Patent Publication Number: US-2016238312-A1

Title: Liquefied gas producing facility and liquefied gas producing method

Description:
TECHNICAL FIELD 
     The present invention relates to a liquefied gas producing facility and a liquefied gas producing method. 
     BACKGROUND ART 
     Liquefied gas producing facilities are facilities for producing desired liquefied gas by refining and liquefying liquefied natural gas (LNG), liquefied petroleum gas (LPG), and synthetic natural gas (SNG), which are natural gases. Examples of liquefied gas producing facilities include an LNG producing facility, an LPG producing facility, and an SNG producing facility. 
     Refrigeration cycles of LNG producing facilities include water-cooling or air-cooling condensers. Water-cooling condensers often use seawater to cool cooling water. However, the influence of the seawater heated as a result of heat exchange on the environment has become a problem, and the number of LNG producing facilities including air-cooling condensers has recently increased. 
     A liquefaction process is essential not only in LNG producing facilities but also in LPG producing facilities and SNG producing facilities. 
     As illustrated in  FIGS. 1 and 2  of PTL 1, a typical LNG producing facility is configured such that a pipe rack is arranged in a central area of the facility and compressors, heat exchangers for cooling natural gas, a distillation column for refining the natural gas, etc., are arranged on both sides of the pipe rack. In an LNG producing facility including an air-cooling condenser, a plurality of air fin coolers (hereinafter referred to also as “AFCs”) are installed at the top of the pipe rack. The AFCs suck in air from below with fans, cause the air to exchange heat with fluids that flow through tubes arranged on the pipe rack, and discharge the air heated as a result of the heat exchange upward. 
     CITATION LIST 
     Patent Literature 
     PTL 1: Japanese Unexamined Patent Application Publication No. 2005-147568 
     SUMMARY OF INVENTION 
     Technical Problem 
     In LNG producing facilities including air-cooling heat exchangers, as the outside temperature increases, the amount of heat exchange in the AFCs decreases, and the output of gas turbines decreases accordingly. This leads to a reduction in the amount of production of LNG. 
     Accordingly, an object of the present invention is to provide an air-cooling liquefied gas producing facility and an air-cooling liquefied gas producing method with which the efficiency of heat exchange performed by the AFCs can be increased and a reduction in the amount of production of liquefied gas due to outside temperature can be suppressed. 
     Solution to Problem 
     According to the present invention, a liquefied gas producing facility and the like as described in the following items can be provided. 
     1. A liquefied gas producing facility which produces liquefied gas by liquefying feed gas which contains methane as a main component, the liquefied gas producing facility comprising: 
     a first heat exchanger that causes a first refrigerant to exchange heat with the feed gas and a second refrigerant to cool the feed gas and the second refrigerant; 
     a first refrigerant compressor that compresses the first refrigerant that is gasified through cooling the feed gas and the second refrigerant in the first heat exchanger; 
     a second heat exchanger that causes the second refrigerant to exchange heat with the feed gas that is cooled by the first heat exchanger to further cool and liquefy the feed gas; 
     a second refrigerant compressor that compresses the second refrigerant that is gasified through cooling the feed gas in the second heat exchanger; 
     air-cooling heat exchangers for the first refrigerant that air-cool the first refrigerant that is discharged from the first refrigerant compressor; 
     air-cooling condensers for the first refrigerant that air-cool the first refrigerant that is cooled by the air-cooling heat exchangers for the first refrigerant to liquefy the first refrigerant; 
     air-cooling heat exchangers for the second refrigerant that air-cool the second refrigerant that is discharged from the second refrigerant compressor; 
     air-cooling condensers for the second refrigerant that air-cool the second refrigerant that is cooled by the air-cooling heat exchangers for the second refrigerant to liquefy the second refrigerant; and 
     a mist spraying device that sprays a mist containing demineralized water toward cooling air supplied to at least one of the air-cooling condensers for the first refrigerant. 
     If the demineralized water is sprayed to all air-cooling heat exchangers (hereunder, “heat exchanger” may also include “condenser”) that the liquefied gas producing facility comprises, an amount of heat exchanged in the heat exchangers increases and an amount of production is maximized. However, it requires a huge amount of demineralized water and is not economical. Therefore, by specifying the air-cooling heat exchangers to which the demineralized water is splayed, the consumption of demineralized water is reduced and an LNG production capacity is efficiently improved. 
     In the air-cooling condensers for the first refrigerant, the feed gas and the second refrigerant are cooled by indirectly exchanging heat with the first refrigerant. The second refrigerant for liquefying the feed gas is cooled by the first refrigerant, and thus, if the refrigeration capacity of the first refrigerant is decreased, the production capacity of the liquefied gas producing facility is significantly decreased. 
     Therefore, in item 1 above, the mist is sprayed to one of the air-cooling condensers for the first refrigerant, thereby reducing the consumption of demineralized water and efficiently improving an LNG production capacity. 
     2. The liquefied gas producing facility according to item 1, further comprising: 
     an acid gas removing device that removes acid gas contained in the feed gas with an amine solution; and 
     a demineralized water producing device that produces demineralized water for diluting the amine solution, 
     wherein the demineralized water contained in the mist is supplied from the demineralized water producing device. 
     3. The liquefied gas producing facility according to item 1 or 2, 
     wherein said at least one of the air-cooling condensers for the first refrigerant that are sprayed with the mist includes an air-cooling condenser for the first refrigerant on which an influence of hot air recirculation (HAR) is large and which is determined on the basis of meteorological field information concerning an area around a location at which the liquefied gas producing facility is installed, the meteorological field information being computed by using three-dimensional fluid dynamic equations. 
     Further, by HAR wherein hot air discharged from one AFC is drawn in the other AFC, there is a problem that the amount of heat exchanged in AFCs is reduced and the production of liquefied gas is decreased. In item 3 above, this problem is avoided. 
     4. The liquefied gas producing facility according to item 3, 
     wherein the meteorological field information concerning an area around a location at which the liquefied gas producing facility is installed is calculated by the steps of: 
     selecting, from a plurality of weather information which are related to areas and times and which include at least temperature data, a plurality of weather information sets related to a plurality of times over a fixed period concerning a first area containing a location at which the liquefied gas producing facility is installed; 
