FM Global

Property Loss Prevention Data Sheets 7-111F

October 2020
Interim Revision January 2023
Page 1 of 8

SULFURIC ACID

Table of Contents
Page

1.0 SCOPE ..................................................................................................................................................... 2

1.1 Hazards ............................................................................................................................................. 2
1.2 Changes ............................................................................................................................................ 2
2.0 LOSS PREVENTION RECOMMENDATIONS ......................................................................................... 2
2.1 Construction and Location ................................................................................................................. 2
2.1.1 General .................................................................................................................................... 2
2.1.2 Sulfur Burning Process ........................................................................................................... 2
2.2 Process Safety .................................................................................................................................. 2
2.3 Protection ........................................................................................................................................... 3
2.3.1 General .................................................................................................................................... 3
2.3.2 Metallurgical/Acid Regeneration Process ............................................................................... 3
2.4 Equipment and Processes ................................................................................................................ 3
2.4.1 Gas Cleaning Plant ................................................................................................................. 3
2.4.2 Blowers .................................................................................................................................... 3
2.4.3 Fuel-Fired Equipment .............................................................................................................. 3
2.4.4 Heat Exchangers ..................................................................................................................... 4
2.4.5 Storage Tanks .......................................................................................................................... 4
2.5 Operation and Maintenance .............................................................................................................. 4
2.5.1 Operation ................................................................................................................................. 4
2.5.2 Maintenance ............................................................................................................................ 4
3.0 SUPPORT FOR RECOMMENDATIONS ................................................................................................. 4
3.1 Loss History ....................................................................................................................................... 4
3.2 Process Overview .............................................................................................................................. 5
4.0 REFERENCES ......................................................................................................................................... 8
4.1 FM Global .......................................................................................................................................... 8
APPENDIX A GLOSSARY OF TERMS ......................................................................................................... 8
APPENDIX B DOCUMENT REVISION HISTORY ......................................................................................... 8

List of Figures
Fig. 1. FM Global client losses by peril from 1977 to 2019 ........................................................................... 5
Fig. 2. Sulfur burning process ......................................................................................................................... 7
Fig. 3. Metallurgical process ........................................................................................................................... 7
Fig. 4. Spent acid regeneration process ......................................................................................................... 8

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7-111F Sulfuric Acid
Page 2 FM Global Property Loss Prevention Data Sheets

1.0 SCOPE
This document provides loss prevention recommendations for sulfuric acid and oleum manufacturing facilities.
The manufacturing methods covering in this data sheet are sulfur burning, metallurgical, and spent acid
regeneration processes.

1.1 Hazards
The main hazards in this occupancy are:
• Corrosive environments
• Weak acid generation
• Hydrogen gas explosions
• High temperature and pressure conditions
• Plastic equipment and piping (FRP)
• Explosions in electrostatic precipitators

1.2 Changes
January 2023. Interim revision. Minor editorial changes were made.

2.0 LOSS PREVENTION RECOMMENDATIONS

2.1 Construction and Location

2.1.1 General
2.1.1.1 For the construction of the plant, use building materials that are compatible and that will resist the
environmental and process conditions. Document and maintain throughout the lifecycle of the plant the
required materials of construction for all piping, process vessels, gaskets, etc. Include any alloy changes in
a management of change program.
2.1.1.2 Use a positive material identification (PMI) program for all piping and vessels requiring high alloy
services. Materials should be verified using alloy analysis tools (e.g., x-ray fluorescence) during construction
and all repair and modification activities.
2.1.1.3 Locate plastic equipment using spacing distribution to prevent equipment to be concentrated in a
single area. Ensure plastic equipment is located away from areas in which potential acid leakage could
damage the integrity and proper function of the equipment.
2.1.1.3.1 Label or identify plastic equipment using placards or other means to alert people about the fire
risk if activities such as hot work (cutting and/or welding) are performed on or near the equipment.
2.1.1.4 Install plastic ducts so they are not exposed to potential fires from equipment with oil fire hazards
and/or combustible storage. For additional guidance refer to Data Sheet 7-78, Industrial Exhaust Systems.
2.1.1.5 For steam turbine generators (STGs), follow the recommendations for construction and location in
Data Sheet 7-101, Fire Protection for Steam Turbines and Electric Generators.

2.1.2 Sulfur Burning Process

2.1.2.1 Locate the outdoor sulfur pile storage in an area that is not subject to prevailing winds. If necessary,
provide wind barriers, water spray or coating with molten sulfur (long term storage) if there are no natural
barriers present.

