Multi-section tandem type gas-liquid parallel flow bubbling reactor

Abstract

The invention relates to a multi-section tandem type gas-liquid parallel flow bubbling reactor which adopts a two-layer barrel structure, an outer barrel is a liquid channel, an inner barrel is a bubbling reactor, and the bubbling reactor is suitable for slow gas-liquid reaction easy to foam. In order to improve the reaction efficiency and prevent liquid phase backmixing, the whole bubble tower reactor is divided into a plurality of sections, the adjacent sections are separated by partition plates, and liquid overflowing from the inner cylinder of the upper section flows into the lower section through a downcomer. Gas passes through the outer barrel from the outside of the outer barrel through a plurality of parallel pipelines, is mixed with liquid flowing out of the downcomer in a rotational flow manner, and then is introduced into the inner barrel from the side wall of the bottom of the inner barrel together with the liquid. The bubbling reactor provided by the invention effectively solves the problems of liquid phase backmixing and fluid foaming, can ensure that a liquid phase obtains a high conversion rate, and can be operated under a wide range of gas / liquid flow velocity ratio.

Description

TECHNICAL FIELD

[0001] The present application relates to bubble column reactors, especially bubble column reactors with multiple stages in series. BACKGROUND

[0002] In a bubble reactor, liquid is continuous phase and gas is dispersed phase, which has the advantages of no moving parts, simple structure, large heat capacity, good heat transfer performance, easy temperature control and high safety. Multi-stage series of bubble reactors are often used in industrial cyclohexane catalytic oxidation reaction to limit the residence time of oxidation products and avoid deep oxidation of reaction products, thereby improving the selectivity and yield of target products. In addition, similarly, it can also be used for series reactions of hydrocarbon oxidation, selective hydrogenation, Fischer-Tropsch synthesis and the like.

[0003] However, when the superficial gas velocity is large, the flow pattern of the bubble reactor will enter the turbulent flow zone from the uniform bubble flow, and the gas will gather to the center of the tower, so that a low-density area appears in the center of the tower, and the liquid in the tower has a parabolic velocity distribution, i.e. the liquid in the center of the tower flows upward, and the liquid near the wall flows downward, causing circulation of the liquid in the tower. Although the circulation of the liquid phase in the bubble column is beneficial to heat and mass transfer, it causes serious backmixing. Backmixing is not conducive to reactions with series steps, which not only affects the selectivity of the reaction, but also affects the conversion rate.

[0004] Therefore, patent application CN2422041Y uses a full-section bubble sieve tray column to form an orderly arranged bubble flow in the synthesis tower, which effectively overcomes longitudinal backmixing. CN 102580630A proposes a bubble column reactor for strengthening acetylene dimerization, which is connected with a circular, rectangular or polygonal baffle on the inner wall of the bubble column, and the included angle between the lower surface of the baffle and the tower wall is 30-120 degrees to reduce the backmixing of acetylene gas. Generally, the function of the baffle is to force the fluid to flow along the baffle route to avoid short circuit. The sieve plate can effectively redistribute the liquid flow in the tower and eliminate the velocity distribution. However, when high temperature and high pressure or solid catalysts exist, the sieve plate will have problems such as sintering, clogging, thermal bending deformation, and difficult cleaning, which seriously affect the reaction.

[0005] Patent application CN 106552577 A proposes a multi-layer draft tube bubble reactor and its use method. The reactor shell is sleeved with a multi-layer draft tube to separate the reactor shell into multiple levels of annular areas and then connected in series with multiple cylinder bodies. This method significantly reduces space utilization efficiency and operational flexibility. The inner and outer annular flow baffles are prone to flow dead angles. Fluids stagnate in the dead angle area and cause local backflow, which destroys the directionality of the overall flow field and causes local backmixing. The blockage of multiple baffles causes uneven pressure distribution in the tower and differential fluctuations in the gas-liquid two-phase flow velocity. The fluid flow rate is too fast or too slow in some areas, and fluids with different residence times are prone to cross-mixing, which increases the degree of backmixing. The baffles easily cause local accumulation of liquid holdup, causing sudden changes in fluid flow state, breaking the original relatively stable plug flow trend, and causing backmixing.

[0006] In general, two measures are currently used to limit liquid backmixing in bubble columns: one is to connect multiple bubble columns in series, and the other is to add multiple sieve plates in the same bubble column for segmentation. The former method has dispersed equipment, high operating and management costs. In addition, once the liquid foams, it will affect the liquid flow between the bubble columns. The latter method cannot fundamentally prevent liquid backmixing because the liquid will flow in the opposite direction under the action of gravity. In addition, the holes on the sieve plate will promote bubble generation, which is not suitable for gas-liquid reactions in foaming systems. SUMMARY

[0007] To solve the above-mentioned problems of the prior art, the present application provides a new gas-liquid co-current bubble reactor that can obtain high conversion rate products and limit liquid backmixing. The specific technical solutions are as follows:

[0008] A multi-stage series gas-liquid co-current bubble reactor, comprising an outer cylinder and a plurality of inner cylinders arranged one after another inside the outer cylinder, characterized in that the inner cylinders are separated by partitions, other than the uppermost layer, which form the bottom of the inner cylinder, and the height of the inner cylinder is less than the distance between the two adjacent partitions; wherein the top of the inner cylinder is open, which is the outlet of the gas-liquid reaction site; the outer cylinder includes a liquid inlet pipe at the top and a gas main pipe communicating with a plurality of gas branch pipes;

[0009] A plurality of downcomers are evenly arranged along the circumference in the annular gap between the outer cylinder and the inner cylinder; liquid is input from the liquid inlet pipe and flows through the downcomers;

[0010] A cyclone mixer is arranged below the side of the inner cylinder and communicates with the downcomer, gas branch pipe, and inner cylinder.

[0011] The outlet end of the downcomer is tangentially connected to the cyclone mixer in the same tower section.

[0012] The outlet end of the gas branch pipe tangentially enters the cyclone mixer of the same tower section.

[0013] The outlet end of the cyclone mixer tangentially enters the inner cylinder of the same tower section.

[0014] A pre-distributor and / or a porous distributor are further arranged above the uppermost layer of the baffle.

[0015] Compared with the prior art, the gas-liquid co-current bubble reactor has the following advantages:

[0016] (1) A plurality of inner cylinders are arranged in the same tower body to form a multi-stage bubble tower with "up-down segmentation and stepwise overflow", a plurality of downcomers are arranged in the annular gap between the inner and outer cylinders to introduce the liquid in the previous tower section into the next tower section through gravitational potential energy, the bubble towers are connected in series, each stage has an independent reaction, the liquid phase backmixing between stages is eliminated, and the space utilization efficiency and operation flexibility are ensured.

[0017] (2) The liquid is once fed from the top of the tower, and the gas is fed from the gas branch pipes on the side of the tower. The liquid first enters the first-stage bubble tower on the uppermost layer to perform a gas-liquid reaction, releases more flow space, further reduces the gas resistance, and thus prevents the liquid phase backmixing.

[0018] (3) The prior art adopts upward feeding from the distributor at the bottom of the tower, which easily causes liquid foaming. Different from the prior art, the cyclone mixer structure of the tangential feeding of the gas and the liquid can fully utilize the potential energy carried by the fluid, and realizes the rotational flow in the three-dimensional space. Since the fluid flows spirally along the horizontal central axis and generates a certain centrifugal force, the influence of gravity can be offset, the gas-liquid stratification problem can be overcome, the gas-liquid contact area is increased, the mass transfer effect between the gas and the liquid phases is strengthened, and the foaming problem is avoided.

[0019] (4) The process has high adaptability and expandability. The multi-stage independent reaction structure design can adjust the process parameters (such as temperature and gas-liquid ratio) according to different reaction stages, and is especially suitable for reaction systems sensitive to liquid phase backmixing and requiring high conversion rate, such as fine chemical synthesis and complex catalytic reaction. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a structure schematic diagram of the gas-liquid bubble tower of Example 1.

[0021] Figure 2 is a structure schematic diagram of the gas-liquid bubble tower of Example 1, which shows the cyclone mixer.

[0022] Figure 3 is a structure schematic diagram of the single-stage bubble tower reactor in Example 1.

[0023] Figure 4is a graph showing the conversion rate of harmful substances in the treatment of wastewater using the bubble column of Example 1 versus the air flow rate.

[0024] Explanation of symbols:

[0025] 1 outer cylinder; 2 pre-distributor; 3 perforated distributor; 4 partition; 5 downcomer; 6 inner cylinder (bubble column); 7 gas main pipe; 8 gas branch pipe; 9 cyclone mixer. DETAILED DESCRIPTION

[0026] Embodiments of the present application will be described below with reference to the accompanying drawings.

[0027] Example 1

[0028] As shown in Figures 1-3 , a multi-stage series gas-liquid co-current bubble reactor includes an outer cylinder 1 and a plurality of inner cylinders (bubble columns) 6 arranged one above another inside the outer cylinder 1. The inner cylinders 6 are separated by partitions 4, the partitions 4 above the uppermost layer form the bottoms of the inner cylinders 6, and the heights of the inner cylinders 6 are less than the distances between adjacent two partitions 4. The tops of the inner cylinders 6 are open, and the gas and liquid react in the inner cylinders 6. The liquid is input from the top of the outer cylinder 1, and the outer cylinder 1 is provided with a gas main pipe 7 communicating with a plurality of gas branch pipes 8.

[0029] A plurality of downcomers 5 are arranged uniformly in the circumferential annular gap between the outer cylinder 1 and the inner cylinders 6.

[0030] A pre-distributor 2 and a perforated distributor 3 are further provided above the uppermost layer of the partitions 4. The pre-distributor 2 and the perforated distributor 3 can be exchanged in position, or one of them is provided.

