MX2008007745A - Method for controlling the temperature of exothermic chemical reactions - Google Patents

Abstract

A method for controlling the temperature of an exothermic reaction with simultaneous production of steam is based on the use of heat exchangers (5a) crossed by a recirculation liquid along an inner path extended between the inlet opening for the recirculation liquid and an outlet opening (5f), the recirculation liquid coming from a steam drum (10) for the separation of the produced steam and being fed to said inlet opening along a path external to the heat exchangers, the produced steam being integrated in the form of an additional liquid flow which is mixed at least in part with the recirculation liquid flowing along the external path.

Description

METHOD TO CONTROL THE TEMPERATURE OF EXOTERMIC CHEMICAL REACTIONS DESCRIPTION Scope In its most general aspect, the present invention relates to a method for conducting exothermic chemical reactions under pseudo-isothermal conditions.

Pseudo-isothermal conditions are understood as conditions for which the reaction temperature is controlled within a restricted range of values around a predetermined optimal value, or a predetermined temperature curve.

In particular, the invention relates to a method for controlling the reaction temperature of the aforementioned type, through the use of tube or plate bundle heat exchangers immersed in a catalytic bed in which such a reaction is carried out. .

Still more particularly, the present invention relates to a method of the type considered above for the control of the temperature of an exothermic reaction and the simultaneous production of steam.

Previous art As is known, the control of a catalytic reaction which is attempted to be carried out under pseudo-isothermal conditions is generally obtained through an exchange of heat between a predetermined operating fluid flowing inside the heat exchangers and the catalytic bed in the which exchangers are immersed and in which the reaction takes place.

In the case of exothermic or highly exothermic reactions, it is also known to use water as an operating fluid to obtain, in addition to the desired heat exchange and the control of the reaction temperature, a considerable production of steam. In such a case, the operating fluid is boiling water.

In particular, the boiling water that passes through the heat exchangers absorbs a certain amount of heat, generating steam. As soon as it leaves the heat exchangers, the steam is then separated from the boiling water in a steam drum and recovered so that it can be used in various applications in the plant in which the exothermic reaction takes place.

The operating fluid is returned instead by feeding a corresponding amount of water into the steam drum from which the steam was removed. The operating fluid is then recirculated to the heat exchangers as boiling water, to carry out its function of heat exchange operative fluid.

This technique, although advantageous and widely applied in this field, has a recognized drawback due precisely to the fact that the temperature of the operating fluid entering into the heat exchangers is the boiling temperature of the water.

For this reason the possibility of controlling the reaction temperature is very limited, the minimum achievable value of which is in any case greater than the boiling temperature of the water.

Summary of the invention The underlying technical problem of the present invention is that of providing a method for controlling the temperature in an exothermic reaction with a simultaneous production of steam having functional characteristics such that the previously mentioned drawbacks with reference to the prior art are completely overcome.

The aforementioned technical problem is solved, according to the invention, by a method of the type considered above based on the use of heat exchangers traversed by a recirculating liquid along an internal path extending between an inlet opening for the recirculating liquid and an outlet opening, said recirculating fluid coming from a steam drum for the separation of said steam produced and being fed in said inlet opening along an external path to said heat exchangers, being said produced vapor reintegrated in the form of an additional liquid flow, characterized in that at least a part of said additional liquid flow is mixed with said recirculating liquid flowing along said external path.

With liquid, it refers to an operative heat exchange fluid that changes phase (vaporizes) when it absorbs the heat of reaction.

Preferably, such liquid is water. In this case, particularly advantageous results were obtained with said at least a portion of said additional liquid flow (water) comprised between 5 and 20% by volume, preferably 10% by volume based on the entire volume of said additional liquid flow ( Water).

Even more preferably, all said additional liquid flow is mixed with said recirculating liquid which flows along said external path.

Advantageously, said additional liquid flow has a temperature lower than the temperature of said recirculating liquid coming from said steam drum.

Preferably, the mixture between said recirculating liquid and said additional liquid flow occurs just upstream of said inlet opening for the recirculating liquid.

Also preferably, the aforementioned additional liquid flow is fed to be mixed with the recirculating liquid at a higher pressure than the recirculating liquid pressure.

