Burner Arrangement Research Articles

CFD modeling of hydrodynamics, combustion and NOx emission in a tangentially fired pulverized-coal boiler at low load operating conditions

With deep peak-load regulations, utility boilers are frequently operated under variable/low load conditions. However, their hydrodynamics, combustion and NOx emission characteristics are uncertain and relevant theoretical guidance are lacking. For this purpose, a comprehensive CFD model including flow, coal combustion and NOx formation is established for a 630 MW tangentially fired pulverized-coal boiler, aiming at solving the problem of decreasing combustion stability and increasing NOx emission in low-load operation. Based on the grid independence and model validation, the flow field, temperature profile, species concentration profile and NOx emission are predicted, and the influences of angle/arrangement of burners are further evaluated. Simulation results indicate that under low-load conditions, residual airflow rotation still persists at the top of boiler regardless of how to adjust the angle/arrangement of burners. With tilting the burner angle upward, flame is more concentrated, combustion becomes more stable, and heat flux rises in the upper zone; the burner arrangement of ABDE gives more uniform temperature distribution in the combustion zone. CO species shows higher content in the combustion zone; the 0° tilt angle gives maximum CO content, followed by the 15° angle, and finally the −15° angle; compared to the ACDE and ABCE arrangement, the ABDE arrangement mode gives much lower CO contents. Burner tilt angle of −15° benefits for lower NOx emission (183 mg/m3) but goes against stable combustion; the burner arrangement mode of ABDE is optimal for the present boiler, which ensures both stable combustion and lower NOx emission (209 mg/m3).

Numerical variational study of the M-shaped boiler invert furnace

Nowadays the world and Russian energy sector seeks to reduce the use of coal for electricity production, however, in the future its significant part will remain in the fuel balance. Due to environmental and economic factors, coal generation has to use technologies to reduce polluting emissions and including also CO2 (HELE technologies) for maintain competitiveness. One of these technologies is the use of a coal for A-USC steam parameters steam turbine cycle. This paper describes the studies conducted to develop the optimal scheme for burning solid fuel in an A-USC M-shaped boiler invert furnace proposed by the Dept. of Thermal Power Plants of the National Research University “Moscow Power Engineering Institute”. Six schemes with a different arrangement of direct-flow burners and nozzles are considered. A test installation for isothermal physical modeling was made for scheme No.1. The results of physical modeling were compared with the results of the numerical simulation model of the test installation. Schemes No. 1-6 were investigated using numerical simulation in the ANSYS software package to identify the best conditions for the organization of staged fuel combustion at low emissions of nitrogen oxides. Scheme 6 is recognized as the most optimal and will be used to create an isothermal physical test installation and conduct numerical simulations of the combustion process for a full-scale furnace model.

Nonpremixed MILD combustion in a laboratory-scale cylindrical furnace: Occurrence and identification

This paper reports a comprehensive investigation into the occurrence and identification of nonpremixed MILD combustion of C3H8/air in a cylindrical furnace. The combustion mode is altered by varying burner arrangement, air-fuel nozzle separation, equivalence ratio and thermal input. Based on the experimental observations, flow analysis and chemical calculations, a new criterion is proposed to identify the occurrence of nonpremixed MILD combustion using local heat release rate (HRR) particularly for CFD simulations. Importantly, unlike the case of CH4, the nonpremixed MILD combustion of C3H8 exhibits a negative HRR (HRR−) region that departs distantly from the positive HRR (HRR+) region, due to complex pyrolysis. This is distinct from the conventional flame where the HRR− region is adjecent to the HRR+ one. The new criterion notably improves the mode identification of nonpremixed combustion operating in various furnaces at different conditions. Moreover, the current study highlights the importance of local HRR in linking the experimental observation, CFD simulation and chemical calculation of MILD combustion.

