The LNG industry is a very promising developing industry for valve manufacturers around the world, but since LNG valves must meet the most stringent requirements, it represents highest level engineering problems.
What is liquefied natural gas?
Liquefied natural gas, or LNG, is ordinary natural gas liquefied by cooling it to −160 °C. In this state, it is an odorless and colorless liquid, the density of which is half that of water. Liquefied gas is non-toxic, boils at a temperature of −158...−163 °C, consists of 95% methane, and the remaining 5% includes ethane, propane, butane, nitrogen.
- The first is the extraction, preparation and transportation of natural gas through a gas pipeline to a liquefaction plant;
- The second is the processing, liquefaction of natural gas and storage of LNG in the terminal.
- Third - loading LNG into gas tankers and sea transportation to consumers
- Fourth - LNG unloading at the receiving terminal, storage, regasification and delivery to end consumers
Gas liquefaction technologies.
As mentioned above, LNG is produced by compressing and cooling natural gas. In this case, the gas decreases in volume by almost 600 times. This process is complex, multi-stage, and very energy-intensive - liquefaction costs can account for about 25% of the energy contained in the final product. In other words, you need to burn one ton of LNG to get three more.
Seven different natural gas liquefaction technologies have been used around the world at different times. Air Products is currently leading the way in technology for producing large volumes of LNG for export. Its AP-SMR™, AP-C3MR™ and AP-X™ processes account for 82% of the total market. A competitor to these processes is the Optimized Cascade technology developed by ConocoPhillips.
At the same time, small-sized liquefaction plants designed for internal use at industrial enterprises. Installations of this type can already be found in Norway, Finland and Russia.
Besides, local installations LNG production can find wide application in China, where today the production of cars powered by LNG is actively developing. The introduction of small-scale units could allow China to scale up its existing LNG vehicle transport network.
Along with stationary systems, in recent years Floating natural gas liquefaction plants are being actively developed. Floating plants provide access to gas fields that are inaccessible to infrastructure (pipelines, marine terminals, etc.).
To date, the most ambitious project in this area is a floating LNG platform, which is being built by Shell 25 km away. from the west coast of Australia (the launch of the platform is scheduled for 2016).
Construction of an LNG production plant
Typically, a natural gas liquefaction plant consists of:
- gas pre-treatment and liquefaction installations;
- technological lines for LNG production;
- storage tanks;
- equipment for loading onto tankers;
- additional services to provide the plant with electricity and water for cooling.
Where did it all start?
In 1912, the first experimental plant was built, which, however, was not yet used for commercial purposes. But already in 1941, large-scale production of liquefied natural gas was established for the first time in Cleveland, USA.
In 1959, the first delivery of liquefied natural gas from the USA to the UK and Japan was carried out. In 1964, a plant was built in Algeria, from where regular tanker transportation began, in particular to France, where the first regasification terminal began operating.
In 1969, long-term supplies began from the USA to Japan, and two years later - from Libya to Spain and Italy. In the 70s, LNG production began in Brunei and Indonesia; in the 80s, Malaysia and Australia entered the LNG market. In the 1990s, Indonesia became one of the main producers and exporters of LNG in the Asia-Pacific region - 22 million tons per year. In 1997, Qatar became one of the LNG exporters.
Consumer properties
Pure LNG does not burn, does not ignite or explode on its own. In open space normal temperature The LNG returns to a gaseous state and quickly mixes with air. When evaporating, natural gas can ignite if it comes into contact with a flame source.
For ignition it is necessary to have a gas concentration in the air of 5% to 15% (volume). If the concentration is less than 5%, then there will not be enough gas to start a fire, and if more than 15%, then there will be too little oxygen in the mixture. To be used, LNG undergoes regasification - evaporation without the presence of air.
LNG is considered a priority or important natural gas import technology by a number of countries, including France, Belgium, Spain, South Korea and the United States. The largest consumer of LNG is Japan, where almost 100% of gas needs are covered by LNG imports.
Motor fuel
Since the 1990s, various projects have emerged for the use of LNG as a motor fuel in water, rail and even road transport, most often using converted gas-diesel engines.
There are already actual working examples of the operation of sea and river vessels using LNG. In Russia, serial production of the TEM19-001 diesel locomotive running on LNG is being established. In the USA and Europe, projects are emerging to convert truck transport to LNG. And there is even a project to develop a rocket engine that will use LNG + liquid oxygen as fuel.
Engines running on LNG
One of the main challenges associated with the development of the LNG market for the transport sector is to increase the number of vehicles and ships using LNG as fuel. The main technical issues in this area are related to the development and improvement various types engines running on LNG.
Currently, three technologies of LNG engines used for marine vessels can be distinguished: 1) spark ignition engine with a lean fuel-air mixture; 2) dual-fuel engine with ignition diesel fuel and working gas low pressure; 3) dual fuel engine with ignition diesel fuel and high pressure working gas.
