20
AN EDE PRIMER ON ALUMINUM SMELTERS An Internal Training Document For distribution to and use by FM Global employees only Larry J. Moore, PE Principal Engineer Mining and Metallurgical Refining Staff Engineering JULY 2008 Copyright 2008 Factory Mutual Insurance Company. All rights reserved. Do not reproduce this report. It is for distribution to and use by FM Global employees only. Do not distribute beyond these groups

Aluminum Industry Primer V2

Embed Size (px)

Citation preview

Page 1: Aluminum Industry Primer V2

AN EDE PRIMER ON

ALUMINUM SMELTERS

An Internal Training Document

For distribution to and use by FM Global employees only

Larry J. Moore, PEPrincipal Engineer

Mining and Metallurgical RefiningStaff Engineering

JULY 2008

Copyright 2008 Factory Mutual Insurance Company. All rights reserved. Do not reproduce this report. It is for distribution to and use by FM Global employees only. Do not distribute beyond these groups

Page 2: Aluminum Industry Primer V2

Aluminum Smelter EDE Primer July 2008

Summary

FM Global has a well developed and institutionalized mine industry specialists program

called the MINERS Program which includes comprehensive engineering standards and

training for mining occupancies. This specialists program also covers as a subset

aluminum refining and smelting but not downstream secondary processes such as

rolling mills.

A fundamentals class entitled “Understanding and Quantifying the Hazards in Aluminum

Smelters” was developed and deployed in 2005 and 2006. There are currently about 40

field (EH and FH) engineers who attended one of the aluminum fundamentals classes or

are seasoned senior engineers with some aluminum smelter expertise.

An industry specific Operating Standard – OS 7-64 Aluminum Industry - has been

published for many years and this covers in detail the entire industry from refining to

consumer products. This standard also includes a comprehensive tutorial on the industry

as a Reference document.

Procedures for field engineering servicing of aluminum facilities are also detailed in the

HRG and Visit Planner.

As a direct result of a pending 2008 summer candidate campaign for Alcoa Aluminum

several operations expressed concern that adequately trained field engineering

resources were not available in all operational locations. The primary concern involves

the smelting part of the aluminum production chain but extends to the upstream refining

and downstream converting operations as well.

To address this gap in geographical resources the Principal Engineer offered to deploy a

“crash” abbreviated class on aluminum smelting for those field engineers who have no

experience in the industry and had not attended one of the fundamentals classes.

FBI operations accepted the offer and a class was deployed July 24th and 25th in the

Paris office for European field engineers.Copyright 2008 Factory Mutual Insurance Company. All rights reserved. Do not reproduce this report. It is for distribution to and use by FM Global employees only. Do not distribute beyond these groups

2

Page 3: Aluminum Industry Primer V2

Aluminum Smelter EDE Primer July 2008

A class for North and South American Operations was discussed but could not be

deployed in a suitable time frame to aid in the upcoming candidate campaign.

Instead the Principal Engineer agreed to develop basic EDE guidelines to help

inexperienced engineers know where to spend their time in complex smelting facilities.

The following EDE Primer supplements OS 7-64 but is not a replacement for studying

and understanding this comprehensive OS and its excellent Reference document.

This is also not a substitute for following the HRG and Visit Planner nor should these

guidelines overrule any Operating Requirements.

The following guidelines only cover aluminum smelting. On site power generation and

other occupancies associated with aluminum industry are not covered.

Aluminum Industry Overview:

The aluminum industry is comprised of the following general manufacturing segments:

• Mining/Concentration: A mine extracts and produces concentrated bauxite ore

• Refining : A refinery produces alumina from bauxite ore in the Bayer digestion

process

• Primary Smelting : A smelter (a/k/a reduction works) produces aluminum metal by

electrolytic reduction of alumina.

• Secondary Melting : These plants process recycled materials or remelt bar stock

from smelters for purification. These plants are heavy industrial occupancies with

principle hazards being molten metals, rolling operations with typical Equipment

and Facility hazards and large robust equipment like presses.

• Consumer products : Downstream metal working processes like rolling, wire

drawing, etc produce final products.

