analyse de cycle de vie-l.pdf

8/10/2019 analyse de cycle de vie-l.pdf

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Analyse de Cycle de Vie (ACV)

Life Cycle Analysis (ACL)

Benjamin Warr

LCA Part I


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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


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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 ofIndustry , (FRED) Framework for ResponsibleEnvironmental Decision Making)


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From Cradle to Grave

1. Manymaterials andenergycombinations(exergy)

2. Complexand linkedprocesses(linked unitprocesses)

3. Consideration of

outputs (allocation to

air, sea, freshwater,

soil)

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


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Partnerships and policies that encourage LCA


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4 main steps of LCA - (SETAC)

1. Goal Definition andScoping

2. Inventory Analysis

3. Impact Assessment

Classification Characterisation

Valuation

4. Interpretation

Iteration

Refinement


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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 andprocurement

Labeling

Developing market strategies

Environmental management systems


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Description of

environmental performanceof products - ISO14040

Improvement of

environmental performance

of products ISO 14062Information about

environmental aspects of

performance ISO14020

Communication of


ISO 14063

Description of


of organisations ISO14030

Information about the

environmental management

systemISO19011


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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)


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Goal and Scope: Functional Units

A functional unit must be defined.

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

Product systems must be comparable

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

Example: cant compare 1L paint with anyother paint, BUT can compare 1m painted

surface with Xmm coating and service life

of 10 years


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Stages

Impacts

Agricultural 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


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Alternative Product Evaluation (APE) : a productsystem (or service) is described by a fixed functional unitthat serves as a reference. Alternative products are then

compared on the basis of their relative environmentalimpact.

Example: What is the environmental impact associatedwith 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 thefunction output. Quotas are then goals which serve as thestarting point for the assessment procedure. Differenttechnical solutions that satisfy the quota are then identified.

What vehicles can be used to carry 1ton of goods 1km ifthe acceptable environmental consequence is limited to acertain environmental impact?

Goal and Scope: Functional Units


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Alternative Functional Units


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Service rather than product

Can consider two valid

approaches

1. Service lifetime2. Raw material life cycle

The System

Functional Units


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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, chemical

performance and costrequirements (need)

2. Develop environmental

requirements and goals

(desire or wish list)


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Industrial Goals driven by R&D


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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 elementaryflows linked to unit processes

There are 2 ways to define the system boundaries (always

considering the goals!) narrow system boundaries:

1. extraction

2. disposal 3. manufacture

4. use

extended system boundaries: cradle to grave


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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:

Reduce

Recover

MaintainUpgrade

And Technology Life Cycles


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Linking Technologies to

Requirements and Goals


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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 ofaluminium for the manufacture of cars and trucks.

Data from over 80% of the worldwide industry including

estimates from Russia and China.


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AL LCA: System Boundaries


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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 sodiumaluminate and undissolved bauxite

residues containing iron, silicon, andtitanium. These residues sink gradually tothe bottom of the tank and are removed.They are known colloquially as "red mud".

Clear sodium aluminate solution is

pumped into a huge tank called aprecipitator. Fine particles of alumina areadded to seed the precipitation of purealumina particles as the liquor cools. Theparticles sink to the bottom of the tank, areremoved, and are then passed through a

rotary or fluidised calciner at 1100C todrive off the chemically combined water.The result is a white powder, pure alumina.The caustic soda is returned to the start ofthe process and used again.

The BAYER PROCESS


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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 bytransferring 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 then sent to a heated

pressure 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 it is delivered to thedecomposer. The mud is thickened and washed so that the caustic soda can be removed andrecycled.

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

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

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


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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 that

can 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 often disposed of on land using one of a variety ofmethods. Once such land has been decommissioned is can be used to grow crops orother vegetation. Alternatively the land can be used for building, depending uponthe moisture of the residue.


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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 150,000amperes. 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 notalways blended to an alloy specification, cleaned and then generallycast.

Across all technologies, electricity consumption averaged 15.95 kWhper kg of molten metal. The consumption of fuels to produce thiselectricity generated 5.8 metric tonnes of CO2 per tonne of metal. Anadditional 1.6 metric tonnes of CO2 per metric tonne are generated inthe electrolytic process.


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Smelting System Diagram

Incremental improvements

have reduced energyintensity.

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.


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Thermodynamic inefficiency in

smelter2Al2O3 + 3C -----> 4Al + 3CO2


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LCA Results: For a target audience? Estimates from car manufacturers and others range from 5-10% 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 ofCO2 equivalents for each tonne of additional automotive aluminiumproducts from enhanced vehicle fuel efficiency over the vehicle'slifetime.

Modelling was also conducted to quantify the effect of using either allrecycled 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

saved

per tonne of Al

95% Recycled60% Recycled30% RecycledAll PrimaryMetal Used


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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 energy to

produce secondary metal as compared to primary metal and

generates only 5% of the green house gas emissions.

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