AU2020260860B2

AU2020260860B2 - Low-sulfur coal production method

Info

Publication number: AU2020260860B2
Application number: AU2020260860A
Authority: AU
Inventors: Takahiro Kato; Ryota Murai; Katsuyasu Sugawara; Ikuhiro Sumi
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 2019-04-24
Filing date: 2020-04-20
Publication date: 2022-11-03
Anticipated expiration: 2040-04-20
Also published as: AU2020260860A1; CA3134533A1; JPWO2020218248A1; WO2020218248A1; CA3134533C; CN113728076A; JP6795132B1; US20220220404A1

Abstract

Provided is a low-sulfur coal production method having an excellent desulfurization effect. The production method comprises bringing coal into contact with a chemical material that is a mixed solution of hydrogen peroxide and acetic anhydride to remove sulfur in the coal. It is preferred that the molar ratio of the acetic anhydride to the hydrogen peroxide (i.e., (acetic anhydride)/(hydrogen peroxide)) is 0.5 to 12.0 inclusive. It is preferred that the acetic anhydride is mixed with the hydrogen peroxide before the chemical material is brought into contact with the coal and the chemical material is brought into contact with the coal after 10 minutes or more has elapsed since the mixing.

Description

LOW-SULFUR COAL PRODUCTION METHOD BACKGROUND OF THE INVENTION

[0001]

The present invention relates to a low-sulfur coal

production method.

BACKGROUND ART

[0002]

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.

[0003]

From such background, the industrial value is high if

sulfur (sulfur content) in coal can be removed before the

coal is used.

[0004]

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

[0005]

Patent Literature 1: JP 3-275795 A

SUMMARY OF INVENTION

[0006]

In producing low-sulfur coal by desulfurizing coal

(removing sulfur in coal), the conventional method had an

insufficient desulfurization effect in some cases.

The present invention seeks to provide a low-sulfur

coal production method having an excellent desulfurization

effect.

[0007]

The present inventors have made an intensive study

and as a result found that when the configuration described below is employed, excellent desulfurization can be achieved.

[0008]

Specifically, the present invention provides the

following [1] to [11].

[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 anhydride 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

anhydride and the hydrogen peroxide (acetic

anhydride/hydrogen peroxide) is not less than 0.5 and not

more than 12.0.

[3] The low-sulfur coal production method according

to [1] or [2] above, wherein the acetic anhydride and the

hydrogen peroxide are mixed before the chemical agent is

brought into contact with the coal, and

wherein when 10 minutes or more have elapsed after

the acetic anhydride and the hydrogen peroxide are mixed,

the chemical agent is brought into contact with the coal.

[4] The low-sulfur coal production method according

to any one of [1] to [3] above, wherein a mass ratio

between the chemical agent and the coal (chemical agent/coal) is not less than 1.0.

[5] The low-sulfur coal production method according

to any one of [1] to [4] above, wherein a temperature of

the chemical agent at a time of being brought into contact

with the coal is not less than 5°C.

[6] The low-sulfur coal production method according

to any one of [1] to [5] above, wherein a temperature of

the chemical agent at a time of being brought into contact

with the coal is not more than 30°C.

[7] The low-sulfur coal production method according

to any one of [1] to [6] above, wherein the coal comprises

sub-bituminous coal.

[8] The low-sulfur coal production method according

to any one of [1] to [7] 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

0 °C.

[9] The low-sulfur coal production method according

to [8] 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

°C/min.

[10] The low-sulfur coal production method according

to any one of [1] to [7] 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.

[11] The low-sulfur coal production method according

to [10] 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.

[0009]

The present invention can provide a low-sulfur coal

production method having an excellent desulfurization

effect.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]

[FIG. 1] 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] 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] FIG. 3 is a schematic view showing an

example of a facility for producing low-sulfur coal.

DETAILED DESCRIPTION OF THE INVENTION

[0011]

[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 anhydride to thereby remove sulfur in

the coal.

[0012]

First, described below is a primary treatment

(chemical treatment) in which coal is brought into contact

with a chemical agent which is a mixed solution of hydrogen

peroxide and acetic anhydride.

[0013]

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 FeS 2

. 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.

[00141

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.

[0015]

Meanwhile, peracetic acid is easy to decompose. In

the invention, therefore, a mixed solution of hydrogen

peroxide and acetic anhydride (hereinafter, also simply

referred to as "mixed solution") is used as a chemical

agent. The mixed solution generates peracetic acid which is

a reaction product of hydrogen peroxide and acetic

anhydride. The mixed solution as above is brought into

contact with coal.

[0016]

A reaction of hydrogen peroxide (H 2 0 2 ) and acetic

anhydride ( (CH 3 CO) 2 0) to obtain peracetic acid (CH 3 CO0 2 H)

and water (120) is represented by Formula (I) below.

