Jet fuel hydrogenation startup and shutdown plan

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The last edit to this post was made by liuquan1100 on 2017-1-19 at 21:11. 2. Typical procedures for shutting down the operation: 1) Reduce temperature and flow rate, stop feeding material, and switch the system to a long-cycle mode. Contact the dispatch team to confirm that preparations for shutting down the kerosene hydrogenation process have been completed, and then proceed with the shutdown according to the planned schedule. Contact the atmospheric/vacuum distillation/tank farm to stop receiving raw materials. Close the manual valve for feed oil inlet to the unit; switch the unit to long-cycle operation. Close the valve for refined kerosene outlet from the unit, and maintain the liquid levels in all containers. Long cycle process: D101→P101→FV11001A→E101 (shell)→F101→R101→E101 (tube)→A101→D102→E202 (shell)→C-201→P-202→E-202 (tube)→A203→E203→SR-201→start long cycle line→SR-101→D101. The reactor temperature at the reaction inlet, TIC10201, is reduced to 200°C at a rate of 5–10°C/h; thereafter, FIC10101A is adjusted at a rate of 20 t/h to reduce the feed rate to around 30 t/h. P101 is then stopped, thereby cutting off the reaction feed. Note: During the reduction process, disable the low flow interlock for the feed pump P101; gradually increase the opening of FV10102 to raise the amount of hydrogen mixed before the furnace, thereby preventing dry burning in the furnace tubes. After stopping the reaction feed pump P-101, promptly close the upstream and downstream valves of the feed control valve FV-10101A, as well as the valve that directs the long-circulation oil to D101, in order to maintain the liquid level in the crude oil tank. Gradually reduce the liquid levels in the raw material tank and the reaction product tank to below 20%, and check the liquid level on the glass panel at site D102. 2) Cool the fractionation section cyclically to maintain the liquid levels in each column; stop feeding reactants, and shorten the circulation in the fractionation system. Open the bypass line for reboiler E204, close the inlet and outlet valves of E204; E204 will operate via the bypass, thereby reducing the temperature at the bottom of C201. Contact the dispatch and tank farm; based on the intermittent level of C201, send the fractionated oil through the unqualified kerosene line to the tank farm in order to stabilize the level in the fractionation tower. Change D201 naphtha to full reflux, close the upstream and downstream valves of LV20201, as well as the valve of the light hydrocarbons to diesel unit. Check the liquid level in the D201 glass plate promptly during the cooling process. After the interruption of C201 reflux, stop the reflux pump P201. Pass the D201 wastewater through LV20102 to send the sulfur-containing wastewater to the sludge oil main pipe; after the level drops, close LV20102 as well as the manual valves upstream and downstream. Change D201 pressure-controlled PV20201 to a flare, and close the main valve leading to the coking area. Reduce the top pressure of D201 to a slight positive pressure. Shut down distillation; all air cooling is in operation. After the C201 liquid level stabilizes at 40%, stop P202 and close the valve at the boundary of the unit for unqualified kerosene. 3) Thermal hydrogen purging and oil expulsion in the reaction system: After the reaction feed was cut off, the temperature at the reactor inlet was maintained at 200°C, with hydrogen being used to circulate and carry away the oil for 4 hours. If the level of D-102 rises, open FV-10301 to divert the oil to the distillation system, and keep the level of D-102 below 30% for 2 hours. If it is confirmed that the D-102 liquid level does not rise, the hot hydrogen purging and oil displacement in the reaction system are completed. During oil reduction in the hot hydrogen cycle, maintain the hydrogen supply at 6000~12000 Nm3/h, making sure not to overload the reciprocating machine and not to disrupt the normal operation of diesel hydrogenation. After stopping the feed pump of the reaction vessel, immediately open the purge hydrogen blind valve at the outlet of P-101, and use hydrogen to displace the oil (the oil remaining in heat exchanger E-101 must be completely drained before hydrogen purging; it can be transferred to an underground oily waste tank via a conveyor belt or discharged in small amounts into the drain). 4) Cooling down of the reaction system and shutdown of the furnace: After the hydrogen supply to the reaction system is ceased, the system is cooled at a rate of 20–25°C/h, with the pressure gradually dropping to 1.5 MPa. During this cooling process, the number of burners is reduced step by step, and the manual valves for those burners are closed. When the temperature drops below 150°C, close the furnace gas valve FV10201 and shut down furnace F101; the reaction catalyst bed continues to cool down. After the burner in the furnace is extinguished, open the air dampers and manway doors fully to maintain negative pressure in the furnace for exhaust and replacement purposes. Keep all 4 A101 air coolers in operation, and maintain the hydrogen supply for jet fuel hydrogenation at 10,000–12,000 Nm3/h. Increase the flow rate through the bypass line of E101 to rapidly lower the temperature of the reactor bed; ensure that the temperature of the reactor bed remains below 80°C before carrying out nitrogen replacement. When the temperature of the reaction catalyst bed is below 80°C, gradually reduce the flow rate through the valve FV10102, which is used to supply fresh hydrogen to E101A. Close the primary outlet kerosene transfer valve of the diesel new hydrogen unit 1113-K-101 and the valve downstream of FV10102, and isolate it promptly using a blind flange. 