Alkali water washing method for reactor of alkylation device

Abstract

The invention provides a method for cleaning a reactor of an alkylation device. The method comprises the steps of material returning replacement, blind plate isolation, reactor alkali washing, water washing and the like. The reactor is cleaned by adopting two-time alkali washing and four-time water washing, so that the problems that the processing amount increase is limited and the product quality is influenced due to overlarge pressure drop of the reactor are effectively solved, and the operation quality of the alkylation device is greatly improved. After the reactor is cleaned by the method and the operation is recovered, the pressure difference of the reactor is reduced from 0.62 MPa to 0.18 MPa, the circulating volume of sulfuric acid is increased from 1950 m to 2500 m, the circulating hydrocarbon volume is increased from 580 m to 600 m, and the processing load is gradually increased to 105%. And the product quality and the energy consumption all meet the design requirements. The method is high in operability and controllable in risk, and can be widely popularized and applied under the condition that the filler layer of the reactor is not replaced, the service life of the filler layer is prolonged, meanwhile, the production cost can be greatly saved, and enterprise benefits are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of safe operation of alkylation units, and particularly relates to an alkaline water washing method for a reactor of an alkylation unit. Background Art

[0002] Currently, the main methods for producing isooctane include the sulfuric acid process, the hydrofluoric acid process, and the solid acid process. Lummus' CDAlky process (low-temperature sulfuric acid process) is widely used due to its significant advantages, including low reaction temperature, high octane number, low energy consumption, and minimal environmental pollution. Nine years have passed since my country's first CDAlky process isooctane unit went into operation. Some alkylation units are experiencing varying degrees of elevated pressure drop in the packing layers of their reactors. The apparent cause of this elevated pressure drop is blockage or poor flow, which prevents proper material penetration and mixing, severely impacting product quality and increasing processing loads. The most effective solution is packing replacement, but this approach is extremely challenging. First, the packing production cycle often far exceeds the planned unit maintenance schedule. Second, packing is expensive. Third, packing replacement is technically challenging and time-consuming, making it generally impractical. Summary of the Invention

[0003] The object of the present invention is to provide an alkaline water washing method for a reactor of an alkylation unit, so as to overcome the above-mentioned technical problems existing in the prior art.

[0004] To this end, the technical solutions provided by the present invention are as follows: A method for cleaning a reactor of an alkylation unit comprises the following steps: Step 1) Material withdrawal and replacement: discharge the acid in the reactor and associated pipelines and replace it with N2; Step 2) Blind plate isolation: Use blind plates to isolate the reactor from other units of the alkylation unit; Step 3) Alkali washing of the reactor: The reactor is cleaned with alkaline solution for multiple cycles until the pH value of the cleaning solution no longer decreases and the pressure drop of the reactor packing bed tends to be stable; Step 4) Water washing: The reactor is washed with water in multiple cycles until the pH value reaches 7-10, and the cleaning is completed.

[0005] The method also includes adding reaction hydrocarbon into the reactor after washing with water to dehydrate and dry the filler layer. Step 1) The specific process of material return and replacement is as follows: First, the sulfuric acid in the reactor is completely drained, and then the reactor is washed with recycled isobutane or alkylate oil. The residual sulfuric acid in the reactor is continuously discharged during the washing process until no sulfuric acid is left. Finally, the reactor is replaced with N2.

[0006] Step 3) Alkali washing of the reactor includes primary alkaline washing and secondary alkaline washing.

[0007] The process of an alkaline wash is as follows: Alkali solution with a mass concentration of 30-35% is injected into the reactor through the filtered acid circulation pump. At the same time, desalted water is injected into the bottom of the reactor through the acid interface measuring point of the reactor. The volume ratio of alkali solution to desalted water is 2-3:1. The alkali solution and desalted water are mixed evenly in the reactor. The acid circulation pump is started to extract the mixed liquid from the bottom and circulate the top of the reactor from top to bottom for alkali washing for 5-6 hours, and the outlet flow of the acid circulation pump is gradually increased; The acid circulation pump is stopped for 2-3 hours, the mixed liquid is withdrawn by 25-30%, and then fresh alkali solution is added to balance the liquid level, and the liquid level does not exceed the gas product outlet of the reactor.

