EPA-600/2-76-119
April 1976
Environmental Protection Technology Series
EFFECT OF EQUIPMENT MAINTENANCE AND
AGE ON SULFURIC ACID PLANT EMISSIONS
% PRO^
Industrial Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development. U.S. Environmental
Protection Agency, have been grouped into five series. These five broad
categories were established to facilitate further development and application of
environmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL PROTECTION
TECHNOLOGY series. This series describes research Derformed to develop and
demonstrate instrumentation, equipment, and methodology to repair or prevent
environmental degradation from point and non-point sources of pollution. This
work provides the new or improved technology required for the control and
treatment of pollution sources to meet environmental quality standards.
EPA REVIEW NOTICE
This report has been reviewed by the U.S. Environmental
Protection Agency, and approved for publication. Approval
does not signify that the contents necessarily reflect the
views and policy of the Agency, nor does mention of trade
names or commercial products constitute endorsement or
recommendation for use.
This document is available to the public through the National Technical Informa-
tion Service, Springfield. Virginia 22161.
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EPA-600/2-76-119
April 1976
EFFECT OF
EQUIPMENT MAINTENANCE AND AGE
ON SULFURIC ACID PLANT EMISSIONS
by
E.L. Calvin and F.D. Kodras
Catalytic, Inc.
P. O. Box 11402
Charlotte, North Carolina 28209
Contract No. 68-02-1322, Task 10
ROAPNo. 21BAV-006
Program Element No. 1AB013
EPA Task Officer: Robert V. Hendriks
Industrial Environmental Research Laboratory
Office of Energy, Minerals, and Industry
Research Triangle Park, NC 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, DC 20460
i
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CONTENTS
Page
List of Figures iv
List of Tables iv
Acknowledgements v
Sections
I Summary and Conclusions 1
II Recommendations 4
III Introduction 6
IV Contact Sulfuric Acid Process and Equipment
Description 9
Contact Sulfuric Acid Plants 9
Single Absorption Process 11
Process Description 11
Critical Equipment Description 15
Process Equipment ^
Instrumentation 2 3
Electrical 30
Piping, Ductwork, Insulation and
Brickwork 34
Dual Absorption Process 38
Process Description 38
Critical Equipment Description 42
V Manufacturer's Recommended Maintenance 44
VI Maintenance and Malfunction History 47
Effect of Maintenance Quality on Equipment
Operability 47
Plant and Equipment Life Cycle 54
Effect of Age on Forced Shutdown Rate 54
ii
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Page
VII Preventive Maintenance 56
Definition of Preventive Maintenance 56
Effect of Preventive Maintenance Program. . . 57
Effect of Equipment Age on Preventive
Maintenance Program 59
Cost of Preventive Maintenance Program. ... 61
Special Materials to Reduce Failures 63
Suggested Preventive Maintenance Program
for Sulfuric Acid Plants 66
Organization of Preventive Maintenance
Program 66
Preventive Maintenance Manual 67
Planning and Scheduling 73
Record Keeping Systems 74
Cost Accounting Systems 75
Refining the System 76
Reports 76
VIII Inspection Technique 78
Inspection Procedure 78
Inspection Check List 81
Inspection Reports 85
IX References 86
X Technical Report Data 87
iii
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LIST OF FIGURES
Number Page
1 Single Absorption-Sulfur Burning-Contact
Sulfuric Acid Plant-Process Flow Diagram ... 12
2 Single Absorption-Sulfur Burning-Contact
Sulfuric Acid Plant-Piping and Instrument
Diagram 25
3 Dual Absorption-Sulfur Burning-Contact
Sulfuric Acid Plant-Piping and Instrument
Diagram 26
4 Dual Absorption-Sulfur Burning-Contact
Sulfuric Acid Plant-Process Flow Diagram ... 39
5 Frequency of Unscheduled Shutdown by
Cause—Single Absorption Plant 51
6 Duration of Plant Shutdown by Cause—
Single Absorption Plant 52-
7 Effect of Equipment Age on Maintenance Cost. . 60
8 Cost of Preventive Maintenance 61
9 Sulfuric Acid Plant Inspection Check List. . . 82
LIST OF TABLES
1 Critical Equipment Description for Single
and Dual Absorption Contact Sulfuric Acid
Plants 16
2 Manufacturer's Recommended Maintenance of
Critical Equipment for Contact Sulfuric
Acid Plants 45
3 Critical Equipment Malfunctions and Mainte-
nance Histories for Contact Sulfuric Acid
Plants 58
4 Preventive Maintenance Manual 68
iv
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ACKNOWLEDGEMENTS
The authors wish to express appreciation to the operations
and maintenance personnel of the plants contacted. Special
appreciation is expressed to the U. S. Army Arsenal, Volunteer
Army Ordinance Plant personnel, especially Mr. R. S. Twichell
for permitting our inspection of the plant and maintenance
records and providing much information on plant equipment
maintenance history. Mr. R. H. Caligiuri, of Air Products
and Chemicals, Inc., provided detailed information on a pre-
ventive maintenance program for a sulfuric acid plant.
v
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SECTION I
SUMMARY AND CONCLUSIONS
The maintenance history for this report was collected from
twenty sulfuric acid plants operated by six companies. Of
the twenty plants three were of the dual absorption type.
Age of the plants range from two years for a dual absorption
plant to fifty years for the oldest single absorption plant.
Information on service life of various pieces of critical
equipment, type and frequency of maintenance required on this
equipment, and the effect of equipment failure was tabulated
and summarized for all plants studied. Neither statistical
data on failures and maintenance performed nor sufficient
data to make a statistical analysis of service life and
maintenance were available. The information tabulated in
the report is a summation of experience in the various plants
with all plants given equal weight. The plants studied varied
from poorly maintained to well maintained as indicated by the
long service life of some of the plants. Quantitative measure-
ment of the degree of maintenance for each of the plants was
not possible, but the estimate of maintenance cost based
upon plant cost was offered by several of the companies
surveyed. A specific differentiation in maintenance cost
between plants of different age was not available but main-
tenance cost ranged from a low of one percent to a high of
seven percent of the plant cost per year. Sufficient records
were obtained to permit a summarization of frequency and
1
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duration of shutdown by cause for the full range of plant ages
covering twelve single absorption plants. These summations
show the most frequent cause of shutdown was gas leaks, with
mechanical equipment failures a close second. Gas leaks were
fifth in the order of shutdown duration, preceded by the two
semi-annual turnarounds, mechanical equipment failures, and
acid leaks.
The following conclusions can be drawn from observation of
the data collected.
1. Shutdown frequency and equipment malfunction are related
to emissions and to preventive maintenance. An adequate
preventive maintenance program will reduce the occurrence
of emissions significantly. A quantitative measure of the
reduction is not possible from the information obtained.
2. The optimum preventive maintenance program to minimize
total plant operating cost including the control of
emissions will cost approximately six percent of the plant
investment annually. This cost will vary somewhat with
the age of the plant, increasing to seven or eight percent
for an older plant.
3. With inadequate maintenance, the service life of a sul-
furic acid plant can be as short as ten years, while with
adequate maintenance the service life will be of up to
fifty years. Neglect of maintenance during the early
years of plant life will require significantly greater
2
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effort after the ten-year point to restore the plant to
a reasonable level of maintenance.
3
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SECTION II
RECOMMENDATIONS
The suggested format for organizing a preventive maintenance
program included in this report is recommended to assist a
company in establishing the optimum preventive maintenance
program for any plant. The details and form of the program
must be tailored to the specific plant needs and facilities.
The inspection technique is recommended for use by an inspector
in determining the quality of plant maintenance and the effect
on emissions. The recommended technique includes a check
list for recording observations and data during the inspec-
tion. The maintenance policy will be evaluated by observing
general plant conditions and checking the maintenance and
production records for key items. The check list should be
submitted with a report describing in more detail the condi-
tions observed in the plant and in the plant records. The
report should include recommendations for improved maintenance
or improved preventive maintenance programs. The check list
and report will serve as a reference to determine future
status and improvements in plant maintenance.
To provide for long term data collection concerning mainte-
nance and equipment failure without undue burden on the plant
operator or EPA personnel, it is recommended that required upset
emissions reports include information concerning the existence
of a preventive maintenance program and a brief maintenance
4
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history of each piece of equipment that caused excessive
emissions. The addition of these simple items to the emis-
sions report will indicate trouble spots in the plant so that
maintenance can be improved or equipment design changed to
eliminate the source of emissions.
5
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SECTION III
INTRODUCTION
Emissions from a well-designed sulfuric acid plant in excess
of the design emission rate usually result from a failure to
properly operate the plant, or from a failure of plant equip-
ment. The frequency and severity of emissions resulting from
equipment malfunction or failure are related to the schedule
and extent of maintaining critical equipment in good working
order and replacing equipment before it wears out. Thus, the
quality of maintenance is an important factor in maintaining
low emissions. This is particularly true in sulfuric acid
production where low emissions depend not on one piece of
control equipment but rather on the fine tuning of the process
operation itself.
Although most emission standards do not usually apply during
periods of process malfunction, reports of these upset condi-
tions are usually required. Their frequency, duration, and
severity are evaluated carefully to ensure that good operator
care is being used; if the malfunctions are considered avoid-
able, then reasonable action will frequently be taken to correct
these situations. A maintenance plan is occasionally required
as a corrective measure for existing plants with excessive
emissions. An enforcement agency may even require plant oper-
ators to submit maintenance plans for critical equipment before
a construction permit is granted. It is also important to
6
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know the effect of age on the plant's capability to consis-
tently meet a standard over its full operating life. As
equipment gets older, malfunctions would be expected to occur
more frequently, causing more frequent periods of abnormally
high emissions.
The relationship between process operating parameters and
emissions has been evaluated in a previous report "Sulfuric
Acid Plant Emissions During Startup, Shutdown, and Malfunc-
tion" .^^The objective of the present study is to evaluate
critical process equipment in both dual and single absorption
sulfuric acid plants burning elemental sulfur and sludge acid
and determine the effects of maintenance on the frequency
and duration of malfunctions resulting in emissions in excess
of the design emission rate. The effect of maintenance pro-
cedures on equipment reliability and emissions will be stud-
ied by using maintenance procedures recommended by equipment
manufacturers and experience of sulfuric acid plant operators.
By reviewing plants of different ages and with different
amounts of preventive maintenance, the effect of age and main-
tenance quality on emissions can be determined. Plant
experience will provide information on life cycles, frequency
of breakdown, and the effectiveness of a preventive maintenance
program in reducing breakdowns and the resulting emissions.
The repair and replacement schedule for an average plant can
also be determined.
The summation of this information can be used as a guide for
7
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establishing an effective preventive maintenance program in-
corporating the suggested Preventive Maintenance program
format. Control reports for management feedback will also
be included in the suggested program.
An inspection technique to be used by an enforcement agency
inspector to evaluate the effectiveness of maintenance in
the plant, including an inspection check list, will be
provided. The approach used in the study and report should
make the report useful for establishing an initial preven-
tive maintenance program for a sulfuric acid plant, and for
evaluating the effectiveness of existing preventive mainte-
nance programs as well.
8
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SECTION IV
CONTACT SULFURIC ACID PROCESS AND EQUIPMENT DESCRIPTION
CONTACT SULFURIC ACID PLANTS
For many years, the basic contact sulfuric acid plant has used
the single absorption process. This process has been used
to develop the basic technology and equipment applied in
today's modern dual absorption process sulfuric acid plants.
Both the single absorption and dual absorption units
contain the same basic unit processes:
(1) Burning sulfur or sulfur bearing feed stocks to produce
sulfur dioxide (SO2)
(2) Cooling the resulting SO2 containing gas
(3) Catalytic oxidation of the SO2 to sulfur trioxide (SO^)
(4) Cooling the resulting oxidized gas containing the SO^
(5) Absorption of SO^ in strong sulfuric acid
The primary difference between the single and dual absorp-
tion acid plants is a second absorber in the dual absorption
plants for removing SO^ from the process gas stream between
the converter beds, in addition to the normal absorber which
is located after the converter. Most of the sulfuric acid
plant designs include variations in the arrangement of heat
exchangers and converter beds and variations in the location
of the primary absorber in the dual absorption plant. All
sulfuric acid plants operate at temperatures up to 175OF and
are exposed to highly corrosive materials. These process
conditions place rigid requirements on the materials of con-
9
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struction, design factors and equipment. In this type of
chemical plant, maintenance assumes a very important place in
determining reliable operation of the plant.
Use of elemental sulfur as feedstock requires the simplest
plant design. Other feedstocks such as spent acid or sludge
acid containing moisture and organics are frequently used,
but require revisions in the design of the SO2 generating
process and impose more difficult problems in emission abate-
ment, operation and maintenance. Feedstock variations can
also affect the sulfur conversion efficiencies in the cata-
lytic converter, the volume of exhaust gases, and the character
and volume of pollutants emitted. When a sulfuric acid plant
uses sludge acid or reclaimed acid as feedstock, varying
quantities of acid mist are generated in the furnace from
combustion of organics in the feed. Oxides of nitrogen and
carbon dioxide (CO2) are also generated from this source.
It is also possible to generate other solid particulate matter
in the furnace by burning reclaimed acid. The generation of
acid mist and other particulates in the furnace requires the
addition of mist entrainment separators or electrostatic
precipitators (ESP) before the recovery boiler and introduces
additional corrosion problems in the ductwork and boiler
areas.
