Climate Impacts and Emission Mitigation of Selected Industrial Processes

10.3.1 Production of Iron and Steel

World raw steel production was 1,200 Mio t in 2006 (USGS, 2007). Markets are growing very fast, especially in China, where annual production has reached about 420 Mio t in 2006. On a global scale steel production GHG emissions are estimated to be 1,500 to 1,600 Mio t CO2-eq., including emissions from coke manufacture and indirect emissions due to power consumption. This is equal to 6 to 7 percent of world's anthropogenic GHG emissions. Chinese steel production accounts for more than 10 percent of countrywide GHG missions.

Iron and steel production is climate relevant for two reasons: First, it is an energy intensive process and thus uses large amounts of fossil energy sources, which result in CO2 emissions. In addition, during the different process steps, non energetic production related emissions of direct climate gases such as CO2 and CH4 occur. Moreover other pollutants with direct greenhouse gas effects are emitted (see table 10.6).

Table 10.6 Emission of selected pollutants in steel production (BREF, 2002)

Pollutant

Amount (g/t liquid steel)

PAH

200

VOC

90

Pollutant

Amount (g/t liquid steel)

CO

14,900

NOX

1,000

SO2

930

The following details of steel production elucidate the sources of emissions:

• Iron is produced by reducing iron oxide from iron ore using metallurgical coke in a blast furnace. Iron is introduced in the form of raw iron ore, pellets, briquettes, or sinter material. The result of this first production step is an impure pig iron. It is the raw material for steel production by specialised steel making furnaces, and for the production of iron products in foundries. During pig iron production CO2 and CH4 are emitted.

• Metallurgical coke which is needed as a reducing agent is produced by heating coking coal in a coke oven in a low oxygen environment. This process is a non-energetic one. Thus, its emissions are considered in the greenhouse balance of steel production. During the process, volatile compounds of the coking coal are driven off as a coke oven gas. When applied in the blast furnace, the metallurgical coke is oxidized. The result is reduced iron and CO2.

• When volatile compounds resulting from metallurgical coke production condensate tar products are generated. Coal tar is the raw material for the production of anodes for electrolytic processes, such as primary aluminum production, and for several other coal tar products. During the processes, CO2 and CH4 are emitted. The relation between these two is about 50:1.

• The majority of the CO2 emissions in the iron and steel production come from the production of pig iron (using metallurgical coke). Smaller amounts originate from the removal of carbon during the steel production. Carbon is also stored in the products, i.e. iron (about 4 percent carbon) and steel (about 0.4 percent carbon).

• Methane which is produced during the processes for coal coke, sinter, and pig iron, is mostly emitted via leaks in the production, only partly through the emission stacks of the plants. Thus a treatment of methane is difficult. The emission factors are 0.5 g CH4/kg produced coal coke, 0.9 for pig iron, and 0.5 for sinter.

Resulting total GHG emissions in steel production are characterised by a high variability depending on the production technology applied. The differences are based on the production route used, fuel mix and production energy efficiency, carbon intensity of the fuel mix, as well as electricity carbon intensity.

Compared to an average emission value of world steel production EU and USA both reach only 50, and Japan only 25 percent, however Russia and China up to 350 percent due to out-date-technology. This fact indicates a high improvement potential by modernisation of plants. In Germany, long term improvement activities of steel making technology resulted in a reduction from 2.5 t CO2-eq. per t of pig iron in 1960 to a value of 1.34 in 2007 (Amelung, 2007). After technology assessment studies a value between 0.5 and 1.5 seems possible. However economic constraints will lower this potential.

Technological improvements refer to reduction of carbon dioxide emissions by CCS (see chapter 9.4), energy efficiency improvements, as well as fuel switching. Energy related measures include enhancing continuous production to reduce heat loss, recovery of waste energy and process gas, or preheating in case of the use of scrap metal. Switching to alternative fuels such as oil and gas could reduce specific CO2 emissions. Other recent options are the use of pre-treated waste components, such as recycled plastics or refuse derived fuel (RDF) (see chapter 12.6). Moreover renewable charcoal is a traditional alternative to coke. By use of hydrogen iron ore could be reduced with much lower CO2 emissions.

Long term total mitigation potential is estimated in the range of 0.32 and 0.76 t CO2-eq./t steel.

