U.S. patent application number 09/864354 was filed with the patent office on 2002-12-19 for method for burning wastes almost without generating dioxin, inhibitor of generating dioxin, and method of producing the inhibitor.
This patent application is currently assigned to Keiji Shiina. Invention is credited to Murakami, Masuzo, Murakami, Tetsuo.
Application Number | 20020189511 09/864354 |
Document ID | / |
Family ID | 27440127 |
Filed Date | 2002-12-19 |
United States Patent
Application |
20020189511 |
Kind Code |
A1 |
Murakami, Masuzo ; et
al. |
December 19, 2002 |
Method for burning wastes almost without generating dioxin,
inhibitor of generating dioxin, and method of producing the
inhibitor
Abstract
The invention provides a technology to largely decrease
generation of dioxin in combustion ashes as well as exhaust gas by
use of an ordinary combustion apparatus. The invention spreads over
wastes being burnt an inhibitor for inhibiting generation of dioxin
that comprises as main contents an adsorbing substance superior in
rate of adsorbing hydrogen chloride gas and a reaction substance
superior in reactivity with hydrogen chloride gas, and additionally
a degradation agent when required, those mixed, granulated and
dried, whereby a powder material removes hydrogen chloride gas in
combustion gas and flying ashes and a granular material removes
hydrogen chloride gas in residual ashes, thereby inhibiting
generation of dioxin.
Inventors: |
Murakami, Masuzo; (Taki-cho,
JP) ; Murakami, Tetsuo; (Taki-cho, JP) |
Correspondence
Address: |
ARMSTRONG,WESTERMAN & HATTORI, LLP
1725 K STREET, NW.
SUITE 1000
WASHINGTON
DC
20006
US
|
Assignee: |
Keiji Shiina
Minoh-shi
JP
|
Family ID: |
27440127 |
Appl. No.: |
09/864354 |
Filed: |
May 25, 2001 |
Current U.S.
Class: |
110/345 ;
588/316 |
Current CPC
Class: |
B01D 53/10 20130101;
B01D 2253/20 20130101; B01D 2253/108 20130101; B01J 20/18 20130101;
B01D 53/685 20130101; F23G 2201/701 20130101; B01D 2257/2045
20130101; B01J 2220/4887 20130101; B01D 53/04 20130101; F23J 7/00
20130101; F23J 2219/60 20130101; B01J 2220/485 20130101 |
Class at
Publication: |
110/345 ;
588/205 |
International
Class: |
F23J 011/00 |
Claims
What we claimed is:
1. A method for burning wastes almost without generating dioxin
comprising spreading over wastes being burnt a mixture of a
granular material and a powder material that comprise as main
contents an adsorbing substance superior in rate of adsorbing
hydrogen chloride gas and a reaction substance superior in
reactivity with hydrogen chloride gas, or a granular material
comprising as the main contents the adsorbing substance and the
reaction substance and partly easily degradable into a powder
material by a mechanical or thermal stimulation, whereby the powder
material removes hydrogen chloride gas in combustion gas, exhaust
gas and flying ashes and the granular material removes hydrogen
chloride gas generated upon burning wastes and hydrogen chloride
gas in residual ashes, thereby inhibiting generation of dioxin.
2. A method for burning wastes almost without generating dioxin
comprising press feeding to a combustion point of wastes being
burnt a powder material that comprises as main contents an
adsorbing substance superior in rate of adsorbing hydrogen chloride
gas and a reaction substance superior in reactivity with hydrogen
chloride gas, whereby removing hydrogen chloride gas generated upon
burning wastes and inhibiting generation of dioxin.
3. A method for burning wastes almost without generating dioxin
comprising previously mixing with wastes before burning operation a
granular material and/or a powder material that comprise as main
contents an adsorbing substance superior in rate of adsorbing
hydrogen chloride gas and a reaction substance superior in
reactivity with hydrogen chloride gas, whereby removing hydrogen
chloride gas in combustion gas, exhaust gas, flying ashes and
residual ashes and inhibiting generation of dioxin.
4. A method for burning wastes almost without generating dioxin as
set forth in claim 1, 2 or 3, wherein the adsorbing substance
employs synthetic zeolite, fly ash, coffee grounds, used tea leaves
or other wastes of plant, or any of these being activated, and the
reaction substance employs at least one compound among calcium
oxide and calcium hydroxide.
