RU2481888C2 - Starting heater for ammonia synthesis reactors - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to reactors intended for production of ammonia, particularly, to internal starting heater. Proposed device comprises several long electric heating elements extending along heater lengthwise axis and several heating element support plates each being composed of outer frame and parallel support bars with their opposite ends secured to said outer frame. Support bars are arranged in plane perpendicular to said lengthwise axis, between said heating elements and in contact therewith. Said support plates are arranged in a group with first and second plate. Note here that first plate support bars are arranged opposite second plate support bars.

EFFECT: resistance to stains creates by gas flow, higher efficiency.

13 cl, 7 dwg

Description

Technical field

The present invention relates to the field of reactors for the production of ammonia. In particular, the invention relates to an internal starting heater with elongated electric heating elements for use in ammonia reactors.

State of the art

Ammonia synthesis is currently carried out in a catalytic reactor or converter (ammonia synthesis column) in which gaseous hydrogen (H ₂ ) and nitrogen (N ₂ ) react at high pressure (usually 130 bar or more) and temperature (about 500 ° C) Various types of ammonia reactors are known; An example of a typical embodiment can be a cylindrical vessel (housing) for radial flow with three catalytic layers and cooling heat exchangers located between them.

When starting up the reactor, it is necessary to heat the gaseous reactants supplied to the reactor to a temperature of about 450-480 ° C in order to start a chemical reaction. For this, in known reactors, a suitable starting heater is used, which can be performed as an external heater, or as an internal electric heater, placed inside the reactor itself.

The internal starting heater is a substantially cylindrical device that is coaxially inserted into the reactor through an opening in the high pressure cap (designed to operate at elevated pressure), and consisting mainly of a mounting flange with the necessary electrical contacts and a beam of elongated heating elements.

In a known embodiment, these electrical elements are made of non-insulated metal tape extending up and down in the longitudinal direction along the electric heater supported by ceramic insulating elements. In another known embodiment, the heating elements are formed by metal rods in a shell, typically U-shaped. These metal rods are usually insulated, but in some cases uninsulated rods are also used.

In the process, gaseous reactants flow along the heater between the heating elements before entering the catalytic reaction zone, for example, into the first catalytic layer.

In a large reactor, the internal heater may have a length of several meters, and it will require appropriate space and means of fastening the heating elements. In known designs, the heating elements are fixed with a metal grid or ceramic supports connected by cross members. Each of these gratings or ceramic supports essentially consists of a ring with intersecting bars forming a square lattice fixing each of the heating elements with a certain gap.

Such internal heaters have disadvantages, especially with regard to reliability and service life. Failures of internal starting heaters are found especially in modern units with high performance and, accordingly, high gas flow rate.

Due to the relatively large gap between the heating elements and the separation elements and the support grid, the heating elements can move relatively freely in any radial direction, i.e. a plane perpendicular to the longitudinal direction, and therefore they are very sensitive to vibrations generated by the flow, to the associated mechanical stress and wear due to relative movements.

Mechanical stress can lead to permanent deformation or mechanical damage to the heating elements. The deformation of the heating elements leads to damage to these elements themselves; the contact of the heating elements can also lead to damage to the surfaces of the heating elements; contact of uninsulated heating elements may cause a short circuit; any damage to the heating element can lead to local overheating, due, for example, to a local decrease in the cross section, with possible melting and destruction of the heating element itself.

If some heating elements become deformed, it can also be difficult to remove the starting heater from the housing for maintenance or replacement. It should also be noted that in most cases, damage to the starting heater is not immediately detected, for example, due to the fact that the reactor continues to work for a long time with the inoperative starting heater. Damage is sometimes detected after some time when the heating elements are irreparably damaged.

Damage to the starting heater can lead to a prolonged shutdown of the ammonia reactor with corresponding costs, expressed in loss of production.

It should also be noted that the internal start-up heater is a critical component, since the total diameter should be as small as possible, since the heater selects part of the volume that can be used by the catalytic layers, and therefore the chemical reaction. For the same reason, the heating elements have a relatively large length and are located close to each other, which allows the small diameter requirement to be fulfilled while obtaining a sufficient cross section between the heating elements for the gas flow. It is usually not possible to design a larger and shorter internal starter heater to make it more resistant to the vibrations generated by the flow.

