USING BLEACHING STAGE MODELS FOR BENCHMARKING HARDWOOD ECF BLEACH PLANTS, 2023 PEERS Conference

Steady-state models estimated the performance of the D₀(EOP)D₁ bleach sequence at two mixed hardwood bleach plants in the southern US. At Mill 1, the full sequence’s chlorine dioxide charge was monitored for two weeks, which brightens the pulp to ~84% ISO. Mill 2 considered the partial sequence for nearly four weeks that brightens the pulp to ~86% ISO. Elevated levels of chlorine dioxide were linked to increased washer carryover in brownstock and extraction areas. For Mills 1 and 2, an extra 0.24% and 0.33% chlorine dioxide was consumed in the D₀ stage. This extra bleach demand was equivalent to an additional 4.8 and 5.5 kappa load to the brownstock, respectively. Some differences were observed for the D₁ stage. Mill 1 had extraction carryover that averaged 1.1 units higher than was measured. It contributed an extra 0.22% chlorine dioxide being used. Mill 2 had extraction carryover that averaged between zero and 0.7 kappa units and consumed up to 0.13% more chlorine dioxide. Another data set from Mill 2 showed high brownstock and extraction carryover, leading to ~0.90% total chlorine dioxide usage to brighten to 84% ISO. Overall, this investigation illustrated that the models could be employed as benchmarks.

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