CH631637A5 - Catalytic reactor plant - Google Patents

Description

The invention relates to a catalytic reactor system which is used, for example, to produce product gases from a feedstock.

Catalytic reaction systems for converting hydrocarbon fuels into usable industrial gases, such as hydrogen, are known. They are generally designed for a high yield of product gas. Plant size is generally of secondary importance because the cost of producing the product gas is a small fraction of the price of the products made from the product gas. The most common method of producing hydrogen is to steam reform a hydrocarbon fuel by passing it through reaction or reactor tubes filled with a heated catalyst and placed within an oven. Typically, the reaction tubes are 6.1 to 12.2 m long and the heat transfer takes place mainly (in the order of 70%) by radiation from the furnace walls onto the reaction tubes. This requires a relatively wide space between the tubes and the placement of the tubes next to the walls of the furnace so that each tube is evenly heated by radiation from the walls. These technical hydrogen production plants have a very high heat transfer capacity in the order of 54 260 to 67 825 kcal / m2 reaction tube surface area and per hour. However, this type of plant is mainly dependent on radiant heat and the thermal reactor efficiency is only 40 to 60%. While high hydrogen conversion rates can be achieved, a large percentage of the thermal energy generated in the furnace leaves the furnace in the form of high temperature exhaust gases (i.e. in the form of waste heat). Large amounts of fuel must therefore be burned to achieve high heating outputs. If the heat energy is not used in a separate process, for example to generate steam, it must be dissipated as energy loss. Even if the waste heat is exploited, it is not used to generate hydrogen, thereby reducing the thermal efficiency of the reactor and increasing the cost of the hydrogen generated.

Along with the development of fuel cell power plants, the need for cheap hydrogen came along

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Fuel and the need for low plant costs in order to make the fuel cell power plants economically competitive with existing power generation plants. This need created an additional incentive to reduce the size and operating costs of fuel processing plants for the production of hydrogen from hydrocarbon fuels. U.S. Patent Nos. 3,144,312 and 3,541,729 describe attempts to reduce the size of reactor plants and to increase thermal efficiency. The extent to which these attempts were successful, if successful at all, cannot be readily determined. In the following description, however, the disadvantages of the constructions known from these US patents are set out in comparison with the invention.

US Pat. No. 3,909,299 describes a steam reforming reactor construction which, while having some desirable features, cannot be as effective or as compact as the system according to the invention described below.

The aim of the invention is to create a catalytic reactor system which can work with high thermal reactor efficiencies and has a compact structure.

Such a reactor plant is characterized by the wording of claim 1.

Several embodiments of the invention are shown in the drawings and are described in more detail below. Show it:

Fig. 1 shows a partial vertical section of a catalytic reactor system and

2 is a cross section through the system of FIG. 1 essentially on the line 2-2 of FIG. 1st

The catalytic reactor system 10 of FIGS. 1 and 2 is considered as an exemplary embodiment of the invention. In this embodiment, the plant is for steam reforming a reformable hydrocarbon fuel in the presence of a suitable catalyst to produce hydrogen. The system 10 contains a furnace 12 with burner nozzles 14, with a burner fuel distributor 16 and with an air distributor 18. A number of tubular reactors 20 are arranged within the furnace 12.

Each reactor 20 has an outer cylindrical wall 22 and an inner cylindrical wall or center tube 24 which define an annular reaction chamber 26 therebetween. The reaction chamber 26 is filled with steam reforming catalyst pellets 28 that rest on a grid 30 located at the inlet 32 of the reaction chamber. Any suitable steam reforming catalyst, such as nickel, can be used to fill the reaction chamber from its inlet 32 to its outlet 36. The cylinder, which is delimited by the outer wall 22, is closed at its upper end 38 by an end cap 40. The middle tube 24 has an upper inlet end 42 and a lower outlet end 44. The inlet end 42 ends below the end cap 40 so that the middle tube is in gas communication with the outlet 36 of the reaction chamber 26.

