A start-up method for a carbon dioxide pre-hydrogenation device

Abstract

The present application relates to a kind of carbon two prehydrogenation device start-up method, comprising the following steps: carbon two prehydrogenation device airtightness check is qualified and after inert gas replacement, in the carbon two prehydrogenation device, ethylene and / or natural gas are punched to 2.0~6.0Mpa, then hydrogenation raw material is introduced into the carbon two prehydrogenation device, and the carbon two prehydrogenation device meets the prehydrogenation condition and starts reaction.This method not only avoids the temperature of the punching process device, effectively improves the efficiency of start-up, and the punching process does not introduce other impurities, also shortens the time of outlet product qualified, improves the economic benefit of device.

Description

Technical Field

[0001] This invention relates to a method for starting up a hydrogenation unit, specifically a method for starting up a pre-hydrogenation unit for C2 hydrocarbons, which is particularly suitable for starting up a selective hydrogenation unit for alkynes. Background Technology

[0002] Ethylene in the C2 fraction is an important product of the ethylene industry, mainly used in the production of downstream products such as polyethylene. In addition to a large amount of ethylene, the cracked C2 fraction also contains a small amount of acetylene (0.5–2.0 vol%), which can seriously affect the polymerization process of ethylene (acetylene participates in the polymerization reaction, poisons the polymerization catalyst, and poses safety hazards to the polymerization system). Therefore, the C2 fraction needs to be selectively hydrogenated to remove acetylene before it can be used in the production of downstream products such as polyethylene. Selective hydrogenation for acetylene removal of C2 fraction plays a crucial role in the ethylene industry.

[0003] In recent years, most of the newly built large-scale ethylene plants in China have adopted the C2 pre-hydrogenation process. Pre-hydrogenation includes pre-propane dehydrogenation and pre-ethane dehydrogenation. Compared with the post-hydrogenation process, the C2 pre-hydrogenation process has the following advantages: (1) The separation process is simplified, the equipment investment is low, and the operating energy consumption is low. (2) It utilizes the hydrogen contained in the material itself, and there is no need to remove acetylene by external hydrogen supply (this method is used in post-hydrogenation). Therefore, its ethylene tower does not have a "Bass distillation section", which avoids the influence of impurities (impurities introduced with hydrogen, such as CO, methane, etc.) on the ethylene product and improves the purity of the produced ethylene. (3) Less green oil is generated in the catalyst, so the catalyst regeneration cycle and service life are long. (4) The operation is very simple. The reactor can run continuously for 3 to 5 years without regeneration or backup reactor. (5) While hydrogenating acetylene, propyne and propadiene (MAPD) ​​are hydrogenated, reducing the load on the separation system and C3 hydrogenation unit, and even completely eliminating the C3 hydrogenation system. However, pre-hydrogenation has fewer control measures for the reactor than post-hydrogenation. Due to the large amount of hydrogen in the material, there is a potential risk of overheating in the reactor bed. If the carbon monoxide content in the material fluctuates (molar fraction 0.05% to 0.3%), the reactor outlet is prone to acetylene leakage. Furthermore, the material needs to be pre-treated; otherwise, catalyst poisons (such as As and S) in the material will poison the catalyst, requiring shutdown and catalyst replacement.

[0004] In the pre-C2 hydrogenation process, the feed entering the hydrogenation reactor contains not only C2 fractions but also some C3 fractions. While removing acetylene, most of the propyne and propadiene must also be removed. Due to numerous side reactions in this hydrogenation process, coupled with high and fluctuating H2 and CO content, the start-up is more difficult and time-consuming compared to post-hydrogenation processes, and it is prone to runaway temperatures. Particularly during the initial start-up pressurization process, the feedstock cracked gas enters the reactor bed. Before the reactor pressure reaches the set pressure, the feedstock gas cannot flow, and alkynes and dienes are statically adsorbed by the catalyst, generating a large amount of adsorption heat. This heat, when accumulated to a certain level, will drive the hydrogenation reaction of alkynes and dienes, further generating reaction heat. If the catalyst reaction temperature is low and the activity is high, the large amount of adsorption and reaction heat will cause the bed temperature to rise rapidly, easily leading to runaway temperatures. Runaway temperatures result in material waste and economic losses, while also prolonging the start-up time. Furthermore, runaway temperatures can cause catalyst coking, covering active sites, reducing catalyst activity, accelerating catalyst deactivation, and severely affecting the long-term stability of the catalyst. Therefore, technicians studied the hydrogenation process, especially the start-up methods of the unit.

[0005] CN200980154641.X discloses a method for selectively hydrogenating acetylene to ethylene, comprising: contacting a feed stream containing ethylene and acetylene with a catalyst under reaction conditions, thereby producing an output feed stream with reduced acetylene content, wherein the feed stream contains 1-8000 ppm carbon monoxide (CO). Specifically, the process feed stream containing ethylene, ethane, and acetylene is compressed, and the temperature is adjusted to cool the compressed gas before it enters a hydrogenation reactor. A layered spherical catalyst is used to selectively hydrogenate the acetylene fraction in the feed, wherein the CO content in the feed is 1-8000 ppm, and the reaction conditions include a pressure of 100 kPa-14.0 MPa and a selective hydrogenation reaction temperature of 10-300 °C. In this process, when a large amount of carbon monoxide is present, the monoxide acts as a reversible inhibitor at the active catalyst site. The acetylene removal method disclosed in this invention does not describe the start-up process and cannot solve the problem of overheating during the start-up of a C2 hydrogenation unit.

[0006] CN201510684013.X discloses a selective hydrogenation method for alkynes and / or dienes in C2 and C3 fractions. The method involves mixing a cracked gas stream from the top of a pre-propane or pre-ethane stripper with a hydrogen-rich gas stream containing carbon monoxide to obtain a carbon monoxide-stable hydrogen-rich gas stream. The carbon monoxide content is 0.15–0.3 mol%, and the carbon monoxide concentration fluctuates within ±20%. This mixed hydrogen-rich cracked gas stream is compressed to 2–4 MPa, subjected to heat exchange, and then reacted with a palladium-supported selective hydrogenation catalyst in a fixed-bed hydrogenation reactor. This pre-hydrogenation method claims to effectively avoid runaway temperatures and alkyne leaks in the hydrogenation reactor caused by large fluctuations in carbon monoxide in the cracked gas generated by the preceding system. Under high space velocity conditions, it can effectively improve catalyst activity and selectivity, and save on the amount of active catalyst components used.

[0007] Wu Hao et al. (Chemical Industry Progress, 2002, 21(9): 673-675) analyzed the influence of CO concentration on the hydrogenation reaction in the pre-hydrogenation process of C2, discussed the factors of CO generation, and proposed effective measures to reduce CO generation and control CO concentration fluctuations: strengthen sulfur injection operation, reduce the feeding temperature of the cracking furnace, and prevent methanol from entering the cracking furnace, etc., to ensure stable operation of the unit. Huang Wenjiao et al. (Industrial Catalysis, 2016, 24(8): 58-63) adopted the cylinder gas injection method to prevent overheating during the start-up process of the unit, ensuring that the CO concentration in the cracked gas is greater than 2000×10. -6 .

