Alkali washing tower system for preparing olefin from methanol

Abstract

The utility model discloses a methanol-to-olefin alkaline washing tower system which comprises a separating tower and an alkaline washing tower, the alkaline washing tower is connected with a gas inlet pipeline, the lower part of the alkaline washing tower is provided with an alkaline liquor circulating unit, the top of the alkaline washing tower is provided with a gas outlet pipeline, and the alkaline washing tower is connected with a water inlet pipeline and a water return pipeline; the bottom of the separation tower is provided with a separation tower bottom circulation, the separation tower bottom circulation is connected with a quenching water unit, and the separation tower bottom circulation is connected with a heater for heating the gas inlet pipeline through a quenching water circulation pipeline; according to the S-MTO device alkaline washing tower water washing system, a washing water recovery system process is arranged, a small part of washing water in the water washing section of the S-MTO device alkaline washing tower is directly fed into the quenching water system, the waste alkali liquid discharge amount of the alkaline washing tower is reduced, the fresh alkali consumption amount is reduced, the energy consumption is reduced, the energy consumption is reduced, and the energy consumption is reduced. Meanwhile, the waste alkali treatment burden of the waste alkali incineration device is reduced, the environmental protection risk is reduced, and device efficiency improvement is achieved.

Description

Technical Field

[0001] The utility model relates to the technical field of alkali washing towers, in particular to a methanol to olefins alkali washing tower system. Background Art

[0002] The methanol to olefins (S-MTO) unit is a methanol to olefins technology that uses the fluidized catalytic cracking process and the continuous reaction-regeneration method of the fluidized bed to convert methanol into basic organic chemical raw materials such as ethylene and propylene.

[0003] The process gas from an S-MTO unit primarily contains acidic gases such as CO2 and methyl / acetic acid. These acidic impurities can harm the unit, causing corrosion of piping and equipment and shortening the life of the molecular sieve. Acidic gases can also harm product synthesis. For example, during low-pressure ethylene polymerization, CO2 and sulfides can destroy catalytic activity. During high-pressure ethylene polymerization, CO2 accumulates in the circulating ethylene gas, reducing the ethylene partial pressure and thus affecting the polymerization rate and molecular weight of the polyethylene. For these reasons, acidic gases must be removed prior to separation. This unit utilizes an alkaline wash method, which involves adding a 20% caustic soda solution (NaOH) to wash the process gas. During the wash process, the NaOH reacts with the acidic gases in the process gas, producing carbonates that dissolve in the waste caustic soda, thereby removing these acidic gases.

[0004] The caustic scrubber is designed with three caustic scrubbing sections and one water scrubbing section. The process gas from the oxide water scrubber, along with crude propylene from the C4 unit, is heated to 45°C in the process gas heater (E-3006) before entering the caustic scrubber. In the middle and bottom sections of the caustic scrubber, the process gas is scrubbed with circulating caustic solutions of strong, medium, and weak alkali, respectively. The top section is the water scrubbing section, which scrubs the process gas after caustic scrubbing to prevent caustic foam from being carried to downstream equipment.

[0005] The process gas enters the bottom of the alkali scrubber, where it comes into countercurrent contact with a circulating weak alkali solution. As the gas flows upward, it is directly scrubbed by the circulating weak alkali solution, removing some of the acidic gases. The weak alkali is circulated by an alkali pump (P-3004A / B). After being scrubbed with the weak alkali, the process gas flows upward to the medium alkali scrubber, where an intermediate scrubber removes some of the acidic gases. The medium alkali is then circulated by an alkali pump (P-3005A / B). The process gas, still carrying a small amount of acidic gases, flows upward to the strong alkali scrubber, where it comes into contact with a circulating strong alkali solution to remove the remaining acidic gases. The strong alkali is circulated by an alkali pump (P-3006A / B). The CO2 content in the process gas leaving the alkali scrubber is less than 1 ml / m³.

[0006] The top of the caustic wash tower is the water wash section, which uses cooled fresh water to wash out entrained caustic foam. The water wash also cools the process gas to near the hydrocarbon dew point, removing excess water vapor before leaving the caustic wash tower. Fresh water from the water wash section (referred to as wash water) is sent to the spent caustic degassing tank (D-3010).

