US20220204880A1

US20220204880A1 - Method for producing low-sulfur coal

Info

Publication number: US20220204880A1
Application number: US17/605,626
Authority: US
Inventors: Ryota Murai; Ikuhiro Sumi; Katsuyasu Sugawara; Takahiro Kato
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 2019-04-24
Filing date: 2020-04-20
Publication date: 2022-06-30
Also published as: AU2020261846B2; WO2020218243A1; CA3134547A1; CN113748186A; AU2020261846A1; JP6992905B2; JPWO2020218243A1

Abstract

A method for producing low-sulfur coal having an excellent desulfurization effect. In the production method, coal is brought into contact with a chemical agent that is a mixed solution of hydrogen peroxide and acetic acid to remove sulfur in the coal. It is preferred that the molar ratio of the acetic acid to the hydrogen peroxide ((acetic acid)/(hydrogen peroxide)) is 1.2 to 60.0 inclusive. It is preferred that the acetic acid is mixed with the hydrogen peroxide before the chemical agent is brought into contact with the coal and the chemical agent is brought into contact with the coal after 30 minutes or more has elapsed since the mixing is performed.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a low-sulfur coal production method.

BACKGROUND ART

In an iron manufacturing process, when coal is used as a reducing material for iron ore, a part of sulfur contained in the coal dissolves as a solid in iron obtained by reducing the iron ore. If sulfur remains, toughness and workability of steel deteriorates, so that a great amount of effort has been made to remove sulfur from iron.
When coal is used as a heat source, a sulfur oxide is mixed in an exhaust gas, so that a great amount of effort has been required to remove a sulfur content from an exhaust gas from the standpoint of prevention of air pollution.
From such background, the industrial value is high if sulfur (sulfur content) in coal can be removed before the coal is used.
As a method of producing coal having a reduced sulfur content (low-sulfur coal), the claim of Patent Literature 1 describes “a chemical desulfurization method for coal, characterized in that an aqueous solution of caustic soda or caustic potash alone, or an aqueous solution of a mixture thereof is mixed with pulverized coal, and the resultant mixture is heated and reacted at a high temperature under an atmosphere of an oxygen gas or air or a mixture thereof, thereby removing a sulfur content in the coal.”

CITATION LIST

Patent Literatures

Patent Literature 1: JP 3-275795 A

SUMMARY OF INVENTION

Technical Problems

In producing low-sulfur coal by desulfurizing coal (removing sulfur in coal), the conventional method had an insufficient desulfurization effect in some cases.
An object of the present invention is therefore to provide a low-sulfur coal production method having an excellent desulfurization effect.

Solution to Problems

The present inventors have made an intensive study and as a result found that when the configuration described below is employed, the foregoing object is achieved. The invention has been thus completed.
Specifically, the present invention provides the following [1] to [16].
[1] A low-sulfur coal production method comprising: bringing coal into contact with a chemical agent which is a mixed solution of hydrogen peroxide and acetic acid to thereby remove sulfur in the coal.
[2] The low-sulfur coal production method according to [1] above, wherein a molar ratio between the acetic acid and the hydrogen peroxide (acetic acid/hydrogen peroxide) is not less than 1.2 and not more than 60.0.
[3] The low-sulfur coal production method according to [1] or [2] above,
wherein the acetic acid and the hydrogen peroxide are mixed before the chemical agent is brought into contact with the coal, and
wherein when 30 minutes or more have elapsed after the acetic acid and the hydrogen peroxide are mixed, the chemical agent is brought into contact with the coal.
[4] A low-sulfur coal production method comprising: bringing coal into contact with a chemical agent which is an aqueous peracetic acid solution to thereby remove sulfur in the coal.
[5] The low-sulfur coal production method according to [4] above, wherein a content of peracetic acid in the chemical agent is not less than 10.0 mass % and not more than 25.0 mass %.
[6] A low-sulfur coal production method comprising: bringing coal into contact with a chemical agent which is a mixed solution of hydrogen peroxide and formic acid to thereby remove sulfur in the coal.
[7] The low-sulfur coal production method according to [6] above, wherein a molar ratio between the formic acid and the hydrogen peroxide (formic acid/hydrogen peroxide) is not less than 1.2 and not more than 60.0.
[8] The low-sulfur coal production method according to [6] or [7] above,
wherein the formic acid and the hydrogen peroxide are mixed before the chemical agent is brought into contact with the coal, and
wherein when 5 minutes or more have elapsed after the formic acid and the hydrogen peroxide are mixed, the chemical agent is brought into contact with the coal.
[9] The low-sulfur coal production method according to any one of [1] to [8] above, wherein a mass ratio between the chemical agent and the coal (chemical agent/coal) is not less than 1.0.
[10] The low-sulfur coal production method according to any one of [1] to [9] above, wherein a temperature of the chemical agent at a time of being brought into contact with the coal is not less than 10° C.
[11] The low-sulfur coal production method according to any one of [1] to [10] above, wherein a temperature of the chemical agent at a time of being brought into contact with the coal is not more than 60° C.
[12] The low-sulfur coal production method according to any one of [1] to [11] above, wherein the coal comprises sub-bituminous coal.
[13] The low-sulfur coal production method according to any one of [1] to [12] above, wherein the coal that has been brought into contact with the chemical agent is heat-treated at a heat treatment temperature of not less than 150° C.
[14] The low-sulfur coal production method according to [13] above, wherein a heating rate at which the coal that has been brought into contact with the chemical agent is heated to the heat treatment temperature is not less than 10° C./min.
[15] The low-sulfur coal production method according to any one of [1] to [12] above, wherein the coal that has been brought into contact with the chemical agent is brought into contact with a hydrogen peroxide solution having a temperature of not more than 40° C.
[16] The low-sulfur coal production method according to [15] above,
wherein a concentration of the hydrogen peroxide solution is not less than 2.0 mass %, and
wherein a mass ratio between the hydrogen peroxide solution and the coal (hydrogen peroxide solution/coal) is not less than 1.0.

Advantageous Effects of Invention

The present invention can provide a low-sulfur coal production method having an excellent desulfurization effect.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing a desulfurization rate with respect to a mass ratio between a chemical agent and coal (chemical agent/coal).

FIG. 2 is a graph (lower part) showing an amount of peracetic acid generated with respect to a temperature of a chemical agent, and a graph (upper part) showing a desulfurization rate (solid line) and a carbon yield (dashed line) with respect to a temperature of a chemical agent.

FIG. 3 is a schematic view showing an example of a facility for producing low-sulfur coal.

DETAILED DESCRIPTION OF THE INVENTION

[Low-Sulfur Coal Production Method]

The low-sulfur coal production method of the invention (hereinafter, also simply referred to as “the method of the invention”) is a low-sulfur coal production method comprising bringing coal into contact with a chemical agent which is a mixed solution of hydrogen peroxide and acetic acid to thereby remove sulfur in the coal.
In addition, the method of the invention is a low-sulfur coal production method comprising bringing coal into contact with a chemical agent which is an aqueous peracetic acid solution to thereby remove sulfur in the coal.
Further, the method of the invention is a low-sulfur coal production method comprising bringing coal into contact with a chemical agent which is a mixed solution of hydrogen peroxide and formic acid to thereby remove sulfur in the coal.