[0008] The aforementioned existing technologies for starting up C2 hydrogenation units all rely on controlling the stability and content of CO in the feedstock to effectively avoid overheating caused by CO fluctuations or excessively low CO content. However, these methods cannot address the issue of overheating during the start-up process. Before the reactor pressure reaches the set pressure, the feedstock gas cannot flow, leading to the static adsorption of alkynes and dienes by the catalyst, generating significant adsorption heat. This accumulated heat can trigger hydrogenation reactions in alkynes and dienes, further generating reaction heat and causing overheating. Furthermore, these disclosed start-up methods require a higher CO concentration than in normal cracked gas. Once the start-up heating process is complete, the concentration needs to be adjusted and reduced to the normal cracked gas CO range, extending the start-up time. Simultaneously, as CO acts as a catalyst activity inhibitor, a reduced CO content "releases" more adsorption sites on the catalyst, further increasing the risk of overheating.

[0009] Liang Yulong et al. (Petrochemical Technology, 2018, 47(2): 192-196) effectively suppressed the initial activity of the C2 pre-hydrogenation catalyst by passivating it. During the start-up of the low space velocity C2 pre-hydrogenation unit, the reactor was directly pressurized to 3.6 MPa with cracked gas. After pressurization, the reactor was heated to the inlet temperature of 64°C at a rate of 10°C every 30 min. The outlet product was qualified and there was no "temperature runaway". In this technology, the initial activity of the catalyst is reduced by passivation, and there is no temperature runaway during the start-up process. However, this start-up method is only suitable for specific passivated catalysts and is not suitable for the stable start-up of all C2 pre-hydrogenation units.

[0010] The isothermal C2 hydrogenation reactor start-up process reported by Xue Xinchao, Zeng Feipeng, et al. (Ethylene Industry, 2016, 28(3):39-43) involved first pressurizing the system with nitrogen to 1.0 MPa during the first start-up process, and then adjusting the CO concentration in the material to 1800 mL / m³. 3 The reactor temperature rises, the unit overheats, and the system shuts down. During the second restart, nitrogen purging is performed, the inlet temperature is set to 15℃, and the inlet CO is adjusted to 5000 mL / m³. 3 The temperature gradually increased, and the start-up process took 7.5 hours. During the first start-up in this report, the unit experienced a temperature runaway, and during the second start-up, the CO concentration was high, and the heating process took a long time.

[0011] In her doctoral dissertation at Lanzhou University, "Development and Application Research of C2 Pre-hydrogenation Catalysts," Che Chunxia recommends a startup method for a C2 pre-hydrogenation unit. This method requires pre-pressurizing the reactor with gas cylinders to a CO content of 5000 μL / L, followed by nitrogen pressurization to a bed pressure of 0.6 MPa, which is maintained for 4–6 hours. The reactor inlet feed valve and pipeline bypass feed valve are then opened, and the bypass pressurization is performed to 3.6 MPa. The flow rate is then adjusted to a higher level to begin reactor preheating and temperature rise. This technology requires a high CO content in the reactor during startup and involves a long pressurization time using N2. Furthermore, the N2 pre-pressurization introduces impurities and fails to address the issue of reducing the pressurization speed during the start-up process to prevent rapid accumulation of adsorbed heat and subsequent temperature runaway.

[0012] Therefore, there is an urgent need to develop a start-up method for a pre-hydrogenation unit of C2 that controls overheating during the stamping process without introducing other impurities, while also having a short start-up time. Summary of the Invention

[0013] Based on the above, the main objective of this invention is to provide a start-up method for a C2 pre-hydrogenation unit. This method not only avoids overheating of the unit during the stamping process and effectively improves start-up efficiency, but also prevents the introduction of other impurities during the stamping process and shortens the time required for the exported products to meet quality standards.

[0014] Therefore, the present invention provides a start-up method for a C2 pre-hydrogenation unit, comprising the following steps: after the C2 pre-hydrogenation unit passes the airtightness test and is purged with inert gas, ethylene and / or natural gas are introduced into the C2 pre-hydrogenation unit and pressurized to 2.0-6.0 MPa, and then hydrogenation feedstock is introduced into the C2 pre-hydrogenation unit. After the C2 pre-hydrogenation unit meets the pre-hydrogenation conditions, the reaction is started.

[0015] The start-up method of the C2 pre-hydrogenation device of the present invention uses nitrogen as an inert gas, for example, but not limited to.

[0016] The startup method of the C2 pre-hydrogenation unit of the present invention preferably involves introducing ethylene and / or natural gas into the C2 pre-hydrogenation unit and pressurizing it to 2.5-4.0 MPa.

[0017] The start-up method for the C2 pre-hydrogenation unit described in this invention refers to the hydrogenation feedstock, which is the hydrogenated material flowing out from the top of the cracking furnace after the cracking furnace is normally and stably put into operation and separated by a propane stripper or an ethane stripper, with a composition that meets the start-up requirements. For example, but not limited to, the representative description of feedstock for C2 pre-hydrogenation in "Ethylene Process and Feedstock," edited by Hu Jie and published by Chemical Industry Press, is shown in Table 1. The book also describes the feedstock composition (mass fraction) of a petrochemical C2 pre-ethane stripper hydrogenation unit as follows: hydrogen 20.09%, methane 25.35%, acetylene 0.99%, ethylene 60.46%, ethane 10.8%, and carbon monoxide 0.092%.

[0018] Table 1. Composition of materials flowing into the C2 hydrogenation reactor inlet before propane removal.

[0019] Components Composition (mole fraction) / % Components Composition (mole fraction) / % hydrogen 14.80 Methylacetylene 0.18 carbon monoxide 0.07 Propylene 0.17 methane 23.53 propylene 14.39 Acetylene 0.66 propane 0.35 ethylene 39.04 <![CDATA[C4 fraction]]> 0.12 Ethane 6.69

[0020] To ensure more stable startup, the start-up method for the C2 pre-hydrogenation unit of the present invention preferably includes, based on the volume of the hydrogenation feedstock, the hydrogenation feedstock comprising: CO 100–10000 ppm, hydrogen 3–40%, methane 0–40%, acetylene 0.01–5.0%, ethylene 20–90%, and ethane 1–30%; more preferably, the hydrogenation feedstock comprises: CO 400–1000 ppm, hydrogen 10–35%, methane 10–30%, acetylene 0.02–1.2%, ethylene 30–55%, and ethane 5–25%.

[0021] The start-up method of the C2 pre-hydrogenation unit of the present invention preferably includes the following step between the inert gas replacement and the ethylene and / or natural gas pressurization: CO is introduced into the C2 pre-hydrogenation unit so that the volume content of CO in the C2 pre-hydrogenation unit reaches more than 1000 ppm, preferably 1000 ppm to 5000 ppm.

[0022] The start-up method for the C2 pre-hydrogenation unit of the present invention preferably includes the following steps:

[0023] (1) After the airtightness of the pre-hydrogenation unit of C2 is qualified, it is replaced with inert gas;

[0024] (2) Ethylene and / or natural gas are introduced into the pre-hydrogenation unit of C2 and pressurized to 2.0–6.0 MPa;

[0025] (3) Use the cracking furnace to generate cracked gas for hydrogenation feedstock. When the C4 content in the top material of the high-pressure ethane / propane de-coupling tower of the cracking furnace is ≤0.1v%, the cracked gas for hydrogenation feedstock is ready for operation. The cracked gas for hydrogenation feedstock is introduced into the pre-hydrogenation unit of C2 and pressurized to the reaction pressure of 2.0 to 6.0 MPa.

[0026] (4) Introduce steam into the steam preheater to heat the cracked gas of the hydrogenation feedstock until the inlet and outlet temperature difference of the hydrogenation reactor of the C2 pre-hydrogenation unit is 3-25℃. The temperature in the hydrogenation reactor rises from top to bottom and forms multiple temperature gradients, the temperature gradients being 1-10℃. Once the acetylene at the end outlet of the C2 pre-hydrogenation unit is qualified, the bed heating is completed.

