CH646618A5 - REACTOR FOR CATALYTIC HETEROGENEOUS SYNTHESIS. - Google Patents

Description

The present invention relates to a reactor for catalytic heterogeneous syntheses, especially for catalytic syntheses of ammonia, methanol, "fuel", higher alcohols, monomers and the like, consisting of at least one external mantle, n catalytic beds formed, each, by granular catalyst placed between a solid bottom and two cylindrical 5-centric walls, the most external one of which is perforated over its entire axial extension and the more internal one has a perforated axial extension lower than that of the said external wall; means for supplying the reaction gases; of means for extracting the reacted gases, and means for regulating the temperature of the reacted gases.

Reactors of this type have been described in recent Italian patent applications (patent applications No. 24 334 A / 79, No. 22 701 A / 80, No. 26 294 A / 80) and in the corresponding Swiss patent in the name of the Applicant and one of the 15 inventors; they are characterized by the fact that the catalytic beds are traversed by the reaction gases in an area with predominantly axial flow, and in another area with mainly radial flow, the catalytic zone with predominantly axial flow, also acting as a sealing pad 20 of gases.

As is known, most of the heterogeneous syntheses are accompanied by a considerable development of heat which is normally recovered outside the reactor itself, cooling the reacted output gas to produce energy 25 (e.g. steam).

The recovery of heat outside the reactors is certainly disadvantageous compared to a recovery inside the reactor because the latter, in the absence of construction complications, would also allow to obtain simultaneously: a) an optimal regulation of the temperature of reaction, thus minimizing the volumes of catalyst; b) maximum yields; and c) maximum thermal level of the recovered heat (e.g. steam produced at higher pressure). Despite these flattering perspectives, the recovery of heat 35 inside the reactors has not yet found widespread application.

In fact, only in exceptional cases has the heat recovered inside the reactor to produce steam and achieve a control of the reaction temperatures (for example in the Fauser-Montecatini ammonia reactor, in the Ammonia-Casale reactor with axial flow catalytic beds of the gas, in the Lurgi methanol reactor always with an axial flow catalytic bed) but this was achieved at the expense of enormous construction complications which in most cases 45 led to the abandonment of this road.

Thus, in the case of the ammonia reactor, modern technologies normally provide for the production of steam outside the reactor itself and this also applies to methanol reactors with the exception of the Lurghi reactor (see-50 dasi E. Supp «Chemtech» July 1973) and the Toyo Engineering reactor (Italian patent application no. 21 172 A / 80) which, however, represent very complex solutions.

In the new radial-axial flow reactors as described in the aforementioned recent Italian patent applications 55 and corresponding Swiss patent application, the regulation of the reaction temperature is obtained either by gas-gas exchange or more generally with the "quenching" system , which however do not allow an in situ recovery of the reaction heat.

60 In the case of quenching, only a part of the quench gas passes through all the catalytic beds and this leads to a consequent decrease in yields.

Continuing her research in the field, the Applicant has found, not surprisingly, that within her 65 new catalytic layer reactors run in series by the reaction gas, with mixed axial radial flow (according to the aforementioned Italian patent applications and related Swiss patent application) can be advantageously recovered

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the heat of reaction, and that this internal recovery with all the other advantages associated with it can be achieved without complications and complexity.

The reactor according to the present invention, by heterogeneous synthesis, especially by catalytic synthesis of ammonia, methanol, "fuel", higher alcohols and monomers, consisting of at least one external mantle, of n catalytic beds each formed by a granular catalyst arranged between a solid bottom and two concentric cylindrical walls of which the outermost one is perforated over its entire axial extension and the innermost one has a perforated axial extension lower than that of the said external wall; means for supplying the reaction gases; of means for the extraction of the reacted gases, and of means for the regulation of the temperature of the reacted gases, is characterized by the fact that inside the central cylindrical space delimited by the internal walls with less perforated extension of at least one of the n catalytic baskets is inserted a heat exchanger which is hit on one side by the gases reacted on the bed with which it is associated, and on the other side is run by water fed from the outside.