Spark ignition engines only run on natural gas, while dual-fuel diesel-gas engines can run on diesel, CNG and heavy fuel oil. Today there are three main manufacturers in this market: Wärtsilä, Rolls-Royce and Mitsubishi Heavy Industries.
In many cases, existing diesel engines can be converted to dual-fuel diesel/gas engines. Such conversion of existing engines may be an economically feasible solution for converting marine vessels to LNG.
Speaking about the development of engines for the automotive sector, it is worth noting the American company Cummins Westport, which has developed a line of LNG engines designed for heavy trucks. In Europe, Volvo has launched a new 13-liter dual-fuel engine running on diesel and CNG.
Notable CNG engine innovations include the Compact Compression Ignition (CCI) Engine developed by Motiv Engines. This engine has a number of advantages, the main one of which is a significantly higher thermal efficiency than existing analogues.
According to the company, the thermal efficiency of the developed engine can reach 50%, while the thermal efficiency of traditional gas engines is about 27%. (Using US fuel prices as an example, a truck with a diesel engine costs $0.17 per horsepower/hour to operate, a conventional CNG engine costs $0.14, and a CCEI engine costs $0.07).
It's also worth noting that, as with marine applications, many diesel truck engines can be converted to dual-fuel diesel-LNG engines.
LNG producing countries
According to 2009 data, the main countries producing liquefied natural gas were distributed in the market as follows:
The first place was occupied by Qatar (49.4 billion m³); followed by Malaysia (29.5 billion m³); Indonesia (26.0 billion m³); Australia (24.2 billion m³); Algeria (20.9 billion m³). Last on this list was Trinidad and Tobago (19.7 billion m³).
The main importers of LNG in 2009 were: Japan (85.9 billion m³); Republic of Korea (34.3 billion m³); Spain (27.0 billion m³); France (13.1 billion m³); USA (12.8 billion m³); India (12.6 billion m³).
Russia is just beginning to enter the LNG market. Currently, only one LNG plant, Sakhalin-2, operates in the Russian Federation (launched in 2009, the controlling stake belongs to Gazprom, Shell has 27.5%, Japanese Mitsui and Mitsubishi - 12.5% and 10%, respectively). At the end of 2015, production amounted to 10.8 million tons, exceeding the design capacity by 1.2 million tons. However, due to falling prices on the world market, revenues from LNG exports in dollar terms decreased by 13.3% year-on-year to $4.5 billion.
There are no prerequisites for an improvement in the situation on the gas market: prices will continue to fall. By 2020, five LNG export terminals with a total capacity of 57.8 million tons will be put into operation in the United States. A price war will begin on the European gas market.
The second major player in the Russian LNG market is Novatek. Novatek-Yurkharovneftegaz (a subsidiary of Novatek) won the auction for the right to use the Nyakhartinsky site in the Yamal-Nenets Autonomous Okrug.
The company needs the Nyakhartinsky site for the development of the Arctic LNG project (Novatek’s second project focused on the export of liquefied natural gas, the first is Yamal LNG): it is located in close proximity to the Yurkharovskoye field, which is being developed by Novatek-Yurkharovneftegaz. The area of the plot is about 3 thousand square meters. kilometers. As of January 1, 2016, its reserves were estimated at 8.9 million tons of oil and 104.2 billion cubic meters of gas.
In March, the company began preliminary negotiations with potential partners about the sale of LNG. The company's management considers Thailand to be the most promising market.
Transportation of liquefied gas
Delivery of liquefied gas to the consumer is a very complex and labor-intensive process. After liquefying the gas at plants, LNG enters storage facilities. Further transportation is carried out using special vessels - gas carriers equipped with cryocankers. It is also possible to use special vehicles. Gas from gas carriers arrives at regasification points and is then transported via pipelines .
Tankers are gas carriers.
A gas tanker, or methane carrier, is a purpose-built vessel for transporting LNG in tanks. In addition to gas tanks, such vessels are equipped with refrigeration units for cooling LNG.
The largest manufacturers of vessels for transporting liquefied natural gas are Japanese and Korean shipyards: Mitsui, Daewoo, Hyundai, Mitsubishi, Samsung, Kawasaki. It was at Korean shipyards that more than two-thirds of the world's gas carriers were built. Modern tankers of the Q-Flex and Q-Max series capable of transporting up to 210-266 thousand m3 of LNG.
The first information about the transportation of liquefied gases by sea dates back to 1929-1931, when the Shell company temporarily converted the tanker "Megara" into a vessel for transporting liquefied gas and built the vessel "Agnita" in Holland with a deadweight of 4.5 thousand tons, intended for simultaneous transportation oil, liquefied gas and sulfuric acid. Shell tankers were named after seashells- they were traded by the father of the company founder Marcus Samuel
Maritime transportation of liquefied gases became widespread only after the end of the Second World War. Initially, ships converted from tankers or dry cargo ships were used for transportation. The accumulated experience in the design, construction and operation of the first gas carriers allowed us to move on to the search for the most profitable methods of transporting these gases.
