Poster presentation delivered at the 2013 CASANZ conference by Katestone Senior air quality consultant Sarah Jane Donnelly. The poster presents a case study for the Tomago Aluminium Smelter to investigate the cause of exceedances of the 24-hour average air quality standard for sulfur dioxide.

1. A CASE STUDY: TOMAGO ALUMINIUM SMELTER
Donnelly, Sarah-Jane1, Shaw,
Natalie2, Killip, Christine3, Roser,
4
Neil
Analysis of measured data
1 Senior
Consultant, Katestone Environmental,
Brisbane
2 Principal Consultant, Katestone Environmental,
Brisbane 3 Managing Director, Katestone
Environmental, Brisbane 4Environment Services
Team Leader, Tomago Aluminium Company,
Newcastle
The Farm
Objective: Determine the source of 24-hour exceedances of SO2
Overview
TAC ambient monitoring for SO2 consists of five sites within 1.1 km
of the site, with monitoring
A review of the monitoring data found:
• 21 exceedances of 24-hr SO2 at School Drive
360
12
315
10
270
Wind Direction (°)
• 9 exceedances of 24-hr SO2 at the Farm
• No exceedances of 1-hr SO2 standard at any site during these periods
8
225
180
6
135
4
Wind Speed (m/s)
Five SO2 monitors
and met station
School Drive
90
• Previous air dispersion modelling of the site did not highlight these
meteorological conditions as a potential issue
• Measured SO2 concentrations at the Highway, Laverick Avenue and at the Met
station comply with 1-hr and 24-hr SO2 NEPM standard of 570 µg/m3 and 228
µg/m3, respectively
The analysis of monitoring
data suggests:
• A wake effected stack
source
•Direction of source
consistent with bake ovens
0
0
Hour
Wind direction
Wind speed
600
500
Concentration (µg/m³)
• Exceedances occurred during extended periods of strong westerly winds
(prevalent in winter months)
2
45
400
300
200
100
0
Hour
School Drive
Emissions
Wind tunnel modelling
Dispersion modelling
Sources of SO2
•2 Bake oven stacks (BO1 & BO2)
•Fugitive emissions from bake oven buildings
•7 Gas treatment stacks
Investigated:
Fugitive emissions:
Investigated side and
roof vents
Side vents not a source
of emissions during
event days
Outcome:
Modelled met file
Building wakes
Source configuration
Side vents on bake oven building
Farm
Met file representative of site
Important to local dispersion
Roof vents modelled as several
volume sources
May be important
Residual emissions occur
Stack tip downwash
Shut down of bake ovens
Modelled source contribution of 24-hour average SO 2 at the School monitoring station
180
Outcome:
160
Bake oven 1 emissions variability
40
700
35
600
30
500
25
400
20
300
15
200
100
5
0
Concentration (mg/m³)
120
10
0
Sources of SO2
2 oven
Emissions stacks (BO1 & BO2) – constant emissions
average emission
measurement: rate
Fugitive emissions from bake oven buildings –
BO1, roofvolume sources with hourly emissions file with
several vents and gas
treatment emissions and modelled 10°C above ambient
constant stacks
7 Gas treatment stacks – constant emissions average
emission rate
SO2 concentration (mg/m3)
Emission rate (g/s)
800
Concentration of SO 2 (µg/m3)
140
100
80
60
40
20
0
30 May
2 Aug
12 Aug
16 Aug
24 Aug
26 Aug
27 Aug
16 Sep
22 Jun
9 Jul
11 Jul
12 Jul
Carbon Bake Fugitive
59.9
42.8
46.4
61.8
65.6
37.4
56.9
45.1
39.0
44.9
62.5
40.4
Gas Treatment Stacks
13.2
20.4
18.4
19.9
20.9
23.0
19.3
26.3
7.8
11.8
12.3
51.1
51.3
51.2
68.3
75.3
35.4
64.6
46.0
54.6
63.3
77.9
Outcome:
•Main source is the gas treatment stacks (290° to 310°)
•Bake oven stacks resulted in lowest concentrations
•Fugitive sources impact at wind speeds of < 5 m/s
19.9
Bake Oven Stacks
•Modelling replicated the
general trend but
concentrations were
underestimated
•Major sources were the bake
oven stacks and roof vents
69.6
Emission rate (g/s)
Risk Assessment
Evaluation of hazard index
2- Assessment of exposure
Identification of sensitive receptor locations
1- Hazard identification
Recognise that there are exceedances and
therefore a hazard
4- Risk characterisation
The
risk
assessment
was
expressed as a hazard index for
each sulphur dioxide air quality
criteria and averaging period
Results showed a number of
receptors in zone 1 were at risk
The hazard index was calculated
as follows:
Sources of SO2
Where:
2 Bake oven stacks (BO1 & BO2) – constant emissions average emission rate
Fugitive emissions from bake oven buildings – several volume sources with hourly emissions file with constant emissions and modelled 10°C above ambient
HI is the hazard
7 Gas treatment stacks – constant emissions average emission rate
Contour of scaled up predicted maximum 24hour average SO2 ground-level concentrations to
match measurements. Shows the
area of
potential exceedance or the areas ‘at risk’
3- Dose response assessment
Evaluate the qualitative and quantitative
toxicity information to estimate the incidence
of adverse effects occurring in humans at
different exposure levels
index
Max Ci is the maximum
concentration
measured
(or
predicted by dispersion model) in
a zone for a particular pollutant
averaging period i
AQCi is the air quality criteria for
the pollutant Max Ci for averaging
period i
Further information
P (07) 3369
3699
Sarah-Jane Donnelly
Conclusions:
TAC should consider options for
mitigating potential impacts at
residences within 1 km to the east
of the smelter.
TAC should consider undertaking
further investigation of sulfur
dioxide levels at the Detention
Centre.
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