Yin R. Metallurgical Process Engineering
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308 Metallurgical Process Engineering
Table 9.1
Comp
arison between the eco-t
ype
factory and the traditional factory
Item Traditional factory Eco-type factory
Enterprise ob
ject
Product-oriented,
high
Function-oriented, economic and ecologic
profit-oriented benefit adjusted
Enterprise structure Chain type, rigidity Network type, adapt each other
Scale trend
Unitary product ion, large- Multi serial producing, reasonable scale of
scale
se
lf
-adaption net
Resources and
en-
High resource
consump-
Low resource consumption in
entirety,
ergy consumption tion, low energy efficiency high energy efficiency
Relationship
of
eco- Lengthways,
department
Transverse, multiplex ecologic economy
nomic system economy
Environment pro- End-pipe treatment,
large
Whole cycle complex control, pay equal
tection
input but low output attention to input-output
Waste, emission
Emissio n
disorder, nega- Recycling utilization in ecosystem facto-
tive benefit
ries, benefit positive
Economic benefit
High partial benefit
of
unit High comparati ve benefit of unit factory,
factory, low in whole high in whole
Social benefit Reduce job chance Increase job chance
On the view
of
technical progress and innovation, the eco-type reforming
of
en-
terprise will come through steps
of
the improvement
of
technology, the innovation
of
product (especially to the equipment manufacturing industry), the innovation
of
manufacturing process integration (especially to the process manufacturing
industry), the function extension and the macro system revolution.
It
proceeds
in a long period (historical age) and also develops from low-level production sys-
tem to high-level gradually. Wang Rusong shows/that the improvement
of
tech-
nology, the innovation
of
product or/and the innovation
of
manufacturing process
integration, the function extension and the macro system revolution will improve
the economic-ecologic benefit in 2 times, 5 times, 10times and 20 times respec-
tively (Fig.9.5).
Type4:
The revolutionof
macroscopic system
Type2:
The innovation of
productorland the exten
s:.;.
'i
o:..;"'-f'
__
processintegration
Typel:
Technology
improvement
Time/year
Fig. 9.5 The ecologic development
of
enterprise grading picture
(Wang and Yang, 2002b)
9.5 Function Extension
of
Steel Plants and Circular Economy
Society
Through the incessant technological development and integration optimization,
Chapter 9 Steel Plants and the Environment Issues
309
the functions
of
steel manufacturing process are broadening. Relationships be-
tween function extension
of
manufacturing process and eco-oriented transforming
of
steel plants will be dissussed in this section.
9.5.1 Function extension
of
manufacturing process and eco-
orientedtransforming
of
steelplants
The processing procedures
of
steel manufacturing process are so many and
each procedure has its own different functions. The collections
of
input and
output
of
materials/and energy for each procedure are different but interde-
pendent on adjacent procedures. They construct several kinds
of
complex
ecological interface with external environment. Fig.9 .6 shows the mate-
rial/energy input and output corresponding to producing 1000 kg
of
hot
metal in blast furnace.
It
can be seen from the Fig.9.6 that the input materi-
als include raw ores, sinter (pellets), recycling converter slag, etc.; the input
energy include coke, pulverized coal and electricity, as well as water, air
(blast, oxygen enriched) etc. The output include the materials such as hot
metal, BF slag and dust, the energy such as BFG , steam, electricity, hot
water and warm water.
Fig.9.6
Material and energy input and output
of
the blast furnace
The input and output
of
materials and energy per tonne liquid steel
of
BOF are
shown in Fig.9.7. The input materials include hot metal, scrap, flux agents, ferro-
alloys, etc.; the energy input includes electricity, coke oven gas, oxygen, nitrogen,
310
Metallurgical
Process
Engineering
argon, steam, as well as water, air etc., and the output include the materials such
as liquid steel, BOF slag, dust and the energy such as converter gas, steam, hot
water, also some drained cooling water.
I
Power
13S.5kW.h/t
~51.08m~/t
I
Water
1
3
1O
k
g/
t
ISteam 1
5
.