Modern standard LNG tanker (methane carrier) can transport 145-155 thousand m3 of liquefied gas, from which about 89-95 million m3 of natural gas can be obtained as a result of regasification. Due to the fact that methane carriers are extremely capital intensive, their downtime is unacceptable. They are fast, the speed of a sea vessel transporting liquefied natural gas reaches 18-20 knots, compared to 14 knots for a standard oil tanker.
In addition, LNG loading and unloading operations do not take much time (on average 12-18 hours). In the event of an accident, LNG tankers have a double-hull structure specifically designed to prevent leaks and ruptures. The cargo (LNG) is transported at atmospheric pressure and a temperature of -162°C in special thermally insulated tanks inside the internal hull of the gas carrier.
A cargo storage system consists of a primary container or reservoir for storing liquid, a layer of insulation, a secondary containment designed to prevent leakage, and another layer of insulation. If the primary tank is damaged, the secondary casing will prevent leakage. All surfaces in contact with LNG are made of materials resistant to extremely low temperatures.
Therefore, the materials typically used are stainless steel, aluminum or Invar (an iron-based alloy with a nickel content of 36%).
A distinctive feature of Moss-type gas carriers, which currently make up 41% of the world's methane carrier fleet, are self-supporting spherical tanks, which are usually made of aluminum and attached to the ship's hull using a cuff along the equator of the tank.
57% of gas tankers use triple membrane tank systems (GazTransport system, Technigaz system and CS1 system). Membrane designs use a much thinner membrane that is supported by the walls of the housing. The GazTransport system includes primary and secondary membranes in the form of flat Invar panels, while in the Technigaz system the primary membrane is made of corrugated stainless steel.
In the CS1 system, invar panels from the GazTransport system, which act as the primary membrane, are combined with three-layer Technigaz membranes (sheet aluminum placed between two layers of fiberglass) as secondary insulation.
Unlike LPG (liquefied petroleum gas) ships, gas carriers are not equipped with a deck liquefaction unit, and their engines run on fluidized bed gas. Given that part of the cargo (liquefied natural gas) supplements the fuel oil, LNG tankers do not arrive at their destination port with the same amount of LNG that was loaded on them at the liquefaction plant.
The maximum permissible value of the evaporation rate in a fluidized bed is about 0.15% of the cargo volume per day. Steam turbines are mainly used as a propulsion system on methane carriers. Despite their low fuel efficiency, steam turbines can be easily adapted to run on fluidized bed gas.
Another unique feature of LNG carriers is that they typically retain a small portion of their cargo to cool the tanks to the required temperature before loading.
The next generation of LNG tankers is characterized by new features. Despite the higher cargo capacity (200-250 thousand m3), the vessels have the same draft - today, for a ship with a cargo capacity of 140 thousand m3, a draft of 12 meters is typical due to the restrictions applied in the Suez Canal and at most LNG terminals.
However, their body will be wider and longer. The power of steam turbines will not allow these larger vessels to develop sufficient speed, so they will use a dual-fuel gas-oil diesel engine developed in the 1980s. In addition, many LNG carriers currently on order will be equipped with an onboard regasification unit.
Gas evaporation on methane carriers of this type will be controlled in the same way as on ships carrying liquefied petroleum gas (LPG), which will avoid cargo losses during the voyage.
Market for maritime transportation of liquefied gas
LNG transportation involves its sea transportation from gas liquefaction plants to regasification terminals. As of November 2007, there were 247 LNG tankers in the world with a cargo capacity of over 30.8 million m3. The LNG trade boom has ensured that all vessels are now fully occupied, compared to the mid-1980s when there were 22 vessels idled.
In addition, about 100 vessels should be put into operation by the end of the decade. The average age of the world's LNG fleet is about seven years. 110 vessels are four years or less in age, while 35 vessels range in age from five to nine years.
About 70 tankers have been in operation for 20 years or more. However, they still have a long useful life ahead of them, as LNG tankers typically have a service life of 40 years due to their corrosion-resistant characteristics. These include up to 23 tankers (small older vessels serving the Mediterranean LNG trade) that are due to be replaced or significantly modernized over the next three years.
Of the 247 tankers currently in operation, more than 120 serve Japan, South Korea and Chinese Taipei, 80 serve Europe, and the remaining vessels serve North America. The past few years have seen a phenomenal increase in the number of vessels serving trade in Europe and North America, while Far East There was only a slight increase due to stagnant demand in Japan.
Regasification of liquefied natural gas
After natural gas is delivered to its destination, the process of regasification occurs, that is, its transformation from a liquid state back into a gaseous state.
