analyse de cycle de vie life cycle analysis

Analyse de Cycle de Vie (ACV)Life Cycle Analysis (ACL)

Benjamin Warr

LCA Part I

History of LCA

• Early 1970s US Net Energy Analysis (NEA) and Materials-Process-Product Models (MPP)

• Society for Environmental Toxicology and Chemistry (SETAC-Europe or US)

• US environmental Protection Agency (USEPA)

• International Standards Organisation (ISO)

– Promote consensus on framework

– Define inventory methodology

– Provide accreditation for enterprises and organisations

– ISO14000 and ISO19000 series

Who uses LCA?(see Methods and Standards\ISO Survey 2003.pdf)

• Industry– Mostly (cautious) multinationals to identify areas of

improvement, working with suppliers to obtain betterquality or « greener » inputs.

– « Less is best » for useable comparisons

– Do not go «beyond regulatory compliance »

– But, a holistic view of the enterprise isproactive, avoids potential problems and isgood for image

• Governments (for France see \DGEMP2003.pdf)– Defining public policy – lag behind industry

– US DOE « Life Cycle Costing », « Greening of Industry », (FRED) Framework for ResponsibleEnvironmental Decision Making)

From « Cradle to Grave »

1. Many materials and energy combinations (exergy)

2. Complexand linkedprocesses(linked unit processes)

3. Consideration of outputs (allocation to air, sea, freshwater, soil)

4. Considering manufacture, use + disposal implies a temporal horizon

Partnerships and policies that encourage LCA

4 main steps of LCA - (SETAC)

1. Goal Definition and Scoping

2. Inventory Analysis

3. Impact Assessment

– Classification

– Characterisation

– Valuation

4. Interpretation

IterationRefinement

Generic Goals• Education and communication• Product design (design for environment)• Product development and improvement• Pollution prevention• Assessment and reduction of potential liability• Strategic planning• Assessing and improving environmental programs• Development of policy and regulations• Individual and organisational purchase and

procurement• Labeling• Developing market strategies• Environmental management systems

•Description of environmental performance of products - ISO14040

•Improvement of environmental performance of products – ISO 14062

•Information about environmental aspects of performance – ISO14020

•Communication of environmental performance– ISO 14063

•Description of environmental performance of organisations – ISO14030

•Information about the environmental management system – ISO19011

1. Goal and Definition Scoping

ISO14041 states• The goal of any study shall unambiguously state

the intended

– application,

– reasons for the study

– target audience• Recognise limitations of LCA (non-spatial at present)

• Identify, justify rules and conventions (data, averages etc.)

• Consider qualitative impacts (i.e. social)

• Involve interested parties early in process (feedback)

• Evaluation of LCA via peer review (check assumptions)

Goal and Scope: Functional Units

A functional unit must be defined.

A reference to which input and output data are related (intensive variable)

Product systems must be comparable

It is the service/performance that iscompared, NOT the product itself

Example: can’t compare 1L paint with anyother paint, BUT can compare «1m paintedsurface with Xmm coating and service life of 10 years »

StagesIm

pact

sAgricultural Life Cycle Index Matrix

Functional unit is YIELD

(rendement)It can be expressed as an intensive variable

relative toquantitative measures

(indices) of the system state

• Alternative Product Evaluation (APE) : a product system (or service) is described by a fixed functional unit that serves as a reference. Alternative products are then compared on the basis of their relative environmental impact.

• Example: What is the environmental impact associated with the activity of driving different vehicles 1km carrying 1 tonne of goods?

• Environmental functional demand (EFD): Based on an an acceptable environmental impact (quota) divided by the function output. Quotas are then goals which serve as the starting point for the assessment procedure. Different technical solutions that satisfy the quota are then identified.

• What vehicles can be used to carry 1ton of goods 1km if the acceptable environmental consequence is limited to a certain environmental impact?

Goal and Scope: Functional Units

Alternative Functional Units

Service rather than productCan consider two valid

approaches1. Service lifetime2. Raw material life cycle

The System

Functional Units

Defining the functional unit,permits answers to a series

of simple questions:• What needs to be

accomplished?• Why does it need to be done?• When does it need to be

done?• What conditions must be

considered?The TEAM must 1. Understand mechanical,

physical, chemicalperformance and costrequirements (need)

2. Develop environmentalrequirements and goals (desire or wish list)

Industrial Goals driven by R&D

Defining the System Boundaries• So that product and service systems can be subdivided into

a set of unit processes.

• Inputs and outputs at the boundaries should be elementary flows linked to unit processes

• There are 2 ways to define the system boundaries (always considering the goals!)

• narrow systemboundaries: – 1. extraction

– 2. disposal

– 3. manufacture

– 4. use

• extended systemboundaries: “cradle to grave”

Proposing Engineering Technologies and Options

• Once requirements and goals are defined, the team should– Identify technologies that combine to form different options to

provide the desired function

• Technologies include materials and equipment.

Keywords:

ReduceRecoverMaintainUpgrade

And Technology Life Cycles

Linking Technologies to Requirements and Goals

LCA of Aluminium• Sponsor: International Aluminium Institute• Stated objectives:

– Increase use of Al in transportation systems– reduce energy consumption and associated GHG emissions of Al

production– Increase use of recycled Al.

• First task: quantification of CO2 and PFC greenhouse gas(GHG) emissions from the worldwide aluminium industry

• Second Task: estimates of the implications (in terms of Greenhouse Gas Emissions) of the increased use of aluminium for the manufacture of cars and trucks.

• Data from over 80% of the worldwide industry includingestimates from Russia and China.

AL LCA: System Boundaries

Bauxite Mining and Benefication• Bauxite is washed, ground and dissolved in

caustic soda (sodium hydroxide) at highpressure and temperature. The resultingliquor contains a solution of sodium aluminate and undissolved bauxite residues containing iron, silicon, and titanium. These residues sink gradually to the bottom of the tank and are removed. They are known colloquially as "red mud".

