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Typical default values for Norwegian plants for C (carbon content in coke) are 97 percent and for S (sequestered carbon in product), 35 per cent. This implies a typicalemission factor of 2.3 tonnes CO2/tonne coke.
More carbon is actually needed in the process than calculated from a stoichiometric
reaction. The suggested emission factors are calculated from coke input in Norwegianplants. The excess carbon is oxidised during the process, little is left as ash (Raaness,1991).
The petrol coke used in this process may contain volatile compounds which will form
methane. Some of this methane will escape to the atmosphere, particularly during thestart up. Measurements at Norwegian plants suggest emission factors of 10.2 kg/tonne
petrol coke or 11.6 kg/tonne carbide product.

2.11.2 CO2 from Calcium Carbide Production
Calcium carbide is made by heating calcium carbonate and subsequently reducing CaO
with carbon (e.g., petrol coke). Both steps lead to emissions of CO2. Some carbon will
be sequestered in the product. The most important application of calcium carbide is
producing acetylene. Consequently, the sequestering will be for a short time only (lessthan a few years) and may be disregarded. On the other hand Ca(OH)2 is produced as aby-product in the acetylene production. This Ca(OH)2 will react with CO2 to form
CaCO3. Hence, the CO2 emitted from the limestone may be said to be recycled.
Production of CaC2:
CaCO3 → CaO + CO2
CaO + 3C → CaC2 + CO (→ CO2)

Use of carbide:
CaC2 + 2H2O → Ca(OH) 2 + C2H2 → 2CO2

The CO gas will in most plants be utilised as energy. 1.8 tonnes CO2/tonne calcium
carbide will be released in the production process. In addition, 1.1 tonnes CO2/tonne
calcium carbide will be released when the carbide is used. The CO2 emissions may belowered by utilising the gas when producing dicyanodiamide from carbide (Olsen 1991).
Limestone contains about 98 per cent CaCO3. 1750 kg limestone (or 950 kg CaO) and640 kg reducing agent (including 20 kg carbon electrodes) are required to produce 1
tonne carbide.
Emissions may be calculated from the use of raw materials (limestone and coke) or fromthe production.

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INDUSTRIAL PROCESSESThe emission factors in Table 2-9 are suggested in the latter case:

TABLE 2-9
EMISSION FACTORS (KG CO2/TONNE CARBIDE)
Limestone

760

Reduction

1090

Use of product

1100

The theoretical emission factor calculated from a stoichiometric reaction is 1.37 tonne
CO2/tonne carbide (for the carbonate and coke step). Excess carbon is howeveroxidised in the process. The suggested emission factors are calculated from the actualuse of raw materials in a Norwegian plant. The emission factor for acetylene use iscalculated from the actual (not stoichiometric) carbon content of carbide.
Also note that the CaO (lime) might be produced at another plant than the carbide plant.
In this case, the emissions from the CaO step should be reported as emissions from lime
production (Section 2.4) and only the emissions from the reduction step and use of
product should be reported as emissions from calcium carbide production.

2.11.3

Precursors
Production

and

SO2

from

CarbideEmission methods have not yet been developed for the EMEP/CORINAIR Guidebook.
SO2 is potentially emitted from the production processes due to sulphur in the raw cokematerial.
Silicon carbide: The emissions are most accurately calculated from the consumption ofcoke, the sulphur content of the coke, and the degree of control. In addition, CO isemitted due to incomplete oxidation of carbon coke. An emission factor of 0.4 tonne
CO/tonne petrol coke has been determined for Norway (Rosland 1987), but this factor
will be highly plant specific.
Calcium carbide: Nearly 100 per cent of the SO2 potentially emitted will be sequesteredin the product (Rypdal 1995, Rosland 1987). An emission factor of 1.5 kg SO2/tonnecoke is given in U.S. EPA 1995, but no experimental methods or assumptions are given.
CO is generated in the process, but is usually oxidised in the process, used as a fuel orflared. This should be checked for the relevant plants.

2.12 Production of Other Chemicals
2 . 1 2 . 1 N 2O E m i s s i o n s
Production of chemicals other than nitric acid and adipic acid may be sources of nitrous
oxide, but more studies are needed to determine whether they represent a significant
source of N2O. Production of caprolactam, acrylonitrile, and catalytic cracking of oil, may
be significant sources. Generally, suggested sources are related to either a process usinga N-compound or a catalytic reduction step. Compared to emissions associated with

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adipic acid and nitric acid production, the N2O emissions from this source category willprobably be small.
Caprolactam is a widely used chemical intermediate. Most of the 3 million tonnes
produced per year is used in the production of nylon-6 (Fisher and Crescenti, 1994).
Different methods are used for the manufacture of caprolactam. They are all based on
catalytic oxidation of ammonia. In the Netherlands, caprolactam production was
identified as a significant industrial source of N2O (Kroeze, 1994).
In order to increase the yield of gasoline from oil, certain fractions from the oil aretreated in a catcracker. Crude oil contains some nitrogen, and the nitrous oxide
emissions from the cracking process may be significant. Depending on the regional
market for light and medium-light oil products, catalytic cracking is more or lessimportant in a specific region. A few studies on emissions from this source have been
performed in the Netherlands but presently data are not available to suggest amethodology (Oonk, 1996).
Therefore, a general recommended method for estimation of N2O emissions from thesesources is not given here.

