JP2007161530A - Reformer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reformer which can reduce the CO concentration and the unreacted gas concentration in a produced reformed gas. <P>SOLUTION: In the double-structured reformer 1 for producing a hydrogen-rich reformed gas by reforming a raw material gas with steam, which is provided with an outside spare reforming chamber 2 having a reforming catalyst layer 4, and an inside main reforming chamber 3 having a mixed catalyst layer 5 filled with a granular mixed catalyst formed by mixing a reforming catalyst and an oxidation catalyst, and a shift catalyst layer 6 filled with a granular shift catalyst; and in which a supply piping 14 for supplying an oxidation air is extended in the central part of the main reforming chamber 3; the average particle size of the mixed catalyst and shift catalyst is made to be 5 mm or smaller, and the distance between the outer surface of the supply piping 14 and the inner surface of the circumferential wall of the main reforming chamber 3 is made to be two times of the average particle size to 12 mm, preferably 2.5 times of the average particle size to 10 mm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a reformer that generates a hydrogen-rich reformed gas by steam reforming a raw material gas, and more particularly, a self-oxidation internal heating type capable of generating a reformed gas that is compact and has high reforming efficiency and low CO concentration. It relates to a reformer.

2. Description of the Related Art Conventionally, there is known a reformer that generates a hydrogen-rich reformed gas by steam reforming a mixture of a source gas and steam (hereinafter referred to as a source-steam mixture) in the presence of a reforming catalyst. The hydrogen-rich reformed gas obtained in the reformer is converted to CO ₂ by reacting residual CO (carbon monoxide) with an oxygen-containing gas in the presence of a catalyst by means of CO reduction, and operates at a particularly low temperature. For solid polymer electrolyte fuel cells, CO is reduced to several ppm level before being supplied as fuel. As the source gas, hydrocarbons such as methane, aliphatic alcohols such as methanol, ethers such as dimethyl ether, city gas, and the like are used. In such a reformer, the reaction formula of steam reforming when methane is used as a raw material gas can be expressed as CH ₄ + 2H ₂ O → CO ₂ + 4H ₂ , and a preferable reforming reaction temperature is 650 to The range is 750 ° C.

  There are an external heating type and an internal heating type as a system for supplying heat necessary for the reforming reaction of the reformer. The external heating type reformer is provided with a heating unit outside, and a reformed gas is generated by reacting a raw material gas and water vapor with a heat source. The internal heating type reformer is provided with a partial oxidation reaction layer on the supply side (upstream side), and the steam reforming reaction layer disposed on the downstream side using the heat generated in the partial oxidation reaction layer is subjected to a steam reforming reaction. Heating to a temperature is performed, and a steam reforming reaction is performed in the heated steam reforming catalyst layer to generate a hydrogen-rich reformed gas.

The partial oxidation reaction can be represented by CH ₄ + 1/2 · O ₂ → CO + 2H ₂ , and the preferable partial oxidation reaction temperature is in the range of 250 ° C. or higher. For example, Patent Documents 1 and 2 describe a self-oxidation internal heating type reformer as an improvement of the internal heating type reformer. The reformers of Patent Documents 1 and 2 have a double structure including an outer preliminary reforming chamber and an inner main reforming chamber. The main reforming chamber is provided with a catalyst layer and a discharge unit, the main reforming chamber receives a discharge from the discharge unit, a supply pipe for oxidized air, a mixed catalyst layer in which the reforming catalyst and the oxidation catalyst are mixed, a shift catalyst layer, and A reformed gas discharge unit is provided.

