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In response to high-temperature corrosion after low NOx transformation with separate over fire air (SOFA), combined arrangement of corner and wall tangential firing burners, as well as anti-tangential and deflecting air technology are studied. Numerical simulation with realizable $$k-\varepsilon$$ two equation and Non-premixed combustion including probability density function model (PDF) is carefully adopted. Result conveys that application of combined arrangement can remarkably reduce the tangent circle in the furnace, lowering the probability that coal particles might strike the furnace wall. Also, lower CO and temperature near the wall would greatly decelerate the high-temperature corrosion. Further studies conclusively show that the performance has no linear relation to the angle in deviation cases. If properly arranged, combined burners layouts behave better than deviation (including anti-tangential) methods in restraint of high-temperature corrosion. All the technologies play effective roles in NOx reduction that the best-performing anti-tangential case 4 has a 50.7% drop from original case. Remission of high-temperature corrosion will have great economic and security importance.

Computational fluid dynamics (CFD) has become an essential tool for optimizing the design and diagnosing the operation of a boiler. However, the validity of the results depends on the degree of numerical diffusion as well as the reliability of the submodels. This study aims to assess mesh sensitivity in the reacting two-phase flow of pulverized coal in a common tangential-firing boiler. Three mesh versions were constructed for the boiler with the number of cells ranging between 1.2 million and 5.4 million, corresponding to 0.0114 -0.0022 m3 per cell in the burner zone. The velocity distribution was found to be highly sensitive compared to temperature, heat flux, and NO concentration. By contrast, the use of key performance parameters such as total wall heat absorption, exit NOx concentration, and carbon conversion, was not appropriate criteria for the mesh sensitivity test. These parameters were determined by integration over the entire surface or volume, which made them sensitive to the overall reaction stoichiometry instead of the mesh fineness. It suggests that the use of a coarse mesh could be acceptable in evaluating the key performance parameters influenced by major operation variables, such as air distribution and fuel properties. However, sufficient mesh fineness is necessary for studies requiring accurate prediction of detailed flow patterns such as the evaluation of burner tilting/yawing or ash deposition on the wall.

A comprehensive numerical study of the combustion optimization of a 660-MW tangentially fired boiler under the constraint of steam tube overheating is presented. To obtain the chemical products and the heat flux at the heating surfaces, a three-dimensional (3D) combustion model was established using computational fluid dynamics (CFD) software. In addition, a 1D + 1D thermal hydraulic model was developed using MATLAB to describe the heating process inside the tubes. Detailed mapping methods were also provided to connect the mesh systems in CFD and MATLAB. As a result, the tube wall temperature can be calculated by considering the coupled heat transfer on the gas and steam sides. The simulation results reveal that under full load conditions, the upward tilting of the separated over-fire air (SOFA) burners can reduce the formation of CO and NOx, which helps achieve higher boiler efficiency. However, when the SOFA tilt angle increases from +20° to +30°, 0.16% of the outer surfaces of the final re-heater would exceed the allowable temperature of the TP347H material; additionally, the improvement in the boiler efficiency and decrease in NOx formation are much less. Thus, considering the unit’s safe operation, the optimal SOFA tilt angle for combustion optimization should be +20°.

Evaluating ash slagging can alleviate the operational problems and improve the efficiency of coal-fired boilers. This paper presents methods to quantify the extent of slagging in a 500 MWe tangential firing boiler by determining the thermal resistance and relating it to ash properties. To determine the thermal resistance by slagging, the operational data of the boiler were extracted for six coal-blend cases and analyzed using a one-dimensional process model. Although the conventional slagging indices based on ash composition have generated conflicting results, new indices based on thermo-mechanical analysis (TMA) of the coal-blend samples provided reasonable agreement with the operational data. In particular, the second peak of the TMA associated with the growth rate was correlated with the thermal resistance of the superheaters, and the third peak representing the slag melting was inversely correlated with that of the furnace wall. It was also found from the numerical modeling of the slag flow on the furnace wall that the critical viscosity temperature at 25 Pa·s can be positively related with the thermal resistance, and consequently, with the slagging propensity of specific coal ashes.

Boilers have contributed significantly to the production of energy and other processes in industry. Understanding the combustion characteristics inside a boiler is essential to increase the efficiency and reduce environmental-related concerns. The novelty of this work is associated with a detailed analysis of the effectiveness of a developed co-firing coal-natural gas burner and the arrangements of the burners in the boiler for efficient combustion. Comparisons were made between the front-wall, the opposite-wall, and the tangential firing types. The characteristics of the flow, the coal particle motion, the temperature distribution, the concentrations of species, and NOx emission levels are examined. The results showed that each burner in the front-wall-fired type creates independent long flame zones. In an opposite-wall fired type, the flames of burners impinge upon the center of the furnace to create turbulence. Results show that front-wall and opposite-wall firing configurations exhibit hot peak zones and temperature imbalances near the furnace sidewall. This emphasizes the need for heavily swirling vanes in the main burner to shorten the flame length and mix the fuel and oxidant well for efficient combustion. The state-of-the-art tangentially fired configuration produced a fireball, ensuring thorough mixing in the furnace and allowing for the complete combustion and uniform distribution of the temperature such that NOx reduction occurs preferentially. Additionally, these results confirm the advantage of combusting coal with natural gas in the main burner, as doing so reduces NOx emissions up to 19%. The technological options identified offer potential for interested manufacturers, researchers, and others in related industries to improve the performance and reduce the emissions of industrial dual-fuel-fired combustion utilities.