First, described below is a primary treatment (chemical treatment) in which coal is brought into contact with a specific chemical agent.
Sulfur in coal is roughly classified into inorganic sulfur (inorganic sulfur content) and organic sulfur (organic sulfur content).
A typical example of inorganic sulfur is FeS₂. Examples of organic sulfur include: an aromatic sulfur compound in which sulfur is present inside an aromatic ring such as dibenzothiophene; an aliphatic sulfur compound such as mercaptan. Of these, sulfur present inside an aromatic ring constituting coal is known to be particularly difficult to be removed.
The present inventors studied various chemical agents (desulfurization agents). As a result, it was found that peracetic acid effectively acts on thiophene form sulfur which is a component particularly difficult to be removed among organic sulfurs in coal, thereby successfully removing sulfur from coal or increasing an efficiency of converting sulfur into an easily removable form. It is assumed that by the action of peracetic acid, thiophene form sulfur is oxidized to be, for example, sulfone form sulfur or sulfide form sulfur, and a bond between carbon and sulfur is relatively weakened to be easily cut off, whereby the sulfur becomes easy to be separated.
Meanwhile, peracetic acid (CH₃COO₂H) is usually generated in a mixed solution of hydrogen peroxide (H₂O₂) and acetic acid (CH₃COOH) (hereinafter, also simply referred to as “mixed solution”) by a reaction represented by Formula (I) below.
$\begin{matrix} H_{2} O_{2} + {CH}_{3} COOH \Leftrightarrow {CH}_{3} {COO}_{2} H + H_{2} O & (I) \end{matrix}$
In Formula (I) above, an equilibrium state changes depending on various conditions such as a temperature and a mixing ratio of a chemical agent. Therefore, the concentration of each component varies depending on the combination of the conditions. Suitable conditions will be described in detail below.
An attempt has also been made to accelerate the forward reaction of Formula (I) above by use of a catalyst and use a means such as distillation, thereby obtaining an aqueous peracetic acid solution. In this case, there is an optimum concentration of peracetic acid, and the details thereof will be described later.
That is, the mixed solution or the aqueous peracetic acid solution as above is used as a chemical agent, and this chemical agent is brought into contact with coal.
When a chemical agent is brought into contact with coal, inorganic sulfur which is easy to be removed dissolves and leaches into the chemical agent in the form of, for example, a sulfate ion. Similarly, a part of organic sulfur is also oxidized and leaches into the chemical agent in the form of, for example, a sulfate ion. Coal is desulfurized (i.e., sulfur in coal is removed) in this manner to thereby obtain coal having a reduced sulfur content (low-sulfur coal).
The present inventors further found that performic acid exhibits a similar effect to that of peracetic acid.
In the invention, therefore, a mixed solution of hydrogen peroxide and formic acid (hereinafter, also simply referred to as “mixed solution”) is used as a chemical agent. The mixed solution generates performic acid (HCOO₂H) which is a reaction product of hydrogen peroxide (H₂O₂) and formic acid (HCOOH) by a reaction represented by Formula (II) below. The mixed solution as above is brought into contact with coal.
$\begin{matrix} H_{2} O_{2} + HCOOH \Leftrightarrow HCOO_{2} H + H_{2} O & (II) \end{matrix}$

<<Molar Ratio (Acetic Acid/Hydrogen Peroxide)>>

When a mixed solution of acetic acid and hydrogen peroxide is used as a chemical agent, a molar ratio between acetic acid and hydrogen peroxide (acetic acid/hydrogen peroxide) in the chemical agent is preferably not less than 1.2 and more preferably not less than 5.0 because peracetic acid which is a reaction product can be formed in a proper amount and the desulfurization effect can become more excellent.
Further, when the molar ratio (acetic acid/hydrogen peroxide) is within the foregoing range, acetic acid can be prevented from becoming excessive with respect to hydrogen peroxide, and residual hydrogen peroxide in the mixed solution can be minimized (as described below, hydrogen peroxide decreases a carbon yield of coal).
The molar ratio (acetic acid/hydrogen peroxide) is preferably not more than 60.0 and more preferably not more than 20.0. When the molar ratio (acetic acid/hydrogen peroxide) is within the foregoing range, as in the above, peracetic acid which is a reaction product can be formed in a proper amount, so that the desulfurization effect can become more excellent. Further, the generated peracetic acid is prevented from being diluted with excessive acetic acid.
The molar ratio (acetic acid/hydrogen peroxide) is calculated as follows.
First, a molar amount [mol] of each component (acetic acid or hydrogen peroxide) in a chemical agent is represented by Formula (a) below. Therefore, the molar ratio between acetic acid and hydrogen peroxide (acetic acid/hydrogen peroxide) in the chemical agent is calculated by Formula (b) below.
$\begin{matrix} Molar amount = (Li \times Ci) / (100 \times Mi) & (a) \end{matrix}$ $\begin{matrix} Molar ratio = (L 1 \times C 1 \times M 2) / (L 2 \times C 2 \times M 1) & (b) \end{matrix}$
Li: amount of i aqueous solution [g/h]
Ci: concentration of i aqueous solution [mass %]
Mi: molecular weight of i [g/mol]
Here, i is 1 or 2, 1 is acetic acid and 2 is hydrogen peroxide.
The molecular weight of acetic acid is assumed to be 60, and the molecular weight of hydrogen peroxide is assumed to be 34. The amount of an aqueous solution Li is adjusted such that the desired molar ratio (acetic acid/hydrogen peroxide) is obtained.

<<Molar Ratio (Formic Acid/Hydrogen Peroxide)>>

When a mixed solution of formic acid and hydrogen peroxide is used as a chemical agent, a molar ratio between formic acid and hydrogen peroxide (formic acid/hydrogen peroxide) in a chemical agent is preferably not less than 1.2 and more preferably not less than 5.0, and, at the same time, preferably not more than 60.0 and more preferably not more than 20.0. The reason therefor is similar to the case where a mixed solution of acetic acid and hydrogen peroxide is used as a chemical agent.
In Formula (II), two substances of one mole each are reacted as in Formula (I) above. Therefore, the molar amount (molar ratio) of reactants required for generation of performic acid is the same.
Regarding determination of the molar ratio (formic acid/hydrogen peroxide), “acetic acid” is replaced with “formic acid” in the description of Formulae (a) and (b) above. The molecular weight of formic acid is assumed to be 46.

