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In one of our previous videos we talked about natural gas. We went through all the detailed steps necessary for its extraction, the types of plant where it is used and we also had an overview of its peculiar features.
As aforementioned, once the gas has been extracted it is refined and transported through gas or methane pipelines, into electrical systems and households.
Anyway, how does the transport of the gas extracted from the field to its final user take place? In the best out of all circumstances, which implies being a Country lucky enough to be directly connected to supplier countries, such as most European countries (including Russia), it is usually transported by land with the help of methane pipelines. Indeed, the Countries that do not have these possibilities must purchase the product from other Nations that transport natural gas by sea.
The transport of natural gas by sea is very delicate. Mind that we are talking about a product composed of 98% methane, which is highly flammable, and transporting it in large tanks installed on a ship can be particularly risky.
This is why natural gas must be brought from its gaseous state to a liquid state. Liquefied natural gas, also called LNG, is not as flammable as in the gaseous state. Moreover, the volume of the gas is reduced by 600 times, increasing the average single-journey transport capacity of LNG carriers. LNG carriers are special ships built specifically for the transport of methane and flammable gases.
Now let’s focus on the natural gas distribution and treatment chain.
After the extraction of the product, with the help of methane pipelines, the gas is transported to special plants which will proceed to liquefy it. The plants can usually be located near the coasts, in port areas, or in floating structures anchored to the seabed, which are called ‘off-shore’ plants.
The process of bringing the gas to a liquid state starts with a treatment to remove carbon dioxide and hydrogen sulphide, then a pre-cooling phase is carried out followed by the extraction of any heavy component. At this point, the gas temperature drastically drops to -163 ° C, below the boiling temperature of methane, the main component of natural gas.
Liquefied natural gas is injected through cryogenic tubes (located on loading docks) into tanks placed on LNG carriers. These particular ships can carry from 150 to 200 thousand cubic meters of methane, and they can be of two different types :
- The first example is that of a ship with integrated tanks developed by Gaztransport & Technigaz. For this type there are 2 versions: the Technigaz model is supplied with tanks consisting of an elastic primary barrier, formed by a membrane with ribs made of steel plates. The arrangement of the plates forms two sets of ribs orthogonal to each other having the function of reducing thermal stresses. The secondary barrier is made with a composite material called "triplex" consisting of an aluminum sheet in a wafer of glass fiber fabric. The tank is fixed to the inner hull with a polyurethane foam reinforced with glass fibers. The typology developed by Gaztransport instead provides two barriers consisting of flat welded planking, made of a particular metal alloy of steel and nickel, called invar. Between the two barriers there are insulating panels and air chambers, into which liquid nitrogen is injected to maintain the cryogenic temperature of the natural gas. In this case the tank is held to the inner hull with balsa wood thermal insulation boxes filled with perlite.
- The other example of a LNG ship with self-supporting tanks was developed by the Moss Rosenberg company. This firm faced the problem of resistance to the stresses induced by the weight of natural gas in the tank. To solve the issue, Moss Rosenberg designed LNG tankers with 4 or 6 spherical tanks. The spheres are insulated with a layer of insulating material, a gap filled with nitrogen is passed between them to increase the insulating capacity and keep the temperature of the tank low. Each sphere is supported by a cylindrical jacket which rests on the ship’s hull; the latter is protected from any gas leaks with a secondary barrier placed at the base of the spheres.
The LNG carrier transports its LNG cargo to the regasification plant; after having been anchored and having connected to the unloading arms of the port facilities, they begin to transfer the LNG to the storage tanks.
As aforementioned, once the gas has been extracted it is refined and transported through gas or methane pipelines, into electrical systems and households.
Anyway, how does the transport of the gas extracted from the field to its final user take place? In the best out of all circumstances, which implies being a Country lucky enough to be directly connected to supplier countries, such as most European countries (including Russia), it is usually transported by land with the help of methane pipelines. Indeed, the Countries that do not have these possibilities must purchase the product from other Nations that transport natural gas by sea.
The transport of natural gas by sea is very delicate. Mind that we are talking about a product composed of 98% methane, which is highly flammable, and transporting it in large tanks installed on a ship can be particularly risky.
This is why natural gas must be brought from its gaseous state to a liquid state. Liquefied natural gas, also called LNG, is not as flammable as in the gaseous state. Moreover, the volume of the gas is reduced by 600 times, increasing the average single-journey transport capacity of LNG carriers. LNG carriers are special ships built specifically for the transport of methane and flammable gases.
Now let’s focus on the natural gas distribution and treatment chain.
