Two-stage hydrocracking method and system for increasing heavy naphtha production

Abstract

The present invention discloses a two-stage hydrocracking method and system for increasing the production of heavy naphtha. The method comprises the following steps: first, the feedstock oil and hydrogen undergo a hydrorefining reaction, and after separation, a first hydrorefining stream and a second hydrorefining stream are obtained; the obtained first hydrorefining stream and hydrogen enter a first hydrocracking reactor, and after reaction and separation, gas, light naphtha, heavy naphtha, and tail oil are obtained; the second hydrorefining stream and tail oil enter a second hydrocracking reactor for reaction, and after the reaction, a second hydrocracking stream is obtained, which is separated into light and heavy components to obtain a light second hydrocracking stream and a heavy second hydrocracking stream; the heavy second hydrocracking stream is circulated to undergo a hydrorefining reaction together with the feedstock oil, and the light second hydrocracking stream is circulated back to be separated from the first hydrocracking stream. The system comprises a hydrorefining reactor, a first separator, a first hydrocracking reactor, a gas-liquid separator, a second separator, a second hydrocracking reactor, and a third separator connected in a certain manner. The method of the present invention can improve the yield of heavy naphtha fraction on the basis of extending the stable operation period of the device.

Description

Technical Field

[0001] The invention belongs to the technical field of petroleum refining, and relates to a hydrocracking method, in particular to a hydrocracking method for processing inferior raw materials to produce more heavy naphtha fractions. Background Art

[0002] As the global energy mix shifts, refineries are undergoing a transformation and upgrade, with oil conversion technology becoming a mainstream development direction. Hydrocracking technology, which transforms macromolecular reactants into lightweight products through reactions like ring opening and chain scission, has become a core component of refineries. Research hotspots in hydrocracking technology mainly focus on three aspects: First, adapting to the deterioration of feedstock. The ability to process even inferior feedstock (high density, high final distillation point, or high content of impurities such as sulfur, nitrogen, and aromatics) enables enterprises to achieve higher economic benefits. However, inferior feedstock will inevitably increase processing difficulty, especially the continuous increase in refining reaction temperature, which will affect the operating cycle of the unit. Second, large-scale units are an inevitable trend in the development of the refining and chemical industry, which can save land costs, equipment costs, and operating and management costs. Two-stage hydrocracking is the development trend of large-scale hydrocracking process. However, in the conventional two-stage full-cycle hydrocracking process, the second-stage circulating oil is directly recycled to the fractionation stage without undergoing the refining process. This causes some difficult-to-react polycyclic aromatic hydrocarbons to circulate and accumulate in the system, thus affecting the long-term stable operation of the unit. Third, the heavy naphtha selectivity of the two-stage full-cycle hydrocracking process has an upper limit. Under the large-scale trend, even a small increase in heavy naphtha yield can bring significant economic benefits.

[0003] CN103773450A discloses a hydrocracking method for processing inferior raw materials. The inferior raw materials are first desulfurized, denitrogenated, and saturated with aromatics through a hydrofining reaction. After passing through a gas-liquid separator, the tail oil fraction in the liquid phase enters a hydrocracking reactor. The upper part of the cracking reactor is loaded with a strong aromatic conversion catalyst and the lower part is loaded with a catalyst with a strong alkane cracking ability. The above design achieves the positive effect of processing inferior raw materials while improving the quality of hydrocracking products. However, this process is not a two-stage circulation process, does not have the conditions for large-scale hydrocracking, and cannot achieve the maximum production of heavy naphtha fractions.

[0004] CN107345154A discloses a hydrocracking method. The hydrocracking catalyst used in this method uses a modified Y-type molecular sieve with the following properties: relative crystallinity of 110% to 150%, a SiO2 / Al2O3 molar ratio of 10 to 50, unit cell parameters of 2.436 to 2.445 nm, a total pore volume of 0.55 to 1.0 mL / g, and a mesopore volume accounting for more than 70% of the total pore volume. This hydrocracking catalyst primarily improves the hydrocracking stage's ability to process low-quality feedstocks, but does not alleviate the pressure that low-quality feedstocks place on the hydrorefining reaction zone.

[0005] CN102876371A discloses a hydrocracking method for inferior raw materials, the method being characterized in that the hydrorefined production oil and hydrogen enter the hydrocracking reactor in reverse, and the hydrocracking catalyst bed portion is provided with a number of cap trays and sieve trays, which play the role of liquid seal and enhanced mass transfer, avoid contact between hydrogen sulfide, ammonia and hydrocracking catalyst, and the tray has a redistribution effect on refined oil, so that refined oil enters the catalyst bed evenly. The inventive method is conducive to the performance of cracking catalyst activity, increases the yield of light oil products, and extends the service life of hydrocracking catalyst. However, this method has limited effect on the operation cycle of the two-stage hydrocracking unit for extending the maximum production of heavy naphtha. Summary of the Invention

[0006] In response to the problems existing in the existing hydrocracking process, the present invention provides a two-stage hydrocracking method and system for increasing the production of heavy naphtha. By optimizing the process flow and catalyst grading scheme, the method can improve the yield of the heavy naphtha fraction while extending the stable operation cycle of the device.

[0007] 1. The present invention provides a two-stage hydrocracking method for increasing the production of heavy naphtha, comprising the following steps:

[0008] S1. Under hydrorefining conditions, the feedstock oil is mixed with hydrogen to undergo a hydrorefining reaction, and the hydrorefined stream obtained after the reaction is separated to obtain a first hydrorefined stream and a second hydrorefined stream;

[0009] S2, the first hydrorefined stream and hydrogen obtained in step S1 enter the first hydrocracking reactor, contact with the catalyst loaded in the reactor, and obtain the first hydrocracking stream after the reaction, which is then separated to obtain gas, light naphtha, heavy naphtha and tail oil respectively;

[0010] S3, the second hydrorefined stream obtained in step S1, and the tail oil obtained in step S2 enter the second hydrocracking reactor, where hydrogen and the hydrocracking catalyst are contacted to react to obtain a second hydrocracking stream;

[0011] S4. The second hydrocracking stream obtained in step S3 is separated into light and heavy components to obtain a light second hydrocracking stream and a heavy second hydrocracking stream. The heavy second hydrocracking stream is circulated together with the crude oil for hydrorefining reaction, and the light second hydrocracking stream is circulated back to be separated from the first hydrocracking stream.

