Major Players in Chemical Kraft’s Recovery Process
The Kraft’s recovery process is an effective and mature technology that ensures an efficient chemical usage for the Kraft’s pulping process. In our previous post, we talked about how Sodium Sulfide plays a major role in the Kraft’s pulping process, the most dominant pulping process to date. However, this pulping process is inefficient in terms of chemical usage. Huge portions of pulping chemicals are wasted in the form of black liquor. To improve chemical efficiency, black liquor will then be processed in the Kraft’s recovery process to recover Sodium Sulfide and Sodium Hydroxide that can be reused again in the pulping process. Globally, over 1.3 billion of black liquor was processed per year to recover up to 50 million tons of pulping chemicals. For this post, we will be talking about Sodium Carbonate (or Soda Ash), the active chemical required to recover pulping chemicals from black liquor.
During the Kraft’s recovery process, a combination of reactions involving Sodium, Calcium and Sulfur forms a closed cycle whereby Sodium Carbonate is reacted to regenerate Sodium Hydroxide. The inclusion of a recovery process drastically improves the chemical efficiency of paper manufacturing process to about 97%.
Soda Ash exists mainly as two different grades, Light and Dense Grade. Both grades exist as white odourless solids with similar purity and impurity content. The main difference between these two grades is their density and size. Soda Ash Light typically has a lower bulk density (400-700 Kg/m3) and is of a smaller particle size (Particle-Median-Diameter ~100 microns) and is more suitable for chemical applications in paper or detergent manufacturing. As for Soda Ash Dense they generally have a higher bulk density (800-1100 Kg/m3) and is of a larger particle size (Particle-Median-Diameter ~300-500 microns) as compared to their Light Grade counterpart. The denser and more granular property of this grade makes it more suitable for applications such as glass manufacturing.
Main industrial production of Soda Ash is via the Solvay process. In this process, aqueous Sodium Chloride solution is bubbled with Carbon Dioxide to form Sodium Hydrogen Carbonate (which will precipitate) and Hydrochloric Acid. Ammonia is also bubbled into the mixture to neutralize the acid form and the mixture is then heated to decompose the Sodium Hydrogen Carbonate into Soda Ash, Water and Carbon Dioxide. The Solvay process is able to recover part of the Carbon Dioxide as well as almost all the Ammonia used in the process. The average price of Soda Ash ranges from 200-230 USD/ton with USA being the major exporter.
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