2.2 Process Safety

2.2.1 Establish a formal process safety program in accordance with Data Sheet 7-43, Process Safety. Place
emphasis on process and equipment integrity (mechanical).

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2.3 Protection

2.3.1 General
2.3.1.1 Provide automatic sprinkler protection for elevated conveyors and combustible buildings handling
or storing solid or molten sulfur. For additional information see Data Sheets 7-11, Conveyors, and 3-26, Fire
Protection for Nonstorage Occupancies.
2.3.1.2 Follow recommendations for protection of steam turbine blowers and generators in Data Sheet 7-101,
Fire Protection for Steam Turbines and Electric Generators.

2.3.2 Metallurgical/Acid Regeneration Process

The protection recommended in this section applies to metallurgical or spent acid regeneration plants where
abundant fiberglass reinforced plastic [FRP] ducts and equipment can normally be found at the gas cleaning
sections.
2.3.2.1 Provide directional water spray protection for important plastic equipment and ductwork. Focus on
concentrations where large ducts cross over each other or multiple vessels are positioned side-by-side.
Design the system to provide a discharge pressure of 20 psi (1.4 bar) for open sprinklers or nozzles greater
than or equal to 1/2 in. (13 mm) or 30 psi (2.1 bar) for smaller nozzles.
2.3.2.2 Institute a policy that ordinary combustibles are not to be staged or stored below long run ducts.
2.3.2.3 Install automatic sprinkler protection inside scrubbers in accordance with Data Sheet 7-78, Industrial
Exhaust Systems.
2.3.2.4 For the protection of stacks with plastic liners, follow the recommendations in Data Sheet 1-13,
Chimneys.

2.4 Equipment and Processes

Equipment, including accessory or utility equipment, should be designed, constructed, installed, operated,
protected, and maintained in a way that minimizes the risk of failures, while providing process reliability.
Selection of building construction materials for equipment is paramount in this occupancy due to harsh
environmental and process conditions.

2.4.1 Gas Cleaning Plant

2.4.1.1 Provide overpressure protection between the Wet Electrostatic Precipitator (WEP) and the drying
tower.
2.4.1.2 Determine, based on a process hazard analysis (PHA), the specific points where alarms and interlocks
need to be installed and the actions to be taken on the gas stream to prevent damage to ducts and equipment.

2.4.2 Blowers
2.4.2.1 Select blower building materials according to compatibility and process conditions. Ensure a slight
over-design is provided to account for normal levels of corrosion and wear expected over the life of the unit.
2.4.2.2 Provide any blower feed duct taking suction after the drying tower with a knock-out pot to collect
all the condensate acid and prevent damage to the blower.
2.4.2.3 Provide blowers with safety interlocks to prevent surging conditions. A surge detection system
interlocked to open a recycle line that discharges back to the inlet of the drying tower may be used. See Data
Sheet 13-24, Fans and Blowers, for additional information.

2.4.3 Fuel-Fired Equipment

2.4.3.1 Provide all fuel-fired equipment, including sulfur burners, gas heating systems, and pre-heaters, with
combustion safeguards and interlocks in accordance with Data Sheet 6-10, Process Furnaces.
2.4.3.2 Interlock the sulfur burner furnace to prevent molten sulfur from entering the chamber if the
temperature is below 850°F (450°C). On natural gas firing equipment, this interlock should be set at 1,400°F
(760°C).

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7-111F Sulfuric Acid
Page 4 FM Global Property Loss Prevention Data Sheets

2.4.4 Heat Exchangers

2.4.4.1 Install an acid detection system interlock after each acid cooler heat exchanger to detect any acid
leaks. Steam quality, water conductivity, or some other acid detection means may be used.
2.4.4.2 For heat recovery boilers, see the guidance in Data Sheet 6-14, Heat Recovery Boilers.

2.4.5 Storage Tanks

2.4.5.1 Molten Sulfur

2.4.5.1.1 Provide molten sulfur storage tanks or pits with temperature monitoring devices to ensure
temperature is maintained in the range of 250-280 °F (120-140 °C) to prevent overheating and fires.
2.4.5.1.2 Provide an inert atmosphere of storage tanks or pits to prevent potential fires using one of the
following options:
A. An inert gas system to maintain an inert atmosphere in the tank head space. See Data Sheet 7-59,
Inerting and Purging of Tanks, Process Vessels, and Equipment, for additional information.
B. Steam snuffing at a delivery rate of 4-8 lb/min per 100 ft3 (0.64 to 1.3 kg/min/m3) of enclosure volume,
interlocked to be activated when the molten sulfur exceeds safe temperature limits.
2.4.5.1.3 Maintain atmospheric vents clear of sulfur build-up.