10.3.2 Cement and lime manufacture 10.3.2.1 Cement manufacture

Cement is a finely ground grey powder of inorganic non-metallic nature. After mixing with water it forms a paste which sets and hardens due to the formation of silicate hydrates from cement constituents. Cement is a critical element of the construction industry. World cement production in 2006 was about 2,500 Mio t (USGS, 2007). It is produced in nearly 40 countries all over the world. The production is growing heavily due to the global economic development, e.g. in China in 2006 a capacity of 1.1 billion t was achieved (USGS, 2007). No shortage of the raw material is envisaged, for limestone is abundant all over the world.

The cement industry strongly contributes to the global CO2 emissions with an amount of 5 percent. In the USA, cement is one of the largest sources of industrial CO2 emissions (see table 10.2). At the current cement production of 94 Mio t of portland cement and 6 Mio t of masonry cement a total of 45.9 Mio t CO2-eq. is emitted.

Comparable with steel production, climate relevant emissions originate from direct energy consumed in making cement, as well as from the chemical proc esses during the reaction. An amount of 60 to 130 kg fuel oil and 110 kWh of electrical energy per ton of cement are used. 50 percent of the greenhouse gas emissions are due to the chemical process, and 40 percent to burning fuels. The remainder splits into transport and electricity needs.

Specific production processes are as follows: In the first process the raw material which is limestone (calcium carbonate CaCO3) is heated at a temperature of about 1,300°C in a cement kiln ("calcination"). This results in lime (calcium oxide CaO) and CO2. The amount of CO2 released is directly proportional to the lime-stone input. In the next step, as an intermediate product, the so-called clinker is produced through the combination of lime with silica-containing material. An average of 0.525 t CO2 is emitted per ton of clinker produced. The clinker is cooled and then mixed with small amounts of gypsum, which results in portland cement. Masonry cement for construction needs is produced by the addition of more lime. This results in additional CO2 emissions.

Also methane is emitted, but in very small amounts, which are in the range of 0.01 percent of the CO2 emissions.

The reduction of CO2 emissions is a first priority in the cement industry. In a Cement Sustainability Initiative a standard ruling for the cement production process and measures to reduce emissions were prepared (CSI, 2005).

One important measure to reduce the climate gas emissions is the substitution of traditional fossil fuels by industrial wastes, which is also one of the most efficient practices of disposing waste components. On the other hand waste components not only substitute energy but also raw material so that a double effect is achieved as long as quality requirements of the target product are met.

A survey of secondary fuels which include such components as used plastics insulation, shredded plastics, paper fractions, and municipal solid waste as well as refuse derived ("secondary") fuels (RDF; see chapter 12.6) is given in table 10.7.

Table 10.7 Secondary fuel use in cement production (UBA, 2007)

Secondary fuel source

CO2 emission factor (kg/ TJ)

Biogenic mass fraction (percent)

Recycled tyres

97.32

27

Recycled oil

78.69

0

Commercial waste - paper

64.88

91

Commercial waste - plastic

83.07

0

Commercial waste - packaging

56.85

40

Secondary fuel source

CO2 emission factor (kg/ TJ)

Biogenic mass fraction (percent)

Textile waste

63.29

70

Commercial waste - other

68.13

52

Animal meals and fats

74.87

100

Processed municipal waste

59.85

55

Waste wood (wood scraps)

95.06

100

Solvents (waste)

71.13

0

Carpet waste

80.42

36.5

Bleaching clay

82.26

0

Sewage sludge

95.11

100

Oil sludge

84.02

0

German cement industry annually applies about 2.8 Mio t of such secondary fuels. Similar activities can be observed in other countries such as Japan and India for the use of waste material, agricultural wastes, sewage sludge and a wide range of organic liquids and solvents. On the level of single companies or cement plants the usage of waste components in an amount of more than three quarters of the fuel was reported (ICCP, 2007c).

In some cases, extra climate benefits are achieved from reduced CO2 emission per energy unit which is due to the biogenic organic carbon content (see table 10.7) which is considered climate neutral (see chapter 12). In the case of refuse derived fuel (RDF) from municipal solid waste (MSW) about 60 percent is of biogenic origin.

