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 164

Table 10.1. Elemental composition black liquor solids (BLS) (Source: KAM report, 2003).

Component [%Mass]

Composition Carbon C 35.7

Oxygen O 35.8

Hydrogen H 3.7

Sulfur S 4.4

Sodium Na 19.0

Potassium K 1.1

Chlorine Cl 0.3

Nitrogen N < 0.1

Black liquor solids (BLS) [%Mass] 80

Higher heating value (HHV) [MJ/kg] 14.5

Lower heating value (LHV) [MJ/kg] 12.3

gas is further processed to bioenergy products e.g. synthetic natural gas (SNG), methanol (MeOH),
dimethylether (DME), hydrogen, FT-liquids etc.
However, there will be an energy deficit in terms of electricity and steam demand in the pulp
mill with biofuel production that shall be compensated by using a biomass-fuelled power boiler.
The synthesis gas obtained in the gasification process requires cleaning from particulates, tars
and sulfur components before it can be converted to biofuels. There is no commercial biofuel
production from black liquor gasification today but the development and interest in producing
transport biofuels has been rising over the last couple of decades. The efficient production
of transport biofuels can be achieved by integrating biorefinery systems at the pulp mills,
co-production pulp together with transport biofuels.

10.2.2 Black liquor gasification-based power generation
Black liquor gasification combined cycle (BLGCC) is another alternative of bioenergy polygen-
eration in the pulp industry achieving higher system energy efficiency with electricity generation
than conventional recovery boiler technology (Larson et al ., 2003). The synthesis gas obtained in
black liquor gasification has similar composition to the synthesis gas obtained from coal-based
gasification and the electricity is generated from the gas turbine fired with the synthesis gas.
The heat recovery steam generator (HRSG) is used to produce high-, medium- and low-pressure
steam by cooling flue gas from the gas turbine.
Figure 10.4 presents a simplified design of a black liquor gasification combined cycle (BLGCC)
system. The BLGCC configuration requires existing falling bark and extra biomass to be com-
busted in the power boiler to generate more high-pressure steam since the high-pressure steam
generated in the HRSG is not sufficient. High-pressure steam from the HRSG and the power
boiler is used in a backpressure steam turbine to generate electricity. The amount of electricity
is increased with pressurized high temperature black liquor gasification and a gas-turbine based
cogeneration system.

10.3 BIOFUEL UPGRADINGWITH PELLET PRODUCTION

Another salient approach is upgrading biomass to a higher energy density fuel like pellet pro-
duction. There is a potential for pellet production in bioenergy systems integrated with the pulp
mills that could be used to replace fossil fuels in the combined heat and power (CHP) plants.
In Sweden, there has been a 300% increase in use of pellets from 1997 to 2005, mainly due to tax-
driven changes in the Swedish energy system (Andersson, 2007). The low quality excess process