Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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A METHOD AND APPARATUS FOR WASTE DISPOSAL
BACKGROUND OF THE IMVENTION
The present invention relates to hazardous waste
disposal systems, and more particularly to an improved
incineration system and method which results in the efficient
destruction of liquid and solid wastes in an apparatus including a
primary incineration combustion means, at least one afterburner
and a flue gas treatment system.
A typical waste incineration system for the destruction
and removal of hazardous wastes consists of a primary incineration
combustion apparatus, an afterburner and a flue gas treatment
system. Additionally, the incineration system may include:
a solid and/or liquid waste feed system;
a system for feeding an auxiliary fuel, usually in
gaseous or liquid form;
a system for feeding oxidizer, usually air anA sometimes
oxygen or an oxygen enriched air;
a system for the evacuation of incombustible solid
products of incineration, such as bottom ash;
a system of heat recovery from the hot exhaust
combustion flue gases with generation of preheated
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combustion air for waste incineration units, hot water,
steam and/or electricity;
a system for preparinq, feeding, recyclinq and treatinq
any water solutions produced for removal of gaseous
and/or particulates ln the flue gas treatment system;
a stack for the discharge of treated flue gases to the
atmosphere;
a control system including flow, pressure and
temperature transducers and controllers for controllinq
the flow of fuel and oxidizers, process temperatures and
pressures at strategic locations in the system; and
a flue gas sampling system.
The primary incineration combustion apparatus for solid
and liquid wastes and sludges may be embodied as rotary kilns,
multiple hearth furnaces, fluidized bed furnaces, grate furnaces
and other combustion apparatus. Liquid and semiliquid pumpable
wastes can also be combusted in cyclonic reactors as well as in
various burners during the inltial thermal destruction step of
incineration process.
The rotary kiln is the preferable embodiment of the
primary incineration process due to its versatility. It is
arranged as a cylindrical refractory lined vessel rotating ahout a
slightly inclined axis. The residence time in the kiln varies
from a fraction of a second to several seconds for gaseous
materials and from several minutes to several hours for solid
materials. Solid wastes can be charqed in a kiln either
continuously as in the case of shredded material or as a batch
charge as in the case of containerized materials such as drums or
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bundles. Special loading devices are used for charqinq solid
wastes while pumpable liquid wastes and sludges are typically
introduced directly into the kiln. The combustible fraction of
wastes is partially pyrolysed and oxidized in the kiln. An
auxiliary fuel such as combustible liquid waste, oil, natural gas
or propane is commonly used for preheating the kiln lining, for
providing supplemental heating while comhustina low caloric value
wastes, and for insuring the combustion stability.
Although the design of other primary incineration
combustion units differs from that of a rotary kiln, they
typically accomplish the same functions and contain many of the
same functional elements as the rotary kilns and exhibit much the
same disadvantages as those discussed below for the kilns.
Afterburners are typically cylindrical refractory lined
vessels equipped with an auxiliary burner which is fed with a
liquid and/or gaseous fuel and an oxidizer. Combustible liguid
wastes can be used instead of, or in addition to, the auxiliary
fuel. Afterburners are used to insure combustion of organic
vapors, soot and other combustible components remainina after the
primary incineration process. ~he afterburners provide a high
temperature, highly oxidizing atmosphere with sufficient residence
time and mixing of combustible vapors with oxygen to insure the
required degree of organics destruction.
The most typical unit for treatment of flue gases
leaving the afterburner is a wet scrubber wherein the combustion
gases are washed by water or water solutions. Soot and halogens
are largely absorbed and sulfur dioxide and nitrogen oxides are
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partially removed in the scrubber. Some polar oraanics and
organics which are adsorbed in the 800t are also partially
removed. An alkali is often added to the scrubbing water to
increase the efficiency of scrubbing of halogens and sulfur
dioxide. Electrostatic precipitators or dust baghouses are often
used for removal of the particulates from flue gases.
Heat recovery units are often installed between thermal
destruction and flue gas treatment units. Heat of hot combustion
flue gases may be used to preheat the combustion air for the
primary incinerator and/or afterburner.
Solid and liquid wastes typically contain orqanic and
inorganic combustible constituents. A fraction of organics may be
Xighly toxic, mutanogenic and teratogenic. This fraction of
organics is usually called principle organic hydrocarbons (POHC~.
Many POHCs are very stable and require oxidation at elevated
temperatures for their destruction. When wastes are charged into
a kiln, a rapid volatilization and partial pyrolysis of organics,
including POHCs and water, if any, occurs. The volatilized
components of organics require an adequate quantity of oxygen for
their oxidation. Fuel and oxygen are also needed to supply heat
for vaporization of water and organics and for raisinq the
temperature to required levels.
The appropriate firing rate and combustion air feed rate
are selected to provide adequate temperatures and excess oxygen
level for the incineration system to achieve the required
destruction efficiency of the POHCs for a given type and quantity
of wastes. This temperature and excess oxygen level will be
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maintained by the control system. Other nonhazardous organics
present as well as the fuel are usually essentially oxidized when
POHCs are oxidized in the primary incineration combustion
apparatus; however, new intermediate products may be formed durinq
the combustion process. These products include carbon
microparticles, carbon monoxide and an array of organic compounds.
Many of these organic compounds are a higher molecular weight
polycyclic or polyaromatic organics such as dioxins, benz(a)
pyrene, dibenzta,c)anthracene, picene, dibenz(a,h)anthracene, 7,
12-dimethyl(a)anthracene, benztb)fluortane,
9,10-dimethylanthracene. These higher molecular weight organics
are often called products of incomplete combustion (PICs). PICs
are often as hazardous as POHCs. A fraction of PICs becomes
absorbed on carbon microparticles. The combined PICs and carbon
particles represent soot. Accordingly, soot is also a hazardous
product. Carbon monoxide is also a toxic constituent and only a
limited quantity of it may be permitted for discharge into the
atmosphere. Therefore, the waste incineration steps must insure
the thermal destruction of carbon monoxide, soot and PICs in the
gaseous phase. Such destruction should be provided prior to the
discharge of the combustion gases from the afterburner.
Both the feed rate and the properties of wastes which
are fed into the combustion system may vary. Extreme variations
in the feed rate occur during the so called batch charge when a
substantial quantity of wastes is rammed or otherwise introduced
into the apparatus in a short period of time. Gradual variations
in the feed rate are also possible for continuously charged waste
streams.
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The operational objective of an incineration system is
to maximize the waste throughput while limiting the total amounts
of discharged flue gases and POHCs as well as PICs under
fluctuating feed conditions. Generally, the maximum allowable
concentration~ of pollutants in the flue gases are specified in
the operating permit which i8 based on the current environmental
requirements and regulations.