<<Elapsed Time After Mixing of Acetic Acid and Hydrogen Peroxide>>

The reaction (forward reaction) of Formula (I) above has a slow rate. Therefore, generation of peracetic acid is insufficient immediately after acetic acid and hydrogen peroxide are mixed in some cases.
The present inventors determined the quantities of various reaction rates and found out that it takes about 30 minutes for the reaction of Formula (I) above to settle into a steady state.
In the invention, therefore, it is preferable that acetic acid and hydrogen peroxide are mixed before a chemical agent is brought into contact with coal, and when 30 minutes or more have elapsed after this mixing, the chemical agent is brought into contact with the coal. This allows peracetic acid to be sufficiently generated, whereby the desulfurization effect of removing sulfur in coal can become more excellent. Further, this allows peracetic acid hydrogen to be decreased, whereby decrease in a carbon yield due to a reaction of hydrogen peroxide with coal can be minimized.
The elapsed time after mixing of acetic acid and hydrogen peroxide is more preferably not less than 45 minutes and even more preferably not less than 60 minutes and, at the same time, preferably not more than 120 minutes and more preferably not more than 80 minutes.

<<Elapsed Time After Mixing of Formic Acid and Hydrogen Peroxide>>

The reaction (forward reaction) of Formula (II) above has a faster rate than that of the reaction of Formula (I) above. Therefore, the elapsed time after mixing and before a chemical agent is brought into contact with coal may be shorter than that in the case where acetic acid and hydrogen peroxide are mixed.
Specifically, the elapsed time after mixing of formic acid and hydrogen peroxide is preferably not less than 5 minutes and more preferably not less than 6 minutes and, at the same time, preferably not more than 90 minutes and more preferably not more than 60 minutes.

<<Concentration of Aqueous Peracetic Acid Solution (Content of Peracetic Acid)>>

When an aqueous peracetic acid solution is used as a chemical agent, the content of peracetic acid in the chemical agent (aqueous peracetic acid solution) is preferably not less than 1.0 mass %, more preferably not less than 5.0 mass % and even more preferably not less than 10.0 mass % because the desulfurization effect can become more excellent.
At the same time, the content of peracetic acid in the chemical agent (aqueous peracetic acid solution) is preferably not more than 25.0 mass %. Although peracetic acid has a risk of ignition and the like on the high concentration side, when the content thereof is within the range, desulfurization can be performed safely and sufficiently.

<<Mass Ratio (Chemical Agent/Coal)>>

The present inventors studied a mass ratio between a chemical agent and coal (chemical agent/coal). In this study, a chemical agent having a molar ratio between acetic acid and hydrogen peroxide (acetic acid/hydrogen peroxide) of 12.0 was used.
FIG. 1 is a graph showing a desulfurization rate with respect to a mass ratio between a chemical agent and coal (chemical agent/coal). As shown in the graph of FIG. 1, as the amount of a chemical agent with respect to coal increases, the desulfurization rate increases, so that the desulfurization effect becomes more excellent. Therefore, the mass ratio (chemical agent/coal) is preferably not less than 0.5 and more preferably not less than 1.0.
As shown in the graph of FIG. 1, when the amount of a chemical agent becomes excessive with respect to the amount of coal, the desulfurization rate barely changes. The mass ratio (chemical agent/coal) is preferably not more than 100.0 and more preferably not more than 50.0 for the sake of reducing the amount of a chemical agent used.
When the molar ratio (acetic acid/hydrogen peroxide) was changed within the range described above, the same tendency as in the graph of FIG. 1 was also seen even when a different agent (an aqueous peracetic acid solution or a mixed solution of formic acid and hydrogen peroxide) was used.
When a mass of coal (solid content) before desulfurization is W₁[kg], a sulfur content of coal (solid content) before desulfurization is % S₁[mass %], a mass of coal (solid content) after desulfurization is W₂[kg], and a sulfur content of coal (solid content) after desulfurization is % S₂[mass %], the desulfurization rate [mass %] is defined by Formula (1) below.
Desulfurization rate[mass %]=100×{1−(W ₂×% S ₂)/(W ₁×% S ₁)} (1)

<<Temperature of Chemical Agent>>

The present inventors also studied a temperature of a chemical agent at the time of being brought into contact with coal (hereinafter, also simply referred to as “a temperature of a chemical agent”). In this study, a chemical agent having a molar ratio between acetic acid and hydrogen peroxide (acetic acid/hydrogen peroxide) of 12.0 was used.
FIG. 2 provides a graph (lower part) showing an amount of peracetic acid generated with respect to a temperature of a chemical agent, and a graph (upper part) showing a desulfurization rate (solid line) and a carbon yield (dashed line) with respect to a temperature of a chemical agent. The amount of peracetic acid generated is an index obtained by setting a calculated value at the time when the reaction contributing substances (hydrogen peroxide and acetic acid) completely react to 1.0.
As shown in the graphs (lower and upper parts) of FIG. 2, when the temperature of a chemical agent at the time of being brought into contact with coal is high, the amount of peracetic acid generated is large, and the desulfurization rate is high, so that the desulfurization effect becomes more excellent. In connection with this, the temperature of a chemical agent is preferably not less than 5° C., more preferably not less than 10° C., even more preferably not less than 20° C. and particularly preferably not less than 50° C.
On the other hand, as shown in the graph (upper part) of FIG. 2, the temperature of a chemical agent is preferably not too high in order to maintain a high carbon yield. Specifically, the temperature is preferably not more than 65° C., more preferably not more than 60° C. and even more preferably not more than 55° C. because the carbon yield can become more excellent.
When the molar ratio (acetic acid/hydrogen peroxide) was changed within the range described above, the same tendency as in the graph of FIG. 2 was also seen even when a different agent (an aqueous peracetic acid solution or a mixed solution of formic acid and hydrogen peroxide) was used.
When a carbon content of coal (solid content) before desulfurization is % C1 [mass %] and a carbon content of coal (solid content) after desulfurization is % C2 [mass %], the carbon yield [mass %] is defined by Formula (2) below.
Carbon yield[mass %]=100×(W ₂×% C ₂)/(W ₁×% C ₁) (2)
The presumable reason why the carbon yield decreases is described below.
Hydrogen peroxide and peracetic acid (or performic acid) may become an oxidizing agent which may destroy a skeleton of coal, and in this case, the carbon yield unintentionally decreases simultaneously with removal of sulfur. The present inventors found, through a study, that peracetic acid first causes cutting off of a bond between sulfur and carbon of thiophene form sulfur, and thereafter destroy of a carbon skeleton (carbon-carbon bond) occurs. The degree of destroy of a carbon skeleton is low with peracetic acid (or performic acid) and high with hydrogen peroxide. In particular, it is remarkable with hydrogen peroxide having a high temperature.
Therefore, by appropriately controlling a condition when a chemical agent is brought into contact with coal (for example, preventing the temperature of a chemical agent from becoming too high, or appropriately adjusting the mixing ratio of hydrogen peroxide in a mixed solution), the thiophene form sulfur can be effectively removed while the destroy of a carbon skeleton is minimized.

