UPDATED DISPERSION MODELLING · 2014-11-12 · The dispersion model software application used was...

UPDATED ATMOSPHERIC

DISPERSION MODELLING

Bellanaboy Bridge Terminal

Shell E&P Ireland Limited

September 2006

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Shell E&P Ireland Ltd Updated Atmospheric Dispersion Modelling Study Bellanaboy Bridge Terminal

RSK ENSR Environment Ltd HH/40036-13 (Rev 0)

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RSK ENSR GENERAL NOTES

Project No: 40036/13 Title: Updated Atmospheric Dispersion Modelling Study Client: Shell E&P Ireland Ltd Issue Date: DRAFT - September 2006 Issuing Office: Hemel Hempstead Prepared by:

Date: 1/9/06

Authorised by:

Project Manager Project QA Rep

Date:

1/9/06

RSK ENSR Environment Ltd (RSK ENSR) has prepared this report for the sole use of the client, showing reasonable skill and care, for the intended purposes as stated in the agreement under which this work was completed. The report may not be relied upon by any other party without the express agreement of the client and RSK ENSR. No other warranty, expressed or implied is made as to the professional advice included in this report. Where any data supplied by the client or from other sources have been used it has been assumed that the information is correct. RSK ENSR can accept no responsibility for inaccuracies in the data supplied by any other party. The conclusions and recommendations in this report are based on the assumption that all relevant information has been supplied by those bodies from whom it was requested. No part of this report may be copied or duplicated without the express permission of RSK ENSR and the party for whom it was prepared. Where field investigations have been carried out these have been restricted to a level of detail required to achieve the stated objectives of the work. This work has been undertaken in accordance with the Quality Management System of RSK ENSR Environment Ltd.

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SUMMARY

An updated air dispersion modelling study has been carried out, using the latest version of the state-of-the-art model AERMOD PRIME, to assess the air quality implications of introducing waste heat recovery to the compressor units. The modelling predicts how releases to air from the Bellanaboy Bridge Terminal will disperse with the proposed modifications and identifies the resulting air quality in the vicinity of the terminal. The model has been developed to ensure meteorological and geographical features are as representative of the local environment as is practicable. Where assumptions have been made, these have been pessimistic (conservative) in nature and are designed to over-predict ground level concentrations to which sensitive locations, including both human and ecological receptors, may be exposed. The modelling however has not taken into account any modifications to plant structures associated with the introduction of the waste heat recovery unit. The modelling has taken into account background air quality.

All significant plant items have been assumed to be operating at full output. Typical emissions will be significantly lower due to fewer plant units operating at lower load and emission rates.

The modelling predicts no relevant ambient air quality standard or guideline will be exceeded at any location beyond the site boundary when the plant is operating at full output (a worst case scenario) with waste heat recovery installed. A minor increase in predicted ambient air quality concentration does however occur due to the reduced exhaust temperature and lower exit velocity in comparison to the baseline assessment where no waste heat recovery is installed. In this report, the effect of successive increase of compressor stack heights at intervals of 10% is examined along with effect of removing heating medium heater. Results in terms of NOx and CO ground level concentrations predict that an increase in the compressor stack heights to 30m optimally compensates for the increase in predicted contributions from the gas compressor units with waste heat recovery facility.

A separate assessment has been carried out to identify the impact of heating medium heater operating for one hour per day. Such an operation of heater medium heater may be required infrequently as a start up till the waste heat recovery system on sales gas compressors pickups the necessary heat. Such frequency of operation of the heating medium heater however is considered to be an overestimate of the frequency of use of the heating medium heater during start up conditions. Assessment with this scenario indicates that there is negligible increase in the ground level concentrations of NO2 and CO pollutants, with environmental concentrations well below the air quality limit values.

Existing air quality has been identified through monitoring surveys to be very good. The modelling predicts good air quality will continue to be present with the terminal in operation.

