Direct-flow Burners Research Articles

Investigation into the Influence of Temperature on the Formation of Nitrogen Oxides during the Staged Combustion of Low-Reactive Coal with the Use of Direct-Flow Burners

Investigation into the Influence of Temperature on the Formation of Nitrogen Oxides during the Staged Combustion of Low-Reactive Coal with the Use of Direct-Flow Burners

The use of numerical simulation to determine the coal combustion efficiency in the A-USC boiler

In this paper, numerical simulation of coal combustion in the invert furnace of a boiler for a 500 MW power unit designed to operate on advanced ultra-supercritical steam parameters (A-USC) is performed. The use of A-USC technology makes it possible to reduce fuel costs for electricity production compared to steam turbine units of previous generations. Also it influences to reduce the level of emissions of harmful substances into the atmosphere. Modeling of the invert furnace at the nominal boiler load was carried out for the developed direct-flow burners and nozzles arrangement of burning coal. After numerical simulation the results were obtained and made it possible to analyze the furnace aerodynamics and the temperature distribution inside the furnace volume. The calculation of the indicators of efficiency and environmental friendliness was carried out and their values appeared smaller than regulatory permissions, which allows us to recommend the developed burners arrangement scheme for its use in invert furnaces. The furnace operation simulation at reduced loads of 70% and 50% was carried out and the results showed the reliability of the developed combustion scheme.

STUDY OF THE AERODYNAMICS OF THE FLOW OF THE COMBUSTION CHAMBER OF A POWER PLANT WITH VARIOUS SUPPLY OF SOLID FUEL

Numerical modeling methods have been used to study the effect of an emergency stop of the fuel mixture supply through individual burners on the aerodynamics of the flow in the combustion chamber of a power boiler. The performed computational experiments made it possible to obtain the main aerodynamic characteristics of heat and mass transfer processes (full velocity vector, pressure, kinetic energy of turbulence and dissipation energy) in the volume of the combustion chamber and at the exit from it in emergency mode (two swirl burners are operating) and compare them with traditional solid fuel combustion (basic mode - four direct-flow burners are working). The results obtained indicate that with a vortex fuel supply in the central region of the combustion chamber, a sharp change in aerodynamic characteristics is observed with the formation of a vortex flow, which weakens as the pulverized coal flow and combustion products move to the exit. The presence of a vortex flow causes stable combustion of solid fuel and uniform distribution of heat flows along the walls of the combustion chamber. In addition, the vortex nature of the flow increases the residence time of coal particles in the combustion chamber, which contributes to a more complete burnout and a decrease in the mechanical underburning of the fuel mixture. Such a detailed study of the aerodynamic flow pattern that takes place in the combustion chamber of power boilers of operating TPPs can only be obtained by numerical simulation methods and by performing computational experiments. The highly informative results obtained make it possible to develop “clean” energy production technologies and solve environmental problems of the emission of harmful substances into the environment.

The Coal Dust Combustion Scheme for an Invert Furnace of an A-USC M-Shaped Boiler

The M-shaped boiler construction for the advanced ultrasupercritical steam parameters (A-USC) is proposed in this work. The boiler was designed to operate in a 500 MW unit on low volatile hard coal. This design allows reducing the pipelines length of the high cost steam pipelines made of nickel alloys. A downstream (invert) furnace is offered for this boiler type. The coal dust burning scheme design using the direct-flow burners and nozzles in a system of vertical and horizontal tangential torches and the solid ash removal are proposed. This approach was extensively used earlier on standard shaped boilers, and it was upgraded now for an invert furnace. The goals are achieved by conducting research on the physical furnace model and thermal furnace processes numerical simulation by computational fluid dynamics software. The most significant research results were as follows: the oxidizer stage supply was performed along the torch length and furnace height; the dynamic jet pressure on the furnace walls was excluded; a high degree of coal burnout was ensured due to the vortex furnace aerodynamics implementation; the uniform furnace section filling with air jets was performed; turbulent jets ejection was significantly higher than that for a flat submerged jet; chemical underburning loss did not exceed 0.1%; and unburned carbon loss was 0.8%. The carbon monoxide concentration at the furnace outlet in terms of air excess ratio equal to α=1.4 was 226 mg/nm3 . The nitrogen oxides concentration in the flue gases (normalized) was 424 mg/nm3 . The results significance obtained during the research is efficient solid fuel use with high technical and economic boiler performance.