In order to achieve thiC operational ob~ective hiqh
temperatures, sufficient retention time and hiqh turhulence should
be provided in both the primary incineration combustion apparatus
and the afterburner. ~ypically, the kiln temperature ranges from
750-C (1400F) to above 1100-C (2500-F). The residence time for
gases in both the kiln and the afterburner ranges from a fraction
of a second to several seconds. Turbulence in either the kiln or
the afterburner is not defined quantitatively, however. It is
usually assumed that mixing is sufficient to heat adequately all
elementary streams of gases and to provide a sufficient contact
between organics and oxygen molecules in t~e furnace. In order to
insure the sufficient contact between organics and oxygen, an
excess of combuqtion air in the range of 5~ to 200~ of
stoichiometric is commonly used.
Temperature, retention time, level of excess air and
turbulence in the primary incineration combustion apparatus and
afterburner effect the destruction efficiency which may be
maintained during the operation of a conventional incineration
system. An increase in any of these parameters will enhance the
destruction efficiency. Attempts to improve destruction
efficiency by increasing one or more of the above parameters,
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however, has not proven to be effective utili2ing currently
available incineration systems because of a corresponding drop in
one of the parameters as one of the others is increased. For
example, a higher level of excess oxygen provided by an increase
in the air feed results in a lower temperature and lower retention
time of gases in the furnace. An increase of the temperature by
raising the amount of auxiliary fuel results in increase of
combustion product volume which reduces retention time.
The incompatible nature of these parameters in existing
incineration systems has limited the capability of existing
incineration systems to dynamically intensify the incineration
process to overcome transient process malfunctions leading to
process failures. Typical transient malfunctions resultinq in
incineration proces~ failure modes are described below using the
kiln as an example for the primary incineration apparatus.
When wastes are charged in large batches or when loading
rates of liquids and sludges are rapidly increased, the quantity
of oxygen present in the kiln and the amount of oxygen being fed
into the kiln during the rapid vaporization stage typically is not
sufficient for complete combustion to occur, resulting in an
overcharginq failure. Only a fraction of combustible constituents
of wastes, including POHC, is completely oxidized, forminq C02
and H20. The remaining organics are partially pyrolyzed and
oxidized, thus forming carbon microparticles, CO and PICs.
Vaporized fractions of POHCs and of wastes together with carbon
microparticles, CO and PICs formed are transferred in an increased
amount into the afterburner, so that afterburner is also
overloaded. Meeting the oxygen requirements during the overload
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period in the kiln by substantially increasinq the level of
continuous combustion air feed rate would result in a shortening
of the retention time for volatilized and partially pyrolyzed
products in the kiln and may degrade the flame stability. This
problem is aggravated by the fact that the substantially excessive
air feed brings along extra nitrogen which absorbs a portion of
the heat generated in the kiln, thus reducing the heat available
for the process and, correspondingly, the temperature level
resulting in reduced destruction efficiency of organics.
When a portion of the waste charged into the kiln durinq
a certain time period has lower caloric value than the expected
design value, the kiln temperature can decline due to reduced heat
release. This may lead to the formation of cold spots in the
furnace when local temperatures decrease below the ignition point
for some organics. The result is a low temperature failure mode
with a substantial breakthrough of the original organics which
cannot be destroyed at lower temperatures. A drastic increase in
PIC formation may also occur due to quenching of pyrolytic
products formed from the original wastes and fuel.
Other failure modes may occur as a result of poor
atomi2ation of liquid wastes and poor mixinq of wastes with
available oxidizers. Poor atomization of liquid wastes leads to
increased size of droplets resulting in incomplete comhustion
while poor mixing may provide an opportunity for the volatilized
wastes to short circuit the combustion process, avoidin~ adequate
contact with an oxidizer. Both of these failure modes result in
products of incomplete combustion being transferred to the
afterburner.
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Flameout failure modes predominantly occur at
unfavorable aerodynamic conditions in the combustion zone. High
velocities of gaseous products near the burner during low fire
conditions, a deficiency of oxidizer, and excessive infiltration
of cold ambient air in the combustion apparatus are typically
events which cause flameout. Excessive increase in the ambient
air moisture content and the high moisture of the wastes being
charged may be other sources of low temperature or flameout
failure.
Failure modes similar to those described ahove for the
kiln may also occur in the afterburner. In addition,
overcharginq, low residence time, low temperature, poor mixing,
the cold wall effect, flameout and poor atomization in the kiln
will always result in an increased PICs loading rate on the
afterburner, and ~ubsequently, in a lower thermal destruction
efficiency overall for existing incineration systems.
Conventional incineration systems are hindered in their
ability to address failure modes because the kiln, the
afterburner, if used, and the air pollution control system are
designed to operate in steady state conditions ignoring the
existence of transient process disturbances which result in
failure modes. Existing incineration systems are also unable to
anticipate transient operational changes of the several individual
elements of the incineration system. For example, they are not
capable of rapidly boosting temperatures and oxygen content in the
afterburner to overcome failure modes in the primary combustion
apparatus.
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Several attempts have been made to improve thermal
destruction efficiency by enriching combustion air in the primary
incineration means with oxygen (see, for example, U. S. Patent
Nos. 4,520,746; 4,462,318 and 4,279,208). The advantage of oxygen
use in incineration processes i8 based on the reduction in the
volume of nitrogen introduced into the incineration-process. This
reduction in the volume of nitrogen decreases the amount of heat
stored in the nitrogen molecules making additional heat available
for waste destruction and for increasing the temperature in the
kiln. In addition, the use of oxygen reduces the quantity of
gases flowing through the kiln, thereby increasing the residence
time and the efficiency of destruction of persistent organics.
The use of oxygen in the waste incineration processes
helps to stabilize combustion and to eliminate the possibility of
failures related to low temperature, insufficient residence time
and the negative impacts of low caloric wastes. However, the
steady flow of additional oxygen may be only marginally effective
in cases of transient overcharging, poor atomization and poor
mixing, which are the failure modes most prone to the breakthrouqh
of POHCs and formation of PICs. Permanently maintaining an
elevated oxygen feed rate can result in overheatinq of primary
incineration combustion apparatus and in damage to the metal parts
and refractories. Moreover, an increased oxygen feed results in
added operational costs. Although the additional use of a
permanent oxygen flow may improve the destruction efficiency of
kilns and afterburners, it cannot solve the problems related to
the transient changes such as those caused by batch charqinq, poor
atomi2ation and poor mixing. This also cannot help to optimize
the destruction efficiency at a given capacity or to maximize the
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capacity of the facility at a given or required efficiency.
Existing methods cannot reconcile the conflict among the desired
factors of high temperature, retention time, turbulence, and
oxygen level in furnaces.
There exists, therefore, a need for an incineration
system and method which results in the efficient destruction of
liquid and solid wastes.