10
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SINGLE ABSORPTION PROCESS
Process Description
A simplified process flow diagram for single absorption con-
tact sulfuric acid plants burning elemental sulfur is presented
in Figure 1.
In this process sulfur is burned with air to form a gas mix-
ture containing approximately eight percent sulfur dioxide,
13 percent oxygen and 79 percent nitrogen. Combustion air
is predryed by passing it through a packed tower circulating
93 to 98 percent sulfuric acid. This tower is constructed
of steel and lined with acidproof brick to provide the neces-
sary corrosion resistance. Predrying the air minimizes the
acid mist formation and resulting corrosion throughout the
system.
A plant burning sludge acid or reclaimed acid may be similar
but will be equipped with electrostatic precipitators (ESP)
or acid mist entrainment filters between the sulfur furnace and
the recovery boiler to remove acid mist and solid particulates.
In addition to mist entrainment separators or ESP's installed
in plants burning acid sludge, it is also common practice
to install filters for removing organic matter before it is
burned in the furnace and scrubbers to remove impurities
from the gas generated. Use of sulfur containing organic
impurities increases the frequency of plugging of the sulfur
guns and other malfunctions in the sulfur handling system.
11
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•H STEAM )
OLEUM TOWER
SULftR>
OLEUM PfiOOUCT
STORAGE TANK
>OLFOW FURNACE BOILER*1
I K 1011
OLEUM
PUMP
TANK
PRl
ECONOMIZER
IV-IOH ~
EMISSION
SOURCE
*>J
COOLER
ABSORPTION
PRODUCTl
acid !
COOLER'
I X-II9I
ACIO COOLER
! nrna
AC©
ACID /
PUMPi
Tank >
< water
SINGLE ABSORPTION
SULFUR BURNING CONTACT
SULFURIC ACID PLANT
PROCESS FLOW DIAGRAM
FIGURE I
-
GASES •
KEY
UQUI06 -
-------
Filtration of the molten sulfur is often required. Additional
problems are also encountered in cleaning the sulfur filter
or plugging of the filter and subsequent loss of sulfur feed.
Combustion products from the sulfur furnace pass through a
waste heat boiler to cool the gas and generate process steam.
The duct work connecting the sulfur furnace to the boiler, as
well as the sulfur furnace, is lined with fire brick to with-
stand the 1750F temperature generated by the combustion of
the sulfur. The combustion products leaving the waste heat
boiler contain sulfur dioxide (SC^) and excess oxygen. Additional
air is added to the gas stream following the waste heat boiler
to provide the necessary oxygen for reaction with SC>2 in the
converter. These gases then pass through a multiple bed con-
verter containing vanadium pentoxide catalyst that promotes the
combination of sulfur dioxide and oxygen to produce sulfur
trioxide (SO^). The catalytic oxidation of SO2 to SO^ in-
creases the temperature of the gas mixture in the catalytic
converter. The heat generated in the first stages of catalytic
oxidation must be removed to control the temperature of suc-
ceeding stages of conversion. This heat is removed in addi-
tional waste heat boilers, economizers and superheaters to
generate process steam. The design and operation of waste
boilers is critical to ensure that condensation does not take
place on cold surfaces in the boiler, causing excessive cor-
rosion. Condensation can occur because of improper operation
of the drying tower, use of dark sulfur or sludge acid, or
improper operation of acid mist removal systems following the
furnace.
13
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The temperature of the gas entering the various catalyst beds
is controlled by adjustment of gas bypass dampers around the
waste heat boilers. Frequently, injection of cool air into the
gas stream entering the converter is also used. This injection
of cool air is called "air quenching". The temperature of gases
leaving the converter is approximately 806F to 815F with approxi-
mately 98 percent of the SOj converted to SO^. The exit gases
are passed through an economizer to preheat the boiler feedwater
being charged to waste heat boilers and to cool the exit gas
to the proper temperature for the absorption operation.
Sulfuric acid is produced by passing the gases leaving the
economizer through an absorption tower where SO^ is absorbed
in hot 9 8.5 to 99.0 percent sulfuric acid. The absorption
tower is constructed of carbon steel lined with acid brick
to prevent corrosion of the steel shell. In the absorption
tower, sulfuric acid of desired strength is produced by con-
trolling the acid concentration, water make-up and tempera-
ture of the feed acid. If fuming sulfuric acid or oleum is
required, the gases containing SO^ leaving the economizer
are first passed through an oleum tower. Here SO^ is dissolved
in recirculating oleum with make-up 98.5 percent acid to produce
oleum. The gas leaving the oleum tower is further stripped
of SO^ by passing through a normal acid absorber containing
98.5 to 98.8 percent sulfuric acid. The majority of single
absorption acid plants is not equipped with an oleum tower,
and can produce acid with a concentration of only 98 to 99
weight percent sulfuric acid.
14
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Critical Equipment Description
Process Equipment
Process equipment critical to the control of excess pollutants
from a single absorption acid plant is described in Table 1
(page 16). The equipment numbers in this table refer to the
equipment shown on the single absorption acid plant flow diagram,
Figure 1, in the previous section. Variations in design of
acid plants by different companies will require some modifica-
tion in this equipment list when applied to a specific type
of plant. Also, different types of equipment are often sub-
stituted in the same service for those indicated on the
equipment list.
One example of the variation in the type of equipment used
in the same service is the waste heat boilers recovering
heat from the process gas. Although fire tube boilers are
most commonly applied in plants of smaller capacity, both
fire tube and water tube boilers have been used in this
service with water tube boilers preferred in larger plants.
Fire tube boilers are normally preferred since they present
less surface for corrosion and less brickwork subject to
high temperatures and sulfur gases. Water tube boilers
are desirable in larger sizes since the high pressure shell
is not required.
The greatest variations in equipment are found in the number,
location and type of heat exchangers used for acid cooling
and gas heating and cooling. Heat exchanger design for
15
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Tibia 1. CRITICAL EQUIPMENT DESCRIPTION FOB SINGLE AND DUAL ABSORPTION CONTACT SULFURIC ACID PLANT*
ITEM
NO.
EQUIPMENT
NAME
EQUIPMENT
DESIGNER'S/
MANUFACTURER'S
NAME
MATERIALS
OF CONSTRUCTION
OPERATING CONDITIONS
TV« OF
EMISSIONS AFFECTED
DESCRIPTION
AND SIZES
TEMP.
®F
PRESSURE
PSIO
SO,
ACID
MIST
REMARKS
C-101
HAM AIR BUWEB
(C-Z03)*
1. Blower
Single otage
Centrifugal
A-C, Clark, Elliott
and Roota
Caat Iron caae
Caat ateel Impeller
Aablent
7
X
Inaufflclent alt (low eanaaa Incomplete
SOj oxidation reaultlng In gOj ealeelona.
2. Turbina
Contending or Don-
condenalng, aultl-
atage
A-C, Coppua, Elliot
and Tarry
Standard aaterlala
330
-
]. Air niter
Oil bath wire mh
type
AAP
Carbon ateel houalng
with oil Impregnated
ateel with filter
media
Frotecta drying ayatea froa plugging
with doata and dirt.
E-101
SULFU1 niRDACB
(E-201)
1. Furnace
Horliontal, refrac-
tory lined, approx.
14* dlaaetar by 30*
long
Cheailco, CB&I, Davy-
Powergae, Ingalla,
Honaanto, Hooter,
n>-H and TIU
Carbon ateel ehell
lneulated with
firebrick
2000
7
X
Aah and ter froa aludge acid coata fire-
brick and cauaea ahell to overheat
2. Burner Syatea
Including aulfur
punpe
Air or preeeura
•tonlilog apray or
chequer type burner*
Chealco, Davy-
Powergae, Honaanto,
Paraona and John
Zlnk
Stalnleoa ateel
X
Plugging of burnare or loaa of aulfur
feed cauaee loaa af converter temperature
control reaultlng In SOj ealeelona froa
upaeta*
B-10S
WASTE BEAT BOILERS
(B-20S
lol B-211)
1-106
eccmonizer
Horliontal firetube
or vertical water
tube type
Gae aide
Water/aide
B4W, CE, r-H. Erie
City, and TIN
Brick lined
Carbon eteel
Carbon ateel
2000
500
I
600
7
X
X
Steaa la noraally generated for turbine
drlvea and export.
Change In temperature of gaa cauaaa SO.
ealaalona reaultlng froa loaa of converter
teaperature.
Leake In tubea cauaea acid alat aalaelooa.
(X-206
Horizontal or verti-
cal, alngle paaa
exchanger
Shell elde-gaaee
Tube alde-BIW
BtU, CE, Erie City
and T-V
Carbon ateel aetal-
llied with alualnua
Carbon ateel
030-400
230-450
1-3
700
X
Leake la tubea cauaea acid alat ealaalona
(X-218)
SUPERHEAT!!
•
Horliontal ahell and
tuba type heat
exchanger
Shall alde-gaa
Tuba aide-attaa
BtU, Brown Plntnba,
CE, Brie City and
Hooter
Carbon ateel aetal-
llaed with alualnua
Carbon ateel
800-930
300-400
2-4
630
X
X
Superheater la optional In alngle abeorp-
tloo planta.
Loaa of teapereture control cauaaa 80.
ealeelona.
Leaks In tubea cauaaa acid alat ealaalona.
-------
Table 1 (Continued). CRITICAL EQUIPMENT DESCRIPTION FOR SINGLE AND DUAL ABSORPTION CONTACT SULFURIC ACID PLANTS
ITEM
NO.
EQUIPMENT
NAME
EQUIPMENT
DESIGNER'S/
MANUFACTURER'S
NAME
MATERIALS
OF CONSTRUCTION
OPERATING CONDITIONS
tvpE OF
EMISSIONS AFFECTED
DESCRIPTION
AND SIZE8
TEMP.
°F
PRESSURE
FSIQ
SO,
ACID
MIST
REMARKS
X-110.
AGIO COOLERS
I-11J and
1-119
(X-210,
1-214.
1-215,
1-219 and
X-220)
Cascade or shell and
tube or Teflon
bundle
Cooling Water slda
Acid side
CIL, DuPont and
Pentex
Caat Iron, atalnleaa
steel or Teflon
80-110
110-220
40
40
X
X
1
Excessive loss of temperature control
csuses S0j from Primary Absorber and
acid mist from Final Absorber.
Wster leaks cause acid dilution and
upset absorption.
Acid leaks cause rapid corrosion of
equipment.
V-104
DRYItU TOWER
,
(V-204)
1. Vesool
2. Entralnment
Separator
3. Distributors
and Piping
4. Packing
Vertical packed
tower appro*.
20' dla. by 45'
high
Knitted nesh pad
Trougha and pipe
Extended surface
packing-Intalox
saddles
Chentco, CB&I, Davy-
Powergas, Ingalls,
Monsanto, Rooter,
Paraons, PD-H and
TIM
ACS, Brink and Tork
Banner Iron Vorks
Knight, Morton
Carbon eteel shell
with acid proof
brick lining
Teflon or Alloy 20
with Alloy 20 grid
Crsy csst Iron
Chemical stonewara
120-170
7
i
X
Malfunction of entralnment separator and
low flow rates, maldistribution, chsnges
In concentrstlon of acid cauaca acid
mlot emlealone.
Plugging and deterioration of packing
causes drying Inefficiencies.
V-I08
CONVEHTER
800-1200
(V-208)
1. Vessel
2. Support Crlds
and Poata
Vertical! multl-
atate packed tower
approx. ]}' dla.
by 4V high
Various types
Chenlco, CB&I, Davy-
Powergas, Ingalls,
Honsanto, Hooter,
Parsons, and PD-H.
Banner Iron Works
Alumlnlted Carbon
ateel or firebrick
lining
Heehanlte cast iron
3
}. Catalyst
Cylindrical or
spherical pellets
Allied Chemicals,
Honsanto, and Stauffei
Vsnadlum pentoxlde
on clay support
X
Dirty or Inactive catalyat causes high
8O2 emissions and high preasure drop.
Exceaalve temperature causes loss of
catalyat by evaporating the vanadium
pentoxlde.
Kolature forma acid mist and causes
formation of hard crusta, plugging and
Inactivating catalyst.
Fluorine compounds sttach carrier form-
ing dust and plugging catalyat.
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Tabla 1 (Continued). CRITICAL EQUIPMENT DESCRIPTION FOR SINGLE AND OUAL ABSORPTION CONTACT SULFURIC ACtP PLANTS
00
ITEM
NO.
EQUIPMENT
NAME
EQUIPMENT
DESCRIPTION
AND SIZES
DESIGNER'S/
MANUFACTURER'S
NAME
MATERIALS*
OP CONSTRUCTION
OPERATING CONDITIONS
TVFE OF
EMISSIONS AFFECTED
TEMP.
°F
PRESSURE
PSIO
SOj
ACID
MIST
REMARKS
7-109
ABSORPTION TOWERS
Malfunction of alst ellalnator and low
flov rates, aaldletributlon, changes
in concentration and tenperature of acid
causes scld alst ealssions and SOj from
Primary Absorber.
Plugging, deterioration and/or attrition
of packing cauaoa loss of absorption.
