System and method for recycling tail gas and cold energy of MTO (methanol to olefin) device

Abstract

The tail gas and cold energy recycling system of the MTO device comprises a demethanizing tower, a condenser I, a reflux tank I, an absorption tower, a condenser II, a reflux tank II, a reflux pump II and a reflux pipeline which are communicated in sequence, wherein the absorption tower is provided with at least one middle-section circulating cooling device; and the top of the absorption tower is respectively communicated with a propane absorbent feeding pipeline and a C3 absorbent feeding pipeline. The recovery method comprises the following steps: tail gas of the MTO device enters the demethanizing tower to be subjected to a demethanizing process, methane, hydrogen and ethylene are preliminarily separated from C2 + components, ethylene is absorbed at the top of the absorption tower through a propane absorbent and a C3 absorbent, and the ethylene is circularly absorbed through the middle-section circulating cooling device; ethylene collected after cooling and absorption is discharged from the bottom end of the absorption tower along with a liquid phase, and a gas phase in the return tank II enters a fuel gas regeneration system. The ethylene recovery device and method disclosed by the invention have the beneficial effects of high efficiency and energy conservation.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of low carbon olefin separation, in particular to a MTO device tail gas and cold energy recycling system and method. BACKGROUND

[0002] With the development of economy, the market demand for low carbon olefins is rising, and the petroleum-based raw materials such as naphtha and light diesel oil as ethylene production raw materials are facing an increasingly serious resource shortage situation, which seriously restricts the sustainable development of related industries. Under this background, the application of methanol to olefins (MTO) technology has attracted attention from all walks of life. MTO technology refers to a process technology that uses coal-based or natural gas-based synthetic methanol or dimethyl ether as raw material, adopts a fluidized bed reaction mode similar to catalytic cracking, and produces low carbon olefins such as ethylene and propylene.

[0003] Generally speaking, after the catalytic conversion of methanol through the MTO reaction device, the product gas produced contains hydrogen, methane, ethylene, ethane, propylene, propane and butene or pentene, and components such as water, carbon monoxide and carbon dioxide. In order to obtain polymerization-grade olefin products, the separation and recovery technology of MTO product gas is crucial. As a high-value core chemical raw material, the loss of ethylene will directly result in huge economic losses for enterprises. Taking an MTO device that processes 1.8 million tons of methanol per year as an example, it is estimated that the direct economic loss of ethylene and related washing material loss due to the entrainment of methane tail gas is more than 30 million yuan per year.

[0004] The existing ethylene recovery process has significant shortcomings: first, the absorbent system is single, and more than 90% of small and medium-sized enterprises only use propane as the absorption medium, but its selective adsorption capacity for C2 components is insufficient, resulting in a high content of ethylene in the fuel gas, and a large amount of high-value ethylene is sent into the pipe network for incineration with the fuel gas; second, the energy recovery efficiency is low, and a large amount of cold energy generated in the process is not effectively recovered, resulting in energy waste; third, the operating cost continues to rise, and with the rise in the price of propane and other washing media, the operating mode of a large amount of circulating washing in the traditional process further increases the production cost. Therefore, it is necessary to provide a recovery system that can efficiently absorb ethylene, select high-efficiency and applicable absorbents, and fully utilize the advantages of cryogenic separation of the cold box system, so as to realize efficient capture of ethylene in the tail gas, reduce the loss of ethylene resources, fully recover the cold energy of the tail gas, reduce energy consumption, and create considerable economic benefits for enterprises. SUMMARY

[0005] In view of the shortcomings of the prior art, the technical problem to be solved by the present application is to provide a MTO device tail gas and cold energy recycling system and method, which can efficiently recover ethylene in the tail gas of the MTO device and has the advantages of energy saving and consumption reduction.

[0006] To solve the above problems, the present application provides the following technical solutions:

[0007] The application discloses an MTO device tail gas recycling system, which comprises an ethylene recycling device for MTO device tail gas.