2.12.2 CH4 Emissions
Although most methane sources from industrial processes individually are small,collectively they may be significant.
Chemical manufacturing processes, e.g., carbon black, ethylene, dichloroethylene, styrene
and methanol, are potential sources of methane. However, sources other than thosementioned here may be of importance.
Few data on emissions are presently available. These are presented in Table 2-10:

TABLE 2-10
EMISSION FACTORS (G CH4/KG PRODUCTION)

Emission factor(g CH4/kg production)

Reference

Carbon black11

Shareef et al., 1988, Stockton and Stelling
1987.

Ethylene1

Shareef et al., 1988, Stockton and Stelling
1987.

Dichloroethylene

0.4

Shareef et al., 1988, Stockton and Stelling
1987.

Styrene4

Shareef et al., 1988, Stockton and Stelling
1987.

Methanol2

Shareef et al., 1988, Stockton and Stelling
1987.

Coke

0.5

Schade, 1980, Barnard, 1990.

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2.12.3 Emissions of Ozone Precursors and SO2
This section is concerned with emissions from small point sources. However, total
emissions from these sources may be important. Only a simple methodology is suggested
here. It should be noted that some of these sources may be individually very important incertain countries. In these cases a more detailed methodology should be used, based onplant specific data. The EMEP/CORINAIR Guidebook and the U.S. EPA guidelines should
be consulted for advise on detailed methodologies and process descriptions.
A summary of default emission factors and ranges is given in Table 2-11. Ranges given for
VOC emissions from many processes are quite large. Emission factors are likely to bequite process specific. For instance, polystyrene is manufactured in various grades bybatch or continuous process. Higher emission factors are associated with the lower
molecular weight of polystyrenes. The variation in emission factors from plants using thecontinuous process is quite large, depending upon the type of vacuum system employed(U.S. EPA 1995).
Evaporative emissions from petrochemical industries may be higher in warm than intemperate countries.

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INDUSTRIAL PROCESSESTABLE 2-11
EMISSION FACTORS FOR MISCELLANEOUS PRODUCTION PROCESSES IN CHEMICAL INDUSTRIES.
(KG/TONNE PRODUCT)
Source

SNAP

SO2

NOx

NMVOC

CO

Acrylonitrile

40520

-

-

1 (0.4-100)-

Acrylonitrile Butadiene Styrene (ABS)Resins

40515

-

-

27.2 (1.4-27.2)-

Carbon black

40409

3.1

0.4

40 (5-90)

10 (5-14)Ethylbenzene

40518

-

-

2 (0.1-2)-

40501/40502

-

-

1.4

-

Formaldehyde

40517

-

-

5 (0-8)-Graphite

40411

-

-

NAV

-

Phtalic anhydride

40519

-

-

6.0 (1.3-6.0)-

Polypropylene

40509

-

-

12 (0.35-12)-

Polystyrene

40511

-

-

5.4 (0.2-5.4)-

Polyethene - Low density

40506

-

-

3

-

-

-

-

2

-

Polyethene - High density

50507

-

-

6.4

-

Polyvinylchloride

40508

-

-

8.5 (0.14-8.5)-

Styrene

40510

-

-

18 (0.25-18)-

Styrene butadiene

40512-14

-

-

NAV

-

1,2, dichloroethane

40503

-

-

7.3 (0.2-7.3)-

Sulphuric acid

40401

17.5 (1-25)

-

-

-

Titanium dioxide

40410

14.6 (0.9-14.6)

-

-

-

Urea

40408

NAV

NAV

NAV

NAV

Vinyl chloridea

40504

1,2, dichloroethane

40505

-

-

2.2

-

Ethylene and propylene

Polyethene - Linear low density

Source: EMEP/CORINAIR guidebook, except the CASPER project (CASPER 1995).
aThe emission factors should be used for the monomer and polymer separately even if they are produced at the same plant unless otherwise specified.
NAV = Not available.
Note: Ranges in brackets.

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2.13 CO2 Emissions from Metal Production
2.13.1CO2 from Metal Production - General
Methodology

With a few exceptions, commercial production of metals from ores requires the use ofcarbon as a reducing agent. If the ore contains carbonate, CO2 originating from the ore
will also be emitted during production. On the other hand, carbon may also besequestered in the metal.
The metal may be reduced by using coal, coke, prebaked anodes and coal electrodes.
Wood chips and charcoal may also be used in some of the processes, but the resulting
CO2 emissions are not counted in Chapter 2 as net emissions. These net emissions of
CO2 should, however, be reported in the Land-Use Change and Forestry Chapter. Cokeis produced from coal or refinery residuals (petrol coke). Prebaked anodes andelectrodes are produced from coal. By-product fuel (coke oven gas and blast furnace gas)
are produced in some of the processes. These fuels may be sold or used within the plant.
They may or may not be included in the national energy balance. Care should
consequently be taken not to double count emissions.
The following general formula may be used to estimate the emissions:
Mass Reducing Agent x Emission Factor + (Carbon ore - Carbon metal) x 3.67 = Emission (tonnes CO2)

The first part of this formula (the amount of reducing agent used combined with anemission factor) will usually be most important and probably be sufficient for making afirst estimate of the emissions.
The emission factors in Table 2-12 are suggested as default.

