JP6631379B2 - Apparatus for separating nitrogen from BOG - Google Patents

Description

  The present invention relates to a nitrogen separation device that removes nitrogen from evaporative gas (BOG) generated from an LNG storage tank that stores LNG obtained by liquefying natural gas.

  Since LNG has a low boiling point of minus 160 ° C., evaporative gas (BOG) is inevitably generated by heat input from the surroundings even while stored in a tank. At this time, since the components having a low boiling point are preferentially evaporated, the BOG is in a state where nitrogen is concentrated.

  BOG is reliquefied and used as a fuel. However, since nitrogen does not have a property as a fuel, the calorific value of BOG containing nitrogen decreases by the amount of nitrogen. Therefore, a technique for removing nitrogen from BOG is required. For example, Patent Literatures 1 and 2 disclose techniques for separating and removing nitrogen components from BOG.

In Patent Literature 1, nitrogen is roughly separated from BOG by a membrane separation device having a separation membrane that selectively allows nitrogen to permeate, and residual nitrogen is adsorbed by an adsorbent under pressure swing of the gas processed by the membrane separation device. It is to do.
Patent Document 2 discloses that nitrogen is adsorbed from BOG by an adsorbent under a pressure swing.

JP 2015-91918 A JP 2012-144628 A

In a membrane separation method in which separation is performed by a separation membrane as in the membrane separation device in Patent Document 1, it is necessary to provide a pressure difference between the upstream side and the downstream side of the separation membrane.
In the case of performing adsorption by an adsorbent, Patent Documents 1 and 2 employ a pressure swing method in which adsorption and desorption are performed using a pressure difference.
In general, since the amount of adsorbent increases as the pressure increases, the adsorbent is adsorbed in a high pressure state and then desorbed in a low pressure state. Therefore, it is necessary to provide a pressure difference in the pressure swing method as in the case of the membrane separation.

In these membrane separation systems and pressure swing systems, when the source gas has a pressure (original pressure) (is in a high pressure state), the source gas may be directly introduced into the separation device. That is, the pressure difference between the original pressure and the atmospheric pressure can be used.
On the other hand, since the pressure of BOG is almost atmospheric pressure, when BOG is used as a raw material gas, in order to apply the membrane separation method or the pressure swing method, it is necessary to first raise the pressure with a compressor and then introduce it into a separation device. There is. Alternatively, it is necessary to introduce a vacuum pump (a kind of compressor that raises the pressure from a vacuum state to an atmospheric pressure state) into the separation device to create a pressure condition lower than the atmospheric pressure.
However, a large power is required to compress the gas. That is, when nitrogen gas is separated from BOG in an atmospheric pressure state by a membrane separation method or a pressure swing method, there is a problem that a large amount of energy is consumed.

  The present invention has been made to solve such a problem, and an object of the present invention is to provide a BOG nitrogen separation apparatus that separates nitrogen gas from BOG without increasing energy consumption.

(1) The apparatus for separating nitrogen from BOG according to the present invention is a nitrogen separator for removing nitrogen gas from BOG discharged from an LNG storage tank,
The first adsorber is filled with an adsorbent that selectively adsorbs nitrogen, as a temperature swing type adsorber for selectively adsorbing nitrogen to the adsorbent at a low temperature and desorbing the adsorbed nitrogen at a high temperature. Having a second adsorption device,
BOG discharge pipes for discharging BOG from the LNG storage tank are connected to the first adsorption device and the second adsorption device respectively via open / close valves,
The first adsorption device and the second adsorption device are provided with a heat medium flow passage for circulating a heating medium, and can be indirectly heated by the heating medium,
BOG is selectively passed from the BOG discharge pipe to the first adsorber and the second adsorber so that the first adsorber and the second adsorber can alternately adsorb and desorb nitrogen. It is characterized by the following.

(2) In the device according to the above (1), the first adsorption device and the second adsorption device flow LNG discharged from the LNG storage tank to indirectly adsorb the adsorbent in the adsorption device. A refrigerant flow path for cooling is provided, and an LNG supply pipe for supplying the discharged LNG is connected to the refrigerant flow path.

  According to the apparatus for separating nitrogen from BOG according to the present invention, there is no need to compress and pressurize the raw material gas or the separated gas, and nitrogen separation is performed by utilizing the cold energy originally possessed by BOG. An excellent effect that the energy consumption is remarkably small as compared with the nitrogen separation technology described above is obtained.

