Análise da recuperação de sódio a partir das cinzas de caldeiras de recuperação na indústria de papel e celulose

Abstract

In recent decades, the pulp and paper industry has grown significantly worldwide in recent decades, with Brazil becoming the second largest producer. In line with this development, the search for cost and environmental impact reduction has become one of the industry's goals. In this context, ash from recovery boilers stands out due to its high generation and the presence of compounds essential to the process, such as sodium carbonate (Na2CO3) and sodium sulfate (Na2SO4). In addition to the salts of interest, ash is also composed of non-processable elements (NPEs), such as chloride (Cl-) and potassium (K+), which represent one of the biggest bottlenecks for the industry, since accumulation within the circuit leads to scale, corrosion and, consequently, changes in adequate operating conditions and reduced production efficiency. To reduce the concentration of NPEs and, simultaneously, ensure satisfactory results for the recovery of sodium salts, leaching or crystallization techniques are used to treat ash. Using electrolyte modeling in the Aspen Plus 2010 process simulator, this study analyzed the purity of the crystals obtained and the adhesion temperature of the deposits at the end of the treatments mentioned above, with the evaluated variables being the concentration of solids (1.1; 1.3, and 1.5), water temperature (35°C and 75°C), ash temperature (90°C and 120°C) and system pressure (0.3 bar and 1 bar). In the leaching process, the optimal operating conditions resulted in the recovery of 92.5% of Na2SO4, 83.2% of Na2CO3, and a sticky temperature in the range of 800 to 850°C. For crystallization, the recovery of sodium sulfate was around 89.7%, in the range of 53.7 to 77.3% for sodium carbonate and a sticky temperature between 750 and 850°C. The results demonstrate that leaching and crystallization techniques are viable and consolidated treatments to ensure operational stability, with higher solids concentration, temperature, and pressure resulting in greater selectivity of the stream of compounds of interest.