JPH06157003A - Hydrogen production method using iron - Google Patents

Abstract

PURPOSE:To effectively generate hydrogen and utilize used scraps as a raw material for steel manufacturing by separately introducing oxygen gas from specific positions between respective introduction positions of a gas containing steam and oxygen and an iron-based raw material capable of catalytically reacting in a countercurrent state. CONSTITUTION:An iron-based raw material (e.g. scrap) 12 housed in a hopper 10 is continuously fed from the top into a reactional column 14. On the other hand, oxygen gas 13 is fed from the middle part of the reactional column 14 and heat is generated while oxidizing the charged iron-based raw material to keep the whole at a prescribed temperature. A gas 15 containing steam and oxygen gas is fed from the bottom of the reactional column 14 and made to react with the iron-based raw material to generate hydrogen gas. The oxygen gas 13 is charged at a position (10) within the range of <=0.5L when the distance between the charging position of the iron-based raw material and the charging position of the gas containing the steam and oxygen is L. The ratio of the quantity of the oxygen charged together with the steam to the charged quantity of the oxygen is (1-5):1. The generated hydrogen gas (H2/H2O-based mixed gas) 16 is led to a separating column 20 to separate and recover the hydrogen gas by cooling the steam.

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 using iron, and more particularly to reforming steam by utilizing energy released when iron contained in iron-based raw materials such as scrap and sponge iron is oxidized. And a method for producing hydrogen.

[0002]

2. Description of the Related Art The consumption of steel in recent years is
It is growing dramatically in building materials, etc.
The amount of scrap generated is increasing year by year, and the effective use of this large amount of scrap is becoming an important issue. However, metals such as Cu, Zn, and Ni are mixed in the scrap, and the range of use as a raw material for steelmaking is generally limited. At present, at most 50% of the generated scrap is used as a raw material for steelmaking. Others are currently left uncollected as waste products.

Not only environmental problems but also effective utilization of them is required from the viewpoint of resource saving. Traditionally,
As a utilization method of iron scrap, it is conceivable to enhance the pretreatment for removing unwanted components in advance, or to expand the usable range of scrap by modifying the steelmaking method itself, and many proposals have already been made today. Has been done.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an effective utilization method that enables large-scale consumption of scrap that is expected to occur in large quantities.

[0005]

[Means for Solving the Problems] In order to achieve such an object, the inventors of the present invention have conducted various studies, focused on the iron content contained in iron scrap, and used it simply as a catalyst in the hydrogen generation reaction from steam. Instead, it can be used in large quantities by using it as one of the reactants, and iron oxide as a reaction product is an unreacted product, that is, recovered as a metal.
As a result of further study of the feasible reaction system, we found that it can be easily separated from metals such as u and Ni by the magnetic separation method and can be advantageously used as a steelmaking raw material. The present invention has been completed by knowing that the introduction position of the oxygen gas to be added is critical.

The steam iron method is known as a method for obtaining hydrogen from water vapor (eg, Shozo Nakaguchi “Petrochemical Journal” Vol. 20, No. 1 (1977) pp. 69-73). However, in this method, the iron content is only used as a catalyst when hydrogen is obtained from steam, and the iron content generated in large quantities such as iron scrap cannot be used effectively. That is, in the steam iron method, iron is used as a type of catalyst that repeats the oxidation-reduction reaction of Fe → FeO (Fe ₃ O ₄ ) → Fe. Of course, the use of iron scrap is considered. Not be
The use of natural ore such as siderite is envisioned.

Here, the gist of the present invention is that the iron-based raw material and the steam + oxygen-containing gas are reacted in a reactor in a counter-current state while being brought into contact with each other, and hydrogen is generated using the heat of oxidation of iron as a heat source. A method, wherein oxygen gas is separately introduced from a position within a distance of 50% from the steam introduction position with respect to the distance between the steam + oxygen-containing gas introduction position and the iron-based raw material charging position in the reactor. It is a method for producing hydrogen utilizing iron.

Therefore, according to the present invention, not only hydrogen can be produced at a low cost, but Cu, Ni, etc. retain a metallic state with respect to oxidized iron (iron oxide), so that they can be obtained by magnetic separation or the like. , Iron and Cu, Ni, etc. can be separated, and one can be used as a metal resource and the other can be used as a raw material for steelmaking as is.