     solving, with the use of the selected plurality of weather information sets as input data, differential equations expressing the weather information based on an analysis model used for conducting a weather simulation, and generating a plurality of first narrow-area weather information sets related to a plurality of second areas which are disposed within the first area and which are smaller than the first area; selecting a second narrow-area weather information set concerning a second area containing the location at which the liquefied gas producing facility is installed from among the generated plurality of first narrow-area weather information sets; and computing the second narrow-area weather information set by using three-dimensional fluid dynamic equations and calculating the meteorological field information concerning the area around the location at which the liquefied gas producing facility is installed. 
     5. A method for producing liquefied gas by liquefying feed gas which contains methane as a main component, the method comprising the steps of: 
     causing, by using a first heat exchanger, a first refrigerant to exchange heat with the feed gas and a second refrigerant to cool the feed gas and the second refrigerant; 
     compressing, by using a first refrigerant compressor, the first refrigerant that is gasified through cooling the feed gas and the second refrigerant in the first heat exchanger; 
     causing, by using a second heat exchanger, the second refrigerant to exchange heat with the feed gas that is cooled by the first heat exchanger to further cool and liquefy the feed gas; 
     compressing, by using a second refrigerant compressor, the second refrigerant that is gasified through cooling the feed gas in the second heat exchanger; 
     air-cooling, by using air-cooling heat exchangers for the first refrigerant, the first refrigerant that is discharged from the first refrigerant compressor; 
     air-cooling, by using air-cooling condensers for the first refrigerant, the first refrigerant that is cooled by the air-cooling heat exchangers for the first refrigerant to liquefy the first refrigerant; 
     air-cooling, by using air-cooling heat exchangers for the second refrigerant, the second refrigerant that is discharged from the second refrigerant compressor; air-cooling, by using air-cooling condensers for the second refrigerant, the second refrigerant that is cooled by the air-cooling heat exchangers for the second refrigerant to liquefy the second refrigerant; and 
     spraying a mist containing demineralized water toward cooling air supplied to at least one of the air-cooling condensers for the first refrigerant. 
     6. The method for producing liquefied gas according to item 5, further comprising the steps of: 
     removing, by using an acid gas removing device, acid gas contained in the feed gas with an amine solution; and 
     producing, by using a demineralized water producing device, demineralized water for diluting the amine solution, 
     wherein the demineralized water contained in the mist is supplied from the demineralized water producing device. 
     7. The method for producing liquefied gas according to item 5 or 6, 
     wherein said at least one of the air-cooling condensers for the first refrigerant that are sprayed with the mist includes an air-cooling condenser for the first refrigerant on which an influence of hot air recirculation (HAR) is large and which is determined on the basis of meteorological field information concerning an area around a location at which the liquefied gas producing apparatus is installed, the meteorological field information being computed by using three-dimensional fluid dynamic equations. 
     8. The method for producing liquefied gas according to item 7, 
     wherein the meteorological field information concerning an area around a location at which the liquefied gas producing facility is installed is calculated by the steps of: 
     selecting, from a plurality of items of weather information which are related to areas and times and which include at least temperature data, a plurality of weather information sets related to a plurality of times over a fixed period concerning a first area containing a location at which the liquefied gas producing facility is installed; 
     solving, with the use of the selected plurality of weather information sets as input data, differential equations expressing the weather information based on an analysis model used for conducting a weather simulation, and generating a plurality of first narrow-area weather information sets related to a plurality of second areas which are disposed within the first area and which are smaller than the first area; 
     selecting a second narrow area weather information set concerning a second area containing the location at which the liquefied gas producing facility is installed from among the generated plurality of first narrow-area weather information sets; and 
     computing the second narrow area weather information set by using three-dimensional fluid dynamic equations and calculating the meteorological field information concerning the area around the location at which the liquefied gas producing facility is installed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram illustrating an example of an LNG producing facility. 
         FIG. 2  is a schematic diagram illustrating an example of an LNG liquefaction facility. 
         FIG. 3  illustrates an example of the functional configuration of a weather predicting apparatus. 
         FIG. 4  illustrates an example of the data table of weather information. 
         FIG. 5  illustrates an example of the hardware configuration of a weather predicting apparatus. 
         FIG. 6  illustrates an example of wide-area weather information. 
         FIG. 7  illustrates an example in which a part of the wide-area weather information illustrated in  FIG. 6  is enlarged. 
         FIG. 8  illustrates an example of narrow-area weather information. 
         FIG. 9  illustrates an example of meteorological field information. 
         FIG. 10  illustrates examples of AFCs at which HAR is occurring. 
         FIG. 11  is a schematic diagram illustrating an embodiment of an LNG liquefaction facility. 
         FIG. 12  is a schematic diagram illustrating an embodiment of the arrangement of components in an LNG producing facility. 
         FIG. 13  is a schematic diagram illustrating an embodiment of a demineralized water supply device. 
         FIG. 14  is a schematic diagram illustrating another embodiment of an LNG liquefaction facility. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     1. Liquefied gas producing facility 
     A liquefied gas producing facility according to the present invention air-cools a refrigerant with air-cooling heat exchangers to liquefy gas. All of heat exchangers described below are air-cooling heat exchangers unless otherwise specified in this specification. 
       FIG. 1  is a schematic diagram illustrating an example of an LNG producing facility. Gas supplied from a gas well is fed to the LNG producing facility after being subjected to a liquid separation process. In the LNG producing facility, LNG is produced by the steps of, for example, mercury removal, acid gas removal, moisture removal, liquefaction, nitrogen removal and the like. 
     In the liquefaction step, the natural gas is liquefied by a vapor compression refrigeration cycle in which power of a compressor and heat exchange in a condenser are utilized. In the refrigeration cycle, a gas refrigerant is compressed by the compressor and cooled by the condenser, so that the gas refrigerant is converted into a high-pressure liquid. Then, the pressure and temperature of the refrigerant are reduced by an expansion valve or the like, and the refrigerant is caused to exchange heat with the natural gas. The refrigerant is gasified as a result of the heat exchange, and is supplied to the compressor. Thus, the refrigerant is circulated. 
     The step of acid gas removal is performed by separating acid gas and process gas by chemical absorption separation using an amine solution. 
