Note: Descriptions are shown in the official language in which they were submitted.
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METHOD OF RECOVERING HYDROGEN FROM ORGANIC WASTE
FIELD OF THE INVENTION
The present invention relates to a method to effectively utilize organic
wastes, such as unused resources and renewable resources, more particularly
to a method to recover hydrogen from the organic wastes.
PRIOR ART
Thinned wood and waste wood were incinerated in the past. Recently
processes to use heat generated in the incineration of these to generate
electricity were studied from viewpoints of energy saving and effective use of
heat. A process to thermally decompose waste plastics into oil or a process to
recycle them as a reducing agent for a blast incinerator was studied and
practically applied. Garbage had been incinerated, but recently a process to
recover methane from garbage by means of methane fermentation and a
process to generate electricity from the methane are being practically used.
As a means to dispose thinned wood or waste wood, direct incineration
and gasification may be mentioned. In the direct incineration, the
above-mentioned materials are completely burnt in an incinerator, such as a
stoker incinerator, a bubbling fluidized bed incinerator, a circulating
fluidized bed incinerator, and a circulating moving bed combustor. What may
be recovered and reused in the direct incineration process is only thermal
energy, by which energy hot water or steam may be produced to generate
electricity. Meanwhile, in the gasification, the above-mentioned materials are
partly oxidized by oxygen or air in a gasification incinerator such as a fixed
bed incinerator, a moving bed combustor, a circulating fluidized bed
incinerator, a two-staged circulating moving combustor, and an entrained
flow bed incinerator. What may be recovered and reused in the gasification
process is thermal energy and gas. The thermal energy may be used to obtain
hot water or electric power. The gas may be used as a fuel to generate hot
water or electric power. In both ways, it is the present situation that
generated heat, hot water, or electric power cannot be used effectively since
there is no factory to consume it.
Due to regulatory measures to reduce dioxin generated in incineration of
wastes, simple incineration of industrial wastes, such as thinned wood, waste
wood from construction, and general waste has been being restricted and,
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therefore, is becoming impossible. Meanwhile, the Construction Material
Recycling Act proclaims promotion of recycling of waste wood from
construction. Therefore, recycling of waste wood from construction is
becoming unavoidable.
SUMMARY OF THE INVENTION
The present invention provides a process to effectively use energy and
gas obtained from organic wastes, such as, thinned wood, driftwood, waste
wood, waste plastics, garbage, sludge, mown grass, and paper industry
sludge.
The present inventors have reached an idea of recovering hydrogen from
the above-mentioned organic wastes so as to promote recycling of unused
resource such as thinned wood, and other organic wastes, such as waste wood,
and to further promote effective utilization thereof as an energy resource. It
has been found that the recovering of energy in a form of hydrogen makes the
energy possible to be stored and transported and, subsequently, to be used to
generate hot water or electric power as required. Further this gives the
environment a less impact since combustion of hydrogen emits no carbon
dioxide, which can contribute to prevention of global warming, and thus the
present invention has been completed.
Namely, the present invention provides
(1) a process for recovering hydrogen, comprising heating organic waste
at a temperature of from 500 to 600 degrees C under a non-oxidative
atmosphere, mixing a pyrolysis gas thus generated with steam at a
temperature of from 900 to 1000 degrees C, and separating hydrogen from a
reformed gas thus obtained.
