Natural gas liquefaction denitrification device and method

Abstract

The invention relates to a natural gas liquefaction denitrification device and method, and the natural gas liquefaction denitrification device comprises a first heat exchanger; a gas phase outlet of the heavy hydrocarbon separator is connected with a second heat exchanger, the second heat exchanger is connected with a third heat exchanger, and the third heat exchanger is connected with the denitrification tower through a pipeline. The natural gas liquefaction denitrification method comprises the following steps: cooling raw material gas; carrying out gas-liquid separation treatment on the cooled feed gas; cooling the gas phase; and carrying out nitrogen removal treatment on the gas phase by using a nitrogen removal tower. The technical scheme provided by the invention has the beneficial effects that the nitrogen is separated by fully utilizing the cold energy produced by the mixed refrigerant, the nitrogen separation efficiency is high, meanwhile, the number of equipment is small, the energy consumption is reduced, the engineering investment is reduced, the economic benefits of enterprises are improved, and the aim of removing the nitrogen is fulfilled by only arranging one denitrification tower. According to the technical scheme, the nitrogen-containing feed gas is subjected to liquefaction denitrification to obtain a product with corresponding purity, so that the economic value of the product is improved.

Description

Technical Field

[0001] This invention relates to the purification and separation of gases, and in particular to a natural gas liquefaction denitrification apparatus and method. Background Technology

[0002] With economic development, the country has increasingly stringent requirements for environmental protection and an increasingly urgent need for green energy. As one of the green energy sources, liquefied natural gas (LNG) is easy to store and transport, so in recent years, the development of LNG plants in China has been booming.

[0003] National standards require that the nitrogen content in LNG not exceed 1% (mol), while the nitrogen content in natural gas usually exceeds 1% (mol), so natural gas needs to be denitrified.

[0004] Chinese invention patent CN201010561795.5 discloses a method for producing natural gas / liquefied natural gas from nitrogen-containing methane gas by denitrification, which includes steps such as precooling of the feed gas, high-pressure tower distillation, low-pressure tower stripping, and product gas reheating / mixed refrigerant circulation. Although the above-mentioned dual-tower technology reduces the tower height and equipment size, this method for producing liquefied natural gas from nitrogen-containing methane gas requires a large number of process equipment, has a complex process, a complicated control loop, and a large engineering investment. Summary of the Invention

[0005] The purpose of this invention is to provide a natural gas liquefaction denitrification device and method that requires fewer pieces of equipment, reduces energy consumption, and lowers engineering investment.

[0006] The natural gas liquefaction denitrification apparatus of the present invention includes: The first heat exchanger used to cool the raw material gas; A heavy hydrocarbon separator is used to perform gas-liquid separation on the cooled feed gas, separating the feed gas into a gas phase and heavy hydrocarbon products. The gas phase outlet of the heavy hydrocarbon separator is connected to a second heat exchanger for cooling the gas phase via a first branch and a second branch. The second heat exchanger is connected to a third heat exchanger for further cooling the gas phase via a pipeline. The third heat exchanger is connected to a denitrification tower via a pipeline. The top of the denitrification tower is connected to a nitrogen-rich gas discharge pipe, and the bottom of the denitrification tower is connected to an LNG storage tank via a pipeline. The second branch passes through the denitrification tower reboiler so that the gas phase in the second branch provides heat to the denitrification tower reboiler.

[0007] The natural gas liquefaction denitrification device of the present invention further includes a mixed refrigerant circulation refrigeration system. The mixed refrigerant circulation refrigeration system includes a mixed refrigerant balance tank, a first mixed refrigerant compressor, a mixed refrigerant compressor interstage separator, a second mixed refrigerant compressor, and a gas-liquid separator. The mixed refrigerant balance tank is connected to the first mixed refrigerant compressor via a pipeline. The first mixed refrigerant compressor is connected to the mixed refrigerant compressor interstage separator via a pipeline. The mixed refrigerant compressor interstage separator is connected to a mixed refrigerant gas phase pipe and a mixed refrigerant liquid phase pipe, respectively. The mixed refrigerant liquid phase pipe is connected to a first throttle valve, and the outlet of the first throttle valve is connected to a first return pipe. The mixed refrigerant liquid phase pipe passes through a second... A heat exchanger is provided. The mixed refrigerant vapor phase pipe is connected to a second mixed refrigerant compressor via a pipeline. The second mixed refrigerant compressor is connected to a gas-liquid separator via a pipeline. The gas-liquid separator is connected to a vapor phase pipe and a liquid phase pipe respectively. The vapor phase pipe is connected to a first reflux pipe. The liquid phase pipe passes through a first heat exchanger, a second heat exchanger, and a third heat exchanger in sequence. The liquid phase pipe is connected to a second throttle valve. The outlet of the second throttle valve is connected to a second reflux pipe. The second reflux pipe passes through a third heat exchanger and a second heat exchanger in sequence before connecting to the first reflux pipe. The first reflux pipe is connected to the inlet of the mixed refrigerant balance tank. The first reflux pipe passes through the first heat exchanger so that the liquid in the first reflux pipe provides cooling capacity to the first heat exchanger.

