Decarbonisation Technology August 2022 issue

venting from the nitrogen rejection unit, boil-off gas venting when boil-off gas compressor is down (usually flared), and ballasting vents during LNG storing and ship loading/unloading (also normally flared). Methane is a far more potent GHG than CO₂, so flaring those emissions (rather than venting them) can reduce their impact by a factor of 35 or more. Means to decarbonise LNG export facilities While decarbonising an LNG export facility is a challenge, various efforts have been taken in the LNG sector to reduce emissions, which basically can be divided into the three following categories: Elimination This category represents the choice of energy forms that power an LNG facility which can eliminate GHG emissions. Due to a proportional relationship between fossil energy or fossil fuel usage and GHG emissions, using a non-fossil fuel energy source will be the ultimate solution to achieve zero emissions. This includes using electrical motors based on electricity generated from renewable energy sources for refrigerant compressors. While partial substitution of fossil fuel by non-fossil fuel is possible for an LNG facility, with current technologies and energy mix, completely substituting fossil fuel is unlikely. It is particularly challenging for those existing LNG facilities that have already installed gas turbines for their refrigerant compressors. Mitigation On the basis of utilising fossil fuel energy, decarbonisation means reducing emissions from fuel gas combustion or methane leaks from piping and instrument leaks. This category includes improving energy efficiency through process design and equipment modifications. This includes utilising more energy-efficient equipment and advanced technologies associated with minimising emissions. It should be noted that, even if all of these mitigation methods are applied, not all GHG emissions associated with operating the facility may be eliminated. Sequestration The amount of CO₂ in the feed gas and the turbine exhaust gas will be released into the atmosphere if it is not captured and

stored. Carbon capture and sequestration (CCS) is considered a must-deploy technology to achieve net-zero emissions by 2050. CCS for LNG plants includes efforts that utilise commercially available CCS technologies to capture and sequester CO₂ emissions, mainly from the AGRU and the gas turbine exhaust. Examples of decarbonisation practices:  Improvement of energy efficiency The energy efficiency for an LNG plant is generally defined as energy input or requirement to produce a unit mass of LNG, such as kWh/kg or kWh per metric ton (MT). Each metric ton of LNG produced is estimated to require approximately 170 to 350 kWh of energy. In the absence of utilising renewable power from the grid, about 8 to 12% of feed gas is needed to produce power to run an LNG plant (including the fuel gas needed for gas turbines that drive refrigerant compressors). This is equivalent to GHG emissions of approximately 0.16 tCO₂e/tLNG to 0.48 tCO₂e/tLNG. For given feed gas conditions (such as pressure, temperature, and compositions), site conditions, and liquefaction technology selected, those values are strongly dependent on the type of drivers used for refrigeration compressors and the level of energy and heat integration. Driver type Efficiency of drivers varies with type. Heavy-duty frame turbines typically have an energy efficiency of 33 to 35%. For aero- derivative turbines, the energy efficiency ranges from 41 to 44%. The energy efficiency of a combined cycle gas turbine (CCGT) can run up to an energy efficiency of 60%. Recently, electrical motors with zero emissions (if the electricity is from a renewable source) have increased interest. Electric drive has been proposed for new LNG facilities that are geographically located where it is feasible to use renewable power from the grid. Heat recovery and integration For LNG plants that use gas turbines, recovering heat from turbine exhaust gas has become a standard design. The recovered waste heat can be used as a heat source for process use, such as providing heat for molecular sieve dehydration regeneration gas and heating medium. This can


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