RU2268086C2 - Countercurrent segmented gas-lift reactor for gas-liquid processes - Google Patents

Abstract

FIELD: chemical industry; heat engineering; apparatuses for realization of the gas liquid chemical processes and heat-exchange and mass-exchange processes.

SUBSTANCE: the invention is pertaining to the apparatuses for realization of the gas liquid chemical processes and heat-exchange and mass-exchange processes with a great release or absorption of heat, in particular, the processes of liquid-phase oxidation of alkyl aromatic monocarboxylic and polycarboxylic acids. The invention presents the reactor consisting of the vertical cylindrical body partitioned in height by horizontal planar septums with holes into sections containing the bundles of the barbotage and circulation pipes fixed on the pipe plates, the fitting pipes for the reactants and heat-carrying agent feeding in and withdrawal. Between the sections there are the separating devices made in the form of the reflective funnels with holes in the center, in internal cavities of which there are the dipped barbotage cylinders and the circulation fitting pipes fixed on the horizontal septums in such a manner that the barbotage cylinders are mounted in the center are established, and the circulation fitting pipes are placed in symmetry outside the barbotage cylinders. At that the bottom parts of the barbotage cylinders located under the horizontal septums have a perforation in the form of slits or holes, and upper parts of the barbotage cylinders located above the horizontal septums are supplied with the heads made in the form of bundles of upright tubes, pellets or perforated plates creating in them resistance to the up-going gaseous current. The invention allows to increase productivity of the reactor by decreasing dispersion of duration of liquid reactants presence in the segmented reaction zone, as well as to raise the hydrodynamic efficiency and stability of the reactor operation due to organization of the discrete gas separation from the gas-saturated liquid in conditions of the countercurrent motion of the gas and the liquid in height of the reactionary volume.

EFFECT: the invention ensures an increase of productivity of the reactor, its hydrodynamic efficiency and stability of operation.

3 cl, 6 dwg, 1 tbl

Description

The invention relates to chemical technology, namely to apparatus for carrying out gas-liquid chemical and heat, mass transfer processes with large heat generation or absorption, in particular processes of liquid-phase oxidation of alkyl aromatic hydrocarbons to aromatic mono- and polycarboxylic acids.

Known shell-and-tube gas lift reactor (KGR) for carrying out gas-liquid reaction processes, for example for the oxidation of p-xylene and other alkylbenzenes (ed. Certificate. No. 129643, bull. Invention No. 13, 1960, authors: Sokolov V.N., Gellis Yu .TO.).

The reactor is a tubular heat exchanger with an enlarged upper separation part. The essence of the reactor device is as follows: the ends of the tube bundle are brought out under the lower tube sheet to a length l = (4,5-5) d, where d is the inner diameter of the pipes. All pipes are divided into bubble and circulation. In the walls of the protruding ends of the bubble tubes at a distance l = 4d from the lower cut, holes are drilled strictly at the same level. When oxygen-containing gas is supplied to the apparatus filled with the reaction mass, a gas layer forms under the lower tube sheet, from which gas enters the bubble tubes through the holes.

The design of the apparatus provides intensive circulation of the reaction mass arising due to the difference in density between the pure liquid in the circulation pipes and the gas-liquid mixture in the bubblers. The apparatus can be effectively used in hydrocarbon oxidation processes with high heat generation (in exothermic reactions). The generated heat is removed by supplying refrigerant to the annulus, and a predetermined temperature is maintained in the reactor throughout the reaction volume. As in the previously known designs of the reaction apparatuses, the essential disadvantages of the described shell-and-tube gas-lift reactor are:

1) An explosive concentration is created in the gas space under the lower tube sheet during the oxidation of a hydrocarbon by air or oxygen, which limits its use.

2) The low coefficient of useful volume of the reaction zone due to the fact that approximately half of it is occupied by the annulus where the coolant or refrigerant is supplied.

3) The device allows you to work only in the direct flow of oxidizing hydrocarbon and oxygen-containing gas, which does not allow to realize the well-known advantages of the countercurrent.

