_________________________________________________________________________ PAPER 2E

Mechanical Integrity Best Practice for Sulphuric Acid Plants

Michael Robert Beaumont

Assistant Vice President, Group Manager Field Engineering FM Global - Australian Operations

Level 15, 255 George Street, Sydney, NSW 2000 Australia Phone: +61 2 8273 1421

michael.beaumont@fmglobal.com

© 2006 Factory Mutual Insurance Company. All Rights Reserved.

Abstract In applying the principles of process safety management to a sulphuric acid plant, Process and Equipment (Mechanical) Integrity is one of the most important elements. The harsh operating environments that exist throughout an acid plant result in the need for careful attention especially to reliability engineering, materials selection, good operating principals and especially good maintenance regimes. Extensive downtime for sulphuric acid plants is really not an option for any company operating one. In most pyrometallurgical smelter complexes, loss of the acid plant would immediately necessitate shut down of the entire plant due to pollution concerns. Where acid is used as a raw material (e.g., fertiliser industry, hydrometallurgical metals production) or regenerated in the chemical process industry, the interruption of raw materials would have an immediate effect on downstream processes. Of particular note, in the metallurgical processing industry, there is a noticeable shift from acid producers (pyrometallurgical processes) to acid users (hydrometallurgical processes). This is resulting in a reduction of available and relatively cheap smelter acid. In turn there has been a large increase the value of sulphuric acid. Because of the issues noted, the drive to improve plant availability and avert catastrophes that could result in long term plant outage is of paramount importance to the industry. Although some industries (such as the Florida fertiliser industry) have gone a long way to developing best practice, there is a need to consolidate these best practices across all industries, especially new hydrometallurgical plant operators now operating large sulphur burning plants. This paper looks at some best practice maintenance and operating procedures for sulphuric acid plants within the scope of mechanical integrity. More specifically, it breaks down the analysis of the plant into six key elements: Environment, Operating Conditions, Age/History, Maintenance, Operators, Safety Devices, and Contingency Planning. The overall goal is to open up a discussion on best practice for the industry. 1. Introduction Sulphuric acid is an extremely important industrial chemical, probably one of the most important in the world. Currently, about 37.9 million tonnes of sulphuric acid is produced worldwide. It is

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used to manufacture a wide variety of other chemicals from fertilizers to pharmaceuticals. It is also used in a variety of important production processes from impurity removal to metal ore leaching. Approximately 70% of the sulphuric acid used is for the manufacture of fertilisers. Most of this acid is produced by sulphur burning plants on-site. The next most important producer would be metallurgical smelters, whose production ranges between 10-15% world-wide. Although demand for sulphuric acid had only been increasing at a rate of about 1% per year in the USA over the past several decades, the rate is now close to 10% and international figures are similar. Subsequently, the price of acid has been driven up substantially (40% in 2004) and the high price and demand appears to be increasing with further rises likely (but more likely on the 10% level). This appears to be especially true with the apparent rise in demand in China. The fertiliser industries in Florida, the traditional major consumers, have been expanding their own on-site capacity to make up for a decrease in the supply of both smelter and merchant acid and the subsequent price increases. The usage of sulphuric acid in a range of new and different industries is also growing. The growth of smaller speciality usage is approximately 3.5% per year. Also, up until the late 1990’s, smelter acid production was increasing by about the same amount and actually reducing in many areas due to the low metal prices leading companies to shut a number of smelters. This brings rise to another trend that is being noticed - the shift of smelter acid from primarily being sold to market, to being used for hydrometallurgical processes on site at the mines/smelters themselves. This is not too surprising because the primary producer of smelter acid has been the copper industry (about 90% of the total in the USA), since its use of heap leaching of copper ores is largely on the rise. High pressure acid leaching processes, used primarily in the nickel/cobalt industry, are also beginning to use much more acid. The daily acid usage is significant and the supply must be readily available, thus resulting in primarily on-site sulphur burning acid plants at these locations. As this paper is not focussed on the financial trends in the sulphuric acid industry, then what is the relevance of presenting this information? The reason relates directly to risk management. Although the safety and environmental aspects of the risks of these plants is critical, they do not stand alone from the business risks – primarily risk of business interruption as a result of an event that causes a plant shut down. Such risks increase dramatically in surging markets like those now being seen with sulphuric acid. Risk can be defined as the product of frequency and consequence. Both are affected dramatically in surging markets. The increase in consequence is obvious – there are more dollars to be lost when the market price is high. The increase in frequency may be less obvious, but it is there all the same. With increasing prices, suppliers will push the plants harder; relax turnaround schedules, and do what is needed to increase production as much as possible. New production plants that are built during these strong markets are built faster and brought on line quicker – construction constraints that can increase the chance of an error in installation or early term operation. These risks are not limited to the sulphuric acid industry. They are trends that are noticed in all industries in strong market conditions. With that said, their impact can be and often is drastically reduced or eliminated with good risk management. And the cornerstone of good risk management for a chemical plant should be based on strong process safety management (PSM) principles. So, it is very important to acknowledge that a sulphuric acid plant is just that – a chemical plant. The process of making sulphuric acid is based on three relatively straightforward equations:

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S + O2 = SO2 [1]1 SO2 + ½ O2 = SO3 + Heat [2] V2O5 Catalyst

SO3 + H2O = H2SO4 + Heat [3] In the scope of chemistry, none of these reactions are overly complex. However, controlling these relatively simple reactions is far from simple. Sulphur dioxide and sulphuric acid are corrosive and difficult to handle, sulphur trioxide intermediate is highly reactive and far from stable, and the amount of heat generated by these exothermic reactions requires special consideration. Balancing all of these issues together and the big picture is complex. That is why it is extremely important to consider this as a complex chemical process – and subsequently to manage it accordingly. There are many excellent resources available on establishing a strong process safety management program for a plant and any sulphuric acid plant operator is very much encouraged to search these out and apply them. However, one element of PSM stands out as extremely important in regards to sulphuric acid plants – Process and Equipment (Mechanical) Integrity. That is what this paper will endeavour to address in a specific manner. The experience of FM Global (Factory Mutual Insurance Company) has shown that when looking at issues of mechanical and electrical integrity, is best and most practical way to address any piece of plant is to look at it in relation to six key elements - Environment, Operating Conditions, Age/History, Maintenance, Operators, Safety Devices, and Contingency Planning. These elements are the key components that link together to produce many of the mechanical and electrical insurance losses seen throughout industry. It is the specific application of these elements to a sulphuric acid plant that will be the primary focus of this paper.2 2. Process and Equipment (Mechanical) Integrity Equipment that processes hazardous materials, as well as the accessory or utility equipment that is important to continued operation of the plant should be designed, constructed, installed, operated, protected and maintained in a way that minimizes the risk, while providing process reliability. This statement is the basic principle of the mechanical integrity element of PSM. In reading it, it becomes obvious that it is something that can be fully applied to sulphuric acid plants. The components of a successful mechanical integrity system are: reliability engineering; materials of construction; fabrication and inspection procedures; installation procedures; 1 Reaction [1] is only applicable to sulphur burning plants, where raw sulphur is burned to produce acid. It is substituted with the roasting of a sulphide ore in the case of metallurgical plants and with the burning of spent acid or hydrogen sulphide in spent acid regeneration plants. Hazards applicable to metallurgical smelting and spent acid regeneration processes upstream of the gas cleaning plants (i.e. primary scrubber) are not within the scope of this paper. 2 It should be noted that this paper has been written from the perspective of the property insurance industry and therefore focuses on issues related to property damage and business interruption. Although life-safety issues are not the focus of the paper, reducing the potential of any property damage event will ultimately render a plant safer in all aspects.

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preventive maintenance; process, hardware, and systems inspection and testing; documented maintenance procedures; alarm, instrument, and safety device management; and demolition procedures. This is the traditional approach to mechanical integrity. However, as described, we will look at this from a slightly different viewpoint, using the six elements already mentioned. These items cover all aspects of mechanical integrity along with other concepts. As noted previously, risk is the product of frequency and consequence. Environment, operating conditions, age/history, maintenance, and operators are elements that impact the frequency side of the equipment risk equation. Safety devices and contingency planning are elements that impact the consequence side of the equipment risk equation. The remainder of the paper shall now focus on specifically exploring these elements as they directly relate to sulphuric acid plants. Figure 1, 2, and 3 are typical simplified sulphuric acid plant flow sheets. These have been included to provide a reference point for the terminology used in this paper.

Figure 1. Typical Flow Sheet for a Metallurgical Sulphuric Acid Plant

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Figure 2. Typical Flow Sheet for Sulphur Burning Acid Plant

Figure 3. Typical Flow Sheet for a Spent Acid Regeneration Plant

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Legend for Figures 1-3

1. Primary

Scrubber/Venturi 2. Gas Cooling Tower 3. Scrubber/Impurity

Removal 4. Wet Electrostatic

Precipitators (WESP)+ 5. Drying Tower 6. Blower

7. Gas Pre-heater 8. Converter 9. Cold Pass Gas-to-Gas

Heat Exchanger 10. Hot Pass Gas-to Gas

Heat Exchanger 11. Interpass/Intermediate

Absorption Tower

12. Final Absorption Tower

13. Stack 14. Air Filter* 15. Sulphur Burner*

16. Combustion Chamber** 17. Boiler**

+ These are also known as Cottrells after their inventor – Dr Frederick Cottrell * Sulphur Burning Plants ** Spent Acid Regeneration

