(617c) Chemical Looping Combustion from Biomass Derived Syngas Using a Fluidizable Ni-Co-La/?-Al2O3 Oxygen Carrier: CLC Performance and CPFD Modelling
AIChE Annual Meeting
2018 AIChE Annual Meeting
Particle Technology Forum
Fluidization in Chemical Looping Processes (Area 20B)
Thursday, November 1, 2018 - 8:42am to 9:03am
In spite of the valuable progress made with OCs by our research team [2,3], the 750ÂºC calcination temperature use was shown to lead to: a) strongly bounded Ni species on alumina and b) undesirable NiAl2O4 . These species inherently limit the OC oxygen capacity in the 550-650ºC operating range. To circumvent this, a new highly performing OC was prepared by reducing all the formed nickel species at 900ºC for 2 hours and this prior to 750ºC calcination. This methodology ensures the complete decomposition of strongly bounded Ni on alumina, as well as that of NiAl2O4. This yields a re-dispersing nickel phase which has little interaction with the g-alumina support. This new highly performing oxygen carrier (HPOC) can provide more than 90% of the nominal oxygen lattice at temperatures between 550-650ºC. The promising HPOC was characterized using BET, XRF, XRD, H2-TPR, NH3-TPD and pulse chemisorption.
CLC runs of syngas and the new OC were performed using the CREC Riser Simulator. This is a mini-fluidized bed reactor with high gas mixing that operates under batch conditions. This unit is designed for oxygen carrier evaluation at expected industrial process conditions. An automatic valve allows the transfer of products to an online gas chromatograph (GC) to detect all product chemical species (CO, CH4, CO2 and H2) accurately. The evaluation of this highly performing OC (HPOC) was developed at 550-650ÂºC, 5-40s and with a ratio of oxygen to be consumed over maximum available oxygen, Ï = 0.5 to 1. A syngas was used in the experimental runs using a 20v% CO, 10v% CH4, 20v% CO2 and 50v% H2 mixture. CLC runs of syngas showed that 60-92% CO2 yields can be obtained within these operating conditions. The CO2 yields and the CH4 conversion steadily increase with reaction time for Ï=1. It is also shown that CO and H2 conversions stabilize and decrease respectively for Ï =1. These trends were attributed to the influence of reforming reactions under OC starving oxygen conditions. An adjustment of the OC oxygen supply to Ï=0.5, leads to all CO, H2 and CH4 species being 78-88% converted.
For the point of view of implementation as an industrial process, a set of twin fluidized bed (oxidizer and reducer) is considered in the present study. Regarding the selected twin fluidized bed configuration, both fluidized beds are interconnected to facilitate oxygen carrier particle circulation. This oxygen carrier particles have a 75 Î¼m mean diameter and a 2500 kg/m3 particle density. Considering 150KW power generation capacity, and Ï =1, the diameter of oxidizer was designed as 780 mm diameter and with an overall length 4500 mm including transport disengaging height. Similarly, reducer was designed as 800 mm and 3750 overall length. Typical 30 seconds total retention time for reducer and 15 seconds for oxidizer were considered. Reduced particles are collected in a loop-seal pot and furthered transported to the top of oxidizer bed. In a similar manner oxidized particle are transported to reducer bed. Product gas (Flue gas) and exhausted air leave from the reducer and oxidizer top section via cyclone particle separators.
To analyze this twin fluidized bed configuration a multi-scale (Wen-Yu) drag model coupled with computational particle-fluid dynamics (CPFD) and CLC volume averaged kinetics are being considered. This Hybrid Barracuda CPFD model uses the Eulerian-Lagrangian approach called MP-PIC (multi-phase particle-in-cell). The softwareâs numerical methodology considers a direct element method wherein solids are modeled as discrete particles with both size and density distributions, and the fluid is modeled as a continuum. The formation of particle cluster is also considered based on cluster size distribution.
On the basis of the data obtained this study allows the following: (a) to establish the twin fluidized bed system performance for CLC; (b) to describe the required oxygen carrier particle circulation; (c) to evaluate the extent of CO2 gas leaking via the loop-seal.
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