Fossil fuel replacement in the pulp mills
Vakkilainen, Esa Kari; Kivistö, Aija (2008)
Post-print / final draft
2008
Lappeenranta University of Technology
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https://urn.fi/URN:ISBN:978-952-214-623-6
https://urn.fi/URN:ISBN:978-952-214-623-6
Tiivistelmä
Many kraft pulp mills have a desire to increase their production capacity. In such cases the recovery boiler is often one of the bottlenecks. Recently two new approaches have become available that promise increased pulp mill capacity and creation of completely fossil-fuel free mill concept. These are lignin removal from black liquor (LignoBoost) and biomass gasification for lime kiln
To study the effect of lignin removal to black liquor an example pulp mill was chosen. The aim was to look at the effects of lignin removal on actual mill conditions. Therefore data was gathered on the mill and the calculations done were based on the actual operation of the mill as far as known.
The removal of lignin decreases the organic content of black liquor, but the inorganic portion remains essentially unchanged. The heating value of the black liquor decreases with increased lignin removal. The new process for extracting lignin from black liquor should not affect the BPR of black liquor very much. Removal of high molecular mass lignin affects only marginally the effective average molecular weight of the non water black liquor portion. The new process for extracting lignin from black liquor may be an opportunity for decreasing the viscosity of black liquor as lignin removal removes high molecular mass components which are a significant source of black liquor viscosity.
For the boiler used in this study we note: At the same steam generation rate, smelt and black liquor flows increase. At lignin removal rate of roughly 20 % the boiler superheating limit is reached. Typically at lower loads auxiliary fuel needs to be added to make full superheating. Lower furnace will start behaving problematically (TRS, SO2, reduction) at about 30 % lignin removal rate. Minimum load that the boiler can run corresponds to about 50 % lignin removal
The main financial benefits are from the lowered operating costs and from debottlenecking the mill. Lowered operating costs are almost solely based on price of natural gas. If recovery boiler is the bottleneck of the mill, then lignin removal also allows further increase of pulp production and brings in quite a lot of new revenue. It seems that taking out lignin to reduce the recovery boiler load does not bring in significant extra revenue because the current price for the sold lignin is rather low.
To study the effect of lignin removal to black liquor an example pulp mill was chosen. The aim was to look at the effects of lignin removal on actual mill conditions. Therefore data was gathered on the mill and the calculations done were based on the actual operation of the mill as far as known.
The removal of lignin decreases the organic content of black liquor, but the inorganic portion remains essentially unchanged. The heating value of the black liquor decreases with increased lignin removal. The new process for extracting lignin from black liquor should not affect the BPR of black liquor very much. Removal of high molecular mass lignin affects only marginally the effective average molecular weight of the non water black liquor portion. The new process for extracting lignin from black liquor may be an opportunity for decreasing the viscosity of black liquor as lignin removal removes high molecular mass components which are a significant source of black liquor viscosity.
For the boiler used in this study we note: At the same steam generation rate, smelt and black liquor flows increase. At lignin removal rate of roughly 20 % the boiler superheating limit is reached. Typically at lower loads auxiliary fuel needs to be added to make full superheating. Lower furnace will start behaving problematically (TRS, SO2, reduction) at about 30 % lignin removal rate. Minimum load that the boiler can run corresponds to about 50 % lignin removal
The main financial benefits are from the lowered operating costs and from debottlenecking the mill. Lowered operating costs are almost solely based on price of natural gas. If recovery boiler is the bottleneck of the mill, then lignin removal also allows further increase of pulp production and brings in quite a lot of new revenue. It seems that taking out lignin to reduce the recovery boiler load does not bring in significant extra revenue because the current price for the sold lignin is rather low.
Lähdeviite
Vakkilainen, Esa and Kivistö, Aija, 2008, Fossil fuel replacement in the pulp mills. Research report EN-35, Lappeenranta University of Technology, Lappeenranta, 49 p. ISBN 978-952-214-623-6.