JP2003321203A - Steam reforming system for hydrocarbon - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steam reforming system which can certainly prevent sulfuric acid corrosion and chlorine SCC (sulfuric acid and chrorine corrosion) corrosion caused on a peripheral surface of a heater tube bundle around an inlet of gas to be heated in a heater by making moisture condensation on all the peripheral surfaces of the heater tube bundle zero. <P>SOLUTION: The steam reforming system involves a water mixing part to mix a raw material hydrocarbon with water and a heat exchanging type steam reforming equipment equipped with a heater to heat the hydrocarbon mixed with water and a combustion chamber. A water preheater is placed at the previous position of the water mixing part. This stream reforming system for the hydrocarbon is characterized by controlling the preheated water temperature at the water preheater to be not higher than boiling temperature. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrocarbon steam reforming system, and more specifically, to a water mixing section for mixing raw hydrocarbons with water, a heater for heating hydrocarbons mixed with water, and combustion. The present invention relates to a steam reforming system including a heat exchange steam reformer having a chamber.

[0002]

2. Description of the Related Art A steam reforming method for hydrocarbons, which is one of the methods for producing hydrogen, uses methane, ethane, propane, butane, city gas, LP gas, natural gas, and other hydrocarbon gases (two or more types). A mixture of hydrocarbons) and alcohols are reformed with steam to produce a hydrogen-rich reformed gas. In the steam reforming method, those hydrocarbons are converted into hydrogen-rich reformed gas by a catalytic reaction in the steam reformer.

FIG. 1 is a diagram showing the principle of a steam reformer. In general, it is composed of a combustion section in which a burner is arranged and a reforming section in which a reforming catalyst is arranged. In the reforming section, the hydrocarbon reacts with steam to produce a hydrogen-rich reformed gas.
Heat is supplied from the outside for the progress of the reaction in the reforming section, and when hydrocarbon is used as a raw material, a temperature of about 750 to 800 ° C. or higher is required. Therefore, the combustion heat (ΔH) generated by the combustion of the fuel gas in the combustion section by the air (combustion air) is supplied to the reforming section. As the reforming catalyst, for example, a Ni-based catalyst, a Ru-based catalyst, or the like is used.

FIG. 2 is a diagram showing an example of the construction of a heat exchange type steam reforming apparatus which uses combustion gas from a burner as a heating source. Although FIG. 2 shows a mode in which the present reformer is arranged vertically, it can also be used in a horizontal mode. As shown in FIG. 2, it is composed of a combustion chamber by a burner arranged in the lower part and a reforming section connected to the combustion chamber. In the combustion chamber, fuel such as city gas is burned with air (combustion air). The reforming section is composed of a double tube consisting of an inner tube and an outer tube surrounding the inner tube.

A raw material gas, for example, desulfurized city gas added with water is supplied from the upper part into the outer pipe (between the outer pipe and the inner pipe) and reformed while descending. The reformed gas returns at its lower end and rises in the inner tube to exchange heat via the inner tube wall, and a part of reaction heat is recovered in the reforming section. FIG. 2B is a diagram showing the state of the lower end portion. Meanwhile, the double pipe is indirectly heated by circulating the combustion gas generated in the combustion chamber to the outer circumference of the outer pipe. A temperature sensor is arranged in each of the combustion chamber and the reforming section as needed.

FIG. 3 shows the use of the steam reformer as described above.
It is a figure explaining a steam reforming system including a process from supply of source hydrocarbon (henceforth, also called source gas or hydrocarbon gas suitably) to a CO shift converter. Since the reforming catalyst is poisoned by the sulfur compounds in the raw material gas such as city gas and deteriorates in performance, it is introduced into the desulfurizer to remove the sulfur compounds. Water is added to the raw material gas after desulfurization, mixed, and introduced into the reforming section of the steam reformer.
Pure water such as distilled water or ion-exchanged water is used as water.

When the source gas is methane, the reforming reaction is
Generally, "CH_Four+ 2H₂O → CO ₂+ 4H₂Indicated by
It Unreacted methane and unreacted methane in the reformed gas produced
In addition to steam and generated carbon dioxide, carbon monoxide (CO)
Around 8 to 15% (volume%) is included. others
For the reformed gas, the by-product CO is converted into carbon dioxide (CO₂) And hydrogen
To a CO transformer to remove it. CO
Shift reaction in a transformer "CO + H₂O → CO₂+ H₂"
Unreacted residual water in the reforming section
Steam is used.