In a particularly simple and advantageous embodiment, the heat exchanger inserted in the cylindrical central space delimited by the internal wall with a smaller perforated extension is a bundle of pipes which are internally traversed by water and are lapped externally by the reacted hot gases which they have passed through axial flow and with radial flow the catalytic bed in which said tube bundle is inserted.

The tube bundle extends substantially over the entire perforated axial length of the internal cylindrical wall of each catalytic basket, and is included in a cylindrical body which has an axial extension slightly less than the axial extension perforated by the internal wall of the basket, called the body. cylindrical by presenting adjustable by-pass openings of the reacted gases at its base.

A process for optimizing the operating conditions of the reactor consists in removing high heat level in situ by heat exchange between the reacted gases on a bed and water circulated from the outside in the central cylindrical part inside the bed itself, so as to obtain , simultaneously with the optimal reaction conditions, also minimizing the volume of catalyst in each bed, and moreover in making an even finer regulation of the temperature of the gases already reacted on a bed and entering the next catalytic bed by dosing the quantity of hot gases reacted on a bed which is sent to the internal cylindrical central part where the heat exchange takes place.

The different aspects and advantages of the invention will become clearer from the description of some exemplary and non-limiting embodiments, such as those represented in the attached drawings in which:

fig. 1 is a schematic and partial section view of a radial axial reactor e.g. according to Italian patent applications n. 24 334 A / 79 and n. 22 701 A / 80, incorporating a heat recovery system according to the present invention, arranged directly inside each catalytic layer; and fig. 2 is a general scheme which illustrates more fully the optimization method.

For the sake of illustrative clarity in fig. 1 schematically represented an axial-radial reactor with only two catalytic baskets C2 and C2, each basket consisting of a support S! (resp. S2) and two cylindrical walls Tj, T2 (resp. T3 and T4); the outermost cylindrical walls and T3 are perforated over their entire axial extension while the innermost walls T2 and T4 have a perforated axial extension lower than that of the said outermost walls Tt and T ,. In fact, as can be seen schematically from fig. 1 the sections T'2, respectively T'4 are without perforations and can be constituted either by a full portion (without perforation) of the internal walls T2 resp. T4, either from a catalytic layer or from any other non-perforated body.

The structure of the non-perforated portion of T2, resp. T4 can therefore be made in different ways; what matters is that the perforated axial extension of the innermost cylindrical wall T2 (T4) is less than the fully perforated one of Tj (T3), so along the area defined by the unperforated sections (T'2 resp. T'4 ) there is a predominantly axial flow Zla of the gases while in the perforated zone T2 (T4) a predominantly radial flow Zlb occurs. This characteristic aspect of the axial-radial reactors is already highlighted in the aforementioned Italian patent applications and Swiss application which must be considered as forming an integral part of this description. In general, the height T'2 (T'4) which defines the predominantly axial flow zone is critical in the sense that it must also be such as to function as a buffer for the flow of gas.

It has now been found, and this constitutes the main feature of the present invention, that in the empty cylindrical space delimited by the internal cylindrical wall T2, (resp. T4) a heat exchanger SCt (resp. SC2) can be inserted, which is surrounded by a cylindrical body BBj (BB2) whose base Bt (B2) is inserted on the support Sx (S2) of the catalytic basket Cj (C2) so that substantially all the flow of reacted gas, that is, is that Zra. (Z2a) which has axially passed through the catalyst in zone Zxa and Zjb (Z2b) which has passed through the catalytic basket radially, go up the whole wall BBX and to the open top B ', (B'2) of this penetrates into the exchanger SC! (resp. SQ) which is supplied with water from an external source SQX (SQ2) and is equipped with a top outlet Uj (U2) in which there is also the steam (high thermal level) produced in situ in SCj (SC2) due to the heat exchange with the hot gases reacted Zla + Zlb.

