Triple-nitrogen expanded natural gas cryogenic liquefaction system

Abstract

The utility model discloses a triple-nitrogen expanded natural gas cryogenic liquefaction system which comprises a nitrogen cooling channel, a first heat flow channel, a second heat flow channel, a third heat flow channel, a first cold flow channel, a second cold flow channel and a third cold flow channel, the first hot flow channel communicates with the first cold flow channel through a first expansion machine, and the second hot flow channel communicates with the second cold flow channel through a second expansion machine. The third hot flow channel is communicated with the third cold flow channel through a third expansion machine; the first-stage compressor assembly, the second-stage compressor assembly, the third-stage compressor assembly and the fourth-stage compressor assembly are communicated in sequence, an outlet of the second cold flow channel is communicated with the input end of the first-stage compressor assembly, an outlet of the third cold flow channel is communicated with the input end of the third-stage compressor assembly, and an outlet of the first cold flow channel is communicated with the input end of the fourth-stage compressor assembly; and the output end of the four-stage compressor assembly is communicated with inlets of the first, second and third heat flow channels. The system has the advantages that the energy consumption of natural gas liquefaction can be effectively reduced, and faults of the compressor can be effectively reduced.

Description

Technical Field

[0001] The utility model relates to the technical field of natural gas deep-cold liquefaction, in particular to nitrogen expansion equipment. Background Art

[0002] At present, the natural gas expansion and liquefaction process is mainly achieved through the reverse Brayton cycle refrigeration principle, using the adiabatic expansion of the expander. The gas does work in the expander to achieve the purpose of cooling, with nitrogen as the refrigerant.

[0003] In the long-term natural gas liquefaction production, it is found that the current single-stage nitrogen expansion provides high comprehensive energy consumption for cooling. In order to improve the economic efficiency of the overall liquefied natural gas process, it is necessary to further optimize the liquefied natural gas production process and further reduce energy consumption. Utility Model Content

[0004] The technical problem to be solved by the utility model is to provide a system for deep-cold liquefaction of natural gas by triple nitrogen expansion, which has a simple structure and can not only provide sufficient cooling capacity for natural gas liquefaction, but also greatly reduce the energy consumption of the entire natural gas deep-cold liquefaction process, thereby effectively reducing the cost of natural gas liquefaction.

[0005] In order to solve the above problems, the technical solution adopted by the utility model is: a triple nitrogen expansion natural gas cryogenic liquefaction system, comprising a cold box, in which a natural gas cooling channel for the natural gas to be liquefied is provided, and a first hot flow channel, a second hot flow channel, a third hot flow channel, a first cold flow channel, a second cold flow channel, and a third cold flow channel for the refrigerant nitrogen to pass through;

[0006] The two ends of the natural gas cooling channel are respectively connected to the natural gas input pipe and the natural gas output pipe, the two ends of the first heat flow channel are respectively connected to the first heat flow input pipe and the first heat flow output pipe, the two ends of the second heat flow channel are respectively connected to the second heat flow input pipe and the second heat flow output pipe, and the two ends of the third heat flow channel are respectively connected to the third heat flow input pipe and the third heat flow output pipe;

[0007] The two ends of the first cold flow channel are respectively connected to the first cold flow input pipe and the first cold flow output pipe, the two ends of the second cold flow channel are respectively connected to the second cold flow input pipe and the second cold flow output pipe, and the two ends of the third cold flow channel are respectively connected to the third cold flow input pipe and the third cold flow output pipe;

[0008] The first hot flow output pipe is connected to the inlet of the first expander, and the outlet of the first expander is connected to the first cold flow input pipe; the second hot flow output pipe is connected to the inlet of the second expander, and the outlet of the second expander is connected to the second cold flow input pipe; the third hot flow output pipe is connected to the inlet of the third expander, and the outlet of the third expander is connected to the third cold flow input pipe;

[0009] It also includes a primary compressor assembly, a secondary compressor assembly, a tertiary compressor assembly, and a quaternary compressor assembly that are connected in sequence; the outlet of the second cold flow output pipe is connected to the input end of the primary compressor assembly, the output end of the secondary compressor assembly and the outlet of the third cold flow output pipe are both connected to the input end of the tertiary compressor assembly, and the output end of the tertiary compressor assembly and the outlet of the first cold flow output pipe are both connected to the input end of the quaternary compressor assembly;

[0010] The output end of the four-stage compressor assembly is connected to the inlets of the first heat flow input connecting pipe, the second heat flow input connecting pipe, and the third heat flow input connecting pipe.

