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OCR for page 105
OCR for page 106
_'{R, SOIL, AND WATER are vital to life on
_lthis planet. We must protect these re-
- _ sources and use them wisely our sur-
vival as a species depends on them. Despite
recent impressive strides in improving the en-
vironment, evidence is overwhelming that more
effective action must be taken to address such
critical issues as acid rain, hazardous waste
disposal, hazardous waste landfills, and ground-
water contamination. It is also vital that we
assess realistically the potential health and en-
vironmental impacts of emerging chemical prod-
ucts and technologies. The problems are clearly
complex and demand a broad array of new
research initiatives.
Technological activities of which chemical
manufacture and processing are key parts-
begin with the extraction of raw materials from
the environment. They then proceed through
numerous steps-processing, storage, handling,
(a
Extraction
\\
/ .~;
Dispose/
......
I'
~N
FRONTIERS IN CHE^~AL E.~llVEERIA7G
transportation, and use and finally end with
the ultimate return of processed materials or
their residues to the environment (Figure 7.1~.
The resulting redistribution of chemicals within
the environment may have adverse impacts.
Harmful compounds of certain elements (e.g.,
nitrogen, sulfur, halogens) may be widely mo-
bilized. Other elements may be converted from
innocuous forms (e.g., mercuric sulfide in cin-
nabar) to highly toxic forms (e.g., methyl mer-
cury). Chemical engineers are involved in all
aspects of chemical manufacture and process-
ing; therefore, it should be their responsibility
to safely manage chemicals in the environment.
Environmental and safety concerns will be cru-
cial challenges to the chemical engineers of the
future. No other group is better trained or more
centrally positioned in the industrial world to
be the cradle-to-grave guardian of chemicals.
Our approach to environmental and safety
Production
/ ENVIRONMENTAL TRANSPORT AND TRANSFORMATION ~
EXPOSURE AND EFFECTS /
,
,~' Storage
~ _~
Transportation
FIGURE 7.1 Life cycle of chemicals in the environment.
OCR for page 107
ENVIRONMENTAL PROTECTION, PROCESS SAFETY, H^474~LS WASTES
MANAGEMENT DECISIONS
· Introduction of new chemicals or
products into the environment
· Introduction or mod fication of
species in the environment
· Technology Utilization (Existing
or new methods)
· Changes in resource utilization
(urban development, fuels, etc)
1
RISK ASSESSMENT AND MANAGEMENT
· Determination of risk to susceptible
populations
· Identification of mitigation measures
1 , 1
I l
1
EFFECTS ON HEALTH AND WELFARE
· Changes in target organs and the
associated health effects
· Changes in the physical environment
(materials, visibility, etc)
RESPONSE OF ECOSYSTEMS
· Physical Changes
-Nutrient and energy flows
-Physical structure of system
-Transport and Transformation
· Biological Changes
-Change in population size
-Mod fications to interactions
-Indirect effects on species
diversity
EXPOSURE ASSESSMENT
· Exposure of human population
· Exposure of animals and plants
of concern to humans
FIGURE 7.2 The effects of human activities on the environment.
problems must change from reactive to proac-
tive; in other words, instead of responding to
crisis and public pressures, we must anticipate
and prevent problems. This will require an
understanding of the detailed chemistry and
physics of processes at the molecular level.
Such basic understanding is crucial if we are to
design plants that are safer and that cause less
pollution, develop better ways to manage and
detoxify hazardous waste, and predict the fate
of chemicals in the environment as well as the
effects of chemicals on humans and ecosystems.
Figure 7.2 diagrams how human activities can
affect environmental quality and human health.
Introduction of new chemical products, adop-
tion of different technologies, or changes in
resource utilization can lead to emissions that
affect the physical, chemical, or biological re-
sponses of the receiving ecosystems. This can
~07
in turn affect human beings and
other resources. A risk assess-
ment of the potential health and
welfare effects of such changes
can indicate whether and to what
extent mitigation measures should
be taken, or original decisions
rethought. Each of the boxes in
the diagram, although greatly
simplified, represents a cluster
of questions that require answers
from environmental research.
IMPACT ON SOCIETY OF
CHEMICALS IN THE
ENVIRONMENT
A number of environmental
issues have received widespread
publicity (Table 7.1), from major
accidents at plants (e.g., Seveso
and Bhopal) to the global and
regional impacts associated with
energy utilization (e.g., carbon
dioxide, acid rain, and photo-
chemical oxidants), the improper
disposal of chemical waste (e.g.,
Love Canal and Times Beach),
and chemicals that have dis-
persed and bioaccumulated af-
fecting wildlife (e.g., PCBs and
DDT) and human health (e.g., cadmium, mer-
cury, and asbestos).
As a consequence, much of the public has
come to believe that most chemicals are haz-
ardous. A recent poll by the Roper Organization
revealed that two out of three American citizens
expect a major chemical disaster, resulting in
thousands of deaths, within the next 50 years.)
The poll also found that a high proportion of
the public lacked confidence that industry would
deal openly with them. A public attitude toward
exposure to chemicals is developing that can
be summed up by the words, "no risk." But,
as a judge recently stated, "In the crowded
conditions of modern life, even the most careful
person cannot avoid creating some risks and
accepting others. What one must not do, and
what I think a careful person tries not to do, is
to create a risk which is substantial."2
OCR for page 108
FRONTIERS I1Y CH~E1~L ENGINEERI.~G
TAR} F. 7.1 Some Well-P~
icize`1 Fnvironmentn1 I.
Global
Regional
Urban
Site-specific
Chlorofluorocarbons and their effect on ozone in the upper
atmosphere
Carbon dioxide and other '~greenhouse" gases (e.g., methane)
and their effect on global temperature
DDT
Polychlorinated biphenyls (PCBs)
Acid rain (NOx, SOx)
Agricultural wastewaters (Kesterson Wildlife Refuge,
Chesapeake Bay)
Airborne lead from automobile exhausts
Carbon monoxide from automobile exhausts
Photochemical oxidants, particularly ozone (Los Angeles)
Sulfur oxides (SOx) and particulate matter (London, Donora)
Dioxins (Seveso, Love Canal, and Times Beach)
Methyl isocyanate (Bhopal)
Methyl mercury (Minamata)
Cadmium (Itai-Itai)
Indoor air (Formaldehyde, asbestos, NO., CO)
What is a substantial risk? How safe is safe
enough? These are questions that trouble the
public, industry, and regulators alike. Scientific
understanding and the available data are inad-
equate to evaluate the true risk to individual
safety, or the true risk of damage to human
health or the environment, from exposure to
most chemicals or to chemical plant or disposal
operations. Yet, legislators and regulators can-
not wait for all the data to come in before they
start to provide the public with the protection
it is demanding. Laws have been passed and
regulations have been developed that require
government approval for production of new
chemicals, design and operation of chemical
plants, workplace exposures, certain product
uses, quantities and concentrations of chemicals
in effluent streams, and disposal of waste and
by-product streams. But because of the uncer-
tainties, some regulations have been written to
protect against the effects of extremely unlikely
worst-case scenarios, resulting in a misalloca-
tion of resources, reduced technical innovation,
and excessive costs. At the same time, other,
less visible hazards that might be the focus of
appropriate regulation have been overlooked.
