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The material resources for the iron and steel industries
The material resources for the iron and steel industries Robert S. Barnes
The
future
coking
supplies
coal
of
iron
ore,
and
ferrous
scrap
discussed. There of the resources
is no of iron
likelihood ore being
until
exhausted twenty-first on
the
other
supply
but
blending by
blast
from
being
shorter
more com-
for
played
an
making
and the
coal
making
greater
will
in the
flexibility
hydrocarbons
considered
stitutes
by and
made
in iron
making,
out coal
non-coking
To ensure
steel
the coal,
furnaces
Briquettes
a part
in
non-coking
making
future. in
is
is being eked
with
pletely
into
Coking
hand,
it
efficient. play
well
century.
are
as
coal.
Scrap
important
are
possible
has always
part
amount
sub-
in
steel
recycled
is
increasing every year. But more effort is needed, that
the
utilised
for steel
example,
to
in car scrap
and that
ensure is fully
refuse is efficiently
recycled.
Steel
demands
the scrap to have few
purities
making
and to be in uniform
pieces.
A cryogenic
paring
such
futuristic non-ferrous
scrap
way
by-products
using
redundant
method
imsized
of
pre-
is described.
A
extracting
iron,
and
sale-
from blast
other refuse, furnaces,
by is
discussed.
Dr Barnes Development,
66
of
metals
eable also
increasingly
is Director of Research and British Steel Corporation
The iron and steel industry has less cause for concern about the possible exhaustion of its necessary resources than most other metal based industries. Many estimates have been made of the reserves of coal and iron ore, not all of which arc consistent. However, an overall picture can be drawn which shows that there are about 5 x 10’ 2 tonnes of hard coal reserves available world-wide. Half of this is in the USSR and China and one-third in the USA. About 10’ * tonnes of coking coal are thought to be available ~- three-quarters in the USA, USSR and China. Estimates of iron ore reserves vary as well, the highest suggested value being greater than 0.5 x 10’ ’ tonnes. One conclusion to be drawn is that there is enough coking coal present to smelt all the reserves of iron ore. However, estimates differ as to how long these reserves will last. According to Voice and Ridgion’ predicted rates of consumption give lifetimes for hard coal reserves of more than 1000 years. Dennis Meadows’ predicts that coal reserves will last another 1300 years at present rates of consumption, while if the rate of use of coal continued to increase exponentially it will run out in a little over 100 years time. Similarly, Meadows predicts that iron ore will last 200 years at present rates of consumption reducing to 100 years if present rates of growth continue. Although predictions differ by large amounts, even the most pessimistic figures provide some comfort for the iron and steel industry, This is illustrated in Figure 1 which shows the expected life-times of some known reserves compared with iron ore and coal. However, as reserves become exhausted, prices will inevitably rise and the exponential rate of increase, which is the foundation stone of most prophecies will change to a more gentle rate of increase, extending the lives of the reserves, and extending them by the encouragement of exploration. This, coupled with developments in mining and refining techniques which will make less rich deposits economically mineable, will ensure that coal and iron ore will last for longer than 100 years. RESOURCES
POLICY
December 1974
a At current rates consumption
Figure
1.
reserves
of
(from
Lifetimes some
Meadows
natural
of
b With consumption growing exponentially at the average annual rate of growth
known resources
et al’ )
Iron ore In the short
term there is little concern about the reserves of iron ore although eventually ores of lower quality may be used lower both in terms of iron content and in terms of suitability for making an acceptable burden to be fed to the blast furnaces. Most of the ores used by the British Steel Corporation (BSC) at present are imported and contain about 60% iron, but some home ore which contains less than 30% iron is still used. It is clear, however, that if lower quality ores are used in blast furnaces in future then more coke or other reductant will be needed to produce a tonne of steel.