3. Frequency 3.1 Environment The operating environment and conditions surrounding equipment relate primarily to outside temperature, humidity, cleanliness, facility siting, and natural hazard exposures (e.g. flood, wind, earthquake, hail, etc). Typical sulphuric acid plants operate as outdoor structures that are exposed to many elements, so the effects of temperature and humidity (primarily atmospheric corrosion issues) are either limited or accounted for in the design. However, as time goes on there are always going to be issues related to small excursions of sulphur dioxide/trioxide, and acid that can accelerate the deterioration of the plant. Limiting damage from these things is largely a function of proper design, good maintenance, and good operators. It is important to consider that any major upset can result in a major sulphur dioxide or trioxide release from the stack. This can send a blanket of acid over the entire plant and surrounding area, but controlling this is a matter of good operating conditions, maintenance, and operator actions. Having a good cleaning program is a fairly straight forward process and really no different from any other industrial facility. A regular program of cleaning up acid spills will lengthen the life of any exposed steel or concrete. Daily checks to determine if there are small excursions is going to allow for faster maintenance or operator actions that will ultimately reduce the chance of any small excursion progressing to a larger event. It is especially important to maintain a high awareness for potential corrosion under any external insulation. General good housekeeping has obvious benefits ranging from reduced corrosion to lessening fire exposures to critical equipment (especially fibreglass reinforced plastic [FRP] equipment normally found in abundance in the gas cleaning sections of a metallurgical or spent acid regeneration plant). There are some specific cleanliness issues to take into account for a sulphur burning plant. In most places where sulphuric acid plants are located, the surrounding conditions can be harsh with significant particulate matter in the atmosphere (especially in locations associated with mining operations). Dust that enters the system can contaminate the acid and also build up between the catalyst nodules in the converter and reduce the overall capacity of the system. Dust can have fluoride and chloride constituents. Although not a common event, fluorides can attack silica acid bricks, mist eliminators, and catalyst supports if they get into the system. Therefore, a

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proper dust filter is needed on the intake to the blower. The most desirable type of filter is a continuous belt filter with a pressure monitor that signals the belt system to change the filter at the appropriate time. Filters that require manual changing are less desirable as they can reduce efficiency if not changed on a suitable interval. Also, there can be a temptation to remove several filters to improve air flow, with the possibility that they will be left out for long periods.

Dust and other contaminants can also enter the plant via dirty sulphur. Although indoor storage is the most desirable way to control this, it is often not practical and outdoor storage is necessary. With outdoor storage, the amount of bulk sulphur should be kept to a minimum. Outdoor storage locations should be chosen such that they are not subject to prevailing winds (loss of sulphur) and to reduce the amount of dust/contaminant that can migrate to the piles. This may require the provision of wind barriers, water sprays, or coating with molten sulphur (for longer term storage) if there are no natural barriers present. Care needs to be taken with water sprays to control the amount of moisture in the sulphur as it can increase energy costs and cause foaming in the sulphur melter. The addition of special water based chemical surfactants may be a solution to minimize this. The location should be chosen so that it is upwind of any dust producing source. When sulphur is stored on the ground, preferably it should be on a concrete or asphalt pad. If this is not done, the first 200 mm of the pile will need to be considered the sacrificial base and not used to feed the plant. Sulphur filtration is recommended after the melter in any plant to reduce contaminant entry, but is all the more important when outdoor storage is used. An alternative to sulphur filtration is a settling pit designed with sufficient residence time to allow suspended solids to settle out of the molten sulphur, however, a larger area will be needed to accommodate the settler pits.

Facility siting is something that can greatly alter the environment of the plant. So, as with any other chemical process unit this should be considered with the principles of process safety management in mind. Exposures to fire, explosion, transportation (aircraft, motor vehicle, rail, ship), and tank farms should be limited. There are also some things in regards to the plant layout that need to be considered. In an effort to conserve space, things like motor control centres and blower rooms may be placed beneath absorption or drying towers, or heat exchangers. There have been cases of leakage from this equipment that makes putting sensitive and important equipment beneath or near them an undesirable option. Suitable bunding and containment should be provided for any area where there is a potential for acid spillage. All foundations should be able to properly resist sulphuric acid (e.g., avoid limestone fill). The keys to ensuring a good operating environment are to maintain the atmosphere free of potentially damaging substances (which is what a metallurgical plant in particular is designed for) and keeping potentially damaging exposures well separated. The aforementioned is going to be relatively easily controlled if the frequency issues covered in the rest of the paper are well managed. The latter is largely going to be subject to the good design of the plant. If the design has not allowed for protection against some of these exposures, then it is all the more important to ensure excellent management of issues related to consequence.

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3.2 Operating Conditions

It is important to compare the actual operating conditions with the design conditions. It is really something that needs to be looked at in three stages – first to assess the suitability and quality of the original design, then to assess whether those initial design criteria still apply (i.e. a measurement of change management), and lastly whether the current operating parameters are in line with the original or modified design. In relation to the traditional mechanical integrity issues, this is very important because it addresses reliability engineering, and materials of construction and fabrication. The best way to begin a discussion on good plant design would be with a quote from John Ruskin (1819-1900), a prominent 19th century English critic who was an astute observer of social and economic issues: “It is unwise to pay too much. But it’s worse to pay too little. When you pay too much, you lose a little money, that is all. When you pay too little, you sometimes lose everything, because the thing you bought was incapable of doing the thing you bought it to do. The common law of business balance prohibits paying a little and getting a lot. It can’t be done. If you deal with the lowest bidder, it is well to add something for the risk you run. And if you do that, you will have enough to pay for something better.” Yes, the old adage that ‘you get what you pay for’ could not be truer than for a chemical process with harsh and often deleterious operating conditions. From alloys to candle filters, blowers to lining bricks – all are going to be subject to a harsh environment. Some parts of the system will need expensive materials designed to operate over a long period, while the only feasible alternative in some areas is to treat some components as consumables and replace accordingly. For a typical sulphuric acid plant, the difference between a first class plant and providing the absolute minimum is only about 3-5% of the total capital. The most important design issue is going to be the choice of the proper materials of construction. Each plant will have different conditions to consider and the range of materials is quite significant. There is an immense amount of information on this subject and no one paper could ever properly cover the topic. So, some issues are addressed here in regards to common best practices. Refer to Table 1 for a summary of some recommended best practices for material selection, a general reference based on common designs and recommended best practice. Careful study of the suitability of the material must be done before specifying it for any application in a sulphuric acid plant.

Once the materials have been chosen, it is critical that they remain the same through the life of the plant. If there are changes, metallurgical studies should verify that the new materials remain completely compatible. So, a strong program for monitoring physical metallurgy issues needs to be in place. This should be factored into the Management of Change procedures. The remainder of this section deals with specific design issues relating to various parts of the plant.

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Table 1 – Recommended Materials

Equipment Preferred Materials Materials to be Avoided Entire Plant - sulphuric acid usage

904L SS, 254 SMO, C-276, Alloy B-2/33, zirconium, tantalum, titanium4

Copper, Brass, Bronze5, Alloy T316SS6, Alloy 400, 316L7, Cast Iron cannot be used in any oleum service

Entire Plant – instrument seals8

304 SS, 316 SS, Hastelloy C (alloy C-276), tantalum, Carpenter 20, Nickel 200, Monel 400, Inconel 600, viton, Buna N, neoprene.

Primary Scrubber/Quench Tower

- Carbon steel with fireclay9 brick lining with furan mortar and 5 mm thick chlorobutyl rubber underlay - high nickel alloys - Quench nozzles – Silicon iron10, Hastelloy C-276, G, X, Alloy 20, stainless steel, PTFE11

FRP

Wet Electrostatic Precipitators

- Lead12 - FRP shell with conductive FRP tubes/PVC tubes with liquid running down surface13 - 904L Stainless Steel

Blower Casing – Grey Cast Iron Impeller – AISI 4130, StE 460, X 5 CrNi 13 4

Converter - Cast iron, carbon steel, and Meehanite - Metallise all such surfaces subject to temperatures >430ºC with aluminium - 2nd bed up – Chromium-Molybdenum steel or use insulating brick. - 304, 304H SS14can be used with no lining or aluminising.

- 304L SS15

Gas-to-Gas Heat Exchangers and associated duct work

Temperature dependent as follows: Up to 450ºC – Carbon Steel 450ºC-480ºC – metallised carbon steel. Above 480ºC – 304/304H, 316L SS or other CrMo steel

Absorption and Drying Towers

- Carbon steel shell, with sheet Teflon®, acid brick (2x95 mm layers) lined16 - Lining bricks – preferably ASTM 279 Type 3 - Halogen-free potassium silicate mortar - Ceramic beams (e.g. Aludur 11) - Filters on drying tower stainless steel or alumet - Shell material austenitic stainless with 4.5% silicon & some calcium17 - Tower packing 80 mm ceramic saddles.

3 In absence of oxidising ions such as cupric, ferric, and fluorides 4 Titanium performs well with cupric, ferric and nickel oxidising atoms present as corrosion inhibitors. 5 Copper, Brass and Bronze perform extremely poorly in sulphuric acid service and need to be avoided in all cases. 6 T316SS Readily attacked at elevated temperatures and pressures especially in dilute (<30% acid) 7 Not used for wetted parts 8 Utilities such as air, water, steam, cooling water, process water do not require chemical seals. 9 In the presence of fluorides, carbon brick can be used on the exposed layer with a less expansive red shale brick below with a thin layer of carbon filled furan mortar trowelled on between the red shale and carbon brick. 10 Good chemical resistance, but brittle. 11 Good chemical resistance, but lacks mechanical strength at high temperatures. 12 Where internals are lead, a homogeneously lead lined tube sheet is preferred. 13 Need to consider fire protection with FRP. 14 Generally an ideal material, but need to consider that at temperatures >540ºC, scaling can occur. 15 Maximum allowable stress values are for maximum temperature of 426ºC. 16 See comments above on acid bricks for quench tower. Mortar would be different as these towers would be handling strong acid. 17 E.g. Sandvik SX® or Seramet®

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Table 1 – Recommended Materials - Chlorobutyl rubber lining beneath acid bricks

Acid Coolers Plate coolers – 316L SS w/anodic protection, Hastelloy – C-22, C-276, D-205, Cronifer 2803 Mo, Alloy 33, Viton seals Shell & Tube coolers – 316L SS w/anodic protection, high Si SS (e.g. Sandvik SX®), Seramet®, ZeCor™

Acid Pumps Wetted pump parts - Alloy 20 or Teflon®-lined Acid Storage Tanks (including pump tanks)

- Carbon steel18, 304SS, 316SS, Alloy 20, or Teflon® coated19. Hastelloy® B and C20

Strong Acid Piping

- Dependent on fluid flow velocities. In general21 (at ambient): 0.3-0.5 m/s: seamless carbon steel piping 0-1.8 m/s – 304/304L SS 0-2.4 m/s – 316/316L SS 0-3 m/s - Mondi™ 2-3 m/s – Sandvik SX® 0-6 m/s - Alloy 20 0-15 m/s - Teflon® & Kynar® lined - Teflon® PTFE-lined hose with 316SS crimped or swaged end fittings and virgin Viton® B gaskets22 - Mondi™, Meehanite, Sandvik SX® Ductile Iron, and Grey cast iron all have some application as well. - Valves – Alloy 2023, lined carbon steel, ductile iron, 316 SS, CDM4Cu, Durimet 20, Durcomet 5/100, Lewmet, DIPA-PFA coated Ni plated ductile cast iron

- Carbon steel for pump tank roofs. - Carbon steel when iron contamination is a concern. - Plastic materials should be avoided wherever possible if there is a potential fire/high temperature exposure. - PVC and CPVC for vent/vapour lines only

Strong Acid Instrumentation

- wetted parts should be Alloy 20 or Teflon®-lined - Vitreous sight glasses.