Similar limitations apply when upgrading an existing ammonia reactor. The maximum size of the internal start-up heater is determined by the existing mounting opening in the housing cover: even if the reactor is retrofitted for higher performance, it is usually impossible or not desirable to install a larger heater, since such an alteration would include an expensive replacement of the entire high-pressure cover. On the other hand, modernization may require increasing the speed of gas reagents to increase productivity, but at the same time the risk of damage to the starting heater by vibrations created by the flow will increase.

Thus, there is an urgent need to create a start-up heater, in which the noted drawbacks can be overcome, in particular the prevention of failures of auxiliary equipment, for example, a start-up heater, affecting the operation and reliability of the entire reactor and ammonia synthesis unit. Despite the existence of such a need, today, however, there is no effective solution to these problems.

SUMMARY OF THE INVENTION

The present invention is based on the task of creating an internal starting heater for an ammonia synthesis reactor (ammonia reactor), more resistant to the stresses generated by the gas stream and, in particular, less sensitive to the vibrations generated by the stream.

This problem is solved by an internal starting heater for an ammonia reactor containing several elongated electric heating elements passing along the longitudinal axis of the reactor, characterized in that:

- the starting heater contains several support plates for the heating elements, each of which has an outer frame and parallel supporting bars, the opposite ends of which are fixed in the outer frame, and which are located in the plane perpendicular to the longitudinal axis, in the passages between the heating elements in contact with heating elements, and

- the support plates are arranged in at least one group having at least a first and second plate, wherein the arrangement of the support bars of the first plate is different from the arrangement of the support bars of the second plate.

Differently arranged support bars of the support plates forming the group of plates create a radial support for the heating elements with a mutually reinforcing effect. According to an aspect of the invention, the support bars of the selected plate act as fixing means for the heating elements in the selected radial direction of the starting heater so that the group of support plates, due to the mutually reinforcing effect, can prevent the heating elements from moving or vibrating in any direction perpendicular to the longitudinal axis.

In an embodiment of the invention, the heater is equipped with a group (s) of support plates, including perpendicular and (or) staggered beams, to support the heating elements, preventing displacement in any radial direction perpendicular to the longitudinal axis of the heater.

In accordance with another aspect of the invention and upon closer examination, the heater includes at least one group of support plates, including at least a first plate with parallel support beams arranged in a first direction in a plane perpendicular to the longitudinal axis of the heater, and at least a second a plate with parallel support bars located in a second direction perpendicular to the first direction.

In accordance with another feature of the invention, the heater includes at least one group of support plates, including at least a first plate with parallel support bars located in the first direction, and at least a second plate with parallel support bars located in the same direction with a shift relative to the bars of the first plate.

In a preferred embodiment, the plates have parallel and equally spaced support bars.

According to another preferred feature of the invention, at least some of the groups of support plates include plates with differently arranged support bars with alternating positions in the aisles between rows and / or columns formed by elongated heating elements so that the group of support plates has at least one support beam in each of these passages. This configuration provides the necessary contact with the heating elements, counteracting displacement and vibration in any radial direction perpendicular to the longitudinal axis of the heater.

In accordance with this feature of the invention, in a preferred embodiment, the heater has at least one group of four plates in the following sequence:

a) the first plate with parallel and spaced along the same interval supporting bars passing in alternating passages between the heating elements;

b) a second plate with support bars passing in alternating passages between the heating elements, the support bars of the second plate being perpendicular to the bars of the first plate;

c) a third plate with support bars parallel and offset (in a checkerboard pattern) relative to the bars of the first plate so that the bars of this third plate pass in parallel and alternating passages with respect to the bars of the first plate;

d) a fourth plate with support bars parallel and offset relative to the bars of the second plate so that the bars of this fourth plate pass in parallel and alternating passages with respect to the bars of the second plate.

In an even more preferred embodiment, the arrangement of the heating elements of the starting heater forms a square grid, and the support bars are located in the aisles in the diagonals between the heating elements. In an equivalent embodiment, the support bars extend in orthogonal (mutually perpendicular) passages between the heating elements.

