3.1 Basics 3.1.1
Scientific Principles
The revised ISO standard 14040:20061) defines ‘life cycle inventory LCI’ analy- sis – as a
phase of life cycle assessment involving the compilation and quantification of inputs and outputs for a product throughout its entire life cycle.
LCI is a material and an energy analysis based on a simplified (linear) systems analysis, whereby loops can only be solved approximately by iteration. Calculation procedures based on matrix inversion can also assess loops.2)However, calculation procedures most frequently used so far are based on spread-sheet analysis to be found in software programmes of the type ‘Microsoft Excel’.
A figurative presentation of the product system is the ‘product tree’ consisting of process units. The product tree should have been developed, at least roughly, in the first phase of life cycle assessment (LCA), the ‘Goal and scope Definition’
(Chapter 2), and has now to be refined. Software packages3)for conducting LCAs help to elaborate the system flow charts.
LCI in its scientific part – by and large – is based on the following laws of nature:
1. Conservation of mass.
2. Conservation of energy (first principle of thermodynamics)
The following applies for the conversion of thermal energy into other forms of energy – part of almost all LCAs – as well as to chemical thermodynamics.
1) ISO (2006a Section 3.3).
2) Heijungs and Suh (2002, 2006).
3) For example, Gabi (PE-International), www.gabi-software.com; SimaPro (Pr´e Consultants) www.pre.nl/software.htm; TEAM (Ecobilan), www.ecobalance.com/fr˙team.php; Umberto (ifu), www.umberto.de. Pionier-Software programs see Vigon (1996), Rice, Clift and Burns (1997) and Siegenthaler, Linder and Pagliari (1997).
Life Cycle Assessment (LCA): A Guide to Best Practice,First Edition.
Walter Kl¨opffer and Birgit Grahl.
c 2014 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2014 by Wiley-VCH Verlag GmbH & Co. KGaA.
3. Increase of entropy (second principle of thermodynamics)
Relevant for the explicit examination of chemical reactions (very frequent in LCI analyses, among others for the production and transformation of chemicals and, for example, the determination of CO2loads by incineration of fossil fuels) 4. Principles of stoichiometry (basis for all chemical reactions)
Transitions of mass into energy and vice versa are only relevant in nuclear reactions, thus providing an exception to the first and second principle.
5. E=m c2(equivalence of mass (m) and energy (E) according to Einstein).4) These principles (1–5) belong to the scientifically best proved laws and thus provide a solid framework for processes analysed within LCIs.5)
These principles can be used as estimations for what quantity of a product can maximally be formed, how much energy can maximally be released or is necessary as aminimumamount for a chemical reaction to occur, how much usable (‘free’) energy can be produced from combustion heat, and so on. Technically attainable yields, efficiencies, and so on, are usually lower than those theoretically predicted, never higher. In the praxis of LCI this means that in the absence of specific, that is, measured data, respective estimations6) can also be made by the use of technical handbooks and manuals or by technical information from the Internet.7) This is often suited for the estimation of main flows (mass, energy) but fails, however, with trace emissions, which often stem from uncontrolled side reactions.
The database in the centre of the inventory with the most important mass and energy flows is usually much more extensive than the data converted into impact categories (classification) in life cycle impact assessment (LCIA, see Section 3.7 and Chapter 4).
The laws of conservation of mass and energy can be used for a strict balance8) (input=output), which, however, most LCAs do not use; for example, oxygen as a seemingly inexhaustible resource on the input side is mostly not assessed and waste heat on the output side is practically not quantitatively recorded.
3.1.2
Literature on Fundamentals of the Inventory Analysis
Fundamentals of a method are often better described in older texts than in newer ones, where much is already assumed to be known. Classical descriptions of LCA have been given by, for example, William Franklin, Robert Hunt and co-workers,9) 4) The use of Einstein’s equation in LCA as a basis for an estimation of energy equivalence has also
been discussed (Heijungs and Frischknecht, 1998).
5) Hunt, Sellers and Franklin (1992) and Hau, Yi and Bakshi (2007).
