CN215676068U - Low-temperature flash evaporation gas recovery and liquefaction device and liquefied natural gas system - Google Patents

Abstract

The utility model provides a low-temperature flash evaporation gas recovery and liquefaction device and a liquefied natural gas system, and relates to the field of chemical equipment. The low-temperature flash evaporation gas recovery and liquefaction device comprises a heat exchanger, a normal-temperature compressor and a cold box, wherein the heat exchanger is used for cooling or reheating pressurized feed gas from the low-temperature compressor, a discharge hole of the heat exchanger is communicated with a feed hole of the normal-temperature compressor, and a discharge hole of the normal-temperature compressor is communicated with the cold box. The temperature of the pressurized feed gas from the outlet of the low-temperature compressor can be below 0 ℃ or above 40 ℃, and the pressurized feed gas is cooled or reheated by the heat exchanger, enters the normal-temperature compressor for pressurization and cooling and then enters the cold box. The normal temperature compressor can be prevented from being damaged, and the working condition stability and the economical efficiency are improved.

Description

Low-temperature flash evaporation gas recovery and liquefaction device and liquefied natural gas system

Technical Field

The utility model relates to the field of chemical equipment, in particular to a low-temperature flash evaporation gas recovery and liquefaction device and a liquefied natural gas system.

Background

The atmospheric boiling point of methane is-161.5 ℃, and liquefied Natural gas is liquid methane gas, which is called LNG (liquefied Natural gas) for short. Liquefied natural gas is generally stored in a low-temperature cold-insulation storage tank, and is commonly stored in various LNG storage and distribution peak shaving stations, LNG receiving stations, natural gas liquefaction plants, and marine LNG carriers. The low-temperature flash Gas is flash Gas of liquefied natural Gas in the process of storage or transportation, and is called BOG (Boil-Off Gas) for short. LNG is a cryogenic liquid stored at temperatures below-162 c, which increases its temperature during storage and transportation due to loss of refrigeration, and thus part of the LNG vaporizes to form flash gas containing methane and nitrogen as the main components. The pressure of the LNG storage container can be increased after the BOG is generated, and if the BOG is directly emptied, the problems of environmental pollution, resource waste and the like can be caused, and safety accidents are easily caused. Therefore, BOG needs to be recycled in the industry.

When the LNG receiving station is connected with an external transmission pipeline network, pressurization external transmission recovery is usually adopted, or BOG is liquefied by using a recondenser and then is pressurized, gasified and output through a booster pump. However, this method is too limited for LNG receiving stations without export pipelines. At present, more and more LNG receiving stations without external transmission pipe networks need to adopt a BOG on-site reliquefaction mode, BOG is conveyed to a reliquefaction recovery device by pressurization of a low-temperature compressor, refrigeration capacity is provided by a refrigeration heat exchanger in an external supply refrigeration cycle, and the BOG is further deep-cooled to below-160 ℃ to obtain an LNG product which is directly returned to an LNG storage tank.

The existing BOG in-situ reliquefaction process generally has the following problems: (1) the normal-temperature BOG compressor is easy to damage, and the risk of stopping production is brought; (2) the existing BOG on-site reliquefaction process can cause cold blockage of a cold box after the operation period, so that the liquid outlet of the device is influenced, and the production stop and the reheating of the cold box takes 2-3 days; when the cold box is reheated in the parking, if raw material gas BOG is in the storage tank, can make storage tank pressure rise constantly, produce huge potential safety hazard, if BOG emptying burning, not only economic loss is huge, also can cause environmental pollution simultaneously.

SUMMERY OF THE UTILITY MODEL

The utility model aims to provide a low-temperature flash evaporation gas recovery and liquefaction device and a liquefied natural gas system, which aim to avoid the problem of damage of a normal-temperature compressor and increase the stability and the economical efficiency of working conditions.

The embodiment of the utility model is realized by the following steps:

in a first aspect, the utility model provides a low-temperature flash evaporation gas recovery and liquefaction device, which comprises a heat exchanger, a normal-temperature compressor and a cold box, wherein the heat exchanger is used for cooling or reheating pressurized feed gas from the low-temperature compressor, a discharge hole of the heat exchanger is communicated with a feed inlet of the normal-temperature compressor, and a discharge hole of the normal-temperature compressor is communicated with the cold box.

