A device and method for deep recovery of ethane from LNG

Abstract

The present invention discloses a device and a method for recovering ethane in LNG in depth, comprising an LNG storage tank, an LNG booster pump, a cold box, a demethanizer, a deethanizer and a reboiler, wherein the reboiler comprises a demethanizer reboiler and a deethanizer reboiler, one end of the LNG booster pump is connected to the LNG storage tank, and the other end is connected to the cold box, three heat exchange channels are arranged in the cold box, namely, a cold logistics LNG heat exchange channel, a high-pressure flash tower top gas phase heat exchange channel and a demethanizer top gas phase heat exchange channel, and also comprises a high-pressure flash washing tower and a washing booster pump, the inlet of the cold logistics LNG heat exchange channel is connected to the outlet of the LNG booster pump, and the outlet of the cold logistics LNG heat exchange channel is connected to the inlet of the high-pressure flash washing tower. The advantages of the present invention are: the recovery rate of ethane in LNG is increased from 90% in the conventional process to 99%; the equipment configuration is simple, and the operation is simple, cheap and feasible.

Description

Technical Field

[0001] The present invention relates to the technical field of natural gas processing, and in particular to a device and a method for deeply recovering ethane from LNG. Background Art

[0002] The main raw materials of domestic LNG receiving stations come from overseas LNG plants, and most LNG contains 2-8% ethane and above. Ethane is recovered from LNG, mainly as a raw material for ethylene production. With the construction and commissioning of ethylene plants using ethane as raw material, the demand for ethane will increase significantly. It has become necessary to deeply recover ethane from LNG. The existing light hydrocarbon recovery device of the receiving station pumps out low-temperature LNG from the LNG storage tank through a low-pressure pump, and after being pressurized by the booster pump of the device, heavy components such as C2 and LPG are extracted through heat exchange and flash evaporation. The problem with the existing process is that since the light hydrocarbon recovery device directly processes the low-temperature LNG output by the booster pump, the device needs to withstand a temperature of -164°C and a certain pressure (about 3MPa), which puts high requirements on the material of the light hydrocarbon recovery device, increases the cost of the device, and also has certain safety risks. The traditional process has a low yield of ethane recovered from LNG. Therefore, it is necessary to design a device for deeply recovering ethane from LNG, the purpose of which is to solve the defect of low yield of ethane recovered from LNG in the prior art. Summary of the invention

[0003] The present invention aims to solve the problem of low ethane recovery rate from LNG in the prior art.

[0004] The present invention is achieved through the following technical solutions:

[0005] A device for deep recovery of ethane in LNG, comprising an LNG storage tank, an LNG booster pump, a cold box, a demethanizer, a deethanizer and a reboiler, wherein the reboiler comprises a demethanizer reboiler and a deethanizer reboiler, one end of the LNG booster pump is connected to the LNG storage tank, and the other end is connected to the cold box, three heat exchange channels are arranged in the cold box, namely, a cold logistics LNG heat exchange channel, a high-pressure flash tower top gas phase heat exchange channel and a demethanizer top gas phase heat exchange channel, and also comprises a high-pressure flash washing tower and a washing booster pump, the inlet of the cold logistics LNG heat exchange channel is connected to the LN The outlet of the cold logistics LNG heat exchange channel is connected to the inlet of the high-pressure flash washing tower, the inlet of the gas-phase heat exchange channel at the top of the high-pressure flash washing tower is connected to the top outlet of the high-pressure flash washing tower, the outlet of the gas-phase heat exchange channel at the top of the high-pressure flash washing tower is connected to the inlet of the washing booster pump, the washing booster pump includes three branches, namely a first branch, a second branch and a third branch, the outlet of the first branch is connected to the inlet of the high-pressure flash washing tower, the outlet of the second branch is connected to the inlet of the demethanizer, and the third branch is connected to the LNG terminal.

[0006] The existing technology is that the existing light hydrocarbon recovery device of the receiving station pumps out low-temperature LNG from the LNG storage tank through a low-pressure pump, and after being pressurized by the device's booster pump, heavy components such as C2 and LPG are extracted through processes such as heat exchange and flash evaporation, but the recovery rate is low.