Copyright 2008 Factory Mutual Insurance Company. All rights reserved. Do not reproduce this report. It is for distribution to and use by FM Global employees only. Do not distribute beyond these groups

3

Page 4: Aluminum Industry Primer V2

Aluminum Smelter EDE Primer July 2008

The following flow diagram demonstrates the aluminum industry production chain.

Some aluminum industry facts:

• Aluminum is the third most abundant element in the Earth's crust and constitutes

7.3% by mass.

• In nature it only exists in very stable combinations with other materials

(particularly as silicates and oxides)

• Its existence was first established in 1808

Is it Aluminium or Aluminum? The word is derived from the Latin Alumen for Alum

(Potassium aluminium sulphate). In 1761 French Chemist Louis-Bernard Guyton de

Morveau proposed the term Alumine.

In 1808 the name Alumium was proposed for the metal.

Copyright 2008 Factory Mutual Insurance Company. All rights reserved. Do not reproduce this report. It is for distribution to and use by FM Global employees only. Do not distribute beyond these groups

Bauxite Mining

Alumina Refining

Aluminum Smelting

Refined Metal

RollingMills

Extrusion ProcessesOther

TransformationProcesses

End Use Recycling

4

Page 5: Aluminum Industry Primer V2

Aluminum Smelter EDE Primer July 2008

Aluminium was adopted by the International Union of Pure and Applied Chemists in

order to conform with the "ium" ending of most elements. By the mid-1800s both

spellings were in common use. Charles Dickens commented that both names were too

difficult for the masses to pronounce.

The first US company was called the Pittsburgh Reduction Aluminum Company and the

metal gradually began to be known only as Aluminum in the US. In 1907 this company

became the Aluminum Company of America (ALCOA).

In 1925 the American Chemical Society decided to adopt the name Aluminum in their

official publications. Most of the world has kept the “i” in Aluminium but it is interesting

to note that the name for the metal's oxide, Alumina has been universally accepted over

its more convoluted alternatives, Alumine and Aluminia.

Both Aluminium and Aluminum thus have an equal claim to etymological and historical

justification.

Exposure Driven Engineering (EDE) Guidelines

The following gives a brief overview of the principal EDE FH and EH hazards found in

electrolytic aluminum reduction smelters.

Protection guidance for various identified exposures is detailed in OS 7-64, Aluminum

Industry, and other operating standards and is not repeated herein except generally.

A smelter consists of distinct and common processes and infrastructure. While there are

variances this is typical of modern smelters using Pre-Baked Anode (PBA) technology.

Older Soderberg technology is not described in this paper as it is now more uncommon

and many of the same hazards and exposures are the same with PBA. Soderberg is well

covered in OS 7-64.

Production of primary aluminum requires the following systems and infrastructure

• delivery, storage, and handling of raw materials

• production of anodes

Copyright 2008 Factory Mutual Insurance Company. All rights reserved. Do not reproduce this report. It is for distribution to and use by FM Global employees only. Do not distribute beyond these groups

5

Page 6: Aluminum Industry Primer V2

Aluminum Smelter EDE Primer July 2008

• production and handling of molten metal

o electrolytic reduction process

o casting

• processing of waste emissions

• electrical supply and distribution

• other utilities and administration support

Figure 1: Modern aluminum smelter with raw material delivery systems and carbon plant

at bottom, potlines at top center, and electrical distribution at top right

Delivery, storage and raw material handling systems

Primary bulk raw materials consist of

• Alumina (a purified form of aluminum oxide) produced in an upstream alumina

refinery and the primary feedstock used for production of aluminum metal.

• Liquid or solid organic pitch (resin binder)

• Petroleum coke (carbon)

• Cryolite, solid sodium aluminum fluoride additive used as a conductive flux and

molten solvent in potline cells

Copyright 2008 Factory Mutual Insurance Company. All rights reserved. Do not reproduce this report. It is for distribution to and use by FM Global employees only. Do not distribute beyond these groups

6

Page 7: Aluminum Industry Primer V2

Aluminum Smelter EDE Primer July 2008

These are often delivered to the site by marine vessel (common for alumina if the

refinery is remote and if there is a nearby port to the smelter) or by surface transport

such as trucks or rail. Cross country rubber belt conveyor systems generally are used to

transport these materials from point of entry to storage silos of bins at the plant site. Hot

liquid pitch is generally delivered by rail or truck and piped into heated tanks.

