A heating furnace and an on-line coke cleaning method

Abstract

The present invention discloses a heating furnace and an on-line decoking method. The heating furnace includes a first radiation chamber, a second radiation chamber and a convection chamber. A first radiation furnace tube and a first burner are arranged in the first radiation chamber. The convection chamber is located above the second radiation chamber, and convection furnace tubes are arranged in the convection chamber. A second radiation furnace tube and a second burner are arranged in the second radiation chamber. The inlet of the second radiation furnace tube is connected to the outlet of the convection furnace tube, and the outlet of the second radiation furnace tube is connected to the outlet of the first radiation furnace tube. An on-line decoking system including the above heating furnace is also provided. The present invention can significantly reduce the coking rate of the heating furnace for easily polymerizable oil products. The on-line decoking system can greatly shorten the shutdown decoking time, thereby prolonging the operation cycle of the heating furnace and saving the decoking cost of the furnace tubes.

Description

Technical Field

[0001] The present invention relates to the field of chemical equipment, and particularly to a heating furnace and an on-line coke cleaning method. Background Art

[0002] A heating furnace is a core equipment in the oil refining and chemical industry, and its design and operation level directly affect the processing capacity, operating flexibility and operation cycle of the unit. When processing easily polymerizable oils such as styrene tar, ethylene tar, coal tar and waste lubricating oil by hydrogenation treatment or thermal conversion process, the raw materials first need to be heated to the feed temperature (usually 370°C - 500°C) in the heating furnace to meet the reaction requirements. However, these oils undergo obvious polymerization reactions at about 300°C, forming a viscous soft coke layer in the furnace tubes of the heating furnace, resulting in problems such as an increase in pressure drop in the furnace tubes, a decrease in heat transfer efficiency, and overheating of the furnace chamber, seriously restricting the operation cycle of the unit. The soft coke layer is a viscous coke layer with a relatively high volatile content adhering to the inner wall of the furnace tube, which is significantly different from the hard coke layer with high hardness and low volatile content in the conventional furnace tubes.

[0003] Currently, during the actual industrial operation process, the heating furnace for such easily polymerizable oils needs to be shut down for coke cleaning after operating for 3 months. On the one hand, it affects the normal production of the enterprise, and on the other hand, it requires additional high start-up, shutdown and coke cleaning costs, resulting in economic losses. More importantly, the current coke cleaning methods such as mechanical coke cleaning balls and air coke burning have poor treatment effects on the soft coke layer in the heating furnace for such easily polymerizable oils. The soft coke layer is easy to adhere to and block the coke cleaning balls or cause overheating of the furnace tubes. In severe cases, the furnace tubes need to be cut and high-pressure water is used for sectional coke cleaning.

[0004] Based on the above analysis, since the target heating temperature required by the processing technology (370°C - 500°C) is higher than the initial polymerization temperature of the easily polymerizable oil (about 300°C), it is inevitable that more serious coking phenomena will occur in the furnace tubes in the high-temperature section. It is difficult to achieve an ideal improvement effect by using conventional uniform heat transfer and coking inhibition technologies. How to develop a heating furnace with a low coking rate and a simple and rapid coke cleaning method is a key technical problem to be solved in the processing of easily polymerizable oils. Summary of the Invention

[0005] The applicant's research found that when the existing technology heating furnace heats and processes conventional raw materials (such as vacuum residue), a hard coke layer is formed in the heating furnace tubes of the conventional raw materials, and the furnace tube coke removal can be achieved by mechanical coke removal, air coke burning or steam stripping coke. However, when the easily polymerizable oil product is heated in the furnace tube, a soft coke layer is formed in the low-temperature section furnace tube, and a hard coke layer is formed in the high-temperature section furnace tube. The soft coke layer has the characteristics of high oil content and high viscosity, and it is very difficult to use the conventional coke removal method. Based on the above findings, the applicant originally proposed a heating furnace with a new structure and a heating furnace system with an on-line coke removal function. First, the easily polymerizable oil product is heated to a lower temperature, and the coking rate is slow at low temperature, and then it is mixed with a high-temperature heat carrier medium that is not easy to coke, and it is quickly heated to the process required temperature, significantly reducing the coking rate in the furnace tube. At the same time, a method of flushing the soft coke with a specific organic solvent is proposed to solve the problem of cleaning the viscous soft coke in the furnace tube.

