Patent Publication Number: US-11029085-B2

Title: BOG processing apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application represents the national stage entry of PCT International Application No. PCT/JP2016/057921 filed Mar. 14, 2016 and claims priority to Japanese Patent Application No. 2015-057309 filed Mar. 20, 2015. The contents of these applications are hereby incorporated by reference as if set forth in their entirety herein. 
     BACKGROUND OF THE INVENTION 
     Technical Field 
     The present invention relates to a BOG processing apparatus for processing boil-off gas generated from liquefied gas. 
     Background Art 
     Conventionally, in a manufacturing facility of liquefied gas (liquefied natural gas, liquefied petroleum gas and so on), storage equipment thereof, and receiving equipment thereof, liquefied gas is stored in a storage tank, drawn from the storage tank, and sent to next processes (a transportation process or a supply process). In such storage tanks of liquefied gas, boil-off gas (BOG) is generated due to vaporization of liquefied gas. As processing measures of such BOG, there are various methods such as a method of delivering it to a utilizing system so as to directly consume it as fuel, a method of re-liquefying the BOG and then returning it to the storage tank, a method of re-liquefying the BOG and mixing it with the liquefied gas, and so on. As a re-liquefying method of the BOG, various methods (for example, see Patent Literatures 1 to 4) are proposed such as a method of cooling the BOG using cool heat of the liquefied gas. Thereby, the re-liquefied BOG liquid and the BOG vapor are separated, and the vapor-liquid is processed. 
     In the BOG processing method described in Patent Literature 1, BOG is introduced to the BOG drum, the LNG taken out from LNG tank is injected to the inside of the BOG drum, the BOG is cooled by contacting with the LNG, and thereby the BOG is liquefied. The liquefied BOG is returned from the BOG drum to the LNG tank as a mixed liquid mixed with the LNG. Meanwhile, the BOG cooled by contacting with the LNG is transmitted from a tip portion of the BOG drum to the BOG compressor, and delivered to a utilizing system after compressed with the BOG compressor. 
     In the BOG processing method described in Patent Literature 2, a mist separation apparatus is provided in the middle of the BOG pipe arranged from the LNG tank to the BOG compressor. Mist is separated from the BOG by a liquid drain drum of the mist separation apparatus. The separated mist is pressurized and sent from a drain pipe arranged on a lower portion of the liquid drain drum to the LNG tank via a drain pump, and returned by spraying it into the LNG tank. On the other hand, the BOG passed through the mist separation apparatus is sent from the BOG discharge pipe to the BOG compressor, and then compressed. Therefore, the BOG passed through the mist separation apparatus is supplied to the utilizing system such as a thermal power device connected to downstream thereof. The liquid drain drum introduces the BOG into an inner space thereof, settles out mist downward by reducing its flow velocity, and thereby drains liquid. Above the inside of the liquid drain drum, a mist eliminator having a mesh filter is arranged. Mist which was not settled out brings into contact with the mesh filter, is taken, and is separated. 
     In the BOG processing method described in Patent Literature 3, BOG is compressed with a compressor, then cooled with a cooler, and supplied to a mixing drum. Further, a part of the LNG is decompressed, and then sprayed into the mixing drum. Thereafter, a mist-shaped LNG by injecting and BOG are contacted, and thereby BOG is re-liquefied. BOG not re-liquefied is returned from a blower line to the compressor. On the other hand, the mixed liquid in which the re-liquefied BOG and LNG are mixed is re-sprayed on the mixed drum, or supplied to the cooler by pressure rising. Thereafter, the mixed liquid is merged to LNG from the LNG tank, supplied to a carburetor, vaporized, and then sent to the utilizing system. 
