JP4758711B2 - Pretreatment method for gas hydrate production - Google Patents

Description

  The present invention relates to a pretreatment method for gas hydrate production, and more particularly to a pretreatment method including a dehydration treatment of a raw material for hydrocarbon mixture gas hydrate containing methane as a main component.

  Gas hydrate is an ice-like solid substance consisting of water molecules and raw gas molecules, and is a kind of stable inclusion compound in which raw gas molecules are included inside a three-dimensional cage structure formed by water molecules. It is. This gas hydrate has a relatively large gas storage capacity, and has characteristic properties such as large generation / decomposition energy and selectivity of hydrated gas. For example, transportation / storage means such as natural gas In addition, various applications such as heat storage systems, actuators, and separation / recovery of specific component gases are possible, and research is being actively conducted.

  Gas hydrate is usually produced under high pressure and low temperature conditions. For example, the following is known as the generation means. By spraying water cooled from the top of the production vessel filled with raw material gas at high pressure, when the water drops fall in the raw material gas, gas hydrate is generated on the surface of the water droplets, so-called "water spray method" There is a so-called “bubbling method” in which gas hydrate is generated on the surface of a bubble when the bubble of the source gas rises in water by introducing gas into the water as a bubble. (For example, see Patent Document 1.)

  The raw material gas for gas hydrate can be used without particular limitation as long as it forms a gas hydrate under a predetermined temperature and a pressure condition higher than atmospheric pressure. For example, methane, natural gas Examples thereof include gas (a mixed gas containing methane as a main component and ethane, propane or the like as a subcomponent), carbon dioxide, and the like.

  In general, as a pretreatment of raw material gas used for hydrocarbon mixture gas hydrate containing methane as a main component, removal of acidic gas such as carbon dioxide, hydrogen sulfide, mercaptan, and separation of heavy components such as butane and heptane Processing is performed. The separation process of heavy components is a process of separating and recovering heavy components at a low temperature of 0 ° C. to −50 ° C. by combining a cooler, a gas-liquid separator, a distillation tower, and the like. If moisture is present in the raw material gas, problems such as pipe blockage due to freezing and poor flow will occur. For this reason, it is necessary to perform a dehydration process before a heavy component separation process.

  In the natural gas liquefaction process, dehydration equipment using physical adsorption by molecular sieves is often used. In this method, the raw material gas is passed through an adsorption tower to adsorb moisture to an adsorbent such as a molecular sieve to remove moisture in the raw material gas, and then sent to a downstream low-temperature treatment step. In general, when the adsorbent adsorbs a predetermined amount of water, it does not adsorb any more, so a regeneration process is required. The regeneration treatment means desorption of moisture from the molecular sieve, and there are a thermal swing method and a pressure swing method, both of which require a regeneration gas. (For example, see Patent Document 2.)

  The thermal swing method is a method in which adsorption is performed at a low temperature, and the temperature is increased and desorbed at a high temperature, since the adsorption performance is higher at a low temperature when compared with a low temperature and a high temperature. The pressure swing method is a method of adsorbing under high pressure under low pressure and high pressure, and adsorbing under high pressure, depressurizing and desorbing under low pressure.

  As the regeneration gas, a gas not containing moisture is used, and in many cases, nitrogen, a raw material gas recirculated from a downstream process, or the like is used. In the case of extracting a raw material gas from a downstream process and using it as a regeneration gas, conventionally, the regeneration gas after regeneration has been used as a fuel gas or recirculated upstream of a dehydration facility. (For example, refer to Patent Document 3.)

However, if the raw material gas extracted from the downstream process is used as a fuel gas after being used as a molecular sieve regeneration gas, the loss of the raw material gas is large, leading to an increase in dehydration costs, and the upstream of the dehydration equipment. When the water is recirculated, water is accumulated in the system and the processing efficiency is lowered. Therefore, there has been a demand for a pretreatment method for gas hydrate production in which dehydration is performed while the processing efficiency is higher and the processing cost is reduced.
JP 2004-10686 A JP 2004-975 A Japanese Patent Publication No. 6-13719

  An object of the present invention is to provide a dehydration method for reducing the processing cost while improving the processing efficiency of a raw material gas mainly composed of methane in the pretreatment for gas hydrate production.

