Method for preventing severe fouling of a flue gas turbine in a catalytic cracking process

Abstract

This invention relates to a method for preventing severe fouling of a flue gas turbine during catalytic cracking. The method includes: during catalytic cracking, cyclically switching the turbine disc temperature between a high-temperature zone and a low-temperature zone, wherein the temperature difference between the high-temperature zone and the low-temperature zone is at least 10°C, and the duration of the high-temperature zone or the low-temperature zone is 1-365 days. This method ensures that the generated thin scale layer will detach and be carried away by the flue gas without causing significant or large-scale flue gas turbine vibration, ensuring long-term operation of the flue gas turbine with no or very thin scale.

Description

Technical Field

[0001] This invention relates to a method for preventing fouling of flue gas turbines during catalytic cracking, and more specifically to a method for preventing severe fouling of flue gas turbines during catalytic cracking. Technical Background

[0002] Flue gas turbines are the main energy recovery equipment in catalytic cracking units of oil refineries, and also one of the components with the highest failure rates. Their function is to convert the pressure and heat energy of the high-temperature flue gas generated during catalyst coking and regeneration into mechanical energy, which not only drives the main blower at full load but also supplies power to the grid. Their operational stability directly affects the entire operating cycle and economic benefits of the catalytic cracking unit. In recent years, the increasing weight and quality of catalytic cracking feedstocks has led to changes in the catalytic cracking process and catalysts. This has resulted in changes in the composition and content of ultrafine catalyst powder entering the flue gas, exacerbating its deposition and scaling in the flue gas turbine. This disrupts the dynamic balance of the flue gas turbine rotor, causing excessive rotor vibration and severely impacting the long-term operation of the flue gas turbine. Ensuring the long-term operation of catalytic cracking flue gas turbines is a major challenge facing the entire industry.

[0003] Currently, there are two main approaches to addressing scale buildup in flue gas turbines. The first approach focuses on reducing the fine powder and scaling properties of catalysts or additives. This requires catalysts or additives to be free of easily scaling chemical components and have sufficiently low wear indices with minimal differences between batches. This, to some extent, affects the possibility and incentive to adopt new catalysts or additives with better catalytic performance, thus impacting the economic efficiency and technological advancement of the equipment. Despite such careful operation, severe scale buildup in flue gas turbines is still common, leading to increased rotor vibration, higher energy consumption, and in most cases, requiring shutdown for cleaning. The second approach is online descaling, including: (1) adding scale inhibitors to the duct before the flue gas inlet of the flue gas turbine, such as CN103865581B and CN10214037B. Due to changes in the composition of scale, scale inhibitors may not be suitable and may even accelerate scale buildup; (2) using online ultrasonic dust removal devices, such as CN205667775U. Because ultrasonic waves require a medium to transmit, and the flow velocity of flue gas in the flow channel is close to the speed of sound, ultrasonic waves are not very effective at removing scale from moving blades; (3) Use an online blade purging device, such as CN110295958A. Because the purging of the blades disturbs the normal operation of the blades, it may damage the equipment; (4) Use a hot scrubbing device for the flue gas turbine, such as CN112483196A. The main method is to add descaling agent to the flue gas turbine, which may affect the stable operation of the flue gas turbine, and the shedding of large scale layers will damage the flue gas turbine; (5) use electrostatic dispersion technology to inhibit scale, such as CN108795497A; (6) use online magnetic separation technology to inhibit scale, such as CN108798799A; (7) thermal cleaning method, when the flue gas turbine is severely scaled, use the thermal washing method to descale the flue gas turbine online (for example, "China and Foreign Energy", 2008(13): 93-94; "Equipment Management and Maintenance", 2013(7), 50-52). The method involves switching a standby flue gas turbine to normal operation. Essentially, this involves removing the scaled flue gas turbine from the operating system and gradually closing the turbine inlet butterfly valve. This alters the flue gas flow rate, temperature, and the relative speed and direction of the turbine blades, causing the catalyst dust deposited on the turbine blades to detach. Then, the amount of cooling steam on the turbine disc is increased, and the temperature difference is widened to further promote complete scale removal. This process is repeated repeatedly over short periods (e.g., 25 minutes to 2 hours) to achieve the desired scale removal. Engineering technicians and unit maintenance personnel must closely monitor the process on-site. However, even with this method, uneven catalyst scale removal can still cause equipment damage. Currently, existing technologies lack effective prevention and treatment measures for flue gas turbine scaling, typically requiring shutdown for cleaning, resulting in significant economic losses. It is estimated that the direct economic loss from shutting down a flue gas turbine for scaling reaches 1-2 million yuan per instance, with indirect economic losses exceeding 5 million yuan per instance.