     In a BOG processing method described in Patent Literature 4, BOG generated in a storage tank is compressed with a compressor, and then sent to a reliquefying device. Further, liquefied gas taken from the storage tank is supplied to the reliquefying device, and BOG is re-liquefied by heat exchanging with the liquefied gas. The mixed liquid in which BOG re-liquefied with the reliquefying device and liquefied gas are mixed is sent to an heat exchanger via a pump, and sent to a carburetor after utilizing the mixed liquid in the heat exchanger so as to cool BOG as a cooling medium. Thereafter, the mixed liquid is supplied to a utilizing system as liquefied gas vaporized in the carburetor. 
     Patent Literature 1: JP 1105-279677 A 
     Patent Literature 2: JP 2001-254898 A 
     Patent Literature 3: JP 2007-155060 A 
     Patent Literature 4: JP 2009-191945 A 
     SUMMARY OF THE INVENTION 
     Technical Problem 
     In a manufacturing facility of liquefied gas, storage facilities thereof, and a receiving facility thereof, the generation amount of BOG generated in the storage tank is not constant, but greatly varies. For this reason, equipment design which can respond to the maximum amount of BOG is required. On the other hand, demand for gas in the utilizing system is further not constant, but also supply of liquefied gas taken from the storage tank greatly varies. Therefore, when sending BOG (re-liquefied BOG) to the utilizing system after joined to the liquefied gas, the consumption of BOG is not stabilized, and extra equipment design is needed to balance the amount of BOG and the consumption. However, in the conventional BOG processing method described in Patent Literatures 1-4, equipment deign that is able to respond to the maximum amount of BOG, and to balance the amount of BOG and the consumption is not sufficiently taken into consideration. Further, when trying to perform such design, specifications of each of equipment becomes excessive, and excessive energy is required for the operation of equipment. 
     An object of the present invention is to provide a BOG processing apparatus which can cut waste of each of apparatus and to improve energy efficiency of apparatus operation. 
     Solution to Problem 
     A BOG processing apparatus of the present invention for processing boil-off gas (BOG) generated from liquefied gas includes a cooling device for cooling the BOG by cold energy of the liquefied gas; and a recovery device for recovering a remaining liquid of the liquefied gas remaining for use in cooling by the cooling device, or a mixed liquid in which liquid of the BOG cooled and liquefied by the cooling device and the liquefied gas are mixed. The cooling device includes a cooling drum formed in a cylindrical shape extending up and down, and circulating BOG from below to above; a BOG inlet part introducing the BOG from a lower portion of the cooling drum into an inside of the cooling drum; a first spray provided above the BOG inlet part and upwardly spraying the liquefied gas; a first filled layer provided above the first spray and bringing the liquefied gas into contact with the BOG; a second spray provided above the first filled layer and downwardly spraying the liquefied gas; a BOG outlet part provided in an upper portion of the cooling drum and sending the BOG cooled; and a liquid outlet part provided in the lower portion of the cooling drum and sending the remaining liquid or the mixed liquid to the recovery device. 
     According to the present invention as described above, the cooling device has the cooling drum, and the BOG inlet part, the first spray, the first filled layer, and the second spray are arranged inside of the cooling drum in order. Therefore, contact efficiency between liquefied gas in the first filled layer and BOG can be improved. That is, liquefied gas is sprayed to BOG introduced from the lower portion of the cooling drum and flowing upwardly, and liquefied gas is sprayed downwardly from the second spray. Thereby, liquefied gas is spread on the top and bottom of the first filled layer positioned between the first spray and the second spray, and BOG passing through the first filled layer can bring into contact with much liquefied gas. Therefore, a predetermined cooling performance for cooling BOG (or for further re-liquefying BOG) can be maintained, the thickness of the first filled layer can be decreased, and the amount of liquefied gas sprayed from each of the sprays can be reduced. 
     Further, it is preferable that the BOG processing apparatus of the present invention further includes a third spray provided above the second spray and downwardly spraying the liquefied gas; a second filled layer provided above the third spray and adsorbing mist in BOG; and a mist eliminator provided above the second filled layer and eliminating mist in BOG passing through the second filled layer. Preferably, the third spray sprays the liquefied gas with a mist form in which liquid drop is small compared with the second spray. 
