On optimization of the coke oven twin-heating flue design providing a substantial reduction of NOx emissions. Part II: Optimized designs for COG- and MG- fired units as well as operating characteristics of the new heating flues

Abstract

This article relates to the optimization of the twin heating flue construction in terms of NOx emission (see also Part I). The novel designs for both mixed-gas (MG) and coke oven gas (COG) have been developed using CFD-based numerical modelling and GRI-Mech 3.0 detailed mechanism (for NOx predictions). By analyzing the results of investigations presented in Part I, the construction modifications of the twin-heating flues have been found, to reduce NOx emission from about 180 ppm (7% O2) and 56 ppm (7% O2) to the values below 100 ppm and 42 ppm for both COG and MG, respectively. These improvements have been achieved by modifying the location\\size of the air and fuel inlets as well as by improving the internal flue gas re-circulation.To test the operation of the optimized heating flues, the operating characteristics for the heating flue temperature range from 1220 °C to 1360 °C have been prepared. The unit operation curves, predicted for the baseline case and modified cases, show that the proposed design modifications decrease NOx emission on average by 25% (MG) and 60% (COG). The flue gas re-circulation for COG has been increased from about 25% to over 70%. For MG, the exhaust gas re-circulation has been improved from about 30% to over 80%. Modifications aimed at intensifying the flue gas re-circulation increase pressure losses inside the heating flues from 10 Pa to 40 Pa for MG and from 5 Pa to 20 Pa for COG.