JP2609956B2 - Pretreatment method for fuel cell material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell power generation system using natural gas, LPG, naphtha, kerosene, and other hydrocarbons as a raw material to generate electricity or a fuel cell power supply system for supplying electricity and heat energy. It relates to a pre-processing method.

[0002]

2. Description of the Related Art In a fuel cell power generation system, natural gas,
Hydrocarbon desulfurization such as LPG, naphtha, and kerosene is hydrodesulfurized, refined, and then reformed at a high temperature to supply a gas having a high hydrogen concentration to the fuel cell.

[0003] Fuel cells include phosphoric acid type fuel cells, molten salt type fuel cells, and solid electrolyte type fuel cells, and the molten salt type or solid electrolyte type fuel cells incorporate a high temperature steam reforming reaction catalyst (internal high temperature type). In this case, the reforming of the raw material and the power generation reaction can proceed in parallel at a high temperature, so that there are various rational aspects. One of the reasons is that steam reforming catalysts and power generation catalysts are less susceptible to sulfur poisoning under high temperature and high concentration hydrogen gas atmosphere, so it is said that coal gasification gas containing sulfur can be used as a raw material. . However, considering that the high-temperature steam reforming catalyst loses part or much of its activity due to sulfur even at a high temperature of 800 ° C., desulfurization of the hydrocarbon raw material must be sufficiently performed even in the internal high-temperature reforming fuel cell. It is an issue.

[0004] In the case of a phosphoric acid type fuel cell, since it cannot be an internal reforming type, a high temperature steam reforming section for a raw material is separately provided. Even in the case of a high-temperature type fuel cell such as a molten salt type or a solid electrolyte type, an internal reforming type is not always used, and a reforming section may be provided separately. Even in the case of these external reforming methods,
It is conceivable that part of the sulfur flowing into the high-temperature steam reforming section deactivates the catalyst in the low-temperature section of the high-temperature steam reforming catalyst, and the remaining part passes through the high-temperature section and adversely affects the downstream catalyst and the fuel cell.

[0005] Considering that the fuel cell power generator can be installed on a narrow site in an urban area or installed in a building, the fuel cell power generator is made small and compact, and a high-temperature steam reforming unit is also installed in an oil refinery. Unlike a reformer installed in a chemical factory, it is made quite compact, so it has a structure that makes operation such as catalyst replacement difficult. Therefore, also in this case, it is necessary to devise sufficient desulfurization of the hydrocarbon raw material so as not to adversely affect the high-temperature steam reforming section, the downstream catalyst, and the fuel cell.

Since the electromotive force of a fuel cell is about 1 V per unit, several tens, hundreds, and tens of units are stacked to form a stack to obtain a high voltage, or a plurality of stacks are combined to obtain a large current and a large power. It is devised like. Since it is difficult to disassemble and maintain this at regular short-term maintenance, the fuel cell is required to have a performance that does not require disassembly and maintenance for 40,000 hours, that is, five years.

A high-temperature steam reforming apparatus in a chemical plant uses high-concentration hydrogen gas containing almost no carbon oxide as hydrogen for hydrodesulfurization, and the continuous operation time may be 8,000 hours. Furthermore, even if there is an error in the driving operation and there is a problem of carbon deposition and sulfur poisoning, it is possible to regenerate by removing carbon and sulfur by steaming. Even in the case where the activity of the catalyst is reduced and the catalyst is replaced without regeneration, the work space for removing the catalyst is sufficient, so that the replacement can be performed relatively easily.

In the fuel cell power generator, not only the phosphoric acid type but also a hydrogen gas containing a large amount of carbon oxide is used as a gas for hydrodesulfurization, so that advanced desulfurization using the gas is difficult. In addition, since the continuous operation time is as long as 40,000 hours, the accumulation of sulfur increases, leading to a decrease in the activity of the high-temperature steam reforming catalyst. Therefore, advanced desulfurization is more strongly required than in the case of high-temperature steam reforming in a conventional chemical plant. Even when the reforming unit is provided outside the fuel cell, it is difficult to perform operations such as catalyst replacement because it is made compact,
Carbon deposition and sulfur poisoning should be avoided more than chemical plant reformers.

