Decoking device and decoking process for cracking furnace

Abstract

The invention discloses a decoking device and a decoking process for a cracking furnace, and belongs to the field of petrochemical engineering, the inlet end and the outlet end of a furnace tube of the cracking furnace are connected with an input electrode, an input end detection electrode, an output electrode and an output end detection electrode, and an electric decoking controller loads voltage and current to the two ends of the furnace tube through the input electrode and the output electrode; current passes through the furnace tube to form an electromagnetic field, and voltages at two ends of the furnace tube are detected in real time through the detection electrodes and uploaded to the detector; in the thermal cracking reaction process, reaction materials containing scorched particles enter from the inlet end of the furnace tube and flow out from the outlet end, the scorched particles carry positive charges in the movement process of the reaction materials, other substances carry negative charges, and due to the fact that the flow direction of the scorched particles in the furnace tube is consistent with the flow direction of current, an electromagnetic field can prevent the scorched particles with the positive charges from getting close to the tube wall of the furnace tube. According to the invention, the coke particle aggregation time is reduced, the operation period of the cracking furnace is prolonged, the decoking effect is improved, the applicable temperature range of the device is expanded, and the yield and selectivity of the target cracking product are not influenced.

Description

Technical Field

[0001] The invention belongs to the technical field of petrochemical industry, and in particular relates to a decoking device and a decoking process for a cracking furnace. Background Art

[0002] More than 85% of ethylene production in the world adopts the tubular furnace steam cracking process. Hydrocarbons and dilution steam undergo thermal cracking reactions in the high-temperature cracking furnace tubes at about 850°C to produce small molecular target products such as ethylene and propylene. At the same time, there are a large number of side reactions. The dehydrogenation of aromatic components produces a large amount of tar and coke (hereinafter referred to as coke particles) and other by-products. These coke particles continue to accumulate and block the cracking furnace tubes, resulting in production interruptions, which has brought many adverse effects on ethylene production, resulting in a series of adverse effects such as reduced target product yields, reduced device processing capacity, increased energy consumption, and shortened operating cycles. Therefore, reducing the aggregation of coke particles and allowing them to pass through the cracking furnace tubes as quickly as possible plays a decisive role in the efficiency of the operating status of the ethylene cracking furnace.

[0003] The mechanism of hydrocarbon thermal cracking coking and its influencing factors are very complicated. The most recognized ones include: catalytic coking, gas phase coking and free radical coking. Among them, gas phase coking is the main form of coking, which refers to the coke generated in the main body of the gas flow. Al-bright and Amnek (Albright LF, Marek J C. Mechanistic model for formation of coke in pyrolysis units producing ethylene [J]. Industrial & Engineering Chemistry Research, 1988, 27 (5): 755-759) used electron microscopes and microphotography and other advanced methods to conduct a detailed study on the gas phase coking process. They believe that coke particles are the main substance in gas phase coking. Some of these coke particles come from the cracking reaction itself, and some are generated through polymerization and polycondensation reactions. The coking process can be expressed as:

[0004]

[0005] Tar particles, referred to as coke particles for short, move at high speed with other gaseous hydrocarbon substances in the cracking furnace tubes at a speed of 50 to 100 m / s. Since the mass of coke particles is much greater than that of other gaseous hydrocarbon substances, their moving speed is also lower than that of other gaseous hydrocarbon substances. This speed difference causes other gaseous hydrocarbon substances to constantly scour and rub the coke particles. In this process, friction generates static electricity, which causes the coke particles to carry a positive charge and other gaseous hydrocarbon substances to carry a negative charge. Since the cracking furnace tubes are made of metal, grounding measures are generally adopted. Under the attractive force of electrostatic force, the positively charged coke particles are easily separated from the reaction materials, adsorbed on the inner surface of the cracking furnace tubes, continuously gathered, and blocked the cracking furnace tubes.

[0006] In recent years, a variety of coking inhibition technologies have been developed to address thermal cracking coking. These include changing cracking reaction conditions, hydrogenation thermal cracking, pretreatment of cracking raw materials, surface treatment of furnace tubes, and adding coking inhibitors. The use of new cracking technologies and cracking furnace tube surface treatment processes requires a huge amount of money to replace cracking furnaces and furnace tubes, which is difficult to achieve in a short period of time. In addition, the price in the chemical market changes rapidly, and the investment returns cannot be guaranteed; changing the cracking dilution ratio and steam measures are conducive to reducing coking, but the effect is limited, and the increased dilution steam affects the processing capacity and output of the device and increases the energy consumption of the device; adding coking inhibitors has a better effect, but it is inevitable that the inhibitors will be entrained into the product, affecting the purity and impurity content of the product, causing unpredictable effects on subsequent separation and processing. How to inhibit and reduce the side reactions of aromatics in the initial stage of the reaction and increase its main reaction of ring opening is an important topic in the current ethylene industry.

