U.S. patent application number 17/605950 was filed with the patent office on 2022-07-14 for low-sulfur coal production method.
This patent application is currently assigned to JFE STEEL CORPORATION. The applicant listed for this patent is JFE STEEL CORPORATION. Invention is credited to Takahiro KATO, Ryota MURAI, Katsuyasu SUGAWARA, Ikuhiro SUMI.
Application Number | 20220220404 17/605950 |
Document ID | / |
Family ID | 1000006299429 |
Filed Date | 2022-07-14 |
United States Patent
Application |
20220220404 |
Kind Code |
A1 |
MURAI; Ryota ; et
al. |
July 14, 2022 |
LOW-SULFUR COAL PRODUCTION METHOD
Abstract
A low-sulfur coal production method having an excellent
desulfurization effect includes 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 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.
Inventors: |
MURAI; Ryota; (Tokyo,
JP) ; SUMI; Ikuhiro; (Tokyo, JP) ; SUGAWARA;
Katsuyasu; (Akita-shi, JP) ; KATO; Takahiro;
(Akita-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
JFE STEEL CORPORATION |
Tokyo |
|
JP |
|
|
Assignee: |
JFE STEEL CORPORATION
Tokyo
JP
|
Family ID: |
1000006299429 |
Appl. No.: |
17/605950 |
Filed: |
April 20, 2020 |
PCT Filed: |
April 20, 2020 |
PCT NO: |
PCT/JP2020/017074 |
371 Date: |
October 22, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C10L 9/06 20130101; C10L
2200/0263 20130101; C10L 2290/544 20130101 |
International
Class: |
C10L 9/06 20060101
C10L009/06 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 24, 2019 |
JP |
2019-082750 |
Claims
1.-11. (canceled)
12. 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, 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, 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.
13. The low-sulfur coal production method according to claim 12,
wherein a mass ratio between the chemical agent and the coal
(chemical agent/coal) is not less than 1.0, and wherein a
temperature of the chemical agent at a time of being brought into
contact with the coal is not less than 5.degree. C. but not more
than 30.degree. C.
14. The low-sulfur coal production method according to claim 12,
wherein the coal comprises sub-bituminous coal.
15. The low-sulfur coal production method according to claim 13,
wherein the coal comprises sub-bituminous coal.
16. The low-sulfur coal production method according to claim 12,
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.degree. C., and 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.degree. C./min.
17. The low-sulfur coal production method according to claim 13,
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.degree. C., and 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.degree. C./min.
18. The low-sulfur coal production method according to claim 14,
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.degree. C., and 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.degree. C./min.
19. The low-sulfur coal production method according to claim 15,
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.degree. C., and 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.degree. C./min.
20. The low-sulfur coal production method according to claim 12,
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.degree. 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.
21. The low-sulfur coal production method according to claim 13,
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.degree. 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.
22. The low-sulfur coal production method according to claim 14,
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.degree. 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.
23. The low-sulfur coal production method according to claim 15,
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.degree. 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.
Description
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.
[0003] 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.
[0004] From such background, the industrial value is high if sulfur
(sulfur content) in coal can be removed before the coal is
used.
[0005] 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
[0006] Patent Literature 1: JP 3-275795 A
SUMMARY OF INVENTION
Technical Problems
[0007] In producing low-sulfur coal by desulfurizing coal (removing
sulfur in coal), the conventional method had an insufficient
desulfurization effect in some cases.
[0008] An object of the present invention is therefore to provide a
low-sulfur coal production method having an excellent
desulfurization effect.
Solution to Problems
[0009] 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.
[0010] Specifically, the present invention provides the following
[1] to [11].
[0011] [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.
[0012] [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.
[0013] [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
[0014] 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.
[0015] [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.
[0016] [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.degree. C.
[0017] [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.degree. C.
[0018] [7] The low-sulfur coal production method according to any
one of [1] to [6] above, wherein the coal comprises sub-bituminous
coal.
[0019] [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 150.degree. C.
[0020] [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 10.degree. C./min.
[0021] [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.degree. C.
[0022] [11] The low-sulfur coal production method according to [10]
above,
[0023] wherein a concentration of the hydrogen peroxide solution is
not less than 2.0 mass %, and
[0024] 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
[0025] The present invention can provide a low-sulfur coal
production method having an excellent desulfurization effect.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a graph showing a desulfurization rate with
respect to a mass ratio between a chemical agent and coal (chemical
agent/coal).