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TABLE OF CONTENTS

1 Introduction ............................................................................................ 1 2 Scope ...................................................................................................... 1

2.1 Pollutants....................................................................................... 1 2.2 Sources ......................................................................................... 1 2.3 Operational Scenarios ................................................................... 1

3 Method .................................................................................................... 2 3.1 The Dispersion Model.................................................................... 2 3.2 Input Data...................................................................................... 2 3.3 Background Air Quality.................................................................. 6 3.4 The Chemistry of Nitrogen Oxides................................................. 6

4 Results .................................................................................................... 7 5 Discussion and Conclusions .............................................................. 18

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1 INTRODUCTION

RSK ENSR Environment Ltd has undertaken an updated air dispersion modelling study on behalf of Shell E&P Ireland Ltd to predict the dispersion characteristics of emissions to atmosphere from the Bellanaboy Bridge Terminal. The updated assessment has been carried out to assess the impact of introducing waste heat recovery on the exhaust of the sales gas compressors for utilisation onsite. Unless specified otherwise, all information is the same as reported in the air dispersion modelling report prepared in support of the IPPC licence application (RSK ENSR report 40036, July 2004).

2 SCOPE

2.1 Pollutants

The pollutants modelled were oxides of nitrogen (NOx) and carbon monoxide (CO). These are generally the most significant pollutants arising from combustion of natural gas, which will be the main fuel used at the terminal. As the hydrocarbon fluids from the Corrib field have been found to contain very low levels of sulphur, emissions of sulphur dioxide will be negligible. Similarly particulate matter (PM) will not be emitted in significant quantities due to the clean-burning nature of the Best Available Technology natural gas combustion systems to be installed. All other substances will be emitted in very small quantities.

2.2 Sources

The sources modelled were those classified as ‘main’ in the body of the IPC licence application (Table 12A.1). These are:

• 2 x gas turbines for sales gas compression (source reference no. A2-1 and A2-2)

• 1 x heating medium heater (reference no. A2-3), fired on gas.

• 2 of the 3 gas engines for power generation (reference no. A2-4, A2-5 and A2-6 – note this is a variation in comparison to the July 2004, which identified all 3 engines operating as the worst case. One generator will always be maintained on standby)

The minor sources such as the emergency generator engine and the firewater pumps are much smaller than the main sources in terms of their power ratings and additionally will only operate for short periods for testing purposes under normal circumstances. Therefore they have not been included in the modelled scenarios.

A review of releases of NOx from the electricity generators is currently being undertaken by Shell E&P Ireland Ltd but is not considered within the context of this report.

2.3 Operational Scenarios

The operating scenarios considered within the modelling include:

1. All the sources listed in Section 2.2 operating (2 gas turbines, 1 heating medium heater, 2 of 3 gas engines for power generation).

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2. As with scenario 1, but an updated assessment with the introduction of waste heat recovery on the sales gas compressor units and removal of the heating medium heater.

3. Additional stack height assessment with the height of the sales gas compressors release points being increased successively in 2.5 m intervals.

4. As with scenario 2, but with operation of heating medium heater for one hour per day as a start up till the time the waste heat recovery system on the sales gas compressor units picks up enough heat. In reality, the frequency of start up will be much lower.

3 METHOD

3.1 The Dispersion Model

The dispersion model software application used was Breeze AERMOD Prime, version 5.1.2. AERMOD is a state-of-the-art, new generation model, accepted by the EPA and many other regulatory bodies worldwide.

3.2 Input Data

The input data used in the modelling study are described in the following sections. Relevant data (locations, emission rates and parameters) are the same as those detailed in Section 12 of the application except for scenario 2 and converted where necessary (e.g emission rates from kg/hr to g/s, temperatures from °C to K) for input to the model. All data are detailed here for convenience.

3.2.1 Source Locations The grid coordinates of the emissions sources are detailed in Table 1 below.

Table 1: Grid Coordinates of Emission Sources

Source ref. no. Source Easting Northing

A2-1 Gas turbine A 86482 333179

A2-2 Gas turbine B 86494 333186

A2-3 Heating medium heater 86598 333151

A2-4 Power generator A 86500 332981

A2-5 Power generator B 86493 332977

A2-6 Power generator C 86485 332973

Note: Only two of the three power generation units are assumed to be in operation.

3.2.2 Source Parameters Table 2 below presents the source parameters input to the model.

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Table 2: Source Parameters

Source Stack height above grade (m)

Stack exit diameter (m)

Exhaust gas temperature (K)

Min efflux velocity (ms-1)

Gas turbines (each) 21.4 for Scenario 1,2,4 only.

