Page 140 - Materials Chemistry, Second Edition

9 Life Cycle Inventory Analysis 125

The economic value approach is recommended as a last resort and is generally
easy to carry out due to the abundance of price data on goods and services. Prices
may be obtained by contacting the company running the multifunctional process in
question or from the stock exchange in case of global markets, e.g. for some metals.
For some co-products there may not be a market because they need to go through
additional processing before they are sold. In that case, the LCA practitioner should
calculate a shadow price. For example, straw, a co-product of wheat production,
needs to be baled before it is sold, and the economic value of baled straw must
therefore be subtracted the cost to the farmer of baling the straw to calculate the
shadow price of the unbaled straw leaving the multifunctional process of wheat
production. Note that the prices of most goods and services are volatile to varying
degrees. It is therefore recommended to calculate average values for the time period
that is relevant to the temporal scope of the study (see Sect. 8.7.2). Once the
economic values have been determined, allocation factors are calculated in the same
way as the above generic example for the representative physical parameter
approach.
It should be noted that although allocation by economic value is the last resort
according to ISO, it is widely used in practice. This is because the other solutions to
the handling of multifunctional processes are often not possible due to the nature of
the multifunctional process or due to lack of the required information and data to
identify the relevant process for a system expansion or to determine a causal
physical relationship, or a common representative physical parameter. By contrast,
the price data needed to carry out economic allocation is generally available. For
this reason, economic allocation is done by some LCA researchers recommended as
a default solution to multifunctionality, e.g. by the Dutch CML Guideline (Guinée
et al. 2002), and the LCI database ecoinvent comes in a version where allocation by
economic value is systematically applied to all multifunctional processes (see
Sect. 9.3.2 below).

9.2.3 Consequential Modelling

In most cases, a consequential LCI will include other processes than an attributional
LCI for the same product system. The attributional LCI includes the processes
which the assessed product ‘sees’ from its journey from the cradle to the grave. If,
for example, the assessed product is a plastic cup, the start of the journey will be
some extracted crude oil, which through a sequence of production processes will be
processed into plastic. This will then be transported to the shop, be bought by a
user, who will use it once and then discard it, after which it will be transported to,
say, an incinerator and burned. In the attributional LCI, each of these processes: the
production of crude oil, the conversion into plastic, the transport and incineration
will be included.
The consequential LCI is different; the goal of the assessment is to identify the
environmental impacts caused by a decision, for example the decision to buy a