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OCR for page 79
OCR for page 80
HE MORAL EQUIVALENT OF WAR. This
summons to respond to the energy
_! crisis, uttered by President Jimmy Carter
less than 10 years ago, today seems so remote
that it might be the subject of a good trivia
question. The mid-1980s are witness to a vast
demobilization of resources and personnel once
committed to energy research. Armies of re-
searchers have been redirected, retired, or laid
off. Pilot and demonstration facilities have been
mothballed. Spending on alternative fuels re-
search has dwindled. The cumulative effect of
this rapid negative change is to discourage
academic investigators and young graduates
from seriously considering the formidable en-
ergy research problems that remain unsolved.
Yet there is nothing trivial about energy. The
cost of energy over the last decade has had a
significant influence on the rate of inflation in
the United States. The energy processing in-
dustries constitute one of the country's largest
industrial segments. In 1985, shipments of pe-
troleum and coal products amounted to $194
billion, and the value of natural gas produced
in the United States exceeded $42 billion.2 The
availability of secure fuel supplies is vital to
national defense. Cheap and abundant energy
supplies are just as important to national eco-
nomic competitiveness in peacetime. No indus-
trial segment has a greater impact on national
well-being, jobs, defense, and economic com-
petitiveness. No industrial segment is more
dependent on chemical engineers for its health
and progress. Research, development, and com-
mercial operations in the energy processing
industries all draw heavily on the knowledge
and techniques of chemical engineers.
There is nothing trivial about our nation's
primary metals industries either in 1985 they
accounted for $126 billion in shipments. This
industrial sector and the energy industries have
a number of characteristics in common. Both
face an uncertain future shaped by the declining
quality of domestic raw materials reserves and
substantially higher quality reserves in countries
that need to obtain foreign exchange through
commodity sales, regardless of market price or
profit considerations. The United States de-
pends heavily on foreign imports for both energy
and metals resources (Figure 6.14. The natural
FRONTIERS IN CH£MICAL ENGI1VEERING
resources industries have experienced cutbacks
in support for industrial and academic research
that are similar to those in the energy industries.
Energy processing and natural resources
processing share numerous fundamental tech-
nical problems, many of which fall squarely in
the domain of the chemical engineer. The cur-
rent retrenchment in research in both fields does
not imply that the problems have largely been
solved. Indeed, the problems are as challenging
as ever, and they are not going to be solved
overnight. Now is the time to conduct the
fundamental research needed for their solution.
How do we take a future-oriented approach
to research on energy and metals? What criteria
do we use to set research priorities? Short-term
projections of prices and availability of re-
sources are poor guides to a national policy for
research. It is virtually impossible to predict
the course that energy prices will take over the
next few years or to prognosticate political
events that might affect the supply of key
minerals to the United States. The most anyone
can say is that oil prices will rise and that a real
threat exists to the stability of our supply of
several key minerals.
What is predictable is that the cost of pro-
ducing oil and minerals in the United States will
be influenced by the rate of depletion of re-
coverable domestic sources. This rate will in
turn be influenced by the economics of recover-
ing usable materials from these domestic sources.
It is certain that there will be a need for engineers
to develop and manage technologies that can
slow the depletion rate by permitting recovery
of a greater fraction of the resources that are
there.
The United States is the recognized world
leader in energy and minerals technology; chem-
ical engineering has been and must continue to
be the key discipline in maintaining that posi-
tion. The primary thrust of chemical engineering
research in these areas should be to provide the
basic knowledge that would give the nation the
capability to react to future shifts in the prices
and availability of energy and minerals. This
capability can be developed by pursuing fun-
damental research in the priority areas laid out
in this chapter. Our ultimate objectives should
be to extract and process current resources
OCR for page 81
PROCESSING OF ENERGY AND NATURAL RESOURCES
20
15
m 10
o
I.: :::: -
~ I.: :~:~:~:~:~:~:~
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% Share
1979 1985 20 -
Net Impose 43 28 ~
......
O ~
1970 1975 1980 1985 1990 1995 2000
Percentage
Niobium
Manganese
Mica (sheet)
Strontium
Bauxite & alumina
Cobalt
Platinum group
Tantalum
Potash
Chromium
Tin
Asbestos
Barite
Zinc
Nickel
Tungsten
Silver
Mercu y
Cadmium
Selenium
100
100
100
100
97
95
92
92
77
73
72
71
69
69
68
68
64
57
55
54
................... .............
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::::::::::::::::::::::::::::::::::
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-
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:::::::::::::::::::::::::::::::::::::::::::::::::::'
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Brazil, Canada, Thailand
South Africa, France, Brazil, Gabon
India, Belgium, France
Mexico, Spain
Australia, Jamaica, Guinea, Surinam
alre, amble, Canada, Norway
South Africa, Great Britain, Soviet Union
Thailand, Brazil, Malaysia, Australia
Canada, Israel
South Africa, Zimbabwe, Yugoslavia, Turkey
Thailand, Malaysia, Bolivia, Indonesia
Canada, South Africa
China, Morocco, Chile, Peru
Canada, Peru, Mexico, Australia
Canada, Australia, Botswana, Norway
Canada, China, Bolivia, Por ugal
Canada, Mexico, Peru, Great Britain
Spain, Algeria, Japan, Turkey
Canada, Australia, Peru, Mexico
Canada, Great Britain, Japan
FIGURE 6.1 The United States is becoming ever more dependent on foreign
sources of oil and minerals. The top graph displays trends in U.S. production
and consumption of petroleum feedstocks from 1970 to 2000. It shows the
growing contribution of imported oil to U.S. consumption, a contribution that
is projected to increase rapidly in the 1990s. The bottom table shows that the
United States depended in 1985 on foreign suppliers for 20 minerals and
metals, some of which are critical to national security. Courtesy, Chevron Oil
Company (top) and the U.S. Bureau of Mines (bottom).
more efficiently and to develop ways of exploit-
ing alternative resources.
TECHNOLOGIES FOR EXPLOITING
ENERGY SOURCES
In the early part of this century, technologies
were developed for exploiting apparently lim-
itless reservoirs of gaseous and liquid fossil
fuels. Because these fuels are easier to handle
and cleaner than coal, they made
great inroads on the use of coal
as a primary energy source.
However, in recent years, it has
become apparent that easily ac-
cessible, high-quality reservoirs
of gaseous and liquid fossil fuels
are not inexhaustible. Moreover,
the demand for energy continues
to increase as the population in-
creases and labor-sparing ma-
chines are developed.
It is a basic premise that this
challenge can best be met by
developing technologies for more
efficient use of existing resources
and for utilizing previously un-
tapped sources of energy. A
number of approaches to these
goals appear to hold promise for
success in the next few decades.
Enhanced Oil Recovery
Technologies for oil produc-
tion can be divided into three
classes: primary recovery, sec-
ondary recovery, and enhanced
oil recovery. In primary recov-
ery, the oil and gas flow naturally
through the reservoir rock to the
production well, impelled b
subterranean pressure. For typ-
ical light oils, only lS-20 percent
of the oil in the formation is
extracted in primary recovery.
Secondary recovery processes
extend primary recovery by in-
jecting water or gas to maintain
reservoir pressure as the oil is
removed. These processes are well established
and generally recover an additional lS-20 per-
cent of the original oil. Thus, for conventional
medium and light crude oils, which have rela-
tively low viscosity at reservoir conditions
about one-third of the original oil can be re-
covered by primary and secondary methods.