This situation must be corrected. Society
needs a clean and safe environment. It also
needs to capitalize fully on new developments
in chemistry, biotechnology, and materials sci-
ence, if the United States is to retain techno
logical leadership and international competi-
tiveness in major segments of industry.
Some of the economic and social costs related
to major environmental issues are discussed in
the following sections.
Chemical Industry Safety
The U.S. chemical and petrochemical indus-
try safety record is generally good. The National
Safety Council's 1985 data show that the chem-
ical industry worker is only one-fourth as likely
to have a fatal on-thejob accident as the average
U.S. employees The Bureau of Labor Statistics
indicates that the 1984 chemical industry rate
for lost work days resulting from occupational
injury was 2.4 per 200,000 man-hours, compared
to 4.7 for manufacturing as a whole and 3.7 for
all private sector employments Over the past
decade, annual fatalities from hazardous chem-
ical accidents have numbered around 40, while
highway fatalities have numbered around 40,000.3
Nevertheless, accidents and unintended
chemical releases pose serious financial risks to
the chemical and petrochemical industry. In
1984 there were five major accidents in the
hydrocarbon-chemical industries, totaling an
estimated loss of $268 million.5 Hundreds of
lesser accidents occur yearly. The total annual
cost to the industry of accidents and unintended
chemical releases is difficult to quantify. It
includes significant costs owing to interruption
OCR for page 109
ENVIRONMENTAL PROTECTIOA7, PROCESS SAFETY, HA718~US WASTES
~E:~-~ ~
FIGURE 7.3 In 1984, 14 years after the passage of the Clean Air Act,
significant areas of the United States were still in violation of National Ambient
Air Quality Standards (NAAQS) for ozone. Courtesy, Environmental Protec-
tion Agency.
of business as well as major liability and liti-
gation costs associated with injuries, deaths,
property damage, and insurance premiums. It
also includes losses of product and feedstock
that are direct profit losses for the manufacturer.
One estimate is that U.S. industry spent $7.7
billion in 1985 for protecting worker safety and
health;6 the total annual cost of accidents and
unintended chemical releases by the U.S. chem-
ical and petrochemical industries is surely many
billions of dollars.
Costs associated with increased government
regulation are also difficult to quantify. Public
concern in response to chemical release acci-
dents affects regulators and community policy
groups. It is evident that the U.S. chemical
industry is already spending large amounts of
money to avoid accidents and to deal with their
consequences when they occur; these costs are
borne in part by the consumers. Continued
expenditures are likely as industry strives to
achieve an "acceptable" level of public safety
throughout all chemical industry operations.
Combustion of Fuels for Power Generation
and Transportation
The burning of fuel for power generation and
transportation presents some of the most long
standing and important problems
in environmental protection.
Fossil fuels are used in such
magnitude that emissions from
combustion sources have a major
impact on urban, regional, and
global air quality. Combustion-
generated pollutants are derived
from contaminants in the fuel
such as sulfur, nitrogen, and in-
organic compounds, from incom-
plete combustion of the fuel, and
from the high-temperature reac-
tion of nitrogen with oxygen in
the air heated by combustion
processes. These pollutants are
emitted both in gaseous form
(e.g., the oxides of nitrogen-the
sum of NO and NO2, denoted as
NOX-sulfur dioxide, and un-
burned hydrocarbons) and in
particulate form (e.g., fly ash and soot). The
1970 Clean Air Act and its amendments are
directed at reducing combustion-generated
emissions through the establishment of National
Ambient Air Quality Standards (NAAQS) for
oxides of sulfur and nitrogen, carbon monoxide,
particulate matter, lead, and ozone. While sub-
stantial reductions in urban levels of carbon
monoxide, sulfur oxides, and particulate matter
have been achieved over the past 15 years,
ozone levels, controlled by an intricate chem-
istry involving organic gases and oxides of
nitrogen, have proved to be more resistant to
control (Figure 7.31. Large-scale air quality
problems arising from combustion-generated
emissions, such as acid rain (Figure 7.4), re-
gional hazes, and volatile toxic compounds,
have also assumed prominence and will likely
be the targets of future legislation.
Adding fluidized gas desulfurization to coal-
fired generating plants is estimated to add 15-
25 percent to their total capital costs, or up to
$125 million on a typical 500-megawatt unit.7
Since the cost of reducing emissions by modi-
fying the combustion process is usually an order
of magnitude lower than that of cleaning the
fuel before burning or removing the pollutants
from the exhaust gases, there are significant
challenges to develop clean, fuel-efficient com
OCR for page 110
/
bustion processes as well as to design more
economical processes for fuel cleaning prior to
combustion and for destroying or removing the
residuals from postcombustion gases.
Hazardous Waste Management
The disposal of hazardous waste may well
have become the Achilles' heel of the American
manufacturing industry. More than 300 million
tons of hazardous waste are generated annually
by about 14,000 installations in the United
States. About 14.7 billion gallons of hazardous
waste is disposed of in or on the land each year,
FRONTIERS IN CHEMICAL ENGINEERING
/'/"/ ~ ;~
\"` ·5. - ~`
~ 622-~__:i
~ ~ , ~-;
\510 5'15-/ ~ ~ ~
Nt W? t6.s2 ~,'
~°~
:5.33- ~ ~
f 5.47 ~ \~ e
~.51 / I ~ L _
aim\\!
~ \ ~
~ )
:'-41\
- _
4 87 .~5.67 ~1
·5.g5
`_!
FIGURE 7.4 Annual mean value of pH (acidity) in precipitation, weighted by
the amount of precipitation in the United States and Canada for 1980. The
low pH values seen in the eastern United States and Canada reflects the high
acidity of the rainfall and other precipitation in this region. This geographic
pattern of acid rain correlates with the emission and transport of sulfur dioxide
from coal-burning plants. From U.S./Canada Work Group #2, Atmospheric
Science and Analysis, U.S. Environmental Protection Agency, Washington,
D.C., 1982.
while around 500 million gallons are incinerated.
Of the total quantity of hazardous waste gen-
erated, manufacturers account for 92 percent.
It has been estimated that the chemical industry
alone generates 71 percent of the manufacturer's
total.8 The Congressional Budget Office has
estimated that the 1984 amendments to the
Resource Conservation and Recovery Act could
increase industrial compliance costs from be-
tween $4.2 billion and $5.8 billion in 1983 to
between $8.4 billion and $11.2 billion in 1990,
depending on the level of waste reduction
achieved by industry.9
A variety of methods have been used over
OCR for page 111
E'i\ YIRONI~1~ TAL PROTECTION, PROCESS SAFETY, HAZARDS US 'WA S TES
the past 100 years to bury hazardous waste.
