Since the inception of Freeport LNG’s gas liquefaction and LNG export project, the central focus was to create a safe, reliable and efficient plant. That meant understanding potential effects on the surrounding communities and impacts on the environment. Environmental stewardship has been our standard of operations since the construction of the original regasification terminal began in 2005.
Today, the Freeport LNG project is becoming the first world-scale electric LNG (eLNG) plant in North America. Using electric motor-driven technology has enabled us to comply with strict local emissions standards and support our ambitious production and export targets. eLNG also means increased plant efficiency and expected availability.
Electric Motors—Revolutionary Solution
The electric motor drive we have selected not only minimizes air emissions; it is also efficient, reliable and simple to operate, while offering longer maintenance intervals. Three General Electric 75 MW motors drive the propane and mixed-refrigerant compressors. Using electric motors with variable frequency drives enables all compressors to restart, even when fully loaded, with no depressurization or loss of refrigerant to the flare.
There are other design features minimizing environmental impact that were incorporated into the design of our liquefaction facilities.
Off-Specification Gas Recycling
The pretreatment trains will remove impurities from the feed gas. These include water, carbon dioxide and heavy hydrocarbons, which could freeze within the pretreatment or liquefaction equipment, plus hydrogen sulfide and mercury.
During start-up, large quantities of off-specification gas are usually flared. Our facilities will have the capability to recycle off-spec gas in a closed loop instead of flaring it, not only during start-up but also during operations.
At the pretreatment facility, undesirable contaminants will be removed from feed gas before liquefaction. They, in turn, will be treated in a regenerative thermal oxidizer from the Eisenmann Corporation coupled with an integrated scrubber and dual-field wet electrostatic precipitator to achieve remarkable contaminant removal efficiency.
Propane and Refrigerant Recovery
Before planned maintenance of compressors and other equipment, propane and mixed refrigerant must be removed from the system. While some facilities recover propane back to storage, in most, everything is flared. Our recovery system is designed to inject both propane and mixed refrigerant into LNG and send the comingled liquid to storage tanks. This greatly reduces emissions from ground-flare combustion.
Lines carrying LNG to storage tanks and to loading docks are designed as vacuum-jacketed piping (a pipe-in-pipe system with vacuum providing thermal insulation). Its performance is ten times better than that of conventional insulation piping and the outer jacket is made of 304 stainless steel capable of withstanding contact with LNG and preventing gas release into the atmosphere should the inner pipe fail.
Primary Dry-Gas-Seal Vent Recovery
Dry seals in refrigeration compressors prevent the process gas from migrating into the atmosphere but some of the sealing gas passes through the primary seal and is typically flared. We have added a vent gas seal recovery system that will send the gas to the BOG system for compression and transfer to the pretreatment facility for use as fuel gas.
Improving Dry-out and Cool-down Procedures
Nitrogen, instead of natural gas, will be used to dry out equipment before LNG production can start. Additional provisions have been incorporated in the design to allow the precool-down process to be performed without flaring hydrocarbons.
Upgrading Manual valves
We have upgraded thousands of manual valves in propane, mixed-refrigerant and ethylene service to bellows seal “zero-leak” valves, which prevent fugitive emissions. It is estimated this will reduce emissions by 6.7 tons per year.
Recovering Boil-off Gas for Fuel
Boil-off gas (BOG) generated at the liquefaction facility is minimized, compressed and transported via a 12” pipeline to the pretreatment facility. It is used as fuel gas to run a gas turbine generator with a waste heat recovery unit to supply process heating to all three pretreatment trains. Excess BOG will be recycled back to the inlet of the liquefaction trains for reprocessing so no flaring is required during LNG carrier loading operations.