Appendix - Ecoprofile methodology (cont'd)

A13. Presentation of results

A13.1. Data categories

All data, with the exception of raw materials requirements have been categorised by the type of operation that gives rise to them. The five categories that have been identified are:

1. Fuel production
2. Fuel use
3. Process
4. Transport
5. Biomass

Although identifying the categories is relatively straightforward, assigning individual data to them can give rise to some problems. For example, transport is used to deliver coal from the coal mine to the power station where it is used to generate electricity. The problem, therefore, that arises is whether this transport operation should be treated as a separate transport operation or whether it should be treated as part of the inputs and outputs of electricity generation; i.e. fuel production. Furthermore, steel is used to construct the vehicle used to transport coal to the power station. Should the inputs and outputs associated with steel production be assigned as process requirements, or transport requirements or fuel production requirements?

There is no simple, unambiguous way of deciding between the different assignment options and so a protocol has been defined and followed in all of the calculations.

Biomass refers to the inputs and outputs associated with the use of biological materials such as wood. The reason for isolating this as a separate category is that such materials absorb carbon dioxide while growing and, given the current interest in CO₂ as a greenhouse gas, there is good reason to hold this parameter separate from the other emissions. Thus biomass CO₂, whether as a negative quantity during tree or plant growth or as a positive quantity if the wood products are eventually burned, is always identified as such. Similarly, biomass fuels are kept as a category separate from other fuels.

Transport operations are easily identified and so the direct energy consumption of transport and its associated emissions are always separated. Thus, in the above example concerning the delivery of coal to a power station, the transport element would separately identified and would not be included as part of the fuel production data. Similarly, any materials inputs to transport operations are also treated as part of the transport operation. Thus the burdens associated with the production of the steel used in vehicle construction would be treated as part of the transport operation.

Fuel production operations are defined as those processing operations which result in the delivery of fuel, or energy, to a final consumer whether domestic or industrial. For such operations all inputs, with the sole exception of transport, are included as part of the fuel production function. So, for example, the burdens associated with the production of the coal used in a power station, any steel used in power station construction, etc., would all be assigned to fuel production.

Fuel use is defined as the use of energy delivered by the fuel producing industries. Thus fuel used to generate steam at a production plant and electricity used in electrolysis would be treated as fuel use operations. Only the fuel used in transport is kept separate.

When all of the above components of the inputs and outputs have been separated from the total inputs and outputs, the residue is assigned to the process.

A13.2. Energy data

The results are presented in two distinct formats. First, the gross or cumulative energy requirements are given as a single table similar to Table 7. These energy requirements refer to the total energy consumption when the production processes are traced back through all operations to the extraction of raw materials from the earth. Masses of fuels have all been converted to energy units using the gross calorific values.

Table 7
Format for presenting energy in terms of the fuel producing industries.

Within the table, the overall energy requirements are analyzed into a number of groups. First, there is a breakdown by fuel producing industry. The electricity supply industry is separately identified because, of all fuel supply industries, the electricity industry exhibits the lowest production efficiency. The oil industry is also separately identified, because, although oil fuels are consumed in a variety of different forms, they are all derived from a common source, crude oil, and they all exhibit approximately the same production efficiency. Finally all of the remaining fuels are grouped under the heading of Other fuels. This group contains coal, coke, gas and any biological fuels. This group also contains entries for any energy recovered as steam or condensate as well as any energy arising from sulphur burning in the production of sulphuric acid. In this report, the main contribution to the Other fuels group is natural gas.

Each of the fuel producing industry contributions is further sub-divided into delivered energy(fuel use), feedstock energy, transport and production & delivery energy.

The delivered energy represents the energy that is received by the final operator who consumes energy. This is independent of country and is directly related to the technology that is used in the various processing operations because this governs the demand for energy. This group also contains any entries that arise as a result of the recovery of energy as steam or condensate because this recovered energy will be used by other processes and so appears as a negative entry (credit) in the energy table.

Feedstock energy represents the energy of the fuel bearing materials that are taken into the system but used as materials rather than fuels. The quantities of hydrocarbon feedstocks that are taken into the system are represented in terms of their gross calorific value because frequently, in the course of processing, some, if not all, of this feedstock may be converted to a fuel. It is a simple matter to convert from feedstock energy to mass if the calorific value is known since the energy content of a feedstock is simply the product (calorific value ( mass). Typical values of calorific values are shown in Table A8 however, in the calculations actual values for specific feedstocks have been used and, for some materials, there can be a large spread of values. It is also important to remember that feedstock energy is not equal to the calorific value of the output products because of materials losses and changes in chemical composition during processing.

