Overview of Chemical-Looping Reduction in Fixed Bed and Fluidized Bed Reactors Focused on Oxygen Carrier Utilization and Reactor Efficiency

Abstract

A model-assisted comparison of two types of chemical-looping (CL) reactors (fixed bed and fluidized bed), with the same oxygen carrier loading and fuel capacity, is carried out to examine performance and efficiency of CL Reducers, operating with methane as the feedstock and nickel oxide as the oxygen carrier. The study focuses on the reduction step of chemical-looping combustion (CLC), for which the reactor efficiency and fuel utilization are crucial in terms of economics and carbon capture efficiency. Process models (a three phase dynamic model for bubbling fluidized beds and a two dimensional homogeneous model for fixed beds) and reaction kinetics developed and validated in previous studies are used. A fluidized bed chemical-looping combustion Reducer is compared to a fixed bed equivalent reactor, scaled-up from a smaller experimental reactor, constrained to bed height to reactor diameter ratios that prohibit excessive temperature and pressure drops across the bed. Through a detailed comparison, CLC operated in the fluidized bed reactor is shown to deliver superior performance, i.e., uniform temperature and pressure distribution; high methane conversion (> 95%) and carbon dioxide selectivity (> 95%) sustained for longer reduction periods; negligible carbon formation (< 2 mol% C basis); and better efficiency in oxygen carrier utilization.

Chemical Looping Gasification of Charcoal with Iron-Based Oxygen Carriers in an Annular Dual-Tube Moving Bed Reactor

“…In addition, the formation of a crystal phase (CuAl 2 O 4 ), crosslinking CuO and γ-Al 2 O 3 , was supposedly to contribute to the stability of copper-based oxygen carrier, whereas the lanthanum contributed speeding the formation of the crosslinking between CuO and γ-Al 2 O 3 . Zhou et al (2014) demonstrated that high CO 2 selectivity and CH 4 conversion for CLC operated in the batch fluidized bed reactor with NiO, and also reported that the operation time of approximately 6 min was achieved for 95% of NiO conversion by CLC operated in the fixed bed reactor, while the operation time of 95% of NiO conversion by CLC operated in the fluidized bed reactor reached lower than 3 min, indicating that the longer reaction times of the gas inside the reactor lead to faster conversions of the oxygen carrier. Wang et al (2016) studied that the kinetic study of Mn-based oxygen carrier for oxygen release by chemical looping air separation (CLAS), and also reported that the first-order chemical reaction model (C1) and Avrami-Erofe'ev random nucleation and subsequence growth model (A2) Kuo et al (2015) reported that the spinel structure of NiFeAlO 4 oxygen carriers presented high CO conversion and H 2 generation has been proved in fixed bed reactor for chemical looping hydrogen generation process (CLHG), because the ability of self-supported and agglomeration resistance were significantly enhanced.…”

Model-assisted analysis of fluidized bed chemical-looping reactors

“…After the initial low reactivity period, the gas product at the exit of the reactor contains mostly CO 2 , due to the relative excess of NiO. The overall CO 2 selectivity is maintained at high levels for the entire reduction time, which is one of the benefits of performing CLC in a fluidized bed compared to a fixed-bed reactor (Zhou et al, 2014a). Chandel et al (2009) studied the reactivity of Ni-and Cu/Fe-based oxygen carriers in a semi-batch fluidized bed reactor by varying the number of redox cycles, reactor temperature (800-900 1C), bed inventory (2.5-6 kg) and fuel flow, with the conclusion that 97% CO 2 capture efficiency was achievable in their setup.…”

“…Alternative reactor concepts for CLC include alternating flow fixed-bed reactors (Noorman et al, 2010), moving bed reactors (Fan et al, 2008), and rotating fixed-bed reactors (Håkonsen and Blom, 2011;Zhao et al, 2013). Compared with fixed-bed reactors, fluidized bed reactors are more suitable to process large inventories of solids with small pressure drop and uniform temperature profiles (Zhou et al, 2014a). Bubbling fluidized bed reactors are the most common implementation of laband pilot-scale CLC Reducers Gayán et al, 2009;Hoteit et al, 2009;Iliuta et al, 2010;Mattisson et al, 2008;Ryu et al, 2008Ryu et al, , 2009.…”

Fabrication of Fe2O3/TiO2 Oxygen Carriers for Chemical Looping Combustion and Hydrogen Generation

“…Numerous technology options are proposed to reduce carbon dioxide (CO 2 ) emissions. Among these technologies, chemical looping combustion (CLC) has been proposed to generate energy with zero to negative carbon emission (Adanez et al, 2012;Reich et al, 2014;Zhou et al, 2014). For CLC process, Fig.…”