5
kg/t
~
23.llm
3
/t
~O
.98m3/t
COG I1.2Sm
3
/t
IOOOkg
Fig.9.7
Material
and
energy
input
and
output
ofBOF
steelmaking
Similarly, we can list the input-output collections
of
coking oven, sinter ma-
chine, electric arc furnace, secondary metallurgy, continuous casting, reheating
furnace, hot rolling, cold rolling etc. Apparently, either for the
BF-BOF
inte-
grated steel plant or for the EAF mini-mill, the manufacturing process's function
should not be limited itselfto the metallurgy-material production. The necessity
and possibility
of
the function extension are shown from the input-output collec-
tions
of
operating and processing procedures.
During the beginning
of
the 21st century, to recognize deeply as well as to
exploit fully the functions
of
steel manufacturing process become a topic
of
epochal significance.
If
only from the point
of
view
of
metallurgy and material
science, the function
of
steelmaking is
just
to produce steel products. But
if
from the view
of
engineering, industry/ and society, that is to say, expanding
our view to resources, energy, environment, ecology, circular economy etc., the
function
of
steelmaking is not only limited in the material production. Therefore,
we should be by broadened viewing field and more positive attitude to think
about the functions
of
steel manufacturing process and the problems
of
iron and
steel enterprises eco-type reforming.
According to above discussion, it can be seen clearly that the modern steel-
Chapter
9
Steel
Plants
andthe Environment
Issues
311
manufacturing process (especialIy
BF-BOF
integrated plant) adaptable to sus-
tainable development will mainly have three functions:
• The function
of
steel product manufacturing;
• The function
of
energy conversion;
• The function
of
waste treatment and recycling.
A.
The
function of steel
product
manufacturing
The main function
of
steel manufacturing is to produce the qualified steel prod-
ucts with low-cost, less emissions on the basis
of
the minimum consumption
of
resources and energy. The steel products ought to meet the users' changing re-
quirements and must be supplied for the social production and the private con-
sumption.
Such steel product manufacturing process is the life cycle system
of
green
steel products, which embodies the concept
of
product life cycle assessment
(LeA).
The life cycle system
of
green steel products wilI relate to the cause-
ef
fect linkage resource and energy exploitation, transportation, manufactur-
ing process, machining and assembling, using phase, abandoning, and recy-
cling processes. The following indicators can assess green degree for steel
products:
I. The specific consumption
of
resources, energy and the emissions (including
greenhouse gases);
2. The use efficiency and service
lif
e
of
products;
3. The environment load
of
steel and its products;
4. The regeneration
of
steel and its products.
F
i
g
.
9
.
8
~ F
i
g
.
9
.
1 1
show the calculated data
of
material, energy and environ-
mental burden for two advanced steel manufacturing processes.
o
100 200
11
Thinslab casting-rolling
300 400 500 600 700 800 900 1000
Time/min
Fig.9.8 Thet
emp
erature
- time
track
of
ma
ss flow inBF
-BOF
proc
ess
I
-I
ron ore; 2
-S
inter; 3- 0 re bin; 4
-B
F tapping; 5- Converter charging; 6- Converter tapping;
7- Retining; 8- Continuous casting;
9-
S1ab conveying; IQ
-R
eheating furnace; II
-R
olling
312
Meta
llurgica
l
Process
Engineering
Iron ore: 1
5UU
kg
Steel
scrap: 282.5 kg
I t steel
Eleclricity@:
0.582 GJ(56.8kW·h)
Tar: 0.621 GJ
Benzene:0.229 GJ
0.390 OJ
Surplus BFG: 1.325 GJ
SurplusCOG:0.375 GJ
Purchased electricity:4.750 GJ(456,8 kW·h)
Flux: 200
kg
Coking coal: 12.290 OJ (490.0kg)
Pulverized coal:4.352 GJ(
I73.5kg)
Others:
Fig. 9.9 Diagram of material, energy and environmental burden in BF
-BO
F
-thin
slab
cast
ing
-ro
lling process (Enterprises without their ow n
power
plant)
CD
BF
-BO
F
-thin
slab casting- rolling process, with the annual slab product ion of 2.8 Mt. The specific
energy consumption is 18.650 GJ/t, i.e. 637.3 kgce/t. While calculated by I tslab, the CO
2
emission is about
1756.4 kg/t, among whic h 1376.4
kg(C0
2)
/t belongs to the emission
of
manufacture procedures, while
380 k
g(C0
2)
/t belongs to the emission of power plant outside. The CO
2
emission factor
of
electricity is 0.95
k
g(C0
2
)1(kW . h).