In an optional implementation mode, a drying tower and a dust filter are further arranged on a communicating pipeline between the normal-temperature compressor and the cold box, a discharge hole of the normal-temperature compressor is communicated with a feed inlet of the drying tower, a discharge hole of the drying tower is communicated with a feed inlet of the dust filter, and a discharge hole of the dust filter is communicated with a feed inlet of the cold box.

In an optional embodiment, a first process pipeline and a second process pipeline are arranged between the normal temperature compressor and the dust filter, the drying tower is installed on the first process pipeline, and a first regulating valve and a second regulating valve are respectively arranged on the first process pipeline and the second process pipeline so as to switch the working states of the first process pipeline and the second process pipeline.

In an alternative embodiment, a dew point detector is installed on the communication line between the dust filter and the cold box.

In an alternative embodiment, the number of the first adjusting valves is two, one first adjusting valve is located between the normal temperature compressor and the drying tower, and the other first adjusting valve is located between the drying tower and the dust filter.

In an alternative embodiment, a purge gas discharge pipeline is further connected to the pipeline between the drying tower and the first regulating valve, and a third regulating valve is further disposed on the purge gas discharge pipeline.

In an alternative embodiment, the drying tower further comprises a purge gas conveying pipeline, and an outlet of the purge gas conveying pipeline is communicated with the drying tower.

In an alternative embodiment, a heater for heating the purge gas is provided on the purge gas delivery pipe.

In an alternative embodiment, a fourth regulating valve is further provided between the heater and the connection point of the purge gas feed line and the first process line.

In a second aspect, the present invention provides a liquefied natural gas system comprising a cryogenic flash gas recovery liquefaction train according to any preceding embodiment.

The embodiment of the utility model has the beneficial effects that: the temperature of the pressurized feed gas from the outlet of the low-temperature compressor can be below 0 ℃ or above 40 ℃, and the pressurized feed gas is cooled or reheated by the heat exchanger, enters the normal-temperature compressor for pressurization and cooling and then enters the cold box. The normal temperature compressor can be prevented from being damaged, and the working condition stability and the economical efficiency are improved.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.

Fig. 1 is a schematic structural diagram of a cryogenic flash gas recovery liquefaction device provided in an embodiment of the present invention;

fig. 2 is a schematic structural diagram of a cryogenic flash gas recovery liquefaction device according to another embodiment of the present invention.

The icon is 100-a low-temperature flash evaporation gas recovery and liquefaction device; 101-raw material gas supply device; 102-a heat exchanger; 103-normal temperature compressor; 104-a drying tower; 105-a dust filter; 106-a heater; 107-dew point detector; 108-a cold box; 110-first process piping; 120-a second process line; 130-purge gas exhaust line; 140-purge gas delivery line; 111-a first regulating valve; 121-a second regulating valve; 131-a third regulating valve; 141-fourth regulating valve.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. The components of embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations.

Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the utility model, as claimed, but is merely representative of selected embodiments of the utility model. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, it need not be further defined and explained in subsequent figures.

In the description of the present invention, it should be noted that the terms "upper", "lower", "inner", "outer", and the like refer to the orientation or positional relationship shown in the drawings, or the orientation or positional relationship which the utility model product is conventionally placed in use, and are only for convenience of describing the present invention and simplifying the description, but do not refer to or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and thus should not be construed as limiting the present invention. Furthermore, the terms "first," "second," "third," and the like are used solely to distinguish one from another and are not to be construed as indicating or implying relative importance.

Furthermore, the terms "horizontal", "vertical" and the like do not imply that the components are required to be absolutely horizontal or pendant, but rather may be slightly inclined. For example, "horizontal" merely means that the direction is more horizontal than "vertical" and does not mean that the structure must be perfectly horizontal, but may be slightly inclined.

In the description of the present invention, it should also be noted that, unless otherwise explicitly specified or limited, the terms "disposed," "mounted," "connected," and "connected" are to be construed broadly and may, for example, be fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

First embodiment

Referring to fig. 1, the embodiment provides a low-temperature flash gas recovery and liquefaction device 100, which includes a heat exchanger 102, a normal-temperature compressor 103, a drying tower 104, a dust filter 105, and a cooling box 108.

