1. Introduction - Firenze University Press

4. The studied system and input data
The studied system consists of a kraft pulp that is planning to increase its production capacity
and has the possibility to invest in energy efficiency measures that reduce the mill steam
demand. The mill is further described in Section 4.1. The studied system is connected to a
surrounding system in which the imported and exported energy and material streams are
priced and the CO2 emissions associated with the imported and exported energy products are
calculated. Section 4.2 presents the data for the surrounding system (energy market
scenarios). Fig. 1 shows a schematic representation of the studied energy system and the
surrounding system.
Fig. 1.A schematic representation of the studied system and surrounding system. Solid lines
represent flows that are relevant for all studied cases, whereas dotted lines represent possible
flows.
4.1. The studied system
The studied mill is a model mill, developed within the national Swedish research programme
“Future Resource Adapted pulp Mill” (FRAM), representing an average Scandinavian market
kraft pulp mill[20]. Table 1 presents an overview of key mill data. Axelsson et al. [11]have
shown that the mill can achieve a steam surplus through investments in process integration
and new efficient equipment, hereafter denoted energy efficiency measures. The energy
efficiency measures in which the studied mill can invest in order to achieve the steam surplus
are described in e.g. [6, 18]. The steam savings of MP and LP steam are approximately
0-20 % and 35-50 % respectively (depending on which energy efficiency measures are
chosen) at a total cost of approximately 10-17 MEUR.
In this study, the mill is assumed to increase its production by 25% (typical number used in
other studies, e.g. Axelsson et al. [16]) to 1250 ADt/d. The use of steam, electricity and oil is
assumed to increase in direct proportion to the production. It is assumed that the recovery
boiler is the bottleneck and to handle the increased amount of black liquor, the mill has to
invest in either a black liquor gasifier (connected to a DME plant or a gas turbine combined
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