[0007] Electrostatic decoking is a new technology that has developed rapidly in recent years. It involves the fields of chemical reactions and separations. At present, it is mainly used in the process of tail gas and air purification. Its electrostatic decoking device is a metal tube with a metal wire installed in the center. The metal tube is grounded as a precipitation electrode, and the metal wire is connected to a high-voltage power supply of 30kV~80kV as a discharge electrode. When the coal gas carries tar dust into the electric field caused by the above two electrodes (i.e., inside the tubular metal shell), the tar dust has the same charge as the discharge electrode due to the charge discharged by the discharge electrode. On the one hand, this charged tar dust attracts other uncharged particles and combines with them to form larger particles, and finally falls from the airflow due to gravity; on the other hand, this charged tar dust moves to the precipitation electrode under the action of the electric field force, and loses its charge when it hits the precipitation electrode and adheres to the precipitation electrode, i.e., the inner wall of the metal tube. Finally, it falls due to gravity or mechanical vibration and is discharged from the tar and dust discharge port. The electrostatic decoking device requires the construction of a complex high-voltage electric decoking tower, and is not suitable for ethylene cracking and coking operations involving oxygen and high temperatures. Since electrostatic decoking requires the use of 30kV to 80kV high voltage electricity, a metal wire is installed in the center as a discharge electrode. Under the high-temperature cracking and coking operation of 850°C, the metal wire is unstable, and the high-voltage discharge may cause the coke and air in the cracking furnace to explode, seriously threatening the safe operation of the device. In addition, the metal wire discharge electrode installed in the center cannot adapt to the high temperature of 850°C and the high-speed airflow of 150m / s, and will soon be damaged and fail.

[0008] For example, a Chinese patent with publication number CN209093613U discloses an electrostatic decoking device. The electrostatic decoking device requires the construction of a complex high-voltage electric decoking tower, including a decoking device body and a DC power supply. The inner cavity of the decoking device body is provided with a partition, and the inner cavity of the partition is evenly provided with air pipes, and the air pipes run through the top and bottom of the partition. The inner cavity of each group of air pipes is provided with a high-voltage electric field negative electrode wire, and the electric field negative electrode wire is connected to the negative electrode of the DC power supply to achieve the effect of gas impurity removal. The electrostatic decoking device only adds a partition, which is essentially no different from ordinary electric decoking. High-voltage discharge cannot be used for cracking and decoking, and can cause explosion of coke and air in the cracking furnace, seriously threatening the safe operation of the device.

[0009] Another example is a honeycomb type high-voltage electrostatic detarring dust collector disclosed in the publication number CN2882795Y. The dust collector needs to build a complex high-voltage electric decoking tower, including a shell with a gas inlet, a gas outlet and a sewage outlet. A high-voltage incoming line box, an intermittent flushing pipeline and an upper frame are respectively provided at the upper end of the shell. The upper frame is connected to the high-voltage DC generator through a high-voltage insulator in the high-voltage incoming line box. A corona wire connected to the upper frame and the lower frame is provided in the hexagonal cylinder. The corona wire and the hexagonal cylinder form a high-voltage DC strong electric field. The dust collector only divides the large cavity into small honeycomb cavities. It is essentially no different from ordinary electric decoking. High-voltage discharge cannot be used for cracking and decoking. It can cause explosion of coke and air in the cracking furnace, seriously threatening the safe operation of the device, and has a complex structure. Summary of the invention

[0010] The object of the present invention is to provide a decoking device and a decoking process for a cracking furnace, so as to solve the problem of hydrocarbon thermal cracking coking existing in the existing tubular furnace steam cracking process.

[0011] The technical solution adopted by the present invention to solve the technical problem is as follows:

[0012] A decoking process for a cracking furnace according to the present invention mainly comprises the following steps:

[0013] An input electrode and an input detection electrode are connected to the inlet end of the cracking furnace tube, and an output electrode and an output detection electrode are connected to the outlet end of the cracking furnace tube. The set voltage and current are loaded to the two ends of the cracking furnace tube through the input electrode and the output electrode by using the electric decoking controller. When current flows through the cracking furnace tube, an electromagnetic field is formed in the cracking furnace tube. At the same time, the voltage at the two ends of the cracking furnace tube is detected in real time through the input detection electrode and the output detection electrode and uploaded to the detector. During the thermal cracking reaction, the reaction material containing coke particles enters from the inlet end of the cracking furnace tube and flows out from the outlet end of the cracking furnace tube. At the same time, the reaction material moves at a high speed in the cracking furnace tube together with other gaseous hydrocarbon substances, so that the coke particles are positively charged and other gaseous hydrocarbon substances are negatively charged. Since the flow direction of the coke particles in the cracking furnace tube is consistent with the flow direction of the current, the electromagnetic field will prevent the coke particles with positive charge from approaching the tube wall of the cracking furnace tube, thereby reducing the coke particle aggregation time and extending the operation cycle of the cracking furnace.

[0014] As a preferred implementation, the set voltage range is 12V to 36V.

[0015] As a preferred implementation, the set current range is 1 mA to 10 mA.

[0016] As a preferred implementation, the electric decoking controller is connected to a power source.

[0017] As a preferred embodiment, the electric decoking controller is used to adjust the voltage and current loaded to both ends of the cracking furnace tube to adapt to different stages of the cracking furnace operation.

[0018] As a preferred implementation, the input end detection electrode, the output end detection electrode and the detector are used to implement sound and light alarms when it is detected that the voltage at both ends of the cracking furnace tube exceeds a set range.