     More specifically, a liquefied gas producing facility according to the present invention includes a liquefied gas producing unit which produces liquefied gas by removing unnecessary substances from feed gas, which contains methane as a main component, and by liquefying the feed gas. The liquefied gas producing unit includes a heat exchanger that cools the feed gas by causing the feed gas to exchange heat with a refrigerant, a compressor that compresses the refrigerant vaporized as a result of heat exchange with the feed gas, an AFC unit that cools the compressed refrigerant, and an expansion unit that further cools the cooled refrigerant by adiabatically expanding the refrigerant. The AFC unit includes a demineralized water supply device which sprays demineralized water. 
     In the liquefied gas producing facility according to the present invention, the demineralized water supply device sprays demineralized water in the form of mists or liquid droplets toward regions below AFCs. The sprayed demineralized water is sucked upward together with air sucked by the AFCs from the regions below. The demineralized water that has been sucked vaporizes while passing between tubes on a pipe rack before being discharged upward from the AFCs. The heat of vaporization generated at this time efficiently cools the refrigerant that flows through the tubes arranged on the pipe rack, so that reduction in the amount of heat exchange due to the outside temperature and HAR can be suppressed. As a result, reduction in the amount of production of the liquefied gas can be suppressed. 
     The demineralized water is water from which salts are removed. Examples of demineralized water include deionized water that has passed through an ion exchange resin, RO water that has passed through a reverse osmosis membrane, distilled water and the like. When the demineralized water is used, formation of scale on the tubes and the AFCs due to salts can be prevented, and a cause of reduction in heat-transfer co-efficient can be removed. 
       FIG. 2  is a schematic diagram illustrating an example of a liquefaction facility included in the LNG producing facility. 
     Feed gas  100  from which CO 2 , H 2 S, and water, which are typical impurities, are removed is transferred to the liquefaction facility as a process fluid. Then, the feed gas is cooled by two refrigerants having different temperatures, and is finally liquefied. The refrigerant having a higher temperature (“first refrigerant”) is, for example, propane. The refrigerant having a lower temperature (“second refrigerant”) is, for example, a mixed refrigerant containing nitrogen, methane, ethane, and propane. 
     In  FIG. 2 , the feed gas is cooled and liquefied by a heat exchanger  101  which uses the first refrigerant as a refrigerant and by a heat exchanger  102  which uses the second refrigerant as a refrigerant. LNG product is transferred to a storage tank  105  by a pump  104 , and is stored until shipment. The LNG is slightly heated in the storage tank, and gas is generated as a result of vaporization of the LNG. This gas is returned to the process, liquefied again by the heat exchanger  102 , and transferred to the storage tank  105  by the pump  104 . 
     In a first refrigerant refrigeration cycle, the first refrigerant collected through intake lines  203 ,  204 , and  205  is pressurized by a first refrigerant compressor  200 , and is then cooled by an air-cooling heat exchanger for the first refrigerant  201 . Then, the first refrigerant is liquefied by an air-cooling condenser for the first refrigerant  211 , de-compressed to a predetermined pressure by an expansion valve  202 , and is transferred to the heat exchanger  101 . The heat exchanger  101  cools the feed gas  100  and the second refrigerant, which is used in a downstream heat exchanger, by causing them to exchange heat with the first refrigerant. 
     In a second refrigerant refrigeration cycle, the second refrigerant collected through intake lines  303  and  304  is pressurized by a second refrigerant compressor  300 , and is then cooled by an air-cooling heat exchanger for the second refrigerant  301 . Then, the second refrigerant is cooled and liquefied as a result of heat exchange with the first refrigerant in the heat exchanger  101 . Next, the second refrigerant is decompressed to a predetermined pressure by an expansion valve  302 , and is transferred to the heat exchanger  102 . The heat exchanger  102  cools and liquefies the feed gas  100  discharged from the heat exchanger  101 . 
     According to the present invention, a demineralized water supply device (not shown) sprays demineralized water from below an AFC  100 A. 
     2. Liquefied gas producing method 
     A liquefied gas producing method according to the present invention is a method for producing liquefied gas by removing unnecessary substances from feed gas, which contains methane as a main component, and by liquefying the feed gas. The liquefied gas producing method includes the steps of cooling the feed gas by causing the feed gas to exchange heat with a refrigerant, compressing the refrigerant vaporized as a result of the heat exchange with the feed gas, cooling the compressed refrigerant with AFCs, and further cooling the cooled refrigerant by adiabatically expanding the refrigerant. Demineralized water is sprayed from below the AFCs. 
     With the liquefied gas producing method according to the present invention, the demineralized water is sprayed from below the AFCs, so that the sprayed demineralized water is sucked upward together with air sucked by the AFCs from below. The demineralized water that has been sucked vaporizes while passing between tubes on a pipe rack before being discharged upward from the AFCs. The heat of vaporization generated at this time efficiently cools the refrigerant that flows through the tubes arranged on the pipe rack, so that reduction in the amount of heat exchange due to the outside temperature and HAR can be suppressed. As a result, reduction in the amount of production of the liquefied gas can be suppressed. 
     The sprayed demineralized water may be in the form of mists or liquid droplets. Although the diameter of the liquid droplets is not particularly limited, the diameter is preferably as small as possible. The amount of demineralized water to be sprayed may be changed as appropriate in accordance with the outside temperature and the occurrence of HAR. Preferably, the amount of demineralized water to be sprayed is set so that all of the demineralized water is vaporized before being discharged upward from the AFCs. 
     The AFCs toward which the demineralized water is sprayed are preferably only some of the AFCs used to produce the liquefied gas. To spray the demineralized water toward all the AFCs used to produce the liquefied gas, a large demineralized water supply device is required. In contrast, when the demineralized water is sprayed toward only some of the AFCs, the required amount of demineralized water can be reduced. Accordingly, the equipment cost for producing and spraying the demineralized water and the operation cost can be reduced. 
     The AFCs toward which the demineralized water is sprayed are preferably the AFCs that have a large influence on the amount of production of the liquefied gas. When the demineralized water is sprayed toward the AFCs that have a large influence on the amount of production of the liquefied gas, the required amount of demineralized water can be reduced. In addition, reduction in the amount of heat exchange and reduction in the amount of production of the liquefied gas due to the outside temperature and HAR can be suppressed. 
     3. Determination of AFCs toward Which Demineralized Water is to be Sprayed Based on Simulation 
     The AFCs which have a large influence on the amount of production of the liquefied gas are, for example, AFCs having a large heat transfer area (amount of heat exchange) and AFCs that are greatly influenced by HAR. The influence of HAR can be analyzed by simulation. 
     3.1 Weather Analysis Models 