[0012] 2. The present invention provides a two-stage hydrocracking system for increasing the production of heavy naphtha, comprising a hydrotreating reactor, a first separator, a first hydrocracking reactor, a gas-liquid separator, a second separator, a second hydrocracking reactor, and a third separator connected in a certain manner, wherein:

[0013] A hydrorefining reactor is used to receive the feedstock oil and hydrogen, and to contact the feedstock oil and hydrogen with the hydrorefining catalyst therein to perform a hydrorefining reaction to obtain a hydrorefining feed stream;

[0014] a first separator, which is used to receive the hydrofinished stream from the hydrofinishing reactor and cut the hydrofinished stream into light and heavy components to obtain a first hydrofinished stream and a second hydrofinished stream after separation;

[0015] a first hydrocracking reactor, which is used to receive the first hydrorefined stream and hydrogen from the first separator, and to react with the catalyst therein to obtain a first hydrocracked stream;

[0016] a gas-liquid separator for receiving and separating the first hydrocracking stream from the first hydrocracking reactor to obtain a gas phase stream and a liquid phase stream after separation;

[0017] A second separator is used to receive and separate the liquid phase stream from the gas-liquid separator to obtain gas, light naphtha, heavy naphtha and tail oil after separation;

[0018] a second hydrocracking reactor for receiving the tail oil from the second separator, the second hydrorefined stream from the first separator, and optionally light naphtha from the second separator, and reacting the resultant with the catalyst therein to obtain a second hydrocracked stream;

[0019] The third separator is used to receive the second hydrocracking stream from the second hydrocracking reactor and cut it into light and heavy components, namely a light second hydrocracking stream and a heavy second hydrocracking stream. The heavy second hydrocracking stream enters the hydrotreating reactor through a pipeline, and the light second hydrocracking stream enters the gas-liquid separator through a pipeline.

[0020] Compared with the two-stage hydrocracking process in the prior art, the two-stage hydrocracking method and system for increasing heavy naphtha production provided by the present invention can bring the following technical effects:

[0021] (1) The hydrorefining stream obtained by the hydrorefining reaction is cut into light and heavy components. The first hydrorefining stream is sequentially processed through the hydrorefining reactor, the first hydrocracking reactor and the second hydrocracking reactor, and the second hydrorefining stream preferably first enters the middle and lower part of the second hydrocracking reactor and is processed by the provided hydrorefining catalyst and the hydrocracking catalyst. The product obtained by the second hydrocracking reactor is again cut into light and heavy components, and the heavy second hydrocracking stream is circulated to the hydrorefining reactor through the pipeline. The above process flow design can reduce the cost of the hydrorefining reactor. The operation severity is reduced by only controlling the nitrogen content of the first hydrorefining feed stream to meet the feed requirement of the first hydrocracking reactor, which greatly alleviates the processing difficulty of the hydrorefining reactor and solves the problems that the hydrorefining process has to operate under higher severity operating conditions due to the high nitrogen content and aromatics content of inferior raw materials and is difficult to remove, and the reaction temperature needs to be continuously increased for temperature compensation, which leads to a shortened operation cycle of the device, and the outlet temperature of the hydrorefining reactor is too high and does not match the required operating temperature of the hydrocracking reactor. The operation cycle of the device can be greatly extended.

[0022] (2) In the two-stage hydrocracking method for increasing the production of heavy naphtha provided by the present invention, a hydrorefining catalyst bed is provided in the second hydrocracking reactor, which is conducive to achieving partial aromatic saturation of the polycyclic aromatic hydrocarbons in the reactor. At the same time, the heavy second hydrocracking material flows through the pipeline into the hydrorefining reactor, which also solves the problem of accumulation of polycyclic aromatic hydrocarbons in the traditional two-stage full-cycle hydrocracking process.

[0023] (3) The applicant discovered that the hydrocracking reaction exhibits a dynamic inhibition-guiding phenomenon in the cracking reaction zone, i.e., during the hydrocracking reaction of the full-fraction reactants, the introduction of substances with a distillation range of A to B°C promotes the reaction of substances with a distillation range of <B°C, while inhibiting the reaction of substances with a distillation range of >B°C. Based on this discovery, the applicant optimized the functional area of ​​the second hydrocracking reactor and the hydrocracking reaction path, significantly improving the selectivity of heavy naphtha while extending the unit's operating cycle. Light naphtha is introduced into the second hydrocracking reactor through a feed port between the hydrorefining catalyst bed II and the hydrocracking catalyst bed III, and a second hydrorefining stream enters the second hydrocracking reactor through a feed port between the hydrocracking catalyst bed I and the hydrorefining catalyst bed II, so that a high concentration zone of light naphtha and heavy fraction reactants is formed in the reactor region below the hydrorefining catalyst bed II, thereby promoting the reaction of the heavy fraction reactants toward the heavy naphtha, reducing the tendency of the heavy naphtha fraction to react toward the light naphtha fraction, and further increasing the heavy naphtha product selectivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of a hydrocracking method in an embodiment of the present invention.

[0025] Among them, 1-feedstock oil; 2-hydrorefining reactor; 3-hydrorefining stream; 4-first separator; 5-second hydrorefining stream; 6-first hydrocracking reactor; 7-first hydrocracking stream; 8-gas-liquid separator; 9-gas stream; 10-liquid stream; 11-second separator; 12-gas; 13-light naphtha; 14-heavy naphtha; 15-tail oil; 16-second hydrocracking reactor; 17-second hydrocracking stream; 18-third separator; 19-heavy second hydrocracking stream; 20-light second hydrocracking stream; 21-circulating hydrogen compressor; 22-circulating hydrogen; 23-fresh hydrogen; 24-first hydrorefining stream; 25-hydrocracking catalyst bed I; 26-hydrorefining catalyst bed II; 27-hydrocracking catalyst bed III;

[0026] Figure 2 Schematic diagram of a conventional two-stage hydrocracking process in a comparative example of the present invention.

[0027] Among them, 1-raw material; 2-hydrogenation refining reactor; 3-hydrogenation refining stream; 4-first hydrocracking reactor; 5-gas-liquid separator; 6-liquid phase stream; 7-fractionation tower; 8-gas; 9-light naphtha; 10-heavy naphtha; 11-tail oil; 12-second hydrocracking reactor; 13-second hydrocracking stream; 14-gas phase stream; 15-circulating hydrogen compressor; 16-first hydrocracking stream; 17-circulating hydrogen; 18-new hydrogen. DETAILED DESCRIPTION

[0028] The technical solutions and technical effects of the present invention are further described below with reference to the accompanying drawings and specific implementations.