[0004] Therefore, there is still an urgent need for a method to prevent severe fouling of the flue gas turbine during catalytic cracking, in order to ensure the long-term operation of the flue gas turbine during catalytic cracking. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preventing severe scaling of flue gas turbines during catalytic cracking, thereby ensuring long-term operation of catalytic cracking flue gas turbines.

[0006] This invention provides a method for preventing severe scaling in flue gas turbines during catalytic cracking, the method comprising:

[0007] During catalytic cracking, the turbine disc temperature is cyclically switched between a high-temperature section and a low-temperature section, wherein the temperature difference between the high-temperature section and the low-temperature section is at least 10°C, and the duration of the high-temperature section or the low-temperature section is 1-365 days.

[0008] In an embodiment of the present invention, the temperature difference between the high-temperature section and the low-temperature section is 10-200°C, and the duration of the high-temperature section or the low-temperature section is 2-180 days.

[0009] In an embodiment of the present invention, the temperature difference between the high-temperature section and the low-temperature section is 20-150°C, and the duration of the high-temperature section or the low-temperature section is 2-90 days.

[0010] In an embodiment of the present invention, the temperature difference between the high-temperature section and the low-temperature section is 20-100°C, and the duration of the high-temperature section or the low-temperature section is 2-60 days.

[0011] In an embodiment of the present invention, the temperature difference between the high-temperature section and the low-temperature section is 20-70°C, and the duration of the high-temperature section or the low-temperature section is 2-30 days.

[0012] In an embodiment of the present invention, the temperature difference between the high-temperature section and the low-temperature section is 20-50°C, and the duration of the high-temperature section or the low-temperature section is 2-15 days.

[0013] Compared with the prior art, the technical advantages of the present invention include:

[0014] (1) Periodically switch the temperature of the flue gas turbine disc between the high temperature range and the low temperature range. Since the expansion coefficients of the fine powder scale layer of the catalyst or additive and the metal of the flue gas turbine rotor are very different, the relatively short duration will only produce a very thin scale layer. This scale layer will fall off and be carried away with the flue gas without causing obvious or large flue gas turbine vibration, ensuring that the flue gas turbine can operate for a long period of time with no scale or a very thin scale layer.

[0015] (2) It avoids the risk of large scale layers falling off during online descaling when there is severe scaling, which may cause the flue gas turbine rotor to vibrate more and shut down or even cause an accident; it also avoids the need to use a backup flue gas turbine and reduce the flue gas flow rate, and avoids the need to frequently raise and lower the flue gas turbine disc temperature in a short period of time, which would reduce the service life of the flue gas turbine.

[0016] (3) When the flue gas turbine operates with no or very thin scale, energy consumption can be greatly reduced.

[0017] (4) No additional descaling equipment and descaling agents are required, greatly reducing investment and operating costs.

[0018] The above and other features and advantages of the present invention will become apparent from the following detailed description. It should be understood that the foregoing general description and the following detailed description are illustrative only and do not constitute a limitation on the claimed aspects. Detailed Implementation

[0019] The "range" disclosed herein is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also expected. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0020] Unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions. Similarly, unless otherwise specified, all technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0021] In this application, unless otherwise specified, the terms "comprising" and "including" as used herein are open-ended or closed-ended. For example, "comprising" and "including" may mean that other components not listed may also be included, or that only the listed components may be included.

