Life-Cycle Inventory Analysis

The second step of the LCA is the life-cycle inventory analysis (LCI). In engineering terms, this is equivalent to a mass and energy balance. The LCA practitioner needs to collect all inputs and outputs within the defined system, including the economic (services and goods) and environmental (resources and emissions) values. This requires that the full flowsheet, including processes required in the manufacture, use, and final disposal are known. The flowsheet starts with raw materials and ends with final use or disposal and includes all emissions (air, water, solid) along the chain, as defined in the goal and scope of the LCA. Data required to perform this stage of the LCA is


Simple schematic diagram showing how system boundaries and allocation of the FU are complicated when recycling and disposal are included.

available from literature, LCA databases, industry data, government records, or may be obtained through physical measurements. This is often the most difficult and time-consuming step in the LCA. Data obtained from systems that were calculated or measured for the specific study is known as the foreground process, while data collected from secondary sources, e.g., databases, is known as the background process (Figure 8.4).


Schematic diagram of foreground (shaded block) versus background processes (everything else).

The ultimate step in the inventory analysis is to construct an inventory table. This involves converting all the material and energy balance numbers, which are typically in the thousands, across the flowsheet into values relative to the FU. For example, one may be looking at the LCA of coal production with a FU of 1 kg. Through investigations, however, one may have the diesel requirements for the entire facility in the entire year. Therefore, it is part of the process to convert an annual diesel value to the equivalent quantity in terms of per kilogram of coal.

The numbers are typically all mass values. In this step, energy values would have become mass values since a kilowatt of energy would require a certain mass of coal or other fuel as may be applicable. While this is a complicated step of the LCA, there are LCA software that may be helpful in analysing and/or dealing with this step.

It is important to note that some issues may not be picked up in numbers, e.g., soil erosion, noise, rainfall/evaporation, or the exact site location, e.g., prime real estates versus more slum-like areas. This should not be forgotten when analysing and reporting results since these issues could play a big part in decision making.

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