JP4744085B2 - Gas hydrate manufacturing apparatus and gas hydrate manufacturing method - Google Patents

Description

  The present invention relates to a gas hydrate manufacturing apparatus and a gas hydrate manufacturing method for manufacturing a hydrate using a mixed gas such as natural gas as a raw material.

A gas hydrate is an ice-like solid crystal consisting of water molecules and gas molecules, and clathrate hydrates (classes) that are formed by gas molecules being taken into the cage of the three-dimensional structure created by water molecules. It is a general term for rate hydrate. This gas hydrate has a high gas storage property, and the amount of natural gas that can be stored in 1 m ³ of natural gas hydrate reaches about 165 Nm ³ .

  At present, a system for storing and transporting natural gas as a gas hydrate (Natural Gas Hydrate System) is being studied for practical use. As a natural gas hydrate production method, water and gas as raw materials are on the high pressure / low temperature side from the hydrate production equilibrium condition (for example, the equilibrium temperature at which hydrate is produced under 5 MPa pressure is about 6 ° C.). A mode of increasing the hydrate conversion rate (meaning the amount of gas contained per unit weight of raw water) by increasing the gas-liquid contact area in the hydrate generation region is considered (for example, Patent Document 1).

JP 2000-302701 A

  Although the main component of natural gas is methane, it often contains ethane, propane, etc. as secondary components. When natural gas is hydrated, methane and the concentration of methane in the gas phase increase because ethane, propane, and other secondary components are easier to hydrate than methane. At this time, the amount of gas contained in the generated hydrate is low and there is an empty cage, but it is difficult for methane molecules to be taken into the empty cage generated by the secondary component. For this reason, in the conventional manufacturing method, even if the gas-liquid contact efficiency is improved, it has been difficult to increase the hydrate conversion rate beyond a certain level.

  A low hydrate conversion rate means that the amount of stored gas per unit weight of natural gas hydrate produced is small, so that the efficiency of storage and transfer is reduced. Therefore, it is necessary to increase the size of the transport tank, the storage tank, the rehydration device, etc., and there is a problem that the equipment cost and the operating cost increase.

  Further, if the generation temperature is lowered or the pressure is increased in order to obtain a high hydrate conversion rate, there is a problem that the cost increases in terms of energy required for the production, equipment, and the like.

  Accordingly, an object of the present invention is to provide a gas hydrate production apparatus and production method for producing a gas hydrate having a high hydrate conversion rate and high transportation and storage efficiency using a mixed gas such as natural gas as a raw material. There is to do.

In order to solve the above-mentioned problem, a first aspect of the present invention is a gas hydride in which a gas hydrate is generated by using a mixed gas containing two or more components composed of a main component and a subcomponent as a raw material and making gas-liquid contact. A rate production apparatus, comprising a first reaction unit for generating a mixed gas hydrate by bringing a mixed gas and water into gas-liquid contact, and water replenishment means, and replenishing the gas that has passed through the first reaction unit A gas hydrate production apparatus comprising: a second reaction unit that brings gas into liquid contact with water to generate gas hydrate.
In the first aspect of the present invention, by separating the first reaction part and the second reaction part, a mixed gas hydrate is generated in the first reaction part, and the main component having high purity in the second reaction part. Gas hydrate can be produced from gas. By generating the gas hydrate separately for the mixed gas and the high-purity main component gas, it becomes possible to improve the hydrate conversion rate and increase the gas storage amount.

  According to a second aspect of the present invention, there is provided the gas hydrate production apparatus according to the first aspect, wherein the first reaction part and the second reaction part are constituted by separate production vessels. . In the second aspect, by forming the first reaction unit and the second reaction unit separately, gas hydrate generation in the second reaction unit is performed separately from the first reaction unit. Gas hydrate produced in the first reaction section and low in hydrate formation rate and gas hydrate produced in the second reaction section and high in hydrate conversion rate. The rate can be easily separated and recovered.

