JPH0685868B2 - Heat transfer method in heat exchanger type reformer - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention utilizes the sensible heat of high temperature gas obtained by burning the exhaust gas of a fuel cell anode in a molten carbonate fuel cell (MCFC) power generation system.
The present invention relates to a heat transfer method in a heat exchanger type reformer having a reforming catalyst tube having a role of producing a gas rich in hydrogen and carbon monoxide by reforming natural gas with steam and supplying the gas to a fuel cell anode. More specifically, the heat exchanger type by controlling the heat flux distribution to the catalyst layer by installing heat transfer promoting means provided on each of the inner tube side and the outer tube side of the catalyst tube in a predetermined positional relationship. The present invention relates to a heat transfer method in a reformer.

[0002]

2. Description of the Related Art A reformer in an MCFC power generation system is required to have a structure resistant to thermal shock, which can withstand frequent start / stop including daily start / shut (DSS) and abrupt load change. A so-called bayonet type catalyst tube having a double tube structure is often used. FIG. 6 is a cross-sectional view showing the outline of the 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. 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 A direction. This natural gas reforming reaction is
For example, the reaction formula CH ₄ + H ₂ O → CO + 3H ₂ ΔH = 49.3Kc
It is an endothermic reaction expressed in al / gram mol. Therefore, in order to promote this reforming reaction, the high temperature combustion gas flow B discharged from the anode exhaust gas combustor and the heat from the reformed gas flowing in the inner tube in the direction opposite to the catalyst layer are transferred to the catalyst layer 4. The catalyst layer 4 is kept at an appropriate temperature.

In a system for supplying a necessary amount of heat from a high temperature combustion gas flowing on the outside (shell side) to such a bayonet type catalyst tube, the following points are particularly important in terms of heat transfer characteristics. (1) To improve heat transfer efficiency. (2) To increase the average value of heat flux and control the distribution from the inlet to the outlet of the catalyst layer to a desired shape not only under full load but also under partial load. (3) To uniformly heat multiple catalyst tubes. Therefore, maintain the pressure loss ΔP at a desired value (0.05 to 0.1 kg / cm ² ) and control its distribution to avoid drift of the combustion gas.

Therefore, in order to improve the heat transfer efficiency to the catalyst layer, various measures have been conventionally made. FIG. 7 is a cross-sectional view of a main part showing a heat transfer promoting means in the prior art. For example, as shown in FIG. 7 (a), a sleeve 5 is provided inside the inner tube of the catalyst tube, and FIG. ), A sleeve 6 is provided as shown in FIG. 7C, an orifice baffle 7 is provided as shown in FIG. 7C, and a wire net 8 is provided outside the outer tube as shown in FIG. 7D. Figure 7
As shown in (e), there is a case where the filling material 9 is applied.

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 it 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 triple structure and becomes complicated. The one provided with the sleeve or the orifice baffle on the combustion gas side (FIG. 7 (b) or (c)) needs to be installed in a wide range because it has a low heat transfer accelerating effect, and it is difficult to control the heat flux distribution. Is. In the case where the wire net is provided on the combustion gas side (Fig. 7 (d)), the heat transfer promotion effect is high, but by itself it is difficult to control the distribution because the pressure loss on the combustion gas side is too small. It is difficult to prevent uneven flow of the combustion gas, and thus it is difficult to uniformly heat the plurality of catalyst tubes. In the case where the sleeve and the wire net are provided on the combustion gas side (combination of FIGS. 7B and 7D), the heat transfer promotion effect is good, but the pressure loss on the combustion gas side is at the optimum level (for example, 0.05-0.1kg
/ cm ² ), it is necessary to enlarge the installation area. Further, if the clearance between the sleeve and the outer tube is reduced in order to enhance the effect of promoting heat transfer, the accuracy in manufacturing and mounting becomes a problem. With the filler on the combustion gas side (FIG. 7 (e)), the effect of promoting heat transfer can be enhanced, but the pressure loss on the combustion gas side becomes excessive, and its distribution cannot be controlled.

[0006]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned drawbacks of the prior art and further not only enhances the heat transfer efficiency but also uniformly heats a plurality of catalyst tubes and heats the catalyst layer. Providing 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 to a desired shape. The purpose is to do.