Heat Recovery Systems

- <400ºC, 450 kPa – carbon steel tubes24 - >400ºC, 450 kPa CrMo stainless steel tubes25

Sulphur Equipment

Melter: Internal – 316SS26, Shell – Carbon Steel, Heating tubes –carbon steel27

18 Acid concentrations of 77-98% (absolute minimum – 70%). Tank corrosion allowance should be 4 mm 19 These alternatives would be used when iron contamination is an issue. Stainless steel acceptable for 100% sulphuric acid - carbon steel is not. Stainless steel is also preferred at low (<20%) acid concentrations. Stainless steels more resistant to hydrogen grooving. 20 For most strengths of acid, but at significant cost (~6x carbon steel). 21 The numbers given here are rules of thumb. 22 For 93-98% acid concentration. They should be designed and hydrostatically tested for a pressure 3.5 bar higher than maximum working pressure, but not less than 14 bar and be full vacuum rated. 23 Plug valves or full-port ball valves. 24 Stainless steel still preferred. 25 Stress corrosion cracking is common so proper bend radius, proper stress relieving etc. should be ensured. 26 Corrosion allowance 3 mm/year 27 Schedule 80

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Gas Cleaning Plant: There are certain designs that do not use wet electrostatic precipitators based on the efficiency of the primary scrubber. There have been issues with the design efficiency matching the actual efficiency. So, it is preferable to include wet electrostatic precipitators (WESPs) in all designs. If a design without WESPs is used, ensure that proper operation has been proven before the plant goes fully on-line. It is acknowledged that there are many designs of all types of gas cleaning plant equipment that use FRP, but there is quite a lot of history of melting or deforming primary scrubbers made of FRP due to over-temperature. If the structure is FRP, then the primary design issues will be either providing protection from over-temperature or sparing. In many traditional designs, this will be an FRP structure with an overflow weir to protect it. Overflow weirs do not provide uniformly wetted surfaces and can result in melting and warping. Interlocks to shut down in the event of temperature excursions can be installed, but this is still not an intrinsically safe design.

Another important issue to consider, especially as it relates to properly understanding the process chemistry is the ‘add-ons’ that are often used for impurity removal. These systems often introduce volatile chemicals that are significantly more hazardous than anything else on site (e.g. ammonia, hydrazine, hydrogen peroxide). Discussion of the particular hazards associated with these is outside the scope of this paper, but careful consideration is critical.

Blower:

For any blowers taking suction after the drying tower, the design of the feed ducting is very important. First and foremost, everything that can be done to limit acid carry-over into the blower should be done. Primarily, that will mean installation of the highest efficiency mist eliminators possible on the drying tower. However, this does not negate the need for good blower feed duct design because there will always be a potential for the condensation of acid in the feed that could damage the blower. Ideally, this would mean a straight feed duct of 5-10 diameters leading into the blower. From a practical point of view, this does not normally occur. However, with some simple design changes in the feed duct, the ingress of condensate to the blower can be controlled to acceptable levels. This is achieved by installing a small lip in the downward duct to deflect condensate on the pipes into a knock-out pot. The knock-out pot will also catch entrained acid condensate that is knocked out by the change in direction. This is shown in Figure 4.

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Figure 4. Good Blower Feed Duct Design Schematic and photo showing external of similar design (Courtesy of Sun Metals)

In addition to reducing the amount of acid carry-over by the methods above, the blower needs to be slightly over-designed to account for the normal levels of corrosion and wear expected over the life of the unit. Typically, and over-design based on 5% of the normal flow is specified. Depending on local conditions, it may be justified to go as high as 10%. Open radial bladed impellers are ideally suited for dirty gas, corrosive or high head applications. Blowers with back-leaning blades and enclosed impellers can also be used where higher head applications are needed. The key is not to under-design the impeller because it will result in cracking. Purchasing a tried and tested design that has been proven prior to delivery is the best practice. This is yet another key area where the prior quote from John Ruskin applies quite aptly.

Material selection will vary widely between sulphur burning plants, where the blower is not in the sulphur dioxide stream, and other plants where it is. Even then, the material selection can vary widely depending on the constituents in the gas. Table 1 offers some example materials but does not represent an exhaustive list. As noted above, it is important to over-design the blower and this would extend to allowing for corrosion as well – especially with the casing, which is not commonly spared. Normally a corrosion allowance of 3 mm/year is used.

Other important considerations regarding blower design include:

• There should be no critical speeds within the normal operating range of the blower. • Use inlet guide vanes to control the blower output when the blower is driven by a

constant speed device such as an induction motor. Otherwise a variable speed drive is suitable.

• Properly seal the shaft of the blower where it exits the casing to prevent the escape of process gas.

• Prior to delivery of the blower, a hydrostatic pressure test of the compressor casing, dynamic balancing of the rotating element at reduced speed, a running test with shop driver at full speed and reduced load, and an impeller over-speed test should be conducted..

Knock-out pot collection point

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Pre-heater: Consider the combustion reaction for natural gas:

CH4 + 2O2 = CO2 + 2H2O [4] Oils can also be used for pre-heating, but the products of combustion are similar. What needs to be acknowledged is that if there is poor combustion, either explosive methane or excess moisture could be introduced the plant. Therefore, it is important to design the turn-down ratio properly. This will be specific to the burner design. However, for natural gas and light fuel oils you would typically specify 8:1. For heavy fuel oils, it would typically be 6:1. This equipment should be provided with all the safeguards that would be expected on any other fuel fired systemi. Because the burner units are not used continually, they are often not left in situ. In these cases, it is important to store the burner assembly in a suitable place out of the elements. To reduce the ingress of moisture, a duct interlock should be provided to exhaust combustion products to atmosphere rather than into the plant. Converter/Catalyst Beds: Proper materials selection to accommodate the expected temperature ranges is extremely important to prevent bulging of the shell, bed collapse, pregnant converters, and bed separation. Although high carbon stainless steel (becoming the material of choice) can be used to allow for a higher temperature range, scaling does occur when temperatures exceed 540ºC. This scale can block the catalyst bed as it falls off and may result in the need to shut the plant down to sift the bed as often as every 6 months. So, metallising (providing a thin metal coating such as aluminium) could also be a consideration. This could even extend to stainless steels. Not only is the proper material selection important, but also the proper fabrication. Bed collapse incidents, for instance, have occurred as a result of poor welding. Also, if consideration is not given in the design phase for the proper plate thicknesses, additional stiffeners may be needed to account for cut-outs required for the core tube. Gas-to-Gas Heat Exchangers/SO3 Coolers: Because the cold pass heat exchanger experiences the lowest temperatures in the plant, it is the first to succumb to possible condensation events. So, these units are usually designed based on the low gas operating condition or the autothermal condition. At the lowest gas strengths, the reaction from conversion of SO2 to SO3 will be at its minimum and therefore the heat from the reaction will be at its minimum, resulting in the lowest temperatures. Keeping a suitable buffer between this temperature and the acid dew point temperature is very important.

Consideration also needs to be given to the effects of intermittent operation (e.g. a copper smelter where the gas is usually only present during charging or slag tapping). The design needs to consider this and allow for the flow of process gases through the heat exchanger only with no gas sent through the SO3 Cooler. This will result in temperature differentials that will need to be accounted for in the mechanical design of the units as well.

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Over the life of the plant it is unlikely that all operating condition excursions will be avoided. Therefore, it must be assumed that some condensation will occur. Also, there will be some mist carry-over from the towers. So, in addition to gas flow and mechanical design considerations, careful consideration should also be given to the material of construction. The material of choice for these units is normally carbon steel because the acid concentrations tend to be well above 77% and they are not normally handling liquid. However, the loss of one of these units will usually result in the acid plant being shut down. This has occurred in the past and caused significant problems for a number of operators. Based on this, it is highly recommended to consider alternative materials like Chromium-Molybdenum (CrMo) stainless steels or at least metallising.

As noted, carry-over from absorption towers is not uncommon in these units and it usually collects in the bottom of the unit. There needs to be a way to monitor and drain this acid at regular intervals. The ideal way to do this is to provide a knock-out pot system that can be checked regularly (see Figure 5). Ideally, this should be set up to be monitored on-line as part of the process control system. Another drain line should also be provided above the tube sheet as shown in Figure 5. This should be checked regularly as well. Running this into a knock-out pot as well would provide the ability to monitor on-line.

Figure 5. Gas-to-Gas Heat Exchanger Acid Drains (Photo courtesy of Sun Metals)

Drying & Absorption Towers: There is another area of the plant where the above quote from John Ruskin distinctly applies – mist eliminators and candle filters. These items are most critical in the drying and absorption towers, however, these principals extend to all mist eliminators used throughout the plant. High efficiency mist eliminators (i.e. designed to remove 100% of particles greater than 1 micron and greater than 99.5% of all particles less than 1 micron) are something that should be as a matter of preference for all applications. However, there will be situations where energy saving type filters

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will be desired to reduce pressure drop across the plant. In spent acid regeneration and metallurgical plants, there should at least be a commitment to only high efficiency eliminators prior to the blower.