Coal
1
Ridgion, J.M. Voice, E.W. and ironmaking and Steelmaking 1.2, (1974) 2 Meadows, D.H., Meadows, D.L., Randers, J. and Behrens, W.W. ‘The limits to growth’, (New York: Universal Books 1972 and Earth Island, London)
RESOURCES
POLICY
The amount of coke needed to produce a tonne of iron has decreased from about 1.5 tonnes in the 1850s to about 0.5 tonnes today. The decrease since 1950 when more than a tonne of coke was needed, is illustrated in Figure 2. This has come about because of better designed blast furnaces, better preparation of the burden, better control of the air flow within the furnace and from the injection of oil into the tuyeres of the furnaces as an alternative reductant to coke. In fact, it is possible with injection to decrease to 0.4 tonne the amount of coke needed to produce a tonne of iron (Figure 3). Another modification which has made blast furnaces more economical in coke has been the use of an increased temperature of the blast ~ for example in the 1940s blast temperatures were between 500-700°C while temperatures of over 1000°C are common now. Even higher temperatures would be welcomed, for a five degree increase in blast temperature is predicted to decrease the coke consumption by 1 kg for each tonne of steel produced. Thus, several factors contribute towards the more efficient use of coke. Making blast furnaces more efficient ekes out the reserves
December 1974
67
/ 1000
900
7’
600
‘\ ‘\
\ ‘\ ‘,, Japan -.-._.A,
500
‘\ ‘\
400 Figure
2. Coke
consumption
1950
52
54
58
56
60
62
64
68
66
70
72
Year
1950-72
:
7
njection
$5001 \ / xtion
\ \ \
1948 Figure
68
3. Best world
coke rate
50
52
54
56
58
60
62
64
66
68
70
72
Year
RESOURCES
POLICY
December
1974
of ‘coking coal as well as contributing towards the cost effectiveness of the industry. In 1973-74, for example, BSC spent 2165 million on buying coal, coke and breeze, and a 1 per cent increase in efficiency will mean an annual saving of 21.7 million - the higher coal prices now will make the saving that much greater. In spite of the relatively abundant supplies of coal world-wide, which it seems are enough to keep all users supplied until at least the end of the twenty-first century, the type of coal needed for making steel is not so abundant. Supplies of indigenous coking coal will become increasingly scarce as old deposits become worked out and new deposits are found to be difficult to mine. In order to counteract any possible shortage, ways have been developed to make use in steelmaking of what was previously considered to be non-coking coal. Blending coking coal with non-coking varieties has been shown to produce coke with acceptable properties. In recent years ways have also been found of making an acceptable substitute for coke using non-coking coal: this non-coking coal results in briquettes and is called formed coke. Although small percentages of coking varieties can be included, formed coke can be made completely from non-coking coal. The briquettes, unlike conventional coke in appearance, have the necessary strength to avoid being crushed so that the reduction gases can flow through the blast furnace. Therefore, blending coking coal with other forms of coal to make formed coke will give the steel industry greater flexibility in its choice of reducing agents. The industry, however, is also considering other methods of reducing iron oxide to iron without using coke as the reducing agent. In particular, methods of direct reduction, which involve making a solid ‘pre-reduced iron’, are being considered, hot hydrogen and carbon monoxide being suitable reducing gases. Direct reduction, however, cannot be considered in isolation, for its use places contraints on the remainder of the steelmaking process in that it normally needs to be followed by an electric arc furnace to produce steel. If a cheap method of producing and heating reducing gases could be obtained then steel making by direct reduction, followed by use of an electric arc furnace, could become an alternative to the conventional blast furnace and basic oxygen route of making steel. A way of making direct reduction such a favoured proposition might lie in using a nuclear reactor to produce the necessary energy. The ways in which a nuclear reactor might be used in steelmaking are being considered by the European Nuclear Steelmaking Club (ENSEC). Most of the major steel makers in Europe are members of the Club which is considering what criteria need to be satisfied by the nuclear reactor. Clearly a high temperature process heat reactor is best suited: the hot helium gas can be used to provide the heat to enable, for instance, the CH, + H, 0 reaction to proceed, giving carbon monoxide and hydrogen. Figure 4 shows a possible way in which a reactor can be incorporated into a steel works. Without going into any detail the potential advantages of relatively cheap heat will be tempered by the high capital costs of the reactor. RESOURCES POLICY December
1974
Figure
4.