[0029] Unless expressly stated otherwise, throughout the specification and claims, the term “comprise” or variations such as “include” or “comprising” will be understood to include the stated elements or components but not to exclude other elements or components.

[0030] In this document, for ease of description, spatially relative terms such as "below," "beneath," "below," "above," "above," etc. may be used to describe the relationship of one element or feature to another element or feature in the accompanying drawings. It should be understood that the spatially relative terms are intended to encompass different orientations of the object in use or operation in addition to the orientation depicted in the drawings. For example, if the object in the drawings is turned over, the element described as being "below" or "beneath" other elements or features will be oriented "above" the elements or features. Therefore, the exemplary term "below" can include both below and above. Objects may also have other orientations (rotated 90 degrees or other orientations) and the spatially relative terms used herein should be interpreted accordingly.

[0031] 1. The present invention provides a two-stage hydrocracking method for increasing the production of heavy naphtha, comprising the following steps:

[0032] S1. Under hydrorefining conditions, the feedstock oil is mixed with hydrogen to undergo a hydrorefining reaction, and the hydrorefined stream obtained after the reaction is separated to obtain a first hydrorefined stream and a second hydrorefined stream;

[0033] S2, the first hydrorefined stream and hydrogen obtained in step S1 enter the first hydrocracking reactor, contact with the catalyst loaded in the reactor, and obtain the first hydrocracking stream after the reaction, which is then separated to obtain gas, light naphtha, heavy naphtha and tail oil respectively;

[0034] S3, the second hydrorefined stream obtained in step S1, and the tail oil obtained in step S2 enter the second hydrocracking reactor, where hydrogen and the hydrocracking catalyst are contacted to react to obtain a second hydrocracking stream;

[0035] S4. The second hydrocracking stream obtained in step S3 is separated into light and heavy components to obtain a light second hydrocracking stream and a heavy second hydrocracking stream. The heavy second hydrocracking stream is circulated together with the crude oil for hydrorefining reaction, and the light second hydrocracking stream is circulated back to be separated from the first hydrocracking stream.

[0036] Further, according to a specific embodiment of the present invention, the feedstock oil may be diesel and / or wax oil; wherein the diesel is one or a mixture of straight-run diesel, coker diesel, catalytic diesel, ebullated bed hydrogenated diesel, and residual oil hydrogenated diesel; and the wax oil is one or a mixture of vacuum wax oil, coker wax oil, ebullated bed hydrogenated wax oil, and deep-drawn wax oil.

[0037] Furthermore, according to a specific embodiment of the present invention, when processing diesel raw materials, the aromatic hydrocarbon content of the raw materials is generally 40% to 90%, preferably 50% to 80%; when processing wax oil raw materials, the distillation range of the raw materials is generally 280°C to 600°C, and the final distillation point is preferably 550°C to 580°C. The sulfur content and nitrogen content in the raw materials can be controlled within a relatively wide range. Under normal circumstances, the sulfur content of the raw materials is not more than 3.0wt%, and the nitrogen content is not more than 3000ppm.

[0038] Furthermore, according to a specific embodiment of the present invention, the splitting temperature of the first hydrorefined stream and the second hydrorefined stream obtained after separation of the hydrorefined stream in step S1 is 10 to 80°C lower than the final distillation point temperature of the raw material, preferably 15 to 30°C lower than the final distillation point temperature of the raw material.

[0039] Further, according to a specific embodiment of the present invention, in the second hydrocracking reactor in step S3, a hydrocracking catalyst bed I, a hydrorefining catalyst bed II, and a hydrocracking catalyst bed III are sequentially arranged according to the flow direction of the liquid phase material, wherein the hydrocracking catalyst bed I and the hydrocracking catalyst bed III are loaded with the same or different hydrocracking catalysts; the volume ratio of the hydrorefining catalyst bed II to the total catalyst bed in the second hydrocracking reactor is 10% to 50%, preferably 12% to 25%; the bottom end of the hydrorefining catalyst bed II is located at 30% to 60% of the height of the second hydrocracking reactor from top to bottom, more preferably 35% to 50%.

[0040] Furthermore, according to a specific embodiment of the present invention, the tail oil enters the second hydrocracking reactor through the feed port at the top of the second hydrocracking reactor.

[0041] Furthermore, according to a specific embodiment of the present invention, the second hydrorefining stream obtained in step S1 enters the second hydrocracking reactor through a feed port provided on the outer wall of the reactor shell between the hydrocracking catalyst bed I and the hydrorefining catalyst bed II.

[0042] Furthermore, according to a specific embodiment of the present invention, light naphtha can enter the second hydrocracking reactor for processing. When entering the second hydrocracking reactor, it preferably enters the second hydrocracking reactor through a feed port on the outer wall of the reactor shell between the hydrorefining catalyst bed II and the hydrocracking catalyst bed III.

[0043] Furthermore, according to a specific embodiment of the present invention, when the light naphtha enters the second hydrocracking reactor, the amount of light naphtha entering the second hydrocracking reactor is 20% to 80% of the total weight of the light naphtha, preferably 25% to 55%.

[0044] Furthermore, according to a specific embodiment of the present invention, the splitting temperature of the light and heavy components of the second hydrocracked material obtained in step S3 is 10-50°C lower than the splitting temperature of the hydrorefined material stream, preferably 15-30°C.

[0045] Furthermore, according to a specific embodiment of the present invention, the specific separation process of the first hydrocracking stream in step S2 to obtain gas, light naphtha, heavy naphtha and tail oil after separation is as follows: the first hydrocracking stream is first subjected to gas-liquid separation to obtain a gas phase stream and a liquid phase stream after separation; the liquid phase stream is further fractionated to obtain gas, light naphtha, heavy naphtha and tail oil; the gas phase stream is further purified (purification generally refers to the removal of sulfur-containing compounds (hydrogen sulfide) in the gas phase stream, and the purification can adopt any of the existing processes for removing hydrogen sulfide) and compressed by a circulating hydrogen compressor to obtain hydrogen, which is then recycled for use as circulating hydrogen.

