3 DESCRIPTION OF PROJECT AND ASSUMPTIONS
3.1.1 It is proposed that the PAFF will be located at an undeveloped newly reclaimed shoreline site at Tuen Mun Area 38. It will consist of the following major elements:
¨
a jetty with two berths, which together will accommodate
a full range of vessels from 10,000 to 80,000 dwt vessels;
¨
a tank farm with gross aviation fuel tankage capacity of
140,000m3 on commissioning and an ultimate tankage of about 420,000m3
as well as pumps and associated facilities;
¨
on site operational facilities including offices;
¨
500mm diameter twin subsea pipelines to transfer the
fuel to the aviation fuel system at the airport.
3.1.2 The planning, design and construction of the project is programmed to take in the region of 4 years, with the commissioning date estimated to be the end of 2005.
3.1.3 The overall study area showing the location of the proposed site in Hong Kong and the proposed pipeline alignment is provided in Figure 3.1. The details of each of the key elements of the facility are discussed below.
3.2 Tank
Farm and Onshore Facilities
3.2.1 Approximately 6.75 ha of land are required to locate the aviation fuel tank farm and associated facilities. The proposed site for the tank farm at Tuen Mun Area 38 has recently been reclaimed by Government and is zoned for industrial use. The site is situated at Siu Lang Shui just southeast of the Castle Peak Power station and is adjoined on the west by the Shui Wing Steel Mill and on the south-east by an area of partially formed land still undergoing reclamation and ultimately earmarked for industrial use in keeping with the other land uses in the area. Further east is the River Trade Terminal. The currently allocated plot has a short length of sea frontage of 60m in width which extends inland for about 140m before widening out to a square area of about 217m in length by 276m in width, see Figure 3.2.
3.2.2 No residential developments are present in the area and the closest substantial development, Melody Garden in Tuen Mun, is at least 3 kilometres from the proposed site. The villages at Lung Kwu Tan are closer at about 2km away but are screened from the site by the Castle Peak topography.
3.2.3 The tank farm will initially house 4 storage tanks each of 40m diameter by 29m in height and providing a storage capacity of 35,000m3. It is intended that the tankage capacity would be increased in stages of several tanks at a time to match the anticipated growth in aviation fuel demand to an ultimate tankage capacity of about 420,000m3 by 2040. The initial capacity of 140,000m3 is expected to be sufficient until about 2010. It is currently forecast that additional tanks would need to be brought on stream at the rate of about 1 new tank every three years up to a maximum of 12 tanks. The tanks would likely be built in clusters of 2, 3 or 4 tanks at each increase. The heights of future tanks would vary between 23m and 32m and their capacities would vary accordingly between 27,000m3 and 39,000m3. The tank farm would be provided with bundwalls and contained drainage. Each tank will be designed with a fixed cone roof. A concept layout of the tank farm is provided in Figure 3.2a and an indicative cross section between the tanks and the lot boundary provided in Figure 3.2b.
3.2.4 Other shore based facilities would include office buildings for administrative and security control, leak detection instrumentation, fire fighting and emergency spill equipment, workshops and basic infrastructure including roads, drains, telecommunications, power supply and lighting.
3.3.1 The PAFF requires the construction of a twin berth jetty. This will be sited approximately 200m offshore with no direct access to shore. The two end to end berths would run approximately parallel to the quay wall and fuel tanker berthing would be provided on the sea facing side. The main activity at the jetty will be unloading of the tankers to the storage tanks in the tank farm. Two or possibly three unloading arms will be provided to unload the fuel at each berth. Fuel lines and services will run to shore through submarine pipes and cabling protected by rock armour not protruding above the existing seabed, so as to provide marine access to other facilities adjoining the tank farm. Details of the jetty are provided in Figure 3.2.
3.3.2 The sea bed level at the site lies between –17 and –18m PD indicating that water depths can reach 19.5-20.5m during the highest high tides. This places considerable constraints upon the types of piling barge which can be used. Conventional anchored pontoons capable of supporting the type of equipment necessary for percussive hammers can be used in these depths of water provided suitable anchors can be deployed to adequately maintain the barge on station during the piling operations.
3.3.3 In order to support oscillatory rigs necessary to install casings deep into the seabed for the purposes of constructing bored piles it will be necessary to mobilise a substantial jack up barge. A suitable barge will be required to support the necessary equipment and to resist large torsional forces imposed by the oscillators during the installation process. Such barges, capable of operating in the proposed depth of water are not common and are usually used for offshore oil exploratory works. They are not available in Hong Kong at the present time and mobilisation of such a barge from exploratory work sites will probably not be economically viable or achievable in the timescale of the project.
3.3.4 Aside for the engineering constraints, consideration of the most appropriate piling method must have due regard for environmental concerns. A particular consideration for this project is the need to protect marine mammals from disturbance during construction. Similar issues were raised when the temporary AFRF was constructed near Sha Chau in 1995. At that time the Airport Authority were advised by a panel of international cetacean experts that percussively driven piles would be preferred over in-situ bored piles, as was the original intention at that time, based upon the decreased time required for this technique, although it would be important to strive to mitigate noise. (ERM 1996).
3.3.5 For the purposes of this assessment it is assumed that the construction would rest on tubular steel piles of diameter between about 900 and 1200mm. It is anticipated that tubular steel piles of the type proposed would be driven into the seabed to achieve the required support. Driving operations will either be undertaken using percussive diesel or hydraulic hammers, as simple drop hammers capable of driving piles of the size required are not readily available. Approximately 200 piles can be expected and the piling period would last about 120 days (60 days for actual pile driving time). A key consideration in the design and construction will be how to mitigate noise. This issue is examined in more detail in Section 7.