By virtue of this exchange, it is possible to maintain the temperature of the reaction zone at the optimal value (equilibrium temperature), to produce high level heat in situ, to have high conversion yields and to minimize the volume of catalyst on each basket. In addition, according to a remarkable aspect of the invention, the temperature of the gases Gj already reacted on a bed (Cj) and directed to the entry of the next bed (C2) can be regulated even more finely due to the fact that almost on the bottom Bt of the body cylindrical BBj openings Fj, F2, F., F6 ... Fn are obtained (ie distributed along the whole cylindrical surface of BBj) whose free light can be adjusted with a closing system (not shown); when the holes Fi-Fn are completely closed the entire flow of reacted gas Zla + Zlb goes up the body BBi and enters the exchanger SCr through B'j In this case the gas leaving the bed Cj has the "cold" temperature set by the exchange thermal and therefore enters the next bed C2 at this temperature which we can call "minimum". On the other hand, when the openings F ^ F ,, are only partially closed, a part of the hot gases reacted G't (e.g. a part of Zlb) will not go up along the body BBt but will pass directly through Fj-Fn to go to the free zone Z2 (between Cx and C2) mixing here with the gases Gt which, through the exchanger SCj, have been brought to a lower temperature.

Therefore adjusting the degree of opening or closing of the holes F ^ Fn will dose the quantity (minority) of hot gas G \ which bypasses the exchanger SCj and arrives hot in Z2 where it will mix with the flow (majority) Gì of the colder gases which has transferred heat to the water from SQt which circulates in the exchanger SCj. In this way, that is, with the insertion of

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exchangers SC1; SC2 etc. etc. in several catalytic beds Cj, C2 etc. etc. and with the by-pass system Fj-F ,,, on the bottom of the body BBj, it is possible not only to optimize the reaction conditions on each single bed but also to make gas flow at optimal temperatures from one bed to another. In fig. 1, the exchangers SCj, SC2 have been schematically represented in their simplest embodiment, i.e. as a bundle of pipes 1 (1 '), 2 (2'), 3 (3 ') etc. etc. inserted between a lower plate Px (P'j) and an upper manifold plate P2 (P'2). It is evident that the exchanger can also be of any other type known per se which allows the best recovery of heat in situ at the highest permitted thermal level. Replacement devices for the tuberous bundle are known per se and their replacement must be considered within reach of the person skilled in the art.

In fig. 2 shows a more generalized scheme of an optimization process and plant, particularly suitable for the synthesis of methanol. The RME methanol reactor was designed here with four C1 catalytic beds; C2, C3, C4; the three heat exchangers SCV SC2, SC3 have been inserted in the internal cylindrical central part of the first three catalytic beds only, the last bed C4 being without an exchanger.

The fresh GSI synthesis gases are sent to the main line 12 and through the lines 12'-12 "they pass, for example, in two exchangers 15 and 16 in which the GRC reacted hot gases leaving the bottom 30 circulate in counter-current through line 20 and distribution lines 20 'and 21'. The GSI 'synthesis gases that passed through the exchangers 15 and 16 and are collected, partially preheated in 17 arrive through lines 18 and 19 at the top of the RME reactor and enter as gas MSI in the first free zone Zt from which they pass with the first axial and then radial flow in the first catalytic bed Cj, then go up the body BBX and travel downward but spiral the exchanger SCj from which a flow of cooled gas Gx (or Gj-G'ì if there is a partial by-pass of SC! For the partial opening of the holes F ^ F ,,) which enters the second catalytic bed C2 runs axially and radially, goes up the body BB2, descends the exchanger SC2, passes as flow G2 (or G2 + G'2 if there is a partial by-pass of SC2 for opening the holes F'rF'n), in the Ietto C3 which runs axially before and radially after,

passes along BB3 in SC3 from which it emerges as a cooled flow G3 (or as a flow G3 + G'a due to partial by-pass due to incomplete closure of the holes F "! - F" n) to finally go through the bed C4 (without exchanger ), exit 5 from 30 and, via lines 20, 20 ', 21, 21' and 22, be sent to the final capacitor CO.

