NL8301737A - Two=stage reactor having vessel contg. annular catalyst bed - with plug between stages, radially outward flows, heat exchanger, and feed mixer - Google Patents

Abstract

Catalytic reactor comprises a vertical cylindrical vessel with inlets for the reactants and outlets for the reaction prods. and contg. an annular catalyst bed divided by a plug into an upper and a lower section through which the reactants pass in radially outward direction. A heat exchanger pre-heats the initial feed stock using the reactants from the first section before these pass into the second section. The bed is contained between concentric outer and inner perforated walls, the inner space contg. a body dividing this space into an upper first-stage and a lower second-stage feed chamber. The initial feed stock leaving the exchanger passes through an external line to a mixer receiving further reactant. The flow from the first section moves through annular passages and via the exchanger tubes, the chamber and the section to separate annular passages and the outlets. Catalytic two-stage reactor with heat exchanger between the stages to pre-heat initial feed stock and act as inter-cooler of reactants between the stages.

Description

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Catalytic reactor.

The invention relates to a catalytic reactor, comprising a vertical, elongated and cylindrical reaction vessel with reactant fluid inlets and outlets, and within that vessel a heat exchanger and two superimposed annular catalyst beds, which flow through in radial direction, as well as a heat exchanger and connecting pipes.

Such a reactor is known from French patent 2,001,518. This patent describes a reactor for ammonia synthesis from nitrogen and hydrogen at high temperature and high pressure, with two or more sequentially run through catalyst beds. In such processes, it is important that the pressure drop across the beds remains small and that the temperature variations in the different beds are limited so that shifting of the equilibrium in an undesired direction is avoided. This can be promoted, inter alia, by heat exchange between supply and partially converted gas and, if necessary, with other fluids. The reactor described there also contains some catalyst beds in the form of a hollow cylinder within the sleeve, while the mixture to be converted is passed through these catalyst layers several times by means of baffles: from the inside to the outside and from the outside to the inside. Heat exchangers are also arranged in that reactor and partly in the catalyst beds themselves in order to control the temperature as well as possible.

However, the construction described there is quite complicated, and this leads to serious difficulties in exchanging the catalyst when its effectiveness has been reduced too far.

French Patent 1,293,205 also describes a catalytic reactor, for example for cracking, reforming or isomerizing gas phase hydrocarbons. A perforated wall is provided within the sleeve at a short distance from the outer wall, which boundary is the catalyst space. A perforated feed pipe and a perforated discharge pipe are arranged in line in the center of the sleeve.

The gases are then fed radially from the feed tube through the catalyst to the outer annular space and from there flow through the lower portion of the catalyst to the exhaust tube. A 55 heat exchanger is often unnecessary in such a process and 8301737 A * -2- it has not been described either. In a variant of this reactor, it has been indicated that the catalyst space is divided by a horizontal metal wall into a lower and an upper part. However, such a partition wall again causes difficulties when replacing the catalyst.

British patent specification 1,140,071 describes a catalytic reactor which is provided with a centrally placed heat exchanger and an annular catalyst space placed around it. This catalytic converter room is divided by radial walls into two or more sec- tors which are passed through consecutively, while the gases passed through in the heat exchanger can be cooled or heated up before passing through a sector.

Besides the mentioned constructions of catalytic reactors, many variations thereof are also known.

A problem with all such reactors is that the catalyst beds are located within the reactor shell and access to it for fresh catalyst replacement is both difficult and expensive, and the downtime can be significant. In many catalytic systems, a separate unit is used for each stage. For example, for a two-stage reaction, two reactors are used with an intermediate heat exchanger used to preheat feed from the first stage. If more than one reactant is present, a separate mixer can be used. For large volume systems such as low pressure or vacuum phase dehydrogenation, where temperatures are very high, the connecting lines present large thermal expansion problems, leading to large pressure drop and excessive residence times. It is further known that in systems where undesired side reactions can take place, a residence time outside the catalyst bed leads to reduced yields of the desired product and to feed losses.

A reactor designed for easier maintenance is described in US Pat. No. 3,475,136. Most of the catalyst is thereby removed by gravity flow through downcomers communicating with each basket, but the remainder must be removed manually.

Double walled tubes are placed in the catalyst bed in the reactor, described in U.S. Pat. No. 3,459,511, wherein 8301737 * + -3 cooling gas is passed through the inner tube and feed gas is distributed through openings in the outer tube. There are many patents which describe reactors of the integral heat exchange type in addition to those just mentioned. United States Patent 3,472,631 5 describes a horizontal reactant flow through the catalyst beds with cold stores on both sides. A common feature consists of a cold feed bypass flow which can be used to control the "hot spots" in the catalyst bed, as described in U.S. Pat. No. 3,475,137. Other typical integral heat exchanger reactors are described in U.S. Pat. Nos. 3,366,461 and 3,372,988.

