98/00815 Flotation of fine coke particles from fly ash

Abstract

Fine coke particles were separated from fly ash in a laboratory flotation cell. Almost 90% of particles by number were below 10 µm and one third of them was less than 2 µm. Fly ash was sampled directly from a surge bin in a power plant and from a refuse dump area. Kerosene and Diesel oil were compared as collectors, and MIBC and polyglycol – based agents – were used as frothers. The best separation coefficient of 0.8 was obtained for 18 kg/t of Diesel oil and 9 kg/t of commercial frother based on polyglycol. LITERATURE REVIEW Fly ash from hard coal combustion can contain 20% or even more combustible residue, usually in the form of coke. This coke with low sulphur content may be considered as valuable ecological fuel. On the other hand, commercial application of fly ash as a component in construction materials requires limited coke content. Up until recently fly ash from Gdansk power plants was deposited at dump sites which harmed the environment. Because several million tons of this waste material have been kept in wet condition, foam flotation was selected for coke removal from the fly ash. Literature review pertaining to fine coal and coke flotation is presented in Table 1. Besides of fly ash, fine coal flotation papers are also included because of many similarities in both flotation systems. Values in bold were calculated or estimated from the data provided by authors of the papers. First seven experimental systems, presented in Table 1, pertain to coal flotation. The coefficient of separation (CS), representing process efficiency, in the range of 31%–73% indicates that fine coal particles do not float easily. It is worth to mention that comparable process efficiency was obtained for the ASH and other flotation equipment, but the flotation time for the ASH was many times shorter. Inferior flotation results can also be attributed to the excess of collector causing increased froth viscosity and greater ash particles entrainment to the froth (Clarkson et al. 1994). Although processing results given by Babatchew are very impressive (raw concentrate grade 75–80%) no processing details were provided (Babatchew 1987).