[0008] The top gas outlet of the absorption tower is sequentially connected with a condenser II and a reflux tank II, the liquid phase discharge end of the bottom of the reflux tank II is sequentially connected with a reflux pump II and a reflux pipeline and the absorption tower, and the gas phase discharge end of the top of the reflux tank II is connected with a fuel gas regeneration system through a cold box.

[0009] The application further discloses that the demethanizing tower is provided with a gas phase feeding port and a liquid phase feeding port.

[0010] The application further discloses that the propane absorbent feeding pipeline comprises a propylene rectifying tower, the bottom discharge end of the propylene rectifying tower is sequentially connected with a propane absorbent pump and a propane absorbent chiller and the feeding end of the condenser II.

[0011] The application further discloses that the C3 absorbent feeding pipeline comprises a high-pressure depropanizing tower, the top discharge end of the high-pressure depropanizing tower is sequentially connected with a condenser III, a reflux tank III, a C3 absorbent pump, a cold box and a propane absorbent chiller and the reflux pipeline, and the discharge end of the reflux tank III is connected with the high-pressure depropanizing tower through a reflux pump III.

[0012] The application further discloses that the side wall of the absorption tower is provided with two middle section circulating cooling devices in parallel, one middle section circulating cooling device and two middle section circulating cooling devices, the one middle section circulating cooling device comprises a one middle section pump and a one middle section cooler which are sequentially connected, and the two middle section circulating cooling device comprises a two middle section pump and a two middle section cooler which are sequentially connected.

[0013] A cold energy recovery and utilization system for an MTO unit includes an ethane discharge pipeline from an ethylene distillation column, the discharge end of the ethylene distillation column being connected to a cold box via an exhaust gas cold box; the gas outlet of reflux tank II being connected to an exhaust gas condensate tank via an exhaust gas cold box, the liquid phase discharge end of the exhaust gas condensate tank being connected to reflux tank II, and the gas outlet of the exhaust gas condensate tank being connected to a fuel gas regeneration system via an exhaust gas cold box and a cold box in sequence.

[0014] A method for recovering and utilizing exhaust gas and cooling energy from an MTO (Mechanical Toll Collection) unit includes the following steps:

[0015] (1) Demethanization process: The tail gas of the MTO unit enters the demethanization tower for the demethanization process. The gas at the top of the demethanization tower is condensed by condenser I and enters reflux tank I. The liquid phase in reflux tank I is returned to the demethanization tower by reflux pump I. The gas phase in reflux tank I enters the bottom feed end of the absorption tower.

[0016] (2) Ethylene absorption process: The gas phase in step (1) enters the bottom of the absorption tower. Propane absorbent and C3 absorbent are added to the top of the absorption tower through the propane absorbent feed line and the C3 absorbent feed line to absorb ethylene. The gas at the top of the absorption tower enters the condenser II for condensation and enters the reflux tank II. The liquid phase in the reflux tank II is returned to the absorption tower through the reflux pump II and the reflux pipeline. The middle section of the absorption tower is a circulating cooling device that circulates the liquid phase repeatedly to absorb ethylene. The ethylene collected after the cooling and absorption process is discharged from the bottom of the absorption tower with the liquid phase. The gas phase in the reflux tank II enters the fuel gas regeneration system after passing through the cold box.

[0017] The technical solution of the present invention also includes that the C3 absorbent from the high-pressure propane removal tower passes through condenser III and reflux tank III, and is then pressurized by the C3 absorbent pump, cooled by the cold box and the propane absorbent quencher, before being connected to the first packing layer of the absorption tower through the reflux pipeline to wash away C2 and C32 entrained in the material. + Components: Propane absorbent from the bottom of the propylene distillation column is pressurized by a propane absorbent pump, cooled by a cooler, and cooled by a propane absorbent quencher before entering the top of the absorption column to absorb ethylene entrained in the material.

