Energy savings combined with lignin extraction for production increase: case study at a eucalyptus mill in Portugal

Abstract

In previous research by the authors, energy savings combined with lignin extraction as a means to debottleneck the recovery boiler were evaluated on a model mill. The study showed that this concept was a profitable alternative to recovery boiler upgrade. In the present paper the concept was taken one step further, and the potential for energy savings and possibilities for lignin extraction were evaluated at a real mill: a market pulp mill in Portugal. The energy-saving methods proved to be applicable also to the real mill and the steam-saving potential was 4.2 GJ/ADt or 33%. Lignin extraction trials with bench scale equipment showed that lignin extraction was fully viable at the studied mill. A full-scale lignin separation plant according to the LignoBoost concept, combined with energy savings, was simulated in a computer environment and compared to installation of a new recovery boiler. A new recovery boiler had an investment cost four times higher than the LignoBoost concept combined with energy savings, but the electricity production would be higher. The profitability for a production increase of 16% was calculated for both cases. Steam savings combined with LignoBoost were found to have better profitability unless the electricity price is very high.