JPH04300642A - Heat transfer method in heat-exchanging-type reformer - Google Patents

Abstract

PURPOSE:To make it possible to easily control heat flux distribution in a catalyst layer by installing a heat transfer accelerating means in almost the central part of the inside of an inner pipe of a catalyst pipe and also installing another heat transfer accelerating means covering from almost the central part of the outside of the catalyst pipe to the upper stream side of the catalyst pipe. CONSTITUTION:A bayonet-type catalyst pipe 1 having a double pipe structure consisting of an inner pipe 3 and an outer pipe 2 to reform natural gas steam into an H2- and CO-rich gas by reaction by bringing the gas steam into contact with the catalyst is installed. A heat transfer accelerating means 12 consisting of a combination of demistar net 10 and an inner pipe wire net 11 is installed in almost the central part of the inside of the inner pipe 3 of the catalyst pipe 1. Also, another heat transfer accelerating means 15 preferably composed of an outer pipe wire net 13 and an orifis buffle 14 is installed covering from almost the central part of the outside of the catalyst pipe 1 to the upper stream side of the catalyst pipe 1. As a result, heat transfer efficiency is enhanced and a plurality of catalyst pipes can be heated uniformly. Furthermore, the heat flux distribution to the catalyst layer can be controlled easily.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention utilizes sensible heat of high-temperature gas obtained by burning fuel cell anode exhaust gas in a molten carbonate fuel cell (MCFC) power generation system.
Regarding the heat transfer method in a heat exchanger-type reformer equipped with a reforming catalyst tube that produces gas rich in hydrogen and carbon monoxide by reforming natural gas with steam and supplies it to the fuel cell anode. , more specifically, a heat exchanger type in which heat transfer promoting means provided on the inner tube side and outer tube side of the catalyst tube are installed in a predetermined positional relationship to control the heat flux distribution to the catalyst layer. This article relates to a heat transfer method in a reformer.

0002

[Prior Art] A reformer in an MCFC power generation system is required to have a structure that is resistant to thermal shock and can withstand frequent startups and stops including daily start/shut (DSS) and rapid load fluctuations. A so-called bayonet type catalyst tube with a double tube structure is often used. FIG. 6 is a sectional view schematically showing its structure, and the bayonet type catalyst tube 1 has a structure in which a catalyst layer 4 is provided between an outer tube 2 and an inner tube 3. The natural gas and steam are reformed into a reformed gas rich in hydrogen and carbon monoxide while passing through the catalyst layer 4 in the direction A. This reforming reaction of natural gas is
For example, the reaction formula CH4 +H2 O→CO+3H2 ΔH=4
It is an endothermic reaction with 9.3 Kcal/gram mole. Therefore, in order to promote this reforming reaction, heat from the high-temperature combustion gas flow B discharged from the anode exhaust gas combustor and the reformed gas flowing in the inner tube in the opposite direction to the catalyst layer is transferred to the catalyst layer 4. The catalyst layer 4 is maintained at an appropriate temperature.

[0003] In such a system that supplies the necessary amount of heat from high temperature combustion gas flowing outside (shell side) to the bayonet type catalyst tube, the following points are particularly important in terms of heat transfer characteristics. (1) Improving heat transfer efficiency. (2) To increase the average value of heat flux and to control its distribution from the inlet to the outlet of the catalyst layer to a desired shape not only at full load but also at partial load. (3) Uniform heating of multiple catalyst tubes. For this purpose, the pressure loss ΔP is set to a desired value (0.05 to 0.1 kg/
cm 2 ) and control its distribution to avoid uneven flow of combustion gas.

[0004] Therefore, various attempts have been made to improve the efficiency of heat transfer to the catalyst layer. FIG. 7 is a sectional view of a main part showing a conventional heat transfer promoting means. For example, as shown in FIG. 7(a), a sleeve 5 is provided inside the catalyst tube inner tube, and as shown in FIG. ) with a sleeve 6 as shown in FIG. 7(c), with an orifice baffle 7 as shown in FIG. 7(d), with a wire net 8 on the outside of the outer tube as shown in FIG. 7(d), Figure 7 (
As shown in e), there are some that are provided with a filler 9.