Experimental air/particle flow characteristics of an 80,000 Nm3/h fly ash entrained-flow gasifier with different multi-burner arrangements

A novel burner arrangement for entrained-flow pulverized coal gasifier with multiple low-set burners, which burners are arranged to be counter-biased, is proposed aimed at mitigating high-temperature corrosion to the wall. To verify the characteristics of this improvement in an 80,000 Nm3/h fly ash entrained-flow gasifier, experiments were conducted on the model to investigate the impact of six burners being co-biased, opposed and counter-biased on the air/particle flow field by using a particle dynamics anemometer. The results show that, on the horizontal cross-section passing through burner centerlines with co-biased burners, opposed burners and counter-biased burners, the radius of mixing zone is 0.196, 0.16 and 0.174; the ratio of total particle volume flux in the near-wall region to the total particle volume flux in the measurement zone was 76.5%, 26.1% and 57.8%, respectively. On the vertical cross-section above burner outlet, the radius of central recirculation zone with co-biased burners remains to expand to 0.88 while that of counter-biased burners gradually shrinks to 0.33. There is no central recirculation zone under opposed burners; air and particle swirl numbers are close to zero. This study shows that new burner arrangement could ease high-temperature corrosion to gasifier wall and strengthens mixing of burner jets.

Thermoacoustics and combustion instability analysis for multi-burner combustors

This paper presents a low-order thermoacoustic model for multi-burner combustors and proposes a control theoretic approach to linear combustion instability analysis in frequency domain, taking acoustic and flame interaction effects among burners into account under a non-zero mean flow condition. Our thermoacoustic model can deal with can-annular and annular combustors in a unified way and is given as a multi-input multi-output transfer function matrix from heat fluctuation input vector to velocity fluctuation output vector. We also propose a flame transfer function matrix description where off-diagonal components describe the effects of a local acoustic field of one burner location on the flame response at another burner location. The discrete rotational symmetry of burner arrangement in a combustor makes it possible to diagonalize both the aforementioned thermoacoustic and flame transfer function matrices analytically from a spatial discrete-time Fourier transformation. The decoupled thermoacoustic transfer function matrix provides a characterization of acoustic resonances, particularly the longitudinal-azimuthal coupled modes unique to multi-burner combustors. In addition, from the Bloch wave interpretation, we find general patterns in the mode shape of a multi-burner combustor and its relations to the mode shape of a single-burner combustor. Furthermore, from a diagonalized closed loop transfer function matrix, a simple combustion instability condition for a multi-burner combustor is developed. This stability condition shows how a single-burner combustor and a multi-burner combustor are different quantitatively, when it comes to combustion instability. Numerical examples are presented to validate our thermoacoustic model against three-dimensional FEM results, and to illustrate our developments and findings.

The working status and deformation risk of membrane walls affected by the arrangement of burners in the arch-fired boiler

The thermal deformation of membrane walls is a severe safety issue in the arch-fired boilers, which is closely related to the combustion and flame inside the furnace. In this paper, various combustion schemes were conducted on a laboratory-scaled arch-fired boiler, exploring the correlations between the working status on membrane walls and the arrangement of burners. The influence mechanisms of the burners on the membrane walls were experimentally determined, with strong impact regions found on the front/rear wall in a relative wide of 0.6. The asymmetric combustion obtained in the furnace increased the temperature and strain/stress on the front wall with greater deformation risk, which should be avoided in the practical operation. The flameout of burners dramatically changed the local temperature and enhances the tearing risk of membrane walls with tension stress, which is consistent with the tearing track in the prototype boiler. Great correlations between the operation parameters (Tg, Tw, Tc, ε1 and σ1) and the and volumetric thermal load (Pv) were experimentally determined and considered applicable to the prototype boiler. While the impact range of burners helps estimating the uniformity of temperature and strain/stress on membrane walls, providing reference to the design and operation of similar boilers.

INCREASING OF REABILITY OF WORK OF BOILERS BY EQUAL DISTRIBUTION OF THE HEAT LOAD OVER THE HEIGHT OF FIREBOX

Detection of one of the methods for reducing the emergency screens of boiler units pipes is in the process of being discovered. Specially used in the even distribution of heat load in the active combustion zone, replacing the burners with 1-2 tier arrangement by 2-4 tier, reducing the single power of the finger. Investigation of the supported solution, with the posture of the boiler. The mathematical calculation model and graphical division of the boiler furnace into combustion zones are presented. The results of the research showed that a large number of burners and a decrease in the unit power of the population, which reaches a greater uniform thermal voltage, are detected by the height of the shielded pipe, reducing peak maximum consumption from 100% to 86.5% (590 kW / m2 to 510 kW / m2) As the number of burners increases, the thermal load in the lower part of the combustion zone increases, which results in more intense boiling, as a consequence of the increase in the velocity of the vapor-liquid mixture in the screen tubes and, accordingly, the cooling of the evaporator tubes in the regions of the highest heat load. The temperature of the screen metal in the zones of maximum heat load of the pipes is reduced by 20-30 0C, which, with a long service life, leads to a decrease in temperature aging, and consequently an extension of the inter-repair life of the boiler. The disadvantage of this method is the complication and complication of the manufacture of screen pipes, increase the hydraulic resistance of the lifting pipes by increasing the number of bends of pipes, complicates the system of supply of fuel and air. The results of the calculations are presented in graphical form, as the dependence of the specific heat load, the temperature of the outer wall of the pipe, the allowable thermal stress, the height of the pipe at one-, two- and four-tier arrangement of burners in the zone of active combustion.

