Technical Field
[0001] The present invention relates to a method of waste melting treatment by thermally
decomposing, burning, and melting waste in a shaft furnace type melting furnace.
Background Art
[0002] As the technology for treating waste, such as city garbage or shredder dust, the
method of waste melting treatment that thermally decomposes and burns the waste, and
melts the pyrolysis residue into slag, discharging it.
[0003] This treating method offers advantages that the waste can be thermally decomposed
to be gasified, thereby allowing the combustion heat to be recovered, and after melting
the pyrolysis residue and discharging it as slag, the volume of the waste to be finally
disposed can be reduced by making land-filling disposal or other. Such a melting treatment
method is available in several types, and as one of them, a method is available which
uses a shaft furnace type waste gassification melting furnace, which is of a vertical
type.
[0004] This shaft furnace type waste gassification melting furnace performs such a treatment
as that in which the coke deposited in the lower section of the furnace is burned,
and onto such coke at high temperature, the waste is charged to be thermally decomposed
and partially oxidized for gasification, with the residue being melted into slag (refer
to Patent Document 1).
[0005] With the shaft furnace type waste gassification melting furnace disclosed in Patent
Document 1, the functions of the furnace body with a vertical and cylindrical shape
are basically divided into three regions along the vertical direction from the viewpoint
of function. In other words, in the lower section of the furnace, there is formed
a high temperature combustion zone having a coke bed in which the coke is deposited;
above this high temperature combustion zone, a waste layer is formed; and in the upper
section of the furnace body above the waste layer, a freeboard section having a large
space is provided.
[0006] With such a gassification melting furnace, in the respective three regions mentioned
above, oxygen-containing gas is blown into the furnace. The high temperature combustion
zone in the furnace lower section is provided with a main tuyere, and therethrough
oxygen rich air is blown in order to obtain a melting heat source for burning the
coke charged and deposited in the coke bed to melt the pyrolysis residue of the waste.
[0007] In addition, the waste layer is provided with a sub-tuyere for slowly fluidizing
the waste which has been charged and deposited, and blowing air to thermally decompose
and partially oxidize the waste. Further, the freeboard section is provided with a
third-level tuyere for blowing air to partially burn the pyrolysis gas (combustible
gas) generated with the waste being thermally decomposed, and thus to maintain the
inside of the furnace at a prescribed temperature.
[0008] Thus, the shaft furnace type waste gassification melting furnace is a provision which,
within a single furnace, can perform both the pyrolysis gassification treatment and
the melting treatment of the waste as it falls in the furnace. The charged waste is
thermally decomposed, thereby gas and residue being generated. By blowing oxygen rich
air from the main tuyere, the coke in the coke bed is burned, a high temperature combustion
zone being formed, and the pyrolysis residue of the waste is melted to be discharged
as slag and metal.
[0009] The high temperature gas generated by the coke combustion in the high temperature
combustion zone heats the waste in the waste layer formed above the high temperature
combustion zone, the waste being thermally decomposed with the air being blown from
the sub-tuyere, and the gas containing combustible gas generated by such pyrolysis
rises in the waste layer, passing through the freeboard section, to be discharged
from a discharge flue provided in the upper section of the furnace into a secondary
combustion chamber outside the furnace. The gas, containing a large quantity of combustible
gas, is burned in the secondary combustion chamber, the heat being recovered at a
boiler to generate steam, which is used for electric power generation, or the like.
[0010] The gas discharged from the boiler is removed of relatively coarse dust particles
by means of a cyclone separator; then is cooled by a temperature lowering apparatus;
is removed of noxious gas through reaction with a harmful substance removing agent;
and is subjected to an exhaust gas treatment, such as that for dust removal with a
dust collector, being dissipated to the atmosphere from a smoke stack.
[0011] With such a waste gassification melting furnace, a coke bed in which coke is deposited
is formed in the furnace bottom section, and the coke is burned to provide a heat
source for melting the pyrolysis residue, however, in recent years, there has been
a demand for reducing the quantity consumed of coal coke originating from the fossil
fuel to cut the carbon dioxide emission amount.
