A natural gas liquefaction device and method for simultaneously removing hydrocarbons and nitrogen

Abstract

The present invention discloses a natural gas liquefaction device and method for simultaneously removing hydrocarbons and nitrogen. The scheme combines dehydrogenation and denitrification, adopts the stable flash steam of the deethanizer as the denitrogenation gas lift gas, and is liquefied while removing nitrogen, thus solving the problem of flash steam removal, increasing the amount of LNG products, and reducing the energy consumption of denitrogenation operation.

Description

Technical Field

[0001] The invention relates to the technical field of petrochemical engineering, and in particular to a natural gas liquefaction device and method for simultaneously removing hydrocarbons and nitrogen. Background Art

[0002] my country's major oil fields have reached the middle and late stages of development. In order to achieve stable production and increased production (enhanced oil recovery, referred to as EOR), nitrogen injection oil recovery technology is often used. Therefore, nitrogen also exists in large quantities in the associated gas of oil fields produced by using nitrogen injection oil recovery as a production increase measure. Another feature of crude oil associated gas is that it is rich in various high-carbon alkane components, especially components above pentane, which have a certain content. In the LNG production process, heavy hydrocarbon components need to be removed to prevent clogging of cold boxes, and nitrogen needs to be removed to prevent the "rollover" phenomenon in the LNG storage and transportation process, while meeting the LNG index requirements. The existing associated gas dehydrogenation usually adopts a low-temperature process. The dehydrogenated condensate contains a part of the light components (methane and ethane). The stabilized light components come out from the top of the deethanizer tower with a low pressure. They are either used as fuel or returned to the inlet of the raw gas compressor for re-pressurization and circulation, resulting in low operating efficiency and high energy consumption of the device.

[0003] The existing natural gas denitrification technology generally uses a denitrification tower for distillation denitrification. During the working process, a reboiler and a condenser are required to be used in conjunction with the denitrification tower, which is costly and consumes a lot of energy. Therefore, a simpler, more economical and energy-saving denitrification method is urgently needed. Summary of the invention

[0004] The purpose of the present invention is to provide a natural gas liquefaction device and method for simultaneous dehydrogenation and denitrification, which combines dehydrogenation and denitrification, uses the stable flash gas of the deethanizer as the denitrogenation gas, and is liquefied while removing nitrogen, thus solving the problem of flash gas removal, increasing the amount of LNG products, and reducing the energy consumption of denitrogenation operation.

[0005] The present invention is achieved through the following technical solutions:

[0006] A natural gas liquefaction device for simultaneous hydrocarbon and nitrogen removal, comprising a cold box, a heavy hydrocarbon removal tower, a low-temperature separator, a nitrogen removal gas-liquid separator, a deethanizer, a denitrogenation tower, a denitrogenation gas circulation compressor and a low-temperature condensate pump;

[0007] The cold box is connected to the heavy hydrocarbon removal tower and the low-temperature separator respectively;

[0008] The gas phase outlet of the low temperature separator is connected to the cold box, and the cold box is connected to the denitrification tower;

[0009] The heavy hydrocarbon removal tower is connected to the deethanizer, and the liquid phase of the low-temperature separator is pressurized by a low-temperature condensate pump and is connected to the heavy hydrocarbon removal tower and the deethanizer respectively;

[0010] The gas phase outlet of the deethanizer is connected to the denitrogenation tower; the gas phase outlet of the denitrogenation tower is connected to the cold box, the cold box is connected to the denitrogenation gas circulation compressor, and the cold box is connected to the denitrogenation gas-liquid separator.

[0011] Furthermore, the raw natural gas enters / exits the cold box 4 times for refrigeration to remove hydrocarbons and nitrogen from it;

[0012] First, the raw gas enters the cold box for precooling, and the outlet of the cold box is connected to the raw gas inlet of the heavy hydrocarbon removal tower. The raw gas from the heavy hydrocarbon removal tower enters the cold box for further precooling. The precooled raw gas outlet of the cold box is connected to the inlet of the low-temperature separator. The gas phase outlet of the low-temperature separator enters the cold box again for liquefaction. The liquefied natural gas outlet of the cold box is connected to the denitrification tower. Finally, the liquid phase outlet of the denitrification tower enters the cold box again for supercooling to obtain the product LNG.