Investigation of the direct-flow burners and nozzles arrangement at the direct-flow-vortex coal combustion in a furnace with solid slag removal

The paper presents results of the furnace aerodynamics investigation using direct-flow burners and air nozzles (DFBAN) with solid slag removal (SSR). The studies were performed using the computational fluid dynamics software ANSYS Fluent. The paper includes recommendations for the development of effective solid fuel combustion schemes with DFBAN, methods for researching and optimization of the combustion aerodynamics with the use of DFBAN, optimization criteria, initial data for the study. The scheme for burning Kuznetsk lean coal with the use of DFBAN and SSR was developed. Several series of calculations were performed for the developed scheme. In these calculations, the dependencies of the indicators of efficiency, furnace ecological safety and reliability on the nozzles and burners positions, which are located in the first zone of the scheme, were found. The first stage of the optimization of the developed scheme burning solid fuel with the SSR was made.

Investigation of the direct-flow jets vortex motion in the M-shaped boiler invert furnace

For advanced ultra-supercritical parameters (A-USC) of steam, the design of an M-shaped boiler is proposed, designed to operate in a 500 MW unit on a lean coal (grade TR). The boiler profile is selected from the condition of minimizing the length of the main steamlines made of expensive nickel-alloy steel. With regard to this boiler, a scheme has been developed for pulverized coal combustion in an invert furnace using direct-flow burners and nozzles. Research has been carried out on the physical model of the furnace in the implementation of this combustion scheme: a qualitative study of the trajectories of the burner jets, jets of secondary and tertiary air obtained by their hot spark visualization; quantitative determination of the main characteristics of burner jets and their weight gain. The studies have shown the high efficiency of the recommended scheme of the furnace-burner device: a staged supply of the oxidizer along the flame length and along the furnace height is organized; the dynamic pressure of jets on the furnace wall tubes is excluded; vortex furnace aerodynamics should provide a high degree of burnout of coal dust particles; air jets evenly fill the horizontal section of the furnace; the ejection capacity of turbulent jets is much higher than for a flat submerged jet.

Development of a simplified methodology for furnace aerodynamics with vortex combustion of organic fuel modeling

This paper describes the process of developing a simplified methodology for furnace aerodynamics during the development or modernization of combustion schemes with direct-flow burners. This technique is based on the use of numerical modeling of air movement and turbulence phenomena in the furnace volume and allows for a relatively short period of time to analyze a large number of options for the burners and nozzles location. This is its advantage in comparison with the use of experimental modeling or numerical simulation with combustion when analyzing a variety of schemes. The model was developed on the basis of validated results of combustion processes numerical simulation in the K-50 boiler furnace. The paper presents the results of calculations performed for several variants of the simplified methodology. For further use, the option that best corresponds to full-scale studies taking into account the fuel combustion process has been selected. The main states of the methodology are formulated.

Numerical simulation of fuel staged swirl combustion in the invert furnace of boiler on advanced ultra-supercritical steam parameters

The paper considers the schemes of Kuznetsky lean coal combustion for the M-shaped boiler. With such a boiler profile, it is possible to significantly reduce the length of main steamlines, which is especially important for the advanced ultra-supercritical parameters of the superheated steam. The furnace in this boiler unit is performed downward (invert). In this work, the aerodynamics of 6 combustion schemes was simulated by means of computational fluid dynamics. All considered schemes were designed on the basis of direct-flow burners and nozzles. For the most aerodynamically reasonable scheme the thermal processes in the boiler furnace firing Kuznetsky lean coal have been simulated by means of computational hydrodynamics. The simulation results showed a high efficiency of fuel burnout: loss due to unburned combustible equaled 0.1%, carbon-in-ash loss equaled 0.8%. Carbon monoxide concentration at the furnace outlet in conversion to excess air equal α = 1.4 amounted 226 mg/m3, the nitrogen oxides concentration in the flue gases (in conversion to normal conditions) equaled 424 mg/m3. It is appropriate to use the results obtained in this research in the development of new solid fuels combustion schemes.

