The fuel consumptions for these categories are taken from DTI (1998). The emissions from most sources in these industries are calculated as in the base combustion module. However, sources involving fuel transformation require a more complex treatment. The problem in estimating emissions from these sources is that fuels are manufactured from other fuels producing process emissions and that subsequently the fuel is burnt elsewhere producing further emissions. Hence it is necessary to define a method of allocating the emissions to the various possible sources without double counting. The approach used by the NAEI is based on a carbon balance over coke production, solid smokeless fuel (SSF) production, blast furnaces and town gas production.

The processes involved are:

coal ® coke + coke oven gas + carbon emission

coal ® SSF + carbon emission

coal ® town gas + carbon emission

coke ® blast furnace gas + carbon emission + carbon in steel

Hence by estimating the carbon content of the coal or coke consumed in these processes and the carbon content of the coke, coke-oven gas, blast furnace gas, steel, town gas and SSF produced, the carbon emission from each process can be calculated.

In reality the carbon emission is in the form of coke oven gas, coal tars used as fuel and blast furnace gas that is unaccounted for in the energy statistics with a contribution from the uncertainty in the estimates of input and output fuels and their carbon content. The calculations are so arranged that the total carbon emission corresponds to the carbon content of the input fuels.

A similar procedure could be applied to sulphur dioxide emissions, however this is complicated by the cleaning of the blast-furnace gas and coke-oven gas produced and possible retention of the sulphur by blast furnace slag. Hence in practice, the treatment of sulphur dioxide depends on the information available and is unique to each process.

Applying the same nomenclature as that used in Section 1.3.2, the emission of carbon from coke production is:

E(car,coke prod,c) = A(coke prod,c) × e(car,coke prod,c)

- cout1

where

cout1 = A(coke made,ck) × e(car,coke made,ck)

+ E(car,coke prod,cog)

+ E(car,I&S, cog)

+ E(car,collieries,cog)

+ E(car,other industry,cog)

+ E(car,TG prod,cog)

and

A(coke made,ck) = Mass of coke made (kg)

e(car,coke made,ck) = Carbon content of coke made (kg/kg)

car = Carbon

ck = Coke

cog = Coke oven gas

c = Coal

The carbon contents of coking coal and coke made are 710 kg/t and 820 kg/t respectively.

For emissions of other pollutants, a mass balance approach is no longer used. It is now assumed that energy emissions arise from the combustion of the blast furnace gas and coke oven gas produced. The emission factors are given in Table A13. Process emissions from coke ovens are estimated on the basis of total production of coke. The emission factors used are given in Table A6.

The inventory also includes emissions from the flaring of coke oven gas. These are based on data on coke oven gas losses given in DTI(1997) and combustion emission factors given in Table A6.

The emission of carbon from SSF production is:

E(car,ssf made,c) = A(ssf prod,c) × e(car,ssf prod,c)

- A(ssf made,ssf) × e(car,ssf made,ssf)

where

A(ssf made,ssf) = Mass of SSF made (kg)

e(car,ssf made,ssf) = Carbon content of SSF made (kg/kg)

ssf = Solid smokeless fuel

The carbon contents of coking coal and coke made are 710 kg/t and 790 kg/t respectively.

For emissions of other pollutants, a mass balance approach is no longer used. It is likely that emissions will arise from the combustion of the coke oven gas produced by some SSF retorts but this combustion is not identified in the energy statistics. Process emissions from SSF plant are estimated on the basis of total production of SSF. The emission factors used are given in Table A8 and are based on USEPA(1997) factors for different parts of the coke production process that are appropriate to the SSF processes used in the UK. Given that there are a number of processes in use these estimates will be very uncertain.

Data is available on the production of SSF and the fuels used (DTI, 1998), however it is clear that in recent years imported petroleum coke has been used in the production of smokeless fuels. Data on the total UK imports and exports of petroleum coke is available but little information is available on its consumption. In these estimates an assumption of an annual 100 kt usage in SSF production since 1992 is used based on DETR (1998f)

Table A8 Emission Factors Used for Coke and Solid Smokeless Fuel Production (kt/Mt fuel produced)

The procedure for town gas is different from the other fuel transformation industries because it is clear from the level of consumption of LPG, natural gas and coke oven gas relative to the production of town gas that much of these fuels were added to the supply of town gas made from coal and oil. The procedure adopted was to perform a carbon balance on the fuels consumed by town gas manufacture and the town gas produced. The carbon emissions were then allocated proportionately to the town gas production fuel consumption categories. The computational scheme is:

E(p, TG Prod, f) = A(TG Prod, f) ´ e(p, TG Prod, f) ´ factor3

where

factor3 = 1 - cout

cin

and

cin = å A( TG Prod, f) ´ e(car, TG Prod, f)

^f

cout = å A(s, tgas) ´ e(car, s, tgas)

^s

where

A(TG Prod, f) = Usage of fuel f in town gas production (kg)

e(p, TG Prod, f) = Emission factor of pollutant p from fuel f in town gas production (kg/kg)

e(car, TG Prod, f) = Carbon content of fuel f in town gas

production (kg/kg)

A(s, tgas) = Usage of town gas in source s (therm)

e(car, s, tgas) = Emission factor of carbon from town gas

in source s (kg/therm)

tgas = Town gas

Emissions of sulphur dioxide are calculated using the simpler scheme:

E(SO₂, TG Prod, f) = A(TG Prod, f) × e(SO₂, TG Prod, f)

The carbon emission from blast furnaces is calculated as:

E(car,I&S BF,ck) = A(I&S BF,ck) × e(car,I&S BF,ck)

- E(car,coke prod,bfg)

- E(car,I&S,bfg)

- A(I&S BF,steel made) × e(car,I&S BF, steel made)

where

A(I&S B F,ck) = Blast furnaces coke consumption (kg)

A(I&S BF,steel made) = Crude steel production (kg)

e(car,I&S BF, steel made) = Carbon content of steel made (kg/kg)

bfg = Blast Furnace Gas

The final term in the equation is the carbon sequestrated in the steel produced. It is assumed that the carbon content of steel is around 1.7 kt C/Mt crude steel. This is a very approximate estimate but the carbon sequestrated is very small compared with the other terms.

For other pollutants the emissions are estimated based on the methodology described in IPCC(1997) for blast furnace charging and pig iron tapping. The emission factors are expressed in terms of the emission per Mt of steel produced and are given in Table A9. Data on steel production is reported in ISSB(1998).

Table A9 Emission Factors for Blast Furnaces (kt/Mt Steel)