Many of these burial sites now pose a threat to
the health of nearby residents and, more broadly,
to the nation's underground water supply (Fig-
ure 7.5~. For example, recent studies by the
state of California have shown that there are
widespread threats to groundwater in Califor-
nia's Silicon Valley; Santa Clara County leads
the nation in the number of sites on the National
Priority List, most of which are associated with
the electronics industry.~° The U.S. Congress
Office of Technology Assessment has recently
projected that there are 10,000 sites nationwide
that belong on the National Priority List of toxic
waste dumps. ~ ~
In 1980, Congress appropriated $1.6 billion
for a 5-year Superfund program. The original
Superfund legislation viewed cleanup of haz-
ardous waste sites as a relatively short-term
program and anticipated that waste could be
contained for several decades by methods such
as building slurry walls and clay caps to elimi-
nate diffusion of buried waste into subsurface
Well
:~_ Disposal
~ ~ Pond
Deep-Well
Injection
waters. After a few years of pursuing such
methods, it is clear that they do not provide a
solution to the problem of containment of waste
in existing landfills; slurry walls leak and clay
caps crack. It is also becoming increasingly
clear that it will require decades to accomplish
an adequate cleanup of hazardous waste sites
nationwide. Thus, when the Superfund act was
reauthorized in 1986, a significant focus was on
the use of new technologies to decontaminate
soil and groundwater and to provide for long-
term containment of wastes (i.e., through en-
capsulation). The level of expenditure could be
as high as $10 billion over the next 5 years.
When one takes the cost of industrial com-
pliance with RCRA to handle currently gener-
ated wastes and adds the cost of Superfund to
clean up the wastes of the past, it becomes
obvious that there are strong incentives for
technology development in the area of waste
minimization and treatment, and many oppor-
tunities for research and employment for chem
. . .
1ca1 engineers.
Spills
Buried
Wastes
it,' '~4 th2`-'2~ 2 2-2 l"2 2' ~
Well
~ A\
FIGURE 7.5 Past methods of waste disposal threaten water supplies today.
Reprinted from Opportunities in Chemistry, National Academy Press, 1985.
OCR for page 112
DESIGN OF INHERENTLY SAFER AND
LESS POLLUTING PLANTS AND
PROCESSES
Few basic decisions affect hazard potential
or have more of an impact on environment than
the initial choice of technology. Thus, when
designing chemical manufacturing processes, it
is important to select sequences of chemical
reactions that avoid the use of hazardous feed-
stocks and the generation of hazardous chemical
intermediates. It is necessary to find reaction
conditions tolerant of transient excursions in
temperature, pressure, or concentration of
chemicals and to use safe solvents when ex-
tracting reaction products during purification
steps. Finally, it is important to minimize stor-
age and in-process inventories of hazardous
substances. The term "inherently safer plants"
has been used to describe this approach. One
further consideration in the design of a new
process or plant is whether it is going to generate
polluting effluents or hazardous wastes. Good
design should result in waste minimization in a
manufacturing process or plant.
Traditional analyses of process economics
might show that inherently safer and less pol-
luting plants are less efficient in terms of energy
or raw materials usage. Indeed, chemical plants
have been designed in the past principally to
maximize reliability, product quality, and prof-
itability. Such issues as chronic emissions, waste
disposal, and process safety have often been
treated as secondary factors. It has become
clear, however, that these considerations are as
important as the others and must be addressed
during the earliest design stages of the plant.
This is in part due to a more realistic calculation
of the economics of building and operating a
plant. When potential savings from reduced
accident frequency, avoidance of generating
hazardous waste that must be disposed of, and
decreased potential liability are taken into con-
sideration, inherently safer and less polluting
plants may prove to cost less overall to build
and operate. And in any case, if the American
public is not convinced that chemical plants are
designed to be safe and environmentally benign,
then the fact that they operate economically
will be of little consequence to the public's
FRO:~RS IN CAL E1YGINEER~G
decision on whether to allow their construction
and operation.
The chemical reaction pathways chosen for
a manufacturing process profoundly influence
chemical plant safety because they determine
the nature and amounts of all substrates, prod-
ucts, and reagents and implicitly govern the
design and operation of all hardware. The ulti-
mate goal of chemical engineering research to
provide inherently safer plants should be to
elucidate the connection between process path-
ways and plant safety and to translate this
connection into a quantitative form amenable
to engineering design calculations. The array of
chemicals, reactions, processes, and types of
physical equipment used in industry is exceed-
ingly diverse and constantly evolving. To effec-
tively address the need for inherently safer
plants, chemical engineering research must be
focused on fundamental issues that span the
entire range of processing activities, from elu-
cidating detailed reaction mechanisms to un-
derstanding and predicting the gross response
of coupled equipment. The goal of such fun-
damental research would be to develop the tools
needed to define, discern, and assess the safety
issues associated with a given process design
and its alternatives.
New approaches to the design of commercial
chemical syntheses should be pursued. A chem-
ical synthesis tree graph with a high-value prod-
uct at its apex, lower-value raw materials at the
base, and reaction steps as nodes connecting
all branches offers a basis for quantitative as-
sessment of feasible and economic process al-
ternatives. It could also serve to define the
safety and environmental impact of a pathway
and offer a basis for safe designs that produce
minimal wastes. Tree graphs could be particu-
larly helpful in evaluating the process safety
implications of highly selective synthesis routes.
Near the apex of the chemical synthesis tree
graph materials that might be used in chemical
reactions are of highest value. Overall raw
material and energy costs are lowest for those
pathways that use the most selective reactions
to achieve the highest yield of the desired
product. However, these selective reactions
often require the handling and storage of more
reactive, and hence more hazardous, chemicals.
OCR for page 113
E1\'Y~.~TAL 6~.N ~ PROCESS SAFETY HAZARDOUS -A7.~/ BEES
For example, in the synthesis of Carbaryl at
Bhopal, a process that required storage of large
quantities of the reactive intermediate methyl
isocyanate was used, rather than a less flexible
and more expensive straight-through reaction
scheme with a minimal inventory of methyl
isocyanate. Developing the methodology of us-
ing process safety and environmental factors in
synthesis tree graphs could provide a better
framework for future plant design.
Most accidents in chemical plants occur when
the plant is not operating at a steady state for
example, when it is starting up or shutting down
or when a transient of temperature, pressure,
or reactant concentration occurs. Fundamental
research in non-steady-state process control and
the management of process transients is there-
fore warranted. Design methodology poses a
related research issue. It is obviously easier for
the designer of a plant or individual reactor to
envision how the equipment will operate during
the normal production mode than to envision
how it will operate under a host of potential
scenarios that derive from process transients.
The safety of chemical plants and reactors could
CH
H
C2H6
H,O,OH
CH3
C ~20
CHO
CO
/
CH3
O H
| H,O,OH | H
H.O.OH
~ CH3CHO- H. O. OH, CH3CO ~ CH3
C H O. OH , CH3, CHoO, CHO
C2H3
O2,H H
OH
C9H2
-
CO2 ~2CH2 CH2O, CHO
O | OH
1 o
~ CH2CO H ~ CH3
FIGURE 7.6 Mechanism of methane combustion.
~3
be improved if designers had the means to
envision the complete reaction topography and
to assess the consequences of straying from
normal operations. This would involve devel-
oping design tools that would incorporate chem-
ical pathway information more systematically
into classical engineering design methods for
reactors and associated equipment.
COMBUSTION
Many of the environmental issues listed in
Table 7.1 are intimately related to combustion.
Combustion contributes significantly to emis-
sions of pollutants into the environment, with
effects ranging from those pertaining to indoor
air pollution to those affecting global climate.
For this reason, combustion has been singled
out to illustrate the progress that can be made
in resolving environmental issues through a
sustained fundamental research program and to
demonstrate the potential added benefits of
continued in-depth study of the physical and
chemical processes underlying combustion.
