A natural-gas purification apparatus includes: a compressor that adjusts the pressure of natural gas, and a separation device that separates natural-gas liquid and carbon dioxide from the natural gas after the pressure adjustment by the compressor through a natural-gas-liquid separation membrane and a carbon-dioxide separation membrane.

TECHNICAL FIELD

The present invention relates to a natural-gas purification apparatus for purifying natural gas from the ground or the like by separating carbon dioxide from the natural gas.

BACKGROUND ART

Natural gases discharged to the surface of the ground from high-temperature high-pressure underground areas such as oil and gas fields include: dry gases with one to two carbon atoms such as methane (CH4) and ethane (C2H6), which are in gaseous form even at normal temperature and pressure; natural-gas liquids containing components with three to four carbon atoms such as propane (C3H8) and butane (C4H10), which are in gaseous format normal temperature and pressure but are easily liquefied when pressurized or cooled, and components with five or more carbon atoms such as pentane (C5H12), which is in liquid form at normal temperature and pressure; and non-hydrocarbon gases such as carbon dioxide (CO2).

As described in, for example, Patent Literature 1, such a natural gas is pressurized (to 0.5 to 2 MPa) by a compressor and cooled (to 0 to 20° C.) by a cooling unit to undergo gas-liquid separation in which a part of its natural-gas liquid is liquefied. The natural gas is then raised in temperature by being heated (to 50 to 80° C.) by a heating unit. Thereafter, the carbon dioxide is passed through a carbon-dioxide separation membrane to a lower pressure side, so that the carbon dioxide is separated and removed. As a result, the natural gas is purified.

CITATION LIST

Patent Literatures

SUMMARY OF INVENTION

Technical Problem

Although the above system described in Patent Literature 1 can purify natural gas, it includes a compressor, a cooling unit, a heating unit, and a carbon-dioxide separation device, and these are arranged in this order from an upstream side in the direction of gas flow. Thus, the system has problems that the system itself is large in size and cannot efficiently separate and remove natural-gas liquid and carbon dioxide from natural gas.

Use of a natural-gas-liquid separation membrane that separates apart of natural-gas liquid from natural gas in the above system has been considered. In this case, the system includes a compressor, a natural-gas-liquid separation device using a natural-gas-liquid separation membrane, and a carbon-dioxide separation device using a carbon-dioxide separation membrane, and these are arranged in this order from an upstream side in the direction of gas flow. Thus, the system has problems that the system itself is large in size and cannot efficiently separate and remove natural-gas liquid and carbon dioxide from natural gas.

In view of the above, the present invention has been made to solve the above-mentioned problems, and an object thereof is to provide a natural-gas purification apparatus which is small in size but is capable of efficiently separating and removing carbon dioxide from natural gas.

Solution to Problem

A natural-gas purification apparatus according to a first aspect for solving the problem described above is a natural-gas purification apparatus for purifying natural gas by separating carbon dioxide from the natural gas, including: a pressure adjuster that adjusts a pressure of natural gas; and a separator that separates natural-gas liquid and carbon dioxide from the natural gas after the pressure adjustment by the pressure adjuster through a natural-gas-liquid separation membrane and a carbon-dioxide separation membrane.

A natural-gas purification apparatus according to a second aspect for solving the problem described above is the natural-gas purification apparatus according to the first aspect in which the separator includes a device body including a gas inlet port through which to receive the natural gas, a natural-gas-liquid outlet port through which to discharge the natural-gas liquid, a carbon-dioxide outlet port through which to discharge the carbon dioxide, and a gas outlet port through which to discharge the natural gas from which the natural-gas liquid and the carbon dioxide have been separated, each of the natural-gas-liquid separation membrane and the carbon-dioxide separation membrane is in a flat shape, and the natural-gas-liquid separation membrane and the carbon-dioxide separation membrane are arranged inside the device body in such a way as to partition an inside of the device body into a first chamber including the gas inlet port and the gas outlet port, a second chamber including the natural-gas-liquid outlet port, and a third chamber including the carbon-dioxide outlet port.