  The gas hydrate production pretreatment method of the present invention that achieves the above object comprises a step of removing acid gas from a raw material gas for gas hydrate containing methane as a main component, an adsorption step of at least two adsorption towers, and a regeneration step. In the pretreatment method for gas hydrate production, including the dehydration step of removing moisture while repeating the step, and the heavy component separation step of separating at least a part of the hydrocarbon component having 2 or more carbon atoms, the regeneration step includes the heavy step. A step of extracting a part of the raw material gas after the separation of the quality component as a regeneration gas, raising the temperature of the regeneration gas and passing it through an adsorption tower to be regenerated, desorbing adsorbed moisture and bringing it into the regeneration gas And a step of returning the regeneration gas accompanied by moisture to the downstream side of the extraction position.

  The pretreatment method for producing gas hydrate according to the present invention includes a step of removing acid gas from a raw material gas mainly composed of methane, a dehydration step of removing moisture, and a heavy component for separating hydrocarbon components having 2 or more carbon atoms. It is a pretreatment method including a separation step, and the dehydration step is a pretreatment method in which moisture is removed while repeating the adsorption step and the regeneration step of at least two adsorption towers.

  In the pretreatment method of the present invention, a part of the raw material gas that has been subjected to the dehydration treatment and the heavy component separation treatment is extracted and used as a regeneration gas, and it is necessary to specially prepare nitrogen or the like as the regeneration gas. Therefore, it is possible to reduce the cost of regeneration processing. In addition, since the raw material gas from which moisture and heavy components have been removed and separated is heated and used as a regeneration gas, the desorption efficiency of adsorbed moisture can be increased, and the desorbed moisture is accompanied by the regeneration gas. Can be removed from the adsorption tower.

  Furthermore, by returning the regeneration gas accompanied by moisture to the downstream side of the regeneration gas extraction position, moisture is not mixed into the newly extracted regeneration gas, and the desorption efficiency of adsorbed moisture is kept high. be able to. Furthermore, it is possible to effectively use raw material gas, which is a precious resource, as gas hydrate raw material gas without using it as fuel gas, improving the utilization efficiency by about 4% and increasing the pretreatment efficiency. Cost can be reduced.

The present invention is described in detail below.
FIG. 1 is a block flow diagram showing an example of a process in a pretreatment method for producing gas hydrate according to the present invention. FIG. 2 is an explanatory diagram showing an example of a process flow of a dehydration step in the pretreatment method of FIG.

  In FIG. 1, the pretreatment for supplying the raw material gas 10 to the gas hydrate production process 4 is a treatment process including an acid gas removal process 1, a dehydration process 2, and a heavy component separation process 3. In the acid gas removal step 1, the acid gas is separated and removed from the raw material gas 10, and in the heavy component separation step 3, the heavy component is separated. The dehydration step 2 has at least two adsorption towers, and an adsorption process for adsorbing and separating moisture from the raw material gas 10 and a regeneration process for desorbing adsorbed water from the adsorbent are alternately repeated. In the pretreatment method of the present invention, the regeneration gas is extracted from the downstream of the heavy component separation step 3 and the moisture of the adsorbent of the adsorption tower for performing the regeneration treatment is desorbed, and then the previous regeneration gas is extracted. It is characterized by returning to the downstream side.

  In FIG. 2, the dehydration process 2 is divided into an adsorption process 2a and a regeneration process 2b. The regeneration process 2b is a part of the raw material gas that has been subjected to the acid gas removal process 1, the adsorption process 2a, and the heavy component separation process 3. Step of extracting heavy component separation step 3 as a regeneration gas, heating the regeneration gas to a predetermined temperature through heat exchangers 5 and 6, and adsorbing tower while desorbing and entraining moisture adsorbed on the adsorbent Removing the moisture from the water, and then adjusting the temperature and pressure of the regeneration gas accompanied by moisture through the heat exchanger 5 and the compressor 7 and returning the regeneration gas downstream to the position where the regeneration gas was previously extracted. The regeneration gas used in the regeneration step 2b is supplied as a raw material gas to the gas hydrate manufacturing step 4.

  The source gas 10 is a natural gas such as a gas field gas produced from a gas field and an accompanying gas that is co-produced when crude oil is produced from an oil field, and combustible containing methane as a main component (80 to 100 vol%). It is a sex gas. In addition to methane, ethane, and propane, the source gas 10 includes acidic components such as hydrogen sulfide, carbon dioxide, and mercaptan, heavy components composed of hydrocarbons having 4 or more carbon atoms such as butane and heptane, moisture, and the like. . The acidic gas in the raw material gas 10 is removed because it hinders stable operation of the plant, and the heavy components are difficult to produce gas hydrates and must be separated and recovered for other effective uses. Furthermore, during the low temperature treatment at a temperature of 0 to -50 ° C. in the heavy component separation step, if moisture is present in the raw material gas, it may freeze and cause clogging of the apparatus piping or flow failure, so that the dehydration treatment is performed. Done.

