Chemical Looping Combustion and Gasification of Fuels. A Review of Studies and New Process Solutions

The current status and research and development on CO2 in chemical looping combustion and gasification of fuels is analyzed. The major results presented in foreign publications are analyzed. At present, this technology is being studied in laboratory and pilot units with a maximum output of 1 MW. It has been demonstrated that the high-temperature chemical looping combustion and gasification technology with metal oxides, which are used as oxygen carriers, can be effective with respect to CAPEX and OPEX. In this type of combustion system, a metal oxide, rather than air, is used to bring oxygen to the fuel. The metal oxide, upon interaction with fuel in a fuel reactor, is reduced to a metal (or a lower oxide) with the formation of CO2 and water vapor. After that, the metal is oxidized in a special reactor, and the produced oxide is returned to the cycle. The gases coming from the fuel reactor after condensation of water vapor consist of more or less pure CO2, which can be used or recycled. Data on the application of various metal oxides are reviewed and analyzed with special attention given to the investigations into the use of natural ores as oxygen carriers. It has been demonstrated that ilmenite is most suitable for this application in terms of its properties (oxygen capacity, abrasion resistance) and cost. The design and operation features of various experimental setups are examined. The main approaches to the design calculation of chemical looping combustion plants are presented. It is shown that, in addition to the properties of oxides themselves, the efficient conversion of fuels requires a sufficient residence time of particles in the reactors and their specific gravity, which are largely determined by the hydrodynamics of interconnected reactors with a fluidized bed and a circulating fluidized bed. In the process, a high circulation rate of particles between the reactors, effective capture of particles, and their stable movement in downcomers and pneumatic loop seals should be maintained. Results are presented of the investigation into the hydrodynamics of interconnected reactors and binary mixtures of particles of different density.

Automated summary

This article analyzes the current status and research and development of CO2 in chemical looping combustion and gasification of fuels. The effectiveness of high-temperature chemical looping combustion and gasification technology using metal oxides as oxygen carriers is demonstrated. Data on the application of various metal oxides, with special attention to the use of natural ores as oxygen carriers, are reviewed and analyzed. The design and operation features of chemical looping combustion plants are examined, along with the fluid dynamics of interconnected reactors.