KR101351440B1 - Membrane-absorption hybrid pretreatment apparatus for lng-fpso - Google Patents

Abstract

An acidic gas processing apparatus suitable for a restricted available space of a floating marine LNG plant is disclosed. The apparatus of the present invention comprises: a separation film array which includes a front film for producing first penetration gas stream and first residue gas stream from natural gas flow that has flowed in, and two rear films for introducing the first penetration gas stream and the first residue gas stream of the front film; an absorption tower which includes an amine-based solution for absorbing acidic gas by introducing gas stream flowed through the separation film array; and a regeneration tower for regenerating the amine-based solution from an amine-based absorbent. The present invention: is able to reduce energy consumption by more than three times, as compared to an amine absorbing process for generally treating acidic gas, by being used as a pretreatment process for acidic gas among marine natural gas for LNG-FPSO; is able to be operated according to the changes in natural gas composition of various marine gas; minimizes the performance degradation of a pretreatment process according to the flowage of a hull; and is suitable for being applied to a restricted space of the LNG-FPSO.

Description

Membrane-Absorption Hybrid Pretreatment Apparatus for LNG-FPSO for Floating Offshore LPN Liquefaction Plants

The present invention relates to a pretreatment apparatus applied to a floating offshore LNG plant, and more particularly to an acid gas removal unit (AGRU) suitable for a limited available space of a floating offshore LNG plant.

Liquefied Natural Gas-Floating Production, Storage and Offloading (LNG-FPSO) moves to gas fields in remote oceans, floating in the ocean, producing LNG, producing, storing, An offshore mobile offshore combined-use plant. The plant consists of floating offshore structures equipped with facilities for pretreatment, liquefaction, and storage of natural gas introduced from subsea gas fields. The plant is reduced in production cost compared to conventional natural gas production methods. This is the way to go.

Natural gas from the offshore gas field is composed mainly of methane and other hydrocarbons such as ethane, propane and butane, and is an impurity acidic gas such as carbon dioxide (CO _{2 )} ) and hydrogen sulfide (H ₂ S). It contains components, moisture (H ₂ O), mercury (Hg), and the like.

Moisture in natural gas, together with natural gas, can cause hydration or ice to shut down the plant when it is cold, and mercury may cause embrittlement of the aluminum plate fin heat exchanger. cause. In addition, the CO ₂ and heavy gas components may cause a CO ₂ freezing problem in the cryogenic facility, which may result in clogging. Therefore, the pretreatment process is introduced before these impurities in natural gas are sent to the liquefaction process, and these impurities must be removed below a certain level.

Meanwhile, the marine pretreatment process takes up to 50% of the available space of the LNG-FPSO deck depending on the impurity content of the raw material gas, which greatly affects the economic efficiency of the FPSO, which is highly dependent on the required space. In addition, since the marine pretreatment process must be able to maintain operational stability and separation performance in the harsh marine environment and ship flow, robust structure and deck design is essential.

In addition, it is necessary to optimize the design for the deterioration of the performance of the pretreatment process according to the natural gas composition change and hull motion of the offshore gas field mined.

As described above, the LNG pretreatment process includes an acid gas removal apparatus for removing carbon dioxide, hydrogen sulfide, and the like, which are acid gas components contained in natural gas.

The amine absorption process (Amine Absorption Process) is mainly used for this acid gas removal technology. The amine-based absorbents used in the amine absorption process include monoethanol amine (MEA) and diethanol amine (DEA), and are currently absorbers (Piperazine) added to the MDEA (Methyldiethanol amine) as an additive. Licensor process) is mainly used, and when the carbon dioxide content is high, piperazine (Piperazine) is used as an additive in the K ₂ CO ₃ aqueous solution to improve the Benfield (Benfield Process).

As such, the process of using a chemical absorbent such as an amine absorber is relatively less sensitive to the partial pressure of carbon dioxide and hydrogen sulfide, which has the advantage of lowering these two components to the ppm level, but it requires a lot of renewable energy in the regeneration column. Has disadvantages. In addition, when the amine absorption process is applied to a floating structure such as LNG-FPSO, there is a problem in that the area and height of the absorber should be sufficiently large in preparation for the flow of the structure.

