LNG - The key energy source in the medium-term on the way to carbon neutrality

Author: Nadja Schmiedl, Ingo Emde, Marco Suleder

LNG stands for Liquefied Natural Gas and refers to natural gas that liquefies as it deep-cools to -162 °C and thereby shrinks to 1/600 of its original gaseous volume. It can therefore be stored or transported by ship or truck. The increasing importance of LNG as an energy source can be traced back to two causes. Firstly, it is widely available at competitive prices in an existing infrastructure. Secondly, it generates fewer and less dangerous emissions during combustion when compared to crude oil and coal. To date, LNG has primarily been used to generate power; however, thanks to its environmental advantages, there is growing interest in LNG as a medium of propulsion in the transport sector, for example in ships, trucks or even passenger vehicles.

Thanks to these properties, LNG has become a key element within the context of the ongoing energy shift from fossil fuels (coal, crude oil, natural gas) to renewable, "green" energy sources.

Since renewable energy sources (wind, solar, hydroelectric, biomethane, etc.) are currently not yet available in sufficient quantities at affordable prices, LNG represents an interim solution on the way to clean, carbon-neutral energy. Although demand for crude oil will have reached its peak within the next three to five years, consumption of natural gas will continue to increase until around 2038, when it will begin to slow down as renewable energy sources are developed further.

Natural gas, or LNG, is predominantly made up of methane, as well as smaller proportions of other gases like ethane, propane and nitrogen. Most of these gases are highly flammable, which means that natural gas and LNG are classified according to ATEX/IECEx as belonging to explosion group IIA, temperature class T1. Accordingly, measures for constructive and electrical explosion protection must be accounted for throughout the entire LNG value chain, and beyond it.

Overview of the LNG supply chain

Überblick über die LNG-Versorgungskette

Until now, LNG has almost exclusively been obtained from natural gas; research into other methods of LNG production, such as the use of biomass or current, is currently ongoing.

The LNG supply chain is made up of a number of steps, starting with natural gas, which is liquefied, and ending with the use of LNG as a fuel by the end customer. The first two stages in the production/exploration of natural gas and the following processing steps are the same as in the natural gas supply chain – the LNG-specific part of the supply chain starts after this. The cleaned natural gas, which has been processed to reach the required quality, is deep-cooled to -162 °C in liquefaction terminals; as a result, it changes to a liquid state. This usually happens immediately before the next step in the supply chain – transportation of the LNG to its destination. It is usually transported on LNG carriers, large specially designed ships. Once it has been delivered to its destination, the LNG is typically returned to its gaseous state in regasification terminals, from which it is fed through pipelines into the local gas network or supplied directly to industrial customers. This is the final stage in the LNG-specific supply chain.

Photo 1: LNG carrier with spherical tanks (Moss Rosenberg type) and a load volume of approx. 150,000 m3

A new development is that LNG is increasingly being used for a purpose other than generating power or heat – it is being used in liquid form as fuel for ships, trucks and buses. Breakbulk terminals are needed in order to divide industrial quantities of LNG into smaller required quantities for end customers. As well as these terminals, prompt and sufficient development of the decentralised LNG infrastructure in the form of bunker stations (bunkering) and filling stations is essential to ensure that LNG can be widely used as a fuel (small scale LNG).

Figure 1: Conventional natural gas extraction and fracking

Natural gas production/upstreaming

If LNG is produced using fossil natural gas reserves, it is extracted from natural gas extraction sites. The first stage of this process is drilling for natural gas. The drilling system essentially comprises a drilling rig and other systems that assist the drilling process. A rotating drill bit is used to drill through the layers of rock. To ensure that the gas cannot escape uncontrollably during the drilling process, the drilled hole is piped, concreted and fitted with safety valves at regular intervals. This helps to protect the surrounding layers of rock and groundwater; the drilled hole must also be continuously measured. The data recorded by the explosion-protected measurement systems is transmitted to the process control system using interface technology from R. STAHL.

Our ISpac isolators, which use conventional point-to-point technology, are often used if the number of signals is low. If the number of signals is higher, our IS1+ Remote I/O system is the more cost-effective solution because this technology transmits the signal quantities via a joint bus using different protocols, such as Profibus DP, Modbus RTU and TCP, PROFINET or Ethernet IP. Furthermore, the sensor technology used transmits a signal as soon as the natural gas reservoir is reached and the drill hole can be finished.

