JP6230183B2 - 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, outside air is introduced into the tank so that workers can enter the tank.

Japanese Patent Laid-Open No. 61-180098

  By the way, since the low-temperature tank has a cold insulation layer, a large amount of heat is required to raise the temperature in the low-temperature tank, and from this, a large amount of nitrogen gas and It is necessary to supply outside air into the low temperature tank. The outside air is supplied after the temperature has been raised to a certain temperature by supplying nitrogen gas, but the outside air generally contains a lot of moisture, although it depends on the season and region, and various other components besides moisture. It is included. When a large amount of outside air containing a large amount of moisture is supplied into the tank in a short period of time, in a temperature and humidity state where the outside air is present, the moisture contained in the outside air is condensed by being cooled in the low temperature tank. Condensation occurs on the inner wall of the. Here, if nitrogen oxides or sulfur oxides are contained in the outside air, these components may be dissolved in water generated by condensation, and nitric acid or sulfuric acid may be generated. Moreover, nitrogen oxides and sulfur oxides may also be contained in the LNG residue, and these components may be dissolved in water generated by condensation to generate nitric acid or sulfuric acid. When the metal material constituting the low-temperature tank is corroded by such nitric acid or sulfuric acid, it is necessary to repair the corroded portion, and the amount of maintenance work increases and the maintenance period is prolonged.

  The present invention has been made in view of the above-described problems, and an object thereof is to prevent the occurrence of corrosive components such as nitric acid and sulfuric acid in the low temperature tank when the low temperature tank is opened.

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

  A first invention is a method for opening a low temperature tank, wherein a residual liquid treatment step of discharging the residual liquid in the low temperature tank, and supplying an inert gas into the low temperature tank after the residual liquid treatment is performed. In the combustible gas purging step for purging the combustible gas in the low temperature tank, the dew condensation determining step for determining whether the temperature of the inner wall surface of the low temperature tank is a temperature at which condensation occurs due to the introduction of outside air, and the dew condensation in the dew condensation determining step An inert gas temperature raising step in which an inert gas is supplied into the low temperature tank to raise the temperature in the low temperature tank and then the process proceeds to the dew condensation determination step again; When it is determined that condensation does not occur in the determination step, a configuration is adopted in which an outside air temperature raising step is performed in which outside air is supplied into the low temperature tank to raise the temperature in the low temperature tank.

  In a first aspect of the present invention, in the first aspect of the present invention, in the dew condensation determination step, a wet line diagram showing a relationship among the temperature of the outside air, the humidity of the outside air, the temperature of the inner wall surface, and the presence or absence of condensation. Based on this, a configuration is adopted in which it is determined whether the temperature at which the dew condensation occurs.

  According to a third aspect of the present invention, in the first or second aspect, when it is determined that dew condensation occurs in the dew condensation determination step, it is determined whether or not a contaminant concentration in the outside air is below a reference value. A configuration in which a transition is made to the inert gas temperature raising step when the pollutant concentration is higher than a reference value, and a contamination concentration determination step is taken to move to the outside air temperature raising step when the pollutant concentration is below a reference value. adopt.

  According to the present invention, when the combustible gas is discharged from the low temperature tank with nitrogen gas or the like, it is determined whether or not dew condensation occurs on the inner wall surface of the low temperature tank. Instead, the temperature of the low temperature tank is raised by supplying an inert gas to the low temperature tank. For this reason, it is possible to prevent condensation on the inner wall surface. Further, according to the present invention, it is determined whether or not dew condensation occurs on the inner wall surface of the low temperature tank while raising the temperature with the inert gas. For this reason, when it is determined that no condensation occurs on the inner wall surface of the low temperature tank, the temperature of the low temperature tank is raised by supplying outside air to the low temperature tank. Therefore, the amount of the inert gas used for raising the temperature of the low temperature tank can be minimized, and the cost for opening the low temperature tank can be reduced.

It is a flowchart for demonstrating the opening operation | work of the tank in 1st Embodiment of this invention. It is explanatory drawing for demonstrating the opening operation | work of the tank in 1st Embodiment of this invention. It is explanatory drawing for demonstrating the opening operation | work of the tank in 1st Embodiment of this invention. It is a flowchart for demonstrating the opening operation | work of the tank in 2nd 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.

(First embodiment)
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 made of 9% nickel steel or aluminum alloy, an outer tank made of carbon steel, an inner tank and an outer tank, It is a metal double shell tank provided with the cold insulation layer which consists of a cold insulation material filled between.

  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 process 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. 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 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, as shown in FIG. 3A, liquid nitrogen supplied from a tank truck T that stores liquid nitrogen is vaporized by the vaporizer 6, and the nitrogen gas Y (inert gas) generated thereby is tank 1 To the inside of the tank 1 from the bottom or side. The nitrogen gas Y may be supplied from other than the tank truck T (for example, a nitrogen tank in the base).