  According to a third aspect of the present invention, there is provided a gas hydrate production method in which a gas mixture is produced by using a mixed gas containing two or more components composed of a main component and a subcomponent as a raw material, and is brought into gas-liquid contact. A first reaction step in which a mixed gas and water are brought into gas-liquid contact to generate a mixed gas hydrate, and a high purity main component from which most of the subcomponents are hydrated and removed in the first reaction step A gas hydrate production method comprising: a second reaction step of additionally introducing water into gas and bringing it into gas-liquid contact to generate gas hydrate.

  In the third aspect, the first reaction step and the second reaction step are separated, and a mixed gas hydrate is generated in the first reaction step, so that the second reaction step starts from a main component gas having high purity. A gas hydrate can be produced. That is, by generating the gas hydrate separately for the mixed gas and the high-purity main component gas, it is possible to improve the hydrate conversion rate and increase the gas storage amount.

  According to a fourth aspect of the present invention, in the third aspect, when the concentration of the main component gas in the gas phase becomes 95% or more in the first reaction step, the second reaction step is performed. This is a method for producing a gas hydrate. In the fourth aspect, by setting the main component gas concentration to 95% or more as the timing for shifting to the second reaction step, it is possible to form a gas hydrate having a high inclusion amount in a substantially single cage in the second reaction step. .

  According to a fifth aspect of the present invention, there is provided the gas hydrate production method according to the third or fourth aspect, wherein the mixed gas is natural gas.

  Natural gas contains ethane and propane as secondary components in addition to the main component methane, and the presence of these components changes the crystal structure of hydrate, resulting in higher purity than methane gas. Therefore, there is a problem that the gas storage amount becomes low. In the present invention, by separating the first reaction step and the second reaction step, it becomes possible to realize a hydrate conversion rate higher than that of the conventional method using natural gas as a raw material.

  According to the present invention, a gas hydrate can be produced from a mixed gas such as natural gas at a high hydrate conversion rate.

<Raw gas>
The raw material gas is not particularly limited as long as it is a mixed gas containing two or more components composed of a main component and subcomponents. For example, in addition to natural gas, biogas (mainly methane, carbon dioxide and sulfide) Anaerobic digestion gas containing hydrogen). As described above, natural gas contains ethane, propane and the like as secondary components in addition to methane as a main component. Examples of general natural gas compositions include methane 86.88%, ethane 5.20%, propane 1.86%, i-butane 0.42%, n-butane 0.47%, i-pentane 0.15. The thing containing% etc. is mentioned.

The relationship between the hydrate generation equilibrium conditions of the main component gas and the sub component gas is preferable because the sub component gas is more likely to be hydrated at a higher temperature and lower pressure than the main component gas, but is limited to this. It is not a thing. The quantitative ratio of the main component gas and the sub component gas is not particularly limited, but the main component gas consumed as the concentration of the main component gas increases as the sub component gas ratio increases (as a mixed gas hydrate). The amount of increases. The subcomponent gas is not limited to one type, and may include two or more types of gases.
<First reaction step>
In the first reaction step, the mixed gas and water are brought into gas-liquid contact to generate a mixed gas hydrate. Here, the temperature and pressure in the reaction can be set to known hydrate generation conditions according to the type of the mixed gas. In the case of natural gas, the equilibrium moves from the case of methane hydrate depending on the composition and ratio of the mixed gas (usually shifts to the high temperature and low pressure side), but it is set to the low temperature and high pressure side from this moved equilibrium condition. By doing so, a hydrate can be produced.

  In the present invention, the gas hydrate is generated by bringing the source gas and water into gas-liquid contact. Here, there is no restriction | limiting in particular as the method of gas-liquid contact, For example, the stirring method, the bubbling method, the method of performing stirring and bubbling simultaneously, the spray method etc. are employable.