[0008] The process of secondary alkaline washing is as follows: Inject alkali solution and desalted water with a mass concentration of 30-35% into the reactor, start the reactor acid circulation pump, and after alkali washing for 4-5 hours, stop the pump to withdraw the alkali; wherein, the volume ratio of alkali solution to desalted water is 1:9-10, and the total liquid volume does not exceed the gas product outlet of the reactor.

[0009] Step 3) During the alkali washing process of the reactor, the temperature inside the reactor is measured every 1-2 hours, the concentration of the circulating alkali solution is detected, the pH value is determined, and the color is recorded.

[0010] Step 4) The specific process of water washing is as follows: Primary water washing: inject deionized water from the bottom of the reactor. When the injection volume reaches 30%-35% of the reactor liquid level, start the acid circulation pump, establish the top circulation of the reactor and maintain the maximum circulation rate. Circulate for 3-4 hours. Analyze the water washing alkali concentration every 1-1.5 hours. After the concentration stabilizes, stop the acid circulation pump and drain the water. Secondary water washing: inject deionized water from the bottom of the reactor, start the acid circulation pump to circulate for 4-5 hours, analyze the water washing alkali concentration every 1-1.5 hours, and stop the acid circulation pump to drain the water after the concentration stabilizes; Three water washes: inject deionized water into the reactor, start the acid circulation pump, analyze the water washing alkali concentration every 1-1.5 hours, stop the acid circulation pump after the concentration stabilizes for 3-4 hours, and then drain the water; four water washes: inject deionized water into the reactor, start the acid circulation pump, analyze the water washing alkali concentration after 3 hours, stop the acid circulation pump after the concentration stabilizes and the pH value reaches 7-10; the amount of deionized water used is 1-1.5 times the volume of the reactor.

[0011] Step 3) During the alkali washing process of the reactor, N2 is filled into the reactor for pressurization, and the reactor safety valve is connected to the flare venting system.

[0012] The post-filtration acid circulation pump is arranged at the bottom of the coalescer after the reactor, and the reactor acid circulation pump is arranged at the bottom of the reactor.

[0013] The beneficial effects of the present invention are: The present invention cleans the reactor through two alkali washes and four water washes. After the reactor resumes operation after alkali-water washing using this method, the reactor pressure difference decreases from 0.62 MPa to 0.18 MPa, the sulfuric acid circulation volume increases from 1950 m³ to 2500 m³, the circulating hydrocarbon volume increases from 580 m³ to 600 m³, and the processing load gradually increases to 105%. Product quality and energy consumption all meet design requirements.

[0014] This invention effectively solves the problem of excessive reactor pressure drop, which restricts processing capacity and affects product quality, significantly improving the operational quality of alkylation units. This method is highly operational, with manageable risks. It can be widely adopted in environments where reactor packing layer replacement is not feasible, extending the packing layer's service life while significantly reducing production costs and improving enterprise profitability. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic flow diagram of the present invention. DETAILED DESCRIPTION

[0016] The following describes the embodiments of the present invention through specific embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification.

[0017] Exemplary embodiments of the present invention are now described. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to provide a thorough and complete disclosure of the present invention and to fully convey the scope of the present invention to those skilled in the art. The terms used in the exemplary embodiments shown in the accompanying drawings are not intended to limit the present invention.

[0018] Unless otherwise specified, the terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art. Furthermore, it is understood that terms defined in commonly used dictionaries should be understood to have meanings consistent with the context of their relevant fields and should not be interpreted as idealized or overly formal.