An experimental cold-model of a simplified tangential firing boiler was established to investigate the mesoscale turbulent flow behaviors, including gas vortex structures, particle motions and interactions between two phases. A modified PIV technology, employing two pairs of lasers and cameras, was applied to measure the velocity and velocity gradient of turbulent flow in foursquare tangential jets alternatively. At a given initial gas velocity and particle mass loading, the interaction between gas and particles was studied at three different particle sizes. It was found that two main coherent vortex structures, circular eddy and hairpin eddy, distributed mainly in low speed area and heavy impingement area, respectively. The characteristics of particle motion in foursquare tangential jets correlated with gas turbulence dissipation, particle size, particle concentration and particle density. Small particles were easily entrained by gas vortex, so that they consumed more turbulence energy and attenuated the gas turbulence intensity. On the contrary, large particles had more inertia and led to heavier impingement in the chamber center, resulting in particle random distribution and complex momentum transfer between gas and particles. Moreover, large particles stretched the coherent vortex to be narrow and long, while small particles pulled down the vortices rotation intensity.

In this study, a numerical and experimental investigation on the flow field in a 500-MW unit of a tangentially fired boiler has been performed to understand the effect of residual swirl on the temperature distribution and inconsistency of flow velocity in the crossover pass. The k–k L –ω turbulence model was used in this study to analyse the possible formation of transition flow in the tangential firing boiler. Furthermore, 1D and 3D hybrid modelling were used for the simulation of the convective heat transfer in the boiler tube assembly. The commercially available code ANSYS Fluent and COMSOL were used for the studies, respectively. The numerical results for the velocity profile and residual swirl in the boiler were validated using the experimental results from the cold air velocity test, in which the flow velocity was directly measured in the full-scale boiler. The computational results agreed well with the experimental findings. Furthermore, from a comparison of the simulation and experiment, it was found that the biased gas flow induces non-uniform tube temperatures at the crossover pass area of the tangential firing boiler. These results aid in the detailed study of the residual swirl effects on the temperature or flue gas at various locations of the boiler. This study indicates that a non-uniform tube temperature at the crossover pass is an inherent problem resulting from residual swirl in the tangential firing boiler. Therefore, the pulverised coal burner should be fine-tuned to avoid tube rupture due to local overheating.

Four-wall tangential firing (FWTF) is a newly developed furnace arrangement used in supercritical and ultra-supercritical 600-MW boilers. In this study, flow characteristics of the flue gas in furnace of a 660-MW boiler firing pulverized coal with FWTF arrangement were investigated through numerical simulations. The variation characteristics of the tangential circle size of the furnace and flue gas bias at the furnace exit were determined. The results show some differences in the flue gas characteristics between the FWTF and traditional four-corner tangential firing (FCTF) in the furnace. In the FWTF, the variation in the actual sizes of the tangential circle in the burner zone is insignificant; the maximum size with respect to geometric limitations is largely maintained. Hence, unlike conventional FCTF, the size of the tangential circle cannot be used as a reliable parameter to analyze the variation in flue gas characteristics in the FWTF. Moreover, the flue gases are uniform and have high fillin...

The use of separated overfire air (SOFA) has become a standard technique of air staging for NOx reduction in the coal-fired boiler and can also be applied to existing boilers by retrofit. This study was to optimize the air distribution for the proposed SOFA installation in a 500 MWe tangential-firing boiler that has 20 identical units in Korea. Using computational fluid dynamics (CFD) incorporating advanced coal combustion submodels, the reference case was established in good agreement with the design data, and different flow ratios of burner secondary air, close-coupled OFA (CCOFA), and SOFA were evaluated. Increasing the total OFA ratio effectively suppressed NO formation within the burner zone but had a negative impact on the boiler performance. With moderate air staging, NO reduction became active between the CCOFA and SOFA levels and, therefore, the OFA distribution could be optimized for the overall boiler performance. For total OFA ratios of 25% and 30% with respective burner zone stoichiometric ratios of 0.847 and 0.791, increasing the SOFA ratio to 15% and 20%, respectively, was ideal for decreasing the unburned carbon release and ash slagging as well as NO emission. Too high or low SOFA ratios rapidly increased the unburned carbon because of inefficient mixing between the strong air jets and char particles. Based on these ideal cases, the actual air distribution can be adjusted depending on the coal properties such as the ash slagging propensity.