[0006] The object of the present invention is to provide a heating furnace and an on-line coke removal system to solve the problems of fast coking rate of the heating furnace for easily polymerizable oil products and difficult coke removal in the furnace tubes.

[0007] To solve the above problems, the technical solution of the present invention includes the following aspects:

[0008] In the first aspect of the present invention, a heating furnace is provided. The heating furnace includes a first radiant chamber, a second radiant chamber and a convection chamber; wherein

[0009] The first radiant chamber is provided with first radiant furnace tubes therein and a first burner at the bottom. The outlet of the first radiant furnace tubes is connected to the outlet of the second radiant furnace tubes;

[0010] The convection chamber is located above the second radiant chamber. Convection furnace tubes are arranged in the convection chamber, and the outlet of the convection furnace tubes is connected to the inlet of the second radiant furnace tubes;

[0011] The second radiant chamber is provided with second radiant furnace tubes therein and a second burner at the bottom. The inlet of the second radiant furnace tubes is connected to the outlet of the convection furnace tubes, and the outlet of the second radiant furnace tubes is connected to the outlet of the first radiant furnace tubes.

[0012] Further, as a preferred embodiment, the first radiant chamber is used to heat the raw material of the easily polymerizable oil product, which can generally be heated to 300°C - 450°C; the easily polymerizable oil product is an oil product that can polymerize to form a soft coke layer at 300°C - 350°C, such as ethylene tar and styrene tar with a high olefin content; or waste lubricating oil with more easily decomposable and polymerizable additives, etc.

[0013] Further, as a preferred embodiment, the first radiant furnace tubes are arranged in any one of the serpentine coil arrangement, horizontal horizontal tube arrangement and vertical riser arrangement. A first feed valve is provided on the inlet pipeline of the first radiant furnace tubes, and a first outlet valve is provided on the outlet pipeline of the first radiant furnace tubes.

[0014] Further, as a preferred embodiment, the convection chamber and the second radiant chamber are used to heat the heat-carrying medium, generally heated to 400°C - 550°C. The heat-carrying medium has the characteristics of being not easily coked at high temperatures and being able to participate in subsequent treatment processes. Preferably, it can be selected from one or several of hydrogen, light distillate oil (final boiling point < 500°C), steam, etc.

[0015] Further, as a preferred embodiment, the second radiant furnace tubes are arranged in any one of the ways such as serpentine coil arrangement, horizontal horizontal tube arrangement, vertical riser tube arrangement, etc., and the convection furnace tubes are arranged in horizontal horizontal tube arrangement.

[0016] The second aspect of the present invention provides an on-line coke cleaning system, which includes a heating furnace and a cleaning agent tank; wherein the heating furnace uses the heating furnace described above.

[0017] The cleaning agent tank is used to store the cleaning agent and provide a place for sedimentation separation of the circulating cleaning agent and soft coke. The inlet of the cleaning agent tank is connected to the cleaning agent circulation pipeline, and the outlet of the cleaning agent tank is connected to the inlet of the cleaning agent circulation pump through a pipeline. A drain valve is provided at the bottom of the cleaning agent tank to discharge the sedimented soft coke.

[0018] The cleaning agent circulation pump provides power for the circulation of the cleaning agent in the system. The inlet of the cleaning agent circulation pump is connected to the outlet of the cleaning agent tank, and the outlet of the cleaning agent circulation pump is connected to the inlet of the first radiant furnace tube.

[0019] The cleaning agent circulation pipeline is sequentially connected to the outlet of the cleaning agent tank, the cleaning agent circulation pump, the cleaning agent inlet valve, the inlet of the first radiant furnace tube, the outlet of the first radiant furnace tube, the cleaning agent outlet valve, and the inlet of the cleaning agent tank.