TABLE 2-12
CO2 EMISSION FACTORS FOR METAL PRODUCTION GENERALLY(TONNE CO2/TONNE REDUCING AGENT)
Reducing Agent

Emission Factora

Coalb

2.5

Coke from coalb

3.1

Petrol coke

3.6

Prebaked anodes and coal electrodes

3.6

a If better information on actual carbon content is not available nationally or cannot be calculated from data in
the Energy Chapter.
b Derived from data in the Energy Chapter

In addition, CO2 will be emitted from baking (prebaked anodes). In the aluminium
industry about 5 per cent of the non-combustion CO2 emissions using the prebaking
technology will be from baking. No data is available for other metal industries using
prebaked anodes.

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2.13.2

Overview
Precursors
ProductionofEmissions
of
and
SO2
from

Ozone
Metal

Production of most metals may generate emissions of SO2, CO, NOx and NMVOC.
Emissions of SO2 originate from sulphur in the reducing agents and in the ores. The
emissions will also depend on control technologies and the extent to which sulphur issequestered in the products.
NOx is produced primarily by the high temperate oxidisation of nitrogen in air. In metal
production, most NOx emissions usually occur as a result of fuel combustion. However,high temperate metal production processes (such as roasting and reduction), which occur
in the presence of air, will also produce nitrogen oxides. These NOx emissions are inprinciple included in this section, but are often impossible to distinguish from the fuelNOx.
CO is formed due to incomplete oxidation of the reducing carbon. This CO may in many
plants be used as a fuel, and double counting of emissions already counted as energy must
be avoided.
In addition, small amounts of NMVOCs may be emitted during parts of some of theprocesses, especially those involving coal.

2.13.3 Iron and Steel2.13.3.1 Overview
Iron is produced through the reduction of iron oxide (ore) using metallurgical coke as the
reducing agent in a blast furnace. Steel is then subsequently made from iron and scrap inother furnaces.
This sector includes two types of facilities. Large integrated primary iron and steel plants
have coking, smelting and refining capacities to produce steel from raw coal and iron ore.
Other, smaller plants produce iron and steel from coke generated off-site. The cokeoven used at an integrated plant is identical to that used at off-site coking facilities. In the
integrated plant, coke oven gases (COGs) are used both for oven under firing andcombustion in the blast furnace and other parts of the process.
Common to all plants is a blast furnace, which reduces raw ore to molten pig iron byheating in the presence of carbon and oxygen. Coke, the source of carbon, has been
estimated to be consumed at a rate of about 450 kg/tonne of hot metal (Rankin andWright, 1992). “Flux” in the form of limestone (CaCO3) or dolomite is also added to thefurnace at a rate of about 250 kg/tonne of iron (U.S. EPA 1986).
Steel may be produced in a basic oxygen furnace (BOF), an electric arc furnace (EAF), an
induction furnace or an open hearth furnace. The open hearth type is the oldest
technology. Low carbon steel is produced in a BOF, where a mixture of pig iron and ironscrap is remelted in the presence of pure oxygen, which oxidises the dissolved carbon tocarbon monoxide or carbon dioxide. Carbon and alloy steels are produced in an EAF, a
refractory-lined pot which utilises electric heating through graphite electrodes which areconsumed in the process. This type is charged with 100 per cent scrap iron.

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2.13.3.2 Emission Estimation Methodology for
CO2
Process emissions of carbon dioxide in an iron and steel plant take place primarily as aresult of coke oxidisation. Additional emissions occur as the limestone flux gives off
carbon dioxide during reduction of pig iron in the blast furnace, but this source iscovered as emissions from limestone use (Section 2.5).
During steel production, CO2 emissions also take place as a result of graphite electrodeconsumption in the EAF.
Pig iron (impure iron) contains about 4-4.5 per cent carbon by weight. In the conversionof pig iron to steel the carbon content is reduced to below 2 per cent by weight. The
process takes place in a steel furnace which has been charged with pig iron, usually
recycled iron or steel and alloying elements to improve material properties. As the
carbon is removed from the pig iron, CO2 and CO are evolved. The lost CO-carbon is
eventually converted to carbon dioxide by combustion. This should not be considered as
an energy emission, as it is inherently part of the iron reduction process. Care should betaken not to double count these emissions (when performing the energy balance).
The most accurate methodology is to calculate the emissions from the amount of
reducing agent used as described in 2.13.1.
Parsons (1977) and ORTECH (1994) have studied the consumption of carbon at iron andsteel production facilities. These results have been summarised by Environment Canada(1996). Emission factors per unit iron or steel produced are shown in Table 2-13.

TABLE 2-13
CO2 EMISSION FACTOR FOR IRON AND STEEL PRODUCTION(TONNES CO2/TONNE IRON OR STEEL PRODUCT)Country

Canadaa

Description

Emission Factor

Integrated facilityb (coke plus ironand/or steel production).

