JPH07215701A - Steam reforming method of hydrocarbon - Google Patents

Abstract

PURPOSE:To reduce the ratio of steam to carbon (S/C) and a quantity of steam consumption and to improve energy saving effect by recycling a part of a re formed gas to a raw material hydrocarbon to suppress carbon formation by the thermal decomposition of hydrocarbon. CONSTITUTION:Hydrocarbon of the raw fuel is introduced to a reformer 4, in which, for example, a Ni based spherical catalyst is setted into layers as a catalyst,, through a hydrodesulfurizer 2 and on the other hand, steam is introduced and supplied to the reformer 4 from a steam generator 3, a part of a produced reformed gas from a CO convertor 5 is returned to the hydrodesulfurizer 2 and is desulfurized by converting the sulfur portion to hydrogen sulfide with hydrogen in the formed gas. A part, about 10vol.%, of the formed gas discharged from the reformer 4 is recycled to the position of (2) in the fore part of the steam introducing position of the reformer 4 by sucking with the ejector system depending on the pressure the steam from the steam generator 3 and as a result, the carbon formation in the reformer 4 is suppressed, the S/C is reduced to 2.5 and the quantity of steam consumption is decreased to 5/6 that of the conventional example.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steam reforming system for hydrocarbons, that is, a steam reforming method for hydrocarbons. More specifically, hydrocarbons such as methane are reformed with steam to produce hydrogen. At the same time, it relates to a steam reforming method for hydrocarbons, which suppresses the formation of free carbon, that is, carbon formation, and reduces the formation as much as possible.

[0002]

2. Description of the Related Art Hydrogen (H ₂ ) contains various unsaturated bonds (C =
C, C = O, C = N, N = N, etc.) for hydrogenation, for the synthesis of ammonia and methanol, for oxyhydrogen flame, for balloon filling gas, and other basic materials having various uses, Recently, it has also been used as fuel for cogeneration and fuel cells.

As industrial methods for producing hydrogen, electrolysis of water, gasification of solid fuels such as coal and coke, gasification of liquid fuel, transformation of gas fuel, and liquefaction of coke oven gas are carried out. Various things are known, such as separation, reaction between iron and water vapor, and decomposition of methanol and ammonia. Among these, methane as a kind of gas fuel conversion method Using natural gas or city gas as a raw material,
A steam reforming system that transforms this by steam (= steam) uses a relatively abundant and clean gas as a raw material, and thus has attracted particular attention.

FIGS. 1 and 2 show an example of a conventional steam reforming system, that is, a method for reforming natural gas, city gas, etc. with steam. 1 in FIG.
Is a gas introduction pipe, 2 is a hydrodesulfurizer, 3 is a steam generator, 4 is a reformer, 5 is a CO shift converter, and 6
Is a reformed gas outlet pipe. In the embodiment of FIG. 2, an adsorptive desulfurizer 2 ′ is used instead of the hydrodesulfurizer 2 of FIG. 1, but the rest is the same as that of the embodiment shown in FIG.
The same reference numerals are used.

A raw material gas such as natural gas is first introduced from the gas introduction pipe 1 into the hydrodesulfurizer 2 or the adsorption desulfurizer 2 ', where sulfur (S) contained as a compound such as mercaptan in the raw material gas. After removing the components, the steam from the steam generator 3 is added and mixed and introduced into the reformer 4, where the raw material gas is reformed into a gas containing hydrogen as a main component.

In the reformer 4, an appropriate catalyst such as Ni-based or Ru-based catalyst is used and reformed by catalytic reaction. When the source gas is CH ₄ as a main component, The reforming reaction here can be represented by the following reaction formula (1). CH ₄ + 2H ₂ O = CO ₂ + 4H ₂ (1)

However, in the reaction according to the above reaction formula (1), some CO gas is contained as a by-product in the reformed gas produced, so that the reformed gas produced from the reformer 4 is contained. Is applied to a CO transformer 5 to convert and remove this by-product CO gas to CO ₂ . The reaction in the shift converter 5 is represented by the following equation (2), and the reformer 4
The unreacted residual water vapor is utilized in. CO + H ₂ O = CO ₂ + H ₂ (2)

The produced gas from the CO shift converter 5 is hydrogen (H ₂ ) and carbon dioxide (CO ₂ ) except for excess steam.
This hydrogen (H ₂ ) is the target gas component, but when the source gas contains methane or methane as the main component, as is clear from the above formula (1), the produced gas is The target gas, namely hydrogen content, is 80 mol%
Close to.