A natural-gas purification apparatus according to a third aspect for solving the problem described above is the natural-gas purification apparatus according to the second aspect in which the gas inlet port and the gas outlet port are arranged opposite to each other, and the natural-gas-liquid separation membrane and the carbon-dioxide separation membrane are arranged parallel to each other.

A natural-gas purification apparatus according to a fourth aspect for solving the problem described above is the natural-gas purification apparatus according to the first aspect in which the separator includes a device body including a gas inlet port through which to receive the natural gas, a natural-gas-liquid outlet port through which to discharge the natural-gas liquid, a carbon-dioxide outlet port through which to discharge the carbon dioxide, and a gas outlet port through which to discharge the natural gas from which the natural-gas liquid and the carbon dioxide have been separated, a first partition plate partitioning an inside of the device body into a first chamber including the gas inlet port and the gas outlet port and a second chamber including the natural-gas-liquid outlet port, and a second partition plate partitioning the inside of the device body into the first chamber and a third chamber including the carbon-dioxide outlet port, each of the natural-gas-liquid separation membrane and the carbon-dioxide separation membrane is in a tubular shape, the natural-gas-liquid separation membrane is arranged inside the first chamber in such a way as to open only to the second chamber through the first partition plate, and the carbon-dioxide separation membrane is arranged inside the first chamber in such a way as to open only to the third chamber through the second partition plate.

A natural-gas purification apparatus according to a fifth aspect for solving the problem described above is the natural-gas purification apparatus according to the fourth aspect in which the gas inlet port and the gas outlet port are arranged opposite to each other, and the natural-gas-liquid separation membrane and the carbon-dioxide separation membrane are arranged parallel to each other.

A natural-gas purification apparatus according to a sixth aspect for solving the problem described above is the natural-gas purification apparatus according to the fifth aspect in which a plurality of the natural-gas-liquid separation membranes and a plurality of the carbon-dioxide separation membranes are arranged adjacently to each other at equal intervals in a front-rear direction.

Advantageous Effect of Invention

According to the present invention, the separator can simultaneously perform the separation and removal of natural-gas liquid from natural gas with the natural-gas-liquid separation membrane and the separation and removal of carbon dioxide from the natural gas with the carbon-dioxide separation membrane. Hence, the natural-gas purification apparatus can be smaller in size than conventional apparatuses including a pressure adjuster, a natural-gas-liquid separator, a heater, and a carbon-dioxide separator arranged in this order from an upstream side in the direction of gas flow. Also, the natural-gas purification apparatus can efficiently separate and remove carbon dioxide from the natural gas while preventing the generation of a liquid film over the carbon-dioxide separation membrane.

DESCRIPTION OF EMBODIMENTS

Embodiments of a natural-gas purification apparatus according to the present invention will be described with reference to the drawings. It is to be noted that the present invention is not limited only to the following embodiments to be described with reference to the drawings.

First Embodiment

A natural-gas purification apparatus according to a first embodiment of the present invention will be described with reference toFIG. 1.

As illustrated inFIG. 1, a natural-gas purification apparatus100according to this embodiment includes a compressor11and a separation device20that separates two components, namely, a part of natural-gas liquid3and carbon dioxide4, from natural gas1. An inlet port of the compressor111is connectable to a natural-gas source10that discharges the natural gas1from, for example, the ground by a gas supply pipe L1provided with an on-off valve V1. An outlet port of the compressor111is connected to a gas inlet port of the separation device20, which will be described later in detail, by a gas supply pipe L2.

The separation device20includes a separation-device body21that serves as a housing, a natural-gas-liquid separation membrane22, and a carbon-dioxide separation membrane23. The separation-device body21includes a gas inlet port21a, a natural-gas-liquid outlet port21b, a carbon-dioxide outlet port21c, and a gas outlet port21d. The gas inlet port21aand the gas outlet port21dare preferably arranged opposite to each other.

Each of the natural-gas-liquid separation membrane22and the carbon-dioxide separation membrane23is in a flat shape, for example.

The natural-gas-liquid separation membrane22and the carbon-dioxide separation membrane23are preferably arranged parallel to each other.

