Self-cementing properties of oil shale solid heat carrier retorting residue

Abstract

Oil shale-type organic-rich sedimentary rocks can be pyrolysed to produce shale oil. The pyrolysis of oil shale using solid heat carrier (SHC) technology is accompanied by large amount of environmentally hazardous solid residue-black ash-which needs to be properly landfilled. Usage of oil shale is growing worldwide, and the employment of large SHC retorts increases the amount of black ash type of waste, but little is known about its physical and chemical properties. The objectives of this research were to study the composition and self-cementing properties of black ash by simulating different disposal strategies in order to find the most appropriate landfilling method. Three disposal methods were simulated in laboratory experiment: hydraulic disposal with and without grain size separation, and dry dumping of moist residue. Black ash exhibited good self-cementing properties with maximum compressive strength values of >6 MPa after 90 days. About 80% of strength was gained in 30 days. However, the coarse fraction (>125 µm) did not exhibit any cementation, thus the hydraulic disposal with grain size separation should be avoided. The study showed that self-cementing properties of black ash are governed by the hydration of secondary calcium silicates (e.g. belite), calcite and hydrocalumite.

Geopolymeric Potential of the Estonian Oil Shale Solid Residues: Petroter Solid Heat Carrier Retorting Ash

“…The solid heat carrier ash studied was sampled at the Petroter-type SHC retort and was provided by VKG. The Petroter SHC process results in dark grey retorting ash (also known as "black ash") that contains up to a few percent of organics [12,13]. During retorting, oil shale is heated in the absence of oxygen to the temperature (approx.…”

Self-Cementing Properties and Alkali Activation of Enefit280 Solid Heat Carrier Retorting Ash

“…As a result, the Enefit280 WHB ash does not contain a CaS (oldhamite) phase. Oldhamite is particularly characteristic of retorting residues [4,16], but does not occur in thermal power plant ashes [17,18]. Oldhamite forms under oxygen deficiency conditions in the reaction between CaO and SO 2 .…”

“…Oldhamite forms under oxygen deficiency conditions in the reaction between CaO and SO 2 . Another mineral indicating oxygen deficiency in the retorting process is a partly oxidised Fe-oxide mineral magnetite Fe 3 O 4 (FeO•Fe 2 O 3 ) in older SHC ashes, whereas in the WHB ash like TPP ashes the hematite Fe 2 O 3 is typically present [16].…”

“…In comparison, the hydration of oil shale ash from thermal power plants and the semi-coke waste from shale oil retorting typically results in a high ettringite content, reaching 30 wt% of crystalline phases [4]. A similar low content of ettringite upon hydration with water was observed in the Petroter ash where ettringite was nearly absent [16] or was found to occur in a low content, < 5 wt% [15]. Ettringite plays an important role in the self-cementing properties of oil shale ash and semi-coke deposits by forming interlocking meshes of needle-like crystals filling the pores space [22].…”

Leaching Thermodynamics and Kinetics of Oil Shale Waste Key Components

“…The resulting solid residue consists mainly of calcite, quartz, K-feldspar, and dolomite, with only trace amounts of CaO free . The composition of this residue is similar to that of ash produced in the circulating fluidized bed furnaces at thermal power plants, but contains up to a few percent of unburnt organic matter due to the short residence time in the combustion stage [8,9].…”