Low-temperature tank field low-temperature system pre-cooling boil-off gas recovery process

Abstract

The invention discloses a low-temperature tank field low-temperature system pre-cooling boil-off gas recovery process, and belongs to the technical field of petrochemical engineering. Comprising a low-temperature storage tank; bOG gas generated in the low-temperature storage tank enters the BOG compressor, and the compressed BOG gas enters the compressor aftercooler to carry out primary heat exchange with water; the BOG gas subjected to primary heat exchange enters the propylene evaporator and is subjected to secondary heat exchange with low-temperature propylene; the BOG gas subjected to secondary heat exchange enters the collecting tank to be subjected to flash evaporation; and the BOG gas after flash evaporation sequentially enters the subcooler and the cooler to be subjected to primary cooling and secondary cooling, and the BOG gas after secondary cooling is connected into a low-temperature material inlet tank hand valve through a recovery pipeline and enters the low-temperature storage tank together with a new low-temperature material. BOG gas generated during precooling of the low-temperature storage tank is recycled to the low-temperature storage tank through the reliquefaction system, so that the recycling rate of the BOG gas is increased, and the cost is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of petrochemical industry, and in particular relates to a pre-cooling evaporation gas recovery process of a low-temperature system in a low-temperature tank area. Background Art

[0002] In the field of petrochemical industry, cryogenic atmospheric pressure storage tanks are widely used to store various volatile liquid raw materials or products. When these storage tanks need to be pre-cooled to prepare to receive new cryogenic liquid materials, the ambient temperature inside the tanks needs to be gradually reduced to a level that can safely store these materials. In this process, since the cryogenic liquid will evaporate quickly after entering the storage tank, a large amount of boil-off gas (BOG) will be generated. If these gases cannot be effectively treated, they will pollute the environment and are also a huge waste of resources.

[0003] In the traditional cryogenic tank precooling stage, the BOG gas generated is usually discharged directly into the atmosphere through the discharge port on the top of the tank or directed to the factory's flare system for combustion treatment. This method not only causes energy loss, but also increases production costs. According to statistics, the recovery rate of BOG gas in this process can only reach 3%, which shows that most of the recyclable resources are not actually effectively reused. Summary of the invention

[0004] The present invention aims at the above problems existing in the prior art and proposes a low-temperature system pre-cooling evaporation gas recovery process in a low-temperature tank area which can improve the recovery rate of BOG gas.

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

[0006] A low-temperature tank area low-temperature system pre-cooling boil-off gas recovery process, comprising:

[0007] Cryogenic storage tank, the cryogenic material enters the cryogenic storage tank through the cryogenic material inlet manual valve to be pre-cooled. During the pre-cooling process, the cryogenic material generates BOG gas due to evaporation and is discharged to the outside;

[0008] BOG compressor and compressor aftercooler, the BOG gas generated in the low-temperature storage tank enters the BOG compressor through the BOG pipeline, and the compressed BOG gas enters the compressor aftercooler to perform heat exchange with water;

[0009] A propylene evaporator is connected to the compressor aftercooler, and the BOG gas after the primary heat exchange enters the propylene evaporator for secondary heat exchange with low-temperature propylene;

[0010] A collecting tank connected to the propylene evaporator, wherein the BOG gas after the secondary heat exchange enters the collecting tank for flash evaporation;

[0011] The subcooler and the cooler, the collecting tank is connected with the subcooler and the cooler in sequence, the BOG gas after flashing enters the subcooler for primary cooling, and then enters the cooler for secondary cooling, the BOG gas is liquefied after the secondary cooling and connected to the low-temperature material inlet valve through the recovery pipeline, and then enters the low-temperature storage tank together with the new low-temperature material.

[0012] As a further improvement of the present invention, the low-temperature storage tank is provided with a storage tank pre-cooling spray ring, and the low-temperature material enters the storage tank pre-cooling spray ring after passing through the low-temperature material tank inlet manual valve.

[0013] As a further improvement of the present invention, the BOG gas output from the cooler is introduced into the low-temperature material feed manual valve through a recovery pipeline and then fed into the storage tank pre-cooling spray ring together with the low-temperature material.

[0014] As a further improvement of the present invention, a BOG compressor inlet buffer tank is further provided between the low-temperature storage tank and the BOG compressor.

