1. Introduction - Firenze University Press

Table 2. Presentation of the different possible outcomes (cases) including case code, case
description and references.
Case code Case description Key data
from
Black liquor gasification
Lignin extraction
Recovery boiler
upgrade
BLGMF 70% of the BL to the BLGMF/DME plant. [21]
BLGMF:CCS 70% of the BL to the BLGMF/DME plant. The
removed CO2 (part of the BLGMF process) is
compressed and sent for storage. If profitable, a part
of the CO2 from the recovery boiler (and bark boiler)
flue gases can also be captured by absorption.
BLGCC 70% of the BL to the BLGCC plant. Possible
investment in a new back-pressure steam turbine
and/or a condensing steam turbine.
BLGCC:CCS 70% of the BL to the BLGCC plant. Possible
investment in a new back-pressure steam turbine
and/or a condensing steam turbine. The BLGCC
plant is modified to include CO2 capture (different
gas cleaning including a water gas shift reactor). If
profitable, a part of the CO2 from the recovery boiler
(and bark boiler) flue gases can also be captured by
absorption.
Lignin:Wood
fuel
Lignin is extracted from the black liquor, which leads
to a decrease of the energy content in the BL to the
RB (max 53%). The lignin is sold as fuel priced as
wood chips.
Lignin:Oil Lignin is extracted from the black liquor, which leads
to a decrease of the energy content in the BL to the
RB (max 53%). The lignin is sold as fuel or
feedstock priced as fuel oil.
RBU:Electricity The RB is upgraded so it can handle the total amount
of BL, 125%. Investment in a new back-pressure
steam turbine and a condensing steam turbine.
RBU:CCS The RB is upgraded so it can handle the total amount
of BL, 125%. Investment in a CO2 capture plant
connected to the recovery boiler flue gases and a new
back-pressure steam turbine.
275
[21], own
calculations
[22, 23]
[21-23],
own
calculations
For all cases, there is also a possibility to invest in heat exchangers and/or heat pumps for
district heating production (DH). It is assumed to be possible to deliver between 10 and
50 MW of district heating depending on season 1 . The falling bark can be fired in an existing
bark boiler and/or be sold. The possibility to import external wood fuel is not considered; the
steam use has to be met by internal resources. Thus, this study shows what can be done at a
kraft pulp mill without importing external biomass, something that could be of interest in the
future when the supply of biomass may be low due to its limited availability.
For technical reasons, the minimum load of the recovery boiler is set to 55% of the maximum
load. For both of the cases with black liquor gasification, the mill’s steam balance is not the
1 The district heating demand that can be supplied with mill excess heat varies according to a duration heat
load curve with a top load of 50 MW.
[8]
[8]
[16]
[24]