[0018] The technical solution of the present invention also includes that, in step (2), the absorption tower is equipped with two intermediate circulation cooling devices. The liquid phase is drawn out from the liquid accumulation tank below the first layer of packing, pumped to the first intermediate cooler by an intermediate pump, and then returned to the liquid distributor above the second layer of packing; the liquid phase is drawn out from the liquid accumulation tank below the second layer of packing, pumped to the second intermediate cooler by a second intermediate pump, and then returned to the liquid distributor above the third layer of packing.

[0019] The technical solution of the present invention also includes that the gas phase of the reflux tank II is partially condensed after exchanging heat with the low-temperature mixed fuel gas of methane, hydrogen and ethane in the exhaust gas cold box, and enters the exhaust gas condensate tank. The liquid phase flows back to the absorption tower reflux tank II, and the gas phase is depressurized and mixed with ethane from the bottom of the ethylene distillation tower to form low-temperature fuel gas. After further recovery of cold energy through the exhaust gas cold box and the cold box, it enters the fuel gas regeneration system.

[0020] The beneficial effects of this invention are:

[0021] The MTO unit tail gas and cold energy recovery and utilization system and method of the present invention achieves efficient ethylene recovery by setting up a demethanizer and an absorption tower. The ethylene content in the tail gas at the top of the absorption tower can be controlled below 2 mol%, and the fuel gas after heat exchange in the cold box meets the regeneration and use standards of the dryer.

[0022] First, the demethanizer can effectively react methane with C2. + The initial separation of components is beneficial for the efficient absorption of ethylene in the subsequent absorption tower.

[0023] Secondly, the absorption tower effectively enhances its ethylene adsorption capacity by employing a dual-stream absorbent system of propane and C3 absorbent. One stream of C3 absorbent from the high-pressure propane stripper reflux tank III is cooled by a cold box and a propane absorbent quencher before entering the reflux pipeline as the absorbent. This efficiently captures ethylene and C2 entrained in methane and hydrogen from the top of the demethanizer. + The two absorption methods work synergistically to effectively improve the ethylene recovery efficiency. One stream of propane absorbent is cooled by a cooler and an absorbent quencher before entering the vapor phase line at the top of the absorption tower to recover the C2 components entrained in the material.

[0024] Furthermore, the absorber is equipped with a mid-section circulating cooling device. Through a closed-loop process of "liquid collection tank - cooling device - distributor return", the absorbent temperature is continuously reduced, enhancing the targeted capture capability of ethylene components. The first layer of packing in the absorber focuses on capturing high-concentration ethylene, while the second layer focuses on capturing low-concentration ethylene. This gradient design of high and low concentrations prevents the absorbent from "saturating and failing", significantly reducing the single consumption of propane absorbent. At the same time, the cyclical steps further improve the absorption effect of ethylene.

[0025] Finally, this invention offers advantages in energy conservation and consumption reduction. On the one hand, by mixing ethane with low-temperature fuel gases such as methane and hydrogen, the latent heat of vaporization of ethane is used to lower the temperature of the mixed fuel gas, further pre-cooling the gas at the top of the absorption tower and promoting the recovery of C3 components. This achieves cascade utilization of cold energy and significantly reduces energy consumption. On the other hand, through the synergistic effect of dual adsorption by propane absorbent and C3 absorbent, the ethylene content in the fuel gas is significantly reduced (controlled below 2 mol%), meeting the dryer regeneration standards. Based on this, a new fuel gas regeneration process replaces the traditional nitrogen regeneration mode, achieving the dual benefits of resource recycling and energy reduction. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the MTO device exhaust gas and cold energy recovery and utilization system in a specific implementation.