Q) Recovered electricity per tonne
of
steel from COQ and TRT is about 56.8 kW • hit.
1800
1600
2
3
1400
P
1200
5
~
=
1000
4
e
6
'"
800
0-
E
600
~
400
200
0 20 40 60 80 100 120 140 160 180
Time/min
Fig.9
.IO
The temperature-
time
track
of
ma ss
flow
in
EAF
- t
hin
sla b casting-
roll
ing
pro
cess
I- Charging; 2- EAF tapping ; 3- Retining; 4
-Con
tinuous casting; 5
-R
eheating; 6
-Rollin
g
Chapter
9 Steel Plants and the Environment Issues 313
.------
J}L...--_----'>
1t steel
Scrap:
1121.5 kg
Ferro alloy:lOA kg
Carbon input:O.321 kg
Natural
gas:2
.019 GJ
Purchased electricity: 5.23 GJ
(503
kW'h)
Oxygen:0.251 Gl(35m
3
)
Electrode :0.154 GJ(4 .6 kg)
Other: 0.934 GJ
COl
C!)
:630.4 kg/ttsteel)
Fig.9.11 Diagram
of
material, energy and environmental burden in EAF- thin
slab casting-rolling process
CD
EAF
-t
hin slab casting- rolling process, with the annual slab production
of
2 Mt. The specific
energy consump tion is 8.91 GJ/t, i.e.304 .2 kgce/t. While calcul ated by I tslab, the CO
2
emissio n is
about 630.5 kg/t, among which 152.5 kg(
C0
2)
/t belongs to the emissio n
of
manu facture procedures,
while 478 kg(
C0
2
)1t belongs to the emission
of
power plant outside. The CO
2
emission factor
of
electricity
is 0.95 kg-(
C0
1
)1(kW . h)
B.
The
function of energy conversion
The steel manufacturing process usually accompanies energy conversion. As an
example
of
the integrated steel enterprise, the
BF-BOF-hot
rolling process is
actually an iron-coal chemical industry. This process may be taken itself for a
reactor to convert coal into energy such as gas, heat, electricity, steam, even hy-
drogen, dimethyl ether etc.
In the integrated steel enterprise, a large quantity
of
combustible gases and high
temperature products (such as red coke, etc.) are co-produced from various reac-
tions in the metallurgical devices. Especially a large amount
of
BF gas with low
sulfur content, a large amount
of
converter gas with high CO content, a lot
of
hy-
drogen-rich coke oven gas, and the
off
gas
of
smelting reduction are already co-
produced together with smelting processes. These are all the symbols
of
the en-
ergy conversion function
of
the steel plants. Meanwhile, a lot
of
high-temperature
waste, steam and hot water are come into being during the steel production. Inte-
grating the above energy forms the self-sustained power generation is risen in the
steel plant. Many large integrated steel complexes are developing to purchase
only coal but no electricity and oil. In China, the steel plants with an annual pro-
duction capacity
of
10 Mt have been equipped with 1.2 million
kW·
h power
plant that generating about 7 billion
kW·
h per year. 1 kW . h only needs
260
~
270 g coal equivalent. The economic-environmental benefit is significant. As to a
314 Metallurgical Process Engineering
large number
of
existing integrated steel enterprises, the production
of
hot metal
in blast furnace is often associated
250
~350
kg/t
of
BF slag supplying to cement
industry. Compared with cement produced by limestone, the cement produced by
BF slag can save limestone about 45% and reduce CO
2
emissions about 44%
(Nobate and Ueki, 2002), as shown in Table 9.2.
Table 9.2 Energyand CO
2
emission
comparsion
of cement
produced
by SF slagand by
limestone
~tem
Limestone cement BF slag cement Reducti on
Index
(A)
( B )
(A -B ) /A
Limestone consumption/kg 1092.0 600.6 45%
Coal/kg 103.6 57.8 44%
Energy consumption
Powe
rlkW·
h
99.2 72.56 27%
CO
2
emission/kg 775.6 437.0 44%
According to the assessment based on calculation (Scaife, Nunn, Cotterll, et aI.,
2002)using the life cycle analysis, if the BF slag used in the production
of
cement
and the BF gas used in power plant are considered, the greenhouse gas emissions
of
the coal-based steel manufacturing and
of
the gas reduction process has little
difference. From the point
of
view
of
greenhouse gas emissions, power generation
and cement production together with integrated steel manufacturing have obvious
profits. This is a very good example about fully bring into play the energy conver-
sion function
of
the steel manufacturing process.
