Fluid catalytic cracking first-stage system and method for establishing a first-stage circulation

Abstract

The present invention belongs to the technical field of petroleum refining, and particularly relates to a catalytic cracking first-stage system and a method for establishing a first-stage circulation therein. The present invention provides a catalytic cracking first-stage system, which improves the original first-stage system, and provides a method for establishing a first-stage circulation in this system, and dehydrates the external tower circulation of the first-stage system during the establishment of the seven-way circulation. It can quickly establish the first-stage circulation of the fractionation tower during the startup of the catalytic cracking unit, stably provide heat sources for the absorption and stabilization system, is conducive to recovering liquefied gas and dry gas components, reducing the emission of toxic and harmful gases, improving economic benefits, and reducing environmental pollution.

Description

Technical Field

[0001] The invention belongs to the technical field of petroleum refining, and in particular relates to a catalytic cracking system and a method for establishing a circulation thereof. Background Art

[0002] At present, most catalytic cracking units use heat combination to save energy, in which the heat circulating in the distillation tower is often used as the heat source for the desorption tower of the absorption stabilization system and the reboiler at the bottom of the stabilization tower. During the startup process, the material and heat balance in the distillation tower has not reached a stable state, and the atomizing steam and stripping steam of the regeneration system condense and accumulate in the extraction tank in the upper part of the distillation tower, making the water content of the system in the first part high and difficult to establish circulation; on the other hand, after the device is sprayed with oil, due to the low initial processing load of the device, the total amount of gasoline and diesel components generated by the reaction is small, and the heat distribution of the distillation tower is relatively lagging behind the reflux adjustment of each middle section, resulting in a large amount of heat taken by the oil slurry and refining system in the lower part of the distillation tower, while the upper heat load is low, especially the diesel component in the middle is relatively small. During this period of operation, there was not enough diesel component in the reflux section of the distillation tower, and the reflux could not be established. Secondly, during the operation of the catalytic cracking unit, the absorption stabilization was in a three-tower circulation state. In order to ensure the safety of the tank area, the stabilized gasoline could not be temporarily discharged from the unit, and all of it entered the absorption tower as a supplementary absorbent, causing the oil-gas ratio in the absorption tower to be too large, excessive absorption, resulting in an increase in the C2 component entering the desorption tower. Due to insufficient heat source at the bottom of the desorption tower, the C2 component will enter the stabilization tower, causing the pressure of the reflux tank of the stabilization tower to increase, and non-condensable gas will be forced to be discharged to the flare system. A combination of various reasons caused the absorption stabilization system to fail to operate normally. It was necessary to release the flare through the air compressor outlet or discharge non-condensable steam from the reflux tank at the top of the stabilization tower into the flare system to ensure that the pressure of the liquid hydrocarbon reflux tank was within the process index range, which not only caused economic losses, but was also not conducive to environmental protection. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a catalytic cracking system, improves the original system, and provides a method for establishing a circulation in the system, which can quickly establish a distillation tower circulation when the catalytic cracking unit is started, and stably provide a heat source for the absorption stabilization system, which is beneficial to recovering liquefied gas and dry gas components, reducing toxic and harmful gas emissions, improving economic benefits, and reducing environmental pollution.

[0004] The FCC first-stage system of the present invention includes a fractionating tower and a diesel stripping tower. The fractionating tower is connected to the diesel stripping tower through a diesel extraction pipeline. The diesel extraction pipeline includes two parallel pipelines, which are respectively provided with a diesel upper extraction outlet valve and a diesel lower extraction outlet valve. The diesel stripping tower is connected to a diesel pump. An external total circulation pipeline of the first-stage tower is provided outside the fractionating tower, which is successively provided with a first-stage extraction layer thermocouple, a first-stage extraction valve, a first-stage pump, a slurry-first-stage heat exchanger, a bottom reboiler of the stabilization tower, a bottom reboiler of the desorption tower, a feedstock-first-stage heat exchanger, a first-stage return valve, and a first-stage return tower thermocouple. Among them, a first-stage filled diesel pipeline is provided in the connecting pipeline between the feedstock-first-stage heat exchanger and the first-stage return valve. An external circulation pipeline of the first-stage tower is provided between the connecting pipeline of the feedstock-first-stage heat exchanger and the first-stage return valve and the connecting pipeline of the first-stage pump and the first-stage extraction valve. A first-stage external circulation cross-over valve is provided on the external circulation pipeline of the first-stage tower;

[0005] In the FCC first-stage system of the present invention, a first-stage external circulation breathing pipeline is provided between the connecting pipeline of the fractionating tower and the first-stage pump and the connecting pipeline of the diesel stripping tower and the diesel pump. A first-stage external circulation breathing line valve is provided on the first-stage external circulation breathing pipeline.

[0006] The method for establishing a first-stage circulation in the FCC first-stage system of the present invention is to dehydrate the external circulation of the first-stage system during the establishment of the seven-way circulation.

[0007] The seven-way circulation includes hot water, sealing oil, first-stage, feedstock oil, recycle oil, slurry, and absorption-stabilization introduced gasoline. During the conventional start-up process of the FCC unit, the pre-steps need to complete purging, pressure testing, airtightness testing of the three reactors and drying of the lining. After the auxiliary combustion furnace is started and the riser reactor and the regenerator are heated up, the next step is to introduce oil and establish the seven-way circulation of the fractionating tower and the absorption-stabilization system. During the establishment of the seven-way circulation, the external circulation of the first-stage system is dehydrated using the process flow. After injecting oil into the riser, a first-stage circulation is quickly established, which plays a key role in promptly incorporating the rich gas at the outlet of the compressor into the absorption-stabilization system.