[0013] Furthermore, the liquid phase outlet of the heavy hydrocarbon removal tower is connected to the deethanizer, and the liquid phase outlet of the low-temperature separator is respectively connected to the heavy hydrocarbon removal tower and the deethanizer after being pressurized by a low-temperature condensate pump, and is used as a low-temperature washing liquid to remove heavy hydrocarbons in the raw gas and the stable flash gas at the top of the deethanizer.

[0014] Furthermore, the gas phase outlet of the deethanizer is connected to the denitrogenation tower, the denitrogenated gas from the denitrogenation tower enters the cold box for reheating, the denitrogenated gas outlet of the cold box is connected to the denitrogenated gas circulation compressor, the denitrogenated gas is pressurized by the denitrogenated gas circulation compressor and then returns to the cold box for liquefaction, the liquefied denitrogenated gas outlet of the cold box is connected to the inlet of the denitrogenation gas-liquid separator for flash evaporation to remove nitrogen from the denitrogenated gas, the gas phase of the denitrogenation gas-liquid separator returns to the cold box for reheating, and the liquid phase outlet of the denitrogenation gas-liquid separator is connected to the denitrogenation tower.

[0015] The present invention also provides a natural gas liquefaction method for simultaneously removing hydrocarbons and nitrogen, comprising the following steps:

[0016] S1: The raw gas enters the heavy hydrocarbon removal tower after being precooled in a cold box. The gas phase at the top of the heavy hydrocarbon removal tower returns to the cold box for further precooling before entering the low-temperature separator. The gas phase in the low-temperature separator returns to the cold box for liquefaction and enters the middle of the denitrification tower. The LNG at the bottom of the denitrification tower is finally supercooled in a cold box to obtain the product LNG.

[0017] S2: The natural gas condensate at the bottom of the heavy hydrocarbon removal tower is sent to the middle of the deethanizer, and the low-temperature condensate at the bottom of the low-temperature separator is divided into two parts, which are respectively sent to the top of the heavy hydrocarbon removal tower and the deethanizer as low-temperature washing liquid, and the low-temperature washing liquid is used to remove heavy hydrocarbons in the feed gas and the stable flash gas at the top of the deethanizer;

[0018] S3: The gas phase at the top of the deethanizer tower enters the bottom of the denitrogenation tower as stripping gas; the gas phase at the top of the denitrogenation tower enters the cold box for reheating and is pressurized by the denitrogenation gas circulation compressor, the pressurized denitrogenation circulation gas returns to the cold box for supercooling and then throttles to enter the denitrogenation gas-liquid separator for flash evaporation, returns to the cold box for reheating and is discharged to a safe point after flash evaporation, and the liquid phase of the denitrogenation gas-liquid separator enters the top of the denitrogenation tower as a low-temperature washing liquid.

[0019] Furthermore, the flash gas in the denitrification gas-liquid separator is used to remove nitrogen.

[0020] Furthermore, the nitrogen content removed is >98%.

[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0022] 1. The present invention provides a natural gas liquefaction device and method for simultaneous dehydrogenation and denitrification, which adopts a construction process and device for natural gas liquefaction that is equipped with a dehydrogenation tower, a deethane tower and a denitrification tower to simultaneously meet the requirements of dehydrogenation and denitrification.

[0023] 2. The present invention provides a natural gas liquefaction device and method for simultaneous dehydrogenation and denitrification, which adopts a heavy hydrocarbon removal tower T1 and a deethanizer T2, and uses low natural gas condensate for washing, and simultaneously removes heavy hydrocarbons in the raw gas and the stable flash gas at the top of the deethanizer tower. The stable flash gas at the top of the deethanizer tower is used as the stripping gas for the denitrification tower, and the flash gas is liquefied at the same time, thereby reducing the energy consumption of the device operation.

[0024] 3. The present invention provides a natural gas liquefaction device and method for simultaneous dehydrogenation and denitrification, which adopts a distillation and washing section set at the top of the denitrification tower T3 to improve the methane recovery rate and significantly reduce the methane content in the discharged nitrogen. The discharged nitrogen concentration is >98%. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0026] Figure 1 It is a flow chart of the present invention.