[0019] Example 1 The present invention provides a method for cleaning a reactor of an alkylation unit, comprising the following steps: Step 1) Material withdrawal and replacement: discharge the acid in the reactor and associated pipelines and replace it with N2; Step 2) Blind plate isolation: Use blind plates to isolate the reactor from other units of the alkylation unit; Step 3) Alkali washing of the reactor: The reactor is cleaned with alkaline solution for multiple cycles until the pH value of the cleaning solution no longer decreases and the pressure drop of the reactor packing bed tends to be stable; Step 4) Water washing: The reactor is washed with water in multiple cycles until the pH value reaches 7-10, and the cleaning is completed.

[0020] Among them, blind plates are used to prevent water / moisture from entering other equipment / pipelines, etc.

[0021] The present invention adopts an alkaline water washing method to carry out technical maintenance on the reactor through steps such as material withdrawal, replacement, blind plate isolation, alkaline washing, and water washing, which effectively solves the problem that the reactor is restricted in processing volume and affects product quality due to excessive pressure drop, and extends the service life of the packing layer.

[0022] Example 2 Based on Example 1, this example provides a method for cleaning a reactor of an alkylation unit, which further includes adding a reaction hydrocarbon into the reactor after water washing, and dehydrating and drying the packing layer. Figure 1 shown.

[0023] Isobutane is introduced into the alkylation reactor, where the circulating hydrocarbon removes the water from the packing layer. Dehydration is then performed at the lowest point of the reactor. Analysis is performed every two hours, and drying is completed after passing the analysis. After the water wash is complete, the packing layer is inspected and repaired, the manhole is sealed, and the packing layer is dehydrated and dried. Finally, the blind plate is removed.

[0024] Example 3 Based on Example 1, this example provides a method for cleaning a reactor of an alkylation unit. The specific process of step 1) material withdrawal and replacement is as follows: First, the sulfuric acid in the reactor is completely drained, and then the reactor is washed with recycled isobutane or alkylate oil. The residual sulfuric acid in the reactor is continuously discharged during the washing process until no sulfuric acid is left. Finally, the reactor is replaced with N2.

[0025] The hydrocarbon wash time is 72-96 hours. Intermittent acid removal is performed on the reactor and associated pipelines to ensure settling time. Pneumatic diaphragm pumps are used to extract and remove the material at certain locations (such as pipeline corners) to minimize residual medium in the reactor. The reactor is purged with N2 to ensure that there is no residual liquefied gas or acid in the reactor.

[0026] Example 4 Based on Example 1, this example provides a method for cleaning a reactor of an alkylation unit, wherein step 3) alkali washing of the reactor includes a primary alkali wash and a secondary alkali wash.

[0027] The process of an alkaline wash is as follows: Alkali solution with a mass concentration of 30-35% is injected into the reactor through the filtered acid circulation pump. At the same time, desalted water is injected into the bottom of the reactor through the acid interface measuring point of the reactor. The volume ratio of alkali solution to desalted water is 2-3:1. The alkali solution and desalted water are mixed evenly in the reactor. The acid circulation pump is started to extract the mixed liquid from the bottom and circulate the top of the reactor from top to bottom for alkali washing for 5-6 hours, and the outlet flow of the acid circulation pump is gradually increased; The acid circulation pump is stopped for 2-3 hours, the mixed liquid is withdrawn by 25-30%, and then fresh alkali solution is added to balance the liquid level. After that, the acid circulation pump is started again, and the liquid level does not exceed the gas product outlet of the reactor.

[0028] The process of secondary alkaline washing is as follows: Inject 30-35% alkali solution and deionized water into the reactor, start the reactor's acid circulation pump, and after 4-5 hours of alkali washing, stop the pump to remove the alkali. The volume ratio of alkali solution to deionized water is 1:9-10, and the total liquid volume does not exceed the gas product outlet of the reactor. The alkali solution is sodium hydroxide solution.

[0029] Among them, the gas product outlet is located at the lower part of the reactor packing layer. When the liquid phase (a mixture of alkali solution and desalted water) overflows through the gas product outlet, it means that the liquid is high enough.

[0030] During the alkali washing process, the temperature in the reactor is measured every 1-2 hours, the concentration of the circulating alkali solution is detected, the pH value is determined, and the color is recorded.