[0008] The method for establishing a first-stage circulation of the present invention includes the following steps:

[0009] S1. The first-stage system receives diesel: Close the first-stage extraction valve and the first-stage return valve, open the external circulation pipeline of the first-stage tower, introduce diesel from the first-stage filled diesel pipeline and fill it into the pipeline of the first-stage system; Open the vent valve at the top of the diesel stripping tower, close the two valves between the diesel stripping tower and the fractionating tower to isolate the fractionating tower from the diesel stripping tower, open the first-stage external circulation breathing line valve, and use the first-stage external circulation breathing pipeline to fill oil into the diesel stripping tower. In this step, the diesel stripping tower serves as a thermal expansion buffer tower for the first-stage circulation;

[0010] S2. Establish the first-stage external circulation: After the first-stage system finishes receiving diesel, start the first-stage pump to establish the first-stage external circulation;

[0011] S3, establish a two-way circulation of raw oil and recycled oil: open the diesel pump, the first valve group, and the first pump inlet to vent to cut water, collect wax oil in the raw oil tank and the recycled oil tank, start the raw oil pump and the recycled oil pump to establish a two-way circulation, and at the same time, use the raw material-first heat exchanger to heat the diesel in the first system pipeline;

[0012] S4. Establish an external circulation of the oil slurry tower: lead wax oil from the recycling oil tank to the inlet of the oil slurry pump to establish an external circulation of the oil slurry tower. At the same time, use the oil slurry-first heat exchanger to heat the diesel in the first system pipeline. When the temperature reaches 95-105°C, open the diesel pump, the first valve group, and the first pump inlet to vent and cut off the water. After the water is cut off, turn off the first pump and stop the external circulation of the first tower;

[0013] S5. Establish a stable absorption gasoline cycle: gasoline is drawn from the unqualified line to each tower and tank, so that the liquid level of each tower and tank is maintained stable at 45-55%;

[0014] S6. In this process, the system is heated up by firing the furnace according to the heating curve of 10-15℃ / h. When the temperature reaches 200℃-300℃, low-pressure protective steam is taken for heat flow. The temperature is kept constant at 300-350℃, and the non-fixed torque flange is thermally tightened. The temperature is raised to 500-550℃ at 10-15℃, and the non-fixed torque flange is thermally tightened.

[0015] S7. Establish a medium cycle: After the above cycles are established, the reaction and regeneration system enters the air drive in turn, removes the large oil and gas line blind plate at the entrance of the fractionation tower, establishes an open oil slurry circulation, and starts to load the agent into the regenerator. When the regenerator material level is 25%-30%, the bed temperature is >380 degrees, and the combustion oil is sprayed; after the combustion oil is sprayed, the auxiliary combustion furnace load is gradually reduced until it is extinguished, and the bed temperature is controlled at 550-600℃, and the reaction and regeneration system is fluidized;

[0016] Start the air compressor to warm up at a low speed. When the outlet temperature of the lifting pipe is >520℃, spray gasoline on the lifting pipe and gradually increase the amount. Within 1-1.5h, the processing capacity will be increased to 70-75% of the processing load. At this time, the temperature in the distillation tower rises rapidly. Close the diesel upper extraction outlet valve and the diesel lower extraction outlet valve. When the thermocouple temperature of the first extraction layer is >240℃ and shows a downward trend, open the first extraction valve, the first return valve and the first pump inlet valve of the distillation tower, close the cross-line valve of the external circulation of the first tower, close the inlet valve of the diesel stripping tower to the first pump, and open the valve of the diesel stripping tower gas return line to the distillation tower, close the vent valve at the top of the diesel stripping tower, and wait until the difference between the inlet pipeline temperature of the first pump and the temperature of the first extraction layer is less than 10℃, start the first pump, establish a circulation, and slowly increase the amount after seeing the flow in the first. Close the air compressor flare valve and open the air compressor outlet gate valve at the same time to merge the rich gas into the absorption stabilization system.

[0017] Preferably, in step S1, after venting and removing the oil phase, the vent valve is closed, the liquid level of the diesel stripping column is filled to 20%-30%, and the diesel in the first intermediate system is stopped from being received.

[0018] Preferably, in step S2, the opening time of the first intermediate pump is 1-2 h.

[0019] Preferably, in step S3, the raw material oil tank and the recycle oil tank receive wax oil until the liquid level reaches 45%-55%, and after stopping receiving wax oil, water drainage is maintained for 30-40 min.

[0020] Preferably, in step S3, the heating rate is 10-15 °C / h, and after heating to 120-130 °C and maintaining a constant temperature to check for thermal tightness, it is then heated to 200-220 °C.

[0021] Preferably, in step S4, the liquid level of the diesel stripping column is maintained at 20%-30%. If the liquid level is low, diesel is introduced through the diesel filling pipeline of the first intermediate system to supplement the first intermediate system.

[0022] Preferably, in step S4, the temperature of the diesel in the pipeline of the first intermediate system is controlled by the temperature control valves of the raw material - first intermediate heat exchanger and the slurry - first intermediate heat exchanger. After the water in the first intermediate system is heated, it is discharged through the vent of the diesel stripping column.

