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科目专业英语
专业冶金工程
姓名仲光绪
学号
1045562137
The
Basic Oxygen Steelmaking (BOS) Process
HISTORY OF THE BASIC OXYGEN STEELMAKING
PROCESS
Basic Oxygen
Steelmaking is unquestionably the
process patented by Sir Henry Bessemer
in 1856. Because oxygen was not available
commercially in those days, air was the
oxidant. It was blown through tuyeres in the
bottom of
the pear shaped vessel. Since
air is 80% inert nitrogen, which entered the
vessel cold but
exited hot, removed so
much heat from the process that the charge had to
be almost 100% hot
metal for it to be
autogenous. The inability of the Bessemer process
to melt significant
quantities of scrap
became an economic handicap as steel scrap
accumulated. Bessemer
production peaked
in the U.S. in 1906 and lingered until the 1960s.
There are two interesting historical
footnotes to the original Bessemer story:
William Kelly was awarded the original
U.S. patent for pneumatic steelmaking over
Bessemer
in 1857. However, it is clear
that Kelly's
blowing rates that the
heat generation barely offset the heat losses. He
never developed a
commercial process
for making steel consistently.
Most
European iron ores and therefore hot metal was
high in sulfur and phosphorus and no
processes to remove these from steel
had been developed in the 1860s. As a result,
Bessemer's steel suffered from both
to phosphorus) that rendered it
unrollable. For his first commercial plant in
Sheffield, 1866,
Bessemer remelted cold
pig iron imported from Sweden as the raw material
for his hot metal.
This charcoal
derived pig iron was low in phosphorus and sulfur,
and (fortuitously) high in
manganese
which acted as a deoxidant. In contrast the U.S.
pig iron was produced using low
sulfur
charcoal and low phosphorus domestic ore.
Therefore, thanks to the engineering genius
of Alexander Holley, two Bessemer
plants were in operation by 1866. However, the
daily
output of remotely located
charcoal blast furnaces was very low. Therefore,
hot metal was
produced by remelting pig
iron in cupolas and gravity feeding it to the 5
ton Bessemer vessels.
The real
breakthrough for Bessemer occurred in 1879 when
Sidney Thomas, a young clerk
from a
London police court, shocked the metallurgical
establishment by presenting data on a
process to remove phosphorus (and also
sulfur) from Bessemer's steel. He developed basic
linings produced from tar-bonded
dolomite bricks. These were eroded to form a basic
slag that
absorbed phosphorus and
sulfur, although the amounts remained high by
modern standards.
The Europeans quickly
took to the
hot metal, and as a bonus,
granulated the phosphorus-rich molten slag in
water to create a
fertilizer. In the
U.S., Andrew Carnegie, who was present when Thomas
presented his paper in
London,
befriended the young man and cleverly acquired the
U.S. license, which squelched
any
steelmaking developments in the South where high
phosphorus ores are located.
Although
Bessemer's father had jokingly suggested using
pure oxygen instead of air, this
possibility was to remain a dream until
cost. A 250 ton BOF today needs about
20 tons of pure oxygen every 40 minutes. Despite
its
high cost, oxygen was used in
Europe to a limited extent in the 1930's to enrich
the air blast for
blast furnaces and
Thomas converters. It was also used in the U.S for
scarfing and welding.
The production of
low cost tonnage oxygen was stimulated in World
War II by the German V2
rocket program.
After the war, the Germans were denied the right
to manufacture tonnage
oxygen, but
oxygen plants were shipped to other countries. The
bottom tuyeres used in the
Bessemer and
Thomas processes could not withstand even oxygen-
enriched air, let alone
pure oxygen. In
the late 1940s, Professor Durrer in Switzerland
pursued his prewar idea of
injecting
pure oxygen through the top of the vessel.
Development now moved to neighboring
Austria where developers wanted to
produce low nitrogen, flat-rolled sheet, but a
shortage of
scrap precluded open hearth
operations. Following pilot plant trials at Linz
and Donawitz, a top
blown pneumatic
process for a 35 ton vessel using pure oxygen was
commercialized by Voest
at Linz in
1952. The nearby Dolomite Mountains also provided
an ideal source of material for
basic
refractories.