[0028] Among them, 11 is condenser I, 12 is condenser II, 13 is condenser III, 21 is reboiler I, 22 is reboiler II, 23 is reboiler III, 31 is reflux tank I, 32 is reflux tank II, 33 is reflux tank III, 34 is reflux pipeline, 41 is reflux pump I, 42 is reflux pump II, 43 is first-stage pump, 44 is second-stage pump, 45 is reflux pump III, 51 is C3 absorbent pump, 52 is propane absorbent pump, 6 is demethanizer tower, 7 is absorber tower, 8 is high-pressure depropanizer tower, 9 is propylene distillation tower, 101 is cold box, 102 is exhaust gas cold box, 103 is exhaust gas condensate tank, 104 is propylene absorbent quencher, 105 is first-stage cooler, 106 is second-stage cooler, and 107 is cooler. Detailed Implementation

[0029] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0030] In the description of this invention, it should be understood that the terms "center", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the purpose of simplifying the description of this invention and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0031] As shown in the attached diagram, an MTO unit tail gas and cold energy recovery and utilization system includes a demethanizer 6, which has a gas phase inlet and a liquid phase inlet. A reboiler I21 is provided at the bottom of the demethanizer 6. The gas outlet at the top of the demethanizer 6 is connected in sequence to a condenser I11 and a reflux tank I31. The liquid phase outlet at the bottom of the reflux tank I31 is connected to the demethanizer 6 through a reflux pump I41. The gas phase outlet at the top of the reflux tank I31 is connected to the bottom inlet of the absorption tower 7.

[0032] The top outlet of the absorption tower 7 is connected in sequence to the condenser II 12 and the reflux tank II 32. The liquid phase outlet of the bottom of the reflux tank II 32 is connected to the absorption tower 7 in sequence through the reflux pump II 42 and the reflux pipeline 34. The gas phase outlet of the top of the reflux tank II 32 is connected to the fuel gas regeneration system through the cold box 101.

[0033] The top of the absorption tower 7 is also connected to a propane absorbent feed line and a C3 absorbent feed line. The propane absorbent feed line includes a propylene distillation tower 9, which has a reboiler Ⅲ23 at its bottom. The bottom outlet of the propylene distillation tower 9 is connected to the inlet of the condenser Ⅱ12 via a propane absorbent pump 52 and a propane absorbent quench 104. The C3 absorbent feed line includes a high-pressure propane stripping tower 8, which has a reboiler Ⅱ22 at its bottom. The top outlet of the high-pressure propane stripping tower 8 is connected to a reflux line 34 via a condenser Ⅲ13, a reflux tank Ⅲ33, a C3 absorbent pump 51, a cold box 101, and a propane absorbent quench 104. A reflux pump Ⅲ45 is also connected between the outlet of the reflux tank Ⅲ33 and the high-pressure propane stripping tower 8.

[0034] The sidewall of the absorption tower 7 is equipped with two intermediate-stage circulating cooling devices in parallel, including a first intermediate-stage circulating cooling device and a second intermediate-stage circulating cooling device. The first intermediate-stage circulating cooling device includes a first intermediate-stage pump 43 and a first intermediate-stage cooler 105 connected in sequence. The second intermediate-stage circulating cooling device includes a second intermediate-stage pump 44 and a second intermediate-stage cooler 106 connected in sequence. The absorption tower 7 is provided with at least three layers of packing. A liquid distributor is provided above the packing layers. The feed end of the first intermediate-stage pump 43 is connected to the liquid accumulation tank below the first layer of packing in the absorption tower 7. The discharge end of the first intermediate-stage cooler 105 is connected to the liquid distributor above the second layer of packing. The feed end of the second intermediate-stage pump 44 is connected to the liquid accumulation tank below the second layer of packing in the absorption tower. The discharge end of the second intermediate-stage cooler 106 is connected to the liquid distributor above the third layer of packing.

[0035] The discharge end of the ethylene distillation column is connected to the cold box 101 via the exhaust gas cold box 102; the gas outlet of the reflux tank II 32 is connected to the exhaust gas condensate tank 103 via the exhaust gas cold box 102; the liquid phase discharge end of the exhaust gas condensate tank 103 is connected to the reflux tank II 32; and the gas outlet of the exhaust gas condensate tank 103 is connected to the fuel gas regeneration system via the exhaust gas cold box 102 and the cold box 101 in sequence.

