Performance of biomass pyrolysis stove from bus wood waste with varying donut briquette compaction pressures

Bus wood (Melaleuca viridiflora) is an underutilized sawmill residue in the Merauke region of South Papua. Converting this residue into densified fuel can support local biomass utilization while reducing unmanaged wood waste. This study evaluates the effect of donut-briquette compaction pressure (30, 40, and 50 bar) on the thermal behavior of a multilayer annular pyrolysis stove. The stove was instrumented with nine K-type thermocouples arranged at outer, middle, and inner radial positions across three vertical layers. Temperature profiles were recorded at 2 min intervals, and thermal output was assessed using Water Boiling Tests (WBTs; n = 16 per pressure). The inner-edge sensors produced the highest temperatures, with transient peaks approaching 900-950 °C, whereas middle-position sensors generally operated between about 400 and 750 °C. Outer-edge sensors remained cooler, although the upper-layer outer sensor reached approximately 450 °C. Mean WBT energy rates were 3.79 ± 0.23, 3.89 ± 0.17, and 3.92 ± 0.26 MJ h⁻¹ for 30, 40, and 50 bar, respectively. One-way ANOVA indicated no significant difference in mean energy rate among the three pressures (p = 0.215). The 40-bar condition showed the lowest coefficient of variation in WBT energy rate and a comparatively sustained intermediate-temperature response. These results indicate that compaction pressure affects temperature evolution and stability more strongly than mean useful energy rate within the tested range.