Appendix - Ecoprofile methodology (cont'd)

A8. The fuel producing industries

Fuels can be divided into two groups; primary and secondary. Primary fuels are those materials, such as oil, coal and gas, which are extracted from the earth and which liberate energy when burned. Secondary fuels are those, such as electricity, coke and manufactured gas, which are produced from primary fuels. The fuel producing industries, which produce both primary and secondary fuels in a form suitable for the ultimate consumer, are little different to any other manufacturing operation; instead of processing materials they process energy. Because energy can be measured in a common unit (the joule) individual fuel production industries are often represented as a single system with their performance being described as an overall energy production efficiency, where

The energy production efficiency of a secondary fuel will always be lower than that of the primary fuel from which it was produced because of losses during the transformation. It is important to recognize, however, that fuel production efficiencies will vary from one country to another. For fossil fuels, these variations tend to be small and are often due to different transport distances but for electricity production, the variations can be very large because of the different mix of fuel types used in its production. Table 2 shows the proportions of the different primary fuels used in electricity production in a number of European countries and gives the values calculated for the overall efficiency of electricity production and delivery, including transmission losses.

The overall efficiency of the electricity supply in any country depends not only on the mix of fuels but also on a number of other factors such as own-use by the electricity producers, transmission/distribution losses and imports from neighbouring countries. The overall efficiencies for the various European countries are given in Table 3.

Table 2.
Percentage of gross electricity generated from different fuels in 1993 in different European countries. ⁹

Table 3.
Overall efficiency of electricity supply in various European countries when all factors are taken into account.

A9. Describing the performance of a system

The performance of a system is described by quantifying the inputs and outputs identified in the simple system diagram of Figure 5. In practice, waste heat is seldom, if ever, measured directly. It can, however, be estimated from the input energy, since, with one exception, all of the energy input will appear as waste heat. The one exception is when a chemical change occurs during processing so that energy is either absorbed or liberated. Usually, however, the reaction energy change is small compared with the total process energy and so seldom invalidates this method of assessing waste heat.

The calculation of input energy and raw materials indicates the demand for primary inputs to the system and these parameters are important in conservation arguments because they are a measure of the resources that must be extracted from the earth in order to support the system. Calculation of the outputs is an indication of the potential pollution effects of the system. Note that the analysis is concerned with quantifying the emissions; it does not make any judgments about deleterious or beneficial properties. Because the inputs and outputs depend upon the definition of the system, any changes to any of the components of the system means that all of the inputs and outputs will change because they are interrelated. One common misconception is that it is possible to change a single input or output while leaving all of the other parameters unchanged. In fact, the reverse is true; because a new system has been defined by changing one input or output, all of the inputs and outputs are expected to change. If they happen to remain the same, it is a coincidence.

The magnitude of the inputs and outputs in any time period will obviously depend upon the throughput of materials and this dependence is usually eliminated by normalizing the inputs and outputs with respect to some measure of the flow. For a true LCI, where there are no usable or saleable products from the system, the system parameters are usually normalized with respect to some internal flow - usually the quantity of product passing through the consumer. For sub-systems which correspond to unit industrial operations, there is normally a usable or saleable product and normalization is usually carried out with respect to the mass of this output. Thus if the total energy input E produces a mass P of saleable product, the normalized energy per unit output is E/P. Similarly, if the total air emission is A for a saleable production P then the normalized air emission is A/P. Any quantity related to throughput can be used as a normalizing parameter although for most materials processing operations, mass of saleable product is usually the most convenient. In the fuel producing industries however, energy output may be more appropriate.

⁹ International Energy Agency. Electricity Information 1994. OECD/IEA, Paris. 1995.