CN110958989A

CN110958989A - Device for producing and distributing nitrogen, in particular for a liquefied gas vessel

Info

Publication number: CN110958989A
Application number: CN201880048321.5A
Authority: CN
Inventors: F.隆巴德
Original assignee: Gaztransport et Technigaz SA
Current assignee: Gaztransport et Technigaz SA
Priority date: 2017-07-19
Filing date: 2018-05-29
Publication date: 2020-04-03
Also published as: WO2019015836A1; RU2020103348A; FR3069237B1; KR102634055B1; SG11202000142UA; RU2756674C2; RU2020103348A3; KR20200029508A; FR3069237A1

Abstract

An apparatus (410) for the production and distribution of nitrogen, in particular for liquid gas transport vessels, comprising: -nitrogen generators (412), each comprising an air inlet (412a) and a nitrogen outlet (412b), at least one of the generators (412) comprising a compressor (426) with an air compression rotor; -a buffer tank (414) for storing nitrogen, characterized in that the apparatus comprises at least one system (464) for varying the frequency or speed of the rotor of the at least one generator with compressor, and in that the apparatus further comprises a primary nitrogen distribution means (416b) for distributing nitrogen exiting from the at least one generator with compressor without passing through the buffer tank, for supplying nitrogen to at least two different consumers (418, 420, 422).

Description

Device for producing and distributing nitrogen, in particular for a liquefied gas vessel

Technical Field

The present invention relates to an apparatus and method for producing and distributing nitrogen, particularly for liquid gas transport vessels.

Background

Transport vessels for liquid gases such as liquefied natural gas are often equipped with devices for generating and distributing nitrogen gas that can be used by a plurality of consumers.

In the present application, a "consumer", in particular a consumer of nitrogen, refers to a system operating with nitrogen or designed to be supplied with nitrogen.

For example, a transport vessel is equipped with three types of nitrogen gas consumers.

A first type (type I) of nitrogen consumer comprises means for supplying nitrogen to a seal, for example a seal of a bearing of a ship compressor. The compressors of ships, for example for pumping boil-off gas, are equipped with sliding bearings for guiding the rotating parts. These bearings are housed in a housing whose labyrinth-seal seals are supplied with nitrogen to prevent outside air from contaminating the housing and disrupting the operation of the bearings.

A second type (type II) of nitrogen gas consumer comprises means for purging a fluid flow line, such as a liquid gas flow line of a ship. In order to clean this type of line and prevent liquid gas from remaining therein, it is known to purge the line with nitrogen.

A third type (type III) of nitrogen gas consumer comprises means for supplying nitrogen gas to an insulated space, such as a liquid gas storage tank on a ship. In fact, this type of tank is equipped with a double wall defining an insulating space supplied with nitrogen.

The nitrogen requirement varies depending on the type of consumer. To be generally comprised between 25 and 70Nm³Flow in the range of/hA type I consumer was continuously supplied with nitrogen at a rate and relatively high pressure of about 5 barg. The continuous supply is due to the fact that nitrogen gas must be continuously supplied to the seal.

Type II consumers are supplied with nitrogen at a considerable flow rate but typically intermittently at a relatively high pressure of about 5 barg.

To be generally comprised between 100 and 200Nm³A considerable flow rate in the/h range and a relatively low pressure of the order of a few mbarg supply nitrogen to type III consumers. The supply is carried out during short and infrequent periods, in particular during the cooling operation before filling the tank with liquid gas.

In the prior art, the apparatus for producing and generating nitrogen comprises: two nitrogen generators, each nitrogen generator comprising an air inlet and a nitrogen outlet; a nitrogen storage buffer tank; and a nitrogen gas distribution device designed to supply nitrogen gas to the consumers.

The generators are placed in parallel and configured to operate in either an all-or-nothing mode (also referred to as start and stop). There are two generators, a main generator and a relay generator, to ensure redundancy and to ensure that the buffer tank is filled with nitrogen when the demand of the consumer for nitrogen is high. The generators are oversized, i.e. they are each configured to be able to provide a nitrogen flow sufficient to supply the largest nitrogen consumer in terms of output, i.e. a type III consumer.

The buffer tank is designed to store the nitrogen produced and supply it to the consumers as required. The generator is typically controlled so that the nitrogen pressure in the buffer tank reaches a maximum. When the nitrogen is consumed and the pressure of the nitrogen in the buffer tank decreases, at least one of the command generators generates nitrogen and increases the pressure in the buffer tank to a maximum pressure value.

However, this technique has drawbacks.

As mentioned previously, the consumption curve of the type I consumer is stable and constant, not suitable for the cyclic operation of the buffer tank and of the nitrogen generator.

This operation imposes a large number of start and stop operating cycles on the generator (about 2000 per year for ships), which shortens the life of the generator and requires frequent maintenance operations.

The present invention represents an improvement over the prior art that is simple, effective and economical.

Disclosure of Invention

According to a first aspect, the invention proposes a device for generating and distributing nitrogen, in particular for a liquefied gas transport vessel, comprising:

-nitrogen generators, each comprising an air inlet and a nitrogen outlet;

-a nitrogen storage buffer tank; and

a nitrogen distribution device designed to supply nitrogen to at least two different consumers,

characterized in that said device comprises:

-first distribution means for distributing the nitrogen exiting from the buffer tank for supplying at least one of the consumers; and

-second distribution means for distributing nitrogen exiting from at least one of said generators without passing through said buffer tank for supplying at least another one of said consumers.

The invention therefore proposes that the nitrogen produced by the generator or generators reach the second distribution device directly without passing through the tank. The first distribution device is supplied with nitrogen gas as such via a tank. Thus, there are two ways of supplying to the dispensing device, i.e. with or without a buffer tank. The tank is therefore used in a different way compared to the prior art. Conversely, the generators are not necessarily oversized and their demand may be small, which reduces the number of start and stop cycles and extends the useful life.

In this application, "nitrogen" refers to air enriched with nitrogen. At sea level, the atmosphere contains almost 78% (by volume) nitrogen, 21% (by volume) oxygen and trace amounts of other gases. Thus, in the present application, "nitrogen" refers to air that contains more than 78% nitrogen by volume, for example more than 80 or 90% by volume. The level is preferably at least 97%.

In this application, "some" generators include at least two, e.g., three generators. At least some of the generators may have common elements such as separators and/or heaters.

