Cracking tail gas recovery method

Abstract

A cracking tail gas recovery method relates to the technical field of tail gas recovery, and comprises the following steps: arranging a fuel pipeline at a tail gas swing head pipeline, and guiding tail gas into a gas-liquid separation tank; acetic anhydride I low-pressure tail gas is guided into a gas-liquid separation tank through a pipeline; a liquid phase valve is arranged at the bottom of the gas-liquid separation tank, the gas-liquid separation tank is connected with a first cracking furnace and a torch, the liquid level condition of the gas-liquid separator is monitored in real time, and liquid is discharged regularly. By optimizing the tail gas treatment process and additionally arranging the recovery device, efficient recovery and reutilization of cracking tail gas are achieved, and the resource utilization efficiency is improved; fuel gas consumption and production cost are reduced, and economic benefits of enterprises are improved; the amount of tail gas discharged to a torch is reduced, the environmental pollution is reduced, and the environmental quality is improved; the transformation process is simple and easy to implement, system operation is stable and reliable, and maintenance cost is low.

Description

Technical Field

[0001] The invention relates to the technical field of tail gas recovery, and in particular to a method for recovering cracking tail gas. Background Art

[0002] In the industrial production process of acetic anhydride II, tail gas treatment is crucial to overall energy efficiency and environmental performance. Traditionally, tail gas is usually directed to the flare system for combustion treatment. Although this treatment method is simple, it fails to fully tap the potential value contained in the tail gas.

[0003] After analyzing the tail gas composition, it was found that the combustible substances contained in the tail gas of the acetic anhydride II unit accounted for more than 80%, mainly including incompletely burned hydrocarbon compounds, hydrogen and other combustible gases. These high concentrations of combustible components not only indicate that the tail gas has significant thermal energy value, but also imply its great potential in energy recycling. The direct emission of a high proportion of combustible components in the tail gas not only causes a huge waste of energy, but also increases the system's dependence on external fuels (such as methanol purge gas), thereby pushing up the production cost of acetic anhydride products.

[0004] In view of the extensive demand for fuel gas and its combustion characteristics in the cracking furnace, recovering the tail gas from the acetic anhydride II unit and introducing it into the cracking furnace as supplementary fuel has become an extremely attractive solution. This move can not only achieve effective recovery and reuse of the energy in the tail gas, but also significantly reduce fuel consumption during system operation, reduce production costs, and improve the environmental friendliness and economic benefits of the unit. Summary of the invention

[0005] The purpose of the present invention is to solve the problems raised in the above background technology, and then propose a method for recovering cracking tail gas.

[0006] The technical solution adopted by the present invention to solve the technical problem is:

[0007] A method for recovering cracking tail gas comprises the following steps:

[0008] S1. A fuel pipeline is separately set at the tail gas head pipeline of the acetic anhydride II device to guide the tail gas to the gas-liquid separation tank for gas-liquid separation to remove the liquid in the tail gas;

[0009] S2, acetic anhydride I low-pressure tail gas is guided to the gas-liquid separation tank through a pipeline;

[0010] S3, a liquid phase valve is provided at the bottom of the gas-liquid separation tank, and the tail gas is separated into gas and liquid in the gas-liquid separation tank. The gas-liquid separation tank is connected to the first cracking furnace, and the gaseous tail gas enters the first cracking furnace along the pipeline, and the liquid is discharged from the liquid phase valve;

[0011] S4. Monitor the liquid level of the gas-liquid separator in real time and drain it regularly.

[0012] Further, in step S3, when the first cracking furnace needs maintenance, the gaseous tail gas is discharged from the first cracking furnace to the flare for combustion.

[0013] Furthermore, in step S3, a nitrogen purge pipeline is provided on one side of the gas-liquid separation tank.

[0014] Furthermore, the top of the gas-liquid separation tank is provided with an on-site flap level gauge, a pressure gauge, a remote level gauge, and a pressure alarm.

[0015] Furthermore, a two-position cut-off valve is provided on the connecting pipeline between the gas-liquid separation tank and the first cracking furnace.

[0016] Furthermore, a two-position shut-off valve is provided on the connecting pipeline between the gas-liquid separation tank and the flare.

[0017] Furthermore, the gas-liquid separation tank is also connected to a second cracking furnace, a third cracking furnace and a fourth cracking furnace.