[0027] In step (4) of the present invention, the temperature gradient refers to the temperature difference between two adjacent temperature measurement points set from top to bottom in the hydrogenation reactor of the C2 pre-hydrogenation device.

[0028] The startup method of the C2 pre-hydrogenation unit of the present invention preferably includes the following steps: In step (3), the cracked gas of the hydrogenation feedstock can be generated by a cracking furnace. The cracked gas of the hydrogenation feedstock enters the quench oil tower, quench water tower, cracked gas compressor sections I-IV, alkaline washing water tower, cracked gas dryer, high-pressure ethane / propane stripper, and cracked gas compressor section V of the cracking furnace in sequence to finally obtain the cracked gas of the hydrogenation feedstock. When the C4 content in the top material of the high-pressure ethane / propane stripper of the cracking furnace is ≤0.1v%, the cracked gas as the hydrogenation feedstock meets the conditions for startup.

[0029] The startup method of the C2 pre-hydrogenation unit of the present invention preferably further includes: adjusting the inlet temperature of the C2 pre-hydrogenation unit after step (4). Specifically, in the startup method of the C2 pre-hydrogenation unit disclosed in the present invention, after step (4), the inlet temperature of the hydrogenation reactor of the C2 pre-hydrogenation unit can be selectively adjusted: after the reaction bed temperature is basically stable, the inlet temperature of each hydrogenation reactor is finely adjusted according to the required load distribution of each hydrogenation reactor of the C2 pre-hydrogenation unit. Preferably, the inlet temperature of the C2 pre-hydrogenation unit is adjusted to 55℃-80℃, and the heating rate during the adjustment process is 0.5-1℃ / h.

[0030] The startup method of the pre-hydrogenation device for C2 according to the present invention is preferably wherein the pre-hydrogenation device for C2 consists of two or three hydrogenation reactors connected in series.

[0031] The startup method of the C2 pre-hydrogenation device of the present invention preferably comprises a three-stage hydrogenation reactor; the inlet temperature of the first stage hydrogenation reactor is adjusted to 55℃-65℃, the inlet-outlet temperature difference is 15-25℃, and the temperature gradient is 5-9℃; the inlet temperature of the second stage hydrogenation reactor is adjusted to 65℃-70℃, the inlet-outlet temperature difference is 8-15℃, and the temperature gradient is 3-6℃; the inlet temperature of the third stage hydrogenation reactor is adjusted to 70℃-80℃, the inlet-outlet temperature difference is 4-10℃, and the temperature gradient is 1-3℃.

[0032] The start-up method of the pre-hydrogenation unit for C2 according to the present invention preferably includes a hydrogenation reactor that is an adiabatic bed or an isothermal bed, with an adiabatic bed being more preferred.

[0033] The start-up method for the C2 pre-hydrogenation unit described in this invention uses pre-hydrogenation conditions commonly used in this technical field, such as, but not limited to, the process conditions disclosed in CN104098426A: reactor inlet temperature 35℃~180℃, reaction pressure 2.0~4.0MPa, and gas hourly space velocity 4000~25000h⁻¹. -1 The preferred pre-hydrogenation conditions recommended by this invention are: 30°C to 100°C, reaction pressure 2.0 to 6.0 MPa, and reaction volume hourly space velocity 2000 to 20000 h⁻¹. -1 Preferred parameters: inlet temperature 50℃~95℃, reaction pressure 2.5~4.0MPa, volumetric hourly space velocity 6000~15000h⁻¹ -1 .

[0034] The start-up method for the C2 pre-hydrogenation unit described in this invention allows for the use of any pressing method, such as pressing with ethylene and / or natural gas pipeline gas, as long as the pressure required by this invention is met. This invention does not impose any particular limitation on the pressing time.

[0035] The start-up method for a C2 front hydrogenation unit according to the present invention is applicable to all acetylene selective hydrogenation units, especially units adopting the C2 front hydrogenation process, such as C2 front deethanization front hydrogenation units, C2 front depropanization front hydrogenation units, and selective hydrogenation acetylene removal units matched with ethylene production by ethane cracking, etc., which selectively hydrogenate acetylene contained in the overhead effluent from a depropanizer tower / deethanizer tower / ethane cracking unit to completely convert it into ethylene, with no loss of ethylene at the same time.

[0036] In the start-up method for a C2 front hydrogenation unit according to the present invention, the selective hydrogenation catalyst used in the front hydrogenation process includes, but is not limited to, supported catalysts. For example, the carrier thereof can be alumina, silica, etc., and the active components thereof can be noble metals Pd, Pt, Au, or non-noble metals Ni, Fe, etc. A selective hydrogenation catalyst with Pd as the main active component is preferred. Of course, the present invention is not particularly limited thereto, and the selective hydrogenation catalyst used in the front hydrogenation process can be adjusted according to the actual requirements of the front hydrogenation process.

[0037] The beneficial effects of the present invention are as follows:

[0038] In the start-up method for a C2 front hydrogenation unit provided by the present invention, pressurization is performed by introducing ethylene and / or natural gas, which avoids impurities introduced by nitrogen pressurization, can shorten the time for the product to reach qualification, and reduces material loss. Compared with the traditional slow pressurization using cracked gas as hydrogenation feedstock, the present invention uses ethylene and / or natural gas to directly pressurize the C2 front hydrogenation unit from a slight positive pressure to a reaction pressure of 2.0 to 6.0 MPa, and the present invention has the characteristics of fast pressurization and short pressurization time; meanwhile, the method of the present invention also avoids the problem of unit temperature runaway caused by the fact that when the feedstock gas cannot flow, the alkynes and dienes therein are statically adsorbed by the catalyst to generate a large amount of adsorption heat, and when the heat accumulates to a certain extent, it will trigger the hydrogenation reaction of alkynes and dienes to further generate reaction heat; in the method of the present invention, the presence of a large amount of ethylene and / or natural gas dilutes the concentrations of alkynes and dienes in the hydrogenation feedstock, effectively reduces the risk of temperature runaway in the unit during the temperature rise process, and shortens the time from the start of hydrogenation reaction to the qualification of the product.

[0039] In addition, in the start-up method of the present invention, before the pressurization with ethylene and / or natural gas, that is, in the early stage of start-up, CO is charged, which can reduce subsequent CO concentration adjustment steps, thereby further effectively shortening the start-up time. Description of Drawings

[0040] Figure 1 is a schematic flow diagram of the C2 front hydrogenation process;

[0041] wherein, after the cracked gas as hydrogenation feedstock passes through a deethanizer / depropanizer, heavy components are separated, and light components enter a hydrogenation reactor as hydrogenation feedstock for hydrogenation, and the hydrogenation product enters a demethanizer for separation;

[0042] Figure labels: 1-Cracked gas of hydrogenation feedstock, 2-Hydrogenation feedstock, 3-Hydrogenation product, 4-Ethane / propane removal tower, 5-C2 pre-hydrogenation unit, 6-Methanation removal tower. Detailed Implementation

[0043] The following provides a detailed description of the embodiments of the present invention: These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and processes. However, the scope of protection of the present invention is not limited to the following embodiments. Experimental methods in the following embodiments without specific conditions are generally performed under conventional conditions. Unless otherwise specified, all percentages in the following embodiments and comparative examples are by weight.

