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

Air staging application effects on overall steam boiler operation

This paper presents the results of calculation system of main processes in power steam boiler, before and after application of air staging. Modified air injection scheme was implemented during 2015 on the power steam boiler within unit 1 of TPP Kostolac B. Measurements performed on site showed that applied reconstruction led to a permanent loss of the steam boiler power. This study was performed in order to define the cause of such an occurrence and to consider the possibility for regaining the designed steam parameters along with keeping NOx concentration in prescribed limits. This paper discusses the influence of repositioning the air injection location on processes within the furnace. Furthermore, the influence of the redistribution of injected air-flow along the furnace height on important boiler operation parameters has been analyzed. Analysis showed that, with appropriate dosing of air along the height of the existing furnace, it is possible to achieve the optimum of the boiler's operation parameters. Results of research showed that air staging throughout the furnace height in best test case additionally reduces NO concentration (195-225 mg/Nm(3)) and increases the power of x considered boiler (828.8-751.1 MW) with an insignificant decrease of the boiler's efficiency (86.27-86.77%). Furthermore, the designed temperatures of superheated (540-498 degrees C) and reheated (540-518 degrees C) steam have been reached again, whereby the safety of the boiler's operation has been significantly increased. Results of this study improve the present explanation of the processes occurred in the furnace with applied primary measures. They also give directions on defining the most influential parameters on considered processes with the final purpose to increase the efficiency and availability of the entire plant

Air staging application effects on overall steam boiler operation

This paper presents the results of calculation system of main processes in power steam boiler, before and after application of air staging. Modified air injection scheme was implemented during 2015 on the power steam boiler within unit 1 of TPP Kostolac B. Measurements performed on site showed that applied reconstruction led to a permanent loss of the steam boiler power. This study was performed in order to define the cause of such an occurrence and to consider the possibility for regaining the designed steam parameters along with keeping NOx concentration in prescribed limits. This paper discusses the influence of repositioning the air injection location on processes within the furnace. Furthermore, the influence of the redistribution of injected air-flow along the furnace height on important boiler operation parameters has been analyzed. Analysis showed that, with appropriate dosing of air along the height of the existing furnace, it is possible to achieve the optimum of the boiler's operation parameters. Results of research showed that air staging throughout the furnace height in best test case additionally reduces NO concentration (195-225 mg/Nm(3)) and increases the power of x considered boiler (828.8-751.1 MW) with an insignificant decrease of the boiler's efficiency (86.27-86.77%). Furthermore, the designed temperatures of superheated (540-498 degrees C) and reheated (540-518 degrees C) steam have been reached again, whereby the safety of the boiler's operation has been significantly increased. Results of this study improve the present explanation of the processes occurred in the furnace with applied primary measures. They also give directions on defining the most influential parameters on considered processes with the final purpose to increase the efficiency and availability of the entire plant

Derivation of transport equations for three-dimensional non-isothermal turbulent flow in cylindrical coordinates

U radu su dati osnovni izrazi u krivolinijskim koordinatama, a zatim su u nastavku rada redom izvedene u cilindričnim koordinatama: jednačina entalpije (temperature), Navije-Stoksove i Rejnoldsove jednačine turbulentnog strujanja, transportne jednačine Rejnoldsovih (turbulentnih) napona, transportna jednačina kinetičke energije turbulencije i na kraju transportna jednačina brzine disipacije kinetičke energije turbulencije. Ovim radom je pokušano popuniti prazninu u našoj i stranoj literaturi u oblasti turbulentnih transportnih procesa u vezi sa izvođenjem turbulentnih transportnih jednačina u cilindričnim koordinatama. Ovaj rad može biti od koristi studentima diplomskih i doktorskih studija, kao i inženjerima i istraživačima u praksi pri rešavanju inženjerskih problema i modeliranju turbulentnih strujanja koja su tako česta u termotehnici i energetici.Paper initially presents the elementary expressions in curvilinear coordinates, and afterwards, the following equations have been derived in cylindrical coordinates, respectively: equation of enthalpy (temperature), Navier-Stokes and Reynolds equation for turbulent flow, transport equations of Reynolds (turbulent) stresses, transport equation of kinetic energy of turbulence, and the transport equation of dissipation rate of turbulent kinetic energy. This paper has been attempted to fill the gap in our and foreign literature with respect to derivation of turbulent transport equations in cylindrical coordinates. This work may be useful to students of graduate and doctoral studies as well as engineers and researchers in practice in solving engineering problems and modeling of turbulent flows, commonly found in thermal engineering and energy

