Feed gas desulfurization process for ammonia synthesis device

Abstract

The invention provides a feed gas desulfurization process for a synthetic ammonia device, relates to the technical field of synthetic ammonia, and solves the technical problem that a large amount of energy is wasted due to the fact that an existing hydrodesulfurization system is started after shutdown and temperature is raised in advance. The feed gas compressor is further provided with a heating gas path used for heating the desulfurization unit in advance, and the heating gas path is communicated with a first gas path used for introducing heating nitrogen and a second gas path used for recycling heating feed gas. The energy consumption is reduced, the heating efficiency is improved, and the driving time is shortened; the regeneration of an active phase in the regeneration process of the catalyst of the desulfurization unit can be ensured, organic sulfide is converted into inorganic sulfide (such as H2S) which is easy to remove, and the desulfurization efficiency is improved; the device is suitable for rapid temperature rising and heating during driving and is also suitable for raw material gas recovery during parking.

Description

Technical Field

[0001] The present invention relates to the technical field of synthetic ammonia, and in particular to a process for desulfurizing raw gas used in a synthetic ammonia device. Background Art

[0002] In the process of synthetic ammonia production, no matter which raw material route is used, coal, oil or natural gas, the raw synthesis gas contains a large amount of CO2, and the synthesis gas using coal as raw material also contains a variety of sulfides. These CO2 and sulfides are highly toxic to the ammonia synthesis catalyst and will affect the synthesis efficiency of ammonia. Therefore, before the synthesis gas enters the ammonia synthesis tower, CO2 and sulfides need to be removed. This process is called desulfurization and decarbonization process.

[0003] The technology of removing sulfide from raw gas is mainly divided into two categories: dry method and wet method. Wet desulfurization is further divided into wet oxidation method and amine method. The wet oxidation method is to oxidize hydrogen sulfide into elemental sulfur in the liquid phase and separate it. It is characterized by high desulfurization efficiency, low residual sulfur content in the purified gas, and can be operated under normal pressure or under pressure. The desulfurizer can be regenerated and recycled, and the operating cost is low. Among them, hydrocatalytic desulfurization promotes the reaction of organic sulfur in the raw material with hydrogen through cobalt-molybdenum catalyst CoMo or nickel-molybdenum catalyst NiMo) to convert organic sulfide into hydrogen sulfide (H2S). The generated hydrogen sulfide gas is then converted into sulfuric acid and low-sulfur hydrocarbons. Sulfuric acid can be sold on the market, while low-sulfur hydrocarbons become the final diesel product. After the hydrodesulfurization equipment has been running for a period of time, the catalyst will gradually lose its activity due to the accumulation of coke on the surface. Therefore, the catalyst needs to be regenerated to remove the coke on its surface to restore the activity of the catalyst. This step does not involve chemical reaction, but rather heat treatment to achieve catalyst cleaning.

[0004] For example, the patent with publication number CN104437032A proposes a synthetic raw gas deep fine desulfurization process and its device, which uses several levels of titanium-based cobalt-molybdenum catalysts, several levels of zinc oxide desulfurizers and a first-level multifunctional fine desulfurizer to make the total sulfur in the raw gas ≤0.01ppm.

[0005] When it is started up after a system overhaul or a long period of troubleshooting, the cobalt-molybdenum hydrogenator and the zinc oxide desulfurization tank need to be heated. Only when the temperature reaches above the reaction temperature, the catalyst surface is activated, and the adsorbed water is removed, can the desulfurization effect of natural gas before feeding be guaranteed. Although it uses titanium-based cobalt-molybdenum or titanium-based cobalt-molybdenum-nickel hydrogenation catalysts, the activation temperature is relatively low. In the actual production of synthetic ammonia, raw gas natural gas is generally used to heat it, and this process still causes a lot of energy waste. Summary of the invention

[0006] The invention provides a raw gas desulfurization process for a synthetic ammonia device, so as to solve the technical problem that the existing hydrodesulfurization system is started up after shutdown and the temperature is raised in advance, resulting in a large amount of energy waste.

[0007] The embodiments of the present invention are implemented by the following technical solutions:

[0008] A process for desulfurizing raw gas for a synthetic ammonia device comprises a raw gas compressor and a desulfurization unit connected to the raw gas compressor, wherein the desulfurization unit comprises a cobalt-molybdenum hydrogenator and a zinc oxide desulfurization tank connected in series in sequence, and the raw gas compressor is also provided with a heating gas circuit for preheating the desulfurization unit, wherein the heating gas circuit is connected to a first gas circuit for introducing heating nitrogen and a second gas circuit for recycling the heated raw gas.

