Catalyst filling method of tubular fixed bed Fischer-Tropsch synthesis reactor

Abstract

The invention discloses a catalyst filling method for a tubular fixed bed Fischer-Tropsch synthesis reactor, which comprises the following steps of: (1) cleaning reaction tubes, and installing plugging springs at the bottoms of the reaction tubes; (2) connecting the bottom end of the reaction tube nest with an outlet pipe of a pump, injecting light oil with a certain height and a distillation range of 100-230 DEG C into the reaction tube nest through the pump, stopping the pump, and maintaining the oil level at the height through a pressure control valve arranged on a crossover line connecting a pump outlet and a pump inlet; (3) filling the reaction tube nests with a catalyst from the top openings of the reaction tube nests, and maintaining the oil level height in the step (2) through a pressure control valve; and (4) after the catalyst is filled, emptying and recovering the light oil from the reaction tube nest. Loss caused by damage of the catalyst is avoided, it is guaranteed that the catalyst is evenly filled in the reaction tube nests, the stacking density is consistent, the axial temperature difference is reduced, and the performance of the catalyst is improved.

Description

Technical Field

[0001] The invention relates to the field of Fischer-Tropsch synthesis, and in particular to a catalyst loading method for a tubular fixed-bed Fischer-Tropsch synthesis reactor. Background Art

[0002] Fischer-Tropsch synthesis is a highly exothermic reaction, and a shell-and-tube reactor is a preferred reactor form. The diameter of the shell-and-tube reactor currently used in Fischer-Tropsch synthesis is generally in the range of 26mm-42mm, and the length can reach 10-12m. The number of reaction tubes in a single reactor can reach tens of thousands. The loading of the catalyst is a key factor affecting the stable operation of the shell-and-tube reactor. Improper loading of the catalyst will not only affect mass transfer and heat transfer, but also cause local over-temperature, and in severe cases, cause the catalyst to deactivate due to thermal runaway. Therefore, how to load the catalyst more evenly in the shell-and-tube reactor is a problem that needs to be solved urgently.

[0003] CN105126709B discloses a loading device and a loading method for catalysts in a reaction tube fixed bed reactor. The loading device consists of a conveying device, a sub-loading device and a feeding device. Through automatic sub-loading and shock loading, the labor intensity of on-site workers is reduced, and the work efficiency and loading accuracy are improved. The invention ensures the consistency of catalyst loading between different reaction tubes, but does not consider how to avoid the occurrence of bridging during the loading process, nor how to avoid the catalyst powdering and cracking caused by the physical impact of the catalyst during the falling process.

[0004] CN1607032A discloses a method for loading catalyst. The method is to insert a chain substance into the reaction tube during the catalyst loading process so that the lower end of the chain substance is higher than the upper end of the catalyst layer. The method can largely avoid the occurrence of the "bridging" phenomenon during the catalyst loading process, and the resistance of the chain substance can reduce the powdering and cracking of the catalyst caused by the physical impact during the catalyst falling process when loading the catalyst in the fixed bed reaction tube reactor. However, since the reaction tube is generally as high as 10-15m, the collision with the chain substance during the catalyst falling process will still cause the catalyst to break, and it is inevitable that the catalyst stacking density at the bottom of the reaction tube is higher than that at the top of the reaction tube, so that the heat release of the bed layer at the bottom of the reaction tube reactor is higher than that at the top, and an axial temperature difference occurs. In addition, the chain substance needs to be continuously pulled up during the catalyst loading process, which inevitably brings about problems such as extending the catalyst loading time and increasing the labor intensity of workers.

[0005] CN102989376B and CN102989375B disclose a catalyst loading method for a reaction tube reactor, which improves the uniformity of catalyst loading in the reaction tube reactor and reduces the difficulty of catalyst loading by controlling the loading rate of the catalyst. However, the method does not consider how to avoid the catalyst powderization and cracking caused by the physical impact of the catalyst during the falling process; nor does it consider the problem of inconsistent stacking density of the upper and lower catalyst beds.

