(664f) Conceptual Analysis of Process Alternatives for Solar Thermochemical Methanol Production: The Role of Chemical Storage

Bruno A. Calfa[1]
and Christos T. Maravelias ^{NOTEREF OLE_LINK1 \h  \* MERGEFORMAT 1 08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000A0000004F004C0045005F004C0049004E004B0031000000}

In
this talk, we study the production of fuels and chemicals from a renewable
source, namely solar energy. In a solar refinery, solar energy is utilized to
convert raw materials, such as CO₂ emitted from fossil fuel power
plants (and sometimes with H₂O), into value-added products; e.g.,
methanol and Fischer-Tropsch (F-T) fuels (Herron et
al., 2015). While different solar-based technologies have been investigated to
carry out the conversion, in this paper, we consider the solar thermochemical
splitting of CO₂ and H₂O (see Meier and Steinfeld (2013) and references therein), which has some
similarities with Concentrated Solar Power (CSP) technology in the electric
power industry.

The
viability, based on systems-level analyses, of a solar-driven (thermochemical
cycle technology) process to produce methanol and/or F-T fuels from syngas
produced from CO₂ and H₂O splitting has recently been
evaluated in the literature (Kim et al., 2011; Kim et al., 2012; Kim et al.,
2013; Rytter et al., 2016; Falter, Batteiger, and Sizmann, 2016). However,
all aforementioned works considered a continuously operated process. However,
one fundamental aspect of the production of solar fuels is the inherent intermittency of solar energy.
Therefore, since the splitting reactions cannot take place when there is not
sufficient solar irradiance (i.e., cloudy days or at night), there is a need to
consider chemical storage.

In
this work, we provide a systems-level analysis of three process configurations,
a base case and two alternatives, which employ solar-thermal technology for the
conversion of CO₂ and H₂O to syngas, which is further
upgraded to methanol. We propose and assess the use of chemical storage to cope
with the intermittency of solar-based chemical technologies. The base case
requires intermediate gas storage, since all streams are treated as continuous
from a high-level perspective (typically assumed in the literature).

First
we determine the number of compression stages that minimizes the total
annualized cost of compression and storage of CO₂/CO and H₂
streams. Material and energy balances followed by an economic analysis indicate
that gas compression and storage significantly contribute to the production
cost in the base case, which makes it less economically favorable than its
alternatives. We perform sensitivity analysis for key process parameters (e.g.,
chemical conversion of the solar reactors, cost of the solar field and solar
reactors, and solar refinery capacity) to investigate their effect on the
production cost of methanol.

The
two alternative process configurations do not require gas storage, since the
syngas production step is operated entirely intermittently. One process
alternative uses a reverse water-gas-shift reactor to further convert CO₂
to CO and correct the stoichiometric number (H₂:CO ratio) required
for the methanol synthesis step, whereas the other process alternative has a
membrane-based CO₂/CO separation that is operated intermittently. Our
analyses show that the process alternatives have overall lower total capital
investment and operating costs than the base case, whose compression, storage,
and amine-based CO₂/CO separation costs represent major components
of the production cost.

References

Falter, C.; Batteiger,
V.; and Sizmann, A. 2016. Climate Impact and Economic
Feasibility of Solar Thermochemical Jet Fuel Production. Environmental Science
& Technology. 50(1):470-477.

Herron, J. A.; Kim, J.; Upadhye, A. A.; Huber, G. W.; and Maravelias,
C. T. 2015. A General Framework for the Assessment of Solar Fuel Technologies.
Energy & Environmental Science. 8(1):126-157.

Kim, J.; Henao,
C. A.; Johnson, T. A.; Dedrick, D. E.; Miller, J. E.;
Stechel, E. B.; and Maravelias,
C. T. 2011. Methanol Production from CO2 Using Solar-Thermal Energy: Process
Development and Techno-Economic Analysis. Energy & Environmental Science.
4(9):3122-3132.

Kim, J.; Johnson, T. A.; Miller, J. E.; Stechel, E. B.; and Maravelias,
C. T. 2012. Fuel Production from CO₂ Using Solar-Thermal Energy:
System Level Analysis. Energy & Environmental Science. 5(9):8417-8429.

Kim, J.; Miller, J. E.; Maravelias, C. T.; and Stechel,
E. B. 2013. Comparative Analysis of Environmental Impact of S2P (Sunshine to
Petrol) System for Transportation Fuel Production. Applied Energy. 111:1089-1098.

Meier, A., and Steinfeld,
A. 2013. Solar Energy. New York, NY: Springer New York. chapter Solar Energy in
Thermochemical Processing, 521-552.

Rytter, E.; Sou__kov‡. F; Lundgren, M. K.; Ge, W.; Nannestad,
. D.; Venvik, H. J.; and Hillestad,
M. 2016. Process Concepts to Produce Syngas for Fischer-Tropsch
Fuels by Solar Thermochemical Splitting of Water And/Or CO₂. Fuel Processing Technology.
145:1-8.