[0007]

Means for Solving the Problems The present inventors have previously provided a heat transfer promoting means, which is a combination of a demister net and a wire net, on the inner tube side of the catalyst tube in order to improve heat transfer efficiency, and a more preferable embodiment. As a result, a heat exchanger type reformer was proposed in which a heat transfer promoting means composed of an outer wire net and an orifice baffle was further provided outside the catalyst tube (Japanese Patent Application No. 3-46891). The present invention further develops this, and if the heat transfer promoting means provided on each of the inner tube side and the outer tube side of the catalyst tube are installed in a predetermined positional relationship, it is extremely possible to solve the above problems. It was completed focusing on its effectiveness.

That is, the heat transfer method in the heat exchanger type reformer of the present invention uses an inner tube and an outer tube for reacting natural gas with steam to reform it into a gas rich in hydrogen and carbon monoxide. In a heat transfer method in a heat exchanger type reformer comprising a bayonet type catalyst tube having a double tube structure as described above, a heat transfer method comprising a combination of a demister net and an inner tube wire net in a substantially central portion inside the inner tube of the catalyst tube. The heat flux distribution to the catalyst layer is controlled by providing heat promoting means and providing another heat transfer means from the substantially central portion outside the catalyst tube to the upstream side of the catalyst tube. . In a preferred aspect of the present invention, the heat transfer promoting means provided outside the catalyst tube may be a heat transfer promoting means including an outer tube wire net and an orifice baffle.

[0009]Detailed explanation of the invention  Hereinafter, the content of the present invention will be specifically described with reference to the drawings.
In the heat transfer method in the heat exchanger type reformer of the present invention,
As a catalytic tube used to reform natural gas with steam
The conventional bayonet type catalyst tube is used for
The outline of its structure is similar to that shown in FIG.
It

FIG. 1 is a sectional view for explaining 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 is provided a heat transfer promoting means 12 which is a combination of a demister net 10 and an inner tube wire net 11, and outside the catalyst tube is another heat transfer promoting means, preferably A heat transfer promoting means 15 including an outer tube wire net 13 and an orifice baffle 14 is provided. Of these, the heat transfer promoting means 12 inside the inner tube is provided in a substantially central portion, preferably over a region of 30 to 80% of the inner tube length, while the heat transfer promoting means 15 outside the catalyst tube is provided in the catalyst tube. It should be provided from approximately the center to the upstream side of the catalyst tube. More specifically, in the heat transfer promoting means 12 inside the inner tube, the difference ΔT ₁ between the inner tube temperature and the average temperature of the catalyst layer 4 is 120 to 180 ° C.,
Preferably, the difference ΔT ₂ between the combustion gas temperature and the average temperature of the catalyst layer 4 of the heat transfer promoting means 15 outside the catalyst tube is 260 ° C. or less, preferably 230 ° C. or less. Provide in the area.

With such a positional relationship, both heat transfer promoting means 1
By installing 2, 15 the inlet 16 of the catalyst layer 4
It is possible to desirably control the heat flux distribution from the outlet to the outlet 17. As a result, the temperature of the reformed gas, which is preferable as the operating temperature of the reformer for the present MCFC power generation system, that is, the reformed gas temperature is 80 at the catalyst layer outlet 17.
It can be maintained at a value of about 0 ° C. and a value of about 600 ° C. at the inner pipe outlet 18.

Such a desired reformed gas temperature can be maintained well not only during steady operation but also during partial load. That is, for example, even at a load of 30 to 50%, it is necessary to maintain the efficiency of the power generation system at the same level as during steady operation, so that the internal pipe outlet temperature of the reformed gas is set to a predetermined value (partial load). This value is equal to the inlet temperature on the anode side of the fuel cell and is around 600 ° C.). Further, the catalyst layer outlet temperature is controlled so as not to rise excessively to cause damage to the catalyst, preferably not more than 800 ° C., or the catalyst outer tube temperature does not exceed its design temperature. Although necessary, such partial load characteristics can be favorably maintained by controlling the heat flux distribution to a desired shape as described above.

