Recycling of iron & steel

transcript

PRESENTATION ONRECOVERY & RECYCLING TECHNOLOGIES OF IRON & STEEL

Presented by: Muhsia Tabassum

M.Sc. Student,

Bangladesh University of Engineering & Technology (BUET).

IRON & STEEL

Iron – from which steel is being manufactured – is produced from iron ore which consists of iron oxide and usually other substances, known as gangue minerals such as oxides of calcium and aluminum, silicates, phosphates and sulphates.

It is smelted in a blast furnace with coke and limestone to produce iron.

IRON & STEEL (CONTINUED)

Steel is an alloy of iron produced by refining iron to remove excess carbon and other elements, particularly silicon and phosphorus.

The carefully controlled amount of carbon and other elements which are left, and some aluminum, nickel and chromium which may be deliberately added, determine the steel’s properties and therefore it’s applications.

PRODUCTION OF IRON & STEEL

Iron Production : (In Blast Furnace)

Iron ore contains iron oxides (Fe2O3) with gangue minerals (SiO2, Al2O3, P2O5 etc.) is used to produce Iron.

Solid charge (iron ore/iron & steel scrap along with coke and limestone)

The hot air – 1,200°C – blown into the base of the furnace induces the combustion of the coke.

PRODUCTION OF IRON & STEEL (CONTINUED..)

The O2 in the air reacts with coke to produce CO which reduces the iron oxide to form iron.

Gangue minerals are absorbed in limestone-forming slag.

Thus iron produced in liquid form tapped from the bottom of the furnace. (Pig iron)

Steel Production (In Basic Oxygen Furnace)

Molten pig iron (hot metal) poured into a large refractory-lined container called a ladle

High purity oxygen at a pressure of 100-150 psi introduced at supersonic speed onto the surface of the iron bath through a water-cooled lance.

Flux are charged Heat generation by the oxidation of

impurities.

STEEL PRODUCTION (IN BASIC OXYGEN FURNACE) CONTINUED..

The addition of oxygen to the charge of the scrap and molten iron leads to the formation of iron oxide and carbon monoxide.

When the carbon content of the molten metal is reduced to the desired level, the steel is tapped into a laddle and cast continuously.

Steel Making (In Electric Arc Furnace)

• Furnace receives energy from a three-phase transformer.

• Cylindrical solid graphite electrodes, suspended from above the shell and extending down through the ports in the roof are used to carry the current and strike an arc with the metal.

• Lime is used as flux & O2 injected into the bath late in the melt to refine the steel.

RECYCLING OF IRON & STEEL

A large number of secondary sources- ‘scrap’

Discarded metal in the form of machinery, auto parts etc.

In the steel making industries scraps are the main source raw materials.

RECYCLING OF IRON & STEEL (CONTINUED..)

Sources of Scrap Mainly three types of scraps- home, new

and old.

Old Scrap Old or obsolete scrap is iron or steel from

postconsumer products.

The largest source is junked automobiles followed by appliances, machinery, worn out railroad cars and tracks, demolished steel structures, and other products.

SOURCES OF SCRAP (CONTINUED..)

New Scrap

Mainly generated from manufacturing plants.

Scrap accumulates when steel is cut, drawn, cast, extruded, or machined.

As it’s chemical and physical characteristics are known, so it is usually transported quickly back to steel plants through scrap processors and dealers or directly back to the steel plant for remelting to avoid storage space and inventory control costs.

SOURCES OF SCRAP (CONTINUED..)

Home Scrapo Home or revert scrap consists of scrap that is

produced in steel mills and foundries as a byproduct of their operations, as well as old plant scrap.

o This scrap has a known composition and is always recycled to the furnace for remelting.

o Technological advances have significantly reduced the generation of home scrap.

DIFFERENT TYPES OF IRON & STEEL SCRAPS

Sheet Iron Scrap (Sheet Tin) Sheet Iron (Sheet Tin) shall consist of

miscellaneous iron & steel and may contain galvanized sheet, painted & coated materials, whole machinery & equipment containing other metals provided Iron is the main content.

Scrap White Goods Major household appliances including stoves,

fridges, freezers, clothes washers, dryers & dish washers.

DIFFERENT TYPES OF IRON & STEEL SCRAPS (CONTINUED..)