[0015] As a further improvement of the present invention, a propylene refrigerator is also included, which is connected to the propylene evaporator. The refrigerant enters the propylene evaporator to cool the propylene and then flows back to the propylene refrigerator to circulate.

[0016] As a further improvement of the present invention, the collecting tank is connected to the supercooler through two parallel pipelines, and the BOG gas after flash evaporation in the collecting tank is split into two pipelines and transported to the supercooler.

[0017] As a further improvement of the present invention, the subcooler is also unidirectionally connected to the BOG compressor through a reflux pipeline, and a portion of the BOG gas after completing primary cooling in the subcooler enters the cooler, and the other portion flows back to the BOG compressor through the reflux pipeline.

[0018] As a further improvement of the present invention, the BOG gas is cooled to -60°C in the subcooler by adopting a 1 / 3 cooling 1 / 2 method.

[0019] As a further improvement of the present invention, the BOG gas is cooled to -70°C in the cooler.

[0020] As a further improvement of the present invention, a storage tank BOG outlet valve and a BOG compressor inlet buffer tank valve are provided on the pipeline between the low-temperature storage tank and the BOG compressor inlet buffer tank;

[0021] A BOG compressor inlet valve is provided on the pipeline between the BOG compressor inlet buffer tank and the BOG compressor;

[0022] A propylene evaporator inlet valve is provided on the pipeline between the compressor aftercooler and the propylene evaporator;

[0023] A reliquefaction return spray ring valve is provided on the pipeline between the cooler and the storage tank pre-cooling spray ring.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. A BOG gas reliquefaction system is added to recycle the BOG gas generated during the precooling of the cryogenic storage tank to the cryogenic storage tank through the reliquefaction system. After optimization, the recovery rate of BOG gas can reach 98%, which greatly improves the recovery rate of BOG gas and reduces costs;

[0026] 2. The entire reliquefaction system gradually lowers the temperature of BOG gas through multiple cooling, and finally completes liquefaction after mixing with cryogenic materials in a cryogenic storage tank, ensuring that BOG gas can be effectively cooled and liquefied, thereby improving the recovery efficiency of BOG gas and reducing energy waste;

[0027] 3. The BOG gas output from the cooler is inserted into the low-temperature material inlet valve through the recovery pipeline, and then sent into the pre-cooling spray ring of the storage tank together with the low-temperature material, ensuring that the temperature of the low-temperature storage tank drops evenly during the pre-cooling process, avoiding the temperature difference stress caused by sudden temperature changes;

[0028] 4. After completing the primary cooling in the subcooler, part of the BOG gas enters the cooler, and the other part flows back to the BOG compressor through the reflux pipeline. The existence of the reflux pipeline allows part of the preliminarily cooled BOG gas to return to the BOG compressor, ensuring that the compressor always has sufficient gas flow to prevent surge. This helps to further optimize the working state of the compressor and can also be used as a means of regulating the system to cope with changes in BOG gas flow and ensure safe operation of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the pre-cooling boil-off gas recovery process of the low-temperature system in the low-temperature tank area of ​​the present invention;

[0030] Figure 2 The present invention is a flow chart of a pre-cooling evaporation gas recovery process of a low-temperature system in a low-temperature tank area.

[0031] In the figure, 100, low-temperature storage tank; 101, manual valve for low-temperature material inlet; 102, storage tank pre-cooling spray ring; 103, storage tank BOG outlet valve; 110, BOG compressor inlet buffer tank; 111, BOG compressor inlet buffer tank valve; 120, BOG compressor; 130, compressor aftercooler; 131, BOG compressor inlet valve; 140, propylene evaporator; 141, propylene evaporator inlet valve; 150, propylene refrigerator; 160, collecting tank; 170, subcooler; 180, cooler; 190, recovery pipeline; 191, reliquefaction return spray ring valve. DETAILED DESCRIPTION

[0032] The following are specific embodiments of the present invention and the accompanying drawings to further describe the technical method of the present invention, but the present invention is not limited to these embodiments.