[0011] Furthermore, in the aforementioned triple nitrogen expansion natural gas cryogenic liquefaction system, the output end of the four-stage compressor assembly is connected to the inlets of the first heat flow input connecting pipe, the second heat flow input connecting pipe, and the third heat flow input connecting pipe through a splitter.

[0012] Furthermore, in the aforementioned triple nitrogen expansion natural gas cryogenic liquefaction system, the first-stage compressor assembly includes a first-stage compressor and a first-stage cooler connected in sequence, the second-stage compressor assembly includes a second-stage compressor and a second-stage cooler connected in sequence, the third-stage compressor assembly includes a third-stage compressor and a third-stage cooler connected in sequence, and the fourth-stage compressor assembly includes a fourth-stage compressor and a fourth-stage cooler connected in sequence.

[0013] Furthermore, in the aforementioned triple nitrogen expansion natural gas cryogenic liquefaction system, the outlet of the second cold flow output pipe is connected to the inlet of the first-stage compressor; the outlet of the second-stage cooler and the outlet of the third cold flow output pipe are both connected to the inlet of the third-stage compressor; the outlet of the third-stage cooler and the outlet of the first cold flow output pipe are both connected to the inlet of the fourth-stage compressor.

[0014] Furthermore, in the aforementioned triple nitrogen expansion natural gas cryogenic liquefaction system, the outlet of the secondary cooler and the outlet of the third cold flow output pipe are connected to the inlet of the third-stage compressor through the first mixer; the outlet of the third-stage cooler and the outlet of the first cold flow output pipe are connected to the inlet of the fourth-stage compressor through the second mixer.

[0015] Furthermore, in the aforementioned triple nitrogen expansion natural gas cryogenic liquefaction system, the natural gas output pipe is connected to the throttle valve.

[0016] The advantages of the utility model are: 1. Three parallel nitrogen expansion cycles provide sufficient cooling capacity for natural gas liquefaction, that is, the first cold flow channel, the second cold flow channel, and the third cold flow channel provided in the cold box provide sufficient cooling capacity for natural gas liquefaction; the first hot flow channel, the second hot flow channel, and the third hot flow channel realize the refrigeration and pre-cooling of the refrigerant nitrogen, which greatly reduces energy consumption. 2. The refrigerant nitrogen in the first cold flow channel, the second cold flow channel, and the third cold flow channel is provided after expansion and cooling by the first expander, the second expander, and the third expander respectively. The use of three expanders can provide refrigerant nitrogen in three different temperature zones, which can make the temperature difference from the hot end to the cold end in the cold box relatively uniform, the temperature gradient between the cold and hot load curves is small, and the irreversible heat loss is reduced, which can reduce the overall energy consumption of the natural gas liquefaction system. 3. Four-stage compression is adopted, in which the refrigerant nitrogen that has released heat in the first cold flow channel enters the four-stage compression component, the refrigerant nitrogen that has released heat in the second cold flow channel enters the first-stage compression component, the refrigerant nitrogen that has released heat in the third cold flow channel enters the third-stage compression component, and the refrigerant nitrogen that has released heat in the first cold flow channel enters the four-stage compressor component. That is, four compressors are used for compression, and the load of the compressor is reasonably distributed, which can greatly reduce the overall energy consumption of the compressor, and can effectively reduce the occurrence of failures caused by overheating of the compressor, and can also distribute refrigerant nitrogen with different cold energy to different compressor sections, thereby further greatly reducing the overall energy consumption of the compressor. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the principle structure of the triple nitrogen expansion natural gas cryogenic liquefaction system described in the utility model. DETAILED DESCRIPTION

[0018] The utility model is further described in detail below in conjunction with the accompanying drawings and preferred embodiments.

[0019] like Figure 1 As shown, the triple nitrogen expansion natural gas cryogenic liquefaction system includes a cold box 1, in which a nitrogen cooling channel 17, a first hot flow channel 11, a second hot flow channel 12, a third hot flow channel 13, a first cold flow channel 14, a second cold flow channel 15, and a third cold flow channel 16 are arranged.