The safety valve is now replaced by a piece known as a "tree". This is used to seal the drilled hole and allows a defined quantity of natural gas to flow out during the extraction process. A riser pipe is used to extract the gas from the reservoir. This procedure requires the use of pumps if the pressure from the natural gas reservoir is insufficient. For this purpose, R. STAHL offers a range of actuation systems in different performance classes. These systems can be supplied with different control variants and can be fitted with a main switch, control transformer, main and control fuses, and control and monitoring devices, depending on the customer's requirements.

Natural gas of fossil origin partially originates from associated gas in the ground, where it escapes as a by-product during the natural gas drilling process or during degasification (targeted removal of gases) of layered crude oil. An alternative method for obtaining natural gas is flaring during the extraction process; however, in light of increasing global greenhouse gas emissions and rising demand, this is no longer environmentally or economically viable.

Onshore and offshore projects for conventional natural gas (and crude oil) extraction that use explosion-protected products and services from R. STAHL include "Zakum Build-up Facilities" and "Zirku Facilities Capacity Enhancement" in the Middle East, "Shah Deniz II" in Azerbaijan, "West Qurna 1" in Iraq, "Kashagan Full Field Development" in Kazakhstan and "Hassi Messaoud Refinery" in Algeria.

The USA has the most ample known shale oil and gas resources in the world. As a result, the fracking method is widely used to extract natural gas in this region. During the fracking process, at depths of several hundred to over a thousand metres, natural gas and crude oil deposits are tapped using a vertical drilled hole and then a horizontal drilled hole (see Figure 1). A perforating gun is used to blast small openings into the shale layers in the horizontal area of the drilled hole. Next, a few million litres of water mixed with solid filler material such as coarse sand, diluted with chemicals to provide antibacterial and corrosion protection, are pumped into the drilled hole at high pressure. The hydrostatic pressure causes the shale layers to open, allowing access for crude oil or natural gas fracking. In the last stage, around 40% of the fracking liquid is pumped out again. The rest of the liquid is primarily composed of solid particles, which keep the fine channels that have been blasted in the shale rock open during the extraction process.

Natural gas can also be obtained from renewable sources such as biomass. For instance, biogas – or biomethane – can be supplied to the natural gas network after biogas treatment, in particular removal of carbon dioxide. This treated biogas is obtained from the unprocessed biogas and is generated in a number of ways, including through fermentation of biomass. Treatment takes place in biogas facilities where biogenic waste and renewable raw materials are fermented.

Currently, natural gas is almost exclusively obtained from fossil natural gas deposits; however, soon it may be possible to replace a proportion of the fossil natural gas, which is generated using bioenergy.

Regardless of the method used to obtain fossil natural gas, explosion protection concepts are always required – whether in the conventional natural gas/natural gas extraction site process or, in the case of more unconventional extraction methods, during raw material extraction, loading, transport, and processing. Due to the relatively low yield from shale deposits, more drilled holes need to be created per extraction site in the fracking process, which means that more drilling equipment is required. Accordingly, typical explosion-protected components needed here include power distribution boards, machine actuation systems, load disconnect switches, safety switches, plugs and sockets, and automation solutions with control and terminal boxes. In biogas plants, however, explosion-protected installation materials are more important.

LNG liquefaction

LNG liquefaction is a practical alternative to transport via pipelines if the natural gas needs to be transported over longer distances. In a liquid state, the volume of LNG is around 600 times smaller than the volume of natural gas under normal atmospheric conditions, which means it can be stored and transported efficiently. Before the natural gas is deep-cooled to -162 °C in a liquefaction plant, also known as an LNG train, which converts it to a liquid state, it must be processed in special treatment plants to ensure that it meets the required quality standards. This process involves separating the raw natural gas from contaminants or dangerous substances in individual process steps. Gas treatment and liquefaction then takes place, usually in a combined large plant.

Natural gas liquefaction processes have been patented by large machine building, oil and gas companies. In general, the processes are based on a one-, two- or three-stage cooling process using pure or mixed coolants. The three main process types for the liquefaction process are the cascade cycle, mixed refrigerant (MR) cycle and expander cycle.

Each process is different in terms of its scalability, investment costs and energy efficiency. For small systems near smaller gas fields, a circular process is ideal thanks to its low investment costs (CAPEX), even though the energy efficiency is significantly lower than that of expander cycle processes. Large LNG trains are always designed with heat exchangers on the coast. Small plants are usually designed with air fin heat exchangers.

