DE102014222333A1 - Reformer with pore or surface burners - Google Patents

Abstract

The invention relates to a reformer, preferably a steam reformer, which comprises a furnace chamber in which reactor tubes are arranged. The reactor tubes are configured to be flowed through by a reaction gas. The furnace chamber is also equipped with pore or surface burners and can be heated with these pore or surface burners preferably from above.

Description

 The invention relates to a reformer, preferably a steam reformer, which comprises a furnace chamber in which reactor tubes are arranged. The reactor tubes are configured to be flowed through by a reaction gas. The furnace chamber is also equipped with several pore or surface burners and can be heated with these pore or surface burners preferably from above.

The necessary heat for operating reformers is usually transferred to the reactor tubes (reaction tubes, reformer tubes) via a cover-fired arrangement of the burners. The fuel gas used is usually natural gas or a mixture of natural gas and process gases, which may contain, for example, H ₂ , CO, CO ₂ and hydrocarbons.

 Propane dehydrogenation (PDH) reformers differ from steam reformers in that they have a significantly lower reaction head height. In addition, in addition to the main reaction (dehydrogenation of propane to propylene) also various side reactions occur (for example, cracking). The small height of the reaction space (length of the reactor tube) causes the flame lengths of the diffusive flames of the jet burners to be too large for a small number of burners (ratio reactor tubes / burners per row of, for example, 4), so that the temperature distribution in the reformer becomes very uneven. It comes thereby to a lower heating of the reactor tubes in the upper area and to a stronger heating in the lower area. The resulting hotter areas result in too high wall temperatures, which can lead to breakage of the catalyst. Furthermore, if the temperatures are too high, the side reactions increase, leading to coking and thus faster deactivation of the catalyst and reduced propylene selectivity.

 Conventional reformers have a comparatively high space requirement because certain minimum distances between the diffusion flames of the jet burners and the reactor tubes must be maintained. Conventional reformers often require several hundred burners for frequently more than a thousand reactor tubes. Therefore, the demand for a uniform application of heat in the production operation is not nearly feasible. Rather, in conventional reformers zones with hot spots and zones with cooler areas on the catalyst outer wall can not be avoided, which has an adverse effect on the behavior of the catalyst (breakage due to overheating and / or different expansion, deactivation of the catalyst, etc.).

DE 199 21 420 A1 discloses tube reformers, which are assigned over their entire length heating tubes, such as radiant tubes with internal burner or tubular pore or surface burner in which the radiant energy exploiting tube spacing. The reformer is designed as a double tube with concentric arrangement of steam / feed feed, supply of an oxidation support and removal of the reformed synthesis gas, wherein a tube surface is formed by a porous, possibly ceramic tube for flameless combustion in the operating position on the surface. The heat transfer takes place mainly by solid state radiation and only to a very small extent by gas radiation. This arrangement has a large footprint, is structurally relatively complex and therefore costly, since each reactor tube is designed as a double tube and is surrounded over its entire length by heating pipes. With this design, it is hardly or not at all feasible for a single burner to heat a plurality of reactor tubes.

 It is an object of the invention to provide reformers that overcome the disadvantages of conventional reformers. The reformers should be characterized by the most uniform temperature distribution, the temperature should be easy, good and safe controllable. Furthermore, the reformers should manage with a small footprint and be as energy efficient as possible and as little maintenance. The reformers should u.a. suitable for carrying out dehydrogenation reactions in which reactors are heated in the form of a bundle of tubes. With regard to the energy distribution, about 2/3 of the necessary energy should be coupled in the first third of the reactor tube, which can not be achieved with the conventional diffusion burner configuration.

 This object is solved by the subject matter of the claims.

 It has surprisingly been found that reformers can be heated with pore or surface burners. In this way, a significantly improved, uniform temperature distribution in the furnace chamber is ensured and the formation of hot spots and zones with cooler areas on the catalyst outer wall is reduced or even completely suppressed. Due to the improved temperature distribution, the reformer can be made more compact, which is why they have a significantly reduced space requirements. This affects u.a. advantageous for the use of materials and energy efficiency.