<Coal>

While the coal used in the invention is not particularly limited and a wide variety of coals can be used, the coal preferably includes coal having a moderate degree of coalification such as sub-bituminous coal, more preferably includes sub-bituminous coal and even more preferably is sub-bituminous coal.
When such coal is used, the desulfurization effect tends to be more excellent than that in the case where coal having a high degree of coalification such as anthracite coal is used, and the carbon yield tends to be more excellent than that in the case where coal having a low degree of coalification such as brown coal is used.
The grain size (mean grain size) of coal used in the invention is not particularly limited. For example, even when the grain size of coal is on the order of several millimeters, there is no significant change in desulfurization performance. When the grain size of coal is equal to or larger than this, a mild pulverization treatment may be performed as necessary.
The primary treatment (chemical treatment) for desulfurizing coal was described above.
Next, two types of secondary treatments are described as a treatment for further removing sulfur remaining in coal having been desulfurized by the primary treatment.

By the action of peracetic acid or performic acid, thiophene form sulfur which is difficult to be removed is changed into an easily removable form; therefore, the thiophene form sulfur can be removed by a heat treatment at a relatively low temperature (about 150° C.)
That is, it is preferable that a heat treatment is further performed on coal which has been brought into contact with a chemical agent because the desulfurization effect can become more excellent. The heat treatment temperature is preferably not less than 150° C., more preferably not less than 250° C., and even more preferably not less than 350° C.
Note that a hydrocarbon-containing gas derived from coal and generated by a heat treatment can be recovered and used as a part of a gaseous fuel in an iron manufacturing process. In consideration of performing a heat treatment using, for example, exhaust heat generated at a factory such as ironworks, a heat treatment at a temperature of up to several hundreds Celsius is preferred.
One example of a furnace for subjecting coal to a heat treatment in iron manufacturing process is a coke oven. The heat treatment temperature in a coke oven is about 1000 to 1200° C., and the coke oven may be operated at a temperature at or above 1200° C. Coal that has been brought into contact with a chemical agent and desulfurized may be introduced into a coke oven to produce low-sulfur coke. While a hydrocarbon gas and a sulfur-containing gas are generated in this case, the sulfur-containing gas can be separately removed. The generated gas after the sulfur-containing gas is removed can be reused as a fuel gas.
Among processes for subjecting coal to a heat treatment, a process having the highest temperature is probably substantially a process of producing coke. As a result of experiments conducted by the present inventors, it was confirmed that a sufficient desulfurization effect was also exhibited even with a heat treatment temperature in a coke oven.
Therefore, the heat treatment temperature is, for example, not more than 1300° C.
Coal that has been subjected to a heat treatment at about 600° C. is generally called semi-coke. Coal that has been brought into contact with a chemical agent and desulfurized can also be used in producing semi-coke. Since semi-coke is generally inferior in strength to coke, it can hardly be used as coke for a blast furnace, but it can be used for other applications. In particular, semi-coke containing less sulfur is useful as, for example, a heating agent (carburizing material) used for heating in a converter.
It is preferable that a heating rate at which coal that has been brought into contact with a chemical agent is heated to the heat treatment temperature (hereinafter, also simply referred to as “heating rate”) is higher. This is because a sulfur compound which has been changed into a form allowing desulfurization by the action of peracetic acid or performic acid may be resynthesized into thiophene form sulfur which is difficult to desulfurize under heating, and this resynthesis is suppressed. Specifically, the heating rate is preferably not less than 10° C./min and more preferably not less than 20° C./min.
While the upper limit of the heating rate is not particularly limited, realization of an excessively high heating rate is difficult for technical and industrial (cost) reasons. Therefore, the heating rate is, for example, not more than 100° C./min.

The present inventors found, through the study, that for further desulfurizing coal that has been brought into contact with a chemical agent, a treatment using low-temperature hydrogen peroxide may be performed separately from the above-described heat treatment.
When hydrogen peroxide acts on coal that has not been subjected to the primary treatment (chemical treatment), as described above, a carbon skeleton is destroyed, and the carbon yield decreases. However, since a sulfur content remaining in coal that has been subjected to the primary treatment is in an easily removable form, the coal can be easily additionally desulfurized with hydrogen peroxide.
That is, it is preferable that the coal that has been brought into contact with the chemical agent is further brought into contact with a hydrogen peroxide solution having a low temperature.
The temperature of a hydrogen peroxide solution is preferably not more than 50° C. and more preferably not more than 40° C. The oxidizing ability of hydrogen peroxide becomes increasingly strong as the temperature of the hydrogen peroxide becomes high, and not only the desulfurization effect but also the carbon yield tends to decrease. When the temperature of a hydrogen peroxide solution is within the above range, the desulfurization effect is further excellent, and the carbon yield is also good.
The lower limit thereof is not particularly limited, and the temperature of a hydrogen peroxide solution is, for instance, not less than 5° C.
The concentration of a hydrogen peroxide solution (the content of hydrogen peroxide in a hydrogen peroxide solution) is preferably not less than 2.0 mass % and more preferably not less than 3.0 mass % because the desulfurization effect can become more excellent.
When the concentration of a hydrogen peroxide solution is not less than 3.0 mass %, the effect thus obtained is substantially constant regardless of the concentration of a hydrogen peroxide solution. Therefore, the upper limit thereof is not particularly limited, and the concentration of a hydrogen peroxide solution is preferably not more than 35.0 mass %, for instance.
Hydrogen peroxide is often commercially available as an aqueous solution of 30 to 35 mass % because it is easy to decompose on the high concentration side. In the present invention, such a commercially available aqueous solution may be appropriately diluted and used.

[Facility for Producing Low-Sulfur Coal]

