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THE hTDbSTRIALECOLOGY OF STEEL
4
FINAL EPORTTo
OFFICEOF BIOLooICAL
AND
EMENTALRESEARCH
U.S. DEPA.RT OF ENERGY
AWARD
NO.
DE-FGO2-97ER62496
BY
-.
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.
.
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. . .
.
Ahma-i26,2001
. . ...... . .
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.
.-
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.
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This report was prepared as an account of work sponsored by an agency of the
United States Government. Neither the United
States
Government nor
any
agency
thereof, nor any of their employees, makes any warranty, cxpnss or implied, or
assumes
any legal liability or responsibility for the accuracy, completeness, or use-
fulness of any inform ation, ap pa rat d, prcduct. or process disclosed, or represents
that its
usc
would not infringe privately owned rights. Reference herein to any
spe-
cific commercial product, process, or service by trade name, trademark, manufac-
turer, or otherwise dots not necessarily constitute or imply its endorsement. recorn-
mcndktion. or favoring by the United States Government or any agency thereof.
The
views
and opinions
of authors
expressed herein do not
necessarily
state or
reflect those of the United Sta tes Government or a n y agency thereof.
7/24/2019 ecologia industrial acero
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._
. .
DISCLAIMER
Por t i ons of this document may be ilkgible
.
in electronic image
produced
f rom the
document.
products. Images
are
best available original
. .
. .
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ABSTRACT
This study
performs
an integratedassessment
of
new technology adoption in the steel
industry. New coke,
iron,
and steel production technologies are discussed and their economic
and environmental characteristics are compared. Based upon
detailed
plant level data
on
ost
and
physical hput-output relations by process,
this
study develops
a
simple mathematical
optimization model of steelprocess choice. This model is then expanded to
a
life cycle
context,
accounting for environmental emissions generated during the production andtransportationof
energy
and
material
inputs into steelmaking. This life-cycle optimization model provides abasis
for evaluating the environmenM impacts of existing and new ironand steel technologies. Five
different plant configurations
are
examined from conventional integrated steel production
to
completely scrapbased operations. Two ost criteria are used o evaluate technoogychoice:
private and socialcost, with the
latter
ncluding the environmen&ldamages associatedwith
emissions. While scrap
based
technologies clearly generate lower em issions in mass
erm,
their
damage cost
estimates reported in the literature suggests that the social costs
associated scrap-
based steel production s slightly higherthan ntegrated steelproduction. Thissuggests adopting
a W -cycle viewpoint can substantiallyaffect environmental assessmentofnew technologies.
Finally, this study also examines the impacts
of
carbon taxes on steel production
costs
and
technology choice.
- -
._
_. _ _ .emissions
of
sulfur,dioxide-andnitrogen.oxides
re
significantly higher.
Using
conventional
. . . . . . . . .
.
..........
., .
_.
.............. . . . . . . . . . . . . .
ii
. . . .
....
-
. . . . . . .
. . . . .
_
.
-.
. . . . . .
. . . . . . . . . . .
. .
. . .
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Y TABLE OF CONTENTS
ABSTRACT ................................................................................................................................I
CHAPTER 1. CNTRODUCTION
.........................................
............................................ ........
CHAPTER
II
.
NEW
TECHNOLOGY
IN
THE STEEL
INDUSTRY
.................................
3
COKEhMCING
.........................................................
.................................................................... 4
No~polluting oking
ofcoal
.................................................................................................
6
Pulverized Coal Injection ...................................................................................................... 7
DIRECTE D U ~ O N
...................................................................................................................
8
Gas-Based Direct Reduction..................................................................................................
8
Midrex................................................................................................................................ 9
HYL .....................................................
:
............................................................................
9
Atex
..........
:......................................................................................................................
9
. . IronCarbide: .........................................................................................................
10
Circofer
&
Circored
.........................................................................................................
10
Coal-Based Direct Reduction
..............................................................................................
11
&rex
................................................................................................................................ 11
. . . . .
HTsmelt
............................................................................................................................. 12
AISI-DOE
irect Steelmaking........................................................................................ 12.
DxOSL._tE................................. ....................% ........................................................... 13
F
.............................................................................................................................
13
Finmet .............................................................................................................................. 13
OXYGEN TEELMAKtNGAND ........................................................................................ 14
SCRAP-BASEDETAL RODU~ON........................................................................................ 14
CASTING ................................................................................................................................... 16
CHAPTER III
.
EMISSIONS FROM IRON AND STEEL INDUSTRY
...................
7
COKEMAKING............................................................................................................................ 17
IRONMAKING
.............................................................................................................................
18
STEELMAIUNG
..........................................................................................................................
18
FACTORS
FFECTING
E~SSIONS.............................................................................................
19
Raw Material Qualiw.......................................................................................................... 19
Sulfur
Content
..................................................................................................................
19
IronContent ofOre. and Ore Type.................................................................................. 20
Fuel Choice and Quality .................................................................................................. 20
.
Physical
form
......................
:........................................................................................... 20
hpmtles
in
~ p u ~
.........................................................................................................
21
Control
Equipment
............................................................................................................... 21
Choice
of
Control Technology......................................................................................... 21
Efficiency of Control Technology....................................................................................
22
Process Characteristics
....................................................................................................... 22
Scrap-Using vs Raw Material Using Technologies......................................................... 23
Coke
vs Coal
Using Technologies
...................................................................................
23
..
. . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . .
. . . . .
. . . . .
. -
. . . . . . . . . . . . . . . -
..-.-.
-
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Batch vs Continuous Processes........................................................................................ 23
Y
Open
vs
Closed Systems.................................................................................................. 24
Positive
(High,
Low)
Vs
Negative Pressure Operation
...................................................
24
Byproduct vs Non-Recovery Coking............................................................................... 24
Degree of
Combustion.....................................................................................................
24
Duration ofOperations
....................................................................................................
25
Desired
Degree ofMetallization...................................................................................... 26
Product qualiv
.................................................................................................................
26
ReguIat0i-y Standards and Monitoring Stringency .............................................................. 26
Economic Vmiables
.............................................................................................................
28
High
temperature
Vs
Low
temperature
process
...............................................................
25
CHAPTER
Y
.
THE
NVIRONMENT & NEW STEEL TECHNOLOGIES
...................9
COKING TEC OL0GI ES ............................................................................................................ 29
................................. ......................................................... 32
......................................................................................................... 33
CHAPTER V
.
THE
IFE
CYCLE
ECONOMIC MODEL
.................................................
5
THE
ECONOMICROCESS ODEL............................................................................................
35
LIFEYCLE
MODEL
ODIFICATIONS
....................................................................................... 36
S~~~ELTING-OLOOIES ........................................................................................................ 29
. . . .-. -.?
Process Emission Coeflcients
.............................................................................................
36
.Ups.e.Acti.e. ...=....==..=...=.....-.=.......................................................................... 38
New
Technology
..................................................................................................................
39
Electric Arc
F
....................................................................................................... 39
Non-Recovery Cokemaking............................................................................................. 41
DirectReduction.............................................................................................................. 41
Natural Gas ShadowProcesses.....:................................................................................. 42
Model
Calibration
...............................................................................................................
43
MATHEMATICALT A ~................................................................................................... 45
CHAPTER VI: MODEL
SIMULATION
RESULTS............................................................
7
BASELINEECHNOLDGY COMPARISONS................................................................................... 47
CARBONTAX POL1.............................................................................................................. 49
Prlvafe Cosf Minlmfiatlon...................... .....................................................................
51
CHAPTERVII.POLICY IMPLICATIONS..
REFERENCES..,..........
............................ ..........W.....................
............................................... 53
APPENDIX
A:
ELECTRICITY BALANCE
.........................................................................
6
...
.
APPENDIX B: PROCESSUNITS..........................................................................................
57
APPENDIX C: COMMODITIES.......................................................................................... 1.58
60
PPENDIX D: EMISSIONS IN THE PROCESS MODEL
.................................................
iv
....