In fact, EAF mini-mill process is also an iron- coal processing. The coal is just
converted into electricity through external power plant, and ferruginous matter
mainly comes from prompt scrap and obsolete scrap in society. Some EAF plant
recovered the hot electric furnace gas to preheat the scrap charge, which can save
100 kW .
hit.
It
is another type
of
energy conversion.
Development
of
hydrogen, a new clean energy, is a worthwhile frontal research
project in steel manufacturing process. Steel plant can use adsorption and separa-
tion method to produce hydrogen from coke oven gas. More noteworthy is using
CO-H
20
reaction from the converter gas with rich CO, or from the smelting re-
duction
off
gas with rich CO & H
2
•
The hydrogen can be further processed to a
liquid energy dimethyl ether (CH
30CH
3
) .
The low exerge waste heat and residual energy in the steel plants can be trans-
ferred into the hot water to provide nearby community residents to use.
e.
The
function of waste
treatment
and
recycling
Many procedures or devices in the steel manufacture possess the capability to
treat and recycle many urban wastes. The resources and energy can be reused.
It
should be emphasized that the waste that the steel plants handled is the bulky
municipal waste, such as:
Chapter 9 Steel Plants and the Environment Issues 315
• Re-melting a variety
of
iron and steel scrap for recovery
of
ferruginous
matter.
• Handling the bulk
of
waste plastics by injecting plastics into blast furnace
(Fig.9.12) or charging into coke oven.
• Recycling waste tires (using liquid nitrogen produced in air separation sta-
tions for the cryogenic treatment).
• Dealing with the social garbage (using combustible gases from steel plants in
special incinerator).
• Treating urban wastewater and sewage (using large water treatment devices
in steel plants), and so on.
In the coming years
of
new century, the social-economic functions
of
steel
plants should be evolved. Steel plants can form eco-industrial chains in different
area, and gradually realize the different eco-type reforming.
Pretreatment
Crushingand grannulating
Plastic film
Injection
"
,,,
8
tuvere
• SF
Fig. 9.12 Injecting waste plastics into SF (recycled plastic containers and package materials
can be injected into
SF)
9.5.2 Steelplants in circular economy society
A.
Circular
economy mode
and
connotation
Down till the beginning
of
21st century, with the marked rise in scientific and
technological level, the social production scale is unprecedented expanding. Hu-
man society seems so powerful and self-satisfied to face the future development.
But people have to face the survive crisis and severe challenge, such as the explo-
sive population growth, the rapid depletion
of
mineral resources and fossil energy,
lack
of
water resource and heavy water pollution, atmospheric pollution and soil
desertification, acid rain area extension, decrease
of
forests and arable land area.
More deep-seated problems are that endangered biodiversity, global warming, and
316 Metallurgical
Process
Engineering
ozonosphere hollow area and so on. Most
of
them are affecting the people's
health and life and severely restricting the economic development. Even the earth
ecosystem that evolved over 40 million years would be brought to a crisis. In
1972 the United Nations conference on Human Environment in Stockholm,
adopted the Declaration
of
United Nations Conference on Human Environment,
which thought-provoking pointed out that "only one Earth" for today's people to
live, "this Earth is not ours from the previous generation inherited, but borrowed
from future generations". This is such a shocking word! Since then, the reports
of
the World Commission on Environment and Development in 1987, the declaration
of
United Nations summit on Environment and Development in Rio de Janeiro,
Brazil in 1992, the new declaration and speeches on the United Nations Summit
on Sustainable Development,
in Johannesburg, South Africa and Assembly
of
Global Environment Facility, in Beijing, China in 2002 constantly repeatedly em-
phasized one idea: Mankind must abide by the principle
of
"development that
meets the needs
of
the present without comprising the ability
of
future genera-
tions to meet their own needs".