6) Boustead and Hancock (1979).
7) Greatest care is to be taken to ensure legitimacy of data.
8) Ecobalance (in German ‘‘ ¨Okobilanz’’ is still the correct translation of LCA) was used prior to the term life cycle assessment. It is derived from the Italian expression bilancio; a reference to economical balance is straightforward.
9) Huntet al. (1992), Janzen (1995) and Boguskiet al. (1996).
James Fava and co-workers,10)and Ian Boustead.11)In a more recent text, Fleischer and Hake12) discuss LCIs in detail. The international standard dealing with LCI has been, from 1998 to 2006, ISO 1404113); since October 2006 LCI has become part of ISO 14044.14) Regional guidelines and standards have been elaborated in Scandinavia, in the USA, France,15) and Canada.16) Scandinavian guidelines are documented in the ‘Nordic Guidelines on Life Cycle Assessment’17) and have been further elaborated in the Danish EDIP programme (Environmen- tal Design of Industrial Products).18) US-EPA has commissioned guidelines for the conduct of LCAs by the Battelle Memorial Institute and by Franklin Asso- ciates.19)A newer publication is available from the European Joint Research Centre (JRC).20)
In German-speaking countries, the Swiss publications of BUWAL21) have for long almost been standard, in particular for Inventory Analysis and its relevant data. The original, German version of the monograph and textbook ‘ ¨Okobilanz (LCA)’22)contains some official variants of LCA, which are typical for Germany.
3.1.3
The Unit Process as the Smallest Cell of LCI 3.1.3.1 Integration into the System Flow Chart
A system flow chart as a diagram of the examined product system consists of small boxes where the processes involved are specified and their mutual dependencies are indicated by one- or two-sided arrows (Figure 3.1).
As long as a linear approximation is adequate, branching will occur at some boxes (see Section 3.1.4) but there will be no formation of networks. The small boxes (1, 2, 3, 4… n,m), which can, for instance, designate production or processing steps of a product, are calledunit processes.
According to ISO 14040, these are the smallest elements considered in LCI for which input and output data are quantified (Figure 3.2). With large data resolution the unit process can correspond to a printing process, a transportation procedure, a metal deformation, a filling, a cleansing, a single chemical reaction, and so on; if less data are available (or for small data resolution), these can refer to a plant or to a side chain, for example, ‘production of electricity’ (see Section 3.4.3).
10) SETAC (1991).
11) Boustead and Hancock (1979) and Boustead (1992, 1995b).
12) Fleischer and Hake (2002).
13) International Standard Organization (ISO) (1998a).
14) International Standard Organization (ISO) (1998a) and ISO (2006b).
15) Association Franc¸aise de Normalisation (AFNOR) (1994).
16) Canadian Standards Association (CSA), 1992.
17) Lindforset al. (1994a,b, 1995).
18) Wenzel, Hauschild and Alting (1997) and Hauschild and Wenzel (1998).
19) EPA, 1993; EPA, 2006; see also EPA’s LCA Web site:www.lcacenter.org/InLCA.
20) http://lct.jrc.ec.europa.eu/pdf-directory/ILCD-Handbook-General-guide-for-LCA-DETAIL-online- 12March2010.pdf, pp. 70–87.
21) BUWAL (1991) and BUWAL (1996, 1998).
22) Kl¨opffer and Grahl (2009).
Unit process 2 Unit process 3 Unit process n
Unit process 4 Unit process m Unit process 1
Figure 3.1 Linear section of a system flow chart.
Inputs
Outputs Energy
(thermal, electrical)
Other inputs
(water, air area) Ancillary material
Raw material pre-product
Material product
Waste heat Emissions into Air Water Soil
Waste water exhaust air Unit process n
Figure 3.2 Schematic illustration of a unit process (without co-products).
As unit processes are also used for data organisation, they are referred to as data collection template.23) For reasons of transparency and data quality, the unit processes should map accurately defined and specific processes. Any time, and if necessary, these unit processes can be aggregated into larger units and be successively averaged; however, not vice versa.