[0023] In step S6, the extraction outlet of the first intermediate is in the liquid accumulation box on the 17th floor of the fractionation tower, and the return port is in the liquid accumulation box on the 14th floor. After the reaction starts injecting oil, sufficient internal liquid reflux should be established in the liquid accumulation boxes on the 14th - 17th floors as soon as possible. Therefore, in the initial stage of oil injection, the diesel extraction valve is closed, no diesel is produced, the liquid accumulation box at the diesel extraction outlet on the 13th floor is quickly filled, overflows to the 14th - floor tray of the first intermediate returning to the tower, provides internal reflux, condenses the heavy components in the rising gas phase, and establishes an equilibrium between the gas - liquid phases on the 14th - 17th floors, and the liquid level in the liquid accumulation box of the first intermediate extraction is quickly established. In the initial stage of oil injection, the temperature of the first intermediate extraction layer will rise rapidly. When the temperature of the extraction layer rises above 240 °C and then shows a decreasing trend, it indicates that there are already liquid components in the liquid accumulation box of the extraction.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The method of the present invention can quickly establish the first intermediate circulation in the fractionation tower during the start - up of the fluid catalytic cracking unit, provide a heat source for the stable operation of the absorption - stabilization system, is conducive to recovering liquefied gas and dry gas components, reducing the emission of toxic and harmful gases, avoiding greenhouse gases generated by flaring, reducing environmental pollution, and creating good social benefits;

[0026] 2. During the normal startup process of a 1.4 Mt / a fluid catalytic cracking unit, about 160 t of liquefied gas components and 20 t of gas are burned off at the flare. Based on the existing startup of the fractionation tower's first-stage recycle in the fluid catalytic cracking unit, the present invention adopts a method of filling diesel oil into the first-stage system for circulation heating and dehydration before injecting oil into the riser. The flare time during the startup of the fluid catalytic cracking unit is shortened by 4 hours, the flare volume of liquefied gas is reduced by about 100 t, and the flare volume of gas is reduced by 14 t. At the same time, the generation of SO2, NO x and particulate pollutants during the flare period is reduced, achieving great economic and environmental benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A simplified structural diagram of the existing first-stage recycle system of the fluid catalytic cracking unit;

[0028] Figure 2 A simplified structural diagram of the first-stage recycle system of the fluid catalytic cracking unit of the present invention;

[0029] In the figure: 1. Fractionation tower; 2. Diesel oil upper extraction outlet valve; 3. Diesel oil lower extraction outlet valve; 4. Diesel oil stripping tower; 5. First-stage tower external recycle breathing pipeline; 6. Diesel oil pump; 7. First-stage tower external recycle breathing line valve; 8. First-stage pump; 9. Slurry - first-stage heat exchanger; 10. Reboiler at the bottom of the stabilizer tower; 11. Reboiler at the bottom of the desorber tower; 12. Feedstock - first-stage heat exchanger; 13. First-stage tower external recycle pipeline; 14. First-stage return valve; 15. First-stage extraction valve; 16. First-stage return to tower thermocouple; 17. First-stage extraction layer thermocouple; 18. First-stage filling diesel oil pipeline; 19. First-stage tower external recycle crossover valve. DETAILED DESCRIPTION OF THE INVENTION

[0030] To further illustrate the method and effect of the present invention, the following describes the present invention in further detail with reference to the embodiments.

[0031] Example 1

[0032] As Figure 1As shown in the figure, the existing first-stage catalytic cracking system includes a fractionating tower 1 and a diesel stripping tower 4. The fractionating tower 1 is connected to the diesel stripping tower 4 through a diesel extraction pipeline. The diesel extraction pipeline includes two parallel pipelines, which are respectively provided with a diesel upper extraction outlet valve 2 and a diesel lower extraction outlet valve 3. The diesel stripping tower 4 is connected to a diesel pump 6. An external total circulation pipeline of the first-stage tower is provided outside the fractionating tower 1, which is successively provided with a first-stage extraction layer thermocouple 17, a first-stage extraction valve 15, a first-stage pump 8, a slurry-first-stage heat exchanger 9, a reboiler at the bottom of the stabilizer tower 10, a reboiler at the bottom of the desorption tower 11, a feedstock-first-stage heat exchanger 12, a first-stage return valve 14, and a first-stage return tower thermocouple 16. Among them, a first-stage filled diesel pipeline 18 is provided in the connecting pipeline between the feedstock-first-stage heat exchanger 12 and the first-stage return valve 14. An external first-stage circulation pipeline 13 is provided between the connecting pipeline of the feedstock-first-stage heat exchanger 12 and the first-stage return valve 14 and the connecting pipeline of the first-stage pump 8 and the first-stage extraction valve 15. A first-stage external circulation bypass valve 19 is provided on the first-stage external circulation pipeline 13.

[0033] As Figure 2 shown in the figure, in the first-stage catalytic cracking system of the present invention, a first-stage external circulation breathing pipeline 5 is provided between the connecting pipeline of the fractionating tower 1 and the first-stage pump 8 and the connecting pipeline of the diesel stripping tower 4 and the diesel pump 6. A first-stage external circulation breathing line valve 7 is provided on the first-stage external circulation breathing pipeline 5.