[0022] In this invention, the method for preventing severe scaling of the flue gas turbine during the catalytic cracking process includes:

[0023] During catalytic cracking, the turbine disc temperature is cyclically switched between a high-temperature section and a low-temperature section, wherein the temperature difference between the high-temperature section and the low-temperature section is at least 10°C, and the duration of the high-temperature section or the low-temperature section is 1-365 days.

[0024] In one embodiment of this application, the temperature difference between the high-temperature segment and the low-temperature segment can be within a numerical range formed by any two of the following listed values ​​as endpoints: 10℃, 20℃, 50℃, 70℃, 90℃, 120℃, 150℃, 180℃, and 200℃. It should be particularly emphasized that although the above values ​​are listed side-by-side, it does not mean that any numerical range formed by any two of the above values ​​as endpoints will yield comparable or similar performance. This also applies to the numerical ranges mentioned below. The preferred embodiments of this application are selected solely based on the specific discussion below and specific experimental data. In optional embodiments of this application, the temperature difference between the high-temperature segment and the low-temperature segment is 10-200℃, 20-150℃, 20-100℃, 20-70℃, or 20-50℃.

[0025] In one embodiment of this application, the duration of the high-temperature or low-temperature segment can be within a numerical range consisting of any two of the following values ​​as endpoints: 1 day, 2 days, 15 days, 30 days, 60 days, 90 days, 180 days, 240 days, and 365 days. In an optional embodiment of this application, the duration of the high-temperature or low-temperature segment is 1-365 days, 2-180 days, 2-90 days, 2-60 days, 2-30 days, or 2-15 days.

[0026] In this invention, those skilled in the art can operate the catalytic cracking process based on their technical knowledge. Furthermore, those skilled in the art can employ well-known technical means to alter the turbine disc temperature during the catalytic cracking process. Currently, the turbine disc temperature in a catalytic cracking unit can be automatically adjusted and maintained online for the required time by a computer system.

[0027] Example

[0028] Unless otherwise stated, the catalytic cracking feedstocks and catalysts used in the embodiments of the present invention are all industrial grade.

[0029] Example 1

[0030] During the operation of a 600,000-ton / year catalytic cracking unit, the disc temperature of the YL-7000C flue gas turbine was periodically maintained at 330℃ for 7 days, then switched to 360℃ for another 7 days, and then switched back to 330℃ for another 7 days. This cycle was repeated for five years, followed by a planned shutdown for inspection. It was found that there was no scaling on the disc of the YL-7000C flue gas turbine, and throughout the entire operating cycle, the rotor of the flue gas turbine did not experience any significant increase in vibration.

[0031] Comparative Example 1

[0032] During the production process of a catalytic cracking unit with a capacity of 600,000 tons / year, after one year of operation using the existing catalytic cracking technology, the YL-7000C flue gas turbine developed severe scaling. The standby flue gas turbine was put into operation, and the scaled flue gas turbine was descaled online by thermal cleaning method (China and Foreign Energy, 2008(13): 93-94; Equipment Management and Maintenance, 2013(7), 50-52). Due to the thick scale layer and large scale pieces, the rotor mass was significantly eccentric and the flue gas turbine rotor vibration exceeded the standard. The on-site workers had to stop the machine and perform manual mechanical scaling, and online scaling was not possible.

[0033] Example 2

[0034] During the operation of a catalytic cracking unit with a capacity of 1 million tons per year, the disc temperature of the YL-7000D flue gas turbine was periodically maintained at 280℃ for 90 days, then switched to 380℃ for 30 days, and then switched back to 280℃ for 90 days. This cycle was repeated for three years, followed by a planned shutdown for inspection. It was found that there was no scaling on the disc of the YL-7000D flue gas turbine, and the rotor vibration of the flue gas turbine did not increase significantly throughout the entire operating cycle.

[0035] Example 3

[0036] In the 600,000-ton / year catalytic cracking flue gas turbine YL-7000C, the turbine disc temperature was periodically maintained at 250℃ for 150 days, then switched to 390℃ for 60 days, then switched to 250℃ for 6 days, then switched to 390℃ for 30 days, then switched to 250℃ for 30 days, and so on, repeating this cycle for four years. A planned shutdown inspection was then conducted. No scaling was found on the YL-7000C flue gas turbine disc, and the rotor vibration did not significantly increase throughout the entire operating cycle.

