A method for decoking a furnace tube of a radiant section of a cracking furnace after the furnace tube is blocked

Abstract

The application discloses a decoking method after the radiation section furnace tube of a cracking furnace is blocked, and relates to the field of decoking of cracking furnaces. The decoking method can be used for the radiation section furnace tube blockage caused by the total shutdown, partial shutdown or large fluctuation of operation conditions of the cracking furnace. In the decoking method, the feeding amount of dilution steam and air is increased for multiple times under different temperature conditions by means of intermittence, the flow of the dilution steam and the coking air is strictly controlled, and the feeding amount and exchange frequency of the dilution steam are repeatedly and greatly adjusted, so that the local overheating points of the furnace tube are prevented from occurring in the coking process, the furnace tube is prevented from being damaged, and the overpressure of the furnace tube is prevented, finally, the blocked furnace tube can be completely decoked in allusion to different situations, the labor and time cost of decoking is reduced, the on-line rate of the cracking furnace is improved, and the energy consumption of the device is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of decoking of cracking furnaces, in particular to a method for decoking of a cracking furnace after plugging of the radiant section tubes. BACKGROUND

[0002] After the industrial cracking furnace runs to a certain condition, due to the reasons of pressure difference reduction of the furnace tube, high surface temperature of the furnace tube and high outlet temperature of the waste heat boiler, it is necessary to carry out the decoking of the material. By introducing the mixture of air and water vapor into the furnace tube of the cracking furnace, carbon dioxide and carbon monoxide are generated by the reaction of the coke blocks at a certain temperature, so as to achieve the purpose of decoking, and the cracking furnace again has the condition of feeding operation. The current coking method is to gradually increase the proportion of air in the water vapor and the coking temperature to control the intensity of the coke block reaction in the furnace tube, so as to prevent the coking process from over-temperature, thereby achieving the purpose of protecting the furnace tube of the cracking furnace.

[0003] The existing coking method is based on the method of decoking after the cracking furnace runs to a certain condition. In the production process of the cracking furnace, it is difficult to avoid the situation of abnormal working condition. In the abnormal working condition, the cracking furnace is stopped, and the phenomenon of plugging of the radiant section tube of the cracking furnace caused by the falling of the coke block is easy to occur, and it is difficult to remove the coke block in the furnace tube by the normal coking program to have the feeding operation state.

[0004] At present, the method adopted after the plugging of the radiant section tube of the cracking furnace is to cut the furnace tube judged to be plugged, to carry out mechanical decoking, and to re-weld to have the feeding operation state. This method has complex construction operation and long time, and consumes a lot of labor cost and time cost. SUMMARY

[0005] The present application provides a method for decoking of the radiant section tube of the cracking furnace after plugging, which can reduce unnecessary construction and construction risk of the cracking furnace after plugging, reduce the labor and time cost of decoking, improve the on-line rate of the cracking furnace, and reduce the energy consumption of the device.

[0006] In order to solve the above technical problems, one of the purposes of the present application provides a method for decoking of the radiant section tube of the cracking furnace after plugging, which is aimed at the plugging of the radiant section tube caused by the complete shutdown of the cracking furnace and the natural cooling to room temperature. The decoking method comprises the following steps:

[0007] (1) Re-igniting and heating the cracking furnace, when the furnace temperature of the cracking furnace reaches 220-250℃, start to input the dilution steam, and at the same time, increase the amount of dilution steam to hot standby steam;

[0008] (2) When the average outlet temperature of the normal furnace tube of the cracking furnace begins to rise to above 600 DEG C, a small amount of coking air is introduced at 100-200 t / h to coke, and when the average outlet temperature of the normal furnace tube of the cracking furnace is at 780-840 DEG C, the coking air is increased to 1.5 t / h and maintained;

[0009] (3) Then, the dilution steam is greatly increased, and the single group of dilution steam is increased to twice the original amount per hour, the maintaining time is controlled to be 1-2 min, then the original amount of the single group of dilution steam is restored, and the maintaining time is 2-4 h, the above operation of increasing and decreasing the single group of dilution steam is repeated in the coking process, the coking time is prolonged to 5-7 days under the condition that the average outlet temperature of the normal furnace tube of the cracking furnace is maintained at 780-840 DEG C, and the radiation section furnace tube of the cracking furnace is completely decoked.