[0007] The present invention adds a washing booster pump and a high-pressure flash washing tower, adopts low-temperature LNG for re-contact washing, and adopts LNG reflux washing in the demethanizer, thereby achieving the purpose of deep recovery of ethane from LNG, and increasing the recovery rate of ethane in LNG from 90% in the conventional process to 99%.

[0008] Working process: LNG from the storage tank is pressurized by the LNG booster pump and sent to the cold box, and enters the high-pressure flash scrubber after heat exchange; the flash gas of the high-pressure flash scrubber returns to the cold box for liquefaction, and is pressurized by the scrubbing booster pump and sent to the top of the high-pressure scrubber and the top of the demethanizer, and is used as a scrubbing liquid to remove and recover ethane in the gas phase at the top of the tower, and the remainder is used as an LNG product; the liquid phase at the bottom of the high-pressure flash scrubber is divided into two parts, one part enters the upper part of the demethanizer, and the other part passes through the ethane supercooler and the top condenser of the demethanizer and enters the lower part of the demethanizer; the gas phase at the top of the demethanizer is returned to the cold box for liquefaction as an LNG product; the lower liquid phase of the demethanizer enters the middle part of the deethanizer.

[0009] Furthermore, the outlet of the first branch is provided with a high-pressure flash washing tower, a high-pressure flash washing tower bottom pump, a demethanizer, a deethanizer and an NGL terminal in sequence along the flow direction.

[0010] Furthermore, the high-pressure flash washing tower bottom pump includes two branches, namely a first branch and a second branch.

[0011] Further, the first branch is connected to the upper part of the demethanizer, and the second branch passes through the ethane subcooler, the deethanizer top condenser, and the lower part of the demethanizer in sequence;

[0012] The liquid phase at the bottom of the high-pressure flash washing tower is divided into two parts, one part enters the upper part of the demethanizer, and the other part enters the lower part of the demethanizer after passing through the ethane subcooler and the deethane tower top condenser.

[0013] Furthermore, the demethanizer reboiler and the demethanizer form a circulation loop.

[0014] Furthermore, the outlet of the demethanizer is connected to the inlet of the demethanizer reboiler, and the outlet of the demethanizer reboiler is connected to the inlet of the demethanizer.

[0015] Furthermore, the deethanizer reboiler and the deethanizer tower form a circulation loop.

[0016] Furthermore, the inlet of the deethanizer reboiler is connected to the outlet of the deethanizer, and the inlet of the deethanizer is connected to the outlet of the deethanizer reboiler.

[0017] A method for recovering ethane from LNG in depth comprises the following steps:

[0018] S1: First pressurization: LNG in the LNG storage tank is pressurized for the first time by the LNG booster pump;

[0019] S2: Heat exchange: After pressurization, it is sent to the cold box for heat exchange;

[0020] S3: First liquefaction: After heat exchange, LNG enters the high-pressure flash scrubber to generate flash gas, which returns to the cold box for the first liquefaction;

[0021] S4: Second pressurization: After liquefaction, the LNG washing booster pump performs the second pressurization;

[0022] S5: Recovery: The LNG after the second pressurization enters the top of the high-pressure flash washing tower and the top of the demethanizer as a washing liquid, and the washing liquid removes and recovers ethane in the gas phase at the top of the high-pressure flash washing tower and the top of the demethanizer;

[0023] S6: splitting: after recovery, the liquid phase at the bottom of the high-pressure flash washing tower is divided into two parts, one part enters the upper part of the demethanizer, and the other part enters the lower part of the demethanizer after heat exchange in the ethane subcooler and the deethane tower top condenser;

[0024] S7: Second liquefaction: The gas phase at the top of the demethanizer is returned to the cold box for a second liquefaction into LNG product.

[0025] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0026] 1. The present invention provides a device for deep recovery of ethane in LNG, which increases the recovery rate of ethane in LNG from 90% in the conventional process to 99%.

[0027] 2. The present invention provides a device for deep recovery of ethane from LNG, which has simple equipment configuration, simple and feasible operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0029] Figure 1 Schematic diagram of the device for recovering ethane from LNG.

