KR20200000771A - gas treatment system and offshore plant having the same - Google Patents

Abstract

The present invention relates to a gas treatment system and an offshore structure having the same. The gas treatment system, which is provided on an offshore structure and is supplied with gas from a gas well to treat the same, includes: a cooling unit cooling the gas produced in the gas well; a distillation unit implementing distillation at extremely low temperature so as to separate carbon dioxide from the cooled gas; a liquefying unit liquefying the gas from which the carbon dioxide is separated; and a vent unit venting the gas in a gaseous state discharged from the distillation unit, wherein the vent unit has a blow-down valve decompressing the discharged gas and preventing the carbon dioxide contained in the gas from freezing by increasing opening when the temperature of the discharged gas is equal to or less than a predetermined value.

Description

Gas treatment system and offshore plant having the same

The present invention relates to a gas treatment system and an offshore structure comprising the same.

As environmental regulations have recently been tightened, the use of natural gas, which is close to an environmentally friendly fuel, is increasing among various fuels. Natural gas can be extracted in gaseous form from wells located in the inland or ocean strata. The extracted natural gas undergoes pretreatment such as mercury removal, drying, or NGL removal, followed by liquefaction for storage and transportation. Can be liquefied through.

Natural gas can be cooled to below the boiling point (for example, -162 ℃ under 1 atm) while being exchanged with a refrigerant, and can be converted into a liquid state. Transport efficiency can be increased.

The liquefaction process as described above may be performed in a land plant or FLNG on the sea, and liquefied natural gas may be stored in an LNG storage tank and then supplied to a consumer.

For example, natural gas may be supplied from LNG storage tanks to onshore city gas facilities or power generation facilities, or may be delivered to cargo tanks of LNG carriers and transported to desired areas by LNG carriers.

At this time, the natural gas may be consumed by being vaporized after being discharged from the LNG storage tank or cargo tank, the vaporization facility may be provided in a land plant or FLNG, or in a facility that consumes natural gas.

As such, natural gas is extracted from gas wells and consumed through pre-treatment, liquefaction, storage, transportation, and gasification processes in turn. Various research and development is conducted to ensure stability and improve efficiency of gas production, treatment, and supply. This is constantly being done.

The present invention was created to solve the problems of the prior art as described above, an object of the present invention, to improve the efficiency of energy use in the process of producing natural gas at sea, which can prevent problems caused by freezing, etc. To provide a gas treatment system and an offshore structure comprising the same.

According to an aspect of the present invention, there is provided a gas treatment system comprising: a cooling unit configured to be provided in a marine structure to receive and process gas from a gas well, and to cool the gas produced in the gas well; A distillation unit for cryogenic distillation to separate carbon dioxide from the cooled gas; A liquefaction unit for liquefying gas from which carbon dioxide is separated; And a vent unit venting gaseous gas discharged from the distillation unit, wherein the vent unit reduces the discharged gas and increases the opening degree when the temperature of the discharged gas is lower than or equal to a preset value to freeze carbon dioxide contained in the gas. It is characterized by having a blowdown valve to prevent.

Specifically, the vent unit, a heater provided downstream of the blowdown valve; And a temperature sensor for measuring the temperature of the gas downstream of the blowdown valve.

Specifically, the vent unit may reduce the gas discharged at the time of initial discharge, but to prevent freezing of carbon dioxide contained in the gas by using the heater, and if the measured value of the temperature sensor is less than or equal to a preset value, By increasing the opening degree, cooling by pressure reduction can be prevented to prevent freezing of carbon dioxide contained in the gas.

Specifically, when the measured value of the temperature sensor is less than or equal to a preset value, the vent part may increase the opening degree of the blowdown valve and prevent freezing of carbon dioxide contained in gas using the heater.

Specifically, the blowdown valve may reduce the discharged gas, but increase the opening degree when the flow rate of the discharged gas is less than or equal to a preset value to prevent freezing of carbon dioxide contained in the gas.

An offshore structure according to an aspect of the present invention is characterized by having the gas treatment system.

Gas treatment system and offshore structure including the same according to the present invention, so that cryogenic distillation, carbon dioxide separation, carbon dioxide re-injection, etc. can be efficiently and safely implemented during the processing of natural gas, it is possible to maximize the gas production efficiency.

1 is a partial conceptual diagram of a gas treatment system according to an embodiment of the present invention.
2 is a partial conceptual diagram of a gas treatment system according to an embodiment of the present invention.
3 is a partial conceptual diagram of a gas treatment system according to an embodiment of the present invention.
4 is a partial conceptual diagram of a gas treatment system according to an embodiment of the present invention.
5 is a graph illustrating a vent of a gas treatment system according to an embodiment of the present invention.

The objects, specific advantages and novel features of the present invention will become more apparent from the following detailed description and the preferred embodiments associated with the accompanying drawings. In the present specification, in adding reference numerals to the components of each drawing, it should be noted that the same components as possible, even if displayed on different drawings have the same number as possible. In addition, in describing the present invention, if it is determined that the detailed description of the related known technology may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Hereinafter, the gas may mean a material having a boiling point lower than room temperature as hydrocarbons such as LPG, LNG, and ethane, but for convenience, the present invention will be limited to the final production and storage of LNG (methane). In the present specification, the gas is not limited to the gas phase despite the term expression.