Primary EDE hazards for raw material delivery and distribution systems are:

• Windstorm exposure at exposed port facilities with large rail mounted cranes and

ship unloaders. Long narrow levees servicing ship ports with conveyor and piping

infrastructure are highly susceptible to hurricane or cyclone wind and sea surge

damage. Wind induced toppling or severe movement of rail mounted cranes and

ship unloaders can occur.

• Fires in semi-mobile equipment like ship unloaders and their on-board electrical

and lubrication systems

• Fires in combustible docks and buildings on docks

• Fires in liquid pitch systems and storage tanks

o Sprinklers

o Interlocks

o Confinement

o Drainage

o Protection Reference: OS 7-99, Thermal Oil Systems; 7-32 Flammable

Liquid Operations.

• Fires in coke (carbon) handling systems

• Possible dust explosion hazard with coke and solid pitch handling systems (Note:

petroleum coke has a low Kst, has been determined in tests to be hard to ignite

and thus represents a very low explosion hazard. Solid pitch fines are similar to

coke fines. Explosion hazards can generally be controlled by good housekeeping

rather than special protection due to very low overall risk)

o Reference: OS 7-76, Combustible Dusts

• Fires in rubber belt conveyors and bucket elevators

o Sprinklers

o Shutdown interlocks

Copyright 2008 Factory Mutual Insurance Company. All rights reserved. Do not reproduce this report. It is for distribution to and use by FM Global employees only. Do not distribute beyond these groups

7

Page 8: Aluminum Industry Primer V2

Aluminum Smelter EDE Primer July 2008

o Reference: OS 7-11, Rubber Belt Conveyor Systems

• Mechanical damage to or toppling of large ship unloaders and cranes due to

stress cracking, corrosion, fatigue or overloading

• Implosion of suction unloading systems

• Breakdown of large motors and suction blowers

• Electrical breakdown or fires in transformers or switchgear

• Impact by marine vessel

• Port blockage

Anode production (PBA processes):

The pre-baked anode smelting process requires anodes and cathodes for the electrolytic

process. The cathode is a carbon liner added when the cell (pot) is newly built and

lasting the life of the pot. Anodes are large carbon blocks “glued” together under

pressure using a pitch resin binder with copper metal rods for conducting electricity from

bus bars. Anodes are consumable products and the carbon that is consumed is the

reducing agent for the reduction process per the following equation.

2 Al2O3 (solid) + 3 C (solid) à 4 Al (liquid) + CO2 (gas)

To put the anode demand in perspective

• 1 ton of aluminum requires 1100 lbs (500 kg) of carbon anode

• The life of one anode is about 30-40 days

• Daily consumption of anodes is from 600 to 1100 t/day

Because of the large continuous demand for anodes a PBA smelter usually requires an

on-site production facility to produce rodded anodes. Anodes can rarely be produced

economically elsewhere and delivered to the plant although there are plants that

specialize only in anode production.

This facility –called the Carbon or Paste Plant - consists of the following primary

processes:

Copyright 2008 Factory Mutual Insurance Company. All rights reserved. Do not reproduce this report. It is for distribution to and use by FM Global employees only. Do not distribute beyond these groups

8

Page 9: Aluminum Industry Primer V2

Aluminum Smelter EDE Primer July 2008

• Mixing of the resin-coke (carbon) blend and forming of a “green” anode block

under pressure and temperature. This is done in a multi-story building

featuring hot liquid pitch pumping and piping systems, mixers and blenders,

thermal oil dryers and hydraulic presses. Hot liquid pitch, thermal oil,

hydraulic oils and carbon combine to produce a high combustible loading with

flammable liquids.

• Adding copper metal conductive rods to the green anode block. Typically

done in a continuous process by drilling openings in the block, and inserting

and “gluing” the rods in place with molten iron. This process can produce fine

dusts of coke and dry pitch that can be combustible.