Specifically, the raw material gas supply device 101 is a pressurized raw material gas M1 from a low-temperature compressor, which may be at 0 ℃ or below or at 40 ℃ or above, the heat exchanger 102 cools or reheats the pressurized raw material gas from the low-temperature compressor to reach a normal temperature state of approximately 20 ℃ to obtain a material flow M2, a discharge port of the heat exchanger 102 is communicated with a feed port of the normal-temperature compressor 103, a material flow M3 output from a discharge port of the normal-temperature compressor 103 is communicated with a feed port of the drying tower 104, a material flow M4 output from a discharge port of the drying tower 104 is communicated with a feed port of the dust filter 105, and a discharge port of the dust filter 105 is communicated with a feed port of the cold box 108. Specifically, the heat exchanger 102 is an air cooler.

Specifically, the drying tower 104 is filled with a molecular sieve-sealed adsorbent to remove water to obtain a material flow M4, and M4 enters a dust filter 105 to filter out solid impurities possibly contained in the material flow.

It should be noted that the inventor utilizes the heat exchanger 102 to cool or reheat the pressurized feed gas from the low-temperature compressor to maintain the temperature at 20 ℃ at normal temperature, thereby reducing the damage to the compressor due to overhigh or overlow temperature in the subsequent BOG pressurization process, prolonging the service life of the compressor, saving the cost, simultaneously reducing the potential safety hazard caused by overhigh pressurized temperature, and improving the feasibility of the feed gas pressurization and the adaptability of various complex feed gas working conditions. In addition, moisture and solid impurities are removed by the drying tower 104 and the dust filter 105, so that the cold blocking problem of the cold box 108 can be effectively prevented, and the working condition stability and the economical efficiency are further improved.

In some embodiments, a first process line 110 and a second process line 120 are disposed between the room temperature compressor 103 and the dust filter 105, the drying tower 104 is mounted on the first process line 110, and a first adjusting valve 111 and a second adjusting valve 121 are disposed on the first process line 110 and the second process line 120, respectively, to switch the working states of the first process line 110 and the second process line 120. A dew point detector 107 is arranged on a communicating pipeline between the dust filter 105 and the cold box 108 and is used for analyzing the water content, and if the water content is lower and reaches the standard, a material flow M5 is obtained, and the material flow enters the cold box for liquefaction; if the water cut is too high, the first process line 110 is closed and the second process line 120 is opened.

Further, there are two first regulating valves 111, one first regulating valve 111 being located between the normal temperature compressor 103 and the drying tower 104, and the other first regulating valve 111 being located between the drying tower 104 and the dust filter 105. The first flow path pipeline 110 and the second flow path pipeline 120 have a short shared pipeline on the connection pipeline with the dust filter, and the material in the second flow path pipeline 120 can be prevented from flowing into the first flow path pipeline 110 by the first regulating valve 111 between the drying tower 104 and the dust filter 105.

When the first process line 110 is closed and the second process line 120 is opened, the drying tower 104 needs to be purged, and the efficiency of the working condition is increased because the drying tower 104 can be purged without stopping. A purge gas discharge line 130 is further connected to a line between the drying tower 104 and the first adjustment valve 111, and a third adjustment valve 131 is further provided on the purge gas discharge line 130 to adjust the opening and closing of the purge gas discharge line 130.

Further, the cryogenic flash gas recovery liquefaction device 100 further comprises a purge gas conveying pipeline 140, and an outlet of the purge gas conveying pipeline 140 is communicated with the drying tower 104. Specifically, the purge gas delivery line 140 is used to deliver purge gas, such as nitrogen.

In some embodiments, a heater 106 for heating the purge gas is provided on the purge gas feed line 140, and a fourth regulating valve 141 is further provided between the heater 106 and the connection point of the purge gas feed line 140 and the first flow line 110. Fourth regulator valve 141 may be closed to prevent material from entering heater 106 when first flow line 110 is in operation. In the purging, a purge gas stream M6 such as nitrogen is heated by a heater 106 to obtain a stream M7, and the stream M7 is introduced into the drying tower 104 to be purged and then is output through a purge gas transfer line 140.

