases from other jets. Investigations carried out on the physical model have confirmed that the proposed combustion arrangement features high efficiency and that a low content of nitrogen oxides in flue gases is obtained.

Experimental investigations of oxyfuel burner for cement production application

The production of cement is one of the CO2 intensive processes, due to the inherent formation of CO2 in the calcination process by decomposition of limestone which is additional to the CO2 generated from fuel combustion. Carbon capture and storage technologies have been seen as a promising way to comply with CO2 reduction targets. As part of the objectives of the Horizon 2020 project CEMCAP, the retrofitting of key parts of the equipment of a conventional cement plant to oxyfuel combustion are investigated. The present study reports the results of several combustion tests employing a downscaled commercial kiln burner to determine its adequacy for oxyfuel operation mode. The investigations were carried out in the 500 kWth top-fired combustion facility at University of Stuttgart, which was previously adapted for these tests, including the installation of an electric preheating system to rise secondary gas temperature up to 800 °C. Fuel used is a German pre-dried lignite previously milled to required fineness in a separate location. A variety of in-flame measurements are performed at a dozen of ports located at different distances from burner outlet in order to characterize combustion behavior in each firing mode. It was observed that under oxyfuel mode additional parameters in burner configuration like total oxygen concentration and oxygen distribution in primary and secondary gas are key variables to adjust flame formation and obtain similar results as in conventional air firing.

Combustion and emission performances of coconut, palm and soybean methyl esters under reacting spray flame conditions

The spray combustion characteristics of coconut (CME), palm (PME) and soybean (SME) biodiesels/methyl esters were compared with diesel by using an axial swirl flame burner. Atomisation of the liquid fuels was achieved via an airblast-type nozzle with varied atomising air-to-liquid ratios (ALR) of 2–2.5. The fully developed sprays were mixed with strongly swirled air to form combustible mixtures prior to igniting at the burner outlet. Under fuel-lean condition, biodiesel spray flames exhibited bluish flame core without the yellowish sooty flame brush, indicating low sooting tendency as compared to baseline diesel. Increasing the atomising air led to the reduction of flame length but increase in flame intensity. Measurements of post-combustion emissions show that SME produced higher NO as compared to CME and PME due to higher degree of unsaturation, while the most saturated CME showed the lowest NO and CO emissions amongst the biodiesels tested across all equivalence ratios. By preheating the main swirl air to 250 °C, higher emissions of NO, CO and CO2 were observed for biodiesels. Higher ALR led to reduced NO and CO emissions regardless of the fuel used, making it a viable strategy to resolve the simultaneous NOCO reduction conundrum. This work shows that despite different emission characteristics exhibited by biodiesels produced from different feedstock, they are in principle potential supplemental fuels for practical combustion systems. The pollutants emitted can be mitigated by operating at higher ALR in a twin-fluid based swirl combustor.

Application of eccentric-swirl-secondary-air combustion technology for high-efficiency and low-NOx performance on a large-scale down-fired boiler with swirl burners

A 300-MWe anthracite and down-fired boiler equipped with swirl burners, which was retrofitted with the previously proposed deep-air-staging combustion technology to reduce particularly high NOx emissions, still suffered from high carbon content in fly ash (despite this content being slightly lower than that before retrofit) on basis of significant NOx reduction. To comprehensively produce a high-burnout and low-NOx setting, a novel combustion technology was proposed in which relative to the axis of the primary air duct, the axes of the inner and outer secondary air ducts of the swirl burner shift away from the furnace center, and this technology is called an eccentric-swirl-secondary-air combustion technology. The coaxial symmetrical arrangements of primary and secondary air ducts for traditional swirl burners are broken. Full-scale industrial measurements under original, deep-air-staging and eccentric-swirl-secondary-air combustion technologies with respect to different loads (i.e., 180, 250, and 300 MWe) were carried out to compare and analyze the validity of and improvement offered by the eccentric-swirl-secondary-air combustion technology. Under different boiler loads, especially at low and middle loads, compared with original and deep-air-staging combustion technologies, eccentric-swirl-secondary-air combustion technology markedly extends the penetration depth of coal/air flow and recirculation regions below arches. The thermal resistance between primary coal/air flow and high-temperature flue gas at the furnace center is reduced further, and the ignition of pulverized coal is timelier. The heating gradient in the burner outlet zone is maintained throughout, and the flame fullness in the primary combustion zone increases. The above three aspects contribute to pulverized coal burnout. Similar to deep-air-staging combustion technology, a low-oxygen and strong reducing atmosphere was formed in the primary combustion zone to reduce NOx formation due to the introduction of overfire air. Compared with deep-air-staging combustion technology, for the eccentric-swirl-secondary-air combustion technology, the air staged combustion in the furnace is improved further, and pulverized coal combustion in the primary combustion zone is more well distributed, which is beneficial to further reducing NOx emissions. The results of low-NOx and high-efficiency performance show that compared with the original boiler, NOx emissions and carbon content in fly ash for the boiler with the eccentric-swirl-secondary-air combustion technology are significantly reduced by above 42% and 32.5 to 20.7% at loads of 180, 250 and 300 MWe, respectively.