US Patent No. 668792

In order to solve the above-mentioned problems of the prior art, an object of the present invention is to provide an LNG-FPSO acid gas pretreatment apparatus suitable for various offshore gas fields.

It is also an object of the present invention to provide an acid gas pretreatment apparatus suitable for application to a limited availability space and structure flow situation of LNG-FPSO.

In addition, an object of the present invention is to provide an acid gas pretreatment apparatus for LNG-FPSO that can be varied depending on the content of impurities contained in the natural gas of the offshore gas field.

In order to achieve the above technical problem, the present invention provides a shear membrane for generating a first permeate gas stream and a first residual gas stream from an introduced natural gas stream, and the first gas stream and the first residual gas stream of the shear membrane, respectively. Membrane Arrays including two incoming membranes; An absorption tower including an amine-based solution for absorbing acid gas by introducing a gas stream introduced through the membrane array; And it provides an acid gas pre-treatment apparatus for LNG-FPSO comprising a regeneration tower for regenerating the amine-based solution from the amine-based absorbent.

In the present invention, one of the two rear membranes may enter the first permeate gas stream to generate a third residual gas stream, and the third residual gas stream may be fed back to the introduced natural gas stream. have.

In addition, in the present invention, the other one of the two rear membranes may enter the first residual gas stream to generate a second permeate gas stream, and the second permeate gas stream may be fed back to the introduced natural gas stream.

At this time, it may further include a multi-stage compressor for compressing the gas stream is generated and fed back from at least one of the two rear membranes.

The present invention may further include means for selectively introducing the natural gas stream into the separator array or the absorption tower.

According to the present invention, it is possible to effectively remove acid gases, which are impurities contained in natural gas, from various marine gas fields while complementing the advantages and disadvantages of the membrane separation method and the absorption method.

In addition, according to the present invention, by applying the acid gas pretreatment process in the marine natural gas for LNG-FPSO can reduce energy consumption up to three times or more compared to the amine absorption process, which is a general acid gas treatment process.

In addition, according to the present invention, it is possible to significantly reduce the amount of the absorbent used in the amine absorption process and column size.

In addition, the present invention can be operated in accordance with the natural gas composition changes of various offshore gas fields, while minimizing the performance degradation of the pretreatment process according to the hull flow and is suitable for applying to the limited space of the LNG-FPSO.

1 is a view schematically showing a membrane array involved in the shear separator process of the hybrid device of the present invention.
2 is a view schematically showing an absorption facility involved in the rear end amine absorption process of the hybrid device of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to the preferred embodiments of the present invention with reference to the drawings.

Membrane separation method is a separation process using the difference in permeation rate of gas mixture membrane. It is energy-saving type because it does not involve phase change. It is simpler than the existing process, so the space required for system installation is simple and operation and control is easy It has the advantages, but there is a limit to the large-capacity gas treatment and it is difficult to use at high temperatures. On the other hand, the absorption method is easy to process a large-capacity gas and can be purified with high purity, but there are disadvantages of high energy consumption and high device cost in the regeneration process.

The present invention provides a membrane separation method (shear process) and an amine absorption method (stage process) to remove acid gases (mainly carbon dioxide), which are impurities contained in natural gas, from various marine gas fields while complementing the advantages and disadvantages of membrane separation and absorption methods. Adopt a new hybrid process to be applied to the mixed LNG-FPSO.

In particular, the present invention can be easily applied to natural gas composition changes of various offshore gas fields, and minimizes the performance degradation of the pretreatment process according to the hull flow and at the same time efficiently minimizes the limited space at the topside of LNG-FPSO. Enables compactness of the device for use.

Existing absorption process consumes a lot of energy due to duty and work generated from reboiler or pump, but it is partially installed by installing membrane in front of absorption process. By removing the acid gas (mainly carbon dioxide), the acid gas load in the amine absorption process can be reduced. In addition, by reducing the amount of Amine Solvent for acid gas removal, the size of the absorption tower and regeneration tower (height, circumference) can be reduced to make it possible to make the most of the limited space on the LNG-FPSO aboard. Operation stability and separation performance can be maintained even in marine environment and ship flow.