Mixed Steel Can Scrap Flattened or whole steel cans. This material is

typically generated from food cans from municipal recycling programs. May contain Bi-Metal (aluminum/steel) beverage cans. CAUTION May not contain aerosol cans.

Bundled Steel Can Scrap Bundled Steel Can Scrap shall consist of compressed

assorted flattened or whole steel cans with a minimum weight density of 75 lb./cubic foot. This material is typically generated from food cans from municipal recycling programs. May contain Bi-Metal (aluminum/steel) beverage cans. CAUTION May not contain aerosol cans.

Briquetted Oil Filters Briquetted Oil Filters shall contain used or spent

automotive or industrial oil filters that have been saturated with motor oil and shall have been compressed to a minimum weight density of 75 lb./cubic foot.

Mixed Scrap Iron & Steel Assorted iron & steel scrap up to any maximum size,

must be free of white goods & light gauge materials under 1/8" in thickness.

No.1 Steel Scrap (HMS1) No.1 HMS shall consist of clean iron & steel with a

minimum thickness of 1/4", and a maximum size of 60"x24", material handling compatible to feed a furnace charge box. This grade may include ISRI code 200.

No.1 Steel Scrap (2 foot) No.1 Steel (2 foot) shall consist of clean iron & steel

with a minimum thickness of 1/4", and a maximum size of 24"x18", material handling compatible to feed a furnace charge box. This grade may include ISRI code 201.

Special Scrap Plate Punchings Special Plate Punchings shall include clean, dry,

uniform plate punchings suitable for ballast material or high density furnaces charging. Material must be free flowing and no piece shall be larger than 2" in any direction and a minimum of 1/4" in any direction. May be any shape provided that there are no protruding edges.

No.2 Steel Scrap No.2 Steel shall consist of clean iron & steel scrap with a

minimum thickness of 1/8", and a maximum size of 60"x18", material handling compatible to feed a furnace charge box.

No.2 Steel Scrap (2 foot) No.2 Steel (2 foot) shall consist of clean iron & steel with a

minimum thickness of 1/8", and a maximum size of 24"x18", material handling compatible to feed a furnace charge box.

No.3 Steel Scrap (Unprepared Bushling) No.3 Steel (Unprepared Bushling) shall consist of clean,

uncoated steel clippings, stappings & sheet skeletons under 1/8" thick.

No.4 Steel Scrap (Silicon Bushling) No.4 Steel (Silicon Bushling) shall consist of clean silicon

bearing steel scrap with a maximum thickness of 1/8"

No.4 Shredded Steel Scrap No.4 Shredded Steel shall consist of course shredded

steel scrap.Mixed Cast Iron Scrap Mixed Cast Iron shall consist of assorted scrap iron

castings.Sorted Machine Cast Scrap Sorted Machine Cast shall consist of sorted broken

or unbroken scrap cast iron machinery scrap, not to exceed 18"x18"

Sorted Scrap Automotive Cast Sorted Automotive Cast shall consist of sorted

broken or unbroken cast iron automotive scrap, not to exceed 18"x18"

Unclean Motor Block Scrap Whole or particle cast iron auto or truck engines.

Transmissions may or may not be attached.Clean Motor Block Scrap Clean Motor Block shall consist of stripped cast

iron motor blocks, free of oil pan, pistons, and all foreign attachments.

Whole Prepared Scrap Car Bodies Unflattened car bodies, with tires, radiator and

battery removed, gas tanks acceptable but must be removed and punctured, (no propane tanks allowed). Engine and transmission may or may not be included.

Flattened Scrap Car Bodies Flattened Car Bodies shall consist of prepared car

bodies that have been flattened & stacked for transportation as auto shredder feedstock. Tires, radiator and battery removed, gas tanks acceptable but must be removed and punctured, (no propane tanks allowed). Engine and transmission must be removed.

Scrap Green Car Bodies Green Car Bodies shall consist of stripped car hulks that

have dismantled through a "Green" Auto Recycling System. The "Green" Car Body shall have most of the manually strippable non-metallic parts removed, including, windows, seats, interior & trunk carpet, head & tail lights, external non-metal body parts, internal dash parts. Fluids reduced or removed.

Scrap Steel Wheel Rims Scrap Steel Wheel Rims shall consist of whole or

crushed steel automobile wheel rims with tires removed, and may contain lead wheel weights.

