The operation of large industrial furnaces will continue to rely on hydrocarbon fuels in the near foreseeable future. Mathematical modeling and numerical simulation is expected to deliver key insights to implement measures to further reduce pollutant emissions. These measures include the design optimization of the burners, the dilution of oxidizer with exhaust gasses, and the mixing of natural gas with hydrogen. In this paper, we target the numerical simulation of non-premixed turbulent combustion of natural gas in a single heating section of a ring pit anode baking furnace. In previous work, we performed combustion simulations using a commercial flow simulator combined with an open-source package for the three-dimensional mesh generation. This motivates switching to a fully open-source software stack. In this paper, we develop a Reynolds-Averaged Navier-Stokes model for the turbulent flow combined with an infinitely fast mixed-is-burnt model for the non-premixed combustion and a participating media model for the radiative heat transfer in OpenFoam. The heat transfer to the refractory brick lining is taken into account by a conjugate heat transfer model. Numerical simulations provide valuable insight into the heat release and chemical species distribution in the staged combustion process using two burners. Results show that at the operating conditions implemented, higher peak temperatures are formed at the burner closest to the air inlet. This results in a larger thermal nitric-oxide concentration. The inclusion of the heat absorption in the refractory bricks results in a more uniform temperature on the symmetry plane at the center of the section. The peak in thermal nitric-oxides is reduced by a factor of four compared to the model with adiabatic walls

Industrial emissions are discussed worldwide for their adverse effects on the global climate change. Nitric oxide (NOx) emissions are harmful among the various flue gases emitted in the atmosphere. There are multiple routes of formation of NOx in industry. The formation of NOx due to local overheating in fuel lean conditions is the most common way. The heavy industries such as aluminium consists of various intermediate processes. Anode baking is one such important process. The anode baking process comprises of a combustion chamber in which natural gas is fired for generating heat. The temperature in the furnace due to the combustion process is as high as 2000oC. This leads to formation of NOx in the anode baking furnace. The Aluminium and Chemie B.V. (Aluchemie) operates industrial anode baking furnaces situated in Rotterdam, The Netherlands. The problems of NOx formation in anode baking furnace of Aluchemie are discussed in this thesis.

Thermal nitric-oxide (NOx) formation in industrial furnaces due to local overheating is a widely known problem. Various industries made significant investments to reduce thermal NOx by varying the operating conditions and designs of the furnace. It is difficult to find the optimal operating conditions that minimize NOx formation in the furnace by trial and error methods. The high temperature in the furnace complicates performing experiments in the furnace. Numerical modeling can provide significant information in such cases. Therefore, the objective of this paper is to obtain a numerical model of the furnace in such a way that the operating conditions can be varied and examined. In this paper, a three-dimensional steady-state finite element model for the anode baking industrial furnace is discussed. The COMSOL Multiphysics software is used for modeling the non-premixed turbulent combustion and the conjugate heat transfer to the insulation lining. The cfMesh software is used for obtaining the mesh. The results show that the simulated temperature agrees well with the measured data from our industrial partner in regions distant from the flames. The analysis shows that by decreasing the fuel mass flow rate and increasing the fuel pipe diameter by 45%, the peak in thermal NOx ppm generated in the furnace decreases by 42%. The model is limited by the use of a single-step chemistry mechanism with an eddy dissipation combustion model and a simplified approach for radiation, such as the P1 approximation model. The model can be further improved by considering a detailed chemistry mechanism model for combustion and a discrete ordinate model for radiation.

Thermal nitric-oxide (NOx) formation in industrial furnaces due to local overheating is a  widely known problem. Various industries made significant investments to reduce thermal NOx by varying the operating conditions and designs of the furnace. Finding optimal operating conditions or design parameters by experimenting in the furnace, however, is difficult. Numerical modeling can provide significant information in such cases. In this paper, a three dimensional steady state finite element model for the anode baking industrial furnace is discussed. The COMSOL Multiphysics software is used for modeling the non-premixed turbulent combustion and the conjugate heat transfer to the insulation lining. The mesh generation using the cfMesh software allows to increase the spatial resolution locally at the outlet of the fuel nozzles while maintaining the overall quality of the mesh. The temperature and species mass fraction obtained from the finite element model are calibrated by adjusting the amount of artificial diffusion in the transport equations for the species. The simulated temperature agrees well with the measured data from our industrial partner in regions distant from the flames. The model underestimates the measured oxygen mass fraction. The spatial gradients in oxygen mass fraction, however, are captured well by the model. The effects of variation of the fuel mass flow rate and the fuel pipe diameter on the NOx generation are studied. The results show that by decreasing the fuel mass flow rate and increasing the fuel pipe diameter by 45%, the peak in thermal NOx ppm generated in the furnace decreases by 42%.

The emissions from the industrial furnaces impact the environment. Among the various factories, those having anode baking furnaces are working on reducing the pollutant emissions. The aerodynamics in the furnace influences the emissions due to the high dependence of combustion and radiation phenomena on the mixing characteristics. Therefore, this paper aims to establish the numerical simulation results for the three-dimensional turbulent flow in a single section of an anode baking furnace with a high rate of fuel injection. The stabilized non-linear finite element approach on the Reynolds-averaged Navier-Stokes (RANS) equation is used with COMSOLMultiphysics. The turbulent viscosity ratio is highly sensitive to the mesh for the standard k-ε model. The requirements of the Cartesian and refined mesh near the jet development region is explained. The comparison of meshes generated by two meshing tools namely cfMesh and COMSOL Multiphysics default Mesher is carried out. The high numerical diffusion in the flow models due to the coarser mesh leads to convergence but deficit the precision in the results. This paper shows that the mesh generated by cfMesh with flow aligned refinement combined with the non-linear finite element solver in COMSOL Multiphysics proves to provide accurate results of turbulent quantities.

The anode baking process is developed and improved since the 1980s due to its importance in Aluminium industry. The process is characterized by multiple physical phenomena including turbulent flow, combustion process, conjugate heat transfer, and radiation. In order to obtain an efficient process with regards to quality of anodes, soot-free combustion, reduction of NOx and minimization of energy, a mathematical model can be developed. A mathematical model describes the physical phenomena and provides a deeper understanding of the process. Turbulent flow is one of the important physical phenomena in an anode baking process. In the present work, isothermal turbulent flow is studied in detail with respect to two turbulence models in COMSOL Multiphysics software. The difference between wall boundary conditions for these models and their sensitivity towards the boundary layer mesh is investigated. A dimensionless distance in viscous scale units is used as a parameter for comparison of models with and without a boundary layer mesh. The investigation suggests that the boundary layer mesh for both turbulence models increase the accuracy of flow field near walls. Moreover, it is observed that along with the accuracy, the numerical convergence of Spalart-Allmaras turbulence model in COMSOL Multiphysics is highly sensitive to the boundary layer mesh. Therefore, development of converged Spalart-Allmaras model for the complete geometry is difficult due to the necessity of refined mesh. Whereas, the numerical convergence of k-ε model in COMSOL Multiphysics is less sensitive to the dimensionless viscous scale unit distance. A converged solution of the complete geometry k-ε model is feasible to obtain even with less refined mesh at the boundary. However, a comparison of a developed solution of k-ε model with another simulation environment indicates differences which enhance the requirement of having converged Spalart-Allmaras model for complete geometry.