Method of treating fly ash of a recovery boiler
AssigneeAndritz Inc.
InventorsKeijo Salmenoja, Niko Metsämuuronen, Marjukka Joutsimo, Ismo Reilama
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Abstract
A method of treating fly ash containing sodium sulfate from a recovery boiler of a chemical pulp mill. This method includes at least the following steps: a) ash is dissolved in an aqueous solution and the pH of the solution is adjusted with alkali for precipitating impurities, b) the solution is filtered for removing the impurities containing precipitate, c) sodium sulfate is crystallized from the solution and the crystals are separated from the solution by filtering or by centrifugation, and d) the crystallized sodium sulfate is used as initial material for producing sodium and sulfur containing chemicals or as process chemical.
Claims17
A method of treating fly ash containing sodium sulfate from a recovery boiler of a chemical pulp mill, wherein the fly ash is removed from a chemical cycle of the chemical pulp mill for adjusting the chemical balance, said method comprising:
- a) dissolving the fly ash in a first aqueous solution, and adjusting the pH of the first aqueous solution with alkali to precipitate impurities from the first aqueous solution with the fly ash,
- b) filtering the first aqueous solution with the fly ash to remove the precipitated impurities,
- c) crystallizing sodium sulfate in the filtered first aqueous solution with the fly ash to form sodium sulfate crystals,
- d) separating the sodium sulfate crystals from the filtered first aqueous solution with the fly ash by filtering or centrifugation,
- e) dissolving the sodium sulfate crystals in a second aqueous solution to form dissolved sodium sulfate crystals,
- f) decreasing with acid the pH of the second aqueous solution with the dissolved sodium sulfate crystals to precipitate calcium from the second aqueous solution, and
- g) after step f), using the dissolved sodium sulfate crystals as an initial material for producing sodium and sulfur containing chemicals and/or as a process chemical.
A method to treat fly ash comprising:
- discharging fly ash from a recovery boiler in a chemical pulp mill;
- dissolving the fly ash in a first aqueous solution;
- precipitating impurities from the aqueous solution with the dissolved fly ash by adding alkaline to increase the pH level to at least eleven of the first aqueous solution with the dissolved fly ash;
- filtering the first aqueous solution with the dissolved fly ash to remove the precipitated impurities and form a filtered first aqueous solution with the dissolved fly ash;
- crystallizing sodium sulfate in the filtered first aqueous solution with the dissolved fly ash,
- after the crystallization, separating crystallized sodium sulfate from the filtered first aqueous solution with the dissolved fly ash by filtering or centrifugation,
- dissolving the crystallized sodium sulfate in a second aqueous solution to form dissolved crystallized sodium sulfate,
- decreasing with acid the pH of the second aqueous solution with the dissolved crystallized sodium sulfate to precipitate calcium from the second aqueous solution, and
- using the dissolved crystallized sodium sulfate to produce sodium and sulfur containing chemicals and/or as a process chemical.
Dependencies are inferred from the claim text.