Bioenergy polygeneration, carbon capture and storage related to the pulp and paper industry and power plants - Biomass as Energy Source: Resources, Systems and Applications - page 166

• Vacuum dryer : the vacuum drying technology requires sub-atmospheric pressure to lower the
boiling temperature of the moisture in the biomass. The moisture is evaporated using hot water
at a temperature of 90 ◦ C (Andersson et al ., 2006).
• Flue-gas dryer : the biomass is circulated in a pneumatic dryer with the flue gas from the
recovery boiler at 160 ◦ C and the moisture is removed with the flue gas leaving the dryer
(Andersson et al ., 2006).
10.4 PERFORMANCE AND SUSTAINABILITY ANALYSIS
The performance analysis presents the objective to integrate bioenergy polygeneration systems
with the pulp industry and to produce bioenergy products in relation with technological limitations
that hinder sustainable commercialization of bioenergy polygeneration. Since a modern pulp mill
has an excess of internal biomass, additional advantages can be achieved with electricity, biofuel
or pellet production with enhanced energy efficiency as a step towards sustainable development.
The integrated bioenergy systems offer significant improvements in the energy efficiency of the
pulp mill as compared to the conventional recovery boiler system.
In this chapter, we have discussed performance of bioenergy systems integrated with the
pulp industry and specific sustainability aspects to analyze, share and compare information
based on technical, economic and environmental perspectives. The environmental performance
of bioenergy polygeneration is presented together with potential of CO 2 reductions and CCS
opportunities as a separate section.
10.4.1 Performance of BLG-based biofuel production
A number of black liquor gasification technologies are available to produce variety of biofuels
e.g. dry black liquor gasification with direct causticization (DBLG) (Dahlquist and Jones, 2005),
Chemrec black liquor gasification (CBLG) (Berglin et al ., 2002; Ekbom et al ., 2005), catalytic
hydrothermal gasification (CHG) (Naqvi et al ., 2010a; Sricharoenchaikul, 2009), etc. The per-
formance of pulp mill integrated bioenergy systems can be evaluated as the energy ratio of the
system which is defined as the sum of mill process steam, net electricity import or export, and
biofuel production divided by the sum of energy inputs i.e. black liquor, biomass to the power
boiler, and biomass to the lime kiln. In recent studies, Naqvi et al . compared and evaluated the
energy conversion performance of different black liquor gasification systems for various biofuel
polygeneration alternatives based on system performance indicators (Naqvi et al ., 2010a, 2012a,
2012b, 2012c). Based on a reference pulp mill capacity of 1000 air dried tonnes per day (ADt) of
pulp production, the study showed better performance results of synthetic natural gas (SNG) pro-
duction from the dry black liquor gasification (DBLG) system as compared to other gasification
systems due to highest energy ratio and biomass-to-biofuel conversion efficiency. The Chemrec
gasification system to produce methanol and dimethyl ether (DME) showed competitive results
with substantial biofuel production. Table 10.2 shows energy efficiencies of different biofuel
options compared with the recovery boiler.
Ekbom et al . (2003) presented a study on black liquor gasification-based motor fuel production
(BLGMF) to investigate the integration of biorefinery systems in terms of technical and economic
feasibility. The energy withdrawn from black liquor to biofuel is compensated by additional
biomass import. Based on 2000 ADt per day of pulp production, about 1183 tonnes per day
(273MW) of methanol and about 824 tonnes per day (275MW) of DME could be produced
with an additional biomass import (414MW) resulting in 66% biomass-to-biofuel conversion
efficiency (Ekbom et al ., 2003). The identical pulp mill could produce 188 tonnes per day of
hydrogen fuel equivalent to 261MW (Andersson and Harvey, 2006). There is a large potential
of motor fuel production as a replacement for fossil fuels especially in countries with a large
pulp industry e.g. Sweden and Finland. Black liquor production in the pulp industry located in
Sweden, Europe, and world is substantial and is estimated about 47TWh, 184TWh, and 733TWh