Patent Application
20210310731
This application claims the benefit of priority under 35 U.S.C. § 119 (a) and (b) to French Patent Application No. 2003456, filed Apr. 7, 2020, the entire contents of which are incorporated herein by reference.
The technical field of the invention is that of the liquefaction of natural gas using a nitrogen refrigeration cycle.
The present invention relates to an installation of a natural gas liquefaction unit using a nitrogen refrigeration cycle and its unit.
Natural gas liquefaction methods need to be used in order to reduce the environmental impact. Market developments promote the use of liquefiers close to public areas in order to ensure more efficient management of deliveries. The available land is generally small and must meet strict environmental restrictions.
Commonly, this type of unit uses mixed coolants that are mixtures of gas with high yields for the liquefaction of natural gas. However, their hazardousness results in factory configurations that are very spread out with a very high societal risk. The invention defines the design of Natural Gas liquefiers using a nitrogen refrigeration cycle called Turbofin™.
The invention offers a solution to the aforementioned problems. An aspect of the invention relates to a natural gas liquefaction unit comprising:
According to other embodiments, the present invention also relates to:
A method for starting a liquefaction unit as defined above, comprising the following steps:
The natural gas is composed of different gases with different physical features, Nitrogen is a pure substance and does not allow all the compounds of the natural gas to be tracked for the liquefaction thereof. However, the method allows the use of the “compression-expansion” principle and therefore allows cold production with high liquefaction yields.
The method is composed of two main parts. The cold creation part identified by the name ‘nitrogen cycle’ and the natural gas liquefaction part. A nitrogen refrigeration cycle is understood to be a cycle in which the coolant is nitrogen, contrary to the cycles with mixed coolants, in which the coolant is a mixture of different constituent elements, in particular a mixture of hydrocarbons.
The nitrogen cycle is a closed loop. The natural gas only passes through the liquefaction zone, called cold box. The nitrogen of the cycle is compressed in a compressor, then cooled, before being compressed a second time, by two boosters, or booster compressors, coupled to two separate turbines.
Preferably, the output pressure of the two boosters of the turbines is identical. Contrary to the configurations in which the outputs of the cold and hot turbines have different pressures and are therefore compressed at two different stages of the cycle compressor, this allows only a single suction pressure to be processed, which simplifies the architecture of the unit and improves its operational efficiency, by simplifying the operating and maintenance operations.
The nitrogen is then pre-cooled before being expanded to create two different cold temperatures. These two latter temperatures correspond to two liquefaction temperatures. Said temperatures themselves correspond to two average temperatures for liquefaction of the gases composed of the natural gas.
Each compression stage corresponds to the heating of the gas. In order to optimize the next compression, the gas must be pre-cooled using equipment called “refrigerators”, operating by exchanging with air or with water.
The consequence of this type of liquefaction is the significant number of connections connecting the equipment to each other. This configuration results in a significant cost compared to the size of the liquefaction cycle.
The liquefaction comprises one or more exchangers, as well as, in general, an element allowing separation of the heavy C6+ type hydrocarbon components contained in the natural gas. The gas that is thus purified, basically composed of methane, is recovered in order to be liquefied through exchangers located in said cold box. The aforementioned separation equipment is located in the same insulating assembly, called cold box.
The liquefaction assembly called cold box can, as a function of the liquefaction volumes, be composed of one or more cold boxes. These can be vertical or horizontal.
The aforementioned equipment and/or sub-assemblies are located around a distribution module comprising all the connections between all the equipment that are required for the method, as well as the connections to the outside of the liquefaction assembly. AH the elements allowing the measurements and the liquefaction assembly to be controlled are also located in this sub-assembly, called central module.
The machines called turbine/booster machines may or may not be, as a function of their capacities, located on the same support structure.
Each of these satellite modules comprises the method function for which it has been identified, as well as the elements allowing it to be controlled and enabling its intrinsic safety.
The connection between the central module and the satellites is adapted for each project condition and/or for each physical variation of each of these satellite modules.
The present invention allows the interconnection zone to be defined as a central distribution module between all the method modules. This can cover the equipment associated with the method or other modules comprising method sub-assemblies. These other method or equipment sub-assemblies are those that are configured to implement method functions that are required for implementing the cold fluid required for the liquefaction of a natural gas stream. The method functions are clearly separate from each other, as well as from those that are associated with the designs of each supplier, and the interconnection allows the possibility of changing suppliers without necessarily changing the circulation of the fluids. The connections are adapted to the modules during the on-site assembly.
In order to meet this requirement, the sub-assemblies and satellite equipment are designed to be autonomous and independent from a method perspective, but also to be mechanical.
The present invention allows a natural gas liquefaction installation to be provided using a nitrogen cooling cycle that adapts to the environment in a manner that is simple and is the least expensive, By virtue of the invention, the system allows a flexible arrangement to be proposed for the installation as a function of the environment.
This also makes it possible to ensure the effectiveness of the method irrespective of the type of hydrocarbon, in particular natural gas.