China is in the transition period that is shifting from pre-industrial to industrial-
development, and the contradiction
of
economy to environment is very prominent.
National leaders have clearly pointed out: "Only take the road
of
circular econ-
omy based on most effective using the resources and protection the environment,
the sustainable development can be achieved."
Circular economy can be regarded as the resources closed-circuit utilization
oriented economy(Jin, Li and Feng, 2003). That is to say, with production expan-
sion and economic growth, the "win-win" goal
of
the survival and development
of
human society can be achieved by building the social economy pattern
of
re-
source-producing-products-consumption-waste recycling, clean closed circulation.
"Circular economy" was first stated in Economics
of
Natural Resources and the
Environment, Harvester wheat-sheaf,
J990 by British environment economist D.
Pearce and R. K. Turner. Circular economy is a new production mode, based on a
closed-cycle mass flow system, and is also a new development method. From an
economic point
of
view, circular economy changes the "environment" from the
economic constraints
of
external factors into a new economic internal production
essentials (Xu, 2004).
Circular economy is the patterns that integrate the cleaner production, compre-
hensive utilization
of
resources, renewable energy development, eco-design
of
products and the ecological consumption, and apply ecological rules to guide the
economic activities
of
society. In accordance with their depth and extent
of
matter
recycling, circular economy can be divided into the following categories:
1. Primary waste recycling. This means that wastes are recycled simply, which
have been industrialized in the early
of
the
zo"
century. For example, steel scrap
recycling, waste paper recycling, glass recycling, which were already in large
Chapter 9 Steel Plants and the Environment Issues 317
scale. Recently that Ricoh in Japan utilizes used Coca-Cola PET bottles for spin-
ning to make dress. In this period substances have not been changed at the mo-
lecular level, limited in the aggregate transformation.
2. Recycling constituted
of
"Producer-decomposer"
. At the end
of
zo"
cen-
tury, as the development
of
the home appliances industry and the auto industry,
the waste appliance dismantling appeared. For example, thermoplastic was granu-
lated as resource. Thermosetting plastic were smashed as filler. Copper, silver,
mercury and other metals recovered with leaching method respectively. So, the
used appliances were decomposited and transformed into raw materials. End-of-
life vehicles could be treated in similar way. This material recycling had been a
step forward.
3. Recycling resources consisted
of
the eco-industrial chains. For example, it
has successfully been developed in China the "Sulfuric Acid Plant
-Phosphate
Fertilizer
Plant-Cement
Plant" eco-industrial chain. Sulfuric acid is supplied to
phosphate fertilizer plant for fertilizer production; its by-product gypsum changes
with pyrolysis position into sulfur dioxide and lime; the lime is used in the pro-
duction
of
cement; and the sulfur dioxide returns into the production
of
sulfuric
acid. Sulfuric acid is used for the production
of
phosphate fertilizer again. The
pollution problems caused by large amount
of
gypsum piling up have been van-
ished, and the element sulfur recycled. This pattern achieves a deep-level matter
recycling where the molecular conversion occurs.
4. Recycling resources with the coupling
of
"Eco-industrial system" and "natu-
ral ecosystems". This is the further advanced mode. For example, as the carbon
dioxide emission in current industrial production is tremendous, some fast-
growing trees and oil phytoplankton are going to develop by biological transgenic
technology. Carbon dioxide in the air will be fixed by them into biomass, and
biomass will be further processed into bio-oil as an energy source. Such use
of
biomass energy will not increase industrial carbon dioxide net emission.
B. Steel
plant
functions
and
modes in
circular
economy society
1. Ecologic requirement and economics
of
industry. The function extension
of
the iron and steel manufacturing process will gradually guide the steel plants to
implement ecological modification in the future development. Steel plant eco-
restructuring is one
of
industrial ecology.
The essence
of
Industrial Ecology is a march that with the development
of
eco-industry and construction
of
eco-industrial park, the input & output
of
industrial economic activities
of
human society can gradually be balanced,
harmonious, smooth and sustained into metabolism
of
natural ecosystem. To
grasp the essence, we must distinguish the similarities and differences be-
tween metabolism
of
natural and industrial processes. Both
of
them consist
of
mass circulation, energy conversion and message transfer. All are the same