EPA/600/R-93/203
November 1993
DuPont Chambers Works
Waste Minimization Project
by
E.I. Du Pont de Nemours
Du Pont Chemicals
Chambers Works Facility
Deepwater, N.J. 08023
Air and Waste Management Division
EPA Region II
U.S. Environmental Protection Agency
New York, N.Y. 10278
RCRA Enforcement Division
Office of Solid Waste and Emergency Response
U.S. Environmental Protection Agency
Washington, D.C. 20460
Risk Reduction Engineering Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
Printed on Recycled Paper
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Notice
This report is being presented by DuPont in satisfaction of
the pollution prevention requirements of Section V of the Consent
Decree in U.S. v. DuPont,Docket Number: 91cv768(JFG), May 22,
1991. This report has been subjected to U.S. Environmental
Protection Agency peer and administrative review and approved for
publication. Approval does not signify that the contents
necessarily reflect the views and policies of the U.S.
Environmental Protection Agency, nor does mention of trade names
or commercial products constitute endorsement or recommendation
for use. This document is intended to provide useful information
about methodologies for pollution prevention in the chemical
process industries and about implementing specific pollution
prevention options on various chemical processes. Compliance
with environmental and occupational safety and health laws is the
responsibility of each individual business and is not the focus
of this report.
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Foreword
In conformance with the U.S. Environmental Protection
Agency's goal of achieving waste minimization and pollution
prevention and in harnessing the enforcement process to aid that
goal, this waste minimization project was undertaken as a
Supplemental Environmental Project.
E.I. Du Pont de Nemours prepared this final report for its
Chambers Works facility in Deepwater, N.J., as a partial
requirement of the judicial Consent Decree entered into by EPA's
Region II and DuPont on May 22, 1991. The primary purpose of the
project was to have DuPont review the existing pollution
prevention and waste minimization activities at the facility and
to identify opportunities for further prevention or minimization.
For the fifteen processes investigated, the potential exists to
reduce the hazardous waste 48 percent and to save $ 14.9 million
each year.
Because of the valuable pollution prevention and waste
minimization information in this report, the technology transfer
of the project is national in scope. The options presented are
of general interest to industry and particularly to others in
chemical processing industries.
This work is consistent with EPA's stress on pollution
prevention, greater reliance on market and economic incentives
and education and outreach.
ill
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Abstract
In a joint U.S. Environmental Protection Agency ( EPA) and
DuPont waste minimization project, fifteen waste streams were
selected for assessment. The intent was to develop assessments
diverse in terms of process type, mode of operation, waste type,
disposal needed, and relative success in identifying good waste
reduction options. The fifteen case study reports describe the
wastes and the processes that produce them, incentives for
reducing the wastes, the options generated by the assessment
teams, the technical and economic evaluation of the best options,
and what others can learn from these efforts.
The EPA assessment methodology is compared with that of
DuPont. The suggestion is made that an upgraded methodology
might combine the strengths of both.
The options generated from the fifteen assessments represent
practical experience that can benefit others in chemical
processing industries. The options were grouped into four types
of waste streams: solvent wash waste, solvent waste other than
wash waste, waste from reaction byproducts, and tar waste. These
options are described so that their suitability to another
organization's needs could be evaluated.
This report was submitted in fulfillment of the pollution
prevention requirements of Section V of the Consent Decree in
U.S. v. DuPont, Docket Number: 91cv768(JFG), May 22, 1991. The
report covers a period from May 1991 to May 1993.
IV
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Table of Contents
Section 1: Executive Summary 1
Project Methodology 2
Case Studies 3
Methodology Critique , 5
Waste Reduction Opportunities for
Organic Chemical Processes ,, 5
Section!: Project Methodology , 7
The Chambers Works Site 8
Project Scope , 8
The EPA/DuPont Project Team 8
Waste Stream Selection 8
Waste Stream Classification 9
EPA Selection Criteria 9
Final Selection 10
Assessment Methodology 10
Assessment Team Formation 10
Area Preparation 11
Option Generation 11
Option Screening 11
Feasibility Evaluation 13
Assessment Results < 16
Section 3: Case Studies 19
Case Study 1: Specialty Alcohols 20
Case Study 2: Organic Salt Process r 25
Case Study 3: Nitroaromatics 32
Case Study 4: Diphenol Ether Process.... 40
Case Study 5: CAP Purification ...t 46
Case Study 6: Polymer Vessel Washout 53
Case Study 7: Reusable Tote Bins 59
Case Study 8: Monomer Production 64
Case Study 9: CAP Isomers Process 72
Case Study 10: Wiped-Film Evaporator 78
Case Study 11: Specialty Surfactant 82
Case Study 12: CAC Process 86
Case Study 13: Solvent Emissions 92
Case Study 14: SAC Process ; 97
Case Study 15: Distillation Train 102
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Section 4: Methodology Critique 105
Methodology Overview 107
Responsible Careฎ .107
The EPA Methodology 107
The DuPont Methodology 108
Application to the Chambers Works Project 109
Methodology Comparison 110
Conclusions 118
Methodology Refinement 119
Section 5: Waste Reduction Opportunities
for Organic Chemical Processes 125
Solvent Wash Waste ...... 126
Solvent Waste (other than solvent wash) , 130
Waste from Reaction By-Products 133
Tar Waste 137
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Tables
Number Page
2-1 Selected Criteria with Relative Weights for
Five Assessments , 12
31- Ranked Summary of Specialty Alcohols Waste
Minimization Options t 23
3-2 Economic Summary of Top Specialty Alcohols Waste
Minimization Option , .. 24
3-3 Ranked Summary of Organic Salt Waste Minimization
Options , 28
3-4 Economic Summary of Top Organic Salt Waste
Minimization Options...., 31
3-5 Ranked Summary of Nitroaromatics Waste Minimization
Options (Reaction Step) 35
3-6 Ranked Summary of Nitroaromatics Waste Minimization
Options(Distillation Step) 36
3-7 Economic Summary of Top Nitroaromatics Waste
Minimization Options...., 38
3-8 Ranked Summary of Diphenol Ether Waste Minimization
Options , 42
3-9 Economic Summary of Top Diphenol Ether Waste
Minimization Options 44
3-10 Ranked Summary of CAP Waste Minimization Options 48
3-11 Economic Summary of Top CAP Waste Minimization
Options 51
3-12 Ranked Summary of Polymer Vessel Waste Minimization
Options 55
3-13 Economic Summary of Top Polymer Vessel Waste
Minimization Options 56
3-14 Ranked Summary of Tote Bin Waste Minimization
Options 61
3-15 Economic Summary of Top Tote Bin Waste Minimization
Options 62
3-16 Ranked Summary of Top Monomers Process Waste
Minimization Options 68
3-17 Economic Summary of Top Monomers Process Waste
Minimization Options 70
3-18 Ranked Summary of CAP Isomers Process Waste
Minimization Options 74
3-19 Economic Summary of Top CAP Isomers Process Waste
Minimization Options 76
3-20 Economic Summary of Wiped-Film. Evaporator Options 80
3-21 Ranked Summary of Specialty Surfactant Waste
Minimization Options 83
3-22 Economic Summary of Top Specialty Surfactant
Waste Minimization Options 84
3-23 Ranked Summary of CAC Process Waste Minimization
Options 89
3-24 Economic Summary of Top CAC Process Waste
Minimization Options 90
vii
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Tables ( cont'd)
Number
3-25
3-26
3-27
Page
Economic Summary of Air Emissions Minimization
Options 94
Economic Summary of Top SAC Waste Minimization
Options 100
Economic Summary of Top Distillation Train Waste
Minimization Options ,.... 104
viii
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Figures
Number Page
3-1 Specialty Alcohols Wash Process 20
3-2 Specialty Alcohols Waste Minimization Options 22
3-3 Organic Salt Process 26
3-4 Organic Salt Waste Minimization Options..... 27
3-5 Nitroaromatics Process 32
3-6 Nitroaromatics Waste Minimizcition Options(Reaction
Step) 33
3-7 Nitroaromatics Waste Minimizeition Options (Distillation
Step) 34
3-8 Diphenol Ether Process .40
3-9 Diphenol Ether Waste Minimization Options 41
3-10 CAP Process 46
3-11 CAP Waste Minimization Options 47
3-12 High-Pressure Water System. 54
3-13 Reusable Tote Bin and Base Tank Assembly 60
3-14 Monomers Process ,. 65
3-15 Monomers Process Waste Minimization Options 66
3-16 CAP Isomers Process 72
3-17 CAP Isomers Process Options 73
3-18 Chlorinated Aromatics Process with Wiped-Film
Evaporator 78
3-19 Wiped-Film Evaporator * 80
3-20 CAC Process , 87
3-21 CAC Product Campaigns 88
3-22 New Catalyst Filtration System 93
3-23 SAC Process , 98
4-1 Comparison of EPA and DuPont Methodologies 106
4-2 Responsible Care Codes for Pollution Prevention 108
4-3 Sources of Waste. 114
4-5 Building Blocks of a Successful Pollution Prevention
Program 120
4-6 Upgraded Methodology 121
4-7 Comparison of Conventional and Upgraded
Methodologies 122
5-1 Solvent Wash Waste Reduction Options 126
5-2 Solvent Waste Reduction Options 130
5-3 Reaction Byproducts Waste Reduction Options 133
5-4 Tar Waste Reduction Options 137
IX
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Acknowledgments
Throughout the two years of this project, an EPA/DuPont
project team coordinated its efforts to produce this Supplemental
Environmental Project Report. Personnel from EPA's Region II( New
York ), from various Headquarters offices in Washington D.C., and
from the Risk Reduction Engineering Laboratory ( Cincinnati, OH)
worked with four chemical and environmental engineers from
DuPont's Research and Development organization at the Chambers
Works facility, Deepwater, N.J.
This project team worked with management to form assessment
teams that varied in size from four to twelve members. Typically,
these assessment teams included an area supervisor, chemists,
engineers, operators, technicians, and at least one ( and as many
as three ) participants from outside the process area to provide
objective input.
Each person's advice and comments were valuable. Our thanks
and appreciation are extended to all these participants and to
the following people:
Emily Chow
Joyce Finkle
Garry Howell
James Ilaria
Davis Jones
Richard Krauser
Haile Mariam
Gale Paul
Mark Pollins
Paul Randall
Conrad Simon
Robert Trebilcock
Melissa Ward
Jocelyn Woodman
EPA, Washington DC
DuPont, Deepwater, NJ
EPA, Cincinnati, OH
EPA, Washington DC
EPA,- Washington DC
EPA, New York, NY
EPA, Washington DC
DuPont, Deepwater, NJ
EPA, Washington DC
EPA, Cincinnati^, OH
EPA, New York, NY
DuPont, Deepwater, NJ
EPA, Washington DC
EPA, Washington DC
Inquiries concerning the information contained in this report
should be directed to: C.S. Hoffman, Jr., E.I. DuPont, Chambers
Works, Deepwater, N.J. 08023.
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SECTION
Executive Summary
This report describes the proceedings and
results of the EPA/DuPont Chambers Works
Waste Minimization Project. The report is
divided into five sections:
Section 1: Executive Summary. An overview
of the entire project.
Section 2: The EPAIDuPont Chambers
Works Waste Minimization Project. A
description of the scope and goals of the
project, its participants, and the methodol-
ogy used to conduct waste minimization
assessments for 15 processes at the Cham-
bers Works site.
Section 3: Case Studies. Fifteen waste
minimization assessment reports.
Section 4: Methodology Critique. An over-
view, comparison, and critique of the EPA
and DuPont methodologies for waste reduc-
tion programs. Also discussed is the
Resjponsible Careฎ program of the Chemical
Manufacturer's Association (CMA), an
important influence upon the DuPont
methodology.
Section 5: Technology Exchange. A sum-
mary of implementation options generated
by the 15 assessments and a post-assessment
search of the technical literature.
SECTION 1: Executive Summary
Pagel
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Project Methodology
The joint waste minimization project of the
EPA and DuPont had three primary goals:
to identify methods for the actual reduction
or prevention of pollution for specific
chemical processes at the Chambers Works
site,
to generate useful technical information
about methodologies and technologies for
reducing pollution which may help the EPA
assist companies implementing pollution
prevention/waste minimization programs,
and
to evaluate and identify potentially useful
refinements to the EPA and DuPont method-
ologies for analyzing and reducing pollution
and/or waste generating activities.
Project Scope
The Chambers Works Waste Minimization
Project involved about 150 people at the site
who devoted more than 12,000 person-hours
to the project. A brief history of the project is
provided below:
May 1991: Creation of the EPA/DuPont
project team
May 1991-June 1992: Selection of 15 waste
streams for inclusion in the project
June 1992-August 1992: Area preparation
* August 1992-November 1992: Assessment
phase
Waste Stream Selection
Five processes each were selected from three
categories:
Category 3: Processes for which no recent
waste minimization and/or pollution preven-
tion assessment analysis has been per-
formed.
Category 2: Processes which have shown
little or no progress in waste minimization
or pollution prevention.
Category 1: Processes which have shown
significant progress in waste minimization
or pollution prevention.
In choosing the 15 waste streams, it was the
intent of the EPA/DuPont project team to
develop a group of assessments that are
diverse in terms of process type, mode of
operation (i.e., batch or continuous), waste
type, disposal media, and relative success in
identifying good waste reduction options.
Assessment Methodology
The assessments typically involved the fol-
lowing steps:
Assessment team formation. The project
team worked with management to form
multidisciplinary assessment teams for the
15 assessments.
Area preparation. Each assessment began
with data collection and an inspection of the
process area.
Option generation. For seven of the 15
assessments, brainstorming sessions were
convened to generate waste reduction
options.
Option screening. The assessment teams for
five assessments applied the weighted-sum
method to screen and prioritize options.
Feasibility evaluation. Economic evalua-
tions determined the net present values
(NPV) and internal rates of return (IRR) for
waste reduction options.
Assessment Results
To date, seven of the 15 processes have
implemented waste reduction options. Without
those implementations, their wastes would
Page 2
SECTION 1: Executive Summary
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have totaled 4,004,000 Ibs per year. They now
total 1,075,000 Ibs per year, a reduction of
73%. The total capital requirement for these
seven processes was $3,085,000.
The other eight processes are now in various
stages of implementing waste reduction
projects. Their combined waste streams total
4,934,000 Ibs per year. The assessments
identified options that could reduce this
number by 34% to 3,250,000 Ibs. Total capital
cost for implementing the waste reductions is
$3,600,000. A brief follow-up note will be
provided to the EPA in one year to summarize
the implementation status for these eight
processes.
If the recommended options for all 15 case
studies are implemented, and if they achieve
the predicted waste reductions, then DuPont
will save $14,900,000 per year (using the
DuPont methodology for economic evalua-
tions). These savings are itemized below:
$1,645,000 in waste disposal costs (treat-
ment, handling, packaging, transportation,
etc.)
$2,185,000 from improved product recovery
(reduced raw materials consumption, re-
duced utilities use, etc.)
$11,070,000 from such process improve-
ment benefits as increased uptime, increased
capacity, improved quality, etc.
Case Studies
In choosing the 15 waste streams, it was the
intent of the EPA/DuPont project team to
develop a group of assessments that are
diverse in terms of process type, mode of
operation (i.e., batch or continuous), waste
type, disposal media, and relative success in
identifying good waste reduction options.
The 13 case studies (assessment reports)
describe waste streams, the processes that
generate them, the incentives for reducing the
wastes, the waste reduction options generated
by members of assessment teams, the techni-
cal and economic evaluations of the best
options, and the key learnings for other waste
reduction efforts.
The 15 assessments are summarized below.
Category 3:
CASE STUDY 1: SPECIALTY ALCOHOLS
A reduction in product impurities permits
elimination of waste from a product wash
step.
CASE STUDY 2: ORGANIC SALT PROCESS
A waste reduction effort extends its scope to
an "upstream process" for possible source
reductions.
CASE STUDY 3: NITROAROMATICS
Improved flow control is the key to waste
reduction in this distillation process.
CASE STUDY 4: DIPHENOL ETHER PROCESS
Balancing the potential for waste reduction
with operational safety.
CASE STUDY 5: CAP PURIFICATION
Viable waste reductions are difficult to
identify in old processes.
Category 2
CASE STUDY 6: POLYMER VESSEL WASHOUT
High-pressure water cleaning eliminates the
use of a hazardous solvent.
CASE STUDY 7: REUSABLE TOTE BINS
Returnable product containers eliminate
55-gallon drums.
CASE STUDY 8: MONOMER PRODUCTION
A reaction/distillation process achieves
waste reduction through better process
control.
SECTION 1: Executive Summary
Page3
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CASE STUDY 9: CAP ISOMERS PROCESS
Switching from batch to continuous feeding
of a chemical stabilizer reduces waste in a
distillation process.
CASE STUDY 10: WIPED FILM EVAPORATOR
Existing technology for reducing waste
through increased product recovery.
Category 1
CASE STUDY 11: SPECIALTY SURFACTANT
A partnership between customer and manu-
facturer leads to the elimination of CFC
from a surfactant product.
CASE STUDY 12: CAC PROCESS
Involving people from all disciplines in
waste reduction effort is a key factor in
eliminating a waste stream.
CASE STUDY 13: SOLVENT EMISSIONS
Upgrading the filtration system for recover-
ing a metal catalyst has eliminated solvent
emissions.
CASE STUDY 14: SAC PROCESS
Improvements in raw material quality open
the door to substantial waste reductions.
CASE STUDY 15: DISTILLATION TRAIN
Relaxing cross-contamination limits in a
multiproduct process helps reduce waste.
The accumulated experience of the 15 assess-
ments yielded a number of key learnings for
waste reductions in the process industries:
It is important to consider all business
objectives when trying to minimize waste.
Waste reduction is often interrelated with
such other business objectives as quality
improvement, increased yield, increased
capacity, shorter cycle time, etc.
The effective elimination or reduction of a
waste stream can often proceed in a series of
small improvements, rather than in the
implementation of a single solution. Waste
reductions in one part of a process often
produce opportunities for further reductions
in other parts of the process.
There is sometimes a trade-off between the
safe operation of a process and pollution
prevention.
Recycling solutions still have their place,
but only after all practical source reductions
have been made.
Waste reductions will increasingly involve
collaboration between producers and
customers.
Waste minimization assessments need not
be confined to the process area. They can be
performed by the sales force to explore
opportunities offered by "green" marketing.
ป Many waste reductions can be identified and
implemented by line workers. Operators and
mechanics should be included on waste
assessment teams.
Equipment startups and shutdowns are a
major source of waste.
Quality need not be sacrificed to achieve
waste reductions.
Improved process control can often result in
dramatic waste reductions.
Page 4
SECTION 1: Executive Summary
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Methodology Critique
Most waste reduction methodologies consist
of the same basic steps:
Chartering
Waste stream selection
Assessment phase
Implementation
Auditing
What distinguishes a methodology in terms of
success or failure is the tools they provide for
assessment teams at the process level. Tools
are methods for accomplishing the tasks
prescribed by a methodology.
The recent publication of the EPA's Facility
Pollution Prevention Guide represents a major
upgrade to the methodology. It places addi-
tional emphasis on the management of a
continuous waste reduction program.
An important strength of the new methodol-
ogy is its recognition that pollution prevention
requires the participation from all levels of the
organization. It contains well-articulated
prescriptions around management commit-
ment. ;
The Pollution Prevention Guide prescribes
flexibility in the choice of assessment tools to
suit local circumstances. But the DuPont
members of the Chambers Works project team
believe that the tools featured by the Guide in
dedicated chapters and appendixes exhibit a
bias toward formal and rigorous tools. Such
featured methods as the total cost assessment,
life cycle analysis, and weighted-sum rating
and ranking all have simpler counterparts. The
DuPont team members feel that the more
rigorous tools work best when applied to very
complex problems with many factors to
consider. But most problems addressed at the
process area level are amenable to quicker,
less formal methods.
An upjgraded methodology might combine the
strengths of the EPA chartering tasks with the
flexibility at the process level of the DuPont
method. Documentation supporting such a
methodology could present a variety of tools,
describe how they are applied, provide clear
examples, and include helpful forms or check-
lists.
Waste Reduction Opportunities for
Organic Chemical Processes
The waste reduction options generated during
the 15 assessments of the Chambers Works
Waste Minimization Project represent a body
of practical experience that can benefit others
throughout the chemical processing industries.
These options are compiled here and grouped
by four waste stream types.
1. Solvent Wash Waste
Cleaning of equipment is one of the most
common areas of waste generation. Three of
the 15 assessments focused on solvent waste
reduction.
2. Solvent Waste (other than wash waste)
Solvents are commonly used in the chemical
industry as carriers to dissolve and dilute
reactants or products, or as washing agents to
wash out impurities from products. Five of the
15 assessments focused on solvent waste
minimization.
3. Waste from Reaction Byproducts
Most processes that involve chemical reac-
tions also involve side reactions which pro-
duce byproducts. The costs associated with the
SECTION 1: Executive Summary
Pages
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byproducts consist not only of the increasing
disposal costs, but also the cost of raw materi-
als and product yield. Six of the 15 assessments
focused on reduction of byproducts.
4. Tar Waste
In many distillation processes, tar wastes
accumulate in the bottoms of distillation col-
umns. The Chambers Works project encoun-
tered three major contributors to tar waste:
Reaction byproducts or impurities in the
product crude.
Thermal decomposition or polymerization
within the column reboiler.
The presence of such additives as stabilizers
or inhibitors within the product crude.
Six of the 15 assessments focused on reduc-
tion of tar wastes.
Pages
SECTION 1: Executive Summary
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SECTION
Project Methodology
This section describes the joint waste minimi-
zation project of the EPA and DuPont. The
project, which lasted from May 1991 to May
1993, had three primary goals:
To identify methods for the actual reduction
or prevention of pollution for specific chem-
ical processes at the Chambers Works site.
To generate useful technical information
about methodologies and technologies for
reducing pollution which may help the EPA
assist companies implementing pollution
prevention/waste minimization programs.
ซ To evaluate and identify potentially useful
refinements to the EPA and DuPont method-
ologies for analyzing and reducing pollution
and/or waste generating activities.
Under the leadership of an EPA/DuPont
project team, waste minimization assessments
were performed for 15 industrial processes at
the DuPont Chambers Works chemical site in
Deepwater, New Jersey. Individual assess-
ment teams from each process applied the
EPA. and DuPont methodologies to identify
and evaluate ideas for reducing waste.
SECTION 2: Project Methodology
Page 7
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The Chambers Works Site
The Chambers Works site, one of the largest
in DuPont, employs nearly 3,000 people and
produces more than 600 different chemicals.
The site contains five operating areas and an
R&D group. Each of the operating areas
contain several production facilities which in
turn can contain several processes. Chambers
Works generates about 1,000 waste streams to
various media, including air, water, and land.
Chambers Works has an ongoing waste
reduction program. Between 1990 and 1991,
this program achieved a number of important
reductions in wastes generated by on-site
processes:
Dissolved organics in wastewater reduced
by 9.5%
Wastes sent to off-site treatment or disposal
facilities reduced by 35.3%
Wastes incinerated on-site reduced by 7.9%
Wastes sent to secure landfill reduced by
45.6%
Most, but not all, of the wastes generated at
Chambers Works are treated at one of three
on-site disposal facilities. These facilities are:
A wastewater treatment plant. This facility
treats all Chambers Works wastewater
streams, as well as wastewater streams from
other companies.
An incineration facility. The incinerator
disposes of the site's liquid waste that is
unsuitable for wastewater treatment. Excep-
tions include some streams that contain
valuable materials (e.g., precious metal
catalysts) which Chambers Works is not
equipped to recover. Those streams are sent
to outside reclamation facilities.
A secure landfill. The landfill receives the
site's solid hazardous waste.
Project Scope
The Chambers Works Waste Minimization
Project evolved from a consent order entered
in May, 1991. Project planning was prescribed
by the terms of the consent order. The project
involved about 150 people at the site who
devoted more than 12,000 person-hours to the
project. The 15 assessments identified 4.6
million pounds of waste reductions, three
million of which have already been imple-
mented. A brief history of the project is
provided below:
May 1991: Creation of the EPA/DuPont
project team
May 1991-June 1992: Selection of 15 waste
streams for inclusion in the project
June 1992-August 1992: Area preparation
(information gathering, creation of assess-
ment teams)
August 1992-November 1992: Assessment
phase (waste minimization assessments
performed)
The EPA/DuPont Project Team
In May of 1991, an EPA/DuPont project team
was formed to implement the Chambers
Works project. The team consisted of EPA
personnel from Region 2 headquarters in New
York, from various EPA headquarters offices
in Washington, DC, and from the Risk Reduc-
tion Engineering Laboratory in Cincinnati.
The DuPont members were four chemical and
environmental engineers from the R&D
organization at Chambers Works.
Waste Stream Selection
In choosing the 15 waste streams, it was the
intent of the EPA/DuPont Project Team to
develop a group of assessments that are
diverse in terms of process type, mode of
Pages
SECTION 2: Project Methodology
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operation (i.e., batch or continuous), waste
type, disposal media, and relative success in
identifying good waste reduction options.
Waste stream selection began with the DuPont
project team members leading a plant-wide
effort to prioritize the waste streams generated
at Chambers Works. They began by collecting
waste information, including a list of waste
streams and their volumes in pounds. The
project team then organized five brainstorming
sessions with key people from each opera-
tional area. These meetings produced a first
cut of 168 waste steams. The project team
then reduced this list to thirty candidates based
on the following two sets of criteria: waste
stream classification and EPA selection
criteria.
From the preliminary list of 30, the EPA team
members selected the final 15 waste streams.
Waste Stream Classification
One of the criteria for selecting processes for
this study is that five would have to be se-
lected from each of three categories:
Category 3: Processes for which no recent
waste minimization and/or pollution preven-
tion assessment analysis has been per-
formed.
Category 2: Processes which have shown
little or no progress in waste minimization
or pollution prevention.
Category 1: Processes which have shown
significant progress in waste minimization
or pollution prevention.
The 15 waste streams eventually chosen for
this project satisfied the classification criteria
at the time of their inclusion on the candidate
list of 30. But before the assessment phase
began, the processes that generated three of
the Category 2 streams began or committed to
implementations that would eliminate or
greatly reduce the wastes. In essence, they
became Category 1 waste streams. This is not
surprising given the definition of Category 2
wastes; the facilities that generated them were
already at work to reduce them.
One of the processes generating Category 3
wastes also implemented a project which
eliminated the waste entirely.
EPA Selection Criteria
The EPA specified a number of additional
criteria to guide DuPont in the selection of the
30 candidate processes. EPA provided these
criteria to ensure a variety of candidate pro-
cesses from which to choose the 15. This in
turn would allow DuPont to assess a well-
rounded set of processes to provide as many
different examples to industry as possible.
The EPA selection criteria were:
ป Only ongoing processes at Chambers Works
could be considered.
The process must produce either a high-
volume waste stream, or a waste stream
containing high concentrations of hazardous
constituents.
At least one process from each Chambers
Works operating area must be selected.
A process could not be rejected because it is
unique or proprietary.
The selected candidates would include both
batch and continuous processes.
ซ Prioritizing waste streams to select pro-
cesses would proceed in accordance with the
process outlined by the EPA methodology.
In addition, the selected processes should meet
as many as possible of the following criteria:
Candidate processes should either use or
release one of the chemicals on the EPA
"list of 17", or else meet all other project-
specific criteria.
SECTION 2: Project Methodology
Pages
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The processes should have the potential for
pollution prevention technology transfer to
the EPA or other companies.
The selected processes should be of types
for which little or no technical information
for pollution prevention is readily available.
The selected candidates should include
processes that release waste to a variety of
media: air, land, and water.
These criteria may not necessarily lead other
plants to choose the best streams for waste
reduction opportunities. However, EPA
believes that they helped to identify 15 Cham-
bers Works processes which had both high
potential for waste reductions and for provid-
ing a good breadth of technical information
for technology transfer.
Final Selection
In February of 1992, EPA project team mem-
bers arrived at Chambers Works to inspect the
facilities that generated the 30 candidate waste
streams and to attend process overview ses-
sions. The information they received during
their visit guided their selection of the final
15 waste streams.
Assessment Methodology
The assessments were performed using the
EPA and DuPont methodologies for waste
reduction, and typically involved the follow-
ing steps:
Assessment team formation
Area preparation
Option generation
Option screening
Feasibility evaluation
For Category 1 assessments, option genera-
tion, screening, and evaluation were per-
formed retrospectively. The assessment teams
did not try to generate new options, but tried
simply to compile the options that had been
considered and reconstruct whatever
prioritization of the options had been per-
formed.
Three Category 2 and one Category 3 pro-
cesses identified successful waste reductions
or eliminations before the start of the project's
assessment phase. Therefore, like the Cat-
egory 1 assessments, option generation,
screening, and evaluation were performed
retrospectively.
Two of the Category 2 processes and all of the
Category 3 processes performed all of the
assessment steps as prescribed by the EPA
methodology.
Assessment Team Formation
The project team worked with management at
the five operating areas to form assessment
teams for the chosen facilities. Assessment
teams varied in size from four to 12 members.
They tended to be smaller at those facilities
which had already implemented successful
waste reductions. They tended to be larger in a
few cases where the scopes of the assessments
expanded to include other related processes at
Chambers Works.
A conscious effort was made to include multi-
disciplinary representation on the assessment
teams. Teams typically included an area
supervisor, chemists, engineers, operators, and
technicians. All of the teams included at least
one, and as many as three, participants from
outside the process area to provide objective
Page 10
SECTION 2: Project Methodology
-------
input. A description of assessment team
dynamics is included in Section 4 of this
report. In general, the project team found that
multidisciplinary participation, and especially
the inclusion of line workers on the teams,
enhanced the number and quality of the
options generated.
Area Preparation
All of the assessments began with data collec-
tion and area inspection.
DATA COLLECTION
For each assessment, the project team col-
lected such process data as operating proce-
dures, flow rates, raw material and product
specifications, records of process changes or
experimental trials, process costs, etc. Where
material balances were not available, the
project team created them using the collected
process data.
Information about the waste stream was also
collected. This included waste stream compo-
sition, amounts, disposal media, disposal
costs, and such special costs as transportation,
handling, and packaging.
Data collection typically took one project
team member from fourjito eight hours, de-
pending on the availability of information and
the complexity of the process.
AREA INSPECTION
Area inspections were performed for all 15
assessments. These usually began with a
meeting of project team members, outside
members of the assessment team, and people
from the process area. At these meetings, the
process operations and material balances were
reviewed. Then the participants toured the
area. The meeting and inspection together
typically took about two hours.
The site inspections were useful for giving
outsiders on the assessment team a good
understanding of the process in a short time.
It also provided an opportunity to talk with
process operators and other people who work
at the process area.
Option Generation
For the seven assessments in which the EPA
methodology was applied, brainstorming
sessions were convened to generate waste
reduction options. At these meetings, the
assessment teams proposed ideas for reducing
the target waste stream. Team members were
encouraged to suggest ideas regardless of
whether they seemed practical at the moment.
Scribes captured suggestions and recorded
them on cause-and-effect "fishbone" charts.
The fishbone charts enabled options to be
grouped into such categories as "chemistry",
"equipment modification", "new technology",
etc. The brainstorming sessions lasted from
two to four hours, and generated about 10 to
20 options each.
For the eight retrospective assessments (i.e.,
assessments on processes which had already
begun or completed implementations), no
attempt was made to generate additional
options. Instead, the assessment teams at-
tempted merely to identify and evaluate the
options that had been considered.
Option Screening
The EPA methodology offers several tools for
screening options which vary in complexity
from simple voting by the assessment team to
the more rigorous weighted-sum ranking and
weighting. Of the seven assessments which
followed the full EPA methodology, five used
weighted-sum ranking and weighting to screen
the options; the other two used simple voting.
SECTION 2: Project Methodology
Page 11
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Table 2-1. Selected Criteria with Relative Weights for Five Assessments
Reduce Safety Hazards
Reduce Treatment/Disposal Costs
Reduce Waste Quantity
Effect on Product Quality
Chance of Success
Fit Corporate Goals
Enhance Consumer Relations
Enhance Community Relations
Reduce Hazardous Toxic'rty
Reduce Raw Mat'l Costs
Low Capital Costs
Low O&M Costs
Short Implementation Period
Ease of Implementation
Success Within DuPont
Success Outside DuPont
Production Not Disrupted
Permit Requirements
Enhance Employee Relations
Source Reduction
Best Available Technology
CAP
Purification
10
8
10
5
10
8
8
8
3
8
8
8
5
8
9
-
4
8
7
10
-
Nitroaromatics
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Organic Salt
Process
10
10
10
10
10
8
5
5
4
10
10
8
7
6
2
1
3
1
1
-
-
Diphenol Ether
Process
10
-
10
10
10
8
8
8
4
10
7
7
7
6
-
-
3
1
-
5
3
Monomer
Production
10
1
5
10
8
-
10
8
5
8
8
8
6
6
-
10
-
8
6
-
In those assessments using the weighted-sum
method, follow-up meetings were held after
the brainstorming sessions. The meetings
began with an open discussion of the options.
Sometimes, a team concluded that an option
did not really reduce waste and removed it
from the list. At other times, interdependent
options were combined into a single option, or
general options were divided into several
more specific options.
After the team agreed on the final option list,
they generated a set of criteria against which
to evaluate the options. Generally, the criteria
Page 12
SECTION 2: Project Methodology
-------
prescribed by the EPA methodology were
adopted as a starting point. Other criteria were
often added to reflect company-specific or
process-specific concerns. Table 21 shows
the criteria and relative weights for the five
waste streams that underwent formal ranking
and weighting.
After the criteria were adopted, each one was
assigned a weight, usually between 0 and 10,
to signify its relative importance. In some
cases, the teams felt that a criterion was not
important to a process, or was adequately
covered by another criterion. They therefore
assigned a value of "0", essentially removing
the criterion from the list.
After the weights were established, each
option was rated according to how well it
fulfilled each criterion with a number from
0 to 10. Multiplying the weight by the rating
provided a score for that criterion, and the sum
of all the scores of all the criteria yielded the
option's overall score.
One assessment team, for the mtroaromatics
process, adopted a simplified method in which
they assigned a weight of "1" to all criteria.
They then assigned ratings of -1,0, or +1
according to how well-an option satisfied each
criterion.
Each assessment team was allowed to assign
their own weights to the criteria. Not surpris-
ingly, the weights varied from assessment to
assessment. The project team did not suggest
common weights for all assessments because
this would not have met process-specific
needs. For example, the criterion "short
implementation time" may be less important
where demand for a product is soft. One thing
that all teams seemed to have in common is
that the criteria "safety" and "probability of
success" were always more decisive than then-
assigned weights. A low score for safety was
not the same as a similar score for another
criterion. If an option ranked high in all
criteria except safety or probability of success,
it stood no chance of being considered for
implementation.
Feasibility Evaluation
Technical evaluations for the top options were
performed by the project team with input from
the assessment teams. No formal method was
used for performing most technical evalua-
tions. The project team found that the discus-
sions of each option during the ranking and
weighting sessions usually determined an
option's practicality, safety, and effectiveness
in reducing waste. Some of the top options
require plant or lab trials to determine their
technical feasibility.
The most difficult part of the feasibility
evaluation was the economic analysis. This
required estimates of equipment cost, installa-
tion cost, the amount of waste reduction, cost
savings to the process, and economic return.
For all options that had not already been
estimated by the individual facilities, the
project team performed the evaluations.
CALCULATING NPV AND IRR
DuPont uses net present value (NPV) and
internal rate of return (IRR) as metrics for
comparing the relative values of waste reduc-
tion options. The NPV is the value to DuPont
of an option over time expressed in today's
after -tax dollars. The value of future cash
flows are discounted to today's dollars using a
given discount rate. All NPV calculations in
this report use a discount rate of 12%. The
IRR is the discount rate at which the NPV of a
given option would equal zero.
The DuPont and EPA methodologies offer
similar tools for performing economic feasi-
bility evaluations. Both offer a simple pay-
back calculation for projects with low capital
costs. Both recommend a calculation of NPV
which incorporates expanded time horizons,
SECTION 2: Project Methodology
Page 13
-------
long-term indicators, and allocation of costs
by area. The DuPont methodology offers a
short-cut formula to quickly calculate NPV
based on a set of assumptions. Otherwise,
NPV is usually calculated using computerized
spreadsheets.
One point on which the DuPont and EPA
methodologies differ is how to handle waste
disposal costs. DuPont calculates only the
direct cost of waste disposal. But there are
other costs associated with waste disposal
such as indirect costs, liability costs, and such
"soft" costs as community relations. Process
engineers make subjective decisions about
how these other costs add to or offset the
results of an NPV calculation. But the EPA
recommends that dollar values be assigned to
these other costs and that they be included in
the NPV calculation.
For the Chambers Works project, NPVs were
calculated in two ways to permit a comparison
of the two methodologies. The NPVs labeled
"DuPont Method" in the assessment reports
use only the direct cost of waste disposal in
the calculation. The NPVs labeled "EPA
Method" were calculated using dollar values
assigned for indirect costs, liability costs, and
soft costs. In both cases, the calculations of
NPV and IRR were based on a number of
assumptions, some of which are listed below:
a time span of 10 years
U.S. tax and depreciation rates
a 4% inflation rate for all cash flows
* startup costs at 10% of investment
40% of permanent investment spent in first
year, 60% spent in second year, and start-up
at the beginning of the third year
achievement of 50% of the costs and rev-
enues in the first year of operation
the only terminal value of a project is its
working capital liquidation
calculation made at beginning of year zero
end-of-year cash flows
When applying the EPA method to calculate
NPV, the project team constructed a comput-
erized spreadsheet to estimate the value of
each variable in the calculation. These in-
cluded costs associated with investment,
revenue, costs savings, working capital, and
one-time charges.
A short-cut method for calculating NPV for
quick evaluation of multiple options has been
developed by DuPont. This formula is math-
ematically equivalent to the EPA methodology
as long as the assumptions given above are
made.
NPV(12%) =
(-.91)*! + (-3.3)*(C-R) + (-.50)* WC + (-.54)*OTC
where: I = Investment
C = Cost
R = Revenue
WC = Working capital
OTC = One-time charges
In this formula, the assumptions determine the
values of the coefficients (the numbers within
parentheses). Changing the assumptions
would require a change in the coefficient
values.