In the first reaction step, the hydrate is formed as it is using the mixed gas as a raw material, so that not only the main component but also the component capable of forming hydrate among the subcomponents is hydrated. For example, in the case of natural gas, ethane or propane, which is easier to hydrate than methane, which is the main component, is preferentially hydrated. Methane also hydrates. However, as described above, if the auxiliary component is first hydrated, methane hydrate formation is less likely to occur, and the amount of gas contained in the hydrate is reduced. Therefore, in the present invention, the first reaction step is completed when the concentration of the main component gas in the gas phase reaches 95% in the first reaction step (preferably when the concentration reaches 99%). Then, the process proceeds to the second reaction step described later. When the concentration of the main component gas in the first reaction step is less than 95% and the transition to the second reaction step is performed, an improvement in the amount of gas inclusion cannot be expected. Note that the first reaction step is not limited to one step, and can be performed in a plurality of steps.
<Second reaction step>
In the second reaction step, water is additionally introduced into the high-purity (approximately 95% or more) main component gas from which most of the subcomponents have been hydrated and removed in the first reaction step, so that gas-liquid contact occurs. Gas hydrate is generated. In the second reaction step, a high-purity main component gas is used as a raw material, so that a gas hydrate having a substantially single cage is formed by the main component gas, not the mixed gas hydrate as in the first reaction step. Is done. For example, when the source gas is natural gas, ethane or propane contained as a subsidiary component is almost hydrated in the first reaction step, so that the purity of 95% or more is obtained in the second reaction step. Methane hydrate is predominantly produced by methane gas.

  The temperature and pressure conditions in the second reaction step can be set according to the hydrate generation conditions of the main component gas, and may be set to the same conditions as in the first reaction step. It can also be changed.

  In the second reaction step, it is important to introduce additional water. In the first reaction step, hydrate formation is mainly performed by the auxiliary component gas. However, since water is consumed at this time, it is necessary to replenish water in the second reaction step. In the first reaction step, type I cages and type II cages are produced in the case of natural gas, but methane gas is difficult to hydrate in the presence of type II cages. It is possible to generate a hydrate of the main component gas having a large gas storage amount by a substantially single gauge by replenishing water. Note that the second reaction step is not limited to one step, and can be performed in a plurality of steps.

Next, embodiments of the present invention will be described in more detail with reference to the drawings.
FIG. 1 is a diagram showing an outline of a natural gas hydrate production apparatus 100 according to an embodiment of the present invention. This hydrate production 100 is a gas-liquid process comprising a first reaction unit 10 that generates a mixed gas hydrate by bringing a mixed gas and water into gas-liquid contact, and a gas that has passed through the first reaction unit 10 and makeup water. And a second reaction unit 20 that is brought into contact with each other to generate a gas hydrate.

  The 1st reaction part 10 respond | corresponds to the said 1st reaction process, and the 2nd reaction part 20 respond | corresponds to the said 2nd reaction process. Each of the first reaction unit 10 and the second reaction unit 20 is formed of a pressure-resistant vessel equipped with a temperature control means, and the internal temperature and pressure are set to the conditions for generating natural gas (methane) hydrate (for example, temperature 3 ˜5 ° C., pressure about 5 MPa).

  The first reaction unit 10 includes a natural gas introduction means 11 and water introduction means 12 as raw materials, and a discharge means 13 for discharging the mixed gas hydrate. Since the first reaction unit 10 mainly hydrates secondary components such as ethane and propane contained in natural gas, the supply amount of raw water may be small, and the second reaction unit 20 Compared to the above, it can be constituted by a small-capacity container.

  The second reaction unit 20 includes a gas introduction unit 21 and a water supply unit 22 for introducing the high-concentration methane gas discharged from the first reaction unit 10, and a hydrate discharge unit 23 for discharging methane gas hydrate. . The second reaction unit 20 passes through the first reaction unit 10 to supply additional water to high-purity methane gas from which ethane or propane, which is a secondary component, has been hydrated and separated, and hydrates. Therefore, it is preferable to use a container having a corresponding volume.