[0012] Then, in order to cut the quantity consumed of coke, there have been proposed a waste
melting method which, as an alternative to coal coke, utilizes lumpy biomass, such
as a carbide produced by heating and pressure molding of sawdust available as a building
waste material for carbonizing it, or charcoal (refer to Patent Document 2), and another
method which charges a biomass solid substance, such as a briquette produced by pressure
molding of biomass, into a waste gassification melting furnace for converting it into
a carbide within the furnace to form a carbide layer (refer to Patent Document 3).
Citation List
Patent Literature
[0013]
- Patent Document 1:
- Japanese Unexamined Patent Application Publication JP-A-09-060 830
- Patent Document 2:
- Japanese Unexamined Patent Application Publication JP-A-2005-249 310
- Patent Document 3:
- Japanese Unexamined Patent Application Publication JP-A-2005-274 122
Disclosure of the Invention
Problems to be Solved by the Invention
[0014] Even if, as an alternative to coke, lumpy biomass of a carbide or a biomass solid
substance is utilized as proposed in Patent Document 2 or 3 for reducing the quantity
consumed of coke in the waste melting furnace to thereby cut the carbon dioxide emission
amount and reduce the cost for operating the waste melting furnace, there will be
presented the following problems.
[0015] In other words, in the case where, as is disclosed in Patent Document 2, lumpy biomass
of a carbide is utilized, or as is disclosed in Patent Document 3, a biomass solid
substance is charged into the waste melting furnace to convert it into a carbide within
the furnace, the combustion heat of the volatile components possessed by a biomass
raw material is consumed in the course of carbonization, the thermal energy corresponding
to the fixed carbon in the biomass raw material being used as a melting heat source
as an alternative to the melting heat source given by the coke.
[0016] Therefore, for the quantity of coal coke that is to be cut, it becomes necessary
to charge a large quantity of lumpy biomass of a carbide or a biomass solid substance,
and since these are expensive, as compared to the coal coke, the expense required
for cutting the quantity consumed of coal coke is increased, thereby the cost for
operating the waste melting furnace being increased, which is a problem. Another problem
is that the combustion heat of the volatile components possessed by the biomass raw
material could have not been effectively utilized.
[0017] Another problem is that the lumpy biomass of a carbide or the carbide produced by
the biomass solid substance being carbonized within the furnace is poor in stability
as a high temperature fire grate, compared to the coal coke, thereby a temperature
decrease in the lower section of the melting furnace or a discharge failure of molten
slag is caused and thus the operation becomes unstable.
[0018] In view of the above-mentioned problems, the present invention has been made, and
it is an object thereof to provide a method of waste melting treatment that can reduce
the quantity consumed of coal coke in a waste melting furnace to cut a carbon dioxide
emission amount, suppressing the cost for operating the waste melting furnace from
being increased, and allowing the combustion heat of the volatile components possessed
by a biomass raw material to be effectively utilized, and a more stable operation
to be performed.
Means for Solving the Problems
[0019] The method of waste melting treatment in accordance with the present invention charges
waste into a shaft furnace type waste melting furnace for thermally decomposing, burning,
and melting the waste.
[0020] Specifically, the method of waste melting treatment in accordance with the present
invention charges coal coke, and a biomass molded article produced by heating a biomass
raw material at a temperature lower than the carbonization temperature thereof while
pressure molding it; forms a high temperature fire grate in a lower section of the
melting furnace with the coal coke; and burns the coal coke and the biomass molded
article to provide a melting heat source.
[0021] Biomass resources have been classified by FAO (Food and Agriculture Organization
of the United Nations), and the biomass resources include woody biomass, such as forest
remaining wood, thinned wood, unutilized tree materials, lumber sawing remaining materials,
and construction scraps; herbaceous biomass, such as straw, and rice hulls; and further,
papermaking biomass; agricultural residues; and unutilized biomass resources, such
as livestock excreta, and food waste.