(V-209
and
V-221)
1. Vessel
2. Hist Eliminator
3. Distributors and
Piping
4. Packing
Vertical packed
toner approx. 20'
dla. by 33' high
Knitted rneah pad
Troughs and plpea
Extended surface
type - Intalox
saddles
Chealco, CB&I, Dsvy-
Povergas, Ingalls,
Honsanto, Hooter,
Paraona and PDH
ACS, Brink, Tork
Banner Iron Works
Knight, Norton and
0. S. Stoneware
Carbon steel vlth
acid proof brick
lining
Alloy 20, Teflon or
flberglaaa pads
vlth Alloy 20 sup-
port grlda or Teflon
rod a
Cray caat iron
Oray east iron
Chealcai atonewaro
430
4
X
X
P-101
ACID CIRCULATING POMPS
'
ant 7-102
(f-201
and P-202)
Vertical submerged
centrifugal praps
mounted on • pump
tank
Labour, Levis, Tabor
and Worthlngton
All vetted parts
Alloy 20 or east
Iron
160-220
33
X
1
X
Pump failure causes acid alst ealssions
and emergency plant shutdown.
(I-Jll
HUT EXCRAHCERS
1
and X-217)
Vertical ahall and
tube type
8hell-gaa
Tube-gag
BSV, CR, F-K, Rooter,
POM and TItt
Carbon ateel
Aluainlced carbon
ateel
130-850
130-700
2-3
2-3
Lose of teaperature control and tube
leaks cauae SOj eaiaalona.
-------
Table 1 Notes
Item numbers in parentheses are for dual absorption
plants. Refer to Process Flow Diagrams Figure 1 and
Figure 4.
Sizes are based on a typical 1500 TPD dual absorption
plant.
Designer/Manufacturer abbreviations used:
AAF—American Air Filter Company Inc.
AC—Allis-Chalmers Corp.
ACS—ACS Industries, Inc.
Allied Chemical—Allied Chemical Corp.
Banner—Banner Iron Works
B&W—Babcock and Wilcox Company
Brink—Monsanto Enviro-Chem Systems Inc.
CB&I—Chicago Bridge and Iron Company
CCI—Catalyst and Chemicals, Inc.
CE—Combustion Engineering, Inc.
Chemico—Chemical Equipment Company
CIL—Canadian Industries Ltd.
Clark—Dresser Clark Division, Dresser Industries
Coppus—Coppus Engineering Corp.
Davy Powergas—Davy Powergas Inc. (Lurgi)
Duriron—Duriron Company Inc.
Elliott—Elliott Company - Carrier Corp.
Erie City—Erie City Iron Works
F-W—Foster Wheeler Corp.
Ingalls—Ingalls Iron Works Co.
Knight—Maurice A. Knight Co.
LaBour—LaBour Pump Co.
Lewis—Charles S. Lewis and Company Inc.
Monsanto—Monsanto Enviro-Chem Systems Inc.
Nooter—Nooter Corp.
Norton—Norton Company
Parsons—Ralph M. Parsons Company
PDM—Pittsburgh DeMoines Steel Co.
Pentex—Pentex Foundry Corp.
19
-------
Roots—Roots-Connersville Division-Dresser Industries
Stauffer—Stauffer Chemical Co.
Taber—Taber Pump Company, Inc.
Terry—Terry Steam Turbine Company
TIW—Tower Iron Works Inc.
Worthington—Worthington Corp.
York—York Separators Inc.
John Zink—John Zink Company
20
-------
acid cooling has evolved from open type, cast iron, cascade
acid coolers used almost exclusively in older plants to the
DuPont Teflon tube exchangers used in some modern plants. The
cast iron cascade coolers still found in many of the older
plants are relatively free from failures but are subject to
corrosion if disruption of the water flow or distribution
allows dry spots to form on the tubes. If the outside of
the tubes are allowed to become dry because of poor water
distribution the dissolved solids in the water will precipi-
tate and form a hard scale on the outer surface of the tubes
reducing heat transfer. Poor water distribution is often
caused by accumulation of algae or other suspended solids
in the distribution trays. This type of cooler requires
frequent cleaning to maintain an even water flow over the
coils and an even heat transfer through the coil surface.
Fouled heat exchanger tubes result in loss of temperature
control on absorber tower acid and result in release of SC^
or acid mist pollutants.
When shell and tube heat exchangers are used for acid cooling,
scale resulting from dry tubes is not a serious problem, but
the heat exchangers must be cleaned periodically to remove
scale from the shell side of the tubes. This is normally
done by acid cleaning and requires careful attention to
prevent corrosion of the outside of the tubes by the cleaning
acid. The frequency of cleaning depends upon the quality
of cooling water used in the exchangers. Fouling on the
water side of the shell and tube exchanger is also aggravated
21
-------
by operating the exchangers at high water temperatures.
Teflon tube exchangers consist of a bundle of very small
diameter Teflon thermal plastic tubes immersed in the pump
tanks. Cooling water flows through the inside of the tubes
and the acid to be cooled flows through the pump tank. Since
the tubes are very small in diameter they are subject to
plugging from scale or suspended solids in the cooling water.
To reduce the frequency of tube plugging, cooling water is
filtered through sand filters to remove particles before
flowing through the exchanger tubes. An air system is also
installed to pulse air through the exchanger periodically
to dislodge any accumulated debris from the tubes. With
properly cleaned cooling water, maintenance requirements on
the Teflon exchangers are low. The Teflon tube bundle is
arranged so that when a single tube breaks it can be easily
plugged to stop the flow of water into the concentrated acid
stream. Since dilution water is added to the acid stream
intentionally, a small amount of leakage in this manner is
usually not detrimental to plant operation.
One of the most common causes of shutdown for maintenance is
the occurrence of leaks in ducts, expansion joints, and
transition pieces. These leaks can occur even in a new
plant and usually result from faults in the welds of the origi-
nal fabrication. Because this duct work is subject to high
temperatures as well as corrosive gases, the combination of
corrosion and mechanical stress causes frequent cracking
22
-------
of expansion joints and transition pieces. These cracks are
a primary source of fugitive SO2 and acid mist emission and
require shutdown of the plant for repairs. The repair of
such cracks by welding is difficult because sulfur will
deposit in the cracks and will alloy with the steel, result-
ing in additional cracking after welding. Such repairs
frequently require the parent metal around the crack to be
removed to eliminate all accumulated sulfur before welding
of a patch to close the opening. In this manner, the welding
is performed on fresh metal not contaminated by absorption
of sulfur.
Instrumentation
The instrumentation for a contact sulfuric acid plant becomes
more critical to pollution-free operation as the reliance
on automatic controls increases. The close control required
to meet the EPA standards requires precise calibration as
well as reliable operation. Instrumentation is not only
required to control the plant and maintain emission levels
within limits but also provides a measurement of the product
flow and analysis of the vent gases required for properly
calculating the emission levels in compliance with federal
regulations.
The most critical instrumentation in a sulfuric acid plant
is that which controls the temperature of the gas entering the
various sections of the catalytic converter. Other critical
process parameters that must be controlled in a sulfuric
23
-------
acid plant are: sulfur and air flow to the sulfur furnace,
acid temperature and concentration into the absorbers and
drying tower, and feed water controls to the waste heat
boilers. Typical instrumentation for a single absorption
acid plant is shown in Figure 2. Instrumentation for a dual
absorption acid plant is similar, consistent with the addition
of the primary absorber and rearrangement of heat exchangers.
Dual absorption plant instrumentation is shown in Figure 3.
The instrumentation system in a sulfuric acid plant can be
either pneumatic or electronic depending upon the preference
of the designer or operator of the plant. Thermocouples
are almost invariably used for sensing temperature of the
gas flows in and out of the catalyst beds. Therefore, elec-
tronic controllers and multi-point electronic temperatures
recorders are most frequently used for temperature measure-
ment. Both electronic and pneumatic instrumentation are
reliable, given proper maintenance, although electronic in-
strumentation usually requires less maintenance for reliable
operation.
Acid flow meters may be installed in the plant for measuring
the flow of acid to the absorbers and drying tower. However,
the most common application of acid flow meters is in the
measurement of product acid to storage. This flow reading
is used to calculate emission levels from the plant. The
most common type of meter for this application is the orifice
meter with a differential pressure (D/P) cell transmitter.
24
-------
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FIGURE 3
-------
Because of the corrosive nature of the hot sulfuric acid
flowing through this meter, the orifice must be checked fre-
quently to ensure the accuracy of the flow readings. D/P
cells or pressure indicators connected to the process fluid
will normally be equipped with chemical seals to prevent
sulfuric acid from entering the instrument. Since the pro-
cess seals are also subject to corrosion they must be checked
frequently to prevent damage to the instrument from a ruptured
seal. Some older plants are equipped with rotameters for
acid flow measurement. These are normally of *the armored
type using a magnetically coupled indicator or transmitter.
This type instrument should also be inspected frequently for
corrosion to prevent inaccuracies in flow measurement.
Control of sulfur feed to the sulfur furnace is important
for maintaining stable operation of a sulfuric acid plant.
In older plants sulfur feed was controlled by the volumetric
or gravimetric measurement of the sulfur feed in the dry
form and constant inventory control of molten sulfur in the
feed tank. This control was accomplished through weigh
belts or batch weighers. This type of instrument may be
found in modern plants to provide information for sulfur
inventory control. A more satisfactory measurement of molten
sulfur feed to the furnace however can be accomplished using
a variety of standard type flow meters adapted for steam
heating to maintain the sulfur in a molten condition. Typi-
cal flow meters that can be used in this service are positive
27
-------
displacement rotameters, orifice meters and variations on
differential pressure type instruments. Where differential
pressure instruments are used, seals must be provided to
prevent molten sulfur from entering the instrument and
causing corrosion or plugging of the instrument with solid
sulfur. The most recent advancement in molten sulfur measurement
is a turbine flow meter designed for use with high tempera-
ture, viscous, molten sulfur. The purity of the sulfur feed
largely determines the type of instrument best suited for
measuring molten sulfur flow. The presence of solid im-
purities in the molten sulfur can cause excessive wear or
plugging of various types of instruments.
The thermocouples used for converter temperature measurement
and control are relatively free from failure or maintenance
requirements. These thermocouples must be installed, how-
ever, in thermowells to prevent corrosive process gases from
contacting the thermocouples. Care must be exercised in
sealing the thermowells to prevent corrosive vapors in the
atmosphere from entering the thermowell. If scale or cor-
rosion occurs on a thermocouple or in a thermowell, errors
in temperature measurement will occur. Periodic inspection
of thermowells should be conducted to permit replacement of
the thermowell before corrosion penetrates into the thermo-
couple space.
If proper design is used in selecting and installing process
transmitters and control instruments are located remotely
28
-------
in an air-conditioned area free from corrosive vapors, the
primary maintenance consideration for instrumentation will
be the protection of the field mounted instruments from
corrosive atmosphere and liquids. This will require special
enclosures, splash protection and corrosion proof coatings
to prevent instrument cases from being corroded. It also
may be necessary to apply air purge to electronic transmit-
ters to prevent the corrosive atmosphere from entering the
transmitter case. Pneumatic transmitters are naturally
purged sufficiently to prevent corrosive gases from entering.
Instrument air lines and electronic cables must be properly
protected and maintained to reduce damage from the corrosive
atmosphere and liquids. Where sulfuric acid leaks may occur,
stainless steel or plastic instrument air lines are generally
used to provide corrosion resistance. Instrument air tubing
racks and cable trays are usually protected in these areas
to reduce the possibility of direct contact with acid.
Proper maintenance of analytical instruments used for measuring
the sulfur dixoide emissions from the vent stack is required
by federal regulation. The instruments used most frequently
for measuring SO^ emissions are types using infra-red or ultra-
violet light absorption or the coulometric titration of iodine.
All instruments in this type of application must be calibrated
on a proper schedule using standard gases of a known concen-
tration. Daily inspection and preventive maintenance must
be performed on these instruments to ensure reliable opera-
tion.
29
-------
The portion of an analytical instrument system most difficult
to maintain in proper operating order is the sampling system.
Sampling systems are subject to corrosion, plugging with
solids and flooding with accumulated condensate. Sampling
systems must be cleaned and inspected regularly and blown
down daily to maintain accurate readings from the analyzer.
The instrument and control system in most sulfuric acid
plants includes only a few control valves in sulfuric acid
service. A control valve in this service usually will have
tungsten carbide internals and Teflon packing for maximum
corrosion resistance. The exterior parts of the control
valve must be protected to prevent atmospheric corrosion
and acid leaks from destroying the diaphragm or piston
housings. Control valves equipped with pneumatic positioners
are particularly vulnerable to corrosion and must be carefully
installed and maintained for reliable service. A control
valve regulating the flow of sulfuric acid in a critical
service should be inspected frequently during plant shutdowns
to determine the condition of the valve internals before
a major failure causes a plant shutdown.
Electrical
The electrical power system for a sulfuric acid plant is
similar to the electrical system for any other type of chemi-
cal plant from the electrical design viewpoint. The area
where sulfuric acid plants differ from many plants in the
30
-------
electrical power system is the requirement for special materials
and special design to prevent corrosion resulting in failure
from liquid acid and acid gases encountered in the service.
In most modern acid plants, the unit substation transformer
is located outside a pressure-ventilated switchgear room with
a secondary throat connection for buswork through the wall
of the room and with a primary connection to an air-filled
terminal box. This pressure-ventilated switchgear room may
also house motor control centers, panelboards, and other
electrical equipment in addition to the switchgear. The air
supplied for this pressure-ventilated room must be clean air
free of acid fumes. This installation method is used:
1. To protect electrical equipment from accumulation of dirt,
dust and other foreign material.
2. To permit the use of less expensive and more easily main-
tained general purpose electrical equipment enclosures
rather than costly corrosion-resistant enclosures.