[0009]

SUMMARY OF THE INVENTION The present invention provides a catalyst for high temperature steam reforming in a fuel cell power generation system,
The purpose is to enable continuous operation for a long period of time while protecting from carbon deposition.

[0010]

Means for Solving the Problems] pretreatment method of a fuel cell material according to the present invention, hydrocarbons containing sulfur compounds
The raw material is mixed with a gas for hydrodesulfurization, and sulfur compounds are
Is converted to hydrogen sulfide and converted to hydrogen sulfide in an adsorption desulfurization reactor.
Is mixed with steam to remove low temperature steam
After treatment with the reforming reactor, high temperature steam of the fuel cell power generation system is provided in the internal or external high-temperature steam reforming unit
It is characterized in that it is supplied to the reforming section .

FIG. 1 shows an example of a specific apparatus configuration for carrying out the present invention, in which a raw material hydrodesulfurization reactor 1, a low temperature steam reforming reactor 2, and a solid electrolyte containing a high temperature steam reforming section are incorporated. And a molten carbonate type twisted-charge battery section 3. Raw natural gas, LPG, naphtha, kerosene is line 4
And supplied from the outside through the hydrogenation gas 5 or the internal circulation.
It is mixed with the ring hydrogenation gas 5 ' and sent to the hydrogenation reactor 1A in the hydrodesulfurization reactor 1, where most of the sulfur compounds are converted to hydrogen sulfide, and the adsorption and desulfurization reactor 1B removes hydrogen sulfide. Is done. Then, the mixture with the steam from the line 6 is supplied to the low-temperature steam reforming reactor 2, and the raw material hydrocarbons are all converted into a mixed gas of methane, hydrogen, carbon dioxide, carbon monoxide and excess steam. The low temperature steam reformed gas is
High-concentration hydrogen-containing gas supplied to a high-temperature steam reforming reactor.
You. FIG. 1 shows a case where the high-temperature steam reforming reactor unit 3A is incorporated in the solid electrolyte type or molten carbonate type fuel cell unit 3, but the high-temperature steam reforming reactor unit is provided outside the fuel cell. May be.

Regarding carbon deposition in a high-temperature steam reforming reactor, in the case of high-temperature steam reforming of LPG, naphtha and kerosene, carbon deposition is more likely to occur due to a decrease in steam ratio and the like than in the case of high-temperature steam reforming of natural gas. However, if the gas has been reformed in the low-temperature steam reforming reactor, there is no hydrocarbon other than CH _{4 in the} gas, so that carbon deposition in the high-temperature steam reforming reactor hardly occurs. Therefore, even when carbon is precipitated due to an extremely low steam ratio, the precipitation occurs on the low-temperature steam reforming catalyst, so that the high-temperature steam reforming reaction catalyst can be protected from carbon deposition.

In order to obtain a desulfurization hydrogen source from within the self-system, an outlet gas of a high-temperature steam reforming reactor or a high-temperature steam reforming reaction section in a fuel cell power generation system having an external high-temperature steam reforming reactor is incorporated. If the outlet gas of a molten salt fuel cell or solid electrolyte fuel cell is used as a gas for hydrodesulfurization, these gases contain a high concentration of carbon monoxide, so that the hydrogenation reaction rate becomes slow, and Becomes insufficient.

When a low-temperature steam reforming reactor is installed, the low-temperature steam reforming gas contains mainly carbon dioxide as carbon oxide and little carbon monoxide, so that reaction inhibition is relatively small. Can be used as a gas for hydrodesulfurization. That is, as shown in FIG. 1, a part of the low-temperature steam reforming gas is extracted from the middle between the low-temperature steam reforming reactor 2 and the fuel cell unit 3, cooled by the cooler 7 to condense the steam, and After removing water, the pressure is increased by the compressor 9 and supplied as hydrodesulfurization gas 5 ' .

In the low-temperature steam reforming reactor, the next reaction has almost reached equilibrium.

The temperature condition of the low-temperature steam reforming reaction (350 ° C.)
(550 ° C), the reaction of (1) is biased to the left and the reaction of (2) is biased to the right, so the carbon monoxide concentration in the low-temperature steam reformed gas is larger than that in the case of the high-temperature steam reformed gas. Lower. As described above, since the low-temperature steam reforming gas has a low concentration of carbon monoxide which strongly adsorbs to the catalyst (CoMo system, NiMo system) for the hydrodesulfurization reaction and inhibits the hydrogenation reaction of the sulfur compound, the hydrodesulfurization gas has a low concentration. It can be used as a source of hydrogen for use.