Further, in the case of the embodiment shown in FIG.
A part of the produced reformed gas obtained through the O shift converter 5 is returned to the hydrodesulfurization unit 2 through the conduit 7, and the sulfur contained in the form of mercaptan or the like is sulfurized by the hydrogen contained in the above proportion. Although it is changed to hydrogen and is adsorbed and desulfurized, in the case of the embodiment shown in FIG. 2, the sulfur content is adsorbed and desulfurized by the adsorbing desulfurizer 2 ′ itself, for example, by the activated carbon method, the molecular sieve method or the like.

[0010]

In general, in the steam reforming method as described above, in the reaction in the reformer 4, free carbon is generated by the thermal decomposition of hydrocarbons in the raw fuel (that is, carbon). (Bon formation), which adheres to the catalyst in the reformer, the wall of the reformer, etc., and significantly inhibits the reaction. To avoid this, this card
Although it is necessary to suppress the bomb formation itself, as one of them, a method of adding a reforming steam in excess has been conventionally adopted.

That is, for example, when a Ni-based catalyst is used as the catalyst, the ratio of S (steam) to C (carbon) must be set to a value exceeding 3 (that is, S / C). Ratio> 3, which is the stoichiometrically required amount of 1.5
(Equivalent to more than double the amount), in the case of Ru system as well,
The ratio is the stoichiometric amount of steam to methane 2
Over (that is, S / C ratio> 2), it is necessary to add excessively.

However, in order to add the reforming steam (steam) in such an excessive amount, it is necessary to increase the amount of steam generated correspondingly, and not only the extra heat is required for that amount. However, excess steam will remain in the produced gas, and in some cases it may be necessary to separately remove the steam in the produced gas. Moreover, these points are particularly related to the continuous steam reforming method over a long period of time. When it is operated, the operation becomes extremely uneconomical and energy saving is a serious problem.

The above-mentioned hydrocarbon steam reforming system is an effective and effective method for obtaining hydrogen from a hydrocarbon as a raw material, and although it is a technique that is almost firmly established, the present inventor nevertheless solves the above-mentioned problems. While continuing various studies and earnestly researching and studying to solve the problems,
The inventors have found that the problem can be solved by recycling the generated gas from the reformer for the bomb formation, and arrived at the present invention.

That is, according to the present invention, steam for reforming hydrocarbons with steam is obtained by sequentially passing a hydrocarbon stream composed of methane, ethane or the like, which is a raw fuel, through a desulfurizer, a steam reformer and a CO converter. In the reforming method, by recycling the reformed gas, carbon formation is suppressed, and the S / C ratio is greatly reduced as compared with the conventional method, and the required water vapor amount is reduced as much as possible. The purpose is to obtain a very effective energy-saving effect by reducing the amount.

[0015]

The present invention is a steam reforming system for hydrocarbons in raw fuel such as natural gas and city gas, that is, a steam reforming method. It is intended to provide a steam reforming method for hydrocarbons, which is characterized by effectively suppressing carbon formation due to thermal decomposition of hydrocarbons in a raw fuel by recycling it into fuel hydrocarbons.

More specifically, according to the present invention, after passing a hydrocarbon stream which is a raw fuel through a desulfurizer, steam is added and mixed and introduced into a reformer, and the reformed gas here is CO 2. In the steam steam reforming method of hydrocarbons, which comprises passing through a converter, a part of the reformed gas discharged from the reformer is recycled to the raw fuel hydrocarbon stream introduced into the reformer. A steam reforming method is provided.