The device according to the invention may comprise one or more of the following features taken in isolation from each other or in combination with each other:

-said second nitrogen distributor member is directly connected to said outlet of at least one of said generators; in the present application, "direct" connection means that the connection is made only by means of a pipe (optionally equipped with a valve);

-the outlets of the generators are connected together by a manifold comprising: a first outlet connected to an inlet of the buffer tank; a second outlet connected to the second distribution means;

-the outlet of at least one of the generators is connected to the inlet of the buffer tank and the outlet of at least another one of the generators is connected to the second dispensing means; in this case, there is no fluid communication between the outlets of all the generators;

-said first distribution means is connected to said second distribution means so that the nitrogen stored in said buffer tank can supply said at least one other of said consumers;

-the outlet of at least one of the generators is connected to the inlet of the buffer tank through a valve;

-said valve is configured as a straight-through valve at all times and has a variable flow rate controlled as a function of the pressure P1 inside said buffer tank and/or as a function of the pressure P2 at the outlet of at least one of said generators and/or as a function of the pressure P3 for supplying said first and/or second distribution means;

-at least some of the inlets of the generator are connected together and to a single air supply port, and/or at least some of the outlets of the generator are connected together and to a single nitrogen outlet port;

-the consumer comprises means for supplying nitrogen to a seal, in particular to a seal of a compressor of the vessel, means for supplying to an insulation space, in particular to a tank of the vessel, and means for cleaning, in particular to a cleaning means for cleaning a supply line of the vessel;

-the generator is configured to operate in an all or nothing mode; and

the generators are identical and have dimensions such that each can supply one of the consumers individually, the consumption of which is designed to be stable and continuous in terms of flow rate.

The invention also relates to a method for producing and distributing nitrogen by means of a device as described above, comprising the following steps:

a) generating nitrogen gas by the generator; and

b) nitrogen was distributed to one of the consumers without passing through a buffer tank.

The method according to the invention may comprise one or more of the following features or steps taken in isolation of each other or in combination with each other:

-supplying nitrogen to the buffer tank during steps a) and b);

-supplying nitrogen to the buffer tanks via valves, the flow rate of nitrogen being regulated as a function of the pressure P1 inside the buffer tanks, and/or as a function of the pressure P2 at the outlet of at least one of the generators, and/or as a function of the pressure P3 for supplying the first and/or second distribution means;

-during steps a) and b), the pressure in the buffer tank is reduced.

According to a second aspect, the invention proposes a device for producing and distributing nitrogen, in particular for liquid gas transport vessels, comprising:

-nitrogen generators, each comprising an air inlet and a nitrogen outlet;

-a nitrogen storage buffer tank; and

characterized in that it comprises at least one nitrogen recirculation line, the inlet of which is connected to the nitrogen outlet of the buffer tank and the outlet of which is connected to the inlet of at least one of the generators.

The recirculation of nitrogen has several advantages. First, it may not waste the excess nitrogen generated, and thus it may be reused. By increasing the level of enrichment of nitrogen in the produced gas, the nitrogen production performance can also be optimized. In fact, the air inlet of the generator receives, in addition to the ambient air, air that has been filled with nitrogen. The recirculation also makes it possible not to stop the generator, limiting the number of start and stop cycles, if the flow rate of nitrogen produced by the generator is not very large. In other words, it is possible to prefer to operate the generator to produce nitrogen and meet the demand of the consumers, while producing excess nitrogen with the same generator, which nitrogen will be recirculated and therefore recirculated, instead of stopping the generator and supplying the consumers with nitrogen stored, for example, in a tank.

the device is configured to recirculate the nitrogen stored in the buffer tank when the pressure in the buffer tank exceeds a certain threshold;

-the recirculation line comprises at least one first valve configured with a variable flow rate controlled as a function of the pressure P1 inside the buffer tank;

-the recirculation line comprises at least one check valve;

-the recirculation line comprises at least one flow meter;

-the device comprises a control system configured to receive information from the flow meter and the pressure sensor of the buffer tank and to control the first valve and the generator accordingly;

-said second valve is configured as a straight-through valve at all times and has a variable flow rate controlled as a function of the pressure P1 inside said buffer tank and/or as a function of the pressure P2 at the outlet of at least one of said generators and/or as a function of the supply pressure P3 of said distribution means;

-the control system is further configured to control the second valve;

-at least some of the inlets of the generators are connected together and to a single air supply port connected to the outlet of the flow-through line; and/or at least some of the outlets of the generators are connected together and to a single nitrogen outlet port;

-the consumer comprises: means for supplying nitrogen to a seal, in particular to a seal of a compressor of the vessel, means for supplying an insulating space, in particular to a tank of the vessel, and ventilation means, in particular for a supply line of the vessel;

-the generator is configured to operate in an all or nothing mode;

a) generating nitrogen gas by the generator; and

b) the nitrogen is recirculated via the recirculation line.

-supplying nitrogen to the dispensing device in steps a) and b);

-monitoring the flow rate of nitrogen recirculation through said recirculation line and stopping at least one of said generators when the value of this flow rate exceeds a predetermined threshold.

According to a third aspect, the invention proposes a device for producing and distributing nitrogen, in particular for liquid gas transport vessels, comprising:

-nitrogen generators, each comprising an air inlet and a nitrogen outlet, at least one of these generators comprising a compressor with an air compression rotor;

-a nitrogen storage buffer tank; and

characterized in that said device comprises at least one system for varying the frequency or speed of said rotor.

The nitrogen production of the generator depends, inter alia, on the frequency or speed of the rotor of the compressor of the generator, and can therefore be adjusted according to the requirements of the consumer. To limit the number of start and stop cycles, for example if the demand for nitrogen is not great, the frequency of the generator rotor may be reduced rather than completely stopping the generator.

-the system is configured to be controlled according to the pressure P1 inside the buffer tank;

-at least some of said generators comprise, from upstream to downstream, i.e. from the inlet to the nitrogen outlet: the compressor; a separator of air and fluid (fluid such as water and/or oil); an air heater; and a filter membrane configured to separate nitrogen from the rest of the air; in practice, membrane separation techniques operate by retaining nitrogen and allowing the permeation of the remaining components of the air;

-the outlet of at least one of the generators is connected to an inlet of the buffer tank;

-the device comprises: first distribution means for distributing the nitrogen exiting from the buffer tank for supplying at least one of the consumers; and a second distribution means for distributing nitrogen exiting from at least one of said generators without passing through said buffer tank for supplying at least another one of said consumers;

-the change system is configured to change the frequency or speed of the rotor of the at least one generator designed to supply the second distribution means;

-the generator is configured to operate in an all or nothing mode; and

a) generating nitrogen gas by the generator; and

b) changing a frequency or speed of a rotor of at least one of the generators.

-supplying nitrogen to the buffer tank and the dispensing means simultaneously during steps a) and b).

-taking nitrogen out of the buffer tank and for supplying the distribution means of all consumers.

