Acrylic acid oxidation unit energy-saving start-up system

Abstract

The utility model relates to the technical field of acrylic acid preparation, in particular to an energy-saving starting system of an acrylic acid oxidation unit. According to the utility model, the turbine fresh fan is connected with the electrically-driven circulating fan in parallel, the outlet of each fan is provided with a check valve, the inlet of the electrically-driven circulating fan is additionally provided with a purified air pipeline and a fresh air suction inlet, the idle electrically-driven circulating fan is utilized to provide fresh air at the initial stage of driving, and when the oxidation load is increased to 40-50%, the byproduct medium-pressure steam is merged into a pipe network, so that the oxidation load is reduced. At the moment, a turbine fresh fan is started, fan switching is conducted, and the stopped electric drive circulating fan is started again to conduct reactor circulating gas switching after follow-up conditions are met. Steam used by the turbine fresh fan can be met only by a small amount of externally supplied medium-pressure steam, and meanwhile, backpressure exhaust steam of the turbine fresh fan is directly sent to a refining system to provide a heat source.

Description

TECHNICAL FIELD

[0001] The utility model relates to acrylic acid preparation technical field, concretely relates to a kind of acrylic acid oxidation unit energy-saving system. BACKGROUND

[0002] Propylene is widely used in acrylic acid generation two-step oxidation method, and propylene and air are used as raw materials, in the presence of water vapor and other inert gases, the first step is that propylene is oxidized to form propylene aldehyde under the action of air and catalyst, and the second step is that propylene aldehyde is further oxidized to form acrylic acid under the action of air and catalyst. The reaction heat is removed by a forced molten salt circulating pump, and 2.0MPa saturated steam is generated by heat exchange with water through a heat exchanger, and then superheated steam is generated by waste gas catalytic incineration unit. The oxidation unit is equipped with a fresh air compressor driven by a turbine and a circulating gas compressor driven by an electric motor. During normal production, the oxidation reaction self-produced steam is used as the power to drive the turbine, and the turbine back pressure exhaust steam is sent to the refining system to provide heat source.

[0003] In order to avoid the reaction into the explosion zone in the initial stage of starting, a large amount of medium-pressure steam is needed as a dilution medium when feeding. After the load is increased to 70% and the parameters are relatively stable, the circulating gas compressor is started, and part of the tail gas rich in water vapor and nitrogen on the top of the absorption tower is recycled back to the reactor to replace part of the medium-pressure steam. At the same time, the amount of waste gas is small and the concentration of organic matter is low in the initial stage of starting, which cannot maintain the catalytic incineration temperature, and the saturated steam cannot be superheated, and the waste gas cannot be discharged up to the standard. The concentration of acrylic acid in the tower kettle of the absorption tower is low, which does not have the condition to be sent to the subsequent refining system for purification, and the turbine back pressure exhaust gas has no steam equipment, which is forced to be empty, resulting in serious energy waste. UTILITY MODEL CONTENTS

[0004] The utility model discloses to solve the problem of large amount of medium-pressure steam used in the initial stage of starting of acrylic acid oxidation unit and reduce energy waste, and provide a kind of acrylic acid oxidation unit energy-saving system.

[0005] In order to solve the above problems, the technical scheme of the utility model is:

[0006] The energy-saving driving system of the acrylic acid oxidation unit, comprising a turbine fresh air fan and an electric driving circulating fan, the outlets of the turbine fresh air fan and the electric driving circulating fan are connected through turbine fan outlet pipelines and circulating fan outlet pipelines respectively, a fan outlet communication valve is arranged on the circulating fan outlet pipeline, a turbine fan inlet guide vane is arranged on the turbine fresh air fan inlet, an electric driving circulating fan inlet guide vane is arranged on the electric driving circulating fan inlet, a purified air pipeline is connected to the inlets of the turbine fresh air fan and the electric driving circulating fan, the purified air pipeline is connected to the inlet of the electric driving circulating fan through a circulating fan inlet pipeline, the turbine fan outlet pipeline and the circulating fan outlet pipeline converge in a gas transportation main pipeline, a circulating fan gas transportation pipeline is arranged on the circulating fan outlet pipeline, the gas transportation main pipeline is connected to a first oxidation reaction device and a second oxidation reaction device arranged in series through a mixer, a circulating fan gas transportation pipeline, a medium-pressure steam pipeline and a preheated propylene pipeline are arranged on the mixer before the first oxidation reaction device, the outlet of the second oxidation reaction device is connected to an absorption tower, the bottom of the absorption tower is connected to a refining system, one end of a tower top waste gas transportation pipeline is connected to the top of the absorption tower, the other end of the tower top waste gas transportation pipeline is divided into a circulating gas transportation pipeline and a burning feed pipeline, the circulating gas transportation pipeline is connected to the circulating fan inlet pipeline, the burning feed pipeline is connected to a plate heat exchanger, an electric heater, a catalytic burning device and a steam superheater in sequence, and the outlet of the steam superheater is connected to the plate heat exchanger through a circulating pipeline; the first oxidation reaction device and the second oxidation reaction device are provided with a heat exchanger, the heat exchanger is connected to a steam superheater through a saturated steam pipeline, the steam superheater is connected to the turbine fresh air fan through a superheated steam pipeline, and the turbine fresh air fan is connected to the refining system through a low-pressure steam pipeline.