Hereinafter, high pressure (HP), low pressure (LP), high temperature, and low temperature are relative and do not represent an absolute value.

The present invention may include a gas treatment system described below, and an offshore structure on which the gas treatment system is mounted. First, the marine structure of the present invention will be briefly described.

Offshore structures are anchored / fixed in the deep sea or offshore, and are facilities that receive, process, refine, liquefy, store, and supply the gas produced from gas wells and supply them to demand destinations, which can mean offshore plants such as FLNG, FSRU, and Fixed Platform. . Of course, the marine structure of the present invention can be used as a concept encompassing general merchant ships, if the gas treatment configuration can be mounted.

The offshore structure includes a hull side, the hull side, and a top side provided on the hull. A storage space may be mainly provided at the hull side of the offshore structure. For example, a liquefied gas storage tank GT may be provided. Liquefied gas storage tank (GT) is a configuration in which the production gas is purified, liquefied and stored, and may be provided as a membrane type to stably store the gas in a cryogenic liquid state, but is not limited thereto.

The liquefied gas storage tank GT may be provided in plural in the longitudinal direction of the hull, and two or more may be provided in the lateral direction of the hull. The number or arrangement of liquefied gas storage tanks GT may vary depending on the size of the product gas that the offshore structure has to process.

The top side includes the structure which processes a gas. The top side may include a gas treatment system to be described later, and the detailed configuration of the gas treatment system will be described in detail below.

The upper side of the hullside may be provided with a cabin, a ventilating engine casing, and a flare tower, in addition to the topside, but most of the upper side of the hullside may be utilized for installation of the topside.

Hereinafter, the gas treatment system of the present invention will be described in detail with reference to FIGS. 1 to 5.

1 to 4 are partial conceptual views of a gas treatment system according to an embodiment of the present invention, and FIG. 5 is a graph illustrating a vent of the gas treatment system according to an embodiment of the present invention.

1 to 5, a gas treatment system 1 according to an embodiment of the present invention is provided in a marine structure and is a system for receiving and treating gas from a gas well, including a cooling unit 10 and a distillation unit 20. ), The carbon dioxide processing unit 30, the after-treatment unit 40, the liquefaction unit 50, the vent unit 60.

The cooling part 10 cools the gas produced by a gas well. The gas produced in the gas well contains methane, which is the main component of natural gas, but also contains carbon dioxide, which must be separated.

In particular, when the gas well is located in tropical regions such as Southeast Asia, carbon dioxide is generated in a large amount because the strata are made of carbonates. At this time, more than 30% (greater than 70%) of the gas produced may be made of carbon dioxide.

In this way, carbon dioxide included in the production gas may be separated by distillation using a boiling point difference from natural gas. However, since the boiling point of carbon dioxide is about -60 degrees Celsius at atmospheric pressure, the cooling unit 10 may cool the production gas so that the carbon dioxide becomes a liquid phase.

To this end, the cooling unit 10 includes a precooler 11, a heat exchanger 12, a gas-liquid separator 13, a pressure reducing valve 14, an expander 15, and an auxiliary heat exchanger 16.

The precooler 11 may be provided on the production gas delivery line L10 connected from the gas well to precool the gas using various refrigerants R134a, nitrogen, and the like. The cooling temperature may be lower than the boiling point of carbon dioxide described above, but since the heat exchanger 12 may be provided downstream of the precooler 11, the temperature of the precooled gas may be higher than the boiling point of carbon dioxide.

The precooler 11 may be provided with a refrigerant circulation part 111 to use a refrigerant. The refrigerant circulation unit 111 may control various types of refrigerants in the order of compression, condensation, expansion, and evaporation so that the gas is cooled when the refrigerant evaporates.

The refrigerant circulation unit 111 includes a refrigerant compressor 111a, a refrigerant expander 111b, and a refrigerant cooler 111c, and the above components may be provided in series along the refrigerant circulation line L111.

The refrigerant condenses in the refrigerant cooler 111c and conversely evaporates in the precooler 11. Therefore, in the coolant cooler 111c, heat included in the coolant may be discharged as waste heat. Since the refrigerant cooler 111c may use outside air or cooling water for cooling the refrigerant, the waste heat is discharged to the outside through the outside air. Outside air flowing into the refrigerant cooler 111c may be sucked from the outside, and the coolant may be transferred from a separate cooling system or shared from a cooling system for cooling other equipment.

The waste heat discharged at this time may be used to prevent freezing of carbon dioxide in the gas treatment process, which will be described later.

R134a, which is a refrigerant that can be used by the precooler 11, causes a problem of environmental pollution due to Freon series, and a cost may be caused due to a price of about 4,000 won per kg.

In order to solve this problem, the present invention utilizes carbon dioxide as a refrigerant of the precooler (11). In this case, the carbon dioxide may be separated from the gas produced in the gas well, and for example, carbon dioxide separated in the distillation unit 20 may be utilized as a refrigerant. This will be described in detail in the section describing the distillation unit 20.

The heat exchanger 12 exchanges and cools gases with each other. For example, the heat exchanger 12 may cool the gas introduced into the distillation unit 20 by heat-exchanging the gas precooled in the precooler 11 with the gas returned from the distillation unit 20.