Regarding steam required for steam reforming, conventionally, water at room temperature is sprayed into hydrocarbons in a water mixing section, and then water is heated in a heater (vaporizer) together with heating of raw material gas. To generate water vapor. The combustion gas from the reformer is used as the heating source. The raw material gas containing water, that is, the heated gas flows in the pipe, the combustion gas flows in the opposite direction (counterflow) to the heated gas around the pipe, and the heated gas is heated by indirect heat exchange.

FIG. 4 is a structural example of a heater having a water mixing section. This heater is a multi-tubular heater, in which water to be heated such as city gas (desulfurized) is mixed with water in the water mixing section and flows through each pipe to preheat water, heat vaporize water, The heated gas (city gas, etc.) is heated and supplied to the reformer. The heating medium flows through the outer circumference of each tube in the opposite direction to the gas to be heated. As the heating medium, high-temperature combustion exhaust gas is used, and in most cases, combustion exhaust gas after being used for the reforming reaction in the reformer is used.

[0010]

DISCLOSURE OF THE INVENTION The present inventors have continuously operated an actual steam reforming system as shown in FIG. 3 in which a heater as shown in FIG. 4 is arranged to produce hydrogen. During operation, the amount of reformed gas decreased and the performance of the steam reforming system deteriorated. It was found that the cause was leakage of raw material hydrocarbons in the heater to the combustion exhaust gas side. Leakage in the heater has a direct adverse effect on the device capacity and is fatal for the entire system.

Then, when the cause of the above-mentioned leakage was pursued and examined, it was observed that sulfuric acid corrosion and chlorine SCC corrosion occurred on the outer peripheral surface of the tube bundle near the inlet of the heated gas of the heater. This is a portion shown as "sulfuric acid corrosion and chlorine SCC corrosion generation portion" in FIG. As a result of further examination and consideration of the cause, it was found that the flue gas contained sulfur and chlorine and was due to condensation of water in the flue gas.

As for the source of sulfur and chlorine in the combustion exhaust gas, the desulfurized city gas has no sulfur and no chlorine component. Therefore, the sulfur content is the fuel introduced into the burner of the reformer. (City gas) and air, and chlorine is due to the air introduced into the reformer burner. In addition, sulfuric acid corrosion and chlorine SCC corrosion due to the sulfur content and chlorine content in the combustion exhaust gas occur in the presence of water, and do not occur in the water vapor state. Moisture is generated by combustion of city gas introduced into the burner in addition to the amount contained in air.

Of these, the sulfur content and the chlorine content are considered to be caused by sulfurous acid gas, chlorine and chlorine compounds in the outside air in the air intake section. On the other hand, regarding water content, in the heater, the deviation of the dispersion of the raw material gas mixed with water, that is, the heated gas into each tube (that is, there is a tube in which the heated gas flows in a large amount and a small amount in the heated gas flows Temperature difference on the flue gas side, which is the heating source, and the temperature of part of the outer circumference of the tube bundle near the inlet of the heated gas in the heater is below the dew point, which causes sulfuric acid corrosion and chlorine. It was found that SCC corrosion occurred.

The present invention solves the above-mentioned problems caused by the heater in the conventional steam reforming system, that is, sulfuric acid corrosion and chlorine SCC corrosion, based on the results of the above investigation and consideration. In a hydrocarbon steam reforming system, long-term continuous operation is possible by avoiding condensation of steam in the combustion exhaust gas that is passed as a heating source to the heater for the raw hydrocarbons. It is an object of the present invention to provide a steam reforming system that enables the above.

[0015]

DISCLOSURE OF THE INVENTION The present invention provides a heat exchange type steam reforming unit having a water mixing section for mixing raw hydrocarbons with water, a heater for heating hydrocarbons mixed with water, and a combustion chamber with a burner. A steam reforming system including a device, wherein a water preheater is arranged in front of a water mixing section.

The present invention is a steam reforming system including a heat exchange type steam reforming device having a heater for heating a hydrocarbon mixed with water and a combustion chamber by a burner. Provided is a steam reforming system for hydrocarbons, wherein a preheater is arranged and a preheating temperature of water by the water preheater is set to a temperature not higher than a temperature at which water does not boil.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention comprises a water mixing section for mixing raw hydrocarbons with water, a heater for heating hydrocarbons mixed with water, and a steam reforming apparatus using combustion gas from a burner as a heating source. For steam reforming system. Further, a water preheater is arranged in the preceding stage of the water mixing section, and the water is preheated by the water preheater and then mixed with the raw material hydrocarbon.

