The Fate of Trace Elements During MTE and HTD Dewatering of Latrobe Valley Brown Coals

Abstract

The nonevaporative brown coal dewatering technologies, Mechanical Thermal Expression (MTE) and Hydrothermal Dewatering (HTD), are being evaluated in an attempt to increase the efficiency of coal drying compared with current evaporative methods.Product waters from each of the three major Latrobe Valley mines were prepared under both MTE (200 C and 15 MPa mechanical pressure) and HTD (300 C and 12 MPa) conditions. Comparison of the relative abundance of individual inorganic components across the two processes generally reflected their form (dissolved, exchanged, or mineral) in the parent coals. For MTE the data were complicated by leaching of rig components (principally bronze). MTE-derived waters contained greater amounts of Ag, As, Cd, Cr, Cu, Hg, Mo, Ni, Sn, and Zn. HTD waters had greater amounts of Al, B, Ba, Ca, Fe, K, Mg, Mn, Na, Pb, Se, Sr, Tl, and V. Dissolved organic carbon was five times higher in the HTD products as a result of the higher processing temperature employed. Many species (Al, Ag, As, Cd, Cr, Cu, Hg, Mo, Ni, Pb, V, Se, and Zn) were found to be above acceptable guidelines for discharge to the environment.

Upgrading of low rank coal by hydrothermal treatment: Coal tar yield during pyrolysis

“…The water can participate in one or more roles with the existing of oxygen functional groups [12] in brown coal: as a catalyst, reactant, and solvent in the aquathermolysis chemistry at the treatment temperature. Compared with these methods, hydrothermal treatment was considered as an effective pretreatment method [13][14][15]. Water removed as liquid may dissolve and leach out some water soluble inorganics and hydrophilic organics containing oxygen functional groups with the waste water, thereby reducing the amount of ash producing constituents [16] and oxygen functional groups [17] in the upgraded solid during hydrothermal treatment.…”

Changes in Physicochemical Properties and the Release of Inorganic Species during Hydrothermal Dewatering of Lignite

“…The seven cations listed in Table , were the most abundant metallic elements in lignites and named as major elements, which are also related to the fouling of boiler during combustion Table shows the concentrations of these major elements in wastewater produced from HTD process.…”

“…15 Xiang et al 16 proposed that HTD process condition is similar to subcritical water condition, and trace elements may also be removed through HTD processing. Although Xiang et al, 16 Butler et al, 17 and Chen et al 18 have reported the fate of trace elements in lignite during HTD, the changes of inorganic substances in raw coal, HTD product, and wastewater were not simultaneously measured and analyzed. Besides, the previous studies about HTD have dealt with a restricted range of coals, and thus it is useful to test whether the conclusions previously reached hold for other coals.…”

Effect of hydrothermal treatment on the carbon structure of Inner Mongolia lignite

“…Because of its high moisture content (25 wt%-60 wt%), the drying/dewatering is an integral step for lignite applications that require high efficiency. Hydrothermal treatment (Butler et al 2007;Sakaguchi et al 2008;Katalambula and Gupta 2009;Ullah et al 2018), a non-evaporative technique, is considered an effective method for dewatering and upgrading lignite. The process enables an improvement in the slurry properties of coal (Yu et al 2012;Fu and Wang 2014;Zhang et al 2018) and can reduce the viscosity of the coal-water slurry.…”