U.S. patent application number 12/734025 was filed with the patent office on 2010-08-19 for apparatus for producing gas hydrate pellet and process for producing gas hydrate pellet with the same.
Invention is credited to Toru Iwasaki, Kenji Ogawa, Kiyoaki Suganoya, Toshio Yamaki.
Application Number | 20100205859 12/734025 |
Document ID | / |
Family ID | 40549000 |
Filed Date | 2010-08-19 |
United States Patent
Application |
20100205859 |
Kind Code |
A1 |
Iwasaki; Toru ; et
al. |
August 19, 2010 |
APPARATUS FOR PRODUCING GAS HYDRATE PELLET AND PROCESS FOR
PRODUCING GAS HYDRATE PELLET WITH THE SAME
Abstract
In producing gas hydrate pellets by compression-molding a gas
hydrate powder, heat generated in a compressing part is removed
with a simple method so as to reduce the degree of gas hydrate
decomposition, and a gas hydrate aggregate blocking the compressing
part is promptly and easily removed. A gas-hydrate-pellet
production apparatus A is characterized by including: a
roll-cooling mechanism which causes cooling water to flow through
outer peripheral portions and/or insides of rolls 6a and 6b,
thereby cooling the rolls 6a and 6b, and also cools the cooling
water 43 discharged after the flow and supplies the cooled cooling
water 43 to the outer peripheral portion and/or the inner portion
of each of the rolls 6a and 6b; and/or heating means provided in a
part of a hopper chamber 5 from which the gas hydrate powder n is
fed to the rolls 6a and 6b.
Inventors: |
Iwasaki; Toru; (Chiba-ken,
JP) ; Yamaki; Toshio; (Chiba-ken, JP) ;
Suganoya; Kiyoaki; (Okayama-ken, JP) ; Ogawa;
Kenji; (Tokyo, JP) |
Correspondence
Address: |
JACOBSON HOLMAN PLLC
400 SEVENTH STREET N.W., SUITE 600
WASHINGTON
DC
20004
US
|
Family ID: |
40549000 |
Appl. No.: |
12/734025 |
Filed: |
October 10, 2007 |
PCT Filed: |
October 10, 2007 |
PCT NO: |
PCT/JP2007/069765 |
371 Date: |
April 6, 2010 |
Current U.S.
Class: |
44/500 ;
425/115 |
Current CPC
Class: |
C10L 3/108 20130101;
C10L 3/10 20130101; C10L 5/363 20130101 |
Class at
Publication: |
44/500 ;
425/115 |
International
Class: |
C10L 5/00 20060101
C10L005/00; C10L 3/06 20060101 C10L003/06 |
Claims
1. An apparatus for producing gas hydrate pellets which
compression-molds a powdery gas hydrate powder into gas hydrate
pellets of a substantially spherical shape or the like, the gas
hydrate powder being generated by contacting and reacting a
raw-material gas and raw-material water with each other, the
production apparatus characterized by comprising: a hopper chamber
which houses the gas hydrate powder; a pair of compression rolls
which are disposed below an opening portion of the hopper chamber;
and a push-in device which feeds the gas hydrate powder in the
hopper chamber to the compression rolls, the apparatus
characterized in that heating means is provided on at least one
side of the hopper chamber.
2. The apparatus for producing gas hydrate pellets according to
claim 1, wherein the heating means supplies hot water to the pair
of compression rolls from a lower portion of the at least one side
of the hopper chamber, and discharges the water from a lower
portion of another side thereof.
3. The apparatus for producing gas hydrate pellets according to
claim 1, wherein a nozzle for jetting any one of the hot water and
water is provided in the lower portion of the at least one side of
the hopper chamber.
4. A roll-type gas-hydrate-pellet production apparatus which
compression-molds a gas hydrate powder to produce gas hydrate
pellets, the gas hydrate powder being generated by contacting and
reacting a raw-material gas and raw-material water with each other,
the gas-hydrate-pellet production apparatus comprising: a hopper
chamber which houses the gas hydrate powder; a pair of compression
rolls which are disposed below an opening portion of the hopper
chamber; and a push-in device which supplies the gas hydrate powder
in the hopper chamber to the compression rolls, the
gas-hydrate-pellet production apparatus further comprising a
roll-cooling mechanism which causes cooling water to flow through
an outer peripheral portion and/or an inside of each roll so as to
cool the roll, and which cools the cooling water discharged after
the flow by use of a cooler.
5. The apparatus for producing gas hydrate pellets according to
claim 1, the production apparatus comprising a roll-cooling
mechanism which causes cooling water to flow through an outer
peripheral portion and/or an inside of each roll so as to cool the
roll, and which cools the cooling water discharged after the flow
by use of a cooler.
6. A process for producing gas hydrate pellets by contacting and
reacting a raw-material gas and raw-material water with each other
so as to generate a gas hydrate powder, and by compression-molding
the gas hydrate powder with a roll-type gas-hydrate-pellet
production apparatus, the process comprising: causing cooling water
to flow through an outer peripheral portion and/or an inside of a
roll of the gas-hydrate-pellet production apparatus so as to cool
the roll; cooling the cooling water discharged after the flow by
use of a cooler; and supplying the cooled cooling water to the
outer peripheral portion and/or the inner portion of the roll.
7. The process for producing gas hydrate pellets according to claim
6, wherein the cooling water is supplied to a hopper chamber from
which the gas hydrate powder is fed to the roll, the cooling water
is thereby brought into contact with the outer peripheral portion
of the roll, and the cooling water is discharged from a
cooling-water outlet of the hopper chamber.
8. The process for producing gas hydrate pellets according to claim
6, wherein a cooling bath is disposed below the roll, the cooling
water is supplied to the cooling bath, and the cooling water is
brought into contact with the outer peripheral portion of the
roll.
9. The process for producing gas hydrate pellets according to claim
6, wherein the cooling water is supplied to a cooling-water jacket
provided inside the roll so as to cool the roll.