Transport energy refers to the energy associated with fuels consumed directly by the transport operations as well as any energy associated with the production of non-fuel bearing materials, such as steel, that are taken into the transport process.

Production and delivery energy represents the energy that is used by the fuel producing industries in extracting the primary fuel from the earth, processing it and delivering it to the ultimate consumer. This will also include the energy associated with the production of any non-fuel materials (such as steel) that are taken into the fuel production process.

Table 8
Conversion factors for various feedstocks.

sequence is evaluated separately and the final result is calculated as the average of the results from the individual production sequences weighted by the output from each production sequence. Averages can be produced for intermediate production steps as shown but these intermediate averages do not affect the final result.

The second method, sometimes referred to as horizontal averaging, is illustrated in Figure 9. In this method, an average is produced for each intermediate step and this average is then used in all of the production sequences to calculate the next step down-stream. The procedure is repeated for the full length of the sequence as shown.

When the performance characteristics of the intermediate steps are similar in all of the production sequences, the results produced by the two methods are expected to be very close to each other. However, when there is a significant divergence in performance characteristics, the average values can be significantly different and these differences can be amplified if the production levels in the different sequences are markedly different.

In the present report, the vertical method of averaging has been used wherever applicable since this most closely approximates to actual practice. It possesses the additional advantage of allowing individual companies to see the precise performance of their own operations; with the horizontal method of averaging, this is not possible because each average involves practices which reflect the behaviour of other companies.

It is perhaps worth noting that the need to choose between these two methods of averaging has only occurred recently. When information about processes was scarce, data were often only available from a single site and this information was usually used in all applications. Thus for many years information on the production of ethylene was based on information from one or two plants. In practice however, there are almost 100 plants in Europe alone and all of these plants do not feed all processes using ethylene. It therefore becomes important to identify, as far as possible, the site specific data for each production sequence, if the results are to be representative of actual practice.

* In practice values vary widely depending on composition.
The values quoted here should be used as a guide only.

The importance of this breakdown is that Delivered energy and Feedstock energy (shown shaded in Table 7) are dependent on the technology used by the process operators. In contrast, the Production and delivery energy depends upon the country in which the processes are carried out. For example, the delivery of one unit of electrical energy in the United Kingdom requires the electricity producers to take in a total of almost 4 units of energy. In contrast, the consumption of 1 unit of electricity in Norway would require the electricity producing industry to take in only about 1.4 units of energy because of the different generating methods and mix of primary fuels. If therefore the aim is to compare technologies or plants that are using the same technology, then the country dependent data can be stripped out of the results by omitting the production and delivery energy column.

Similarly, transport depends on the relative locations of the suppliers to a plant and this again is something over which the process operator usually has little control. Therefore this element of energy needs to be stripped out of the results when attempting to compare technologies.

The second format for presenting energy data is in terms of the primary fuel and feedstock inputs as shown in Table 9. Unlike Table 7 which referred to the fuel producing industries, Table 9 refers to the primary fuels actually extracted from the earth. Strictly the entries for nuclear, hydro, hydrogen and recovered energy are not 'primary' energy sources but are included in the table to obtain and energy balance and to show their relative importance.

Table 9
Fuel/energy inputs referred to primary fuels.

In the input-output tables, energy requirements are analyzed in terms of primary fuels that are extracted from the earth; the headings coal, oil, gas, etc. do not refer to the coal industry, the oil industry, etc. but to the quantities of coal, oil and gas, etc. that are removed from the earth. Recovered energy from steam and condensate recovery processes are entered into these tables as a separate entry. Similarly, any energy recovered from sulphur burning is also entered in the fuel table. As in the case of the energy table, the primary fuels are kept separate from the feedstocks. It should be noted that the feedstock quantities in both representations are the same. Similarly the raw materials sector of the table refers to the primary raw materials that are extracted from the earth.

A13.3. Emission data

The emission data refer again to the cumulative totals arising when all operations are traced back to the extraction of raw materials from the earth. The emissions recorded, refer to those remaining after any on-site treatment and so do not necessarily reflect the output of the production sequence to the on-site air or water treatment facilities. These are categorised as fuel production, fuel use, transport, process and biomass as described earlier.

A13.4. Raw materials inputs

Raw materials inputs are simply the sum of all of the materials that are extracted from the earth. There is however one exception. Sulphuric acid is manufactured from both elemental sulphur and from sulphur dioxide recovered from oil refining and metallurgical processes. These different sources of sulphur are entered separately in the raw materials table.