5. A method for burning wastes almost without generating dioxin as
set forth in claim 1 or 3, wherein spreading over wastes being
burnt at more than 450.degree. C. an inhibitor for inhibiting
generation of dioxin that comprises as main matters at least one
compound among calcium oxide and calcium hydroxide and powder of an
adsorbing substance superior in rate of adsorbing hydrogen chloride
gas, such as synthetic zeolite, fly ash, coffee grounds, used tea
leaves, other wastes of plant or any of these being activated, and
additionally, a degradation agent, those materials being into
granules and dried, whereby causing the inhibitor to be partly
degraded into a powder material.
6. A method for burning wastes almost without generating dioxin as
set forth in claim 1, 2, 3, 4 or 5 wherein the dioxin-generation
inhibitor is spread over wastes to be burnt at a proportion of 0.2
to 5 wt % or preferably of 0.5 to 1.5 wt % with respect to a weight
of wastes when in dry state.
7. An inhibitor for inhibiting generation of dioxin comprising a
mixture of a granular material and a powder material that composed
of as main contents an adsorbing substance superior in rate of
adsorbing hydrogen chloride gas and a reaction substance superior
in reactivity with hydrogen chloride gas, or a granular material
comprising as the main contents the adsorbing substance and the
reaction substance and partly easily degradable into a powder
material by a mechanical or thermal stimulation.
8. An inhibitor for inhibiting generation of dioxin as set forth in
claim 7 wherein the adsorbing substance employs synthetic zeolite,
fly ash, coffee grounds, used tea leaves or other wastes of plant,
or any of these being activated, and the reaction substance employs
at least one compound among calcium oxide and calcium
hydroxide.
9. An inhibitor for inhibiting generation of dioxin as set forth in
claim 7 or 8 wherein an organic matter or oyster shell powder as
the degradation agent is added and the mixed materials are
granulated and dried.
10. A method of producing a dioxin-generation inhibitor comprising
the steps of mixing a powder of an adsorbing substance superior in
rate of adsorbing hydrogen chloride gas, such as synthetic zeolite,
fly ash, coffee grounds, used tea leaves, other wastes of plant or
any of these being activated, and a powder of at least one compound
among calcium oxide and calcium hydroxide, and adding a little
amount of powder of an organic matter or oyster shell as a
degradation agent when required, and then granulating and drying
these mixed materials.
11. A method of producing a dioxin-generation inhibitor as set
forth in claim 10 wherein the granules material after drying is
subjected to a granulator to be partly made powdery.
12. A method of producing a RDF having less generation of dioxin
comprising a process of adding to crushed wastes when crushed,
compressed and made solid a mixture of a powder of an adsorbing
substance superior in rate of adsorbing hydrogen chloride gas, such
as synthetic zeolite, fly ash, coffee grounds, used tea leaves,
other wastes of plant or any of these being activated, and a powder
of at least one compound among calcium oxide and calcium
hydroxide.
13. A method of producing a RDF having less generation of dioxin as
set forth in claim 12 wherein the powder mixture is added at a
proportion of 0.2 to 5 wt %, preferably 0.5 to 1.5 wt % with
respect to a weight of wastes being dry.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method for burning wastes
almost without generating dioxin, an inhibitor inhibiting
generation of dioxin, and a method of producing such inhibitor.
[0003] 2. Prior Art
[0004] In order to decrease dioxin generated upon burning wastes,
various inhibitors inhibiting generation of dioxin, such as
resolvent catalyst containing titanium oxide, and an inhibitor for
removing a precursor of dioxin, or hydrogen chloride, and various
technologies of burning wastes by use of those inhibitors have been
hitherto developed. Furthermore developed is a gasification and
dissolution technology in which exhaust gas from high temperature
combustion gas of burnt wastes in a combustion chamber or zone is
to be burnt again at a temperature of 1000 to 1500.degree. C. by
making use of the fact that dioxin when burnt at a very high
temperature of 1000 to 1500.degree. C. is dissolved.
[0005] The conventional dioxin removal technologies aim principally
at removing or decreasing dioxin contained in the exhaust gas from
that high temperature combustion gas. The foregoing conventional
inhibitors inhibiting generation of dioxin and the
dissolving-burning (gasification/dissolution) technique have an
effect of removing or decreasing dioxin in that exhaust gas. In
this respect, many attempts have been hitherto proposed as: a
technique or method of dechlorination reaction by adding potassium
carbonate into a low oxygen atmosphere between a boiler and a
cyclone (Japanese Unexamined Patent Application No. Hei
11-9959(1999)); that an exhaust gas from combustion gas in an
incinerator is cooled to 220 to 230.degree. C. and is subjected to
spraying of calcium hydroxide and activated carbon, so that calcium
hydroxide neutralizes acidic gas and activated carbon adsorbs
dioxin and mercury (Japanese Unexamined Patent Application No. Hei
7-204432(1995)); that exhaust gas at a point during its treatment
processes before becoming less than 400.degree. C. is applied with
an adsorbing/removing material for a precursor of dioxin (by making
use of the fact that dioxin is unlikely to be produced at more than
400.degree. C. while easily produced around 200 to 400.degree.
