Experimental investigation of the flowability of oxygen carriers for Chemical-Looping Combustion

Abstract

questration in an innovative way. Air and fuel are separately handled in two fluidized bed reactors. Interconnection and reaction are achieved by circulating an oxygen carrier between both reactors. The oxygen carrier is a crucial component, as it is responsible for the performance of the overall process. As the carrier is consistently oxidized in the air reactor and reduced in the fuel rector, a high reaction rate and a high oxygen ratio are required. Furthermore the melting point has to be sufficiently high and solid carbon formation should not be catalysed. Besides these chemical properties, the mechanical nature of the material must be taken into account. Attrition is the process when the material undergoes fragmentation in smaller particles and is consequently elutriated from the system. This has to be avoided since it can decrease the lifetime of the carrier significantly. Another important aspect is the flowability of the carrier which is investigated in this work. The bulk of oxgen carrier would ideally behave as a fluid, flowing freely through the CLC unit. However, the actual CLC environment is not ideal. The flow behavior is altered by phenomenons like clogging or slugging. Because flowability describes the global behaviour of a granular system, which is influenced by a variety of parameters, material investigations as well as simple experiments were conducted. Investigated material properties are related to size, shape, density and surface characteristics. The experimental part consisted of measurements of a flow through a funnel, the Angle of Repose, the Hausner Ratio and the minimum fluidization velocity.