4) In the reactor it is possible to maintain one predetermined temperature regime throughout the reaction zone, although in the vast majority of cases, for example, during the oxidation of polyalkylbenzenes, as the reaction depth increases, a change in the temperature regime is required, since the reactivity of the initial hydrocarbon and intermediate products can vary within wide limits (1.5-5 times). This greatly reduces the performance of the reactor.

5) The presence of a large number of holes in the lower part of the bubbler pipes for gas passing through them does not allow the apparatus to be used in processes accompanied by the formation of crystallized and precipitated reaction products or catalyst due to clogging of these holes and violation of the hydrodynamic parameters of the reactor.

A device is known for a gas-lift apparatus for carrying out gas-liquid chemical and heat, mass transfer processes with high heat generation (RF patent 2040940, bull. No. 22 from 08/09/95, author: Savelyev N.I., Zharikov L.K., Zharov I.F., Savelyeva L.A., Nikolaev E.G., Militsin I.A., Shkurko V.G.). The gas-lift apparatus comprises a vertical cylindrical body with a bundle of bubblers and circulation pipes and tube sheets, an upper chamber with vertical plates, a lower chamber with a gas distribution device, fittings for supplying and discharging reagents and a coolant. A distinctive feature of the apparatus is that the gas distribution device is made in the form of a horizontal partition with holes, the axes of which coincide with the axes of the bubble tubes, vertical bridges are installed between the partition and the lower tube sheet, offset from the vertical plates in the upper chamber with the formation of a multi-pass channel for the fluid to move from inlet to outlet.

In the specified gas-lift apparatus, a decrease in the dispersion of the residence time of the liquid reagent is achieved by organizing its multi-way movement through the working area. Due to the presence of new elements in the apparatus, not only multi-way fluid movement is realized, but also its circulation through bubbled and circulation pipes is localized.

The proposed gas-lift apparatus has a number of disadvantages inherent in the previously described device shell-and-tube gas-lift reactor, namely:

- low coefficient of net volume of the reaction zone, because approximately half of the volume is occupied by the annulus where the coolant is supplied;

- it is impossible to ensure the operation of the device in countercurrent conditions, because in about half of the bubbler pipes, the gas and liquid flow are straight-through, which does not allow to realize the known advantages of the counterflow;

it is possible to maintain one predetermined temperature regime in the apparatus throughout the reaction zone, which does not allow physicochemical processes to be realized in it, for example, the liquid-phase oxidation of methylbenzenes to benzene-polycarboxylic acids, which require different temperature limits at the initial and final stages of the reaction transformations.

Closest to the claimed reactor is known from the patent of the Russian Federation No. 2147922 (bull. No. 12, 04/27/2000, author: Potekhin V.M., Ivanov V.A., Domansky I.V. and others.) The reactor for liquid-phase oxidation of hydrocarbons, consisting of a vertical cylindrical body with internal circulation pipes, elements for supplying and removing heat, pipes for the input and output of liquid reagents and gas. The internal cavity of the housing is divided in height by horizontal partitions with holes in sections, in each of which a bubbler pipe is installed, the upper section of which is located under the upper annular partition, and the lower section above the lower ring partition at a distance that ensures the movement of the liquid phase from the bubbler pipe into the circulation pipes fixed in tube sheets.

The reactor operates as follows. The initial reaction mixture (IRS), consisting of the components of the catalyst and hydrocarbon dissolved in it, is continuously fed into the upper section of the reactor through the inlet of the IRS, which is lowered down the bubbler pipe, and is distributed in the reaction volume over the holes located along the height of the pipe. Oxygen-containing gas, such as air, is supplied to the lower section of the reactor through an air inlet. The start of the reactor begins after filling the reactor with the reaction mixture and heating it in an inert gas atmosphere. The reaction mixture is heated by supplying a coolant to the annulus of the shell-and-tube heater of the lower section.