[0007] The waste caustic soda from the bottom of the caustic wash tower and the wash water from the top of the tower enter the waste caustic soda degassing tank (D-3010). The hydrocarbon gas flashed out of the waste caustic soda degassing tank is recovered and sent to the first suction tank of the process gas compressor. The degassed waste caustic soda is ultimately sent to the waste caustic soda treatment facility.

[0008] When the S-MTO unit is operating normally, the water washing section of the caustic scrubber must maintain a certain amount of fresh water. Excessive water flow will prevent the complete removal of caustic foam carried by the process gas, causing corrosion to downstream production equipment and pipelines, and damage to the desiccant. The washing water from the water washing section is sent to the spent caustic degassing tank for degassing, and some of the process gas is recovered.

[0009] To ensure the alkali washing effect, when the S-MTO unit is in normal production, the amount of fresh water in the water washing section needs to be increased. However, the increase in the amount of fresh water in the water washing section will lead to an increase in the amount of washing water sent to the waste alkali degassing tank, an increase in the generation of waste alkali, and ultimately an increase in the discharge of waste alkali, affecting the efficiency of the unit. Utility Model Content

[0010] The purpose of the utility model is to provide a methanol to olefins alkaline washing tower system to solve the problems raised in the above background technology.

[0011] To achieve the above objectives, the present invention provides the following technical solutions:

[0012] A methanol to olefins alkali scrubber system comprises a separation tower and an alkali scrubber, wherein the alkali scrubber is connected to an air inlet pipeline, an alkali solution circulation unit is provided at the bottom of the alkali scrubber, an air outlet pipeline is provided at the top of the alkali scrubber, and the alkali scrubber is connected to a water inlet pipeline and a water return pipeline;

[0013] The bottom of the separation tower is provided with a separation tower bottom circulation, the separation tower bottom circulation is connected to a quenching water unit, and the separation tower bottom circulation is connected to a heater for heating the air inlet pipeline through a quenching water circulation pipeline;

[0014] The return water pipeline is connected to the water outlet of the heater on the quenching water circulation pipeline through a connecting pipeline.

[0015] As a further solution of the present invention: the alkali solution circulation unit includes a weak alkali circulation pipeline, a medium alkali circulation pipeline, and a strong alkali circulation pipeline arranged in sequence from bottom to top.

[0016] As a further solution of the present invention: a strong alkali liquid inlet pipe is connected to the strong alkali circulation pipeline, and the strong alkali liquid inlet pipe is connected with the water inlet pipeline and the return water pipeline through a regulating pipeline.

[0017] As a further solution of the present invention: a waste alkali liquid discharge pipe is provided at the bottom of the alkali washing tower.

[0018] As a further solution of the present invention: a separation tower top circulation is provided at the upper portion of the separation tower, and a separation tower middle circulation is provided at the middle portion of the separation tower.

[0019] As a further solution of the present invention: a circulating pump is provided in the bottom circulation of the separation tower, the water outlet end of the circulating pump is respectively connected to the heater and the quenching water unit, a quenching water heater is provided in the quenching water unit, the water outlet end of the quenching water heater is connected to a reboiler group, and the reboiler group is provided with a bypass pipeline.

[0020] As a further solution of the present invention: the water outlet of the heater, the water outlet of the connecting pipe, and the water outlet of the reboiler group are connected to the propylene tower reboiler, and the water outlet of the propylene tower reboiler is connected to the separation tower through a circuit breaker.

[0021] As a further solution of the present invention: the reboiler group includes a deethanizer reboiler, a C2 hydrogenation reactor feed heater, and a depropanizer reboiler arranged in parallel.

[0022] Compared with the prior art, the beneficial effects of the present invention are: the present invention has a novel structure.

[0023] 1. This application sets up a washing water recovery system process, which directly sends a small portion of the washing water from the washing section of the alkali washing tower of the S-MTO unit into the quenching water system, thereby reducing the discharge of waste alkali liquid from the alkali washing tower, reducing the consumption of fresh alkali, and at the same time reducing the waste alkali treatment burden of the waste alkali incineration device, reducing environmental risks, and achieving device efficiency improvement.