21.5 Varied for Scenario 3.

1.7 All scenarios

Scenario 1: 753

Scenario 2,3,4: 473

29.7 for Scenario 1:

23.4 for Scenario 2,3,4:

Heating medium heater – on gas

20.0 for Scenario 1,4 only


555 Scenario 1,4 only


Power generators (each)

15.8 for All scenarios


773 for All scenarios


3.2.3 Emission Rates Table 3 presents the pollutant emission rates input to the model.

Table 3: Pollutant Emission Rates

NOx emission rate (g/s)

CO emission rate (g/s)

Source type Maximum Maximum

Gas turbines (each) 1.72 for All scenarios


Heating medium heater – on gas


0.17 for Scenario 1 only

Power generators (each)



3.2.4 Meteorological Data The predominant wind direction is from the south-west and will disperse emissions away from the nearest residential dwellings for the majority of time. The frequency of wind direction and windspeed during 2001 is illustrated in Figure 1. Other years used in the study show a very similar pattern. The windrose included in Figure 1 identifies the frequency of the wind direction from where the wind is coming from as opposed to going to. Winds are typically moderate to strong and periods of very low winds or calm when dispersion characteristics can be restricted are shown to be very infrequent. The meteorological data was collated at Belmullet, which is the nearest and most representative meteorological station where data is collated in sufficient detail for use in this assessment. Local geographic features are not considered to significantly impair dispersion from emission sources or change local wind conditions.

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Five years (1997 - 2001) of hourly sequential meteorological data were purchased from Met Eireann and used in the model (separate runs for each year). The data includes all required parameters to simulate both horizontal and vertical movements in the atmosphere. The data is adjusted to reflect the land use around the terminal site.

Figure 1: Windrose - Belmullet 2001

3.2.5 Buildings A three-dimensional representation of the site was incorporated into the model to ensure that the effect of on-site structures on the air flow was taken into account. Figure 2 below shows the site model as used. The exact individual building dimensions and locations can be viewed in the electronic input files supplied with this report. It should be noted that detailed design for the waste heat recovery unit structures was not available at the time of writing this report and the modelling assessment will be reviewed and where required, updated once such information is available.

Figure 2: Three-dimensional Site Model

Not to scale. HMH = Heating Medium Heater. GTs = Gas Turbines. Powergen = Power Generation Engines

HMH GTs

Powergen Site boundary

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3.2.6 Output Grid Output concentrations were calculated on a 4 x 4 km Cartesian grid, with output points equally spaced at 100 m intervals along both the east-west and north-south axes. This grid was selected following test runs to ensure that a suitable area was covered whilst still calculating at a high enough resolution to ensure that important features of the plume were not obscured. Receptors were also placed at the boundary vertices, which can be seen in Figure 2 above. No output points were placed within the site boundary.

3.2.7 Terrain Elevations To account for the effects of the relatively complex terrain on the airflow in the area, digital terrain elevations were included in the model. These were purchased from Ordnance Survey Ireland.

3.2.8 Averaging Periods & Assessment Criteria The model calculated pollutant concentrations over averaging periods designed for direct comparison with air quality standards and objectives set by Irish statute. These standards implement the EU daughter directives on air quality (Air Quality Standards Regulations, 2002 (SI No. 271 of 2002). Such standards have been set by environmental and health professionals across Europe following extensive worldwide research and are designed to protect the most sensitive of receptors, including for example elderly humans with existing respiratory ailments and areas valued for their flora and fauna.

A number of the standards are expressed as percentile concentrations. The percentile represents the percentage of time for which the concentration is below that stated value. A concentration expressed as a 99.8th percentile for example, is the concentration that is below the value for 99.8 percent of the time (or is exceeded for just 0.2% of the time). Standards expressed as percentiles hence allow concentrations higher than the stated limit value for a certain percentage of time without adverse impact on health or ecosystems.

