Official website of the New Zealand Farm Forestry Association


Supercritical CO2 dewatering of E. nitens. Results of Scion’s core funded experiments

By Bernie Dawson, Hamish Pearson, Rosie Sargent, August 2018.

Download SWP-T062 (pdf)

Executive summary

The objective of this study was to see if removing sap from Eucalyptus nitens via supercritical CO2 dewatering reduces the level of checking and collapse

This project

Eucalyptus nitens was sourced from Southwood Exports in Southland, and small boards were either air dried from green to ~12% moisture content, or dewatered with supercritical CO2 to remove sap from the lumens prior to air drying to 12%. Levels of collapse, and numbers of checks were measured following drying.

Key results

The dewatered boards had significantly lower levels of collapse compared to the air dried boards. The average depth of collapse was reduced from 1 mm per board face to 0.25 mm per board face.

The number of checks on the faces and ends of the dewatered boards were higher than in the air dried boards.

Implications of results for the client

Dewatering with supercritical CO2 has potential to reduce levels of collapse in E. nitens. Levels of end checking are increased, but these may not necessarily correlate with the presence of internal checking.

Further work

As a next step, it is recommended that the economics of the dewatering process be compared to that of air drying from green.

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