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Knowledge for
the Sulphuric Acid Industry
Introduction
General
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Instrumentation
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Sulphur Burning
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Lead Chamber
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Equipment Life
April 15, 2006
Introduction
The life span for a piece of equipment varies with many
factors such as:
Original design parameters
Materials of construction
Fabrication and erection
Operating conditions (normal and
excursions)
Type and frequency of maintenance
The original design parameters for a piece
of equipment play an important role in the expected life of a piece of equipment.
The corrosion allowance and vessel wall thickness specified for a piece of equipment
directly affects its life span. For lined equipment, the specification of the lining
system and thickness is also an important factor. If a piece of equipment is subject
to erosion then design velocities will affect equipment life. In corrosive services,
the material of construction used to construct a piece of equipment affects its expected
life span. Constructing a heat exchanger from stainless steel rather than carbon
steel may cost more but its increased life span may justify the initial higher cost.
The quality of the fabrication and erection for a piece of equipment is important in
extending the life of a piece of equipment. Poor welds can result in premature
failure or increased corrosion. All equipment is designed to operate within a set
limit of temperature, pressure, concentration, velocity, etc. Operating outside of
the design limits may result in increased corrosion or stress on the equipment that will
lead to premature failure. No piece of equipment is expected to operate its entire
life without some preventative maintenance. Vendors will often provide maintenance
schedules and activities to be performed in order to maximize the life of a piece of
equipment. When a piece of equipment has reached the end of its useful life it must
be replaced. Equipment must be replaced when the cost to maintain it becomes so high
that the cost of replacement can be justified. As well, if a piece of equipment is
no longer reliable and results in frequent and costly outages, it should be
replaced. Finally, complete failure of a piece of equipment such that it can no
longer be operated means that replacement is required. A piece of equipment may also
be replaced in conjunction with a plant expansion even though it still has years of
serviceable life remaining.
Converters
The converter is the largest single piece
of equipment in the plant. A decision to
replace a converter is not taken lightly because it is a major undertaking. Converters that are being replaced at this time
are the cast iron grid and post and the brick internal designs. There are no known cases of newer stainless steel
converters being replaced. The older
converters typically suffer from gas leaks, bulging shells, collapsed grids,
internal/external gas leaks, etc. Since the
converter is a major piece of equipment, a replacement converter is often accompanied with
an increase in plant capacity and an increase in the size of the converter.
| Owner/Operator |
Details |
Mosaic (Cargill)
Florida |
Original 1961 cast iron grid and post converter
replaced in 1999 with a new stainless steel design. Service life of 38 years.
The converter was replaced as part of a plant increase in capacity from 2200 to 3200 STPD. |
Mosaic (Cargill)
Florida |
Original 1965 cast iron grid and post converter
replaced in 2004 with a new stainless steel design. Service life of 39 years. |
Lucite (Ineos)
Memphis Site |
Sulphuric acid regeneration plant converter,
originally built in 1972 was replaced in 1996 after a service life of 24 years. |
J.R. Simplot
Pocatello, Idaho |
Original 35 year old cast iron grid and post
converter replaced in 2001 with a new stainless steel converter |
Sasol Agri
Phalaborwa, South Africa |
Plant built in 1975. Original converter
replaced after a service life of 24 years with a stainless steel converter. Plant
capacity also increased. |
Agrium
Redwater, Alberta |
Original cast iron grid and post converter replaced in 2002 with a
new stainless steel converter after a service life of 33 years. |
TeckCominco
Trail, British Columbia |
Original converter in No. 8 acid plant was installed in 1966.
Converter replaced in 2006 after a 40 year service life. The converter had
undergone numerous repairs. |
Gas-to-Gas Heat Exchangers
A gas-to-gas heat exchanger reaches the end
of its useful life when it can no longer perform the required heat transfer duty or when
the pressure drop through the exchanger is excessive. The major reason for both of
these conditions occurring is corrosion of the heat exchanger. Poor heat transfer
can be caused by fouling of the heat exchange surface and corrosion of tubes the causes
tube to be plugged. High pressure drops are the result of corrosion products
accumulating inside the exchanger.
| Owner/Operator |
Details |
| Cold Exchanger |
Typical service life: 5 to 15 years |
J.R. Simplot
Lathrop, California |
Two 13 year-old exchangers replaced with Monplex
units. Old units corroded, tubes plugged. High pressure drop low heat transfer
|
CODELCO
El Teniente, Chile |
SO3 cooler originally installed in
1998. Exchanger re-tubed after 6 years in early 2004. Tube failures continue
through 2004 and exchanger re-tubed at end of 2004. |
INCO
Coppercliff, Ontario |
Plant built in 1991. Cold reheat
exchangers replaced in 2004 after a service life of 13 years. The hot and hot reheat
exchangers were replaced in 2005 after a service life of 14 years. The replacement
of the heat exchangers was part of a plant expansion. The cold reheat exchangers
were showing high pressure drops which necessitated their replacement. |
Tessenderlo Chemie
Belgium |
Cold heat exchanger replaced in 1997 after a 7
year service life. During previous shutdowns corrosion was noted at the lower inlet
tubesheet and some tubes were plugged. Although the unit was still serviceable, a
decision was made to replace the unit to ensure reliable operation. |
Sasol Agri
Phalaborwa, South Africa |
Plant built in 1975. Hot heat exchanger
replaced after a service life of 24 years. Cold exchanger replaced after a service
life of 26 years. |
Bunge Fertilizantes
Cubatão, Brazil |
Replacement of heat exchanger E104 in 1995 after
a service life of 17 years. Exchanger E104 is a hot exchanger in a sulphur burning
plant. |
Tesoro Refining
Martinez, California |
Original hot heat exchanger installed in 1962
was replaced in 1971, 1980 and 1991 with a similar design (carbon steel with alonized
tubes). In 2003, the hot exchanger was replaced with a stainless steel design. |
Distributors
There are two types of distributors in
common use: pipe and trough distributors. The material of construction is cast iron,
high silicon stainless steel or 310 SS. The life of a distributor depends in the
material of construction, acid temperature and concentration. For cast iron
distributors longer service life is achieved by using thicker the walls for the pipe,
trough and downcomers. Unfortunately, the thicker walls increase the weight and cost
of the distributor. Alloy stainless steel distributors rely on the fact that
corrosion rates are much lower so thinner material can be used in the fabrication of the
distributor. Distributors are somewhat unique because they experience corrosion from
both sides of the material whereas piping experiences corrosion only from the inside.