Calculating the investment for an option
required an understanding of the impact the
option will have upon operating procedures
and equipment. At times, the project team
used computer modeling to determine this
impact. Estimates for equipment costs were
aided by the availability of an in-house data-
base of such costs, vendor information, and
trade books. These estimates also had to
Page 14
SECTION 2: Project Methodology
-------
include costs associated with the installation
of equipment, such as piping, instrumentation,
contingency, escalation, etc.
Estimating changes in operating costs required
data for the annual generation of waste, waste
disposal media, disposal costs, and any appli-
cable special waste costs such as transporta-
tion, handling, and packaging. Operating costs
include raw materials, utilities, and labor. The
economic evaluations in this report also
considered cost savings which are triggered by
waste reduction options, but are not directly
related to waste reduction. These include
improved equipment uptime, increased pro-
ductivity, faster product changeovers in
multiproduct facilities, improved quality, and
reduced working capital.
Many options claimed additional product
recovery as a benefit. Estimating the value of
the additional product depended on whether
the generating process was "sold out" (i.e.,
every pound of product had an immediate
buyer) or had slack demand. In slack-demand
processes, production can be reduced by an
amount equivalent to the amount of product
recovered. Thus, the value of additional
product recovery equals the variable cost of
producing the equivalent amount of new
product. In the sold-out processes, there would
be no production decrease since every avail-
able pound of product is quickly sold. Thus,
the value of the recovered product equals its
selling price less any additional selling costs.
Many options require laboratory or plant trials
to demonstrate their technical feasibility. The
cost of these trials were handled as one-time
charges and include the cost of engineering,
chemists, lab time, etc.
EPA METHOD VS. DuPONT METHOD
The DuPont method calculates only real
changes in cash flow resulting from a project.
The method recognizes that the economic
evaluation is not always the chief determinant
of whether a waste reduction option gets
approval for implementation. So-called "soft
costs" are also considered. But no attempt is
made to place a dollar value on these costs.
Examples of such costs are safety, occupa-
tional health, and community relations. Soft
costs can cause an economically acceptable
option to be rejected, or an economically
marginal option to be approved. In one of the
case studies included in this report, a waste
reduction option which had a negative NPV
was implemented because of the soft cost of
regulatory compliance. Another of the case
studies reports implementation of a negative-
NP V option because the implementation
would enhance customer relations. Con-
versely, several assessments identified cost-
effective options that were rejected because of
negative soft costs, i.e., they would compro-
mise safety.
The EPA method suggests a "total cost assess-
ment", which considers four elements:
extended time horizon
use of long-term indicators
allocation of costs by area
expanded cost inventory
All of these elements are accounted for in the
DuPont methodology except for the expanded
cost inventory. This element attempts to place
dollar values on what DuPont would regard as
soft costs. Such intangibles as enhanced public
SECTION 2: Project Methodology
Page 15
-------
image are quantified and included in the NPV
calculation. For the 15 assessments, NPVs and
IRRs that were calculated by the EPA method
include an allowance for future liability and
full disposal costs. But they don't include the
intangible benefits as these were judged to be
too difficult to estimate.
Another difference between the EPA and
DuPont methods is in the way waste disposal
costs are estimated. Most of the waste streams
in this report are disposed on-site at one of the
Chambers Works disposal facilities. The
accounting system at Chambers Works
charges a process the full fixed and variable
costs for the waste it generates. This is the
allocation of cost by area recommended by the
EPA's total cost assessment. However, the
DuPont methodology for calculating disposal
cost savings uses only the actual cost saved by
DuPont, i.e., the variable costs of waste
disposal. The fixed costs associated with the
on-site treatment facilities do not significantly
decrease with smaller waste volume. These
costs are redistributed among the remaining
users. In other words, the on-site treatment
cost used by a process in economic evalua-
tions is lower than the cost actually paid by
the process for waste treatment.
To some extent, the existence of on-site
treatment facilities does tend to reduce the
incentive for waste reduction when economics
are calculated using the DuPont methodology.
For marginal cases, an NPV using the full cost
of disposal is often calculated in addition to
the variable cost-only NPV. In these instances,
the direct-cost NPV is the primary evaluation
tool and the full-cost NPV is considered as a
soft benefit. In those cases where waste is
disposed off site, the NPV calculated by the
DuPont and EPA methodologies are the same.
For most of the 15 assessments, the DuPont
and EPA economics did not differ greatly.
Discounting of future cash flows diminished
the differences between the two calculations,
especially for economically attractive options.
In fact, disposal costs represented only a small
portion (about 11%) of the savings in most
cases. Savings from such process improve-
ments as shorter cycle times, yield increases,
reduced raw material costs, etc. were usually
decisive. The value of these savings is exactly
the same whether one uses the EPA or the
DuPont method of calculating NPV.
Assessment Results
To date, seven of the 15 processes have
implemented waste reduction options. Without
those implementations, their wastes would
have totaled 4,004,000 Ibs per year. They now
total 1,075,000 Ibs per year, a reduction of
73%. The total capital requirement for these
seven processes was $3,085,000. The largest
capital project required $2,200,000, while
some projects required no capital money at all.
The total NPV for the waste reductions was
$15,574,000 (using the DuPont methodology).
They all had positive economic returns, except
for one implementation that was regulatory
driven. Economic returns for the implementa-
tions tended to be very high because most of
them provided benefits other than waste
minimization, such as increased yield, produc-
tivity, reduced cycle time, etc. All seven
implementations achieved source reductions,
although some combined source reductions
with recycling as well.
The other eight processes are now in various
stages of implementing waste reduction
projects. Their combined waste streams total
4,934,000 Ibs per year. The assessments
identified options that could reduce this
number by 34% to 3,250,000 Ibs. Only one of
the eight processes identified an option that
would completely eliminate the waste stream.
The others identified reductions ranging from
Page 16
SECTION 2: Project Methodology
-------
21% to 50%. Total capital cost for implement-
ing the waste reductions is $3,600,000. All
eight of the processes identified options with
positive economic returns for a total NPV of
$23,681,000 (using the DuPont methodology).
Most of the processes have begun implementa-
tions, but several have placed their implemen-
tations on hold pending commitment of re-
sources. A brief follow-up note will be pro-
vided to the EPA in one year to summarize the
implementation status for these eight processes.
If the recommended options for all 15 case
studies are implemented, and if they achieve
the predicted waste reductions, then DuPont
will save $14,900,000 per year (using the
DuPont methodology). These savings are
itemized below:
$1,645,000 in waste disposal costs (treat-
ment, handling, packaging, transportation,
etc.)
$2,185,000 from improved product recovery
(reduced raw materials consumption, reduced
utilities use, etc.)
$ 11,070,000 from such process improve-
ment benefits as increased uptime, increased
capacity, improved quality, etc.
Not all waste minimization assessments
identify cost-effective waste reductions. The
high rate of return for the assessments in this,
project are probably due to the EPA methodol-
ogy criteria by which the waste streams were
selected. These criteria select waste streams in
part for their waste minimization potential,
weeding out the streams that are less likely to
be reducible. The criteria also tend to select
large waste streams which offer more pounds
of waste reduction per dollar of capital
spending.
When large streams contain valuable products,
the value of recovering the product often
exceeds the cost of disposal. In fact, disposal
costs represented only a small fraction of the
savings for many of the assessments in this
project. Most of the savings come from other
process improvements that result from the
waste reduction option, such as improved
yield, quality, cycle time, and productivity.
SECTION 2: Project Methodology
Page 17
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-------
SECTION
Case Studies
This section presents the assessment reports
for the 15 waste streams that comprised the
Chambers Works project. The reports describe
the wastes and the processes that produce
them, the incentives for reducing the wastes,
the waste reduction options that were gener-
ated by assessment teams, the technical and
economic evaluations of the best options, and
key learnings for other waste reduction efforts.
In each report, only the best waste reduction
options are described in any detail. The full
list of generated options are presented in
tables, along with the pros and cons of each.
The economic evaluations of the best options
are also summarized in tables.
Before reading these reports, be sure to review
Section 2: Project Methodology for a descrip-
tion of the methods used for option generation
and screening, and for performing the techni-
cal and economic feasibility analyses.
Section 2 also describes the selection and
classification of the waste streams included in
the project, and the formation of assessment
teams and the tasks they performed.
The reports provide economic and waste
reduction totals for individual assessments.
The combined totals for all 15 assessments are
presented in Section 2.
SECTION 3: Case Studies
Page 19
-------
CATEGORY 3
Case Study 1: Specialty Alcohols
A reduction in product impurities permits elimination of waste from a
product wash step
Abstract
This case study describes a successful effort to
eliminate a waste stream generated by wash-
ing a specialty alcohol product of impurities
and residual acidity. Improvements in the
purity of the crude product have enabled the
business to explore ways of neutralizing the
residual acidity and eliminating the wash step
entirely. This effort began not as a waste mini-
mization project, but as part of an overall
process improvement program. Acid neutral-
ization will replace washing because it attains
most of the goals of the program, of which
waste minimization is but one. This study
highlights the importance of considering all
business objectives when trying to minimize
waste. Waste minimization is often interre-
lated with such other business objectives as
quality improvements, increased capacity, and
reduced cycle times. This assessment also
demonstrates how improvements in one area
of a process can produce opportunities for
improvement in other areas.
Wash #1/Wash #2
Water
Chemical scavenger
Isopropyl alcohol (IPA)
SIGHT GLASS
A batch of alcohol crude
enters the wash kettle
and is mixed with wa-
ter, chemical scavenging
agents, and isopropyl alcohol
(IPA). The mixture is agitated
and then allowed to settle. The
specialty alcoholproduct sepa-
rates from the wash and settles
to thebottom of thekettle. The
mixture is then drained from
thebottom of thekettle through
a sight glass monitored by an
operator. The settled product
leaves the kettle bottom first
and is sent to an accumulator
tank. When the operator sees
that the product layer has
drained and the aqueous wash
has started to exit the kettle,
he/she diverts the flow from
the accumulator tank to a sump
for disposal.
The product layer in the accumulator tank is then
returned to the wash kettle for a second wash with water,
scavengers, and IPA. Again, the mixture is agitated and
then allowed to settle. The kettle is drained, with the
specialty alcohol product going to the accumulator
Specialty alcohol crude
ACCUMULATOR
TANK
Specialty alcohol crude
(to wash #2)
Aqueous wash
(waste stream)
Specialty alcohol crude
(from wash #1/wash #2)
FILTER
Finished
product
tank. Again, the operator diverts the aqueous wash to
the wastewater sump for disposal. From the accumula-
tor tank, the specialty alcohol is filtered and drummed
for shipment as final product.
Figure 3-1. Specialty Alcohols Wash Process
Page 20
SECTION 3: Case Studies
-------
CASE STUDY 1: Specialty Alcohols
CATEGORY 3
Background
DuPont produces several specialty alcohols at
its Chambers Works site. When manufactured,
these alcohols contain residual acidity which
must be removed before the product can be
sold. Historically, the crude alcohol also
contained halogenated impurities. These
corrosive compounds shortened the service
life of process equipment and were respon-
sible for high maintenance costs. But over the
years, an ongoing process improvement
program has steadily reduced these impurities.
Today, the amount of impurities in the alcohol
crude is low enough that further processing is
not required except to remove the residual
acidity.
In the mid-1970s, the Chambers Works plant
implemented a process that washes residual
acidity and impurities out of the alcohol crude.
The process, illustrated in Figure 3-1, consists
of washing the crude twice in aqueous solu-
tions containing inorganic chemical "scaven-
gers", which removed residual acidity and
impurities. Isopropyl alcohol (IPA) is added to
the solutions to assist the separation of the
alcohol product from the wash water at the
end of each wash. ;'
The used wash water is sent to the on-site
wastewater treatment plant for disposal. With
the exception of a small amount of alcohol
product that leaves the process as a yield loss,
IPA is the only organic component of this
waste stream.
The improved purity of the alcohol crude
presented a good opportunity for a dramatic
waste reduction. The only purpose now served
by the wash process is to remove residual
acidity from the crude. So a method for
neutralizing the crude with a chemical agent
was developed. This neutralization option will
be implemented in early 1993, and will com-
pletely eliminate the wash process and its
attendant waste.
The improved purity of the alcohol crude and
the resulting elimination of the wash process
originated not from a dedicated waste minimi-
zation effort, but from an ongoing process
improvement program that has waste minimi-
zation as just one of its goals. The other goals
are improved quality, shorter cycle times,
reduction of inventories, etc. Nevertheless, a
formal waste minimization assessment was
undertaken to generate additional options and
to compare them against acid neutralization.
At an informal review of these options, the
assessment team agreed that acid neutraliza-
tion was clearly the best and only option for
reducing wastes and satisfying other process
improvement goals.
The process improvement program imple-
mented acid neutralization for a variety of
reasons:
Process simplification. Acid neutralization
frees the washing equipment for other uses.
It simplifies operating procedures and
enhances process flexibility.
Reduction in raw material costs. This
includes the cost of IPA and the chemical
scavengers used in the wash process.
Waste reduction. Acid neutralization re-
duces disposal costs by eliminating the need
for treatment at the wastewater treatment
plant.
Improved product yield. The small amounts
of alcohol product that were lost in the
wash water are now saved.
Increased capacity. The elimination of the
wash process removes a significant bottle-
neck in the production of specialty alcohols.
SECTION 3: Case Studies
Page 21
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CATEGORY 3
CASE STUDY 1: Specialty Alcohols
Wash product
crude once
Instead of twice
Rocyde second
wash to first wash
of next batch
Replace wash process with
acid neutralization step
Vacuum-strip IPA from wash for recycling
.r*
Replace washing with alternative^^1
separationtechnology
~
Substitute a less toxic
solvent for IPA x
Use salt solution ii
of IPA, and wash product
once instead of twice
Employ alternative
chemistry to eliminate acid"
residual in product crude
Wash product crude at 4\
higher temperatures^^
?6r
Figure 3-2. Specialty Alcohols Waste Minimization Options
Description of Waste Stream
A typical analysis of the waste stream result-
ing from the specialty alcohol wash process
would reveal:
Water 93.6%
IPA 5.1%
Alcohol (product) 0.7%
Inorganic chemicals 0.6%
Excluding water, IPA accounts for 80% (by
weight) of the waste stream, and 94% of the
total organic content (TOC). At present, the
wash process produces 0.15 Ibs of waste TOC
for every pound of specialty alcohol produced.
This waste stream is sent to the on-site waste-
water treatment plant for disposal.
Costs associated with this waste stream in-
clude the replacement cost of the IPA and
chemical scavengers, the yield loss repre-
sented by the specialty alcohol component,
and the wastewater treatment cost.
Previous Waste Minimization Efforts
A series of small process changes over the
course of 15 years gradually reduced impuri-
ties in the specialty alcohol crude. These
changes were driven by a desire to improve
product quality. The possibility that impurities
had been reduced enough to eliminate the
solvent wash was not explored, during this
period because the wash step was still thought
to be necessary for good quality.
In 1991, a process improvement team identi-
fied elimination of the wash step as an option
for simplifying the process. A subsequent
laboratory study, completed in mid-1992,
determined that washes were not needed for
removing impurities, and that neutralizing the
residual acid in the alcohol was all that was
required.
Aside from continuous improvement in the
purity of specialty alcohol crude, there has
been no previous effort to reduce waste from
the specialty alcohols wash process.
Waste Minimization Options
The specialty alcohols assessment team met in
a brainstorming session and generated nine
possible options for reducing waste. They
recorded their ideas by constructing a cause-
and-effect "fishbone" chart, shown in
Figure 3-2. Given the clear superiority of the
acid neutralization option, the assessment
team did not perform formal weighting and
Page 22
SECTION 3: Case Studies
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CASE STUDY 1: Specialty Alcohols
CATEGORY 3
Table 3-1. Ranked Summary of Specialty Alcohols Waste Minimization Options
Option
Pros
Cons
1. Replace wash process with acid
neutralization step.
2. Substitute a less toxic solvent
for IPA.
3. Use salt solution instead of IPA,
and wash product once instead
of twice.
4. Employ alternative chemistry to
eliminate acid residual in
product crude.
5. Wash product crude once
instead of twice.
6. Recycle second wash to first
wash of next batch.
7. Wash product crude at higher
temperatures.
8. Vacuum-strip IPA from wash for
recycling.
9. Replace washing with alterna-
tive separation technology.
Elimination of the waste stream
Attainment of other process
improvement goals
Substitution of waste IPA with a
less toxic substance
Reduction of TOO load in waste
stream by about 94%
Elimination of the waste stream
Reduction of the IPA component of
the waste stream by half
Reduction of the IPA component of
the waste stream by half
Elimination or reduction of IPA
component of waste stream
Elimination of IPA component of
waste stream
Elimination of waste stream
Alternative solvent is undefined
Alternative solvent would pose
disposal problems of its own
No real reduction in the amount
of waste produced
Uncertain whether salt facilitates
separation as well as IPA
Would not attain other process
improvement goals
Alternative chemistry is undefined
High research cost
High capital cost
Long implementation time
Would not attain other process
improvement goals
Would not attain other process
improvement goals
Uncertain chance of success
Would not attain other process
improvement goals
Not a source reduction
High research cost
High capital cost
Long implementation time
Uncertain chance of success
High research cost
High capital cost
Long implementation time
ranking using the weighted-sum method. The
acid neutralization option satisfied all of the
process improvement program goals, includ-
ing complete source reduction of organic
waste from the wash process. Table 3-1
summarizes the assessment team's informal
evaluation of each option.
Technical and Economic Feasibility
Technical Evaluation
The acid neutralization option had been
chosen before this waste minimization assess-
ment. But the assessment provided a method
for testing the validity of this option against
SECTION 3: Case Studies
Page 23
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CATEGORY 3
CASE STUDY 1: Specialty Alcohols
Table 3-2. Economic Summary of Top Specialty Alcohols Waste Minimization Option
Option
Replace wash
process with acid
neutralization step
Waste
Reduction
100%
Capital Cost
$40,000
EPA Method
NPV(12%) IRR
$725,000
162%
DuPont Method
NPV(12%) IRR
$272,000
93%
Implemen-
tation Time
1 year
Comments: For an explanation of terms used in this analysis, see the discussion under "Feasibility
Evaluation" in Section 2: Project Methodology.
other options generated by the interdiscipli-
nary assessment team.
Because acid neutralization offered a complete
source reduction of waste with little capital
cost, all options that prescribed variations on
the present washing method were quickly
eliminated. Options that prescribed changes in
reaction chemistry or separation technology
were poorly defined, and could not be imple-
mented without significant research and
capital expenditures, and long development
times. This left acid neutralization as the only
option worthy of an economic evaluation. It
not only provided a complete source reduction
of waste, but also met all of the other process
improvement goals.
Economic Evaluation
The results of the economic analysis are
presented in Table 3-2. The analysis consid-
ered such environmental cost savings as yield
improvement, wastewater treatment costs, and
replacement costs for the wash solutions. Also
considered were cost savings from the attain-
ment of process improvement goals such as
shortened cycle times and lower maintenance
costs.
The majority of the cost savings from imple-
menting acid neutralization resulted from
eliminating the waste stream. But adding the
process improvement benefits significantly
enhanced the attractiveness of this option. It's
conceivable that marginal waste reduction
options for other processes could become
justifiable if they were evaluated on the basis
of both waste minimization and process
improvement results.
Barriers to Implementation
The Chambers Works site expects to imple-
ment the acid neutralization option in early
1993. There are no perceived barriers to
implementation.
Opportunities for Others
This case study, like others in this series,
highlights the importance of considering all
business objectives when trying to minimize
waste. There were many incentives for change
in addition to waste minimization, and the
combination of these incentives led to a suc-
cessful effort. Waste reductions are often
interrelated with other goals of a process im-
provement program, and solutions which
satisfy all of these goals are solutions that are
likely to be implemented.
The specialty alcohols experience also demon-
strates how improvements made in one area of
the process can produce opportunities in other
areas. The elimination of the wash process
was made possible by improving product
purity over a period of years. Significantly,
some time had passed between the attainment
of virtually impurity-free production and the
realization that the wash process might no
longer be necessary. It's important for process
improvement teams to periodically reevaluate
the entire manufacturing process as continu-
ous improvements are implemented.
Page 24
SECTION 3: Case Studies
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CATEGORY 3
Case Study 2: Organic Salt Process
A waste reduction effort extends its scope to an upstream process for
possible source reductions
Abstract
This report describes a waste minimization
assessment performed for a process that
neutralizes and purifies an acidic crude to
recover an organic salt. The assessment
revealed opportunities for waste reduction not
only in the purification process itself, but also
in the upstream process that produces the
crude. Several options that combine source
reductions with recycling were adopted for
implementation. Some of these options have
broad application throughout the process
industries.
Background
The DuPont Chambers Works site produces
an organic salt used in the textile industry. The
salt is produced in two separate processes
(illustrated in Figure 3-3) at the site. The first
process makes an acidic crude (called "crude
acid") through a series of reactions. A reactant
in one of the reactions is methanol, and excess
amounts of it are required to achieve a high-
yield crude acid.
In the second process, the crude acid is neu-
tralized with an alkaline compound, and then
cooled to allow organic salt crystals to form.
These crystals are filtered out, and the remain-
ing process stream is sent to a distillation
column where the excess methanol is recov-
ered. The remaining waste from the
distillation column is sent to the on-site
wastewater treatment plant for disposal.
This waste minimization assessment began as
an attempt to reduce waste from the process
for neutralizing and purifying the organic salt.
But the assessment team found opportunities
for waste reduction in the crude acid process
as well. The most promising waste minimiza-
tion candidates were found to be:
a source reduction through the minimization
of a byproduct generated in the process that
makes the crude,
a source reduction through improved recov-
ery of product in the purification process,
and improved recycling of a process reactant
through elimination of wastes caused by
equipment startups and shutdowns.
Implementation of these options would result
in an estimated waste reduction of 25%.
Description of Waste Stream
A typical analysis of the waste stream leaving
the methanol recovery column would reveal:
Water
Reaction byproducts
Organic salt (product)
Alkaline compound
Methanol
88.0%
8.3%
2.2%
1.0%
0.5%
The amount of waste from this process has
been constant for several years and equals
0.14 Ibs of nonaqueous waste for every pound
of organic salt produced.
Costs associated with this waste stream in-
clude the yield loss represented by the
unrecovered organic salt, replacement cost of
unrecovered methanol, and the costs of treat-
ing the stream at the wastewater treatment
plant.
SECTION 3: Case Studies
Page 25
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CATEGORY3
CASE STUDY 2: Organic Salt Process
Reactants
Excess mathano).
Alkaline compou
CRUDE ACID
REACTIONS
METHANOL
RECOVERY
COLUMN
CRYSTALLCER
Alkaline compound
ROTARY
VACUUM
FILTER
DRYER
Neutralized
filtrate
Itrate ^J""
Mathano!
(recycled to crude
acid process)
Waste stream (to
wastewater
treatment plant)
Organic
salt
FILTRATE
NEUTRALIZATION
TANK
Organic salt
' (product) "
A series of reactions produces the crude acid
which is processed into saleable organic salt
One of the reactants is methanol, and excess
amounts of it are required to force one of the reac-
tions to completion.
The crude acid is then fed into a neutralizer, where it
is mixed with an alkaline compound and heated. From
the neutralizer, the crude passes on to a crystallizer
which cools the mixture, causing organic salt crystals
to form. The crystal-bearing mixture then passes on to
a rotary vacuum filter. Here the organic salt crystals
collect in the outer part of the filter, forming a solid
"filter cake". The remaining liquid, called the
"filtrate", consists of methanol, byproducts, and
uncrystallized organic salt
The acidic filtrate exits the rotary filter and enters a
neutralizing tank, where it is mixed with an alkaline
compound to protect the downstream process equip-
ment From the neutralizing tank, the filtrate is sent to
the methanol recovery column. There the filtrate is
heated, causing the methanol to boil off and exit the
process from the top of the column. The distilled
methanol is collected and recycled back to the crude
acid process. The remaining liquid exits the column
bottom and is sent to the on-site wastewater treatment
plant for disposal.
Figure 3-3. Organic Salt Process
Page 26
SECTION 3: Case Studies
-------
CASE STUDY 2: Organic Salt Process
CATEGORY 3
Previous Waste Minimization Efforts
There are three waste minimization projects
now being implemented in the organic salt
process:
Optimize the reactant ratio in the crude acid
process to reduce byproduct formation. The
reaction that produces the crude acid is the
source of the byproducts in the waste
stream.
Recirculate the column bottoms stream back
to the methanol recovery column during
startup. During startup of the methanol
recovery column, before the column has
reached its operating temperature for opti-
mum takeoff of methanol product, some
methanol leaves with the column bottoms
and is diverted to the wastewater treatment
plant. A project is now under way to
recirculate the column bottoms to a holding
tank until the column has reached its operat-
ing temperature. The material in the holding
tank would then be reintroduced to the
column for normal methanol recovery.
Successful implementation of this project
would reduce the amount of methanol in the
waste stream.
Install chiller to reduce the temperatures
within the crystallizer. Lower crystallizer
temperatures will increase the amount of
organic salt that crystallizes out from the
crude acid. Successful implementation of
this project will reduce the organic salt
content of the waste stream.
These three projects were begun in an effort to
increase process productivity by improving
product yield and reducing waste.
Waste Minimization Options
The assessment team for the organic salt
process met in a brainstorming session and
generated 19 possible options for reducing
waste. They recorded their ideas by construct-
ing a cause-and-effect "fishbone" chart, shown
in Figure 3^4. In subsequent meetings, the
Use new technology
to make the crude acid
Cool first-filter wash stream >
Use evaporative cooling
technique to crystallize product
vฃ, Isolate filter wash stream &
n* recirculate it to the neutralizer
Cool rotary vacuum filter filtrate
& recirculate it to the neutrallzer
Improve filter cloths in
rotary vacuum filter
Redesign methanol
recovery column
Add agent to enhance the
crystallization of organic salt
Decrease amount of
alkaline compound added _
before distillation step. '
y
W
Optimize reactant ratio In _
crude acid process
Add water to combine with
excess reactants in the s-g
crude acid process ^-&
Upgrade PH controllers
at the neutrallzer
Optimize addition & mixing of
sJkallne compound
Methanol distillation column
Figure 3-4. Organic Salt Waste Minimization Options
SECTION 3: Case Studies
Page 27
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CATEGORY 3
CASE STUDY 2: Organic Salt Process
Table 3-3. Ranked Summary of Organic Salt Waste Minimization Options
Option
1. Optimize
reactant ratio in
crude acid
process.
2. Use new
technology to
make the crude
acid.
3. Add water to
combine with
excess reac-
tants in the
crude acid
process.
4. Recirculate
methanol
column bottoms
during startups
and shutdowns.
5. Install chiller for
the crystallizer.
6. Add agent to
enhance the
crystallization of
organic salt.
7. Improve filter
cloths in rotary
vacuum filter.
8. Optimize
addition and
mixing of
alkaline
compound.
9. Optimize
column control
point.
Pros
Addresses a major
cause of waste
Low capital and
operating costs
Very high source
reduction potential
High source
reduction potential
Low operating cost
Moderate recycling
potential
Very good chance
of success
Moderate source
reduction potential
Very good chance
of success
Low source
reduction potential
Low source
reduction potential
Low capital and
operating costs
Presumptive
source reduction
Small recycling
potential
Cons
Very high capital
cost
Moderate capital
cost
Safety concerns
Moderate capital
cost
Moderate capital
cost
Unknown chance
of success
Low chance of
success
Low chance of
success
Low chance of
success
Comments
This option would reduce the
amount of byproducts which
form in the crude acid
process.
This option would ensure
that virtually all of the
reactants are consumed in
the reaction that produces
the crude acid.
This option would prevent
excess reactants in the
crude acid process from
forming byproducts.
This option requires the
installation of piping and
control equipment.
Lower temperatures would
cause more organic salt to
crystallize, improving the
product yield and reducing
waste.
A chemical agent that would
enhance crystallization has
not yet been identified.
At present, some organic
salt is lost through the filter
cloths. Previous attempts to
identify better filter cloths
have failed.
The prevailing view among
assessment team members
is that present method is
already efficient.
This option involves finding a
better location on the
methanol recovery column
for placing temperature and
pressure controls.
Score*
946
822
792
682
636
521
504
487
465
'maximum score - 1,210
Page28
SECTION 3: Case Studies
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CASE STUDY 2: Organic Salt Process
CATEGORY 3
Table 3-3. Ranked Summary of Organic Salt Waste Minimization Options (cont'd)
Option
1 0. Install larger
cooling coils
within the
crystallizer.
11. Install auto-
matic tempera-
ture controller.
12. Use brine as
cooling medium
within coils.
13. Decrease the
amount of alkali
added before
distillation step.
14. Use evapora-
tive cooling
technique to
crystallize
product.
15. Upgrade PH
controllers at
the neutralizer.
16. Isolate filter
wash stream
and recirculate
it to the
neutralizer.
17. Cool filter wash
stream.
1 8. Cool rotary
vaccum filter
filtrate and
recirculate it to
the neutralizer.
19. Redesign
methanol
recovery
column.
*maximum score =
Pros
Moderate source
reduction potential
Moderate chance
of success
Moderate source
reduction potential
Moderate chance
of success
Moderate source
reduction potential
Moderate chance
of success
Low capital cost
Moderate source
reduction potential
Moderate chance
of success
Presumptive
source reduction
1,210
Cons
Very high capital
cost
Moderate capital
cost
High capital cost
High operation
and maintenance
costs
Low waste
minimization
potential
Low chance of
success
Very high capital
cost
Very high opera-
tion and mainte-
nance costs
Low chance of
success
Low waste
minimization
potential
Low chance of
success
Low waste
minimization
potential
Low chance of
success
Low waste
minimization
potential
Low chance of
success
Low recycling
potential
Very high capital
cost
Comments
Larger cooling coils would
cause more organic salt to
crystallize, improving yield
and reducing waste.
This option would provide
better control of the rate of
cooling within the crystal-
lizer.
Replacing water with brine
would permit cooler tem-
peratures within the crystal-
lizer.
The alkali protects process
equipment from the acidic
crude. This option would
reduce waste by the amount
of the alkali reduction, a very
low amount.
This option would replace
the present method of
crystallizing the product.
Assessment team achieved
consensus that present pH
control is not a problem.
This option seeks to recover
the small amount of organic
salt that is lost in the filter
wash stream.
Water in the rotary filter
washes impurities out of the
filter-cake. Inevitably, some
crystals dissolve and wash
away. This option would
reduce this (small) yield loss
by cooling the washwater.
This would recover more
product, but requires a
method for separating the
salt from the rest of the
filtrate before it recirculates
to the neutralizer.
This option hopes to achieve
a more efficient distillation of
the methanol from the waste
stream.
Score*
442
435
432
402
396
382
332
296
285
252
SECTION 3: Case Studies
Page 29
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CATEGORY 3
CASE STUDY 2: Organic Salt Process
team discussed the options and ranked them
using the weighted sum method described in
Section 2 of this document.
Table 3-3 summarizes these discussions, and
presents the options in rank order.
The 19 options generated during the brain-
storming session fall into three categories:
Source reduction of waste stream constitu-
ents (11 options)
* Recovery and recycling of methanol or
organic salt (five options)
Increased crude acid purity to reduce impu-
rities which end up in the waste stream
(three options)
Technical and Economic Feasibility
After considering the pros and cons of each
option listed in Table 3-3, the assessment
team chose five options for technical and
economic feasibility analysis:
Optimize reactant ratio in crude acid process
Use new technology to make the crude acid
Add water to combine with excess reactants
in the crude acid process
* Recirculate methanol column contents
during startups and shutdowns
Install chiller for the crystallizer
Technical Analysis
The "optimize reactant ratio" and "add
water...in crude acid process" options both
involve changes to the present process for
making crude acid. The former option requires
no capital investment, while the latter requires
a moderate investment. Both options have
high source reduction potentials. Both are
technically feasible, although only plant trials
can confirm their effectiveness.
The new technology for making crude acid
process has been successfully demonstrated in
other applications. Although the waste mini-
mization potential of this option is significant,
the cost of implementing this option cannot be
justified.
Recirculating the methanol column bottoms
during startups and shutdowns is a recycling
option that is easy to implement for a small
capital investment. The installation of a chiller
for the crystallizer is also easy to implement,
although it does require a moderate capital
investment Neither option represents new
technology, and both are technically feasible.
Economic Analysis
The economic analysis of these five options is
presented in Table 3-4-. Results are provided
using both DuPont and EPA methodologies.
The DuPont methodology uses the variable
costs of wastewater treatment because the
company uses its own wastewater facility.
Thus, the DuPont methodology does not take
into account the fixed costs of wastewater
treatment, whereas the EPA methodology uses
both the fixed and the variable costs in eco-
nomic analyses.
The analysis reveals the most promising
options to be:
Optimize reactant ratio in crude acid process
Recirculate the column contents during
startup/shutdown
Install chiller for the crystallizer
The three options have short implementation
periods and high "internal rates of return"
(ERR) with little capital investment. Imple-
mentation of the three options would yield a
combined waste reduction of 25%.
Page30
SECTION 3: Case Studies
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CASE STUDY 2: Organic Salt Process
CATEGORY 3
Barriers to Implementation
There are no anticipated barriers to implemen-
tation of any of the three options. Projects for
optimizing the reactant ratios and installing
the chiller are well under way. A project for
recirculating the contents of the methanol
column is still in the planning stage, and
completion is expected some time in 1993.
Opportunities for Others
The waste minimization options examined in
this case study have general application for
other processes. In most chemical processes,
there is an inverse relationship between
product yield and waste. If reactant ratios are
not in balance, then an excess reactant is likely
to. become involved in a side reaction that
produces byproducts. This lowers the product
yield on raw materials and increases waste.
Equipment startups and shutdowns are fre-
quent sources of waste. When process
equipment is started up, there usually is a
"line-out" period before the equipment
achieves its standard operating conditions.
Process streams that pass through the equip-
ment during line-out usually emerge off spec
and contain large amounts of waste. Methods
for reintroducing these streams to the equip-
ment after line-out can result in significant
waste reductions.
Table 3-4. Economic Summary of Top Organic Salt Waste Minimization Options
Option
Optimize reactant
ratio in crude acid
process
Add water... in
the crude acid
process
Recirculate
methanol column
bottoms...
Install chiller...
Use new technol-
ogy to make the
crude acid
Waste
Reduction
5%
19%
13%
7%
54%
Capital Cost
$0
$206,000
$25,000
$190,000
$5,230,000
EPA Method
NPV(12%) IRR
$5,700,000
$1,100,000
$700,000
$9,700,000
($600,000)
oo
79%
211%
209%
9%
OuPont Method
NPV(12%) IRR
$5,500,000
$400,000
$200,000
$9,400,000
($2,700,000)
oo
42%
103%
205%
<0%
Implemen-
tation Time
6 months
1 year
1 year
6 months
2 years
Comments: The economics for these options are given on a stand-alone basis, and do not consider
possible synergies from implementing more than one option.
Parentheses denote negative numbers.
For an explanation of terms used in this analysis, see the discussion under "Feasibility
Evaluation" in Section 2: Project Methodology.
SECTION 3: Case Studies
Page 31
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CATEGORY 3
Case Study 3: Nitroaromatics
Improved flow control is the key to waste reduction in this distillation process
Abstract
A waste minimization assessment was per-
formed for a process that produces
nitroaromatic compounds. Continuous distilla-
tion separates the compounds into their
constituent isomers and removes reaction
byproducts. The chief impediment to reducing
waste was found to be difficulties in control-
ling the rate of flow from the detarring column
that discharges the wastes. The full benefit of
a source reduction in reaction byproducts will
not be realized unless the flow control prob-
lem is solved. Waste reduction for this process
will consist of a series of small improvements
rather than the implementation of a single
solution.
Aromatic
compound
Product
A
Nitric acid-
Crude
REACTION
STEP
DISTILLATION
STEP
CONTROLLER
FLOW METER VALVE
REBOILER
Aromatic compounds and nitric acid enter
the reactor where they are mixed to create
nitroaromatic compounds and reaction
byproducts. The crude leaving the reactor pro-
ceeds to the distillation step, where nitroaromatic
compounds are removed from the crude and
purified. Among the distillation equipment is a
detarring column where nitroaromatic product
boils off, leaving the reaction byproducts,
unrecovered product, and distillation tars to
accumulate within the reboiler. A pump removes
PUMP
these wastes continuously. The flow from the
reboiler must be carefully measured and controlled
to prevent a buildup of reaction byproducts to
unsafe levels. This flow control is accomplished
by means of a flow meter and valve. The flow rate
is so low that a 1/8" flow-tube is used to obtain
accurate measurements. At extremely low flows
the valve and flow meter become plugged, forcing
a process shutdown. To prevent this occurrence,
the operation runs at a higher-than-optimal
flow rate.
Figure 3-5. Nitroaromatics Process
Page32
SECTION 3: Case Studies
-------
CASE STUDY 3: Nttroaromatics
CATEGORY 3
Background
The Chambers Works site produces several
nitroaromatic compounds which have a
variety of commercial uses. The continuous
process for producing these compounds,
illustrated in Figure 3-5, consists of a reaction
step and a distillation step.
In the reaction step, aromatic feedstock is
combined with nitric acid within a reactor to
produce a crude consisting of nitroaromatic
compounds and some reaction byproducts.
One of these byproducts, which has a higher
boiling point than the others, has low thermal
stability. This high-boiling byproduct could
pose a safety hazard during distillation if
allowed to concentrate above a certain thresh-
old within the crude as product is removed.
The formation of the high-boiling byproduct
can be minimized through careful control of
the ratio of feedstock to nitric acid within the
reactor. Nevertheless, a certain amount of the
high-boiling byproduct inevitably forms.
From the reactor, the crude undergoes a series
of distillations to remove the byproducts and
purify the nitroaromatic compounds to product
specifications. Distillation exploits differences
in the boiling points of each compound within
the nitroaromatic crude, separating com-
pounds with lower boiling points (low-boilers)
from those with higher boiling points (high-
boilers). The process stream enters a distilla-
tion column where it is subjected to heat. The
low-boilers leave the top of the column as
vapor, while the high-boilers leave the column
reboiler as liquid. By controlling the tempera-
ture and pressure within the process equip-
ment, one can control the chemical composi-
tion of the vapors and liquids leaving the
column.
