Modeling of the reactions of a calcium-based sorbent with sulfur dioxide

A mathematical model of calcium sorbent reactions for the simulation of sulfur dioxide reduction from pulverized coal combustion flue gasses was developed, implemented within a numerical code and validated against available measurements under controlled conditions. The model attempts to resemble closely the reactions of calcination, sintering and sulfation occurring during the motion of the sorbent particles in the furnace. The sulfation was based on the partially sintered spheres model (PSSM), coupled with simulated particle calcination and sintering. The complex geometry of the particle was taken into account, with the assumption that it consists of spherical grains in contact with each other. Numerical simulations of drop down tube reactors were performed for both CaCO3 and Ca(OH)(2) sorbent particles and results were compared with experimental data available from the literature. The model of the sorbent reactions will be further used for simulations of desulfurization reactions in turbulent gas-particle flow under coal combustion conditions

Development of mathematical model for co-firing pulverized coal and biomass in experimental furnace

A comprehensive mathematical model for prediction of turbulent transport processes and reactions during co-combustion of pulverized fuels in furnace fired by 150 kW swirl stabilized-burner has been developed. Numerical simulations have been carried out by using an in-house developed computer code, with Euler-Lagrangian approach to the two-phase flow modelling and sub-models for individual phases during complex combustion process: evaporation, devolatilization, combustion of volatiles, and char combustion. For sub-model of coal devolatilization the approach of Merrick is adopted, while for biomass devolatilization the combination models of Merrick, and of Xu and Tomita are selected. Products of devolatilization of both the pulverized coal and biomass are considered to contain the primary gaseous volatiles and tar, which further decomposes to secondary gaseous volatiles and residual soot. The residual soot in tar and carbon in coal and biomass char are oxidized directly, with ash remaining. For volatiles combustion the finite rate/eddy break-up model is chosen, while for char oxidation the combined kinetic-diffusion model is used. The comprehensive combustion model is validated against available experimental data from the case-study cylindrical furnace. The agreement of the simulations with the data for the main species in the furnace is quite good, while some discrepancies from experimental values are found in the core zone. The presented model is a good basis for further research of co-combustion processes and is able to provide analysis of wide range of pulverized fuels, i. e. coal and biomass. At the same time, the model is relatively simple numerical tool for effective and practical use

Numerical Tracking of Sorbent Particles and Distribution During Gas Desulfurization in Pulverized Coal-Fired Furnace

Furnace sorbent injection for sulfur removal from flue gas presents a challenge, as the proper process optimization is of crucial importance in order to obtain both high sulfur removal rates and good sorbent utilization. In the simulations a two-phase gas-particle flow is considered. Pulverized coal and calcium-based sorbent particles motion is simulated inside of the boiler furnace. It is important to determine trajectories of particles in the furnace, in order to monitor the particles heat and concentration history. A two-way coupling of the phases is considered influence of the gas phase on the particles, and vice versa. Particle-to-particle collisions are neglected. Mutual influence of gas and dispersed phase is modeled by corresponding terms in the transport equations for gas phase and the equations describing the particles turbulent dispersion. Gas phase is modeled in Eulerian field, while the particles are tracked in Lagrangian field. Turbulence is modeled by the standard k-epsilon model, with additional terms for turbulence modulation. Distribution, dispersion and residence time of sorbent particles in the furnace have a considerable influence on the desulfurization process. It was shown that, by proper organization of process, significant improvement considering emission reduction can be achieved.Turbulence Workshop, Aug 31-Sep 02, 2015, Univ Belgrade, Fac Mech Engn, Belgrade, Serbi

Influence of Application of Hottels Zonal Model and Six-Flux Model of Thermal Radiation on Numerical Simulations Results of Pulverized Coal Fired Furnace