[0034] The method for establishing a first-stage circulation in the first-stage catalytic cracking system of the present invention is to perform external circulation dehydration on the first-stage system during the establishment of the seven-way circulation; the seven-way circulation includes hot water, sealing oil, first-stage, feedstock oil, recycle oil, slurry, and gasoline introduced from the absorption and stabilization section. Specifically, it includes the following steps:

[0035] S1. The first-stage system receives diesel: Close the first-stage extraction valve 15 and the first-stage return valve 14, open the first-stage external circulation pipeline 13, introduce diesel from the first-stage filled diesel pipeline 18 and fill it into the first-stage system pipeline; open the vent valve at the top of the diesel stripping tower 4, close the two valves between the diesel stripping tower 4 and the fractionating tower 1 to isolate the fractionating tower 1 and the diesel stripping tower 4, open the first-stage external circulation breathing line valve 7, and use the first-stage external circulation breathing pipeline 5 to fill the diesel stripping tower 4 with oil. In this step, the diesel stripping tower 4 serves as a thermal expansion buffer tower for the first-stage circulation;

[0036] Among them, in step S1, after venting and removing the oil phase, close the vent valve. When the liquid level of the diesel stripping tower 4 is filled to 25%, the first-stage system stops receiving diesel;

[0037] S2. Establish the first-stage external circulation: After the first-stage system finishes receiving diesel, start the first-stage pump 8 to establish the first-stage external circulation;

[0038] Among them, the starting time of the first-stage pump 8 is 1.5 h;

[0039] S3. Establish two-way circulation of feedstock oil and recycle oil: Start the diesel pump, the first-stage valve group, and the vent at the inlet of the first-stage pump to drain water. The feedstock oil tank and the recycle oil tank receive wax oil. Start the feedstock oil pump and the recycle oil pump to establish two-way circulation. At the same time, put into use the feedstock-first-stage heat exchanger 12 to heat up the diesel oil in the first-stage system pipeline;

[0040] Among them, the feedstock oil tank and the recycle oil tank receive wax oil until the liquid level reaches 50%. After stopping receiving wax oil, continue to drain water for 30 minutes; The heating rate is 10°C / h. Heat up to 130°C and keep it constant for heat tightening inspection, and then heat up to 220°C;

[0041] S4. Establish the external circulation of the slurry tower: Draw wax oil from the recycle oil tank to the inlet of the slurry pump to establish the external circulation of the slurry tower. At the same time, put into use the slurry-first-stage heat exchanger 9 to heat up the diesel oil in the first-stage system pipeline. When the temperature reaches 100°C, start the diesel pump 6, the first-stage valve group, and the vent at the inlet of the first-stage pump 8 to drain water. After draining water is completed, close the first-stage pump 8 and stop the external circulation of the first-stage tower;

[0042] Among them, keep the liquid level of the diesel stripping tower 4 at 25%. If the liquid level is low, diesel oil is introduced into the first-stage system through the diesel filling pipeline 18 of the first stage; The temperature of the diesel oil in the first-stage system pipeline is controlled by the temperature control valves of the feedstock-first-stage heat exchanger 12 and the slurry-first-stage heat exchanger 9. After the water in the first-stage system is heated, it is discharged through the vent of the diesel stripping tower 4;

[0043] S5. Establish the gasoline circulation for absorption and stabilization: Draw gasoline from the unqualified line to each tower and tank to keep the liquid level of each tower and tank at 50% and stable;

[0044] S6. In this process, the reactor-regenerator system lights the furnace and heats up. Heat up according to the heating curve at a rate of 15°C / h. When heating up to 250°C, introduce low-pressure protective steam into the internal heat extraction. Keep it constant at 350°C, tighten the non-fixed moment flange thermally. Heat up to 550°C at a rate of 15°C and keep it constant, and tighten the non-fixed moment flange thermally;

[0045] S7. Establish the first-stage circulation: After the above circulations are established, the reactor-regenerator system successively enters the process of purging air, removes the blind flange of the large oil and gas line at the inlet of the fractionating tower 1, establishes the open-circuit circulation of the slurry, and starts loading the catalyst into the regenerator. When the material level in the regenerator is 30%, the bed temperature > 380 degrees, spray combustion oil; After the combustion oil is sprayed, gradually reduce the load of the auxiliary combustion furnace until it goes out, control the bed temperature at 600°C, and fluidize the reactor-regenerator system;

[0046] Start the air compressor for low-speed warm-up operation. When the temperature at the outlet of the first reactor in the riser reaches above 520 °C, inject gasoline into the riser and gradually increase the flow rate. Raise the processing volume to 70% of the processing load within 1 hour. At this time, the temperature in the fractionation tower rises rapidly. Close the upper diesel extraction outlet valve 2 and the lower diesel extraction outlet valve 3. When the temperature measured by the thermocouple 17 at the first-stage extraction layer > 240 °C and shows a downward trend, open the first-stage extraction valve 15, the first-stage return valve 14, and the inlet valve of the first-stage pump 8 in the fractionation tower, close the external circulation bypass valve 19 of the first stage, close the valve from the diesel stripping tower 4 to the inlet of the first-stage pump 8, and open the valve of the gas return line from the diesel stripping tower 4 to the fractionation tower 1. Close the vent valve at the top of the diesel stripping tower 4. When the temperature difference between the inlet pipeline of the first-stage pump 8 and the temperature at the first-stage extraction layer is less than 10 °C, start the first-stage pump 8 to establish the first-stage circulation. After the first-stage circulation shows flow, gradually increase the flow rate. Close the compressor flare valve and open the outlet gate valve of the compressor at the same time, and incorporate the rich gas into the absorption and stabilization system.

[0047] During the conventional start-up process of an original 1.4 Mt / a fluid catalytic cracking unit, about 160 t of liquefied gas components and 20 t of gas were burned off by flaring. By establishing the first-stage circulation through the above method, the flaring time of the fluid catalytic cracking unit during start-up was shortened by 4 hours, the flaring volume of liquefied gas was reduced by about 100 t, and the flaring volume of gas was reduced by 14 t. At the same time, the generation of SO2, NO x and particulate pollutants was reduced, achieving great economic and environmental benefits.