• Curing (baking and drying) of the green anode block to form the final product

which is sent to the potline. The green anodes are delivered to in-ground

baking furnaces, which consist of a series of refractory brick lined pits with

hollow, surrounding interconnected flue walls. Anodes are packed into the

pits with a blanket of coke covering the anodes and filling the space between

the anode blocks and the walls of the pits.

• The pits are heated with natural gas for a period of several days. The flue

system of the furnace is arranged so that hot gas from the pits being fired is

drawn through the next few sections of pits to preheat the next batch of

anodes before they are fired. Air for combustion of the gas travels through the

flues of previously fired sections, cooling these anodes while reheating the

air. The anodes are fired to approximately 2100o F (1150°C), and the cycle of

placing green anodes, preheating, firing, cooling, and removal is approx. two

weeks.

• Large waste emission systems associated with anode forming and baking

ovens consisting of off-gas collection ducts (often called ring mains),

scrubbers, precipitators etc.

• Automated or manual systems for delivering pre-baked anodes to the potline

Copyright 2008 Factory Mutual Insurance Company. All rights reserved. Do not reproduce this report. It is for distribution to and use by FM Global employees only. Do not distribute beyond these groups

9

Page 10: Aluminum Industry Primer V2

Aluminum Smelter EDE Primer July 2008

Figures 2 and 3: Enclosed and open multi-story carbon plants

Primary EDE hazards for Carbon (Paste) Plants are:

• Fires in thermal oil systems in multi-story buildings

o Sprinklers

o Interlocks

o Confinement

o Drainage

o Protection Reference: OS 7-99, Thermal Oil Systems; 7-32 Flammable

Liquid Operations; 7-14, Protection of Chemical Process Structures

• Fires in hydraulic oil systems with high pressure spray potential

o Sprinklers

o Interlocks

o Protection Reference: OS 7-98, Hydraulic Fluid Oil Systems

• Fires in hot liquid pitch storage, pumping and piping systems with pool potential

o Sprinklers

o Interlocks

o Confinement

o Drainage

Copyright 2008 Factory Mutual Insurance Company. All rights reserved. Do not reproduce this report. It is for distribution to and use by FM Global employees only. Do not distribute beyond these groups

10

Page 11: Aluminum Industry Primer V2

Aluminum Smelter EDE Primer July 2008

o Protection Reference: 7-32 Flammable Liquid Operations

• Fires in conveyor systems (both rubber belt and bucket)

o Sprinklers

o Shutdown interlocks

o Protection Reference: OS 7-11, Rubber Belt Conveyor Systems

• Fires in pitch or bake oven fumes collection (waste emission) systems

(combustible deposits inside ducts, precipitators, scrubbers etc)

o Housekeeping

o Internal fire protection

• Fires in electrical cables, transformers and switch rooms

o Products of combustion (POC) detection at minimum

o Additional fire protection as needed

• Low dust explosion hazard with coke and solid pitch handling systems (See

Material Handling above)

• Mechanical damage to gears and motors on ball mills, extruders, and presses

o Maintenance

o Vibration analysis

o Spares

o NDE

• Electrical breakdown of transformers and switchgear

o Maintenance, inspection and testing

o Spares

o Clean, cool and dry environments

Production and handling of aluminum metal

At a primary smelter this generally consists of

• Electrolytic reduction process

• Casting of ingots, billets or other shapes to customer specification

Electrolytic reduction process

Copyright 2008 Factory Mutual Insurance Company. All rights reserved. Do not reproduce this report. It is for distribution to and use by FM Global employees only. Do not distribute beyond these groups

11

Page 12: Aluminum Industry Primer V2

Aluminum Smelter EDE Primer July 2008

The Hall-Heroult process is the method by which alumina (Al2O3) is separated into its

component parts of aluminum metal and oxygen gas by electrolytic reduction. It is a

continuous process with alumina being dissolved in cryolite bath material (sodium

aluminum fluoride) in electrolytic cells called pots and with oxidation of the carbon

anodes. The bath is kept in its molten state by the resistance to the passage of a large

electric current. Pot temperatures are typically around 1688-1769° F (920°- 980°C). The

aluminum is separated by electrolysis and regularly removed by siphoning for

subsequent casting. The pots are connected electrically in series to form a ‘potline.’

