The implication of emission control systems on the mass and energy balances of the kraft pulp mill process - A case study of Södra Cell Mönsterås’s recovery boiler
Publicerad
Författare
Typ
Examensarbete för masterexamen
Master's Thesis
Master's Thesis
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
This master’s thesis concludes on the mass and energy balances of the kraft pulp
mill process and investigates the possible implications in connection to new emis sion control systems. The work is based on a case study of the recovery boiler at
Södra Cell in Mönsterås. Key aspects include the energy and element balances oc curring in the boiler and the emission of NOx and SOx . Three primary emission
control measures are evaluated: injection of ammonia solutions (SNCR), injection
of ammonia-containing gas (dissolver off gas), and the injection of scrubber effluent.
The process model is based on previous work and validated by comprehensive data
collection from the reference plant. The model is implemented in the software Aspen
Plus. The model is zero-dimensional and equilibrium-based and cannot describe the
effects of spatial distribution of air and temperature within the boiler or processes
controlled by kinetic-based reactions.
The result shows that the implementation of water-diluted ammonia injection with
the potential to reduce NOx emissions by 45 % does not significantly affect flue
gas temperature. While the use of dissolver off gas is advantageous, due to the
utilisation of a waste stream, current ammonia levels from the dissolver off gas is
insufficient for achieving significant SNCR effects compared to water-diluted am monia injection, with a difference of 0.69 mol NH3/s. Recycling scrubber effluent
does not significantly alter the sulphidity of the flue gas but does increase reduction
efficiency of the smelt, thereby reducing the need for make-up chemicals.
The derived model is useful for describing the overall implications of the recovery
boiler’s mass and energy balances and could be used to quantify the effects of other
process modifications. The work should be complemented with more detailed design
tools.
Beskrivning
Ämne/nyckelord
Södra Mönsterås, kraftmassabruk, sodapanna, Aspen Plus, utsläppskontroll, primära åtgärder, NOx, SOx