[0010] As a preferred solution, when the outlet temperature of part of the furnace tube is always <100 DEG C and the inlet pressure and the cross-section pressure of the furnace tube are consistent during the temperature rising process of the cracking furnace, it is indicated that the radiation section furnace tube of the cracking furnace is blocked.

[0011] As a preferred solution, in steps (1) and (3), the pressure of the introduced dilution steam is 0.5-0.8 MPa, and the temperature is 180-230 DEG C.

[0012] As a preferred solution, in step (1), the temperature rising rate of the cracking furnace is >50 DEG C / h.

[0013] In order to solve the above technical problems, the second object of the present application provides a decoking method for the radiation section furnace tube of a cracking furnace after the furnace tube is blocked, aiming at the radiation section furnace tube being blocked due to the local shutdown of the cracking furnace, and the decoking method comprises the following steps:

[0014] The average outlet temperature of the normal furnace tube of the cracking furnace is maintained at 800-840 DEG C, the dilution steam is maintained to the amount of the hot standby steam, the coking air is increased to 1.5 t / h and maintained, then the single group of dilution steam is greatly increased to twice the original amount per hour, the maintaining time is controlled to be 1-2 min, the maintaining time is 2-4 h, then the original amount of the single group of dilution steam is restored, the above operation of increasing and decreasing the single group of dilution steam is repeated in the coking process, the coking time is prolonged to 2-5 days under the condition that the average outlet temperature of the normal furnace tube of the cracking furnace is maintained at 800-860 DEG C, and the radiation section furnace tube of the cracking furnace is completely decoked.

[0015] As a preferred solution, when the outlet temperature of part of the furnace tube is reduced to be more than 100 DEG C different from that of other furnace tubes and the inlet pressure and the cross-section pressure of the furnace tube are consistent due to the local shutdown of the cracking furnace, it is indicated that the radiation section furnace tube of the cracking furnace is blocked.

[0016] As a preferred solution, the pressure of the introduced dilution steam is 0.5-0.8 MPa, and the temperature is 180-230 DEG C.

[0017] In order to solve the above technical problems, the third object of the present application provides a decoking method for the blocked radiant section furnace tube of a cracking furnace, which is aimed at the blockage of the radiant section furnace tube caused by the large fluctuation of the operating conditions of the cracking furnace, and comprises the following steps:

[0018] The cracking furnace is returned to the decoking state, after purging the cracking furnace, the average temperature of the normal furnace tube outlet of the cracking furnace is maintained at 800-840 DEG C, the dilution steam is maintained to the amount of the hot standby steam, the decoking air is gradually increased to 1.5 t / h and maintained, then the dilution steam is greatly increased to twice the original amount / h, the maintaining time is controlled at 1-2 min, then it is restored to the original amount of the single group of dilution steam, and maintained for 2-4 h, the above single group of dilution steam rising and falling operation is repeated in the decoking process, the decoking time of the cracking furnace is extended to 24-72 h under the condition that the average outlet temperature of the normal furnace tube of the cracking furnace is maintained at 800-860 DEG C, and the radiant section furnace tube of the cracking furnace is completely decoked.

[0019] As a preferred scheme, when the outlet temperature of part of the furnace tube is reduced to more than 100 DEG C different from that of other furnace tubes, and the inlet pressure and the transverse section pressure of the furnace tube are consistent, it is found that the radiant section furnace tube of the cracking furnace is blocked.

[0020] As a preferred scheme, the pressure of the dilution steam is 0.5-0.8 MPa, and the temperature is 180-230 DEG C.