1.6

Reference

Environment Canada(1996)a Includes CO produced by coke and coke oven gas consumption. It does not include any form of2
conventional energy consumption. The emission factor applies to both iron or iron plus steel production, since
uncertainty in the estimates overshadow the incremental difference in CO2 emissions.
b Environment Canada has reported an emission factor of approximately 1.5 tonnes CO /tonne iron or steel
2
for a non-integrated facility. This is, however, a rather uncertain value.
Note: Figures exclude CO2 from flux (CaCO3) consumption.

2.13.3.3 Emission Estimation Methodology for
Ozone Precursors and SO2
Emissions from iron and steel may originate from various stages of the production
process.
Iron production:• Blast Furnace Charging: Primary iron production in smelters. No process emission
factors are given in the EMEP/CORINAIR Guidebook (SNAP 40202). In the CASPER
model (CASPER 1995) emission factors of NMVOC are given as 100 g/tonne product(range 20-200) and CO is given as 1330 g/tonne product (range 1180-20000).

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Preliminary research from Environment Canada suggests that sulphur dioxide emissions
from the blast furnace may be 1000-3000 g SO2/tonne of iron produced.
• Pig Iron Tapping: This involves the removal of the molten pig iron from the smelter.
While it does give rise to emissions of a range of heavy metals, according to the
EMEP/CORINAIR Guidebook no appreciable emissions of the four gases occur. In the
CASPER model (CASPER 1995) the following emission factors are given: SO2: 30 g/tonne
product, NOx: 76 g/tonne product, CO: 112 g/tonne product and NMVOC: 20 g/tonne
product.
Steel production:• Open Hearth Furnace: Steel is produced in the open hearth furnace fired by gas orfuel oil. No data exist for process emission from open hearth furnaces.
• Basic Oxygen Furnace Steel Plant: Pure oxygen is blown into the furnace via a lance.
Burning CO maintains exothermic conditions. Most CO emissions are therefore
eliminated. The EMEP/CORINAIR Guidebook (SNAP 40206) provides no emission
factors for the gases.
• Electric Furnace Steel Plant: This type of furnace is usually charged with 100 per centscrap iron. Graphite electrodes conduct current through the metal to heat the charge.
Emissions are dependent upon the quality of scrap metal and operating conditions. The
EMEP/CORINAIR Guidebook (SNAP 40207) does not give any emission factors for thegases of interest.
Steel processing:• Rolling Mills: Rolling mills use a range of different processes and emit differing amountsof pollutants according to the specific processes used. Most of the emissions from rollingmills are from the fuel used to heat the process. However cold-rolling will emit a rangeof gases in addition to the fuel combustion emissions. The emission factors expressed as
the amount of steel cold rolled are taken from the EMEP/CORINAIR Guidebook (SNAP40208) and are shown in Table 2-14. Note that SO2, NO2 and CO emission factors are
only given for process smelter gas (as sometimes used for rolling pretreatment).

TABLE 2-14
EMISSION FACTORS FOR ROLLING MILLS (G/TONNE STEEL PRODUCED)
Pollutant

Emission Factor (default)

Emission Factor (Range)

SO2 a

45

30-60

NOx a

40

20-50

CO a

1

0.3-1

NMVOC

30

20-30

a from process smelter gas

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2.13.4 Ferroalloys
2.13.4.1 Overview
Ferroalloy is the term used to describe concentrated alloys of iron and one or moremetals such as silicon, manganese, chromium, molybdenum, vanadium and tungsten.
These alloys are used for deoxidising and altering the material properties of steel.
Ferroalloy facilities manufacture concentrated compounds which are delivered to steel
production plants to be incorporated in alloy steels. Ferroalloy production involves a
metallurgical reduction process which results in significant carbon dioxide emissions.
In ferroalloy production, raw ore, coke and slagging materials are smelted together underhigh temperature. A commonly used technology is the submerged-arc open-top electric
furnace (EAF) (Environment Canada, 1983; Ontario Research Foundation, 1981). In the
EAF, heating is accomplished by passing current through graphite electrodes suspended ina cup-shaped, refractory-lined steel shell. Carbon reduction of the metallic oxides occurs
as both coke and graphite electrodes are consumed.
During ferroalloy smelting, the reduction reaction takes place at a high temperature.
Carbon captures the oxygen from the metal oxides to form CO, while the ores are
reduced to molten base metals. The component metals then combine in the solution.
For example, the following reaction occurs in the production of 50 per cent ferrosilicon(AWMA, 1993):
Fe2O3 + 2 SiO2 + 7C → 2FeSi + 7COPrimary emissions in covered arc furnaces consist almost entirely of CO as opposed toCO2, due to the strong reducing environment (ORTECH, 1994). All CO is assumed,
however, to be converted to CO2 within days afterwards.