Another problem arises if unit processes are too large because necessary attri- butions will cause problems, for example, the distribution of the total electricity consumption of a plant and the attribution to a single product analysed. It is, however, easier to obtain data for a complete manufacturing plant (especially for emissions) than for a single process. Site-specific data may be available, for 23) Boguskiet al. (1996).
instance, via an operational input–output analysis of a factory in the context of an environmental management system (see Section 1.1.5). In general, however, a factory producesseveralproducts; inputs and outputs need to be attributed to these products according to defined rules. For data acquisition in a factory in line with the processes leading to a specific product, assignment is unnecessary because the data are already available. This procedure is recommended by ISO but requires much more data collection work.
Data acquisition is one of the most complex phases of LCA (see the Pellston Workshop on Global Guidance Principles for LCA Databases24)), especially when site-specific upstream and downstream data are required.
3.1.3.2 Balancing
Theoretically, a complete energy and mass assessment (input and output) should be conducted for every unit process. In praxis this often fails due to the inadequacy of the data: Usually the waste heat is not measured, the waste water output is set equal to the fresh water input, the greenhouse gas CO2 formed during combustion is usually not measured but calculated assuming an approximate stoichiometry, for example, for long-chain aliphatic hydrocarbons. In the simplest case, the combustion of methane (main part of natural gas), Equation 3.1a is valid:
CH4+2O2→CO2+2H2O (3.1a)
For petrol, for example, Equation 3.1b is valid on the simplified assumption that it contains pure Octane.25)
2C8H18+25O2→16CO2+18H2O (3.1b)
According to this equation, the combustion of 1 l petrol (average density 740 g l−1) results in the release of 2.28 kg CO2.
The principle conservation of mass cannot be applied in such cases as its validity is a prerequisite of the equation. If the empirical basis of the chemical equation is known, calculations as quoted are very precise. This, for instance, applies for the formation of sulphur dioxide from the sulphur content of fuels, as it can very securely be presumed that, via combustion, one molecule of SO2is formed from every single sulphur atom (Equation 3.1c).
S+O2→SO2 (3.1c)
24) Sonnemann and Vigon (2011).
25) Falbe and Reglitz (1995, p. 351).
Exercise: Sample case for a calculation of CO2-emissions
An energy concern supplies natural gas to its customers (original data).
The following figures are known (even though the unit kilowatt hour should only be used for electricity, it is also applied in technical contexts, as in this case, to indicate low and high heat values):
Natural gas component
Average fraction
Unit
Methane CH4 87.535 mol%
Ethane C2H6 5.545 mol%
Propane C3H8 2.000 mol%
i-Butane C4H10 0.248 mol%
n-Butane C4H10 0.351 mol%
i-Pentane C5H12 0.056 mol%
n-Pentane C5H12 0.004 mol%
Nitrogen N2 3.260 mol%
Carbon dioxide CO2 0.960 mol%
Other data Average value Unit
High heat value 11.580 kWh m−3
Low heat value 10.457 kWh m−3
Density 0.821 kg m−3
Calculate the CO2 emissions in g MJ−1 that are released due to the incineration of the natural gas. Use the low heat value. Energy expenditure for extraction and transport of the natural gas to the customer (upstream) is not considered here.
If detailed data procurement is possible, it should be made. As for data procured in the factory, the primary data (sometimes calledforeground data26)) can be combined with an operational input–output analysis or be taken from it as the same data are required at the process level. An operational input–output analysis,27)however, does not require an allocation of inventory parameters to particular products.
Besides, it should be considered that many unit processes do not refer to industrial products as such, but to agri- or silvicultural processes or to those of disposal or to those of use/consumption of a product. The latter depend on consumers’ attitudes and behaviours in daily life, which is a field that has rarely been investigated quantitatively.
26) According to our knowledge, a distinction between foreground and background data was first made in a SETAC Europe Working Group on Life Cycle Inventory Analysis with Roland Clift as chair (unpublished, about 1997).