Further, there exists a need for a system and method
which solves the problems related to the transient changes such as
those caused by batch charging, poor atomization and poor mixing.
Also, there exists a need for a system and method
capable of identifying critical prefailure conditions of the
process and providing optimum levels of fuel, oxygen and air to be
fed into the system.
lS SUMMARY OF THE INVENTION
The present invention relates to a waste incineration
system comprised of a primary incineration combustion means which
preferably includes a kiln, an afterburner means, and a flue gas
treatment means. Both the lncineration means and the afterburner
means may utilize at least two oxidizing gases having different
oxygen concentrations, for example, oxygen and air or oxygen and
oxygen enriched air. By varying the ratio of these oxidizers the
amount of total oxygen and nitrogen delivered in either the
primary incineration combustion means, the afterburner means, or
both can be adjusted. In the course of this adjustment the
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required temperature, retention time, turbulence and oxygen supply
level can all be provided simultaneously and without negative side
effects.
Additional oxidizing agents can be optionally used. For
example, water or steam may be introduced to reduce soot and NOX
formation. Additionally, water can be used for the temperature
control in either the primary incineration apparatus or in the
afterburner. Ozonated oxygen or air may also be used as an
initiator of chain reactions.
Dynamic variations in the rates of feed of these
different oxidizing gases insures the optimization of the
combustion process so that the quantity of oxygen and nitrogen and
water supplied conforms with that required for complete combustion
whenever fluctuations in the demand for oxygen for combustion of
waste occurs. In particular, such fluctuations are related to
charging of large batches or other transient events that may
potentially reduce the efficiency of thermal waste destruction.
Improvements in incineration processes by the use of
oxygen may be achieved with the use of traditional combustion
apparatus such as oxy-fuel burners, oxygen enriched burners and
oxygen lances. Further improvements can be accomplished by the
separate introduction of two different oxidizing gases such as air
and oxygen into the combustion tunnel of the burner, as
previously described in U.- S. Patent No. 4,622,077 and U. S.
Patent No. 4,642,047 granted February 10, 1987.
In accordance with these patents, the
oxygen stream is introduced primarily as a high pressure, high
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vel~city jet or jets directed through the hot core of the flame.
The excess oxygen directed throughout the flame core has a
substantially elevated temperature as compared with excess oxygen
being introduced around flame pattern in a mixture with combustion
air into a primary incineration combustion apparatus. Such hot
oxygen has an increased ability to oxidize organics.
Additionally, the axial introduction of a high velocity oxygen
stream enveloped by fuel and/or fluid waste stream which in turn
is enveloped by air or oxygen enriched air, insures a more
effective mixing of combustible components of the fuel and/or of
the waste stream inside the flame pattern, thus reducing NOX and
PICs formations. The transport of oxidizer toward the fuel or
liguid waste particles in the flame pattern is also intensified
due to better conditions for mixing of oxygen with combustibles
from both outside and inside the flame pattern.
Stable combustion under dynamically changing operational
conditions may be provided by the use of a burner described in
U. S. Patent No. 4,797,087 granted January 10, 1989. This burner
design provides a high temperature oxidizing gas being delivered
for incineration purposes through a controllable flame pattern
capable of uniform heating of the primary incineration combustion
means and the afterburner means. This increased controllability
reduces the possibility of cold spot formation or local overheating
of the incineration system. Additionally, the high flame velocity
of this burner is used to improve mixing and to reduce short
circuiting.
The present invention also includes a dynamic control
system containing transducers for measuring process variables such
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a8 temperature, pressure and flows of fuel, fluid waste, oxidizinq
gases and hot combustion products in order to identify critical
prefailure conditions of the process based on signals received
from the transducers and on such signals received by the process
controller. The system prescribes the new "emergency" levels of
fuel, oxygen and air to be fed into the primary incineration
combustion means and the afterburner means to brinq the process
back to the desired mode of operation and to prevent process
failure. Fuel, oxygen and air are supplied to the primary
incineration combustion means by a gas train system containinq the
necessary valves and actuators communicating with the computerized
control system to control fuel, oxygen and air flows according
with the prescription of the process controller.
The present invention also relates to a method of waste
lS incineration including the steps of identifying transient
prefailure events and responding to such events by properly
raising the ratio between the "emergency" amounts of oxygen and
nitrogen being delivered into the afterburner means. An increase
in the oxygen/nitrogen ratio immediately increases the temperature
of the gaseous atmosphere of the afterburner vessel due to
reduction of the ballast nitrogen flow. Also, a reduction in the
nitrogen feed into the process results in an increase of the
residence time for waste destruction and, therefore, in an
improved destruction efficiency of the afterburner.
A further step in response to prefailure modes may be a
rapid decrease of the flow of fuel being introduced in primary
incineration means, without creating a problem with flame
stability, to slow down the rate of volatilization in the primary
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incineration combustion means, to increase the auantity of oxygen
available for the oxidation of the wastes and to further increase
the retention time, simultaneously.
When two oxidizing gases are also utilized in the
S primary combustion incineration means, similar "emergency" changes
in flow rates of these oxidizing gases may be implemented. If
during an "emergency" operation, the kiln or afterburner
temperatures rise for a prolonged period of time to a level above
that allowable for the refractories, water or steam injection may
be used for cooling purposes.
Mixing in the gaseous atmosphere and heat transfer in
the afterburner means may be improved by tangentially feeding flue
gases exhausted from the primary incineration combustion means
into a vortex chamber of the afterburner vessel, thus eliminating
short circuiting. Introduction of a high velocity flame in the
afterburner may be arranged to create a venturi effect to move the
entering stream of combustion products into the combustion chamber
with less of a pressure drop. Alternatively, the flue gases may
be fed into the vortex chamber axially, while a burner is fired
into this chamber tangentially so that the hot exhaust gases from
the primary combustion means are enveloped by and mixed with the
hot oxidizing gases discharged from the burner.
The present method and apparatus are also capable of
minimizing unplanned shutdowns of the incineration system and
inappropriate transient releases of the POHCs and PICs to the
atmo~phere during shutdowns and transient surge conditions such as
those caused by batch charging or unexpected changes in the
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caloric value of the waste as well as by other system
malfunctions.
