1.1 Adjustment of Background NO₂ at Black Point

1.1.1 Background

An extensive set of wind tunnel tests for the Black Point Power Station was conducted as parte 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 NO_x emission rates assumed in 1993 for the particular set of wind tunnel tests remain relevant for the present situation, the NO_x 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.

1.1.2 NO_x to NO₂ Conversion in BPPS EIA Study

The methodology for determination of NO_x 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/NO_x = 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.

1.1.3 Adjustment for NO_x/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 0.33 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 2^nd 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 operation of BPPS is about 2,500 MW which is approximately 50% of the BPPS EIA Study, therefore, a factor of 0.5 is applied to adjust the NO₂. Using adjusted Janssen coefficient, the maximum hourly NO₂ concentrations at ASRs at Lung Kwu Tan are calculated.

ASRs at Lung Kwu Tan (x=2, C₁ = 30% of AQO, wind speed of 12 m/s):

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)

CPPS Contribution

For ASRs A2 to A7 located at Lung Kwu Sheung Tan area, since the wind angles from LNG terminal and from the CPPS are opposite, therefore, no cumulative short-term impact is anticipated.

Long-term NO₂ Concentrations

The 2^nd 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 NO_x reduction of 10% and 50% for CPA and CPB ([2]), respectively. The 2^nd daily and annual average NO₂ concentrations in the BPPS EIA Study, Part B, Table 6.2b are summarized below.

	Lung Kwu Tan
Worst wind speed adopted in Wind Tunnel Testing (m/s)	12
2^nd Highest Daily NO2 Concentration	12.1% of AQO (18 µgm^-3)
Annual NO2 Concentration	0.6 % of AQO (0.33 µgm^-3)
Note: (a) Reference to Table 6.2b of BPPS EIA Study

CAPCO considers further reducing the NO_x 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 NO_x reduction technology is proposed to further reduce 80% of current NO_x 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 new licence NO_x limit in future and hence the future NO_x limit is not yet confirmed at this stage. However, it is expected that is likely to be tightened to meet the NO_x 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, in view of the current generating capacity of BPPS (2,500 MW) and the further NO_x reduction at CPB, the 2^nd daily and annual average NO₂ concentrations at Lung Kwu Tan in the above table will be reduced.

However, since the above results are the cumulative results taking into account the contribution from BPPS and CPPS, 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 (which is shorter than CPPS to Lung Kwu Tan) is used for the calculation to obtain the worst 2^nd highest daily NO₂ concentration.

The detailed calculations are shown as below.

2^nd 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)

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)

Summary

A summary of adjusted short-term and long-term NO₂ concentrations are presented as below.

	Lung Kwu Tan
Worst wind speed adopted in Wind Tunnel Testing (m/s)	12
Adjusted Maximum Hourly NO2 Concentration	54 µgm^-3 (BPPS ONLY)
Adjusted 2^nd Highest Daily NO2 Concentration (BPPS + CPPS with NOx mitigation)	22 µgm^-3
Adjusted Annual NO2 Concentration (BPPS + CPPS with NOx mitigation)	0.6 µgm^-3

Of note, in accordance with the indicative commencement programme in the Emission Control Project to CPPS “B” Units, the low NO_x 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 2^nd highest daily and annual average SO₂ concentration should be much lower due to the current BPPS power generating capacity and future NO_x reduction programme at CPB.

Therefore, the cumulative short-term and long-term NO₂ impact assessment in this Study will be the worst-case assessments.

4B.1 Emission Rate Calculations

Submerged Combustion Vaporizers (SCVs)

Total emissions : NO_x = 51 tonnes/yr and CO = 257 tonnes/yr (provided by Vendor’s equipment information, emissions are based upon 30 t/hr and fuel gas produced per 100 t/hr LNG vaporization)

No. of SCVs = 5

Emission rate of each SCV:

NO_x = (51 tonnes / 365 days / 24 hours / 3600 s) x 1x10⁶ / 5 = 0.32 g/s

CO = = (257 tonnes / 365 days / 24 hours / 3600 s) x 1x10⁶ / 5 = 1.63 g/s

Total flowrate = 130,000 Nm³hr^-1 (at 0 °C & 101.3 kPa)