The natural-gas-liquid separation membrane22is a membrane capable of separating and removing a part of the natural-gas liquid3from gas. For example, the membrane with the product name LPG-Sep, manufactured by Membrane Technology and Research Incorporated (US), or the like is usable as the natural-gas-liquid separation membrane22.

The carbon-dioxide separation membrane23is a membrane capable of separating and removing carbon dioxide from gas. For the carbon-dioxide separation membrane23, it is preferable to use a membrane of cellulose acetate, polyimide, a fluororesin, or the like with a withstand temperature of 50 C or lower, and more preferable to use a membrane with a withstand temperature of 80 C or lower.

The natural-gas-liquid outlet port21bis connected to the outside of the system by a natural-gas-liquid discharge pipe L11provided with an on-off valve V2. The carbon-dioxide outlet port21cis connected to the outside of the system by a carbon-dioxide discharge pipe L12provided with an on-off valve V3. The post-separation-gas outlet port21dis connected to the outside of the system by a gas discharge pipe L13provided with an on-off valve V4.

In the above natural-gas purification apparatus100, components such as the compressor11, the gas supply pipes L1and L2, the natural-gas-liquid discharge pipe L11, the carbon-dioxide discharge pipe L12, the gas discharge pipe L13, and the on-off valves V1to V4constitute a pressure adjuster.

Next, a natural-gas purification method using the above natural-gas purification apparatus100according to this embodiment will be described.

First, the composition of the natural gas1from the natural-gas source10(the proportions of dry gas2, the natural-gas liquid3, the carbon dioxide4, and the like) is figured out in advance using analysis equipment such as a gas chromatograph (GC).

The actuation of the compressor111and the opening degrees of the on-off valves V1to V4are adjusted and controlled according to this composition of the natural gas1. Meanwhile, the opening degrees of the on-off valves V1to V4may be adjusted and controlled automatically by an arithmetic control device (not illustrated) or manually by an operator.

Thus, the natural gas1supplied from the natural-gas source10is pressurized (to 0.5 to 2 MPa) by the compressor11and then supplied to the inside of the first chamber31of the separation device20.

When the natural gas1pressurized by the compressor11is supplied to the inside of the first chamber31of the separation device20, a part of the natural-gas liquid3in the natural gas1is moved through the natural-gas-liquid separation membrane22to the second chamber32, which is a lower pressure side (natural-gas-liquid flow side), and then discharged to the outside of the system through the natural-gas-liquid outlet port21b, the natural-gas-liquid discharge pipe L11, and the on-off valve V2. Also, the carbon dioxide4in the natural gas is moved through the carbon-dioxide separation membrane23to the third chamber33, which is a lower pressure side (carbon-dioxide flow side), and then discharged to the outside of the system through the carbon-dioxide outlet port21c, the carbon-dioxide discharge pipe L12, and the on-off valve V3. On the other hand, the remaining gas (the dry gas2and the remaining part of the natural-gas liquid3) is discharged to the outside of the system through the gas outlet port21d, the gas discharge pipe L13, and the on-off valve V4without being liquefied.

Here, as the carbon-dioxide separation membrane23separates and removes the carbon dioxide4from the natural gas1, the carbon-dioxide separation membrane23is cooled and experiences a temperature drop that can cause generation of a liquid film. However, since the natural-gas-liquid separation membrane22separates and removes a part of the natural-gas liquid3simultaneously with the separation and removal of the carbon dioxide4, the generation of a liquid film is prevented.

Since the liquefaction of apart of the natural-gas liquid3is prevented as above, the natural gas1can be efficiently purified.

Thus, according to this embodiment, the separation device20can simultaneously perform the separation and removal of a part of the natural-gas liquid3from the natural gas1with the natural-gas-liquid separation membrane22and the separation and removal of the carbon dioxide4from the natural gas1with the carbon-dioxide separation membrane23. Hence, the natural-gas purification apparatus100can be smaller in size than conventional apparatuses including a compressor, a cooling unit, a heating unit, and a carbon-dioxide separation device arranged in this order from an upstream side in the direction of gas flow. Also, the natural-gas purification apparatus100can efficiently separate and remove the carbon dioxide4from the natural gas1while preventing the generation of a liquid film over the carbon-dioxide separation membrane23.

