Note: Descriptions are shown in the official language in which they were submitted.
Wo 95118667 PCT/CA95/00012
2 1 80633
TITLE OF INVENTIQN
rKrV~ . lUr~l OF r~ ' AND V--;Lr~U~ OF
clDr-~ ~T.OnF~ ~Ur~L~S IN l~ OF
Wllq~ TFDTl~T.Q
FTr~r~n OF INVENTION
The present invention relates to the prevention of
formation and destruction of organohalogen compounds
including dioxins and furans in incineration of waste
materials .
R~rRr7R~uND TO T~ J~ TIoN
The formation of organohalogen ~ ol~n~ (OHC),
including polychlorinated dibenzo-p-dioxins ~PCDD) and
dibenzo furans (PCDF), OCCUrB in all combustion processes
which provides the n~r~a~ry favourable conditions and
ingredients, such as c~rh~nPous, organohalogenated and
20 metallic materials. Municipal, medical and industrial
waste incinerators are large contributors to the release
of O~IC to the environment. Municipal solid waste
incinerators are called "Resource Recoveryl1 plants,
promising to provide steam and electricity while
25 simult~n~n1~1 y reducing trash volume by 90 percent .
Reduction in trash volume results in less transportation
costs and land fill space. Due to these benefits,
incineration is a viable alternative to landfill.
Ilundreds of such incinerators are in operation around the
3 0 world .
One of the significant drawbacks to the incineration
procedure is that several hundred stable and toxic
compounds, including polychlorinated dibenzo-p-dioxins
(abbreviated herein as PC3D and collectively commonly
35 termed "dioxins") and polychlorinated dibenzo~urans
(abbreviated herein as PCDF and collectively commonly
termed "furans"), are formed and are present in parts-
per-million ~-nrr~ntrations both in the flyash formed
dur~ng c~mbustion and in the stack emissions. The
~ WO95JI8667 2 1 8 0 6 3 3 PCT/CA95100012
formation of OHC, including PCDD and PCDF, in the process
of combustion and pyrolysis of organic compounds in
presence of inorganic halogenated compounds has been
known for some time. The major sources of release of
OHC, including dioxins and furans, are various
incineration processes involving combustion of municipal
waste, municipal 51udge, medical waste, polyvinyl
chloride and other ha1Ogen-cnnt~;nin~ plastics.
Our research work shows that the formation of OHC,
including dioxins and furans, occurs in municipal solid
waste ;nr;n~ tr,rS (MSWI) around the world. It has been
shown in our laboratories that combustion of PVC resulted
in the formation of dioxins. Increased levels o~ dioxins
and furan3 have been observed in stack emissions and in
flyash when PVC was incinerated. One of the r -h~ni mq
proposed for the formation of PCDD and PCDF is by
reactions of molecular precursor species that are present
during incineration, resulting in surface catalyzed
synthesis of PCDD/PCDF on the flyash via recL~ J
free radical condensation, dechlorination,
dehydL~ ation, t,rans-chlorination, isomeri2ation and
other similar molecular r~rt;onq. From the fact that
uncontrolled rf~isrt j on~ occur during the lncineration
process, it can be presumed that all above m~nt i onF~d
reactions can proceed due to the presence of different
kinds of metal~metal-oxides, inorganic halides, organic
materials and gaseous compounds, such as CH2-CH" CH=CE~,
HzO, CO2 and HCl in the flue gas stream. Inorganic
halides and acid gases can form in the incineration
process at high temperatures from halogen-cnn~ininr
plastics, moisture and small amounts of metals present in
waste materials. These compounds constitute catalytic
sites on the sur~ace on the f lyash produced during
incineration to enhance the formation of PCDD/PCDF.
We have studied flyash samples from different
' incinerators around the world. The dioxins and furans
2180633
have been detected in all incinerators studied. More
than 600 compounds were detected in flyash samples that
includes a large number of OHC.
Release of OHC, including dioxins and furans, by
5 MSWI through the stack emissions and flyash is of
significant public concern. MSwI flyash containing high
levels of dioxins and furans when dumped in landfill
sites can leach dioxins in water system. Hence, there is
a need for a technology which can provide safe
10 incineration of waste materials. The present invention
relates to a method of reducing the OHC in the stack
emissions and in flyash of the MSWI. There has been
previously described in our U. S . Patents Nos . 4, 793, 270
and 5 ,113, 772, the provision of material acting as a
15 catalyst inhibitor in association with the f lyash so as
to inhibit the catalytic activity of the f lyash towards
the formation of chlorinated compounds, including dioxins
and f urans .
