JP6225539B2 - Opening the cryogenic tank - Google Patents

Description

  The present invention relates to a method for opening a cryogenic tank.

  A low-temperature tank that stores a low-temperature liquefied gas such as LNG (Liquefied Natural Gas) performs an open operation to form an environment for workers to enter in the tank, for example, during maintenance. In such an open operation, first, residual liquid remaining in the low temperature tank is discharged, and then nitrogen gas is supplied to the low temperature tank to purge methane gas. After that, the temperature is increased by nitrogen gas, the temperature is increased by the outside air, and the air is replaced to create an environment where workers can enter the tank.

Japanese Patent Laid-Open No. 61-180098

  By the way, a low temperature tank called a so-called double shell tank has an outer tub and an inner tub, and has a cold insulating layer made of a cold insulating material filled between the outer tub and the inner tub. This cold insulation layer has a huge heat capacity. For this reason, even if nitrogen gas is introduced into the inner tank to raise the temperature, much of the heat supplied to the inner tank is absorbed by the cold insulation layer, and it takes a very long time to raise the temperature in the inner tank. Is required. One reason for this is that a very large amount of time is required for the temperature raising operation in the inner tank. For example, in the case of a general ground-type metal double shell tank, the operation for opening the low temperature tank is performed. It takes several months to complete.

  The present invention has been made in view of the above-described problems, and an object thereof is to shorten the time required for opening a low-temperature tank.

  The present invention adopts the following configuration as means for solving the above-described problems.

  The first invention is a method for opening a low-temperature tank having a cold insulation layer between an outer tank and an inner tank, the residual liquid treatment step for discharging the residual liquid in the low-temperature tank, and after the residual liquid treatment, A combustible gas purging step for purging the combustible gas in the low temperature tank by supplying an inert gas into the low temperature tank, and the inside of the inner tank by supplying an inert gas into the inner tank and the cold insulation layer. A configuration of including an inert gas temperature raising step for raising the temperature is adopted.

  According to a second aspect of the present invention, in the first aspect of the present invention, a configuration in which at least a part of the inert gas discharged from the inner tank is supplied to the cold insulation layer in the inert gas temperature raising step.

  According to a third aspect of the present invention, in the second aspect of the present invention, a configuration is used in which the inert gas discharged from the inner tank is heated and supplied to the cold insulation layer.

  According to the present invention, the inert gas is supplied into the inner tank and also supplied to the cold insulation layer. For this reason, the cold insulation layer itself is directly heated by the inert gas, and the amount of heat supplied to the inner tank can be prevented from being taken away by the cold insulation layer, and the inner tank can be heated in a short time. It becomes. Therefore, according to the present invention, it is possible to shorten the time required for opening the low temperature tank.

It is a flowchart for demonstrating the opening operation | work of the tank in one Embodiment of this invention. It is explanatory drawing for demonstrating the opening operation | work of the tank in one Embodiment of this invention. It is explanatory drawing for demonstrating the opening operation | work of the tank in one Embodiment of this invention.

  Hereinafter, an embodiment of a method for opening a cryogenic tank according to the present invention will be described with reference to the drawings. In the following drawings, the scale of each member is appropriately changed in order to make each member a recognizable size.

  FIG. 1 is a flowchart for explaining a method for opening a low-temperature tank (work for opening a tank 1) according to this embodiment. Note that the low temperature tank opened by the low temperature tank opening method of the present embodiment is the tank 1 shown in FIGS. 2 and 3 to be described later, for example, an LNG tank that stores the liquefied gas X such as LNG. This tank 1 is schematically shown in FIGS. 2 and 3, but for example, an inner tank 1a made of 9% nickel steel or aluminum alloy, an outer tank 1b made of carbon steel, and an inner tank 1a It is a metal double shell tank provided with a cold insulation layer 1c made of a cold insulation material filled between the outer tub 1b. For example, pearlite is used as the cold insulation material for forming the cold insulation layer 1c.

  Further, as shown in FIGS. 2 and 3, the tank 1 is provided with a monitoring control unit 4 including various sensors (thermometer, liquid level gauge, pressure gauge), and the tank is used by using the monitoring control unit 4. One opening operation is managed.