The gas inlet port21aand the gas outlet port21dof the separation device20are arranged opposite to each other, and the natural-gas-liquid separation membrane22and the carbon-dioxide separation membrane23are arranged parallel to each other. Thus, the natural gas1pressurized by the compressor11equally contacts the natural-gas-liquid separation membrane22and the carbon-dioxide separation membrane23from when the natural gas1is supplied to the inside of the first chamber31of the separation-device body21through the gas inlet port21ato when the natural gas1is discharged to the gas discharge pipe L13through the gas outlet port21d. Hence, a part of the natural-gas liquid3and the carbon dioxide4can be efficiently separated and removed from the natural gas1.

Second Embodiment

A natural-gas purification apparatus according to a second embodiment of the present invention will be described with reference toFIG. 2toFIG. 4.

In this embodiment, the configuration of the separation device included in the above-described natural-gas purification apparatus is changed. Besides this, the natural-gas purification apparatus according to this embodiment includes the same devices as the above-described natural-gas purification apparatus.

As illustrated inFIG. 2toFIG. 4, the natural-gas purification apparatus according to this embodiment includes a separation device20A. The separation device20A includes a separation-device body21A that serves as a housing, natural-gas-liquid separation membranes22A, and carbon-dioxide separation membranes23A. The separation-device body21A includes a gas inlet port21Aa, a gas outlet port21Ad, a natural-gas-liquid outlet port21Ab, and a carbon-dioxide outlet port21Ac. The gas inlet port21Aa and the gas outlet port21Ad are preferably arranged opposite to each other.

As in the natural-gas-liquid separation membrane22, each natural-gas-liquid separation membrane22A is a membrane capable of separating and removing a part of the natural-gas liquid3from the natural gas1. For example, the membrane with the product name LPG-Sep, manufactured by Membrane Technology and Research Incorporated (US), or the like is usable as the natural-gas-liquid separation membrane22A.

As in the carbon-dioxide separation membrane23, each carbon-dioxide separation membrane23A is a membrane capable of separating and removing carbon dioxide from gas. For the carbon-dioxide separation membrane23A, it is preferable to use a membrane of cellulose acetate, polyimide, a fluororesin, or the like with a withstand temperature of 50 C or lower, and more preferable to use a membrane with a withstand temperature of 80 C or lower.

The above separation device20A further includes: a first partition plate41that partitions the inside of the separation-device body21A into a first chamber31A including the gas inlet port21Aa and the gas outlet port21Ad and a second chamber32A including the natural-gas-liquid outlet port21Ab; and a second partition plate42that partitions the inside of the separation-device body21A into the first chamber31A and a third chamber33A including the carbon-dioxide outlet port21Ac.

Each natural-gas-liquid separation membrane22A is in, for example, a tubular shape opened at one end22Aa and closed at the other end22Ab. In the first partition plate41, openings41aare formed at positions coinciding with the positions at which the natural-gas-liquid separation membranes22A are attached. The natural-gas-liquid separation membranes22A are arranged inside the first chamber31A in such a way as to open to (communicate with) only the second chamber32A through the first partition plate41. Each carbon-dioxide separation membrane23A is in, for example, a tubular shape opened at one end23Aa and closed at the other end23Ab. In the second partition plate42, openings42aare formed at positions coinciding with the positions at which the carbon-dioxide separation membranes23A are attached. The carbon-dioxide separation membranes23A are arranged inside the first chamber31A in such a way as to open to (communicate with) only the third chamber33A through the second partition plate42.

The natural-gas-liquid separation membranes22A and the carbon-dioxide separation membranes23A are arranged parallel to each other. The natural-gas-liquid separation membranes22A and the carbon-dioxide separation membranes23A are arranged adjacently to each other at equal intervals in the front-rear direction (the left-right direction inFIG. 3and FIG.4).

In the above natural-gas purification apparatus, components such as the compressor11, the gas supply pipes L1and L2, the natural-gas-liquid discharge pipe L11, the carbon-dioxide discharge pipe L12, and the on-off valves V1to V4constitute a pressure adjuster.