The tanker delivers LNG to special regasification terminals, which consist of a berth, a discharge rack, storage tanks, an evaporation system, installations for processing evaporation gases from tanks and a metering unit.
Upon arrival at the terminal, LNG is pumped from tankers into storage tanks in liquefied form, then the LNG is converted into a gaseous state as needed. Conversion into gas occurs in an evaporation system using heat.
In terms of capacity of LNG terminals, as well as in the volume of LNG imports, Japan is the leader - 246 billion cubic meters per year according to 2010 data. In second place is the United States, more than 180 billion cubic meters per year (2010 data).
Thus, the main task in the development of receiving terminals is primarily the construction of new units in various countries. Today, 62% of receiving capacity comes from Japan, the USA and South Korea. Together with the UK and Spain, the receiving capacity of the first 5 countries is 74%. The remaining 26% is distributed among 23 countries. Consequently, the construction of new terminals will open up new and increase existing markets for LNG.
Prospects for the development of LNG markets in the world
Why is the liquefied gas industry developing at an ever-increasing pace in the world? Firstly, in some geographical regions For example, in Asia, transporting gas by tankers is more profitable. At a distance of more than 2,500 kilometers, liquefied gas can already compete in price with pipeline gas. Compared to pipelines, LNG also has the advantages of modular expansion of supplies, and also eliminates border crossing problems in some cases.
However, there are also pitfalls. The LNG industry occupies its niche in remote regions that do not have their own gas reserves. Most LNG volumes are contracted at the design and production stage. The industry is dominated by a system of long-term contracts (from 20 to 25 years), which requires developed and complex coordination of production participants, exporters, importers and carriers. All this is seen by some analysts as a possible barrier to the growth of liquefied gas trade.
Overall, in order for liquefied gas to become a more affordable source of energy, the cost of LNG supplies must compete successfully in price with alternative fuel sources. Today the situation is the opposite, which does not negate the development of this market in the future.
Continuation:
- Part 3: Butterfly valves for cryogenic temperatures
When preparing the material, data from the following sites was used:
- lngas.ru/transportation-lng/istoriya-razvitiya-gazovozov.html
- lngas.ru/transportation-lng/morskie-perevozki-spg.html
- innodigest.com/liquefied-natural-gas-LNG-as-alta/?lang=ru
- expert.ru/ural/2016/16/novyij-uchastok-dlya-spg/
LNG carrier is a sea transport vessel transporting liquefied gases (propane, butane, methane, ammonia, etc.).
According to the types of transported gases, differing in liquefaction temperature, there are:
- gas carriers for liquefied petroleum gases(CIS), ammonia, etc. (liquefaction temperature up to 218 K);
- gas carriers- ethylene carriers for liquefying ethane, ethylene, etc. (liquefaction temperature up to 169 K);
- gasoses for liquefied natural gas (LNG) or methane carriers (liquefaction temperature up to 110 K).
According to the architectural and structural type, gas carriers are vessels with a stern arrangement of the main engine and superstructure, a double bottom, often double sides and isolated ballast tanks.
For liquefied by increasing pressure, inserted cargo tanks are used with a design pressure of usually no more than 2 MPa. They are placed both on the deck and in the holds on special foundations. The material of the tanks is carbon steel. For gas carriers with a combined gas liquefaction method, the insert tanks are thermally insulated and installed only in the holds. The material of tanks for gas with a temperature of 223K is heat-treated fine-grained unalloyed steel.
Gas, liquefied at atmospheric pressure, is transported in thermally insulated insert and membrane (semi-membrane) tanks (the membrane is a thin metal shell supported through load-bearing insulation on the inner lining of the housing). The material of the tanks (cargo temperature 218K and below) is aluminum alloys, steels alloyed with nickel and chromium, special alloys (for example, Invar containing 36% nickel).
Insert tanks have different shapes (for example, spherical, cylindrical, prismatic). LNG carriers and ethylene carriers have refrigeration units to re-liquefy cargo vapors generated during transportation. On LPG carriers, these vapors can be used as additional fuel for the main engine. To transport gas with temperatures below 236K, tanks are equipped with a secondary continuous barrier that serves as a temporary container for leaked cargo.
When transporting flammable gases, the hold space around the tank shell is filled with inert gas stored in containers or produced by the ship's installation.
Depending on the degree of danger of the cargo being transported, there are 3 degrees of structural protection for the gas carrier, with the 1st degree being the highest. Each degree characterizes the level of tank survivability and a certain distance between the cargo tanks and the outer plating. To ensure safety, gas carriers are equipped with instruments for measuring the temperature of the cargo and the ship’s hull, pressure, tank filling level, gas analyzers, etc.
