Program for North American Mobility in Higher
Education
Introducing Process Integration for Environmental
Control in Engineering Curricula
Module 3: Environmental Challenges –
Pulp & Paper Industry
Caroline Gaudreault
Created at:
École Polytechnique de Montréal &
Texas A&M University, 2003
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2
Tier III:
Open-Ended Problem
Tier III: Statement of Intent
Tier III: Statement of Intent
The purpose of this is to provide students
with an open-ended problem which
assimilates the concepts of minimum
impact manufacturing including process
integration and LCA .
4
Problem Statement
You are an environmental engineer in a
pulp and paper mill. The head office
wants to enhance its competiveness by
putting together a technology roadmap
with the ultimate goal to be a minimum
impact manufacturing mill.
Some information about the mill is given
at the following page.
5
Mill Description
 Conventional pulping technology, ECF bleaching, drying,
activated sludge plant
 Debarking: dry
 Lime kiln: normal
 Lime kiln fuel: heavy fuel oil
 Lime kiln flue gas: high eff. ESP
 Bark boiler (HW bark):
 Total efficiency 0.87
 Fluidized bed boiler
power generation from excess heat in mill
 Electric
condensation turbine
 Since no information is available concerning the effluent
treatment plant, its efficiency will be consider constant. As a
consequence of that, from a relative point of view, the
effluent ion loads can be considered proportional to the ones
before the effluent treatment.
6
Question 1
A few months ago the company as ordered a partial
LCA study in order to have an idea about its life cycle
environmental impacts. As a first step, your boss ask
you to look at this study as well as at the mill simulation
and make him your recommendations for environmental
improvement.
To do this look at unit process
contribution to each impacts and perform sensibility
analysis. Do not use any normalization or weighting.
Without doing calculations, you can also use cost
arguments. Also determine, by mass balances by how
much fresh water can be theoretically reduced (by
recycle).
System boundaries are defined in the LCA study and
the main hypothesis are presented next pages.
7
Functional Unit
 All LCA results are presented relative to
the functional unit. The functional unit
has been defined as follow:

8
The production of 1 admt of pulp.
Chemical Production
 Chemical production as been included into
the system boundaries.
Chemical are
considered to be transported on an average
distance of 100 km using 40 ton diesel trucks
and empty trucks return to the supplier. For
calculation purpose a weight of 1/10 of the
transported chemicals has been assumed for
the return of the truck.
 No data was available for talc manufacturing.
Therefore it has been excluded from the
system
boundaries.
However,
its
transportation has been considered.
9
Birch Growth and Harvesting
 Birch growth and harvesting as been
included in the boundaries. The wood
is transported on an average of 100 km.
The same assumptions as for chemicals
apply.
10
Others
 By product have been located.
 A credit has been considered for the
generated energy (but only on the energy).
 Pulp is transported on an average distance of
200 km to the customer (same assumptions
as chemicals).
 Industrial landfill is located at 5 km of the mill.
16 ton diesel trucks are used to transport the
solid wastes, the return of the trucks is
considered negligible.
11
Necessary documents
 LCA Base Case
 Process Simulation
12
Question 2
 Your boss is convinced that most of the
competitive advantages that can be gain with
environmental improvement are related with
fresh water rereduction.
 In this case, recycling the effluent water is the
most obvious way to reduce fresh water
consumption, but this can result in the buildup of non-process elements and so reduce
process performance.
 For this reason, he has also mandated a
consulting company to perform a water pinch
study subject to process constraints.
13
Question 2 (Cont’d)
 The consultant has first evaluated possibility of direct recycle
because it does not implicate major capital costs. Major results
are presented in the following table.
14
Water Consumption
23% reduction
Liquid Effluent
Reduction of ion content of
2.3%
Gas Effluent
Cl, K: 0.2% increase
Na: 6.8% increase
Energy produced
5% reduction (need more
energy to pump)
Dust
13.4% increase
Solid wastes
Neglictible difference
Question 2 (Cont’d)
 Using the LCA model, discuss if this
represent a real environmental improvement.
To compare results, normalize against the
base case.
 A panel of experts has determined that the
importance of each impact category can be
described by the weights in the following
tables.
Resources and emissions are
weighted separatly.
 What is the influence of the weights on the
final decision.
15
Question 2 (Cont’d)
Resource depletion:
Impact
Raw water
consumption
16
Weigth
0.83
Energy
consumption
0.08
Virgin Fiber
consumption
0.01
Other
resources
0.08
Emissions:
Impact
Weigth
Carcinogenic
substances
0.70
Heavy metals
0.07
Acidification
0.01
Eutrophication
0.01
Summer smog
0.07
Winter smog
0.07
Solid Wastes
0.005
Global
Warming
0.065
Solution – Q1
 The process simulation does not give a
lot of insights on the environmental
impacts of the process. However it is
obvious that the bleaching plant
consumes a lot on fresh water and
rejects a lot in the environment. The
following is the solution for potential
water reduction
17
Solution – Q1 (Cont’d)
Water balances can be
summarized by this picture.
The
total
fresh
water
consumption
is
9.33+0.97+3.83+20.66=34.7
9 ton/ton of dry pulp.
Only liquid water can be
“directly”
recycle:
0.967+5.92+0.681+20.66=
28.23 ton/ton of dry pulp.
For
mass
conservation
reasons, only the min of
fresh water or liquid effluent
can be recycle ie. 28.23 ton.
So the minimum water
consumption
is
34.7928.23=6.56
ton
(ie
a
reduction of 81%).
18
Solution – Q1 (Cont’d)
 The following graph show the contribution of each process unit
to resource consumption.
Process Contributions - Input Impact Categories
100%
90%
80%
70%
60%
Landfill
Transport
Chemical Production
Pulp Manufacturing
50%
40%
30%
20%
10%
0%
Raw Water
Consumption
19
Virgin Fiber
Consumption
Natural Resources
Consumption
Energy Consumption
Solution – Q1 (Cont’d)
 The last figure show that the
manufacturing activities consumes a lot
of resources: water, virgin fiber and
other natural resources.
 It also shows that chemical production
is particularly energy-consuming.
 From a first look, reducing chemical and
water consumption will result in a
significant environmental benefit.
20
Solution – Q1 (Cont’d)
 The following graph show the contribution of each process unit
to emission-related environmental impacts.
Process Contributions - Output Impact Categories
100%
80%
Growth
Harvesting
Landfill
Transport
Chemical Production
Pulp Manufacturing
60%
40%
20%
C
ar
ci
te
W
as
id
er
in
t
W
So
l
Sm
og
og
Su
m
m
er
Sm
s
no
ge
ni
c
H
ea
v
y
Su
bs
M
ta
nc
e
n
Eu
tro
ph
ic
at
io
n
Ac
i
di
fic
at
io
g
ar
m
in
W
ba
l
G
lo
21
et
al
s
0%
Solution – Q1 (Cont’d)
 From this graph it is possible to note that:




22
Manufacturing activities are a large contributor to
acidification, eutrophication, winter smog and solid
wastes;
Chemical production is a large contributor to all
impact
categories
but
more
specifically
eutrophication, heavy metals and summer smog.
Transportation seems also to be a large
contributor to several impact categories: global
warming, carcinogenic substances and summer
smog.
Global warming is due to almost all unit
processes.
Solution – Q1 (Cont’d)
 Even if it is impossible to talk about the relative importance of
each impacts since no weighting has been performed, it is clear
from the to last graphs that manufacturing activities, including
chemical consumption must be targeted in order to reduce the
overall environmental impacts. Transport is also a significant
contributor.
 The followings results show how much a 5% reduction in
transportation and chemical consumption will affect the
environmental impacts. Manufacturing is more difficult to
assess but the impact of an increase of 5% of the yield (from
50% to 52.5%) is also presented. It as been assumed that an
increased yield will only impact the quantity of wood required
and not the chemical consumption in order to keep both effect
separate.
23
Solution – Q1 (Cont’d)
 It is important to note that here only easily
manipulable variable have been modified in order to
determine which changes will influence the more the
environmental impacts.
 The most important results are the following:
 A 5% increase in the yield will result in a:




A 5% reduction in transportation will result in a:



24
5.64% reduction in fresh water consumption;
4.70% reduction in virgin fiber consumption;
4.39% reduction in natural resources consumption.
4.86% reduction in energy consumption;
4.26 reduction in carcinogenic substances.
A 5% reduction in chemical will not affect
significantly the environmental impacts.
Solution – Q1 (Cont’d)
 As an environmental engineer, you will
propose the followings:




25
Increase the process performance, which will also
reduce costs.
Since reducing transportation distance is not
easily realizable, you suggest to find a mode of
transportation less pollutant.
Even if a reduction of chemical consumption will
necessarily reduce the cost, it is not an
environmental priority.
The mass balances have shown that there is a lot
of potential for fresh water reduction.
Solution - Q2
Question 2 - Normalized Results - Resources
1.2
1
0.8
Pulp Manufacturing
Chemical Production
Transport
Harvesting
Total
0.6
0.4
0.2
0
Raw Water Consumption
26
Virgin Fiber Consumption
Natural Resources
Consumption
Energy Consumption
Solution - Q2 (Cont’d)
 The last graph shows the LCA results
(resources) for the direct water recycle option.
The results have been normalized against the
reference case.
From this graph, it is
possible to say that:



27
Raw water consumption from the manufacturing
process unit has been reduced to 70% of the
reference case.
Energy consumption by the manufacturing has
been increase by 5%.
Everything else is constant.
Solution - Q2 (Cont’d)
Question 2 - Normalized Results - Resources - Emissions
1.2
1
0.8
Pulp Manufacturing
Chemical Production
Transport
Landfill
Harvesting
Growth
Total
0.6
0.4
0.2
te
W
as
So
lid
og
te
rS
m
m
og
m
er
S
W
in
og
en
ic
ci
n
ar
Su
m
an
ce
Su
bs
t
M
vy
ea
H
C
28
s
et
al
s
n
Eu
t
ro
p
hi
ca
tio
n
Ac
id
ifi
ca
tio
G
lo
ba
l
W
ar
m
in
g
0
Solution - Q2 (Cont’d)
 The preceding graph shows a reduction
in the following impact categories:

Acidification
process unit.
from
the
manufacturing
 It also shows an increase in:

Winter smog
process unit.
from
the
manufacturing
 All the remaining impact categories are
almost constant.
29
Solution - Q2 (Cont’d)
 The aggregated indicators are:


Resources: 0.76
Emissions: 1.00
 From this it is possible to conclude that
the direct water recycle solution has a
positive impact on the resource impact
categories (almost 25% improvement)
and almost no impact on the emissions.
30
Solution - Q2 (Cont’d)
 A lot of importance has been
given to the raw water
consumption. A sensitivity
analysis on the weights has
been conducted.
First,
weight of raw water has
been
decreased
while
maintaining the other relative
weights constant.
 The results are presented in
the table. It can be seen
than even if the raw water
importance passes from 83%
to 10%. There is still an
environmental benefit.
31
Weight of the
Aggregated
raw water
Indicator
consumption
0.83
0.76
0.50
0.85
0.30
0.91
0.10
0.97
Solution - Q2 (Cont’d)
 The impact category the
most influenced by the direct
recycle other than raw water
is the energy.
 By increasing the weight of
energy while maintaining the
other ratios constant we
obtain the results presented
in the table.
 The conclusion of the 2
tables
is
that
the
environmental improvement
is robust to the weights.
32
Weight of the Aggregated
Energy
Indicator
0.08
0.76
0.16
0.78
0.32
0.82
0.64
0.90
0.83
0.96
Solution - Q2 (Cont’d)
 The same strategy has been
applied to the emission impact
categories. Sensitivity analysis
have been conducted on the
acidification and winter smog
weights.
 Acidification has been reduced
so the sensitivity analysis try to
determine if more weight on this
impact category will reduce
significantly the aggregated
indicator.
 The table shows that even if
acidification weight passes from
1% to 80% this will results in
only 2% improvement.
33
Weight of the Aggregated
Acidification
Indicator
0.01
1.00
0.10
1.00
0.20
1.00
0.40
0.99
0.80
0.98
Solution - Q2 (Cont’d)
 Winter smog has been
increased so the sensitivity
analysis try to determine if
more weight on this impact
category
will
increase
significantly the aggregated
indicator.
 The table shows that even if
winter smog weight passes
from 7% to 80% this will
results
in
only
1%
degradation.
 The 2 previous tables show
that the emissions indicator
is robust to the weights.
34
Weight of the Aggregated
Winter Smog
Indicator
0.07
1.00
0.14
1.00
0.28
1.00
0.56
1.00
0.80
1.01
Solution - Q2 (Cont’d)
 Overall conclusion:



35
Direct water recycle results in a positive
resource
saving
(24%)
without
compromising the other impact categories.
Furthermore, it is a low cost solution.
In consequence, its implementation is
highly recommended.