A first aspect of the invention relates to a reformer, preferably a steam reformer, which comprises a furnace chamber in which reactor tubes are arranged. The reactor tubes are configured to be flowed through by a reaction gas. The furnace chamber is also equipped with pore or surface burners and can be heated with these pore or surface burners preferably from above.

 Compared to conventional reformers, in particular conventional steam reformers, in the reformer according to the invention, flame-guided diffusion burners (nozzle burners) are replaced by pore burners or area burners, which are preferably of planar design in the sense of surface burners. The heat transfer takes place almost exclusively by gas radiation and only to a very small extent by convection and solid state radiation; the flue gas leaving the pore or surface burner penetrates the furnace space and flows around the reactor tubes, whereby they are heated uniformly. For physical reasons, with the same output of all pore burners or surface burners, a negative temperature gradient in the flow direction is formed (warmer at the top than at the bottom), while the temperatures in the horizontal plane are relatively constant over the entire furnace space.

 Reactor tubes (reaction tubes, reformer tubes) within the meaning of the invention are the structures through which a reaction gas flows, in which the chemical reaction of the reaction gas takes place. Since this chemical reaction is usually catalytically, the reactor tubes are preferably filled with a catalyst or with a mixture of a plurality of catalysts, which may optionally be applied to a carrier. Suitable catalysts are known to a person skilled in the art. The wall of the reactor tubes is preferably made of metal. However, in principle, other materials can also be used, for example ceramics. Suitable materials are known to a person skilled in the art.

 In a preferred embodiment, the reformer of the invention comprises at least 100 or at least 200 reactor tubes, more preferably at least 300 or at least 400 reactor tubes, more preferably at least 500 or at least 600 reactor tubes, most preferably at least 700 or at least 800 reactor tubes, and especially at least 900 or at least 1000 reactor tubes. which are preferably all arranged together in a furnace chamber.

 Diameter and length of the reactor tubes depend on the chemical reaction which is to take place in the reformer. Typical internal diameters of the reactor tubes are in the range of 5 to 15 cm, more preferably 8 to 12 cm. Typical heated lengths of the reactor tubes are in the range of 1 m to 5 m, more preferably 2 m to 3 m.

 Preferably, the reactor tubes are arranged substantially parallel to one another and / or substantially vertically. Particularly preferably, the reactor tubes are arranged in a plurality of rows, wherein the individual reactor tubes within a row are preferably arranged parallel to one another and / or vertically and wherein the rows are arranged substantially parallel to each other, so that lanes are formed between the rows of reactor tubes. The pore or surface burners are then particularly preferably arranged above the lanes, preferably along the lanes, so that the pore burners or area burners are also arranged in rows. In plan view, a sequence of parallel rows of reactor tubes - pore reactor tubes - pore burners, etc. are then preferably obtained. In the side view, the pore burners are preferably located above the top of the reactor tubes, i. the pore burners do not extend the length of the reactor tubes. The heat input is thus preferably exclusively from above, in which case the flue gas flowing into the furnace chamber from above reaches the reactor tubes, surrounds them and heats them in this way.

 If the reactor tubes are arranged in rows, the shortest distance A between two adjacent rows of reactor tubes is preferably at most 180 cm or at most 160 cm, more preferably at most 140 cm or at most 120 cm, even more preferably at most 100 cm or at most 80 cm, wherein in each case Center point of the cross-sectional area of the reactor tubes for the determination of the distance A is based. Due to the virtually flameless combustion taking place outside the furnace space, it is not necessary to keep the distance to the reactor tubes to avoid hot spots due to flame contact, as can occur with diffusion burners. This leads to very significant potential savings with respect to the space. Thus, the distance between reactor tube and burner can be halved if necessary.

Reaction gas in the context of the invention is basically any gas or gas mixture which can be converted, preferably catalytically, in a gas phase reaction. Preferred reaction gases include propane, which is catalytically dehydrogenated to propene and hydrogen; as well as natural gas, which is catalytically converted to synthesis gas, which can then be obtained from the synthesis gas subsequent products such as ammonia or methanol. Typical gas compositions include, for example, (i) H ₂ 83%, CH ₄ 5%, C ₂ H ₆ 3.5%, CO ₂ 7%, remainder 1.5%; or (ii) H ₂ 49%, CH ₄ 45%, C ₂ H ₆ 3.7%, balance 2.3%.