10. The process for producing gas hydrate pellets according to
claim 6, wherein the temperature difference T-T.sub.0 between the
temperature T of the gas hydrate pellets and the temperature
T.sub.0 of the gas hydrate powder is set to be below 3.degree.
C.
11. The process for producing gas hydrate pellets according to
claim 6, wherein the amount of heat removed by the cooler is set to
be not less than the amount of heat Q1 obtained by the following
expression (I): Q1=(T-T.sub.0)cM+qM.beta./100 (I), (in the
expression (I), Q1 is the amount of heat [w] which the gas hydrate
powder receives in the pelletization, c is the specific heat
[kJ/kgK], q is the decomposition heat [kJ/kg], M is the
pelletization speed [kg/s] for the gas hydrate powder, and .beta.
is the degree of decomposition [%] in the pelletization of the gas
hydrate powder).
Description
TECHNICAL FIELD
[0001] The present invention relates to an apparatus for producing
gas hydrate pellets and a process for producing gas hydrate pellets
with the same. More specifically, the present invention relates to:
an apparatus for producing gas hydrate pellets that is designed to
promptly remove a blockage formed of a gas hydrate aggregate
generated between rolls used for compression molding; an apparatus
for producing gas hydrate pellets that is designed to reduce the
degree of decomposition in pelletizing a gas hydrate powder; and a
process for producing gas hydrate pellets with the same.
BACKGROUND ART
[0002] In these days, natural gases, which are mainly composed of
methane, propane, and the like, have attracted attention as clean
energy sources. Such natural gases are liquefied into liquefied
natural gases (LNGs) for the transportation and storage of the
natural gases. However, the transportation and storage of gases in
the form of LNGs need to be conducted under very low temperature
conditions (at -162.degree. C. or below); accordingly, the
transport system and the storage system therefor are expensive.
[0003] A gas hydrate is an ice-like solid substance composed of
water molecules and raw-material gas molecules, and is a kind of
stable clathrate compound in which the raw-material gas molecule is
included inside a three-dimensional cage-like structure formed of
the water molecules. The gas hydrate has a relatively large gas
content and has characteristic properties such as large
generation/decomposition energies and a high selectivity of gas to
be hydrated. For these reasons, the gas hydrates have a variety of
possible applications including transportation/storage means for
natural gases and the like, heat storage systems, actuators,
separation and recovery of specific component gases, for example,
and have been actively studied.
[0004] Gas hydrates are generally generated under high pressure and
low temperature conditions. As generating means for gas hydrates, a
so-called "water spray system" and a so-called "bubbling system"
are known, for example. In the water spray system, cooled
raw-material water is sprayed within a generating vessel that is
filled with a raw-material gas at a high pressure from the top
thereof, whereby gas hydrates are generated in the surfaces of
water droplets while the water droplets are falling down in the
raw-material gas. In the bubbling system, a raw-material gas is
introduced as bubbles (is bubbled) into raw-material water, whereby
gas hydrates are generated in the surfaces of the bubbles of the
raw-material gas while the bubbles are rising in the water.
[0005] The gas hydrate thus produced is in the form of a so-called
powder like a powder snow or a crushed ice. The gas hydrate powder
has been proposed to be transported and stored while being
maintained at a temperature (for example, approximately -20.degree.
C.) at which the gas hydrate effects the self-preservation. The
filling fraction of the gas hydrate powder in a storage tank ((the
volume of the gas hydrate powder)/(the volume of the container)) is
small. For this reason, the transportation or storage of the gas
hydrate powder require a tank or the like having a large volume.
Moreover, there is a problem in that the gas hydrate powder has a
large surface area because of its powder form, and thus is
decomposed into the natural gas and water at a very high
decomposition rate. There is also a problem in that, if a large
amount of the gas hydrate powder is stored, lower part of the
powder is hardened into a bedrock-like form, thus becoming
difficult to take out.
[0006] In this regard, the present inventors have proposed so far a
technique in which the powdery gas hydrate powder is
compression-molded into a product in the form of pellets of a
substantially spherical shape or the like by using a molding
apparatus, and then the gas hydrate pellets are transported or
stored (refer to, for example, Patent Document 1).
[0007] An apparatus F for producing gas hydrate pellets of this
technique is configured as follows, as illustrated in FIG. 8. A gas
hydrate powder n supplied into a hopper chamber 30 is fed to a pair
of rolls 33a and 33b having facing pockets 34 (molding concave
portions). The gas hydrate powder n filled in the pockets 34 is
then compressed and molded along with the rotations of the rolls
33a and 33b. In addition, a screw-type push-in device 31 for
filling the gas hydrate powder n into the pockets 34 is disposed in
the hopper chamber 30, and the gas hydrate powder receives, in
addition to its own weight, a predetermined pressure applied by the
push-in device 31.
[0008] Meanwhile, according to the observation of the inventors, it
has been found that, in the above-described production apparatus F,
water may exude from the snow-powder-form gas hydrate powder n if
the compression molding is conducted under conditions similar to
those for generating the powder n (for example, approximately at 4
to 6 MPa and 2 to 5.degree. C.). The following facts have also been
found: since having a specific gravity smaller than that of water,
the gas hydrate powder n has a nature to float up as the exuding
water is accumulated in the hopper chamber 30; and the higher the
molding pressure, the larger the amount of water to exude.
[0009] In the compression molding with the production apparatus F
using the gas hydrate powder n as a raw material, pellets p can be
steadily produced in the initial stage of the operation because no
exuding water has been accumulated. However, since the gas hydrate
that has been pressed and consolidated is filled in a gap between
the rolls 33a and 33b, water squeezed out by the rolls 33a and 33b
(squeezed water) is not discharged through the gap but accumulated
in the hopper chamber 30.
[0010] As the operation continues in such a state, the water level
keeps rising in the hopper chamber 30. Buoyancy is provided to the
gas hydrate powder along with the rise of the water level.
Consequently, the gas hydrate powder n pushed in by the push-in
device 31 and the gas hydrate powder n floating up are successively
accumulated near the tip of the screw of the push-in device 31, and
are thus compressed into an aggregate.
