A Galvanised Cold Rolled C Section Engineering Essay

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In this report the sustainability of a galvanised cold rolled C-section to be used as a rafter in a portal Frame building will be examined. The entire life cycle will be examined, staring with the extraction of the iron ore and finishing with the decommissioning of the building. In the report the key points will be energy consumption, CO2 emissions, toxic waste, biodiversity and climate change will be examined.

Extraction

The two methods for extracting iron ore are surface mining known as open-pit mining and underground mining known as shaft mining. Both types of mining need to be done on a large scale to be competitive consuming a lot of energy in the process, according to Swedish mining company LKAB's annual report 2010 (LKAB, 2010), in the year 2010 the total energy requirement for their mines and processing plants in Kiruna, Svappavaara and Malmberget and their ports in Lulea and Narvik amounted to about 4.1 TWh. Their mines and ports produced and delivered 26 million tonnes of iron ore, 21 million tonnes was in the form of pellets produced at their pelletizing plants (LKAB, 2010). This gives an approximate energy consumption per tonne of pellets of 0.19 MWh/tonne (LKAB, 2010).

Due to the large amounts of energy consumed and quantity of fossil and other fuels used in the process of mining and pelletizing there is a considerable amount of atmospheric emissions, in 2010 the mines and processing plants in Kiruna, Svappavaara and Malmberget produced 696,000 tonnes of CO2 (LKAB, 2010). According to the report Methodology for the free allocation of emission allowances in the EU ETS post 2012 Sector report for the iron ore industry in 2007 the three mines and pelletizing plants in Sweden owned by LKAB produced 38.3 kg CO2/tonne of ore and pellets produced (European Commission, 2009).

The amount of CO2 produced in the mining and production process can vary depending on the production process used to refine the ore and the type of ore mined. Table 1 below taken from LKAB's 2010 annual report shows the difference in CO2 emissions of sintering and pelletizing as well as LKAB's form of pellets. Swedish iron ores are oxides, for example hematite Fe2O3, while Austrian ores are carbonates, for example siderite FeCO3, this means that during the pelletizing process significantly higher process emissions are expected from the plant due to open in 2013 in Austria, due to the carbon content of the Austrian ore and the increased energy requirements to produce the pellets due to special treatments the plant expects to produce 130 kg CO2/tonne of ore and pellets an increase of 91.7 kg CO2/tonne when compared to the Swedish plants (European Commission, 2009).

process emissions.jpgImage and statistics taken from LKAB (2010)

Mining creates a large amount of waste rock, in modern mines this rock is now sorted and sold on for other uses such as construction material or for its mineral and metal content, the Swedish mines owned by LKAB sorted 89% of the waste extracted. The Carajas mine in Brazil in 2007 extracted 296 million tonnes of iron ore, by sorting its waste rock it also relinquished 17.6 million metric tons of pellets; 247,900 metric tons of finished nickel; 9.1 million metric tons of bauxite; 4.3 million tons of alumina; 551,000 metric tons of aluminium; 1.3 million metric tons of kaolin; 2,500 metric tons of cobalt (Net Resources International, 2012).

Other wastes are generated during the mining and refining of the iron ore including fluids from spills and breakages on the machinery used, residue from explosives and contaminated water from treatment and refining processes. The contaminated water is purified in onsite treatment plants and as long as it meets certain environmental criteria can be pumped back into the environment, any water deemed to be unsafe can be re-used in the iron mining process.

Both types of mine can have a negative ecological impact both in the destruction to habitat and by accidental release of containments into the local environment. Open pit mines such as the Carajas mine in Brazil cause significantly more destruction to wildlife than shaft mines. Mining companies in modern times have to have a plan in place to return the habitat to its original state. Jaymilson Magalhaes, the operations manager for the Carajas mine in Brazil states in an interview with BBC reporter David Shukman, that their mine only covers about 3% of the area of the national forest and the company has to have a plan in place to restore the forest to its natural state before any digging can commence (BBC, 2012), this includes using any spoil from the mine to reshape the topography before a massive replanting process using native species can be undertaken (BBC, 2012). Magalhaes claims that he genuinely believes that the forest can be restored after mining, by careful planning they know exactly which plants are needed and they have nurseries with the original vegetation in, so that when they finish mining and the topography is reformed the forest will be able to grow back to its original state (BBC, 2012).