[0009] Preferably, it also includes a compressor interstage separator for separating the liquid generated in the compression process, and the compressor interstage separator is also provided with an input pipeline and an output pipeline for connecting the raw gas compressor, and the input pipeline and the output pipeline are also provided with an anti-kick valve for preventing the raw gas compressor from surging.

[0010] Preferably, the raw gas compressor is also provided with a heat exchanger for recovering heat generated during the compression process, and the heat exchanger is arranged in the input pipeline.

[0011] Preferably, the output pipeline is also provided with a first recovery pipeline for recovering part of the raw gas to the combustion engine as fuel gas.

[0012] Preferably, it also includes a compressor inlet separator connected to the raw gas compressor for separating liquid from the raw gas, and the compressor inlet separator is provided with a second recovery pipeline for recovering part of the raw gas to a first furnace as fuel gas.

[0013] Preferably, the raw gas compressor comprises a first inlet connected to the compressor inlet separator, a first outlet connected to the input pipeline, a second inlet connected to the output pipeline, and a second outlet connected to the desulfurization unit.

[0014] Preferably, the second gas path is connected to the zinc oxide desulfurization tank, which is provided with two groups of stop valves for controlling the opening and closing thereof and a blind plate provided between the two groups of stop valves.

[0015] Preferably, the desulfurization unit is also connected to a first-stage furnace raw gas coil for heating raw gas and nitrogen, and a reaction pipe for transporting raw gas to a first-stage furnace. The reaction pipe is provided with a vent pipe for venting nitrogen and heating raw gas, and the second gas path is connected to the vent pipe for venting nitrogen and part of the raw gas.

[0016] A start-up method for a raw gas desulfurization process of a synthetic ammonia device comprises the following steps:

[0017] S1: Nitrogen preheating: close the second gas line and preheat the desulfurization unit to 80℃-120℃ through the first gas line;

[0018] S2; Raw gas replacement: close the first gas line, introduce the raw gas to vent the nitrogen in the pipeline, and then open the second gas line;

[0019] S3; Raw gas heating: Heat the desulfurization unit to 280℃-300℃ and start the operation.

[0020] A shutdown method for a raw gas desulfurization process of a synthetic ammonia device, when shutting down and cooling down, closing a venting pipeline for venting the raw gas and opening a second gas path.

[0021] With this technical solution, the organic sulfides in the raw gas are pre-treated by a cobalt-molybdenum hydrogenator to convert them into easily removable inorganic sulfides (such as H2S), and then these sulfides are further removed by a zinc oxide desulfurization tank. This method can greatly improve the desulfurization efficiency and ensure that the sulfur content in the raw gas meets the strict standards required for synthetic ammonia. By introducing heated nitrogen through the heating gas line and recycling the heated raw gas, the desulfurization unit can be quickly heated during startup, shortening the preheating time and reducing energy consumption. At the same time, recycling the heated raw gas further improves energy utilization;

[0022] It is used to recover the heat generated by the compression process, which helps to maintain the temperature balance of the system and reduce the need for additional cooling. It is used to recover part of the raw gas to the gas turbine as fuel gas and to recover the liquid in the raw gas. This not only reduces resource waste, but also improves the economic benefits of the overall process. By preheating the desulfurization unit with nitrogen first, then replacing the nitrogen with raw gas, and finally heating it to the operating temperature, it ensures that the system can smoothly transition during the start-up process and avoids equipment damage or safety accidents caused by sudden temperature changes. When stopping and cooling, closing the venting pipeline and opening the second gas line helps to safely reduce the system temperature and prevent harmful gases from escaping, ensuring the safety of the shutdown process. By setting up multiple recovery pipelines, the flow direction of the raw gas can be flexibly adjusted according to actual needs, which improves the operational flexibility and adaptability of the system. It can not only be used for preheating during start-up, but also provide heating during parking and cooling, which enhances the versatility of the system. By separating the liquid, the corrosion and wear inside the equipment are reduced, the service life of the equipment is extended, and the maintenance cost is reduced. The stop valve and blind plate are set on the heating gas line to facilitate the cutting off of the heating gas line during maintenance or overhaul, which improves the maintainability of the system;