  In the above configuration, the first reaction unit 10 generates mixed gas hydrate until the concentration of the main component gas (methane gas) in the gas phase reaches about 95%. The high-concentration main component gas that has passed through the first reaction unit 10 is introduced into the second reaction unit to be hydrated. Here, hydration can be performed under substantially the same temperature and pressure conditions as pure methane gas, and methane hydrate with a high gas storage amount is generated. The total amount of gas hydrates thus obtained (the total of the first reaction unit 10 and the second reaction unit 20) is higher than when gas hydrate is generated in a single reaction unit. . In the present embodiment, one each of the first reaction unit 10 and the second reaction unit 20 is illustrated, but each may be configured by a plurality of reaction units (production containers).

  The mixed gas hydrate recovered from the first reaction unit 10 and the methane hydrate recovered from the second reaction unit 20 can be separately stored and transported. It is also possible to store and transfer.

<Action>
When the mixed gas is hydrated with a single-stage gas hydrate production apparatus, there is a problem that the amount of gas taken into the cage (the amount of inclusion) does not increase as described above, and the gas reaches a peak. The reason for this is not clear, but a rational explanation is possible if the following is considered. Here, natural gas hydrate will be described as an example.

  FIG. 2 is a graph showing the relationship between the amount of gas contained in a mixed gas hydrate produced by a single-stage hydrate production apparatus (conventional method) using a mixed gas containing methane and propane as a raw material and the concentration of propane in the raw material gas. It is. This graph shows a tendency for the gas storage amount to increase at a propane concentration of 5% or less. From this result, in the gas hydrate production using a mixed gas such as natural gas as a raw material, the amount of gas hydrate contained in the raw material gas is suppressed by keeping the amount of subcomponents (for example, ethane, propane, etc.) low. It is suggested that can be improved.

  It is known that gas hydrates have different types of cages (cages) such as type I and type II depending on the type of hydrate-forming substance. In the case of natural gas hydrate, it is produced with a mixture of Type I and Type II cages. This is because ethane, propane and the like are contained in addition to methane, and the ratio of the type I and type II cages is considered to change depending on the amount of these subcomponents. For example, it is known that when propane is contained, a type II cage is formed, and methane is taken into the propane as well, but its filling rate is low, and it is considered that many cages remain empty. On the other hand, in the case of pure methane, a hydrate is constituted only by a substantially I-type cage.

  In the present invention, the reaction part for producing the gas hydrate is divided into a plurality of parts, and in the first reaction part, the auxiliary components such as propane and ethane are made into the gas hydrate and consumed as the mixed gas hydrate. The production rate of the cage (for example, type II cage with propane) is kept low, and the gas hydrate of a single cage (for example, type I cage with methane) is formed from the high purity main component gas in the second reaction section. Let As a result, even if the gas storage amount of the mixed gas hydrate generated in the first reaction section is low, it remains at a low ratio, so that a high gas storage amount can be obtained as a whole. It is guessed.

  In addition, when the hydrate formation is performed by separating the first reaction part and the second reaction part, the first reaction part and the second reaction part are separated in order to efficiently generate the gas hydrate. It was experimentally confirmed that it was effective to supply water directly to the second reaction section. This is also because the gas is contained in the empty cage in the state where the type I cage and the type II cage coexist, and fresh water is separately introduced into the second reaction part, thereby providing the type I cage. It is presumed that methane hydrate can be easily generated by the cage.

  Furthermore, one of the factors that lower the hydrate conversion rate in the generation of mixed gas hydrate is that the viscosity of the liquid phase increases as the amount of mixed gas hydrate generated increases. Therefore, if the hydrate generation is continued as it is, the gas-liquid contact efficiency is reduced and the hydrate conversion rate is also suppressed. However, as a result of additionally introducing water into the second reaction section, the viscosity of the liquid phase is reduced. Hydrate generation efficiency may be improved.

EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in more detail, this invention is not restrict | limited at all by this. 3 and 4 in the following examples and comparative examples, reference numerals 34a to 34c and reference numeral 52 denote pressure adjusting means, and reference numerals 35a to 35c and reference numeral 53 denote temperature adjusting means.
Example 1
Production with a two-stage mixed gas hydrate production device:
Natural gas hydrate was produced using the test apparatus shown in FIG.
<Experimental procedure>
The reaction vessel 31a and the reaction vessel 31b of the two-stage mixed gas hydrate production apparatus 30 were each charged with 0.5 liters of purified water. The accumulator 51 was filled with a mixed gas having a predetermined pressure and concentration, and from there, the mixed gas was charged into the reaction vessel 31a from the accumulator 51 to a predetermined pressure of 5 MPa.

  After the reaction vessel 31a is adjusted to a predetermined production temperature condition (3 to 5 ° C.) by the cooler 33a, the water in the reaction vessel 31a is agitated by the stirrer 32a to bring the gas and water into gas-liquid contact, and gas hydrate Started generating. Gas was supplied from the pressure accumulator 51 to the reaction vessel 31a, and the temperature was kept constant by the cooler 33a.

  When gas hydrate generation in the reaction vessel 31a proceeds to some extent and the methane concentration in the gas phase reaches 98% or more, the valve 55 is opened to allow the gas phase gas in the reaction vessel 31a to flow out. Introduced into the phase.

  The inside of the reaction vessel 31b was adjusted to a predetermined temperature (0 to 5 ° C.) by the cooler 33b, and the water in the vessel was stirred by the stirrer 32b to start the production of gas hydrate. The temperature was kept constant by the cooler 33b.

  When the gas hydrate formation in the reaction vessel 31b ceased, stirring in the reaction vessel 31b was stopped, and both reaction vessels 31a and 31b were cooled to -20 ° C. After cooling, the pressure in both reaction vessels 31a and 31b was reduced to atmospheric pressure. The gas phase gas was appropriately collected and the gas composition was measured. Moreover, the gas hydrate produced | generated by reaction container 31a, 31b was extract | collected, respectively, and the amount of stored gases and gas composition of gas hydrate were measured.

Comparative Example 1
Production with single-stage mixed gas hydrate production equipment:
Natural gas hydrate was produced using the test apparatus shown in FIG.
<Experimental procedure>
The reaction vessel 31c was filled with 0.5 liters of purified water. The pressure accumulator 51 was filled with a mixed gas having a predetermined pressure and concentration, and from there, the mixed gas was filled into the reaction vessel 31c until the predetermined pressure reached 5 MPa.

  After the inside of the reaction vessel 31c is adjusted to a predetermined generation temperature condition (3 to 5 ° C.) by the cooler 33c, the water in the reaction vessel 31c is agitated by the stirrer 32c to bring the gas and water into gas-liquid contact. Started generating rates. The pressure in the reaction vessel 31c was maintained at a constant pressure by supplying gas from the accumulator 51 through the pressure reducing valve 54, and the gas decreased by the generation of gas hydrate was constantly supplied. The temperature in the reaction vessel 31c was kept at a constant temperature by the cooler 33c.

  When the generation of gas hydrate ceased, stirring in the reaction vessel 31c was stopped, and the reaction vessel 31c was cooled to -20 ° C. After cooling, the internal pressure of the reaction vessel 31c was reduced to atmospheric pressure. The gas phase gas in the pressure vessel 31C was appropriately collected and the gas composition was measured. The produced gas hydrate was collected, and the amount of gas contained in the gas hydrate and the gas composition were measured.

<Result>
FIG. 5 shows the concentration of propane in the initial source gas and the gas phase gas obtained in the reaction vessel 31a (that is, the source gas in the reaction vessel 31b; the secondary source gas), and FIG. 6 shows the one-stage gas hydrate production apparatus 40. The gas storage amount of the gas hydrate (Comparative example 1) produced | generated by (2) and the gas hydrate (Example 1) produced | generated by the reaction container 31b of the two-stage type gas hydrate manufacturing apparatus 30 is shown.