[0044] Detection methods

[0045] The composition of each component in the cracked gas of the hydrogenation feedstock and the outlet gas of each stage of the hydrogenation reactor was analyzed using gas chromatography under the following operating conditions:

[0046] a) Detector: Hydrogen flame detector;

[0047] b) Chromatographic column: a stainless steel column with a length of 3.0m and an inner diameter of 3mm;

[0048] c) Inlet temperature: 70℃;

[0049] d) Column temperature: 110℃;

[0050] e) Detector temperature: 150℃.

[0051] Calculation formula

[0052]

[0053] Figure 1 This is a schematic diagram of the pre-hydrogenation process for C2. (See also...) Figure 1 As shown, the cracked gas 1, the feedstock for hydrogenation, passes through the ethane / propane dehydrogenator 4, where the heavy components are separated. The light components are used as feedstock 2 and enter the pre-hydrogenation unit 5 for hydrogenation. The resulting hydrogenated product 3 is then separated in the demethanizer 6.

[0054] Example 1 (CO charging, ethylene pressurization)

[0055] A domestic 270,000-ton / year ethylene C2 pre-propane dehydrogenation unit employs a three-stage series adiabatic bed process for selective acetylene hydroremoval. The hydrotreating catalyst used is Shell's 7741B-T, which uses alumina as a support and approximately 0.03% Pd as the active component. The composition of the hydrotreating feedstock is shown in Table 2. The start-up method for this C2 pre-propane dehydrogenation unit includes the following steps:

[0056] (1) After the air tightness of the pre-hydrogenation unit of C2 is qualified, the nitrogen replacement is qualified.

[0057] (2) After the cracking furnace is put into operation, the cracked gas of the hydrogenation feedstock enters the quench oil tower, quench water tower, cracked gas compressor I-IV section, alkaline washing water tower, cracked gas dryer, high pressure propane removal tower, and cracked gas compressor V section in sequence.

[0058] (3) CO is injected into the first, second and third stage hydrogenation reactors of the C2 pre-hydrogenation unit. The catalyst loading of each hydrogenation reactor is 9m³, and CO is injected into 4 steel cylinders (40L / cylinder, pressure 11 MPa) with a CO content of 1500ppm. The CO injection time is 10h.

[0059] (4) Ethylene pressurization: Pressurize the hydrogenation reactor of the C2 pre-hydrogenation unit to 2.0 MPa for 30 min.

[0060] (5) Open all the feed valves and continue to pressurize the reactor bed with the bypass pyrolysis gas for 2 minutes at a pressure of 3.5 MPa. The reactor inlet temperature is preheated to 32°C by the pyrolysis gas. The bed temperature rises by 2°C after the pressing is completed.

[0061] (6) Introduce steam into the steam preheater to heat the cracked gas of the hydrogenation feedstock until a positive temperature difference appears in the first stage hydrogenation reactor, that is, the temperature in the first stage hydrogenation reactor gradually increases from top to bottom. There are 3 temperature measuring points from the inlet to the outlet in the first stage hydrogenation reactor. When an 8°C temperature gradient is formed between two adjacent temperature measuring points, that is, the inlet and outlet temperature difference of the first stage hydrogenation reactor is 16°C, and the online display shows that the acetylene conversion rate reaches 58%, the heating of the first stage hydrogenation reactor ends; start heating the second stage hydrogenation reactor until a positive temperature difference appears in the second stage hydrogenation reactor, that is, the temperature in the second stage hydrogenation reactor gradually increases from top to bottom, and the temperature in the second stage hydrogenation reactor gradually increases from the inlet to the outlet. Five temperature measuring points are set up at the inlet. Heating of the second-stage hydrogenation reactor ends when a temperature gradient of 3.5°C is formed between two adjacent measuring points (i.e., the inlet-outlet temperature difference is 14°C) and the acetylene concentration at the outlet of the second-stage hydrogenation reactor is below 90 ppm. Heating of the third-stage hydrogenation reactor then begins until a positive temperature difference appears, meaning the temperature gradually increases from top to bottom. Five temperature measuring points are set up from the inlet to the outlet of the third-stage hydrogenation reactor. Heating of the third-stage hydrogenation reactor ends when a temperature gradient of 2°C is formed between two adjacent measuring points (i.e., the inlet-outlet temperature difference is 8°C) and the acetylene concentration at the outlet of the third-stage hydrogenation reactor is below 1 ppm.

[0062] (7) After the reaction bed temperature is basically stable, the inlet temperature of each hydrogenation reactor is finely adjusted according to the load distribution required by each hydrogenation reactor to ensure that the acetylene at the outlet of the third-stage hydrogenation reactor is less than 1 ppm, the total ethylene selectivity of the first, second and third-stage hydrogenation reactors is ≥60%, and the total start-up time from the commissioning of the cracking furnace to the qualified acetylene at the outlet of the third-stage hydrogenation reactor is 14 hours. The start-up is completed at a reaction pressure of 3.5 MPa and a reaction volume hourly space velocity of 7500 h⁻¹. -1 The inlet reaction temperatures of the first, second, and third stage hydrogenation reactors are 58.4℃, 68.1℃, and 74.9℃, respectively.

[0063] Table 2 Composition of Hydrogenation Feedstock

[0064] Hydrogenation feedstock <![CDATA[H2]]> <![CDATA[C2H2]]> <![CDATA[C2H4]]> <![CDATA[C2H6]]> <![CDATA[CH4]]> CO <![CDATA[C3H6]]> <![CDATA[C3H8]]> MAPD Volume content (%) 17.95 0.45 43 11.2 12 0.06 11.98 2.9 0.46

[0065] Example 2 (no CO charging, ethylene pressurization)

[0066] A domestic 270,000-ton / year ethylene C2 pre-propane removal and pre-hydrogenation unit employs a three-stage series adiabatic bed process for selective acetylene hydroremoval. The hydrogenation catalyst used is Shell's 7741B-T, which uses alumina as a support and approximately 0.03% Pd as the active component. The composition of the hydrogenation feedstock is shown in Table 3. The start-up method for this C2 pre-propane removal and pre-hydrogenation unit includes the following steps:

[0067] (1) After the air tightness of the pre-hydrogenation unit of C2 is qualified, the inert gas replacement is qualified.

[0068] (2) After the cracking furnace is put into operation, the cracked gas of the hydrogenation feedstock enters the quench oil tower, quench water tower, cracked gas compressor I-IV section, alkaline washing water tower, cracked gas dryer, high pressure propane removal tower, and cracked gas compressor V section in sequence.

[0069] (3) Ethylene pressurization: Pressurize the hydrogenation reactor of the C2 pre-hydrogenation unit to 3.5 MPa for 30 min.

[0070] (4) Open all the feed valves and introduce pyrolysis gas into the reactor bed through the bypass for 2 minutes at a pressure of 3.5 MPa. The reactor inlet temperature is preheated to 32°C by the pyrolysis gas. After the pressurization is completed, the bed temperature rises by 2°C.