[0019] As a preferred embodiment, the input electrode, the output electrode, the input end detection electrode and the output end detection electrode are all equipped with a cooling radiator, and the cooling radiator is selected from one or more of an air-cooled heat dissipation structure, a water-cooled heat dissipation structure, a fin heat dissipation structure, and a microchannel heat dissipation structure.

[0020] As a preferred embodiment, the cross-sections of the input electrode, the output electrode, the input end detection electrode and the output end detection electrode are selected from one of a circle, a square, a triangle and a polygon; the end faces of the input electrode, the output electrode, the input end detection electrode and the output end detection electrode are flat or curved.

[0021] A decoking device for a cracking furnace of the present invention is used to realize the electric decoking process of a quencher, and mainly comprises: a power supply, an electric decoking controller, an input electrode, an output electrode, an input end detection electrode, an output end detection electrode and a detector; the power supply is connected to the electric decoking controller, the electric decoking controller is respectively connected to the input electrode and the output electrode, the input electrode and the output electrode are respectively connected to the inlet end and the outlet end of the furnace tube of the cracking furnace, the input end detection electrode and the output end detection electrode are respectively connected to the inlet end and the outlet end of the furnace tube of the cracking furnace, and the input end detection electrode and the output end detection electrode are both connected to the detector.

[0022] The beneficial effects of the present invention are:

[0023] The invention is provided with an input electrode and an input end detection electrode connected to the inlet end of the cracking furnace tube, and an output electrode and an output end detection electrode connected to the outlet end of the cracking furnace tube. The electric decoking controller is used to load the set voltage and current to the two ends of the cracking furnace tube through the input electrode and the output electrode. When the current passes through the cracking furnace tube, an electromagnetic field is formed in the cracking furnace tube. At the same time, the voltage at the two ends of the cracking furnace tube is detected in real time through the input end detection electrode and the output end detection electrode and uploaded to the detector. When the voltage at the two ends of the cracking furnace tube is too low or too high, an audible and visual alarm is performed, thereby improving the safety of the cracking furnace decoking process and solving the problem of high-voltage discharge safety. Problem: During the thermal cracking reaction, the reaction materials containing coke particles enter from the inlet end of the cracking furnace tube and flow out from the outlet end of the cracking furnace tube. At the same time, during the high-speed movement of the reaction materials in the cracking furnace tube together with other gaseous hydrocarbon substances, the coke particles are positively charged and other gaseous hydrocarbon substances are negatively charged. Since the flow direction of the coke particles in the cracking furnace tube is consistent with the flow direction of the current, the electromagnetic field will prevent the positively charged coke particles from approaching the tube wall of the cracking furnace tube, thereby reducing the coke particle aggregation time, extending the operation cycle of the cracking furnace, and improving the decoking effect, solving the problems of rapid coking, short operation cycle, short service life of the furnace tube, high energy consumption and low production efficiency in the cracking furnace.

[0024] In addition, the electrodes used in a cracking furnace decoking device of the present invention can withstand a high temperature of 1300°C, which expands the applicable temperature range of the device and makes it suitable for most high and low temperature environments, including minus 100°C to plus 1300°C, solving the problem that the existing decoking device is only used for low-temperature tail gas purification below 250°C and cannot operate under the high temperature conditions of 850°C in the cracking furnace.

[0025] The decoking device and decoking process of a cracking furnace of the present invention can inhibit the aggregation of coke particles in the furnace tube without affecting the yield and selectivity of the target product of the cracking product, thereby extending the operation cycle of the cracking furnace and the economic benefit of the device, and complying with the technical specifications of low-carbon green chemical industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a structural schematic diagram of a cracking furnace decoking device of the present invention.

[0027] In the figure, 1. power supply, 2. electric decoking controller, 3. input electrode, 4. output electrode, 5. input end detection electrode, 6. output end detection electrode, 7. detector, 8. cracking furnace tube, 9. reaction material, 10. coke particle flow direction, 11. current flow direction. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0029] In a first aspect, the present invention provides a decoking device for a cracking furnace.

[0030] See also Figure 1 To illustrate, a decoking device for a cracking furnace of the present invention can be installed in an explosion-proof control cabinet, and specifically includes the following components:

[0031] A power source 1, an electric decoking controller 2, an input electrode 3, an output electrode 4, an input end detection electrode 5, an output end detection electrode 6 and a detector 7.

[0032] Wherein, the power supply 1 is connected to the electric decoking controller 2, and the electric decoking controller 2 is respectively connected to the input electrode 3 and the output electrode 4, and the input electrode 3 and the output electrode 4 are respectively connected to the inlet end and the outlet end of the cracking furnace tube 8, that is, the input electrode 3 is connected to the inlet end of the cracking furnace tube 8, and the output electrode 4 is connected to the outlet end of the cracking furnace tube 8; the input end detection electrode 5 and the output end detection electrode 6 are respectively connected to the inlet end and the outlet end of the cracking furnace tube 8, that is, the input end detection electrode 5 is connected to the inlet end of the cracking furnace tube 8, and the output end detection electrode 6 is connected to the outlet end of the cracking furnace tube 8; the input end detection electrode 5 and the output end detection electrode 6 are both connected to the detector 7.