Mechanism analysis on the pulverized coal combustion flame stability and NOx emission in a swirl burner with deep air staging

Low NOx burner and air staged combustion are widely applied to control NOx emission in coal-fired power plants. The gas-solid two-phase flow, pulverized coal combustion and NOx emission characteristics of a single low NOx swirl burner in an existing coal-fired boiler was numerically simulated to analyze the mechanisms of flame stability and in-flame NOx reduction. And the detailed NOx formation and reduction model under fuel rich conditions was employed to optimize NOx emissions for the low NOx burner with air staged combustion of different burner stoichiometric ratios. The results show that the specially-designed swirl burner structures including the pulverized coal concentrator, flame stabilizing ring and baffle plate create an ignition region of high gas temperature, proper oxygen concentration and high pulverized coal concentration near the annular recirculation zone at the burner outlet for flame stability. At the same time, the annular recirculation zone is generated between the primary and secondary air jets to promote the rapid ignition and combustion of pulverized coal particles to consume oxygen, and then a reducing region is formed as fuel-rich environment to contribute to in-flame NOX reduction. Moreover, the NOx concentration at the outlet of the combustion chamber is greatly reduced when the deep air staged combustion with the burner stoichiometric ratio of 0.75 is adopted, and the CO concentration at the outlet of the combustion chamber can be maintained simultaneously at a low level through the over-fired air injection of high velocity to enhance the mixing of the fresh air with the flue gas, which can provide the optimal solution for lower NOx emission in the existing coal-fired boilers.

Effect of producer gas addition and air excess ratio on natural gas flame luminescence

This paper presents the emission spectroscopy method for registering chemiluminescent radical species of OH∗,CH∗,C2∗ by means of optical flame imaging using optical bandpass filters, corresponding to emission wavelengths of the radicals of interest, and by scanning the flame using optical fibers coupled to a spectrometer for recording the emission spectra. The aim of this research is to analyse the distribution of chemiluminescence intensity along the flame axis from various angles simultaneously in order to determine the effect of the air equivalence ratio (ER) and mixing of producer gas (PG) from biomass gasification into the natural gas flow to spectral characteristics of flame at specific wavelengths representing formation reactions of OH∗ radical species. The experiments were carried out with pure natural gas (NG) and air mixture and a premixed air/gas mixtures (80%NG and 20% PG, 65%NG and 35%PG). Flows of air, NG and PG were premixed before entering the combustion chamber. For flame emission spectroscopy, two different methods were used: 1) imaging by an ICCD camera through optical bandpass filters suitable for OH∗,CH∗,C2∗ chemiluminescence intensity registration; 2) by a combination of a spectrometer and five optical fibers to collect the flame spectra from 5 different angles and in various heights from the burner outlet. The distribution of chemiluminescent species intensity along the burner vertical axis was analyzed and zones with most intense OH∗,CH∗,C2∗ generation in flame were identified, and the effect of addition of PG to NG and ER to the OH∗ chemiluminescence was analysed.

Dynamics of diffusion jet combustion in an ejection burner

In this work we present the results of computational and experimental studies on the burnout dynamics of diffusion gas jets in an ejection burner with a two-stage air ejection scheme. It is shown that usage of this scheme leads to an increase in the uniformity of the distribution of thermogasdynamic parameters at the burner outlet, an increase in the completeness of combustion of the fuel, and a more stable operation of the device.

