Esterification purge gas treatment device in process of preparing ethylene glycol from synthesis gas

Abstract

The utility model belongs to the technical field of ethylene glycol preparation, and particularly relates to an esterification purge gas treatment device in a process of preparing ethylene glycol from synthesis gas, which comprises an MN recovery tower, a gas mixer, a tail gas heater, a tail gas reactor, a cooler and a tail gas absorption tower, tower top outlet gas of the MN recovery tower and purge gas from PSA desorption gas of a hydrogenation unit enter a gas mixer, are mixed in the gas mixer, then enter a tail gas heater to be heated and then enter a tail gas reactor to react, an outlet of the tail gas reactor is connected with an inlet of a cooler, an outlet of the cooler is connected with a tail gas absorption tower, and an outlet of the tail gas absorption tower is connected with an outlet of the MN recovery tower. The tail gas absorption tower is connected with a spray water inlet pipe and a waste gas discharge pipe; and the tail gas reactor is a fixed tubular reactor. According to the device, nitrogen oxide which cannot be directly discharged in esterification purge gas can react to generate harmless gas such as nitrogen and nitrogen dioxide, environmental pollution is avoided, the device can adapt to the shutdown working condition of an esterification system, air does not need to be supplemented to the MN recovery tower, and the technological operation risk is reduced.

Description

Technical Field

[0001] The utility model belongs to the technical field of ethylene glycol preparation, and particularly relates to an esterification purge gas processing device in a synthesis gas to ethylene glycol process. Background Art

[0002] The existing synthesis gas to ethylene glycol process mainly consists of two parts. The first part is the oxidative carbonylation of synthesis gas to produce dimethyl oxalate, and the second part is the hydrogenation of oxalate to produce ethylene glycol. The main reaction formula is as follows:

[0003] CO coupling reaction: 2CH3ONO+2CO→(COOCH3)2+2NO;

[0004] Esterification regeneration reaction: 2CH3OH+2NO+1 / 2O2→2CH3ONO+H2O;

[0005] Oxalate hydrogenation reaction: (COOCH3)2+4H2→(CH2OH)2+2CH3OH;

[0006] Overall reaction: 2CO+4H2+1 / 2O2→(CH2OH)2+H2O.

[0007] Therefore, the existing synthesis gas to ethylene glycol esterification purge gas generally adopts the method of adding air for oxidative esterification to produce methyl nitrite, and then uses low-temperature methanol to absorb the methyl nitrite and return it to the esterification system ("esterification system" refers to the large oxidative carbonylation esterification system). When the esterification system is shut down and the conditions for receiving nitrogen oxides are not met, it can only be discharged to the flare, causing environmental pollution. Moreover, adding air to the methyl nitrite recovery tower can easily create an oxygen-containing explosive environment, and the process operation risk is relatively high. Therefore, it is necessary to design a new esterification purge gas treatment device to adapt to the working conditions when the esterification system is shut down and the conditions for receiving nitrogen oxides are not met. Utility Model Content

[0008] The utility model aims to provide an esterification purge gas processing device in a synthesis gas to ethylene glycol process, so as to adapt to the working condition that the esterification system is shut down and does not have the conditions for receiving nitrogen oxides.

[0009] In order to achieve the above-mentioned purpose, the scheme of the utility model is as follows: a device for processing esterification purge gas in a synthesis gas to ethylene glycol process, comprising a gas mixer, a tail gas heater, a tail gas reactor, a cooler and a tail gas absorption tower, wherein the esterification purge gas and the purge gas from the PSA analysis gas of the hydrogenation unit enter the gas mixer, are mixed in the gas mixer, enter the tail gas heater for heating, and then enter the tail gas reactor for reaction, the outlet of the tail gas reactor is connected to the inlet of the cooler, the outlet of the cooler is connected to the tail gas absorption tower, and the tail gas absorption tower is connected to a spray water inlet pipe and an exhaust gas discharge pipe; the tail gas reactor is a fixed shell and tube reactor.