Design of a combined burner based on the patterns of interaction between an external swirling jet and an axial direct-flow jet

The issue of providing fuel and energy resources to the population depends to a large extent on the wear of thermal networks, as well as heat-generating equipment, which, accordingly, forces the consumer to abandon the centralized heating supply in favor of decentralized supply. However, low-power heat-generating units for autonomous consumers do not most of the time operate under the rated mode. The most promising way to solve the issue of energy conservation is to improve the utilization rate of fuel and energy resources in heat-generating units for decentralized heating systems that operate under non-stationary regimes. An experimental study of the velocity field of interaction between the coaxial axial direct-flow and external swirling jets has established that the performance efficiency of a heat-generating plant at a change in the thermal load could be improved by controlling the resulting velocity field. For a more even distribution of temperature within the furnace volume, it has been proposed to supply fuel with an oxidizer in the furnace by the axial direct-flow and swirling coaxial jets. It was revealed that at a distance of 2 diameters of the axial branch pipe from the cut there occurs a transverse toroidal vortex. The appearance of such a vortex is explained by the emergence of low-pressure regions due to the different angles of opening of the swirling outer jet and axial direct-flow jet. The considered dependence of change in the gas flow rate at a decrease in power has demonstrated that the gas flow rate in the proposed burner is less than that in analogs (vortex burner or direct-flow burner) by 10‒15 % when the power of the burner is reduced. At the same time, the specified advantage is limited to the range of the burner's power of 50‒130 kW. The results reported confirm the possibility of controlling the velocity field and temperature distribution when the total fuel and oxidizer flow rate changes within the operational range of low-power heat-generating plants. The correspondence between the temperature field and the velocity field in the interaction of non-isothermal jets has also been shown

Physical modeling of the M-shaped boiler furnace aerodynamics

In order to increase the thermodynamic efficiency of the Rankine cycle, in Russia, China, the USA, and EU countries, new-generation power units with advanced ultra-supercritical (A-USC) steam parameters are being developed. Using A-USC steam parameters (temperature – 700-760 °C, pressure – 35 MPa) will lead to the need to use expensive nickel steels. A single-shell design of the M-shaped boiler for burning Kuznetsk coal grade TP with solid slag removal (SSR) was proposed to reduce the total length of the main steam pipelines. A solid fuel combustion scheme with direct-flow burners, nozzles and system of vertical-horizontal tangential flames (VHTF) has been developed for this boiler, which will ensure: emissions of nitrogen oxides into the atmosphere at a level lower than standard; continuous operation of the boiler in the absence of slagging of the furnace walls and overheating of the pipe metal; a high degree of burnout of coal dust, with the provision of the standard value of the mechanical underburning of fuel; long minimum boiler load at a level not exceeding 40% of the nominal one according to the conditions of coal dust combustion stability.

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.

Investigation of the interaction of turbulent jets in furnaces with direct-flow burners for high-power boilers

The aim of the study is to develop a highly efficient scheme of combustion of low-grade solid fuels with the realization of regulatory requirements for emissions of hazardous substances into the atmosphere. One of the directions of practical application of such a scheme is conversion of boilers with liquid slag removal to solid slag removal. Liquid slag removal boilers have a number of disadvantages that make their use in modern conditions impractical: reducing the reliability of the liquid slag at low loads and high emissions of NOx nitrogen oxides, which exceed the standard values 2-3 times. In light of amendments to the environmental legislation of the Russian Federation, changing the order and rates of payment for emissions of hazardous substances from 2020, thermal power plants will be forced to implement environmental measures to ensure normative values of specific emissions. The basic principles of effective solid fuel burning organization with the application of direct-flow burners have been formulated on the basis of the conducted research.

Investigation of the Combustion Process of Solid Fuel in Furnaces with Direct-Flow Burners