Notwithstanding the detailed summary herein, the
invention in one broadly claimed aspect provides an afterburner
apparatus for oxidizing combustible components of a gaseous
stream, comprising means for providing containment for
combustion and thermal destruction of combustible components of
the stream, means for delivering the gaseous stream into the
containment meàns, at least one auxiliary burner means for
generating hot auxiliary combustion products by combustion of a
fluid combustible material in the burner and means for
adjustably delivering the fluid combustible material into the
auxiliary burner. Means provide for two oxidizing gases having
different oxygen and nitrogen concentrations from each other to
the apparatus, at least one of the oxidizing gases being
provided into the auxiliary burner and sensing means comprising
a plurality of transducers senses process characteristics
inside the apparatus and generates signals indicative of the
value of the process characteristics sensed. Means is provided
for controlling the means for providing oxidizing gases to
simultaneously control process temperature, the amount of
oxygen in exhaust gas leaving the apparatus and the retention
time of gases inside the apparatus and there is means for
comparing the transducer signals with predetermined values for
the process characteristic which insure reduction of hazardous
components in the stream below a desired level and for
communicating a signal indicative of the value of the results
of the comparisons to the means for controlling the means for
providing oxidizing gases.
Another claimed aspect of the invention provides an
apparatus for disposing of wastes, comprising primary
incineration combustion means for combustion of the wastes into
residue and gaseous stream, means for controllably delivering a
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primary oxidizing gas into the primary incineration combustion
means and first means for providing containment for combustion
and thermal destruction of combustible components of the
gaseous stream. Means is provided for delivering the gaseous
stream from the primary incineration combustion means to the
containment means and auxiliary burner means generates hot
auxiliary combustion product by burning fluid combustible
material in the burner communicating with the first containment
means. Means deliver the fluid combustible material into the
auxiliary burner and means provides for two oxidizing gases
having different oxygen and nitrogen concentrations from each
other to the apparatus, at least one of the oxidizing gases
being provided into the auxiliary burner. Sensing means
comprising a plurality of transducers senses process
characteristics inside the apparatus and generates signals
indicative of the value of the process characteristics sensed
and means control the means for providing oxidizing gases to
simultaneously control process temperature, the amount of
oxygen in exhaust gas leaving the apparatus and the retention
time of gases inside the apparatus. Means compare the
transducer signals with predetermined values for the process
characteristics which insure reduction of hazardous components
in the stream below a desired level and communicate a signal
indicative of the value of the results of the comparisons to
the means for controlling the means for providing oxidizing
means.
The invention in a further aspect provides various
methods of thermal destruction of wastes, one of which
comprises the steps of introducing solid waste material into a
primary incineration means, providing a primary oxidizing gas
to the primary incineration means, incinerating the solid waste
material in the primary incineration means to produce solid
residue and gaseous exhaust, directing the gaseous exhaust from
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the primary incineration means to a containment means having an
auxiliary burner generating hot auxiliary combustion product,
controllably introducing fluid combustible material into the
auxiliary burner, providing two secondary oxidizing gases
having different oxygen and nitrogen concentrations from each
other to the containment means, at least one of the oxidizing
gases being provided into the auxiliary burner, combusting the
residual combustible components of the gaseous exhaust in the
containment meàns and combusting the fluid combustible material
introduced into the auxiliary burner, sensing process
characteristics of the primary incineration means and the
containment means and generating signals indicative of the
values of the process characteristics sensed, comparing at
least one of the sensed process characteristic signal with a
predetermined value for the process characteristic which
ensures reduction of hazardous components of the gaseous
exhaust below a desired level and communicating the result of
the comparison to means for controlling the flow of at least
one of the two secondary oxidizing gases provided to the
containment means, sensing when a batch of the solid waste
material is about to be introduced into the primary
incineration means and generating a signal indicative of the
introduction and in response to the signal indicative of the
introduction of solid waste material, adjusting the flow of at
least one of the oxidizing gases provided to the containment
means to increase the total amount of oxygen momentarily
provided to the containment means and to increase the
proportion of oxygen to nitrogen provided with the oxidizing
gases.
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Other advantages of the invention will in part be
obvious and in pa-t appear hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a process flow diagram of an incineration
system.
Fig. 2 iS a longitudinal cross-sectional view of a
burner mixer chamber used in the afterburner means.
Fig. 3 is a side cross-sectional view of a vortex
chamber taken along lines 3-3 in Fig. 2.
Fig. 4 is a longitudinal cross-sectional view of an
alternative burner mixer chamber used in the afterburner means.
Fig. 5 is a side cross-sectional view of a vortex
chamber taken along line 5-5 in Fig. 4.
DESCRIPTION OF THB PREFERRED EMBODIMENT
The preferred embodiment of the invention, comprisinq a
primary incineration combustion means, an afterburner means and
flue gas treatment system means, is now described with reference
to the drawings in which like numbers indicate like parts
throughout the views.
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Apparatus
Fig. 1 shows a flow diagram including a primary
incineration combustion vessel, or kiln 1, which is a part of
the primary incineration combustion means 70 and a means for
S providing containment for combustion and destruction 2
connected to the kiln by a connecting duct 5. A fluid waste
burner 3 is attached to kiln 1, preferably a water cooled
burner as described in detail in U.S. patent No. 4,797,087
granted January 10, 1989. A means for feeding solid wastes 29
is attached to kiln 1. The burner 3 has a waste port 9 for the
introduction of pumpable fluid wastes, a first gas port 6 for
the introduction of a first oxidizing gas (for example, air), a
second gas port 7 for the introduction of a second oxidizing
gas having a different oxygen concentration from the first
oxidizing gas (for example, oxygen), a fuel port 8 for the
introduction of an auxiliary fuel, a water port 30 for the
introduction of cooling water and a cooling water discharge
outlet 31. A collecting container 4 for ash residue is
connected to kiln 1. A first flame supervising means 18 which
determines the existence of a flame, such as an ultraviolet
sensor, is built into the burner 3.
Figs. 2 and 3 show a vortex mixing chamber 10
attached to the containment means 2 which receives hot flue
gases from the kiln 1 by flue gas inlet 11. A
first oxidizing gas, for example oxygen, is supplied through a
first oxidizing gas inlet 13 to the fluid waste burner
26 and then into vortex mixing chamber 10. A second
oxidizing gas having a different oxygen concentration from the
first oxidizing gas, for example air, is supplied to the burner
26 through a second oxidizing gas inlet 12. Auxiliary fuel
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is supplied through an auxiliary fuel inlet 14. Pumpable fluid
waste may be supplied in some cases through a liquid waste inlet
15. Cooling water for the liquid waste burner 26 is supplied
through a cooling water inlet 16 and evacuated through a cooling
water discharge outlet 17. A second flame supervising means 19 is
used to identify the existence of the flame. The burner 26 is
preferably designed as described in U. S. Patent No. 4,797,087
granted January lO, 1989 to maintain a hot stable flame core
during continuous incineration operation, to prevent flame
failure and to minimize NOX formation.
Figs. 4 and 5 show an alternative afterburner means
which includes a vortex mixing chamber 101 with inlet 102 for flue
gases fed from the primary combustion means 1 and a hurner 103
which is similar in design to burner 26. ~urner 103 is equipped
with lines 104 and 105 for feeding primary and secondary oxidizing
gases such as oxygen, oxygen enriched air or air, 106 for an
auxiliary gaseous fuel and 107 for an auxiliary liquid fuel, and
108 and 109 for cooling water.