     According to the above structure, the third spray, the second filled layer, and the mist eliminator are arranged above the second spray in the inside of the cooling drum in this order. Further, the third spray sprays liquefied gas having a mist shape in which liquid drop is smaller than that of second spray. Therefore, cooling performance for cooling BOG and controlling BOG temperature (or further re-liquefying BOG) can be improved. Furthermore, mist in BOG is adsorbed by the second filled layer arranged above the third spray, and mist in BOG passing through the second filled layer is removed by the mist eliminator. Thereby, BOG in which mist is not included as much as possible can be delivered from the BOG outlet part. When the compressor is provided above the BOG outlet part, BOG can be compressed without decreasing performance of the compressor. 
     Further, in the BOG processing apparatus of the present invention, it is preferable that the recovery device includes an ejection introducing the liquefied gas, drawing the remaining liquid or the mixed liquid by injection pressure of the liquefied gas, and mixing the liquefied gas and the remaining liquid or the mixed liquid and delivering. 
     According to the above structure, the recovery device includes an ejection. The ejection draws the remaining liquid or the mixed liquid from the liquid outlet part of the cooling drum by injection pressure of liquefied gas, and delivers it. Therefore, liquid can be recovered without using a pump driven by external power, and configuration of the device can be simplified. Herein, when the recovery device is constructed by using driving components such as a pump or valve for sending liquid, it is necessary to use driving components of cryogenic specification. Further, installation of driving components of a plurality of systems is required in maintenance or failure. As a result, the recovery device is complexed, becomes large in size, and thereby cost of the installation is increased. In contrast, in the present invention, the recovery device is constructed with the ejector for using pressure of liquefied gas. Therefore, it is not necessary to use driving components such as a pump or valve, and thereby structure of the recovery device can be simplified, and decreased in size. Further, cost of equipment can be reduced. 
     According to the BOG processing apparatus of the present invention as described above, a predetermined cooling performance for cooling BOG (or cooling and re-liquefying) can be kept, and the amount of liquefied gas for spraying can be reduced. Therefore, waste of each device can be eliminated, and energy efficiency of device operation can be increased. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic configuration showing a BOG processing apparatus according to an embodiment of the present invention; 
         FIG. 2  is a sectional view showing a cooling device in the BOG processing apparatus; and 
         FIG. 3  is a schematic configuration showing a BOG processing apparatus before improving the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Hereinafter, an embodiment of the preset invention will be explained with reference to drawings. A BOG processing apparatus  1  of the embodiment of the present invention for example is installed in a manufacturing equipment of liquefied natural gas (LNG), a storage equipment thereof, a receiving equipment thereof and so on, and processes Boil-off gas (BOG) caused by vaporizing LNG in a LNG storage tank. The BOG processing apparatus  1  is constructed to cool the BOG and returns the remaining liquid (or the mixed liquid including the re-liquefied liquid) to the LNG storage tank, and to send BOG to a utilizing system. Herein, as the utilizing system, a thermal power equipment for burning BOG as a fuel gas so as to generate electric power is illustrated. 
     As shown in  FIG. 1 , in the BOG processing apparatus  1 , a LNG supply line A for supplying LNG from the LNG storage tank, a BOG supply line B for supplying BOG from the LNG storage tank, a liquid return line C for returning liquid remaining in the treatment (or the mixed liquid in which the re-liquefied BOG and LNG are mixed, hereafter it is simply described as liquid ML) to the LNG storage tank, and a BOG outlet line D for delivering the processed BOG to the utilizing system are connected. LNG which is extracted from a lower portion of the LNG storage tank and boosted by a pump is supplied via a flow control valve A 1  to the LNG supply line A. Further, BOG which is extracted from an upper portion of the LNG storage tank, boosted by a compressor, and cooled by a precooling apparatus is supplied to the BOG supply line B. 
