JPH0669881B2 - Hydrocarbon steam reforming method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a steam reforming method for producing hydrogen-rich gas from a raw material hydrocarbon such as LPG and naphtha.
More specifically, it relates to improvement of a two-stage steam reforming method using a combination of a medium temperature steam reforming reactor and a high temperature steam reactor.

As one of the methods for producing hydrogen-rich gas by steam reforming raw hydrocarbons such as LPG and naphtha, the raw hydrocarbons and steam are first treated in an external heating type medium temperature steam reforming reactor, and then the produced gas is treated. A two-stage steam reforming method in which a high temperature steam reforming reactor is used is known. Since this method can utilize the outlet gas of the high temperature steam reforming reactor to heat the medium temperature steam reforming reactor, it has an advantage that the heat load required for the heating furnace can be reduced. However, even if the heat recovery of the flue gas is attempted by this method, the flue gas still retains a considerable amount of heat. Therefore, this method cannot fully recover the heat of the flue gas. However,
If only the heat recovery rate is a problem, the heat recovery rate can be improved by using the above flue gas as a heat source to generate steam in an amount that exceeds the amount of steam required for the steam reforming reaction. It is possible. However, in the current steam reforming process, it is sufficient if the steam required for this can be covered by the residual heat of the flue gas, and even if more steam can be obtained, the steam can be evaluated exceptionally. The reality is that it cannot be done. Therefore, it is most desired to reduce the amount of fuel used in the heating furnace that heats the high temperature steam reforming reactor.

The present invention revises the idea of generating excess steam to recover the residual heat of flue gas, and the flue gas is preheated from the medium temperature steam reforming reactor to the high temperature steam reforming reactor. By utilizing the residual heat of the gas, the heat load of the heating furnace used for maintaining the high temperature steam reforming reactor at a desired reaction temperature can be further reduced.

Thus, the method for steam reforming of hydrocarbons according to the present invention is a method in which the gas supplied from the medium temperature steam reforming reactor to the high temperature steam reforming reactor is heated again by the flue gas to obtain high temperature steam. The purpose is to reduce the heat load of the heating furnace required to maintain the reforming reactor at a desired temperature.

That is, the two-stage steam reforming method according to the present invention comprises (a)
The raw material hydrocarbons and steam are supplied to a flue gas of a heating furnace in which a high temperature steam reforming reactor is housed or a medium temperature steam reforming reactor which is heated by an outflow gas from the high temperature steam reforming reactor, Contacting the first reforming catalyst under a first reforming condition to generate a primary reformed gas containing hydrogen and methane as main components, and (b) using the primary reformed gas as a flue gas of the heating furnace. (C) The heated primary reforming gas is supplied to the high temperature steam reforming reactor and contacted with the second reforming catalyst under the second reforming condition. The secondary reformed gas containing hydrogen as a main component is generated.

In the two-stage steam reforming method of the present invention, the preheating of the raw material hydrocarbon is limited to a temperature (approximately 520 ° C.) that does not accompany olefin formation as in the conventional method, but the preheated raw material hydrocarbon is the medium temperature steam. Since it is reformed in the reforming reactor, it is converted to primary reformed gas that does not generate olefins even if it is heated to 520 ° C or higher. Can be supplied to the reactor, and thus the heat load required for the heating furnace of the high temperature steam reforming reactor can be highly reduced.