Drying and absorption towers should be designed with a dish bottom, which are much easier to brick. If the tower has a flat bottom, an expansion joint needs to be provided at the bottom to allow it to move with changes in temperature without displacing the lining bricks. Flat bottom towers tend to have many more problems with leakage through the bricks to the shell at these points.

The choice of lining bricks and liner is also important in preventing acid seepage through to the shell. Ideally bricks with acid porosity less than 1% should be chosen. ASTM type 3 bricks will provide that and provide a lower porosity for the minimal cost differential to Type 2 bricks. The need to minimise leaks through brick and mortar porosity is especially true of towers with carbon steel shell construction. If there is seepage, the shell steel will corrode forming iron sulphate between the lining and the core, which can cause bulges. This is more common around inlets and outlets. Any one instance of this is unlikely to interrupt production because these can be cut out and repaired. However, ongoing leakage can result in a situation where the tower may have to be brought off line earlier than scheduled. Unlined towers can be used with carefully chosen alloys; however, the allowance for excursions from design operating conditions is much more limited than with lined towers.

Packing is normally 3-3.6 m thick. Thicknesses up to 4.6 m are used in some plants to increase the efficiency of acid distribution and prevent sulphur trioxide carry-over. Acid must be fed in below the packing surface. Normally, the design strives to achieve about 0.1 kPa pressure differential over the tower. Ideally in the packing, there should be a minimum of one acid distributor per 0.1 sq m. Some designs use up to five. Distributor pipes need to be large enough to ensure that they are not blocked. There are certain designs that do not use a drying tower based on the efficiency of the gas cleaning plant. At these plants, there have been issues with the design efficiency matching the actual efficiency. So, it is preferable to include drying towers in all designs. If a design without a drying tower is used, ensure that proper operation has been proven before the plant goes fully on-line. Acid Cooling: Where there is an interface between cooling water system and strong acid systems, the hazard of mixing the acid with water is there. There have been cases where minor leaks have occurred, progressively grown to major leaks, and large amounts of acid have mixed with water with explosive effects due to the high heat of mixing. In order to get around this, the pressure in the acid side needs to be kept higher than the pressure on the water side to allow only acid to flow into the water system. The pH of the cooling water can then be easily monitored and action taken immediately should a leak occur. Consideration can be given to anodic protection to reduce the chance of corrosion issues. However, it can be difficult to install, especially for air-cooled heat exchangers. The best possible way to deal with corrosion issues on acid coolers is to choose the best possible material for the conditions.

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Acid Pumps, Pump Tanks, and Piping:

When sulphuric acid first contacts carbon steel, iron sulphate (FeSO4) is produced, coating the steel and forming a "passivating" film which protects the carbon steel from further corrosion. Hydrogen gas (H2) is also produced according to this reaction.

Fe + H2SO4 = FeSO4 + H2 [5] With carbon steel, if the velocity is too low, then reaction [5] can occur, producing hydrogen gas. The hydrogen gas bubbles will float and scrape off the iron sulphate coating, exposing bare metal. This will form more iron sulphate and more hydrogen bubbles. The bubbles tend to follow the same track, exposing more bare metal. Eventually the metal will have grooves corroded/eroded into the surface from the repeating cycle, which is termed hydrogen grooving. So, it is important to both choose the correct materials and ensure that proper velocities are maintained. There may even be a need to consider hydrogen detection in tanks if there has been a history of hydrogen grooving.

Similar to the effects of hydrogen grooving, overly high velocities will not allow the iron sulphate passivating layer to form. Whether in pump tanks or piping, turbulence should be prevented that can cause this. In order to keep the velocity/turbulence in the pump tank to a minimum, the feed should be beneath the surface and well off the walls. Acid flowing down the tank walls and erosion-corrosion caused by turbulence both can result in hydrogen grooving. Pump tanks should be either a vertical cylindrical tank with dish bottom or a horizontal cylindrical tank. A centrifugal, seal-less magnetic-drive pump is the preferred pump for sulphuric acid transfer. Piping materials should be selected based on conditions (Table 1). All metal piping should be welded per established standards and specificationsii. Screwed fittings should be avoided. Sight glasses should be limited, but when used, they should be protected from mechanical damage.

There is a significant heat of dilution when sulphuric acid is mixed with water. With water feed into the tank to control concentration, the flow rate should be the minimum possible. The water feed flow valve should be interlocked with a concentration monitor. Similar to fuel fired equipment, a double-block arrangement on the water line is recommended.

Sulphur Furnace: A good sulphur furnace design is going to achieve the best possible gas mixing and most importantly, the full combustion of sulphur prior to leaving the furnace. This is not only important to the efficiency of the plant, but also in limiting moisture produced in the combustion reaction. Cold shell and hot shell designs both have their advantages, each depending on the conditions at the location. Cold shell design will minimise shell expansion, but allow for some corrosion potential at the brick/shell interface due to condensation. Hot shell designs will have larger shell expansion, but the internals will be above the gas dew point and reduce the chance of any internal corrosion. To provide sufficient residence time and complete combustion, good practice would be to size the furnace for about 0.1 m³/tonne per day of acid production based on 12% sulphur dioxide, with a length to diameter ratio of 2:1 to 4:1. Insulation is required on the tank to minimize heat loss. A detailed engineering design is needed to properly take into account

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all the site specific issues. High efficiency sulphur guns are recommended. It is important to maintain temperature in the proper range as well to ensure proper viscosity. This entails both maintaining the furnace at proper temperature and ensuring that all lines and pumps are heated.

Heat Recovery Systems: Any sort of steam generation (waste heat boilers, economisers, or proprietary heat recovery systems) within an acid plant presents a unique exposure where water (in steam or liquid form) can be introduced into the system. This can upset the water balance and dew points. Fairly straightforward pH monitoring systems can be used to monitor acid water interfaces in acid coolers, but for obvious reasons something this simple will not work in the steam application. The most important thing to do with a heat recovery system is to carefully and strictly follow all of the manufacturer’s recommendations. This extends not only to design, but also operating the plant within the recommended ranges (e.g., temperature, pressure, and acid concentration ranges). General Operating Parameters: The most critical aspect is the control of moisture, most of which is generated in the absorber system. In a metallurgical or regeneration acid plant, considerably more water enters the absorbers because it is delivered from the gas cleaning system. To avoid excess moisture being introduced (especially to the gas to gas heat exchangers), careful balancing must be maintained. As noted, special care needs to be taken in managing the combustion process as well.

To monitor these conditions requires instrumentation. Instrumentation will include pressure monitoring, transmissometers (opacity), dewpoint monitors, photometric meters (dust and acid mist), corrosion monitors, and pH monitors. There are some basic things that should be adhered to in regards to instrumentation. It is always preferable to use instruments that draw gas from the system instead of working directly in-line. In-line instruments cannot be removed during operation for calibration, maintenance and repair without having to shut down the plant. Also, the seals on in-line instruments are subject to harsher conditions and can fail more readily.

The acid dewpoint is probably one of the most critical conditions to monitor. It is extremely important that this is monitored at the exit of the Cold Pass Heat Exchanger to Absorber Tower and the exit of the Hot Pass Heat Exchangers to Absorber Tower (Economizers/SO3 Coolers in parallel). Not only is this critical in minimising the condensation of acid in these areas, it will also allow maximum heat recovery if such equipment is in use.

Blockage of the catalyst bed is an extremely important thing to monitor as scale can form in many ways such as high temperature scaling as noted, metallised coatings can flake off, and dust ingress can block the bed. If the bed becomes blocked and is not cleared, the blower can over-pressurise the system causing damage. Also, it has the potential to send the blower into a surge condition.

Refer to Table 2 for a summary of some key monitoring equipment and operating parameters.

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Table 2 – Important Operating Parameters/Monitoring Equipment Equipment Operating Parameters/Monitoring Equipment Entire Plant – instrumentation

- Instrument air dew point – variable based on lowest outdoor temperatures. - Measurement of sulphuric acid concentration: Conductivity (0-25%, 35-75%, 95-100%), Sound Velocity (60-100% & oleum).

Primary Scrubber/Quench Tower

- Over-temperature alarm set to maximum allowable working temperature for upstream plant28 - Overall temperature limit of 240ºC29

Wet Electrostatic Precipitators

- Provide sight glasses located 180° apart at the exit of the ESP which can be used to check the clarity of the gas. If present, acid mist will appear as a fog.

Blower - For steam turbine driven units, is water quality suitable (sodium analyser provided and set for 80 ppb or less)

Converter/Catalyst Bed

- No excessive pressure drop30 - Pressure profiling done once per day31 - Maximum catalyst temperature ~620ºC

Gas to Gas Heat Exchangers

- Dew Point – 140-180°C - Acid carryover concentration maintained between 99% and 99.9% - Knock-out pot level monitored and volume of acid measured).

Draying and Absorption Towers

- Final tower acid concentration maintained between 98.5% and 99%32 - High level contact probe (conductivity) in bottom of tower.33 - Ideally provide a sampling system with vacuum pump, pitot tubes, glass sampling tubes, etc. to monitor mist carry-over from towers. - Acid inlet temperatures can range from 50°C to 90°C - Outer wall temperature <60°C34

Acid Cooling - pH of the cooling water Acid Storage Tanks - Minimum possible temperature in tanks (Carbon Steel <40°C, Stainless Steel <50ºC,

Alloy 20 <60ºC, Teflon® coated <200ºC) - Minimum possible velocity/turbulence in tanks. - Level gauges (differential pressure cells, sonar probes, radar probes, capacitance probes, and floats). - Dry instrument air or nitrogen should be used for bubblers. - Hydrogen detection in tanks

Heat Recovery Systems

- Acid strength maintained between 99% and 99.9% - Water quality monitoring should be monitored by the process control system with suitable alarms.

Sulphur Equipment - Raw sulphur moisture content – 0.5-1.5%

- Molten sulphur temperature - 130ºC to 145°C (never to reach 158ºC35) - Sulphur pumps shaft free to turn and steam heating on before feed is started and ensure pump shaft is free to turn.