Next, an example in which the present invention is implemented using a specific facility will be described with reference to FIG. 3.
FIG. 3 is a schematic view showing an example of a facility for producing low-sulfur coal (hereinafter, also simply referred to as “production facility”).
The production facility shown in FIG. 3 has a hydrogen peroxide storage tank 1 for storing hydrogen peroxide and an acetic acid storage tank 3 for storing acetic acid.
The hydrogen peroxide inside the hydrogen peroxide storage tank 1 is supplied to a chemical agent mixing tank 5 via a hydrogen peroxide transport pipe 2. The acetic acid inside the acetic acid storage tank 3 is supplied to the chemical agent mixing tank 5 via an acetic acid transport pipe 4. The hydrogen peroxide transport pipe 2 and the acetic acid transport pipe 4 are each provided with a suitable flow rate control device (not shown), and the flow rates of the hydrogen peroxide and the acetic acid can be controlled.
The chemical agent mixing tank 5 is provided with a heating device 6 and a mixing device 7. The hydrogen peroxide and the acetic acid supplied to the chemical agent mixing tank 5 are heated to a predetermined temperature using the heating device 6 as necessary and mixed using the mixing device 7.
A chemical agent which is a mixed solution obtained by mixing in the chemical agent mixing tank 5 is supplied to a desulfurization treatment tank 9 via a chemical agent transport pipe 8. The chemical agent transport pipe 8 is provided with a suitable flow rate control device (not shown), and the flow rate of the chemical agent can be controlled.
The desulfurization treatment tank 9 is further supplied with coal from a coal storage tank 10 for storing coal via a coal transport pipe 11. The coal transport pipe 11 is provided with a suitable flow rate control device (not shown), and the flow rate of the coal can be controlled.
The desulfurization treatment tank 9 is provided with a heating device 12. The heating device 12 controls the chemical agent supplied from the chemical agent mixing tank 5 and the coal supplied from the coal storage tank 10 to an appropriate temperature as necessary. Further, the desulfurization treatment tank 9 is provided with a mixing device 13. The mixing device 13 mixes the chemical agent and the coal well as necessary.
Thus, in the desulfurization treatment tank 9, the coal is brought into contact with the chemical agent and desulfurized, thereby obtaining coal with low sulfur content (low-sulfur coal) (hereinafter, also referred to as “chemical-treated coal”)
The desulfurization treatment tank 9 is provided with discharge holes at two places. A chemical agent circulation pipe 14 is provided at one discharge hole. Peracetic acid or acetic acid may remain in a part of the chemical agent after use in desulfurization of the coal. In this case, the chemical agent may be flown back from the desulfurization treatment tank 9 to the chemical agent mixing tank 5 and reused.
However, sulfur may leach into the chemical agent after desulfurization. Reuse of the chemical agent into which sulfur leaches may adversely affect desulfurization. Therefore, a chemical agent discharge pipe 15 is connected to the chemical agent circulation pipe 14, and a part or all of the chemical agent after desulfurization can be discharged through the chemical agent discharge pipe 15.
A chemical-treated coal transport pipe 16 is provided at the other discharge hole of the desulfurization treatment tank 9. The chemical-treated coal transport pipe 16 is further branched into three pipes, i.e., a chemical-treated coal discharge pipe 16 a, a heat treatment device connection pipe 16 b and a hydrogen peroxide treatment device connection pipe 16 c.
The chemical-treated coal discharge pipe 16 a discharges the chemical-treated coal obtained in the desulfurization treatment tank 9 without performing the secondary treatment. The heat treatment device connection pipe 16 b transports the chemical-treated coal to a heat treatment device 17. The hydrogen peroxide treatment device connection pipe 16 c transports the chemical-treated coal to a hydrogen peroxide treatment device 23.
First, the heat treatment device 17 will be described.
When low-sulfur coal (chemical-treated coal) is subjected to a heat treatment in the heat treatment device 17, sulfur is further volatilized, so that the desulfurization proceeds further. The coal that has been subjected to the heat treatment in the heat treatment device 17 and has been further reduced in sulfur content (hereinafter, also referred to as “heat-treated coal”) is taken out through a heat-treated coal discharge pipe 18 and used for a predetermined use.
Further, the heat treatment device 17 is provided with a heat treatment gas exhaust pipe 19. A gas generated by a heat treatment may include a combustible gas. In this case, the gas can be taken out through the heat treatment gas discharge pipe 19 and used for a predetermined use.
Next, the hydrogen peroxide treatment device 23 will be described.
The hydrogen peroxide treatment device 23 is supplied with the chemical-treated coal via the hydrogen peroxide treatment device connection pipe 16 c. In the hydrogen peroxide treatment device 23, the chemical-treated coal is subjected to the above-described secondary treatment (hydrogen peroxide treatment).
The hydrogen peroxide treatment device 23 is supplied with the hydrogen peroxide via a hydrogen peroxide supply pipe 20. The hydrogen peroxide supply pipe 20 is connected to the hydrogen peroxide storage tank 1. When the hydrogen peroxide is diluted, water may be supplied from a dilution water tank 21 through a dilution water supply pipe 22. Another hydrogen peroxide storage tank (not shown) may be provided exclusively for the hydrogen peroxide treatment device 23.
The hydrogen peroxide treatment device 23 is provided with a cooling device 24. The cooling device 24 controls a temperature inside the hydrogen peroxide treatment device 23 to an appropriate temperature as necessary.
Further, the hydrogen peroxide treatment device 23 is provided with a mixing device 25. The mixing device 25 mixes the hydrogen peroxide solution and the chemical-treated coal well as necessary.
The hydrogen peroxide treatment device 23 is provided with discharge holes at two places.
A hydrogen peroxide circulation pipe 27 is provided at one discharge hole. Hydrogen peroxide may remain in a part of the hydrogen peroxide solution after use in desulfurization of the coal (chemical-treated coal). In this case, the hydrogen peroxide solution may be flown back from the hydrogen peroxide treatment device 23 to the hydrogen peroxide storage tank 1 and reused. A destination of the flowback may be a separately provided hydrogen peroxide storage tank (not shown) or the chemical agent mixing tank 5.
However, sulfur may leach into the hydrogen peroxide solution after desulfurization. Reuse of the hydrogen peroxide solution into which sulfur leaches may adversely affect desulfurization. Therefore, a hydrogen peroxide discharge pipe 28 is connected to the hydrogen peroxide circulation pipe 27, and a part or all of the hydrogen peroxide solution after desulfurization can be discharged through the hydrogen peroxide discharge pipe 28.
A discharge pipe 26 is connected to the other discharge hole of the hydrogen peroxide treatment device 23. Coal that has been further desulfurized inside the hydrogen peroxide treatment device 23 (hereinafter, also referred to as “hydrogen peroxide-treated coal”) is taken out through the discharge pipe 26 and used for a predetermined use.
Note that since the chemical-treated coal transported to the heat treatment device 17 or the hydrogen peroxide treatment device 23 is already reduced in sulfur content, it may be taken out through the heat-treated coal discharge pipe 18 or the discharge pipe 26 without being subjected to the secondary treatment (heat treatment or hydrogen peroxide treatment).
Each part of the production facility described with reference to FIG. 3 need not have a special specification, and existing devices can be used as appropriate. For example, the heat treatment device 17 may be a heat exchanger using exhaust heat as a heat source, and it may be a furnace such as a semi-coke oven or a coke oven.
When formic acid is used instead of acetic acid in the production facility shown in FIG. 3, the “acetic acid” is replaced with “formic acid,” and the “peracetic acid” is replaced with “performic acid.”
In this case, the production facility shown in FIG. 3 has a “formic acid storage tank 3” instead of the “acetic acid storage tank 3” and a “formic acid transport pipe 3” instead of the “acetic acid transport pipe 3.”
When an aqueous peracetic acid solution is used as a chemical agent, the production facility shown in FIG. 3 has a “peracetic acid storage tank 1” instead of the “hydrogen peroxide storage tank 1,” a “peracetic acid transport pipe 2” instead of the “hydrogen peroxide transport pipe 2,” a “dilution water storage tank 3” instead of the “acetic acid storage tank 3” and a “dilution water transport pipe 4” instead of the “acetic acid transport pipe 4.”
In this case, the peracetic acid storage tank 1 stores peracetic acid. The dilution water storage tank 3 stores dilution water for diluting peracetic acid. The peracetic acid inside the peracetic acid storage tank 1 is supplied to the chemical agent mixing tank 5 via the peracetic acid transport pipe 2. The dilution water inside the dilution water storage tank 3 is supplied to the chemical agent mixing tank 5 via the dilution water transport pipe 4. The peracetic acid transport pipe 2 and the dilution water transport pipe 4 are each provided with a suitable flow rate control device (not shown), and the flow rates of the peracetic acid and the dilution water can be controlled.
In the chemical agent mixing tank 5, the supplied peracetic acid and dilution water are mixed to thereby prepare an aqueous peracetic acid solution.
Since the other points are the same as those described above, their description is omitted.