[0046] Further, according to a specific embodiment of the present invention, the operating conditions of the hydrotreating reactor include: a reaction temperature of 320 to 430°C, preferably 340 to 400°C; a reaction pressure of 6.0 to 20.0 MPa, preferably 8.0 to 16.0 MPa; a volume space velocity of 0.2 to 10.0 h -1 , preferably, the volume space velocity is 0.8~2.0h -1 ; The hydrogen-to-oil volume ratio is 100 to 3000, preferably, the hydrogen-to-oil volume ratio is 400 to 1200. Unless otherwise specified, the pressures described herein are gauge pressures. The hydrotreating reactor is filled with at least one hydrocracking refining catalyst, preferably comprising 1 to 3 hydrotreating refining catalysts. The hydrotreating refining catalyst can be an existing commercially available catalyst or prepared according to an existing method. When a commercially available hydrotreating refining catalyst is selected, specifically, commercial hydrogenation catalysts such as FF-12, FF-56, FF-66, and FHUDS-8 developed by Dalian (Fushun) Petrochemical Research Institute of Sinopec can be selected.

[0047] Further, according to a specific embodiment of the present invention, the operating conditions of the first hydrocracking reactor include: a reaction temperature of 350 to 425°C, preferably 360 to 400°C; a reaction pressure of 6.0 to 20.0 MPa, preferably 8.0 to 16.0 MPa; a volume space velocity of 0.6 to 8.0 h -1 , preferably, the volume space velocity is 0.8~2.0h -1; The volume ratio of hydrogen to oil is 100 to 2500; preferably, the volume ratio of hydrogen to oil is 500 to 1800. Unless otherwise specified, the pressures described herein are gauge pressures. The first hydrocracking reactor is loaded with at least one hydrocracking catalyst, which can be an existing commercially available hydrocracking catalyst or prepared according to an existing method. When a commercially available hydrocracking catalyst is selected, specifically, commercial hydrocracking catalysts such as FC-52, FC-32, and FC-76 (developed by Dalian (Fushun) Research Institute of Petrochemicals (FRIPP) of Sinopec) can be selected.

[0048] Further, according to a specific embodiment of the present invention, the operating conditions of the second hydrocracking reactor include: a reaction temperature of 320 to 400°C, preferably 330 to 390°C; a reaction pressure of 6.0 to 18.0 MPa, preferably 8.0 to 16.0 MPa; a volume space velocity of 0.6 to 8.0 h -1 , preferably, the volume space velocity is 1.0 to 2.5 h -1 ; The volume ratio of hydrogen to oil is 500 to 2500, and preferably, the volume ratio of hydrogen to oil is 600 to 2000. Unless otherwise specified, the pressures described herein are gauge pressures. The hydrocracking catalyst bed I and the hydrocracking catalyst bed III in the second hydrocracking reactor are both loaded with at least one hydrocracking catalyst, and the hydrocracking catalyst can be an existing commercially available hydrocracking catalyst or prepared according to an existing method. The hydrocracking catalysts used in the hydrocracking catalyst bed I and the hydrocracking catalyst bed III can be the same or different. When a commercially available hydrocracking catalyst is selected, commercial hydrocracking catalysts such as FC-76 and FC-50 (developed by Dalian (Fushun) Research Institute of Petrochemicals (FRIPP) of Sinopec) can be selected for the specific hydrocracking catalyst bed I. Specifically, commercial hydrocracking catalysts such as FC-76 and FC-14 (developed by Dalian (Fushun) Research Institute of Petrochemicals (FRIPP) of Sinopec Corporation) can be selected for use in hydrocracking catalyst bed III. The hydrorefining catalyst bed in the second hydrocracking reactor is loaded with at least one hydrorefining catalyst. This hydrorefining catalyst can be a commercially available catalyst or prepared according to existing methods. Specifically, commercial hydrorefining catalysts such as FF-56, FF-66, FHUDS-7, FHUDS-8, and FTX, developed by Dalian (Fushun) Research Institute of Petrochemicals (FRIPP) of Sinopec Corporation, can be selected. The hydrorefining catalyst can be the same as or different from the hydrorefining catalyst used in the hydrorefining reactor.

[0049] 2. The present invention provides a two-stage hydrocracking system for increasing the production of heavy naphtha, comprising a hydrotreating reactor, a first separator, a first hydrocracking reactor, a gas-liquid separator, a second separator, a second hydrocracking reactor, and a third separator connected in a certain manner, wherein:

[0050] A hydrorefining reactor is used to receive the feedstock oil and hydrogen, and to contact the feedstock oil and hydrogen with the hydrorefining catalyst therein to perform a hydrorefining reaction to obtain a hydrorefining feed stream;

[0051] a first separator, which is used to receive the hydrofinished stream from the hydrofinishing reactor and cut the hydrofinished stream into light and heavy components to obtain a first hydrofinished stream and a second hydrofinished stream after separation;

[0052] a first hydrocracking reactor, which is used to receive the first hydrorefined stream and hydrogen from the first separator, and to react with the catalyst therein to obtain a first hydrocracked stream;

[0053] a gas-liquid separator for receiving and separating the first hydrocracking stream from the first hydrocracking reactor to obtain a gas phase stream and a liquid phase stream after separation;

[0054] A second separator is used to receive and separate the liquid phase stream from the gas-liquid separator to obtain gas, light naphtha, heavy naphtha and tail oil after separation;

[0055] a second hydrocracking reactor for receiving the tail oil from the second separator, the second hydrorefined stream from the first separator, and optionally light naphtha from the second separator, and reacting the resultant with the catalyst therein to obtain a second hydrocracked stream;

[0056] The third separator is used to receive the second hydrocracking stream from the second hydrocracking reactor and cut it into light and heavy components, namely a light second hydrocracking stream and a heavy second hydrocracking stream. The heavy second hydrocracking stream enters the hydrotreating reactor through a pipeline, and the light second hydrocracking stream enters the gas-liquid separator through a pipeline.

[0057] Furthermore, according to a specific embodiment of the present invention, a hydrocracking catalyst bed I, a hydrorefining catalyst bed II, and a hydrocracking catalyst bed III are sequentially arranged in the second hydrocracking reactor according to the flow direction of the liquid material. The volume ratio of the hydrorefining catalyst bed II to the total catalyst bed in the second hydrocracking reactor is 10% to 50%, preferably 12% to 25%; the bottom end of the hydrorefining catalyst bed II is located at 30% to 60% of the height of the second hydrocracking reactor from top to bottom, and more preferably 35% to 50%.