3. To enable the substation to be positioned at the center
of electrical load requirements, resulting in shorter
runs of feeder cables.
4. To prevent access by unauthorized people.
All electrical equipment located in the production area and
subjected to acid fumes must be housed in the proper type of
enclosure to protect the equipment. NEMA type 4X water
tight corrosion-resistant enclosures are used for control
stations and must be coated with an appropriate acid proof
31
-------
paint to protect the metal. Aluminum conduit is frequently
used to minimize corrosion of conduit runs. A substitute for
aluminum conduit is PVC coated steel, although this type of
conduit is subject to damage, leaving the bare metal exposed
to acid corrosion. For this reason alumunum conduit is pre-
ferred. All electrical wire in an acid plant must have acid
resistant insulation.
All electric motors in a sulfuric acid plant should be of a
type suitable for chemical service. These motors are totally
enclosed with alloy steel bolts and double sealed bearings.
The outside of the motor housing is treated with an acid
proof paint such as epoxy to protect the motor housing.
Careful inspection and planned preventive maintenance of the
complete electrical system must be conducted frequently to
find points of acid attack so repairs can be performed and
the protective coatings replaced. All control devices such
as motor starters and other contacting devices should be
inspected frequently to detect corrosion of the electrical
parts. Before opening, all enclosures should be cleaned to
remove corrosive particles. If evidence of corrosive gas or
liquid is found in the enclosure, the system should be in-
spected to locate the source of entry and gaskets or seals
replaced to prevent further corrosion of electrical parts.
All motor windings should be checked periodically with a
megger to detect any deterioration of motor winding insula-
tion. When maintenance is performed on any portion of the
32
-------
electrical system, care should be exercised to replace all
covers and gaskets in proper condition to ensure continued
seal of the system against entry of corrosive gases and
liquids.
A sulfuric acid plant requires an extensive interlock system
to prevent operation of the plant in an unsafe condition for
personnel and equipment. Safety trips are connected to pro-
cess services such as low water level in the boilers, high
temperatures in the furnace, converter overtemperature, low
combustion air flow and many others. The existence of these
safety trips in electrical systems makes this type of plant
control system susceptible to shutdown during electrical
storms from voltage surges and momentary interruptions.
Electrically held motor starters can also drop out and shut
down the plant if voltage is interrupted for a very short
period of time. To prevent unnecessary shutdowns from these
surges and momentary voltage losses the safety trip system
is equipped with time delays to prevent drop out on short
interruption. Motor starters are frequently equipped with
under voltage time delay relays to prevent drop out and
plant shutdown on momentary interruptions. When equipped
with these devices, maintained in good working order and
correctly adjusted, the acid plant will experience fewer
shutdowns from electrical service problems. If maximum
security of operation is desired, an alternate electrical power
service can be installed with automatic load transfer features.
With this arrangement, the second source of power will be
33
-------
selected automatically if the primary source fails, reducing
the chance of power loss. This service is expensive but may
be justified for a large plant in areas of unreliable electri-
cal service.
Piping, Ductwork, Insulation and Brickwork
Based on plants surveyed, in an average sulfuric acid plant
approximately 34 percent of all of the forced shutdowns result
from acid or gas leaks in the piping, coolers, ducts or vessels.
Small leaks that occur are often patched temporarily while the
plant is operating. The repair is then performed at a later
time during a shutdown for other purposes. Many factors affect-
ing the frequency of acid and gas leaks are dependent upon
design of the plant equipment rather than maintenance. Many
shutdowns however result from failures that could be prevented
or postponed by proper preventive maintenance.
Sulfuric acid plants use both external and internal insulation
to control heat losses and protect equipment from excess heat.
Internal insulation is generally firebrick inside a carbon
steel shell. Brick linings are also used in other vessels
in sulfuric acid plants to protect the carbon steel shell
against the effects of the hot sulfuric acid contained in the
vessel. This brick is acid proof brick installed with acid proof
mortar. External insulation is generally of foamed plastic,
magnesia, or foam glass, depending upon the temperature level.
Piping acid leaks are caused primarily by corrosion of the
carbon steel piping by the hot, concentrated sulfuric acid.
34
-------
Carbon steel is used rather than alloy steel for these ser-
vices to reduce cost. The accepted design practice is to
include a corrosion allowance in determining the thickness
of the pipe and allow for its replacement. Careful inspec-
tion of all plant piping is required to locate badly corroded
pipe so it can be replaced before failure or a leak occurs.
Special attention should be given to flanges and joints that
are most subject to leaks. Use of proper gasket material is
especially important in preventing leaks in flange joints.
Ductwork for transporting hot acid gases is subject to cor-
rosion as well as stress cracking from thermal expansion of
equipment. Corrosion of the ductwork and the production of
corrosion products that foul the catalyst are reduced by
flame coating the inside surfaces of carbon steel ductwork
and vessels subject to corrosive gases with aluminum. This
treatment reduces the corrosion rate of the carbon steel and
decreases the frequency of gas leaks.
Major equipment in the plant is usually arranged to require
the minimum length of duct to interconnect the furnace,
boilers and converter. The short duct run reduces the cost
of construction and corrosion possibilities but introduces
other problems of stress from thermal expansion. These
problems are accentuated with the high temperature ducts (up
to 1700F) because of the need to install insulating fire
brick linings with different coefficients of thermal
35
-------
expansion than the steel ducts.
The thermal expansion of ducts is controlled by installation
of expansion joints and by the use of elbows to permit flexure
of the duct. The furnace is often mounted on a movable base
to permit it to move to compensate for expansion of the outlet
duct. All of these measures decrease the stress applied to
the ducts, but failures still occur in both brickwork and
ducts at points of high stress. The expansion joints, duct
elbows and flanges should be inspected regularly to detect
cracking that will develop into a major leak. Expansion
joints must be replaced on a regular schedule established
by operating experience.
Thermal expansion of steel shells lined with brick causes
frequent cracking of the brick lining. If the brick lining
is not repaired regularly to maintain a strong mortar seal,
the brick lining can fail completely and cause rapid de-
struction of the duct and force shutdown. Repointing the
mortar in the acid proof and firebrick is normally done
during the semi-annual shutdowns when equipment is open for
inspection.
The absorber, drying tower and acid pump tanks are lined
with acid proof brick to prevent hot concentrated sulfuric
acid from contacting the carbon steel shell. If the integrity
of the brick lining is maintained, the steel vessel will have
a long service life. If the acid proof brick is permitted
36
-------
to deteriorate, early failure of the steel shell will occur
resulting in leaks requiring shutdown and extensive
repairs. An important factor in obtaining a long service
life from acid proof brick linings is the workmanship used
in installing the brick. Poor workmanship will result in
gaps and cracks in the mortar causing leaks.
The insulation of the sulfuric acid plant is both internal
and external. These types of insulation are illustrated by
the external insulation on the absorber towers, pumps, tanks
and acid piping; and internal insulating fire brick in the
furnace, waste heat boiler, and converter. Additional
insulation is applied to maintain the temperature in
the gas ducts above the condensation point to prevent acid
condensation in the ducts. If the ducts are allowed to cool
below the dew point, the vapor carried in the gas stream
will condense on the metal surfaces and cause extensive
corrosion.
Fire brick linings in high temperature vessels must be
maintained regularly to prevent massive failure of the carbon
steel vessel shells resulting from high temperatures and
corrosive gases. Careful maintenance of the external insula-
tion will extend the life of equipment and permit high oper-
ating efficiency in terms of energy consumption.
37
-------
DUAL ABSORPTION PROCESS
Process Description
The average single absorption sulfuric acid plant will produce
SO2 emissions in the range of 1600 ppm to 2500 ppm when
operating at normal efficiencies. Since this level of sulfur
dioxide emissions is in excess of federal or state regulations,
the need for lower sulfur dioxide emissions is accomplished
by secondary absorption equipment. The need for more effi-
cient sulfuric acid plants initiated the development of the
dual absorption plant. The dual absorption process can convert
99.7 to 99.9 percent of the sulfur dioxide to sulfur trioxide
for producing sulfuric acid., The increased complexity of the
dual absorption acid plant also requires more reliable equip-
ment and more effective control systems to maintain a low
level of SO2 emissions.
A typical modern dual absorption process burning elemental
sulfur is shown in Figure 4. The primary difference between
the single absorption and the dual absorption process is the
addition of a primary SO^ absorber for gas leaving the third
catalyst bed. One process (Lurgi) uses the absorber after
the second bed. Since the addition of an absorber between
catalyst beds requires cooling and reheating the process gas,
a change in the heat recovery system is also required.
Comparison of Figures No. 1 and 4 will show that the sulfur
combustion portions of the single and dual absorption plants
38
-------
VD
WSir BSD
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CXJAL ABSORPTION
SULFUR SURNtNG CONTACT
SULFURIC ACID PLANT
PROCESS FLOW DIAGRAM
FIGURE 1
ZEE-
-------
are similar. Air is compressed and dried in a drying tower
with 93 to 98 percent sulfuric acid before it is used for
combustion of sulfur in the sulfur furnace. The hot gases
from a sulfur furnace then pass through the waste heat boiler
to generate process steam. The waste heat boiler is designed
to permit further cooling of the combustion products to ap-
proximately 795 to 820F in the No. 1 heat exchanger by re-
heating part of the gas from the primary absorber. The cool
gases are then passed through the first bed of the catalytic
converter where the gas temperature is increased by oxidation
to SO^ to approximately 1100 to 1130F. The high temperature
gas exiting the first catalyst bed is cooled in the No. 2
heat exchanger to approximately 82OF for reaction in the
second catalyst bed. The heat is used to reheat the remainder
of the gas from the primary absorber. Heat generated in the
second catalyst bed is removed by a steam superheater in the
process steam line from the waste heat boiler. Heat generated
in the third catalyst bed is removed by an economizer in the
boiler feedwater system before the gas is fed to the primary
absorption tower. In the primary absorption tower the concen-
tration of SO3 in the gas is reduced to about 100 parts per
million by contact with 98.5 percent sulfuric acid.
Cool gas leaving the primary absorption tower must be reheated
before introduction to the fourth catalyst bed. This is
accomplished by passing through No. 1 and No. 2 heat exchangers
in parallel.
40
-------
Variations in location of these heat exchangers is one of the
major differences between plants from various designers. In
a single absorption plant, the gas passing through the exchangers
is not cooled below the condensation point at any time while
passing through the catalytic converter. With proper design
of heat exchangers and control of the process, condensation
will not occur in the heat exchangers and not cause a corrosion
problem. In a dual absorption plant, however, gases are cooled
to 170F in the primary absorber. This low temperature results
in more possibilities for condensation in the heat exchangers
that follow the primary absorber. This high probability of
condensation results in this being a major location of cor-
rosion failure. These exchangers have received extensive
attention in design to minimize or eliminate corrosion prob-
lems through variations in materials of construction, configura-
tion and location. Although design improvements have in-
creased the life of this exchanger, it still remains one of
the major maintenance problems in many acid plant designs.
Approximately 97 percent of the SO2 remaining in the gas stream
is converted to SO^ in the fourth catalyst bed. This gives
a much higher overall conversion rate (99.7 to 99.9 percent)
than is possible in the single absorption plant. The increased
conversion efficiency results from the lower partial pressure
of SO^ in the gas, permitting the reaction to be driven more
nearly to completion. The gases leaving the fourth catalyst
41
-------
bed are finally cooled in a second economizer that heats boiler
feedwater before contacting 98.5 percent sulfuric acid in the
secondary absorption tower. The gases leaving the secondary
absorption tower will contain approximately 100 to 200 parts
per million SC^ under normal operating conditions and will
meet the existing emission standards without further processing.
If oleum is required, an oleum tower is installed upstream "
of the primary absorber in a manner similar to the single
absorption process.
With the exception of the location of the primary absorber
and heat exchangers previously discussed, all major designers
of dual absorption sulfuric plants use much the same basic
equipment configuration. Important differences between these
designs are found in the details of the converter, heat ex-
changers and absorbers. Air quench is also used in some dual
absorption plants but is not frequently used because of waste
in energy.
Critical Equipment Description
The major differences in critical equipment between the single
absorption plant and the dual absorption plant is the addition
of the primary absorber and substitution of gas-to-gas heat
exchangers in place of the No. 2 waste heat boiler that is
used in the single absorption plant. Additional critical equip-
ment required for a dual absorption plant is shown in Table 1,
page 16. Equipment numbers in this table refer to the process
flow sheet for the dual absorption plant shown in Figure 3.
42
-------
All dual absorption acid plants use gas-to-gas shell and tube
heat exchangers to reheat the gas from the primary absorber.
The location and arrangement of the gas heat exchangers will
vary with different plant designers. The arrangement of the
heat exchangers is important to the operation, maintenance
and life expectancy of the exchangers.
The heat exchangers are normally constructed of carbon steel
with all surfaces in contact with sulfur gases aluminized.
These exchangers will not contribute to plant shutdowns or
increased emissions if plant operation maintains the gas dry
and free from acid mist. Efforts to minimize this problem
are the primary reason for variations in heat exchanger
arrangement between plant designers. Failure of temperature
control equipment or malfunction of the plant that causes
the temperatures to run abnormally low in the exchangers will
accelerate corrosion and subsequent failure of exchangers.
Since these variations are more prone to occur during start-
up of the plant, malfunctions resulting in a shutdown and
start-up will accentuate the corrosion problems.
