(335a) Chemical Looping Technology for Fossil Energy Conversion - Solids Flow Issues

Chemical Looping Technology for Fossil Energy Conversion - Solids Flow
Issues*

by

L.- S. Fan

Distinguished University Professor

C John Easton Professor in Engineering

Professor of Chemical and Biomolecular Engineering

 The
Ohio State University

*to be presented at the Fluidization Session of the 2011 AIChE Annual Meeting in honor of Ted Knowlton

Abstract

The concept of
chemical looping reactions has been widely applied in chemical industries, e.g.,
the production of hydrogen peroxide (H₂O₂) from hydrogen
and oxygen using 9,10-anthraquinone as the looping
intermediate. Fundamental research on chemical looping reactions has also been
applied to energy systems, e.g., the splitting of water (H₂O) to
produce oxygen and hydrogen using ZnO as the looping
intermediate. Fossil fuel chemical looping applications had been used
commercially with the steam-iron process for coal from the 1900s to the1940s and
had been demonstrated at a pilot scale with the carbon dioxide acceptor process
in the 1960s and 1970s. There are presently no chemical looping processes using
fossil fuels in commercial operation. A key factor that hampered the continued
use of these earlier processes for fossil energy operation was the inadequacy of
the reactivity and recyclability of the looping particles. This factor led to
higher product costs for using the chemical looping processes, compared to the
other processes that were petroleum or natural gas based.  With CO₂ emission control now being
considered as a requirement, interest in chemical looping technology has
resurfaced. In particular, chemical looping processes are appealing due to
their unique ability to generate a sequestration-ready CO₂ stream while
yielding high energy conversion efficiency. Renewed fundamental and applied
research since the early 1980s has emphasized improvement over the earlier
shortcomings. New techniques have been developed for direct processing of coal
or other solid carbonaceous feedstock in chemical looping reactors. Significant
progress is underway in particle design, reactor development, and looping
system integration, as demonstrated by the operation of several pilot or
sub-pilot scale units worldwide, making it possible that chemical looping
technology may be commercially viable in the future for processing carbonaceous
fuels.

This
presentation will describe the fundamental and applied aspects of modern
chemical looping technology that utilizes fossil and biomass as feedstock. The
presentation will discuss solids flow issues associated with this technology.
Specifically, it will highlight solids-gas contact modes with respect to the
optimum feedstock conversion and relationship among the metal oxide conversion,
solids flux and reactor size. Opportunities and challenges for chemical looping
process scale-up and commercialization will also be illustrated from the solids
flow standpoint.