3.3.6 Defensive fenders would be provided off the shore side of the jetty to prevent any possible collision from small craft straying into the prohibited area. Coupling points on the ship would be provided with slop trays to catch occasional minor spills of unloaded fuels during coupling and de-coupling and the vessels will deal with the spills.
3.4.1 A short buried submarine twin pipeline will connect the reception jetty to the onshore tank farm, together with the utilities required for the jetty. The fuel from the jetty to the tank farm will be transferred at a rate of 3,500m3 per hour. It is proposed that the fuel would then be delivered to the airport site by means of further buried twin subsea pipelines which would connect to the existing facility at Sha Chau. The total length of the pipelines would be about 4.8km including a 400m stretch within the Lung Kwu Chau and Sha Chau Marine Park in the approach to the existing AFRF pipeline.
3.4.2 The twin pipelines would each have an outside diameter of 500mm. The pipelines will be operated at a pressure of 30 barg (gauge pressure) and have a pumping rate of 30,000m3 per day or 1,500m3 per hour based upon 20 hours per day of pumping. It is assumed that these would be continuously welded, encased in concrete and lowered into a trench of approximately 3 - 3.5m depth. Future dredging activities are planned along the pipeline route for a coal berth for CLP in Urmston Road and, therefore, in this section of the alignment, the pipeline depth will be increased to around 6-7m below seabed. In both cases, the trench would then initially be backfilled with sand and protected with graded stones and rock armour (150-300mm) for about 1m up to the existing seabed. Schematic illustrations of the proposed pipelines and utilities from the jetty to shore and from the tank farm to the connection with the AFRF at Sha Chau are provided in cross sections (A) and (B) respectively in Figure 3.3.
3.4.3 The pipeline from the PAFF to the existing AFRF would be connected by brought up one of the existing dolphin piles and flanged together with the existing pipeline using a new valve arrangement incorporated in-between.
3.4.4 The trench is assumed to be formed by a combination of trailer suction hopper dredger for the deeper areas in Urmston Road and by grab dredging for the remaining length. Sand for the pipeline backfill would be placed by bottom dumping from barges. Graded rock would be subsequently placed either down pipe directly into the trench or lowered by grab.
3.4.5 A possible alternative to dredging a trench for the pipelines would be horizontal directional drilling, tunnel and ploughing. These techniques have been discussed in Section 2 of this report and dismissed on engineering, programming, environmental and cost constraints.
3.5.1 The fuel reception jetty will provide two berths to allow flexibility to accommodate a full range of vessels within the size range 10,000 to 80,000dwt. Fuel would typically be received at a frequency of twice per week ring to a forecast average of 3.6 occasions per week at the 2040 planning horizon.
3.5.2 A detailed breakdown of the expected tanker offloading frequency assumptions is provided in Table 3.1 below.
Table 3.1 Tanker
Frequency Estimate
|
Year |
Volume in tonnes |
Source/ Frequency |
No. of vessels |
Parcel size |
Volume |
Market share |
|
2006 |
3,679,200 |
China |
36 |
20000 |
720,000 |
20% |
|
Singapore |
56 |
40000 |
2,240,000 |
61% |
||
|
Middle
East |
12 |
60000 |
720,000 |
20% |
||
|
Total volume Vessels/ Year Vessels/ Week |
|
|
3,680,000 |
100% |
||
|
104 |
|
|
|
|||
|
2.0 |
|
|
|
|||
|
2010 |
5,256,000 |
China |
60 |
20000 |
1,200,000 |
23% |
|
Singapore |
62 |
45000 |
2,790,000 |
53% |
||
|
Middle
East |
21 |
60000 |
1,260,000 |
24% |
||
|
Total volume Vessels/ Year Vessels/ Week |
|
|
5,250,000 |
100% |
||
|
143 |
|
|
|
|||
|
2.8 |
|
|
|
|||
|
2040 |
8,740,000 |
China |
70 |
30000 |
2,100,000 |
24% |
|
Singapore |
80 |
45000 |
3,600,000 |
41% |
||
|
Middle
East |
38 |
80000 |
3,040,000 |
35% |
||
|
Total volume Vessels/ Year Vessels/ Week |
|
|
8,740,000 |
100% |
||
|
188 |
|
|
|
|||
|
3.6 |
|
|
|
|||
3.6 Emergency Backup Facilities
3.6.1 In order to ensure the security of fuel supply to the airport, it will be necessary to maintain the existing aviation fuel reception facilities and associated pipeline as an emergency backup following commissioning of the PAFF. This strategic need was recognised at the time that the temporary facility was gazetted. The existing temporary AFRF could not be abandoned because of need to safeguard supply in the event that that the new PAFF ever became damaged or inoperable for whatever reason. This eventuality is considered to be remote but nonetheless must be guarded against given the strategic and economic necessity of guaranteeing constant fuel supply to the airport. For this reason it will continue to be necessary to maintain the dredged access channel and also to maintain the existing pipeline. Based upon the selected pipeline option, regular flushing of the existing pipeline at a frequency of approximately once every 6 weeks to avoid stagnation of the sitting pipe volume and potential contamination of the down stream fuel supply is not required.