[0027] 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.
[0028] 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]
[0029] 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.
<Primary Treatment (Chemical Treatment)>
[0030] 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.
[0031] Sulfur in coal is roughly classified into inorganic sulfur
(inorganic sulfur content) and organic sulfur (organic sulfur
content).
[0032] A typical example of inorganic sulfur is FeS.sub.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.
[0033] 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.
[0034] 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.
[0035] A reaction of hydrogen peroxide (H.sub.2O.sub.2) and acetic
anhydride ((CH.sub.3CO).sub.2O) to obtain peracetic acid
(CH.sub.3COO.sub.2H) and water (H.sub.2O) is represented by Formula
(I) below.
2H.sub.2O.sub.2+(CH.sub.3CO).sub.2O.revreaction.2CH.sub.3COO.sub.2H+H.su-
b.2O (I)
[0036] 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.
[0037] 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).
<<Molar Ratio (Acetic Anhydride/Hydrogen
Peroxide)>>
[0038] 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.
[0039] 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).
[0040] 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.
[0041] The molar ratio (acetic anhydride/hydrogen peroxide) is
calculated as follows.
[0042] 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.times.Ci)/(100.times.Mi) (a)
Molar ratio=(L1.times.C1.times.M2)/(L2.times.C2.times.M1) (b)
[0043] Li: amount of i aqueous solution [g/h]
[0044] Ci: concentration of i aqueous solution [mass %]
[0045] Mi: molecular weight of i [g/mol]
[0046] Here, i is 1 or 2, 1 is acetic anhydride and 2 is hydrogen
peroxide.
[0047] 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.
<<Elapsed Time after Mixing>>
[0048] 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.
[0049] 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.
[0050] 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 10 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.
[0051] The elapsed time after mixing is more preferably not less
than 20 minutes and even more preferably not less than 30 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.
<<Mass Ratio (Chemical Agent/Coal)>>
[0052] 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.
[0053] 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.
[0054] 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.
[0055] When a mass of coal (solid content) before desulfurization
is W.sub.1 [kg], a sulfur content of coal (solid content) before
desulfurization is % S.sub.1 [mass*], a mass of coal (solid
content) after desulfurization is W.sub.2 [kg], and a sulfur
content of coal (solid content) after desulfurization is % S.sub.2
[mass %], the desulfurization rate [mass %] is defined by Formula
(1) below.
Desulfurization rate[mass %]=100.times.{1-(W.sub.2.times.%
S.sub.2)/(W.sub.1.times.% S.sub.1)} (1)
<<Temperature of Chemical Agent>>
[0056] 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.
[0057] 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.
[0058] 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.degree. C., more preferably not less
than 10.degree. C., even more preferably not less than 20.degree.
C. and particularly preferably not less than 25.degree. C.
[0059] 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 40.degree. C., more
preferably not more than 35.degree. C. and even more preferably not
more than 30.degree. C. because the carbon yield can become more
excellent.
[0060] 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.times.(W.sub.2.times.%
C.sub.2)/(W.sub.1.times.% C.sub.1) (2)
[0061] The presumable reason why the carbon yield decreases is
described below.
[0062] 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.
[0063] 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>
[0064] 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.
[0065] 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.
[0066] 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.
[0067] The primary treatment (chemical treatment) for desulfurizing
coal was described above.
[0068] 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.
<Secondary Treatment (Heat Treatment)>
[0069] 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.degree. C.)
[0070] 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.degree. C., more preferably not less than 250.degree. C.,
and even more preferably not less than 350.degree. C.
[0071] 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.
[0072] 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.degree.
C., and the coke oven may be operated at a temperature at or above
1200.degree. 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.
[0073] 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.
[0074] Therefore, the heat treatment temperature is, for example,
not more than 1300.degree. C.
[0075] Coal that has been subjected to a heat treatment at about
600.degree. 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.
[0076] 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.degree. C./min and more preferably not less than 20.degree.
C./min.
[0077] 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.degree. C./min.
<Secondary Treatment (Hydrogen Peroxide Treatment)>
[0078] 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.
[0079] 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.
[0080] 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.
