JP7200977B2 - Blast furnace gas dust collection method - Google Patents

Description

The present invention relates to a dust collection method for blast furnace gas.

In a steelworks, a blast furnace produces pig iron by reducing and melting main raw materials such as iron ore and sintered ore using limestone as an auxiliary raw material and coke as a reducing agent.
These raw materials (raw fuel) are charged into the blast furnace from above. On the other hand, hot air is blown from the lower part of the blast furnace to burn the coke. Therefore, in the blast furnace, gases such as carbon monoxide and carbon dioxide generated by combustion of coke and nitrogen in hot air flow upward. When this gas reaches the upper part of the blast furnace, it is discharged to the outside of the blast furnace together with the raw fuel, which is partly fine grained.
Since the gas discharged from the blast furnace (blast furnace gas) contains combustible components such as carbon monoxide, it is effectively used as clean gas in ironworks, etc. after removing the entrained raw fuel as dust. Specifically, for example, it is used as fuel for combustion devices such as burners.

Conventionally, there are various methods for collecting dust from blast furnace gas, including dry methods and wet methods. Among them, wet methods are often used.
The dry method causes a small gas temperature drop (small energy loss), but may not have dust removal performance that meets the specifications of the combustion apparatus.
On the other hand, in the wet method, blast furnace gas is brought into contact with water (collected dust water) to collect collected dust water (dust slurry) in which dust is suspended. In the wet method, the temperature of the gas is greatly lowered, so the energy loss is large, but clean gas with low dust concentration can be obtained.

By the way, as described above, blast furnace gas contains carbon dioxide. Therefore, when the dust-collected water comes into contact with the blast furnace gas, carbon dioxide dissolves in the dust-collected water, and the pH of the dust-collected water decreases. As a result, easily soluble minerals in the dust are eluted into the collected water. Thereafter, when the dust-collected water is exposed to the atmosphere, carbon dioxide is released from the dust-collected water and the pH rises. As a result, the mineral content in the dust collection water becomes supersaturated.
When the dust collection water supersaturated with minerals is circulated through the pipes, the minerals may precipitate or deposit as scales in the pipes, which may hinder the circulation.
Techniques for preventing such scale deposition are disclosed in Patent Documents 1 and 2, for example.

JP-A-49-133209 JP-A-2002-126787

In recent years, the operation of blast furnaces has progressed, and the raw materials and fuels used in blast furnaces have been improved.
For example, the strength of sintered ore is improved, and sintered ore is sorted by particle size before being charged into a blast furnace to remove fine particles.

Moreover, when producing sintered ore and coke, it has become possible to use raw materials with many impurities. As a result, the components of the dust have changed compared to before, and the amount dissolved in the dust collection water has also changed.

For this reason, a new problem that has not existed in the past has arisen.
First, dust-collected water (dust slurry) that collects dust in contact with the blast furnace gas is then introduced into a solid-liquid separator such as a thickener, and solid-liquid separated. That is, the dust collection water and the dust contained therein are separated.
At this time, a phenomenon occurs in which the dust aggregates or solidifies within the solid-liquid separator. When the dust agglomerates (including solidification; the same shall apply hereinafter), the electric power required to operate the rake (stirring blade) installed in the solid-liquid separator increases. If the dust agglomerates severely, the operation of the rake will be stopped, and as a result, it may be necessary to stop the entire installation for wet dust collection.

The techniques disclosed in Patent Documents 1 and 2 cannot suppress such dust agglomeration.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to suppress aggregation or solidification of dust in collected dust water in which dust contained in blast furnace gas is collected.

As a result of intensive studies, the inventors of the present invention have found that the above object can be achieved by adopting the following configuration, and completed the present invention.

That is, the present invention provides the following [1] to [5].
[1] A method for collecting dust from blast furnace gas, in which the cation-anion ratio of dust-collected water containing dust contained in blast furnace gas is adjusted to 1.01 or more. However, the cation-anion ratio is the sum of the products of the valences and molar concentrations of the cations contained in the dust-collected water, and the sum of the products of the valences and molar concentrations of the anions contained in the dust-collected water. is a value divided by
[2] The method for collecting dust from blast furnace gas according to [1] above, wherein the cation/anion ratio is 1.20 or less.
[3] The cations are Ca ²⁺ , Na ⁺ , K ⁺ , Mg ²⁺ and NH ₄ ⁺ , and the anions are SO ₄ ²⁻ , S ₂ O ₃ ²⁻ , Cl ⁻ , F ⁻ and The dust collection method for blast furnace gas according to the above [1] or [2], wherein the five types are CH ₃ COO ^- .
[4] The method for collecting blast furnace gas dust according to any one of [1] to [3] above, wherein a cation source is added to the collected dust water to adjust the cation-anion ratio.
[5] The dust collection method for blast furnace gas according to the above [4], wherein the cation-anion ratio of the dust collection water introduced into the solid-liquid separator is adjusted.