[0048] Example 2

[0049] As Figure 2 shown, the fluid catalytic cracking first-stage system of the present invention includes a fractionation tower 1 and a diesel stripping tower 4. The fractionation tower 1 is connected to the diesel stripping tower 4 through a diesel extraction pipeline. The diesel extraction pipeline includes two parallel pipelines, which are respectively provided with an upper diesel extraction outlet valve 2 and a lower diesel extraction outlet valve 3. The diesel stripping tower 4 is connected to a diesel pump 6. An external total circulation pipeline of the first stage is provided outside the fractionation tower 1, which is successively provided with a thermocouple 17 at the first-stage extraction layer, a first-stage extraction valve 15, a first-stage pump 8, a slurry-first-stage heat exchanger 9, a reboiler at the bottom of the stabilization tower 10, a reboiler at the bottom of the desorption tower 11, a feedstock-first-stage heat exchanger 12, a first-stage return valve 14, and a first-stage return-to-tower thermocouple 16. Among them, a first-stage filled diesel pipeline 18 is provided on the connecting pipeline between the feedstock-first-stage heat exchanger 12 and the first-stage return valve 14. An external circulation pipeline of the first stage is provided between the connecting pipeline of the feedstock-first-stage heat exchanger 12 and the first-stage return valve 14 and the connecting pipeline of the first-stage pump 8 and the first-stage extraction valve 15. An external circulation bypass valve 19 is provided on the external circulation pipeline of the first stage;

[0050] An external circulation breathing pipeline 5 of the first stage is provided between the connecting pipeline of the fractionation tower 1 and the first-stage pump 8 and the connecting pipeline of the diesel stripping tower 4 and the diesel pump 6. A valve 7 of the external circulation breathing pipeline of the first stage is provided on the external circulation breathing pipeline 5 of the first stage.

[0051] The method for establishing a first-stage recycle in the fluid catalytic cracking first-stage system according to the present invention is to dehydrate the first-stage system outside the tower during the establishment of the seven-way recycle; the seven-way recycle includes hot water, sealing oil, first-stage oil, feedstock oil, recycle oil, slurry, and gasoline drawn from the absorption and stabilization unit. The specific steps are as follows:

[0052] S1. The first-stage system receives diesel: Close the first-stage extraction valve 15 and the first-stage return valve 14, open the first-stage external recycle pipeline 13, introduce diesel from the first-stage diesel filling pipeline 18 and fill it into the first-stage system pipeline; open the vent valve at the top of the diesel stripping column 4, close the two valves between the diesel stripping column 4 and the fractionating column 1 to isolate the fractionating column 1 from the diesel stripping column 4, open the first-stage external recycle breather line valve 7, and use the first-stage external recycle breather pipeline 5 to fill the diesel stripping column 4 with oil. In this step, the diesel stripping column 4 serves as a thermal expansion buffer column for the first-stage recycle;

[0053] Among them, in step S1, after venting and removing the oil phase, close the vent valve, fill the diesel stripping column 4 to a liquid level of 20%, and the first-stage system stops receiving diesel;

[0054] S2. Establish the first-stage external recycle: After the first-stage system finishes receiving diesel, start the first-stage pump 8 to establish the first-stage external recycle;

[0055] Among them, the starting time of the first-stage pump 8 is 1 h;

[0056] S3. Establish the two-way recycle of the feedstock oil and the recycle oil: Start the diesel pump, the first-stage valve group, and the vent at the inlet of the first-stage pump to drain water. The feedstock oil tank and the recycle oil tank receive wax oil, start the feedstock oil pump and the recycle oil pump to establish the two-way recycle. At the same time, put into use the feedstock-first-stage heat exchanger 12 to heat up the diesel in the first-stage system pipeline;

[0057] Among them, the feedstock oil tank and the recycle oil tank receive wax oil to a liquid level of 45%, stop receiving wax oil and keep draining water for 30 min; the heating rate is 10 °C / h, heat up to 130 °C and keep it at a constant temperature to check for thermal tightness, and then heat up to 220 °C;

[0058] S4. Establish the slurry external recycle: Draw wax oil from the recycle oil tank to the inlet of the slurry pump to establish the slurry external recycle. At the same time, put into use the slurry-first-stage heat exchanger 9 to heat up the diesel in the first-stage system pipeline. When the temperature reaches 95 °C, start the diesel pump 6, the first-stage valve group, and the vent at the inlet of the first-stage pump 8 to drain water. After draining water is completed, close the first-stage pump 8 and stop the first-stage external recycle;

[0059] Among them, keep the liquid level of the diesel stripping column 4 at 20%. If the liquid level is low, introduce diesel from the first-stage diesel filling pipeline 18 to supplement the first-stage system; control the diesel temperature in the first-stage system pipeline through the temperature control valves of the feedstock-first-stage heat exchanger 12 and the slurry-first-stage heat exchanger 9. The water in the first-stage system is heated and discharged through the vent of the diesel stripping column 4;

[0060] S5. Establish the recycle of absorbed and stabilized lead gasoline: Draw gasoline from the unqualified line to each tower and tank to keep the liquid levels in each tower and tank stable at 45%.

[0061] S6. During this process, ignite the furnace in the reaction-regeneration system and heat up according to the heating curve at a rate of 10 °C / h. When the temperature rises to 200 °C, introduce low-pressure protective steam for the internal heat exchanger. Keep the temperature constant at 300 °C, thermally tighten the non-fixed moment flange, then heat up to 500 °C at a rate of 10 °C and keep the temperature constant, and thermally tighten the non-fixed moment flange.