[0022] The present invention uses a biomass molded article produced by heating such a biomass
resource as a raw material (to be called a biomass raw material) at a temperature
lower than the carbonization temperature thereof while pressure molding it.
[0023] In the present specification, the term "carbonization temperature" refers to a temperature
at which the volatile components of a biomass raw material starts volatilization,
which is also a temperature at which dry distillation is started.
[0024] The biomass molded article, which is produced by heating a biomass raw material at
a temperature lower than the carbonization temperature thereof while pressure molding
it, contains volatile components, and therefore, by charging such biomass molded article
into a melting furnace to be burned in the lower section thereof for use as a melting
heat source, the combustion heat of the volatile components possessed by the biomass
raw material can be effectively utilized.
[0025] In accordance with the present invention having such a configuration, the coal coke
forming a high temperature fire grate provides a function which assures passing of
gas and liquid through the high temperature fire grate, by creating voids between
lumps of coke, on the basis of its inherent lumpy geometry, and a function which serves
as a heat source for melting. On the other hand, the biomass molded article can be
used regardless of its high temperature strength, geometry, and dimensions, having
a function as a melting heat source which supplements the heat quantity of the coal
coke for melting.
[0026] Therefore, as the required quantity of coal coke, a minimum quantity required for
forming a high temperature fire grate will suffice, and the shortage as the melting
heat source can be supplemented with the above-mentioned biomass molded article, whereby
both can secure a sufficient melting heat source, while, with a minimum quantity of
coal coke, a high temperature fire grate layer can be formed.
[0027] If only the biomass molded article is to be used to form a high temperature fire
grate, it will be required to provide a biomass molded article having a high temperature
strength and a size larger than a prescribed one, the cost of which is high. In addition,
the stability thereof as a high temperature fire grate will be poor as compared to
the coal coke.
[0028] On the other hand, if the biomass molded article is required to play a role only
as a source for supplying melting heat, in other words, a melting heat source, it
is not required to have a high temperature strength. Therefore, there is no need for
using an expensive biomass carbide, whereby the cost for operating the waste melting
furnace can be suppressed from being increased.
[0029] Then, if the coal coke is used to form a high temperature fire grate, the coal coke
and the biomass molded article are burned with the air for combustion being fed from
the main tuyere, the combustion gas well rising and passing through the high temperature
fire grate for heating and thermally decomposing the waste to burn and melt it, and
the melt well falling and flowing through the above-mentioned high temperature fire
grate.
[0030] In the present invention, the biomass molded article is preferably a molded article
containing the volatile components by 50 weight percent or more. By heating the biomass
raw material while pressure molding it so as to provide a molded article containing
the volatile components by 50 weight percent or more, the combustion heat of the volatile
components possessed by the biomass raw material can be effectively utilized.
[0031] In the present invention, it is preferable that the biomass molded article be a molded
article which is produced by heating the biomass raw material at a temperature of
115 °C to 230 °C while pressure molding it. By heating the biomass raw material at
a temperature of 115 °C to 230 °C while pressure molding it, a biomass molded article
with which the volatile components possessed by the biomass raw material are left
can be obtained, whereby the combustion heat of the volatile components possessed
by the biomass raw material can be effectively utilized.
[0032] In the present invention, it is preferable that the biomass molded article be a prismatic
body one side of which has a length of 50 mm or longer, or a cylindrical body having
a diameter of 50 mm or larger and a length of 50 mm or longer. By using a biomass
molded article having such dimensions and a geometry, the biomass molded article,
after having been charged into the melting furnace, can reach the lower section of
the furnace, while the volatile components being suppressed from being thermally decomposed
and burned in the furnace, whereby the combustion heat of the volatile components
possessed by the biomass raw material can be effectively utilized as a melting heat
source.
[0033] In the present invention, it is preferable that the quantity of coal coke to be charged
into the furnace be at least a quantity required for forming a high temperature fire
grate, and the heat quantity required to provide a melting heat source be supplemented
by the biomass molded article.