Even the efficient MR design, which is the most frequently used design, requires large amounts of energy in order to cool the natural gas. The typical power required by an LNG train is approximately 28 MW per mtpa (million tonnes per annum). Additional consumers in the gas treatment and pre-compression processes
also increase the overall power consumption, increasing it to around 35–40 MW per mtpa. In small LNG plants, the power value increases to far above 50 MW for a capacity of less than 1 mtpa.

Figure 2: Modular structure of an explosion-protected energy distribution system for Zone 1

For this reason, high-performance explosion-protected motor actuation systems and power distribution boards are required in order to actuate the pumps and/or ventilators required by the heat exchangers. Depending on the customer's needs, the solution can be made up of a range of types of protection.
The main types of protection that R. STAHL use are flameproof enclosure "Ex d", pressurised enclosure "Ex p", increased safety "Ex e" and encapsulation "Ex m". The outstanding variety of the product range and numerous national and international certificates means that the switchgears and protective devices can be planned and installed individually according to the customer's requirements. Equipment specified by the customer can be provided with the modular technology in the form of individually encapsulated modules.

In this process, the electrical components are installed in separately designed and hermetically sealed enclosures, or even designed as an integral explosion protection solution, according to the product function, in a corresponding overall construction. Thanks to the modular construction of the enclosure technology, the control systems and power distribution boards can be designed in a number of sizes, making sure that very high power levels with multiple current outlets are available even in explosion-protected areas. Figure 2 shows an example of a power distribution board in combination with Ex e and Ex d enclosures. If the auxiliary contacts, miniature circuit breaker, residual current circuit breaker, load disconnect switch or safety switch are linked to a Remote I/O system, the fault outputs for the power distribution board can be read out and monitored using the distributed control system. This function reduces the maintenance and servicing costs of the entire LNG train.

[Translate to Englisch:] Foto 3: Der LNG-Carrier, die „Gallina“, legt Seite an Seite mit der „Prelude“ an und wird mit den Entladearmen der „Prelude“ verbunden. — Photo 3: The Gallina, an LNG carrier, rests side-by-side with the Prelude plant and is connected to the Prelude plant using offloading arms

A number of LNG trains have been equipped with lighting, automation and low-voltage technology by R. STAHL. Notable examples in this context include the "Wheatstone LNG plant", "Yamal LNG plant" and "Arctic LNG II".

Liquefaction plants are often installed as onshore facilities near a body of water. A Floating LNG (FLNG) plant represents a more flexible, often more cost-effective variant. FLNG plants can be designed as natural gas extraction sites or as LNG storage facilities, also known as Floating Storage Units or FSUs. Floating plants that extract, liquefy and store natural gas are referred to as Floating Production, Storage and Offloading Units (FPSOUs). "Prelude", the world's first and to date largest FLNG plant, supplies the western coast of Australia with 3.6 million tonnes of LNG per year. Its area is approximately the size of four football fields. R. STAHL provided the Prelude plant with terminal boxes for the electrical installation technology, among other items of equipment. Additional FLNG projects for which R. STAHL provided Remote I/O systems, control systems, plugs and sockets and isolators include the "Petronas Floating LNG 2" and "Golar Hilli FLNG"

Photo 4: Example representation of a Remote I/O (IS1+)

and HMI station (SHARK device platform) from R. STAHL

LNG transport

Natural gas is liquefied in order to make it suitable for transport. Since natural gas is usually liquefied right on the coast, LNG tankers are primarily used to transport it. In many cases, gas producers and gas buyers have agreed long-term supply contracts, which guarantee a secure, sustainable power supply. Transport often takes place over significant distances; suppliers build entire fleets of tankers for this purpose.

Larger and larger LNG tankers are being built in order to keep transport costs as low as possible. The sizes of the LNG tankers range from 120,000 to 180,000 m³ (small scale IMO-type B, conventional IMO-type B) and up to 265,000 m³ (Q-flex and Q-max) for the LNG tanker carrier classes developed in the last few years.

Although the LNG tanks on board LNG tankers are insulated, slow heating can cause part of the load to evaporate – this gas is referred to as Boil-Off Gas (BOG). To make optimum use of the load capacity, special compressors are used on board to cool the BOG and liquefy it again. Explosion-protected Remote I/O control stations are used in hazardous areas to control these compressors and the associated plants. The intrinsically safe signals from sensors and actuators regarding the compressors, which are connected via the IS1+ Remote I/O system, are transmitted via PROFIBUS DP, for instance, to the decentralised control system.