EXAMPLES

The present invention is specifically described below with reference to examples. However, the present invention should not be construed as being limited to the following examples.

Examples 1 to 31 and Comparative Examples 1 and 2

By using the production facility described with reference to FIG. 3, a test was conducted in which coal was desulfurized to produce low-sulfur coal by the method of the present invention.
As the coal, at least one selected from the group consisting of Coal A (sub-bituminous coal), Coal B (sub-bituminous coal) and Coal C (semi-anthracite coal) was used. The details of the coals used are shown in Table 1 below. The granularity of each coal was about 300 μm in a mean grain size. With all coals, permeability of peracetic acid is high, and the desulfurization performance did not vary greatly depending on the granularity.

TABLE 1

	Industrial analysis value	Industrial analysis value
	[mass % d.a.f.]	[mass % d.b.]

	C	H	N	S	V.M	Ash

Coal A	78.5	4.6	0.8	0.2	38.2	6.8
Coal B	77.1	4.9	1.5	0.5	33.2	6.7
Coal C	82.1	1.2	1.4	2	9.4	8.1

In Table 1 above, “d.a.f” indicates a dry ash free basis, and means an analytical value of net coal excluding moisture and ash.
“d.b.” means an analysis value on a dry basis.
“V.M” means a content of volatile matter in industrial analysis.
“Ash” means a content of ash in industrial analysis.
Test conditions such as supply amounts (flow rates) of coal are shown in Tables 2 to 4 below.
In Examples 1 to 8, 20 to 22 and 24 to 27 as well as Comparative Examples 1 and 2, only the above-described primary treatment (chemical treatment) was performed. That is, the coal after being brought into contact with the chemical agent was taken out, and the desulfurization rate and the carbon yield were determined.
In Examples 9 to 13, 23, 28 and 29, the above-described secondary treatment (heat treatment) was further performed. That is, after the primary treatment (chemical treatment), the coal was further introduced into the heat treatment device capable of raising the temperature to 1200° C. and then subjected to heat treatment under a nitrogen atmosphere, and the desulfurization rate and the carbon yield after the heat treatment were determined.
In Examples 14 to 19, 30 and 31, the above-described secondary treatment (hydrogen peroxide treatment) was further performed. That is, after the primary treatment (chemical treatment), the coal was further introduced into the hydrogen peroxide treatment device and then subjected to the hydrogen peroxide treatment, and the desulfurization rate and the carbon yield after the hydrogen peroxide treatment were determined.
In the primary treatment, an aqueous solution having a concentration of hydrogen peroxide of 35 mass % was used as hydrogen peroxide. As acetic acid, acetic acid having a purity of 99 mass % was used. As peracetic acid, an aqueous solution having a concentration of peracetic acid of 30 mass % was used. As formic acid, formic acid having a purity of 99 mass % was used.

TABLE 2

																						Comparative

Example

		Unit	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	1	2

Coal	Coal A	g/h	100	0	0	100	100	100	100	100	100	100	100	100	100	100	100	0	100	100	100	100	0
	Coal B	g/h	0	100	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
	Coal C	g/h	0	0	100	0	0	0	0	0	0	0	0	0	0	0	0	100	0	0	0	0	100
	Total amount	g/h	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100
Chemical agent	Hydrogen peroxide	g/h	29	17	29	7	170	11	12	29	29	29	29	29	29	29	29	29	29	29	29	300	300
and	Acetic acid	g/h	220	193	220	247	80	125	79	220	220	220	220	220	220	220	220	220	220	220	220	0	0
primary	Molar ratio	mol/mol	12.1	18.2	12.1	56.5	0.8	18.2	10.5	12.1	12.1	12.1	12.1	12.1	12.1	12.1	12.1	12.1	12.1	12.1	12.1	0.0	0.0
treatment	(acetic acid/hydrogen peroxide)
(chemical	Elapsed time after mixing	min	60	67	120	60	30	20	30	30	60	60	60	60	60	60	60	120	60	60	60	—	—
treatment)	Mass ratio	g/g	2.5	2.1	2.5	2.5	2.5	1.4	0.9	2.5	2.5	2.5	2.5	2.5	2.5	2.5	2.5	2.5	2.5	2.5	2.5	3.0	3.0
	(chemical agent/coal)
	Chemical agent temperature	° C.	56	18	54	56	21	50	25	9	56	56	56	56	56	56	56	54	56	56	56	30	30
	Desulfurization rate	mass %	53	52	42	51	49	49	49	49	53	53	53	53	53	53	53	42	53	53	53	28	23
	(after primary treatment)
	Carbon yield	mass %	96	96	98	98	80	97	97	96	96	96	96	96	96	96	96	98	96	96	96	71	75
	(after primary treatment)
Secondary treatment	Heat treatment temperature	° C.	—	—	—	—	—	—	—	—	150	600	1200	135	150	—	—	—	—	—	—	—	—
(heat treatment)	Heating rate	° C./min	—	—	—	—	—	—	—	—	20	30	25	20	5	—	—	—	—	—	—	—	—
	Desulfurization rate	mass %	—	—	—	—	—	—	—	—	65	66	68	54	61	—	—	—	—	—	—	—	—
	(after secondary treatment)
	Carbon yield	mass %	—	—	—	—	—	—	—	—	95	94	94	96	95	—	—	—	—	—	—	—	—
	(after secondary treatment)
Secondary treatment	Temperature of hydrogen	° C.	—	—	—	—	—	—	—	—	—	—	—	—	—	20	40	40	45	30	30	—	—
(hydrogen peroxide	peroxide solution
treatment)	Concentration of hydrogen	mass %	—	—	—	—	—	—	—	—	—	—	—	—	—	35.0	35.0	20.0	20.0	1.5	3.0	—	—
	peroxide solution
	Mass ratio	g/g	—	—	—	—	—	—	—	—	—	—	—	—	—	2.5	2.5	1.2	1.5	2.5	0.9	—	—
	(hydrogen peroxide solution/coal)
	Desulfurization rate	mass %	—	—	—	—	—	—	—	—	—	—	—	—	—	65	66	55	56	62	63	—	—
	(after secondary treatment)
	Carbon yield	mass %	—	—	—	—	—	—	—	—	—	—	—	—	—	95	93	97	67	95	95	—	—
	(after secondary treatment)

