A method for refining heavy wax oil in a hydrocracking unit

Abstract

The present invention discloses a method for refining heavy wax oil feedstock in a hydrocracking unit. Using heavy wax oil blended with light fractions as the feedstock, it successively passes through a hydrofining reaction zone and a hydrocracking reaction zone. In the hydrofining reaction zone, reactions such as desulfurization, denitrification, deoxidation, and aromatic saturation mainly occur; in the hydrocracking reaction zone, hydrofining and cracking reactions mainly take place. The reaction products enter the fractionation system to separate out liquefied gas, light naphtha, heavy naphtha, diesel, and unconverted oil. The method of the present invention can effectively solve the problems of severely excessive nitrogen content in the refined oil and large radial temperature difference in the catalyst bed layer of the reactor when the hydrocracking unit processes wax oil feedstock; at the same time, it also solves the problem that the wax oil hydrotreating unit cannot provide feedstock for the fluid catalytic cracking unit during shutdown and maintenance, making it difficult to balance the production of the whole plant.

Description

Technical Field

[0001] The invention discloses a hydrogenation process method, in particular to a hydrogenation process method for refining heavy wax oil raw materials in a hydrocracking unit. Background Art

[0002] As oil resources become increasingly depleted and environmental protection requirements become increasingly stringent, the proportion of hydrogenation units in refineries is also increasing. In order to maximize the yield and quality of light oil, the severity of the reaction of the wax oil hydrotreating unit has gradually increased, resulting in a shortened catalyst operation cycle. For newly built single-series refineries with a capacity of tens of millions of tons, the wax oil hydrotreating unit has a large processing volume and limited capacity in the intermediate tank area. After the raw materials of the wax oil hydrotreating unit are deteriorated, the unit operation cycle is generally about 3 years, and usually at least one "skimming" treatment is required in the middle, resulting in a failure to synchronize with the 4-year major overhaul cycle of the entire plant. During the shutdown of the wax oil hydrotreating unit for agent replacement / skimming, a large amount of heavy wax oil raw materials will not be able to be stored; at the same time, the wax oil hydrotreating unit cannot provide raw materials for the catalytic cracking unit, and it is difficult to balance the production of the entire plant.

[0003] The hydrocracking unit has strong adaptability to raw materials, and has the advantages of good product quality, high yield of liquid products, and high flexibility of product structure. In order to ensure the material balance of the whole plant during the shutdown and maintenance of the wax oil hydrotreating unit, maintain the normal production of all units in the whole plant, and reduce the loss of the shutdown of the wax oil hydrotreating unit to the benefits of the whole plant, during the shutdown and replacement of the wax oil hydrotreating unit, the production plan of the hydrocracking unit is changed from the hydrocracking plan to the wax oil hydrotreating plan to replace the role of the wax oil hydrotreating unit in the whole plant process. The raw materials of the wax oil hydrotreating unit are generally three-line wax oil and coking wax oil, and a small amount of deasphalted oil can also be blended. The main products are naphtha, diesel and hydrogenated wax oil. Since naphtha cannot meet the reforming feed requirements and the diesel cetane number is low, naphtha and diesel have been discontinued for energy saving and consumption reduction. After the production regulation of the hydrocracking unit was gradually switched from the hydrocracking scheme to the wax oil hydrotreating scheme, it was found that the nitrogen content of the refined oil was high, with the highest exceeding 600 mg / kg, far exceeding the control value of ≯20 mg / kg. At the same time, due to the heavier raw materials and poor material distribution, the radial temperature difference of the catalyst bed in the refining reactor increased from the original ≯3°C to 10-15°C, seriously affecting the smooth operation of the hydrocracking unit and the performance of the cracking catalyst. Summary of the invention

[0004] In view of the deficiencies of the prior art, the object of the present invention is to provide an improved wax oil hydrogenation method, which is applicable to the processing of heavy wax oil raw materials by a hydrocracking unit during the shutdown and maintenance period of a wax oil hydrotreating unit. Compared with the existing hydrocracking process, the method of the present invention can solve the problems of serious over-standard nitrogen content in the refined oil and large radial temperature difference in the reactor when the hydrocracking unit processes heavy wax oil raw materials during the shutdown and maintenance period of the wax oil hydrotreating unit, provide high-quality raw materials for the fluid catalytic cracking unit, and ensure the production balance of the whole plant.