Specifically, the heater 106 may be a general electric heater.

The operation of the apparatus is described in detail below with reference to fig. 1:

the first process is described as follows: the valves of the third, second, and fourth regulating valves 131, 121, and 141 are closed, and the remaining valves are opened. The pressurized feed gas M1 from the cryogenic compressor had a temperature of 0 ℃ or less or 40 ℃ or more and a pressure of 0.7 MPa. M1 enters heat exchanger 102 and is cooled or reheated to 20 ℃ to obtain stream M2. M2 was cooled under increased pressure in a warm compressor 103 to give stream M3, M3 at 40 ℃. M3 enters a drying tower 104 to remove moisture through molecular sieve adsorption, and a stream M4 is obtained. M4 enters a dust filter 105 to filter out solid impurities possibly contained, a dew point analyzer analyzes moisture, and if the moisture content is too high, the process flow II is carried out; if the water content is lower and reaches the standard, a material flow M5 is obtained, and M5 enters a cold box for liquefaction.

It should be noted that: when the moisture of the drying tower is saturated, the BOG takes the moisture of the drying tower out, and the BOG enters a second process flow after being seen by a dew point analyzer.

The second process is described as follows: two first regulator valves 111 are closed and the remaining valves are open. And after reheating or cooling by the inlet heat exchanger 102, the material flow M2 is subjected to pressurization and cooling by the normal temperature compressor 103 to obtain a material flow M8. In this case, the physical property parameters of M8 were the same as those of M4. M8 bypassed to dust filter 105, yielding stream M5. M5 entered the cold box for liquefaction. At the same time, nitrogen stream M6 was reheated in heater 106 to provide stream M7. M7 purges the drying tower 104 and is directly vented by the purge gas exhaust line 130 after purging.

It should be noted that: as the water dew point of BOG is only about-60 ℃, the BOG can directly bypass and go to a dust filter without passing through a drying tower; the reheating nitrogen purging and the driving can be carried out simultaneously.

The operation time of the second flow is about 1 day, and then the first flow is restarted and the operation is carried out according to the process cycle.

Second embodiment

Referring to fig. 2, the difference from the first embodiment is that the heat exchanger 102 is not in the form of an air cooler but instead is a circulating water heat exchanger, and the temperature of the circulating water is 20 ℃.

The utility model provides a liquefied natural gas system, which comprises the low-temperature flash gas recovery and liquefaction device 100 in any one of the previous embodiments and also comprises a storage tank.

The utility model has the following advantages:

(1) simple equipment, stable working condition, high product purity and yield and good economic benefit.

Specifically, the dew point of water in the raw material gas obtained by the embodiment of the utility model can reach below-70 ℃, a high-quality LNG product is obtained by further cryogenic liquefaction, and the purity of the liquefied natural gas product can reach above 99%. The water-containing dew point in the pretreated raw material gas is low, so that the economic loss caused by freezing and blocking of the cold box is reduced, meanwhile, the condition that the pressure of the BOG storage tank is continuously increased due to freezing and blocking of the cold box is avoided, the potential safety hazard is reduced, and the BOG cannot be emptied to cause resource waste. The device provided by the utility model is suitable for the working condition of BOG on-site reliquefaction due to moisture and solid impurities contained in the purged pipeline or equipment.

(2) The energy is cleaner, and the environmental pollution is avoided.

According to the embodiment of the utility model, air is used as the heating medium and the cooling medium of the inlet air cooler, so that heat transfer among air, materials and air is realized, energy is cleaner, and environmental pollution is avoided.

(3) The working condition is applicable widely.

The temperature of the raw material gas after being pressurized and cooled by the compressor in the embodiment of the utility model can be stabilized at about 40 ℃, and the utility model is suitable for various working conditions, in particular the working condition that BOG transmits inlet air through the compression of the low-temperature compressor.