the DR/EAF
Nuclear
power
applied
to
route
Nuclear reactor
Total steel 24-
-___----8-
Figure
60 Year
5. Scrap usage in steelmaking
Scrap
Nearly one-half the steel produced by BSC every year comes from scrap. The remainder is made directly from iron ore. Figure 5 shows this and the relative contributions of the different methods for making steel. The open hearth method is being run down in favour of the more efficient and economical basic oxygen method and by 1980 all open hearth operation will have been phased out. Up to 30% of scrap is fed into a basic oxygen furnace while the electric arc furnace is fed exclusively on scrap. Of the scrap used by the Corporation about a half is bought and the remainder is self generated within the works. There is a need for even greater efforts in recovering ferrous scrap, particularly in view of its high inherent energy content. With time, less scrap will become available from within the Corporation’s works, in a large part because of the widespread introduction of continuous casting. Similarly, it is expected that high quality process scrap from outside the industry, which is usually returned within a short time, will decrease as the efficiency of processes in other industries similarly improves. More effort will then be needed to recover capital scrap - the long term scrap 70
RESOURCES
POLICY
December
1974
from, for example, bridges, buildings and ships -~ and merchant scrap - the medium term scrap ranging from tin cans to motor cars. The problem is to ensure that in spite of changing procedures and habits a regular supply of scrap will be returned to the steel works. At present, the Corporation buys about 10’ tonnes of With internally arising scrap scrap per week from merchants. expected to decrease and steel output expected to increase there is a need for an even greater supply of scrap at the right price.
140/o dust and cinder
17%
vegetable
matter
43%
Paper
9Olo metal
3%
9%
5%
0
Steel from refuse
rags
glass
plastics
I
I
IO
20 010
Figure domestic
6.
I 30
I
I
40
50
by weight
Projected
composition
of
refuse (1980)
RESOURCES
POLICY
December
Two sources of scrap are domestic refuse and cars. Little is done at present to extract iron and steel from refuse and more can be done to make more efficient use of car scrap. At present the local authorities in Britain have to dispose of more than 14 x 1Oh tonnes of refuse a year. As the population, and the standard of living, increases the amount of refuse will also increase. It is difficult to predict how much refuse there will be for disposal in ten years time, not only because of the difficulty in predicting the population at that time but also because public awareness of the problems caused to the environment by refuse will force manufacturers to change packaging habits. Whatever the amount of refuse to be disposed of in the future the percentage of recyclable iron it will contain is not likely to be less than it is at present. It is estimated that refuse in 1980 will contain 9 per cent metal (Figure 6) and more than 90% of this metal will be iron. Even at the present rate of production of refuse about 1.6 x lo6 tonnes of iron are being disposed of each year. Most of the refuse in Britain is at present used as a land fill and little attempt is made to recover usable materials from it. Some of the refuse is incinerated, but this is carried out chiefly to reduce its volume before disposal (by up to 9OYu) and not in order to extract a recyclable product. The heat generated by incineration is sometimes put to use, the ferrous part recovered and the clinker used for road making. But this is the exception rather than the rule. It is possible in principle to make more use of refuse than is done at present. This problem has been considered recently not only with a view to alleviate the waste disposal problem in Britain but also with a view of making use of some of the redundant blast furnaces which are situated in different parts of the country. The essentials of the process which is envisaged are shown in Figure 7. The first stage would involve the separation of the refuse into an organic and inorganic part. The organic fraction would then be introduced to a pyrolysis unit where it would be heated in the absence of air. The organic compounds will dissociate into fuel oils and gas. Some of the recovered gas can be used to heat the pyrolysis unit and also to fire the high temperature incinerator. Excess gas will then be used elsewhere as a source of energy. The inorganic fraction of the refuse will be fed into a high temperature incinerator which can possibly be a blast furnace. There is a high degree of similarity between a conventional high temperature incinerator and a blast furnace. For example they both have preheated blasts with auxiliary fuel supplies and they both have waste gas cleaning systems, and there seems to be no fundamental 1974
71
r
Inorganic fraction
Organic fraction
I
I
Figure combined
7.
Treatment
of
refuse
by
Recovered oil
Slag processing unit
Hightemperature incinerator
Pyrolysis unit
Recovered surplus gas
Recovered metal
Recovered glass
Recovered slab
pyrolysis/incineration
reason why incineration can not be carried out in blast furnaces. The molten iron and the slag will be tapped from the furnace as is done for a conventional blast furnace. A schematic diagram of a combined pyrolysis unit and a blast furnace working as a high temperature incinerator is shown in Figure 8. From one tonne of refuse about 680 kg of organic waste is expected which, when pyrolysed, produces oil and gas which have an inherent energy of 11 900 MJ. More than 500 MJ is recirculated to heat and melt the inorganic fraction as well as to keep the residue molten. The net output is 11 300 MJ in the form of gas and oil as well as 90 kg of metals, 90 kg of glass and 140 kg of dust. These residues can then be turned into saleable metallic and ceramic residues. If the entire refuse produced in Britain every year is turned into useful energy in this way then 53 400 GWh of useful energy would be produced (equivalent to 6.6 x lo6 tonnes of coal).