[0027] Reference numerals and corresponding component names:

[0028] E1-cold box; T1-heavy hydrocarbon removal tower; V1-low-temperature separator; V2-denitrogenation gas-liquid separator; T2-deethanizer; T3-denitrogenation tower; C2-denitrogenation gas circulation compressor; C1-refrigerant compressor unit; P1-low-temperature condensate pump. DETAILED DESCRIPTION

[0029] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0030] In the following description, a large number of specific details are set forth in order to provide a thorough understanding of the present invention. However, it is obvious to those of ordinary skill in the art that these specific details do not have to be adopted to implement the present invention. Throughout the specification, reference to "one embodiment", "embodiment", "one example" or "example" means that the specific features, structures or characteristics described in conjunction with the embodiment or example are included in at least one embodiment of the present invention. Therefore, the phrases "one embodiment", "embodiment", "one example" or "example" that appear in various places throughout the specification do not necessarily refer to the same embodiment or example. In addition, specific features, structures or characteristics can be combined in one or more embodiments or examples in any appropriate combination and / or sub-combination. In addition, it should be understood by those of ordinary skill in the art that the illustrations provided herein are all for illustrative purposes, and the illustrations are not necessarily drawn to scale. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0031] [Example 1]

[0032] like Figure 1 As shown, a natural gas liquefaction device for simultaneous hydrocarbon and nitrogen removal comprises a cold box E1, a heavy hydrocarbon removal tower T1, a low-temperature separator V1, a denitrification gas-liquid separator V2, a deethanizer T2, a denitrification tower T3, a denitrification gas circulation compressor C2 and a low-temperature condensate pump P1; the cold box E1 is connected to the heavy hydrocarbon removal tower T1 and the low-temperature separator V1 respectively; the gas phase outlet of the low-temperature separator V1 is connected to the cold box E1, and the cold box E1 is connected to the denitrification tower T3; the heavy hydrocarbon removal tower T1 is connected to the deethanizer T2, and the liquid phase of the low-temperature separator V1 is pressurized by the low-temperature condensate pump P1 and is connected to the heavy hydrocarbon removal tower T1 and the deethanizer T2 respectively; the gas phase outlet of the deethanizer T2 is connected to the denitrification tower T3; the gas phase outlet of the denitrification tower T3 is connected to the cold box E1, the cold box E1 is connected to the denitrification gas circulation compressor C2, and the cold box E1 is connected to the denitrification gas-liquid separator V2.

[0033] This scheme designs a heavy hydrocarbon removal tower and a deethanizer, which use low-temperature condensate for washing, and remove heavy hydrocarbons from the feed gas and the stable flash gas at the top of the deethanizer. At the same time, this scheme also sets up a denitrogenation tower, which uses stable flash gas as the denitrogenation tower gas lift gas, and is liquefied while removing nitrogen, increasing the amount of LNG products. A distillation and washing section is set at the top of the denitrogenation tower in this scheme, which improves the methane recovery rate and greatly reduces the methane content in the discharged nitrogen. The washing liquid comes from the denitrogenation flash tank, which is obtained after the nitrogen-rich gas at the top of the denitrogenation tower is reheated, pressurized, liquefied and throttled flash.

[0034] Furthermore, the raw natural gas enters / exits the cold box E1 4 times for refrigeration to remove hydrocarbons and nitrogen from it;

[0035] First, the raw gas enters the cold box E1 for precooling, and the outlet of the cold box E1 is connected to the raw gas inlet of the heavy hydrocarbon removal tower T1. The raw gas of the heavy hydrocarbon removal tower T1 enters the cold box E1 for further precooling. The precooled raw gas outlet of the cold box E1 is connected to the inlet of the low-temperature separator V1, and the gas phase outlet of the low-temperature separator V1 enters the cold box E1 again for liquefaction. The liquefied natural gas outlet of the cold box E1 is connected to the denitrification tower T3, and the liquid phase outlet of the denitrification tower T3 finally enters the cold box E1 for supercooling to obtain the product LNG.

[0036] Furthermore, the liquid phase outlet of the heavy hydrocarbon removal tower T1 is connected to the deethanizer T2, and the liquid phase outlet of the low-temperature separator V1 is respectively connected to the heavy hydrocarbon removal tower T1 and the deethanizer T2 after being pressurized by the low-temperature condensate pump P1, and is used as a low-temperature washing liquid to remove heavy hydrocarbons in the raw gas and the stable flash gas at the top of the deethanizer.