1 is a schematic diagram illustrating a membrane array for performing a membrane process which is a shearing process of the present invention.

Referring to FIG. 1, inflow natural gas (FEED) is introduced into the mixer 110, the front membrane 120, and the rear membranes 130 and 140.

In the present invention, the shear membrane 120 and the rear membrane 130 and 140 may be made of, for example, a hollow fiber membrane (Hollow fiber membrane, OD 400 μm, ID 200 μm) made of polysulfon. The membrane can also be used in the form of a membrane module, such as, for example, MC1507P from Airrane.

In the present invention, the membrane separation process consisting of the front membrane (120) and the rear membrane (130, 140) to remove the ratio of carbon dioxide in the natural gas flowing into the subsequent amine absorption process up to 85% compared to the incoming natural gas, methane recovery rate You can raise it by more than 98%.

Hereinafter, the membrane process consisting of the illustrated three-stage (3-stage) will be described in detail.

For example, a fed gas of a predetermined temperature and pressure (eg, 45 ^° C., 60 bar) passes through the shear membrane 120. The shear membrane generates a first residual stream having a low acid gas concentration (residue 1) and a first permeate stream having a high acid gas concentration (Permeate 1) with respect to the introduced natural gas.

The first residual stream (residue 1) is recovered through a second after-layer 140, as a second residual stream (residue 2) consisting of a high concentration of methane gas, such as 98.8% or more methane. The second residual stream (residue 2) is passed through a flash tank 150 which separates gas and liquid during liquid production as needed into the subsequent amine absorption process.

Meanwhile, the first permeate stream (Permeate 1) of the shear membrane 120 forms a third permeate stream (Permeate 3) and a third residual stream (Residue 3) while passing through the second rear membrane 130. The third residual stream (Residue 3) is passed through the multi-stage compressor (170, 180, 190) and the heat exchanger (175, 185, 195) to increase the methane recovery rate to the temperature and pressure conditions of the inlet gas (FEED) Can be adjusted and fed back to the mixer 110.

Similarly, the second permeate 2 of the first after-layer 140 may be fed back, and the feedback path may be provided with a mixer 160 for mixing with the third permeate 2. .

On the other hand, although not shown separately, the permeate stream (permeate 3) of the second rear membrane 130 having a high acid gas concentration may be sent to a flare and burned and then released into the atmosphere.

Natural gas having a low acid gas concentration, which has passed through the above membrane process, is introduced into a subsequent amine absorption process.

Figure 2 is a schematic representation of an amine absorption plant for carrying out the subsequent amine absorption process in the present invention.

Referring to FIG. 2, the apparatus constituting the amine absorption process is largely composed of an absorber 210 and a regenerator 250.

The natural gas stream 1 from which some acid gas is removed is introduced into the absorption tower 210 through the membrane process of the previous stage. The introduced natural gas stream 1 is first discharged as sweet gas 15 through the absorption tower by lean amine 14 injected into the absorption tower top. At this time, CO ₂ concentration in the discharged natural gas is limited to 50 ppm or less, H ₂ S concentration is limited to 4 ppm or less.

The absorption tower may use an amine-based absorption as an absorbent. The amine-based absorbent is provided in an aqueous solution, the concentration of the absorbent is preferably 10 to 65 wt%. In addition, the absorbent may be used, such as MEA, DEA, MDEA or DIPA.

Rich amine (2) having high acid gas concentration by absorbing acid gas in the gas stream through the absorption tower is reduced to atmospheric pressure through the valve and then flows into the flash tank (3). The introduced amines are hydrocarbons removed and discharged through the flash process (4). Rich amine (5), which has absorbed acid gas through the flash tank, enters the subsequent regeneration tower (250) (6). Due to the influx of rich amine, a large amount of CO ₂ and H ₂ S are discharged to the upper part of the regeneration tower 250 (7). The lean amine is discharged to the lower part of the regeneration tower through the regeneration process (8), and the discharged lean amine is heat-exchanged with the rich amine (5) of the flash tank in a heat exchanger (230). The heat exchanged lean amine 9 is subjected to a make-up process by the inflow of amine (MEA) and water (WATER) while passing through the mixers 260 and 270 and the heat exchanger 265 (10, 11). Lean amine, which maintains a constant amine concentration through the make-up process, is sent to the absorption tower through a pump (272) and a heat exchanger (275) (12), and this circulation process is continuously performed. The acid gas removal process in natural gas is performed while repeating.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to preferred embodiments of the present invention.

