This section presents the air
quality impact assessment for the Project during the construction and operation
phases. Air Sensitive Receivers
(ASRs) and the potential sources of impacts have been identified and
assessed. Mitigation measures are
recommended, where necessary.
3.2
Legislative
Requirement and Evaluation Criteria
The principal legislation for
the management of air quality in
Table
3.1 Hong Kong Air
Quality Objectives (mg m-3) (a)
|
Air Pollutant |
Averaging Time |
|||
|
|
1 Hour (b) |
24 Hour (c) |
3 Months (d) |
1 Year (d) |
|
Total Suspended Particulates (TSP) |
- |
260 |
- |
80 |
|
Respirable Suspended Particulates (RSP) (e) |
- |
180 |
- |
55 |
|
|
800 |
350 |
- |
80 |
|
Nitrogen Dioxide (NO2) |
300 |
150 |
- |
80 |
|
Carbon Monoxide (CO) |
30,000 |
- |
- |
- |
|
Photochemical Oxidants (as ozone
(O3)) (f) |
240 |
- |
- |
- |
|
Lead (Pb) |
- |
- |
1.5 |
- |
|
Notes: (a)
Measured at 298K (25°C) and 101.325 kPa
(one atmosphere) (b)
Not to be exceeded more than three times per year (c)
Not to be exceeded more than once per year (d)
Arithmetic means (e)
Suspended airborne particulates with a nominal aerodynamic diameter of
10 micrometres or smaller (f)
Photochemical oxidants are determined by measurement of ozone only |
||||
In addition, the Technical
Memorandum on Environmental Impact Assessment Ordinance (EIAO-TM) also stipulates an hourly TSP
criterion of 500 mg m-3
for construction dust impacts.
3.3
Baseline
Conditions and Air Sensitive Receivers
3.3.1
Existing Conditions
The Emission Control Project is to be located at the existing Castle
Peak Power Station. The existing
air quality in the area is influenced by the emissions from a number of industrial
establishments in the nearby area and in the Pearl River Delta region,
including the existing Castle Peak Power Station.
One of the nearest EPD Air Quality Monitoring Stations (AQMS) is located
in Tung Chung, about 10 km from the site.
The annual average concentrations of major air pollutants measured at
the Tung Chung AQMS in 2005 are presented in Table 3.2.
Table 3.2 Annual
Average Pollutant Concentrations in the Study Area
|
Pollutant |
Annual Average Concentration (μg m-3)(a) |
|
Total Suspended Particulates (TSP) |
65 |
|
Respirable Suspended Particulates (RSP) |
57 |
|
|
21 |
|
Nitrogen Dioxide (NO2) |
46 |
|
Note: (a) Tung Chung AQMS, 2005 |
|
3.3.2
Air Sensitive Receivers (ASRs)
The Air Sensitive Receivers identified in the
Study Area are listed in Table 3.3 and their locations shown in Figure A.2 of
Annex A. ASRs are representative of
residential and commercial areas at various distances from the project site, as
required by the Study Brief.