  FIG. 1A is a longitudinal sectional view schematically showing a self-oxidation internal heating type reformer, and FIG. 1B is a sectional view taken along line BB in FIG. The reformer 1 includes an outer preliminary reforming chamber 2 and an inner main reforming chamber 3 arranged in a double cylinder shape. The preliminary reforming chamber 2 and the main reforming chamber 3 are made of a metal cylinder. Each of them is formed in a rectangular shape having a long and flat cross section (in the illustrated example, a flat square shape), and the long sides of the cross sections are arranged in parallel to each other. The preliminary reforming chamber 2 is formed between the outer cylinder 2a and the inner cylinder 3a, and the main reforming chamber 3 is formed inside the inner cylinder 3a. A reforming catalyst layer 4 is provided in the preliminary reforming chamber 2, and a mixed catalyst layer 5 and a shift catalyst layer 6 in which the reforming catalyst and the oxidation catalyst are mixed are provided in the main reforming chamber 3. Is provided with a heat insulating layer 3b at the boundary with the outer cylinder 2a and forms a heat transfer section at the boundary with the shift catalyst layer 6. The shift catalyst layer 6 includes a high temperature shift catalyst layer 7 and a low temperature shift catalyst layer 8. In addition, the catalyst with which these catalyst layers are filled generally has a spherical or cylindrical shape.

The reforming catalyst is a steam reforming of the raw material gas. For example, a Ni-based reforming reaction catalyst such as NiO—A1 ₂ O or NiO—SiO ₂ .A1 ₂ O ₃ or WO ₂ —SiO ₂ .A1 ₂ O ₃ NiO-WO ₂ · SiO ₂ · A1 ₂ O ₃ or the like is used. The reforming catalyst constituting the mixed catalyst layer 5 is the same as described above, and the oxidation catalyst uniformly dispersed therein is the temperature required for the steam reforming reaction by oxidizing the raw material gas in the raw material-steam mixture. For example, platinum (PT), rhodium (Rh), ruthenium (Ru), or palladium (Pd) is used. The mixing ratio of the oxidation catalyst to the reforming catalyst is selected in the range of about 1 to 15% according to the type of the raw material gas to be steam reformed. For example, when methane is used as the raw material gas, it is about 5% ± 2%. In the case of methanol, the mixing ratio is about 2% ± 1%.

  A raw material-steam mixture supply unit 9 is provided at the lower part of the preliminary reforming chamber 2, and a discharge unit 10 for discharging the effluent after the preliminary reforming is provided at the upper part of the preliminary reforming chamber 2. A supply unit 11 communicating with the discharge unit 10 of the preliminary reforming chamber 2 is provided at the upper part of the main reforming chamber 3, and a supply pipe 14 for supplying oxidized air to the central portion of the main reforming chamber 3 is extended. An air ejection portion 17 having a large number of nozzle holes is formed in a portion where the supply pipe 14 extends to the mixed catalyst layer 5. Further, a reformed gas discharge section 12 is provided at the lower portion of the main reforming chamber 3. The supply pipe 14 has a flat cross section (in the example shown, a flat square shape, but the short side of the cross section may be semicircular), and the main reforming chamber 2 and the main reforming chamber 14 are modified. The cross section of the pawn chamber 3 is substantially similar.

  The main reforming chamber 3 is provided with a mixed catalyst layer 5, a high temperature shift catalyst layer 7, and a low temperature catalyst layer 8 in order from the top to the bottom, and the low temperature shift catalyst layer 8 including the boundary portion of each catalyst layer and the discharge portion 12 is provided. A support plate 15 that supports the catalyst particles is disposed on the lower side. (Similar support plates 15 are also disposed in the preliminary reforming chamber 2.) These support plates 15 have a gas flowability but have a hole diameter that does not allow the passage of catalyst particles, and are usually plate-like punch metal. Porous members such as mesh and mesh are used.

  The discharge unit 12 includes a manifold provided in a space below the support plate 15 and an outlet tank connected to an end portion of the manifold extending outside the reformer 1. Then, the reformed gas that has flowed out to the discharge unit 12 passes through the support plate 15 and enters the manifold, and is discharged from there through the outlet tank.

  On the other hand, a starting preheater 13 is connected to the upper portion of the main reforming chamber 3. The preheater 13 quickly raises the mixed catalyst layer 5 to the oxidation reaction temperature when the system is started up. An electric heater is disposed in the preheater 13 and an oxidation catalyst such as platinum (PT) or palladium (Pd) is provided. Filled. At the start-up, the preheater 13 is supplied with the raw material gas and the start air from the suction mixing means 16, and the raw material gas is oxidized by oxygen in the air, and the mixed catalyst layer 5 can be oxidized by the high temperature gas generated by the oxidation heat. Heats up to a certain temperature.