C.)(Japanese Unexamined Patent Application No. Hei 9-220438(1997));
that dioxin is adsorbed and removed from exhaust gas (Japanese
Unexamined Patent Application No. Hei 10-128062(1998)); that an
adsorbent for dioxin, such as acid clay, is blown on a flue in an
incinerator (Japanese Unexamined Patent Application No. Hei
11-9963(1999)); that dioxin in exhaust gas is dissolved by use of
catalyst containing titanium and others (Japanese Unexamined Patent
Application Nos. Hei 2-35914(1990); Hei 3-8415(1991); Hei
4-265122(1992), and so on).
[0006] However, the conventional dioxin-generation inhibitors that
utilize titanium oxide as the chief material are expensive to
produce and need to be applied frequently, thereby wholly taking a
great cost. And the device based on the dissolving-burning
technique (gasification/dissolution oven) is about 10 times more
expensive than ordinary incinerators for wastes, and hard to be
made small-sized, so that it cannot be spread broadly. The
gasification/dissolution oven inevitably requires large quantities
of wastes to be disposed of continuously, which has problems of
collecting and transporting wastes broadly from various places and
obtaining understanding, in this regard, of inhabitants near the
transporting routes.
[0007] Besides, those methods do substantially not remove dioxin in
ashes from burnt wastes (residual ashes). The ashes from burnt
wastes are disposed of merely in such manner as mixed with a setup
agent (e.g., cement) to be solidified and buried in the ground.
Recently, removal of dioxin in the exhaust gas from that high
temperature combustion gas can be almost achieved in case that the
cost is not a problem. But huge quantities of wastes are disposed
of and burnt all over the world. Limitlessly preventing at a low
cost the generation of dioxin discharged in the atmosphere from the
burnt wastes is quite serious and important matter. Also, it is no
exaggeration to say that there are not at all any other solutions
for removal of dioxin in ashes from burnt wastes than the foregoing
manner of burying solidified ashes in the ground.
[0008] The inventor has studied minutely to solve those defects and
succeeded in developing such a unique method of burning wastes that
generation of dioxin discharged in the atmosphere is prevented at a
quite low cost and dioxin in ashes from burnt wastes can be removed
almost completely, and a dioxin-generation inhibitor for use in the
unique wastes-burning method.
SUMMARY OF THE INVENTION
[0009] The present invention relates to a method for burning wastes
with quite less generation of dioxin, a dioxin-generation inhibitor
optimum for realizing the wastes-burning method, and a method of
producing such inhibitor.
[0010] The present invention also relates to a method of producing
RDF which has quite less generation of hydrogen chloride gas and
dioxin.
[0011] The dioxin-generation inhibitor according to the present
invention comprises a granular or powder material or a mixture of
the same consisting as a main content an adsorbing substance
superior in rate of adsorbing hydrogen chloride gas and a reaction
substance superior in reactivity with hydrogen chloride gas. The
inhibitor is spread over wastes being burnt so as to remove
hydrogen chloride gas in the combustion gas, flying ashes and
residual ashes, thereby inhibiting generation of dioxin.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a side view showing a small-sized incinerator for
a small plant.
[0013] FIG. 2 is a plan view showing a scattering means assembled
in the small-sized incinerator in FIG. 1.
[0014] FIG. 3 is a sectional view showing a principal part of a
large incinerator mounting a scattering means.
[0015] FIG. 4 is a schematic diagram showing a structure of the
dioxin-generation inhibitor according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0016] The present invention quickly and surely removes halogen
compounds (called hereunder "hydrogen chloride gas", and being a
source of generation of dioxin), such as hydrogen chloride gas and
bromine chloride gas, being generated during burning wastes, in
order to prevent generation of dioxin.
[0017] Dioxin comprises benzene ring, chlorine (bromine) and oxygen
and is produced from chemical reaction between chloride and organic
substances in wastes under presence of heavy metal and heat of 200
to 600.degree. C. It is well known that hydrogen chloride gas
reacts with calcium oxide (quick lime) or calcium hydroxide (slaked
lime) to become calcium chloride. Hence, most of the conventional
dioxin-generation inhibitors are made of quick lime and slaked lime
and take a long reaction time and cannot sufficiently capture
hydrogen chloride gas that occurs in succession.
