E-book material~Lecture on the Basics of Catalytic Reforming Units (Chapter 1, Section 5)

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Section 5: Introduction to the Continuous Reforming Process Flow 1. Process Flow of the Naphtha Hydrorefining Unit: Straight-run naphtha from atmospheric pressure, along with a small amount of hydrorefined naphtha provided by this unit, is mixed together and fed into the feed buffer tank. After buffering and dehydration, it is pressurized using a feed pump under flow control; thereafter it is mixed with recycled hydrogen. It then exchanges heat with the reaction products in the shell side of the mixed feed heat exchanger (the heat exchanger is equipped with temperature control lines that allow adjustment of the load on the heating furnace). Finally, after being heated to the reaction temperature by the feed heating furnace, it enters the pre-hydrogenation reactor. The crude oil undergoes hydrorefining in the presence of a catalyst and hydrogen, to remove organic sulfur, nitrogen, chlorine compounds and metal impurities from it, as well as to saturate the olefins. After the chlorine in the reaction products is removed using a high-temperature dechlorination reactor, they proceed to the tube side where heat exchange takes place with feed water. There, they mix with demineralized water supplied from the demineralized water tank via a water injection pump; this mixture is used to wash out the ammonium salts present in the products. Following cooling through an air cooler and a water-cooled condenser, the reaction products enter the reaction product separation tank. The reaction products undergo gas-liquid separation in the separator; hydrogen is drawn out from the top, combined with additional hydrogen from the reforming section, and then enters the buffer tank at the inlet of the recycle hydrogen compressor to have any liquid carried away. From there, it passes through insulated heating pipes to the recycle hydrogen compressor where it is pressurized before being circulated back to the reaction system ； The liquid product passes through the feed/top heat exchanger tubes of the evaporation tower and the feed/bottom heat exchanger tubes of the evaporation tower under level control, exchanges heat with the top and bottom streams, and then enters the evaporation tower. The light components at the top of the tower, hydrogen sulfide, and trace amounts of water are sequentially cooled by heat exchange, the evaporator air cooler, and water-cooled condensers before entering the evaporator reflux tank. The gas containing hydrogen sulfide in the reflux drum is discharged from the unit under pressure to the dry gas desulfurization unit for hydrogen sulfide removal. A portion of the liquid phase is pressurized by the evaporation tower reflux pump and then returned to the tower under cascade control of liquid level and flow rate ； The other portion, under the cascade control of flow rate and top sensitive plate temperature, is pressurized by the feed pump of the header oil stripping tower and heated in the stripper feed heat exchanger before entering the header oil stripping tower. Most of the gasoline at the bottom of the evaporation tower is pumped by a reboiler and fed into the reboiler of the stripping tower under flow control; after being heated, it returns to the evaporation tower. The remaining portion undergoes heat exchange in the shell side of the feed/bottom heat exchanger of the evaporation tower and is used as feed for the reforming reaction. The light naphtha coming from the evaporation tank’s reflux drum is separated in the overhead oil stripping tower. Part of the refined light naphtha at the bottom of the tower is used as feed for the butane removal tower after being heated in exchange with heat from the feed heater, while another part is heated by the reboiler of the overhead oil stripping tower and sent back to the bottom of the tower as a heat source. The material at the top of the tower is cooled by water cooling at the tower top and then enters the reflux tank. The gas from this reflux tank, along with the gas from the top of the pre-hydrogenation gas-liquid separation tank, is sent to the dry gas desulfurization unit for treatment, while the liquid phase in the reflux tank is pumped back. To prevent hydrogen sulfide corrosion of the pipeline systems in the equipment at the top of the evaporation tower and the overhead oil stripping tower, a corrosion inhibitor injection system is installed, which includes a corrosion inhibitor tank, a corrosion inhibitor injection pump, and injection pipelines at the tower top. If wet pre-sulfurization is required when starting up the naphtha hydrogenation catalyst, sulfur injection tanks, sulfur injection pumps, and injection pipelines for feeding sulfur into the pre-hydrogenation reactor are provided. http://down1.hcbbs.com/attachment/album/201705/28/100207a3a35kqg5vqgm6jm.jpg 2. Reforming reaction section: The purpose of the reforming reaction section is to use reforming catalysts to convert the naphthenes and alkanes with low octane numbers present in refined naphtha into high-octane gasoline components rich in aromatics, while also producing hydrogen as a by-product. Refined naphtha is pressurized by the reforming feed pump and then mixed with the reforming cycle hydrogen that has been pressurized by the reforming cycle hydrogen compressor. After exchanging heat with the reforming reaction products, it is heated in the first reforming heater before entering the upper part of the first reforming reactor, where it reacts via radial contact with the catalyst flowing from top to bottom. From there, it passes through the central tube from the upper part of the first reforming reactor into the second reforming heater, and then sequentially enters the second reforming reactor, the third reforming heater, the fourth reforming heater, until it exits from the upper part of the fourth reforming reactor. There, it exchanges heat with the feed in the reforming feed heat exchanger, and after being condensed and cooled in an air cooler, vapor-liquid separation takes place. The hydrogen-containing gas is pressurized by the reforming cycle hydrogen compressor and divided into two parts: one part of the hydrogen is used as reforming cycle hydrogen and mixed with the reaction feed, while the remaining part is sent to the hydrogen re-contact section as reforming hydrogen. After coming into contact with hydrogen again, the reformate enters the stabilizer tower. The liquefied petroleum gas at the top of the tower is pumped out via the pumping unit, while the stable gasoline at the bottom of the tower is sent to the aromatic extraction section. 