Referring again to Fig. 1, temperatures of combustion
products exhausting from the kiln 1 are registered by a first
thermocouple 20. Temperatures in the afterburner vessel 55 of
containment means 2 are registered by a second thermocouple 21.
The absolute pressure and the effluent flue gas flow rate from the
kiln 1 are determined by first and second transducers 22 and 23,
respectively, and the absolute pressure and the effluent flue gas
flow rate from containment means 2 are monitored by third and
fourth transducers 24 and 25, respectively.
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A control system for detecting and ad~usting to
operational conditions in the apparatus is provided. ~he system
includes a feed indicating means 33 for indication to a control
means 34 of a hatch charge approachinq the feeding means 29. The
feed indicating means 33 may be arranged, for example, as a limit
switch which is energized when the batch charge passes its
location. The control means 34 communicates with the feed
indicating means 33. The control means 34 receives sianals from
thermocouples 20 and 21, electrical flow transducers 23 and 25,
and pressure transducers 22 and 24. An optional smoke detection
means 35 may be used to detect smoke in combustion products
entering the flue duct 5. Such detection means 35 may include an
ultraviolet flame detector or an electrical opacity sensor
communicating with the control means 34. The control means 34 is
also connected to operate a first air flow modulatinq means 47 on
the first air line 80, a second air flow modulating means 51 on
the second air line R1, a first oxygen flow modulatinq means 48 on
the first oxygen line 82, a second oxygen flow modulatina means 50
on the second oxygen line 83, a first auxiliary fuel flow
modulating means 52 on the first auxiliary fuel line 84, a second
fuel flow modulating means 49 on the second auxiliary fuel line
85, a first waste flow modulating meàns 36 on the first pumpable
fluid waste line 8fi, and a second waste flow modulatinq means 37
on the second pumpable liquid waste line 87. The instant input
flows to burner 3 are sensed for feedback control of the inputs bv
control means 34 as follows: air is measured by the first air flow
metering means 38; oxygen is measured by the first oxygen flow
metering means 39; auxiliary fuel is measured bv the first
auxiliary fuel flow metering means 41; and, pumpable wastes are
30 measured by the first waste flow meterina means 40. Similarly,
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for the second burner means 26, instant flow of air is measured by
the second air flow metering means 45; oxygen is measured by the
second oxygen flow metering means 44; auxiliary fuel is meafiured
by the second auxiliary fuel flow metering means 43; and, pumpable
wactes are measured by the second waste flow meterinq means 42.
The burner means 2fi is fired into the interior of the
vortex mixing chamber 10, shown in Figs. 2 and 3, which is filled
with hot flue gases being delivered from the kiln 1. The flue
gases preferably enter tangentially to the interior 27 of the
vortex mixing chamber 10, shown in Figs. 2 and 3, therehy causing
a rotating mixing movement. The flame of the fluid waste burner
means 26, along with a controlled amount of excess oxygen, is
directed through the burner combustion chamber 28 at hiqh
velocity, thereby creatinq a venturi effect for infipirating the
kiln flue gases into the flame directed toward the afterburner
vessel 55. This creates intensive mixing of the qaseous stream
prior to entering a refractory lined afterburner vessel 55 of the
containment means 2.
Referring now to Figs. 1, 4 and 5, there is shown an
alternative embodiment of the afterburner. This afterburner
consists of a vortex mixing chamher 101 with inlet 102 for the
flue gas transferred from the primary incineration means 1 and
outlet 110 for transferring the hot gases in the afterburner
vessel 55. The burner means 103 is tanqentially attached to the
25 vortex chamber 101. The burner means 26 has inlets 107, 104, 10
and 105 for feeding a combu~tible fluid ~waste or fuel), a first
oxidizer such as oxygen, an auxiliary fuel ~when needed) and a
second oxidizer, such as air, respectively.
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Means for feeding additional amounts of oxyqen 12n may
also be provided. This means 120 allows oxygen to be fed directly
into the vortex mixing chamber 101, if desired, rather than
through input port 104. The vortex chamber 101 is attached to the
afterburner vessel 55 by outlet 110 and is connected to the flue
gas duct 5 by inlet 102. Alternatively, means 120 may be attached
to the contracted section of the outlet 110. AdditionAllv, a
secondary burner ~imilar to burner meanq 120 may be installed
downstream of means 2~. A further modification of afterburner
shown in Figs. 4 and 5 may include two or more consecutive rapid
mix chambers similar to vortex chamber 101, having preferably
burner means similar to means 103. These rapid mix chambers are
communicating with each other by apertures allowinq the flow of
gases from the first rapid mix chamber into the second and
followinq rapid mix chambers. Optionally, water or steam feedinq
means may be provided in either first, or second or all rapid
mix chambers. Said rapid mix chamhers may include afterburner
vessels communicating with each mixing chamber to proviAe
additional retention time.
Operation
Referrinq now to all of the fiqures, the operation of
the system will be described. Solid waste may be continuously or
batch charged into kiln 1 through feeder 29. At the same time
pumpable fluid waste may be introduced for incineration throuqh
the waste port 9 into the fluid waste burner 3 and further with a
flame into the kiln 1 interior.
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For lower caloric value waste streams, auxiliary fuel
may be introduced through auxiliary fuel port 8 into the hurner 3
and further directed through the burner combustion chamber 2
towards the kiln 1 interlor. A first oxidizinq gas with low
oxygen concentration (for example, air) enters the burner through
first gas port 6 and is further directed through the burner
combustion chamber 28 toward the kiln 1 interior. A second
oxidizing gas with higher oxygen concentration tfor example,
oxygen) may be supplieA from a li~uid oxyqen tank or from an
on-site oxyqen generation unit through second gas port 7 to fluifl
waste burner 3 anA further through burner comhustion chamber 28
toward kiln 1 interior.
To satisfy the required temperature in kiln 1 measured
by thermocouple 20, the waste feeding rate, the auxiliary fuel
flow and the first and second oxidizinq gas flows to burner 3 and
kiln 1 are maintained essentially constant during steady state
operation. The kiln 1 temperature has to exceed sufficiently the
temperature of volatilization of all organic components of the
waste to a qaseous state during the solids retention time in the
kiln 1. Additionally, the temperature should be above the
ignition point of volatilized components oriqinating from soli~
waste as well as comhustible components formed durinq pyrolysis of
pumpable waste and auxiliary fuel so that said volatilized
combustion components undergo thermal destruction.
