Ash and Flue Gas from Oil Shale Oxy-Fuel Circulating Fluidized Bed Combustion

Abstract

Carbon dioxide emissions are considered a major environmental threat. To enable power production from carbon-containing fuels, carbon capture is required. Oxy-fuel combustion technology facilitates carbon capture by increasing the carbon dioxide concentration in flue gas. This study reports the results of calcium rich oil shale combustion in a 60 kW th circulating fluidized bed (CFB) combustor. The focus was on the composition of the formed flue gas and ash during air and oxy-fuel combustion. The fuel was typical Estonian oil shale characterized by high volatile and ash contents. No additional bed material was used in the CFB; the formed ash was enough for the purpose. Two modes of oxy-fuel combustion were investigated and compared with combustion in air. When N 2 in the oxidizer was replaced with CO 2 , the CFB temperatures decreased by up to 100 • C. When oil shale was fired in the CFB with increased O 2 content in CO 2 , the temperatures in the furnace were similar to combustion in air. In air mode, the emissions of SO 2 and NO x were low (<14 and 141 mg/Nm 3 @ 6% O 2 , respectively). Pollutant concentrations in the flue gas during oxy-fuel operations remained low (for OXY30 SO 2 < 14 and NO x 130 mg/Nm 3 @ 6% O 2 and for OXY21 SO 2 23 and NO x 156 mg/Nm 3 @ 6% O 2 ). Analyses of the collected ash samples showed a decreased extent of carbonate minerals decomposition during both oxy-fuel experiments. This results in decreased carbon dioxide emissions. The outcomes show that oxy-fuel CFB combustion of the oil shale ensures sulfur binding and decreases CO 2 production.

Long-term mineral transformation of Ca-rich oil shale ash waste

“…OS deposits are found worldwide but these large reserves are exploited only in a few countries, mostly because of the low heating value and environmental concerns. Even the best quality OS like the Estonian kukersite OS have heating values of 8-12 MJ/kg (Ots, 2006) and generate~45-53% of solid residues upon combustion (Loo et al, 2018). This is much greater than the 5-20% solid waste left from typical coal firing.…”

Research and Development of the Oxy-Fuel Combustion Power Cycles with CO2 Recirculation

“…The power production industry produces a remarkable amount of harmful emissions [2], so the mitigation of power facility emissions is a topical direction. Today, thermal power plants successfully reduce nitrogen and sulfur oxide emissions [3][4][5][6][7]. Organic fuel combustion produces huge amounts of carbon dioxide, and its emissions still are a difficult problem [8,9].…”

Carbon dioxide sequestration in power plant Ca-rich ash waste deposits

“…High-temperature (> 1200-1400 °C) pulverized combustion (PC) technology was the main method for processing OS up until 2018, but has been replaced by circulated fluidized bed combustion (CFBC) technology operating at 700-800 °C, which had been gradually implemented since 2004. PC boilers emit up to one tonne of CO 2 per tonne of fuel [23], but CFBC emits up to 13% less [24], largely due to the lower extent of carbonate decomposition in low-temperature combustion (decomposition extent 0.97 in PC and 0.60 in CFBC) [25].…”