Table 4: Relevant Air Quality Standards

Substance Averaging Period Limit value

concentration (µµµµgm-3)

NO2 Annual average 40

NO2 99.8th percentile of hourly means

200

CO Maximum daily 8 hour running mean

10,000

An additional oxide of nitrogen (NOx) air quality standard exists for the protection of ecosystems (30 µgm-3) expressed as an annual average. The assessment has included comparison with this air quality standard though it is not strictly applicable within 5km of a facility of this nature. The World Health Organisation has set guideline values for the protection of health and ecosystems. These are generally similar to the levels specified in Table 4. Slight variations to the limits specified in the Air Quality Standards Regulations include a one hour guideline for NO2 (200 µgm-3) and a guideline NO2 value for the protection of sphagnum dominated vegetation (expressed as an annual average) of 12µgm-3. WHO guidelines are not described in statute but many of their recommendations are

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incorporated into the standards identified in the Air Quality Standards Regulations, 2002. Additional information on model parameters is included in the electronic data files that accompany this report and the IPC licence application.

3.3 Background Air Quality

In the absence of any publicly available air quality data for the region, RSK ENSR undertook a sampling survey on behalf of Shell. The full report of this survey is available separately to this report. The survey did not measure CO, however NO2 was included in the scope. Whilst CO has not been measured, very low concentrations of this parameter would be expected and exceedances of the CO 8-hour standard are only typically observed in highly congested urban environments. Three sampling periods were carried out between 2001 and 2003.

The long-term average concentration of NO2 for all locations during the sampling period was identified to be less than 3.4 µgm-3 (typically 2 µgm-3). As expected for a rural area with little industry or traffic, this is a very low concentration in comparison to the ambient air quality standard and is indicative of very good air quality. This value has been used in the assessment to add to the modelled long-term process contributions and hence predict total concentrations resulting from terminal operations.

The average background concentration of NOx measured during the monitoring surveys (across all sampling locations) was 11 µgm-3. Background concentrations of NOx over short periods (such as an hourly average) have been predicted using a recommended approach by the UK Environment Agency whereby short period modelling results are added to twice the long-term background concentration (Guidance Note H1: IPPC – Environmental Assessment and Appraisal of BAT). This takes into account the potential for peak process contributions to coincide with high short period background concentrations. It is rare however for peak background concentrations and the highest process contributions from a site of this nature, to coincide both spatially and temporally. In order to ensure a robust assessment, the highest value of NO2 measured over the shortest sampling period available has been used. This corresponds to 12 µgm-3, measured in close proximity to the R314 road.

3.4 The Chemistry of Nitrogen Oxides

The modelled pollutant was total NOx – a mixture of nitrogen monoxide (NO) and NO2. In combustion plant such as the units that will be installed at the terminal, most NOx is released as NO. Upon release NO is partially and gradually oxidised to NO2 by complex chemical reactions in the atmosphere. The speed and eventual equilibrium point of the reaction are dependent on factors such as the incident sunlight and the concentrations of ozone in the vicinity. NO is not a substance of great concern in terms of air quality. The air quality standards are set for NO2 only, not NOx for the protection of human health. The modelling study has assumed that 75% of the NOx released is oxidised to NO2 by the time it reaches the receptor point. This is considered to be a conservative assumption. In reality much of the NOx (perhaps 50-80%) will still be in the form of NO, especially when the maximum concentrations are found relatively close to the sources.

The average proportion of background NOx in the form of NO2 identified during the monitoring survey outlined in Section 3.3 was 45%. Given the low proportion of NO2 anticipated within any exhaust plumes emitted from the facility and only 45% of NOx

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being in the form of NO2 in the background environment, the use of a 75% conversion factor is likely to lead to a significant overestimate of both short term and long term concentrations within the modelling study.

4 RESULTS

The highest predicted results of the dispersion model for any location at or beyond the site boundary, assuming the maximum number of plant operating onsite are summarised in Table 5 (with background air quality incorporated) for all the three scenarios identified in section 2.3. The highest concentrations are found at, or in close proximity to the site boundary.