Advantages of the Invention
[0034] As described above, the present invention can provide a method of waste melting treatment
with which, upon making a melting treatment of waste in a shaft furnace type melting
furnace, coal coke and a biomass molded article are charged, and therefore, in the
furnace, a high temperature fire grate is formed by the coal coke, whereby, in the
state in which the combustion gas rising and passing through the high temperature
fire grate and the melt falling and flowing through the same are well maintained,
the melting heat source can be secured with a minimum quantity of coal coke required
for forming a high temperature fire grate and the biomass molded article supplementing
the coal coke; the quantity consumed of coal coke can be reduced to cut the carbon
dioxide emission amount with the cost for operating the waste melting furnace being
reduced; in addition, the combustion heat of the volatile components possessed by
the biomass raw material can be effectively utilized, and a more stable operation
can be carried out.
Brief Description of the Drawing
[0035] Figure 1 is a diagrammatic view showing a schematic configuration of an apparatus
of an embodiment of the present invention.
Best Mode for Carrying Out the Invention
[0036] Hereinbelow, an embodiment of the present invention will be explained with reference
to the attached drawing, i.e., Figure 1. In the present embodiment, coal coke and
a biomass molded article are supplied to a shaft furnace type waste gassification
melting furnace as fuel, however, prior to explaining such a feature, the schematic
configuration of the shaft furnace type waste gassification melting furnace will be
explained.
[0037] With the shaft furnace type waste gassification melting furnace shown in Figure 1
in one embodiment of the present invention, the upper section of the gassification
melting furnace 1 is provided with a charging port 2 for charging waste as an object
to be treated, coal coke and a biomass molded article as fuel, and lime stone as a
material for adjusting the slag composition into the furnace, and the side of the
upper section is provided with a gas discharge port 3 for discharging the gas in the
furnace to the outside thereof. In addition, the bottom section of the gassification
melting furnace 1 is provided with a residue discharge port 4 for discharging the
molten slag and the molten metal.
[0038] With the shaft furnace type waste gassification melting furnace, the internal space
of the gassification melting furnace 1 is basically divided into three regions along
the vertical direction; from bottom, the three regions providing a lower shaft section
I, which is formed in the lower section of the furnace, a middle shaft section II,
which is located above the lower shaft section I, and a freeboard section III, which
is formed in the upper section. These sections I, II, and III are regions having the
following functions, respectively.
[0039] In other words, the lower section shaft section I is a region where the coal coke
and biomass molded article deposited are burned to form a high temperature combustion
zone; the middle shaft section II is a region where the waste in the waste layer,
which is formed by the deposition of the waste charged onto the high temperature combustion
zone, is thermally decomposed; and the freeboard section III is a region where the
combustible gas generated is partially burned.
[0040] Above the waste gassification melting furnace 1, there is disposed a supply apparatus
(not shown) which supplies waste, such as municipal waste, coal coke, biomass molded
article, and lime stone for use as a material for adjusting the composition of slag
generated, respectively. The waste, the coal coke and biomass molded article, and
the lime stone are conveyed by a carrying conveyor (not shown), and charged into the
furnace from the above-mentioned charging port 2 in the furnace upper section.
[0041] On the furnace wall, there are provided tuyeres for blowing oxygen-containing gas
into the respective lower shaft section I, middle shaft section II, and freeboard
section III mentioned above, which are formed in the waste gassification melting furnace.
[0042] In other words, in the lower shaft section I, there is provided a main tuyere 5 through
which oxygen rich air is blown to burn the coal coke and biomass molded article which
have been deposited in the lower shaft section I for forming a high temperature combustion
zone to melt the pyrolysis residue; in the middle shaft section II, there is provided
a sub-tuyere 6 through which air is blown to partially burn the charged and deposited
waste, and slowly fluidizing the waste while thermally decomposing and burning it;
and in the freeboard section III, there is provided a third-level tuyere 7 for blowing
air to partially burn the combustible gas generated by thermally decomposing the waste
for maintaining the inside of the furnace at a prescribed temperature.