Steel from cars
Whilst the extraction of useful by-products from refuse should be pursued, making sure that all the useful steel in cars which are scrapped is also important. In Britain at present more than 700 000 cars are scrapped annually and according to some estimates the number could be as high as a million. On average, each car weighs about 0.8 tonne and 80% of this is iron and steel. Therefore this is a source of 6.5 x lo5 tonnes of useful scrap to the steel industry. It is not unreasonable to assume that by the end of the century twice the present number of cars will be scrapped each year. While increasing the efficiency of the scrap industry as 72
RESOURCES
POLICY
December 1974
far as old cars are concerned will not contribute as much as the recycling of refuse - a great deal of the steel from old cars is already reused - it is nevertheless a source of scrap which cannot be neglected. A useful development in this line, from the USA, is a furnace designed to melt cars. The cars are first stripped of easily removable and worthwhile parts (such as radiators, cables, generators and batteries), lime is placed in the car and it is then compressed. Light scrap and steelmaking dusts can also be placed in the cars before they are compressed. The compressed car is fed into the top of the furnace, and air is injected half way down the stack to oxidise any lead or zinc present and remove it as a dust. The car then passes into the combustion chamber, which can be fired by oil or gas; the temperature here is more than 1600°C. Molten steel and slag are tapped from the bottom of the furnace. As yet such a full scale plant has not been built, but it is designed to process 22 cars ----North American size - an hour and produce 2 x lo5 tonnes of hot metal/year. At the same rate of feeding with British cars this would amount to 1.93 x lo5 cars a year and an output of 1.2 x lo5 tonnes of iron.
El I tonne
raw refuse
iegregated
into,\
, 680
90kq glass 90 kg metals 140 kg dust, etc.
kg organics
(paper, plastics, veqtable waste, etc.)
376 MJ to‘ heat and melt
Figure
8. Heat
flows
pyrolysis/high-temperature
RESOURCES
l35MJ to keep residue molten
-11300 MJ oil and gas for storage and sale ie-- 1.86 barrels oil
in a combined inciner-
ation system
i”
Saleable metallic an
1 POLICY
December
1974
73
3
Steel research
Corporationl
73
(British
Steel
Cryogenic scrap
The value of scrap depends to a great extent on its quality ~ that is its chemical composition and on its size. Ideally the steel industry would very much like all the scrap it uses to be uniform size. In an attempt to improve the quality, scrap has been cooled to liquid nitrogen temperatures and then fragmented. The net result is that the scrap is transformed into a product which is much more manageable. The size of the fragments is less than 50 mm and the density of the scrap increased from about 960 kg/m3 to a value of 3 100 kg/mj. The non-ferrous component can be more effectively separated by this process. One of the problems with using a cryogenic method to break up the scrap is the cost, but efforts in the Corporation’s laboratories” to develop a new closed loop process for producing low temperatures using methane as a coolant have been encouraging and are being pursued.
Conclusions It would be foolish
to say that the iron and steel industry is satisfied with the state of its resources but developments in making coke from coals which were previously thought to be inferior for iron making, together with the consideration now being given towards using direct reduction for the preparation of iron will give the industry a flexibility in the use of fuels which it has not previously enjoyed. Gas and oil from the North Sea can be used as reductants as well as fuels. These indigenous sources of energy could add greatly to the Corporation’s flexibility and security of supply making it less vulnerable to sudden shortages of other fuels and reductants. Iron ore is, of course, essential to the industry although a greater availability of scrap of improved quality and quantity is needed to increase output to meet the greater demands of the future. There is no immediate concern about the supply of ore but more needs to be done to ensure that as much usable scrap as possible is recycled if only to conserve energy.
Acknowledgement I wish to thank Mr Norman
Davis and Dr Alun Jones
for their
assistance.
