Electrochemical Salt Split for Mill Sodium Sulfur Balance Control

摘要

Controlling the sodium/sulfur (Na/S) balance is critical for successful pulp mill operation. In recent years, technical, economic and environmental drivers have tightened the degrees of freedom for pulp mill operation. As stricter regulatory standards can be expected, mills will need to focus extra attention on complying with new and potentially demanding constraints. It is documented that certain types of mills (e.g. those with lignin production) are particularly sensitive to disruptions in the Na/S balance. Recent spikes in the price of chemicals, especially caustic, have provided motivation for considering alternative makeup and recovery technologies. By applying "salt split" technology to the recovery boiler fly-ash or chlorine dioxide salt cake, the mill can improve the mill's Na/S balance control, along with other components in the Kraft cycle (e.g. potassium and chloride) and at the same time produce valuable chemicals. This technical paper provides results from a commercial scale pilot plant of an electrochemical process in which sodium sulfate is converted to caustic and sulfuric acid. This process, as such, has been proven before; what is new with this particular application is the technology scope and the length of operation. The scale of the current application has provided the potential to discuss the application in terms of performance and economic impact, as well as the influence on pulp mills' Na/S balances. The technology may be considered for mill expansions, stricter emission requirements, lignin and viscose production units and bio-refinery type mill solutions. The paper will present data from a pilot plant which has now been in operation for almost three years; during which various operating conditions and raw materials have been tested. This technology is now available for commercial implementation.