ADVANTAGE OF THE INVENTION According to this invention, it can suppress that dust aggregates or solidifies in the dust collection water which collected the dust contained in blast furnace gas.

It is a schematic diagram which shows an example of the cleaning equipment of blast furnace gas. 1 is a schematic diagram showing an experimental apparatus for experimentally confirming the effects of the present invention; FIG.

The dust collection method for blast furnace gas of the present invention (hereinafter also referred to as the "method of the present invention") is a method of collecting dust contained in blast furnace gas and collecting dust to make a cation-anion ratio of 1.01 or more. It is a gas dust collection method.
However, the cation-anion ratio is the sum of the products of the valences and molar concentrations of the cations contained in the dust-collected water, and the sum of the products of the valences and molar concentrations of the anions contained in the dust-collected water. is a value divided by
As a result, when the collected dust water (dust slurry) in which the dust contained in the blast furnace gas is collected is subjected to solid-liquid separation by a solid-liquid separation device such as a thickener, the dust aggregates (including solidification, hereinafter the same). can be suppressed.

The phenomenon of dust agglomeration depends on the charge state of dust (dust particles). The charge state of dust particles is commonly referred to as the zeta potential.
The zeta potential can take both positive and negative values, but since dust particles have the same sign, they act as a repulsive force (electrical repulsive force).
On the other hand, van der Waals forces act as attractive forces between dust particles. If the absolute value of the zeta potential is large, the electrical repulsive force exceeds the van der Waals attractive force, so dust aggregation does not occur.

However, the zeta potential is not always a constant value and changes depending on the surrounding conditions. Shinnosuke Usui, Journal of the Society of Powder Technology, 1987, Vol. 24, No. 12, p. 798-804, the zeta potential ζ is described as:

here,
ζ: Zeta potential [V]
ν': valence of potential-determining ion (described later) [-]
c: ion concentration [mmol/L]
c ₀ : c [mmol/L] at which ζ=0
pH: Hydrogen ion concentration [-]
pH ₀ : pH at which ζ=0 [-]
is.

Strictly speaking, an index called activity should be used for c, but in the scope of the present invention, the activity and ion concentration are approximately the same, so c is the ion concentration for simplification of calculation. .

Formula 1 above is a formula that holds when the particles are ionically bonded. The zeta potential ζ varies depending on the valence and concentration of ions around the particle that have a high affinity for the compound that constitutes the particle (called “potential-determining ions”).
Equation 2 above is said to hold when the particles are oxides, and the zeta potential ζ varies with pH.

The present inventors measured the ion concentration and pH of various dust-collected waters, and measured the zeta potential of dust particles in the dust-collected waters.
As a result, it was confirmed that the current zeta potential of dust particles in collected water tends to be governed mainly by Equation 1 above.
Since the dust particles in the collected water are a mixture of various substances, the type of potential-determining ions is not singular. Only single cations (eg Ca ²⁺ , Na ⁺ ) correlated poorly with zeta potential.
On the other hand, there is a good correlation between the ratio of cations and anions present in the collected water (cation-anion ratio), which considers the valence numbers, and the zeta potential. A tendency to increase was found.
Therefore, if the cation-anion ratio of the dust collection water is appropriately controlled, aggregation of dust in the dust collection water can be suppressed.

All kinds of cations and anions contained in the dust collection water may be quantified.
However, the zeta potential is a major component of
Cations: Ca ²⁺ , Na ⁺ , K ⁺ , Mg ²⁺ and NH ⁴⁺ Anions: SO ₄ ²⁻ , S ₂ O ₃ ²⁻ , Cl ⁻ , F ⁻ and CH ₃ COO ⁻ high.
In practice, these 10 kinds of ions in total should be considered.

The cation-anion ratio is the sum of the products of the valences and molar concentrations of the cations contained in the dust-collected water divided by the sum of the products of the valences and molar concentrations of the anions contained in the dust-collected water. be.
Hereinafter, the "total value of the product of the cation valence and the molar concentration" is also referred to as the "cation concentration", and the "total value of the product of the anion valence and the molar concentration" is also referred to as the "anion concentration".
Specifically, the anion-cation ratio is calculated based on Equation 3 below.

here,
ν _ki : valence of i-th cation in collected water [-]
C _ki : molar concentration of i-th cation in collected water [mmol/L]
ν _aj : the valence of the j-th anion in the collected water [-]
C _aj : molar concentration of the j-th anion in collected water [mmol/L]
is.