[0031] The reactor volume is 663m 3 Taking the reactor as an example, the alkali washing is described in detail: One alkaline wash: 286 tons of water were added; about 100 tons of alkali (30% concentration) were added; after 30 minutes, the alkali concentration was 5.07% at the upper end and 14.83% at the lower end; The acid circulation pump was started to establish top circulation (spraying from top to bottom), with a total outlet flow of 2000m³. After 4 minutes, the temperature reached a maximum of 114.5°C, and after 6 minutes, the temperature dropped to 80°C. After 11 minutes, the average temperature of the reactor dropped to 65°C and stabilized.

[0032] After one hour, analysis of the acid circulation pump outlet revealed acidity, with an acid concentration of 19.3%. After two hours, the acid circulation pump was stopped, and approximately 100 tons of material was withdrawn from the reactor. 30 tons of 30% alkali solution were then added. The acid circulation pump was restarted, and laboratory analysis revealed the following: after three hours of circulation, the alkali concentration was 17.18%; after four hours, it was 11.32%; and after five hours, it was 10.36%. Once the analysis results stabilized, the acid circulation pump was stopped, and the alkali was withdrawn to the neutralization tank. The pH of the reactor after the withdrawal of alkali was measured to be 12.94.

[0033] Secondary alkaline washing 25 tons of alkali solution and 225 tons of demineralized water were added. The acid circulation pump was started. After 30 minutes, the concentration of the deionized water was analyzed to be 4.56% and the pH was 12. After 1 hour, the concentration of the deionized water was analyzed to be 3.79% and the pH was 12. After 2 hours, the concentration of the circulating alkali solution was analyzed to be 3.84% and the pH was 12. The concentration of the circulating alkali solution in the reactor stabilized, and after 4 hours, the acid circulation pump was stopped to deionize the alkali solution.

[0034] When the pH value stops decreasing, the black color of the alkali solution tends to be stable, and the pressure drop of the reactor packing layer tends to be stable, it indicates that the alkali solution cleaning is completed and all waste alkali is discharged from the reactor system to the neutralization tank.

[0035] Example 5 Based on Example 4, this example provides a method for cleaning a reactor of an alkylation unit. The specific process of step 4) water washing is as follows: Primary water washing: inject deionized water from the bottom of the reactor. When the injection volume reaches 30%-35% of the reactor liquid level, start the acid circulation pump, establish the top circulation of the reactor and maintain the maximum circulation rate. Circulate for 3-4 hours. Analyze the water washing alkali concentration every 1-1.5 hours. After the concentration stabilizes, stop the acid circulation pump and drain the water. Secondary water washing: inject deionized water from the bottom of the reactor, start the acid circulation pump to circulate for 4-5 hours, analyze the water washing alkali concentration every 1-1.5 hours, and stop the acid circulation pump to drain the water after the concentration stabilizes; Three water washes: inject deionized water into the reactor, start the acid circulation pump, analyze the water washing alkali concentration every 1-1.5 hours, and stop the acid circulation pump after the concentration stabilizes for 3-4 hours; Four water washes: inject deionized water into the reactor, start the acid circulation pump, analyze the water washing alkali concentration after 3 hours, and stop the acid circulation pump to drain the water after the concentration stabilizes and the pH value reaches 7-10; the amount of deionized water used is 1-1.5 times the volume of the reactor.

[0036] After the alkaline cleaning of the reactor system is completed and the drainage is completed, close all the drain valves and perform water washing.

[0037] The reactor volume is 663m 3 Taking the reactor as an example, water washing is described in detail: One wash 154 tons of desalted water was injected in one water wash; the acid circulation pump was started, and the pH value was analyzed to be 12.98 after 1 hour, 1.11% after 2 hours, and 1.18% after 3 hours; the alkali concentration in the water wash tended to be stable and the pump was stopped to drain the water.