At the same time, the total amount of oxyaen beinq
delivered with oxidizing qases into the kiln 1 has to be kept hiah
enough to insure its availability to completely combust auxiliary
fuel and fluid waste, and to provide extra oxygen flow to destroy
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the bulk of combustible components beinq formed in the interior of
the kiln 1.
Flue gases exhausted from the kiln 1 are directed into
the first vortex mixing chamber 1n throuqh flue qas inlet t1 and
further throughout the interior 27 of the vortex mixina chamber lO
toward the interior of the afterburner vessel 55. At the same
time, pumpable fluid wastes may be incinerated by introduction
through liquid waste inlet 15 into combustion chamber 2~ of the
fluid waste burner 26 and further through the interior 27 of the
vortex mixing chamber 10 toward the refractory lined vessel 55 of
the containment means 2. Auxiliary fuel may be introduced when
needed to insure flame stability and/or additional heat input to
maintain the required afterburner temperature (for instance, as
required by requlations), throuqh auxiliary fuel inlet 14 into
burner 26 then throughout burner combustion chamber 2~ and further
through the interior 27 of the mixing chamber 10 toward
afterburner vessel 55. The first oxidi2inq gas with a hiqher
oxygen content (for example, oxygen) than second oxidizinq qas is
directed into the burner 26 through the first oxidizinq gas inlet
13, and further throughout combustion chamber 28, thus discharginq
hot oxidizinq agent originated as auxiliary combustion products
from the flame envelope of burner means 26 toward the interior 27
of vortex mixing chamber 10 and further toward afterhurner vessel
55. A second oxidizing gas with low oxygen content (for example,
air or oxygen enriched air) is directed into burner 26 throuqh the
second oxidizing gas inlet 12 and further throughout combustion
chamber 28 thus discharging said hot oxi~izinq qas aqent toward
the interior 27 of the mixing chamber 10 and further toward
afterburner vessel 55. At least 2% to 3% of residual oxyaen
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content in the combustlon gases leavinq afterburner preferrably
should be provided during steady-state operating conditions.
Referring now to Figs. 4 and 5, an alternative
émbodiment of the vortex chamber will he operated as follows: The
flue gases from the primary combustion means will be fed axiallv
into the vortex mixing chamber 1n1 through inlet 102. The burner
means 103 will be fed with a combustible fluid (waste or fuel), a
first oxidizer such as oxygen, and a second oxidizer, such as air,
or oxygen enriched air, through portæ 10~, 104 and 105,
respectively. Auxiliary fuel may also be fed throuah port l0fi
when needed. The burner means 103 fires tanqentially into mixinq
chamber 101 so that the hot auxiliary combustion product which may
be, depending on operational mode, a hot oxidi2ing or reducinq
agent, originating as hot auxiliary comhustion product from the
flame envelope of burner means 103 mix with the flue gases fed
from the primary combustion means 1 in the vortex chamber.
Several operational modes of afterburner may be used. The
selection of the operation mode depends on the composition of flue
gases fed in the afterhurner and environmental requlations.
When substantial quantities of POHCs, PICs, soot and CO
are expected in the flue qases fed in the afterburner and NOX is
of no concern, the burner means 26 is fired to produce a hot
oxidizing auxiliary combustion product. Under this operational
conditions, heat and oxygen are added to the flue gases in the
afterburner, thus providin~ the re~uired destruction of POHCs,
PIC, soot and CO. In order to reduce NOX formation in the
burner means 26, a fraction of oxidizing qas can be fed downstream
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of the hot flame zone at the burner means 26 by the u.se of the
oxidizer injecting means 120.
When in addition to POHCs, PICs, soot and CO the
concentration of NOX must also be controlled, the operation of
the afterburner may be further improved as follows. ~he burner
means 26 will be fired using fuel rich conditions to produce hot
reducing auxiliary combustion products rich with CO and H2.
Since CO and H2 are fielective reducinq species for NOX, NOX
will be reduced while oxygen in the flue gases will be consumed to
a lesser extent. Simultaneously PO~Cs and PICs will undergo a
further thermal destruction due to the additional heat provided
with the hot reducinq auxi].iary combustion products qenerated in
the burning means 26. By feeding additional oxidizinq qas throuqh
the injectinq means 120 downstream of the flame zone of the burner
means 26, additional oxidative destruction of POHCs, PICs, soot
and CO will be achieved to satisfy environmental requlations. A
further improvement of this operating mode may be accomplished by
the injection of a hot oxidizing auxiliar.y comhustion product bv
the use of burner means similar to means 26 instead of or together
with injecting a plain oxidizer by means 120. In this improvement
additional heat is provided simultaneously with oxygen. A further
improvement of this operating mode may include injection of water
or steam into the burner means 26 thus increaslng the CO anfl H2
content in the hot reducing auxiliary combustion products.
When multiple consecutive rapid mix chamhers are used,
the chambers at the head of the afterburner can be fed with hot
reducing auxiliary combustion products while the final staaes will
be fed with hot oxidizing auxiliary combustion product thus
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insuring NOX reduction and POHCs, PICs, soot and CO
destruction.
Said hot auxiliary oxidizing combustion products have
high temperatures and high momentum and provide hiqh turhulence,
extra heat to raise mix temperature and excess oxyqen. ~s a
result, rapid and uniform mixing occurs in chamber 101 and a final
hot combustion product with at least 2% to 3~ of residual oxyqen
is transferred through outlet 110 into afterburner vessel 55,
wherein the required retention time is provided. Such operation
of afterburner insures accelerated burninq of residual POHCs, CO,
soot and gaseous PICs and provides higher destruction efficiency
than that achievable with air above.
A negative pressure will be maintained in the ki]n and
in the afterburner in order to prevent gas leakaqe outside the
system. An exhaust fan is used for creatinq the reouired neqative
pressure.
In the preferred embodiment and its operation, the ratio
of air to oxygen or oxygen enriched air, the fuel feed rate and
the oxygen excess level are selected for a particular compositlon
and a particular feed rate of waste so that the reauired
temperature, retention time, partial pressure of oxyqen and
turbulence in the afterburner and in the kiln are provided and the
required destruction efficiency of POHCs is insured to comply with
environmental standards.
~he desired settings for temperature in the kiln and the
afterburner, the maximum flow rates of combustion products from
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the kiln and the afterburner, and the safe level of negative
pressure in the kiln and the afterburner vessel will be entered by
the operator into the controller means 34.
Control means 34 will maintain the temperature of
combustion product exhausted from the kiln according to a set
point chosen by the operator. When temperature measured by
thermocouple 20 drops below the desired set point, control means
34 will increase the amount of auxiliary fuel beinq delivered to
the burner by raisinq the instant flow settinq for the auxiliary
fuel supply line and accordingly on oxyqen supply line so that the
chosen oxygen excess level is proviAed until the temperature
measured by thermocouple 20 has reached the desired set points
chosen by the operator. Similar temperature control is proviAed
for burner 10 of containment means 2.
