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Research Papers

Solar Gasification of Biomass: Kinetics of Pyrolysis and Steam Gasification in Molten Salt

[+] Author and Article Information
Brandon J. Hathaway, David B. Kittelson

Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN 55455jhd@me.umn.edu

Jane H. Davidson1

Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN 55455jhd@me.umn.edu

1

Corresponding author.

J. Sol. Energy Eng 133(2), 021011 (Apr 08, 2011) (9 pages) doi:10.1115/1.4003680 History: Received September 07, 2010; Revised January 24, 2011; Published April 08, 2011; Online April 08, 2011

The use of concentrated solar energy as a heat source for pyrolysis and gasification of biomass is an efficient means for production of hydrogen rich synthesis gas. Utilizing molten alkali carbonate salts as a reaction and heat transfer media promises enhanced stability to solar transients and faster reaction rates. The present study establishes and compares the reaction kinetics of pyrolysis and gasification of cellulose from 1124 K to 1235 K in an electric furnace. Data are presented in an inert environment and in a bath of a ternary eutectic blend of lithium, potassium, and sodium carbonate salts. Arrhenius rate expressions are derived from the data supported by a numerical model of heat and mass transfer. The molten salt increases the rate of pyrolysis by 74% and increases gasification rates by more than an order of magnitude while promoting a product gas composition nearer to thermodynamic equilibrium predictions. These results justify using molten carbonate salts as a combined catalyst and heat transfer media for solar gasification.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Flow diagram of the system used to carry out the gasification and pyrolysis reactions

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Figure 2

Detail cross section diagram of the reactor assembly

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Figure 3

Computation domain representing the cross section through the midplane of the feed tablet. The half outlined with a dashed line was not modeled due to assumed symmetric behavior.

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Figure 4

Extent of carbon conversion for steam gasification reactions at various temperatures in (a) gaseous and (b) molten salt environments. The dashed lines represent the conversion predicted by the optimized shrinking grain reaction model.

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Figure 5

Arrhenius plot of steam gasification data with and without molten alkali carbonate salt

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Figure 6

Average measured product gas yield for cellulose tablets undergoing flash pyrolysis at 1200 K and above with and without molten salt present

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Figure 7

Data and simulations of pyrolysis of cellulose tablets at 1235 K with and without molten salt present

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Figure 8

Cumulative extent of conversion for 10 mm diameter cellulose tablets undergoing pyrolysis at 1235 K with and without molten salt present

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