Included among the distillation equipment in
the nitroaromatics process is a distillation
column known as the "detarring column". It
receives a continuous feed of crude, boiling
off nitroaromatic products and discharging a
viscous waste stream containing the reaction
Remove reaction byproduct
before separation and sell it
Find alternative way
to synthesize products
Redesign reactor
Modify reaclanl mixing mechanism
Use online instrument
to monitor strength of
acid leaving reactor
Improve reactor agitation
Reduce reactor feed rates
Modify feedstock ratios
Figure 3-6. Nitroaromatics Waste Minimization Options (Reaction Step)
SECTION 3: Case Studies
Page 33
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CATEGORY 3
CASE STUDY 3: Nitroaromatics
byproducts, unrecovered product, and a small
amount of tars which form during distillation.
The waste stream leaving the detarring col-
umn is incinerated.
The waste stream contains two major compo-
nents and arises from two sources. The first
component consists of the byproducts formed
during the reaction step. These are chemically
unstable and would pose a safety hazard if
allowed to concentrate within the waste
stream. The second component consists of
nitroaromatic product purged as waste with
the reaction byproducts from the detarring
column reboiler. The source of this yield loss
is an inability to adequately control the rate at
which the wastes are purged. Waste leaves the
reboiler through a flow meter that has a diam-
eter of just 1/8". The flow meter controls a
valve which opens to achieve the desired flow
rate. When flow rates are extremely low, both
flow meter and valve clog up, causing flow to
stop completely and the process to shut down.
To avoid this development, the process runs at
higher flow rates. But at higher flows, larger
amounts of otherwise recoverable product are
removed with the waste.
The lower the purge rate, the more product is
recovered in the detarring column. But at very
low flows, reaction byproducts would accu-
mulate to an unsafe level within the reboiler.
Thus, process improvements aimed exclu-
sively at reducing the purge rate can achieve
only marginal waste reductions. Similarly,
reducing the formation of reaction byproducts
alone would not achieve much waste reduc-
tion because of the high purge rate at the
detarring column. However, implementing
both improvements together would greatly
reduce the waste from the nitroaromatics
process.
Description of Waste Stream
A typical analysis of the waste stream leaving
the nitroaromatics column is provided below.
Unrecovered product 76%
Byproducts 20%
Distillation tars 4%
The amount of waste from this process has
been constant for several years, and equals
0.014 Ibs for every pound of nitroaromatic
Run wastes through
an additional product
recovery slap
Add a stabilizing agent to
crude to prevent tar formation
during distillation
Replace distillation with
a different technology
-------
CASE STUDY 3: Nitroaromatics
CATEGORY3
Table 3-5, Ranked Summary of Nitroaromatics Waste Minimization Options (Reaction Step)
Option
1. Use online
instrument to
monitor
strength of acid
leaving reactor.
2. Improve reactor
agitation.
3. Modify feed-
stock ratios.
4. Modify reactant
mixing mecha-
nism.
5. Reduce reactor
feed rates.
6. Find alternative
way to synthe-
size products.
7. Redesign
reactor.
8. Remove
reaction
byproduct
before separa-
tion and sell it.
'maximum score = 21
Pros
May achieve
source reduction
of reaction
byproducts
May achieve
source reduction
of reaction
byproducts
Would achieve
source reduction
of reaction
byproducts
Speculative source
reduction of
reaction
byproducts
May achieve
source reduction
of reaction
byproducts
Has the potential
for reducing
reaction
byproducts
Several possible
designs offer
promise for
byproduct
reduction
Virtually eliminates
a significant
component of
waste
Reduces the major
component of the
waste by permit-
ting greater
product recovery
Cons
Could be difficult
to implement
Uncertain chance
of success
Reduced produc-
tion capacity
Increased operat-
ing costs
Uncertain chance
of success
Reduced produc-
tion capacity
May require
redesign of reactor
Uncertain chance
of success
because alterna-
tives are not well
understood
High development
cost
High implementa-
tion cost
High development
cost
High implementa-
tion cost
Low concentra-
tions of byproduct
in crude before
separation make
chance of success
unlikely
Large capital cost
Safety limitations
Comments
The strength of the spent
acid leaving the reactor
would control the rate of feed
acid addition. Acid strength
could be measured by a
variety of instruments,
including pH or density
meters.
Improved agitation could
reduce the formation of
reaction byproducts.
Decreasing nitric acid would
increase the amount of
unreacted aromatic feed-
stock to be removed during
the distillation step.
Based on the assumption
that improved mixing would
reduce byproduct formation.
Reduced reactor feed rates
would result in longer
residence times within the
reactor. Some studies
indicate that byproduct
formation may decrease
under these conditions.
High costs make this option
unattractive at this time.
High costs make this option
unattractive at this time.
The low concentration of
byproduct within the crude
and high capital costs make
this option unattractive.
Score*
18
14
12
11
9
7
7
6
SECTION 3: Case Studies
Page 35
-------
CATEGORY 3
CASE STUDY 3: Nitroaromatics
Table 3-6. Ranked Summary of Nitroaromatics Waste Minimization Options (Distillation Step)
Option
1. Use computer
tracking system
to monitor
wastes.
2. Improve flow
meter and
valve at
detarring
column and
add online
Instrumenta-
tion.
3. Implement
batch purging
of waste from
detarring
column.
4. Improve flow
meter and
valve at
detarring
column.
'maximum score ป 21
Pros
Permits optimiza-
tion of waste
purge control
Easy implementa-
tion
Reduction in major
component of
waste through
better product
recovery
Implementation
required to realize
benefits from
source reduction
of reaction
byproduct
Reduction in major
component of
waste through
better product
recovery
Reduction in major
component of
waste through
better product
recovery
Implementation
required to realize
benefits from
source reduction
of reaction
byproduct
Cons
Does not solve
flow control
problems and,
therefore, doesn't
reduce wastes
Uncertain chance
of success
* May present a
more difficult
control problem
than continuous
purging
Uncertain chance
of success (may
already be using
the best available
technology)
Safety concerns
Comments
Capability of implementing
this option exists in present
process control equipment.
On-line instrumentation may
allow lower flow rates
without compromising
safety.
This option would allow
waste to accumulate in
column reboiler to be purged
periodically in batches.
Batch purging would create
additional safety concerns
that would have to be
addressed.
Investigation required to
determine if better equip-
ment is available. It's
possible that online instru-
mentation will also be
required to enhance safety.
Score*
16
14
14
14
crude produced. At present, wastes from the
detarring column are incinerated.
Costs associated with this waste stream
include the yield loss represented by unre-
covered product and the cost of incinerating
the waste stream.
Previous Waste Minimization Efforts
In recent years, several attempts have been
made to reduce the waste stream from the
nitroaromatics process:
A study was performed on the effect of
increasing the ratio of aromatic feedstock to
nitric acid within the reactor. The study
showed that changing the ratio could de-
crease byproducts. But these changes could
not achieve its full measure of waste reduc-
tion unless the flow rate problem at the
detarring column were solved.
A process control software program was
installed to track the amounts of waste
discharged from the detarring column. The
information provided by the program helped
Page36
SECTION 3: Case Studies
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CASE STUDY 3: Nilroaromatics
CATEGORY 3
Table 3-6. Ranked Summary ofNitroaromatics Waste Minimization Options (Distillation Step, cont'd)
Option
5. Add a stabiliz-
ing agent to
crude to
prevent tar
formation
during distilla-
tion.
6. Optimize
temperature
and pressure
control during
distillation step.
7. Redesign
detarring
column reboiler
to permit
removal of
more wastes.
8. Replace
distillation with
a different
technology.
9. Sell wastes as
a product.
10. Run wastes
through an
additional
product
recovery step.
'maximum score = 21
Pros
Would reduce the
tars formed in
isomer separation
column
Lower tempera-
tures and pres-
sures could
reduce distillation
tars
Would permit
operation at
greater flow rates
Reduces the
major component
of the waste by
permitting greater
product recovery
Would eliminate
the waste stream
Reduces the
major component
of the waste by
permitting greater
product recovery
Cons
Stabilizing agents
in distillation
columns greatly
complicate waste
management
Addresses a very
small component
of the waste
stream
Uncertain chance
of success
Tars constitute
only a small part
of the waste
stream
High capital cost
Long development
and implementa-
tion time
High capital cost
ซ Long development
and implementa-
tion time
May be difficult to
find buyers
High capital cost
Long implementa-
tion time
Comments Score*
See "Case Study 5: CAP 1 2
Purification" in this series for
a description of the problems
associated with using
stabilizers in distillation
columns.
Although some tars do form 1 1
during the distillation step,
reaction byproducts are the
major source of waste from
this process.
Source reductions in the 9
reaction step would be more
cost effective.
Source reductions in the 8
reaction step would be more
cost effective.
6
Possible technologies 3
include use of a wiped-film
evaporator. Source reduc-
tions in the reaction step
should be considered first.
to decrease wastes somewhat. More impor-
tantly, it heightened awareness about the
amount of waste produced and identified
flow control as a major impediment to waste
reduction.
Waste Minimization Options
The assessment team for the nitroaromatics
process met in a brainstorming session and
generated 18 options for reducing waste. They
recorded their ideas by constructing the two
cause-and-effect "fishbone" charts shown in
Figures 3-6 and 3-7. One chart contains
options which address reaction byproduct
formation, and the other contains options for
reducing wastes from the distillation step. In
subsequent meetings, the assessment team
discussed the options and ranked them using
the weighted-sum method described in Section
2 of this document. Tables 3-5 and
3-6 summarize these discussions, and presents
the options in rank order.
SECTION 3: Case Studies
Page 37
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CATEGORY3
CASE STUDY 3: Nrtroaromatics
Determining how options generated for one
process would affect conditions at the other
process introduced a level of complexity not
encountered in other case histories in this
series. For this reason, the assessment team
used the flexibility afforded by the DuPont
and EPA methodologies to simplify the
weighted-sum ranking method described in
Section 2 of this document. The team assigned
a weight of "1" to each criterion. They then
assigned a score of "+1", "0", or "-1" to each
option according to how well it satisfied the
criterion.
Technical and Economic Feasibility
After considering the pros and cons of each
option listed in Tables 3-5 and 3-6, the
assessment team chose four options for techni-
cal and economic feasibility analysis:
Improve flow meter and valve at detailing
column
Improve flow meter and valve at detarring
column and add online instrumentation
Use online instrument to monitor strength of
acid leaving reactor
Improve reactor agitation
Table 3-7. Economic Summary of Top Nitroaromatics Waste Minimization Options
Option
REACTION STEP:
Use online instal-
ment to measure
strength of acid...
&
Improve reactor
agitation
DISTILLATION STEP:
Improve flow
meter & valve
Improve flow
meter & valve...
online instrumen-
tation
Waste
Reduction
17%
16%
23%
Capital Cost
$63,000
$37,000
$109,000
EPA Method
NPV(12%) IRR
$398,000
$396,000
$484,000
87%
75%
54%
DuPont Method
NPV(12%) IRR
$291,000
$243,000
$267,000
72%
57%
39%
Implemen-
tation Time
6 months
6 months
1 year
Comments: The economics for these options are given on a stand-alone basis, and do not consider
possible synergies from implementing more than one option.
The waste reduction percentages for the distillation step options are not fully additive if
both options are implemented.
Implementing the reaction step option and one of the distillation step options would give a
combined waste reduction of about 37%.
For an explanation of terms used in this analysis, see the discussion under "Feasibility
Evaluation" in Section 2: Project Methodology.
Page38
SECTION 3: Case Studies
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CASE STUDY 3: Nitroaromatics
CATEGORY 3
The results of the analysis are presented in
Table 3-7.
These four options were chosen because taken
together, they seem to represent a coherent,
stepwise plan for waste reduction, rather than
a collection of disparate projects. The options
"new flow meter and valve" and "new flow
meter, valve, and online instrumentation" are
designed to bring the detarring column flow
rate under control, a necessary precondition
for meaningful source reduction. The addition
of online instrumentation will not improve
waste reduction, but may be required to ensure
that the present margin of safety is main-
tained.
The last two options (improve reactor agita-
tion, continuous monitoring of acid strength)
are designed to achieve source reductions in
byproduct formation. These two options were
combined for the economic evaluation be-
cause it may be necessary to implement both
to achieve the desired source reduction. It's
worth repeating that these source reductions
will not reduce waste until the flow rate from
the detarring column is brought under control.
Barriers to Implementation
It seems likely that the waste reduction from
the detarring column purge stream can be
achieved by improving the flow control,
although there is some feeling among assess-
ment team members that the present flow
control mechanisms already represent the best
available technology.
Methods for achieving source reductions in
byproduct formation are more experimental.
The waste reduction figures given in
Table 3-7 are based on the assumption that
these options will work. But in fact, the causes
of byproduct formation require more study.
Previous tests have yielded mixed results. It's
possible that the options identified here will
achieve less waste reduction than the figure
given in Table 3-7.
In a best case scenario, implementing waste
reduction options in both the reaction and
purification steps will yield a 37% reduction.
In the; worst case, solving the flow rate prob-
lem should reduce waste by 16%. These steps
would also provide a better understanding of
the process, and prepare the nitroaromatics
area for a future waste minimization effort.
Opportunities for Others
The nitroaromatics process demonstrates how
waste minimization is sometimes an iterative
process in which progress is made in small
steps, and not in a single great leap.
This case history, like others in this series,
also demonstrates how a waste reduction
effort:'must often expand beyond its original
scope. The assessment team originally focused
only on the reaction step. But it soon became
apparent that significant reductions could be
achieved only by expanding the scope of the
assessment to include the distillation step
as well.
SECTION 3: Case Studies
Page 39
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CATEGORY3
Case Study 4: Diphenol Ether Process
Balancing the potential for waste reduction with operational safety
Abstract
This case study focuses on a waste stream
from a batch process for making a substituted
diphenol ether. The process uses a solvent as a
reaction stabilizer. A recovery step recycles
some of the solvent for future reuse, but safety
concerns limit the amount of solvent recov-
ered. Unrecovered solvent constitutes the
greatest part of the waste. The chosen waste
reduction option permits the recovery of more,
but not all, of the added solvent. This report
illustrates an increasingly frequent situation in
which process engineers must balance safety
considerations with the need to minimize
waste.
Solvent
Organic salt
SLURRY
VESSEL
Chlorinated
phenol
REACTION
VESSEL
DROWNING
TANK
Recovered
solvent
Waste stream
(to waste-water
treatment plant)
Crude product
FILTERS
I
Rnal product
A
SOLVENT
RECEIVING
TANK
solid organic salt is
slurried with solvent
within the slurry tank and
then introduced to the reaction
vessel. There, the slurry is mixed
with chlorinated phenol, and the
mixture is heated. The resulting
reaction produces diphenol ether
and a small amount of byproducts.
When the reaction is completed, a vacuum is
applied to the equipment to lower the boiling
point of the solvent. The solvent then boils up
the distillation column and collects in the
solvent receiving tank for eventual reuse.
About half of the solvent in the reaction vessel
is recovered in this way, enough to nearly fill
the receiving tank.
After the solvent recovery step, the reaction
mass is dumped into a drowning tank full of
water. It is then washed with a large, continu-
ous stream of water. The diphenol ether settles
to the bottom of the tank, while the remaining
solvent and reaction byproducts dissolve in the
aqueous wash. The waste-bearing water is
siphoned off contiuously from the top of the
tank and sent to the on-site wastewater
treatment plant for disposal. After the wash
step, the free liquid is filtered off. The diphenol
ether is then sent to another facility on-site for
further processing.
Figure 3-8. Diphenol Ether Process
Page40
SECTION 3: Case Studies
-------
CASE STUDY 4: Diphenol Ether Process
CATEGORY 3
Background
The DuPont Chambers Works facility pro-
duces a substituted diphenol ether which, after
further processing at another facility on-site,
becomes a raw material for the manufacture of
various polymers. The process produces an
aqueous waste stream containing a solvent and
small amount of reaction byproducts.
The process for producing diphenol ether is
illustrated in Figure 3-8. A solid organic salt
is slurried with a solvent, introduced to a
reaction vessel, and mixed with a chlorinated
phenol. The subsequent reaction produces the
diphenol ether and byproducts. When the
reaction is complete, about half of the solvent
is recovered for reuse by means of a distilla-
tion column connected to the reaction vessel.
The reaction mass is then drowned and
washed with copious amounts of water to
remove the solvent and byproducts.
The solvent performs double duty in this
process. It serves as a transport medium,
carrying the organic salt to the reactor. Within
the reactor, the solvent performs an important
safety role. Both the raw material and reaction
byproducts are extremely volatile and can
explode; when dry. The solvent prevents
drying of the volatile compounds. Thus, there
is a limit to how much solvent can be removed
from the reaction vessel before process safety
is compromised.
An additional recovery step for removing
solvent from the drowning tank wash water
cannot be seriously considered. The wash
water is so dilute that no known recovery
method, can be made cost-effective. Reuse of
the wasih water is not an option because the
byproduct it removes is at its solubility limit.
Description of Waste Stream
Water comprises almost 99% of the waste
from the drowning tank. A typical analysis of
the waste (excluding water) would reveal:
Inorganic salt 50%
Solvent 36%
Unreacted raw material 11 %
Reaction byproducts 3%
The amount of waste from this process has
been constant for several years and (excluding
water) equals 0.24 Ibs for every pound of
Send reaction mass to
downstream process for
further processing
Use chemical extraction to remove
solvent from reaction mass
Install larger solvent receiving tank
Upgrade solvent distillation
Develop more accurate test ^jy
for raw material purity ,/ฃ*-
f&
&
ซ?
&
Increase the amount of chlorinated phenol in
reactor to achieve more complete reaction
Isolate reaction mass after drowning
Use alternative chemistry toy?Use less solvent
manufacture product ^^Sparge nitrogen into the reactor to
I isป different solvent ./inhibit formation of reaction byproduct
Figure 3-9. Diphenol Ether Waste Minimization Options
SECTION 3: Case Studies
Page 41
-------
CATEGORY3
CASE STUDY 4: Diphenol Ether Process
Table 3-8. Ranked Summary of Diphenol Ether Waste Minimization Options
Option
1. Useless
solvent.
2. Install larger
solvent
receiving tank.
3. Upgrade
solvent
distillation step.
4. Isolate reaction
mass after
drowning.
5. Develop more
accurate test
for raw material
purity.
6. Use chemical
extraction to
remove solvent
from reaction
mass.
'maximum score ซ
Pros
Less solvent in
waste
Lower raw material
costs
Less solvent in
waste
Lower raw material
costs
Less solvent in
waste
Less reaction
byproduct in waste
Lower raw material
costs
Less solvent in
waste
Lower raw material
costs
Reduced reaction
byproducts in
waste
Low cost
High chance of
success
Easy implementa-
tion
Lower solvent
costs
Less solvent in
waste
1,170
Cons
Safety concerns
Moderate capital
investment
Safety concerns
Prohibitive capital
cost
Based in part on
speculative
hypothesis of how
reaction byproduct
forms
Safety concerns
High capital cost
Poor chance of
success because
of safety concerns
Very low waste
minimization
potential
Increased raw
material cost (for
chemical extractor)
Produces a new
waste stream
Moderate capital
cost
Safety concerns
Comments
Present tank size imposes a
limit on how much solvent
can be recovered.
This option proposes the
installation of a new and
larger distillation column as
well as a larger solvent
receiving tank.
Would require installation of
a solvent purification system.
More precise knowledge of
raw material purity would
help reduce unreacted raw
materials by permitting
optimization of reactant
ratios. But reaction
byproducts are a very small
part of the waste stream.
Score*
900
875
800
674
639
627
diphenol ether product produced. The waste
stream is treated at the on-site wastewater
treatment facility.
Major costs associated with this waste stream
are the costs of wastewater treatment and the
raw material costs represented by the
unrecovered solvent. Yield losses from this
process are extremely low.
Previous Waste Minimization Efforts
Past efforts to reduce solvent waste have
consisted of incremental attempts to reduce
the amount of solvent left unrecovered within
the reactor. Each attempt is preceded by
testing to ensure that the new target amount
will still be sufficient to keep the reaction
mass stable. As a result of these attempts, the
Page 42
SECTION 3: Case Studies
-------
CASE STUDY 4: Diphenol Ether Process
CATEGORY 3
Table 3-8. Ranked Summary ofDiphenol Ether Waste Minimization Options (cont'd)
Option
7. Increase the
amount of
chlorinated
phenol in
reactor to
achieve more
complete
reaction.
8. Use different
solvent.
9. Use alternative
chemistry to
manufacture
product.
10. Send reaction
mass to
downstream
process for
further process-
ing.
11. Sparge nitrogen
into reactor to
inhibit formation
of reaction
byproduct.
'maximum score =
Pros
Product yield
improvement
Lower raw material
cost
Less unreacted
raw material in
waste
Speculative
reduction in
solvent waste
Speculative
reduction in waste
Improved safety
Less solvent in
waste
Lower raw material
costs
Less byproduct in
waste
1,170
Cons
More reaction
byproduct in waste
Alternative solvent
not specified (poor
chance of suc-
cess)
Alternative
chemistry not
specified (poor
chance of suc-
cess)
High capital cost
Introduces
additional process
steps to down-
stream process
High capital
investment for
emission abate-
ment system
Could produce a
waste stream of
its own
Air permit modifi-
cation needed
Comments
Previous attempts to use a
different process to manu-
facture product have failed.
The additional processing
would stabilize the otherwise
unstable compounds within
the reaction mass.
This high-cost option
addresses a very small
component of the waste
stream.
Score*
598
509
501
432
417
amount of unrecovered solvent has been
reduced by about 40% over the past ten years.
Waste Minimization Options
The assessment team for the diphenol ether
process met in a brainstorming session and
generated 11 possible options for reducing
waste. They recorded their ideas by construct-
ing a cause-and-effect "fishbone" chart, shown
in Figure 3-9. In subsequent meetings, the
team discussed the options and ranked them
using the weighted-sum method described in
Section; 2 of this document. Table 3-8 summa-
rizes these discussions, and presents the
options in rank order.
The options with the highest waste minimiza-
tion potential are those which attempt to
reduce the amount of solvent in the waste.
Options which attempt to reduce the formation
of byproducts or improve the purity of the raw
materiails have a very low potential for waste
reduction because the reaction in this process
is already very efficient, and the amount of
byproducts in the waste is very small.
SECTION 3: Case Studies
Page 43
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CATEGORY3
CASE STUDY 4: Diphenol Ether Process
Table 3-9. Economic Summary of Top Diphenol Ether Waste Minimization Options
Option
Use less solvent
Install larger...
receiving tank
Upgrade solvent
distillation step
Waste
Reduction
58%
47%
47%
Capital Cost
$0
$128,000
$376,000
EPA Method
NPV(12%) IRR
$3,070,000
$2,100,000
$2,100,000
Comments: For an explanation of terms used in this analys
Evaluation" in Section 2: Project Methodology.
oo
153%
78%
DuPont Method
NPV(12%) IRR
$1,290,000
$750,000
$550,000
CO
83%
38%
Implemen-
tation Time
1 year
1 year
1 .5 years
s, see the discussion under "Feasibility
Technical and Economic Feasibility
Technical Evaluation
After considering the pros and cons of each
option in Table 3-8, the assessment team
chose three for technical and economic feasi-
bility analysis:
Use less solvent
Install larger solvent receiving tank
Upgrade solvent distillation step
Option 1 simply calls for using less solvent to
slurry the organic salt. This option scores well
in terms of ease of implementation and waste
minimization potential. But any attempt to
reduce solvent before the reaction step raises
serious safety issues because of the volatility
of the unreacted chlorinated phenol.
Option 2, "Install larger solvent receiving
tank", is also relatively easy to implement.
This option calls for distilling off more solvent
after the reaction is complete and before the
reaction mass is sent to the drowning tank.
The extra distillation is not possible at this
time because the solvent receiving tank is too
small to accept additional solvent. Installing a
larger tank would make implementation of
this option possible.
Option 3, "Upgrade solvent distillation step",
would require a significant capital investment
in that it calls for the installation of both a
larger distillation column and a new receiving
tank. This option would reduce waste in two
ways. First, an upgraded column would permit
the removal of more solvent. (This is why the
larger receiving tank is required.) Secondly,
the new column would improve the purity of
the solvent removed from the reactor. At
present, some unreacted raw material boils up
the column with the solvent, and this material
ultimately becomes waste.
Economic Evaluation
Table 3-9 summarizes the results of the
economic feasibility study for the three top-
rated options. Option 1 is the most economi-
cally attractive since it requires no capital
investment, and its Net Present Value (NPV)
is higher than the other options. But safety
concerns associated with this option offset its
economic attractiveness, and move it to the
bottom of the list of three as a candidate for
implementation.
Option 2, "Install larger solvent receiving
tank", was chosen as the best option. It has an
acceptable NPV, and is far safer than
Page 44
SECTION 3: Case Studies
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CASE STUDY 4: Diphenol Ether Process
CATEGORY 3
Option 1. The larger tanks enable additional
solvent distillation after the volatile chlorinated
phenol has been consumed in the reaction.
Option 3, "Upgrade distillation step", would
require significant capital expenditure for a
waste reduction that is approximately equal to
that of the less costly Option 2. For this reason,
it is not a candidate for implementation.
Barriers to Implementation
Safety concerns frustrate most attempts to
reduce wastes from this process. Recently, the
process chemist and representatives from the
DuPont central research organization met to
consider alternative chemistries for producing
diphenol ether. The group concluded that none
of the alternatives they identified resolved the
safety issues or produced less waste.
A project for installing a larger receiving tank
is currently in the planning stages. However,
neither the capital nor the human resources to
implement this option have yet been assigned.
Opportunities for Others
Several case studies in this series examine
processes where a stabilizing agent is added
for safety reasons. In all of those studies, the
stabilizing agent either comprises the chief
component of the waste stream, or otherwise
frustrates attempts at waste reduction. All of
these processes were designed long before
waste reduction became a serious concern. As
a rule, the original process designers allowed
themselves large margins of safety by recom-
mending the use of far more stabilizing agent
than necessary. In these processes, waste
reductions often can be achieved by simply
reevaluating the amount of stabilizing agent
required for safety so that the amount of
stabilizer can be reduced.
SECTION 3: Case Studies
Page 45
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CATEGORY 3
Case Study 5: CAP Purification
Viable waste reductions are difficult to identify in old processes
Abstract
A waste minimization assessment was per-
formed for a process which uses a distillation
column to purify a chloroaromatic compound
from a product crude. The addition of a solid
stabilizing agent to minimize tar formation
indirectly increases the process waste stream
and frustrates attempts to reduce waste. Thus,
the inauguration of a program to reduce the
amount of stabilizer used was chosen as the
best waste minimization option. This assess-
ment exposes a possible flaw in the methodol-
ogy for weighting and ranking waste reduction
options. By not giving enough weight to an
option's probability for success, several
unworkable options placed near the top of the
list.
Intermediate cut
Product cut ^-
Foreshot cut
RECEIVING TANKS
BATCH
DISTILLATION
COLUMN
- CAP crude
-Stabilizer
STILL
Waste stream
PUMP
The CAP crude and stabilizer
enter the still and are heated
while the column operates
under normal atmospheric pressure.
Water boils off, rises to the top of the
column, and exits the process. The
pressure within the column is then
reduced.
During the transition from atmo-
spheric to operating pressure, low-
boilers continue to rise up the column.
At first, the material consists largely
of water, low-boiling impurities, and
some CAP. This material, called the
"foreshot cut", enters a receiving tank
to be held until the end of the product
campaign. At that time, it will be used
to flush the process equipment in
preparation for the next campaign.
As column pressure continues to drop,
the amount of CAP boiling up the
column with the low-boiling impuri-
ties increases. At some point, this
"intermediate cut" is diverted to
another receiving tank to be recycled
back into the still with the next batch
of the campaign. When the column
has at last achieved its operating
pressure, virtually pure CAP boils up
in a final "product cut".
Figure 3-10. CAP Process
Page46
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CASE STUDY 5: CAP Purification
CATEGORY 3
Background
The DuPont Chambers Works site produces a
chlorinated aromatic product (CAP) in two
separate processes at the site. One process
makes CAP crude, and the other purifies the
crude to product specifications.
The process which purifies CAP crude is
among the oldest at the Chambers Works site.
The process equipment is not dedicated to
CAP purification, but is used to purify other
products as well. Each CAP product "cam-
paign" can purify a maximum of three batches
of CAP crude before the amount of waste
accumulating within the equipment precludes
further processing.
The CAP is essentially boiled off from the
crude by a heated still which is connected to a
batch distillation column. This method exploits
differences in the temperatures at which each
constituent of the crude will boil. Lowering the
pressure within the process equipment has the
effect of lowering all boiling points. At the
right temperature and pressure, compounds
with lower boiling points (low-boilers) will
vaporize and rise to the top of the column.
There they condense, and either leave the
process or pass to a receiving tank to be held
for further processing. By controlling the
temperature of the crude and the pressure
within the process equipment, one can control
the chemical content of the vapor taken off the
top of the column.
Heating the CAP crude causes the formation of
byproducts, some of which are heavy tars. To
minimize byproduct formation, a stabilizing
agent is added to the crude. If an insufficient
amount of stabilizer is present, byproduct
formation can be very rapid, causing damage
to the process equipment. Although the
stabilizer is a nonhazardous solid, its
accumulation during a product campaign
Increase purity of raw
materials used to
make CAP crude
\
Sell crude CAP crude
without purifying it
Install an external stabilizer column
Implement continuous ^
monitoring of stabilizer level ya
Use different Stabilizer
Reduce operating pressure /;
Install equipment to remove ^&"
stabilizer from waste stream /j?
Improve CAP color
(eliminate still)
Figure 3-11. CAP Waste Minimization Options
SECTION 3: Case Studies
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CATEGORY 3
CASE STUDY 5: CAP Purification
Table 3-10. Ranked Summary of CAP Waste Minimization Options
Option
1. Reduce
stabilizer by
50%.
2. Use chemical
"color scaven-
ger".
3. Install equip-
ment to remove
stabilizer from
the waste
stream.
4. Sell CAP crude
without
purifying it.
5. Implement
continuous
monitoring of
stabilizer level.
6. Install pump to
circulate the
stabilizer within
the still.
7. Reduce
operating
pressure.
8. Install an
external
stabilizer
column.
"maximum score -
Pros
Addresses a major
cause of waste
Low-to-moderate
capital and
operating costs
Would eliminate
the need for
distillation process
Would reduce
waste
Would permit
recycling of
stabilizer
Would eliminate
the need for
distillation process
Would reduce the
amount of stabi-
lizer used
Would reduce the
amount of stabi-
lizer used
Low-to-moderate
capital cost
Would permit
distillation at lower
temperatures,
which would in
turn reduce tars
formed during
distillation and
allow a reduction
of stabilizer used
Would greatly
increase CAP
recovery by
keeping stabilizer
out of the still
1,450
Cons
Would require
implementation of
at least one and
perhaps several
other options to
assure that the
process remains
stable
Virtually no chance
of success
High capital cost
Long implementa-
tion time
Virtually no chance
of customer
acceptance
Developing a
suitable measuring
device could be
difficult
May be difficult to
implement
Very high capital
costs
May be difficult to
implement
technically
Comments
Ideas for reducing the
amount of stabilizer include
adding stabilizer only to the
first batch of a campaign, or
adding progressively smaller
amounts to each batch.
The chief reason for purify-
ing CAP crude is to eliminate
color and produce a water-
white liquid. But a search of
the chemical literature failed
to identify a scavenger that
would eliminate color.
Assumes that more precise
control would reduce
stabilizer while maintaining
an acceptable margin of
safety.
A pump would circulate CAP
within the still to keep the
stabilizer in suspension.
(Mechanical agitation is not
an option because of still
geometry.)
Score*
1,060
1,010
950
910
890
870
840
830
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CASE STUDY 5: CAP Purification
CATEGORY 3
Table 3-10. Ranked Summary of CAP Waste Minimization Options (cont'd)
Option
9. Increase
number of
charges per
campaign.
10. Crystallize CAP
instead of
distilling it.
1 1 . Replace
heating coils
in still with
external heat
source.
12. Use different
stabilizer.
13. Increase purity
of raw materials
used to make
CAP crude.
'maximum score =
Pros
Would eliminate
the need for
stabilizer
May improve CAP
recovery
Would reduce
amount of stabi-
lizer by improving
circulation within
still
Presumed
increase in CAP
recovery
1,450
Cons Comments
Accumulating
stabilizer buildup
probably renders
this option
undoable in
present process
Prohibitive capital
cost
High capital cost
Very low probabil- Previous attempts to find
fty of success alternative stabilizers have
High research cost failed.
Would merely shift
some of the waste
disposal problem
to another process
Score*
820
780
780
780
480
indirectly contributes to waste by preventing
complete recovery of CAP product. Moreover,
the stabilizer is chiefly responsible for the
gritty, extremely viscous consistency of the
waste stream.
Figure 3-10 illustrates the CAP purification
process. The distillation process consists of
three phases:
the "foreshot cut". Water and low-boiling
impurities boil off first. This material is
stored in a holding tank to eventually flush
the still after the final batch of the campaign.
the "intermediate cut". A transition period
during which increasing amounts of CAP
boil up with the last of the low-boilers. This
material is stored for recycling into the still
during the next batch.
the "product cut". With the low-boilers
gone,, virtually pure CAP boils up the
column.
After the third and final batch of the campaign,
a viscous "heel" of tar and stabilizer remains at
the bottom of the still. The still is heated to
maximum temperature and pressure to recover
as much residual product from the heel as
possible. Then the tank that holds the foreshot
cut empties into the still to flush the heel. The
flush is dewatered and incinerated.
SECTION 3: Case Studies
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CATEGORY 3
CASE STUDY 5: CAP Purification
Description of Waste Stream
A typical analysis of the waste stream leaving
the CAP still is provided below.
CAP (unrecovered product) 60%
Stabilizer 34%
Impurities 3%
High-boiling tars 3%
The consistency of the organic portion of the
waste stream is much like that of heavy motor
oil. However, the stabilizer thickens the waste
considerably, and limits the amount of CAP
that can be recovered from the crude.
The amount of waste from this process has
been constant for several years, and equals
0.12 Ibs for every pound of CAP product
recovered. At present, wastes from CAP
purification are incinerated.
Costs associated with this waste stream in-
clude the yield loss represented by the
unrecovered CAP, replacement cost of the
stabilizer, and the costs of incinerating the
waste stream.
Previous Waste Minimization Efforts
Over the years, several efforts were made to
reduce wastes from the CAP purification
process:
The practice of recycling the intermediate
cut was designed into the process to increase
the amount of CAP recovered. This yield
improvement reduced the CAP component
of the waste.
Successful introduction of the stabilizer to
the process minimized the formation of tars
during distillation. These tars would other-
wise contribute to the organic component of
the waste.
An effort to eliminate the stabilizer failed.
Had it succeeded, it would have removed a
major cause of waste generation.
Waste Minimization Options
The assessment team for CAP purification met
in a brainstorming session and generated 13
possible options for reducing waste. They
recorded their ideas by constructing a cause-
and-effect "fishbone" chart, shown in
Figure 3-11. In subsequent meetings, the team
discussed the options and ranked them using
the weighted-sum method described in
Section 2 of this document. Table 3-10 sum-
marizes these discussions, and presents the
options in rank order.
Most of the options focus on the solid stabi-
lizer. One option that was not suggested
during brainstorming is changing the method
of stabilizer addition from batch to continu-
ous. This was among the most promising
options in Case Study 9: "CAP Isomers
Process". But that case study examined a
continuous distillation process. The CAP
purification process is a batch distillation;
adding stabilizer in continuous mode would
result in no waste reductions at all.
Technical and Economic Feasibility
After considering the pros and cons of each
option listed in Table 3-10, the assessment
team chose six options for technical and
economic feasibility analysis:
Option 1: Reduce stabilizer by 50%
Option 3: Install equipment to remove
stabilizer from the waste stream
Option 5: Implement continuous monitoring
of stabilizer level
Option 6: Install pump to circulate the
stabilizer within the still
Option 7: Reduce operating pressure
Option 8: Install an external stabilizer
column
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CASE STUDY 5: CAP Purification
CATEGORY 3
Table 3-11. Economic Summary of Top CAP Waste Minimization Options
Option
Reduce stabilizer
by 50%
Install equipment
to remove stabi-
lizer...
Implement contin-
uous monitoring
of stabilizer level
Install pump to
circulate
stabilizer...
Reduce operat-
ing pressure
Install an exter-
nal stabilizer
column
Waste
Reduction
34%
59%
34%
34%
34%
59%
Capital Cost
$20,000
$331,000
$57,000
$48,000
$104,000
$237,000
EPA Method
NPV(12%) IRR
$66,000
($156,000)
$32,000
$41 ,000
($9,000)
($73,000)
59%
<0%
24%
29%
10%
3%
DuPont Method
NPV(12%) IRR
$66,000
($156,000)
$32,000
$41 ,000
($9,000)
($73,000)
59%
<0%
24%
29%
10%
3%
Implemen-
tation Time
6 months
1 year
6 months
6 months
1 year
1 year
Comments: The economics for these options are given on a stand-alone basis, and do not consider
possible synergies from implementing more than one option.
Waste reduction percentages for these options are not fully additive if more than one
option is implemented.
Parentheses denote negative numbers.
For an explanation of terms used in this analysis, see the discussion under "Feasibility
Evaluation" in Section 2: Project Methodology.
The results of the economic analysis are
presented in Table 3-11. Option 1 is easy to
implement, has a good chance of reducing
waste, and has a good economic return.
However, safety concerns will probably
prevent it from being implemented. Options 5,
6, and 7 achieve the same waste reduction as
Option 1, but provide additional process
controls that would maintain the present level
of safety.
Option 3 offers greater waste reductions and
would be fairly easy to implement, but the
capital cost is prohibitive. Similarly, Option 8
would reduce wastes substantially but at a
high cost
Of the options considered, Option 6, "Install
pump to circulate the stabilizer within the
still", offers the best chance of success.
