Innovation: Using less energy to liquefy natural gas

Dual Internally and Externally Structured Tube for Air Coolers (or DIESTA) technology, the product of a public-private partnership, improves the efficiency of air coolers used in natural gas liquefaction plants. This innovation has a positive impact on both the cost and environmental performance of liquefied natural gas (LNG) plants.

The LNG industry is experiencing rapid growth, driven in particular by its advantages in the fight against climate change. To find out more, we talked with Total, a major LNG player that is pursuing a comprehensive approach to energy efficiency.

It takes natural gas to liquefy natural gas

Natural gas is currently on a roll because it emits the least carbon dioxide (CO2) and pollutants of all the fossil fuels, comparing particularly favorably to coal. Global consumption of natural gas rose a strong 3 percent in 2017, or twice as much as in 20161. Most of this growth is being driven by demand from China (up 15 percent), which will be the top importer of natural gas by 20192, consuming 40 percent of global supply.

Today, the most efficient way to ship natural gas from where it is produced to where it is used is by sea, on LNG carriers, given that the distances involved are often very large. Maritime transportation offers greater flexibility in adjusting supply to demand and less exposure to geopolitical changes. Liquefaction, which reduces the volume of natural gas by a factor of 600, is therefore a crucial step in the process.

But it's a step that needs to become more energy efficient. To become a liquid, natural gas must be cooled to -163 Celsius in a process that requires a considerable amount of energy. Several cryogenic units equipped with huge turbocompressors3 are needed to compress and then expand propane in order to generate cold energy4 that is transferred directly to the feed gas to be cooled.

As a result, a liquefaction plant can use up to 10 percent of the feed gas to pre-treat and cool the gas to be exported. Reducing this percentage is therefore a top priority from both a cost and an environmental standpoint.

DIESTA technology in action

A public-private partnership to drive innovation

This is where Dual Internally and Externally Structured Tube for Air Coolers (DIESTA) technology comes in. It started with a partnership between Total and the French Environment and Energy Management Agency (ADEME)5, initiated in 2008 via the ADEME-Total Energy Efficiency Program.

Sylvie Padilla, head of the companies and green technology department at ADEME, remembers the encounter between two players interested in energy efficiency. "At the time, Total was looking to get involved in this type of initiative and promote a type of open innovation for its customers and itself."

As part of this Energy Efficiency Program, a public-private partnership was formed to launch calls for energy-related projects in the industry. Out of a total of 163 projects submitted, 55 were shortlisted and 35 went on to the demonstrator stage. Eight are now "in the catalog" and at least four are in use at industrial sites.

DIESTA is one of the four. Co-developed with three international companies — Wieland, Kelvion and TechnipFMC — this technology is applied to finned tubes in air-cooled heat exchangers. Air coolers chill, condense and subcool the propane used as a coolant in liquefaction trains. Their finned tubes ensure the heat exchange between the fluid to be chilled or condensed (propane) and the cold source (the air fanned through the air cooler). DIESTA finned tubes were specifically designed with modifications to the interior surface of both the tube and the outside fins to optimize the air-cooling process. The new design improves the rate of heat exchange between the tube-side propane and fin-side air by around 15 percent.

As Thierry Schuhler, head of Total's cross-functional Energy Efficiency R&D Program, explains: "The aluminum alloy sleeve that covers DIESTA's exterior surface holds fins that are dimpled and grooved, rather than smooth as they would be on a standard tube. This allows for better air distribution and increased turbulence, two factors that help to improve the heat transfer coefficient."

Cost and environmental benefits

Reducing the size of liquefaction trains also reduces their construction cost. "Since DIESTA increases the amount of heat exchanged in each unit, the total number of units — and therefore the LNG train's length — can be decreased by up to 20 percent," Schuhler said. A LNG train's footprint depends on the number of air cooler units that must be lined up to obtain the necessary cooling power. "LNG trains that process millions of tons of LNG annually can be two hundred meters long," he added.

A substantial reduction in each train's footprint yields cost savings that go beyond the price of the air coolers themselves.

Higher-efficiency air coolers improve turbocompressor performance. These compressors are the most energy-intensive components of liquefaction trains and play a key role in their overall size. Optimization of cryogenic unit efficiency can be harnessed either to reduce energy consumption or to increase LNG output.

"This innovative technology can help LNG plants lower their costs and improve their environmental performance," Schuhler said. "From now on, it will be systematically taken into consideration for greenfield projects, as well as for revamping projects."

More than technology

Feedback from companies involved in the DIESTA project has been very positive, now that the understandable questions that arose during launch have been answered and the initial wrinkles ironed out.

"The financial benefits were obvious right away," Schuhler said. "But beyond that, our work with technicians and users and the installation of an on-site demonstrator also created value for industrial operators and small businesses. It's a good example of what we should do when we offer innovative new projects to other industrial players."

While DIESTA addressed energy efficiency in terms of equipment and processes, it also took a new approach by involving the different links in the chain.

"The concept of an identifiable community, combining users, equipment manufacturers and public and private researchers, has had a hard time getting off the ground in the area of energy efficiency," Schuhler said.

Padilla recognizes that DIESTA has helped jump-start such a community, now embodied in a newly created alliance known as ALLICE6.

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1 Source: Global Gas Consumption,

2 Source: International Energy Agency.

3 Gas turbine-driven compressors.

4 Expressed in small or gram calories. A calorie is the amount of heat or cold needed to raise or lower the temperature of one gram of water by 1°C to or from 14.5°C to or from 15.5°C at standard atmospheric pressure (1 bar).

5 The French Environment and Energy Management Agency (ADEME) is active in the implementation of public policy in the areas of the environment, energy and sustainability. The agency provides expertize and advisory services to businesses, local authorities and communities, government agencies and the public at large, to enable them to establish and consolidate their environmental action.

6 ALLICE (Alliance industrielle pour la compétitivité et l'efficacité énergétique) is a new alliance created by CETIAT, CETIM, CTCPA and ENEA Consulting, soon to be joined by the Liten Institute. The alliance aims to strengthen the energy efficiency community in industry and support innovation by bringing together players from across the value chain (solution providers, design and engineering firms, users) and from different industrial channels to enhance cross-functional cooperation.

This page was paid for by Total. The editorial staff of CNBC had no role in the creation of this page.