Unravelling the improved permeability of wet granular packed bed via embedding dry particles: From multi-scale mechanisms to combustion enhancements

The permeability of wet granular packed beds inevitably deteriorate as their thickness increases. Therefore, a wide variety of technologies have been developed to improve bed permeability. Return fines embedding (RFE) is a promising technology owing to its simplicity and efficiency. Improved bed permeability using RFE was validated by increasing the moisture content from 7.5% to 9.0%. Return fines larger than 3 mm, particularly those between 4 mm and 5 mm, played a key role in improving bed permeability, and the corresponding mass ratio to the total weight of return fines is not expected to exceed 60%. It was also found that the return fines embedded in the lower zone had better permeability than those embedded in the upper zone owing to the formation of an overly wet zone close to the bottom. As a result, the particle-scale porous structures and the meso-scale moisture transfer phenomena were investigated to unravel the bed-scale improved permeability. In addition to the multi-scale mechanisms, the combustion enhancements in the wet granular packed bed by applying the RFE strategy were visually demonstrated.