28 Redundant sensors (high and high-high) for FRP equipment at gas exit interlocked with protection system. 29 Where brick lined – this is the normal maximum operating temperature of mortar compatible with weak acid. 30 What constitutes excessive pressure drop is determined on a plant by plant basis, but should be a known parameter from the design. 31 Once per week would be acceptable if no unusual conditions. 32 This is a range - the optimum acid concentration must be found by operating experience 33 A brick dropped in the unit can block acid outlet. This can cause a wave that may damage the arch and drop the packing. This can also cause blower surge. 34 This is the maximum working temperature for most rubber linings. 35 158ºC is the temperature at which sulphur will caramelise and become impossible to pump.

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In summary, the key to ensuring good operating conditions is to get the plant design right in the first place. It is often going to be worthwhile to invest additional capital up front to achieve this. This is difficult in the economies of today’s turn-key projects; however, it is something that has proven to pay back many times over in the way of risk reduction. Unfortunately, it is difficult to measure things that are avoided, but recorded loss history alone demonstrates a definite trend in this area. Again, failing to do this may also have other cost implications down the line in form of costs to retrofit more expensive safety devices and an increase in emergency spare inventory (i.e. take steps to reduce the consequence of the risk). Once the plant is in operation, the focus then shifts to running the plant within the parameters of the design, which can and is achieved in many well run plants around the world.

3.3 Age/History Deterioration due to age or a past history of problems plays a major role in the mechanical integrity of the plant. It stands to reason that equipment that is within its useful design life and has a history of consistently good operation, is going to be of better risk quality than one where there is a lack of design details, the equipment is old/obsolete, and it is being operated beyond its design life, or has had past problems. These are truths that can be accepted about any equipment, and it is completely applicable to a sulphuric acid plant. The first thing to look at is whether the equipment exceeds its design life. What is the design life of the plant – is it commensurate with the planned duration of operations? Manufacturers sell similar plants with various expected life times (e.g. 5 year, 10 year, or premium plant for long term use). Most of the acid plants being built today have a planned period of usage of greater than 10 years and should really be designed with longevity in mind. Generally, sulphuric acid plants are not designed to operate more than 30 years without major refurbishments (i.e. all parts completely replaced/rebuilt at some stage in that period). For some parts of the plant, like carbon steel cold pass heat exchangers, it would probably be more realistic to work on a 15 year maximum design life for that part of the plant. In cases where no drying tower was provided in the design, after 5 years the plant condition should be monitored more closely. Action should be taken quickly whenever signs appear that indicate that refurbishment of part of the plant may be needed. Even if the plant is within its design life, consideration needs to be given to how the plant has been operated during that period. Has there been a history of excursions (e.g. pressure, temperature, acid concentration, excessive misting)? Has this resulted in an abnormal number of operating problems or unplanned repairs? If so, it is quite likely that the original design life of the plant can no longer be relied on. A typical sulphuric acid plant can probably go through about 25-30 cold starts before it needs to undergo a life study and major refurbishments. If there has been a history of excessive cycling (i.e. many stop/starts or turnarounds), then the plant may have become stressed beyond its useful life because the most onerous conditions that the plant sees are when it is starting up and shutting down. If this is the case, a life study will probably be needed. In general, a life study should be done for any areas of the plant that may have been affected by any major excessive moisture or acid condensation incident. Lastly, consider if the plant is a new or unproven design. Most sulphuric acid production provides feed stock for another finished product (e.g. fertilisers), or is used to get rid of waste (e.g., spent acid or sulphur dioxide from a metallurgical plant). Given the potential business

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interruption exposure to the main product of manufacture, it is advisable to remain slightly more conservative in the design of the sulphuric acid plant and adhere to tried and tested design. This is not to say that process efficiency improvements should not be considered, but rather that making slow and well thought out design choices in the sulphuric acid plant will benefit the entire operation in the long run. The idea of using only a tried and tested design should not only extend to the initial overall design, but also to the components used within the plant – from catalyst to candle filters. There have been a number of incidents where what was thought to be a suitable replacement or a like-for-like replacement has not been the case as the design of the actual component had changed. This highlights the need for strong management of change procedures that take into account all potential changes at the plant. Because of the relative simplicity of this concept (i.e., equipment wears out, especially under harsh operating conditions), this section has been relatively brief in comparison to others, but that does not reduce the overall importance of age and operating history. Sulphuric acid plants operate under a variety of harsh conditions and will ultimately need major refurbishments several times in their life. Also, it does not take that long for major implications to arise when an excursion from the operating design occurs. So, the key is to address problems quickly when they occur and action repairs and refurbishments as soon as they are needed.

3.4 Maintenance A good maintenance regime will follow the manufacturer’s requirements or equivalent and the procedures are documented and proven. It should be at a level commensurate with what would be expected at any high hazard chemical plantiii. It should also be predictive or preventive instead of reactive maintenance. Being a single line process, there is little in the process chain that can be allowed to fail. If the plant has been properly designed and is being properly operated, then over the life of the plant it is good maintenance that will most affect the ability to maintain the highest level of mechanical integrity. And it will not extend only to frequency (i.e. operational and process issues), but also to the consequence because having safety devices in proper working order and spares in good working condition are both critical to ensuring the consequence can actually be reduced if the need arises. Preventive and predictive maintenance both play an important role in sulphuric acid plants. Preventive maintenance is good for items where the wear/corrosion rate is well established, items that can be changed without taking the plant fully off line, or things that can be done during scheduled turnarounds. Predictive maintenance also plays a very important role in sulphuric acid plants. Because excess cycling is not desirable in a sulphuric acid plant, predicting the right maintenance intervals can assist in limiting excess shut downs. One thing that is very important to good predictive maintenance is an established program of internal inspections. Good predictive maintenance cannot be based on guess work. Because most of the plant is not visible during normal operations, internal checks are the only reliable method to ensure that all problems are discovered. Breakdown maintenance should be minimised. In most cases, a mechanical integrity failure is going to result in a hazardous chemical release and therefore even things like pumps with an in-situ spare beside them can pose risks to the operation.

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As with any maintenance program, all required maintenance (preventive and predictive) needs to be documented, preformed as scheduled, and records kept. Records of ongoing maintenance are especially important in trouble-shooting non-routine problems that occur in the plant and to trend information that may feed back into the predictive maintenance program. Also, good maintenance records are an essential for proper management of change. As we turn to the specifics of best practice maintenance regimes, we will look at things in four categories - regular inspections/checks, internal inspections, other general maintenance issues, and maintenance procedures and training. Regular Inspections/Checks: The checks referred to here can be either part of the duties of the maintenance staff or the operators. Also, it is critical that the information from these checks is fed back from the operators to the maintenance staff and visa versa. Critical inspections and checks you would expect to be included are listed in Table 3. This only focuses on some critical aspects and is not considered exhaustive. Three checks stand out above all others in Table 3 – draining acid condensate from the gas-to-gas heat exchangers, stick testing, and pressure monitoring. These are the most effective tests to monitor for acid carry-over, which is probably the most detrimental issue for sulphuric acid plants. Both tell you a considerable amount about what is going on inside the plant.

Table 3 – Regular Inspections/Checks

Equipment Inspections/Checks Entire Plant - Weekly (preferably daily) pressure profiling of the plant36

- Daily checks of all critical alarm components, sensors, probes, etc. - Checks for corrosion under insulation at least at each turnaround or more frequent if local conditions dictate. - Daily visual inspections of the supporting structures for signs of accelerated corrosion that may lead to structural collapse.

Gas-to-Gas Heat Exchangers

- Each shift, acid condensate carefully monitored and drained from cold pass heat exchanger (once per hour on start-up)37. - Open all drains on shut down.

Drying and Absorption Towers

- Stick testing once per day, preferably once per shift

Acid Storage Tanks & Piping

- Annual external "walk-around" inspection (with strong focus on welds) - Biennial ultrasonic thickness test.

Acid Coolers - Daily checks for leakage or abnormal conditions on plate heat exchangers. Stack - Opacity monitored a minimum of once every two hours (or on-line monitoring)

The stick test can indicate the type of problem that is occurring (sulphur trioxide burns stick uniformly, many burn spots, all sizes – probably a hole in mist eliminator, large spots – probably re-entrainment, small spots – probably low efficiency from mist eliminators). When a stick test is performed, it is also important to record a number of other factors so that trending will be meaningful. These include acid condition in the tower (temperature, concentration, & flow of

36 Indication of a displaced/leaking mist eliminator should be attended to and repaired immediately. 37 On-line monitoring systems would negate the need for going on plant to check.

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acid, mist eliminator pressure drop, gas flow and temperature, and any other observations that may be out of the ordinary). The stick test results in addition to these other parameters should be tracked in a database to allow for proper trending and analysis.

A better form of acid detection would be a proper sampling system with a vacuum pump, glass sampling tubes etc, but they are uncommon and expensive. With such a system, regular stick tests would not be needed, but periodic stick testing would still be needed to ensure that the system is working properly. Where this indicates that there is a displaced/leaking mist eliminator, it should be attended to and repaired preferably within an hour or being detected. The acid drain also gives us some key information – how much carryover there and the carryover concentration (can be tested). In particular carryover with particles below 3-5 microns are picked up. Stick tests are ineffective at detecting this. If in a 24 hour period, the amount of acid drained exceeds 7 litres, action should be taken immediately. Pressure monitoring is something that is preferably done on-line as part of the process control system, but this is not he case in many older plants still in service. Pressure monitoring is another way to determine if there is a potential for fine carry-over that is resulting from mist eliminators displacement or misalignment. Internal Inspections: Internal inspections for a sulphuric acid plant warrant a discussion on their own. There are many parts of the plant that often go without proper internal inspections due to the difficulty of access. However, the harsh operating conditions within an acid plant make internal inspections a necessity as the difficulty of conducting them does not often outweigh the consequences of foregoing them. Table 4 lists typical equipment and what to look for on an internal inspection. A thorough internal inspection should be conducted at each turnaround. This should be at least annually, but may be extended up to two years if based on sound risk based inspection protocols. When problems are discovered during the internal, they should be addressed immediately and not left until the next turnaround, even if that means an extension of the shut down. It is likely that this time will be paid back in avoiding future unplanned shut downs.