[0011] Then, the powder n fed by the push-in device 31 causes the
aggregate having a substantially wedge-shaped cross section and
extending in the axial direction of the rolls 33a and 33b to grow
to be an aggregate b of a substantial size. The aggregate b acts
like a blockage in an opening portion 35 of the hopper chamber 30
and between the rolls 33a and 33b, so that the gas hydrate powder n
cannot be fed to the rolls 33a and 33b, causing a problem in that
the gas hydrate pellets p cannot be produced.
[0012] Moreover, operating the production apparatus Fat normal
pressure (atmospheric pressure) also brings about a similar
problem. When the pressurizing force of the push-in device 31 is
increased for securing the filling into the pockets 34, the
particles of the powder n are fixed together to form the aggregate
b, eventually acting like a blockage.
[0013] Once the aggregate b is generated as described above, the
operation of the production apparatus F has to be interrupted for
removal of the gas hydrate aggregate b, requiring works such as
disassembly, reassembly, and adjustment of the apparatus F. As a
result, the operating efficiency of the gas-hydrate-powder
production apparatus is significantly deteriorated. In particular,
when the production apparatus F produces the gas hydrate pellets p
through compression molding in a high-pressure atmosphere (4 to 6
MPa) that is conditions similar to those for generating the gas
hydrate powder, the following problems occur. In this case, the
work for removing the gas hydrate aggregate b is extremely
difficult because the entire apparatus is accommodated in a robust
pressure-tight container having a thickness of 200 mm or more. It
takes a long time (for example, 24 hours) for the aggregate b to be
dissolved, and the production apparatus F has to stop the operation
for such a long time. Eventually, the production amount of the
production apparatus for the gas hydrate powder n, which is the raw
material, has to be considerably reduced, or the production has to
be stopped.
[0014] On the other hand, another problem would occur in
pelletizing a gas hydrate powder through compression molding.
Specifically, the surface temperature of the rotating rolls 33a and
33b increases accompanying the compression work in the
pelletization. If the surface temperature reaches the decomposition
temperature of the gas hydrate, the gas hydrate powder is
decomposed. For example, after a gas hydrate powder is generated
under conditions of a pressure of 5.4 MPa and a temperature of 2 to
3.degree. C., if the gas hydrate powder is continuously formed into
pellets through compression molding by using a rotating-roll-type
pelletizer, the surface temperature of the rolls increases. Then,
if the atmosphere reaches conditions of a pressure of 5.4 MPa and a
temperature of 8.degree. C., the gas hydrate is decomposed. The
decomposition of the gas hydrate reduces the concentration, in turn
causing a problem in that the advantages of the gas hydrate cannot
sufficiently be exerted.
[0015] As a countermeasure to this problem, the temperature of the
gas hydrate powder may be lowered in advance prior to the supply
thereof to the pelletizer. However, this approach requires another
cooling device to be disposed between the gas hydrate generator and
the pelletizer. Thus, there is a concern that the number of
manufacturing processes increases, leading to an increase in
producing cost.
[0016] Accordingly, no process for producing gas hydrate pellets
has been established yet, the process being capable of pelletizing
a gas hydrate powder while suppressing the decomposition of the
powder by a method that is simple and does not lead to a cost
increase.
Patent Document 1: Japanese patent application Kokai publication
No. 2002-220353
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0017] The present invention has been made for solving the
above-described problems. A first object of the present invention
is to provide an apparatus for producing gas hydrate pellets which
is designed to promptly melt a blockage formed of a gas hydrate
aggregate generated between rolls when gas hydrate pellets are
produced by compression-molding a gas hydrate powder by using a
rotating-roll-type pellet production apparatus. A second object
thereof is to provide: an apparatus for producing gas hydrate
pellets which is designed to reduce the degree of decomposition of
a gas hydrate by removing, with a simple method, heat generated in
a compressing part on a roll surface; and a process for producing
gas hydrate pellets with the same.
Means for Solving the Problems
[0018] An apparatus for producing gas hydrate pellets of a first
invention for achieving the above object is a production apparatus
which compression-molds a powdery gas hydrate powder into gas
hydrate pellets of a substantially spherical shape or the like, the
gas hydrate powder being generated by contacting and reacting a
raw-material gas and raw-material water with each other. The
production apparatus is characterized as follows. The production
apparatus includes: a hopper chamber which houses the gas hydrate
powder; a pair of compression rolls which are disposed below an
opening portion of the hopper chamber; and a push-in device which
feeds the gas hydrate powder in the hopper chamber to the
compression rolls. Heating means is provided on at least one side
of the hopper chamber.
[0019] The heating means preferably supplies hot water to the pair
of compression rolls from a lower portion of the at least one side
of the hopper chamber, and discharges the water from a lower
portion of another side thereof. Moreover, a nozzle for jetting the
hot water or water is preferably provided in the lower portion of
the at least one side of the hopper chamber.
[0020] An apparatus for producing gas hydrate pellets of a second
invention is a roll-type gas-hydrate-pellet production apparatus
which compression-molds a gas hydrate powder to produce gas hydrate
pellets, the gas hydrate powder being generated by contacting and
reacting a raw-material gas and raw-material water with each other.
The gas-hydrate-pellet production apparatus is characterized as
follows. The gas-hydrate-pellet production apparatus includes: a
hopper chamber which houses the gas hydrate powder; a pair of
compression rolls which are disposed below an opening portion of
the hopper chamber; and a push-in device which supplies the gas
hydrate powder in the hopper chamber to the compression rolls. The
gas-hydrate-pellet production apparatus further includes a
roll-cooling mechanism which causes cooling water to flow through
an outer peripheral portion and/or an inside of each roll so as to
cool the roll, and which cools the cooling water discharged after
the flow by use of a cooler.
[0021] Furthermore, the apparatus for producing gas hydrate pellets
of the first invention may include a roll-cooling mechanism which
causes cooling water to flow through an outer peripheral portion
and/or an inside of each roll so as to cool the roll, and which
cools the cooling water discharged after the flow by use of a
cooler.
