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The aim of this work is the determination of the combustion characteristics of two different fuel gases for their blast furnace utilization. The availability of gas from the coke production as well as from the basic oxygen furnace (BOF) process in an integrated metallurgical plant makes it possible to substitute reducing agents like oil. For a description of the varieties of the gases, coke oven gas (COG) and a mixture of COG and BOF gas, four independent modeling approaches were applied to cover all aspects. The different applied modeling approaches are the thermodynamic equilibrium, the plug flow reactor (PFR) model with detailed chemistry with or without, resp., consideration of the mixing time and computational fluid dynamics (CFD). This guarantees an improved understanding of the whole combustion process.The earlier ignition of the COG/BOF gas mixture in comparison to the COG can be ascribed to the higher excess air ratio, in spite of the better ignition propensity of COG. The higher net calorific value of the COG results in higher combustion temperatures, which implicates a higher thermal strain on the tuyere. In addition, greater amounts on CO and H 2 in the raceway result from the COG combustion.KEY WORDS: ironmaking; blast furnace; gas injection; modeling; combustion. time, it is possible to study the influence of different mixing lengths on the resulting temperature and species concentrations at the end of the tuyere.Computational Fluid Dynamics (CFD) allows a more detailed description of the predominant flow of gas injection. Because of the high resource demanding flow calculation, simplified models are used for the simulation of the reactions. The simplest assumption is the thermodynamic equilibrium again which is now based on the local composition. Basic Facts Plant LayoutThe layout of the blast furnace with the gas injection plant is shown in Fig. 1. In the mixing station, gas from the coke production (coke oven gas, COG) and gas from the basic oxygen furnace (BOF gas) are mixed if it is necessary. Then the process gas is conveyed via a screw compressor and a gas cooler to a bustle pipe, wherefrom it is directed to 17 tuyeres spread over the circumference of the blast furnace.The injection of the reducing gas is done by using two lances per tuyere, which is represented by the cases in this study (Fig. 2). The lances end 10 cm inside from the end of the tuyere. Input ParameterFor calculation, two gases with different compositions are used. These are the coke oven gas (COG) and a mixture of COG and BOF gas (COG/BOF). The different compositions of the two gases and their net calorific values as well as the predominant excess air ratios of the combustion process are listed in Table 2. The appointed boundary conditions valid for one tuyere can be seen in Table 3. Reaction MechanismsThe reaction mechanisms of the combustion are radical chain reactions. These chain reactions consist of starting reactions that build radicals, chain propagation reactions, chain branching reactions that increase the amount o...

NO x (i.e., NO and NO2) and N2O are known as harmful pollutants. In fluidized bed combustion these are formed from the nitrogen in the fuel. To develop effective primary measures reducing the emissions, more knowledge on the mechanism of formation and destruction ongoing in fluidized beds has to be obtained. In this work, a detailed chemistry model is combined with a two-phase model for a stationary fluidized bed to calculate the emissions of a single fuel particle in a laboratory-scale stationary fluidized bed. The single particle model consists of a simple model for the H2O release during drying, a model for the volatiles composition, and a model for the nitrogen chemistry during char combustion. The detailed reaction mechanism consists of a homogeneous part, heterogeneously catalyzed reactions on the bed material, and radical recombination reactions on the solids’ surface. The results confirm that devolatilization and char combustion are of nearly equal importance for NO and N2O formation. During devolatilization, NO is formed from HCN and NH3, while N2O is formed almost exclusively from HCN. During char combustion, NO is mostly formed by heterogeneous oxidation of char nitrogen, while N2O is formed from homogeneous oxidation of HCN. On the other hand, there is also a back coupling of NO on the homogeneous burnout of the carbon containing species, by sensitizing the oxidation of CH4.