A cylindrical plug 46 is disposed within the central tube 24, the outer diameter of which is slightly smaller than the inner diameter of the central tube, whereby an annular regeneration chamber 48 is formed between the plug and the central tube and has an inlet 49. The plug 46 may be a solid rod, but in the embodiment described here, it is a tube which is closed by an end cap 50 at one end, so that reaction products leaving the reaction chamber 26 around the plug 46 through the

Regeneration chamber 48 must flow. The distance between the plug 46 and the central tube 24 is maintained by bulges 52 in the plug wall.

The regeneration chamber 48 serves the purpose of returning heat from the reaction products leaving the outlet 36 into the catalyst bed of the reaction chamber 26. Therefore, outlet 54 of reaction chamber 48 is considered adjacent to inlet 32 of the catalyst bed rather than located at outlet end 44 of the center tube, despite the fact that the actual ring formed between plug 46 and center tube 24 extends to outlet end 44. The arrangement shown in Fig. 1 provides a certain preheating of the process fuel before it enters the catalyst bed. However, this is not critical to the present invention. In addition, in this embodiment, the plug 46 extends over the entire length of the reaction chamber, so that the inlet 49 of the regeneration chamber is located next to the outlet 36 of the reaction chamber. While this is preferred for maximum regeneration, the regeneration chamber inlet can be located anywhere between the inlet and outlet of the reaction chamber using a shorter plug.

It should be noted that the regeneration chamber 48 is essentially isolated from the hot furnace gases. In order to achieve maximum overall reactor efficiency, it is important to prevent the thermal energy of the furnace gas from heating the reaction products within the regeneration chamber 48. It is also important to prevent the burning of additional fuel or hydrogen within the regeneration chamber 48. Only internal heat that is already present in the reaction products at outlet 36 is transferred to the reaction chamber.

Each reactor 20 can be regarded as a reactor which has an upper part 56 and a lower part 58. The upper part 56 is arranged in a space which is referred to below as the combustion chamber 60. The combustion chamber 60 is the volume of the furnace 12 within which the actual combustion of the fuel and air which are introduced into the furnace takes place. This space is characterized by very high temperatures, considerable radiant heating and convection heating of the reactors 20 and by axial (i.e. in the direction of the axis of the reactors 20) and radial mixing of the gases therein.

The lower part 58 of each reactor is surrounded by a cylindrical wall 62 which is arranged at an outer distance from the wall 22 and with which it delimits an annular burner gas channel 64 with an inlet 66 and an outlet 67. The outlet 67 is located next to the inlet 32 of the reaction chamber 26. The channel 64 is filled with a heat transfer packaging material which rests on a grid 68 and, in the present example, consists of balls 70 made of aluminum. The space 72 between adjacent cylindrical walls or channels 62 is filled with a non-heat conductive material, such as ceramic fiber insulation, which rests on a plate 74 which extends across the furnace and in which holes are formed through which the reactors 20 pass. The plate 74 and the material within the space 72 prevent the furnace gases from flowing around the outside of the cylindrical walls 62.

In addition to plate 74, plates 76, 78 and 80 also extend over the furnace and define manifolds between them. The plate 80 rests on the bottom wall 82 of the furnace. The plates 78 and 80 define one between them

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Reaction product manifold 84. Plates 76 and 78 define a process fuel inlet manifold 86 therebetween. Plates 74 and 76 define a furnace gas outlet manifold 88 therebetween. Plugs 46 and center tubes 24 abut bottom plate 80. The outer walls 22 of the reactors abut plate 78. The cylindrical walls 62 abut the plate 74.

In operation, a mixture of steam and reformable hydrocarbon fuel from manifold 86 enters inlet 32 of reaction chamber 26 through holes 90 in wall 22; the distributor 86 is supplied via a line 92. Immediately, the mixture begins to be heated by the furnace gases flowing through it in countercurrent through the channel 64, and the mixture begins to react in the presence of the catalyst particles 28. As the fuel, steam, and reaction products move upward within the reaction chamber 26, they continue to react and absorb additional heat. The temperature of the reaction products reaches a maximum at the outlet 36. The hot reaction products enter the inlet 49 of the regeneration chamber 48. As the reaction products travel the length of the annular regeneration chamber, heat is returned from them to the reaction chamber 26. They then enter the reaction product distributor 84 through holes 94 in the central tube 24 and are led away from the reactor via a line 96 for further processing, storage or consumption.