In this case, the recycle gas is introduced into the conduit in front of the steam introduction site, and the recycle compressor is sucked by utilizing the pressure of the steam with the increased pressure of the steam. The pressure of the mixed steam can be effectively used without the need for a separate one. Further, it is advantageous to introduce an ejector type for this suction, but in the present invention, if necessary,
It is also possible to appropriately use the recycling compressor and the ejector together.

According to the present invention, with the above-mentioned constitution, carbon formation can be effectively suppressed and its generation can be substantially eliminated, but the amount of supplied steam, that is, the S / C ratio is greatly increased. The amount of water vapor introduced can be reduced to the minimum necessary. And this point is an extremely effective effect in terms of energy saving, considering the case where the steam reforming method is continuously operated for a long period of time, and at the same time, mixing of steam into the produced gas can be avoided. It is possible to obtain various effects.

In the present invention, the reason or the causal relationship for obtaining such remarkable effects is unknown in detail. However, perhaps the hydrocarbon is reformed by a reformer,
It is presumed that this is due to the dilution effect of the obtained hydrogen-rich produced gas and the O ₂ supply action of the produced CO ₂ .

That is, the recycled gas dilutes the hydrocarbons in the raw fuel, and this has the same effect as the diluting action by the steam (by the excess steam as in the conventional method) so that the hydrocarbon concentration is increased. In addition to lowering, carbon dioxide formation is suppressed by the action of O ₂ supplied by produced CO ₂ , or carbon formation is suppressed by returning produced free carbon to CO or CO ₂ . I think that the.

Further, as described above, the reforming gas itself is recycled in the conventional manner shown in FIG.
This is for hydrodesulfurization of the raw fuel and for supplying hydrogen in the reformed gas to it (for that purpose, the recycling rate is at most about 3%). Therefore, the recycling operation in the present invention is performed. Is completely different from this in terms of its technical significance, and its ratio is also 10
%, Or it exceeds this value for recycling.

[0022]

EXAMPLES Examples of the present invention will be described below, but it goes without saying that the present invention is not limited to these examples. FIG. 3 and FIG. 4 are diagrams showing the outline of the steam reforming system for hydrocarbons according to the present invention.
The symbols have the same meanings as those in FIGS.

In FIG. 3, the arrangement of the steam generator 3, the hydrodesulfurizer 2, the reformer 4 and the CO converter 5, the hydrodesulfurizer 2 is shown.
Introducing and supplying steam from the steam generator 3 to the raw fuel guided to the reformer 4 via the CO converter 5
It is the same as in the case of FIG. 1 in that part of the reformed gas produced from No. 1 is returned to the hydrodesulfurizer 2, and the sulfur in the produced gas is desulfurized, and FIG. This corresponds to FIG.

In FIGS. 3 and 4, reference numeral 8 is a recycling conduit. In the present invention, a part of the product gas discharged from the reformer 4 is added to the raw fuel hydrocarbons introduced into the reformer 4 by the conduit 8 and mixed to be recycled to remove the free carbon in the reformer 4. The production, that is, the carbon formation is suppressed, the production of free carbon is reduced as much as possible as compared with the conventional system, and the amount of steam used can be greatly reduced.

In this case, the reformed gas discharged from the reformer 4 is recycled by the conduit 8 and mixed with the raw fuel, and its introduction part is located before the steam introduction part of the reformer (in FIGS. 3 to 4,
Point), and this by the steam from the steam generator,
The pressure can be used for suction and the pressure of the mixed steam can be effectively used, but the suction can be performed more advantageously by performing the suction in the ejector type.

Further, as the reformed gas in the present invention,
In addition to the case where the reformed gas from the reformer 4 is used (in Fig. 3 to 4), the gas from the outlet of the CO shifter 5 (in Fig. 3 to 4) is recycled. You can also let it. Also, the gas can be recycled before the hydrodesulfurizer 2 (in Fig. 3 to 4),
In this case, in particular, in the embodiment of FIG. 3, it is also possible to combine the recycling of the hydrogen gas for hydrodesulfurization.