At the same time, the control means 34 continuously
compares the pressure measured by pressure transducer 22, with the
pressure set point chosen by the operator as re~uired to maintain
a safe negative pressure condition within the kiln, insuring that
any looseness in the kiln will result in a leakage of ambient air
into the kiln rather than a leakage of comhustion products from
the kiln. Anytime the negative pressure measured by the pressure
transducer 22 exceeds the safe set point chosen by the operator,
the control means 34 will reduce the air flow set point anA raise
the oxygen flow set point in such fashion that each 4.76 volumes
of air will be substituted by approximately 1 volume of oxyqen fed
in kiln 1 maintaining the total amount of the oxygen feed
approximately constant until the negative pressure reaches the
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1 333973
safe set point. Similar pressure requlation involvinq pressure
transducer 24 is utili2ed in the afterburner.
To insure a maintenance of the desired retention time
and to avoid additional air pollution volumes beinq produced in
the kiln, the control means 34 continuously compares the allowed
combust~on product flow setting for the kiln dischar~e with the
actual flow belnq measured by the flow transducer 23. When the
actual flow exceeds the allowed set point chosen by the operator,
the control means 34 reduces the air flow and increases the oxygen
flow supplied to burner 1 in such a manner that the reduction in
every 4.76 volumes of air flow will result in approximately a t
volume increase in oxygen flow maintaining the total amount of the
oxyqen feed approximately constant until the combustion product
flow reaches the allowed flow rate.
The control system 34, by means of thermocouples 20 and
21, will recogni2e an excessive increase in combustion product
temperatures which result from the ad~ustments in pressures and
flows and will reduce auxiliary fuel flow to brin~ the
temperatures down to the desired levels. Simultaneously with the
reduction of the auxiliary fuel flow, the oxygen flow will he
reduced accordinq to the approximately stoichiometric fuel/oxygen
ratio.
Additionally, feed forward controls may be preferrahly
used for both the primary incineration combustion mean~ and
containment means 2 when solid wastes are batch chargeA. Prior to
the feeding of a batch charge, the feed indicatinq means 33
located upstream of the loaAing chute of feedinq means 29
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1 333973
transmits a signal to the controlling means 34 identifyinq that a
charge is approaching loadin,q chute 29. In response, the control
means 34 changes air, oxygen and auxiliary fuel set points to a
special "emergency" set of values, insuring the supply of
additional excess oxygen durin,q, such transient loadinq conditions,
and activates modulating means 47-52 so that the feedinq of air is
reduced and the feedinq of oxyqen is increased in both the kiln
and the afterburner prior to loading of the incineration system,
resulting in a rapid rise in oxygen concentration in the kiln and
afterburner as well as the temperature in the afterburner. The
emergency set of values should provide for maximum prestored
oxygen mass in the primary combustion incineration means and
afterburner while maintaining the flame stability, as well as the
required temperatures and retention time of gases during the
lS transient event. The excess mass of oxygen accumulated in the
kiln 1 in anticipation of the approaching batch chaeqe is utilized
to provide sufficient oxidizer durinq the first staqe of waste
charge volatilization. Optionally, the auxiliary fuel feed and/or
the liquid waste feed delivered to primary incineration combustion
means may also be reduced while maintaining the temperature in the
kiln under venting conditions substantially above the temperature
of ignition of organics in the waste to be charqed, thus leavinq
more oxygen in the kiln volume availahle for incineration of a
batch of wastes, and increasing the retention time for gaseous
products in the kiln.
When the batch charge enters the kiln 1, there exists a
substantial prestored oxygen mass in the primary incineration
combustion means as well as the afterburner and the temperature
conditions necessary for the combustion of organics in said batch
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in the primary incineration combustion means and afterburner. The
levels of oxygen, air and fuel feed will be returned to those
corresponding to the nominal feeding rates when the destruction of
volatilized organics created during the transient overload
condition is complete. The duration of such "emergency" cycle can
be predicted by experience and the timer of control means 34 will
maintain the initial duration settinq of such "emerqency"
transient air, auxiliary fuel and oxygen flows based upon this
prediction maintaining maximum partial pressure of oxygen and
temperature in afterburner. During such an "emergency" cycle,
thermocouples 20 anA 21 may indicate temperature levels beyond
steady state operating conditions. However, the control means 34
will overrule these signals during an "emer~ency" cycle so that
overheating for a short time period is allowed.
lS After the "emerqency" cycle ends, the control means 34
begins an "approaching cycle" which is designed to chanqe
gradually the auxiliary fuel flow anfl the oxygen flow towards a
steady state ratio first in primary incineration comhustion means
and then in the afterburner. If during such cycle the smoke
indicating means indicates smoke formation, the increase in the
fuel flow will be discontinued but the oxygen flow will be raised
again for a preset short time interval. After this time interval
elapses, the "approachinq cycle" will be initiated aqain. The
control system will repeat the approachinq cycle until the smoke
is eliminated and the temperature and the level of excess oxyqen
in the kiln reach a normal level for steady operation. After such
event the additional flow of oxygen being supplied to the
afterburner to insure the complete combustion of any excess PICs
during transient loading in the kiln will be discontinued and the
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afterburner will reach steady operational conditions. Proper
temperature will be further maintained by thermocouples 20 and 21
and by control means 34.
Sensor means 20, 22, 23 and 35 located after the exit
from kiln 1 and prior to containment means 2 will provide feedback
control of the primary incineration combustion means and feed
forward control of the afterburner means during the incineration
process. These means supply electrical signals to control means
34 indicating the temperature, pressure or flow rate of gas
leaving kiln 1 or the presence of excess smoke or flame. These
signals are received and interpreted by control means 34, which in
turn chanqes the oxygen, air and fuel flow into the kiln l anfl/or
containment means 2.
Signals from thermocouples 20 and 21 are continuously
compared with desired set points by the control means 34. A
decrease or increase of the kiln 1 temperature beyond a desired
set point triggers an increase or decrease, respectively, in the
flow of auxiliary fuel by the use of the first fuel flow
modulating means 52. The afterburner temperature is measured with
thermocouple 21 and is compared by the control means 34 with a
desired set point. A decrease or increase of the afterburner
temperature beyond the desired set point triqqers an increase or
decrease, respectively, in the flow of auxiliary fuel by the use
of the second fuel flow modulating means 49. An increase or
decrease in the auxiliary fuel flow into the primary incineration
combustion means 70 or the containment means 2 will be identified
by control means 34 through communication with flow metering means
41 and 43. The control means 34 will also respond by ad~ustina
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the flow of oxygen to control the proper ratio between auxiliary
fuel and oxidizer.