[0033] The voltage range of the power supply 1 can be specifically 0.01V to 36V. Different voltages all have a decoking effect, but the decoking effects of different voltages are different, and the higher the voltage, the better the decoking. Therefore, in order to comply with the national standard "Safety Voltage" GB3805-83 and operational safety, in the present invention, the power supply 1 is designed to be a DC safety voltage of less than 36V. In order to take into account both the decoking effect and the safety design, the voltage range of the power supply 1 is preferably a DC safety voltage of 12V to 36V.

[0034] In addition, the power supply range of the power supply 1 can be specifically 0.01mA to 10000mA. Different currents all have a decoking effect, but the decoking effects of different currents are different, and the decoking is relatively good for a higher current. Therefore, in order to comply with the national standard "Safety Voltage" GB3805-83 and operational safety, in the present invention, the power supply 1 is designed to be a direct current safety current of less than 10mA. In order to take into account both the decoking effect and the safety design, the current range of the power supply 1 is preferably a direct current safety current of 1mA to 10mA.

[0035] The input electrode 3 and the output electrode 4 are respectively connected to the inlet and outlet ends of the cracking furnace tube 8, and the input end detection electrode 5 and the output end detection electrode 6 are respectively connected to the inlet and outlet ends of the cracking furnace tube 8. Specifically, the input electrode 3, the output electrode 4, the input end detection electrode 5 and the output end detection electrode 6 can be respectively connected to the cracking furnace tube 8 through metal materials.

[0036] Among them, the connection method between the input electrode 3, the output electrode 4, the input end detection electrode 5 and the output end detection electrode 6 and the cracking furnace tube 8 can be bolt connection or welding connection. Preferably, welding connection is adopted to achieve seamless connection, which can prevent the loss of current energy and the attenuation of detection signals.

[0037] The input electrode 3, the output electrode 4, the input-end detection electrode 5 and the output-end detection electrode 6 can be made of high-temperature resistant materials and can withstand a high temperature of 1300°C.

[0038] Among them, the high-temperature resistant material used is preferably nickel-based high-temperature alloy, titanium-based high-temperature alloy or molybdenum-based high-temperature alloy, more preferably titanium-based high-temperature alloy. Titanium alloy has good corrosion resistance as well as good anti-oxidation, heat resistance, acid and alkali resistance, and is not easily corroded by the atmosphere, water, chemicals, etc.

[0039] Among them, cooling radiators are installed on the input electrode 3, the output electrode 4, the input end detection electrode 5 and the output end detection electrode 6. The installed cooling radiators can increase the heat dissipation area and optimize the heat conduction path, thereby improving the heat dissipation effect and being able to reduce the high temperature of about 1300°C in the cracking furnace tube 8 to the tolerance temperature of the electrode cable.

[0040] The cooling radiator may be an active heat dissipation structure or a passive heat dissipation structure, preferably a passive heat dissipation structure.

[0041] Among them, the active heat dissipation structure can be an air-cooled heat dissipation structure or a water-cooled heat dissipation structure, and is preferably an air-cooled heat dissipation structure.

[0042] The passive heat dissipation structure may be a fin heat dissipation structure or a microchannel heat dissipation structure, preferably a fin heat dissipation structure.

[0043] The cross-sections of the input electrode 3 , the output electrode 4 , the input-end detection electrode 5 and the output-end detection electrode 6 may be circular, square, triangular or any polygonal.

[0044] The end surfaces of the input electrode 3 , the output electrode 4 , the input-end detection electrode 5 and the output-end detection electrode 6 may be flat surfaces or curved surfaces.

[0045] The structures of the input electrode 3, the output electrode 4, the input end detection electrode 5 and the output end detection electrode 6 are preferably cylindrical structures.

[0046] The main function of the electric decoking controller 2 is to adjust the different working voltages and different working currents of the decoking device of the cracking furnace of the present invention to adapt to different stages of the operation of the cracking furnace. For example, in the initial stage of the operation of the cracking furnace, the surface of the cracking furnace tube 8 is relatively clean, and the working voltage and working current can be relatively low. At this time, the preferred voltage range is 12V to 30V, and the preferred current range is 1mA to 5mA; at the end of the operation of the cracking furnace, the surface of the cracking furnace tube 8 is covered with a coke layer, and the working voltage and working current should be increased. At this time, the preferred voltage range is 24V to 36V, and the preferred current range is 5mA to 10mA.

[0047] The decoking device for a cracking furnace of the present invention has an operating power of 0.1 watt to 1000 kilowatts and a conversion efficiency of about 90%. The preferred operating power is 100 watts to 10 kilowatts.

[0048] After the decoking device for a cracking furnace of the present invention is started, the electric decoking controller 2 converts the alternating current into direct current, and the current output by the electric decoking controller 2 enters the cracking furnace tube 8 through the input electrode 3, and flows out through the output electrode 4 or grounding to form a closed loop. According to the Ampere's law of electromagnetics, in any section of a conductor, the magnitude and direction of the current determine the magnitude and direction of the generated magnetic field. This law explains that the essence of the current is a moving charge and generates a magnetic field. Therefore, when a current passes through the cracking furnace tube 8, an electromagnetic field is formed in the cracking furnace tube 8. At the same time, an input end detection electrode 5 and an output end detection electrode 6 are respectively arranged at the inlet and outlet ends of the cracking furnace tube 8. The voltage of the input end detection electrode 5 and the output end detection electrode 6 is detected in real time by the detector 7, that is, the voltage at both ends of the cracking furnace tube 8 is detected in real time. Once the voltage is too low or too high, the detector 7 will give an audible and visual alarm.