Loading and unloading of gases, liquefied at ambient temperature or in a combined way, is carried out by ship booster pumps, the gas supply to which is carried out due to the pressure difference provided by the compressor in the cargo tank of the ship and the shore tank. Unloading of gas liquefied at atmospheric pressure is carried out by ships submersible pumps, and loading - by shore means.
The displacement of the gas carrier, depending on the type and method of gas liquefaction, is 15-30 thousand tons, speed is 16-20 knots. The power plant is usually diesel.
There are combined gas carriers for simultaneous transportation of liquefied gases and other bulk cargo (oil, chemicals, etc.).
development of maritime transport for the transportation of liquefied natural gas
Transporting liquefied natural gas by sea has always been only a small part of the overall natural gas industry, which requires large investments in the development of gas fields, liquefaction plants, cargo terminals and storage facilities. Once the first vessels for transporting liquefied natural gas were built and proved to be quite reliable, changes in their design and the resulting risks were undesirable for both buyers and sellers, who were the main persons of the consortiums.
Shipbuilders and shipowners also did not show much activity. The number of shipyards being built to transport liquefied natural gas is small, although Spain and China have recently announced their intentions to begin construction.
However, the situation on the liquefied natural gas market has changed and continues to change very quickly. There were many people who wanted to try themselves in this business.
In the early 1950s, technological developments made it possible to transport liquefied natural gas over long distances by sea. The first ship to transport liquefied natural gas was a converted bulk carrier " Marlin Hitch", built in 1945, in which aluminum tanks with external balsa insulation stood freely. was renamed to " Methane Pioneer"and in 1959 made its first flight with 5000 cubic meters. meters of cargo from the USA to the UK. Despite the fact that the water that penetrated into the hold wetted the balsa, the ship operated for quite a long time until it began to be used as a floating storage facility.
The world's first gas carrier "Methane Pioneer"
In 1969, the first dedicated liquefied natural gas vessel was built in the UK for voyages from Algeria to England, called the Methane Princess». Gas carrier had aluminum tanks, a steam turbine, in the boilers of which it was possible to utilize boiled-off methane.
gas carrier "Methane Princess"
Technical data of the world's first gas carrier "Methane Princess":
Built in 1964 at the shipyard " Vickers Armstong Shipbuilders» for the operator company « Shell Tankers UK»;
Length - 189 m;
Width - 25 m;
Power plant - steam turbine, 13750 hp;
Speed - 17.5 knots;
Cargo capacity - 34500 cubic meters. m methane;
Dimensions gas carriers have changed little since then. In the first 10 years of commercial activity, they increased from 27,500 to 125,000 cubic meters. m and subsequently increased to 216,000 cubic meters. m. Initially, the flared gas was free of charge for shipowners, since due to the lack of gas supply gas, it had to be released into the atmosphere, and the buyer was one of the parties to the consortium. Delivering as much gas as possible was not the main goal as it is today. Modern contracts include the cost of burned gas, and this falls on the shoulders of the buyer. For this reason, the use of gas as fuel or its liquefaction have become the main reasons for new ideas in shipbuilding.
design of cargo tanks of gas carriers
gas carrier
First ships for transportation of liquefied natural gas had cargo tanks of the Conch type, but they were not widely used. A total of six ships with this system were built. It was based on prismatic self-supporting tanks made of aluminum with balsa insulation, which was later replaced by polyurethane foam. When building large vessels up to 165,000 cubic meters. m, they wanted to make cargo tanks from nickel steel, but these developments never came to fruition, as cheaper projects were proposed.
The first membrane containers (tanks) were built on two gas carrier ships in 1969. One was made of 0.5 mm thick steel, and the other was made of 1.2 mm thick corrugated stainless steel. Perlite and PVC blocks for stainless steel were used as insulating materials. Further developments in the process changed the design of tanks. The insulation was replaced with balsa and plywood panels. The second stainless steel membrane was also missing. The role of the second barrier was played by triplex aluminum foil, which was covered with glass on both sides for strength.
But the most popular tanks were the MOSS type. The spherical containers of this system were borrowed from ships transporting petroleum gases and quickly became widespread. The reasons for this popularity are self-sustaining, cheap insulation and construction separate from the vessel.
The disadvantage of a spherical tank is the need to cool a large mass of aluminum. Norwegian company Moss Maritime"the developer of MOSS type tanks, proposed replacing the internal insulation of the tank with polyurethane foam, but this has not yet been implemented.
Until the end of the 1990s, the MOSS design was dominant in the construction of cargo tanks, but in recent years, due to price changes, almost two thirds of those ordered gas carriers have membrane tanks.
Membrane tanks are built only after launching. This is a fairly expensive technology and also takes quite a bit long time built 1.5 years.