The air introduced through the Teflon nozzle into the lower section of the reactor enters the bubbler pipe, creating an airlift effect as it moves from bottom to top, causing circulation of the reaction mass along the circuit: upper cavity of the bubbler pipe → separation cavity above the bubbler pipe, limited by an annular partition and the tube sheet, circulation pipes → lower cavity of the section → lower cavity of the bubbler pipe. The gas-liquid mixture emerging from the inner cavity rises up to the annular partition, the cross-sectional area of which is equal to or less than the cross-sectional area of the bubbler pipe. As a result of this, the gas-liquid flow experiences resistance to its rise upward and is partially separated.

The gas bubble torch, having passed a hole in the annular partition, enters the lower zone of the upper section by a countercurrent reaction mass moving from top to bottom from the above sections, and then into the bubbler pipe of the upper section of the reactor. The reaction mass discharged from the lower section of the reactor is subjected to cooling, followed by isolation of the desired products by known methods, and the exhaust gas from the upper section is cooled and subjected to purification after separation of the water-vinegar condensate. The proposed reactor has several advantages. Due to the presence of annular partitions and their arrangement as new elements in comparison with the known reaction apparatus described above, longitudinal mixing between sections is limited, the volume of local separation zones under the annular partitions is minimized, which prevents the possibility of explosion of a vapor-gas mixture under conditions of increased oxygen concentration. This in turn allows one to increase the concentration of the oxidizing agent O ₂ in the lower sections, i.e. at the final stages, limiting the rate of reaction transformations, from 5% to 12-20% and intensify the process. In addition, the design of the reactor allows you to use the known advantages of the counterflow of liquid reagents and gas (vapor-gas) mixtures.

At the same time, the reactor under consideration has drawbacks, the essence of the main ones is as follows: a separation device created by an annular partition with a hole and bounded below the tube plate of the wall of the reactor vessel is inefficient and does not provide stability of the hydrodynamic regime in the reactor. This is due to the fact that a pulsating regime of piston-like gas movement from bottom to top occurs in the hole of the annular partition, i.e. from the lower sections to the upper ones due to the enlargement (association) of gas bubbles to sizes commensurate with the cross-section of the bubbler pipe of the upstream section, and, as a result of this, the appearance of an uncontrolled pulsating outflow of liquid reagents from top to bottom, i.e. from the upper sections to the lower. The mixing of liquid reagents between sections occurs much faster than is required by the time of their stay in each section to achieve the necessary degree of conversion of reagents at specific concentration and temperature parameters of oxidation that are predetermined and do not coincide in sections. Under these conditions, the dispersion of the residence time of liquid reagents in the working area of a partitioned reactor can increase to a value close to the maximum, which in turn will significantly reduce the efficiency of the reactor.

The aim of the invention is to increase the productivity of the reactor by reducing the dispersion of the residence time of liquid reagents in a partitioned reaction zone and increasing the hydrodynamic efficiency and stability of the reactor by organizing discrete separation of gas from a gas-filled liquid under conditions of countercurrent movement of gas and liquid along the height of the reaction volume.

This goal is achieved by the fact that in the reactor, consisting of a vertical cylindrical body, divided in height by horizontal flat partitions with holes in the sections containing bundles of bubbler and circulation pipes fixed to the tube sheets, pipes for the input and output of reagents and coolant, in addition between the sections Separation devices are installed, made in the form of reflective funnels with holes in the center, into the internal cavities of which bubbler glasses and circulation branch pipes mounted on horizontal partitions in such a way that the bubble tubes are installed in the center, and the circulation nozzles are located symmetrically outside the bubble bottles, while the lower parts of the bubble glasses under the horizontal partitions have perforations in the form of slots and holes, and the upper parts of the bubble glasses above the horizontal partitions equipped with a nozzle that creates resistance to them in the upward gaseous flow, in the form of bundles of vertical tubes, granules or perforated plates in. Moreover, between the horizontal flat partition and the upper section of the reflecting funnel, vertical partitions are installed with a length less than 0.5 of the radius of the funnel in the form of flat blades tangentially overlapping the upper section of the funnel at an angle of 45 ° with respect to the radial line, and the lower sections of the circulation pipes are located below the horizontal plane, secant bubbling glasses at the top of the perforated sections.