Difference of results of numerical simulation of pulverized coal fired furnace when mathematical models contain various radiation models has been described in the paper. Two sets of numerical simulations of pulverized coal fired furnace of 210 MWe power boiler have been performed. One numerical simulation has contained Hottels zonal model, whereas the other numerical simulation has contained six-flux model. Other details of numerical simulations have been identical. The influence of radiation models has been examined through comparison of selected variables (gas-phase temperature, oxygen concentration, and absorbed radiative heat rate of surface zones of rear and right furnace walls), selected global parameters of furnace operation (total absorbed heat rate by all furnace walls and furnace exit gas-phase temperature). Computation time has been compared as well. Spatially distributed variables have been compared through maximal local differences and mean differences. Maximal local difference of gas-phase temperature has been 8.44%. Maximal local difference of absorbed radiative heat rate of the surface zones has been almost 80.0%. Difference of global parameters of furnace operation has been expressed in percents of value obtained by mathematical model containing Hottels zonal model and has not been bigger than 7.0%. Computation time for calculation of 1000 iterations has been approximately the same. Comparison with other radiation models is necessary for assessment of differences

Assessing the impact of primary measures for NOx reduction on the thermal power plant steam boiler

The European normatives prescribe content of 200 mg/Nm(3) NO for pulverized coal combusting power plants. In order to reduce content of NOx in Serbian thermal power plant (TPP) square Kostolac B square its necessary to implement particular measures until 2016. The mathematical model of lignite combustion in the steam boiler furnace is defined and applied to analyze the possibility of implementing certain primary measures for reducing nitrogen oxides and their effects on the steam boiler operation. This model includes processes in the coal-fired furnace and defines radiating reactive two-phase turbulent flow. The model of turbulent flow also contains sub-model of fuel and thermal NOx formation and destruction. This complex mathematical model is related to thermal and aerodynamic calculations of the steam boiler within a unified calculation system in order to analyze the steam boiler overall work. This system provides calculations with a number of influential parameters. The steam boiler calculations for unit 1 (350 MWe) of TPP square Kostolac B square are implemented for existing and modified combustion system in order to achieve effective, reliable and ecological facility work. The paper presents the influence analysis of large number of parameters on the steam boiler operation with an accepted concept of primary measures. Presented system of calculations is verified against measurements in TPP square Kostolac B square. (C) 2015 Elsevier Ltd. All rights reserved

A numerical study of a utility boiler tangentially-fired furnace under different operating conditions

For prediction of complex processes in two-phase turbulent reactive flows within large-scale boiler furnaces firing pulverized coal, a comprehensive 3D differential mathematical model and CFD computer code have been developed in-house. The model incorporates trade-offs between submodels sophistication and computational practicality. An easy-to-use interface for introducing input data and grid generation has been build within the code. The main purpose of the paper is to present numerical predictions of processes in the case-study furnace under different operating conditions, obtained by the developed model. The paper also provides information on characteristics and evaluation of the model, with a grid refinement study and comparisons with comprehensive data. The effects of different operating conditions on the processes in the case-study furnace are correctly predicted, demonstrating the ability of the developed model to perform parametric studies. (c) 2008 Elsevier Ltd. All rights reserved

A computer code for the prediction of mill gases and hot air distribution between burners sections at the utility boiler

One of the main tasks during the design or simulation and analyses of the utility steam boiler operation is the prediction of a distribution of mill gases and hot air flow rates between burners sections. These are the boundary conditions for the combustion process in the boiler furnace, and they strongly influence the steam boiler economy and reliability of operation. A computer code for the prediction of mill gases and hot air distribution between boiler burners has been developed. The code is based on simultaneous calculations of material and heat balances for the fail mill and corresponding air tracts. This paper presents a methodology of performed calculations, the code structure, and results obtained for the steam boiler furnace of 350 MWe thermal power plant equipped with eight fall mills. (C) 2008 Elsevier Ltd. All rights reserved

Three-dimensional modeling of utility boiler pulverized coal tangentially fired furnace

