Page 107 - Materials Chemistry, Second Edition

92 A. Bjørn et al.

(a) Alternative
Combined
heat and Power plant 2 production of
power plant 1 district
heating

1 GWh 1.5 GWh 1 GWh 1.5 GWh
electricity heat electricity heat

(b)
Combined Alternative
heat and production of Power plant 2
power plant 1 district heating

1 GWh 1.5 GWh 1.5 GWh 1 GWh
electricity heat heat electricity

Fig. 8.7 Equivalent modelling approach when dealing with multifunctionality. a System
expansion: to ensure equal functionality system 2 is expanded to include the secondary function
of system 1. b Crediting: system 1 is credited for the production of the secondary function, in order
to have equal functionality of system 2

crediting the milk for the avoided impacts from alternative production of beef and
other co-products. This alternative production might be the raising of cattle in a
pure beef production system (which includes hides and other low-value
co-products). Note that quality differences between dairy cow meat and cattle
meat means that they may not be functionally equivalent. This may require the
application of a value correction factor to the crediting.
An important task in system expansion is to identify the process (or combination
of processes) which is superseded by the co-product. This relates to the decision
context (Situation A, B or C1/C2) identified in the goal definition (Sect. 7.4) and
will be dealt with in Sect. 8.5.3.
Allocation
Sometimes it is not feasible to obtain complete functional equivalency between the
compared systems or to isolate the primary function of a process from the sec-
ondary functions through system expansion. This may be the case when there is no
alternative way to produce the secondary functions. A classic example of such a
multi-output process is a petrochemical refinery with a variety of different organic
substances as output without any mainstream alternative routes of production for
these. It may also be the case when the most likely alternative route also has
secondary functions, creating the need for further system expansion introducing
alternative routes for the new level of secondary functions, which again may have
secondary functions, creating the need for further system expansion and so on. In
the milk example, the alternative production of meat from raising of cattle for
example leads to the co-production of horn (for example used in jewellery