[0037] Furthermore, the gas phase outlet of the deethanizer T2 is connected to the denitrogenation tower T3, the denitrogenated gas from the denitrogenation tower T3 enters the cold box E1 for reheating, the denitrogenated gas outlet of the cold box E1 is connected to the denitrogenated gas circulation compressor C2, the denitrogenated gas is pressurized by the denitrogenated gas circulation compressor C2 and then returns to the cold box E1 for liquefaction, the liquefied denitrogenated gas outlet of the cold box E1 is connected to the inlet of the denitrogenation gas-liquid separator V2, which is used to flash remove the nitrogen in the denitrogenated gas, the gas phase of the denitrogenation gas-liquid separator V2 returns to the cold box E1 for reheating, and the liquid phase outlet of the denitrogenation gas-liquid separator V2 is connected to the denitrogenation tower T3.

[0038] The working principle of the present invention comprises the following steps:

[0039] S1: The raw gas is pre-cooled in cold box E1 and then enters the heavy hydrocarbon removal tower T1. The gas phase at the top of the heavy hydrocarbon removal tower T1 returns to the cold box E1 for further pre-cooling and then enters the low-temperature separator V1. The gas phase in the low-temperature separator V1 returns to the cold box E1 for liquefaction and then enters the middle of the denitrification tower T3. The LNG at the bottom of the denitrification tower T3 is finally supercooled in the cold box E1 to obtain the product LNG.

[0040] S2: The natural gas condensate at the bottom of the heavy hydrocarbon removal tower T1 is sent to the middle of the deethanizer T2. The low-temperature condensate at the bottom of the low-temperature separator V1 is divided into two parts and sent to the top of the heavy hydrocarbon removal tower T1 and the deethanizer T2 as low-temperature washing liquid. The low-temperature washing liquid is used to remove heavy hydrocarbons from the feed gas and the stable flash gas at the top of the deethanizer.

[0041] S3: The gas phase from the top of the deethanizer T2 enters the bottom of the denitrogenation tower T3 as the stripping gas; the gas phase from the top of the denitrogenation tower T3 enters the cold box E1 for reheating and is pressurized by the denitrogenation gas circulation compressor C2, the pressurized denitrogenation circulation gas returns to the cold box E1 for supercooling and then throttles to enter the denitrogenation gas-liquid separator V2 for flash evaporation, returns to the cold box E1 for reheating and is discharged to a safe point after flash evaporation, and the liquid phase of the denitrogenation gas-liquid separator V2 enters the top of the denitrogenation tower T3 as the low-temperature washing liquid.

[0042] Furthermore, the flash gas in the denitrification gas-liquid separator V2 is used to remove nitrogen.

[0043] Furthermore, the nitrogen content is removed to >98%.