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Table 4 – Internal Inspections

Equipment Items to Inspect Primary Scrubber/Venturis

- Where brick lined, the brick condition should be investigated. - Check weak acid distributors38 - Check mist eliminator pads/candle filters are secured in place and in good repair.

Wet Electrostatic Precipitators

- Check for tube sheet leakage39. - Check for collection tube burn through - Ensure that each discharge electrode is centred in the collecting tube. - Check for broken discharge electrodes, remove and block off tube. - Check for tube sheet bulging

Pre-heater - Check refractory, burner condition Converter/Catalyst Bed

- Inspect catalyst bed supporting beams - Check for screen plugging, brick/refractory deterioration40, collapsed/partially collapsed beds, bulging of supports, cracked support grids41, shifted support columns.

Gas-to-gas Heat Exchangers

- Inspect for iron sulphate build up in and on the tubes as well as any other signs of corrosion

Drying & Absorption Towers

- Inspect lining brick condition, all candle filters/mist pads, condition of the packing, and condition of acid distributors and clear any blockages.

Steam Equipment & Heat Recovery Systems

- Complete internal as would be expected for any boiler or other piece of steam producing equipment.

Acid Storage Tanks & Piping

- 5 yearly internal visual inspection42

Exhaust Stacks - Lined stacks - check the lining every 3-5 years - Concrete stack – check for spalling every 3-5 years. - Steel/alloy stacks – check for corrosion issues every 3-5 years. - Large FRP stacks do not require internal inspections, but if quite high, may need to access internally to investigate UV degradation.

General Maintenance: Beyond the regular inspections/checks, and internal evaluations, there are a number of other actual maintenance items that will follow on from this. For the predictive maintenance aspects, they will largely follow on from the results of the above inspections. Other preventive maintenance items are recommended based on normal manufacturer’s recommendations and experience. Table 5 lists some other items you would expect to find in a normal maintenance plan. This just provides some examples of key items and is far from exhaustive. For a typical acid plant, it would be expected that the maintenance schedule (normally computer based) if printed out would be of considerable length.

38 Normally can be done by pulling them out. 39 Look for signs of liquid running down from tube sheet staining outside of tubes - indicator that WESP is approaching the end of its life. 40 If there is damage to the brick lining, there may be hot spots that can be detected with infrared scanning. Although it is a good practice to conduct these checks, they are not a substitute for internal inspections. 41 A support post could be placed under the grid if the damage is not major – preferable to avoid this temporary fix. 42 On large flat bottom tanks, internal inspections will be the only way to see the condition of the tank bottom as UT thickness testing cannot be done.

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Table 5 – Other Maintenance Items

Equipment Maintenance Items Entire Plant - Corrosion thickness measurement inspection program (focussing on

areas of high gas velocity and past problems) at each turnaround - Comprehensive maintenance checks of all critical alarm components, sensors, probes, etc.

Wet Electrostatic Precipitators

- Maintenance should be at the same level normally expected for any high voltage equipmentiv - Repair tube sheet leaks by fixing the tube-to-tube sheet weld

Pre-heater - Burner maintenance as per gas fired equipment best practices (e.g. functional testing of components, leak testing of safety shut-off valves, proper turn-down ratio etc)v

Blower - Monitor even build-up of iron sulphate, wash excess build-up, and balance blower impellers at each turn-around

Converter/Catalyst Bed

- Screen catalyst bed. - Remove scale from unit using a light brushing or vacuuming to prevent damage to chromium oxide layer on stainless steel units - Where there is grid separation, reset grids and post and reposition grids, replace supports with larger ones and weld additional support to the shell if necessary. - Replace cracked grids

Drying & Absorption Towers

- Stainless steel filters on drying tower inlet should be changed annually. - Wash internals43

Steam Equipment & Heat Recovery

- Water treatment for boiler/superheater/economiser carefully controlled in accordance with highest possible standards. Ensure that there is no sodium contamination.

Acid Storage Tanks & Piping

- Maintain in accordance with suitable standardsvi

Acid Coolers - When visual signs of leakage appear, dismantle plate heat exchangers, check for corrosion issues, repair and reassemble.

43 Water washing should not be done for any unlined metal tower and water washing should only be conducted on lined towers once the integrity of the lining has been established via a thorough internal inspection.

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Maintenance Training and Procedures: Training precedes application of the procedures. Also, it is important that training not be limited to just maintenance task specific items. Maintenance personnel must understand the plant and process chemistry in order to properly understand the hazards and subsequently to properly apply procedures. In addition to the training, there are specific skills that may be needed that may not be available in-house. A good example is a lead burner if there are still lead components within the plant (e.g. wet electrostatic precipitators). Also, special experience needs to include items like acid wash testing and the use of potassium ferrocyanide solution for finding defects. This should be reviewed regularly to ensure that the skills are still available locally when needed in a potential emergency. Permit systems should be used and in line with chemical industry standards. In particular, hot work management is a key issue at acid plantsvii. Often the acid plant and gas cleaning plants are seen as relatively benign areas in regards to hot work. However, with the potential for build up of hydrogen gas (reference reaction [5] above), the build up of methane during start up (reference reaction [4] above), and potentially large amounts of FRP, there are actually a number of fire/explosion risks. Hot work procedures and training should be suitably detailed to address these unique exposures. These things can include labelling of plastic and rubber/plastic lined equipment, specialty welding procedures for special metals [stainless steels, exotic alloys, lead], precautions for potential hydrogen build-up, and potentially the presence of sulphur either as part of the process in an sulphur burning plant or as a potential product of a plant upset causing the plant to go into reducing conditions. Care should be extended to caked on solid sulphur on equipment such as sulphur pumps. Use of direct flame to assist in removing this material can generate sulphur dioxide gas and there is potential to damage the metal parts by ‘flame-hardening’ them. Good maintenance procedures will underpin a well run plant. Some additional time, effort and money invested in maintenance will reap benefits in the long run. Sulphuric acid plants are not commonly erected to last only a few years, so there should be an expected risk reduction pay back in the life of the plant. However, considering the harsh operating conditions that exist in sulphuric acid plants, if the proper time, effort, and money are not invested in the plant, it can take very little time for the plant to begin to have operational issues. If not kept in check with good maintenance, the failure rate of various components will accelerate very rapidly and soon result in plant downtime. Not only will this have immediate economic impact on the entire operation, it could start a vicious circle of plant cycling that could lead to a marked decrease in overall acid plant life.

3.5 Operators A good operation will have operators with good knowledge/skills, full authority to control the equipment in emergencies, good supervision, and be adequately staffed. This is critical in ensuring that the operation will continue running well over an extended period. At operations where the training is poor, emergency procedures are not posted or practiced, staff are overworked, have limited experience, have staff shortages, and take short cuts, have the elements already in place to result in significant property damage or business interruption incidents. These

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deficiencies can add up to overcome even the best designed safety devices and contingency plans. If a sulphuric acid plant is being run outside of its operating parameters, damage can be done very quickly and the vicious circle of cycling can begin as noted previously. Of primary importance is a complete and up-to-date operating procedure that is easily available and used by all the operators. The procedures need to deal with both routine and non-routine operations. Routine procedures are those that focus on the ongoing operation of the plant within its safe design operating limits – pressure, temperature, acid concentration, etc. Non-routine procedures include those for emergency situations, experimental operations (especially when process control interlocks are to be overridden), standby operations (idling part of the plant during a problem). In a sulphuric acid plant, the start-up and shut down procedures would need to be considered a non-routine event, given the desire to avoid cycling these plants excessively. Check-list type procedures are good and the more straightforward way these procedures are presented, the easier they will be to understand. It is best if experienced operators are part of the process of writing and updating the procedures. In new plants, operators should be brought on board early to assist with this. The human /process interfaces need to be carefully considered. This is an important part of plant design, but also should be a key element taken into account when writing procedures. Process control software needs to be clear to the operator – anything that can be done to simplify or clarify on screen information or procedures should be done. All the right instruments need to be there for monitoring important criteria (e.g. acid concentration instruments [conductivity meters, refractometers, and sonic liquid analysers], etc.). All manual controls need to be available and understood in an emergency. The same holds true for safety protective systems. At existing plants especially, re-writes of the procedures should carefully consider what can and cannot be easily accomplished in an emergency with the exiting human/process interfaces. Also, with existing plants, the spontaneous response of experienced operators based on their past experience is very important to consider. Once procedures are established, regular checks for updates need to be made to ensure that procedures are correct and up to date. One thing that is very important is to continually check that the operating practices and procedures match. If they do not, then corrective action needs to be taken quickly. This may be accomplished by updating or simplifying the procedures. Alternatively, the procedures may be fine and stopping bad practices may be a matter of better supervision or refresher training. It is also important to establish roles and responsibilities between various groups in the operation and establish good lines of communication. This includes the role of the operational staff versus that of the maintenance staff. Operations staff will always have the primary roles because they are running the process, but there are some questions to ask to establish some important responsibility issues. Who will conduct which inspection? Are there minor maintenance items that will normally be done by the operational staff and how are these accounted for in the maintenance plan? Is the operational staff keeping maintenance up to date on all changes and plant upgrades? Establishing roles also extends beyond the operations and maintenance staff. Modern sulphuric acid plants rarely, if ever stand alone. So, responsibilities need to be determined between various operations within a plant and communication needs to be very open between the various operations. For instance, at a fertiliser plant, when will the phosphoric acid plant operators take