When a low-temperature steam reforming gas containing carbon oxide is used instead of pure hydrogen as the hydrodesulfurization gas, it is difficult to completely desulfurize with the hydrodesulfurization reactor. The sulfur compounds that cannot be completely desulfurized are decomposed in the low-temperature steam reforming reactor, and the sulfur is removed by combining with the low-temperature steam reforming catalyst. As a result, the activity of the low-temperature steam reforming catalyst decreases, but there is no problem if a sufficient amount of the catalyst is filled in consideration of the decrease in the activity.

The outlet gas of a fuel cell (internal high-temperature reforming type fuel cell) having a high-temperature steam reforming reactor built therein is one in which a part of hydrogen gas in the high-temperature reforming gas is consumed for power generation reaction. Although the hydrogen concentration is higher than that of the low-temperature steam reformed gas, it is desirable to use it as a gas for hydrodesulfurization. However, at high temperatures, the reaction of the above formula (2) is biased to the left, and the carbon monoxide concentration is high. There is a disadvantage that the addition reaction is inhibited. Therefore, a CO shift reactor 10 is provided as shown in FIG. 2 and a part of the outlet gas of the fuel cell is guided to perform a CO shift reaction at about 200 ° C. to 450 ° C., and the reaction of equation (2) proceeds to the right. After reducing the carbon oxide concentration to improve the hydrogen concentration, the mixture is cooled to condense and remove the steam, and the pressure is increased by the compressor 9 to be supplied as the hydrodesulfurization gas 5 ' . As a result, a hydrogenation gas having a relatively high hydrogen concentration and a low carbon monoxide concentration is obtained, and desulfurization can be performed using this gas.

The embodiment of the present invention is not limited to those illustrated in FIGS. 1 and 2. For example, a pretreatment system for a plurality of fuel cells in a series of pretreatment systems may be used. A plurality of low-temperature steam reforming reactors can be provided in the treatment system so that the low-temperature steam reforming reactor can be switched during operation.

[0020]

Example 1 Raw naphtha (EP = 180 ° C.) 2 L (liter) / Hr (1.4 kg / Hr) was used as a hydrodesulfurization gas. Of low-temperature steam reforming gas having a composition of 57.7 NL / Hr, and LHSV = 1.0 using a NiMo-based / ZnO catalyst.
L / Hr, P = 8 Kg / cm ² G, T = 360 ° C. for desulfurization purification, and then 4.4 Kg / cm ² of steam for the desulfurization purified naphtha.
H, and then supplied to a low-temperature steam reforming reactor filled with 1.0 kg of a Ni-based low-temperature steam reforming catalyst, and P = 7 kg /
cm ² G, steam reforming at T = 500 ° C. Low-temperature steam reformed gas of 3.3N composition (after removing steam)
m ³ / Hr was obtained. At this time, the sulfur content in the raw naphtha and the desulfurized purified naphtha was 130 ppm and 0.2 ppm, respectively.
Met. Further, no hydrogen sulfide was detected in the low-temperature steam reformed gas. From these results, it can be seen that (1) sulfur in the raw material naphtha can be desulfurized to 0.2 ppm even when low-temperature steam reforming gas is used as the gas for hydrodesulfurization, and (2) low concentration of 0.2 ppm in the purified desulfurized naphtha. It was also found that the sulfur of the sulfur was not combined with the low-temperature steam reforming catalyst and flowed downstream (source gas to the fuel cell system). In other words, it can be seen that if the hydrocarbon feedstock supplied to the fuel cell power generation system is hydrodesulfurized and then treated in a low-temperature steam reforming reactor, the downstream catalyst is protected from sulfur poisoning.