However, in the case where a sleeve is provided inside the inner tube of the catalyst tube (FIG. 7(a)), the effect of promoting heat transfer is low, so it is necessary to install the sleeve in almost the entire area of the inner tube. It becomes difficult to control the flux (heat flux) distribution, and the catalyst tube has a three-layered structure, making it complicated. Those with a sleeve or orifice baffle on the combustion gas side (Figure 7 (b) or (c)) have a low heat transfer promotion effect when used alone, so they must be installed over a wide area, making it difficult to control the heat flux distribution. It is. A wire net provided on the combustion gas side (Fig. 7(d)) has a high heat transfer promotion effect, but if it is used alone, the pressure loss on the combustion gas side is too small and it is difficult to control its distribution. It is difficult to prevent uneven flow of combustion gas, and therefore it is difficult to uniformly heat a plurality of catalyst tubes. The one in which a sleeve and wire net are provided on the combustion gas side (the combination of FIGS. 7(b) and (d)) has a good heat transfer promotion effect, but the pressure loss on the combustion gas side cannot be maintained at an optimal level (for example, 0.05~0.1k
g/cm 2 ), it is necessary to expand the installation area. Furthermore, when attempting to reduce the clearance between the sleeve and the outer tube in order to enhance the heat transfer promotion effect, manufacturing and mounting accuracy becomes a problem. In the case of filling the combustion gas side (Fig. 7(e)), the heat transfer promotion effect can be enhanced, but the pressure loss on the combustion gas side becomes excessive.
Moreover, its distribution cannot be controlled.

[0006]

[Problems to be Solved by the Invention] The present invention solves the drawbacks of the prior art, and not only further increases the heat transfer efficiency, but also uniformly heats a plurality of catalyst tubes, and reduces heat to the catalyst layer. Provides a heat transfer method in a heat exchanger type reformer that can maintain the reformed gas temperature at a predetermined desired value not only at full load but also at partial load by controlling the flux distribution in a desired manner. The purpose is to

[0007]

[Means for Solving the Problems] In order to increase the heat transfer efficiency, the present inventors provided a heat transfer promoting means in combination with a demister net and a wire net on the inner tube side of the catalyst tube, and a more preferred embodiment As a result, a heat exchanger type reformer was proposed in which a heat transfer promoting means consisting of an outer tube wire net and an orifice baffle was further provided on the outside of the catalyst tube (Japanese Patent Application No. 3-46891). The present invention further develops this by installing heat transfer promoting means provided on each of the inner tube side and outer tube side of the catalyst tube in a predetermined positional relationship, in order to solve the above problems extremely. It was completed with a focus on being effective.

[0008] That is, the heat transfer method in the heat exchanger type reformer of the present invention is such that natural gas and steam are reacted and reformed into a gas rich in hydrogen and carbon monoxide from an inner tube and an outer tube. In a heat transfer method in a heat exchanger type reformer equipped with a bayonet type catalyst tube having a double tube structure, a heat transfer method consisting of a combination of a demister net and an inner tube wire net is installed approximately at the center inside the inner tube of the catalyst tube. The present invention is characterized in that the heat flux distribution to the catalyst layer is controlled by providing a heat promoting means and providing another heat transfer means from a substantially central portion on the outside of the catalyst tube to an upstream side of the catalyst tube. . In a preferred embodiment of the present invention, the heat transfer promoting means provided outside the catalyst tube may be a heat transfer promoting means comprising an outer tube wire net and an orifice baffle.

DETAILED DESCRIPTION OF THE INVENTION The contents of the present invention will be specifically explained below, including the drawings. In the heat transfer method in the heat exchanger type reformer of the present invention,
As a catalyst tube used for reforming natural gas with steam, a conventionally used bayonet type catalyst tube is used, and the outline of its structure is the same as that shown in FIG. 6.