[0008] In the natural gas liquefaction denitrification device of the present invention, the outlet of the second throttling valve is connected to the first pipeline, the first pipeline is connected to the second return pipe, and the first pipeline passes through the denitrification tower condenser so that the liquid phase after throttling and cooling provides cooling capacity to the denitrification tower condenser.

[0009] The natural gas liquefaction denitrification method of the present invention includes: Cooling the raw gas; The cooled raw gas is subjected to gas-liquid separation to separate the gas phase and heavy hydrocarbon products. Cooling the gas phase; A denitrification tower is used for gas phase denitrification treatment.

[0010] Compared with existing technologies, the beneficial effects of the technical solution of this invention are as follows: It fully utilizes the cooling capacity and pressure energy of the mixed refrigerant, providing cooling capacity to the denitrification tower condenser through a first pipeline, while simultaneously recovering the nitrogen cooling capacity by returning the nitrogen separated from the top of the denitrification tower to the liquefaction cold box; it fully utilizes the cooling capacity produced by the mixed refrigerant to separate nitrogen, employing a denitrification tower for nitrogen removal, resulting in high nitrogen separation efficiency and fewer pieces of equipment. The reboiler and condenser are integrated inside the denitrification tower, reducing energy consumption and engineering investment, improving the economic benefits for enterprises. Only one denitrification tower is needed to achieve nitrogen removal, completely solving the problem of excessive nitrogen content in liquefied natural gas. The technical solution of this invention denitrifies nitrogen-containing feed gas through liquefaction to obtain products of corresponding purity, improving the economic value of the products. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the structure of the natural gas liquefaction denitrification device of the present invention. Detailed Implementation

[0012] like Figure 1 As shown, the natural gas liquefaction denitrification apparatus of the present invention includes: The first heat exchanger LNG1 is used to cool the feed gas; A heavy hydrocarbon separator V3 is used to perform gas-liquid separation on the cooled feed gas, separating the feed gas into a gas phase and heavy hydrocarbon products. The gas phase outlet of the heavy hydrocarbon separator is connected to a second heat exchanger LNG2 for cooling the gas phase via a first branch 11 and a second branch 12. The second heat exchanger LNG2 is connected to a third heat exchanger LNG3 for further cooling the gas phase via a pipeline. The third heat exchanger is connected to a denitrification tower T1 via a pipeline. The top of the denitrification tower is connected to a nitrogen-rich gas discharge pipe 14, and the bottom of the denitrification tower is connected to an LNG storage tank via a pipeline. The second branch 12 passes through the denitrification tower reboiler E3, so that the gas phase in the second branch provides heat to the denitrification tower reboiler.

[0013] The natural gas liquefaction denitrification device of the present invention further includes a mixed refrigerant circulation refrigeration system. The mixed refrigerant circulation refrigeration system includes a mixed refrigerant balance tank (not shown in the figure), a first mixed refrigerant compressor K1, a mixed refrigerant compressor interstage separator V1, a second mixed refrigerant compressor K2, and a gas-liquid separator V2. The mixed refrigerant balance tank is connected to the first mixed refrigerant compressor via a pipeline. The first mixed refrigerant compressor is connected to the mixed refrigerant compressor interstage separator via a pipeline. The mixed refrigerant compressor interstage separator is connected to a mixed refrigerant gas phase pipe 21 and a mixed refrigerant liquid phase pipe 22, respectively. The mixed refrigerant liquid phase pipe 22 is connected to a first throttle valve 31. The outlet of the first throttle valve 31 is connected to a first return pipe 41. The mixed refrigerant liquid phase pipe passes through a first exchanger... Heat exchanger; the mixed refrigerant vapor phase pipe is connected to the second mixed refrigerant compressor via a pipeline. The second mixed refrigerant compressor K2 is connected to the gas-liquid separator V2 via a pipeline. The gas-liquid separator is connected to the vapor phase pipe 51 and the liquid phase pipe 52 respectively. The vapor phase pipe is connected to the first return pipe 41. The liquid phase pipe passes through the first heat exchanger, the second heat exchanger, and the third heat exchanger in sequence. The liquid phase pipe is connected to the second throttle valve 32. The outlet of the second throttle valve is connected to the second return pipe 42. The second return pipe 42 passes through the third heat exchanger and the second heat exchanger in sequence and is then connected to the first return pipe. The first return pipe 41 is connected to the inlet of the mixed refrigerant balance tank. The first return pipe 41 passes through the first heat exchanger LNG1 so that the liquid in the first return pipe 41 provides cooling capacity to the first heat exchanger LNG1.

