Agglomeration

Many investigations are focused on the mechanisms of formation and distribution of agglomerates inside fluidized beds. In high temperature applications, such as gasification or combustion, the presence of ash acts as a homogeneous glue layer for the formation of agglomerates, leading to the partial or total bed defluidization. Low temperature applications, such as coating and drying processes, present fluidization problems due to the appearance of agglomerates. In our group, we study the defluidization process by agglomerates formation using cold and high temperature experiments.

The group measures pressure fluctuation signals in order to detect the onset of the agglomeration process, which is carried out adding liquid to the bed in the cold conditions, or through the fuel agglomeration in the high temperature setup. Pressure measurements are analyzed in time and frequency domains, employing the analysis procedures and the control scheme developed by our group. Two experimental setups are used in order to analyze the agglomeration and defluidization phenomena:

• Cold setup: fluidized bed equipped with a rotating distributor

Liquid is added to the bed in order to reproduce the experimental conditions found in literature when agglomerates are formed during fluidization. The rotating distributor is used as a counteracting measurement against the defluidization phenomena. In the video we can see that the swirl effect of the distributor breaks the agglomerates settled on top of the distributor, improving the recuperation of the fluidized conditions. The video also shows the analysis of the pressure fluctuations with the wide band energy.

• High temperature setup: small facility

A lab-scale bubbling fluidized bed with an inner diameter of 52.8 mm has been used to compare two different bed materials, silica sand and sepiolite during Cynara cardunculus L. gasification. The results showed two types of agglomerates: (i) formed on top of the bed, and (ii) formed on the bottom of the bed, which leads to different defluidization processes. Figure 1 shows snapshots obtained during these gasification experiments. Figure 2 presents the influence of the air excess on the agglomerates.

Figure 1. Cynara cardunculus L. gasification using silica sand and sepiolite.

Figure 2. Agglomeration for silica sand and sepiolite for different air excess.