Low-alloy and heat-resistant steel generally shows good anti-corrosion performance. Also unlike CFB boiler, there is little serious erosion happening in furnace of the pulverized coal boiler due to the low particle concentration. But when subjected to the coupled effect of high-temperature corrosion-erosion, serious failures would occur. This study analyzed the reason for eroded failure of water wall tubes of a 660 MW supercritical boiler with pulverized coal combustion, concluding that such failure resulted from the coupled effect of high-temperature corrosion-erosion. Analysis of the failed sample determined that failure was caused by the combination of high-temperature corrosion-erosion and the rate of failure was faster than that occurring solely by erosion. The numerical simulation result also showed that the H2S concentrations of the fault areas are much higher than others which are coincide with the fact. Furthermore, the study proposed the way of improving the situation for the special four-wall tangential firing through numerical simulation.

In this work, an integrated numerical model combining combustion and fluid heating was established for a 660 MW coal-fired boiler. To validate the accuracy of the developed model, related experiment was also conducted, and shows that the relative errors (REs) of several predicted parameters on both flue-gas side and water-steam side of the boiler are less than 7 %, which meets the requirement of analysis. The results indicate that the effect of SOFA tilt angle on gas temperature deviation (GTD) is greatest, and that of SOFA’s proportion follows; while GTD presents a smallest sensitivity to the concentration of O2. This is because O2 concentration mainly affects the average value of the gas temperature, but barely changes its distribution. By contrast, altering SOFA’s tilt angle and its proportion directly varies the shape, location, and area of the high-temperature and low-temperature regions at the entrance profile of the horizontal crossover pass, so these two factors play a more important role in the variation of GTD.

The NOx emissions prediction modeling of a coal-fired boiler is a complicated problem because of its highly nonlinear and strongly correlated multi-variables. To address this problem, this paper presents a novel deep structure using continuous restricted Boltzmann machine (CRBM) with support vector regression (SVR). A new steady-state identification method is first established by applying kernel principal component analysis (KPCA). Subsequently the stationary samples are subjected to the stacked CRBM network for extracting implied features. The combination of the optimal features and target NOx values are further utilized for training SVR to establish the regression pzmart of the CRBM-SVR prediction model. Additionally, particle swarm optimization (PSO) is applied for optimizing hyper-parameters of SVR, and weights of CRBMs are fine-tuned with gradient descent on account of prediction errors. Compared with the existing state of the art, the proposed structure achieves a good performance of 4.83 mg/m3, 3.55 mg/m3 and 0.963 of RMSE, MAE and R2.

Complete fuel switching from heavy fuel oil (HFO) to bioliquid (BL) was demonstrated in a 100 MWe-capacity boiler with a tangential firing configuration. The BL from the residue of palm oil production successfully replaced HFO at the full load (103 MWe) with new atomizers and minor adjustments to the operating parameters. The detailed combustion and heat transfer characteristics of the two fuels were analyzed using computational fluid dynamics (CFD). Compared to the HFO firing case, more uniform distributions of the gas temperature and heat transfer rate were observed in the combustion zone for the BL firing case. The total heat transfer rate was slightly lower on the furnace wall (evaporator), but this disadvantage was offset by the increased convection in the downstream heat exchangers. Because of the low soot concentration, the contribution of convection in the BL-firing case was larger in the lower furnace. A significant reduction in SOx and NOx emissions was achieved due to the low S and N content of BL, which would be the main benefit of fuel switching, in addition to the minimization of greenhouse gas emissions. In the future, the CFD model established in this study could be applied to the evaluation of BL different candidates and various co-firing cases with HFO.

The furnace core temperature (FCT), wall temperature, and tangential circle diameter in a 1 MW four-wall tangential firing furnace (FWTF(F)) were investigated in detail. The FCT and wall temperature of the primary air section of corner tangential firing furnace (CTF(F)) were also studied for comparison. Results show that compared with CTF that exhibited higher temperature distribution in the center of the furnace wall and lower at the corner where the burners are installed, FWTF is more conducive for gas-powder mixture timely ignition and burnout because of the higher temperature and heat flux in the burner zone. FWTF can efficiently prevent slagging in the burner zone because of the small temperature difference of the primary air section. The wall temperature in FWTFF exhibited uniformity, became an uneven parabola-like distribution, and exhibited uniformity again along the flue gas. The maximum temperature difference in CTFF was 1.48 (anthracite) and 3.65 (bituminous) times of that in FWTFF. The actual tangential circle diameters of anthracite and bituminous in FWTFF were approximately 3 and 7.6 times of imaginary tangential circle diameter, respectively.