[0010] The working principle and beneficial effects of this solution are as follows: In this solution, the esterification purge gas and the purge gas from the hydrogenation unit PSA decomposition gas enter the gas mixer and are mixed to obtain a mixed gas. After the mixed gas is heated to 230°C by the tail gas heater, it enters the tail gas reactor. Under the action of the catalyst, the NO and MN gases in the mixed gas that cannot be directly discharged undergo an oxidation-reduction reaction with H2 to produce harmless N2 and H2O (reaction formula: 2MN+H2→2CH3OH+2NO; NO+H2→0.5N2+H2O; 2NO+5H2→2NH3+2H2O); at the same time, part of the NO in the esterification non-condensable gas reacts with the CO in the carbonylation non-condensable gas to produce CO2 and N2 (reaction formula: 2NO+2CO→2CO2+N2). The reacted mixed gas is cooled in the cooler and enters the tail gas absorption tower, where it comes into countercurrent contact with the esterification acid-containing wastewater sprayed from the top of the tail gas absorption tower, and ammonia is absorbed (reaction formula: NH3+H + =NH4 + ), organic matter (primarily methanol) dissolves in the acidic esterification wastewater, and the washed gas is discharged to the incinerator through the exhaust pipe. The wastewater from the tail gas absorption tower kettle is sent to the wastewater treatment station. In this way, this solution can recover methyl nitrite when the esterification system is shut down, and react nitrogen oxides and CO in the esterification off-gas to produce harmless gases such as nitrogen, carbon dioxide, and ammonia, and discharge nitrogen and carbon dioxide to avoid environmental pollution. Moreover, this solution can also be operated during the esterification system startup, thus avoiding the addition of air to the methyl nitrite recovery tower and reducing process operation risks.

[0011] Optionally, the treatment device also includes an exhaust gas heat exchanger, which is arranged between the gas mixer and the exhaust gas heater. The outlet of the gas mixer and the inlet of the exhaust gas heater are both connected to the tube side of the exhaust gas heat exchanger, and the outlet of the exhaust gas reactor and the inlet of the cooler are both connected to the shell side of the exhaust gas heat exchanger.

[0012] In this solution, the gas after the reaction in the tail gas reactor and the gas mixed in the gas mixer exchange heat in the tail gas heat exchanger, thereby cooling the gas after the reaction and heating the gas before the reaction, improving the utilization rate of heat and reducing the amount of steam used in the tail gas heater.

[0013] Optionally, the processing device further comprises an MN recovery tower, and the esterification purge gas enters the MN recovery tower, is sprayed and washed with methanol, and is discharged from the top of the tower, and enters the gas mixer with the purge gas from the hydrogenation unit PSA analysis gas.

[0014] In this scheme, before the esterification purge gas enters the gas mixer, it is first washed by the MN recovery tower to recover the methyl nitrite in the esterification purge gas.

[0015] Optionally, the treatment device further comprises a steam drum, and the water inlet and the water outlet of the steam drum are both connected to the shell side of the tail gas reactor.

[0016] In this solution, boiler water is used as the heat removal medium between the tubes of the tail gas reactor, and the by-produced medium-pressure steam in the steam drum removes the reaction heat, thereby improving the utilization rate of the reaction heat and avoiding heat energy waste.

[0017] Optionally, the outlet of the cooler includes a gas outlet and a condensate outlet, the gas outlet is connected to the bottom of the tail gas absorption tower, and the condensate outlet is connected to the top of the tail gas absorption tower.

[0018] In this scheme, after the reaction products of the tail gas reactor are condensed by the condenser, N2, CO2 and NH3 are gaseous, H2O is liquid, and most of CH3OH is liquid, with a small part being gaseous. Therefore, the gaseous products enter from the bottom of the tail gas absorption tower, and the liquid products enter from the top of the tail gas absorption tower, so that the gaseous products rise in the tail gas absorption tower and countercurrent with the spray water and liquid products in the tower.

[0019] Optionally, a branch pipe is connected to the spray water inlet pipe, and control valves are installed on both the spray water inlet pipe and the branch pipe.

