Chemical‐looping combustion process: Kinetics and mathematical modeling

Abstract

Chemical Looping Combustion technology involves circulating a metal oxide between a fuel zone where methane reacts under anaerobic conditions to produce a concentrated stream of CO 2 and water and an oxygen rich environment where the metal is reoxidized. Although the needs for electrical power generation drive the process to high temperatures, lower temperatures (600-800 C) are sufficient for industrial processes such as refineries. In this paper, we investigate the transient kinetics of NiO carriers in the temperature range of 600 to 900 C in both a fixed bed microreactor (WHSV ¼ 2-4 g CH 4 /h/g oxygen carrier) and a fluid bed reactor (WHSV ¼ 0.014-0.14 g CH 4 /h per g oxygen carrier). Complete methane conversion is achieved in the fluid bed for several minutes. In the microreactor, the methane conversion reaches a maximum after an initial induction period of less than 10 s. Both CO 2 and H 2 O yields are highest during this induction period. As the oxygen is consumed, methane conversion drops and both CO and H 2 yields increase, whereas the CO 2 and H 2 O concentrations decrease. The kinetics parameter of the gas-solids reactions (reduction of NiO with CH 4 , H 2 , and CO) together with catalytic reactions (methane reforming, methanation, shift, and gasification) were estimated using experimental data obtained on the fixed bed microreactor. Then, the kinetic expressions were combined with a detailed hydrodynamic model to successfully simulate the comportment of the fluidized bed reactor.

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

“…A semibatch fluidized bed unit from the literature (Chandel et al, 2009) is chosen as the prototype reactor in this analysis. A fixed bed reactor is designed, based on the experimental setup of Iliuta et al (2010) to match the feed flow and solids inventory of the fluidized bed reactor. Both prototype reactors are assumed to process preheated, undiluted methane and to not be externally heated, which are realistic conditions for an industrial-scale application.…”

“…Early experimental studies on CLC were conducted in thermogravimetric analyzers (TGA) and fixed bed reactors. Both are commonly used for kinetic studies because of their simplicity, favoring reaction rates to be extracted easily from experimental data (Abad et al, 2007;Iliuta et al, 2010;Jin and Ishida, 2002). These systems however, implement semi-batch processes and as a result flow rates must be switched periodically.…”

Reduction and oxidation kinetics of nickel-based oxygen-carriers for chemical-looping combustion and chemical-looping reforming

“…Temperature programmed reduction or oxidation (TPR, TPO) technique has also been used but at lower temperatures [28,29,31]. Other facilities such as fluidized-bed [40,44] or fixed-bed reactors [33] have been used to determine reaction kinetics too. The kinetic parameters have been obtained using the shrinking core, the changing grain size and the nucleation models.…”

“…The kinetic parameters have been obtained using the shrinking core, the changing grain size and the nucleation models. Nevertheless, most of these studies carried out only a partial analysis without considering either the effect of the gas concentration or temperature [25][26][27][28][29][30][31][32][33][34]. In this case, limited information can be extracted from the reactivity data for design purposes, although they can be used to compare different oxygen carriers.…”

“…Several works where the kinetics of reaction for the reduction with CH 4 , CO and H 2 and the oxidation with oxygen have been determined for Cu-, Ni-, Fe 2 O 3 -and Mn 3 O 4 -based oxygen carriers [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] can be found in the literature. Most of these experimental studies have been done in a thermogravimetric analyzer.…”