A potline is a group of 100 to 300 electrolytic cells or "pots" that are connected in

electrical series. An aluminum smelter consists of one or more potlines

In each pot, direct current passes from carbon anodes, through the cryolite bath

containing alumina in solution, to the carbon cathode cell lining and then to the anodes

of the next pot and so on (see Figures 4 and 5). Steel bars embedded in the cathode

carry the current out of the pot while the pots themselves are connected through an

aluminum bus-bar system. The pot consists of a steel shell in which the carbon cathode

lining is housed. This lining holds the molten cryolite and alumina in solution and the

molten aluminum created in the process. An electrically insulated superstructure

mounted above the shell stores alumina automatically delivered via a sealed system and

holds the carbon anodes, suspending them in the pot.

The electrolyte, which fills the space between the anodes in the pot, consists of molten

cryolite containing dissolved alumina. A solid crust forms at the surface of the electrolyte.

The crust is broken periodically and alumina is stirred into the electrolyte to maintain the

alumina concentration.

Approximately 13 -16 kilowatt-hours of direct current electrical energy, 2.2 lbs (1/2 kg) of

carbon, and 4.4 lbs (2 kg) of aluminum oxide are consumed per kg of aluminum

produced.

Copyright 2008 Factory Mutual Insurance Company. All rights reserved. Do not reproduce this report. It is for distribution to and use by FM Global employees only. Do not distribute beyond these groups

12

Page 13: Aluminum Industry Primer V2

Aluminum Smelter EDE Primer July 2008

Figures 4 and 5: Cross section views of pot

Figures 5 and 6: Photo of a modern PBA pot and series of pots in a potline building.

Copyright 2008 Factory Mutual Insurance Company. All rights reserved. Do not reproduce this report. It is for distribution to and use by FM Global employees only. Do not distribute beyond these groups

13

Page 14: Aluminum Industry Primer V2

Aluminum Smelter EDE Primer July 2008

As the electrolytic reaction proceeds, aluminum, which is slightly denser than the pot

bath material, is continuously deposited in a metal pool on the bottom of the pot while

oxygen reacts with the carbon material of the anodes to form oxides of carbon, primarily

large amounts of carbon dioxide. As the anodes are consumed during the process, they

must be continuously lowered to maintain a constant distance between the anode and

the surface of the metal, which electrically is part of the cathode. The anodes are

replaced on a regular schedule.

The vigorous evolution of carbon dioxide at the anode helps mix the added alumina into

the electrolyte but carries off with it any other volatile materials and even some fine

solids. If any carbon monoxide does form it usually burns to carbon dioxide when it

contacts air at the surface of the crust. Compounds of fluoride formed in side reactions

are the other main volatile product.

As electrolysis progresses, the aluminum oxide content of the bath is decreased and is

intermittently replenished by feed additions from the pot's alumina storage to maintain

the dissolved oxide content at about 2 to 5 percent. If the alumina concentration falls to

about 1.5 to 2 percent, the phenomenon of "anode effect" may occur. During anode

effect, the bath fails to wet the carbon anode, and a gas film forms under and about the

anode. This film causes a high electrical resistance and the normal pot voltage, about 4

to 5 volts, increases 10 to 15 times the normal level. Correction is obtained by computer

controlled or manual procedures resulting in increased alumina content of the bath.

The most critical issues associated with potline operation are

• Power supply and all electrical equipment must be designed to provide maximum

reliability and continuity of operations.

• Raw material handling, pneumatic systems, instrumentation, computer and

process controls must be arranged, protected and maintained in good working

order.

• Centralized exhaust and effluent treatment systems must be protected and

maintained.

• Back up systems or alternative operating capabilities must be in place for all

critical support systems.

Copyright 2008 Factory Mutual Insurance Company. All rights reserved. Do not reproduce this report. It is for distribution to and use by FM Global employees only. Do not distribute beyond these groups

14

Page 15: Aluminum Industry Primer V2

Aluminum Smelter EDE Primer July 2008

• Loss of critical support systems for more than a few hours can cause pots or

potlines to freeze.

A Potline process consists of the following systems and infrastructure:

• Electrical power

o Electrolysis power to pots and potlines is delivered from rectiformers by

metal (usually aluminum) bus bars. Control systems power is usually by

electrical cable. Both systems are typically in a space or basement below

the pots.

