B3 Unrefereed conference proceedings

Firing practices in modern recovery boilers

Publication Details
Authors: Vakkilainen Esa
Publication year: 2019
Language: English
Title of parent publication: 55th Anniversary International Recovery Boiler Conference
JUFO-Level of this publication: 0
Open Access: Not an Open Access publication


This work updates liquor firing practices in Finnish recovery boilers
from the previous 2004 data with new 2018 data. It was prepared under FRBC
Liquor firing subcommittee by sending all boilers a questionnaire that was
filled. Results from 2018 are compared to results to 2004.

The average liquor firing in a Finnish
recovery boiler increased 330 tsd/d and the average boiler burned 2800 tds/d.
Because several small boilers have been shut and the installed new boilers are
big the average size increased significantly. The liquor to be burned changed
slightly. The black liquor dry solids increased 1 % and the heating value
decreased 0.3 MJ/kgds. Liquor firing per unit area of boiler bottom has clearly
increased. Average value increased 17.4 " 19.4 tds/d m2 and the HHRR 2820 "
3100 kW/m2. Increase in firing capacity can be explained by new big
boilers and progress in black liquor combustion, enabling more liquor to be
burnt per unit area. All boilers except two use primary-air of less than 30 %. Most
recovery boilers are using high over 30 % tertiary and quaternary air.

Liquor firing temperature corresponds to
BPR. Also pressures have been kept at
the same level. This is significant because the liquor firing per gun has
increased a lot.

NOx emissions show a wide spread; 50–230
mg/Nm3. Highest values have not decreased, but two boilers have a
very low value. No boiler reported TRS that is higher than detection limit. Only
few boilers gave dust emission close to 100 mg/Nm3. The dust
emissions have gone down significantly.

The main reasons for increased firing capacity are new, bigger boilers
and development of black liquor firing. Now we can fire more liquor per same
bottom area than before. Because the black liquor dry solids increased only
moderately the main explanations are probably the improved control systems, new
air systems and general improvements in liquor firing.

Last updated on 2020-28-02 at 09:03