[0021] As a preferred scheme, the cracking furnace is a 28U1-1 type ethylene cracking furnace with an annual output of 35,000 tons, and has two groups of feed, and the hot standby steam of each group of feed is 4.5 t / h.

[0022] Compared with the prior art, the embodiments of the present application have the following beneficial effects:

[0023] The decoking method of the present application is aimed at the blocked furnace tube, and the amount of the dilution steam and air is increased several times under different temperature conditions by intermittence, the flow of the dilution steam and the decoking air is strictly controlled, and the different amount of the dilution steam and the exchange frequency are repeatedly adjusted, the local overheating point of the furnace tube is prevented in the decoking process, the furnace tube is prevented from being damaged, and the overpressure of the furnace tube is prevented, so that the decoking of the blocked furnace tube caused by different conditions can be effectively realized. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0025] Embodiment one

[0026] A decoking method after the plugging of the radiant section furnace tube of a cracking furnace, the cracking furnace tube plugging situation is: due to the complete shutdown of the cracking furnace, the natural cooling to room temperature, resulting in the plugging of the radiant section furnace tube, specifically due to the failure of the fan, resulting in the complete shutdown of the cracking furnace, causing up to 1 / 2 of the furnace tube to exist plugging phenomenon, taking a 28U1-1 type ethylene cracking furnace with an annual output of 35,000 tons as an example, there are two groups of feed, and the hot standby steam of each group of feed is 4.5t / h, the decoking method comprises the following steps:

[0027] (1) Re-igniting the cracking furnace according to the temperature rising rate of the temperature rising curve > 50℃ / h, when the cracking furnace hearth temperature reaches 220-250℃, dilution steam is introduced, the pressure of the dilution steam is about 0.5-0.8MPa, and the temperature is 180-230℃, and the furnace hearth temperature is continued to be raised according to the temperature rising rate of the temperature rising curve > 50℃ / h, and the amount of dilution steam is gradually increased to the amount of hot standby steam, i.e. 4.5t / h per group;

[0028] (2) During the temperature rising process of the cracking furnace, it is found that the outlet temperature of part of the furnace tube is always <100℃, and the inlet pressure and the transverse section pressure of the furnace tube are consistent, indicating that the current cracking furnace radiant section furnace tube is plugged, when the average outlet temperature of the normal furnace tube rises to above 600℃, a small amount of 100-200t / h coking air is introduced to start coking, when the average outlet temperature of the normal furnace tube is 780-840℃, the coking air is increased to 1.5t / h and maintained;

[0029] (3) Then the dilution steam is greatly increased, the pressure of the dilution steam is about 0.5-0.8MPa, and the temperature is 180-230℃, the single group dilution steam is increased from 4.5t / h to 9t / h, the maintaining time is controlled in 1-2min, then it is restored to 4.5t / h, and maintained for 2-4h, the above single group dilution steam rising and falling operation is repeated for several times during the coking process, under the condition that the average outlet temperature of the furnace tube is maintained at 780-840℃, the coking time is prolonged to 5-7 days, and the radiant section furnace tube of the cracking furnace can be completely decoked.

[0030] Corresponding to the plugging condition of the cracking furnace, if the cutting of the cracking furnace tube and the mechanical decoking method is adopted, it will take more than 14 days to complete the complete decoking.

[0031] Example two

[0032] A method for decoking after the radiation section of a cracking furnace is blocked, the cracking furnace is blocked due to partial shutdown of the cracking furnace, the outlet temperature of part of the furnace tube is found to be reduced by more than 100 DEG C from that of other furnace tubes, and the inlet pressure and the cross-section pressure of the furnace tube are consistent, which indicates that the radiation section of the cracking furnace is blocked, and the cracking furnace is partially shut down due to interruption of the feed of the cracking furnace, which causes 1 / 4 of the furnace tube to be blocked, for example, a 28U1-1 type ethylene cracking furnace with an annual output of 35,000 tons, which has two groups of feeds, and the standby steam for each group of feeds is 4.5 t / h, the method for decoking includes the following steps:

[0033] When the average outlet temperature of the normal furnace tube is maintained at 800-840 DEG C, the amount of dilution steam is maintained to the amount of standby steam, the incineration air is increased to 1.5 t / h and maintained, then the dilution steam is greatly increased, the pressure of the dilution steam is about 0.5-0.8 MPa, the temperature is 180-230 DEG C, the amount of dilution steam is increased from 4.5 t / h to 9 t / h, the maintaining time is controlled to be 1-2 min, and then it is restored to 4.5 t / h and maintained for 2-4 h, the above single group of dilution steam rising and falling operation is repeated for several times during the incineration process, the average outlet temperature of the normal furnace tube is maintained at 800-860 DEG C, the incineration time is extended to 2-5 days, and the radiation section of the cracking furnace can be completely decoked.

[0034] Corresponding to the blocking condition of the cracking furnace, if the cutting of the furnace tube of the cracking furnace and the mechanical decoking are adopted, it takes more than 7 days to complete the complete decoking.

[0035] Example three

[0036] A method for decoking after the radiation section of a cracking furnace is blocked, the cracking furnace is blocked due to partial shutdown of the cracking furnace, the outlet temperature of part of the furnace tube is found to be reduced by more than 100 DEG C from that of other furnace tubes, and the inlet pressure and the cross-section pressure of the furnace tube are consistent, which indicates that the radiation section of the cracking furnace is blocked, and the cracking furnace is partially shut down due to interruption of the feed of the cracking furnace, which causes 1 / 4 of the furnace tube to be blocked, for example, a 28U1-1 type ethylene cracking furnace with an annual output of 35,000 tons, which has two groups of feeds, and the standby steam for each group of feeds is 4.5 t / h, the method for decoking includes the following steps:

[0037] The pyrolysis furnace is returned to the coking state, after the pyrolysis furnace is purged, the normal furnace tube outlet average temperature is maintained at 800-840℃, the dilution steam is maintained at 4.5t / h, the coking air is gradually increased to 1.5t / h and maintained, then the dilution steam is greatly increased, the pressure of the dilution steam is about 0.5-0.8MPa, the temperature is 180-230℃, from every group 4.5t / h to 9t / h, the maintaining time is controlled at 1-2min, then returned to 4.5t / h, maintained for 2-4h, the above single group dilution steam rising and falling operation is repeated for several times in the coking process, under the condition of maintaining the normal furnace tube average outlet temperature at 800-860℃, the coking time is prolonged to 24-72h, the pyrolysis furnace radiation section furnace tube can be completely decoked.

[0038] Corresponding to the pyrolysis furnace blockage condition, if the cutting pyrolysis furnace tube and mechanical decoking mode is adopted, it needs more than 5 days to complete the complete decoking.

[0039] The above specific embodiments further illustrate the purpose, technical scheme and beneficial effects of the present application, it should be understood that the above only is the specific embodiment of the present application, and does not limit the protection scope of the present application. It is particularly pointed out that for those skilled in the art, any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A method for decoking a furnace tube of a radiant section of a cracking furnace after the furnace tube has been plugged, characterized in that, The method for clearing the coking in the radiation section of the cracking furnace includes the following steps: (1) Re-ignite the cracking furnace and raise the temperature, when the temperature of the furnace reaches 220-250 DEG C, start to pass in the dilution steam, and at the same time, raise the temperature of the furnace, and gradually increase the amount of the dilution steam to the amount of the hot standby steam; (2) When the average outlet temperature of the normal furnace tubes of the cracking furnace starts to rise to above 600 DEG C, pass in a small amount of 100-200 t / h coking air to coke, when the average outlet temperature of the normal furnace tubes of the cracking furnace is 780-840 DEG C, increase the coking air to 1.5 t / h and maintain; (3) Then, greatly increase the dilution steam, increase the amount of the single group of dilution steam to twice the original amount per hour, maintain for 1-2 min, then restore to the original amount of the single group of dilution steam, maintain for 2-4 h, repeat the above operation of increasing and decreasing the single group of dilution steam during the coking process, maintain the average outlet temperature of the normal furnace tubes of the cracking furnace at 780-840 DEG C, extend the coking time to 5-7 days, and complete the coking clearing in the radiation section of the cracking furnace; In steps (1) and (3), the pressure of the dilution steam is 0.5-0.8 MPa, and the temperature is 180-230 DEG C.