[0030] 1-LNG storage tank, 2-LNG booster pump, 3-cold box, 4-high-pressure flash washing tower, 5-washing booster pump, 6-high-pressure flash washing tower bottom pump, 7-demethanizer, 8-demethanizer reboiler, 9-deethanizer, 10-deethanizer reboiler, 11-ethane subcooler, 12-deethanizer reflux tank, 13-reflux pump, 14-deethanizer top condenser. DETAILED DESCRIPTION

[0031] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0032] Embodiment 1:

[0033] like Figure 1 As shown, the present invention is a device for deep recovery of ethane in LNG, comprising an LNG storage tank 1, an LNG booster pump 2, a cold box 3, a demethanizer 7, a deethanizer 9 and a reboiler, wherein the reboiler comprises a demethanizer reboiler 8 and a deethanizer reboiler 10, one end of the LNG booster pump 2 is connected to the LNG storage tank 1, and the other end is connected to the cold box 3, three heat exchange channels are arranged in the cold box 3, namely, a cold logistics LNG heat exchange channel, a high-pressure flash tower top gas phase heat exchange channel and a demethanizer top gas phase heat exchange channel, and also comprises a high-pressure flash washing tower 4 and a washing booster pump 5, the cold logistics LNG heat exchange channel The inlet of the channel is connected to the outlet of the LNG boosting pump 2, the outlet of the cold logistics LNG heat exchange channel is connected to the inlet of the high-pressure flash washing tower 4, the inlet of the high-pressure flash tower top gas-phase heat exchange channel is connected to the top outlet of the high-pressure flash washing tower 4, the outlet of the high-pressure flash tower top gas-phase heat exchange channel is connected to the inlet of the washing boosting pump 5, the washing boosting pump 5 includes three branches, namely the first branch, the second branch and the third branch, the outlet of the first branch is connected to the inlet of the high-pressure flash washing tower 4, the outlet of the second branch is connected to the inlet of the demethanizer 7, and the third branch is connected to the LNG terminal.

[0034] Embodiment 2:

[0035] like Figure 1As shown, this embodiment is based on embodiment 1, and the outlet of the first branch is sequentially provided with a high-pressure flash washing tower 4, a high-pressure flash washing tower bottom pump 6, a demethanizer 7, a deethanizer 9 and an NGL terminal along the flow direction; the high-pressure flash washing tower bottom pump 6 includes two branches, namely a first branch and a second branch; the first branch is connected to the upper part of the demethanizer 7, and the second branch passes through an ethane subcooler 11, a deethanizer top condenser 14, and a lower part of the demethanizer 7 in sequence; the deethanizer top condenser 14 is connected to the deethanizer reflux tank 12; the demethanizer re The boiler 8 and the demethanizer 7 form a circulation loop; the outlet of the demethanizer 7 is connected to the inlet of the demethanizer reboiler 8, and the outlet of the demethanizer reboiler 8 is connected to the inlet of the demethanizer 7; the deethanizer reboiler 10 and the deethanizer 9 form a circulation loop; the inlet of the deethanizer reboiler 10 is connected to the outlet of the deethanizer 9, and the inlet of the deethanizer 9 is connected to the outlet of the deethanizer reboiler 10, the top gas phase of the demethanizer 7 is returned to the cold box 3 for liquefaction as an LNG product, and the lower liquid phase of the demethanizer 7 enters the middle part of the deethanizer 9.

[0036] Embodiment 3:

[0037] like Figure 1 As shown, this embodiment is based on Embodiments 1 and 2 to implement a recovery method of a device for deep recovery of ethane in LNG, comprising the following steps:

[0038] S1: First pressurization: LNG in LNG storage tank 1 is pressurized for the first time by LNG booster pump 2;

[0039] S2: heat exchange: after pressurization, it is sent to cold box 3 for heat exchange;

[0040] S3: First liquefaction: After heat exchange, LNG enters the high-pressure flash scrubber 4, and the flash gas generated is returned to the cold box 3 for the first liquefaction;

[0041] S4: Second pressurization: After liquefaction, the LNG washing booster pump 5 performs a second pressurization;

[0042] S5: Recovery: The LNG after the second pressurization enters the top of the high-pressure flash washing tower 4 and the top of the demethanizer 7 as a washing liquid, and the washing liquid removes and recovers ethane in the gas phase at the top of the high-pressure flash washing tower 4 and the top of the demethanizer 7, and the remainder is used as the LNG product;

[0043] S6: splitting: after recovery, the liquid phase at the bottom of the high-pressure flash washing tower 4 is divided into two parts, one part enters the upper part of the demethanizer 7, and the other part enters the lower part of the demethanizer 7 after heat exchange through the ethane subcooler 11 and the deethane tower top condenser 14;

[0044] S7: Second liquefaction: The gas phase at the top of the demethanizer 7 is returned to the cold box 3 for a second liquefaction to produce LNG product;

[0045] S8: The lower liquid phase of the demethanizer 7 enters the middle of the deethanizer 9.