     Herein, a BOG processing apparatus  100  before the improvement having substantially the same function as the BOG processing apparatus  1  of the embodiment in the present invention will be explained with reference to  FIG. 3 . In the BOG processing apparatus  100 , as well as the BOG processing apparatus  1 , a LNG supply line A, a BOG supply line B, a liquid return line C, and a BOG outlet line D are connected. The BOG processing apparatus  100  has a cooling device  101  for cooling BOG by cool heat of LNG, a compression device  102  for compressing BOG cooled by the cooling device  101 , a second cooling device  103  for cooling BOG compressed by the compression device  102 , and a recovery device  104  for recovering the remaining liquid (or the mixed liquid in which re-liquefied BOG liquid and LNG are mixed) ML remaining after used in the cooling device  101  so as to cool BOG. 
     The cooling device  101  has a cooling drum  110 , a BOG inlet part  111 , a filled layer  112 , a spray  113 , a mist eliminator  114 , a BOG outlet part  115 , and a liquid outlet part  116 . The cooling drum  110  is formed in a cylindrical shape extending vertically, and circulates BOG from below to above. The BOG inlet part  111  introduces BOG from a lower portion of the cooling drum  110  into an inside thereof. The filled layer  112  is arranged above the BOG inlet part  111 , and brings LNG into contact with BOG. The spray  113  is arranged above the filled layer  112 , and sprays LNG downwardly. The mist eliminator  114  is arranged above the spray  113 , and eliminates mist in BOG. The BOG outlet part  115  is arranged above the cooling drum  110 , and ejects the cooled BOG toward the compression device  102 . The liquid outlet part  116  is arranged in a lower side of the cooling drum  110 , and ejects liquid ML toward the recovery device  104 . 
     The cooling drum  110  is formed as a close container. In an inside of the cooling drum  110 , the BOG inlet part  111 , the filled layer  112 , the spray  113 , and the mist eliminator  114  are installed. In a lower portion of the cooling drum  110 , a storage part  117  is arranged so as to store liquid ML, and is formed with a semi-ellipsoid shape of 2 to 1. The BOG inlet part  111  is constructed with a current plate for evenly diffusing BOG supplied from the BOG supply line B into an inside of the cooling drum  110 . BOG introduced from the BOG inlet part  111  rises in the inside of the cooling drum  110 , and passes through the filled layer  112  and the mist eliminator  114 . 
     The filled layer  112  is a layer for cooling BOG (or re-liquefying a part of BOG by cooling) with cool heat of LNG after coming into gas-liquid contact with BOG introduced from the BOG inlet part  11  into the inside of the cooing drum  110  and LNG sprayed from the spray  113 . Further, in order to bring LNG and BOG into gas-liquid contact with a large contact area, the filled layer  112  is constructed by one for example filled with a metal forming ring or one formed by overlapping a net-like molded body made of metal, and is formed in a layer shape with a height dimension of about 2 m. The mist eliminator  114  removes the mist from BOG raised with a gas state through the filled layer  112 , and is constructed with a metal or ceramic filter having fine meshes so as to absorb mist and drop it. 
     The compression device  102  compresses BOG which is cooled by the cooling device  101  and introduced from the BOC outlet part  115 . For example, a turbo type compressor is used for the compression device  102 . The second cooling device  103  cools BOG boosted by the compression device  102 . For example, an air-cooling type air fin cooler is used for the second cooling device  103 . Herein, while BOG introduced from the BOG outlet part  115  is cooled to for example −100° C. to −120° C., and raised to 60° C. to 70° C. by compressed with the compression device  102 , it is delivered to the utilizing system after cooled to normal temperature of approximately 30° C. by the second cooling device  103 . 