In this case, the heat exchanger 12 is provided downstream of the precooler 11, but the heat exchanger 12 may be provided upstream of the precooler 11.

Heat exchanger 12 may be provided with four or more streams. For example, the heat exchanger 12 is a gas stream parallel to the production gas delivery line L10 which is delivered to the distillation unit 20 through the precooler 11, and the heat exchanger 12 of the heat exchanger 12 in the production gas delivery line L10. In the gas stream parallel to the production gas return line (L11) branching from the downstream, the gas stream parallel to the gas phase delivery line (L21) through which the gaseous gas discharged from the distillation unit 20 is delivered, and in the distillation unit 20 It may comprise a gas stream parallel to the gas phase circulation line (L22) circulating to the heat exchanger (12).

At this time, the production gas return line (L11) may be connected to the distillation unit 20 by joining the gas supply line (L13), which will be described later, via the heat exchanger (12), and the gas delivery line (L21) and the gas phase circulation line ( L22 is a flow of the gas cooled by the reduced pressure, it is possible to cool the gas on the production gas delivery line (L10).

The stream of the heat exchanger 12 is not limited to the above, for example, one or more gas phase circulation lines (L22) may be provided. That is, the heat exchanger 12 may also have five or more streams.

The gas-liquid separator 13 gas-separates the gas cooled by the precooler 11 and the heat exchanger 12 in order. In this case, the separated gas may be mostly carbon dioxide, and in contrast, the gas may be in a state where carbon dioxide is removed.

Both liquid gas and gaseous gas separated from the gas-liquid separator 13 are connected to the distillation unit 20, and the liquid gas is delivered through the liquid supply line L12 and the gaseous gas is a gaseous supply line. May be delivered via L13.

At this time, the pressure reducing valve 14 is provided in the liquid supply line L12, and the expander 15 is provided in the gas phase supply line L13. Of course, since the pressure reducing valve 14 and the expander 15 placed between the gas-liquid separator 13 and the distillation unit 20 have the same function in terms of lowering the pressure, they may be replaced / mixed with each other.

The auxiliary heat exchanger 16 may heat-exchange the gas in the gas state discharged from the distillation unit 20 through the gas phase transmission line L21 and the gas passed through the heat exchanger 12 in the production gas return line L11. have.

Gas heat exchanged in the auxiliary heat exchanger 16 via the heat exchanger 12 along the production gas return line L11 is cooled under reduced pressure through a pressure reducing valve 161 provided on the production gas return line L11, It can be joined to the supply line (L13). In this case, the production gas return line L11 may be connected to the downstream of the expander 15 in the gas phase supply line L13, but is not limited thereto.

The distillation unit 20 performs cryogenic distillation to separate carbon dioxide from the cooled gas. In general, distillation is performed at room temperature / high temperature, such as fractional distillation of LPG, gasoline, kerosene, diesel, heavy oil, and lubricating oil from crude oil, but the distillation in the present invention is required to separate carbon dioxide from natural gas. Given that the boiling point is cryogenic, it is distilled after cooling rather than heating.

Therefore, the distillation performed by the distillation unit 20 of the present invention may be referred to as cryogenic distillation, wherein cryogenic temperature means a temperature lower than the boiling point of carbon dioxide. Of course, the exact value of the cryogenic temperature is not limited, and especially considering that the boiling point of carbon dioxide depends on the pressure, the temperature of the gas delivered by the distillation unit 20 is also not fixed.

For example, the pressure of the gas flowing into the distillation unit 20 is about 30 bar, and may have a temperature cooled to about -40 degrees by the cooling unit 10.

The distillation unit 20 may include a distillation column 21, a turbine 22, and a cooler 23. The distillation column 21 may cryogenically distill the gas introduced through the liquid supply line L12 and the gas phase supply line L13 to separate carbon dioxide from the gas.

In this case, the gas that is separated by the distillation column 21 and then delivered to the liquefaction unit 50 may have a ratio of carbon dioxide within 20% and methane of about 80%. Carbon dioxide still contained in the gas is further separated by the aftertreatment unit 40.

A gas circulation line L20 may be provided in the distillation column 21 so that a part of the gas in the distillation column 21 may be delivered to the heat exchanger 12 of the cooling unit 10 and then returned. In addition, the gaseous delivery line (L21) is provided in the distillation column 21, the gas in the gas state can be supplied to the after-treatment unit 40 or a separate demand through the auxiliary heat exchanger 16 and the heat exchanger (12). .

In addition, the gas phase circulation line (L22) is provided in the distillation column (21), and the gas phase circulation line (L22) increases the separation efficiency of carbon dioxide by returning to the distillation column (21) after gaseous gas is cooled / liquefied.

At this time, the gas phase circulation line L22 is provided with a turbine 22 and a cooler 23 sequentially along the flow of gas, and a heat exchanger 33 for exchanging heat with carbon dioxide of low temperature separated from the distillation column 21. Can be.

Both the turbine 22 and the cooler 23 are configured to cool the gas in a gaseous state, the turbine 22 may be cooled by pressure drop, and the cooler 23 may implement cooling using a refrigerant. Of course, if carbon dioxide can be sufficiently liquefied using the heat exchanger 33, at least one of the turbine 22 and the cooler 23 can be omitted.