Mixed Steel Turnings & Iron Borings Mixed Turnings & Borings shall consist of assorted cast

iron or steel turnings, borings or grindings.Short Shoveling Borings Scrap Short Shoveling Borings and Turnings shall consist of

clean free flowing cast iron borings or steel turnings. Must be free of fluffy, tangled, springy turnings and free of lumps or clumps.

Steel Mill Scale Mill Scale shall consist of magnetic iron surface scale

produce while working steel.

Iron Oxides Iron Oxides shall consist of clean sized iron

and iron oxide particles or powdered material. Maximum particle size of -10 mesh.

Manganese Steel Scrap Manganese Steel Scrap shall consist of non-

magnetic manganese/steel alloy materials. May include Manganese Grinder Plates.

Other Scrap Iron & Steel Other Scrap Iron & Steel shall include any

iron & steel materials not covered in the other iron & steel grades.

GENERAL PROCEDURE OF IRON & STEEL RECYCLING

Collection and Sorting The first step in metal recycling is the collection

of all the materials which are made up of metals. There should be an organized system for the collection of metals. Containers should be used to collect them.

For that there should be recycling centers in all big cities and there should be recycling bins at home and in the shopping malls that should be taken directly to industry.

The second important step is sorting the kind of metals which are good for recycling. The quality of metals matters a lot when it comes to recycling.

GENERAL PROCEDURE OF IRON & STEEL RECYCLING (CONTINUED..)

Processing The next step is to compact the metal. All the appliances are squeezed and squashed

in the machines so that they don’t occupy that much space in conveyor belts.

Sweat Furnace The furnace is used by many metal scrap

recyclers for the purpose of separating aluminum, zinc, and or/or lead from Iron in composite parts. It can also be used to remove contaminants like dirt, rubber, plastics and other combustibles from aluminum, zinc, and/or lead bearing scrap.

Shredding By shredding with massive hammer mills

automobile hulls, appliances and other large goods are reduced to fist-sized pieces.

Three streams of material are produced: ferrous metals (iron and steel), a light fraction residue and a heavy fraction residue.

The ferrous metals (iron & steel) are recovered by the shredder operator through magnetic separation and sold to steel mills.

Melting and Purification The next step is to melt all this scrap metal

in a large furnace.

Each metal has a specially designed furnace depending on its properties.

Then after melting the metals are purified by using different methods. Electrolysis is also used for metal purification.

GENERAL PROCEDURE OF IRON & STEEL RECYCLING (CONTINUED..) Magnetic Separation When large quantities of ferrous

scrap are to be separated from other materials magnetic separation is the obvious choice.

Magnetic separators can be of the belt type or drum type.

In the drum a permanent magnet is often located inside a rotating shell. Material passes under the drum on a belt.

A belt separator is similar except that the magnet is located between pulleys around which a continuous belt travels.

Eddy Current Separation Eddy current separators are used to separate

non-ferrous metals from waste and automobile shredder residue.

The simplest device follows this principle is the inclined ramp separator. This uses a series of magnets on a sloped plate covered with a non-magnetic sliding surface.

When a feed of mixed materials are fed down the ramp, non-metals slide straight down, while metals are deflected sideways by the interaction of the magnetic field and the induced eddy current.

The two streams are then collect separately.

Heavy Media Separator Heavy media separation (HMS) utilizes a

medium normally consisting of finely ground magnetic or ferrosilicon and water.

By varying the relative proportion of the solids the relative density of the medium can be adjusted.

The specific gravity of the medium is typically halfway between the densities of the two materials being separated.

Once separated, the products are allowed to drain; the medium recovered is returned to the process.

Incineration

Some scrap processors use incineration to remove combustible materials including oil, grease, wood, plastic & paper and volatile metals such as lead & zinc.

Dezincing Technologies: Two main processes of dezincing technologiesI. Thermal and Thermo-Mechanical

Removal: In the first method galvanized parts are heated

to a temperature greater than 900ᵒC to evaporate the zinc.

In the second method galvanized parts are heated to a temperature sufficient to embrittle the coating, which is then removed by abrasion.

In a third process coating is heated and subsequently removed by abrasion.

II. Chemical and Electrolytically Aided Removal of Chemicals:

In the first sulfuric acid is used to dissolve the zinc coating.