The list of figures drawings.

Figure 1. Scheme of a counterflow sectioned gas-lift reactor (cross section).

Figure 2. Reactor model diagram.

Figure 3. Graph of tracer concentration versus time for sections of a reactor model.

Figure 4. Graph of tracer concentration versus time for sections of a reactor model (comparative example).

Figure 5. Scheme of the reaction unit.

6. A graph of the change in tracer concentration versus time for sections of the reactor in the reaction unit.

Figure 1 shows a cross section of a countercurrent sectioned gas-lift reactor. The latter includes a vertical cylindrical housing 1, divided in height by horizontal partitions 2 into a series of sections C1, C2, C3, equipped with bubblers 4 and circulation 3 pipes fixed in tube sheets 5, reflective funnels 6 with holes in the center 7, into the inner cavity of which are lowered bubbling glasses 8 and circulation nozzles 9, mounted on horizontal partitions and located so that the bubbling glasses are installed in the center, and the circulation nozzles are symmetrically different from the outside of the glasses to a friend.

The lower part of the bubbler glass under the horizontal partition has perforations in the form of slots or holes 10, and the upper part of the bubbler glass above the plate is equipped with a nozzle 11 in the form of rings or a bundle of vertical tubes. Between the horizontal partition and the upper section of the reflecting funnel, vertical partitions 12 are installed in the form of flat blades tangentially overlapping the upper section of the funnel to a depth of not more than 0.5 of the radius of the funnel at an angle of 45 ° with respect to the radial line.

The upper section of reactor C1 is equipped with fittings A for the inlet of the initial reaction mixture containing hydrocarbon, B for the outlet of the exhaust gases, and C and D for the inlet and outlet of the coolant. The middle section of reactor C2 is equipped with fittings D for introducing catalyst components, as well as fittings B and D for entering and leaving the coolant. The lower section of the reactor C3 is equipped with a gas distributor 13, fittings B, D for the input and output of the coolant, E for the introduction of gas, as well as a fitting Zh for the output of reaction products.

Countercurrent sectional gas-lift reactor operates as follows. After filling the reactor with a mixture of liquid reagents, subject to chemical or physical transformations involving gas, gas is supplied to the lower part of section C3 through nozzle E, which, passing through the gas distributor 13, enters the bubbler pipes of the lower section C3. In them, he interacts with the fluid and draws it into the upward movement. The ascending gas-liquid flow exiting the bubble tubes 4 of the lower section reaches the outer surface of the reflecting funnel 6 and then the conical surface of the funnel directs it into the separation space bounded on the sides by the wall of the reactor 1 and the outer conical surface of the reflecting funnel 6, and on top by a horizontal partition 2.

The liquid stream with a part of the bubbles enters the circulation pipes and moves along them down the section C3, where the upward gas stream is again drawn into the upward movement through the bubbled pipes, closing the continuous circuit of the liquid circulation.

Partially separated from the liquid, a gas-liquid stream in the form of enlarged gas bubbles fills the cavity bounded above by a horizontal partition, from below by the upper cut of the reflecting funnel, on the sides by the outer surface of the bubblers and circulation tubes, as well as the inner surface of the reactor vessel. Squeezing the liquid to the level of the cracks in the bubblers, the gas-liquid flow swirls around the bubblers with the help of tangentially arranged plates installed above the reflective partition and, additionally separating from the liquid, enters the internal cavities of the bubblers and then, passing the nozzle, enters in the form of gas bubbles in bubbling pipes 4 of the upper middle section C2.

The liquid flow from the upstream section C2 through the circulation tubes enters the internal cavity of the reflecting funnel 6 and then is drawn into the upward movement by the gas flow in the bubbler glasses, which returns the liquid to the upstream section and thereby closes the local liquid circulation circuit: the upstream section → the downstream reflecting funnel sections → upstream section.

Similarly, the countercurrent movement of liquid and gas occurs in the remaining sections.

