4A.1 Adjustment
of Background NO2 at Black Point
4A.1.1
BackgroundBackground
An
extensive set of wind tunnel tests for the Black Point Power Station was
conducted as part of the EIA of the Proposed
6000 MW Thermal Power Station at Black Point in 1993 (hereafter called BPPS
EIA Study). Maximum 1-hour average
nitrogen dioxide (NO2) concentrations were modelled for a number of
ASRs. However, even that the NOx emission rates assumed in 1993 for the
particular set of wind tunnel tests remain relevant for the present situation,
the NOx to NO2 conversion rates
may have had changed over the years due to the increase in background ozone
concentrations. The update of such
conversion rates and the re-assessment of NO2 at the interested ASRs
is summarized as below.
4A.1.2
NOx to NO2 Conversion in BPPS EIA Study
The
methodology for determination of NOx to NO2
conversion used was based on the commonly used Janssen’s formula ([1]) that
links the conversion rate to the prevailing meteorological conditions, distance
to the receptor and the background ozone concentrations:
NO2/NOx
= A (1 – exp (-ax)) [1]
where A and a are coefficients depending on wind speed,
ambient ozone concentration and the season of the year that can be determined.
In
the BPPS EIA Study, the values of coefficients used were obtained from Janssen
tables for summer conditions using linear interpolation of wind speeds. The ambient ozone concentration was
assumed as 35 ppb for A and 50 ppb for a
determination. The artificial
increase of O3 concentration assumed for a
estimates was substantiated by the higher solar radiation in HK as compared to
Holland, where the Janssen’s study was conducted.
The
value of A was calculated to be 0.74 and the values of a
were 0.21 km-1 for wind speed of 8 m/s and 0.29 km-1 for
wind speed of 12 m/s in the BPPS EIA Study.
4A.1.3
Adjustment for NOx/NO2 Conversion Rate and NO2
Concentration
Adjustment of Janssen’s
Coefficients
The
annual average of daily hour maximum ozone concentration measured at EPD AQMS
in Tung Chung for the year 2004 is 108 μgm-3, i.e., about 55
ppb. Assuming again the summer
conditions, from the Janssen Table 4,
A will be equal to 0.81 for wind speeds from 5 to 15 m/s.
For
the a
estimation, to be consistent with the BPPS EIA Study, the ozone level is
increased by 15 ppb, i.e., from 55 to 70 ppb. Using again Janssen Table 4 and applying interpolation between the 50 and 90
ppb levels in a way consistent with the BPPS EIA Study approach, a
will be 0.175 km-1 for 70 ppb of ozone and wind speed of 5 m/s and
0.40 km-1 for the 15 m/s wind speed.
By linear
interpolation for wind speeds, a will be 0.24 km-1 for wind speed of 8 m/s and
0.33 km-1 for 12 m/s.
Adjustment of NO2
Concentrations
If
C1 is NO2 concentration obtained in the BPPS EIA Study
and C2 is the NO2 concentration in this Study, the
adjustment of NO2 concentrations can obtain from the Janssen’s
formula (1):
C2
= C1 [A2 (1 – exp(-a2x))]
/ [A1 (1 – exp(-a1x))] [2]
where x is the distance (km) between ASR and the source
The
formula [2] using the appropriate values of A and a
coefficients is applied to recalculate the maximum hourly and 2nd
highest NO2 concentrations shown in Table 3.3a and 6.2b of the BPPS EIA Study, respectively.
Short-term NO2
Concentration
BPPS
Contribution
The
maximum hourly NO2 concentrations, presented in the BPPS EIA Study, Part A, Table 3.3a, was predicted based on the
generating capacity of 4,800 MW of BPPS.
The
current generating capacity of BPPS is about 2,500 MW which is approximately
50%, therefore, a factor of 0.5 is applied to adjust the NO2 based
on the current operation mode.
Using adjusted Janssen coefficient, the maximum hourly NO2 concentrations
at ASRs at Lung Kwu Tan, Ha Pa Nai
and Sheung Pak Nai are
calculated.