[0007] The waste gas catalytic burning unit is provided with a plate heat exchanger and an electric heater, is used for waste gas heating, and maintains the waste gas catalytic burning temperature at 450-500 DEG C.

[0008] The first oxidation reaction device and the second oxidation reaction device are provided with catalysts in the tube banks, the shell sides are filled with molten salt, and a molten salt circulating pump, a heat exchanger and a steam drum are arranged outside, the molten salt circulation removes the reactor, and 2.0 MPa saturated steam is generated.

[0009] The first oxidation reaction device and the second oxidation reaction device are used in series, propylene generates propylene aldehyde in the first oxidation reaction device, and generates acrylic acid in the second oxidation reaction device, and the peroxidation reaction problem is effectively avoided.

[0010] Further, the plate heat exchanger outlet is connected to a tail gas discharge port.

[0011] Further, the upper portion of the absorption tower is provided with a quenching water pipeline.

[0012] Further, the gas transportation main pipeline is divided into a first gas transportation branch pipeline and a second gas transportation branch pipeline, the first gas transportation branch pipeline is connected with the first mixer inlet of the medium-pressure steam pipeline, the circulating fan gas transportation pipeline is connected with the first mixer inlet, the first mixer outlet is connected with the second mixer inlet, the preheated propylene pipeline is connected with the second mixer inlet, the second mixer outlet is connected with the first oxidation reaction device through a pipeline, the outlet of the first oxidation reaction device and the second gas transportation branch pipeline are connected with the inlet of the third mixer, and the outlet of the third mixer is connected with the inlet of the second oxidation reaction device through a pipeline.

[0013] Further, the circulating fan outlet pipeline is provided with a first check valve, and the turbine fan outlet pipeline is provided with a second check valve.

[0014] Further, the circulating fan outlet pipeline is provided with a circulating fan anti-surge pipeline, and the circulating fan anti-surge pipeline is provided with a circulating fan anti-surge valve.

[0015] Further, the turbine fan outlet pipeline is provided with a turbine fan anti-surge pipeline, and the turbine fan anti-surge pipeline is provided with a turbine fan anti-surge valve.

[0016] The turbine fresh fan and the electrically-driven circulating fan are provided with turbine fan inlet guide vanes, circulating fan inlet guide vanes, outlet turbine fan anti-surge valves and circulating fan anti-surge valves, the inlet guide vanes and the outlet anti-surge valves are adjusted according to the operating conditions of the fans, and the two fans are switched stably.

[0017] Further, the circulating gas transportation pipeline is provided with a circulating gas inlet valve, and the purified air pipeline is provided with a purified air cut-off valve.

[0018] Working principle:

[0019] The purification air cut-off valve on the purification air pipeline connected with the electric drive circulating fan inlet is opened, the circulating gas inlet valve is closed, the circulating fan anti-surge valve is fully opened, the circulating fan inlet guide vane is closed to the minimum opening degree, the fan outlet communication valve is opened, the electric drive circulating fan is started, the purification air provided by the electric drive circulating fan passes through the circulating fan outlet pipeline, the gas transportation main pipeline, the first gas transportation branch pipeline and the medium-pressure steam pipeline, is mixed in the first mixer, enters the second mixer, is mixed with the hot propylene in the preheated propylene pipeline, enters the first oxidation reaction device, is discharged from the first oxidation reaction device after oxidation reaction, enters the third mixer and is mixed with the purification air from the second gas transportation branch pipeline, enters the second oxidation reaction device for further reaction, then enters the absorption tower, is absorbed by the quenching water from the tower upper quenching water pipeline, the aqueous solution of acrylic acid exists at the tower bottom, is transported to the refining system, the tail gas generated at the tower top is transported through the tower top waste gas transportation pipeline, is transported through the incineration feed pipeline after being heated by the plate heat exchanger and the electric heater, enters the catalytic incineration device for incineration treatment of the organic matter, returns to the plate heat exchanger after being heated by the steam superheater to heat the tail gas from the tower top, is transported to the tail gas discharge port for treatment and discharge after being treated, when the oxidation load is increased to 40-50%, the 2.0MPa saturated steam from the heat exchangers of the first oxidation reaction device and the second oxidation reaction device is transported to the steam superheater through the saturated steam pipeline to heat the saturated steam to 300 DEG C by using the temperature of the gas after incineration to obtain superheated steam, the superheated steam is transported to the turbine fresh fan through the superheated steam pipeline, at this time, the turbine fan anti-surge valve is fully opened, the turbine fan inlet guide vane is closed to the minimum opening degree, the turbine fresh fan is started, the inlet guide vanes and the anti-surge valves of the two fans are adjusted, the switching of the two fans is gradually completed, until the electric drive circulating fan is stopped, the fan outlet communication valve is closed, the electric drive circulating fan returns to the standby state, and the low-pressure steam discharged by the turbine fresh fan back pressure is transported to the refining system as steam for the refining system.

[0020] The utility model has the advantages that:

[0021] 1) the utility model discloses a method for reducing the medium-pressure steam consumption of the acrylic acid oxidation unit in the initial stage of starting, reducing energy waste, connecting the turbine fresh fan and the electric drive circulating fan in parallel, providing fresh air by the idle electric drive circulating fan in the initial stage of starting, when the oxidation load is increased to 40-50%, the by-product medium-pressure steam is connected to the pipeline network, the turbine fresh fan is started to switch the fans, and the electric drive circulating fan is started to switch the reactor circulating gas when the subsequent conditions are met. Only a small amount of external medium-pressure steam can meet the steam demand of the turbine fresh fan, and the steam discharged by the turbine fresh fan back pressure is directly sent to the refining system to provide heat.

[0022] 2) The utility model discloses a compressor of different forms of power drive in the initial stage of starting is optimized, and low-pressure steam emptying is greatly reduced, and energy waste is reduced. The turbine fresh air fan provides fresh air, and the air volume is large. The electric drive circulating fan provides circulating air, and the air volume is small. In the initial stage of starting, the acrylic acid concentration is low, and the condition of sending to the subsequent refining system is not provided. The turbine fresh air fan back pressure steam has no heat user, and steam is emptied, causing energy waste. At the same time, the steam amount required for starting the turbine fresh air fan is also large. The electric drive circulating fan is used to start first, and the turbine fresh air fan is not started, so that the steam amount of external acquisition is reduced. With the load increasing, the fresh air volume gradually increases. After 40-50% load, the electric drive circulating fan air volume is insufficient to provide the reactor air volume requirement, and the turbine fresh air fan is started. At this time, part of the self-produced steam is connected into the pipe network, and steam can be provided for the turbine fresh air fan start, so that the steam of external acquisition is reduced.

[0023] 3) The utility model discloses a waste gas catalytic incineration unit is provided with electric heater, realizes the treatment of waste gas, and the superheat of saturated steam reaches the initial stage of starting waste gas discharge up to standard. ACCURACY

[0024] The drawings described here are used to provide further understanding of the utility model, and constitute a part of the utility model. The illustrative embodiment and the description of the utility model are used to explain the utility model, and do not constitute improper limitation to the utility model. In the drawings:

[0025] Figure 1 The structure diagram of the acrylic acid oxidation unit energy-saving starting system of the utility model discloses a structure diagram of the acrylic acid oxidation unit energy-saving starting system.

[0026] In the figure: 1, turbine fresh air fan; 101, turbine fan inlet guide vane; 2, electrically driven circulating fan; 201, circulating fan inlet guide vane; 3, purified air pipeline; 301, purified air shut-off valve; 4, circulating fan inlet pipeline; 5, circulating fan outlet pipeline; 6, turbine fan outlet pipeline; 7, circulating fan anti-surge valve; 8, turbine fan anti-surge valve; 9, fan outlet communication valve; 10, first check valve; 11, second check valve; 12, gas transportation main pipeline; 13, circulating fan gas transportation pipeline; 14, medium-pressure steam pipeline; 15, preheated propylene pipeline; 16, first mixer; 17, second mixer; 18, second gas transportation branch line; 19, first oxidation reaction device; 20, second oxidation reaction device; 21, third mixer; 22, saturated steam pipeline; 23, absorption tower; 24, quenching water pipeline; 25, tower top waste gas transportation pipeline; 26, incineration feed pipeline; 27, circulating gas transportation pipeline; 2701, circulating gas inlet valve; 28, plate heat exchanger; 29, electric heater; 30, catalytic incineration device; 31, steam superheater; 32, circulating pipeline; 33, superheated steam pipeline; 34, tail gas discharge port; 35, low-pressure steam pipeline; 36, first gas transportation branch line; 37, refining system. DETAILED DESCRIPTION