  As shown in FIG. 1, when the tank 1 is opened, the liquid is first drained (step S1). As shown in FIG. 2A, a liquefied gas X is normally stored in the tank 1, and a discharge pump 2 for discharging the liquefied gas X from the tank 1 based on an instruction from the outside is connected. (See FIG. 2). In the draining (step S1), the discharge pump 2 is used to discharge most of the liquefied gas X stored in the tank 1 to the outside of the tank 1.

  Further, a boil-off gas discharge line 3 for discharging gas (boil-off gas) vaporized in the tank 1 is connected to the ceiling portion of the tank 1. When draining (step S1), the boil-off gas generated in the tank 1 is discharged from the boil-off gas discharge line 3 to the outside of the tank 1, and a boil-off gas processing unit (not shown) including a compressor or the like that compresses the boil-off gas. ).

  Subsequently, a residual liquid process (step S2) is performed in which the liquefied gas X accumulated at the bottom of the tank 1 that cannot be completely discharged by the discharge pump 2 is discharged to the outside of the tank 1. Here, as shown in FIG. 2B, the temporary pump 5 is connected to the bottom of the tank 1, the temporary pump 5 and the like are purged with nitrogen gas, and then the temporary pump 5 is operated to operate the tank 1. The liquefied gas X collected at the bottom is discharged to the outside of the tank 1. Further, the liquefied gas X discharged from the tank 1 by the temporary pump 5 is supplied to a pipe that transports the liquefied gas X discharged from the above-described discharge pump 2. This residual liquid processing (step S2) corresponds to a residual liquid processing step of discharging the residual liquid in the low temperature tank in the present invention. Further, after the residual liquid treatment (step S2), the liquefied gas X remaining in the tank 1 is vaporized by natural heat input to the tank 1 as necessary. It is also possible to perform the residual liquid treatment without using the temporary pump 5. In this case, as much liquefied gas X as possible is discharged by the discharge pump 2, and then the remaining liquid is processed by natural heat input or heat input by supplying heated combustion gas and nitrogen gas.

  When all of the liquefied gas X is discharged from the inside of the tank 1 by the residual liquid treatment (step S2), the combustible gas exhaust and the hot up (step S3) are subsequently performed as shown in FIG. Here, liquid nitrogen supplied from a tank truck T (see FIG. 3) for storing liquid nitrogen is vaporized by a vaporizer 6 (see FIG. 3), and nitrogen gas Y (inert gas) generated thereby is tank 1 To the inside of the tank 1 from the bottom or side.

  When the nitrogen gas Y is supplied to the tank 1 in this way, the combustible gas M (for example, methane gas) remaining in the tank 1 is pushed up to the upper part of the tank 1 by the nitrogen gas Y heavier than the combustible gas M. The combustible gas M is discharged (purged) from the boil-off gas discharge line 3 to the outside of the tank 1. When the concentration of the combustible gas M discharged to the outside of the tank 1 is high, the combustible gas M is discharged from the boil-off gas discharge line 3, but when the concentration of the combustible gas M is low (for example, 5%) In the following case, the combustible gas M is diffused into the atmosphere via the inner tank nozzle 7, for example.

  Further, the nitrogen gas Y supplied from the vaporizer 6 to the tank 1 is generated by warming liquid nitrogen with warm water or the like in the vaporizer 6. For this reason, the temperature of the nitrogen gas Y can be adjusted by adjusting the temperature of the warm water that warms the liquid nitrogen. Such nitrogen gas Y is adjusted to a temperature that raises the temperature in the tank 1 and supplied to the tank 1. As a result, the temperature in the tank 1 is raised (hot up).

  This combustible gas exhaust and hot-up (step S3) corresponds to a combustible gas purging step in which purging the combustible gas in the low temperature tank by supplying an inert gas into the low temperature tank after the residual liquid treatment in the present invention. To do.