The
receptor heights were chosen at 1.5 m for all locations, and at selected
locations at an additional level depending on the properties of each ASR (20 m
or 30 m for low-rise buildings, 100 to 150 m for high-rises). It is believed that these assessment
levels are adequate to capture the plume properties under a range of different
wind speeds, both for the low-rise structures and also for the high-rise ASRs,
considering the size of the plume and the distance to the ASRs
Table 3.3 Air
Sensitive Receivers
|
Label |
Location |
Approximate distance (km) |
Height above ground (m) |
|
A1 |
Lung Kwu Tan ( |
1.3 |
1.5 |
|
A2 |
Lung Kwu Tan ( |
1.8 |
1.5 |
|
A3 |
Lung Kwu Sheung Tan (village house) |
3.3 |
1.5 |
|
A4 |
Ha Pak Nai (village house) |
6.2 |
1.5 |
|
A5 |
Sheung Pak Nai
(village house) |
8.7 |
1.5 |
|
A6a |
Hung Shui Kiu, |
10.3 |
1.5 |
|
A6b |
Hung Shui Kiu, |
10.3 |
30 |
|
A7a |
Lam Tei, Botania Villa |
8.4 |
1.5 |
|
A7b |
Lam Tei, Botania Villa |
8.4 |
30 |
|
A8a |
Tuen Mun North |
6.1 |
1.5 |
|
A8b |
Tuen Mun North |
6.1 |
120 |
|
A9a |
Tuen Mun Centre |
5.6 |
1.5 |
|
A9b |
Tuen Mun Centre |
5.6 |
120 |
|
A10a |
Tuen Mun South,
Butterfly Estate |
4.3 |
1.5 |
|
A10b |
Tuen Mun South, Butterfly
Estate |
4.3 |
110 |
|
A11a |
So Kwun Wat, |
7.3 |
1.5 |
|
A11b |
So Kwun Wat, |
7.3 |
100 |
|
A12a |
Tai Lam
Chung (Tai Lam Correctional Institution) |
10.4 |
1.5 |
|
A12b |
Tai Lam
Chung (Tai Lam Correctional Institution) |
10.4 |
15 |
|
A13 |
River Trade Golf |
3.0 |
1.5 |
|
A14a |
Tung Wah Group of Hospital Youth |
1.8 |
1.5 |
|
A14b |
Tung Wah Group of Hospital Youth |
1.8 |
20 |
|
A15a |
Proposed |
1.0 |
1.5 |
|
A15b |
Proposed
|
1.0 |
30 |
|
A16 |
Siu Ho Wan (village house) |
10.3 |
1.5 |
|
A17 |
Tai Ho
Wan (village house) |
10.0 |
1.5 |
|
A18a |
Tung
Chung (residential building along coast) |
9.2 |
1.5 |
|
A18b |
Tung
Chung (residential building along coast) |
9.2 |
150 |
|
A19a |
HK
International Airport (hotel, offices) |
6.4 |
1.5 |
|
A19b |
HK
International Airport (hotel, offices) |
6.4 |
30 |
|
A20 |
Sha Lo Wan (village house) |
9.2 |
1.5 |
|
A21a |
Tin Shui Wai, |
11.9 |
1.5 |
|
A21b |
Tin Shui Wai, |
11.9 |
110 |
|
A22 |
So Kwun Wat, So Kwun Wat Tsuen |
8.6 |
1.5 |
|
A23a |
Tuen Mun South, |
5.7 |
1.5 |
|
A23b |
Tuen Mun South, |
5.7 |
110 |
Most of the near-field ASRs are village houses or
low-rise structures with representative receptor heights at 1.5 m. The ASR closest to the project site is
the proposed
3.4
Construction
Phase Air Quality Impact Assessment
3.4.1
The Project
Construction, Demolition and Site Formation Activities and their Potential Air
Quality Impacts
The following
construction/demolition works are the subject of this assessment:
·
Demolition
of existing facilities at CPB, including: the 4,680 tonne Fuel Oil Day Tank and
Dangerous Goods (DG) Store;
·
Relocation
or re-routing of existing facilities, including: 2,626 litre Carbon Dioxide
(CO2) Storage Tank, two 4,600 litre Liquefied Petroleum Gas (LPG) Storage
Tanks, and Intermediate Pressure Reduction Station;
·
Installation
of new emission control equipment and facilities (SCR and FGD) and associated
site formation works;
·
Provision
of Reagent and By-Product Handling and Storage Facilities, including: limestone
silos, limestone slurry tanks, gypsum dewatering and storage facilities for the
LS-FGD operations and the urea storage silos, urea dissolving tanks, urea
solution storage tanks and urea-to-ammonia reactors for the SCR operations;
·
Provision
of additional berthing facility for loading and unloading of the process
reagents, including up to 40,000 tonnes per year of urea, up to 150,000 tonnes
per year of limestone and up to 257,000 tonnes per year of gypsum as
by-products.
It is expected, that due to
the limited scale of the construction and demolition works and the remoteness
of ASRs, gaseous and particulate emissions (of CO, SO2, NOx
and RSP) from the construction machinery and vehicles are of secondary
importance and do not have the potential to cause any exceedances
of Air Quality Objectives listed in Table 3.1.