Conveniently, the aforementioned exothermic reaction is a catalytic reaction carried out in a catalytic bed.

Advantageously, the aforementioned heat exchangers are of the so-called plate type.

Advantages and additional features of the method for controlling the temperature of exothermic reactions according to the present invention will be more apparent from the detailed description of an embodiment thereof, made hereinafter with reference to the accompanying drawings, given as indicative and not limitations.

Brief description of the figures FIG. 1 shows, in a longitudinal section, a schematic view of a reactor for carrying out the method according to the invention; FIG. 2 shows schematically the reactor of FIG. 1 in a cross-sectional view along the line I-I.

FIG. 3 shows, in a longitudinal section, a schematic view of the reactor of FIG. 1 according to an alternative embodiment of the method according to the invention.

Detailed description of the invention With reference to the aforementioned figures, a reactor is generally indicated with 1 to carry out the method according to the present invention.

The reactor 1 comprises a cylindrical housing 2 having a vertical axis X-X, an upper bottom 3 equipped with an inlet opening 3a of reagent, and a bottom bottom 4 equipped with an outlet opening 4a of product.

The reactor 1 further comprises a plurality 5 of plate type heat exchangers 5a, positioned therein and included in a space of defined reaction between opposite horizontal planes, indicated with A and B in FIG. 1.

In particular, such plate-type heat exchangers 5a are accommodated on planes that are parallel to each other and parallel to the axis XX of the cylindrical housing 2 of reactor 1. However, the possibility of providing a radial arrangement of the components is not included. exchangers with respect to the aforementioned axis XX.

The reactor 1 also comprises a catalytic bed 6, supported therein in a known manner and therefore not shown in the figures, defined between the horizontal planes A and B, in which the plurality 5 of heat exchangers 5a is immersed. .

In detail, each heat exchanger 5a has a substantially flattened shape, and comprises a pair of opposite side walls 20, preferably metal. The side walls 20 are connected along their perimeters so as to define a chamber 21 therein for the passage of a predetermined operational cooling fluid.

More in detail, each heat exchanger 5a comprises opposite horizontal sides 5b and 5c, upper and lower, respectively, and opposite vertical sides, indicated with 5d and 5e, which delimit the chamber 21 mentioned above for the passage of the operating fluid.

Each chamber 21 is in fluid communication with an operating fluid inlet opening 5h of the corresponding heat exchanger 5a through a distributor conduit 5i accommodated on the lower horizontal side 5c. The chamber 21 is also in fluid communication with an outlet opening 5f of the corresponding heat exchanger 5a through a collecting conduit 51 located on the opposite lower horizontal side 5b.

The exchangers 5a are therefore in fluid communication with the outside of the reactor 1, by means of recirculation and discharge conduits. suitable, 8 and 9 respectively. The conduits 8 and 9 are connected to said inlet openings 5h and outlet 5f, respectively, as will be described in more detail below.

In particular, the recirculation duct 8 is connected to a collector-distributor 18, which in turn is connected to the above-mentioned inlet openings 5h through respective connection conduits 28, so that a fluid communication is obtained between the recirculation duct 8 and the chamber 21 of the exchangers 5a.

Similarly, the outlet openings 5f of the exchangers 5a are connected through respective connection conduits 29 to a collector-distributor 19, which in turn is connected to said discharge conduit 9, so as to obtain a fluid communication. between the discharge conduit 9 and the chamber 21 of the exchangers 5a.

The recirculation duct 8 and the discharge duct 9 are in turn connected to a steam drum, indicated in its fullness with 10, located outside the reactor 1. In particular, the recirculation duct 8 is connected to the steam drum in a lower position thereof, while the discharge conduit 9 is connected in an upper portion of the steam drum 10. A fluid communication is thus obtained between the chamber 21 of the exchangers 5a and the steam drum 10 through the recirculation and discharge ducts 8, 9.

In accordance with the present invention, an additional supply conduit 7 is provided, which is in fluid communication with the chamber 21 of the heat exchangers 5a through a first portion 7a thereof connected to said recirculation conduit 8.

With reference to the example of FIG. 1, the supply conduit 7 is also in fluid communication with the steam drum 10, through a second portion 7b thereof, directly connected to the steam drum 10.