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responsibility for the sulphuric acid piping/storage? For a metallurgical plant, there will be numerous cases where an upset in the furnace will require an emergency shut down, resulting in the need to idle the acid plant, so the acid plant operators need to be ready to respond quickly and effectively to a condition that they may not be monitoring. Similarly, a situation in the acid plant may necessitate an emergency shut down of the entire plant. With the acid plant going quickly off line, there may be a need to have dampers opened and other actions taken as part of the emergency procedures. Above all, good communication is the key between all parties. Ideally, experience should be shared regularly at tool box discussions, safety meetings, and meetings between maintenance and the operational bodies. Also, the communication between shifts is important. It is important that the changing shift crews communicate all information to the next crew both in regards to the specific plant issues as well as other issues with operations and maintenance that have the potential to affect the plant. Another good idea is to bench-mark against other operations, either within your organisation, as part of a wider industry group, or possibly just with mutual agreement with a few other similar plants in your geographical area. The Florida fertiliser industry are a good example of a group of operators who regularly share ideas. Another good example of this is the Monsanto “Heat Recovery System HRS Users Conference,” which was started to address the complexities of running their proprietary system as part of the plant. Good training is the foundation of any good operating procedures. People are only going to be able to apply the procedures if they understand why and how. Training should include an understanding of the process detailed enough to allow for the safe completion of any. It is important to ensure operators understand the process chemistry, especially potential upset conditions. (e.g., rapid corrosion that can occur in a cold pass gas-to-gas heat exchanger or heat recovery system, potential for hydrogen explosions with economizer leaks, etc.). Ideally, the training should be a mixture of class room, self study and on-the-job. Certification that training has been successfully completed should be performance based, with verification by experienced operators on-the-job. Ensure that other key aspects of process safety management are included in the training (e.g., management of change – identifying and handling changes including temporary changes, recognising incidents and near-misses, etc). This raises an exceptionally important issue for plants associated with metallurgical processes. Consider that a spent acid regeneration plant will usually be part of a petroleum refinery site with well established process safety management procedures. The staff at these plants will likely have been working in the chemical industry for some time and will usually be familiar with these chemical process industry concepts. This may not necessarily be the case where a sulphuric acid plant is located at a remote mining/metallurgical refining location, where there will be a mixture of backgrounds, some who have not worked within the procedures of a fully integrated chemical plant. Bridging that knowledge gap is a critical consideration in training design. Similarly, with experienced operators hired from other locations, have other potential gaps been bridged? For example, if all previous plants the operator worked at did not have steam systems associated with the acid plant, would they know that if there is a steam leak and acid is turned off quickly, but then turned back on, you could cause a massive vacuum as the highly hygroscopic acid combines with the steam? It is critical to ensure that such hazards are understood and the

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proper action will be taken (e.g., in this case - keeping all man-ways open when this operation is conducted). If they are not addressed, the operator may not know what to do until it is too late. In addition, there needs to be consideration for any additional outside training that may be required. For instance, if the plant is of Monsanto design and equipped with a Heat Recovery System, the operators should attend the special Monsanto training course “HRS General Awareness Training.” These are special proprietary systems that have very specific manufacturer’s operating instructions. Refresher training needs to be provided regularly. This is especially important for non-routine conditions. A good idea is to run regular ‘what if’ sessions with operators for abnormal conditions. Records of all training need to be kept up to date. Also, there should be an effort to keep abreast of incidents at other plants where the lessons can be built into refresher training at your plant. Lastly, it is important to establish at the outset that operators have complete authority to shut down distressed equipment with management support. This message should carry through from initial training to day-to-day operations with management seen as actively supporting it. Operators sit at the coal face and are often the last line of defence before safety devices take over. However, the wrong actions of operators can even render certain safety devices ineffective. So, their actions could be the difference between a small process upset and a major incident. Their knowledge of the overall process is critical to ensure that they can make the right choices in the right situations. Ensuring that the training to do this is correct and keeping it up to date is critical. 4. Consequence 4.1 Safety Devices

A good plant will have all safety devices in working order with proper records kept. Constructing the plant properly and operating the plant within its design limits is the key issue for a sulphuric acid plant. Therefore, a large number of additional safety devices are not necessarily required outside of the alarms and interlocks on the control system. This underscores the importance of the operators and their actions as discussed above. When alarms occur (e.g., acid concentration out of range) or inspections/checks reveal an abnormal condition (e.g., excess acid condensate in gas-to-gas heat exchanger), action needs to be taken quickly. However, there are some safety devices that do need to be considered.

One issue that is often overlooked is the need for pressure relief throughout the acid plant. The blower provides high volumes of gas and therefore can increase the pressure within the acid plant to unacceptable levels without proper relief. Blowers can potentially pressurise to 60-70 kPa. The usual design for about 90% of plants is about 30 in. water (7.5 kPa). Operating history has shown that lack of pressure relief can result in incidents severe enough to bulge converter beds. A key area where over-pressure protection is needed is between the wet electrostatic precipitators and the drying tower. This is usually done with a water seal, but some designs use a weighted vent. Some systems have also been designed with an oil seal. However,

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an oil seal is less desirable because it has the potential to allow oil into the system, which could cause further upstream problems. Vacuum conditions also need to be considered because sulphuric acid plants are not designed to work under vacuum either. Low pressure alarms should be in place throughout the plant. Also there should be some vacuum protection as well (i.e., with a water seal as noted above). Acid storage tanks should be provided with suitable vacuum breakers. Being a critical piece of rotating equipment, the blower needs some special consideration in regards to safety devices. The following aspects need to be considered that regard:

• A method of protection needs to be provided for surging conditions. This can be a surge

detection system that ideally is interlocked to open a recycle line. Because sulphur dioxide cannot be emitted to atmosphere, the recycle line should discharge back to the inlet of the drying tower. A simple high pressure monitor is not suitable as a detection/actuation device. The system needs to be either able to monitor differential pressure (complex systems that are often overridden) or simply monitor low pressure to catch the low pressure cycle of the surge. This is really not unique to sulphur dioxide, but rather used in many gas compressor installations.

• For steam turbine driven blowers: o Proper PRV provided.

o Also, use a low pressure trip for turbine driven blower surge protection. (Turbine over-speed could cause a larger problem because it can get much higher pressure if the over-speed trip fails).

o Careful consideration of the mechanical and lubrication oil hazards is needed. Although not usually large units, these turbines need to be designed with all of the considerations that would normally be applied to larger power turbines.viii

As noted above, there is often a large amount of FRP used to construct the gas cleaning plant at metallurgical and spent acid plants. To deal with this, various levels of over-temperature protection are needed. The first level is over-temperature alarms and interlocks. If the temperature excursion is going to reach a level that could damage the plant, there may be an option to divert the hot gases or stop the upstream processes. However, because of the nature of sulphur dioxide, venting to atmosphere is not something that is encouraged and in many locations will not be allowed. So, consideration of other protection needs to be considered as well.

If the primary scrubber/quench tower is FRP, then a flow of emergency water through the quench nozzles should be established immediately. The source of emergency water must be an uninterruptible, preferably the fire water main or water supply of similar reliability. In the absence of suitable water supply, an alternative may be an elevated head tank having sufficient volume for the expected duration of the high temperature. If PTFE quench nozzles are used, they are probably not something that can be relied on in such circumstances, so consideration may need to be given to using alloy nozzles. However, if they are already in use, it is still a good idea to connect them to an emergency water supply.

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Corrosion protection systems may also be needed in some places. A common application of this is anodic protection for acid coolers (primarily tube and shell type). Providing this type of protection is a good idea where the conditions warrant it. However, as any corrosion protection system relies on ongoing maintenance, power supplies, and other items that can fail, it is always better to try to select a material of construction more suited to the application than an additional protection system. With the proper materials of construction, a suitable level of protection can be provided through the process control of the plant. The above mentioned items are the most common safety devices seen and needed at sulphuric acid plants. However, there are numerous other hazards specific to any one plant that may need additional protective devices. Impurity removal is a good example – this can see the introduction of any number of hazardous materials such as hydrogen peroxide, hydrazine, and ammonia to the site. The only successful way to ensure that all necessary safety devices are provided in the design is to subject the entire plant to a thorough process hazard analysis. That will allow final decisions to be made on what needs to be provided with additional protection, what can be handled with process control or operating procedures, what needs to be intrinsically safe, and what can be handled through some sort of contingency planning. 4.2 Contingency Planning

Being prepared to minimise business impact associated with equipment or system outages if an unexpected event occurs is extremely important. However, once this point is reached, the failure has already occurred. As noted previously, this is not a desired situation to be in for a sulphuric acid plant. If there has been a significant excursion, there are not a lot of truly effective contingencies if major damage has already been done to a large part of the plant. Being a single line process, it will immediately have a business impact. So, contingencies should be the last resort after designing and building the plant correctly and providing suitable safety devices. An ideal approach to take for new plants is to design them based on two independent plants sized at least at 50% capacity. With sulphuric acid plants usually critical to another process, this is an excellent way to keep the plant operating at partial production while repairs are made. It will also allow for upstream and downstream processes to have more controlled and safer shut downs if deemed necessary. If the plants are built within a suitable distance of each other, there may also be a potential to cross connect between plants, ultimately avoiding the need for a full shut down and cold re-start. This would need to be balanced with the risk posed from the facility siting. The choice of spares is going to be dependent on the original design, materials of construction, safety devices in place, and ultimately by process hazard analysis. Some typical spares that could be considered include:

• FRP duct material (capable of replacing longest duct length if practical).

• Primary scrubber/quench tower if constructed of FRP.

• Wet Electrostatic Precipitator

• Blower(s) (at a minimum spare impellers),

• Catalyst

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• Cold pass gas-to-gas heat exchanger (or at least tube bundle) if constructed of carbon steel

• Acid cooler

• Spare tube bundles for boilers/economisers/heat recovery systems (If so, are they removable for quick change)

• Pressure Filters for sulphur burners.

