A low-cost oxygen carrier material realized through an Al-based skeleton encapsulating iron–titanium oxides with long-term chemical reactivity and mechanical stability for commercial chemical looping applications.
The methane-to-syngas
(MTS) chemical looping process is an advanced
methane reforming technology for the production of high purity syngas.
The developed MTS process utilizes metal oxide oxygen carriers in
a cocurrent moving bed reactor to partially oxidize the methane such
that the resulting syngas stream is undiluted by nitrogen in air or
H2 from overconversion and directly suitable for downstream
processing. The oxygen carriers are regenerated with air in a separate
fluidized bed reactor producing a spent air stream separate from the
product syngas, circumventing the need for cryogenic air separation
units. In this work, a 15 kWth subpilot unit is designed
and operated in a continuous manner to experimentally confirm the
viability of the MTS process. Reactor design considerations and methodology
are discussed in detail. An iron–titanium composite oxygen
carrier is used as the oxygen carrier for its ability to achieve high
methane conversion while regulating the product syngas to the partial
oxidation products, CO and H2. Syngas is produced with
an H2/CO ratio of ∼2, and a purity of ∼97%
is produced with methane conversion exceeding 99%. The coinjection
of methane with H2 and/or H2O is explored for
the purpose of H2 utilization and flexible H2/CO ratios, allowing the MTS process to produce syngas for a variety
of downstream processes without reactor modification. The results
indicate that syngas with H2/CO ratios ranging from 1.19
to 2.50 with high methane conversion and syngas purity can be produced
with coinjection. No evidence of carbon deposition on the oxygen carrier
is revealed, and the oxygen carrier retained structural integrity
after subjection to reaction and circulation in the subpilot unit.
Syngas production is highly critical
to the manufacturing of many
value-added products, and its economic prospects can be increased
through the enhancement of fuel conversion and the syngas yield. This
study explores the thermodynamic characteristics of syngas production
through chemical looping reforming (CLR) of natural gas using dicalcium
ferrite (Ca2Fe2O5) as the oxygen
carrier in a cocurrent moving-bed reactor. The effects of temperature,
pressure, and steam addition are studied for both isothermal and adiabatic
conditions. A natural gas conversion of 99.78% and a yield of 2.86
mol of syngas/mol of natural gas are obtained for CLR as compared
to 95.97% and 2.70, respectively, for autothermal reforming (ATR).
A fluidized bed and a countercurrent moving bed are employed for the
regeneration of reduced solids using air and a steam/CO2 mixture, respectively, thereby achieving operational flexibility.
The syngas yield increases by ∼41% using the steam/CO2 mixture, whereas a high-purity H2 is obtained from the
oxidation of reduced solids in pure steam. The process analyses indicate
an increase in the effective thermal efficiency from 86.4% to 92.2%
and the exergy efficiency from 79.5% to 85.3% on using the Ca2Fe2O5-based CLR over ATR, rendering
the syngas production using CLR economically attractive.
Production of various value-added chemicals through natural gas conversion with syngas as an intermediate is becoming increasingly popular because of the abundance of natural gas and maturation of syngas-producing technologies. Chemical looping reforming is one such technology that is envisioned as a substitute to the existing syngas production processes such as steam methane reforming, autothermal reforming, and partial oxidation of natural gas (POX) because of its superior thermodynamic capabilities and less parasitic energy requirements. The proposed work makes use of CuO-modified Ca 2 Fe 2 O 5 -based oxygen carriers for syngas production through chemical looping, where the system performance is subjected to thermodynamic scrutiny. The main objective of the proposed work is to assess the change in syngas production capability and other process parameters because of reduced endothermicity of the process through CuO incorporation. Thermodynamic simulations are carried out to assess the system performance at various operating temperatures, pressures, and lattice oxygen availability. Parameters such as the effective thermal efficiency, cold gas efficiency, and exergy efficiency are calculated to evaluate the performance of oxygen carriers with varying compositions of CuO. These parameters are measured for two process configurations: isothermal and thermoneutral. An overall process simulation is further carried out to gain a deeper perspective of the changes occurring in the chemical-looping system because of CuO modification of the oxygen carrier.
Chemical looping partial oxidation (CLPO) is a novel technology for converting methane into high quality syngas that can be further converted into liquid fuels. In the present work, Ni-doped Ca2Fe2O5...
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