A best available technology for reliable and cost-effective chlorine dioxide used in ECF pulp production

Our large-scale, single-vessel processes (SVP) generate chlorine dioxide in a vacuum environment and produce a solid salt cake byproduct. Systems are available that use methanol and hydrogen peroxide as a reducing agent.

Reaction chemistry
Our patented SVP-SCW process generates chlorine dioxide (ClO2) by reducing sodium chlorate (NaClO3) using methanol (CH3OH or MeOH) in a sulfuric acid (H2SO4) solution, according to the following reaction: 9 NaCIO3 + 2 CH3OH + 6 H2SO4 → 9 ClO2 + 3 Na3H(SO4)2 + 0.5 CO2 + 1.5 HCOOH + 7 H2O. The byproduct of this reaction is an acidic salt cake, sodium sesquisulfate Na3H(SO4)2, that is approximately 18 wt% sulfuric acid. By recovering the sulfuric acid from the sodium sesquisulfate salt, acid feed requirements and salt cake volume can be reduced approximately 17% and 25%, respectively respectively. Recovering this acid is the function of the salt cake wash (SCW).

SCW – sulfuric acid recovery
To recover the sulfuric acid from the sodium sesquisulfate salt, it is filtered from the generator solution by the first salt cake filter. Then it is transferred to a metathesis tank where it is dissolved in hot water. The sesquisulfate is partly converted to sodium sulfate and a weak sulfuric acid solution, according to the following equation: 4 Na3H(SO4)2 + H2O → 2 H2SO4 + 6 Na2SO4. The slurry from the metathesis tank is pumped to a second salt cake filter where the sodium sulfate is recrystallized and sent to the mill's recovery system or other applications.

SVP-SCW Benefits

This SVP-SCW process is an ideal choice for pulp mills that want to:

  • Reduce their salt cake byproduct (approximately 25%)
  • Lower their acid consumption (approximately 17%)

In addition to acid recovery, SVP-SCW features all the same benefits as SVP-LITE® . It is possible to convert any SVP process to another with only minor equipment changes.

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