Abstract:
A refrigerating method and a refrigerating system utilizing a large decomposition heat absorbed at the time of decomposition of the gas hydrate and building up, by a pump, the pressure of liquid components generated due to the decomposition of gas hydrate and compressing only gas components by a compressor, the refrigerating method comprising the steps of generating the gas hydrate (H) by a hydrate generating reactor ( 11 ), decomposing the gas hydrate (H) into the liquid components (L) and the gas components (G) after depressurization to absorb heat, separating the decomposed liquid components (L) and gas components (G) from each other, building up the pressure of the liquid components (L) by the pump ( 16 ) and transferring to the hydrate generating reactor ( 11 ), and pressurizing and compressing only the gas components (G) by the compressor ( 17 ) and transferring to the hydrate generating reactor ( 11 ).

Description:
TECHNICAL FIELD 
     The present invention relates to a refrigerating method and a refrigerating system, particularly to a refrigerating method and a refrigerating system utilizing gas hydrate for a refrigerant. 
     BACKGROUND ART 
     A refrigerating system is widely used in fields such as food storage and air conditioning. As shown in  FIG. 2 , a refrigerating system  40  of the prior art is constituted by including a compressor  41 , a condenser  42 , a liquid receiver  43 , an expansion valve (depressurizing unit)  44 , and an evaporator (chiller)  45 . 
     Moreover, ammonia and fluorocarbon gas which are very volatile liquids are used for refrigerants. The ammonia has a low temperature of −33.3° C. at the atmospheric pressure and when this cold liquid becomes a gas, it wrests heat from the surrounding area to refrigerate the area. 
     In the case of the refrigerating system  40  of the prior art, the compressor  41  sucks in and compress a cold gas G 1  gasified by the evaporator  45  and compresses to generate a high-temperature high-pressure gas G 2 . The compressed gas G 2  is cooled and condensed by water or air in the condenser  42  to generate a liquid L 1 . The refrigerant L 1  becoming a liquid is temporarily stored in the liquid receiver  43  and then sent to the expansion valve  44  set to the entrance of the evaporator  45 . 
     The high-temperature and high-pressure refrigerant L 1  is expanded in the expansion valve  44  to depressurize it. When the refrigerant L 1  passes through the expansion valve  44 , some of the refrigerant L 1  is evaporated and reduced in temperature to become a low-temperature and low-pressure refrigerant L 2 . The refrigerant L 2  is evaporated in the evaporator  45  to wrest heat from the surrounding area of the evaporator  45 , and when evaporated, it cools the surrounding area of the evaporator  45 , and generates a refrigerating action. 
     However, the conventional refrigerating system uses a single fluid such as ammonia or fluorocarbon gas as a refrigerant for forming a refrigerating cycle and compresses the whole quantity of the refrigerant which is a single fluid, in a gas state by the compressor. Therefore, there are problems that the required motive power of the compressor increases, the system increases in size, and the power consumption increases. 
     That is, the “coefficient of performance (COP)” indicating the refrigeration efficiency obtained by dividing the refrigerating capacity by the thermal equivalent of compression, particularly, the “actual coefficient of performance =refrigerating capacity (kW)/motor(kW)” obtained by dividing the refrigerating capacity by the heat quantity corresponding to the output of a motor for operating a refrigerator deteriorates. 
     However, there is gas hydrate used for Japanese Patent Laid-Open Nos. 157005/1982, 340035/1992, 58646/1994, and 2001-10990 as the motive power source of a turbine and the like, cold heat storing material, and gas occlusion substance. 
     This gas hydrate is referred to as a hydrate clathrate compound or a gas clathrate compound, which is obtained by mixing a gas such as low-class carbon hydride with a liquid (hydrate) such as water. In the case of the decomposition heat of this gas hydrate, it is known that the decomposition heat in terms of the unit mass of gas is very large and becomes approx. 1.3 times larger than that of water. 
     The present invention is made to solve the above problems by obtaining the above knowledge, and its object is to provide a refrigerating method and a refrigerating system capable of using a large decomposition heat absorbed, when decomposing gas hydrate by utilizing gas hydrate as the refrigerant of a refrigerating system and capable of greatly decreasing the motive power necessary for the refrigerating system by boosting the liquid components generated due to decomposition of gas hydrate by a pump, compressing only the gas components by a compressor, and thereby, decreasing the gas quantity to be compressed by the compressor. 