  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 is low (for example, in the case of methane gas) Is 5% or less), the combustible gas M is diffused into the atmosphere through the diffusion pipe 7.

  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. It is determined whether the temperature is generated (step S4). Here, the monitoring control unit 4 acquires the temperature of the inner wall surface of the tank 1 from the thermometer installed in the tank 1, acquires the temperature and humidity of the outside air from the temperature and humidity meter installed outside the tank 1, By applying the temperature of the inner wall surface and the temperature and humidity of the outside air to a wet diagram that stores in advance, when the outside air touches the inner wall surface of the tank 1, the moisture is condensed and the temperature of the inner wall surface where condensation occurs. Determine if there is any. The wetness diagram shows the relationship between the temperature of the outside air, the humidity of the outside air, the temperature of the inner wall surface, and the presence or absence of condensation.

  The step of determining whether or not the temperature at which dew condensation is caused by the introduction of the outside air (step S4) is the dew condensation determination step of determining whether or not the temperature of the inner wall surface of the low-temperature tank is a temperature at which dew condensation is caused by the introduction of outside air It corresponds to.

  In step S4, when it is determined that the temperature of the inner wall surface is a temperature at which dew condensation occurs due to the introduction of outside air, nitrogen gas Y is subsequently supplied into the tank 1 as shown in FIG. 1 (step S5). It can be understood that the nitrogen gas Y does not contain moisture. For this reason, when the nitrogen gas Y is supplied into the tank 1, the temperature inside the tank 1 is raised without causing condensation on the inner wall surface of the tank 1. When a certain time has passed or supply of a certain amount of nitrogen gas Y is completed, a step (step S4) is performed again to determine whether the temperature is such that condensation occurs due to the introduction of outside air.

  In the present invention, when the nitrogen gas Y is supplied (step S5) in the present invention, when it is determined that condensation occurs in the condensation determination process, the inert gas is supplied into the low temperature tank to raise the temperature in the low temperature tank. This corresponds to an inert gas temperature raising step that subsequently shifts again to the dew condensation determination step.

  When it is determined in step S4 that the temperature of the inner wall surface is a temperature at which condensation does not occur due to the introduction of outside air, outside air is introduced into the tank 1 as shown in FIG. 1 (step S6). Here, as shown in FIG. 3B, the outside air introduction device 8 is connected to the tank 1, and the outside air Z is supplied from the outside air introduction device 8 into the tank 1. The outside air introduction device 8 includes a ventilation fan 8a that pumps the outside air Z and an air lock chamber 8b that is connected to the tank 1. The outside air Z that is pumped by the ventilation fan 8a is passed through the air lock chamber 8b. To tank 1. The ventilation fan 8a may be an air conditioner.

  The tank 1 is heated by the outside air Z supplied by the outside air introduction device 8. This outside air Z is the atmosphere, and the amount of water varies depending on the season, but it contains a little moisture. Such outside air Z is cooled by touching the inner wall surface of the tank 1, but does not cause condensation because the temperature of the inner wall surface is a temperature at which no condensation occurs as described above. Since the outside air Z supplied into the tank 1 becomes a large amount, 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 above-described diffusion pipe 7.

  In the process of introducing outside air into the tank 1 (step S6), in the present invention, when it is determined that condensation does not occur in the dew condensation determination process, the outside air is supplied into the low temperature tank to rise in the low temperature tank. This corresponds to an outside air temperature raising step for heating.

  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 oxygen concentration contained in the gas discharged from the diffusion tube 7 and the nozzle 9 is acquired from the oxygen concentration meter, the temperature in the tank 1 is acquired from the thermometer installed in the tank 1, and these oxygens are obtained. The determination is made by comparing the 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 S4 again, and it is determined whether or not the temperature causes condensation due to the introduction of outside air. That is, in the present embodiment, monitoring in the tank 1 is continued by repeating Step S4 and Step S6 until the temperature and oxygen concentration in the tank 1 reach the set values. Among these, when an environment in which dew condensation occurs due to temperature fluctuations or component fluctuations in the outside air, switching to supply of nitrogen gas Y (step S5) is performed.

  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, it is determined whether the temperature of the inner wall surface of the tank 1 is a temperature at which condensation occurs due to the introduction of the outside air Z, and when it is determined that condensation occurs, the nitrogen gas Y is supplied into the tank 1. When it is determined that the temperature inside the tank 1 is raised and no condensation occurs, the outside air Z is supplied into the tank 1 to raise the temperature inside the tank 1.