     The descriptions are made on examples of the simulation (computational fluid analysis) that is performed with a weather predicting apparatus using output data of weather analysis models that are to be described below. 
     When measuring the temperature and the direction of the wind in an area in which a liquefied gas producing facility will be placed, measurements over several years are required since it is necessary to design a liquefied gas producing facility by considering the influence of an annual change, such as whether or not the El Nino phenomenon is observed. However, if there is no data over the years, a liquefied gas producing facility has to be designed on the basis of low-precision environmental data, since it is difficult to measure the temperature and the direction of the wind for several years in future from a present time point. 
     Weather analysis models include various physical models, and by analyzing such physical models by using a computer, calculations for predicting the weather having a higher spatial resolution are performed, thereby making it possible to conduct weather simulations. Weather simulations have an advantage over field observation that weather information having a higher spatial resolution can be estimated. 
     In order to conduct weather simulations, it is necessary to load data of initial values and boundary values from a weather database downloaded from a network. A sufficiently detailed spatial resolution for designing an LNG producing facility is not available. However, as weather information concerning a wide area including an area in which an LNG producing facility is placed (hereinafter referred to as a “wide-area weather information”), for example, NCEP (National Centers for Environmental Prediction), which is global observation analysis data reanalyzed every six hours and which is provided by NOAA (National Oceanic and Atmospheric Administration) etc., is available. NCEP data as the wide-area weather information include weather elements (wind direction, wind speed, turbulence energy, solar radiation, atmospheric pressure, precipitation, humidity, and temperature) on three-dimensional grid points obtained by dividing the world into a grid pattern (grid spacing is 1.5 through 400 km), and are updated every six hours. In this embodiment, it is necessary to design an LNG producing facility by considering the influence of an annual change, such as whether or not the El Nino phenomenon is observed. Accordingly, wide-area weather information over the several years (for example, the above-described NCEP data) is used as data of initial values and boundary values. 
     An example of physical models included in weather analysis models is the WRF (Weather Research &amp; Forecasting Model). The WRF include various physical models. Examples of the physical models are radiation models for calculating the amount of solar radiation and the amount of atmospheric radiation, turbulence models for expressing a turbulence mixed layer, and ground surface models for calculating the ground surface temperature, soil temperature, field moisture, snowfall amount, and surface flux. 
     The weather analysis models include partial differential equations expressing the motion of fluid in the atmosphere, such as Navier-Stokes equations concerning the motion of fluid and empirical equations derived from atmospheric observation results, and partial differential equations expressing the law of conservation of mass and the law of conservation of energy. By solving these simultaneous partial differential equations, weather simulations can be conducted. Thus, by using wide-area weather information as input data indicating initial values and boundary values, differential equations based on weather analysis models for weather simulations are solved, thereby making it possible to generate weather information concerning a location area of an LNG producing facility related to a region having a narrower spatial resolution than that of wide-area weather information. Weather information generated in this manner is referred to as “narrow-area weather information”. 
     3.2 Computational Fluid Analysis 
     Computational fluid analysis refers to a numerical analysis and simulation technique for observing the flow of fluid by applying Computational Fluid Dynamics (CFD) in which equations concerning the motion of fluid are solved by using a computer. More specifically, by using Navier-Stokes equations, which are fluid dynamics equations, the state of fluid is spatially calculated by utilizing the Finite Volume Method. The procedure for computational fluid analysis includes a step of creating 3D model data reflecting a structure of a facility, which is a subject to be examined, a step of generating grids by dividing a range of the subject to be examined into grids, which are the minimum calculation units, a step of loading initial values and boundary values and solving fluid dynamic equations concerning each grid by using a computer, and a step of outputting various values (flow velocity, pressure, etc.) obtained from analysis results, as images, such as contours and vectors. 
     By conducting computational fluid analysis, fluid simulations having a higher resolution than those obtained by weather analysis models can be implemented. Thus, it is possible to provide information concerning air current phenomena unique to a space scale of a subject to be examined, such as small changes in the wind speed and the wind direction, a disturbance of an air current on a scale from several centimeters to several meters, and a change in air current around a building, which are very difficult to predict by weather simulations. 
     3.3 Functional Configuration and Hardware Configuration of Weather Predicting Apparatus 
     A weather predicting apparatus uses weather analysis models or conducts computational fluid analysis, thereby calculating narrow-area weather information concerning a narrow area in which an LNG producing facility is placed. 
       FIG. 3  illustrates an example of the functional configuration of a weather predicting apparatus. A weather predicting apparatus  90  shown in  FIG. 3  includes a storage section  12  which stores therein data and programs and a processor  14  which executes arithmetic operations. In the storage section  12 , a weather analysis program  901 , such as the WRF, a computational fluid analysis program  903 , a design temperature calculating program  905 , a wind rose generating program  907 , a layout output program  909  for generating a layout, a weather database  800 , wide-area weather information  801 , such as NCEP data, narrow-area weather information  803  obtained by weather simulations, air flow field information  805  obtained by computational fluid analysis, temperature analysis data  807 , wind direction analysis data  808 , and layout data  809 . The weather database stores therein the wide-area weather information  801 , which is obtained as a result of downloading it from an external source or is obtained from a storage medium. 
     The processor  14  executes the weather analysis program  901  and thereby performs weather analysis processing in which the narrow-area weather information  803  is generated from the wide-area weather information  801  and is stored in the storage section  12 . The processor  14  also executes the computational fluid analysis program  903  and thereby performs computational fluid processing in which the air flow field data  807  is generated from the narrow-area weather information  803  and is stored in the storage section  12 . 
     Further, the processor  14  executes the layout generating program  909  and outputs the layout data  809  on the basis of the wind direction analysis data  808 . 