Enhanced oil recovery (EOR) processes (also
called tertiary recovery processes) are used to
recover a portion of the remaining two-thirds
OCR for page 82
82
of the original oil. Adverse reservoir properties
and conditions limit both the applicability of
EOR processes and the extent of recovery from
those reservoirs to which the processes can be
applied effectively. In addition, there are entire
oil deposits so viscous "ultraheavy" crudes,
bitumens, and tars that primary recovery is
not possible and secondary recovery processes
are generally ineffective. Such deposits in the
United States approach the potential of con-
ventional oil reserves, and on a worldwide basis
they are several-fold greater than total reserves
of the lower viscosity conventional crude oils.
Much of the total resource of these extremely
viscous oils is in Canada and Venezuela.
The ability to recover as much as possible of
the remaining two-thirds of conventional oils in
known formations and to utilize ultraheavy
crude deposits will become increasingly impor-
tant as U.S., and ultimately worldwide, reserves
of conventional crude oils are depleted.
The three classes of EOR technologies that
have been studied extensively are thermal re-
covery, miscible flooding, and chemical flood-
ing. For each of these methods, the following
two basic problems must be overcome if we are
to recover a significant part of the remaining
oil.
· Oil deposits are found in porous sedimen-
tary rocks with limited pathways (permeability)
for flow of oil through the reservoir formation
to a producing well. The first problem is to
achieve microscopic recovery efficiency to
displace the oil from the rock matrix and cause
it to How through the formation along a specific
pathway. Figure 6.2 depicts an oil droplet in
porous sand. Because of interracial tension, the
oil cannot be moved by water pumped into the
formation. If the interracial tension of the oil is
lowered whether by increased temperature,
by an oil-miscible sweeping fluid, or by chemical
additives-the oil can move from its original
location through the porous sand.
· The second problem is to achieve macro-
scopic sweep efficiency recovery of oil from
a significant fraction of the reservoir formation.
This problem is generally more intractable than
the first. The reservoir formation is not homo-
geneous in porosity or permeability, which causes
FRONTIERS IN CHEMICAL E.VGINEERING
FIGURE 6.2 Interfacial tension imprisons residual oil in
rock, preventing its displacement by water. Without inter-
facial tension, oil flows freely, leaving no residual portion
in the rock. Courtesy, Amoco Production Company.
phenomena such as fingering and allows pockets
of oil to be bypassed, dramatically lowering the
sweep efficiency of all current EOR methods
(Figure 6.31. A basic challenge for chemical
engineers is how to detect and/or model the
movement of oil, water, gas, and injected chem-
icals in the heterogeneous environment of the
reservoir. This problem is discussed in detail in
Chapter 8, which is devoted to computer-
assisted process and control engineering.
Thermal recovery methods involve the use
of steam and in-situ combustion. Thermal EOR
processes add heat to the reservoir to reduce
the viscosity of the oil or to vaporize it. In
addition, these processes use steam or oil com
OCR for page 83
PROCESSING OF E^~Y AND NATURAL RESOURCES
FIGURE 6.3 Oil can be recovered from reservoirs by
pumping in steam, gas, or specialty chemicals. All methods
face common problems posed by inhomogeneities in the
rock containing the oil. Some major problems include poor
vertical coverage, inefficient sweeping that bypasses pock-
ets of oil, and severe channelling of fluids along fissures or
highly permeable layers of rock. Chemical methods of
compensating for these inhomogeneities would boost the
yields and cut the operating costs of enhanced oil recovery.
Courtesy, Amoco Production Company.
bustion products as a drive fluid to move oil to
producing wells. Thermal processes are most
often used in reservoirs of viscous oils and tars
on which tests have established that primary
production will be small and waterflooding will
be largely ineffectual. Thus, thermal methods
are usually used in place of, rather than after,
secondary or primary methods.
The first EOR method to achieve widespread
commercial acceptance, steam injection (Figure
6.4), has been used commercially in California
for more than 20 years and now accounts for
more than 80 percent of U.S. EOR production.
A less well developed thermal method, in-
situ combustion, holds much promise but also
poses a tremendous challenge to the theory and
practice of chemical engineering. The in-situ
combustion process involves many processes
occurring simultaneously. Heat is generated
within the reservoir by injecting air or oxygen
to burn part of the reservoir oil (Figure 6.51. It
is common practice to co-inject water with or
above the oxidant to scavenge energy from hot
rock lying behind the burn front. In-situ com-
bustion often achieves considerably higher tem-
peratures than steam flooding, and the heat not
only physically and chemically reduces the oil
viscosity but also partially vaporizes the oil,
83
which is driven forward by a combination of
steam, hot water, and gas.
The earth itself is the reaction vessel and
chemical plant. The complicated reaction chem-
istry and thermodynamics involve mixers, re-
actors, heat exchangers, separators, and fluid
flow pathways that are a scrambled design by
nature. Only the sketchiest of flowsheets can
be drawn. The chemical reactor has complex
and ill-defined geometry and must be operated
in intrinsically transient modes by remote con-
trol. Overcoming these difficulties is a true
frontier for chemical engineering research.
Another EOR approach to reducing the vis-
cosity of oil in the reservoir is miscible flood-
ing-the injection of fluids that mix with the oil
under reservoir conditions. Such fluids include
carbon dioxide, light hydrocarbons, and nitro-
gen. Supply and cost of carbon dioxide are often
more favorable than for other injectants. Ex-
tensive research and field testing have estab-
lished the technical viability of miscible flood-
ing, and a number of commercial carbon dioxide
miscible flooding projects are in operation.
Chemical EOR methods are based on the
injection of chemicals to develop fluid or inter-
facial properties that favor oil production. The
three most common of these methods are poly-
mer flooding, alkaline flooding, and surfactant
flooding.
Commercial implementation of polymer
flooding and alkaline flooding is in progress, and
there is confidence that research can make these
processes more cost-effective and extend their
applicability to a greater fraction of the known
reservoirs. The research focus is on improving
the thermal, chemical, and biological stability
of polymers and making them more cost-effec-
tive. Research targets in alkaline flooding in-
clude better definition of the reactions of alkaline
materials with the rock formation and the use
of ancillary chemicals to improve performance.
As with polymer flooding, a primary objective
is to extend the applicability to more severe
conditions.
Of the chemical EOR technologies, surfactant
flooding is the most complex, the farthest from
commercial feasibility, and the most challenging
in terms of research needs, yet it has the greatest
ultimate potential. It involves injecting surfac
OCR for page 84
~4
il. I I I I I I I 1` ,, I, i, L, ~ I,
FRONTIERS IN CHEMICAL ENGINEERING
STACK GAS
SCRUBBER
PRODUCTION FLUIDS (OIL, GAS, WATER)
SEPARATION AND
PRODUCTION WELL
(a) OIL AND WATER ZONE NEAR ORIGINAL RESERVOIR TEMPERATURE (a) HOT WATER ZONE
(a) HEATED OIL ZONE
tents, such as sulfonated crude oil, to mobilize
the oil for subsequent recovery by a waterflood.
The most recent National Petroleum Council
(NPC) study of EOR3 estimates that chemical
EOR technologies constitute more than 60 per-
cent of the additional EOR potential for ad-
vanced technology and that surfactant flooding
represents more than 90 percent of this poten-
tial. Research objectives are to extend surfac-
tant flooding to more severe conditions and to
make it more cost-effective.
The stakes in continued research and devel-
opment of EOR technologies are enormous.
They involve decreasing U.S. dependence on
imported oil and extending the useful lifetime
of the world's exhaustible supply of petroleum.