Since the main objectives of shipbuilding today are to increase cargo capacity with unchanged hull dimensions and reduce the cost of insulation, currently three main types of cargo tanks are used for ships transporting liquefied natural gas: the spherical type of tank "MOSS", the membrane type of the "Gas" system Transport No. 96" and a membrane tank of the Technigaz Mark III system. The “CS-1” system has been developed and is being implemented, which is a combination of the above membrane systems.
MOSS type spherical tanks
Membrane tanks of the Technigaz Mark III type on the LNG Lokoja gas carrier
The design of tanks depends on the design maximum pressure and minimum temperature. Built-in tanks- are a structural part of the ship’s hull and experience the same loads as the hull gas carrier.
Membrane tanks- not self-supporting, consisting of a thin membrane (0.5-1.2 mm), which is supported through insulation fitted to the inner casing. Thermal loads are compensated by the quality of the membrane metal (nickel, aluminum alloys).
transportation of liquefied natural gas (LNG)
Natural gas is a mixture of hydrocarbons that, after liquefaction, forms a clear, colorless and odorless liquid. Such LNG is usually transported and stored at a temperature close to its boiling point, about -160C°.
In reality, the composition of LNG is different and depends on the source of its origin and the liquefaction process, but the main component is, of course, methane. Other components may be ethane, propane, butane, pentane and possibly a small percentage of nitrogen.
For engineering calculations, of course, they take physical properties methane, but for transmission, when an accurate calculation of thermal value and density is required, the actual composite composition of LNG is taken into account.
During sea crossing, heat is transferred to the LNG through the tank insulation, causing part of the cargo to evaporate, known as boil-off. The composition of LNG changes due to boil-off, as lighter components, which have a low boiling point, evaporate first. Therefore, the unloaded LNG has a higher density than that which was loaded, a lower percentage of methane and nitrogen content, but a higher percentage of ethane, propane, butane and pentane.
The flammability limit of methane in air is approximately 5 to 14 percent by volume. To reduce this limit, before loading, air is removed from the tanks using nitrogen to an oxygen content of 2 percent. In theory, an explosion will not occur if the oxygen content in the mixture is below 13 percent relative to the percentage of methane. The boiled-off vapor of LNG is lighter than air at a temperature of -110C°, and depends on the composition of the LNG. In this regard, steam will rush up above the mast and quickly dissipate. When cold vapor is mixed with the surrounding air, the vapor/air mixture will be clearly visible as a white cloud due to condensation of moisture in the air. It is generally accepted that the flammability limit of a vapor/air mixture does not extend very far beyond this white cloud.
filling cargo tanks with natural gas
gas processing terminal
Before loading, the inert gas is replaced with methane, since during cooling, the carbon dioxide included in the inert gas freezes at a temperature of -60C° and forms a white powder that clogs nozzles, valves and filters.
During purging, the inert gas is replaced by warm methane gas. This is done in order to remove all freezing gases and complete the tank drying process.
LNG is supplied from shore through a liquid manifold where it enters the stripping line. After which it is supplied to the LNG evaporator and methane gas at a temperature of +20C° is supplied through a steam line to the top of the cargo tanks.
When 5 percent methane is detected at the mast inlet, the escaping gas is sent through compressors to shore or to boilers via a gas combustion line.
The operation is considered complete when the methane content measured at the top of the load line exceeds 80 percent of the volume. After filling with methane, the cargo tanks are cooled.
The cooling operation begins immediately after the methane filling operation. For this purpose, it uses LNG supplied from shore.
The liquid flows through the cargo manifold to the spray line and then into the cargo tanks. Once the cooling of the tanks is completed, the liquid is switched to the load line to cool it. Cooling of tanks is considered complete when the average temperature, with the exception of the two upper sensors, of each tank reaches - 130C° or lower.
When this temperature is reached and the liquid level in the tank is present, loading begins. The steam generated during cooling is returned to shore using compressors or by gravity through a steam manifold.
loading of gas carriers
Before the cargo pump starts, all unloading columns are filled with liquefied natural gas. This is achieved using a stripping pump. The purpose of this filling is to avoid water hammer. Then, according to the cargo operations manual, the sequence of starting the pumps and the sequence of unloading the tanks is carried out. During unloading, sufficient pressure is maintained in the tanks to avoid cavitation and to have good suction at the cargo pumps. This is achieved by supplying steam from the shore. If it is impossible to supply steam to the ship from shore, it is necessary to start the ship's LNG evaporator. Unloading is stopped at pre-calculated levels, taking into account the remainder necessary to cool the tanks before arriving at the loading port.
After stopping the cargo pumps, the unloading line is drained and the steam supply from the shore is stopped. The coastal stander is purged using nitrogen.