 Pore or area burners in the context of the invention are known to a person skilled in the art. These are gas burners of special design, in which the combustion reaction of the premixed fuel-air mixture takes place in a porous structure and not in an open flame. The result is a flameless, volumetric combustion, which is sometimes referred to as "glowing foam". Since an exiting free flame is dispensed with, pore burners, unlike conventional diffusion burners, do not have a combustion chamber but a reactor comprising a large number of small reactors filled with ceramic foam or other structures. Here, the combustion takes place within a ceramic or metallic porous matrix. The fact that the exhaust gas flow is divided and merged over and over again improves the heat transfer from the flame to the porous structure. The burner emits a smoke stream which is very homogeneous in temperature and which at first releases the heat mainly to the environment by means of gas radiation and only to a small extent by convection and solid state radiation.

 The pore or surface burner according to the invention preferably comprises two zones, a blocking zone which contains comparatively small pores, and a reaction zone, which is preferably larger than the blocking zone and contains comparatively larger pores or cavities. The small pores of the blocking zone are preferably chosen so that an ignition of the fuel-air mixture is not possible. Likewise, the barrier zone serves as a flame arrestor to prevent flashbacks and flashbacks at low loadings or low gas-air flows. In the reaction zone connected to the exclusion zone, combustion is stabilized. The good heat transfer properties of the porous medium prevent the lifting of the flame at high loads or high gas-air flows. Since flame lift-off and flashback are prevented, the performance of the pore burner can be modulated in a wide range, typically e.g. 1: 4. The result is a compact, low-emission combustion system with high power density and energy efficiency.

 While conventional burner systems are characterized by inhomogeneous, flow stabilized reaction zones with local temperature spikes and high emissions, the pore burner of the present invention allows homogeneous temperature ranges at higher power density with greater dynamics as well as the use of low calorific value fuels (such as landfill gas). In comparison to conventional diffusion burners, the pore burner according to the invention has u.a. the advantage that it allows a homogeneous and stable combustion process in a reactor, whereby a significant acceleration of the combustion reaction is achieved.

In comparison with conventional diffusion burners, the flameless pore or surface burners according to the invention have a number of advantages in the reformer according to the invention: the energy densities are very high; the solid-state radiation component is very high in the entire power range with a radiator temperature of up to 1400 ° C; in terms of performance, a high modulation capability is ensured; the temperature distribution over the combustion chamber cross-section is very homogeneous; the distribution of the flue gas (exhaust gas) over the combustion chamber cross-section is very homogeneous; and there are no free flames that cause local overheating. The result is minimal emissions (CO and NO _x ); uniform emission of hot flue gases (exhaust gases) and solid state radiation over the entire burner surface; Avoidance of local overheating; No flames in the combustion chamber, burn-out length and flame stabilization zone; Adaptation of the burner geometry to the material to be heated; stepless modulation of the burner output; no significant change in the flow and temperature fields in the modulation range; Improvement of heat transfer and thus energy savings (eg up to 60%); Reduction of CO ₂ emissions; Increase in product quality; Increase in product throughput; Reduction of noise emissions; Improvement of working conditions and ergonomics.

 The pore or surface burners according to the invention can be made very variable in shape. It is possible to install the pore burners as burner runners along an aisle of the reactor tubes. This arrangement has the advantage that along a groove only a limited number of ignition points (2 to 3 electrical ignitions) and also only a small number of monitoring elements for a comprehensive monitoring are necessary. This leads to significant savings in the instrumentation of a reformer.

 In a preferred embodiment, each pore or surface burner comprises a plurality of burner heads through which the heat generated emerges.

Preferably, each pore burner comprises at least 3 burner heads, more preferably at least 4, even more preferably at least 5, most preferably at least 6, and most preferably at least 7, at least 8, at least 9, at least 10, at least 11 or at least 12 burner heads.