In the present paper, computational fluid dynamic modelings were established to research a newly presented re-heat steam temperature deviation solution on the basis of FLUENT 6.3.26 considering a 700 MWe tangentially fired pulverised-coal boiler, which confronted with severe flue gas and re-heat steam temperature deviation. The model was solidly validated by grid independence test and comparison with the experimental data obtained from a series of on-site measurements. Upon reliable validation, the model was further used to investigate the forming mechanism of re-heat steam temperature deviation as well as the influence of burner tilt angle on it. The conclusions mainly include (1) Residual swirling flow in the upper furnace caused the flue gas velocity and temperature deviations in crossover pass. For a typical anticlockwise tangential firing system, the flue gas velocity and temperature were lower in left part of crossover pass. The deviation of flue gas further generated the convective heat transfer imbalance of final re-heater, therefore, the temperature deviation of re-heat steam was severe. (2) Tilting the burner upward can effectively reduce the intensity of residual flow as well as the flue gas deviation degree. The + 11° tilt angle of burner was relatively optimum considering the flue gas deviation and final re-heater overheating potential. Specifically, the intensity of residual swirl flow dropped 44% with burner tilting upward for + 11°. Practical operation of boiler demonstrated that the reheat steam temperature deviation was reduced from 22 °C to 10 °C in this case. (3) When the tilt angle of additional air (AA) was bias set, the flow field of upper furnace was changed. Consequently, the residual swirl flow intensity and the flue gas deviation were reduced considerably. On-site measurements indicated that the combination of tilting burner upward for + 11° and setting the bias of AA tilt angle for 10° can further reduce the re-heat steam temperature deviation to 4 °C.

A new kind of tangential firing—four-walls tangential firing (FWT)—has been gradually adopted in large utility boilers, particularly supercritical boilers. It is necessary to determine the airflow characteristics of this new method. In this study, we use a cold modeling experimental device in laboratory based on the prototype of one 660 MW power supercritical boiler with FWT. From results of particle tracing and particle dynamic analyzer measurements, we study the airflow characteristics in the furnace. We also compare the observed airflow characteristics with those of traditional four-corners tangential firing (FCT). We are able to discern differences in airflow characteristics between FWT and FCT. We find that for FWT, the rigidity of the jets is not only influenced by the rotating airflows, but also by the adjacent upstream jets. Furthermore, the airflow velocities close to the wall of FWT are significantly higher than those of FCT and the directions of the airflow are almost all oriented toward the wall.

Based on a corner tangential boiler in a power plant, Temperature field, flow field, velocity field and other factors in furnace is simulated with FLUENT software at different boiler bottom air leakage ratio. These study results provides a further evidence for high efficient and safe operation of boilers.

With the use of computational fluid mechanics software – FLUENT, the numerical simulation computation of combustion process inside a certain 200MW corner tangential firing boiler whose combustor is transformed by the multi-grade efficient low-nitrogen combustion technology was conducted, thus the furnace temperature, velocity, mixture and NOx concentration field at rated conditions before and after the transformation were obtained. The calculation results were highly identical with the industrial test results. The results show that after using the multi-grade efficient low-nitrogen combustion technology, the NOx emissions significantly lowered down with the drop of about 40% compared with the emissions before transformation, while the furnace coking and high temperature corrosion were effectively controlled, achieving good economic and social benefits and providing a reference to the design and transformation of the same types of boilers.

By using the computational fluid dynamics software Fluent and the choice of the reasonable mathematical model, the flow, heat transfer and combustion are simulated in a 300 MW tangential firing boiler furnace. In the process of numerical simulation in the furnace, the gas phase turbulent flow usesRealizable model for both sides and solves the governing equations using SIMPLEC algorithm. Calculation results show that the highest temperature in the furnace is in the burner area,the whole furnace space rotates flow field, residual rotation still exists in the exit of the furnace, and the smoke temperature deviation causes in the residual rotation of furnace exit.

The FLUENT computational fluid dynamics software package was used to model outlet velocity and temperature inhomogeneity in a 1000 MW dual circle tangential firing single furnace ultra-supercritical boiler. These computations allowed a theoretical analysis of thermal deviations at the furnace outlet and suggested means of reducing such deviations. This work involved study of radiative and convective heat transfer of the upper furnace platen superheaters, the radiative–convective heating surfaces above the furnace nose and the convective heating surfaces in the horizontal flue. The results demonstrated that the radiant heat load of the heating surfaces of the platen superheaters is related to the sectional dimensions of the furnace and exhibits a bimodal distribution in the boiler modeled during this work. It was also determined that a large recirculation zone is formed in the central section of the horizontal flue owing to velocity superposition. After establishing the thermal load distribution characteri...

An IFA300 constant temperature anemometer system is adopted to perform cold air experiments on a scale model of a dual circle tangential firing single furnace ultra supercritical boiler to investigate the causes and influencing factors of jet deviation in the furnace, which is the main cause of the elliptical aerodynamic field. The elliptic aerodynamic field could cause heat imbalance in the burner zone, in which case high temperature corrosion and slagging might happen on the high-temperature furnace wall. Theoretical derivations and analysis have been carried out before any experimental studies, and an equation determining the influencing factors of the jet deviation has been established. The experimental results agree well with the equation. The jet deviation becomes more problematic when the velocity ratio of the impacting jet and the impacted jet increases from 0.85 to 1.30. A reduction in the distance from the impacting position to the root of the impacted jet also increases the jet deviation as well as the angle between the impacting jet and impacted jet. The results of the theoretical analysis and experiments provide some transformations within the boiler that could be adopted to avoid the formation of the oblique ellipse flow field.

