Precipitator Ash Addition to Black Liquor to Reduce Evaporator Scaling – Understanding 1 the Fate of the Ash, 2023 PEERS Conference

Precipitator ash is often added into the black liquor to the concentrators to help reduce sodium salt scaling. In most cases it is added to as-fired black liquor which is then partially recycled back to the concentrator body operating just above the solubility limit. In this scenario, the ash added to liquor above the solubility limit and is intended to increase the crystal mass to provide surface area for sodium salts to precipitate on. Some mills have observed a positive effect while others have not. In some other mills, precipitator ash is added below the solubility limit so that the ash dissolves to increase the dissolved sulfate levels sufficiently that burkeite precipitates first rather than dicarbonate. This is because burkeite scaling is less severe in falling film evaporators than dicarbonate.

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