US-A-5113772 descri~es the inhibition in an
20 incinerator of the ~ormation of dioxins and furans
categorized by flyash from precursors using certain
organic a ~ kA 1 i n~ and inorganic ~ l k~ 1 i n~ materials
US-A-5021229 defines the addition of calcium-based
sorbents, including calcium oxide, calcium hydroxide and
25 calcium carbonate in dry or slurry form to a flue gas
stream from an incinerator to react with HCl in the f lue
gas, by i n j ection at t emp eratures o f 4 0 0 o to 9 0 0 C .
WO-A-8800672 describes the formation of dioxins in
the incineration of wastes using sodium carbonate or
30 sodium bicarbonate in solid form added to the waste.
DE-A--3527615 describes an incineration process in
which HCl gas is reacted with a basic powdery material.
DE-A-3628043 describes a filter iL, ~l~Lu~ for
purifying inhaled air comprising a plurality of layers of
35 absorption material including a calcium ammonium silicate
material impregnated with glycol.
GEANDERTES BLATT
-
2~80633
DE-A-3632366 describes a procedure for ~icp~c~l of
halogenated cu~ uuu-,ds by bringing the halogenated
materials into contact with a nucleophilic reaction
partner at high temperature.
SI~MMARY t~F JNVRNTION ~ ~c
It has now been found that inorganic bases, either
alone or in combination with aliphatic hydroxy or
polyllydLu~y compounds (such materials being herein termed
de-LLUy~L:~ and inhibitor/de~LLuy~ ,,), are very effective
in destroying OHC, including dioxlns and furans, on ~SWI
flyash. It i5 believed that the destroyers, when heated
with flyash, react with the OHC and extract halogen to
f orm neutral stable inorganic salts and organohydroxy
~ lllp-.:UII-15, which then react with more destroyer and
metallic constituents in flyash at higher temperatures,
resulting in their decomposition. Formation of dioxins
and furans by the catalytic activity of f lyash and
precursors in f lue gases at temperature between about
250 and about 400~C has been reported in our previous
U.s. Patents Nos. 4,793,270 and 5,133,772. Inorganic
bases have been used traditionally for conversion of OHC
into organohydroxy compounds under strictly controlled
conditLons . The use of destroyers under drastic
conditions, such as high temperatures and presence of air
and steam, as provided herein, results in the reaction of
OHC in the f lue gases and on f lyash particles with the
destroyer to f orm the organohydroxy compounds, which
ultimately decompose due to ~urther reactions with
de~LLuy~ at higher temperatures. Hence, according to
one aspect, the present investigation is directed towards
the destruction of OHC on f lyash and in f lue gases
produced during MSWI by the utilization of the destroyers
in ~he manner described herein.
In another aspect, the present invention is directed
towards the deac~ivation of the flyash and thus the
prevention of the f ormation of OHC, including dioxins and
GEANDER~Es ELA~
2 ~ ~0633
f urans . Research in our laboratories and a study of the
correlation of operational conditions with levels of
dioxins and furans detected in the stack emissions and in
the flyash show that up to about 15% OHC compounds is
s formed in the combustion process and the rr~-;n;n~ about
85% is formed by catalytic activity o~ flyash and small
molecules, such as C~=CH~, CH=CH, H O, CO2 and HCl,
present in f lue gas stream .
Thus, based on previous U.S. Patents Nos. 4,793,270
and 5 ,113, 772, inhibition of the formation of about 85%
of the OHC compounds, including dioxins and furans, was
possible by the Introduction of inhibitors in the
postcombustion zone of the incinerators at about 400C.
Since it is possible to introduce the presently-
15 investigated destroyer compounds at a wide range of
temperatures, from about 300 about 1100C, the present
invention enables a higher destruction effLciency to be
achieved. In laboratory experiments, complete
destruction of all OHC on flyash has been found when
20 flyash was heated with inorganic bases at 400C.
Mixtures of inorganic bases and aliphatic hydroxy
compounds (AHC) are highly effective when they were used
in smaller amounts and even at lower temperatures (about
300O to about 500C) and the specific utilization of such
25 organic-inorganic complexes in decreasing PCDD/PCDF on
flyash and stack emissions forms an aspect of the
invention. Destroyer compounds also act as inhibitors
and deactivate flyash sites responsible for the formation
of the OHC . The ef f ect of temperature on the OHC on the
3 0 f lyash shows that the amount of dioxins and furans
increases with temperature up to about 400OC When
f lyash containing OHC was covered with destroyer
compounds and heated, then destruction of OHC started at
about 300OC and complete destruction of OHC had occurred
35 by the time the temperature reached about 400OC. Various
destroyers have shown different destruction efficiency
- - 21 80633
l~or OHC. An increase in the amount of destroyer (when
only inorganic bases were used) increases its efficiency
for destruction of OHC compounds. EIowever, the mixture
of inorganic bases and AHC at 2 . 59~ (by Wt) of flyash
shows optimum destruction efficiency for OHC. The
destruction ef f iciency does not improve signif icantly by
increasing the amount of inhibitor mixture. The
technique described here is useful for the destruction of
OHC, including dioxins and furans, at the source, i.e.
in the post combustion zone of ~SWI, using destroyers in
the postcombustion zone.
