AUTHOR: SHAWN HUANG, SENIOR ADIVSOR
This technical paper was presented by Shawn Huang, Senior Advisor, September 19th, at Gastech 2024 Technical & Commercial Commercial Conference, in Houston, TX.
To learn more about the event or future Gastech events, visit https://www.gastechevent.com/.
INTRODUCTION
Liquefied Natural Gas (LNG) is not only a way to monetize stranded natural gas reserves or dispose of the associated gas from liquid productions for the resource owners, but also is a method to deliver a lower carbon content energy source. Producing LNG consumes energy. LNG plants vary Liquefied Natural Gas (LNG) is not only a way to monetize stranded natural gas reserves or dispose of the associated gas from liquid productions for the resource owners, but also is a method to deliver a lower carbon content energy source. Producing LNG consumes energy. LNG plants vary in size
and use different technologies and energy sources to produce LNG. Figure 1 depicts the carbon emissions from producing each tonne of LNG from various sizes of LNG production trains. Regardless of the size of the train ranging from 1 MTPA to 12 MTPA, carbon emissions varied between -75% to +60% relative to the average of all trains.
The amount of carbon emissions released by LNG plants has attracted increasing attention from corporate sustainability initiatives. The simplistic approach of carbon emissions per tonne of LNG produced does not consider the train size, technology type, and energy source. Have the LNG trains been operating at the highest attainable energy efficiency with the lowest attainable carbon emissions? How should the carbon emissions performance of an LNG plant be measured?
CARBON EMISSIONS PERFORMANCE MEASUREMENT
Solomon uses a Carbon Emissions Index (CEI) to measure the carbon emissions performance of LNG plants. Equation 1 is Solomon’s Carbon Emissions Index calculation method.
In the equation, the CO2e is a carbon dioxide equivalent that includes CO2 equivalent of methane and nitrous oxide and is calculated with the recommended methodology from IPCC (Intergovernmental Panel on Climate Change of United Nations).
As shown in Equations 2 to 4, actual CO2e emissions are from fuel combustion, flare combustion, fugitive gas, vented gas, and vented CO2. The fuel combustion includes both direct and indirect combustions.
Through Indirect Emissions, the carbon emissions performance measurement accounts for different types of energy sources to produce LNG.
Standard CO2e emissions is where the normalization occurs for “apples-to-apples” comparison between LNG plants of different sizes and technology types. As shown in Equation 5, standard energy emissions are calculated from Reference Energy Carbon Emissions Factor and Energy Intensity Index™ (EII®) standard energy. The Reference Energy Carbon Emissions Factor assumes natural gas as fuel. The EII standard energy of an LNG Plant is calculated from unique process units including compression and utilities of the plant, as shown in Equation 6.
The standard flare emissions, fugitive emissions, and vent methane emissions are based on industry operations data. The standard vent CO2 emissions include all CO2 removed from feedstock of the LNG plant.
The process units may include acid gas removal, heavy hydrocarbon removal, liquefaction compression, power generation, utilities, etc., that the LNG plant has. The EII standard energy of process units are based on industry operations data, among which the LNG liquefaction compression data is licensed from Shell Global Solutions International BV. Through the EII standard energy, each plant is normalized to a standard that is unique to its own facilities configuration for comparative measurement of its performance.
APPLICATION FOR LNG PLANTS
Carbon Emissions Index (CEI) is calculated for LNG production facilities that participated in Solomon’s benchmarking study (see Figure 2). The CEI varied from 60 to 160 relative to the average CEI of 100 for all participating LNG production facilities. The figure also shows the components of the
CEI, namely direct and indirect combustion, CO2 removed from the plant feedstock net of sequestration, plant flare, and fugitive and vented gas from the plant.
Among all contributors in the calculation of CEI, combustion emission is the major contributor to CEI, followed by carbon dioxide removed from the plant feedstock net of carbon sequestration. Plant flare includes both normal plant operations flaring and plant shutdown, and process upset flaring. Emissions from plant flaring, and fugitive and vented gas are not negligible for some plants.
Since standards CO2e emissions for CEI includes all CO2 removed from feedstock of the LNG plant, any carbon sequestration of this portion of feedstock CO2 improves CEI.
KEY DRIVERS OF PERFORMANCE
Direct and indirect combustion emissions from energy consumption are major contributors to CEI. Solomon uses EII to measure the performance of energy consumption, as shown in Equation 7.
Figure 3 shows the breakdown of EII of LNG production facilities and the contributors of EII. EII varied from 70 to 150, relative to the average EII of 100 for all participating LNG production facilities. In the calculation of EII, EII standard energy is based on industry operations data, and each plant is first compared against its own standard. Each plant’s relative EII should be 100 if its performance is industry average. As seen in Figure 3, regardless of plant size or configuration, the energy to make LNG through compression is less than 35% of the EII standard energy.
Up to 79% of EII standard energy is lost in compression. This loss can be attributed to fired-gas-turbine exhausts for gas-turbine driven LNG plants. Only up to 19% of waste heat from direct combustion gas turbines is recovered. For indirect combustion, such as electric motor-driven compression, this loss is captured through the efficiency of the imported electrical power generation.