[0009]

Next, the operation of the present invention will be described. The basic reaction utilized in the present invention can be described as follows.

3 / 4Fe (s) + H ₂ O (g) = 1 / 4Fe ₃ O ₄ (s) + H ₂ (g) ΔH ⁰ = 6.708
kcal / mol ・ ・ (1) Fe (s) ＋ H ₂ O (g) ＝ FeO (s) ＋ H ₂ (g) ΔH ⁰ ＝ 3.880 kca
l / mol ··· (2) (1) (2) is an exothermic reaction, and in an isothermal system without heat removal from the equipment, this reaction can be performed without applying external energy due to the heat of oxidation of Fe. It is possible to maintain.
Therefore, it is possible to oxidize the scrap with steam and replace this energy with hydrogen. Moreover, since Cu, Ni, etc. are less likely to be oxidized than Fe, Fe is selectively oxidized, so that Cu, Ni can be separated from the iron scrap.

The basic reaction in the present invention is as described above, but process heat removal occurs in an actual reaction vessel. Further, in order to give a sufficient reaction rate to the equations (1) and (2),
It is necessary to keep the reaction system at a high temperature, and in this case, sensible heat loss occurs due to the substance entering and leaving the container. In order to compensate for this, it is necessary to give energy, but electric energy is expensive, and in the present invention, 3 / 4Fe (s) + 1 / 2O ₂ (g) = 1 / 4Fe ₃ O ₄ (s) ΔH ⁰ = -65.8kcal
/ mol ・ ・ (3) Fe (s) ＋ 1 / 2O ₂ (g) ＝ FeO (s) ΔH ⁰ ＝ −63.0kcal / mo
The amount of heat that oxidizes Fe with oxygen, which has a heating value an order of magnitude larger than that of equations (4), (1), and (2), is used as an auxiliary heat source to further promote the effective use of scrap. According to the present invention, a part of the oxygen added as the auxiliary heat source is charged with steam, and the rest is charged into the reaction vessel on the downstream side thereof.

FIG. 1 is a flow chart for carrying out the method according to the present invention. In the figure, iron scrap (hereinafter simply referred to as scrap) 12 as an iron-based raw material contained in a hopper 10 is continuous from the top. To the reaction tower 14. From the point of reaction promotion, the finer the shape of the scrap, the better.
Considering handling and cost, and considering movement within the reaction column, it is preferable to subdivide the product into a thickness of 0.5 to 5 mm and a length of 3 to 300 mm with a shredder or the like. On the other hand, the oxygen gas 13 is sent to the reaction tower 14 from the middle, and the generated scrap is heated while being oxidized to maintain the entire scrap layer at a predetermined temperature. Steam 15 is sent from the bottom of the reaction tower 14,
Hydrogen gas is generated by reacting with scrap heated to a predetermined temperature. At this time, the temperature may decrease due to heat removal from the process or the like, so it is preferable to add oxygen together with steam from the bottom of the reaction column. Assuming that the distance between the iron scrap 12 charging position and the steam + O ₂ charging position is L, the position l _{0 at} which oxygen is charged from the middle of the reaction tower is within 0.5 L.

The amount of oxygen to be added may be sufficient to compensate for the decrease in heat. In that case, a suitable ratio of the amount of oxygen added together with the steam and the amount of oxygen added halfway is 1 to 5: 1. Hydrogen gas generated by scrap oxidation reaction 16
Is recovered from the top of the reaction column. Hydrogen gas concentration is usually 30 ~
Since it is 60% by volume, hydrogen gas is further guided to the separation tower 20 to separate and recover hydrogen gas by cooling the steam.

On the other hand, the reacted scrap 18 mainly composed of iron oxide is continuously recovered from the bottom of the reaction tower, and if necessary magnetic separation is performed to remove unreacted metals (eg Ni, Cu) and iron oxide. The separated and recovered iron oxide is reused, for example, as a steelmaking raw material. The discharging mechanism may be as shown in FIG. 2, for example.

The reaction tower 14 usable in the present invention may be a vertical vertical furnace such as a shaft furnace, may be shaped like a blast furnace, and may be a horizontal rotary furnace such as a kiln furnace. It may be. In any case, the scrap layer may move continuously and come into contact with the steam gas in a countercurrent to react. Here, considering the heat and mass balance of the hydrogen production method according to the present invention, it is as follows.