[0027] The utility model can be understood in combination with the following examples.

[0028] In one embodiment, as Figure 1As shown, the energy-saving starting system of the acrylic acid oxidation unit comprises a turbine fresh air fan 1 and an electrically-driven circulating fan 2. The outlets of the turbine fresh air fan 1 and the electrically-driven circulating fan 2 are connected through a turbine fan outlet pipeline 6 and a circulating fan outlet pipeline 5 respectively. The circulating fan outlet pipeline 5 is provided with a fan outlet communication valve 9. The turbine fresh air fan 1 is provided with turbine fan inlet guide vanes 101. The electrically-driven circulating fan 2 is provided with circulating fan inlet guide vanes 201. A purified air pipeline 3 is connected to the inlets of the turbine fresh air fan 1 and the electrically-driven circulating fan 2 respectively. The purified air pipeline 3 is connected to the inlet of the electrically-driven circulating fan 2 through a circulating fan inlet pipeline 4. The turbine fan outlet pipeline 6 and the circulating fan outlet pipeline 5 converge at a gas transportation main pipeline 12. The circulating fan outlet pipeline 5 is provided with a circulating fan gas transportation pipeline 13. The gas transportation main pipeline 12 is connected to a first oxidation reaction device 19 and a second oxidation reaction device 20 arranged in series through a mixer. The mixer before the first oxidation reaction device 19 is provided with the circulating fan gas transportation pipeline 13, a medium-pressure steam pipeline 14 and a preheated propylene pipeline 15. The outlet of the second oxidation reaction device 20 is connected to an absorption tower 23. The bottom of the absorption tower 23 is connected to a refining system 37. One end of a tower top waste gas transportation pipeline 25 is connected to the top of the absorption tower 23. The other end of the tower top waste gas transportation pipeline 25 is divided into a circulating gas transportation pipeline 27 and a burning feed pipeline 26. The circulating gas transportation pipeline 27 is connected to the circulating fan inlet pipeline 4. The burning feed pipeline 26 is sequentially connected to a plate heat exchanger 28, an electric heater 29, a catalytic burning device 30 and a steam superheater 31. The outlet of the steam superheater 31 is connected to the plate heat exchanger 28 through a circulating pipeline 32. The first oxidation reaction device 19 and the second oxidation reaction device 20 are provided with heat exchangers. The heat exchangers are connected to the steam superheater 31 through a saturated steam pipeline 22. The steam superheater 31 is connected to the turbine fresh air fan 1 through a superheated steam pipeline 33. The turbine fresh air fan 1 is connected to the refining system 37 through a low-pressure steam pipeline 35.

[0029] The waste gas catalytic burning unit is provided with the plate heat exchanger 28 and the electric heater 29 for heating the waste gas so that the catalytic burning temperature of the waste gas is maintained at 450-500℃.

[0030] The first oxidation reaction device 19 and the second oxidation reaction device 20 are provided with catalysts in the tube banks and are filled with molten salt in the shell sides. A molten salt circulating pump, a heat exchanger and a steam drum are arranged outside the first oxidation reaction device 19 and the second oxidation reaction device 20. The molten salt circulation removes the reactors, thereby generating 2.0MPa saturated steam.

[0031] The first oxidation reaction device 19 and the second oxidation reaction device 20 are used in series. Propylene generates propylene aldehyde in the first oxidation reaction device and generates acrylic acid in the second oxidation reaction device, thereby effectively avoiding the problem of peroxidation reaction.

[0032] It can be understood that the outlet of the plate heat exchanger 28 is connected to a tail gas discharge port 34.

[0033] It can be understood that the absorption tower 23 is provided with a quenching water pipeline 24 at the upper part.