     In the BOG outlet line D for delivering BOG to the utilizing system, a BOG valve D 1  is provided so as to control flow rate depending on demand of BOG in the utilizing system and to close circulation of BOG. In an upstream side than the BOG valve D 1  (a side of the second cooling device  103 ), a BOG circulation line E is connected. The BOG circulation line E is to connect the BOG outlet line D and the BOG supply line B. In the middle of the BOG circulation line E, a BOG valve E 1  is arranged so as to control flow rate of BOG circulating BOG into the BOG supply line B and to close circulation of BOG. That is, when demand of BOG is low in the utilizing system, the BOG valve D 1  is throttled, the BOG valve E 1  is opened, and BOG from the BOG circulation line E to the BOG supply line B is circulated. Thereby, the delivery from the compression device  102  to the BOG outlet line D is reduced, and BOG circulating from the cooling device  101  to the compression device  102  is increased. As a result, the operation of the compression device  102  can be performed without delay. 
     The recovery device  104  extracts liquid ML stored in the storage part  117  of the cooling drum  110 , and returns the extracted liquid ML to the LNG storage tank through the liquid return line C. The recovery device  104  has extraction pipes  121 ,  122  connected to the liquid outlet part  116  of the cooling device  101  and divided into two system, pumps  123 ,  124  arranged in each of the extraction pipes  121 ,  122 , and pipes  125 ,  126  extending from each of the pumps  123 ,  124  to the liquid return line C. In the extraction pipes  121 ,  122 , gas pipes  127 ,  128  for returning BOG vaporized from liquid ML to the cooling drum  110  are connected. Furthermore, in the middles of the pipes  125 ,  126 , a pair of switching valves  129 ,  130  for switching flow of liquid ML and adjusting flow rate thereof are arranged, respectively. 
     In such recovery device  104 , the switching valves  129 ,  130  is switched, and one of the pumps  123  and  124  is driven. Thereby, liquid ML is extracted from the cooling drum  110  by using a path on one side, and delivered to the liquid return line C. At this time, although the other of the pumps  123  and  124  is stopped, a small amount of liquid ML flows through a path on the other side by the switching valves  129 ,  130 . In the other words, liquid ML is delivered in the path of the one side, and the path of the other side is made to wait as a backup. By switching between one side and the other side appropriately, maintenance and equipment exchange can be performed without stopping the operation. Further, by draining a small amount of liquid ML to the path of the other side standing-by and cooling liquid ML, an available state is always maintained on the path of the other side. 
     As described above, according to the BOG processing apparatus  100  before the improvement, liquid of LNG remaining after used in the cooling device  101  for cooling (or the mixed liquid in which the re-liquefied BOG and LNG are mixed) as liquid ML can be returned to the LNG storage tank via the liquid return line C. Further, mist from BOG cooled by the cooling device  101  is eliminated, and BOG is compressed by the compression device  102 , and cooled by the second cooling device  103 . Thereafter, BOG can be sent to the utilizing system as a fuel gas via the BOG outlet line D. Therefore, BOG generated in the LNG storage tank can be effectively utilized without waste. 
     However, in the BOG processing apparatus  100  before the improvement, the filled layer  112  for bringing into gas-liquid contact with BOG and LNG and cooling BOG by cool heat of LNG becomes excessive in the cooling device  101 . Further, LNG sprayed from the spray  113  tends to become large amounts. That is, BOG introduced from the BOG inlet part  111  lower than the filled layer  112  comes into gas-liquid contact with LNG sprayed from the spray  113  upper than the filled layer  112 . In order to increase the contact area, a thickness dimension of the filled layer  112  becomes large, and thereby the supply of LNG for spraying is increased so as to spread LNG to the thick filled layer  112 . In this manner, when the supply of LNG is increased, operation power of the pump used for supplying is increased. As a result, problem such that operation energy of the entire system is increased is caused. 