[0033] like Figure 1-2 As shown, the present invention provides a low-temperature tank area low-temperature system pre-cooling boil-off gas recovery process, comprising:

[0034] Cryogenic storage tank 100, the cryogenic material enters the cryogenic storage tank 100 through the cryogenic material inlet manual valve 101 to be precooled. During the precooling process, the cryogenic material generates BOG gas due to evaporation and is discharged to the outside;

[0035] BOG compressor 120 and compressor aftercooler 130. BOG gas generated in the cryogenic storage tank 100 enters the BOG compressor 120 through the BOG pipeline, and the compressed BOG gas enters the compressor aftercooler 130 to perform heat exchange with water.

[0036] The propylene evaporator 140 is connected to the compressor aftercooler 130. The BOG gas after the primary heat exchange enters the propylene evaporator 140 and performs secondary heat exchange with the low-temperature propylene.

[0037] The collecting tank 160 is connected to the propylene evaporator 140, and the BOG gas after the secondary heat exchange enters the collecting tank 160 for flash evaporation;

[0038] The subcooler 170 and the cooler 180, and the collecting tank 160 are connected to the subcooler 170 and the cooler 180 in sequence. The BOG gas after flashing enters the subcooler 170 for primary cooling, and then enters the cooler 180 for secondary cooling. After the secondary cooling, the BOG gas is liquefied and connected to the low-temperature material inlet valve 101 through the recovery pipeline 190, and then enters the low-temperature storage tank 100 together with the new low-temperature material.

[0039] It should be noted that, during the pre-cooling of the current cryogenic storage tank 100, the BOG gas generated by the evaporation of the cryogenic material entering the cryogenic storage tank 100 is generally directly discharged to the flare system for combustion treatment, resulting in a very low recovery rate of the BOG gas, approximately about 3%, causing waste.

[0040] To solve this problem, a BOG gas reliquefaction system is added in this embodiment, and the BOG gas generated during the precooling of the cryogenic storage tank 100 is recovered to the cryogenic storage tank 100 through the reliquefaction system. After optimization, the recovery rate of the BOG gas can reach 98%, which greatly improves the recovery and utilization rate of the BOG gas and reduces the cost.

[0041] Specifically, the liquefaction process of BOG gas is as follows:

[0042] 1. Compression phase

[0043] BOG compressor 120: The BOG gas is first compressed by the BOG compressor 120 to increase its pressure. The higher pressure is helpful for the subsequent liquefaction of the gas.

[0044] 2. Initial cooling stage

[0045] Compressor aftercooler 130: The compressed BOG gas enters the compressor aftercooler 130 and is cooled by heat exchange with cooling water to prepare for the next cooling step.

[0046] 3. Secondary cooling stage

[0047] Propylene evaporator 140: After the initial cooling, the BOG gas enters the propylene evaporator 140 to exchange heat with the low-temperature propylene. The propylene evaporator 140 further reduces the temperature of the BOG gas by using a refrigerant (usually propylene) to make it close to the liquefaction point.

[0048] 4. Flash stage

[0049] Collecting tank 160: The BOG gas after secondary cooling enters the collecting tank 160 for flash evaporation. In this process, the BOG gas expands rapidly under a lower pressure, and part of the gas is liquefied due to the drop in temperature.

[0050] 5. Supercooling stage

[0051] Subcooler 170: The flashed BOG gas enters the subcooler 170 to further reduce its temperature to make it closer to the liquefaction point. The low temperature condition in the subcooler 170 helps more gas to liquefy.

[0052] 6. Final cooling stage

[0053] Cooler 180: The BOG gas from the subcooler 170 enters the cooler 180 for final temperature reduction treatment. The cooler 180 cools the BOG gas to a temperature very close to its liquefaction point. At this time, most of the gas should have been liquefied or very close to the liquefied state.

[0054] 7. Liquefaction completed

[0055] Cryogenic storage tank 100: The BOG gas after cooling finally enters the cryogenic storage tank 100 together with the new cryogenic material through the recovery pipeline 190. In this process, the BOG gas is mixed with the cryogenic material to further complete the liquefaction process.

[0056] That is, the liquefaction of BOG gas is a gradual cooling process. These devices work together to gradually reduce the temperature of BOG gas through multiple cooling, and finally complete liquefaction after mixing with low-temperature materials in the low-temperature storage tank 100. The entire process is designed to ensure that BOG gas can be effectively cooled and liquefied, thereby improving the recovery efficiency of BOG gas and reducing energy waste.