The number and type of the modules used for a wide range of signal types are tailored precisely to meet the requirements of the application. The use of 8- or 16-channel Ex i modules means that the stations can be built to be very compact, significantly reducing space and weight in comparison with conventional solutions.

The compressors and systems are installed below deck, where there is limited space available around the gas tanks. For this reason, the machines and corresponding Remote I/O stations with I/O modules and various digital display and message elements must be small, meet the requirements for explosion protection in Zone 1 and be robust enough for use around the world under the toughest ambient conditions.

The vibration-resistant structure of the IS1+ Remote I/O systems, combined with 12 different ship certifications such as DNV-GL, ABS and ClassNK, make the system suitable for operation on ships – both above and below deck.

The IS1+ stations are designed primarily to ensure that they are very easy to install on board. Robust stainless steel enclosures with increased safety "Ex e" type of protection are used for the compressor control stations. The design of the enclosure, featuring narrow single, double or even triple doors, enables easy access without blocking the narrow passages on ships. High-quality sealing materials reliably protect the installed devices against the saline atmosphere.

LNG regasification

After the LNG has reached its destination, the natural gas is converted back to its gaseous form in regasification units. If the regasification units are required for a long period of time at a specific location with high capacity, an onshore plant can be established. Alternatively, Floating Storage and Regasification Units (FSRUs) can be used. Thanks to their size, the offshore plants incur lower capital investments and are outstandingly flexible, since they can be relocated to a different site. Currently, the highest regasification capacity is found in Asia, for instance in Japan, South Korea, China, and India, as well as in Europe, for example in Spain, France, the UK, and Turkey, because these two continents are the largest LNG importers.

During the regasification process, the LNG must be supplied with the required evaporation heat. Due to the low boiling point of natural gas, a particularly high quantity of heat energy is required; for cost reasons, this process often uses seawater. Figure 3 shows an example of a pump unit that conveys seawater to the heat exchanger. The pump skid is also equipped with safety switches from R. STAHL, as well as alarm signal emitters and terminal boxes. The safety switches safely disconnect the electrical energy supply from machines and system parts for cleaning and repairs. All of the installed load disconnect switches have an AC-3 switching capacity, meaning that inductive loads such as squirrel cage motors can be switched.

After the evaporation process, the gas is compressed in a compression plant before being fed into the natural gas network. R. STAHL's new patented EXpressure technology is a practical option for onshore and, in particular, offshore projects where the plant weight is a crucial cost factor. Motor actuators and power distribution boards, which are required for a number of tasks including actuation of compressors or supplying the heat exchangers and evaporation systems, can be made significantly lighter and more compact through the use of this technology. This development in "Ex d" flameproof enclosure technology safely dissipates the explosion pressure in control cabinets and control boxes via flow channels. This means that the enclosure, which has been manufactured to industrial control cabinet dimensions, and the control system made up of industrial components can be located in Zone 1 or 2.

The hazardous zones in regasification plants extend over large areas of the system. As a result, solutions from R. STAHL are not only suitable for the process sequence, such as actuating and supplying system parts, but also for the entire functional sequence of the plant. For instance, the linear luminaires, tubular light fittings, floodlights and portable lamps from R. STAHL can be used to provide lighting for work equipment and objects, both inside and outside. The explosion-protected emergency luminaires with battery operation ensure that the lighting is safe in case of an error. Audible and/or visual alarm signal emitters are used to indicate alarms, warnings or information in the event of a device malfunction in the hazardous area. Installation technology such as switches, terminal/control boxes or sockets can be used to provide lighting in individual areas. The explosion-protected camera systems are used for monitoring, while the network technology, such as WLAN access points, is used for communication within the entire system.

The regasification plants are located near the coast, either onshore or offshore, similar to the liquefaction process. The saline, humid environment poses significant challenges for the electrical equipment. Furthermore, the requirements for maritime applications must be considered for floating systems. In this respect, particular importance is placed on the explosion-protected components and systems made of seawater-resistant enclosure materials and high-quality sealing materials, and designed to be resistant to vibrations and electromagnetic influences. Thanks to R. STAHL's comprehensive range of products with international ship approvals, the products can be installed both below deck and universally above deck.