As preferred embodiments, mention may be made of
(2) the process according to the above-described (1), wherein the organic
waste is one selected from the group consisting of thinned wood, driftwood,
waste wood, waste plastics, garbage, sludge, mown grass, and paper industry
sludge;
(3) the process according to the above-described (1), wherein the organic
waste is one selected from the group consisting of thinned wood, driftwood
and waste wood;
(4) the process according to any one of the above-described (1) - (3),
wherein a means to separate hydrogen from the reformed gas for recovering
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hydrogen is one selected from the group consisting of PSA, membrane
separation, and cryogenic separation;
(5) the process according to any one of the above-described (1) - (3),
wherein a means to separate hydrogen from the reformed gas for recovering
hydrogen is PSA;
(6) the process according to any one of the above-described (1) to (5),
wherein the temperature at which said organic waste is heated under a
non-oxidative atmosphere is in a range of from 530 to 570 degrees C;
(7) the process according to any one of the above-described (1) to (6),
wherein the temperature at which the generated pyrolysis gas is mixed with
steam is in a range of from 950 to 1000 degrees C;
(8) the process according to any one of the above-described (1) to (7),
wherein a pressure at which said organic waste is heated under a
non-oxidative atmosphere and a pressure at which the generated pyrolysis
gas is mixed with steam are 1 MPa or less;
(9) the process according to any one of the above-described (1) to (7),
wherein a pressure at which said organic waste is heated under a
non-oxidative atmosphere and a pressure at which the generated pyrolysis
gas is mixed with steam are in a range of from 0.1 MPa to 1 MPa; and
(10) the process according to any one of the above-described (1) to (9)
further comprising producing hydrogen by reacting carbon monoxide and
water with each other both contained in said reformed gas obtained after the
mixing with steam.
According to the process of the present invention, unused resources or
organic wastes can be recycled and used as an energy resource.
Conventionally, wastes disposal and energy generation were performed
separately. Now energy efficiency can be raised by performing them in one
and the same equipment. Hydrogen can also be recovered without generating
carbon dioxide.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a flow chart of the equipment used in the Example.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Examples of the organic waste used in the present invention include
thinned wood, driftwood, bamboo, rice straw, rice hull, corn, sweet sorghum,
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vegetable, fruits, flower, sea weed, other unused resources such as wood or
plants recovered in forests, rivers, dams or sea coasts, as well as waste
wood,
waste materials from lumber mills, waste bamboo, trimmed branches, mown
grass, waste plastics, garbage, food residues, residues from vegetable
processing, residues from fruit processing, sewage sludge, animal and. human
waste sludge, community sewage sludge, activated sludge, and paper
industry sludge. A mong these, preferably use is made of thinned wood,
driftwood, waste wood, waste plastics, garbage, mown grass, and paper
industry sludge. Use of thinned wood, driftwood or waste wood is particularly
preferred,
The organic waste may have a dimension such as that of coarsely
crushed one. The organic waste may be in a solid state in the form of, for
instance, plate, stick, sheet or other forms with a dimension of from 1 mm to
cm. When the organic waste is smaller than 1 mm, it may be in any form of
15 particulates, powder, or sludge. A water content of the organic waste
depends
on its form and is preferably 50 weight % or less, more preferably 30 weight %
or less.
In the present invention, the organic waste is first heated under a
non-oxidative atmosphere, whereby the organic waste is decomposed to
generate a pyrolysis gas.
The upper limit for a heating temperature is 600 degrees C, preferably
570 degrees C, and the lower limit is 500 degrees, preferably 530 degrees C.
The above-described range may increase the amount of the generated gas. If
the temperature is lower than the lower limit, the organic waste is not
decomposed enough. If the temperature is higher than the upper limit, the
amount oft he generated gas cannot be raised. The upper limit for t he
pressure in the heating step is preferably 1 MPa, more preferably 0.3 MPa,
and the lower limit is preferably 0.1 MPa, more preferably 0.103 MPa.
Nitrogen is preferably used as the non-oxidative atmosphere.
The form or type of the heating furnace that may be used is not
particularly limited as far as it can heat the raw material organic waste to
the above-described temperature. Examples include a retort incinerator, a
shaft incinerator, a rotary kiln, a fixed bed incinerator, a moving bed
combustor, and a fluidized bed incinerator. Alumina, silica, sand, and so on
may be used as a circulating medium in the moving bed combustor and the
fluidized bed incinerator, and there is no particular restriction on their
shape.
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In the present invention, the organic waste is heated as described above,
and then the pyrolysis gas thus generated is mixed with steam, whereby the
pyrolysis gas and steam react with each other to reform the pyrolysis gas into
a hydrogen-enriched gas.