[0049] For reliable and stable decoking devices suitable for industrial use, the maximum output power can generally only reach about 20 kilowatts. In actual applications, the rated power that can operate stably for a long period is only about 10 kilowatts. Therefore, in order to enhance the decoking effect and adapt to more decoking occasions, multiple groups of cracking furnace decoking devices of the present invention can be set up to work in parallel to obtain a better and more ideal decoking effect.

[0050] In a second aspect, the present invention provides a cracking furnace decoking process, which is mainly implemented by using a cracking furnace decoking device provided in the first aspect.

[0051] A decoking process for a cracking furnace of the present invention has the following specific implementation steps:

[0052] During the thermal cracking reaction, the reaction material 9 containing coke particles moves at a high speed in the cracking furnace tube 8 together with other gaseous hydrocarbon substances, and its speed is about 50 to 100 m / s. Since the mass of the coke particles is much greater than that of other gaseous hydrocarbon substances, its moving speed is also lower than that of other gaseous hydrocarbon substances. This speed difference will cause other gaseous hydrocarbon substances to continuously scour and rub the coke particles. In this process, friction generates static electricity, which makes the coke particles positively charged and other gaseous hydrocarbon substances negatively charged. Since the cracking furnace tube 8 is made of metal, grounding measures are generally adopted. According to Coulomb's law of electromagnetism, there is an interaction force between different charges. The positively charged coke particles are easily separated from the reaction material 9 under the attractive force of electrostatic force, adsorbed on the inner surface of the cracking furnace tube 8 and continuously aggregated, which may block the cracking furnace tube 8. At this time, when the cracking furnace decoking device of the present invention is started, current flows through the cracking furnace tube 8 and an electromagnetic field is formed on the surface of the cracking furnace tube 8; when the magnetic lines of force of the electromagnetic field reach a suitable direction and intensity, the electromagnetic field will hinder the positively charged coke particles from approaching the wall of the cracking furnace tube 8, thereby achieving the purpose of slowing down their aggregation on the wall of the cracking furnace tube 8, allowing them to pass through the cracking furnace tube 8 as much as possible, reducing their aggregation time on the wall of the cracking furnace tube 8, and extending the operation cycle of the cracking furnace.

[0053] Among them, when the coke particle flow direction 10 in the cracking furnace tube 8 is consistent with the current flow direction 11, that is, the current output by the electric decoking controller 2 enters the cracking furnace tube 8 through the input electrode 3, flows out of the cracking furnace tube 8 through the output electrode 4 or grounding, and the reaction material 9 enters the cracking furnace tube 8 through the input electrode 3 end, and flows out of the cracking furnace tube 8 through the output electrode 4 end, the coke particles in the cracking furnace tube 8 generate repulsive force due to the electromagnetic field effect of the tube wall of the cracking furnace tube 8, and are not easy to be adsorbed on the tube wall of the cracking furnace tube 8 and then pass through the cracking furnace tube 8, thereby greatly reducing the amount of coking and extending the operation cycle of the cracking furnace.

[0054] Among them, when the flow direction 10 of the coke particles in the cracking furnace tube 8 is inconsistent with the flow direction 11 of the current, that is, the current output by the electric decoking controller 2 enters the cracking furnace tube 8 through the input electrode 3, and flows out of the cracking furnace tube 8 through the output electrode 4 or the ground, and the reaction material 9 enters the cracking furnace tube 8 through the output electrode 4 end, and flows out of the cracking furnace tube 8 through the input electrode 3 end, the coke particles in the cracking furnace tube 8 generate a deflection force due to the electromagnetic field effect of the tube wall of the cracking furnace tube 8. The coke particles are prone to radial movement in the process of moving forward, and then deflect in the direction of the tube wall of the cracking furnace tube 8, and are easily adsorbed on the tube wall of the cracking furnace tube 8, which greatly increases the amount of coking, resulting in the operation cycle of the cracking furnace being shorter than the operation cycle under normal conditions.

[0055] The working principle of the present invention is that the electric decoking of the thermal radiation furnace tube of the cracking furnace acts on a thermal reaction environment above 1000°C, and the cracking coking mechanism of thermal radiation is free radical coking, that is, the coking matrix such as polycyclic aromatic hydrocarbons in the high-temperature gas continues to dehydrogenate into coke particles, and the coke material is in the form of solid coke particles. The outside of the cracking furnace tube 8 is a furnace flame of 1100°C, and the safety requirements are relatively high. According to the safety design specifications of the cracking furnace, a DC stable current of 36V or less should be used. Therefore, the present invention applies a safety voltage electric field of less than 36V (national standard "Safety Voltage" GB3805-83) at both ends of the inlet and outlet of the cracking furnace tube 8, and sets a safety current. By effectively controlling the voltage and current of the electric field, a stable electromagnetic field can be formed in the cracking furnace tube 8. When the flow direction of the coke particles in the cracking furnace tube 8 is consistent with the direction of the electric field (that is, the coke particle flow direction 10 is consistent with the current flow direction 11), the coke particles are more likely to pass through the cracking furnace tube 8 under the action of the electromagnetic field, rather than being adsorbed on the inner surface of the cracking furnace tube 8, thereby achieving the effect of slowing down the carbon deposition in the cracking furnace tube 8, greatly reducing the amount of coking, and extending the operation cycle of the cracking furnace.