[0071] (5) Introduce steam into the steam preheater to heat the cracked gas of the hydrogenation feedstock until a positive temperature difference appears in the first stage hydrogenation reactor, that is, the temperature in the first stage hydrogenation reactor gradually increases from top to bottom. There are 3 temperature measuring points from the inlet to the outlet in the first stage hydrogenation reactor. When an 8°C temperature gradient is formed between two adjacent temperature measuring points, that is, the inlet and outlet temperature difference of the first stage hydrogenation reactor is 16°C, and the online display shows that the acetylene conversion rate reaches 50%, the heating of the first stage hydrogenation reactor ends; start heating the second stage hydrogenation reactor until a positive temperature difference appears in the second stage hydrogenation reactor, that is, the temperature in the second stage hydrogenation reactor gradually increases from top to bottom, and the temperature in the second stage hydrogenation reactor gradually increases from the inlet to the outlet. Five temperature measuring points are set up. Heating of the second-stage hydrogenation reactor ends when a temperature gradient of 3.5°C is formed between two adjacent measuring points, i.e., the inlet-outlet temperature difference of the second-stage hydrogenation reactor is 14°C and the acetylene at the outlet of the second-stage hydrogenation reactor is below 110 ppm. Heating of the third-stage hydrogenation reactor then begins until a positive temperature difference appears in the reactor bed, i.e., the temperature in the third-stage hydrogenation reactor gradually increases from top to bottom. Four temperature measuring points are set up in the third-stage hydrogenation reactor from inlet to outlet. Heating of the third-stage hydrogenation reactor ends when a temperature gradient of 3°C is formed between two adjacent measuring points, i.e., the inlet-outlet temperature difference of the third-stage hydrogenation reactor is 9°C and the acetylene at the outlet of the third-stage hydrogenation reactor is below 1 ppm.

[0072] (6) After the reaction bed temperature has basically stabilized, the inlet temperature of each hydrogenation reactor is finely adjusted according to the required load distribution of each hydrogenation reactor to ensure that the acetylene outlet of the third-stage hydrogenation reactor is below 1 ppm, the total ethylene selectivity of the first, second, and third-stage hydrogenation reactors is ≥60%, and the total start-up time from the commissioning of the cracking furnace to the qualified acetylene outlet of the third-stage hydrogenation reactor is 6 hours. The start-up is completed at a reaction pressure of 3.5 MPa and a reaction volume hourly space velocity of 7500 h⁻¹. -1 The inlet reaction temperatures of the first, second, and third stage hydrogenation reactors are 55.7℃, 68.5℃, and 75.1℃, respectively.

[0073] Table 3 Composition of Hydrogenation Feedstock

[0074] Hydrogenation feedstock <![CDATA[H2]]> <![CDATA[C2H2]]> <![CDATA[C2H4]]> <![CDATA[C2H6]]> <![CDATA[CH4]]> CO <![CDATA[C3H6]]> <![CDATA[C3H8]]> MAPD Volume content (%) 17.95 0.45 43 11.2 12 0.06 11.98 2.9 0.46

[0075] Example 3 (CO charging, ethylene pressurization)

[0076] A domestic 450,000-ton / year ethylene C2 pre-propane removal and pre-hydrogenation unit employs a three-stage series adiabatic bed process. It uses PetroChina's PEC-21 catalyst for selective acetylene hydroremoval. The PEC-21 catalyst uses alumina as a support and is loaded with approximately 0.03% Pd as the active component. The hydrogenation feedstock conditions are shown in Table 4. The start-up method for this C2 pre-propane removal and pre-hydrogenation unit includes the following steps:

[0077] (1) After the air tightness of the pre-hydrogenation unit of C2 is qualified, the inert gas replacement is qualified.

[0078] (2) After the cracking furnace is put into operation, the cracked gas of the hydrogenation feedstock enters the quench oil tower, quench water tower, cracked gas compressor I-IV section, alkaline washing water tower, cracked gas dryer, high pressure propane removal tower, and cracked gas compressor V section in sequence.

[0079] (3) CO was injected into the first, second and third stage hydrogenation reactors of the C2 pre-hydrogenation unit. The catalyst loading of each hydrogenation reactor was 13 m³. A total of 8 steel cylinders of CO (40 L / cylinder, pressure 11 MPa) were injected, with a CO content of 3000 ppm. The CO injection time was 5 h.

[0080] (4) Ethylene pressing: Press the hydrogenation reactor of the C2 pre-hydrogenation unit to 4.5 MPa for 30 min.

[0081] (5) Open all the feed valves and continue to pressurize the reactor bed with the bypass pyrolysis gas. The pressing time is 2 minutes and the pressure is 3.6 MPa. The reactor inlet temperature is preheated to 34°C by the pyrolysis gas. The bed temperature rises by 2°C after the pressing ends.

[0082] (6) Introduce steam into the steam preheater to heat the cracked gas of the hydrogenation feedstock until a positive temperature difference appears in the first stage hydrogenation reactor, that is, the temperature in the first stage hydrogenation reactor gradually increases from top to bottom. There are 4 temperature measuring points from the inlet to the outlet in the first stage hydrogenation reactor. When a temperature gradient of 6°C is formed between two adjacent temperature measuring points, that is, the inlet and outlet temperature difference of the first stage hydrogenation reactor is 18°C, and the online display shows that the acetylene conversion rate reaches 58%, the heating of the first stage hydrogenation reactor ends; start heating the second stage hydrogenation reactor until a positive temperature difference appears in the second stage hydrogenation reactor, that is, the temperature in the second stage hydrogenation reactor gradually increases from top to bottom, and the temperature in the second stage hydrogenation reactor gradually increases from the inlet to the outlet. Six temperature measuring points are set up. Heating of the second-stage hydrogenation reactor ends when a temperature gradient of 3°C is formed between two adjacent measuring points, i.e., the inlet and outlet temperature difference of the second-stage hydrogenation reactor is 15°C and the acetylene at the outlet of the second-stage hydrogenation reactor is below 100 ppm. Heating of the third-stage hydrogenation reactor then begins until a positive temperature difference appears in the third-stage hydrogenation reactor, i.e., the temperature in the third-stage hydrogenation reactor gradually increases from top to bottom. Six temperature measuring points are set up in the third-stage hydrogenation reactor from inlet to outlet. Heating of the third-stage hydrogenation reactor ends when a temperature gradient of 1°C is formed between two adjacent measuring points, i.e., the inlet and outlet temperature difference of the third-stage hydrogenation reactor is 5°C and the acetylene at the outlet of the third-stage hydrogenation reactor is below 1 ppm.

[0083] (7) After the reaction bed temperature is basically stable, the inlet temperature of each hydrogenation reactor is finely adjusted according to the load distribution required by each hydrogenation reactor to ensure that the acetylene outlet of the third-stage hydrogenation reactor is less than 1 ppm, the total ethylene selectivity of the first, second and third-stage hydrogenation reactors is ≥60%, and the total start-up time from the commissioning of the cracking furnace to the qualified acetylene outlet of the third-stage hydrogenation reactor is 7 hours. When the product at the outlet of the third-stage hydrogenation reactor is qualified, the reaction pressure is 3.6 MPa and the reaction volume hourly space velocity is 12000 h⁻¹. -1 The inlet reaction temperatures of the first, second, and third stage hydrogenation reactors are 63.2℃, 65.7℃, and 72.8℃, respectively.

[0084] Table 4 Composition of Hydrogenation Feedstock

[0085] Hydrogenation feedstock <![CDATA[H2]]> <![CDATA[C2H2]]> <![CDATA[C2H4]]> <![CDATA[C2H6]]> <![CDATA[CH4]]> CO <![CDATA[C3H6]]> <![CDATA[C3H8]]> MAPD Volume content (%) 15.80 0.59 31.62 6.29 26.52 0.06 11.93 1.24 0.53

[0086] Example 4 (CO charging, natural gas ramming)

[0087] A domestic 800,000-ton / year ethylene C2 pre-hydrogenation unit employs a three-stage series adiabatic bed process, using PetroChina's PEC-21 catalyst for selective acetylene hydrogenation removal. The PEC-21 catalyst uses alumina as a support and is loaded with approximately 0.03% Pd as the active component. The composition of the hydrogenation feedstock is shown in Table 5. The start-up method for this C2 pre-propane removal pre-hydrogenation unit includes the following steps:

[0088] (1) After the air tightness of the pre-hydrogenation unit of C2 is qualified, the inert gas replacement is qualified.