[0036] The recycling method using the above-mentioned exhaust gas and cold energy recovery and utilization system includes the following steps:

[0037] The tail gas from the MTO unit enters the demethanizer for demethanization. The operating parameters of the demethanizer are: top temperature -20 to -30°C, top pressure 2.0 to 3.0 MPa, with the most preferred parameters being a top temperature of -26°C and a top pressure of 2.7 MPa. The demethanizer feed is divided into gas-liquid two-phase separate feeds, entering the 10th and 14th trays respectively. The gas at the top of the demethanizer is condensed by condenser I and enters reflux tank I. The liquid phase in reflux tank I is returned to the demethanizer via reflux pump I, while the gas phase in reflux tank I enters the bottom feed end of the absorber. The demethanizer adopts a segmented feed design for the gas phase (10th tray) and liquid phase (14th tray). Based on the density difference between the gas and liquid components, this design avoids the decrease in mass transfer efficiency caused by mixed gas-liquid feed, enhances the initial separation effect of methane, hydrogen, and ethylene from C2+ components, and is beneficial for the efficient capture of ethylene in the subsequent absorber. After the demethanizing process, the gas at the top of the demethanizing tower mainly consists of methane, hydrogen, and entrained ethylene.

[0038] After the demethanizing process, the gas phase (a mixture of light components such as methane, hydrogen, and ethylene) enters the absorption tower and undergoes cooling and absorption. The absorbed ethylene is discharged from the bottom of the absorption tower along with the liquid phase. The ethylene content in the tail gas at the top of the absorption tower can be controlled below 2 mol%. The operating parameters of the absorption tower are: top temperature -10 to -20℃, top pressure 2.0 to 3.0 MPa, and most preferably, top temperature -14℃ and top pressure 2.6 MPa.

[0039] The addition process for the two absorbents is as follows: Propane absorbent and C3 absorbent are added at the top of the absorption tower via the propane absorbent feed line and the C3 absorbent feed line to absorb ethylene; the C3 absorbent from the high-pressure propane stripper passes through condenser III and reflux tank III, then is pressurized by the C3 absorbent pump, cooled by the cold box heat exchanger and the propane absorbent quencher, and finally enters the first packing layer of the absorption tower via the reflux line to wash away C2 and C3 precipitates entrained in the material. + Components: Propane absorbent from the bottom of the propylene distillation column is pressurized by a propane absorbent pump, cooled by a cooler, and cooled by a propane absorbent quencher before entering the top of the absorption column to absorb ethylene entrained in the material.

[0040] The absorber tower is equipped with two intermediate circulating cooling devices. Liquid phase is drawn from a sump below the first layer of packing, pumped to a first intermediate cooler by an intermediate pump, and then returned to a liquid distributor above the second layer of packing. Liquid phase is drawn from a sump below the second layer of packing, pumped to a second intermediate cooler by a second intermediate pump, and then returned to a liquid distributor above the third layer of packing. The intermediate circulating cooling devices in the absorber tower further improve the ethylene recovery efficiency by repeatedly circulating the liquid phase during ethylene absorption.

[0041] The gas from the top of the absorber tower is condensed by condenser II and then enters reflux tank II. The liquid phase in reflux tank II is returned to the absorber tower. Ethylene collected after cooling and absorption processes is discharged from the bottom of the absorber tower along with the liquid phase. The gas phase in reflux tank II partially condenses after heat exchange with the low-temperature mixed fuel gas of methane, hydrogen, and ethane in the exhaust gas cold box, and enters the exhaust gas condensate tank. The liquid phase flows back to the absorber tower reflux tank II. After depressurization, the gas phase mixes with ethane from the bottom of the ethylene distillation tower to form low-temperature fuel gas. This gas then passes through the exhaust gas cold box and the cold box for further recovery of cold energy before entering the fuel gas regeneration system. The ethane cooled by throttling at the bottom of the ethylene distillation tower mixes with the low-temperature fuel gases such as methane and hydrogen. Due to the reduced partial pressure of the gas phase in the system, the liquid ethane absorbs heat and vaporizes, gradually lowering the temperature of the mixed fuel gas. Heat exchange is then conducted between the exhaust gas cold box and the gas from the top of the absorber tower, further pre-cooling the gas from the top of the absorber tower, promoting the separation of C3 components, and realizing the resource utilization of cold energy.