[0037] Example 4

[0038] In the 600,000-ton / year catalytic cracking flue gas turbine YL-7000C, the disk temperature of the flue gas turbine was maintained at 250°C for 15 days periodically, then switched to 350°C for 15 days, and then switched back to 250°C for 15 days. After repeating this cycle for one year, the catalyst LBO-16 used in the catalytic cracking process was replaced with LDO-70. Because of the different compositions and the large difference in the attrition index between the new and old catalysts, the amount of catalyst fines in the flue gas doubled. During this period, the disk temperature of the flue gas turbine was maintained at 250°C for 5 days, switched to 350°C for 5 days, and then switched back to 250°C for 5 days, repeating the cycle until the new catalyst completely replaced the old catalyst, and then restored to maintaining the disk temperature of the flue gas turbine at 250°C for 15 days, switching to 350°C for 15 days, and then switching back to 250°C for 15 days, repeating the cycle. After four years, a planned shutdown inspection was carried out. It was found that there was no fouling on the disk of the flue gas turbine YL-7000C, and during the entire operation cycle, there was no obvious increase in the vibration of the rotor of the flue gas turbine.

[0039] Comparative Example 2

[0040] During the production process of a 1,000,000-ton / year catalytic cracking unit, after operating according to the existing catalytic cracking technology for half a year, the catalyst LBO-16 used in the catalytic cracking process was replaced with LDO-70. Because of the different compositions and the large difference in the attrition index between the new and old catalysts, the amount of catalyst fines in the flue gas doubled, and serious fouling occurred on the flue gas turbine YL-7000D. The standby flue gas turbine was put into use, and the fouled flue gas turbine was cleaned online by the "thermal cleaning" method (Sino-Global Energy, 2008(13): 93-94; Equipment Management & Maintenance, 2013(7), 50-52). Due to the thick scale layer and large falling scale blocks, the rotor mass eccentricity was relatively large and the vibration of the flue gas turbine rotor exceeded the standard. The on-site workers had to stop the machine for manual mechanical cleaning and could not carry out online cleaning.

[0041] It should be noted that this application is not limited to the above embodiments. The above embodiments are only examples, and embodiments with the same structure and the same effect as the technical idea within the scope of the technical solution of this application are included in the technical scope of this application. In addition, within the scope of not departing from the main idea of this application, various modifications that can be thought of by those skilled in the art to the embodiments and other ways constructed by combining some constituent elements of the embodiments are also included in the scope of this application.

Claims

1. A method for preventing severe scaling of a flue gas turbine during catalytic cracking, the method comprising: During catalytic cracking, the turbine disc temperature is periodically switched between high-temperature and low-temperature zones, causing the flue gas... gas turbine Long-term operation with no or very thin scale, wherein the temperature difference between the high-temperature section and the low-temperature section is at least 10°C, and the duration of the high-temperature section or the low-temperature section is 1-365 days.

2. The method according to claim 1, characterized in that, The temperature difference between the high-temperature and low-temperature sections is 10-200℃, and the duration of the high-temperature or low-temperature section is 2-180 days.

3. The method according to claim 1, characterized in that, The temperature difference between the high-temperature and low-temperature sections is 20-150℃, and the duration of the high-temperature or low-temperature section is 2-90 days.

4. The method according to claim 1, characterized in that, The temperature difference between the high-temperature and low-temperature sections is 20-100℃, and the duration of the high-temperature or low-temperature section is 2-60 days.

5. The method according to claim 1, characterized in that, The temperature difference between the high-temperature and low-temperature sections is 20-70℃, and the duration of the high-temperature or low-temperature section is 2-30 days.

6. The method according to claim 1, characterized in that, The temperature difference between the high-temperature and low-temperature sections is 20-50℃, and the duration of the high-temperature or low-temperature section is 2-15 days.