But the disadvantages is that it is difficult to separate the dissolved iron & zinc.

In the second the zinc coating is leached by ammonia.

In the third, caustic soda is used to dissolve the zinc coating.

CHEMICAL AND ELECTROLYTICALLY AIDED REMOVAL OF CHEMICALS (CONTINUED..)

The caustic soda dezincing process is considered to be the most promising.

Two major steps: Zinc is first dissolved from the steel scrap in a caustic

soda electrolyte by applying an electric current Then the sodium zincate solution is electrolyzed to

recover zinc in powder form on the cathode. The process can be applied to all types of galvanized

steel scrap. After electrolysis the material is passed through a multi-

station, counter-current rinsed cycle to remove entrained sodium zincate.

The zinc-enriched electrolyte is then treated in the electrowinning section using convetional cells with nickel anodes and cathodes.

Detinning Technologies The electrolytic detinning process consists of

leaching in a hot alkaline solution. The scrap is suspended in baskets in a bath

containing about 10% caustic soda, at a temperature of 80ᵒC.

Steel cathodes surround the baskets. A spongy tin deposit is formed on the

deposits. It is manually removed, compacted melted and cast into ingots and sold to tin refiners.

RECOVERING IRON POWDER FROM SCRAP

There are four methods to recover iron powder from scrap:

Atomization: A stream of molten metal produced from

home, industrial or processed obsolete scrap, is broken up with high pressure air, water or gases, such as nitrogen or argon.

Iron powder is produced by direct high pressure water atomization of molten scrap.

The powder is collected, dried and annealed.

The non-magnetic materials, if any, are segregated in a magnetic separator.

RECOVERING IRON POWDER FROM SCRAP (CONTINUED..)

Chemical Methods: o One of the most important chemical methods for the

production of iron powder is direct reduction of the scrap by using gaseous or solid reducing agents.

o The dried and ground mill scale is loaded in ceramic saggers using special charge heads, which are so designed that alternate sub-divisions can be filled with the mill scale and reducing agent, which is a mixture dried and ground coke limestone.

o The loaded saggers are stacked and heated at 1100ᵒC in a continuous tunnel kiln.

o The sponge iron then removed from the cooled saggers, crushed to powder, magnetically separated and subsequently reduced.

o The reduced powder is screened and blended depending upon the end use.

CHEMICAL METHODS (CONTINUED..)

Another chemical process has been developed to utilize low-grade scrap such as turnings, borings, tin cans and other types of ferrous scrap.

The process consists of dissolving the scrap in hydrochloric acid, followed by evaporation and crystallization of the resultant solution to yield ferrous chloride crystals, which are dried, briquetted and converted to iron sponge by reduction in hot hydrogen.

Electrolytic Deposition:

In this process, iron scrap is treated with hydrochloric or sulfuric acid to produce chloride or sulfate or mixed chloride-sulfate electrolyte bath.

Iron powder is produced by using a graphite or carbon anode or a stainless steel cathode.

Pulverization:o These methods use cast iron turnings or

machining swarf as the material.o The machining chips are degreased, heavy

pieces are removed by air-separator, and the chips are hammer-milled to produce the particles of less than 0.8 mm size.

o These chips are then impact-fractured by throwing them against a target surface by a high velocity stream.

o The powders are collected, classified and annealed.

PULVERIZATION (CONTINUED..)

In another method, the cutting fluid is separated from machining swarf and the cleaned and dried material is pulverized in a hammer-mill at room temperature.

INTERMEDIARY PRODUCTS & WASTE TREATMENT (IN THE STEEL-MAKING INDUSTRY)

Type Process Source

Characteristics

Treatment/Reuse/Recycle

Spent waste acid and pickle liquor

Finishing Non-metallic Processed & recovered iron chlorides are used for phosphate removal. Neutralized with lime and land-filled.

Pickling Non-metallic, Hazardous waste

Neutralized with lime and land-filled. Processed and recycled for pickling or sewage treatment.

Alkali cleaner

Non-metallic Land-filled.

Tin line Non-metallic Waste sludge is treated by an ion-exchange process, chromic acid is recovered and recycled. Land-filled.

Spent refractory

Melting Non-metallic Reused or processed and recycled. Land-filled or stockpiled.