1) Evaluation of sensible heat loss The best heat exchange efficiency is that the temperature of the substance discharged by performing countercurrent heat exchange is the same as the temperature of the substance charged into the system. The heat balance was calculated by dividing the reaction vessel into a central reaction system and a countercurrent system for upper / lower heat exchange, as shown in FIG.

The calculation was performed per 1.0 mol of H ₂ O, and x represents the conversion rate of water vapor to hydrogen. The reaction system temperature was 1300K. The temperature at which H ₂ O was introduced into the countercurrent system was 600K, and the temperature at which scrap was introduced into the countercurrent system was 298K.

From equation (I) in Table 1, the minimum value of exhaust gas sensible heat loss lost in the counterflow system is when the scrap entering the reaction system from the counterflow system is heated to 1300K (reaction system temperature). Given (1), (minimum exhaust gas sensible heat) = (1−x) H _{1300, H2O} ＋ x ・ H _{1300, H2}
Substitute the thermodynamic value at −3/4 ・ x ・ H _{1300, Fe} 1300K.

(Minimum exhaust gas sensible heat loss in countercurrent system) = 9.2
98-9.04x (kcal / mol, H ₂ O) (5) On the other hand, the minimum value of sensible heat loss in the countercurrent system is 600 K of Fe ₃ O ₄ discharged from the countercurrent system. And the difference from the introduced steam sensible heat (600K) is the same as the above equation (5) (minimum sensible heat loss in countercurrent system) = 2.509-3.266x ・ ・ ・ ・ ・ (6)

[0020]

[Table 1]

On the other hand, the heat of reaction is assumed to produce Fe ₂ O _3.
Heat of reaction = 6.708 ・ x ・ ・ ・ ・ ・ ・ (7) From equation (1), the best heat balance in equations (5) to (7) is taken as (7) − (5) − (6) = −6.789 ＋12.48 ・ x ・ ・ ・ (8) Further, FIG. 3 is a state diagram showing the equilibrium relationship between iron and iron oxide and H ₂ —H ₂ O based gas. Is. Horizontal axis is temperature, vertical axis is H ₂ −
The H ₂ content in the H ₂ O based gas is shown. In the figure, 3 / 4Fe +
The curve of H ₂ O = Fe ₃ O ₄ + H ₂ shows that Fe is Fe ₃ O ₄ in the low temperature range.
₂ shows the equilibrium H ₂ content when changing to.

[0022] Since FeO becomes phase is present in the high temperature region, curves and shows the balance containing H ₂ ratio when Fe is changed to FeO, the equilibrium containing H ₂ ratio when FeO is changed to Fe ₃ O ₄ There is a curve shown. 1000 to 11 to maintain the oxidation rate of scrap due to water vapor and to always maintain an H ₂ ratio of about 60%
It can be seen that it is desirable to maintain the temperature around 00 ° K.

FIG. 4 shows the conversion of the heat balance at each temperature into H ₂ x
The graph shows that the heat balance improves (that is, surplus heat is generated) as the conversion rate of H ₂ O to H ₂ increases, when the steam preheating temperature is constant. , H ₂
The lower the conversion rate to, the worse the heat balance (ie, insufficient heat). Also, it can be seen that the heat balance improves as the preheating temperature of the introduced steam increases.

However, in this reaction system, the above (2)
Since the equilibrium H ₂ conversion rate at 1300 K in the equation is 0.61, it is equilibrium-difficult to set the conversion rate of H ₂ O to H ₂ to 0.61 or more. Further, in FIG. 3, when the value on the vertical axis is a positive value, excess heat is generated (the temperature of the system tends to rise), and when it is a negative value, the amount of heat is insufficient (system Temperature tends to decrease).

From the above, it is necessary to supplement the heat even when the treatment is performed on the premise of the best heat exchange in the countercurrent, and in order to position this method as a large-scale scrap treatment process.
Auxiliary heating according to equations (3) and (4) is required.

2) Introducing position of oxygen (1), (2) and (3), (4) are all gas-solid reactions, and are generally more reactive than the gas-gas reaction shown in (9). The speed is slow.