The distillation column 21 may be provided with a gas supply line L23, and the gas supply line L23 is connected to the aftertreatment unit 40 from the distillation column 21. At this time, the gas flowing into the gas supply line (L23) is composed of 80% of methane, 20% of carbon dioxide, etc., as described above, which requires additional separation of carbon dioxide.

The carbon dioxide processing unit 30 processes the carbon dioxide separated from the distillation unit 20. In particular, the carbon dioxide processing unit 30 may re-inject the separated carbon dioxide into the underground injection well.

In the case of carbon dioxide, which is involved in the production of natural gas, if it is large, it cannot be discharged to the atmosphere due to environmental regulations.

As described above, in the case of Southeast Asia and the like, since the ratio of carbon dioxide is high in the gas produced by the formation of carbonate, a carbon dioxide reinjection process is required.

In this case, the reinjection well is different from the gas well in which natural gas is produced, and is a portion in which only carbon dioxide is injected without producing gas. The injection of carbon dioxide is made through the bottom hole BH in the ground layer, and the well head WH provided with the choke valve 38 may be provided above the bottom hole BH.

In order to keep the pressure of the strata stable, it is necessary to keep the reinjection pressure of carbon dioxide stable. In particular, the re-injection pressure of carbon dioxide should be kept constant even in disturbances such as ramp-up where gas flow rate increases or turndown situation where gas flow rate decreases.

In this case, if the choke valve 38 provided in the well head WH is used, the pressure of the carbon dioxide flowing into the bottom hole BH can be adjusted, but the choke valve 38 is located at the bottom of the sea, making it difficult to operate and control reaction speed. There is a problem that is slow.

In particular, the re-injected carbon dioxide may be 95% to 98% of carbon dioxide, not pure carbon dioxide, and even if only 3% to 5% changes, the phase envelope may be changed and the phase may be changed, thereby changing the density and changing the pressure.

Therefore, the present invention can stabilize the pressure of the re-injected carbon dioxide by using the control valve 35 in addition to the choke valve 38, the carbon dioxide processing unit 30, the reboiler 31, the pressure reducing valve 32 , Heat exchanger 33, carbon dioxide pump 34, control valve 35, cooler 36, choke valve 38, controller 39, and the like.

Reboiler 31 (reboiler), the liquid carbon dioxide separated from the distillation column 21 through the carbon dioxide discharge line (L30) is heated again to flow into the distillation column (21). Since the gas discharged from the distillation column 21 along the carbon dioxide discharge line L30 may include methane, the reboiler 31 may be used to bring the separated carbon dioxide closer to pure carbon dioxide.

The pressure reducing valve 32 depressurizes and cools the carbon dioxide separated from the distillation column 21. The pressure reducing valve 32 may implement cooling using the Joule-Thomson effect as a Joule-Thomson valve, similarly / similarly to the valves used in the same representation herein. The carbon dioxide cooled by the pressure reducing valve 32 may be used as a refrigerant in the heat exchanger 33.

The heat exchanger 33 cools the gas in a gaseous state flowing along the gas phase circulation line L22 by using the reduced pressure carbon dioxide. Since gaseous gas may include gaseous carbon dioxide, carbon dioxide flowing into the gas phase circulation line L22 is liquefied by heat exchange with carbon dioxide in a low temperature liquid state in the heat exchanger 33, and then returned to the distillation column 21. Can be separated from methane.

The carbon dioxide pump 34 pressurizes carbon dioxide for reinjection. The carbon dioxide may enter the carbon dioxide pump 34 in the liquid phase at a temperature lower than the boiling point and at a pressure lower than the critical point.

At this time, the carbon dioxide pump 34 pressurizes the carbon dioxide to a pressure higher than the critical point (for example, about 160 bar), thereby changing the carbon dioxide into a supercritical state as the heating by the pressurization is accompanied.

The carbon dioxide discharged from the carbon dioxide pump 34 may be, for example, a supercritical state having a temperature of 70 to 80 degrees Celsius at 161 bar, but may have various temperatures and pressures corresponding to the supercritical state.

In the supercritical state, since the pressure is very unstable and a sudden change in physical properties occurs, measurement of pressure or the like may not be accurately performed.

Therefore, the present invention can secure the accuracy of the pressure measurement by measuring the pressure of the carbon dioxide upstream of the carbon dioxide pump 34 with respect to the carbon dioxide phase change from the carbon dioxide pump 34 as a starting point.

To this end, a transmitter 37a is provided upstream of the carbon dioxide pump 34 in the carbon dioxide discharge line L30, and the transmitter 37a may measure the pressure of carbon dioxide in a liquid state.

The control valve 35 is provided downstream of the carbon dioxide pump 34, and the opening degree is adjusted based on the pressure measurement value for the carbon dioxide in the liquid state. The pressure of the carbon dioxide re-injected into the re-injection well by the carbon dioxide pump 34 is inevitably fluctuate. The control valve 35 adjusts the opening degree based on the change in the pressure value measured by the transmitter 37a. 35) It may be possible to stabilize the pressure of carbon dioxide downstream.

Therefore, the present invention through the control valve 35 can reduce the pressure fluctuation of the carbon dioxide in the re-injection well, even if the pressure of the re-injection carbon dioxide is shaken because the amount of carbon dioxide generated in the production gas is changed, the re-injection is stable Can be.