[0005] The method for refining heavy wax oil raw materials in the hydrocracking unit provided by the present invention includes the following contents:

[0006] (1) Provide a hydrofining reaction zone and a hydrocracking reaction zone; the hydrofining reaction zone includes a hydrofining catalyst, and the hydrocracking reaction zone contains a hydrocracking catalyst;

[0007] (2) Using heavy wax oil blended with a part of light distillate oil as the feedstock, together with hydrogen, first pass through the hydrofining reaction zone to produce hydrofined product oil;

[0008] (3) The hydrofined product oil obtained in step (2) enters the hydrocracking reaction zone and successively passes through more than three hydrocracking catalyst beds together with hydrogen;

[0009] (4) The hydrocracking stream obtained in step (3) undergoes gas-liquid separation and fractionation to obtain a mixture of jet fuel fraction and diesel fraction as wide-cut diesel, and the tail oil is taken out of the unit as the raw material for the fluid catalytic cracking unit.

[0010] Further, the initial boiling point of the heavy wax oil is generally 350-400 °C, preferably 370-390 °C; the final boiling point is generally 550-700 °C, preferably 580-600 °C; the initial boiling point of the light distillate oil is generally 40-200 °C, preferably 50-180 °C; the final boiling point is generally 330-400 °C, preferably 350-380 °C. In the feedstock, the mass fraction of the blended light distillate oil is generally 5%-50%, preferably 10%-30%. The blended light distillate oil can be one or several of the fractions such as straight-run gasoline and diesel, coker gasoline and diesel, and catalytic gasoline and diesel of crude oil.

[0011] Further, in the hydrocracking reaction zone, it is generally controlled that the conversion of heavy components in the feedstock > 350 °C is as little as possible.

[0012] Further, in order to enable the hydrocracking unit to maintain the wax oil hydrotreating production plan (that is, to maintain a relatively high tail oil yield as much as possible) and meet the need to temporarily replace the wax oil hydrotreating unit. For more than three hydrocracking catalyst beds in the hydrocracking reaction zone, among two adjacent hydrocracking catalyst beds, the inlet temperature T of the downstream catalyst bed should be controlled. nLower than the inlet temperature T of the upstream catalyst bed n-1 (n is an integer greater than or equal to 2, and the maximum is the number of hydrocracking catalyst beds). Preferably, T n is lower than T n-1 by 1 to 10 °C, more preferably by 2 to 8 °C. Those skilled in the art are familiar that the purpose of adjusting the inlet temperature of the hydrocracking catalyst bed can be achieved by adjusting the opening degree of the cold hydrogen valve between adjacent two catalyst beds.

[0013] Further, the operating conditions of the hydrotreating reaction zone generally include: the reaction temperature is 300 - 480 °C, the reaction pressure is 5.0 - 20.0 MPa, the hydrogen-oil volume ratio is 100:1 - 4000:1, and the liquid hourly space velocity is 0.2 - 10.0 h -1 ; the preferred operating conditions are: the reaction temperature is 330 - 450 °C, the reaction pressure is 8.0 - 17.0 MPa, the hydrogen-oil volume ratio is 400:1 - 2000:1, and the liquid hourly space velocity is 0.5 - 4.0 h -1 .

