Solubility of ESP Dust and Optimization of the Recovery of Sodium Sulphate Crystals, 2005 Engineering, Pulping & Environmental Conference

The effluent-free concept, first proposed by Rapson in 1967 and pioneered by Great Lakes Forest Products in 1978, involves the internal recycle of all the contaminated process streams, to eliminate all pulp mill effluent. Any closed-cycle technology must use a process for removal of problematic non-process elements, such as chloride and potassium. Chloride and potassium are minor components which can accumulate in kraft pulping chemical recovery cycles. Previous studies indicated that Cl- and K+ have adverse effects on thermal properties of fireside deposits in the kraft recovery boiler, accelerating plugging of the flue gas passages and increasing the rate of the corrosion of the superheater tubes by lowering the melting point of the deposits. The removal of Cl- and K+ from liquor cycle has become more important with the trend of increasing mill system closure, and most particularly with the prospects of incorporating bleach plant closure. There is an enrichment of Cl- and K+ in recovery boiler electrostatic precipitator dust(EPD) and so it is a good place from which to remove them. The five major components in the precipitator dust are sodium, sulfate, carbonate, chloride and potassium and once the common denominator to all the techniques for Cl- and K+ removal of the recovery cycle, is the dilution of the ashes, firstly on water, with the preferential crystallization of sodium sulfate, in relation to the other salts presents on the EPD, the objective of this work is to evaluate the solubility of the eletrostatic precipitator dust on mixtures such as H2O / H2SO4 or H2O / Spent Acid (H2SO4 + Na2SO4) in order to obtain sodium sulfate crystals with largest purity and size, minimizing the losses of this salt, which will be re-used on the paper manufacture process, and optimizing its removal from the liquor enriched in Cl- and K+.