(Example)

Simulation was performed on the pretreatment process consisting of the hybrid process of the present invention. Process simulation was applied to the hybrid process consisting of the three-stage membrane process described in Figures 1 and 2 and the amine absorption process consisting of the absorption tower and the regeneration tower, compared with the conventional amine absorption process. Process simulations were performed using Invensys PRO / II.

To this end, first, the process simulation for the conventional amine absorption process was as follows. The content of feed natural gas and feed stream conditions used in the process simulation are shown in Table 1.

As a conventional amine absorption process, as shown in Figure 2, it was composed of a process consisting of one absorption tower and one regeneration tower, MEA 30 wt% was used as the amine solvent. Natural gas under the feed gas stream conditions shown in Table 1 was introduced into the FEED of FIG. 1 (1), so that the solvent of the MEA of lean amine (11) reacted in the absorption tower and combined with carbon dioxide was rich amine (2). Will be moved to. Sweet gas (15) is discharged to the top of the absorption tower, where CO ₂ is limited to 50 ppm or less and H ₂ S to 4 ppm or less. Rich amine (2) enters the regeneration tower and is discharged as acid gas (7) at the top, and the bottom is circulated after heat exchange with rich amine streams (8, 9). After the up process (10, 11) was again diluted with lean amine (14) was applied to the circulation process to the absorption tower. Table 2 shows the main stream results derived from process simulation using Invensys' PRO / II.

On the other hand, the process simulation for the hybrid process of the present invention. The hybrid process of the present invention was combined with the membrane process of FIG. 1 at the front end of the amine absorption process described above.

In the process simulation, a three-stage membrane separation method was used, and the residual stream (residue 1) from which natural gas passed through the shear membrane and some acid gas was removed was passed through the lower rear membrane 140 to recover 98% or more of methane. A stream (residue-2) was generated and passed through the flash tank 220 to be introduced into the amine absorption process (post process) of FIG. 2. In addition, the permeate stream (permeate 1) passing through the shear membrane is passed through the upper rear membrane 130, and the residual stream (residue 3) passed through the recycle to increase the methane recovery (methane recovery). Permeate 2 and residual 3 were recycled to feed gas conditions (40 ^o C) and pressure (60 bar) using a multistage compressor and heat exchanger to increase the recovery of methane. At this time, the membrane permeate side (Membrane permeate side) pressure was set to 7.8 bar, the permeance coefficient of the membrane (Permeance coefficient) was as shown in Table 3. Components not shown are assumed to follow the permeation coefficient of methane. This is because the methane component is the most difficult to separate, so when the methane component is separated, all components not shown are also separated. The natural gas (1) after the membrane separation process was introduced into the amine absorption process, which is a subsequent process, so that CO ₂ in the sweet gas (15) was limited to 50 ppm or less through the absorption tower and the regeneration tower.

The main streams of process simulations to which the present invention is applied are shown in Tables 4 and 5 below. Table 4 shows the main stream values for the membrane process, which is a shearing process, and Table 5 shows the main stream values for the amine absorption process.

Table 6 is a table showing the process simulation results for the amine absorption process and the hybrid process according to the embodiment of the present invention.

Referring to Table 6, the carbon dioxide concentration of the sweet gas (sweet gas) is 48.85 ppm when applying the conventional amine absorption process, it can be seen that the circulation flow rate of the amine solution used at this time needs 122,349.49 kg / hr. In this case, the lower temperature of the regeneration tower was 111.7 ° C., the upper pressure was 1.1 bar, and the reboiler duty was 15.5926 Mkcal / hr.

