Numerical simulation of coal-air mixture flow in a real double-swirl burner and implications on combustion anomalies in a utility boiler (original) (raw)
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Study on Combustion Performances of Burners in Furnace in Coal Fired Power Plants
Steam generation are one of the critical components of a thermal powerplant. Studies of the performance of combustion in a steam generator are very complex in nature. In this work numerical simulations are used to investigate the characteristics of gas and coal particle two-phase flow in boiler furnaces. In order to examine the detailed behavior of the flow different load conditions were given with varying the velocity of flow of air and fuel. Flow characteristics with multiple number of burners and firing at different locations resembeling variation of load is studied. Studies of effect of different operating conditions are studied using commercial code FLUENT. To determine velocity, temperature characteristics a 3D combustor model isused in this case study. Change of size in burners is done in order to find the temperature profiles changes in furnace. Analyses of particle trajectories are done so as to study the emission characteristics, fouling on burners etc.
Modeling Issues in CFD Simulation of Brown Coal Combustion in a Utility Furnace
The Journal of Computational Multiphase Flows, 2010
This paper describes the mathematical formulation and modelling issues of a computational fluid dynamics (CFD) model of a 375 MW utility furnace. This tangentially-fired furnace is fuelled by high moisture content brown coal from coal mines at Latrobe Valley in Victoria, Australia. The influences of different turbulence models, particle dispersion, and radiation models on the CFD prediction are investigated. Two turbulence models, standard k-ε model and Shear-Stress Transport (SST) model, provide similar predictions that are in good agreement with the plant data. The effect of particle dispersion on the prediction is found to be insignificant for this high-volatile brown coal. The predicted wall incident radiation flux based on two radiation models, namely, discrete transfer (DT) model and P-1 model are compared against power plant measurements. The comparison reveals that the DT model provides good prediction of the radiation profiles, while the P-1 model considerably underpredicts the wall incident radiation flux.
This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright " CFD modeling study was performed for the combustion of the brown coal in a large-scale tangentially-fired furnace. " Performance of the boiler under ten different operating conditions was investigated. " The temperature distributions were better when the turned off burners are set in the opposite direction. " The results showed improvements on the combustion characteristics in comparison with the standard operating case. a b s t r a c t In the present paper, a computational fluid dynamics (CFD) modeling study was performed for the combustion of the brown coal in a large-scale tangentially-fired furnace (550 MW) under different operating conditions. The AVL Fire CFD code has been used to model the combustion processes. The mathematical models of coal combustion with the appropriate kinetic parameters were written and incorporated to the code as user defined functions. These models consist of pulverised coal (PC) devolatilization, char burnout , and heat and mass transfer. The simulation of the PC combustion was carried out using multi-step reaction chemistry mechanisms. The level of confidence of this numerical model was based on the previous validations of the lignite combustion in a lab-scale furnace, as well as the validation parameters of the present furnace at the standard existing conditions in terms of temperature values and species concentrations. Performance of the boiler under ten different operating conditions was investigated. The strategy of operation schemes for the first six combustion scenarios were based on the change of the out-of-service (turned off) burners under full load operation, while the rest cases were carried out at 20% lower and 20% higher loads than the standard operating conditions. The validated model was used to perform the following investigation parameters: furnace gas temperatures, species concentrations (O 2 , CO and CO 2), velocity distributions, and char consumption. The predictions demonstrated that there are good temperature distributions in the furnace when the turned off burners are set in the opposite direction under full load operation. For higher aerodynamic effect, the numerical results showed improvements on the combustion characteristics in terms of species concentrations and char burnout rates in comparison with the standard operating case. The findings of this study provide good information to optimize the operations of the utility tangentially coal-fired boiler with less emission.
Large Eddy Simulation of coal combustion in a large-scale laboratory furnace
2014
A detailed Large Eddy Simulation (LES) of pulverised coal combustion in a large-scale laboratory furnace is presented. To achieve a detailed representation of the flow, mixing and particle dispersion, a massively parallel LES was performed. Different phenomenological network models were applied and compared to each other in order to obtain the most adequate devolatilization kinetic data for the LES. An iterative procedure allowed to optimise the devolatilization kinetic data for the studied coal and operating conditions. The particle combustion history is studied by analysing particle instantaneous properties giving a perspective on coal combustion that currently is not available by other means than LES. Predicted major species and temperature were compared with measurements and a good agreement was obtained. The finely resolved near burner region revealed that the flame is stabilised very close to the burner. Furthermore, two distinct zones of CO 2 production were found-one in the internal recirculation zone (IRZ) due to gaseous combustion, and one downstream of the vortex breakdown, due to intense char combustion. It was found that particle properties are inhomogeneous within the IRZ, whereas in the external recirculation zone (ERZ) and downstream of the vortex breakdown they were found to be homogeneous.