Accordingly, in one aspect of the present invention,
there i5 provided a method for incinerating waste
materials h~herein dioxins and furans formed in the
incineration are destroyed, which comprises incinerating
waste materials selected from municipal solid waste,
medical waste, municipal sludge, industrial waste and
other materials, to form fly ash and gaseous products of
incineration, comprising dioxins and furans; and passing
the gaseous products of incineration to a precipitation
step, wherein the fly ash is precipitated from the
gaseous products of the inciner~tion; characterized by:
introducing at least one destroyer compound directly into
the gaseous products of incineration during the passage
of the gaseous products of incineration to the
precipitation step to react with and destroy dioxins and
furans present in the gaseous products of incineration
prior to destroyer compound introduction to decrease
dioxin and furan concentrations in stack emissions from
the precipitation step.
In another aspect of this invention, any material,
such as flyash, soil, sediment or sludge, containing high
levels of OHC can be detoxicated by mixing the material
with a suitable destroyer and heating the resulting
mixture at about 300 to about 900C or, preferably, by
incinerating such material in the existing incinerators
Dtn~
~ 2180633
alony with other waste material~, and using destroyers in
a postcombustion zone as described above. Accordingly,
materials containing high levels o~ organohalogen
compounds, including dioxins and furans, including soil,
5 sediment, sludge or flyash formed in an incineration
operation, may be mixed with the waste materials to be
incinerated according to the procedure provided herein to
ef f ect destruction of the OHC in such materials .
,,C~s~ TFS ~
~ Wo 9S/18667 2 t 8 0 6 3 3 PcT~cAgsl0ool2
In another aspect of the invention, certain
materials are used to effect inhibition/destruction of
PCDD and PCDF which are mixtures of certain alkali metal
hydroxides and certain ~l;rh~t;c hydroxy or polyhydroxy
5 c~ ...~,u1-d~. Such alkali metal hydroxide . ~s~u~ds may
comprise ~zodium hydroxide or potassium hydroxide,
particularly potassium hydroxide, while such a1 ;rh~t j c
hydroxy or polyhydroxy compounds may comprise ethylene
glycol or polytetrahydrofuran. A particularly preferred
lO mixture of materials is a mixture of potassium hydroxide,
ethylene glycol and silica gel.
Such materials may be effectively employed by direct
injection as an aqueous solution into a post-combustion
zone of an incinerator at a temperature of about 300 to
about 500-C, preferably about 350 to about 450 C, more
particularly around 400'C.
Accordingly, in this aspect of the invention, there
is provided a method of decreasing the rnnnpntration Of
organohalogen compounds in flyash and vent gas stream
20 formed in the incineration of combustible r~tP~; ;~
which comprises effecting combustion of combustible
materials in a combustion zone to form gaseous combustion
products nnnt~;nin~ e~trained flyash; conveying the
gaseous combustion products from the combustion zone to
25 a precipitation zone; precipitating flyash from the
gaseous combustion products in the precipitation zone;
venting the gaseous combustion products from the
precipitation zone to provide the vent gas stream; and
introducing to the gaseous combustion products during the
3 0 conveying step an aqueous solution of at least one
mixture o~ alkali metal hydroxide and aliphatic hydroxy
or polyhydroxy compounds at a temperature of the gaseous
combustion products of about 300 to about 500 C.
The introduction of such organic-inorganic nnrrl P~Pq
35 to the combustion gas stream also may be c ' inP~ with
introduction of an alkali metal hydroxide, in the form of
.
