CH652047A5 - Axial-radial reactor for heterogeneous syntheses - Google Patents

Abstract

In a reactor having an external shell and an internal cartridge, preferably obtained by assembling a number of stackable elementryal cartridges, each of which contains, from the outside to the inside, at least one solid wall forming a clearance with the inner wall of the shell, a continuous bottom of the solid wall, a first wall perforated over its entire length, a second inner wall only partially perforated, and a catalytic bed inserted between said bottom and said totally or partially perforated walls, at least one heat exchanger is arranged centrally and axially in a catalytic bed; the feed gases, which have cooled the outer wall of the shell, are collected in a pipe in the centre of the heat exchanger, through which pipe they run in one direction (for example downwards), then run back through the exchanger in the other direction inside the exchange tubes thereof, exiting preheated in the free zone above the free top of the catalytic bed where they are mixed with fresh gas fed directly from the outside into this zone. This mixture of preheated gas and fresh gas passes, at first axially and then radially, into the catalytic bed, is collected in the centre, is brought into contact with the outside of the heat exchanger tubes and, from the bottom thereof, is conveyed directly to the next catalytic bed.

Description

The present invention relates to reactors for heterogeneous synthesis and more particularly for catalytic synthesis of ammonia, methanol, "fuel" and higher alcohols, monomers and the like, consisting of an external shell, an internal cartridge comprising a full forming wall of interspace with the inner wall of the mantle (M), of at least one catalytic bed (QQ) formed by granular catalyst placed between a bottom (Fo) and two concentric cylindrical walls (Tj-Tj) of which the outer one (T \) is perforated on all its axial and innermost extension (T2) it has no perforations on its minority extension; of means for the supply of the reaction gases, of means for the extraction of the reacted gases, of at least one heat exchanger, and of means for the supply of fresh exchange gas to it. Such reactors are described in Italian patent applications n. 24334A / 79 and n. 22701A / 80 of the Applicant; they are characterized by the fact that each catalytic layer or bed is crossed by the reaction gases in an area with predominantly axial flow, and in another area with predominantly radial flow, the area with predominantly axial flow, also acting as a buffer or stopper held between catalytic layers. Preferably, the internal cartridge is advantageously obtained by simple assembly of elementary cartridges, each formed (proceeding from the outside to the inside) by a full cylindrical side wall, by a full bottom which can be the continuation of the full external wall, by a first cylindrical wall perforated along its entire axial extension and by an internal cylindrical wall perforated only partially, i.e. having at least one small axial extension not perforated: the catalytic layer is disposed on said bottom and is delimited by said side walls completely respectively partially perforated. Each catalytic layer or bed is open at the top where the predominantly axial flow area acts as a sealing pad. Furthermore, between a catalytic bed and the next 10 there is always a separation zone in which cold gases are sent to be used for heat exchange (direct or indirect) with hot ones preheated and / or already partially reacted. In the case of indirect heat exchange, the heat exchanger between cold synthesis gas 15 and partially synthesized hot synthesis gas is arranged axially to the reactor in the central part of the catalytic layers: the tubes of these individual exchangers are crossed internally by the cold supply gases and they are externally lapped by the hot gases which have passed (axially 20 and radially) the catalytic bed enveloping the exchanger in question, as well as the catalytic layer or layers which precede it.

Continuing her research, studies and experiments in the vital and important field of axial-radial reactors (today even more vital for the substantial energy savings 25 that are achieved), the Applicant has managed to create an axial-radial flow and exchange reactor Indirect thermal with great efficiency and great construction simplicity.

The reactor according to the invention of the type specified in the preamble of this description is now characterized in that a heat exchanger is arranged centrally and axially to a catalytic bed; that the fresh process gases that have cooled the inner wall of the casing are collected in a central duct to the exchanger and run it in one direction (e.g. from top to bottom) and then repeat the same path in the other sense inside the tubes of said exchanger, opening preheated in the free area above the free surface of the catalytic bed, where they are mixed with the fresh exchange gas 40 fed directly from the outside and diffused in said area; that the mixture of pre-heated process gas and fresh exchange gas thus obtained crosses the entire catalytic layer axially and then radially, is collected in a central interspace, and is brought to touch the outside 45 of the heat exchanger pipes from the bottom of which it is conveyed directly to the subsequent catalytic bed which it will pass first axially then radially to be collected at the center of the reactor.

One of the advantages of the invention is that it allows a simple and effective construction of the whole reactor and its use without loss of volume due to the process temperature regulation system. In particular, the internal cartridge can now be made with several modular stackable cartridges, light (they have only one full wall) that can be assembled in situ, and with an open-air catalytic bed.