FIGS. 1 and 2 attached hereto are examples of flow sheets for carrying out the two-stage steam reforming method of the present invention.
In the mode shown in FIG. 1, it is supplied from the line 1 into the system.
In the flue 6 of the heating furnace 5 in which the raw material hydrocarbon such as LPG or naphtha is mixed with the steam supplied from the line 2 and the high temperature steam reforming reactor 4 is housed, usually 500 to 520.
Preheated to about ℃. As already mentioned, raising the temperature of the feedstock hydrocarbons to above 520 ° C with this preheating results in the formation of a small amount of olefins in the flue preheater, which results in the formation of carbon on the catalyst of the high temperature steam reforming reactor. Will be deposited and the reaction activity will be significantly reduced. The mixture of the raw hydrocarbon and the steam preheated to a predetermined temperature is supplied to the medium temperature steam reforming reactor 3 heated by the outflow gas from the high temperature steam reforming reactor 4 as shown in the figure, By contacting the first reforming catalyst under the first reforming condition, it is converted into a primary reformed gas containing hydrogen and methane as main components and containing carbon monoxide, carbon dioxide and unreacted steam. The first reforming conditions include a temperature of 520 to 620 ° C., a pressure of 10 to 30 kg / cm ² G,
A steam ratio of 1.5 to 3.0 (H ₂ O mol / C atom of hydrocarbon component) and a gas hourly space velocity of 2000 to 6000 hr ⁻¹ are generally adopted. As the first reforming catalyst, 2 wt% of Ru is an alumina carrier. The catalyst supported above is usually used.

The primary reformed gas obtained from the medium temperature steam reforming reactor 3 is
Next, after the temperature is raised in the flue 6 of the heating furnace 5, it is supplied to the high temperature steam reforming reactor 4, and the second reforming condition is applied to the second reforming condition.
By contacting with the reforming catalyst, the secondary reformed gas containing 50 mol% or more of hydrogen is converted. The second reforming conditions are a temperature of 700 to 850 ° C., a pressure of 10 to 30 kg / cm ² G, and a pressure of 2.5.
A steam ratio (H ₂ O mol / C atom of hydrocarbon component) of ˜5.5 and a gas hourly space velocity of 2,000˜6000 hr ⁻¹ can be adopted, and the second reforming catalyst is made to have nickel supported on alumina. Ordinary natural gas reforming catalysts can be used. From the high temperature steam reforming reactor 4, a secondary reformed gas of about 800 to 850 ° C. is obtained.
Is used as a heat source for maintaining the first reforming condition of 520 to 620 ° C.

FIG. 2 shows a mode in which the heating of the medium temperature steam reforming reactor 3 is performed by the flue 6 of the heating furnace 5 instead of by the outflow gas (secondary reforming gas) from the high temperature steam reforming reactor 4. The raw material hydrocarbons supplied from the line 1 are mixed with the steam supplied from the line 2 and preheated in the flue 6, and then introduced into the medium temperature steam reforming reactor 3. The reactor 3 is heated by the flue 6 of the heating furnace 5, and the mixture of the raw material hydrocarbon and steam in the reactor 3 becomes the first reforming catalyst under the above-mentioned first reforming condition. When converted into primary reformed gas, it is converted into primary reformed gas. This primary reformed gas is further heated by heat exchange in the flue 6, and then supplied to the high-temperature steam reforming reactor 4 to be subjected to the second reforming catalyst under the second reforming condition described above. When contacted with, it is converted to a secondary reformed gas containing 50 mol% or more of hydrogen.

In addition, in the embodiment shown in FIG. 1, the mixture of the raw material hydrocarbon and steam is preheated in the flue 6 and supplied to the intermediate temperature steam reforming reactor 3. However, instead of this, as shown in FIG. It is also possible to preheat only the steam in the flue 6, mix this with the raw material hydrocarbons and supply it to the medium temperature steam reforming reactor 3. Similarly, also in the embodiment shown in FIG. 2, instead of preheating only steam, the raw material hydrocarbon can be preheated together with steam. Although not shown in FIG. 1 and FIG. 2, in the method of the present invention, steam is additionally added to the outflow gas from the medium temperature steam reforming reactor, that is, the primary reformed gas to perform high temperature steam reforming. It is also possible to increase the steam ratio in the reactor.