Dust nuisance is therefore
the remaining concern during the construction, demolition and site formation
works and, in accordance with the Study Brief, constitutes the main subject of
this assessment.
The Construction Dust
generation potential of different construction activities are discussed below.
Demolition and
Relocation Works
Most of the demolition and
relocation works concerns steel/concrete structures with most of the caissons
and concrete foundations remaining intact. The principal potential sources of
construction dust will include:
· Demolition of
concrete structures in the Dangerous Goods Store, Fuel Oil Day Tank, and LPG
switch room & vaporiser room, and LPG Tank areas (about 1,300 m3 in total)
· Underground
excavation (soil/concrete) for the new piping locations (about 800 m3 in total)
· Backfilling with
soil the trenches following relocation of the piping.
Construction and Installation
of the FGD and SCR Equipment
The superstructures and
equipment installed will mainly be of prefabricated steel construction, so the dust
generation potential of the construction works is low.
Site Formation
Site
formation activities with the potential for dust generation will be very
limited. The main area of such works
will be the northern coal yard, where some filling is anticipated.
Provision of Additional
Berthing Facility
These will involve the
handling of wet materials, and therefore their potential for construction dust
generation is low.
3.4.2
Conclusion
Due to relatively small scale
of the dust generating activities during the construction phase of the Project
and the distance from the ASRs (the closest sensitive receiver is approximately
1 km away from the project site), no adverse dust impact is anticipated. Although dust emissions and gaseous
emissions are not expected to affect the nearby ASRs during the construction
phase, the dust control measures stipulated in the Air Pollution Control (Construction
Dust) Regulation should be implemented to comply with the Regulation.
3.5
Operational
Phase Assessment
3.5.1
Emission Reductions under the CPB Emission
Control Project
The Emission Control Project is a
project aimed to achieve a significant reduction in emissions from the Castle
Peak Power Station.
The
following reduction efficiencies are used as the basic assumptions for the
operational air quality assessment:
·
SO2
emission reduction by up to 90%; and
·
NOx emission reduction by up to 80%.
Some
reduction in particulate emissions is also anticipated as a result of FGD operation,
details of which will be assessed during the design optimisation.
3.5.2
Other Potential Sources of Impact
Increased Marine
Traffic
To achieve the significant
reductions in the SO2 and NOx emissions from CPB,
the project will create a slight increase in the marine traffic, due to the
need for limestone and gypsum transportation. It is anticipated that marine vessels, in the
size range of 1,000 DWT to 10,000 DWT, will arrive at a rate of about one per
week, with 2 days berthing time for loading / unloading activities. This will constitute only an
insignificant fraction of the existing marine traffic emissions in
Ammonia Slip
The
operation of the SCR and SNCR systems may result in a phenomenon known as
“ammonia slip”, i.e. excess, unreacted ammonia making
its way to the flue gas. For
typical SCR and SNCR systems in a coal-fired power station, the ammonia slip is
kept at a range of few parts per million, the potential ammonia emissions from
the Project would be negligible. It should be noted that ammonia required for the SCR and SNCR NOx reduction is generated from urea on a
supply-on-demand basis. There will
not be any bulk ammonia storage on-site.
The design of the SCR and SNCR facilities will allow for the ammonia
slip in the flue gas to be closely monitored and in case of sign of
deterioration, adequate control and measures will be implemented. Immediate control measures include
adjustment to the injection rate of ammonia. Other longer-term actions include the
addition or replacement of SCR catalyst.
Potential Dust Impact from
Limestone Storage and Handling
The unloader of limestone at the berthing
facility will be of low dust emission potential, consisting of dust control
measures like telescoping chute.
Conveyor belts will be covered; transfer towers and storage of limestone
will be enclosed and provided with dust collection system. The potential dust impact from the
limestone handling operation is therefore expected to be negligible.