The primary absorber used in the dual absorption units, with
its associated pumps and acid coolers, is similar to that used
in the single absorption plant and normally presents no
additional maintenance or operational problems not encountered
in the single absorption plant.
43
-------
SECTION V
MANUFACTURER'S RECOMMENDED MAINTENANCE
Major maintenance functions recommended by the equipment manu-
facturers are presented in Table 2. This list covers only
the critical equipment contributing to plant emissions and
does not include many items of auxiliary equipment necessary
for plant operations. The maintenance tasks listed are typ-
ical and will vary in kind and frequency of recommended
maintenance between manufacturers. Since the tendency is
for manufacturers to claim longer service life than can nor-
mally be obtained, the periods between major overhauls and
estimated service life will probably be shorter in most
applications. The final schedule for preventive maintenance
and overhaul operations will be adjusted to reflect operating
experience as shown in the sample preventive maintenance
manual discussed in Section VII .
Table 2 shows most of the tasks scheduled to be performed
annually. This period is influenced by the common practice
of shutting down plants for annual overhaul. All maintenance
possible is usually done during these annual shutdowns to
reduce the number of forced shutdowns during the remainder of
the year. Even when the service life on equipment is expected
to be several years, it is normally inspected on an annual
basis to provide assurance of reliable operation during the
following year.
44
-------
Mil I. MANUFACTURER* RECOMMENDED MAINTENANCE OF CRITICAL EQUIPMENT FOB CONTACT SULFURIC ACID HANTS
ITEM
NO.
EQUIPMENT
NAME
TYPE OF MAINTENANCE
RECOMMENDED
FREQUENCY OF MAINTENANCE
ESTIMATED
rtn
SHIFT
DAILY
WEEKLY
AS
INDICATED
SERVICE
LIFE
(YEARS)
REMARKS
C-10J
HAIN AIR BLOWER
I *-10
(C-I01)
1. 1lower
2. Turbine
). iif niter
Change oil la tiulap
check lubrication ifttn
Coaplete overhaul
Inepect for do!m, vibration and hot taarlogi
Change oil
Check all filter pressure differential
Replace or clean oil flltera
Check oil preeeure and tsaperatnre
Coaplat* cnrerhnul
Check lor nolaoi vibration and hot tearing*
Change oil bath
Replace filter vedle
Check filter stadia drive and oil level
X
I
S
¦
S
X
Annually
I yro.
Annually
6 mo.
S yre.
As req'd.
Frequency depends upon environmental
condition*.
C-101
SULFUR ruuuci
U-20
(I-J01)
1. Shell
2. Burner Syatea
Repaint sorter
Replace refractory
Itelubrlcate aulfur pimps
Check puapa for nolee and vibration
Replace aulfur spray noaela
I
Annually
Ae req'd.
y-t mo.
Annually
•-10J
UASTK BEAT BOILERS
20-21
and III
(B-201)
Inepect tubea and clean
Test safety valvea
Kydroetatlc teat
Annually
Annually
Annually
1-106
ECONOMIZERS
20-21
(1-206
and 207)
Inspect tubes sod clean
Hydrostatic teat
Annually
Annually
' V-10S
CONVERTER
20-2}
IS
20-2)
(V-20S)
T-109
1. iiiint
2. Support grid*
«nd post*
J. Catalyst
ABSoimoN timers
Inspect firebrick
Repleco broken firebrick
Inspect for themel dlatortlon
Replace daaaged lteaa
Screen catslyst
Mska-up lost catalpat
Annually
Ae req'd.
Annually
As req'd.
6 ae<
6 ao>
Stock 10X of catalyat charge for
replaceaent.
(»-10»
and 221)
1. Veeael
2. Hist gllnlaator
]. Dlatrlbutora and
Piping
4. hoUoi
Ropolnt Barter
Replace daaaged acid proof brick
Inepect and clean
Replace corroded part*
1Depict
Replace corroded parte
Inepect for aettllng and clean
Add pecking
Unpeck end ttaah packing
Annually
Ae req'd.
Annually
Aa req'd.
Annually
Aa req'd.
Annually
Aa req'd.
3-J yre.
1-J
20-2)
20-2S
Weeh sulfate dsposlts oat it required.
Stock 101 nf packing charge for
replecenent.
-------
Ml* I (Cortland). MANUFACTURER'S WCCOMMgWPEO MAIWTEWAWCg OP OPTICAL EQUIPMENT FOR COOT ACT BUtfURIC ACHI PLANT!
at
ITEM
NO.
EQUIPMENT
NAM!
TYPE Of MAINTENANCE
RECOMMENDED
FREQUENCY OF MAINTENANCE
ESTIMATED
PER
SHIFT
DAILY
WEEKLY
AS
INDICATED
SERVICE
LIFE
(YEARS)
REMARKS
r-101
ACID C1RCUUTIK0 whps
M
Spar* pump nnrnally lnatallcd to
and 101
(r-ioi
and 201)
Check blaring fabrication and teaperatura
telabrlcata
Iaapaet (or ootaa and vibration
lufict and ovarhiul
Inapact and claaa puap tank
tapolnt nortar la puap tank
I
S
J-* pa.
Annually
Annually
la req'd.
7-10
H
prevent ahutdnm o( plant fcecauaa
of puap (allure.
Check (or eccumlatlon of packing chip a.
(X-lil
BEAT UCHMtOUl
2-J
and 217)
(1-218)
SUPERHEATER
Annually
20-2)
Inapact tabaa and clean
Mull;
1-110,115
ACID COOLIBS
u-u
•ad 111
1. Cnc*d« trpt
2. Shall and tube
1. Teflon bum! la
Claaa tubea and trougha
Iuapect total and claaa
Ida pact tnbaa and tub* ahaeta
/La req'd.
>-12 ¦».
1 no.
OaboM
Frequency o( cleaning dependa og
ueter quality,
lequlroe filtered water.
*-104
DR11SO TOWtB
'
21- JO
(V-204)
1. Veaeel
2. Intralnrat
Separator
1. Dlat«Ibutora
and fiptaj
4. racking
Repolat sorter
Replace damaged acid pool brick
iaapaet aad claaa
laplaca corrodad pitta
Inapact
taplaca corroded parte
Iaapaet (or Battling
Add packing to replace loat packing
Unpack and oaab packing
Imuall;
Ae req'd.
Annually
Aa taq'li
Anonally
Aa req'd.
Annul ly
Aa raq'd.
I-J yra.
1-J
20-2J
20-2S
Stock 101 at packing charge (or
replacement.
-------
SECTION VI
MAINTENANCE AND MALFUNCTION HISTORY
A summary of maintenance and malfunction history for the
critical sulfuric acid plant equipment is given in Table 3.
This history was compiled from maintenance data from several
plants of various ages and types and with a. variety of feed-
stock. The data shown represents typical or average experi-
ence. Another presentation of the frequency and duration of
plant downtime is given in Figure 5 and Figure 6. These
represent data from 12 plants with a wide variation in age
and maintenance quality.
THE EFFECT OF MAINTENANCE QUALITY ON EQUIPMENT OPERABILITY
The effect of maintenance quality on plant operability is
difficult to evaluate from plant maintenance data since the
quality of maintenance performed in the plant cannot ade-
quately be evaluated without firsthand experience. Plant
operators seldom provide judgement on the quality of main-
tenance performed in their plants. Certain general relation-
ships however, can be stated on a qualitative basis as demon-
strated by plant maintenance history.
The rotating equipment such as pumps and blowers will probably
be the most affected by maintenance neglect. Failure to pro-
perly lubricate pump bearings as well as over lubrication of
bearings can cause premature bearing failure. Failure to
replace damaged bearings in pumps when needed can cause
pumps to seize and shear shafts or damage casings beyond
47
-------
Table 1.
CRITICAL EQUIPMENT MALFUNCTIONS AND MAINTENANCE HISTORIES FOR CONTACT SULFURIC ACID PLANTS
ITEM
NO.
EQUIPMENT
NAME
TYPE OF
MALFUNCTION
CAUSE OF
MALFUNCTION
MEAN
TIME
BETWEEN
XCURENCES
MAINTENANCE
REQUIRED
MEAN
TIME TO
REPAIR
THEORETICAL EFFECT
OF MAINTENANCE
NEQLECT
AVOIDABLE BY
PREVENTIVE
MAINTENANCE
G-10J
HAIR AIR BLOWER
1 day
(C-203)
1. Blower
Kxceaalre vibration
Sulfate buildup on
1-2 yrs.
Vaah with vater and
Vear on bearlnga and nechanl-
Tea
lnpeller
csuatlc, drain and
cal failure
dry-out
Bearing* overheating
Inproper lubrication
Unknown
Lubricate
1 hour
Bearing failure-replace
Tea
2. Turbine
Excessive vibration
Scale on rotor becauaa
Unknown
Wash rotor
1 day
Vear on bearing* and mechani-
Tea
of ateaa quality
4 hour
cal failure
1
Bearing* overheating
Inproper lubrication or
Unknown
Lubricate, cleen oil
Bearing failure-replace
T«s
or oil cooling
filter, check oil
punp, clean oil
cooler or check
doling vater supply
Tea '
3. Air niter
Insufficient air (low
Dirty filter
Unknown
'lira filter media,
1 hoar
SOj emissions and blower
c'isnge oil bath.
overheating
check drive
K-101
SULFUR FUR*ACE
(K-201)
1. Shall
Bot spot la shall
Deterioration ol firebrick
1-2 yrs.
lining
Repair firebrick and
1 «fc.
Failure of furnace ahall
Ro
ahell
Generation •( Mid al't
Staaa leak* froa Jacketing
l/2-l yr.
Replace burner or
1-4 to*.
Corroalon Of plant equipment
Ro
Into aolfur
pip*
down atreAa and catalyat
2. Burner-System
Ro colfur feed
Sulfur punp failure, plugged
1/1-1 yr.
Replace poop
2-4 hrs.
deterioration
Loaa of converter tetap-
Ro
pipeline* because of cold.
eratura control
sulfur
Unplug line*
1 day
Tea
B-10S
WA3TB BEAT BOILERS
and 111
Corrosion of tubsa
1 yr.
Replace tub*
1 wk.
Internal corroalon of down-
Tea
(B-203)
atream equipment and
Inaufflclent ateaa flow
catalyst deterioration
Tube scaling beceuse of
Jnknoun
Clean tubea
1 days
Tuba failure-replace
Te*
vater quality
Ho feed water flow
Failure of feedvater ayatea
I yr.
Check and repair
1 wk.
Tube failure-replace
Tea
feedwater aystem
*-106
ECONOMIZERS
(1-2OS
Ruptured tuba or seal
l®sk
and 207)
3-12 do.
Plug tubea
4-6 lira.
Internal corroalon of down-
Ro
Replace tube*
? daya
atrean equlpnent end
catalyst deterioration
Insufficient cooling
Plugged or coated tubea
6-12 ao.
Clean tubes
1 day
Ruptured tubea
Te*
(1-218)
S0FERHCATKR9
Steaa leak to gaa strain
Ruptured tube or seal
l yr.
Replace tube
1-2 daya
Internal corroalon of down-
No
leak
atreaa equipment and
catalyst deterioration
-------
Table 1 (Continued). CRITICAL EQUIPMENT MALFUNCTIONS AND MAINTENANCE HISTORIES FOR CONTACT SULFURIC ACIO PLANTS
ID
ITEM
NO.
EQUIPMENT
NAME
TYPE OF
MALFUNCTION
CAUSE OF
MALFUNCTION
MEAN
TIME
BETWEEN
3CCURENCE2
MAINTENANCE
REQUIRED
MEAN
TIME TO
REPAIR
THEORETICAL EFFECT
OF MAINTENANCE
NEGLECT
AVOIDABLE BY
PREVENTIVE
MAINTENANCE
x-uo
ACID COOLERS
Water blaat, acrap or
wire brush
3-7 daya
Acid nlat emissions and
opacity froa atack
Tea
11J, and
119
1. Cascade type
Insufficient and cooling
Scale on outside of tubee
Unknown
(X-210
21J, 219
and 220)
2. Shell and tube
). Teflon bundle
Acid leak
Inaufflclent acid cooling
Acid leak
Insufficient cooling
Hater leak to acid
Corrosion
Scaling of tubes
Corrosion
Plugged tubes
Leaking tubea
3-6 bo.
Jnknown
Unknown
Inknown
Unknown
Blankoff section
Replace tube aectlon
Acid clean tubee
Plug or replace tuba
Back fluah '
Plug or replace tube
4 hra.
2 daya
4-8 hrs.
2 daya
1 hr.
1 hr.
Hater pollution -
acidic cooling
water ayatea
Acid nlat emissions and
opacity froa stack
Hater pollution - acidic
cooling water lyitei
Acid mlat enlsalona and
opacity froa stack
Eiceaalva leakage cause*
acid alst emissions and
atack opacity
Tea
Tes
Ho
Tee
Tea
V-109
ABSORPTION TOWERS
(V-209
and 221)
1. Vessel
2. Hist Eliminator
Acid leaks
Acid* mist carry-over
Corroalon
By-passing or plugged pad
DnVnown
!-3 yre.
Patch or weld
Repair or replace
4-8 hra.
1 day
Shell failure and water
pollution
Acid aiat emission
Internal corroalon of heat
exchangers and catalyat
deterioration froa Primary
Absorber. Acid alst emis-
sion and opacity froa Pinal
Do
Do
). Dlatilbutore and
Piping
4. Packing
Low ebaorptlon efficiency
Low absorption efficiency
Haldlatribution of acid
Flooding, channelling,
aettling or dlalntegra-
tlon of packing
Unknown
1-2 yra.