The NPC study of EOR estimates that with
currently implemented EOR technologies the
_'
~ STEAM AND CONDENSED WATER ZONE
FIGURE 6.4 Steam flooding is one of two principal thermal methods for oil
recovery and has been commercially applied since the early 1960s. A mixture
of steam and hot water is continuously injected into the oil-bearing formation
to displace mobilized oil to adjacent production wells. Reprinted with per-
mission from Enhanced Oil Recovery. Copyright 1984 by the National
Petroleum Council.
total ultimate EOR potential for the United
States is 14.5 billion barrels (Figure 6.6), which
is more than 50 percent of the U. S. total
estimated future recovery by primary and sec-
ondary processes. The NPC study also esti-
mates that successful development of projected
advanced EOR technologies could make pos-
sible the recovery of 27.5 billion barrels of
domestic oil (Figure 6.61. This is more than 10
years of U.S. production at current rates and
could provide an important augmentation of
domestic supplies well into the next century.
Shale Oil Production
Oil shales are a large, virtually untapped
source of hydrocarbons. U.S. reserves repre-
sent several hundred billion barrels of oil and
OCR for page 85
INJECTION WELL
WATER PUMP ~ ~ ,
~ ~ rim_=
~SSI.\G OF ENERGY AND NATURAL RESOURCES
AIR COMPRESSOR
PRODUCTION WELI
COMBUSTION GASES T
- 1 - l- (it) COLD COMBUSTION GASES (0 COKING REGION I I , I
J ~ - ~ 1 _r~ (at) OIL BANK (NEAR INITIAL TEMPERATURE) (is) BURNING FRONT AND COMBUSTION ZONE am, I I I I
L ~ I ~ r =- - ~-\ CONDENSING OR HOT WATER ZONE A_ , ' - ~ ' ,
- 1- . --' - - J- ~J (50° - 200°F ABOVE INITIAL TEMPERATURE) W AIR AND VAPORIZED WATER ZONE ~L
(is) STEAM OR VAPORIZING ZONE . (is) INJECTED AIR AND WATER ZONE
(APPROXIMATELY 400°F) (BURNED our
FIGURE 6.5 In-situ combustion is a major thermal means of oil recovery. Heat is
generated in the reservoir by injecting air and burning part of the oil. This partially
vaporizes the remaining oil, which is then driven forward by a combination of steam,
hot water, and gas. Any oil left behind becomes fuel for the in-situ process. Water
is also injected into the well; it improves the efficiency of the process by transferring
heat from the rock behind the combustion zone (7) to the rock immediately ahead
of the combustion zone (4). Reprinted with permission from Enhanced Oil Recovery.
Copyright 1984 by the National Petroleum Council.
are located in both the western and eastern
states. Eastern oil shales are intimate mixtures
of inorganic silts and insoluble organic material
that have been consolidated into rock. In west
ern oil shales, the matrix is a carbonate-based
marlstone. The organic content of both shales
is typically 5-30 percent, and most of it is a
polymeric, insoluble petroleum precursor called
kerogen. Shale oil can be recovered by heating
the rock through the range from 250 to 500°C,
where the kerogen is thermally decomposed to
liquid and gaseous products, leaving 20-35 per
cent of the organic matter as coke (Figure 6.7~.
Because of the insolubility of kerogen and the
difficulty of physically separating it from the
shale, this retorting method is the only recovery
process that has been developed.
Retorting can be carried out above ground or
in situ. The former process involves mining the
shale and heating it in a vessel. Process devel-
opment has been concentrated on three impor-
tant engineering problems. The first is how to
handle the large quantities of solids that must
be processed. The second involves how to
transfer heat to those solids. And the third
concerns the effect of shale particle size on the
efficiency of oil recovery. In-situ retorting is an
alternative to mining the shale, but only if the
shale bed can be made sufficiently porous to
allow injection of air to burn part of the kerogen
OCR for page 86
~6
and the resulting coke and to
permit outflow of the retorting
products. In shallow beds, blast
ing can lift the overburden and
fracture the shale to permit these
necessary flows. In deeper de
posits, partial mining followed
by blasting shale into the result
ing space is used to create a
porous rubble bed underground.
Engineering research has fo
cused on ways of producing po
rosity, on gas How and combus- ADVANCEDTECHNOLOGY
tion in porous beds, and on As BlLLlON BARRELS
recovery of products from the
large quantities of off-gas. Much
of this research and development
must be done in the field on a
large and costly scale.
It is possible that greater po
rosity in shale beds could be
achieved by chemical commi
nution of the shale. For example,
the treatment of western oil shales
with acid solutions might result
in comminution by inducing cor
rosive stress fracture of the car
bonate rock. Chemical engineering research in
this area, as well in the elucidation of oil-rock
interactions, might provide insights for new
strategies for oil shale production.
Conversion of Coal to Gaseous and
Liquid Fuels
Coal is the giant of fossil fuel resources.
World reserves are many times those of petro-
leum, and the United States is one of the major
resource holders. Coal can be used directly in
combustion or converted to gas or liquid. Only
combustion consumes significant amounts of
coal today.
Coal is currently economically useful only in
plants that are equipped for large-scale handling
of solids, and it is used only indirectly as a raw
material for chemical synthesis. Accordingly,
there has been considerable research on pro-
cesses for converting coal into gaseous or liquid
fuels and chemicals. Only gasification has ad-
vanced to commercial status.
FRONTIERS IN CHE^~lCAL ENGINEERI1YG
Miscible
Thermal ~ Chemical
IMPLEMENTED TECHNOLOGY
14.5 BILLION BARRELS
FIGURE 6.6 Prospects for enhanced oil recovery using implemented and
advanced technologies are shown above. The ultimate amount of U.S. oil that
can be recovered by ''implemented technology," technology that presently
exists in at least the proven field test stage, is estimated to be 14.5 billion
barrels. Using "advanced technology," technology that might be conceivably
developed before 2013, adds another 13 billion barrels of oil to the estimate,
for a total of 27.5 billion barrels. A comparison of the distribution of ultimate
recoveries by method is also shown. Most of the increase in the estimate
from applying advanced technology comes from improvements in chemical
flooding methods. The projections assume that crude oil has a nominal price
of $30 per barrel and that the minimum rate of return on capital is 10 percent.
Reprinted with permission from Enhanced Oil Recovery. Copyright 1984 by
the National Petroleum Council.
Coal is gasified by heating it in the presence
of steam to make synthesis gas (syngas), a
mixture of carbon monoxide and hydrogen. A
variety of processes for coal gasification have
evolved, and several U.S. pilot facilities have
been built on scales of 100 to 1,000 tons per
day during the last 10 years. The Great Plains
coal gasification plant in North Dakota is op-
erating at 10,000 tons per day. Coal syngas has
lower energy content than natural gas for fuel
use, but is widely used for the synthesis of
liquid fuels and other chemicals. For example,
Tennessee Eastman is operating a commercial
plant that converts 900 tons of coal per day into
syngas that is in turn converted into acetic an-
hydride and other chemicals by a series of cata-
lytic reactions. The Tennessee Eastman process
is an excellent example of innovative chemical
engineering in the design and construction of
an efficient plant to synthesize organic chemi-
cals from nonpetroleum raw materials. (See
"Acetic Anhydride from Coal" on pp. 88-89.)
OCR for page 87
PROCESSING OF E1VERGY A^~D VA TURAL RESOURCES
CRUSHED OIL & FINES
SHALE RETORT
IT
FINES
COMBUSTION .
1
SPENT
SHALE
UNDERGRADE _
MATERIAL
, GAS TO CLEANUP
SOLID
LIQUID
SEPARATION
FIGURE 6.7 Steps in oil shale retorting are shown. Oil shale is crushed and
then heated in a retort to drive off the oil that is trapped in the rock. Any oil
left behind, as well as particulates returned to the process as the recovered
oil is processed, is burned to provide heat for the retorting. The oil that is
recovered from the shale is chemically treated to produce synthetic crude for
further processing in conventional refineries. Courtesy, Amoco Oil Company.