-
Wo 95/186~7 2 t 8 0 6 3 3 PCT/C~95100012
8
an ar~ueous solution thereof, particularly sodium
hydroxide or potassium hydroxide, directly into the
combustion gas stream, at a higher temperature above
about 500'C, which may include multiple introductions at
dif ferent higher t 1 ~ aLu~e levels of approximately
500 C, 600-C and 700 C.
R~7T~ DESt~TPTION OF DR~WINGS
Figure l is a 8- ~;r diagram of the experimental
set-up used for the studies of the destruction, the
inhibition of formation and catalytic formation of OHC on
flyash;
Figure 2 is a graphical repr~C~.nt~t;nn of the native
PCDD and PCDF present on MSWI flyash prior to ~no heat~
and after heat treatment of the flyash at various
temperatures;
Figure 3 rn7~t~;nc a graphical repres~nt~tinn of the
amounts of native PCDD (A) and PCDF ~B) on MSWI flyash
heated without and with typical destroyers at various
temperatures;
20 Figure 4 rnnt~;nc chromatograms showing the response
of electron captor ~l~t~rtor for the O~C. Samples
analyzed were l) MSWI flyash, no treatment, 2) MSWI
~lyash heated to 400 C without destroyer, 3) MSWI flyash
heated at 400 C with destroyer (NaOH 5~ by wt . );
Figure 5 is a graphical repres~nt~t;nn of the amount
of 13C PCDD produced on the flyash prior to (BG) and after
destroyer tr~ tq of the flyash at 300-C;
Figure 6 is a graphical repres~nt~tinn of the effect
of temperature on formation of dioxins from ''3C
p~ntarhlorophenol precursor on flyash coated by different
destroyers (2~) at various t~ ~ aLuLes; and
Figure 7 rnnt~inc graphical representation of the ~
decomposition of native dioxins and furans at various
temperatures using ~rious destroyers.
-
~ WO 95118667 2 1 8 0 6 3 3 PCT~C~35/00012
,. g
r.T~NT'T~T, DESrT~TPTI~ OF INVENTION
In the present invention, inorganic bases, either
alone or in A~m; ~t~re with aliphatic hydroxy or
polyhydroxy 'q (here termed destroyers) are
5 employed and their effect on organohalogen ~ uul,ds
lOHC), including dioxins and furans, on flyash was
investigated. It has been found that the destroyer
U ~ lc, when coated on the flyash, effectively destroy
OHC on the flyash at temperatures above about 300 C. The
l0 destroyer compounds may be selected from inorganic bases
which are hydroxides, oxides, ~rh~n~t~q, 1~yd- uue~
on:~t~q and silicates of one or more alkali metals or
~qlkPllinF~ earth metals. The destroyer compounds that have
been found to be particularly effective are sodium
15 hydroxide ~NaOH), potassium hydroxide (KOH), calcium
hydroxide (Ca (OH) 2) ~ calcium oxide (CaO), magnesium oxide
(MgO), sodium carbonate (Na2CO3), potassium carbonate
(K2CO3), calcium carbonate (CaCO3), sodium orthosilicate
(NacSiOi), sodium metasilicate (Na2SiO3) and either used
20 alone or in ~ ;Ytllres with aliphatic hydroxy or
polyhydroxy compounds (AHC). Such aliphatic hydroxy or
polyhydroxy compounds may include ethylene glycol, l, 2-
propanediol, l,4-b~t~ne~;ol, polytetrahydrofuran or
mixtures of these ~u- ,~uul-ds . These destroyer compounds
25 can be used to effectively destroy OHC on the flyash and
in the flue gases of solid waste incineration by
introduction to the combustion gas stream at suitable
temperature. In the laboratory tests, it has been found
that the flyash coated with NaOX and XOH (2 to 43~)
30 destroys the formation of PCDD up to 99~ compared to the
formation of pr-DD on untreated flyash. A similar effect
was observed using an even smaller percentage of mixtures
of NaOH or KOH in conjunction with aliphatic hydroxy
compounds .
3~ Several experiments were conducted using the
laboratory experimental set-up shown in Figure l. A MSWI
Wo 95/l8667 2 t 8 0 6 3 3 PCT/C~95/00012
, ~ 10
flyash (with native dioxins a~d furans produced in the
inci~eration proce66 on it) was heated at temperatures
200- to 500 C in air under d~ _~' -ric pressure. It was
found that the amount of native dioxins and furans
5 increased up to 350 C, probably due to presence of
precursors on the flyash, which by catalytic activity of
the 1yash, were converted into PCDD/PCDF. Above 350-C,
the amount of PCDD/PCDF on the flyash decreased, probably
due to a decreasing rate of forr~t;nn against the rate of
10 ~ ition of PCDD/PCDF. The flyash heated at 400 C
to 500 C showed very little amount of both PCDD/PCDF.
After the heat treatment at various temperatures, flyash
samples were dried by heating at 150 C to remove toluene
used for extraction. A catalytic activity test of the
15 flyash samples next was conducted at 300-C. The
procedures for catalytic activity tests were similar to
that reported in our previous U.S. Patents Nos. 4,793,270
and 5,113,772. It was found that flyash heated up to
500 C retained its catalytic activity to produce PCDD
20 from precursors, such as PCP, at lower temperatures such
as 250- to 400 C.
In another set of laboratory experiments, heat
treatment of 1yash coated by 2 to 5~ destroyer compounds
shows that destruction of PCDD/PCDF started at 300 C and
25 was completed by the time the temperature reached 400-C.