As another climate control option considerable amounts of foundry sand, which is a by-product of steel making, can be used in cement production in place of cement clinkers. One ton of cement clinker can be replaced by one ton of foundry sand, and this relationship defines the pertinent CO2 emission reduction. In Germany, in 2004, 5.11 Mio t of cement clinker were replaced by foundry sand. This is also a waste reducing activity (UBA, 2007).

The total long term mitigation effect is estimated between 0.65 and 0.89 t CO2-eq./t cement (IPPC, 2007c).

10.3.2.2 Lime manufacture

The term lime refers to a broad variety of chemical substances, which includes high-calcium quicklime (calcium oxide, CaO), hydrated lime (calcium hydro xide, Ca(OH)2, dolomite quicklime (CaO*MgO), and dolomite hydrate (e.g. Ca(OH)2*Mg(OH)2).

Lime is not only used in the cement production, but is also a manufactured product, which has many industrial, chemical, and environmental applications, mainly in steel making, as a purifier in metallurgical furnaces, in cleaning (desulfurisation) of flue gas (FGD) from coal-fired electric power plants, in construction, in water purification, or as raw material in glass manufacturing and magnesium production from dolomite.

World annual lime production amounted to about 130 Mio t in 2006 (USGS, 2007), with China and USA as main producers, which produced 25 and 21.2 Mio t, respectively, followed by Russia (8.5), Japan (8.9), and Germany (6.8 Mio t). Lime ranks high among the most important chemicals, in the U.S. industry it was historically fifth in total production of all chemicals.

The main technological step - in analogy to the cement production - is the calcination, where CaO is produced and CO2 is emitted to the atmosphere. Theoretical process emissions are 0.785 t CO2 per ton of calcium oxide and 1.092 t CO2/t magnesium oxide produced. In efficient lime kilns about 60 percent of the emissions are due to the chemical processes. In Europe they are estimated at 0.750 t CO2/t lime. The value can be up to 2-3fold, e.g. in small vertical kilns in Thailand. Emissions from fuel depend on the kiln type, energy efficiency and fuel mix and are 0.2 to 0.45 t CO2/t lime (IPPC, 2007).

More efficient and better managed kilns are a pre-condition of emission reductions. Further reductions are possible by switching to low-fossil carbon fuels as in case of cement. For small scale facilities the use of solar energy seems promising.

A major reduction is possible by recovering of CO2 for use in sugar refining and for the production of precipitated calcium carbonate (PCC), which is applied as special filler in premium-quality coated and uncoated papers. In the U.S. industry in 2004 1.125 Mio t CO2 were used in this way which is equal to about 7 percent of the total U.S. CO2 emission in the lime industry. 90 percent of the CO2 input in the U.S. sugar refining and PCC production were from this source.

10.3.3 Ammonia manufacture and urea application

Ammonia and urea are nitrogen fertilizers for application in agriculture to improve plant yields. Annual world ammonia production in 2006 was about 122 Mio t (USGS, 2007).

At present, feed-stocks of ammonia production are natural gas, but also petroleum coke. In the case of production from natural gas, there are five main process steps, including a primary and a secondary reforming and a shift reforming process, by which CO2 is removed from the process. During the following ammonia synthesis, NH3 is formed by a catalytic process from H2 and N2.

CO2, together with process impurities, is a constituent of the waste gas. It is washed out by a scrubber from which it is released into the atmosphere during regeneration of the scrubber solution. A part of the CO2 is used as a raw material in the production of urea (CO(NH2)2) together with ammonia. The carbon in the urea is released into the environment after application of the urea fertilizer in agriculture. Hence, the whole amount of CO2 produced in the ammonia synthesis is finally emitted into the atmosphere. For greenhouse gas budgets these CO2 emissions are allocated to ammonia or urea production according to the amount of both fertilizers.

The emission factor is 1.2 t CO2-eq. per t of NH3 in the case of natural gas feedstock. For each ton of urea 0.73 t CO2-eq. are emitted. The long term mitigation effect is about 0.5 CO2-eq./t (IPPC, 2007c).

10.3.4 Aluminum production

Aluminum is a light weight metal with high corrosion resistance and high heat and electric conductivity. Its annual global production in 2005 was about 31.2 Mio t (USGS, 2007) with highest capacities in China (7.2 Mio t), Russia (3.7), Canada (2.8), and the USA (2.5). Production is expected to grow at a rate of 3 percent per year during the next decade.

