The present trend in recovery boilers is to raise the steam parameters to increase power generation, but higher steam temperatures are known to increase the risk of corrosion in superheaters. However, other factors may be involved. The pulp mill industry is relocating to areas where pulping operations commonly use eucalyptus and acacia, typically resulting in relatively low white liquor sulphidity (28-33%). Together with increased floor loadings of recovery boilers, this has led to an increase in the carbonate content (CO3); for example, in ESP ash, it may reach a level of 20% or higher.
This paper focusses on the effect of the CO3/SO4 ratio in ash on both high temperature corrosion and the first melting temperature. Several laboratory-scale corrosion studies were conducted with synthetic ashes having different CO3/SO4 ratios and with two commonly used superheater materials: the low alloy ferritic steel 10CrMo9-10, and the austenitic stainless steel TP347H. The results were discussed and compared to corrosion measurements in full-scale recovery boiler.
It was concluded that the CO3/SO4 ratio affects the melting behavior of superheater deposits to some extent. With TP347H, significant differences in corrosion resistance with varying CO3/SO4 ratios were observed at the two highest test temperatures: 525° and 550 °C. No correlation was found between the CO3/SO4 ratios and the corrosion resistance of the low alloy steel 10CrMo9-10.
|Title of host publication||Proceedings of the 2014 International Chemical Recovery Conference|
|Editors||Markus Nieminen, Päivi Lampinen|
|Publisher||Suomen Soodakattilayhdistys / Finnish Recovery Boiler Committee|
|ISBN (Electronic)||978-952-68166-2-3, 978-952-68166-1-6|
|Publication status||Published - 2014|
|MoE publication type||A4 Article in a conference publication|
|Event||conference; 2014-06-09; 2014-06-12 - Tampere Hall, Tampere|
Duration: 9 Jun 2014 → 12 Jun 2014
|Conference||conference; 2014-06-09; 2014-06-12|
|Period||09/06/14 → 12/06/14|