Numerical Investigation of Sorption Enhanced Steam Methane Reforming Process Using Computational Fluid Dynamics Eulerian-Eulerian Code A. Di Carlo,* E. Bocci, F. Zuccari, and A. Dell’Era CIRPS-InteruniVersity Research Center for Sustainable DeVelopment, UniVersity of Rome “La Sapienza”, Rome, Italy This paper highlights the use of a fluidized bed reactor of 10 cm i.d. for producing hydrogen by sorption- enhanced steam methane reforming (SE-SMR). The model used for the hydrodynamic behavior of the bed is Eulerian-Eulerian. The kinetics of the steam methane reforming, water-gas shift, and carbonation reactions are based on literature values. Intra- and extraparticle mass transfer effects are considered together with the kinetics in the chemical models. The bed is composed of an Ni catalyst and calcined dolomite. A static bed height of 20 cm is investigated. A volume ratio of dolomite/catalyst is varied from 0-5 during the simulation. Dry hydrogen mole fraction of >0.93 is predicted for temperatures of 900 K and a superficial gas velocity of 0.3 m/s with a dolomite/catalyst ratio >2. Furthermore, the bubble formation in the fluidized bed influence product yields and product oscillations are observed. Another important aspect is that when the dolomite/ catalyst ratio is higher than 2 the necessary heat for the reforming endothermic reaction can be almost entirely supplied by the exothermic reaction of carbonation. Introduction Hydrogen is considered to be an important potential energy carrier; however, its advantages are unlikely to be realized unless efficient means to produce it with reduced generation of CO 2 can be found. Sorption-enhanced steam methane reforming (SE-SMR) is a potential route to energy efficient hydrogen production with CO 2 capture. The reactions with CaO as sorbent are when a kinetic approach is used the following reaction must also be considered: CO 2 is converted into a solid carbonate as soon as it is formed, shifting the reversible reforming and water-gas shift reactions beyond their conventional thermodynamic limits. Regeneration of the sorbent (the reverse reaction 3) releases relatively pure CO 2 , suitable for geological and deep-ocean storage or industrial usage. The CaO-CO 2 reaction has been found to consist of two stages, a fast stage followed by an extremely slow stage. 1 As the reaction produces an expanded solid product, the slow stage is believed to be controlled by product-layer diffusion. The sudden change from a fast to a slow stage of reaction is of interest with respect to CaO-based sorbents for CO 2 removal. Alvarez and Abanades 1 attributed the sharp transition to a critical thickness of the product layer. The findings of Abanades and Alvarez 2 suggest that the pore size distribution plays a crucial role for the CaO-CO 2 reaction. When the pore size distribution changes during calcination/carbonation cycles, the reactivity of the sorbent is altered accordingly. The proportion of the maximum conversion attributable to the reaction-controlled phase diminishes with the number of capture-and-release cycles due to a change in the particle morphology resulting from sintering. Thus, the maximum conversion achieved during carbonation of a fixed duration decreases with cycle number as it is limited by the rate of conversion during the (slow) diffusion- controlled phase. Bhatia and Perlmutter 3 first suggested that the diffusion-controlled phase may involve a solid-state mass transfer mechanism. Strategies for enhancing multicycle per- formance include steam hydration and thermal treatments (e.g., the works of Manovic and Anthony 4,5 and Lysikov et al. 6 ). In the work of Kuramoto et al., 7 an intermediate hydration treatment was found to enhance the reactivity and durability of the sorbents for multicycle CO 2 sorption. Because of the presence of eutectics in the CaO-Ca(OH) 2 -CaCO 3 ternary system, the formation of sorbent melts was observed in repetitive calcination-hydration-carbonation reactions at elevated pres- sures at 923 and 973 K. Even under eutectic conditions, the sorbents retained their high reactivity for CO 2 sorption. Tailored CaO-based sorbents, whereby the active material is supported on high surface area solids, such as alumina (Al 2 O 3 ) or mayenite (Ca 12 Al 14 O 33 ) have also been proposed (e.g., the works of Li et al. 8 and Feng et al. 9 ). In order to be competitive with the alternative strategy of simply using large quantities of limestone, tailored sorbent materials must achieve a significantly enhanced average conversion through a much larger number of cycles, in order to offset the economic penalties associated with their manufacture. For example, Li et al. 10 estimated that CaO/Ca 12 Al 14 O 33 (75/25 wt %) was approximately on par with CaO in terms of the cost of electricity and CO 2 mitigation for coal combustion with CO 2 removal from the flue gas. Calcium-based natural sorbents have the advantage of being low cost and readily available, but as mentioned previously, they have been proven to be unable to maintain their capture capacity over multiple reforming/regeneration cycles. 11 Re- cently, it has been reported that lithium-containing materials (mainly Li 2 ZrO 3 and Li 4 SiO 4 ) are promising candidates with high CO 2 capture capacity and high stability. Numerical studies have already been carried out with these new sorbents by Rusten et al., 12,13 Ochoa-Fernandez et al. 14 and Lindborg et al. 15 However, kinetic limitations are still the main drawback as * To whom correspondence should be addressed. E-mail: andrea.dicarlo@uniroma1.it. CH 4 + H 2 O S 3H 2 + CO - 206.2 kJ/kmol (1) CO + H 2 O S H 2 + CO 2 + 41.2 kJ/kmol (2) CaO + CO 2 S CaCO 3 + 178 kJ/kmol (3) CH 4 + 2H 2 O S 4H 2 + CO 2 - 165.0 kJ/kmol (4) Ind. Eng. Chem. Res. 2010, 49, 1561–1576 1561 10.1021/ie900748t  2010 American Chemical Society Published on Web 01/19/2010