Arc Steel Furnace Operation at Changing Working Space Aerodynamic Flows

Results of the design analysis carried out using computer software are presented for boundary data complying with the currently operating state-of-the-art arc steel furnace. Flow of natural gas combustion products and oxygen are reviewed for the radial and tangential burner arrangement in the working space between the wall and the electrodes. Location of high temperature fields is determined and the expected heat transfer to the charge materials through the active surface participating in heat exchange is evaluated. Precipitation degree is determined for the dust participating in scull generation on a wall water-cooled surface and significant reduction of dust effect on electrodes.

Inner aerodynamics of the improved four-vortex furnace model

The internal aerodynamics of a perspective vortex furnace chamber of a pulverized coal boiler with a diagonal arrangement of burners is studied using the non-contact optical method of flow diagnostics: Particle Image Velocimetry - PIV. The results of PIV measurements, characterizing the complex spatial structure of a swirled flow in an isothermal laboratory model of the furnace device, are presented. The velocity distribution in the vortex chamber volume is obtained, and the flow structure in the form of four conjugate closed vortices with curved axes is visualized.

Numerical Research on the Influence of Declination Angle on Carrying Capacity of Tertiary Air, Ignition, and Combustion Characteristics of Pulverized Coal of 300 MW Down-Fired Utility Boiler with Multi-Injection and Multi-Staging Combustion Technology

AbstractA new burner arrangement mode is proposed for a 300-MW down-fired boiler burning bituminous coal (Vdaf=23.59%). Under the new burner arrangement, 21.99% of the total air volume is arranged ...

Hyperspectral imaging and analysis of swirling flames issued from two and four slots circumferential burners

A spectroscopy and visual investigation for turbulent swirling flames formed by four-circumferential swirling turbojet EV in comparison with a two-circumferential swirling air entries configuration burner using hyper spectral camera. The special design of the EV-burner guarantees flame stabilization at the burner exit by a recirculation of hot gases and entrained fresh reactance mixture. A recirculation zone (vortex breakdown) can be generated when a sufficient strong swirling flow exist. The main parameter of combustion diagnostics based on optical devices is the flame itself, whose spectrum is closely related to the process state, as a fingerprint of the instantaneous operational condition, in terms of energetic yield, fuel consumption and pollutants emissions. The hyperspectral imaging technique in the aspect of flame analysis to give a complete description for the flame zones behavior and distribution of reactions through the whole flame. The spectral peaks for issued flames have been studied to give complete vision for the effect of changing the equivalence ratio and different burner arrangement four and two circumferential swirling entries.

Numerical simulation study on the influences of the secondary-tertiary air proportion on the airflow mixing effects and pulverized coal combustion characteristics in a 300-MW down-fired boiler

In this paper, based on the MIMSC (multi-injection and multi-stage combustion) technology, new burner arrangement and air distribution parameter settings were proposed for a 300-MW subcritical down-fired boiler originally using MBEL (Mitsui Babcock Energy Limited) combustion technology. Numerical simulations were conducted to study the influences of the secondary-tertiary air proportion on the airflow mixing effect in the furnace, the ignition and pulverized coal combustion characteristics. The airflow mixing effect in the furnace is characterized by the size of the dimensionless vertical velocity decay area (Vda) and the fluctuation of the maximum vertical velocity decay curve (Vdc). During the research, the sum of the secondary and tertiary air rate remained constant, and the secondary air rate was set to 30.54%, 33.54%, 36.54%, 39.54%, and 42.54%. It was found that under the condition of using new type burner, with the secondary air rate increased from 30.54% to 42.54%, the ignition distance of pulverized coal decreased from 1.30m to 0.84m, the dimensionless penetration depth decreased from 1.46 to 1.27, and the NOx emission and carbon in the fly ash decreased first and then increased. The variation of Vdc showed the following regulation. At the secondary air rate of 30.54% to 33.54%, increasing the secondary air rate decreased the fluctuation amplitude. While at the secondary air rate of 39.54% to 42.54%, increasing the secondary air rate increased the fluctuation amplitude. Only at the secondary air rate of 36.54%, Vdc in the tertiary air mixing area was smooth. When Vdc was smooth, Vda was small at 0.043, the carbon in fly ash at the furnace outlet was the lowest at 4.19%, and the NOx emission was low at 675.9 mg/m3 at 6% O2. An optimal secondary air rate of 36.54% is recommended. For the subsequent design of burner structure and parameters, it is suggested that Vdc in the tertiary air mixing area should be smooth.