. - ..
1
. . .
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LIST OF TABLES
Table
1: Resource
use
and
env irom enta l performance ofcok ing technologies
........................ 30
Table 2:
Resource
use and
environmental
erformance
of
iron echnologies
............................ 31
Table
3:
Comparison of Alternative DIU Technologies .............................................................
32
Table 4: Resource use and environmental performance of steel re-g technologies.............. 3
Table
6:
Comparison of energy and
material
use for alternative steel technologies.
.................
47
Table 7: Air and solid
wastes
emissions fiom alternative steel technologies intons.................8
Table
8:
Incremental
costs for
new steel technologies
(millions
of dollars)...............................
50
Table
9:
Steel technology choice under various
carbon
axes
.................................................... 51
Table Al:
Comparison
OfElectricity Consumption
in Base
Case..............................................
56
Y
Table
5:
Process
associations
between
LCA and the
process
mode1
..........................................
37
LIST OF FIGURES
Figure 1
:
Future
steel
plant
configurations
...................................................................................
4
.-. -.Figure2: -Comparison-ofX?~-emissions-acrosslternative echnologies...................................
19
F i W 3:
Coking
duration
vs
wall
t e r n w e
..........................................................................
25
Figure 4: Relationshipbetween%green
coke
and PAH
emissions
..........................................
27
Figure
5
.Electricity
consumption
per
percent
DRI
e
...................................................... 40
Figure 6
Processmap ofthe LCA coke and coke oven
gas
production.
................................... .44
.
.......
_. .. .
.__-..T~.------- - -_-_I ..... . . . .
V
. . . . . . . . . . . . . .
..-
. . .
-., _ - .........
.~
-
...........................
-
....... . . . . . . . .
. . . . . . . .
....._lX...
...
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CI&PTER I. INTRODUCTION
The steel industry provides a classic example of anevolving industrial ecosystem.
During
the
late
19th and early 20th century, ntegmted steel plants in Pittsburgh and Chicago provided
neighboring communities with coke oven gas for lighting and district heating. Today, these same
plants recycle off-gases to generate
steam
and electricity
within
the plant. By-product coke ovens
were also a major
source
ofpetrochemicals during
this
era before modem petroleum refining
became prevalent. Post consumer recycling is also important with roughly 50 percent
of
all steel
in the
U.S. oming
from recycled scrap steel. Like the Kalundborg case discussed by Ehrede ld
and Gertler (1997), these loop clos ing activities slowly developed over time as firms identified
and characterized waste sources and
sinks.
Steel companies in theU.S. ollowed a similar course
but were driven more by intense competition from producers both home and abroad.
Technological innovations have always
been
mportant in steelmaking (Barnett and
- .- ._Cmdall, 1986),,SteeLmills use one of two types of furnaces o make new steel. Both
f uraaces
recycle old s teel into new, but each is
used
to create different products for varied applications.
The
first,
the basic
oxygen furnace
(BOF),
uses
about
28
percent steel
scrap
to
make new steel.
The other 72 percent is molten
iron
produced h m last furnaces,which require
iron ore
fiom
mines, limestone fiom quarries, and coke from batteries ofovens. The BOF furnace produces
d o r m and
high
quality fiat-rolled steel products used in
cans,
appliances, and automobiles.
The other type of steelmaking f i unace, he electric
scrap
to make-new steel;-Steel mim'mills-using-these
totaiU.S.
teel production. This steel is used
such as steel plates, rebars and
structuralbeams.
Steel
than
ntegrated d s ecause they do not require blast furnacesand coke ovens. Their reliance
on steel scrap also
affords
them anenvironmental advantage in lower energy and virginmaterial
consumption.
that can yield relatively highquality sheet steel. Thisadditional competitive forcecomes at a
time
when many integrated steel
firm
are seriously
reevaluating
their plants
in
light of the recent
regulationscontrolling oxic emissions
iom
coke
ovens.
Most existing methods of producing
coke generate Iigitive emissions &it
contain
potentially carcinogenic substances, such as
benzene soluble organics (BSOs). A variety of strategies, some entailing additional investment
andor hi@er operating costs, can educe these emissions. Considine, Davis, and hk akov it s
(1992) conducted a study estimating the benefits and costs
of
coke oven regulations,
incorporating closure decisions and new technology adoption, and found
that
investment in new
coking technologies
is
profitable under the new regulations.
Inkt nland Steel is currently building a large battery of coke ovens using the
Thompson non-recovery process, heralded as a possible clean technology breakthrough. This
design allows the controlled burning of coal that destroys the Benzene Soluble Organics
(BSOs)
and other potentially carcinogenic
compounds
contained
in
the offgases of the coking process.
There are, however, relatively large amounts
of
sulk dioxide emissions h m he waste heat,
which can be recovered via heat exchangers and used toproduce steam for electricity generation.
Minimills have entered the last domain of integrated steel, employing thnslab casting
. .
.
_ -
_ ._..---
.
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Iron
&
Steel - 2
0
There
are
several other
nev
iron
and steelmaking technologies that could either
substantially reduce or eliminate coking coal consumption in the production of steel. Pulverized
coal injection (PCI), replacing up
to
40 percent of the coke needed in ironmaking, is widely used
inEurope, Asia, and Japan and
is
now gaining favor in the United States (McManus
1992a).
Natural gas injection isa similar technology being promoted by the
Gas
Research Institute
(Brooks
1992).
There are also threenew steelmaking technologies that could totally eliminate the need
for coke. First, there
is
d rect reduction DR), a coal or
natural
gas-based
ironmaking
process,
that producqs an iron substitute for scrap in electric arc finances. Another coke eliminating
option is the Corex process, which does not requi recoke and produces a large volume ofwaste
heat that
can
be used
to
cogenerate electricity. Finally, there is direct steelmaking (DSM),
a
process that could eliminate the need for coking and ironmaking
in
traditional integrated steel
mills. Unlike
PCI
DR, nd CORFX, this echnology is currently not under commercial
development. -
these technological options.
our
analysis
is
based
upon
an engineering-txonomic model of steel production with environmental
coefficients from a life cycie assessment (LCA) of steelproduction tiom primary resource
extraction
to
the plant gate. Our model selects the optimal combination
of
activitiestominimize
cost subject
to
a numberof constraints, includingmass and energy balances for
intermediate
products. Substitute activities represent new technologies available for possible
many aggregate process models, cour.mociel is -fora-specific steel plant with cde
uponactualoperating~ormance.
The analysispresented below uses thismodel in three
ways.
The
first
application
compares the economic and environmental
performance
of steel technologies, ensuring
technical
feasibility.
This
analysis provides insights into the tradeoffs between cost and environmental
objectives, such as educing greenhouse
gas
emissions, toxic discharges, and acidic residuals.r
The second a p p l i k o n solves the model under
two
different definitions of
cost:
private and
social. The latter includes private costs and the environmental damages associated with the LCA
impacts. This
allowsus
o determinewhether steelproduction echnology would
be different if
environmenU externalities were internalized through a system
of taxes or
permits. Finally,
we
examine the impact of carbon
technological development in the steel industry. A
discussion
of fkctok
affecting emissions appears in Chapter
III. A
comparison of the resource
and environmental characteristics
of
alternative steel production paths appears in Chapter IV.
The development of the economic-engineering process model with Me-cycle impacts is
ChapterV.
This
model is then used in Chapter VI o compare the cost and environmental
emissions for technically feasible plant configurations using these technologies. The
final
chapter
summafizes our
main points and discusses the policy implications of
this
research.
- - . - - ~ i
-.-,
ia.-*.Z.=-,.
This study prese
technology choice in the steel industry.
The next chapter dis
. .
. .
. .
.
.
.
.
. ..
-.
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Industrial Ecology
-
3
CHAPTER
11.