Coal syngas can be converted into liquid
hydrocarbon fuels by catalytic reactions. One
process for this conversion, the Fischer-Tropsch
process, was developed in Germany during
World War II and is being operated on a large
scale in South Africa. Today's pilot facilities
and pioneering uses of syngas are establishing
a technical and economic basis for the genera-
tion of commercial coal gasification projects
that is expected to emerge in the 1990s.
Coal gasification research and development
have concentrated on handling of solids, prob-
lems with ash, and dealing with the sulfur and
nitrogen compounds present in coal. The newest
pilot plants are investigating catalytic gasifica-
tion. The integration of coal gasifiers with elec-
tric power generators in a combined-cycle mode
(Figure 6.8) is an emerging field for design
studies and economic evaluation. Much of the
combined-cycle equipment is being perfected in
natural-gas-burning plants that will come on
stream in the next few years.
In-situ coal gasification has been demon-
strated in small-scale field tests. Compared with
aboveground gasification, in-situ gasification has
the potential advantage of mitigating many of
87
l
OILHYDRO-
TREATING ~ SYNCRUDE
_
SOUDS
DISPOSAL
the problems associated with materials corro-
sion and mechanical solids handling; the main
environmental problem is groundwater contam-
ination. A further benefit of in-situ coal gasifi-
cation is the potential for exploiting coal re-
serves that cannot be mined economically.
However, it is no less complex than in-situ
recovery of heavy tars or shale oil, and the
engineering challenges are comparable.
The conversion of coal into liquid materials
can be accomplished by pyrolysis or by direct
liquefaction heating coal in the presence of a
hydrogen source. Neither of these routes is yet
economically feasible.
In pyrolysis, coal is split into a hydrogen-rich
liquid and a hydrogen-depleted solid char. The
liquid contains significant amounts of nitrogen
and sulfur compounds, as well as high-molec-
ular-weight aromatic compounds such as as-
phaltenes. It is difficult to upgrade this liquid
to a fuel suitable for transportation uses. Fur-
thermore, while the liquid might be used in
boilers, it would pose severe problems of nitro-
gen and sulfur oxide emissions from power
plants. Research to date has uncovered few
uses for the char, and it must be disposed of.
OCR for page 88
FRONTIERS ^~N CHE.~AL ENCINEERIiN'6
There are challenges and oppor-
tunities in developing a process
for in-situ pyrolysis of coal in
which the char is the principal
fuel.
In direct liquefaction, coal is
heated in the presence of hydro-
gen and a catalyst such as cobalt-
molybdenum or nickel-molyb-
denum on alumina to give a
greater yield of high-quality hy-
drocarbons than that produced
by pyrolysis. This hydrogenation
process has been demonstrated
in several 50- to 250-ton-per-day
plants.
Chemical engineering research
on direct liquefaction has fo-
cused on improving hydrogena-
tion efficiency, for example, by
treating a coal slurry in a hydro-
gen-donor solvent in a high-pres-
sure reactor. Basic knowledge of
coal structure and reactivity as
well as scientific understanding
of hydrogen-transfer reactions has
been crucial in improving the
process. Equally important has
been the realization that the de-
sired reaction products can
undergo secondary reactions that
diminish yields and quality of
final products. Accordingly, two-
stage liquefaction with a catalyst
in one or both stages is being
tested on a small scale. Although
catalyst performance is improv-
ing, there is still a need for cata-
lysts that will perform even bet-
ter in such severely fouling
conditions.
New Raw Materials for
Petroleum Refineries
As the domestic mix of fossil
fuel resources changes over the
coming years, new challenges will emerge for
the design and renovation of our nation's in-
stalled base of refineries. While the practical
aspects of this task must be left to the petroleum
and gas industries, there is a need for funda-
mental research to provide new design concepts
and for trained engineering personnel to main-
tain international competitiveness in these in
OCR for page 89
4~R ~ CESSING OF ENER ~ ~ A.~D HA TU~ ~ RES ~ ~ ~ CES
dustries. The challenges arise from the prop-
erties of the new raw materials that are already
finding their way into the process mix. In
comparison with the crudes for which
refineries have been designed,
both heavy crudes and shale oil
contain hydrocarbons of higher
molecular weight and higher car-
bon-to-hydrogen ratio; more un-
wanted sulfur, nitrogen, and cat-
alyst-poisoning metals like
vanadium and nickel; and a bi-
tumen-like residue that is diffi-
cult to refine. Such resources
must be upgraded by chemically
adding hydrogen or chemically
removing carbon, by redistrib-
uting hydrogen among hydrocar-
bon fractions, and by removing
compounds of heteroatoms and
metals. Research has already led
to improved thermal upgrading
methods such as fluid-bed coking
with coke gasification to remove
carbon (Figure 6.9) and to cata-
lytic hydrotreating schemes to
add hydrogen and remove com-
pounds of nitrogen, sulfur, vana-
dium, and nickel (Figure 6.101.
The co-processing of coal with
heavy crude oil or its heavier
fractions is being developed to
lower capital requirements for
coal liquefaction and to integrate
processing of the products of
coal conversion into existing pe-
troleum refineries. This devel-
opment appears to represent the
main route by which coal-based
liquid fuels will supplement and
perhaps someday displace petro-
leum-based fuels.
At the low-molecular-weight
end of the spectrum, a process
newly commercialized by Mobil
for converting methanol into gas-
oline has significantly expanded
opportunities in C-1 chemistry-
the upgrading of one-carbon mol-
ecules to multicarbon products.
The process involves the use of
ZSM-5, a shape-selective zeolite catalyst. (See
"Zeolite and Shape-Selective Catalysts" in
Chapter 9.)
Since methanol can be made from coal, nat
OCR for page 94
so
~1 ~1~, 11
,1r! ~
FUEL FABRICATION
.~
E. it' h
PROCESSING
URANIUM
MINING
1 1
:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:
·:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:
~_ I ~l_ ~_ r
Van ~0
~ · . o · · ~ · . b .. v ~ ~ . ;- ~ ;', '.
MILLING
. ,
. ~
such fields as pyrometallurgy, thermodynamics
of metal-salt systems, ceramics, distillation of
metals, waste processing, and remote process
control technology.
Nuclear Fusion
Although generation of power from nuclear
fusion has not yet been demonstrated, it is
potentially a huge source of energy. Fusion
power, the source of the sun's energy, results
from the release of energy through the combi
FR0~RS I,\ CHE1~AL E.\GINEERING
l
it,
REACTOR
I In
SPENT FUEL STORAGE
~ ~ ~ ~ ,,_~_.~
SPENT FUEL SHIPMENT
DEEP GEOLOGIC ISOLATION
·-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:
·:::::::::::::::::::
....................
.: . - · ~ ~
J '
:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:
in;- i'' 0;; _ ~
. 0.`'··O~ ·~>
_ ~r=~ r _ ~1
O-0 ~. ;·0;~ ~';-02 ~° ACE
FIGURE 6.12 Chemical process steps lie at the heart of the nuclear fuel cycle
used in the United States. Uranium from mining and milling operations is
converted to UFO, a volatile gas, which can then be separated so as to isolate
the radioactive isotope of uranium. Further chemical steps are used to convert
UFO into UO' for fuel assemblies, to isolate the long-lived isotopes generated
in nuclear power plants, and to encapsulate these isotopes for eventual storage
in nuclear waste respositories. Courtesy, Argonne National Laboratory.
nation of light elements into heavier ones. The
reaction currently under study is fusion of
deuterium and tritium to produce helium and
neutrons. Deuterium, an isotope of hydrogen
present in low concentration in water, can be
obtained by separating it from seawater. Tri-
tium, another hydrogen isotope, is generated
by reacting lithium with neutrons. In a fusion
reactor, it would be generated in the lithium
blanket of the reactor by neutrons derived from
the reactor.