As described above, the greater the absolute value of the zeta potential, the greater the electrical repulsion, and the dust particles are less likely to agglomerate.
The zeta potential can be theoretically determined from calculations of electrical repulsion and van der Waals forces.
As a result of investigation by the present inventors, the value of zeta potential increased as the cation-anion ratio increased. When the cation-anion ratio was less than 1.01, there was a tendency for dust to aggregate.
Therefore, the cation-anion ratio of the dust collection water is 1.01 or more from the viewpoint of suppressing aggregation of dust.
The cation-anion ratio of the dust collection water is preferably 1.03 or more, more preferably 1.06 or more, still more preferably 1.11 or more, and particularly preferably 1.16 or more, because it can further suppress dust aggregation. .

The inventors of the present invention measured the zeta potential while varying the cation-anion ratio. As a result, for example, when the cation-anion ratio was 1.01, the zeta potential was 20 mV, and when the cation-anion ratio was 1.03, the zeta potential was 25 mV (see [Examples] described later).

Although the upper limit of the cation-anion ratio is not particularly limited, the cation-anion ratio is preferably 1.20 or less for reasons described later.

Examples of methods for adjusting the cation-anion ratio of collected water include a method of supplying cations to increase the cation-anion ratio and a method of removing anions.
Any method may be used, but the method of supplying cations is simple and preferable.

Examples of the method of supplying cations include a method of adding a cation source in the form of an aqueous solution (hereinafter also referred to as "cation source liquid").
Specific examples of cation sources include caustic soda, sodium carbonate, sodium hydrogencarbonate, calcium hydroxide, calcium carbonate, calcium hydrogencarbonate, aqueous ammonia, ammonium carbonate, ammonium hydrogencarbonate, and magnesium hydroxide.

The cation concentration of the cation source solution takes into consideration the valence of the cations and the degree of ionization of the cation source.
For example, when the cation source solution is an aqueous sodium hydroxide solution, Na ⁺ is monovalent, and almost all of sodium hydroxide is ionized (that is, the degree of ionization is 1), so the cation source solution (sodium hydroxide aqueous solution) becomes the cation concentration as it is.
In addition, for example, when the cation source liquid is an aqueous calcium hydroxide solution, Ca ²⁺ is divalent and the degree of ionization of calcium hydroxide is 0.8. The cation concentration is obtained by multiplying the molarity by 2×0.8.
Literature values such as chemical handbooks are used for the degree of ionization. More precisely, it is measured in advance.

Next, an embodiment of the present invention will be described based on FIG.
FIG. 1 is a schematic diagram showing an example of blast furnace gas cleaning equipment (hereinafter simply referred to as "cleaning equipment"). The gas discharged from the blast furnace 1 (blast furnace gas) contains combustible components and dust such as iron ore powder, sintered ore powder, limestone powder, silica stone powder and coke powder.
The cleaning facility shown in FIG. 1 includes a blast furnace 1, a dry dust collector 3, a wet dust collector 7, a thickener 9, and the like.
The blast furnace 1 and the dry dust collector 3 are connected by an exhaust gas pipe 2 . The dry dust collector 3 has an outlet 4 . A dry dust storage place 5 is provided at the end of the discharge port 4. - 特許庁
The dry dust collector 3 and the wet dust collector 7 are connected by a pipe 6 .
A gas holder 20 is connected to the wet dust collector 7 via a clean gas transport pipe 19 . Further, the wet dust collector 7 is provided with a pipe 8a, and a thickener 9, which is a solid-liquid separator, is disposed at the tip of the pipe 8a.
The thickener 9 has a rake 10 which is a stirring blade. The rake 10 agitates the inside of the thickener 9 and rakes the solid content that has settled inside the thickener 9 to a discharge port (not shown) at the bottom center of the thickener 9 . Furthermore, the thickener 9 comprises a motor 11 for rotating the rake 10 .
The wet dust collector 7 is connected to the upper portion of the thickener 9 via a pipe 16 , a cooler 17 and a pipe 18 . Furthermore, a pipe 12, a dehydrator 13 and a pipe 14 are connected to the discharge port of the thickener 9, and a wet dust storage place 15 is provided at the end thereof.

In such a configuration, gas discharged from the blast furnace 1 (blast furnace gas) passes through the exhaust gas pipe 2 and is introduced into the dry dust collector 3 .

