On optimization of the coke oven twin-heating flue design providing a substantial reduction of NOx emissions Part I: General description, validation of the models and interpretation of the results

Abstract

The paper presents an altered design of the coke oven twin-heating flues which is optimized in terms of NOx emission. The heating flue modifications relate to the position and size of the air inlets as well as an improved internal exhaust gas re-circulation. The optimization process was carried out using CFD-based numerical modeling. To ensure better accuracy, the formation of NOx within the heating flues was predicted using full GRI-Mech 3.0 mechanism.Improvement of the flues construction significantly reduced nitrogen oxides emission. When burning coke oven gas (COG) the NOx concentration in the flue gas drops from 182 ppm (7% O2) to the value below 100 ppm (7% O2). In the case of mixed gas (MG), the content of nitrogen oxides (in exhaust gases) decreases from about 56 ppm (7% O2) to 42 ppm (7% O2). The predicted results indicate a satisfactory agreement with the measured values. The correlation coefficients for measured and predicted NOx concentrations are equal to 0.99 (COG) and 0.81 (MG). The standard deviations are at the level of ±23.5 ppm (COG) and ±17.1 ppm (MG).This paper is Part I and contains: selected 1D and 3D simulations results, predictions interpretation, investigation of the internal flue gas re-circulation as well as validation of the model developed for the optimization procedure. In the associated publication (Part II) the optimized designs of the unit under consideration (for both MG and COG) have been described. Moreover, for the baseline and optimized cases, a number of the operating characteristics have been presented.