According to the invention, a catalytic reactor of the type described in the preamble comprises an elongated, annular catalyst bed (26) concentric with the vessel, which bed is enclosed between an outer perforated wall (28) and an inner perforated wall (30). ), which bed is divided by one or more plugs (34) into a first stage (20) and a second stage (22), the space within the wall (30) being divided by a filler body (72) into a first ( 50) and a second (48) supply chamber, while further inlet (10) is connected to supply chamber (50) via the heat exchanger (12), a conduit (14) mounted outside the reactor vessel and mixer (16), and outside the perforated wall (28) chambers (54a, 56B) plates (71) and openings (68, 70) are provided to direct the fluid discharge from the first stage through heat exchanger (12) and the second supply chamber (48) to the second catalyst stage (22) and chambers (54B, 56A), plates (71) and openings (68, 70) to allow fluid from the second stage to the outlet (24).

Figure 1 schematically illustrates a two-stage catalytic reactor system with an intermediate supply-exhaust heat exchanger and pre-reaction mixing. As indicated, a feed stream 10 is passed through the core side of a heat exchanger 12 in heat exchange ratio with the effluent from the first stage catalytic bed 20 passing through the tube side of the heat exchanger 12. The preheated feed in conduit 14 is fed to mixer 16 and mixed with a second feed in line 18.

The combined stream is then passed through the first stage catalytic bed (20), the tube side of heat exchanger 12, and the second stage (22) catalytic bed (22), respectively. A product stream 24 is discharged from the catalyst bed 22 to a reprocessor. It will be understood that when such a system is constructed from individual units, numerous connection lines are required with associated thermal expansion problems, large pressure drops and long residence times. Even a system in which, for example, the mixer 16 is integral with the first stage 20, and the exchanger 12 is integral with the second stage 22, would require multiple external connections.

Figure 2 schematically illustrates the general arrangement and flow patterns for a two-stage reactor R according to the invention, in which all the functions shown above are performed with a single vessel, which is only dotted for clarity in Figure 2.

The invention is based at least in part on the use of a single catalyst bed 26, in the form of a cylinder with an outer perforated wall 28, an inner perforated wall 30 and a catalyst 32 filling the space therebetween. This bed is divided into a lower zone constituting the first reaction stage, generally designated 20 and an upper zone constituting the second reaction stage, generally designated 22. The heat exchanger 12 is integral with reactor R and is placed at one end of the catalyst bed 26, while mixer 16 is placed at the other end thereof. (It will be understood that the reactor can also be designed upside down, but in Fig. 2 the heat exchanger 12 is placed at the top end). In operation, the reactants are fed into conduit 10 and passed through the core side of heat exchanger 12 and from there through conduit 14 to mixer 16. A second reactant may or may not be added to mixer 16 at 18 as shown by the dashed flow lines the reactants 30 from mixer 16 upwardly through the space, defined by filler body 72 and inner wall 30, and radially outwardly through the lower, first reaction zone 20. The reactants and the reaction products of the first stage are then introduced into upward through an annular channel to the top of the reactor where they enter the tube side of heat exchanger 12. From heat exchanger 12, the reactants flow back into the space defined by filler body 72 and inner wall 30, but now flow downward rather than upward. The reaction components flow out radially through the upper, second stage reaction zone 22, in a second annular form, in a radial direction. channel, after which they are removed from the reactor through outlet 24. The catalyst 32 is exchanged by dropping spent catalyst from the bottom of bed 26 under the influence of gravity and feeding fresh catalyst at the top. Since, according to the invention, only a single bed 26 is used for both reaction stages, it is necessary to ensure that the reactants flow in radial outward direction through them and not down or up, which would lead to mixing of first and second stage reaction components. nents. This is accomplished by inserting horizontal plugs, designated 34, along with the catalyst so that plugs are periodically present in the column and provide a "neutral zone" between the upper and lower stages where the reactants cannot enter radially, and which is long enough to have a plug in it at all times. A simplified vertical cross-section of a reactor R according to the invention is illustrated in Fig. 5. A pressure vessel 36 is constructed such that it is suitable for the intended use of the reactor R. The reactor R is provided with a removable cover 38, a 20 number of inlet openings 4 (1 to introduce the catalyst at the top and a number of outlet openings 42 at the lower end to discharge the catalyst. The arrangement of internal parts is generally similar to that shown schematically in Figure 2 and the same reference numerals have been used It will be seen that a difference between FIG. 2 and FIG. 3 is that what is placed in FIG. 2 above is in FIG. 3 just below, with the exception, of course, of the intermediate and discharge openings. In particular, the heat exchanger 12 is of a general construction, the core side of which is in communication with the inlet pipes 10 and at the top end with a pipe 14. D The line 14 has a length almost equal to the total length of the reactor and is mounted outside the reactor vessel. The top end of line 14 communicates with a mixing zone 16, where a supply line 18 for a second reaction component also exits. It can be seen that a filler body 72 is placed in the central portion of the bath structure at the neutral zone so that the space between the inner wall 30 of the catalyst bed is divided by this filler body 72 into an upper chamber 50 and a lower chamber 48, which correspond with the 8301737 „λ -6- second and first reaction zones adjacent to each other, respectively.

