Liquid Discharges
Liquids will be discharged into the ocean as part of the normal, day-to-day activities of the Prelude FLNG facility. Shell has implemented control systems to ensure the liquid wastes on Prelude are appropriately managed.
Planned liquid discharges
The liquids which may be discharged into the environment include:
- Drainage and bilge effluent
- Food waste, greywater and sewage
- Cooling water
- Desalination brine, boiler blowdown and mixed bed polisher effluent
- Produced water
- Use and release of chemicals in ad-hoc discharges.
Impacts upon environmental receptors
Impacts have been assessed for receptors in the:
- Physical environment (water quality and sediment quality)
- Biological environment (fish, marine mammals and other underwater species, birds and marine plants)
There are no assessed negative impacts on socio-economic environment receptors from planned liquid discharges.
As discharges will rapidly dilute and disperse in the open ocean environment, modelling studies indicate impacts to water quality are likely to be highly localised around the point of discharge. Because of the deep ocean environment and strong currents, there will be no expected impacts to sediment on the sea floor.
Therefore all impacts and risks to receptors have been assessed as being as low as reasonably possible, and therefore of an acceptable level.
For a detailed summary, select your area of interest:
Drainage and bilge effluent
Drainage and bilge effluent
Where it comes from
Process drainage, wash-down water, storm-water, sea spray, rainwater and water generated from routine operations.
It may contain small quantities of oil, grease, metals, detergents (surfactants) and other residual chemicals present on the deck.
For safety reasons, run-off from areas containing LNG, mixed refrigerant or LPG is not contained to ensure that these do not develop into flammable gas clouds on the facility.
How it may impact environment
Small quantities of metal, chemicals or oil is discharged into the ocean which may affect water quality.
Biological receptors that come into contact with affected water may be impacted.
Mitigation strategies in place
- Drainage and bilge discharge will not be discharged if contamination levels are higher than defined acceptable levels.
- Drainage discharge will not be discharged if contamination levels are too high.
- Assurance will be undertaken of marine support vessels, including a check for valid and in date International Oil Pollution Prevention certificates as required by vessel class requirements.
- Spill kits are available on Prelude and marine support vessels to clean up small accumulations of contaminants.
Food waste, sewage and greywater
Food waste, sewage and greywater
Where it comes from
Grey water and sewage from accommodation, hospital, toilets, sinks, washbasins, showers, laundry and sweat drains.
Food waste is also macerated (softened and broken up) for disposal as liquid waste.
How it may impact environment
Extra nutrients discharged could increase turbidity, increase pathogens (bacteria, viral agents and / or parasites) or increase oxygen demand in the water.
Mitigation strategies in place
- Food wastes will be macerated to < 25 mm particle size if discharged within 500m of the FLNG.
- Vacuum toilets are designed to reduce sewage wastes to <25mm particle size prior to discharge to sea.
- Assurance will be undertaken of marine support vessels to check for valid and in date International Sewage Pollution Prevention Certificates, as required by vessel class requirements.
- Marine support vessels have a current Waste Management Plan (or equivalent) in accordance with MARPOL.
Cooling water
Cooling water
Where it comes from
Seawater is used for cooling and then discharged back into the ocean at slightly higher temperatures.
Chlorine is added to the cooling water to reduce the potential for any marine growth within the cooling system’s pipework.
How it may impact environment
Localised water quality may be impacted by increased chlorine levels discharged.
Chlorine has the potential to harm marine organisms in high doses.
Increased surface water temperatures may cause alteration of the physiological processes of exposed organisms.
Mitigation strategies in place
- The electrochlorination unit is maintained to ensure dosing is undertaken in a controlled manner.
- Online chlorine analysers are maintained and have associated critical alarms at defined limits.
- Online monitoring or manual sampling conducted to confirm free chlorine discharge do not exceed levels described in the full Environment Plan.
Desalination brine, boiler blowdown and mixed bed polisher effluent
Desalination brine, boiler blowdown and mixed bed polisher effluent
Where it comes from
A number of water-based effluents are produced on Prelude. To understand them, visit the glossary for definitions of desalination brine, boiler blowdown and mixed bed polisher.
How it may impact environment
There is potential for water quality to be impacted by the presence of chemicals in this discharge.
Mitigation strategies in place
- The pH of the boiler blow-down and mixed bed polisher discharges are monitored either by online analyser or manually to ensure pH levels are within range.
Produced water
Produced water
Where it comes from
Produced water is water which has permeated into the gas reservoir over time and includes condensate.
How it may impact environment
Produced water can contain a range of potential inherent and added contaminants, when added to ocean water, could impact the water quality.
Fauna may be exposed to potentially toxic concentrations of contaminants.
Mitigation strategies in place
- The online analyser will be validated to ensure readings are accurate and reliable.
- Automatic shut-off of the discharge is implemented to meet the set limits.
- Strict protection limits for water quality are in place within the 1km mixing zone for produced water discharges.
- Critical equipment associated with the produced water system will have preventative and corrective maintenance carried out on it.
- Lab technicians are suitably qualified for managing and evaluating the systems.
Chemicals in ad-hoc discharges
Chemicals in ad-hoc discharges
Where it comes from
Chemicals are used for various processes and may be present in discharge streams.
How it may impact environment
Chemicals used on the facility could cause impacts to water quality.
Mitigation strategies in place
- All other chemicals discharged will be rated and managed according to their content and will be managed to a level that is as low as possible.
- Ad hoc/non-routine discharges with chemical additives are required to meet strict criteria prior to release.
- Subsea chemical injection valves are maintained and ensure discharges are undertaken in a controlled manner.