[0044] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A natural gas liquefaction device for simultaneous dehydrogenation and denitrification, characterized in that: It includes a cold box (E1), a heavy hydrocarbon removal tower (T1), a low-temperature separator (V1), a denitrogenation gas-liquid separator (V2), a deethanizer (T2), a denitrogenation tower (T3), a denitrogenation gas circulation compressor (C2) and a low-temperature condensate pump (P1); The cold box (E1) is connected to the heavy hydrocarbon removal tower (T1) and the low-temperature separator (V1) respectively; The gas phase outlet of the low temperature separator (V1) is connected to the cold box (E1), and the cold box (E1) is connected to the denitrification tower (T3); The heavy hydrocarbon removal tower (T1) is connected to the deethanizer (T2), and the liquid phase of the low-temperature separator (V1) is pressurized by a low-temperature condensate pump (P1) and then connected to the heavy hydrocarbon removal tower (T1) and the deethanizer (T2) respectively; The gas phase outlet of the deethanizer (T2) is connected to the denitrogenation tower (T3); the gas phase outlet of the denitrogenation tower (T3) is connected to the cold box (E1), the cold box (E1) is connected to the denitrogenation gas circulation compressor (C2), and the cold box (E1) is connected to the denitrogenation gas-liquid separator (V2); The raw natural gas enters / exits the cold box (E1) 4 times for refrigeration and dehydrogenation; First, the raw gas enters the cold box (E1) for precooling, the outlet of the cold box (E1) is connected to the raw gas inlet of the heavy hydrocarbon removal tower (T1), the raw gas of the heavy hydrocarbon removal tower (T1) enters the cold box (E1) for further precooling, the precooled raw gas outlet of the cold box (E1) is connected to the inlet of the low-temperature separator (V1), the gas phase outlet of the low-temperature separator (V1) enters the cold box (E1) again for liquefaction, the liquefied natural gas outlet of the cold box (E1) is connected to the denitrification tower (T3), and the liquid phase outlet of the denitrification tower (T3) finally enters the cold box (E1) for supercooling to obtain the product LNG; The liquid phase outlet of the heavy hydrocarbon removal tower (T1) is connected to the deethanizer (T2), and the liquid phase outlet of the low-temperature separator (V1) is respectively connected to the heavy hydrocarbon removal tower (T1) and the deethanizer (T2) after being pressurized by a low-temperature condensate pump (P1), and is used as a low-temperature washing liquid to remove heavy hydrocarbons in the feed gas and the stable flash gas at the top of the deethanizer; The gas phase outlet of the deethanizer (T2) is connected to the denitrogenation tower (T3), the denitrogenated gas of the denitrogenation tower (T3) enters the cold box (E1) for reheating, the denitrogenated gas outlet of the cold box (E1) is connected to the denitrogenated gas circulation compressor (C2), the denitrogenated gas is pressurized by the denitrogenated gas circulation compressor (C2) and then returns to the cold box (E1) for liquefaction, the liquefied denitrogenated gas outlet of the cold box (E1) is connected to the inlet of the denitrogenation gas-liquid separator (V2) for flash evaporation to remove nitrogen from the denitrogenated gas, the gas phase of the denitrogenation gas-liquid separator (V2) returns to the cold box (E1) for reheating, and the liquid phase outlet of the denitrogenation gas-liquid separator (V2) is connected to the denitrogenation tower (T3).

2. A natural gas liquefaction method for simultaneous dehydrogenation and denitrification, characterized in that: The following steps are involved: S1: The raw gas is pre-cooled in a cold box (E1) and then enters a heavy hydrocarbon removal tower (T1). The gas phase at the top of the heavy hydrocarbon removal tower (T1) is returned to the cold box (E1) for further pre-cooling and then enters a low-temperature separator (V1). The gas phase in the low-temperature separator (V1) is then returned to the cold box (E1) for liquefaction and then enters the middle of a denitrification tower (T3). The LNG at the bottom of the denitrification tower (T3) is finally supercooled in a cold box (E1) to obtain product LNG. S2: The natural gas condensate at the bottom of the heavy hydrocarbon removal tower (T1) is sent to the middle of the deethanizer (T2), and the low-temperature condensate at the bottom of the low-temperature separator (V1) is divided into two parts, which are respectively sent to the top of the heavy hydrocarbon removal tower (T1) and the deethanizer (T2) as low-temperature washing liquid, and the low-temperature washing liquid is used to remove heavy hydrocarbons in the feed gas and the stable flash gas at the top of the deethanizer; S3: The gas phase at the top of the deethanizer (T2) enters the bottom of the denitrogenation tower (T3) as stripping gas; the gas phase at the top of the denitrogenation tower (T3) enters the cold box (E1) for reheating and is pressurized by the denitrogenation gas circulation compressor (C2), and the pressurized denitrogenation circulation gas returns to the cold box (E1) for supercooling and throttling and enters the denitrogenation gas-liquid separator (V2) for flash evaporation, and then returns to the cold box (E1) for reheating and is discharged to a safe point after flash evaporation, and the liquid phase of the denitrogenation gas-liquid separator (V2) enters the top of the denitrogenation tower (T3) as a low-temperature washing liquid.

3. A natural gas liquefaction method for simultaneous dehydrogenation and denitrification according to claim 2, characterized in that: The flash gas in the denitrogenation gas-liquid separator (V2) is used to remove nitrogen.

4. A natural gas liquefaction method for simultaneous dehydrogenation and denitrification according to claim 3, characterized in that: The nitrogen content removed is >98%.

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