 In this case, the plurality of burner heads are preferably distributed along the main direction of extent of the pore or surface burner, particularly preferably in the form of a line. The aspect ratio (length to width) of each pore or surface burner is preferably at least 3: 1, more preferably at least 4: 1, and in particular at least 5: 1. A typical pore or surface burner according to the invention has, for example, a length of 4 m and a width of 70 cm, wherein along the main extension direction 10 individual burner heads with a length of 40 cm and a width of 70 cm are arranged.

 In a preferred embodiment, a plurality of pore or surface burners or their burner heads are arranged in rows and thereby preferably form a burner trough.

 If the pore burners are arranged in rows, the shortest distance C between two adjacent rows of pore burners is preferably at most 180 cm or at most 160 cm, more preferably at most 140 cm or at most 120 cm, even more preferably at most 100 cm or at most 80 cm, wherein in each case the central axis of the furnace chamber facing cross-sectional area of the pore or surface burner for the determination of the distance C is used.

 In a preferred embodiment, the pore burners are arranged to heat the oven cavity from above, i. the heat exits of the pore burners or burner heads are aligned so that they release the heat from top to bottom into the furnace chamber (cover-fired arrangement of the burners to the reactor tubes). For this purpose, the pore or surface burners can be integrated into the ceiling of the furnace chamber or alternatively be arranged below the ceiling of the furnace chamber. The burned flue gas then flows from above into the furnace chamber and heats the reactor tubes, in particular by gas radiation. The burners mounted on the furnace roof emit the hot combustion gases into the furnace chamber evenly distributed over the burner surface. The reactor tubes are thus washed around by a negative temperature gradient in the flow direction of the exhaust gas (warmer at the top than below) from the hot exhaust gases. The heat transfer is done by mainly by gas radiation and only to a very small extent by solid state radiation and convection without that it can lead to local overheating due to impinging flames. Figuratively speaking, the reactor tubes are located in a hot exhaust gas bath which, due to the flat inflow, has a significantly higher homogeneity with respect to the temperatures compared with the flame-type diffusion burners. This makes it possible to heat the reactor tubes with a high average heat transfer. Furthermore, most of the heat in the region of the highest reaction rate of the main endothermic reaction of the reaction gas is introduced in the upper region of the reactor tubes. The uniform temperature distribution prevents damage to the catalyst.

 The pore or area burners according to the invention are preferably fully premixing gas burners.

The pore or surface burners according to the invention preferably have an energy density of at least 120 kW / m ² , more preferably at least 250 kW / m ² , even more preferably at least 300 kW / m ² .

 Preferably, the pore burners of the present invention produce a radiation temperature of at least 800 ° C, more preferably at least 1000 ° C, and even more preferably at least 1400 ° C.

 In a preferred embodiment, the heat outputs of the pore burners are flanked laterally by radiation transformers along an upper region B of the reactor tubes. By such specially positioned radiation transformers, such as radiation plates or radiation plates, which may be arranged for example parallel to the upper parts of the reformer tubes, the heat flux density can be increased by the local increase of the radiation component targeted in the required range. The radiant panels can be provided with slots so that they can be adjusted in height according to the operational requirements. In addition to the aforementioned radiation plates and radiation plates, it is also possible according to the invention to form the radiation transformers from highly heat-conductive metal foams. The upper region B preferably makes up at most 50% of the longitudinal extent of the reactor tubes, more preferably at most 40%, even more preferably at most 30% and in particular at most 20%.

 In a preferred embodiment, a plurality of pore or surface burners are arranged in rows and the burner lines thus formed are provided with burner hoods. The burner hoods are then preferably mounted on the furnace roof. On the one hand, the burner hoods have the advantage that the thermal separation of the pore or surface burners from the hot furnace chamber is ensured and, on the other hand, the installation and replacement of pilot burners is simplified. This offers advantages in the assembly and maintenance of the systems.

Preferably, the number ratio of pore burners to reactor tubes is in the range of 1: 1 to 1: 100, more preferably 1: 3 to 1:30, even more preferably 1: 5 to 1:25, most preferably 1: 8 to 1: 22 and especially 1:10 to 1:20.

