ecologia industrial acero

7/24/2019 ecologia industrial acero

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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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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.


3/66

._

. .

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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. . . . .

_

.

-.

. . . . . .

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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

.

.......

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. . . . . . . . . . . . . .

..-

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-., _ - .........

.~

-

...........................

-

....... . . . . . . . .

. . . . . . . .

....._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


11/66

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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... .. ....... - .-


12/66

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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13/66

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

._%_.

-.

. .

. . . . . . _


14/66

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 .~


15/66

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


27/66

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.-_


28/66

Industrial Ecology

-

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,

.

_.

..

.

.

.

.

.

. .

.

..

.

.

.

.

.


39/66

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

-

..

.


40/66

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


41/66

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


42/66

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


43/66

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__- --

-

-


44/66

Industrial Ecology

-

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


45/66

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).


46/66

Industrial Ecology

- 39

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:


47/66

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


48/66

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,


49/66

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

ecologia industrial acero

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