N~TECHNOLOGYIN
HE
STEEL
INDUSTRY
Competition and recent environmental regulations are inducing technological innovations
that
will
transformmetal refining and smelting. The steel industry has been evolving fiom
a
highly capital intensive, batch processing production technologies to less capital intensive,
continuous
processing systems that
are
cleaner and
more
energy efficient. There
are
many
hdications
suggesting that this ransformation is accelerating. Moreover, faced with ever more
stringent environmental controls, many
firm
are redesigning their production process
to
eliminate pollution or to u t i l i wastes
as
resources.
This strategy is gaining hold in many
industries and
is
likely to become more widespread as firm learn that reducing pollution in some
cases may lower energy and material costs. Investments in new technology often hold the key to
these cost savings. Understanding the key characteristicsof these technologies and their
prospects
for
commercial
development
is
the primary objective ofthis chapter.
_-V~,beginut discussion by
.providing
an overview
of
the production process
to
establish
a context for
our
discussion ofnew ironand steel production technologies. With the recent large
Capacity
additions by steel
minimill
companies in flat rolled sheet production, there
is
increasing
concern
about the
availability ofiron
bearing raw
materials. As a
result, new iro
technologies, ironwaste recovery systems, and steel scrap purification techni
developmentthat could potentially offer steelmakersmore l e x i b ~ t yn their raw material
choices. Further down the production line, the success ofthin
-
castingappearstobeusheririg
in developing &~g~chnnaogies---- --- ----
- - - =
--
The distinction between integrated plants and steel m i n im i l l s is beginning
to
blur.
Most
steel plants in the United States are either traditional ore based integrated plants producing high
quality sheet and stripproducts or traditional scrap based electricarc h c e EAF) plants
producing bars, wire, structural shapes, and other long products. These polar opposites
appear
n
Figure 1.Note the difference in scale and the greater number of steps involves
with
integrated
steel production. Recently, some hybrid plant designs are emerging. Perhaps the best example is
the Nucor plant in Cradordsv ille,
Indiana
that produces sheet products using athin slab caster
fed
by
steel
produced
in E A F s using
a
mixture
of
scrap and
iron
carbide, a new ferrous material
input. Thisplant configuration
appears
in the third sectionof Figure 1.
Another
variation
involves integrated firm adopting
-
steel technologies, such as direct ironmaking,
advanced EAFs, and thin slab casting, a configurationknown as mini-integrated (see section 2
of
Figure 1). The concern over the availability of
high
quality ironmaterial inputs appears to be
main
impetus
or these innovations. Energy costs, capital availability, transportation costs, and
access toproduct markets are additional considerations. While there may be no unique optimal
mill configuration, the trend is toward so-called market
mills
that supply
a
market niche within
a
geographical area.
modernize across the entire production process
from
cokemaking
to
rolling and finishing
operations. For nstance, Wand Steel constructednon-recovery
coke
ovens and most ntegrated
firms
in the US are substantially raising their rates
of
pulverized coal injection into blast
furnaces. Minimills continue to advance electric arc
furnace
echnology. There is
a
g r o h g ist
New te c h d o g y adoption continues across all plant types. Integratedmills continue
to
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Iron
& Steel
-
4
of new ironmaking technologies designed to provide a substitute for
high
quality scrap, which is
in greaterdemand since
d s
re employing new casting technologies to produce high
quality products for appliance and automotive markets. Innovations in electricarc furnaces, such
as oxygen
injection,
arematching thisnew flexibility in raw material supply.
are
discussed in the
following sections.
Figure
1:
Future
steel plant configurations
ConventionaI Integrated Procaw:
4
mtll ion
tons
peryear
Sw
-
Mini
Integreted P&tion.-
1-2
miIIion tonsperyear
These innovations
+
Continuous
m
Thinslab
AdvancedScrqp Based Production.-1-2
mill ion
tonsperyear
-
Obsolete Mclter
Proccssin
castin
TmditionuISeng,Based Producton.-0.5-1
mill ion
tonsperyear
PCI
- pulverizedeoal njection
EAOF -HeCtric a r ~xygen
f i vnact
New
OSM--cOnvtntional
orcontinuous
refining with
scrap
preheating
AdvancedMeltg - Fossil fuel
or hybrid
melterwith scrap preheating
SOW: -(FnUhan.RJ.,d I.,-1995) .
.
COKEMAKING
Coke is
abasic
material used o manufacture iron n the s teel industry.
Iron
naturally
occurs
n oxide
ores,
and
a
chemical reaction
called
reduction
is
necessary
to
remove
the
oxygen,
leaving the ironinmetallic form. Carbon bonds strongly withoxygen, and coke, the residual
char
after heat forces
he organic volatile matter fiom
coal, is
composed primarily of f i xed
carbon.
In
the
blast f urnace,
he carbon rom coke reducesironores into molten ironor pig iron.
Subsequently, controlled oxidation forces
added
oxygen
to
react with large
k o u u t s
of xcess
carbon eaving anironproduct with about 1% carbon-steel.
.,
,.
.....
...
_,.
-
..
.
..
, .
.
..
. . .
. .
.
... .. ....... - .-
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I
Industrial Ecology
-
5
Since the nineteenth century, the steel industry
has
been manufacturingcoke
in
by-
product recovery ovens, designed to capture the volatile matter driven from coal during coking.
When cooled, the by-product matter condenses into coal tar,a source of many chemical products
such as synthetic tars, plastics, and crude light oil.
Operators
of by-product recovery coke oven batteries are contendingwith several market
forces and regulatory issues. One-fifth of
the
coke oven batteries in the United States
are
operating well beyond their expected productive life of
thi rt y
to thirty-five years (Peters 1992, .
18). Emissions
from
by-product recovery coke ovens contain everal carcinogenic compounds
such as benzene soluble organics @SO), which affect public health. The Clean Air Act
Amendments
CAAA)
f 1990 pecify minimumemission limits, Maximum Available Control
Technology (MAC) and the more stringent Lowest Achievable Emission Rate (LAER),
intended to reduce air
toxic
emissions by 90% by 2003. Ifresidual emissions do not provide
an
ample
margin
of safety to protect the most exposed individual, EPAwillpromulgate even
more stringent
conmlson
coke oven emissions.
.. ..
- ~ -r 1-T .-.--
I n a C iceoven emission controls
on
he united
States steel i n d w , Considine,
Davis,
nd Marakovits
(1993a)
use
an
engineering-economic
approachto
measure the economic consequences of regulation
and
its effect
on
adoption in the
steel
industry.
In
a
later,
p r e w tudy
estimating
he
costs
coke oven emission controls, hey incorporate untxx&ty surzounding key parameters, such as
EPAs controversialestimateofunit
risk,
the p
one UIiit of coke oven emissions (Considhe
distributions for eight parameters and generate one hundred
stochastic analysis. As
in
the earlier study,
emissionlimits
on
he steel industry in 1995and 1998, espectively, and compare the results with
the base year solutions to estimate the industry costs due to regulation.
In the earlier d y s i s , Considine et
al.
conclude that coke oven
emission
controls would
accelerate the current trend towards electric 8ty: steelmaking and nonpolluting coking
technologies (Considine et al. 1993% pp. 452-3). However, lengthy plant construction lead times
would createcoke
shortages,
causing
imports
o rise. The older coke batteries shut downunder
MACT, but newer,
low cost
batteries shut down in 1998 or exceeding LAER missionlimits.
Steel producers have continually adopted innovative steelmaking technologies. Aging
coke oven batteries and declining cokingcapacities over time have been forcing integrated
producers to examine alternatives to traditional coking and ironmaking practices (Davis and
Considine 1992, . 57). In addition, environmental regulations on coke oven emissions may
stimulate technological innovation though regulators intend the MACT standard to encourage-
increased use
of
proven technologies
Graham
and Holtgrave
1990,
p.
243-4).