According to a fourth aspect, the invention proposes a device for producing and distributing nitrogen, in particular for liquid gas transport vessels, comprising:

-nitrogen generators, each comprising an air inlet and a nitrogen outlet, at least one of these generators comprising a compressor with an air compression rotor; and

-a nitrogen storage buffer tank; and

characterized in that it comprises at least one system for varying the frequency or speed of the rotor of said at least one generator with compressor and it also comprises main distribution means for distributing the nitrogen exiting from said at least one generator with compressor without passing through said buffer tank, for supplying nitrogen to at least two different consumers.

The inventors have found that at a given pressure of supplied nitrogen, the purity of molecular nitrogen increases as the flow rate decreases. Thus, for a purity of molecular nitrogen of 97% specified at the nominal flow rate, a reduction in flow rate would result in the production of excess mass of nitrogen and an excessive supply of air upstream. The variation of the frequency or speed of the rotor of the compressor of the nitrogen generator makes it possible to guarantee a sufficient nitrogen production with sufficient purity, while optimizing the air consumption of the generator.

In this case, the buffer tank is used as an additional source of nitrogen, and the generator is directly connected to the consumer and is therefore configured to supply the consumer directly.

In this application, a "primary" device for distributing nitrogen gas refers to a device designed to deliver most or all of the nitrogen gas stream produced by the generator(s) being operated. On the other hand, the "secondary" means for distributing nitrogen are designed to deliver only a small part of the nitrogen flow produced.

-said at least one generator with a compressor comprising, from upstream to downstream, i.e. from the inlet to the nitrogen outlet: the compressor, a separator of air and fluid (e.g., water and/or oil), a heater, and a filter membrane configured to separate nitrogen from the remainder of the air; in practice, membrane separation techniques operate by retaining nitrogen and allowing the permeation of the remaining components of the air;

-said single nitrogen outlet port is connected to the inlet of said buffer tank and to said main distribution means for distributing nitrogen, preferably through a valve;

-the apparatus comprises secondary distribution means for distributing the nitrogen exiting from the buffer tank for supply to at least some of the consumers;

-the primary dispensing means is connected to the secondary dispensing means through a valve;

-said primary means for distributing nitrogen directly supplies at least said means for supplying nitrogen to the seal and said means for supplying the insulating space;

-said primary means for distributing nitrogen comprise at least one pressure and/or flow rate sensor connected to the control system of said system for varying the frequency or speed;

the generators are identical and oversized, so that each generator is able to supply at least one of the consumers individually, when the generator is regulated by the change system to a load lower than 100%, the consumption of the consumers being designed to be stable and continuous in terms of flow rate.

a) generating nitrogen gas by the generator;

b) varying a frequency or speed of a rotor of the at least one generator having a compressor; and

c) at least some of the consumers are supplied without passing through the buffer tank.

-controlling the frequency or speed of the rotor of said at least one generator with compressor so that the pressure or flow rate is greater than or equal to a threshold value in said primary means for distributing nitrogen;

-a pressure threshold of 5barg in the main means for dispensing nitrogen; and

-supplying nitrogen to the buffer tank if and only if the pressure measured in the primary dispensing means is greater than the pressure threshold and the pressure measured in the buffer tank is lower than a lower limit value.

When the nitrogen flow rate required by the consumers is lower than the maximum nitrogen flow rate that the generator can produce alone, a single one of the generators can be used to produce nitrogen.

At least two generators, or all generators, may be used to generate nitrogen when the required nitrogen flow rate for the consumer is higher than the maximum nitrogen flow rate that each of these generators can generate, but the required nitrogen flow rate is lower than the maximum cumulative nitrogen flow rate that these generators can generate when operated simultaneously.

At least two generators, or all generators, can be used to generate nitrogen when the nitrogen flow rate required by the consumer is greater than the maximum cumulative nitrogen flow rate that can be generated when the generators are operating simultaneously. The buffer tank can be used to provide a supplemental nitrogen flow rate that is sufficient to meet the needs of the consumers, particularly during cooling of the tanks to which they are connected.

Advantageously, the consumers, in particular individual ones of the consumers, require a maximum nitrogen flow rate in order to cool the liquefied gas tank.

The consumer(s) may require a nitrogen flow rate for cooling of the tank without the tank having to be subjected to inerting beforehand, since the tank is supplied with nitrogen, it may be brought to a temperature higher than-40 ℃.

The consumer(s) may require a nitrogen flow rate to cool the tank after inerting the tank, and may bring the tank temperature above-10 ℃ or 0 ℃ due to the nitrogen supply to the tank.

The features of the different aspects of the invention may be combined with each other even if these combinations do not have to be described in detail in the embodiments described below.

Drawings

The invention will be better understood and other details, features and advantages thereof will become more apparent from reading the following description, given by way of non-limiting example with reference to the accompanying drawings, in which:

FIG. 1 is a schematic view of an apparatus for producing and distributing nitrogen;

FIG. 2 is a schematic view of an embodiment of an apparatus for producing and distributing nitrogen in accordance with the present invention;

fig. 3 to 5 are schematic diagrams corresponding to fig. 1, illustrating the steps of the method according to the invention;

FIG. 6 is a schematic view of a variant embodiment of the apparatus for producing and distributing nitrogen according to the present invention;

FIG. 7 is a schematic view of another variant embodiment of the apparatus for producing and distributing nitrogen according to the present invention;

FIG. 8 is a schematic view of another variant embodiment of the apparatus for producing and distributing nitrogen according to the present invention;

fig. 9 to 14 are schematic diagrams corresponding to fig. 8, illustrating steps of a method according to the invention;

FIG. 15 is a schematic diagram showing, highly schematically, the nitrogen produced by the generator of the apparatus according to the prior art, with respect to the nitrogen demand of the main nitrogen consumer;

FIG. 16 is a schematic diagram schematically illustrating nitrogen produced by generators of another plant relative to the nitrogen demand of the primary nitrogen consumer, in this case each generator having a fixed flow rate;

FIG. 17 is a schematic diagram highly schematically illustrating the generation of nitrogen by the generators of the apparatus according to the invention, in this case each having a variable flow rate, relative to the demand for nitrogen by the main nitrogen consumer; and

fig. 18 is a schematic diagram summarizing and comparing the devices in fig. 15 to 17.

Detailed Description

In the following description, the terms "upstream" and "downstream" refer to the flow of a fluid, such as a gas or a liquid, in a pipe or a circuit.

Fig. 1 shows an apparatus 10 for generating and distributing nitrogen, the apparatus 10 being particularly useful for liquid gas transport vessels.

The apparatus 10 basically includes a nitrogen generator 12, each of which includes: an air inlet 12a and a nitrogen outlet 12 b; a buffer tank 14 for storing nitrogen gas; and a distribution device 16 for distributing nitrogen, designed to supply nitrogen to the

consumers

18, 20 and 22.

