Transcript IO-LCA - Civil and Environmental Engineering

Economic Input-Output Life
Cycle Assessment
12-714/19-614 Life Cycle Assessment and
Green Design
Structure of a Process-based LCA Model
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Criticism of LCA
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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.
How Research is Done…
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Sitting around in an office, we were
complaining about problems of LCA
methodology.
Realized economic input-output models could
solve boundary and circularity problems.
Then hard work – assembling IO models,
linking to environmental impacts and testing.
Found out later that Leontief and Japanese
researchers had done similar work, although
not directly for environmental life cycle
assessment.
Economic Input-Output Analysis
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Developed by Wassily Leontief (Nobel Prize in
1973)
“General interdependency” model: quantifies the
interrelationships among sectors of an economic
system
Identifies the direct and indirect economic inputs of
purchases
Can be extended to environmental and energy
analysis
The Boundary Issue
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Where to set the boundary of the LCA?
“Conventional” LCA: include all processes, but at least
the most important processes if there are time and
financial constraints
In EIO-LCA, the boundary is by definition the entire
economy, recognizing interrelationships among
industrial sectors
In EIO LCA, the products described by a sector
are representing an average product not a specific
one
Circularity Effects
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Circularity effects in the economy must be accounted for:
cars are made from steel, steel is made with iron ore, coal,
steel machinery, etc. Iron ore and coal are mined using
steel machinery, energy, etc...
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waste
product
emissions
system
boundary
Building an IO Model
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Divide production economy into sectors (Note:
could extend to households or virtual sectors)
Survey industries: Which sectors do you
purchase goods/services from and how
much? Which sectors do you sell to? (Note:
Census of Manufacturers, Census of
Transportation, etc. every 5 years)
Building an IO Model (II)
Form Input-Output Transactions Table –
Flow of purchases between sectors.
 Constructed from ‘Make’ and ‘Use’ Table
Data – purchases and sales of particular
sectors. (Note: need to reconcile
differing reports of purchases and
sales...)
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Economic Input-Output Model
Input to sectors
Output from sectors
1
2
3
n
Intermediate input I
Va lue added V
Total input X
 Xij + Yi = Xi;
 (Aij*Xj) + Yi =
1
X1 1
X2 1
X3 1
Xn 1
I1
V1
X1
2
X1 2
X2 2
X3 2
Xn 2
I2
V2
X2
Xi = Xj;
3
X1 3
X2 3
X3 3
Xn 3
I3
V3
X3
n
X1 n
X2 n
X3 n
Xn n
In
Vn
Xn
Intermediate
output O
Final
demand Y
Total
output X
O1
O2
O3
On
Y1
Y2
Y3
Yn
X1
X2
X3
Xn
using Aij = Xij / Xj
Xi
in vector/matrix notation:
A*X + Y = X =>
Y = [I - A]*X
or X = [I - A]-1*Y
GDP
Building an IO Model (III)
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Sum of Value Added (non-interindustry
purchases) and Final Demand is GDP.
Transactions include intermediate product
purchases and row sum to Total Demand.
From the IO Transactions Model, form the
Technical Requirements matrix by dividing
each column by total sector input – matrix A.
Entries represent direct inter-industry
purchases per dollar of output.
Scale Requirements to Actual Product
Engine
$20,000
Car:
$2500
Engine:
Steel
...
$2500 $2000 $1200
$800
Other
Parts
Plastics
$300
Steel
$200
$150
$10
...
Aluminum
$10
Example: Requirements for Car
and Engine
Engine
0.125
Car:
Steel
0.1
0.06
Other
Parts
Engine:
0.12
Steel
...
0.04
0.0005
Plastics
0.08
0.06
...
Aluminum
0.004
Using a Requirements Model
Columns are a ‘production function’ or
recipe for making $ 1 of good or service
 Strictly linear production relationship –
purchases scale proportionally for
desired output.
 Similar to Mass Balance Process Model
– inputs and outputs.
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Mass Balance and IO Model
Racing
Engine
Steel
Etc.
Car Production
(Motor Vehicle Assembly)
Etc.
Final Demand
Supply Chains from
Requirements Model
Could simulate purchase from sector of
interest and get direct purchases
required.
 Take direct purchases and find their
required purchases – 2 level indirect
purchases.
 Continue to trace out full supply chain.
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Leontief Results
Given a desired vector of final demand
(e.g. purchase of a good/service), the
Leontief model gives the vector of sector
outputs needed to produce the final
demand throughout the economy.
 For environmental impacts, can multiply
the sector output by the average impact
per unit of output.
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Supply Chain Buildup
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First Level: (I + A)Y
Second Level: A(AY)
Multiple Level: X = (I + A + AA + AAA + … )Y
Y: vector of final demand (e.g. $ 20,000 for
auto sector, remainder 0)
I: Identity Matrix (to add Y demand to final
demand vector)
A: Requirements matrix, X: final demand
vector
Direct Analysis – Linear
Simultaneous Equations
Production for each sector:
 Xi = ai1 X1 + ai2 X2 + …. + ainXn + Yi
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Set of n linear equations in unknown X.
 Matrix Expression for Solution:
X(I - A) = Y <==> X = (I - A)-1 Y
 Same as buildup for supply chain!
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Effects Specified
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Direct
» Inputs needed for final production of product
(energy, water, etc.)
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Indirect
» ALL inputs needed in supply chain
» e.g. Metal, belts, wiring for engine
» e.g. Copper, plastic to produce wires
» Calculation yields every $ input needed
EIO-LCA Implementation
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Use the 491 x 491 input-output matrix of the U.S.
economy from 1997
Augment with sector-level environmental impact
coefficient matrices (R) [effect/$ output from
sector]
Environmental impact calculation:
E = RX = R[I - A]-1 Y
In Class Exercise
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Two Sector
Economy.
Model Final Demand
$100 for Sector 1.
Haz Waste of 50
gm/$ in Sector 1 and
5 gm/$ in Sector 2.
Transaction Flows ($
billion) are:
1
2
Final
Dmd.
1
150
500
350
2
200
100
1700
V.A.
650
1400
1100
Solution
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Requirements Matrix: Row 1: 0.15 and 0.25,
Row 2: 0.2 and 0.05
(I-A) inverse Matrix: Row 1: 1.2541 and 0.33,
Row 2: 0.264 and 1.1221
Direct intermediate inputs: $15 of 1 and $20 of
2
Total Outputs: $125.4 of 1 and $26.4 of 2
Hazardous Waste: 6402 gm.