Howevb,
environmental regulations raise the costs of coke production. For example, only twelve percent
of
the batteries existing in 1991 can economically achieve the less stringent MACT emission
l imts,
and 83% of those batteries requi rerebuilding (Peters 1992,p. 15). As a result,
environmentalcontrolscould accelerate the steel industrys aatural rate of technology adoption
towards processes that reduce or even eliminate coke requirements.
. . . . .
~. _ . _
. . .
. .
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Iron& Steel
-
6
The steel industry has se vpil technological choices to reduce coke oven emissions. The
viability of each option varies by coke plant based on he age and conditionof the batteries,
existing coke oven emission levels, availability of capital, plant location, and relative material
and energy prices, among others. In addition to importing foreign coke, steel producers
can
retrofit or rebuild existing coke ovens,
as
well as
install
new w e ta k in g batteries (Considine et
al. 1993%p. 445). Retrofitting involves replacing the coke ovens doors and their jambs. New
jambs may necessitate replacement of the refractory bricks, depending
on
he condition
of
the
oven walls (Struthers Corporation 1991, p. 14). A pad-up rebuild involves demolishing the
existing
battery to
he
concrete
"pad" or foundation and building a new battery of the same
dimensions in its place (Struthers Corporation 1991, p. 15).
Besides additional investment in the wet-coking technology, steel producers have several
new processes
to
consider, which we describe below. Coke producers
can
nvest innonpolluting
coking echnology calledJewell. Alternatively, the industry
can
adopt ironand steelmaking
processes, such
as
pulverized coal injection, d rect reduction, and scrapbased steelmaking,
whichsave-oreliminate,wke@to
coke oven emissions
to
re@
Nonpolluting Coking of Coal
nonpolluting coke oven presently being
used
in
Vansant, Virginia
by Jewell Coal and Coke
Company, owned by Sun Coal Company. Ironically, the Jewell-Thompson
to theObSXete-ve oven ~ ~ ~ ~ g ~ ~ e e ~ ~ ~ e ~
oven, the Jewell oven operates onnegative pressure, which
minimizes
coal
tars
and
gas
combust nside the oven and flues (Knoezner et
al.
1
process recovers
no
by-products, eliminating the need for by-product recovery facilities
and
he
disposal
of hazardous wastes. Provisions for the recovery of excess heat will permit
cogeneration
of
electricity (Knoezner
et al.
1992,
p.
50).
;nallv, fcoke producers cannot economicallycontrol
can
cease operations.
CAAA requixe the sdministrator
of
EPA to evaluate the Jewell-Thompson oven, a
A Jewell oven is about twelve feet wide and forty-five feet long,
accommodating
a coal
charge of twenty-five to B y tons (Knoezner et al. 1992, p. 50). Oven charging is by
a
cOnveyOr
machine
through he pusher
side door
and not from above (Knoemer
et
al. 1992, p.
52).
The
operatoradmits
a l i mtedamount of air
into
the oven to combust some
of
the volatile matter
being driven fiom the coal, which generates heat required for coking. The partially combusted
gas
escapes
through
ole flues
located
below the oven
floor,
combusting further within the flues
and creating additional heat underneath the coal bed (Knoener et al. 1992, p. 5 1). Coking time
can
range between wenty-four to forty-eight hours (Knoezner et
al.
1992, p.
50). Pushing
and
quenching
operationsare
similar to the wet-coking process (Knoezner et
al. 1992, p. 52).
Other
no-recovery coke even designs include the European
Jumbo
Coking Reactor and
the American Calderon coking process cunently under development may completely eliminate
all cokesv en emissions
(Wrona, 1997,
p.
60). Dry
quenching
is
another technique to
reduce
emissions, recovering heat fiom the hot coke during quenching to generate steam. Thisprocess,
however, uses more electricity thanother coking processes and requires greater inputs of coking
coal. Another process is form coking that produces briquettes by drying and partially oxidizing
._%_.
-.
. .
. . . . . . _
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Industrial
E C O ~ O ~ Y
7
lower
quality
noncoking p u l v e q d coal with
steam
in a fluidized-bed reactor, followed by
carbonization at higher temperatures (Lankford, et, al, 1985, p. 142). Both of these processes
offer a relatively environmentally acceptable means
of
producing coke and are extensivelyused
in Japan and Russia but have yet to find extensive use in
North
America.
Aging cokemaking facilities, stringent emission controls
on
coke oven emissions, and
perhaps increased scarcity
of
metallurgical coal
in
some
areas
have forced plant
operators
o
examine alternatives to traditional ironand steelmaking (Davis and Considine 1992, p.
57).
Below we discuss several new technologies that lower coke requirements or eliminate the need
for coke.
Pulverized
Cod
Injection
coke. To
reduce
ironore to
its
metallic
form
suitable for production, ironmakers can inject
pulverized coal
intoa
blast fUmace proper to lower coke requirements (Davis and Considine
1992,p.
3-7).
One pound ofpu ive rhd coal can
replace one
pound of coke
as
a fuel and
as
a
reducing agent (Unsworth et
al.
1989,
p.
1-20).
Because pulverized
coal
cannot
substi=
for the
permeability of porouscoke or support the blast f i vnaceburden, it cannot completely
replace
coke.
Pulverized coal injection
(PCI)
nd continuous casting reduce the need for metallurgical
-
The U.S.Department of Energys
project atBethlehem Steel Corporations Burns
techn d o . - . -
used in many plants today. In the process, both
blast furnace in place of naturalgas (or o
generated by the blast furnace itselfremain
exiting the blast firmace is clean, containing
no
measurable SO2 or NO,. Sulfur
removed by the limestone flux and bound up in the
slag,
which
is
a marketable
addition to the net
emission
eduction
realized
by coke displacement,
high
blast furnace
production.
Coal injection
also
allows the use of a wide range of relatively
inexpensive
coals,
in contrast
to
coke,which
can
only
be
made fiom certainhigh
quality
coals.
Two
high-capacity
blast furnacesat the Burns Harborplant, eachwith aproduction
capacity of 7,000 net
tons per
day of hot metal, have been etrofitted with the coal injection
technology.
The
two units
will use about
2,800
tons/day of
coal
during
full operation,
eplacing
about 40% of the coke needed in the furnaces. Bituminous coals with sulfur content ranging fivm
0.8% to 2.8% fiom West
Virginia,
Pennsylvania, Illinois, and Kentucky are to be used. A western
sub-bituminous coal having 0.4-0.9%
sulfur
might be ested also.
Construction was completed
in
February 1995. Bethlehem Steel submitted
a
public
design report in March 1995. Start-up testing
has
been completed, and the plant
is
complete.
Operational testing began n November 1995. Furnace C hasbeen operated with an average coal
injection rate
of 275
lbdnet
ton
ofhot metal, using low-volatile bituminous coals. Bethlehem
Steel has determined
that
thisinjection ate will be the new operating baseline for Furnace
C
for
all future test coal comparisons. Furnace C also
has
been operated with a coke rate of
approximately 650 lbdnet ton
of
hot metal without coal injections, down from
770
lbdnet
ton.
...
, . . .- .
...
.
,
. .
. . ..
. I .~
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Iron & Steel - 8
Furnace D
as
been operated
with
a coal injection rate of approximately 190 lbdnet
ton
of hot
metal, which is above its design N i t of 180 lbdnet ton. Bethlehem Steel has completed
repairs
to a coalpreparation plant necessitated by tramp organics in recent coal supplies. Bethlehm Steel
plans to increase substantially the coal feed rate through all 52 tuyeres for comparison
with
he
baseline standard of 275 lbdnet tonof hot metal
on
Furnace C.
The
granular
coal injection project at Bethlehem Steels
Bums
Harbor plant
in
Northern
Indiana
offers he U.S. steel ind- a way to become more co mpti tive while impmving its
environmental performance. The echnology can be applied to essentially allU.S. blast furnaces.
It should be applicable to any rank coal commercially available in the United States
that
has
a
moisture contentno higher than 12%. The environmental impacts
of
commercial application
come .primarily
from
a reduction in the need for coke, the production of which can elease
emissions
of
sulfurdioxide and
air
toxics.