The iron ore and pellets are transported by train to harbours, then transported by ship to harbours located near to steel mills where the iron ore is turned into usable steel products. In an effort to make the trains ecologically friendly as well as to make them more profitable the companies make them very long and able to carry a large quantity of ore, LKAB in their 2010 annual report claim that they operate trains of 68 cars in length, each able to carry 100 tonnes, with a total capacity of 6,800 tonnes (LKAB, 2010), whilst BHP Billiton (Australian Government, 2012), a mining company from Australia, operate trains consisting of up to three locomotives and over 250 wagons. Trains of this size carry over 25,000 tonnes of ore and can be over 2km in length (Australian Government, 2012).

Manufacturing

Generally steel is produced in integrated iron and steel plants, these are usually located near the mines in countries that produce their own ore or near deep water harbours in countries that import their ore. The United Kingdom imports the iron ore and coal it needs for steel production due to the resources of good quality coking coal and ore being limited and not economically viable (EEF, 2011). These plants produce many varieties of steel in many forms. In 2011 the United Kingdom produced 9,481 k tonnes of crude steel (World Steel Association, 2012). The steel making process is energy intensive and uses fossil fuels in the process, table 2 below shows the CO2 emissions and energy consumption of different steel products, values are per tonne of finished product.

Plate

Sections

Tubes

Hot Dip

Galvanised

(generally)

Purlins and

Side Rails

CO2

(t/t)

0.919

0.76

0.857

1.35

1.10

Energy

(GJ/t)

17.37

13.12

15.42

21.63

19.38

(TATA Steel, 2012)

The steel process also produces a large varieties of by products, most of these can be re-used in the steel process or sold on for other uses. Table 3 below shows some of the by products generated and how they are used in other industries.

By-product

Use/industry

Ground granulated blast furnace slag

Cement in the concrete sector

Air-cooled blast furnace and basic oxygen steelmaking slag

Agricultural fertiliser and civil engineering

Tar, benzene, toluene and xylene

Chemical industry

Ammonium sulphate and sulphuric acid

Agricultural fertiliser

Iron oxide

Electronics, cement and paint

Ferrous chloride solution

Water treatment, effluent and dye industries

Zinc dross

Non-ferrous metal recovery industries

(TATA Steel, 2012)

Steel can also be produced by re-cycling steel from its previous service. For every tonne of steel that is re-cycled 1.9 tonnes of iron ore and 0.6 tonnes of coal are saved (EEF, 2011), it also takes 75% less energy to re-cycle steel than it takes to produce steel from iron ore (The NEED Project, 2012)

Due to the weight of galvanised cold rolled steel members weighing less than hot rolled members for the same application it means you get more members per tonne therefore you are able to transport more members per lorry, using less lorries to deliver the materials for a building/structure. From my own experience if all the steel members of a building are of cold rolled steel, a building of dimensions 18m x 18m x 5.5m can be delivered on one transport lorry, this includes all bolts and connection plates needed for construction and all rails, purlins, door jambs and headers needed to complete the frame.

Erection

Due to the C-section to be used as a rafter is galvanised it is protected from the elements and can be stored outside until it is required for installation. Due to the lower weight per metre of C-sections compared to I beams the entire structure can be erected quickly, with minimal machinery, from experience the building mentioned above (18m x 18m x5.5m) can have its structure completed by 3 men, 1 14m telescopic handler and 1 small diesel powered scissor lift in about 5 working days. Buildings over 22m in width generally can't be erected using a telescopic handler due to the weight of the completed rafter being too close to the maximum lifting capacity of the machinery and health and safety require the use of a crane for these operations, which will increase the cost of erection, energy consumed and CO2 emissions.

The C-section rafter and all other components are pre-fabricated, so once the materials are onsite they have to be bolted together and are ready for lifting and installation, the sketches below show the typical connection process for a C-section rafter.

Once the rafter is completed the telehandler is used in conjunction with a sling and lifted into position. While 1 man operates the telehandler holding the rafter in position, and making any adjustments needed to align bolt holes, the other men use the scissor lift to access the required height to bolt the rafter the eaves plate and secure the rafter in position by installing some of the roof purlins. This assembly can be done in any weather as long as health and safety permit the operations to commence, many sites are closed by health and safety due to severe weather conditions such as snow, electrical storms and high winds, MEWP's must not be used in wind speeds above 12.5m/s.