[0057] Preferably, the cryogenic storage tank 100 is provided with a tank precooling spray ring 102. The cryogenic material enters the tank precooling spray ring 102 after passing through the cryogenic material inlet manual valve 101, and then is evenly distributed inside the cryogenic storage tank 100, avoiding local overcooling or uneven precooling, and making the precooling of the entire cryogenic storage tank 100 more uniform.

[0058] Preferably, a BOG compressor inlet buffer tank 110 is further provided between the cryogenic storage tank 100 and the BOG compressor 120. The BOG compressor inlet buffer tank 110 is provided to stabilize the pressure of the BOG gas entering the compressor, thereby ensuring that the intake pressure of the compressor is relatively stable.

[0059] Preferably, a propylene refrigerator 150 is further included, which is connected to the propylene evaporator 140. The refrigerant enters the propylene evaporator 140 to cool the propylene and then flows back to the propylene refrigerator 150 and circulates in this way, ensuring that the propylene evaporator 140 can continuously and effectively cool the BOG gas.

[0060] Preferably, the collecting tank 160 is connected to the subcooler 170 through two parallel pipelines, and the BOG gas after flash evaporation in the collecting tank 160 is divided into two pipelines and transported to the subcooler 170, wherein the subcooler 170 is also unidirectionally connected to the BOG compressor 120 through a reflux pipeline, and a part of the BOG gas after primary cooling in the subcooler 170 enters the cooler 180, and the other part flows back to the BOG compressor 120 through the reflux pipeline.

[0061] The existence of the return line allows part of the preliminarily cooled BOG gas to return to the BOG compressor 120, ensuring that the compressor always has sufficient gas flow to prevent surge. This helps to further optimize the working state of the compressor and can also be used as a means of regulating the system to cope with changes in the BOG gas flow and ensure safe operation of the system.

[0062] Preferably, the BOG gas is cooled to -60°C in the supercooler 170 by adopting a 1 / 3-cold-1 / 2 method, that is, the BOG gas is cooled in stages in the supercooler 170, first cooled to a certain intermediate temperature, and finally cooled to -60°C, so as to more accurately control the cooling process. Subsequently, the BOG gas enters the cooler 180 and is cooled to -70°C, and the material is liquefied.

[0063] Preferably, the BOG gas output from the cooler 180 is inserted into the low-temperature material tank inlet manual valve 101 through the recovery line 190, and then sent into the storage tank precooling spray ring 102 together with the low-temperature material. This is because the material temperature has reached -70°C at this time, and the low-temperature storage tank 100 has just started precooling. Therefore, the reliquefied -70°C material cannot directly enter the low-temperature storage tank 100, but enters the storage tank precooling spray ring 102 together with the low-temperature material to precool the low-temperature storage tank 100, thereby ensuring that the temperature of the low-temperature storage tank 100 drops evenly during the precooling process and avoiding temperature difference stress caused by sudden temperature changes.

[0064] Preferably, a storage tank BOG outlet valve 103 and a BOG compressor inlet buffer tank valve 111 are provided on the pipeline between the low-temperature storage tank 100 and the BOG compressor inlet buffer tank 110;

[0065] A BOG compressor inlet valve 131 is provided on the pipeline between the BOG compressor inlet buffer tank 110 and the BOG compressor 120;

[0066] A propylene evaporator inlet valve 141 is provided on the pipeline between the compressor aftercooler 130 and the propylene evaporator 140;

[0067] A reliquefaction return spray ring valve 191 is provided on the pipeline between the cooler 180 and the tank pre-cooling spray ring 102.

[0068] By correspondingly controlling the flow at the location through various valves and setting valves on key pipelines, accurate control of each stage of the pre-cooling boil-off gas (BOG) recovery process of the cryogenic storage tank 100 can be achieved to ensure the safety and efficient operation of the system.

[0069] The technical means disclosed in the scheme of the present invention are not limited to the technical means disclosed in the above technical means, but also include technical schemes composed of any combination of the above technical features. The above is a specific implementation of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications are also regarded as the protection scope of the present invention.

