JPH08225302A - Production of hydrogen - Google Patents

Abstract

PURPOSE: To provide a method for producing hydrogen, capable of making the concentration of carbon monoxide in a mixed gas to be fed to a PSA process into not larger than fixed value, minimizing the capacity of an adsorption column of the PSA process and surely reducing the residual CO concentration in a product hydrogen gas to not larger than an allowable value. CONSTITUTION: This method for producing hydrogen comprises subjecting a desulfurized petroleum-based hydrocarbon and steam to high-temperature steam reforming reaction in a reaction tube of external heating type packed with a catalyst, subjecting a formed reformed gas comprising hydrogen, carbon monoxide, carbon dioxide and methane to CO modifying reaction on a catalyst of a high-temperature column, treating the prepared mixed gas rich in hydrogen by a PSA device to produce high-purity hydrogen. In this method, when operation load of a hydrogen production device is raised, steam is injected into the reformed gas to be sent to the high-temperature modifying column to reduce the concentration of carbon monoxide in the gas to be sent to the PSA device to not larger than a fixed value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing hydrogen in which high-purity hydrogen is produced by refining a reformed gas obtained by a steam reforming reaction using a petroleum hydrocarbon as a raw material.

[0002]

2. Description of the Related Art A large amount of hydrogen gas required for hydrocracking of petroleum heavy fractions, hydrodesulfurization, etc. has been conventionally produced by the following method. That is, the raw material LP
After removing sulfur from petroleum hydrocarbons such as G and naphtha using a cobalt-molybdenum hydrogenation catalyst and an adsorption catalyst such as zinc oxide (desulfurization process), an external heating system filled with a nickel catalyst 8 with superheated steam in the reaction tube of
By performing a high temperature steam reforming reaction at a high temperature around 00 ° C,
In order to generate a reformed gas with a high hydrogen concentration (high temperature steam reforming process) and then to convert carbon monoxide in the reformed gas into hydrogen, a CO shift reaction is carried out on a high temperature shift catalyst composed of iron oxide or the like. To obtain a hydrogen-rich mixed gas (CO shift process).

After that, a high-purity gas having a hydrogen purity of, for example, 99.99 vol% or more is produced by treating with a PSA device to remove carbon dioxide, methane and carbon monoxide in the hydrogen-rich mixed gas ( PSA step). PSA equipment (Pres
sure Swing Adsorption) is a multiple adsorption tower (4-10 towers) filled with an adsorbent that selectively adsorbs components other than hydrogen under high pressure and desorbs it under reduced pressure. -A system (hereinafter referred to as a PSA system) designed to operate as an automatic continuous adsorption system as a whole by performing cyclic operation consisting of substitution and pressurization and shifting the cycle between each tower in time. is there.

Since the PSA device is a device that utilizes the pressure of the raw material gas itself, it has the advantages that it does not require a utility, it has a low operating cost and is economical, and that it is easy to maintain and manage. Although it is widely used, it also has the following problems.

As described above, the hydrogen-rich mixed gas processed by the PSA device is composed of hydrogen, carbon dioxide, carbon monoxide and methane components in descending order of content. Among these components, The component required to have the lowest content from the above-mentioned hydrocracker or hydrodesulfurizer using product hydrogen is carbon monoxide, and its allowable content is very low, for example, about 20 ppm. .

On the other hand, when viewed from the adsorbent of the PSA device, the most difficult component to adsorb among the components in the above mixed gas is carbon monoxide. Therefore, the device capacity of the PSA device depends on the device. It is largely influenced by the designed maximum concentration of carbon monoxide in the incoming gas mixture and the acceptable concentration of residual carbon monoxide in the product hydrogen leaving the PSA unit. That is,
It can be seen that in order to economically make the PSA device compact, it is most effective to make the maximum concentration of carbon monoxide in the mixed gas entering the device as small as possible.

Considering the CO conversion reaction, this reaction is an exothermic reaction, and in equilibrium, the lower the temperature, the more the reaction proceeds and the less carbon monoxide remains. As a catalyst for carrying out the reaction at this low temperature, for example, there is a low temperature shift catalyst which is active even at around 200 ° C. The low-temperature shift catalyst is a catalyst whose main component is copper oxide, zinc oxide, etc., but it requires a special reduction operation with hydrogen gas at the time of start, and it is easily poisoned by a small amount of sulfur compounds and its activity decreases. However, it has become obsolete these days.