It is worth noting that reactors with heat exchanger arranged centrally and axially to a catalytic bed are already known; in particular, US patent number 60 4 181 701 describes an exclusively radial flow reactor in which a heat exchanger is arranged in the central area of a catalytic bed and is fed with fresh exchange gases. However, not only are the type of reactor (exclusively radial) different and complex (with respect to the invention) but also the structure and behavior of the exchanger in the economy of the whole system for regulating the process conditions; volume losses are not indifferent in said patent 4 181 701.

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The different aspects and advantages of the invention will become clearer from the following description of the preferred but not limiting embodiment represented in the attached drawing which is a schematic and partial longitudinal section of a reactor according to the invention.

As described in the previous Swiss patent 643 752 of the Applicant whose description is to be considered as an integral part of this text, the reactor consists of an outer jacket or pressure pressure housing M and an internal cartridge which in the attached drawing is advantageously represented in its form realization obtained by in situ assembly of several CU1 modular cartridges; CU2 .. CUj ... CUn-j, CUn. For illustrative and representative simplicity, only two cartridges CL ^ and CU2 have been shown, each formed by an external wall T0 which preferably forms a single body with a bottom FO and a cover CO. Inside T0 there is a first cylindrical wall Tj which is perforated over its entire axial extension, and a second cylindrical wall T2 which is also perforated but also has an unperforated extension T'2. In other words, the internal wall T2 is perforated on an extension corresponding to the difference of the axial extensions of Tx and T'2, that is to TrT'2. The side walls Tj and T2 + T'2 delimit with the bottom FO the catalytic layer or bed Ct formed by granular catalyst. The same modular cartridge structure (i.e. assembled for simple stacking) is obtained with CU2 whose catalytic basket C2 is enclosed between the bottom FO ', the internal wall completely perforated The internal wall perforated on section T2: 2 and not perforated on section T'2.2. At the top said basket is free, i.e. between the bottom FO of the upper basket Cj and the upper free surface of the basket C2 there is a free zone Z2 substantially similar to the free zone Z1 which is between the internal wall of the cover CO and the top free layer of the catalytic layer Cj. By virtue of the non-perforated wall T'2 (resp. T'22) of each basket the catalyst zone Zla having the axial extension of T'2 will be crossed by mainly axial gas flows while the zone Zlb of catalyst having the extension of the perforated wall T2 will be crossed by mainly radial flow.

According to the most important aspect of the invention, a catalytic basket, in particular the one closest to one end of the reactor, preferably at the opposite end to that of the inlet of the process gases IG, has its central annular zone occupied by an exchanger of indirect heat HE which with its central duct 15 for the collection of process gases, with its lower closing cap 10 and with its series of heat exchanger tubes U realizes an arrangement and a critical and advantageous combination with a short adduction of fresh EGI exchange gas, blossoming directly in the free zone Zl of the catalytic bed Cj.

In fact, it will be seen that with a happy combination of the process gas paths in the exchanger, and the exchange gas in the free area of the catalytic bed, an efficient system for regulating the process conditions is created with a simple and effective construction reactor .

As can be seen from the drawing, the cold process gases (inlet gas) enter IG and follow the path from bottom to top indicated by the arrows Fj along the cavity I between the external walls T0 and Tn-2 of the cartridges CUj, CU2 and the inner wall of the mantle M which is thus cooled. At the top of the reactor this main flow Fj is conveyed to the center in the duct 15 arranged centrally to the heat exchanger HE which is thus traversed by Fi in a direction e.g. from the top to bottom. The exchanger HE (arranged centrally and axially to the catalytic bed Q) is closed at the bottom by the cap 10 so that the gases Fj are forced by 10 to go up in the other direction, e.g. upwards passing into the tubes U of the exchanger from which they emerge in the free zone Z1 as preheated gas Flp. In this same zone Z1; that is, inside the cover CO, however, also the conduit 8 fed by a flow of fresh exchange gas EGI (exchanger by-pass inlet) arrives: the conduit 8 ends with a toroidal outlet 9 and diffuses a fresh gas Fe in Z1 (exchange gas) which mixes with the main gas flow Flp (exiting from the top of the heat exchanger HE) so in Z1 there is the gas mixture F2 = Flp + Fe which will pass through the first zone Zla of Cj axially and then continue in the zone Zlb of the basket with mainly radial flow, collecting in the interspace 21 beyond the perforated wall T2. Said gas flow F3 (which to be the mixed gas flow F2 = Fip + Fe which first crossed the zone Zla axially and then radially inwards the zone Zlb of the catalytic bed Cj and is therefore partially reacted and therefore hot) when it collects at 22 it is obliged to pass through the heat exchanger HE, that is, to touch the tubes U of HE externally; this path of the gases F3 outside the pipes U is indicated by the semicircular arrows F4. These gases indicated with F4 transfer heat to the main flow of gas F \ (which is Ft after having traveled the top tube 15 of HE from top to bottom) which, due to the closure by means of the cap 10, returns the exchanger inside the pipes U from which it comes out at the top as a preheated flow Flp to mix with the secondary exchange flow Fe in the free zone Zx.

