Case study - Elemental chlorine free kraft pulp bleaching and chlorine dioxide scrubbing

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Courtesy of Raschig USA Inc.

Chlorine Dioxide - CIO2 Scrubber Packing at Kraft Pulp Mills

Elemental Chlorine Free - ECF - bleaching of wood pulp using Chlorine Dioxide, CIO2, as the primary bleaching agent eliminates dioxin emissions. This is a reflection of the fact that as a bleaching agent CIO2 is 10 times more reactive than elemental Chlorine, Ck. As a powerful oxidizing agent CIO2 must be generated on site - it is too dangerous to transport by either rail or highway. Approximately 90% of white papers today are made using ECF bleached wood pulp. And also any trace amount of CICMhat escapes either the CIO2 generator or the bleach plant at the kraft mill must be captured and scrubbed in a packed tower. At just 5 ppm concentration CIO2 if breathed is capable of causing serious lung damage.

A typical CIO2 generator and kraft mill bleach sequence are shown above. Note that in addition to the generatorthat in the bleaching process that there are several places where fugitive emissions of CIO2 must be addressed-Typically, these emissions are captured and passed through a counter-current scrubbing tower. The packing of choice for the tower being 3.5' Jaeger Tri-Packs?1 in PVDF resin, seen left below,to resist the powerful oxidizing power of CIO2.

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