MXPA97008707A

MXPA97008707A - Converse apparatus

Info

Publication number: MXPA97008707A
Application number: MXPA/A/1997/008707A
Authority: MX
Inventors: Filippi Ermanno; Rizzi Enrico
Original assignee: Ammonia Casale Sa
Priority date: 1996-11-12
Filing date: 1997-11-12
Publication date: 1998-10-30

Abstract

A conversion apparatus of the type comprising an indirect heat exchange zone (5) for the conversion reaction of a gaseous flow comprising methane and vapor to CO, Co2, and H2, is distinguished by the fact that it advantageously comprises a plurality of floating head tubes (6) containing a conversion catalyst, a chamber (9) for collecting the reaction products placed downstream of the tubes (6), and a duct (15) opened in said chamber ( 9) for the extraction of reaction products from the apparatus

Description

CONVERSION APPARATUS Field of Application The present invention relates to a conversion apparatus of the type comprising an indirect heat exchange zone for the conversion reaction of a gaseous flow comprising methane and vapor in CO, C02 and H2. In the description given below and in the following claims, the term "methane" is generally understood to refer to a raw material, which is a source of hydrogen and carbon such as, for example, methane itself or a mixture of liquid and / or gaseous hydrocarbons such as natural gas and naphtha. As is known, in the field of the conversion of methane to obtain hydrogen and carbon, which are indispensable for the synthesis of products such as ammonia and / or methanol, the requirement to make available an apparatus, which on the one hand allows to obtain a methane conversion reaction as complete as possible, and on the other hand requires low energy consumption, maintenance and investment costs and is easy to implement, is always more urgent. Prior Art To satisfy the aforementioned requirement, a permutator type conversion apparatus has been proposed in the industry, that is, it has a thermal exchange zone for the methane conversion reaction. In this apparatus, the high amount of heat necessary for the endothermic conversion reaction is supplied by indirect heat exchange with a flow of heating gas fed to such an apparatus. In particular, in ammonia plants where the conversion reaction of methane is carried out in two different sections called primary and secondary conversion, with the second operating at a higher temperature than the previous one, it is possible to use the hot reaction gas from the secondary conversion section as a thermal source for the primary conversion section. The permutation type conversion apparatus is generally used in the state of the art in the synthesis processes of ammonia, methane or hydrogen to replace the conventional primary reformer, as described for example in EP-A-0 298 525. Although advantageous in several ways, the apparatus described above shows a series of disadvantages, the first of which is that it is of a very complex construction, which requires high investment costs.

In fact, this apparatus comprises therein a plurality of bayonet-type tubes, that is to say consisting of an external tubular element with a capped end for indirect heat exchange between the flow of heating gas and the gaseous reactants (methane and steam) , and an internal tube for the extraction of the reaction products. As can easily be imagined, such a structure is complex and expensive to construct, difficult to access for maintenance operations, and involves a large diameter conversion apparatus. Furthermore, since the conversion reaction is of the catalytic type, it is necessary that the annular space defined between the outer tubular element and the inner tube be uniformly filled with the catalyst and that the catalyst be periodically replaced. These operations are clearly hindered or at least made difficult by the presence of the inner tube. Finally, the use of bayonet-type tubes shows disadvantages even from the point of view of energy, since there is a significant undesired heat exchange between the flow of reacted gas and the flow of reaction gas, with the additional risk of the occurrence of the metal disintegrating corrosion of the inner tube due to the reacted gas if the latter cools excessively.

JP-A-4154601 discloses an exchange type conversion apparatus comprising a plurality of individual tubes filled with the catalyst and through which the heating gas flows out. The tubes are adhered at their ends to the respective tube plates, which also adhere properly to the conversion apparatus. Although the heat exchange tubes described in JP-A-4154601 are simpler to construct and operate than bayonet tubes, they show the serious disadvantage that they are not free to expand if subjected to high temperatures, and damage the apparatus , as in the case of the conversion reaction, with the risk of cracking or even rupture thereof and therefore the mixing of the reaction gas with the heating gas and the damage to the apparatus. It is understood that this type of apparatus not only causes high maintenance costs for the replacement of defective tubes, but that it is not capable of ensuring optimal and reliable long-term operation. Due to these disadvantages, it has been found of little application until now, to the exchange type conversion apparatus according to the prior art despite the ever more urgent requirement perceived in the industry.