There are two generators 12 mounted in parallel with their inlets 12a connected together and to a single port 24 for supplying air to the generators. Their outlets 12b are connected together by a manifold and to the inlet 14a of the buffer tank 14.

From upstream to downstream, i.e., from inlet 12a to outlet 12b, each generator 12 includes an air compressor 26, a separator 28 of air and fluid (e.g., water and/or oil), an air heater 30, and a filter membrane 32, the filter membrane 32 configured to separate nitrogen from the remainder of the air. The compressor 26 of each generator is, for example, of the type having a compression rotor. The rotor has, for example, pistons, screws or blades.

Buffer tank 14 is equipped with an overpressure valve 34, which overpressure valve 34 is configured to allow the release of nitrogen contained in tank 14 to the outside when the pressure inside tank 14 exceeds a predetermined threshold (e.g. 11 barg).

The buffer tank 14 is also equipped with a pressure sensor 36 configured to measure the pressure of nitrogen inside the tank 14, referred to as P1.

The buffer tank 14 also includes a nitrogen outlet 14b, the nitrogen outlet 14b being connected to the

consumers

18, 20 and 22 by a distribution device 16. In this case, the distribution means 16 comprises a pressure relief valve 38, 38', the inlet of which is connected to the outlet 14b and the outlet of which is connected to the

consumer

18, 20, 22. Each pressure reducing valve is configured to be supplied with nitrogen at any pressure upstream (through tank 14) and to provide a constant pressure downstream to the corresponding consumer. The valve 38 connected to the

consumers

20, 22 is configured to provide nitrogen at a known consumption pressure Pc1, for example 5 barg. Valve 38' connected to consumer 18 is configured to provide nitrogen at a known consumption pressure Pc2 (e.g., 0.5 barg).

In the example shown, the consumers 18 are of type III and comprise, for example, means for supplying nitrogen to an insulating space, for example a liquid gas storage tank of a ship. The consumer 20 is of type II and comprises means for example for cleaning a fluid flow line of a ship. The consumer 22 is of type I and comprises means for supplying nitrogen to the seals of the bearings of the ship's compressor. Types I, II and III have been described previously.

The device 10 also comprises a system 40, which system 40 controls the generator 14, in particular the compressor 26 of the generator, in particular as a function of the signal emitted by the pressure sensor 36.

One of the generators 12 is considered a primary generator and the other of the generators is considered a relay generator. Each generator is configured to operate in an all-or-nothing mode and is controlled by the system 40.

The primary generator is configured to generate nitrogen when the pressure in the tank 14, as measured by the sensor 36, is contained in the range of 6 to 9 barg. The relay generator is configured to generate nitrogen when the pressure in the tank 14 measured by the sensor 36 is comprised in the range of 5 to 8 barg. System 40 controls generator 14 according to the nitrogen demand of the consumer so that the pressure P1 in the buffer tank is at a maximum of about 10 barg. Therefore, whenWhen the nitrogen consumption drops the pressure P1 below 9bar, the system 40 activates the main generator to generate nitrogen and fill the buffer tank 14. When nitrogen consumption causes pressure P1 to drop below 8bar, system 40 activates the main and relay generators to generate nitrogen and fill buffer tank 14. This start and stop operation makes it possible to guarantee the maximum amount of nitrogen available in the buffer tank 14, but causes accelerated wear of the generators and therefore reduces their service life. These generators are also expensive because they are oversized (and identical) so that they can each be sufficient to supply the largest nitrogen consumer, i.e. the largest in terms of flow rate, i.e. the type III consumer 18. For example, they each have, for example, 150Nm at 10barg³The nitrogen making capability is/h.

Fig. 2 to 5 show a first embodiment of a device 110 according to the invention, which essentially comprises the same elements as the device 10. Accordingly, the foregoing description relating to the device 10 applies to the device 110, so long as it does not contradict the subsequent description.

In the following description, elements that have been previously described are denoted by the same reference numerals increased by one hundred.

In this case, the apparatus 110 comprises three generators 112, but it may comprise more generators. The generators 112 are mounted in parallel with their inlets 112a connected together and to a single port 124 and their outlets 112b connected together and to the inlet 114a of the surge tank 114.

In contrast to the prior art, the generator 112 is not oversized in this case. They are identical and are configured such that they can individually supply type I consumers 22 with stable consumption. In practice, each generator is preferably dimensioned so as to produce a nitrogen flow rate slightly greater than the constant nitrogen consumption flow rate of the type I consumer. For example, they each have 50Nm at 6barg³The nitrogen making capability is/h.

From upstream to downstream, i.e., from inlet 112a to outlet 112b, each generator 112 includes an air compressor 126, a separator 128 of air and fluid (e.g., water and/or oil), an air heater 130, and a filter membrane 132, the filter membrane 132 configured to separate nitrogen from the remainder of the air.

Certain elements of the generator 112 may be shared. This is the case, for example, for the separator 128 and heater 130 of the generator, as shown by the dashed rectangle in fig. 2. Thus, the device 110 may comprise a separator 128 which is common to the three generators 112 or only to two of them. In the same manner, the apparatus 110 may include a heater 130 that is common to three generators 112 or to two of the generators.

The outlet 112b of the generator 112 is connected to the inlet 14a of the buffer tank 114 via a valve 142. Upstream of the valve 142 there is provided a pressure sensor 114, which pressure sensor 114 makes it possible to measure the pressure of nitrogen, called P2, at the outlet of the generator 112. The buffer tank 114 is also equipped with two

pressure sensors

136 and 146 configured to measure the pressure P1 inside the tank. The

sensors

136, 146 may be replaced by a single sensor. The signals emitted by the

sensors

144 and 136 are designed to be received by a system 140, which system 140 controls the operation of a device 148 for controlling the valve 142. In the same manner, the signal emitted by sensor 146 is designed to be received by system 140, which system 140 controls the operation of device 150 for controlling nitrogen recirculation valve 152.

The device 110 includes a nitrogen recirculation line 154 connected at an upstream end thereof to the nitrogen outlet 114b of the canister 114 and at an opposite downstream end thereof to the inlet 112a of the generator 112.

Line 154 is equipped with valve 152 and check valve 156. It may also be equipped with a flow meter 158 whose signals are designed to be transmitted to the system 140. The flow meter 158 makes it possible to determine the amount of nitrogen produced in excess. In the event of overproduction and excessive flow rates of nitrogen gas flowing in line 154, the system 140 may command one of the generators 112 to stop when both generators are operating.