This also makes it possible to guarantee construction with a manageable cost, since the modules can be constructed in the factory and delivered directly to the site, while being able to be adapted to the environment of the site.
A cold box integrates one or more heat exchangers in an insulating enclosure that is generally made of steel or of carbon. The cold box combines the exchangers with their associated cryogenic equipment: separator tanks, two-phase supply tanks, distillation columns, connection pipes, valves and instrumentation.
Therefore, the present invention allows the aforementioned problem to be resolved in at least two points:
The present invention will basically cover the cryogenic part of the method. It forms the liquefaction area thereof. In order to limit thermal losses, this part of the method is installed in an insulating box, called cold box. The temperatures vary between +20° C. to −196° C. The equipment is therefore subject to significant mechanical stresses. In order to reduce the mechanical effects, it is common to distribute the stresses over the whole of the relevant method line. The solution implemented in the present invention allows an approach for managing stresses to be provided by defining the cold box as being autonomous. The stresses inside the cold box will be managed by placing a fixed point at the limit of the cold box or by providing permissible stresses for other parts.
This installation allows the cold-part modules (heat-exchange module and separator module) to be aligned together and allows the hot part (compressor module) to be added in line with or perpendicular to this alignment, thus reducing the ground footprint and also reducing the lengths of the interconnections.
The invention and the various applications thereof will be better understood from reading the following description and from studying the accompanying FIGURES.
For a further understanding of the nature and objects for the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein:
The FIGURE shows a representation of a schematic diagram of a liquefaction system according to one embodiment of the invention.
In
The interconnection module 4 rests on a frame that allows it to be handled and is connected to the cold box in the vicinity of said assembly zone.
Advantageously, the interconnection module comprises one or more elements selected from among control valves, manual valves, valve actuators. Thus, the important elements for controlling the liquefaction assembly are arranged in the interconnection module, the assembly and the on-site handling of which are simpler and safer, which facilitates the assembly of these elements and facilitates access for maintenance. The safety of the unit is improved. In particular, one or more valves are of the Pressure Safety Valve (PSV) type. According to a particular embodiment, the unit comprises one or more pressure safety valves, all of which are arranged in the interconnection module.
The feed stream NG can be a stream of natural gas, which can be pre-treated, in which one or several substances, such as sulphur, carbon dioxide, water, are reduced, so as to be compatible with cryogenic temperatures, as is known in the prior art.
The heat exchangers are known from the prior art and can have various arrangements of their feed flows and refrigerant streams.
When the flow of liquefied, or at least partially liquefied, hydrocarbons is liquefied natural gas (LNG), the temperature can be approximately −150° C. to −160° C.
The liquefaction of the feed stream NG is carried out by virtue of a fluid or an expanded cooling nitrogen current in one or more coolant circuits for pre-cooling the feed stream NG.
A heat exchange module comprises walls for thermally insulating the heat exchanger from the outside and comprises a framework allowing the heat exchange module to be transported so that it can be fixed.
The framework can be made of stainless steel bars in order to reduce the effects of thermal diffusion. Furthermore, this framework can assume the form of a container, thus forming the edges of a rectangular parallelepiped, also referred to as a right cuboid. Thus, it is simple to transport. The framework of the heat exchange module can also comprise means for facilitating installation.
An element is understood to be a module, or a compressor, or an expansion device or a circuit of a module, or a cooler, or a separator.
Connections are understood to be a tube or pipe that may or may not be insulated and that can comprise valves or restrictors.
A stream is understood to be one or more fluids, that may be in the liquid phase or in the gaseous phase or both, circulating through elements of the system.
An inlet is understood to be a point at which the fluid enters, therefore giving the stream a direction of circulation. In other words, an inlet of a first element is connected downstream of an outlet of a second element.
An outlet is understood to mean that the fluid exits an element and therefore provides a direction of circulation for the stream. In other words, an outlet of a first element is connected upstream of an inlet of a second element.
Connected means connected for transporting a fluid, for example, an inlet connected to an element implies that a fluid can transition from the element to the inlet either directly or via other elements.
Connected is understood to mean the connection of two elements (the outlet of one element to an inlet of another element) for transporting fluid using connections or connected directly to one another (an outlet directly connected to an inlet of an element (without pipe)). In other words, there are no other elements between the two elements.
Fixed is understood to mean the physical assembly of one element to another element in order to secure them together.
An expanded stream is understood to mean the stream downstream of an expansion circuit and upstream of a compressor.
A compressed stream is understood to mean the stream upstream of an expansion circuit and downstream of a compressor.
The liquefied natural gas resulting from the method that is the subject matter of the present invention subsequently can be, for example, transferred to a storage or transportation device.
The method that is the subject matter of the present invention particularly enables the investment expenditure to be optimized. Indeed, having a modular system allows several arrangements of the modules to be proposed and thus allows the installation research costs, as well as the manufacturing cost, to be reduced.
It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus; the present invention is not intended to be limited to the specific embodiments in the examples given above.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003456 | Apr 2020 | FR | national |