[0062] S7. Establish the first-stage recycle: After the above recycle is established, the reaction-regeneration system is successively purged of air, the blind flange of the large oil and gas line at the inlet of the fractionating tower 1 is removed, an open-circuit recycle of slurry oil is established, and catalyst is charged into the regenerator. When the inventory level in the regenerator reaches 25%, the bed temperature > 380 °C, and combustion oil is sprayed. After the combustion oil is ignited, gradually reduce the load of the auxiliary combustion furnace until it is extinguished, control the bed temperature at 600 °C, and fluidize the reaction-regeneration system.

[0063] Start the air compressor for low-speed warm-up operation. When the temperature at the outlet of the first stage of the riser reaches above 520 °C, spray gasoline into the riser, gradually increase the flow rate, and increase the processing volume to 75% of the processing load within 1.5 h. At this time, the temperature inside the fractionating tower rises rapidly. Close the upper draw-off valve 2 and the lower draw-off valve 3 of diesel oil. When the temperature measured by the thermocouple 17 at the first-stage draw-off layer > 240 °C and shows a downward trend, open the first-stage draw-off valve 15, the first-stage return valve 14, and the inlet valve of the first-stage pump 8 of the fractionating tower, close the cross-line valve 19 for the first-stage external recycle of the fractionating tower, close the valve from the diesel stripping tower 4 to the inlet of the first-stage pump 8, open the valve from the gas return line of the diesel stripping tower 4 to the fractionating tower 1, close the vent valve at the top of the diesel stripping tower 4. When the temperature difference between the inlet pipeline of the first-stage pump 8 and the temperature at the first-stage draw-off layer is less than 10 °C, start the first-stage pump 8 to establish the first-stage recycle. After the first-stage recycle shows flow, gradually increase the flow rate, close the blowdown valve of the air compressor and open the outlet gate valve of the air compressor at the same time, and incorporate the rich gas into the absorption and stabilization system.

[0064] Example 3

[0065] As Figure 2As shown in the figure, the first-stage catalytic cracking system of the present invention includes a fractionating tower 1 and a diesel stripping tower 4. The fractionating tower 1 is connected to the diesel stripping tower 4 through a diesel extraction pipeline. The diesel extraction pipeline includes two parallel pipelines, which are respectively provided with a diesel upper extraction outlet valve 2 and a diesel lower extraction outlet valve 3. The diesel stripping tower 4 is connected to a diesel pump 6. An external total circulation pipeline of the first-stage tower is provided outside the fractionating tower 1, which is successively provided with a first-stage extraction layer thermocouple 17, a first-stage extraction valve 15, a first-stage pump 8, a slurry-first-stage heat exchanger 9, a reboiler at the bottom of the stabilizer 10, a reboiler at the bottom of the desorber 11, a feedstock-first-stage heat exchanger 12, a first-stage return valve 14, and a first-stage return tower thermocouple 16. Among them, a first-stage filled diesel pipeline 18 is provided on the connecting pipeline between the feedstock-first-stage heat exchanger 12 and the first-stage return valve 14. An external first-stage circulation pipeline 13 is provided between the connecting pipeline of the feedstock-first-stage heat exchanger 12 and the first-stage return valve 14 and the connecting pipeline of the first-stage pump 8 and the first-stage extraction valve 15. A first-stage external circulation cross-line valve 19 is provided on the first-stage external circulation pipeline 13.

[0066] A first-stage external circulation breathing pipeline 5 is provided between the connecting pipeline of the fractionating tower 1 and the first-stage pump 8 and the connecting pipeline of the diesel stripping tower 4 and the diesel pump 6. A first-stage external circulation breathing line valve 7 is provided on the first-stage external circulation breathing pipeline 5.

[0067] The method for establishing a first-stage circulation in the first-stage catalytic cracking system of the present invention is to dehydrate the external circulation of the first-stage system during the establishment of the seven-way circulation. The seven-way circulation includes hot water, sealing oil, first-stage, feedstock oil, recycle oil, slurry, and gasoline introduced from the absorption and stabilization unit. The specific steps are as follows:

[0068] S1. The first-stage system receives diesel: Close the first-stage extraction valve 15 and the first-stage return valve 14, open the first-stage external circulation pipeline 13, introduce diesel from the first-stage filled diesel pipeline 18 and fill it into the first-stage system pipeline; Open the vent valve at the top of the diesel stripping tower 4, close the two valves between the diesel stripping tower 4 and the fractionating tower 1 to isolate the fractionating tower 1 from the diesel stripping tower 4, open the first-stage external circulation breathing line valve 7, and use the first-stage external circulation breathing pipeline 5 to fill the diesel stripping tower 4 with oil. In this step, the diesel stripping tower 4 serves as a thermal expansion buffer tower for the first-stage circulation.

[0069] Among them, in step S1, after venting and removing the oil phase, close the vent valve. When the liquid level of the diesel stripping tower 4 is filled to 30%, the first-stage system stops receiving diesel.

[0070] S2. Establish the first-stage external circulation: After the first-stage system finishes receiving diesel, start the first-stage pump 8 to establish the first-stage external circulation.

[0071] Among them, the starting time of the first-stage pump 8 is 2 hours.