[0018] The inventors conceived under the circumstances a
combination of quick lime or slaked lime with an adsorbing
substance that quickly and surely catches and captures hydrogen
chloride gas generated in succession during burning wastes and
achieved the present invention. For the purpose, the inventors
developed various adsorbing substances excellent in rate of
adsorbing hydrogen chloride gas and also shapes and methods of
applying of the dioxin-generation inhibitor to be applied to wastes
being burnt.
[0019] Next, the present invention will be detailed. The
dioxin-generation inhibitor according to the present invention
does, as foregoing, comprise as the main contents an adsorbing
substance that quickly and surely catches and captures hydrogen
chloride gas and a reaction substance that reacts on hydrogen
chloride gas to hold chlorine. The reaction substance may employ
calcium oxide (quick lime) or calcium hydroxide (slaked lime), or a
mixture of the same. The dioxin-generation inhibitor according to
the present invention which is shaped into granules uses slaked
lime for most of the reaction substance.
[0020] Materials superior in rate of adsorbing are preferable for
the adsorbing substance. Table 1 shows the adsorbing rates of
various substances. Measurement operation was carried out in such
manner that 0.5 g of each specimen is placed in respective
polypropylene containers each having a capacity of 3000 ml and a
plug, followed by applying 2 ml of 99.999% hydrogen chloride gas to
each container and plugging and leaving. Concentration of hydrogen
chloride gas in the containers was measured by use of Kitagawa
indicator tube at a time immediately after plugging, 10 minutes
after application of hydrogen chloride gas, and 20 minutes after
such application (Measured by: Himec Ltd., Chugoku district
office). Initial concentration of less than 0.1 in Table 1
indicates the fact that 30 ppm hydrogen chloride gas was wholly
adsorbed in an instant.
1 TABLE 1 Concentration of hydrogen chloride gas (ppm) Specimen
Initial 10 min after 20 min after Blanks 30 30 30 Coffee grounds 10
4 under 0.1 Activated coffee under 0.1 under 0.1 under 0.1 grounds
Fly ash 3 0.3 under 0.1 Activated fly ash under 0.1 under 0.1 under
0.1 Used tea leaves under 0.1 under 0.1 under 0.1 Activated carbon
5 2 under 0.1 Squeezed soybeans 17 8 under 0.1 Dolomite 12 12 under
0.1 Synthetic zeolite 1 4 0.4 under 0.1 Synthetic zeolite 2 under
0.1 under 0.1 under 0.1
[0021] The reason that the present invention attaches importance to
the adsorbing rate with respect to the adsorbing substances is as
follows. In detail, it takes about 5 to 10 seconds with more or
less difference depending upon scales of incinerators that
combustion gas changes to exhaust gas which is then discharged
through a chimney to the atmosphere. In this course of process, the
gases react on organic substances to produce dioxin. Hence, in case
that it takes a minute to adsorb hydrogen chloride gas, in which
time dioxin is generated, and residual hydrogen chloride gas is
discharged in the atmosphere.
[0022] Next, explanation will be given upon those in Table 1
showing the initial concentration under 0.1. The activated coffee
grounds are the used coffee material which already provided coffee
and having about 50% water content and dried at 100 to 140.degree.
C. and comminuted under 100 mesh, more preferably, under 200 mesh,
further preferably under 300 mesh since the adsorbing substances
that are fine are superior in flotation. Also, since coffee grounds
are more readily comminuted when having low water content, they are
preferably dried to have 2% or less water content. Drying is
carried out preferably at around 120 to 130.degree. C., more
preferably about 125.degree. C. since drying at 100.degree. C. or
less takes long and drying at 140.degree. C. causes the coffee
grounds to have oil oozed out on the surface and become poor in
ability of adsorbing hydrogen chloride gas. Used coffee grounds
merely dried to 5 to 10% water content was poor in adsorbing rate
in comparison with activated carbon. Used tea leaves are dried and
ground in the same manner as coffee grounds and are a little poor
in adsorbing ability in comparison with coffee grounds, so that the
used tea leaves need to be applied a little at a larger quantity.
Furthermore, coffee grounds when applied with lime (about 5 to 10
wt %) or having 5 to 10% water content can be advantageously ground
as effectively or easily.