~ence, the addition of destroyers makes the flyash
complex destructive for organic compounds, even at 300-C,
otherwise flyash promotes the formation of dioxins and
furans (see Figures 2 and 3). The effectiveness of
30 destruction depends upon the amount of destroyer used and
the temperature employed for the destruction. About 6
wt9~ destroyer at 300-C has the same effect as about 1 wt~i
destroyer at 400 C. This result indicates that very
little destroyer is required to achieve complete
35 destruction of the O~C, if destroyer can be introduced at
temperatures ~etween 400 and 900 C, or up to llOO C, in
WO 95118667 2 ~ 8 0 6 3 3 PCr1C~95100012
11
the postcombustion zone of the incinerator, ~erf~n~in~
upon the type of the destroyer used. Destruction
efficiency also depends upon the melting point of the
destroyer used. NaOH and ICOH are highly effective when
used above about 390 C, Na2CO3 above about 800-C, and
sodium meta- and ortho-silicates above about 900 C.
In general, destroyer compounds are used in any
amount within a range of from about 0.5 to about 6 wt~ of
the flyash produced in the incineration step. This
quantity generally corresponds to about 0 . 025 to about
0.3 wt9~ of- the waste material incinerated.
The destroyer may be introduced to the post-
combustion zone of the incinerator in any convenient
form, for example, granular form, powder form or,
preferably, as an aqueous solution.
Depending on the destroyer compound or compounds
used, the destroyer compound may be introduced between
the combustion chamber and precipitation zone of the
incinerator at a suitable temperature of from about 300-
to about ll00-C, preferably from about 300 to about 800 C
and particularly from about 300 to about 600 C.
The destroyer effect achieved herein also may be
combined with the inhibition of formation of OHCs by
flyash catalysis, as described in USPs 4,793,270 and
5, 113, 772, by introduction of a suitable inhibitor
material as described therein, to the incinerator gas
stream between the combustion zone and the precipitation
zone, generally at a temperature o~ from about 300- to
about 500 C. The present invention employs, in one
emho~;m~nt, mixtures of materials as inhibitor~destroyers
not contemplated in our earlier patents.
As will be apparent from the disclosure of USP
5 ,113, 772, some of the rnmrm-nrlq which were used as
inhibitors of OHC formation in that patent are used
herein as destroyers of OE~C. It is preferred herein to
employ the same compounds for destruction and inhibition.
Wo 9S118667 2 1 8 0 6 3 3 PCT1CA95100012
12
In general, higher temperatures are required to effect
destruction of OHC tqith such , 'R than inhibition of
OHC formation. The destroyer and inhibitor compounds,
therefore, may be added at different lor~t;nnq, and
5 accordingly, different temperatures, between the
incinerator and the precipitator. The present invention
employs, in one ~nhn~;r^nt, mixtures of ~-t~ as
inhibitor/destroyers not cnnt~ _ 1 ^ted in our earlier
patents .
Several mixtures of the above described inorganic
bases and - their combination with AHCs were tested in
laboratory experiments. A coating of 5 wt% NaOH on
flyash completely destroyed all the OHC, including
PCDD/PCDF, on the flyash at 400 C. In addition, the
15 flyash was F~rr~n~ntly deactivated for the formation of
PCDD/PCDF. Deactivation of flyash is very important
because it provides the means to introduce destroyers at
any temperatures above 400 C for higher efficiency with
a lower amount of destroyer. In this way, destroyers
20 effectively destroy an estimated l0 to lS~ OHC compounds
produced in the furnace when introduced at about 400 to
ll00-C in the post combustion zone of the incinerator.
The procedure also deactivates the flyash to prevent
further formation of PCDD/PCDF (about 35 to go~) by
25 catalytic activity of the flyash in the cooler parts of
the incinerator.
Acid ga6es which may be present in the incinerator
gas stream, such as HCl, SO2 and M2~ also may react with
the ~ inQ destroyer compounds, so that such acid gases
30 are removed from the gas stream, whereby their
con^^n~tinn in the stack emissions decreases.
The dioxins and the furans exhibit varying degrees
of toxicity, rl~renrlinj on the number of chlorine atoms
present and the position of the chlorine substitution.
35 Usually toxicity of a particular sample is estimated
` based on amount of tetra- to octa- chlorinated dioxins
Wo 95/18667 2 1 8 0 6 3 3 PCT/CJ~95/00012
13
and furans present. The formation of PCDD and PCDF for
precursor m~q, such as chlornhen7~nrq~
chlorophf~nnl R and chlorodiphenyl ethers on flyash is
illustrated by the following equation:
_ _
a ~ .~o ~ 7
+ ~T + >~ 1
~Y AS~ ~ P~::DF
10 m= I _ 6 n-- I - 5 ~)
rT~ r)~ ~H~ ~Lu~ur~ul5 ~ 8
Cl, P~DD
~lrZ~MpT.~.':
15 Exam~le l:
This Example shows the effect of heat on the amount
of native dioxins and furans present on MSWI flyash.