The optimization of the boiler furnace’s aerodynamics is considered in order to increase the efficiency of burning power-generating fuel by the example of burning lean Kuznetsk coal in a solid slag removal scheme. Combustion options have been proposed and investigated in schemes with direct injection of coal dust and with an intermediate coal dust hopper. The schemes use direct-flow burners with an counter-displaced arrangement and nozzles with a downward inclination, and staged combustion of fuel is used. A study of the furnace’s aerodynamics on an isothermal bench was carried out. The results of physical modeling were compared with the data of numerical modeling of an isothermal bench. It is noted that combustion schemes differ in the intensity of vortex formation in the active combustion zone. A numerical simulation of fuel combustion in the boiler furnace was performed using the two indicated combustion schemes. The purpose of the simulation was to obtain the distribution of temperatures, gas velocities, concentrations of combustion products, nitrogen oxide emissions, degree of burnout in the furnace volume and other characteristics that affect the efficiency, reliability, and environmental safety of the boiler. The results of model studies showed that the developed schemes provide high efficiency of burning lean Kuznetsk coal with solid slag removal and, at the same time, low emissions of nitrogen oxides. An additional verification of the numerical model was carried out by comparing the gas temperatures by the height of the furnace obtained by its numerical simulation and thermal zone calculations. A comparison of the temperatures of the gases at the outlet of each zone showed their good agreement (the difference was no more than 30°C).

3-D modelling of heat and mass transfer during combustion of low-grade coal

Using numerical methods, the basic characteristics of heat and mass transfer processes in the furnace chamber of the BKZ-75 boiler of the Shakhtinskaya TPP (Kazakhstan) were studied during a forced partial stop of the supply of coal dust through the burners. Two modes of fuel supply were studied; a direct-flow method of supplying air mixtures, when two direct-flow burners are working and two are in emergency mode and vortex method of supplying air mixtures - two vortex burners with a swirl angle of the air mixture flow and their inclination the center of symmetry of the boiler by 30? and two are in emergency mode. The computational experiments allowed to obtain the distributions of the total velocity vector, temperature fields, concentration fields of CO, NO2 throughout the entire volume of the combustion chamber and conduct a comparative analysis for the two investigated emergency mode (direct-flow and vortex). Based on the results, it can be concluded that in the case of a forced partial stop of the supply of coal dust, the use of the vortex method of supplying air mixtures improves heat and mass transfer processes and allows minimizing emissions of harmful substances.

Numerical study of the methane-air combustion in the direct-flow burner of the boiler 300 MW TGMP-314 boiler

This paper presents the results of the numerical simulation of the methane-air combustion in the direct-flow burner. The construction of the burner was proposed by the Department of Thermal power plants MPEI for organization the staged combustion. the burners are designed for installation on boiler 300 MW TGMP-314 at thermal power plane in Moscow. The simulation of five modes of operation of the burner depending on the boiler load was carried out using modern packages of computational fluid dynamics ANSYS. The goal of this work is to investigate effects of replacement of existing vortex burners in previously described facilities with the direct-flow burners with organization of the new combustion process. As results after the simulation, the parameters of the numerical values of the turbulence parameters and the mass fractions of various substances for the gas-air flow in the boiler inlet plane was obtain. On the basis of the obtained results analysis of the proposed design of the burner was made. Numerical values of the parameters of the gas-air flow in the plane of the inlet to the boiler will be used later as input data for the numerical simulation of the boiler furnace.

SLOW-UP GENERATION OF NITROGEN OXIDES BY TURNING THE PRIMARY AIR FLOW IN THE SWIRL BURNER OF THE BOILER TPP 312

The aim of the work is computer simulation of the formation of nitrogen oxides in the furnace of the boiler TPP 312 with the swirl of the primary air in the boiler burners. The organization of the vortex flow allows reducing the generation of nitrogen oxides due to the formation of a return flow, which ballasts the combustion zone by oxidation products. The limitation of this technique is the reduction of the combustion temperature which can lead to underburning.
 The objective of the study is to determine the formation of nitrogen oxides based on computer simulation of the gas dynamics of the firing space of the boiler TPP 312 DTEK Ladyzhyn TES when swirling streams of air are used in the burner channels.
 Efficient combustion of fuel, in particular solid, is ensured by three factors: mixing of the fuel and the oxidizing agent, residence time in the temperature zone necessary for the combustion of fuel particles and temperature. The selection of the parameter is under pressure from requirements operating in opposite directions. On the one hand, a higher temperature contributes to better fuel burning, but, on the other hand, the formation of nitrogen oxides increases at a higher temperature.
 Analysis of the data on the quality of coal that comes to the station made it possible to derive the averaged characteristics of coal that were used to improve the combustion model of the software package.
 Conclusions
 In the presence of swirling flow, the maximum temperature is 108 K lower than in the case of a direct-flow burner, which causes a 5% reduction in the generation of nitrogen oxides. Centrifugal flows created a rarefaction zone at the burner axis and the reaction products begin to heat the fuel mixture in the burner itself. The surface area of ​​the beginning of combustion during the application of twisting reduces by 30%.
 The results of the study showed that the twisting of the primary air does not lead to a significant reduction of nitrogen oxides.

