Partial Borate Autocausticising Technology Mill Trial Experiences

摘要

A trial of Partial Borate Autocausticising (PBAC) technology was completed at Carter Holt Harvey’s Kinleith kraft pulpmill during 2004. The trial aimed to demonstrate the technology was compatible with mill operation and to characterise the benefits in liquor circuit de-bottlenecking. The trial confirmed PBAC technology was compatible with the mill operation. The presence of borate in the liquor circuit posed no threat to normal operations and did not have any affect on finished pulp or paper products. PBAC reactions produced significant quantities of caustic in green liquor, prior to recausticising. On average an additional 34 t/day of caustic was present in green liquor during the trial period when compared to the baseline period. In addition, lime demand for causticising decreased by an average of 24 t/day. This meant that every tonne of borate added to the liquor circuit, on average reduced lime demand for white liquor production by 13 t/day. Addition of sodium metaborate into the mill liquor circuit required some process adjustments. Tuning of recovery boiler operations was necessary due to the change in black liquor composition and heat value. Tuning of slaker control was also required – to maintain optimum causticising operations with borate present. Increased levels of boron were present in recovery boiler particulate emissions, while total particulate discharge decreased. Boron levels in mill waste streams, both aqueous and solid, increased above pre-trial levels as was expected. None of the observed process changes are considered to be significantly different from emissions during normal mill operation.