The new process was
officially dubbed the
was seen globally
as a viable, low capital process by which the war
torn countries of Europe
could rebuild
their steel industries. Japan switched from a
rebuilding plan based on open
hearths
to evaluate the LD, and installed their first unit
at Yawata in 1957.
Two small North
American installations started at Dofasco and
McLouth in 1954. However,
with the
know-how and capital invested in 130 million tons
of open hearth capacity, plans for
additional open hearth capacity well
along, cheap energy, and heat sizes greater by an
order
of magnitude (300 versus 30
tons), the incentive to install this untested,
small-scale process in
North America
was lacking. The process was acknowledged as a
breakthrough technically but
the
timing, scale, and economics were wrong for the
time. The U.S
，
which
manufactured about
50% of the world's
total steel output, needed steel for a booming
post-war economy.
There were also
acrimonious legal actions over patent rights to
the process and the
supersonic lance
design, which was now multihole rather than single
hole. Kaiser Industries
held the U.S.
patent rights but in the end, the U.S. Supreme
Court supported lower court
decisions
that considered the patent to be invalid.
Nevertheless, the appeal of lower
energy, labor, and refractory costs for the LD
process could
not be denied and
although oxygen usage in the open hearth delayed
the transition to the new
process in
the U.S., oxygen steelmaking tonnage grew steadily
in the 1960's. By 1969, it
exceeded
that of the open hearth for the first time and has
never relinquished its position as
the
dominant steelmaking process in the U.S. but the
name LD never caught on in the U.S.
Technical developments over the years
include improved computer models and
instrumentation for improved turn-down
control, external hot metal desulfurization,
bottom
blowing and stirring with a
variety of gases and tuyeres, slag splashing, and
improved
refractories.
INTRODUCTION
Accounting for 60% of the world's total
output of crude steel, the Basic Oxygen
Steelmaking
(BOS) process is the
dominant steelmaking technology. In the U.S., that
figure is 54% and
slowly declining due
primarily to the advent of the
flat-
rolled mills. However, elsewhere its use is
growing.
There exist several variations
on the BOS process: top blowing, bottom blowing,
and a
combination of the two. This
study will focus only on the top blowing
variation.
The Basic Oxygen Steelmaking
process differs from the EAF in that it is
autogenous, or
self-sufficient in
energy. The primary raw materials for the BOP are
70-80% liquid hot metal
from the blast
furnace and the balance is steel scrap. These are
charged into the Basic
Oxygen Furnace
(BOF) vessel. Oxygen (>99.5% pure) is
velocities. It oxidizes the carbon and
silicon contained in the hot metal liberating
great
quantities of heat which melts
the scrap. There are lesser energy contributions
from the
oxidation of iron, manganese,
and phosphorus. The post combustion of carbon
monoxide as it
exits the vessel also
transmits heat back to the bath.
The
product of the BOS is molten steel with a
specified chemical anlaysis at
2900°
F-3000°
F.
From here it may undergo further
refining in a secondary refining process or be
sent directly to
the continuous caster
where it is solidified into semifinished shapes:
blooms, billets, or slabs.
Basic
refers to the magnesia
(MgO) refractory lining which wears through
contact with hot,
basic slags. These
slags are required to remove phosphorus and sulfur
from the molten
charge.
BOF
heat sizes in the U.S. are typically around 250
tons, and tap-to-tap times are about 40
minutes, of which 50% is
with the continuous casting of slabs,
which in turn had an enormous beneficial impact on
yields
from crude steel to shipped
product, and on downstream flat-rolled quality.
BASIC OPERATION
BOS process replaced open hearth
steelmaking. The process predated continuous
casting. As
a consequence, ladle sizes
remained unchanged in the renovated open hearth
shops and
ingot pouring aisles were
built in the new shops. Six-story buildings are
needed to house the
Basic Oxygen
Furnace (BOF) vessels to accommodate the long
oxygen lances that are
lowered and
raised from the BOF vessel and the elevated alloy
and flux bins. Since the BOS