 Preferably, the number ratio of burner heads to reactor tubes is in the range of 1: 1 to 1:50, more preferably 1: 1 to 1:20, more preferably 1: 1 to 1:10, most preferably 1: 1 to 1: 7 and especially 1 : 1 to 1: 5.

 A further aspect of the invention relates to a method for carrying out a gas phase reaction comprising passing a reaction gas through the reactor tubes of a reformer according to the invention described above and heating the furnace chamber with the pore burners.

 Preferably, the combustion air is not preheated in the inventive method. In normal operation, the air ratio is preferably in the range of 1.0 to 2, more preferably 1.0 to 1.2.

 All preferred embodiments which have been described above in connection with the reformer according to the invention apply analogously to the process according to the invention.

 Another aspect of the invention relates to the use of a reformer according to the invention described above for carrying out the inventive method described above. Another aspect of the invention relates to the use of a pore or surface burner according to the invention described above for heating a reformer, preferably a reformer according to the invention described above.

 All preferred embodiments which have been described above in connection with the reformer or the process according to the invention apply analogously to the uses according to the invention.

 In summary, the exchange according to the invention of conventional diffusion burners by means of pore or area burners according to the invention for reformers, inter alia. the following advantages: reduction of the burner to be individually set and controlled; Reduction of the necessary width of the "oven" i. significant reduction in footprint; no flames in the area of the reactor tubes, which lead to undesired local overheating or do not allow the desired heat input in the upper area; the burners emit only hot exhaust gas between the reactor tubes, which flows around them evenly and heats the reactor tubes along its entire length; for physical reasons, a negative temperature gradient arises from top to bottom (in the flow direction) (warmer at the top than below); temperature uniformity in a horizontal plane is significantly improved over conventional reformers; the variation of the burner power does not qualitatively change the heat transfer.

The invention is described below by the 1 to 5 explained in more detail. A person skilled in the art will recognize that the embodiments of the invention explained in the figures are not to be construed restrictively and that certain features are not essential to the functioning of the invention, so that these features need not necessarily be realized, but may even be omitted.

1 schematically illustrates in plan view a section through a reformer according to the invention ( 1 ), which has a furnace space ( 2 ), in the reactor tubes ( 3 are arranged, which are configured to be flowed through by a reaction gas, wherein the furnace chamber ( 2 ) with pore or area burners ( 4 ) is heated. Each pore or area burner ( 4 ) is formed linearly in the sense of a burner trough, wherein in each case 10 burner heads ( 5 ) along the main extension direction of the pore or area burner ( 4 ) are evenly distributed. In this way, the 10 burner heads ( 5 ) of each pore or area burner ( 4 ) arranged in rows. The reactor tubes ( 3 ) are also vertically in several rows ( 6 ), wherein between two adjacent rows ( 6 ) one lane each ( 7 ), above which the pore or surface burner ( 4 ) in parallel alignment with the rows ( 6 ) is arranged. Two adjacent rows ( 6 ) have the distance (A) to each other.

Illustrated for comparison 2 schematically in plan view a section through a conventional reformer, in which the not with pore or area burners, but with conventional diffusion burners ( 8th ) is heated. The diffusion burners thereby produce vertically downwardly directed flames which extend into the furnace chamber. In order to ensure sufficient heating of the reactor tubes, a significantly larger number of diffusion burners is required than in 1 ,

3 schematically illustrates a preferred embodiment in side view as a section through a reformer according to the invention ( 1 ). In this case, three mutually parallel, vertically oriented reactor tubes ( 3 ) arranged below the furnace roof, in which two pore or area burners ( 4 ) or burner heads ( 5 ), the burned flue gas (long dashed arrows) into the furnace space in the areas between the reactor tubes ( 3 ) emit. Flanking in the embodiment shown in the upper region (B) of the reactor tubes ( 3 ) Radiation transformers ( 9 ) the outlet openings of the pore or area burners ( 4 ) or burner heads ( 5 ) and ensure improved heat distribution (short arrows) in this upper region (B) to the reactor tubes ( 3 ).