The following describes an application example of the cryogenic flash vapor recovery liquefaction apparatus 100 according to an embodiment of the present invention:

application example 1

The raw material gas is BOG pressurized by a low-temperature compressor, and the pipeline equipment contains moisture and solid impurities. The method comprises the following steps of obtaining clean raw material gas at 40 ℃ after inlet heat exchange, pressurization, cooling, drying and filtering, wherein the raw material gas can be directly sent to a cold box for cryogenic liquefaction, and the specific process flow is as follows:

the valves of the third, second, and fourth regulating valves 131, 121, and 141 are closed, and the remaining valves are opened. The pressurized feed gas M1 from the cryogenic compressor had a temperature of-40 ℃ and a pressure of 0.7 MPa. M1 enters heat exchanger 102 and is cooled or reheated to 20 ℃ to obtain stream M2. M2 was cooled under increased pressure in a warm compressor 103 to give stream M3, M3 at 40 ℃. M3 enters a drying tower 104 to remove moisture through molecular sieve adsorption, and a stream M4 is obtained. M4 enters a dust filter 105 to filter solid impurities possibly contained, a dew point analyzer analyzes moisture, if the moisture content is lower and reaches the standard, a material flow M5 is obtained, and M5 enters a cold box to be liquefied; if the water content is too high, two first regulating valves 111 are closed, the remaining valves are opened, stream M1 continues to be aerated, and stream M5 continues to enter the cold box. And (3) simultaneously feeding a nitrogen material flow M6, reheating M6 by a heater 106 to obtain a material flow M7, purging the drying tower 104 by M7, and directly emptying after purging.

The physical parameters of the product in this case are shown in Table 1:

TABLE 1 physical Properties of the product at each step

The results show that the feed gas obtained had a methane content of 92.14%, a nitrogen content of 7.86% (inlet feed gas nitrogen content) and a water content of essentially 0.

The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes will occur to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. The utility model provides a low temperature flash distillation gas recovery liquefying plant which characterized in that, includes heat exchanger, normal atmospheric temperature compressor and cold box, the heat exchanger is used for cooling or reheat the pressure boost feed gas that comes from the low temperature compressor, the discharge gate of heat exchanger with the feed inlet intercommunication of normal atmospheric temperature compressor, the discharge gate of normal atmospheric temperature compressor with the cold box intercommunication.

2. The device for recovering and liquefying flash evaporation gas at low temperature according to claim 1, wherein a drying tower and a dust filter are further arranged on a communicating pipeline between the normal temperature compressor and the cooling box, a discharge port of the normal temperature compressor is communicated with a feed port of the drying tower, a discharge port of the drying tower is communicated with a feed port of the dust filter, and a discharge port of the dust filter is communicated with a feed port of the cooling box.

3. The device as claimed in claim 2, wherein a first flow line and a second flow line are disposed between the normal temperature compressor and the dust filter, the drying tower is mounted on the first flow line, and the first flow line and the second flow line are respectively provided with a first regulating valve and a second regulating valve to switch operating states of the first flow line and the second flow line.

4. The cryogenic flash gas recovery liquefaction device of claim 3, characterized in that a dew point detector is installed on a communication pipeline between the dust filter and the cold box.

5. The cryogenic flash gas recovery liquefaction device of claim 3, wherein the number of the first regulating valves is two, one first regulating valve is located between the normal temperature compressor and the drying tower, and the other first regulating valve is located between the drying tower and the dust filter.

6. The cryogenic flash gas recovery liquefaction device according to claim 5, wherein a purge gas discharge pipeline is further connected to a pipeline between the drying tower and the first regulating valve, and a third regulating valve is further arranged on the purge gas discharge pipeline.

7. The cryogenic flash gas recovery liquefaction device of claim 6, further comprising a purge gas delivery line, an outlet of the purge gas delivery line being in communication with the drying tower.

8. The cryogenic flash gas recovery liquefaction device according to claim 7, wherein a heater for heating the purge gas is provided on the purge gas delivery line.

9. The cryogenic flash gas recovery liquefaction plant of claim 8, wherein a fourth regulating valve is further provided between the heater and the connection point of the purge gas delivery line and the first process line.

10. A liquefied natural gas system comprising the cryogenic flash gas recovery liquefaction plant defined in any one of claims 1 to 9.

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