In a preferred embodiment, the outer frame of the support plates is a ring substantially perpendicular to the direction of arrangement of the elongated heating elements. The supporting bars are, for example, made of metal pipes welded at the ends to this outer ring frame. As it should be clear to the specialist, the terms perpendicular and parallel are used taking into account the usual tolerances in the structures.

Heating elements are made in the form of resistive elements (electrical resistances). In preferred embodiments of the invention, each of the heating elements mainly includes an outer shell and an electric heating element located inside the shell and electrically isolated from it to prevent the possibility of a short circuit.

The object of the invention is also a converter or reactor (column) for the synthesis of ammonia, equipped with said starting heater. Another object of the invention is a method for upgrading an ammonia synthesis reactor, comprising at least the steps of extracting an existing starting heater and installing a starting heater in accordance with the invention in the original reactor vessel.

The main advantage of the invention is that the elongated heating elements of the starting heater are supported efficiently and reliably to counteract the stresses and vibrations created by the gas stream of the reactants supplied to the ammonia reactor. More specifically, direct contact with the support bars provides the heating elements with a support that counteracts any radial displacements in directions perpendicular to the longitudinal axis of the heater.

As shown above, plates with differently arranged support bars have a mutually reinforcing effect in preventing the vibrations created by the flow. The alternating arrangement of the support bars of the plates forming the group of plates is most preferable, since any heating element is secured against displacement in some direction by direct contact with at least the support bars of one of the plates from each group of plates, with little or no clearance.

As a result, the heating elements are reliably protected from destructive vibrations created by the flow.

These and other advantages will be more apparent when reading the following description of the preferred option and the attached drawings, where:

Brief Description of the Drawings

figure 1 presents a schematic sectional view of an ammonia converter equipped with an internal starting heater, in accordance with an embodiment of the invention;

figure 2 presents a fragment of the starting heater of the ammonia converter shown in figure 1;

figure 3-6 presents the layout of the support bars and plates of the starting heater shown in figure 2;

7 is a view of a typical cross section of a starting heater.

Detailed Description of the Invention

Figure 1 shows a three-layer ammonia reactor or converter 1 having a housing 2 containing catalyst layers 3, 4 and 5 with cooling heat exchangers 6 and 7 located between them. The reactor 1 is equipped with an internal electric starting heater 10. FIG. 1 also shows a high pressure cap (bottom) 12.

The heater 10 is generally a cylindrical device, coaxial with the housing 2, surrounded by a wall 8.

The main components of the starting heater 10 are: a mounting flange 13 for connecting to the high pressure cover 12, electrical contacts 14, a mounting plate 15 for several elongated heating elements extending in a direction parallel to the longitudinal axis XX of the heater 10 itself. The axis XX coincides with the axis of the main body 2 .

In the process, gaseous reagents enter the housing 2 through the upper inlet 11 and flow into the annular space 2a, undergo preliminary heating, flowing upward in the heat exchangers 7 and 6, then flow through the gap 8a around the wall 8, enter the space 8c through the inlet the hole 8b, and then passing along the axis through the heater 10 and in contact with its heating elements, reach the desired temperature of about 450-480 ° C. From the output of the starting heater 10, the reagents pass to the first catalytic layer 3, where the formation of ammonia begins. The path of movement of the gaseous reactants is shown by the arrows in FIGS. 1 and 2. An ammonia converter of this type is well known to specialists and therefore will not be described in detail.

In a preferred embodiment, the heating elements are electrical resistances in the form of metal-clad U-shaped rods 16 having an outer thin shell and an inner heating element electrically isolated from this outer shell. In a preferred embodiment, the rods are filled with a compacted powder of magnesium oxide, isolating the heating element from the outer shell. The internal element is heated by passing electric current.

In a typical cross section of the heater 10, the electric rods 16 are arranged in a square grid, that is, in parallel rows and columns (FIGS. 2-7).

The heater 10 also has support plates 20 for heating elements, i.e. for electric heating rods 16. The support plates 20 are located in planes perpendicular to the longitudinal axis XX and are connected by longitudinal crossbars 23, forming a support frame for the rods 16. The plates 20 generally consist of an outer ring frame and parallel bars attached at their ends to this ring frame.