Fuel for the furnace enters the manifold 16 via a line 98 and then enters the combustion chamber 60 via the nozzles 14. Air enters the manifold 18 via a line 100 and passes through annular passages 102 which surround each nozzle 14. into the combustion chamber 60. The combustion of the fuel and the air takes place within the combustion chamber 60. The hot gases from the combustion chamber move through the channels 64 into the distributor 88 and are discharged via a line 103. The temperatures within the combustion chamber are generally sufficiently high that high heating powers are achieved in the area of the upper parts 56 of the reaction chambers in spite of the relatively low heat transfer coefficient in this area. If the temperature of the furnace gases drops as the gases move away from the burner nozzles, the heating output would normally become unduly low. However, this is counteracted according to the invention by using the annular burner gas channels 64 above the lower parts 58 of the reactors. If properly dimensioned, these channels increase the local heat transfer coefficients and therefore the heat transfer efficiency values. This leads to high heating outputs both over the upper parts and over the lower parts, despite the lower temperatures of the furnace gases in the area of the lower parts. The annular gap size of the burner gas channel, the reaction chamber and the regeneration chamber is of primary importance in achieving high heating outputs. These gaps are dimensioned in such a way that the highest possible degree of heat transfer efficiency results, which is compatible with the desired exhaust gas temperatures of the furnace gases and the reaction products. Although theoretically the heat transfer efficiency increases as the burner gas channel becomes narrower and the regeneration chamber gap decreases, practical limit values such as the maximum permissible wall temperatures and pressure drops within the rings are important factors when determining the minimum permissible gap sizes for a special application. The annular gap size of the reaction chamber is selected in connection with the gap sizes of the burner gas channel and the regeneration chamber such that sufficiently high temperatures result in the entire catalyst bed without furnace gases in the burner gas channel heating the reaction products within the regeneration chamber 48 on the other side of the catalyst bed. The regeneration chamber 48 must, as already mentioned above, be essentially insulated from the heat effects of the furnace gases.

At this point it is interesting to compare the invention with the systems known from the above-mentioned US Pat. Nos. 3,541,729 and 3,144,312. In the plant known from US Pat. No. 3,541,729, the furnace heating current flows in the same direction as the current through the annular catalyst bed along the inner wall thereof. This solution is clearly less effective and differs from the counterflow which, according to the invention, goes along the outer wall of the bed. In the plant known from U.S. Patent 3,541,729, the highest furnace gas temperatures are at the inlet end of the catalyst bed, which is the coolest end, and the heat transfer in this area is likely to be so great that a significant amount of the heat from the furnace gases is applied to the upper parts of the regeneration stream is transmitted in the ring 113. This heat leaves the furnace along with the reaction products, thereby reducing overall thermal reactor efficiency. This is not the case with the invention because the burner gas at the reaction chamber inlet is coldest due to the counterflow.

The plant known from US Pat. No. 3,144,312 differs from the plant according to the invention in that the furnace gases are located on the inner annular catalyst bed. In addition, the furnace gases flow alongside the inner as well as the outer reaction stream, which is in contrast to the invention, in which the regeneration stream is essentially isolated from the hot furnace gases, which is an important requirement. It should also be noted that the relatively cool cylindrical outer wall 10 is rigidly attached to the relatively hot inner cylindrical wall 9. Stresses caused by different thermal expansion between these two walls are likely to be impermissibly high and can cause interference. Furthermore, none of the plants known from the two US patents is suitable for use with multiple reactors in a single furnace.