• Compressed air

o Used for control air for regulating equipment and for pneumatic power for

raw materials (alumina, Cryolite, etc.) delivery systems

• Raw materials conveying system

o Alumina and Cryolite are delivered to storage bins by elevated rubber belt

conveyor systems and are fed continuously into pots by pot tending

machines

o Anodes are delivered by mobile pot tending machines and inserted into

pots as they are consumed

• Fumes and effluent exhaust and handling system

o Off-gases consisting primarily of CO2 and fines containing alumina and

Cryolite fluorides are captured in waste emission ducts and sent to

scrubbers and precipitators for recovery of valuable feed stock and air

cleaning

• Service cranes and mobile equipment

o Replenishing feed hoppers

o Changing PB anodes (or feeding Soderberg pots with anode paste)

o Tapping metal

Primary EDE hazards for potline processes are:

• Loss of a critical utility can cause potline freeze

o A potline freeze is caused when there is an interruption to the pot or

potline for more than “several “(4 to 8) hours. This can result in the metal

and electrolyte in the pot freezing (solidifying) and this cannot generally

Copyright 2008 Factory Mutual Insurance Company. All rights reserved. Do not reproduce this report. It is for distribution to and use by FM Global employees only. Do not distribute beyond these groups

15

Page 16: Aluminum Industry Primer V2

Aluminum Smelter EDE Primer July 2008

be re-melted by electrical means due to poor conductivity. The frozen

electrolyte often needs to be physically removed. This can result in all or

many of the pots needing to be torn apart and rebuilt, a long and costly

process. (Refer to OS 7-64, Aluminum Industry - Reference Document -

for a more detailed description. Also refer to OS 7-64 – Section 5.0 Loss

Expectancy Guidelines - for a procedure to quantify potline freeze.)

o A potline freeze might be caused by many different sub- events including:

• Uncontrolled fire at anode paste plant

• Fire/explosion anode baking ovens/fume extraction system

• Loss of main electrical switchgear/substation

• Loss of main auxiliary power switchgear

• Loss of more than one power group/transformer

• Fire exposure to DC bus bars

• Molten metal pot tap out damaging DC bus bar

• Loss of potline gas treatment center

• Electrical utility service interruption

• Loss of compressed air service

• Loss of environmental waste effluent treatment (fume handling)

• Loss of shipping facility (unloader, conveyers)

• Loss of casting center (molten metal explosion)

• Loss of critical production equipment (ball mill, induction furnace,

paste mixer)

• Loss of main DCS control system

• Loss of cooling water

• Events that can cause a loss of electrical power:

o Area-aide power outage such as weather event destroying power lines

o Failure of on-premises generation

o Switchgear or transformer failure

o Failure involving component within the DC bus bar network

o Sudden tap out from a pot damaging bus bars or control cables

o Transformer fire damaging bus bars

o Poor coordination of electrical system resulting in failure

Methods to reduce risk of electrical failure

Copyright 2008 Factory Mutual Insurance Company. All rights reserved. Do not reproduce this report. It is for distribution to and use by FM Global employees only. Do not distribute beyond these groups

16

Page 17: Aluminum Industry Primer V2

Aluminum Smelter EDE Primer July 2008

o Redundant incoming power supply lines

o Proper layout of power lines, transformers, bus bars

o Testing, inspection and maintenance of electrical equipment

o Conduct thermography of welds, joints, risers.

o Perform milli-volt drop tests of welds, joints, risers and DC

isolators.

o Conduct thermography of DC isolators.

o Protection of electrical equipment

o Availability of emergency equipment

o Conduct thermography of welds, joints, risers.

o Perform milli-volt drop tests of welds, joints, risers and DC isolators.

o Conduct thermography of DC isolators.

o Equipment and procedures to handle failure of

welds and joints (similar to handling a pot tap out that washes away a

section of busbars).

o Visually inspect welds for cracking.

o Protection References: UTH - Service Interruption

(P0229); UTH – Electrical Hazards; OS 7-64 Aluminum Industry;