The device 150 is configured to actuate the valve 152 when the pressure in the tank 114 as measured by the sensor 146 exceeds a certain threshold (e.g., about 10 barg).

In the case of overproduction of nitrogen, line 154 allows the overproduction of nitrogen to be reused to avoid generator shutdowns, thereby limiting the number of start-up and shut-down cycles.

The buffer vessel 114 is equipped with an overpressure valve 134 and its outlet 114b is connected to the consumers of types II and III, i.e. the

consumers

118 and 120, by means of a first distribution device 116 a.

In this case, the distribution means 116a comprises a pressure relief valve 138, 138', the inlet of which is connected to the outlet 14b and the outlet of which is connected to the

consumer

118, 120.

The apparatus 110 also includes a second device 116b for dispensing nitrogen directly to a type I consumer, consumer 122. In this case, these distribution means 116b comprise a pressure relief valve 138, the inlet of which is connected to the outlet 112b of the generator 112 and the outlet of which is connected to the consumer 122.

The outlets 112b of the generators 112 are therefore connected together to form a first branch of a connection in the form of a "Y", the second branch of which is connected to the inlet 114a of the tank through a valve 142, and the third branch of which is connected to the valve 138 and the consumer 122. The direct supply to the consumers 122 requires a constant nitrogen flow rate to be maintained over a considerable period of time, so that multiple start and stop cycles of generator operation can be avoided, thereby limiting wear of the generator. Additionally, the tank 114 may employ a nitrogen storage function and have a storage pressure that varies between a minimum and maximum value, rather than just a buffer function, for which the operating pressure must be held constant.

According to a variant not shown, the consumer directly supplied by the generator 112 may be a type II consumer 120.

Fig. 3-5 illustrate the operational steps of the apparatus 110, and in particular, the steps of a method for generating and dispensing nitrogen.

The steps shown in fig. 3 represent supplying nitrogen directly to the consumer 122 and, if desired, recirculating the nitrogen.

One of the generators 112 is actuated by the system 140 and generates nitrogen at a flow rate and pressure sufficient to meet the requirements of the type I consumer 122. The nitrogen pressure is equal to 5barg downstream of the valve 138 of the device 116b and higher than 5barg upstream of the valve. Excess nitrogen generated by the generator is delivered to the buffer tank 114 through valve 142, and valve 142 is permanently left open.

In the event that the pressure of the nitrogen inside the tank 114, as measured by the sensor 146, exceeds a certain threshold (e.g. 10barg), valve 152 is opened and the nitrogen is vented from the tank to reduce its pressure and returned to the inlet 112a of the generator. Thus, this nitrogen will be reprocessed by the generator to increase the nitrogen production output of the plant, i.e. the enrichment of the nitrogen in the gas at the generator outlet.

The steps shown in fig. 4 also represent supplying nitrogen directly to the consumer 122 and, if desired, recirculating the nitrogen.

Two of the generators 112 are actuated by the system 140 and produce nitrogen at a flow rate and pressure sufficient to meet the demand of the type I consumer 122 or other consumers. The nitrogen pressure is equal to 5barg downstream of the valve 138 of the device 116b and higher than 5barg upstream of the valve. Excess nitrogen generated by the generator is delivered to the buffer tank 114 through valve 142, and valve 142 is open.

In the event that the pressure of the nitrogen gas inside the tank 114, as measured by the sensor 146, exceeds the aforementioned threshold value, the valve 152 is opened and the nitrogen gas is vented from the tank to reduce its pressure and returned to the inlet 112a of the generator.

When the consumer does not require nitrogen or requires a flow rate of nitrogen lower than that produced, the nitrogen pressure in the tank 114 increases. Above the pressure threshold, device 150 commands valve 152 to open and therefore to recirculate a portion of the nitrogen contained in the tank, in order to maintain its internal pressure at 10 barg. In the event that the flow rate of the recirculated nitrogen is below the threshold, the generator remains operational. In the event that the flow rate is greater than the threshold, the system 140 may stop one of the generators.

When the consumer requires a nitrogen flow rate that is greater than the generated nitrogen flow rate, the nitrogen pressure in the tank 114 is reduced. The system may then command the activation of the third generator 112 to prevent the pressure in the tank from reaching a minimum value, for example 1 barg. However, the device is configured such that the pressure in the tank can be lowered to such a low level, which is not the case in the prior art.

Before activating a generator, such as the third generator, the system 140 may command activation of the heater of that generator. This makes it possible to pre-heat the generator for its intended purpose.

The steps represented in fig. 5 represent the supply of nitrogen to the

consumers

118 and 122. The consumer 118 requires a higher nitrogen flow rate. This is the case in particular during cooling and filling of the liquid gas tank, since the insulation space of the tank must be supplied with nitrogen at a high flow rate and low pressure.

Two of the generators 112 are driven by the system 140 and produce nitrogen, one of which is supplied directly to the consumer 122 and the other to the buffer tank 114. In distribution device 116b, the pressure of the nitrogen is equal to 5barg downstream of valve 138 and higher than or equal to 5barg upstream of this valve. In dispensing device 116a, the pressure of the nitrogen is equal to 0.5barg downstream of valve 138' and higher than 0.5barg upstream of the valve.

Valve 142 is controlled to ensure that the pressure upstream of valve 138 of dispensing means 116b is always above 5 barg. To this end, valve 138 may be nearly closed so that all or nearly all of the nitrogen produced by the generator is supplied to the consumer 122.

In general, the valve 142 preferably remains open regardless of the operating conditions of the device 110. This allows nitrogen to be supplied to the buffer tank 114 at any time and rebalancing of the pressures upstream and downstream of the valve 142, i.e., in the nitrogen outlet manifold of the generator 112 and in the tank 114. If the flow rate of the consumed nitrogen is high and greater than the flow rate of nitrogen generated by the generator 112, the pressure in the tank will decrease. If the nitrogen consumption stops, or the consumed flow rate is lower than the supply flow rate, the pressure in the tank will increase until a maximum value is reached.

In particular, valve 142 is configured to open fully when the pressure inside the tank is above 5barg, and partially when the pressure inside the tank is less than 5barg, so that the pressure upstream of the valve is higher than or equal to 5 barg.

As a variant, the valve 142 may be replaced by a valve having two states, i.e. all or none. Thus, an additional conduit for connecting the generator outlet to the buffer tank inlet in parallel with the valve is required to ensure fluid communication between the generator outlet and the buffer tank inlet even when the valve is closed.

Fig. 6 shows a second embodiment of a device 210 according to the invention, which essentially comprises the same elements as the device 110. Accordingly, the foregoing description relating to device 110 applies to device 210 so long as it does not contradict the following description.

