ODOUR DISPERSION STUDY NESS ENERGY PROJECT, ABERDEEN

ODOUR DISPERSION STUDY

NESS ENERGY PROJECT, ABERDEEN (SCOTLAND)

IN/MA-21/0464-001/01

July, 2021

Environment Division

IN/MA-21/0464-001/01 8th July 2021 1

Odour Dispersion Study

Ness Energy Project, Aberdeen (Scotland)

INDEX

Página

1. INTRODUCTION AND OBJECTIVES ............................................................................. 2

2. ODOUR IMMISSION CRITERIA ..................................................................................... 3

3. SELECTION OF THE REPRESENTATIVE METEOROLOGICAL YEAR ........................ 4

3.1 WRF METEOROLOGYCAL DATA ........................................................................ 5

3.1 DYCE (NOAA) ......................................................................................................10

4. ODOUR EMISSION POINT SOURCE ...........................................................................16

5. DESCRIPTION AND INPUT DATA TO THE CALPUFF DISPERSION

MODEL ..........................................................................................................................18

5.1 Introduction ...........................................................................................................18

5.2 General review .....................................................................................................19

5.3 Data required for the calmet application................................................................21

5.4 Data required for the calpuff application................................................................22

5.5 Information and input data to the dispersion model ...............................................25

5.5.1 Selected area of study for modelling ..............................................................................25

5.5.2 Generation of the wind field in the study area ................................................................26

5.5.3 Definition of odour emission source ...............................................................................32

6. CONTRIBUTION OF THE PROJECT TO THE ODOUR LEVELS ..................................35

7. CONCLUSIONS ............................................................................................................37


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1. INTRODUCTION AND OBJECTIVES

This document presents the odour dispersion study carried out for the facilities projected

by ACCIONA in the West Tullos industrial area, at the south of Aberdeen (Scotland). The Project

consists of an “energy from waste power plan”t which will process residual household and

commercial waste that would have otherwise been disposed into landfill.

The project will have a deodorization system, so the purpose of the study is to estimate

odour levels in the surroundings and to verify through the use of modeling techniques if the

emission levels provided for this deodorization system are appropriate to verify the standards set

by the Scottish Environmental Protection Agency, SEPA.

For the development of the previous analyses, the CALPUFF dispersion model will be

used, which is included in the Guideline on Air Quality Models1 of the Unites States

Environmental Protection Agency (US EPA) and which depends, among others many factors, on

the characterization of the emissions, the meteorology and the topography of the area.

The selection of the representative meteorological year for the simulations with Calpuff

model, will be carried out analysing the period 2018-2020.

So, considering the objectives expressed above, the document presented will have the

following structure:

1. Introduction and objectives

2. Odour immission criteria

3. Selection of the representative meteorological year

4. Odour emissions point source

5. Description and input data to the CALPUFF dispersion model

6. Contribution of the Project to the odour levels

7. Conclusions

1 Appendix W to 40 cfr part 51


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2. ODOUR IMMISSION CRITERIA

SEPA, in “H4 Odour Management” Technical Guidance, provides ‘benchmark levels’ that

indicate the likelihood of unacceptable odour pollution. The benchmarks are based on the 98th

percentile of hourly average concentrations of odour modelled over a year at the site/installation

boundary. The benchmarks are:

- 1.5 odour units for most offensive odours;

- 3 odour units for moderately offensive odours;

- 6 odour units for less offensive odours.

Processes involving decaying animal or fish remains, processes involving septic effluent

or sludge and biological landfill odours are considered as “most offensive odours”. So, an odour

concentration of 1.5 ou/m3 is considered as target to be met at the boundary of the Plant.


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3. SELECTION OF THE REPRESENTATIVE METEOROLOGICAL YEAR

According to “H4 Odour Management” Technical Guidance, to represent conditions for

an “average year”, hourly meteorological data for a period of at least three should be used.

So, for the selection of the representative meteorological conditions of the project site,

three years of meteorological data generated with the Weather Research and Forecasting (WRF)

model have been evaluated (2018-2020). Additionally, the meteorological data available on the

NOAA (National Oceanic and Atmospheric Administration, U.S. Department of Commerce)

website from station “Dyce”, located 11 km from the project, have also been evaluated.