The characteristics of the WGZ170/9.8-3 pulverized coal boiler were obtained based on cold test，Including the air velocity distribution in tangential firing boiler and the relation between air distribution with opening of each secondary air dampe，The test results had determined that the baffle of blower at around 40% and two parallel draft fan about 45% were relatively appropriate. and the air distribution and opening of each secondary air dampe and balancing the distribution of primary air and second air along the width direction of the boiler hearth were confirmed through test，and the aerodynamic field inside the boiler was investigated based on the tie-floating test．and good aerodynamic field can be obtained after distributing the primary air and second air reasonably，which guarantee the ignition and stable operation of the boiler．

Thermal power plants are a large source of greenhouse gas emissions among energy industry facilities. Emission factors for methane and nitrous oxide depend on combustion technologies and operating conditions and vary significantly with individual thermal power plants. Due to this variability, use of average emission factors for these gases will introduce relatively large uncertainties. This study determined the CH4 emission factors of thermal power plants currently in operation in Korea by conducting field investigations according to fuel type and type of combustion technique. Through use of the Monte Carlo simulation, the uncertainty range for the CH4 emission factor was determined. The estimation showed, at the 95% confidence level, that the uncertainty range for CH4 emission factor from a tangential firing boiler using bituminous coal was &minus, 46.6% to +145.2%. The range for the opposed wall-firing boiler was &minus, 25.3% to +70.9%. The range for the tangential firing boiler using fuel oil was &minus, 39.0% to 93.5%, that from the opposed wall-firing boiler was &minus, 47.7% to +201.1%, and that from the internal combustion engine boiler was &minus, 38.7% to +106.1%. Finally, the uncertainty range for the CH4 emission factor from the combined cycle boiler using LNG was &minus, 90% to +326%.

In this paper, the flow field characteristics of over fired air (OFA) for novel low NO x pulverized coal combustion technology are studied. The research was conducted with a 300 MWe tangential firing boiler that was adapted for this technology, and a three-dimensional particle-dynamics anemometer (PDA) was employed on the model to measure the characteristics of gas flow in the burnout area and gas/particle flows under the front panel superheater. The impact of a positive offset at 15°, counter offset at 15° and design case without an offset the OFA relative to the direction of the secondary air jet in the main combustion were considered. With different OFA offsets, the deflection characteristics, the velocity and root mean square (RMS) fluctuation velocity of OFA jet are obtained, as well as the gas/particle flows characteristics under the front panel superheater. The results show that, with a positive offset, an over-large tangential circle is formed, which produces slagging and temp-bias under the panel superheater. However, with a counter offset, the OFA is sent into the center of the chamber, and the particle is forced to the water wall. Compared with the other two conditions and combined with the counterflow of primary air, OFA without an offset for the jet contains a proper tangential circle, strong inflexibility and turbulence, which prevents slagging and burn out.

In this paper, a new technology for a tangential firing pulverized coal boiler, high efficiency and low NO x combustion technology with multiple air-staged and a large-angle counter flow fuel-rich jet (ACCT for short) is proposed. To verify the characteristics of this technology, experiments of two combustion technologies, ACCT and CFS-1 (Concentric Firing System-1), are carried out under a cold model of a 1025 t/h tangential firing boiler with a PDA (particle dynamics anemometer). The distributions of velocity, particle concentration, particle diameters and the particle volume flux of primary air and secondary air are obtained. The results show that the fuel-rich primary air of ACCT can go deeper into the furnace and mix with the main flow better, which means that the counter flow of fuel-rich jets in ACCT can realize stable combustion, low NO x emission and slagging prevention.

An experimental and numerical study on the effect of opposing tangential primary air jets with different biased angles on aerodynamic fields in the furnace and the flue gas velocity deviation in the horizontal flue gas pass was carried out in a tangentially fired boiler model of a 600 MW unit. The results show that the flow fields in the left and right sides of the upper furnace are obviously different and the gas velocity deviation in the horizontal flue gas pass is large for the original tangentially fired system. However, the actual tangential circle diameter in the furnace, the residual swirl intensity at the furnace exit, and the flue gas velocity deviation in the horizontal flue gas pass will be reduced when the appropriate opposing tangential angle of primary air jets is adopted in a new tangential firing system. The appropriate opposing tangential angle of primary air jets is 10−15° relative to the original primary air jets, and the ratio of opposing tangential momentum flux moment to tangential m...

The Computational fluid dynamics (CFD) code PHOENICS is applied to simulate and evaluate the combustion process within the furnace of a 1,000 MW dual circle tangential firing single furnace lignite-fired ultra supercritical (USC) boiler. The dependence on overfire air (OFA) positioning on the combustion process is studied. The results show that the highest temperature appears on the upside of the burner zone close to the front wall, and the high temperature zone rises with elevated OFA positions. However, the temperature field distributions are similar despite differing OFA positions. The char content near the rear wall is higher than that near the front wall, and below the furnace arch, coal particles concentrate towards the front wall. Also with elevated OFA positions, nitrogen oxide (NOx) concentrations at the outlet fall, but char content increases. In regard to NOx emission and char burnout, the suggested optimal distance from the OFA center to the center of the uppermost primary air nozzle should be 6 meters.