     SUMMARY OF THE INVENTION 
     A refrigerating method of the present invention utilizing gas hydrate as a refrigerant comprises the steps of: generating gas hydrate by a hydrate generating reactor; depressurizing the generated gas hydrate; decomposing the depressurized gas hydrate into liquid components and gas components by a hydrate decomposing reactor to absorb heat; separating the decomposed gas components and the decomposed liquid components from each other; and boosting the decomposed liquid components by a pump and transferring it to the hydrate generating reactor, pressurizing and compressing the decomposed gas components by a compressor to transfer the gas components to the hydrate generating reactor, and is characterized in that an additive separated by the hydrate generating reactor is mingled in the liquid components transferred via a liquid line through an additive feed line connected to the hydrate generating reactor and the liquid line. 
     According to the refrigerating method, by utilizing gas hydrate as the refrigerant of a refrigerating system, it is possible to cool the surrounding area by using a large decomposition heat of the gas hydrate when decomposing the gas hydrate in a hydrate decomposing system and thereby efficiently absorbing heat. Therefore, refrigerating can be efficiently performed and the system becomes compact. 
     Therefore, by using sea water, cooling water, low-temperature water, brine and the like which are easy to use relatively, it is possible to make the brine of about −5° C. to 15° C. 
     Moreover, because the liquid components and gas components obtained by decomposing gas hydrate are separated into gas and liquid and the liquid components are boosted by a pump and only the gas components which are part of the gas hydrate are compressed by a compressor, the gas quantity passing through the compressor, that is, the gas quantity compressed by the compressor decreases compared to the case of the refrigerating system of the prior art and the required motive power of the compressor is extremely decreased. 
     For example, the required motive power of the compressor used for this refrigerating method becomes ⅓ to ⅙ compared to the case of a compressor shown in  FIG. 2  of a conventional refrigerating system for compressing the whole gas quantity of a refrigerant by using the gas as a refrigerant. 
     Moreover, in the generating step of the gas hydrate, a mixed liquid or liquid components containing solids generated in the hydrate generating reactor is (or are) transferred to a cooler and cooled, and the cooled mixed liquid or liquid components containing the cooled solids are returned to the hydrate generating reactor, so temperature is lowered by radiating heat to external gas or liquid by the cooler and it is possible to efficiently generate gas hydrate. 
     Furthermore, the gas hydrate is cooled by the liquid components generated by the hydrate decomposing system before putting the gas hydrate in the hydrate decomposing system, so it is possible to increase a cold heat recovery quantity in the hydrate decomposing system. 
     Furthermore, a refrigerating system utilizing gas hydrate of the present invention is a refrigerating system utilizing gas hydrate as a refrigerant and having a hydrate generating reactor, a cooler, a depressurizing unit, a hydrate decomposing system, a pump, and a compressor, comprising: a hydrate line constituted by connecting in order the hydrate generating system, the depressurizing unit, and the hydrate decomposing system to transfer the gas hydrate; a gas line constituted by connecting in order the hydrate decomposing system, the compressor, and the hydrate generating reactor to transfer gas components decomposed from the gas hydrate; a liquid line constituted by connecting in order the hydrate decomposing system, the pump, and the hydrate generating reactor to transfer liquid components decomposed from the gas hydrate; and a cooling line constituted by connecting in order the hydrate generating reactor, the cooler, and the hydrate generating reactor to cool and return a mixture solution or liquid components solids generated in the hydrate generating reactor, the system further comprising an additive feed line connecting the hydrate generating reactor and the liquid line to each other for mingling an additive separated by the hydrate generating reactor into the liquid components transferred via the liquid line. 
     This configuration makes it possible to execute the above refrigerating method utilizing gas hydrate. 
     Moreover, in the case of the above refrigerating system utilizing gas hydrate, a cold heat recovery unit for cooling the gas hydrate in the hydrae line by the liquid components transferred through the liquid line is set between the hydrate generating reactor and the depressurizing unit in the hydrate line, so it is possible to cool gas hydrate by the liquid components generated by the hydrate decomposing system and then put the gas hydrate in the hydrate decomposing system and increase the cold heat recovery quantity by the hydrate decomposing system. 
     Furthermore, in the case of the above refrigerating system utilizing gas hydrate, in order to mix an additive separated by the hydrate generating reactor in the liquid components transferred through the liquid line, an additive line for connecting the hydrate generating reactor and the liquid line is set, so it is possible to circulate the additive and efficiently accelerate the generation of gas hydrate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustration showing a configuration of a refrigerating system of an embodiment of the present invention; and 
         FIG. 2  is an illustration showing a configuration of a refrigerating system of the prior art. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A refrigerating method and a refrigerating system utilizing gas hydrate of the present invention are described below by referring to  FIG. 1 . 
     A refrigerating system used for a refrigerating method utilizing gas hydrate of the present invention uses gas hydrate (gas clathrate compound) H constituted by gas components G of low-class hydrocarbon such as ethane and liquid components L such as water (or oil) as a refrigerant. 