[0014] Further, the operating conditions of the hydrocracking reaction zone generally include: the reaction temperature is 250 - 500 °C, the reaction pressure is 5.0 - 20.0 MPa, the hydrogen-oil volume ratio is 100:1 - 4000:1, and the liquid hourly space velocity is 1.0 - 10.0 h -1 ; preferably: the reaction temperature is 300 - 440 °C, the reaction pressure is 8.0 - 17.0 MPa, the hydrogen-oil volume ratio is 400:1 - 2000:1, and the liquid hourly space velocity is 1.0 - 4.0 h -1 .

[0015] In the method of the present invention, the hydrotreating reaction zone mainly undergoes reactions such as desulfurization, denitrification, deoxidation, and aromatics saturation of the raw materials, and the hydrocracking reaction zone mainly conducts hydrocracking reactions.

[0016] Those skilled in the art generally believe that there will not be major problems in using a hydrocracking unit to process heavy wax oil raw materials. In fact, there are no major problems from the perspective of the reaction itself. When the contents of impurities such as metals and asphaltenes do not exceed the standards, the dry point of the raw materials processed by the current hydrocracking unit has reached up to 600 °C. However, due to design condition limitations, catalyst grading selection for specific raw materials, etc., there are problems such as unreasonable matching of the temperatures of the refining and cracking reactors when the existing hydrocracking unit processes heavy wax oil raw materials, resulting in insufficient hydrotreating temperature, relatively high outlet temperature of the refining reactor, relatively large radial temperature difference, relatively high hydrocracking reaction depth, and the need for the cracking reactor to have as low a temperature as possible. When the cold hydrogen valve is at the maximum opening degree allowed by safety, the cracking temperature is still relatively high, thus resulting in problems such as high hydrogen consumption and low yield of hydrocracking tail oil.

[0017] The inventors of the present application found through research that by reducing the viscosity of the feedstock to the hydrocracking unit, it is an effective measure to solve the problems of large radial temperature difference in the hydrofining reactor, too high refining reaction temperature, and temperature mismatch between the refining and cracking reactors. That is, it is necessary to control the bed temperature rise of the hydrocracking catalyst as low as possible, so that the hydrocracking unit operates in the hydrofining operation mode. In the present invention, by blending a part of light distillate oil into the heavy wax oil feedstock, the composition of the feedstock oil is changed, making the viscosity of the feedstock oil smaller. Due to the decrease in the raw material viscosity, the material distribution is more reasonable, and the radial temperature difference of the hydrofining reactor is greatly reduced. At the same time, due to the incorporation of light distillate oil, the difficulty of the hydrodenitrogenation reaction is reduced, the average reaction temperature of hydrofining and the outlet temperature of the hydrofining reactor are reduced, making the temperature matching between the hydrofining and hydrocracking reactors more reasonable. The temperature at the inlet of the hydrocracking reactor bed decreases from top to bottom, thereby reducing the cracking depth, reducing hydrogen consumption, and improving the economic benefits of the whole plant.

[0018] In the existing hydrocracking units, the feedstock for the hydrocracking unit is diesel or wax oil, and the operation mode of equal inlet temperature is generally adopted for each catalyst bed of the hydrocracking reactor. In this way, the catalyst load of each bed can be similar, and the deactivation rate is also similar, maximizing the effectiveness of all catalysts. In the present invention, the operation mode of gradually decreasing the inlet temperature of the cracking catalyst bed is adopted. This is because the hydrocracking feedstock is much heavier than the design value. To ensure that the nitrogen content of the refined oil meets the control value of ≤20 mg / kg, a higher temperature is required for hydrofining. In order to provide more tail oil feedstock, the hydrocracking reaction depth should be as low as possible, making it difficult to match the hydrofining and hydrocracking reaction temperatures. If the operation of equal inlet temperature is adopted, the hydrocracking conversion rate is relatively high. In the present invention, it is preferably to adopt the operation mode of gradually decreasing the inlet temperature of the second, third, and fourth beds (if there is a fourth bed), so as to reduce the conversion depth as much as possible and save precious hydrogen resources.