Major research programs in the United States
OCR for page 95
~SSi.~76 OF ENERGY AND '\~^L RESOURCES
and the Soviet Union have concentrated on
proof of principle and on containment of the
extremely high-temperature nuclear reaction.
Although the research is expensive, U.S. federal
funding had been relatively ensured until recent
budgetary problems. Chemical engineering re-
search is needed on the preparation of solid
breeder materials, blanket tritium recovery,
blanket coolant technology, high-temperature
heat transfer, low-activation materials, and tri-
tium containment.
Electrochemical Energy Conversion and
Storage
The last 25 years have witnessed a rapid rise
in the numbers and capabilities of batteries, fuel
cells, and electrolysis cells. Developments in
batteries and fuel cells open the way to new
and improved schemes for energy storage and
power generation (see "Fuel Cells for Trans-
portation" in Chapter 91. Devices invented for
military and aerospace applications have moved
quickly into civilian use for example, in con-
sumer electronic products, stationary energy
storage, and electric vehicles. Significant ad-
vances in electric vehicle technology could
significantly reduce demand for transportation
fuels derived from petroleum.
The areas of important electrochemical en-
gineering research can be grouped by the desired
results. Initial costs can be lowered by devising
better or less costly corrosion-resistant mate-
rials for inactive components of cells, superior
catalysts for electrodes in fuel cells and elec-
trolysis cells, and innovations that reduce the
complexity of electrochemical transformation
systems. The useful lifetimes of systems can be
lengthened by reducing corrosion, improving
electrodes, and understanding how porous elec-
trodes perform and change in structure during
cyclic operation. Finally, battery and cell per-
formance can be improved by developing new
materials that permit higher electrode reaction
rates and lower internal electrochemical losses
and by new designs based on modern electro-
chemical engineering.
Solar Power
The challenge of solar energy research is to
discover or develop efficient processes for trans
forming radiant solar energy into usable elec-
trical energy or chemical fuels. Solar energy
has inherent advantages over other energy
sources. It is plentiful, ubiquitous, free, and
continuously replenished, and it can be con-
verted into electricity or fuels by processes that
are environmentally benign. Yet, because it is
a dilute and highly variable source of energy,
conversion costs are high, and the construction
of large (1,000-MW) commercial plants for elec-
tric power or fuels production is not likely in
this century. Solar energy falls on the earth at
about 1 kW/m2 at noon on a sunny day. A solar
cell area of about 40 km2 (15.5 mill would be
required to construct a 1,000-MW power station
with solar cells that are 12 percent efficient,
assuming an average of 5 hours of sunlight per
day throughout the year. The cost of siting and
constructing a plant of this size, based on current
technology, would be great. On the other hand,
smaller photovoltaic arrays are being used as a
peaking resource by some electric utility grids.
For example, Southern California Edison main-
tains an array of about 0.1 km2 to produce about
7.5 MW of power. It operates unattended and
has low maintenance expenses.
Solar power research should be continued to
make smaller scale applications of solar energy
more cost-effective. Specific research areas for
chemical engineers in photovoltaics include de-
velopment of low-cost methods for producing
the cell materials and for fabrication of the other
components that are proportional to cell area.
Solar-induced temperature gradients afford op-
portunity for ocean thermal energy conversion.
Research is needed on convective and phase-
change heat transfer as well as on biofouling
control to minimize resistance to heat transfer
on the seawater side. Development of low-cost
materials and methods of construction for heat
exchangers will be key to the success of this
technology.
Research on the molecular basis of photoex-
citation and electron transfer, including inter-
actions of electron donor and acceptor mole-
cules, could lead to new photochemicals.
Development of model photosensitive com-
pounds and methods of incorporating them into
membranes containing donor, acceptor, or in-
termediate excitation transfer molecules, and
.
OCR for page 96
~6
eventual development of photo-
chemical reactor systems, could
involve the use of sunlight to re-
place less-specific energy sources.
Geothermal Energy
In some situations, it makes
good economic sense to tap the
earth's heat as an energy source.
One approach to utilizing this
resource is illustrated in the side-
bar on this page.
Plant Biomass as a Fuel
Source
During the 1970s, considerable
attention was given to fuels from
renewable resources. Use of
wood-burning stoves increased
markedly in some parts of the
country. A subsidized industry
to prepare ethanol as a gasoline
supplement was started. But de-
spite this, it is unlikely that plant
biomass will ever satisfy more
than a small percentage of U.S.
energy demands. The reasons are
primarily technological and lo-
gistical.
Much of the plant biomass pro-
duced on U.S. land and water
areas is used for food or forest
products or exists in designated-
use areas such as parks and na-
tional forests. If 10 percent of
the total biomass were available
for conversion to energy, it would
represent about 5.7 x 10~8 J/yr
(5.4 x 10'5 BTU/yr). With the
generous assumption of 50 percent conversion
efficiency, this biomass would produce about
2.8 x 10'8 J/yr (2.7 x 10'5 BTU/yr) of energy as
fuel, or only about 3 percent of current U.S.
energy demand. Furthermore, the logistics of
collecting today's available biomass would be
forbidding. If a large area for producing biomass
for energy were to be set up, it would almost
certainly have to be on marginal land and would
FRONHERS IA' ~L ENGI.~NG
require greater than average use of fertilizer,
irrigation, and mechanical work, all of which
consume fuel energy themselves. The cost of
net energy contributed by biomass will always
be substantially higher than that calculable for
the gross (i.e., apparent) fuel product. Thus,
economic considerations would appear to rule
out production of large amounts of energy from
this source for the foreseeable future, and en
OCR for page 97
PROCESSING OF ENERGY AND ^~ATU^L RESOURCES
gineering research for such schemes does not
merit high priority.
The development of bioreactor systems for
the production of large-volume chemicals (see
Chapter 3) could be the basis for reconsidering
the production of biomass in limited quantities
for fuel uses. This would require efficient mi-
crobial organisms to catalyze fermentation,
digestion, and other bioconversion processes,
as well as efficient separation methods to re-
cover fuel products from process streams.
TECHNOLOGIES FOR EXPLOITING
MINERAL AND METAL RESOURCES
The technologies involved in the minerals
processing industry can be broken down into
those where the desired metal component~is in
high concentration, such as scrap iron, iron ore,
phosphate ore, and bauxite, and those where
the concentration of the valuable constituent is
low, such as gold and silver ore, lean copper
ore, and certain types of scrap and wastes.
High-Concentration Raw Materials
The economics of extraction processes re-
quire the primary raw materials industries to
locate near the richest ore deposits. Many such
deposits are now outside the United States. The
combination of high U.S. labor costs, foreign
government subsidies, and very dilute domestic
ore deposits (0.5 percent or less) has driven a
substantial portion of the copper mining and
refining industry to foreign countries. The de-
velopment or acquisition of technology abroad
for the smelting of nonferrous metal sulfides,
electrolytic extraction of zinc, and production
of steel has drawn portions of those industries
overseas. Although U. S. industry has been slow
to adopt the new technologies, there are indi-
cations that the pace of U.S. research and
development in these areas may quicken. An
example is the steel industry/federal government
initiative in steel making. Projects now under
way or planned include electromagnetic contin-
uous casting, direct reduction of ore, and de-
velopment of processes to remove copper and
tin from scrap steel.
97
High concentrations of valuable elements ex-
ist in the earth's crust but cannot be economi-
cally recovered because they are buried too
deep. The challenge to the chemical engineer is
to develop methods for extracting these valuable
materials in place without having to move and
process enormous amounts of rock. The general
concepts for in-situ recovery by solution mining
or leaching are practiced for the recovery of
uranium, soda ash, and potash. Despite these
successes, most of the opportunities remain
untapped because of technological barriers. Each
mineral deposit has its own characteristics, and
the processing environment deep beneath the
earth's surface has been constructed by nature;
our ability to modify it is limited.