Barriers to Implementation
The addition of stabilizer is a safety practice
that prevents rapid byproduct and tar forma-
tion and consequent equipment damage. It will
be difficult to arouse interest in reducing the
amount of stabilizer unless other changes are
made that will maintain the margin of safety at
SECTION 3: Case Studies
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CATEGORY 3
CASE STUDY 5: CAP Purification
current levels. Moreover, CAP purification is
a batch process which shares equipment with
several other products. Economics would
make changes that benefit just one product
difficult to justify.
Opportunities for Others
This series of assessments examines six
processes in which the waste streams exit
from distillation columns. The CAP process
features a unique combination of process-
specific considerations, i.e., the age of the
process, the particular stabilizer it requires,
and its sharing of equipment with other pro-
cesses. Thus the ideas generated for reducing
the waste stream seem specifically relevant to
the CAP process. However, many of the
options generated for the other distillation
waste streams will surely be relevant for other
processes throughout industry.
Several case studies in this series examine
processes where a stabilizing agent is added
for safety reasons. In all of those studies, the
stabilizing agent either comprises the chief
component of the waste stream, or otherwise
frustrates attempts at waste reduction. As a
rule, the designers of such processes allowed
large margins of safety by recommending the
use of more stabilizing agent than necessary.
Thus, waste reductions often can be achieved
by simply reevaluating the amount of stabiliz-
ing agent required for safety so that the
amount of stabilizer can be reduced. However,
it is likely that such reductions will have to be
accompanied by such additional changes as
better process controls, different operating
conditions, or equipment changes in order to
maintain the present margin of safety.
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SECTION 3: Case Studies
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CATEGORY 2
Case Study 6: Polymer Vessel Washout
High-pressure water cleaning eliminates the use of a hazardous solvent
Abstract
This report describes a successful effort to
achieve a 98% source reduction in a waste
stream generated by the washing of a process
vessel with a flammable solvent. The solvent
wash has been replaced by a high-pressure
stream of water. The method used to identify
and evaluate alternatives to the solvent wash
contained some essential features of the EPA
waste minimization methodology. However,
this effort began not as a waste minimization
project, but as part of an overall process
improvement program. The new washout
system was implemented because it attained
most of the goals of the program, of which
waste minimization was but one. This assess-
ment highlights the importance of considering
all business objectives when trying to mini-
mize waste; waste reduction is often inter-
related with such other business objectives as
quality improvement, increased capacity, and
reduced cycle times.
Background
The DuPont Chambers Works site produces
several grades of polymer. The process uses
an agitated vessel which must be cleaned
periodically to maintain product quality.
During processing, polymer accumulates on
the vessel walls, agitator blades, and baffles.
Cleanup is complicated by the vessel's con-
struction, which renders opening the vessel
to facilitate cleaning difficult and time-
consuming.
Until recently, the vessel was cleaned by
washing with a flammable solvent. The sol-
vent was pumped into the vessel, agitated, and
drained through a bottom flange. This process
was typically repeated six times per cleaning.
The solvent and dissolved polymer were
drummed for eventual incineration on site.
In December of 1991, the polymers process
area implemented a waste minimization option
that has completely eliminated the solvent
component of the waste stream. Moreover, the
potential exists for eliminating the small
amount of polymer waste as well. Solvent
washing of the vessel has been replaced by
cleaning with a high-pressure water jet.
The alternative cleaning method originated not
from a dedicated waste minimization effort,
but from a process improvement program that
had waste minimization as just one of its
goals. The other goals were improved quality,
shorter cycle times, reduction of inventories,
etc. This waste minimization effort did not
conform to the EPA methodology in that
responsibility for its implementation fell to a
single person in consultation with other area
personnel. But the process contained some
basic features of the EPA methodology, i.e.,
option generation and economic/technical
feasibility analysis.
The process improvement program focused on
vessel washout for several reasons:
The solvent waste. The copious amounts
of solvent required for washout produced
a large waste stream that had to be
incinerated.
Safety concerns during washout. Solvent
fumes constitute an explosion hazard, and
special safety precautions had to be ob-
served in the vicinity of the vessel during
washout.
SECTION 3: Case Studies
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CATEGORY 2
CASE STUDY 6: Polymer Vessel Washout
Safety concerns associated with handling
and storing solvent-filled drums. Solvent
fumes released during loading and unload-
ing posed a safety hazard, as did the ergo-
nomics of drum handling.
Product quality considerations. The solvent
wash never really did a thorough job of
cleaning the vessel.
The need to improve uptime. The amount of
time required for vessel washout frustrated
attempts to increase production.
Figure 3-12 illustrates the new cleaning
system. A special nozzle and lance assembly
is connected to a high-pressure water source
and inserted through the flange at the vessel
bottom. The flange itself has been enlarged to
accommodate the equipment and to enhance
draining of the wash water. A stream of water
at a pressure of 10,000 psi with a flow rate of
16 gpm blasts the residual polymer from the
interior surfaces. For safety reasons, the entire
system is operated remotely, and no high-
Vessel
Rotated
Lance
High Pressure
Water Feed
Nozzle
Clamped
Attachment
Swivel
Joint
The high-pressure water
lance is attached to a
carriage, which is in turn
affixed to the bottom of the
vessel. A chain-drive moves the
lance up and down the carriage as
needed. A swivel joint at the base
of the lance permits free rotation.
The nozzle at the dp of the
spinning lance has two
aperatures, which emit cone-
shaped sprays of water at 10,000
psi with a combined flow rate of
16 gpm.
Operation of the lance is con-
trolled from a panel well re-
moved from the vessel. The
process is designed such that no
high-pressure spray leaves the
interior of the vessel. These
precautions assure operator safety
during vessel washout.
Figure 3-12. High-Pressure Water System
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SECTION 3: Case Studies
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CASE STUDY 6: Polymer Vessel Washout
CATEGORY 2
pressure spray escapes the vessel. The system
was designed with the help of an external
vendor. With the exception of the nozzle and
lance assembly, the system is operated using
leased equipment.
Description of Waste Stream
A typical analysis of the waste stream result-
ing from the solvent washout of the polymer
vessel would reveal:
Solvent 98%
Residual polymer 2%
Costs associated with this waste stream in-
cluded the replacement cost of the solvent, the
yield loss represented by the accumulation of
residual polymer, and the costs of incinerating
the waste stream.
Before the waste minimization effort, the
solvent washout produced 0.013 Ibs of hazard-
ous waste to be incinerated for every pound of
polymer product made. After implementation
of the high-pressure water system, waste
generation fell to 0.0001 Ibs of nonhazardous
waste for evey pound of polymer produced.
Table 3-12. Ranked Summary of Polymer Vessel Waste Minimization Options
Option
Pros
Cons
Comments
1. Replace solvent
washout with
cleaning by high-
pressure water jet.
2. Use a still to recover
and recycle solvent.
3. Use an antistick
coating (such as
glass) on vessel
walls.
4. Open process vessel
and clean it manually.
Complete source
elimination of solvent
wash
Potential for applying
residual polymer to as
yet unexplored uses
Attainment of other
process improvement
goals
Would achieve 90%
reuse of solvent
Would reduce the
number of solvent
washes required
Would attain other
process improvement
goals
Complete source
elimination of solvent
wash
Potential for applying
residual polymer to as
yet unexplored uses
Safety concerns
Equipment modification
(i.e., enlargement of
flange at vessel bottom)
required
Would not achieve other
process improvement
goals
Requires significant
capital cost and in-
creased operation and
maintenance costs
Would not eliminate
solvent washes because
some polymer would still
stick to coated vessel
walls
Requires equipment
modification
Would significantly
increase maintenance
costs
Poor attainment of other
process improvement
goals
Would not enhance
employee relations
To prevent injuries to
employees, spray equip-
ment must be operated
remotely, and spray must
be completely enclosed
within the vessel.
The polymer is insoluble in
water and can easily be
separated from the wash.
ft will be landfilled until
uses for it are found.
A dirty and tedious job for
whomever must perform it.
SECTION 3: Case Studies
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CATEGORY 2
CASE STUDY 6: Polymer Vessel Washout
This represents a source reduction of 98% in
the amount of waste generated.
The new cleaning system does produce a
small wastewater stream, which is sent to the
on-site wastewater treatment plant. Because
the residual polymer is virtually insoluble in
water, the wastewater contains no TOC or
other contaminants and adds only a small
hydraulic load on the wastewater treatment
plant.
Previous Waste Minimization Efforts
In 1989, a project was started for which waste
minimization was the chief goal. The project
would have used a still to separate the solvent
from the dissolved polymer and recycle it for
future washes. Some of the process equipment
required for this project was actually procured,
but never installed. Work on the project
stopped once the high-pressure washout
process was demonstrated.
The solvent recycling project would have
eliminated about 90% of the waste sent to the
incinerator. However, this option was judged
to be less satisfactory than the water-jet option
because:
it represented a recycling of waste rather
than a source reduction, and
it did not meet the other goals established
for the process improvement program.
Waste Minimization Options
In 1990, four options were considered for
achieving waste minimization, and these are
summarized in Table 3-12. Option 1, "Re-
place solvent washout with cleaning by high-
pressure water jet", emerged as the clear best
choice. It satisfied all of the process improve-
ment goals, including complete source reduc-
tion of solvent waste.
Technical and Economic Feasibility
Technical Evaluation
By April of 1991, a prototype nozzle had been
designed with the help of the vendor and was
ready for testing. The system operated at a
pressure of 10,000 psi and a flow rate of 16
gpm. The test was not a complete success in
that the nozzle failed to reach all of the re-
quired interior surfaces. Nevertheless, results
were judged good enough to warrant further
development.
Table 3-13. Economic Summary of Top Polymer Vessel Waste Minimization Options
Opllon
Replace solvent...
wrth...high-pres-
sure water jet
...recover and
recycle solvent
Waste
Reduction
98%
90%
Capital Cost
$125,000
$500,000
EPA Method
NPV(12%) IRR
$2,720,000
($358,000)
181%
DuPont Method
NPV (12%) IRR
$2,690,000
($393,000)
180%
Implemen-
tation Time
1 year
2 years
Comments: Parentheses denote negative numbers.
For an explanation of terms used in this analysis, see the discussion under "Feasibility
Evaluation" in Section 2: Project Methodology.
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CASE STUDY 6: Polymer Vessel Washout
CATEGORY 2
Economic Evaluation
Only two options were subjected to an eco-
nomic analysis: Option 1 "Replace solvent
washout with cleaning by high-pressure water
jet", and Option 2 "Use distillation column to
recover and recycle solvent". Results are
summarized in Table 3-13 using both DuPont
and EPA methodologies.
When evaluating waste minimization projects,
it's important to consider all factors that can
contribute to their cost effectiveness. Focusing
narrowly on waste minimization objectives
could cause a business to overlook cost-saving
options that have a better chance of implemen-
tation. The high-pressure water jet option had
a very attractive internal rate of return (IRR)
when considered for its attainment of both
waste minimization and process improvement
goals. Had it been evaluated on the basis of
waste minimization alone, the IRR would
have been marginal, and its chances for
implementation would have been diminished.
The recovery of solvent option (Option 2)
began as a low capital project with a limited
scope. It had assumed the use of drums to
handle and store the recovered solvent, and ,
this helped keep the capital cost down. How-
ever, the handling of drums was later deemed
to be inconsistent with other process improve-
ment goals, and the scope of the project was
changed to eliminate the use of drums. This
required the use of holding tanks and associ-
ated equipment, which increased capital costs
prohibitively.
Barriers to Implementation
Barriers to implementing the high-pressure
water option included concerns over safety.
The same technology is employed in some
industries to cut rock! A wayward jet stream
could easily disable a person. A way had to be
found to operate the system remotely, and to
completely enclose the water jet within the
polymer vessel. Moreover, a specialized
nozzle which could reach all interior surfaces
of this particular vessel had to be designed.
Evaluation of Performance
The experimental lance/nozzle assembly was
modified to achieve complete washing of the
vessel interior. The flange at the bottom of the
vessel was enlarged to accommodate the lance
and to improve drainage. The new system was
tested in December of 1991 and resulted in
flawless cleaning of the vessel. Since then, the
system, has met all of its process improvement
program goals. The solvent waste has been
completely eliminated. The remainder of the
waste stream, i.e., a small amount of non-
hazardous polymer, is now being landfilled.
But process area management is already
considering ways in which this waste can be
sold for various applications.
This waste minimization success story is
being communicated throughout the DuPont
community in a number of ways, including a
description of the technology in an internal
technical bulletin distributed to engineers.
This waste minimization effort has won an
"Environmental Excellence Award", a DuPont
award which recognizes people or teams that
have made significant contributions toward the
company's goal of global environmental
leadership.
Opportunities for Others
Many industrial processes depend upon
solvent washes for cleaning equipment. High-
pressure water cleaning now presents an
environmentally sound alternative. Nozzle
SECTION 3: Case Studies
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CATEGORY 2
CASE STUDY 6: Polymer Vessel Washout
designs and ancillary equipment have ad-
vanced sufficiently to permit automated and
safe high-pressure water cleaning systems.
Even in those processes where water cannot
be introduced into the equipment, an alterna-
tive exists. Vessels can be cleaned with solid
carbon dioxide (dry ice) particles suspended in
a nitrogen gas carrier. The solid CO2 cleans in
a manner similar to that of sandblasting, but
evaporates, leaving only the material removed
from the equipment
This assessment highlights the importance of
considering all business objectives when
trying to minimize waste. Waste reduction is
often interrelated with such goals as quality
improvement, cycle time reduction, and lower
materials cost. Solutions which satisfy all of
these goals are those which are most likely to
be implemented. The lesson for option genera-
tion is to look at the big picture, and not to
focus narrowly on a waste stream.
Page 58
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CATEGORY 2
Case Study 7: Reusable Tote Bins
Returnable product containers eliminate 55-gallon drums
Abstract
This report describes the successful imple-
mentation of an environmentally friendly
product packaging system to reduce the use of
single-use 55-gallon drums. This effort both
conserves landfill space and reduces a waste
stream consisting of the chemical residue
remaining within thousands of empty drums.
The new packaging system uses returnable
metal tote bins which drain much more com-
pletely than drums, and provide better ergo-
nomics for users and handlers. Customers
view the new packaging as a value-adding part
of the product offering because it relieves
them of the burden of drum disposal. The
combination of product improvement with
waste minimization helped to ensure the
success of this effort.
Background
The Chambers Works site produces a line of
more than 500 specialty chemicals which are
sold in small-volume orders to customers in a
variety of industries. These chemicals, some
of which are custom-made for specific cus-
tomer applications, are collectively known as
"small-lot" chemicals. Until recently, all
customers of small-lot chemicals received
their products in single-use containers such as
55-gallon drums. When emptied, the drums
could contain about a pound of product resi-
due. Customers had to wash out the drums and
properly dispose of the wash and residue, and
then dispose of the empty drum, usually with-
in a landfill. Given the rising costs of waste
disposal, customers clearly had great value for
an alternative packaging method that would
relieve them of this waste disposal burden.
Recently, a DuPont assessment team of
business leaders and plant personnel com-
pleted, an effort to identify and implement
alternative packaging for several customers of
small- lot chemicals. The team had established
several goals that the chosen alternative would
have to meet:
relieve customers of the waste disposal
burden
provide better ergonomics and ease of use
than that afforded by drums
have no adverse affect on product quality or
shelf life
The chosen alternative, illustrated in
Figure 3-13, is a returnable metal tote bin
with am optional base tank. Customers receive
a full tote bin and mount it atop the base tank
which; dispenses the product. When the tote
bin is empty, the customer ships it to a third-
party cleaning vendor located near the Cham-
bers Works site. The cleaning vendor uses a
high-pressure water system to clean the tote
bins, and then sends the clean bins and the
washwater to Chambers Works. There, the
empty tote bins are refilled with whatever
small-lot chemical is ready for shipment. The
washwater goes to the on-site wastewater
treatment plant for disposal.
The returnable tote bins are purchased by
DuPont, which retains ownership of them
throughout their service life. The base tanks
are the property of the customer. DuPont bears
the costs for the return shipment of the tote
bins and for their cleaning.
SECTION 3: Case Studies
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CATEGORY 2
CASE STUDY 7: Reusable Tote Bins
The totes bins are specially designed for
complete drainage. Any residue left behind in
an empty tote bin is an extremely small frac-
tion of that left behind in the equivalent
number of empty drums. Moreover, the
elimination of the drums themselves is a waste
reduction which conserves landfill space. And
because the tote bins meet the,goals estab-
lished for this effort, they have won accep-
tance by those customers who receive them.
Description of the Waste Stream
The waste stream from drum packaging
originates not from the Chambers Works
plant, but from the customer's site. After the
product is consumed, about one pound of
waste remains within each drum. Disposal of
this waste is the responsibility of the cus-
tomer. Costs to the customer include labor
cost for washing the drum, disposal cost for
the residue, disposal cost for the empty drum,
RETURNABLE
TOTE BIN
BASE
TANK
SLOPED
INTERIOR
BOTTOM
VAPOR LINE/
SIGHT TUBE
The returnable tote bin is a 345-gal, stainless
steel container. It meets all DOT specifications
for shipping the chemicals it contains. The tote
bin has a stacking pad and leg positioners to permit
stacking. The container is designed to be assessible to
a fork lift from three sides. The inner bottom of the
container is sloped to allow material to drain quickly
and completely.
The base tank holds about 500 gallons. The returnable
tote bin is placed on top of the base tank and feeds its
contents to the tank. A vapor line attached between the
tote bin and base tank prevents vapor from escaping to
the atmosphere. The base tank contains an instrument or
site tube to indicate fluid level. The tote bin/base tank
assembly provides a steady supply of product, even
during tote bin changeovers.
Figure 3-13. Reusable Tote Bin and Base Tank Assembly
Page 60
SECTION 3: Case Studies
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CASE STUDY 7: Reusable Tote Bins
CATEGORY'2
and yield loss represented by the residue.
These costs can easily total more than $25
per drum.
The use of returnable containers virtually
eliminates this cost for the customer. It also
greatly reduces the total wastes represented by
product residue in empty drums. But a more
dramatic waste reduction is the number of
drums that will not occupy space in landfills.
One returnable tote bin holds as much product
as six drums. Over its expected service life,
the tote bin will package as much product as
360 drums.
Shifting the waste disposal burden from many
customers to DuPont helps to ensure that
wastes will be disposed of properly. It also
protects DuPont from liabilities resulting from
improper disposal of drums by customers.
Previous Waste Minimization Efforts
The small-lot chemicals business had previ-
ously studied the use of 275-gallon polyethyl-
ene totes. However, permeation of the poly-
ethylene by the solvent was observed, and it
was judged an unsuitable material of construc-
tion for this end use. Implementation of this
option would have required either costly
modification to the polyethylene or the adop-
tion of an alternative polymer with specific
resistance to the solvent. No such polymer is
known to be commercially available.
Waste Minimization Options
The assessment team examined four waste
minimization options, and these are summa-
rized in Table 3-14. Option 1, "Stainless steel,
returnable container", emerged as the best
choice because it satisfies to some degree all
of the goals established for this waste minimi-
zation effort.
Technical and Economic Feasibility
Only two options would result in waste elimi-
nation: Options 1 and 2, both of which use the
same container. Option 1 requires a cleanout
of the tote bins between uses, whereas Op-
tion 2 eliminates cleaning by dedicating tote
bins to single products.
Option 1 simplifies the packaging process.
Cleaning a tote makes it suitable for packag-
ing any product for shipment to any customer.
Given the great number and low volume of
Table 3-14. Ranked Summary of Tote Bin Waste Minimization Options
Option
Pros
Cons
1. Stainless steel, returnable
container.
2. Dedicated returnable
containers.
3. Make on-demand deliveries
("milk run" option) using multi-
compartment tankers.
4. Use plastic totes with vapor
barrier.
Eliminates disposal at customer
sites
Reduces total waste by 50%
Complete elimination of waste
stream
Eliminates drum disposal
Much lower cost than stainless
steel tote bins
Does not completely eliminate
waste
High capital cost
Too many containers required
Quality concerns from potential
contamination or decomposition of
product remaining in tote
Impractical and costly because of
number of products and customers
Would not eliminate waste
because tanker trucks would have
to be cleaned between runs
Can be used only once, and would
not ameliorate disposal problems
SECTION 3: Case Studies
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CATEGORY2
CASE STUDY 7: Reusable Tote Bins
Table 3-15. Economic Summary of Top Tote Bin Waste Minimization Options
Option
Returnable
containers, six
trips per year
with washout
Returnable
containers, six
trips per year
with no washout
Waste
Reduction
50%
100%
Capital Cost
per Container
$1,500
$1,500
NPV(12%) IRR
($1,997)
$360
<0%
17%
Change In Product Cost
for Acceptable IRR
$0.07/lb increase
None required
Comments: Parentheses denote negative numbers.
For an explanation of terms used in this analysis, see the discussion under "Feasibility
Evaluation" in Section 2: Project Methodology.
small-lot chemicals sold to individual custom-
ers, dedicating totes to single products would
lengthen their turnaround time and require a
greater number of tote bins. Cleaning the totes
for reuse with any product available for
shipment shortens their turnaround time, and
helps to offset the cost of the bins.
Because Option 2 eliminates washout, the tote
bins would have to be modified with seals and
check valves to prevent contamination from
the surrounding environment in which the
totes are used. But dedicating tote bins to
customers who buy a product in high volume
could make economic sense.
The economic feasibility of reusable tote bins
depends on such customer-specific factors as
distance from Chambers Works and tote bin
turnaround frequency. The evaluation pre-
sented in Table 3-15 assumes a shipping
distance of about 1000 miles, six round trips
per-tote per-year, and a tote bin service life of
10 years. It factors in cost savings to DuPont
from the elimination of drums, pallets, and
stretch wrapping. No customer cost savings
were assumed.
Offsetting these savings are costs associated
with washing the tote bins, shipping them
back to Chambers Works, and tracking them
throughout the product cycle. The greatest of
these costs is the washing, accounting for
about 60% of the total.
Table 3-15 presents evaluations for two cases:
Case 1: Six turnovers per year with wash-
out between uses. An acceptable internal
rate of return (IRR) for purchasing the totes
would require additional revenue equal to
about $0.07 per pound of product shipped.
Case 2: Six turnovers per year using prod-
uct-dedicated totes and no washout. Not
only does this option provide a 100% reduc-
tion in waste, but it also provides sufficient
IRR to support purchase of the returnable
totes without any additional revenue.
The products within the small-lot chemicals
line generally are sold in such low volume that
dedicated tote bins are not likely to have six
turnovers per-tote per-year as Case 2 assumes.
But other product lines now packaged in
drums are sold in sufficient volume to benefit
Page 62
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CASE STUDY 7: Reusable Tote Bins
CATEGORY 2
from a switch to dedicated, returnable totes.
Each product and customer has to be evalu-
ated on a case-by-case basis.
Such "soft" benefits as increased customer
satisfaction and maintenance of market posi-
tion will undoubtedly influence the decision of
whether to use drums or totes.
Evaluation of Performance
In the spring of 1991,50 tote bins were or-
dered to demonstrate the validity of the return-
able container concept. There were some
initial problems with the materials used for
sight glass tubes and gaskets, but these were
solved by fall 1991. The small-lot chemicals
business now uses the tote bins for many
products and expects to extend their use to
more products in the future.
Opportunities for Others
This assessment demonstrates that good waste
reductions don't always originate in the pro-
cess area. The replacement of drum packing
with reusable bins was suggested by the sales
force and driven by the business organization.
There are probably many products for which
switching from drum packing to returnable
containers would benefit both supplier and
customer. For the supplier, the cost of a
returnable tote over its service life could be
less than the cost of the nonreturnable drums
that would otherwise be used. But the real
beneficiaries of returnable containers are
customers, happy at last to be rid of a disposal
headache. Switching to reusable containers
in businesses still dominated by drums can
confer upon a supplier a competitive
advantage.
The Chemical Manufacturer's Association
(CMA) promulgates Product Stewardship
guidelines as part of its Responsible Careฎ
program. These guidelines are intended to
promote the safe handling of chemicals, from
initial manufacture to ultimate disposal, by
member organizations, their distributors, and
customers. In many cases, returnable contain-
ers are a good way to advance the objectives
of the Product Stewardship guidelines.
SECTION 3: Case Studies
Page 63
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CATEGORY 2
Case Study 8: Monomer Production
A reaction'distillation process achieves waste reduction through better
process control
Abstract
A process for making monomers uses a
reactor to create the product, and a distillation
column to separate the product from the
reaction mass. Some of the reaction mass
polymerizes within the reaction vessel, form-
ing waste and entrapping a large quantity of
otherwise good product. To increase product
yield and reduce waste, the monomers process
will replace its outmoded process control
system with a modern distributed control
system (DCS). This assessment demonstrates
the importance of process control to waste
reduction. It also demonstrates the interrela-
tionship between waste reduction and other
business objectives such as reduced cycle
time, higher product yield, and greater process
productivity.
Background
A batch process at the DuPont Chambers
Works site produces several monomers used
to manufacture various polymers. One of the
raw materials used in the process, methyl
methacrylate (MMA), is itself a monomer.
During processing, MMA tends to polymerize
within the process equipment, forming a very
viscous tar and entrapping a large quantity of
otherwise recoverable product. These wastes
are currently drummed and landfilled on site.
Figure 314 illustrates the process for produc-
ing monomers. MMA and long-chain alcohol
are reacted in the presence of a catalyst to
form the product monomer. Despite the
addition of a polymerization inhibitor, some
MMA polymerizes when heated to process
temperatures. When processing of a product
batch is complete, the polymer tar is drained
from the bottom of the reactor into 55-gal
drums, mixed with wax to enhance solidifica-
tion, and landfilled.
A waste minimization assessment was per-
formed to generate options for reducing the tar
stream from the monomers process. The
assessment team determined that the best
option for implementation would be the
complete replacement of the present pneu-
matic control system with an electronic dis-
tributed control system (DCS). This project
will require considerable capital investment,
but is expected to cut the tar stream in half. In
addition to reducing waste, the DCS will also
improve product yield, shorten cycle time, and
improve quality. Indeed, it is for all of these
reasons that the DCS option was selected. It's
questionable whether such a high-capital
project could have been justified based on
reducing the waste stream alone.
Description of the Waste Stream
A typical analysis of the tars leaving the
monomers reactor would reveal:
Unrecovered product monomer 50%
Polymer tars 45%
Decomposition products 5%
The tars leave the hot reactor as a viscous
liquid, but form a solid mass upon cooling.
Some wax is added to help solidify the tars.
Decomposition products include inhibitors
and catalyst left over from the reaction.
Page 64
SECTION 3: Case Studies
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CASE STUDY 8: Monomer Production
CATEGORY 2
I
Water, Methanol, MMA
I
Alcohol
I
Product Monomer
FORESHOT
RECEIVER
DISTILLATION
COLUMN
MIDSHOT
RECEIVER
PRODUCT
RECEIVER
MMA. Water
Product Monomer
Alcohol
REACTOR
Alcohol,
-MMA,
Catalyst,
Inhibitor
Waste stream
Virgin MMA and alcohol, a recycle stream of
MMA and water, a recycle stream of alcohol,
and a polymerization inhibitor are placed in a
heated reactor. Water boils off, rises as vapor to the
top of the column, and exits the process. Then a
catalyst is introduced to the reactor. The resulting
reaction produces the product monomer and methanol
byproduct. As the methanol forms, it boils up the
column and passes to the foreshot receiver, taking
some MMA with it. The reaction continues until
methanol ceases to form. Then the pressure within the
reactor and column is reduced. This causes unreacted
alcohol to boil up the column and pass on to the
midshot receiver. The pressure within the process
equipment is reduced again, and the product monomer
boils up the distillation column to the product receiver.
Despite the addition of the inhibitor, some MMA and
product monomer polymerizes upon exposure to heat
and form!; a viscous tar. At the end of each product
batch, the tar is drained from the bottom of the reactor
into drums and then landfilled.
Methanol is washed out of the foreshot receiver with
water. Some residual water remains behind with the
MMA. At the start of the next product batch, the
contents of the foreshot and midshot receivers are
reintroduced to the reactor.
Figure 3-14. Monomers Process
SECTION 3: Case Studies
Page 65
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CATEGORY 2
CASE STUDY 8: Monomer Production
The amount of waste currently generated by
this process is 0.12 Ibs of waste for every
pound of monomer produced. The wastes are
currently landfilled on site.
The major costs associated with this waste
stream are the costs of landfilling and the yield
loss represented by the unrecovered product.
Included in the landfilling costs are the costs
of purchasing and handling drums, and the
cost of the wax which is used to solidify the
tars.
Previous Waste Minimization Efforts
Over the years, several efforts have been made
to reduce wastes from the monomers process.
In 1970, the process began operating at lower
reactor and column pressure. This allowed the
reaction and distillation steps to run at lower
temperatures. Lower temperature retarded
polymerization of the reaction mass, resulting
in a waste reduction of about 25%. Unfortu-
nately, the lower temperature increased both
the reaction time and distillation time, result-
ing in reduced production. So in 1975, the
pressure and temperature were raised back to
their previous levels.
In 1975, the amount of inhibitor added to the
reactor was doubled, which improved product
yield and reduced wastes by about 14%.
This measure is still in effect in the current
process.
In 1990, the monomers process tested an
alternative method for disposing of tars:
mixing the tars with solvent and then inciner-
ating the mixture. This option was tested
because of concern about off-site landfill
costs in the event that the Chambers Works
landfill became full. Also, adding solvent
would make the tars pumpable, eliminating
the ergonomic safety concerns associated
with drum handling. However, test results
showed that the cost of incineration and
solvent were greater than the cost of off-site
landfilling.
In 1992, an alternative inhibitor was tested for
its possible waste minimization value. Labo-
Change reaction chemistry\
Use different Inhibitor to\
retard tar formation \<ฃ
Use a different process \&
Uso filtration to separate product
from decomposition products
Improve reactor heat
distribution or agitation to
prevent localized over heating
Reduce water entering process by/
using multistage extraction ฃง
Add additional equipment /**
for recovering more /
product from tars /
Add additional catalyst to
permit running process at \
tower temperatures \ j,
"Milk" the charge (longer distillation >&
time) to recover more product v
ฃ Reduce reactor pressure during
tfjs. reaction and purification
\ Increase amount of inhit
/
?" Sell tars as product
Improve process \
control, especially \
P . temperature control \Q
\^i \S*
\ \
\ \ Red
"""" \ \ Wash
/ / Mont
SeS' /& Pro
/^ Slurry tars in water and f^
/ฃ send to wastewater /&
/& treatment plant Jfy
Add inhibitor continuously /^
to distillation column /&
r
uce
:from
mcrs
cess
Figure 3-15. Monomers Process Waste Minimization Options
Page 66
SECTION 3: Case Studies
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CASE STUDY 8: Monomer Production
CATEGORY 2
ratory tests indicated that the new inhibitor
might decrease tar formation. However, a
plant trial revealed no decrease in tars. It is
often difficult to reproduce laboratory results
in an actual process because the control of a
large scale process usually lacks the precision
of control in the laboratory. However, this
option may be reconsidered after the DCS is
installed.
Waste Minimization Options
An assessment team consisting of the area
chemist, area engineer, two operators, and
three people from outside of the process area
generated 15 waste minimization options.
They recorded their ideas by constructing a
cause-and-effect "fishbone" chart, shown in
Figure 315. In subsequent meetings, the team
discussed the options and ranked them using
the weighted-sum method described in Section
2 of this document. Table 3-16 summarizes
these discussions, and presents the options in
rank order.
Both the MMA raw material and the product
monomer tend to polymerize when heated to
process temperatures, and this produces the tar
stream. For this reason, source reduction
options tended to address reactor temperature,
the polymerization inhibitor, or residence time
of the reactants within the reactor. Because the
tar stream contains a large percentage of
unrecovered product monomer, several
recyling options looked at ways to recover
additional product from the waste stream.
Technical and Economic Feasibility
After considering the pros and cons of each
option listed in Table 3-16, the assessment
team chose five options for technical and
economic feasibility analysis:
Option 1: Reduce reactor pressure during
reaction and purification
Option 2: Add additional catalyst to permit
running process at lower temperatures
Option 4: Increase amount of inhibitor
added to the reactor
Option 5: Improve process control, espe-
cially temperature control
Option 11: "Milk" the charge (longer distil-
lation time) to recover more product
The results of the economic analysis are
presented in Table 3-17.
Option 5, "Improve process control...", is
currently being implemented. The process
area is replacing their outmoded pneumatic
controls with a DCS. The more precise control
afforded by the DCS will permit shorter
residence times within the reactor. This in turn
will reduce waste by perhaps 50%.
The DCS project, did not rank at the top of the
option list, and might not have been selected
for waste reduction alone. But other benefits
from the DCS, such as increased production,
higher product yield, shorter cycle time, and
higher product quality, all contributed the
additional cost savings required to justify this
project.
After the DCS has been installed, several
other options might be considered to achieve
further reductions. The economic analysis for
these options as well as for the DCS are
presented in Table 3-17.
Option 4, "Increase amount of inhibitor added
to the reactor", could be implemented quickly
and with no capital cost. In the past, doubling
the amount of inhibitor reduced tar formation.
It's possible that doubling it again, or chang-
ing the method or location of inhibitor addi-
tion, could achieve further reductions. The
analysis in Table 3-17 assumes several
person-months of a chemist's time to evaluate
SECTION 3: Case Studies
Page 67
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CATEGORY 2
CASE STUDY 8: Monomer Production
Table 3-16. Ranked Summary of Top Monomers Process Waste Minimization Options
Option
1. Reduce reactor
pressure during
reaction and
purification.
2. Add additional
catalyst to
permit running
process at
lower tempera-
tures.
3. Slurry tars in
water and send
to wastewater
treatment plant.
4. Increase
amount of
inhibitor added
to the reactor.
5. Improve
process
control,
especially
temperature
control.
6. Improve reactor
heat distribu-
tion or agitation
to prevent
localized
overheating.
7. Sell tars as
product.
8. Change
reaction
chemistry.
Pros
May reduce
amount of tars
which form in
reactor
Little or no capital
cost
Lower tempera-
tures would
reduce tar
formation
Little or no capital
cost
Would eliminate
waste stream from
landfill
Would reduce
amount of tars
which form in
reactor
Little or no capital
cost
Better process
control could
reduce residence
time in reactor,
thus reducing tar
formation
May reduce
amount of tars that
form in reactor
The tars could be
formed into
shapes and sold
Totally new
chemistry could
reduce tar
formation
Cons
May require plant
to run at lower
production rates
Longer residence
time in reactor
could actually
increase tar
formation
Increased raw
material cost (cost
of additional
catalyst)
May require plant
to run at bwer
production rates
Much more
expensive than
landfilling
No waste reduc-
tion
Increased raw
material cost (cost
of additional
inhibitor)
High capital cost
High capital cost
Underlying
assumption (that
localized high
temperatures
cause tar forma-
tion) is uncertain
Low molecular
weight of the tars
makes it unlikely
to have many
uses
Alternative
chemistry could
compromise
process safety
High capital cost
Long development
time
Uncertain chance
of success
Comments
Modifications to the distillation
column packing may permit
operation at lower pressures
without reducing production
rates.
May require laboratory trials to
determine optimum amount of
catalyst.
This option would not reduce
waste, but it would conserve
landfill space.
Experience has shown that
increasing inhibitor does reduce
tar formation. This option may
require laboratory trials to
determine optimum amount of
inhibitor.
Cost savings in areas other
than waste minimization would
be needed to help justify this
option.
The project team speculated
that reactor agitation may
splash the reaction mass onto
exposed heating coils. Exposed
coils are considerably hotter
than coils that are continually
covered with reaction mass.
It may be possible to add a
catalyst to increase the molecu-
lar weight of the tars.
Cost savings from other areas
would be required to make this
option economically feasible.
Score*
811
787
773
713
711
677
659
653
'maximum score ^ 1,1 70
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CASE STUDY 8: Monomer Production
CATEGORY 2
Table 3-16. Ranked Summary of Top Monomers Process Waste Minimization Options (cont'd)
Option
9. Use different
inhibitor to
retard tar
formation.
10. Use a different
process.
11. "Milk" the
charge (longer
distillation time)
to recover more
product.
12. Reduce water
entering
process by
using multi-
stage extrac-
tion.
13. Add inhibitor
continuously to
distillation
column.
14. Add additional
equipment for
recovering
more product
from tars.
15. Use filtration to
separate
product from
decomposition
products.
'maximum score =
Pros
Tests show that
other inhibitors
can be used
Fair chance of
success
The yield increase
can reduce waste
by about 50%
Good chance of
success (option
has been demon-
strated)
Reduced raw
materials loss
(cost savings)
Shorter batch
cycle time
Increased
production
Reduced tar
formation through
shorter residence
time in reactor
Could reduce tar
formation in
column
ซ Possible waste
reduction of 50%
ฐ Eliminates
distillation
Increased yield
Reduces waste
by 50%
Shorter cycle time
Increase produc-
tion
Low capital cost
1,170
Cons
Plant trials with
alternative
inhibitors showed
no reduction in tar
formation
Alternative
process produces
a large waste-
water stream
Concentrated tars
are difficult to
remove from the
reactor
Option tends to
force tars up the
column with
product, thus
affecting quality
Option could
cause tar forma-
tion in the column
High capital cost
Requires installa-
tion of a multi-
stage extractor
Tar reduction is
likely to be small if
tars are formed
primarily in the
reactor
High capital cost
Long implementa-
tion time
Unacceptable
quality deteriora-
tion (some tars
would remain in
product)
Comments
This option could be reconsid-
ered after installation of the
new DCS.
An alternative process for
producing a similar product
does exist on site.
Past experience shows that
concentrated tars are extremely
difficult to remove from reactor.
Perhaps high-pressure water
cleaning with subsequent
filtration of tars could be used.
The process currently uses a
single-stage extraction to
recover excess raw materials.
This extraction uses water,
which must be removed from
the process. Using additional
extraction stages reduces both
the amount of water in the
process and the time that the
reactor is held at elevated
temperatures.
It remains to be determined
whether tars are formed
primarily in the reactor or the
distillation column.
One possible method is the use
of a wiped-f ilm evaporator.
Implementation of this option
would require customers to
agree to lower product quality
specifications.
Score*
649
619
612
577
575
464
463
SECTION 3: Case Studies
Page 69
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CATEGORY 2
CASE STUDY 8: Monomer Production
in a laboratory the optimum amount of inhibi-
tor and to conduct a trial on the actual process
equipment The analysis also assumes an
additional 50% reduction in waste. Combined
with the waste reduction achieved by the
DCS, total waste reduction would be about
75%.