[0019] Compared with the prior art, the method of the present invention has the following beneficial effects:

[0020] 1. Aiming at the phenomena of large radial temperature difference, difficult temperature matching, and high conversion rate that occur when using the existing hydrocracking unit to process heavy wax oil feedstock, through in-depth analysis of the causes of the problems, the present invention creatively proposes to blend a certain proportion of light distillate oil into the heavy wax oil feedstock, solves the problem of large radial temperature difference when the existing hydrocracking unit processes heavy wax oil feedstock, reduces the difficulty of temperature matching, and effectively protects the performance of the hydrocracking catalyst.

[0021] 2. By blending a certain proportion of light distillate oil into the heavy wax oil feedstock processed in the hydrocracking unit, and preferably adopting the inlet temperature reduction operation for the cracking bed layer of the hydrocracking reactor, the tail oil yield is further ensured. At the same time, the safety risk caused by the excessive cold hydrogen valve position between the refining and cracking reactors can be reduced, the hydrogen consumption of the unit can be effectively reduced, and the economic benefits of the unit can be improved.

[0022] 3. Blending a certain proportion of light distillate oil into the heavy wax oil feedstock of the hydrocracking unit can ensure the overall plant material balance during the shutdown and maintenance of the wax oil hydrotreating unit, maintain the normal production of each unit in the whole plant, and reduce the loss of the overall plant benefit caused by the shutdown loss of the wax oil hydrotreating unit.

[0023] 4. Blending a certain proportion of light distillate oil into the heavy wax oil feedstock processed by the hydrocracking unit can reduce the nitrogen content of the feed, and more importantly, reduce the viscosity of the feedstock oil, thereby reducing the difficulty of hydrodenitrogenation. The nitrogen content of the refined oil can be effectively reduced, and the performance of the hydrocracking catalyst can be effectively protected. Brief Description of the Drawings

[0024] Figure 1 is a principle process flow diagram of the present invention.

[0025] Wherein: 1 - heavy wax oil feedstock, 2 - light component feedstock, 3 - recycle hydrogen, 4 - hydrorefining reactor, 5 - hydrocracking reactor, 6 - fractionation system, 7 - liquefied gas, 8 - light naphtha, 9 - heavy naphtha, 10 - diesel oil, 11 - unconverted oil. Detailed Embodiments

[0026] The process flow of the present invention is as follows: The heavy wax oil feedstock, light component feedstock and hydrogen are mixed and then enter the hydrorefining reactor for reactions such as desulfurization, denitrification and aromatics saturation. The effluent of the refining reaction enters the hydrocracking reactor directly without separation. The reaction products enter the fractionation system, and liquefied gas, light naphtha, heavy naphtha, clean diesel oil and tail oil are separated. The tail oil is used as the feedstock for catalytic cracking.

[0027] The heavy wax oil feedstock used in the present invention can be one or several of the fractions such as vacuum gas oil of crude oil, coker gas oil, deasphalted oil, shale oil and coal synthetic oil. The blended light component oil can be one or several of the fractions such as straight-run gasoline and diesel oil of crude oil, coker gasoline and diesel oil, catalytic gasoline and diesel oil.

[0028] The hydrofining catalyst used in the method of the present invention is usually a conventional heavy oil hydrofining catalyst, generally composed of a carrier and a hydro-metallic component supported on the carrier, including the Group VI B active metal component in the periodic table, such as tungsten and / or molybdenum, generally 8% to 35% by weight of the metal oxide, preferably 12% to 30%; and the Group VIII active metal component promoter, such as nickel and / or cobalt, 1% to 10% by weight of the metal oxide, preferably 1.5% to 6%. The carrier used for the hydrofining catalyst is an inorganic refractory oxide, such as alumina, amorphous silica-alumina, silica, titanium oxide, etc.