For this reason, in recent hydrogen production apparatuses, the CO shift process is generally constituted only by a high-temperature shift catalyst whose main component is iron oxide, which is easy to operate and manage. Another characteristic of the equilibrium of the CO shift reaction is that the higher the steam content in the gas entering the shift tower, the more favorable the reaction. However, in recent hydrogen production equipment, the steam reforming process is mainly due to thermal economy, and the amount of steam relative to the raw material hydrocarbons (called steam / carbon ratio).
Therefore, the steam content in the reformed gas entering the CO shift process is also decreasing.

[0009]

The present invention has been made in view of the above-mentioned problems of the prior art. In the mixed gas entering the PSA step when the load on the hydrogen production apparatus becomes large. Keep the concentration of carbon monoxide below a certain level,
An object of the present invention is to provide a method for producing hydrogen which can reduce the capacity of the adsorption tower in the PSA step and can surely make the residual CO concentration in the product hydrogen gas to be less than or equal to the allowable value.

[0010]

The object of the invention as set forth in claim 1 is to carry out a high temperature steam reforming reaction in an externally heated reaction tube in which a desulfurized petroleum hydrocarbon is filled with a catalyst together with steam. The produced reformed gas composed of hydrogen, carbon monoxide, carbon dioxide, and methane is subjected to a CO shift reaction on the catalyst of the high-temperature shift tower, and the resulting hydrogen-rich mixed gas is treated with a PSA device to obtain high purity. In the method for producing hydrogen for producing hydrogen as described above, when the operation load of the hydrogen production apparatus becomes high, steam is injected into the reformed gas that enters the high temperature shift tower to remove carbon monoxide in the gas that enters the PSA apparatus. A method for producing hydrogen characterized in that the concentration is set to a certain value or less, and the gist of the invention according to claim 2 is that in the method for producing hydrogen according to claim 1, in the product gas leaving the PSA apparatus. Monoacid If the concentration thereof continuously measuring the concentration of carbon tends to increase, in the production method of the hydrogen, characterized by increasing the amount of steam injected into the reformed gas entering the high temperature shift tower.

[0011]

[Function] Gas composition (including steam) entering the high temperature shift tower
If the same, the concentration of carbon monoxide in the gas exiting the high temperature shift tower will be high as shown in FIG. 2 because the space velocity will increase with increasing equipment load. Therefore,
If the maximum inlet concentration of the PSA device is designed at the point B in FIG. 2, the capacity of the adsorption tower of the PSA device becomes considerably large, but if it is designed at the point A as in the present invention, The capacity can be made quite compact. Furthermore, in the hydrogen production equipment installed for the hydrodesulfurization of petroleum, the capacity of the hydrogen production equipment is determined with a considerable margin in consideration of some conditions, and therefore it is operated at a high load exceeding point A. It can be said that the number of days required for the steam injection is not so large even during the whole year, and the cost of steam injection required when the device load exceeds point A does not increase so much.

The amount of steam injected in the CO conversion process is
The steam content in the reformed gas determined by the steam / carbon ratio in the steam reforming process, the equilibrium constant determined by the reaction temperature in the CO conversion process, and the predetermined CO at the CO conversion process outlet.
Since it can be easily calculated by using the concentration and the like, it is possible to control so as to inject a minimum required and small amount of steam. However, for safety, the concentration of carbon monoxide in the product gas leaving the PSA process is constantly measured, and if there is an increasing tendency, by adopting the control method for increasing the amount of injected steam, The CO concentration in the product gas can be surely kept below the allowable value.

[0013]

EXAMPLES Examples of the method for producing hydrogen according to the present invention will be described below. FIG. 1 is a schematic system diagram of an embodiment of the present invention. Petroleum hydrocarbons such as LPG and naphtha, which are raw materials, are preheated to around 400 ° C in a heating furnace together with a recycling gas for desulfurization that uses a part of product hydrogen, and then a cobalt-molybdenum hydrogenation catalyst and oxidation are performed. After entering the desulfurization tower filled with the zinc adsorption catalyst, all the sulfur compounds in the raw material are hydrogenated to hydrogen sulfide, and then by the adsorption catalyst,
Almost completely removed.

The desulfurized raw hydrocarbon is then 400
Along with steam for reforming, which is a gasifying agent overheated to ℃ or above, enters a reforming furnace consisting of a reaction tube filled with a nickel-based catalyst, and the reaction required for high-temperature steam reforming reaction by the combustion heat of fuel. The heat is supplied to complete the reaction at around 800 ° C., and a high temperature reforming process is performed after forming a reformed gas composed of hydrogen, carbon monoxide, carbon dioxide, methane and the like. After that, the reformed gas is subjected to heat recovery in a waste heat boiler or the like, and is cooled to around 350 ° C., which is suitable for high temperature shift reaction, and moves to the next step.