2.13.4.2 Emission Estimation Methodology for
CO2
The most accurate methodology is to calculate the emissions from the amount of
reducing agent used as described in Section 2.13.1. Alternatively, the emissions may be
calculated from the production volume. However, it is impossible to suggest default
factors for this process. Ferroalloy production may more or less be based on biologicalcarbon (wood and wood waste). To the extent that the biocarbon is replaced and thatelectricity is produced from e.g., hydro power, the production of ferroalloys may inprinciple be CO2 free. However, in most countries a production based on biocarbon
only will not be economical feasible. The suggested emission factors (Table 2.15) assume(if not otherwise specified) that all carbon is fossil and are derived from a material balance
made by SINTEF (SINTEF 1991a) and Streibel (1974).

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INDUSTRIAL PROCESSESTABLE 2.15
CO2 EMISSION FACTORS FOR FERROALLOY PRODUCTION(TONNES/TONNE PRODUCT)
Type Ferroalloy

Emission Factor

Ferrosilicon - 50%Si

2-2.7

Ferrosilicon - 75%Si

3.9

Ferrosilicon - 90%Si

4.8-6.5

Silicon metala

4.3

Ferromanganese

1.6

Silicon manganese

1.7

Ferrochromium

1.3

Ferrochromium-silicon

NAVa All producers probably use some biocarbon in order to obtain the desired product properties. 1.6 tonne bioCO2/tonne silicon may be considered as a minimum value and is not included in the emission factor in the table.
NAV = Not Available

2.13.4.3 Emission Estimation Methodology for
Ozone Precursors and SO2
SO2, CO, NOx and NMVOC are potentially emitted in the production process as
described in Section 2.13.2.
Sulphur may be sequestered in the products. For ferromanganese and silicon manganese98-99 per cent of the sulphur from ore and coke will be sequestered. Of the remaining
ferroalloys, assume 5 per cent of the sulphur is sequestered (Rypdal 1995, Rosland 1987).
In the CASPER model (CASPER 1995) a factor of 35 g/tonne product has been suggested
for ferrosilicon.
NOx will originate from production of ferrosilicon and silicon metal. A factor of
11.7 kg/tonne product has been determined (Rypdal 1995). However, this factor is highly
uncertain, and there may also be emissions from the production of other ferroalloys. In
the CASPER model (CASPER 1995) 0.05 kg/tonne has been suggested.
The emissions of NMVOC originate from coal or coke. The emissions are calculated
from the consumption of coal and coke. An emission factor of 1.7 kg/tonne is suggested(Rypdal 1995).
The U.S. EPA has published uncontrolled CO emission factors for various ferroalloy
products (U.S. EPA 1985). These vary with furnace type. Some of these factors arepresented in Table 2-16.

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INDUSTRIAL PROCESSESTABLE 2-16
CO EMISSION FACTORS FOR FERROALLOY PRODUCTION(KG CO/TONNE METAL)
Metal

Covered Furnace

Sealed Furnace

Ferrosilicon - 50%Si

1.09

NAV

Ferrosilicon - 75%Si

1.62

NAV

Silicon Manganese

NAV

0.84

Source: U.S. EPA reported by ORTECH (1994).
NAV = not available.

2.13.5 Aluminium
2.13.5.1 Overview
Primary aluminium is produced in two steps. First bauxite ore is ground, purified andcalcined to produce alumina. Following this, the alumina is electrically reduced toaluminium by smelting in large pots.
During the reduction process, the aluminium smelting pot acts as the electrolysis cell.
The pot itself, a shallow steel container, forms the cathode, while the anode consists of
one or more carbon blocks suspended in it. In the pot, alumina (Al2O3), is dissolved in afluoride bath consisting primarily of cryolite, Na3AlF6. Passing electrolysis current
through the cell also causes a heating effect through the resistance of the cell which
maintains the electrolyte in a liquid state.
Molten aluminium is evolved while the anode is consumed in the reaction. However, thecarbon functions as a fuel cell and as such substitutes electrical energy consumption. The
aluminium forms at the cathode and gathers on the bottom of the pot. The favoured
gaseous reaction product is CO2:
Al2O3 + 3/2C → 2Al + 3/2 CO2

Most carbon dioxide is evolved from the reaction of the carbon anode with alumina, butsome is formed as the anode reacts with other sources of oxygen (especially air). Thisoccurs during cell operation and, in the case of prebaked electrodes, during anodeproduction at the aluminium plant.
Three types of reduction cells are in use: prebaked anode, horizontal stud S;derberg
anode and vertical stud S;derberg anode. Prebaked anodes have been preferred overS;derberg cells during the last 20 years because they are more productive and efficientwith respect to electrical energy consumption and emit fewer organic compounds (U.S.
EPA 1995).

2.13.5.2 Emission Estimation Methodology forCO2
CO2 emissions may be calculated from the amount of reducing agents used as describedin Section 2.13.1. Alternatively, the emissions may be estimated from the production
volume of primary metal and the specific consumption of carbon. Emissions factors for

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CO2 are suggested in Table 2-17 based on SINTEF 1991b and ORTECH 1994. The
production and use of carbon anodes for aluminium smelting is a very well establishedprocess. Evidence suggests that there is little variation in CO2 emissions from plants
utilising similar technologies. It is very likely that use of the appropriate emission factor,
along with the correct activity data, will produce accurate estimates.