  According to the opening operation of the tank 1 of this embodiment, when the combustible gas M is discharged from the tank 1, it is determined whether or not condensation occurs on the inner wall surface of the tank 1, and it is determined that condensation occurs. In such a case, the temperature of the tank 1 is raised by supplying nitrogen gas Y instead of the outside air Z into the tank 1. For this reason, it is possible to prevent condensation on the inner wall surface. Further, according to the opening operation of the tank 1 of the present embodiment, it is determined whether or not dew condensation occurs on the inner wall surface of the tank 1 while the temperature is increased by the nitrogen gas Y. For this reason, when it is determined that condensation does not occur on the inner wall surface of the tank 1, the temperature of the tank 1 is raised by supplying the outside air Z to the tank 1. Therefore, the amount of nitrogen gas Y used for raising the temperature of the tank 1 can be minimized, and the cost for opening the tank 1 can be reduced.

  Further, according to the opening operation of the tank 1 of the present embodiment, is the temperature at which condensation occurs based on the wet diagram showing the relationship between the temperature of the outside air, the humidity of the outside air, the temperature of the inner wall surface, and the presence or absence of condensation? Judgment is made. For this reason, it is possible to easily determine whether the temperature of the inner wall surface is a temperature at which condensation occurs.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. In the present embodiment, it is assumed that the residue of the liquefied gas X does not contain a substance that corrodes the tank 1 by being dissolved in water. FIG. 4 is a flowchart for explaining the opening operation of the tank 1 of the second embodiment. As shown in this figure, in this embodiment, it is determined whether or not the temperature is the temperature at which condensation occurs due to the introduction of the outside air described in the first embodiment (step S4). Then, it is determined whether the contaminant concentration of the outside air Z is equal to or lower than the reference value (step S8).

  In step S8 in FIG. 4, the concentration of nitrided oxide or sulfur oxide, which is a contaminant in the outside air Z, is measured by sampling the atmosphere and performing ion chromatography or the like. The determination is made by comparing the measured value with a reference value. The reference value is a value determined so that nitric acid or sulfuric acid having high acidity that corrodes the tank 1 is not generated when nitrided oxide or sulfur oxide contained in the outside air is dissolved in water. It is set based on experiments and the like.

  When the contaminant concentration in the outside air Z is higher than the reference value, the process proceeds to the step of supplying the nitrogen gas Y described in the first embodiment (step S5). On the other hand, when the contaminant concentration in the outside air Z is equal to or less than the reference value, the process proceeds to the step (step S6) of introducing outside air into the tank 1 described in the first embodiment. In such a case, dew condensation occurs when the outside air Z touches the inner wall surface of the tank 1, but the tank 1 is not corroded because the concentration of contaminants in the outside air Z is small.

  The step of determining whether or not the concentration of contaminants in the outside air Z is below a reference value (step S8) in the present invention determines whether or not the concentration of contaminants in the outside air is below a reference value. It corresponds to a contamination concentration determination step that shifts to an inert gas temperature raising step when higher than the reference value and shifts to an outside air temperature raising step when the pollutant concentration is below the reference value.

  According to such an opening operation of the tank 1 of the present embodiment, even when dew condensation occurs due to the introduction of the outside air Z, the temperature of the tank 1 is increased by the outside air Z when the concentration of contaminants in the outside air Z is small. Is done. For this reason, the usage-amount of nitrogen gas Y can be reduced more, and it becomes possible to hold down the cost for opening the tank 1 more.

  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), 2 ... Discharge pump, 3 ... Boil-off gas discharge line, 4 ... Monitoring control part, 5 ... Temporary pump, 6 ... Vaporizer, 7 ... Dissipation pipe, 8 ... ... Outside air introduction device, 8a ... Ventilation fan, 8b ... Air lock chamber, 9 ... Nozzle, M ... Flammable gas, T ... Tank truck, X ... Liquefied gas, Y ... Nitrogen gas (inert Gas), Z ... open air

Claims (3)

A method for opening a cryogenic 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;
A condensation determination step for determining whether the temperature of the inner wall surface of the low-temperature tank is a temperature at which condensation occurs due to introduction of outside air; and
Not a condition that said a determination that condensation occurs in the condensation determination step, moves the inside cold said tank by supplying an inert gas cold tank followed again the condensation determining step while raising the temperature An active gas heating step;
Cold, characterized in that the condition that the determination is that the condensation in the condensation determining step does not occur, and an outside air Atsushi Nobori step of raising the temperature of said cold tank by supplying outside air into said cold tank How to open the tank. In the dew condensation determination step,
The temperature of the outside air, the humidity of the outside air, the temperature of the inner wall surface, and the temperature at which the condensation occurs is determined based on a wetness diagram showing a relationship between the presence or absence of condensation. The method for opening a low-temperature tank according to 1. On the condition that the dew condensation is determined in the dew condensation determination step, it is determined whether the contaminant concentration in the outside air is below a reference value, and the inert gas when the contaminant concentration is higher than the reference value. 3. The method for opening a low-temperature tank according to claim 1, further comprising a contamination concentration determination step that shifts to a temperature raising step and moves to the outside air temperature raising step when the pollutant concentration is below a reference value. .

Images