The location of the point where the WRF data have been extracted (on the location of the

Project) and the Dyce station (NOAA) are presented below:

FIGURE 3.1

LOCATION OF WRF DATA POINT AND DYCE STATION (NOAA)

To select an “average year” hourly meteorological data, Pearson's correlation coefficient

will be used.


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The correlation coefficient of the frequency distribution of the wind components (speed

and direction) is determined for each of the years of the period (2018-2020) in comparison with

the accumulated of the three years.

The calculation of the correlation coefficient establishes a comparison between the

distribution of frequencies of appearance of wind blowing in each sector of wind directions for

each range of speeds, for two periods of time reflected in a matrix way.

The equation for the correlation coefficient is:

Where and are the sample means average (matrix 1) and average (matrix 2).

3.1 WRF METEOROLOGYCAL DATA

The following table presents the correlation coefficients calculated for each year:

TABLE 3.1

CORRELATION COEFFICIENT

WRF METEOROLOGYCAL DATA

Periods Correlation coefficient

2018 vs. 2018-2020 0,87

2019 vs. 2018-2020 0,91

2020 vs. 2018-2020 0,84

Below are the wind roses generated from the WRF data:


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FIGURE 3.2

WIND ROSE WRF DATA

2018


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FIGURE 3.3

WIND ROSE WRF DATA

2019


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FIGURE 3.4

WIND ROSE WRF DATA

2020


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FIGURE 3.5

WIND ROSE WRF DATA

2018-2020 (ACCUMULATED PERIOD)


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3.1 DYCE (NOAA)

The following table presents the correlation coefficients calculated for each year:

TABLE 3.2

CORRELATION COEFFICIENT

DYCE STATION DATA (NOAA)

Periods Correlation coefficient

2018 vs. 2018-2020 0,98

2019 vs. 2018-2020 0,98

2020 vs. 2018-2020 0,98

Below are the wind roses generated from Dyce station data (NOAA):


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FIGURE 3.6

WIND ROSE DYCE STATION DATA

2018


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FIGURE 3.7


2019


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FIGURE 3.8


2020


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FIGURE 3.9


2018-2020 (ACCUMULATED PERIOD)


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As main conclusion after the meteorological study seen before, taking into account that

the correlation coefficient of the Dyce station (NOAA) is the same for all years, the year 2019 will

be simulated since it is the year with the highest correlation coefficient of the WRF data (0.91).


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4. ODOUR EMISSION POINT SOURCE

The odour emission point source is associated with the deodorization system. The

location of the stack in the Project facilities is presented below.

FIGURE 4.1

LOCATION OF THE STACK ON THE PLOT PLAN

The plant will have a deodorization system based on an adsorption process with

activated carbon. Considering the type of effluents to be treated and based on the supplier's

experience, it is expected that the efficiency of the process will allow reaching an odor

concentration in the exhaust gases around 780 ou/m3.


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The characteristics of the flue gases and the odour emissions associated are presented

below:

TABLE 4.1

PHYSICAL CHARACTERISTICS OF THE EMISSION SOURCE

AND CHARACTERIZATION OF FLUE GASES

Parameters Data

UTM coordinates (m) (1) X: 555,897

Y: 6,331,948

Diameter (m) 1.25

Height (m) 25

Flue gas flow (m3/h) 54,000

Flue gas velocity (m/s) 12.2

Flue gas temperature (ºC) 9.1 (2)

Odour concentration (uo/m3) 780

Odour emissions (uo/s) 11,700

(1) Google Earth (WGS-84) (2) Annual average ambient temperature (Dyce station, NOAA, 2019).


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5. DESCRIPTION AND INPUT DATA TO THE CALPUFF DISPERSION

MODEL

5.1 INTRODUCTION

CALPUFF is an advanced non-steady state air quality and weather simulation system

developed by scientists at Exponent, Inc2.

It is a multi-layer, multi-species, non-stationary and dispersion model using puffs, which

allows simulating the effects (in time and space) of weather conditions on the transport,

transformation and deposition of pollutants.

FIGURE 5.1

CALPUFF MODELING SYSTEM

This model includes algorithms to simulate near-source effects such as building

downwash, plume elevating, partial plume penetration, etc. and effects that occur in areas far

from the source such as the deposition of pollutants, chemical transformations, vertical wind

shear, transport on water and coast effects.