  As shown in FIG. 5, in the two-stage gas hydrate production apparatus 30, the propane concentration in the gas phase is reduced to a value close to 0% by the reaction vessel 31a, and this is used as the raw material gas for the reaction vessel 31b. As a result, as shown in FIG. 6, a higher gas storage amount was obtained as compared with the mixed gas hydrate produced by the single-stage gas hydrate production apparatus 40.

  From the above examples and comparative examples, the hydrate conversion rate is increased and the gas inclusion amount is increased when the reaction is divided into two or more stages as compared with the case where the mixed gas is gas hydrated by one stage reaction. It was shown that it can.

  The present invention has been described above with reference to various embodiments. However, the present invention is not limited to the above embodiments, and can be applied to other embodiments within the scope of the invention described in the claims. It is.

For example, in FIG. 1, the first reaction unit 10 and the second reaction unit 20 are configured by separate containers. For example, as shown in FIG. 7, in the integrated hydrate generation container 110, the first reaction unit 111 is used. It is also possible to distinguish between the second reaction part 112 and the second reaction part 112.
That is, in a system in which hydrate formation is performed while flowing the generated water and gas (for example, natural gas) as raw materials into the tubular hydrate generating device 110, the source gas has a predetermined concentration (for example, 95%). A region in which the water supply means 22 is provided at the start site of the second reaction unit 112 as the first reaction unit 111 can be adopted.

  The present invention can be advantageously used when a mixed gas including natural gas is hydrated and stored, transported, or the like.

The drawing which shows the outline | summary of the hydrate manufacturing apparatus which concerns on one Embodiment of this invention. The graph figure which shows the relationship between the gas storage amount of mixed gas hydrate, and a propane density | concentration. BRIEF DESCRIPTION OF THE DRAWINGS Drawing which shows the outline | summary of the two-stage type mixed gas hydrate manufacturing apparatus used in Example 1. FIG. The figure which shows the outline | summary of the 1 step | paragraph type mixed gas hydrate manufacturing apparatus used in the comparative example 1. FIG. Drawing which shows the comparison of the propane density | concentration in source gas. The drawing which shows the comparison of the amount of gas occlusion in the gas hydrate of Example 1 and Comparative Example 1. Drawing which shows the outline | summary of the hydrate manufacturing apparatus which concerns on another embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 1st reaction part 11 Gas introduction means 12 Water introduction means 13 Gas discharge means 20 2nd reaction part 21 Gas introduction means 22 Water supply means 23 Hydrate discharge means 100 Hydrate manufacturing apparatus 110 Hydrate production | generation container 111 1st Reaction section 112 second reaction section 200 hydrate production apparatus

Claims (3)

A gas hydrate production apparatus that uses a mixed gas containing two or more components composed of a main component and subcomponents as a raw material, and generates gas hydrate by gas-liquid contact,
The mixed gas is natural gas, the main component of which is methane,
A first reaction section including a single reaction vessel in which a mixed gas and water are brought into gas-liquid contact to generate a mixed gas hydrate until the concentration of the main component gas in the gas phase reaches 95% or more;
A second reaction section comprising water replenishing means, wherein the gas that has passed through the first reaction section and the makeup water are brought into gas-liquid contact to generate gas hydrate;
A gas hydrate production apparatus comprising:   2. The gas hydrate production apparatus according to claim 1, wherein the first reaction unit and the second reaction unit are configured by separate production vessels. A gas hydrate production method in which gas liquefaction is generated by using natural gas , which is a mixed gas containing two or more components composed of a main component and subcomponents, as a raw material,
The main component of the mixed gas is methane,
A first reaction step in which natural gas and water are brought into gas-liquid contact in one reaction vessel to generate a mixed gas hydrate;
Second reaction step of generating gas hydrate by introducing water into gas-liquid contact by additionally introducing water into the high-purity main component gas from which most of the auxiliary components have been hydrated and removed in the first reaction step. And comprising
A method for producing a gas hydrate, characterized in that, in the first reaction step, the second reaction step is performed when the concentration of the main component gas in the gas phase becomes 95% or more.

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