5) Nitrogen purging of the reaction system: Open the valve from the bottom of D102 to the sludge tank, transfer the oil stored in D102 to the sludge tank, and then close it. Use PV10301 to control the pressure of the reaction system, releasing it to a slight positive pressure into the low-pressure gas system at a rate of 1.0 MPa/h. Then, prepare to introduce low-pressure nitrogen from Exit 1 of K101 to purge the reaction system. This process is estimated to take about 6 to 10 hours. This process requires special attention to ensuring that the oil stored in heat exchanger E-101 is cleaned up in advance; otherwise, it will severely hinder the progress of nitrogen displacement. The displacement process is as follows: Nitrogen → P101 outlet → F101 → R101 → D102 → PV10301 → low pressure → atmosphere. After consulting the laboratory and confirming that the gas concentration in the reaction system (hydrogen + hydrocarbons) is less than 3% V, the discharge path from the top of D102 is changed to the atmosphere for displacement; this process continues until it is confirmed that the gas concentration in the reaction system (hydrogen + hydrocarbons) is less than 0.5% V, at which point it is considered acceptable. 3. Precautions during shutdown
1) Adhere to the principle of cooling down first before reducing the flow rate, to prevent the bed temperature from exceeding limits. 2) During the cooling and pressure reduction of the reaction system, operations must be carried out strictly in accordance with the prescribed plan to prevent significant fluctuations and avoid leaks in the equipment, flanges, etc. 3) If the reactor needs to be restarted after a shutdown, an analysis of the CO content in the circulating gas (<30 ppm) should be conducted before the temperature of any bed in the reaction system drops to 205°C, in order to prevent the formation of nickel carbonyl during the shutdown process. 4) During the shutdown process, closely monitor the changes in bed pressure drop and bed temperature rise. Outdoor operators should strengthen inspections and promptly report and handle any abnormal situations. 5) During the shutdown, the reaction system is depressurized, while the nitrogen line continues to supply nitrogen. The fractionation system and the nitrogen lines of the new hydrogen generator system are isolated using blind flanges. When purging the system with nitrogen, implement proper isolation procedures to prevent mixing of nitrogen with gases such as hydrogen. 6) The pipelines of the inlet and outlet devices have had all materials removed as required for maintenance, been purged thoroughly, and fitted with blind flanges. 7) Fire-fighting water and fire-fighting steam must be supplied during maintenance. 8) When removing or installing blind flanges, control the construction time (it should not be too long) to prevent excessive air from entering the heating furnace pipelines and systems, which could lead to spontaneous combustion of ferrous sulfide. 9) Parts that need to be isolated using blind flanges after shutdown: System Serial Number, Pipeline, Status, Diameter (DN), Nominal Pressure (PN), Person who conducted the inspection, Date. Reaction section: 1. P101 outlet – new hydrogen purge line: Open, Diameter 50, Nominal Pressure 5.0; 2. K101 primary outlet – nitrogen purge line: Open, Diameter 80, Nominal Pressure 5.0; 3. K101 primary outlet – line leading to the plant: Closed, Diameter 100, Nominal Pressure 11.0; 4. F101 outlet isolation flange: Closed, Diameter 250, Nominal Pressure 5.0; 5. R101 inlet large cover pipeline flange: Closed, Diameter 250, Nominal Pressure 5.0; 6. Reactor outlet flange: Closed, Diameter 250, Nominal Pressure 5.0; 7. D102 top to silencer: Open, Diameter 100, Nominal Pressure 5.0 – for gases. 8. Heating furnace burners, 8 units: Closed, Diameter 50, Nominal Pressure 2.0; 9. Heating furnace pilot lights, 4 units: Closed, Diameter 25, Nominal Pressure 2.0. Startup plan for kerosene hydrogenation (after skimming): 1. Dehydration and drying of the heating furnace tubes. After professional cleaning and blasting of the furnace tubes, it is possible that some cleaning water may remain and not be completely removed. It is planned to heat the furnace and dry the tubes at a later stage. The specific procedure is as follows: Use gas from the heating furnace to ignite and raise the temperature so that it does not exceed 200°C; then heat the furnace tubes. Add a small amount of nitrogen from the inlet pipeline, using it as a carrier medium to carry the steam generated by heating out of the furnace tubes, until no white vapor is present at the outlet pipeline. 2. Airtightness of the reaction system 2.1 System purging 1) Verify that the blind flanges installed at various locations such as the reactor’s inlet and outlet have been removed or restored, ensuring unobstructed flow. 2) Ensure that the high-pressure airtightness process is unobstructed; isolate the following components: close the manual valves at the outlets of P-101/AB as well as the second valve in the heating pump line. Close the two valves on the nitrogen purge line at the outlet of P-101/AB; keep the intermediate drain valve open. Close the first valve for hydrogen coming from the diesel hydrogenation area, as well as the two valves on the DN80 nitrogen line from that same area; keep the intermediate drain valve open. Close the downstream valve controlled by liquid pressure in D-102, as well as the bypass valve, the manual valve on the main line for removing contaminants from D-102, and the two valves on the nitrogen line at the top of D-102; keep the intermediate drain valve open. Close the manual valve on the line leading to the vacuum pump in D-102, and also the manual valve for venting hydrogen-containing gases. 