In order to maintain the required temperature in each section, the coolant is supplied and removed to the annular space of the shell-and-tube heat exchangers through fittings B and D. Depending on the nature of the physical or chemical process (exothermic or endothermic), heat is removed or supplied through the heat transfer surface of the shell-and-tube heat exchangers by changing the flow of heat carrier.

After the completion of physical or chemical processes, the resulting product in the form of a solution or suspension is discharged from the lower section C3 through the nozzle G and then processed and emitted by known methods, and the exhaust gas is removed from the upper section C1 through the nozzle B and then subjected to the necessary working out (cooling, cleaning and etc.) known techniques.

The following is a comparison of the effectiveness of the application proposed by the present invention, the reactor and known reaction apparatuses on the examples of physical and chemical processes.

Example 1. In a glass physical model of the reactor (figure 2), consisting of 3 sections (case diameter 150 mm, total height 2.5 m, working volume 40 l), the device of which corresponds to the present invention, an aqueous solution of acetic acid is fed and chromium acetate with a space velocity of 0.2 l / min. After filling the reaction volume, open the control valve at the outlet of the liquid solution from the lower section so that the amount of the introduced reaction solution is equal to the amount of liquid removed from the reactor and the height of the liquid column in the separation zone of the upper section C1 is at the same level. In the lower section C3 of the reactor through the nozzle E serves gas (air) in an amount of 40 nl / min, ensuring a reduced linear velocity of at least 2 m / s. The exhaust gas is removed from the upper section C1 through the nozzle B, subjected to cooling and purification. After establishing a stable hydrodynamic regime in all sections of the reactor and stabilizing the costs introduced into and leaving the reactor of liquid and gas flows, the control valve on the supply line of the reaction solution is closed and at the same time the valve is opened to supply the watered solution of acetic acid without chromium acetate. The change in chromium concentration over time in all three sections was determined by the spectral method on a spectrophotometer by sampling every 5 min and analyzing them. The main objective of the experiment:

- to establish the nature of the curves of changes in the concentration of chromium in each section over a period of time of continuous washing out under conditions of a counterflow of gas and liquid;

- determine the degree of longitudinal mixing in the liquid and gas phase in countercurrent conditions;

- experimentally confirm the degree to which the dispersion of the residence time of the liquid components in each section and in the reactor as a whole is minimized;

- to assess the feasibility of providing in each section local, independent concentration and temperature parameters required by a chemical or physical process.

The results are shown in figure 3. As can be seen from the results, each section of the reactor under the conditions of countercurrent passage of gas and liquid through them performs the functions of localized mixing apparatuses, which make it possible to maintain the required technological parameters of chemical and physical processes in them.

The data presented indicate that the longitudinal mixing of the liquid reactants between the sections and the dispersion of the residence time of the liquid reactant in the reactor are minimized.

Example 2. A comparative experiment is carried out in a glass model of the same size and by the same methodology as in example 1, with the only difference that the reactor device corresponds to the previously known invention (patent No. 2147922, RF, 2000), t. e. without separation devices.

From the results obtained (Fig. 4), it follows that after almost 6-8 minutes, the concentration of the analyzed component (chromium) in all sections is leveled and the proposed design, as a result of a high degree of longitudinal mixing of the liquid phase between the sections, approaches a single gas-lift reactor.

Example 3. The experiment is carried out in a 3-section reactor made of titanium alloy VT1-0, the device of which corresponds to the present invention. Dimensions of the reactor: diameter - 330 mm, height - 14 m. Total working volume - 300 l.

To conduct the experiment using a pilot plant with a countercurrent gas lift reactor, the strapping scheme of which is presented in figure 5. In the collector E1, an acetic acid solution of chromium acetate is prepared, which is pumped into the countercurrent gas lift reactor in the upper section. Gas (air) is supplied to the lower section. The drainage of the liquid containing the analyzed component of the reaction mixture (chromium acetate) is carried out in the collection E6.