3.5.3
Scope and Objectives of the Operational
Phase Assessment
The Study
Brief stipulates that “The Applicant may carry out a comparative study to
demonstrate if the stack emission impacts of the “B” Units before and after the
Project will lead to lower air quality impacts at the Air Sensitive Receivers
(ASRs) by using either a simple screening tool such as ISCST3 Gaussian model or
a more sophisticated tool, such as wind tunnel test, if necessary”. The
following sub-sections summarise the methodology and results of such
comparative assessment, using a Wind Tunnel testing methodology. More details
on this comparative wind tunnel study are provided in Annex A.
It should be noted that, as
described in Section 3.5.6, the
comparative study demonstrated that the Project will result in an improvement
of air quality at all locations; therefore, a quantitative assessment of
cumulative air quality impacts under Section
3.4.1.5 of the Study Brief is not
necessary.
3.5.4
Wind Tunnel Test Methodology
General
The spatially and temporally variable meteorological and atmospheric
dispersion conditions associated with complex terrain pose several challenges
to assessing the dispersion of airborne pollutants in a coastal, mountainous
region such as the Study Area.
Physical scale wind tunnel modelling accounts for building wake and
complex terrain effects, and is one of the most accurate methods for the
simulation of these near-field influences for neutrally stable atmospheric
conditions.
In general, wind tunnel air quality studies involve placing a physical
model of the emission sources and surrounding terrain in a wind tunnel,
emitting a passive tracer from the sources and measuring its concentrations at
a number of receivers inside the wind tunnel for different wind speeds and
directions.
The Present Study
Wind tunnel tests for this study were conducted by Rowan Williams Davies
& Irwin Inc. (RWDI) of
The wind tunnel simulated the winds
approaching the Study Area, the exhaust discharged from the source being tested
and the dispersion of the exhaust in the atmosphere.
3.5.5
Results: Air Quality Improvements under
Worst-Case Conditions
The estimated relative decreases in
concentrations of SO2 and NOx
after the retrofit for the worst-case meteorological conditions (ie those for which the highest concentration ratios were
measured) have been presented for each receptor in Table A.4 of Annex A.
The results shown in Table A.4 of Annex A represent the resultant reduction of SO2
and NOx concentrations, hence air quality
improvements at the ASRs, under the worst-case conditions measured in the wind
tunnel for each of the two scenarios tested. The results demonstrate that the
percentage reductions in the measured SO2 and NOx
concentrations at the ASRs are very similar to the corresponding reductions of
SO2 and NOx emissions from the
CPB units after retrofit. The slight
changes in the percentage reduction of the measured concentrations can be
explained by the changes in the plume characteristics (i.e. a lower exit
velocity and a lower efflux temperature after implementation of the retrofit
programme) and the effects of the complex terrain on the exhaust
dispersion.
In conclusion, the effects of changes in
dispersion characteristics (due to changes in flue gas physical properties) on
the pollutant concentrations at ASRs after the retrofit are much lower in
magnitude when compared with those of the expected emission reductions of SO2
and NOx. The combined effects of the emission
reductions and the changes in physical characteristics of the plume result in
air quality improvements at all the identified ASRs ranging from 86% to 91% for
SO2, 72% to 83% for NOx.
It should be noted that the above NOx and SO2 reductions in predicted
worst-case concentrations are related to the Castle Peak Station “B” emissions
only and do not include cumulative effects. While the assessment of cumulative
impacts is not the focus of this EIA Study, it is anticipated that (with all
other emissions assumed constant) the Project will result in an improvement in
SO2 and NOx levels in the
vicinity of the Castle Peak Power Station.
The magnitude of such improvements will of course be lower for sensitive
receivers located further away from the CPPS.
Based on the
current licence limit for particulate emissions (125 mg Nm-3) and
the likely achievable particulate emissions level after FGD retrofit (50 mg Nm‑3),
the potential reduction in particulate emissions would be around 60%. Assuming this 60% reduction rate in
particulate emissions, it can be concluded based on the concentration ratios
measured in wind tunnel (see Annex A)
that the particulate concentrations will decrease at all ASRs and that,
depending on location, these concentration decreases will range from 44% to
66%. Further studies will be needed
with FGD manufacturers during design to confirm if additional particulate
emissions reduction through FGD is feasible.