  On the other hand, water vapor from a water vapor generating means (not shown) and raw material gas from a raw material supply part are introduced into the fluid introducing part of the suction mixing means 16 constituted by an ejector. Further, the discharge part of the suction mixing means 16 is communicated with the supply part 9 of the preliminary reforming chamber 2.

  Next, the operation of the reformer 1 of FIG. 1 will be schematically described. The raw material-steam mixture supplied from the supply unit 9 is partly reformed by the action of the reforming catalyst in the preliminary reforming chamber 2 to generate a hydrogen-rich reformed gas, and the generated reformed gas The gas and the remaining raw material-water vapor mixture flow from the discharge unit 10 to the supply unit 11 of the main reforming chamber 3.

  The raw material-steam mixture flowing into the main reforming chamber 3 reacts with the oxygen in the air (oxidation reaction) due to the action of the oxidation catalyst contained in the mixed catalyst layer 5, and the raw material gas is generated by the oxidation heat. Reacts with water vapor (reforming reaction) to generate a reformed gas. The generated reformed gas converts CO (carbon monoxide) remaining in the high temperature shift catalyst layer 7 into hydrogen, and then further converts the remaining CO into hydrogen in the low temperature shift catalyst layer 8 to be discharged from the discharge unit 12 to the outside. Is done.

JP 2001-192201 A JP-A-2005-149860

  In the reformer 1 having the structure as described above, there are heat generation due to oxidation reaction, heat absorption due to reforming reaction, and heat generation due to shift reaction, and the overall heat energy is released by heat release from the heat generation portion and heat absorption by the heat absorption portion. Balance of balance. Specifically, in the mixed catalyst layer, thermal energy roughly corresponding to the difference between the heat generated by the oxidation reaction and the endotherm by the reforming reaction is held in the generated reformed gas, and the thermal energy held by the reformed gas is Along with the gas, it flows into a heat transfer layer (not shown) on the downstream side. Part of the heat energy flowing into the heat transfer layer is transferred to the reforming catalyst layer 4 in the preliminary reforming chamber 2 through the inner cylinder 3a, and the rest flows into the shift catalyst layer 6 further downstream along with the reformed gas. To do. A part of the heat energy of the mixed catalyst layer 5 is also transferred to the supply pipe 14.

  However, according to experiments, during the operation of the reformer 1 having such a structure, the temperature in the vicinity of the air ejection portion in the supply pipe of the oxidized air extended into the mixed catalyst layer 5 becomes relatively high, and the surroundings away from it It has been found that there is a phenomenon in which a temperature distribution occurs in which the temperature of the portion becomes lower than that, and a part of the unreacted raw material gas (for example, methane gas) flows out from the low temperature portion to the downstream side. Thus, when a part of the unreacted source gas flows out downstream, the reforming efficiency is lowered accordingly.

  Further, the heat energy of the shift catalyst layer 6 is not efficiently transferred to the preliminary reforming chamber 2, the shift catalyst layer 6 becomes higher than the design range, and the high-temperature reformed gas is discharged from the reformer 1 to the outside. It was also found that there is a phenomenon that. As described above, when the shift catalyst layer 6 has a higher temperature than the design range, the shift reaction efficiency decreases, and as a result, the reformed gas containing a relatively high concentration of CO flows out. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve these problems in the conventional reformer, and to provide a reformer having a new structure therefor.

As a result of various experiments, it has been found that the above-mentioned problem occurs mainly when the distance between the outer surface of the supply pipe for oxidizing air and the inner surface of the peripheral wall of the main reforming chamber is not appropriate. That is, as shown in FIG. 2, when the distance between the outer surface of the air supply pipe and the inner surface of the main reforming chamber is too wide (T: 12 mm), the temperature distribution in the mixed catalyst layer 5 is narrow (T: 8mm) (the temperature in the short side direction of the cross section decreases as it goes outward), the outflow of unreacted raw material gas increases, and the shift catalyst layer 6 in the shift catalyst layer 6 moves from the shift catalyst layer to the preliminary reforming chamber 2. The heat transfer coefficient decreases, the temperature of the shift reaction catalyst layer 6 increases, and the CO concentration in the reformed gas flowing out therefrom increases.
On the other hand, when the interval is too narrow, the balance between the heat generated by the oxidation reaction in the mixed catalyst layer 5 and the heat absorption due to the reforming reaction tends to be disturbed, and in this case also, the unreacted raw material gas tends to flow downstream. Further, when the interval is too narrow, the filling rate of the catalyst particles for forming the mixed catalyst layer 5 or the shift catalyst layer 6 is reduced, the interparticle space is increased, and the internal volume of the main reforming chamber 3 is increased accordingly. Need to be large.