Also,
because 8 wide range of relatively low-cost
coals can
be
used
to
replace processed coke, the ironmaking process is less expensive. The cost
of more expensive &els such as
MW
as and oil
can
be avoided.
- -
yx-- - Iu.x- .-7 1-
-- --I-
Industrial Ecology - 19
produce zinc-rich dust that also indudes lead and cadmium. During steelmaking various kinds of
scrap and oily mill scale are generated. Home scrap, generated during various finishing and
shaping operations, is recycled back to the EAFBOF. The pickling process during steelmaking,
in which the contaminated coating on steel is removed with HCl, generates water emissions with
suspended and dissolved solids.
Figure
2:
Comparison of C02 missions across alternative technologies
Kilogramsof carbon dioxide per ton hot rolled
strip product
2500
ntegrated Steel DRI+EAF based EAF based
I
Mill Mill Minimill
Source: VAI (Sapphire: Advanced Solutions for
Waste
Free Iron
&
Steel Plants)
FACTORS
3 W X G
EMISSIONS
The conversion of iron ore to steel is a complex process involving various processes, raw
materials, equipment, and physicdchemical reactions. Emissions during these processes are a
function of several factors, the more important of which are discussed briefly.
RawMaterial Quality
coal, iron content of ore,BTU (or fixed carbon) content of he l, and impurities in raw materials.
These are discussed below:
Su&r Content
The sulfurcontent of coal
has
a direct bearing on emissions of
SO,
and H2S during the
coking process. Russell and Vaughan (1
976)
report that
as
an approximation, the percent
sulfur
in coke oven
gas
is 1.7 times the percent sulfur in coal input to coking units.
Sulfur
n coalalso
affects the sulfurcontent in pig iron, which necessitates a hot metal desulfurizing step during
steelmaking.
Quality parameters that influence environmental releases include the sulfbrcontent
of
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Iron Steel - 20
Iron Content
of Ore
and Ore
T p e
The iron content
of
ore determines the bulk that needs to
be
crushed, transported and
handled. These operations
are
associated with energy use as well
as
C02 and PM emissions.
Hence processes that use less ore,
ceterispuribus, are
associated with less emissions and
higher
energy efficiency.
FuelChoiceand Qual
The quality of industrial fuels
-
coal, fuel oil, esidual oil, and natural
gas
- determine the
amounts of criteriapollutants, and metallic hazardousair pollutant emissions from industrial
combustion sources within an ironand steelmaking plant. For example, the BTU content of a
coal determines the
total
mass of fie1thatmust be transported, crushed and conveyed.Hence,
low
BTU
coal, even ifpriced
at
a discount in the market, exacts its full cost, albeit
on
he
environment.
YI..--T.-_
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Industrial Ecology
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21
Coal too
is
available
in
many s%s ranging fiom -6mm to -32 mm. Transport and handling
of
iron
ore fines and pulverized mal releases some fine ironore and coal particles in to the
immediate atmosphere. Processes that use lumpy ores and coarser coals, or processes that bypass
the use of raw
materials
will naturally be associated with less particulate emissions.
hl J W ' & S ill hp
Chattexjee (1993) reports that the amount of slag generated during
ironmaking
is directly
related to the amount of gangue present in the iron feed in the heat, The ash content of
coalis
a
fm o r in the generation of slag in blast furnace operations. Since the removal of
ash
silica)
generates COZ during
slag
fo m ti on , higher silica content
in
coal and ironore generates
i n m e n t a l C& emissions. Chatterjee (1993) M e r sserts that good quality
coals
with low
levels
of
ash,
s u b
nd volatile matter are likely to yield higher fuel efficiency, and require less
additives
(fluxes
and detd fbrm m
).
Similarly, EPA (1999)
reports
ead emissions
in
particulates
from EAF operationsare a h c t i o n of the lead in the
scrap
charged to the process.
determine
emissions. A
case in point
is
the emissions
of
polyaromatic
hydrocarbons
PAH)
emissions during the quenching operation in cokemaking. Quenching
pedorined
with
con amhated waters releases order of magnitude higher amounts of PAH thanquenching with
clean water.
-
---Inthwcases, the strength and quality of reagents
as
well
as
operating practices may
-----.---x-.- -.--_--- - - ----__-
~ -
,._--. --
ontrol Equipment
Both the choice and efficiency'ofpollution control equipment has an important impact
on
emissions n ironand steel production. There is substantial diversity in the typeand efficiency of
pollution
control equipment in the industry that complicates estimation of emissions at the
aggregate level.
Choke
of Control
Technology
Numerous pollution abatement technologies are available. These technologies are
typically
specific
o one medium - air, water, or solid. Within each medium however, several
variants exist thatcontrol one or multiple pollutantstodifferent degrees. Particulate abatement
equipment include simple cyclones, high efficiency cyclones, electro-static precipitators (ESP)
with a continuugi. of efficiencies,scrubbers, wet ESPs, fabric filters,and ceramic
filters.
Cyclones achieve
about
a 90%cbntrol
of
particulates by
mass.
However, their
capacity to
control
finer particles
(lidWaste Emissions
Ted
Blast Furnace
1600
up
to 33% with PC
0.3 -0.45
22-34
0.3
07 I
__ i b )
760 - 1410
12.25 - 100.7
SOO(c)
6.2097
180(c)
3.8(d)
0.25
17.5 - 25
1487 (1344
-
160s
1175 (1050
-
134:
0
60
656.8 (525
-
788)
0.6
0.4 - 0.6(a)
130
53
114
16.5 - 17.28
60
0.01
0.04
0.42
50
145
95:
60E
0.6
estimatebasedon conversion
of
volume share CO2 to mass using exhaust flow of 1650-1728m3/thrn
FromTable2 t is evident that COREX has several desirable features. First, its iron
ore
nput
coefficient
(1344
-
1609Kgs per
ton) is modestly
lower
than he 1600Kgs of ironore
required
for blast furnace reduction. It requires modestly higher electricity and more oxygen thandoes the
blast h c e eduction process. Second, the process does not require coke, and hence eliminates,
.
_.
..
.
.
.
.
.
. .
.
..
.
.
.
.
.
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Iron& Steel -
32
inl
1
.4
0
at leastpartidry, the emissions wsociated with cokemaking.
It
is also environmentally superior to
blast f urnacetechnology.
This
advantage derives fiom the partial use of hydrogen as a reductant
rather thancomplete reliance on
carbon.
PM and
SO,
missions are significantly lower, though
NOx emissionsmay be higher than hat fiom the blast fimace. In addition, he
use
of
coal release
some methane during the reduction. C O W lso
boasts
of significantreductions
in
ammonia,
phenol and sulfide discharges
to
water effluents
during
the
reduction
process.
The
echnology,
however, produces higher amounts of
slag,
possibly due
to
the direct inputs of impurity-
containing coal in to smelting reduction fiunace.
leso urce Requirements
____-.-.._._-I
Iron
ore
Coal
Coke
.
Electricity
o w e n
Natural
Gas
Water
Labor
ir Emissions
co2
PM/Dust
SOX
NO,
Methane
raterEmissions
Ammonia
BOD
Sulfides
Phenol
>lid
Waste Emissions
Slag
Dust and
Sludge
DRI
T E C O L O G ~ S
There
are
at least half a dozen, and probably a dozen competing DRI technologies. The
evaluation here is limited
to
those that have
are
commercially established.
All
DRI rocesses in
Table
3
consume approximately the same amount of ironore. FASTMET and Circofer use coal
8s
the reductant,
wlkreas
other technolo
Table
3:
Comparison of Alternative
DRT
Teclqologies
use
natural
gas for
providing
thermal
energy
and
-1 -r
- - ~. -....