[0023] The setting of the second gas circuit can ensure that the raw gas disk does not dry burn during the shutdown and cooling period, and the natural gas introduced can be fully reused to reduce its waste; it can also reuse the heated raw gas during startup, which reduces the heating energy consumption and reduces the need to heat the raw gas again, and then heats the desulfurization unit by the raw gas, greatly shortening the heating time; after the nitrogen is heated to a certain temperature, the heating effect is limited, and the front heating is performed by heating the nitrogen, and the second half of the heating process is heated by raw gas, which can ensure the regeneration of the active phase in the desulfurization unit catalyst regeneration process, while taking into account the efficiency of industrial production, reducing energy consumption while improving heating efficiency and shortening the startup time.

[0024] The technical solution of the embodiment of the present invention has at least the following advantages and beneficial effects:

[0025] 1. The present invention reduces energy consumption, improves heating efficiency and shortens start-up time;

[0026] 2. The present invention can ensure the regeneration of the active phase in the desulfurization unit catalyst regeneration process, convert organic sulfides into inorganic sulfides (such as H2S) that are easy to remove, and improve the desulfurization efficiency;

[0027] 3. The present invention is suitable for rapid heating during start-up and also suitable for raw gas recovery during shutdown. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0029] Figure 1 A schematic diagram of a process flow for a raw gas desulfurization process for a synthetic ammonia device provided in Example 1 of the present invention;

[0030] Icons: 1. Raw gas compressor; 3. Compressor interstage separator; 4. Cobalt-molybdenum hydrogenator; 5. Zinc oxide desulfurization tank; 6. Heating gas circuit; 61. First gas circuit; 62. Second gas circuit; 7. Heat exchanger; 81. Input pipeline; 82. Output pipeline; 821. First recovery pipeline; 822. Anti-surge valve; 2. Compressor inlet separator; 21. Second recovery pipeline; 13. First inlet; 11. First outlet; 12. Second inlet; 14. Second outlet; 91. Stop valve; 9. Blind plate; 41. First-stage furnace raw gas coil; 51. Reaction pipeline; 52. Vent pipeline. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0032] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. 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.

[0033] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0034] In the description of the present invention, it should be noted that if the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside" and the like appear, the orientation or position relationship indicated is based on the orientation or position relationship shown in the accompanying drawings, or is the orientation or position relationship in which the product of the application is usually placed when used. It is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0035] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0036] Example 1

[0037] A process for desulfurizing raw gas for a synthetic ammonia device comprises a raw gas compressor 1 and a desulfurization unit connected to the raw gas compressor 1, wherein the desulfurization unit comprises a cobalt-molybdenum hydrogenator 4 and a zinc oxide desulfurization tank 5 which are connected in series in sequence, and the raw gas compressor 1 is also provided with a heating gas circuit 6 for preheating the desulfurization unit, and the heating gas circuit 6 is connected to a first gas circuit 61 for introducing heating nitrogen and a second gas circuit 62 for recycling the heated raw gas.

[0038] In this embodiment, a compressor interstage separator 3 is also included for separating the liquid generated in the compression process. The compressor interstage separator 3 is also provided with an input pipeline 81 and an output pipeline 82 for connecting the raw gas compressor 1. The input pipeline 81 and the output pipeline 82 are also provided with an anti-kick valve 822 for preventing the raw gas compressor 1 from surging.

[0039] In this embodiment, the raw gas compressor 1 is further provided with a heat exchanger 7 for recovering heat generated during the compression process, and the heat exchanger 7 is provided in the input pipeline 81 .

[0040] In this embodiment, the output pipeline 82 is further provided with a first recovery pipeline 821 for recovering part of the raw gas to the combustion engine as fuel gas.

[0041] In this embodiment, it also includes a compressor inlet separator 2 connected to the raw gas compressor 1 for separating liquid from the raw gas. The compressor inlet separator 2 is provided with a second recovery pipeline 21 for recovering part of the raw gas to a first furnace as fuel gas.

[0042] In this embodiment, the raw gas compressor 1 includes a first inlet 13 connected to the compressor inlet separator 2, a first outlet 11 connected to the input pipeline 81, a second inlet 12 connected to the output pipeline 82 and a second outlet 14 connected to the desulfurization unit.