TABLE 3

	Example	Example

		Unit	20	21	22	23

Coal	Coal A	g/h	100	50	100	50
	Coal B	g/h	0	50	0	50
	Coal C	g/h	0	0	0	0
	Total amount	g/h	100	100	100	100
Chemical agent	Peracetic acid	g/h	150	120	80	120
and	Dilution water	g/h	250	60	250	60
primary treatment	Content of peracetic acid (after dilution)	mass %	12.7	25.0	7.8	25.0
(chemical treatment)	Mass ratio (chemical agent/coal)	g/g	4.0	1.8	3.3	1.8
	Chemical agent temperature	° C.	60	10	30	10
	Desulfurization rate	mass %	57	51	48	51
	(after primary treatment)
	Carbon yield
	(after primary treatment)	mass %	95	97	96	97
Secondary treatment	Heat treatment temperature	° C.	—	—	—	250
(heat treatment)	Heating rate	° C./min	—	—	—	18
	Desulfurization rate
	(after secondary treatment)	mass %	—	—	—	66
	Carbon yield
	(after secondary treatment)	mass %	—	—	—	96
Secondary treatment	Temperature of hydrogen peroxide solution	° C.	—	—	—	—
(hydrogen peroxide	Concentration of hydrogen peroxide solution	mass %	—	—	—	—
treatment)	Mass ratio (hydrogen peroxide solution/coal)	g/g	—	—	—	—
	Desulfurization rate	mass %	—	—	—	—
	(after secondary treatment)
	Carbon yield	mass %	—	—	—	—
	(after secondary treatment)

TABLE 4

	Example	Example	Example

		Unit	24	25	26	27	28	29	30	31

Coal	Coal A	g/h	100	0	0	100	100	100	100	100
	Coal B	g/h	0	100	0	0	0	0	0	0
	Coal C	g/h	0	0	100	0	0	0	0	0
	Total amount	g/h	100	100	100	100	100	100	100	100
Chemical agent	Hydrogen peroxide	g/h	36	21	36	14	36	36	36	36
and	Formic acid	g/h	209	183	209	122	209	209	209	209
primary treatment	Molar ratio (formic acid/hydrogen peroxide)	mol/mol	12.1	18.2	12.1	18.2	12.1	12.1	12.1	12.1
(chemical treatment)	Elapsed time after mixing	min	6	60	20	3	6	6	6	6
	Mass ratio (chemical agent/coal)	g/g	2.5	2.0	2.5	1.4	2.5	2.5	2.5	2.5
	Chemical agent temperature	° C.	55	12	34	26	55	55	55	55
	Desulfurization rate
	(after primary treatment)	mass %	55	54	46	52	55	55	55	55
	Carbon yield
	(after primary treatment)	mass %	95	96	98	96	95	95	95	95
Secondary treatment	Heat treatment temperature	° C.	—	—	—	—	150	150	—	—
(heat treatment)	Heating rate	° C/min	—	—	—	—	20	5	—	—
	Desulfurization rate	mass %	—	—	—	—	66	61	—	—
	(after secondary treatment)
	Carbon yield	mass %	—	—	—	—	94	95	—	—
	(after secondary treatment)
Secondary treatment	Temperature of hydrogen peroxide solution	° C.	—	—	—	—	—	—	20	30
(hydrogen peroxide	Concentration of hydrogen peroxide solution	mass %	—	—	—	—	—	—	35.0	3.0
treatment)	Mass ratio (hydrogen peroxide solution/coal)	g/g	—	—	—	—	—	—	2.5	0.9
	Desulfurization rate	mass %	—	—	—	—	—	—	66	63
	(after secondary treatment)
	Carbon yield	mass %	—	—	—	—	—	—	95	94
	(after secondary treatment)

It was revealed that Examples 1 to 19 using a mixed solution of hydrogen peroxide and acetic acid as a chemical agent exhibited a higher desulfurization rate than those of Comparative Examples 1 and 2 in which such a solution was not used, thus having a sufficient desulfurization effect. The carbon yield also tended to be good.
The comparison between Example 1 and Example 5 revealed that Example 1 in which a molar ratio (acetic acid/hydrogen peroxide) was 12.1 had a higher desulfurization rate than that of Example 5 in which a molar ratio (acetic acid/hydrogen peroxide) was 0.8, thus having a more excellent desulfurization effect.
The comparison between Example 1 and Example 6 revealed that Example 1 in which the elapsed time after mixing of acetic acid and hydrogen peroxide was 60 minutes had a higher desulfurization rate than that of Example 6 in which the time was 20 minutes, thus having a more excellent desulfurization effect.
The comparison between Example 1 and Example 7 revealed that Example 1 in which the mass ratio (chemical agent/coal) was 2.5 had a higher desulfurization rate than that of Example 7 in which the mass ratio (chemical agent/coal) was 0.9, thus having a more excellent desulfurization effect.
The comparison between Example 1 and Example 8 revealed that Example 1 in which the temperature of the chemical agent at the time of being brought into contact with coal was 56° C. had a higher desulfurization rate than that of Example 8 in which the temperature was 9° C., thus having a more excellent desulfurization effect.
The desulfurization rates (after the secondary treatment) of Examples 9 to 13 were equal to or higher than the desulfurization rates (after the primary treatment) of Examples 1 to 8.
The comparison between Example 9 and Example 12 revealed that Example 9 in which the heat treatment temperature was 150° C. had a higher desulfurization rate (after the secondary treatment) than that of Example 12 in which the heat treatment temperature was 135° C., thus having a more excellent desulfurization effect.
The comparison between Example 9 and Example 13 revealed that Example 9 in which the heating rate at which the temperature was raised to the heat treatment temperature was 20° C./min had a higher desulfurization rate (after the secondary treatment) than that of Example 13 in which the heating rate was 5° C./min, thus having a more excellent desulfurization effect.
The desulfurization rates (after the secondary treatment) of Examples 14 to 19 were equal to or higher than the desulfurization rates (after the primary treatment) of Examples 1 to 8.
The comparison between Example 14 and Example 17 revealed that Example 14 in which the temperature of the hydrogen peroxide solution was 20° C. had a higher desulfurization rate (after the secondary treatment) than that of Example 17 in which the temperature was 45° C., thus having a more excellent desulfurization effect.
The comparison between Example 14 and Example 18 revealed that Example 14 in which the concentration of the hydrogen peroxide solution was 35.0 mass % had a higher desulfurization rate (after the secondary treatment) than that of Example 18 in which the concentration was 1.5 mass %, thus having a more excellent desulfurization effect.
The comparison between Example 14 and Example 19 revealed that Example 14 in which a mass ratio (hydrogen peroxide solution/coal) was 2.5 had a higher desulfurization rate (after the secondary treatment) than that of Example 19 in which a mass ratio (hydrogen peroxide solution/coal) was 0.9, thus having a more excellent desulfurization effect.

