Abstract
© Copyright © 2020 Gulec, Meredith and Snape. Heavy industries including cement, iron and steel, oil refining, and petrochemicals are collectively responsible for about 22% of global CO2 emissions. Among these industries, oil refineries account for 4–6%, of which typically 25–35% arise from the regenerators in Fluid Catalytic Cracking (FCC) units. This article reviews the progress in applying CO2 capture technologies to FCC units. Post combustion and oxyfuel combustion have been investigated to mitigate CO2 emissions in FCC and, more recently, Chemical Looping Combustion (CLC) has received attention. Post combustion capture can readily be deployed to the flue gas in FCC units and oxyfuel combustion, which requires air separation has been investigated in a pilot-scale unit by Petrobras (Brazil). However, in comparison, CLC offers considerably lower energy penalties. The applicability of CLC for FCC has also been experimentally investigated at a lab-scale. As a result, the studies demonstrated highly promising CO2 capture capacities for FCC with the application of post combustion (85–90%), oxyfuel combustion (90–100%) and CLC (90–96%). Therefore, the method having lowest energy penalty and CO2 avoided cost is highly important for the next generation of FCC units to optimize CO2 capture. The energy penalty was calculated as 3.1–4.2 GJ/t CO2 with an avoiding cost of 75–110 €/t CO2 for the application of post combustion capture to FCC. However, the application of oxyfuel combustion provided lower energy penalty of 1.8–2.5 GJ/t CO2, and lower CO2 avoided cost of 55–85 €/t CO2. More recently, lab-scale experiments demonstrated that the application of CLC to FCC demonstrate significant progress with an indicative much lower energy penalty of ca. 0.2 GJ/t CO2.
Highlights
CO2 released from the industries beyond power generation can be captured using post combustion, pre-combustion, oxyfuel combustion, and chemical looping combustion (CLC) technologies (Kohl and Nielsen, 1997; Straelen et al, 2009, 2010; Ali et al, 2011; Digne et al, 2014; Pérez-Fortes et al, 2014; Clarens et al, 2016; Quader et al, 2016; Zhou et al, 2016)
The results indicated that a proper design of heat integration would significantly decrease the energy penalties for CO2 capture in Fluid Catalytic Cracking (FCC) units
Chemical Looping Combustion (CLC) is another promising technology for CO2 capture from the FCC regenerator
Summary
The average CO2 concentration has reached nearly 415 ppm in 2019, which is 40% higher than the level in the 1850s of only 280 ppm. In FCC-oxyfuel combustion capture, oxygen mixed with recycled CO2 is used instead of air to oxidize the coke that deposited on the FCC catalyst during cracking reaction (Melien and Roijen, 2009; Mello et al, 2009a, 2013, 2015a; Miracca, 2015). In the FCC-CLC capture, the coke is combusted with oxygen carriers, which are supplied by an additional circulation through an air reactor integrated with the FCC regenerator (Güleç et al, 2019a,b, 2020). To define the technical feasibility of oxyfuel combustion, heat balance and volumetric flow rate tests were carried out with two FIGURE 6 | Process flow diagram presenting three different heat integration options with post-combustion capture for the flue gas released from the regenerator of the FCC unit, adapted from Wei et al (2018) with permission from Elsevier. To keep product selectivity and conversion the same, circulating reduced oxygen
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