FIG. 5 is a view showing an example of a mode in which a water preheater is arranged in the preceding stage of the water mixing section. Water is first passed through a water preheater to be preheated and then mixed with a heated gas such as city gas (desulfurized) in a water mixing section. The heated gas mixed with preheated water flows through each tube in the heater, and is supplied to the reformer through the process of vaporizing water and heating the heated gas. High-temperature combustion exhaust gas, which is a heating medium, flows through the outer circumference of each tube in the opposite direction to the gas to be heated.

As a heating medium in the preheater, as shown in FIG. 5 and FIG. 6 which will be described later, it is generated from a steam reforming device (reformer) and discharged through a heater for heating hydrocarbon mixed with water. The combustion exhaust gas may be used, or the combustion exhaust gas discharged from the steam reforming device (reformer) may be used.

As described above, by heating water in advance with the water preheater and then supplying it to the water mixing section so that the combustion exhaust gas in the heater has a temperature higher than the moisture dew point, all the outer peripheral surfaces of the tube bundles in the heater are heated. It is possible to reduce the water condensation at 0 to prevent sulfuric acid corrosion and chlorine SCC corrosion that occur on the outer peripheral surface of the tube bundle near the inlet of the heated gas of the heater.

Since the reason for disposing the water preheater in the present invention is as described above, it is important to heat the water in the water preheater to the dew point temperature of water in the combustion exhaust gas or higher. As a result, the possibility of water condensation on the outer surface of the tube bundle of the heater can be reduced to zero. Even if the fuel supplied to the combustion chamber by the burner contains sulfur and the supplied air contains chlorine, the moisture in the combustion exhaust gas flowing through the heater is in the state of water vapor. The outer surface of the tube bundle does not corrode.

In the present invention, the preheating temperature of water in the water preheater is preferably controlled so as to be equal to or lower than the temperature at which water does not boil at the operating pressure and equal to or higher than the moisture dew point temperature of combustion exhaust gas. As a result, the preheating of water in the water preheater is heating of the liquid (water), not under gas-liquid mixing, so that the heat transfer efficiency is improved and the heat transfer area can be reduced. For this reason, the heat transfer area as a whole (water preheater + heater) can be reduced (water preheater + heater according to the present invention) as compared with the case of a conventional heater alone (see FIG. 3). Heat transfer area <heat transfer area of conventional heater alone).

FIG. 6 is a view showing an example of a mode in which the water preheater according to the present invention is arranged in the preceding stage of the water mixing section in the steam reforming system as shown in FIG. In FIG. 6, the arrow (→) indicates the flow direction when the corresponding gas is flowing. Water is preheated by a water preheater having a combustion exhaust gas generated from a reformer and discharged through a heater for heating hydrocarbon gas mixed with water as a heat source, and then mixed with hydrocarbon gas. Here, instead of the heat source, the combustion exhaust gas discharged from the reformer may be used as the heat source.

After passing through the desulfurizer, the raw material gas such as city gas is mixed with the water preheated as described above, and the hydrocarbon gas mixed with the water is heated by the heater. In FIG. 6, the preheated water is shown to be supplied into the conduit from the desulfurizer to the heater. However, when the heater as shown in FIG. Supplied.

The steam-containing hydrocarbon gas heated by the heater is introduced into the reforming section of the reformer (reformer). The reformer is equipped with a reformer and a combustion chamber by a burner, and burner burns city gas with air. The produced combustion gas is discharged from the reformer after being used as a heat source for heating and reforming the steam-containing hydrocarbon gas heated by the heater. The exhaust flue gas is further used as a heat source for the heater and the subsequent water preheater. The reformed gas generated by the reformer is used as a heat source for the air preheater.

[0026]

The present invention will be described in more detail based on the following examples, but it goes without saying that the present invention is not limited to these examples.

Example A steam reforming system shown in FIG. 6, that is, a steam reforming system equipped with a water preheater was used. As the reforming device, a heat exchange type steam reforming device using a combustion gas from a burner shown in FIG. 2 as a heating source was used, and the reforming section was filled with a reforming catalyst (a catalyst in which Ni was supported on alumina). The structure of the part including the water preheater and the heater is as shown in FIG. City gas (13A) was used as a raw material gas.

