Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
  • F23G5/00—Incineration of waste; Incinerator constructions; Details, accessories or control therefor
  • F23G5/008—Incineration of waste; Incinerator constructions; Details, accessories or control therefor adapted for burning two or more kinds, e.g. liquid and solid, of waste being fed through separate inlets
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
  • F23G5/00—Incineration of waste; Incinerator constructions; Details, accessories or control therefor
  • F23G5/08—Incineration of waste; Incinerator constructions; Details, accessories or control therefor having supplementary heating
  • F23G5/14—Incineration of waste; Incinerator constructions; Details, accessories or control therefor having supplementary heating including secondary combustion
  • F23G5/16—Incineration of waste; Incinerator constructions; Details, accessories or control therefor having supplementary heating including secondary combustion in a separate combustion chamber
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
  • F23G2204/00—Supplementary heating arrangements
  • F23G2204/10—Supplementary heating arrangements using auxiliary fuel
  • F23G2204/103—Supplementary heating arrangements using auxiliary fuel gaseous or liquid fuel

Definitions

• 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.
• 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 and 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 combustion air for waste incineration units, hot water, steam and/or electricity; a system for preparing, feeding, recycling and treating any water solutions produced for removal of gaseous and/or particulates in 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 controlling the flow of fuel and oxidizers, process temperatures and pressures at strategic locations
• 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 initial 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 about 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 charged 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 bundles.
• Special loading devices are used for charging 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 combusting low caloric value wastes
• 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 liquid 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 remaining after the primary incineration process. The 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 partially removed in the scrubber. Some polar organics and organics which are adsorbed in the soot 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 organic and inorganic combustible constituents.
• a fraction of organics may be highly toxic, mutanogenic and teratogenic. This fraction of organics is usually called principle organic hydrocarbons (POHC).
• POHC principle organic hydrocarbons
• Many POHCs are very stable and require oxidation at elevated temperatures for their destruction.
• 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 raising 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 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 during the combustion process. These products include carbon microparticles, carbon monoxide and an array of organic compounds.
• organic compounds are a higher molecular weight polycyclic or polyaromatic organics such as dioxins, benz(a) pyrene, dibenz(a,c)anthracene, picene, dibenz(a,h)anthracene, 7, 12-dimethyl(a)anthracene, benz(b)fluortane, 9,1O-dimethylanthracene.
• PICs products of incomplete combustion
• 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.
• 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.
• the maximum allowable concentrations of pollutants in the flue gases are specified in the operating permit which is based on the current environmental requirements and regulations.
• the kiln temperature ranges from 750°C (1400°F) 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 the furnace. In order to insure the sufficient contact between organics and oxygen, an excess of combustion 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 has not proven to be effective utilizing 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 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.
• Failure modes similar to those described above for the kiln may also occur in the afterburner.
• overcharging, 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 subsequently, in a lower thermal destruction efficiency overall for existing incineration systems.
• 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.
• 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 incineration 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.
• oxygen and air oxygen and oxygen enriched air.
• Additional oxidizing agents can be optionally used.
• water or steam may be introduced to reduce soot and N0 X formation.
• 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.
• the oxygen stream is introduced primarily as a high pressure, high velocity 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.
• 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 N0 X and PICs formations.
• the transport of oxidizer toward the fuel or liquid 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 Application No. 883,769.
• 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 as temperature, pressure and flows of fuel, fluid waste, oxidizing 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 bring 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 containing 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 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.
• 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 incineration combustion means, to increase the quantity of oxygen available for the oxidation of the wastes and to further increase the retention time, simultaneously.
• 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.
• 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 atmosphere during shutdowns and transient surge conditions such as those caused by batch charging or unexpected changes in the caloric value of the waste as well as by other system malf nctions.
• 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.
• 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 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 watercooled burner as described in detail in U. S. Patent Application Serial No. 883,769.
• 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, oxygen), 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, air), 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
• a second oxidizing gas having a different oxygen concentration from the first oxidizing gas for example air
• Auxiliary fuel 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 Application No. 883,769 to maintain a hot stable flame core during continuous incineration operation, to prevent flame failure and to minimize N0 X 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 burner 103 which is similar in design to burner 26.
• Burner 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.
• temperatures of combustion products exhausting from the kiln 1 are registered by a first thermocouple 20.
• thermocouple 21 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
• a control system for detecting and adjusting to operational conditions in the apparatus includes a feed indicating means 33 for indication to a control means 34 of a batch charge approaching 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 signals 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 modulating means 47 on the first air line 80, a second air flow modulating means 51 on the second air line 81, a first oxygen flow modulating means 48 on the first oxygen line 82, a second oxygen flow modulating 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 means 36 on the first pumpable fluid waste line 86, and a second waste flow modulating 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 by 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 by the first auxiliary fuel flow metering means 41; and, pumpable wastes are measured by the first waste flow metering means 40.
• 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 by the first auxiliary fuel flow metering means 41; and, pumpable wastes are measured by the first waste flow metering means 40.