Option 2, "Add additional catalyst..", could
also reduce tars if the catalyst caused a faster
reaction and at lower temperatures. Again, this
option would require no capital costs, but
would require several man-months of lab
evaluation and trials.
Option 11, "Milk the charge...", i.e., prolong
the distillation step to recover more product)
has been shown to reduce waste by about
50%. However, the concentrated tars at the
bottom of the reactor become too thick to
remove easily. (These tars are actually molten
polymer.) This option could be implemented if
a way were found for easily removing the
waste from the reactor. A high-pressure water
system has been successfully adopted for
cleaning a process vessel at another process
area on site. (See Case Study 6: "Polymer
Vessel Washout".) If this option were imple-
Table 3-17. Economic Summary of Top Monomers Process Waste Minimization Options
Option
Improve process
control...
Waste
Reduction
50%
Capital Cost
$1,200,000
EPA Method
NPV(12%) IRR
$2,600,000
51%
DuPont Method
NPV(12%) IRR
$2,600,000
51%
Implemen-
tation Time
1 .5 years
The evaluation of the following options assumes successful implementation of
"Improve process control..."
Increase amount
of inhibitor...
Add additional
catalyst...
"Milk" the
charge...
Reduce reactor
pressure
75%*
75%*
75%*
75%*
$0
$0
$150,000
$100,000
$205,000
$166,000
$120,000
$109,000
51%
45%
28%
25%
$165,000
$126,000
$81 ,000
$69,000
45%
39%
23%
20%
6 months
6 months
1 year
1 year
Comments: Waste reductions given for options with an asterisk (*) assume an additional 50% waste
reduction after implementation of "Improve process control..." This results in a total
reduction of 75%. The economics for asterisked options include cost savings resulting
only from the reduction of waste from 50% to 75%.
The economics for these options are given on a stand-alone basis, and do not consider
poss ble synergies from implementing more than one option.
For an explanation of terms used in this analysis, see the discussion under "Feasibility
Evaluation" in Section 2: Project Methodology.
Page 70
SECTION 3: Case Studies
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CASE STUDY 8: Monomer Production
CATEGORY 2
mented for the monomers process, it would
combine with the new DCS to achieve a waste
reduction of about 75%.
Option 1, "Reduce and column pressure..."
has been tried before, and is known to reduce
tar formation. But it also reduces production
by requiring longer reaction and distillation
times. However, it may be possible to redesign
the distillation column to speed up the distilla-
tion step. The column contains "packing",
specially shaped material that increases the
interior surface area of the column thereby
enhancing the distillation. A different kind of
packing called "structured" packing might
permit lower column pressures without de-
creasing the production rate.
It's probably a good idea to defer implementa-
tion of any additional waste minimization
options until after the DCS startup. Past
experience with DCS conversions shows that
the wealth of data that a DCS can provide
leads to better understanding of the causes of
byproduct formation. It is possible that new
options for reducing waste will become
apparent after the process has begun operating
under DCS control.
Barriers to Implementation
The high capital cost of a DCS conversion is
an impediment to implementation, but people
at the monomers process are confident that
they will secure the funding. Most of the
planning, installation, and system configura-
tion will be done by process area personnel,
with the full participation of operators and
mechanics. They expect to have the DCS
installed and running by the end of 1993.
Opportunities for Others
This case study, like others in this series,
demonstrates the interrelationship between
process improvement goals and waste minimi-
zation. Control system improvements can
reduce waste in many processes. But these
improvements are often expensive, and can be
justified economically only after considering
the returns expected from improved quality,
increased productivity, better product yields,
etc.
This assessment also demonstrates how impor-
tant the? assessment team composition is to the
success of a waste minimization effort. The
monomers assessment team included represen-
tatives from among those who actually run the
process: operators and mechanics. One of the
most promising waste minimization options,
that of increasing distillation time to recover
more product, was suggested by an operator.
The hands-on experience that such people
have is an important complement to the theo-
retical understanding possessed by process
engineers and chemists.
SECTION 3: Case Studies
Page 71
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CATEGORY 2
Case Study 9: CAP Isomers Process
Switching from batch to continuous feeding of a chemical stabilizer
reduces waste in a distillation process
Abstract
This case study examines a waste reduction
project for a distillation process that purifies
chloroaromatic isomers from a product crude.
The project will reduce the amount of a chemi-
cal stabilizer that is used to prevent dechlori-
nation of the crude. This stabilizer ultimately
forms a substantial part of the process waste
stream. The project will replace the current
method of batch feeding the stabilizer with
continuous feeding. Although this change will
significantly reduce wastes, a waste assess-
ment was nevertheless performed to identify
additional waste reduction options. These
options could have general application to
other distillation processes.
Recovered isomers^
(to start of process)
ISOMEB
COLUMN
High-boiling isomer (product)
DETARRING,
TheCAPcnideis Low-boiling isomer
fed continu-
ously to the iso-
merdistillationcolumn
where it is subjected to
heat at reduced pres-
sure. The low-boiling
isomer vaporizes, ex-
its the top of the col-
umn, and collects as a CAP crude
liquid in a product
catch tank.
Tolimitdechlorination
of the crude, a 50/50
mixture of solid stabi-
lizer and carriersolvent
is added to the isomer
column in batches
through theisomer col-
umn pump. The pump
impellers ensure good
mixingofstabilizerand PUMP
CAP crude. Atpresent,
the stabilizer level in the isomer column is monitored by
drawing samples from the column and sending them to a lab
for analysis. The turnaround time from the drawing of
samples and the communication of the lab results is several
hours.
The crude passes from the isomer column reboiler to the
detaning column, where it is again subjected to heat at
reduced pressure. The high-boiling isomer vaporizes and
exits theprocess through the top of the column. The heavier
VACUUM
STILL-POT
crude
1
CAP
^i
^\_^/
REBOILER
REBOILER
CATCH
TANK
Low-boiling
isomer
(product)
Low-boiling isomer (thinner)
WASTE
COLLECTION
TANK
Waste (tar) stream
material remaining at the column bottom then passes on to
a vacuum still-pot. This material is again heated, and much
of the remaining isomers boil off to be recycled back to the
start of the process. The material which remains at the
bottom of the still-pot consists of tars, stabilizer, and
unrecovered isomers. This tar stream is pumped to a waste
collection tank where it is thinned with a stream of the low-
boiling isomer. The thinned tar stream is thensent to the on-
site incineration plant for disposal.
Figure 3-16. CAP Isomers Process
Page 72
SECTION 3: Case Studies
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CASE STUDY 9: CAP Isomers Process
CATEGORY 2
Background
A process area at the DuPont Chambers
Works site purifies chlorinated aromatic
products (CAP) from a feedstream of crude
produced elsewhere on site. The crude con-
tains two CAP isomers, both of which have
commercial value when separated. Isomers are
structural variations of the same chemical
formula. The molecules of a compound's
isomers contain the same atoms, but differ-
ences in the way these atoms are arranged
impart different chemical properties to each
isomer. The two CAP isomers have different
boiling points, and therefore are known as the
"low-boiling isomer" and the "high-boiling
isomer".
Figure 3-16 illustrates the CAP isomer purifi-
cation process. A series of distillations re-
moves first the low-boiling isomer, then the
high-boiling isomer. A final distillation recov-
ers isomers trapped within the spent crude and
recycles it back to the start of the process. The
remaining tar stream is routed to a waste
collection tank, where it is mixed with some
of the low-boiling isomer to thin it in prepara-
tion for incineration on-site.
Exposing CAP to the high temperatures of
distillation can cause a dechlorination reac-
tion. This reaction is exothermic (i.e., it
generates its own heat), and could become a
safety hazard if it proceeds undetected and
uncontrolled. Moreover, dechlorination
reaction byproducts are corrosive and can
cause equipment damage. To prevent dechlo-
rination, a solid stabilizing agent is slurried
with an organic solvent and added to the crude
in batches. Stabilizer levels are monitored by
drawing samples of the in-process crude and
analyzing them in a laboratory. The turn-
around time between the drawing of samples
and the receipt of results is several hours. This
lag times forces process operators to increase
their margin of safety by adding large amounts
of stabilizer.
The CAP isomers process has undertaken a
waste reduction project that will reduce waste
by 25%. The project will replace the present
method of batch feeding the stabilizer with
continuous feeding. This will reduce waste in
two ways. First, it will permit a reduction in
the amount of stabilizer used. Second, it will
Use a waste stream from another ^
process to thin the CAP waste ^
Add acid to the waste stream
to make it water soluble
Use a different stabilizeryffi'
Add a high-boiling compound /
to the waste to displace CAP/
Improve stabilizer
agitation within the reboiler
Recycle waste stream
back to the isomer column
Use online measurement
of stabilizer levels
Replace the vacuum still-pot *$,
with a wiped-fllm evaporator /.ง
Add stabilizer in solid form
Use CAP to slurry the stabilizer
Figure 3-17. CAP Isomers Process Options
.SECTION 3: Case Studies
Page 73
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CATEGORY 2
CASE STUDY 9: CAP Isomers Process
Table 3-18. Ranked Summary of CAP Isomers Process Waste Minimization Options
Option
Pros
Cons
Comments
1. Use CAP to slurry the
stabilizer.
2. Use online measure-
ment of stabilizer
levels.
3. Add acid to the waste
stream to make it
water soluble.
4. Recycle waste
stream back to the
isomer column.
5. Add a high-boiling
compound to the
waste to displace
CAP.
Source reduction
through elimination of
the organic carrier used
to slurry the stabilizer
Low-to-moderate capital
cost
Good source reduction
potential through
reduction in the amount
of stabilizer required for
safe column operation
Elimination of the
incinerated waste
stream
Source reduction by
withholding the low-
boiling isomer from the
waste stream
Low capital cost
Reduction in the amount
of stabilizer required for
safe column operation
Moderate capital cost
Uncertain chance of
success
Creation of a waste-
water stream
Moderate capital cost
Moderate capital cost
Yield improvement
through increased
product recovery
Low capital cost
Small overall waste
reduction
Increased operating cost
This option would elimi-
nate the organic solvent
that is now used to slurry
the stabilizer.
This option would replace
manual sampling and lab
analysis with real-time
measurement of stabilizer
levels.
This option would change
the waste disposal
medium from incineration
to wastewater treatment.
This option would reuse
the stabilizer that remains
in the waste stream. It
would have to be imple-
mented in conjunction with
Option 2 ("Use online
measurement of stabilizer
levels") to ensure that safe
levels of stabilizer were
being maintained.
This option would use
waste from another
Chambers Works process
to displace CAP from the
waste in the detarring
column. The difficulty lies
in finding a process that
emits a suitable waste
stream.
Page 74
SECTION 3: Case Studies
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CASE STUDY 9: CAP Isomers Process
CATEGORY 2
Table 3-18. Ranked Summary of CAP Isomers Process Waste Minimization Options (cont'd)
Option
Pros
Cons
Comments
6. Use a different
stabilizer.
7. Use a waste stream
from another process
to thin the CAP
waste.
8. Add stabilizer in solid
form.
9. Replace the vacuum
still-pot with a wiped-
film evaporator.
Presumptive source
reduction through a
reduction in the amount
of stabilizer required for
safe column operation
- Low capital cost
ฐ Increased product yield
of the low-boiling CAP
isomer
ซ Waste reduction by
withholding the low-
boiling isomer from the
waste stream
ซ Low capital cost
Source reduction
through elimination of
the organic carrier used
to slurry the stabilizer
Source reduction
through increased
product recovery
10. Improve stabilizer
agitation within the
reboiler.
Poor chance of success
Low chance of success
High capital cost
Ergonomic safety
concerns associated
with handling the solid
stabilizer
Low chance of success
Very high capital cost
Good source reduction
potential through
reduction in the amount
of stabilizer required
Moderate capital cost
Low chance of success
Previous informal efforts to
identify an alternative
stabilizer have yielded
nothing.
This option would use
liquid waste from another
Chambers Works process
to thin the CAP waste in
the waste tank, replacing
the present method of
using the low-boiling
isomer as the thinner. The
difficulty lies in finding a
process that emits a
suitable waste stream.
No technique for adding a
solid to equipment under
vacuum has been identi-
fied.
The wiped-film evaporator
would probably recover
more product than the
present still-pot. For
information about the
operation of a wiped-film
evaporator, see Case
Study 10, "Wiped-Film
Evaporator".
Good mixing of stabilizer
means that more of it
reacts with the process
stream. But the present
method of adding the
stabilizer to the reboiler
pump already provides
good mixing.
SECTION 3: Case Studies
Page 75
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CATEGORY 2
CASE STUDY 9: CAP Isomers Process
permit a reduction in the amount of the low-
boiling isomer required to thin the waste at the
end of the process.
A waste assessment team was recently formed
to identify other possible waste reduction
options. Their efforts are motivated by a
desire to both cut cost and reduce waste. At
present, the CAP isomer process produces the
largest stream of incinerated waste on the
Chambers Works site.
Description of the Waste Stream
A typical analysis of the waste stream leaving
the CAP isomer process is provided below.
Tars 33%
Low-boiling isomer 33%
Stabilizer and solvent 24%
High-boiling isomer 10%
The amount of waste from this process has
been constant for several years, and equals
0.12 pounds for every pound of CAP product
recovered. Wastes from CAP isomers purifica-
tion are incinerated.
Costs associated with this waste stream in-
clude the yield loss represented by the
unrecovered CAP (including the low-boiling
isomer used to thin the waste), replacement
cost of the stabilizer, waste handling and
storage costs, and the costs of incinerating the
waste stream.
Previous Waste Minimization Efforts
Over the past decade, several options for
reducing waste have been considered. These
include:
Use a different stabilizer. It was hoped that a
different stabilizer, used in smaller amounts,
would maintain the current level of process
safety. But this idea was rejected after
preliminary studies failed to identify such
a stabilizer.
Use less of the present stabilizer while
continuing to add it to the process in
batches. This idea too was rejected after a
preliminary study concluded that reductions
in the amount of stabilizer would corre-
spondingly reduce the margin of process
safety.
Use less stabilizer by replacing batch
feeding with continuous feeding. Studies
showed this idea to be workable and effec-
tive, and it is currently being implemented.
Waste Minimization Options
The CAP isomers assessment team met in a
brainstorming session and generated 10
options for achieving additional waste reduc-
tions. They recorded then- ideas by construct-
ing a cause-and-effect "fishbone" chart, shown
in Figure 3-17. In subsequent meetings, the
team discussed the options and subjectively
Table 3-19. Economic Summary of Top CAP Isomers Process Waste Minimization Options
Option
Use CAP to slurry
the stabilizer
Use online
measurement...
Waste
Reduction
10%
15%
Capital Cost
$100,000
$40,000
EPA Method
NPV (12%) IRR
$1,640,000
$1,640,000
151%
257%
DuPont Method
NPV (12%) IRR
$1,300,000
$1,160,000
133%
209%
Implemen-
tation Time
6 months
1 year
Comments: For an explanation of terms used in this analysis, see the discussion under "Feasibility
Evaluation" in Section 2: Project Methodology.
Page 76
SECTION 3: Case Studies
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CASE STUDY 9: CAP Isomers Process
CATEGORY 2
ranked them according to their practicality and
waste minimization potential. Table 3-18
summarizes these discussions, and presents
the options in approximate rank order.
Technical and Economic Feasibility
After considering the pros and cons of each
option listed in Table 3-18, the assessment
team chose two options for technical and
economic feasibility analysis:
ซ Option 1: Use CAP to slurry the stabilizer
Option 2: Use online measurement of
stabilizer levels
Option 1 would eliminate the solvent compo-
nent of the waste stream. Option 2 would
reduce waste by permitting more precise
control of stabilizer levels, thus eliminating
the tendency to use excess stabilizer to ensure
a good margin of safety.
The results of the economic analysis are
presented in Table 3-19. Both options have
very high internal rates of return (IRR).
Barriers to Implementation
The addition of stabilizer is a safety practice
that prevents an exothermic dechlorination
with its attendent risks to people and equip-
ment. Any attempt to alter the amount of
stabilizer or the manner in which it is intro-
duced: to the process must take safety into
account.
Opportunities for Others
This series of assessments examines six
processes in which the waste streams exit
from (distillation columns. The CAP isomers
process is typical of many distillation pro-
cesses in use today throughout industry.
Therefore, many of the options generated for
the CAP isomers process may be more gener-
ally applicable.
Several case studies in this series examine
processes where a stabilizing agent is added
for safety reasons. In all of those studies, the
stabilizing agent either comprises the chief
component of the waste stream, or otherwise
frustrates attempts at waste reduction. The
amount of stabilizer added to such processes is
dictated by worst-case scenarios and the need
for comfortable margins of safety. Therefore,
waste reductions must usually be accompanied
by such additional changes as better process
controls, different operating conditions, or
equipment changes.
SECTION 3: Case Studies
Page 77
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CATEGORY 2
Case Study 10: Wiped-Film Evaporator
Existing technology for reducing waste through increased product recovery
Abstract
This case study examines an attempt to reduce
waste through enhanced product recovery in a
process which produces chlorinated aromatics.
The process area will install a wiped-film
evaporator to recover residual product from a
distillation tar stream. This effort is part of an
ongoing waste reduction program which has
also achieved source reductions in the process
byproducts that create the tar stream. This
case study demonstrates that improved prod-
uct recovery is a way to continue reducing
waste even after all practical source reductions
have been made.
Product
DISTILLATION
COLUMN
Reactants-
Catalyst
Product
crude
REACTOR
Reactants are mixed and heated in a reactor
in the presence of a catalyst. The resulting
reaction produces chlorinated aromatics
and heavy reaction byproducts. The reaction
mass then proceeds to the distillation step.
In the reduced pressure of a distillation column,
the lighter chlorinated aromatics begin to boil off
as the remainder of the hot reaction mass falls to
the bottom of the column. The reaction mass is
then recycled through a reboiler back into the
column. Part of this recycle stream will pass
through the wiped-film evaporator. The evapora-
Waste
stream
(recycle)
REBOILER
V
T
WIPED FILM
EVAPORATOR
Waste stream
NEUTRALIZER
TANK
Neutralized waste stream
(to wastewater treatment)
tor will boil off most of the unrecovered product
and reintroduce it back into the column. As is the
current practice, the remaining waste will pass to
a neutralization tank to be mixed with caustic
and water before passing on to the wastewater
treatment plant
Figure 3-18. Chlorinated Aromatics Process with Wiped-Film Evaporator
Page 78
SECTION 3: Case Studies
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CASE STUDY 10: Wiped-Film Evaporator
CATEGORY 2
Background
The DuPont Chambers Works site includes a
process, illustrated in Figure 3-18, that manu-
factures chlorinated aromatics. The continu-
ous process consists of a reaction step which
produces a product-crude, followed by a
distillation step which purifies the product.
The reaction step produces heavy tar as a
byproduct. The tar entraps significant amounts
of otherwise saleable product, and carries it
away from the distillation step as waste.
The chlorinated aromatics process has long
pursued waste minimization as a key strategy
for increasing production. Over the years, the
process area reduced reaction byproducts to a
point where each additional pound of reduc-
tion has become very costly. So the process
area is now implementing a product recovery
project that will further reduce waste.
The project involves the design, testing, and
installation of a wiped-film evaporator. The
evaporator will receive the tar stream that
emerges from the distillation step and recover
some of the chlorinated aromatics that are
trapped within the tar. The process area first
considered this project in the mid-1970s, and
rejected it as being too costly. But rising
waste disposal costs and the need for produc-
tion increases forced a subsequent reconsid-
eration. To date, the wiped-film evaporator
project has completed its design and testing
phases. Installation is expected in 1994.
Figure 3-19 illustrates the principles of
operation of a wiped-film evaporator. In
general terms, a wiped-film evaporator ex-
poses a tar stream to a heated surface upon
which the lighter compounds are boiled off
and recovered. In the chlorinated aromatics
process, the material recovered by the evapo-
rator will be recycled back to the distillation
step for further purification.
Description of the Waste Stream
A typical analysis of the present waste stream
from the chlorinated aromatics process would
reveal:
Chlorinated aromatics 60%
Heavy byproduct 40%
These acidic wastes are neutralized with an
alkaline compound, dissolved in water, and
sent to the on-site wastewater treatment plant
for disposal.
Costs associated with this waste stream in-
clude the yield loss represented by the
unrecovered product, preparation costs associ-
ated with wastewater treatment, and the
wastewater treatment itself.
At present, the chlorinated aromatics process
produces 0.015 Ibs of waste for every pound
of product. When operation of the wiped-film
evaporator begins, this total will fall to 0.007
Ibs of v/aste.
Previous Waste Minimization Efforts
The need to continuously increase production
has ingrained waste minimization into the
working culture at the chlorinated aromatics
process. Over the years, byproduct formation
in the reaction step has been substantially
reduced. The marginal cost of reducing
byproducts even more is now high. Therefore,
the process area has focused on recovering
more product per pound of crude. The wiped-
film evaporator will help to accomplish this.
Waste Minimization Options
Few records exist of past option generation
activity.. Suggestions for waste minimization
projects were made informally, and little effort
has been made to maintain recorded proceed-
ings. The area is continuously evaluating its
performance in decreasing wastes.
SECTION 3: Case Studies
Page 79
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CATEGORY 2
CASE STUDY 10: Wiped-Film Evaporator
DRIVE
A
FEED
HEATING
MEDIUM
VAPOR
HEATING
MEDIUM
The waste stream
enters the wiped-
film evaporator
through the feed inlet. As
gravity draws the material
down, the rotor blades
spread the material over
the heated surface and
create effective film
turbulence. Lighter
compounds evaporate. The
vapors rise up the evapora-
tor and pass through the
vapor outlet The remain-
ing wastes are sent to a
neutralization tank to be
prepared for wastewater
treatment
Figure 3-19. Wiped-Film Evaporator
Technical and Economic Feasibility
Not all waste streams are suitable for wiped-
film evaporation. By removing the recoverable
product, the evaporator effectively concen-
trates the wastes. Several streams in this series
of reports consist of thermally unstable com-
ponents which cannot safely be concentrated
above a certain threshold.
Although the waste produced by the chlori-
nated aromatics process is thermally stable, it
is highly corrosive. Off-the-shelf wiped-film
evaporators are generally constructed of
stainless steel, which will corrode if exposed
to the chlorinated aromatics waste. Therefore,
a specially designed evaporator constructed of
a corrosion-resistant alloy is required.
Initial testing of the wiped-film evaporator at a
DuPont laboratory yielded mixed results,
probably because of problems with material
flows and operating parameters. But a subse-
quent test at the vendor's site in 1991 proved
successful. The test demonstrated a 50%
reduction in the waste stream, concentrating it
from 40% to 77% byproducts.
Table 3-20 summarizes the economic analysis
of the wiped-film evaporator.
Table 3-20. Economic Summary ofWiped-Film Evaporator Option
Option
Wiped-film
evaporator
Waste
Reduction
52%
Capital Cost
$1,450,000
EPA Method
NPV(12%) IRR
$2,869,000
45%
DuPont Method
NPV(12%) IRR
$135,500
14%
Implemen-
tation Time
1 year
Comments: For an explanation of terms used in this analysis, see the discussion under "Feasibility
Evaluation" in Section 2: Project Methodology.
Page80
SECTION 3: Case Studies
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CASE STUDY 10: Wiped-Film Evaporator
CATEGORY 2
Barriers to Implementation
Over the years, the chief barrier to the imple-
mentation of the wiped-film evaporator option
has been its large capital cost. Three factors
offset this barrier:
the rising cost of waste disposal
the need for production increases
the cost of unrecovered product in the waste
Another barrier to implementation has been
the corrosive nature of the waste, which has
important implications for the evaporator's
materials of construction. This barrier was
overcome by working closely with the vendor
to develop the evaporator, and by extensive
testing.
Opportunities for Others
The chlorinated aromatics process delayed
implementation of the wiped-film evaporator
option until after substantial source reductions
in generated waste were made. The process
area found that the source reductions were for
a time less costly than recycling or product-
recovery schemes. By waiting to install the
evaporator until after the source reductions,
the process area realized the maximum benefit
from both options. This case study demon-
strates that improved product recovery is a
way to continue reducing waste even after all
practical source reductions have been made.
SECTION 3: Case Studies
Page 81
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CATEGORY 1
Case Study 11: Specialty Surfactant
A partnership between customer and manufacturer leads to the elimination
ofCFCfrom a surfactant product
Abstract
This case study describes a successful effort to
eliminate the chlorofluorocarbon (CFC)
content of a specialty surfactant product. The
CFC, which served as a solvent for dissolving
the surfactant, has been replaced by water.
This effort was undertaken in response to
customer demand for a non-CFC product.
Customers played a crucial role in the success
of this effort by providing input in the devel-
opment of the new product formulation. This
study illustrates the increasing value custom-
ers place on environmental friendliness. Many
future waste reduction efforts are likely to
involve collaborations between producers and
customers.
Background
The DuPont Chambers Works site produces a
surfactant which is sold to manufacturers of
cleaning products. In its pure state, the surfac-
tant is a waxy solid with the consistency of bar
soap. But customers require a liquid for their
manufacturing processes. Liquification is
achieved by dissolving the surfactant in a
mixture of solvents. This enables the surfac-
tant to be sold as a nearly transparent liquid
with the viscosity of a light oil.
An important quality consideration is that the
surfactant be well-dissolved within the sol-
vent. The appearance of sediment in the
product is evidence of undissolved surfactant.
Quality improvement efforts over time have
been directed at reducing the amount of high-
molecular weight compounds within the
surfactant, as these compounds are largely
responsible for sediment formation.
Before waste minimization, a combination of
three solvents had been used: water, isopropyl
alcohol (IPA), and Freonฎ 113. The Freon
113 had been particularly effective in dissolv-
ing high-molecular weight compounds, and
was thus considered crucial to maintaining
product quality and customer acceptance.
Unfortunately, Freon 113 is a CFC, and its use
is believed to contribute to the depletion of
ozone in the upper atmosphere.
In 1989, the Chambers Works site began a
program to eliminate Freon 113 from the
surfactant product. The impetus for this
program was a growing desire among DuPont
and its customers to eliminate CFCs from their
processes. Eliminating Freon 113 required a
reformulation of the product. Customers
cooperated in the effort by agreeing to evalu-
ate the product reformulation.
In 1991, a plant trial successfully produced a
surfactant in which the CFC had been replaced
with water. The new product has since re-
placed the old formulation, thus achieving a
100% source reduction in CFC released to the
environment.
Description of the Waste Stream
Wastes from production of the old surfactant
product consisted of airborne emissions of
CFC and IPA, both volatile organic com-
pounds (VOCs). These emissions occurred
primarily at the sites where the surfactant
product was consumed, with a very small
amount occurring as fugitive emissions from
the Chambers Works site.
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CASE STUDY 11: Specialty Surfactant
CATEGORY 1
Table 3-21. Ranked Summary of Specialty Surfactant Waste Minimization Options
Option
Pros
Cons
1. Replace CFG with
water.
2. Replace CFC with a
non-ozone depleting
alternative.
3. Eliminate both CFC
and IPA.
4. Manufacture and sell
material as a solid.
Elimination of CFC from product
Reduction of VOCs from product
Elimination of CFC from product
Elimination of CFC from product
Elimination of VOCs from product
Elimination of CFC from product
Elimination of VOCs from product
5. Use basic or acidic
water to dissolve
product.
6. Use other solvents.
7. Reduce IPA and
replace with water.
8. Replace CFC with
IPA.
Elimination of CFC from product
Elimination of VOCs from product
Elimination of CFC from product
Reduction of VOCs from product
Small materials cost savings
Elimination of CFC from product
Risk of customer resistance to slightly
increased sediment in product
Little or no reduction in VOCs from
product
Non-ozone depleting alternative is
more costly than CFC
High development cost (new manu-
facturing and handling processes
required)
Very poor chance of success
High development cost (new manu-
facturing and handling processes
required)
Very poor chance of success
Merely shifts the burden of waste
disposal to customers (customers will
have to add solvents to the product)
Poor chance of success
Customer resistance
Poor chance of finding combination of
solvents having less VOC emissions,
flammability, or toxicity than IPA and
water
Customer resistance to increased
sediment in product
No reduction of VOCs from product
A typical analysis of the product leaving the
Chambers Works process before the reformu-
lation would have revealed:
Water/surfactant 67%
IPA 22%
CFC 11%
Virtually all of the organic solvents added to
the surfactant were inevitably released into the
atmosphere.
Costs associated with this waste stream in-
clude the cost of the solvents added to the
product, and the small amount of solvent lost
as fugitive emissions at Chambers Works.
More importantly, failure to remove CFC
from l:he product would have eventually
forced it off of the market.
Previous Waste Minimization Efforts
No previous attempts to eliminate CFC from
the surfactant products had been made. In
1986, a new product development effort
successfully reduced the amount of high-
molecular weight compounds in this surfac-
tant, and this in turn reduced the amount of
sediment in the product. Given that the pur-
pose of adding CFC was to dissolve such
compounds, this product development effort
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CATEGORY 1
CASE STUDY 11: Specialty Surfactant
set the stage for CFC elimination. In 1989, the
business organization learned that a product
with a small amount of sediment could gain
customer acceptance if it were CFC-free. This
customer acceptance made the CFC elimina-
tion possible.
Waste Minimization Options
In 1989, a team was formed to consider ways
in which CFC might be removed from the
surfactant product They generated eight
possible options, and these are summarized in
Table 3-21. With the exception of Option 7,
"Manufacture and sell surfactant as a solid",
the options involve reformulations of the
solvent system used in the product. Responsi-
bility for evaluating these options and imple-
menting the elimination of CFC fell to the
process chemist, who performed these tasks in
consultation with surfactant customers.
Technical and Economic Feasibility
Technical Evaluation
A series of laboratory experiments were
performed to evaluate alternative solvent
systems. Replacing CFC with water was
determined to be the best option. It was the
only option which eliminated CFC and re-
duced VOC emissions without forcing major
changes to the process or to product quality.
Removing CFC did slightly increase the
amount of sediment in the product, but the
amount was still low enough to gain customer
acceptance. The new solvent system contains
33% less VOCs than the old one, and elimi-
nates all CFC.
Economic Evaluation
Table 3-22 summarizes the economic evalua-
tion of the chosen option. Although CFC
elimination required modifications to the
procedures used to manufacture the surfactant,
equipment modifications or other capital
expenditures were not required. Cost savings
resulted from replacing CFC with water. The
evaluation did not assume an increase in sales
resulting from CFC elimination, nor did it
assume loss of sales resulting from the failure
to eliminate CFC.
Barriers to Implementation
The chief impediment to this waste minimiza-
tion effort was a possible lack of customer
acceptance for the new product formulation.
In the absence of CFC, a small amount of
sediment forms within the surfactant product.
Keeping the amount of this sediment low was
the key to achieving customer acceptance.
Evaluation of Performance
The chosen waste reduction option eliminated
100% of the CFC emissions and 33% of VOC
emissions. This was accomplished without
Table 322. Economic Summary of Top Specialty Surfactant Waste Minimization Option
Option
Replace CFC with
water
Waste
Reduction
100% CFC
33% VOCs
Capital Cost
$0
EPA Method
NPV(12%) IRR
$2,000
13%
DuPont Method
NPV(12%) IRR
$2,000
13%
Implemen-
tation Time
1 year
Comments: For an explanation of terms used in this analysis, see the discussion under "Feasibility
Evaluation" in Section 2: Project Methodology.
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CASE STUDY 11: Specialty Surfactant
CATEGORY 1
affecting the quality of the finished product.
The new product has met with good customer
acceptance.
Opportunities for Others
This case study demonstrates the opportunity
that exists to eliminate CFCs from those
products that use them as solvents. More
importantly, this case study shows that a great
potential for waste minimization exists in
partnerships between producers and custom-
ers. Customers have traditionally represented
a major impediment to waste reduction.
Failure to place value on environmentally
friendly products provided producers with
little incentive to reduce wastes. But this
situation is likely to change as the growing
public demand for waste reductions affects
customers and producers alike. In the new
business climate, the development of environ-
mentally friendly products will increasingly
become a collaborative effort between produc-
ers and customers.
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CATEGORY 1
Case Study 12: CAC Process
Involving people from all disciplines in waste reduction effort is a
key factor in eliminating a -waste stream
Abstract
This study describes a successful effort to
eliminate a waste stream of solvent from a
multiproduct chemical processing area. The
solvent had been used to flush the process
equipment at the conclusion of each product
campaign. Elimination of the solvent wash
was accomplished by installing drainage
valves at low elevations on the process equip-
ment, and building a wheeled collection vessel
to collect the drainage at the conclusion of a
product campaign. In addition to eliminating a
large waste stream, the new drainage system
has shortened product changeover time and
increased product yield through recovery of
the product residue. This waste elimination
solution was conceived and implemented by
line workers, highlighting the importance of
including representatives from all disciplines
on waste assessment teams.
Background
One process area at the DuPont Chambers
Works site makes two types of chlorinated
aromatic compounds (CAC), and from them
produces three products. The pure forms of
both compounds, known as CAC-1 and
CAC-2, account for two of the products; the
third is a mixture of the two compounds. The
process area uses many pieces of equipment to
produce these products, including reactors,
distillation columns, heat exchangers, and
storage tanks. The two compounds cycle
through the equipment in separate product
"campaigns".
At the conclusion of each campaign, a large
amount of residual product remains within the
process equipment. This residue must be
removed before the start of the next campaign
to prevent it from contaminating the new
product. In the past, this was done by flushing
the process equipment with solvent. The
solvent wash has long been the focus of
remediation efforts for a variety of reasons.
It created a large waste stream for
incineration.
It was a major contributor to long equipment
setup times between product campaigns.
It made reprocessing large amounts of
product necessary because the solvent
contaminated the initial product made in a
new campaign.
The residual product washed away by the
solvent represented a significant yield loss.
In 1990, a waste minimization team at the
CAC process area conceived and subsequently
implemented an equipment drainage system to
completely eliminate the solvent wash. Drain-
age valves were installed at strategic locations
of low elevation on the process equipment. A
movable, insulated collection vessel was
designed and built by area personnel. At the
conclusion of a product campaign, workers
drain the residue from each valve in turn. The
collected product residue is held in a storage
tank for reintroduction to the process during
that product's next campaign. Figure 3-20
illustrates the operation of the new drainage
system.
In deciding whether or not to implement the
system, the assessment team had to consider
its effect upon product quality. After the
process equipment is drained, only a fraction
of the original residue remains. The team was
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CASE STUDY 12-. CAC Process
CATEGORY 1
-CAC-1 Flush
PROCESS
EQUIPMENT
CAC-1 Flush
FLUSH
TANK
DRAINAGE
VALVES
MOBILE
COLLECTION
VESSEL
Residual product
CAC-1
DRAINAGE
TANK
To beginning of
process for new
product campaign
At the end of a product campaign, residual
product is drained from the process equip-
ment into a specially built "mobile collection
vessel". This vessel is emptied into the product
drainage tanks, where product residues accumulate
until they are eventually recycled back to the process
at the start of a future campaign.
During changeovers from CAC-2 to CAC-1 produc-
tion, the drainage procedure is supplemented with a
washout of the process equipment. A reserve of
CAC-1 is held in a flush tank until it is released to
flush away any remaining CAC-2. The amount of
CAC-2 within the flush tank is held constant by
periodically drawing down small quantities of the
flush to either recycle back to the process or to make
the mixed CAC product This drawdown amount is
replaced with virgin CAC-1.
CAC-2
DRAINAGE
TANK
The mobile collection vessel was designed and built
by CAC process operators and mechanics. It consists
essentially of a SS-gallon tank securely fastened to a
wheeled carriage. The tank has been insulated to
prevent solidification of the product residue upon
exposure to ambient temperatures. A flexible hose is
used to connect the mobile vessel to the drainage
valves to permit drainage from the most hard-to-
reach drain points. The mobile vessel is designed to
be operated by a single person.
The mobile collection vessel offers several advan-
tages over the use of drums for collecting the
drainings. It's built low to the ground, allowing
collection from low spots that drums could not
service. ITie mobile vessel provides better ergonom-
ics than drums, and avoids the disposal problems that
occur with drum use.
Figure 3-20. CAC Process
SECTION 3: Case Studies
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CATEGORY 1
CASE STUDY 12: CAC Process
uncertain if even this small amount would
have to be flushed to avoid unacceptable
contamination of the next product to be made.
In the case of CAC-2, the team found that
flushing was not required. However, the purity
specifications for CAC1 are much stricter
and require flushing. But instead of using
solvent for this flush, the new system uses an
amount of CAC-1 product held in reserve for
this purpose. The CAC-1 flush is recovered
and stored for repeated reuse in future cam-
paigns. Over time, residual CAC-2 builds up
within the CAC-1 flush. When it exceeds an
acceptable level, the flush is reworked back
into the process or is used to make the mixed
CAC products.
Figure 3-21 depicts the CAC campaign
strategy and product purity requirements.
Description of the Waste Stream
A typical analysis of the waste stream result-
ing from the solvent wash would reveal:
Unrecovered product residue 20%
Solvent
The costs associated with this waste stream
included the replacement cost of the solvent, <
costs associated with the disposal of the
solvent wash, the yield loss represented by the
unrecovered product residue, lost productivity
and capacity due to lengthy setup time be-
tween campaigns, and the cost of reprocessing
solvent-contaminated product.
Before the waste elimination effort, the CAC
process generated 0.015 Ibs of waste for every
pound of product produced. This waste was
once treated at the on-site wastewater treat-
ment plant. In later years, the waste was
incinerated after a pretreatment that reduced
its chlorine content.
Implementation of the new drainage system
has eliminated this waste stream completely.
Previous Waste Minimization Efforts
Over the years, the CAC process area has
devoted considerable effort to address the
problems posed by the solvent wash. At first
these efforts focused on end-of-pipe waste
treatment. Later, a recycling scheme was
implemented to reduce the amount of waste.
Finally, the area began looking at source
reductions to reduce and then eliminate the
waste entirely.
In the original process, the solvent flush and
its load of residual product simply passed
through the process equipment and on to the
on-site wastewater treatment plant. In 1987,
the CAC area began incinerating the solvent
CAC-1
CAMPAIGN
NO tiusn
required
te-
CAC-2
CAMPAIGN
Flush
required
w.