74
RESOURCES
POLICY
December 1974
The
future
coking
supplies
coal
of
iron
ore,
and
ferrous
scrap
discussed. There of the resources
is no of iron
likelihood ore being
until
exhausted twenty-first on
the
other
supply
but
blending by
blast
from
being
shorter
more com-
for
played
an
making
and the
coal
making
greater
will
in the
flexibility
hydrocarbons
considered
stitutes
by and
made
in iron
making,
out coal
non-coking
To ensure
steel
the coal,
furnaces
Briquettes
a part
in
non-coking
making
future. in
is
is being eked
with
pletely
into
Coking
hand,
it
efficient. play
well
century.
are
as
coal.
Scrap
important
are
possible
has always
part
amount
sub-
in
steel
recycled
is
increasing every year. But more effort is needed, that
the
utilised
for steel
example,
to
in car scrap
and that
ensure is fully
refuse is efficiently
recycled.
Steel
demands
the scrap to have few
purities
making
and to be in uniform
pieces.
A cryogenic
paring
such
futuristic non-ferrous
scrap
way
by-products
using
redundant
method
imsized
of
pre-
is described.
A
extracting
iron,
and
sale-
from blast
other refuse, furnaces,
by is
discussed.
Dr Barnes Development,
66
of
metals
eable also
increasingly
is Director of Research and British Steel Corporation
The iron and steel industry has less cause for concern about the possible exhaustion of its necessary resources than most other metal based industries. Many estimates have been made of the reserves of coal and iron ore, not all of which arc consistent. However, an overall picture can be drawn which shows that there are about 5 x 10’ 2 tonnes of hard coal reserves available world-wide. Half of this is in the USSR and China and one-third in the USA. About 10’ * tonnes of coking coal are thought to be available ~- three-quarters in the USA, USSR and China. Estimates of iron ore reserves vary as well, the highest suggested value being greater than 0.5 x 10’ ’ tonnes. One conclusion to be drawn is that there is enough coking coal present to smelt all the reserves of iron ore. However, estimates differ as to how long these reserves will last. According to Voice and Ridgion’ predicted rates of consumption give lifetimes for hard coal reserves of more than 1000 years. Dennis Meadows’ predicts that coal reserves will last another 1300 years at present rates of consumption, while if the rate of use of coal continued to increase exponentially it will run out in a little over 100 years time. Similarly, Meadows predicts that iron ore will last 200 years at present rates of consumption reducing to 100 years if present rates of growth continue. Although predictions differ by large amounts, even the most pessimistic figures provide some comfort for the iron and steel industry, This is illustrated in Figure 1 which shows the expected life-times of some known reserves compared with iron ore and coal. However, as reserves become exhausted, prices will inevitably rise and the exponential rate of increase, which is the foundation stone of most prophecies will change to a more gentle rate of increase, extending the lives of the reserves, and extending them by the encouragement of exploration. This, coupled with developments in mining and refining techniques which will make less rich deposits economically mineable, will ensure that coal and iron ore will last for longer than 100 years. RESOURCES
POLICY
December 1974
a At current rates consumption
Figure
1.
reserves
of
(from
Lifetimes some
Meadows
natural
of
b With consumption growing exponentially at the average annual rate of growth
known resources
et al’ )
Iron ore In the short
term there is little concern about the reserves of iron ore although eventually ores of lower quality may be used lower both in terms of iron content and in terms of suitability for making an acceptable burden to be fed to the blast furnaces. Most of the ores used by the British Steel Corporation (BSC) at present are imported and contain about 60% iron, but some home ore which contains less than 30% iron is still used. It is clear, however, that if lower quality ores are used in blast furnaces in future then more coke or other reductant will be needed to produce a tonne of steel.