Next, the heat transfer promoting means 12 and 15 will be described more specifically. The demister net 10 used for the heat transfer promoting means 12 is formed by randomly forming thin metallic wires in the form of an integrated body such as a gold scourer. For example, the porosity is 99% and the density is 80 kg.
/ M ³ is used. Further, the inner pipe wire net 11 has a form in which the above-mentioned demister net is compressed, and the void thereof is, for example, about 20 mesh. This inner tube wire net has an effect of promoting heat transfer by itself, holds the demister net, and also has a function of rectifying the reformed gas flow.

The reason why such a metal wire assembly has a heat transfer promoting action is as follows. That is, in the case of such an aggregate of metal wires, the specific surface area is large,
By being placed in the passage of the hot reformed gas fluid,
It is easily heated to high temperature by the reformed gas fluid. Since the radiant power of this high-temperature metal wire assembly is high, the surface to be heated, that is, the inner surface of the catalyst layer tube, is subjected to radiant heating due to thermal radiation from the metal wire assembly in addition to convection heating by the reforming gas fluid. Moreover, the amount of heat transfer by the heat radiation is large. As a result, the overall heat transfer from the reformed gas fluid to the heated surface is significantly greater than that without the metal wire assembly.

The demister net 10 and the inner tube wire net 11 are preferably provided alternately in the vertical direction of the inner tube of the catalyst tube as shown in FIG. 1 and combined in multiple stages in order to hold the demister net. The thickness of the demister net (ln) and the thickness of the inner pipe wire net (lw)
The ratio (ln / lw) of 3 to 20, preferably 8 to 1
The range is 2.

As described above, the operating temperature of the reformer for the MCFC power generation system is 800 at the reformed gas catalyst layer outlet.
C., about 600.degree. C. at the catalyst pipe outlet, but in this temperature range, the Boudard reaction from CO-rich gas,
That is, there is a high possibility of carbon deposition due to 2CO → C + CO ₂ . In order to prevent this, as a material used not only for the inner tube of the catalyst tube but also for the heat transfer promoting means inside the inner tube,
A material that suppresses the Boudart reaction or at least has no catalytic action is selected. In addition, even under operating conditions, the steam / carbon ratio (S / C) of about 3 which is larger than 2 to 2.5, which is generally adopted as a natural gas raw material, is adopted to suppress the Boudard reaction. It is preferable.

In the present invention, the heat transfer promoting means provided on the outer side of the catalyst tube has a function of promoting heat transfer and enables uniform heating of a plurality of catalyst tubes provided in the heat exchanger type reformer. It is essential for the stable operation of the device to uniformly heat these multiple catalyst tubes from the combustion gas side, and for that purpose it is necessary to distribute the combustion gas evenly from its inlet to its outlet without uneven flow. It is necessary to control the value of pressure loss ΔP from the inlet to the outlet and its distribution.

Therefore, in the present invention, the orifice baffle is preferably installed as a heat transfer promoting means provided on the outer side of the catalyst tube, and the installation position is installed upstream from the substantially central portion of the catalyst tube. It is a thing. That is, the high-temperature combustion gas flow path becomes narrow at the position where the orifice baffle 14 is installed, which causes turbulence in the flow of the combustion gas to accelerate the heat transfer and also allows the combustion gas to flow without uneven flow. 0.05-0.1 kg / cm ² can be given. And, by installing an orifice baffle on the upstream side, that is, on the downstream side of the combustion gas, from the substantially central portion of the catalyst tube,
Since most of the pressure loss ΔP can be concentrated in the orifice baffle portion, uniform heating of a plurality of catalyst tubes can be realized without causing a non-uniform flow in the flow of combustion gas. In this way, the pitch and the number of stages of the orifice baffle 14 are determined in order to obtain the desired pressure loss value and its distribution.

The heat transfer promoting means 15 preferably comprises the orifice baffle 14 and the outer tube wire net 13, of which the outer tube wire net 1 is used.
3 has a heat transfer function by convection heating and radiant heating, which is similar to the heat transfer promoting means formed by combining the demister net and the inner tube wire net described above.
Φ, about 8 mesh is preferably used.

[0020]

EXAMPLES An example of the present invention will be described in more detail below. The invention is not limited in scope by these examples.

