Chemical looping technology - a manifestation of a novel fluidization and fluid-particle system for CO2 capture and clean energy conversions

Chemical looping is broadly defined to represent processes that use chemical intermediates to decompose a reaction into two or more sub-reaction steps. Metal oxides are the typical chemical intermediates used for the chemical looping reactions although other metal derivatives are also used. Based on its intended applications, chemical looping encompasses calcium looping for CO2 capture and redox looping for clean energy conversion applications. The redox looping has a longstanding history and has been demonstrated at multiple scales under various operating conditions since its conceptual inception about 120 years ago. Even with such extensive and prolonged efforts, redox looping is yet to be realized sustainably at a commercial level, while the calcium looping has been demonstrated for commercial applications. With growing concerns of climate change due to emissions of industrial greenhouse gases, efforts in developing redox looping processes as a promising fossil energy conversion technology with CO2 emission control have been invigorated since the beginning of the 21st century. Metal oxide reaction engineering and particle science and technology have been the two enabling technical thrust areas, pivotal to advance the chemical looping concept to industrial practice. This article highlights some salient features of the chemical looping processes including a description of their historical development and illustration of the material screening and synthesis of oxygen carrier particles along with the representative process operational behavior. Recognizing that the configuration of chemical looping systems in their key operational scheme is established on the framework of circulating fluidized bed (CFB) systems, this article emphasizes the relevant characteristics of fluidization and fluid-particle systems with which the chemical looping technology is conducted. Both the fundamental and applied aspects of chemical looping processes and their associated CFB operation are discussed.

Automated summary

Chemical looping is a process that uses chemical intermediates to decompose a reaction into multiple sub-reaction steps. Calcium looping and redox looping are two applications of chemical looping, with the former being commercially demonstrated and the latter yet to be realized sustainably. With increasing concerns about climate change, efforts to develop redox looping as a promising fossil energy conversion technology with CO2 emission control have been invigorated. Metal oxide reaction engineering and particle science and technology are crucial technical areas to advance the industrial practice of chemical looping.