In particular, the control valve 35 utilizes the measured pressure value change for the liquid state carbon dioxide upstream of the carbon dioxide pump 34, not the supercritical state carbon dioxide downstream of the carbon dioxide pump 34, thereby providing more accurate and faster response to the pressure change. Can cope.

The cooler 36 cools carbon dioxide in a supercritical state. The cooler 36 may utilize a non-limiting refrigerant to cool 70-80 degrees C. of supercritical carbon dioxide to about 40 degrees C. and deliver the same to the reinjection well.

Since the cooler 36 is provided downstream of the control valve 35, the pressure variation of the carbon dioxide flowing into the cooler 36 may be attenuated. Therefore, according to the present invention, the fatigue pressure of the cooler 36 can be prevented by extending the injection pressure to the cooler 36 and the life of the equipment can be extended.

The choke valve 38 injects carbon dioxide in a supercritical state underground. The choke valve 38 is provided in the well head WH described above, and may be provided in the deep sea. Therefore, the choke valve 38 may not be sensitive and rapid pressure adjustment.

However, the present invention can stabilize the carbon dioxide pressure through the control valve 35 by using the change in the measured value of the transmitter 37a, it is possible to respond quickly to the change in carbon dioxide pressure.

In addition, the present invention can reduce the pressure fluctuation of the carbon dioxide by using the choke valve 38 in addition to the control valve 35 through the change in the measured value of the transmitter 37a. Specifically, in the present invention, when the measured value change of the transmitter 37a is within the reference range, only the control valve 35 may reduce the pressure fluctuation of carbon dioxide.

On the other hand, when the measured value change of the transmitter 37a is greater than or equal to the reference range, the control valve 35 alone is considered to be large enough to control the pressure, and by using at least the choke valve 38 of the control valve 35 and the choke valve 38. Pressure fluctuations of carbon dioxide can be reduced.

The choke valve 38 may operate in accordance with the measured value change of the transmitter 37a and / or is provided downstream of the carbon dioxide pump 34 to measure the secondary transmitter 37b for measuring the pressure of carbon dioxide in a supercritical state. It can work according to the value change.

That is, the control valve 35 reduces the pressure fluctuation of carbon dioxide when the measured value change of the transmitter 37a is within the reference range, and when the measured value change of the transmitter 37a is above the reference range, the control valve 35 and the choke valve ( At least the choke valve 38 of 38 may adjust the opening degree based on the measured value of the auxiliary transmitter 37b to reduce the pressure fluctuation of carbon dioxide.

Through this, the present invention, primarily based on the pressure change to the carbon dioxide in the liquid state to reduce the pressure fluctuations of the carbon dioxide to the control valve 35 in front of the cooler 36, and secondly carbon dioxide in the liquid / supercritical state By reducing the pressure fluctuations of the carbon dioxide with the choke valve 38 based on the pressure change on, the pressure change of the carbon dioxide can be pre-adjusted at the top side before reaching the refilling well to block the pressure disturbance in advance.

In addition, the present invention can maintain a constant pressure against the re-injection well, it is possible to reduce the pressure drop of the choke valve 38 to increase the life of the choke valve 38. The control of the control valve 35 and the choke valve 38 can be made by the controller 39 receiving measurement values such as the transmitter 37a.

In addition, the carbon dioxide processing unit 30 may include a carbon dioxide delivery line L31 branched from the carbon dioxide discharge line L30. At this time, the branch point of the carbon dioxide delivery line (L31) is not particularly limited, which will be described later.

The carbon dioxide delivery line L31 delivers the carbon dioxide separated from the distillation unit 20 to the cooling unit 10. Carbon dioxide may be delivered to the precooler 11 through a carbon dioxide delivery line (L31). The precooler 11 may use R134a as a refrigerant as described above, but since R134a (4,000 won per kg) is considerably more expensive than carbon dioxide (200 won per kg), the present invention uses carbon dioxide instead of R134a as a refrigerant. Can be.

In this case, carbon dioxide may be replenished in the refrigerant circulation part 111 through the carbon dioxide delivery line L31. In the case of using R134a, a facility for replenishing the refrigerant from the outside is required, but since the present embodiment can use a large amount of carbon dioxide separated from the produced gas as the refrigerant, there is no need to use a separate refrigerant replenishment facility.

The carbon dioxide separated in the distillation unit 20 may be replenished upstream of the refrigerant compressor 111a in the refrigerant circulation unit 111. This is because downstream of the refrigerant compressor 111a may be difficult to replenish due to the high refrigerant pressure.

However, when the refrigerant circulation unit 111 uses carbon dioxide as the refrigerant, and the carbon dioxide separated from the distillation unit 20 is replenished with the refrigerant circulation unit 111, the point where the carbon dioxide delivery line L31 branches is a carbon dioxide pump ( 34).

This is because the pressure of the carbon dioxide is high (for example, about 130 bar) downstream of the carbon dioxide pump 34, so that the refrigerant can be sufficiently delivered to the refrigerant circulation part 111. Therefore, carbon dioxide may be supplied to the refrigerant circulation unit 111 without further pressurization downstream of the carbon dioxide pump 34.

The carbon dioxide used in the refrigerant circulation unit 111 may be returned to the carbon dioxide processing unit 30 again, but may be decompressed by the refrigerant expander 111b in the process of being used as the refrigerant. Compressors (not shown) may be placed to increase the pressure again.