CALPUFF has the ability to model inert pollutants and to employ pseudo-first order

transformation mechanisms. Furthermore, it allows considering the influence of sea breezes on

the dispersion of pollutants, allowing the user to define regions affected by the phenomenon

mentioned.


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The system also has the peculiarity of including simple modules of chemical

transformation, which allow studying and calculating some secondary species such as sulphates

(SO42-) and nitrates (NO3

-).

The United States Environmental Protection Agency (US EPA) presents the CALPUFF

modelling system (Guideline of Air Quality Models) as one of the systems applicable to the

transport of pollutants on a large scale (from 50 to 200 km from the source) and also for its

application at local scales where non-stationary effects can be important (calms of wind, breezes,

recirculation and other effects due to the type of terrain or coast).

5.2 GENERAL REVIEW

The CALPUFF model consists of three main components: Calmet, Calpuff and Calpost

and a long list of pre-processor and post-processor programs designed to provide the model with

meteorology and topographic databases in a suitable format.

Calmet is a meteorological model that develops hourly wind fields on a three-

dimensional grid that covers the entire modelling domain. In addition to reproducing the wind

fields of the region, Calmet has a micrometeorology module that describes the characteristics of

the mixing layer and develops three-dimensional temperature fields, as well as other parameters

that Calpuff uses to model the dispersion of pollutants. Additionally, Calmet has an option that

allows the use of wind fields generated by the WRF forecast model, either as the initial wind field

or as pseudo-observations together with other input data to the model.

Calpuff is a transport and dispersion model that models puffs of pollutants emitted from

the sources considered, simulating the dispersion and transformation processes along their route

and considering the wind fields designed by Calmet. The main characteristics of this pollutant

dispersion modelling system are:

2 http://www.src.com/


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- Modelling of the emission plume as discrete pollutant packages that change position

and size over time (puffs).

- Possibility of considering various types of sources (point, area, volume and line).

- Applicability for modelling domains that extends from tens of meters to hundreds of

kilometres from the source.

- Analysis for periods of time that can go from an hour or less to a year.

- Ability to model inert pollutants and to use pseudo-first order transformation

mechanisms.

- Applicability in complex terrain situations.

- Ability to work with meteorological information in three dimensions.

Calpost is a post-processing program that compiles the results obtained by Calpuff

producing as a result meteorological data output fields, concentrations and deposition fluxes.

Figure 5.2 represents a global scheme of the system configuration.

FIGURE 5.2

CALMET/CALPUFF SYSTEM MODULES

Geophysical and

meteorological data

processors

CALMET

Meteorological model

WRF

Meteorological model

CALPUFF

Dispersion model

CALPOST

Post-processing model

PRTMET

Post-processing model

METEOROLOGICAL

MODULE

MODULE

DISPERSION

MODULE

POST-PROCESSED


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5.3 DATA REQUIRED FOR THE CALMET APPLICATION

Calmet is a diagnostic model composed of a wind field generation module and a

micrometeorological module. It uses data from meteorological observations and information from

the terrain and land uses to construct the wind field and determine the structure of boundary layer

over land and over water (in this case), throughout the computational domain.

The following data will be required to run the Calmet meteorological model:

a) Geophysical data

The geophysical data required by the model are the following:

- Land elevation data.

To reproduce the effect of the terrain orography on the behaviour of the plumes, a digital

grid is elaborated from a Digital Terrain Elevation Model.

- Land use data.

The model also requires the definition of the types of land uses existing in the entire grid

that has been considered in the study.

b) Meteorological data

To select the most representative meteorological data for the study area and use them in

the application of the dispersion model it is necessary to include:

- Data from meteorological stations of Surface observations that include, hourly

observations of:

Wind velocity.

Direction of the wind.

Temperature.

Cloud cover.

Height of cloud ceiling.

Pressure on the surface.

Relative humidity.


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- Data from an altitude observation station that provides representative vertical profiles

(twice a day) of:

Wind velocity.

Direction of the wind

Temperature

Pressure

- In case of needing to calculate concentration or wet deposition flows, the input of

precipitation data to the model will be required, the required hourly data being:

Precipitation rates

Precipitation type code (part of the Surface data file)

- Besides, meteorological data can be optionally included in stations located in the sea

(buoys, boats, etc.). These data can be hourly, daily, monthly or even seasonal and

must contain:

Air-sea temperature difference

Air temperature

Relative humidity

Mixing height

Wind velocity

Direction of the wind

Temperature gradients above and below the mixed layer.