Replace
Wash and replace
2-3 daya
1-2 daya i
Absorber.
High SOj froa Primary Ab-
sorber and high SOj froa
Pinal Absorber
High SO2 froa Primary Ab-
sorber. nigh SO) and
opacity froa Pinal Absorber
Do
Tes
P-101
ACID CIRCULATING PUMPS
and 102
Low acid flow
No add flow
Flagged suction
Damaged Impeller
Bearing selture
Unknown
1-2 yrs
Unknown
Clean puop and tank
Replace
Rebuild pump
2-3 days
1 day
1-2 daya
High SOj fron Primary Ab-
sorber. Internal corroalon
of downatreaa equipment
froa Drying Tower SO] and
opacity froa Pinal Absorber
Plant anutdown
Do
Tes
No
-------
Table 1 (Continued). CRITICAL EQUIPMENT MALFUNCTIONS AND MAINTENANCE HISTORIES FOR CONTACT SULFURIC ACID PLANTS
ITEM
NO.
EQUIPMENT
NAME
TYPE OF
MALFUNCTION
CAUSE OF
MALFUNCTION
MEAN
TIME
BETWEEN
OCCURENCE!
MAINTENANCE
REQUIRED
MEAN
TIME TO
REPAIR
THEORETICAL EFFECT
OF MAINTENANCE
NEOLECT
AVOIDABLE BY
PREVENTIVE
MAINTENANCE
V-104
DtYMO TOVEK
(V-204)
1. Vessel
Acid leak
Corroalon
Unknown
Patch
<-8 hra.
Uater pollution and ahell
failure
Internal corroalon of
downatreaa equipment
catalyat deterloretlon
end acid alat eolaalon
Internal corroalon of down-
atreaa equlpnent, catalyat
deterioration and acid
alat enlealM
Internal corroalon of down-
atreaa equipment, catalyat
deterioration and acid
alet ealeelon
Ko
2. Entralnaent
3. Distributors and
Piping
4. Packing
Acid alat carry-over
laproper drying
Ioproper drying
Corroded fraae or pad
bjr-pagaing end plugging
Haldlatrlbutlon of acid
froa corroded or plugged
dlatrlbutora
Flooding or channelling
froa dirty or settled
pecking
2-3 yre.
Unknown
1-2 yra.
Replace
Replace
Vseh and replace loat
packing
1 day
2-3 daya
1-2 wka.
Bo
Ho
fas
?t108
CCHVERTER
'
(V-208)
1. Vesael.
2. Support Crlde
and Poata
3. Catalyst
¦tickling
Collapse or tackling
Von converalon efficiency
Overheating
Overheating
Dirty catalyat
Damaged catelyts
(over-heated)
Unknown
Unknown
6 ao.
Unknown
Bapalr
Repair, replace or
tebulld
Screen catalyat
Replace catalyat
3 daya
2-4 wka.
5-T days
High SOj ealaalona
Plugged converter
High SO. ealaalona
High ealaalona
High 30j ealaalona
Ho
Ho
Tea
Ho
(1-211
BEAT EXCHANCERS
Plug tubas
Replace tubes
Plug tube*
Replace tubas
1 day
1 wfc.
1 day
1 wk.
High SO] because of loaa
of teapereture control
Acid alat ealaalona
Ho
Ho
and 217)
Low beat transfer
Tube leaka
Corroalon froa acid
carry-over
Corroalon froa acid
carry-over
1-1 yre.
1-2 yre.
-------
ACID LEAKS FROM
PIPING
9.3%
INSTRUMENT AND
CONTROL FAILURE/
9.5%
COOLING WATER
AND BOILER
MAKEUP
7.9%
ACID MIST
EMISSIONS
9.5%
ACID LEAKS
FROM COOLERS
7.1%
MECHANICAL
EQUIPMENT
FAILURES
17.4%
ELECTRIC POWER
LOSS
6.3%
SULFUR
PUMPS
AND
BURNERS
6.3%
i
GAS LEAKS
FROM DUCTS
21%
# ,
# /
-------
MECHANICAL
EQUIPMENT
FAILURE
15%
ACID LEAKS
FROM PIPING
8%
GAS LEAKS
FROM DUCTS
7%
COOLING WATER
AND BOILER MAKE-UP
6%
BOILER
INSPECTION AND
CATALYST
CLEANING
15%
ACID MIST
EMISSIONS
5%
%
k. a
f///
£
/
/O
S'S
03
tc
it
**i
o
s|
o ^
UJ -J
¦J rf
Ul 2
s
u
cc
111
z
I-
o
SEMI-ANNUAL CATALYST
CLEANING AND
TURNAROUND
29%
DURATION OF PLANT SHUTDOWN
BY CAUSE
SINGLE ABSORPTION PLANT
Figure 6
52
-------
repair. Serious damage caused by neglect will always result
in increased plant emissions. Obviously, the cost of plant
operation also will be increased by such maintenance neglect.
One of the most significant indicators of the quality of
plant maintenance is the frequency of unplanned shutdowns.
Plants being forced to shut down often by a variety of
failures invariably have poor maintenance programs and per-
sonnel usually do not detect and repair damaged equipment
before a failure occurs.
Leaks in acidic gas and liquid lines represent one of the most
frequent causes of shutdowns in any acid plant. A poorly main-
tained plant will experience more frequent leaks. One reason
for failure of acid proof brick linings can be maintenance
neglect. Improper or inadequate repair of leaks will result
in reoccurrence of the leaks and cause more frequent shutdowns.
A plant covered with temporary patches to stop leaks will
also have a high emission rate at the start-up that follows
forced shutdowns for repairs and will also have higher fugi-
tive emissions.
The failure rates and resulting emissions from a poorly main-
tained plant are not corrected by a sudden change in maintenance
philosophy from a minimum maintenance program to a more ade-
quate maintenance program. Several years of high quality
maintenance will be required to bring the plant up to the
desired level of repair. The life of a well-maintained plant
will be as long as twenty to fifty years while one receiving
53
-------
minimum maintenance will become almost inoperable in about
ten years. This comparison is illustrated by data obtained
from similar operating plants with different maintenance phi-
losophies. Experience has shown that a single absorption plant
will require a major overhaul on the average of every fourteen
years. Sufficient operating history is not available to deter-
mine this period for dual absorption paints.
PLANT AND EQUIPMENT LIFE CYCLE
The useful plant life reflects the life of all items of equipment
installed in the plant. The normal life expectancy of critical
equipment is shown in Table 2. The service life shown is in
excess of twenty years for most of the major equipment. Some
of the smaller pieces of equipment such as pumps have a shorter
service life and must be replaced during the normal life ex-
pectancy of the plant. The life expectancy shown in Table 2,
page 45, is based upon an optimum preventive maintenance pro-
gram to obtain maximum economically, justifiable, useful life
from the plant.
EFFECT OF AGE ON FORCED SHUTDOWN RATE
After the initial shake down period when the inherent weak-
nesses of a plant are detected and corrected, the failure
rate in a plant is inversely proportional to the amount and
quality of preventive maintenance. A slight rise in the rate
will occur after the first few years, but this will be small
if the preventive maintenance program is flexible and is up-
dated frequently to compensate for the age of plant equipment.
54
-------
This trend will continue until the amount of preventive main-
tenance required to achieve satisfactory on-stream time is
no longer economically justifiable. At this point the plant
will either require excessive maintenance expenditures or
have a higher unit production cost for the product resulting
from reduced on-stream time. Increased emissions will also
occur as a result of the frequent shutdown and operational
failures. The final result of maintenance neglect is shown
in Table 3, Page 48, for the critical equipment considered.
55
-------
SECTION VII
PREVENTIVE MAINTENANCE
DEFINITION OF PREVENTIVE MAINTENANCE
Eventually, all plant equipment must be repaired if it is to
continue to fulfill a useful function. The need for these
repairs can be prevented or deferred by proper servicing, or
accomplished by replacement before failure, or replacement
after failure occurs. The choice of the type of maintenance
practiced in a plant is a management function.
Breakdowi maintenance is always precipitated by the failure
of some component in the plant to perform its necessary
function. The breakdown maintenance philosophy makes
no provisions for maintenance of equipment until failure
occurs and is generally characterized by frequent plant
shutdowns and long production outages.
The preventive maintenance philosophy, however, includes
the first two functions illustrated above; i.e., servicing
equipment to prevent or defer its failure and replacement and
repair before failure occurs. Thus, with a preventive
maintenance philosophy, equipment failure is less frequent,
shutdown of plant operations occurs less frequently and
forced shutdown periods are shorter. The preventive
maintenance philosophy requires the establishment and imple-
mentation of a program tailored to accomplish management
goals for a specific plant.
56
-------
EFFECT OF PREVENTIVE MAINTENANCE PROGRAM
An effective preventive maintenance program affects several
aspects of plant operation. The most significant effect is
to reduce the total downtime and lost production resulting
from equipment failure. Since lost production can be equated
to money, the cost of lost production must be added to the
cost of maintenance to determine the total cost of a mainten-
ance program. As the amount of money spent on preventive
maintenance is increased, the amount of money lost through
production outage tends to decrease. Considering only produc-
tion quantity and maintenance cost, the most desirable
preventive maintenance program is one that produces the
lowest overall production cost consistent with safe operation
of the plant. Since preventive maintenance is a long range
program, the long range overall cost of plant operation must
be considered in optimizing a preventive maintenance program.
When market conditions demand maximum production, preventive
maintenance can be tailored to provide .a higher on-line time
to maximize production volume. Frequently, optimization
for production volume will require a preventive maintenance
program similar to optimization for overall minimum cost. If
the market advantage is temporary, however, emphasis on
production may override maintenance considerations on the short
term and cause maintenance to be deferred to a later time,
although deferred maintenance may "cost more over the long
period. When market conditions are bad and the market for the
57
-------
product is not expected to improve within the life expectancy
of the plant, a policy of minimum maintenance expenditure may
be the wisest choice. With this type of program, plant life is
shortened and any subsequent rebuilding of the plant will cost
more than proper preventive maintenance during the period.
However, if the plant is expected to be retired, operation with
minimum maintenance can provide the most income for the plant
during the final short period of the plant life.
Selecting a management policy for maintenance for maximizing
the production rates, optimizing overall operating cost, or
minimizing production cost in the short term is a management
decision based on many factors. An additional factor that
must be considered, however, in establishing a maintenance
program is the legal requirement for maintaining plant emis-
sions within established standards. In a sulfuric acid
plant, this necessity may prevent the selection of the minimum
cost route since equipment failure and malfunctions causing
shutdowns and start-up of the plant will contribute to excessive
emissions. When control of plant emissions is considered
along with maximizing profit from the plant, a preventive
maintenance program optimized on total cost and providing
operation within emission standards must be established. The
preventive maintenance program must be tailored for each specific
plant based on operating and maintenance experience and judgement
of plant management.
58
-------
EFFECT OF EQUIPMENT AGE ON PREVENTIVE MAINTENANCE PROGRAM
A preventive maintenance program that is optimal for a
new sulfuric acid plant, and produces the maximum return
on the investment, and emissions within the standards, will be
changed as the plant becomes older. During the first year
of operation, most plants go through a shake-down period when
weaknesses and faults in the design and equipment are
located and corrected. After this shake-down period, the
preventive maintenance program can be established at the
optimum point. As the plant becomes older, the equipment
failure rate will increase, and more replacement of equipment
will be required rather than repair to keep the plant in
proper operating condition. The general shape of a life
cycle-repair curve is shown in Figure 7. The frequency of
performing many preventive maintenance tasks will be increased
as the plant becomes older. The required frequency of preven-
tive maintenance tasks must be established based upon experi-
ence and modified as experience in the older plant dictates.
A major rebuilding or reconditioning of the plant will also
modify the preventive maintenance program and permit lengthen-
ing the period between preventive maintenance tasks to a point
similar to that required for a new plant. A preventive main-
tenance program must be flexible to permit change with age
of the plant if optimum maintenance is to be performed and
emissions from the plant are to be maintained within the
standard.
59
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BREAK-IN
o\
o
§>20%
USEFUL LIFE
WEAR-OUT \
PERIOD . *
SHAKEDOWN PERIOD ENDS
OPTIMUM REPLACEMENT POINT
10
15 20 25 30
ACID PLANT AGE IN YEARS
35
40
45
50
EFFECT OF EQUIPMENT AGE ON MAINTENANCE COST
Figure 7
-------
COST OF PREVENTIVE MAINTENANCE PROGRAM
The cost of maintenance varies widely depending upon the type
of plant, age and the philosophy of maintenance adopted by
management. A philosophy of minimum maintenance may require
an expenditure of as little as one percent of the capital
investment for the plant per year. This low rate can be main-
tained for only a short period, however, before major renova-
tion of the plant will be required. Most modern sulfuric acid
plants that start with a good preventive maintenance program
when the plant is new will spend about five percent of the plant
capital investment per year for the maintenance program. This
percentage will vary from three percent for the marginal program
to a maximum of seven percent where great emphasis is placed
upon maintenance. The higher figures represent expenditures
by a company dedicated to good plant maintenance. Another
company with a different philosophy of maintenance indicated
an expenditure of less than one percent for a poorly maintained
plant to a maximum of two percent for a preventive maintenance
program considered to be excellent. Other companies indicated a
maintenance cost between one and seven percent. The optimum
expenditure is probably near five percent. A curve illustrating
the relationship between the amount spent on preventive maintenance
and the controllable maintenance cost is shown in Figure 8.
