Tecnologías de la Información y Comunicación

4.9.5

Source Specific Recalculations

The revision to methodology regarding CO2 emissions from ammonia production that are

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series, with an increase in emissions of 170kt CO2 in 2009. This recalculation has been

made to ensure that the estimates are in line with the 1996 IPCC Guidelines.

4.9.6

Source Specific Planned Improvements

Emission factors and activity data will be kept under review.

4.10

SOURCE CATEGORY 2B2 – NITRIC ACID PRODUCTION

4.10.1 Source Category Description

Nitric acid is produced by the catalytic oxidation of ammonia: 4NH3 + 5O2⇒ 4NO + 6H2O

2NO + O2⇔ 2NO2

3NO2 + H2O ⇔ 2HNO3 + NO

Nitrous oxide is also formed by oxidation of ammonia: 4NH3 + 3O2⇒ 2N2O + 6H2O

Nitrous oxide is emitted from the process as well as a small percentage of the NOx. At the

end of 2010, nitric acid was being manufactured at 2 UK sites with a total of 4 production plants. One of the plants has NOx/N2O abatement fitted to all units since commissioning

(pre-1990), while the other three plants have no nitrous oxide abatement fitted to any units.

4.10.2 Methodological Issues

Across the 1990-2009 time-series, the availability of emissions and production data for UK Nitric Acid (NA) plant is inconsistent, and hence a range of methodologies have had to be used to provide estimates and derive emission factors for this sector.

For plant in England, emissions data from plant operators are available for all sites from 1998 onwards from the EA’s Pollution Inventory. For the plant (now closed) in Northern Ireland, emissions data from plant operators became available from 2001.

Site-specific production estimates are largely based on production capacity reported directly by the plant operators. This approach may overestimate actual production. No data are available for two sites operating between 1990 and 1994, and production at these sites is calculated based on the difference between estimates of total production and the sum of production at the other sites.

Emission estimates for N2O are derived for each NA site using:

a) Emissions data provided by the process operators directly or via the Pollution Inventory (1998 onwards for plant in England, 2001 onwards for plant in N Ireland); b) Site-specific emission factors derived from reported emissions data for the same site

for another year (1990-1997 for some plant in England, 1994-1997 for other plant in England, 1990-2000 for plant in N Ireland); and

c) A default emission factor of 6 kt N2O /Mt 100% acid produced in cases where no

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default factor is the average of the range quoted in IPCC Guidelines (IPCC, 1997) for medium pressure plant

Emissions of NOx are derived for each nitric acid site using emissions data provided by the

process operators directly or via the Pollution Inventory. No emissions data are available before 1994 and so a default NOx emission factor of 3.98 tonne NOx / kt of 100% acid

produced and nitric acid production data (CIS, 1991) is used up to 1988 with emissions between 1989 and 1993 being calculated by linear interpolation.

The default emission factor 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 is based on data on UK manufacturing plant provided by the Nitric Acid Association for the year 1985 (Munday, 1990).

Some nitric acid capacity is associated with a process that manufactures adipic acid. For the years 1990-1993, its emissions are reported combined with those from the adipic acid plant (see Section 3.10) but emissions from 1994 onwards are reported separately. This causes some inconsistency in between reporting categories, although total emissions are not affected.

4.10.3 Uncertainties and Time Series Consistency

The Approach 1 (error propagation) uncertainty analysis in Annex 7 provides estimates of uncertainty according to IPCC source category and fuel type.

Emissions from nitric acid production are estimated based on a combination of emission factors and reported emissions data. The methodology used to estimate N2O for this sector

does vary through the time-series depending upon the availability of data. The calculated N2O EF for UK nitric acid production facilities varies quite significantly across the time

series, and this may be a reflection of the lack of availability of a consistent time-series of emissions data. However, the variable N2O EF for this sector is also a reflection of nitric

acid production patterns across UK sites that utilise different process conditions with only one plant fitted with N2O abatement.

For all plants in England, emissions of N2O used in the GHG inventory are taken from

emissions reported in the Pollution Inventory data from 1998 onwards. For the plant in Northern Ireland, reported emission data became available from 2001 onwards. Prior to these years in England, emissions of N2O are estimated using either plant-specific EFs (in

terms of plant capacity) based on 1998 PI data and applied to known historic plant capacity, or by applying a default emission factor of 6 kt N2O /Mt 100% acid produced for some plant

in 1990-1993. A similar approach has been used for the nitric acid plant in Northern Ireland prior to 2001.

The nitric acid plant emissions data are considered to be reliable since they are subject to internal QA/QC checks by the plant operators and the Environment Agency before being reported in the Pollution Inventory. More details have been obtained regarding the abatement plant and N2O monitoring methodologies at the one UK plant with N2O

abatement fitted, and this has clarified some previous uncertainties regarding their process emissions.

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4.10.4 Source Specific QA/QC and Verification

This source category is covered by the general QA/QC of the greenhouse gas inventory in

Section 1.6.

4.10.5 Source Specific Recalculations

No recalculations have been made for emission estimates in this category.

4.10.6 Source Specific Planned Improvements

Emission factors and activity data will be kept under review.

4.11

SOURCE CATEGORY 2B3 – ADIPIC ACID PRODUCTION

4.11.1 Source Category Description

Adipic acid is manufactured in a multi-stage process from cyclohexane via oxidation with nitric acid. Nitrous oxide is produced as a breakdown product from the nitric acid. A single company produced adipic acid in the UK until closure of the plant in April 2009.

4.11.2 Methodological issues

Production data and emission estimates have been estimated based on data provided by the process operator (Invista, 2010). The emission estimates are based on the use of plant- specific emission factors for unabated flue gases, which were determined through a series of measurements on the plant, combined with plant production data and data on the proportion of flue gases that are unabated. In 1998 an N2O abatement system was fitted to

the plant. The abatement system is a thermal oxidation unit and is reported by the operators to be 99.99% efficient at N2O destruction. In 2004 it was operational 92.6 % of the

time (when compared to plant operation). Variation in the extent to which this abatement plant is operational, account for the large variations in emission factors for the adipic acid plant since 1999.

A small nitric acid plant is associated with the adipic acid plant that also emits nitrous oxide. From 1994 onwards this emission is reported as nitric acid production but prior to 1994 it is included under adipic acid production. This will cause a variation in reported effective emission factor for these years. This allocation reflects the availability of data.

4.11.3 Uncertainties and Time Series Consistency

The Approach 1 (error propagation) uncertainty analysis in Annex 7 provides estimates of uncertainty according to IPCC source category and fuel type.

Emissions of N2O from adipic acid production are now taken from emissions reported in the

Pollution Inventory, with more process-specific details also provided directly by the plant operators. In the early 1990s, emissions were received direct from the plant operators. The level of uncertainty associated with reported emissions of N2O is not fully understood.

However these data are considered to be reliable since they are subject to internal QA/QC checks within the company producing the adipic acid, and QA/QC checks by the Environment Agency before being reported in the Pollution Inventory.

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Fluctuations in the N2O EF from this plant are apparent since the installation of the

abatement plant. Following direct consultation with the plant operators, it has been determined that the variability of emissions is due to the varying level of availability of the abatement plant. A small change in the availability of the abatement system can have a very significant impact upon overall plant emissions and hence upon the annual IEF calculated.

4.11.4 Source Specific QA/QC and Verification

This source category is covered by the general QA/QC of the greenhouse gas inventory in

Section 1.6. During summer 2005, consultation between Defra, AEA, plant operators and