In the dry dust collector 3, the cross-sectional area of the pipe through which the gas flows is widened, and the gas flow velocity is slowed down. Dust has different terminal velocities according to particle size. Relatively coarse dust whose terminal velocity is higher than the gas flow velocity stays inside the dry dust collector 3 without being entrained.
The dust (referred to as “dry dust”) that remains and accumulates inside the dry dust collector 3 is discharged from the outlet 4 and stored in the dry dust storage area 5 .
On the other hand, the gas accompanied by fine dust particles discharged from the dry dust collector 3 passes through the pipe 6 and is introduced into the wet dust collector 7 .

The wet dust collector 7 is a device that brings water (collected dust water) into contact with a gas accompanied by fine dust particles to collect the dust in the collected water.
There are various forms of the wet dust collector 7, for example, a device that sprays water in order to improve the efficiency of gas-solid-liquid contact, a device that uses a Raschig ring or a ring slit as a filler, and the like. be done. The wet dust collector 7 is not particularly limited, and a device having necessary dust removal performance can be used as appropriate.

The wet dust collector 7 separates the fine dust-entrained gas from clean gas and dust-containing water (dust slurry).
The clean gas is transported through clean gas transport pipe 19 to gas holder 20 and stored. The clean gas stored in the gas holder 20 is fed to a combustion device such as a burner as required.

On the other hand, the dust slurry is introduced into the thickener 9 through the pipe 8a.
A branch pipe 8b is connected to the pipe 8a. A tank (not shown) in which the above-described cation source liquid is stored is connected to the branch pipe 8b. From the tank, a necessary amount of cation source liquid is added to the dust slurry introduced into the thickener 9 as required.
Furthermore, a branch pipe 8c, which will be described later, is connected to the pipe 8a.

The thickener 9 separates the dust slurry into solid and liquid. More specifically, by allowing the dust slurry to stay for a certain period of time, the solid content is allowed to settle and separated from the supernatant water. The sedimented solid content is scraped to a discharge port at the bottom center of the thickener 9 by driving the motor 11 to rotate the rake 10 .

By the way, in the dust slurry introduced into the thickener 9 via the pipe 8a, the dust may aggregate or solidify as described above. In this case, the rotation load of the rake 10 increases, the power consumption of the motor 11 increases, and in the worst case, the motor stops (trips) due to overload.
Therefore, in this embodiment, an appropriate amount of cation source liquid is supplied from a tank connected to the branch pipe 8b of the pipe 8a. As a result, the cation/anion ratio of the dust slurry introduced into the thickener 9 is set to a value that satisfies the range described above. In this way, the zeta potential of the dust contained in the dust slurry is increased, and aggregation of the dust is suppressed.

Concentrated dust slurry (concentrated dust slurry) is discharged from the outlet of the thickener 9 . The concentrated dust slurry passes through pipe 12 and reaches dehydrator 13 . In the dehydrator 13, the concentrated dust slurry is dewatered to a moisture content suitable for storage.
Examples of the dehydrator 13 include a device that sandwiches an object between filterable cloths and applies pressure to dehydrate the object, a device that dehydrates the object using centrifugal force, and the like. It can be used without any particular limitation.
A concentrated dust slurry (referred to as “wet dust”) dehydrated by the dehydrator 13 passes through a pipe 14 and is stored in a wet dust storage location 15 .

The supernatant water of the thickener 9 is extracted from the pipe 16, passes through the cooler 17 as necessary, and is returned to the wet dust collector 7 for use.

Each part of the cleaning equipment described with reference to FIG. 1 does not need to have special specifications, and existing equipment can be used as appropriate. For example, as the wet dust collector 7, a wet electric dust collector can be used. Multiple devices may be used in combination.

EXAMPLES The present invention will be specifically described below with reference to Examples. However, the present invention is not limited to the examples described below.

<Experimental device>
FIG. 2 is a schematic diagram showing an experimental apparatus for experimentally confirming the effects of the present invention.
The experimental apparatus shown in FIG. 2 is mainly composed of a reaction stirring tank 21 . The reaction stirring tank 21 is equipped with a stirrer 22 and a motor 23 for rotating the stirrer 22 .
Dust slurry is supplied to the reaction stirring tank 21 from the wet dust collector 7 (see FIG. 1) via the branch pipe 8c of the pipe 8a (see FIG. 1).
A tank 24 storing the above-described cation source liquid is arranged in the vicinity of the reaction stirring tank 21 . A supply pipe 25 is connected to the tank 24 . A necessary amount of the cation source liquid is supplied from the tank 24 to the reaction stirring tank 21 via the supply pipe 25 .