FIG. 1 is a sectional view illustrating an example of the installation position of the heat transfer promoting means in the heat transfer method of the present invention. Inside the inner tube 3 of the bayonet type catalyst tube 1, a heat transfer promoting means 12 consisting of a combination of a demister net 10 and an inner tube wire net 11 is provided, and on the outside of the catalyst tube, another heat transfer promoting means, preferably A heat transfer promoting means 15 consisting of an outer tube wire net 13 and an orifice baffle 14 is provided. Among these, the heat transfer promoting means 12 on the inside of the inner tube is provided approximately at the center, preferably over an area of 30 to 80% of the length of the inner tube, while the heat transfer promoting means 15 on the outside of the catalyst tube is provided at the center of the inner tube. It is provided on the upstream side of the catalyst tube from approximately the center. More specifically, the heat transfer promoting means 12 inside the inner tube has a difference ΔT1 between the inner tube temperature and the average temperature of the catalyst layer 4 of 120 to 180°C.
, preferably in the range of 130 to 150°C, while the heat transfer promoting means 15 on the outside of the catalyst tube has a temperature difference ΔT2 between the combustion gas temperature and the average temperature of the catalyst layer 4 of 260°C or less, preferably 230°C or less. Provided in the area.

With such a positional relationship, both heat transfer promoting means 12
, 15, it becomes possible to desirably control the heat flux distribution from the inlet 16 to the outlet 17 of the catalyst layer 4. As a result, the temperature of the reformed gas was adjusted to a preferable operating temperature of the reformer for the present MCFC power generation system, that is, the temperature of the reformed gas was adjusted to 800°C at the catalyst bed outlet 17.
℃, and can be maintained at a value of about 600°C at the inner tube outlet 18.

[0012] Such a desirable reformed gas temperature can be well maintained not only during steady operation but also during partial load. In other words, since it is necessary to maintain the efficiency of the power generation system at the same level as during steady operation even at a load of 30 to 50%, the inner pipe outlet temperature of the reformed gas is kept at a predetermined value ( This value needs to be maintained at around 600° C., which is equal to the fuel cell anode side inlet temperature. In addition, the temperature at the outlet of the catalyst bed is controlled so that it does not rise too much to cause damage to the catalyst, preferably so that it does not rise too much above 800°C, or the temperature of the outer catalyst tube does not exceed its design temperature. Although necessary, such partial load characteristics can also be maintained well by controlling the heat flux distribution in a desired shape as described above.

Next, each heat transfer promoting means 12 and 15 will be explained in more detail. The demister net 10 used as the heat transfer promoting means 12 is made by randomly forming thin metal wires into an aggregate shape like a metal scrubber, and has a porosity of 99% and a density of 80 kg, for example.
/m3 is used. Further, the inner tube wire net 11 has a shape similar to that of the above-mentioned demister net compressed, and has, for example, a gap of about 20 meshes. This inner tube wire net itself has a heat transfer promoting effect, holds the demister net, and also functions to rectify the reformed gas flow.

The reason why such an aggregate of metal wires acts to promote heat transfer is as follows. In other words, in the case of such an aggregate of metal wires, the specific surface area is large;
By being placed in the path of the hot reformate gas fluid,
Easily heated to high temperatures by reformed gas fluid. Since the radiation power of this high-temperature metal wire assembly is large, the surface to be heated, that is, the surface of the tube inside the catalyst layer, is subjected to radiant heating due to thermal radiation from this metal wire assembly in addition to convective heating by the reformed gas fluid. , and the amount of heat transfer due to thermal radiation is large. As a result, the overall heat transfer from the reformate gas fluid to the heated surface is significantly greater than that without the metal wire assembly.

For holding the demister net, it is preferable that the demister net 10 and the inner tube wire net 11 be arranged alternately in the longitudinal direction of the catalyst tube inner tube and combined in multiple stages as shown in FIG. Also, the thickness of the demister net (ln) and the thickness of the inner tube wire net (lw)
The ratio (ln/lw) is 3 to 20, preferably 8 to 1
The range shall be 2.