As described above, in the two-stage steam reforming method of the present invention, an external heat type medium temperature steam reforming reactor and a high temperature steam reforming reactor are combined to heat the medium temperature steam reforming reactor. The effluent gas from the reforming reactor or the flue gas of the heating furnace for the high temperature steam reforming reactor is used, and the effluent gas from the medium temperature steam reforming reactor is further heated by heat exchange with the flue gas. Since it is supplied to the high-temperature steam reforming reactor after the heating, the heat load of the heating furnace for the high-temperature steam reforming reactor can be significantly reduced. When hydrogen-rich gas is produced from a raw hydrocarbon such as LPG or naphtha by a two-stage steam reforming method, it is preferable to maintain the high temperature steam reforming reactor in the latter stage at a high temperature in terms of chemical equilibrium. The composition of the hydrogen-rich gas flowing out depends exclusively on the outlet temperature of the reactor. Therefore, in order to obtain the hydrogen-rich gas having the desired composition, the high temperature steam reforming reactor must be heated by the heating furnace so that the outlet temperature corresponding to it can be maintained. Therefore, if the temperature of the gas supplied to the reactor is low, the heat load of the heating furnace required to maintain the outlet temperature of the reactor at a desired temperature is correspondingly increased. However, according to the method of the present invention, the temperature of the gas supplied to the high temperature steam reforming reactor can be increased for the reason described above, so that the heat load of the heating furnace can be reduced accordingly.

Next, the two-stage steam reforming method of the present invention will be described more specifically with reference to examples.

Comparative Example A mixture of desulfurization LPG of 5800 kg / hr and superheated steam of 21624 kg / hr was prepared according to the same flow as in FIG. 1 except that the outlet gas of the medium temperature steam reforming reactor 3 was directly introduced into the high temperature steam reforming reactor 4. It is supplied to the medium temperature steam reforming reactor 3 filled with a ruthenium-based catalyst at ℃, pressure 16kg / cm ² G, outlet temperature 600 ℃
Under the conditions described above, a primary reformed gas having the composition shown in column A of Table 1 was obtained.

Next, this primary reformed gas was supplied to the high temperature steam reforming reactor 4 and brought into contact with a nickel catalyst under the conditions of a pressure of 15 kg / cm ² G and an outlet temperature of 830 ° C., and the composition shown in column B of Table 1 was obtained. Secondary reformed gas of 28740 Nm ³ / hr (dry gas) was obtained. The heat load of the heating furnace 5 (the amount of heat absorbed in the reactor 4) in this example is 13.6 × 10.
^{It was 6} Kcal / hr.

Example Next, the case of carrying out the present invention will be described. Desulfurization LPG 5800 kg /
21624 kg / hr of superheated steam was mixed into hr, and it was introduced into the medium temperature steam reformer 3 (using the reformed gas at the outlet of the high temperature steam reforming reactor as a heat source) at 450 ° C, and the outlet temperature was external heat exchange. Up to 600 ℃. The pressure is 16 kg / cm ² G. The composition of this reaction gas is shown in column A of Table 2. This gas was further heated to 700 ° C by a flue and supplied to the high temperature steam reforming reactor 5, and when the outlet temperature was 830 ° C and the pressure was 15 kg / cm ² G, the gas having the composition shown in column B of Table 2 was used. 28740 Nm ³ / hr (dry gas) was obtained. Heat load of heating furnace at this time (amount of heat absorption in reactor 4)
Was 11.9 × 10 ⁶ Kcal / hr.

[Brief description of drawings]

1 and 2 show an example of the flow sheet of the method of the present invention. 1; Raw hydrocarbon introduction line 2; Steam introduction line 3; External heat type medium temperature steam reforming reactor 4; High temperature steam reforming reactor 5; Heating furnace 6; Flue

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-49-91096 (JP, A) JP-A-59-100190 (JP, A) JP-A-53-64202 (JP, A)

Claims (1)

[Claims] 1. A medium temperature steam in which (a) a raw material hydrocarbon and steam are heated by a flue gas of a heating furnace containing a high temperature steam reforming reactor or an outflow gas from the high temperature steam reforming reactor. The reforming reactor is supplied with a first reforming condition under the first reforming condition.
To produce a primary reformed gas containing hydrogen and methane as main components, and (b) heat-exchange the primary reformed gas with the flue gas of the heating furnace to raise the temperature. (C) The heated primary reformed gas is supplied to the high temperature steam reforming reactor, and is brought into contact with the second reforming catalyst under the second reforming condition so as to contain hydrogen as a main component. A steam reforming method for hydrocarbons, characterized in that a reformed gas is produced.