[0022] A process for producing gas hydrate pellets of the present
invention is a process for producing gas hydrate pellets by
contacting and reacting a raw-material gas and raw-material water
with each other so as to generate a gas hydrate powder, and by
compression-molding the gas hydrate powder with a roll-type
gas-hydrate-pellet production apparatus. The process is
characterized by including: causing cooling water to flow through
an outer peripheral portion and/or an inside of a roll of the
gas-hydrate-pellet production apparatus so as to cool the roll;
cooling the cooling water discharged after the flow by use of a
cooler; and supplying the cooled cooling water to the outer
peripheral portion and/or the inner portion of the roll.
[0023] In the production process, preferably, the cooling water is
supplied to a hopper chamber from which the gas hydrate powder is
fed to the roll, the cooling water is thereby brought into contact
with the outer peripheral portion of the roll, and the cooling
water is discharged from a cooling-water outlet of the hopper
chamber. A cooling bath may be disposed below the roll. The cooling
water may be supplied to the cooling bath. The cooling water may be
brought into contact with the outer peripheral portion of the roll.
Additionally, the cooling water may be supplied to a cooling-water
jacket provided inside the roll so as to cool the roll.
[0024] The temperature difference T-T.sub.0 between the temperature
T of the gas hydrate pellets and the temperature T.sub.0 of the gas
hydrate powder is preferably set to be below 3.degree. C. The
amount of heat removed by the cooler is preferably set to be not
less than the amount of heat Q1 obtained by the following
expression (I):
Q1=(T-T.sub.0)cM+qM.beta./100 (I),
[0025] (in the expression (I), Q1 is the amount of heat [w] which
the gas hydrate powder receives in the pelletization, c is the
specific heat [kJ/kgK], q is the decomposition heat [kJ/kg], M is
the pelletization speed [kg/s] for the gas hydrate powder, and
.beta. is the degree of decomposition [%] in the pelletization of
the gas hydrate powder).
EFFECTS OF THE INVENTION
[0026] According to the apparatus for producing gas hydrate pellets
of the first invention, a substantially wedge-shaped aggregate
(blockage) of a gas hydrate powder, which is formed between the
compression rolls, is directly melted with the hot water, so that
the aggregate is melted at a high melting rate. Accordingly, the
time for which the pellet production is interrupted by the clogging
in the production apparatus is shortened. In particular, the
operation for removing a blockage is significantly improved in
producing pellets at a high pressure under conditions similar to
those for generating a gas hydrate powder. As a result, the
production amount of gas hydrate pellets is prevented from being
deteriorated.
[0027] Moreover, since the hot water or water is jetted, such hot
water or the like collides intensively against a gas hydrate
aggregate at a high pressure. Accordingly, the aggregate can be
further efficiently melted.
[0028] The apparatus for producing gas hydrate pellets of the
second invention includes the roll-cooling mechanism which causes
the cooling water to flow through the outer peripheral portion
and/or the inside of each roll so as to cool the rolls, which cools
the cooling water discharged after the flow by use of the cooler,
and which circulates the cooled cooling water so as to again flow
through the outer peripheral portion and/or the inside of the roll.
Accordingly, the temperatures of the gas hydrate and the roll
surfaces are prevented from reaching the decomposition temperature
of the gas hydrate. As a result, the degree of decomposition of the
gas hydrate can be reduced.
[0029] The process for producing gas hydrate pellets of the present
invention uses the roll-type gas-hydrate-pellet production
apparatus. In producing gas hydrate pellets by compression-molding
a gas hydrate powder, the cooling water is circulated to flow
through the outer peripheral portion and/or the inside of the roll
of the gas-hydrate-pellet production apparatus so as to cool the
roll surface. Accordingly, even when heat is generated by the
compression work in the pelletization of the gas hydrate powder,
the cooling water removes the heat, so that the temperatures of the
gas hydrate and the roll surfaces are prevented from reaching the
decomposition temperature of the gas hydrate. As a result, the
degree of decomposition of the gas hydrate can be reduced.
[0030] In addition, after the cooling water flows through the outer
peripheral portion and/or the inside of the roll so as to cool the
roll surface, the discharged cooling water is cooled to a
predetermined temperature, and then, is circulated again through
the outer peripheral portion and/or the inner portion of the roll.
This securely prevents the temperature of the roll surface from
increasing. Accordingly, it is possible to produce firmly compacted
gas hydrate pellets while removing generated heat and suppressing
an increase in production cost with a simple method.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] [FIG. 1] Part a of FIG. 1 and Part b of FIG. 1 are schematic
configuration views of an embodiment of an apparatus for producing
gas hydrate pellets of a first invention, and Part a of FIG. 1 is a
side view while Part b of FIG. 1 is a top view.
[0032] FIG. 2 is a perspective view of FIG. 1.
[0033] FIG. 3 is an explanatory view illustrating the overview of a
gas-hydrate-pellet production apparatus of a rotating roll type
that is an embodiment of an apparatus for producing gas hydrate
pellets of a second invention.
[0034] FIG. 4 is a block flow diagram showing an example of
processes in a process for producing gas hydrate pellets of the
present invention.
[0035] FIG. 5 is an explanatory view schematically showing an
example of processes according to a first embodiment of the
production process of the present invention.
[0036] FIG. 6 is an explanatory view schematically showing an
example of processes according to a second embodiment of the
production process of the present invention.
[0037] FIG. 7 is an explanatory view schematically showing an
example of processes according to a third embodiment of the
production process of the present invention.
[0038] FIG. 8 is a schematic configuration view of a conventional
apparatus for producing gas hydrate pellets.