       FIG. 4  illustrates an example of the data table of weather information. The data table shown in  FIG. 4  indicates the wide-area weather information  801 , but may also be applied to the narrow-area weather information  803 . The wide-area weather information indicates weather information concerning a wider area than narrow areas corresponding to the narrow-area weather information, and such a wider area includes the narrow areas corresponding to the narrow-area weather information. The weather information is, as shown in  FIG. 4 , a plurality of record sets constituted by various data indicating the wind direction, wind speed, turbulence energy, solar radiation, atmospheric pressure, precipitation, humidity, and temperature, by using the time as a primary key. In other words, the data table shown in  FIG. 4  is constituted by weather information sets classified based on the temperature, and each of the wide-area weather information  801  and the narrow-area weather information  803  is constituted by a plurality of weather information sets classified based on the area. 
       FIG. 5  illustrates an example of the hardware configuration of a weather predicting apparatus. The weather predicting apparatus  90  shown in  FIG. 5  includes a processor  12 A, a main storage device  14 A, an auxiliary storage device  14 B, which is a hard disk or an SSD (Solid State Drive), a drive  15  that reads data from a storage medium  900 , and a communication device  19 , such as an NIC (network interface card). These components are connected to one another via a bus  20 . The weather prediction apparatus  90  is connected to a display  16 , which serves as an output device, and an input device  17 , such as a keyboard and a mouse, which are externally disposed. The processor  12  shown in  FIG. 3  corresponds to the processor  12 A, and the storage section  14  corresponds to the main storage device  14 A. 
     In the storage medium  900 , the weather database  800 , the weather analysis program  901 , the computational fluid analysis program  903 , the design temperature calculating program  905 , the wind rose generating program  907 , and the layout generating program  909  shown in  FIG. 3  may be stored as data. These data  800  through  909  are stored in the storage section  12 , as shown in  FIG. 3 . 
     The weather predicting apparatus  90  may be connected to an external server  200  or a computer  210  or  220  via a network  40 . The computer  210  and the external server  200  may have the same components as those of the weather predicting apparatus  90 . For example, the weather predicting apparatus  90  may receive the weather database  800  stored in the server  200  via the network  40 . Alternatively, among the programs shown in  FIG. 3 , only the weather analysis program  901  concerning weather simulations having a high system load may be stored in the weather predicting apparatus  90 , and the other programs may be stored in any of the computers  210  and  220  and may be executed therein. 
     Additionally, a description has been given above in which the weather predicting apparatus  90  is restricted to hardware, such as a computer. However, the weather predicting apparatus  90  may be a virtual server in a data center. In this case, the hardware configuration may be as follows. The programs  901  through  909  may be stored in a storage section in a data center, and a processor in the data center may execute the stored programs  901  through  909 , and data may be output from the data center to a client computer. The external server  200  may include a weather database, in which case, the weather predicting apparatus  90  may obtain wide-area weather data from the external server  200 . 
     3.4 Reproduction of Weather Information around LNG Producing Facility 
       FIG. 6  illustrates an example of wide-area weather information. In  FIG. 6 , wide-area weather information A 100  on a map of Japan is shown. 
       FIG. 7  illustrates an example in which the wide-area weather information shown in  FIG. 6  is enlarged. In the wide-area weather information A 100  shown in  FIG. 7 , an area in which the LNG producing facility  100  is placed is shown. Reference numeral  1100  designates a coastline. The left side of the coastline  1100  in the plane of the drawing is the sea, and the right side thereof is the land.  FIG. 8  illustrates an example of narrow-area weather information.  FIG. 8  illustrates an area for which weather simulations are conducted, and the area is partitioned into a plurality of zones A1 through A16 in order to conduct weather simulations, and each zone corresponds to a calculation grid. For example, if the grid resolution is 9 km, the calculation zone is 549 km×549 km. If the grid resolution is 1 km, the calculation zone is 93 km×93 km. Accordingly, in these zones A1 through A16, estimation points are set in a grid pattern at intervals of 1 through 9 km in the north-south direction and the east-west direction. 
     The LNG producing facility  100  is placed, as shown in  FIG. 8 , and in order to obtain the temperature or the direction of the wind in the zone in which the LNG producing facility  100  is placed, the processor  12  generates narrow-area weather information A1 through A16 from the wide-area weather information A 100  by solving partial differential equations expressing weather information based on weather analysis models. 
       FIG. 9  illustrates an example of meteorological field information. The processor  12  conducts computational fluid analysis on the narrow-area weather information A16 shown in  FIG. 9 , thereby calculating meteorological field information concerning a region smaller than the zones of narrow-area weather information. After calculating the meteorological field information concerning the zone A16, by using the meteorological field information concerning the zone A16 as an initial value, the processor  12  may determine detailed meteorological field information around the LNG producing facility  100  by using fluid dynamic models (CFD models). In this case, the detailed meteorological field information can be determined with a resolution in increments of 0.5 m, which is much smaller than the grid resolution (for example, 1 km) used in weather simulations. 
     The meteorological field information concerning the target zone A16 in which the LNG producing facility  100  is placed can be determined by using fluid dynamic models. Thus, precise data taking the configurations of buildings into consideration can be obtained. Examples of fluid dynamic models are K-Epsilon, LES, and DNS. 
     It is sufficient that a computer of this embodiment obtains detailed data of meteorological field information concerning the target zone only, and thus, it is not necessary to conduct analysis for all the zones A1 through A16 by using CFD models. Accordingly, a lot of computation times taken by conducting analysis using CFD models are not necessary, and CFD analysis is conducted only for the target zone, thereby making it possible to improve the precision and decrease the processing time. 
     Reference numeral  320  shown in  FIG. 9  designates a recirculating flow of an exhaust gas. By conducting CFD analysis, the flow in which heated air discharged from the LNG producing facility is returned to and recirculates in the suction unit of the LNG producing facility can be calculated and clarified, which has not been clarified by conducting weather simulations. Additionally, the recirculating flow is clarified, and thus, AFCs that are greatly influenced by HAR can be determined. 
     Moreover, for example, if there is, for example, an aerodrome in A3 shown in  FIG. 8  and required observation data, such as temperature data and wind direction data, is available, first narrow-area weather information sets may be recalculated by using such data as input values. With this arrangement, it is possible to improve the precision of weather simulations by using available local data. 