In accordance with the method according to the present invention, a reagent stream is fed into the reactor 1 through the reagent inlet opening 3a.

Such reagent flow advances towards the bottom bottom 4 of the reactor 1, parallel to the axis X-X, which crosses the catalytic bed 6 where it reacts exothermically with the formation of reaction products.

Such reaction products, for example ammonia or methanol, then leave the reactor 1 through the product outlet opening 4a, provided in the bottom bottom 4 mentioned above.

For the cooling of the catalytic bed 6, a flow of recirculating water coming from the steam drum 10 is sent to the heat exchangers 5a.

In particular, the flow of recirculating water is fed to the inlet openings 5h mentioned above along a path external to the heat exchangers 5a.

With reference to the examples illustrated in the figures, such an external path is obtained by means of the recirculation conduit 8, the collector-distributor 18 and the connection conduits 28 and is therefore comprised between the steam drum 10 and the apertures of entrance 5h.

Then, the flow of recirculating water crosses the plurality of exchangers 5 along an internal path which extends, for each heat exchanger 5a, between the inlet opening 5h and the outlet opening 5f mentioned above.

In the non-limiting example illustrated in FIG. 1, the recirculating water flows countercurrent to the flow of the reactants within the catalytic bed 6, absorbing heat.

In other words, the water flowing within the heat exchangers 5a absorbs, through the walls of the exchangers themselves, the heat of reaction developed by the exothermic reaction in the catalytic bed 6 and suffers, followed by such heat absorption, a partial change of state with steam generation.

At the outlet of the heat exchangers 5a, a flow of boiling water and steam is therefore sent, via the connection conduits 29, the manifold-distributor 19 and the discharge conduit 9, to the steam drum 10, where the steam is then separated by means of a steam outlet duct 11.

On the other hand, the boiling water of recirculation is forwarded to the heat exchangers 5a by means of the aforementioned external path obtained with the circulation conduit 8, the manifold-distributor 18 and the connection conduits 28.

An additional flow of water is also fed through the conduit 7 to reintegrate the operating fluid portion (water) removed as vapor through the steam outlet conduit 11. In accordance with the invention, at least a portion of such a flow of additional water is advantageously mixed, through the aforementioned first portion 7a of the duct 7, with the recirculating water flowing along the aforementioned external path, and thus with the recirculating boiling water leaving the steam drum 10 and therefore it is free of steam.

Preferably, such at least one part is comprised between 5 and 20% by volume, for example 10% by volume, based on the entire volume of said additional water flow.

Still in accordance with the invention, such at least a part of the additional water flow is mixed with the recirculating water flowing along the aforementioned external path at a lower temperature with respect to the temperature of the recirculating water itself ( boiling) that exits from the steam drum 10, and preferably is at a higher pressure.

Advantageously, therefore, the operating fluid (water in the present case) fed to the chamber 21 of the exchangers 5a has a temperature smaller with respect to the temperature of the recirculating water that leaves directly from the steam drum 10.

According to the non-limiting example illustrated in FIG. 1, the mixture between the recirculating water and the additional water flow occurs in the recirculation duct 8, at the entrance of the first portion 7a of the duct 7 in such duct 8, which is accommodated in the example in proximity with the inlet 5h of the exchanger 5a.

The possible remaining part of the additional water flow is instead sent conventionally to the steam drum 10. In particular, with reference to FIG. 1, such remaining part of the additional water flow is fed directly to the steam drum 10 by means of the aforementioned second portion 7b of the feed conduit 7.

In accordance with an alternative embodiment of the invention, schematically illustrated in FIG. 3, the additional water flow for the reintegration of the operating fluid (water) removed as steam is entirely mixed with the recirculating water that comes out from the steam drum 10.

In this case, the supply conduit 7 does not comprise the second portion 7b for its direct connection with the steam drum 10, and is only composed of the first portion 7a. Thus, the entire additional water flow is mixed with the recirculating fluid flowing along the aforementioned external path between the steam drum 10 and the inlet opening 5h of the heat exchangers 5a.

Advantageously, the present method makes it possible to reach, inside the heat exchangers 5a, a temperature of the cooling operating fluid, which is considerably lower than the temperature of the boiling water.