Next, various conditions were set using the above-mentioned apparatus system, and operation was performed for each set condition. As an example thereof, the case of using the embodiment of FIG. 3 will be described. As the reforming catalyst, a Ni-based spherical catalyst (manufactured by Toyo CCI Co., Ltd.) was prepared and set in the reformer 4 in layers. .

Next, natural gas (city gas 13A) is supplied from the gas introduction pipe 1 [space velocity (SV): about 100].
0 hr ⁻¹ ], 10 (volume)% of the reformed gas is recycled to the reformer 4 (→ in the figure), and the steam (gas pressure: 7 kg / cm ² G) from the steam generator 3 is ejected.
Mixed by format.

According to this, in the case of the conventional example (FIG. 1), in order to suppress the carbon formation, it is necessary to set the S / C ratio to at least 3.0. According to the above operation example of the invention, the S / C ratio can be reduced to 2.5, and the required steam amount in this case is 6 minutes compared with the conventional method. However, these advantages and effects were almost the same under other setting conditions.

As described above, according to the present invention, the hydrocarbon stream having the steam generator 3 and composed of methane, ethane and the like as raw fuel is desulfurizer 2, 2 ', reformer 4 and CO converter. 5
In the steam reforming method using steam for reforming hydrocarbons, a part of the reformed gas discharged from the reformer 4 is recycled to the front of the reformer 4 to make a carbon-frame-form. The S / C ratio can be significantly reduced while suppressing the vibration. Therefore, this makes it possible to reduce the required amount of water vapor as much as possible and obtain a very effective energy saving effect.

[0031]

As described above, according to the present invention, a hydrocarbon stream composed of methane, ethane, etc., which is a raw fuel, is desulfurized,
In a steam reforming method in which hydrocarbons are reformed by steam by sequentially passing through a steam reformer and a CO converter, by recycling a part of the reformed gas discharged from the reformer before the reformer. The S / C ratio can be greatly reduced while suppressing carbon formation. In addition, the required amount of water vapor can be reduced as much as possible, and a very effective energy saving effect can be obtained.

Further, by introducing the recycled gas before the steam introducing portion to the reformer and sucking the recycled gas with steam having an increased pressure, the pressure of the mixed steam can be effectively utilized. You can Further, in this case, if the suction is performed by an ejector type, it is more effective in terms of energy saving and the like.

[Brief description of drawings]

FIG. 1 is a diagram showing a conventional steam reforming system.

FIG. 2 is a view showing a conventional steam reforming system using an adsorptive desulfurizer 2 ′ in place of the hydrodesulfurizer 2 of FIG.

FIG. 3 is a diagram showing an embodiment in which the steam reforming system of the present invention is applied to FIG.

FIG. 4 is a diagram showing an embodiment in which the steam reforming system of the present invention is applied to FIG.

[Explanation of symbols]

 1 Gas Inlet Pipe 2 Hydrodesulfurizer 2'Desulfurizer 3 Steam Generator 4 Reformer 5 CO Converter 6 Reformed Gas Outlet Pipe 7 Recycle Pipe for Hydrodesulfurizer 8 Recycle Pipe

Claims (3)

[Claims] 1. In a steam reforming method for hydrocarbons, a part of the reformed gas is recycled to a raw material hydrocarbon before reforming, whereby a carbon foam by thermal decomposition of the raw material hydrocarbons.
A steam reforming method for hydrocarbons, characterized in that it suppresses messation. 2. A steam reforming of hydrocarbon, which comprises passing a raw material hydrocarbon through a desulfurizer, adding and mixing steam and introducing the mixture into a reformer, and passing the reformed gas there through a CO converter. In the quality method, a hydrocarbon steam reforming method, characterized in that a part of the reformed gas discharged from the reformer or the CO converter is recycled to the raw material hydrocarbon before the reformer. 3. The steam reforming method for hydrocarbons according to claim 2, wherein the recycled gas is introduced into the front part or the rear part of the desulfurizer.