[0081] The temperature of a hydrogen peroxide solution is
preferably not more than 50.degree. C. and more preferably not more
than 40.degree. 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.
[0082] The lower limit thereof is not particularly limited, and the
temperature of a hydrogen peroxide solution is, for instance, not
less than 5.degree. C.
[0083] 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.
[0084] 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.
[0085] 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]
[0086] Next, an example in which the present invention is
implemented using a specific facility will be described with
reference to FIG. 3.
[0087] 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").
[0088] 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.
[0089] 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 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.
[0090] 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.
[0091] 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.
[0092] 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.
[0093] 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.
[0094] 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")
[0095] 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.
[0096] 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.
[0097] 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.
[0098] 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.
[0099] First, the heat treatment device 17 will be described.
[0100] 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.
[0101] 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.
[0102] Next, the hydrogen peroxide treatment device 23 will be
described.
[0103] 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).
[0104] 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.
[0105] 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.
[0106] 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.
[0107] The hydrogen peroxide treatment device 23 is provided with
discharge holes at two places.
[0108] 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.
[0109] 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.
[0110] 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.
[0111] 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).
[0112] 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
[0113] 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 16 and Comparative Example 1
[0114] 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.
[0115] 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 .mu.m 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-US-00001 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
[0116] 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.
[0117] "d.b." means an analysis value on a dry basis.
[0118] "V.M" means a content of volatile matter in industrial
analysis.
[0119] "Ash" means a content of ash in industrial analysis.
[0120] Test conditions such as supply amounts (flow rates) of coal,
hydrogen peroxide and acetic anhydride are shown in Table 2
below.
[0121] 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.
[0122] 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 capable of raising the temperature
to 1200.degree. 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.
[0123] 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.
[0124] 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.
TABLE-US-00002 TABLE 2 Example Example Unit 1 2 3 4 5 6 7 8 9 Coal
Coal A g/h 100 50 0 100 100 100 100 100 100 Coal B g/h 0 50 0 0 0 0
0 0 0 Coal C g/h 0 0 100 0 0 0 0 0 0 Total amount g/h 100 100 100
100 100 100 100 100 100 Chemical Hydrogen peroxide g/h 50 100 50 95
50 20 240 50 50 agent and Acetic anhydride g/h 265 55 265 40 350 70
60 265 265 primary Molar ratio mol/mol 5.0 0.5 5.0 0.4 6.6 3.3 0.2
5.0 5.0 treatment (acetic anhydride/ (chemical hydrogen peroxide)
treatment) Elapsed time after min 30 60 30 30 8 30 30 30 30 mixing
Mass ratio (chemical g/g 3.2 1.6 3.2 1.4 4.0 0.9 3.0 3.2 3.2
agent/coal) Chemical agent .degree. C. 20 22 20 20 17 20 35 20 20
temperature Desulfurization rate mass % 52 51 50 48 51 45 58 52 52
(after primary treatment) Carbon yield mass % 96 93 97 96 94 96 90
96 96 (after primary treatment) Secondary Heat treatment .degree.
C. -- -- -- -- -- -- -- 150 1200 treatment temperature (heat
Heating rate .degree. C./min -- -- -- -- -- -- -- 20 25 treatment)
Desulfurization rate mass % -- -- -- -- -- -- -- 65 68 (after
secondary treatment) Carbon yield mass % -- -- -- -- -- -- -- 95 94
(after secondary treatment) Secondary Temperature of .degree. C. --
-- -- -- -- -- -- -- -- treatment hydrogen peroxide (hydrogen
solution peroxide Concentration of mass % -- -- -- -- -- -- -- --
-- treatment) hydrogen peroxide solution Mass ratio (hydrogen g/g
-- -- -- -- -- -- -- -- -- peroxide solution/coal) Desulfurization
rate mass % -- -- -- -- -- -- -- -- -- (after secondary treatment)
Carbon yield mass % -- -- -- -- -- -- -- -- -- (after secondary
treatment) Comparative Example Example Example Unit 10 11 12 13 14
15 16 1 Coal Coal A g/h 100 100 100 100 100 100 100 100 Coal B g/h
0 0 0 0 0 0 0 0 Coal C g/h 0 0 0 0 0 0 0 0 Total amount g/h 100 100
100 100 100 100 100 100 Chemical Hydrogen peroxide g/h 50 50 50 50
50 50 50 300 agent and Acetic anhydride g/h 265 265 265 265 265 265
265 0 primary Molar ratio mol/mol 5.0 5.0 5.0 5.0 5.0 5.0 5.0 0.0
treatment (acetic anhydride/ (chemical hydrogen peroxide)
treatment) Elapsed time after min 30 30 30 30 30 30 30 -- mixing
Mass ratio (chemical g/g 3.2 3.2 3.2 3.2 3.2. 3.2 3.2 3.0
agent/coal) Chemical agent .degree. C. 20 20 20 20 20 20 20 20
temperature Desulfurization rate mass % 52 52 52 52 52 52 52 2.8
(after primary treatment) Carbon yield mass % 96 96 96 96 96 96 96
96 (after primary treatment) Secondary Heat treatment .degree. C.