[0020] Further, as a preferred embodiment, the cleaning agent tank is cylindrical or cylindrical-conical. A partition baffle is arranged inside the cleaning agent tank. The partition baffle is located above the outlet of the cleaning agent tank. Further preferably, the partition baffle can be provided with openings, and the opening ratio is 10 - 50%. The opening ratio = the total opening cross-sectional area of the partition baffle / the total area of the partition baffle × 100%.

[0021] The third aspect of the present invention provides a method for on-line coke cleaning of furnace tubes. The on-line coke cleaning method uses the on-line coke cleaning system described in the second aspect of the present invention. The on-line coke cleaning method includes the following contents:

[0022] Step S10, when implementing on-line coke cleaning, start the cleaning agent circulation pump, open the cleaning agent feed valve and the cleaning agent discharge valve, and close the first feed valve to establish a cleaning agent circulation loop.

[0023] Step S20: The circulating cleaning agent in step S10 is heated to 20°C - 200°C in the first radiant furnace tube, gradually flushing the soft coke in the furnace tube, realizing online coke cleaning.

[0024] Step S30: The material flow (including the cleaning agent and the flushed soft coke) discharged from the outlet of the first radiant furnace tube in the first radiant chamber in step S20 returns to the cleaning agent tank. Through sedimentation separation, the soft coke is discharged from the blowdown valve at the bottom of the cleaning agent tank, and the cleaning agent is recycled.

[0025] In the above method, the cleaning agent is an organic solvent, specifically one or more of petroleum ether, toluene, light distillate oil (final boiling point < 500°C), and anthracene oil.

[0026] Compared with the prior art, the advanced effects of the heating furnace and the online coke cleaning system provided by the present invention are mainly reflected in:

[0027] 1. The applicant's research found that the polymerization and coking rate of easily polymerizable oil products at low temperatures is significantly reduced. Based on this, it is proposed to first heat the easily polymerizable oil products to a temperature with a lower coking degree, and then mix them with a high-temperature heat carrier that is not prone to coking, and quickly heat them to the process required temperature, significantly reducing the coking rate of the easily polymerizable oil products in the furnace tube and extending the operation cycle of the device.

[0028] 2. The applicant's research found that the viscous soft coke generated by easily polymerizable oil products at low temperatures is soluble in some organic solvents. Therefore, a special method of circulating and flushing with an organic cleaning agent is proposed to achieve online cleaning of the viscous soft coke, solve the problem of difficult cleaning of the viscous soft coke in the furnace tube, and greatly save the coke cleaning and start-up / shutdown costs.

[0029] 3. In the online coke cleaning method of the present invention, through sedimentation separation of the soft coke in the cleaning agent tank, the recycling of the cleaning agent is realized, which can further reduce the coke cleaning cost. Description of the Drawings

[0030] Figure 1 is a schematic diagram of a prior art heating furnace;

[0031] Figure 2 is a schematic diagram of the first embodiment of the heating furnace system with online coke cleaning function of the present invention;

[0032] Figure 3 is a schematic diagram of the second embodiment of the heating furnace system with online coke cleaning function of the present invention;

[0033] Description of the Reference Numerals

[0034] 10 - Convection chamber of the prior art heating furnace; 11 - Convection furnace tube of the prior art; 20 - Radiation chamber of the prior art heating furnace; 21 - Radiation furnace tube of the prior art; 22 - Burner of the prior art.

[0035] 1 - Heating furnace; 101a - First burner; 101b - Second burner; 110a - First radiant chamber; 110b - Second radiant chamber; 111a - First radiant furnace tube; 111b - Second radiant furnace tube; 120 - Convection chamber; 121 - Convection furnace tube; 2 - Cleaning agent tank; 201 - Partition baffle; 202 - Drain valve; 3 - Cleaning agent circulation pipeline; 301 - Cleaning agent feed pump; 302 - Cleaning agent feed valve; 303 - First feed valve; 304 - First outlet valve; 305 - Cleaning agent discharge valve. Detailed implementation mode

[0036] In the present invention, unless otherwise stated, the orientation terms such as "upper, lower, left, right" generally refer to the orientation shown in the accompanying drawings and the orientation in actual application, and "inner, outer" refer to the inside and outside of the contour of the component.