As a plant gets older, the expenditure required to maintain
good operating conditions will increase to approximately
seven percent when the plant is fifteen to twenty years
of age. This expenditure level will maintain the
61
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8%
HIGH
CONTROLLABLE MAINTENANCE COST
W
:cost
K°f;
1 /oci
UJ
111
COST OF
PRODUCTION
LOSSES CAUSED
BY FAILURES
IT OF PM
LOW
HIGH
LOW
+* LEVEL OF PREVENTIVE MAINTENANCE ~
MANY REPAIRS & FAILURES FEW FAILURES & REPAIRS
Controllable maintenance cost = cost of PM + cost of repairs + cost of production
losses caused by failures.
COST OF PREVENTIVE MAINTENANCE
Figure 8
62
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plant in approximately the same operating condition with
failure rates similar to a new plant. The maintenance cost
figures presented include the maintenance of emission
control equipment. Installation of emission control equip-
ment has increased* the cost of maintenance of dual absorption
acid plants, by approximately 20 - 25 percent. This increase may
be different for plants employing various types of tailgas
cleaning systems.
SPECIAL MATERIALS TO REDUCE FAILURE
The use of special materials and alloys to reduce corrosion
in the sulfuric acid plant is standard for some types of
equipment. The submersible acid pumps supplying hot acid
to the absorbers and drying towers are constructed of Alloy
20 to withstand the corrosion of hot sulfuric acid. These
pumps would have very short lives if cast iron or a less resis-
tant alloy was used. With proper maintenance, pumps made of
Alloy 2 have a service life of five to eight years.
Acid coolers are most frequently made of cast iron or carbon
steel with sufficient corrosion allowance to give a long
service life. If the cooler tubes, however, are allowed to
operate at a higher than normal temperature, very rapid cor-
rosion and early failure will result. In modern sulfuric
acid plants, there is an increasing use of coolers made of
stainless steel and special tube bundles made of Teflon.
Sufficient operating time is not available on the Teflon
63
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exchanger to evaluate economic justification, but service
life should be indefinite as far as corrosion of tubes is
concerned.
The most common maintenance problem that causes plant shut-
down is leaks in the gas ducts, duct transition pieces and in
expansion joints. These components are usually constructed of
carbon" steel with a flame sprayed coating of aluminum on the
inside surfaces. This coating reduces corrosion and failure
rate of the ducts and vessels and reduces the accumulation of
corrosion products in the catalyst. The use of alloys for
these massive sections is not economically justified. Addi-
tional studies, in view of the need to minimize the shutdown
frequency and the resultant pollution, could show that special
treatment is justified for transition pieces and expansion
joints subject to the most severe conditions.
For many years, the carbon steel shell of the absorbers and
drying towers has been protected from corrosion by installing
a layer of asbestos, cemented with sodium silicate, between
the acid proof brick liner and the shell. Frequently, an
acid leak through a crack in the acid brick liner will pene-
trate the asbestos sheet and attack the carbon steel shell.
In some recently built plants, a Teflon membrane is installed
next to the steel shell in addition to the asbestos to provide
additional corrosion protection. The result or economic
justification of this modification is not known.
64
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One of the most severe services in a sulfuric acid plant is
removal of acid mist from the gases leaving the drying towers
and absorbers. The mist eliminators are most frequently built
with type 316 stainless steel frames and 316 stainless steel
knitted wire mesh demister pads. The life of these units is
usually short because of the effect of corrosion in the fine
wire of the mesh pads. Longer service life can be obtained
by using a knitted demister pads of Teflon in place of the type
316 stainless steel. Frequent failures occur in the type
316 stainless steel frame that supports the demister pad
causing by-passing of acid mist. More corrosion resistant
materials for the demister frame have not been used and
probably could not be economically justified. The high effi-
ciency mist eliminator, installed after the final absorption
tower, usually incorporates a fiberglass pad. The fiberglass
pad is not subject to corrosion deterioration but the 316
stainless steel frame and screen holding the pad is a likely
point of corrosion failure.
With the increasing need for reliability and higher cost of
replacement for the more complex dual absorption acid plants,
the use of special materials to reduce corrosion and failure
rates will probably increase. It is doubtful, however, that
substitution of special materials for major pieces of equip-
ment will be justified because the materials presently being
used and the techniques of construction have been developed
over a long period of time and have provided reasonable
reliability in the severe service of a sulfuric acid plant.
65
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SUGGESTED PREVENTIVE MAINTENANCE PROGRAM FOR SULFURIC ACID PLANTS
Organization of Preventive Maintenance Program
When a preventive maintenance program is organized, certain
document systems and procedures must be established if the
program is to effectively reduce the cost of maintenance,
frequency and length of shutdown and emission of pollutants
from the plant.
The first requirement of a preventive maintenance program is
the development of a preventive maintenance manual that com-
pletely defines and describes the process equipment to be
maintained, the maintenance task to be performed and the
schedule for performing the maintenance.
Based upon the schedule for maintenance proposed by the manual,
an overall maintenance schedule must be developed and main-
tenance plans formulated to integrate the maintenance within
the operation of the plant. An evaluation of the effective-
ness of the preventive maintenance program will require com-
plete records of when and what maintenance is performed on
each piece of equipment. A record of equipment failures and
production downtime is also required in the recordkeeping
system. The overall long range objective of the preventive
maintenance program is minimizing the cost of plant operation
and keeping plant emissions within standards. The emissions
monitoring program required by law will evaluate the success
of maintaining emissions within standards, but a cost account-
ing system must be established to determine the effectiveness
66
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of the overall maintenance program. As with any such plan
and operating system, historical information must be used
to modify and refine the program to achieve the goals set by
the management when the program was established.
Preventive Maintenance Manual
The preventive maintenance manual provides a basis for
establishing a preventive maintenance program. This manual
must list all plant equipment subject to maintenance and
describe the maintenance tasks required for each piece of
equipment. Equipment manufacturer's recommendations should
be used for establishing the type of maintenance required
if extensive maintenance experience is not available on the
equipment. The preventive maintenance manual should be re-
fined as data on the frequency and techniques of maintenance
are developed from analysis of maintenance records and from
economic analysis of the cost accounting system. Revision of
the manual should be perpetual using data feedback from
these sources to compensate for aging of plant equipment.
A typical preventive maintenance manual listing the critical
equipment for a typical single absorption and dual absorption
acid plant is illustrated in Table 4. In an actual established
program more pieces of equipment will be included depending
upon variations in the design of the specific plant. The
manual includes those maintenance tasks either recommended
by the manufacturer or indicated by experience. Routine in-
67
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Table 4
PREVENTIVE MAINTENANCE MANUAL
EQUIPMENT
NUMBER
EQUIPMENT
NAME
MAINTENANCE TASK
DESCRIPTION
FREQUENCY
TYPE (1)
MANHOURS
REQUIRED
SHIFT
DAILY
WEEKLY
AS IN-
DICATED
C-103
Main Air
(C-203)
Blower
1. Blower
Check Lubrication System
X
0
Check for Unusual Noise
and Vibration
X
0
Check Bearing Temperature
X
0
Clean and Inspect Bear-
ings and Lub System
12 Mo.
S
Wash and Inspect Rotor
12 Mo.
S
2. Turbine
Check Oil Pressure, Temp-
erature and Level
X
0
Bleed Air from Lube Oil
Filter
X
0
Wash and Inspect Rotor
12 Mo.
S
Clean and Inspect Bearings
and Lube System
12 Mo.
S
Clean and Inspect Seals
12 Mo.
S
Test Governor and Trips
12 Mo.
S
F-102
3. Filter
Check Filter Media Drive
X
0
(F-202)
Wash Filter Media and
Change Oil in Bath
12 Mo.
S
Surface
Furnace
K-101
1. Furnace
Inspect Shell for Hot Spots
X
0
(K-201)
Inspect and Repair Fire
Brick
12 Mo.
S
2. Burner
Check Flame Pattern and
System
Rod as Required
X
0
Check Pumps for Noise and
Vibration
X
0
Check Pump and Motor Bear-
ing Temperature
X
0
Check Steam Traps for
Operation
X
0
Relubricate Sulfur Pump
Bearings
3-6 Mo.
0
11) S = SHUTDOWN REQUIRED
O = MAINTENANCE PERFORMED WHILE OPERATING.
68
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Table 4
PREVENTIVE MAINTENANCE MANUAL
EQUIPMENT
NUMBER
EQUIPMENT
NAME
MAINTENANCE TASK
DESCRIPTION
FREQUENCY
TYPE (1)
MANHOURS
REQUIRED
SHIFT
DAILY
WEEKLY
AS IN-
DICATED
B-105
Boilers
Inspect Tubes and Fire-
Brick
12 Mo.
S
(B-205)
Clean Gas and Waterside
of Tubes
12 Mo.
S
Repair Tube Leaks or
Bulged Tubes
12 Mo.
s
Test Boiler and Safety
Valves
12 Mo.
s
Clean, Lubricate & Check
Alignment of Dampers
6 Mo.
s
X-106
Economizers
Inspect Gas Side for Cor-
rosion
12 Mo.
s
(X-206)
Clean and Repair Tubes
12 Mo.
s
(X-207)
Test Economizer and Safety
Valves
12 Mo.
s
Clean, Lubricate & Check
Alignment of Dampers
6 Mo.
s
(X-218)
Superheater
Inspect Shell Side for
Corrosion
12 Mo.
s
Test Superheater & Safety
Valves
12 Mo.
s
Clean, Lubricate & Check
Alignment of Dampers
6 Mo.
s
X-110
Acid Cooler
Inspect for Leaks and
X
0
X-115
Corrosion
X-119
(X-210)
Clean Water Side of Tubes
As
s
Needed
(X-214)
(X-215)
Clean Water Distributers
As
0
on Cascade Coolers
Needed
(X-219)
(X-220)
(1) S = SHUTDOWN REQUIRED
O = MAINTENANCE PERFORMED WHILE OPERATING.
69
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Table 4
PREVENTIVE MAINTENANCE MANUAL
EQUIPMENT
NUMBER
EQUIPMENT
NAME
MAINTENANCE TASK
DESCRIPTION
FREQUENCY
TYPE (1)
MANHOURS
REQUIRED
SHIFT
DAILY
WEEKLY
AS IN-
DICATED
V-104
Drying
(V-204)
Tower
1. Vessel
Clean and Acid Proof Brick
and Shell for Corrosion
and Leaks
12 Mo.
S
2. Entrain-
Wash and Inspect for Cor-
ment
rosion and Bypassing
12 Mo.
S
Separator
3. Distribu-
Check for Corrosion
12 Mo.
S
ters and
Piping
4. Packing
Inspect for Attrition &
Channeling—Clean and
Replace as Required
12 Mo.
s
V-108
Converter
Clean and Inspect Fire
6 Mo.
s
(V-108)
1. Vessel
Brick and Shell for Cor-
rosion and Leaks
2. Mist
Check for Corrosion and
Eliminator
Bypassing
12 Mo.
s
3. Support
Check for Corrosion and
Grids and
Warping
12 Mo.
s
Posts
4. Packing
Inspect for Attrition and
Channeling—Clean and
12 Mo.
s
Replace as Required
(1) S = SHUTDOWN REQUIRED
O = MAINTENANCE PERFORMED WHILE OPERATING.
70
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Table 4 •
PREVENTIVE MAINTENANCE MANUAL
EQUIPMENT
NUMBER
EQUIPMENT
NAME
MAINTENANCE TASK
DESCRIPTION
FREQUENCY
TYPE (1)
MANHOURS
REQUIRED
SHIFT
DAILY
WEEKLY
AS IN-
DICATED
V-109
Absorption
(V-209).
Towers
(V-221)
1. Vessel
Clean and Inspect Acid
12 Mo.
S
Proofbrick and Shell for
Leaks and Corrosion
2. Mist
Wash and Inspect for Cor-
12 Mo.
S
ELlminatoi
rosion and Bypassing
3. Piping &
Check for Corrosion
12 Mo.
s
Distri-
buters
4. Packing
Inspect for Attribution
12 Mo.
s
and Channeling—Clean
and Replace as Required
(1) S = SHUTDOWN REQUIRED
O = MAINTENANCE PERFORMED WHILE OPERATING.
71
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Table 4
PREVENTIVE MAINTENANCE MANUAL
FREQUENCY
z ce
T—
LLI HI
1 1
a 2
LU
EQUIPMENT
MAINTENANCE TASK
>
. o
* '
oE
NAME
DESCRIPTION
SHIFT
DAILY
_i
LU
Ul
S
AS IN-
DICATE
UJ
O-
>
H
13
20
-------
spections, lubrications and checking by operating and main-
tenance personnel are not included in the sample manual but
should be included in any established program. Emphasis is
placed upon the completion of major maintenance during the
annual plant turnaround to minimize breakdown maintenance.
Planning and Scheduling
As previously indicated, the schedule developed for a pre-
ventive maintenance program is based initially upon an
equipment manufacturer's recommendation and previous experience
of plant operations. As experience is gained, the frequency
of maintenance tasks and the time required to perform these
tasks will be refined to improve the efficiency of the main-
tenance program. The time required to complete a task is
important when scheduling either on-line or shutdown mainte-
nance to ensure all required tasks can be completed within
the total scheduled downtime. Maintenance task plans for
a specific shutdown must also be compatible with manpower
availability.