The embodiment in fig. 6 differs from the embodiment in fig. 2 to 5 in that the first distribution means 216a is connected to the second distribution means 216b by a bypass line 260, the bypass line 260 being equipped with a valve 262 and/or a check valve.

Bypass line 260 is configured to allow nitrogen to flow from distribution device 216a, and thus from buffer tank 114, to consumer 122. Line 260 may have an upstream end connected to distribution means 216a upstream of valves 138, 138' and a downstream end connected to distribution means 216b upstream of valve 138.

To simplify the device 210, in this case the outlets 212b of the two generators 212 are connected to the inlet 214a of the buffer tank 214 by a pipe without a valve. Device 210 also has no recirculation line, although it may include one.

In addition, the apparatus 210 includes at least one system 264 for varying the frequency or speed of the rotor of the compressor 226 of at least one of the generators 212'. System 264 can be controlled by system 240. As a variant, it can be controlled manually, the frequency or speed of the rotor being adjusted manually.

In the example shown, the system 264 is associated with a single one of the compressors, the outlet 212 b' of which is directly connected to the distribution means 216b, without being connected to the outlets 212b of the other generators. As previously described, the outlets 212b of the other two generators are connected to the inlet 214a of the tank.

Fig. 7 shows a third embodiment of a device 310 according to the invention, which comprises substantially the same elements as the device 210. Accordingly, the foregoing description relating to device 210 applies to device 310, so long as it does not contradict the following description.

The embodiment in fig. 7 differs from the embodiment in fig. 6 in particular in that the apparatus 310 comprises only a first distribution device 316a and therefore no second device for distributing nitrogen directly from the outlet 312a of the generator 312. Thus, the distribution device 316a is connected to the outlet 314b of the buffer tank 314 and to all the

consumers

318, 320 and 322 by means of pressure reducing valves 338, 338'. The generator outlets 312b are all connected together and to the buffer tank inlet 314 a.

Furthermore, the device 310 comprises means 366 for controlling the system 364, in particular controlling the system 364 depending on the pressure in the buffer tank 314 measured by the pressure sensor 346.

In the embodiment of fig. 7, the generator associated with the system 364 may be smaller in size than the other generators. This generator is for example similar to those

generators

112, 212 described previously, while the other generators may be of the type used in the prior art (generally oversized).

In general, the present invention proposes a solution to the technical problem of accelerated wear of nitrogen generators due to their all or nothing or start and stop modes of operation.

Fig. 8 to 14 show a further variant embodiment of the device 410 according to the invention, which comprises substantially the same elements as those of the device 10. Accordingly, the foregoing description relating to the device 10 applies to the device 110, so long as it does not contradict the subsequent description.

In the following description, elements that have been previously described with reference to fig. 1 are denoted by the same reference numerals increased by one hundred.

In this case, the apparatus 410 comprises two generators 412, but it may comprise more generators. The generators 412 are mounted in parallel with their inlets 412a connected together and to a single port 424 and their outlets 112b connected together.

From upstream to downstream, i.e., from inlet 412a to outlet 412b, each generator 412 includes an air compressor 426, a separator 428 of air and fluid (e.g., water and/or oil), an air heater 430, and a filter membrane 432 configured to separate nitrogen from the remainder of the air. In practice, membrane separation techniques operate by retaining nitrogen and allowing permeation of the remaining components of the air.

As previously described, certain elements of the generator 412 may be common.

The outlet 412b of the generator 412 is connected to the inlet 414a of the buffer tank 414 through a valve 442. The outlet 421b is also connected to the main device 416b for distributing nitrogen to the

consumers

418 and 422.

The direct supply to the consumers makes it possible to avoid a large number of start and stop operating cycles of the generator, thus limiting the wear of the generator. Additionally, the tank 414 may employ a nitrogen storage function and have a storage pressure that varies between a minimum and maximum value, rather than just a buffer function, for which the operating pressure must be held constant.

The outlet 414b of the buffer tank 414 is also connected by a secondary device 416a for distributing nitrogen to at least one of the consumers, in this case a type III consumer 418. The buffer tank 414 may comprise a further outlet 414c connected to a type II consumer 420.

The primary means for dispensing 416b is equipped with

pressure sensors

444a, 444b and flow rate sensor 445. A pressure sensor 444a and a flow rate sensor 445 are located just at the outlet of the generator 412, and another pressure sensor 444b is located further downstream. The

sensors

444a, 444b are configured to measure the pressures P1 and P2 of the nitrogen in the device 416 b.

The buffer tank 414 is also equipped with a pressure sensor 446a, the pressure sensor 446a being configured to measure the pressure P4 inside the tank. The secondary distribution means 416a is provided with a pressure sensor 446b, which pressure sensor 446b is configured to measure a pressure P3.

Downstream of each

consumer

418, 420, 422, the

distribution device

416a, 416b includes a pressure relief valve 438, 438' \438 ".

In the example shown, the main distributor piece 416b comprises two respective supply lines of

consumers

418, 420, 422. A first line 416b1 extends from the outlet 412b of the generator 412 to the consumer 422 and is equipped with

sensors

444a, 444b and 445 and a valve 438. The second line 416b2 extends between the first line 416b1 and the consumer 418 and is provided with a valve 438 'and a further valve 462 arranged downstream of the valve 438'. The second line 416b2 is connected to the first line 416b1 downstream of the

sensors

444a, 444b, 445 and upstream of the valve 438. The third line 416b3 extends between the first line 416b1 and the consumer 420 and is equipped with a valve 438'. Line 416b3 is connected only to outlet 414c of buffer tank 414. The secondary distribution device 416a is connected to the second line 416b2, downstream of the valve 462 and upstream of the valve 438'. These dispensing devices 416a are provided with valves 443.

The signals emitted by the

sensors

446a, 444b are designed to be received by the

control devices

448a, 448b, the

control devices

448a, 448b controlling the

valves

442 and 462 accordingly. In the same way, the signal emitted by the sensor 446b is designed to be received by the control device 448c, which controls the valve 443 accordingly.

The signals emitted by the

sensors

444a, 445 are designed to be received by the control system 440 of the system 464 for varying the frequency or speed of the rotor of the compressor 426 of each generator 412.

Thus, it will be appreciated that the speed or frequency of each compressor rotor is controlled in accordance with the pressure and/or flow rate of the nitrogen circulating in the primary distribution device 416 b.

Unlike the device 110, in the device 110, the capacity of each generator (with or without all) is slightly greater than the conventional consumers 422, in which case the capacity of the generator 412 of the device 410 is greater, so that the modification system 464 can cause the generator to operate at a reduced load ("low" operation) and meet the requirements of the conventional consumers 422. The system 464 makes it possible to increase the generator's production when the demand increases, for example due to the extra demand of the consumers 418.