• Clear sodium aluminate solution ispumped into a huge tank called a precipitator. Fine particles of alumina are added to seed the precipitation of pure alumina particles as the liquor cools. The particles sink to the bottom of the tank, are removed, and are then passed through a rotary or fluidised calciner at 1100°C to drive off the chemically combined water. The result is a white powder, pure alumina. The caustic soda is returned to the start of the process and used again.

• The BAYER PROCESS

The BAYER PROCESS in REFINERY• The Bayer process can be considered in three stages:• Extraction The hydrated alumina is selectively removed from the other (insoluble) oxides by

transferring it into a solution of sodium hydroxide (caustic soda): – Al2O3.xH2O + 2NaOH ---> 2NaAlO2 + (x+1)H2O– The process is far more efficient when the ore is reduced to a very fine particle size prior to reaction.

This is achieved by crushing and milling the pre-washed ore. This is thensent to a heatedpressure digester.

– Conditions within the digester (concentration, temperature and pressure) vary according to the properties of the bauxite ore being used. Although higher temperatures are theoretically favouredthese produce several disadvantages including corrosion problems and the possibility of otheroxides (other than alumina) dissolving into the caustic liquor.

– After the extraction stage the liquor (containing the dissolved Al2O3) must be separated from the insoluble bauxite residue and purified as much as possible and filtered before itis delivered to the decomposer. The mud is thickened and washed so that the caustic soda can be removed and recycled.

• Decomposition Crystalline alumina trihydrate is extracted from the digestion liquor by hydrolysis:– 2NaAlO2 + 4H2O ---> Al2O3.3H2O + 2NaOH– This is basically the reverse of the extraction process, except that the product's nature can be

carefully controlled by plant conditions (including seeding or selective nucleation, precipitationtemperature and cooling rate). The alumina trihydratecrystals are then classified into size fractions and fed into a rotary or fluidised bed calcination kiln.

• Calcination Alumina trihydrate crystals are calcined to remove their water of crystallisation and prepare the alumina for the aluminium smelting process.

– The mechanism for this step is complex but the process, when carefully controlled, dictates the properties of the final product.

Additional Info. on the Bayer Process• The amount of residue« red mud » generated, per tonne of alumina produced,

varies greatly depending on the type of bauxite used, from 0.3 tonnes for highgrade bauxite to 2.5 tonnes for very low grade.

• The following data gives some idea of the wide range in chemical composition thatcan be found in residue from different bauxites.

• Fe2O3 30 - 60%

• Al2O3 10 - 20%

• SiO2 3 - 50%

• Na2O 2 - 10%

• CaO2 - 8%

• TiO2

• Trace - 10%

• Apart from the alkalinity that is imparted by liquors in the process, the residue ischemically stable and non-toxic.

• Bauxite residue is most oftendisposed of on land using one of a variety of methods. Once such land has been decommissioned is canbe used to grow crops or other vegetation. Alternatively the land can be used for building, depending uponthe moisture of the residue.

Al Smelting: the Hall-Heroult Process• Alumina is dissolved in an electrolytic bath of molten cryolite

(sodium aluminium fluoride) within a large carbon or graphite linedsteel container known as a "pot". An electric current is passed throughthe electrolyte at low voltage, but very high current, typically 150,000 amperes. The electric current flows between a carbon anode (positive), made of petroleum coke and pitch, and a cathode (negative), formed by the thick carbon or graphite lining of the pot.

• Molten aluminium is deposited at the bottom of the pot and issiphoned off periodically, taken to a holding furnace, often but not always blended to an alloy specification, cleaned and then generallycast.

• Across all technologies, electricity consumption averaged 15.95 kWh per kg of molten metal. The consumption of fuels to produce thiselectricity generated 5.8 metric tonnes of CO2 per tonne of metal. An additional 1.6 metric tonnes of CO2 per metric tonne are generated in the electrolytic process.

Smelting System Diagram

Incremental improvements have reduced energy intensity.

2Al2O3 + 3C -----> 4Al + 3CO2

•PFC emissions at 0.30 kg of CF4 and 0.03 kg of C2F6 per mt per metric tonne of Al.

•Equivalent to 2.2 metric tonnes of CO2 for every tonne of Al.

Thermodynamic inefficiency in smelter

2Al2O3 + 3C -----> 4Al + 3CO2

LCA Results: For a target audience?• Estimates from car manufacturers and others range from5-10% of

fuel economy savings per 10% weight reduction for today's averagevehicles.

• Thus an automobile driven for 200,000 km could save 6-13 litres of gasoline for every kg of aluminium used to replace 2 kg of heaviermaterials

• Modelling indicates the potential to save over 20 metric tonnes of CO2 equivalents for each tonne of additional automotive aluminium products from enhanced vehicle fuel efficiency over the vehicle'slifetime.

• Modelling was also conducted to quantify the effect of using either all recycled or all primary aluminium. The table below shows that evenwith all virgin (primary) metal, net carbon dioxide savings are substantial.

26.722.918.113.9Tonnes CO2e savedper tonne of Al

95% Recycled60% Recycled30% RecycledAll PrimaryMetal Used

Future Efforts• Easier dismantling of aluminium components from cars to

improve the recovery of aluminium.

• Recycling rates for transport applications range from 60-90 per cent.

• Close to 40% of the global demand for aluminium in all markets is based on recycled metal from process scrap and scrap from old products.

• Increasing use of recycled metal saves on both energy and mineral resources needed for primary production.

• Recycling of aluminium requires only 5% of the energyto produce secondary metal as compared to primary metal and generates only 5% of the green house gas emissions.