[0020] Two ends of the natural gas cooling channel 17 are respectively connected to a natural gas input pipe 171 and a natural gas output pipe 172 , and the natural gas output pipe is connected to a throttle valve 173 .

[0021] The two ends of the first heat flow channel 11 are respectively connected to the first heat flow input pipe 111 and the first heat flow output pipe 112, the two ends of the second heat flow channel 12 are respectively connected to the second heat flow input pipe 121 and the second heat flow output pipe 122, and the two ends of the third heat flow channel 13 are respectively connected to the third heat flow input pipe 131 and the third heat flow output pipe 132.

[0022] The two ends of the first cold flow channel 14 are respectively connected to the first cold flow input pipe 141 and the first cold flow output pipe 142, the two ends of the second cold flow channel 15 are respectively connected to the second cold flow input pipe 151 and the second cold flow output pipe 152, and the two ends of the third cold flow channel 16 are respectively connected to the third cold flow input pipe 161 and the third cold flow output pipe 162.

[0023] The first hot flow output pipe 112 is connected to the inlet of the first expander 100, and the outlet of the first expander 100 is connected to the first cold flow input pipe 141; the second hot flow output pipe 122 is connected to the inlet of the second expander 200, and the outlet of the second expander 200 is connected to the second cold flow input pipe 151; the third hot flow output pipe 132 is connected to the inlet of the third expander 300, and the outlet of the third expander 300 is connected to the third cold flow input pipe 161.

[0024] It also includes a first-stage compressor assembly 2, a second-stage compressor assembly 3, a third-stage compressor assembly 4, and a fourth-stage compressor assembly 5 that are connected in sequence. The outlet of the second cold flow output pipe 152 is connected to the input end of the first-stage compressor assembly 2, the output end of the second-stage compressor assembly 2, and the outlet of the third cold flow output pipe 162 are both connected to the input end of the third-stage compressor assembly 4, and the output end of the third-stage compressor assembly 4 and the outlet of the first cold flow output pipe 142 are both connected to the input end of the fourth-stage compressor assembly 5.

[0025] The output end of the four-stage compressor assembly 5 is connected to the inlets of the first heat flow input pipe 111, the second heat flow input pipe 121, and the third heat flow input pipe 131. In this embodiment, the output end of the four-stage compressor assembly 5 is connected to the inlets of the first heat flow input pipe 111, the second heat flow input pipe 121, and the third heat flow input pipe 131 through the diverter 6. The setting of the diverter 6 can distribute and adjust the amount of refrigerant nitrogen in the first heat flow input pipe 111, the second heat flow input pipe 121, and the third heat flow input pipe 131, so that the temperature of the inlet and outlet of the refrigerant in the cold box can be adjusted according to the actual production situation, ensuring that the natural gas can be effectively liquefied while further optimizing the overall process energy consumption. Preferably, after the diversion by the diverter 6, the diversion molar ratio of the refrigerant nitrogen in the first heat flow input pipe 111, the second heat flow input pipe 121, and the third heat flow input pipe 131 is 0.1:0.2:0.7.

[0026] In this embodiment, the first-stage compressor assembly 2 includes a first-stage compressor 21 and a first-stage cooler 22 connected in sequence, the second-stage compressor assembly 3 includes a second-stage compressor 31 and a second-stage cooler 33 connected in sequence, the third-stage compressor assembly 4 includes a third-stage compressor 41 and a third-stage cooler 42 connected in sequence, and the fourth-stage compressor assembly 5 includes a fourth-stage compressor 51 and a fourth-stage cooler 52 connected in sequence.

[0027] Specifically, the outlet of the second cold flow output pipe 152 is connected to the inlet of the first-stage compressor 21; the outlet of the second-stage cooler 32 and the outlet of the third cold flow output pipe 162 are both connected to the inlet of the third-stage compressor 41; the outlet of the third-stage cooler 42 and the outlet of the first cold flow output pipe 142 are both connected to the inlet of the fourth-stage compressor 51.

[0028] In this embodiment, the outlet of the secondary cooler 32 and the outlet of the third cold flow output pipe 162 are both connected to the inlet of the third-stage compressor 41 through the first mixer 7; the outlet of the third-stage cooler 42 and the outlet of the first cold flow output pipe 142 are both connected to the inlet of the fourth-stage compressor 51 through the second mixer 8. The first mixer 7 and the second mixer 8 are provided to ensure that the refrigerant nitrogen is mixed evenly.