[0006] The above inventions all involve catalyst loading technology for reaction tube reactors, which mainly improve the uniformity of catalyst loading by automatic subpackaging, inserting chain materials, controlling the loading rate, etc. However, the above methods only partially alleviate or solve the problem of catalyst loading uniformity, but there are still problems such as easy breakage of the catalyst, inconsistent stacking density of the upper and lower catalyst beds, and large axial temperature difference. Summary of the invention

[0007] In view of the deficiencies in the prior art, an object of the present invention is to provide a catalyst loading method for a shell-and-tube fixed-bed Fischer-Tropsch synthesis reactor, so as to avoid the loss caused by catalyst loading breakage, facilitate uniform loading of catalyst in the reaction shell and tube, and improve the catalytic reaction effect.

[0008] In order to achieve the above-mentioned invention object, the present invention adopts the following technical solutions:

[0009] A catalyst loading method for a tubular fixed-bed Fischer-Tropsch synthesis reactor, the catalyst loading method comprising:

[0010] (1) Clean the reaction tubes and install a plugging spring at the bottom of the reaction tubes;

[0011] (2) Then, the bottom end of the reaction tube is connected to the outlet pipe of the pump, and a certain height of light oil with a distillation range of 100-230° C. is injected into the reaction tube through the pump, and then the pump is stopped and the oil level is maintained at this height through a pressure control valve provided on the crossover line connecting the pump outlet and the pump inlet;

[0012] (3) loading the catalyst into the reaction tubes from the top opening of the reaction tubes so that the catalyst settles in the reaction tubes and forms a catalyst bed, while maintaining the oil level in step (2) by a pressure control valve to prevent the oil level from rising and overflowing during the addition of the catalyst to the reaction tubes;

[0013] (4) After the catalyst is loaded, the light oil is discharged from the reaction tubes and recovered.

[0014] In some embodiments, when cleaning the reaction tubes in step (1), the reaction tubes can be cleaned by a high-pressure water gun or a steel brush to make the inner wall of the reaction tubes smooth and free of dirt; then a plugging spring is installed at the bottom of the reaction tube, and the distance from the top of the plugging spring to the bottom of the reaction tube is represented by L, which can be 5-40 cm, preferably 10-30 cm, such as 15, 20 or 25 cm.

[0015] Those skilled in the art understand that the distance (L) between the top of the plugging spring and the bottom of each reaction tube should be kept consistent to ensure consistent catalyst loading. In some embodiments, the deviation between the distance L between the top of the plugging spring and the bottom of the plugging spring in different reaction tubes should be controlled within ±3 cm (that is, the difference between the L value in any reaction tube and the L value in any other reaction tube is within ±3 cm), preferably the L deviation is within ±1 cm, such as ±0.5 cm or 0.

[0016] In step (2) of the present invention, light oil is injected into the reaction tube from the bottom of the reaction tube by a pump, and the oil level is subsequently maintained by a pressure control valve provided on the crossover line. It is understood by those skilled in the art that the pressure control valve can be opened when the pressure exceeds a set value, and closed when the pressure is lower than the set value, so that when the oil level in the reaction tube increases due to the addition of the catalyst, the light oil can be discharged from the bottom of the reaction tube in time to maintain the oil level.

[0017] Preferably, the light oil used is selected from light hydrocarbons with a distillation range of 100°C to 230°C produced by Fischer-Tropsch synthesis, such as 100-200°C or 140-230°C. The use of Fischer-Tropsch synthetic oil can prevent the S element in the oil from poisoning the catalyst. The light oil distillation range is selected to be in the range of 100°C to 230°C. On the one hand, it prevents the light oil from volatilizing during the catalyst loading process, causing safety hazards, and on the other hand, it prevents the light oil from hydrogenating during the catalyst reduction process, causing carbon deposition on the catalyst, and promotes subsequent Fischer-Tropsch synthesis; preferably, the light oil can be selected from light white oil with a grade of W-20, W-30, W-40 or W-60;

[0018] In some embodiments, the distance between the light oil injected in step (2) and the upper end of the reaction tubes is in the range of 100 cm-150 cm, which prevents the catalyst from being damaged during the falling process due to the oil level being too far away from the upper end of the tubes, and prevents the oil level from being too far away from the upper end of the tubes from splashing oil droplets during the catalyst loading process.