Many research needs in this area parallel
those of in-situ processing of oil shale and
recovery of heavy crude oils. Additional re-
search needs cover a broad spectrum of mining,
metallurgical, environmental, and chemical en-
gineering: solids handling and comminution,
separations and concentration processes for ore
beneficiation, electrolytic processing, solvent
extraction, and treatment and disposal of waste
products. It will take the best-trained chemical
engineers using the most sophisticated tools of
chemistry, physics, and computer technology
to unlock economically the vast reserves of
metals and minerals that cannot be recovered
at present.
Low-Concentration Raw Materials
The ascendant method for economically pro-
cessing deposits low in the desired component
is solvent extraction. This is most commonly
done in processing plants above ground, and all
the spent ore must be restored to its original
location or otherwise disposed of in a way that
meets environmental constraints. The restora-
tion cost can be borne by high-value products
like gold, silver, and uranium. In the production
of moderate-value products such as copper from
lean ores, magnesium from dolomite, and alu-
minum from raw materials other than bauxite,
the only economically viable way to process
deposits may be to extract more than one
product. This requires designing and building
more complex chemical plants, with all the
OCR for page 98
attendant challenges to chemical engineering
research.
Waste Streams as Sources of Minerals and
Metals
Substantial quantities of aluminum, copper,
and steel are reused as scrap. The challenge is
to purify the scrap metal sufficiently to process
it for reuse. There is opportunity for new pro-
cesses that can remove unwanted elements-
either alloyed or piece contaminants more ef-
fectively and at lower cost than current pro-
cesses.
Many of the waste streams from U. S. process
industries are water containing small quantities
of metal ions that the law requires be removed
before the wastewater is disposed of. There is
an economic incentive to recoup at least some
of the cost of wastewater treatment by recover-
ing and selling the metal content instead of
merely disposing of the metals as sludge. Be-
cause the waste streams are dilute in desired
materials, research is needed to devise efficient
extraction and separation processes.
Likewise, fly ash from power plant combus-
tors often contains small amounts of metals or
their oxides, which require costly disposal in
the ever-shrinking number of approved hazard-
ous waste landfills. Thus, there are economic
incentives to recover the metal values as well
as to reduce the costs of ultimate disposal.
Here, too, the metal content is low, and research
is needed to develop economical separation
processes. In principle, advances in this area
could be translated into recovery of metal values
from mine tailings.
INTELLECTUAL FRONTIERS
The basic technologies used in the energy and
natural resource processing industries have many
elements in common, and the chemical engi-
neering profession has a long history of finding
and adapting basic technologies to the needs of
diverse industries. No profession is better suited
by tradition and training to attack the many
difficult technical problems of these industries.
And these problems must be attacked and solved
if our country is to maintain its high standard
FRO1~S IN CH^£~AL E\&~.~G
of living and its position in the worldwide
economy.
The demands for energy and materials con-
tinue to increase, and the accessibility of natural
resources to meet them continues to fall as the
most easily recovered fossil fuel and mineral
deposits are depleted. The gap between rising
demand and falling availability must be bridged
by technology that improves the efficiency of
extraction, conversion, and use of energy and
materials. The development of such technology
takes long lead times, and there is a paramount
long-term need to maintain momentum in re-
search on the frontiers of chemical and process
engineering. The problems enumerated here
offer challenges equal to any that chemical
engineers have faced in the past.
In-Situ Processing
Available resources of fuels and materials in
the accessible parts of the earth's crust are
becoming increasingly scarce. The alternative
to moving greater and greater amounts of crust,
whether it is mixed with the valued substance
or simply overlies it, is in-situ processing. A1-
though this technology is well established in
petroleum recovery, the long-term incentive to
increase its efficiency is great. The incentives
for other in-situ technologies vary but are bound
to intensify in the future. The development of
in-situ processes involves long lead times in
research and development. Field tests are large-
scale, prolonged projects that may last many
months. The potential environmental problems
are considerable. By the time the need for an
in-situ process becomes acute, it is too late to
commence research. The prize goes to those
who are prepared.
Problems with in-situ processing share certain
elements. Fluid phases move through a vast,
complex network of passages in a porous me-
dium. The process is inherently nonsteady state.
The physical transformations or chemical re-
actions proceed in zones or fronts that migrate
through the porous structure. The fluids interact
physically with the solid walls that define the
passages. The passages are irregular, and their
dimensions and structure change with distance.
This structural inhomogeneity imposes uncer
OCR for page 99
PROCESSING OF ENERGY AND NAP URAL RESOURCES
tainties that make processing in situ riskier than
processing in designed and constructed plants.
Further, the potential adverse environmental
impacts of in-situ processing have proved to be
important barriers to the widespread commer-
cialization of in-situ processes for oil shale and
coal. Sustained research in the following areas
is needed to reduce both environmental and
process risks:
· porous structures, both at the microscopic
scale and larger;
· methods for creating or enhancing perme-
ability in nonporous formations of oil shale,
coal, and ore bodies;
· combustion processes under reservoir con
. .
citrons;
· mechanisms of oil displacement;
· the distribution and flow of viscous fluids
in porous media and the motion of complex
fronts;
· surface and colloidal phenomena involved
in fluid-rock interactions, such as wetting and
spreading, and adhesion and release;
· phase equilibria, phase thermodynamics,
and chemical reactions between injected fluids
and solids in the reservoir;
· phase behavior, colloidal aspects, adsorp-
tion, and rheology of surfactant formulations;
· rheology and degradation of hydrophilic
polymers and their interactions with rock;
· the chemistry involved in winning a desired
component from a given type of deposit;
· separation of fines from produced mate-
rials;
· treatment and disposal of tailings;
· mathematical models of such phenomena;
and
· process synthesis, design, management, and
optimization with severely limited information.
Geochemistry, geophysics, geology, environ-
mental science, and chemical engineering must
be more closely linked if advances are to be
made in these areas.
.
Processing Solids
Solids handling is ubiquitous in the processing
of energy and natural resources. To liberate the
desired components, crystalline solids (e.g.,
99
rocks) must be broken into grains; these may
have to be comminuted to yet finer particles.
Current crushing and grinding processes are
highly energy inefficient; typically 5 percent or
less of the total energy expended is used to
accomplish solids fracture. These processes also
produce a broad distribution of particle sizes,
including fines that are difficult to process fur-
ther. Solids comminution could be greatly im-
proved by a process that fractured crystalline
solids selectively along grain boundaries.
Fundamental understanding of crushing,
grinding, and milling is deplorably limited. For
example, there is no rational basis for the design
of a ball mill, a commonly used industrial device.
Mineral processing and chemical engineering
researchers need a deeper understanding of
solid-state science and fracture mechanics, just
as they have mastered and are contributing to
colloid and interface science. There are great
challenges in devising chemical comminution
aids as well as processes for handling solids
that become plastic, sticky, or reactive at tem-
peratures reached in comminution.
Just as important as finding better ways to
prepare granular solids and powders is finding
ways to move them, to contact them with fluids,
to allow them to react in chemical processes,
and to separate the residues. A major study in
19816 showed that cost overruns on large proj-
ects involving solids processing depended di-
rectly on the throughput rate of solids. Much
of the current equipment design for mineral
processing dates from earlier times when ores
were richer and costs of processing not as high.
