Ash and material handling — bottom ash, fly ash and fuel feed

A biomass boiler island moves three solid streams continuously. Bottom ash — the coarse fraction falling through the grate, typically 20–40 % of total ash on bagasse firing — leaves through a water-sealed conveyor under the furnace. Fly ash — the fine fraction carried in the gas — is collected at every hopper in the gas path: boiler bank, economizer, cyclone or multicyclone, and ESP or bag filter, then conveyed to a silo. Fuel — bagasse, rice husk, wood chip — arrives through feeders that meter it to the furnace. Within the boiler products range this is the system that decides whether the collectors upstream can actually perform: every hopper in the gas path is a hole in the pressure boundary, and the material-handling equipment is what keeps those holes sealed.

The fuels set the duty. Bagasse arrives at ~50 % moisture with high char carryover, and its fly ash is high in silica — abrasive enough that erosion, not corrosion, is the dominant wear mechanism in chutes, rotary valves and conveying bends. Rice husk ash is more abrasive still, at 85–90 % amorphous silica, which is simultaneously its commercial value (see below).

The submerged scraper conveyor (SSC) is the standard bottom-ash solution: ash falls from the grate into a water trough that quenches clinker, kills sparks, and — critically — seals the furnace bottom against air in-leakage, protecting the draught balance. A slow chain (typically 1–3 m/min) drags the quenched ash up a dewatering incline to a bunker at 15–25 % surface moisture. Design points that decide service life on bagasse duty: chain and flight material hard enough for silica ash, water-level control that maintains the seal at all boiler loads, and trough plate thickness treated as a wear allowance, not a structural minimum.

Drag-chain (en-masse) conveyors handle dry fly ash from economizer and collector hoppers where distances are short and layout is linear — a sealed casing, a slow chain, and inlet/outlet flanges that hold the system's air-tightness. Their enemies are the same as the rotary valve's: abrasion at the return strand and in-leakage at worn casing joints. For fuel feed, the same family reappears on the other side of the furnace: metering drag conveyors and screw or chute feeders that spread bagasse or husk across the grate. Fuel feeders are combustion equipment as much as handling equipment — uneven feed is the usual root cause behind the O₂ swings that force operators to carry high excess air.

Rice husk ash is 85–90 % amorphous silica — a reactive pozzolan for concrete and the feedstock for precipitated-silica production, where its amorphous (non-crystalline) state is exactly what the chemistry needs. A plant on rice husk that keeps its fly ash dry, unmixed with bottom ash and free of tramp material can turn a disposal cost into a revenue line; Arrow's silica extraction from rice husk ash service covers the process route and the ash-quality requirements, which reach back into combustion control — burning temperature decides whether the silica stays amorphous. Bagasse ash finds use in concrete blends and as a potassium-bearing soil amendment returned to cane fields. In every case the material-handling design choices on this page — dry conveying, dedicated silo, sealed transfer — are what preserve the value; a single wet, mixed ash stream is only ever waste. Handling-system supply, from single rotary valves and conveyor chains as boiler spares up to complete hopper-to-silo systems engineered with the collector retrofit they serve, is quoted per project after the technical assessment, with capacities and wear-material selections stated on the plant's measured ash rate and abrasiveness.