National Atmospheric Emissions Inventory

Appendix 1

The Methodology of the National Atmospheric Emissions Inventory


2.5 Industrial Processes

 2.5.1 Cement Manufacture

In a cement kiln, calcium carbonate (CaCO3) is broken down to CaO and carbon dioxide. The emission was estimated from the annual UK production of clinker (DETR, 1997d) and an emission factor of 138.3 t/ kt clinker produced (IPCC, 1997). The clinker produced is then ground up with gypsum to produce cement. Since clinker may be imported or exported the production of cement is not precisely related to the production of clinker. Hence it is preferable to use clinker data to estimate carbon dioxide emissions.

2.5.2 Lime Manufacture

Lime (CaO) is manufactured from limestone (CaCO3 ) and dolomite (CaCO3MgCO3) by heating in a lime kiln resulting in the evolution of carbon dioxide. UK limestone use is given in BGS(1998) and an emission factor of 120 t carbon/kt limestone was used based on the stoichiometry of the chemical reaction assuming pure limestone. For dolomite an emission factor of 130 t carbon /kt dolomite would be used, however dolomite calcination data is not given explicitly but included in the limestone data. Hence emissions will be under estimated. Dolomite calcination is believed to be a small proportion of the total hence the over estimate is unlikely to be significant. The limestone calcination data used excludes limestone calcined in the chemical industry since a large proportion of this is used in the production of sodium carbonate by the Solvay process. The limestone is calcined to produce carbon dioxide but nearly all this is recovered and is sequestrated in the sodium carbonate produced. Some of the subsequent uses of sodium carbonate result in the emission of CO2 (e.g. glass manufacture) but others do not (e.g. water softening). More data on sodium carbonate consumption by use is required before an estimate can be made. Hence the current estimate of lime calcination emissions are low.

2.5.3 Limestone and Dolomite Use

Emissions from the use of limestone and dolomite were estimated from the following sources:

  • iron and steel manufacture
  • glass manufacture
  • agricultural soils (liming of soils)

Usage data is available in BGS(1998) and ISSB(1997) for iron and steel use. The emission factors were 120 t carbon/kt limestone or chalk and 130 t carbon /kt dolomite and assume all the carbon is released to the atmosphere.

2.5.4 Cement and Lime Fuel Combustion

Sections 2.5.1 and 2.5.2 describe the emission of CO2 from the degradation of limestone and dolomite used in cement and lime manufacture. The category cement & lime fuel covers emissions of all pollutants arising from the combustion of fuels in kilns. In DUKES (DTI,1997), this fuel consumption is included under 'other industries'. An estimate was made of the fuel consumed by cement and lime kilns and emissions estimated from emission factors specific to the process (see Tables A3-A6). The fuel estimates were for 1990-1993 (Blyth et al., 1996) and were extrapolated to other years by using clinker production data (DETR, 1997d) and limestone calcination data (BGS, 1998). Having estimated the consumption of coal, fuel oil and natural gas by the lime and cement sector, the fuel consumption by other industry was adjusted so that the total consumption agreed with DUKES (DTI,1997). Estimates were also made of emissions from the combustion of scrap tyres and waste oils in cement kilns. The emission factors used are reported in Tables A3 and A5. The non-CO2 factors for scrap tyres are the same as for coal, because this fuel is normally burnt mixed with a larger proportion of coal. The carbon content of scrap tyres was estimated from data in Ogilvie (1995). The fuel consumption was taken from Collingwood (1997).

2.5.5 Nitric Acid Manufacture

The manufacture of nitric acid produces emissions of both NOx and nitrous oxide. Up to 1988 estimates of NOx are estimated from the annual production of nitric acid (CIS, 1991). The NOx emission factor is 3.98 t/kt of 100% acid produced. This is an aggregate factor based on CORINAIR (1989) emission factors for the different types of processes ranging from 3-12 t/kt of 100% acid produced. The aggregate factor was based on data on UK Manufacturing plant provided by the Nitric Acid Association for the year 1985 (Munday, 1990)

UK production data have not been published since 1988. Since then a number of plants have either closed down, changed ownership, moved or have been fitted with abatement technology. Since 1994 estimates of NOx were made based on returns from manufacturers. These data comprise HMIP authorisations which are likely to be higher than actual emissions. Emissions from 1989 to 1993 were estimated by linear interpolation.

Only Dupont (1997) were able to supply data on nitrous oxide emissions. For the remaining plant, the emissions were calculated from production data and an emission factor of 6 t/kt. This is an average factor based on manufacturers estimates (ICI, 1997) and is consistent with the range quoted in IPCC Guidelines (IPCC, 1997) for medium pressure plant. Up to 1988, the production data from (CIS, 1991) was used. Since 1994 production estimates based on returns from manufacturers were used. These are based mainly on plant capacity data which may over estimate true production levels. Production from 1989 to 1993 was estimated by linear interpolation.