Photo 5: Pump skid with audible and visual alarm signal emitters, safety switches and terminal boxes from R. STAHL

There are also application cases in which the LNG is not regasified immediately after transport, but initially stored in cryogenic tanks. Efficient tank insulation can reduce the amount of Boil-Off Gas (BOG) to a relatively low level. Sensors detect the amount of Boil-Off Gas that is fed into the local natural gas pipeline network in compressed form. In this process, which takes place in the hazardous area, the data transmission to the control system is performed using interface technology from R. STAHL (e.g. Remote I/O, isolators). The LNG can also be loaded onto ships or trucks as fuel via bunker stations, or transported to large consumers (e.g. business) using transport vehicles or barges. Electronic and electrical equipment such as panel PCs and thin clients for process monitoring and control within the hazardous area round off the R. STAHL product range for LNG.

Photo 6: Plant overview of a finished regasification terminal

LNG at the end consumer

LNG is used in a number of ways around the world. Its main areas of use are heat generation, power generation and as an energy source for the process industry. However, the use of LNG as a fuel is currently on the rise. Thanks to its good environmental properties and its positive effect on carbon dioxide emissions, LNG is used as a fuel for both trucks and ships.

The new IMO 2020 regulation is a specification set out by the International Maritime Organization (IMO) to reduce marine pollution. It stipulates that, from 1st January 2020, ships may only use fuels with a sulphur content of maximum 0.5%. The upper sulphur content limit of 3.5% remained in place until 2020. As a result, combustion of heavy fuel oils in ship motors is now only possible if significant effort is spent on subsequent exhaust gas purification. In the past, the use of heavy fuel oil not only caused around two to three percent of global CO2 emissions; it also released fine dust, nitrogen oxide and sulphur dioxide into the air, significantly contributing to air and water pollution. Accordingly, low-sulphur fuels such as LNG are a key solution for the global shipping industry.

Retrofitting existing ships powered by heavy fuel oil or constructing new ships with LNG drives requires the use of Fuel Gas Supply Systems (FGSSs). This means that additional hazardous areas are created on board, where only explosion-protected equipment can be used. The Fuel Gas Supply System (FGSS) that supplies fuel to the motors in the LNG drive comprises the gas tanks, as well as evaporators, compressors, pumps and a central automation system. A Remote I/O system installed on-site in the hazardous area and an HMI system are used to monitor the process.

The temperature, pressure and flow values measured in these system parts, the valve positions, the device status, etc. must be provided to the ship control system and the self-sufficient Alarm Control Monitoring System (ACMS), if present.

The FGSS represents a hazardous area due to the high volatility and ignitability of the conveyed gas; as a result, the measured values must only be determined and transmitted using explosion-protected, often intrinsically safe sensors and network components. In this context, it is not only essential to transmit the sensor data out of the Ex zones to the control centres. The recorded data, visualisation and alarm control management monitoring in Zone 1 must also be made available in an operating system.

An ET-598 operating system is used for on-site visualisation and FGSS alarm management. This thin client from the SHARK device range, certified according to ATEX, IECEx, ABS and DNV GL, is specially designed for Zone 1 and extreme ambient conditions such as those on board ships. The operating system is fitted with a seawater-resistant IP66 enclosure and is resistant to the extreme vibrations generated on ships. Ethernet multimode fibre optics designed with the "Ex op is" type of protection are used for communication with the other system components. This eliminates electromagnetic influences from components installed nearby, such as motors and converters. The capacitive 21.5" touch screen display allows the user to control the entire system. This type of touch screen is installed behind a thick, toughened glass pane, limiting the system's susceptibility to mechanical damage. The entire system is designed to be extremely robust in order to guarantee high availability, since repairs are very difficult to perform once a ship is at sea.

In conclusion, it is clear to see that LNG will become more and more important within the context of the global energy revolution over the next few years.
The R. STAHL Group offers a comprehensive, diversified explosion protection range – from automation solutions and energy technology to lighting systems and marine-specific products – to meet customers' needs throughout the entire LNG supply chain. A portfolio including more than 20,000 explosion-protected, certified products and the variety of detailed variants available establish a basis for implementing customer-specific solutions.

Thanks to their extensive expertise in explosion protection and their experience combining different types of protection with conventional technology, R. STAHL AG is able to offer clients the perfect solution to any Ex challenge.