For the temperature at which the gas is mixed with steam, the upper
limit is 1000 degrees C and the lower limit is 900 degrees C, preferably 950
degrees C. If the temperature is lower than the above-described lower limit,
the reforming reaction does not proceed. If the temperature is higher than
the upper limit, the material of the reforming furnace is adversely affected,
which is undesirable.
Heat required to promote the above-described reforming reaction is
supplied by a heat medium, which has been heated. As a heat source for the
heat medium, use is made of heat obtained by burning tar and char, including
carbon and ash, which is generated in the heating of the above-described
organic waste under a non-oxidative atmosphere. The burning is conducted
preferably separately from the aforementioned system in which the organic
waste is heated under a non-oxidative atmosphere.
Since tar among others tends to disturb a continuous operation in the
heating of the above-described organic waste under a non-oxidative
atmosphere, the tar is preferably removed at the bottom of the furnace,
whereby a continuous operation can be conducted smoothly. If tar and char
by-produced simultaneously are withdrawn and burnt, it is possible not only
to avoid malfunction of the equipment and secure safe operations, but also to
effectively use the tar and char.
Steam to reform the pyrolysis gas can be obtained from industrial water
or clean water through a heat exchanger by using heat of the hot reformed
gas obtained from the reforming furnace. Alternatively, a boiler may be
installed to obtain steam. The temperature of the steam supplied is
preferably 140 degrees or higher, and the pressure is preferably 0.376 MPa or
higher. The temperature and the pressure may be, for instance, 180 degrees
C and 1 MPa but are not restricted thereto. Steam may be fed into the
reforming furnace by continuous or intermittent spraying.
There is no particular limitation on the form or type of the reforming
furnace that may be used. Mention may be made of, for instance, a retort
incinerator, a shaft incinerator, a rotary kiln, a fixed bed incinerator, a
moving bed combustor, and a fluidized bed incinerator. In general, a furnace
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of the same form as that of the above-described heating furnace is used.
However, this is not limitative. For instance, a combination of a rotary kiln
as
a heating furnace and a retort incinerator as a reforming furnace may be
used. As a circulating medium for the moving bed incinerator and the
fluidized bed incinerator, use may be made of, for instance, alumina, silica,
and sand, and there is no particular limitation on their shape.
The reformed gas out of the reforming furnace is passed preferably
through a shift reaction bed, whereby carbon monoxide contained in the
reformed gas is reacted with an excessive amount of steam, so that more
hydrogen is recovered. The shift reaction is known. For instance, a two-stage
process is used. In the first stage, the reaction takes place preferably at a
temperature of from 350 to 500 degrees C using a high temperature
conversion catalyst of iron-chromium system so that a content of remaining
carbon monoxide in the gas is 3 -4 volume %. Then in the second stage, the
reaction takes place preferably at a temperature of from 200 to 250 degrees C
using a low temperature conversion catalyst of copper-zinc system so that the
content of remaining carbon monoxide in the gas is 0.3 -0.4 volume %.
Pressure during the reaction is preferably 1 MPa or higher, more
preferably from 1 to 3 MPa. The pressure may be determined so that it is
matched to the pressures of the steps before and after the shift reaction bed.
The gas thus obtained is cooled preferably with water and then
hydrogen is recovered. As a means to recover hydrogen from the gas, any
known method can be used. Mention may be made of, for instance, a pressure
swing adsorption method or PSA, a membrane separation method, and a
cryogenic separation method. Among these, PSA is suitable since a gas
content can be controllable freely and the cost is lower. In PSA, a hydrogen
content in the recovered gas can be controlled by changing, for instance, an
adsorption time or a height of an adsorption bed. Thus the gas is separated
into hydrogen and the other gases to recover hydrogen obtained in the
above-described procedures.