  From the above knowledge, the reformer of the present invention that solves the above problems is a mixture filled with an outer preliminary reforming chamber having a reforming catalyst layer and a particulate mixed catalyst in which the reforming catalyst and the oxidation catalyst are mixed. An internal main reforming chamber having a shift catalyst layer filled with a catalyst layer and a particulate shift catalyst, and a supply pipe for supplying oxidized air to the center of the main reforming chamber is extended to convert the raw material gas into steam reforming. In the reformer having a double structure that generates a hydrogen-rich reformed gas, the average particle diameter of the mixed catalyst and the shift catalyst is 5 mm or less, and the outer surface of the supply pipe and the peripheral wall of the main reforming chamber The distance from the inner surface is set to be twice to 12 mm of the average particle diameter (Claim 1).

  In the reformer, the outer preliminary reforming chamber, the inner main reforming chamber, and the supply pipe have cross-sections each having a flat rectangular shape, and their long side planes are arranged in parallel to each other, An air ejection portion of the supply pipe is formed on the long side plane, and the distance between the long side plane of the supply pipe and the inner surface on the long side of the main reforming chamber is set to 2 to 12 mm of the average particle diameter. (Claim 2).

  In any one of the above reformers, the interval can be 2.5 times to 10 mm of the average particle diameter.

In the reformer of the present invention, the average particle diameter of the mixed catalyst and the shift catalyst is 5 mm or less, and the interval between the outer surface of the oxidizing air supply pipe and the inner surface of the peripheral wall of the main reforming chamber is twice the average particle diameter or more. It is characterized by being 12 mm. In this way, by setting the distance between the outer surface of the oxidizing air supply pipe and the inner surface of the peripheral wall of the main reforming chamber to be 12 mm or less, in the mixed catalyst layer, a uniform temperature distribution is ensured in each part of the reforming reaction. Can be promoted. In other words, if the dimension is larger than the upper limit, the temperature of the mixed catalyst layer decreases as the distance from the oxidizing air supply pipe decreases, and there arises a disadvantage that unreacted raw material gas flows out from the low temperature portion to the downstream side.
In the shift catalyst layer, the temperature increase of the shift catalyst layer due to a decrease in the heat transfer coefficient (decrease in heat transfer to the reforming catalyst layer on the outside if the interval is too wide) suppresses the shift reaction efficiency. It is possible to prevent the increase in the CO concentration in the reformed gas flowing out from the shift catalyst layer.

  Further, by making the interval between the outer surface of the oxidizing air supply pipe and the inner surface of the peripheral wall of the main reforming chamber at least twice the average particle diameter, it is possible to prevent the balance of heat generation and endothermic balance in the mixed catalyst layer, and It is possible to prevent a decrease in the catalyst filling rate in the mixed catalyst layer and the shift catalyst layer (when the interval is too narrow, voids are easily generated between the catalyst particles).

In the reformer, as described in claim 2, the outer preliminary reforming chamber, the inner main reforming chamber, and the supply pipe have cross-sections each having a flat rectangular shape and their long side planes. Are arranged in parallel, and the air ejection portion of the supply pipe is formed on the long side plane, and the distance between the long side outer surface of the supply pipe and the long side inner surface of the main reforming chamber is the average particle. The diameter can be 2 to 12 mm.
With such a configuration, the reformer can be configured to be thin, and the air blowing portion in the oxidizing air supply pipe can be dispersed on the long side having a large area to uniformly supply the oxidizing air to each part of the mixed catalyst layer. it can.