[0020] In this solution, a branch pipe is connected to the spray water inlet pipe to switch the source of the spray water, so that the spray water can be switched from esterified acid-containing wastewater to desalted water, or from desalted water to esterified acid-containing wastewater according to actual working conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic structural diagram of an esterification purge gas treatment device in a synthesis gas to ethylene glycol process according to Example 1 of the present invention;

[0022] Figure 2 This is a schematic structural diagram of the esterification purge gas treatment device in the synthesis gas to ethylene glycol process in Example 2 of the present utility model. DETAILED DESCRIPTION

[0023] The following is further described in detail through specific implementation methods:

[0024] The marks in the drawings of the specification include: MN recovery tower 1, gas mixer 2, tail gas heat exchanger 3, tail gas heater 4, tail gas reactor 5, cooler 6, tail gas absorption tower 7, steam drum 8, methanol spray inlet pipe 9, esterification purge gas inlet pipe 10, drain pipe 11, liquid pump I 12, liquid pump II 13, spray water inlet pipe 14, waste gas discharge pipe 15, wastewater discharge pipe 16, liquid pump III 17, branch pipe 18, control valve 19.

[0025] Example 1

[0026] This embodiment is basically as Figure 1Figure 1 shows an esterification purge gas processing apparatus in a synthesis gas to ethylene glycol process, comprising an MN recovery tower 1, a gas mixer 2, an exhaust gas heat exchanger 3, an exhaust gas heater 4, an exhaust gas reactor 5, a cooler 6, an exhaust gas absorption tower 7, and a steam drum 8. The top of the MN recovery tower 1 is connected to a methanol spray inlet pipe 9, and the bottom of the MN recovery tower 1 is connected to an esterification purge gas inlet pipe 10 and a liquid discharge pipe 11. Liquid pump I 12 is installed on the liquid discharge pipe 11, so that the methanol that has absorbed methyl nitrite is pumped to the esterification tower by liquid pump I 12. The top outlet gas of the MN recovery tower 1 and the purge gas from the PSA analysis gas of the hydrogenation unit enter the gas mixer 2, the outlet of the gas mixer 2 is connected to the inlet of the tube side of the tail gas heat exchanger 3 through a pipeline, and the inlet of the tail gas heater 4 is connected to the outlet of the tube side of the tail gas heat exchanger 3 through a pipeline; the outlet of the tail gas reactor 5 is connected to the inlet of the shell side of the tail gas heat exchanger 3 through a pipeline, the inlet of the cooler 6 is connected to the outlet of the shell side of the tail gas heat exchanger 3 through a pipeline, and the inlet of the tail gas reactor 5 is connected to the outlet of the tail gas heater 4 through a pipeline.

[0027] The tail gas reactor 5 is a fixed shell-and-tube reactor, and the vent gas enters the tube side of the tail gas reactor 5, and the water inlet of the steam drum 8 is connected to the outlet of the shell side of the tail gas reactor 5 through a pipeline, and the water outlet of the steam drum 8 is connected to the inlet of the shell side of the tail gas reactor 5 through a pipeline, and a liquid pump II 13 is installed on the pipeline between the water outlet of the steam drum 8 and the tail gas reactor 5, so that the boiler water is pumped into the shell side of the tail gas reactor 5 by the liquid pump II 13.

[0028] The outlet of the cooler 6 is connected to the tail gas absorption tower 7. Specifically, the outlet of the cooler 6 includes a gas outlet and a condensate outlet. The gas outlet is connected to the bottom of the tail gas absorption tower 7 via a pipeline, and the condensate outlet is connected to the top of the tail gas absorption tower 7 via a pipeline. The top of the tail gas absorption tower 7 is connected to a spray water inlet pipe 14 and an exhaust gas discharge pipe 15. The bottom of the tail gas absorption tower 7 is connected to a wastewater discharge pipe 16. A liquid pump III 17 is installed on the wastewater discharge pipe 16, so that the wastewater is pumped to the sewage treatment station by the liquid pump III 17. In addition, each pipeline is equipped with a valve for controlling the on-off of the pipeline. Figure 1 Not shown in .

