Influence of Coal Blending Methods on Unburned Carbon and NO Emissions in a Drop-Tube Furnace

Abstract

The influence of coal-blending methods, such as out-furnace and in-furnace methods, on unburned carbon and NO emissions of blending coal combustion in a drop-tube furnace (DTF) has been analyzed using experimental and numerical approaches for binary coals (sub-bituminous and bituminous coals) used by Korean power plants. In the out-furnace method, as the blending ratio of sub-bituminous coal based on bituminous coal (SBR) increases up to 50%, the unburned carbon fraction gradually decreases. The worst condition is found at a SBR of 75%, which is caused by the occurrence of highly oxygen-deficient conditions in the furnace. Furthermore, the emission index of NO (EINO) is proportional to the SBR. In addition, the in-furnace blending method is applied using a modified DTF to improve the efficiency of unburned carbon fractions and the involvement of NO emissions. The results show that unburned carbon fractions as well as the EINO decrease over time because of improvements in oxygen deficiency and NO reduction mechanisms. The numerical modeling strongly supports these phenomena and provides insights into the mechanisms that affect the blending methods during the combustion of coal blends.

Experimental Investigation of Ash Deposit Behavior during Co-Combustion of Bituminous Coal with Wood Pellets and Empty Fruit Bunches

“…The first is supply retention by the screw feeder at the beginning of the experiment due to the densely packed samples, and the second is rate reduction at the end of the experiment due to the loosely packed samples, leading to decreased self-loading of fuel particles. The rate of air transport was adjusted so that the excess O2 content was maintained at 1.16 (v/v, dry), the typical furnace exit value for pulverized fuel boilers [29]. The mass of deposited ash particles was obtained by calculating the difference between the clean and fouled samples, and Approximately 200 mg of an ash sample was placed in a crucible and the top of the sample was flattened with a jig by applying a constant pressure of 260 kPa.…”

“…To examine the ash deposition tendencies according to the type of coal and biomass co-combustion, a DTF apparatus (600 mm long with an internal diameter of 70 mm) was used [29]. Figure 2 shows schematics of the DTF apparatus and deposition probe.…”

Unburned carbon from coal combustion ash: An overview

“…[8,26,45] -effect of coal mineral matter [8,16,26,46] -coal blending [32,39,44,[47][48][49] -co-combustion of coal with alternative fuels [50][51][52][53][54].…”

Empirical Formula to Predict the NOx Emissions from Coal Power Plant using Lab-Scale and Real-Scale Operating Data

“…Therefore, the input heat was calculated to be 1.68 kcal/min considering that the standard fuel supply was 0.3 g/min. By applying a stoichiometric ratio of 1.16, the total gas flow rate was 5 L/min [17].…”