[0014] In the natural gas liquefaction denitrification device of the present invention, the outlet of the second throttling valve is connected to the first pipeline 61, the first pipeline is connected to the second return pipe 42, and the first pipeline passes through the denitrification tower condenser E4 so that the liquid phase after throttling and cooling provides cooling capacity to the denitrification tower condenser.

[0015] The natural gas liquefaction denitrification method of the present invention includes: Cooling the raw gas; The cooled raw gas is subjected to gas-liquid separation to separate the gas phase and heavy hydrocarbon products. Cooling the gas phase; A denitrification tower is used for gas phase denitrification treatment.

[0016] In operation, the natural gas liquefaction denitrification device of the present invention cools the feed gas through a heat exchanger and then enters the heavy hydrocarbon separator. The liquid phase is sent out of the cold box for rewarming, while the gas phase continues to cool in the plate-fin heat exchanger. After cooling to a certain temperature, it enters the denitrification tower. LNG products with a high methane concentration are discharged at the bottom of the tower and sent to the LNG storage tank after supercooling. Gas with a high nitrogen concentration, i.e., nitrogen-rich gas, is discharged at the top of the tower.

[0017] The refrigerant in the natural gas liquefaction denitrification device of the present invention can be a mixture of substances such as nitrogen, methane, ethylene, propane, and isopentane.

[0018] After primary compression, the mixed refrigerant enters the interstage separator of the mixed refrigerant compressor. The liquid phase provides cooling capacity to the plate-fin heat exchanger in the cold box, while the gas phase enters the secondary compression and gas-liquid separation stage, and then enters the cold box. The gas phase refrigerant is cooled and throttled after passing through the heat exchanger in sequence, and then enters the denitrification tower condenser to cool the top of the tower. The liquid phase refrigerant is cooled and throttled after passing through the plate-fin heat exchanger (first heat exchanger LNG1), and then provides cooling capacity to the plate-fin heat exchanger.

[0019] The feedstock gas can be a mixture of methane-rich gases such as natural gas and shale gas.

[0020] Denitrification towers can be packed towers, plate towers, or sieve plate towers.

[0021] The compressor can be a reciprocating compressor, a centrifugal compressor, or a screw compressor.

[0022] The refrigerant can be a mixture of substances including nitrogen, methane, ethylene, propane, isopentane, etc.

[0023] The technical solution of this invention is particularly applicable to natural gas and petrochemical tail gas.

[0024] The working process of the natural gas liquefaction denitrification device of the present invention is as follows: The feed gas C1, after being cooled by the first heat exchanger LNG1, enters the heavy hydrocarbon separator V3. The exiting gas phase is divided into two parts. The first part continues to be cooled in the second heat exchanger LNG2 and the third heat exchanger LNG3. After being cooled to a certain temperature, it enters the denitrification tower T1. At the bottom of the tower, LNG product C2 with a high methane concentration is discharged. After subcooling, C2 is sent to the LNG storage tank. The top of the denitrification tower T1 discharges a gas with a high nitrogen concentration, namely nitrogen-rich gas FN1, which is discharged after being reheated in a cold box. The second part directly enters the reboiler E3 of the denitrification tower to exchange heat with the product at the bottom of the tower. Afterward, the ambient temperature natural gas is depressurized and the nitrogen component is separated.

[0025] The natural gas liquefaction denitrification device of the present invention adopts a mixed refrigerant refrigeration process, and the refrigerant can be a mixture of substances including nitrogen, methane, ethylene, propane, isopentane, etc.

[0026] The mixed refrigerant first passes through the mixed refrigerant balance tank for buffering before entering the compression inlet of the mixed refrigerant compressor. After primary compression, the mixed refrigerant enters the interstage separator V1 of the mixed refrigerant compressor. The liquid phase directly enters the plate-fin heat exchanger LNG1, which cools to -40°C to provide cooling capacity for the plate-fin heat exchanger in the cold box. The gas phase in the interstage separator of the mixed refrigerant compressor enters the secondary compression stage and then enters the gas-liquid separator V2 at the outlet of the mixed refrigerant compressor. After gas-liquid separation, they enter the cold box separately.