Of
note, A2 (EPD Office at WENT Landfill) is located at Nim
Wan and the distance between BPPS and A2 is about 2.1 km. No assessment point was identified in
the wind tunnel testing. But in
view of the detailed wind tunnel testing results in the BPPS EIA Study Annex D (NO2 results under Option 3 at wind
direction of 232°), the results
at 2.4 km away from BPPS emission sources is lower than that predicted at 3.2
km which is at Ha Pak Nai, therefore, the predicted
results at Ha Pak Nai will be used to represent the
worst NO2 concentration attributable to BPPS at A2 (EPD Office at
WENT Landfill).
ASRs
at Lung Kwu Tan (x=2, C1 = 30% of AQO,
wind speed of 12 m/s), Ha Pak Nai (x=3.2, C1
= 10% of AQO, wind speed of 8 m/s) and Sheung Pak Nai (x=7.5, C1 = 5% of AQO, wind speed of 8
m/s):
Lung Kwu
Tan
C2 = 30 [0.81 (1 – exp
(-0.33 x 2))] / [0.74 (1 – exp (-0.29 x 2))] x 0.5 = 18%of AQO (54 mgm-3)
Ha Pak Nai
C2 = 10 [0.81 (1 – exp
(-0.24 x 3.2))] / [0.74 (1 – exp (-0.21 x 3.2))] x 0.5 = 6%of AQO (18 mgm-3)
Sheung
Pak Nai
C2 = 5 [0.81 (1 – exp
(-0.24 x 7.5))] / [0.74 (1 – exp (-0.21 x 7.5))] x 0.5 = 2.9%of AQO (9 mgm-3)
CPPS
Contribution
For ASRs A3 to
A8 located at Lung Kwu Sheung
Tan area, since the worst wind direction from LNG terminal and from CPPS to
ASRs A3 to A8 are opposite, therefore, no cumulative short-term impact is
anticipated.
For ASRs A1
and A2 located at Sheung Pak Nai
and Nim Wan, respectively, contribution from the CPPS
is likely to cause cumulative air quality as well as BPPS with the LNG Terminal
contribution.
The CPPS
contribution assessed in the BPPS EIA Study is used in the following
calculation. In the BPPS EIA Study,
no wind tunnel testing was performed at Sheung Pak Nai. However, Sheung Pak Nai (8 km) is located
further away from CPPS than Ha Pak Nai (i.e., 5.5 km)
and the NO2 concentration at Sheung Pak Nai should be lower than that at Ha Pak Nai. Therefore, NO2 concentrations
predicted at Ha Pak Nai are used as worst case NO2
concentration at Sheung Pak Nai.
The
worst wind direction of CPPS “A” and “B” Units (CPA and CPB) to Ha Pak Nai is about 195°. With reference to BPPS
EIA Study, Annex H, Table H.1b, the maximum hourly NO2
concentration under wind speed of 8 ms-1 are 59.9 µgm-3
and 46.6 µgm-3, contributed from CPA and CPB, respectively.
CPA
is currently operating with low-NOx
burners and the current licence limit of NOx
is 1,500 mgm-3. In the BPPS EIA Study, Annex B, the source NOx concentration at source for CPA in the wind
tunnel testing was 1,577 mgm-3.
Therefore, about 5% of NOx is
reduced by the operation of low-NOx
burners and hence, a reduction factor of 0.05 will be applied to adjust the NO2
concentration attributable to CPA at Ha Pak Nai.