3) Nitrogen at 0.7 MPa is drawn from the primary outlet of the diesel hydrogenation fresh hydrogen unit (K-101) to purge the reaction system, with the gas being vented from the top of D-102 for purification. 4) Contact the quality inspection center in a timely manner to take samples and analyze the oxygen content in the reaction system. 5) Decide whether to continue the purging based on the test results: If the oxygen content in the system is higher than 0.5% (V), continue with the purging process. If the oxygen content in the system is below 0.5% (V), the displacement is completed. 2.2 Nitrogen airtightness testing of the reaction system: 1) Slowly pressurize the reaction system from the nitrogen line at the primary outlet of the diesel hydrogenation fresh hydrogen unit (K-101) to 0.7 MPa in order to conduct the nitrogen airtightness test. 2) After the airtightness test with 0.7 MPa nitrogen is successful, proceed with the airtightness test using 2.5 MPa nitrogen (if such 2.5 MPa nitrogen is not available, move directly to the next step). 3) For any airtightness leakage points detected, promptly contact Qilu Construction for handling. 4) After passing the test, maintain the pressure for 2 hours; the pressure is allowed to drop by no more than 0.03 MPa per hour. 5) After the reaction system is proven airtight, reduce the pressure to 1.5 MPa. 2.3 Hydrogen airtightness of the reaction system: 1) After the gas analysis of the furnace chamber of the reaction heating furnace (F-101) shows satisfactory results, light the permanent lamp in F-101, and control the temperature of its furnace chamber to be no higher than 150°C, in preparation for introducing new hydrogen to displace the gas in the reaction system. 2) After analyzing that the oxygen content in the recycle gas is <0.5%, slightly open the first and second hand valves of the hydrogen supply from diesel hydration to introduce fresh hydrogen to displace the reactant mixture in the system; after regulating the pressure in D102, vent it to the flare. 3) Sample and analyze the purity of hydrogen in the circulation system; when the hydrogen content is greater than 80%, it indicates that the hydrogen has successfully replaced the nitrogen. 4) After the nitrogen has been successfully replaced by hydrogen, the reaction system is pressurized to 2.2 MPa to verify its airtightness to hydrogen. After checking for any leaks, maintain a constant pressure for 2 hours; the static pressure drop should not exceed 0.07 MPa to be considered acceptable. 5) After the hydrogen gas shows satisfactory airtightness, establish a hydrogen circulation in the reaction system. 3. Normal production 3.1 Oil feeding into the reaction system 1) Hydrogen circulation in the reaction system, with system pressure controlled at ≤1.5 MPa. Establish a short cycle for the self-circulation and temperature rise within the fractionation stripper system. Special attention must be paid when putting the bottom reboiler (E-204) into operation, to prevent too rapid heating that could cause leaks at the heat exchanger flanges! 2) The temperature at the outlet of the heating furnace shall be increased at a rate of ≯20°C/h, with the outlet temperature reaching around 150°C; care should be taken to ensure that the maximum temperature in the reactor bed remains ≯150°C. 3) Activate the pressure control for the feed oil tank D-101, inform the dispatch team, and send kerosene to the feed oil buffer tank. When the liquid level reaches 70%, start the reaction feed pump and control the flow rate at ~40 t/h. Maintain the D-102 liquid level at 40–60%. When the liquid level in D-102 is high, oil is discharged into the stripper (C-201), establishing a long-cycle operation. 4) When the system temperature reaches 150–200°C, contact the construction unit to perform the first comprehensive and uniform thermal tightening of the modified parts. 3.2 Adjustment procedures 1) After the reaction temperature reaches 200°C, the temperature at the furnace outlet is increased at a rate of 5~8°C/h. The pressure in the reaction system rose to 2.2 MPa, while the temperature at the reactor inlet was maintained between 230 and 240 degrees℃ ； Coordinate with the construction unit to perform a second thermal tightening on the modified areas. 2) Control the make-up hydrogen flow rate from the first-stage outlet of the new hydrogen compressor K-101 for diesel hydrogenation to the kerosene hydrogenation unit (approximately 4,000–6,000 m³/h), ensuring that the hydrogen-to-oil ratio is ≥50 (V/V). 3) In accordance with the specifications in the process card, further adjustments are made to the reaction system and distillation system to optimize various process parameters. 4) After the process parameters of the reaction and distillation systems have been stable for 2 hours, arrange for laboratory analysis of the refined aviation fuel; once two consecutive analyses show satisfactory results, contact the dispatch and storage teams to transfer the product to the finished product tanks (it is advisable to first check whether the product is free from corrosion; if possible, transfer it to refined diesel first to avoid the formation of excessive contaminated oil).