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@PHDTHESIS{Falter:695878,
author = {Falter, Christoph},
othercontributors = {Pitz-Paal, Robert and Sizmann, Andreas},
title = {{E}fficiency potential of solar thermochemical reactor
concepts with ecological and economic performance analysis
of solar fuel production},
school = {Rheinisch-Westfälische Technische Hochschule Aachen},
type = {Dissertation},
address = {Aachen},
reportid = {RWTH-2017-06526},
pages = {1 Online-Ressource (XVIII,234 Seiten) : Illustrationen,
Diagramme},
year = {2017},
note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
University; Dissertation, Rheinisch-Westfälische Technische
Hochschule Aachen, 2017},
abstract = {The alternative fuel production pathway by solar
thermochemical splitting of water and carbon dioxide into
hydrogen and carbon monoxide by redox reactions of a metal
oxide, and their subsequent conversion into liquid fuels by
Fischer-Tropsch synthesis, is investigated. These fuels
could provide a means to completely decarbonize the
transport sector and thus to significantly reduce its
climate impact. A generic model is developed for the
description of solar thermochemical reactors including heat
exchangers, where reduced elements of redox material move
from the reduction to the oxidation chamber through a number
of heat exchanger chambers, in which they transfer energy by
radiation to the cold elements moving in counter-flow. In a
first implementation of the model, infinitely fast thermal
diffusion within the material is assumed and the influence
on heat exchange of the wall separating the hot from the
cold elements is neglected. A heat exchanger efficiency
potential of over $80\%$ is determined, where efficiency is
increased towards higher reaction temperatures and reaches
its maximum value in the reduction pressure range of 10-100
Pa due to a trade-off between additional energy requirements
for vacuum pumping and enhanced fuel productivity. In a
second implementation of the model, the effect of the
separating wall is considered and heat diffusion in the
porous redox material is solved. Heat exchanger efficiency
is found to have a potential of about $70\%,$ where heat
diffusion in the redox material is identified to be a
limiting factor for heat exchange. The system can be
enhanced by increasing the porosity as well as optimizing
material thickness and total residence time of the elements
in the heat exchanger. Through an efficient design of the
heat exchanger, efficiencies close to the optimal case of
infinitely fast heat diffusion can be reached. The model is
adapted for the description of heat exchange between two
unmixed particle beds moving in opposite directions in a
cylindrical enclosure. Heat exchanger efficiency is found to
have a potential of close to $60\%$ and to be limited by
heat transfer within the particle beds which can be enhanced
e.g. by optimizing the bed diameter, heat exchanger length,
particle size, and the velocity of the beds. The analysis is
complemented by an assessment of ecological and economic
performance of a baseline case fuel production plant. The
baseline assumptions are that the plant has an output of
1000 barrels per day (bpd) of jet fuel and 865 bpd of
naphtha, uses water from seawater desalination and carbon
dioxide by capture from the atmosphere, has a thermochemical
efficiency of $20\%,$ and uses heat and electricity provided
by conversion of solar primary energy and combustion of the
gaseous Fischer-Tropsch products. The energy conversion
efficiency from incident sunlight to lower heating value of
the produced fuels is determined to be $5.0\%.$ A life cycle
analysis shows greenhouse gas (GHG) emissions of 0.49
kgCO2-eq. per liter of jet fuel, which is a reduction of
over $80\%$ compared to conventional jet fuel. The main
drivers of the GHG emissions are identified to be the
origins of carbon dioxide and electricity, the combustion of
gaseous Fischer-Tropsch products, and the construction of
the solar concentration infrastructure. The water
consumption is 7.4 liters per liter jet fuel for on-site
processes and 40.2 liters for off-site processes, which is
orders of magnitude lower than that of biofuels and about
equal to that of fossil fuels. The area-specific
productivity is 3.3 × 104 liters of jet fuel equivalents
per hectare and year, which is lower than the best
power-to-liquid pathways but about an order of magnitude
higher than that of biofuels. An economic model based on the
annuity method shows production costs of 2.23 € per liter
of jet fuel for the baseline case. The economic drivers are
the construction and operation of the solar concentration
facility, the provision of electricity by an on-site
concentrated solar power plant, carbon dioxide capture, and
the lifetime of the fuel production plant. Thermochemical
efficiency and solar irradiation have an important influence
both on the GHG emissions and the plant economics through
their determination of the required size of the solar
concentration facility. It is found that jet fuel production
with emissions significantly lower than conventional fuel
requires a renewable source both for carbon dioxide and for
electricity, such as carbon dioxide capture from the
atmosphere and electricity generation from sunlight.
Assuming favorable development of the involved process
steps, production costs of 1.28 € per liter jet fuel at
greenhouse gas emissions of 0.10 kgCO2-eq. per liter are
estimated. The realization of high thermochemical
efficiencies is crucial for the development of an economic
fuel production pathway due to its direct influence on the
required size of the solar concentration facility. The
developed models can be used for the continued comprehensive
analysis of the fuel production pathway including the large
parameter space in the design of solar thermochemical
reactors and thus provide a valuable tool for further
research and design.},
cin = {412910},
ddc = {620},
cid = {$I:(DE-82)412910_20140620$},
typ = {PUB:(DE-HGF)11},
doi = {10.18154/RWTH-2017-06526},
url = {https://publications.rwth-aachen.de/record/695878},
}
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