     As the gas components G for forming the gas hydrate H, it is possible to use a single component of low-class hydrocarbon such as methane, ethane, propane, and butane, or a mixed gas of a plurality of components of these substances. Moreover, it is possible to use water or oil as the liquid components L. 
     Furthermore, to adjust a condition of generating and decomposing the gas hydrate H in a refrigerating system  10 , it is also possible to use an additive A. As the additive A to be added to the liquid components L of the gas hydrate H, there are substances referred to as a hydration clathrate accelerator, a hydrate stabilizer, and a hydrate decomposer. In this case, however, the hydration clathrate accelerator for accelerating generation of hydrate is used. By using the hydration clathrate accelerator, it is possible to lower the pressure and raise temperature when generating hydrate. 
     As the hydrate clathrate accelerator A, it is possible to use any one of 1,3-dioxolane, tetrahydrofuran, furan, cyclobutanone, cyclopentanone, special saline, lecithin, PVA, PVCap, acetone, methanol, common salt, glycol, and so on. 
     Moreover, as shown in  FIG. 1 , the refrigerating system  10  is constituted by including a hydrate generating reactor  11 , a cooler  12 , a cold heat recovery unit  13 , a depressurizing unit  14 , a hydrate decomposing system (chiller)  15 , a pump  16 , and a compressor  17 . 
     Furthermore, the refrigerating system  10  connects units by a hydrate line  31 , a gas line  32 , a liquid line  33 , a cooling line  34 , and an additive line  35 . 
     The hydrate line  31  is constituted by connecting the hydrate generating reactor  11 , the cold heat recovery unit  13 , the depressurizing unit  14 , and the hydrate decomposing system  15  in order and the gas line  32  is constituted by connecting the hydrate decomposing system  15 , the compressor  17 , and the hydrate generating reactor  11  in order. 
     Moreover, the liquid line  33  is constituted by connecting the hydrate decomposing system  15 , the pump  16 , the cold heat recovery unit  13 , and the hydrate generating reactor  11  in order and the cooling line  34  is constituted by connecting the hydrate generating reactor  11 , the pump  36 , the cooler  12 , and the hydrate generating reactor  11  in order. 
     Furthermore, the additive line  35  is constituted by connecting the hydrate generating reactor  11 , an additive catching vessel  22 , and the liquid line  33  at the upstream side of the pump  16 . 
     In the refrigerating system  10 , the slurry-like gas hydrate H generated in the hydrate generating reactor  11  is cooled at the cold heat recovery unit  13  by the liquid components L pressurized and sent to the hydrate generating reactor  11  from the pump  16  and then enters the depressurizing unit  14  and is decompressed and absorbs heat from the surrounding area in the hydrate decomposing system  15  at the downstream side of the depressurizing unit  14  and is decomposed into the gas components G and liquid components L. 
     The hydrate decomposing system  15  is constituted by a hydrate decomposing reactor  15   a , a liquid-gas separator  15   b , and a liquid receiver  15   c , which can efficiently cool the surrounding area by using a large decomposition heat of the gas hydrate H when decomposing the gas hydrate H. 
     The hydrate decomposing reactor  15   a , the liquid-gas separator  15   b , and the liquid receiver  15   c  can be set as an integrated system or when the absorbed heat quantity is large, a heat sink can be set to the external circulating line of the integrated system. However, it is also possible to form the reactor  15   a , the separator  15   b , and the receiver  15   c  by separated vessels as described above. 
     Moreover, the liquid components L and gas components G decomposed in the hydrate decomposing reactor  15   a  are separated in the liquid-gas separator  15   b  and the liquid components L stored in the liquid receiver  15   c  is pressurized by the pump  16  in the liquid line  33  to cool the gas hydrate H in the cold heat recovery unit  13  before depressurized and sent to the hydrate generating reactor  11 . Furthermore, the separated gas components G is pressurized and compressed by the compressor  17  in the gas line  32  and sent to the hydrate generating reactor  11 . 
     In the case of the above configuration, liquid and gas are separated by the hydrate decomposing system  15  and then, the gas components G and liquid components L decomposed by the gas hydrate H are separately boosted. Therefore, because the liquid components L is boosted by the pump  16  and sent to the hydrate generating reactor  11 , the required motive power can be decreased. 
     Moreover, because the gas components G to be compressed by the compressor  17  are part in the gas hydrate H, the gas quantity decreases compared to the case of the refrigerating system of the prior art, the required motive power of the compressor  17  is extremely decreased, and the required motive power of the compressor  17  having the configuration in  FIG. 1  becomes ⅓ to ⅙ compared to the case of the compressor  41  of the conventional refrigerating system  40  for compressing the whole gas quantity of a refrigerant by using the gas as the refrigerant as shown in  FIG. 2 . 