At exhaust temperature of 30 °C, the total flowrate = 144.285.71 m³hr^-1

Stack velocity = 144.285.71 / 3600 / 5 / (p x 0.6²) = 7.09 ms^-1

Gas Turbine Generators

Total emissions : 128 tonnes of NO_x and 156 tonnes of CO a year (based on Solar Turbines Mar-90, by Caterpillar)

Gas turbine generator operation time : continuous

No. of gas turbine = 4 + 1 (spare)

Emission rate of each gas turbine generator:

NO_x = (128 tonnes / 365 days / 24 hours / 3600 s) x 1x10⁶ / 4 = 1.01 g/s

CO = (156 tonnes / 365 days / 24 hours / 3600 s) x 1x10⁶ / 4 = 1.24 g/s

Total flowrate = 382,800 Nm³hr^-1 (at 0 °C & 101.3 kPa)

At exhaust temperature of 500 °C, the total flowrate = 1,083,899 m³hr^-1

Stack velocity = 1,083,899 / 3600 / 4 / (2.3 x 2.3) = 14.2 ms^-1

LNG Carrier – Auxiliary Engines

· Total generator capacity = 9,350 kW (under 75% load factor)

· Generator load factor = 75%

· Burning Marine Diesel Oil (MDO) or Heavy Fuel Oil (HFO)

According to IMO MARPOL Annex VI, NO_x is limited by the formula:

45.0 x rpm^-0.2 g/kWh

The auxiliary generator will be operating at 720 rpm and therefore, NO_x emission will be 12.07 g/kWh. At 75% load, the NO_x can vary from 7% to 15% and therefore, upper limit of NO_x emission will be 12.07 x 1.15 = 13.88 g/kWh.

NO_x emission factor = 13.88 g/kWh

SO₂ emission factor = 6 g/kWh (based on 1.5% sulphur content)

CO emission factor = 0.6 g/kWh

Emission rate from one chimney:

NO_x = (13.88 g/kWh x 9,350 kW) / 3600 = 36 g/s

SO₂ = (6 g/kWh x 9,350 kW) / 3600 = 15.6 g/s

CO = (0.6 g/kWh x 9,350 kW) / 3600 = 1.56 g/s

As 3 individual stacks are enclosed in a single chimney, therefore, effective diameter = 0.78 m

Exhaust gas velocity = 25 ms^-1

Exhaust temperature = 320 °C

Gas Heaters at Gas Receiving Station at Black Point

Total emissions : 72 tonnes of NO_x and 45 tonnes of CO a year (based on Vendor’s equipment information, 4.1 MMSCFD for the Design Case)

Total no. of stack = 4

Emission rate of each stack:

NO_x = (72 tonnes / 365 days / 24 hours / 3600 s) x 1x10⁶ /4 = 0.57 g/s

CO = (45 tonnes / 365 days / 24 hours / 3600 s) x 1x10⁶ / 4 = 0.36 g/s

Total flowrate = 73,900 Nm³hr^-1 (at 0 °C & 101.3 kPa)

Assuming at exhaust temperature of 280 °C, the total flowrate = 149,695 m³hr^-1

Stack velocity = 149,695 / 3600 / 4 / (p x 0.54²) = 11.56 ms^-1

Summary of Modelling Parameters

	SCV	Gas Turbine Generator	LNG Carrier – Auxiliary Engine	Gas Heaters at GRS
No. of Emission Source	5	4	1	4
Stack Height (m)	13	8	41	15
Stack Diameter (m)	1.2	2.6 ^(a)	0.78	1.07
Exit Temperature (°C)	30	500	320	280
Exit Velocity (m/s)	7.09	14.2	25	11.56
NO2 Emission Rate (g/s)	0.32	1.01	36	0.57
SO2 Emission Rate (g/s)	-	-	15.6	-
CO Emission Rate (g/s)	1.63	1.24	1.56	0.36
Note: (a) The stack diameter is an equivalent diameter in which the stack emission area is 2.3 m x 2.3 m.

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([1]) Janssen L.H.J.M. et al. A Classification of NO Oxidation Rates in Power Plant Plumes based on Atmospheric Conditions. Atmospheric Environment, 22, 43-53, 1988.

([2]) Reference to the BPPS EIA Study, Part A, Section 3.2.3, 1,100 ppm reduced to 1,000 ppm for CPA (about 10% reduced) and 1,100 ppm reduced to 6,00 ppm for CPB (about 50% reduced).