An experimental apparatus shown in the Figure l was
used to test the effect of heat treatment and catalytic
20 activity of flyash samples. The apparatus comprised a
glass tube (25 X l cm I .D. ) passing through the oven.
Part of the ~low tube was a re6ervoir where f lyash to be
tested was packed. A flyash sample rom MSWI with all
compounds produced in the process of the incineration on
25 it was heated at various temperatures to examine the
effect of heat. In each experiment, 1.5 g of the flyash
was placed in the glass tube. The section of the tube
rnntAininrJ flyash was heated at various temperatures for
60 minutes using 3 ml/minute flow of air through the
30 tube. After completing the experiment, the flyash was
spiked with an int~rnAl standard for recovery estimates.
Orga~ic rnmro~n~lc present on the flyash were extracted by
eluting with 220 ml toluene. Extracts were cnnr~nt~ated
by rotary evaporation to a few ml and final rnnr~nt~ation
35 in a sample vial to 500 ~Ll under a gentle stream o~ N2.
~ WO95118C67 2 1 8 0 6 3 3 PCTICA95100012
14
Figure 2 shows a graph of the amount o~ native
dioxins and furans present on ~SWI flyash prior to ~no
heat) and after heat tL~ ~`. t of the flyash at various
temperatures. The results of these experiments reveal
5 that the flyash produced in the incineration process
rnntRinc high levels of dioxins/furans (no heat plot) and
precursors. The MSWI flya3h is highly catalytically
active, which produces more dioxins/furans, probably from
native precursors present on the flyash, when heated from
200- to 400'C.
After the heat treatment at various temperatures,
flyash samples were dried by heating at l50 C to remove
toluene used f or extraction . Then a catalytic activity
test of these flyash samples was conducted at 300 C. In
15 the catalytic activity test, a volume of 50 /ll of 5 ~g/~Ll
13C_pCp solution in tl~;lnnl wag deposited on the gl~ss
beads on top of the flyash and the solvent was allowed to
evaporate. The section of the tube ~nnt~ ;ng flyash and
13C-PCP was heated at 300'C for 60 minutes using 3
20 ml/minute flow of air. After completing the experiment,
the flyash was spiked with an internal standard for
recovery estimates and extracted as - ;~nn~d above.
Analysis of extracts shows the f ormation of 33C PCDD .
This result indicates that merely heating the flyash does
25 not affect its catalytic activity.
mnle 2:
This Example shows the effect of 5~ destroyers on
native PCDD/PCDF on the flyash.
In these experiments, fresh flyash (l0 g) rnnt~ining
30 native PCDD/PCDF was coated with a 5~ destroyer solution
in water. A l . 5 g portion of destroyer coated and dried
flyash was used in the heat treatment described in
Example l. The amount of PCDD/PCDF detected in flyash
coated by typical destroyers, namely NaOH and PSEGC (a
35 polysilicate-ethylene glycol complex formed from
KOH:ethylene glycol:silicagel in respective weight ratios
~ WO 95/18667 2 1 8 0 6 3 3 PCTtCA9~100012
15
17: 60: 23 ) and heated at various temperature6 is shown in
Figure 3 . Comparing the amounts of PCDD/PCDF on f lyash
heated at various temperatures without (Figure 2) and
with NaOX, PSEGC and SMSEG (a sodium metasilicate-
5 ethylene glycol complex formed from sodium--t:~c;l;r~te:ethylene glycol in a weight ratio of 15:85)
destroyers (Figure 3 ), it can be seen that no PCDD/PCDF
was produced between 300 C and 500 C on destroyer-coated
flyash. In fact, the native PCDD/PCDF content of
10 destroyer-coated flyash was reduced at 300 C and
completely eliminated at 400 C. The experiment at 500 C
also did not reveal any residual native PCDD/PCDF.
Similar results were obtained f or KPTHF, a mixture of
KOH:PTHF (KOH:polytetrahydrofuran:: 25 :75) and other
15 destroyers with vary little variation in the destruction
ef f iciency .
Figure 4 shows the plot of gas chromatography/
electron capture detector response f or various
chlorinated rn7nroun~q on flyash from MSWI, the flyash
20 heated at 400-C, and the flyash coated by 5 wt~ NaOH and
heated at 400-C. It is clear from Figure 4 that a large
number of organohalogen ~ -c, including PCDD/PCDF,
are present on flyash from MSWI (bottom tracing) . Merely
heating the flyash at 400-C does not destroy the OHC on
25 the flyash (middle tracing) . However, 5 wt~ destroyer on
the ~lyash effectively destroys all the OHC, including
PCDD/PCDF, on the flyash ~top tracing) .