     Topographical features of the zone A16 in which the LNG producing facility is placed may be different from those described in weather information due to a reason of any of land leveling, land use, and equipment installation. Even in such a case, first narrow-area weather information sets may be recalculated on the basis of topographical information reflecting any of the land leveling, land use, and equipment installation caused by placing the LNG producing facility. With this arrangement, it is possible to precisely simulate weather conditions after the LNG producing facility is placed. 
       FIG. 10  illustrates examples of AFCs at which HAR is occurring.  FIG. 10  shows that the high/low temperature is indicated by the color shading, and the more the color become dark, the greater the influence of HAR is. The AFCs of propane condenser that greatly influenced by HAR can be determined. 
     As described above, for the design of the gas liquefaction facility, the narrow-area weather information is provided to predict the weather by the weather simulation, by which the CFD analysis is performed, and thereby the AFCs that HAR is greatly influenced can be clarified. Accordingly, even if there is no available data over the years, it becomes possible to design and construct the gas liquefaction plant in which measures to HAR are considered and implemented. 
     In the above example, CFD analysis is performed based on calculation results of weather simulation, for the design of gas liquefaction plant; however, CFD analysis can be performed without performing the weather simulation. In that case, CFD analysis can be performed by using the measured weather data, or in case not requiring the higher accuracy. 
     An air-cooling LNG producing facility includes a plurality of AFCs, and consumption of the demineralized water is increased when the demineralized water is sprayed toward all the AFCs. Therefore, among the air-cooling condenser for the first refrigerant  211 , AFCs that are greatly influenced by HAR are determined by simulation, and the demineralized water is sprayed toward the determined AFCs. Thus, the amount of consumption of the demineralized water can be suppressed. 
     In addition, preferably, CFD analysis is performed and the demineralized water is intermittently sprayed so that the demineralized water is sprayed when the influence of HAR is large. Accordingly, reduction in the amount of production of the liquefied gas due to HAR can be suppressed. 
     Embodiments of the present invention will now be described below with reference to the accompanying drawings. The scope of the present invention is not limited to the embodiments described below. 
     Embodiments 
     First Embodiment 
       FIG. 11  is a schematic diagram illustrating an embodiment of a liquefaction facility included in an LNG producing facility. In this process, propane (hereinafter also referred to as “C3”) and a mixed refrigerant (hereinafter also referred to as “MR”) containing nitrogen, methane, ethane, and propane are used as refrigerants for cooling and liquefying natural gas. This process is referred to as a C3-MR method. 
       FIG. 11  shows a flow of natural gas (or LNG) which is a process fluid (shown by thin solid lines), a flow of a first refrigeration cycle in which propane is used as a working fluid (shown by thick solid lines), and a flow of a second refrigeration cycle in which the mixed refrigerant is used as a working fluid (shown by dashed lines). The flow of propane and the flow of mixed refrigerant form closed loops through which the respective fluids are circulated by respective compressor driving devices and that are independent of each other. A propane (C3)compressor  20  and two mixed refrigerant (MR) compressors  40  and  42 , which are connected in series, are connected to respective gas turbines and motors (not shown) for driving the compressors. 
     The C3 compressor  20  pressurizes propane, which is the refrigerant of the first refrigeration cycle, and is driven by a single-shaft gas turbine (not shown). The low-pressure-stage MR compressor  40  and the high-pressure-stage MR compressor  42  pressurize the mixed refrigerant, which is a mixture of nitrogen, methane, ethane, and propane and which is the refrigerant of the second refrigeration cycle, in two stages. The MR compressors  40  and  42  are simultaneously driven by a gas turbine and a motor (not shown). 
     The propane refrigerant pressurized by the C3 compressor  20  circulates through the first refrigeration cycle shown by the thin solid lines, and the mixed refrigerant pressurized by the MR compressors  40  and  42  circulates through the second refrigeration cycle shown by the dashed lines. 
     Refined natural gas  10 , from which carbonic acid gas and hydrogen sulfide are removed in advance by an acid gas processing device, is cooled to about 21 degrees C. under a pressure of about 5 MPa (50 bar) in a heat exchanger  11  through which high-pressure propane refrigerant (pressure 770 kPa (7.7 bar), temperature 17 degrees C.) flows. Accordingly, most of the moisture contained in the refined natural gas  10  is condensed, and is removed afterwards by a drum  12 . The thus-dewatered natural gas is cooled to −10 degrees C. in a heat exchanger  13  through which intermediate-pressure propane refrigerant (pressure 320 kPa (3.2 bar), temperature −13 degrees C.) flows, and is then cooled to −30 degrees C. by a heat exchanger  14  through which low-pressure propane refrigerant (pressure 130 kPa (1.3 bar), temperature −37 degrees C.) flows. Next, the natural gas is supplied to a scrub column  15 , where heavy fraction is removed. Then, the natural gas is cooled by a main heat exchanger  16  through which the mixed refrigerant of the second refrigeration cycle flows, and is further cooled to −162 degrees C. and liquefied by being adiabatically expanded by an expansion valve  17 . The liquefied natural gas is transferred to an LNG tank  18 . 
     In the first refrigeration cycle, the propane refrigerant collected from the heat exchangers  11 ,  13 , and  14  and chillers  24 ,  25 , and  26  is pressurized to 1.6 MPa (16 bar) by the C3 compressor  20 . Then, the propane refrigerant is cooled to 47 degrees C., which is close to the condensation temperature, as a result of heat exchange with cooling water in a C3 compressor desuperheater  21 , and is further cooled and completely condensed as a result of heat exchange with cooling water in a C3 condenser  22 . The condensed propane refrigerant is further cooled by a C3 subcooler  23 , decompressed by expansion valves  27  to  32  to respective predetermined pressures, and transferred to each of the heat exchangers  11 ,  13 , and  14  and the chillers  24  to  26 . 
     In the second refrigeration cycle, the mixed refrigerant that has exchanged heat with the natural gas in the main heat exchanger  16  is compressed in two stages by the MR compressors  40  and  42 , and is cooled to 45 degrees C. by cooling water in a low-pressure-stage MR compressor aftercooler  41  and a high-pressure-stage MR compressor aftercooler  43 . The pressurized mixed refrigerant is successively subjected to heat exchange in the chillers  24  to  26 , through which the propane refrigerant decompressed to the respective pressures flows, and is eventually cooled to −35 degrees C. and partially condensed. Then, a separation drum  44  separates the mixed refrigerant into liquid and gas, both of which are caused to flow into the main heat exchanger  16 . The mixed refrigerant that has flowed into the main heat exchanger  16  is cooled by being adiabatically expanded by expansion valves  45  and  47 , and is dispersed into the main heat exchanger  16  through nozzles  46  and  48 . The dispersed mixed refrigerant cools the natural gas by exchanging heat with the natural gas while exchanging heat with the mixed refrigerant that flows through pipes in the main heat exchanger  16 . 
       FIG. 12  is a schematic diagram illustrating the arrangement of components in the LNG producing facility according to the embodiment. Table 1 shows the relationship between the model numbers of the components illustrated in  FIG. 12  and the names of the components. 
     