Efficiency of application of various layout arrangements of oil-gas burners in thermal power plant boilers

The necessary intensity of burning and completeness of fuel burning out in furnace volume are reached by the correct supply organization and the subsequent mixture of fuel with secondary air that is provided with burner devices. Experimental research of fuel oil and gas combustion efficiency in boiler furnaces of thermal power plant has shown that, the peripheral axial twist executed in the form of two channels with axial scapular air rotator is preferable. The combined gas supply is perspective: tubular peripheral and pilot central. For fuel oil combustion at large expenses the most effective burning is reached due to application of steam-mechanical nozzles which main lack is the considerable length of a torch. The two-tiered arrangement of burners in boiler at combustion of gas and fuel oil is more effective, in comparison with single-tier, both at the counter direction, and at unilateral frontal. For increasing the efficiency of combustion of fuel at some burners types in a boiler furnace the ascending vertical rotation of a torch can be created by the asymmetrical counter arrangement of burners of the first and second tiers. Use of the smoke exhauster of gases recirculation for reduction of harmful emissions of nitrogen oxides with boilers flue gases gives bigger effect in comparison with optimization of the choice of a layout arrangement of burners and parameter of a twist.

Physical and mathematical modeling of solid fuel combustion in the application of direct-flow burners

The tightening of standards for emissions of harmful substances into the air makes it increasingly important to pay attention to fuel combustion technology. The concentration of nitrogen oxides in flue gases on solid fuel boilers, in most cases, exceeds the standard value. The most significant excess in NOx emissions occurs in boilers wit slag-tap removal. The possibility of influence on the aerodynamics of the furnace when using vortex burners, which are individual action burners, on powerful boilers is severely limited. When direct-flow burners, which are collective action burners, there is a possibility of significant impact on the aerodynamics of the active combustion zone. With a rational arrangement of direct-flow burners and nozzles and the use of step combustion, it is possible to provide a significant reduction in the formation of nitrogen oxides, mechanical underburning of solid fuel particles and to prevent the possibility of slag of the screen system. The main problem of using direct-flow burners is the need to study the aerodynamics of each specific combustion volume of different boilers. On the basis of research on physical and mathematical models developed schemes of solid fuel combustion in steam boilers using direct-flow burners and nozzles in the presence of a large number of horizontal and vertical vortices, which should contribute to the efficient combustion of fuel with low emissions of nitrogen oxides.

Unification of Design Solutions for Two Groups of Drum-Type Gas-Fired Boilers with Different Capacities and Steam Parameters

Difficulties in implementing methods for unification of design solutions for power-generating boilers of different capacities are considered. The unification of the designs could result in cost reduction at all stages of boiler manufacturing. Approaches are described that were used to search for solutions for two groups of drum-type gas-fired boilers with capacities of 75–150 and 200–320 t/h that function at different values of the superheated steam pressure and temperature. The selection of the design solutions for the boiler-flow diagrams and the method for the arrangement of the burning process common for all boilers, as well as the evaluation of the efficiency and reasonability of the adopted solutions, have been validated. Considering the experience of manufacturing and operating the boilers and the reliability and efficiency of the heating surfaces, the design solutions are set forth and justified, which include the selection of the material of the tubes and their diameters and wall thickness, the number of parallel coils from one cross section, the coil spacing, and the arrangement of the coils. The criteria for determining the geometry of the heating surfaces for the basic boilers of each group have been established. The possibility of extending the geometric parameters on the boilers of other capacities is considered. The variants of the thermal designs for the boilers operating at 100, 50, and 30% loads calculated using the Boiler Designer and Furnace software programs are provided. The causes as to why the required superheated steam temperature cannot be achieved in all boilers at low loads at the excess air coefficients at the furnace exist specified in the current normative documents have been analyzed. Depending on the parameters that determine the arrangement of swirl burners in the furnace, two different but stable burning process patterns are possible.