"Low" operation corresponds, for example, to 6bar50Nm at g³An operating point of/h, which corresponds to about 30% to 50% of the rated capacity of the generator. This "low" operation corresponds to a steady regular consumption, i.e., meets the requirements of the consumer 422.

The maximum capacity of the generator is no longer related to the maximum demand, which remains intermittent.

Fig. 9-14 illustrate the operational steps of the apparatus 410, and in particular, the steps of a method for generating and dispensing nitrogen.

The steps shown in fig. 9 represent supplying nitrogen directly to the consumer 422 or alternatively to the consumer 418.

One of the generators 412 is actuated by the system 440 and generates nitrogen at a flow rate and pressure sufficient to meet the demand of the type I consumer 422. The nitrogen pressure is equal to 5barg downstream of valve 438 of device 116b and higher than 5barg upstream of the valve. Unlike apparatus 110, there is no longer excess nitrogen gas produced because the generator is controlled to produce any desired level. In the case of the operating rate in FIG. 9, essentially only consumer 422 is consuming. The consumer 418 can potentially consume a low flow rate or no consumption, which then passes through the open valves 462, 438'.

The compressor of the generator 412 in operation may be at a load of 30% to 50% of its nominal capacity. The load is adjusted by the system 440 according to the consumption flow rate measured by the sensor 444 a. Sensor 445 makes it possible to guarantee the operating rate and, in fact, to supply valve 438 with a pressure at least equal to 5 barg.

Valves

442 and 443 are closed. Valve 462 is fully open to meet the small nitrogen demand of the consumer 418. Valve 438' is thus open. Thus, fig. 9 shows a stable normal consumption state of the apparatus.

The steps in FIG. 10 represent an increase in the demand for nitrogen from the

consumers

422 and 418. The pressure or flow rate of nitrogen production is higher than in the previous step.

In this case, an increase in the consumption flow rate measured by sensor 444a and a pressure measured by sensor 445 indicate an increase in the flow rate. The system 440 increases the load on the compressor to meet demand.

Valves

442 and 443 are closed. Valve 462 is fully open to meet the small nitrogen demand of the consumer 418. Valve 438' is thus open.

The single generator 412 operates in step 10, as compared to the two generators in the subsequent steps shown in fig. 11, which show the device status corresponding to high consumption.

Both generators 412 are actuated by the system 440 and produce nitrogen at a flow rate and pressure sufficient to meet the demands of the

consumers

422 and 418. In this case, the consumer 418 requires a higher nitrogen flow rate. This is the case in particular during cooling and filling of the liquid gas tank, since the insulation space of the tank must be supplied with nitrogen at a high flow rate and low pressure.

After this increase in consumption, the compressor is first started to about 80% of its load, and the compressor of the second generator is started accordingly. To obtain a balanced outlet pressure, the total load is distributed to both compressors. For example, both compressors may be adjusted to approximately 40% load. In the case of "high consumption", the required flow rate is considered to be less than or equal to the total capacity of the two compressors (2 × 100%).

Valves

The consumption peak corresponds to the case where the required flow rate is greater than the total capacity of the two compressors (2 × 100%). When the consumption exceeds capacity, the supplied pressure will drop. When the pressure is close to 5barg, a buffer tank 414 will be used to complete the production of nitrogen and maintain the necessary pressure required for the consumer (fig. 12). Then, the nitrogen pressure in the tank 414 is reduced. Valve 443 opens and dispenses the stored nitrogen so as to maintain sufficient pressure upstream of valve 438'. Valve 462 is gradually closed to maintain sufficient pressure upstream of valve 438. Valve 442 remains closed. When the pressure P2 measured by sensor 444b rises again to a sufficient value, it is considered that the consumption peak has been exceeded.

The situation where the nitrogen flow rate or pressure required by the consumer is reduced (fig. 13) is similar to the situation where the flow rate or pressure is increased, as shown in fig. 11.

The steps shown in fig. 14 represent the supply of nitrogen to the consumer and buffer tank 414. Two of the generators 412 are activated by the system 440 and produce nitrogen, one of which is supplied directly to the consumer 422 and the other of which is supplied to the buffer tank 414. In the dispensing device 416b, the nitrogen pressure is equal to 5barg downstream of the valve 438 and higher than or equal to 5barg upstream of the valve. In dispensing device 416a, the nitrogen pressure is equal to 0.5barg downstream of valve 438' and higher than 0.5barg upstream of the valve.

When the consumer does not require nitrogen or requires a flow rate of nitrogen lower than that produced, the nitrogen pressure in tank 414 increases. Beyond the pressure threshold, device 448c commands valve 443 to open.

At normal operating rates, when there is no peak, the tank 414 must be kept full, preferably at the highest pressure that the generator 412 can produce, for example in the range of 10 to 12 barg. Valve 442 begins to open to allow nitrogen to be supplied to the canister to increase its pressure if and only if, for example, pressure P2 measured by sensor 444b is greater than 5barg and pressure P4 measured by sensor 446a is less than 8 barg. To obtain this maximum filling pressure of 10 to 12barg, two compressors may be used at 100%.

In any event, valve 442 is controlled to ensure that the pressure upstream of valve 438 of dispensing device 416b is always above 5 barg. To this end, valve 438 may be nearly closed so that all or nearly all of the nitrogen produced by the generator is supplied to consumer 122.

Fig. 15 illustrates the prior art of the present invention and these generators are identical and oversized, for example suitable to provide a sufficient nitrogen flow rate to supply nitrogen to the maximum consumer in terms of flow rate, i.e. type III consumer. N1 and N2 are the low and high demand levels for nitrogen by the consumers, respectively. Levels L1 and L2 are the nitrogen making capacity of the two generators G1 and G2, respectively. The capability of the first generator, L1, makes it possible to override level N1 instead of level N2. To cover level N2, it is necessary to operate both generators simultaneously and then produce a nitrogen flow rate greater than N2, which corresponds to the nitrogen flow rate (MAX) of the maximum nitrogen consumer of type III.

Fig. 16 shows a similar situation, with three generators (G1, G2 and G3) instead of two, and a buffer tank (RT). N1 and N2 are the low and high demand levels for nitrogen by the consumers, respectively. Levels L1, L2, and L3 are the nitrogen making capacity of the three generators, respectively. The capability of the first generator, L1, makes it possible to cover level N1. The accumulation capacities L1, L2 and L3 may cover the level N2. Beyond this level, the buffer tank is used to supply more nitrogen in addition to the three generators and to complete the flow rate supplied until the nitrogen flow rate (MAX) of the maximum nitrogen consumer of type III is reached.

