Design of advanced industrial furnaces using numerical modeling method

Sammanfattning: This doctoral thesis describes the fundamentals ofmathematical modeling for the industrial furnaces and boilersand presents the results from the numerical simulations of sometypical applications in advanced industrial furnaces andboilers. The main objective of this thesis work is to employcomputational fluid dynamics (CFD) technology as an effectivecomputer simulation tool to study and develop the newcombustion concepts, phenomena and processes in advancedindustrial furnaces and boilers. The applications concern onfrom retrofitted conventional grate boilers to the mostadvanced highly preheated and diluted air combustion (HPDAC)furnaces. In this work, several topics are specially concernedwhen applying CFD technology to combustion cases. These topicsare including grate bed model, NOxmodeling, mixing problem, air staging system, andhighly preheated and diluted air combustion technology. In thiswork, a black-box grate bed model is developed and used inmodeling of grate fired furnaces and boilers. It is based onthe thermodynamic calculations and a set of conservationequations of mass, energy of fuel and air on the grate bed. Oneof benefits of this bed model is simple and feasible to be putinto use in industry. For NOxmodeling, besides the thermal NO and prompt NO,the HCN route fuel NO has been employed to predict the fuel NOemissions in coal/biomass fired furnaces. In addition, based onNH3route of fuel NO formation, a SNCR scheme for NOxabatement has been proposed also. For mixingproblem, the concepts of global degree of mixing and individualdegree of mixing have been proposed and used successfully inpractical applications. The new definition of degree of mixingovercomes some shortages of existed mixing parameters, such asthe mixing factor and the degree of non-mixing, which arenon-normalized and may lose physical meaning in some regions ofthe system. A new air staging system has been studied. It isused to improve the secondary or over-fire air configuration,thus to reduce the pollutant emissions and to enhance thecombustion facilities' efficiencies. In this work, the airstaging system has been employed in coal and biomass combustionfor grate fired furnaces/boilers. The performance of the newair staging system has been evaluated and optimized by usingnumerical modeling method together with physical modelingmethod. Results show that the new air staging system has a goodpotential of improving the combustion quality and reducing thepollutant emissions in industrial furnaces and boilers.Recently, the highly preheated and diluted air combustiontechnology has been regarded as the new generation energytechnology for advanced industrial furnaces and boilers. Inthis work, the highly preheated and diluted air combustionphenomena have been studied by using different numericalmodels. A hybrid procedure of both the large eddy simulationusing subgrid-scale stress Smagorinsky model and the Reynoldsstress model with eddy dissipation model has been alsoinvestigated to study the dynamic combustion process under theconditions of highly preheated and diluted air combustion.Results show that HPDAC technology possesses advantages ofsaving energy and low NOxemission, thus it has high potential to be usedfor the next generation of industrial furnaces and boilers. Thelarge eddy simulation using subgrid-scale stress Smagorinskymodel together with Reynolds stress model / eddy dissipationmodel are possible to study the HPDAC dynamic process. Finally,this work shows that numerical modeling method is a verypromising tool to deal with the complicated combustionprocesses even for practical applications in industry.Keywords: air staging, bed model, boiler, burner,computational fluid dynamics (CFD), Ecotube, fuel staging,furnace, grate combustion, highly preheated and diluted aircombustion (HPDAC), large eddy simulation (LES), mathematicalmodeling, nitrogen oxides (NOx), numerical simulation