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.

Combustion of liquid hydrocarbons in a jet of superheated steam

The process of combustion of liquid hydrocarbons with spraying by a jet of superheated steam in a direct-flow burner is studied experimentally in this work at the example of diesel fuel. The aim of research is to study the effect of regime parameters (steam and fuel flow rate) on the main characteristics of the process. Specific amount of heat and useful thermal power were determined from the measurements on a flow calorimeter, a gas analyzer Testo 350 was used to perform the gas analysis of combustion products. A regime map was plotted and results of characteristic combustion conditions were presented. The regimes of high completeness of fuel combustion with low production of toxic combustion products were determined.

Development of the scheme of stepwise combustion of coal in the inverter firebox of a power unit of 1000 MW power

The desire to increase the efficiency of using the heat of burned solid fuel leads to the significant growth of the initial steam parameter at steam-turbine plants. At the maximum temperatures of fresh and secondary steam of 700–720°С, the price of connecting of steam pipelines between the boiler and turbine is up to 20% of the price of a power plant unit, which dictates the necessity to decrease their length. One of the methods to achieve this is the application of an inverter firebox. An M-shaped profile of boiler, allowing one to decrease the length of heat-resistant steam pipelines, was developed at NRU MPEI. A distinctive feature of the profile is two inclined connecting gas flues between the firebox and convective shaft, starting from the gas windows located in the lower third of the firebox height. The boiler was designed for the steam production of 2493 t/h with the parameters of fresh steam of 35 MPa and 710°C. Thermal and aerodynamic calculations made it possible to get the sizes of boiler and dimensions of heating surfaces, and they also allow one to get the values of temperatures in the characteristic points along the gas path. On the basis of the results of calculations, the coefficient of efficiency of the boiler was 93.07% and the fuel consumption was 91.13 kg/s. For this boiler, the technology of effective stepwise burning of coal in a direct-flow-vortex torch (DFVT) in a system of vertical and horizontal tangential torches in the mode of solid slag removal, previously successively used in boilers with a traditional profile and upgraded to an inverter firebox, is proposed. The layouts of the direct-flow burners and nozzles for even and odd vertical sections of the firebox and also in a horizontal section were proposed. Organization of staged air supply in the vertical direction with a high fraction of in-firebox recycle of hot gases leads to low concentration of nitrogen oxides.

Efficiency of using direct-flow burners and nozzles in implementation of dry-bottom ash removal at the TPP-210A boiler furnace

In reconstruction of operating pulverized coal-fired boilers, one of the main factors is the choice of a method for slag removal: dry bottom ash removal (DBAR) or slag-tap removal (STR). In this case, ecological and economic aspects should be taken into account, and also the early ignition of pulverized coal fuel, the reliability of operation of the furnace walls in the mode without slagging, and the stability of slag removal should be provided. In this work, issues of changeover of the pulverized coal-fired boilers of the TPP-210A type from the STR mode to the DBAR mode are considered. As of today, the main problems during the operation of these boilers are the high emissions of nitrogen oxides together with flue gases into the atmosphere and the appropriated payoffs, a small range of loads available, the necessity of stabilization of the pulverizedcoal flame sustainability by using the highly reactive fuel, large mechanical fuel underburning, etc. Results of studying aerodynamics of a furnace with DBAR obtained in the process of physical simulation are given; technical solutions and preliminary design (configuration of burners and nozzles in the boiler furnace, conceptual design of the pulverized coal burner, configuration of TPP-210A boiler with the low heat liberation of furnace cross-section and volumetric heat release) are set forth, which are associated with the optimization of aerodynamics of furnace volume, when the direct-flow burners and nozzles are used, and with organization of the efficient staged combustion of solid fuel. Two versions of possible modernization of a boiler unit are considered. Under conditions of the planned increase in the steam production capacity, the most promising measures are as follows: the DBAR implementation with reducing heat releases of the cross-section and volume of the furnace approximately by half, the installation of the direct-flow burners and nozzles with injection of recirculation gases into the active combustion zone by bleeding them from the turning chamber.