[0021]Example 1  FIG. 2 is a heat exchanger for 1 MW power generation used in the method of the present invention.
It is sectional drawing explaining the outline | summary of the structure of a type | mold reformer. This reform
At the top of the body of the vessel is the inlet nozzle for natural gas and steam.
Having a reforming gas outlet nozzle 20 and a reforming gas outlet nozzle 20.
Combustion gas inlet nozzle 21 is at the bottom and its exit is at the top.
A mouth nozzle 22 is provided. Do not touch inside the reformer body.
Install six medium tubes (only two are shown in the figure) and touch them.
Heat transfer promoting means are provided on the outside of the medium pipe 1 and on the inside of the inner pipe, respectively.
They are provided, but the detailed installation positions of them are described later.
It

The inner wall corresponding to the installed portion of the catalyst tube 1 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 lower part of the 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 portion of the reformer body is made of another heat insulating material 27.

Then, natural gas and steam are introduced into the 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, the high-temperature combustion gas is introduced into the reformer main body from the inlet nozzle 21, transfers heat to the catalyst tube 1, and is then discharged from the outlet nozzle 22.

As shown in FIG. 1, the installation position of the heat transfer promoting means provided inside the catalyst tube and outside the catalyst tube is a heat transfer promoting means 12 formed by combining a demister net 10 and an inner tube wire net 11. The inside of the catalyst pipe inner tube corresponding to a range of 3.18 to 1.5 m from the most upstream end of the catalyst layer 4, specifically, the demister net 10 and the inner tube wire net 11. Were alternately arranged in the vertical direction in five stages. On the outside of the catalyst tube, a heat transfer promoting means 15 including an outer tube wire net 13 and an orifice baffle 14 is provided on the upstream side of the catalyst layer, specifically, in the range from the vicinity of the most upstream end of the catalyst layer to 2.0 m. Installed in position. The orifice baffle 14 was supported by the tie rods 23 and provided in five stages. A thermometer 28 is attached inside the inner tube.

The operating conditions of this device having such a configuration are as follows. As process side conditions, at the inlet nozzle 19, a natural gas flow rate of 171 Nm ³ / h, a steam flow rate of 596 Nm ³ / h, a temperature of 434 ° C., and a pressure of 4.8.
kg / cm ² G, and at the outlet nozzle 20, the reformed gas flow rate is 1151 Nm ³ / h (H ₂ : 56.55 vol%, CO:
_{7.69vol%, CO 2: 8.96vol%} , CH 4: 0.64vol%, H 2
O: 26.18 vol%), temperature 600 ° C, pressure 2.3 kg / c
m ² G, and at the catalyst layer outlet 17 (bottom of the catalyst tube), the temperature was 800 ° C. and the pressure was 2.4 kg / cm ² G.

On the other hand, the combustion gas side conditions are as follows: at the inlet nozzle 21, the flow rate of the combustion gas is 1805 Nm ³ / h, temperature is 1170 ° C., pressure is 2.5 kg / cm ² G, and at the outlet nozzle 22, the flow rate is 1805 Nm ³ / h, temperature. 600
° C., was carried out under a pressure of 2.4kg / cm ² G.

[0027]Comparative Example 1  As a means to promote heat transfer, the inner surface of the inner surface of the catalyst tube should be
A sleeve is provided across the sleeve, while a sleeve is provided on the combustion gas side.
And the wire net on the upstream side of the catalyst tube
The same as Example 1 except that it is installed in a range from 1 to 2.5 m)
It was operated under the conditions.

[0028]Heat flux  Outer tube of the catalyst tube in the above-mentioned Example 1 and Comparative Example 1
Fig. 3 shows the results of measuring the heat flux on the inner and inner tubes.
Shown in. In the figure, 29 is the inner tube of Example 1 and 30 is the inner tube of Comparative Example 1.
The side heat flux is shown in FIG.
The outer tube side heat flux of the comparative example 1 is shown.