Comparison of radiative heat transfer models used in numerical simulations of boiler furnaces

Toplotno zračenje je dominantni mod prostiranja toplote sa vrućih produkata sagorevanja ka zidovima ložišta. Tačnost računanja flukseva zračenja je od suštinskog značaja za tačnost numeričkih simulacija, kojima se mogu predvideti performanse celokupnog procesa. Do sada je razvijeno nekoliko modela razmene toplote zračenjem, koji se mogu svrstati u fluksne, zonalne i hibridne modele. Reprezentativni modeli zračenja svake grupe opisani su u radu. Poređenje modela predstavljeno je za laboratorijsko ložište, za koje su prethodno određene tačne vrednosti neto razmenjenih energija zapreminskih zona i neto razmenjenih flukseva površinskih zona. Poređenje pokazuje da su zonalni modeli tačniji od fluksnih modela, čime se preporučuje njihova primena za numeričke simulacije ložišta za sagorevanje fosilnih goriva.Thermal radiation is dominant mode of heat transfer from hot combustion products to the furnace walls. Accuracy of calculation of the heat exchanged by thermal radiation is essential for the accuracy of numerical simulation, by which performances of the whole process can be predicted. So far, several models of radiative heat exchange have been developed, which can be grouped into flux, zonal, and hybrid models. Representative models of each group have been described. Comparison of the models have been performed for the laboratory furnace, for which the exact values of radiative source term and net exchanged heat of furnace walls have been previously determined. Comparison shows that zonal models are more accurate than flux models and suggests their application for the numerical simulation of furnace for fossil fuel combustion

Numerical determination of the pulverized coal flame radiative properties

Ispitan je uticaj broja čestica letećeg pepela koje nastaju fragmentacijom jedne čestice koksnog ostatka na radijaciona svojstva disperzne faze plamena ugljenog praha, kao i da li se primenom tako dobijenih radijacionih svojstava disperzne faze može dobiti slaganje rezultata numeričkih istraživanja sa rezultatima merenja. Za uslove sagorevanja unutar ložišta bloka A2 TENT snage 210 MNJ, koncentracija čestica letećeg pepela i funkcija raspodele su određeni pod pretpostavkom da jedna čestica koksnog ostatka formira od jedne do pet čestica letećeg pepela. Radijaciona svojstva oblaka čestica letećeg pepela izračunata su metodom nepravilne difrakcije. Rezultati pokazuju da sa porastom broja čestica letećeg pepela koje nastaju od jedne čestice koksnog ostatka rastu vrednosti koeficijenata apsorpcije i rasipanja zračenja, ali opada njihov odnos. Vrednosti radijacionih svojstava upotrebljene su u diferencijalnom matematičkom modelu procesa unutar izabranog ložišta. Koeficijent apsorpcije gasne faze određen je modelom jednog sivog gasa i u svim ispitivanim slučajevima bio je konstantan. Istraživanje je pokazalo da porast koeficijenta apsorpcije disperzne faze dovodi do porasta temperature gasne faze i flukseva upadnog zračenja, kao i da se slaganje sa rezultatima merenja postiže za sve izračunate vrednosti radijacionih svojstava disperzne faze.Influence of the number of particles that are formed by fragmentation of one char particle on radiative properties of the dispersed phase of the pulverized coal flame, as well as on the results of numerical investigation of the process have been investigated. For the combustion conditions inside the furnace of A2 TENT 210 MW thermal unit, concentration of the flyash particles and particle size distribution parameters have been determined under assumption that one char particle forms from one to five flyash particles. Radiative properties of the cloud of flyash particles have been determined using anomalous diffraction method. Results show that increase of the number of flyash particles leads to the increase of the absorption and scattering coefficients. The differential mathematical model has been formed, for the process inside the chosen furnace. The absorption coefficient of the gas phase has been obtained by application of the simple gray gas model, and its value has been kept constant in all examined cases. Results show that increase of the dispersed phase absorption Coefficient leads to the increase of the gas-phase temperature and incident radiative fluxes. Agreement with the results of measurement has been achieved for all values of the dispersed phase radiative properties