SUMMARY OF THE INVENTION The fundamental problem in the present invention is to make available a conversion apparatus, which would be simple to implement, reliable, and would provide a methane conversion reaction as complete as possible with low investment, maintenance and operation costs. as well as low energy consumption. The problem mentioned above is solved according to the present invention by means of a conversion apparatus for the conversion of methane and vapor to CO, C02 and H2 of the type comprising: an external substantially cylindrical coating, in which an exchange zone is defined indirect thermal and a zone to feed a gaseous flow comprising methane and vapor to the zone of indirect thermal exchange; an opening formed in said coating for feeding in said indirect heat exchange zone a flow of heating gas as a thermal source for said conversion; and which is characterized in that it also comprises: a plurality of floating head tubes containing a conversion catalyst, which extends longitudinally in said indirect heat exchange zone and in fluid communication with said feed zone; a chamber for collecting a gaseous flow comprising CO, C02 and H2 obtained from said conversion and located downstream of said tubes; an open duct in said collection chamber for the extraction from the coating of said gaseous flow comprising CO, C02 and H2. In the description given below and in the following claims, the term "floating head tubes" is understood to mean tubes having at least one end (head) structurally free to move (floating) to allow the thermal expansion of the tubes. Advantageously, the conversion apparatus according to the present invention requires a collection chamber for the reacted gas in fluid communication with a plurality of tubes containing the catalyst for indirect heat exchange, and a duct for the extraction of this gas coming from the coating. In this way, all the gas, once the conversion reaction took place, is collected in the same chamber and extracted by means of a single duct. Thanks to this particular structure, it is possible to obtain the exchange type conversion apparatus, which is reliable, extremely simple to build and has low implementation costs, which is at the same time effective in terms of the methane conversion reaction without the typical drawbacks of the prior art apparatus. In particular, the operations of maintenance and loading or replacement of the catalyst in the tubes are facilitated by the presence of a plurality of individual floating head tubes independent of one another. In addition, since all the reacted gas is collected in a single chamber and is extracted from the coating by means of a pipeline, which is thermally independent of the heat exchange tubes, the undesired thermal exchange between the reacted gas and the reaction gas it is advantageously removed to avoid the danger of corrosion of metal disintegration of the extraction duct and to reduce operating costs in comparison with the prior art apparatus. According to a preferred embodiment of the apparatus according to the present invention, the extraction duct is advantageously installed coaxially with said lining and extends parallel to said tubes through the indirect heat exchange zone and the feeding zone, from the collection chamber to a gas outlet opening from the lining. In the same way, a very simple and compact structure is obtained, allowing at the same time an effective compensation for the expansion of the different parts of the apparatus caused by the different thermal stress, to which these parts are subjected and by the use of different materials. In particular, it is possible to reliably and appropriately compensate the different proportions of expansion to which the heat exchange tubes and the reacted gas extraction duct are subjected, if it is necessary to renounce the extremely simple apparatus from the structural point of view. Indeed, thanks to the special installation of the extraction duct, there is an advantageously obtained collection chamber, which is also of floating type, with the heat exchange tubes and the extraction duct free to expand in mutually opposite directions with respect to the feeding area. In this way, the different proportions of expansion of the materials not only do not create mechanical problems for the apparatus, but they can compensate each other in a certain way. Advantageously, according to this embodiment, between said duct and said tube plate