  When the combustible gas M in the tank 1 is exhausted to a concentration below the lower explosive limit by the combustible gas exhaust and hot-up (step S3), then, as shown in FIG. Nitrogen gas Y is supplied to the cold insulation layer 1c (step S4). The tank 1 is generally provided with a pipe for supplying nitrogen gas to the space between the inner tank 1a and the outer tank 1b. For this reason, the nitrogen gas Y supplied to the cold insulation layer 1c is supplied to the space between the inner tank 1a and the outer tank 1b through the pipe, for example. Since the cold insulation layer 1c is made of granular pearlite, the nitrogen gas Y supplied to the cold insulation layer 1c passes through the cold insulation layer 1c and is finally discharged from the outer tank nozzle 12 or the like to the outside of the tank 1. The

  Moreover, in this embodiment, as shown to Fig.3 (a), the nitrogen gas Y exhausted from the inner tank nozzle 7 (or roof nozzle) is supplied to the cold insulation layer 1c. Thereby, at least a part of the nitrogen gas Y supplied to the cold insulation layer 1c can be made the nitrogen gas Y discharged from the inner tank 1. Since the nitrogen gas Y discharged from the inner tank nozzle 7 (or the roof nozzle) is normally diffused into the atmosphere, the nitrogen gas Y as a whole is supplied to the cold insulation layer 1c in this way. Can be reduced. Note that all of the nitrogen gas Y discharged from the inner tank nozzle 7 (or the roof nozzle) may be supplied to the cold insulation layer 1c, but may be a part thereof.

  Further, in the present embodiment, the nitrogen gas Y discharged from the inner tank nozzle 7 is heated by the heater 10, boosted by the blower 11, and then supplied to the cold insulation layer 1 c. For example, the heater 10 is wound around a pipe that guides the nitrogen gas Y, and indirectly heats the nitrogen gas Y flowing through the pipe from the outside of the pipe. Thereby, the heated nitrogen gas Y is supplied to the cold insulation layer 1c.

  The step (step S4) of supplying the nitrogen gas Y to the inner tank 1a and the cold insulation layer 1c is performed in the present invention by raising the temperature in the inner tank by supplying an inert gas to the inner tank and the cold insulation layer. This corresponds to the inert gas temperature raising step.

  When supply of the nitrogen gas Y to the inner tank 1a and the cold insulation layer 1c is started and a certain time has passed or a certain amount of nitrogen gas Y is supplied, it is determined whether the temperature of the inner tank 1a has reached a predetermined value. (Step S5). Here, the monitoring control unit 4 acquires the temperature in the inner tub 1a from the thermometer installed in the tank 1, and compares the acquired temperature with a predetermined value to make the above determination. The predetermined value is determined so that condensation does not occur in the introduction of outside air in a later process. In step S5, the concentration of the combustible gas is also monitored.

  In step S5, when it is determined that the temperature of the inner tank 1a is not a predetermined value, the process returns to step S4 again. That is, the nitrogen gas Y is supplied to the inner tank 1a and the cold insulation layer 1c until the temperature of the inner tank 1a reaches a predetermined value. On the other hand, when it is determined in step S5 that the temperature of the inner tank 1a is a predetermined value, outside air is introduced into the inner tank 1a as shown in FIG. 1 (step S6). Here, as shown in FIG. 3B, the outside air introduction device 8 is connected to the inner tank 1a, and the outside air Z is supplied from the outside air introduction device 8 into the inner tank 1a. The outside air introduction device 8 includes a ventilation fan 8a (or an air conditioner) that pumps the outside air Z and an air lock chamber 8b that is connected to the inner tank 1a, and the ventilation fan 8a (or an air conditioner). The outside air Z to be pumped in is supplied into the inner tank 1a through the air lock chamber 8b.

  The tank 1 is heated by the outside air Z supplied by the outside air introduction device 8. Since the outside air Z supplied into the tank 1 becomes large, the outside air Z is diffused into the atmosphere from the nozzle 9 provided in the upper part of the tank 1 in addition to the inner tank nozzle 7 described above.

  When a certain time has elapsed from the supply of the outside air Z into the tank 1 or when the supply of a certain amount of the outside air Z is completed, it is determined whether the temperature and oxygen concentration in the tank 1 have reached the set values (step S7). Here, the monitoring control unit 4 acquires the oxygen concentration contained in the gas discharged from the inner tank nozzle 7 (or roof nozzle) or nozzle 9 from the oxygen concentration meter, and from the thermometer installed in the tank 1. The determination is made by acquiring the temperature in the tank 1 and comparing these oxygen concentration and temperature with set values. The set value is determined based on the amount of components necessary for the environment in which the worker can work in the tank 1.