| Owner/Operator |
Details |
| General |
Cast Iron: Downcomers will typically last about 4 to 5 years
Alloy:
Expected life of more than 20 years based on corrosion rates of less than 0.025 mm/y (1
mpy) |
Bricklined Towers
Properly design, installed and operated
brick lined equipment should last the life of an acid plant. Properly specified and
installed acid resistant lining will provide the necessary protection of the carbon steel
shell. However, if there is a failure of the lining that allows acid to penetrate to
the shell, the equipment will quickly begin to show the signs of deterioration. The
first indication of a problem will be the characteristic bulging of the metal shell as
iron sulphates form between the shell and the brick lining. The next stage will be
actual acid leaks through the steel shell. Various techniques can be used to repair
and extend the life of the equipment but eventually the equipment will need to be
replaced.
| Owner/Operator |
Details |
DuPont
Wurtland, KY |
40 year old drying tower replaced.
37 year old absorber tower replaced. |
Mosaic Co.
Uncle Sam, LA |
Absorber tower originally installed in 1968.
The tower lasted 36 years but had been repaired numerous times.
Approximately, 60 to 70% of the shell had been repaired or replaced. |
| Pasminco Zinc |
Original Lurgi venturi absorber was built in
1978. Over the years the tower developed bulges, leaks and degradation of the carbon
steel shell. In 1998, Lurgi replaced the tower with an increase in capacity (+15%
flow). The tower had a life of 20 years. |
Lucite (Ineos)
Memphis Site, TN |
Drying and absorbing towers were replaced as
part of a plant upgrade to increase capacity by a factor of 2 times. The original
1972 drying tower was replaced in 1994 after a 22 year life. The original absorber
tower was replaced in 2000 after a 28 year life. |
| CF Industries |
Original 1965 drying tower was replaced in 1997
after a service life of 32 years. The original tower had a flat bottom design that
was repaired numerous times. This was done in both the A and B plants. |
Mosaic Co.
South Pierce, FL |
Original 1975 absorber tower in the No. 10 plant was replaced in 1992 after a
service life of 17 years.
Absorber tower in No. 11 plant was replaced in 1996 after a
service life of 21 years. |
PCS Phosphates
Aurora, NC |
Original final absorption tower on the No. 5
plant built in 1982 replaced in 1989 and again in 1995. In 2002, tower was replaced
with an alloy design. |
Copebrás Limitada
Cubatão, Brazil |
Final absorption tower replaced in 2001 after a
service life of 27 years. |
Falconbridge
Timmins, Ontario |
Original absorber tower built in 1972 replaced
in 1993 after 21 years of service. The replacement tower experienced problems early
in its life and was eventually replaced in 2005 after only 12 years of service. |
Sasol Agri
Phalaborwa, South Africa |
Plant built in 1975. Original dry and
absorber towers suffered from leaks and the integrity of the brick lining was in question.
Both towers were replaced in 2001 with alloy towers after a 26 year life. |
Climax Molybdenum
Fort Madison, Iowa |
Plant built in 1977. Original drying tower
and pump tank replaced in 2005 after a service life of 28 years. New drying tower is
an alloy design. |
Sulphur Furnaces
A sulphur furnace is basically a refractory lined carbon steel
shell. The factors that most affect the life of a sulphur furnace are the operating
temperature, thermal cycling and condensation of acid on the shell. Refractory
lining failures are probably the most common problem associated with sulphur furnaces.
Loss of refractory bricks from the lining will create hot spots on the shell
causing damage to the shell. Collapsed baffle walls will change the flow pattern in
the furnace and affect burning efficiency.
| Owner/Operator |
Details |
Bunge Fertilizantes
Cubatão, Brazil |
After 18 years of operation the sulphur furnace
was requiring frequent maintenance and repairs. The sulphur furnace and boiler were
replaced and the plant capacity was increased at the same time. |
Marsulex
Prince George, BC |
Plant originally built in 1966. Sulphur
furnace replace in 1989 as part of a plant expansion and addition of liquid SO2 plant.
Service life of 23 years. |
Mosaic (Cargill)
Florida |
No. 8 acid plant originally built in 1966.
Sulphur furnace replaced in 2003 after a service life of 37 years. |
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