This paper presents selected results of numerical simulations of processes in utility boiler pulverized coal tangentially fired dry-bottom furnace. The simulations have been performed by specially developed comprehensive mathematical model. The main features of the model are a three-dimensional geometry, k-epsilon gas turbulence model, Eulerian-Lagrangian approach, particles-to-turbulence interaction, diffusion model of particle dispersion, six-flux method for radiation modeling and pulverized coal combustion model based on the global particle kinetics and experimentally obtained kinetic parameters. Five operation regimes of 210 MW, boiler furnace burning Serbian lignites, with different grinding fineness of coal and coal quality, have been simulated. The model successfully predicts the influence of the parameters on the furnace processes and operation characteristics (like the flue gas temperature and the furnace walls radiation fluxes). The predicted flame temperature and percentage combustibles in bottom ash are in good agreement with the measurements. The developed model can find different applications, both in research and practice. (c) 2006 Elsevier Ltd. All rights reserved

Possibilities for reconstruction of existing steam boilers for the purpose of using exhaust gases from 14 MW or 17 MW gas turbine

Within the energy system in Methanol vinegar complex (MVC) in Kikinda, beside process boiler and auxiliary equipment, there are three equal steam boilers made by Minel Kotlogradnja, provided for combustion of natural gas, fuel oil and process gases. Aiming to increase the MVC Kikinda energy plant capacity, one gas turbine of 14 MW or 17 MW is going to be installed. In regard to relatively high gas temperature and a large amount of the unused oxygen from the air in the exhaust gas, it is specified to split exhaust gas into the two equal streams and import them into the two existing steam boilers, each having production of 16.67 kg/s (60 t/h). In order to use the exhaust gas heat, as well as oxygen contained within, it is necessary to replace the existing burners and to reconstruct the heat exchangers in the steam boiler vertical convective pass. Besides, it is necessary to verify if the existing flue gases fan can comply with the new operating regime, during which a half of the turbine exhaust gas is imported into the steam boiler. (c) 2013 Elsevier Ltd. All rights reserved

Predicting effects of air staging application on existing coal-fired power steam boiler

The results of an extended research performed with the aim of investigating influence air staging application on processes occurred in boiler furnace have been presented in this paper. This subject was developed as a result of the need to obtain valid engineering methods for estimating the intensity of combustion and heat transfer processes under sub-stoichiometric conditions. The used calculation method, presented in previous publications, has been established by linking the differential mathematical model of processes in the furnace and conventional integral calculation procedures of all heating surfaces within the boiler. Such verified calculation method provided the algorithm for qualitative analysis of steam boiler operation regardless of the applied combustion scheme. In this research, by use of such approach, the operation of power boiler within TPP Kostolac has been assessed where combustion system was reconstructed during 2015. Calculation results in case of application of designed combustion system (UNR) and alternative air staging configuration (TC1) have been considered. In addition, the present air distribution scheme with the applied primary measures (R) has been analyzed. Comparison of such gained results listed in the same table ensures the trend of the change occurred by application of the air-staging system which needs to be more closely defined. Results of research showed that air staging throughout the furnace height slows down the combustion with the simultaneous intensification of the heat transfer process. Although this phenomenon led to the reduction in NOx concentration (195/470 mg/Nm3, dry, 6% O2), it decreased the power of considered boiler (725.5/774.0 MW) and increased boiler's efficiency (86.49/85.52%). Furthermore, due to the temperatures of superheated (517.0/540.0 °C) and reheated (524.0/540.0 °C) steam being below the designed level, the safety of the boiler's operation was significantly affected. The study also reveals that the boiler's efficiency rate is, in any considered case with applied air staging system, higher due to the possibility to run the boiler with the lower value of excess air ratio (1.15/1.22). Additionally, results demonstrate that distribution of the amount of air, as well as air introduction location, can significantly influence parameters of superheated and reheated steam as well as the regulation area of the same. © 2018 Elsevier Lt