H ₂ O (g) = H ₂ (g) + 1/2 O ₂ (g) (9) Therefore, when a large amount of O ₂ is present, the reduction of steam by scrap does not occur. , O ₂ is sufficiently separated from the container outlet, and the reaction shown in Eqs. (3) and (4) must be completed, but the reaction shown in Eqs. (1) and (2) needs to proceed to some extent. is there. For this reason, there is a restriction on the O ₂ introduction position, and as shown in FIG. 5, the blowing position is a dimensionless distance from the steam inlet (lower part of Table 1) to the outlet (upper part of Table 1) of 0.5, that is, the intermediate position. It was found that the conversion to hydrogen proceeded most favorably when it was on the inlet side.

As can be seen from FIG. 5, the H ₂ content is 40% even when l ₀ / L = 0, and the additional oxygen may be added as a mixture of water vapor and H ₂ , but preferably l ₀ / L = 0.
It is divided into 2 to 0.4.

[0029]

EXAMPLES The present invention will be described in more detail by way of examples. In the reaction tower with an inner diameter of 1.2 m and a height of 11 m (outer diameter of 2.5 m) shown in Fig. 1, first, LPG / air was introduced before the test, the inside of the tower was preheated to 1200 to 1400 K, and then crushed with a shredder. 25 tons of scrap scrap with a size of 0.5 to 1.2 mm and a size of about 5 cm square was charged.

Even after charging, LP until the temperature in the furnace reaches 1100K
After the temperature was raised by introducing G / air, water vapor was introduced at 3500 Nm ³ / h from the lower portion (15 shown in FIG. 1), and oxygen 500 Nm ³ / h was introduced from the water vapor introduction hole at the lower portion. In addition, steam from the bottom
A test was conducted in which 3000 Nm ³ / h was introduced, and gas was introduced from the side wall (13 shown in Fig. 1) from four double tube tuyeres (inner tube oxygen 500 Nm ³ / h, outer tube steam 500 Nm ³ / h). . The tuyere positions were 20%, 40%, 60% and 80% of the distance between the steam inlet and the outlet (Examples 2 and 3 and Comparative Examples 1 and 2). Table 2 shows the proportion of H ₂ content in the outlet gas.

In Examples 1 to 3 in which the oxygen introduction position was within the range of 40% from the H ₂ O introduction port, the proportion of H ₂ produced was 41%.
To 54% and higher concentrations of H ₂ gas is obtained. On the other hand, as in Comparative Examples 1 and 2, the oxygen introduction position is 60
It can be seen that the H ₂ concentration decreases as the distance from the H ₂ O introduction port becomes 80% and 80%. Further, since the iron oxide obtained in this example contained 1.2% of copper (metal state), iron oxide was used as a cooling agent for the steelmaking furnace after being recovered by magnetic separation.

[0032]

[Table 2]

Further, in order to compare with Example 2 having the highest reforming rate, the blowing of oxygen from the tuyere was stopped under the same conditions as Example 2 (only water vapor in the outer tube was used). In this case, the temperature of the reactor center 2 m above the tuyere was measured in Example 2
1260 to 1350K, but 800K in 1 hour after the stop of blowing
And the H ₂ content in the outlet gas became 2%.

[0034]

According to the present invention, it is possible to obtain hydrogen from steam by using scrap as a heat source. At that time, a large amount of scrap can be used, and the used scrap can be effectively used as a steelmaking raw material.

[Brief description of drawings]

1 is a schematic illustration of an apparatus for carrying out the method according to the invention.

FIG. 2 is an explanatory diagram of a mechanism for discharging reacted scrap.

FIG. 3 is a graph showing an H ₂ O / H ₂ equilibrium diagram.

FIG. 4 is a graph showing heat balance calculation values in the method according to the present invention.

FIG. 5 is a graph showing the effect of tuyere position in the method according to the present invention.

Claims (1)

[Claims] 1. A method for reacting an iron-based raw material with steam and an oxygen-containing gas in a countercurrent state in a reactor to generate hydrogen by using the heat of oxidation of iron as a heat source, wherein steam in the reactor is used. Using iron, which is characterized by separately introducing oxygen gas from a position within 50% of the steam introduction position with respect to the distance between the oxygen-containing gas introduction position and the iron-based raw material charging position. Hydrogen production method.