[0019] In a preferred embodiment, the pump outlet is provided with a pump outlet valve, and the pump outlet valve is connected to the bottom end of the reaction tube through an oil inlet pipeline and to the pump inlet through a jumper line; the oil inlet pipeline is provided with an oil inlet valve, and a pressure gauge and the pressure control valve are provided in sequence along the logistics direction of the jumper line.

[0020] Preferably, when the pump is started, first ensure that the pump is in a self-circulating state through the cross-line, then gradually adjust the cross-line pressure control valve to input light oil into the reaction tubes, and after the oil level rises to a predetermined height H, record the corresponding oil pressure P, then stop the pump and maintain the oil level at this height H through the pressure control valve.

[0021] In the present invention, the pump can be a centrifugal pump, a gear pump, a screw pump, a plunger pump, a diaphragm pump, etc. The pump head must be higher than the length of the reaction tube, and a centrifugal pump and a diaphragm pump are preferred. The pressure control valve can be a needle valve, a regulating valve, a back pressure valve, etc., and a back pressure valve is preferred.

[0022] In some embodiments, the pump inlet connected to the jumper is further connected to a light oil storage tank, thereby providing light oil for injection and recovering light oil when adding catalyst, thereby improving the injection and recovery efficiency of light oil.

[0023] In step (3) of the present invention, the catalyst is loaded into the reaction tubes from the top opening of the reaction tubes so that the catalyst settles in the reaction tubes and forms a catalyst bed. Considering that the sedimentation of the catalyst in light oil is different from that of conventional catalyst loading, in order to prevent the occurrence of "bridging", "channeling" and "biased flow" in the catalyst loading in light oil, in a preferred embodiment, the ratio of the diameter of the reaction tubes to the equivalent diameter of the catalyst should be 15:1-30:1, such as 25:1, preferably 15:1-20:1.

[0024] Preferably, in order to ensure the strength of the catalyst while reducing the methane selectivity of the catalyst, the cross-sectional diameter of the catalyst should not exceed 2 mm, and the cross-sectional diameter of the catalyst is preferably 1.4 mm-1.8 mm.

[0025] In a preferred embodiment, to ensure the catalyst loading effect, the catalyst loading rate (i.e., the rising rate of the catalyst bed height formed) should not exceed 10 cm / s, such as 4-6 cm / s or 8-10 cm / s, to prevent the occurrence of catalyst "bridging". In the present invention, in order to avoid the problem of overflow caused by the rise of the oil level during the catalyst loading process, the oil pressure (P) in step (2) is maintained unchanged by the pressure control valve, and the excess light oil is returned through the pressure control valve.

[0026] It is understood by those skilled in the art that, in order to prevent the catalyst from leaking, before loading the catalyst in step (3), it is well known in the art that, for example, Porcelain balls and The filling height of the porcelain balls should be consistent, for example, it can be 15-25cm, such as 20cm.

[0027] In a preferred embodiment, in step (4), after the catalyst is loaded, the oil pressure is released to normal pressure through the pressure control valve to allow the light oil to withdraw from the reaction tubes, and then the catalyst bed is purged from top to bottom with an inert gas, preferably nitrogen, to remove the light oil adsorbed on the catalyst; at the same time, since the catalyst is added to the light oil, the catalyst dust is easier to separate from the catalyst, and with the subsequent purging, the catalyst dust removal effect is significantly better.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] (1) In the present invention, the injection and discharge recovery of light oil are all carried out through the bottom of the reaction tube, the required equipment is simple, the operation is convenient, and light oil is saved; and after adding light oil, the activity of the catalyst is significantly improved compared with no addition, and the C5+ space-time yield is also improved;