[0024] 2. A smaller portion of the washing water in the device of the present application is directly fed into the quenching water system. Firstly, the washing water can be degassed in the reverse regeneration separation tower; secondly, the reverse regeneration process gas is weakly acidic and needs to be injected into the separation tower with a 3% concentration of alkali solution for neutralization. A small portion of the washing water is introduced into the quenching water system, which can reduce the amount of alkali injected into the separation tower.

[0025] 3. The device of this application is implemented internally, which is simple to implement, with a short process and low investment. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the caustic washing tower system diagram of this embodiment;

[0027] In the figure: 1-separation tower, 2-separation tower top circulation, 3-separation tower middle circulation, 4-separation tower bottom circulation, 5-air inlet pipeline, 6-alkali washing tower, 7-heater, 8-quenching water unit, 9-quenching water circulation pipeline, 10-air outlet pipeline, 11-water inlet pipeline, 12-regulating pipeline, 13-return pipeline, 14-waste alkali liquid discharge pipe, 15-weak alkali circulation pipeline, 16-medium alkali circulation pipeline, 17-strong alkali circulation pipeline, 18-alkali liquid inlet pipe, 19-connecting pipeline, 20-reboiler group, 21-quenching water heater, 22-propylene tower reboiler. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0029] See also Figure 1 In an embodiment of the present invention, a methanol-to-olefins alkali washing tower system includes a separation tower 1 and an alkali washing tower 6. A separation tower top circulation 2 is provided at the upper portion of the separation tower 1, a separation tower middle circulation 3 is provided at the middle portion of the separation tower 1, and a separation tower bottom circulation 4 is provided at the bottom of the separation tower 1.

[0030] The alkali washing tower 6 is connected to the air inlet pipeline 5, the top of the alkali washing tower 6 is provided with an air outlet pipeline 10, the alkali washing tower 6 is connected to the water inlet pipeline 11 and the return water pipeline 13, the bottom of the alkali washing tower 6 is provided with a waste alkali liquid discharge pipe 14, and the lower part of the alkali washing tower 6 is provided with an alkali liquid circulation unit, which includes a weak alkali circulation pipeline 15, a medium alkali circulation pipeline 16, and a strong alkali circulation pipeline 17 arranged from bottom to top. The strong alkali circulation pipeline 17 is connected to a strong alkali liquid inlet pipe 18, and the strong alkali liquid inlet pipe 18 is connected to the water inlet pipeline 11 and the return water pipeline 13 through the regulating pipe 12.

[0031] The bottom circulation 4 of the separation tower is connected to a quenching water unit 8, and the bottom circulation 4 of the separation tower is connected to a heater 7 for heating the air inlet pipeline 5 through a quenching water circulation pipeline 9. The heater 7 adopts a horizontal floating head heat exchanger, and the return water pipeline 13 is connected to the water outlet of the heater 7 on the quenching water circulation pipeline 9 through a connecting pipeline 19.

[0032] A circulating pump is provided in the bottom circulation 4 of the separation tower, and the water outlet of the circulating pump is connected to the heater 7 and the quenching water unit 8 respectively. A quenching water heater 21 is provided in the quenching water unit 8, and the water outlet of the quenching water heater 21 is connected to the reboiler group 20. The reboiler group 20 is provided with a bypass pipeline. The water outlet of the heater 7, the water outlet of the connecting pipeline 19, and the water outlet of the reboiler group 20 are connected to the propylene tower reboiler 22. The water outlet of the propylene tower reboiler 22 is connected to the separation tower 1 through a circuit breaker. The reboiler group 20 includes a deethanizer reboiler, a carbon two hydrogenation reactor feed heater, and a depropanizer reboiler arranged in parallel.

[0033] When the utility model is in use, a DN40 pipeline is connected from the washing water return pipeline of the alkali washing tower washing section of the alkali washing unit of the S-MTO device to the outlet pipeline of the process gas heater of the alkali washing unit of the quenching water system of the device.