[0023] Fly ash is those discharged at a huge quantity from a
thermal power plant or station or the like and is various in pH as
3 to 13 depending upon kinds of coal used and specific facilities
of thermal power plant to thereby have or show separate adsorbing
rates for adsorbing hydrogen chloride gas. Fly ash in Table 1 shows
the adsorbing ability of fly ash showing pH 10 (and CEC (cation
exchange capacity) about 120 at maximum) provided by mixing various
fly ashes having different pH values. Thus, fly ash in Table 1 is
hard to be into practical use. For the present invention, it is
preferable to employ activated fly ash provided by activating
freely selected fly ash. Activation of fly ash involves mixing fly
ash with slaked lime, which water is added to and is agitated and
left for 2 to 3 hours. The mixing ratio of fly ash and slaked lime
may be at discretion but the proportion of fly ash may be
preferably more than slake lime, for example, fly ash of 60 to 80
wt % and slaked lime 20 to 40 wt %. Precipitate in the mixture is
then dried and comminuted under 100 to 200 mesh, more preferably,
300 mesh to obtain an excellent adsorbing substance that shows pH
12 to 13 and CEC 150 to 200 and is quite high in rate of adsorbing
hydrogen chloride gas.
[0024] Next, synthetic zeolite will be detailed. An ordinary
synthetic zeolite (synthetic zeolite 1 in Table 1) used for
synthetic detergent or the like has the adsorbing rate that is only
a little higher than the activated carbon and is therefore not so
preferable for the present invention. Another zeolite, the
synthetic zeolite 2 (provided by Tosoh Corporation under tradename
"Zeolum") shows the adsorbing rate equivalent to those of the
activated coffee grounds and activated fly ash. The "Zeolum" is
superior in adsorbing also hydrogen sulfide gas, sulfur dioxide or
other gases as well as hydrogen chloride gas, but is problematic
due to a high cost.
[0025] Other materials such as the activated carbon of coconut
shell, squeezed soybeans, and dolomite show the concentration under
0.1 of hydrogen chloride gas 20 minutes after the gas-application
but are not usable for the present invention that needs or requires
quick adsorbing. Any other adsorbing materials than those shown in
Table 1 that can show or have the same or equivalent adsorbing rate
as the activated coffee grounds and activated fly ash can be fully
applicable to the present invention provided that it can be
preferably available at a low cost. Rice hull when carbonized shows
a rather high adsorbing rate but takes trouble and time for
carbonization. In case that an effective carbonizing method is
available, rice hull can be usable for the present invention.
Besides, wastes from agricultural products produced at a vast
quantity, such as wheat hull or squeezed sugarcane, may be
attempted to be given any treatment to achieve materials showing
high adsorbing rate and convenience in the aspect of disposing of
the wastes.
[0026] The dioxin-generation inhibitor according to the present
invention adsorbs and holds immediately or quickly hydrogen
chloride gas generated upon burning wastes and then causes the
hydrogen chloride gas to react on slaked lime and/or quick lime and
become extinct. In this respect, it is preferable to employ as
calcium compound any materials having excellent efficiency of
reaction on hydrogen chloride gas.
[0027] The dioxin-generation inhibitor according to the present
invention is provided in such manner that 50 to 85 wt % of calcium
compound (slaked lime, quick lime, etc.) is mixed with 50 to 15 wt
% of adsorbing substance, followed by adding a proper amount of
water to the mixture and making granulation and drying. More
preferable mixing proportion is around 65 to 75wt % of calcium
compound and around 35 to 25 wt % of adsorbing substance with which
mixing proportion there can be provided a dioxin-generation
inhibitor C in which an adsorbing substance A is covered at most of
the outer surface with calcium compounds B smaller in granular
diameter than the adsorbing substance A as seen in the schematic
diagram of FIG. 4. The actual or practical dioxin-generation
inhibitors comprise a quite large number of the schematically shown
dioxin-generation inhibitors C combined together. When the
inhibitor C mixes and contacts with combustion gas or exhaust gas,
the adsorbing substance A adsorbs hydrogen chloride gas contained
in the gases in an instant or quickly. The adsorbed hydrogen
chloride gas then reacts on calcium compound B to make calcium
chloride and be removed from the system of combustion gas and
exhaust gas, whereby generation of dioxin on the basis of hydrogen
chloride gas as a material is largely inhibited.