[0029] The working principle is as follows: the refrigerant nitrogen is compressed and cooled to a pressure of 2.07MpaA and a temperature of 30°C by the first-stage compressor assembly 2; it is compressed and cooled to a pressure of 3.0MpaA and a temperature of 30°C by the second-stage compressor assembly 3; it is compressed and cooled to a pressure of 5.5MpaA and a temperature of 30°C by the third-stage compressor assembly 4; it is compressed and cooled to a pressure of 10.0MpaA and a temperature of 30°C by the fourth-stage compressor assembly 5.

[0030] The refrigerant nitrogen output by the four-stage compressor assembly 5 is split through the splitter 6, and the split molar ratio in the first heat flow input connecting pipe 111, the second heat flow input connecting pipe 121, and the third heat flow input connecting pipe 131 is 0.1:0.2:0.7.

[0031] The refrigerant nitrogen enters the first hot flow channel 11 in the cold box 1 through the first hot flow input pipe 111 and is cooled to -24°C, and then expands through the first expander 100, the temperature drops to -123.3°C, and the pressure is 3.10MpaA; the cooled refrigerant nitrogen enters the first cold flow channel 14 through the first cold flow input pipe 141 as a refrigerant. The refrigerant nitrogen that has released coldness in the first cold flow channel 14 then enters the second mixer 8 through the first cold flow output pipe 142.

[0032] The refrigerant nitrogen enters the second hot flow channel 12 in the cold box 1 through the second hot flow input pipe 121 and is cooled to -78°C, and then expands through the second expander 200, with the temperature dropping to -157.2°C and the pressure being 1.40MpaA; the cooled refrigerant nitrogen enters the second cold flow channel 15 through the second cold flow input pipe 151 as a refrigerant. The refrigerant nitrogen that has released coldness in the second cold flow channel 15 then enters the first compressor 21 through the second cold flow output pipe 152.

[0033] The refrigerant nitrogen enters the third hot flow channel 13 in the cold box 1 through the third hot flow input pipe 131 and is cooled to -24°C, and then expands through the third expander 300, the temperature drops to -85.05°C, and the pressure is 3.10MpaA; the cooled refrigerant nitrogen enters the third cold flow channel 16 through the third cold flow input pipe 161 as a refrigerant. The nitrogen released from the third cold flow channel 16 then enters the first mixer 7 through the third cold flow output pipe 162.

[0034] The natural gas to be liquefied at a temperature of 40°C is transported through the natural gas input pipe 171 into the natural gas cooling channel 17 and cooled to -157°C. It is then transported through the natural gas output pipe 172 and further throttled and liquefied through the throttle valve 173 to form liquefied natural gas at -163°C and a pressure of 1.0 atmosphere.

[0035] The advantages of the utility model are as follows: 1. The first cold flow channel 14, the second cold flow channel 15, and the third cold flow channel 16 are provided in the cold box 1, that is, three channels for providing refrigerant for cold capacity are provided, so as to provide sufficient cold capacity for natural gas liquefaction; the first hot flow channel 11, the second hot flow channel 12, and the third hot flow channel 13 realize the refrigeration and pre-cooling of the refrigerant nitrogen, which can effectively reduce energy consumption. 2. The refrigerant nitrogen in the first cold flow channel 14, the second cold flow channel 15, and the third cold flow channel 16 are provided after expansion and cooling by the first expander 100, the second expander 200, and the third expander 300 respectively. The use of three expanders can provide refrigerant nitrogen in three different temperature zones, which can make the temperature difference from the hot end to the cold end in the cold box relatively uniform, the temperature gradient between the cold and hot load curves is small, and the irreversible heat loss is reduced, that is, the overall energy consumption of the natural gas liquefaction system can be reduced. Fourth, a four-stage compression is adopted, wherein the refrigerant nitrogen that has released heat in the first cold flow channel 14 enters the four-stage compression assembly, the refrigerant nitrogen that has released heat in the second cold flow channel 15 enters the first-stage compression assembly, the refrigerant nitrogen that has released heat in the third cold flow channel 16 enters the third-stage compression assembly, and the refrigerant nitrogen that has released heat in the first cold flow channel 14 enters the four-stage compressor assembly, that is, four compressors are used for compression, which can reasonably distribute the load of the compressor, thereby greatly reducing the overall energy consumption of the compressor, and can effectively reduce the occurrence of failures caused by overheating of the compressor, and can also distribute refrigerant nitrogen with different cold energy to different compressor sections, thereby further greatly reducing the overall energy consumption of the compressor.