2H 2 0 2 + (CH 3 CO) 2 0 4> 2CH3 COO 2H + H 2 0 ... (I)

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.

[0017]

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).

[0018]

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

A molar ratio between acetic anhydride and hydrogen

peroxide (acetic anhydride/hydrogen peroxide) in a chemical

agent is preferably not less than 0.1 and more preferably

not less than 0.5 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

anhydride/hydrogen peroxide) is within the foregoing range,

acetic anhydride 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).

[0019]

The molar ratio (acetic anhydride/hydrogen peroxide)

is preferably not more than 15.0 and more preferably not

more than 12.0. When the molar ratio (acetic anhydride/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 anhydride.

[00201

The molar ratio (acetic anhydride/hydrogen peroxide)

is calculated as follows.

First, a molar amount [mol] of each component (acetic

anhydride or hydrogen peroxide) in a chemical agent is

represented by Formula (a) below. Therefore, the molar

ratio between acetic anhydride and hydrogen peroxide

(acetic anhydride/hydrogen peroxide) in the chemical agent

is calculated by Formula (b) below.

Molar amount = (Li x Ci)/(100 x Mi) ... (a)

Molar ratio= (L1 x C1 x M2)/(L2 x C2 x M1) ... (b)

Li: amount of i aqueous solution [g/h]

Ci: concentration of i aqueous solution [mass%]

Mi: molecular weight of i [g/moll

Here, i is 1 or 2, 1 is acetic anhydride and 2 is

hydrogen peroxide.

The molecular weight of acetic anhydride is assumed

to be 102, 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 anhydride/hydrogen peroxide) is obtained.

[0021]

<<Elapsed Time After Mixing>>

The reaction (forward reaction) of Formula (I) above

has a relatively slow rate. Therefore, generation of

peracetic acid is insufficient immediately after acetic

anhydride 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 10

minutes for the reaction of Formula (I) above to settle

into a steady state.

In the invention, therefore, it is preferable that

acetic anhydride and hydrogen peroxide are mixed before a

chemical agent is brought into contact with coal, and when

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 is more preferably not

less than 20 minutes and even more preferably not less than

minutes and, at the same time, preferably not more than

120 minutes, more preferably not more than 90 minutes, and

even more preferably not more than 60 minutes.

[0022]

<<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

anhydride and hydrogen peroxide (acetic anhydride/hydrogen

peroxide) of 5.0 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, more preferably not less than 1.0 and even more

preferably not less than 2.0.

[0023]

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.

[0024]

When a mass of coal (solid content) before

desulfurization is W [kg], a sulfur content of coal (solid

content) before desulfurization is %S 1 [mass%], a mass of

coal (solid content) after desulfurization is W2 [kg], and

a sulfur content of coal (solid content) after

desulfurization is %S 2 [mass%], the desulfurization rate

[mass%] is defined by Formula (1) below.

Desulfurization rate [mass%] = 100 x {l - (W2 x

%-S2)/(W1x %S1)) . . (1)

[0025]

<<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

anhydride and hydrogen peroxide (acetic anhydride/hydrogen

peroxide) of 5.0 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 anhydride) completely react to 1.0.

[0026]

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

0 °C, more preferably not less than 10 C, even more

preferably not less than 200 C and particularly preferably

not less than 25 0 C.

[0027]

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 400C, more preferably not more than 350C and even more preferably not more than 30 0 C because the carbon yield can become more excellent.

[0028]

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 x (W 2 x %C 2 )/(W 1 x %CA) ...

(2)

[0029]

The presumable reason why the carbon yield decreases

is described below.

Hydrogen peroxide and peracetic 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 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.

[0030]

<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.

[0031]

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.

[0032]

By the action of peracetic acid which is a reaction

product of hydrogen peroxide and acetic anhydride,

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 0 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

0 temperature is preferably not less than 150 C, more

preferably not less than 2500 C, and even more preferably not less than 3500 C.

[0033]

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.

[0034]

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 12000 C, and the coke oven may be operated at

a temperature at or above 1200 0 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 13000 C.

[00351

Coal that has been subjected to a heat treatment at

about 600 0 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.

[00361

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 a mixed solution of hydrogen peroxide and acetic anhydride 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

°C/min.

[0037]

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.

[0038]

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.

[00391

The temperature of a hydrogen peroxide solution is

preferably not more than 50 0 C and more preferably not more

than 400 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.

[00401

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.

[00411

[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.

[0042]

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 anhydride storage tank 3 for storing acetic anhydride.