[0037] The present invention provides a heating furnace, which includes a first radiant chamber 110a, a second radiant chamber 110b and a convection chamber 120. Among them, the first radiant chamber is provided with a first radiant furnace tube 111a and a first burner 101a, and the outlet of the first radiant furnace tube is connected to the outlet of the second radiant furnace tube 111b; the convection chamber is located above the second radiant chamber, and a convection furnace tube 121 is arranged in the convection chamber, and the outlet of the convection furnace tube is connected to the inlet of the second radiant furnace tube; the second radiant chamber is provided with a second radiant furnace tube 111b and a second burner 101b, the inlet of the second radiant furnace tube is connected to the outlet of the convection furnace tube, and the outlet of the second radiant furnace tube is connected to the outlet of the first radiant furnace tube.

[0038] The on - line decoking system includes the heating furnace described above, a cleaning agent tank 2, a cleaning agent feed pump 301, and a cleaning agent circulation pipeline 3. Among them, the inlet of the cleaning agent tank is connected to the cleaning agent circulation pipeline, the outlet of the cleaning agent tank is connected to the inlet of the cleaning agent feed pump through a pipeline, and a drain valve 202 is arranged at the bottom of the cleaning agent tank; the inlet of the cleaning agent feed pump is connected to the outlet of the cleaning agent tank, and the outlet of the cleaning agent feed pump is connected to the inlet of the first radiant furnace tube 111a; the cleaning agent circulation pipeline is sequentially connected to the outlet of the cleaning agent tank, the cleaning agent feed pump, the cleaning agent feed valve 302, the inlet of the first radiant furnace tube, the outlet of the first radiant furnace tube, the cleaning agent outlet valve 305, and the inlet of the cleaning agent tank.

[0039] The specific decoking process of the on - line decoking system includes the following content:

[0040] Step S10, when implementing on - line decoking, start the cleaning agent feed pump 301, open the cleaning agent feed valve 302 and the cleaning agent discharge valve 305, close the first feed valve 303 and the first outlet valve 304, and establish a cleaning agent circulation loop;

[0041] In step S20, the circulating cleaning agent in step S10 is heated to 20°C - 200°C in the first radiant furnace tube 111a, and the soft coke in the furnace tube is gradually rinsed off to achieve online coke cleaning.

[0042] In step S30, the soft coke rinsed off in step S20 is carried into the cleaning agent tank 2 by the cleaning agent and discharged through the drain valve 202 at the bottom of the cleaning agent tank through sedimentation separation.

[0043] Figure 1 The following shows a prior art heating furnace, including a prior art convection chamber 10 and a radiant chamber 20 of the prior art heating furnace. Among them, prior art convection furnace tubes 11 are arranged in the prior art convection chamber of the prior art heating furnace; prior art radiant furnace tubes 21 and a prior art burner 22 are arranged in the prior art radiant chamber of the prior art heating furnace. The oil product first enters the inlet of the prior art convection furnace tube, enters the inlet of the prior art radiant furnace tube from the outlet of the prior art convection furnace tube, is heated to the process required temperature, and then flows out from the outlet of the prior art radiant furnace tube. The prior art burner provides the heat required for heating the oil product. Since the target heating temperature required by the process (370°C - 500°C) is higher than the starting polymerization temperature of the oil product (about 300°C), there is a relatively serious coking phenomenon in the furnace tubes in the high-temperature section.

[0044] Example 1

[0045] As Figure 2 shown, in this embodiment, both the first radiant chamber and the second radiant chamber are of cylindrical furnace type. The radiant furnace tubes are all arranged in a serpentine coil around the cylindrical radiant chamber from top to bottom, and the convection furnace tubes are arranged horizontally. During normal production, the first radiant chamber heats 5 t / h of waste lubricating oil to 300°C, and the second radiant chamber heats 630 kg / h of hydrogen to 500°C. After the waste lubricating oil and hydrogen are mixed, the reaction required temperature of 380°C is reached. When online coke cleaning of the furnace tubes is carried out, toluene is used as the cleaning agent. The first radiant chamber heats the toluene to 50°C and circulates and cleans for 10 h. The cleaning agent tank is of cylindrical type.