EXPLANATION OF REFERENCE SIGNS
[0039] 1, 1a, 1b side plate [0040] 2 heat-transfer-medium line
[0041] 3 ejecting nozzle [0042] 4 water pipe (cooling-water outlet)
[0043] 5 hopper chamber [0044] 6a, 6b molding roll [0045] 7 pocket
[0046] 9a, 9b roll shaft [0047] 10a, 10b feeder base [0048] 12
push-in device [0049] 21 generator [0050] 22 gas-hydrate-pellet
production apparatus (pelletizer) [0051] 41, 42 cooling water
[0052] 43 discharged cooling water [0053] 57 cooler [0054] 58
cooling bath [0055] A production apparatus [0056] h1 hot water
[0057] h2 discharged water [0058] h3 squeezed water [0059] g
raw-material gas [0060] w raw-material water [0061] n gas hydrate
powder [0062] p gas hydrate pellets
BEST MODES FOR CARRYING OUT THE INVENTION
[0063] Hereinafter, an embodiment of a production apparatus A
according to a first invention will be described with reference to
FIG. 1 and FIG. 2.
[0064] As illustrated in Parts a and b of FIG. 1 as well as FIG. 2,
the production apparatus A includes: a hopper chamber 5 for storing
a gas hydrate powder n; a pair of compression rolls 6a and 6b
disposed below an opening portion 5a of the hopper chamber 5; and a
push-in device 12 for feeding the gas hydrate powder n in the
hopper chamber 5 to the compression rolls 6a and 6b. The hopper
chamber 5 is formed of: side plates 1a and 1b that are disposed on
side surfaces of the rolls 6a and 6b in such a way as to face each
other; and feeder bases 10a and 10b that are disposed to face each
other while being inclined to extend toward a gap between the roll
6a and the roll 6b. Note that the illustration of the screw-type
push-in device 12 disposed in the hopper chamber 5 is omitted in
Part b of FIG. 1 and FIG. 2.
[0065] Hot water h1 is supplied to the pair of compression rolls 6a
and 6b through a lower portion of the side plate 1a of the hopper
chamber 5, and is discharged through a lower portion of the other
side plate 1b. Further, nozzles 3 for ejecting the hot water are
provided to the lower portion of the side plate 1a.
[0066] As the hot water h1, water such as discharged water h2
discharged from a water pipe 4, squeezed water h3 from the gas
hydrate powder, or unreacted water in a gas-hydrate-powder
production apparatus; or water such as ion-exchange water or pure
water may be used with control of the temperature. The hot water h1
is maintained at a predetermined temperature (for example, in a
range of 60 to 80.degree. C.) in a thermostatic chamber (not
illustrated) formed of a temperature control unit, a transfer pump,
a water storage tank, and a heat exchanger. The hot water h1 is
supplied into the hopper chamber 5 through the nozzles 3 from
heat-transfer-medium lines, and the squeezed water h3 and the
discharged water h2 resulting from the supplied hot water are
circulated back to the thermostatic chamber through the water pipe
4.
[0067] In addition, the side plate 1a as well as the rolls 6a and
6b can be cooled by causing cooling water (for example, pure water
at approximately 1.degree. C.) to flow through the
heat-transfer-medium line 2 in the side plate 1a as necessary
during the compression molding of gas hydrate pellets p.
[0068] The compression production apparatus A for the gas hydrate
pellets p, which has the above-described structure, operates as
follows. The gas hydrate powder n supplied from the unillustrated
gas-hydrate-powder production apparatus is once retained in the
hopper chamber 5 under the conditions similar to those for
generating the gas hydrate powder (for example, approximately at 5
MPa and 3.degree. C.). Then, the powder n is fed to the pair of
rolls 6a and 6b disposed below the opening portion 5a of the hopper
chamber 5 by the action of the screw-type push-in device 12. The
gas hydrate powder n is securely filled in pockets 7 formed in the
rolls 6a and 6b, and is compressed along with the rotation of the
rolls 6a and 6b, so that the pellets p are produced.
[0069] In the compressing part between the rolls 6a and 6b, water
(unreacted water) contained in the gas hydrate powder n exudes out
as if being squeezed out. The squeezed water h3 is not discharged
to the outside through the gap between the rolls 6a and 6b because
the gas hydrate has been pressed and consolidated in the gap.
Instead, the squeezed water h3 is discharged all the time through
the water pipe 4 provided in the lower portion of the side plate 1b
of the hopper chamber 5.
[0070] When the pellets p are produced using the apparatus A, the
aforementioned substantially wedge-shaped aggregate b (blockage) is
generated in some cases between the rolls 6a and 6b and in the
opening portion 5a of the hopper chamber 5. Such generation of the
aggregate is caused due to variations in the pressing force of the
push-in device 12, the property of the gas hydrate powder n, which
is the raw material, and the like.
[0071] In such a case, the hot water h1 (for example, at 60.degree.
C.) is supplied from the thermostatic chamber into the hopper
chamber 5 through the heat-transfer-medium line 2 in the side plate
1a. The supply amount and temperature of the hot water h1 are
preferably adjusted as appropriate in accordance with the interior
size of the hopper chamber, the length of the rolls in the axial
direction thereof, the temperature of the gas hydrate powder to be
supplied, and the like.
[0072] With the supply of the hot water h1, the aggregate b
(blockage) of the gas hydrate powder receives the heat of the hot
water h1, and is thereby melted (decomposed) in a short time period
(for example, 3 to 6 minutes) while emitting a gas (a natural gas
such as methane or propane). Then, the hot water h1 which has given
the heat to the aggregate b (blockage) is discharged as the
discharged water h2 through the water pipe 4. The gas generated in
the melting of the aggregate b (blockage) is recovered through a
gas recovery conduit so as to be reused as a raw-material gas for
the gas-hydrate-powder production apparatus or the like.
[0073] The production apparatus A according to the first invention
significantly reduces the burden on the operation of removing the
substantially wedge-shaped aggregate (blockage) generated in the
hopper chamber 5 of the production apparatus, and also shortens the
time taken for the removal from several hours to several
minutes.
[0074] It should be noted that, although the configuration to
supply the hot water into the hopper chamber 5 has been described
in the embodiment illustrated in FIGS. 1 and 2, it is also possible
to cause a highly-pressurized jet flow to collide against the
aggregate b through the nozzle 3, and hot water or cool water (for
example, approximately at 1 to 4.degree. C.) may be used as the jet
flow.