  When it is determined in step S7 that the temperature and oxygen concentration in the tank 1 have reached the set values, the opening operation of the tank 1 in the present embodiment is terminated, assuming that an environment in which an operator can enter the tank 1 is formed.

  On the other hand, when it is determined in step S7 that the temperature and oxygen concentration in the tank 1 are not set values, the process returns to step S6 again. That is, outside air Z is supplied into the tank 1 until the temperature and oxygen concentration of the inner tank 1a reach the set values.

  In the opening operation of the tank 1 of the present embodiment as described above, the residual liquid in the tank 1 is discharged, and the combustible gas M in the tank 1 is purged by supplying the nitrogen gas Y into the tank 1 after the residual liquid treatment. Then, the nitrogen gas Y is supplied to the inner tank 1a and the cold insulation layer 1c to raise the temperature of the inner tank 1a, and finally the outside air Z is supplied to the tank 1.

  According to the opening operation of the tank 1 of this embodiment, the nitrogen gas Y is supplied into the inner tank 1a and also supplied to the cold insulation layer 1c. For this reason, the cold insulation layer 1c itself can be directly heated by the nitrogen gas Y, and the amount of heat supplied into the inner tank 1a can be suppressed from being taken away by the cold insulation layer 1c, and the temperature in the inner tank 1a is increased in a short time. It becomes possible to make it. Therefore, according to the opening operation of the tank 1 of the present embodiment, it is possible to shorten the time required for opening the low temperature tank.

  Moreover, according to the opening operation | work of the tank 1 of this embodiment, at least one part of the nitrogen gas Y discharged | emitted from the inner tank 1a is supplied to the cold insulation layer 1c. For this reason, the nitrogen gas Y can be supplied to the cold insulation layer 1c without increasing the amount of nitrogen gas Y used.

  Moreover, according to the opening operation | work of the tank 1 of this embodiment, the nitrogen gas Y discharged | emitted from the inner tank 1a is heated, and it supplies to the cold insulation layer 1c. For this reason, it becomes possible to warm the cold insulation layer 1c in a short time, and it becomes possible to heat up the inside of the inner tank 1a in a short time.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to the said embodiment. Various shapes, combinations, and the like of the constituent members shown in the above-described embodiments are examples, and various modifications can be made based on design requirements and the like without departing from the spirit of the present invention.

  For example, in the above embodiment, the configuration in which the present invention is applied to the opening operation of the tank 1 for storing LNG has been described. However, the present invention is not limited to this, and can be applied to an opening operation of a tank for storing LPG (Liquefied Petroleum Gas). In such a case, the combustible gas in the present invention is propane gas or butane gas.

  Moreover, in the said embodiment, the structure which uses nitrogen gas as an inert gas was demonstrated. However, the present invention is not limited to this, and other inert gas may be used.

  DESCRIPTION OF SYMBOLS 1 ... Tank (low temperature tank), 1a ... Inner tank, 1b ... Outer tank, 1c ... Cold storage layer, 2 ... Discharge pump, 3 ... Boil-off gas discharge line, 4 ... Monitoring control part, 5 ... ... Temporary pump, 6 ... Vaporizer, 7 ... Inner tank nozzle, 8 ... Outside air introduction device, 8a ... Ventilation fan, 8b ... Air lock chamber, 9 ... Nozzle, 10 ... Heater, 11 ... Blower, 12 ... Outer nozzle, M ... Combustible gas, T ... Tank truck, X ... Liquefied gas, Y ... Nitrogen gas (inert gas), Z ... Outside air

Claims (2)

A method for opening a low-temperature tank having a cold insulation layer between an outer tank and an inner tank,
A residual liquid treatment step of discharging the residual liquid in the low-temperature tank;
A combustible gas purge step of purging the combustible gas in the low temperature tank by supplying an inert gas into the low temperature tank after the residual liquid treatment;
Possess the inert gas heating step of the inner tank to raise the temperature by supplying an inert gas into the tank and the cold layer,
The method for opening a low-temperature tank , wherein in the inert gas temperature raising step, at least a part of the inert gas discharged from the inner tank is supplied to the cold insulation layer . Open method of cold tank according to claim 1, wherein the supply to the cold layer warmed the discharged the inert gas from the inner tank.

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