2.5.6 Adipic Acid Manufacture

Adipic acid is manufactured from cyclohexane by oxidation with nitric acid. Nitrous oxide is produced unavoidably with an emission factor of around 300 kg/t of adipic acid produced (IPCC, 1997). Production figures and emission estimates are provided by DuPont (1997).

2.5.7 Sulphuric Acid Manufacture

The UK emissions of SO2 from sulphuric acid manufacture were supplied by NSAA(1997).

2.5.8 Mining and Quarrying

Emissions of PM10 from mining and quarrying were estimated using USEPA (1995) factors. This gives an average factor of 0.1g/kg of material throughput. Clearly this is a rather crude estimate and so no time series has been estimated.

2.5.9 Industrial Process NMVOC Emissions

The NAEI category Processes total is based on the work of the Emission Monitoring and Abatement Department at NETCEN. It comprises emissions from the following industrial processes.

  • Oil Refineries
    • Petroleum products processing
    • Storage and handling of petroleum products in refineries
  • Iron and Steel Rolling Mills
  • Processes in organic chemical industry
  • Other industries
    • Bread
    • Wine
    • Beer
    • Spirits
  • Road paving with asphalt

The methodology of the estimates is discussed in Passant et al (1998). The breakdown into speciated categories is based on Rudd(1995).

2.5.10 Industrial Processes PM10

The CRI (Environment Agency, 1997a) contains estimates of total particulate emissions from large industrial processes (part 'A' processes). However the CRI is incomplete. Table A9 lists the emissions in the CRI from industrial processes. The increasing trend of the figures is due to the increasing coverage of the database and not a real increase in emissions.

Table A9 1996 CRI Particulate Emissions (tonnes)
Industry Process 1992 1993 1994 1995 1996
FUEL AND POWER PRODUCTION AND ASSOCIATED PROCESSES CARBONISATION AND ASSOCIATED PROCESSES 106 473 626 400 392
  GASIFICATION AND ASSOCIATED PROCESSES   152 109 64 62
  PETROLEUM PROCESSES   183 1614 1575 1613
  Total 9350 12125 15071 24453 27230
METAL PRODUCTION AND PROCESSING IRON AND STEEL 0 2 3 4788 5179
  NON-FERROUS METALS 0 0 0 49 276
  Total 0 3 3 4837 5455
MINERAL INDUSTRIES CEMENT\LIME MANUFACTURE AND ASSOCIATED PROCESSES 2 1938 5012 4361 4933
  CERAMIC PRODUCTION   371 723 621 592
  GLASS MANUFACTURE AND PRODUCTION   13 113 18 8
  OTHER MINERAL FIBRES   228 536 586 351
  PROCESSES INVOLVING ASBESTOS   1 11 9 5
  Total 2 2551 6395 5594 5888
OTHER INDUSTRY COATING PROCESSES AND PRINTING         3
  DI-ISOCYANATE PROCESSES   0 0 0 2
  PAPER AND PULP MANUFACTURING PROCESSES       1 107
  PROCESSES INVOLVING URANIUM     0 0 0
  TAR AND BITUMEN PROCESSES         30
  TIMBER PROCESSES   0 0 0  
  Total 0 0 0 1 141
THE CHEMICAL INDUSTRY ACID PROCESSES     8473 216 164
  CHEMICAL FERTILISER PRODUCTION     132 436 499
  INORGANIC CHEMICAL PROCESSES   0 347 229 302
  MANUFACTURE AND USE OF ORGANIC CHEMICALS 0 37 533 620 248
  PESTICIDE PRODUCTION 0 0 1 0 0
  PETROCHEMICAL PROCESSES     21 22 21
  PROCESSES INVOLVING HALOGENS     88 79 34
  Total 0 37 9595 1603 1268
Total of 1996 CRI Part 'A' Processes   107 3399 18342 14073 14819

An estimate of the total emissions of PM10 of 'about 30 ktonnes' from industrial processes was given in the third report of the Quality of Urban Air Review Group. This estimate was made by taking the total production and using emission factors from the USEPA (1995). However, this calculation is fairly crude. It was compared with the CRI data for 1994 (the latest year at the time). The total for 1994 was 19,764 (since revised by the Environment Agency to 31,064; see Table A9). As the CRI estimate includes all suspended particulates not just PM10 it was thought that the estimate of 32 ktonnes was reasonable.

Now, the CRI includes more sources and the total has been revised upwards. The total for 1996 of 39983 tonnes probably represents less PM10 that the 32000 tonnes quoted above. However, as the CRI does not cover smaller sources it is likely that the current figure is an underestimate. Also the USEPA data has been revised with more detailed emission factors. Work is continuing to match these emission factors to the UK and to revise the current estimates. When this is completed revised estimates for the industrial process sector will be produced.