located between said feed zone and said heat exchange zone as between said duct and said liner, suitable gas seal means are provided in order to avoid deviation undesired reaction gas or reacted gas, and at the same time allow the different proportions of thermal expansion of the apparatus. Thanks to the present invention, the seal means for gas, which ensure the correct operation of the apparatus, are minimized and only concentrated between the extraction duct, the tube plate and the external coating. Preferably, the gas seal means is installed near said outlet opening, in order to facilitate access to the gas sealing means and thereby simplify and assist in the maintenance thereof. The features and advantages of the present invention are set forth in the description of one embodiment thereof given below by way of the non-limiting example with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: Figure 1 shows a longitudinal cross-sectional view of a conversion apparatus according to the present invention; Figure 2 shows a longitudinal cross-sectional view of a part of the apparatus of Figure 1, modified according to a preferred embodiment of the present invention; 3 shows a longitudinal cross-sectional view in enlarged scale of a detail of the apparatus of FIG. 2. DETAILED DESCRIPTION OF A PREFERRED MODE With reference to FIGS. 1-3, reference number 1 indicates as a whole an apparatus of FIG. conversion according to the present invention for the conversion reaction of a gaseous flow comprising methane and steam. The apparatus 1 comprises a substantially cylindrical external liner 2, in which a tube plate 3 dividing the liner 2 into an indirect heat exchange zone 5 and in a zone 4 for feeding a total of the cross section thereof extends. gaseous flow comprising methane and vapor to the zone 5. A plurality of tubes of floating heads, all indicated by the reference numeral 6, extend longitudinally in the zone of indirect thermal exchange 5 from the plate 3 tube. Tubes 6 define within them a zone (not shown) for housing a conversion catalyst of the known type. In addition, the tubes 6 have a first end 7 in fluid communication with the zone 4 and a second end 8 in fluid communication with a chamber 9 for the collection of a gaseous flow comprising CO, C02, and H2 obtained from the reaction The reference number 10 indicates a tube plate installed between the tubes 6 and the chamber 9, at the second end 8. The lining 2 is also equipped, in the zone of indirect heat exchange, with openings 11 and 12, which are respectively for the inlet and outlet of a heating gas as a thermal source for the conversion reaction. The openings 13 and 14 are also defined in the coating 2 in zone 4, respectively for the inlet of the reaction gas comprising methane and steam and the outlet of the reacted gas comprising CO, C02, and H2. Advantageously, a duct 15 is provided in the coating 2 for extracting the reacted gas coming from the apparatus 1. The duct 15 is in fluid communication with the chamber 9 and the outlet opening of the gas 14. Thanks to the particular structure that results in From the presence of a plurality of individual tubes 6 in combination with the chamber 9 and the reacted gas extraction duct 15, it is possible to ensure an apparatus that is mechanically very simple and easy to implement with respect to the construction, and which it is at the same time extremely reliable and effective from the point of view of the energy and conversion efficiency of the conversion reaction. In the example of figure 1, the extraction duct 15 is installed coaxially with the liner 2 and extends parallel to the pipes 6 through the indirect heat exchange zone 5 and the supply zone 4. According to a method alternative of the present invention (not shown), the duct 15 extends from the chamber 9 to the lower end of the apparatus 1, and the outlet 14 is defined coaxially with and at the lower end of the coating 2. With respect to the example of figure 1, it is thus possible to increase in the zone 5 the space useful for the installation of the tubes 6 with the resulting increase of the heat exchange surface. The reference number 16 indicates in a general manner the sealing means to prevent undesired diversion of the reaction gas or gas reacted. These means 16 also allow the different thermal expansions, in particular of the pipes 6 and the duct 15, in order to ensure the optimum and reliable operation of the apparatus 1.