The hydrogen peroxide inside the hydrogen peroxide

storage tank 1 is supplied to a chemical agent mixing tank

via a hydrogen peroxide transport pipe 2. The acetic

anhydride inside the acetic anhydride storage tank 3 is

supplied to the chemical agent mixing tank 5 via an acetic

anhydride transport pipe 4. The hydrogen peroxide transport

pipe 2 and the acetic anhydride 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 anhydride 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 anhydride 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

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")

[0043]

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 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.

[0044]

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 16a, a heat treatment device

connection pipe 16b and a hydrogen peroxide treatment

device connection pipe 16c.

The chemical-treated coal discharge pipe 16a

discharges the chemical-treated coal obtained in the

desulfurization treatment tank 9 without performing the

secondary treatment. The heat treatment device connection pipe 16b transports the chemical-treated coal to a heat treatment device 17. The hydrogen peroxide treatment device connection pipe 16c transports the chemical-treated coal to a hydrogen peroxide treatment device 23.

[0045]

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.

[0046]

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 16c. 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.

[0047]

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.

[00481

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.

[0049]

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).

[0050]

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.

[EXAMPLES]

[00511

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.

[0052]

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 pm 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.

[00531

[Table 1]

Table 1 Industrial analysis value [mass% d.a.f.] Industrial analysis value [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

[0054]

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.

[0055]

Test conditions such as supply amounts (flow rates)

of coal, hydrogen peroxide and acetic anhydride are shown

in Table 2 below.

In Examples 1 to 7 and Comparative Example 1, 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 8 to 11, 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

0 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 12 to 16, 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.

[00561

In the primary treatment, an aqueous solution having

a concentration of hydrogen peroxide of 35 mass% was used

as hydrogen peroxide. As acetic anhydride, acetic anhydride

having a purity of 99 mass% was used.

[0057]

[Table 21

Ea.0 000 m E,-0o 000o 0 .00 00m c. ro .- 4C 6 ,4 N 0

U

0 0L 0 Lo n o N Ln m0A m in 00 Ln N n C 0 rTh 0 - ooU n N L ~0 0 Lfl 0 0 0 N N 0D a%

a- ~0 o 0 f0 ON N 'f

E NkD inm' n 0) Un in N 0 LU roC, Ln 0 .i n o0 co 0 0 O0 Lf 0 L oNro N iD 0)fl

000 f 2- LN" L n mr n 0 0 N 0 i 0 CND ND" f tD qn in n 000 0 LO1II

L-4n mj F-j i 1

0 C, CD 0 m 0 0N N 0 10 C)0 (ii Lii 0 ,-4n 0- U- ) Ln L 0 Lii 0 E-0 x C CD00) 0 O r 0 0) Loi 0 0N N 0 Ott CD 2 Wu ,0 CD 4 N C:> tinj r, 0 10

0 l 00 0 0 0 ~C 00> in ON c NI %DI C, 0 ci '-I N, LI m uD m4

0 O0 ND ODi 2 0 nI N 0 0 0~ ;1ui 0 0N 0 mi m mo Ui 10

o 0 0O~ 0 i CY C) 0

0~~1 C>00 0, ,N Nt 0

cs 6 C - a,,,

I= ' 0 0 i ON 0 N C: N- m-- ;1 (5)

0U 0 oiln 0 OND N C)CD r -4.1 N Lfi ti5 i-n 0

r, EC) 0 C:> 01 In I

n 10 Eo* 1 C:)~ ~ 0n0

E.- c CID(A n m Co C D u -n ID I E E E Ew E E E E

~ ~0* 1 IDDEDI a)0 -U -0 E0 -2 c~ c cl 2 ~ ~UC C0 3 0 CX X 0 (1 0) (10 >< c E~U~ I Cwn InO. 4E E In- j, u E 2-' 2 -2 (

2W . -0 g.I 1F 3 00 c 2 -F -Fo -Fa E c)- -r >m '

m 2cIO 0 00mc E a)N r 0 o 0 0-02 - c u u u E a ') cID 0 0 0)~~ ~ a)' CEID2-

-uu >r C Ef U LA a) V)~ 0 0 0 a

=IDa) - o = Z C 2 .

[00581

It was revealed that Examples 1 to 16 using a mixed

solution of hydrogen peroxide and acetic anhydride as a

chemical agent exhibited a higher desulfurization rate than

that of Comparative Example 1 in which such a solution was

not used, thus having a sufficient desulfurization effect.

The carbon yield was also good.

[0059]

The comparison between Example 1 and Example 4

revealed that Example 1 in which a molar ratio (acetic

anhydride/hydrogen peroxide) was 5.0 had a higher

desulfurization rate than that of Example 4 in which a

molar ratio (acetic anhydride/hydrogen peroxide) was 0.4,

thus having a more excellent desulfurization effect.