     Further, in the BOG processing apparatus  100  before the improvement, two systems of piping and pumps  123 ,  124  for operation and backup are installed in the recovery device  104  from the need for continued operation. Therefore, installation of equipment and maintenance become a major liability. Furthermore, two systems of piping, valves, and pumps  123 ,  124  are used for circulating the remaining LNG liquid ML (or the mixed liquid in which the re-liquefied BOG and LNG are mixed). For this reason, it is necessary to use a cryogenic equipment. Therefore, installation burden of equipment is increased. In addition, since flowing a small amount of liquid ML in a path on a stand-by side as its backup and cooling are required, energy used for the operation is increased. In this manner, in the BOG processing apparatus  100  before the improvement, problem that not only burdens of installation of equipment and maintenance in the recovery device  104  is increased but also energy for used for the operation is increased is caused. 
     For the BOG processing apparatus  100  before the improvement as described above, the improved point will be explained in detail below with reference to  FIGS. 1 and 2 . A BOG processing apparatus  1  is constructed with a cooling device  2 , a compression device  3 , a second cooling device  4 , and a recovery device  5 . In the BOG processing apparatus  1 , the cooling device  2  and the recovery device  5  are improved from the cooling device  101  and the recovery device  104  of the BOG processing apparatus  100 . The compression device  3  and the second cooling device  4  are used in the same manner as the compression device  102  and the second cooling device  103 . 
     The cooling device  2  has a cooling drum  10 , a BOG inlet part  11 , a first spray  12 , a first filled layer  13 , a second spray  14 , a third spray  15 , a second filled layer  16 , and a mist eliminator  17 . The cooling drum  10  is formed in a cylindrical shape extending up and down, and circulates BOG from below to above. The BOG inlet part  11  introduces BOG from a lower portion of the cooling drum  10  into an inside of the cooling drum  10 . The first spray  12  is arranged above the BOG inlet part  11 , and upwardly spraying LNG. The first filled layer  13  is arranged above the first spray  12 , and brings into contact with LNG and BOG. The second spray  14  is arranged in au upper side of the first filled layer  13 , and downwardly sprays LNG. The third spray  15  is arranged above the second spray  14 , and downwardly sprays LNG. The second filled layer  16  is arranged above the third spray  15 , and adsorbs mist in BOG. The mist eliminator  17  is arranged above the second filled layer  16 , and eliminates mist in BOG. Further, in an upper portion of the cooling drum  10 , a BOG outlet part  18  for sending BOG toward the compression device  3  is arranged. In a lower portion of the drum  10 , a liquid outlet part  19  for sending liquid ML toward the recovery device  5  is arranged. 
     The cooling drum  10  is formed as a closed container. The BOG inlet part  11 , the first spray  12 , the first filled layer  13 , the second spray  14 , the third spray  15 , the second filled layer  16 , and the mist eliminator are installed inside of the cooling drum  10 . Further, a storage part  20  for storing liquid ML in which LNG and BOG are mixed is formed in a lower portion of the cooling drum  10 . The storage part  20  is formed in a substantially conical shape projecting downward so as to store mixed liquid ML. The  130 G inlet part  11  is constructed with a current plate for evenly diffusing BOG supplied from the BOG supply line B into an inside of the cooling drum  10  in common with the BOG inlet part  111 . BOG introduced from the BOG inlet part  11  moves up inside of the cooling drum  10 , and passes through the first filled layer  13 , the second filled layer  16 , and the mist eliminator  17 . 
     The first spray  12  sprays LNG upwardly. That is, the first spray  12  sprays LNG along flow of BOG introduced from the BOG inlet part  11  and moving up, and LNG is upward moved toward the first filled layer  13  while including BOG in LNG. The first filled layer  13  is formed in a layer shape overlapping a metal ring or metal net similar to the filled layer  112 . The first filled layer  13  is different from the filled layer  112 . For example, the height dimension thereof is thinly made with about 600 mm. In common with the spray  113 , the second spray  14  downwardly sprays LNG, but LNG sprayed from the second spray  14  is greatly reduced than the spray  113 . The third spray  15  sprays mist-like LNG having a small droplet diameter compared with the second spray  14 . 