- Finally, initial hourly wind field data can be included from forecast model output files

such as:

WRF model output

5.4 DATA REQUIRED FOR THE CALPUFF APPLICATION

Calpuff is a transport and dispersion model that models “packets” (puffs) of pollutants

emitted from the sources considered, simulating the dispersion and transformation processes

along its route and considering the wind fields designed by Calmet.


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The Calpuff atmospheric dispersion model is composed of a series of modules that must

be completed in order to carry out the model. The information to include is indicated below:

a) Emission source data and aerodynamic effect of structures

The data of the emission sources for the application of the model are geometric or

operational:

- Geometrics:

Coordinates of location and height above sea level.

Height and diameter at the stack outlet.

- Operative:

Temperature and exit velocity of the gases emitted.

Pollutant emissions

Nevertheless, the parameters to be defined for each of the emission sources will depend

on the type of source selected (point, line, area, etc.).

On the other hand, it should be noted that the CALPUFF model has the BPIP (Building

Profile Input Program) module to consider the aerodynamic effect of the structures. Therefore, the

model includes algorithms to simulate effects close to sources such as building downwash.

b) Receptors

Receptors are defined as those points where the concentration of pollutants at ground

level is to be calculated. These are obtained from a grid created in the environment of the

installation’s emission sources.

Additionally, discrete receptors are defined at those points in the study area where it is of

interest to calculate the contribution of pollutant emissions (inhabited areas, spaces of ecological

interest, etc.).

c) Other model options

Among the different options offered by the Calpuff model, it is possible to select those

that achieve a simulation closer to the reality of the process of atmospheric dispersion. The main

options are:


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- Dispersion

For the simulation of pollutant dispersion, the Calpuff model requires the definition of the

following issues:

· Selection of the type of element to be used in the modelling (puffs or slugs).

· Characterisation of the dispersion plume.

· Definition of the methodology used in the calculation of the dispersion coefficient.

· Direct measurement of turbulence.

· Micro-meteorological parameters.

· PGT dispersion coefficients or MESOPUFF II coefficients.

- Elevation of the plume.

Emissions from a stack can rise above the height of the stack. This is owing to the

difference in temperature between the ambient temperature and the flue gas temperature. The

vertical position of the plume depends on the magnitude of this gradient and the speed of output.

Calpuff supplies various algorithms for calculating the dimensions and development of

the plume, taking into account several factors such as:

· Calculation of the plume at different distances or calculation of the final height of

the plume.

· Stacktip downwash effect (plume below source).

· Vertical shearing.

· Partial plume penetration in the inversion layer.

- Dry deposition

Calpuff includes a module that calculates the dry deposition rates of gases and particles

as a function of the physical parameters, the meteorological conditions and the pollutant species

being modelled. The model has the option of allowing the user to enter daytime deposition rates.

- Wet deposition

Calpuff uses an empirical sweep coefficient to consider pollutant carryover and wet

deposition flows as a result of precipitation. The sweep coefficients are constituted as a function

of the type of pollutants and the type of precipitation (liquid, frost, …).


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- Coastal effects

Calpuff can simulate the effects of pollutant transport, dispersion and deposition on water

surfaces.

When sources are located in close proximity to large bodies of water, effects on

emissions can occur. It can be shown that, if the temperature of the water body does not change,

during the day it will have a lower mixing layer than the surrounding water.

- Chemical transformations

The model includes a module to consider chemical transformations following a 5 species

scheme (SO2, SO42-, NOx, HNO3 y NO3

-) known as MESOPUFF II or a 6 species scheme (SO2,

SO42-, NO, NO2, HNO3 y NO3

-) known as RIVAD/ARM3.

- Complex terrains.

The shock of the scattering plume on a hill is evaluated considering that the current line

(Hd) is divided in two:

· A part surrounding the hill (low Hd).

· Another part that rises above it (high Hd).