Bir Elektrik Ark Ocağındaki Enerji Üretiminin ve Transferinin HAD Modeli

Modeling of energy production and heat transfer by carbon combustion and electrical arc is performed using Fluent computational fluid dynamic (CFD) software in this manuscript. The heat energy generated by carbon burning and electric arc radiation during combustion of the scrap in the EAO has been examined in detail. For this reason, modeling studies have utilized the combustion reactions of carbon particles and electromagnetically emitted radiation. Firstly, particle surface and gas reactions are investigated in terms of injected carbon burning. The result of the chemical reaction at the burner outlet is about 3000 K of the core temperature during combustion. It has been determined that the temperature which acts on the slag is 2200 K. The radiation temperature was found to be highest in the area under the electrodes and fell to 1850 K in the area where the melt was poured. Under steady operating conditions, it was seen that electric energy was absorbed by about 5.5% of the electrodes. As a result of this study, CFD software can be used to model combustion and radiation and energy generation and heat transfer for an electric arc furnace at the design study.

Swirl stability and emission characteristics of CO-enriched syngas/air flame in a premixed swirl burner

There is significant variation in the composition of synthesis gas derived from biomass, coal or waste. The inconsistency of syngas constituents poses challenges and requires thorough characterisation prior to use as alternative fuel in practical combustion system. The present study investigates the combustion and emission characteristics of CO-enriched syngases by using an atmospheric premixed swirl flame burner. High (CO/H2 = 3) and moderate (CO/H2 = 1.2) CO-enriched syngases were fully premixed with air and diluents of CH4 and CO2 prior to ignition at the burner outlet. Direct flame imaging shows that moderate CO-enriched syngas produces less luminous flames than high CO-rich syngas, signifying less tendency to form soot. Moderate CO-rich syngases show more compact flames with higher intensity owing to higher H2 contents. The blowout test shows that higher CO content syngases result in lean blowout at higher equivalence ratios, posing stability issues. High fractions of unreactive CO2 and reactive CH4 in syngases result in higher lean blowout limit. Emissions wise, high CO-rich syngases show evidently less NOx emissions as compared to baseline pure CO flames at increasing equivalence ratios. Moderate CO-rich flame exhibits higher NOx level than high CO-rich at ϕ < 0.8. However, at fuel-stoichiometric and fuel-rich regions they display similar levels of NOx. Higher fraction of CO2 dilution results in reduction of NOx emissions, with pronounced impact on fuel-rich cases. There was minimal effect on CO emissions with increased dilution of CO2.

Experiment and numerical simulation investigations of the combustion and NOx emissions characteristics of an over-fire air system in a 600 MWe boiler

ABSTRACTSeveral numerical simulations are conducted to investigate the influence of pulverized-coal combustion characteristics and NOx emissions with different configurations of nozzle and arrangements of an over-fire air device for a 600 MWe boiler unit. It is found by a series of comparisons that the numerical simulation results are almost in agreement with the in-situ experimental results, including the flue gas temperature of the burner outlet, the flue gas temperature along the furnace height, the NOx concentration, and combustible content in the fly ash of the air preheater outlet, which indicates that the numerical model and the grid are reasonable. Numerical simulation results show that setting the over-fire device in which the inner is straight flow and the outer is swirl flow and the staggered arrangement of two layers of over-fire air (OFA) in the boiler are both conducive to the pulverized-coal combustion in the furnace and to the reduction of NOx emissions. The results also show the values of 241.64 mg/m3 @ 6% O2 for the lowest NOx concentration at the furnace outlet. Compared with the boiler without OFA, the NOx concentration decreased by 60.4%. Using the staggered arrangement of two layers of OFA in the practical 600 MW boiler unit, the gas temperature can reach 1100 K at the height of 100 mm away from the burner outlet, leading to coal particle ignition immediately; moreover, the NOx emission concentration reduced to 284 mg/m3 @ 6% O2 and heat loss due to unburned carbon in refuse of the air preheater outlet is 3.17%.