• f 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 measured by the second auxiliary fuel flow metering means 43; and, pumpable wastes are measured by the second waste flow metering means 42.
• the burner means 26 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, thereby 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 high velocity, thereby creating a venturi effect for inspirating the kiln flue gases into the flame directed toward the afterburner vessel 55. This creates intensive mixing of the gaseous stream prior to entering a refractory lined afterburner vessel 55 of the containment means 2.
• FIG. 1, 4 and 5 there is shown an alternative embodiment of the afterburner.
• This afterburner consists of a vortex mixing chamber 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 tangentially attached to the vortex chamber 101.
• the burner means 26 has inlets 107, 104, 106 and 105 for feeding a combustible fluid (waste or fuel), a first oxidizer such as oxygen, an auxiliary fuel (when needed) and a second oxidizer, such as air, respectively.
• Means for feeding additional amounts of oxygen 120 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.
• means 120 may be attached to the contracted section of the outlet 110.
• a secondary burner similar to burner means 120 may be installed downstream of means 26.
• 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 allowing the flow of gases from the first rapid mix chamber into the second and following rapid mix chambers.
• water or steam feeding means may be provided in either first, or second or all rapid mix chambers.
• Said rapid mix chambers may include afterburner vessels communicating with each mixing chamber to provide additional retention time. Operation
• Solid waste may be continuously or batch charged into kiln 1 through feeder 29.
• pumpable fluid waste may be introduced for incineration through the waste port 9 into the fluid waste burner 3 and further with a flame into the kiln 1 interior.
• auxiliary fuel may be introduced through auxiliary fuel port 8 into the burner 3 and further directed through the burner combustion chamber 28 towards the kiln 1 interior.
• a first oxidizing 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 (for example, oxygen) may be supplied from a liquid oxygen tank or from an on-site oxygen generation unit through second gas port 7 to fluid waste burner 3 and further through burner combustion chamber 28 toward kiln 1 interior.
• the waste feeding rate, the auxiliary fuel flow and the first and second oxidizing 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 gaseous state during the solids retention time in the kiln 1. Additionally, the temperature should be above the ignition point of volatilized components originating from solid waste as well as combustible components formed during pyrolysis of pumpable waste and auxiliary fuel so that said volatilized combustion components undergo thermal destruction.
• the total amount of oxygen being delivered with oxidizing gases into the kiln 1 has to be kept high enough to insure its availability to completely combust auxiliary fuel and fluid waste, and to provide extra oxygen flow to destroy the bulk of combustible components being formed in the interior of the kiln 1.
• Flue gases exhausted from the kiln 1 are directed into the first vortex mixing chamber 10 through flue gas inlet 11 and further throughout the interior 27 of the vortex mixing chamber 10 toward the interior of the afterburner vessel 55.
• pumpable fluid wastes may be incinerated by introduction through liquid waste inlet 15 into combustion chamber 28 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 regulations), through auxiliary fuel inlet 14 into burner 26 then throughout burner combustion chamber 28 and further through the interior 27 of the mixing chamber 10 toward afterburner vessel 55.
• the first oxidizing gas with a higher oxygen content (for example, oxygen) than second oxidizing gas is directed into the burner 26 through the first oxidizing gas inlet 13, and further throughout combustion chamber 28, thus discharging hot oxidizing 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 afterburner vessel 55.
• a second oxidizing gas with low oxygen content (for example, air or oxygen enriched air) is directed into burner 26 through the second oxidizing gas inlet 12 and further throughout combustion chamber 28 thus discharging said hot oxidizing gas agent toward the interior 27 of the mixing chamber 10 and further toward afterburner vessel 55.
• At least 2% to 3% of residual oxygen content in the combustion gases leaving afterburner preferrably should be provided during steady-state operating conditions.
• an alternative embodiment of the vortex chamber will be operated as follows:
• the flue gases from the primary combustion means will be fed axially into the vortex mixing chamber 101 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 ports 107, 104 and 105, respectively.
• a combustible fluid waste or fuel
• a first oxidizer such as oxygen
• a second oxidizer such as air, or oxygen enriched air
• the burner means 103 fires tangentially into mixing chamber 101 so that the hot auxiliary combustion product which may be, depending on operational mode, a hot oxidizing or reducing agent, originating as hot auxiliary combustion 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.
• the hot auxiliary combustion product which may be, depending on operational mode, a hot oxidizing or reducing agent, originating as hot auxiliary combustion 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 afterburner and environmental regulations.
• 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 providing the required destruction of POHCs, PIC, soot and CO.
• a fraction of oxidizing gas can be fed downstream of the hot flame zone at the burner means 26 by the use of the oxidizer injecting means 120.
• the operation of the afterburner may be further improved as follows.
• the 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 selective reducing species for N0 X , NO x will be reduced while oxygen in the flue gases will be consumed to a lesser extent. Simultaneously POHCs and PICs will undergo a further thermal destruction due to the additional heat provided with the hot reducing auxiliary combustion products generated in the burning means 26.
• a further improvement of this operating mode may be accomplished by the injection of a hot oxidizing auxiliary combustion product by 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 increasing the CO and H2 content in the hot reducing auxiliary combustion products.