[0046] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A device for deep recovery of ethane from LNG, comprising an LNG storage tank (1), an LNG booster pump (2), a cold box (3), a demethanizer (7), a deethanizer (9) and a reboiler, wherein the reboiler comprises a demethanizer reboiler (8) and a deethanizer reboiler (10), one end of the LNG booster pump (2) is connected to the LNG storage tank (1), and the other end is connected to the cold box (3), and three heat exchange channels are arranged in the cold box (3), namely, a cold logistics LNG heat exchange channel, a high-pressure flash tower top gas phase heat exchange channel and a demethanizer top gas phase heat exchange channel, characterized in that: It also comprises a high-pressure flash washing tower (4) and a washing booster pump (5), wherein the inlet of the cold logistics LNG heat exchange channel is connected to the outlet of the LNG booster pump (2), the outlet of the cold logistics LNG heat exchange channel is connected to the inlet of the high-pressure flash washing tower (4), the inlet of the gas-phase heat exchange channel at the top of the high-pressure flash washing tower is connected to the top outlet of the high-pressure flash washing tower (4), the outlet of the gas-phase heat exchange channel at the top of the high-pressure flash washing tower is connected to the inlet of the washing booster pump (5), and the washing booster pump (5) comprises three branches, namely a first branch, a second branch and a third branch, the outlet of the first branch is connected to the inlet of the high-pressure flash washing tower (4), the outlet of the second branch is connected to the inlet of the demethanizer (7), and the third branch is connected to the LNG terminal; The outlet of the first branch is provided with a high-pressure flash washing tower (4), a high-pressure flash washing tower bottom pump (6), a demethanizer (7), a deethanizer (9) and an NGL terminal in sequence along the flow direction; The high-pressure flash washing tower bottom pump (6) comprises two branches, namely a first branch and a second branch; the first branch is connected to the upper part of the demethanizer (7), and the second branch passes through the ethane subcooler (11), the demethanizer top condenser (14), and the lower part of the demethanizer (7) in sequence; The demethanizer reboiler (8) and the demethanizer (7) form a circulation loop.

2. The device for deep recovery of ethane from LNG according to claim 1, characterized in that: The outlet of the demethanizer (7) is connected to the inlet of the demethanizer reboiler (8), and the outlet of the demethanizer reboiler (8) is connected to the inlet of the demethanizer (7).

3. The device for deep recovery of ethane from LNG according to claim 1, characterized in that: The deethanizer reboiler (10) and the deethanizer (9) form a circulation loop.

4. The device for deep recovery of ethane from LNG according to claim 3, characterized in that: The inlet of the deethanizer reboiler (10) is connected to the outlet of the deethanizer (9), and the inlet of the deethanizer (9) is connected to the outlet of the deethanizer reboiler (10).

5. A recovery method of a device for deep recovery of ethane from LNG according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1: First pressurization: The LNG in the LNG storage tank (1) is pressurized for the first time by the LNG boosting pump (2); S2: Heat exchange: After the first pressurization, it is sent to the cold box (3) for heat exchange; S3: Liquefaction: After heat exchange, the LNG enters the high-pressure flash scrubber (4) to generate flash gas, which then returns to the cold box (3) for liquefaction; S4: Second pressurization: After liquefaction, the LNG is pressurized for the second time via a washing and boosting pump (5); S5: Recovery: The LNG after the second pressurization enters the top of the high-pressure flash washing tower (4) and the top of the demethanizer (7) as a washing liquid. The LNG removes and recovers the gaseous ethane at the top of the high-pressure flash washing tower (4) and the top of the demethanizer (7).

Images