Health & Environmental Research Online (HERO)


Print Feedback Export to File
6558233 
Journal Article 
The Generator Acid Purification (GAP) system reduces caustic make-up requirements at kraft mills 
Paleologou, M; Berry, RM; Gillis, T; Thompson, R; Sheedy, M; Brown, C 
1999 
0 
Pulp and Paper Canada
ISSN: 0316-4004 
Annex Publishing & Printing, Inc. 
100 
2 (Feb 1999) 
34 
The APU can be operated under different conditions, separating acid from salt with varying degrees of efficiency. The most cost-effective operation for the mill occurs when the amount of acid in the product salt solution and the amount of salt in the product acid solution are minimized. Table IV shows the throughput rates and concentrations of products obtained under a set of operating conditions chosen to minimize the amount of acid in the salt product. This was accomplished by using a relatively large volume of water to elute the acid from the resin. In this experiment, a simulated modified [Mathieson] chlorine dioxide generator spent acid solution (500g/L [Symbol Not Transcribed] and 440g/L [Symbol Not Transcribed]) was fed to the APU at a rate of 2.3 L/h and was separated into two streams: a sodium sulphate-rich stream (210 g/L [Symbol Not Transcribed] and 17 g/L [Symbol Not Transcribed]) produced at a rate of 4.0 L/h and a sulphuric acid-rich stream (260 g/L [Symbol Not Transcribed] and 34g/L [Symbol Not Transcribed]) produced at a rate of 4.2 L/h.


In the GAP-S system, the sodium sesquisulphate obtained from the vacuum filter is first fully dissolved. The solution which contains sulphuric acid and sodium sulphate is then fed to an APU. Because of the lower sulphuric acid concentration of the solution, reduction of the small amount of residual chlorate present is not necessary. As with the basic GAP system, the de-acidified sodium sulphate by-product is recycled back to recovery. A portion of the purified dilute sulphuric acid obtained by water elution of the APU resin is recycled back to the dissolving tank to dissolve the sodium sesquisulphate. Using this approach, the acid concentration in the solution is fortified beyond what is possible by simply dissolving the sesquisulphate in water.


We have demonstrated that chlorine dioxide generator spent acid can be separated into its component sulphuric acid and sodium sulphate using the GAP or GAP-S systems. The de-acidified sodium sulphate generated from these systems can be returned to the recovery cycle for sodium and sulphur make-up without destroying alkalinity in pulp mill liquors. The pure sulphuric acid product can be used for brownstock acidification or other mill uses. Attractive paybacks are anticipated in all mills which have atmospheric chlorine dioxide generators (e.g. Mathieson, modified Mathieson and Solvay) but the system can be used with sub-atmospheric generators (e.g. R8, SVP-LITE) as well, with economics competitive with Eka Chemicals' Saltcake Washer and Sterling's R10 processes. The GAP and GAP-S systems are presently being marketed by Eka Chemicals in North America and Cellchem in the rest of the world. 
Pulp bleaching; Pulp & paper mills; Recovery of chemicals