[0029] During actual use, the esterification purge gas (esterification purge gas components: nitrogen 45%, carbon monoxide 25%, methyl nitrite 13%, nitric oxide 8%, and others 9%) enters the bottom of the MN recovery tower 1 through the esterification purge gas inlet pipe 10, forming an upward airflow in the tower; at the same time, fresh methanol enters the upper part of the MN recovery tower 1 through the methanol spray inlet pipe 9 for spraying, and the upward airflow contacts the sprayed methanol in countercurrent, and the methyl nitrite in the esterification purge gas dissolves in the methanol. The methanol after dissolving the methyl nitrite is transported to the esterification tower through the discharge pipe 11 under the action of the liquid pump I 12. The esterification purge gas from which most of the methyl nitrite has been removed enters the gas mixer 2 through the top of the MN recovery tower 1. At the same time, the purge gas from the PSA analysis gas of the hydrogenation unit (containing 72.2% hydrogen) also enters the gas mixer 2. The two are mixed in the gas mixer 2 to obtain a mixed gas. The mixed gas then enters the tube side of the tail gas heat exchanger 3, exchanges heat with the high-temperature reaction product at the outlet of the tail gas reactor 5, and achieves initial heating of the mixed gas. The mixed gas then enters the tail gas heater 4, is indirectly heated to 230°C by medium-pressure steam, and then enters the tail gas reactor 5 for reaction.

[0030] In tail gas reactor 5, under the action of a catalyst, NO and MN gases in the mixed gas, which cannot be directly discharged, undergo an oxidation-reduction reaction with H2, producing harmless N2 and H2O. The specific reaction equations are as follows: 2MN + H2 → 2CH3OH + 2NO; NO + H2 → 0.5N2 + H2O; 2NO + 5H2 → 2NH3 + 2H2O. Simultaneously, some NO in the esterified non-condensable gas reacts with CO in the carbonylated non-condensable gas to produce CO2 and N2, using the reaction equation 2NO + 2CO → 2CO2 + N2. During the reaction, boiler water is used as a heat removal medium between the tubes of tail gas reactor 5, and medium-pressure steam is produced as a byproduct in steam drum 8 to remove the reaction heat, thereby improving heat utilization.

[0031] The high-temperature reaction products are discharged from the outlet of the tail gas reactor 5. The high-temperature reaction products enter the shell side of the tail gas heat exchanger 3 and exchange heat with the mixed gas in the tube side of the tail gas heat exchanger 3 to achieve initial cooling of the reaction products. Subsequently, the reaction products enter the cooler 6, where circulating water indirectly cools the reaction products. The N2, CO2, and NH3 in the reaction products are gaseous, the H2O is liquid, and the CH3OH is mostly liquid, with a small portion being gaseous. In this way, the gaseous products enter the tail gas absorption tower 7 from the bottom of the tower and form an updraft within the tower. The liquid products are sprayed down from the top of the tail gas absorption tower 7. At the same time, the esterification acid-containing wastewater entering the top of the tail gas absorption tower 7 through the spray water inlet pipe 14 is sprayed down. The updraft countercurrently contacts the liquid products and the esterification acid-containing wastewater. The liquid products and the esterification acid-containing wastewater dissolve the organic matter (mainly methanol) in the updraft, and the ammonia in the updraft reacts with the nitric acid. The reaction formula is NH3+HNO3=NH4NO3. In this way, the rising airflow after washing is mainly composed of nitrogen and carbon dioxide, which is discharged to the incinerator through exhaust gas discharge pipe 15 for incineration. The final emissions are nitrogen and carbon dioxide, which are harmless to the environment and avoid causing environmental pollution. The liquid product in the bottom of tail gas absorption tower 7 and the esterification acid wastewater are discharged to the sewage treatment station through wastewater discharge pipe 16 under the action of liquid pump III 17.

[0032] In another embodiment, the MN recovery tower 1 is not provided, and the esterification purge gas directly enters the gas mixer 2. Although methyl nitrite in the esterification purge gas is lost, the equipment investment cost can be reduced.