Returning to the present invention, it should be noted that it has been found that a relatively narrow range of gap sizes results in good thermal reactor efficiencies at both high and low process fuel throughputs. The heat transfer packing material 70 disposed within the channels 64 provides a further improvement in the heat transfer efficiency and uniformity of the heat distribution compared to a ring of the same size but without the heat transfer packing material. Since the heat transfer efficiency increases with decreasing annular gap size, the heat transfer packing material 70 could be omitted if the size of the annular burner gas channel were reduced. While this is within the scope of the invention, a wider annular channel with heat transfer packing material is preferred because it is more difficult and expensive to maintain allowable dimensional tolerances as the gap becomes smaller. Permissible ranges for gap sizes with and without heat transfer packaging material are given in Table 1, while the best results achieved using the preferred ranges are given in Table 2. The specified4

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The areas mentioned are reliable estimates, which are largely based on test results. It should be noted that the specified ranges can be extended for reactors with a very small or very large diameter.

Table 1 Permissible annular gap sizes

Reaction chamber 7.6-50.8 mm

Regeneration chamber 2.5-25.4 mm

Burner gas duct (without packing material) 2.5-25.4 mm

Burner gas duct (with packing material) 12.7-76.2 mm

Table 2 Preferred ring gap sizes

Reaction chamber 12.7-38.1 mm

Regeneration chamber 3.2-12.7 mm

Burner gas duct (without packing material) 6.4-12.7 mm

Burner gas duct (with packing material) 12.7-50.8 mm

Some other factors that determine the choice of the gap size are: properties of the gases and catalyst particles, the thickness and thermal conductivity of the walls that separate the heating gases and the heated gases, and the Reynold number of the different flows. The walls that separate the countercurrents from each other are usually made as thin as possible, as is compatible with the structural integrity, and made from materials that are not very expensive but have good thermal conductivity. The catalyst is generally chosen so that it has good reactivity and a long life. The catalyst particle size is generally chosen to be as small as possible to maximize the catalyst surface area, but not so small as to create an unacceptable pressure drop in the reaction chamber.

Although not shown in the drawings, means should be provided to prevent fluidization of the catalyst bed due to the upward flowing process gas.

Example I

In a steam reforming reactor plant similar to that of FIGS. 1 and 2 with nineteen tubular reactors, each reactor had a length of approximately 1524 mm, measured from inlet 32, and an outer wall diameter of 229 mm. Half of the length (762 mm) of the reactor extended into the combustion chamber 60. The outer walls 22 of adjacent reactors were 76 mm apart. The reactors on the furnace wall were between 102 and 127 mm away from it. The gap between the outer wall 22 and the inner wall 24 was 27.9 mm, that between the inner wall 24 and the plug 46 was 6.4 mm and that between the cylindrical wall 62 and the outer wall 22 was 31.8 mm. The burner gas channel was filled with 12.7 mm diameter Raschig rings made of aluminum oxide. The catalyst was in the form of cylindrical pellets. The process fuel was naphtha, which entered the catalyst bed as a vapor mixed with about 4.5 parts by weight of water vapor. The process fuel throughput was about 11.3 kg / h per reactor with a total fuel throughput of about 215 kg / h. A conversion rate of 95% and a total thermal reactor efficiency of 90% were achieved.

Example II

In a steam reforming reactor plant with a single tubular reactor, the reactor length was

1524 mm, measured from inlet 32, and the reactor had an outer wall diameter of 229 mm. Half of the length (762 mm) of the reactor extended into the combustion chamber 60. The furnace wall was all around 76 mm from the outer wall of the reactor. The gap between the outer wall 22 and the inner wall 24 was 27.9 mm, that between the inner wall 24 and the plug 46 was 6.4 mm and that between the cylindrical wall 62 and the outer wall 22 was 31.8 mm. The burner gas channel was filled with aluminum oxide balls with a diameter of 12.7 mm. The catalyst was in the form of cylindrical pellets. The process fuel was naphtha, which entered the bed as a vapor mixed with about 4.5 parts by weight of water vapor. The process fuel throughput was 12.7 kg / h. A conversion performance of 88% and a total thermal reactor efficiency of 87% were achieved.

The manifold assembly and burner construction shown in the drawings are given by way of example only and are not critical to the invention or to part of the same, because the invention is applicable to a single-reactor reactor system within a furnace as well as a multiple system Reactors, as shown above examples. There are particular advantages to placing multiple reactors in a single furnace, since it allows the reactors to be packed tightly by ensuring both uniform and extremely effective heating of the lower parts of the reactors.

