Process LCA

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There are four stages in the traditional process life cycle assessment approach

  • Scoping: definition of the purpose of the LCA. What is the LCA going to be used for? Comparing two similar products? Determining the effect of a new product on the environment? Is the desired information for internal or external use?
  • Inventory: quantification of inputs (energy, raw material) and outputs (environmental releases) throughout the life of the product or activity. How much energy is required to produce, distribute, use and dispose the product? What materials are consumed during all the life-cycle stages of a product? What wastes and pollutants are generated?
  • Impact Assessment: quantitative and/or qualitative assessment of the effect of the environmental loads identified in the inventory component. What are the environmental effects of producing the product? How much landfill space will be required for disposal? How do the pollutants affect the environment: Acid rain, ozone depletion?
  • Improvement Assessment: assessment of opportunities for improvement of economic impact. Can the amounts of pollutants be reduced? Can the product be reused, recycled, refurbished? Can energy be recuperated from the product by incineration?

Life-Cycle Assessment deals with a systematic interpretation (qualitatively and quantitatively) of the ‘cradle-to-grave’ interactions between that product and its environment. Therefore, it is important to understand the model that is used to interpret this progression of the product from cradle-to-grave. This is the generalized Life-Cycle Model; the product system.

The product system is defined by a combination of unit processes that together perform one or more functions. Unit Processes are analogous to control volumes/systems. The complex system (product system) is modeled by viewing the life cycle as a system broken down into subsystems (unit processes) that have inputs and outputs that can be both intermediate and elemental.


Contents

Goal and Scope

In order to adequately understand, organize, and relate the results of a Life-Cycle Assessment, the goals and scope must be clearly stated, with all subsequent developments “consistent with the goal and scope”.

There is a very specific list of elements that define the scope of an LCA in ISO 14040/14041:

  • The functions of the product system, or, in the case of comparative studies, the systems;
  • The functional unit;
  • The product system to be studied;
  • The product system boundaries;
  • Allocation procedures;
  • Types of impact and methodology of impact assessment, and subsequent interpretation to be used;
  • Data requirements;
  • Assumptions;
  • Limitations;
  • Initial data quality requirements;
  • Type of critical review, if any;
  • Type and format of the report for the study.

[ISO 14040:1997(E)]

Defining the system, system function, functional unit, and reference flow is vital; inventory data gathered based on the model developed as defined by the system function is referenced to the functional unit and reference flow. More importantly, the functional unit and reference flow allow for comparative assertions to be made when more than one system is compared.

System function is self-explanatory; it is simply what the system is meant to do. The functional unit is a clearly defined, measurable unit of this function. The reference flow is the amount of product that satisfies the intended function as quantified by the reference flow.

“EXAMPLE In the function of drying hands, both a paper towel and an air-dryer system are studied. The selected functional unit may be expressed in terms of the identical number of pairs of hands dried for both systems. For each system, it is possible to determine the reference flow, e.g. the average mass of paper or the average volume of hot air required for one hand-dry, respectively. For both systems, it is possible to compile an inventory of inputs and outputs on the basis of the reference flows. At its simplest level, in the case of paper towel, this would be related to the paper consumed. In the case of the air-dryer, this would be largely related to the energy input to the air dryer.” [ISO 14041:1998(E)]

Defining the system boundaries is accomplished by defining:

  • The unit processes to be included in the product system;
  • The emissions to be measured.

“Several life cycle stages, unit processes and flows should be taken into consideration, e.g.:”

  • Inputs and outputs in the main manufacturing/processing sequence;
  • Distribution/transportation
  • Production and use of fuels, electricity and heat;
  • Use and maintenance of products;
  • Disposal of process wastes and products;
  • Recovery of used products (including reuse, recycling and energy recovery);
  • Manufacture of ancillary materials;
  • Manufacture, maintenance and decommissioning of capital equipment;
  • Additional operations, such as lighting and heating;
  • Other considerations related to impact assessment (if any).

[ISO 14041:1998(E)]

ISO gives a qualitative impression of how boundaries can be drawn: “Resources need not be expended on the quantification of such inputs and outputs that will not significantly change the overall conclusions of the study.” [ISO 14041:1998(E)] In addition, cutoffs can be made by marking a threshold of mass, energy, or specific emissions as a percentage of the total for a unit process, and excluding inputs and outputs that do not meet that threshold.