[0038] Secondary water washing 150 tons of desalted water was injected for the secondary water washing; the acid circulation pump was started, and the alkali concentration was analyzed to be 3.32% after 1 hour, 3.2% after 2 hours, and 3.05% after 3 hours; the alkali concentration of the water washing tended to be stable, and the pump was stopped and the water was drained. After 4 hours, the pH value of the neutralization tank was analyzed to be 13; after 5 hours, the alkali solution concentration was analyzed to be 1.04 and the pH value was 12.63.

[0039] Three washes 236 tons of desalted water were injected into the three water washes; the acid circulation pump was started, and the concentration of water wash alkali was analyzed every 1-1.5 hours. After the water wash alkali concentration became stable for 3 hours, the pump was stopped and the water was discharged.

[0040] Four washes 251 tons of desalted water were injected in four water washes; the acid circulation pump was started, and the alkali concentration was analyzed to be 0.03% after 3 hours and 0.03% after 4 hours, with a pH value of 10; the pump was stopped and the water was drained after the alkali concentration in the water wash stabilized.

[0041] According to statistics, this alkaline-water wash operation involved two alkaline washes and four water washes, consuming a total of 155 tons of 30% concentrated alkali solution and 1,302 tons of demineralized water. The first alkaline wash, due to excessively high liquid levels, resulted in the discharge of 100 tons of acidic liquid, so this alkali consumption is not included in the final alkali consumption.

[0042] After the alkaline water wash was completed and passed, nitrogen was injected into the reactor, and the low-point drain was opened to drain all accumulated water from the system. After drying with nitrogen and passing the ventilation inspection, damaged internal components of the reactor were replaced and maintenance work began. After operations resumed, the reactor's differential pressure dropped from 0.62 MPa to 0.18 MPa, the sulfuric acid circulation rate increased from 1950 m³ to 2500 m³, the circulating hydrocarbon rate increased from 580 m³ to 600 m³, and the processing load gradually increased to 105%. Product quality and energy consumption fully met design requirements.

[0043] This method effectively addresses the issue of excessive reactor pressure drop, which limits processing capacity and impacts product quality, significantly improving the operational quality of the alkylation unit. This method is highly operational, with manageable risks. It can be widely adopted in environments where reactor packing replacement is not an option, extending the packing's service life while significantly reducing production costs and improving enterprise profitability.

[0044] Example 6 Based on Example 4, this example provides a method for cleaning a reactor of an alkylation unit. In step 3), during the alkali washing process of the reactor, N2 is filled into the reactor for pressurization, and the reactor safety valve is connected to the flare venting system.

[0045] The post-filtration acid circulation pump is arranged at the bottom of the coalescer after the reactor, and the reactor acid circulation pump is arranged at the bottom of the reactor.

[0046] The caustic wash process releases a large amount of heat, and the volatilization of residual liquefied gas causes a rapid pressure rise. This gas is then sent to the caustic wash tower through a bypass line from the safety valve, where it is then released into the low-wattage system. This heat release can also cause foaming in the liquid, making it difficult for the pump to operate. Therefore, N2 is used to pressurize the system to ensure normal pump operation.

[0047] The above examples are merely illustrative of the present invention and do not limit the scope of protection of the present invention. Any design that is identical or similar to the present invention falls within the scope of protection of the present invention.

Claims

1. A method for cleaning a reactor of an alkylation unit, characterized in that: The following steps are involved: Step 1) Material withdrawal and replacement: discharge the acid in the reactor and associated pipelines and replace it with N2; Step 2) Blind plate isolation: Use blind plates to isolate the reactor from other units of the alkylation unit; Step 3) Alkali washing of the reactor: The reactor is cleaned with alkaline solution for multiple cycles until the pH value of the cleaning solution no longer decreases and the pressure drop of the reactor packing bed tends to be stable; Step 4) Water washing: The reactor is washed with water in multiple cycles until the pH value reaches 7-10, and the cleaning is completed.

2. The method for washing the reactor of an alkylation unit with alkaline water according to claim 1, characterized in that: The method also includes adding reaction hydrocarbon into the reactor after washing with water to dehydrate and dry the filler layer.