Before leaving, the steam line is purged with nitrogen until the methane content is no more than 1 percent of the volume.
gas carrier protection system
Before commissioning gas carrier, after docking or long-term parking, cargo tanks are drained. This is done in order to avoid the formation of ice during cooling, as well as to avoid the formation of aggressive substances if moisture combines with some components of the inert gas, such as oxides of sulfur and nitrogen.
gas carrier tank
Drying of tanks is carried out with dry air, which is produced by an inert gas installation without the process of burning fuel. This operation takes about 24 hours to reduce the dew point to - 20C. This temperature will help avoid the formation of aggressive agents.
Modern tanks gas carriers designed with minimal risk of load sloshing. Ship tanks are designed to limit the force of liquid impact. They also have a significant margin of safety. However, the crew is always mindful of the potential risk of cargo sloshing and possible damage to the tank and equipment within it.
To avoid sloshing of the cargo, the lower liquid level is maintained at no more than 10 percent of the tank length, and the upper level at least 70 percent of the tank height.
The next measure to limit sloshing of the load is to limit the movement gas carrier(rolling) and those conditions that generate splashing. The amplitude of splashing depends on the state of the sea, the list and speed of the vessel.
further development of gas carriers
LNG tanker under construction
Shipbuilding company " Kvaerner Masa-Yards» production started gas carriers type "Moss", which significantly improved economic performance and became almost 25 percent more economical. New generation gas carriers allows you to increase the cargo space with the help of spherical expanded tanks, not to burn evaporated gas, but to liquefy it using a compact UPSG and significantly save fuel using a diesel-electric installation.
The principle of operation of the gas treatment unit is as follows: methane is compressed by a compressor and sent directly to the so-called “cold box”, in which the gas is cooled using a closed refrigeration loop (Brayton cycle). Nitrogen is the working cooling agent. The cargo cycle consists of a compressor, a cryogenic plate heat exchanger, a liquid separator and a methane recovery pump.
The evaporated methane is removed from the tank by an ordinary centrifugal compressor. Methane vapor is compressed to 4.5 bar and cooled at this pressure to approximately - 160C° in a cryogenic heat exchanger.
This process condenses hydrocarbons into a liquid state. The nitrogen fraction present in the steam cannot be condensed under these conditions and remains in the form of gas bubbles in liquid methane. The next separation phase occurs in the liquid separator, from where liquid methane is discharged into the tank. At this time, nitrogen gas and partially hydrocarbon vapors are released into the atmosphere or burned.
Cryogenic temperature is created inside the “cold box” by the cyclic compression-expansion method of nitrogen. Nitrogen gas with a pressure of 13.5 bar is compressed to 57 bar in a three-stage centrifugal compressor and is cooled with water after each stage.
After the last cooler, the nitrogen goes to the “warm” section of the cryogenic heat exchanger, where it is cooled to -110C°, and then expanded to a pressure of 14.4 bar in the fourth stage of the compressor - the expander.
The gas leaves the expander at a temperature of about -163C° and then enters the “cold” part of the heat exchanger, where it cools and liquefies the methane vapor. The nitrogen then passes through the "warm" part of the heat exchanger before being suctioned into the three-stage compressor.
The nitrogen expansion unit is a four-stage integrated centrifugal compressor with one expansion stage and promotes compact installation, reduced cost, improved cooling control and reduced energy consumption.
So, if anyone wants to gas carrier leave your resume and as they say: “ Seven feet under keel».
Which is designed for the transportation of liquefied natural gas and is undoubtedly considered the best in technical equipment gas carrier, type Liquefied Natural Gas Carrier (LNGC) « British Emerald» . It became the flagship of a series of four ships of the same type in the British tanker fleet: "British Ruby", "British Sapphire" and "British Diamond".
Gas carriers owned by a British company BP Shipping Limited", which plays a leading role in the global natural gas market, offering innovative methods in delivering such a valuable resource to customers.
All built in 2008 at the shipyard " Hyundai Heavy Industries"in South Korea. When developing the vessel design, engineers were guided by the principles of efficiency and safety.
The first principle was realized thanks to the new concept DFDE (dual-fuel diesel-electric), which means two fuels in one diesel-electric installation. DFDE technology allows engines to use transported gas vapor as fuel, and in addition diesel fuel as standard. This technology is not new, but it has not been used on such devices before. This innovation gives gas carrier uniqueness. The new electromechanical system is more expensive to install, but within a year it pays for itself due to its high efficiency gas carrier.
This principle makes it possible to significantly reduce the cost of diesel fuel, which is used on ships of this class, and also reduce emissions harmful substances into the atmosphere. Safety gas carrier was primarily achieved through the double hull.
largest gas carrier in the world
gas carrier British Emerald
gas carrier "British Diamond"
LNG carrier "British Sapphire"
gas carrier "British Ruby"
gas carrier tank
LNG carrier "British Emerald" in the terminal
Secondly, on gas carrier a system is provided that cools the gas in containers to a temperature of - 160 degrees Celsius, thereby transforming it into a liquid state, therefore reducing the volume in a ratio of 600:1 and volatility, which makes it possible to transport gas more profitably and safely. This system made it possible to free up space, which was used in the process to increase the usable volume. In addition, the hull showed high hydrodynamic characteristics, which significantly reduced water resistance.