[0028] The method for burning wastes according to the present
invention involves spreading the foregoing dioxin-generation
inhibitor over wastes being burnt in which the powder material of
the invention removes hydrogen chloride gas in the combustion gas
and flying ashes and the granular material removes hydrogen
chloride gas generated upon burning wastes and hydrogen chloride
gas contained in residual ash. The more the powder material is
fine, the higher its flowability becomes, so that the powder
material can have higher efficiency of contacting with combustion
gas and exhaust gas and achieve excellent efficiency of adsorbing
hydrogen chloride gas. Hence, the inhibitor according to the
present invention adopts the mixture of the powder material and
granular material whose mixing proportion may be about fifty-fifty.
The power material may be simply or readily provided by that the
granular material (granulated product) is subjected to a granulator
to be partly made powdery, or by that granular material is caused
to undergo mechanical or thermal (i.e., combustion heat about
450.degree. C.) stimulation or irritation in the incinerator to be
partly made powdery. For this purpose, a degradation agent may be
added for excellent efficiency of degradation. In case that the
powder material is provided by causing the granular material to be
partly degraded into powder in the incinerator, it is needed to
apply the inhibitor only comprising the granular material which
application is easily carried out. The efficiency of degradation is
also required for the case that the granular material is subjected
to the granulator or the case that the granular material mixed with
wastes adsorbs effectively hydrogen chloride gas.
[0029] Next, the degradation agent will be explained. Granulated
and dried products generally tend to tighten. Hence, the present
invention provides the shape of granule that is easily degradable.
A degradation agent when added a little facilitates the efficiency
of degradation. The degradation agent may employ organic
substances, particularly, ground product of plant, such as squeezed
soybeans, used tea leaves, coffee grounds, or ground product of
oyster's shell. The degradation agent may be added about 3 to 10 wt
%, preferably around 5 wt % with respect to a total of calcium
compounds and the adsorbing substance. It is preferable to use a
degradation agent whose granular diameter is about under 40 to 60
mesh since too small granular diameter provides poor efficiency of
degradation.
[0030] The combustion gas referred to in the present invention is a
high temperature gas generated upon wastes burning in a combustion
chamber or zone. Combustion exhaust gas (called herein or hereunder
the "exhaust gas") is the combustion gas taken out and discharged
from the combustion chamber or zone. The flying ashes is solid
content or matter flying together with the combustion gas and/or
exhaust gas. Also, the residual ash refers to a residue from
combustion.
[0031] Disposing of wastes by use of fire involves burning wastes
for disposal or making use of combustion as fuel. The present
invention is applicable to either case. The present invention is
also applicable to an extremely large-scale incinerator or
combustion furnace of over several dozens to several hundreds tons
of daily disposal, to a large or middle-sized incinerator or
combustion furnace of about several dozens to several tons of daily
disposal, or to a small or extremely small-sized incinerator or
combustion furnace for a small scale plant or domestic use.
[0032] The present invention can be applied to the middle-sized or
larger incinerator or combustion furnace merely by mounting a
spreader to the conventional incinerator or combustion furnace
without necessity of modification of the facilities or newly
provision of expensive facilities, resulting in large reduction of
cost. The reason why the spreader is used here is that wastes are
continuously supplied by a movable floor or the like, so that the
inhibitor according to the present invention at an amount
corresponding to wastes supplied per unit time is to be applied
continuously. Hence, the capacity of the spreader needs to
correspond to a specific amount of wastes. Spreading the inhibitor
by the spreader is precisely aimed at wastes to be burnt. The
inhibitor of the present invention comprising only the powder
material needs to be force-fed to a combustion point.
[0033] A small-sized incinerator or combustion furnace may be
fabricated mounting a spreader on the outside and a scattering
device at an upper part inside the furnace, so that hydrogen
chloride gas is substantially completely removed. Furthermore, a
small or extremely small-sized incinerator may burn wastes that
previously mix with the inhibitor according to the present
invention. Upon burning off a field or a bonfire, the inhibitor
according to the present invention may be spread over wastes to
largely reduce or decrease generation of dioxin.
[0034] Next, the "RDF" (refuse derived fuel, provided by shattering
wastes or refuse, and causing them to set hard, i.e., drying,
compressing and forming them in a bar-like shape) will be
explained. In detail, RDF is a material obtained by that wastes or
refuse containing thermoplastic resin, such as plastic film, is
shattered and dried, and compressed and shaped into a solid matter
in size of fingers. Since RDF has less water content and
well-regulated shapes, they are suitable for solid fuel. RDF when
burnt does generate dioxin "naturally" since RDF often contains
vinyl chloride film in the material.