[0043] The gas discharge port 3 is connected to a secondary combustion chamber 10 for burning
the combustible gas generated by thermally decomposing the waste. For secondary combustion,
an air blowing port 11 is provided through which air is blown. In addition, adjacent
to this secondary combustion chamber 10, a boiler 12 is provided in order to recover
the heat from the combustion gas produced by burning the combustible gas in the secondary
combustion chamber 10.
[0044] On the other hand, the biomass molded article is of the type produced as a prismatic
body one side of which has a length of 50 mm or longer, or a cylindrical body having
a diameter of 50 mm or larger and a length of 50 mm or longer, by filling a molding
container with a pulverized biomass raw material, and heating it at a temperature
of 115 °C to 230 °C, while pressure molding it.
[0045] By heating and pressure molding under such a heating condition, the biomass raw material
can be provided as a biomass molded article without being carbonized, and containing
the volatile components by 50 weight percent or more. The pressure for pressure molding
may be 8 to 25 MPa. As the method for biomass molded article manufacturing, the manufacturing
method disclosed in Domestic Re-publication of
PCT International Application WO2006/078023 A may be applied.
[0046] By performing molding under the above-mentioned heating and pressure conditions,
the biomass molded article can be provided with a surface which is extremely dense
and free from pores. By using a biomass molded article produced as a prismatic body
one side of which has a length of 50 mm or longer, or a cylindrical body having a
diameter of 50 mm or larger and a length of 50 mm or longer, and having a surface
which is extremely dense and free from pores, the biomass molded article, after having
been charged into the melting furnace, can reach the lower section of the furnace,
while the volatile components being suppressed from being thermally decomposed and
burned in the furnace, the combustion heat of the volatile components possessed by
the biomass raw material can be effectively utilized as a melting heat source.
[0047] With the present embodiment apparatus configured as thus, gasified melting treatment
of the waste is performed in the following manner.
[0048] The waste, the coal coke and biomass molded article, and the lime stone from the
supply apparatus are charged into the furnace by a prescribed quantity, respectively,
through the charging port 2 provided in the upper section of the gassification melting
furnace 1, and from the main tuyere 5, the sub-tuyere 6, and the third-level tuyere
7, oxygen rich air or air is blown into the furnace, respectively.
[0049] The waste which has been charged from the above-mentioned charging port 2 is deposited
in the middle shaft section II in the furnace to form a waste layer, being dried by
the high temperature gas rising from the high temperature combustion zone in the lower
shaft section I and the air blown from the sub-tuyere before being thermally decomposed.
[0050] The combustible gas generated by the pyrolysis is burned in the freeboard section
III with the air blown from the third-level tuyere, being maintained at a temperature
of 850 °C or higher, and after being subjected to a treatment for decomposing the
harmful gas and the tar component, is fed to the secondary combustion chamber provided
outside the furnace, the heat of the combustion gas being recovered by the boiler.
[0051] The coal coke falls to the lower shaft section I; the biomass molded article falls
to the lower section shaft section I, while the volatile components being suppressed
from being thermally decomposed and burned on the way of falling, as a result, a high
temperature combustion zone is formed, the coal coke and biomass molded article being
burned; the pyrolysis residue which has been produced as a result of thermal decomposition
of the waste in the waste layer in the middle shaft section II falls and reaches the
lower section shaft section I, where a high temperature combustion zone is formed,
the coal coke and biomass molded article being burned; and in the lower section shaft
section I, the volatile components in the biomass molded article, and the fixed carbon
in the coal coke and biomass molded article are burned, the noncombustibles being
melted to be changed into molten slag and molten metal.
[0052] The molten slag and the molten metal are discharged from the residue discharge port
4 to be fed to a water granulating apparatus provided outside of the furnace, and
cooled and solidified, the cooled and solidified water granulated slag and the water
granulated metal being recovered.
[0053] Thus, the coal coke and biomass molded article are charged into the waste gassification
melting furnace; the coal coke forms a high temperature fire grate in the lower section
of the gassification melting furnace 1; and the coal coke and biomass molded article
are burned to provide a melting heat source for melting the pyrolysis residue (ash)
of the waste, and the noncombustibles.