Hydrocarbons and Fuel-
Bound Nitrogen
The burning of fuel in a prac-
tical combustion system, such as
a power plant boiler or the cyl-
inder of an internal combustion
engine, is at first glance very
simple: a mixture of hydrocarbon
and air is ignited and burned to
carbon dioxide and water. On
closer examination this burning
turns out to be one of the most
complex processes in all engi-
neering. For example, the com-
bustion of the simplest hydro-
carbon fuel, methane, involves
more than 50 chemical reactions
(Figure 7.61. During the past four
decades, major progress has been
made in developing a mechanis-
tic understanding of the combus-
tion of methane and C-2 hydro-
carbons and their derivatives.
Rate constants of many individ
OCR for page 114
ual free-radical reactions have
been measured, and a good num-
ber of those not measured can
be estimated from thermochem-
ical kinetics and unimolecular re-
action theory.
Major unknowns in the mech-
anism by which a hydrocarbon
fuel burns concern the pyrosyn-
thesis reactions that lead to the
formation of polycyclic aromatic
hydrocarbons (PAHs) and soot
and the oxidation chemistry of
atoms other than carbon and hy-
drogen (heteroatoms) in the fuel,
particularly nitrogen, sulfur, and
halogens.
Nitrogen oxide emissions from
furnaces and boilers come mostly
from oxidation of the nitrogen
atoms in the fuel, whereas in
internal combustion engines these
emissions are derived largely from
oxidation of atmospheric nitrogen. Burners of
advanced design currently reduce the emissions
of nitrogen oxides by a factor of 2 from uncon-
trolled combustion systems by staging the ad-
dition of oxygen to produce an initial fuel-rich
regime in which the bound nitrogen is partially
converted to N2 (Figure 7.71. Potentially greater
reduction in nitrogen oxides can be attained by
adding hydrocarbons downstream of the fuel.
This is called reburning (Figure 7.81. To deter-
mine the optimal sequence of air and fuel
addition requires detailed knowledge of both
the fuel nitrogen chemistry and the hydrocarbon
chemistry.
The development of staged combustors for
the control of nitrogen oxides is constrained
partly by the formation of PAHs and soot
(Figure 7.9~. The PAHs are potential carcino-
gens whose biological activity depends strongly
on their molecular structure. It is postulated
that they are formed under locally fuel-rich
conditions by the successive addition of C-2
through C-5 hydrocarbons to aromatic rings
followed by ring closure. On the other hand, a
staged combustor cannot be operated on too
lean a fuel mixture because formation of nitro-
gen oxides is favored under this regime. Con
~~A'~RS £rN £~E,~IC:~1L ~.7~/~ll\TEERIlYG
SECONDARY
COAL AND /y AIR
PRIMARY AIR 1 ~/
INTERIOR MUTT-STAGE
BURNER WALL
~O~yC~
\
~/
/
FIGURE 7.7 Schematic of a 10w-NOx/SOx pulverized coal burner. The addition
of oxygen is staged to produce an initial fuel-rich zone in the burner that
results in reduced emissions of nitrogen oxides.
tinned experimental and theoretical study of the
combustion chemistry of higher molecular weight
hydrocarbons should provide the understanding
needed for the design of combustors in which
the fuel/oxygen regime is selected to minimize
emissions of PAHs and nitrogen oxides.
Soot
Combustion processes are a major source of
particles emitted to the atmosphere. Particles
formed in combustion systems fall roughly into
X~
FUEL MOLECULE
CONTAINING FUEL
NITROGEN ATOMS
| 0:,, NO
COMBUSTION NH
- N2
FIGURE 7.8 NOx control in combusion by reburning. Ad-
dition of hydrocarbons (CHn) late in the combustion process
leads to the reduction of nitrous oxide (NO) to nitrogen gas
(No)
OCR for page 115
Ei\~.~ENTAL PROTECTION, PROCESS SAFETY, ^~AY,4~0US -BASTES
Hydrocarbon , C4Hs + C2H2 ~ [2
Fuel Butadienyl Acetylene
Radical
~ +C2 ~
Pyrene Phenanthrene
Benzene
i+C4 =\
+C4 ~ +C2 [4
Naphthalene Acenapthylene
FIGURE 7.9 Mechanism of formation of polycyclic aromatic hydrocarbons
(PAHs) during combustion.
two categories. The first, referred to as soot,
consists of carbonaceous particles formed by
pyrolysis of the fuel molecules. The second,
referred to as ash, is composed of particles
derived from noncombustible constituents in
the fuel and from heteroatoms in the organic
structure of the fuel.
Soot can be produced in the combustion of
gaseous fuels and from the volatilized compo-
nents of liquid or solid fuels. Soot formation is
a complex process involving the chemistry of
fuel destruction under fuel-rich conditions where
hundreds of aromatics and other intermediate
~5
compounds are formed (Figure
7.10~. An understanding of the
mechanism of soot formation has
become more important because
soot hampers the use of such
important technologies as staged
combustion and diesel engines.
In addition, the sooting tendency
of aromatic compounds is higher
than that of aliphatics, and the
i: aromatic content of fuels is ex
~pected to increase in the future
my> as petroleum resource availabil
Fluoranthene ity forces refiners to use fuel
feedstocks with lower ratios of
hydrogen to carbon.
Soot is objectionable not only
because of its opacity but also
because soot particles are car
riers of toxic compounds. When combustion
products cool, soot particles provide conden
sation sites for hydrocarbon vapors, particularly
PAHs. Soot particles are agglomerates of small,
roughly spherical units. The small vary in di
ameter from O.OOS to 0.2 ~m, with most in the
range of 0.01 to 0.05 ~m, while the size and
morphology of the clusters can range from
aggregates of several particles to large contrails
several micrometers in diameter and hundreds
of micrometers in length. Soot particles are not
pure carbon. The atomic ratio of hydrogen to
carbon decreases from around 1.0 at the point
H H H
, ~
C C C C'
:4 + C2H2(-H) ~+H(-H ~=. +C2H2 ~C_H
~3 _
it+
SOOT
-+H(-H2) ~3 +C2H2(-H) it) +C2H2(-H) ~3
FIGURE 7.10 A possible mechanism for soot formation.
OCR for page 124
_ if. /
aqueous particles may participate in oxidation-
reduction reactions with the particles, undergo
chemical transformations in which the particle
surface serves as a catalyst, or participate in
heterogeneous photochemical processes. The
design of effective engineering processes for the
treatment of water supplies to remove toxic
compounds by adsorption/reaction/particle-re-
moval sequences demands fundamental data on
the kinetics of the individual steps and the
incorporation of the data into process models.
A major challenge is to describe all relevant
chemical influences on the efficiency of removal
of specific toxic compounds. Among these are
the physical and chemical properties of the
absorbing particle surface, the alteration of
these properties by reactions or dissolution-
precipitation processes, and the stability of
aqueous particles to coagulation. In contrast to
the chemical conditions of conventional munic-
ipal water and wastewater processing, the con-
ditions selected or imposed by the special cir-
cumstances for control of hazardous substances
may include extremes of pH, redox potential,
ionic content, and organic content. These fac-
tors may become critical in the design of optimal
processes combining adsorption, reaction, and
coagulation steps.
