Utilization of biomass when combined with carbon capture and sequestration (CCS) is one feasible solution for "bioenergy with carbon capture and storage" (BECCS), which can reduce the CO2 emissions in the atmosphere. Rice husk is a unique biomass resource because its ash content is typically higher than 15% and more than 88% of this mineral matter is composed of silica. Ash partitioning and deposition mechanisms in rice husk combustion are still under investigation and will be the focus of this paper. Two different rice husk resources were tested in this work: one is from China, and another is from the United States, which are abbreviated as RH_CN and RH_US, respectively. The experimental work was performed in a 100 kW down-fired oxy-fuel combustor (OFC), and both fuels were co-fired with natural gas to achieve combustion conditions that are comparable to coal combustion. Two conditions were tested: (1) air combustion and (2) oxy-combustion with 70% O-2 and 30% CO2 in oxidant gas (denoted as OXY70). Results suggested that similar sub-micrometer accumulation modes and super-micrometer fragmentation modes appeared for both rice husks. Although the composition of super-micrometer particles was similar and enriched in silica for both rice husks, the sub-micrometer particles from RH_CN are mainly composed of volatile elements (K, Na, Cl, and P), while these from RH_US are mainly composed of Si. This compositional difference in sub micrometer aerosols subsequently affects the ash deposit formation; for example, the tightly bound inside deposits from RH_CN have much more volatile elements than those from RH_US. More importantly, apparent ash shedding on deposits occurred after 0.5 h for RH_CN, but this cannot be observed in RH_US until the maximum sampling time (2 h).