Effect of heating process on the wettability of fine coals of various ranks

Abstract

Spontaneous coal combustion can produce a condition of heating process because the atmosphere of coal underground is usually poor in oxygen. Even though the spontaneous combustion of coal is prevented by people, the surface properties of coal are greatly changed. The changes in the wettability of coal influence the flotation of fine coals. This paper investigates the effect of the heating process on the wettability of fine coals of various ranks. Lignite, bituminous, and anthracite coals were used as experimental samples. The heating temperature and time were 500 °C and 2 h. X‐ray photoelectron spectroscopy (XPS) and contact angle measurements were used to indicate the changes in wettability of fine coals before and after the heating process. The results showed that the wettability of bituminous coal was significantly increased whereas that of lignite was greatly decreased after the heating process. However, the wettability of anthracite coal was increased only a little after the heating process.

Experimental methods in chemical engineering: Contact angles

“…In five of these papers, CA is only an inlet parameter in a model or a numerical simulation. The twelve remaining involve experimental measurements, all of which were performed with an optical goniometer or derived instruments . The latter enables analysis at a liquid/liquid/solid or a liquid/gas/solid interface instead of a gas/liquid/solid one (Figure ).…”

“…The latter enables analysis at a liquid/liquid/solid or a liquid/gas/solid interface instead of a gas/liquid/solid one (Figure ). Works performed with an optical goniometer mainly employed the static sessile drop method with only two employing dynamic methods . Three studies included qualitative surface analysis through scanning electron microscopy images to estimate the substrate roughness: Ahmmed et al published the only manuscript in which both advancing and receding contact angles are reported and in which an estimation of the hysteresis is provided.…”

“…Studies containing experimental work on contact angles were mostly interested in investigating the wettability of powders: nanoparticles and microparticles . Other surfaces of interest included polymeric films, rocks, and glass .…”

“…Other applications involve nanofluids: in one case, a nanopowder was used as an interfacial modifier to alter the wettability of a reservoir surfaces; in two others, nanoparticles were left in suspension to act as modifiers of the physical properties (viscosity, thermal conductivity, surface tensions) of water or bitumen . Probe liquids employed include water, salted water, toluene, denatured ethanol, n ‐dodecane, bitumen, and various oils …”

“…Contact angle measurements were performed in order to probe the wetting behaviour (usually hydrophobicity or oleophilicity) and assess the success of a modification method (application (1), red cluster in the Figure ). In two circumstances the hysteresis was investigated (application (2)), either in terms of kinetic hysteresis (penetration of the liquid in a porous substrate) or in terms of surface anisotropy, while in another the free surface energy of the solid was estimated through the OWRK model (application (3)).…”