Innovative Technologies in the Repowering of the Nizhnekamsk CHPP by Upgrading the TGME-464 Boiler to Combust Pulverized Petroleum Coke

The repowering project of the Nizhnekamsk CHPP involves upgrading the main and accessory boiler equipment to allow flame combustion of pulverized petroleum coke (petcoke) produced by a TANEKO delayed coking unit. The scope of work includes equipping the gas-and-oil fired boiler with a burner arrangement for petcoke combustion and providing central coal pulverization and pneumatic ash handling. To meet the atmospheric emission requirements, it is necessary to equip the boilers with a selective catalytic reduction installation, high-efficiency electrostatic precipitators, and a desulfurization plant.

Application of overfire air technology on an example of a steam boiler PK-39 of the Aksu TPP (Kazakhstan)

When burning any fossil fuels, one of the most harmful combustion products are nitrogen oxides NOx, which damage both the environment and human health in particular. Reduction of NOx emissions from fuel combustion at TPPs plays an important role in reducing the total level of nitrogen oxides NOx emitted into the atmosphere. One way to reduce the concentration of nitrogen oxides NOx is the stepwise combustion of the pulverized coal mixture, in particular the «Overfire Air» technology. The essence of this method is that the main volume of air is fed into the pulverized burners, and the rest of the air is further along the height of the torch through special nozzles. Structurally, the method of stepwise combustion of fuel can be carried out in boilers with a two-tier arrangement of burners along the height of the combustion chamber. In this case, practically no significant reconstruction of the boiler is required, which is associated with additional costs. In the present work, computational experiments on the use of modern overfire air technology (OFA) in the combustion chamber of the PK-39 boiler of the Aksu TPP were carried out and the fields of the main characteristics of heat and mass transfer, as well as the influence of the mass flow of the oxidant through the OFA injectors on the combustion process were obtained.

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.

BURNING FUEL OIL IN BOILERS WITH DIFFERENT CONFIGURATIONS OF BURNERS

The article presents the results of experimental research of efficiency of fuel oil combustion in power boilers at TPPs with different layout of burners at different steam loads. Given the values of efficiency of boilers and of emissions of nitrogen oxides when burning fuel oil. The efficiency of using bunk steel counter arrangement of burners.

Furnaces of the Unified-Family Drum-Type Gas-Fired Boilers

The article deals with supporting calculations of the furnace dimensions and the method for combustion of natural gas for two types of unified-family drum-type boilers with steam capacities of 75–150 and 200–320 t/h at superheat steam pressures of 3.9, 6.9, 9.8, and 13.8 MPa and temperatures of 440, 510, 540, and 560°C. An approach to unification and the requirements of environmental sustainability, economic efficiency, and flexibility and the basic engineering solutions for each boiler type are set forth. A method was proposed and implemented that allows, using the Boiler Designer software, finding the temperatures of the flue gases, hot air, and recycle gases that are necessary for conducting the thermal analysis of the boiler furnace with a single-stage tubular air preheater and determining the most rational unified design of the latter. The basic concepts and criteria are set forth that underlie the calculations of the furnace size in its plan, the furnace height, and the number and arrangement of swirl burners. With the furnace software for expanded thermal analysis of the furnace, the effect of the superheated steam pressure and the furnace height on the enthalpy increment of 1 kg of the working medium in the evaporating heating surfaces was determined for all boilers of the series in question at the nominal load under conventional fuel combustion conditions without recirculation. For the furnace outlet screen, the increment was calculated using the Boiler Designer software. The correspondence between the obtained enthalpy increments and the recommended values was evaluated. For the case of a significant divergence between the above figures, additional engineering solutions were proposed that facilitate the unification of the boilers. Based on the results of the analysis of the boiler furnaces and the expert estimations of the required convection pass height, a furnace height value was selected for each boiler group. The possibility of reducing the nitrogen oxide concentrations in the combustion products of the unified boilers was studied. The calculation investigations show that it is possible to achieve the required nitrogen oxide concentrations in all boilers at the selected furnace heights by stepwise and staged combustion or by injecting the recycle gasses into the burner box. Specific recommendations for the implementation of the above measures are provided.