It is explanatory drawing of the nitrogen separation apparatus from BOG which concerns on this Embodiment, Comprising: The state which performs the adsorption process of nitrogen by the 1st adsorption device, and performs the desorption process of nitrogen by the 2nd adsorption device is shown. It is explanatory drawing of the nitrogen separation apparatus from BOG which concerns on this Embodiment, and has shown the state which performs the desorption process of nitrogen by the 1st adsorption device, and performs the adsorption process of nitrogen by the 2nd adsorption device.

The nitrogen separating apparatus 1 from BOG according to the present embodiment (hereinafter sometimes simply referred to as “nitrogen separating apparatus 1”) removes nitrogen from BOG discharged from LNG storage tank 3, as shown in FIG. The apparatus has two suction devices, a first suction device 5 and a second suction device 7.
The first adsorption device 5 and the second adsorption device 7 have the same structure, are filled with an adsorbent for selectively adsorbing nitrogen, selectively adsorb nitrogen on the adsorbent at a low temperature, and It is a temperature swing type adsorption device for desorbing adsorbed nitrogen.

  As an example of the structure of the temperature swing type adsorption apparatus, there is a heat exchanger in which one flow path is filled with a granular adsorbent. For example, a shell and tube type heat exchanger in which the shell side is filled with an adsorbent, or a plate and fin heat exchanger disclosed in, for example, JP-A-2003-260327, in which one flow path is filled with an adsorbent. And the like.

The first adsorption device 5 and the second adsorption device 7 are provided for alternately adsorbing and desorbing nitrogen, and therefore, the first adsorption device 5 and the second adsorption device 7 are provided with the LNG storage tank 3. A first refrigerant flow path 9 and a second refrigerant flow path 11 for distributing the discharged LNG are provided, respectively, so that the discharged LNG can indirectly cool the adsorbent (adsorption step). The first adsorption device 5 and the second adsorption device 7 are provided with a first heat medium passage 13 and a second heat medium passage 15, respectively, through which a heating medium flows. It can be heated indirectly (regeneration step).
Various piping systems and on-off valves are provided as specific modes for realizing such functions. Hereinafter, these piping systems and on-off valves will be described.

As shown in FIGS. 1 and 2, a BOG discharge pipe 17 that discharges BOG from the LNG storage tank 3 is branched into a first BOG discharge pipe 19 and a second BOG discharge pipe 21 on the way, and the first BOG discharge pipe 19 has a first BOG discharge pipe 19. The first adsorption device 5 is connected to the second BOG discharge pipe 21, and the second adsorption device 7 is connected to the second BOG discharge pipe 21.
The first BOG discharge pipe 19 is provided with a first on-off valve V1, and the second BOG discharge pipe 21 is provided with a second on-off valve V2. Although the operation of the nitrogen separator 1 will be described later, a white on-off valve indicates an "open" state, and a black on-off valve indicates a "closed" state.

The first adsorption device 5 is connected to a first gas discharge pipe 23 for discharging an adsorption treatment gas subjected to a nitrogen adsorption treatment or a regeneration gas subjected to a nitrogen gas desorption treatment.
Similarly to the first adsorber 5, the second adsorber 7 has a second gas discharge for discharging the adsorbed gas subjected to the nitrogen adsorption process or the regeneration gas subjected to the nitrogen gas desorption process. Tube 25 is connected.

  The first gas discharge pipe 23 is connected to a first adsorption processing gas discharge pipe 27 for flowing an adsorption processing gas having been subjected to nitrogen adsorption processing via a third on-off valve V3, and is connected to the second gas discharge pipe 25. Is connected to a second adsorption processing gas discharge pipe 29 through which an adsorption processing gas subjected to nitrogen adsorption processing flows through a fourth on-off valve V4.

  Further, the first gas discharge pipe 23 is connected to a first regeneration gas discharge pipe 31 for discharging a regeneration gas subjected to nitrogen gas desorption processing via a fifth on-off valve V5, and a second gas discharge pipe. A second regeneration gas discharge pipe 33 for discharging the regeneration gas subjected to the desorption process of the nitrogen gas through the sixth on-off valve V6 is connected to 25.