2.4.5.2 Sulfuric Acid

2.4.5.1 Provide acid storage tanks with suitable vacuum breakers.
2.4.5.2 Install hydrogen gas detection to prevent hydrogen accumulation and explosions in the tank.
2.4.5.3 Provide acid storage tanks with high level alarms and high-high level interlocks.

2.5 Operation and Maintenance

2.5.1 Operation
2.5.1.1 Establish operational procedures for all operation modes, including normal startup and shutdown,
process upsets, emergency shutdown, and restart, that include activities to prevent conditions such as weak
acid generation or hydrogen formation and explosions.
2.5.1.2 Ensure updated procedures exist for fuel-fired equipment with all the activities/instructions to be
followed for cold start and hot restart operations.

2.5.2 Maintenance
2.5.2.1 Establish an asset integrity monitoring program in accordance with Data Sheet 9-0, Asset Integrity.
2.5.3 Inspect, test and maintain safety controls, alarms and interlocks according to Data Sheet 7-45, Safety
Controls, Alarms, and Interlocks.

3.0 SUPPORT FOR RECOMMENDATIONS

3.1 Loss History

FM Global client losses to this occupancy from 1977 to 2019 are presented in Figure 1, where the three
largest categories of loss by peril were explosion, natural hazards, and equipment breakdown.
The largest losses in sulfuric acid plants were related to explosions in which electrostatic precipitators and
furnaces were involved.
Natural hazards occupied the second place with 16% of the total losses during this period, were flood
represented the main cause for these losses.
Heat exchangers and coolers were the main equipment driven the equipment breakdown losses. One of
the largest losses in this category involved a weak acid scenario, where sulfuric acid corroded the heat

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Sulfuric Acid 7-111F
FM Global Property Loss Prevention Data Sheets Page 5

Equipment
Breakdown

9% 4% 3%
Natural
Hazards
16%

2%

Explosion
67%

Collapse Electrical Breakdown Explosion

Other Natural Hazards Equipment Breakdown

Fig. 1. FM Global client losses by peril from 1977 to 2019

exchanger tube bundle, allowing higher pressure water to enter process stream and reduce concentration
to corrosive levels, with ensuing damage to multiple pieces of equipment.

3.2 Process Overview

Sulfuric acid is an extremely important industrial chemical, probably one of the most important in the world.
In 2015, about 250 million tons of sulfuric acid were produced worldwide, with a forecast production for 2021
of 278 million tons. The leading producers in the world are China, United States, India, and Russia, which
together contribute with more than 60% of the global production of sulfuric acid.
Sulfuric acid is used in a wide variety of industries and processes around the world. Approximately 60% of
the sulfuric acid produced is used to manufacture fertilizers (i.e., superphosphate of lime and ammonium
sulfate). In the chemical industry, it is used to manufacture chemicals such as hydrofluoric acid, nitric acid,
sulfate salts, synthetic detergents, dyes and pigments, explosives, and drugs. Sulfuric acid is also used for
metal processing and in petroleum refining to wash impurities out of gasoline and other refinery products.
Some other industries include pulp/paper and fiber.
Most of the sulfuric acid is produced by sulfur-burning plants. The next most important producer would be
metallurgical smelters, whose production ranges between 10% and 15% worldwide. Sulfuric acid can also be
produced by a spent acid regeneration (SAR) process. These last two processes are commonly used as
an option to minimize air pollution or dispose of unwanted by-products.
The sulfuric acid process is based on the following chemical equations:
S + O2 → SO2
SO2 + O2 ↔ SO3 + Heat

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7-111F Sulfuric Acid
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SO3 + H2O → H2SO4 + Heat