Spares should be properly stored, weather-proofed, and maintained in a condition that will allow for immediate installation in the event of a failure. Regardless of what spares are kept on hand, written plans should be provided for all critical equipment. They should be up to date in regards to availability, alternative suppliers, and special transportation needs. These plans should be routinely reviewed and updated. Also, in the analysis of the risk to the plant, even with spares provided there will usually be downtime associated with installing them. Whether this risk is considered acceptable will vary between operations, but it will always be worse than avoiding failure in the first place. 5. Conclusion Each year, there is more sulphuric acid made than any other manufactured chemical and its importance as an industrial chemical does not appear to be set for a reduction in the near future. Many new uses are actually being found each year, with some significant volume applications like the leaching operations in the copper industry. This underlines the importance of keeping these plants operating continuously and reliably – and that can be done with good risk management techniques. These techniques include sound PSM systems. Of particular note for sulphuric acid plants a strong Process and Equipment (Mechanical) Integrity program is critical. These programs are used routinely in the mainstream chemical process industry and incidents have consistently resulted in reduced number of incidents and improved risk quality. Where acid plants are used in these industries, they benefit from this improved risk quality as well. However, all acid plants are not necessarily associated with mainstream chemical process industries and this is on the increase with the wider applications for sulphuric acid use in the mineral and metals industry. This paper has focussed primarily on the mechanical integrity aspects critical to ensuring high risk quality at a sulphuric acid plant. The approach has been slightly different in that is has been done by looking at six key elements that will shut the plant down. A best practice can be defined as “An activity or procedure that has produced outstanding results in another situation and could be adapted to improve effectiveness, efficiency, ecology, and/or innovativeness in another situation.” Therefore, the challenge now will be to continue with these ideas towards a more all inclusive best practice. This will need to include further technical documents and more established lines of communications across all industries involved with sulphuric acid production.

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6. Special Acknowledgements The author would like to extend some special acknowledgment and thanks to some particular parties. First, thank you to Mr. Leonard J. Friedman, Acid Engineering & Consulting, Inc. Mr. Friedman has assisted FM Global on various issues regarding claims and engineering. His insights have helped FM Global to gain a proper understanding of the hazards and risk associated with these plants and what is needed to avoid them and protect against them. FM Global engineers, including the author, visit many sites in the course of their job. These sites include locations that are insured, have been insured; have been visited prior to quoting on an insurance policy, and for training courses. During the site visits, much is learned about the hazards and risks at particular sites and through discussions with plant personnel, insights are often gleaned. So, thanks are extended to all these sites which include: Grupo Mexico Ray Smelter, Arizona, USA; Anaconda Murrin Murrin Nickel Mine, Leonora, Western Australia; Western Mining Company, Olympic Dam, South Australia; Western Mining Company Kalgoorlie Nickel Smelter; Western Australia; Zinifex Port Pirie Smelter, South Australia; Zinifex Hobart Smelter, Tasmania, Australia; Zinifex Budel Smelter, Netherlands; Zinifex Clarkesville Smelter, Tennessee, USA; IMC Fertiliser, New Wales, Florida, USA. Special thanks goes to Mr. Reg O’Connell, General Manager and his staff at Sun Metals Zinc Refinery, Townsville, Queensland, Australia not only for their time on site, but also for the permission to utilise photos from their site. 7. References ASM International. ASM Handbook, Volume 13A Corrosion: Fundamentals, Testing and

Protection. 0-87170-705-5. Materials Park, OH. ASM International, 2003.

ASM International. ASM Metals Reference Book, Third Edition. 0-87170-478-1. Materials Park, OH. ASM International, 1993.

Berger, Dan “Re: What are the economic and technological implications of sulfuric acid?” MadSci Network: Chemistry 3 September 1997. Online. Available at: http://www.madsci.org/posts/archives/dec97/873378197.Ch.r.html 16 November 2005.

Centre for Chemical Process Safety of the American Institute of Chemical Engineers. Auditing Mechanical Integrity. 0-8169-0423-5. New York, American Institute of Chemical Engineers, 1989.

Centre for Chemical Process Safety of the American Institute of Chemical Engineers. Guidelines for Auditing Process Safety Management Systems. 0-8169-0556-8. New York, American Institute of Chemical Engineers, 1993.

Centre for Chemical Process Safety of the American Institute of Chemical Engineers. Guidelines for Safe Process Operations and Maintenance. 0-8169-0627-0. New York, American Institute of Chemical Engineers, 1995.

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Centre for Chemical Process Safety of the American Institute of Chemical Engineers. Guidelines for Writing Effective Operating and Maintenance Procedures. 0-8169-0658-0. New York, American Institute of Chemical Engineers, 1996.

Chemical Economics Handbook. Menlo Park, Calif.: SRI International, 2000. Online Available from: The Dialog Corporation, Cary, North Carolina at http://www.collectionscanada.ca/iso/tc46sc9/standard/690-2e.htm 22 November 2005.

European Sulphuric Acid Association (ESA) a sector group of CEFIC/European Fertilizer Manufacturers’ Association. "Best Available Techniques for Pollution Prevention and Control in the European Sulphuric Acid and Fertilizer Industries Booklet No. 3 of 8: Production of Sulphuric Acid” 2000.

Friedman, Leonard J. 2003, Sulphuric Acid Plant Consultant [Interview by author] April 23.

"Getting the Details Right (Sulphuric Acid Technology)" Northern Light. 1995 British Sulphur Publishing (UK).

Graff, Gordon. "A snug market—and spiralling prices" Purcahsing.com. 9 December 2004. Online. Available at: http://www.purchasing.com/article/CA487724.html 18 November 2005.

Louie, Douglas “Maintenance Spend as % of Asset Value” Forum The Sulphuric Acid Network. Posted 10 July 2002. Online. Available at: http://www.h2so4network.com/forum/topic.asp?TOPIC_ID=174&FORUM_ID=2&CAT_ID=1&Topic_Title=Maintenance+Spend+as+%25+of+Asset+Value&Forum_Title=Forum+Archives 18 November 2005.

"Market Expansion" The Sulphur Institute. Online. Available at: http://www.sulphurinstitute.org/usex.html 17 November 2005.

Moore, L J. "Using Process Safety Management to Manage Risk in Mineral and Metals Processing Facilities" Mining Risk Management Conference Proceedings May 2003.

Muller, Thomas L. "Sulphuric Acid and Sulphur Trioxide" Kirk-Othmer Encyclopaedia of Chemical Technology. 1997, John Wiley & Sons, Inc. Article Online Posting Date: December 4, 2000.

National Association of Corrosion Engineers Unit Committee T-5A on Corrosion in Chemical Processes. Corrosion in Sulphuric Acid – Proceedings of the Corrosion/85 Symposium on Corrosion in Sulphuric Acid. 0-915567-11-3. Houston, Texas, National Association of Corrosion Engineers, 1987.

Oliverson, Raymond J. "Benchmarking: a reliability driver." Hydrocarbon Processing. August 2000, pp 71-76.

Sanders, Roy E. Chemical Process Safety – Learning From Case Histories. 0-7506-7022-3. Woburn, MA: Butterworth-Heinemann, 1999.

Shoemaker, L.E. and J. R. Crum “Experience in Effective Application of Metallic Materials for Construction of FGD Systems” Special Metals. Online. Available http://www.specialmetals.com/documents/Metallic%20Materials%20for%20Construction%20of%20FGD%20Systems.pdf 19 November 2005.

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“Sulphuric Acid Plants & Products” Monsanto Enviro-chem Systems Online. Available at: http://www.mecsglobal.com/MECS/layout/SulfuricAcid/sulfuric_acid.asp 2 November 2003.

Sulphuric Acid Plant Training Manual. Online. Available: http://members.rogers.com/acidmanual/index.htm 4 November 2003.

"Sulphuric Acid" The Columbia Encyclopaedia, Sixth Edition. 2001-05. Online. Available at: http://www.bartleby.com/65/su/sulfuric.html 14 November 2005.

"Sulphuric Acid" Wikipedia. Online. Available at: http://en.wikipedia.org/wiki/Sulfuric_acid#Uses 17 November 2005.

TAPPI. "TIP 0606-26: Sulphuric acid (H2SO4) safe storage and handling" 2003.

"Technical Data - Equipment" DuPont Sulphur Products 1995-2003. Online. Available at http://www.dupont.com/sulfurproducts/techdata/equipment.html 19 November 2005.

i Reference FM Global Property Loss Prevention Data Sheets 6-0 “Elements of Industrial Heating Systems,” 6-4 “Oil and Gas Fired Single Burner Boilers,” 6-5 “Oil and Gas Fired Multiple Burner Boilers,” 6-9 “Industrial Ovens and Dryers,” NFPA 8501 “Prevention of Furnace Explosions in Fuel Oil and Natural Gas-Fired Single Burner Boiler-Furnaces” ASME CSD-1 “Controls and Safety Devices for Automatically Fired Boilers,” NFPA 86 “Oven and Furnaces Standard,” NFPA 54 “National Fuel Gas Code” ii E.g. ANSI B31.3 - Normal Service iii A good reference is the American Institute of Chemical Engineers Centre for Process Safety book “Guidelines for Safe Process Operations and Maintenance.” The program should address traditional chemical plant issues such as having a program to ensure double blocking and no short-bolting. iv Reference FM Global Property Loss Prevention Data Sheet 5-20 “Electrical Testing” v Reference FM Global Property Loss Prevention Data Sheets 6-0 “Elements of Industrial Heating Systems,” 6-4 “Oil and Gas Fired Single Burner Boilers,” 6-5 “Oil and Gas Fired Multiple Burner Boilers,” 6-9 “Industrial Ovens and Dryers,” NFPA 8501 “Prevention of Furnace Explosions in Fuel Oil and Natural Gas-Fired Single Burner Boiler-Furnaces” ASME CSD-1 “Controls and Safety Devices for Automatically Fired Boilers,” NFPA 86 “Oven and Furnaces Standard,” NFPA 54 “National Fuel Gas Code” vi E.g. API 653, API 570, etc. vii Reference U.S. Chemical Safety and Hazard Investigation Board report on the 17 July 2001 incident at the Motiva Enterprises LLC Delaware city refinery.

This is available on-line at: http://www.csb.gov/completed_investigations/docs/DS-MotivaIR-090602.pdf A brief summary: An explosion occurred when a crew of contractors was repairing grating on a catwalk in a sulphuric acid storage tank farm when a spark from their hot work ignited flammable vapours in one of the storage tanks. The tank separated from its floor, instantaneously releasing its contents. Other tanks in the tank farm also released their contents. A fire burned for approximately one-half hour. viii Specific details on protection and maintenance of these units can be found in FM Global Property Loss Prevention Data Sheets 7-101 “Fire Protection for Steam Turbines and Electric Generators” and 13-3 “Steam Turbines.”