Page 145 - Materials Chemistry, Second Edition
P. 145

130                                                     A. Bjørn et al.

              It may also happen that the freed supply resulting from a decreased demand does
            not lead other users to utilise the product. If this is the case, it can be assumed that
            less will be produced of the product, or if the product is a co-product of another and
            more valuable product, and its production therefore bound, it may end up as waste,
            implying that a decrease in the demand for the product will simply imply more
            waste.
              It may seem an enormous task to try to identify whether all the commodities
            included in the life cycle are constrained in their production. However, in practice
            the assumption will often be that a product is constrained if:

            • It is a co-product from a process that has another more valuable product, as it
              will never be the less valuable product that will control the overall output of the
              production (e.g. waste from a slaughterhouse that may be utilised for biodiesel
              production is constrained by the amount of meat produced).
            • Its production is limited by regulation (e.g. regulation may set a limit for the
              overall annual catch of commercial fish species).
            • Its production is limited physically (for example the production of wood on an
              island is restricted by e.g. forest area and a high cost of transportation may mean
              that import is not an economic option).
              Identifying whether a commodity is produced as a less valuable by-product will
            often be quite easy, but the identification of both regulatory and physical constraints
            may be more difficult. It will in many cases require knowledge about the specific
            market in which the change in demand is made, which will often require advice
            from experts. Furthermore, one must know whether the production capacity for the
            product, for which demand is changed, is already filly utilised. Figure 9.4 presents a
            decision tree for dealing with potential market constraints.
              In case of unconstrained markets, go directly to Step 4. Constrained markets
            must in some cases (see Fig. 9.4) be studied in Step 3 first to identify what other
            users prefer as a substitute (in the case of increased demand) or which substitute
            other users stop using (in the case of decreased demand).
            Step 3: Product substitution
              As noted in Step 1 it is commonly assumed in consequential LCA that supply
            follows demand. This implies that if we change supply, we will not change the
            demand but rather affect the competition between suppliers to cover the demand.
            For example, if we reduce the supply of crude oil on the market, it is assumed that
            the crude oil users will attempt to find a substitute for the crude oil, creating a
            demand for other products satisfying the same service as offered by the crude oil.
            The demand for the service that the crude oil is providing is thereby assumed to be
            constant, but there is a change in the way the demand is met.
              Following this assumption about demand driven consumption, changes in how
            the demand is met may arise if the supply of a product is changed, or if we change
            demand for a product whose production is constrained (as explained in Step 2).
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