[0043] In this embodiment, the second gas path 62 is connected to the zinc oxide desulfurization tank 5 , which is provided with two groups of stop valves 91 for controlling the opening and closing thereof and a blind plate 9 provided between the two groups of stop valves 91 .

[0044] In this embodiment, the desulfurization unit is also connected to a first-stage furnace raw gas coil 41 for heating raw gas and nitrogen, and a reaction pipe 51 for transporting raw gas to a first-stage furnace. The reaction pipe 51 is provided with a vent pipe 52 for venting nitrogen and heating raw gas. The second gas path 62 is connected to the vent pipe 52 for venting nitrogen and part of the raw gas.

[0045] Working principle and usage:

[0046] The organic sulfides in the raw gas are pre-treated by the cobalt-molybdenum hydrogenator 4 and converted into inorganic sulfides (such as H2S) that are easy to remove, and then these sulfides are further removed by the zinc oxide desulfurization tank 5. This method can greatly improve the desulfurization efficiency and ensure that the sulfur content in the raw gas meets the strict standards required for synthetic ammonia. By introducing heated nitrogen through the heating gas line 6 and recycling the heated raw gas, the desulfurization unit can be quickly heated during startup, shortening the preheating time and reducing energy consumption. At the same time, recycling the heated raw gas further improves energy utilization;

[0047] It is used to recover the heat generated by the compression process, which helps to maintain the temperature balance of the system and reduce the need for additional cooling. It is used to recover part of the raw gas to the gas turbine as fuel gas and to recover the liquid in the raw gas. This not only reduces resource waste, but also improves the economic benefits of the overall process. By preheating the desulfurization unit with nitrogen first, then replacing the nitrogen with raw gas, and finally heating it to the operating temperature, it ensures that the system can smoothly transition during the start-up process and avoids equipment damage or safety accidents caused by sudden temperature changes. When parking and cooling, closing the venting pipeline 52 and opening the second gas path 62 helps to safely reduce the system temperature and prevent harmful gases from escaping, ensuring the safety of the parking process. By setting up multiple recovery pipelines, the flow direction of the raw gas can be flexibly adjusted according to actual needs, which improves the operational flexibility and adaptability of the system. It can not only be used for preheating during start-up, but also provide heating during parking and cooling, enhancing the versatility of the system. By separating the liquid, corrosion and wear inside the equipment are reduced, the service life of the equipment is extended, and the maintenance cost is reduced. A stop valve 91 and a blind plate 9 are provided on the heating gas circuit 6, so as to facilitate cutting off the heating gas circuit 6 during maintenance or overhaul, thereby improving the maintainability of the system;

[0048] The second gas path 62 can be set up to ensure that the raw gas disk does not dry burn during the shutdown and cooling period, and the natural gas introduced can be fully reused to reduce its waste; it can also reuse the heated raw gas during the start-up period, which reduces the heating energy consumption and reduces the need to heat the raw gas again, and then the process of heating the desulfurization unit by the raw gas, greatly shortening the heating time; after the nitrogen is heated to a certain temperature, the heating effect is limited, and the front heating is performed by heating the nitrogen, and the second half of the heating process is heated by the raw gas, which can ensure the regeneration of the active phase in the regeneration process of the desulfurization unit catalyst, while taking into account the efficiency of industrial production, reducing energy consumption while improving heating efficiency and shortening the start-up time.

[0049] Example 2

[0050] A start-up method for a raw gas desulfurization process of a synthetic ammonia device comprises the following steps:

[0051] S1: Nitrogen preheating: close the second gas line 62 and preheat the desulfurization unit to 120°C for 5 hours through the first gas line 61;

[0052] S2; Raw gas replacement: close the first gas line 61, introduce the raw gas to vent the nitrogen in the pipeline and then open the second gas line 62;

[0053] S3; Raw gas heating: Heat the desulfurization unit to 300℃ for 5h and then start the operation.

[0054] A shutdown method for a raw gas desulfurization process of a synthetic ammonia device, when shutting down and cooling down, closing a venting pipeline 52 for venting the raw gas and opening a second gas path 62.

[0055] In this embodiment, after startup, the total sulfur in the raw gas leaving the desulfurization unit is ≤0.01 ppm.