The
source NOx concentration at source for CPB
in the wind tunnel testing was 1,578 mgm-3 in accordance with the BPPS EIA Study, Annex B. Currently, CPB is also operating with
low-NOx burners and the current licence
limit of NOx is 1,500 mgm-3. Also, CAPCO considers further reducing
the NOx emission at CPB to meet emission
cap in 2010. Therefore, an EIA for Emission Control Project to CPPS “B”
Units was conducted and approved in November 2006. In the approved EIA for Emission Control Project to CPPS “B” Units, new NOx reduction technology is proposed to further
reduce 80% of current NOx emission. Based on the findings in the approved EIA for Emission Control Project to CPPS “B”
Units, CAPCO is negotiating with the EPD to obtain a reasonable licence NOx limit in future and hence the future NOx limit is not yet confirmed at this stage. However, it is expected that is likely
to be tightened to meet the NOx limit
specified in the Best Practicable Means
for Electricity Works (Coal-fired Plant, Gas-fired Gas Turbine and Oil-fired
Gas Turbine (Peak Lopping Plant) (BPM 7/1) which is 670 mgm-3. Therefore, with the consideration of
existing low-NOx burner and future
implementing of new NOx reduction
technology, a NOx reduction factor of 0.57
([2])
will be applied to adjust the NO2 concentration contributed from CPB
at Ha Pak Nai.
The indicative commencement date of future low NOx
technology at CPB is in end of 2009 to 2011 in accordance with the approved EIA for Emission Control Project to CPPS “B”
Units which is likely to be earlier than this Study.
Hence the
maximum hourly NO2 concentration contributed from CPA and CPB will
be adjusted by
(a) higher
ozone level (108 µgm-3) in 2004;
(b) NOx reduction by
current implementation of low NOx burners
at CPA (a factor of 0.05) and
(c) current
low-NOx burner and future new NOx reduction technology at CPB (a factor of
0.57).
The
calculation is shown as below
Ha Pak Nai
CPA
C2
= 59.9 [0.81 (1 – exp (-0.24 x 5.5))] / [0.74 (1 – exp (-0.21 x 5.5))] x
(1-0.05)
= 67 mgm-3
CPB
C2 =
46.6 [0.81 (1 – exp (-0.24 x 5.5))] / [0.74 (1 – exp (-0.21 x 5.5))] x (1-0.57)
= 23 mgm-3
Therefore,
the total maximum hourly NO2 concentration at Ha Pak Nai contributed from CPA and CPB is 67 mgm-3
+ 23 mgm-3
= 90 mgm-3
Long-term
NO2 Concentrations
The
2nd daily and annual average NO2 concentrations,
presented in the BPPS EIA Study, Part B,
Table 6.2b, had considered the contribution from BPPS as well as CPPS with NOx reduction of 10% and 50% for CPA and CPB ([3]),
respectively. The 2nd
daily and annual average NO2 concentrations in the BPPS EIA Study, Part B, Table 6.2b are
summarized below.
|
|
Lung Kwu Tan |
Ha Pak Nai |
|
Worst wind speed adopted in Wind Tunnel Testing (m/s) |
12 |
8 |
|
2nd Highest Daily NO2 Concentration |
12.1% of AQO (18 µgm-3) |
11.3 % of AQO (17 µgm-3) |
|
Annual NO2 Concentration |
0.6 % of AQO (0.33 µgm-3) |
0.5 % of AQO (0.28 µgm-3) |
|
Note: (a)
Reference
to BPPS EIA Study, Part B, Table 6.2b |
||
As
discussed before, the current licence NOx limit
is likely to be further tightened to meet 670 mgm-3 specified in the
Best Practicable Means for Electricity
Works (Coal-fired Plant, Gas-fired Gas Turbine and Oil-fired Gas Turbine (Peak
Lopping Plant) (BPM 7/1) for CPB.
Therefore, in view of the current generating capacity of BPPS (2,500 MW)
and the further NOx reduction at CPB, the
2nd daily and annual average NO2 concentrations at Lung Kwu Tan and Ha Pak Nai in the
above table will be reduced.
However,
since the above results are the cumulative results taking into account of
emissions from BPPS and CPPS in the Wind Tunnel Testing, therefore, the results
could only be adjusted with ozone level of 108 μgm-3, i.e., about 55
ppb in 2004 as worst case assessment.