       
         
           
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Model No. 
                 Name 
               
               
                   
               
             
            
               
                 1000 
                 Dryer Regen Gas Cooler 
               
               
                 1001 
                 Regenerator Overhead Condenser 
               
               
                 1002 
                 Demethanizer Bottom Cooler 
               
               
                 1003 
                 C3 Condenser 
               
               
                 1004 
                 Debutanizer Bottom Cooler 
               
               
                 1005 
                 Debutanizer Overhead Condenser 
               
               
                 1006 
                 Demethanizer Condenser 
               
               
                 1007 
                 Lean Amine Cooler 
               
               
                 1008 
                 LP MR Compressor Aftercooler 
               
               
                 1009 
                 C3 Subcooler 
               
               
                 1010 
                 C3 Compressor Desuperheater 
               
               
                 1011 
                 HP MR Compressor Aftercooler 
               
               
                 1012 
                 End Flash Gas Compressor Aftercooler 
               
               
                 1013 
                 End Flash Gas Compressor 3rd Intercooler 
               
               
                 1014 
                 End Flash Gas Compressor 2nd Intercooler 
               
               
                 1015 
                 End Flash Gas Compressor 1st Intercooler 
               
               
                 1016 
                 MR Gas Turbine 
               
               
                 1017 
                 C3 Gas Turbine 
               
               
                   
               
            
           
         
       
     