Recent development of the use of reversed
micelles (aqueous surfactant aggregates in or-
ganic solvents) to solubilize significant quan-
tities of nonpolar materials within their polar
cores can be exploited in the development of
new concepts for the continuous selective con-
centration and recovery of heavy metal ions
from dilute aqueous streams. The ability of
reversed micelle solutions to extract proteins
and amino acids selectively from aqueous media
has been recently demonstrated; the results
indicate that strong electrostatic interactions
are the primary basis for selectivity. The high
charge-to-surface ratio of the valuable heavy
metal ions suggests that they too should be
extractable from dilute aqueous solutions.
The potential of reversed micelles needs to
be evaluated by theoretical analysis of the metal
ion distribution within micelles, by evaluation
of the free energy of the solvated ions in the
reversed micelle organic solution and the bulk
aqueous water, and by the experimental char
acterization of reversed micelles by small-angle
neutron and x-ray scattering.
Wet Oxidation
Incineration achieves high destruction effi-
ciencies by fast free-radical reactions in the
presence of water vapor at high temperatures
(1,500-2,300°C) and 1 atm. Waste can also be
destroyed by oxidation at much lower temper-
atures by operating at high pressures, including
conditions above the critical point for water.
For example, high destruction efficiencies (greater
than 99.99 percent) of toxic organic compounds
can be achieved in 2 seconds at moderate
temperatures (1,000-1,200°C) at 250 atm. The
lower reaction temperature permits the destruc-
tion of waste of much lower heating value than
can be incinerated, at least without the use of
auxiliary fuels. The chemistry of such reactions
at high pressures and moderate temperatures
needs to be further elucidated before wet oxi-
dation processes can be more widely used in
hazardous waste management.
Remediation of Toxic Waste Sites
Only two processes, high-temperature pyrol-
ysis and mobile incineration, have proved ef-
fective for soil decontamination and are consid-
ered to be commercially viable. Both involve
heating the contaminated soil to a high temper-
ature, which is costly in terms of energy use
and materials handling. There are substantial
opportunities for innovation and development
of processes for the separation of contaminants
from soils and the in-situ treatment of contam-
inated soils. Examples of each are given in the
following subsections.
Separation Processes
One generic problem in site remediation is
the removal or deactivation of small quantities
of toxic organics from highly porous and sur-
face-active media such as soil. Alternative pro-
cesses to pyrolysis and high-temperature oxi-
dation of soil, such as thermal Resorption, steam
stripping, and supercritical extraction, require
less energy and thus should be investigated
OCR for page 125
further. Fundamental research on the nature of
the adsorbed state of organics in soil could have
as a significant payoff the identification of al-
ternative process paths. Basic measurements of
Resorption kinetics and pore diffusion in clas-
sified fractions of soil components (e.g., clays,
silts, and sand) can provide the basis for de-
veloping accurate models of such processes as
soil Resorption and migration of contaminated
plumes. This information could be used to
determine the conditions necessary for thermal
Resorption and steam stripping.
Extraction with supercritical fluids, such as
carbon dioxide or methanol in carbon dioxide,
offers the potential for combining the high mass-
transfer coefficients of gases with the moder-
ately high absorption capacities of liquid sol-
vents. In addition, the solubility characteristics
are highly sensitive to relatively small changes
in temperature and pressure. Thus, the contam-
inants can be recovered from the supercritical
fluid after extraction and the supercritical fluid
recycled at moderate cost. The method is being
applied to tertiary oil recovery by the petroleum
industry, a process somewhat akin to the re-
moval of organics from soil. Fundamental re-
search on the solubilities of organic compounds
in supercritical fluids would expedite the eval-
uation and application of this promising tech-
nology.
Biodegradation
The use of biodegradation for the treatment
of dilute waste streams has already been dis-
cussed; it also has potential for in-situ treatment.
The critical need is to learn how to select and
control microorganisms in a soil environment
to achieve the desired degradation of organics.
Monitoring
One of the most important elements in the
remediation of existing waste sites is early
detection and action. As an example, the cost
of cleanup at Stringfellow, California, increased
from an estimated $3.4 million to $65 million
because of pollutant dispersal during a decade
of inaction after the first identification of the
problem. The opportunities for innovative sam
,~ ~
~ ~ lo.
pling strategies responsive to this need are
discussed in the following section.
BEHAVIOR OF EFFLUENTS IN THE
ENVIRONMENT
It has been recognized for some time that
fluids in motion, such as the atmosphere or the
ocean, disperse added materials. This property
has been exploited by engineers in a variety of
ways, such as the use of smoke stacks for boiler
furnaces and ocean outfalls for the release of
treated wastewaters. It is now known that
dilution is seldom the solution to an environ-
mental problem; the dispersed pollutants may
accumulate to undesirable levels in certain niches
in an ecosystem, be transformed by biological
and photochemical processes to other pollut-
ants, or have unanticipated health or ecological
effects even at highly dilute concentrations. It
is therefore necessary to understand the trans-
port and transformation of chemicals in the
natural environment and through the trophic
chain culminating in man.
The Atmospheric Environment
Over the last two decades, significant progress
has been made in understanding the mechanisms
of transport and transformation of pollutants in
the atmosphere. Mathematical models have been
developed to describe the spatial and temporal
distributions of sulfur dioxide, carbon monox-
ide, nitrogen oxides, hydrocarbons, and ozone.
These models now serve as the backbone for
the development of state plans for implementing
the 1977 Clean Air Act amendments. Region-
wide air pollution and acid rain are current
subjects of intensive mathematical modeling
efforts. But in spite of the strides that have
been taken, a number of important research
problems remain in understanding the behavior
of atmospheric contaminants.
Organic compounds constitute about 25-30
percent of the fine aerosol mass (the mass
contained in particles smaller than 2.5 Am di-
ameter) in urban areas. They are of considerable
interest because some of them, such as PAHs,
are either suspected carcinogens or known mu-
tagens. Still, little headway has been made
OCR for page 126
126
toward engineering their systematic reduction
in the atmosphere.
The problem is complex because many dif-
ferent sources contribute to atmospheric load-
ings of organic compounds. Not only do toxic
waste incinerators have to be considered, but
so do more than 50 classes of mobile and
stationary combustion sources and industrial
processes that release small amounts of toxic
organics mixed with other exhausts. In addition,
reliable aerosol source samples of PAHs and
their oxygenated or nitrated derivatives are
difficult to collect because these compounds are
present in both gas and aerosol phases. Special
stack-sampling equipment must be designed to
acquire meaningful samples. Emissions undergo
transport and chemical transformation in the
atmosphere. For example, mutagenic nitro com-
pounds can be created by the reaction of PAHs
with HNO3, NO', or NOOK. One way to analyze
these atmospheric transformations is to com-
pare the chemical composition of primary source
effluents with that of ambient aerosol samples.
However, source and ambient samplings now
vary in methodology and analysis so that dif-
ferences between them may be due to laboratory
procedures. A comprehensive study, in which
source and ambient measurements are made
and analyzed the same ways, is needed. Source
emission data could then be correlated with
atmospheric transport calculations, and the rel-
ative importance of source contributions to
ambient organics could be identified.
When spills and releases of hazardous gases
or liquids occur, the concentration of the haz-
ardous material in the vicinity of the release is
often the greatest concern, since potential health
effects on those nearby will be determined by
the concentration of the substance at the time
of the acute exposure. There are many models
of routine continuous discharges (e.g., dis-
charges arising from leaky valves in chemical
plants), but these cannot be applied to single
episodic events. Research on the ambient be-
havior of short-term environmental releases and
the development of models for concentration
profiles in episodic releases are crucial if we are
to plan appropriate safety and abatement mea-
sures.