[0058] Furthermore, according to a specific embodiment of the present invention, the second hydrocracking reactor is provided with two or more feed ports, preferably three feed ports, which are respectively denoted as feed port A, feed port B, and feed port C; wherein,

[0059] Feed port A is provided at the top of the second hydrocracking reactor, and the tail oil enters the second hydrocracking reactor through the feed port A;

[0060] A feed port B is provided on the outer wall of the reactor shell between the hydrocracking catalyst bed I and the hydrorefining catalyst bed II. The second hydrorefining stream obtained in step S1 enters the second hydrocracking reactor through the feed port B.

[0061] The feed port C is provided on the outer wall of the reactor shell between the hydrorefining catalyst bed II and the hydrocracking catalyst bed III, and the light naphtha enters the second hydrocracking reactor through the feed port C.

[0062] Furthermore, according to a specific embodiment of the present invention, the first separator, the second separator, and the third separator may be devices that can separate materials according to their distillation ranges, such as fractionating towers.

[0063] Furthermore, according to a specific embodiment of the present invention, depending on actual needs, the gas-liquid separator generally includes but is not limited to a hot high-pressure separator, a hot low-pressure separator, a cold high-pressure separator, and a cold low-pressure separator; the connection method between the separators and between the separator and the distillation tower can adopt the existing connection method in the field, and those skilled in the art can freely choose according to actual needs.

[0064] Furthermore, according to a specific embodiment of the present invention, the hydrotreating reactor, the first hydrocracking reactor, and the second hydrocracking reactor can be selected from at least one of a fixed bed hydrogenation reactor, a suspended bed hydrogenation reactor, and a fluidized bed hydrogenation reactor; preferably, a fixed bed reactor is used.

[0065] In conjunction with the instructions Figure 1The two-stage hydrocracking method provided by the present invention is further illustrated in the specific embodiments: in the presence of hydrogen (including new hydrogen 23 and recycled hydrogen 22), the raw material 1 enters the hydrorefining reactor 2 and contacts the hydrorefining catalyst filled in the reactor to react, the hydrorefining stream 3 obtained by the reaction enters the first separator 4 for light and heavy component separation to obtain the first hydrorefining stream 24 and the second hydrorefining stream 5, wherein the first hydrorefining stream 24 enters the first hydrocracking reactor 6, and in the presence of hydrogen and hydrocracking The reaction is carried out under the presence of a catalyst, and after the reaction, a first hydrocracking stream 7 is obtained, which enters a gas-liquid separator 8 for gas-liquid separation to obtain a gas stream 9 and a liquid stream 10, wherein the gas stream 9 is compressed by a circulating hydrogen compressor 21 and recycled as circulating hydrogen 22 (which can be recycled back to the hydrofining reactor, the first hydrocracking reactor, and the second hydrocracking reactor), and the liquid stream 10 enters a second separator 11 for separation to obtain gas 12, light naphtha 13, heavy naphtha 14 and tail oil 15. The second hydrocracking reactor 16 is provided with a hydrocracking catalyst bed I25, a hydrorefining catalyst bed II26, and a hydrocracking catalyst bed III27 in sequence according to the flow direction of the liquid phase material. The second hydrocracking reactor is provided with three feed ports, which are respectively recorded as feed port A, feed port B, and feed port C; wherein, feed port A is provided at the top of the second hydrocracking reactor, and the tail oil 15 enters the second hydrocracking reactor 16 through feed port A; feed port B is provided on the outer wall of the reactor shell between the hydrocracking catalyst bed I25 and the hydrorefining catalyst bed II26, and the second hydrorefining material stream 5 enters the second hydrocracking reactor through feed port B. 16; a feed port C is provided on the outer wall of the reactor shell between the hydrorefining catalyst bed II26 and the hydrocracking catalyst bed III27, and the optional light naphtha 13 enters the second hydrocracking reactor 16 through the feed port C; the second hydrocracking stream 17 obtained after the reaction enters the third separator 18 for cutting light and heavy components to obtain a light second hydrocracking stream 20 and a heavy second hydrocracking stream 19; the obtained heavy second hydrocracking stream 19 is circulated through a pipeline to the hydrorefining reactor 2 for treatment together with the raw material, and the obtained light second hydrocracking stream 20 is circulated through a pipeline to the gas-liquid separator 8 for treatment together with the first hydrocracking stream 7.

[0066] In this paper, the detailed physical property analysis results of the raw materials used (including wax oil raw materials and diesel raw materials) are shown in Table 1.

[0067] In the examples and comparative examples herein, the hydrotreating reactor, the first hydrocracking reactor, and the second hydrocracking reactor are all fixed-bed hydrogenation reactors.

[0068] Table 1 Properties of inferior raw materials

[0069]

[0070] Example 1

[0071] This embodiment adopts Figure 1 The process flow for the two-stage hydrocracking method is shown in Table 1. The properties of the processed wax oil feedstock are shown in Table 1. The hydrotreating reactor is loaded with FF-56 hydrotreating catalyst, the first hydrocracking reactor is loaded with FC-46 hydrotreating catalyst, and the second hydrotreating reactor is loaded with FC-76 hydrotreating catalyst, FF-66 hydrotreating catalyst, and FC-50 hydrotreating catalyst, respectively. The volume of the FF-66 hydrotreating catalyst in the second hydrotreating reactor accounts for 20% of the total volume of the catalyst in the second hydrotreating reactor. The bottom of the hydrotreating catalyst bed is located 50% of the height of the second hydrotreating reactor. The light-heavy split temperature for the hydrotreating stream is 555°C, and the light-heavy split temperature for the second hydrotreating stream is 540°C. The amount of light naphtha entering the second hydrotreating reactor is 30 wt% of the total weight of the light naphtha. The operating conditions of the hydrotreating reactor are as follows: reaction pressure of 16.0 MPa, reaction temperature of 370 °C, volume space velocity of 1.2 h -1 The reaction conditions of the first hydrocracking reactor are as follows: reaction pressure of 16.0 MPa, reaction temperature of 370 °C, volume space velocity of 1.0 h -1 , the hydrogen-to-oil volume ratio is 1300. The reaction conditions of the second hydrocracking reactor are as follows: reaction pressure is 16.0 MPa, reaction temperature is 350°C, volume space velocity is 2.0 h -1 , the volume ratio of hydrogen to oil was 1500. The reaction results are shown in Table 2.

