As floating LNG players explore innovative power solutions, clear guidance keeps safety the top priority while pursuing operational and environmental objectives, argues Terrance Roberts, ABS Business Development Manager, Global Offshore, in the second part of a two-part article.
Power system design considerations
LNG production requires substantial energy – liquefying 1 kg of natural gas consumes around 0.25 kWh of power. That means an installation designed to process 5 million tpy of LNG would require approximately 140 MW of electrical power.
External power can come from land-based grid supply, renewable onshore or offshore energy sources, power service vessels, or a combination of these sources.
A hybrid power system configuration with a combination of conventional marine power sources such as diesel and gas engines or turbines and non-conventional sources can be designed to meet the reliability and redundancy requirements of FLNG installation projects.
Installations located near shore can take advantage of the power from the main power grids or localised energy sources based on wind, solar, hydro, fuel cells, or nuclear power plants. A combination of these sources is known to offer high reliability and availability and are more efficient from a sustainability perspective than the onboard power generation systems.
The number of power connection lines from the external source depends on project risk tolerance, source reliability, environmental factors, and hazards associated with power loss.
An important consideration, external power supply should be supplemented by backup local power generation onboard the installation to immediately support essential services and safety-critical loads if external power is lost. Duration of the backup system’s availability should be designed based on evacuation plans, project risk tolerance, risk associated with loss of process systems, environmental assessment and Classification rules and requirements in the installation area.
ABS’s aforementioned publication covers three FLNG configurations with specific technical advisories for:
- FLNG with propulsion and accommodation.
- FLNG without propulsion but with accommodation.
- FLNG without propulsion and without accommodation.
Additional installation criteria
Power transmission from external power sources uses ultra-high voltage or high voltage alternating current or direct current subsea or overhead cables. This choice depends on distance from the external source, transmitted power requirements, space constraints, and cost considerations.
With incoming UHV/HVAC power from the external power source, installations require an external power switchboard and step-down transformer, along with mitigation measures for voltage variation, resonance and reactive power generation by subsea cables.
Cable support structures also must maintain optimal cable length that minimises slack while preventing excessive tension. The support system must avoid interfering with mooring systems and other equipment while accommodating the full range of the FLNG installation’s draught and tidal variations.
The ABS approach offers an opportunity to use recognised industry standards in the design and construction, with consideration for thermal and electrical monitoring and distance protection relays.
Documenting hazards and risk
FLNG owners and operators exploring electrification can look to class society publications to address complex operations that demand rigorous adherence to established safety standards. Floating LNG assets combine high-voltage electrical systems with cryogenic liquefied gas in a dynamic marine environment – a combination that creates compounding hazards where conventional offshore electrical practices may be insufficient.
Conducting a comprehensive hazard and risk assessment is essential to identify how electrical system failures could trigger cascading events affecting personnel, the environment or asset integrity. This assessment must systematically evaluate how equipment failures, operational errors or other external factors can lead to dangerous scenarios.
All foreseeable hazards, their root causes, potential consequences and risk controls must be thoroughly documented. At a minimum, some aspects that must be addressed include equipment layout, arrangement and location; mechanical faults, electrical faults and human errors; electrical shock precautions; cybersecurity gaps; flammable and toxic gas dispersion and other environmental factors. Additionally, some of the hazards specific to this novel concept include damage to external power supply cables, loss of any single component in the stationkeeping/mooring system, extreme weather conditions and impact or collision, among others.
A safe global energy transition
Keeping safety at the forefront of decision-making is essential risk management for novel and new technologies that have no direct precedent in either traditional offshore oil and gas or onshore LNG facilities.
ABS’ publication addresses critical aspects – from power system configuration to goal-based standards – to help ensure externally powered FLNG installations protect personnel health and safety, offshore and nearshore assets and the environment.
As leaders of the offshore classification industry, ABS offers information and reports to address critical aspects – from power configurations and systems design to safety and environmental protection systems – with an innovative goal-based approach. These principles represent a path to class and statutory compliance based on specific characteristics and risk profile, providing a customised approach to novel technology. Once implemented in the design criteria and systems configuration, the ABS requirements would provide a solid basis for project development, helping to ensure externally powered FLNG installations protect personnel health and safety, offshore and nearshore assets and the environment.
You can read the first part of the article here.