[0027] The liquid refrigerant is cooled to -40°C and throttled in the first heat exchanger LNG1, then returns to the first heat exchanger LNG1 to provide cooling. The gaseous refrigerant is cooled to -162°C in heat exchangers LNG1, LNG2, and LNG3 in sequence before entering the throttling valve for further throttling. The throttled refrigerant then enters the denitrification tower condenser E4 to cool the top of the tower, providing cooling before returning to the first heat exchanger LNG1 to exchange heat with each section of the main heat exchanger. After mixing with the liquid refrigerant in the opposite flow, it is reheated to room temperature and then enters the mixed refrigerant balance tank for buffering before entering the next cycle.

[0028] The first heat exchanger, LNG1, is a plate-fin heat exchanger.

[0029] Compared with the prior art, the beneficial effects of the technical solution of the present invention are as follows: 1. This invention fully utilizes the cooling capacity and pressure energy of the mixed refrigerant by throttling the mixed refrigerant. By setting up a first pipeline, it provides cooling capacity to the denitrification tower condenser. At the same time, it recovers the nitrogen cooling capacity by returning the nitrogen gas separated from the top of the denitrification tower to the liquefaction cold box. 2. This invention fully utilizes the cooling capacity produced by the mixed refrigerant to separate nitrogen. It uses a denitrification tower to remove nitrogen, which has high nitrogen separation efficiency and requires fewer pieces of equipment. The denitrification tower integrates a reboiler and a condenser, which reduces energy consumption and engineering investment, improves the economic benefits of enterprises, and only requires one denitrification tower to achieve the purpose of nitrogen removal, completely solving the problem of excessive nitrogen content in liquefied natural gas.

[0030] The technical solution of this invention denitrifies nitrogen-containing raw gas through liquefaction to obtain products of corresponding purity, thereby improving the economic value of the products.

[0031] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A natural gas liquefaction denitrification device, characterized in that, include: The first heat exchanger used to cool the raw material gas; A heavy hydrocarbon separator is used to perform gas-liquid separation on the cooled feed gas, separating the feed gas into a gas phase and heavy hydrocarbon products. The gas phase outlet of the heavy hydrocarbon separator is connected to a second heat exchanger for cooling the gas phase via a first branch and a second branch. The second heat exchanger is connected to a third heat exchanger for further cooling the gas phase via a pipeline. The third heat exchanger is connected to a denitrification tower via a pipeline. The top of the denitrification tower is connected to a nitrogen-rich gas discharge pipe, and the bottom of the denitrification tower is connected to an LNG storage tank via a pipeline. The second branch passes through the denitrification tower reboiler so that the gas phase in the second branch provides heat to the denitrification tower reboiler.

2. The natural gas liquefaction denitrification device as described in claim 1, characterized in that, It also includes a mixed refrigerant cycle refrigeration system, which comprises a mixed refrigerant balance tank, a first mixed refrigerant compressor, a mixed refrigerant compressor interstage separator, a second mixed refrigerant compressor, and a gas-liquid separator. The mixed refrigerant balance tank is connected to the first mixed refrigerant compressor via pipelines. The first mixed refrigerant compressor is connected to the mixed refrigerant compressor interstage separator via pipelines. The mixed refrigerant compressor interstage separator is connected to a mixed refrigerant gas phase pipe and a mixed refrigerant liquid phase pipe, respectively. The mixed refrigerant liquid phase pipe is connected to a first throttle valve, and the outlet of the first throttle valve is connected to a first return pipe. The mixed refrigerant liquid phase pipe passes through a first heat exchanger. The vapor phase pipe is connected to the second mixed refrigerant compressor via a pipeline. The second mixed refrigerant compressor is connected to the gas-liquid separator via a pipeline. The gas-liquid separator is connected to the vapor phase pipe and the liquid phase pipe respectively. The vapor phase pipe is connected to the first reflux pipe. The liquid phase pipe passes through the first heat exchanger, the second heat exchanger, and the third heat exchanger in sequence. The liquid phase pipe is connected to the second throttle valve. The outlet of the second throttle valve is connected to the second reflux pipe. The second reflux pipe passes through the third heat exchanger and the second heat exchanger in sequence before connecting to the first reflux pipe. The first reflux pipe is connected to the inlet of the mixed refrigerant balance tank. The first reflux pipe passes through the first heat exchanger so that the liquid in the first reflux pipe provides cooling capacity to the first heat exchanger.

3. The natural gas liquefaction denitrification device as described in claim 2, characterized in that, The outlet of the second throttling valve is connected to the first pipeline, which in turn is connected to the second return pipeline. The first pipeline passes through the denitrification tower condenser so that the liquid phase cooled by throttling provides cooling capacity to the denitrification tower condenser.

4. A method for denitrification of natural gas liquefaction, characterized in that, include: Cooling the raw gas; The cooled raw gas is subjected to gas-liquid separation to separate the gas phase and heavy hydrocarbon products. Cooling the gas phase; A denitrification tower is used for gas phase denitrification treatment.

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