The outer surface of filler body 72 is preferably formed to act as a deflector of the reactants to the catalyst 32 so that the bed is used evenly. Between the catalyst bed 32 and the inner wall of the pressure vessel 36 is arranged an annular inner wall 52 which divides the available space into two approximately equal, annular chambers 54 and 56. Both chambers 54 and 56 are divided into upper and lower sections, the lower parts being indicated by B and the upper parts by A. At the level 10 of the neutral zone 34 there is a transition arrangement, generally designated 58, so that the lower inner annular chamber 54 B is in fluid communication with the upper, outer annular chamber 56 A.

Similarly, the upper, inner chamber 54A is in fluid communication with the lower, outer chamber 56B. Each of the inner chambers 54B and 54A are in communication with the. neighboring portions of the catalyst bed 32 through the perforated wall 30, but they are not in communication with each other. The lower, outer chamber 56 B is open at the bottom and communicates with the tube side of exchanger 12. Thereby, the reactants are passed through chamber 50 to the upper first 20 stage 20 and from there through chambers 54 A and 56 B to exchanger 12. .

The reactants are passed upwardly through the tubes from exchanger 12 to chamber 48 from which the reactants are uniformly passed through the second reaction stage 22. The bottom end of chamber 54B is closed such that reaction products leaving the second reaction zone 22 by chamber 54 B must pass to chamber 56 A, the latter communicating with outlet 24 of vessel 36.

The top end of the bed 26 is closed, and a plurality of drop tubes 68 communicate with catalyst inlet ports 40 (one is shown). The outlet openings 42 communicate directly with the bottom of the bed. It should be noted that mixer 16 is a minimum distance from the feed deflector (i.e. the wall of filler body 72) to minimize non-catalytic residence time. The same relationship applies to the top of exchanger 12 and the second reaction stage 22.

The structure of a suitable dynamic seal or plug that will move down with the catalyst and prevent gas leakage between the stages is shown in Figure 3. A plug may consist of a number of layers of an inert granular material with selected particle size, which is chemically inert, such as sand. By a suitable choice of particle size, the system can be arranged to avoid migration of fine particles in the lower catalyst bed and leakage between stages. Referring to Figure 3, seal 34 is composed of a five-layer sandwich comprising top and bottom layers 60 of overlapping pieces of metal wool, intermediate layers 62 of fine catalyst particles, and a central layer 64 of pieces of metal foil. It will be appreciated that details of the reactor construction, instrumentation, isolation and the like will clearly differ depending on the intended use, and will be readily determined by one skilled in the art of these types of reactions and reaction conditions. However, it will be apparent that reactors of the invention are particularly suitable for vacuum or low pressure systems whose reactivity proceeds outside the catalytic environment. All flows are annular or radial, and the internal walls are designed for pressure drop and catalyst support only. if an internal structural failure should occur, it will remain limited within the vessel and present no danger. The design of the filler body 72 should provide a gradual decrease in the inlet cross-section along the inlet wall 30 of the catalyst bed as well as fill pre-reaction space to reduce the residence times of hot reactants.

Internal thermal expansion problems are solved by providing expansion seals for concentric cylinders. Many types are known. A variety of means are also available for the construction of the transition section, but one example is illustrated in more detail in Figures 4 and 6. Thus, at the transition point, the annular wall 52 is tapered to adapt to the perforated wall 28 (a portion of which is shown) on one side and outer wall 3 & on the other side, with expansion joints and seals 66 in particular provided at the last point. Horizontally extending plates 71 are arranged in the shape of transition section 58 to form transition sub-sections. A number of openings 68 and 70 are provided with tapered sections which face each other in alternating sub-sections, whereby a fluid connection is obtained between chambers 56 A and 54 B. The chambers 56 B and 54 A are constructed entirely analogously .

8301737

Claims (1)

CONCLOSI E. Catalytic reactor, comprising a vertical, elongated and cylindrical reactor vessel with inlets and outlets for reaction fluid and within that vessel two superimposed annular catalyst beds, which are flowed in radial direction, as well as a heat exchanger 5 and connecting pipes, with characterized in that the reactor is provided with an elongated, annular cat alys at orbed (26) concentric with the vessel, which bed is enclosed between an outer perforated wall (28) and an inner perforated wall (30) which bed or more plugs (34) is divided into a first stage (20) and a second stage (22), the space within wall (30) being divided by a filler body (72) into a first (50) and a second (48) supply chamber, while further inlet (10) via the heat exchanger (12), a conduit (14) mounted outside the reactor vessel and mixer (16) is connected to supply chamber (50), which is outside the perforated wall (28) ers (54 A, 56 B), plates (71) 15 and openings (68, 70) are provided to direct the first stage fluid discharge through the heat exchanger (12) and the second supply chamber (48) to the second catalyst stage (22) and chambers (54 Bv 56 A), plates (71) and openings (68, 70) to direct second stage fluid drain to outlet (24). 8301737