[0030] (2) By adding light oil to the reaction tubes, the falling rate of the catalyst is slowed down, reducing the probability of catalyst damage. At the same time, by controlling the ratio of the reactor inner diameter to the catalyst equivalent diameter and the catalyst loading rate, the pressure drop and stacking density of the catalyst bed in multiple tubes are improved, which is beneficial to reducing the axial temperature difference, thereby improving the catalyst activity and time-space yield, and reducing the methane selectivity; under the premise of ensuring a good loading effect, the catalyst loading efficiency is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A schematic diagram of a filling device for implementing the filling method of the present invention;

[0032] Description of reference numerals:

[0033] 3-reaction tubes; 4-oil level; 5-sealing spring; 6-oil inlet pipeline; 7-oil inlet valve; 8-pump outlet valve; 9-pump; 11-cross-line; 12-pressure control valve; 13-pressure gauge. DETAILED DESCRIPTION

[0034] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention and the accompanying drawings. Obviously, the described embodiments are only embodiments of a part of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0035] Figure 1A schematic diagram of a filling device for implementing the filling method of the present invention is shown, wherein the pump outlet is provided with a pump outlet valve 8, and the pump outlet valve 8 is connected to the bottom end of the reaction tube 3 through an oil inlet pipeline 6 and connected to the pump inlet through a jumper 11; the oil inlet pipeline 6 is provided with an oil inlet valve 7, and the jumper 11 is provided with a pressure gauge 13 and the pressure control valve 12 in sequence along the logistics direction.

[0036] After cleaning the reaction tubes 3 and installing the plugging spring 5 at a distance L from the bottom, the pump 9 can be started to prepare to inject light oil into the reaction tubes; when the pump 9 is started, first, the cross-line 11 is used to ensure that the pump 9 is in a self-circulating state, and then the cross-line pressure control valve 12 is gradually adjusted to input the light oil into the reaction tubes 3. After the oil level 4 rises to a predetermined height H, the corresponding oil pressure P is recorded, and then the pump is stopped and the oil level 4 is maintained at this height H through the pressure control valve 12.

[0037] The catalyst is loaded into the reaction tubes 3 from the top opening so that the catalyst settles in the reaction tubes 3 and forms a catalyst bed, and the oil level 4 is maintained at a height by a pressure control valve. After the catalyst is loaded, the oil pressure is released to normal pressure through the pressure control valve 12 to allow the light oil to exit from the reaction tubes, and then the catalyst bed is purged from top to bottom with an inert gas, preferably nitrogen, to remove the light oil adsorbed on the catalyst.

[0038] The present invention is further described below with reference to the embodiments.

[0039] Example 1

[0040] The tube-type fixed bed reactor has 113 reaction tubes, each tube is 6m long and has an inner diameter of 25mm. Figure 1 The catalyst is loaded using the loading device shown. A plugging spring is installed 15 cm from the bottom of the reaction tube. W-20 (distillation range 120-160°C) light white oil is used as the light oil raw material. The oil is slowly injected into the tube through a centrifugal pump and a pressure control valve (back pressure valve is selected). The oil level is 5 m and the oil pressure is 35 KPa. Stop the pump. Add the following into the tubes in sequence: Porcelain balls and The porcelain balls prevent the catalyst from leaking, and the height of the porcelain balls is 20 cm. Weigh 2.3 kg of clover-type catalyst (for the preparation of the catalyst, please see Example 2 in CN201810200988.4, 4-8 mm long, 1.7 mm cross-sectional diameter, and 1.5 mm equivalent diameter) and add it to the reaction tubes in 3 batches at a rate of 4-6 cm / s. After filling, the oil pressure is reduced to zero through the back pressure valve, and N2 is purged from the top of the tubes to remove dust and clear the light white oil in the catalyst. After the purge is completed, the bed pressure drop of 113 tubes is measured and the bulk density is calculated and the data is recorded. The statistical and experimental results are shown in Tables 1, 2 and 3.

[0041] Example 2

[0042] The difference from Example 1 is that the light oil used is W-30 (distillation range is 135-170° C.), the catalyst cross-sectional diameter is 1.8 mm, the equivalent diameter is 1.6 mm, and the catalyst filling rate is 8-10 cm / s.