     In this manner, by coming into gas-liquid contact with LNG which is sprayed from each of the first spray  12 , the second spray  14  and the third spray  15  and BOG introduced from the BOG inlet part  11 , BOG is cooled by cold energy of LNG (or a part of BOG is re-liquefied by cooling). When passing through the second filled layer  16 , mist is adsorbed on BOG cooled by the first filled layer  13  and rising as a vapor. Further, when passing through the mist eliminator  17 , mist is removed and sent from the BOG outlet part toward the compression device  3 . Liquid ML of the first filled layer  13  falls into the lower storage part  20  and is stored. 
     In common with the first filled layer  13 , the second filled layer  16  is constructed with in the form of laminate overlapping a metal forming ring or a metal mesh shaped body, but the size of the ring or mesh is formed smaller than the first filled layer  13 . Thereby, the second filled layer  16  is configured to facilitate adsorption of mist. Further, in common with the mist eliminator  114 , the mist eliminator  17  is constructed with metal or ceramic having fine mesh so as to adsorb mist in BOG and drop it. In this way, mist of LNG adsorbed on the second filled layer  16  and the mist eliminator  17  are combined and then the drop become large. Thereby, the mist falls into the lower side of storage part  20  and stored with liquid ML. 
     The recovery device  5  extracts liquid ML stored in the storage part  20  of the cooling drum  10 , and returns the extracted liquid ML from the liquid return line C to the LNG storage tank. The recovery device  5  is constructed with an ejector  21  connected to the liquid outlet part  19  of the cooling device, a branch pipe A 2  connecting the front of the flow control valve A 1  on the LNG supply line A with the ejector  21 , and a control valve A 3  arranged on a middle of the branch pipe A 2  and controlling flow rate of LNG. The ejector  21  introduces liquid ML extracted from the liquid outlet part  19  into an inside thereof, and draws liquid ML by injection pressure of LNG supplied from the branch pipe A 2 . Further, the ejector  21  apples pressure after mixing LNG and liquid ML, and sends the liquid ML from the liquid return line C to the LNG storage tank. 
     According to such recovery device  5 , liquid ML can be drawn by the injection pressure of LNG supplied from the LNG storage tank without using the pumps  123 ,  124 , and can be sent from the liquid return line C to the LNG storage tank. Therefore, power for driving the pumps and so on can be reduced. Further, by using LNG as a driving medium and returning liquid ML to the LNG storage tank, energy efficiency of the whole BOG processing process can be boosted without adding a separation apparatus required when using another driving medium. 
     According to the BOG processing apparatus  1  of the embodiment in the present invention as described above, there are effects as below. More specifically, while BOG is introduced from the lower portion of the cooling drum  10  and flows upward, LNG is upwardly sprayed from the first spray  12  along a direction in which BOG flows, and is downwardly sprayed from the second spray  14 . Thereby, LNG can be spread on the top and lower of the first filled layer  13  positioned between the first spray  12  and the second spray  14 , and BOG passing through the first filled layer  13  can be brought into contact with much LNG. Thus, a predetermined cooling performance for cooling BOG (or cooling and re-liquefying BOG) can be maintained, and a thickness in the first filled layer  13  can be decreased. Furthermore, an amount of LNG sprayed from each of the sprays  12 ,  14  can be reduced by the minimum necessary. 
     The third spray  15  is arranged upward the second spray  14 , LNG having a mist shaped is sprayed from the third spray  15 , and thereby cooling performance for cooling BOG (or cooling and re-liquefying BOG) can be improved. Further, mist in BOG is adsorbed by the second filled layer  16  arranged upward the third spray  15 , and mist in BOG passing through the second filled layer  16  is eliminated by the mist eliminator  17 . Therefore, BOG in which mist is not included as much as possible can be sent from the BOG outlet part  18  to the compression device  3 , and BOG can be compressed without reducing the function of the compression device  3 . 