Unlike the above case, the carbon dioxide separated from the distillation unit 20 and supplied to the re-injection well may be used as a refrigerant without additional treatment. That is, the precooler 11 may have a stream passing through the low temperature carbon dioxide separated from the distillation unit 20 and delivered to the carbon dioxide treatment unit 30.

In this case, the carbon dioxide may be separated from the distillation unit 20, decompressed by the pressure reducing valve 32, and then passed through the precooler 11, and a separate refrigerant circulation unit 111 may be omitted. At this time, the portion through which the precooler 11 passes on the carbon dioxide discharge line L30 may be downstream of the pressure reducing valve 32, but is not limited thereto.

As described above, the present invention utilizes the carbon dioxide delivered to the reinjection well by the carbon dioxide treatment unit 30 as a refrigerant of the precooler 11, thereby eliminating the need for using an expensive refrigerant and replenishing the refrigerant from the outside, thereby reducing operating costs. It can greatly reduce.

The aftertreatment unit 40 further separates carbon dioxide from the distilled gas. Although carbon dioxide is primarily separated from the distillation column 21, about 20% of carbon dioxide may still be mixed in the gas.

Therefore, the after-treatment unit 40 may separate the carbon dioxide from the gas by using a chemical action, etc., it may have a configuration shown in FIG.

First, referring to FIG. 2, the aftertreatment unit 40 includes an amine absorption column 41, an amine regeneration column 42, an amine heat exchanger 43, an amine pump 44, and the like. The gas discharged from the distillation column 21 and flowing to the liquefaction unit 50 along the gas supply line L23 may pass through the amine absorption column 41.

The amine absorption column 41 can separate carbon dioxide from a gas through a chemical action using an amine. In addition, the amine absorption column 41 may have an amine circulation part 411 to perform carbon dioxide separation while the amine is circulated.

The amine regeneration column 42 is treated to recycle the amine used for separation of carbon dioxide in the amine absorption column 41. Some of the liquid amine separated from the amine regeneration column 42 is heated and circulated through the reboiler 422 to allow carbon dioxide to vaporize, and another portion of the amine pump 44 along the amine circulation line L40. May be returned to the amine absorption column 41 and then returned again.

In this case, the amine transferred from the amine regeneration column 42 to the amine absorption column 41 and the amine returned from the amine absorption column 41 to the amine regeneration column 42 may be heat-exchanged with each other by the amine heat exchanger 43. have.

On the other hand, the gaseous amine separated from the amine regeneration column 42 may be carbon dioxide separated through the carbon dioxide separation unit 421. The carbon dioxide separation unit 421 heat exchanges (heats) the amine with fresh water or the like to vaporize the carbon dioxide. The liquid amine is returned to the amine regeneration column 42 using the knockout drum 421a, and the carbon dioxide in the gas phase is separated from the carbon dioxide. It can be delivered to the carbon dioxide processing unit 30 through (L41).

Through this series of processes, the after-treatment unit 40 may remove carbon dioxide remaining in the gas by using an amine as a secondary, so that the carbon dioxide may be sufficiently removed from the gas delivered to the liquefaction unit 50.

On the other hand, referring to FIG. 3 unlike the above, the aftertreatment unit 40 may include a pressure reducing valve 45 and an ice maker 46. In the case of the above configuration, while the carbon dioxide is separated by a chemical method using an amine, the after-treatment unit 40 in FIG. 3 may separate the carbon dioxide by a physical method using the freezing of carbon dioxide. Of course, the after-treatment unit 40 of the present invention may be provided in combination with the configuration of FIG.

The pressure reduction valve 45 reduces the distilled gas. Among the gases cooled by reduced pressure, carbon dioxide may be at least partially liquefied. However, since the pressure reducing valve 52 is also provided in the liquefaction unit 50, the degree of pressure reduction of the pressure reducing valve 45 of the after-treatment unit 40 may be higher than the internal pressure of the liquefied gas storage tank GT.

Excessive cooling of the gas by depressurization may result in freezing of carbon dioxide before the freezer 46 and clogging the line. Therefore, the pressure reducing valve 45 may be installed adjacent to the ice maker 46, or the rear end of the pressure reducing valve 45 may be directly connected to the inlet / inside of the ice maker 46.

The ice maker 46 freezes the carbon dioxide contained in the decompressed gas. The ice maker 46 may freeze carbon dioxide using a refrigerant such as liquefied nitrogen. After the frozen carbon dioxide is removed from the foreign matter through the filter 461, the frozen carbon dioxide is stored in the carbon dioxide storage tank 462 as carbon dioxide crystals.

The carbon dioxide stored in the carbon dioxide storage tank 462 may be used for reinjection into a reinjection well or may be supplied to a separate demand destination. However, since the carbon dioxide is stored as a crystal in the carbon dioxide storage tank 462, the natural sublimed carbon dioxide may be discharged from the carbon dioxide storage tank 462 to be delivered to the re-injection through the carbon dioxide processing unit 30.

In the case of using the aftertreatment unit 40 of FIG. 3, the aftertreatment unit 40 may omit the separation of carbon dioxide using an amine, and thus, it is not necessary to have an amine absorption column 41 or an amine regeneration column 42. In this case, the energy consumption of the whole process and the maintenance cost can be reduced.