Densely packed reactors represent a non-linear, regular arrangement of at least three reactors, the arrangement essentially filling the combustion chamber volume and the reactors being essentially uniformly distributed and arranged essentially at equal and close mutual distances within the combustion chamber volume. For example, if a cylindrical combustion chamber is assumed, an arrangement of three tightly packed reactors can have the shape of an equilateral triangle, with one reactor at each corner. An array of four densely packed reactors can have the shape of a square, with one reactor on each corner. A five reactor arrangement can include a central reactor surrounded by a quadratic arrangement of four reactors. Nine reactors can have a square arrangement of three parallel rows, each with three reactors. A hexagonal arrangement with nineteen reactors is shown in FIG. 2. In all cases, at least a portion of each reactor in the array receives a much smaller amount of direct radiation from the combustion chamber wall. For example, reactors on the wall receive significantly less radiation on the side facing away from the wall. In addition, parts of the reactors receive a significantly smaller amount of radiation due to the blocking of the radiation by other reactors in the regular arrangement.

The catalytic reactor system explained is compact, has high thermal reactor efficiencies and is able to work with high heating outputs.

It contains an annular reaction chamber located within a furnace, heat for the reaction being generated by 1) hot furnace gas which flows in countercurrent to the flow through the reaction chamber within a narrow ring coaxial with and adjacent to the outer wall surface of the annular reaction chamber is arranged, and 2) is generated by regenerative heat from the reaction products that leave the reaction chamber and countercurrent to the flow through the reaction chamber within a narrow Rin5

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ges flow, which is arranged coaxially to and immediately adjacent to the inner wall of the reaction chamber and the reaction products, which are substantially isolated from the heating effects of the hot gases within the furnace. A large number of reactors can be accommodated in a compact furnace volume.

To achieve low costs, high heating powers (i.e. high speeds at which heat from the hot gases in the furnace is transferred to the reaction stream per unit of wall surface area that separates the two streams from each other) and a compact arrangement are required. A high thermal reactor efficiency requires a high rate of conversion of process fuel to hydrogen while burning a minimal amount of fuel in the furnace. Complex and expensive designs to avoid excessive thermal stresses, which are generated by temperature differences between interconnected parts, should not be necessary.

Two streams are used to heat the reaction stream. The main source of heat is the counterflow of furnace gases through a narrow ring along the outer wall of an annular reaction chamber. The other heat source is regenerative heat from the reaction products, which leave the annular reaction chamber and flow in counterflow through a narrow ring along the inner wall thereof. The use of counter currents and narrow annular heating gas channels are critical factors for maximizing the heating output and the thermal reactor efficiency. A high re-generator heat transfer efficiency reduces the furnace heating power required per unit of process fuel supply. The system therefore works with a higher overall thermal efficiency. In this regard, the size of the annular gap of each of the two annular channels that carry hot gases in heat exchange relationship with the reaction chamber is a critical factor in determining how much of the available heat in the heating streams is actually transferred to the reaction stream.

For explanation, it is useful to consider a parameter called heat transfer efficiency s. The heat transfer efficiency is equal to the change in the enthalpy of the heating current divided by the theoretical maximum change in the enthalpy. In other words, when the heating current has an enthalpy Ei at its entry temperature Tx and an enthalpy E2 at its exit temperature T2 and when the heated stream has a temperature T3 when it enters, the heat transfer efficiency between the two flows is given by the following equation given.

= Egg -E2

Ej-E3

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where E3 is the enthalpy of the heating current, calculated at temperature T3.

It is also important to determine the thermal reactor efficiency t | define:

15 (Nh2HLHVh2)

11 (Fr) (LHVr) + Ff (LHVf)

where NH2 is the total amount of hydrogen produced, 2o LHVH2 is the lower heating value of hydrogen, Fr is the amount of process fuel fed to the reactor, Ff is the amount of fuel fed to the furnace, and LHVr and LHVf are the lower heating values of the process fuel and the furnace fuel, respectively. It has been assumed above that hydrogen is the desired reaction product. The equation can easily be modified for other reaction products.