After the extraction of the product, with the help of methane pipelines, the gas is transported to special plants which will proceed to liquefy it. The plants can usually be located near the coasts, in port areas, or in floating structures anchored to the seabed, which are called ‘off-shore’ plants.
The process of bringing the gas to a liquid state starts with a treatment to remove carbon dioxide and hydrogen sulphide, then a pre-cooling phase is carried out followed by the extraction of any heavy component. At this point, the gas temperature drastically drops to -163 ° C, below the boiling temperature of methane, the main component of natural gas.
Liquefied natural gas is injected through cryogenic tubes (located on loading docks) into tanks placed on LNG carriers. These particular ships can carry from 150 to 200 thousand cubic meters of methane, and they can be of two different types :
- The first example is that of a ship with integrated tanks developed by Gaztransport & Technigaz. For this type there are 2 versions: the Technigaz model is supplied with tanks consisting of an elastic primary barrier, formed by a membrane with ribs made of steel plates. The arrangement of the plates forms two sets of ribs orthogonal to each other having the function of reducing thermal stresses. The secondary barrier is made with a composite material called "triplex" consisting of an aluminum sheet in a wafer of glass fiber fabric. The tank is fixed to the inner hull with a polyurethane foam reinforced with glass fibers. The typology developed by Gaztransport instead provides two barriers consisting of flat welded planking, made of a particular metal alloy of steel and nickel, called invar. Between the two barriers there are insulating panels and air chambers, into which liquid nitrogen is injected to maintain the cryogenic temperature of the natural gas. In this case the tank is held to the inner hull with balsa wood thermal insulation boxes filled with perlite.
- The other example of a LNG ship with self-supporting tanks was developed by the Moss Rosenberg company. This firm faced the problem of resistance to the stresses induced by the weight of natural gas in the tank. To solve the issue, Moss Rosenberg designed LNG tankers with 4 or 6 spherical tanks. The spheres are insulated with a layer of insulating material, a gap filled with nitrogen is passed between them to increase the insulating capacity and keep the temperature of the tank low. Each sphere is supported by a cylindrical jacket which rests on the ship’s hull; the latter is protected from any gas leaks with a secondary barrier placed at the base of the spheres.
The LNG carrier transports its LNG cargo to the regasification plant; after having been anchored and having connected to the unloading arms of the port facilities, they begin to transfer the LNG to the storage tanks.
The regasification plants can be located in:
- port areas. Namely, on onshore plants located on the mainland;
- a platform resting on the seabed, also defined as an “offshore gravity based” plant;
- a floating storage and regasification unit (FSRU): a LNG carrier, converted for regasification, anchored to the seabed (we will cover this type of platform later in the video).
With the pumps on board of the LNG carrier, the LNG is unloaded into the tanks of the plant. Curiously, for a standard load of LNG, it takes approximately 12 hours. LNG is always stored in liquid form which is why special cryogenic tubes are adopted, which are able to manage and maintain the liquefied gas temperature of -163 ° C.
LNG is stored in double-shell tanks at atmospheric pressure. The inner shell, in contact with the LNG, is made of special varieties of steel with 9% nickel to avoid breakage problems due to low temperatures. The outer shell, on the other hand, is made of prestressed concrete. Between the interspace of the two shells there is an insulating coating and another coating on the bottom in glass foam. All LNG tanks are cylindrical in shape and rest on a base where there are seismic isolators, to avoid breakages and losses during the shocks of an earthquake for instance. The phases of filling and extracting the LNG take place on the upper part, with the aid of an immersion pump; the ceiling consists of a layer of insulation held by suspension cables and a steel cladding, covered with a reinforced concrete wall. The tanks can be buried, to have a lower visual impact, but have very high construction and maintenance costs, which is why they prefer to be installed on the surface, where costs are decidedly lower; the capacity of a tank can vary between 7,000 cubic meters and 160,000 cubic meters.
Once the LNG has been stored in the tanks, the regasification phase starts in plants that vaporize the liquefied gas. This treatment is very delicate and can be carried out with different technologies, which are distinguished according to the operating temperature, i.e. processes at room temperature and higher than ambient temperature.
An open rack vaporizer is used for the process at room temperature. Operation is very simple: inside the vaporizer there are vertical tube bundles, made of aluminium alloy and coated with a zinc alloy to prevent corrosion phenomena induced by sea salt, through which the LNG flows from bottom to top. Sea water is rained down on these pipes at room temperature, which transfers its heat to the tube bundle, allowing the vaporization of the LNG inside. Paying particular attention to the containment of substances harmful to the environment, the sea water is subsequently collected to be returned to the sea at a temperature of 4-5 ° C. This is a very proven technology in the LNG industry, used mainly in Europe, which by not using a heat source to heat the LNG allows to reduce CO2 emissions into the atmosphere.