As is apparent from FIG. 3, the heat flux distribution of Example 1 was found to be in the range where the heat transfer promoting means was installed (catalyst layer length 1.
In the range of 5 to 3.18 m and the range of 0 to 2.0 m on the outer pipe side, it is understood that the improvement is achieved. That is, the heat flux in the middle portion is increased and the value in the outlet portion of the inner pipe is decreased. As a result, the heat transfer at the outlet is reduced, and the excessive reduction of the reformed gas temperature is prevented. By controlling such a preferable heat flux distribution, as described below, the reformed gas temperature at the catalyst layer outlet and the inner pipe outlet is maintained at a preferable value not only at full load but also at partial load. be able to.

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

[0031]Reformed gas temperature distribution  FIG. 4 shows the 100% raw materials of Example 1 and Comparative Example 1 described above.
A graph showing the temperature distribution of the catalyst layer and reformed gas during normal operation
And 33 indicated by the solid line is the catalyst layer in Example 1.
, 34 shows the temperature distribution of the reformed gas, respectively, and is indicated by the dotted line.
Reference numeral 35 denotes the catalyst layer in Comparative Example 1, and 36 denotes the reforming gas.
The respective temperature distributions of the gas are shown.

As can be seen from this graph, in Example 1, the distribution of the heat flux on the outer tube side and the inner tube side of the catalyst tube was preferably controlled as shown in FIG. The temperature at the point of 4.0 m) is kept at a preferable temperature of about 800 ° C., and the temperature of the reformed gas outlet (at a point of 0 m of the catalyst layer) is about 60 at the preferable temperature.
It was possible to maintain at 0 ° C. On the other hand, in Comparative Example 1, the distribution of the heat flux on the outer tube side and the inner tube side of the catalyst tube was unfavorable as shown in FIG. 3, so that the catalyst layer outlet temperature was about 820 ° C. and the reformed gas outlet was The temperature was about 580 ° C., which was different from the preferable value.

FIG. 5 is a graph showing the temperature distribution of the catalyst layer and the reformed gas at the time of 30% load operation, which is indicated by the solid line 3
7 is the catalyst layer in the example of the present invention, 38 is the temperature distribution of the reformed gas, 39 is the dotted line 39 is the catalyst layer in the comparative example, and 40 is the temperature distribution of the reformed gas.

As can be seen from this graph, in the embodiment of the present invention, the catalyst layer outlet temperature can be kept at about 820 ° C. even at 30% load, and the reformed gas outlet temperature can be maintained at about 590 ° C. I was able to. On the other hand, in the comparative example, the catalyst layer outlet temperature is about 850 ° C.,
Further, the reformed gas outlet temperature was about 570 ° C., which was a large deviation from the preferable value.

[0035]

According to the present invention, a heat transfer promoting means composed of a combination of a demister net and an inner tube wire net is provided at a substantially central portion inside the inner tube of the catalyst tube, and from a substantially central portion outside the catalyst tube. Since the heat flux distribution to the catalyst layer is controlled by providing another heat transfer means on the upstream side of the catalyst tube, the heat transfer efficiency can be improved and uniform heating of a plurality of catalyst tubes can be realized. Further, it becomes easy to control the heat flux distribution to the catalyst layer, and the reformed gas temperature and the catalyst layer outlet temperature can be maintained at desired values not only under full load but also under partial load.

[Brief description of drawings]

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

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

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

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

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

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

FIG. 7 is a cross-sectional view of essential parts showing a heat transfer promoting means in a conventional technique.

[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 provided inside the inner tube of the catalyst tube 13 Outer tube wire net 14 Orifice baffle 15 Provided outside the catalyst tube Another means for promoting heat transfer

Claims (2)

[Claims] 1. A heat exchanger comprising a bayonet type catalyst tube having a double tube structure composed of an inner tube and an outer tube for reacting natural gas with steam to reform it into a gas rich in hydrogen and carbon monoxide. In a heat transfer method in a type reformer, a heat transfer promoting means composed of a combination of a demister net and an inner wire wire net is provided in a substantially central portion inside the inner tube of the catalyst tube, and a substantially central portion outside the catalyst tube. A heat transfer method in a heat exchanger type reformer, characterized in that the heat flux distribution to the catalyst layer is controlled by providing another heat transfer promoting means from above to the upstream side of the catalyst tube. 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 including an outer tube wire net and an orifice baffle. Heat transfer method.