[0034] It can be understood that the gas transportation main pipeline 12 is divided into a first gas transportation branch pipeline 36 and a second gas transportation branch pipeline 18, the first gas transportation branch pipeline 36 is connected with the inlet of the first mixer 16, the circulating fan gas transportation pipeline 13 is connected with the inlet of the first mixer 16, the outlet of the first mixer 16 is connected with the inlet of the second mixer 17, the preheated propylene pipeline 15 is connected with the inlet of the second mixer 17, the outlet of the second mixer 17 is connected with the inlet of the first oxidation reaction device 19 through a pipeline, the outlet of the first oxidation reaction device 19 is connected with the inlet of the third mixer 21 through the second gas transportation branch pipeline 18, and the outlet of the third mixer 21 is connected with the inlet of the second oxidation reaction device 20 through a pipeline.

[0035] It can be understood that the circulating fan outlet pipeline 5 is provided with a first check valve 10, and the turbine fan outlet pipeline 6 is provided with a second check valve 11.

[0036] It can be understood that the circulating fan outlet pipeline 5 is provided with a circulating fan anti-surge pipeline, and the circulating fan anti-surge pipeline is provided with a circulating fan anti-surge valve 7.

[0037] It can be understood that the turbine fan outlet pipeline 6 is provided with a turbine fan anti-surge pipeline, and the turbine fan anti-surge pipeline is provided with a turbine fan anti-surge valve 8.

[0038] The turbine fresh fan 1 and the electrically driven circulating fan 2 are provided with turbine fan inlet guide vanes 101, circulating fan inlet guide vanes 201, and the outlets are provided with a turbine fan anti-surge valve 8 and a circulating fan anti-surge valve 7, according to the operating conditions of the fan, the inlet guide vanes and the outlet anti-surge valves are adjusted, and stable switching of the two fans is realized.

[0039] It can be understood that the circulating gas transportation pipeline 27 is provided with a circulating gas inlet valve 2701, and the purified air pipeline 3 is provided with a purified air cut-off valve 301.

[0040] Working principle:

[0041] The purification air cut-off valve 301 on the purification air pipeline 3 connected with the inlet of the electrically driven circulating fan 2 is opened, the circulating gas inlet valve 2701 is closed, the circulating fan anti-surge valve 7 is fully opened, the circulating fan inlet guide vane 201 is closed to the minimum opening degree, the fan outlet communication valve 9 is opened, the electrically driven circulating fan 2 is started, the purification air provided by the electrically driven circulating fan 2 enters the first mixer 16 after being mixed with the medium-pressure steam in the medium-pressure steam pipeline 14 through the circulating fan outlet pipeline 5, the gas transportation main pipeline 12 and the first gas transportation branch pipeline 36, enters the second mixer 17 after being mixed with the hot propylene in the preheated propylene pipeline 15, enters the first oxidation reaction device 19 after being mixed with the purification air from the second gas transportation branch pipeline 18 in the third mixer 21, is discharged from the first oxidation reaction device 19 after oxidation reaction, enters the second oxidation reaction device 20 for further reaction, then enters the absorption tower 23, is absorbed by the quenching water from the quenching water pipeline 24, the aqueous solution of acrylic acid is discharged at the bottom of the tower and is transported to the refining system 37, the tail gas generated at the top of the absorption tower 23 is transported through the tower top waste gas transportation pipeline 25, is heated after passing through the plate heat exchanger 28 and the electric heater 29, enters the catalytic incineration device 30 for incineration treatment of the organic matter, returns to the plate heat exchanger 28 after being heated by the steam superheater 31, then is transported to the tail gas discharge port 34 for treatment and discharge after being treated, when the oxidation load is increased to 40-50%, the 2.0MPa saturated steam from the heat exchangers of the first oxidation reaction device 19 and the second oxidation reaction device 20 is transported to the steam superheater 31 through the saturated steam pipeline 22, the saturated steam is heated to 300 DEG C by using the temperature of the gas after incineration to obtain superheated steam, the superheated steam is transported to the turbine fresh fan 1 through the superheated steam pipeline 33, at this time, the turbine fan anti-surge valve 8 is fully opened, the turbine fan inlet guide vane 101 is closed to the minimum opening degree, the turbine fresh fan 1 is started, the inlet guide vanes and the anti-surge valves of the two fans are adjusted, the switching of the two fans is gradually completed, until the electrically driven circulating fan 2 is stopped, the fan outlet communication valve 9 is closed, the electrically driven circulating fan 2 returns to the standby state, and the low-pressure steam discharged by the turbine fresh fan 1 is transported to the refining system 37 through the low-pressure steam pipeline 35 as steam for the refining system 37.