According to an embodiment of the invention, the starting heater 10 includes support plates 20 with perpendicular and offset bars that touch the heating rods 16.

In the above example, plates 20 are assembled in groups of four plates. Each group of plates includes a sequence of four plates 20A, 20B, 20C and 20D with a different structure. Figure 2 shows a group 20 'of four plates, including the aforementioned plate 20A-20D, and another adjacent group 20' 'of four plates. The plates 20A-20D of the second group 20 '' are arranged in the same sequence as the plates of the first group 20 ', and so on.

The configuration of the first plate 20A is shown in detail schematically in FIG. The plate 20A is mainly formed by a ring 21 and parallel support bars 22A extending into alternating diagonal passages N between the rods 16. The dimensions (for example, diameter or equivalent size) of the bars 22A substantially coincide with the gap “t” between the diagonal rows of the rods 16 (FIG. 3) so that each bar 22A touches two diagonal rows adjacent to this bar 22A. In a preferred embodiment, the bars 22A are made of pipes welded to the ring 21, and the nominal diameter of these pipes is equal to the mentioned gap t.

The next plate 20B of the plate group 20 ′ is shown in FIG. The support bars 22B of the plate 20B are located diagonally, but lie in a direction perpendicular to the bars of the plate 20A. Thus, the bars 22B are placed in the passages P between the rods 16 formed at an angle of 90 ° to the passages N in which the bars 22A of the first plate 20A are placed.

The third plate 20C (FIG. 5) includes parallel bars 22C located in the same direction as the bars 22A of the first plate 20A and extending in the diagonal passages N. The bars 22C of the third plate 20C, however, are offset relative to the bars 22A of the first plate 20A by the distance equal to the distance between two consecutive diagonal rows of heating rods 16. This can be seen in the drawings, comparing FIG. 3 and FIG. 5, considering a rod having the designation 16 *, which is in contact with the first extreme right bar 22 * of the plate 20A, while at emya the first rightmost bar plate 20C to 22C, passing around the next diagonal passage is not in contact with the same rod 16 *.

The fourth plate 20D includes bars 22D extending in the same direction as the bars 22B of the second plate 20B located in the diagonal passages P and offset in the same way.

Depending on the length of the heater 10 and the location of the heating elements 16, the number of plate groups can vary, as well as the number of plates 20 in each group. Some groups of plates, for example the last group, may be incomplete, including, for example, only three plates or less.

It should be noted that, in accordance with the embodiment described here as an example, the support bars of the plates 22A and 22C or, respectively, 22B and 22D are complementary, i.e. placed in complementary groups of diagonal passages N or P.

Figure 7 presents a typical section of the heater 10, which shows that the sequence of different groups of plates allows you to create a radial support for the heating rods 16 on each side. The rod 16 is supported by the interaction of each of the rods 22A-22D, which prevents its possible vibrations in any direction perpendicular to the axis X-X.

It should be borne in mind that due to contact with the bars 22A-22D, the natural vibrations of the heating rods 16 are shifted to higher frequencies, as a result of which the starting heater 10 is much less sensitive to destructive vibrations caused by the flow. At the same time, the rods 16 are not affected by any mechanical restrictions and, for example, thermal expansion can occur freely.

7 also shows that the heating rods 16 occupy about 50% of the available cross section of the heater, leaving another 50% of the cross section for the passage of the gas stream through the gaps 24.

In accordance with the invention, configurations of plates and support bars with a different geometry can be made. For example, an equivalent embodiment is possible in which the support bars enter the orthogonal passages L and M between the heating elements 16 (FIG. 3). The first plate 20A, in this equivalent embodiment, has vertical bars in alternating passages M, and the second plate 20B has horizontal bars in alternating passages L. The bars of the third and fourth plates 20C and 20D in this embodiment are parallel to the bars of plates 20A and 20B and are offset regarding them.

In other embodiments, the bars of the plates 20 can, for example, be placed in the next two passages between the heating rods 16, then the two passages can be skipped, after which the next two beams, etc., or any other variants of such a configuration are installed.