[0046] Compared with the prior art ( Figure 1 ) that directly heats the waste lubricating oil and hydrogen to 380°C, in the first radiant chamber of the present invention, only the easily polymerizable waste lubricating oil needs to be heated to 300°C, significantly reducing the coking rate of the first radiant furnace tube, and the furnace tube operation cycle can be increased from 3 months to more than 6 months. The present invention uses a cleaning agent for online coke cleaning. Compared with the prior art high-pressure water coke cleaning, the shutdown coke cleaning time is shortened from 7 days to 10 h of online coke cleaning, saving the shutdown coke cleaning time and cost.

[0047] Example 2

[0048] As Figure 3As shown in the figure, the first radiation chamber and the second radiation chamber in this embodiment both adopt a square box furnace type. The radiant furnace tubes are arranged horizontally, and the burners are located on both sides of the radiant furnace tubes. The convective furnace tubes are arranged horizontally. During normal production, the first radiation chamber heats 10 t / h of ethylene tar to 350 °C, and the second radiation chamber heats 10 t / h of light wax oil to 520 °C. After the ethylene tar and the light wax oil are mixed, the temperature required for the reaction, 385 °C, is reached. When online coke cleaning of the furnace tubes is carried out, the light distillate oil (boiling range < 350 °C) in the product is used as the cleaning agent. The first radiation chamber heats the light distillate oil to 100 °C and circulates for cleaning for 24 h. The cleaning agent tank is in a cylindrical-conical shape.

[0049] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any suitable combination of each specific technical feature. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods. But these simple modifications and combinations should also be regarded as the content disclosed by the present invention and all fall within the protection scope of the present invention.

Claims

1. A method for heating easily polymerizable oil products using a heating furnace, the heating furnace comprising a first radiation chamber, a second radiation chamber and a convection chamber; Among them A first radiant chamber, in which first radiant furnace tubes are provided, and a first burner is provided at the bottom. The outlet of the first radiant furnace tubes is connected to the outlet of the second radiant furnace tubes; the first radiant chamber is used to heat the easily polymerizable oil product to 300°C - 450°C; the easily polymerizable oil product is an oil product that polymerizes to form a soft coke layer at 300°C - 350°C. A convection chamber, which is located above the second radiant chamber. Convection furnace tubes are arranged in the convection chamber, and the outlet of the convection furnace tubes is connected to the inlet of the second radiant furnace tubes. A second radiant chamber, in which second radiant furnace tubes are arranged, and a second burner is provided at the bottom. The inlet of the second radiant furnace tubes is connected to the outlet of the convection furnace tubes, and the outlet of the second radiant furnace tubes is connected to the outlet of the first radiant furnace tubes; the convection chamber and the second radiant chamber are used to heat the heat-carrying medium to 400°C - 550°C; the heat-carrying medium is selected from one or more of hydrogen, light distillate oil, and steam. The method for heating the easily polymerizable oil product using a heating furnace includes the following steps: Step S10: Heat the easily polymerizable oil product in the first radiant chamber, and the heated easily polymerizable oil product is discharged from the outlet of the first radiant furnace tubes. Step S20: The easily polymerizable oil product discharged from the outlet of the first radiant furnace tubes is mixed with the heat-carrying medium discharged from the outlet of the second radiant furnace tubes, and the heat-carrying medium heats the easily polymerizable oil product to the process-required temperature.

2. The method for heating easily polymerizable oil products using a heating furnace according to claim 1, characterized in that: The first radiant furnace tubes adopt any one of the serpentine coil arrangement, horizontal horizontal tube arrangement, and vertical riser arrangement. A first feed valve is provided on the inlet pipeline of the first radiant furnace tubes, and a first outlet valve is provided on the outlet pipeline of the first radiant furnace tubes.

3. The method for heating easily polymerizable oil products using a heating furnace according to claim 1, characterized in that: The second radiant furnace tubes adopt any one of the serpentine coil arrangement, horizontal horizontal tube arrangement, and vertical riser arrangement, and the convection furnace tubes adopt the horizontal horizontal tube arrangement.

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