[0042] The above merely illustrates the embodiments of the present application and is not intended to limit the present application. The present application can be variously changed and modified by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of the claims of the present application.

Claims

1. An energy saving start-up system for an acrylic acid oxidation unit, characterized by, The turbine fresh air fan (1) and the electric drive circulating fan (2) are connected through turbine fan outlet pipeline (6) and circulating fan outlet pipeline (5) respectively, the circulating fan outlet pipeline (5) is provided with fan outlet communication valve (9), the purification air pipeline (3) is connected to the inlet of turbine fresh air fan (1) and electric drive circulating fan (2) respectively, the purification air pipeline (3) is connected to the inlet of electric drive circulating fan (2) through circulating fan inlet pipeline (4), turbine fan outlet pipeline (6) and circulating fan outlet pipeline (5) are connected to gas transportation main pipeline (12), circulating fan gas transportation pipeline (13) is arranged on circulating fan outlet pipeline (5), the mixer before first oxidation reaction device (19) is provided with circulating fan gas transportation pipeline (13), medium pressure steam pipeline (14) and preheated propylene pipeline (15), the outlet of second oxidation reaction device (20) is connected to absorption tower (23), the bottom of absorption tower (23) is connected to refining system (37), one end of overhead waste gas transportation pipeline (25) is connected to absorption tower (23), the other end of overhead waste gas transportation pipeline (25) is divided into circulating gas transportation pipeline (27) and incineration feed pipeline (26), circulating gas transportation pipeline (27) is connected to circulating fan inlet pipeline (4), the incineration feed pipeline (26) is sequentially connected to plate heat exchanger (28), electric heater (29), catalytic incineration device (30) and steam superheater (31), the outlet of steam superheater (31) is connected to plate heat exchanger (28) through circulating pipeline (32); first oxidation reaction device (19) and second oxidation reaction device (20) are provided with heat exchanger, the heat exchanger is connected to steam superheater (31) through saturated steam pipeline (22), steam superheater (31) is connected to turbine fresh air fan (1) through superheated steam pipeline (33), turbine fresh air fan (1) is connected to refining system (37) through low pressure steam pipeline (35).

2. The energy saving start-up system for an acrylic acid oxidation unit according to claim 1, characterized in that, The outlet of plate heat exchanger (28) is connected to tail gas discharge port (34).

3. The energy efficient start-up system for an acrylic acid oxidation unit of claim 1, wherein, The upper part of absorption tower (23) is provided with quenching water pipeline (24). The upper part of absorption tower (23) is provided with quenching water pipeline (24).

4. The acryl oxidation unit energy saving start-up system according to claim 1, characterized by, The gas transportation main line (12) is divided into a first gas transportation branch line (36) and a second gas transportation branch line (18), the first gas transportation branch line (36) is connected with the inlet of a first mixer (16), the circulating fan gas transportation line (13) is connected with the inlet of the first mixer (16), the outlet of the first mixer (16) is connected with the inlet of a second mixer (17), the preheated propylene line (15) is connected with the inlet of the second mixer (17), the outlet of the second mixer (17) is connected with the inlet of a first oxidation reaction device (19) through a pipeline, the outlet of the first oxidation reaction device (19) is connected with the inlet of a third mixer (21) through a pipeline, and the outlet of the third mixer (21) is connected with the inlet of a second oxidation reaction device (20) through a pipeline.

5. The acryl oxidation unit energy saving start-up system according to claim 1, characterized by, A first check valve (10) is arranged on the circulating fan outlet pipeline (5), and a second check valve (11) is arranged on the turbine fan outlet pipeline (6).

6. The acryl oxidation unit energy saving start-up system according to claim 1, characterized by, A circulating fan anti-surge pipeline is arranged on the circulating fan outlet pipeline (5), and a circulating fan anti-surge valve (7) is arranged on the circulating fan anti-surge pipeline.

7. The acryl oxidation unit energy saving start-up system according to claim 1, characterized by, A turbine fan anti-surge pipeline is arranged on the turbine fan outlet pipeline (6), and a turbine fan anti-surge valve (8) is arranged on the turbine fan anti-surge pipeline.

8. The acrylic acid oxidation unit energy efficient start-up system of claim 1, wherein, A circulating gas inlet valve (2701) is arranged on the circulating gas transportation pipeline (27), and a purified air cut-off valve (301) is arranged on the purified air pipeline (3).

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