4 schematically illustrates in plan view a section through a reformer according to the invention ( 1 ), which in comparison to the embodiment according to 1 requires less space. This is especially due to a smaller distance (A) of adjacent rows (A). 6 ) of reactor tubes ( 3 ) to expression.

5 schematically illustrates a preferred pore or surface burner according to the invention ( 4 ), which with a burner hood ( 10 ) is equipped. 5A shows a side perspective view, 5B a perspective view from below. 5A shows a total of three burner heads ( 5 ) on the side facing away from the furnace chamber. 5B shows these three burner heads ( 5 ) on the furnace chamber facing side with the respective burner surfaces ( 11 ). The three burner surfaces ( 11 ) are of a thermal insulation ( 12 ) and a flange surface ( 13 ), which for attachment of the pore or area burner ( 4 ) on the furnace roof.

LIST OF REFERENCE NUMBERS

1

 reformer

2

 furnace

3

 reactor tube

4

 Pore or area burners

5

 burner head

6

 string

7

 streets

8th

 diffusion burner

9

 radiation transformer

10

 burner hood

11

 burner surface

12

 thermal insulation

13

 flange

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 19921420 A1 [0005]

Claims (16)

A reformer ( 1 ) comprising a furnace space ( 2 ), in the reactor tubes ( 3 are arranged, which are configured to be flowed through by a reaction gas, characterized in that the furnace chamber ( 2 ) with pore or area burners ( 4 ) is heated. The reformer ( 1 ) according to claim 1, wherein each pore burner ( 4 ) several burner heads ( 5 ). The reformer ( 1 ) according to claim 2, wherein each pore or area burner ( 4 ) at least three burner heads ( 5 ). The reformer ( 1 ) according to claim 2 or 3, wherein the plurality of burner heads ( 5 ) line along the main extension direction of the pore or surface burner ( 4 ) are distributed. The reformer ( 1 ) according to any one of the preceding claims, wherein the pore or area burners ( 4 ) - are arranged in rows and / or - heat the furnace chamber from above. The reformer ( 1 ) according to any one of the preceding claims, wherein the pore or area burners ( 4 ) - are fully premixed gas burners; and / or - have an energy density of at least 120 kW / m ² ; and / or - produce a radiation temperature of at least 800 ° C. The reformer ( 1 ) according to any one of the preceding claims, wherein the reactor tubes ( 3 ) - are arranged substantially parallel to one another and / or - substantially vertically. The reformer ( 1 ) according to any one of the preceding claims, wherein the reactor tubes ( 3 ) in rows ( 6 ) are arranged, which are arranged substantially parallel to each other, so that between the rows ( 6 ) of reactor tubes ( 3 ) Alleys ( 7 ) are formed. The reformer ( 1 ) according to claim 8, wherein the pore burners ( 4 ) above the streets ( 7 ) are arranged. The reformer ( 1 ) according to claim 8 or 9, wherein the shortest distance A between two adjacent rows ( 6 ) is at most 180 cm. The reformer ( 1 ) according to one of the preceding claims, wherein the heat escapes from the pore burners ( 4 ) along an upper region B of the reactor tubes ( 3 ) side of radiation transformers ( 9 ) flanked. The reformer ( 1 ) according to any one of the preceding claims, wherein the number ratio of pore or area burners ( 4 ) to reactor tubes ( 3 ) ranges from 1: 1 to 1: 100. The reformer ( 1 ) according to one of claims 2 to 12, wherein the number ratio of burner heads ( 5 ) to reactor tubes ( 3 ) ranges from 1: 1 to 1:50. A process for carrying out a gas phase reaction comprising passing a reaction gas through the reactor tubes ( 3 ) of a reformer ( 1 ) according to one of claims 1 to 11 and the heating of the oven space ( 2 ) with the pore or area burners ( 4 ). Use of a reformer ( 1 ) according to one of claims 1 to 13 for carrying out the method according to claim 14. Use of a pore or surface burner ( 4 ) as claimed in any one of claims 1 to 6 for heating a reformer ( 1 ).

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