Since the catalyst must be cleaned semi-annually in most
plants, many of the annual tasks are scheduled during alter-
nate semi-annual shutdowns. This minimizes the length of
such shutdowns and provides the maximum opportunity for major
maintenance or replacements during these periods. A well-
organized and scheduled program will also have provisions
for completing all task work that is due in the event of an
73
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unscheduled shutdown caused by equipment failure. Maintenance
accomplished during these periods may prevent additional down-
time resulting from equipment failure before maintenance can
be performed during the next scheduled plant shutdown. These
techniques for spreading work through the various planned
shutdowns and taking advantage of opportunities for maintenance
during unscheduled shutdowns will reduce the amount of work
required during the semi-annual turnaround. Efficient plan-
ning of work to be performed during a shutdown will reduce
the length of shutdown, and proper scheduling of maintenance
will reduce unscheduled shutdowns resulting from equipment
failure.
Recording Keeping Systems
A preventive maintenance program for a plant cannot be op-
timized without appropriate records of the maintenance history
of that plant. Many forms of recordkeeping systems have been
employed for preventive maintenance programs. These systems
have been described at length in various books on the subject
and will only be mentioned briefly in this report.
The most frequently used recordkeeping systems include single
card, three card and punched edge card systems for manual
sorting and retrieving of information. Also, various computer
sorting and retrieval systems have been applied in larger
installations. Regardless of the form of recordkeeping,
certain basic information about the equipment and maintenance
74
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must be recorded for later analysis in order to evaluate and
update the preventive maintenance program. The recordkeeping
system must include, generally, a complete description of
equipment, a record of what maintenance is performed, when
the maintenance was performed and manpower requirements for
completing the task. The equipment description part of the
record will include the manufacturer's model, name, location
within the plant and plant identification number. The main-
tenance tasks to be performed are detailed and special in-
structions concerning lubrication type, coatings and special
parts or materials are included in the records.
The recommended maintenance frequency is also shown on the
card. A record of maintenance performed is recorded by the
maintenance mechanic or foreman after each maintenance task.
The records of maintenance performed should include parts and
materials used and time required to complete the task.
Cost Accounting Systems
Another part of the recordkeeping system necessary to evaluate
the effect of the preventive maintenance program and establish
the optimum schedule is the cost accounting system. This
system must determine and record the cost of each maintenance
task. These combined costs are the cost of the preventive
maintenance program. The lowest overall cost results from
the optimum amount of maintenance performed and should be the
maintenance goal established by plant management.
75
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Refining the System
Because of variations in plant design and operating conditions,
there is no single optimum preventive maintenance program that
can be applied to all plants. After the initial program
schedule has been established, the process of refinement must
begin. Each equipment failure should be analyzed to determine
the cause of the failure and if the schedule or maintenance
plan can be changed to prevent the failure from re-occurring
and causing an unplanned shutdown. Careful revision of the
system in this manner and proper analysis of cost provided
by the cost accounting system will yield a preventive mainte-
nance program that permits operation of the plant with a
minimum number of unplanned shutdowns and therefore minimum
emissions resulting from plant start-ups and operating mal-
functions .
Reports
If a preventive maintenance program is to be effective, there
must be feedback from the recordkeeping system to management
to show status and effectiveness of the program. This feed-
back is provided by the monthly "Preventive Maintenance
Performance Report" listing the maintenance tasks scheduled
during the month and the number of tasks either performed on
time, performed late or deferred. A percent compliance to
the schedule for tasks requiring a shutdown and those per-
formed while on line is a useful evaluating tool.
76
-------
In addition to the Performance Report, a list of delinquent
tasks should be provided with the original schedule, and a
new schedule for their completion should be made. This report
is often called the "P.M. Non-Compliance Report" and should
include a statistical summary of the items appearing on the
report.
A "Maintenance Operating Report" showing total downtime re-
sulting from equipment failure and scheduled maintenance
along with a list of shutdown causes, will assist in evalu-
ating the established schedule and refining the P. M. Program.
The report should include the last maintenance performed on
the equipment causing the shutdowns and the date of the last
and next scheduled maintenance.
77
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SECTION VIII
INSPECTION TECHNIQUE
INSPECTION PROCEDURE
An inspector entering a sulfuric acid plant for the purpose
of evaluating maintenance procedures usually will not have
access to the internals of the plant equipment to determine
the condition of the equipment and the expected
Without direct access to the working parts of the machinery,
the quality of maintenance must be inferred from the general
plant appearance and a review of operating and maintenance
records. In most instances, a plant that looks well cared for
on the outside will be well maintained in the important
areas. A plant that looks rundown will usually be in a bad
state of repair and subject to frequent equipment failures
and resulting emissions. A plant without a preventive
maintenance program or one with an inadequate program will
also be more subject to occurrences of high emissions from
equipment failure and shutdown.
The most obvious indication that a sulfuric acid plant is
not in compliance with the NSPS is high opacity of the
plume from the stack. An inspector entering the plant
will observe the stack and estimate the opacity of the
plume. This observation will be preliminary to a general
observation of plant conditions and will help form an
opinion of the quality of plant maintenance.
78
-------
A walk through the plant will provide an appraisal of the
overall condition of the plant. Special attention should
be given to liquid and gas leaks from the equipment and the
presence of patches for temporary repair of plant leaks.
The condition of external insulation should also be noted
as an indication of the emphasis placed on maintenance.
The primary source of specific information concerning the
status of maintenance of the plant is the maintenance record
system. Satisfactory operation with a minimum of equipment
failures and a minimum amount of emissions cannot be obtained
without an effective preventive maintenance program. An
effective program will have all of the elements, in some form,
of the program suggested in Section VIII. A review should
be made of the recordkeeping system, schedule and status
reports to determine if the plant has established a suitable
preventive maintenance program. Many variations in the form
of the P.M. program are possible but the effectiveness of the
program is the basis for determining its adequacy.
The effectiveness of the preventive maintenance program
can be determined by reviewing the maintenance records
for the past several months. The number of forced shutdowns
resulting from equipment failures, normally reported in the
operating log or maintenance reports, is a good indication
of the adequacy of the preventive maintenance program and of
the effectiveness of its application. The number of maintenance
j)
tasks scheduled but not completed should be shown in the monthly
"Delinquent Maintenance" report. A large number of delinquent
79
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tasks and tasks that appear on several monthly reports in
succession indicates the preventive maintenance program is
not adequately followed. The total downtime for maintenance
during previous months may indicate either excessive equipment
failure or poor scheduling of maintenance tasks. This data
must be weighed with factors such as delinquent maintenance
tasks to determine the cause of high downtime.
Another significant source of information for evaluating
maintenance quality is the quarterly report submitted by the
plant operator to EPA explaining any occurrence of emissions
in excess of the NSPS. Emissions resulting from equipment
failure should be analyzed to determine if the failure
resulted from a lack of preventive maintenance. Repetitive
occurrences caused by the same plant equipment will almost
always point to a deficiency in maintenance or design.
The net result of the review of records and reports will
be a judgement on the adequacy of the preventive maintenance
program and the application of the program by plant maintenance
personnel. Shortcomings in the program should be noted
and recommendations for improvement should be offered. It
is doubtful that a single inspection can produce many
conclusive evaluations. The accumulation of data from
several inspections will establish the true picture of
plant maintenance quality and its effect on emissions.
80
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INSPECTION CHECK LIST
Figure 9 presents a check list that can be used to record data
needed to evaluate a preventive maintenance program during a
plant inspection. A maintenance inspection may be combined
with an inspection of plant operations in which case the
check lists for the two inspections can be combined and the
first page will be common to the combined check list. The
first page of the check list is for recording general plant
identification information and description and data obtained
from a spot check of stack emission opacity. The second page
can be used to record the general appearance of the plant.
Gas and liquid leaks should be recorded on this page with
an indication of the severity of the leak. Since this part
of the inspection is subjective, comments to qualify each
observation will be helpful in the overall evaluation of plant
maintenance quality.
The third page of the check list is used for recording a
summary of data taken from the preventive maintenance records
and operating and maintenance reports. Actual numbers should
be entered in the form to provide a quantitative measure of
the key points thereby indicating the effectiveness of the
preventive maintenance program. The final summation of the
form is a question calling for a judgement by the inspector
on the adequacy of the preventive maintenance program. This
judgement should be qualified by any pertinent comments and
suggestions.
81
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FIGURE 9
SULFURIC ACID
PLANT INSPECTION
CHECK LIST
Company Name
Source Code Number
Company Address
Name of Plant Contact
Unit Designation
Plant Capacity
Type of Feed Stock
Inspection Date
PRE-ENTRY OBSERVATIONS
STACK PLUME:
WEATHER CONDITIONS:
Clouds:
Wind: 1
Humidity:
Precipitation:.
Temperature:.
Time:
EQUIVALENT OPACITY (Circle One)
0 10 20 30 40 50 75
OPACITY REGULATION
PLUME COLOR
~ In Compliance
~ Not in Compliance
82
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EQUIPMENT MAINTENANCE
PLANT INSPECTION
GENERAL HOUSEKEEPING
Below Average Average Above Average
~ ~ ~ ~ ~
Comments:
EQUIPMENT APPEARANCE
Below Average Average Above Average
~ ~ ~ ~ ~
Comments:
THERMAL INSULATION CONDITION
Below Average Average Above Average
~ ~ ~ ~ ~
Comments:
ACID LEAKS OBSERVED: Number Severity
GAS LEAKS OBSERVED: Number Severity
-------
EQUIPMENT MAINTENANCE RECORDS
Preventive Maintenance Program Established? Yes CD No I I
Is P.M. Program being followed? Yes ~ No ~
Number of P.M. Tasks Not Completed Last Month
Previous Month
Number of Forced Shutdowns Last Month
Previous Month
Percent Down Time for Maintenance Last Month
Previous Month
Number of Occurrences of High Emissions Resulting from Equipment Malfunction
Reported Last Quarter
Equipment Causing More Than One Occurrence
Number
Number
Number
Number
Is P.M. Program Adequate? Yes ~ No ~
Comments:
84
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The recommended check list should be completed while the
inspection of the plant and the records is made. It should
be supplemented with additional facts or observations con-
sidered important to the task of evaluating the effect of
maintenance on emissions.
INSPECTION REPORTS
The reports recommended for the preventive maintenance program
in Section VII are primarily to assist the plant operator
in managing the program. Although these reports should be
available to the EPA inspector during a plant visit, routine
submission of the reports to EPA would place an unneccessary
burden on the operator and EPA. Some amount of routine
evaluation of the maintenance program in the plant could be
obtained by revising the format of the Quarterly Emissions
Violation Report submitted by the operator to EPA. Data on
the last date of overhaul and total service life of any piece
of equipment responsible for emissions in excess of the NSPS
could be included. Statements could also be required concerning
the establishment of a preventive maintenance program and
compliance with the program as indicated by the number of
delinquent preventive maintenance tasks during the report
period.
85
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SECTION IX
REFERENCES
1. Calvin, E. L., F. D. Kodras. Evaluation of Emissions During
Start-Up, Shutdown and Malfunction of Sulfuric Acid Plants.
Industrial Environmental Research Laboratory, EPA by
Catalytic, Inc., Charlotte, N. C. EPA-600/2-76-010.
January 1976. 353 pages.
86
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SECTION X
TECHNICAL REPORT DATA
f Please read Instructions on the reverse before completing)
1. REPORT NO. 2.
EPA-600/2-76-119
3. RECIPIENT'S ACCESSIOWNO.
4. TITUS ANO SUBTITLE
Effect of Equipment Maintenance and Age on
Sulfuric Acid Plant Emissions
8. REPORT OATH
ADril 1976
8. PERFORMING ORGANIZATION COOE
7. AUTHOR(S)
E.L. Calvin and F. D. Kodras
8. PERFORMING ORGANIZATION REPORT NO.
Project 42470
9. PERFORMING ORGANIZATION NAME ANO AOORS5S
Catalytic, Inc.
P.O. Box 11402
Charlotte, North Carolina 28209
10. PROGRAM ELEMENT NO.
1AB013; ROAP 21BAV-006
14. 4onY ract/grant no.
68-02-1322, Task 10
12. SPONSORING AGENCY NAM8 ANO ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Task Final: 4/75-1/76
14. SPONSORING AGENCY COOS
EPA-ORD
18. supplementary notes Task officer for this report is R. V.H
Ext 2557.
endriks r Mail Drop 62,
i«. abstract rep0r£ describes the effect of equipment maintenance and age on emis-
sions from single- and dual-absorption sulfuric acid plants, using both elemental
sulfur and recycled sulfur-containing acid sludge feedstock. A description is inclu-
ded of the critical equipment, manufacturer's recommended maintenance data,
and malfunction history from 20 sulfuric acid plants. From this data, a recommen-
ded preventive maintenance program is provided for the critical equipment. A check-
list is provided for an inspector to use in evaluating maintenance in an operating
plant.
17. KEY WORDS ANO DOCUMENT ANALYSIS
a. DESCRIPTORS
b.l08NTIPIERS/OPBN ENDED TERMS
c. COSATI Field/Group
Air Pollution
Preventive Maintenance
Chemical Plants
Sulfuric Aci d
Air Pollution Control
Stationary Sources
Effects of Aging
13B
15E
07A
07B
18. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
92
2a SECURITY CLASS (ThUpage)
Unclassified
22. PRICE
SPA Form 2230*1 (*>73)
87
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