3.5.6
Conclusion
A comparative air quality assessment was
conducted for the existing CPB units.
Scale model testing was performed in RWDI's
Boundary Layer Wind Tunnel to simulate the behaviour of the exhaust plume
before and after installation of the proposed emission control equipment.
Each
configuration was tested for a wide range of wind speeds and directions, as
required to measure the plume impacts at the receptor locations. The results of
the wind tunnel study are presented in Table
A.4 of Annex A as percentage changes measured at each receptor location by
comparing the pre-retrofit concentrations against the corresponding reductions
in the pollutant concentrations after the retrofit.
The following is a summary of the major
findings:
·
The
measured percentage reduction in SO2, NOx
and particulates concentrations at the receptor locations before and after
implementation of the retrofit programme are similar in magnitude to the
proposed emission reductions at source.
The effects of changes in flue gas characteristics on the dispersion of
emissions were minor and insignificant when compared to the corresponding
reductions in SO2, NOx and
particulates emissions from CPB after retrofit.
·
This
comparative study demonstrated that the worst case predicted SO2, NOx and particulates concentrations
at all the identified ASRs will have an improvement in air quality after the
retrofit as required in Section 3.4.1.2
of the Study Brief.
3.6
Mitigation
Measures
3.6.1
Construction Phase
The following dust control
measures stipulated in the Air Pollution
Control (Construction Dust) Regulation are recommended.
· The area at which
demolition work takes place should be sprayed with water prior to, during and immediately
after the demolition activities so as to maintain the entire surface wet;
· Dust screens or
sheeting should be provided to enclose the structure to be demolished to a
height of at least 1 m higher than the highest level of the structure;
· Any dusty
materials should be wetted with water to avoid any fugitive dust emission;
·
All temporary
stockpiles should be wetted or covered by tarpaulin sheet to prevent fugitive
emissions;
· All the dusty
areas and roads should be wetted with water;
· All the dusty materials
transported by lorries or barges should be covered entirely by impervious sheet
to avoid any leakage; and
· The falling height
of fill materials should be controlled.
3.6.2
Operational Phase
Since the project will
significantly reduce SO2 and NOx
emissions and further reduce particulate emissions from the Castle Peak
Station “B” units, and the potential impacts of ammonia slip and dust from
limestone handling will be dealt with at the design and equipment procurement
stage, no further mitigation measures are required.
3.7
Environmental
Monitoring and Audit
Due to the relatively small scale of the
demolition and construction works and the remoteness of the Air Sensitive
Receivers, no EM&A is required for the Construction Phase.
Since the Project will
achieve reductions in SO2,
NOx and particulates emissions,
no additional EM&A activities are required for the Operational Phase, other
than those already required by the Specified Process Licenses for the operation
of the Castle Peak Power Station.
3.8
Summary
and Conclusion
3.8.1
Construction Phase
Dust from demolition, site formation and
construction activities is the key concern during the construction of the
Project.
Demolition of concrete
structures in the Dangerous Goods Store, Fuel Oil Day Tank, and LPG storage compound
(about 1300 m3 in total), underground excavation (soil/concrete) for
the new piping locations (about 800 m3 in total), filling with soil
of the existing trenches of the piping to be relocated, limited foundation
works at the FGD, SCR and reagent and by-product handling and storage facilities locations, as well as
limited site filling works in the northern coal yard area are the major
construction/demolition works of the Project with dust-generating
potential. Due to the relatively
small scale of these works, the remoteness of Air Sensitive Receivers (the
closest ASR is at approximately 1 km away) and with the implementation of the
dust control measures stipulated in the Air
Pollution Control (Construction Dust) Regulation, no adverse air quality impact
is envisaged from the construction of the Project.
3.8.2
Operational Phase
A
comparative wind tunnel modelling study demonstrated that the operation of the
Project will result a significant reduction in SO2, NOx and particulates concentrations at the receptor locations,
similar in magnitude to the proposed emission reductions at the source after
the implementation of the retrofit programme.