[0033] In summary, this embodiment can adapt to operating conditions where the esterification system is shut down and the conditions for receiving nitrogen oxides are unavailable. By mixing the esterification purge gas with the hydrogenation unit purge gas for reaction, the nitrogen oxides in the esterification purge gas that cannot be directly discharged are converted into nitrogen and carbon dioxide harmless gases for discharge, thus avoiding environmental pollution. Furthermore, this embodiment can also be operated during the esterification system startup, thereby avoiding the need to replenish air to the MN recovery tower 1, thereby reducing process operation risks and generating medium-pressure steam as a byproduct.

[0034] Example 2

[0035] The difference between this embodiment and the first embodiment is that: Figure 2 As shown, in this embodiment, a branch pipe 18 is connected to the spray water inlet pipe 14, and a control valve 19 is installed on both the spray water inlet pipe 14 and the branch pipe 18. In this example, the esterification acid-containing wastewater enters the tail gas absorption tower 7 through the spray water inlet pipe 14. If the esterification acid-containing wastewater is exhausted or the supply pipeline fails, the control valve 19 on the spray water inlet pipe 14 can be closed and the control valve 19 on the branch pipe 18 can be opened to supply desalted water to the tail gas absorption tower 7, thereby switching the spray water source.

[0036] The above description is merely an embodiment of the present invention. Commonly known details such as the specific structure and characteristics of the solution are not described in detail here. It should be noted that those skilled in the art may make various modifications and improvements without departing from the structure of the present invention. These modifications and improvements should also be considered within the scope of protection of the present invention and will not affect the effectiveness and practicality of the implementation of the present invention. The specific embodiments and other descriptions in the specification may be used to interpret the content of the claims.

Claims

1. A device for treating esterification purge gas in a synthesis gas to ethylene glycol process, characterized by: It includes a gas mixer, a tail gas heater, a tail gas reactor, a cooler and a tail gas absorption tower. The esterification purge gas and the purge gas from the hydrogenation unit PSA analysis gas enter the gas mixer, are mixed in the gas mixer, enter the tail gas heater for heating, and then enter the tail gas reactor for reaction. The outlet of the tail gas reactor is connected to the inlet of the cooler, and the outlet of the cooler is connected to the tail gas absorption tower. The tail gas absorption tower is connected to a spray water inlet pipe and an exhaust gas discharge pipe. The tail gas reactor is a fixed shell and tube reactor.

2. The device for treating esterification purge gas in the synthesis gas to ethylene glycol process according to claim 1, characterized in that: The processing device also includes an exhaust gas heat exchanger, which is arranged between the gas mixer and the exhaust gas heater. The outlet of the gas mixer and the inlet of the exhaust gas heater are both connected to the tube side of the exhaust gas heat exchanger, and the outlet of the exhaust gas reactor and the inlet of the cooler are both connected to the shell side of the exhaust gas heat exchanger.

3. The device for treating esterification purge gas in a synthesis gas to ethylene glycol process according to claim 1, characterized in that: The processing device also includes an MN recovery tower. The esterification purge gas enters the MN recovery tower, is sprayed and washed with methanol, and then discharged from the top of the tower. The purge gas enters the gas mixer with the purge gas from the hydrogenation unit PSA analysis gas.

4. The device for treating esterification purge gas in the synthesis gas to ethylene glycol process according to any one of claims 1 to 3, characterized in that: The processing device further comprises a steam drum, the water inlet and the water outlet of the steam drum are both connected to the shell side of the tail gas reactor.

5. The device for treating esterification purge gas in a synthesis gas to ethylene glycol process according to claim 1, characterized in that: The outlet of the cooler includes a gas outlet and a condensate outlet, the gas outlet is connected to the tower kettle of the tail gas absorption tower, and the condensate outlet is connected to the tower top of the tail gas absorption tower.

6. The device for treating esterification purge gas in a synthesis gas to ethylene glycol process according to claim 1, characterized in that: The spray water inlet pipe is connected to a branch pipe, and control valves are installed on both the spray water inlet pipe and the branch pipe.

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