3. The method for washing the reactor of an alkylation unit with alkaline water according to claim 1, characterized in that: Step 1) The specific process of material return and replacement is as follows: First, the sulfuric acid in the reactor is completely drained, and then the reactor is washed with recycled isobutane or alkylate oil. The residual sulfuric acid in the reactor is continuously discharged during the washing process until no sulfuric acid is left. Finally, the reactor is replaced with N2.

4. The method for washing the reactor of an alkylation unit with alkaline water according to claim 1, characterized in that: Step 3) Alkali washing of the reactor includes primary alkaline washing and secondary alkaline washing.

5. The method for washing the reactor of an alkylation unit with alkaline water according to claim 4, characterized in that: The process of an alkaline wash is as follows: Alkali solution with a mass concentration of 30-35% is injected into the reactor through the filtered acid circulation pump. At the same time, desalted water is injected into the bottom of the reactor through the acid interface measuring point of the reactor. The volume ratio of alkali solution to desalted water is 2-3:

1. The alkali solution and desalted water are mixed evenly in the reactor. The acid circulation pump is started to extract the mixed liquid from the bottom and circulate the top of the reactor from top to bottom for alkali washing for 5-6 hours, and the outlet flow of the acid circulation pump is gradually increased; The acid circulation pump is stopped for 2-3 hours, the mixed liquid is withdrawn by 25-30%, and then fresh alkali solution is added to balance the liquid level, and the liquid level does not exceed the gas product outlet of the reactor.

6. The method for washing the reactor of an alkylation unit with alkaline water according to claim 4, characterized in that: The process of secondary alkaline washing is as follows: Inject alkali solution and desalted water with a mass concentration of 30-35% into the reactor, start the reactor acid circulation pump, and after alkali washing for 4-5 hours, stop the pump to withdraw the alkali; wherein, the volume ratio of alkali solution to desalted water is 1:9-10, and the total liquid volume does not exceed the gas product outlet of the reactor.

7. The method for washing the reactor of an alkylation unit with alkaline water according to claim 1, wherein: Step 3) During the alkali washing process of the reactor, the temperature inside the reactor is measured every 1-2 hours, the concentration of the circulating alkali solution is detected, the pH value is determined, and the color is recorded.

8. The method for washing the reactor of an alkylation unit with alkaline water according to claim 1, characterized in that: Step 4) The specific process of water washing is as follows: Primary water washing: inject deionized water from the bottom of the reactor. When the injection volume reaches 30%-35% of the reactor liquid level, start the acid circulation pump, establish the top circulation of the reactor and maintain the maximum circulation rate. Circulate for 3-4 hours. Analyze the water washing alkali concentration every 1-1.5 hours. After the concentration stabilizes, stop the acid circulation pump and drain the water. Secondary water washing: inject deionized water from the bottom of the reactor, start the acid circulation pump to circulate for 4-5 hours, analyze the water washing alkali concentration every 1-1.5 hours, and stop the acid circulation pump to drain the water after the concentration stabilizes; Three water washes: inject deionized water into the reactor, start the acid circulation pump, analyze the water washing alkali concentration every 1-1.5 hours, stop the acid circulation pump after the concentration stabilizes for 3-4 hours, and then drain the water; four water washes: inject deionized water into the reactor, start the acid circulation pump, analyze the water washing alkali concentration after 3 hours, stop the acid circulation pump after the concentration stabilizes and the pH value reaches 7-10; the amount of deionized water used is 1-1.5 times the volume of the reactor.

9. The method for washing the reactor of an alkylation unit with alkaline water according to claim 1, characterized in that: Step 3) During the alkali washing process of the reactor, N2 is filled into the reactor for pressurization, and the reactor safety valve is connected to the flare venting system.

10. The method for washing the reactor of an alkylation unit with alkaline water according to claim 5, characterized in that: The post-filtration acid circulation pump is arranged at the bottom of the coalescer after the reactor, and the reactor acid circulation pump is arranged at the bottom of the reactor.

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