The gas sealing means 16 are installed, with reference to Figure 1, between the duct 15 and the tube plate 3 and between the duct 15 and the lining 2, although in the example of Figure 2 they are installed between the duct 15 and the tube plate 3 and between the tube plate 3 and the liner 2. According to the embodiment of figure 1, all gas sealing means 16 are advantageously installed in relation to a single part of the apparatus 1, that is, to the extraction duct 15, to simplify the installation of these means within the apparatus as much as possible. To facilitate the maintenance operations of the gas sealing means 16, as shown in Figure 2, the latter can be installed near the reacted gas outlet opening 14. According to this preferred embodiment of the present invention, the Sealing means for gas 16 are installed in relation to a tubular accessory 17 of the tube plate 3 extending from the latter towards the opening 14. Advantageously, the gas sealing means 16 are of the labyrinth type or of the ring type of the gas. compression and preferably of the compression ring type. In the description given below, the term "labyrinth sealing means" is understood to mean a seal created by the coupling of two parts of generally tubular shape, a male part and a female part, the first having its external toothed surface Such a way that, once coupled, solid rims and empty spaces (labyrinth) are created between the coupled parts, which prevents the passage of gas. In the description given below, the term "compression ring sealing means" is understood to mean a seal created by a compression ring installed between a male part and a female part coupled to prevent passage of the gas. Thanks to this type of sealing means 16, it is possible to ensure the gas seal and allow the expansion compensation to be durable and reliable even for large expansion proportions as in the case of the conversion apparatus. Figure 3 shows an enlarged scale in detail of the conversion apparatus 1 of Figure 2, making the sealing means for gas 16 of the compression ring type between the extraction duct clearer and the tubular accessory 17 of the tube plate 3. The sealing means 16 comprise a plurality of compression rings 18 (preferably at least two), housed in respective cavities 19 of a cylindrical element 20 adhered to the end 21 of the duct extraction 15 preferably in a removable manner, for example by means of screws (not shown). The presence of the compression rings 18 between the duct 15 (male) and the accessory 17 (female) prevents the passage of the reacted gas into the heat exchange zone 5 and at the same time allows the duct 15 to extend along the length of the accessory 17 to compensate for its expansion. The gas sealing means 16 of the conversion apparatus 1 in the example of FIGS. 1 and 2 are preferably of the type shown in FIG. 3. With respect to the labyrinth seal, the use of the compression rings allows a series of advantages among which it is worth mentioning: a more effective gas seal (less gas diversion through the seal); greater structural flexibility (the opening between male and female can be raised 10 times more than with the labyrinth seals), and greater strength of the sealing means (shorter for an equal seal). This means that the piston ring sealing means can ensure a good gas seal, even in the case of deterioration and / or misalignment of the female and male parts, as well as greater flexibility when assembling and adjusting the operations in the apparatus. Conversion 1, less sensitivity to the entry of foreign bodies and less risk of retention. The use of piston ring sealing means advantageously extends to an apparatus for performing generally endothermic or exothermic chemical reactions, for example, even for methane or ammonia synthesis reactors, to ensure the gas seal between the parts structurally different ones that have different proportions of thermal expansion. In Figures 1 and 2, the arrows Fl and F2 indicate the various trajectories taken in the conversion apparatus 1, by the gas flow comprising methane and steam (reaction gas) and by the flow of hot gas for thermal exchange indirect, respectively. The operation of the conversion apparatus according to the present invention is described below. The operating conditions of the temperature indicated in the present description are for a primary conversion apparatus. With reference to Figure 1, a gas flow Fl comprising methane and steam (reaction gas), preheated to a temperature between 300 ° C and 500 ° C is fed to the feed zone 4 of the apparatus 1 through the gas inlet opening 13 and arranged to pass to tubes 6 (tube side) for the conversion reaction at a temperature between 500 ° C and 1000 ° C. For this purpose, tubes 6 are properly filled with the catalyst. The conversion reaction is made possible by the heat transmitted by a flow of hot gas F2 having a temperature between 900 ° C and 1100 ° C fed to the heat exchange zone 5 through the gas inlet opening 11. The flow of hot gas F2 flows out of the tubes 6 (coating side) and is discharged from the coating 2 through the gas outlet opening 12 at a temperature of between 300 ° C and 600 ° C. In particular, the flow of hot gas F2 transmits the reaction heating by indirect heat exchange to the colder reaction gas flow Fl. The gas stream Fl comprising CO, C02, and H2 obtained from the conversion reaction is discharged from the tubes 6 through the end 8, collected in the chamber 9 and extracted from the apparatus 1 through the pipeline. 15 and the gas outlet opening 14 at a temperature between 500 ° C and 1000 ° C. As stated above, the gaseous flow Fl, once collected and fed to the duct 15, is no longer in thermal connection with the passage of reaction gas to - l. through the tubes 6, and thus the undesired thermal exchange between the reacted gas and the reaction gas is advantageously avoided. Furthermore, the expansion rates of the various parts of the apparatus 1, especially of the tubes 6 and of the duct 15, due to the different materials and thermal forces to which they are subjected, are effectively compensated for by the particular structure of the chamber 9 and of the duct 15 and by means of the installation of the sealing means 16, which allow the movement of the various parts and at the same time prevent the undesired leakage of gas. It is important to note that the use of these sealing means does not adversely affect the simplicity of the construction of the apparatus according to the present invention. In the examples of FIGS. 1 and 2, the tubes 6 are advantageously installed in a packet of tubes in order to optimize the occupation ratio of the heat exchange zone 5. In addition, to increase the available surface area and thus improve the thermal exchange, the tube package is preferably equipped with appropriate diaphragms 22 and the tubes 6 have fins (not shown). For an ammonia synthesis process, the flow of hot gas F2 preferably comprises the gaseous flow coming from the secondary conversion section. From the above, the numerous advantages achieved by the present invention are clear, in particular that which obtains a reliable conversion apparatus, which is structurally simple and easy to construct and which allows the conversion of methane with low consumption costs. of energy, operation and maintenance.