Ingot hot tops

Batch ingot casting

Metallic Metal is recovered magnetically and remaining material sold for use as roadbed aggregate.

Mill scale Finishing Metallic Sintered and recycled.

STAINLESS STEEL (SORTING & PREPARATION TECHNOLOGIES)

Manual Sorting: This involves the removal of components from

the scrap by hand. Example- the removal of catalytic converters from scrap automobiles.

Large items such as storage tanks and platforms must be cut to allow them to be changed into a furnace.

This is done using torches, crushers and shredders.

Magnetic Separation:o This is used to separate the magnetic stainless

steels and nickel from the non-magnetic stainless steels.

STAINLESS STEEL (SORTING & PREPARATION TECHNOLOGIES) (CONTINUED..)

Baling & Compaction: Loose scrap and thin-walled low density scrap (tanks and

tubing) are normally compacted by bailing or briquetting.

A baler is a heavy piece of equipment that uses up to three hydraulic rams to compress the scrap.

In the briquetter, small scraps are compacted into pockets as it passes between two counter rotating drums.

The use of bales and briquettes reduce transportation costs and facilitates the charging of the furnace.

Shredding: It is used to reduce the size of large stainless steel parts. Stainless steel found in automobiles is recovered from

automotive shredder residues.

STAINLESS STEEL (SORTING & PREPARATION TECHNOLOGIES) (CONTINUED..)

Eddy Current Separation:• Some non-ferrous metal separators utilize eddy

current technology to recover the non-ferrous metals and stainless steels from shredder residue.

Heavy Media Separation:• It is used in some non-ferrous metal separators to

recover the non-ferrous metals and stainless steels from shredder residue.

Sweat Furnace: • This is used for the purpose of separating

aluminum, zinc and lead from stainless steels, which coexist in composite parts and to remove contaminants.

GENERAL DESCRIPTIONS OF RECOVERY TECHNOLOGIES OF STAINLESS STEELS

The following are some of the ladle-refining processes: Ladle without-cover:• Composition adjustment by sealed argon bubbling(CAS)

process;• Sealed argon bubbling (SAB) process; and• Argon-oxygen decarburization (AOD) process. Ladle with-cover: • Thyssen-Niederrhein (TN) process;• Kimitsu Injection Process (KIP); and• Capped Argon Bubbling (CAB) process. Vacuum Processes:• Stream degassing process;• Rheinstahl Huttenwerke & Heraeus (RH) process;• Vacuum-oxygen decarburization (VOD) process; and• Dortmund-Hoerder (HD) process.

ECONOMIC FACTS IN RECYCLING IRON AND STEEL Almost 40% of the world’s steel production is made from scrap. Every ton of recycled steel can help save 1.4 ton of iron ore. Conversely, a steel can land-filled will take 100 years to vanish. Steel is the most recycled material on earth! In Luxembourg, 2,292 tons of

steel packaging have been collected in 2013. Recycling one ton of steel saves 1,100 kgs of iron ore, 630 kgs of coal, and

55 kgs of limestone. CO2 emissions are reduced by 58% through the use of ferrous scrap.

Recycling one ton of steel saves 642 kWh of energy, 1.8 barrels (287 litres) of oil, 10.9 million Btu's of energy and 2.3 cubic metres of landfill space.

Recycling steel uses 75% less energy compared to creating steel from raw materials - enough to power 18 million homes.

Steel recycling uses 74% less energy, 90% less virgin materials and 40% less water; it also produces 76% fewer water pollutants, 86% fewer air pollutants and 97% less mining waste.

Steel automobile frames contain at least 25% recycled steel and a typical electrical appliance will usually be made of 75% recycled steel. Steel cans consist of at least 25% recycled steel.

ECONOMIC FACTS IN RECYCLING IRON AND STEEL (CONTINUED)..

USES OF STEEL

Steel is present in many different areas: A car is made of 65% recyclable and recycled

steel – engine parts, body, doors, etc. Electrical appliances: Washing machine: 57%

steel; Cooker: 80% steel. This steel is recyclable.

Fridge: 51% steel Food packaging: cans and beverage cans

mainly. This steel is recyclable and recycled.

Building products: 70% of all building products made of steel – concrete rebars, metallic frames, etc. – are recycled.

THANKS TO ALL