Assessment of the Scale-Up and Operational Design of the Fuel Reactor in Chemical Looping Combustion
Conference contribution, 2011
Chemical looping combustion is expected to play a major role as Carbon Capture and Storage technology due to its intrinsic separation of the flue gas stream from the nitrogen contained in the fed air, thus avoiding the energy and capital cost penalty deriving from the presence of an air separation unit. Having been successfully tested in units ranging up to 120 kWth in the last decade, chemical looping combustion starts to face the challenge of scale-up to commercial scale.
While results obtained at lab-scale units are rellevant to the initial development of the technology, scale-up implies the appearance of new key phenomena such as limited lateral gas and solids mixing, modified solids flow patterns and increased residence times. Having this, experience from large-scale fluidized bed units is highly valuable for further development of the chemical looping combustion technology through scale-up and is an essential resource to get a more complete understanding of the process.
The current work presents the first version of a 3-dimensional model for the fuel reactor of a large-scale chemical looping combustion unit. The model is based on validated models available in literature for combustion in large-scale fluidized beds. Thus, expressions for the fluid dynamics of the solids and gas phases, gas-solids contact and heat transfer derived from investigations in large-scale fluidized bed boilers are combined with kinetic data obtained from chemical looping experiments at lab-scale. From this, a model is obtained that is able to describe the performance trends of a large-scale fuel reactor upon variation of different inputs and operational strategies, such as feeding points for fuel and oxygen carriers, physical properties of these, operational conditions (fluidization velocity, pressure drop over the reactor) and design of the reactor. Such a modeling tool is used to obtain suitable large-scale designs and operational strategies for the fuel reactor, which are presented in the current paper.