[0060]

The comparison between Example 1 and Example 5

revealed that Example 1 in which the elapsed time after

mixing of acetic anhydride and hydrogen peroxide was 30

minutes had a higher desulfurization rate than that of

Example 5 in which the time was 8 minutes, thus having a

more excellent desulfurization effect.

[0061]

The comparison between Example 1 and Example 6 revealed that Example 1 in which the mass ratio (chemical agent/coal) was 3.2 had a higher desulfurization rate than that of Example 6 in which the mass ratio (chemical agent/coal) was 0.9, thus having a more excellent desulfurization effect.

[00621

The comparison between Example 1 and Example 7

revealed that Example 1 in which the temperature of the

chemical agent at the time of being brought into contact

with coal was 20 0 C had a better carbon yield than that of

0 Example 7 in which the temperature was 35 C.

[0063]

The desulfurization rates (after the secondary

treatment) of Examples 8 to 11 were equal to or higher than

the desulfurization rates (after the primary treatment) of

Examples 1 to 7.

The comparison between Example 8 and Example 10

revealed that Example 8 in which the heat treatment

temperature was 150 0C had a higher desulfurization rate

(after the secondary treatment) than that of Example 10 in

which the heat treatment temperature was 100 0 C, thus having

a more excellent desulfurization effect.

The comparison between Example 8 and Example 11

revealed that Example 8 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 11 in

which the heating rate was 5°C/min, thus having a more

excellent desulfurization effect.

[0064]

The desulfurization rates (after the secondary

treatment) of Examples 12 to 16 were equal to or higher

than the desulfurization rates (after the primary

treatment) of Examples 1 to 7.

The comparison between Example 12 and Example 14

revealed that Example 12 in which the temperature of the

hydrogen peroxide solution was 20 0C had a higher

desulfurization rate (after the secondary treatment) than

that of Example 14 in which the temperature was 45 0 C, thus

having a more excellent desulfurization effect.

The comparison between Example 12 and Example 15

revealed that Example 12 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 15 in which the concentration was 1.5

mass%, thus having a more excellent desulfurization effect.

The comparison between Example 12 and Example 16

revealed that Example 12 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 16 in which a mass ratio (hydrogen peroxide solution/coal) was 0.9, thus having a more excellent desulfurization effect.

REFERENCE SIGNS LIST

[0065]

1: Hydrogen peroxide storage tank

2: Hydrogen peroxide transport pipe

3: Acetic anhydride storage tank

4: Acetic anhydride 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

16a: Chemical-treated coal discharge pipe

16b: Heat treatment device connection pipe

16c: 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

[0066] The reference in this specification to any prior

publication (or information derived from it), or to any

matter which is known, is not, and should not be taken as

an acknowledgment or admission or any form of suggestion

that that prior publication (or information derived from

it) or known matter forms part of the common general

knowledge in the field of endeavour to which this

specification relates.

38a

[0067] Throughout this specification and the claims which

follow, unless the context requires otherwise, the word

"comprise", and variations such as "comprises" and

"comprising", will be understood to imply the inclusion of

a stated integer or step or group of integers or steps but

not the exclusion of any other integer or step or group of

integers or steps.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS

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

anhydride to thereby remove sulfur in the coal.

2. The low-sulfur coal production method according to

claim 1, wherein a molar ratio between the acetic anhydride

and the hydrogen peroxide (acetic anhydride/hydrogen

peroxide) is not less than 0.5 and not more than 12.0.

3. The low-sulfur coal production method according to

claim 1 or 2, wherein the acetic anhydride and the hydrogen

peroxide are mixed before the chemical agent is brought

into contact with the coal, and

wherein when 10 minutes or more have elapsed after

the acetic anhydride and the hydrogen peroxide are mixed,

the chemical agent is brought into contact with the coal.

4. The low-sulfur coal production method according to

any one of claims 1 to 3, wherein a mass ratio between the

chemical agent and the coal (chemical agent/coal) is not

less than 1.0.

5. The low-sulfur coal production method according to

any one of claims 1 to 4, wherein a temperature of the

chemical agent at a time of being brought into contact with

the coal is not less than 5°C.

6. The low-sulfur coal production method according to

any one of claims 1 to 5, wherein a temperature of the

chemical agent at a time of being brought into contact with

the coal is not more than 30°C.

7. The low-sulfur coal production method according to

any one of claims 1 to 6, wherein the coal comprises sub

bituminous coal.

8. The low-sulfur coal production method according to

any one of claims 1 to 7, 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

0 °C.

9. The low-sulfur coal production method according to

claim 8, 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

°C/min.

10. The low-sulfur coal production method according to

any one of claims 1 to 7, 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.

11. The low-sulfur coal production method according to

claim 10,

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.