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Research Papers

Integration of Solar Gasification With Conventional Fuel Production: The Roles of Storage and Hybridization

[+] Author and Article Information
Jane H. Davidson

e-mail: jhd@me.umn.edu
Department of Mechanical Engineering,
University of Minnesota,
111 Church Street S.E.,
Minneapolis, MN 55455

1Corresponding author.

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING. Manuscript received June 24, 2013; final manuscript received October 2, 2013; published online December 12, 2013. Assoc. Editor: Aldo Steinfeld.

J. Sol. Energy Eng 136(1), 010906 (Dec 12, 2013) (10 pages) Paper No: SOL-13-1177; doi: 10.1115/1.4025971 History: Received June 24, 2013; Revised October 02, 2013

The use of concentrated solar radiation as the source of process heat to drive biomass gasification offers potential increases in yield and efficiency over conventional approaches to gasification but requires that temporal variations in output be alleviated with thermal storage or hybridization. The impacts of thermal storage and degree of hybridization on the efficiency, specific yield, and variation in output of a solar gasification facility are explored through parametric simulations of a generalized 100 MWth solar receiver facility. Nominal syngas yield rates from 1.5 to 50 tonnes/h are considered along with molten carbonate salt storage volumes from 200 to 6500 m3. High solar fractions (95%) result in a maximum thermal efficiency of 79% and specific syngas yield of 139 GJ/ha while low solar fractions (10%) for highly hybridized facilities reduce the thermal efficiency to 72% and specific yield to 88 GJ/ha, akin to conventional gasification processes. Solar fractions greater than 95% result in large variation in synthesis gas yield rate, varying as much as 30:1 throughout the year. This variation can be reduced to below a 4:1 ratio, more acceptable for downstream processes, through either hybridization to achieve solar fractions less than 50% with little to no thermal storage, or alternately the use of 5600 m3 of molten carbonate salt to allow for solar fractions up to 87%.

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Figures

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Fig. 1

Schematic of the generalized geometry for a molten salt solar gasification reactor

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Fig. 2

Simplified diagram of a solar gasification facility. (1) Heliostat field, (2) beam-down tower, (3) receiver/reactor, (4) feedstock inlet to reactor and syngas outlet to downstream process.

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Fig. 3

System schematic for the modeled concentrating solar gasification facility. The boundaries of the analysis are represented by the dotted lines. The components and flows with dashed lines are used to assist the solar-driven gasification process when insufficient sunlight is available. Potential downstream processes are shown in the dash-dotted lines at the right.

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Fig. 7

Comparison of normalized syngas yield rate over the course of a typical summer week for a facility achieving a solar fraction of fsolar  = 50% with heat capacity values of Ceff = 6 GJ/K for the dashed line and Ceff = 21 GJ/K for the solid line. The incident solar power is included for reference.

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Fig. 6

Surface plot of annual average thermal efficiency as a function of the nominal syngas yield rate and the heat capacity of the reactor

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Fig. 5

Surface plot of specific yield of synthesis gas for facilities of various heat capacities and annual solar fractions

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Fig. 8

Comparison of normalized syngas yield rate over the course of a typical summer week for a facility with heat capacity Ceff = 11 GJ/K with nominal feed throughputs resulting in solar fractions of fsolar = 80% for the solid line and fsolar = 40% for the dashed line. The incident solar power is included for reference.

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Fig. 9

Contours of maximum synthesis gas overrate as a function of the facility heat capacity or carbonate salt volume and annual solar fraction. The shaded region indicates a maximum overrate unacceptable for continuously feeding a downstream power production process.

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Fig. 10

Contours of required CSGS tank volume in thousands of cubic meters at 30 bar and 300 K in order to allow for a steady rate of consumption in a downstream fuel production process as a function of the facility heat capacity or carbonate salt volume and annual solar fraction

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Fig. 4

Surface plot of the annual solar fraction as a function of the nominal syngas yield rate and heat capacity of the reactor

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