It should always be kept in mind that T) is approximately directly proportional to e and that therefore a high degree of efficiency requires a high degree of heat transfer efficiency.

The main advantage of this reactor plant is that it has a high thermal reactor efficiency in a wide range of heating capacities (including very high heating capacities), while the plant has a compact size. The result is a durable, compact, economical and effective design that is capable of working with high process fuel throughputs.

40 The invention is not limited to steam reforming hydrocarbon fuels to produce hydrogen. The heat transfer principles on which the invention is based could just as well be applied to other endothermic catalytic reactions.

s

2 sheets of drawings

Claims (10)

631 637 PATENT CLAIMS 1. Catalytic reactor system, characterized by a combustion chamber (60) for burning fuel to generate hot gases; by at least one tubular reactor (20) with a first part (56), which extends into the combustion chamber, with an outer wall and with an inner wall (24), the inner wall being arranged at a distance from the outer wall and with this one annular reaction chamber (26) for receiving a reaction catalyst (28), wherein the reaction chamber (26) has an inlet end (32) and an outlet end (36) and the outlet end is arranged in that part of the reactor which is in the combustion chamber ( 60) extends; by a wall arrangement (62) which is arranged at a distance from the outer wall (22) of the reaction chamber and with which it defines an annular burner gas channel which extends coaxially with and directly adjoins the reaction chamber and an inlet end (66) in gas connection with the Combustion chamber and an outlet end (67) substantially at the inlet end (32) of the reaction chamber, wherein the burner gas channel (64) is designed to direct hot gas from the combustion chamber over the outer wall of the reactor in counterflow to the flow passing through the reaction chamber to add heat to it; and by means (46) spaced inwardly of the inner wall of the reactor and defining an annular regeneration chamber therewith which is coaxial with and immediately adjacent to the annular reaction chamber (26) and an inlet end (49) and an Has outlet end (54), the total amount of the reaction products entering the regeneration chamber through the inlet end being determined by the reaction chamber outlet end, and the regeneration chamber being designed to direct the reaction products in countercurrent to the flow passing through the reaction chamber and only internal heat, which is already present in the reaction products at the outlet end of the reaction chamber, to be transferred back to the reaction chamber. 2. Reactor system according to claim 1, characterized in that the device (46) which is arranged at a distance inwards from the inner wall (24) of the reactor is a cylindrical plug which is arranged within the channel. 3. Reactor system according to claim 1 or 2, characterized in that the distance between the walls of the regeneration chamber is between 2.5 and 25.4 mm, that the distance between the walls of the burner gas channel is between 2.5 and 76.2 mm, and that the distance between the walls of the reaction chamber is between 7.6 and 50.8 mm. 4. Reactor system according to one of claims 1 to 3, characterized in that the reaction chamber contains a steam reforming catalyst and that the reactor system means for introducing a reformable hydrocarbon fuel and water vapor into the reaction chamber inlet end (32) and devices for introducing a fuel and an oxidizing agent into the Combustion chamber has. 5. Reactor system according to one of claims 1, 2 or 4, characterized in that the burner gas channel (64) is essentially filled with a heat transfer packing material. 6. Reactor system according to one of claims 1 to 5, characterized in that the distance between the walls of the regeneration chamber is between 3.2 and 12.7 mm, that the distance between the walls of the burner gas channel is between 12.7 and 50.8 mm lies, and that the Distance between the walls of the reaction chamber is between 12.7 and 38.1 mm. 7. Reactor system according to one of claims 1 to 6, characterized in that the reactors (20) are arranged vertically within a furnace (12), and that the outlet end of the reaction chamber (26) is located at the upper end of the reaction chamber. 8. Reactor plant according to one of claims 1 to 7, characterized in that a plurality of tubular reactors are arranged within the furnace. 9. Reactor system according to claim 8, characterized in that the regeneration chamber (48) extends substantially over the full length of the reaction chamber (26). 10. Reactor system according to claim 8 or 9, characterized in that the Vorrichtimg associated with the reaction chamber is a cylindrical stopper which has a cylindrical outer surface which is spaced from the inner wall arrangement of the reactor.