  A first LNG supply pipe 39 for supplying LNG as a coolant for cooling the adsorbent to the first adsorption device 5 is connected to the LNG discharge pipe 37 for discharging LNG from the LNG storage tank 3 by the pump 35. I have. The first LNG supply pipe 39 is branched from the LNG discharge pipe 37 and connected to the inlet side of the first refrigerant flow path 9 for indirectly cooling the adsorbent in the first adsorption device 5. It is connected to the outlet side and is again connected to the LNG discharging pipe 37. A seventh on-off valve V7 is provided on a pipe on the entry side of the first LNG supply pipe 39. Further, an eighth on-off valve V8 is provided between a connection part on the entrance side and a connection part on the exit side of the first LNG supply pipe 39 in the LNG discharge pipe 37.

  Similarly to the first adsorption device 5, the second adsorption device 7 is also connected to the second adsorption device 7 with a second LNG supply pipe 41 for supplying LNG as a refrigerant for cooling the adsorbent. . The second LNG supply pipe 41 branches from the LNG discharge pipe 37 and is connected to the inlet side of the second refrigerant flow path 11 that indirectly cools the adsorbent in the second adsorption device 7. It is connected to the outlet side and is again connected to the LNG discharging pipe 37. A ninth on-off valve V9 is provided in the pipe on the entry side of the second LNG supply pipe 41. In addition, a tenth on-off valve V10 is provided between the connection part on the entry side and the connection part on the exit side of the second LNG supply pipe 41 in the LNG discharge pipe 37.

Further, the first adsorber 5 is connected to the first heat medium flow path 13 of the first adsorber 5 and heat medium for indirectly heating the adsorbent (for example, seawater or air at room temperature). The first heat medium supply pipe 43 is connected to the first heat medium supply pipe 43. The first heat medium supply pipe 43 is provided with an eleventh on-off valve V11.
Similarly, the second adsorber 7 is connected to the second heat medium flow path 15 in the second adsorber 7 and heats the adsorbent indirectly (for example, seawater or air at room temperature). ) Is connected to the second heat medium supply pipe 45, and the second heat medium supply pipe 45 is provided with a twelfth on-off valve V12.

The operation of the nitrogen separator 1 according to the present embodiment configured as described above will be described with reference to FIGS.
1 and 2, a white on-off valve indicates an "open" state, and a black on-off valve indicates a "closed" state.
The state shown in FIG. 1 shows a state in which nitrogen is adsorbed from BOG using the first adsorption device 5 and a desorption process of nitrogen is performed in the second adsorption device 7, and the state shown in FIG. 2 shows a state in which nitrogen is adsorbed from BOG using the second adsorber 7 and nitrogen is desorbed in the first adsorber 5.

  As shown in FIG. 1, LNG is stored in the LNG storage tank 3 at a low temperature of −160 ° C., and the evaporative gas (BOG) is also discharged from the LNG storage tank 3 through the BOG discharge pipe 17 at a low temperature, It is supplied to the first adsorption device 5. When the low-temperature evaporative gas (BOG) is passed through the first adsorber 5, the adsorbent is cooled by the low-temperature evaporative gas and the nitrogen gas in the evaporative gas is adsorbed by the adsorbent (adsorption step).

In general, the adsorption capacity of the adsorbent increases as the temperature decreases, so that nitrogen is adsorbed more than the adsorbent in the normal temperature state. In the present embodiment, in order to obtain a cooling effect, LNG discharged from the LNG storage tank 3 is caused to flow through the first refrigerant flow path 9 provided in the first adsorption device 5 by the first LNG supply pipe 39, Since the adsorption device (adsorbent) is cooled, the adsorption capacity is further improved.
The LNG supplied to the first adsorption device 5 by the first LNG supply pipe 39 is heated, for example, from -160 ° C to -150 ° C, and returned to the LNG discharge pipe 37 again.

The nitrogen-removed BOG that has been subjected to the nitrogen adsorption treatment in the first adsorption device 5 is discharged downstream by the first adsorption treatment gas discharge pipe 27 via the first gas discharge pipe 23 and the third on-off valve V3. .
The nitrogen gas removed from the first adsorption processing gas discharge pipe 27 after the nitrogen removal is removed from the BOG, and has a higher calorific value than the BOG before the nitrogen removal and has a higher value as a fuel. For example, in the case where BOG is compressed by a compressor, mixed with LNG discharged by the LNG discharging pipe 37 and supplied to a demand destination, if BOG generated from the LNG storage tank 3 is compressed as it is, nitrogen which has no calorific value will also be obtained. Useless compression power is consumed because they are compressed together, but the compression power can be reduced by compressing the BOG after removing nitrogen discharged from the first adsorption processing gas discharge pipe 27. It becomes.

