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.

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A double-slit model de®eloped can predict the frictional two-phase pressure drop, external liquid holdup, pellet-scale external wetting efficiency, and gas ᎐ liquid interfacial area in cocurrent downflow trickle-bed reactors operated under partially wetted condi-( tions in the trickle flow regime. The model, an extension of the Holub et al. 1992, ) 1993 mechanistic pore-scale phenomenological approach, was designed to mimic the actual bed ®oid by two inclined and interconnected slits: wet and dry slit. The external wetting efficiency is linked to both the pressure drop and external liquid holdup. The model also predicts gas ᎐ liquid interfacial areas in partially wetted conditions. An exten-si®e trickle-flow regime database including o®er 1,200 measurements of two-phase pressure drop, liquid holdup, gas ᎐ liquid interfacial area and wetting efficiency, published in 1974 ᎐ 1998 on the partial-wetted conditions, was used to ®alidate the modeling approach. Two new impro®ed slip-factor functions were also de®eloped using dimensional analysis and artificial neural networks. High-pressure and -temperature wetting efficiency, liquid holdup, pressure drop, and gas ᎐ liquid interfacial area data from the literature on the trickle-flow regime using con®entional monosized beds and catalyst bed-dilution conditions were successfully forecasted by the model.

The original and extended Holub phenomenological models for pressure drop and liquid holdup in trickle flow regime systematically under-predicted frictional pressure drops at elevated pressure and at high gas throughputs. On the basis of an extensive historic trickle flow regime database and Ergun bed constants (over 4000 measurements from 34 references between 1959 and 1998), state-of-the-art correlations for shear and velocity slip factors and Ergun single-phase flow bed constants (Blake−Kozeny−Carman and Burke−Plummer bed parameters) were developed. The correlations involved combination of feed-forward neural networks and dimensional analysis. The shear and velocity slip factors were expressed as a function of the six most expressive dimensionless groups (Re L, Re G, Fr L, We L, X L, St L), whereas Blake−Kozeny−Carman and Burke−Plummer bed parameters were correlated to particle equivalent diameter, sphericity factor, bed porosity, and column diameter. These correlations fed into Holub's phenomenological model improved noticeably the prediction of frictional pressure drop and liquid holdup in trickle flow reactors.

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