The proposed starting heater 10 can be used to replace the existing internal heater of the ammonia reactor, with its modernization. According to figure 1, the main steps of modernization are to remove the existing heater through the upper hole in the cover 12, and install a new heater with the same overall diameter as the previous one, through the existing hole in the cover 12. Thanks to the use of a new heater, less sensitive to vibration caused by the flow, it is possible to increase the input speed of the reactants and their specific mass flow rate in the catalyst layers and the performance of the reactor 1 as a whole. It should be noted that these advantages are obtained without reducing the reaction space and without any changes in the housing 2 or the cover 12.

Claims (13)

1. An internal starting heater (10) for an ammonia synthesis reactor (1), comprising several elongated electric heating elements (16) extending along the longitudinal axis (XX) of the heater (10), characterized in that it comprises several support plates ( 20) for heating elements (16), each of which includes an outer frame (21) and parallel supporting bars (22A-22D), the opposite ends of which are attached to the outer frame, and these supporting bars are located in a plane perpendicular to said longitudinal axis and (X-X), in the passages (L, M, N, P) between the heating elements (16) and in contact with these heating elements, and the support plates (20) are located at least one group (20 ', 20' ' ) having at least a first and a second plate, and wherein the support bars (22A) of the first plate (20A) are arranged differently from the support bars (22B) of the second plate (20B). 2. The heater (10) according to claim 1, in which at least one group (20 ') includes at least a first plate (20A), with parallel support bars (22A) located in the first direction in the said plane perpendicular to the longitudinal axis (X-X) of the heater (10), and at least another plate (20B), with parallel support bars (22B) located in the second direction in the said plane and perpendicular to the first direction. 3. The heater (10) according to claim 1, in which at least one group (20 ') includes at least a first plate (20A) with support bars (22A) located in the first direction in said plane perpendicular to the longitudinal axis ( X-X) of the heater (10), and at least another plate (20C) with support bars (22C) parallel to the bars (22A) of the first plate and staggered relative to them. 4. The heater (10) according to claim 1, in which the parallel support bars (22A-22D) of the plates (20) are located at the same interval. 5. The heater (10) according to claim 1, in which at least some of the groups (20 ', 20' ') include plates (20A-20D), support bars (22A-22D) of which pass in alternating passages (L, M, N, P) between the rows and / or columns formed by the elongated heating elements (16) so that each group of plates has at least one support bar in each of these passages. 6. The heater (10) according to claim 5, comprising at least one group (20 ') of four plates, sequentially containing:
the first plate (20A) with parallel and equally spaced support bars (22A) passing in alternating passages between the heating elements (16),
a second plate (20B) with support bars (22B) passing in alternating passages between the heating elements (16) and perpendicular to the bars of the first plate,
a third plate (20C) with support bars (22C) parallel and offset from the first plate so that they extend in parallel and alternating passages with respect to the bars (22A) of the first plate (20A), and
a fourth plate (20D) with support bars (22D) parallel and offset from the second plate so that they extend in parallel and alternating passages with respect to the bars (22B) of the second plate (20B). 7. The heater (10) according to claim 6, in which the arrangement of the heating elements (16) forms a square grid. 8. The heater (10) according to claim 5, in which the bars (22A-22D) of the plates extend in diagonal passages (N, P) between the heating elements (16). 9. The heater (10) according to claim 5, in which the bars (22A-22D) of the plates extend in orthogonal passages (L, M) between the heating elements (16). 10. The heater (10) according to claim 6, containing several successively arranged groups (20 ', 20' ') of four plates. 11. The heater (10) according to claim 1, in which each of the heating elements (16) is a resistive element with a shell, including an outer shell and an electric heating element inside it, electrically isolated from this shell. 12. Converter (1) synthesis of ammonia for the reaction of hydrogen and nitrogen to produce ammonia, comprising a housing (2) and an internal starting heater (10) according to any one of the preceding paragraphs. 13. A method for upgrading an ammonia synthesis converter (1) having a housing (2) and a starting heater located inside it, during which an existing starting heater is removed from the housing (2) and a starting heater (10) is inserted into the housing (2) according to any one of claims 1-10.

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