[0035] Under the circumstance, the inventors attempted to add the
dioxin-generation inhibitor according to the present invention upon
producing RDF and succeeded in manufacturing RDF that involves less
generation of dioxin. Conventionally, upon manufacturing RDF, quick
lime is added a little for drying (removing water content). In
place of quick lime, the inventors added the dioxin-generation
inhibitor of the present invention in powdery state at an amount of
0.2 to 5 wt % with respect to dried wastes. The loadings when less
than 0.2 wt % shows less effect of removal of dioxin, and it takes
much cost to have a problem in the aspect of cost and effect when
the loadings is more than 5wt %. A sufficient effect of removing
dioxin can be provided at the loadings around 0.5 to 1.5wt %,
particularly, around 0.7 to 1 wt %.
[0036] Preferred Embodiments of the Invention
EXAMPLE 1
[0037] High reactive quicklime of 66 wt % (made by Ashidachi Lime
Co., Ltd., containing CaO of 73%) used as the calcium compound was
mixed with activated coffee grounds (under 200 mesh) of 19 wt % and
activated fly ash of 9 wt % used as the adsorbing substance and
shown in Table 1, and used tea leaves under 40 mesh of 5 wt % as
the degradation agent, followed by adding water of 25 wt % and
kneading, extrusion shaping into granules 2 mm.times.5 mm, and
drying the shaped granules at 120.degree. C. to obtain the
dioxin-generation inhibitor.
[0038] The resultant dioxin-generation inhibitor was spread to RDF
(5 kg) burning in a small incinerator (or combustion furnace) 1 in
FIG. 1. The amount of spreading was 0.7wt % with respect to RDF.
The incinerator 1 shown in FIG. 1 is for use in a small-scale plant
and comprises a spreader 2 at the outside of the furnace for
feeding the dioxin-generation inhibitor into the furnace, and a
scattering means 3 for scattering the inhibitor over wastes being
burnt. The capacity of the incinerator 1 is 1 m.sup.3. The powder
material removes hydrogen chloride gas in the combustion gas and
flying ashes and the granular material removes hydrogen chloride
gas in the residual ash, thereby inhibiting generation of dioxin.
FIG. 2 is a plan view of the scattering means 3 whose four blades
31 each twists at the middle.
[0039] At a time when burning is stable, the combustion gas was
taken through the measuring port to measure concentration of
hydrogen chloride gas in the combustion gas and find that
concentration was 118.2 mg/m.sup.3 as shown in Table 2 (measured by
Himec Ltd., Chugoku district office).
2 TABLE 2 Concentration of hydrogen chloride Specimen Gas
(mg/m.sup.3) Example 1 118.2 Comparative example 1 442.0
COMPARATIVE EXAMPLE 1
[0040] RDF (5 kg) was similarly burnt in the same incinerator as
Example 1 without using the dioxin-generation inhibitor of the
present invention. Concentration of hydrogen chloride gas in the
combustion gas was measured and shown to be 442.0 mg/m.sup.3 as
seen in Table 2.
[0041] From the above, it will be appreciated that using the
dioxin-generation inhibitor according to the present invention
causes generation of hydrogen chloride gas to be reduced to about
1/4 in a small incinerator for general domestic use.
EXAMPLE 2
[0042] A large-scale combustion furnace or incinerator 4 may carry
out spreading of the dioxin-generation inhibitor over wastes being
burnt on the wastes-burning/moving grid 5 by use of an inhibitor
spreader 6 mounted on the outside as shown in FIG. 3. In this case,
the combustion furnace 4 having been being used may be enough to
only mount the spreader 6 without necessity of modification,
thereby being quite economical.
[0043] A manufacturing plant for RDF burns RDF partly for drying
wastes material. A combustion furnace used in this case may have
substantially the structure shown in FIG. 3. RDF (according to the
present invention) mixing and kneading the dioxin-generation
inhibitor of the invention at a proportion of 1.5 wt % (with
respect to dried wastes), and RDF (as conventional) mixing and
kneading lime of 2 wt % as conventionally were produced and burnt
separately in the same large-scale combustion furnace for drying
wastes to measure generated dioxin according to JIS K 0311-1999
method and gas chromatography mass analysis method. Measurement
results are as shown in Table 3 (Measurer: Bab-Hitachi Industrial
Co.).