In addition, as will be described later, the pressure reducing valve 45, the ice maker 46, and the like of the present embodiment may be used as the configuration of the vent part 60 for blowdown.

The liquefaction unit 50 liquefies the gas from which carbon dioxide was isolate | separated. The liquefaction unit 50 flows along the gas liquefaction line (L50), passes through the after-treatment unit 40, and receives the gas flowing through the gas liquefaction line (L50). It can liquefy the gas which occupies.

The liquefaction unit 50 includes a liquefier 51, a pressure reducing valve 52, and a flash drum 53. The liquefier 51 liquefies gas by using a refrigerant, and may include a refrigerant supply unit 511 similarly or similarly to that of the precooler 11.

The refrigerant supply unit 511 may include a refrigerant compressor 511a, a refrigerant expander 511b, a refrigerant tank 511c, and the like, and a refrigerant cooler (not shown) may be added.

The gas flowing into the liquefaction unit 50 may be about 30 bar (when the after-treatment unit 40 uses an amine), in which case the boiling point of the gas may be higher than the boiling point at atmospheric pressure, the liquefaction unit 50 is a gas At least a portion of the gas may be liquefied even if it is cooled to a temperature higher than the boiling point at atmospheric pressure.

The pressure reducing valve 52 may further reduce the pressure of the gas cooled by the liquefaction unit 50 and further cool through the Joule-Thomson effect. In this case, the pressure reducing valve 52 may drop the pressure of the gas to a level corresponding to the internal pressure of the liquefied gas storage tank GT (for example, atmospheric pressure), so that the gas is at least mostly liquefied.

The flash drum 53 may discharge some components (nitrogen or the like) that are not liquefied to the outside along the flash gas discharge line L51 even though the pressure is reduced by the pressure reducing valve 52. At this time, the flash gas discharge line (L51) may be connected to the atmosphere or to a separate demand destination.

For example, since the flash gas contains nitrogen or the like, the flash gas may be used as a refrigerant of the precooler 11. That is, a line may be connected to the refrigerant circulation part 111 connected to the precooler 11 to replenish the flash gas.

The liquid gas separated from the flash drum 53 is delivered to and stored in the liquefied gas storage tank GT, and the stored gas may be treated as a final product. The gas can then be transported by gas carrier.

The vent unit 60 vents a gas in a gaseous state discharged from the distillation unit 20. The vent part 60 may implement a blowdown for discharging the gas to the outside in a shut-down situation in which the process is stopped.

However, since the pressure of the gas introduced into the distillation unit 20 is higher than about 30 bar and the atmospheric pressure, when the blowdown, the vent unit 60 decompresses the discharged gas to be discharged to the outside (for example, the atmosphere) along the vent line L60. Can be.

The vent part 60 includes a blowdown valve 61, a heater 62, and a temperature sensor 63. The blowdown valve 61 lowers the pressure of the gas being blowdown. In this case, decompression occurs, and as the exhaust gas is cooled, there is a fear of freezing of carbon dioxide.

In order to solve this problem, the vent part 60 may provide a heater 62. The heater 62 is provided upstream and / or downstream of the blowdown valve 61 to heat the gas utilizing various heat sources, thereby freezing carbon dioxide when cooled due to the pressure drop of the gas due to the blowdown valve 61. Can be prevented.

In this case, the heater 62 may use waste heat of the refrigerant used for cooling the gas in the cooling unit 10. The cooler 11 of the cooling unit 10 is provided with a refrigerant circulation unit 111, the refrigerant circulation unit 111 is provided with a refrigerant cooler (111c) for cooling the refrigerant, the refrigerant in the cooler (111c) As it cools, it can transfer waste heat to outside air or cooling water.

In this case, the waste heat transfer line L112 through which the outside air or the coolant is transferred is connected to the heater 62, and the heater 62 heat-exchanges the outside air or the coolant with the waste heat, and heats the gas to freeze carbon dioxide. Can be suppressed. At this time, the outside air or the cooling water cooled while heating the gas may be discarded to the outside or circulated to the refrigerant cooler 111c to be reused, but the flow is not limited thereto.

Alternatively, the heater 62 may be provided in the form of a line surrounding the flow of the gas vented to heat the gas, and may form a double pipe structure by surrounding the vent line L60.

Of course, the waste heat of the refrigerant can be used in various parts in addition to the heater 62 to prevent freezing of carbon dioxide.

In addition, the present invention can suppress the freezing of carbon dioxide by controlling the opening degree of the blowdown valve 61. To this end, the vent line (L60) is provided with a temperature sensor 63 for measuring the temperature of the gas upstream or downstream of the blowdown valve 61, the blowdown valve 61 is the temperature of the discharged gas is a preset value If it is below, the opening degree can be raised and the freezing of the carbon dioxide contained in gas can be prevented.

Since the gas is cooled as much as the blowdown valve 61 depressurizes the gas, when the blowdown valve 61 reduces the degree of depressurizing the gas, the temperature drop of the gas can be suppressed.

However, if the blowdown valve 61 increases the opening degree and lowers the decompression degree during the initial blowdown, the flow rate and the flow rate of the discharged gas may become strong.

