Novel Recovery Process for Small-Scale Non-Wood Pulp Mills, 1998 International Chemical Recovery Conference Proceedings

A major difficulty in non-wood pulping is the recovery of heat and chemicals from the cooking liquor. The main reason for this is the silicon present in the liquor. The silicon content can be reduced by precipitating silica by re-ducing the liquor pH with carbon dioxide. A co-precipitation of lignin makes the separation of silica very difficult. Experiments have shown that by saturating the liquor with carbon dioxide at a high temperature, the precipitate is readily separated at a high dry solids content. However, because lignin is separated from the liquor, its heating value is reduced. For liquor combustion a novel device is proposed. The device operates at an elevated pressure and uses pure oxygen for combustion. Oxygen can be produced on site by VSA technology. Mass and energy balances show that this is an energy-efficient and environmentally friendly way to recover chemicals from the cooking liquor when processing non-wood fiber with a high silicon content.