[0056] In summary, the decoking device and decoking process of a cracking furnace of the present invention do not require the construction of a complex high-voltage electric decoking tower, thereby solving the technical problems of the traditional decoking process, such as the need to build a complex and expensive electric capture tower or cylinder, the safety problem of high-voltage discharge, and the inability to be applicable to ethylene cracking and coking operations containing oxygen and high temperature.

[0057] In addition, the traditional decoking process is only applicable to low-temperature tail gas purification below 250°C, and its electrodes cannot operate at the high temperature of 850°C in the cracking furnace. The decoking device and decoking process of the cracking furnace of the present invention have a wider and more extensive applicable temperature range and can be applied to most high-temperature and low-temperature environments, including -100°C to 1300°C, solving the high-temperature decoking problem of the traditional decoking process.

[0058] The decoking device and decoking process for a cracking furnace of the present invention have been experimentally verified to have no influence on improving the yield and selectivity of the target product of the cracking product, and can inhibit the aggregation of coke particles in the furnace tube 8 of the cracking furnace, thereby solving the problems of rapid coking of the cracking furnace, short operation cycle, short service life, high energy consumption and low production efficiency existing in the traditional decoking process.

[0059] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0060] Example 1

[0061] First, a blank test was conducted without opening the cracking furnace decoking device, and a blank test was conducted in a simulated cracking pilot plant with a feed rate of 5 kg per hour. Before the thermal cracking reaction, the cracking furnace tube 8 was removed and weighed separately, and the weight M1 obtained was the empty tube weight of the cracking furnace tube 8 (8220.00 grams).

[0062] Install the cracking furnace tube 8, the cracking raw material is selected as naphtha, the cracking temperature is 830 ℃, the cracking pressure is 0.18MPa, and the cracking dilution ratio is 0.5. After other process parameters reach the set value, feed the naphtha raw material. After the cracking furnace is operated for 6 hours, stop feeding the naphtha raw material, after the cracking furnace tube 8 is purged and dried, remove the cracking furnace tube 8 and weigh it, and obtain that weight M2 is the sum of the empty tube weight and the blank coking amount (8222.50 grams), and weight M2 minus weight M1 is the blank coking amount (2.50 grams).

[0063] Then, a decoking test was carried out in a simulated cracking pilot plant with an hourly feed rate of 5 kg. The cracking raw material was selected as naphtha, the cracking temperature was set to 830°C, the cracking pressure was 0.18 MPa, and the cracking dilution ratio was 0.5. After other process parameters reached the set values, the naphtha raw material was introduced. The voltage and current output by the electric decoking controller 2 were set to 30V and 0.3 mA respectively, and the cracking furnace decoking device of the present invention was started. The current output by the electric decoking controller 2 entered the cracking furnace tube 8 through the input electrode 3 and flowed out of the cracking furnace tube 8 through the output electrode 4, forming a closed loop. Current passed through the cracking furnace tube 8, and an electromagnetic field was formed on the surface of the cracking furnace tube 8. The electromagnetic field would prevent the positively charged coke particles from approaching the wall of the cracking furnace tube 8, thereby achieving the purpose of slowing down the aggregation of coke particles on the wall of the cracking furnace tube 8, allowing the coke particles to pass through the cracking furnace tube 8 as much as possible, reducing the coking time on the wall of the cracking furnace tube 8, and playing the effect of extending the operation cycle of the cracking furnace. After the cracking furnace has been running for 6 hours, the introduction of naphtha raw material is stopped, and the cracking furnace tube 8 is purged and dried, and then the cracking furnace tube 8 is weighed. The weight M3 is the sum of the empty tube weight and the decoking amount (8220.46 grams). The weight M3 minus the weight M1 is the decoking amount compared to the coking amount (0.46 grams), which is 2.04 grams less than the blank coking amount (2.50 grams), and the reduction ratio is 81.60%, and the decoking effect is obvious.

[0064] Example 2 Decoking Test with Reverse Current

[0065] A decoking test was conducted in a simulated cracking pilot plant with a feed rate of 5 kg per hour. Naphtha was selected as the cracking raw material, the cracking temperature was 830°C, the cracking pressure was 0.18 MPa, and the cracking dilution ratio was 0.5. After other process parameters reached the set values, the naphtha raw material was introduced. The voltage and current output by the electric decoking controller 2 were set to 30V and 3mA respectively, and the cracking furnace decoking device of the present invention was started. The current output by the electric decoking controller 2 entered the cracking furnace tube 8 through the input electrode 3 and flowed out of the cracking furnace tube 8 through the output electrode 4, and the reaction material 9 entered the cracking furnace tube 8 through the output electrode 4 end and flowed out of the cracking furnace tube 8 through the input electrode 3 end. After the cracking furnace has been stably operated for 6 hours, the feeding of naphtha raw material is stopped, and the cracking furnace tube 8 is purged and dried, and then the cracking furnace tube 8 is weighed, and the weight M4 is the sum of the empty tube weight and the decoking amount (8224.40 grams). The weight M4 minus the weight M1 is the decoking amount compared with the coking amount (4.40 grams), which is increased by 1.90 grams compared with the blank coking amount (2.50 grams), and the increase ratio is 76.00%. Not only is there no decoking effect, but the coking amount is obviously increased on the contrary.