[0054] The quantity of coal coke to be charged into the furnace is a quantity required for
forming a high temperature fire grate, and the heat quantity necessary as the melting
heat source is supplemented by the biomass molded article, a prescribed quantity being
charged, respectively.
[0055] In such a course of gasified melting treatment of waste, the coal coke of the coal
coke and biomass molded article as fuel has a lumpy geometry at the beginning of being
charged into the furnace, and in the high temperature combustion zone in the lower
shaft section I, the voids between coal cokes form a high temperature fire grate.
[0056] The top face of the layer of the high temperature fire grate is located above the
main tuyere 5; the oxygen rich air or air from the main tuyere 5 rises and passes
through the above-mentioned voids, the combustion of the coal coke and biomass molded
article being well carried out; and a sufficient quantity of the combustion gas reaches
the waste layer.
[0057] On the other hand, in the high temperature combustion zone, the noncombustibles and
ash of the waste are sufficiently melted by the quantity of heat obtained by the combustion
of the coal coke and biomass molded article, thereby molten slag and molten metal
being produced. The molten slag and the molten metal well fall and pass through the
above-mentioned voids of the high temperature fire grate, reaching the residue discharge
port 4.
[0058] According to such a gasified melting treatment method for waste, the coal coke forming
a high temperature fire grate provides a function which assures passing of gas and
liquid through the high temperature fire grate, by creating voids between lumps of
coke, on the basis of its inherent lumpy geometry, and a function which serves as
a heat source for melting.
[0059] On the other hand, the biomass molded article can be used regardless of its high
temperature strength, geometry, and dimensions, providing a function as a melting
heat source which supplements the heat quantity of the coal coke for melting.
[0060] Therefore, as the required quantity of coal coke, a minimum quantity required for
forming a high temperature fire grate will suffice, and the shortage as the melting
heat source can be supplemented with the above-mentioned biomass molded article, whereby
both can secure a sufficient melting heat source, while, with a minimum quantity of
coal coke, a high temperature fire grate layer can be formed.
[0061] If the biomass molded article is required to play a role only as a source for supplying
melting heat, in other words, a melting heat source, it is not required to have a
high temperature strength. Accordingly, inexpensive biomass molded article can be
used, whereby the cost for operating the waste melting furnace can be reduced.
[0062] Then, if the coal coke is used to form a high temperature fire grate, the coal coke
in the high temperature fire grate and the biomass molded article deposited in the
high temperature fire grate are burned with the air for combustion fed from the main
tuyere, the combustion gas well rising and passing through the high temperature fire
grate for heating and thermally decomposing the waste to burn and melt it, and the
melt well falling and flowing through the above-mentioned high temperature fire grate.
[0063] In this way, with the high temperature fire grate, the combustion gas rising and
passing therethrough and the molten slag and molten metal falling and flowing therethrough
are well maintained, while the coal coke and the biomass molded article as fuel being
burned.
[0064] Upon the combustion, as the quantity of coal coke to be charged, a minimum quantity
required for forming a high temperature fire grate will suffice, and the shortage
to the heat quantity required for gasification melting of the waste is supplemented
with the biomass molded article. Further, the combustion heat of the volatile components
possessed by the biomass raw material can be effectively utilized as the melting heat
source.
[0065] Thus, the quantity consumed of coal coke can be minimized, while the biomass molded
article can be charged regardless of its high temperature strength, geometry, and
dimensions, and even an inexpensive biomass molded article can be used as fuel. In
this way, the quantity consumed of coal coke can be reduced to cut the carbon dioxide
emission amount with the cost for operating the waste melting furnace being reduced,
whereby waste treatment allowing stable operation can be carried out.
[0066] Biomass is preferably molded under the above-mentioned heating and pressure conditions,
and to the above-mentioned dimensions and geometry, however, heating and pressure
molding of biomass may be performed under other conditions, provided that the volatile
components of the biomass raw material are effectively left.
Description of Symbols
[0067] The symbol 1 denotes a gassification melting furnace.