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Research Papers

A Thermodynamic and Cost Analysis of Solar Syngas From the Zn/ZnO Cycle

[+] Author and Article Information
Julia Haltiwanger Nicodemus

Engineering Studies,
Lafayette College,
Easton, PA 18042
e-mail: nicodemj@lafayette.edu

Morgan McGuinness

Math and Physics,
Lafayette College,
Easton, PA 18042

Rijan Maharjan

Mechanical Engineering,
Lafayette College,
Easton, PA 18042

From NREL solar resource data.

Based on CCPC+TR=C/9.43×10-5, derived from Ref. [2].

Peters et al. [16], Figs. 13 and 14, p. 627.

Based on EIA data and the lower heating value of natural gas.

1Corresponding author.

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING: Including Wind Energy and Building Energy Conservation. Manuscript received July 25, 2014; final manuscript received August 1, 2014; published online August 25, 2014. Editor: Gilles Flamant.

J. Sol. Energy Eng 137(1), 011012 (Aug 25, 2014) (10 pages) Paper No: SOL-14-1214; doi: 10.1115/1.4028189 History: Received July 25, 2014; Revised August 01, 2014

We present a thermodynamic and cost analysis of synthesis gas (syngas) production by the Zn/ZnO solar thermochemical fuel production cycle. A mass, energy, and entropy balance over each step of the Zn/ZnO syngas production cycle is presented. The production of CO and H2 is considered simultaneously across the range of possible stoichiometric combinations, and the effects of irreversibilities due to both recombination in the quenching process following dissociation of ZnO and incomplete conversion in the fuel production step are explored. In the cost analysis, continuous functions for each cost component are presented, allowing estimated costs of syngas fuel produced at plants between 50 and 500 MWth. For a solar concentration ratio of 10,000, a dissociation temperature of 2300 K, and a CO fraction in the syngas of 1/3, the maximum cycle efficiency is 39% for an ideal case in which there is no recombination in the quencher, complete conversion in the oxidizer, and maximum heat recovery. In a 100 MWth plant, the cost to produce syngas would be $0.025/MJ for this ideal case. The effect of heat recuperation, recombination in the quencher, and incomplete conversion on efficiency and cost are explored. The effects of plant size and feedstock costs on the cost of solar syngas are also explored. The results underscore the importance improving quencher and oxidizer processes to reduce costs. However, even assuming the ideal case, the predicted cost of solar syngas is 5.5 times more expensive than natural gas on an energy basis. The process will therefore require incentive policies that support early implementation in order to become economically competitive.

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References

Figures

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Fig. 1

Model flow diagram of the solar thermochemical cycle for syngas production via ZnO dissociation

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Fig. 2

Oxidation temperature dependence of cycle efficiency for multiple CO:H2 ratios for the “ideal” case and the “realistic” case, both with and without heat recuperation

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Fig. 3

Cost of syngas as a function of the plant size for the ideal case (α = 1, β = 1) and the realistic case (α = 0.8, β = 0.61), both with heat recuperation (dashed lines) and without heat recuperation (solid lines)

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Fig. 4

Fuel cost versus solar resource (beam radiation) 50 MW, 100 MW, 250 MW, and 500 MW plants

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Fig. 5

Cost of syngas over a range of possible feedstock CO2 costs for a 100 MWth (solid lines) and a 500 MWth (dashed lines) plant for a feedstock water cost of $0.01/l (thin lines) and $0.1/l (thick lines)

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Fig. 6

Sensitivity of the cost of syngas to a ±1% change in component and financing assumptions

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