In the high temperature shift process, carbon monoxide in the reformed gas is converted into hydrogen by the following CO shift reaction on the high temperature shift catalyst containing iron oxide as a main component. CO + H ₂ O = H ₂ + CO ₂ Kp = (H ₂ ) (CO ₂ ) / (CO) (H ₂ O) Kp is an equilibrium constant, which is a function of the reaction temperature and increases as the reaction temperature decreases. When the apparatus load is less than the point A in Fig. 2, the space velocity of the shift converter catalyst becomes small, so the reaction temperature can be lowered to increase the equilibrium constant; Kp, and the CO concentration at the shift tower outlet can be increased accordingly. Can be reduced.

However, when the load on the apparatus increases and becomes larger than point A, the space velocity also increases, so that the reaction temperature cannot be lowered. Instead, if the amount of steam in the gas entering the high temperature shift converter is increased, it can be seen from the above equilibrium equation that the amount of residual carbon monoxide in the outlet gas of the high temperature shift tower decreases when Kp is constant. If Kp is constant, if carbon monoxide in the high-temperature shift tower outlet gas is determined,
The amount of steam injected from the above equilibrium equation can be easily calculated. Therefore, when the concentration of carbon monoxide at the outlet of the high temperature shift process is constantly measured and the concentration becomes higher than the predetermined concentration, calculate the steam amount required for this equilibrium with a calculator, and adjust the steam amount close to this calculated value to the controller. Set and inject.

Further, the concentration of carbon monoxide in the product hydrogen leaving the PSA process is constantly measured, and if an increasing tendency is observed, by injecting a steam amount larger than the amount required for equilibrium, The CO concentration in the product gas can be reliably maintained below the allowable value.

Specifications of the gas composition, flow rate, etc. in the case where the present invention is applied to a reformed gas obtained by high temperature steam reforming at a steam / carbon ratio of 3.0 using naphtha as a raw material hydrocarbon are shown. Show. Reformed gas Modified gas * 1 Modified gas * 2 CO 16.1% 5.0% 3.0% CO ₂ 11.2 19.7 21.2 H ₂ 68.8 71.8 72.3 CH ₄ 3. 9 3.5 3.5 100.0 100.0 100.0 Dry gas amount (Kmol / H) 100.0 110.6 112.7 Steam amount (〃) 55.1 44.5 81.9 Wet gas amount (〃) 155.1 155.1 194.6 * 1; CO-transformed case without steam injection * 2; CO-transformed case with modified steam injection (invention) Injection steam amount; 81.9-44.5 + (112) 7-110.6) = 39.5 (mol / H) From above, about 25% of the amount of gas entering the CO shift process
It can be seen that the amount of CO adsorbed can be reduced by 40% by injecting the steam amount of (at 100% load).

[0019]

According to the method for producing hydrogen described above,
By keeping the CO concentration in the gas entering the PSA unit below a certain value when the load of the hydrogen production unit is high, the capacity of the adsorption tower of the PSA unit can be reduced and the CO concentration in the product gas leaving the PSA unit can be reduced. It is possible to obtain the effect that the value can be surely made equal to or less than the allowable value.

[Brief description of drawings]

FIG. 1 is a schematic system diagram of an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between CO concentration in a gas exiting a shift converter and an apparatus load.

Claims (2)

[Claims] 1. A reformer comprising hydrogen, carbon monoxide, carbon dioxide and methane produced by performing a high temperature steam reforming reaction in an externally heated reaction tube filled with a catalyst together with desulfurized petroleum hydrocarbons and steam. CO gas on the catalyst of the high temperature shift tower
The metamorphic reaction is performed, and the resulting hydrogen-rich mixed gas is added to P
In a method for producing hydrogen for producing high-purity hydrogen by processing with an SA device, steam is injected into the reformed gas that enters the high temperature shift tower when the operating load of the hydrogen production device becomes high, and the PSA device is provided with the steam. A method for producing hydrogen, characterized in that the concentration of carbon monoxide in the incoming gas is kept below a certain value. 2. The method for producing hydrogen according to claim 1,
When the concentration of carbon monoxide in the product hydrogen leaving the PSA device is continuously measured and the concentration tends to increase, the amount of steam injected into the reformed gas entering the high temperature shift converter is increased. Method for producing hydrogen.