(391d) Design of a Chemical-Looping Combustion System for Solid Fuels

Fossil fuels, such as coal, oil and natural gas are widely used in the power and industrial sectors. Their demand is gradually increasing in spite of a growing international concern about climate change and an increasing desire to control greenhouse gas (GHG) emissions. Carbon capture and storage (CCS) has significant potential to decrease anthropogenic carbon dioxide emissions. A great majority of the carbon dioxide capture R&D is focused on the power generation sector, particularly coal-fired power generation. Chemical looping combustion (CLC) promises to by an energy efficient carbon capture technology because of its inherent separation of carbon dioxide. A CLC system usually consisted of two fluidized bed reactors, an air reactor (AR) and a fuel reactor (FR), and uses a granular oxygen carrier to transfer oxygen from combustion air to the fuel. The oxygen carrier is oxidized by the air in the AR and is reduced by the fuel in the FR. Hence, air is not mixed with the fuel, and the outgoing carbon dioxide stream is not diluted by nitrogen. Successful commercialization of power generation processes using coal directly, utilizing CL technology, requires a suitable process design, which is currently under development. A steady state model of a CLC process has been developed, based on mass and energy balance. The model is used to estimate the reactors dimensions using iron oxide as oxygen carrier, as an example. Coal is represented in a general way so as to be able to include a wide range of fuels. Mass balance is based on an effective molecular formula for the carrier particles and the solid circulation rate is partitioned into metal, oxygen and inert flow rates. The solid circulation rate in the system is calculated as a function of the difference in conversion of the carrier particles and other operating parameters.