[0089] (2) After the cracking furnace is put into operation, the cracked gas of the hydrogenation feedstock enters the quench oil tower, quench water tower, cracked gas compressor I-IV section, alkaline washing water tower, cracked gas dryer, high pressure propane removal tower, and cracked gas compressor V section in sequence.

[0090] (3) CO is injected into the first, second and third stage hydrogenation reactors of the C2 pre-hydrogenation unit. The catalyst loading of each hydrogenation reactor is 20m³, and a total of 10 steel cylinders of CO (40L / cylinder, pressure 11 MPa) are injected. The CO content in the reactor is 3700ppm, and the CO injection time is 12h.

[0091] (4) Natural gas pressurization: pressurize the hydrogenation reactor of the C2 pre-hydrogenation unit to 5.0 MPa for 25 min.

[0092] (5) Open all the feed valves and introduce pyrolysis gas into the reactor bed through the bypass for 2 minutes at a pressure of 3.8 MPa. The reactor inlet temperature is preheated to 35°C by the pyrolysis gas, and the bed temperature rises by 3°C after the pressurization ends.

[0093] (6) Introduce steam into the steam preheater to heat the cracked gas of the hydrogenation feedstock until a positive temperature difference appears in the first stage hydrogenation reactor, that is, the temperature in the first stage hydrogenation reactor gradually increases from top to bottom. There are 4 temperature measuring points from the inlet to the outlet in the first stage hydrogenation reactor. When a temperature gradient of 5°C is formed between two adjacent temperature measuring points, that is, the inlet and outlet temperature difference of the first stage hydrogenation reactor is 15°C, and the online display shows that the acetylene conversion rate reaches 50%, the heating of the first stage hydrogenation reactor ends; start heating the second stage hydrogenation reactor until a positive temperature difference appears in the second stage hydrogenation reactor, that is, the temperature in the second stage hydrogenation reactor gradually increases from top to bottom, and the temperature gradient from the inlet to the outlet in the second stage hydrogenation reactor reaches 50%. Four temperature measuring points are set up at the inlet. Heating of the second-stage hydrogenation reactor ends when a 4°C temperature gradient is formed between two adjacent measuring points (i.e., the inlet-outlet temperature difference is 12°C) and the acetylene concentration at the outlet of the second-stage hydrogenation reactor is below 200 ppm. Heating of the third-stage hydrogenation reactor then begins until a positive temperature difference is achieved, meaning the temperature gradually increases from top to bottom. Four temperature measuring points are set up from the inlet to the outlet of the third-stage hydrogenation reactor. Heating of the third-stage hydrogenation reactor ends when a 2°C temperature gradient is formed between two adjacent measuring points (i.e., the inlet-outlet temperature difference is 6°C) and the acetylene concentration at the outlet of the third-stage hydrogenation reactor is below 1 ppm.

[0094] (7) After the reaction bed temperature is basically stable, the inlet temperature of each hydrogenation reactor is finely adjusted according to the required load distribution of each hydrogenation reactor to ensure that the acetylene outlet of the third-stage hydrogenation reactor is below 1 ppm, the total ethylene selectivity of the first, second, and third-stage hydrogenation reactors is ≥50%, and the total start-up time from the commissioning of the cracking furnace to the qualified acetylene outlet of the third-stage reactor is 18 hours. When the product at the outlet of the third-stage hydrogenation reactor is qualified, the reaction pressure is 3.8 MPa and the reaction volume hourly space velocity is 14000 h⁻¹. -1 The inlet reaction temperatures of the first, second, and third stage hydrogenation reactors are 58.2℃, 68.0℃, and 73.4℃, respectively.

[0095] Table 5 Composition of Hydrogenation Feedstock

[0096] Hydrogenation feedstock <![CDATA[H2]]> <![CDATA[C2H2]]> <![CDATA[C2H4]]> <![CDATA[C2H6]]> <![CDATA[CH4]]> CO <![CDATA[C3H6]]> <![CDATA[C3H8]]> MAPD Volume content (%) 18.7 0.74 32.31 6.09 24.44 0.08 11.93 1.09 0.33

[0097] Example 5 (No CO charging, natural gas ramming)

[0098] A domestic 800,000-ton / year ethylene C2 pre-hydrogenation unit employs a three-stage series adiabatic bed process, using PetroChina's PEC-21 catalyst for selective acetylene hydrogenation removal. The PEC-21 catalyst uses alumina as a support and is loaded with approximately 0.03% Pd as the active component. The composition of the hydrogenation feedstock is shown in Table 6. The start-up method for this C2 pre-propane removal pre-hydrogenation unit includes the following steps:

[0099] (1) After the air tightness of the pre-hydrogenation unit of C2 is qualified, the inert gas replacement is qualified.

[0100] (2) After the cracking furnace is put into operation, the cracked gas of the hydrogenation feedstock enters the quench oil tower, quench water tower, cracked gas compressor I-IV section, alkaline washing water tower, cracked gas dryer, high pressure propane removal tower, and cracked gas compressor V section in sequence.

[0101] (3) Natural gas pressurization: pressurize the hydrogenation reactor of the C2 pre-hydrogenation unit to 6.0 MPa for 25 min.

[0102] (4) Open all the feed valves and introduce pyrolysis gas into the reactor bed through the bypass for 2 minutes at a pressure of 3.8 MPa. The reactor inlet temperature is preheated to 35°C by the pyrolysis gas, and the bed temperature rises by 3°C after the pressurization ends.

[0103] (5) Introduce steam into the steam preheater to heat the cracked gas of the hydrogenation feedstock until a positive temperature difference appears in the first stage hydrogenation reactor, that is, the temperature in the first stage hydrogenation reactor gradually increases from top to bottom. There are 6 temperature measuring points from the inlet to the outlet in the first stage hydrogenation reactor. When a temperature gradient of 5°C is formed between two adjacent temperature measuring points, that is, the inlet and outlet temperature difference of the first stage hydrogenation reactor is 25°C, and the online display shows that the acetylene conversion rate reaches 70%, the heating of the first stage hydrogenation reactor ends; start heating the second stage hydrogenation reactor until a positive temperature difference appears in the second stage hydrogenation reactor, that is, the temperature in the second stage hydrogenation reactor gradually increases from top to bottom, and the temperature gradient from the inlet to the outlet in the second stage hydrogenation reactor reaches 70%. Five temperature measuring points are set up at the inlet. Heating of the second-stage hydrogenation reactor ends when a 3°C temperature gradient is formed between two adjacent measuring points (i.e., a 12°C temperature difference between the inlet and outlet of the reactor) and the acetylene concentration at the outlet of the reactor is below 100 ppm. Heating of the third-stage hydrogenation reactor then begins until a positive temperature difference is achieved, meaning the temperature gradually increases from top to bottom. Three temperature measuring points are set up from the inlet to the outlet of the third-stage reactor. Heating of the third-stage reactor ends when a 2°C temperature gradient is formed between two adjacent measuring points (i.e., a 4°C temperature difference between the inlet and outlet of the reactor) and the acetylene concentration at the outlet of the reactor is below 1 ppm.