[0031] A cyclone mixer 9 is provided below the side of each inner cylinder 6 and communicates with the downcomer 5, the gas branch pipe 8, and the inner cylinder 6, respectively.

[0032] The outlet end of the downcomer 5 and the outlet end of the gas branch pipe tangentially enter the cyclone mixer 9 of the same column stage.

[0033] The liquid is input from the liquid inlet pipe, first passes through the pre-distributor 2 to slow down the liquid flow and pre-distribute the liquid, then further uniformly distributes the liquid through the perforated distributor 3, reaches the first layer of partitions 4, and then tangentially enters the first cyclone mixer 9 through the first downcomer 5 on the first layer of partitions 4, while the gas tangentially enters the first cyclone mixer 9 from the first gas branch pipe 8. After the gas and liquid are mixed, they tangentially enter the first inner cylinder 6. As the liquid continuously flows in, the liquid level in the first inner cylinder 6 continuously rises, and the first-stage bubble reaction is carried out. After the liquid overflows, it reaches the second layer of partitions 4, and then tangentially enters the second cyclone mixer 9 through the second downcomer 5 on the second layer of partitions 4, while the gas tangentially enters the second cyclone mixer 9 from the second gas branch pipe 8. The same applies to the subsequent stages.

[0034] Finally, liquid and gas exit the reactor from the bottom.

[0035] Example 2

[0036] This example uses Figures 1-3 a multi-stage gas-liquid bubble reactor to treat industrial wastewater using air oxidation method with enzymes as homogeneous catalysts. Tangential mixing of gas and liquid in the reactor and multi-stage bubble reaction are used to degrade harmful substances in the wastewater into harmless compounds. The bubble column used in this example has a three-stage series structure. Other multi-stage series structures such as two-stage and four-stage can also be used according to actual needs such as industrial wastewater treatment capacity and harmful substance concentration.

[0037] In the experiment, the wastewater flow rate was fixed at 0.16 m 3 / h, and the concentration of harmful substances was about 10 mol / m 3 . The air flow rate was adjusted for gas-liquid bubble reaction. To study the effects of gas-liquid mass transfer area and liquid phase residence time on the reaction, a three-stage series bubble bed was used for testing. The bed height was two kinds, 0.40 m and 0.6 m, and the total volume of the bubble bed was 0.35 m 3 and 0.52 m 3 , respectively, and the liquid phase residence time was 2.2 h and 3.3 h, respectively. The measured conversion rate of harmful substances at the reactor outlet as a function of gas flow rate is shown in Figure 4 . It can be seen that increasing the gas flow rate and increasing the volume of the bubble column are beneficial to increasing the conversion rate, but the conversion rate increases slowly when the gas flow rate is large.

[0038] When the air flow rate is small, the oxygen supply cannot meet the needs of the reaction, so the conversion rate of harmful substances is low. After increasing the air flow rate, the conversion rate increases significantly. When the air flow rate continues to increase, the conversion rate increases slowly, because the solubility of oxygen is very low, and the increase in air flow rate shortens the gas residence time, and the oxygen cannot be dissolved before leaving the reactor.

[0039] The volume of the reactor has a great effect on the conversion rate of the reaction, which is mainly due to the change in the liquid phase reaction time. When the volume of the reactor is small, even if the air flow rate is large, it is also difficult to achieve a high conversion rate.

[0040] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent replacements to some technical features, as long as they are within the spirit and principles of the present application. Any modification, equivalent replacement, improvement, etc. made within the scope of the present application should be included in the protection scope of the present application.

Claims

1. A multi-stage series gas-liquid co-current bubble reactor comprising an outer cylinder and a plurality of inner cylinders arranged one above the other inside the outer cylinder, characterized in that, The inner cylinders are separated by partitions, other than the uppermost layer, which form the bottom of the inner cylinders, the height of the inner cylinders being less than the distance between two adjacent partitions; the top of the inner cylinders being open; The outer cylinder comprises a liquid inlet pipe at the top and a gas main pipe communicating with a plurality of gas branch pipes; A plurality of downcomers are arranged uniformly in the annular gap between the outer cylinder and the inner cylinder; liquid is input from the liquid inlet pipe and flows through the downcomers; A cyclone mixer arranged below the side of the inner cylinder communicates with the downcomers, the gas branch pipes and the inner cylinder respectively.

2. The bubble column reactor according to claim 1, characterized in that The outlet end of the downcomer is tangentially connected to the cyclone mixer of the same tower section.

3. The bubble column reactor according to claim 1, characterized in that The outlet end of the gas branch pipe is tangentially connected to the cyclone mixer of the same tower section.

4. The bubble column reactor of claim 1, wherein The outlet end of the cyclone mixer is tangentially connected to the inner cylinder of the same tower section.

5. The bubble column reactor of claim 1, wherein, A pre-distributor and / or a perforated distributor are further arranged above the uppermost layer of the partitions.

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