As mentioned above, the operating temperature of the reformer for the present MCFC power generation system is 800℃ at the exit of the catalyst layer of the reformed gas.
℃, and about 600℃ at the outlet of the catalyst tube, but in this temperature range, the Boudoir reaction from CO-rich gas,
That is, there is a high possibility of carbon precipitation due to 2CO→C+CO2. In order to prevent this, a material that suppresses Boudoir reaction or at least does not have catalytic action is selected as the material used not only for the inner tube of the catalyst tube but also for the heat transfer promoting means inside the inner tube. In addition, in terms of operating conditions, the Boudoir reaction is suppressed by adopting a steam/carbon ratio (S/C) of about 3, which is slightly larger than the 2 to 2.5 generally adopted for natural gas raw materials. It is preferable.

In the present invention, the heat transfer promoting means provided outside the catalyst tubes not only promotes heat transfer but also enables uniform heating of the plurality of catalyst tubes provided in the heat exchanger type reformer. It is essential for the stable operation of the device to heat these multiple catalyst tubes evenly from the combustion gas side.To do this, it is necessary to distribute the combustion gas evenly from the inlet to the outlet without drifting. It is necessary to control the value of the pressure loss ΔP from the inlet to the outlet and its distribution.

Therefore, in the present invention, this object is achieved by preferably installing an orifice baffle as a heat transfer promoting means provided outside the catalyst tube, and by installing the orifice baffle upstream from approximately the center of the catalyst tube. It is something. In other words, the high-temperature combustion gas flow path becomes narrow at the installation position of the orifice baffle 14, which creates turbulence in the flow of combustion gas and promotes heat transfer, while also achieving an optimal pressure loss that allows combustion gas to flow without uneven flow. 0
．． 05 to 0.1 kg/cm 2 . In addition, by installing the orifice baffle upstream from the approximate center of the catalyst tube, that is, on the downstream side of the combustion gas, most of the pressure loss ΔP can be concentrated in the orifice baffle portion, causing uneven flow in the combustion gas flow. Uniform heating of multiple catalyst tubes can be achieved without any problems. In this way, the pitch and number of stages of the orifice baffle 14 are determined in order to obtain the desired value and distribution of pressure loss.

The heat transfer promoting means 15 preferably includes the orifice baffle 14 and the outer tube wire net 13, of which the outer tube wire net 1
No. 3 has a heat transfer effect by convection heating and radiation heating, similar to the heat transfer promoting means formed by combining the above-mentioned demister net and inner pipe wire net. For example, 1.1φ
, about 8 mesh is preferably used.

[0020]

[Example] Hereinafter, the present invention will be explained in more detail by giving an example. The scope of the present invention is not limited by these Examples.

Example 1 FIG. 2 is a sectional view illustrating the outline of the structure of a 1 MW power generation heat exchanger type reformer used in the method of the present invention. The upper part of the reformer body has an inlet nozzle 19 for natural gas and steam, and the outlet nozzle 20 for reformed gas. The lower part of the reformer body has an inlet nozzle 21 for combustion gas, and the upper part has an outlet nozzle 21 for combustion gas. A nozzle 22 is provided. Six catalyst tubes 1 (only two are shown in the figure) were installed inside the reformer main body, and heat transfer promoting means were installed on the outside of the catalyst tubes 1 and on the inside of the inner tube, but the details of their installation are as follows. The position will be described later.

The inner wall corresponding to the part where the catalyst tube 1 is installed is lined with a ceramic fiber blanket 24 having a small heat capacity, and the inner wall near the combustion gas inlet nozzle 22 at the bottom of the main body is lined with a refractory castable 25. The outer wall is made of a heat insulating castable material 26, and the outer wall of the upper part of the reformer body is made of another heat insulating material 27.

Natural gas and steam are introduced into the main reformer through the inlet nozzle 19, reformed into a gas rich in hydrogen and carbon monoxide while passing through the catalyst tube 1, and discharged through the outlet nozzle 20. . On the other hand, high-temperature combustion gas is introduced into the reformer main body from the inlet nozzle 21, transfers heat to the catalyst tube 1, and then is discharged from the outlet nozzle 22.