Coal
1
Ridgion, J.M. Voice, E.W. and ironmaking and Steelmaking 1.2, (1974) 2 Meadows, D.H., Meadows, D.L., Randers, J. and Behrens, W.W. ‘The limits to growth’, (New York: Universal Books 1972 and Earth Island, London)
RESOURCES
POLICY
The amount of coke needed to produce a tonne of iron has decreased from about 1.5 tonnes in the 1850s to about 0.5 tonnes today. The decrease since 1950 when more than a tonne of coke was needed, is illustrated in Figure 2. This has come about because of better designed blast furnaces, better preparation of the burden, better control of the air flow within the furnace and from the injection of oil into the tuyeres of the furnaces as an alternative reductant to coke. In fact, it is possible with injection to decrease to 0.4 tonne the amount of coke needed to produce a tonne of iron (Figure 3). Another modification which has made blast furnaces more economical in coke has been the use of an increased temperature of the blast ~ for example in the 1940s blast temperatures were between 500-700°C while temperatures of over 1000°C are common now. Even higher temperatures would be welcomed, for a five degree increase in blast temperature is predicted to decrease the coke consumption by 1 kg for each tonne of steel produced. Thus, several factors contribute towards the more efficient use of coke. Making blast furnaces more efficient ekes out the reserves
December 1974
67
/ 1000
900
7’
600
‘\ ‘\
\ ‘\ ‘,, Japan -.-._.A,
500
‘\ ‘\
400 Figure
2. Coke
consumption
1950
52
54
58
56
60
62
64
68
66
70
72
Year
1950-72
:
7
njection
$5001 \ / xtion
\ \ \
1948 Figure
68
3. Best world
coke rate
50
52
54
56
58
60
62
64
66
68
70
72
Year
RESOURCES
POLICY
December
1974
of ‘coking coal as well as contributing towards the cost effectiveness of the industry. In 1973-74, for example, BSC spent 2165 million on buying coal, coke and breeze, and a 1 per cent increase in efficiency will mean an annual saving of 21.7 million - the higher coal prices now will make the saving that much greater. In spite of the relatively abundant supplies of coal world-wide, which it seems are enough to keep all users supplied until at least the end of the twenty-first century, the type of coal needed for making steel is not so abundant. Supplies of indigenous coking coal will become increasingly scarce as old deposits become worked out and new deposits are found to be difficult to mine. In order to counteract any possible shortage, ways have been developed to make use in steelmaking of what was previously considered to be non-coking coal. Blending coking coal with non-coking varieties has been shown to produce coke with acceptable properties. In recent years ways have also been found of making an acceptable substitute for coke using non-coking coal: this non-coking coal results in briquettes and is called formed coke. Although small percentages of coking varieties can be included, formed coke can be made completely from non-coking coal. The briquettes, unlike conventional coke in appearance, have the necessary strength to avoid being crushed so that the reduction gases can flow through the blast furnace. Therefore, blending coking coal with other forms of coal to make formed coke will give the steel industry greater flexibility in its choice of reducing agents. The industry, however, is also considering other methods of reducing iron oxide to iron without using coke as the reducing agent. In particular, methods of direct reduction, which involve making a solid ‘pre-reduced iron’, are being considered, hot hydrogen and carbon monoxide being suitable reducing gases. Direct reduction, however, cannot be considered in isolation, for its use places contraints on the remainder of the steelmaking process in that it normally needs to be followed by an electric arc furnace to produce steel. If a cheap method of producing and heating reducing gases could be obtained then steel making by direct reduction, followed by use of an electric arc furnace, could become an alternative to the conventional blast furnace and basic oxygen route of making steel. A way of making direct reduction such a favoured proposition might lie in using a nuclear reactor to produce the necessary energy. The ways in which a nuclear reactor might be used in steelmaking are being considered by the European Nuclear Steelmaking Club (ENSEC). Most of the major steel makers in Europe are members of the Club which is considering what criteria need to be satisfied by the nuclear reactor. Clearly a high temperature process heat reactor is best suited: the hot helium gas can be used to provide the heat to enable, for instance, the CH, + H, 0 reaction to proceed, giving carbon monoxide and hydrogen. Figure 4 shows a possible way in which a reactor can be incorporated into a steel works. Without going into any detail the potential advantages of relatively cheap heat will be tempered by the high capital costs of the reactor. RESOURCES POLICY December
1974
Figure
4.