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Table 5: Summary of Results. Highest Predicted Process Contributions at or Beyond the Site Boundary (with background ambient concentrations incorporated)

Maximum concentrations (µµµµgm-3)

Scenario* Year of meteorological data

NO2 annual average

NO2 1-hour average, 99.8th percentile

CO 8-hour average

1997 9.5 130.8 94

1998 12.8 129.2 100

1999 13.4 137.7 102

2000 11.7 135.2 94

Scenario 1: Maximum plant operation without waste heat recovery

2001 11.8 136.1 105

1997 9.7 152.2 111

1998 12.8 149.0 109

1999 13.7 150.6 113

2000 11.9 151.4 113

Scenario 2: Maximum operation with waste heat recovery, but without heating medium heater 2001 12.0 147.8 114

Year of meteorological data

Stack height of sales gas compressor units

NO2 annual average

NO2 1-hour average, 99.8th percentile

CO 8-hour average

1999 21.4 13.7 150.6 113

1999 23.9 13.4 141.8 106

1999 26.4 13.1 133.1 96

1999 28.9 12.9 127.8 84

1999 31.4 12.8 127.5 77

1999 33.9 12.6 127.1 73

Scenario 3: Same as Scenario 2, but with additional sales gas compressor units stack height assessment

1999 36.4 12.6 127.1 73

1997 9.7 152.2 111

1998 12.8 149 109

1999 13.7 150.6 114

2000 11.9 151.5 113

Scenario 4: Same as Scenario 2 but with operation of heating medium heater for one hour per day for start up

2001 12.0 147.8 115

Air Quality Standard 40 200 10,000

Notes: The predicted 8-hour CO average is not expressed as a running average but is the highest predicted value for sequential 8-hour periods (e.g 00:00-08:00, 08:00-16:00, 16:00-24:00). There is unlikely to be a

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significant difference between the two types of averaging period. The highest predicted concentration of CO is less than 2% of the air quality standard with all plant operating at maximum output.

Referring to Table 5, Scenario 1 which represents plant operation in combination with the highest predicted process contribution with all plant operating at full output, a combined long period environmental concentration below the ambient air quality standard of 30 µgm-3 for the protection of ecosystems is predicted. Even lower concentrations will be predicted under typical operation. Predicted concentrations of NOx and CO fall rapidly with distance from the site boundary.

Table 5 identifies that NOx and CO ground level concentrations resulting from the plant operation as per scenario 2 will be marginally more when compared to scenario 1. However, this minor increase in pollutant concentrations will be compensated by increase of sales gas compressors release heights as illustrated with 1999 meteorological data as scenario 3 in Table 5. Stack height assessment results presented for Scenario 3 are graphically presented in Figures 3 to 5. These results suggest that an optimal increase of stack height to 30m will compensate for the minor increase in ground level concentrations resulting from the introduction of the waste heat recovery unit. Scenario 4 identifies that the increase in NOx and CO ground level concentrations resulting from the operation of heating medium heater for one hour per day is negligible. Such events of operation of heating medium heater are very infrequent with waste heat recovery system on sales gas turbines in operation.

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Figure 3: Effect of Sales Gas Compressors stack height on NO2 1 hour 99.8 percentile environmental ground level concentrations

Figure 4: Effect of Sales Gas Compressors stack height on NO2 annual average environmental ground level concentrations

NO2 1 hr 99.8 p Average Environmental GLC, µµµµg m-3. Scenario 3.

125

130

135

140

145

150

155

20 25 30 35 40

Sales Gas Compressor Release Height, m

NO

2 1

ho

ur

99.8

p G

LC

NO2 Annual Average Environmental GLC, µµµµg m-3. Scenario 3.

12.00

12.50

13.00

13.50

14.00

20 25 30 35 40


NO

2 A

nn

ual

Ave

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GL

C,

µµ µµg m

-3

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Figure 5: Effect of Sales Gas Compressors stack height on CO 8 hour average environmental ground level concentrations

CO 8 hour Average Environmental GLC, µµµµg m-3. Scenario 3.

70

80

90

100

110

120

20 25 30 35 40


CO

8 h

ou

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vera

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GL

C,

µµ µµg m

-3

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Figure 6: NO2 1 hour 99.8 percentile average environmental offsite ground level concentrations for scenario 1.


Predicted Ground Level NO2 (1 hour 99.8 percentile) ConcentrationScenario 1. 1999 Met Data.

