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Research Papers: Fuel Combustion

# Chemical-Looping Combustion of Hard Coal: Autothermal Operation of a 1 MWth Pilot Plant

[+] Author and Article Information
Peter Ohlemüller

Institute for Energy Systems and Technology,
Otto-Berndt-Str. 2,

Jan-Peter Busch

Institute for Energy Systems and Technology,
Otto-Berndt-Str. 2,

Michael Reitz

Institute for Energy Systems and Technology,
Otto-Berndt-Str. 2,

Jochen Ströhle

Institute for Energy Systems and Technology,
Otto-Berndt-Str. 2,

Bernd Epple

Institute for Energy Systems and Technology,
Otto-Berndt-Str. 2,

Contributed by the Advanced Energy Systems Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received August 3, 2015; final manuscript received December 28, 2015; published online January 13, 2016. Assoc. Editor: Yiannis Levendis.

J. Energy Resour. Technol 138(4), 042203 (Jan 13, 2016) (7 pages) Paper No: JERT-15-1297; doi: 10.1115/1.4032357 History: Received August 03, 2015; Revised December 28, 2015

## Abstract

Chemical-looping combustion (CLC) is an emerging carbon capture technology that is characterized by a low energy penalty, low carbon dioxide capture costs, and low environmental impact. To prevent the contact between fuel and air, an oxygen carrier is used to transport the oxygen needed for fuel conversion. In comparison to a classic oxyfuel process, no air separation unit is required to provide the oxygen needed to burn the fuel. The solid fuel, such as coal, is gasified in the fuel reactor (FR), and the products from gasification are oxidized by the oxygen carrier. There are promising results from the electrically heated 100 kWth unit at Chalmers University of Technology (Sweden) or the 1 MWth pilot at Technische Universität Darmstadt (Germany) with partial chemical-looping conditions. The 1 MWth CLC pilot consists of two interconnected circulating fluidized bed reactors. It is possible to investigate this process without electrically heating due to refractory-lined reactors and coupling elements. This work presents the first results of autothermal operation of a metal oxide CLC unit worldwide using ilmenite as oxygen carrier and coarse hard coal as fuel. The FR was fluidized with steam. The results show that the oxygen demand of the FR required for a complete conversion of unconverted gases was in the range of 25%. At the same time, the carbon dioxide capture efficiency was low in the present configuration of the 1 MWth pilot. This means that unconverted char left the FR and burned in the air reactor (AR). The reason for this is that no carbon stripper unit was used during these investigations. A carbon stripper could significantly enhance the carbon dioxide capture efficiency.

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## Figures

Fig. 1

Simplified process scheme of CLC of solid fuels

Fig. 2

Simplified configuration of the 1 MWth CLC pilot plant at Technische Universität Darmstadt

Fig. 3

Particle size distribution of ilmenite

Fig. 4

Top: coal feed to FR and propane feed to AR (propane was used only during the first 20 minutes). Middle: pressure drops of FR and AR. Bottom: temperatures of FR and AR.

Fig. 5

Average pressure profile of AR (left, ♦, total height 8.66 m) and FR (right, ▲, total height 11.35 m)

Fig. 6

Top: dry concentrations of CO2 and O2 at the AR outlet. Middle: dry concentration of CO2 at the FR outlet. Bottom: dry concentrations of H2, CO and CH4 at the FR outlet.

Fig. 7

Oxygen demand and CO2 capture efficiency

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