5.5 INFORMATION AND INPUT DATA TO THE DISPERSION MODEL

5.5.1 Selected area of study for modelling

The area of study selected for the simulation of the odour dispersion from the new

facilities in Aberdeen (Scotland), consists of a square of dimensions 6 km in a North-South

direction and 6 km in an East-West direction, focused on the location of the facilities

themselves. Below is an image of the study area:


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FIGURE 5.3

AREA OF STUDY

5.5.2 Generation of the wind field in the study area

The dispersion conditions of the pollutants depend largely on the existing climatology of

the study area. Therefore, in order to establish the climatological conditions of the area, the

Calmet meteorological module is run, which uses data from meteorological observations and

information on the terrain and land uses to build the wind field for the entire domain.

As mentioned above, in the description of the model, in addition to reproducing the wind

fields of the region, Calmet has a micrometeorology module that describes the characteristics of

the boundary layer, above the land and water, and develops three-dimensional fields of

temperature, as well as other parameters used by Calpuff for modelling the dispersion of

pollutants.

Therefore, the following data will be necessary to run the Calmet meteorological model:


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5.5.2.1 Initial wind field

The final wind field generated with the Calmet meteorological module starts from an

initial wind field, generated by the Weather Research and Forecasting (WRF) weather model,

which is adjusted considering the effects of the terrain and the meteorological data from stations

available in the area.

The WRF model is a numerical climate prediction system designed for both operational

and research applications. The following entities have participated in the development of WRF:

National Center for Atmospheric Research (NCAR), National Oceanic and Atmospheric

Administration (represented by the National Center for Environmental Prediction (NCEP) and the

Forecast Systems Laboratory (FSL), Air Force Weather Agency (AFWA), Naval Research

Laboratory, University of Oklahoma and Federal Aviation Administration (FAA).

WRF reflects advanced, flexible and portable code that is efficient in computing

environments from a large number of parallel supercomputers to portable computers. Its

individual modular source code can be configured for both research and operational applications.

WRF is maintained and supported as a community model to facilitate its wide use

internationally, for research, operations and teaching. It is valid for a wide range of applications

from small scales to global simulations. These applications include real-time numerical prediction,

data assimilation study and development, parameterised physical properties research, regional

climate simulations, air quality models and ideal simulations.

The configuration of the WRF model used for the generation of meteorological data is as

follows:


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TABLE 5.1

SPECIFICATIONS OF MODELLING WITH WRF

Modelling specifications – WRF Model

Temporary nature of the series Year 2019

Domain area 50 km * 50 km

Resolution 1 km

No. vertical levels 18

Topography (DEM) GTOPO30 (30s)

Land use model (LULC) USGS GLCC (1000m)

Height data Every 6 h

Initialization time 00:00, 06:00, 12:00, 18:00 UTC

Sides edges and initialization NCEP FNL (Final) Operational Global Analysis data

(1-degree)

Data output frequency Hourly

5.5.2.2 Topography

To reproduce the effect of the topography on the behaviour of the plumes, the elevations

above sea level of each of the receptor nodes are used.

For this purpose, a digital grid has been created with dimensions of 20 km in the North-

South direction and 20 km in the East-West direction, obtained from a Digital Terrain Elevation

Model with a resolution of 30 m (Shuttle Radar Topography Mission-SRTM- 1 Arc-Second

Global).

A digitised image of the terrain in the study area is presented below:


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FIGURE 5.4

DIGITAL TERRAIN MODEL

5.5.2.3 Land uses

The CALPUFF model also requires the definition of land uses throughout the grid which

has been considered in the study.

The land uses to be considered in the modelling have been obtained from the CORINE

LAND COVER land use database (100 m resolution). The main objective of this database is the

capture of numerical data and for the creation of a European database at a scale of 1:100,000 on

the coverage and use of the territory through interpretation using images collected by the LandSat

and SPOT series of satellites. Figure 5.5 shows the land use grid used in the dispersion model.


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FIGURE 5.5

LAND USE GRID

Land Use Codes: 80 (Tree-free Plain), 55 (Seas and Oceans), 40 (Forest Lands), 20 (Agricultural Lands) y 10

(Urban or Construction Land).

5.5.2.4 Surface meteorological data and upper air data

In order to take into account surface meteorological data representative of the

climatological conditions in the area, the meteorological data from the following station have been

included in the model:

- “Dyce” station (available on the NOAA website).

Wind rose from Dyce was shown in Figure 3.7.


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In addition to weather data recorded on the surface, the model requires vertical weather

data profiles. Since no station is available to record meteorological upper air data, data from the

WRF forecast meteorological model have been used throughout the study area.