<Examples 1 to 5 and Comparative Example 1>
In Examples 1 to 5 and Comparative Example 1, experiments were conducted using the experimental apparatus shown in FIG.
Specifically, first, 100 L of dust slurry was supplied to the reaction stirring tank 21 through the branch pipe 8c. The cation concentration and anion concentration of this dust slurry were measured to calculate the cation/anion ratio. Furthermore, the zeta potential (absolute value) of the dust particles was obtained.

In addition, when calculating the cation anion ratio of the dust slurry,
Cations: Ca ²⁺ , Na ⁺ , K ⁺ , Mg ²⁺ and NH ⁴⁺ Five anions: only SO ₄ ²⁻ , S ₂ O ₃ ²⁻ , Cl ⁻ , F ⁻ and CH ₃ COO ⁻ were quantified. (same below).

After that, the cation source liquid was added to the dust slurry from the tank 24 through the supply pipe 25 . A sodium hydroxide aqueous solution or a calcium hydroxide aqueous solution was used as the cation source liquid. The cation concentration of the aqueous sodium hydroxide solution was 500 mmol/L, considering the valence of Na ⁺ (1) and the degree of ionization of sodium hydroxide (1). The cation concentration of calcium hydroxide was 37 mmol/L, taking into account the valency of Ca ²⁺ (2) and the ionization degree of calcium hydroxide (0.8).
Thus, the cation-anion ratio of the dust slurry was adjusted.

During this time, the motor 23 was driven to keep the stirrer 22 rotating. The output of the motor 23 was recorded before and after adjusting the cation-anion ratio of the dust slurry.
The results are shown in Table 1 below.

<Summary of evaluation results>
As shown in Table 1 above, in Examples 1 to 5, the cation-anion ratio before adjustment of the dust slurry was 0.97 to 0.98, the absolute value of the zeta potential was 10.5 to 13 mV, The output of the motor was a high value of 70-82%.
Therefore, when the cation source solution was added to adjust the cation-anion ratio to 1.01 to 1.23, the absolute value of the zeta potential became 20 to 36 mV and the motor output decreased to 21 to 26%. Therefore, it can be said that the aggregation of dust could be suppressed. Therefore, the dust can be stably settled and separated.

When comparing Example 3 (cation-anion ratio after adjustment: 1.20) and Example 5 (cation-anion ratio after adjustment: 1.23), the motor output after adjusting the cation-anion ratio was Both were the same 21%.
Therefore, from the viewpoint of saving the amount of the cation source liquid to be added, it is found that the cation-anion ratio should be 1.20 or less.

On the other hand, in Comparative Example 1, as in Examples 1 to 5, the cation-anion ratio before adjustment of the dust slurry was 0.97, the absolute value of the zeta potential was 10.5 mV, and the motor output was 82%. was a high value.
However, the cation to anion ratio was still 0.98 after adding the cation source solution. In this case, the absolute value of the zeta potential increased to 13 mV, but the motor output remained high at 70%. Therefore, it can be said that suppression of dust aggregation was insufficient.

1: Blast furnace 2: Exhaust gas pipe 3: Dry dust collector 4: Discharge port 5: Dry dust storage place 6: Pipe 7: Wet dust collector 8a: Pipe 8b: Branch pipe 8c: Branch pipe 9: Thickener 10: Rake 11: Motor 12: Piping 13: Dehydrator 14: Piping 15: Wet dust storage place 16: Piping 17: Cooler 18: Piping 19: Clean gas transport pipe 20: Gas holder 21: Reaction stirring tank 22: Stirrer 23: Motor 24: Tank 25: Supply pipe

Claims (4)

A dust collection method for blast furnace gas, wherein the cation-anion ratio of dust-collected water in which dust contained in blast furnace gas is collected is 1.01 or more.
However, the cation-anion ratio is the sum of the products of the valences and molar concentrations of the cations contained in the dust-collected water, and the sum of the products of the valences and molar concentrations of the anions contained in the dust-collected water. is the value divided by
the cations are Ca ²⁺ , Na ⁺ , K ⁺ , Mg ²⁺ and NH ₄ ⁺ , and
The anions are SO ₄ ^2- , S ₂ O ₃ ^2- , Cl ^- , F ^- and CH ₃ COO ^- . The dust collection method for blast furnace gas according to claim 1, wherein the cation/anion ratio is set to 1.20 or less. 3. The method for collecting dust from blast furnace gas according to claim 1, wherein a cation source is added to said dust collection water to adjust said cation-anion ratio. The dust collection method for blast furnace gas according to claim 3 , wherein the cation-anion ratio of the dust collection water introduced into the solid-liquid separator is adjusted.

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