Claims

NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and therefore the property described in the following claims is claimed as property. A conversion apparatus for the conversion of methane and vapor to CO, C02, and H2, of the type comprising: an external substantially cylindrical coating (2), in which an indirect heat exchange zone (5) is defined and a zone (4) for feeding a gaseous flow comprising methane and steam to the zone of indirect thermal exchange (5); an opening (11) formed in said lining (2) for feeding in said indirect heat exchange zone (5) a flow of heating gas as a thermal source for said conversion; characterized in that it also comprises: a plurality of floating head tubes (6) containing a conversion catalyst, which extends longitudinally in said indirect heat exchange zone (5) and in fluid communication with said feed zone (4); a chamber (9) for collecting a gaseous flow comprising CO, C02 and H2 obtained from said conversion and located downstream of said tubes (6); a duct (15) opened in said collection chamber (9) for extracting from said lining (2) said gaseous flow comprising CO, C02 and H2.
2. An apparatus according to claim 1 characterized in that said extraction duct (15) is installed coaxially with said lining (2) and extends parallel to said tubes (6) through said zone of indirect thermal exchange (5) and said feeding zone (4), from said collection chamber (9) towards a gas outlet opening (14) of said lining (2).
An apparatus according to claim 2 characterized in that suitable gas sealing means (16) are provided between said duct (15) and a tube plate (3) located between said feeding zone (4) and said zone of indirect thermal exchange (5). .
An apparatus according to claim 3 characterized in that suitable gas sealing means (16) are provided between said duct (15) and said lining (2).
5. An apparatus according to claim 3 characterized in that suitable gas sealing means (16) are provided between said tube plate (3) and said liner (2).
6. An apparatus according to claims 3 to 5 characterized in that said gas sealing means (16) are installed near said outlet opening (14).
7. An apparatus according to claims 3 to 5 characterized in that said gas sealing means (16) are of the compression ring type.
8. The use of a seal of the type of compression ring in an apparatus to carry out endothermic or exothermic chemical reactions, in particular conversion reactions, to ensure the gas seal between the structurally distinct parts that have different proportions of thermal expansion .