As an example, the wind rose generated from the WRF meteorological data at surface

level for a point on the location of the project was presented in Figure 3.2.

5.5.2.5 Wind field

Once the Calmet meteorological module has been executed, the hourly wind fields are

obtained in the study area for all selected heights.

Below is an image of the wind field generated by Calmet, for a specific hour and for a

height of 10 m.

As can be seen in the images of the hourly wind fields, for each point of the defined grid

a vector is obtained that defines the direction of the wind and which has a different colour

depending on the speed.


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FIGURE 5.6

WIND FIELD (04/01/20 - 08:00; HEIGHT = 10 m)

5.5.3 Definition of odour emission source

The characterisation of the emissions considered in the modelling is included in Chapter

4 of this document. It should be noted that the definition of the odour emission source in the

dispersion model is carried out as a point source.

The definition of point sources in the CALPUFF model requires the determination of the

following parameters:

- Coordinates of emission source location (X, Y in m)


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- Ground level at that point (m)

- Stack height (m)

- Stack diameter (m)

- Flue gas velocity (m/s)

- Flue gas temperature (K)

- Pollutant emission rates (g/s)

In the simulations that have been carried out, the effect of the structures of the

installation that, due to their dimensions, may have some effect on the dispersion of pollutants,

has also been considered.

5.5.4 Receptors

Receptors are defined as those points where the concentration of pollutants at ground

level is going to be calculated. They are obtained from a grid of dimensions 6 km in the North-

South direction and 6 km in the East-West direction, with a resolution of 100 m. Furthermore,

three nested grids and centred on the installation have been included, with resolutions of 50 m (2

km x 2 km), 25 m (1 km x 1 km) and 10 m (0.5 km x 0.5 km), as shown in the following Figure:

FIGURE 5.8

RECEPTOR GRIDS


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Additionally, receptors have been located at the boundary of the Plant, every 5 m. The

Figure 5.9 shows the location of these receptors.

FIGURE 5.9

LOCATION OF RECEPTORS AT THE BOUNDARY OF THE PLANT


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6. CONTRIBUTION OF THE PROJECT TO THE ODOUR LEVELS

Through the application of the CALPUFF model, the contribution of the Project to the 98th

percentile of the hourly mean values of odour immission has been obtained. The graphical

representation of the results in the environment of the facilities is presented in Figures 6.1 and

6.2. The levels corresponding to 1.5 and 1 ou/m3 have been represented. Since the odour

threshold is set at 1ou/m3, quantification below this level makes no physical sense.

FIGURE 6.1

CONTRIBUTION OF THE PROJECT TO THE 98th PERCENTILE

OF THE HOURLY MEAN VALUES OF ODOUR IMMISSION (I)


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FIGURE 6.2

CONTRIBUTION OF THE PROJECT TO THE 98th PERCENTILE

OF THE HOURLY MEAN VALUES OF ODOUR IMMISSION (II)

As can be seen in the Figures, in relation to the contribution of the Project to the levels of

odour immission (valued through the 98th percentile of the hourly average values), it should be

noted that level corresponding to 1.5 ou/m3 is found located on the facilities themselves.

Likewise, level corresponding to 1 ou/m3 extends up to a maximum distance of 50-60 m

from the boundaries of the facilities, without affecting inhabited sites.


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7. CONCLUSIONS

This document presents the odour dispersion study carried out for a Waste Power Plant

projected by ACCIONA in the West Tullos industrial area, at the south of Aberdeen (Scotland).

According to “H4 Odour Management” Technical Guidance (SEPA), an odour

concentration of 1.5 ou/m3 has to be met at the boundary of the Plant, based on the 98th

percentile of hourly average concentrations.

From the results obtained with CALPUFF model, it is concluded that with an emission

level of 780 uo/m3, the contribution of the Project to the levels of odour immission would mainly

affect to the facilities and its surrounding. Thus, it should be noted that the level corresponding

to 1.5 ou/m3 is located within the boundary of the facilities, without affecting inhabited sites.

Seville, 8th July 2021

Signed by: Signed by:

Chemical Engineer Industrial Engineer

Master in Engineering and

Environmental management

Head of Environmental Modelling

Area

Documents

ODOUR DISPERSION STUDY NESS ENERGY PROJECT, ABERDEEN