DIESTA ACHE CO2 emissions reduction for LNG trains
Author: Nicolas Bilbault, Xavier Guérif, Falk Mohasseb
Due Date: 06.10.2023
This abstract aims to demonstrate the possibilities to generate CO2 emission reduction by improving the ACHE performances using enhanced finned tube technology on LNG trains.
According to one definition carbon credits are “permits that allow the owner to emit a certain amount of carbon dioxide or other greenhouse gases” . A carbon credit represents the right to emit greenhouse gases equivalent to one ton of carbon dioxide. Companies can sell unused credits to other companies.
The end of the past decade and the start of 2020s are showing a continuous global development of the LNG liquefaction capacity with a huge increase in the supply and treading capacity and a large number of final investment decision in 2018 and 2022.
According to the International Energy Agency (IEA), energy demand increased by 2.1% in 2022..The fuel that had the biggest gain was natural gas, which accounted for 45% of this growth in energy consumption. Global gas demand is expected to continue to grow at a rate of 1.6% until 2024. Natural gas is projected to overtake coal and become the second leading source of energy consumption globally by 2030 in order to achieve net-zero emissions targets.
According to the International Gas Union (IGU) 2023, the current liquefied natural gas production capacity is 478.4 mtpa. The proposed aspirational LNG supply capacity at pre-FID stage is 997.1 mtpa as of end-April 2023.
Despite the development of small to medium size liquefied natural gas plants, this capacity increase is still lead by giant liquefied natural gas trains requiring more and more cooling capacity and facing significant challenges related to carbon neutrality, affordability and profitability. In order to meet COP21 targets, reducing emissions should be very much on the radar of new projects developers.
The current second wave of LNG market is showing a growth and return of the large trains. The average size of an LNG train moved from 2.5 mtpa in 1985 to 5.2 mtpa in 2020. Increasing the LNG trains capacity means increasing the required heat exchange surface and consequently the weight and CO2 emissions related to the heat exchangers production.
How to optimize the required Air Cooled Heat Exchangers on a large LNG train?
This is the challenge that Kelvion Thermal Solutions (KTS) / TechnipEnergies (T.EN) / Wieland decided to address through the DIESTA finned tube technology development.
DIESTA (Dual Internal & External Structured Tube for Air fin cooler) allows optimizing the efficiency of the ACHe resulting in reducing its footprint on the LNG trains. Reducing footpring of the ACHe means reducing the size of the train itself.
Reducing the size of the train means reducing its cost and carbon footprint.
How to optimize the size of the ACHe using DIESTA?
Air coolers are used to chill, condense and subcool the propane used as a coolant in liquefied natural gas trains. The finned tubes of the air coolers are essential components for the heat transfer between the fluid to be cooled down or condensed and the air.
Dedicated to air coolers and optimized for propane condensation, DIESTA is a Dual Enhanced finned tube jointly developed by KTS, Wieland and T.EN with the support of the French Agency for Energy (ADEME) and TOTALEnergies.
This technology combines and improves the legacy of two technologies: the enhanced Groovy fins developed by KTS and the GEWA-PB tube inner geometry developed by T.EN and Wieland.
By proposing an optimized grooved structure on the fins, DIESTA delivers a higher air side heat transfer coefficient, while limiting the impact on the pressure drop. For a propane condenser, the air side thermal resistance represents approximately 60% of the total resistance. The tube side resistance on the same propane condenser represents 30% of the total resistance. When the size of the air cooler footprint is reaching about 200 m long by 16 m wide, it is quite valuable to improve the tube side heat transfer coefficient.
DIESTA allows to do that on the tube side and on the fins side simultaneously.
After developing the product for the propane condensation, we also focused on gas cooling application therefore allowing us to address the complete propane loop and mixed refrigerant loop of an LNG train.
Consequently, DIESTA allows reducing the global LNG train heat exchangers footprint by 10 to 20%. Reducing the footprint means reducing the produced heat exchanger and their consequences in terms of carbon emissions and global LNG train CAPEX.
The development program included a rigorous testing campaign including fouling tests, cleaning test and thermal testing validations following the stepwise approach of API 17N, Technology readiness Levels in the oil and gas industry.
LNG Train CAPEX savings:
For an LNG train capacity of 5 mtpa, here is below an example of the global savings that can be reached considering a 10% AFC footprint reduction leading to a 10% LNG Train footprint reduction:
The above study case highlights the global scale savings that can be generated on the LNG Train global cost. This global saving representing a very consequent level versus the initial AFC commodity cost:
10% footprint reduction can generate 7% global scale saving on the Train.
Knowing that the costing ratio between AFC commodity and global train costing may vary depending on the site conditions, the country restrictions, the erection mode (stick built or modular concept), we could save the equivalent of 80 to 250% of the initial AFC commodity cost as a global saving. In the present case, the global savings are equivalent to 85.7% of the ACHe cost.
Numerous LNG projects studies are showing the interest of DIESTA versus conventional solution in terms of global scale CAPEX savings.
How to value the AFC DIESTA CO2 emissions savings?
ACHE requires a certain number of raw materials such as carbon steel tubes and plates resulting from the steel smelter manufacturing process, aluminum strip resulting from the aluminum smelter industry for the manufacturing of the heat exchangers and other steel components such as supporting structure, casing and fan rings also coming from the steel smelter industry.
Those components are generating CO2 emissions before reaching our factories.
The method of calculation is consisting on evaluating all the emissions associated to the outsourced components, adding the transportation to the factory, adding the factory emissions and then the finished product transportation to final location of the plant.
With an average estimated emission of 10 T CO2 / T of production, the Aluminum appeared quickly as the main source of emission to be compared to 1.9 T CO2/T of produced steel.
Emissions associated to the factory consumptions and transportations appeared negligible versus the raw material smelters ‘one.
We selected then a typical large liquefied natural gas project considering customer base design of the ACHe versus the DIESTA enhancement on finned tubes.
Initial design is leading to 400 ACHe for a total weight of 1860 T of aluminum material versus DIESTA design leading to 300 ACHe for 1278 T of aluminum, to achieve the same duty on the plant.
The DIESTA design optimization is leading to a 32% reduction of the aluminum quantity representing this same 32% CO2 emissions reduction.
Moreover, reducing the size of the ACHE means reducing the number of fans required to achieve the duty leading to less power consumption.
Thus, on this same project example, the 400 ACHe were requiring 600 fans leading to a total installed power of: 22.4 MW
The DIESTA design solution with 300 ACHE requires 450 fans leading to a total installed power of: 21.5 MW
The below table is summarizing the CO2 emissions reduction resulting from the optimized ACHe design & OPEX.
IGU 2019 World LNG report
EIC DataStream reports
API RP 17N
Worldsteel association, Steel’s contribution to al ow carbon future
ECTA, CEFIC associations, Guidelines for Measuring and Managing CO2 Emissions from Freight transport operations
BSR, How to calculate and Manage CO2 Emissions from Ocean Transport
The Oxford institute for Energy Studies, Challenges to the future of LNG: decarbonisation, affordability and profitability