3 TABLE 3 Specimen Dioxin (ng-TEQ/m.sup.3) Example 2 0.063
Comparative example 2 0.11 Dioxin: PCDDs + PCDFs + CoPCB
[0044] As shown in Table 3, the amount of generated dioxin from RDF
according to the present invention was 0.063 ng-TEQ/m.sup.3
(nanogram). The value clears 1 nanogram provided in the already
given Heisei 14 (2002) Regulation for the large-scale combustion
furnaces and also 0.1 nanogram newly provided in Heisei 14
regulation. Regarding small combustion furnaces for domestic use,
the values provided in the regulation are 10 nanogram and 5
nanogram, respectively, and do not at all lead any problems.
COMPARATIVE EXAMPLE 2
[0045] The conventional RDF does not clear the newly provided
Heisei 14 Regulation. In this comparative example, the
dioxin-generation inhibitor was partly mixed, resulting in a
possibility of a low value of generated dioxin deviated from an
actual state. This could be inferred from the fact that measurement
results of hydrogen chloride gas on the basis of specimens taken
simultaneously with measurement of dioxin do not have definite
difference as seen in Table 4, i.e., that there shows merely quite
little difference in comparison with the measurement results of
hydrogen chloride gas shown in Example 1 and the comparative
example 1, and that the case in Table 4 has merely quite little
difference between the examples in view of difference of dioxin
concentration in residual ash described later referring to Example
3 and comparative example 3. The above inference is possibly
explained also on the basis of such fact and any difference arising
therefrom that Examples 1 and 3 employ a small-sized combustion
furnace while Example 2 uses a large-scale combustion furnace.
4 TABLE 4 Concentration of hydrogen Specimen chloride gas
(mg/m.sup.3/N) Example 2 3.9 Comparative example 2 4.8
Concentration of hydrogen chloride gas: O.sub.2 12% conversion JIS
K 0107 Mercury thiocyanate method (II) Absorptiometric method
EXAMPLE 3
[0046] Measurement results of concentration of dioxin in residual
ash taken in the burning test in Example 1 are shown in Table 5
(measured by: Bab-Hitachi Industrial Co.).
5 TABLE 5 Specimen Dioxin (ng-TEQ/m.sup.3) Example 3 0.033
Comparative example 3 0.12 Dioxin: PCDDs + PCDFs + CoPCB
[0047] Toxicity equivalent concentration
COMPARATIVE EXAMPLE 3
[0048] Measurement result of concentration of dioxin in residual
ash taken in the burning test in the comparative example 1 is also
shown in Table 5.
[0049] As seen in Table 5, concentration of dioxin contained in the
residual ashes with the dioxin-generation inhibitor according to
the present invention having been spread was about 1/4in comparison
with the case not spreading the inhibitor. In view of concentration
of dioxin in residual ash 6.6 nanogram according to a certain
measurement result, that in the comparative example in this
invention is quite little. This is so inferred as resulting from
using the RDF as wastes material in this Example and comparative
example (to be noted here is that RDF mixes quicklime.).
[0050] Effect of the Invention
[0051] As seen from the above, the inhibitor for inhibiting
generation of dioxin according to the present invention comprises
an adsorbing substance superior in rate of adsorbing hydrogen
chloride gas and a reaction substance superior in reactivity with
hydrogen chloride gas, as main contents, and a degradation agent
additionally used when required, the mixture of these materials
being granulated and dried.
[0052] Hence, the dioxin-generation inhibitor is superior in
ability of adsorbing hydrogen chloride gas and is capable of
largely reducing generation of dioxin contained in the combustion
gas and residual gas, thereby making a great contribution to
environmental sanitation. Also, the present invention can make use
of industrial wastes as the adsorbing substance to thereby be
excellent in the respect of saving resources while providing such
advantage as being manufactured at a low cost and with a simple
apparatus and technology.
[0053] The method for burning wastes according to the present
invention involves spreading over wastes being burnt the
dioxin-generation inhibitor that comprises a granular material,
powder material or a mixture of the same, so that the powder
material removes hydrogen chloride gas in combustion gas and flying
ashes and the granular material removes hydrogen chloride gas in
residual ash, whereby inhibiting generation of dioxin.
[0054] The dioxin-generation inhibitor according to the present
invention can be used selectively correspondingly to the scale of
incinerators and combustion furnaces to burn wastes or refuge. The
dioxin-generation inhibitor is also usable in burning off dead
grass or a field or in a bonfire without use of incinerators or the
like.
[0055] Hence, the present invention provides that concentration of
dioxin contained in the exhaust gas can be largely reduced or
decreased with a simple device (although hitherto realized at a
quite high cost), and concentration of dioxin in the residual ashes
is also largely decreased (which has been almost impossible
conventionally), providing a good news to the serious environmental
problem.
* * * * *