[0072] Example 2

[0073] This embodiment adopts Figure 1The two-stage hydrocracking process flow chart is shown in Table 1. The properties of the processed gas oil feedstock are shown in Table 1. The hydrotreating reactor is loaded with FF-66 hydrotreating catalyst, the first hydrocracking reactor is loaded with FC-52 hydrocracking catalyst, and the second hydrocracking reactor is loaded with FC-46 hydrotreating catalyst, FTX hydrotreating catalyst, and FC-14 hydrotreating catalyst, respectively. The FTX hydrotreating catalyst in the second hydrocracking reactor accounts for 12% of the total catalyst volume in the second hydrocracking reactor. The bottom of the FTX hydrotreating catalyst bed is located 35% of the height of the second hydrocracking reactor from the top. The light-heavy split temperature for the hydrotreating stream is 545°C, and the light-heavy split temperature for the second hydrocracking stream is 520°C. The amount of light naphtha entering the second reactor is 50 wt% of the total light naphtha weight. The operating conditions of the hydrotreating reactor are as follows: reaction pressure of 14.0 MPa, reaction temperature of 375 °C, volume space velocity of 0.8 h -1 The hydrogen-to-oil volume ratio is 1000. The reaction conditions of the first hydrocracking reactor are as follows: reaction pressure of 14.0 MPa, reaction temperature of 380°C, volume space velocity of 1.5 h -1 , the hydrogen-to-oil volume ratio is 1200. The reaction conditions of the second hydrocracking reactor are as follows: reaction pressure is 14.0 MPa, reaction temperature is 340 ° C, volume space velocity is 1.0 h -1 , the hydrogen to oil volume ratio is 1200. The reaction results are shown in Table 2.

[0074] Example 3

[0075] This embodiment adopts Figure 1 The two-stage hydrocracking process flowsheet is shown in Table 1. The hydrotreating reactors were loaded with FF-66 hydrotreating catalyst and FTX hydrotreating catalyst in a 1:1 volume ratio, in the direction of liquid flow, from top to bottom. The first hydrocracking reactor was loaded with FC-76 hydrocracking catalyst, while the second hydrocracking reactor was loaded with FC-50 hydrocracking catalyst, FF-66 hydrotreating catalyst, and FC-50 hydrocracking catalyst, in the direction of liquid flow, from top to bottom. The volume of the FF-66 hydrotreating catalyst in the second hydrocracking reactor accounted for 25% of the total catalyst volume in the second hydrocracking reactor. The bottom of the FF-66 hydrotreating catalyst bed was located 45% of the height of the second hydrocracking reactor. The light-heavy split temperature for the hydrotreating stream was 350°C, and the light-heavy split temperature for the second hydrocracking stream was 330°C. The amount of light naphtha entering the second reactor was 40 wt% of the total weight of light naphtha. The operating conditions of the hydrotreating reactor were as follows: reaction pressure of 10.0 MPa, reaction temperature of 365 °C, volume space velocity of 1.8 h-1 The hydrogen-to-oil volume ratio is 800. The reaction conditions of the first hydrocracking reactor are as follows: reaction pressure 10.0 MPa, reaction temperature 370 ° C, volume space velocity 1.2h -1 The reaction conditions of the second hydrocracking reactor are as follows: reaction pressure of 10.0 MPa, reaction temperature of 350 ° C, volume space velocity of 1.8 h -1 , the hydrogen to oil volume ratio is 1200. The reaction results are shown in Table 2.

[0076] Comparative Example 1

[0077] This comparative example uses Figure 2 The process flow of the two-stage hydrocracking method is shown in Table 1. The properties of the processed wax oil feedstock are shown in Table 1. The specific process is as follows: In the presence of hydrogen (including new hydrogen 18 and recycled hydrogen 17), the feedstock 1 enters the hydrorefining reactor 2 and contacts and reacts with the hydrorefining catalyst filled in the hydrorefining reactor. The hydrorefining stream 3 obtained by the reaction enters the first hydrocracking reactor 4, contacts and reacts with the hydrogen and the hydrocracking catalyst filled in the first hydrocracking reactor. After the reaction, the first hydrocracking stream 16 is obtained and enters the gas-liquid separator 5 for gas-liquid separation. Then a gaseous stream 14 and a liquid stream 6 are obtained, wherein the gaseous stream 14 is compressed by a circulating hydrogen compressor 15 and circulated as circulating hydrogen 17. The liquid stream 6 enters a fractionating tower 7 for separation to obtain gas 8, light naphtha 9, heavy naphtha 10 and tail oil 11. The tail oil 11 enters the second hydrocracking reactor through the feed port at the top of the second hydrocracking reactor, contacts with hydrogen and the hydrocracking catalyst loaded in the second hydrocracking reactor to react. The second hydrocracking stream 13 obtained after the reaction is circulated to the gas-liquid separator 5 through a pipeline for treatment.

[0078] The hydrofining reactor was loaded with FF-56 hydrofining catalyst, the first hydrocracking reactor was loaded with FC-46 hydrocracking catalyst, and the second hydrocracking reactor was loaded with FC-76 hydrocracking catalyst. The operating conditions of the hydrofining reactor were as follows: reaction pressure of 16.0 MPa, reaction temperature of 370°C, volume space velocity of 1.2 h -1 The reaction conditions of the first hydrocracking reactor are as follows: reaction pressure of 16.0 MPa, reaction temperature of 370 °C, volume space velocity of 1.0 h -1 , the hydrogen-to-oil volume ratio is 1300. The reaction conditions of the second hydrocracking reactor are as follows: reaction pressure is 16.0 MPa, reaction temperature is 350°C, volume space velocity is 2.0 h -1 , the volume ratio of hydrogen to oil was 1500. The reaction results are shown in Table 2.

[0079] Comparative Example 2

[0080] use Figure 2 The two-stage hydrocracking process shown in Table 1 uses the wax feedstock properties processed. The hydrotreating reactor is loaded with FF-66 catalyst, the first hydrocracking reactor is loaded with FC-52 catalyst, and the second hydrocracking reactor is loaded with a graded catalyst. The upper hydrocracking catalyst A is FC-46, the hydrotreating catalyst is FTX, and the lower hydrocracking catalyst B is FC-14. The hydrotreating catalyst in the second hydrocracking reactor accounts for 12% of the volume, and the bottom of the hydrotreating catalyst bed is located at 35% of the height of the second hydrocracking reactor (from top to bottom). The operating conditions of the hydrotreating reactor are as follows: reaction pressure of 14.0 MPa, reaction temperature of 375°C, and volumetric space velocity of 0.8 h / min. -1 The reaction conditions of the first hydrocracking reactor are as follows: reaction pressure of 14.0 MPa, reaction temperature of 380 °C, volume space velocity of 1.5 h -1 , the hydrogen-to-oil volume ratio is 1200. The reaction conditions of the second hydrocracking reactor are as follows: reaction pressure is 14.0 MPa, reaction temperature is 340 ° C, volume space velocity is 1.0 h -1 , the hydrogen to oil volume ratio is 1200. The reaction results are shown in Table 2.

