Page 176 - Materials Chemistry, Second Edition

9 Life Cycle Inventory Analysis 161

Appendix: Example of Consequential LCA on Biodiesel
Made from Poultry Fat

To help you get an overview of the 4-step procedure for performing a consequential
LCI (presented in Sect. 9.2.3), an example is here presented, which shows some
parts of a consequential LCI looking at the decision to supply additionally
200 tonnes of biodiesel based on poultry fat. It should be noted that this is a
constructed example and that the factual claims made may not be completely
accurate.
To start the procedure, we go to Step 1. Here we are asked to consider whether
the assessed decision leads to changes in demand or supply. Clearly, this decision
leads to changes in supply. This implies that we move directly to Step 3.
Step 3 is based on the assumption that demand is constant, and given that we
increase supply of poultry fat biodiesel we therefore have to consider what other
products it substitutes. According to the procedure given in Step 3, we need to
identify a user and a satisfying substitute for the user which fulfils the same
functions terms of functionality, technical quality, costs, etc.
Biodiesel is only used by drivers of diesel vehicles and can be blended with
petrochemical diesel or used as a full substitute for petrochemical diesel in ordinary
diesel engines. As it is often sold under favourable tax conditions, it seems rea-
sonable to assume that it will substitute ordinary diesel. However, another scenario
which may also in some cases be realistic to consider is that it will substitute other
types of biodiesel (e.g. based on other substrates). Ordinary diesel and other types
of biodiesel can both be produced without constraints (the answer to the second
question of the decision tree in Fig. 9.5 is ‘no’) and can therefore both be con-
sidered reasonable alternatives. In this example, however, we will only consider the
former.
Having found petrochemical diesel as a substitute, we go to Step 4 to identify
which technology will produce the diesel, which is substituted. Here, we need to
consider the trend in the market, the scope of the decision, and whether the decision
leads to an increase or decrease in demand. Having addressed these issues, we find
that the substituted diesel is produced by the least cost-efficient technology sup-
plying the market at the time of our decision, which we find to be crude oil
produced from tar sand.
Biodiesel does not contain the same amount of energy per weight unit as
ordinary diesel, implying that we will need more biodiesel than diesel to drive a
certain distance. The ratio is around 37:42, implying that for each kg of poultry fat
biodiesel we produce and use extra, we will reduce the production and use of diesel
made from tar sand by 37/42 kg.
The production of biodiesel inevitably leads to the co-production of glycerol.
When we decide to increase the production of biodiesel by 200 tonnes, we will also
increase the production of glycerol by approximately 20 tonne. As this is a result of
our decision to produce more biodiesel, it needs to be included in the assessment.
We therefore start again in Step 1 by asking the question: “What happens if we