As shown in FIG. 1, the installation positions of the heat transfer promoting means provided on the inner side of the catalyst tube and the outside of the catalyst tube are as shown in FIG. A demister net 10 and an inner tube wire net 11 are placed approximately at the center of the catalyst layer 4, specifically inside the catalyst tube inner tube corresponding to a range of 3.18 to 1.5 m from the most upstream end of the catalyst layer 4. were arranged in five rows alternately in the vertical direction. On the outside of the catalyst tube, a heat transfer promoting means 15 consisting of an outer tube wire net 13 and an orifice baffle 14 is installed on the upstream side of the catalyst layer, specifically, in a range up to 2.0 m from the vicinity of the most upstream end of the catalyst layer. installed in position. The orifice baffle 14 is supported by tie rods 23 and provided in five stages. Note that a thermometer 28 is attached to the inside of the inner tube.

The operating conditions of this apparatus having such a configuration are as follows. As process conditions, at the inlet nozzle 19, natural gas flow rate is 171 Nm3/h, steam flow rate is 596 Nm3/h, temperature is 434°C, and pressure is 4.8°C.
kg/cm2
vol%, CO: 7.69 vol%, CO2: 8.9
6vol%, CH4: 0.64vol%, H2O
:26.18 vol%), temperature 600°C, pressure 2.3
kg/cm2 G, catalyst layer outlet 17 (bottom of catalyst tube)
In this case, the temperature was 800° C. and the pressure was 2.4 kg/cm 2 G.

On the other hand, as conditions on the combustion gas side, at the inlet nozzle 21, the combustion gas flow rate is 1805 Nm3/h, the temperature is 1170°C, and the pressure is 2.5 kg/cm2 G, and at the outlet nozzle 22, the flow rate is 1805 Nm3/h, the temperature is 600°C, The test was carried out at a pressure of 2.4 kg/cm2G.

Comparative Example 1 As a heat transfer promoting means, a sleeve was provided on the inner tube side of the catalyst tube over the entire inner tube, and on the other hand, on the combustion gas side, a sleeve and a wire net were installed on the upstream side (the furthest side) of the catalyst tube. Operation was carried out under the same conditions as in Example 1, except that the device was installed within a range of 2.5 m from the vicinity of the upstream end.

Heat flux The results of measuring the heat flux on the outer tube side and inner tube side of the catalyst tube in Example 1 and Comparative Example 1 are shown in FIG.
Shown below. In the figure, 29 indicates the inner tube side heat flux of Example 1, 30 indicates the inner tube side heat flux of Comparative Example 1, 31 indicates the outer tube side heat flux of Example 1, and 32 indicates the outer tube side heat flux of Comparative Example 1.

As is clear from FIG. 3, the heat flux distribution in Example 1 is different from the range where the heat transfer promoting means is installed (
On the inner tube side, the catalyst layer length is 1.5 m for the total catalyst layer length of 4 m.
It can be seen that improvements were made in the range of 3.18 m and 0 to 2.0 m on the outer tube side). That is, the heat flux at the intermediate portion is increased, and the value at the exit portion of the inner tube is decreased. As a result, heat transfer at this outlet portion is reduced, and an excessive drop in the temperature of the reformed gas is prevented. By controlling such a preferable heat flux distribution, the reformed gas temperature at the outlet of the catalyst layer and the outlet of the inner tube can be maintained at a preferable value not only during full load but also during partial load, as described below. be able to.

On the other hand, the heat flux distribution in Comparative Example 1 cannot be controlled, especially on the inner tube side, so that the reformed gas at the outlet of the catalyst layer and the outlet of the inner tube at full load and especially at partial load. It becomes difficult to maintain the temperature at the desired value.

Reformed gas temperature distribution FIG. 4 is a graph showing the catalyst layer and reformed gas temperature distribution during 100% load operation in the above-mentioned Example 1 and Comparative Example 1, and 33 shown by a solid line is a graph showing the temperature distribution of the reformed gas in the example 1 and comparative example 1. Reference numeral 34 indicates the temperature distribution of the reformed gas in the catalyst layer in Comparative Example 1, and 36 indicates the temperature distribution of the reformed gas in the catalyst layer in Comparative Example 1.

