Attrition & Breakage Fundamentals

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Development of First Principles Attrition Model to Determine Solid Makeup Cost of Novel CFB Technologies at NETL

Ronald Breault, National Energy Technology Laboratory

A number of technologies are being developed worldwide that utilize the circulating fluidized bed concept, particularly for efficient energy conversion with carbon capture and chemicals production. One prominent example is chemical looping combustion for carbon capture, which circulates a metal oxide between a fuel reactor and an air reactor. The fuel reactor reduces the metal oxide with a carbonaceous fuel and captures carbon in situ, while the air reactor regenerates the metal oxide using air, which generates energy to power a steam cycle. While great strides have been made in the development of chemical looping, a great uncertainty in the development of economic models for this technology is the metal oxide makeup cost, which is dependent on the attrition rate. The attrition rate is highly dependent on the process conditions, such as velocity and temperature, and the material properties; that very widely between the fuel reactor and the air reactor. While numerous attrition models for unit operations in a CFB exist, these models are not based strictly on material properties, and consist of “efficiency” terms which are unknown before experiments. In order to utilize these models, the material needs to be tested in small-scale pilot unit operations to attain the material constant in the attrition expression, and it is difficult to determine the attrition rate a priori. Thus, it is desirable to develop first principles attrition models for unit operations in a CFB that are only dependent on material properties and knowledge of the process conditions so that important economic decisions can be made for a material in a certain process without performing extensive scale-up. The models are being developed by combining knowledge of hydrodynamics with the fields of wear and fracture mechanics for particulate solids, which give the volume of attrited product for a given material. The development of these models will allow for quick screening of materials and CFB designs to minimize the material makeup cost. NETL has plans for a four to five year effort in this area, which began last July. This paper will present our results to date and our plans for the next 4-plus years.