[0056] Comparative Example 1

[0057] The only difference between this comparative example and Examples 1 and 2 is that in this comparative example, the second gas circuit 62 is not provided, and the start-up preheating process is directly heated by circulating nitrogen, and the nitrogen is heated for 22 hours to 280° C. before start-up.

[0058] Comparative Example 2

[0059] The only difference between this comparative example and Examples 1 and 2 is that in this comparative example, the second gas circuit 62 is not provided, and the start-up preheating process is first heated to 120°C with circulating nitrogen for 5 hours, and then heated with raw gas, but the raw gas is not recycled, and is heated to 300°C for 8 hours before start-up.

[0060] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A process for desulfurizing raw gas for a synthetic ammonia plant, characterized by: The invention comprises a raw gas compressor (1) and a desulfurization unit connected to the raw gas compressor (1), wherein the desulfurization unit comprises a cobalt-molybdenum hydrogenator (4) and a zinc oxide desulfurization tank (5) which are connected in series in sequence, and the raw gas compressor (1) is also provided with a heating gas path (6) for preheating the desulfurization unit, and the heating gas path (6) is connected to a first gas path (61) for introducing heating nitrogen and a second gas path (62) for recycling the heating raw gas.

2. A process for desulfurizing raw gas for a synthetic ammonia plant according to claim 1, characterized in that: It also includes a compressor interstage separator (3) for separating liquid generated during the compression process, and the compressor interstage separator (3) is also provided with an input pipeline (81) and an output pipeline (82) for connecting the raw gas compressor (1), and the input pipeline (81) and the output pipeline (82) are also provided with an anti-kick valve (822) for preventing the raw gas compressor (1) from surging.

3. A process for desulfurizing raw gas for a synthetic ammonia plant according to claim 2, characterized in that: The raw gas compressor (1) is also provided with a heat exchanger (7) for recovering heat generated during the compression process, and the heat exchanger (7) is arranged on the input pipeline (81).

4. A process for desulfurizing raw gas for a synthetic ammonia plant according to claim 2, characterized in that: The output pipeline (82) is also provided with a first recovery pipeline (821) for recovering part of the raw gas to the combustion engine.

5. A process for desulfurizing raw gas for a synthetic ammonia plant according to claim 2, characterized in that: It also includes a compressor inlet separator (2) connected to the raw gas compressor (1) for separating liquid from the raw gas, and the compressor inlet separator (2) is provided with a second recovery pipeline (21) for recovering part of the raw gas to the first stage furnace.

6. A process for desulfurizing raw gas for a synthetic ammonia plant according to claim 5, characterized in that: The raw gas compressor (1) comprises a first inlet (13) connected to the compressor inlet separator (2), a first outlet (11) connected to the input pipeline (81), a second inlet (12) connected to the output pipeline (82), and a second outlet (14) connected to the desulfurization unit.

7. A process for desulfurizing raw gas for a synthetic ammonia plant according to any one of claims 1 to 6, characterized in that: The second gas path (62) is connected to the zinc oxide desulfurization tank (5), and is provided with two groups of stop valves (91) for controlling the opening and closing thereof and a blind plate (9) provided between the two groups of stop valves (91).

8. A process for desulfurizing raw gas for a synthetic ammonia plant according to any one of claims 1 to 6, characterized in that: The desulfurization unit is also connected to a first-stage furnace raw gas coil (41) for heating raw gas and nitrogen, and a reaction pipeline (51) for conveying raw gas to a first-stage furnace. The reaction pipeline (51) is provided with a venting pipeline (52) for venting nitrogen and heating raw gas. The second gas path (62) is connected to the venting pipeline (52) for venting nitrogen and part of the raw gas.

9. A start-up method for a raw gas desulfurization process for a synthetic ammonia plant according to any one of claims 1 to 8, characterized in that: The steps include: S1: Nitrogen preheating: close the second gas line (62) and preheat the desulfurization unit to 80°C-120°C through the first gas line (61); S2; Raw gas replacement: close the first gas line (61), introduce the raw gas to vent the nitrogen in the pipeline and then open the second gas line (62); S3; Raw gas heating: Heat the desulfurization unit to 280℃-300℃ and start the operation.

10. A shutdown method for a raw gas desulfurization process of a synthetic ammonia plant according to any one of claims 1 to 8, characterized in that: When the vehicle is stopped for cooling, the venting pipeline (52) for venting the raw gas is closed and the second gas path (62) is opened.

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