[0070] It should be noted that all directional indications in the embodiments of the present invention (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0071] In addition, in the present invention, descriptions such as "first", "second", "one", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0072] In the present invention, unless otherwise clearly specified and limited, the terms "connection", "fixation", etc. should be understood in a broad sense. For example, "fixation" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0073] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

Claims

1. A low-temperature tank area low-temperature system pre-cooling boil-off gas recovery process, characterized in that: include: Cryogenic storage tank, the cryogenic material enters the cryogenic storage tank through the cryogenic material inlet manual valve to be pre-cooled. During the pre-cooling process, the cryogenic material generates BOG gas due to evaporation and is discharged to the outside; BOG compressor and compressor aftercooler, the BOG gas generated in the low-temperature storage tank enters the BOG compressor through the BOG pipeline, and the compressed BOG gas enters the compressor aftercooler to perform heat exchange with water; A propylene evaporator is connected to the compressor aftercooler, and the BOG gas after the primary heat exchange enters the propylene evaporator for secondary heat exchange with low-temperature propylene; A collecting tank connected to the propylene evaporator, wherein the BOG gas after the secondary heat exchange enters the collecting tank for flash evaporation; The subcooler and the cooler, the collecting tank is connected with the subcooler and the cooler in sequence, the BOG gas after flashing enters the subcooler for primary cooling, and then enters the cooler for secondary cooling, the BOG gas is liquefied after the secondary cooling and connected to the low-temperature material inlet valve through the recovery pipeline, and then enters the low-temperature storage tank together with the new low-temperature material.

2. A low-temperature tank area low-temperature system pre-cooling boil-off gas recovery process according to claim 1, characterized in that: The low-temperature storage tank is provided with a storage tank pre-cooling spray ring, and the low-temperature material enters the storage tank pre-cooling spray ring after passing through the low-temperature material tank inlet manual valve.

3. A low-temperature tank area low-temperature system pre-cooling boil-off gas recovery process according to claim 2, characterized in that: The BOG gas output from the cooler is introduced into the low-temperature material feed hand valve through a recovery pipeline, and then is sent into the pre-cooling spray ring of the storage tank together with the low-temperature material.

4. A low-temperature tank area low-temperature system pre-cooling boil-off gas recovery process according to claim 1, characterized in that: A BOG compressor inlet buffer tank is also provided between the low-temperature storage tank and the BOG compressor.

5. A low-temperature tank area low-temperature system pre-cooling boil-off gas recovery process according to claim 1, characterized in that: It also includes a propylene refrigerator, which is connected to the propylene evaporator. The refrigerant enters the propylene evaporator to cool the propylene and then flows back to the propylene refrigerator to circulate.

6. A low-temperature tank area low-temperature system pre-cooling boil-off gas recovery process according to claim 1, characterized in that: The collecting tank is connected to the supercooler through two parallel pipelines, and the BOG gas after flash evaporation in the collecting tank is split into two pipelines and transported to the supercooler.

7. A low-temperature tank area low-temperature system pre-cooling boil-off gas recovery process according to claim 1, characterized in that: The subcooler is also unidirectionally connected to the BOG compressor via a return line. After completing a cooling process in the subcooler, a portion of the BOG gas enters the cooler, and the other portion flows back to the BOG compressor via the return line.

8. A low-temperature tank area low-temperature system pre-cooling boil-off gas recovery process according to claim 1, characterized in that: The BOG gas is cooled to -60°C in the subcooler by using a 1 / 3 cooling 1 / 2 method.

9. A low-temperature tank area low-temperature system pre-cooling boil-off gas recovery process according to claim 1, characterized in that: The BOG gas is cooled to -70°C in the cooler.

10. A low-temperature tank area low-temperature system pre-cooling boil-off gas recovery process according to claim 1, characterized in that: The pipeline between the low-temperature storage tank and the BOG compressor inlet buffer tank is provided with a storage tank BOG outlet valve and a BOG compressor inlet buffer tank valve; A BOG compressor inlet valve is provided on the pipeline between the BOG compressor inlet buffer tank and the BOG compressor; A propylene evaporator inlet valve is provided on the pipeline between the compressor aftercooler and the propylene evaporator; A reliquefaction return spray ring valve is provided on the pipeline between the cooler and the storage tank pre-cooling spray ring.

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