2. A method of decoking a furnace tube of a radiant section of a cracking furnace after the furnace tube has been plugged as claimed in claim 1, characterized in that, During the temperature raising process of the cracking furnace, when the outlet temperature of part of the furnace tubes is always below 100 DEG C, and the inlet pressure of the furnace tubes is consistent with the cross section pressure, it is indicated that the radiation section of the cracking furnace is coked.

3. A method of decoking a furnace tube of a radiant section of a cracking furnace after the furnace tube has been plugged as recited in claim 1, wherein, In step (1), the temperature raising rate of the cracking furnace is greater than 50 DEG C / h.

4. A method for decoking a furnace tube of a radiant section of a cracking furnace after the furnace tube has been plugged, characterized in that, The method for clearing the coking in the radiation section of the cracking furnace includes the following steps: Maintain the average outlet temperature of the normal furnace tubes of the cracking furnace at 800-840 DEG C, maintain the amount of the dilution steam to the amount of the hot standby steam, after increasing the coking air to 1.5 t / h and maintaining, greatly increase the single group of dilution steam to twice the original amount per hour, maintain for 1-2 min, maintain for 2-4 h, then restore to the original amount of the single group of dilution steam, repeat the above operation of increasing and decreasing the single group of dilution steam during the coking process, maintain the average outlet temperature of the normal furnace tubes of the cracking furnace at 800-860 DEG C, extend the coking time to 2-5 days, and completely clear the coking in the radiation section of the cracking furnace; The pressure of the dilution steam is 0.5-0.8 MPa, and the temperature is 180-230 DEG C.

5. A method of decoking a furnace tube of a radiant section of a cracking furnace after plugging of the furnace tube according to claim 4, characterized in that When the outlet temperature of part of the furnace tubes is lowered to be more than 100 DEG C different from the outlet temperature of the other furnace tubes, and the inlet pressure of the furnace tubes is consistent with the cross section pressure, it is indicated that the radiation section of the cracking furnace is coked.

6. A method of decoking a furnace tube of a radiant section of a cracking furnace after the furnace tube has been plugged, characterized in that, The method for clearing the coking in the radiation section of the cracking furnace includes the following steps: The cracking furnace is returned to the coking state, after purging the cracking furnace, the average temperature of the normal furnace tube outlet of the cracking furnace is maintained at 800-840℃, the dilution steam is maintained to the amount of the hot standby steam, the coking air is gradually increased to 1.5t / h and maintained, then the dilution steam is greatly increased to twice the original amount / h, the maintaining time is controlled at 1-2min, then it is returned to the original single group dilution steam input amount, maintained for 2-4h, the above single group dilution steam rising and falling operation is repeated during the coking process, the average outlet temperature of the normal furnace tube of the cracking furnace is maintained at 800-860℃, and the coking time is extended to 24-72h, so that the radiation section furnace tube of the cracking furnace is completely decoked; The pressure of the input dilution steam is 0.5-0.8MPa, and the temperature is 180-230℃.

7. A method of decoking a furnace tube of a radiant section of a cracking furnace after plugging of the furnace tube according to claim 6, characterized in that Due to the large fluctuation of the operation condition of the cracking furnace, it is found that the outlet temperature of part of the furnace tube is reduced to more than 100℃ different from that of other furnace tubes, and the furnace tube inlet pressure and the transverse section pressure are consistent, which indicates that the radiation section furnace tube of the cracking furnace is blocked.