TABLE 2-17
CO2 EMISSION FACTORS FOR PRIMARY ALUMINIUM PRODUCTION(TONNES/TONNE PRODUCT)
Pollutant

Soderberg Process

Prebaked Anode Process

CO2

1.8

1.5

2.13.5.3 Emission Estimation Methodology for
Ozone Precursors and SO2
Emissions of carbon monoxide, nitrogen oxide and sulphur dioxide can be estimated fromthe amount of aluminium produced. Emissions may originate from the production
process and baking of anodes. No distinction between the Soderberg and prebaked
method is given in the EMEP/CORINAIR Guidebook (SNAP 40301). The suggested
emission factors are shown in Table 2-18. No information is given about the degree ofcontrol.

TABLE 2-18
EMISSION FACTORS FOR ALUMINIUM PRODUCTION(KG/TONNE PRIMARY ALUMINIUM PRODUCED)
Pollutant

SO2

NOx

CO

Process

Emission Factor (Default)

Emission Factor (Range)

Electrolysis

14.2

10-17.5

Anode baking

0.9

0.8-1.0

Electrolysis

2.15

1.3-3.0

Anode baking

NE

NE

Electrolysis

135

27-680

Anode baking

400

NAV

NE = negligible.
NAV = not available.

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2.13.6

PFCs from Aluminium Production

2.13.6.1 Overview
Two PFCs, carbon tetrafluoride (CF4) and carbon hexafluoride (C2F6), are known to be
emitted from the process of primary aluminium smelting.
Aluminium is smelted in large pots by an electrolytic reduction process using carbon
electrodes. The pot itself forms the cathode, while the anode consists of one or morecarbon blocks. During production, alumina (Al2O3) is dissolved in a fluoride melt
consisting primarily of cryolite, Na3AlF6. PFCs are formed during a phenomenon known
as the Anode Effect (AE), when alumina levels are low. A forced reaction results whenmolten fluoride salts at high temperature combine with carbon at the anode to favour theformation of CF4 and C2F6. This occurs because, during an AE, voltage rises to a level
greater than that corresponding to the Gibbs energy of formation for these gases (Laval
University, 1994).
When the melt becomes depleted of alumina (reduction to a level of 1.5-2.0 wt %), theAE occurs and the cell voltage rises from the normal value of 4-5 volts to 20-50 volts.
This happens very suddenly and, in theory, is due to a sudden increase in electricalresistance across the anode-bath interface. As a result, the voltage rises to continue
delivering current across the higher resistance. Competing reactions begin to occur to
produce CO, CF4 and C2F6 in addition to CO2. It is believed that the carbon anodebecomes completely covered by gas during the AE. The two reactions of interest at thispoint are:
Na3AlF6 + 3/4C = Al + 3NaF + 3/4CF4

Na3AlF6 + C = Al + 3NaF + 1/2C2F6The overall anode gas composition below the anode during an anode effect may beapproximately 15 % wt CF4, 20 wt % CO2, 65 wt % CO and 1 wt % C2F6 (Thonstad,Oygard and Diep, 1994). AEs typically occur between 0.3 to 3 times daily on a given celland last on the order of 2 to 20 minutes (Unisearch, 1994).

2.13.6.2 Emission Data
Measured Emission Data
In 1992, the Norwegian aluminium industry measured the emissions of PFCs from theirsmelters. The measurements in production cells were performed with a photoacoustic
gas monitor (Norsk Hydro, 1996), (See Table 2-19). The results were different for
prebaked lines (0.02 to 0.18 kg CF4/tonne Al) and Søderberg lines (0.15 to
0.9 kg CF4/tonne Al).

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INDUSTRIAL PROCESSESTABLE 2-19
MEASURED EMISSIONS OF PFCS FROM PRIMARY ALUMINIUM PRODUCTION
Norway(Norsk Hydro, 1996)

Canada(Schiff ,1994)

CF4

C2F6

CF4

C2F6

kg/tonne Al

kg/tonne Al

kg/tonne Al

kg/tonne Al

Side Worked Prebaked (SWPB)

NAV

NAV

1.19 a0.067 aHorizontal Stud Søderberg (HSS)

NAV

NAV

0.82 a0.14 aVertical Stud Søderberg (VSS)

0.15-0.9

0.006-0.04

0.4 b

NAV

0.001-0,008

0.045-0.53 c

0.007-0.032 c

Cell Technology

Centre Worked Prebaked (CWPB)

0.02-0.18

a Based on samples from one plant.
b Samples from one plant-value has been adjusted to compensate for error.
c Based on sampling 5 plants.
NAV = Not Available.