Electrical operating standards

• Events that can cause a loss of

compressed air

Loss will shut down plant causing possible potline freeze

Power outage

Fire

Mechanical breakdown

• Environmental waste effluent handling systems (fume system)

o Power outage

o Fire in combustible components (e.g. bag house)

o Protection References: OS 7-64, Aluminum Industry Section

2.1.3.3; OS 7-73 Dust Collection Systems; OS 7-78 Industrial Exhaust

Systems

• Molten Material – See casting operations below

Copyright 2008 Factory Mutual Insurance Company. All rights reserved. Do not reproduce this report. It is for distribution to and use by FM Global employees only. Do not distribute beyond these groups

17

Page 18: Aluminum Industry Primer V2

Aluminum Smelter EDE Primer July 2008

Figure 7: Closely spaced regulating transformers exposing main AC bus bars

Casting Operations

Molten aluminum is tapped from pots and transferred (usually by mobile carriers with

crucibles) to holding furnaces in a cast house. Furnaces are generally oil or gas fired but

may be electric.

From furnaces molten aluminum is cast into shapes such as ingots, billets, sows, or

slabs. Casting stations often use water cooling baths.

Aluminum metal is highly reactive in both solid and liquid (molten) forms. Solid particles

can cause dust explosions. Solid particles however are usually not found in or near

casting operations unless there is a powder making operation or cutting of metal in the

area.

Liquid aluminum in aerosol (mist droplet) form in air can cause a violent mist explosion.

Aerosols can be formed in casting operations when chemical reactions occur or when a

strong disturbing force such as a lightning strike or a precursor explosion occurs. This

phenomenon is rare but has occurred in industrial settings with molten metal mists.

Copyright 2008 Factory Mutual Insurance Company. All rights reserved. Do not reproduce this report. It is for distribution to and use by FM Global employees only. Do not distribute beyond these groups

18

Page 19: Aluminum Industry Primer V2

Aluminum Smelter EDE Primer July 2008

Molten aluminum is reactive in the presence of water and some other materials such as

hydrated lime, iron and copper oxides, and fertilizers. The reaction with water is partially

a steam expansion event compounded with formation of hydrogen gas by the rapid

decomposition of water. Reaction with oxides (i.e., iron rust) is called a thermite reaction.

The presence of hydrated lime (i.e., concrete) can cause a rapid exothermic reaction

under certain ideal conditions.

Since casting operations include water cooled casters and sometimes metal lined or

concrete pits these explosion potentials can exist in modern smelters.

Fire hazards are also present from potential molten metal spills contacting combustibles.

Primary EDE hazards for casting operations are:

• Fuel explosion in furnace

Proper fuel burner combustion safeguards

• Molten metal-water explosion

Eliminate water from furnace charge

Proper design and maintenance of water cooling on casters

Good operator training

Organic coatings on metal and concrete surfaces in pits

• Chemical reaction between aluminum and lime, metal catalysts or

oxidizers

Proper understanding of hazards

Elimination of potential catalysts

Proper grounding and bonding against lightening

• Molten metal spill

Can cause fires in other combustibles

Can damage control systems

Proper location of cables, control an utility systems

Dikes and curbs

Pits

Copyright 2008 Factory Mutual Insurance Company. All rights reserved. Do not reproduce this report. It is for distribution to and use by FM Global employees only. Do not distribute beyond these groups

19

Page 20: Aluminum Industry Primer V2

Aluminum Smelter EDE Primer July 2008

• Fire hazards in hydraulic (furnace lifting jacks), lube oil and fuel oil

systems

Proper location

Shielding against molten metal spill

AS protection if not near molten metal

Interlocks

• Fire hazards in grouped cables or switchgear

Proper location

Shielding against molten metal spill

AS protection if not near molten metal

• Mechanical and electrical breakdown

Maintenance of equipment

• Primary protection Reference: OS 7-64 Aluminum Industry

Administrative and support facilities

The plant will have warehousing, offices, maintenance shops, buildings housing

electrical and other utilities. These buildings will typically be non-combustible in modern

smelters. Fire protection might be needed for combustible occupancy.

Copyright 2008 Factory Mutual Insurance Company. All rights reserved. Do not reproduce this report. It is for distribution to and use by FM Global employees only. Do not distribute beyond these groups

20