Data quality is an important issue for LCA, and ISO makes reference to the following as issues to address in the scope:

  • Time
  • Geography
  • Technology
  • Source
  • Measured/Calculated/Estimated
  • Precision
  • Completeness
  • Representativeness
  • Consistency
  • Reproducability


Life Cycle Inventory Analysis

The goal and scope provide the framework for the inventory. During preparation for data collection, the full and detailed sequence of unit processes with inputs and outputs is developed. Any other relevant issues for data collection must also be addressed (units, responsibility, data categories, etc.). ISO 14041 contains a sample data collection sheet.

Data collection itself is carried out, through data gathering on site or through published sources (which must of course be properly referenced).

“Following the data collection, calculation procedures are needed to generate the results of the inventory of the defined system for each unit process and for the defined functional unit of the product system that is to be modeled.” [ISO 14041:1998(E)] Calculating is broken down into the following:

  • Validation:
    • Mass/energy balances (as a check);
    • Comparative analyses of emissions factors (as a check);
    • Reporting and treatment of data gaps.
  • Relating data to unit processes:
    • “For each unit process, an appropriate reference flow shall be determined (e.g. 1 kg of material or 1 MJ of energy). The quantitative input and output data of the unit process shall be calculated in relation to this reference flow.” [ISO 14041:1998(E)]
  • Relating data to functional unit and data aggregation:
    • “ … normalizing the flows of all unit processes in the system to the functional unit. The calculation should result in all system input and output data being referenced to the functional unit.” [ISO 14041:1998(E)]
  • Refining the system boundaries:
    • Sensitivity analysis should be used to validate scope decisions;
    • Refine and re-collect relevant data if necessary.

Allocation deals with the inherent nature of coupled life cycles in industrial activity. Multiple product systems exist within any system to be studied, and allocation procedures define how they are linked to one product versus another. Allocation must be done according to a more rigid set of rules than most of the other elements in the LCI according to ISO. As such, consult the standard itself for further information.


Life Cycle Impact Assessment

The purpose of the Life-Cycle Impact Assessment (LCIA) is to assign quantities of environmental relevance to the Life-Cycle Inventory Results. ISO defines the following stages in the progression from LCI results to indicator results:

  • Selection of:
    • Impact categories;
    • Category indicators;
    • Characterization models;
    • Category endpoints.
  • Classification:
    • “Assignment of LCI results to the impact categories.” [ISO 14042:2000(E)]
  • Characterization:
    • Calculation of category indicator results;
  • Optional:
    • Normalization (“Calculation of the magnitude of category indicator results relative to reference information” [ISO 14042:2000(E)]);
    • Grouping;
    • Weighting;
    • Data quality analysis.

The standard discusses in detail criteria for the selection of impact categories, category indicators, and characterization models. It is best to access the standard for this information.

LCI results are assigned to impact categories (classification) in order to make the environmental issues embedded within the inventory apparent.

Characterization: “The calculation involves the conversion of LCI results to common units [through characterization factor] and aggregation of converted results within the impact category [aggregation results in the indicator result].” [ISO 14042:2000(E)]

With a body of indicator results compiled from the inventory, a full Life-Cycle Impact Profile is composed.

The optional activities are left to the standard.


Life Cycle Interpretation

“The objectives of life cycle interpretation are to analyse results, reach conclusions, explain limitations and provide recommendations based on the findings of the preceding phases of the LCA or LCI study and to report the results of the life cycle interpretation in a transparent manner.” [ISO 14043:2000(E)]

The elements of a Life-Cycle Interpretation are defined as:

  • Identification of the significant issues based on the results of the LCI and LCIA phases of LCA;
  • Evaluation which considers completeness, sensitivity and consistency checks;
  • Conclusions, recommendations and reporting.

[ISO 14043:2000(E)]

Some Criticisms of (Process) LCA

  • There is lack of comprehensive data for LCA.
  • Data reliability is questionable.
  • Defining problem boundaries for LCA is controversial and arbitrary. Different boundary definitions will lead to different results.
  • LCA is too expensive and slow for application in the design process.
  • There is no single LCA method that is universally agreed upon and acceptable.
  • Conventional, SETAC-type LCA usually ignores indirect economic and environmental effects.
  • Published LCA studies rarely incorporate results on a wide range of environmental burdens; typically only a few impacts are documented.
  • Equally credible analyses can produce qualitatively different results, so the results of any particular LCA cannot be defended scientifically.
  • Modeling a new product or process is difficult and expensive.
  • LCA cannot capture the dynamics of changing markets and technologies.
  • LCA results may be inappropriate for use in eco-labeling because of differences in interpretation of results.

Links

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