[0029] The hydrocracking catalyst described in the present invention can be selected from conventional hydrocracking catalysts in the art. The hydrocracking catalyst generally includes a cracking component and a hydrogenation component. The cracking component usually includes amorphous silica-alumina and / or molecular sieves, such as Y-type or USY molecular sieves. The binder is usually alumina or silica. The hydrogenation component is selected from metals, metal oxides or metal sulfides of Group VI, VII or VIII, more preferably one or more of iron, chromium, molybdenum, tungsten, cobalt, nickel, or their sulfides or oxides. Based on the weight of the catalyst, the content of the hydrogenation component is 5% to 40%. The commercially available hydrofining catalysts that can be selected mainly include: HC-K, HC-T, HC-P developed by UOP, and 3936, 3996, FF-16, FF-26, FF-36, FF-46, FF-56, FF-66 developed by Fushun Research Institute of Petroleum and Petrochemicals. The hydrocracking catalyst can use conventional commercial hydrocracking catalysts, such as DHC-32, DHC-39, HC-43, HC-115 of UOP, and 3974, 3976, FC-12, FC-16, FC-26, FC-32, FC-46, FC-50, FC-76 developed by Fushun Research Institute of Petroleum and Petrochemicals.

[0030] The present invention will be further explained below in conjunction with the drawings and embodiments. The heavy wax oil raw material, light component raw material and hydrogen are mixed and then enter the hydrofining reactor for reactions such as desulfurization, denitrification and aromatics saturation. The reactants directly enter the hydrocracking reactor without separation, and the reaction products enter the fractionation system to separate out liquefied gas, light naphtha, heavy naphtha, clean diesel and tail oil, and the tail oil is used as the catalytic cracking raw material.

[0031] The heavy wax oil feedstock 1 is mixed with the light component feedstock 2 and the circulating hydrogen 3 and then enters the hydrotreating reactor 4, where desulfurization, denitrogenation and aromatic saturation reactions are carried out under the action of hydrogen and the catalyst; the reactants directly enter the hydrocracking reactor 5 for hydrocracking reaction without separation, and the reaction products enter the fractionation system 6 to separate liquefied gas 7, light naphtha 8, heavy naphtha 9, clean diesel 10 and unconverted oil 11. The unconverted oil 11 can be used as a catalytic cracking feedstock, or can be recycled back to the hydrotreating reactor 4 or the hydrocracking reactor 5 for further refining.

[0032] The scheme and effect of the present invention are described below by examples. The catalysts used are commercial catalysts developed and produced by Dalian Petrochemical Research Institute, FF-36 is a hydrofining catalyst, and FC-32 is a hydrocracking catalyst. In the examples and comparative examples, the aviation fuel fraction is mixed with the diesel fraction as a wide-fraction diesel.

[0033] In the embodiment and comparative example, the hydrocracking reactor adopts four catalyst beds with equal volume loading. The reaction pressure is 15 MPa, and the volume space velocity is 1.1 and 2.0 h -1 .

[0034] The first stage series process hydrocracking unit processes wax oil raw materials. Example 1 is a heavy component raw material mixed with 10% light component raw material (raw material 1), and the inlet temperature of the cracking reactor is the same. Example 2 is a heavy component raw material mixed with 10% light component raw material (raw material 1), and the inlet temperature of the cracking reactor decreases. Example 3 is a heavy component raw material mixed with 20% light component raw material (raw material 2), and the inlet temperature of the cracking reactor decreases. Comparative Example 1 processes all the same heavy component raw materials (raw material 3) as Example 1, and the inlet temperatures of each bed of the cracking reactor are the same; Comparative Example 2 processes all the same heavy component raw materials (raw material 3) as Example 1, and the inlet temperature of the cracking reactor decreases, to illustrate the advanced nature of this hydrocracking process in processing heavy component raw materials. The process conditions and results are shown in Table 2 below.