CAC-1
CAMPAIGN
0.1% CAC-2
Permitted
1.0% CAC-1
Permitted
0.1% CAC-2
Permitted
Figure 3-21. CAC Product Campaigns
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CASE STUDY 12: CAC Process
CATEGORY 1
Table 3-23. Ranked Summary of CAC Process Waste Minimization Options
1.
2.
3.
4.
5.
Option
Drain the process
equipment and
eliminate the solvent
wash.
Drain the process
equipment and flush
with CAC product.
Loosen product
specifications to
eliminate the need
for cleaning equip-
ment.
Substitute solvent
flush with water.
Use waste solvent
from another
process to flush
equipment.
Pros
Eliminates use and
disposal of solvent
Recovers saleable
product
Low capital cost
Shortens product
changeover time
Eliminates solvent
storage and associated
working capital charges
Eliminates use and
disposal of solvent
Recovers saleable
product
Low capital cost
Shortens product
changeover time
Eliminates solvent
storage and associated
working capital charges
No risk to product purity
Eliminates use and
disposal of solvent
Recovers saleable
product
Low capital cost
Shortens product
changeover time
Eliminates solvent
storage and associated
working capital charges
Eliminates use and
disposal of solvent
Low capital cost
Eliminates solvent
storage and associated
working capital charges
A reduction in total
solvents used on site
Cons
Product purity concerns
t
Costs associated with
recovering and repro-
cessing the flush
streams
Low chance for success
(customer resistance)
No reduction in product
changeover time
Creation of an aqueous
waste stream
No product yield
increase
Risk to product quality
by contamination with
water
Not a source reduction
No reduction in product
changeover time
No product yield
increase
Comments
This option requires the
installation of drainage
valves on the process
equipment and a means of
collecting the product
residue. The assessment
team judged the risk to
product purity to be a
prudent one in view of the
potential benefits of this
option.
This option requires the
installation of drainage
valves on the process
equipment and a means of
collecting the product
residue. The potential
benefits are less than
those of Option 1 , but so
are the risks to product
quality.
Discussions with customer
reinforced the need to
maintain the present
product specifications.
Although this option is
known to be suitable for at
least some of the process
equipment, it clearly is less
desirable than Options 1
and 2.
Clearly the least
desirable option.
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CATEGORY 1
CASE STUDY 12: CAC Process
Table 3-24. Economic Summary of Top CAC Process Waste Minimization Options
Option
Eliminate the
solvent wash by
implementing
Options 1 & 2
Waste
Reduction
100%
Capital Cost
$10,000
EPA Method
NPV(12%) IRR
$2,212,000
671%
DuPont Method
NPV(12%) IRR
$2,212,000
671%
Implemen-
tation Time
6 months
Comments: For an explanation of terms used in this analysis, see the discussion under "Feasibility
Evaluation" in Section 2: Project Methodology.
wash on-site. The waste first had to be pre-
treated with a nitroaromatic compound to
reduce its chlorine content. Later, the area
arranged to have the waste incinerated at
another DuPont site where pretreatment was
not required.
The first waste reduction was achieved when
the CAC area developed a method for recover-
ing and recycling much of the solvent from
the spent wash. However, this still left a
considerable amount of residual product and
unrecovered solvent to be incinerated. In
1990, the area reduced the number of flushes
between campaigns. This measure alone
reduced waste by 33%, and represented the
area's first successful source reduction.
Waste Minimization Options
In 1990, an interdisciplinary CAC assessment
team met in a brainstorming session and
generated five options for eliminating or
improving the solvent washout. These options
are summarized in Table 3-23. Option 1,
"Drain the process equipment and eliminate
the solvent wash", and Option 2 "Drain the
process equipment and flush with CAC
product", were the only options seriously
considered.
Technical and Economic Feasibility
Technical Evaluation
Both Options 1 and 2 required the installation
of drainage valves on the process equipment,
and a way to collect and accumulate the
product residue. An insulated 55-gal tank was
mounted securely onto a specially built hand-
cart. This mobile collection vessel would be
wheeled to each drainage point to collect
product residue. The contents of the mobile
vessel would then be emptied into a storage
tank for eventual recycling to a future cam-
paign. Because the CAC residual has a very
low volatility, air emissions were not a consid-
eration in the design of the cart.
Option 1 was implemented and tested in 1991.
The new drainage system removed about 75%
of the residual product from the process
equipment. This was good enough for starting
a CAC-2 campaign. Although some initial
product left the process contaminated with
residue, the amount was small enough to
permit easy reprocessing.
Unfortunately, the new system was not ad-
equate for starting a campaign of CAC-1,
which has much more demanding purity
specifications than CAC-2. Contamination of
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CASE STUDY 12: CAC Process
CATEGORY t
the CAC-1 continued well into the campaign,
producing a volume of off-spec material that
was simply too great to reprocess.
Option 2 was then tested for a CAC-1 cam-
paign, using a small reserve of CAC-1 to flush
the process equipment. This test proved
successful. When the campaign began, opera-
tors were able to bring the product within
specifications quickly. The amount of con-
taminated material was small enough to
permit reprocessing.
Economic Evaluation
Implementation of Options 1 and 2 was
completed by plant personnel with only
minimal cost. The low capital cost coupled
with the benefits realized by the waste reduc-
tion made these waste minimization options
very attractive. The economics of implement-
ing both options are summarized together in
Table 3-24.
Barriers to Implementation
Concern about product quality was the only
barrier to the implementation of these options.
Flushing the equipment with CAC-1 solved
this problem. Once it was demonstrated that
product quality could be maintained without
generating an additional waste stream, it was
possible to implement these options.
Evaluation of Performance
The CAC area has successfully demonstrated
the complete elimination of washwaste be-
tween product campaigns, and has achieved
the cost savings identified in Table 3-24. The
people involved with this waste elimination
effort have been recognized with a site
achievement award.
Opportunities for Others
This study illustrates the importance of includ-
ing representatives from all process disciplines
on the assessment team. The new drainage
system was conceived and implemented by a
process operator with help from two mechan-
ics. The mobile collection vessel they de-
signed avoided the ergonomic and disposal
problems associated with drums, and can
reach lower spots on the process equipment.
Their solution for eliminating the waste
stream was achieved with low capital cost and
short implementation time, and demonstrates
that waste reduction need not require technical
solutions and elaborate equipment.
This study also shows that waste reduction is
often an iterative process. The CAC team
implemented a number of options over time
that gradually reduced the waste. Had they
stopped after a few initial successes, the waste
stream would not have been eliminated. In
hindsight, then- solution for eliminating the
waste stream seems simple and obvious. In
reality, the team gained the confidence to
implement a somewhat risky solution through
then- experience with incremental waste
reductions.
Finally, this assessment shows that taking
prudent risks can yield big waste reductions.
Conventional wisdom held that quality would
suffer unless the process equipment received
an overkill of solvent washing. But the assess-
ment team made the imaginative leap to a
breakthrough solution that eliminated the
waste a.nd greatly reduced costs. And they did
it without compromising the quality of their
products.
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CATEGORY 1
Case Study 13: Solvent emissions
Upgrading the filtration system for recovering a metal catalyst has
eliminated solvent emissions to the atmosphere
Abstract
This case study describes a successful effort to
reduce air emissions of a volatile solvent by
99%. The emissions originate from an in-
process filtration system that recovers a
precious metal catalyst for shipment to a
reclamation facility. The emissions were
reduced by replacing a plate-and-frame filter
press with an alternative filtration system. The
waste reduction effort was undertaken to
comply with stricter state regulation of air
emissions. Cost savings generated by the new
filtration system were not great enough to
offset capital investment. This study discusses
some aspects of waste reduction efforts that
are regulatory driven.
Background
A batch process at the DuPont Chambers
Works site produces a specialty aromatic
product. The process includes a reaction step
that produces a product crude, and a purifica-
tion step that separates the product from the
impurities in the crude. The reaction step uses
a precious metal catalyst. A volatile solvent is
used to slurry the catalyst and one of the
reactants before the reaction step.
Before arriving at the purification step, the
product crude passes through a filtration
system to remove the metal catalyst. The
filtered catalyst, which is wet with solvent and
aromatic product, is drummed and shipped to
an off-site reclamation facility. There the
catalyst is recovered through an incineration
process that burns off the combustible
impurities.
In the past, the filtration was performed by a
plate-and-frame filter press. This type of filter
consists of a series of perforated plates that are
covered with filter cloths and sandwiched
between two metal frames. As the crude
passed through the filter press, the catalyst
collected on the filter cloths, forming a wet
cake. After each filtration, the press had to be
opened manually to remove the cake.
The old filtration system released solvent
vapors to the atmosphere in two ways:
Opening the filter press caused some of the
solvent in the cake to evaporate.
When reassembling the press, it was impos-
sible to create a perfect seal due to wicking
of the filter cloths. The filter leaked during
operation, and this leakage was the source of
fugitive solvent emissions.
Reducing solvent emissions became a priority
because of stricter air emissions standards
imposed by the New Jersey Department of
Environmental Protection (NJDEP). In 1989,
the specialty aromatics process area began
looking for an alternative filtration system.
In 1991, the process area replaced the filter
press with the modern dual-filtration system
illustrated in Figure 3-22. The system uses a
"back-pulse" type primary filter and a "hori-
zontal-leaf' secondary filter. This design
offers several advantages over the old press:
The new filters do not have to be opened to
remove the filter cake. This virtually elimi-
nates leakages and fugitive emissions. Only
trace amounts of solvent are released to the
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CASE STUDY 13: Solvent Emissions
CATEGORY 1
Nitrogen (to atmosphere)
Product crude
(from reaction step)
COMPRESSOR/CONDENSER
ENSEMBLE
-Solvent, product (recycle)-
Nitrogen
BACK-PULSE
FILTER
FEEDTANK
Product crude
Filter cloth
Vapor (solvent, product, nitrogen)
Filtered crude
HORIZONTAL-LEAF
FILTEFt
Filter leaf
-Solvent, product (recycle)-
(to purification step)
Hot solvent
Nitrogen
In the new filtration system, a batch of product
crude passes from a feed tank through a back-
pulse filter. The filter concentrates the
catalyst, which collects in the filter bottom along
with some solvent and product. This slurry is then
sent to a horizontal-leaf filter to remove additional
solvent and product. The liquid from the horizon-
tal-leaf filter is recycled back to the feed tank for
reprocessing with the next batch of crude. The
catalyst-bearing filter cake is sent to an off-site
reclamation facility.
The back-pulse filter contains tubes covered with
filter cloths. The liquid portion of the crude passes
through these tubes, while the filter cake collects
on the outside of the filter cloths. The back-pulse
filter is so named because periodic back-pulses of
nitrogen gas dislodge the wet cake from the filter
cloths, causing it to collect on the filter bottom
along with a "heel" of product and solvent.
, *- Dry filter-cake
(to recovery
incinerator)
The horizontal-leaf filter contains an assembly of
filter leaves connected to a central shaft. The
catalyst-bearing slurry cascades over the leaves
from the top to the bottom of the filter. The liquid
portion is recycled to the feed tank, while the filter
cake collects on the leaves. Hot solvent is then
introduced to the filter to wash recoverable product
out of the cake. The solvent wash is pumped to the
feed tank. Then hot nitrogen is blown into the
secondary filter to dry the cake. The nitrogen is
vented to the atmosphere after first being stripped
of solvent and product vapors by a cooler/con-
denser ensemble. At the end of the drying step, the
central shaft rotates. The filter cake is spun off of
the leaves and falls by gravity to the bottom of the
filter. The cake is then drummed and sent to the
reclamation facility.
Figure 3-22. New Catalyst Filtration System
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CATEGORY 1
CASE STUDY 13: Solvent Emissions
atmosphere from solvent/product recovery
equipment. Solvent emissions have been
reduced by 99%.
Most of the saleable product that was previ-
ously lost in the filter cake is now recovered.
Description of the Waste Stream
The air emissions from this process consist of
100% volatile solvent. Costs associated with
these emissions consist of the replacement
cost of the solvent. Had the alternative filtra-
tion system not been implemented, regulatory
noncompliance would have forced a shutdown
of the process.
Before the emissions reduction, the catalyst
filtration produced 0.09 Ibs of solvent emis-
sions for every pound of product produced.
After the reductions, this figure fell to 0.001
Ibs of waste.
Previous Waste Minimization Efforts
Although the specialty aromatics process area
has reduced waste streams in other parts of the
process over the years, no known attempts
have previously been made to reduce solvent
emissions to the atmosphere from the filter-
press operation.
Waste Minimization Options
The dual-filtration system described in this
report was the only option seriously consid-
ered for reducing the solvent emissions. It
would have been possible to comply with the
NJDEP regulations by installing the back-
pulse filter alone. The reduction in air emis-
sions would have been as great with one filter
as with two. But the single-filter "option"
would have actually increased net waste. The
filter cake from the back-pulse filter contains
more solvent than was previously lost to air
emissions. This solvent would have added to
the incinerable waste that is sent to the recla-
mation facility. Dual-filtration provides a net
waste reduction by producing a dryer filter
cake and recycling most of the liquid filtrate.
An upgrade to the new filtration system
currently under investigation would reduce the
solvent in the filter cake even more. The hot
nitrogen that is used to dry the filter cake
Table 3-25. Economic Summary of Air Emissions Minimization Options
Option
Install dual
filtration system
Install dual
filtration system
& steam drying
Waste
Reduction
99%
air emissions
99%
air emissions
62%
reclamation
Capital Cost
$2,200,000
$2,200,000
EPA Method
NPV(12%) IRR
($1,880,000)
($1,390,000)
<0%
<0%
DuPont Method
NPV(12%) IRR
($1,880,000)
($1,390,000)
Comments: Parentheses denote negative numbers.
<0%
<0%
Implemen-
tation Time
6 months
6 months
For an explanation of terms used in this analysis, see the discussion under "Feasibility
Evaluation" in Section 2: Project Methodology.
Page 94
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CASE STUDY -43: Solvent Emissions
CATEGORY 1
would be replaced with steam. The steam
would promote better drying by displacing the
solvent in the cake. Most of the displaced
solvent would then be recycled back into the
process.
Although not seriously considered, another
option for reducing the solvent emissions
would have been to shut the process down. As
the economic analysis reveals, replacing the
filtration system required a large capital
investment with little offsetting return. If the
product were one that was considered mar-
ginal, shutting the process down would have
received more serious consideration as a waste
reduction option.
Technical and Economic Evaluation
Technical Analysis
In designing the new filtration system, the
specialty arornatics project team first consid-
ered a primary filter that used sintered (perme-
able) metal elements as the filter medium.
Although this type of filter works well in other
applications, lab testing proved it to be unsuit-
able for the specialty aromatics process. The
catalyst tended to clog the element pores,
forcing frequent replacement of the filter
elements.
After further investigation and testing, the
project team selected a primary filter that uses
disposable filtercloths. The new filtration
system was installed in 1991, and has met its
waste reduction goals.
Economic Analysis
Table 3-25 summarizes the economic analysis
of the dual-filtration system, both with and
without the steam-drying upgrade. Although
the filtration system resulted in an economic
loss, a substantial part of the operating cost
can be reduced by using steam instead of hot
nitrogen to dry the filter cake. Neither option
yields an internal rate of return (IRR), and
both have a negative net present value (NPV).
Implementation of the new filtration system
has resulted in a financial loss to DuPont,
which often happens in cases of regulatory
driven waste reductions.
Barriers to Implementation
The chief barrier to implementation of the new
filtration system was the identification of an
appropriate filtration technology. Precious
metal recovery requires very efficient filtra-
tion, and the choice of a filter medium must be
made carefully. The specialty aromatics
process considered and tested a filtration
technology (sintered metal) that proved
unsuitable before adopting the chosen design.
Opportunities for Others
If a process area is going to make a substantial
capital investment for new equipment, it's
better to install equipment that will actually
reduce waste rather than merely shift the
waste to another medium. It would have been
easy for the specialty aromatics process to
comply with tougher emissions regulations
while creating a new waste stream. Installing
the primary filter alone would have brought
the process into compliance for air emissions,
but would also have generated additional
liquid waste.
In an existing process, the additional amounts
of solvent and product recovered by a new
filtration system may not be enough to offset
the capital costs of the implementation. Had
this waste assessment not been regulatory
driven, it is unlikely that the new system
would have been installed.
Regulatory driven waste reductions have the
potential of killing off existing processes. The
specialty aromatics business described here
SECTION 3: Case Studies
Page 95
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CATEGORY 1
CASE STUDY 13: Solvent Emissions
was judged by the corporation to be strong
enough to absorb the cost of the capital invest-
ment in the new filtration system. This is not
true of all businesses. There are always two
other options that don't appear on option
generation tables. One is to do nothing, a
credible option if all others have negative
NPVs with no "soft" benefits, and if the waste
is handled in an environmentally sound man-
ner. But if regulatory waste reduction is
imposed upon a business, then doing nothing
is not an option. Under these circumstances,
if the value of a business does not justify the
cost of regulatory compliance, then shutting
down could well become the chosen "waste
reduction" option.
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CATEGORY 1
Case Study 14: SAC Process
Improvements in raw material quality open the door to substantial
waste reductions
Abstract
This case study examines ongoing waste
reduction efforts for a process that manufac-
tures aromatic compounds. The process
produces a waste stream of heavy tars which
are incinerated. Extreme variability in the
quality of one of the incoming raw materials
had previously frustrated waste reduction
efforts by creating uncertainty about the
causes of waste generation. But recent im-
provements in the quality of the raw materials
have made waste reduction possible. The
waste reductions described in this study result
from improvements in process control,
changes in reaction conditions, and improved
waste handling.
Background
A continuous process at the DuPont Chambers
Works site uses reaction and distillation to
produce specialty aromatic compounds (SAC).
The process, illustrated in Figure 3-23, pro-
duces a waste stream containing heavy tars
which form during the reaction step and exit
the process from the distillation step. These
viscous tars entrap significant amounts of
SAC product and carry it away from the
process as waste. In fact, saleable SAC prod-
uct constitutes the greatest proportion of the
waste stream. The yield loss represented by
the entrapped SAC provided a strong incen-
tive for tar reduction from the SAC process.
The SAC reaction step produces two types of
tar. So-called "thermal" tars are an inevitable
consequence of the high-temperature reaction.
"Acid" tars, on the other hand, form when one
of the; raw materials enters the process with
excessively low pH, i.e., it is acidic. The
presence of acids during the reaction step
triggers a side reaction which produces the tar.
The ratio of thermal tar to acid tar in the SAC
waste is unknown because there is no practical
way to distinguish between them in waste
stream samples. This fact used to discourage
waste reduction efforts at the SAC process.
Poor pH control at the on-site process that
makes the raw material caused substantial and
unpredictable fluctuations in acidic content.
This in turn caused the level of tar formation
to fluctuate, and made it impossible to mea-
sure the impact of a waste reduction effort.
Not only did acidic raw material directly
produce tar, it increased waste in an indirect
way as well. In time, uncertainty over the acid
content of the raw material prompted the SAC
process area to add a neutralizing agent to the
reaction step. This neutralizing agent itself
became part of the waste stream.
In 1990, the raw materials process installed
online instrumentation to provide rapid and
continuous readouts of pH levels. Operators
could now control their process more effec-
tively and keep acidity low. This resulted in an
immediate tar reduction at the SAC process
area. Moreover, reliable knowledge of raw
material pH enabled the SAC area to imple-
ment successful waste reduction options of
their own. These include running the SAC
reaction at lower temperatures, and reducing
the amount of a neutralizing agent added to
the reaction.
SECTION 3: Case Studies
Page 97
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CATEGORY 1
CASE STUDY 14: SAC Process
Neutralizing
agent
SAC products
RAW MATERIALS
PROCESS
PH
METER
Reactant Catalyst
Raw
material
FEED
TANK
Raw material
REACTION
STEP
SAC crude ,
DISTILLATION
STEP
The process for making SAC raw material
includes a neutralization step in which an
alkaline compound is added to reduce acidity.
The amount of alkali is controlled by operators
according to pH-level readouts from a recently
installed online pH meter.
The raw material enters the SAC process through a
feed tank, from which it is fed continuously into the
reaction step. There it is mixed with another reactant
and a catalyst Historically, a neutralizing agent has
been added to the reaction step to ensure against
Wastes
(to on-site incineration plant)
excess acidity in the raw material. The neutralizing
agent is still added, but in much reduced amounts
since the improvement in pH control back at the raw
materials process.
The SAC crude which leaves the reaction step
contains several saleable compounds, each of which
must be separated out from the crude. This is accom-
plished through a complex series of distillations. The
resulting waste stream is sent to the oiri-site incinera-
tion facility for disposal.
Figure 3-23. SAC Process
A waste minimization team was formed to
find ways of improving product yield and
reducing wastes from the SAC process. Their
efforts to date, together with the control
improvement in the raw materials process,
have reduced waste by almost 60%.
Description of Waste Stream
Before the waste reductions, a typical analysis
of the SAC process waste stream would have
revealed:
SAC product 93.5%
Tars 5.8%
Neutralizing agent 0.7%
Costs associated with this waste stream in-
cluded the yield loss represented by the
unrecovered product, the cost of incineration,
waste handling and storage costs, and the
replacement cost of the neutralizing agent.
Before the waste reductions, the SAC process
produced 0.07 Ibs of incinerated waste for
every pound of product recovered. After
implementation of the waste reductions, this
figure fell to 0.03 Ibs. This represents a source
reduction of 58.5%.
Previous Waste Minimization Efforts
Uncertainty over the pH of the incoming raw
material had long discouraged the SAC pro-
cess area from investigating tar reductions.
Instead, attention was directed at ways to
upgrade the distillation step to recover more
Page98
SECTION 3: Case Studies
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CASE STUDY 14: SAC Process
CATEGORY1
product from the SAC crude. Changes in such
distillation variables as temperature, pressure,
and flow rate were considered but never
implemented. Such measures would certainly
not have matched the waste reductions
achieved by the tar reductions described in
this case study.
Waste Minimization Options
The implementation of four waste reduction
options accounts for the waste reductions so
far at the SAC process:
Install online pH meter at the raw materials
process. The raw materials process controls
pH by adding an alkaline compound to the
raw material. In the past, pH had been
measured by sampling and laboratory
analysis, with a turnaround time of several
hours between sample collection and the
receipt of lab results. This made it difficult
to know how much alkali to add. Undetected
changes in acidity occurred, and this caused
concurrent fluctuations in tar formation at
the downstream SAC process.
The new instrumentation now provides
operators with rapid and continuous feed-
back of process conditions. This enables
them to more effectively control the acidity
of the outgoing material.
Improving the pH consistency of the raw
material made subsequent waste reductions
possible by permitting the accurate evalua-
tion of proposed options.
Improved pH control has resulted in a direct
waste reduction of 7.1 %.
Run SAC reaction step at lower tempera-
ture. This option targets the formation of
thermal tars. Lower temperature reduces tar
formation, but it also slows the reaction. The
resulting productivity decrease would have
prevented the implementation of this option.
But people at the SAC process area were
able to adjust other process parameters to
permit operation at lower temperature with
no reduction in productivity.
Reducing reaction temperature has resulted
in a waste reduction of 42.9%.
Reduce the amount of neutralizing agent in
the reaction step. The use of this agent was
made necessary by uncertainty about the pH
of the incoming raw material. But now that
better pH control in the raw materials pro-
cess has eliminated the uncertainty and has
reduced acidity, the amount of neutralizing
agent added to the reaction step has been
reduced. Further reductions are now under
consideration.
Implementation of this option has reduced
waste from the SAC process by 1.4%.
Improve waste handling. Tars are pumped
from the process equipment into a tank truck
for transportation to the on-site incinerator.
In the past, trucks were dispatched to the
incinerator only when full. But it takes
several days to fill a truck. During that time,
the SAC waste can solidify into an
unflowable sludge and become difficult to
handle at the incinerator. So hot SAC prod-
uct was routinely added to the waste to thin
it and make it flowable.
Today, the trucks are dispatched from the
SAC process to the incinerator daily while
the waste is still partially fluid. This mini-
mizes the need for the S AC-product thinner.
This waste handling improvement has
contributed 7.1% to the overall waste reduc-
tion effort with no capital costs or reductions
in productivity.
The impetus for these waste reduction efforts
has been the need to improve yield by reduc-
ing tars, and the need to reduce the cost of
waste disposal.
SECTION 3: Case Studies
Page 99
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CATEGORY 1
CASE STUDY 14: SAG Process
Table 3-26. Economic Summary of Top SAC Waste Minimization Options
Option
Install online pH
meter
Lower reaction
temperature
Reduce
neutralizing agent
Improve waste
handling
Waste
Reduction
7.1%
42.9%
1.4%
7.1%
Capital Cost
$50,000
$0
$0
$0
EPA Method
NPV(12%) IRR
$990,000
$6,180,000
$30,000
$1,030,000
195%
CO
oo
CO
DuPont Metfiod
NPV(12%) IRR
$920,000
$5,810,000
$10,000
$970,000
189%
CO
CO
CO
Implemen-
tation Time
6 months
3 months
1 month
1 month
Comments: For an explanation of terms used in this analysis, see the discussion under "Feasibility
Evaluation" in Section 2: Project Methodology.
With the exception of the improved pH con-
trol, the waste minimization team generated
these options at informal, undocumented
brainstorming sessions. The idea for reducing
reaction temperature emerged after extensive
research into reaction kinetics by the engineer
who led the team. Sources for the research
included site records and technical literature in
the public domain.
The SAC area continues to pursue additional
waste reductions. Changes in distillation
strategies to recover more product from the
waste are now under consideration. In 1992,
people from the SAC area and experts from
other DuPont organizations convened a
technical symposium to examine ways to
achieve greater process improvement and
waste reduction. The symposium produced
two long-term options that are worthy of
investigation: develop entirely new reaction
chemistry, or keep the current reaction but
install state-of-the art reaction equipment.
Either of these long range solutions could
virtually eliminate tar formation from the
reaction step.
Technical and Economic Feasibility
Studies conducted before implementation of
the four waste reduction options had shown
them all to be technically feasible and effec-
tive. Economic evaluation of the options,
summarized in Table 3-26, had shown them
all to be cost effective.
Barriers to Implementation
For years, the variable pH of the incoming raw
material discouraged tar reductions at the SAC
process. Uncertainty of the amount of acid tars
forming in the reaction step made it impos-
sible to measure the success of any tar reduc-
tion efforts. This barrier was removed when
the raw materials process area improved its
pH control.
Improved pH control removed the only barrier
to reducing the amount of neutralizing agent
in the reaction step.
The proposal to lower reaction temperature
met with some organizational resistance
because of its possible effect upon process
productivity. This resistance was overcome by
Page 100
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CASE STUDY 14: SAC Process
CATEGORY 1
demonstrating that productivity could be
maintained by adjusting other process
conditions.
There were no barriers to the waste handling
improvement described in this report.
Opportunities for Others
This case study demonstrates how problems in
one manufacturing process can exacerbate
waste generation at subsequent "downstream"
processes. The failure to control pH at the raw
materials process was a direct cause of waste
generation at the SAC process, and made it
extremely difficult to pursue any significant
waste reductions. Variability in acid-tar
formation would have hidden any waste
reduction successes in the SAC process. But
once raw material pH was brought under
control, it became possible for the SAC
process area to test improvements for their
effectiveness in reducing tars.
Like other studies in this series, this study
demonstrates the importance of good process
control to any waste reduction effort. There is
usually hesitancy about upgrading the control
systems of older processes because of the
capital investment that's usually required. But
several processes at the Chambers Works site
have been able to reduce the cost of upgrades
by relying heavily upon site personnel, instead
of outside resources, to implement the control
upgrades. These processes typically realize
greater than anticipated process improvements
from upgraded control, and find the capital
investment well justified.
SECTION 3: Case Studies
Page 101
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CATEGORY 1
Case Study 15: Distillation Train
Relaxing cross-contamination limits in a multiproduct process helps reduce waste
Abstract
This case study describes an effort to reduce
incinerated wastes from the washing of distil-
lation equipment during product changeovers.
A waste reduction of nearly 80% was
achieved through several steps requiring little
capital investment The effort was prompted
by rising incineration costs and the need to
increase product yields. A key to the reduction
was the finding that product cross-contamina-
tion limits could be relaxed with no negative
impact upon final product quality. This finding
could be of general interest to the chemical
processing industry.
Background
The Chambers Works "distillation train" is a
collection of separation equipment that oper-
ates continuously to purify products from two
crude streams produced at another process on-
site. The product crudes cycle through the
equipment in separate "campaigns". At the
conclusion of each campaign, a portion of the
product crude from the next campaign is used
to wash out the equipment to prevent contami-
nation of the new product with residue from
the old. This washout crude becomes too
contaminated with residue to recycle back into
the process. It therefore leaves the distillation
train as waste for incineration.
Three types of equipment in the distillation
train are relevant to this study:
Distillation columns. The distillation train
includes a series of distillation columns, the
largest of which contains packing to enhance
separation. The amount of residue left on the
packing is sufficient to cause unacceptable
cross-contamination. Cleaning the packing
actually begins after the new campaign has
started. The initial material (distilled by the
column carries away the old product residue
and becomes part of the washout waste.
Piping and storage tanks. Pipe interiors and
tank bottoms are flushed between campaigns
to remove residue.
Decant tank. The distillation train includes a
decant tank that separates liquids of different
densities. Historically, large amounts of new
product crude have been used to flush the
decant tank between campaigns.
In 1990, a project team was formed to identify
ways to reduce waste from equipment wash-
out. Their goals included a reduction in incin-
eration costs and improvement in product
yields. As a result of the team's activities, four
options for reducing waste have been imple-
mented. These have reduced the washout
waste by about 78%. The four options are:
Reduction in the amount of material used to
flush the decant tank. The waste reduction
team performed an evaluation of how much
material is actually required to do an ad-
equate cleaning job. They found that just
one-tenth the amount that had been used was
sufficient. Reducing the material used for
cleaning the decant tank contributed 27.4%
to the overall waste reduction effort.
Installation of a dedicated pipeline. Previ-
ously, a single pipeline had been used to
transport both of the product crudes from the
process that made them to the distillation
train. In 1990, another pipeline was installed
to provide dedicated pipelines for both
crudes. This eliminated the need for flushing
between campaigns and contributed 20.6%
to the overall reduction effort.
Page 102
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CASE STUDY 15: Distillation Train
CATEGORY 1
Implementation of a column drain and
pump-out procedure. In the new procedure,
the large distillation column is placed under
slight positive pressure for a period of 24 to
48 hours. During this time, operators peri-
odically pump out the column as residue
blows off of the packing. The pumped
residue is sent to a storage tank to be re-
cycled back to the process during a future
campaign. The new procedure permits a
reduction in the amount of contaminated
product taken as waste from the column at
the start of a campaign, and accounts for
17.1% of the overall waste reduction.
Relaxation of cross-contamination limits.
The waste reduction team found that a
greater amount of old product residue could
be tolerated without compromising the
purity specifications for the new product.
This finding enabled waste reduction in two
ways. First, the amount of material used to
clean the piping and tanks was simply
reduced. Secondly, the amount of material
taken as waste from the large column at the
start of a new campaign was further reduced.
Some cross-contaminated product from the
column is allowed to enter the product
collection tank where it mixes with the purer
product that arrives later. The overall
amount of product contamination is kept
within product purity specifications. Relax-
ation of cross-contamination limits has
contributed 13.1% to the overall waste
reduction.
Description of the Waste Stream
The waste stream from this process consists
entirely of product crude. Thus the cost of this
waste stream, in addition to the costs of
incineration, includes the yield loss repre-
sented by unrecovered product.
Before implementation of the four options
described above, the distillation train washout
produced 0.032 Ibs of waste per pound of
product produced. After implementation, this
figure dropped to 0.007 Ibs.
At present, the replacement of product crude
with waste material for flushing the decant
tank is under consideration. If implemented,
this option would reduce the washout waste to
0.006 pounds per pound of product.
Previous Waste Minimization Efforts
Over the years, reductions in other waste
streams from the distillation train have been
achieved. However, no known attempts to
reduce washout waste were made before
formation of the waste reduction team in
1990,,
Waste Minimization Options
The waste reduction team generated a number
of waishout waste reduction options in addition
to the four that were implemented. These
include:
Use, waste material to flush the decant tank.
The option would use the high-boiler waste
from one of the distillation columns to clean
the decant tank instead of good product
crude. Implementation of this option is
seriously being considered.
Flush the column packing with water. This
option involves pouring water over the
large-column packing to wash out the
residue. This option is not being seriously
considered because of concerns about
equipment corrosion.
Simply reduce further the amount of mate-
rial used for equipment washout. The waste
reduction team determined that no such
reduction can now be made without compro-
mising product quality.
SECTION 3: Case Studies
Page 103
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CATEGORY 1
CASE STUDY 15: Distillation Train
Table 3-27. Economic Summary of Top Distillation Train Waste Minimization Options
Option
Install dedicated
pipeline
Relax cross-
contamination
limits
Reduce flush in
decant tank
Column drain &
pump-out
procedure
Use waste
material as flush
Waste
Reduction
20.6%
13.1%
27.4%
17.1%
3.4%
Capital Cost
$700,000
$0
$0
$0
$0
EPA Method
NPV(12%) IRR
$3,280,000
$400,000
$840,000
$530,000
$110,000
79%
oo
00
00
00
DuPont Method
NPV(12%) IRR
$3,080,000
$270,000
$570,000
$360,000
$70,000
76%
oo
oo
00
00
Implemen-
tation Time
6 months
6 months
3 months
3 months
1 month
Comments: For an explanation of terms used in this analysis, see the discussion under "Feasibility
Evaluation" in Section 2: Project Methodology.
Technical and Economic Evaluation
No technical problems were encountered in
implementing the waste reduction options.
Table 3-27 summarizes the economic evalua-
tion of the four implemented options, as well
as the option, "Use waste material to flush the
equipment set", which is now under consider-
ation. The option, "Install dedicated pipeline",
is the only one that required capital invest-
ment. This option nevertheless had a favorable
internal rate of return (IRR) and net present
value (NPV).
Barriers to Implementation
Concern about product quality was the only
barrier to relaxing the cross-contamination
limits. Once it was demonstrated that product
quality could be maintained, it was possible to
implement that option.
Capital investment was a barrier to implemen-
tation of the dedicated pipeline option. This
barrier was removed when the option was
shown to have favorable IRR and NPV.
There were no barriers to implementing the
reduction in decant tank washout material and
the new procedure for cleaning the packing
inside the large distillation column.
Opportunities for Others
This case study, like others in this series,
demonstrates mat equipment washouts pro-
vide a good opportunity for significant waste
reductions with little capital cost. The experi-
ence of the distillation train team shows that
waste reductions can be achieved through a
series of small, inexpensive steps rather than
by a great leap of investment in new
equipment.
Reevaluation of product specifications and
cross-contamination limits presents more
waste reduction opportunities. There are
probably many older processes that have
overly strict purity standards that were estab-
lished at a time when waste generation was
less of an issue. Today, these "purity cush-
ions" seem unnecessary in view of the increas-
ing importance of waste reduction.
Page 104
SECTION 3: Case Studies
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SECTION
Methodology Critique
In recent years, a number of waste reduction
methodologies have been developed in
government, industry, and academe. Their
purpose is to provide manufacturers with a
systematic approach to identifying and
reducing waste from their processes.
Cataloging these methodologies is beyond
the scope of this report, but extensive
literature exists about programs promulgated
by various levels of government, industry
organizations, and individual companies.1"6
This section examines the EPA and DuPont
methodologies in light of the experience of
the Chambers Works Waste Minimization
Project. As a participating member of the
Chemical Manufacturers Association
(CMA), DuPont has committed to
implementing CMA's Responsible Careฎ
Codes. Any discussion of the DuPont
methodology must also include a description
of the codes.
In applying the EPA methodology, the
Chambers Works project team performed
those tasks defined in this critique as "waste
stream selection" and "assessment". In
general, the team did not perform tasks
defined herein as "chartering", "implementa-
tion", or "auditing", and the discussions of
those tasks in this critique are based on the
experience that DuPont and the Chambers
Works site have accumulated in the course
of their own waste reduction efforts.
SECTION 4: Methodotogy Critique
Page 105
-------
EPA Methodology
r
Establish the Pollution Prevention Program
Executive level decision
Policy statement
Consensus building
I
Organize Program
Name task force
State goals
I
Do Preliminary Assessment
1 Collect data
Review sites
Establish priorities
Write Program Plan
Consider external groups
Define objectives
Identify potential obstacles
Develop schedule
I
Do Detailed Assessment
Name assessment team(s)
Review data and siie(s)
> Organize and document information
I
Define Pollution Prevention Options
Propose options
Screen options
I
Do Feasibility Analysis
Technical
Environmental
Economic
I
Write Assessment Report
Implement the Plan
Select projects
Obtain funding
Install
Measure Progress
Acquire data
Analyze results
I
Maintain Pollution Prevention Program
DuPont Methodology
Start with Commitment & Awareness
Adopt policy, guidelines, & goals
Provide resources
Assign "cheerleader" to head program
Publicize policy, objectives, & goals
Empower individuals to carry out program
Start visible program with Immediate results
Establish awards for individuals and groups
Base compensation on environmental
performance
Keep employees & community informed
I
Organize to Facilitate Waste Minimization
Central team to coordinate effort
Operation area teams for data/actions
R&D and engineering for long-range projects
Define Problem: "Know Your Waste"
Identify, list, & characterize all streams
Trace primary streams to their sources
Define waste cost-reduction benefits
Track Waste Data
Set up data-base system for all streams
Track primary streams
Establish Targets & Goals
Divide streams into "now" & "later"
> Prioritize "later" streams for projects
Set goals for each stream
I
Reduce Waste & Emission Streams
Do short-term, low-cost streams as
they are Identified
Define options for reducing each
priority stream
Analyze technical & economic
feasibility of each option
Select best option & initiate project action
Incorporate disciplined environmental
analysis early in project design phase
Audit Progress
Set up an area audit to control waste
> Provide management summaries
against goals
Report good project results broadly
Figure 4-1. Comparison of EPA andDuPont Methodologies
Page 106
SECTION 4; Methodology Critique
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Methodology Overview
Figure 4-1 provides a side-by-side compari-
son of the basic steps prescribed by the EPA
and DuPont methodologies. The EPA method-
ology shown is taken from the newly pub-
lished Facility Pollution Prevention Guide7,
Both methods can be said to contain the
following elements:
Chartering-in which the highest organiza-
tional levels commit to a waste reduction
program, policies are articulated and com-
municated, goals are set, and participants are
identified.