Because most people spend the majority of
FRO~N TIERS I.\' iCHEMICALL ENGIATEERI~`'G
their time indoors, the quality of the indoor
atmospheric environment is now receiving greater
attention from researchers and regulators. There
has been a reported increase in both the con-
centration and diversity of pollutants in indoor
environments; formaldehyde, nitrogen dioxide,
carbon monoxide, and a diverse range of organic
compounds have been identified. It is not certain
whether this should be attributed to the use of
new building materials and to changes in build-
ing ventilation resulting from increased insula-
tion or to the use of more sophisticated analyt-
ical techniques. Since the principal indoor air
pollutants are known or suspected to adversely
affect health (Figure 7.16), there is a need to
engineer systems that can reduce their genera-
tion. Chemical engineers can assist in devel-
oping such systems, including
· home heating and cooking burners that
minimize the generation of oxides of nitrogen;
~ improved heat transfer devices that will
allow for air exchange with the outside envi-
ronment while avoiding excessive loss of heat;
and
~ resins, binders, coatings, and glues for
building materials that do not emit hazardous
compounds, such as formaldehyde.
Finally, there is a need for simple instrumen-
tation that can be used to quantify occupant
exposure to air pollution.
The Aquatic and Soil Environments
Disturbingly little is known about the mech-
anisms of groundwater contamination, including
not only those for transport and dispersion but
also those for chemical transformation. Under-
ground pollutant transport is often represented
with rather simplistic plume models, in much
the same way as traditionally done for the
atmosphere. These models do not take into
account the fact that, for the underground trans-
port process alone, the detailed mechanisms of
flow through inhomogeneous porous media rep-
resent a major source of added complexity that
cannot be ignored (Figure 7.171. Chemical en-
gineering expertise in petroleum reservoir mod-
eling can be applied to this area.
OCR for page 127
ENVIRONMENT.4L PROTECTION, PROCESS SAFETY, HAZARDOUS WASTES
:~ ~ NASAL CAVITY
:~FORMALDEHYDE
~ /_ ~ -ORAL CAVITY
TRACHEA ~ 1 ~ ~
_~IIT-~-~] DIOXIDE
BRONCHUS i-\ L4§ ~ ~ AMMONIA, SULFUR DIOXIDE
\ ; ~PARTICLES UNDER3
N1 R O
I ~ 1lN ~ ~_NllTR~rFKI nlm~lnF
I I \\ I ~ f ~= - \ ~ ''''me '' 'a'''
a\ _ ~ (FROM ALVEOLI INTO
\ BLOODSTREAM)
I ( ~ :~ CARBON DIOXIDE
y / ~ t~w (FROM BLOODSTREAM
PINTO ALVEOLI)
ALVEOLI
FIGURE 7.16 Health effects of indoor air pollution. Gaseous and particulate
contaminants frequently found in indoor air pollution affect different parts of
the respiratory system. Some, such as carbon monoxide and nitrogen dioxide,
move from the lungs into the bloodstream.
Models of chemical reactions of trace pollut-
ants in groundwater must be based on experi-
mental analysis of the kinetics of possible pol-
lutant interactions with earth materials, much
the same as smog chamber studies considered
atmospheric photochemistry. Fundamental re-
search could determine the surface chemistry
of soil components and processes such as ad-
sorption and Resorption, pore diffusion, and
biodegradation of contaminants. Hydrodynamic
pollutant transport models should be upgraded
to take into account chemical reactions at sur-
faces.
Considerable work has been done on the
behavior of pollutant species at air-water and
air-soil interfaces. For example, wet and dry
deposition measurements of various gaseous
and particulate species have been made over a
wide range of atmospheric and land-cover con-
ditions. Still, the problem is of such complexity
that species-dependent and particle-size-de-
pendent rates of transfer from the atmosphere
to water and soil surfaces are not completely
understood. There is much to be learned about
pollutant transfer at water-soil interfaces. Con-
cern about groundwater contamination by min
OCR for page 128
~8
.
\',Compilance point Aqulfer \
Flow I\__
1 1~
b:-------:-:-:-:-:-:-::::-~-------:
~.~..................
. _ .. .
Waste ~ ~ B
constituent ~ I;;;;
source | ~
-K ~ Aqulfer
I..
::::::::::::: Plume of contaminants
Sampilng wells, downgradlent
· Upgradlent well
eral processing leachates, by rainwater leaching
of landfills, and by runoff of contaminated
surface water has heightened the opportunities
for further work in this area.
Ambient Monitoring
Advances in understanding the transport and
fate of chemicals in the environment will depend
on substantial improvements in measurement
capabilities. Attention should be directed to-
ward instrumental techniques that can deter-
mine the oxidation state of inorganic species,
which often has a marked influence on reactiv-
ity, transport properties, and toxicity of the ion.
Free radicals and other highly reactive trace
species play important roles in the chemistry of
the environment. Detection of these species
FRONTIERS IN CHEMICA.L E.\G1NEERING
it,
1
if Acted fracture
Waste
constituent
l source
Ground water flow
l
~ 1
Compilance
olnt
FIGURE 7.17 Oversimplified and more realistic views of plume migration in
underground water. Plume migration is affected by inhomogeneities in the
aquifer. The diagram on the right shows that gravitational influences or
fractures on the aquifer might cause plumes to flow in directions different
from the direction of groundwater flow. Courtesy, Office of Technology
Assessment.
requires rugged and reliable instrumentation
that can be transported and used in the field.
Remote sensing technology should be explored
as a means of characterizing regional pollutant
distributions.
The extent of groundwater contamination
from landfills and storage tank leakage is often
unknown (Figure 7.181. It is important to devise
measurement strategies to characterize the spa-
tial, chemical, and temporal nature of this prob-
lem. Chemical engineers have been at the fore-
front in using advanced mathematical tools and
instrumentation to characterize the size and
extent of petroleum reservoirs. This technology
should be transferred to the groundwater prob-
lem and, in particular, to the task of designing
cost-effective sampling strategies. Other options
include probing potential subsurface sources of
OCR for page 129
ENVIRONMENTAL PROTECTION, PROCESS SAFETY, 0.47,4~6TS WASTES
·
-
1' 1
2 e ""
~ ~ ~ ~storage\, <~.~!~( 4~ ~: ~ ~ ~ -it Con am'na ng l;; ~ ~
' ... Soil Contaminated ~
' ' ' 22', By Residual Gasoline
................................... , , it. ~ ., ,.,.,.,. A.,., , ,., . ,. ~.
.................. ' 2,'. Accumulated'. ~ :
FIGURE 7.18 Leakage from underground storage tanks. Some 2 million
underground steel storage tanks are buried beneath service stations throughout
the country. Another 1.5 million steel gasoline tanks are buried on farms.
Thousands of "orphan" tanks are believed to have been left behind when
service stations were razed for redevelopment. Leaks from these tanks could
allow hazardous organic compounds to migrate beneath the surface, polluting
soil and aquifers and releasing fumes to the surface. Courtesy, E.I. du Font
de Nemours and Company, Inc.
pollutants by nondestructive methods such as
acoustic probing, eddy current techniques to
assess tank corrosion, magnetometers for lo-
cation of buried drums, and electrical resistivity
measurements.