the DR/EAF
Nuclear
power
applied
to
route
Nuclear reactor
Total steel 24-
-___----8-
Figure
60 Year
5. Scrap usage in steelmaking
Scrap
Nearly one-half the steel produced by BSC every year comes from scrap. The remainder is made directly from iron ore. Figure 5 shows this and the relative contributions of the different methods for making steel. The open hearth method is being run down in favour of the more efficient and economical basic oxygen method and by 1980 all open hearth operation will have been phased out. Up to 30% of scrap is fed into a basic oxygen furnace while the electric arc furnace is fed exclusively on scrap. Of the scrap used by the Corporation about a half is bought and the remainder is self generated within the works. There is a need for even greater efforts in recovering ferrous scrap, particularly in view of its high inherent energy content. With time, less scrap will become available from within the Corporation’s works, in a large part because of the widespread introduction of continuous casting. Similarly, it is expected that high quality process scrap from outside the industry, which is usually returned within a short time, will decrease as the efficiency of processes in other industries similarly improves. More effort will then be needed to recover capital scrap - the long term scrap 70
RESOURCES
POLICY
December
1974
from, for example, bridges, buildings and ships -~ and merchant scrap - the medium term scrap ranging from tin cans to motor cars. The problem is to ensure that in spite of changing procedures and habits a regular supply of scrap will be returned to the steel works. At present, the Corporation buys about 10’ tonnes of With internally arising scrap scrap per week from merchants. expected to decrease and steel output expected to increase there is a need for an even greater supply of scrap at the right price.
140/o dust and cinder
17%
vegetable
matter
43%
Paper
9Olo metal
3%
9%
5%
0
Steel from refuse
rags
glass
plastics
I
I
IO
20 010
Figure domestic
6.
I 30
I
I
40
50
by weight
Projected
composition
of
refuse (1980)
RESOURCES
POLICY
December
Two sources of scrap are domestic refuse and cars. Little is done at present to extract iron and steel from refuse and more can be done to make more efficient use of car scrap. At present the local authorities in Britain have to dispose of more than 14 x 1Oh tonnes of refuse a year. As the population, and the standard of living, increases the amount of refuse will also increase. It is difficult to predict how much refuse there will be for disposal in ten years time, not only because of the difficulty in predicting the population at that time but also because public awareness of the problems caused to the environment by refuse will force manufacturers to change packaging habits. Whatever the amount of refuse to be disposed of in the future the percentage of recyclable iron it will contain is not likely to be less than it is at present. It is estimated that refuse in 1980 will contain 9 per cent metal (Figure 6) and more than 90% of this metal will be iron. Even at the present rate of production of refuse about 1.6 x lo6 tonnes of iron are being disposed of each year. Most of the refuse in Britain is at present used as a land fill and little attempt is made to recover usable materials from it. Some of the refuse is incinerated, but this is carried out chiefly to reduce its volume before disposal (by up to 9OYu) and not in order to extract a recyclable product. The heat generated by incineration is sometimes put to use, the ferrous part recovered and the clinker used for road making. But this is the exception rather than the rule. It is possible in principle to make more use of refuse than is done at present. This problem has been considered recently not only with a view to alleviate the waste disposal problem in Britain but also with a view of making use of some of the redundant blast furnaces which are situated in different parts of the country. The essentials of the process which is envisaged are shown in Figure 7. The first stage would involve the separation of the refuse into an organic and inorganic part. The organic fraction would then be introduced to a pyrolysis unit where it would be heated in the absence of air. The organic compounds will dissociate into fuel oils and gas. Some of the recovered gas can be used to heat the pyrolysis unit and also to fire the high temperature incinerator. Excess gas will then be used elsewhere as a source of energy. The inorganic fraction of the refuse will be fed into a high temperature incinerator which can possibly be a blast furnace. There is a high degree of similarity between a conventional high temperature incinerator and a blast furnace. For example they both have preheated blasts with auxiliary fuel supplies and they both have waste gas cleaning systems, and there seems to be no fundamental 1974
71
r
Inorganic fraction
Organic fraction
I
I
Figure combined
7.
Treatment
of
refuse
by
Recovered oil
Slag processing unit
Hightemperature incinerator
Pyrolysis unit
Recovered surplus gas
Recovered metal
Recovered glass
Recovered slab
pyrolysis/incineration
reason why incineration can not be carried out in blast furnaces. The molten iron and the slag will be tapped from the furnace as is done for a conventional blast furnace. A schematic diagram of a combined pyrolysis unit and a blast furnace working as a high temperature incinerator is shown in Figure 8. From one tonne of refuse about 680 kg of organic waste is expected which, when pyrolysed, produces oil and gas which have an inherent energy of 11 900 MJ. More than 500 MJ is recirculated to heat and melt the inorganic fraction as well as to keep the residue molten. The net output is 11 300 MJ in the form of gas and oil as well as 90 kg of metals, 90 kg of glass and 140 kg of dust. These residues can then be turned into saleable metallic and ceramic residues. If the entire refuse produced in Britain every year is turned into useful energy in this way then 53 400 GWh of useful energy would be produced (equivalent to 6.6 x lo6 tonnes of coal).
