Influence of comminution and briquetting parameters on the agglomeration behaviour of wheat straw

The low bulk density of wheat straw necessitates a processing and densification for the ease of handling, storage and transportation for a later use as fuel or as raw material for thermal conversion. This densification could be done by briquetting. For this purpose, the wheat straw was comminuted in five different ways, with a twin-screw extruder, a cutting mill, a beater mill, a hammer mill and a swing mill. Subsequently, the comminuted material was agglomerated with a hydraulic piston press with cylindrical press channel of 50 mm diameter at pressures of 100 MPa, 140 MPa, and 240 MPa without any binders. In order to evaluate the compression, the compression work as well as briquette-quality parameters were determined, such as the apparent density and the abrasion resistance. We describe the obtained results using three different models, namely Heckel (1961), Cooper-Eaton (1962) and Kawakita-Lüdde (1971). With these models, it becomes possible to compare the compaction behaviour of the comminuted wheat straw with other materials. In addition, the modelling can be used to design the compaction process on a larger scale. While the models by Heckel and Kawakita-Lüdde are suitable for the description of the compression of the comminuted material (R2 = 0.99), the model by Cooper-Eaton was found unsuitable without further adaption.