       FIG. 12  is a schematic top view illustrating the arrangement of the pipe rack disposed in a central region of the LNG producing facility, gas turbines of the C3 compressor ( 1017 ), and gas turbines of the MR compressor ( 1016 ). A plurality of AFCs are disposed at the top of the pipe rack. The sizes of the components in  FIG. 12  reflect the sizes of the areas occupied by the actual components. 
     Referring to  FIG. 12 , among the AFCs included in the LNG producing facility, a C3 compressor desuperheater ( 1010 ), a C3 condenser ( 1003 ), a C3 subcooler ( 1009 ), a low-pressure-stage MR compressor aftercooler ( 1008 ), and a high-pressure-stage MR compressor aftercooler ( 1011 ) occupy large areas on the pipe rack. These AFCs are used for liquefaction, and the heat transfer areas (amounts of heat exchange) thereof are large. Therefore, the effect of spraying of the demineralized water is also large. In particular, the C3 condenser occupies the largest area, and variation in the amount of heat transfer (amount of heat exchange) of the C3 condenser significantly affects the amount of production of the LNG. 
     Therefore, in the present embodiment, from the viewpoint of occupation areas of the components, the AFCs toward which the demineralized water is to be sprayed are preferably the C3 compressor desuperheater, the C3 condenser, the C3 subcooler, the low-pressure-stage MR compressor aftercooler, and the high-pressure-stage MR compressor aftercooler, and more preferably, the C3 condenser. 
     The refined natural gas, which is the process fluid, is cooled from ambient temperatures to around −30 degrees C. by propane, and is further cooled to around −162 degrees C. by the mixed refrigerant in the main heat exchanger. Thus, an LNG product is produced. The mixed refrigerant is also cooled from ambient temperatures to around −30 degrees C. by propane, and is then supercooled in the main heat exchanger. 
     Since both the process fluid and the mixed refrigerant need to be cooled to around −30 degrees C. by propane as described above, reduction in the amount of heat exchange of the propane greatly affects the amount of production of the LNG. The propane is compressed by the C3 compressor  20  to have an increased pressure, and is completely condensed by the C3 condenser  22 . The heat of vaporization generated at this time is used to cool the process fluid and the mixed refrigerant to around −30 degrees C. The condensation temperature of the propane depends on the intake temperature of the C3 condenser  22 . Therefore, when the intake temperature is increased by the influence of HAR, the pressure increase achieved by the compressor also increases. As a result, energy loss increases. 
     Therefore, in the present embodiment, from the viewpoint of the process, the AFCs toward which the demineralized water is to be sprayed are preferably those of the C3 condenser  22 , and more preferably, some of the AFCs included in the C3 condenser  22  that are greatly affected by HAR. 
       FIG. 13  is a schematic diagram illustrating an embodiment of a demineralized water supply device. 
     A demineralized water supply device  70  includes a plurality of spray nozzles  59 , and sprays the demineralized water through the spray nozzles  59  so that the cooling air of an AFC can be cooled when the sprayed demineralized water is vaporized. The demineralized water is supplied from a demineralized water tank  50  to a water supply header  57  through a foreign-matter removing strainer  51 , a water supply pump  52 , a water supply cutoff valve  53 , a water-supply-rate control valve  54 , a water flowmeter  55 , and a foreign-matter removing filter  56 . The water supply header  57  guides the supplied water to a plurality of demineralized water pipes. The demineralized water is supplied from the water supply header  57  to the demineralized water pipes through a water-supply-header outlet-flow-rate control valve  58 , and is sprayed from the spray nozzles  59 . The sprayed demineralized water is sucked upward together with air sucked by an AFC  61 . The demineralized water that has been sucked vaporizes while passing between tubes  60  arranged on the pipe rack before being discharged upward from the AFC  61 . 
     A signal representing the amount of supplied demineralized water measured by the water flowmeter  55  is transmitted to a control device  62 . The control device  62  is capable of calculating the amount of water required on the basis of the operational state of the AFC  61 , and controlling the water-supply-rate control valve  54 . 
     The demineralized water supply device illustrated in  FIG. 13  is applied to particular AFCs, such as the C3 condenser, and the demineralized water is sprayed toward the AFCs from below. 
     Most LNG producing facilities are constructed in a desert or a barren land where a gas well is present, and the surrounding air is generally hot and dry. In particular, during daytime when the sun is up, the maximum temperature increases to around 35 degrees C. The difference between the dry-bulb temperature (temperature of air) and wet-bulb temperature during daytime is often as large as around 10 degrees C. Since the dew point at which water vapor condenses is lower than the wet-bulb temperature, there is a possibility that the air temperature can be reduced to the wet-bulb temperature by about 10 degrees C. by adiabatic cooling achieved by vaporization of the sprayed demineralized water. Thus, it is clear that adiabatic cooling of air introduced into the AFCs by spraying of the demineralized water according to the present invention is very effective. 
     Second Embodiment 
       FIG. 14  is a schematic diagram illustrating another embodiment of a liquefaction facility included in an LNG producing facility. In this process, propane, ethylene, and methane are successively used as refrigerants. This process is referred to as a cascade method. 
       FIG. 14  shows a flow of natural gas (or LNG), which is a process fluid (shown by thin solid lines), a propane cooling cycle in which propane is used as a working fluid (shown by two-dot chain lines), an ethylene cooling cycle in which ethylene is used as a working fluid (shown by dashed lines), and a methane cooling cycle in which methane is used as a working fluid (shown by thick solid lines). The flows of propane, ethylene, and methane form closed loops through which the respective fluids are circulated by respective compressor driving devices and that are independent of each other. A propane compressor  200 , an ethylene compressor  300 , and a methane compressor  400  are connected to respective gas turbines and motors (not shown) for driving the compressors. 
     The main components of the propane cooling cycle are the propane compressor  200 , a propane cooler  201 , a propane condenser  211 , an expansion valve  202 , a high-pressure intake line  203 , an intermediate-pressure intake line  204 , and a low-pressure intake line  205 . 
     The main components of the ethylene cooling cycle are the ethylene compressor  300 , an ethylene cooler  301 , an expansion valve  302 , a high-pressure intake line  303 , and a low-pressure intake line  304 . 
     The main components of an indirect heat exchange portion of the methane cooling cycle are the methane compressor  400 , a methane cooler  401 , a high-pressure intake line  402 , an intermediate-pressure intake line  403 , and a low-pressure intake line  404 . 
     Refined natural gas  100  from which CO 2 , H 2 S, and water, which are typical impurities, are removed is transferred to the liquefaction facility as a process fluid, and is cooled and liquefied by three heat exchangers with different temperatures that are arranged successively. The three heat exchangers are a heat exchanger  101  which uses propane as a refrigerant, a heat exchanger  102  which uses ethylene as a refrigerant, and a heat exchanger  103  which uses methane as a refrigerant. LNG product is transferred to a storage tank  105  by a pump  104 , and is stored until shipment. The LNG is slightly heated in the storage tank and vaporized. The thus-generated gas is returned to the process, liquefied again by the heat exchanger  103 , and transferred to the storage tank  105  by the pump  104 . 
     In the propane cooling cycle, the propane refrigerant collected through the intake lines  203 ,  204 , and  205  is pressurized by the propane compressor  200 , and is then cooled by the propane cooler  201 , and is liquefied by the propane condenser  211 . Then, the propane refrigerant is decompressed to a predetermined pressure by the expansion valve  202 , and is transferred to the heat exchanger  101 . The heat exchanger  101  cools the refined natural gas  100  as well as the ethylene refrigerant and methane refrigerant, which are used in the downstream heat exchangers, by causing them to exchange heat with the propane refrigerant. 
     In the ethylene cooling cycle, the ethylene refrigerant collected through the intake lines  303  and  304  is pressurized by the ethylene compressor  300 , and is then cooled by the ethylene cooler  301 . Then, the ethylene refrigerant is further cooled as a result of heat exchange with the propane refrigerant in the heat exchanger  101 . Next, the ethylene refrigerant is decompressed to a predetermined pressure by the expansion valve  302 , and is transferred to the heat exchanger  102 . The heat exchanger  102  cools the refined natural gas  100  discharged from the heat exchanger  101  and the methane refrigerant, which is used in the downstream heat exchanger, by causing them to exchange heat with the propane refrigerant. 
     In the methane cooling cycle, the methane refrigerant collected through the intake lines  402 ,  403 , and  404  is pressurized by the methane compressor  400 , and is then cooled by the methane cooler  401 . Then, the methane refrigerant is cooled as a result of heat exchange with the propane refrigerant in the heat exchanger  101 , further cooled as a result of heat exchange with the ethylene refrigerant in the heat exchanger  102 , and is transferred to the heat exchanger  103 . The heat exchanger  103  cools and liquefies the refined natural gas  100  discharged from the heat exchanger  102  by causing it to exchange heat with the methane refrigerant. 
     Fuel gas  405  is combustible gas which contains a large amount of nitrogen and which has not been liquefied. The fuel gas is used as fuel for gas turbines that drive the compressors. In the case where large power is required to produce the LNG, the amount of fuel gas is increased and the amount of liquefied gas is reduced. When the amount of heat exchange at the AFCs is increased by spraying the demineralized water, the power of the gas turbines can be reduced and the amount of production of the LNG can be maximized. 
     In the embodiment illustrated in  FIG. 14 , an AFC toward which the demineralized water is to be sprayed in accordance with the present invention is preferably the propane condenser  211 . The demineralized water is sprayed by using the demineralized water supply device illustrated in  FIG. 13 . 
     Industrial Applicability 
     The liquefied gas producing apparatus and liquefied gas producing method according to the present invention are suitable for production of LNG, LPG, and SNG. 
     Although only some exemplary embodiments and/or examples of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments and/or examples without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention. 
     The documents described in the specification and the Japanese application specification claiming priority under the Paris Convention are incorporated herein by reference in its entirety.