On the modelling of turbulent reacting flows in furnaces and combustion chambers
Acta Astronautica, 1979
A general computer programme was developed to calculate the local flow properties in turbulent reactive and non reactive flows with recirculation; these calculations were obtained by solving the appropriate conservation equations in finite difference form with the corresponding boundary conditions. The calculation procedure employs a two equation turbulence model, and embodies various combustion models appropriate to diffusion, premixed and arbitrary fuelled flames. The phenomenon of unmixedness caused by turbulent fluctuations, which lead to a situation where the instantaneous value of fuel and/or oxidant concentrations and, therefore, their corresponding chemical reaction rates vanish, is investigated. The combustion models considered here are characterized by, for instance, instant reaction with clipped Gaussian probability distribution of concentration, which corresponds to random variation of fuel concentration with time, finite reaction rate with an eddy break up formulation, and finite reaction rate with a second order closure which accounts for temperature and concentration fluctuations. The radiative heat flux, which appears in the energy conservation equation, is obtained using a coupled four flux representation and integrating the radiation intensity distribution over a solid angle of 2w. The validity of the computational procedure incorporating the proposed turbulence, combustion and radiation models was assessed by comparisons with the experimental data in reacting and non reacting flows, and indicated satisfactory agreement. The obtained agreement assesses the validity of the physical assumptions of the models and supports the use of such procedure for furnace design purposes.
Modeling of volatiles combustion and alkali deposition in a fluidized bed coal combustor
Chemical …, 2002
A simplified kinetic model, coupled with the bed hydrodynamics and a volatile evolution region within the bed, was formulated to predict the extent of gas-phase combustion in a laboratory-scale fluidized bed coal combustor (FBC). A close examination has also been made to highlight the relevance of the reducing/oxidizing environment (computed with the present theoretical model) in relation to FBC materials exposed to fireside corrosion at high temperature, under various operating conditions. The model results revealed that, for high-volatile coals with particle diameters (d c ) of 1±3 mm and sand particle size (d s ) of 0.674 mm, over one third of the original coal volatiles may burn in the freeboard region at bed temperature (T b ) £ 850 C and excess air (XSA) £ 10 %. These values, together with the computed equilibrium conversion of alkali chlorides to sulfates, may suggest that sodium and potassium salts present in the vapor phase are likely to accelerate hot corrosion of heat exchange tubes above the bed when an FBC operates at T b £ 840 C, XSA £ 20 %, d c < 5 mm, d s < 1 mm, H s £ 0.2 m and U o < 1 m/s. Conversely, at T b > 890 C and XSA > 30 %, high oxidation rates may be present for the in-bed tubes. At these higher T b values and XSA < 10 %, a sulfidation mechanism presumably influences the extent of corrosion on the metallic components within the bed.
Simplified numerical modelling of oxy-fuel combustion of pulverized coal in a swirl burner
2D simulation has been carried out to analyze pulverized coal combustion in oxy-fuel environment. Radiation and turbulence models have been evaluated. The proposed simplified model has been validated against experimental data. Validated model has been used to evaluate the effects of combustion environments. a b s t r a c t In this work, a computational fluid dynamics (CFD) modelling has been performed to analyze pulverized coal combustion in a vertical pilot-scale furnace. The furnace with swirl burner is located at the Institute of Heat and Mass Transfer at RWTH Aachen University, where O 2 /CO 2 combustion environment was adopted to study pulverized coal combustion experimentally (Toporov et al., 2008). A two-dimensional axisymmetric domain has been used in this work with a Lagrangian method to track coal particles. Performances of different Reynolds-Averaged-Navier-Stokes (RANS) turbulence models have been investigated. The radiative heat transfer using discrete ordinate (DO) model coupled with variants of weighted-sum-of-grey-gases (WSGGM) methods has been examined. The results obtained by these models have been compared with the experimental data. The DO radiation model with domain based WSGGM and SST k-omega turbulence model showed a very good match with the experimental data among other tested models. The accuracy of predicted results was comparable to LES results available in the literature. It is observed that to get preliminary results the current simplified model is good enough with accuracy comparable to LES modelling. By using this validated model, the influence of combustion environments such as air, oxy-steam (O 2 /H 2 O) and oxy-RFG (O 2 /CO 2) on temperature and NO concentration distribution has been investigated. NO x produced was least in the oxy-steam environment.
A Numerical Analysis of Pulverized Coal Combustion in a Multiburner Furnace
Energy & Fuels, 2007
A three-dimensional numerical simulation is applied to a pulverized coal combustion field in a furnace equipped with three burners, and the trajectories of the coal particles with respect to each burner, which are hardly obtained experimentally, are also investigated in detail. Simulation results are compared with experimental results. The results show that the numerical and experimental results are consistent generally. Also, the examination of the particle trajectories shows that most of the unburned carbon originates from the upperstage burner. This result suggests that the overall unburned fraction can be reduced by supplying coal with a low combustibility to lower-or middle-stage burners and supplying coal with a high combustibility to the upper-stage burner.
Journal of Physics: Conference Series, 2017
This paper presents an investigation on the effects of primary airflow to coal fineness in coal-fired boilers. In coal fired power plant, coal is pulverized in a pulverizer, and it is then transferred to boiler for combustion. Coal need to be ground to its desired size to obtain maximum combustion efficiency. Coarse coal particle size may lead to many performance problems such as formation of clinker. In this study, the effects of primary airflow to coal particles size and coal flow distribution were investigated by using isokinetic coal sampling and computational fluid dynamic (CFD) modelling. Four different primary airflows were tested and the effects to resulting coal fineness were recorded. Results show that the optimum coal fineness distribution is obtained at design primary airflow. Any reduction or increase of air flow rate results in undesirable coal fineness distribution.