After achieving a steady hydrodynamic regime and a stable liquid level in the upper section of the reactor, samples are taken from each section and the chromium concentration is determined. Next, the collector E1 is turned off by closing the valve on the output line of the chromium acetate solution and turn on the supply of the acetic acid solution (without chromium acetate) from the collector E2, resulting in a decrease in chromium in time in each section. [Cr] control is carried out by analysis of samples taken every 10 min from each section. The results of example 3 are shown in Fig.6.

From the obtained results of example 3 it follows that all sections of the countercurrent gas lift reactor, by the nature of the change in their concentrations of the analyzed component (Cr) in the liquid phase, perform the functions of flow-through complete mixing apparatuses installed in series.

Example 4. The experiment is carried out in a pilot plant (Fig. 5) using the chemical process of liquid-phase catalytic oxidation of pseudocumene in an acetic acid medium.

An acetic acid catalyst solution containing soluble salts of heavy metals, for example, Co, Mn, Ni acetates and hydrobromic acid (HBr), is prepared in a collector with a stirrer and heated jacket E1 and then pump H3 is fed into reactor P4 to fill 70% of the total reaction volume . After filling the reactor, the coolant is fed into the annulus of the lower section and the solution in the reactor is heated to 160 ° C with an inert gas flow through all sections of the reactor. After reaching the indicated temperature, the feed of the initial reaction mixture containing pseudocumene is switched on, and air is supplied instead of inert gas. The required temperature in each section is supported by heat removal in the upper and lower sections due to evaporation of water supplied to the annular space of the heat exchangers of the upper and middle sections, in the lower section - by supplying heat by supplying a heat carrier (BOT) to the annular space of the heat exchanger of the lower section.

The reaction products are removed from the lower section to a collector E6 with a mixer, where, if necessary, gas (air) is supplied, and then they are sent for processing to trimellitic acid anhydride through an airlock E9. The exhaust gases are removed from the upper section of the countercurrent gas lift reactor, which, after cooling in the condensers T51, T52 and purification, are discharged into the atmosphere. To ensure the activity of the catalytic system, a solution of hydrobromic acid is fed into the middle and lower sections of the PGR.

The results of example 1 are shown in the table.

Table
Distribution of concentrations and temperature in sections of the reactor. Section Number C1 C2 C3 The concentration of pseudocumene in the liquid phase,% weight 0.9 0.2 traces The concentration of trimellitic acid in the liquid phase,% weight 11,4 38.8 40.8 Temperature ° C 176 181 188

Thus, an advantage of the claimed invention is to increase the productivity of the reactor by reducing the dispersion of the residence time of liquid reagents in a partitioned reaction zone and increasing the hydrodynamic efficiency and stability of the reactor by organizing discrete separation of gas from a gas-filled liquid under conditions of countercurrent movement of gas and liquid along the height of the reaction volume.

Claims (3)

1. Countercurrent sectioned gas-lift reactor for gas-liquid processes, consisting of a vertical cylindrical body, divided by height of horizontal flat partitions with openings into sections containing bundles of bubbler and circulation pipes mounted on tube sheets, pipes for the input and output of reagents and coolant, characterized in that between the sections there are separation devices made in the form of reflective funnels with holes in the center, in the internal cavities of which puppies have bubblers and circulation nozzles fixed to the horizontal partitions so that the bubblers are installed in the center, and the circulation nozzles are symmetrically outside the bubblers, while the lower parts of the bubblers under the horizontal partitions have perforations in the form of slots or holes, and the upper parts bubbling glasses above the horizontal partitions are equipped with a nozzle that creates resistance in them to an upward gaseous flow, in the form of beams vertically flax tubes, granules or perforated plates. 2. A counterflow sectioned gas-lift reactor for gas-liquid processes according to claim 1, characterized in that between the horizontal flat partition and the upper cut of the reflective funnel, vertical partitions are installed with a length less than 0.5 of the funnel radius in the form of flat blades tangentially overlapping the upper funnel cut at an angle of 45 ° with respect to the radial line. 3. Countercurrent sectioned gas-lift reactor for gas-liquid processes according to claim 1 or 2, characterized in that the lower sections of the circulation pipes are located below the horizontal plane, cutting bubblers at the upper points of the perforated sections.

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