27) Hulpke and Marsmann (1994), Schaltegger (1996), Schmidt and Schorb (1995), Finkbeiner, Wiedemann and Saur (1998) and Rebitzer (2005).
Unit process x Material A
Material B
Pre-product Intermediate
product
Figure 3.3 Branching due to several main inputs (multi-input process).
3.1.4 Flow Charts
Each box in a flow chart represents a unit process that requires full attention from the LCA experts. Less important unit processes have already been cut-off in the first phase (see Section 2.2.2.1). However, an iterative approach is preferable whereby, in an LCI overview, unit processes to be neglected and side chains are first determined with the use of estimated data. At the beginning of data acquisition at the latest, a decision must be made concerning side chains to be cut-off and those to be considered using estimated values.
The distinction between main and side chains cannot easily be made in complex product systems.28)Starting with the use phase the main chain follows the produc- tion of the product upstream: production of product, production of intermediate products, and finally reaches the extraction of raw material (thecradle). The disposal chain runs in the opposite direction (‘downstream’) until the final destruction, for example, by incineration (thegrave).29)
A flow chart as a ‘bead thread’ according to Figure 3.1 is too simplistic. Real flow charts always produce branches. Two fundamental process types, multi-input and multi-output processes, can be distinguished.
1. Several materials, pre-products and intermediate products, and so on, enter the main chain by a unit process. This is called amulti-input process. In Figure 3.3 a pre-product and two materials, A and B, enter the unit process X. A and B are 28) Fleischer and Hake (2002), Lichtenvort (2004) and Kougoulis (2007).
29) The methaphorcradle to gravehas strongly contributed to a fundamental understanding of LCA, see Chapter 1.
Unit process x
Co-product A
Co-product B
Pre-product Intermediate
product
Figure 3.4 Branching due to several main outputs (multi-output process).
essential, not negligible ancillary materials and cannot be cut off. For clarity, in this and the following illustrations all further inputs and outputs such as energy, ancillary materials and emissions are omitted.
2. A unit process yields several usable products of which only one is further processed within the product system (multi-output process). Besides an inter- mediate product, which is necessary for the product assessment under study, in Figure 3.4, two further products A and B are released for use in other production chains. These are calledco-products(see Section 2.2.2.2), because the formation processes of the intermediate product as well as the products A and B are necessarily coupled.
In systems analysis each unit process must be examined with respect too its co-products. The data are needed either to allocate material and energy demand as well as emissions to the intermediate products and co-products or to be able to make an adequate system expansion (see Sections 2.2.2.2 and 3.3). Co-products of the product system under examination arenotintegrated into the system flow chart; theyleavethe system and can be presented outside its boundary (Figure 3.5, case A). This is different in the case of system expansion; here co-products remain within the system boundary, which can lead to very large systems (Figure 3.5 case B), especially if such a system expansion has to be performed more than once in a given product system.
Another possibility of branching in a product tree occurs if several processes are considered as an output (Figure 3.6). This is true for the life cycle phase ‘disposal’ if there are several ways of disposal or recycling. Closed-loop recycling (CLR) occurs if waste from the production is re-inserted into the production; open-loop recycling (OLR) occurs if waste is used in other production processes. As in the case of co-products, a decision has to be made concerning the position of the system boundary. The quantitative handling of recycling processes is discussed in Sections 3.3.3 and 3.3.5.
A real, although highly simplified, flow chart is depicted in Figure 3.7. It describes the production of linear alkylbenzene sulfonate (LAS) (sodium-n-dodecyl benzene
Unit process x
Co-product A
Pre-product Intermediate
product
Co-product B
(a)
(b)
Unit process x Pre-product
Co-product A
Intermediate product
Co-product B
System boundary
Figure 3.5 Allocation or system expansion with multi-output processes. (a) Case A: alloca- tion necessary and (b) Case B: system expansion.
Product after use phase
Incineration
Landfill
Recycling (closed loop)
Recycling (open loop) Production
and use of product
System boundary
Figure 3.6 Branching through several process options for an output.