[0072] S3. Establish two-way circulation of feedstock oil and recycle oil: Start the diesel pump, the first-stage valve group, and the vent at the inlet of the first-stage pump to drain water. The feedstock oil tank and the recycle oil tank receive wax oil. Start the feedstock oil pump and the recycle oil pump to establish two-way circulation. At the same time, put into use the feedstock-first-stage heat exchanger 12 to heat up the diesel oil in the first-stage system pipeline;

[0073] Among them, the feedstock oil tank and the recycle oil tank receive wax oil until the liquid level reaches 55%. After stopping receiving wax oil, keep draining water for 40 minutes; The heating rate is 15 °C / h. Heat up to 120 °C and keep it constant for heat tightening inspection, and then heat up to 200 °C;

[0074] S4. Establish the external circulation of the slurry tower: Draw wax oil from the recycle oil tank to the inlet of the slurry pump to establish the external circulation of the slurry tower. At the same time, put into use the slurry-first-stage heat exchanger 9 to heat up the diesel oil in the first-stage system pipeline. When the temperature reaches 105 °C, start the diesel pump 6, the first-stage valve group, and the vent at the inlet of the first-stage pump 8 to drain water. After draining water is completed, close the first-stage pump 8 and stop the external circulation of the first-stage tower;

[0075] Among them, keep the liquid level of the diesel stripping tower 4 at 30%. If the liquid level is low, diesel oil is introduced into the first-stage system through the diesel filling pipeline 18 of the first stage; Control the diesel oil temperature in the first-stage system pipeline through the temperature control valves of the feedstock-first-stage heat exchanger 12 and the slurry-first-stage heat exchanger 9. After the water in the first-stage system is heated, it is discharged through the vent of the diesel stripping tower 4;

[0076] S5. Establish the gasoline circulation for absorption and stabilization: Draw gasoline from the off-specification line to each tower and tank to keep the liquid level of each tower and tank at 55% and stable;

[0077] S6. In this process, the reactor-regenerator system lights up the furnace and heats up. Heat up according to the heating curve at 15 °C / h. When heating up to 300 °C, introduce low-pressure protective steam into the internal heat extraction. Keep it constant at 350 °C, conduct heat tightening for the non-fixed torque flange, heat up to 550 °C at 15 °C and keep it constant, and conduct heat tightening for the non-fixed torque flange;

[0078] S7. Establish the first-stage circulation: After the above circulations are established, the reactor-regenerator system sequentially enters the air purging process, removes the blind flange of the large oil and gas pipeline at the inlet of the fractionating tower 1, establishes the open-circuit circulation of the slurry, and starts loading the catalyst into the regenerator. When the material level in the regenerator is 30%, the bed temperature > 380 °C, spray combustion oil; After the combustion oil is sprayed, gradually reduce the load of the auxiliary combustion furnace until it goes out, control the bed temperature at 600 °C, and the reactor-regenerator system conducts fluidization;

[0079] Start the air compressor for low-speed warm-up operation. When the temperature at the outlet of the first reactor in the riser reaches above 520 °C, inject gasoline into the riser and gradually increase the flow rate. Raise the processing volume to 70% of the processing load within 1 hour. At this time, the temperature in the fractionating tower rises rapidly. Close the upper diesel extraction outlet valve 2 and the lower diesel extraction outlet valve 3. When the temperature measured by the thermocouple 17 at the first intermediate draw layer > 240 °C and shows a downward trend, open the first intermediate draw valve 15, the first intermediate return valve 14, and the inlet valve of the first intermediate pump 8 in the fractionating tower. Close the external circulation bypass valve 19 of the first intermediate. Close the valve from the diesel stripping tower 4 to the inlet of the first intermediate pump 8, and open the valve from the gas return line of the diesel stripping tower 4 to the fractionating tower 1. Close the vent valve at the top of the diesel stripping tower 4. When the temperature difference between the inlet pipeline of the first intermediate pump 8 and the temperature at the first intermediate draw layer is less than 10 °C, start the first intermediate pump 8 to establish the first intermediate circulation. After the first intermediate shows flow, slowly increase the flow rate. Close the compressor flare valve and open the compressor outlet gate valve at the same time to merge the rich gas into the absorption and stabilization system.

Claims

1. A catalytic cracking first-stage system includes a fractionating tower (1) and a diesel stripping tower (4). The fractionating tower (1) is connected to the diesel stripping tower (4) through a diesel extraction pipeline. The diesel extraction pipeline includes two parallel pipelines, which are respectively provided with a diesel upper extraction outlet valve (2) and a diesel lower extraction outlet valve (3). The diesel stripping tower (4) is connected to a diesel pump (6). An external total circulation pipeline of the first-stage tower is arranged outside the fractionating tower (1), and successively provided with a first-stage extraction layer thermocouple (17), a first-stage extraction valve (15), a first-stage pump (8), a slurry-first-stage heat exchanger (9), a stabilizer bottom reboiler (10), a desorber bottom reboiler (11), a feedstock-first-stage heat exchanger (12), a first-stage return valve (14), and a first-stage tower return thermocouple (16). Among them, A connecting pipeline between the raw material, a heat exchanger (12) and a return valve (14) is provided with a diesel filling pipeline (18); a middle tower external circulation pipeline (13) is provided between the connecting pipeline between the raw material, a heat exchanger (12) and a return valve (14) and a connecting pipeline between a pump (8) and a withdrawal valve (15); a middle tower external circulation cross-line valve (19) is provided on the middle tower external circulation pipeline (13); and the invention is characterized in that a middle tower external circulation breathing pipeline (5) is provided between the connecting pipeline between the fractionating tower (1) and the pump (8) and the connecting pipeline between the diesel stripping tower (4) and the diesel pump (6); and a middle tower external circulation breathing line valve (7) is provided on the middle tower external circulation breathing pipeline (5).