[0081] Comparative Example 3

[0082] This embodiment adopts Figure 1 The two-stage hydrocracking process flowsheet is shown in Table 1. The properties of the processed diesel feedstock are shown in Table 1. The hydrotreating reactor was loaded with FF-66 hydrotreating catalyst and FTX hydrotreating catalyst (1:1 volume ratio) in a graded pattern from top to bottom, following the direction of liquid feed flow. The first hydrocracking reactor was loaded with FC-76 hydrocracking catalyst. The second hydrocracking reactor was loaded with FC-50 hydrocracking catalyst (45% V) and FC-50 hydrocracking catalyst (55% V) in a graded pattern from top to bottom, following the direction of liquid feed flow. No hydrotreating catalyst was added. The light-heavy split temperature for the hydrotreating stream was 350°C, and the light-heavy split temperature for the second hydrocracking stream was 330°C. The amount of light naphtha entering the second reactor was 40 wt% of the total light naphtha weight. The operating conditions of the hydrotreating reactor are as follows: reaction pressure of 10.0 MPa, reaction temperature of 365 °C, volume space velocity of 1.8 h -1 The hydrogen-to-oil volume ratio is 800. The reaction conditions of the first hydrocracking reactor are as follows: reaction pressure 10.0 MPa, reaction temperature 370 ° C, volume space velocity 1.2h -1The reaction conditions of the second hydrocracking reactor are as follows: reaction pressure of 10.0 MPa, reaction temperature of 350 ° C, volume space velocity of 1.8 h -1 , the hydrogen to oil volume ratio is 1200. The reaction results are shown in Table 2.

[0083] Table 2 Results of Examples and Comparative Examples

[0084]

[0085] The experimental results of the above embodiments and comparative examples show that the yield of heavy naphtha in the hydrocracking method of the present invention is significantly increased, while solving the problems of aromatic accumulation in the circulating oil and insufficient hydrodenitrogenation capacity during long-term operation of the two-stage cycle hydrocracking when processing inferior raw materials.

Claims

1. A two-stage hydrocracking method for increasing the production of heavy naphtha, comprising the following steps: S1. Under hydrorefining conditions, the feedstock oil is mixed with hydrogen to undergo a hydrorefining reaction, and the hydrorefined stream obtained after the reaction is separated to obtain a first hydrorefined stream and a second hydrorefined stream; the splitting temperature of the first hydrorefined stream and the second hydrorefined stream is 10 to 80° C. lower than the final distillation point temperature of the feedstock oil; S2, the first hydrorefined stream obtained in step S1 and hydrogen enter the first hydrocracking reactor, contact with the hydrocracking catalyst loaded in the reactor, and obtain the first hydrocracking stream after the reaction, which is then separated to obtain gas, light naphtha, heavy naphtha and tail oil respectively; S3, the second hydrorefined stream obtained in step S1, and the tail oil obtained in step S2 enter the second hydrocracking reactor, where hydrogen and the hydrocracking catalyst are contacted to react to obtain a second hydrocracking stream; S4, the second hydrocracked stream obtained in step S3 is split into light and heavy components to obtain a light second hydrocracked stream and a heavy second hydrocracked stream, the heavy second hydrocracked stream is circulated and subjected to a hydrofining reaction together with the feed oil, and the light second hydrocracked stream is circulated and separated from the first hydrocracked stream; the splitting temperature of the light and heavy components of the second hydrocracked stream is 10 to 50° C. lower than the splitting temperature of the hydrofined stream; The second hydrocracking reactor is provided with a hydrocracking catalyst bed I, a hydrorefining catalyst bed II, and a hydrocracking catalyst bed III in sequence according to the flow direction of the liquid phase material. The volume ratio of the hydrorefining catalyst bed II to the total catalyst beds in the second hydrocracking reactor is 10% to 50%. The bottom end of the hydrorefining catalyst bed II is located at 30% to 60% of the height of the second hydrocracking reactor from the top down. The second hydrorefining feed stream enters the second hydrocracking reactor through a feed port provided on the outer wall of the reactor shell between the hydrocracking catalyst bed I and the hydrorefining catalyst bed II. The tail oil enters the second hydrocracking reactor through a feed port at the top of the second hydrocracking reactor. The light naphtha enters the second hydrocracking reactor through a feed port provided on the outer wall of the reactor shell between the hydrorefining catalyst bed II and the hydrocracking catalyst bed III. The amount of light naphtha entering the second hydrocracking reactor is 20% to 80% of the total weight of the light naphtha.

2. The two-stage hydrocracking method for increasing heavy naphtha production according to claim 1, wherein: The hydrocracking catalyst bed I and the hydrocracking catalyst bed III are loaded with the same or different hydrocracking catalysts.

3. The two-stage hydrocracking method for increasing heavy naphtha production according to claim 1, wherein: The volume ratio of the hydrorefining catalyst bed II to the total catalyst bed in the second hydrocracking reactor is 12% to 25%; the bottom end of the hydrorefining catalyst bed II is located at 35% to 50% of the height of the second hydrocracking reactor from top to bottom.

4. The two-stage hydrocracking method for increasing heavy naphtha production according to claim 1, wherein: The splitting temperature of the first hydrorefined stream and the second hydrorefined stream obtained after separation of the hydrorefined stream in step S1 is 15 to 30° C. lower than the final distillation point temperature of the raw material.

5. The two-stage hydrocracking method for increasing heavy naphtha production according to claim 1, wherein: The amount of light naphtha entering the second hydrocracking reactor is 25% to 55% of the total weight of the light naphtha.

6. The two-stage hydrocracking method for increasing heavy naphtha production according to claim 1, wherein: The splitting temperature of the light and heavy components of the second hydrocracking stream obtained in step S3 is 15-30° C. lower than the splitting temperature of the hydrorefined stream.