[0075] Moreover, it is possible that a plurality of movable nozzles
are provided in the lower portions of the side plates 1a and 1b of
the hopper chamber 5, and thus a highly-pressurized jet flow is
caused to collide intensively against a predetermined part by these
movable nozzles. This configuration makes it possible to further
effectively dissolve the aggregate b.
[0076] Furthermore, in order to prevent the gas hydrate powder from
clogging the inside and the opening portion of the water pipe 4 on
the hopper chamber 5 side, a conduit may be provided through which
the hot water h1 is caused to flow in a side portion of the opening
portion in the side plate 1b and around the water pipe.
[0077] FIG. 3 is a perspective view illustrating an example of an
embodiment of a production apparatus of a second invention.
[0078] In FIG. 3, a production apparatus A is a rotating-roll-type
gas-hydrate-pellet production apparatus, and is a so-called
briquetting-roll-type gas-hydrate-pellet production apparatus
including a hopper chamber 5 above a pair of rotating rolls 6a and
6b. As has already been illustrated in Part a of FIG. 1, the hopper
chamber 5 includes a screw-type push-in device (not illustrated)
for pushing a gas hydrate powder to the rotating rolls with
increased pressure while the gas hydrate powder is supplied to the
inside of the hopper chamber 5. The gas hydrate powder is taken in
by pockets 7 formed in the roll surfaces of the rotating rolls 6a
and 6b, and is pelletized through compression molding between the
rolls. The shape of each pocket 7 is not particularly limited, and
preferably is a semi-spherical shape, a semi-oval shape, a
semi-columnar shape, a rectangular shape, an almond shape, or a
pillow shape. It is particularly preferable that the pockets 7 have
the semi-spherical shape, the pillow shape, or the semi-oval shape,
and are arranged in such a way that the longitudinal directions
thereof are substantially parallel to the circumferential
directions (rotating directions) of the rolls. This is because the
formed pellets are easily removed off the pockets 7, in other
words, provides a better releasability.
[0079] In the production apparatus A, the pressure to be applied
between the pair of rotating rolls 6a and 6b is preferably 5 MPa to
200 MPa. Compression-molding with a pressure within this range
enables the pelletization while suppressing the decomposition of
the gas hydrate powder as much as possible. On the other hand, the
amount of heat generated from the gas hydrate powder due to the
compression work and friction acting between the rotating rolls as
described above is approximately 1 kJ/kg to 100 kJ/kg. Along with
the heat generation, the temperature of the roll surfaces is
increased, in turn increasing also the temperatures of the gas
hydrate powder and the pellets, which are in contact with the roll
surfaces. If the temperature of the gas hydrate powder or the
pellets reaches the decomposition temperature of the gas hydrate,
part thereof is decomposed.
[0080] In the second invention, the production apparatus A includes
a roll-cooling mechanism. The roll-cooling mechanism cools the
rolls 6a and 6b by causing cooling water to flow through the outer
peripheral portions and/or the insides of the respective rolls 6a
and 6b. Accordingly, the temperatures of the gas hydrate and the
roll surfaces can be prevented from reaching the decomposition
temperature of the gas hydrate. As a result, the degree of gas
hydrate decomposition can be reduced. In addition, the roll-cooling
mechanism is configured as follows. The cooling water 43 that has
flowed through the outer peripheral portions and/or the insides of
the rolls is discharged from a cooling-water outlet 4 and recovered
to a cooling-water tank; thereafter, the cooling water 43 is cooled
and circulated again through the outer peripheral portions and/or
the inner portions of the rolls.
[0081] The roll-cooling mechanism may be installed in the
production apparatus of the aforementioned first invention. The
installation makes it possible to reduce the degree of gas hydrate
decomposition by removing, with a simple method, the heat generated
in the compressing part in producing the gas hydrate pellets by
compression-molding the gas hydrate powder. As a result,
high-quality gas hydrate pellets can be stably produced. In
addition, consider a case where an aggregate (blockage) of the gas
hydrate powder has been generated between the compression rolls due
to disturbance or the like. In this case, supplying hot water
instead of the cooling water makes it possible to promptly melt the
aggregate (blockage), to shorten the time for which the production
apparatus is stopped, and thus to prevent the production efficiency
of the gas hydrate pellets from being deteriorated.
[0082] FIG. 4 is a block flow diagram showing an example of
processes in a process for producing gas hydrate pellets of the
present invention. In FIG. 4, reference numeral 21 denotes a
generator; 22 denotes a gas-hydrate-pellet production apparatus
(hereinafter, sometimes called a "pelletizer"); 23 denotes a
chilling machine; 24 denotes a depressurizer; and 25 denotes a
storage tank. In the generator 21, a raw-material gas g and
raw-material water w are brought into contact with each other, so
that a powdery gas hydrate powder n is generated under
predetermined low-temperature, high-pressure conditions. The gas
hydrate powder n is supplied to the pelletizer 22, which thus
produces gas hydrate pellets p. The gas hydrate pellets p are
cooled to a further low temperature by the chilling machine 23.
After the high pressure is released by the depressurizer 24, the
gas hydrate pellets p are stored at a low temperature in the
storage tank 25. In addition, cooling water 41 is supplied to the
pelletizer 22 for cooling. Discharged cooling water 43 after the
cooling is cooled and circulated as cooling water 42. Moreover,
part of the discharged cooling water may be supplied to the
generator 21 as raw-material water 45.
[0083] The conditions for generating the gas hydrate powder n in
the generator 21 are given as follows. When methane hydrate is
taken as an example, what is generally required is a pressure
higher than or a temperature lower than a temperature/pressure
curve that connects points of 253 K/2 MPa, 273 K/3.5 MPa, and 284
K/8 MPa, of (generating temperature)/(generating pressure). By
contrast, if exposed to a pressure lower than or a temperature
higher than the temperature/pressure curve, the gas hydrate powder
is decomposed into the raw-material gas and water. The generator 21
may be formed of a single unit or a plurality of units. In
particular, it is preferable to increase the gas hydrate
concentration by using a generator formed of two units. In
addition, the generator may include dewatering means (not
illustrated) to increase the gas hydrate concentration.