  In addition, the temperature in the vicinity of the air ejection portion in the mixed catalyst layer is likely to increase in temperature, and the temperature gradient in the short side direction of the cross section in the mixed catalyst layer is also likely to decrease rapidly. The synergistic effect of being able to disperse the jetting part makes the temperature of each part in the mixed catalyst layer uniform, and the increase in temperature distribution can be prevented more effectively.

In any one of the above reformers, as described in claim 3, the interval can be 2.5 times to 10 mm of the average particle diameter. Thus, by setting the interval to 10 mm or less, the effect of preventing an increase in unreacted raw material gas outflow from the mixed catalyst layer, the effect of preventing the increase in CO concentration in the reformed gas flowing out from the shift catalyst layer, and the like are further enhanced. be able to.
Further, by setting the interval to 2.5 times or more of the average particle diameter, the effect of preventing the balance between heat generation and endotherm in the mixed catalyst layer, the effect of preventing the catalyst filling rate from decreasing in the mixed catalyst layer and the shift catalyst layer, etc. Easier to achieve.

  Next, the best mode for carrying out the present invention will be described with reference to the drawings. The reformer of the present invention has the same basic structure as the reformer of FIGS. 1A and 1B described above. Therefore, the description which overlaps with the already described content is omitted as much as possible.

  The reformer 1 of the present invention has an average particle diameter of the mixed catalyst and shift catalyst forming the mixed catalyst layer 5 of the reformer 1 shown in FIG. And the inner surface of the peripheral wall of the main reforming chamber 3 is characterized in that the distance T is 2 to 12 mm of the average particle diameter, preferably 2.5 to 10 mm of the average particle diameter. FIG. 1B shows the interval T.

More specifically, in the reformer 1 having a double structure, the outer preliminary reforming chamber 2, the inner main reforming chamber 3, and the supply pipe 14 have flat cross sections (flat squares), respectively. Moreover, they are formed in a substantially similar shape. An air ejection portion 17 of the supply pipe 14 is formed on the long side of the cross section, and an interval T between the long side outer surface of the cross section of the supply pipe 14 and the long side inner surface of the peripheral wall of the main reforming chamber 3 is The average particle diameter is 2 to 12 mm, preferably 2.5 to 10 mm.
The distance between the outer surface on the short side of the cross section of the supply pipe 14 and the inner surface on the short side of the peripheral wall of the main reforming chamber 3 is not particularly limited, but is set to about 2 to 3 times the average particle diameter of the catalyst. It is desirable.

  The air ejection part 17 is comprised by many nozzle holes. In the illustrated example, the nozzle hole group is arranged in two rows, and a large number of nozzle holes are evenly distributed at predetermined intervals in each row. In this way, by arranging a large number of nozzle holes evenly distributed, the oxidized air can be uniformly distributed and supplied to the mixed catalyst layer 5.

  Next, examples and comparative examples in which reforming operation is performed using the reformer 1 of the present invention will be described. The reformer 1 shown in FIG. 1 was used. The dimensions of the outer cylinder 2a of the standard reformer 1 are 700mm in height, horizontal length (long side) 145mm, width (short side) 110mm, and the inner cylinder 3a has dimensions of 520mm in height and horizontal length ( The long side of the cross section is 120 mm, the width (short side of the cross section) is 25 mm, and the dimensions of the supply pipe 14 are a horizontal length (long side of the cross section) of 110 mm and a width (short side of the cross section) of 5 mm.

  The reformer 1 changes the width (short side) of the inner cylinder 3a a plurality of times so that the distance T between the outer surface on the long side of the supply pipe 14 and the inner surface on the long side of the peripheral wall of the main reforming chamber 3 is 4 mm ( Comparative examples), 6 mm (twice the average particle diameter), 7.5 mm (2.5 times the average particle diameter), 10 mm, 12 mm, and 14 mm (comparative example) were set for experiments. The average particle size of the mixed catalyst and shift catalyst was 3 mm. At this time, as shown in FIG. 1A, the width (short side) of the outer cylinder 2a is set so that the distance A between the inner surface of the outer cylinder 2a and the outer surface of the inner cylinder 3a is 8 mm. Set.