FIG. 17 illustrates an aspect of the invention, and the apparatus includes a generator having a variable flow rate. One or more generators supply nitrogen as needed. If the demand for nitrogen is low, one of the generators is put into operation and the speed or frequency of its rotor is controlled to supply the required flow rate. If the required flow rate is greater than the maximum flow rate that a single generator can produce, then both generators are put into operation. The generators' accumulation capacities L1 and L2 are equal to N2. The buffer tank is used to intermittently supply the excess flow rate required to meet the demand, thus requiring an additional flow rate from level N2 to level MAX.

According to one embodiment of the invention, level N2 corresponds to the flow rate required by a type III consumer during cooling of the tank. The tank may be emptied and brought to a temperature above-40 ℃. The tank may be filled again with the liquid gas without performing an inerting step including injecting an inert gas into the tank to expel air. However, before that, due to the type III consumer, it was necessary to cool the water tank. The flow rate N2 therefore corresponds to the flow rate necessary for the supply of the consumer.

The maximum level MAX corresponds to the flow rate required by the same consumer during the tank that has been inerted before cooling. The tank may be emptied and brought to a temperature above-10 ℃ or 0 ℃. It may be subjected to one or more inerting steps, including the injection of an inert gas into the tank in order to evacuate the air that enters it as a result of, for example, maintenance operations carried out in the tank. The tank may be refilled with liquid gas. However, before that, due to the type III consumer, it was necessary to cool the water tank. The flow rate NMAX therefore corresponds to the flow rate necessary for the supply of the consumer.

Level N1 may correspond to a flow rate that is continuously required by one or another of the other consumers (e.g., type I consumers).

Claims

1. An apparatus (410) for the production and distribution of nitrogen, in particular for liquid gas transport vessels, comprising:

nitrogen generators (412), each nitrogen generator comprising an air inlet (412a) and a nitrogen outlet (412b), at least one of the generators (412) comprising a compressor (426) having an air compression rotor; and

a nitrogen storage buffer tank (414),

characterized in that it comprises at least one system (464) for varying the frequency or speed of the rotor of said at least one generator with compressor and in that it also comprises a main distribution means (416b) for distributing the nitrogen exiting from said at least one generator with compressor without passing through said buffer tank, for supplying nitrogen to at least two different consumers (418, 420, 422).

2. The apparatus (410) of claim 1, wherein the at least one generator with a compressor comprises, from upstream to downstream, i.e. from an inlet (412a) to an outlet (412 b): the compressor (426); a separator (428) of air and fluid, such as water and/or oil; a heater (430); and a filter membrane (432), the filter membrane (432) configured to separate nitrogen from a remainder of air.

3. The device (410) of any preceding claim, wherein at least some of the inlets (412a) of the generators (412) are connected together and to a single air supply port, and/or at least some of the outlets (412b) of the generators are connected together and to a single nitrogen outlet port.

4. The apparatus (410) of claim 3, wherein the single nitrogen outlet port is connected to an inlet (414a) of the buffer tank (114) and a primary nitrogen distribution means (416b), preferably via a valve (442).

5. An apparatus (410) according to any of the preceding claims, wherein the apparatus comprises secondary distribution means (416a) for distributing nitrogen exiting from the buffer tank (414) for supplying at least some of the consumers (418, 420, 422).

6. The apparatus (410) of any preceding claim, wherein the primary dispensing means (416b) is connected to the secondary dispensing means (416a) via a valve (462).

7. The device (410) of any one of the preceding claims, wherein the consumer (418, 420, 422) comprises: means (422) for supplying nitrogen to a seal, in particular to a seal of a compressor of said vessel; means (418) for supplying an insulation space, in particular a tank of the vessel; and a purification device (420), in particular for purifying a supply line of the vessel.

8. The device (410) according to claim 7, wherein the primary means (416b) for distributing nitrogen directly supply at least the means (422) for supplying nitrogen to the seal and the means (418) for supplying nitrogen to the insulating space.

9. The device (410) according to any one of the preceding claims, wherein the primary distribution means (416b) for distributing nitrogen comprise at least one pressure and/or flow rate sensor (470, 472) connected to a control system (440) of the system (464) for varying the frequency or speed.

10. The device (410) of any one of the preceding claims, wherein the generators (412) are identical and oversized, such that each generator is capable of individually supplying at least one of the consumers whose consumption is designed to be stable and continuous in terms of flow rate, when the generator is adjusted to a load below 100% by the change system.

11. A method of producing and distributing nitrogen gas by the apparatus (410) of any one of the preceding claims, the method comprising the steps of:

a) generating nitrogen gas by the generator (412);

b) changing a frequency or speed of a rotor of the at least one generator (412) having a compressor; and

c) supplying at least some of the consumers (418, 420, 422) without passing through the buffer tank (414).

12. The method according to claim 11, wherein the frequency or speed of the rotor of the at least one generator with compressor is controlled such that the pressure or flow rate is higher than a threshold value in the primary distribution means (416b) for distributing nitrogen.

13. A method according to claim 12, wherein the pressure threshold in the primary dispensing means (416b) for dispensing nitrogen is 5 barg.

14. Method according to any one of claims 11 to 13, wherein the buffer tank (414) is supplied with nitrogen if and only if the pressure measured in the primary distribution means (416b) is above the pressure threshold and the pressure measured in the buffer tank (414) is below a lower limit value.

15. The method of any one of claims 11 to 14,

using a single one of the generators to generate nitrogen when the nitrogen flow rate required by the consumer is less than the maximum nitrogen flow rate that the generator can generate alone;

at least two generators or all generators are used to generate nitrogen when the required nitrogen flow rate for the consumer is higher than the maximum nitrogen flow rate that each of these generators can generate, but the required nitrogen flow rate is lower than the maximum cumulative nitrogen flow rate that these generators can generate when operated simultaneously; and is

At least two generators, or all generators, are used to generate nitrogen gas when the nitrogen flow rate required by the consumers is greater than the maximum cumulative nitrogen flow rate that these generators can generate when operating simultaneously, and the buffer tank is used to provide an additional nitrogen flow rate sufficient to meet the demands of the consumers.

16. The method of claim 15, wherein the consumers, in particular individual ones of the consumers, require a maximum nitrogen flow rate to cool a liquid gas storage tank.

17. The method of claim 16, wherein one or more of the consumers require a nitrogen flow rate in order to cool the tank, the tank having not been previously inerted, the tank being capable of being brought to a temperature above-40 ℃ due to the nitrogen supply to the tank.

18. The method of claim 16, wherein one or more of the consumers require a nitrogen flow rate to cool the tank after inerting the tank and the temperature of the tank can be higher than-10 ℃ or 0 ℃ due to the tank being supplied with nitrogen.