Influence of pressure and retention time on briquette volume and raw density during biomass densification with an industrial stamp briquetting machine

Biomass densification is a key technology for economic and environmental use of biomass in bio economy. Thus, the aim of the study was to analyze and simulate the influence of process-related parameters of briquetting on the product quality. The densification of woody biomass was performed with an industrial stamp briquetting machine with a throughput of 60 kg/h. On the one hand, briquettes were produced using statistical methodologies by varying the pre-densification pressure (i.e., 13-40 MPa), main densification pressures (i.e., 100-200 MPa) and the retention time (i.e., 0-10 s). On the other hand, the pressure distribution in the forming mold was calculated numerically. The equations were solved iteratively. Subsequently, the data set of the statistical model was used to validate the numerical results. The investigation shows: (1) due to friction, pressure and density differences occur on the forming mold walls; (2) the retention time is the main influencing factor for biomass densification; (3) significant agreements between experimental and simulation data were possible. Based on the results, new forming molds for industrial biomass compaction could be developed. With a slightly conical briquette geometry, these could favor a more even pressure distribution and thus increase briquette stability.