Chapter 11

Life-Cycle Concepts, Product Stewardship and Green

Engineering

Introduction

Products, services and processes all have a life cycle.

The product life-cycle stages are illustrated in the next slide, along the horizontal axis.

The same figure, along the vertical axis, illustrates the main elements of a process life cycle.

Life-Cycle Assessment1. The first step in an LCA is to determine the scope and

boundaries of the assessment.2. The 2nd step is to inventory the inputs (e.g., raw materials

and energy) and outputs (e.g., products, byproducts, wastes, and emissions) that occur and are used during the life cycle.

3. The 3rd step is to assess the environmental impacts of the inputs and outputs compiled in the inventory. (life-cycle impact assessment)

4. The 4th step is to interpret the results of impact assessment, suggesting improvements whenever possible.

System Boundaries and Functional Unit

The system boundaries are simply the limits placed on data collection for the study.

The functional unit for a product is necessary for determining equivalence between choices, e.g., paper, plastic and cloth grocery sacks.

Life-Cycle Inventories

A life-cycle inventory is a set of data and material and energy calculations that quantifies the inputs and outputs of a product life cycle.

Some of the values are objective quantities derived using tools such as M&E balances.

Other values are more subjective and depend on choices and assumptions.

Steel from junked cars;Paper from used wooden furniture

Allocation of Inputs and Emissions to Co-Products and By-Products

Allocation to co-products based on mass:

crude oil assigned to naphtha production mass of naphtha produced crude oil use for the entire refinery

total mass of product produced

Allocation to by-prod

ucts based on value:

crude oil assigned to naphtha production value of naphtha produced crude oil use for the entire refinery

total value of product produced

Allocation of Inputs and Emissions for Products that are Made from

Recycled Goods• Treat products made from recycled material

s as if they had no raw material requirements.

• Allocate a portion of the raw material requirements from original product to the product made from recycled materials.

• Example: A synthetic garment made out of the polyethylene terephthalate (PET) recovered from recycled milk bottles.

Data Aggregation

Data Aggregation

Life-Cycle Impact Assessments• Classification: where inputs and outputs

determined during the inventory process are classified into environmental impact categories.

• Characterization: where the potency of effect of the inputs and outputs on their environmental impact categories is determined.

• Valuation: where the relative importance of each environmental impact category is assessed, so that a single index indicating environmental performance can be calculated.

Environmental Impact Categories

• Global warming• Stratospheric ozone

depletion• Photochemical smog

formation• Human

carcinogenicity• Atmospheric

acidification

• Aquatic toxicity• Terrestrial toxicity• Habitat destruction• Depletion of nonrenew

able resources• Eutrophication

Example of Classification –Selected Air Emissions from Polyethylene Production

Kg emission/kg polyethylene

Classification

Nitrogen oxides 0.0012 Photochemical smog precursor; global warming gases; acid precipitation and acid deposition precursor

Sulfur dioxide 0.0090 Acid precipitation and acid deposition precursor

Carbon monoxide 0.0009 Smog precursor

Characterization• The second step of impact assessment quantifies impact

for each inventory item by integrating the inventory amount with the potential to cause an impact, i.e., potency factor.

• Once the potency factor s are established, the inventory values for inputs and outputs are combined with the potency factors to arrive at impact scores.

• Energy use, material use and emissions are summed over the life cycle and the weighting or potency factors are then applied to these summed inventory elements.

• Most life-cycle impact assessments assume that inventory data can be summed over the entire life cycle without accounting for spatial and temporal distributions.

Valuation

The final step in life-cycle impact assessment consists of weighting the results of the characterization step so that the environmental impact categories of the highest importance receive more attention that those of least concern.

There is no generally accepted method for aggregating values obtained from the evaluations of different categories to obtain a single environmental impact score.

Solution

2 2

x x

x x

The ELUs due to air emissions are0.53 kg CO 0.09 ELU/kg CO 0.0477 ELU0.006 kg NO 0.22 ELU/kg NO 0.00132 ELU0.0006 kg CO 0.27 ELU/kg CO 0.000162 ELU0.004 kg SO 0.10 ELU/kg SO

0.0004 ELU

__________________________________________TOTAL: 0.049462 ELU

Streamlined Life-Cycle Assessments

The use of life-cycle studies fall along a spectrum from a complete spatial and temporal assessment of all inputs and outputs due to the entire life cycle to an informal consideration of the environmental stresses that occur over a product or process life cycle.

Life-Cycle Thinking

Life-Cycle Assessment

Streamlined Life-cycle Assessment

Streamlined Life-Cycle Assessments

Streamlined life-cycle assessments are conducted in order to find– most important life-cycle stages– type of inputs and outputs for more detailed

study– where the most significant environmental issues

occur.

Streamlined Data Gathering• A study might build extensive on previously comp

leted life-cycle assessment, e.g., ethylene versus polyethylene.

• Omission of product component or material causing insignificant environmental impacts based on itseconomic value– weight– energy use– toxicity

• Leave out life-cycle stages

Environmentally Responsible Product Assessment

• Developed at Bell Laboratories/Lucent Technologies.

• Replies on the use of expert evaluations of extensive checklists, surveys and other information.

• Scores from 0 to 4 (with 4 indicating the best performance) are assigned to the life stages and inventory categories.

Example

Results

LCA Goals

• Minimizing the magnitude of pollution• Conserving non-renewable resources• Ensuring that every effort is being made to

conserve ecological systems• Developing alternatives to maximize the

recycling and reuse of materials and waste• Applying the most appropriate pollution

prevention or abatement techniques

Uses of Life-Cycle Studies

• Product comparison, e.g., cloth and disposable diapers, plastic and paper cups, and polystyrene clamshells and paper wrappings for sandwiches.

• Strategic planning for manufacturer concerning product design and materials

Uses of Life-Cycle Studies

• Public sector uses– Helping to develop long-term policy regarding overall

material use, resource conservation, and reduction of environmental impacts and risks posed by materials and processes throughout the product life cycle.

– Evaluating resource effects associated with source reduction and alternative waste management techniques

– Providing information to the public about the resource characteristics of products or materials

Ecolabel

Uses of Life-Cycle Studies

• Product design and improvement– To identify processes, ingredients, and systems

that are major contributors to the environmental impacts

– To compare different options within a particular process with the objective of minimizing environmental impacts