Kunio Okiura

Effect of coal particle and spray droplet sizes on combustion characteristics of coal—water mixtures

Abstract An experimental study was carried out to clarify the effect of the droplet and coal particle sizes of coal—water mixtures (CWM) on combustibility, using a twin-fluid atomizer in a small-scale test furnace of 80 kg CWM/h. It was found that the spray mean droplet size became smaller as the coal particle size decreased, while other conditions remained constant, giving rise to better combustibility. However, the combustion efficiency decreased by the blow-off of flame phenomena when the atomizing speed increased even though the spray mean droplet size decreased. It was also confirmed that the combustion efficiency was influenced by the specific surface area of coal particles even if the spray mean droplet sizes did not change. When CWM with a nominal top size of 150 μm was compared with that of 590 μm but containing more fines of less than 5 μm, the size distribution of fly ash was found to be independent of coal particle size distributions of CWM, resulting in no difference in the unburned content in the fly ash.

Fundamental study on behavior of coal nitrogen in pulverized coal combustion.

For the development of de-NOx combustion technique of pulverized coals, a fundamental combustion test was carried out using a combustion electrically outer heated test furnace (the inside diameter : 115, the length : 1500) with co-axial burner. This report is concerned with behavior of coal nitrogen in combustion. The main results are as follows. The high swirl of the secondary air is effective for low-NOx emission because emitted NOx is deoxidized by NH3 which is produced in the reduction zone near the burner. NOx reduction process is very much influenced by the temperature of the reduction zone. The formation of NH3 from coal nitrogen results from volatile matter in coal, and the formation of HCN results from chemical combinations of fuel-N.