  The acidic gas removal step 1 is not particularly limited as long as it removes acidic gases such as hydrogen sulfide, carbon dioxide, and mercaptans. However, the acidic gas is removed by contacting with an alkaline component such as amine. It is preferable to do.

  The heavy component separation step 3 is a treatment step for separating and recovering a part of heavy components composed of hydrocarbons having 2 or more carbon atoms such as ethane, propane, butane, and heptane from the raw material gas. It consists of a separator, a distillation tower, etc., and separates and recovers heavy components using the difference in liquefaction temperature of each hydrocarbon component. In particular, the hydrocarbon component having 5 or more carbon atoms is separated and recovered because it is difficult to produce gas hydrate and there are useful uses other than gas hydrate. In the separation and recovery of heavy components, a part of ethane and propane may be separated and recovered at the same time, and it is not necessary to separate and recover the entire amount of hydrocarbon components having 5 or more carbon atoms. That is, the heavy components are separated and recovered so that the amount of unreacted gas in the gas hydrate production process is within a predetermined range.

  The dehydration process of the present invention is a dehydration process that removes moisture while repeating the adsorption process 2a and the regeneration process 2b using at least two adsorption towers. In FIG. 2, a part of the piping related to the adsorption process 2a and the regeneration process 2b is omitted, but any adsorption tower is arranged so that the adsorption process and the regeneration process can be alternately repeated.

  In the present invention, by using at least two adsorption towers, it is possible to simultaneously proceed with the regeneration process of the other adsorption tower in parallel with the moisture adsorption process by passing the raw material gas through one of the adsorption towers. it can. The number of adsorption towers is not limited to two. For example, three adsorption towers can be used, and the dehydration process can be efficiently advanced by mutually shifting the timing of the adsorption process and the regeneration process. In this case, when one adsorption tower is performing an adsorption process, the other two adsorption towers may perform a regeneration process, and when two adsorption towers are performing an adsorption process, the remaining one adsorption tower The tower may perform the regeneration process.

  In the present invention, the adsorbent of the adsorption tower is not particularly limited as long as it selectively adsorbs moisture contained in the raw material gas and desorbs under appropriate conditions. Alumina, impregnated alumina, molecular sieve (synthetic zeolite), activated carbon, sulfate anhydride, carbonate anhydride and the like can be mentioned, preferably molecular sieve (synthetic zeolite) and activated alumina. Moreover, it is also possible to use a combination of a plurality of adsorbents among these adsorbents as appropriate.

  In the present invention, the adsorption step 2a is a step of removing the moisture in the raw material gas by passing the raw material gas through the adsorption tower, and the condition is that the temperature is preferably 10 to 45 ° C., more preferably 15 to 15. The pressure is preferably 40 ° C and 1 to 20 MPa, more preferably 5 to 15 MPa.

  The amount of water in the raw material gas that has passed through the adsorption step 2a is preferably 5 ppm or less, more preferably 1 ppm or less. By setting the amount of water in the raw material gas to 5 ppm or less, it is possible to prevent the occurrence of problems due to freezing of water in the downstream heavy component separation step 3, and when part of it is used as a regeneration gas. In addition, the desorption efficiency of adsorbed water can be increased, which is preferable.

  In the pretreatment method for gas hydrate production according to the present invention, the regeneration step 2b is a step of extracting a part of the raw material gas after the heavy component separation step 3 as a regeneration gas, and the regeneration gas is heated to regenerate. The step of passing through the adsorption tower and desorbing the moisture and entraining the regeneration gas, and the step of returning the regeneration gas accompanied by the moisture to the downstream side of the extraction position of the raw material gas. is there. Further, the regeneration gas accompanied by moisture and the raw material gas after the heavy component separation step are both used as the raw material gas for gas hydrate production mainly composed of methane.

  In the regeneration step 2b, a part of the raw material gas that has been subjected to the dehydration process and the heavy component separation process is extracted and used as a regeneration gas, and it is necessary to prepare a special gas such as nitrogen as the regeneration gas. Therefore, the processing cost can be suppressed.

  In addition, since the raw material gas from which moisture and heavy components have been removed and separated is heated to a predetermined temperature and then passed through an adsorption tower to be regenerated as a regeneration gas, the desorption efficiency of the moisture adsorbed on molecular sieves and the like The moisture can be desorbed in a short time and can be removed from the adsorption tower along with the regeneration gas. The temperature of the regeneration gas is preferably raised through heat exchange with the regeneration gas that has been subjected to regeneration treatment (heat exchanger 5) and heat exchange (heat exchanger 6) that supplements the heat exchange.