It was revealed that Examples 20 to 23 using an aqueous peracetic acid solution as a chemical agent exhibited a higher desulfurization rate than those of Comparative Examples 1 and 2 in which such a solution was not used (see Table 2), thus having a sufficient desulfurization effect. The carbon yield also tended to be good.
The comparison between Example 20 and Example 22 revealed that Example 20 in which the content of the peracetic acid in the chemical agent (aqueous peracetic acid solution) was 12.7 mass had a higher desulfurization rate than that of Example 22 in which the content was 7.8 mass %, thus having a more excellent desulfurization effect.
The desulfurization rate (after the secondary treatment) of Example 23 was equal to or higher than the desulfurization rates (after the primary treatment) of Examples 20 to 22.

It was revealed that Examples 24 to 31 using a mixed solution of hydrogen peroxide and formic acid as a chemical agent exhibited a higher desulfurization rate than that of Comparative Examples 1 and 2 in which such a solution was not used, thus having a sufficient desulfurization effect. The carbon yield also tended to be good.
The comparison between Example 24 and Example 27 revealed that Example 24 in which the elapsed time after mixing of formic acid and hydrogen peroxide was 6 minutes had a higher desulfurization rate than that of Example 27 in which the time was 3 minutes, thus having a more excellent desulfurization effect.
The desulfurization rates (after the secondary treatment) of Examples 28 to 29 were equal to or higher than the desulfurization rates (after the primary treatment) of Examples 24 to 27.
The comparison between Example 28 and Example 29 revealed that Example 28 in which the heating rate at which the temperature was raised to the heat treatment temperature was 20° C./min had a higher desulfurization rate (after the secondary treatment) than that of Example 29 in which the heating rate was 5° C./min, thus having a more excellent desulfurization effect.
The desulfurization rates (after the secondary treatment) of Examples 30 to 31 were equal to or higher than the desulfurization rates (after the primary treatment) of Examples 24 to 27.
The comparison between Example 30 and Example 31 revealed that Example 30 in which a mass ratio (hydrogen peroxide solution/coal) was 2.5 had a higher desulfurization rate (after the secondary treatment) than that of Example 31 in which a mass ratio (hydrogen peroxide solution/coal) was 0.9, thus having a more excellent desulfurization effect.

REFERENCE SIGNS LIST

- 1: Hydrogen peroxide storage tank (peracetic acid storage tank)
- 2: Hydrogen peroxide transport pipe (peracetic acid transport pipe)
- 3: Acetic acid storage tank (formic acid storage tank, dilution water storage tank)
- 4: Acetic acid transport pipe (formic acid transport pipe, dilution water transport pipe)
- 5: Chemical agent mixing tank
- 6: Heating device
- 7: Mixing device
- 8: Chemical agent transport pipe
- 9: Desulfurization treatment tank
- 10: Coal storage tank
- 11: Coal transport pipe
- 12: Heating device
- 13: Mixing device
- 14: Chemical agent circulation pipe
- 15: Chemical agent discharge pipe
- 16: Chemical-treated coal transport pipe
- 16 a: Chemical-treated coal discharge pipe
- 16 b: Heat treatment device connection pipe
- 16 c: Hydrogen peroxide treatment device connection pipe
- 17: Heat treatment device
- 18: Heat-treated coal discharge pipe
- 19: Heat treatment gas exhaust pipe
- 20: Hydrogen peroxide supply pipe
- 21: Dilution water tank
- 22: Dilution water supply pipe
- 23: Hydrogen peroxide treatment device
- 24: Cooling device
- 25: Mixing device
- 26: Discharge pipe
- 27: Hydrogen peroxide circulation pipe
- 28: Hydrogen peroxide discharge pipe

Claims

1-16. (canceled)

17. A low-sulfur coal production method comprising:

bringing coal into contact with a chemical agent which is a mixed solution of hydrogen peroxide and acetic acid to thereby remove sulfur in the coal,

wherein a molar ratio between the acetic acid and the hydrogen peroxide (acetic acid/hydrogen peroxide) is not less than 1.2 and not more than 60.0,

wherein the acetic acid and the hydrogen peroxide are mixed before the chemical agent is brought into contact with the coal, and

wherein when 30 minutes or more have elapsed after the acetic acid and the hydrogen peroxide are mixed, the chemical agent is brought into contact with the coal.

18. A low-sulfur coal production method comprising:

bringing coal into contact with a chemical agent which is an aqueous peracetic acid solution to thereby remove sulfur in the coal,

wherein a content of peracetic acid in the chemical agent is not less than 10.0 mass % and not more than 25.0 mass %.

19. A low-sulfur coal production method comprising:

bringing coal into contact with a chemical agent which is a mixed solution of hydrogen peroxide and formic acid to thereby remove sulfur in the coal,

wherein a molar ratio between the formic acid and the hydrogen peroxide (formic acid/hydrogen peroxide) is not less than 1.2 and not more than 60.0,

wherein the formic acid and the hydrogen peroxide are mixed before the chemical agent is brought into contact with the coal, and

wherein when 5 minutes or more have elapsed after the formic acid and the hydrogen peroxide are mixed, the chemical agent is brought into contact with the coal.

20. The low-sulfur coal production method according to claim 17,

wherein a mass ratio between the chemical agent and the coal (chemical agent/coal) is not less than 1.0,

wherein a temperature of the chemical agent at a time of being brought into contact with the coal is not less than 10° C. but not more than 60° C.

21. The low-sulfur coal production method according to claim 19,

22. The low-sulfur coal production method according to claim 17,

wherein the coal comprises sub-bituminous coal.

23. The low-sulfur coal production method according to claim 19,

wherein the coal comprises sub-bituminous coal.

24. The low-sulfur coal production method according to claim 20,

wherein the coal comprises sub-bituminous coal.

25. The low-sulfur coal production method according to claim 21,

wherein the coal comprises sub-bituminous coal.

26. The low-sulfur coal production method according to claim 17,

wherein the coal that has been brought into contact with the chemical agent is brought into contact with a hydrogen peroxide solution having a temperature of not more than 40° C.,

wherein a concentration of the hydrogen peroxide solution is not less than 2.0 mass %, and

wherein a mass ratio between the hydrogen peroxide solution and the coal (hydrogen peroxide solution/coal) is not less than 1.0.

27. The low-sulfur coal production method according to claim 19,

28. The low-sulfur coal production method according to claim 20,

29. The low-sulfur coal production method according to claim 21,

30. The low-sulfur coal production method according to claim 22,

31. The low-sulfur coal production method according to claim 23,

32. The low-sulfur coal production method according to claim 24,

33. The low-sulfur coal production method according to claim 25,