[0021]

Example 2 The same raw material naphtha (E) as used in Example 1 was used.
P: 180 ° C.) 2 L / Hr (1.4 Kg / Hr) as hydrodesulfurization gas Water vapor was removed from the simulated gas at the outlet of the twisting battery with the composition Gas (composition after removal of water vapor) of 35.0 NL / H
r, and using a NiMo / ZnO catalyst, the LHSV
= 1.0 L / Hr, P = 8 Kg / cm ² G, T = 360
The sulfur content in the purified naphtha was 0.4%.
ppm. The purified desulfurized naphtha is steamed with 4.4.
Kg / Hr, Ni-based low temperature steam reforming catalyst 1.0
Pg is supplied to a reactor filled with Kg, and P = 7 Kg / cm ²
G, T = After steam reforming at 500 ° C, introduced into a reactor filled with a Ni-based high-temperature steam reforming catalyst, and P = 6.5Kg
/ Cm ² G, T = 500 ° C. to 800 ° C., High temperature steam reformed gas 7.15 (after removing steam)
Nm ³ / Hr was obtained. After the 50 hour reaction experiment, the high temperature steam reforming catalyst was taken out and observed, but no carbon deposition was observed.

[0022]

[Comparative Example 1] Using the same raw material naphtha and the same apparatus as the hydrodesulfurization gas, bypassing the low-temperature steam reformer and directly subjecting the desulfurized purified naphtha to high-temperature steam reforming, High temperature steam reformed gas 7.14 (after steam removal)
Nm ³ / Hr was obtained. After conducting a 50-hr reaction experiment, the high-temperature steam reforming catalyst was taken out and observed.
Carbon deposition was observed in the catalyst layer having a temperature distribution of 50 ° C.

The following two points can be seen from Examples 1 and 2 and Comparative Example 1. (1) Using the low-temperature steam reforming gas as the hydrodesulfurization gas (Example 1) has better desulfurization results than using the fuel cell outlet gas as it is as the hydrogenation gas (Example 2). (2) Conditions for carbon deposition when desulfurized purified naphtha is directly subjected to high-temperature steam reforming (Comparative Example 1) (raw material type,
Even when the steam ratio, temperature, and pressure are the same, reforming in a low-temperature steam reforming reactor and then high-temperature steam reforming (Example 2) can avoid carbon deposition.

[0024]

Example 3 Same as used in Example 2. The fuel cell outlet simulated gas (including water vapor) having the composition of
-Led to a CO shift reactor filled with a Cr-based catalyst, P = 2
Kg / cm ² G, reaction at T = 350 ° C., cooling to condense and remove water vapor, Was obtained in the same manner as in Example 1 except that the gas was pressurized by a compressor and supplied as 31.7 NL / Hr as a gas for hydrodesulfurization. As a result, the sulfur content in the purified naphtha could be desulfurized to S <0.1 ppm. Next, when the desulfurized purified naphtha was subjected to low-temperature steam reforming in the same manner as in Example 1, Low-temperature reformed gas having a composition of (after removing water vapor) 3.28 Nm ³
/ Hr. Further, the sulfur content in the reformed gas could not be detected. From this example, it can be seen that even at the outlet gas of the fuel cell, the performance of hydrodesulfurization can be improved by converting CO into CO ₂ in the CO shift reactor and reducing the effect of inhibiting the hydrogenation reaction.

[0025]

As described above, the high-temperature steam reforming catalyst in the fuel cell power generation system is protected from sulfur poisoning and carbon deposition, thereby enabling long-term continuous operation.

[0026]

[Brief description of the drawings]

FIG. 1 is an example of a specific device configuration for carrying out the present invention.

FIG. 2 is an example of another device configuration.

Claims (3)

(57) [Claims] 1. A hydrocarbon raw material containing a sulfur compound is treated with water.
Most of the sulfur compounds are mixed with the gas for hydrodesulfurization and
Is converted to hydrogen sulfide and hydrogen sulfide is removed by an adsorption desulfurization reactor.
Low temperature steam reforming reaction
A method for pretreating fuel cell raw materials, comprising: supplying a high-temperature steam reforming section to a high-temperature steam reforming section of a fuel cell power generation system having a built-in or external high-temperature steam reforming section . 2. The method according to claim 1, wherein a gas treated in a low-temperature steam reforming reactor is used as a gas for hydrodesulfurization in the hydrogenation reactor . 3. In the case where the fuel cell is an internal high temperature reforming type fuel cell incorporating a high temperature steam reforming section, after a part of the fuel cell outlet gas is denatured to reduce the carbon monoxide content.
The method according to claim 1, which is used as a gas for hydrodesulfurization in a hydrogenation reactor .