This technology is also used on LNG carriers converted to FSRUs, or Floating Storage and Regasification Units. This particular platform allows at the same time the transport and regasification of LNG once it arrives in the unloading area near the coast. These ships vary in length from 250 to 280 meters and they are around 40 meters wide, with a capacity of approximately 140,000 cubic meters and an annual production of 2.5 / 3 million tons.
With a temperature higher than room temperature, a submerged combustion vaporizer is used for the process, let’s see together how it works: for submerged combustion systems a burner placed in a water bath, which constitutes the fluid that will heat the LNG, will do the work. A small amount of imported natural gas is used to start the precautionally preheated burner, generally 1.5%. The hot gases produced are conveyed through a distribution system inside the hot water bath, which is crossed by a tube bundle that carries the LNG that vaporizes inside the bundle itself. The vaporized gas is sent to the compression stage and to storage in spherical tanks, and then it will be injected into the transport and distribution network.
We have thus come to the end of our video. We have seen all the stages of the liquid natural gas supply chain, from liquefaction in coastal plants to its regasification with constantly evolving technologies.
- port areas. Namely, on onshore plants located on the mainland;
- a platform resting on the seabed, also defined as an “offshore gravity based” plant;
- a floating storage and regasification unit (FSRU): a LNG carrier, converted for regasification, anchored to the seabed (we will cover this type of platform later in the video).
With the pumps on board of the LNG carrier, the LNG is unloaded into the tanks of the plant. Curiously, for a standard load of LNG, it takes approximately 12 hours. LNG is always stored in liquid form which is why special cryogenic tubes are adopted, which are able to manage and maintain the liquefied gas temperature of -163 ° C.
LNG is stored in double-shell tanks at atmospheric pressure. The inner shell, in contact with the LNG, is made of special varieties of steel with 9% nickel to avoid breakage problems due to low temperatures. The outer shell, on the other hand, is made of prestressed concrete. Between the interspace of the two shells there is an insulating coating and another coating on the bottom in glass foam. All LNG tanks are cylindrical in shape and rest on a base where there are seismic isolators, to avoid breakages and losses during the shocks of an earthquake for instance. The phases of filling and extracting the LNG take place on the upper part, with the aid of an immersion pump; the ceiling consists of a layer of insulation held by suspension cables and a steel cladding, covered with a reinforced concrete wall. The tanks can be buried, to have a lower visual impact, but have very high construction and maintenance costs, which is why they prefer to be installed on the surface, where costs are decidedly lower; the capacity of a tank can vary between 7,000 cubic meters and 160,000 cubic meters.
Once the LNG has been stored in the tanks, the regasification phase starts in plants that vaporize the liquefied gas. This treatment is very delicate and can be carried out with different technologies, which are distinguished according to the operating temperature, i.e. processes at room temperature and higher than ambient temperature.
An open rack vaporizer is used for the process at room temperature. Operation is very simple: inside the vaporizer there are vertical tube bundles, made of aluminium alloy and coated with a zinc alloy to prevent corrosion phenomena induced by sea salt, through which the LNG flows from bottom to top. Sea water is rained down on these pipes at room temperature, which transfers its heat to the tube bundle, allowing the vaporization of the LNG inside. Paying particular attention to the containment of substances harmful to the environment, the sea water is subsequently collected to be returned to the sea at a temperature of 4-5 ° C. This is a very proven technology in the LNG industry, used mainly in Europe, which by not using a heat source to heat the LNG allows to reduce CO2 emissions into the atmosphere.
This technology is also used on LNG carriers converted to FSRUs, or Floating Storage and Regasification Units. This particular platform allows at the same time the transport and regasification of LNG once it arrives in the unloading area near the coast. These ships vary in length from 250 to 280 meters and they are around 40 meters wide, with a capacity of approximately 140,000 cubic meters and an annual production of 2.5 / 3 million tons.
With a temperature higher than room temperature, a submerged combustion vaporizer is used for the process, let’s see together how it works: for submerged combustion systems a burner placed in a water bath, which constitutes the fluid that will heat the LNG, will do the work. A small amount of imported natural gas is used to start the precautionally preheated burner, generally 1.5%. The hot gases produced are conveyed through a distribution system inside the hot water bath, which is crossed by a tube bundle that carries the LNG that vaporizes inside the bundle itself. The vaporized gas is sent to the compression stage and to storage in spherical tanks, and then it will be injected into the transport and distribution network.
We have thus come to the end of our video. We have seen all the stages of the liquid natural gas supply chain, from liquefaction in coastal plants to its regasification with constantly evolving technologies.