-- ---1-
I - . --_
Units
. -
K g a m
Tondton
KwH
per
ton
(N)m3lthm
GcaVthm
m3Iton
Manhrs per thrr
TonsiVlm
glthm
m3tthm'
g/thm
mgMl
g m m
Ton/thm
Kglton
DIRECTLY
REDUCED IRON TECHNOLOGIES
ClRCOFEl
1442
380
0
90
190
-
195
0
2
0.315
- . -_-_-
50mgMm3
10- 100
1.1mgnitre
CIRCORE
1483
0
0
100
0
2.75
1.5
0.31
5
-_..- ---?
50mg/Nm?
10
86ngIJ
FASTMEl
1380- 143(
270 - 380
0
60 - 90
0
0.6
-
0.65
1-1.5
0.2
-
0.3
1.05-
1.18
H n
11
1450
0
0
90
0
2.55
-
2.8&
1.6
- 1.8
0.34
3.039kgftor
0.2
0.05kgEton
26.7
-
m4
0
0
1.97
i
-
..
.
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Industrial E co lo ~ y 33
U n i l
carbon
& hydrogen for reductio% The
DFU
processes consume different combinations
of
reductants, oxygen and energy and other inputs. Midrex DRI
is
relatively electricity intensive
thanother
DRI
technologies. However, consistentwith higher labor c o s t s in the US, abor input
at 0.16 manhoursper ton ron is the least among he set
of
DRI echnologies. Unfortunately,
emissions
coefficients are missing for many echologies.
This
is acritical
idonnationgap
that
must be filled to
facilitate
comparison
of
nvironmental performance.
Technology
BOF QBOP
EAF
1EEEFI G ECHNOLOGIES
._ -_--
-~ ~ m
m3lton
KwH per
ton
Nm3/thm
Manhrs per thm
Manhrs per thm
Basic Oxysen Furnace @OF) technology once
dominated
the steel industry in theUS.
The EAF ased minimills have, however, gained a substantial shareof he steel refiningmarket.
A few
steel mills employ the Q-BOP rocess.Table
4
presents he resource use and emissions
coefficients or BOF, QBOP, nd EAF technologies.
Table 4: Resource use and environmental perormance
of
teel refining technologies
_----
0.932- -
101-201
0.097
0.32
I
STEELMAKING TECHNOLOGIES
0.58 -
38
0.066 -
1.w
0.07
0.066
-0.54
esource Requirements
IrOdSeiiiii
Nitrogen
Electricity
Oxygen
Labor
Maintenance
ir Emissions
c 0 2
- . . ..
I
M/ PMlO
Tondthm
Lb per thm
Lb per thrn
Lb per
thm
g/thm
Ton/thm
Kgbn
olid Waste Emisslons
0.0068
- 28.5 0.056(a
0.1 17 - 0.220
0.0038
0.02-0.1
100-440
8-62
Ranges
often
indicate differences in controlequipment
0.8
1.13
30
0.048
0.967
430 -600
350
110-420
20 -40
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Iron
& Steel
-
34
The Q-BOP pparently iqa little more efficient at converting iron to steel. It is
also
very
energy
efficient,consuming only 30 KwH* per tonof steel, which is at least
an
order of
magnitLlce lower
thanBOF
nd
EAF
processes.
EAF
generate approximately the same amount of slag, dust and sludge. Emission coefficient
ranges
overlap for these competing technologies, negating any basis for
ranking
them.
coking,
ironmaking and
steelmaking
echnologies revealsmany datagaps, especially pertaining
to emissions coefficients. The only notable observation is the a p k n t superiorityof COREX
over the traditional blast furnace reductionof iron
both
in
term
of resource use and
environmentalpedormance.
Data for comparison of environmental p e r f o m c e ishard
to
come by. The BOF and the
The above examhation of the resource use and environmental performance of alternative
. . . . . . . . . . . . . . -.
.......
i ..-.. . . . . . . . . . . . . .
. . . . . . . . . . .
. . . . . . . . . . . . . . . .
8 according to
the
EPRI
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Industrial Ecology - 35
CHAPTERV.
k~
IFECYCLECONOMIC MODEL
The sequential
natureof
production w ith multiple joint products
has
motivated m y
researchers ta develop linear programming or process models of the steel production process.
Early studies include
Tsao
and Day (1970) and Russell and Vaughan (1976) while more recent
efforts include those by Sparrow,
et.
al. (1984) and ,Considhe, et.al. (1992). These models are at
the industry level with aggregate inputsutput relations determined either fiom representative
process
uni ts
or
h m
ggregate industry data.
In
contrast,
this
study develops a detailed process model for
a
specific steel plant, the
Mon Valley Steel Works,owned and operated by U.S.Steel Corporation
(USX).
The Mon
Valley Works ncludes the Clairton Coke Works, he largest coke oven batteries in the U.S., he
historic Edgar Thompson blast fixrnace and BOF mill developed by
Andrew
Carnegie, and the
Irvin finishing
mill.-
Thiscomplex
is
somewhat unique because it generates excess coke, which
is
transferred
to otherUSXmills and sold to other steel producers. Nevertheless, thisplant is
representative
of
many integrated
steel
mi l l s
in the
U.S.
because technical efficiencies
of
coke
ovens, blast furnaces,and other equipment do not vary substantially between firms.
The model development occurred in two phases. The first step entails the development of
8 simple
hear
programming model based upon estimates
of
the costs by process based
upon data
provided by Don
Barnet$
(1997).
This
dorm ation, however, does not provide a
very
detailed
picture-of
~ - ~ p r o d ~ & : i a r i dl~cric-@~-bdanr@Sietweenhe
various process units
in the plant. The
ife
cycle inventory
data
collected by Rhodes et. al.
(2000)
provides information
to develop these balances and
to
estimate and the environmental emissions by process. The ife
cycle assessment(LCA)ncludes
raw
material extraction through steel product manufacturig.
Both sources
of
infoxmation provide a fairly detailed view of he steel production process,
including
iron
and
coal
mining, coking, blast fiunace production, steel production,
and
rolling
and finishing operations.
naEECONOMIC
ROCESSMODEL
world.
His
data includes input-output relations, factor prices, and capacities by process.
Companies operating hese plants voluntarily subscribe
to
his service under he condition that
their detailed process cost
data
remainsconfidential. Based upon this idormation, Barnett
provides analysis that allows companies to detemine where their plant costs
rank
n relation to
others in he industry.
Barnett calculates the average cost of production by process by
summing
the product of
the inputsutpu t coefficient and the respective input prices, which provides
an
average cost per
unit
of
output. The
per
unit
costs
of intermediate inputs, such as coke and pig iron, hen
essentially become input prices for
downstream
processes, such
as
steelmaking.
'Barnett (1997) collects detailed process
data
for many integrated steel plants around the
Barnett provided uswith his data for the
Mon
Valley Steelworks. This allowed the
specification
of a
simple linear programming model with 16 process activities. The
first
two
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Iron& Steel - 36
include screening of metallurgicql coal and
the
production of coke fiom conventional by-product
slot coke ovens. The coefficients
of
these activities include coal, labor, energy, and maintenance
requirements per unit of coke produced
as
well as an estimate of the amount of coke oven off-gas
generated. The next group of activities involve
iron
production, including sintering, pulverized
coal injection, and blast
f urnace
operation. The third group of activities entails steelmaking;
including basic oxygen f i unaceoperation,
vacuum
de-gasification, and continuous casting. The
final
group of activities includes rolling and f i s h i n g operations hat produce hot-rolled band,
cold rolled steel sheet, and galvanized steel products. Our base model solution provides an
estimate of total variable production costs very close to the costs estimated by
Bamett
(1997).
LIEE
CYCLE
MODELMODIFICATIONS
The life cycle inventory
data
provides considerable detail that
permits
significant
enhancement of the process model initially developed using the idormation rovided by Bamett.