In quantity and value aluminum is the second in the range of metals after steel and is important in all segments of the economy. Uses include transportation (aircraft, automobiles, bicycles), construction (windows, doors), packaging (cans, foil), and consumer durables for daily life, such as kitchen ware and material. By the so-called eloxation a thin surface cover is generated which improves the primarily high corrosion resistance and makes aluminum even better applicable in the construction sector.

In nature, aluminum occurs as a low soluble oxide and as a silicate. The production of primary aluminum from the ores (especially bauxite) is very energy consuming (via electrolytical processes), so that a reduction of the power input seems to be the best choice of process and climate improvements. However latest worldwide efforts to reduce electricity needs in primary aluminum production were without result due to the fact that the production is currently optimised, and the energy need is close to the theoretical minimum (by a factor of 2) (Schon, 2004).

The best option to reduce power input for total aluminum production is recycling, since the energy need for recycled aluminum is only 8.5 percent of the primary production for Western European or German energy mix, respectively. Sources for recycled aluminum include automobiles, windows and doors. However, recycling of aluminum cans has the highest profile. In the USA in 2006 aluminum recovered from purchased scrap was about 3 Mio t, of which 64 percent came from manufacturing scrap and 36 from discarded aluminum products (old scrap). Aluminum from old scrap was equivalent to 16 percent of apparent consumption (USGS, 2007). For details of aluminum recycling effects on CO2 emissions see chapter 12.

In additions to the energy aspect also process related emissions of CO2 and PFCs occur, especially perfluormethane (CF4) and perfluoroethane (C2F6), both characterised by very high global warming potentials (see table 7.1).

The emission of CO2 occurs during the aluminum smelting process, when aluminum oxide from the ores is reduced (Hall-Heroult reduction process) through electrolysis in reduction cells. The cells contain a molten bath of cryolite (Na3AlF6) which is of natural or synthetic origin. For the cathode in the electrolytic process a carbon lining is used. As anode, also carbon containing material is applied. Carbon is oxidised during the process and emitted into the atmosphere as CO2.

The amount of CO2 released is approximately 1.5 t/t aluminum produced. In another technology (so-called Soderberg cell) 1.8 t/t are released. A technology shift from this cell would reduce the emissions by 20 percent.

Aluminum production industry in addition to CO2 is a source of PFC emissions. The reason is the so-called anode effect by which the voltage in the electrolysis bath rapidly increases due to reduced levels of the smelting bath. Then reactions of carbon and fluorine of the molten cryolite bath take place, and fugitive emissions of CF4 and C2F6 occur. Their magnitude depends on the process conditions and can be massively reduced if anode effects are minimised by better control technologies. In the U.S. aluminum industry PFC emissions declined by a factor of 6.6 in the last 15 years. The relation of CO2 emissions to PFC emissions currently is about 1:0.7 compared to 1:2.6 in 1990. Further drastic reduction is expected by use of an inert anode type that would eliminate CO2 and PFC emissions from the smelting process. Commercially viable results are expected by 2020.

Current climate efficient measures mostly rely on enhanced recycling of scrap aluminum.

10.3.5 Carbon Dioxide Use

CO2 is used for food processing, in chemical production, for beverages, refrigeration, as a greenhouse fertilizer, or in the petroleum industry for enhanced oil recovery (EOR). In the case of EOR, CO2 is injected into the underground to rise the reservoir pressure, so that additional oil can be extracted (see also chapter 9.4).

CO2 is a by-product of many industrial processes (e.g. ammonia production, fossil fuel combustion, bioethanol production, lime processing), but also emanates during extraction of crude oil and natural gas of which it is a naturally occurring constituent. Other feed-stocks of CO2 are natural CO2 reservoirs.

The methodology for the accounting of CO2 used in industry is not yet fully available. Typically the following assumptions are made: In the case of enhanced oil recovery the CO2 applied is assumed to remain sequestered in the reservoirs (see chapter 9.3; CCS). For all other CO2 uses it is assumed to be released into the atmosphere during or after the process.

Fossil fuel burning related CO2 is not considered in this chapter.

Under these conditions 1.2 Mio t CO2-eq. are emitted in the USA. This is less than one percent of the total greenhouse gas emissions there.

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