7. The two-stage hydrocracking method for increasing heavy naphtha production according to claim 1, wherein: The operating conditions of the hydrotreating reaction in step S1 include: reaction temperature of 320-430°C, reaction pressure of 6.0-20.0 MPa, volume space velocity of 0.2-10.0 h -1 , the hydrogen-to-oil volume ratio is 100-3000.

8. The two-stage hydrocracking method for increasing heavy naphtha production according to claim 1, wherein: The operating conditions of the hydrotreating reaction in step S1 include: reaction temperature of 340-400°C, reaction pressure of 8.0-16.0 MPa, volume space velocity of 0.8-2.0 h -1 , the hydrogen-to-oil volume ratio is 400-1200.

9. The two-stage hydrocracking method for increasing heavy naphtha production according to claim 1, wherein: The operating conditions of the first hydrocracking reactor include: reaction temperature of 350-425°C, reaction pressure of 6.0-20.0 MPa, volume space velocity of 0.6-8.0 h -1 , the hydrogen-to-oil volume ratio is 100-2500.

10. The two-stage hydrocracking method for increasing heavy naphtha production according to claim 1, wherein: The operating conditions of the first hydrocracking reactor include: reaction temperature of 360-400°C, reaction pressure of 8.0-16.0 MPa, volume space velocity of 0.8-2.0 h -1 , the hydrogen-to-oil volume ratio is 500-1800.

11. The two-stage hydrocracking method for increasing heavy naphtha production according to claim 1, wherein: The operating conditions of the second hydrocracking reactor include: reaction temperature of 320-400°C, reaction pressure of 6.0-18.0 MPa, volume space velocity of 0.6-8.0 h -1 , the hydrogen-to-oil volume ratio is 500-2500.

12. The two-stage hydrocracking method for increasing heavy naphtha production according to claim 1, wherein: The operating conditions of the second hydrocracking reactor include: reaction temperature of 330-390°C, reaction pressure of 8.0-16.0 MPa, volume space velocity of 1.0-2.5 h -1 , the hydrogen-to-oil volume ratio is 600-2000.

13. The two-stage hydrocracking method for increasing heavy naphtha production according to claim 1, wherein: The raw oil is diesel and / or wax oil; the diesel is one or more of straight-run diesel, coker diesel, catalytic diesel, ebullated-bed hydrogenated diesel, and residual oil hydrogenated diesel; the wax oil is one or more of vacuum wax oil, coker wax oil, ebullated-bed hydrogenated wax oil, and deep-drawn wax oil.

14. The two-stage hydrocracking method for increasing heavy naphtha production according to claim 13, wherein: When processing diesel raw materials, the aromatic content of the raw materials is 40% to 90%. When processing wax oil raw materials, the distillation range of the raw materials is 280℃ to 600℃.

15. The two-stage hydrocracking method for increasing heavy naphtha production according to claim 13, wherein: When processing diesel raw materials, the aromatic content of the raw materials is 50% to 80%; when processing wax oil raw materials, the final distillation point of the raw materials is 550℃ to 580℃.

16. A two-stage hydrocracking system for increasing heavy naphtha production, comprising a hydrotreating reactor, a first separator, a first hydrocracking reactor, a gas-liquid separator, a second separator, a second hydrocracking reactor, and a third separator connected in a certain manner, wherein: A hydrorefining reactor is used to receive the feedstock oil and hydrogen, and to contact the feedstock oil and hydrogen with the hydrorefining catalyst therein to perform a hydrorefining reaction to obtain a hydrorefining feed stream; a first separator, which is used to receive the hydrofinished stream from the hydrofinishing reactor and cut the hydrofinished stream into light and heavy components to obtain a first hydrofinished stream and a second hydrofinished stream after separation; a first hydrocracking reactor, which is used to receive the first hydrorefined stream and hydrogen from the first separator, and to react with the catalyst therein to obtain a first hydrocracked stream; a gas-liquid separator for receiving and separating the first hydrocracking stream from the first hydrocracking reactor to obtain a gas phase stream and a liquid phase stream after separation; A second separator is used to receive and separate the liquid phase stream from the gas-liquid separator to obtain gas, light naphtha, heavy naphtha and tail oil after separation; a second hydrocracking reactor, which is used to receive the tail oil from the second separator, the second hydrorefined stream from the first separator, and the light naphtha from the second separator, and to obtain a second hydrocracked stream after contact reaction with the catalyst therein; a third separator, which is used to receive the second hydrocracked material stream from the second hydrocracking reactor and split the second hydrocracked material stream into light and heavy components to obtain a light second hydrocracked material stream and a heavy second hydrocracked material stream, the heavy second hydrocracked material stream enters the hydrofining reactor through a pipeline, and the light second hydrocracked material stream enters the gas-liquid separator through a pipeline; The second hydrocracking reactor is provided with a hydrocracking catalyst bed I, a hydrorefining catalyst bed II, and a hydrocracking catalyst bed III in sequence according to the flow direction of the liquid phase material. The volume ratio of the hydrorefining catalyst bed II to the total catalyst bed in the second hydrocracking reactor is 10% to 50%. The bottom end of the hydrorefining catalyst bed II is located at 30% to 60% of the height of the second hydrocracking reactor from the top down. The second hydrocracking reactor is provided with three feed ports, which are respectively denoted as feed port A, feed port B, and feed port C. Feed port A is provided at the top of the second hydrocracking reactor, and the tail oil enters the second hydrocracking reactor through the feed port A; The feed port B is provided on the outer wall of the reactor shell between the hydrocracking catalyst bed I and the hydrorefining catalyst bed II, and the second hydrorefining stream enters the second hydrocracking reactor through the feed port B; The feed port C is provided on the outer wall of the reactor shell between the hydrorefining catalyst bed II and the hydrocracking catalyst bed III, and the light naphtha enters the second hydrocracking reactor through the feed port C.

17. The two-stage hydrocracking system for increasing heavy naphtha production according to claim 16, wherein: The volume ratio of the hydrorefining catalyst bed II to the total catalyst bed in the second hydrocracking reactor is 12% to 25%; the bottom end of the hydrorefining catalyst bed II is located at 35% to 50% of the height of the second hydrocracking reactor from top to bottom.

18. The two-stage hydrocracking system for increasing heavy naphtha production according to claim 16, wherein: The hydrotreating reactor, the first hydrocracking reactor and the second hydrocracking reactor are selected from at least one of a fixed bed hydrogenation reactor, a suspended bed hydrogenation reactor and a fluidized bed hydrogenation reactor.

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