  The conditions for regeneration by desorbing moisture from the adsorbent are preferably a temperature of 200 to 350 ° C., more preferably 260 to 300 ° C., and a pressure of preferably 4 to 6 MPa, more preferably 5 to 5.6 MPa. Good. By setting the conditions for regenerating the adsorption tower within the above range, it is preferable because the adsorbed water can be efficiently desorbed.

  The regeneration gas entrained with moisture in this way passes through the heat exchanger 5 and the compressor 7, performs heat recovery and pressure adjustment, and then returns to the raw material gas piping supplied to the gas hydrate production process 4. The temperature of the regeneration gas at this time is preferably 0 to 10 ° C., more preferably 1 to 6 ° C., and the pressure is preferably 5 to 6 MPa, more preferably 5.4 to 5.6 MPa.

  The raw material gas supplied to the gas hydrate production step 4 includes the regeneration gas used in the regeneration step, and the temperature is preferably 0 to 10 ° C., more preferably 1 to 6 ° C., and the pressure is preferably 5 It is good that it is-6MPa, More preferably, it is 5.4-5.6MPa.

  By returning the regeneration gas used in the regeneration process to the downstream side of the position where a part of the raw material gas is extracted as the regeneration gas, it is possible to prevent moisture from being mixed into the newly extracted regeneration gas.

  In addition, the pretreatment method of the present invention combines the gas for regeneration accompanied by moisture with the raw material gas, so that the raw material gas, which is a valuable resource, is not used as a fuel gas, but as a raw material gas for gas hydrate. Since it is used effectively, the preprocessing cost can be reduced.

  For example, in a gas hydrate production facility with annual production of 1 million tons, the required amount of raw material gas is 163 tons / hour, although it depends on the difference in raw material composition. Here, as a standard, if the raw material gas contains about 0.18% by weight of water, the amount of dehydration from the raw material gas is 0.3 tons / hour, which is obtained from an adsorbent such as molecular sieve. The amount of water to be desorbed is the same amount. In the regeneration process, for example, when a raw material gas having a moisture content of 1 ppm or less is used as a regeneration gas under the conditions of a temperature of 260 ° C. and a pressure of 5.5 MPa, the necessary amount of the regeneration gas is estimated to be 7 tons / hour.

  At this time, when the regeneration gas used in the regeneration process is used as a fuel gas as in the prior art, in order to secure the amount of raw material gas to be supplied to the gas hydrate production process 4, 163 tons / hour, A raw material gas of 170 tons / hour added with a gas amount of 7 tons / hour must be pretreated.

  In contrast, the pretreatment method for gas hydrate production according to the present invention circulates and uses a part of the pretreated raw material gas as a regeneration gas, so that the raw material gas supply amount is 163 tons / hour. Thus, it is possible to reduce the raw material gas by about 4%, and it is possible to achieve a significant reduction in pretreatment costs while reducing the pretreatment burden and increasing the treatment efficiency.

It is a block flow figure showing an example of a process of a pretreatment method of gas hydrate manufacture concerning the present invention. It is explanatory drawing which shows an example of the process flow of the dehydration process in the pre-processing method of gas hydrate manufacture of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Acid gas removal process 2 Dehydration process 2a Adsorption process 2b Regeneration process 3 Heavy component separation process 4 Gas hydrate manufacturing process 5 Heat exchanger 6 Heat exchanger 7 Compressor 10 Source gas

Claims (2)

A process for removing acid gas from a raw material gas for gas hydrate containing methane as a main component, a dehydration process for removing moisture while repeating an adsorption process and a regeneration process for at least two adsorption towers, and a hydrocarbon component having 2 or more carbon atoms In a pretreatment method for gas hydrate production, comprising a heavy component separation step of separating at least a part of
The regeneration step is a step of extracting a part of the raw material gas that has undergone the heavy component separation step as a regeneration gas, and the adsorption gas is desorbed by raising the temperature of the regeneration gas and passing it through an adsorption tower to be regenerated. A pretreatment method for gas hydrate production, including a step of entraining the regeneration gas with the regeneration gas and a step of returning the regeneration gas entrained with the moisture to the downstream side of the extraction position. The pretreatment method for gas hydrate production according to claim 1, wherein the regeneration gas accompanied by moisture and the raw material gas after the heavy component separation step are supplied to the gas hydrate production step.

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