As can be clearly seen from the figure, the flow of gas F4 (which is the flow partially reacted on the bed Cx inside which, that is, at 21, it had collected as flow Fs) exits from the lower annular ports 18 of the exchanger HE and goes to the second catalytic bed C2 of which it crosses the first section (the one having extension equal to the height of the unperforated wall T'2 2) with mainly axial flow, and the second section (the one having the extension of the perforated part T2 2) with flow mainly radial; the radial flow is inward (centripetal) as in the Zji area of the first basket C1; whereby all the gas that also has through the second catalytic basket collects as flow F5 and exits via the T5 tube from the GO outlet (gas outlet). The system for regulating the temperature of the gases inside the reactor, according to the invention, has proved to be extremely efficient, flexible and reliable. In fact, it is sufficient to adjust the quantity of exchange gas flow EGI = Fe as a function of the flow Fj and the conditions of these after preheating (Flp) to arrive at establishing the optimal process conditions.

The structure of the reactor which allows to achieve these optimal process conditions is constructively simple and effective; in fact there are no useful volume losses (as in the prior art), the cartridge can be made with stackable elements that do not require fixing elements, are light because they have only one solid wall, and are mounted in situ; there are no exchange gas supply pipes (EGI) that pass through the reactor; each catalytic basket remains open at the top so there is no need for divisional walls between basket and basket; the first upper piece of catalyst (which is not exploited in the prior art) is also exploited (axially), etc. etc.

It is clear that the invention, even if described for illustrative clarity with reference to the simpler embodiment shown in the drawing, is by no means limited to this type of execution but is suitable for use.

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used on reactor with any number of catalytic baskets and with any type of cartridge. Thus, if the number of baskets is greater than two, it will be possible to exploit either a single exchanger according to the invention or insert at least another exchanger in a basket subsequent to the second.

Although the cartridge is preferably made up of several stackable cartridges, the invention applies equally well to a one-piece cartridge. Similarly, the exchanger HE can be replaced with a different type of exchanger 5 but with equivalent behavior.

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1 sheet of drawings

Claims (2)

652047 2 CLAIMS 1. Reactor for heterogeneous and catalytic synthesis of ammonia, methanol, combustible mixtures, higher alcohols, polymerizable monomers and the like, consisting of an external shell (M), an internal cartridge (CU1-CU2) involving a solid wall (To ) cavity forming machine with the inner wall of the mantle ', of at least one catalytic bed or basket (Ç [-C2) formed by granular catalyst placed on a bottom (FO) and between two concentric cylindrical walls (TrT2) of which the outer one (TJ is perforated on all its axial extension while the innermost one (T2) does not have perforations only on a minority stretch (T ') of its extension, of means (Fj) for the supply of synthesis gases (or process) (IG), of means for the extraction of the reacted gases (GO), of a heat exchanger of the process gases (HE), and of means for the adduction to the exchanger of fresh heat exchange gas, characterized in that centrally and axially to a catalytic bed (C x) a heat exchanger (HE) is arranged; that the fresh process gases (Fj) which have cooled the internal wall of the casing (M) are collected in a central duct (15) to the exchanger and run it in one direction and then repeat the same path in the other direction inside of the pipes (U) of said exchanger (HE), opening preheated in the free zone above the free surface (Zx) of the catalytic bed, where they are mixed with the fresh exchange gas (Fe) (EGI) fed directly from the outside and diffused in said area (Zj); that the mixture (F3) of preheated process gas (Fjp) and fresh exchange gas (Fe) thus obtained crosses the entire catalytic layer (Cj) axially and then radially, is collected in a central interspace (21), it is brought to touch the outside of the tubes (U) of the exchanger (ME) from the bottom of which it is conveyed directly to the next catalytic bed (C2) which will pass first axially and then radially to be collected at the center of the reactor. 2. Reactor according to claim 1, wherein the cartridge inside the shell is made up of several stacked elementary cartridges, each cartridge comprising a catalytic basket which can be traveled axially and radially.