Steel from cars
Whilst the extraction of useful by-products from refuse should be pursued, making sure that all the useful steel in cars which are scrapped is also important. In Britain at present more than 700 000 cars are scrapped annually and according to some estimates the number could be as high as a million. On average, each car weighs about 0.8 tonne and 80% of this is iron and steel. Therefore this is a source of 6.5 x lo5 tonnes of useful scrap to the steel industry. It is not unreasonable to assume that by the end of the century twice the present number of cars will be scrapped each year. While increasing the efficiency of the scrap industry as 72
RESOURCES
POLICY
December 1974
far as old cars are concerned will not contribute as much as the recycling of refuse - a great deal of the steel from old cars is already reused - it is nevertheless a source of scrap which cannot be neglected. A useful development in this line, from the USA, is a furnace designed to melt cars. The cars are first stripped of easily removable and worthwhile parts (such as radiators, cables, generators and batteries), lime is placed in the car and it is then compressed. Light scrap and steelmaking dusts can also be placed in the cars before they are compressed. The compressed car is fed into the top of the furnace, and air is injected half way down the stack to oxidise any lead or zinc present and remove it as a dust. The car then passes into the combustion chamber, which can be fired by oil or gas; the temperature here is more than 1600°C. Molten steel and slag are tapped from the bottom of the furnace. As yet such a full scale plant has not been built, but it is designed to process 22 cars ----North American size - an hour and produce 2 x lo5 tonnes of hot metal/year. At the same rate of feeding with British cars this would amount to 1.93 x lo5 cars a year and an output of 1.2 x lo5 tonnes of iron.
El I tonne
raw refuse
iegregated
into,\
, 680
90kq glass 90 kg metals 140 kg dust, etc.
kg organics
(paper, plastics, veqtable waste, etc.)
376 MJ to‘ heat and melt
Figure
8. Heat
flows
pyrolysis/high-temperature
RESOURCES
l35MJ to keep residue molten
-11300 MJ oil and gas for storage and sale ie-- 1.86 barrels oil
in a combined inciner-
ation system
i”
Saleable metallic an
1 POLICY
December
1974
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3
Steel research
Corporationl
73
(British
Steel
Cryogenic scrap
The value of scrap depends to a great extent on its quality ~ that is its chemical composition and on its size. Ideally the steel industry would very much like all the scrap it uses to be uniform size. In an attempt to improve the quality, scrap has been cooled to liquid nitrogen temperatures and then fragmented. The net result is that the scrap is transformed into a product which is much more manageable. The size of the fragments is less than 50 mm and the density of the scrap increased from about 960 kg/m3 to a value of 3 100 kg/mj. The non-ferrous component can be more effectively separated by this process. One of the problems with using a cryogenic method to break up the scrap is the cost, but efforts in the Corporation’s laboratories” to develop a new closed loop process for producing low temperatures using methane as a coolant have been encouraging and are being pursued.
Conclusions It would be foolish
to say that the iron and steel industry is satisfied with the state of its resources but developments in making coke from coals which were previously thought to be inferior for iron making, together with the consideration now being given towards using direct reduction for the preparation of iron will give the industry a flexibility in the use of fuels which it has not previously enjoyed. Gas and oil from the North Sea can be used as reductants as well as fuels. These indigenous sources of energy could add greatly to the Corporation’s flexibility and security of supply making it less vulnerable to sudden shortages of other fuels and reductants. Iron ore is, of course, essential to the industry although a greater availability of scrap of improved quality and quantity is needed to increase output to meet the greater demands of the future. There is no immediate concern about the supply of ore but more needs to be done to ensure that as much usable scrap as possible is recycled if only to conserve energy.
Acknowledgement I wish to thank Mr Norman
Davis and Dr Alun Jones
for their
assistance.
74
RESOURCES
POLICY
December 1974