[0104] (6) After the reaction bed temperature has basically stabilized, the inlet temperature of each hydrogenation reactor is finely adjusted according to the required load distribution of each hydrogenation reactor to ensure that the acetylene outlet of the third-stage hydrogenation reactor is below 1 ppm, the total ethylene selectivity of the first, second, and third-stage hydrogenation reactors is ≥50%, and the total start-up time from the commissioning of the cracking furnace to the qualified acetylene outlet of the third-stage hydrogenation reactor is 8 hours. When the product at the outlet of the third-stage hydrogenation reactor is qualified, the reaction pressure is 3.8 MPa and the reaction volume hourly space velocity is 14000 h⁻¹. -1The inlet reaction temperatures of the first, second, and third stage hydrogenation reactors are 58.5℃, 68.2℃, and 72.8℃, respectively.

[0105] Table 6 Composition of Hydrogenation Feedstock

[0106] Hydrogenation feedstock <![CDATA[H2]]> <![CDATA[C2H2]]> <![CDATA[C2H4]]> <![CDATA[C2H6]]> <![CDATA[CH4]]> CO <![CDATA[C3H6]]> <![CDATA[C3H8]]> MAPD Volume content (%) 18.7 0.74 32.31 6.09 24.44 0.08 11.93 1.09 0.33

[0107] Comparative Example 1 (CO charging, but without ethylene or natural gas ramming).

[0108] A domestic 270,000-ton / year ethylene C2 pre-propane dehydrogenation unit employs a three-stage series adiabatic bed process for selective acetylene hydroremoval. The hydrotreating catalyst used is Shell's 7741B-T, which uses alumina as a support and approximately 0.03% Pd as the active component. The composition of the hydrotreating feedstock is shown in Table 2. The start-up method for this C2 pre-propane dehydrogenation unit includes the following steps:

[0109] (1) After the air tightness of the pre-hydrogenation unit of C2 is qualified, the nitrogen replacement is qualified.

[0110] (2) After the cracking furnace is put into operation, the cracked gas of the hydrogenation feedstock enters the quench oil tower, quench water tower, cracked gas compressor I-IV section, alkaline washing water tower, cracked gas dryer, high pressure propane removal tower, and cracked gas compressor V section in sequence.

[0111] (3) CO is injected into the first, second and third stage hydrogenation reactors of the C2 pre-hydrogenation unit. The catalyst loading of each hydrogenation reactor is 9m³, and CO is injected into 4 steel cylinders (40L / cylinder, pressure 11 MPa) with a CO content of 1500ppm. The CO injection time is 10h.

[0112] (4) Open all the feed valves and continue to pressurize the reactor bed with the bypass pyrolysis gas. The pressing time is 2 minutes and the pressure is 3.5 MPa. The reactor inlet temperature is preheated to 32°C by the pyrolysis gas. The bed temperature rises by 2°C after the pressing is completed.

[0113] (5) Water vapor is introduced into the steam preheater to heat the cracked gas of the hydrogenation feedstock. The temperature in the first stage hydrogenation reactor rises rapidly and heat is quickly removed. The device overheats and the highest temperature of the bed in the first stage hydrogenation reactor reaches 216°C. The reactor is depressurized in a chain. Due to the overheating during the pressurization process, the device fails to start up.

[0114] Comparative Example 2 (CO charging, but without ethylene or natural gas ramming)

[0115] A domestic 800,000-ton / year ethylene C2 pre-hydrogenation unit employs a three-stage series adiabatic bed process, using PetroChina's PEC-21 catalyst for selective acetylene hydrogenation removal. The PEC-21 catalyst uses alumina as a support and is loaded with approximately 0.03% Pd as the active component. The composition of the hydrogenation feedstock is shown in Table 5. The start-up method for this C2 pre-propane removal pre-hydrogenation unit includes the following steps:

[0116] (1) After the air tightness of the pre-hydrogenation unit of C2 is qualified, the inert gas replacement is qualified.

[0117] (2) After the cracking furnace is put into operation, the cracked gas of the hydrogenation feedstock enters the quench oil tower, quench water tower, cracked gas compressor I-IV section, alkaline washing water tower, cracked gas dryer, high pressure propane removal tower, and cracked gas compressor V section in sequence.

[0118] (3) CO is injected into the first, second and third stage hydrogenation reactors of the C2 pre-hydrogenation unit. The catalyst loading of each hydrogenation reactor is 20m³, and a total of 10 steel cylinders of CO (40L / cylinder, pressure 11 MPa) are injected. The CO content in the reactor is 1500ppm, and the CO injection time is 12h.

[0119] (4) Open all the feed valves and introduce pyrolysis gas into the reactor bed through the bypass for 2 minutes at a pressure of 3.8 MPa. The reactor inlet temperature is preheated to 35°C by the pyrolysis gas, and the bed temperature rises by 3°C after the pressurization ends.

[0120] (5) Water vapor is introduced into the steam preheater to heat the cracked gas of the hydrogenation feedstock. The temperature in the first stage hydrogenation reactor rises rapidly and heat is quickly released. The device overheats and the highest temperature of the bed in the first stage hydrogenation reactor reaches 328°C. The first stage hydrogenation reactor is depressurized in a chain. Due to the overheating during the pressurization process, the device fails to start up.

[0121] Comparative Example 3 (CO charging and ethylene stamping, but insufficient stamping pressure)

[0122] A domestic 450,000-ton / year ethylene C2 pre-propane removal and pre-hydrogenation unit employs a three-stage series adiabatic bed process. It uses PetroChina's PEC-21 catalyst for selective acetylene hydroremoval. The PEC-21 catalyst uses alumina as a support and is loaded with approximately 0.03% Pd as the active component. The hydrogenation feedstock conditions are shown in Table 4. The start-up method for this C2 pre-propane removal and pre-hydrogenation unit includes the following steps:

[0123] (1) After the air tightness of the pre-hydrogenation unit of C2 is qualified, the inert gas replacement is qualified.

[0124] (2) After the cracking furnace is put into operation, the cracked gas of the hydrogenation feedstock enters the quench oil tower, quench water tower, cracked gas compressor I-IV section, alkaline washing water tower, cracked gas dryer, high pressure propane removal tower, and cracked gas compressor V section in sequence.

[0125] (3) CO was injected into the first, second and third stage hydrogenation reactors of the C2 pre-hydrogenation unit. The catalyst loading of each hydrogenation reactor was 13 m³. A total of 8 steel cylinders of CO (40 L / cylinder, pressure 11 MPa) were injected, with a CO content of 3000 ppm. The CO injection time was 5 h.

[0126] (4) Ethylene pressurization: Pressurize the hydrogenation reactor of the C2 pre-hydrogenation unit to 1.5 MPa for 10 min.

[0127] (5) Open all the feed valves and continue to pressurize the reactor bed with the bypass pyrolysis gas. The pressing time is 2 minutes and the pressure is 3.6 MPa. The reactor inlet temperature is preheated to 34°C by the pyrolysis gas. The bed temperature rises by 2°C after the pressing ends.