Service Life

Due to steel's low specific heat capacity of 480 J/kg and its high thermal conductivity of 45 W/mK (Greenspec, 2013) means that it is ill suited for uses where thermal mass is used to store and release heat, however it would be a good choice of material for low or reverse thermal mass design.

C-sections are easy to modify onsite without the need of specialist equipment, from my own experience they can be cut and drilled onsite making them a flexible material. Extending the building is also an easy process, by the removal of the external cladding and gaining access to the structure, the building can be extended either by adding another portal and a valley gutter or by adding more bays at either end.

Steel is a strong, hard and tough material so it takes a considerable force to damage it.

There is little or no maintenance required for a galvanised C-section rafter.

End Of Life

A cold rolled steel frame building/structure can be disassembled as easily as it is erected. All of the materials used in the frame can be re-cycled or re-used, there is a large market for second hand portal frame buildings. From my own experience a building 5m x 90m x 4m with a building 20m x 20m x 4m connected to the gable (see photo below) can be taken down in a controlled manner by 6 men, 1 14 m telescopic handler and 2 diesel powered scissor lifts in 9 working days, the frame of the building along with the single skin cladding, personal and roller doors was loaded into 1 40' and 1 20' shipping containers and stored for future use, this was done for Sub Sea 7 at their temporary spool base in Limassol, Cyprus.

recycled.jpg

This Diagram depicts what percentage of concrete, timber and steel used in construction is re-cycled, re-used, down cycled and sent to land fill (BCSA, 2011).

Conclusion

Due to the amount of steel that is now re-used and re-cycled it can be a fairly sustainable material. Only when steel products are made from iron ore is it not really sustainable as we have no way of creating more ore.

LKAB ANNUAL REPORT AND SUSTAINABILITY REPORT 2010 (2010) LKAB Annual Report 2010, 29th March 2011. Sweden : Lulea Grafiska, pp. 3-41.

EUROPEAN COMMISSION (2009) Methodology for the free allocation of emission allowances in the EU ETS post 2012 ,Sector report for the iron ore industry, November 2009. European Union : Fraunhofer Institute for Systems and Innovation Research, pp. 3-7.

BCSA (2011) The Whole Story from Cradle To Grave, 18th November 2011. Great Britain : United Business Media, pp. 12-13.

THE NEED PROJECT (2012) Secondary Energy Infobook, June 2012. USA : Great Lakes Fuel Cell Education Partnership, pp. 69.

MINING TECHNOLOGY.COM (2012) Carajas Iron Ore Mine, Brazil, [WWW] Net Resources International. Available from: http://www.mining-technology.com/projects/carajas/ [Accessed 20/12/2012].

NEWS SCIENCE & ENVIRONMENT (2012) Forests and Caves of Iron: An Amazon Dilemma [WWW] BBC. Available from http://www.bbc.co.uk/news/science-environment-18483647 [Accessed 21/12/2012].

AUSTRALIAN ATLAS OF MINERALS, RESOURCES, MINES & PROCESSING CENTRES (2012) Iron Fact Sheet [WWW] Australian Government, Geoscience Australia. Available from http://www.australianminesatlas.gov.au/education/fact_sheets/iron.html [Accessed 23/12/2012].

EEF UK STEEL (2011) Ironmaking [WWW] EEF. Available from http://www.eef.org.uk/uksteel/About-the-industry/How-steel-is-made/step-by-step/Ironmaking.htm [Accessed 26/12/2012].

WORLD STEEL ASSOCIATION (2012) Steel Productioon 2011 [WWW] World steel Association. Available from http://www.worldsteel.org/statistics/statistics-archive/2011-steel-production.html [Accessed 28/12/2012].

TATA STEEL (2012) The Carbon Footprint Of Steel [WWW] TATA Steel. Available from http://www.tatasteelconstruction.com/en/sustainability/carbon_and_steel/ [Accessed 29/12/2012].

TATA STEEL (2012) By-product [WWW] TATA steel. Available from http://www.tatasteeleurope.com/en/company/activities/strip_products_uk/the_environment/making_strip_steel_better/by-products/ [Accessed 30/12/2012].

GREENSPEC (2013) Thermal Mass [WWW] Greenspec. Available from http://www.greenspec.co.uk/thermal-mass.php [Accessed 1/1/2013].

EEF UK STEEL (2011) About The Steel Industry [WWW] EEF. Available from http://www.eef.org.uk/uksteel/About-the-industry/default.htm [Accessed 1/1/2013].

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