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Research Papers: Fuel Combustion

A New Subgrid Model for the Heat and Mass Transfer Between a Hot Gas and Char Particles in Dense-Bed Reactors

[+] Author and Article Information
S. Schulze

Institute of Energy Process Engineering and
Chemical Engineering,
Technische Universität Bergakademie Freiberg,
Fuchmühlenweg 9,
Freiberg 09596, Germany

P. Nikrityuk

Associate Professor
Mem. ASME
Donadeo Innovation Centre for Engineering,
Department of Chemical and
Materials Engineering,
University of Alberta,
9211-116 Street,
Edmonton, AB T6G 1H9, Canada
e-mail: nikrityu@ualberta.ca

1Corresponding author.

Contributed by the Advanced Energy Systems Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received July 30, 2015; final manuscript received February 8, 2016; published online March 1, 2016. Assoc. Editor: Terry Wall.

J. Energy Resour. Technol 138(4), 042206 (Mar 01, 2016) (7 pages) Paper No: JERT-15-1291; doi: 10.1115/1.4032732 History: Received July 30, 2015; Revised February 08, 2016

This work is devoted to the development and verification of a new intrinsic-based subgrid model for moving char particles gasifying in a hot flue gas or syngas environments consisting of CO2/H2O/CO species. The distinguishing feature of our model relative to the submodels published in the literature is that it takes into account the thermal and chemical nonequilibrium between the particle's surface and its center. Thus, our model is able to predict temperature and species gradients inside the particles. The main focus of the new submodel is to demonstrate the crucial role of intrinsic-based heterogeneous reactions in the adequate prediction of carbon conversion rates for char particles gasification in fixed-bed and fluidized-bed gasifiers. The new model is verified against steady-state, particle-resolved computational fluid dynamics (CFD)-based, three-dimensional simulations carried out for different volume fractions of solid phase in a control volume (CV). Acceptable agreement has been demonstrated. Finally, to demonstrate our new model's predictions, we carried out several unsteady simulations for different ambient temperatures and Reynolds numbers. The importance of simultaneous change of char porosity and particles size during gasification has been demonstrated for different regimes indicated by the Damköhler numbers.

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Figures

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Fig. 1

Principal scheme of a CV and char particles inside

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Fig. 2

Contour plots of temperature and species mass fractions predicted for T = 1200 K, Rep = 30, εb = 0.46, YCO2,∞=0.3, and YH2O,∞=0.7. Here, the gas flow is directed along the z-axis from southwest to northeast.

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Fig. 3

Contour plots of temperature and species mass fractions predicted for T = 1200 K, Rep = 30, εb = 0.738, YCO2,∞=0.3, and YH2O,∞=0.7. Here, the gas flow is directed along the z-axis from southwest to northeast.

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Fig. 4

Three-dimensional CFD computational domain and division into segments each consisting of three particles with a diameter of 2 cm used for comparison with submodel predictions. The gas flow is directed from the left to the right side.

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Fig. 5

Comparison of the temperature (a) and carbon mass flux (b) on the carbon particle surface predicted using 3D CFD and submodel for T = 1200 K and εb = 0.46, Rep = 30

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Fig. 6

Comparison of the temperature (a) and carbon mass flux (b) on the carbon particle surface predicted using 3D CFD and submodel for T = 1200 K and εb = 0.738, Rep = 30

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Fig. 7

Submodel calculations for an intrinsic reactions case: the time history of normalized particle density and radius (a), Damköhler number (b), temperatures Tp and Ts (c), and the carbon mass flow (d) of char particle. The initial particle temperature is Tp,0 = 800 K, gas-phase temperature T = 1200 K. The Reynolds number Rep = 30 is fixed for t  > 0 s.

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