Optimization of pulverised coal combustion by means of CFD/CTA modeling

Abstract

The objective of the work presented in this paper was to apply a method for handling two-phase reacting flow for prediction of pulverized coal combustion in large-scale boiler furnace and to assess the ability of the model to predict existing power plant data. The paper presents the principal steps and results of the numerical modeling of power boiler furnace with tangential disposition of the burners. The computational fluid dynamics/computational thermal analysis (CFD/CTA) approach is utilized for creation of a three-dimensional model of the boiler furnace, including the platen superheater in the upper part of the furnace. Standard k-e model is employed for description of the turbulent flow. Coal combustion is modeled by the mixture fraction/probability density function approach for the reaction chemistry, with equilibrium assumption applied for description of the system chemistry. Radiation heat transfer is computed by means of the simplified P-N model, based on the expansion of the radiation intensity into an orthogonal series of spherical harmonics. Some distinctive results regarding the examined boiler performance in capacity range between 65 and 95% are presented graphically. Comparing the simulation predictions and available site measurements concerning temperature, heat flux and combustion efficiency, a conclusion can be drawn that the model produces realistic insight into the furnace processes. Qualitative agreement indicates reasonability of the calculations and validates the employed sub-models. After the validation and verification of the model it was used to check the combustion efficiency as a function of coal dust sieve characteristics, as well as the impact of burners modification with introduction of over fire air ports to the appearance of incomplete combustion, including CO concentration, as well as to the NOx concentration. The described case and other experiences with CFD/CTA stress the advantages of numerical modeling and simulation over a purely field data study, such as the ability to quickly analyze a variety of design options without modifying the object and the availability of significantly more data to interpret the results. .

Improvement of environmental aspects of thermal power plant operation by advanced control concepts

“…Coal combustion and NO x emission modelling can be conducted through computational fluid dynamic (CFD) models [13,14], but their very long computation time imposes need for different model that will be practical for on-line power plant control. Artificial neural networks and neuro-fuzzy models are currently the most researched approaches to and NO x emission modelling [15].…”

Pulverised-Coal Combustion with Staged Air Introduction: CFD Analysis with Different Thermal Radiation Methods

“…One of the most important segments of the furnace modelling is the way of radiative heat transfer incorporation. Thermal radiation in the furnaces can be modelled by means of various approaches, like discrete transfer method [15], discrete ordinates method [16,[19][20][21], six-fluxes method [18], Monte Carlo method [10], or so called P-N approximation method [25], including its P-1 variant, as it is used in [26,27]. In general, it should be pointed out that a comprehensive model of the furnace processes must balance sub-models sophistication with computational practicality.…”

“…In this case, there are totally 688,886 tetrahedral hybrid cell elements in the domain. According to the previous experiences with simulations of other boiler furnaces with comparable domain dimensions and complexity, the grid is fine enough to give gridindependent solutions, showing satisfactory convergence and accuracy and, at the same time, to meet the restrictions in computational time [26,27,29]. Thermocouple pyrometry, as a practical and reliable method of measuring gas temperature in full-scale boilers, is used in this case.…”

Modeling of pulverized coal combustion for in-furnace NOx reduction and flame control

“…Research efforts continuously focus on modeling NO x formation/destruction reactions in pulverized coal combustion [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. Nitric oxide (NO) is the most abundant NO x from coal combustion.…”