[0043] The statistical and experimental results are shown in Tables 1, 2 and 3.

[0044] Example 3

[0045] The difference from Example 1 is that the light oil used is W-60 (distillation range is 185-225° C.), the catalyst cross-sectional diameter is 1.6 mm, the equivalent diameter is 1.4 mm, and the catalyst filling rate is 3-5 cm / s.

[0046] The statistical and experimental results are shown in Tables 1, 2 and 3.

[0047] Comparative Example 1

[0048] The tube-type fixed bed reactor has 113 reaction tubes, each of which is 6m long and has an inner diameter of 25mm. A plugging spring is installed 15cm from the bottom of the reaction tube. Porcelain balls and The porcelain balls prevent the catalyst from leaking, and the height of the porcelain balls is 20 cm. Weigh 2.3 kg of clover-shaped catalyst (length 4-8 mm, diameter 1.7 mm, equivalent diameter 1.5 mm) and add it to the reaction tubes in 3 batches at a free fall rate of 4-6 cm / s. After loading, N2 is used to purge from the top of the tubes to remove dust from the catalyst. After the purge is completed, the bed pressure drop and bulk density of 113 tubes are measured and the data is recorded. During the purge process, it was found that there was a lot of catalyst dust, the pressure drop deviation was large, and the bulk density of the lower catalyst was significantly higher than that of the upper part, resulting in a large axial temperature difference in the tube reactor.

[0049] Comparative Example 2

[0050] The W-20 light white oil in Example 1 was replaced with a heavy diesel fraction at 300-400°C, and the rest was the same as in Example 1. Although the catalyst stacking density in the upper, middle and lower parts was relatively uniform, when the heavy diesel fraction was desorbed from the catalyst, it was found that the heavy diesel fraction had a large viscosity and was difficult to desorb from the catalyst, which not only affected the accuracy of the pressure drop measurement data, but more seriously, the residual heavy diesel fraction underwent a chemical reaction (hydrogenolysis reaction) during reduction to generate carbon deposits, resulting in fewer catalyst active sites and reduced catalyst performance.

[0051] Comparative Example 3

[0052] The cross-sectional diameter of the cloverleaf catalyst in the embodiment is increased to 3 mm, and the equivalent diameter is 2.7 mm, and the rest is the same as the embodiment. It is found that the catalyst has a larger particle size, which leads to an enhanced internal diffusion effect. Compared with CO, H2 is easier to enter the interior of the catalyst particles, resulting in a higher hydrogen-to-carbon ratio inside the catalyst particles, a larger amount of methane generated, and a smaller amount of the target product C5+.

[0053] Comparative Example 4

[0054] The catalyst addition rate of 4-6 cm / s in the embodiment was replaced by random addition, and the rest was the same as the embodiment. During the implementation, it was found that the catalyst was easy to bridge, especially the tubes with thermocouples inside, which caused multiple reworks and was very time-consuming.

[0055] It can be seen from Tables 1 and 2 that when the method of the present invention is used for catalyst loading, the pressure drop deviation of multiple reaction tubes is small, the number of rework is small, and the packing density of the upper, middle and lower parts of the catalyst bed is more uniform. It can be seen from the results in Table 3 that after the catalyst loading method of the present invention is adopted, the axial temperature difference of the catalyst bed is low, which means that the catalyst utilization rate is improved, so its CO conversion rate and the target product C5+ space-time yield are high.

[0056] Table 1 Statistics of pressure drop of 113 reaction tubes

[0057]

[0058]

[0059] Table 2 Bed bulk density

[0060]

[0061] The catalysts loaded in the examples and comparative examples were reduced under the same conditions and heated at 215°C, 3MPa, 800h -1 Fischer-Tropsch reaction was carried out under the conditions of H2 / CO=2. The axial temperature difference and experimental results are shown in Table 3.