The handling of coal, oil shale, and ores would
be improved by research on the mechanics of
pneumatic and slurry transport of particulate
solids, particularly on the mechanisms of failure
through plugging, attrition, and erosion. Im-
proved processes for coal liquefaction and gas-
ification could come from research on particu-
late transport in fluidized beds, including high-
pressure gas-fluidized beds of large particles,
ebulated beds, and liquid slurry reactors. We
must also understand chemical reaction pro-
cesses in systems of moving particles, especially
at high temperatures and pressures. There are
the related critical issues of particles being
consumed or created by chemical reaction,
OCR for page 100
particle agglomeration and sintering, and trans-
port and separation of hot sticky particles. For
example, Plate 5 shows the stages of retorting
of an oil shale particle as the temperature is
increased by an external hot gas. The kerogen
is reacted, cracked, volatilized, and coked in
an idealized series of concentric volumes. Lib-
erated products must flow through the coked
zone to exit the particle. If the temperature falls
too rapidly, particles can become wet and sticky.
These problems are related to the more general
problem of chemical reactions involving liquids
or gases inside porous solid particles.
Equipment design and scale-up present par-
ticularly great challenges whenever solids are
to be processed on a large scale. Consequently,
advances in the basic understanding of solids
processing will be for naught if they are not
translated into practical, reliable designs. This
will require close cooperation among the fields
of mechanical, mineral, and chemical engineer-
ing and between disciplines in the earth and
physical sciences.
Separation Processes
Separations play a vital role in the processing
of energy and natural resources.7 Improved
separations can lead to improved efficiency of
existing processes or to economical means for
exploiting alternative resources. For example,
the petroleum refining industry is based on
separations of natural and synthetic hydrocar-
bons. Improved separations could lead to better
concentrations of aromatic hydrocarbons in gas-
oline to enhance the octane rating and paraffinic
hydrocarbons in jet fuel to improve burning
characteristics. The winning of critical metals
such as copper, uranium, and vanadium from
low-grade domestic ores requires chemical ex-
traction followed by recovery from the dilute
extractant solution. More selective extractants
are needed, as are better separations to remove
fly ash, sulfur oxides, and nitrogen oxides from
power plant and other gaseous emissions to
protect air and water quality.
Every separation process divides one or more
feeds into at least two products of different
composition. Separation processes that operate
on heterogeneous feeds usually involve screen
.~RS Alar CHE!~L F^NGlYEERING
ing or settling. Those that involve physically
homogeneous mixtures must use more subtle
means to create products of different compo-
sition. These latter processes are pervasive in
industry; they consume large amounts of energy
and require sophisticated research and design.
Separation processes are based on some dif-
ference in the properties of the substances to
be separated and may operate kinetically, as in
settling and centrifugation, or by establishing
an equilibrium, as in absorption and extraction.
Typical separation processes are shown in Table
6.1. Better separations follow from higher se-
lectivity or higher rates of transport or trans-
formation. The economics of separation hinges
on the required purity of the separated substance
or on the extent to which an unwanted impurity
must be removed (Figure 6.131.
Most methods of separating molecules in
solution use direct contact of immiscible fluids
or a solid and a fluid. These methods are helped
by dispersion of one phase in the other, fluid
phase, but they are hindered by the necessity
for separating the dispersed phase. Fixed-bed
adsorption processes overcome the hindrance
by immobilizing the solid adsorbent, but at the
cost of cyclic batch operation. Membrane pro-
cesses trade direct contact for permanent sep-
aration of the two phases and offer possibilities
for high selectivity.
There is already intensive research on mem-
brane separations for energy and natural re-
source processing. Applications have so far
centered on organic polymeric membranes for
mild service conditions, but research could lead
to both organic and inorganic membranes that
can operate under harsher conditions. Zeolites
and other shape-selective porous solids like
pillared clays appear to offer a fertile field of
research for separation applications. Chemically
selective separation agents that distinguish be-
tween absorptive, chelating, or other molecular
properties are also attracting study.
Research should continue on traditional sep-
aration methods. For example, there is a con-
tinning need for more selective extraction agents
for liquid-liquid and ion-exchange extractions.
High-temperature processes that use liquid met-
als or molten salts as extraction agents should
have potential in nuclear fuel reprocessing and
OCR for page 101
PROCESSI;~G OF FNERGY ACID NA TURAL RE5~ES
TABLE 6.1 Methods for Separating Mixtures
Property Difference
Examples of Processes
Particle size
Magnetism
Density
Solubility
Surface affinity
Solid/liquid phase
Molecular character
Molecular size
Dielectric constant
Solidification temperature
Rate of phase change
Ionic character
Screening, mechanical jigging
Magnetic separation
Centrifugation, settling, jigging
Extraction
Adsorption
Filtration
Dialysis, membrane gas separation
Molecular sieve separation
Electrophoresis
Zone refining
Crystallization, distillation
Ion exchange
metals recovery; basic thermodynamic data on
such high-temperature systems are lacking.
Many of the ores of base metals are sulfide
deposits. They must be milled to exceedingly
fine size in order to free the wanted grains from
the rest of the mineral. The desired grains are
semiconducting colloidal particles, and the
mechanisms of leaching and flotation-the pre
1o6
104
~2
_~
- 2
1
lo-2
ferred methods of concentrating them depend
on both their electrochemical and colloidal prop-
erties. The separation processes leave a large
quantity of unwanted fines that must be rejected
as slimes. Better understanding of these pro-
cesses should permit separation of complex
sulfides and discovery of paths to recovering
individual metals from dilute, impure solutions.
/
/ · Radium
Vitamin B-12
Penicillin ~ ~
/
uranium from Ore
Id Gold
Copper ./ Magnesium from Seawater
/ .. ~ Bromine from Seawater
Mined Sulfur Sulfur from Stack Gas
/ ~ Oxygen
L Factor of 2
~ differential in price
100 percent 1 percent
1 percent
1 thousandth of 1 millionth of
1 percent
D I LUTI O N (expressed as percent concentration
FIGURE 6.13 The importance of separation processes in determining the
eventual cost of materials and products is illustrated in this figure. Product
prices correlate with the degree of dilution of the raw material in the matrix
from which it must be isolated. A factor of two in product price is shown in
the figure. Courtesy, Norman N. Li, Allied-Signal Corporation.
1 billionth of
1 percent
OCR for page 102
A hypothetical separation of a homogeneous
mixture, carried out in a thermodynamically
reversible manner, would require the theoretical
minimum expenditure of energy. In practice,
however, separations of such mixtures need 50
to 100 times this minimum. Thus, there is
significant opportunity for improvement of sep-
arations by creating ways to reduce energy
consumption without a commensurate increase
in capital and operating costs.
Researchers in separation science and tech-
nology draw on and contribute to a variety of
related fields, including
· phase-equilibrium thermodynamics;
· mass transfer and transport phenomena;
· interracial phenomena, including surface
and colloid chemistry;
· mechanisms of chemical reactions, espe-
cially complexation reactions;
· analytical chemistry; and
· computer-assisted process and control en
glneerlng.
Future progress in separation science and tech-
nology will require continued cooperative re-
search between scientists and engineers in these
fields.
Materials
Research on materials can lead to more eco-
nomical processing under extreme conditions
and to reduced capital and operating costs.
There are strong incentives to find construction
materials for process units that are derived from
domestic resources, that are less contaminating
of process and environment, and that have the
following properties:
· greater strength and more resistance to
abrasion and corrosion;
· longer life and less subject to degradation
by cycling conditions;
· serviceability under more severe conditions
of temperature, pressure, or neutron flux; and
· greater resistance to hydrogen embrittle-
ment.
There are comparable incentives to develop
new process-related materials that are more
selective as catalysts, extractants, or separation
FRON' - lERS IV CHExiUlCAL EM
membranes and more effective in controlling
flow in porous media. In addition, the devel-
opment of materials that are less energy inten-
sive in terms of production and use is a goal
equivalent to other means of energy conserva-
tion.