On the basis of counter flow of primary air with fuel rich in company with overall air-staged technology, this paper introduces a new pulverized coal combustion technology that can realize low NO x emission, high combustion efficiency, slagging, and high-temperature corrosion prevention by employing overall air-staged combustion, large-angle counter flow of primary air with a fuel-rich jet and forming a partial area of high-temperature and high pulverized coal concentration in the furnace. To verify technical data, research has been conducted on a 1025 t/h tangential firing boiler adopting this technology and a three-dimensional particle-dynamics anemometer (PDA) is employed on this prototype for measurement of the characteristics of two-phase gas/particle flows in the burner area. The distribution of the particle concentration and size distribution of the primary air, as well as the gas/particle velocity field were obtained. The experiments also measure the flowing characteristics of over-fired air (OFA) and secondary air. The results show that, with counter flow of fuel-rich jet technology, more particles can be injected into the high-temperature side in the furnace, the concentration of the particle is higher at the high-temperature side than that near the water wall, and the particle concentration of large particles is also lower near the water wall. The research shows that the counter-flow technology combined with overall air-staged technology of the tangential firing boiler can realize low NOx emission and high efficiency combustion and can prevent slagging on the surface of the water wall and high-temperature corrosion.

Accurate prediction of percentage unburnt carbon in fly ash in the case of high ash content Indian coal, at the design stage, is generally difficult. In the present paper, a large number of laboratory test data and site data are used to understand the mechanism of unburnt carbon in fly ash as well as in bottom ash. Rigorous statistical analysis of the performance data taken from tangentially fired boilers shows that empirical correlation between a combination of coal properties and percentage unburnt carbon in fly ash exist. Equations to predict percentage unburnt carbon in fly ash and bottom ash have been proposed.

The purpose of this paper is to present the flow field in the 300MW tangential firing utility boiler that used the Low NOx Concentric Firing System (LNCFS). Using the method of cold isothermal simulation ensures the geometric and boundary condition similarity. At the same time the condition of self-modeling is met. The experimental results show that the mixture of primary air and secondary air becomes slower, the average turbulence magnitude of the main combustion zone becomes less and the relative diameter of the tangential firing enlarges when the secondary air deflection angle increases. When the velocity pressure ratio of the secondary air to the primary air (p2/p1) enlarges, the mixture of the secondary air and the primary air becomes stronger, the average turbulence magnitude of the main combustion zone increases, and the relative diameter of the tangential firing becomes larger. Because the over fire air (OFA) laid out near the wall has a powerful penetration, the relative diameter of the tangential firing on the section of the OFA is very little, but the average turbulence magnitude is great. When the velocity pressure ratio of the OFA to the primary air pOFA/p1 increases, the relative diameter of the tangential firing on the section of the OFA grows little, the average turbulence magnitude becomes larger and the penetration of the OFA becomes more powerful.

This paper presents an investigation on the influence of different furnace cross sectional configurations on the flow and velocity distribution in a small-scale tangential firing furnace. The flow and combustion of natural gas in three furnaces of different cross section are simulated numerically using CFD. The results show that velocity distribution is non-uniform along the width and depth of the furnace in rectangular furnace while square cross section gives uniform distribution. The effect of furnace cross section on the tangential velocity is more obvious when the length difference of the width and depth of the furnace is larger. The axial velocity is found to be highly influenced by the furnace cross section.

A fuel nitrogen conversion model has been superimposed onto the computational fluid dynamics (CFD) model Furnace. The combined model has been applied to seven pulverised coal-fired boilers serving the Australian power industry in order to predict the emission levels of nitric oxide NO in the flue gases. The nitrogen model is comprised of a gas phase reaction system and a char nitrogen gasification step. Two approaches to char N-to-NO conversion were trialled; one taking experimentally measured conversion percentages and the other assuming that NO is the primary nitrogen product from char nitrogen. The furnaces modelled include units with outputs from 120 to 660 MWe having front-wall, opposed and tangential firing systems burning a range of coals. The predictions were good for some configurations but poor for other configurations under the same firing conditions. The CFD model used cannot be regarded as reliable in its current stage of development. The areas of concern exposed in the application of the model for predictive purposes are simulating the flame structure of swirl burners, and establishing the gasification mechanism of char nitrogen. The latter represents the highest area of uncertainty in the simulation. To get good fits with measured values it was necessary to adjust the degree to which NO penetrates the char particles and is reduced to N2. Further experimental information and an improved char model should rectify this situation within a few years.