Improvements in the monitoring and opera-
tion of incinerators could minimize the acciden-
tal release of hazardous effluents. In particular,
fast-acting, continuous, on-line monitors are
needed to detect excursions in operating con-
ditions that could lead to toxic emissions.
Development of methodologies for charac-
terizing and measuring human exposure to
chemicals is a challenging scientific and engi-
neering undertaking. Data are needed for studies
of risk assessment and health effects. During
the past decade, rudimentary monitors have
become available to determine a person's ex-
posure by measuring concentrations of a given
pollutant in the air breathed. Efforts should be
directed to lowering the cost and increasing the
sensitivity, chemical selectivity, and accuracy
of these monitors. Widespread use of personal
exposure monitors offers the potential for im-
proving epidemiological studies and for devel-
oping a more rigorous scientific basis for setting
standards in the workplace and the general
environment.
129
Multimedia Approach to
Integrated Chemical
Management
_ - .
'| ll'Current laws and programs fo
1111lllIlllllcus on the removal of pollutants
from the medium-air, water, or
land in which they are found,
often with little regard for chem
ical management of the environ
ment as a whole. Because mod
ern analytical techniques have
revealed trace amounts of many
toxic chemicals throughout the
environment, however, the me
dium-specific approach to pol
lution control is now questiona
ble.15 The diverse effects of acid
rain and of leachates from haz
ardous waste sites illustrate the
mobility of chemicals in the en
vironment ([Figure 7.19~. The
following list gives many areas
of research opportunity in a multimedia ap
proach to chemical management of the environ
ment:
~ characterization of background levels of
chemicals and geochemical cycles;
· basic kinetic studies of chemical degrada-
tion;
· field experiments to measure pollutant fluxes
among media;
· fundamental studies of interracial dynam-
~cs;
· better determination of Henry's Law con-
stants for volatile species;
· study of chemical speciation, including
binding of organic compounds in soil and surface
waters (Figure 7.201;
· studies of sorption and Resorption of heavy
metals on suspended organic matter; and
· formation of precipitates in response to
changes in pH.
ASSESSMENT AND MANAGEMENT OF
HEALTH, SAFETY, AND
ENVIRONMENTAL RISKS
Two of the biggest challenges facing chemical
engineering in the near future are (1) the iden
1
OCR for page 130
HERS IN CHEA8~CAL ENGEtYE£~.~\G
Prevailina Winds
_ , , . ~ 1, . ., ;, by ·.,
__c5 ~ ~\ Photochemistrv
Mu merit ~::~r~Pc
tification and evaluation of the risks- both real
and perceived to human health and to the
environment from exposure to chemicals (risk
assessment) and (2) the adequate control of
these risks (risk management). The ultimate
objective in meeting these challenges is to en-
sure that risks in the chemical and processing
industries are viewed as acceptable by the
public, regulatory bodies, and the courts, while
maintaining worldwide technological leadership
and cost competitiveness in these industries
by capitalizing fully on advances in chem-
istry, biotechnology, materials, and microelec-
tronics.
These challenges are critical to the profession
of chemical engineering, the chemical industry,
and our country. Risk assessment and manage-
ment involve input from a multitude of differ-
ent disciplines. The methodology is rapidly
changing and extremely complex and requires
both technical input and input from profes-
sionals with expertise in legal, economic, judi-
cial, medical, regulatory, and public perception
issues.
· ~:
*,,.\. , ~. ,,.~
Aauatic Ecosvstem
FIGURE 7.19 Mobility of acid rain a multimedia problem. Reprinted from
Opportunities in Chemistry. National Academy Press, 1985.
Risk Assessment
Risk assessment, an obvious precursor to risk
management, first identifies a hazard and then
quantifies the likelihood of occurrence (hazard
assessment) and the impact (exposure assess-
ment) associated with each hazard event.
Hazard Identification arid Assessment
Two main hazards associated with chemicals
are toxicity and flammability. Toxicity mea-
surements in model species and their interpre-
tation are largely the province of life scientists.
Chemical engineers can provide assistance in
helping life scientists extrapolate their results
in the assessment of chemical hazards. Chemical
engineers have the theoretical tools to make
important contributions to modeling the trans-
port and transformation of chemical species in
the body from the entry of species into the
body to their action at the ultimate site where
they exert their toxic effect. Chemical engineers
are also more likely than life scientists to ap
OCR for page 131
~NV^'RO.~-TAL PR0~' I0,A~, ~63~£SS Satisfy
preciate realistic conditions and exposure scen-
arios for the use of hazardous chemicals in
industrial settings. Their assistance in interdis-
ciplinary efforts is needed to relate toxicity
measurements to actual practice.
Identification of hazards of unexpected, epi-
sodic events such as transportation accidents,
equipment failure, fires, and explosions is largely
the responsibility of the chemical engineer. The
most difficult problem in the quantification of
toxicity, explosion, and fire hazards of unex-
pected and episodic natures is the estimation of
the probability of occurrence. Risk analysts
draw on both analysis and experience to gen-
erate sequences of component and subsystem
failures that might lead to significant accidents.
Methods such as fault-tree analysis can be used
to display failure sequences in a logical format.
Mechanical failures, operator errors, and man-
agement system deficiencies must all be consid-
ered in identifying and quantifying risks.
Risk assessment for complex systems involv-
ing hazardous chemicals requires deep under
IS WASTES
)37
standing of the full spectrum of operations. It
is highly interdisciplinary and potentially re-
quires manipulation of massive amounts of in-
formation, some of which may be missing or of
uncertain validity. While the techniques and
governing rules for risk assessment are generally
straightforward, much creative work needs to
be done before the methodology can be used
efficiently and effectively to anticipate and cor-
rect safety problems or to analyze operating
abnormalities for precursors of danger.
New techniques employing expert systems
for analysis of complex chemical processes can
be used to anticipate safety problems associated
with various design decisions. In many major
accidents, the relevant fundamental phenomena
involved were totally unanticipated and were
understood only after considerable investiga-
tion. Some of these abnormal conditions might
have been identified by a priori research guided
by techniques for anticipating interactions that
might be overlooked in conventional approaches
to design. Other serious accidents were pre
F1GURE 7.20 The binding properties of chemicals can affect their distribution
and retention in various environmental media. For example, the hypothetical
environmental fates of two chemicals are contrasted. The profile on the left
shows the loading in various media over time for a chemical that binds strongly
with lipid material. The profile on the right shows the loading in various media
over time for a chemical that binds strongly with organic material. Courtesy,
Office of Technology Assessment.
Water
OCR for page 132
ceded by abnormalities in operation that were
ignored until it was too late. Again, techniques
for identifying and investigating such warning
signals might have avoided disaster.
Exposure Assessment
There is a dearth of information and meth-
odology in the area of human and environmental
exposure assessment. Standardized methodol-
ogies have not been developed; monitoring of
personnel exposure is rare; and suitably sensi-
tive, rapid-response, portable analytical equip-
ment is limited. Fortunately, the exposure factor
is a controllable variable, at least theoretically,
and is largely within the province of the chemical
engineer, who selects and designs processes,
sites and expands plants, and develops plant
operating procedures and transport systems. To
determine the likely dispersion of flammable
materials, as well as the transport of toxic
chemicals in the environment, dispersion/reac-
tion models (both near field and far field) for
realistic accident scenarios (e.g., heavy gases,
dusts, aerosols) must be developed and verified
experimentally.