Thus, particularly in its lower portion, the reactor operates at a temperature that is lower than the boiling temperature of the water, which advantageously can still be varied as desired within certain limits.

The upper portion of the reactor, on the other hand, operates at a temperature higher than the boiling temperature of the water.

It is possible, therefore, through a method according to the invention, to overcome the drawbacks mentioned above with reference to the prior art.

The main advantage resulting from the present invention lies in the possibility of cooling the catalytic bed 6, in particular in proximity with the bottom bottom 4 of the reactor 1, and thus in correspondence with the final section of the catalytic bed traversed by the reagent flow.

Such cooling makes it possible to improve the conversion of reactants into products, and thus the yield of production, particularly for equilibrium-limited reactions, such as the synthesis reactions of ammonia and methanol.

Even more advantageously, it should be said that, in the case where circulation of the circulating liquid (e.g., water) from the steam drum occurs by natural circulation, mixing with the additional liquid (water) flow, which is fed at a higher pressure, it allows to minimize the effects of possible pressure drops of the recirculation liquid that occur along its circulation path, both inside and outside the reactor.

An additional advantage lies in the structural simplicity with which it is possible to manufacture a reactor to carry out the method according to the present invention.

Such structural simplicity advantageously makes it possible to integrate the present method even in reactors which currently employ methods of the prior art, by means of simple modifications and economic structural modifications.

Of course, to the method for controlling the temperature of exothermic reactions described above, a person skilled in the art can provide numerous modifications with the intention of satisfying contingent and specific needs, all however within the scope of protection of the invention, as defined in the following claims.

Claims (10)

1. A method for controlling the temperature of an exothermic reaction with simultaneous production of steam by the use of heat exchangers (5a) traversed by a recirculating liquid along an internal path extended between an inlet opening (5h) for the recirculating liquid and an outlet opening (5f), said recirculating liquid coming from a steam drum (10) for the separation of said steam produced and being fed to said inlet opening (5h) along a path ( 8, 18, 28) external to said heat exchangers (5a), said steam produced being reintegrated in the form of an additional liquid flow, at least a portion of said additional liquid flow being mixed with said flowing recirculating liquid along said external path (8, 18, 28), characterized in that said additional liquid flow has a temperature lower than the temperature of said recirculating liquid that comes from said steam drum (10).

2. The method according to claim 1, characterized in that said liquid is water and said at least a portion of said additional liquid flow is comprised between 5 and 20% by volume, preferably 10% by volume, based on the whole volume of said additional liquid flow.

3. The method according to claim 1, characterized in that said additional flow of additional liquid is mixed with said recirculating liquid flowing along said external path (8, 18, 28).

4. The method according to any of the preceding claims, characterized in that the mixture between said recirculating liquid and said additional liquid flow occurs just upstream of said inlet opening (5h) for the recirculating liquid.

5. The method according to any of the preceding claims, characterized in that said additional liquid flow is fed at a higher pressure than the recirculating liquid pressure.

6. The method according to any of the preceding claims, characterized in that said exothermic reaction is a catalytic reaction.

7. The method according to any of the preceding claims, characterized in that said heat exchangers (5a) are of the so-called plate type.

8. A chemical reactor for carrying out exothermic reactions under pseudo-isothermal conditions of the type comprising a cylindrical shell (2), closed at opposite ends by an upper bottom (3) and a bottom bottom (4), respectively, a reaction space (6) defined within said cylindrical casing (2) in which a plurality (5) of heat exchangers (5a) in fluid communication with a steam drum (10) is positioned, a path being defined (8, 18) , 28) external to said heat exchangers (5a) between said steam drum (10) and an inlet opening (5h) of said exchangers (5a) for the recirculation to said heat exchangers of a heat exchange operative fluid comprising a boiling liquid, characterized in that it further comprises a conduit (7, 7a) connected to said external path (8, 18, 28) for feeding an additional liquid flow into said operating fluid of heat exchange of recirculation.

9. The reactor according to claim 8, characterized in that the connection between said conduit (7, 7a) and said external path (8, 18, 28) is positioned just upstream of said inlet opening (5h) of said exchangers ( 5a).

10. The reactor according to claim 8, characterized in that said heat exchangers (5a) are of the so-called plate type.