Reduction of carbon monoxide emission from a solid-fuel thermo-accumulation furnace

Many households in Serbia, using electric thermo-accumulation furnaces for heating, have been forced to find an alternative solution, due to a significant increase in electricity prices during the last decade. A possible solution is replacing electric heating appliances with the solid fuel-fired ones. A prototype of a new concept of thermo-accumulation solid fuel-fired furnace has been developed to meet these growing needs, providing electricity saving together with considerable environmental benefits. Two strategies for reduction of carbon monoxide emission are examined in the paper: application of Pt/Al2O3 catalyst, in the form of 3 ± 0.3 mm spheres, providing further combustion of flue gases within the furnace, as well as an additional emission reduction by means of the air excess control. Experimental investigations of the catalyst influence on the conversion of carbon monoxide have been done for different operation regimes and positions of the catalyst. The paper presents selected results regarding carbon monoxide emission during wood and coal combustion. Investigations suggest a considerable effect of the catalyst and a strong influence of the catalyst position within the furnace to carbon monoxide emission reduction. In addition, experimental tests have been conducted to asses the effect of the air excess control in the furnace on carbon monoxide emission. The amount of combustion air, the flue gas flow rate, and the fuel feeding regime have been adjusted in order to keep the flue gas oxygen content in a relatively narrow range, thus obtaining controlled combustion conditions and lower carbon monoxide emission. In this way, the furnace has been made able to respond to the changes in heating needs, fuel quality and other parameters, which is advantageous in comparison with similar solid-fuel fired furnaces

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

Numerical optimisation of processes in the furnace considering NOx emission and efficiency of utility boiler

Razvijen je matematički model, namenjen za predviđanje procesa u energetskim parnim kotlovima TE Kostolac B tangencijalno loženim sprašenim lignitom. Model je primenjen za numeričku analizu rada kotla radi smanjenja emisije NOx, uz istovremeno održavanje visokog stepena korisnosti kotla. Kompleksni dvofazni tok gas-čestice modeliran je Ojler-Lagranževim pristupom. Povezivanje faza je ostvareno kuplovanjem pomoću PSI-Cell koncepta. Radi ostvarivanja željenih analiza, ugrađen je pod-model formiranja/destrukcije NO, unutar složenog koda za sagorevanje, koji se koristi za predviđanje emisije na izlazu iz ložišta. Modelirani su termički i gorivi NO, kao najuticajniji oksidi azota pri sagorevanju ugljenog praha. Proračunski program je razvijen radi lakše upotrebe od strane inženjerskog osoblja prilikom analiza procesa u kotlovskim postrojenjima. Numeričke simulacije su izvršene za različite radne uslove kotla, prilikom loženja lignitom sa kopa Drmno. Suprotstavljeni zahtevi a smanjenjem emisije i efikasnim sagorevanjem, sa osvrtom na bezbedan rad pregrejača pare često zahtevaju rad kotla u uskim granicama radnih parametara, koji su utvrđeni pomoću termičkog proračuna kotla.Mathematical model, aimed for prediction of processes in TE Kostolac B power plant utility boiler furnace tangentially fired by pulverized lignite, was developed in-house. The model was applied in numerical analysis of boiler operation, in order to reduce NOx emission by combustion modifications in the furnace, while maintaining high efficiency of the boiler unit. Complex two-phase gas-particle flow was modelled using Euler-Lagrange approach. Coupling between phases was done by using PSI-Cell concept. In order to perform necessary analysis, NO formation/destruction sub-model was implemented, within comprehensive combustion code, used to predict emission from the furnace. Thermal and fuel NO were modelled, as the most influential nitrogen oxides during pulverized coal combustion process. The computational code was developed to be easily used by engineering staff dealing with the process analysis in boiler units. Numerical simulations were performed for the boiler fired by the lignite Drmno, under different operating conditions. Contradictory requirements with respect to emission reduction and efficient combustion with safe operation of super-heaters often require boiler to operate within narrow limits of operation parameters, which is determined by means of the boiler thermal calculation

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