2.5.11 The Feedstock Use of Natural Gas

Natural gas is used as a feedstock for the manufacture of ammonia (for fertilizer), methanol and acetic acid. The largest use is for ammonia manufacture by the steam reforming of natural gas to make hydrogen:

  CH4 + H2O Û CO + 3H2
  CO + H2O Û CO2 + H2

The hydrogen is then reacted with nitrogen from air to form ammonia

  N2 + 3H2 Û 2NH3

If there is no use of the by-products CO and CO2 formed then these are emitted to atmosphere. The CO is oxidised to CO2 prior to emission. Hence the CO2 emission can be estimated from the natural gas usage or the amount of ammonia produced. In principle the emission is 0.97 t CO2 /t NH3 produced based on the reaction stoichiometry.

In the UK some ammonia plants are integrated with methanol and acetic acid manufacture for greater efficiency. Thus hydrogen formed as a by-product from acetic acid manufacture is used as the feedstock for ammonia manufacture. Some carbon monoxide and carbon dioxide from the reforming process is used to manufacture methanol. This carbon is sequestrated as methanol and is not emitted to atmosphere.

Methanol is manufactured from natural gas using a process similar to the steam reforming process:

  CO + 2H2 Û CH3OH

so that all the carbon content of the natural gas is sequestrated as methanol.
Acetic acid is manufactured from methanol and natural gas and again the carbon content of the natural gas is sequestrated.
Two estimates were made:

  • The amount of CO2 emitted from ammonia manufacture
  • The amount of natural gas used in the manufacture of products. This can then be deducted from the total combustion of gas by industry in order to calculate the combustion emissions of the non- CO2 pollutants.

The procedure adopted for the emission of CO2 from ammonia manufacture was:

  1. Data on the plant capacity, natural gas consumption or CO2 emission from
    • ammonia plant
    • acetic acid plant
    • methanol plant
    were collected from manufacturers. This included a breakdown between natural gas used as a feedstock and natural gas used as a fuel.

  2. The ammonia capacity of the plants using hydrogen by-product from acetic acid manufacture was excluded.
            
  3. The emissions of CO2 (and natural gas consumption) were scaled to be consistent with the total UK ammonia production reported in BGS (1998)
            
  4. Corrections were made based on manufacturers advice on the 'recovery ' of carbon in methanol manufacture.

    The procedure used to estimate the natural gas use as a feedstock was to perform a carbon balance over the three processes:

    1. Methanol plant capacity data was used to estimate its natural gas use
    2. The natural gas usage of the acetic acid plant was available
    3. The natural gas use equivalent to the CO2 emission from ammonia manufacture was calculated
    4. The total feedstock use of natural gas was estimated as the sum of items 1-3

    The 1996 Inventory includes an estimate of the NO    x emission from the ammonia reformer reported under ammonia combustion. This arises from the combustion of natural gas to produce the high temperatures required by the process. The estimate was based on data provided by the manufacturers.

    The necessary data were supplied by ICI, Kemira and BP Chemicals.

    2.5.12 Catalytic Crackers

    The regeneration of spent catalyst used in the catalytic cracking of petroleum to produce gasoline and gas oil results in a significant emission of sulphur dioxide. Emission data for catalytic crackers in the UK was supplied by UKPIA(1997). For earlier years estimates were obtained by scaling on petrol production.

    2.5.13 Aluminium Production

    Aluminium is produced by the electrolytic reduction of alumina in large pots. During the reduction, the carbon anode is consumed resulting in the emission of CO    2 , SO2 and other pollutants. In the UK most aluminium is produced by the prebaked anode cell process, though one plant operates the older Soderberg Cell process. Emissions were estimated based on the production of aluminium for each type of process and the carbon emission factors shown in Table A10. The carbon emission factors reflect current practice, and higher emission factors were used for earlier years. For the other, pollutants the same factors were used for each process.

    Table A10 Emission Factors for Aluminium Production (kt/Mt Al production)

      CO2 a SO2 b NOx b CO a
    Soderberg 520 15.1 2.15 93
    Prebake 420      
    a CO2 as carbon, Alcan (1997).
    b IPCC (1997)

    2.5.14 Electric Arc Furnaces

    Emissions from electric arc furnaces were estimated for the first time. These are used in the production of stainless and mild steel and also for recycling scrap. Emissions are based mainly on default emission factors taken from the UNECE/CORINAIR Draft Chapter on electric arc furnaces. The CO    2 emission arises from the consumption of a graphite anode and is based on manufacturer's data.

    Table A11 Emission Factors for Electric Arc Furnaces

      CO2 a CH4b N2Ob NOxb SO2b NMVOCb COb
    Emission Factor kt/Mt Steel 3.6 0.01 0.005 0.2 0.13 0.09 1
    a BISPA(1997)
    b Berdowski et al (1997)