Four gas supertankers can easily enter 44 ports and more than 50 terminals around the world. They replace eight previous "peers".
Technical data of the gas carrier "British Emerald":
Length - 288 m;
Width - 44 m;
Draft - 11 m;
Deadweight - 102064 tons;
Marine propulsion system- four diesel-electric engines " Wartsila»;
Speed - 20 knots;
Cruising range - 26,000 miles;
Crew - 29 people;
Vessels over 300 meters long to transport liquefied natural gas will be able to cut through ice up to 2 meters thick.
Until factories are built on the Moon or Mars, it will be difficult to find a less hospitable industrial enterprise than Yamal LNG is a $27 billion natural gas processing plant located in Russia 600 kilometers north of the Arctic Circle.
In winter, when the sun does not appear for more than two months, temperatures here reach -25 on land and -50 in the blinding fog of the sea. But this desert contains a lot of fossil fuels, about 13 trillion cubic meters, which is equivalent to about 8 billion barrels of oil.
Therefore, Yamal LNG, controlled by a Russian natural gas producer Novatek, brought together partners to spend an unprecedented amount on a new type of fuel transportation.
Conventional tankers are still unable to break through the Arctic ice of the Kara Sea, despite its melting due to global warming. Using small icebreaking vessels as tanker escorts remains extremely costly and labor intensive. That's why international cooperation naval designers, engineers, builders and owners plan to spend $320 million to create at least 15 three-hundred-meter tankers capable of independently breaking through ice.
The ship will have to perform its tasks in extremely harsh conditions,” Bloomberg said Mika Hovilainen, icebreaker specialist in Aker Arctic Technology Inc., a Helsinki-based company engaged in ship design. “Its systems must operate correctly over a very wide temperature range.
These tankers are the largest gas carriers ever built, measuring 50 meters in width. When fully loaded, each can carry just over 1 million barrels of oil. All 15 will be able to transport 16.5 million tons of liquefied natural gas per year - enough to supply half of South Korea's annual consumption and close to the capabilities of Yamal LNG. They will travel west to Europe in winter and east to Asia in summer, passing through two meters of ice.
Icebreakers do not break ice, as many people think. Ship hulls are designed to bend the edge of the ice cap and distribute the weight evenly across its entire surface. When moving in ice, the tanker uses its stern section, which is specially adapted for grinding thick ice.
Tests of the first tanker took place in December last year. When moving stern first in thick ice, its speed was 7.2 knots (13.3 km/h). This is the first ship of this type to sail along the Northern Sea Route from Siberia to the Bering Strait in 6.5 days.
Building such ships is part of a much larger game. “This is perhaps the biggest step forward in the development of the Arctic,” said the Russian President Vladimir Putin in December at the launch of the first gas tanker at the Yamal LNG plant. Talking about the 18th century poet's prediction Mikhail Lomonosov On the expansion of Russia and Siberia, Putin emphasized: “Now we can safely say that Russia will expand through the Arctic in this and the next century. The largest mineral reserves are located here. This is the site of the future transport artery – the Northern Sea Route, which, I am sure, will become very effective.”
In order to cut through the ice, enormous effort is required, which is why the tankers received three natural gas generators with a capacity of 15 megawatts. Any one of these vessels can “charge” about 35 thousand standard American homes.
To avoid excessive work of generators, a special thruster produced by the Swedish-Swiss engineering giant ABB Ltd., disconnects the engines from the propellers. That is, the propellers can spin faster or slower without causing the engine to howl, says Peter Terwiesch, President of ABB's Industrial Automation Division. Separating the engine and propeller workload improves fuel efficiency by 20 percent, he said. As a bonus, “you get much better maneuverability,” Terwiesch says. Operating a supertanker has never been so easy.
Although liquefied natural gas tankers have been sailing for about half a century, ferrying fuel from the arid Middle East, until the last decade there was no need for special "ice" models, when the Norwegian Snohvit and Russian project "Sakhalin-2" for the first time began gas production in colder climates. Yamal LNG Port, Sabetta, was designed and built in tandem with the ships that would serve it.
The second reason why the creation of massive icebreaker tankers became economically feasible is the tremendous climate pollution. The Russian half of the Arctic is becoming navigable much faster than the American-Canadian side.
Carriers chartered to Yamal LNG are expected to have a service life of 40 years. So they are likely to still be at sea in the 2040s, when climate scientists predict the Arctic will be ice-free during the summer. “Further development of the Arctic and its resources is inevitable,” says Keith Haynes Professor of Meteorology at the University of Reading, studying Arctic shipping.
Translation Stanislav Prygunov, especially for BV