According to the process of the present invention, unused resources and
renewable resources can be utilized effectively. It is also possible to
recover
hydrogen, which is useful, without generating carbon dioxide. Therefore, the
process of the present invention can be used in a variety of industrial
fields,
such as timber industry, lumbering industry, livestock industry, construction
industry, environment conservation industry, transportation industry, fuel
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supply industry, gas supply industry, and plastic manufacturing industry.
The present invention will be further elucidated in detail with reference
to the following Example, but is not limited thereto.
EXAMPLE
The equipment used in the Example is as shown in Fig. 1. Here, A is a
heating furnace, B is a reforming furnace, C is a gas cooling instrument, and
D is a hydrogen separating instrument, PSA. P represents a pump; 1
represents waste wood; 2, steam; 3, a cooling gas; 4, a hydrogen-enriched gas;
5, a waste gas; 6, tar and char; and 7, a heat medium. Retort furnaces with a
cone-shaped bottom were used as the heating furnace and the reforming
furnace. PSA was used as the hydrogen separating instrument.
Example 1
Waste wood of cedar, disposed of from a lumber mill, was used for
gasification. The waste wood had been subjected to coarse crushing into a
mixture of sticks having almost the same dimension as that of disposable
chop sticks, ones of a size of saw dust, and thin plates having almost the
same
dimension as that of a playing card. Properties of the waste wood are
presented in Table 1.
Table 1 Properties of Waste Wood
Water content 30 weight %
Ash content 5 weight %
Total Calorie 19,600 kJ/kg
Element Composition C 49.90 weight %
H 5.78 weight %
N 0.36 weight %
0 43.59 weight %
S 0.37 weight %
Each value in Table 1 was determined according to the methods
described below.
Water and ash contents: JIS-M8812 (1993)
Total calorie: JIS-M8814 (1993)
Element composition: JIS-M8819 (1997)
The waste wood was continuously introduced into a heating furnace
kept at a temperature of 550 degrees C and a pressure of 0.103 MPa. The
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amount of the waste wood fed was 286 kg/h and an apparent residence time
in the heating furnace was about 1 hour.
The pyrolysis gas generated by thermal decomposition was obtained at
the top of the heating furnace at a rate of 244 kg/h. The gas was introduced
into the reforming furnace kept at a temperature of 950 degrees C and a
pressure of 0.103 MPa. Simultaneously, overheated steam (180 degrees C and
1 MPa) was introduced into the reforming furnace at a rate of 50 kg/h to
reform the gas.
The reformed gas of 950 degrees C was obtained at a rate of 294 kg/h.
Then the gas was brought into contact with water in the cooling
instrument to be cooled down to a temperature of 40 degrees C. The
composition of the gas is as shown in Table 2.
Table 2. Gas Composition after Reformed (in volume %)
N2 02 CO2 CO H2 CH4 C.,H, H2O
Gas 0.00 0.00 21.4 16.7 58.5 1.4 0.0 2.0
Composition
The gas composition in Table 2 was determined with gas
chromatography, from Shiamadzu Co. Ltd., GC8A.
Then the cooled gas was introduced into the hydrogen purifying
instrument and the hydrogen-enriched gas with a hydrogen content of 95
volume % was recovered at a rate of 30 kg/h.
The composition of the hydrogen-enriched gas is as shown in Table 3.
Table 3. Gas Composition after the Purification (in volume %)
N2 02 CO2 CO H2 CH4 C,,H H2O
Gas 0.00 0.00 2.1 1.0 95.5 1.4 0.0 0.0
Composition
The gas composition in Table 3 was determined with the same gas
chromatography for Table 2.
INDUSTRIAL APPLICABILITY
The present invention provides a process to effectively utilize energy
and gas obtained from organic waste, such as thinned wood, driftwood, waste
wood, waste plastics, garbage, sludge, mown grass, and paper industry
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sludge. With the present invention, unused resources or organic waste can be
recycled as energy source. Conventionally, waste disposal and energy
production were performed separately but energy efficiency can be raised by
performing these in one and the same equipment. It is also possible to
recover hydrogen without generating carbon dioxide.