The steam reforming system, which produces hydrogen gas of 500 Nm ³ / h in a steady operation, is started, and thereafter, it is continuously operated for a long period of time. In FIG. 6, the flow rate and temperature at each location during steady operation are also shown. Although the operation was continued in this way, sulfuric acid corrosion and chlorine SCC corrosion were not observed at all on the outer peripheral surface of the tube bundle near the inlet of the gas to be heated of the heater. Thus, the effect of the present invention is clear.

Comparative Example As a comparative example, continuous operation was carried out using the steam reforming system shown in FIG. As shown in FIG. 7, this reforming system is a reforming system without a water preheater. The heater shown in FIG. 4 was used as the heater, and other than this, continuous operation was performed in the same manner as in the example. In FIG. 7, the flow rate and temperature at each location during steady operation are also shown. After three years of operation, the amount of hydrogen produced decreased. In pursuit of the cause, it was observed that sulfuric acid corrosion and chlorine SCC corrosion occurred on the outer peripheral surface of the tube bundle near the inlet of the heated gas of the heater, and the raw hydrocarbon gas leaked to the combustion exhaust gas side. It was

[0030]

According to the present invention, it is possible to reduce the water condensation on all the outer peripheral surfaces of the tube bundle in the heater, and thereby the heated gas (water + hydrocarbon gas) in the heater.
Sulfuric acid corrosion and chlorine SC on the outer surface of the tube bundle near the inlet of the
C corrosion can be reliably prevented. As a result, various useful effects can be obtained such as it is not necessary to consider sulfuric acid corrosion and chlorine SCC corrosion as the constituent material of the heater.

[Brief description of drawings]

FIG. 1 is a diagram showing a steam reformer in principle.

FIG. 2 is a diagram showing a configuration example of a heat exchange type steam reforming apparatus using a combustion gas from a burner as a heating source.

FIG. 3 is a diagram illustrating a steam reforming system including a process from a supply of hydrocarbon gas to a CO shifter using a steam reformer.

FIG. 4 is a diagram showing a configuration example of a heater having a water mixing unit.

FIG. 5 is a diagram showing an example of an embodiment of the present invention in which a water preheater is arranged in the preceding stage of a water mixing section.

FIG. 6 is a diagram showing an example of a mode in which a water preheater is arranged in a preceding stage of a water mixing section in a steam reforming system.

FIG. 7 is a diagram showing a steam reforming system without a water preheater (comparative example).

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yoshifumi Takano             Tokyo Shinjuku 3-7-1 Nishishinjuku Tokyo Gas             Within Chemical Co., Ltd. (72) Inventor Haruhiko Nakamura             2-1 Okawa-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Mitsubishi             Kakoki Co., Ltd. (72) Inventor Katsura Kuragaki             2-1 Okawa-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Mitsubishi             Kakoki Co., Ltd. F-term (reference) 4G140 EA03 EA06 EB03 EB12 EB43                       EB44

Claims (5)

[Claims] 1. A steam reforming system comprising a heat exchange type steam reforming apparatus comprising a water mixing section for mixing raw hydrocarbons with water, a heater for heating hydrocarbons mixed with water, and a combustion chamber. A steam reforming system for hydrocarbons, characterized in that a water preheater is arranged in the preceding stage of the water mixing section. 2. A steam reforming system including a heat exchange type steam reforming apparatus comprising a water mixing section for mixing raw hydrocarbons with water, a heater for heating hydrocarbons mixed with water, and a combustion chamber. Arranging a water preheater in front of the water mixing section, and
A steam reforming system for hydrocarbons, characterized in that the preheating temperature of water by a water preheater is controlled to be equal to or lower than a temperature at which water does not boil. 3. The heating source of the water preheater is a combustion exhaust gas discharged through a heater for heating a hydrocarbon mixed with water generated from a steam reformer. 3. The hydrocarbon steam reforming system according to any one of 2 above. 4. The steam reforming of hydrocarbon according to claim 1, wherein the heating source of the water preheater is combustion exhaust gas discharged from the steam reforming device. system. 5. The hydrocarbon steam reforming system according to any one of claims 3 to 4, wherein the preheating temperature of water in the water preheater is not higher than the temperature at which water does not boil and the moisture dew point of the combustion exhaust gas. A hydrocarbon steam reforming system characterized by being controlled to a temperature or higher.