Influence of the technique for injection of flue gas and the configuration of the swirl burner throat on combustion of gaseous fuel and formation of nitrogen oxides in the flame

How the points at which the flue gas was injected into the swirl burner and the design of the burner outlet influence the formation and development of the flame in the submerged space, as well as the formation of nitrogen oxides in the combustion products, have been studied. The object under numerical investigation is the flame of the GMVI combined (oil/gas) burner swirl burner fitted with a convergent, biconical, cylindrical, or divergent throat at the burner outlet with individual supply of the air and injection of the gaseous fuel through tubing. The burners of two designs were investigated; they differ by the absence or presence of an inlet for individual injection of the flue gas. A technique for numerical simulation of the flame based on the CFD methods widely used in research of this kind underlies the study. Based on the summarized results of the numerical simulation of the processes that occur in jet flows, the specific features of the aerodynamic pattern of the flame have been established. It is shown that the flame can be conventionally divided into several sections over its length in all investigations. The lengths of each of the sections, as well as the form of the fields of axial velocity, temperatures, concentrations of the fuel, oxygen, and carbon and nitrogen oxides, are different and determined by the design features of the burner, the flow rates of the agent, and the compositions of the latter in the burner ducts as well as the configuration of the burner throat and the temperature of the environment. To what degree the burner throat configuration and the techniques for injection of the flue gas at different ambient temperatures influence the formation of nitrogen oxides has been established. It is shown that the supply of the recirculation of flue gas into the fuel injection zone enables a considerable reduction in the formation of nitrogen oxides in the flame combustion products. It has been established that the locations of the zones of intensive fuel burnout and generation of nitrogen oxides do not coincide over the flame length, and the ambient temperature has a significant impact on the combustion stability at low values and on the concentration of nitrogen oxides in the combustion products at high values.

Energy, exergy and sensitivity analyses of a hybrid combined cooling, heating and power (CCHP) plant with molten carbonate fuel cell (MCFC) and Stirling engine

A hybrid combined cooling, heating and power (CCHP) system which consists of molten carbonate fuel cell (MCFC), Stirling engine and double effect LiBr/H2O absorption chiller is introduced and analyzed. Molten carbonate fuel cell is the main power production source which its exhausted heat is used as heat source of the Stirling engine. Exhausted heat from the Stirling engine is used as heat source of the absorption chiller’s generator. The produced power of the process is 6482 kW, also it provides 2137 kW heat duty and 1372 kW cold duty. Performance of the process is evaluated by energy and exergy analysis methods. Also sensitivity of the overall and electrical efficiencies to the fuel utilization factor, air flow rate to the burner, burner outlet temperature and oxidant flow rate are analyzed. Results of the energy analysis show that overall and electrical efficiencies are 71.71% and 42.28% respectively. Exergy analysis shows that molten carbonate fuel cell, Stirling engine and gas turbine have considerable efficiencies. Highest exergy destruction rate is related to the CH4 and H2 burners that mostly is because of the irreversible nature of the combustion.

Dissociative influence of H2O vapour/spray on lean blowoff and NOx reduction for heavily carbonaceous syngas swirling flames

Recent studies have described and evidenced the enhancement of fundamental combustion parameters such as laminar flame speed due to the catalytic influence of H2O with heavily carbonaceous syngas mixtures. In this study, the potential benefits of these subtle changes in water loading and hence reaction pathways are explored in terms of delayed lean blowoff, and primary emission reduction in a premixed turbulent swirling flame (Ø = 0.6–0.8), scaled for practical relevance. Chemical kinetic models initially confirm that H2O has a substantial impact on the employed fuel behaviour; increasing flame speed by up to 60% across an experimental range representative of fluctuation in atmospheric humidity (∼1.8 mol%). OH* chemiluminescence and OH planar laser induced fluorescence (PLIF) were employed to analyse the changes in heat release structure resulting from the experimental addition of H2O vapour to the combustor. Equivalent concentrations of liquid H2O were introduced into the central recirculation zone of the premixed flame as an atomised spray, to investigate the influence of phase changes on the catalytic effect. Near the lean stability limit, H2O addition compresses heat release to shorten the elongated flame structure. Whereas with a stable and well-defined flame structure, the addition triggers a change in axial heat release location, causing the flame front to retract upstream toward the burner outlet. Higher quantities of two-phase flow were combined to explore the possibility of employing the spray as a stabilising mechanism, effectively dampening the observed influence of humidity. The chemical enhancement induced by the controlled supply was shown to reduce the lean blowoff stability limit, enabling an increase in additional air flow of almost 10%. However, the catalytic effect of H2O diminishes with excessive supply and thermal quenching prevails. There is a compound benefit of NOx reduction from the use of H2O as a flame stabiliser with the practically-relevant syngas: First NOx production decreases due to thermal effect of H2O addition, with potential for further reduction from the change in lean stability limit; leanest experimental concentrations reduced by up to a factor of four with two-phase flow at the highest rates of supply. Hence, the catalytic effect of H2O on reaction pathways and reaction rate predicted and observed in the laminar environment, is shown to translate into practical benefits in the challenging environment of turbulent, swirl-stabilised flames.