Next, a natural-gas purification method using the above natural-gas purification apparatus according to this embodiment will be described.

First, the composition of the natural gas1from the natural-gas source10(the proportions of the dry gas2, the natural-gas liquid3, the carbon dioxide4, and the like) is figured out in advance using analysis equipment such as a gas chromatograph (GC).

The actuation of the compressor111and the opening degrees of the on-off valves V1to V4are adjusted and controlled according to this composition of the natural gas1. Meanwhile, the opening degrees of the on-off valves V1to V4may be adjusted and controlled automatically by an arithmetic control device (not illustrated) or manually by an operator.

Thus, the natural gas1supplied from the natural-gas source10is pressurized (to 0.5 to 2 MPa) by the compressor11and then supplied to the inside of the first chamber31A of the separation device20A.

When the natural gas1pressurized by the compressor11is supplied to the inside of the first chamber31A of the separation device20A, apart of the natural-gas liquid3in the natural gas1is moved through the natural-gas-liquid separation membranes22A to the second chamber32A, which is a lower pressure side (natural-gas-liquid flow side), and then discharged to the outside of the system through the natural-gas-liquid outlet port21Ab, the natural-gas-liquid discharge pipe L11, and the on-off valve V2. Also, the carbon dioxide4in the natural gas1is moved through the carbon-dioxide separation membranes23A to the third chamber33A, which is a lower pressure side (carbon-dioxide flow side), and then discharged to the outside of the system through the carbon-dioxide outlet port21Ac, the carbon-dioxide discharge pipe L12, and the on-off valve V3. On the other hand, the remaining gas (the dry gas2and the remaining part of the natural-gas liquid3) is discharged to the outside of the system through the gas outlet port21Ad, the gas discharge pipe L13, and the on-off valve V4without being liquefied.

Here, as the carbon-dioxide separation membranes23A separate and remove the carbon dioxide4from the natural gas1, the carbon-dioxide separation membranes23A are cooled and experience a temperature drop that can cause generation of a liquid film. However, since the natural-gas-liquid separation membranes22A separate and remove a part of the natural-gas liquid3simultaneously with the separation and removal of the carbon dioxide4, the generation of a liquid film is prevented.

Since the liquefaction of apart of the natural-gas liquid3is prevented as above, the natural gas1can be efficiently purified.

Thus, according to this embodiment, the separation device20A can simultaneously perform the separation and removal of a part of the natural-gas liquid3from the natural gas1with the natural-gas-liquid separation membranes22A and the separation and removal of the carbon dioxide4from the natural gas1with the carbon-dioxide separation membranes23A. Hence, the natural-gas purification apparatus can be smaller in size than conventional apparatuses including a compressor, a cooling unit, a heating unit, and a carbon-dioxide separation device arranged in this order from an upstream side in the direction of gas flow. Also, the natural-gas purification apparatus can efficiently separate and remove the carbon dioxide4from the natural gas1while preventing the generation of a liquid film over the carbon-dioxide separation membranes23A.

The gas inlet port21Aa and the gas outlet port21Ad of the separation device20A are arranged opposite to each other, and the natural-gas-liquid separation membranes22A and the carbon-dioxide separation membranes23A are arranged inside the first chamber31A. Thus, a part of the natural-gas liquid3and the carbon dioxide4can be gradually separated and removed from the natural gas1inside the first chamber31A. Generation of a liquid film due to abrupt temperature drop can be prevented.

The natural-gas-liquid separation membranes22A and the carbon-dioxide separation membranes23A are arranged parallel to each other. Thus, the natural gas1after the pressure adjustment by the compressor11equally contacts the natural-gas-liquid separation membranes22A and the carbon-dioxide separation membranes23A from when the natural gas1is supplied to the inside of the first chamber31A of the separation-device body21A through the gas inlet port21Aa to when the natural gas1is discharged to the gas discharge pipe L13through the gas outlet port21Ad. Hence, a part of the natural-gas liquid3and the carbon dioxide4can be efficiently separated and removed from the natural gas1.

REFERENCE SIGNS LIST