Sulfonation and neutralisation
1000 kg LAS Crude oil
extraction Refinery
n-paraffin production Benzene production
LAB- production
NaCl- mining
NaOH production S pro-
duction
Cl2 841
263
516 251
721
127 100
99 516
System boundary
Figure 3.7 Flow chart of LAS produc- tion. LAS – linear alkyl benzene (predom- inantlyn-dodecylbenzene) – is transferred by sulfonation into LAS. Numbers with- out unit refer to kilogram of the substance specified in the left unit process. Chlorine
(Cl2) is the co-product of sodium hydroxide (NaOH) in the electrochemical production from common salt (NaCl) and leaves the system (allocation necessary); a further co- product is hydrogen (not indicated).
sulfonate). In this synthesis four components (n-paraffin, benzene, sulphur tri- oxide via sulphur and sodium hydroxide) are gradually produced and set into reaction.30)
3.1.5
Reference Values
With the exception of Figure 3.7, the definition of unit processes and their integration into flow charts have so far not implied quantification. However, in business practice basic information on unit processes of production systems are often procured related to operating time (per hour or per annum) or are related to various other reference values depending on the cause of measurement or 30) Janzen, 1995; Berna, Cavalli and Renta, 1995.
procurement of the data. In LCI data have to be related to the part of the output relevant to the production of the assessed product, and therefore the original data used in the inventory have to be converted accordingly.
The most frequent unit with goods (contrary to services) is a certain mass of the final product, for example, 1 (metric) ton=1000 kg=1 Mg, as in the LAS example. The numbers in Figure 3.7 indicate European averages similar to those of APME plastics31); and current updates. ECOSOL data are completely and openly published32)as opposed to APME data, which are only accessible as short-cuts with restricted transparency.33)The study, conducted by Franklin Associates (USA) and commissioned by ECOSOL on behalf of the European industries, is best described as inventory analysis with thecradle-to-factory gateas the technical system boundary.
With these data, surfactants, the surface-active ingredients of detergents, can make an entry as a complete unit process (from raw material extraction to surfactant) to LCIs of divers detergents. Depending upon goal definition, these must then also assess further components of the detergents, packaging, distribution, washing and the ultimate destination of the chemicals (waste water purification plant, degradation, etc.). The surfactant data of the ECOSOL study are typical generic data which are highly valuable as background data to LCA practitioners. They are presently (2013) updated within a project coordinated by CEFIC, the European association of the chemical industry.
The mass data in Figure 3.7 give an overview on the quantitative flow of material that is necessary to produce 1 Mg LAS: for an environmental assessment of loads related to the production of 1 Mg LAS, 127 kg of NaOH, 100 kg S (by SO3) and 721 kg LAB must be included, which means that these production lines must be traced back, step by step, to the raw materials. Thus, for example, 251 kg benzene and 516 kgn-paraffin are needed for the production of 721 kg LAS . As processes usually do not have a 100% yield and the figures already consider allocations (see Sections 2.2.2.2 and 3.3), figures cannot be simply added. The quantitative data in Figure 3.7 are discussed more precisely in Section 3.3 (allocation).
The aggregation of data, which are standardized on a certain mass of the final product, is done by simple multiplication and addition which can be accomplished with spread-sheet programmes of the type Microsoft Excel.
In doing this, the data for partial aggregations for the individual unit processes must not be lost, because the processes causing the load cannot be deduced from the aggregated values. The analysis of final results on the basis of unit processes or groups of unit processes (=sectors, for example, all transportation or all waste disposal units) is calledsectoral analysis. It can be accomplished during the inventory analysis or following the impact assessment (see Chapter 5).
In comparative LCA studies, the data calculated per mass unit can easily be converted into the functional unit (fU) or reference flow.
LCI s can be seen as a special case of material flow analysis (MFA). MFA with other system boundaries and reference values (usually not ‘from cradle to grave’
31) Boustead, 1993a,b,c, 1994a,b, 1995a,b, 1996a,b, 1997a,b,c; Boustead and Fawer, 1994.
32) www.plasticseurope.org.
33) Complete quote in Section 1.5.