The relatively mature technology of upgrading
heavy oils by reaction with hydrogen is illus-
trative. Reactors are required to withstand hy-
drogen embrittlement at high pressures and
temperatures. Present practice is to use foot-
thick reactors lined with alloy steels. The largest
of these can no longer be constructed in the
United States because the cessation of nuclear
power construction has led to the closing of
facilities capable of such fabrication. Cheaper
reactor materials would improve the economics
of the process; better materials could lead to
operability under more severe conditions that
would provide higher conversions.
Materials problems abound in the energy
storage field. For example, cheap materials with
large effective thermal capacity are needed to
store thermal energy in solar heating systems.
Some systems use chemically reactive materials
and store energy as enthalpy of reaction. There
is an opportunity to develop photosensitive
catalysts to improve the coupling between the
solar energy input and the energy converter.
High-temperature thermal energy storage sys-
tems confront corrosion problems aggravated
by thermal cycling and temperature-sensitive
solubilities that conspire to shorten system life,
signifying the need for better materials. Like-
wise, battery storage of electrical energy is
limited by the cost of materials and by corrosion
and microstructural changes aggravated by the
inherently cyclic operation.
Materials science is an intrinsically interdis-
ciplinary field. Materials scientists include phys-
icists, chemists, metallurgists, mechanical en-
gineers, and chemical engineers. It is the latter
who have the best opportunity to establish
specifications for needed materials and to join
in research on ways to meet those specifications.
Advanced Methods for Design and Scale-up
Many of the shortcomings of energy and
natural resource processing arise from lack of
OCR for page 103
PROCESSING OF ENERGY Aide .~A TURAL RESOURCES
sufficiently powerful design and scale-up pro-
cedures for the practicing chemical engineer
(see Chapter 81. A goal of research is to design
large units from first principles and small-scale
experiments. This has been done in the past;
scale-up factors of 50,000 are common in petro-
leum refining technology. However, in much of
energy and natural resource production, there
is such complexity and lack of basic data,
especially for large-scale solids processing, that
empiricism will continue to prevail until pilot
plants and demonstration projects are success-
fully modeled. Scale-up factors in solids pro-
cessing typically range from two to five.
For example, research on moving hot solids
will require individual pieces of equipment, then
whole systems, from which reliable data for
scale-up can be obtained. Costs of such research
would be out of reach for all but the largest
industrial and government laboratories. The
application of research results to improved com-
mercial oil shale retorting would require large
pilot plants costing tens of millions of dollars,
followed by demonstration plants or single com-
mercial modules costing hundreds of millions.
Experimentation on an equivalent scale can be
imagined for a new steel-making technology,
for in-situ leaching of uranium, or for solution
mining of hydrothermal mineral deposits such
as soda ash. Such research will require inter-
disciplinary teams and sustained activity over
periods of years.
The problem of ever-increasing construction
costs dates from the mega-project concept of
World War II and the race toward an overnight
synthetic fuels industry. Nevertheless, large
construction projects will be needed to bring
coal gasification, coal liquefaction, and oil shale
processing to fruition. Construction costs are
not small in the minerals processing industries,
and the more dilute the ore, the larger must be
the economically viable plant. The incentives
are great to develop lower cost designs and
construction methods. Noteworthy ideas in-
clude modular construction from preassembled
units and the organization of construction into
multiple small projects. Substitute materials that
can be produced with lower energy or raw
material cost need to be developed. Chemical
engineers must be cognizant of the construction
cost implications when they select construction
materials and prepare flowsheets.
Other Important Research
Many additional intellectual challenges for
chemical engineers are relevant to energy and
natural resource processing. These include res-
ervoir modeling (Chapter 8), combustion (Chap-
ter 7), catalysis (Chapter 9), and electrochemical
engineering (Chapter 94. A recent report entitled
Future Directions in Advanced Exploratory Re-
search Related to Oil, Gas, Shale, and Tar
Sand Resources discusses some of the chemical
engineering research challenges described in
this chapter in a broad, multidisciplinary context
that includes the earth sciences.
[Finally, it should not be forgotten that chem-
istry plays an important role as a fundamental
science for these industries. Major contributions
to be expected from chemistry in energy and
natural resources are discussed in the 1985
report Opportunities in Chemistry.9
IMPLICATIONS OF RESEARCH
FRONTIERS
Each of the generic research areas discussed
in this chapter has a strong multidisciplinary
character. While the underlying fundamentals
of some are amenable to investigation by indi-
vidual chemical engineers, in many cases col-
laboration will be required between chemical
engineers and other scientists and engineers
skilled in geology, geophysics, hydrology, me-
chanical engineering, physics, mineralogy, ma-
terials science, metallurgy, surface and colloid
science, and all branches of chemistry. It will
be necessary to generate creative interactions
that overcome traditional academic compart-
mentalization of outlook, experience, and ed-
ucation. Academic departments of chemical
engineering should take the lead in establishing
interdisciplinary teams to carry out fundamental
research in these high-priority research areas.
They should seek ways to involve government
and industrial scientists in interdisciplinary ac-
tivities. There must be freer flow of information
between industry, university, and government;
professional disciplines; and academic depart-
ments.
OCR for page 104
The educational background of chemical en-
gineers makes them particularly well suited to
solve problems in the areas discussed herein.
Chemical engineers are used to working with
concepts from all the related fields, and their
training has evolved to cover most of the skills
needed to solve technical problems. Interdis-
ciplinary research in the relevant areas can only
strengthen the chemical engineering cadre in
the energy and natural resource processing
industry.
The funding needs for the research described
in this chapter will be large and long term; they
can be met only by some combination of gov-
ernment and industry. Government support is
appropriate because efficient processing of en-
ergy and natural resources is key to continued
national growth and prosperity. Appropriate
initiatives for the Department of Energy, the
U. S. Bureau of Mines, and the National Science
Foundation all in cooperation with industry-
are laid out in Chapter 10. Industry support is
mandatory because commercialization is a goal
and because companies will be the eventual
profit-driven proprietors of the technology de-
veloped. There is advantage and precedent for
companies to band together in consortia or
through institutes to provide continued funding
particularly of basic research. In addition, such
long-term commitment will allow academic re-
searchers the freedom to set up ongoing pro-
grams to feed basic data and concepts into the
centers and consortia without fear of sudden
shifts in funding priorities.
FRONTIERS IN CHEMICAL ENGINIEJE]R]!1~G
NOTES
1. 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 Of lice, 1986, Table 1310.
2. 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, Tables 1233, 1215.
3. National Petroleum Council. Enhanced Oil Re-
covery. Washington, D.C.: National Petroleum
Council, 1984.
4. J. Haggin. "Methane-to-Gasoline Plant Adds to
New Zealand Liquid Fuel Resources.'' Chem.
Eng. News, 65 (25), 22 June 1987, 22.
5. E. Berenyi. "Overview of the Waste-to-Energy
Industry." Chem. Eng. Prog., 82 (11), November
1986, 13.
6. E. W. Merrow et al. Understanding Cost Growth
and Performance Shortfalls in Pioneer Processing
Plants (Report R-2569-DOE). Santa Monica, Calif.:
Rand Corporation, September 1981.
This section draws, in part, on a recent NRC
report; Separation and Purification: Critical Needs
and Opportunities. Washington, D.C.: National
Academy Press, 1987.
8. National Research Council, Board on Chemical
Sciences and Technology. Future Directions in
Advanced Exploratory Research Related to Oil,
Gas, Shale, and Tar Sand Resources. Washington,
D. C.: National Academy Press, 1987.
9. National Research Council, Board on Chemical
Sciences and Technology. Opportunities in Chem-
ist~y. Washington, D.C.: National Academy Press,
1985.
Representative terms from entire chapter:
oil shale