3. Hydrogen re-contact section: The hydrogen produced through reforming is pressurized by a reforming hydrogen compressor and then mixed with the reformate oil. After further cooling in an ammonia refrigeration system, oil and gas are separated, thereby increasing the purity of the hydrogen and the yield of the reformate oil. The purified reforming hydrogen is used; the remaining hydrogen undergoes dechlorination treatment. A small portion of the dechlorinated reforming hydrogen is sent to the pretreatment section as supplementary hydrogen, another small portion is used for catalyst regeneration purposes, and part of it is sent to a PSA unit for further purification. The reformate oil after re-contact is sent to a stabilizer tower. 4. Catalyst regeneration section ① Catalyst regeneration: The catalyst to be regenerated, which comes from the reforming reaction section, first has the hydrocarbons it contains removed there by hydrogen gas (coming from the outlet of the reforming cycle hydrogen compressor) in the catalyst collector at the bottom of the fourth reactor. It then enters the “L” valve assembly, where nitrogen gas supplied by the lift gas blower is used as the primary and secondary lift gas to carry it to the separation hopper at the upper part of the regenerator. There, dust on the catalyst is blown off using leaching gas, after which it enters the regenerator. The catalyst to be regenerated passes through the regenerator from top to bottom, undergoing processes of coking, reheating, chlorination, and drying before exiting the regenerator. After being sealed with nitrogen, it enters a closed hopper placed in a hydrogen environment. A logic control system controls the five steps of preparing the hopper for use, pressurizing it, discharging material from it, depressurizing it, and loading it, all via pressure balancing, in order to regulate the amount of catalyst that circulates. After flowing out of the lockhopper, the catalyst passes through another \"L\"-valve assembly, and is lifted to the reduction zone at the top of the first reactor by the primary and secondary lift gases provided by the reformed pressurized hydrogen. The reformed hydrogen that comes into contact with the catalyst is then subjected to heat exchange and heating, and is used as reducing hydrogen to reduce the catalyst from its oxidized state. Thus, the catalyst completes one cycle; the regenerated reforming catalyst, having regained its activity, is returned to the reforming reactor to carry out the reforming reaction. ② Regeneration air washing with alkali: The air released after regeneration due to burning contains chlorides; these chlorine-containing gases come into full contact with alkali in the washing tower, resulting in the formation of water-soluble salts. After the chlorides are removed through washing, the air is released, while the waste alkaline solution is sent to a dedicated treatment facility for disposal. ③ Catalyst dust recovery: The leaching gas containing catalyst dust enters a dust collector, where the catalyst dust is recovered using filters; thereafter, the dust collection tank is sent to a catalyst factory on a regular basis to have the precious metals recovered. The dust-free leaching gas is pressurized by the dust removal fan and then recycled back to the separation hopper, thus completing the cycle for catalyst dust recovery. 5. Extraction section: The stabilized gasoline coming from the catalytic reformer is sent to the depentanizer for pentane removal after passing through the feed/bottom heat exchanger of the depentanizer. After being cooled by the cooler, the material at the top of the tower enters the pentane reflux tank. The material at the top of the tower is pressurized by a reflux pump; part of it is sent back to the tower as reflux, while the remaining part is discharged as product. The heat source for the depentane tower is provided by the reboiler of the depentane tower, with the heating medium being medium-pressure steam after temperature and pressure reduction (2.3 MPa). After being pressurized, the depentanizer bottoms oil passes through the depentanizer feed/bottoms heat exchanger; it then exchanges heat with the feed/bottoms gasoline components in the feed/bottoms heat exchanger of the feed splitter tower, before being fed to the C6 removal tower as feedstock for separation and extraction. The tower overhead material, after being cooled by the de-C6 tower overhead air cooler, enters the de-C6 tower reflux drum. The material at the top of the tower is pressurized by a reflux pump; part of it is sent back to the tower as reflux, while the remaining part is cooled in an extraction feed cooler before being fed into the extraction feed tank. The heat source for the C6 removal tower is provided by the reboiler of that tower, while the gasoline fraction at the bottom of the C6 removal tower is sent to the heptane removal tower. The C6 (C6 and C7 components) coming from the reformation unit is first fed into the extraction distillation feed tank; the aromatic feed enters the middle section of the extraction distillation column after heat exchange, while the lean solvent is fed in near the top of the extraction distillation column. In vapor-liquid operation, the solvent extracts and carries the aromatics to the bottom of the tower, while the non-aromatics reach the top of the tower as raffinate oil. The raffinate gas phase is condensed and cooled before being collected in the top reflux tank. Part of the liquid material is pumped out and returned to the extractive distillation column to remove trace amounts of solvent from the raffinate oil. The remaining material is cooled to storage temperature and used as a raffinate product in gasoline blending. The reboiler at the bottom of the extraction distillation column uses hot lean solvent as the heat medium for reuse, with medium-pressure steam serving as another heat medium.