CHAPTER 4 . Urban watershed services for improved ecosystem management and
4.1 Introduction
The Project will include the construction of an LNG Carrier unloading facility consisting of a dredged basin with an LNG Carrier berth and a berth for the temporary mooring attending tugs or mooring craft. The LNG unloading facility will have the capability of unloading in the order of 180 ships per year. Each tanker will have an approximate unloading time of 18 hours at Bradwood Landing and full turnaround time of up to 36 hours (from open sea to open sea).
The LNG berth will be located at, approximately, river mile 39 of the Columbia River.
The location of the berth is such that it is over 1000 ft from the main river navigation channel providing a significant clear safety distance from the main channel for a passing vessel.
All maneuvering and docking of the LNG Carriers at the berth will be under tug assistance and pilot supervision. All berthing and mooring operations will be closely monitored by the Berthing Master/Jetty Controller from a berth control office located on the Jetty Head to ensure safety of operations.
The Columbia River navigation channel starts at the Columbia River bar and continues five miles upriver at a depth of 55-feet and a width of 2,640-feet. It then maintains a depth of 40-feet and a width of 600-feet to beyond the berth site. The channel passes under Astoria Bridge with 205-feet air clearance and 1070-feet clear width. A project
(the US Army Corps of Engineers’ Columbia River Federal Navigation Channel Improvement Project) is currently underway to deepen the existing 40-foot deep shipping channel by 3 feet to allow continued navigation access. Work to deepen the navigation channel began in June 2005. Additional work is expected to take place in 2006 and 2007.
A dredged maneuvering and turning area will connect the berth with the navigation channel. This dredged area will be approximately 2000 feet by 2000 feet and will be dredged to a depth of at least 42 feet below Columbia River Datum (CRD).
Construction of the marine basin will require the dredging of approximately 650,000 cubic yards of material. The dredge disposal method to be used will be approved by the US Army Corps of Engineers (USACE).
The unloading facilities will be sized to handle LNG Carriers with a capacity of 100,000 m3 up to 200,000 m3 and drafts up to 40 feet. Carriers with larger capacities may be evaluated in the future. Four breasting structures and four mooring structures will be provided at the berth, consisting of steel pipe piles with concrete caps. The breasting structures will be equipped with fenders suitable to safely berth and moor the full range of vessel sizes being considered. Access catwalks will be provided at each berth to connect the breasting structures to the jetty head and to the mooring structures. For the safety of personnel emergency egress catwalks will provide an alternative route to shore should the primary route be blocked. Mooring points comprising Quick Release Hooks (QRH) will be provided at each berth on the mooring dolphin structures for bow & stern breast lines (holding the vessel onto the berth) and on the berthing dolphin structures for spring lines (maintaining the vessels position along the berth).
Mooring structures will be provided with ladders to provide access from small craft on the Columbia River and protective hand railing around the working surface of the structures except on the mooring line faces. Floodlighting to the QRH moorings will be provided, angled downwards and shielded to ensure that there is no danger to the safe navigation of vessels on the Columbia River.
The mooring hooks will be provided with strain gauges enabling measurement of the forces arising in the mooring lines to be displayed on a screen located within the Berth Control Office. This will enable the safe mooring of the Carrier to be monitored at all times. There will also be fitted to the berth face a display screen enabling the velocity and angle of approach of the berthing vessel to be continuously monitored until the Carrier is safely berthed.
The two extreme up and downriver mooring dolphins will each be provided with a navigation light marking the extent of the structure in the river.
The jetty head will be a reinforced concrete beam structure, approximately 115 feet wide by 125 feet long supported on steel pipe piles. Outside the LNG pipework area the slab will be sloped to drain storm water into the marine basin. Operational and pipework areas will be curbed and laid to slopes such that any liquid that falls into the curbed area below the pipes will flow to the onshore containment pit. Drainage from this point will be via the LNG spill collection trough along the approachway to an onshore spill impoundment basin.
The approachway will be approximately 20’ wide (24 feet over safety barriers and curbs) to permit a small mobile rubber tired crane to pass to the unloading arm area.