Anthracite combustion characteristics and NOx formation of a 300 MWe down-fired boiler with swirl burners at different loads after the implementation of a new combustion system

A new combustion system has been applied to a 300MWe down-fired boiler with swirl burners to reduce NOx emissions. The unit provided the introduction of overfire air (OFA) and a decrease in the flow area of the inner and outer secondary air ducts of the swirl burners. Industrial experiments on the retrofitted boiler were performed at different loads. Full-scale measurements of the flue gas temperature distribution in the burner outlet region, the furnace temperature distributions measured by a pyrometer and the local mean gas species concentrations in the region near the sidewall were made at loads of 180, 250, and 300MWe. The results show that the ignition distance increased with decreasing load, especially as the load decreased from 250MWe to 180MWe. At three different loads, the retrofitted coal/air flow could be all ignited in time at a distance in the range of 0.6–1.4m from the burner outlet. Compared with the original combustion system, the ignition distance of the coal/air flow was significantly reduced at a load of 300MWe. In addition, at a load of 300MWe, the temperature of the boiler hopper was much higher than that at loads of 180MWe and 250MWe. Compared with the original combustion system, the upper furnace temperature decreased slowly with increasing measurement height at a load of 300MWe after the retrofit. Measurements of the O2 and CO concentrations in the region near the sidewall indicate that the fullness degree of the coal flame in the furnace at different loads was different. After the retrofit, the reheat steam temperatures reached the design temperature of 541°C at loads of 180MWe and 250MWe, and the average reheat steam temperatures increased by approximately 13°C. Compared with the original combustion system, a significant NOx reduction (more than 40%) at different loads was achieved without increasing the levels of unburnt carbon in the fly ash.

Large Eddy Simulations of Unconfined Non-reacting and Reacting Turbulent Low Swirl Jets

The low swirl flow is a novel method for stabilizing lean premixed combustion to achieve low emissions of nitrogen oxides. Understanding the characteristics of low swirl flows is of both practical and fundamental interest. In this paper, in order to gain better insight into low swirl stabilized combustion, large eddy simulation and dynamically thickened flame combustion modeling are used to characterize various features of non-reacting and reacting low swirl flows including vortex breakdown, shear layers’ instability, and coherent structures. Furthermore, four test cases with different equivalence ratios are studied to evaluate the effects of equivalence ratio on the flame and flow characteristics. A finite volume scheme on a Cartesian grid with a dynamic one equation eddy viscosity subgrid model is used for large eddy simulations. The obtained results show that the combustion heat release and increase in equivalence ratio toward the stoichiometric value decrease the local swirl number of the flow field, while increasing the flow spreading at the burner outlet. Results show that the flame becomes W shaped as the equivalence ratio increases. Moreover, the combination of the swirling motion and combustion heat release temporally imposes a vortex breakdown in the post-flame region, which leads to occurrence of a transient recirculation zone. The temporal recirculation zone disappears downstream of the burner outlet due to merging of the inner shear layer from all sides at the centerline. Also, various analyses of shear layers’ wavy and vortical structures show that combustion heat release has the effect of decreasing the instability amplitude and vortex shedding frequency.