The first improvem&t involves the inclusion of emission coefficients by pn>cess. In general, the
K d % y B
&&
those defined by Rhodes et.al. The required
aggregations
re discussed in the next section. Unlike
Barnett
(1993, the
life
cycle inventory
data
ncludes emissions generated in upstream activities, such as coal and
ironore
mining, which
are
discussed in the second sub-section below. As the previous discussion indicates, our
surveys
of the industry did not yield a complete emissions profile ofnew technologies, which necessitates
several
assumptionsthat are discussedbelow.
Finally,
a carefbl
comparison of
emissionsreported
by Rhodes et. al. with those fiom
our
model provides
a
good check for 8ccuracy. The complicating factor in
this
comparison, however,
arises fiom the hypothetical nature of the plant output in their study. As mentioned above, the
Mon
Valley steelworks is imbalanced, producing substantiallymore coke thanrequired,
As
a
result, he
Rhodes
tudy only included those emissions associated with coke requirements at the
plant.
Other
plants consum ing the excess coke would include, at least in theory, the associated
emissions. From a plant optimization viewpoint, not accounting for these emissions and in
particular
the off-gases
that
coke ovens generate would be a
serious
distortion. Thismodel
calibration
issue
and related
matters
are
discussed in
more detail below.
Process Emission Coefficients
In calculating the emission coefficients, the first step was to match processes
in
the life
cycle inventory data by Rhodes to those
in
the base process model
so
that emission coefficients
from the
Rhodes
study
could be properly assigned to processes within the process model.
Comparison of the two models yielded the following associations and subsequent assignments
shown
in Table 1.
Where single LCA processes
are
associated with multiple processes, emission
coefficients have only been attached to the irst of the associated processes listed inTable 1.The
units
of emissions were given
in
a variety
ofunits,
and allwere converted
to
a
pound
~ e rhort
ton basis tomatch process levels
as
defined in the existing process model. All emissionswere
then added to the existing set of commodities.
,
---...
-----------
-___.?-I.iT--I__- --
-
-
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37
COKE-SLOT
SCREEN
SINTER
~ ~~
Table 5: Process,associations between LCA nd the process model
Making
Coke
Coke
Sintering
GAL-HD
8305
HOt-DipGalvanizing '
@&)
Galv Hot dipped 8324
Coke Oven Products
(mg/MJ)
No
changes were made
to
the input profiles
materials,
abor, operating costs), except
in a
very few specific cases noted below. The Barnett data did not include the
three
power plants at
the
Mon
Valley works. Their steam output significantly
alters
the energy flows
within
the plant.
The ife cycle datacollected by Rhodes, however, provide a more accurate representation of the
plant's energy flows
The first step in ncorporating the power plants was to add them
as
new processes, and to
complete'their input
/
output profile. The power plants
are
at the coke ovens, the steel works,
and the
rollingmill.
Second, the emission coefficients were calculated. This
was
straighgorward,
and coefficients were taken fkom the LCA Model and converted to pounds per MJ of steam
d. Steam is tracked in UT hroughout the model.
Third, power plant fuel inp& and by-product electricity generatio
added to the
input/output profiles
in
the proper
unts.
The steam output
fiom
the three power plants
is
clearly
assigned to consumption points within the plant
and,
therefore, each power plant's steam
output
is
designated accordingly. These three items were added to the set
of
ommodities and the set of
intermediate products.
Since steam was not yet entered as an input into any process, this was the next and final
step to complete for the power plants. There are only four processes that use steam
as
an nput,
and these processes were amended to include a steam input in the appropriate
units
of
MJ
team
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Iron
Steel - 38
per shorttonof process level. Adetailed electricity balance, which appears in Appendix A,
indicates that kilowatts of consumption and production
are
vlrithin5 'percent of each other, which
may reflect transmission losses and slight discrepancies between the LCA data and Bamett's
technical coefficients.
The
main
solid waste fiom steelmaking is the slag h m he blast iiunaceand fiom the
steel furnace. Waste slag
has
no
e-use within the plant, and all of the slag exits the steel
mill.
Waste slag is commonly sold for use in road building and cement production. In the LCA model,
waste slag totals790,000
MT
per year. Most of the slag is sold for productive use, and
approximately 5% is landfilled as solid
waste.
In the LCA report,Table 3-4, page 30,the slag
figure
reported only includes the landfilled quantity, not the slag sold for productive use.
The LCA slag output coefficients were apparently adjusted so that only the landfilled
portion
is represented. In the present model, al l slag coefficients were readjusted upwardusing
the implied
waste
ratio. Slag exiting the plant
as
waste is
accounted
for as a solid waste and
landfill
costs accrue
to
the total cost ( t h e
are no
other costs associated with landfilled slag),
while slag sold earns
a
credit that accrues
to
the total cost.
Upstream
Activities
mining, iron pelletproduction, fluxmining, zinc mining, and electricity.generation. The addition
outphfthese five processeso
~ e . . ~ ~ u - ~ ~ u ~ ~ ~ ~ p ~ e ~ ~ f o - r - ~ h - p , r - ~ s s ~
as
straightforward.
Emissions were converted-
to pounds
pei
short
ton
emissions were added to he
commodities and emissions sets as required. Labor, energy, and material inputs were not
included because he
process
model optimizes plant activities not the entire vertically integrated
supply chain.
The challenge
is
to
decide where to draw the line
as
we move upstream and m e r
The next modification includes the addition of
six
upstream processes:
coal
mining, iron
outside of the steel mill. We have bcluded ironand coal mining operations, pellet production,
flux mining, and
zinc mining
as hese are key inputs. But should we include the inputs that are
required
to
execute the pellet production process? Fuelsare consumed, but they are
not part of
the plant's optimization
hction,
i.e. the
cost
of
upstream
inputs is
accounted
for in the price of
the product purchased. In essence, what processes do
we
exclude? The answer to this question
can be based onavariety of arguments, but sophisticatedarguments were not necessary
to
reach
a
conclusion. This isdue to the fact that the LCA documentation does not permit further
upstream analysis or inclusion. Although items such as "2237-Fuel
Oil
Produce/Deliver" is
itemized as an input to several processes, there is no corresponding inputloutpdemission profile
for
this
process, hence we cannot include it directly.
This
orces a different approach.
When we examined our model's performance in replicating LCA totalemission figuresby
source, we found our model
was
quite accurate in all respects, but slightly underestimated
. emissions for these five upstream processes which rely on nputs like "2237" above, where
no
inputloutputlemission profiles are available. Therefore, based on inal delivered quantities in the
hypothetical case, we adjusted he emission coefficients on these five processes slightly upward
in order to calibrate the model based on he
total
emissions reported in SCSI (1998, p. 29-30).
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Industrial Ecology
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The external electricity gqneration emission profile for the Middle Atlantic region is
calculated based
on
he LCA report. The Rhodes report provided a basis for estimating emissions
per
ki lowatt of purchased electricity
New Technology
New technology
is
represented in the model
as
process options. For example, the model
allows two different types of coke production: conventional by-product coking and non-recovery
cokemaking.
Several W er en t kinds of iron echnologies
are
available: Corex and
two
coal and
three gas-based
DRI
echnologies. To absorb any possible DRI production, the model allows
switchingfrom basic oxygen
steel
k c e s o five different EAF fimaces,
each
with different
DRI-scrap blends. Similarly, the electricity co-generating plants have the option of usingby-
product gases or purchased
natural
gas.
Some emissions coefficients for the new technologies were estimated due to incomplete
survey results. Newtechnologies
are
relatively early
in
their development, and process
coefficients varied
among
datasources and specific and proposed installations. We have
attempted
to
reconcile these variations and the coefficients sometimes represent averages,
estimates, and interpolations. We believe that we have achieved an accurate accountingof the
input,
output,
and emission profiles of the new technologies. The new technologies include
electric arc furnaces,non-recovery cokemaking, and direct iron reduction.
In order to constrainthe addition of new
.-_
echnologies
___ _j
to - r j
easonable levels,
a
set of capital
comtr&&we;e ~~-~h~w~echnologys assigned a lump sum capital cost in aprice
table. These capital costs
are
aken h m Considine et
ut.