Concentration contours in micrograms per cubic metreAssumes 75% conversion ratio

1999 meteorological data from BelmulletIncorporates short period background value of 12 micrograms per cubic metre

3035404550556065707580859095100105110115120125

84500 85000 85500 86000 86500 87000 87500 88000331000

331500

332000

332500

333000

333500

334000

334500

335000

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Figure 7: NO2 annual average environmental offsite ground level concentrations for scenario 1.


Predicted Ground Level NO2 (Annual Average) ConcentrationScenario 1. 1999 Met Data.

Concentration contours in micrograms per cubic metreAssumes 75% conversion ratio

1999 meteorological data from BelmulletIncorporates long period background value of 3.4 micrograms per cubic metre

84500 85000 85500 86000 86500 87000 87500 88000331000

331500

332000

332500

333000

333500

334000

334500

335000

3.5

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Figure 8: CO 8 hour average environmental offsite ground level concentrations for scenario 1.


Predicted Ground Level CO (8 hour average) ConcentrationScenario 1. 1999 Met Data.

Concentration contours in micrograms per cubic metre

1999 meteorological data from Belmullet

84500 85000 85500 86000 86500 87000 87500 88000331000

331500

332000

332500

333000

333500

334000

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Figure 9: NO2 1 hour 99.8 percentile average environmental offsite ground level concentrations for scenario 2.


Predicted Ground Level NO2 (1 hour 99.8 percentile) ConcentrationScenario 2. 1999 Met Data.

Concentration contours in micrograms per cubic metreAssumes 75% conversion

1999 meteorological data from BelmulletIncorporatres short term background concentration of 12 micrograms per cubic metre

3035404550556065707580859095100105110115120125130

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Figure 10: NO2 annual average environmental offsite ground level concentrations for scenario 2.


Predicted Ground Level NO2 (Annual Average) ConcentrationScenario 2. 1999 Met Data.

Concentration contours in micrograms per cubic metreAssumes 75% conversion

1999 meteorological data from BelmulletIncorporatres long term background concentration of 3.4 micrograms per cubic metre

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Figure 11: CO 8 hour average environmental offsite ground level concentrations for scenario 2.


Predicted Ground Level CO (8 hour Average) ConcentrationScenario 2. 1999 Met Data.

Concentration contours in micrograms per cubic metre

1999 meteorological data from Belmullet

5101520253035404550556065707580859095100

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5 DISCUSSION AND CONCLUSIONS

Numerous assumptions have been incorporated into this dispersion modelling study that are designed to over predict ground level concentrations and therefore provide a conservative assessment of air quality impacts. The highest predicted concentrations using these assumptions occur at or in close proximity to the site boundary. Whilst it is unlikely that members of the public will be exposed at such a location for a relevant period of time, predicted concentrations for all scenarios are within air quality standards for the protection of health taking into account background concentrations. The modelling predicts no relevant ambient air quality standard or guideline will be exceeded at any location beyond the site boundary when all installed plant is operating at full output (a worst case scenario) with waste heat recovery installed on the sales gas compressors. A minor increase in predicted ambient air quality concentration does however occur in comparison to the baseline assessment where no waste heat recovery is installed due to the reduced exhaust temperature and lower exist velocity. This minor increase will be adequately compensated with an optimal increase to 30m for the gas compressors’ stack height. Further, the increase in NO2 and CO ground level concentrations resulting from the operation of heating medium heater for one hour per day is negligible. Such frequency of operation of the heating medium heater however is considered to be an overestimate of the frequency of use of the heating medium heater during start up conditions.

Conclusions Operations at the terminal site will not result in a significant impact on local air quality. This conclusion is based on a comparison of the ground level NO2 concentrations predicted by highly conservative dispersion modelling with relevant air quality standards and guidelines. Such standards and guidelines have been set by environmental and health professionals across Europe following extensive worldwide research. They are designed to protect the most sensitive of receptors, including for example elderly humans with existing respiratory ailments and sensitive areas valued for their flora and fauna. Existing air quality is very good and is predicted to remain so with the terminal in operation with or without waste heat recovery in operation.

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EPA Export 12-11-2014:23:34:12

UPDATED DISPERSION MODELLING · 2014-11-12 · The dispersion model software application used was...

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Transcript of UPDATED DISPERSION MODELLING · 2014-11-12 · The dispersion model software application used was...