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 169

From the economic perspectives, there are some limitations that must be resolved for sustain-
able commercialization of transport biofuel polygeneration with black liquor gasification e.g.
incremental biofuel production cost, biofuel distribution cost that is an area of concern especially
for gaseous fuels (e.g. DME, compressed natural gas (CNG), H 2 gas) but less important for liquid
fuels (e.g. methanol, bio-diesel), high cost of fuel-flexible vehicles, high cost of fuel cell vehicles
(e.g. using hydrogen fuel cells). Moreover, the economic risks would be considerable in terms of
poor operational reliability and absence of technical guarantees from technology suppliers.
10.4.2 Performance of BLG-based electricity generation
Black liquor gasification combined cycle (BLGCC) has a net electricity efficiency of 22%, which
means twice the electricity output as compared to a conventional recovery boiler system (Näsholm
and Westermark, 1997). The increased electricity generation is mainly due to efficient energy
utilization of the gas turbine and a large amount of latent heat recovered from the synthesis gas.
Maunsbach et al . (2001) studied the combined cycle with the integration of advanced gas turbines
e.g. evaporative gas turbine (EvGT) (Jonsson and Yan, 2005), steam injected gas turbine (STIG)
and externally fired gas turbine (EFGT) (Eidensten et al ., 1996; Wolf et al. , 2002; Yan et al .,
1995; Yan and Eidensten, 2000). The STIG cycle showed better energy efficiency, cost and load
performance as compared to the combined cycle. For a pulp mill producing 1000 ADt per day
of pulp, the STIG cycle has potential to double 576 kWh/ADt electricity surplus meeting the
internal steam demand of the mill (Maunsbach et al ., 2001). However, the gas turbine without
steam injection results in electricity surplus with reduced steam demand and the EvGT cycle has
high net electricity efficiency.
Based on a reference mill producing 2700 tonnes dry solids of black liquor, a high efficiency
of the BLGCC system can be achieved with a net electricity generation of about 115MW as
compared to about 65MW of electricity generation in the conventional recovery boiler system
(Larson et al ., 2003). The conventional recovery boiler system is required to purchase electricity
from the grid whereas the BLGCC system has potential to export about 14MW of electricity to
the grid. To produce identical process steam in the BLGCC system relative to the recovery boiler
system, additional biomass is required to be combusted in the bark boiler to generate steam to
meet the steam demand of the reference pulp mill. The BLGCC systemwith Chemrec gasification
results in higher lime-kiln load resulting in increased demand for additional fuel for the lime kiln.
For a base capacity of 2000 ADt per day of pulp production, the BLGCC system can export
electricity to the grid generating about 87MW of electricity as compared to about 45MW of
electricity from the recovery boiler system (Andersson and Harvey, 2006). The combined heat and
power (CHP) plant configurations with the recovery boiler systemand the black liquor gasification
system were studied by Eriksson and Harvey (2004). The study showed that the integrated black
liquor gasification CHP units had electrical efficiency between 60% and 70% as compared to the
heat-only powerhouses requiring extra biomass import. Table 10.5 shows combined performance
results from black liquor gasification-based biofuel and electricity polygeneration systems.
10.4.3 Performance of pellet production system
Andersson (2007) conducted a detailed study on the possibilities of integrating pellet production
with the pulp mills. The study evaluated different options to integrate drying and pellet production
with the Ecocyclic pulp mill (KAM) producing 630,000 air-dried tonnes of pulp per year (KAM,
2003). The excess heat from the pulp mill was used to dry the biomass that contributed to an
efficient integrated pellet production and pulp mill. Three technologies for biomass drying were
studied i.e. steam drying, flue gas drying and vacuum drying, based on the energy demand, CO 2
emissions and economics of pellet production. Table 10.6 shows results from drying technologies.
The flue gas dryer using flue gas from the recovery boiler showed better performance than other
dryer options (Andersson, 2007) and about 70,000 tonnes per year of potential pellet production
based on the reference pulp mill capacity at a production cost of about 25 Euro per tonne of