Af ter the heat treatment at various temperatures of
the flyash samples coated by various destroyers, they
30 were extracted using toluene, after that they were dried
by heating at 150 C to remove toluene used for
extraction. A catalytic activity test of these flyash
samples then was conducted using 13C PCP at 300 C, as
described in the Example 1. Only traces of 13C labelled
35 PCDD were produced on these flyash samples from l3C-PCP
Wo 95118667 2 1 8 0 6 3 3 PCT1C~95100012
16
This result indicates that the catalytically active sites
on the f lyash were removed by the destroyer .
Exam~le 3:
This Example shows the effect o~ amount and type of
S destroyer used for coating the flyash in the forT~~t;nn of
C PCDD f rom 13C PCP .
In these experiments, nine f lyash samples ( l . 5 y
each) were coated by three different de~LL~,y~ namely
Na,CO3, KOH and NaOH (l wt%, 2 wtg~ and 6 wt~) separately.
Catalytic activity tests were conducted on each coated
sample at 300 C, as described in Example l. The analyses
of the f lyash extracts are shown in Figure 5 .
Background(BG) represents the amount of 13C PCDD produced
from 13C PCP on the flyash with no destroyer at 300 C.
From the plots, it can be seen that, as the amount of
destroyer (wt~) increases, the formation of PCDD
decreases. The effect is consistent for all three
destroyers used. There was a slight difference i~
activity of the destroyers to prevent the formation of
2 0 PCDD .
mn l e 4:
This Example shows the effect of temperature on the
formation of 13C PCDD from 13C PCP on the flyash coated by
variou6 destroyers.
In these experiments, three different destroyers,
namely Na2CO3, KOH and ~aOH were coated ~2 wt~) separately
on flyash samples. Catalytic activity tests were
conducted on each coated sample at 300, 350 and 400 C,
as described in Example l. The analyses of the flyash
extracts are shown in Figure 6. Background(BG) represents
the amount of 13C PCDD produced rom ~3C PCP on the flyash
with no destroyer at 300-C. From the plots, it can be
seen that the effectiveness of the destroyer increased
with the temperature increases.
3 5 Figure 7 shows the percentage reduction or
destruction of native dioxins and furans using various
Wo 95/l8667 2 1 8 0 6 3 3 PCT/CA95/000l2
17
inhibitor/destroyers. The inhibitor/destroyers used were
in these experiment6, namely:
i) KPTHF, a mixture of KOH:polytetrahydrofuran
(25 : 75), 5% ~by wt)
ii) SMSEG, sodium metasilicate:ethylene glycol
~15:85, 5% (by wt)
iii) NaOH, 5~ (by wt)
iv) PSEGC, potassium hydroxide:ethylene
glycol:silica gel:: :17:60:23, 5~ ~by wt)
The results seen in Figure 7 are compared with those
f ound earlier .
From the results of Examples 3 and 4, it can be seen
that the catalytic activity of flyash for the formation
of PCDD from precursors was effectively reduced, either
by using smaller amounts of destroyers at higher
temperatures or by using larger amounts of destroyers at
lower temperatures.
Exam~le 5:
This Example illustrates a commercial scale plant
test.
A waste incinerator plant had three i n~ep~nr~nt
incineration lines comprising an incineration grate for
municipal waste, a waste to heat boiler (100 ton per day)
and a multi-stage flue gas purification plant. From a
refuse bunker, the waste is supplied to the incineration
grate where it is burned at lD00-C. Flue gases flc>w
through the boiler at a velocity of 6 to 12 M/second.
The inhibitor/destroyer mixtures were injected into
the waste flue gas stream. KOH or NaOH as the de~L.~y~La
were injected in a temperature window of 590 + 50 C and
PSEGC or SMSGC (see Fxample 4) as the
inhibitor/destroyers were inj ected in a temperature
window of 375- + 50 C. The amount ~f each inhibitor and
destroyer injection was 7 to 10~ by weight of the flyash
produced. An injection nozzle unit was employed
containing a pressure atomizer with a mixing chamber in
wo 95rl866~r 2 ~ 8 0 6 3 3 PCT/CA95100012
18
which the destroyer or inhibitor was mixed with 13 times
the amount of water by volume. The nozzles had a outside
diameter of 12 mm and an opening of l, 6 mm and were
operated with water at an inj ection pressure of 6 to 8
5 bar to distribute the destroyer/inhibitor uniformly
thLUu~lluuL the flue gas.