[0066] Example 3 Decoking Test at Different Voltages

[0067] A decoking test was conducted in a simulated cracking pilot plant with a feed rate of 5 kg per hour. Naphtha was selected as the cracking raw material, the cracking temperature was 830°C, the cracking pressure was 0.18 MPa, and the cracking dilution ratio was 0.5. After other process parameters reached the set values, the naphtha raw material was introduced. The voltage and current output by the electric decoking controller 2 were set to 36V and 3mA respectively, and the cracking furnace decoking device of the present invention was started. The current output by the electric decoking controller 2 entered the cracking furnace tube 8 through the input electrode 3 and flowed out of the cracking furnace tube 8 through the output electrode 4, forming a closed loop. After the cracking furnace has been running for 6 hours, the introduction of naphtha raw material is stopped, the cracking furnace tube 8 is purged and dried, and then the cracking furnace tube 8 is removed and weighed. The weight M5 is the sum of the empty tube weight and the decoking amount (8220.35 grams). The weight M5 minus the weight M1 is the decoking amount compared to the coking amount (0.35 grams), which is 2.15 grams less than the blank coking amount (2.50 grams), with a reduction rate of 86.00%. Relative to the decoking voltage of 30V, the decoking effect of the decoking voltage of 36V is further improved.

[0068] Example 4 High voltage decoking test above safe voltage

[0069] A decoking test was conducted in a simulated cracking pilot plant with a feed rate of 5 kg per hour. Naphtha was selected as the cracking raw material, the cracking temperature was 830°C, the cracking pressure was 0.18 MPa, and the cracking dilution ratio was 0.5. After other process parameters reached the set values, the naphtha raw material was introduced. The voltage and current output by the electric decoking controller 2 were set to 48V and 3mA respectively, and the cracking furnace decoking device of the present invention was started. The current output by the electric decoking controller 2 entered the cracking furnace tube 8 through the input electrode 3 and flowed out of the cracking furnace tube 8 through the output electrode 4, forming a closed loop. After the cracking furnace has been running for 6 hours, the introduction of naphtha feedstock is stopped, the cracking furnace tube 8 is purged and dried, and then the cracking furnace tube 8 is removed and weighed. The weight M6 is the sum of the empty tube weight and the decoking amount (8220.32 grams). The weight M6 minus the weight M1 is the decoking amount compared to the coking amount (0.32 grams), which is 2.18 grams less than the blank coking amount (2.50 grams), with a reduction rate of 87.20%. Relative to the decoking voltage of 30V, the decoking effect of the decoking voltage of 48V is further improved.

[0070] Example 5 Decoking Tests at Different Currents

[0071] A decoking test was conducted in a simulated cracking pilot plant with a feed rate of 5 kg per hour. Naphtha was selected as the cracking raw material, the cracking temperature was 830°C, the cracking pressure was 0.18 MPa, and the cracking dilution ratio was 0.5. After other process parameters reached the set values, the naphtha raw material was introduced. The voltage and current output by the electric decoking controller 2 were set to 30V and 5mA respectively, and the cracking furnace decoking device of the present invention was started. The current output by the electric decoking controller 2 entered the cracking furnace tube 8 through the input electrode 3 and flowed out of the cracking furnace tube 8 through the output electrode 4, forming a closed loop. After the cracking furnace has been running for 6 hours, the introduction of naphtha feedstock is stopped, the cracking furnace tube 8 is purged and dried, and then the cracking furnace tube 8 is removed and weighed. The weight M7 is the sum of the empty tube weight and the decoking amount (8220.31 grams). The weight M7 minus the weight M1 is the decoking amount compared to the coking amount (0.31 grams), which is 2.19 grams less than the blank coking amount (2.50 grams), with a reduction rate of 87.60%. Relative to the decoking current of 3 mA, the decoking effect of the decoking current of 5 mA is further improved.

[0072] Example 6 Decoking Test Using Alternating Current

[0073] A decoking test was conducted in a simulated cracking pilot plant with a feed rate of 5 kg per hour. Naphtha was selected as the cracking raw material, the cracking temperature was 830°C, the cracking pressure was 0.18 MPa, and the cracking dilution ratio was 0.5. After other process parameters reached the set values, the naphtha raw material was introduced. The AC voltage and AC current output by the electric decoking controller 2 were set to 30V and 5mA respectively, and the cracking furnace decoking device of the present invention was started. The current output by the electric decoking controller 2 entered the cracking furnace tube 8 through the input electrode 3 and flowed out of the cracking furnace tube 8 through the output electrode 4, forming a closed loop. After the cracking furnace has been running for 6 hours, the introduction of naphtha feedstock is stopped, the cracking furnace tube 8 is purged and dried, and then the cracking furnace tube 8 is removed and weighed. The weight M8 is the sum of the empty tube weight and the decoking amount (8222.49 grams). The weight M8 minus the weight M1 is the decoking amount compared to the coking amount (2.49 grams), which is basically unchanged compared to the blank coking amount (2.50 grams). This shows that the alternating current has no decoking effect.