For the operation of the exchangers according to the invention SCu SC2, SC3, the main water source SQ feeds the pump Pj through line 42, 43 and 44 which through line 45 and the three lines 46, 47 and 48 circulate water in the pipes associated with SC1; SC2 and SC3 whose outputs U1; U2 and U3 are carried by a single line Uc which feeds an RC collector in the upper part of which there will be the steam ST (produced in the individual exchangers SC1; SC2 and SC3) which goes to the 15th use ST '. At the bottom of the RC collector there is SQ 'water which is recirculated together with fresh water from SQ.

It has been found that by adopting a scheme of the type of fig. 2 for a methanol plant of 1000 tons per day with an operating pressure of 80 bar, the recovery of saturated vapor at around 18 bar, and the volume of catalyst assume the values shown in the following table when recovery is carried out internal to the reactor according to the present invention, or external recovery according to the previous methodology.

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Production 1000 t / d CH3OH at 80 bar. Steam recovery at 18 bar with 4 catalytic beds

Total MM Kcal per Volume in 30 Kcal / h tons ms catalyze-

4-bed methanol

Internal recovery of the reactor 17 MM 410.000 85 35 according to the invention

External recovery at 7.8 190,000 96

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2 drawings sheets

Claims (5)

646618 1. Reactor for catalytic heterogeneous syntheses, especially for catalytic synthesis of ammonia, methanol, "fuel", higher alcohols, monomers, consisting of at least one external mantle, n catalytic beds formed, each with a granular catalyst placed between a solid bottom (S 1) and two concentric cylindrical walls (T 1, T 2) of which the outermost one is perforated over its entire axial extension and the innermost one has a perforated axial extension lower than that of the said external wall; means for supplying the reaction gases; of means for extracting the reacted gases, and means for regulating the temperature of the reacted gases, characterized in that inside the central cylindrical space delimited by the internal walls (T 2, T 4) with less perforated extension than at least one of the In the catalytic baskets there is a heat exchanger (SC 1) which is hit, on the one hand, by the hot gases reacted on the bed with which it is associated and, on the other hand, is run through by water supplied from the outside (SQ 1 ). 2. Reactor according to claim 1, characterized in that the exchanger inserted in the cylindrical central space defined by the internal wall with a smaller perforated extension is a bundle of tubes, which are internally crossed by water and are lapped externally by the gases they have passed through both with predominantly axial flow and with mainly radial flow, said catalytic bed into which said tube bundle is inserted. 2 Reactor according to the preceding claims, characterized in that the tube bundle (SC 1) extends substantially over the entire perforated axial length (T 2) of the internal cylindrical wall of each catalytic basket, and is included in a cylindrical body (BB 1) which has an axial extension slightly less than the perforated axial extension of the internal wall (T 2) of the basket, said cylindrical body having at its base, adjustable by-pass openings of the reacted gases. Process for commissioning a reactor according to claims 1, 2 and 3 to obtain the optimization of heterogeneous catalytic syntheses, in particular of ammonia, methanol, «fuel», higher alcohols, monomers, and for heat recovery of the gases reacted on the catalytic baskets crossed by the synthesis gases on an area with mainly axial flow and on another area with mainly radial flow, characterized in that the hot gases reacted by predominantly axial passage, before, and radial, after, on a catalytic bed passes through a central cylindrical area inside the said bed in relation to heat exchange, with water which is circulated in said area and with which heat is removed in situ. Method according to claim 4, characterized in that the fresh gases to be reacted pass through at least one heat exchanger (15, 16) through which the hot gases reacted leaving the catalytic bed pass, that the said fresh gases thus preheated pass through each basket catalytic with predominantly axial flow and with predominantly radial flow and are led to lap a heat exchanger which is arranged within an internal cylindrical body (BB 1) to the cylindrical internal wall (T 2, T 4) with a perforated area with less axial extension ( T2 ', T4'), which is fed, on the one hand, with water and gives out a mixture of water and steam which is conveyed together with those coming from the other tube bundles arranged inside the other catalytic baskets to a collector ( RC) of water-steam.