In the modern era of the coal fired boilers combustion optimization plays a vital role for increasing the boiler efficiency and reducing the production of hazardous waste gases like NOX, SOX etc. Hence to optimize the combustion there are different ways to control the parameters of boiler combustion like 3T method, which includes Time, Temperature and Turbulence. Each of them can be controlled by controlling variety of parameters available in boiler combustion. One of the methods to control the turbulence of the fire ball is to control firing of the coal and the oil burner's angle and the direction in accordance to get proper tangential firing. In this paper we propose a method based on digital image processing for measurement of furnace oil gun nozzle spray angle measurement using Hough transform.

A three-dimensional numerical simulation was carried out to study the pulverized-coal combustion process in a tangentially fired ultra-supercritical boiler. The realizable k- ε model for gas coupled with discrete phase model for coal particles, P-1 radiation model for radiation, two-competing-rates model for devolatilization, and kinetics/diffusion-limited model for combustion process are considered. The characteristics of the flow field, particle motion, temperature distribution, species components, and NOx emissions were numerically investigated. The good agreement of the measurements and predictions implies that the applied simulation models are appropriate for modeling commercial-scale coal boilers. It is found that an ideal turbulent flow and particle trajectory can be observed in this unconventional pulverized-coal furnace. With the application of over-fire air and additional air, lean-oxygen combustion takes place near the burner sets region and higher temperature at furnace exit is acquired for better heat transfer. Within the limits of secondary air, more steady combustion process is achieved as well as the reduction of NOx. Furthermore, the influences of the secondary air, over-fire air, and additional air on the NOx emissions are obtained. The numerical results reveal that NOx formation attenuates with the decrease in the secondary air ratio ( γ2nd) and the ratio of the additional air to the over-fire air ( γAA/ γOFA) was within the limits.

The process of the pulverized coal combustion in tangential firing boiler has prominent significance on improving boiler operation efficiency and reducing NOX emission. This paper aims at researching complex turbulent vortex coherent structure formed by the four corners jets in the burner zone, a cold experimental model of tangential firing boiler has been built. And by employing spatial correlation analysis method and PIV (Particle Image Velocimetry) technique, the law of Vortex scale distribution on the three typical horizontal layers of the model based on the turbulent Integral Length Scale (ILS) has been researched. According to the correlation analysis of ILS and the temporal average velocity, it can be seen that the turbulent vortex scale distribution in the burner zone of the model is affected by both jet velocity and the position of wind layers, and is not linear with the variation of jet velocity. The vortex scale distribution of the upper primary air is significantly different from the others. Therefore, studying the ILS of turbulent vortex integral scale is instructive to high efficiency cleaning combustion of pulverized coal in theory.

With the help of CFD ( computational fluid dynamics) software Fluent and by choosing a rational mathematical model，a numerical simulation was performed of a 680 MW ultra-supercritical wall-type-arranged tangentially-fired boiler．Value simulation of the combustion process inside the furnace can be developed. Values simulated are particle movement, temperature, speed and thermal differentials inside the furnace and at the furnace outlet. The value simulation shows that the pulverized particles ignited easily, had good stable combustion characteristics, good radiation firmness, good penetration ability, low sulphur content in flyash, flow stream not easily diverted or form slag, tangential diameter slightly smaller, furnace thermal difference slightly smaller, thermal load in the furnace was uniform, and thermal differential at furnace outlet very small.

In order to know about coke phenomena of 130t/h boiler with tangential firing, velocity and valves characteristics of primary and secondary air were measured. Fireworks test and numerical simulation were done at the condition of actual working and uniform air distribution, and the tangential circle diameter of actual working and uniform air distribution were obtained. The results show that the boiler will be satisfied basically with uniform air distribution in four corners on the condition that air velocity is adjusted uniformly in different jet, the ideal aerodynamic field in boiler will be obtained, and it provides reference for hot state run

The numerical study on furnace flow, heat transfer and combustion process for the 600MW tangential firing boiler in a power plant under the O 2 /CO 2 atmosphere has been researched. The results showed that: With the oxygen molar concentration increasing, the temperature in furnace increases and the high temperature region in furnace becomes larger which is favorable to pulverized coal ignition under the O 2 /CO 2 atmosphere. But considering the safety of burner and water wall slagging, the oxygen molar concentration is not too high. Oxygen-enriched combustion has little effect on the upper layer pulverized coal combustion, but it has great effect on under layer pulverized coal combustion. Compared with pulverized coal combustion under the air atmosphere, the furnace flame central position moves upward, and the characteristic of temperature distribution in furnace is beneficial to preventing water wall from slagging when the oxygen molar concentration is not too high.

The ignition stability and burnout behaviors of the blend coals to be used in the 2 A— 680 MW ultra-supercritical boilers of second stage project of Xisaishan Power Generation Co. Ltd are analyzed by using the thermal gravimetric analyzer. The results showed that the ignition and combustion stability of the design coals were not nice and the coals were difficult to be burnt out. At the meantime, according to the combustion behavior of the blend coals, the primary suggestions for type selection of boiler equipments and the selection of operating parameters were proposed. Analysis of the combustion behaviors of the blend coals to be used in the boiler and adaptability of the boiler to coal rank variations indicated that the tangential firing is a better choice for the boiler.