  On the other hand, in the second adsorption device 7, a heat medium such as seawater is supplied from the second heat medium supply pipe 45, and the desorption process of the nitrogen gas is performed. When the adsorbent is heated, the adsorption capacity is reduced, so that the desorption treatment is performed. The desorbed regeneration gas is discharged through the second gas discharge pipe 25, the sixth on-off valve V6, and the second regeneration gas discharge pipe 33.

If the nitrogen purity of the desorbed regeneration gas is sufficiently high, in other words, if the concentration of flammable gas components such as methane in the regeneration gas is sufficiently low, the desorbed regeneration gas should be released to the atmosphere as it is. Can be done. If the nitrogen purity of the desorbed regeneration gas is not sufficiently high, the nitrogen purity is further increased. To dissipate. Here, the amount of regeneration gas discharged from the nitrogen separation device 1 is significantly smaller than the amount of BOG (the amount of generated BOG) discharged from the LNG storage tank 3, and the amount of the generated BOG is directly used for high-purity nitrogen separation. As compared with the case where the process is performed, the equipment capacity of the subsequent process can be significantly reduced. The combustible gas component separated in the subsequent process can be used as fuel, and the nitrogen component may be recovered as product nitrogen without being released.
The heat medium of, for example, 20 ° C. supplied to the second adsorption device 7 through the second heat medium supply pipe 45 is discharged at, for example, 10 ° C. by exchanging heat with the adsorbent.

When the first adsorption device 5 adsorbs nitrogen to the adsorption capacity limit, the first adsorption device 5 is switched to the nitrogen gas desorption process, and the second adsorption device 7 is switched to the nitrogen gas adsorption process.
This switching is performed by switching the opening and closing of the on-off valve, and the state shown in FIG. 2 shows the opened and closed state of the on-off valve after the switching.

In the state shown in FIG. 2, the evaporating gas (BOG) in a low temperature state is circulated to the second adsorption device 7, and the LNG discharged from the LNG storage tank 3 is placed in the second adsorption device 7 by the second LNG supply pipe 41. Is circulated through the second refrigerant flow path 11 disposed in the first refrigerant passage.
The BOG that has been subjected to the nitrogen adsorption treatment in the second adsorption device 7 and has been subjected to nitrogen removal is discharged downstream by the second adsorption treatment gas discharge pipe 29 via the second gas discharge pipe 25 and the fourth on-off valve V4. .

  On the other hand, in the first adsorption device 5, a heat medium such as seawater is supplied by the first heat medium supply pipe 43 to perform a desorption process of nitrogen gas, and the desorbed regeneration gas is supplied to the first gas discharge pipe 23. Are discharged through the fifth on-off valve V5 and the first regeneration gas discharge pipe 31.

In the state shown in FIG. 2, when nitrogen is adsorbed to the adsorption capacity limit by the second adsorption device 7, the second adsorption device 7 is switched to the nitrogen gas desorption process, and the first adsorption device 5 is switched to the nitrogen gas adsorption process.
Thus, by switching the processing mode of the first adsorption device 5 and the second adsorption device 7, the adsorption and desorption of the nitrogen gas can be continuously performed.
In addition, as the determination that the first adsorption device 5 or the second adsorption device 7 has adsorbed nitrogen to the adsorption capacity limit, the gas components are measured in the BOG discharge pipe 17, the first gas discharge pipe 23, and the second gas discharge pipe 25. A measuring device for performing the measurement may be provided, and the switching may be performed according to the measured value of the nitrogen component concentration. For example, while the adsorption process is being performed by the first adsorption device 5, the nitrogen component concentration in the BOG discharged from the first gas discharge pipe 23 after the nitrogen removal is changed to the nitrogen component concentration (nitrogen removal) in the BOG discharge pipe 17. When the ratio becomes equal to or more than a predetermined ratio with respect to the nitrogen component concentration in the previous BOG, the first adsorption device 5 determines that nitrogen has been adsorbed to the adsorption capacity limit. Generally, a threshold of a predetermined ratio often takes a value of about 1/50 to 1/5.