     Further, the recovery device  5  has the ejector  21  in which LNG becomes the driving medium. Therefore, when compared with a case of using driving components the pumps  123 ,  124  or valves  129 ,  139  like the BOG processing apparatus before the improvement, the structure of the recovery device  5  can be simplified and downsized. Furthermore, cost of equipment can be reduced. That is, in the BOG processing apparatus  100  before the improvement, it is necessary to use cryogenic driving components such as the pumps  123 ,  124 , the valves  129 ,  130  and the like, and to install driving components of a plurality of systems for inspection or failure. As a result, the recovery device  104  becomes complex and large in size, and thereby cost of installation is increased. On the other hand, in the BOG processing apparatus  1  of the embodiment in the present invention, the recovery device  5  is constructed with having the ejector  21  in which LNG is the driving medium. Therefore, the structure thereof can be simple, and the configuration of a standby equipment can be reduced without having mechanical moving parts. 
     Also, the present invention is not limited to the above embodiments. The present invention includes various constitutions in which the object of the present invention can be achieved, and the following modifications are includes in the present invention. For example, in the above embodiment, the BOG processing apparatus  1  installed in a manufacturing equipment of liquefied natural gas (LNG), a storage equipment thereof, a receiving equipment thereof and so on is explained, however the present invention is not limited to liquefied natural gas. The present invention can be used in a manufacturing equipment of any liquefied gas such as liquefied petroleum gas (LPG), liquefied nitrogen, liquefied oxygen, and liquid hydrogen as the BOG processing apparatus. 
     Further, in the embodiment, the second device  2  having the third spray  15  and the second filled layer  16  are illustrated, however the third spray  15  and the second filled layer  16  are additional things for increasing cooling effect of BOG, and they are not an essential configuration in the present invention. Therefore, they can be omitted as appropriate. Furthermore, the recovery device  5  has the ejector  21  in the embodiment, but the recovery device  5  of the present invention may have a pump like the recovery device  104  before the improvement. In addition, the recovery device  5  has one of the ejector  21  in the embodiment, but the ejector may be provided in each of positions branched into a plurality of systems as the recovery device  104  before the improvement. 
     Further, the BOG processing apparatus  1  of the embodiment is constructed to return liquid ML to the LNG storage tank by the recovery device  5 , but it is not limited to return the recovered liquid to the LNG storage tank as the recovery device. The remaining liquid (or the mixed liquid in which the re-liquefied BOG and LNG are mixed) may be joined to a line sending LNG to the utilizing system. Moreover, the BOG processing apparatus  1  of the embodiment is constructed to compress BOG cooled in the cooling device  2  by the compression device  3 , and to send it the utilizing system after cooled in the second cooling device  4 , but it is not limited to send BOG cooled in the cooling device  2  to the utilizing system. The BOG processing apparatus  1  may be constructed to re-liquefy almost all of BOG and to discharge the small remaining BOG to the atmosphere via a flare stack. In this case, the compression device  3  and the second cooling device  4  can be omitted. 
     The best mode configurations, methods and the like for carrying out the present invention are disclosed in the above description, but the present invention is not limited thereto. In the other words, the present invention is illustrated with reference to a specific embodiment, and explained. However, various modifications can be made by those skilled in the art to the above-described embodiments, in shapes, materials, quantities, and other detailed configurations without departing from the technical idea and the scope of the object of the present invention. Thus, descriptions that restrict the shape, material, etc. disclosed above is exemplarily described in order to facilitate understanding of the present invention, and the present invention is not limited thereto. So, descriptions in the name of members excluding a part of the limitation of the shape, material, etc. or all of the limitation are included within the scope of the present invention.