(1992). The plant
can
be constrained
to
a
fixed amount of total capital
outlay
(say
$500
million over the planning horizon . But these
costs
are not incurred as lump sums, instead we assume they are financed by some combinafion
of debt and equity, and we amortizepayments o these sources based on
a
twenty year lifeand a
average
cost
of capital of ten percent in the base case. Costs must be
amortized
and included
in
this
manner o support the structure of the optimization
of
annual operating
costs.
Electric
Arc Furnaces
Obviously, electricarc furnaces0re not new but they do representan alternative
not
employed in the
existing
plant. Moreover, EAFs
can
be fed different
ratios
of scrapand
directly reduced irondepending upon the relative
cost
these twomaterials. Data by Barnett for
the Cravdordsville plant operated by Nucor, Inc. provide the labor, energy, and materials
requirements for the E M options. Emissions are based upon hose presented above.
Direct
CO
and C02 missions are assumed to be negligible. The range of the PMlO coefficient was very
large, and using an average has significant impacts in a social planning
context.
A figureof 0.05
was used in consideration of BF and BOF coefficients.
To
permit evaluation of different input ratios of scrap and DFU, ultiple E M rocesses
are
included in the model to represent the different fixed input ratios.
An
analysis was made of
the effect of the input ratio of these two items has onother factors, mainly electricity
consumption. There
are
many important factors that affect the
amount
of energy consumption in
the
EAF
as a function
of
percent DRI charged. Some of these include:
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Iron
&
Steel
-
40
Physical form of the
DIU
(particle size)
Friability (leads to excess fines and yield decline)
Temperature of the DRI harge
Batch versus Continuous Charging
Composition (unreduced iron oxides, FeO)
Gaugue
(mainly silica and
alumina)
We assume continuous charging at low-medium charge rates
of 1040%.
Batch charging
generally leadsto lower productivity, while continuous charging generally leads to improved
productivity (Stephenson,
1980).
The inclusion of
DRI
n the
EAF
charge may affect electricity
consumption positively or negatively based on he relative influence of the tors itemized
above,
it
is the net effect that is important for this study.
As
described in Stephenson
(1980,
p. 1 o), "continuous
ofDRIresults
n
several improvements
in
the melting processwhich tend to
e t he detrimentaleffects of
DRI
composition. The improvement inpower consumption
occurs at relatively small additions, in the range of 10 to
30
percent
of
the charge, where savings
onand help
Figure 5. Electricity consumption per percent
DRI
harged
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Industrial
E C O ~ O ~ Y41
inpower consumption of
3
to log ercent have been reported when the optimum quantity of DRI
is used. When more
than
30percent DRI is continuously fed, the overall effectis toward
increased power consumption relative to an a l l scrap charge. With DRI constituting
60-75
percent of the charge, the electric power consumption experienced by most commercial DRI
users is
in
the range of
550-650
kwh
ton
apped.
An
approximation of this relationship is
depicted in Figure
1.
The electricity consumption coefficients applied in the process model
are
based onFigure
1. It is
important
to note
that in addition to the factors mentioned above regarding sensitivity of
energy requirements, other items such as electrode, oxygen, and lime consumption may go up or
down. Also,yields may vary
as
well.
In
order to keep the model concise, and for lack of
scientific description of the complex interrelationships of these factors, none
of
these other
fkt ors have beenaccounted for in the
EAF
profiles.
Non-Recovery
Cbkemaking
power generation. The input
data
are
updated h m he study by Considine et
al.
(1
992),
collected h m lant operators. Steam output canbe used downstream in the BF, since he Jewell
process does not require steam
as
an input and we typically consider conventional by-product and
Jewell
to
be mutually exclusive. Emissionsare based
upon
Table 1above by adding emissions
fiom
charging, coking, pushing, and quenching to calculate a totalemission (averaging where
this
emission coefficient. Power generation emissions
are
e based upon the previously
discussed Unit emissions
for
the existing power plants. PMlO emissions are estimated fiom the
by-product cokingemissions coefficients. Finally, our coefficients assume
that
a l lCO and C&
emissions h m ewell
are in
the offgas stream, which
are
emitted during the power generation
process.
-
ThenonLiveryCokenAcingproces-involves
coking, flue-gas desulfurization, and
needed). - p o l Y ~ ~ ~ c ~ Y ~ ~ ~ ~ - ~ - ~ ~ ~ e ~ oue.to.high uncertainty of
Direct Reduction
The first
direct
reduction process includes COREX. The resource requirements
are
h m
Considine
et
aZ.
(1992)
Unlikeconventional blast furnaces, COREX, requires
ironore not
pellets
and c811accept
a
wide range of coal types, including steam coal. Emissions based
upon
Table
2 above except that CO emissions
are
estimatedbased upon the blast furnace coefficient and coal
consumption.
The Unit
resource
equirements fo r the remaining direct reduction technologies are based
upon Table 3above. For the Circofer process, CO, NO,, and PMlO emissions
are
based on
Corex coefficients, using coal
as
a reference. The
CG,
lag, Phenol, C1, and
3
e m i s s i o 9 - p
fiom the manufkhuer. Unit methane emissions are an average of the other DRI technologies.
The C@ emissions coefficient for the Circored process is from estimates by the technology
vendor. NOx and PMlO coefficients
are
based upon two other natural gas based processes,
Mdrex and HYLIIIprocesses for which data are available. Emissions of COY O,, NO,, PMlO,
and CH4 by the coal-based Fastmet process are estimated based upon Circofers unit
coal
consumption. C Q missions fiom the HYLIII and M drex process are estimated based upon the
unit gas consumption of the Circored process. The process emissions coefficients for PM10, SOX,
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Iron& Steel - 42
NO,, and
CO
are very close to thsose from a DRI plant permit application in Convent Louisiana in
1997. VOC and dust figures were taken fiom the permit and added to the emission profile for a l l
five DRI processes.
Reduction gases are produced on site in a gas reformer. Reducing gases are generated
from a mixture of
naturiil
gas
and recycled top gas fiom the reduction
furnace.
The t h d
efficiency of the reformer is enhanced with a heat recovery system. Sensible heat is recovered to
preheat the combustion air used in the reformer burners and the mixture of top gas and naturiil
gas fed to the refomer.
The majority of the top gas fiom the reduction furnace is recycled either fo r reinjection to
the f urnace after cleaning) or for heat recovery. In addition, top-gases are consumed within the
plant
in
avariety of other utilities services such
as
steam generation, electricity generation, and
otherpower and preheating activities. Inthis analysis, we ssuIl[ie that a l l such utilities
are
required components of the DRI module
as
a whole. That is, these off-gases cannot
be
exported
to
other
uses
within an integrated production process.
What we are
concerned with
are
those
excess gases, however
small,
that
are
available for
export
and their respective heat values.
But
due to the variety of arrangements of reformer,
furnace,
and
utilities, one
cannot h o w he
amount of off-gas available for export without a detailed schematic
of
a plant.
Estimates
of
export gas heat d u e s are equally elusive due to changes in heat value, pressure, and temperature
as op-gases
pass
hrough
a
maze of reuses.
Multiple technical s o ~ $ W e r e - ~ ~ l ~ ~ ~ - y i e l ~ g ~ - f e w ,ide ranging estimates for
export gas volume and heat values. For gas-based processes, estimates ranged fiom 1.188
mmBTUIton metal to 5.840
mmBTU/ton
metal, depending on he particular plant schematic. For
gas-based
DRI processes,
this
study
assumes
2.5 &TU
off-gas ton
Fe
nd 0.5
mmBTU /ton Fe
or
coal-BasedDRI
processes.
The gas-based figure compares with a figure of 4mmBTU/tonmetal
exported fiom the Blast Furnace.
In
the present model, the Blast Furnace sim ilarly recycles
much of its top
gas,
and
is
actually
a
net electricity produce