  The reforming catalyst layer 4 in the preliminary reforming chamber 2 of the reformer 1 is formed by filling a Ni-based reforming catalyst, and the mixed catalyst layer 5 in the main reforming chamber 3 is composed of a noble metal-based oxidation catalyst and a Ni-based reforming catalyst. The shift catalyst layer 6 (the high temperature shift catalyst layer 7 and the low temperature catalyst layer 8) was formed by filling Fe—Cr and Cu—Zn shift catalysts.

For the reformer 1 having the intervals T, the raw material-steam mixture having a methane gas-steam ratio of (1: 3) is supplied to the pre-reformer 2 of the reformer 1, and the temperature of the mixed catalyst layer 5 is adjusted. The reforming reaction was carried out at 700 ° C. 3 and 4 show the results of measuring the CO concentration in the reformed gas flowing out from the reformer 1 and the unreacted raw material gas concentration flowing out from the mixed catalyst layer to the shift catalyst layer. In these graphs, the horizontal axis represents the interval T, and the vertical axis represents the CO concentration relative to the reformed gas and the unreacted raw material gas concentration as a volume ratio. From these results, it was confirmed that the reformer 1 set in the range of the present invention has a low CO concentration in the reformed gas and a small outflow amount of unreacted raw material gas.
Next, the CO concentration in the reformed gas when the interval T is set to 8 mm, which is the median value in FIGS. 3 and 4, and the interval A between the inner surface of the outer cylinder 2a and the outer surface of the inner cylinder 3a is changed. Changes in the reaction raw material gas concentration were examined. As a result, similar to the preferable range of the interval T, it was found that when A was in the range of 6 mm to 12 mm, the concentration thereof was small, and it was confirmed that it was preferable. This means that A is preferably 2 to 12 mm of the average particle diameter of the mixed catalyst and the shift catalyst.

  The reformer of the present invention can be used for a reformer that generates a hydrogen-rich reformed gas by steam reforming a raw material gas.

The longitudinal cross-sectional view and BB cross-sectional view of the reformer of this invention. The figure which shows distribution of internal temperature with respect to each distance from an outer cylinder to an oxygen supply pipe | tube. The figure which shows the change of CO concentration in reformed gas The figure which shows the change of the unreacted gas density | concentration in reformed gas.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reformer 2 Preliminary reforming chamber 2a Outer cylinder 3 Main reforming chamber 3a Inner cylinder 4 Reforming catalyst layer 5 Mixed catalyst layer 6 Shift catalyst layer 7 High temperature shift catalyst layer 8 Low temperature shift catalyst layer 9 Supply section

DESCRIPTION OF SYMBOLS 10 Discharge part 11 Supply part 12 Discharge part 13 Preheater 14 Supply pipe 15 Support plate 16 Suction mixing means 17 Air ejection part

Claims (3)

  An outer preliminary reforming chamber 2 having a reforming catalyst layer 4, a mixed catalyst layer 5 filled with a particulate mixed catalyst obtained by mixing a reforming catalyst and an oxidation catalyst, and a shift catalyst layer 6 filled with a particulate shift catalyst. And a supply pipe 14 for supplying oxidized air to the central portion of the main reforming chamber 3 is extended to produce a hydrogen-rich reformed gas by steam reforming the raw material gas. In the reformer 1 having a double structure, the average particle diameter of the mixed catalyst and the shift catalyst is 5 mm or less, and the distance between the outer surface of the supply pipe 14 and the inner surface of the peripheral wall of the main reforming chamber 3 is the average particle. A reformer having a diameter of 2 to 12 mm.   In Claim 1, the cross sections of the outer preliminary reforming chamber 2, the inner main reforming chamber 3 and the supply pipe 14 are flat rectangular shapes, and their long side planes are arranged in parallel to each other. The air blowing portion 17 of the supply pipe 14 is formed on the long side plane, and the distance between the long side plane of the supply pipe 14 and the long side side inner surface of the main reforming chamber 3 is the average particle diameter. A reformer characterized by being 2 to 12 mm.   The reformer according to claim 1 or 2, wherein the interval is 2.5 times to 10 mm of the average particle diameter.

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