[0018] Furthermore, the connecting pipeline between the gas-liquid separation tank and the first cracking furnace, the connecting pipeline between the gas-liquid separation tank and the second cracking furnace, the connecting pipeline between the gas-liquid separation tank and the third cracking furnace, and the connecting pipeline between the gas-liquid separation tank and the fourth cracking furnace are arranged in parallel.

[0019] Furthermore, the step S3 further includes the following steps:

[0020] S31. After the tail gas is cracked, the cracked tail gas enters the flare through the tail gas recovery buffer tank, ensuring that the tail gas recovery buffer tank can safely discharge the tail gas through the flare in the early stage of the transformation;

[0021] S32, after the vacuum pumps of the cracking furnace and the absorption unit are running stably, open the valve of the tail gas recovery buffer tank into the reaction furnace, and slowly close the valve into the flare to achieve the transfer of tail gas from the flare to the cracking furnace;

[0022] S33. The control room personnel need to monitor the outlet pressure of the absorption vacuum pump and conduct online analysis of the exhaust gas emissions after cracking, and adjust the amount of exhaust gas recovery in time according to indicators such as nitrogen oxides to ensure stable operation of the system.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention realizes efficient recovery and reuse of cracking tail gas by optimizing the tail gas treatment process and adding a recovery device, thereby improving resource utilization efficiency; reducing fuel gas consumption and production costs, thereby improving the economic benefits of the enterprise; reducing the amount of tail gas discharged to the flare, thereby reducing environmental pollution and improving environmental quality; the transformation process is simple and easy to implement, and the system operates stably and reliably with low maintenance costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A simplified process flow diagram of the first embodiment of the present invention;

[0025] Figure 2 A schematic diagram of the process flow of the second embodiment of the present invention;

[0026] Among them: 1 tail gas head pipeline, 2 fuel pipeline, 3 acetic anhydride I low-pressure tail gas, 4 liquid phase valve, 5 nitrogen purge pipeline, 6 pressure gauge, 7 pressure alarm, 8 torch, 9 the first cracking furnace, 10 the second cracking furnace, 11 the third cracking furnace, 12 the fourth cracking furnace, 100 gas-liquid separation tank. DETAILED DESCRIPTION

[0027] 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 described embodiments 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 creative work are within the scope of protection of the present invention. The present invention is further described in combination with the drawings and embodiments:

[0028] First embodiment

[0029] like Figure 1 As shown, a method for recovering cracking tail gas comprises the following steps:

[0030] S1. A fuel pipeline 2 is separately set at the tail gas head pipeline 1 of the acetic anhydride II device to guide the tail gas to the gas-liquid separation tank 100 for gas-liquid separation to remove the liquid in the tail gas;

[0031] S2, acetic anhydride I low-pressure tail gas 3 is guided to the gas-liquid separation tank 100 through a pipeline;

[0032] S3, a liquid phase valve 4 is provided at the bottom of the gas-liquid separation tank, and the tail gas is separated into gas and liquid in the gas-liquid separation tank, and the gaseous tail gas enters the first cracking furnace 9 along the pipeline, and the liquid is discharged from the liquid phase valve;

[0033] S4. Monitor the liquid level of the gas-liquid separator in real time and drain it regularly.

[0034] In an emergency situation, it is necessary to set up tail gas flow switching measures. When the first cracking furnace needs maintenance, the gaseous tail gas is discharged from the first cracking furnace to the flare 8 for combustion;

[0035] In at least one embodiment, the top of the gas-liquid separation tank is provided with an on-site flap level gauge, a pressure gauge 6 and a remote level gauge, and a pressure alarm 7 to achieve real-time monitoring.

[0036] In step S3, a nitrogen purge pipeline 5 is provided on one side of the gas-liquid separation tank.

[0037] In at least one embodiment, in step S1, the fuel pipeline can be provided with necessary valves, flow meters and other accessories according to actual conditions. At the same time, appropriate pipe materials and pipe diameters are selected according to parameters such as exhaust gas flow and pressure to ensure smooth exhaust gas transportation.

[0038] In at least one embodiment, a two-position shut-off valve is provided on the connecting pipeline between the gas-liquid separation tank and the first cracking furnace; and a two-position shut-off valve is provided on the connecting pipeline between the gas-liquid separation tank and the flare.

[0039] Second embodiment

[0040] The difference from the first embodiment is that the gas-liquid separation tank is further connected to a second cracking furnace 10, a third cracking furnace 11 and a fourth cracking furnace 12.