The pipeway will be 16 feet wide (19 feet overall width) located over the spill collection trough such that any liquid escape dropping into the trough will be directed to the onshore spill containment pit.
The surface of the trough will be lined with a sacrificial layer of concrete designed to minimize thermal shock to the underlying structural concrete in the event of an LNG leak or spill.
Onboard ship pumps will deliver the LNG to the LNG storage tanks. A total of four marine unloading arms will be installed on the unloading arm platform, three for liquid delivery to the LNG storage tanks and one for vapor return to the ship. One of the liquid lines can be valved to flow vapor return to the ship in the event of a problem with the primary vapor return arm. Space for a possible future fifth arm will be reserved on the platform. The unloading arms will be designed with swivel joints to provide the required range of movement between the ship and the shore connections. Each arm will be fitted with powered emergency release coupling (PERC) valves to protect the arm and the ship. The PERC valves also minimize spillage of LNG in their operation. Each arm will be operated by a hydraulic system and a counterbalance weight will be provided to reduce the deadweight of the arm on the shipside connection and to reduce the power required to maneuver the arm into position. The unloading arms will be a nominal 16-inch diameter capable of a combined unloading rate of 12,000 m3/hour. The LNG will then be transferred to the storage tanks onshore by a 32-inch diameter liquid (cryogenic) transfer line.
Maneuvering and docking of the LNG tankers can be accomplished with no more than three Z-drive tugs under most weather conditions of weather, current, tide, etc. The berth layout was first reviewed by experienced pilots, and changes made based on their recommendations. The final berth layout was then successfully confirmed in computer simulations of the maneuvering and berthing conducted at the U.S. Army Corps of Engineers Engineering Research and Development Center's (ERDC) Ship and Tow Simulator located in Vicksburg, Mississippi. A full report can be found in Resource Report 11.
The facilities have been designed to provide safe berths for the receipt and support of LNG Carriers and to ensure the safe transfer of LNG cargoes from the ships to on-shore storage facilities. Design is in accordance with applicable codes and standards, including but not limited to Oil Companies International Marine Forum (OCIMF), Society of International Gas Tanker and Terminal Operators (SIGTTO), International Navigation Association (PIANC), American Petroleum Institute (API), and American Society of Civil Engineers (ASCE).
13.7.1.1 Carrier Unloading Arms
Refer to P&ID’s W00031-000-PR-PI-004/005/006/007.
A set of four unloading arms (2 liquid unloading arms, 1 hybrid arm, normally used in liquid unloading service and 1 vapor return arm) will be provided on the jetty. The transfer of LNG from carrier to shore will be by means of these four articulated arms.
Each unloading arm will be provided with two isolating valves and a Powered Emergency Release Coupling (PERC). The PERC system will protect the arm and the carrier in the event of excessive movement of the arm, and help to minimize spillage of LNG if emergency uncoupling of an arm occurs. The arms will be operated by means of an hydraulic system and counter-weights will be provided to facilitate rapid disconnection and to reduce the deadweight of the arms on the shipside connections.
The unloading arms are designed for an unloading rate of 52,834 gpm (12,000 m3/hr).
Operating conditions will be in the region of 95 psia and –255 oF.
In case of non-availability of the vapor return arm, one LNG unloading arm (the hybrid arm) can be changed to vapor service. A DB&B connection between the vapor return arm and the hybrid arm is provided for this purpose. In this event, the unloading flowrate is decreased by 33% and the unloading time increased correspondingly.
The main technical characteristics of the unloading arm set are as follows:
• Manufacturer: FMC Energy Systems or similar
• Service: Natural Gas / LNG
• Unloading Arm Size: 16 in
• Design Temperature: –274 oF / +99 oF
• Range of Carrier Capacities: 26.4 – 52.8MM gallons (100,000 m3 – 200,000 m3)
The unloading arms manufacturer will be selected based on compliance to specifications and will have prior experience with LNG operations.
See Appendix B13 for LNG Unloading Arms Datasheet (W00031-664-PR-DS-011).