Therefore, as shown in Figure 5, during the initial discharge blowdown valve 61 to reduce the discharged gas to the normal range to prevent the freezing of carbon dioxide contained in the gas using the heater 62, the temperature sensor 63 If the measured value of is less than or equal to a preset value (for example, -60 degrees Celsius), the opening degree of the blowdown valve 61 is increased to reduce cooling due to reduced pressure, thereby preventing carbon dioxide freezing.

If the measured value of the temperature sensor 63 is equal to or less than the preset value, the carbon dioxide freezing in the vent line L60 can be effectively suppressed by increasing the opening degree of the blowdown valve 61 and using the heater 62.

However, the timing of increasing the opening degree of the blowdown valve 61 may be determined by the measurement temperature of the gas, but may also be determined by the pressure or flow rate of the gas, and thus the temperature sensor 63 may be replaced or replaced with other sensors. .

In this case, the blowdown valve 61 prevents freezing by reducing the Joule-Thomson effect by reducing the Joule-Thomson effect when the gas temperature / pressure / flow rate or the like is measured by the sensor below the preset value. Can be implemented. Control of the blowdown valve 61 and the heater 62 according to the measured value of this sensor can be made by the controller 64.

Thus, the present invention, while preventing the freezing of carbon dioxide in the process of producing gas, it is possible to achieve a stable operation and to reduce the energy, cost, and the like.

The present invention is not limited to the above-described embodiments, and of course, a combination of the above embodiments or a combination of at least one of the above embodiments and known technologies may be included as another embodiment.

The present invention has been described above with reference to the embodiments of the present invention. However, the present invention is only an example, and is not intended to limit the present invention. Those skilled in the art will not depart from the essential technical details of the present embodiment. It will be appreciated that various combinations or modifications and applications which are not exemplified in the embodiments are possible in the scope. Therefore, technical matters related to modifications and applications easily derivable from the embodiments of the present invention should be interpreted as being included in the present invention.

1: gas treatment system GT: liquefied gas storage tank
WH: Well Head BH: Bottom Hole
10: cooling unit L10: production gas delivery line
L11: Production Gas Return Line L12: Liquid Supply Line
L13: Weather Supply Line 11: Precooler
111: refrigerant circulation section 111a: refrigerant compressor
111b: refrigerant expander 111c: refrigerant cooler
L111: Refrigerant circulation line L112: Waste heat transfer line
12: heat exchanger 13: gas-liquid separator
14: pressure reducing valve 15: expander
16: auxiliary heat exchanger 161: pressure reducing valve
20: distillation unit L20: gas circulation line
L21: weather delivery line L22: weather circulation line
L23: gas supply line 21: distillation column
22: turbine 23: cooler
30: carbon dioxide treatment unit L30: carbon dioxide discharge line
L31: CO2 Delivery Line 31: Reboiler
32: pressure reducing valve 33: heat exchanger
34: carbon dioxide pump 35: control valve
36: cooler 37a: transmitter
37b: Auxiliary transmitter 38: Choke valve
39: controller 40: post-processing unit
L40: amine circulation line L41: carbon dioxide separation line
41: amine absorption column 411: amine circulation
42: amine regeneration column 421: carbon dioxide separation unit
421a: knockout drum 422: scourer
43: amine heat exchanger 44: amine pump
45: pressure reducing valve 46: ice machine
461: filter 462: carbon dioxide storage tank
50: liquefaction unit L50: gas liquefaction line
L51: flash gas discharge line 51: liquefier
511: refrigerant supply unit 511a: refrigerant compressor
511b: refrigerant expander 511c: refrigerant tank
52: pressure reducing valve 53: flash drum
60: vent part L60: vent line
61: blowdown valve 62: heater
63: temperature sensor 64: controller

Claims (6)

The system is provided in the offshore structure to receive gas from the gas well and process it,
Cooling unit for cooling the gas produced in the gas well;
A distillation unit for cryogenic distillation to separate carbon dioxide from the cooled gas;
A liquefaction unit for liquefying gas from which carbon dioxide is separated; And
It includes a vent for venting the gas of the gas state discharged from the distillation unit,
The vent part,
And a blowdown valve to reduce the pressure of the discharged gas and increase the opening degree to prevent freezing of carbon dioxide contained in the gas when the temperature of the discharged gas is lower than or equal to a preset value. The method of claim 1, wherein the vent portion,
A heater provided downstream of the blowdown valve; And
And a temperature sensor for measuring the temperature of the gas downstream of said blowdown valve. The method of claim 2, wherein the vent portion,
Normally depressurize the gas discharged during initial discharge, but prevent freezing of carbon dioxide contained in the gas by using the heater, and if the measured value of the temperature sensor is less than or equal to a preset value, increase the opening degree of the blowdown valve to cool by reduced pressure Gas treatment system, characterized in that to prevent the freezing of carbon dioxide contained in the gas. The method of claim 2, wherein the vent portion,
When the measured value of the temperature sensor is less than a predetermined value increases the opening degree of the blowdown valve and at the same time using the heater to prevent freezing of carbon dioxide contained in the gas. The method of claim 1, wherein the blowdown valve,
Depressurizing the discharged gas, but if the flow rate of the discharged gas is less than the predetermined value to increase the opening degree to prevent the freezing of carbon dioxide contained in the gas. An offshore structure comprising the gas treatment system according to any one of claims 1 to 5.

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