posted on 2024-03-07, 13:08authored byFredrik Weiland, Daniel Jacobsson, David Wahlqvist, Martin Ek, Henrik Wiinikka
Changed utilization
of black liquor in the pulp and paper industry
has the potential to offer simplified carbon capture and, thus, negative
net emissions from these large point sources. This can be achieved
either by adapting existing recovery boilers to oxyfuel combustion
or by replacing them with black liquor gasification technology. In
this work, the chemistry during black liquor conversion was therefore
studied in detail under different atmospheres relevant for pyrolysis,
gasification, and oxyfuel combustion. Experiments were performed using
environmental scanning transmission electron microscopy (ESTEM) and
thermogravimetric analysis (TGA), supported with thermodynamic equilibrium
calculations (TECs) to understand and interpret the results. Black
liquor conversion was found to be generally similar in air and oxyfuel
atmospheres containing approximately 20–25 mol % oxygen. The
results however indicated that there was a higher probability of forming
carbonates in the melt at higher carbon dioxide (CO2) partial
pressures, which in addition was found to be associated with potentially
higher sulfur loss during black liquor conversion. Both of these characteristics
can negatively affect the chemical recycling at the pulp mill by increasing
the need for lime and makeup chemicals.