Plant test I was conducted using combination I
consisting of KOH as destroyer and l?SEGC as
inhibitor/destroyer, plant test II was conducted using
10 combination II consisting of ~NaO}l as destroyer and SMSGC
as inhibitor/destroyer and plant test III was conducted
using ~ ' in~t;on I and activated carbon. On the fourth
day of each test, the flue gas samples were collected for
PCDD/PCDF measurements. Several flyash samples were
l~ collected from the electrostatic -precipitator on the
third and fourth day of each test. Sampling and analysis
of the flue gas for PCDD/PCDF t~f~n~ n~ration were done
with standard techniques.
The amount of PCDD/PCD~ detected on the f lyash
20 samples during the three tests is shown i~ the ollowing
Table I:
WO 95/18667 2 ~ 8 0 6 3 3 PCT/CA9~100012
19
a , o ~D N ~ N ~D
~,
~: a
O ~J
P~
.. ~
~ u7 r N Lt~ N
-
. .
N ~ N H 0~ D
~ m .~ o~
A
~'
O ~ O r~
ZJl 1~ N N N H . ~D
H
Jq
O
a ~ ~ H ~ N H N .-1 N
f-l ~ r .
o ~
~ ~ f ~
E~ Z
C~ ~ N f'~
m
E~ d
Wo 95/18667 2 1 8 0 6 3 3 PCTIC~95/00012
AB may be seen from these results, with all other
conditionB ,~ ;nin~ the same, injecting the de~L.uye-
and inhibitors into the post combustion zone att -- aLuLes of 550 C and 350 C respectively, caused a
5 marked re~llrt;~n in the amount of PCDD/PCDF on the flyash
samples from the electrostatic precipitator A
comparison between the individual tests shows that the
best re~ ti~n of PCDD/PCDF of 999~ was achieved in Test
III An overall reduction in PCDF of about 80 to 94~ was
lO achieved in Tests I to III
The amount of total PCDD/PCDF detected in flue gases
in background samples and samples collected during Tests
I to III are shown in the following Table II
WO9!i/18667 2 1 8 0 6 33 PCT/CA9S1000~2
21
~ .
E~
~C\ N ~ CO L~l Ul O
~ ~ E ~ ~ ~ N
E~ -'t~) C~ o 1'~ N :1 0 1''1 0~ N _I
~0 E~ r ~ ~ r ~D ~ N r 1`'1
S~ _
o
D~ '
c4 E o rl ~ N Ir) ~ ~ r~ L~ ~ .1'
N ~' ~`7 N ~I' ~ ~') ~ t~
C) Cq
H
~n
~ ~ a E N N ~D ~D N ~ t~ Ll) t` r~
O H N N ~D N ~ I`') ~ ~ ~I N
U~
H
H
H H
_ ~ ~ H
Cl ~ V 3
a) 3 Il~
S~ H H H H C~ 3 3 c) s~
O -- H H H H H H 3 ~ ~t Il~
O ~ IJ CJ O a) H H H H H
O O O O O O G) C) C) ~q
O -LLIl~i ~I W tlJ ~ E-' E- E-' ~U
C~ ~-l ., .. .. . .,
H C~ ~ .-- .. . ..
W ~ _ L . L L
~1 ~ ~ ' ,
t I t
Wo 95/18667 2 i 8 0 6 3 3 PCIIC~95/00012
22
As may be seen from the result3 of Table II, the
PCDD/PCDF cono~ntration related to the toxic e~auivalent
(TE) of USEPA was reduced in Te9ts I to III up to gl9~ in
raw gas and up to 95% in pure gas.
The results crntAinpd in this Example demonstrate
that the formation of ~CDD/PCDF during the incineration
of waste can be PRs~nt;A~ly suppressed both the flyash
from the electrostatic precipitator and in the flue gas
by injection of desL~ uyc:~ ~ and inhibitors into the flue
gas from the i~cinerators.
- SVMM~RY OF DISCL~)SURE
In the summary of thi6 disclosure, the present
invention provides a method for destruction of
organohalogen compounds (ûHC), including dioxins and
furans, and for the prevention of formation of the O~C
and the acid gases in the combustion gas stream from
waste inr;n~rA~rrs by employing certain inorganic bases,
alone or their combination with aliphatic hydroxy
rrrnrollnrlq (collectively called herein destroyers). The
destroyers, such as alkali metal/AlkAl;n~ earth metal
oxides, hydroxides, carbonates, bicarbonates and
silicates and mixtures of alkali metal/~lkAl inP earth
metals oxides, hydroxides, carbonates, bicArhr~n~tes,
silicates and their mixtures with AliphAt;c hydroxy
and/or polyhydroxy ~ o~n~lq, proved to be highly
effective in the destruction and the prevention of
formation of the O~C, including toxic dioxins and furans,
in the post combustion zone of incinerators.
Modif ications are possible withi~ the scope of this
3 0 invention
.