[0128] (6) Introduce steam into the steam preheater to slowly heat the cracked gas of the hydrogenation feedstock until a positive temperature difference appears in the first hydrogenation reactor. There are 4 temperature measuring points from the inlet to the outlet in the first hydrogenation reactor. However, there are signs of temperature runaway during the heating process, and it is impossible to achieve a temperature gradient from top to bottom. The heat is quickly removed, and the temperature rises and falls back. After the temperature at each point of the bed stabilizes, the slow heating continues. Once the inlet and outlet temperature difference of the first-stage hydrogenation reactor reaches 18℃ and the online display shows an acetylene conversion rate of approximately 50%, the heating of the first-stage hydrogenation reactor is complete. Heating of the second-stage hydrogenation reactor then begins until a positive temperature difference appears in the reactor bed, meaning the temperature gradually increases from top to bottom. Six temperature measuring points are set up from the inlet to the outlet of the second-stage reactor. Heating of the second-stage reactor ends when a 3℃ temperature gradient is formed between adjacent measuring points (i.e., the inlet and outlet temperature difference is 15℃) and the acetylene concentration at the outlet is below 100 ppm. Heating of the third-stage hydrogenation reactor then begins. Heating of the third-stage hydrogenation reactor ends when a positive temperature difference appears, meaning the temperature gradually increases from top to bottom. Six temperature measuring points are set up from the inlet to the outlet of the third-stage reactor. Heating of the third-stage hydrogenation reactor ends when a 1℃ temperature gradient is formed between adjacent measuring points (i.e., the inlet and outlet temperature difference is 5℃) and the acetylene concentration at the outlet is below 1 ppm.

[0129] (7) After the reaction bed temperature is basically stable, the inlet temperature of each hydrogenation reactor is finely adjusted according to the load distribution required by each hydrogenation reactor to ensure that the acetylene outlet of the third stage hydrogenation reactor is less than 1 ppm, the total ethylene selectivity of the first, second and third stage hydrogenation reactors is ≥50%, and the total start-up time from the commissioning of the cracking furnace to the qualified acetylene outlet of the third stage hydrogenation reactor is 37 hours. When the product at the outlet of the third stage hydrogenation reactor is qualified, the reaction pressure is 3.6 MPa and the reaction volume hourly space velocity is 12000 h⁻¹. -1The inlet reaction temperatures of the first, second, and third stage hydrogenation reactors are 63.1.0℃, 65.1℃, and 72.5℃, respectively.

[0130] The results from Comparative Example 1 and Example 1, and Comparative Example 2 and Example 4 show that in the pre-hydrogenation units of Comparative Example 1 and Comparative Example 2, the reactor bed temperature rose rapidly due to the lack of ethylene / natural gas pressurization, resulting in overheating and unit start-up failure. The results from Comparative Example 3 and Example 3 show that in Comparative Example 3, insufficient pressurization pressure caused overheating during the reaction process, and the total start-up time was 5.2 times that of the present invention.

[0131] In summary, the start-up method for the C2 pre-hydrogenation unit provided by this invention, which uses ethylene and / or natural gas for pressurization, avoids the impurities introduced by nitrogen pressurization, shortens the product qualification time, and reduces material loss. Compared to the traditional slow pressurization using cracked gas as hydrogenation feedstock, this invention uses ethylene and / or natural gas to directly pressurize the C2 pre-hydrogenation unit from a slightly positive pressure to a reaction pressure of 2.0–6.0 MPa. This invention features rapid pressurization and short pressurization time. Simultaneously, this method avoids the problems caused by the static adsorption of alkynes and dienes by the catalyst due to the stagnant feedstock gas, resulting in a large amount of adsorption heat. This heat accumulation can then drive the hydrogenation reaction of alkynes and dienes, further generating reaction heat and causing overheating issues. Furthermore, the presence of a large amount of ethylene and / or natural gas dilutes the concentration of alkynes and dienes in the hydrogenation feedstock, effectively reducing the risk of overheating during the heating process and shortening the time from the start of the hydrogenation reaction to product qualification.

[0132] In addition, the start-up method of the present invention introduces CO before the ethylene and / or natural gas pressurization, i.e. in the early stage of start-up, which can reduce the subsequent CO concentration adjustment steps and thus further shorten the start-up time.

[0133] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the present invention.

Claims

1. A method for starting up a pre-hydrogenation unit for C2, characterized in that, Includes the following steps: (1) After the airtightness of the pre-hydrogenation unit of C2 is qualified, it is replaced with inert gas; (2) CO is introduced into the pre-hydrogenation unit of C2 so that the volume content of CO in the pre-hydrogenation unit of C2 reaches more than 1000 ppm; (3) Introduce ethylene and / or natural gas into the pre-hydrogenation unit of C2 and pressurize it to 2.0-6.0 MPa; (4) Use a cracking furnace to generate cracked gas for hydrogenation feedstock. The cracked gas for hydrogenation feedstock passes through a high-pressure ethane / propane dehydrogenator. When the C4 content in the top material of the high-pressure ethane / propane dehydrogenator is ≤0.1v%, it is ready to be used as hydrogenation feedstock. The hydrogenation feedstock is fed into the pre-hydrogenation unit of C2 and pressurized to a reaction pressure of 2.0 to 6.0 MPa. (5) Introduce steam into the steam preheater to heat the hydrogenation feedstock until the inlet and outlet temperature difference of the hydrogenation reactor of the C2 pre-hydrogenation unit is 3-25℃. The temperature in the hydrogenation reactor rises from top to bottom and forms multiple temperature gradients, the temperature gradients being 1-10℃. Once the acetylene at the end outlet of the C2 pre-hydrogenation unit is qualified, the bed heating is completed. Based on the volume of the hydrogenation feedstock, the hydrogenation feedstock includes: CO 100-10000 ppm, hydrogen 3-40%, methane 0-40%, acetylene 0.01-5.0%, ethylene 20-90%, and ethane 1-30%.

2. The start-up method of the pre-hydrogenation unit for C2 according to claim 1, characterized in that, The inert gas is nitrogen.

3. The start-up method of the pre-hydrogenation unit for C2 according to claim 1, characterized in that, Ethylene and / or natural gas are introduced into the pre-hydrogenation unit of C2 and pressurized to 2.5–4.0 MPa.

4. The start-up method of the pre-hydrogenation unit for C2 according to claim 1, characterized in that, Based on the volume of the hydrogenation feedstock, the hydrogenation feedstock includes: CO 400-1000ppm, hydrogen 10-35%, methane 10-30%, acetylene 0.02-1.2%, ethylene 30-55%, and ethane 5-25%.

5. The start-up method of the pre-hydrogenation unit for C2 according to claim 1, characterized in that, In step (2), CO is introduced into the pre-hydrogenation device of C2 so that the volume content of CO in the pre-hydrogenation device of C2 reaches 1000ppm~5000ppm.

6. The start-up method of the pre-hydrogenation unit for C2 according to claim 1, characterized in that, Also includes: After step (5), the inlet temperature of the C2 pre-hydrogenation unit is adjusted to 55℃-80℃, and the heating rate during the adjustment process is 0.5-1℃ / h.

7. The start-up method of the pre-hydrogenation unit for C2 according to claim 1, characterized in that, The pre-hydrogenation unit for C2 consists of two or three hydrogenation reactors connected in series.

8. The start-up method of the pre-hydrogenation unit for C2 according to claim 7, characterized in that, The C2 pre-hydrogenation unit is a three-stage hydrogenation reactor; the inlet temperature of the first stage hydrogenation reactor is adjusted to 55℃-65℃, the inlet-outlet temperature difference is 15-25℃, and the temperature gradient is 5-9℃; the inlet temperature of the second stage hydrogenation reactor is adjusted to 65℃-70℃, the inlet-outlet temperature difference is 8-15℃, and the temperature gradient is 3-6℃; the inlet temperature of the third stage hydrogenation reactor is adjusted to 70℃-80℃, the inlet-outlet temperature difference is 4-10℃, and the temperature gradient is 1-3℃.

9. The start-up method of the pre-hydrogenation unit for C2 according to claim 7, characterized in that, The hydrogenation reactor is an adiabatic bed or an isothermal bed.

Images