posted on 2020-03-17, 20:29authored byYitao Zhang, Fanhe Kong, Andrew Tong, Liang-Shih Fan
Chemical looping is an advanced material
and energy conversion
technology that can achieve both high-level process intensification
and efficiency. To analyze chemical looping processes, it is essential
to include process conditions that are realistic and comparable to
those that are expected in industrial systems. Relevant variations
in these conditions as occurred in bench versus industrial-scale systems
include isothermal versus adiabatic operation of the reactors and
local versus global process heat integration. Naturally, the types
of reactors employed dictate how the reactor operation is to be conducted
from the heat integration viewpoint in the overall process arrangement.
As an example, in industrial applications, a fluidized bed reactor
is operated near uniform temperature conditions. A fixed bed or a
moving bed reactor, on the other hand, is typically operated adiabatically,
and thus under the autothermal operation, the nonisothermal condition
prevails, leading to different strategies for process simulations
and heat integration requirements. This study presents the chemical
looping process simulation based on a moving bed reactor used as a
reducer for two H2 generation process configurations under
autothermal operating conditions. The two process configurations are
represented by the two-reactor (reducer–combustor followed
by the water–gas shift reaction) and the three-reactor (reducer–oxidizer–combustor
with water splitting for H2 generation in the oxidizer)
chemical looping systems with each configuration producing H2 in a different operating scheme. The simulation results are compared
with the conventional steam methane reforming (SMR) system as a baseline
case to underscore the attractiveness of the chemical looping configurations.
Specifically, for each configuration, the parametric study under the
adiabatic conditions is used to optimize the operating conditions
that can satisfy the heat balance requirements and can achieve a maximum
H2 yield. The exergy analysis indicates that the two-reactor
chemical looping and three-reactor chemical looping systems can achieve,
respectively, a 4.0 and 11.4% increase in relative percentage in the
overall process exergy efficiency over the conventional steam methane
reforming system.