Approximately 26% of EII standard energy is lost in in-plant electrical power generation, while up to 9% of waste heat from direct combustion gas turbine power generation is recovered. Around 16% of EII standard energy is used for electrical power for process cooling and other plant operations, and approximately 26% of EII standard energy is used for direct fired process heating. There is up to 52% of EII standard energy not accounted for in some LNG production facilities.
CASE STUDY AND PERFORMANCE GAP
How do we use carbon emissions performance measurement to help LNG plant operations? Figure 4 is an example of LNG production facilities’ Carbon Emissions Index compared against the average of the top half CEI performers. As mentioned earlier, combustion emission is the major contributor to the CEI performance indicator. Combustion emissions are analyzed by EII.
Figure 5 represents the EII of these example production facilities compared against the average top half EII performers. On further analysis, the EII top half performers use waste heat recovery from compression and power generation, while the example LNG production facilities do not. The example LNG production facilities have a higher energy loss in compression, energy loss in power generation, and have higher energy consumption on direct fired heating and energy unaccounted for.
Analyzing the drivers of EII against peer top performance gives insight into what has been achieved by peer LNG plant production facilities. Figure 6 shows the gaps and advantages of the EII of the example LNG production facilities compared against the average of top half EII performers. The example facilities only have one advantage over the top performers in energy for making LNG through compression. The other energy consumption categories are gaps. The example facilities have no waste heat recovered from compression or power generation for its energy consumption, therefore the less consumption of waste heat in total energy consumption is shown as a gap rather than as an advantage.
From the detailed EII gap analysis, the top opportunities are in energy loss in compression, waste heat recovered from compression, direct fired heating, and energy unaccounted for (see Figure 7). Among these opportunities, the first three could be interrelated. When the example facilities use waste heat recovered from compression, the energy loss in compression gap would be reduced. When the waste heat recovered from compression replaces the heating duties required by the direct fired heating, the direct fired heating gap would be reduced.
The energy unaccounted for is a result of inaccurate tracking of energy consumption. It could be from direct fired heating or other energy consumptions. This gap can be significant for some LNG production facilities, as shown previously in Figure 3.
Table 1 shows there is a 3.5% energy gap between the example facilities and the top performers on direct fired heating. To close this gap, the energy could be supplied by waste heat recovery from compression. The energy loss in compression gap is 11.0%, which is sufficient to cover the required energy. The 8.8% gap on waste heat recovered from compression indicates that peers have done more on waste heat recovery from compression than the example facilities.
The 2.3% energy unaccounted for gap shows that if the direct fired heating is higher than the data reported, there is still sufficient energy to capture from energy loss in compression through waste heat recovery.
Waste heat recovery from compression or power generation gas fired turbine exhaust has been successfully used in many LNG production facilities. Some LNG production facilities are using waste heat from an adjacent power plant to make LNG.
VALUATION OF CLOSING THE GAP
Closing the gap on direct fired heating versus the top performers would allow the example LNG production facilities to produce 1.1 extra LNG cargo per year from the saved plant fuel gas. Each LNG cargo of approximately 64 thousand (k) tonnes of LNG is about 41 million United States dollars (M USD) at an average price of 12 USD per million British thermal units (Btu) in 2023. The loading arms and the jetty are between the LNG cargo tanker and the
LNG storage tanks.
If the energy unaccounted for of the example LNG production facilities is from the inaccurate measuring of the energy consumption of the direct fired heating, the extra LNG cargos produced per year is close to 2. The 1.1 extra LNG cargos is 46M USD per year. The close to two extra LNG cargos is about 70M USD per year. This information was leveraged by the example facilities to make an investment decision on a brownfield project to install waste heat recovery units on fired gas turbines, recognizing that it could reduce the plant’s carbon emissions and enhance its LNG production.
Once the brownfield project is implemented, the gap of the energy consumption (EII) of the example LNG production facilities versus top performers is expected to turn into an advantage, as shown in Figure 8 and Figure 9. The gap of the CEI after the gap closure is expected to be smaller than the top half performers (see Figure 10).
CONCLUSIONS
There are other LNG production facilities that have potential key opportunities like that of the example LNG production facilities, as shown in Figure 11. The analysis demonstrates that:
- CEI, accompanied by EII, provides an effective measurement of LNG production facilities’ carbon emissions and energy consumptions performance.
- Detailed analysis of performance helps identify gaps against what has been achieved by peer LNG production facilities.
- Closing the gaps with peers would not only improve carbon emissions performance, but also increase LNG production.
- Accurately tracking energy consumptions of LNG production facilities enables identifying opportunities for LNG production enhancement.
Shawn Huang, Senior Advisor, HSB Solomon Associates LLC
Shawn began his career with Exxon in 1990 and has served in technical and managerial roles in the industry. That included being an operations management team member of an LNG plant and leading technical departments at ConocoPhillips for 8 years in supporting global operations and project developments.
As Senior Advisor with Solomon for LNG and gas plant operations comparative performance analysis, he conducts studies and delivers insights for study participants. Shawn holds a PhD in Chemical Engineering, an MBA, and a PE license.
Shawn chaired sessions and presented papers in international forums as a member of Technical Committee of Offshore Technology Conference (2005–2015).