In the scope of chemistry, none of these reactions are overly complex. However, controlling these relatively
simple reactions is far from simple. Sulfur dioxide and sulfuric acid are corrosive and difficult to handle, sulfur
trioxide intermediate is highly reactive and far from stable, and the amount of heat generated by these
exothermic reactions requires special consideration.
As mentioned above, sulfuric acid can be produced using the following processes:
• Sulfur burning (see Figure 2)
• Metallurgical (see Figure 3)
• Spent acid regeneration (see Figure 4)
Basically, the main difference between these three processes is the type of raw materials used, and the
cleaning or production process required to obtain the necessary SO2 that will be transformed by catalytic
oxidation into SO3 in the converter. The catalytic oxidation of SO2 to SO3 is a highly exothermic reaction and
converters are commonly designed as multistage adiabatic units with gas cooling between each stage.
Gas leaving the converter is normally cooled to improve SO3 absorption in the absorption towers. The process
gas is not cooled below certain temperature ranges to avoid the possibility of corrosion from condensing
sulfuric acid originating from trace water in the gas stream. In some cases, a gas cooler is used instead of
an economizer.
Once the SO3 stream is cooled, it goes to packed absorption towers, where SO3 is absorbed and converted
to H2SO4. Concentrated sulfuric acid circulates in the tower and cools the gas to within a few degrees of
the acid inlet temperature. Acid temperatures rise within the tower due to the exothermic reaction that is
produced when sulfuric acid is generated. The hot product acid leaving the tower is cooled in heat exchangers
before being recirculated or pumped into storage tanks.
The sulfur burning process use horizontal brick-lined combustion chambers with dried air and atomized molten
sulfur introduced at one end. Atomization can be achieved by pressure spray nozzles or by mechanically
driven spinning cups, the degree of atomization being a key factor in producing efficient combustion. Plants
using this process produce considerable heat from the sulfur combustion, which can be used to produce
steam and generate power via turbines.
Burners used for spent acid can have some similarities with those used for sulfur burning. Very high
temperatures are reached in the combustion chamber that can also be used to generate steam or power.

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Sulfuric Acid 7-111F
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Comb.
Sulfur Hot
S Gases

Sulfur SO + O
Drying Tower
Air Burner

HSO
Natural Gas

HSO Stack Converter

Cold Interpass
Exchanger

Final SO + HO

Absorbing
Tank Tower
HSO SO + HO Interpass
Absorbing
Tower
HSO

HSO

Tank Tank
HSO HSO

99% HSO
To Storage

Fig. 2. Sulfur burning process

Wet
Electrostatic Final Gas Cooling Primary SO + other comp.
Precipitator Scrubber Tower Scrubber from metallurgical
WESP processes

Gas Cleaning

Gas SO + O
Drying Tower Blower
Pre-heating

HSO

HSO Stack Converter

Cold Interpass
Exchanger

Final SO + HO

Absorbing
Tank Tower
HSO SO + HO Interpass
Absorbing
Tower
HSO

HSO

Tank Tank
HSO HSO

99% HSO
To Storage

Fig. 3. Metallurgical process

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7-111F Sulfuric Acid
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Final Gas Cooling Primary Combustion

Boiler Spent Acid
Scrubber Tower Scrubber Chamber

Gas SO + O
Drying Tower Blower
Pre-heating

HSO

HSO Stack Converter

Cold Interpass
Exchanger

Final SO + HO

Absorbing
Tank Tower
HSO SO + HO Interpass
Absorbing
Tower
HSO

HSO

Tank Tank
HSO HSO

99% HSO
To Storage

Fig. 4. Spent acid regeneration process

4.0 REFERENCES

4.1 FM Global
Data Sheet 1-13, Chimneys
Data Sheet 3-26, Fire Protection for Nonstorage Occupancies
Data Sheet 6-10, Process Furnaces
Data Sheet 6-14, Heat Recovery Boilers
Data Sheet 7-11, Conveyors
Data Sheet 7-43, Process Safety
Data Sheet 7-45, Safety Controls, Alarms and Interlocks
Data Sheet 7-59, Inerting and Purging of Tanks, Process Vessels and Equipment
Data Sheet 7-98, Hydraulic Fluids
Data Sheet 7-78, Industrial Exhaust Systems
Data Sheet 7-99, Heat Transfer by Organic and Synthetic Fluids
Data Sheet 7-101, Fire Protection for Steam Turbines and Electric Generators
Data Sheet 9-0, Asset Integrity
Data Sheet 13-24, Fans and Blowers

APPENDIX A GLOSSARY OF TERMS

See Data Sheet 7-111, Chemical Process Industries.

APPENDIX B DOCUMENT REVISION HISTORY

The purpose of this appendix is to capture the changes that were made to this document each time it was
published. Please note that section numbers refer specifically to those in the version published on the date
shown (i.e., the section numbers are not always the same from version to version).
January 2023. Interim revision. Minor editorial changes were made.
October 2020. This is the first publication of this document.

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