Detailed estimation of generated woody biomass ash for use as fertilizer material

The physical and chemical characteristics of woody biomass ash (WBA) are highly dependent on the ash type, fuel, and furnace type. WBA recycling requires knowledge of its amount and characteristics. In this study, the amount of WBA recoverable as fertilizer in Japan was estimated considering the ash type, furnace type, and fuel type, using data obtained in a questionnaire-based survey of 105 of the 220 biomass power plants in Japan. The results showed that the amount of ash was > 1.5 times larger than that calculated according to fuel type. The discharged ash contained moisture, sand, and impurities. The slopes of the estimation model of the actual versus calculated amount were larger for gasification power generation, followed by stoker furnaces and fluidized bed furnaces. The bottom ash ratio in WBA from all furnace types was 0.37. With an estimated biomass combustion by the 220 biomass power plants in Japan of 3.4 × 10⁷ t in 2026, the amount of generated ash would be 6.9–12 × 10⁵ t. Bottom ash accounted for 2.7–4.7 × 10⁵ t, with circulated fluidized bed furnace-derived ash comprising > 60 % of the total. The estimated annual amount of ash suitable for fertilizer use was 6.2–11 × 10⁵ t. The K content of WBA in 2026 was estimated to be 1.8 times larger than that in annually imported fertilizer. This K resource should be fully exploited and the efficient use of K extraction residue should be pursued to achieve an effective circular economy.