In Australia, all aluminium smelters use pre-baked cell technology. Emission factors fromthe Australian aluminium industry are reported to be 0.53 kg CF4/tonne Al, and 0.05 kg
C2F6/tonne Al (Workbook, Australia, 1995).
A study of Canadian aluminium plants found CF4 emission factors to be between 0.045
and 1.2 kg. per tonne of aluminium produced (Unisearch, 1994). The emission factor for
C2F6 was between 0.007 and 0.14 kg per tonne. The Canadian study further subdivided
the Søderberg and Prebaked technologies into two separate categories (Table 2-19). Thissubdivision narrows the emission range for each category.
PFC emissions increase with frequency, intensity and duration of anode effects. The
Norwegian study reported the frequency variation to be 0.03-0.24 AE per cell-day in
Prebaked lines, and 1.0-2.76 AE per cell-day in Søderberg lines. Canadian data show AE
frequency to vary between 0.2 and 2.6 per cell-day in all lines. Uncertainty in allmeasurements is relatively high (of the order of 50 per cent).
Estimated Emission Data
A preliminary U.S. EPA study suggested a range of 0.01 to 1.2 kg of CF4 per tonne ofaluminium produced by any technology (U.S. EPA, 1994a). This range is an average basedon measured emissions from aluminium smelters in the United States, Canada and
Norway. These values may underestimate emissions from other aluminium producing
regions.
CICERO (1992) and, Khalil and Rasmussen (1985) have studied trends in atmosphericCF4. The studies made projections based on the assumption that all atmospheric CF4
originates from aluminium production. Though data are subject to large uncertainties,
both papers lead to the conclusion that the average emission rate from aluminium
smelting is around 1 kg per tonne metal.
The global emissions of PFCs to the atmosphere from all aluminium smelters was reestimated for 1995 (Harnisch and Borchers, 1995), and reported to be closer to 1.4 kg
CF4/per tonne Al, and 0.2 kg C2F6/per tonne Al (Tabereaux, 1995). The distribution offour different cell technologies on a global scale is given in Table 2-20, together withestimated CF4 emissions.

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INDUSTRIAL PROCESSESTABLE 2-20
ESTIMATED GLOBAL CF4 EMISSIONS FROM SMELTERS WITH
VARIOUS CELL TECHNOLOGIESType of Cell Technology

Per Cent of World
Production

kg CF4 /tonne Al

Modern Prebaked

20

0.05

HS Søderberg

11

1.0

“Older” Prebaked

40

1.75

VS Søderberg

29

2.0

Weighted average for all plants
world-wide

100

1.40

Source: Tabereaux, 1995.

Calculation of Emission Data
Tabereaux (1995) has proposed a method for PFC emission calculation. He states thatthe generation of CF4 in electrolysis cells follows Faraday’s Law (i.e., the quantity of gas
generated depends on the flow of electrical current in the cell). At 100 per centefficiency, 13.68 g of CF4 is formed for every kiloampere-minute (kA min) duration of theanode effect. For example, CF4 emissions for an aluminium smelter having an average
percentage (p) of 16 per cent CF4 in pot gas during anode effects (AE), 91 per centcurrent efficiency (CE) for aluminium production, 0.5 anode effects per pot day (AEF),
and anode effect duration (AED) of 2.5 minutes can be calculated from:
Kg CF4 / tonne Al =(kg CF4/kA min) / (kg Al/kA min) x (1000kg/tonne) x (p/CE) x AEF x AED=

13.68 / 8.05) x (0.16 / 0.91) x (0.5) x (2.5)

=

0.373

2.13.6.3 Emission Estimation Methodology for
PFCs
Measurements
Since emissions of CF4 and C2F6 vary so significantly from one aluminium smelter to thenext, depending on cell type and AE parameters, the estimations will be highly uncertain
unless actual emission measurements have been made. Every effort should be made toobtain such data.

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INDUSTRIAL PROCESSES

Calculations
It is recognised that measurements are both expensive and time-consuming. It may,
however, be much easier to make a limited survey of AE frequency and duration at
smelters. In such cases, it is recommended that specific CF4 emissions for anode effects
longer than 2 minutes are calculated as follows:
kg CF4/tonne Al = 1.698 x (p / CE) x AEF x AED

p=average fraction of CF4
in the pot gas during anode effects

Prebaked: p=

0.08 (8%)

Søderberg: p=

0.04 (4%)

CE=current efficiency expressed as afraction, rather than a percentage

AEF=

number of anode effects per pot day

AED=

anode effect duration in minutes

It is recommended that the default rate for C2F6 emissions be 1/10 that of CF4.
Estimations
It is recommended that estimates are used only when no measured data exist. Specificemission factors should be chosen according to the type of technology used as shown in
Tables 2-19 and 2-20 and applied to national primary aluminium production data for eachtechnology. The following method may then be used to give an estimate of the annual
CF4 emissions from a smelter with a given cell technology.
CF4 emission (kg) = EF(tech) (kg CF4/tonne Al) x pp(tech) (tonnes)

where:EF(tech)=emission factor by technology (from Table 2-20)

pp(tech)=primary aluminium production by technology

2.13.7 Other Metal Production
2.13.7.1 Emissions of CO2
This includes production of all non-ferrous metals except aluminium. The metals may be
produced using carbon as reducing agents or by other methodologies.
Whether carbon is emitted or not depends on the production process. Some ores are
not reduced with carbon. Hence, CO2 emissions from these processes are low. The
general methodology suggested, where emissions are calculated from the consumption of
reducing agents and the carbon content of ores, is recommended. An overview of
production processes is given in Table 2-21. Some metals may be produced fromalternative production methods.

