(559z) Hydrogen Production from Carbonaceous Feedstocks Using a Novel Solar Rotary Kiln Reactor
AIChE Annual Meeting
2019
2019 AIChE Annual Meeting
Topical Conference: Advances in Fossil Energy R&D
Poster Session: Advances in Fossil Energy R&D
Wednesday, November 13, 2019 - 3:30pm to 5:00pm
HYDROGEN PRODUCTION FROM
CARBONACEOUS FEEDSTOCKS USING A NOVEL SOLAR ROTARY KILN REACTOR
Summary
Synthesis gas production using
solar energy as a means to valorize carbonaceous feedstocks is an interesting
source of hydrogen and an effective alternative to hybridize existing thermal
power plants operating with fossil fuels. Some of the benefits of providing
solar heat to run endothermic processes such as pyrolysis and gasification are:
(i) no combustion products in the resulting gas; (ii) storage of solar energy
as chemical energy; and (iii) energy upgrading of the feedstock, among others. The present work presents the
design of a novel solar rotary kiln tilted and bottom indirectly irradiated for
the thermochemical conversion of carbonaceous feedstocks, as well as the
hydrogen yield obtained from the gasification of bituminous coal. A peak
hydrogen concentration of 26% was found in the product gases and a maximum
temperature of 1,200 K was achieved in the reaction zone.
1.
Introduction
Solar synthesis gas (syngas) production from carbonaceous
feedstock is a desirable technology to develop in Chile, since it would
represent an alternative on foreign imports of fossil fuels and would provide a
path to valorize, initially, national sub-bituminous coal reserves, and other
carbonaceous feedstocks, such as agroindustrial and municipal solid wastes.
Previous studies by Piatkowski et al have demonstrated the
feasibility of converting several feedstocks into syngas using solar energy,
achieving energy upgrades by factors up to 1.30. However, the high temperatures
required for gasifying solid fuels, as well as the poor thermal conductivity of
packed beds Wieckert et al, make the development of a continuous reactor an
engineering challenge.
This study was focused on the design, development and operation
of a novel solar rotary reactor for thermochemical conversion of coal. The
conversion processes observed consisted of pyrolysis, allothermal steam
gasification and autothermal steam gasification.
2.
Methods and experimental apparatus
Experiments on solar thermochemical conversion were conducted
in a batch rotary kiln solar reactor. Rotary kilns for solar applications have
been widely reviewed by Alonso et al, but no mention of the design proposed in
this research have been made previously. The concentration optics used for the
experiments consisted of a 10 heliostats array (1 m2 of reflective
surface each one)
focused to a 1.5 m2 Cassegrain concentrator, with its hyperbolic focal
point located behind its parabolic vertex. The reactor featured a cavity
receiver, with its entry located on the hyperbolic focal point of the
concentrator, coupled to a CPC-3D, responsible of redirecting the radiation
spillage into the cavity receiver. Inside the cavity an emitter plate of
graphite coated with SiC was used to reradiate the solar flux to the reaction
chamber. Steam was supplied to the reaction chamber using a custom-built
electric boiler. Coal particles showed a uniform size distribution with an
average particle size of 5 mm. Alongside with the fuel particles, inert alumina
hollow spheres of similar size were mixed in order to enhance the effective
thermal conductivity of the bed. The product gas was cooled and filtered
through a stage filled with water and collected vaccum sealed vessel in order
to control the total amount of product gas obtained from each gasified sample.
The
reactor was implemented at the Renewable Energy Laboratory of the Department of
Mechanical Engineering from the UTFSM, and all experiments featured irradiances
greater than 1,000 W m-2. Synthesis gas was determined by discrete
sampling of the product gas and gas chromatograph analysis. Temperature
measurements were achieved using type-S thermocouples uniformely distributed
along the reactor walls.
3.
Results
Solar thermochemical conversion of bituminous coal was
achieved under the presence of steam at a fixed tilt angle of 45°. Peak
hydrogen concentration found in the product gases was of 27%. Peak temperature
recorded inside the reaction chamber was 1,200 K.
4.
Discussion
Solar assisted hydrogen production, was successfully achieved
in a novel bottom indirectly irradiated solar rotary kiln reactor operating
with bituminous coal and steam. The emitter plate, as recommended by Piatkowski
et al, effectively transferred the solar heat to the reaction chamber without
signs of damage. Finally, a design for a continuous reactor should consider an
ash collection system.
5.
References
Alonso, E., Gallo, A., Roldán, M. I., Pérez-Rábago, C. A.
& Fuentealba, E. Use of rotary kilns for solar thermal applications: Review
of developed studies and analysis of their potential. Sol. Energy 144,
90–104 (2017).
Piatkowski, N., Wieckert, C., Weimer, A. W., Steinfeld, A.
Solar-driven gasification of carbonaceous feedstock—a review. Energy
Environ. Sci. 4, 73–82 (2011).
Wieckert, C., Obrist, A., Zedtwitz,
P. Von, Maag, G. & Steinfeld, A. Syngas production by thermochemical
gasification of carbonaceous waste materials in a 150 kWth Packed-Bed Solar
Reactor. Energy and Fuels 27, 4770–4776 (2013).