Claims

1. A triple nitrogen expansion natural gas cryogenic liquefaction system, including a cold box, characterized in that: The cold box is provided with a natural gas cooling channel for the natural gas to be liquefied, and a first hot flow channel, a second hot flow channel, a third hot flow channel, a first cold flow channel, a second cold flow channel, and a third cold flow channel for the refrigerant nitrogen to pass through; The two ends of the natural gas cooling channel are respectively connected to the natural gas input pipe and the natural gas output pipe, the two ends of the first heat flow channel are respectively connected to the first heat flow input pipe and the first heat flow output pipe, the two ends of the second heat flow channel are respectively connected to the second heat flow input pipe and the second heat flow output pipe, and the two ends of the third heat flow channel are respectively connected to the third heat flow input pipe and the third heat flow output pipe; The two ends of the first cold flow channel are respectively connected to the first cold flow input pipe and the first cold flow output pipe, the two ends of the second cold flow channel are respectively connected to the second cold flow input pipe and the second cold flow output pipe, and the two ends of the third cold flow channel are respectively connected to the third cold flow input pipe and the third cold flow output pipe; The first hot flow output pipe is connected to the inlet of the first expander, and the outlet of the first expander is connected to the first cold flow input pipe; The second hot flow output pipe is connected to the inlet of the second expander, and the outlet of the second expander is connected to the second cold flow input pipe; the third hot flow output pipe is connected to the inlet of the third expander, and the outlet of the third expander is connected to the third cold flow input pipe; It also includes a primary compressor assembly, a secondary compressor assembly, a tertiary compressor assembly, and a quaternary compressor assembly that are connected in sequence; The outlet of the second cold flow output pipe is connected to the input end of the first-stage compressor assembly, the output end of the second-stage compressor assembly and the outlet of the third cold flow output pipe are both connected to the input end of the third-stage compressor assembly, and the output end of the third-stage compressor assembly and the outlet of the first cold flow output pipe are both connected to the input end of the fourth-stage compressor assembly; The output end of the four-stage compressor assembly is connected to the inlets of the first heat flow input connecting pipe, the second heat flow input connecting pipe, and the third heat flow input connecting pipe.

2. The triple nitrogen expansion natural gas cryogenic liquefaction system according to claim 1, characterized in that: The output end of the four-stage compressor assembly is connected to the inlets of the first heat flow input connecting pipe, the second heat flow input connecting pipe, and the third heat flow input connecting pipe through a flow divider.

3. The triple nitrogen expansion natural gas cryogenic liquefaction system according to claim 1, characterized in that: The first-stage compressor assembly includes a first-stage compressor and a first-stage cooler connected in sequence, the second-stage compressor assembly includes a second-stage compressor and a second-stage cooler connected in sequence, the third-stage compressor assembly includes a third-stage compressor and a third-stage cooler connected in sequence, and the fourth-stage compressor assembly includes a fourth-stage compressor and a fourth-stage cooler connected in sequence.

4. The triple nitrogen expansion natural gas cryogenic liquefaction system according to claim 3, characterized in that: The outlet of the second cold flow output pipe is connected to the inlet of the first-stage compressor; the outlet of the second-stage cooler and the outlet of the third cold flow output pipe are both connected to the inlet of the third-stage compressor; the outlet of the third-stage cooler and the outlet of the first cold flow output pipe are both connected to the inlet of the fourth-stage compressor.

5. The triple nitrogen expansion natural gas cryogenic liquefaction system according to claim 4, characterized in that: The outlet of the secondary cooler and the outlet of the third cold flow output pipe are connected to the inlet of the third-stage compressor through the first mixer; the outlet of the third-stage cooler and the outlet of the first cold flow output pipe are connected to the inlet of the fourth-stage compressor through the second mixer.

6. The triple nitrogen expansion natural gas cryogenic liquefaction system according to claim 1, characterized in that: The natural gas output pipe is connected to the throttle valve.

Images