[0034] During normal operation of the S-MTO unit, the original wash water from the caustic wash column, which was discharged to the waste caustic degassing tank, is now fed into the quench water system. This water enters the quench water system and is then fed to the propylene column reboiler before entering the reactor-reprocessor separation tower. This streamlined process allows for increased fresh wash water usage at the caustic wash column overhead, improving process gas washing efficiency, further enhancing product quality, and reducing the risk of corrosion in system equipment without increasing the amount of waste caustic liquid discharged. The recycled wash water is then fed into the quench water system. The S-MTO unit's quench water system feeds this water to the reactor-reprocessor separation tower for degassing, recovering a portion of the process gas. This increased volume of recycled wash water allows the weakly alkaline wash water to neutralize the weakly acidic process gas in the separation tower, effectively reducing the caustic injection rate in the separation tower by approximately 13%. The maximum amount of recycled wash water accounts for approximately 42% of the fresh water injected into the caustic wash column overhead. A portion (approximately 58%) of this wash water is fed to the caustic wash column's strong caustic pump inlet to adjust the fresh caustic concentration and maintain the circulating caustic concentration in each stage.

[0035] Domestically, waste caustic soda discharged from caustic wash towers is typically sent to incinerators for combustion, increasing production costs and environmental risks. Furthermore, the high failure rate of incinerators presents a production challenge within the industry. The present invention significantly reduces the amount of waste caustic soda discharged from caustic wash towers while increasing the amount of fresh wash water used at the top of the towers, improving the effectiveness of process gas water washing, further enhancing product quality, and reducing the risk of corrosion in system equipment. The recovered wash water ultimately enters a separation tower for degassing, recovering a portion of the process gas from this water stream, meeting original design requirements while also reducing the amount of caustic soda injected into the separation tower, thereby reducing costs and increasing efficiency.

[0036] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the present invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be encompassed within the present invention. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

[0037] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A methanol to olefins alkali washing tower system, comprising a separation tower (1) and an alkali washing tower (6), characterized in that: The alkali washing tower (6) is connected to an air inlet pipeline (5), an alkali solution circulation unit is provided at the lower part of the alkali washing tower (6), an air outlet pipeline (10) is provided at the top of the alkali washing tower (6), and the alkali washing tower (6) is connected to a water inlet pipeline (11) and a water return pipeline (13); A separation tower bottom circulation (4) is provided at the bottom of the separation tower (1), the separation tower bottom circulation (4) is connected to a quenching water unit (8), and the separation tower bottom circulation (4) is connected to a heater (7) for heating an air inlet pipeline (5) via a quenching water circulation pipeline (9); The return water pipeline (13) is connected to the water outlet of the heater (7) on the quenching water circulation pipeline (9) through a connecting pipeline (19).

2. A methanol to olefins alkali scrubber system according to claim 1, characterized in that: The alkali solution circulation unit comprises a weak alkali circulation pipeline (15), a medium alkali circulation pipeline (16), and a strong alkali circulation pipeline (17) which are arranged in sequence from bottom to top.

3. A methanol to olefins alkali scrubber system according to claim 2, characterized in that: The strong alkali circulation pipeline (17) is connected to a strong alkali liquid inlet pipe (18), and the strong alkali liquid inlet pipe (18) is communicated with the water inlet pipeline (11) and the water return pipeline (13) through a regulating pipeline (12).

4. A methanol to olefins alkali scrubber system according to claim 1, characterized in that: A waste alkali liquid discharge pipe (14) is provided at the bottom of the alkali washing tower (6).

5. A methanol to olefins alkali scrubber system according to claim 1, characterized in that: The upper part of the separation tower (1) is provided with a separation tower top circulation (2), and the middle part of the separation tower (1) is provided with a separation tower middle circulation (3).

6. A methanol to olefins alkali scrubber system according to claim 1, characterized in that: A circulation pump is provided in the bottom circulation (4) of the separation tower, and the water outlet of the circulation pump is respectively connected to the heater (7) and the quenching water unit (8). A quenching water heater (21) is provided in the quenching water unit (8), and the water outlet of the quenching water heater (21) is connected to a reboiler group (20), and the reboiler group (20) is provided with a bypass pipeline.

7. A methanol to olefins alkali scrubber system according to claim 6, characterized in that: The water outlet end of the heater (7), the water outlet end of the connecting pipe (19), and the water outlet end of the reboiler group (20) are connected to the propylene tower reboiler (22), and the water outlet end of the propylene tower reboiler (22) is connected to the separation tower (1) through a circuit breaker.

8. The methanol to olefins alkali scrubber system according to claim 6, characterized in that: The reboiler group (20) includes a deethanizer reboiler, a C2 hydrogenation reactor feed heater, and a depropanizer reboiler arranged in parallel.

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