     Furthermore, the hydrate generating reactor  11  is kept at a high pressure, a mixed liquid or liquid components Lh containing solids are heat-exchanged with an external cooling medium formed by sea water, cooling water, low-temperature water, brine and the like by the cooler  12  to radiate the heat of the gas hydrate H side to the external cooling medium and cooled to return to the hydrate generating reactor  11  and cool the gas hydrate H side. 
     Furthermore, the additive A for accelerating generation of the gas hydrate H separated when generating the gas hydrate H in the hydrate generating reactor  11  is supplied to the upstream side of the pump  16  through the additive line  35  to mix it with the liquid components L. 
     The gas components G are incorporated into the liquid components L in a high-pressure and low-temperature state by cooling by the cooler  12  and boosting by the pump  16  and the compressor  17 , and the gas hydrate H is generated. 
     By repeating the above refrigerating cycle, a refrigerating function is exhibited in the hydrate decomposing system  15 . 
     Moreover, in the case of the hydrate generating reactor  11 , it is important to keep proper pressure and temperature, because the pressure resistance of a vessel causes a undesirable problem when the pressure is high, the gas hydrate H is not generated when the pressure is low, the gas hydrate H is decomposed when the temperature is high, and the generation efficiency of the gas hydrate H is deteriorated through freeze of the liquid components L when the temperature becomes 0° C. or lower. 
     Therefore, circulating quantities of the gas hydrate H, the liquid components L, and the gas components G, and heat exchange quantities of the hydrate decomposing system  15 , the cold heat recovery unit  13 , and the cooler  12  are controlled by a sensor and a pressure controller not-illustrated to adjust the pressure and the temperature of each unit. 
     Pressures and temperatures of units are shown below. In the case of pressures, the hydrate generating reactor  11  uses 1.0 MPa to 10 MPa and the depressurizing unit  14  uses 2.0 MPa or lower at its downstream side. The temperature of the external cooling medium of the cooler  12  ranges between 10° C. and 35° C. and the temperature of the brine which is cooled in the hydrate decomposing system  15  and supplied to the outside ranges between −5° C. and 15° C. 
     Moreover, balanced data is shown below. When using a mixed gas of methane and ethane and an additive, a pressure of 5.0 MPa and a temperature of 25° C. are obtained at the high-pressure side where the gas hydrate H is generated and 0.5 MPa and 2° C. are obtained at the low-pressure side where the gas hydrate H is decomposed and the gas components G are generated. 
     Then, calculation examples of decomposition heat of the gas hydrate H are shown below. In the case of methane hydrate having a weight ratio of methane:water of 1:6.75, MW (molecular weight) is 125, the molecular decomposition heat is 12.95 kcal/mol, and the decomposition heat for 1 kg of hydrate is 103.6 kcal/kg. 
     Moreover, in the case of ethane hydrate having a weight ratio of ethane:water of 1:4.60, MW is 168, the molecular decomposition heat is 16.16 kcal/mol, and the decomposition heat for 1 kg of hydrate is 102.1 kcal/kg. 
     Furthermore, in the case of propane hydrate having a weight ratio of propane:water of 1:6.95, MW is 350, the molecular decomposition heat is 30.88 kcal/mol, and the decomposition hear for 1 kg of hydrate is 88.2 kcal/kg. 
     As described above, according to a refrigerating method and a refrigerating system utilizing the gas hydrate H of the present invention, by utilizing the gas hydrate H as the refrigerant of the refrigerating system, refrigeration can be efficiently made because a large decomposition heat absorbed when decomposing the gas hydrate H can be used. 
     Therefore, it is possible to make the brine of approx. −5° C. to 15° C. by using sea water, cooling water, low-temperature water, brine and the like which can be comparatively easily used. 
     Moreover, because the liquid components L generated through decomposition of the gas hydrate H are boosted by the pump  16  to compress only the gas components G by the compressor  17 , it is possible to decrease the gas quantity to be compressed by the compressor  17  and extremely decrease the motive power necessary for a refrigerating system. Therefore, the present invention makes it possible to decrease the required motive power of a compressor to approx. ⅓ to ⅙ compared to a compressor of a conventional refrigerating system for compressing the whole gas quantity of a refrigerant by using the gas as a refrigerant. 
     Industrial Applicability 
     The present invention provides a refrigerating method and a refrigerating system capable of using a large decomposition heat absorbed through decomposition of gas hydrate and extremely decreasing the motive power necessary for the refrigerating system by boosting a liquid components generated through decomposition of the gas hydrate by a pump and compressing only a gas components by a compressor. 
     Therefore, the present invention can be used as a refrigerating method and a refrigerating system widely used in fields such as food storage, air conditioning and the like.