As can be seen from this graph, in Example 1, as a result of preferably controlling the distribution of heat flux on the outer tube side and the inner tube side of the catalyst tube as shown in FIG. The temperature at the reformed gas outlet (at the point where the catalyst layer length is 0 m) is kept at about 60° C., which is the preferable temperature.
It was possible to maintain the temperature at 0°C. On the other hand, in Comparative Example 1, the distribution of heat flux on the outer tube side and the inner tube side of the catalyst tube was unfavorable as shown in FIG. The temperature was about 580°C, which was different from the desired value.

FIG. 5 is a graph showing the temperature distribution of the catalyst layer and reformed gas during 30% load operation.
7 shows the temperature distribution of the catalyst layer in the example of the present invention, 38 shows the temperature distribution of the reformed gas, and 39 shown by a dotted line shows the temperature distribution of the catalyst layer in the comparative example, and 40 shows the temperature distribution of the reformed gas.

As can be seen from this graph, in the embodiment of the present invention, even at 30% load, the catalyst bed outlet temperature can be kept at about 820°C, and the reformed gas outlet temperature can be maintained at about 590°C. was completed. On the other hand, in the comparative example, the catalyst layer outlet temperature was approximately 850° C., and the reformed gas outlet temperature was approximately 570° C., which were large deviations from the respective preferred values.

[0035]

According to the present invention, a heat transfer promoting means consisting of a combination of a demister net and an inner tube wire net is provided at approximately the center of the inside of the inner tube of the catalyst tube, and the heat transfer promoting means is provided at approximately the center of the outside of the catalyst tube. Since the heat flux distribution to the catalyst layer is controlled by providing another heat transfer means upstream of the catalyst tubes, heat transfer efficiency is increased and uniform heating of a plurality of catalyst tubes can be realized. Furthermore, the heat flux distribution to the catalyst layer can be easily controlled, and the reformed gas temperature and the catalyst layer outlet temperature can be maintained at desired values not only at full load but also at partial load.

[Brief explanation of drawings]

FIG. 1 is a sectional view illustrating an example of the installation position of a heat transfer promoting means in the heat transfer method of the present invention.

FIG. 2 is a sectional view illustrating the outline of the structure of a 1 MW heat exchanger type reformer for power generation used in the method of the present invention.

FIG. 3 is a graph showing the results of measuring the heat flux on the outer tube side and the inner tube side of the catalyst tube in Examples and Comparative Examples.

FIG. 4 is a graph showing the catalyst layer and reformed gas temperature distribution during 100% load operation.

FIG. 5 is a graph showing the catalyst layer and reformed gas temperature distribution during 30% load operation.

FIG. 6 is a sectional view showing an outline of the structure of a bayonet type catalyst tube.

FIG. 7 is a sectional view of a main part showing a heat transfer promoting means in the prior art.

[Explanation of symbols]

1 Bayonet type catalyst tube 2 Outer tube 3 Inner tube 4 Catalyst layer 10 Demister net 11 Inner tube wire net 12 Heat transfer promoting means 13 provided inside the inner tube of the catalyst tube
Outer tube wire net 14 Orifice baffle

Claims (2)

[Claims] Claim 1: A heat exchanger equipped with a bayonet type catalyst tube having a double tube structure consisting of an inner tube and an outer tube for reacting natural gas and steam to reform it into a gas rich in hydrogen and carbon monoxide. In the heat transfer method in a type reformer, a heat transfer promoting means consisting of a combination of a demister net and an inner tube wire net is provided approximately at the center of the inner side of the catalyst tube, and a heat transfer promoting means consisting of a combination of a demister net and an inner tube wire net is provided at approximately the center of the outer side of the catalyst tube. A heat transfer method in a heat exchanger type reformer, characterized in that heat flux distribution to the catalyst layer is controlled by providing another heat transfer promoting means from the upstream side of the catalyst tube to the catalyst layer. 2. The heat exchanger type reformer according to claim 1, wherein the heat transfer promoting means provided outside the catalyst tube is a heat transfer promoting means comprising an outer tube wire net and an orifice baffle. Heat transfer method.