[0041] Furthermore, the connecting pipeline between the gas-liquid separation tank and the first cracking furnace, the connecting pipeline between the gas-liquid separation tank and the second cracking furnace, the connecting pipeline between the gas-liquid separation tank and the third cracking furnace, and the connecting pipeline between the gas-liquid separation tank and the fourth cracking furnace are arranged in parallel.

[0042] In order to fully recover the cracking tail gas and ensure the effective use of the cracking tail gas, the tail gas of the cracking absorption unit is recycled and reused, thereby reducing the absorption unit tail gas entering the flare combustion, reducing the flare emission index, and stabilizing the safe, environmentally friendly and energy-saving operation of the device, the step S3 also includes the following steps:

[0043] S31. After the tail gas is cracked, the cracked tail gas enters the flare through the tail gas recovery buffer tank, ensuring that the tail gas recovery buffer tank can safely discharge the tail gas through the flare in the early stage of the transformation;

[0044] S32, after the vacuum pumps of the cracking furnace and the absorption unit are running stably, open the valve of the tail gas recovery buffer tank into the reaction furnace, and slowly close the valve into the flare to achieve the transfer of tail gas from the flare to the cracking furnace;

[0045] S33. The control room personnel need to monitor the outlet pressure of the absorption vacuum pump and conduct online analysis of the exhaust gas emissions after cracking, and adjust the amount of exhaust gas recovery in time according to indicators such as nitrogen oxides to ensure stable operation of the system.

[0046] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for recovering cracking tail gas, characterized in that: The following steps are involved: S1. A fuel pipeline is separately set at the tail gas head pipeline of the acetic anhydride II device to guide the tail gas to the gas-liquid separation tank for gas-liquid separation to remove the liquid in the tail gas; S2, acetic anhydride I low-pressure tail gas is guided to the gas-liquid separation tank through a pipeline; S3, a liquid phase valve is provided at the bottom of the gas-liquid separation tank, and the tail gas is separated into gas and liquid in the gas-liquid separation tank. The gas-liquid separation tank is connected to the first cracking furnace, and the gaseous tail gas enters the first cracking furnace along the pipeline, and the liquid is discharged from the liquid phase valve; S4. Monitor the liquid level of the gas-liquid separator in real time and drain it regularly.

2. The method for recovering cracking tail gas according to claim 1, characterized in that: In step S3, when the first cracking furnace needs maintenance, the gaseous tail gas is discharged from the first cracking furnace to the flare for combustion.

3. The method for recovering cracking tail gas according to claim 1 or 2, characterized in that: In step S3, a nitrogen purge pipeline is provided on one side of the gas-liquid separation tank.

4. The method for recovering cracking tail gas according to claim 3, characterized in that: The top of the gas-liquid separation tank is equipped with an on-site flap level gauge, a pressure gauge, a remote level gauge, and a pressure alarm.

5. The method for recovering cracking tail gas according to claim 1, characterized in that: A two-position cut-off valve is arranged on the connecting pipeline between the gas-liquid separation tank and the first cracking furnace.

6. The method for recovering cracking tail gas according to claim 2, characterized in that: A two-position cut-off valve is arranged on the connecting pipeline between the gas-liquid separation tank and the flare.

7. The method for recovering cracking tail gas according to claim 1, characterized in that: The gas-liquid separation tank is also connected to a second cracking furnace, a third cracking furnace and a fourth cracking furnace.

8. The method for recovering cracking tail gas according to claim 7, characterized in that: The connecting pipeline between the gas-liquid separation tank and the first cracking furnace, the connecting pipeline between the gas-liquid separation tank and the second cracking furnace, the connecting pipeline between the gas-liquid separation tank and the third cracking furnace, and the connecting pipeline between the gas-liquid separation tank and the fourth cracking furnace are arranged in parallel.

9. The method for recovering cracking tail gas according to claim 1, characterized in that: The step S3 also includes the following steps: S31. After the tail gas is cracked, the cracked tail gas enters the flare through the tail gas recovery buffer tank, ensuring that the tail gas recovery buffer tank can safely discharge the tail gas through the flare in the early stage of the transformation; S32, after the vacuum pumps of the cracking furnace and the absorption unit are running stably, open the valve of the tail gas recovery buffer tank into the reaction furnace, and slowly close the valve into the flare to achieve the transfer of tail gas from the flare to the cracking furnace; S33. The control room personnel need to monitor the outlet pressure of the absorption vacuum pump and conduct online analysis of the exhaust gas emissions after cracking, and adjust the amount of exhaust gas recovery in time according to indicators such as nitrogen oxides to ensure stable operation of the system.

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