  As described above, according to the present embodiment, there is no need to compress and pressurize the raw material gas and the separation gas, and nitrogen separation is performed by utilizing the cold energy originally possessed by LNG. An excellent effect that energy consumption is remarkably small as compared with nitrogen separation technology can be obtained.

  In the above embodiment, the first adsorber 5 and the second adsorber 7 are used to indirectly cool the adsorbent when performing the nitrogen adsorption process in the first adsorber 5 and the second adsorber 7. However, as described above, since the BOG discharged from the LNG storage tank 3 is at a low temperature, the adsorption efficiency is higher than when the gas in a normal temperature state is circulated. In this sense, it is meaningful to use a temperature swing type adsorption apparatus for adsorbing nitrogen from BOG, and the present invention includes a case where there is no mechanism for indirectly cooling the adsorbent by LNG.

  Further, in the above-described embodiment, the example in which the two suction devices of the first suction device 5 and the second suction device 7 are provided has been described. However, the number of the suction devices is not limited to two. Any number may be used, and three or more may be used.

DESCRIPTION OF SYMBOLS 1 Nitrogen separation device 3 LNG storage tank 5 1st adsorption device 7 2nd adsorption device 9 1st refrigerant flow path 11 2nd refrigerant flow path 13 1st heat medium flow path 15 2nd heat medium flow path 17 BOG discharge pipe 19th 1 BOG discharge pipe 21 Second BOG discharge pipe 23 First gas discharge pipe 25 Second gas discharge pipe 27 First adsorption processing gas discharge pipe 29 Second adsorption processing gas discharge pipe 31 First regeneration gas discharge pipe 33 Second regeneration gas discharge pipe 35 pump 37 LNG discharge pipe 39 first LNG supply pipe 41 second LNG supply pipe 43 first heat medium supply pipe 45 second heat medium supply pipe V1 to V12 First open / close valve to twelfth open / close valve

Claims (3)

A nitrogen separator for removing nitrogen gas from BOG discharged from an LNG storage tank,
The first adsorber is filled with an adsorbent that selectively adsorbs nitrogen, as a temperature swing type adsorber for selectively adsorbing nitrogen to the adsorbent at a low temperature and desorbing the adsorbed nitrogen at a high temperature. Having a second adsorption device,
The BOG discharge pipe for discharging the BOG from the LNG storage tank is connected respectively via an on-off valve to the first suction device and the second adsorption unit,
Wherein the first adsorber and said second adsorber, is arranged heating medium passage for circulating a heating medium, being adapted to be indirectly heated by the heating medium,
The first adsorption device and the second adsorption device are provided with a refrigerant flow path for indirectly cooling the adsorbent in the adsorption device by flowing LNG discharged from the LNG storage tank, The inlet side of the refrigerant flow path is connected to an LNG supply pipe branched from an LNG discharge pipe that supplies LNG to a demand destination, and the output side of the refrigerant flow path returns to the LNG discharge pipe again via the LNG supply pipe. Has been
BOG is selectively passed from the BOG discharge pipe to the first adsorber and the second adsorber so that the first adsorber and the second adsorber can alternately adsorb and desorb nitrogen. An apparatus for separating nitrogen from BOG. 2. The adsorption processing gas from which nitrogen gas has been removed from BOG by the first adsorption device and the second adsorption device is mixed with LNG discharged by an LNG discharge pipe leading to a demand destination . A device for separating nitrogen from BOG. A nitrogen separator for removing nitrogen gas from BOG discharged from an LNG storage tank,
The first adsorber is filled with an adsorbent that selectively adsorbs nitrogen, as a temperature swing type adsorber for selectively adsorbing nitrogen to the adsorbent at a low temperature and desorbing the adsorbed nitrogen at a high temperature. Having a second adsorption device,
The BOG discharge pipe for discharging the BOG from the LNG storage tank is connected respectively via an on-off valve to the first suction device and the second adsorption unit,
Wherein the first adsorber and said second adsorber, is arranged heating medium passage for circulating a heating medium, being adapted to be indirectly heated by the heating medium,
From BOG discharge tube BOG to the second adsorber and the first adsorber by selectively passing flow, adsorption and desorption of nitrogen so as to perform alternately by said first adsorber and said second adsorber Yes,
The nitrogen gas is removed from the BOG by the first adsorption device and the second adsorption device, and the adsorption process gas is mixed with LNG discharged by an LNG discharge pipe leading to a demand destination. apparatus.

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