In orde`r to prevent excess flue gas discharge from the
incineration syQtem, the control system will raise the flow of
oxygen and reduce the flow of air based upon signals from the
transducers 22, 23, 24, and 25 indicating that an excess amount of
flue gases are being generated.
When the sensor means 35 detects excessive smoke or
flame existing in the flue exhaust fluct 5, indicating to the
control means 34 a deficiency of oxygen in kiln 1, the control
means 34 will activate first oxygen flow modulating means 48 to
increase the oxygen supply and modulating means 52 and 36 to
reduce auxiliary fuel flow and/or pumpable waste. When the second
sensor means 65 detects excessive smoke or flame existing in the
flue exhaust duct 32 indicating to the control mean.s 34 a
deficiency of oxygen in the containment means 2, the control means
34 will activate second oxygen flow modulating means 50 to
increase the oxygen supply and modulatinq means 49 and 37 to
reduce auxiliary fuel flow and/or pumpable waste.
Within the allowed magnitude of the batch charae and
gradual fluctuations in the flow rate and composition of wastes,
the process insures the required destruction efficiency of PO~Cs,
prevents formation of PICs and minimizes formation f ~x due to
the following features:
(a) The controlled oxygen to air ratio permits the
change in the oxidizer flow in order to meet the oxyqen demand and
simultaneously to maintain the required temperature, retention
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1 333973
time and turbulence. This eliminates such failure modes as
overcharginq or burning of wastes with low caloric value at
temperatures below the reauired level. Ad~itionally, the
destruction and efficiency of POHCs, PICs and soot are increased,
the negative effect of poor atomiæation of liquid wastes is
minimized, and the possibility of a flame out failure is virtually
eliminated;
(b? Uniform heating and intensive mixinq due to the u.se
of the burner means as described and due to rapid mixinq of the
hot oxidiæing auxiliary combustion products with the flue gases,
as presently described, eliminates cold spots and breakthrough of
POHCs;
tc) The use of hot oxidizing and reducinq auxiliary
combustion products in combination with the hot oxidizinq
auxiliary combustion products in the afterhurner further improves
removal of NOx and destruction of POHCs, PICs and soot in the
afterburner;
(d) The use of water or steam and 020ne permits further
optimiæation of either the oxidiæing or reducing hot auxiliary
combustion products which are used for NOx reduction and POHCS,
PICs, soot and CO elimination;
~ e) The use of rapid mix of the hot auxiliary
combustion products with the flue gases in the afterburner
provides uniform temperature and gaseous constituents distrihution
in the rapid mix chamber; and
(f) Rapid control of oxygen, air and fuel feed into the
primary combustion means and afterburner pro~ide fast response to
changes in the waste feed and composition. ~he feed-forward
control of batch combustion in both the primary and the secondary
30 combustion means allows the maximiæation of the size of the batch
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charge for a given system, while feedback control of the primary
and feed-forward control of the secondary combustion means allows
the maximization of the magnitude of the qradual chanqes in the
waste feed. In either case the temperature, retention time and
turbulence are maintained at reauired levels.
A possible modification to the system is the conversion
of a portion of the oxygen stream to ozone prior to its use as an
exclusive oxidizer or in combination with air, oxyaen or oxygen
enriched air. Ozone can be most heneficially used as an oxidizer
in situations where the need for additional heat input into the
afterburner is insignificant. Ozone initiates chain reactions in
the flame, thus resulting in faster and more complete destruction
of POHC and reduction in the PIC formation.
A further modiflcation is the use of water as an
additional oxidizing-reducing agent by its introduction into the
combustion process in the primary incineration combustion means
and afterburner. Water will disassociate at hiqh temperatures
into hydrogen, oxygen and hydroxide, which are heneficial to the
combustion process. These species prevent formation of soot and
cyclic and aromatic hydrocarbons including halogenated and
oxygenated compounds which are freauently PICs. The use of water
is most advantageous when the caloric value of the wastes being
incinerated in the primary incineration comhustion means is hiqh
and/or the ratio of H:C is low. The hydrogen formed from water
reacts with haloqens which are often found in the POHCs forminq
HCl, HF, etc., thus making halogens mobilized and not available
for the formation of halogenated PICs.
1 333973
charge for a given system, while feedback control of the primary
and feed-forward control of the secondary combustion means allows
the maximization of the magnitude of the qradual chanqes in the
waste feed. In either case the temperature, retention time and
turbulence are maintained at reauired levels.
A possible modification to the system is the conversion
of a portion of the oxygen stream to ozone prior to its use as an
exclusive oxidi2er or in combination with air, oxyaen or oxyqen
enriched air. Ozone can be most heneficially used as an oxidizer
in situations where the need for additional heat input into the
afterburner is insignificant. Ozone initiates chain reactions in
the flame, thus resulting in faster and more complete destruction
of POHC and reduction in the PIC formation.
A further modification is the use of water as an
additional oxidizing-reducing agent by its introduction into the
combustion process in the primary incineration combustion means
and afterburner. Water will disassociate at hiqh temperatures
into hydrogen, oxygen and hydroxide, which are heneficial to the
combustion process. These species prevent formation of soot and
cyclic and aromatic hydrocarbons including halogenated and
oxygenated compounds which are freauently PICs. The use of water
is most advantageous when the caloric value of the wastes being
incinerated in the primary incineration comhustion means is hiqh
and/or the ratio of H:C is low. The hydrogen formed from water
reacts with haloqens which are often found in the PORCs forminq
HCl, HF, etc., thus making halogens mobilized and not available
for the formation of halogenated PICs.
1 333973
A further modification of the vortex mixinq chamher is
the use of co-current or counter-current feed of flue gases from
the primary incineration chamber and the hot auxiliary combustion
product generated in the afterburner burner.
In cases where further improvements of the destruction
level of hazardous waste is needed, a second afterburner means may
be utilized with an embodiment similar to those described above to
provide an additional step of afterburning the hot gaseous
- products leaving the first afterburner means. A partial recyclinq
of the gaseous products between the primary incineration
combustion means and the afterburner, or between a first and
second afterburner, may be utilized for further reduction of PICs
and POHCs. Partial recycling of flue gases provides mixing of
high and low concentrated portions of flue gases and eaualization
of fluctuations of POHC an PIC in the gaseous effluent from the
system. Optionally, a reducing atmosphere may be maintained in
the first afterburner and/or in recycled gases thus provifling
NOX reduction in the flue gases entering the final afterburner.
An oxidizing atmosphere may be provided in the second
afterburner.
Alternative probes, such as thermal pyrometers,
combustible gas analyzers, oxygen analyzers and ~V scanners, may
be used to indicate to the control system the existence of
prefailure conditions.
While the above description contains many specificities,
these should not be construed as limitations on the scope of the
invention, but rather as an amplification of one preferrefl
embodiment thereof.
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