On the other hand, when the amine absorption process including the three-stage membrane separation method, the carbon dioxide concentration of the sweet gas was maintained at 49.09 ppm, it can be seen that the circulation flow rate of the amine solution used at this time requires 18,233 kg / hr. At this time, the regeneration tower had a lower temperature of 111.7 ° C, an upper pressure of 1.1 bar, a reboiler duty of 2.3147 Mkcal / hr, a compressor actural work of 2,846 kw, and a compressor duty of compressor duty) is 2.4478 Mkcal.

Based on the results of Table 6, the results of the column size of the absorption tower and the regeneration tower required in the conventional amine absorption process and the hybrid process of the present invention are shown in Table 7 and Table 8, respectively. The column size of the absorption tower and regeneration tower was calculated by computer simulation considering gas velocity and contact area.

Tables 7 and 8 show that the column size is reduced by about 50% when the hybrid process of the present invention is applied compared to the conventional amine absorption process. The membrane separation method, which is a shearing process, removes about 85% of the CO ₂ from the raw material, thereby reducing the CO ₂ load on the amine absorption process, which is a post-stage process, to reduce the amine solvent circulate rate, thereby reducing the total column size by about half. The effect is to reduce.

Therefore, the membrane separation process applied to the front end of the present invention is a process that is not influenced at all by the marine environment and vessel flow, and the absorption tower and regeneration tower size (height, circumference, etc.) of the amine absorption process of the latter stage affected by the marine environment, etc. In addition, the process can be made compact to maximize the limited space of LNG-FPSO, while maintaining operational stability and separation performance in harsh marine environments and ship flows.

Table 9 below shows a comparison of energy consumption in the conventional amine absorption process (membrane not applied) and the hybrid process (membrane application) of the present invention. As can be seen in Table 9, it can be seen that the difference in energy consumption is apparent between the conventional amine process and the hybrid process of the present invention. The amount of energy consumed in the conventional amine absorption process is 15.5926 Mkcal / hr, while in the present invention, the amount of energy consumed is 4.7625 Mkcal / hr. That is, the present invention is reduced energy consumption up to three times or more compared with the conventional amine absorption process.

As described above, the hybrid process of the present invention has excellent effects in adaptability to marine environments including ship flow, applicability to narrow space constraints, and energy saving. In addition to this, the hybrid apparatus of the present invention may further have the advantage of applying a variable process depending on the components of natural gas as a raw material. For example, the apparatus of the present invention may further include a branch valve for inflow of natural gas, and when the carbon dioxide component is low in natural gas, the natural gas flow may be operated by an amine absorption process without inflow into the membrane process. On the other hand, otherwise, natural gas may be introduced into the membrane process so that a hybrid process including a shear membrane process is applied.

While the preferred embodiments of the present invention have been described above, the above-described embodiments illustrate the present invention and limit the present invention.

100 Membrane Arrays 110, 160, 260, 270 Mixers
120 Shear 130, 140 Shear
150 flash tanks 170, 180, 190 compressor
175, 185, 195 heat exchanger
200 amine absorption plant
210 Absorption Tower 220 Flash Tank
230, 252, 254, 265, 275 Heat Exchanger
250 tower

Claims (5)

Membrane array comprising a shear membrane for generating a first permeate gas stream and a first residual gas stream from the introduced natural gas stream, and two trailing membranes for respectively introducing the first gas stream and the first residual gas stream of the shear membrane. ;
An absorption tower including an amine-based solution for absorbing acid gas by introducing a gas stream introduced through the membrane array; And
Acid-gas pretreatment device for LNG-FPSO comprising a regeneration tower for regenerating the amine solution from the amine-based absorbent. The method of claim 1,
One of the two rear membranes is introduced into the first permeate gas stream to generate a third residual gas stream, the third residual gas stream is fed back to the introduced natural gas flow for LNG-FPSO Acid gas pretreatment device. The method of claim 1,
One of the two downstream membranes may enter the first residual gas stream to produce a second permeate gas stream, and the second permeate gas stream is fed back to the introduced natural gas stream. Acid gas pretreatment device. 3. The method according to claim 1 or 2,
And a multistage compressor for compressing the gas stream generated and fed back from at least one of the two rear membranes. The method of claim 1,
The acid gas pre-treatment apparatus for LNG-FPSO further comprises means for selectively introducing the natural gas flow into the membrane array or the absorption tower.

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