[0042] This embodiment utilizes a dual setup of propane and C3 absorbents to significantly improve ethylene recovery. The C3 absorbent recovers and utilizes C2 and C3 components while reducing the operating load on the subsequent propylene distillation column, enhancing the unit's operational flexibility and stability. Through the synergistic adsorption effect of the propane and C3 absorbents, the ethylene content in the fuel gas is significantly reduced (controlled below 2 mol%), meeting the dryer regeneration standards. This allows for the addition of a fuel gas regeneration process to replace the traditional nitrogen regeneration mode, significantly reducing nitrogen consumption and achieving the dual benefits of resource recycling and energy reduction. Furthermore, the propane absorbent is located at the top vapor line of the absorption tower, improving the capture efficiency of ethylene components. Due to the change in material composition within the reflux tank, a centrifugal reflux pump can be used, significantly reducing the difficulty and cost of subsequent maintenance. By mixing ethane with cryogenic fuel gases such as methane and hydrogen, the latent heat of vaporization of ethane lowers the temperature of the mixed fuel gas, further pre-cooling the top gas of the absorption tower and promoting C3 component recovery. This achieves cascaded utilization of cooling capacity, significantly reducing energy consumption.

[0043] Although the present invention has been described in detail with reference to the accompanying drawings and preferred embodiments, the invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should also be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the scope of the claims.

Claims

1. A system for recovering and utilizing exhaust gas from an MTO (Mechanical Toll Collection) device, characterized in that: The system includes a demethanizing tower, with the top outlet of the demethanizing tower connected in sequence to a condenser I and a reflux tank I. The liquid phase outlet at the bottom of the reflux tank I is connected to the demethanizing tower via a reflux pump I, and the gas phase outlet at the top of the reflux tank I is connected to the bottom feed outlet of the absorption tower. The top outlet of the absorption tower is connected in sequence to condenser II and reflux tank II. The liquid phase outlet at the bottom of reflux tank II is connected to the absorption tower in sequence through reflux pump II and reflux pipeline. The gas phase outlet at the top of reflux tank II is connected to the fuel gas regeneration system through a cold box. The absorption tower is equipped with at least one intermediate circulating cooling device. The top of the absorption tower is also connected to a propane absorbent feed pipeline and a C3 absorbent feed pipeline, respectively.

2. The MTO unit exhaust gas recovery and utilization system as described in claim 1, characterized in that, The demethanizer is equipped with a gas phase inlet and a liquid phase inlet.

3. The MTO unit exhaust gas recovery and utilization system as described in claim 1, characterized in that, The propane absorbent feed line includes a propylene distillation column, and the bottom outlet of the propylene distillation column is connected in sequence to the inlet of the propane absorbent pump, the propane absorbent quencher, and the condenser II.

4. The MTO unit tail gas recovery and utilization system as described in claim 1, characterized in that, The C3 absorbent feeding pipeline includes a high-pressure propane removal tower. The top discharge end of the high-pressure propane removal tower is connected to the reflux pipeline in sequence through condenser III, reflux tank III, C3 absorbent pump, cold box, and propane absorbent quencher. The discharge end of the reflux tank III is also connected to the high-pressure propane removal tower by a reflux pump III.

5. The MTO unit exhaust gas recovery and utilization system as described in claim 1, characterized in that, The absorption tower has two intermediate-section circulating cooling devices connected in parallel on its sidewall, including a first intermediate-section circulating cooling device and a second intermediate-section circulating cooling device. The first intermediate-section circulating cooling device includes a first intermediate-section pump and a first intermediate-section cooler connected in sequence, and the second intermediate-section circulating cooling device includes a second intermediate-section pump and a second intermediate-section cooler connected in sequence. The absorption tower has at least three layers of packing material, and a liquid distributor is provided above the packing material. The feed end of the first intermediate-section pump is connected to the liquid accumulation tank below the first layer of packing material in the absorption tower, and the discharge end of the first intermediate-section cooler is connected to the liquid distributor above the second layer of packing material. The feed end of the second intermediate-section pump is connected to the liquid accumulation tank below the second layer of packing material in the absorption tower, and the discharge end of the second intermediate-section cooler is connected to the liquid distributor above the third layer of packing material.

