Program for North American Mobility in Higher Education Introducing Process Integration for Environmental Control in Engineering Curricula

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Program for North American Mobility in Higher
EducationIntroducing Process Integration for
Environmental Control in Engineering Curricula

• Module 3 Environmental Challenges Pulp Paper
  Industry
• Caroline Gaudreault
• Created at
• École Polytechnique de Montréal
• Texas AM University, 2003

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LEGEND

• Go to the web site
• Go to next subject
• More information on the same subject
• Look for the answer to the question

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Tier IIIOpen-Ended Problem
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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 .

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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.

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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
• Electric power generation from excess heat in
  mill 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.

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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.

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Functional Unit

• All LCA results are presented relative to the
  functional unit. The functional unit has been
  defined as follow
• The production of 1 admt of pulp.

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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.

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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.

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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.

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Necessary documents

• LCA Base Case
• Process Simulation

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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 build-up
  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.

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Question 2 (Contd)

• 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.

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
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Question 2 (Contd)

• 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.

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Question 2 (Contd)

• Resource depletion

• Emissions

Impact Weigth
Raw water consumption 0.83
Energy consumption 0.08
Virgin Fiber consumption 0.01
Other resources 0.08
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
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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

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Solution Q1 (Contd)

• Water balances can be summarized by this picture.
• The total fresh water consumption is
  9.330.973.8320.6634.79 ton/ton of dry pulp.
• Only liquid water can be directly recycle
  0.9675.920.68120.66 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
  34.79-28.236.56 ton (ie a reduction of 81).

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Solution Q1 (Contd)

• The following graph show the contribution of each
  process unit to resource consumption.

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Solution Q1 (Contd)

• 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.

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Solution Q1 (Contd)

• The following graph show the contribution of each
  process unit to emission-related environmental
  impacts.

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Solution Q1 (Contd)

• From this graph it is possible to note that
• 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.

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Solution Q1 (Contd)

• 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.

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Solution Q1 (Contd)

• 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
• 5.64 reduction in fresh water consumption
• 4.70 reduction in virgin fiber consumption
• 4.39 reduction in natural resources consumption.
• A 5 reduction in transportation will result in
  a
• 4.86 reduction in energy consumption
• 4.26 reduction in carcinogenic substances.
• A 5 reduction in chemical will not affect
  significantly the environmental impacts.

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Solution Q1 (Contd)

• As an environmental engineer, you will propose
  the followings
• 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.

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Solution - Q2
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Solution - Q2 (Contd)

• 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
• 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.

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Solution - Q2 (Contd)
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Solution - Q2 (Contd)

• The preceding graph shows a reduction in the
  following impact categories
• Acidification from the manufacturing process
  unit.
• It also shows an increase in
• Winter smog from the manufacturing process unit.
• All the remaining impact categories are almost
  constant.

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Solution - Q2 (Contd)

• 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.

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Solution - Q2 (Contd)

• 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.

Weight of the raw water consumption Aggregated Indicator
0.83 0.76
0.50 0.85
0.30 0.91
0.10 0.97
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Solution - Q2 (Contd)

• 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.

Weight of the Energy Aggregated Indicator
0.08 0.76
0.16 0.78
0.32 0.82
0.64 0.90
0.83 0.96
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Solution - Q2 (Contd)

• 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.

Weight of the Acidification Aggregated Indicator
0.01 1.00
0.10 1.00
0.20 1.00
0.40 0.99
0.80 0.98
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Solution - Q2 (Contd)

• 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.

Weight of the Winter Smog Aggregated Indicator
0.07 1.00
0.14 1.00
0.28 1.00
0.56 1.00
0.80 1.01
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Solution - Q2 (Contd)

• Overall conclusion
• 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.