Risk Management
Once the hazard and exposure assessments
are complete for any specific hazard, it is
relatively simple to determine how many people
will be affected and the severity of the effect
(i.e., the risk). It is considerably more difficult
to decide whether these risks are warranted
compared to the benefits. This is particularly
true if the risks are uncertain, involuntary, or
not understood by those at risk; if those at risk
are not primarily those who benefit; or if alter-
natives are unknown, uncertain, or impractical.
The process is complex because the goals are
multiple and frequently contraindicating.
Economic, liability, public image, and opinion
considerations are involved. Catastrophic haz-
ards are less acceptable than smaller ones even
if the absolute risk is identical. Voluntary risks
are a way of life for most people, but there is
minimal tolerance for involuntary risks, partic-
ularly if they are unknown or not understood.
In today's heavily regulated and litigious
society, it is becoming increasingly essential
that risk assessments be conducted and ade-
quately and carefully documented for all existing
industrial plants and transport systems that
handle or store significant quantities of toxic or
flammable chemicals. The same must be done
in siting new facilities, selecting processes,
designing processes and equipment, developing
operating and maintenance procedures, and de-
signing transport systems.
Policies and procedures for risk management
decisions must be established and be clear and
simple if the massive, but necessary, workload
of risk assessment and management is not to
cripple the chemical industry's worldwide com-
petitive position and consume inordinate re-
sources through inefficiency.
Managing chemical risk must proceed in the
absence of perfect information on risks and how
to avoid them. The lack of critical information
or good alternatives is no excuse for inaction.
IMPLICATIONS OF RESEARCH
FRONTIERS
This chapter has made clear the challenges
to chemical engineers in research related to
environmental protection, process safety, and
hazardous waste management. Chemical engi-
neering education must become strongly ori-
ented to these topics, as well. For example,
what might be characterized as the traditional
approach to environmental concerns in process
design- establishing the process and then pro-
viding the necessary safety and environmental
controls must give way to a new approach
that considers at the earliest stages of design
such factors as
process resilience to changes in inputs,
~ minimization of toxic intermediates and
products, and
~ safe response to upset conditions, startup,
and shutdown.
As chemical engineering research develops new
design and control tools to deal with these
factors, these tools should be integrated into
the curriculum. Process safety research is gen-
erally more advanced in industry than it is in
OCR for page 133
academia. Closer interaction between industrial
researchers and academic researchers and ed-
ucators is needed to disseminate insights and
knowledge gained by industry in this area.
Other problems in environmental science and
technology as well as an introduction to the
social, economic, and political aspects of en-
vironmental issues should receive broad ex-
posure in the curriculum. They should be in the
content of existing courses wherever possible.
Industry has strong developmental research
programs in areas such as process safety, but
more fundamental research on process design
tools, on emerging environmental problems, or
on general topics linked to public health and
environmental protection requires stable, long-
term research support from the federal govern-
ment. The chemical engineering profession stands
ready to tackle these issues aggressively; does
the federal government?
The principal federal agencies that have sup-
ported environmental research generally have
been the Environmental Protection Agency, the
National Science Foundation, the National
Oceanic and Atmospheric Administration, the
National Institute of Environmental Health Sci-
ences, and the Department of Energy. In recent
years, many of these agencies have experienced
budget cuts that threaten their ability to maintain
vital research programs that anticipate environ-
mental problems, instead of reacting to the latest
crisis. Cutting back on basic research on envi-
ronmental problems is a false economy. Small
savings today on anticipatory research may
result in very large costs to society in the future,
since dealing with the consequences of envi-
ronmental problems is invariably more expen-
sive than research to anticipate and prevent
these problems.
Because of the critical importance of main-
taining our environmental quality and improving
process safety and hazardous waste manage-
ment, the committee recommends that these
federal agencies undertake new initiatives in
chemical engineering research. The details of
proposed initiatives for EPA and NSF are spelled
out in more detail in Chapter 10 and Appendix
A of this report. An investment in research to
anticipate and prevent environmental problems
is likely to be highly cost-effective. The costs
of responding to unforeseen environmental
problems have certainly been great. Signifi-
cantly increased support for fundamental re-
search is vital if universities are to preserve
their role in long-term environmental research
and in the education of tomorrow's researchers,
process designers, and regulators.
NOTES
1. J. L. Makris. Natural Hazards Observer, 10~3),
January 1986, 1.
2. J. McLoughlin. "Risk and Legal Liability" in
Dealing with Risk, R. F. Griffiths, ed. New York:
John Wiley & Sons, 1982.
3. National Safety Council. Accident Facts. Chi-
cago: National Safety Council, 1985.
4. U.S. Department of Commerce, Bureau of the
Census. Statistical Abstract of the United States:
1987, 107th ed. Washington, D.C.: U.S. Govern-
ment Printing Office, 1986, Table 697.
5. One Hundred Largest Losses-A Thirty- Year
Review of Property Damage Losses in the Hy-
drocarbon-Chemical Industries (OHL-9-86-71.
Chicago: Marsh and McLennan, 1986.
6. McGraw-Hill Economics. Survey of Investment
in Employee Safety and Health, 13th ed. New
York: McGraw-Hill, 1985.
7. James L. Regens, "The Regulatory Environment
for Coal Development," in Costs of Coal Pol-
lution Abatement: Results of an International
Symposium. Paris: Organisation for Economic
Cooperation and Development, 1983.
8. The National Survey of Hazardous Waste Gen-
erators and Treatment, Storage, and Disposal
Facilities Regulated Under RCRA in 1981.
WESTAC, Inc., 1984.
9. U. S. Congress, Congressional Budget Of lice.
Hazardous Waste Management: Recent Changes
and Policy Alternatives. Washington, D.C.:
Congressional Budget Office, May 1985.
10. U.S. Congress, Committee on Public Works and
Transportation, Subcommittee on Investigations
and Oversight. Hazardous Waste Contamination
of Water Resources (Concerning Groundwater
Contamination in Santa Clara Valley, CA) (99-
321. Washington, D.C.: U.S. Government Print-
ing Office.
11. U.S. Congress, Office of Technology Assess-
ment. Superfund Strategy (OTA-ITE-2521.
Washington, D.C.: U.S. Government Printing
Office, 1985.
OCR for page 134
734
12. T. A. Kletz. Simpler, Cheaper Plants or Wealth
and Safety at Work Notes on Inherently Safer
and Simpler Plants. London: Institution of
Chemical Engineers, 1984.
13. U.S. Environmental Protection Agency, Science
Advisory Board. Incineration of Hazardous Liq-
uid Waste. Washington, D.C.: U.S. Environ-
mental Protection Agency, 1984.
FF ON IFS ER ~ IN IDEA ~ ~ ^~iA\E~^ ^\ ~
14. U.S. Congress, Office of Technology Assess-
ment. Technologies for Hazardous Waste Man-
agement. Washington, D.C.: U.S. Government
Printing Office, 1981.
15. For a detailed discussion of this topic, see Y.
Cohen, ed. Pollutants in a Multimedia Environ-
ment. New York: Plenum Press, 1986.
Representative terms from entire chapter:
process safety