Waste stream selection-in which informa-
tion about wastes are collected and waste
streams are prioritized for reduction.
Assessment phase-in which options for
reducing the target waste stream are gener-
ated, prioritized, evaluated, and selected for
implementation.
Implementation-m which action is taken to
reduce the target waste stream.
Auditing-an ongoing process in which
wastes are monitored and reductions are
measured.
One difference between the two methodolo-
gies is that "waste stream selection" is actually
a part of the EPA method's chartering activi-
ties. It constitutes a separate process in the
DuPont methodology.
Responsible Care
The CMA has recently published its Respon-
sible Care Codes6, to which all member
organizations, including DuPont, have com-
mitted. The codes aim to improve the chemi-
cal industry's management of chemicals,
safety, health, and environmental perfor-
mance. They prescribe specific management
practices in six areas: community relations,
pollution prevention, chemicals distribution,
process safety, employee health and safety,
and product stewardship.
Figure 4-2 presents the Responsible Care
Codes for pollution prevention. The codes do
not constitute a methodology in that they do
not prescribe how an organization implements
them. Rather, they describe hallmarks that
successful pollution programs share. The
codes also provide a series of checkpoints for
an organization to incorporate into its own
methodology.
The EPA Methodology
At the start of the Chambers Works project,
the EPA's methodology was embodied in its
Waste Minimization Opportunity Assessment
Manual9. As its name implies, it placed great
emphasis on the assessment phase of a waste
reduction program, and offered tools for
conducting a waste assessment. The Manual
placed less emphasis on the establishment and
management of an ongoing waste reduction
program.
The recent publication of the EPA Facility
Pollution Prevention Guide1 represents a
major upgrade to the methodology. It places
additional emphasis on the management of a
continuous waste reduction program. For
example, the single chartering step prescribed
in the old manual has expanded to four itera-
tive steps in the new guide. And whereas
auditing had been a constituent task of imple-
mentation in the manual, the guide presents it
as a discrete, ongoing step. The guide's
inclusion of "maintain pollution prevention
program" as part of the methodology is
also new.
SECTION 4: Methodology Critique
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Codet
A clear commitment by senior management through policy, communications, and re-
sources to ongoing reductions at each of the company's facilities in releases to air,
water, and land.
Code 2
A quantitative inventory at each facility of wastes generated and released to the air,
water, and land measured or estimated at the point of generation or release.
CodeS
Evaluation, sufficient to assist in establishing reduction priorities, of the potential impact
of releases on the environment, and the health and safety of employees and the public.
Code 4
Education of, and dialog with, employees and members of the public about the inven-
tory, impact evaluation, and risks to the community.
CodeS
Establishment of priorities, goals, and plans for waste and release reduction, taking into
account both community concerns, and the potential safety, health, and environmental
impacts as determined under Codes 3 and 4.
Code6
Ongoing reduction of wastes and releases, giving preference first to source reduction,
second to recycle/reuse, and third to treatment.
Code?
Measure progress at each facility in reducing the generation of wastes and in reducing
releases to the air, water, and land, by updating the quantitative inventory at least annu-
ally.
CodeS
Ongoing dialog with employees and members of the public regarding waste and release
information, progress in achieving reductions, and future plans. This dialog should be at
a personal, face-to-face level, where possible, and should emphasize listening to others
and discussing their concerns and ideas.
Figure 4-2. Responsible Care Codes for Pollution Prevention
The methodology described in the guide is a
major step forward. The old manual correctly
assumed that assessments are at the heart of a
waste reduction program. But the new meth-
odology increases the likelihood that assess-
ments will actually be performed because it
prescribes waste reduction roles for people at
all levels of the organization.
The DuPont Methodology
The DuPont methodology, like that of the
EPA, has also evolved over the years. It began
in 1988 as a set of tools for tracking waste. In
fact, "waste stream selection" is still the
methodology's most explicitly articulated
step. The DuPont methodology provides more
detailed prescriptions for chartering and waste
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SECTION 4: Methodology Critique
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Code 9
Inclusion of waste and release prevention objectives in research and in the design of
new or modified facilities, processes, or products.
Code 10
An ongoing program for promotion and support of waste and release reduction by
others.
Code 11
Periodic evaluation of waste management practices associated with operations and
equipment at each member company facility, taking into account community concerns
and health, safety, and environmental impacts, and implement ongoing improvements.
Code 12
Implementation of a process for selecting, retaining, and reviewing contractors and toll
manufacturers, that takes into account sound waste management practices that protect
the environment, and the health and safety of employees and the public.
Code 13
Implementation of engineering and operating controls at each member company facility
to improve prevention of and early detection of releases that may contaminate ground-
water.
Code 14
Implementation of an ongoing program for addressing past operating and waste man-
agement practices, and for working with others to resolve identified problems at each
active or inactive facility owned by a member company taking into account community
concerns, and health, safety, and environmental impacts.
Figure 4-2. Responsible Care Codes for Pollution Prevention (cont'd)
stream selection than for the assessment phase.
The company views the commitment of all
organizational levels as crucial to the success
of the program. Given the number and diver-
sity of the DuPont manufacturing facilities, it
is felt that how-to prescriptions for conducting
assessments are best left to the site.
The development of the present methodology
has been greatly influenced by the CMA's
Responsible Care Codes. Many of the activi-
ties prescribed for each step came directly
from the codes. Today, the DuPont methodol-
ogy can best be viewed as a plan for imple-
menting the Responsible Care Codes.
Application to the Chambers Works Project
At the start of the Chambers Works project,
the old EPA methodology was current. An
original goal of the project was to apply the
Chambers Works experience to a critique of
the EPA's assessment methodology. Because
the assessments were of primary interest, the
project's chartering and waste stream selection
activities were governed less by adherence to
a methodology, and more by project-specific
requirements. (See Section 2: Project Method-
ology.) However, the project team did apply
tools provided by the EPA methodology in a
preliminary selection of waste streams.
SECTION 4: Methodology Critique
Page 109
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The assessment phase of the project included
seven assessments involving waste streams
that had not yet been eliminated or greatly
reduced. These applied the EPA's tools for
conducting assessments. The remaining eight
assessments featured waste streams that had
already been eliminated or reduced. The
purpose of including them was to share suc-
cessful experiences with others in the process-
ing industries. They applied the EPA's
assessment tools retrospectively. (The full
assessment reports are contained in Section 3:
Case Studies.)
Methodology Comparison
Most methodologies consist of the same basic
steps of chartering, waste stream selection,
assessment, implementation, and auditing.
What distinguishes them in terms of success
or failure is the tools they provide for assess-
ment teams at the process level. Tools are
methods for accomplishing the tasks pre-
scribed by a methodology. Ideally, publica-
tions which support methodologies contain
descriptions of these tools, describe how they
are applied, provide clear examples, and
perhaps include helpful forms or checksheets.
The EPA Pollution Prevention Guide provides
a variety of tools for performing waste mini-
mization assessments. The 15 assessment
teams that participated in the Chambers
Works project used many of these tools. The
discussions which follow, particularly those
concerning the assessment phase, focuses on
the assessment teams' experiences with the
tools they chose.
Chartering Activities
The five tasks that the EPA prescribes under
"Establish the pollution prevention program"
and "Organize program" are essentially the ,
same as the tasks included in the DuPont steps
called "Start with commitment and aware-
ness" and "Organize to facilitate waste mini-
mization".
In the DuPont methodology, chartering occurs
not just at the executive level, but is repeated
at each organizational level. The replication of
commitment from the highest levels down to
the line organizations is intended to integrate
waste minimization into the way that people
work everyday. It's the key to the success of
the waste minimization program.
At the executive level, the commitment to a
waste reduction program began with DuPont
CEO Edgar Woolard, who has declared, "I
want to create a corporate culture in which
there is no such thing as industrial waste". A
policy statement has been written and commu-
nicated throughout the corporation which
states: "It is DuPont policy to minimize the
generation of waste to the extent that it is
technically and economically feasible, and to
handle all waste in an environmentally sound
manner. Treatment or disposal will be on-site
whenever practicable, or at other DuPont sites
with suitable waste management facilities as a
first choice if it becomes necessary to send
waste off-site."
At the corporate level, waste reduction goals
have been articulated. These are:
reduction of hazardous waste by 35% from
1990 to 2000.
reduction of toxic emissions to the air (from
U.S. sites) by 60% from 1987 to 1993.
reduction of emissions of the EPA's special
list of 17 hazardous chemicals by 50% from
1988 to 1995.
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SECTION 4: Methodology Critique
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DuPont has also committed to goals for
reducing or eliminating CFC production,
energy consumption, carcinogenic air emis-
sions, and toxic discharges to landfill.
DuPont has established a corporate level core
competency group to provide vision and
determine goals for waste reduction. The
Environmental Stewardship Core Competency
of the Safety, Health, and Environmental
Excellence Center (SHEEC) is directly ac-
countable to the Vice President of Safety,
Health, and Environmental Affairs. Among
SHEEC's responsibilities are:
establishing guidelines for waste reduction
goals
tracking wastes and waste reductions
implementing the Responsible Care Codes
administering environmental excellence
awards and compensations
auditing sites for compliance with regula-
tions and company policy
training for waste reduction
At Chambers Works, the site staff has repli-
cated Mr. Woolard's commitment, and has
adopted similar waste reduction goals for the
site. The staff has established a task team to
develop the site commitment, achieve consen-
sus among all operating areas of the plant,
organize the program at the site level, and
implement the Responsible Care codes. The
team consists of plant staff members, environ-
mental professionals, supervisors, R&D
people, and line workers. It has developed and
maintains a six-month action plan for imple-
menting long-term waste reductions. The plan,
which is updated frequently, is also concerned
with eliminating unplanned releases.
The site commitment has been replicated in
each of the five operating areas and has
worked its way down to the line organizations.
Some line organizations have adopted ongoing
waste nsduction efforts, and some have been
pursuing them for years. Some of these facili-
ties are featured in the project assessments.
What they have in common are a willingness
to abandon old ways of thinking about waste
and the ongoing participation of cross-func-
tional groups of people in waste reduction
activities.
The experience at Chambers Works so far
reveals that driving the commitment down-
ward gets harder the closer one gets to the line
organizations. The ongoing demands of
production, maintenance, safety, and so on
seem to compete with waste reduction. The
successful facilities are those that have made
the paradigm shift that views all of these
demands as complementary, and not compet-
ing, activities.
Waste Stream Selection
The EPA includes waste stream selection in its
chartering phase under "Do preliminary
assessment", whereas DuPont devotes three
discrete steps to waste stream selection. In
both methodologies, waste steam selection
involves data collection and prioritization of
the waste streams. Both methods suggest
collecting the minimum amount of informa-
tion needed to prioritize the streams.
The primary tool offered by the EPA for
prioritizing waste streams is a formal ranking
and weighting procedure. In practice, the
amount of data to be collected is proportional
to the number of criteria used to prioritize the
waste streams. For example, collecting data
about waste costs requires information about
the cost of treating the waste, the cost of
product lost to waste, handling costs, and
transportation costs. For large sites with many
waste streams, formal ranking and weighting
can be too time-consuming to be practical.
Moreover, much of this effort will be dupli-
cated during the assessment phase.
SECTION 4: Methodology Critique
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An alternative tool for prioritizing wastes is
offered by the DuPont methodology, and is
known internally as "Know Your Waste"10.
The method requires a production area or site
to identify all wastes streams and to collect
sufficient information about them to permit
prioritization. It suggests the creation of flow
diagrams or material balances to help quantify
previously unaccounted for losses and emis-
sions.
Once the major streams have been identified,
they are prioritized into "do now" and "do
later" streams by cross-site, cross-disciplinary
teams without formal ranking and weighting.
This tool is similar to one offered by the EPA
for screening waste reduction options.
Of course, the group which identifies the
waste streams to work on should also be
empowered to allocate resources for waste
assessments upon those streams. An important
criteria for selection of "do now" streams is
waste minimization potential. This was true
for the brainstorming teams that chose the
candidates for the 15 assessments. This is
probably why most of the assessments in the
Chambers Works project identified options
that would significantly reduce waste while
producing high economic returns. The Re-
sponsible Care Codes take "Know Your
Waste" a step further by including input from
employees and the community during waste
stream prioritization.
Other tools for prioritizing waste streams can
be considered. For example, Pareto diagrams
are a simple way to rank waste streams by
volume. Smaller waste streams could be given
high priority if they are particularly toxic or
for anticipated regulatory imperatives. A
Pareto analysis for a typical chemical plant is
likely to show that the top 20% of the waste
streams account for more than 80% of the
total waste volume. Of the 15 assessments
included in the Chambers Works project, 13
addressed waste streams that were among the
top 20% for each operating area,' and among
the top 20% for each disposal medium.
Assessment Phase
DuPont actually combines its assessment and
implementation phases, whereas the EPA
methodology expands the assessment phase
into four discrete steps. In the assessment
phase of the Chambers Works project, the
project team performed the tasks listed under
"Do detailed assessment", "Define pollution
prevention options", and "Do feasibility
analysis" of the EPA methodology.
Some general observations from the assess-
ment phase of the Chambers Works project
are summarized below:
Assessments should be quick, uncom-
plicated, and structured to suit local
conditions. Otherwise, they're viewed as
annoyances intruding upon the day-to-day
concerns of running a production process.
Assessment teams should be kept small,
about six to eight people, to encourage open
discussion during option generation.
Including at least one line-worker on an
assessment team provides insight into how
the process really operates.
Including at least one person from outside
the process on an assessment team provides
a fresh perspective.
Area inspections and brainstorming meet-
ings are valuable tools during the assessment
phase.
It's important to determine the source of a
waste stream, as opposed to identifying the
equipment that emits it, before the option
generation step.
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Overly structured methods for screening
options do not overcome group biases and
are regarded as time-wasters by most teams.
What follows is a task-by-task analysis of the
assessment phase of the Chambers Works
project.
ASSESSMENT TEAMS
The formation of interdisciplinary assessment
teams at the process area level was considered
a good approach and is probably the reason
why all of the project assessments identified at
least some good waste minimization options.
The teams numbered from six to ten people,
and typically included supervisors, production
people, engineers, chemists, and operators.
The operators provided valuable input in most
of the assessments. They see things that are
not part of written procedures, and know
better than anyone else what happens during
day-to-day process operation.
Particularly helpful was the inclusion of
people from outside of the process on each
assessment team. Outsiders provide an objec-
tive view. Their presence promotes creative
thinking because they don't know the process
well enough to be bound by local conventions.
Appointing outsiders as assessment team
leaders could be a way of capitalizing on the
fresh perspectives they provide.
In the Chambers Works project, project team
members led the assessment teams. This
provided two advantages. First, doing assess-
ments became easier as project team members
gained experience. Second, project team
members were able to share ideas generated in
earlier assessments with participants in the
later assessments. The accumulated learnings
of the project team are the basis for the infor-
mation in Section 5: Waste Reduction Oppor-
tunities for Organic Chemical Processes.
DATA COLLECTION
For each assessment, some combination of the
following kinds of information proved useful
during the assessment phase:
Operating procedures
Flow rates
Batch sizes
Waste concentrations within streams
Raw material and finished product specs
Documentation on process changes
Information about lab experiments or plant
trials
The project team feels it is important to obtain
or generate a material balance before the area
inspection. The material balance proved to be
the most useful single piece of documentation.
In most cases, having sufficient data to com-
pile a material balance was nearly all the data
that was required for an assessment.
Energy balances were not considered to be
useful because of a bias in the waste stream
selection. Energy consumption was rated low
as a criterion for selecting the streams, and
few of the options generated during the assess-
ments had a significant impact upon energy
consumption. However, energy costs were
included in calculations for economic feasibil-
ity. Similarly, water balances were not consid-
ered useful, but water costs were included in
the calculations for economic feasibility.
AREA INSPECTION
All 15 of the project assessments included an
area inspection by members of the assessment
teams. These proved to be a useful team-
building exercise, and provided everyone with
a common grounding in the process. Outside
participants would probably have had trouble
understanding the discussions during the
subsequent brainstorming meeting without
these inspections.
SECTION 4: Methodology Critique
Page 113
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Raw materials
1%
Unrecovered product
46%
Reaction byproducts Tars formed during distillation
50% 3%
Figure 4-3. Sources of Waste
The experience that outsiders bring to the site
inspections can sometimes result in a break-
through. On one inspection, an outsider
noticed a waste stream similar in composition
to the raw material used by another Chambers
Works process. She is now conducting an
independent assessment on this waste stream
to determine if it can indeed be used as a feed
stock for the other process.
OPTION GENERATION
Options were generated at brainstorming
meetings of the assessment teams. The project
team concluded that the best format for these
meetings is to freely collect ideas, and to
avoid discussion of them beyond what is
necessary to understand them.
It is important to determine the true source of
the waste stream before the option generation
part of the assessment phase. Impurities from
an upstream process, poor process control, and
many other factors may all combine to con-
tribute to waste. Unless these sources are
identified and their relative importance estab-
lished, option generation can focus on the
piece of equipment that emits the waste stream
and which may in fact produce only a small
part of the waste. As Figure 43 shows, one of
the project assessments examined a waste
stream that had four sources. Two of these
sources were responsible for about 97% of the
waste. But because these sources were not
identified beforehand, roughly equal numbers
of options addressed all four sources. Fortu-
nately, the causes of the waste came to be well
understood before the assessment was com-
pleted. But knowing the major sources of the
waste beforehand would have saved time by
allowing team members to concentrate on
them.
Several tools might be provided to help
identify the actual source of the waste. A
material balance provides a good starting
point. A cause-and-effect "fishbone" diagram
such as that in Figure 4-3 can help identify the
sources of waste and indicate where to look
for reductions. Sampling to identify compo-
nents of the waste stream can provide clues to
their sources. Control charts, histograms, and
scatter diagrams can depict fluctuations in
waste stream components and thus provide
more clues.
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SECTION 4: Methodology Critique
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The value of brainstorming meetings was
demonstrated by at least one of the "retrospec-
tive" project assessments. A group was devel-
oping an option that would have reduced
waste, and had actually begun to procure the
required equipment. Later, another option that
eliminated the waste stream entirely was
identified and implemented. The wasteful
procurement might have been avoided if a
good cross-section of people from the process
had been brought together for brainstorming.
OPTION SCREENING
The EPA methodology offers several tools for
option screening. These include such simple
methods as categorizing and simple voting, as
well as the more rigorous weighted-sum rating
and ranking method. Five of the assessments
performed rating and ranking of options using
the weighted-sum method described in Section
2. These exercises were very time-consuming,
and four of the five assessment teams did not
find them useful. For those assessments, it
would have been better to apply one of the
simpler tools. The one team that did find the
weighted-sum method helpful had a very
complicated process with many options.
The assessment teams uncovered some pos-
sible pitfalls with the weighted-sum method.
The method is designed to provide an objec-
tive measure of an option's worthiness. In
practice, some teams incorporated local biases
into the weights assigned to the criteria or the
rankings they gave to an option. Thus, options
which outside observers subjectively consid-
ered to be innovative and promising some-
times didn't fare well when ranked against
more conventional, "popular" options.
On several occasions, an option ranked at or
near the top of the list because it scored high
in every criteria except probability of success
or safely. But an unsatisfactory score in either
of these two criteria is enough to reject an
option, no matter what its other merits are.
The high scores achieved by some impractical
options; probably indicates that the assessment
teams used too many weighted criteria.
Another problem with the ranking and weight-
ing is that many options could not be evalu-
ated on the fly. Some options had to be better
defined or required laboratory analysis. This
made it difficult to rank them at a meeting.
Often, the options that were worth pursuing
were obvious to many team members before
the ranking exercise began. These people
tended to view the subsequent exercise as a
waste of time.
The weighting and ranking meetings were not
entirely fruitless. Often the discussions about
each option provided a good basis for deter-
mining its technical and environmental feasi-
bility.
One of the simpler tools offered by the EPA is
to classify options into three categories:
implement immediately, marginal or impracti-
cal, and more study required. This is similar to
a DuPont tool designed to quickly identify the
best options for further evaluation. It pre-
scribes placing all of the generated options
into four categories:
Do now
Do later
Insufficient knowledge
(Apparently) impractical
The terms "do now" and "do later" do not
refer to timing but to the waste reduction
value of an option. A do-now option is one
with high waste minimization potential or
high chance of success. The do-later options
have lower waste reduction potential and
perhaps longer implementation times. The do-
later options should be reconsidered after the
do-now options have been implemented. The
"insufficient knowledge" options require
SECTION 4: Methodology Critique
Page 115
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additional study before they can move into
one of the other categories. The "impractical"
options, while not dismissed outright, have
very low waste reduction value or chance of
success.
Many other tools can be used to quickly
screen options. These include cost/benefits
analysis, simple voting, and listing option
"pros" and "cons".
FEASIBILITY ANALYSIS
The economic analysis portion of the assess-
ment is the most difficult and time-consuming
part of the assessment. The use of long-term
economic indicators as prescribed by both the
EPA's total cost assessment and the DuPont
methodology, while necessary, is a source of
potential problems. Estimating investment,
cost savings, and revenue changes is within
the competence of the people who will actu-
ally be doing the analysis at the area level.
The difficulties arise when dealing with the
other factors required for calculating net
present value (NPV). These include multiyear
estimates of inflation, taxes, tax depreciation,
fixed costs, selling expenses, working capital,
etc. Most chemists and engineers do not
perform enough NPV calculations to become
expert in the method. Computers have helped
to simplify the calculation of NPV, but not the
determination of the factors cited here.
Section 2 contains a description of how the
project team determined the economic feasi-
bility of selected options. That description
includes a "short-cut" method which standard-
izes the assumptions about the factors needed
to calculate NPV, and simplifies the calcula-
tion to terms familiar to the people who
perform assessments. The short-cut method
provides good results for a minimum of effort.
Frequently, the project team had to evaluate
an option with only a rough idea of its waste
reduction potential. Determining the precise
waste reduction through lab testing or plant
trials is expensive and time-consuming. To
select the best options during the assessment
phase, the project team had to make quick
estimates of waste reduction potential. The
short-cut method was a great help in these
situations.
In calculating NPV, DuPont uses only actual
costs and then considers the impact of such
"soft costs" as safety or regulatory compli-
ance. The EPA method encourages the assign-
ment of dollar values to these soft costs to
improve the attractiveness of waste reduction
options. But determining actual values for
future liability and intangibles is difficult at
the organizational level where most assess-
ments are done. Most assessment teams can
identify the "soft" costs and benefits associ-
ated with an option, and these can be factored
into the final decision to implement or not
implement. In practice, using the DuPont or
EPA methods made no real difference in
determining option feasibility in the 15 assess-
ments. However, it is conceivable that the
choice of method might make a difference for
marginal options.
The economic feasibility part of the assess-
ments uncovered several possible pitfalls\
associated with either methodology:
failure to consider non-waste minimization
improvement options
overestimating sales, savings, or waste
minimizations
underestimating additional operating costs
underestimating required capital investment
taking credit for cost savings that merely
shift the costs to other areas of the plant
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WRITE ASSESSMENT REPORT
Writing the assessment reports in Section 3
was difficult for those processes that had
committed to waste reduction before the start
of the project's assessment phase. This is
because the typical waste assessment is done
informally. No report is written at the end of
assessments, and only the most promising
options are investigated in depth. Documenta-
tion about past reduction efforts is, of course,
available. But lost are the waste reduction
options that were suggested and rejected.
Because waste reduction is an iterative pro-
cess, it would be useful to capture those
options for reconsideration in a future
assessment.
For this reason, the project team feels that
assessment reports are a useful part of the
assessment process. However, writing reports
such as those in Section 3 is time-consuming.
A list of the generated options, a summary of
the pros and cons of each, and the feasibility
results may be all that is necessary.
Implementation
Several assessment reports in Section 3 de-
scribe a variety of waste reduction implemen-
tations. Some of these consisted of stepwise
changes to the process, each incrementally
reducing the amount of waste. Such changes
can often be made without large capital
expenditures, and can be accomplished
quickly. This is a common approach to waste
reduction. Because expenditures are small,
facilities are willing to make the changes
without extensive study and testing. Several
iterations of incremental improvement are
often sufficient to virtually eliminate the waste
stream. Other implementations require large
capital expenditures and do require laboratory
testing, piloting, allocating resources, and
capital, installation, and testing.
Many of the waste reductions described in the
Chambers Works project assessments were
performed, as part of ongoing process im-
provements, and were classified as such. For
example, a major upgrade to a process control
system might be considered by people at the
area to be a "process improvement", even
though it resulted in a significant waste
reduction. It's important for an organization to
take full waste reduction credit for such
improvements.
It is fell: that implementations should be
performed at the lowest organizational level
possible. Several project assessments describe
implementations in which operators and
mechanics played a major role in reducing
large waste streams. Many smaller waste
streams can escape the notice of the site team.
But at the area level, they can be reduced as
part of ongoing process improvement pro-
grams.
Product Life Cycle
An important feature of the DuPont methodol-
ogy is that it considers the environmental
impact of products from the design phase,
through manufacture and use, to final disposal.
The DuPont methodology step called "Orga-
nize to Facilitate Waste Minimization" covers
the design of new products and processes, as
do the Responsible Care Codes. DuPont has
developed a method for designing more
environmentally friendly processes, and has
shared it with the process industries12. Cham-
bers Works has developed guidelines for
reducing product and process waste by build-
ing pollution prevention into the research and
development of new products. Wastes gener-
ated during manufacturing are addressed by
the DuPont waste reduction program, well-
describsd in this report. The final disposal of
DuPont products and packaging is addressed
SECTION 4: Methodology Critique
Page 117
-------
by the Responsible Care Codes for Product
Stewardship. In short, DuPont attempts to
build pollution prevention into each stage of a
product's life cycle.
The EPA prescribes a more holistic approach
to product life cycle issues. Although not
specified as a step in the EPA methodology,
the Facility Pollution Prevention Guide
recommends the use of life cycle analysis
(LCA). The guide does not provide much
information about how to perform a life cycle
assessment, but the subject has been covered
in the open literature.13-14 The virtue of LCA is
that it considers the complete environmental
impact of a product during the earliest stages
of design and development. In practice, LCA
is perceived as being difficult, time-consum-
ing, and expensive. Moreover, LCA is not
always free from bias given the speculative
nature of the many assumptions it requires as
assessment inputs.
The point is that more tools should be offered
for addressing product life cycle issues. LCA
seems best suited for the design of new prod-
ucts. For established products, the approach
taken by DuPont may be more appropriate.
Conclusions
The EPA methodology has already evolved
from a how-to for conducting assessments to a
comprehensive pollution prevention program.
It will no doubt evolve again as experience
with its application grows. Joint projects
between EPA and industry, such as the Cham-
bers Works project, provide a wealth of real
world input to future iterations. The increasing
volume of technical literature on the subject of
methodologies will also be influential. The
EPA seems well-placed to develop what will
be recognized as an industry standard for
pollution prevention methodologies.
An important strength of the current method-
ology is its recognition that pollution preven-
tion requires the participation from all levels
of the organization. It contains well-articu-
lated prescriptions around management com-
mitment.
In prescribing the expanded cost inventory,
the EPA is asking the right question, i.e., how
does one accurately value the benefits of
pollution prevention? Unfortunately, the
expanded cost inventory is full of ambiguities
and is difficult to apply. Economic feasibility
evaluations are often performed at the process
area level, and by people who are unable to
place a value upon future liability or intan-
gible benefits. As this report has noted, such
evaluations are already difficult. Having
people attempt to estimate dollar values for
such intangibles as "improved public image"
seems too much to ask. Other methods are
easier. These include the subjective consider-
ation of soft costs/benefits during option
evaluation.
The EPA Pollution Prevention Guide rightly
prescribes flexibility in the choice of assess-
ment tools to suit local circumstances. How-
ever, the DuPont members of the project
Team believe that the tools featured by the
guide in dedicated chapters and appendixes
exhibit a bias toward the more formal and
rigorous assessment tools. Such featured
methods as the total cost assessment, life cycle
analysis, and weighted-sum rating and ranking
all have simpler counterparts. The DuPont
team members feel that the more rigorous
tools work best when applied, to very complex
problems with many factors to consider. But
most problems addressed at the process area
level are amenable to quicker, less formal
methods. Application of the formal methods to
the typical process-level assessment does not
ensure elimination of group biases, and tends
to dampen the enthusiasm of the busy people
who participate in such assessments.
Page 118
SECTION 4: Methodology Critique
-------
The Chambers Works project uncovered
several key learnings that may be helpful to
other pollution prevention efforts:
A successful waste reduction program
requires the commitment of the entire
organization. An important strength of the
DuPont methodology is its "cascading
commitment" approach in which the com-
mitment to pollution prevention is made by
the top management and then replicated at
all levels of the organization. Over time, this
approach integrates pollution prevention into
the corporate culture, and empowers indi-
vidual facilities to implement waste reduc-
tions. Today, pollution prevention is taking
hold and growing roots at facilities across
Chambers Works.
Vision is important for successful waste
reduction. During the Chambers Works
project, the project team observed that what
the successful facilities have in common is a
vision of a process that becomes ever better
in terms of productivity, quality, and waste
reduction. At those facilities where wastes
were eliminated, people already knew that
they wanted to reduce waste and had general
ideas about how to do it.
Success breeds success. A waste reduction
methodology should provide for quick, early
results to provide examples and encourage-
ment to others. This can be accomplished by
keeping the assessment phase simple and
flexible.
Methodology Refinement
Process Improvement Programs
and Pollution Prevention
Many businesses in DuPont have adopted
formal process improvement programs to
achieve such goals as greater capacity, shorter
cycle times, and higher quality. Indeed, many
of the pollution prevention success stories
occurred at facilities which were really pursu-
ing these goals. One of the strengths of the
DuPont process improvement methodology is
that it recognizes "visioning" as a discrete and
ongoing activity that underlies the entire
effort. At a high level, business teams create a
vision of a nimble, flexible organization able
to quickly meet new competitive challenges.
At the facility level, people create a vision of a
world-class process mat is appropriate for
their circumstances and their role within the
high-level vision.
The ideal pollution prevention program would
combine the commitment enjoyed by the
DuPont waste minimization methodology with
the visioning that is a part of the process im-
provement methodology.-And it would be
simple to allow facilities to achieve quick
successes. The key determinants of success for
any pollution prevention program is organiza-
tion-wide commitment, vision, and visible
success. If these ingredients are present, it
almost doesn't matter which prescriptive
methodology an organization adopts.
Methodology Upgrade
An upgraded methodology would begin by
identifying the building blocks upon which a
successful pollution prevention program might
be based. These are depicted in Figure 4-5. At
the base of the pyramid are the four "stake-
holders" in pollution prevention: community,
employees, stockholders, and customers. All
have a role to play in the methodology.
The commitment to pollution prevention, in
which policies and goals are articulated, is
built upon interactions with the four entities at
the base of the pyramid.
With the commitment in place, a vision can be
created to provide a road map for meeting the
goals. A vision depicts a future-state process or
organization that meets the pollution preven-
tion goals, and is accompanied by a general,
evolutionary plan for achieving the vision.
SECTION 4: Methodology Critique
Page 119
-------
IMPLEMENTATION
'Feedback to stakeholders^
ASSESSMENT
Options for achieving the vision
VISION
Guides the pollution prevention effort
COMMITMENT
"Cascading" commitment throughout organization
STAKEHOLDERS
Community, Employees, Stockholders, Customers
Figure 4-5. Building Blocks of a Successful Pollution Prevention Program
With the vision in place, an analysis of the
organization or facility can be performed. The
vision influences the option generation activ-
ity, and helps to resolve ambiguities about the
relative merits of waste reduction options. The
extent to which an option advances the facility
toward the future state becomes a criterion by
which the option is evaluated.
The results of implementations cycle back to
the interaction with the stakeholders. Through
this interaction, the goals and the vision are
upgraded to achieve additional waste reduc-
tions. Continual iterations of the methodology
advance an organization toward the state of
"no waste" at the top of the pyramid.
A suggested methodology is presented in
Figure 4-6. One unique feature is that it
requires all of the steps to be performed at all
organizational levels. This concept is illus-
trated in Figure 4-7. Most methodologies
consist of a series of steps, the first few of
which are performed at the highest levels of
the organization, and the last of which are
performed at the line organization. But the
new methodology could prescribe that each
step of the plan be performed at each level of
the organization.
The activities recommended for each step
would consider the limited time and resources
available for pollution prevention. Instead of
prescribing "how-tos", the methodology
would provide a variety of tools from which
local sites can choose. The hope is that waste
reduction opportunities will be identified
quickly, leaving more time for people to
perform the implementations that actually
reduce waste.
Page 120
SECTION 4: Methodology Critique
-------
\f
^~~
CHARTERING
Establish Pollution prevention
program
- Start with commitment &
awareness
- Policy statement
-Goals
Establish team to coordinate
effort
Organize program
\
r
INFORMATION GATHERING
Identify and characterize
waste
Identify sources of waste
Waste tracking system
\
r
VISIONING
Articulate vision of future-
state organization/process
Establish targets & goals
- Divide targets into "do now"
& "do later
Write program plan
Build consensus for vision
,
-
ANALYSIS
Define, prioritize, and select
pollution prevention options
l
r
IMPLEMENTATION
Implement the pollution
prevention option
}
AUDITING
Use tracking s
distinguish wa
from other typi
Provide mana
summaries ag
Communicate
stakeholders
r
ystem to
ste reductions
as of projects
s
gement
ainst goals
progress to
A Common Plan for All
An upgraded methodology could have people
at all levels of the organization working to the
same plan. At the corporate level, a company
commits to a pollution prevention program
and creates a vision to depict a future-state
corporation that meets the pollution preven-
tion goals. During the analysis phase, options
to advance the company toward the vision are
generated. Such options might include tools
that help sites establish their pollution preven-
tion goals, recognition programs for environ-
mental excellence, provisions for pollution
prevention training, etc.
The facility level is where wastes are gener-
ated land where waste reductions will occur.
Chartering at this level involves, among other
things, forming an interdisciplinary pollution
prevention team. In those facilities that have
established a formal process improvement
progiram, that program's core team can double
as the pollution prevention team provided they
are given appropriate training. The facility
team then creates a vision of a future-state
process that makes high-quality products with
a minimum of waste. The options generated
during the assessment phase are evaluated in
part for the extent to which it advances the
facility toward the vision.
The facility level implementations provide the
feedback that the rest of the organization
needs to develop new goals and update then-
visions. Thus, pollution prevention becomes a
perpetual effort to achieve ever greater levels
of environmental excellence.
Figure 4-6. Upgraded Methodology
SECTION 4: Methodology Critique
Page 121
-------
c
onventional Methodology
STEP1
f
STEP 2
I
\
STEPS
'
STEP 4
i
STEPS
1
STEP 6
1
STEP?
^
STEPS
1
STEP 9
Corporate
Level
Site
Level
Facility
Level
r>
>
L
*
H
Upgraded Methodology
| CHARTERING
\
INFORMATION GATHERING
|
VISIONING
^
ANALYSIS
j
IMPLEMENTATION
*
| AUDITING
^^>
\J^
CHARTERING
j
INFORMATION GATHERING
^
VISIONING
{
ANALYSIS
^
IMPLEMENTATION
|
AUDITING
-SJ'^.
\J^
CHARTERING
j
INFORMATION GATHERING
|
VISIONING
J
ANALYSIS
^
IMPLEMENTATION
J
AUDITING
Figure 4-7, Comparison of Conventional and Upgraded Methodologies
Page 122
SECTION 4: Methodology Critique
-------
REFERENCES
1. Freeman H, Harten T, Springer J, Randall P, Curran M A & Stone K. Industrial pollution preven-
tion: a critical review. /. Air Waste Manage. Assoc. (42)5:618-56,1992.
2. Pojasek R B & Call L J. Contrasting approaches to pollution prevention auditing.
Pollution Prevention Review (1)3:225-35,1991.
3. Center for Industrial Services. University of Tennessee. Writing a waste reduction program.
Univ. Tenn., 45 p.
4. Hannan P W. Methodology used to reduce incinerable wastes using source reduction in the chemical
industry. Proceedings: incinerable hazardous waste minimization workshops.
Calif. Dept of Health Services & Assoc. of Bay Area; Govts., 1991. p. 79-83.
5. Texas Water Commission. Pollution prevention assessment manual for Texas businesses.
Austin: Texas Water Commission, 1992.98 p.
6. Rittmeyer R W. Waste minimization part 1: prepare an effective pollution prevention program.
Chemical Engineering Progress, May, 1991. p. 55-62.
7. U.S. Environmental Protection Agency. Facility pollution prevention guide. Washington: EPA, 1992.
8. Chemical Manufacturers Association. Pollution prevention resource manual.
Washington: CMA, 1991.
9. U.S. Environmental Protection Agency. Waste minimization opportunity assessment manual.
Washington: EPA, 1988.
10. LaBar G. Du Pont watching its waste. Occupational Hazards, July 1990.
11. Kraft R L. Incorporate environmental reviews into facility design.
Chemical Engineering Progress, August 1992. p. 46-52.
12. Bailey P E. Life-cycle costing and pollution prevention.
Pollution Prevention Review (1)1:27-39,1991.
13. Baker R D & Warren J L. Management of the product life cycle to promote pollution prevention.
Pollution Prevention Review (1)4:357-67,1991.
14. U.S. Environmental Protection Agency. Pollution prevention benefits manual, volume 1: the manual.
Washington: EPA, 1989.
15. White A L, Becker M & Goldstein J. Total cost assessment: accelerating industrial pollution
prevention through innovative project financial analysis. Boston: Tellus Institute, 1991.
16. Spitzer M A, Pojasek R, Robertaccio F L & Nelson J. Accounting and capital budgeting for pollu-
tion prevention. Proceedings: Engineering Foundation Conference.
San Diego: Engineering Foundation, 1993.