[0074] Example 7 Decoking Comparison Test of Pyrolysis Product Yield

[0075] In order to investigate whether the decoking device of the cracking furnace of the present invention affects the yield of the cracking product while suppressing coke, a decoking test was carried out in a simulated cracking pilot plant with an hourly feed of 5 kg. The cracking raw material was selected as naphtha, the cracking temperature was 830°C, the cracking pressure was 0.18MPa, and the cracking dilution ratio was 0.5. After other process parameters reached the set values, the naphtha raw material was introduced. The AC voltage and AC current output by the electric decoking controller 2 were set to 30V and 3mA respectively, and the decoking device of the cracking furnace of the present invention was started. The current output by the electric decoking controller 2 entered the cracking furnace tube 8 through the input electrode 3 and flowed out of the cracking furnace tube 8 through the output electrode 4 to form a closed loop. After the cracking furnace was operated for 3 hours, the cracking products were collected at the outlet of the cracking furnace tube 8 for chromatographic analysis, and the comparative data of the cracking product yield after decoking and the blank cracking product were obtained, as shown in Table 1.

[0076] Table 1 Mass yield of decoked pyrolysis products and blank pyrolysis products, %

[0077]

[0078]

[0079] It can be seen from Table 1 that the yields of cracking products of the blank group and the decoking group are very close, which indicates that the decoking device for a cracking furnace of the present invention will not affect the yield of cracking products while suppressing coke.

[0080] The present invention discloses a decoking device and decoking process for a cracking furnace. Those skilled in the art can refer to the content of this article and appropriately improve the process parameters to achieve the above. It should be particularly noted that all similar replacements and modifications are obvious to those skilled in the art and are considered to be included in the present invention. The product of the present invention has been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the product of this article without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention.

Claims

1. A decoking process for a cracking furnace, characterized in that: The following steps are involved: An input electrode and an input detection electrode are connected to the inlet end of the cracking furnace tube, and an output electrode and an output detection electrode are connected to the outlet end of the cracking furnace tube. The set voltage and current are loaded to the two ends of the cracking furnace tube through the input electrode and the output electrode by using the electric decoking controller. When current flows through the cracking furnace tube, an electromagnetic field is formed in the cracking furnace tube. At the same time, the voltage at the two ends of the cracking furnace tube is detected in real time through the input detection electrode and the output detection electrode and uploaded to the detector. During the thermal cracking reaction, the reaction material containing coke particles enters from the inlet end of the cracking furnace tube and flows out from the outlet end of the cracking furnace tube. At the same time, the reaction material moves at a high speed in the cracking furnace tube together with other gaseous hydrocarbon substances, so that the coke particles are positively charged and other gaseous hydrocarbon substances are negatively charged. Since the flow direction of the coke particles in the cracking furnace tube is consistent with the flow direction of the current, the electromagnetic field will prevent the coke particles with positive charge from approaching the tube wall of the cracking furnace tube, thereby reducing the coke particle aggregation time and extending the operation cycle of the cracking furnace.

2. A decoking process for a cracking furnace according to claim 1, characterized in that: The set voltage range is 12V to 36V.

3. A decoking process for a cracking furnace according to claim 1, characterized in that: The set current range is 1 mA to 10 mA.

4. A decoking process for a cracking furnace according to claim 1, characterized in that: The electric decoking controller is connected to a power source.

5. A decoking process for a cracking furnace according to claim 1, characterized in that: The electric decoking controller is used to adjust the voltage and current loaded on both ends of the cracking furnace tube to adapt to different stages of the cracking furnace operation.

6. A decoking process for a cracking furnace according to claim 1, characterized in that: The input end detection electrode, the output end detection electrode and the detector are used to realize sound and light alarm when it is detected that the voltage at both ends of the cracking furnace tube exceeds a set range.

7. A decoking process for a cracking furnace according to claim 1, characterized in that: The input electrode, the output electrode, the input end detection electrode and the output end detection electrode are all equipped with cooling radiators, and the cooling radiators are selected from one or more of air cooling structure, water cooling structure, fin cooling structure and microchannel cooling structure.

8. A decoking process for a cracking furnace according to claim 1, characterized in that: The cross-section of the input electrode, output electrode, input end detection electrode and output end detection electrode is selected from one of circular, square, triangular and polygonal; the end faces of the input electrode, output electrode, input end detection electrode and output end detection electrode are flat or curved.

9. A decoking device for a cracking furnace, used to implement the quencher electric decoking process as claimed in any one of claims 1 to 8, characterized in that: include: Power supply, electric decoking controller, input electrode, output electrode, input end detection electrode, output end detection electrode and detector; The power supply is connected to the electric decoking controller, and the electric decoking controller is respectively connected to the input electrode and the output electrode, and the input electrode and the output electrode are respectively connected to the inlet end and the outlet end of the cracking furnace tube, and the input end detection electrode and the output end detection electrode are respectively connected to the inlet end and the outlet end of the cracking furnace tube, and the input end detection electrode and the output end detection electrode are both connected to the detector.

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