[0084] The process for producing gas hydrate pellets of the present
invention includes cooling the rolls 6a and 6b by causing the
cooling water to flow through the outer peripheral portions and/or
the insides of the rolls. The cooling water set at a predetermined
temperature is brought into direct contact with the roll surfaces
and is further caused to coexist with the gas hydrate powder,
whereby the amount of heat generated by the compression work and
friction can be directly removed and the temperatures of the gas
hydrate and the roll surfaces are thus prevented from increasing.
Moreover, the cooling water is caused to flow in the insides of the
rolls and is further circulated, whereby the roll surfaces can be
set at a predetermined temperature without reduction of the cooling
water.
[0085] In the present invention, the cooling water that has flowed
through the outer peripheral portions and/or the insides of the
rolls is recovered to the cooling-water tank; thereafter, the
cooling water is cooled and is circulated again through the outer
peripheral portions and/or the inner portions of the rolls. The
cooling-water tank may be supplied with new water in addition to
the recovered cooling water. In addition, the water pooled in the
cooling-water tank may be not only used as the cooling water but
also supplied to the generator as the raw-material water of the gas
hydrate.
[0086] In a first embodiment of the production process of the
present invention, as illustrated in FIG. 5, a gas hydrate powder n
is fed to the rolls 6a and 6b from a hopper chamber 5, and is
formed into gas hydrate pellets p through compression molding,
which are transferred to the chilling machine 23 to be cooled. In
this event, the cooling water 42 is supplied to the hopper chamber
5, the cooling water is brought into contact with the outer
peripheral portions of the rolls 6a and 6b, and then, the
discharged cooling water 43 after the cooling process is discharged
through a cooling-water outlet 4 of the hopper chamber 5. In other
words, the cooling water 42 supplied to the hopper chamber 5 is
brought into contact with the outer peripheral portions of the
rolls, and thereby removes heat generated due to the compression
work and friction and cools the roll surfaces. Part of the cooling
water after the cooling process is consumed as a binder for the gas
hydrate powder n, and the rest thereof is discharged through the
cooling-water outlet 4 provided to the hopper chamber. The
discharged cooling water 43 is recovered to a cooling-water tank
55. The cooling-water tank 55 is supplied as necessary with the new
cooling water 41 and/or water that is obtained through dewatering
of the gas hydrate by the dewatering means of the generator, or the
like. With a pump 56, cooling water 44 pooled in the cooling-water
tank 55 is cooled to a predetermined temperature by a cooler 57 and
is circulated as the cooling water 42 to the hopper chamber 5. Note
that, part of the cooling water 44 may be supplied to the generator
as the raw-material water 45. With this configuration, the heat
generated due to the compression work and friction in the
compression molding of the gas hydrate pellets can be efficiently
removed, so that the gas hydrate can be prevented from being
decomposed.
[0087] In the production process of the present invention, the
temperature difference T-T.sub.0 between the temperature T of the
gas hydrate pellets p and the temperature T.sub.0 of the gas
hydrate powder n is set to be preferably below 3.degree. C., and
more preferably below 0.degree. C., that is, it is preferable that
the temperature T of the pellets p be set to be lower than the
temperature T.sub.0 of the powder n. Setting the temperature
difference T-T.sub.0 in such a range makes it possible to securely
suppress the decomposition of the gas hydrate. Here, the amount of
removed heat Q2 removed by the cooler 57 may be set to be equal to
or more than the amount of heat Q1 which the gas hydrate powder
receives in the pelletization, whereby an increase in temperatures
of the rotating rolls and the gas hydrate can be suppressed.
[0088] It should be noted that setting the temperature of the
cooling water too low is not preferable because the cooling water
is frozen and thus does not function as the binder in the
compression molding of the gas hydrate powder as described above.
Specifically, the gas hydrate powder having a high concentration is
dry and unlikely to be hardened like a loose snow even being
compressed. For this reason, the cooling water is supplied to the
gas hydrate powder, so that part of the cooling water functions as
the binder for the particles of the gas hydrate powder. The gas
hydrate powder, thus, can be compression-molded into firmly
compacted gas hydrate pellets. Note that the surplus of the cooling
water is removed upward with the gap between the pair of rotating
rolls becoming narrower, and no excessive amount of water is
contained in the gas hydrate pellets. In addition, the water
serving as the binder is further cooled to be frozen by the
chilling machine 23 provided downstream of the pelletizer 22, and
thus the gas hydrate pellets can be further firmly compacted.
[0089] In the production process of the present invention, the
degree of decomposition .beta. in the pelletization of the gas
hydrate powder is set to be ideally 0%, but preferably not more
than 10%, and more preferably 0% to 5%. Note that the degree of
decomposition p is determined as follows. Each of the gas hydrate
powder and the gas hydrate pellet is sampled, and each sample is
decomposed into water and the raw-material gas. Then, the gas
content [% by weight] of each sample is measured. The ratio [%] of
the gas content of the gas hydrate pellets to the gas content of
the gas hydrate powder is obtained as the degree of decomposition
p.
[0090] Moreover, it is preferable that the amount of heat removed
by the cooler 57 be set to be not less than the amount of heat Q1
obtained in accordance with the following expression (I).
Q1=(T-T.sub.0)cM+gM.beta./100 (I)
[0091] Here, Q1 is the amount of heat [w] which the gas hydrate
powder receives in the pelletization, and c is the specific heat
[kJ/kgK], which is, for example, 1.8 to 2.0 kJ/kgK in the case of
natural gas hydrates. q is the decomposition heat [kJ/kg], which
is, for example, approximately 440 kJ/kg in the case of natural gas
hydrates. M is the pelletization speed [kg/s] for the gas hydrate
powder. The temperature T of the gas hydrate pellets p, the
temperature T.sub.0 of the gas hydrate powder n before supplied to
the pelletizer, and the degree of decomposition p are actual
measurement values.