In
accordance with the Equation [1] for adjustment of NO2
concentrations, shorter distance from the source will give higher NO2
concentration. Therefore, the
distance between the BPPS and Lung Kwu Tan or Ha Pak Nai (which is shorter than CPPS to Lung Kwu
Tan or Ha Pak Nai) is used for the calculation to
obtain the worst 2nd highest daily NO2 concentration.
The detailed
calculations are shown as below.
2nd
Highest Daily NO2 Concentration
Lung Kwu
Tan
C2 = 12.1 [0.81 (1 – exp
(-0.33 x 2))] / [0.74 (1 – exp (-0.29 x 2))] = 14.5%of AQO (22 mgm-3)
Ha Pak Nai
C2 = 11.3 [0.81 (1 –
exp (-0.24 x 3.2))] / [0.74 (1 – exp (-0.21 x 3.2))] = 13.6%of AQO (20 mgm-3)
Annual Average
NO2 Concentration
Lung Kwu
Tan
C2 = 0.6 [0.81 (1 –
exp (-0.33 x 2))] / [0.74 (1 – exp (-0.29 x 2))] = 0.7%of AQO (0.6 mgm-3)
Ha Pak Nai
C2 = 0.5 [0.81 (1 –
exp (-0.24 x 3.2))] / [0.74 (1 – exp (-0.21 x 3.2))] = 0.6%of AQO (0.5 mgm-3)
Summary
A summary of
adjusted short-term and long-term NO2 concentrations are presented
as below.
|
|
Lung Kwu Tan |
Ha Pak Nai |
Sheung
Pak Nai (a) |
|
Worst wind speed adopted in Wind Tunnel Testing (m/s) |
12 |
8 |
8 |
|
Adjusted Maximum Hourly NO2 Concentration |
54 µgm-3 (BPPS ONLY) |
108 µgm-3 (BPPS + CPPS) |
99 µgm-3 (BPPS + CPPS) |
|
Adjusted 2nd Highest Daily NO2
Concentration |
22 µgm-3 |
20 µgm-3 |
- |
|
Adjusted Annual NO2 Concentration |
0.6 µgm-3 |
0.5 µgm-3 |
- |
|
Note: (a)
No
wind tunnel testing was performed at Sheung Pak Nai in the BPPS EIA Study; the NO2
concentrations predicted at Ha Pak Nai is used as
worst case assumption. |
|||
Since
the adjusted 2nd highest daily and annual average NO2
concentrations at Lung Kwu Tan and Ha Pak Nai are similar, the adjusted 2nd highest daily
and annual average NO2 concentrations (22 mgm-3
and 0.6 mgm-3,
respectively) at Lung Kwu Tan which is the highest
will be adopted for the cumulative long-term impact assessment at all identified
ASRs and for plotting the contours to assess the worst case cumulative impacts.
Of
note, in accordance with the indicative commencement programme in the Emission Control Project to CPPS “B” Units,
the low NOx reduction technology will be
operated in end of 2009 to 2011 which should be earlier than the LNG Terminal
operation. Therefore, during the
LNG Terminal operation, the 2nd highest daily and annual average SO2
concentration should be much lower due to the current BPPS power generating
capacity and future NOx reduction
programme at CPB.
Also,
the maximum hourly NO2 concentration from CPPS contribution at Nim Wan/Ha Pak Nai and Sheung Pak Nai is estimated at
195°. However, the worst wind angle from LNG
terminal to Nim Wan/Ha Pak Nai
and Sheung Pak Nai is about
232°. According to Wind Tunnel Tests for Castle Peak “A” and “B Station, by Central
Electricity Research Laboratories, 1981, at the worst wind angle of 232°
the NO2 plume contributed from CPPS is very narrow and will not
contribute NO2 to Nim Wan, Ha Pak Nai and Sheung Pak Nai areas.
Therefore, the cumulative short-term NO2 impact assessment
due to LNG terminal and CPPS will rarely occur and therefore, the cumulative
short-term NO2 impact assessment considering the above adjusted maximum
hourly NO2 concentration from CPPS is the worst-case assessment.