100 150 -- -- -- -- -- -- treatment temperature (heat Heating rate
.degree. C./min 10 5 -- -- -- -- -- -- treatment) Desulfurization
rate mass % 53 61 -- -- -- -- -- -- (after secondary treatment)
Carbon yield mass % 95 95 -- -- -- -- -- -- (after secondary
treatment) Secondary Temperature of .degree. C. -- -- 20 40 45 30
30 -- treatment hydrogen peroxide (hydrogen solution peroxide
Concentration of mass % -- -- 35.0 35.0 5.0 1.5 3.0 -- treatment)
hydrogen peroxide solution Mass ratio (hydrogen g/g -- -- 2.5 2.5
2.5 2.5 0.9 -- peroxide solution/coal) Desulfurization rate mass %
-- -- 65 66 55 62 63 -- (after secondary treatment) Carbon yield
mass % -- -- 95 93 71 95 95 -- (after secondary treatment)
<Summary of Test Results>
[0125] 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.
[0126] 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.
[0127] 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.
[0128] 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.
[0129] 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.degree. C. had
a better carbon yield than that of Example 7 in which the
temperature was 35.degree. C.
[0130] 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.
[0131] The comparison between Example 8 and Example 10 revealed
that Example 8 in which the heat treatment temperature was
150.degree. C. had a higher desulfurization rate (after the
secondary treatment) than that of Example 10 in which the heat
treatment temperature was 100.degree. C., thus having a more
excellent desulfurization effect.
[0132] 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.degree. C./min
had a higher desulfurization rate (after the secondary treatment)
than that of Example 11 in which the heating rate was 5.degree.
C./min, thus having a more excellent desulfurization effect.
[0133] 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.
[0134] The comparison between Example 12 and Example 14 revealed
that Example 12 in which the temperature of the hydrogen peroxide
solution was 20.degree. C. had a higher desulfurization rate (after
the secondary treatment) than that of Example 14 in which the
temperature was 45.degree. C., thus having a more excellent
desulfurization effect.
[0135] 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.
[0136] 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
[0137] 1: Hydrogen peroxide storage tank [0138] 2: Hydrogen
peroxide transport pipe [0139] 3: Acetic anhydride storage tank
[0140] 4: Acetic anhydride transport pipe [0141] 5: Chemical agent
mixing tank [0142] 6: Heating device [0143] 7: Mixing device [0144]
8: Chemical agent transport pipe [0145] 9: Desulfurization
treatment tank [0146] 10: Coal storage tank [0147] 11: Coal
transport pipe [0148] 12: Heating device [0149] 13: Mixing device
[0150] 14: Chemical agent circulation pipe [0151] 15: Chemical
agent discharge pipe [0152] 16: Chemical-treated coal transport
pipe [0153] 16a: Chemical-treated coal discharge pipe [0154] 16b:
Heat treatment device connection pipe [0155] 16c: Hydrogen peroxide
treatment device connection pipe [0156] 17: Heat treatment device
[0157] 18: Heat-treated coal discharge pipe [0158] 19: Heat
treatment gas exhaust pipe [0159] 20: Hydrogen peroxide supply pipe
[0160] 21: Dilution water tank [0161] 22: Dilution water supply
pipe [0162] 23: Hydrogen peroxide treatment device [0163] 24:
Cooling device [0164] 25: Mixing device [0165] 26: Discharge pipe
[0166] 27: Hydrogen peroxide circulation pipe [0167] 28: Hydrogen
peroxide discharge pipe
* * * * *