In this paper, High-Temperature Air Combustion (HiTAC) method utilizing coal as fuel is studied numerically using Computational Fluid Dynamics (CFD). A case study was performed using the CFD code FLUENT 6.2 to investigate the effects of utilizing high temperature air combustion on a real 700MW coal-powered boiler operating on a tangential firing mechanism. The results obtained were consistent with the ones reported in the literature. For high temperature air, a bigger flame structure and higher average temperature inside the boiler was found. The firing performance is found to be improved mainly due to formation of stable flame which further leads to the reduction in ignition delay.

The computational fluid dynamics (CFD) code PHOENICS was applied to evaluate the combustion process in the furnace of a 1000 MW dual circle tangential firing single furnace lignite-fired ultra supercritical (USC) boiler. The influence of different primary air ratios (35%, 39% and 43%) on the flow and mixing characteristics of the gas-solid two-phase flow and the combustion process in the furnace was focused on. The results indicate that in the furnace with double tangential firing, the flow field shows two well-symmetrical ellipses at different primary air ratios. The surface temperatures of the burners at which, the long axis of the ellipses pointed, are much higher than those in the other four corners. Thus the phenomena of 'Hot corners' and 'Cold corners' arise. In practical operating, the flow erodes the walls in the hot corner which may lead to high temperature corrosion and slagging. With the increase of primary air ratio, the average concentration of NO x at the outlet of furnace rises while the char distributions in the furnace are similar. By the comparisons of the characteristics of the airflow, the temperature distributions, the NO x formation amounts and the char burnout rates, the situation with the 35% primary air ratio is preferable. The results of this paper have great value because of the support they lend to the design of USC lignite-fired boilers.

In a large capacity tangentially fired boiler, the final reheater tubing sustained abnormal oxidation and localized excessive metal wastage in a short time of the unit operation. The root causes of the problem are identified by test data analysis. The test data indicated that the reheater tubing metal temperatures in the affected areas exceeded the recommended limit of the metal oxidation temperature due to higher than expected local gas temperatures and velocities. A soot-blower facing the overheated portion of the reheater leading tubes accelerated the process of metal wastage by periodically removing the oxide layer. The configuration of the boiler internals upstream of the reheater section is found to be the main cause of the localized overheating. Side-to-side gas flow/temperature stratification due to tangential firing contributed to a lesser degree to the problem. The results and conclusions presented in this paper should be a beneficial guide to the designer of large capacity boilers.

Boiler can also be called as ＂the Burner＂. The main Function of the Boiler is to Burn the Fuel and Make Combustion possible. In this project we are going to study how coal is pulverized and burnt in order to gain more heat. Most coal fired power station boilers use pulverized coal. This technology is well developed, and there are thousands of units around the world, accounting for well over 90% of coal fired capacity. The coal is pulverized to a fine powder, so that less than 2% is +300 micro meter (μm) and 70-75 % is below 75 microns, for a bituminous coal. This system has many advantages such as ability to fire varying quality of coal, quick responses to changes in load, use of high pre-heat air temperatures etc. One of the most popular systems for firing pulverized coal is the tangential firing using four burners corner to corner to create a fireball at the centre of the furnace.

The present work deals with the numerical transient simulation of load changes in a pulverised coal-fired utility boiler. The boiler is a tangential firing system with an electrical output of 750 MW. The code used for the calculations is the in-house developed 3D combustion code AIOLOS. The implemented solution procedure is based on either the well-known SIMPLEC method (Semi Implicit Method for Pressure Linked Equations Consistent) or the PISO approach (Pressure Implicit with Splitting of Operators). The stability of the procedure is independent of the time step, since an implicit temporal discretisation scheme (Euler Implicit) is used. A validation exercise is presented by comparing the numerical results with temperature measurements available from LSE (Lehrstuhl fur Systemtheorie in der Elektrotechnik), Saarland University, Saarbrucken.

A 293 kW pilot-scale facility was used to develop a low-NO x pulverized coal-fired tangential system. Low NO x is achieved by directing the fuel and 20 percent of the secondary combustion air into the center of the furnace with the remaining 80 percent of the secondary combustion air directed parallel to the furnace walls. The separation of secondary combustion air in this manner creates a fuel rich zone in the center of the furnace where NO x production is minimized. This combustion modification technique has lowered NO x 60 percent relative to conventional tangential firing. In addition, CO, UHC and unburned carbon emissions are substantially unaffected by the modification. Also, the modification places a blanket of air on the furnace walls which is beneficial from a wall corrosion and slagging point of view. Finally, the modification shows a decrease in NO x emissions as firebox gas temperature is increased. This characteristic might be beneficially applied in a large-scale system to reduce furnace volume, and thereby capital cost, for a given combustion heat release. Tests are now underway to further optimize and characterize this low-NO x combustion modification technique.