SECTION 4: Methodology Critique
Page 123
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-------
SECTION
Waste Reduction Opportunities
for Organic Chemical Processes
The Chambers Works Waste Minimization
Project examined 15 waste streams from the
DuPont site in Deepwater, New Jersey. Scores
of people with diverse skills and experiences
generated well more than a hundred options
for reducing these streams. Some of the
options were duplicates of each other, gener-
ated by assessment teams working on separate
but similar processes. Some were "blue sky",
futuristic suggestions thrown out at brain-
storming meetings as much to stimulate
thought as to identify immediate reductions.
But nearly all of them were generated by
people who actually work the processes every
day. Taken together, these options represent a
body of practical experience that can benefit
others throughout the chemical processing
industries.
This section compiles those options that are of
general interest to industry, and augments
them with options gleaned from a post-assess-
ment search of the technical literature. They
are grouped by four waste stream types:
1. Solvent Wash Waste
2. Solvent Waste (other than solvent wash
waste)
3. Waste Incurred from Reaction Byproducts
4. Tair Waste
The information in this section is offered to
stimulate thought during the assessment phase
of a waste reduction effort. It is not an exhaus-
tive compilation of possibilities, and its
inclusion here cannot be regarded as an
endorsement of an option's viability in any
particular situation. Your organization should
independently evaluate the suitability of these
or any other options for its own needs and
circumstances.
SECTION 5: Waste Reduction Opportunities for Organic Chemical Processes
Page 125
-------
Solvent Wash Waste
Cleaning of equipment is one of the most
common areas of waste generation. Much
literature exists on the reduction of solvent
wash waste from metal cleaning and
degreasing applications as well as from vari-
ous applications in the paint industry. This
section focuses on the chemical industry's
reduction of solvent wash waste (i.e., vessels
and associated piping requiring clean-out).
However some of the waste minimization
techniques presented in this section can be
applied to other industries (and, in fact, were
derived from literature on other industries'
wash waste reduction techniques).
Three of the fifteen case studies presented in
Section 3 of this report focus on solvent waste
reduction. These are:
Case Study 6: Polymer Vessel Washout
Case Study 12: CAC Process
Case Study 15: Distillation Train
Waste minimization options from the three
case studies were combined with information
from the technical literature. Figure 5-1
presents a fishbone chart of some alternatives
for reducing solvent wash waste. The options
are neither all-inclusive nor applicable to all
situations.
Discussion of Options
The first 10 options are grouped under the
Operating Procedures category. For the most
part, they can be implemented quickly and at
little or no cost.
Clean equipment manually. Manual
cleaning could reduce the amount of
solvent used because:
the manual washing may be more
efficient than an automated wash system
personnel can vary the amount of
solvent needed from wash-to-wash
depending on the condition of the
equipment (cleanliness)
jns\
ilutioiAC
Loosen finished -,
product specifications Vft
=^A
Use anit-sBck coating on equipment walls
Use distillation or other techno-
logy to recover solvent
Use dedicated equipment to
make products
Install better draining
equipment
Clean equipment manually
Drain equipment between campaigns
Pre-wash equipment with detergent/water solull
Flush equipment with product and recycle to processV^i.
Flush with waste solvent from another process v*>
_ iy^
Minimize amount of solvent used to wash equipment
Increase campaign lengthsV-X.
Optimize order of product change-overs
Wash vessels Immediately to avoid solidification^
Replace solvent with non-hazardous wash (e.g., water)
Wiping or brushing system
High-pressure water Jet
Rotating spray head /^
Figure 5-1. Solvent Wash Waste Reduction Options
Page 126
SECTION 5: Waste Reduction Opportunities for Organic Chemical Processes
-------
A variation of this option could involve
personnel entering the equipment and
wiping the product residue off the equip-
ment interior walls with hand held wipers
or spatulas1 which would minimize or
eliminate the necessity of a subsequent
solvent wash. The safety aspects of this
option, particularly the nature and extent
of personnel exposure, should be thor-
oughly reviewed before implementation.
Drain equipment between campaigns.
Better draining would lessen the product
residue on the equipment walls and
thereby minimize or eliminate the solvent
used in a subsequent wash. This could be
accomplished by simply increasing the
time between the end of a production
batch or cycle and the start of the washout
procedure. This option was adopted in
Case Studies 12 and 15. In Case Study 15,
to facilitate draining of a packed distilla-
tion column, a slight positive pressure is
maintained (with nitrogen) on the column
for 24 to 48 hours. The residual product is
thereby "swept" off the packing, and
accumulates in the bottom of the column.
Prewash equipment with a detergent/water
solution. This option has to do with per-
forming a prewash on the contaminated
equipment using a soap and water solu-
tion2. This step would minimize or elimi-
nate the solvent needed in a subsequent
wash step.
Flush equipment with product and recycle
to process. This option applies to situa-
tions where two or more different products
are produced in the same equipment. A
small reserve of the next product to be
campaigned can be withheld from a
previous similar campaign and then be
used as a flush for the equipment. The
contaminated product (which had been
used as flush) can then be reworked or
reprocessed to make it acceptable for use.
This option was adopted in Case Study 12.
Flush with waste solvent from another
process. Instead of using a fresh solvent, a
waste solvent from another process on the
plant can be used for the equipment flush.
This procedure would reduce the plant's
total waste load.
Minimize amount of solvent used to wash
equipment. This option was adopted in
Case Study 15. Many times, a process will
be started up and a procedure written
calling for a certain volume of solvent
flush to clean out the equipment set be-
tween batches or cycles. The procedure
often times goes unchallenged. Often, the
amount of solvent used for the flush can be
minimized1 with no change in the resulting
cleanliness of the equipment.
Increase campaign lengths1. By careful
scheduling and planning, product cam-
paign lengths can be increased thereby
reducing the number of equipment wash-
outs needed.
Optimize order of product changeovers1.
Many times, specifications for products
produced in the same equipment are
different. One set of specifications may be
more stringent than another. Through
careful planning and inventory control,
product changeovers can be made from
products with tighter specs to those with
looser specs.
Wash vessels immediately to avoid solidifi-
cation1. Often times, product residue will
dry and thicken or harden in the equipment
between solvent washouts. By immedi-
ately washing out vessels between cam-
paigns, the residue is more easily removed
when it does not have the opportunity to
set on equipment interior walls.
SECTION 5: Waste Reduction Opportunities for Organic Chemical Processes
Page 127
-------
Replace solvent with non-hazardous wash.
Solvent wash can be replaced by a less
hazardous or non-hazardous (i.e., water)
flush material. Another variation of this
option would be to replace the solvent
with a less volatile solvent thus reducing
fugitive emissions. The solvent could then
be recovered and recycled.
The next group of options belong to the
Unique Technology category. These usually
involve capital investment. The costs incurred
during waste reduction associated with the
new technology must result in a sizable return
on investment to justify the capital cost.
High-pressure water jet. This option was
adopted in Case Study 6. The new clean-
ing system involves a special nozzle and
lance assembly which is connected to a
high-pressure water source and inserted
through a flange at the vessel bottom. All
solvent waste is eliminated. Product
removed from the equipment walls can be
separated from the water and recovered for
further waste reduction. Even in those
processes where water cannot be intro-
duced into the equipment, an alternative
exists. Vessels can be cleaned with solid
carbon dioxide (dry ice) particles sus-
pended in a nitrogen gas carrier. The solid
CO2 cleans in a manner similar to that of
sand blasting, but evaporates, leaving only
the material removed from the equipment.
Rotating spray head3. A rotating spray
head can be used to clean vessel interiors.
This system would minimize solvent use
by allowing solvent to contact all contami-
nated surfaces in an efficient manner.
Pipe-cleaning "pigs". These are pipe
cleaning mechanisms made of any number
of materials. They are actuated by high-
pressure water, product, or air. Pigs re-
move residual buildup on pipe walls
thereby minimizing or eliminating subse-
quent washing.
Wiping or brushing system. A system of
wipers or brushes that would clean off
residual product. (Perhaps analogous to a
car wash except on interior vessel walls as
opposed to the outside of a car.) This
system would be appropriate for situations
where the product hardens on the vessel
walls. The wipers or brushes would then
dislodge the material which would subse-
quently fall to the vessel bottom. This
would not be appropriate for viscous
material that would adhere to the brushes
or wipers then have to be washed off; this
could create as much, if riot more waste,
than the original situation.
Any options falling under the Product Specifi-
cation category would usually not involve
capital expenditures. Investigation, perhaps
including R&D efforts, would probably have
to take place before any product spec changes
could be incorporated so that finished product
quality would not be adversely affected.
Loosen finished product specifications.
Loosening finished product specs would
allow higher levels of impurities or cross-
contamination of products which would
allow reduction or elimination of solvent
wash. This option was adopted for Case
Study 15.
The final five options fall under the Equip-
ment/Process Modification category. Options
in this category usually involve significant
capital costs. Options for implementation are
chosen such that the resulting waste reduc-
tions are large enough to support the large
capital expenditures.
Use anti-stick coating on equipment walls.
Application of an anti-stick agent, such as
Teflonฎ, to equipment interior walls would
Page 128
SECTION 5: Waste Reduction Opportunities for Organic Chemical Processes
-------
enable easy removal of leftover residue.
The subsequent flush could then be ac-
complished with less solvent resulting in
less waste.
Use distillation or other technology to
recover solvent^. Recycle and reuse of
solvent can reduce waste significantly.
Depending on the situation, there are
several processes that can be considered
for recovery. A non-inclusive list includes
crystallization, filtration, membrane
separation, distillation, and wiped-film
evaporation. Ultrasonics, which involves
an extremely high level of mixing, should
also be considered. For small volumes,
sending the solvent to a commercial
recovery operation may be considered.
The purchase or rental of a mobile solvent
recovery process5 may also be cost-
effective.
Initially, Case Study 6 selected the use of
distillation to recover solvent wash waste.
But as source reduction option was subse-
quently investigated, and proved to be a
better alternative.
Use dedicated equipment to make prod-
ucts. This option eliminates the necessity
of having to wash out equipment between
production campaigns thus eliminating the
flush solvent waste stream. Case Study 15
adopted this option, installing second
pipeline for dedicated transfer of raw
material to the distillation process.
Install better draining equipment. During
the design of a new process, flush solvent
waste can be significantly minimized by
designing equipment to facilitate better
draining. This would include vessels that
contain sloping interior bottoms and
piping arrangements with valved low
points or valves that drain back into the
main vessels. In Case Study 12, drainage
valves were installed at strategic "low
point" locations on the process equipment.
A movable, insulated collection vessel was
designed and built by facility personnel.
After a product campaign, the residue is
drained from each equipment section into
the collection vessel. The collected mate-
rial is then reintroduced into the process
during the product's next campaign.
SECTION 5: Waste Reduction Opportunities for Organic Chemical Processes
Page 129
-------
Solvent Waste (other than solvent wash)
Solvents are commonly used in the chemical
industry as carriers to dissolve and dilute
reactants or products, or as washing agents to
wash out impurities from products. Often, it is
necessary to isolate the finished product from
the solvent at the end of a production cycle or
after a washing cycle. A major source of waste
exists in the use and isolation of the solvent.
Other times, product is sold in solution with a
solvent Many customers are requiring manu-
facturers to look into ways of replacing or.
eliminating the solvents used in this manner.
Five of the case studies examined in Section 3
of this report focused on solvent waste (other
than solvent flush) minimization. These are
listed below:
Case Study 1: Specialty Alcohols
Case Study 2: Organic Salt Process
Case Study 4: Diphenol Ether Process
Case Study 9: CAP Isomers Process
Case Study 11: Specialty Surfactant
Waste minimization options from the five case
studies were combined with information from
the technical literature. Figure 5-2 presents a
fishbone chart of some alternatives for reduc-
ing solvent waste. The options are neither all-
inclusive nor applicable to all situations.
Discussion of Options
The first category of waste minimization
options is chemistry. Any options falling into
this category usually involve significant
technical research before being adopted. Such
areas as safety and product quality have to be
investigated prior to any change.
Replace solvent with a less hazardous
material. This option was adopted in Case
Study 11. In this study, the chlorofluoro-
carbon, which served as a solvent for
dissolving the surfactant product, has been
replaced with water.
Develop new chemistry that minimizes or
eliminates solvent. Waste reductions can
Upgrade equipment to
minimize/eliminate
teaks & emissions V%.
Improve recycle loop
Recover solvent and
recycle to process
Replace solvent with less
hazardous material
\
Develop new chemistry that
minimizes or eliminates solvent
Use different solvent
Use product as solvent
Develop technology that minimizes /ffr
or eliminates solvent use or losses
Use or new technology to remove &
recycle solvent to minimize losses
7
*W Improve maintenance
procedures to detect & reduce
fugitive emissions
Establish an equipment
leak testing program
Use |ess ^
Figure 5-2. Solvent Waste Reduction Options
Page 130
SECTION 5: Waste Reduction Opportunities for Organic Chemical Processes
-------
result from the development of new
chemistry that eliminates the necessity of
using solvent as a carrier for solids, or
eliminates the need for a solvent wash.
This type of "breakthrough" option should
always be sought and considered in a
waste minimization program.
Use different solvent. Use of a less hazard-
ous or non-hazardous solvent or use of a
similarly hazardous solvent that would
require less volume would all be waste
minimizing options: A typical example
would be the use of a high boiling solvent.
VOC would be reduced and the company
would save on solvent costs.
Use product as solvent. This option is
currently under investigation for Case
Study 9. In that process a stabilizer used to
prevent dechlorination is slurried in a
solvent and then added to the distillation
column reboiler. The solvent finally leaves
the process as a significant portion of a tar
waste stream. The waste minimization
strategy is to use the product as the carrier
component of the stabilizer. The product
would then be removed from the product
stream during the distillation. This option
would eliminate the solvent.
The next three options fall under the Operat-
ing Procedures category. These options usu-
ally do not require any capital investment and
can be implemented quickly.
Use less solvent. Many times processes are
started up and run unchallenged under a
certain set of operating procedures. The
procedures may have been developed in a
laboratory and sized up for production
scale. Investigation may reveal that lessen-
ing the amount of solvent used in the
process may not affect the process or
product. Such a reduction would probably
result in a corresponding waste reduction.
In Case Study 4 this option was explored
but not adopted due to safety concerns.
Improve maintenance procedures to detect
and reduce fugitive emissions. Fugitive
emissions (emissions from valves, gaskets,
pump seals, fittings, etc., in a process) can
be significant if gone undetected. Routine
testing for fugitives coupled with an action
plan for reduction or elimination of the
emission can reduce the air emission waste
stream from these sources significantly.
Establish leak testing program. This
option refers to equipment and piping
leaks. Establishment of a routine leak
detection program coupled with an action
plan for reduction or elimination of the
leak would result in significant waste
reductions.
Options from the Product Specification cat-
egory would usually not involve capital
expenditures. They do require investigation to
ensure that product quality is not adversely
affected. This category contains one option.
Eliminate solvent. Elimination of solvent,
either the solvent wash or the solvent
added to the product (whatever is appli-
cable), would completely eliminate the
associated wastes. Case Study 1 adopted
l:his waste minimization option. This study
featured a process that included a solvent
wash for removing impurities, but continu-
ous improvements in the as-made purity of
the product eliminated the need for the
solvent wash.
Options from the Unique Technology category
usually involve capital investment, and require
a sizable return on investment to justify the
cost. This category contains two options.
SECTION 5: Waste Reduction Opportunities for Organic Chemical Processes
Page 131
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Develop technology that minimizes or
eliminates solvent use or losses. Wastes
can be minimized or eliminated with the
development of new technology.
Use new technology to remove and recycle
solvent to minimize losses. Some new
technologies to explore might include
extraction, wiped-film evaporation, and
membrane separation.
The final three options fall under the Equip-
ment/Process Modification category. Options
in this category typically involve significant
capital expenditures. Options for implementa-
tion are chosen such that the resulting waste
reductions are large enough to support the
large capital expenditures.
Upgrade equipment to minimize or elimi-
nate leaks and emissions. Upgrading could
require significant replacement of old
equipment or merely repair of existing
equipment.
For example, steam jets for dropping
pressure in distillation columns could be
replaced with mechanical vacuum sys-
tems, such as liquid-ring vacuum pumps.
Another example would be the repair of
leaky or faulty equipment, pipes, and
valves.
Improve recycle loop. This option refers to
processes that already employ a solvent
recovery/recycling system. Improvement
could include installing larger or higher
tech equipment or simply making the
current system more reliable or more
efficient. In Case Study 2, this option was
adopted. Startup solvent wastes are gener-
ated from a solvent recovery distillation
column during startup before the column
reaches its operating temperature and
pressure. These wastes will be reduced by
channeling the startup wastes to a holding
tank until the column has reached its
operating temperature and pressure. The
startup wastes will then be reintroduced to
the system after the column has attained
steady-state conditions.
Recover solvent and recycle to process.
This option calls for waste reduction by
the installation of a recovery/recycling
process such as distillation, separation,
filtration, crystallization,. For a small
operation that cannot justify the costs of
installing such a process, a mobile solvent
recovery process5 may be a viable option.
Page 132
'SECTION 5: Waste Reduction Opportunities for Organic Chemical Processes
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Waste from Reaction Byproducts
Most processes that involve chemical reac-
tions also involve side reactions which pro-
duce byproducts. The byproducts end up as
waste downstream. The costs associated with
the byproducts consist not only of the increas-
ing disposal costs, but also the cost of raw
materials and product yield. Many times,
inexpensive changes can be made to decrease
byproduct formation. However, when these
are exhausted some more detailed, expensive
changes can be implemented with high
returns.
Six of the case studies in Section 3 of this-
report dealt with reduction of byproducts.
These are listed below:
Case Study 1: Specialty Alcohols
Case Study 2: Organic Salt Process
Case Study 3: Nitroaromatics
Case Study 4: Diphenol Ether Process
Case Study 8: Monomer Production
Case Study 14: SAC Process
\V>
Sell by-products \~-bf Improve quality ol raw materials
Optimize reactant ratio
Provide mores accurate measure
Went of raw material purity
Add or optimize catalyst
Document operating parameters
Document operating &
maintenance procedures
Redesign reactor /
Optimize agitation
Optimize residence time
\YCL
Optimize reaction kinetics \%
Upgrade or introduce preventive^ <^
maintenance schedule \^*
Improve operator awareness\
Change reactant addition
mechanism
Implement new process
- ~
Modify reactor cooling/heating
mechanism
Convert to continuous process
-
Provide online analysis
Upgrade process controls
/ "^
Implement routine calibration^^
Figure 5-3. Reaction Byproducts Waste Reduction Options
SECTION 5: Waste Reduction Opportunities for Organic ChemicalProcesses
Page 133
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Waste minimization options from the six case
studies were combined with information from
technical literature. Figure 5-3 presents a
fishbone chart of some alternatives for reduc-
ing byproduct formation. The options are
neither all-inclusive, nor applicable to all
situations.
Discussion of Options
The first category of options is Operating
Procedures. Any option falling under this
category usually does not require any signifi-
cant capital expenditure. The options can often
be implemented quickly.
Optimize reactant ratio. Optimization of
the reactant ratio can reduce the excess
constituents that may be involved in side,
byproduct forming reactions. This option
will also increase production yield. This
technique was adopted in Case Study 2.
Provide more accurate measurement of
raw material purity. This can be accom-
plished by either providing an upgraded
measurement device, or by changing the
measurement technique. By knowing the
accurate raw material purity, the reactants
can be added in the appropriate amounts
thus reducing excesses and under-addi-
tions. This in turn reduces constituents
available for side reactions and byproduct
formation. This option will also increase
production yield. Although explored in
Case Study 4, this option was not adopted
because in this particular situation,
byproducts constituted a very small por-
tion of the waste stream.
Optimize operating parameters. Many
times, processes are operated within a
range of operating conditions. Narrowing
this range, or even changing the range
altogether, may help to reduce the
byproducts.
Document operating and maintenance
procedures. Documentation of good work
practices, both operational and mainte-
nance, will ensure that they are performed
correctly. This could include modified or
narrower operating ranges, calibration
methods and cycles, and maintenance
procedures.
Optimize residence time. A common cause
of byproduct formation is a reaction time
that is either too short or too long. In such
cases, increasing or decreasing reactor
residence time may reduce byproducts.
Among the options examined in Case
Study 3 is one that would reduce feed rates
to increase residence time.
Optimize reaction kinetics. Optimizing
reaction kinetics, (temperature and pres-
sure) can reduce byproduct formation.
This option was demonstrated in Case
Study 14.
Upgrade or introduce preventative main-
tenance (PM) schedule. Preventative
maintenance can identify and correct
problem areas that cause waste formation.
This includes process parameter measure-
ment and control equipment and raw
material feed systems, as well as reactor
functionality (agitators, baffle integrity,
etc.).
Improve operator awareness. Making
operators aware of the need to reduce
waste can, in fact, result in waste reduc-
tions. Education as to how waste can be
controlled, (i.e., through better control of
process parameters, good housekeeping
practices, etc.) can lead to significant
waste reductions.
The next three options fall under the Process
Control category. These options are ones
related to the measurement and control of
Page 134
SECTION 5: Waste Reduction Opportunities for Organic Chemical Processes
-------
process parameters, raw material feed rates, or
reaction conversion rates. Byproduct forma-
tion, often times, can be minimized by good
process control.
Provide online analysis. Online analysis
and control of process parameters, raw
material feed rates, or reaction conversion
rates can significantly reduce byproduct
formation and waste. If online analysis and
control is too costly, more frequent opera-
tor checks or manual sampling and control
will also serve to enhance control of the
process and thus reduce waste. Online
analysis was examined in Case Study 3. In
this situation, the reaction mass exiting the
reactor was to be measured for acidity in
order to control raw material feed rate. It
was theorized that this control scheme
would minimize reaction byproduct
formation.
Implement routine calibration. Routine
calibration of process measurement and
control equipment can minimize inaccu-
rate parameter set-points and faulty
control.
Upgrade process controls. Upgrades of
process parameter measurement and
control equipment to ensure more accurate
control within perhaps a narrower range,
can help to reduce process conditions that
contribute to byproduct formation. This
option was selected for Case Study 8. In
this case,,the upgraded control system will
be costly, but is expected to reduce waste
generation significantly as well as increase
product yield. These combined factors
justify the high capital cost.
The next category of options is chemistry.
Options falling into this category generally
involve a certain amount of R&D work not
only to come up with the change, but also to
ensure safety and product quality.
Improve quality of raw materials. Provid-
ing high-quality raw materials with mini-
mum impurities can reduce waste. This
option could entail working with vendors
to provide higher quality materials or
providing some online means of ensuring
optimal raw material properties. For
example, in Case Study 14, an online pH
meter was installed to ensure that the pH
of the incoming raw material is at an
optimal level. Process adjustments are
made to correspond to any deviations.
Add or optimize catalyst. The addition of a
catalyst, or optimization of the amount or
type of catalyst, may minimize side reac-
tions and improve reaction conversion.
Changes in the chemical makeup of a
catalyst, the method by which it is pre-
piared, or its physical characteristics (size,
shape, porosity, etc.) can substantially
improve catalyst life and effectiveness.6
The following four options fall under the
Equipment category. Options under this
category usually involve significant capital
expenditures. Options for implementation are
usually chosen so that the resulting waste
reductions are large enough to support the
large capital expenditures.
Redesign reactor. Reactor design plays an
important role in whether or not byproduct
formation is a problem. Reactors should be
designed so that "dead spots" are avoided,
there is good heat transfer to the reaction
mass, and there is adequate residence time.
Reactor size and shape, agitation device,
baffles, a plug-flow versus continuous
stirred reactor, etc., all have an effect on
the efficiency of the reaction and, thereby,
the formation of byproducts. This option
was considered in Case Study 3 but was
deemed to be too costly.
SECTION 5: Waste Reduction Opportunities for Organic Chemical Processes
Page 135
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Optimize agitation. Increasing agitation or
changing agitation mechanisms many times
results in better contact of the reactants,
resulting in a more efficient reaction with
less byproduct formation. Such modifica-
tions to the reactor as adding or improving
baffles, installing a higher-r.p.m. motor on
the agitator(s), or using a different mixer
blade or multiple impellers can improve
mixing. Some examples of various mixing
mechanisms include impellers, jet mixers,
and mixing pipe tees, as well as the utiliza-
tion of the impeller of a pump to mix.
Improvement of reactor agitation was
chosen as a top option in Case Study 3.
Change reactant addition mechanism.
Improving the way in which reactants are
added in a reaction process is another way
in which byproduct formation can be
inhibited. This usually means adding the
reactant or reactants in a way that promotes
better contact of all the reaction compo-
nents. Traditional feed methods can be
replaced with spargers or other distribution
systems. Adding a compound to a pump
impeller containing the other reaction
compounds or adding a reactant into a pipe
mixing tee should also be considered to
promote better distribution.
Modify reactor cooling/heating mecha-
nism. Modification of the mechanism for
cooling or heating a reactor can also limit
byproduct formation and increase product
yield. Avoidance of hot or cold spots in the
reactor should be considered in making the
choice of mechanisms. Heat-up and/or cool
down times should also be considered.
Convert to continuous process. The
startups and shutdowns associated with
batch processes are a common source of
wastes and byproduct formation. Convert-
ing a process from batch to continuous
mode would reduce these wastes. This
option may require modifications to piping
and equipment.
Options in the Product Specification category
do not require capital expenditure, although.
development and marketing efforts are usually
necessary. Both of the following options
appear in several of the case studies in
Section 3.
Sell byproducts. It's worth considering
whether a market can be identified for a
byproduct.
Sell product as is. Loosening product
specifications, if accepted by the customer,
could allow the product to be sold without
the prior removal of byproducts thus
eliminating the associated waste. Some-
times, however, this could simply move
the waste problem from one area to an-
other. The entire process and product loop
requires examination prior to adoption of
this option.
Waste minimization alternatives in the Unique
Technology category are long-term projects
that require capital investment. The savings
associated with the resulting waste reduction
would, of course, have to be large enough to
justify the capital cost.
Implement new chemistry. An existing
process may involve chemistry that can be
significantly upgraded or changed due to
newer findings and technology. The new
chemistry could result in significant waste
reductions and should be considered.
Implement new process. An existing
process that was installed before waste
minimization was considered could be
replaced with a newer, environmentally
friendly process. One such example is the
use of ultrasound techniques that enable a
reaction to proceed at lower temperatures,
thus reducing tar and/or byproduct forma-
tion. Another example is a laser system
that enables reactions to proceed at lower
temperatures because selection of the
proper frequency enables activation of the
specific chemical bond of interest7.
Page 136
SECTION 5: Waste Reduction Opportunities for Organic Chemical Processes
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Tar Waste
Many distillation processes build up tar waste
in the column bottoms. The distillation pro-
cess is used to purify components in a crude
product stream which was produced in an
upstream reaction process. Typical analyses of
tar streams vary drastically from process to
process. A starting point for investigating
waste minimization options should be deter-
mining the major components and causes of
the tar waste stream. There are three major
contributions to tar:
1. If byproducts or impurities are present in
the crude product stream from the up-
stream reaction process, they may signifi-
cantly contribute to the tar waste load.
2. Another major component of the tar may
be thermally decomposed or polymerized
, product or raw material. The thermal
decomposition or polymerization may
have occurred in the distillation column's
reboiler because of high-temperatures.
3. Additives such as stabilizers and, inhibitors
that have been added to the distillation
process or to the .upstream process may
also significantly contribute to the waste
load.
After the composition of the waste stream has
been determined, the direction of the option
generation session is more clearly defined.
The previous section, "Reduce Byproduct
Formation" deals with all the options related
to byproduct and impurity reduction. The
options presented below focus mainly on
reduction of tars formed as a result of thermal
decomposition and polymerization as well as
reduction of additives.
Convert to continuous process
Improve tiar purge rate
Upgrade stabilizer addition system
Redesign column
Redesign reboiler
Improve feed distribution
Use different technology for detarring
Insulate column/reboiler \ of.
Preheat column feed
Treat the column bottoms to
further concentrate tars
.
Increase size of vapor line\>>
Reduce reboiler temperature
Automate column con
Reduce pressure in column
Increase distillation time
Optimize handling of tar stream
Add, change, or eliminate stabilizerA
Increase charge s\ze
Increase operator awareness,/ ,>>
Document operating &
maintenance procedures
Figure 5-4. Tar Waste Reduction Options
SECTION 5: Waste Reduction Opportunities for Organic Chemical Processes
Page 137
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Six of the case studies in Section 3 of this
report dealt with reduction of tars. These are
listed below:
Case Study 3: Nitroaromatics
Case Study 5: CAP Purification
Case Study 8: Monomer Production
Case Study 9: CAP Isomers Process
Case Study 10: Wiped-Film Evaporator
Case Study 14: SAC Process
Waste minimization options from the six case
studies mentioned above were combined with
information from the technical literature to
come up with the waste minimization alterna-
tives shown in Figure 5-4. The options are
neither all-inclusive nor applicable to all
situations.
Discussion of Options
The first category of options is Equipment/
Process Modification. Options under this
category usually involve significant capital
expenditures. Options for implementation are
usually chosen because the resulting waste
reductions are large enough to support the
large capital investment.
Convert to continuous process. The
startups and shutdowns associated with
batch processes are a common source of
wastes and byproduct formation. Convert-
ing a process from batch to continuous
mode would reduce these wastes. This
option may require modifications to piping
and equipment;
Improve tar purge rate. Continuous
distillation processes require a means of
removing tar waste from column bottoms.
Optimizing the rate at which tars are
purged may reduce waste. An automatic
purge that controls at the lowest possible
purge rate is probably best. If an automatic
purge is not possible, then there are other
ways to improve a manually controlled or
batch-operated tar purge.- If a batch purge
is used, more frequent purges of smaller
quantities may reduce overall waste.
Some processes that purge continuously
may purge at excessively high rates to
prevent valve-plugging. More frequent
cleaning, or installing a new purge system
(perhaps with anti-stick interior surfaces)
would permit lower purge rates. This
option was chosen as one of the top alter-
natives in Case Study 3. The
nitroaromatics process has difficulty
maintaining low purge rates because at
low flows, the valve and flow-meter
become plugged with tar. To avoid plug-
ging, the process runs at higher flow rates.
Area personnel are now exploring a new
flow-meter and valve that would be sensi-
tive enough to permit lower flow rates
without plugging.
Upgrade stabilizer addition. Many distilla-
tion processes use stabilizers which reduce
the formation of tars as well as minimize
unfavorable side reactions. The stabilizers
not only wind up as large components of
the tar waste stream but also typically
make the waste stream more viscous. The
more viscous the waste stream, the rriore
saleable product the waste stream carries
with it. Upgrade of the stabilizer addition
system would allow for less stabilizer to
be added in the process. Upgrades may
include continuous versus batch addition
of stabilizer (adopted in Case Study 9) or
continuous or more frequent analysis of
the presence of the stabilizer coupled with
automatic addition or enhanced manual
addition of the stabilizer.
Optimization of the point of addition,
column versus reboiler, is another area to
be explored along with method of addi-
Page 138
SECTION 5: Waste Reduction Opportunities for Organic Chemical Processes
-------
tion. One inventive option generated at the
Case Study 5 brainstorming session was to
put the stabilizer in a packed column,
separate from the process distillation
column. Process material would then be
circulated through the packed column
containing the stabilizer.
Stabilizer typically consists of a solid
material slurried in a solvent used as a
carrier. Options for waste reduction also
focus on selective reduction of one of the
two components. Addition of the stabilizer
in powder form eliminates the solvent. Use
of product as the carrier component was
selected as one of the best options in Case
Study 9.
Redesign column. Many of the case studies
evaluated this option in some fashion. A
better design may include changes in size
or packing. The focus is on making the
column more efficient for the particular
process.
Redesign reboiler. Depending on the
process, a better design may include use of
a different heat source in the reboiler to
limit thermal degradation of materials, a
better agitation system to allow more
efficient use of the stabilizer, or a different
reboiler design altogether (i.e., smaller,
larger, different shape). Case Study 5
looked at two options focusing on redesign
of the reboiler: 1) installation of spargers
in the still to circulate the stabilizer, and 2)
installation of an external heat source to
replace the current heating coils.
Improve feed distribution. The effective-
ness of feed distributors (particularly in
packed columns) needs to be analyzed to
be sure that distribution anomalies are not
lowering overall column efficiency.6
Insulate column and/or reboiler. Good
insulation is necessary to prevent heat
losses. Poor insulation requires higher
reboiler temperatures and also allows
column conditions to fluctuate with
weather conditions6.
& Preheat column feed. Preheating the feed
should improve column efficiency. Sup-
plying heat in the feed requires lower
temperatures than supplying the same heat
to the reboiler, and it reduces reboiler load.
Often, the feed is preheated by cross-
exchange with other process streams6.
Increase size of vapor line. In low pressure
or vacuum columns, pressure drop is
especially critical; installing a large vapor
line reduces pressure drop and decreases
the reboiler temperature6.
Reduce reboiler temperature. Several
techniques could be used to reduce
reboiler temperature such as de-superheat-
ing steam, using lower pressure steam, and
using an intermediate heat transfer fluid.
Automate Column Control. For a given
distillation process, there is one set of
operating conditions that is "optimum" at
any given time. Automated control sys-
tems are capable of responding to process
fluctuations and product changes swiftly
and smoothly, minimizing waste produc-
tion.
The next category of options is Operating
Procedures. Typically the options in this
category can be done in a relatively short
amount of time for little or no capital cost.
Reduce pressure in column. Reduction of
the pressure in a column allows the distil-
lation to be run at a lower temperature.
This option was evaluated in Case
Study 3.
SECTION 5: Waste Reduction Opportunities for Organic Chemical Processes
Page 139
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Increase distillation time. This option
would be considered for a batch process
where extending the distillation time
would allow more product to be extracted
from the tar waste. This option was ex-
plored in Case Study 8. It was not chosen
because the more concentrated tars at the
bottom of the reactor would become too
thick to remove easily. A way of easily
removing the thick tars would have to be
implemented along with this option.
Increase charge size or campaign size. Tar
waste streams usually carry with them a
certain amount of product. Increase in
charge size (batch size) could possibly
reduce the tar waste stream if the tars are
removed from the still bottom after every
charge. Also, in the case of a campaign
where the tars are removed at the end of a
campaign, increasing the charges per
campaign can lessen the number of tar
clean-outs per year thus resulting in less
tar waste. This option was explored in
Case Study 5.
Increase operator awareness. Making
operators aware of the need to reduce
waste can, in fact, result in waste reduc-
tions. Education on how waste can be
controlled can lead to significant waste
reductions.
Document operating and maintenance
procedures5. Documentation of good
operating practices, both operational and
maintenance, will ensure that they are
performed correctly. This could include
modified or narrower operating ranges,
calibration methods and cycles, and
maintenance procedures.
The next two options fall under Unique
Technology. Options in this category usually
involve a significant amount of capital invest-
ment and R&D effort. Most of the case studies
examined in this report looked at some sort of
new technology for minimizing the waste.
Use different technology for detarring.
Some other means of purification of a
crude product stream may reduce the tar
formation. The types of technology may
include crystallization, membrane separa-
tion, extraction, filtration, or the use of a
wiped-film evaporator.
Treat the column bottoms to further
concentrate tars. Treating the tar stream
from the bottom of a distillation for further
removal of product may be a viable op-
tion. In Case Study 10, a wiped-film
evaporator will be installed to further
concentrate the tar waste stream. Other
methods should also be investigated such
as extraction and crystallization.
One option falls under the Chemistry cat-
egory. Options in this categoiy require signifi-
cant R&D research by chemists and engineers
to ensure adequate product quality as well as
process safety.
Add, change, or eliminate stabilizer. This
option focuses on increasing or optimizing
the addition of stabilizer. This could also
mean using a different stabilizer that
requires smaller quantities to provide the
same stabilizing effect. Since the stabilizer
represents such a large portion of the
waste stream, emphasis in this area should
be given. Case Studies 3,9, and 5 focused
on this area.
Any options falling under the Product Specifi-
cation category would usually not involve
capital expenditures. Investigation, perhaps
including R&D efforts, would probably have
to take place before any product spec changes
could be incorporated so that finished product
quality would not be adversely affected.
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SECTION 5: Waste Reduction Opportunities for Organic Chemical Processes
-------
Sell tars as product. Selling tars to be
made into a useful product is a way of
eliminating the stream as a waste. This
option may be difficult to implement,
especially if the tars contain a hazardous
component.
The Tars Handling category contains one
option.
Optimize handling of tar waste stream. In
several of the processes used in the case
studies, the tars from the bottoms of the
distillation column had to be thinned with
a solvent to make them pumpable. Often
times this solvent is product from the
process. The added solvent adds to the
volume of the waste stream. In Case Study
14, tars were pumped from the process
equipment into a tank truck for transporta-
tion to the on-site incinerator. In the past,
trucks were dispatched to the incinerator
only when full. During the several days it
took to fill the truck, the tar waste solidi-
fied which would make it difficult to
handle at the incinerator. Hot product was
therefore added just prior to the discharge
of the truck to thin the waste. To rectify
this situation, the area is now discharging
die trucks on a daily basis. The material in
the trucks stays warm enough to enable
adequate handling at the incinerator.
In Case Study 9, low boiler product was
added to a tar waste collection tank as a
solvent to thin the tars. Two options were
explored to minimize the need for addition
of this solvent: 1) Use of an already
existing waste stream from another pro-
cess to thin the tars. 2) The addition of
acid to the tar waste stream to make it
water soluble. The stream could then be
mixed with water and disposed of at the
wastewater treatment plant.
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Mid-Atlantic Industrial Waste Conference (Kugelman I J, ed.) Technomic: Lancaster (PA), 1985.
p. 334-42.
3. Jorgensen B. Alternative Technologies in Chemical Processes. Proceedings: Incinerable Hazardous
Waste Minimization Workshops Calif. Dept. of Health Services & Assoc. of Bay Area Govts., 1991.
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4. Chemical Manufacturers Association. Pollution Prevention Resource Manual
Washington: CMA, 1991.
5. Keener T C. The Application of a Mobile Solvent Recovery Process to Minimize Hazardous Waste.
Hazardous and Industrial Solid Waste Minimization Practices, ASTM STP1043
Conway R A, Frick J H, Warners D J, Wiles C C, Duckett E J, eds. Philadelphia: ASTM, 1989.
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ซU.S. GOVERNMENT PRINTING OFFICEU993-550-001/80312
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