[0035] Table 1 Raw oil properties

[0036]

[0037] Table 2 Process conditions and results

[0038]

[0039] *Average reaction temperatures of hydrotreating / hydrocracking reactors, respectively.

[0040] The above embodiments show that when using a hydrocracking unit to process the heavy wax oil, the feedstock of the wax oil hydrotreating unit, mixing a part of the light fraction oil feedstock into the heavy wax oil feedstock can effectively solve the problems of high nitrogen content in the refined oil and large radial temperature difference in the refined reactor, and can reduce the hydrogen consumption, increase the tail oil yield, provide high-quality feed for the fluid catalytic cracking unit, and improve the economic benefits of the enterprise.

Claims

1. A method for refining heavy wax oil raw materials in a hydrocracking unit, characterized in that, It includes the following contents: (1) Provide a hydrotreating reaction zone and a hydrocracking reaction zone; the hydrotreating reaction zone includes a hydrotreating catalyst, and the hydrocracking reaction zone contains a hydrocracking catalyst; (2) Use heavy wax oil blended with light distillate oil as the feedstock, together with hydrogen, first pass through the hydrotreating reaction zone to produce hydrotreated product oil; (3) The hydrotreated product oil obtained in step (2) enters the hydrocracking reaction zone and sequentially passes through more than three hydrocracking catalyst beds with hydrogen; (4) The hydrocracked product stream obtained in step (3) undergoes gas-liquid separation and fractionation to obtain a jet fuel fraction and a diesel fraction. After mixing the jet fuel fraction and the diesel fraction, it is used as wide-cut diesel, and the tail oil obtained is sent out of the unit as the feedstock for the fluid catalytic cracking unit; Among them, the mass fraction of the light distillate oil blended in the feedstock is 5% - 50%, the initial boiling point of the light distillate oil is 40 - 200 °C, and the final boiling point is 330 - 400 °C; In two adjacent hydrocracking catalyst beds, the inlet temperature T of the downstream catalyst bed n is lower than the inlet temperature T of the upstream catalyst bed n-1 , T n is 5 - 10 °C lower than T n-1 , where n is an integer greater than or equal to 2.

2. The method according to claim 1, wherein The initial boiling point of the heavy wax oil is 350 - 400 °C, and the final boiling point is 550 - 700 °C.

3. The method according to claim 1, wherein The mass fraction of the light distillate oil blended in the feedstock is 10% - 30%.

4. The method according to any one of claims 1 to 3, characterized in that, The light distillate oil is one or several of straight-run gasoline and diesel, coker gasoline and diesel, and catalytic gasoline and diesel fractions of crude oil.

5. The method according to claim 1, wherein The operating conditions of the hydrofining reaction zone include: a reaction temperature of 300 to 480 °C, a reaction pressure of 5.0 to 20.0 MPa, a hydrogen-oil volume ratio of 100:1 to 4000:1, and a liquid hourly space velocity of 0.2 to 10.0 h -1 .

6. The method according to claim 5, wherein The operating conditions of the hydrofining reaction zone are as follows: the reaction temperature is 330 to 450 °C, the reaction pressure is 8.0 to 17.0 MPa, the hydrogen-oil volume ratio is 400:1 to 2000:1, and the liquid hourly space velocity is 0.5 to 4.0 h -1 .

7. The method according to claim 1, characterized in that, The operating conditions of the hydrocracking reaction zone include: the reaction temperature is 250 to 500 °C, the reaction pressure is 5.0 to 20.0 MPa, the hydrogen-oil volume ratio is 100:1 to 4000:1, and the liquid hourly space velocity is 1.0 to 10.0 h -1 .

8. The method according to claim 7, wherein The operating conditions of the hydrocracking reaction zone include: the reaction temperature is 300 to 440 °C, the reaction pressure is 8.0 to 17.0 MPa, the hydrogen-oil volume ratio is 400:1 to 2000:1, and the liquid hourly space velocity is 1.0 to 4.0 h -1 .

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