2. A method for establishing a cycle in a catalytic cracking system according to claim 1, characterized in that: In the process of establishing the seven-way circulation, one of the systems is subjected to external circulation dehydration; The seven-way circulation includes hot water, sealing oil, first medium, raw oil, recycled oil, slurry oil and absorption stable gasoline circulation; The method for establishing a one-cycle catalytic cracking system comprises the following steps: S1. Collecting diesel in the first system: close the first extraction valve (15) and the first return valve (14), open the first tower external circulation pipeline (13), introduce diesel from the first diesel filling pipeline (18) and fill it into the first system pipeline; open the vent valve at the top of the diesel stripping tower (4), close the two valves between the diesel stripping tower (4) and the fractionation tower (1), isolate the fractionation tower (1) and the diesel stripping tower (4), open the first tower external circulation breathing line valve (7), and use the first tower external circulation breathing line (5) to fill the diesel stripping tower (4) with oil. In this step, the diesel stripping tower (4) serves as a thermal expansion buffer tower of the first circulation; S2, establishing a middle tower external circulation: after the first system finishes collecting diesel, the first pump (8) is turned on to establish a middle tower external circulation; S3, establishing a two-way circulation of raw oil and recycled oil: start the diesel pump, the first valve group, and the first pump inlet to vent to cut off water, collect wax oil in the raw oil tank and the recycled oil tank, start the raw oil pump and the recycled oil pump to establish a two-way circulation, and at the same time, use the raw material-first heat exchanger (12) to heat the diesel in the first system pipeline; S4, establishing an oil slurry tower external circulation: wax oil is introduced from the recycling oil tank to the inlet of the oil slurry pump to establish an oil slurry tower external circulation. At the same time, the oil slurry-first-stage heat exchanger (9) is used to heat the diesel in the first-stage system pipeline. When the temperature reaches 95-105° C., the diesel pump (6), the first-stage valve group, and the inlet of the first-stage pump (8) are opened to vent and cut off the water. After the water is cut off, the first-stage pump (8) is closed and the first-stage tower external circulation is stopped; S5. Establish a stable absorption gasoline cycle: gasoline is drawn from the unqualified line to each tower and tank, so that the liquid level of each tower and tank is maintained stable at 45-55%; S6. In this process, the system is heated up by firing the furnace according to the heating curve of 10-15℃ / h. When the temperature reaches 200℃-300℃, low-pressure protective steam is taken for heat flow. The temperature is kept constant at 300-350℃, and the non-fixed torque flange is thermally tightened. The temperature is raised to 500-550℃ at 10-15℃, and the non-fixed torque flange is thermally tightened. S7. Establishing a medium cycle: After the above cycles are established, the air is driven out of the reaction and regeneration system in turn. The large oil and gas line blind plate at the entrance of the fractionation tower (1) is removed to establish an open oil slurry circulation. The regenerator is charged with agent. When the regenerator material level is 25%-30%, the bed temperature is >380 degrees, and the combustion oil is sprayed. After the combustion oil is sprayed, the auxiliary combustion furnace load is gradually reduced until it is extinguished. The bed temperature is controlled at 550-600°C, and the reaction and regeneration system is fluidized. Start the air compressor to warm up at a low speed. When the outlet temperature of the first riser pipe is >520℃, spray gasoline on the riser pipe and gradually increase the amount. Within 1-1.5 hours, the processing capacity is increased to 70-75% of the processing load. At this time, the temperature in the distillation tower rises rapidly. Close the diesel upper outlet valve (2) and the diesel lower outlet valve (3). When the temperature measured by the thermocouple (17) of the first extraction layer is >240℃ and shows a downward trend, open the first extraction valve (15), the first return valve (14) and the inlet valve of the first pump (8) of the distillation tower, and close the second extraction valve (15). Close the cross-line valve (19) for the external circulation of the first tower, close the inlet valve from the diesel stripping tower (4) to the first pump (8), and open the valve of the gas return line from the diesel stripping tower (4) to the distillation tower (1), close the vent valve at the top of the diesel stripping tower (4), and when the difference between the inlet pipeline temperature of the first pump (8) and the temperature of the first extraction layer is less than 10°C, start the first pump (8) to establish the first circulation. After the flow rate is seen in the first, slowly increase the volume, close the flare valve of the air compressor and open the outlet gate valve of the air compressor to merge the rich gas into the absorption stabilization system.

3. The method for establishing a first-stage recycle in the first-stage catalytic cracking system according to claim 2, wherein: In step S1, after the oil phase is vented and removed, the vent valve is closed, the liquid level of the diesel stripping tower (4) is filled to 20%-30%, and the first system stops receiving diesel.

4. The method for establishing a one-cycle system in a catalytic cracking system according to claim 2, characterized in that: In step S2, a pump (8) is turned on for 1-2 hours.

5. The method for establishing a one-cycle system in a catalytic cracking system according to claim 2, characterized in that: In step S3, the raw oil tank and the refining oil tank collect wax oil until the liquid level is 45%-55%, and the water is cut off for 30-40 minutes after the wax oil collection is stopped.

6. The method for establishing a one-cycle system in a catalytic cracking system according to claim 2, characterized in that: In step S3, the heating rate is 10-15°C / h, the temperature is raised to 120-130°C, and then the temperature is raised to 200-220°C after constant temperature inspection to ensure heat tightness.

7. The method for establishing a one-cycle system in a catalytic cracking system according to claim 2, characterized in that: In step S4, the liquid level of the diesel stripping tower (4) is maintained at 20%-30%. If the liquid level is low, a diesel filling pipeline (18) is used to introduce diesel to supplement the system.

8. The method for establishing a one-cycle system in a catalytic cracking system according to claim 2, characterized in that: In step S4, the temperature of the diesel in the pipeline of the first system is controlled by the temperature control valves of the raw material-first heat exchanger (12) and the oil slurry-first heat exchanger (9), and the water in the first system is heated and discharged through the diesel stripping tower (4).

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