6. The cold energy recovery system of the MTO device as described in any one of claims 1-5, characterized in that, The discharge end of the ethylene distillation tower is connected to the cold box via the exhaust gas cold box; the gas outlet of reflux tank II is connected to the exhaust gas condensate tank via the exhaust gas cold box; the liquid phase discharge end of the exhaust gas condensate tank is connected to reflux tank II; and the gas outlet of the exhaust gas condensate tank is connected to the fuel gas regeneration system via the exhaust gas cold box and the cold box in sequence.

7. A method for recovering and utilizing exhaust gas and cooling energy from an MTO (Mechanical Toll Collection) unit, characterized in that, Includes the following steps: (1) Demethanization process: The tail gas of the MTO unit enters the demethanization tower for the demethanization process. The gas at the top of the demethanization tower is condensed by condenser I and enters reflux tank I. The liquid phase in reflux tank I is returned to the demethanization tower by reflux pump I. The gas phase in reflux tank I enters the bottom feed end of the absorption tower. (2) Ethylene absorption process: The gas phase in step (1) enters the bottom of the absorption tower. Propane absorbent and C3 absorbent are added to the top of the absorption tower through the propane absorbent feed line and the C3 absorbent feed line to absorb ethylene. The gas at the top of the absorption tower enters the condenser II for condensation and enters the reflux tank II. The liquid phase in the reflux tank II is returned to the absorption tower through the reflux pump II and the reflux pipeline. The intermediate circulating cooling device in the absorption tower absorbs ethylene by repeatedly circulating the liquid phase. After cooling and absorption, the collected ethylene is discharged from the bottom of the absorption tower along with the liquid phase, and the gas phase in the reflux tank II enters the fuel gas regeneration system after passing through the cold box.

8. The method for recovering and utilizing exhaust gas and cold energy as described in claim 7, characterized in that, The C3 absorbent from the high-pressure propane stripper passes through condenser III and reflux tank III, then is pressurized by the C3 absorbent pump, cooled by a cold box heat exchanger and a propane absorbent quencher, before entering the first packing layer of the absorption tower via the reflux pipeline to wash away C2 and C3 entrained in the material. + Components: Propane absorbent from the bottom of the propylene distillation column is pressurized by a propane absorbent pump, cooled by a cooler, and cooled by a propane absorbent quencher before entering the top of the absorption column to absorb ethylene entrained in the material.

9. The method for recovering and utilizing exhaust gas and cold energy as described in claim 7, characterized in that, In step (2), the absorption tower is equipped with two intermediate circulation cooling devices. The liquid phase is drawn out from the liquid collection tank below the first layer of packing, pumped to the first intermediate cooler by an intermediate pump, and then returned to the liquid distributor above the second layer of packing. The liquid phase is drawn out from the liquid collection tank below the second layer of packing, pumped to the second intermediate cooler by a second intermediate pump, and then returned to the liquid distributor above the third layer of packing.

10. The method for recovering and utilizing exhaust gas and cold energy as described in claim 7, characterized in that, After the gas phase in reflux tank II exchanges heat with the low-temperature mixed fuel gas of methane, hydrogen and ethane in the exhaust gas cold box, it partially condenses and enters the exhaust gas condensate tank. The liquid phase flows back to the absorption tower reflux tank II. After the gas phase is depressurized, it mixes with ethane from the bottom of the ethylene distillation tower to form low-temperature fuel gas. After further recovery of cold energy through the exhaust gas cold box and the cold box, it enters the fuel gas regeneration system.

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