[0062] Table 3 Axial temperature difference of reaction tubes and experimental results

[0063]

[0064] It can be seen from Tables 1, 2 and 3 that, compared with the comparative example, when the embodiment is used for catalyst loading, the catalyst loading uniformity is better, the pressure drop of the catalyst bed of different tubes can be controlled within ±5%, the catalyst stacking density is more consistent, and the axial temperature difference is lower when the catalyst performs the Fischer-Tropsch reaction; and the activity of the catalyst is significantly improved, the methane selectivity is reduced, and the C5+ space-time yield is improved.

[0065] It is easy to understand that the above embodiments are only examples for clear explanation and do not mean that the present invention is limited thereto. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from this are still within the protection scope of the present invention.

Claims

1. A catalyst loading method for a tubular fixed-bed Fischer-Tropsch synthesis reactor, the catalyst loading method comprising: (1) Clean the reaction tubes and install a plugging spring at the bottom of the reaction tubes; (2) Then, the bottom end of the reaction tube is connected to the outlet pipe of the pump, and a certain height of light oil with a distillation range of 100-230° C. is injected into the reaction tube through the pump, and then the pump is stopped and the oil level is maintained at this height through a pressure control valve provided on the crossover line connecting the pump outlet and the pump inlet; (3) loading the catalyst into the reaction tubes from the top opening of the reaction tubes so that the catalyst settles in the reaction tubes and forms a catalyst bed, while maintaining the oil level in step (2) by a pressure control valve to prevent the oil level from rising and overflowing during the addition of the catalyst to the reaction tubes; (4) After the catalyst is loaded, the light oil is discharged from the reaction tubes and recovered.

2. The catalyst according to claim 1, characterized in that In step (3), the ratio of the diameter of the reaction tube to the catalyst equivalent diameter is 15:1 to 30:1, and the catalyst cross-sectional diameter is 1.4-1.8 mm.

3. The catalyst loading method according to claim 1 or 2, characterized in that: In step (3), the catalyst is uniformly added into the reaction tube at a rate of ≤10 cm / s.

4. The catalyst loading method according to any one of claims 1 to 3, characterized in that: In step (4), after the catalyst is loaded, the oil pressure is released to normal pressure through the pressure control valve to allow the light oil to exit from the reaction tubes, and then the catalyst bed is purged from top to bottom with an inert gas to remove the light oil and catalyst dust adsorbed on the catalyst.

5. The catalyst loading method according to any one of claims 1 to 4, characterized in that: In step (1), the distance between the top of the plugging spring and the bottom of the reaction tube is 5-40 cm, preferably 10-30 cm, represented by L; Preferably, the deviation of the distance L between the top of the blocking spring and the bottom of the blocking spring in different reaction tubes is within ±3 cm, and preferably the deviation of L is within ±1 cm.

6. The catalyst loading method according to any one of claims 1 to 5, characterized in that: In step (2), the distance between the injected light oil and the upper end of the reaction tube is in the range of 100 cm to 150 cm.

7. The catalyst loading method according to any one of claims 1 to 6, characterized in that: The light oil used is selected from light hydrocarbons with a distillation range of 100°C to 230°C produced by Fischer-Tropsch synthesis, preferably light white oil with grades of W-20, W-30, W-40 or W-60.

8. The catalyst loading method according to any one of claims 1 to 7, characterized in that: The pump outlet is provided with a pump outlet valve, which is connected to the bottom end of the reaction tube through an oil inlet pipeline and to the pump inlet through a jumper line; the oil inlet pipeline is provided with an oil inlet valve, and a pressure gauge and the pressure control valve are provided in sequence along the upper side of the jumper line in the logistics direction.

9. The catalyst loading method according to claim 8, characterized in that: When the pump is started, first ensure that the pump is in a self-circulating state through the cross-line, then gradually adjust the cross-line pressure control valve to input light oil into the reaction tubes. After the oil level rises to the predetermined height H, record the corresponding oil pressure P, then stop the pump and maintain the oil level at this height H through the pressure control valve.

10. The catalyst loading method according to claim 8 or 9, characterized in that: The pump is a centrifugal pump or a diaphragm pump, and the pressure control valve is a back pressure valve.

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