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INDUSTRIAL PROCESSESTABLE 2-21
PRODUCTION PROCESSES FOR SOME METALS
Metal

Main Ore(s)CarbonReduction

Electrolysis(without carbon)

Other(non-CO2)

Chromiuma

FeCr2O4, PbCrO4

CopperCu2S, CuFeS2, Cu2O,xx (SO2)Gold

Element

x

x

Lead

PbS

x

Magnesium

Carbonatex

Mercury

HgS

x (SO2)

Molybdenium

MoS2

x (SO2)

Nickel

NiS, NiO

Platinum
Siliconb

Element, PtS

Silver

Ag2S, element

Tin

SnO2

Titanium

TiO2, FeTiO3Tungsten

WO3

Uranium

UxOy

Zinc

ZnS, ZnCO3xxx (SO2)xxx (SO2)x

SiO2, Si-O-alkali

x
x
x
xc
x
x
x

a See also ferroalloy productionb See also ferroalloy production and carbide production
c Two step reduction process, involving first C + Cl , then Mgxx (SO2)2

Note: The appearance of (SO2) in the final column indicates that the production process is a major world-wide source ofSO2 emissions.

In the case of magnesium and other metals in a carbonate ore, the carbon emitted fromthe ore should be taken into account in addition to the coke reducing agent.

2.13.8SF6 Used in Aluminium
Foundries

and Magnesium

In the magnesium industry, SF6 is used as a cover gas in foundries to prevent oxidation ofmolten magnesium. The Norwegian producer of magnesium has assessed whether SF6
used as a cover gas reacts with other components in the furnaces. The results so far
indicate that SF6 is quite inert. For the time being it is therefore assumed that all SF6
used as cover gas is emitted to the atmosphere. The consumption figures are therefore
used as emission estimates.

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INDUSTRIAL PROCESSESIn the aluminium industry SF6 is used as a cover gas only for special foundry products. As
SF6 is assumed to be inert, SF6 emissions should equal consumption:
Emission of SF6 = Consumption of SF6 in magnesium and aluminium foundries

2.14 Pulp and Paper Industries
2.14.1 Overview
Pulp and paper production has three major processing steps: pulping, bleaching and paper
production. The type of pulping and the amount of bleaching used depend on the natureof the feedstock and the desired quality of the end product. Kraft (sulphate) pulping is
the most widely used pulping process and is typically used to produce strong paper
products. The Kraft pulping process includes bleaching, chemical recovery and byproduct recovery.
Sulphite pulping is another chemical pulping process. It produces a weaker paper thansome other types of pulping, but the pulp is less coloured, making it more suitable forprinting, often with little bleaching.

2.14.2

SimpleMethodology
Precursors and SO2

for

Ozone

Simpler methodologies are presented in the EMEP/CORINAIR Guidebook for threepaper pulping processes;• Kraft (SNAP 40602),• Acid sulphite (SNAP 40603)• Neutral sulphite semi-chemical process (SNAP 40604).
Only data for the Kraft and Acid sulphite processes are available.
In the Kraft pulping process sodium sulphide and sodium hydroxide are used tochemically dissolve the lignin that binds the cellulose fibres. Emission factors are based on
the production of air-dried pulp and are shown in Table 2-22 as suggested in the
EMEP/CORINAIR Guidebook. The emissions of SO2 may be lower in new mills than theolder ones (U.S. EPA 1995).

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INDUSTRIAL PROCESSESTABLE 2-22
NON-COMBUSTION EMISSION FACTORS FOR PAPER AND PULP PRODUCTION KRAFT PULPING(KG/TONNE DRIED PULP)
Pollutant

Emission Factor (Default)

Emission Factor (Range)

SO2

70.005-10NOx

1.5

0.017-1.5

VOCa

3.7

0.1-4.9

COb

5.6

NAV

a

Note, VOC is defined as the total gaseous non-methane organic compounds which include sulphur
compounds.
b Ref: U.S. EPA 1995.
NAV = Not Available

The acid sulphite pulping process is similar to the Kraft process except that a sulphurous
acid solution is used to dissolve the lignin in the wood. This solution is buffered by theuse of bisulphide of sodium, magnesium, calcium or ammonium. SO2 is considered to be
the major pollutant. There are at least four types of processes: ammonium based (NH3),
calcium based (Ca), magnesium based (MgO) and sodium based (Na) (U.S. EPA, 1995).
Emissions factors from U.S. EPA, 1995 are given in Table 2-23.

TABLE 2-23
NON COMBUSTION EMISSIONS FROM PAPER AND PULP PRODUCTION ACID SULPHITE PULPING(KG/TONNE DRIED PULP)
Pollutant

Type of Process

Emission Factor(Default)

Emission Factor(Range)SO2

NH3, Ca, MgO and Na

30

8-50

2.14.3

Detailed
Methodology
Precursors and SO2

for

Ozone

The preferred methodology is to use continuous measurements data which may beavailable for SO2 and NOx. This is only feasible in modern plants where the number ofmeasure points to be monitored is limited. Detailed emission factors related to thevarious processes are given in the EMEP/CORINAIR Guidebook.

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