A comparison between the stabilization of premixed swirling CO2-diluted methane oxy-flames and methane/air flames

Revamp of air powered industrial boilers to oxy-combustion operation raises several issues. In this study, the stabilization of CO2-diluted premixed swirling CH4/O2 flames is compared to operation with CH4/air flames by a set of experiments in a generic labscale combustor equipped with an axial-plus-tangential swirler. The investigated flames are stabilized aerodynamically within the swirling flow without help of any solid anchoring device. The structure of the turbulent swirling flames is examined by recording their OH∗ chemiluminescence. Laser induced OH fluorescence measurements are carried out to delineate the location of the flame front and burnt gases and infer the shape taken by the flame. Particle imaging velocimetry measurements reveal the corresponding velocity field. The temperature is also recorded with thermocouples in the internal and the external recirculation zones of the flow and inside the combustion chamber walls. These diagnostics reveal similarities between the topology of CH4/air and CH4/O2/CO2 flames near their stabilization point. For a fixed swirl number, it is found that N2- and CO2-diluted CH4/O2 flames at the same equivalence ratio feature very similar shapes provided the adiabatic flame temperature and the ratio of bulk velocity to laminar burning velocity are kept the same although the absolute value of bulk velocity and the general velocity level inside the combustor are different. This result was found for injection Reynolds numbers varying from Re=8500–28000 and for swirl numbers ranging from S0=0.5 to 1.2. The operability range of well stabilized CO2-diluted flames is however reduced. It is also found that the temperature of the burnt gases in the outer recirculation zone differs between the CO2- and N2 diluted combustible mixtures sharing the same adiabatic temperature, but this does not affect the stabilization of the flames near the burner outlet, the temperature in the burnt gases and inside the combustor sidewalls. The flame leading edge is stabilized on average off-axis due to the structure of the W axial velocity profile produced by the axial-plus-tangential swirler at the burner outlet. This study indicates that CO2-diluted CH4/O2 premixed swirling flames can be stabilized with similar shapes as CH4/air flames without design modification provided the suggested similarity is obeyed.

Quantitative and qualitative relationship between swirl burner operatingconditions and pulverized coal flame length

Currently, there are used in power plants two types of burners to combustion the pulverized coal: jet burners and swirl burners. Most of the published works in the field of analysis of burners operating conditions are related to jet burners and are limited to initial region of the flame at the outlet of the burner. For jet burners an offset between the burner outlet and the flame beginning point could be analyzed. In the case of swirl burners with the pre-mixing diffuser chamber an offset between flame ignition point and burner outlet is usually not visible. Because already in the pre-mixing diffuser chamber of swirl burner occurs the ignition of coal-dust together with oxidant-gas cloud and thereby the formation of the flame. Therefore, the analysis of operating conditions for this types of burners requires a different approach. There is a lack of researches, in which will be analyzed changes of the flame length, that are caused by changes of design and operating parameters of swirl burner with the pre-mixing diffuser chamber. Therefore the aim of this study was to implement and verify the methodology for estimating the flame length, which will allow monitoring changes of operating conditions, that are caused by changes of design and operating parameters of swirl burner with the pre-mixing diffuser chamber. To carry out the analysis of the image of the coal flame, the two algorithms have been presented. This two algorithms, being based on the video images of the coal flame allows to specify and detect the end point of the flame and on that basis the length of the flame, as well as the fluctuation changes of flame length can be later determined. Both, the change thermal loads of coal burner, streams of secondary air, as well as the constructional change of the angle of swirler assemblies, resulted in distinct changes in the length of the pulverized coal flame.

Influence of the type of the pulverized coal concentrator on the operation of a tangential fired boiler with horizontal bias combustion

In this paper, the problems of combustion instability and high-temperature corrosion of pulverized coal fired boiler are investigated by numerical simulation and analysis of the momentum moment. Elbow and twisting plate type of burners are used in the boiler, and the reverse moment of momentum is formed at the outlet of the fuel-rich side of the burner. The momentum moment in the boiler is opposite to the designed tangential circle, and the tangential circle in the boiler is reversed rotation. The reverse moment of momentum at the burner outlet can be eliminated by using louver horizontal bias pulverized coal burner, while the problems of combustion instability and high-temperature corrosion of the boiler are solved, and the combustion efficiency is improved. Accordingly, economic benefit is obviously got.