[0092] To be specific, the temperature T.sub.0 of the gas hydrate
powder n before supplied to the pelletizer and the temperature T of
the gas hydrate pellets p are measured. The degree of decomposition
p is obtained by measurement according to the above-described
method. The amount of heat Q1 is calculated in accordance with the
expression (I). Then, the coolant temperature of the cooler 57 and
the flow rate of the pump 56 may be adjusted so that the amount of
heat Q2 removed by the cooler should be not less than the amount of
heat Q1.
[0093] A second embodiment of the production process of the present
invention is, as illustrated in FIG. 6, a process in which: cooling
baths 58 are arranged respectively below the rolls 6a and 6b; the
cooling water 42 is circulated to the cooling baths 58; and gas
hydrate pellets are produced while the cooling water 42 is brought
into contact with the outer peripheral portions of the rolls 6a and
6b to thereby cool the roll surfaces. When the lower portions of
the rolls are dipped into the cooling water 42 supplied to the
cooling baths 58, water films are formed on the roll surfaces,
whereby the roll surfaces are effectively cooled. In addition, the
compression molding is carried out while the rolls are rotated with
the roll surfaces being wet and thus catch the gas hydrate powder
in the hopper chamber 5. Accordingly, the cooling water
appropriately functions as the binder in the same manner as the
above-described first embodiment of the production process.
[0094] Instead of the dipping of the lower portions of the rolls in
the cooling baths, the cooling water may be sprayed onto the roll
surfaces for the heat removal. It is preferable that a cooling bath
be disposed in a lower portion for recovering the surplus of the
cooling water thus sprayed. Further, both of the cooling by dipping
the lower portions of the rolls in the cooling bath and the cooling
by spraying may be employed in combination. These methods are also
preferable because the methods make it possible to effectively
remove the heat of the roll surfaces and to supply a proper amount
of water as the binder.
[0095] It should be noted that it is preferable to perform the
treatment process for the discharged cooling water 43 after the
cooling process as well as the removal of heat in amount Q2 by the
cooler 57 in the same manner as the first embodiment of the
production process of the present invention. Moreover, it is
preferable to set the temperature difference T-T.sub.0 between the
temperature T.sub.0 of the gas hydrate powder n before supplied to
the pelletizer and the temperature T of the gas hydrate pellets p
as well as the degree of gas hydrate decomposition .beta. in the
same manner as the first embodiment.
[0096] A third embodiment of the production process of the present
invention is, as illustrated in FIG. 7, a process for producing gas
hydrate pellets while cooling the rolls 6a and 6b from the insides
thereof with the cooling water 42 supplied to cooling-water jackets
provided respectively inside the rolls 6a and 6b. The cooling water
is introduced to the insides through roll shafts 59, and flows
through the cooling-water jackets provided inside the rolls. The
temperature of the roll surfaces can be set at a predetermined
temperature with no decrease of the cooling water by causing the
cooling water to flow into the insides of the rolls and then to
circulate while being cooled to a predetermined temperature by the
cooler.
[0097] It should be noted that it is preferable to perform the
treatment process for the discharged cooling water 43 after the
cooling process as well as the removal of heat in amount Q2 by the
cooler 57 in the same manner as the first embodiment. Moreover, it
is preferable to set the temperature difference T-T.sub.0 between
the temperature T.sub.0 of the gas hydrate powder n before supplied
to the pelletizer and the temperature T of the gas hydrate pellets
p as well as the degree of gas hydrate decomposition .beta. in the
same manner as the first embodiment.
[0098] In each of the above-described embodiments, the gas hydrate
powder n is formed into the gas hydrate pellets p while the cooling
water is supplied at the stage before the pressure release to
atmospheric pressure conducted by the depressurizer 24. The process
for producing gas hydrate pellets of the present invention is not
limited to the embodiments, and is also effective in producing gas
hydrate pellets, for example, at atmospheric pressure, after
depressurization. Specifically, consider a case where an atmosphere
that does not allow a gas hydrate to be decomposed is set for
production of gas hydrate pellets. Even in this case, the
production process of the present invention makes it possible to
produce firmer gas hydrate pellets with the degree of gas hydrate
decomposition reduced by preventing the set atmospheric conditions,
from being changed by heat generated due to the compression work
and friction, and thus from being converted into a state where the
gas hydrate is likely to be decomposed.
[0099] Hereinafter, although the present invention will be further
described by giving an example, the scope of the present invention
is not limited to the example.
EXAMPLE
Comparative Example
[0100] In accordance with the gas hydrate pellet production
processes illustrated in FIG. 5, a gas hydrate powder having a
temperature T.sub.0 of 6.degree. C. (with an equilibrium
temperature of 7.degree. C.) was generated from a natural gas as a
raw-material gas. The gas hydrate powder was compression-molded at
a pelletization speed M of 0.06 kg/s, with no supply of cooling
water. The temperature T of gas hydrate pellets thus produced was
7.degree. C., that is, the temperature difference T-T.sub.0 was
1.degree. C. The degree of decomposition .beta. measured by the
aforementioned method was 3.2%. In the production, the amount of
heat Q1 calculated in accordance with the expression (I) was 1.8
kw, where the specific heat was set at 1.6 kJ/kgK and the
decomposition heat q was set at 440 kJ/kg.
Example
[0101] In accordance with the gas hydrate pellet production
processes illustrated in FIG. 5, gas hydrate pellets were produced
in the same manner as Comparative Example except that cooling water
was circulated to the hopper chamber of the rotating-roll-type
pelletizer while being cooled so that the amount of heat Q2 removed
by the cooler should be 1.8 kw. As a result, the temperature
difference T-T.sub.0 between the gas hydrate powder before the
pelletization and the pellets after the pelletization was 0.degree.
C., and the degree of gas hydrate decomposition .beta. was 0%. In
addition, the gas hydrate pellets obtained in Example were more
firmly compacted than those obtained in Comparative Example.
* * * * *