• the chambers at the head of the afterburner can be fed with hot reducing auxiliary combustion products while the final stages will be fed with hot oxidizing auxiliary combustion product thus insuring N0 X reduction and POHCs, PICs, soot and CO destruction.
• Said hot auxiliary oxidizing combustion products have high temperatures and high momentum and provide high turbulence, extra heat to raise mix temperature and excess oxygen.
• rapid and uniform mixing occurs in chamber 101 and a final hot combustion product with at least 2% to 3% of residual oxygen is transferred through outlet 110 into afterburner vessel 55, wherein the required retention time is provided.
• Such operation of afterburner insures accelerated burning 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 kiln and in the afterburner in order to prevent gas leakage outside the system.
• An exhaust fan is" used for creating the required negative pressure.
• the ratio of air to oxygen or oxygen enriched air, the fuel feed rate and the oxygen excess level are selected for a particular composition and a particular feed rate of waste so that the required temperature, retention time, partial pressure of oxygen 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.
• the desired settings for temperature in the kiln and the afterburner, the maximum flow rates of combustion products from 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 being delivered to the burner by raising the instant flow setting for the auxiliary fuel supply line and accordingly on oxygen supply line so that the chosen oxygen excess level is provided until the temperature measured by thermocouple 20 has reached the desired set points chosen by the operator. Similar temperature control is provided for burner 10 of containment means 2.
• control means 34 continuously compares the pressure measured by pressure transducer 22, with the pressure set point chosen by the operator as required 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 combustion 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 and raise the oxygen flow set point in such fashion that each 4.76 volumes of air will be substituted by approximately 1 volume of oxygen fed in kiln 1 maintaining the total amount of the oxygen feed approximately constant until the negative pressure reaches the safe set point.
• Similar pressure regulation involving pressure transducer 24 is utilized in the afterburner.
• the control means 34 continuously compares the allowed combustion product flow setting for the kiln discharge with the actual flow being 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 1 volume increase in oxygen flow maintaining the total amount of the oxygen 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 recognize an excessive increase in combustion product temperatures which result from the adjustments in pressures and flows and will reduce auxiliary fuel flow to bring the temperatures down to the desired levels. Simultaneously with the reduction of the auxiliary fuel flow, the oxygen flow will be reduced according to the approximately stoichiometric fuel/oxygen ratio.
• feed forward controls may be preferrably used for both the primary incineration combustion means and containment means 2 when solid wastes are batch charged.
• the feed indicating means 33 located upstream of the loading chute of feeding means 29 transmits a signal to the controlling means 34 identifying that a charge is approaching loading chute 29.
• 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 during such transient loading conditions, and activates modulating means 47-52 so that the feeding of air is reduced and the feeding of oxygen 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 transient event.
• the excess mass of oxygen accumulated in the kiln 1 in anticipation of the approaching batch charge is utilized to provide sufficient oxidizer during the first stage of waste charge volatilization.
• 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 charged, thus leaving more oxygen in the kiln volume available for incineration of a batch of wastes, and increasing the retention time for gaseous products in the kiln.
• the control means 34 begins an "approaching cycle” which is designed to change gradually the auxiliary fuel flow and the oxygen flow towards a steady state ratio first in primary incineration combustion 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 "approaching cycle” will be initiated again. The control system will repeat the approaching cycle until the smoke is eliminated and the temperature and the level of excess oxygen in the kiln reach a normal level for steady operation.
• thermocouples 20 and 21 and by control means 34 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 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 changes the oxygen, air and fuel flow into the kiln 1 and/or containment means 2.
• thermocouples 20 and 21 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 triggers 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 adjusting the flow of oxygen to control the proper ratio between auxiliary fuel and oxidizer.
• 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.
• the control means 34 When the sensor means 35 detects excessive smoke or flame existing in the flue exhaust duct 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.
• the control means 34 When the second sensor means 65 detects excessive smoke or flame existing in the flue exhaust duct 32 indicating to the control means 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 modulating means 49 and 37 to reduce auxiliary fuel flow and/or pumpable waste.
• the process insures the required destruction efficiency of POHCs, prevents formation of PICs and minimizes formation of N0 X due to the following features:
• the controlled oxygen to air ratio permits the change in the oxidizer flow in order to meet the oxygen demand and simultaneously to maintain the required temperature, retention time and turbulence. This eliminates such failure modes as overcharging or burning of wastes with low caloric value at temperatures below the required level. Additionally, the destruction and efficiency of POHCs, PICs and soot are increased, the negative effect of poor atomization of liguid wastes is minimized, and the possibility of a flame out failure is virtually eliminated; (b) Uniform heating and intensive mixing due to the use of the burner means as described and due to rapid mixing of the hot oxidizing auxiliary combustion products with the flue gases, as presently described, eliminates cold spots and breakthrough of POHCs;
• 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, oxygen or oxygen enriched air.
• Ozone can be most beneficially 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 high temperatures into hydrogen, oxygen and hydroxide, which are beneficial to the combustion process. These species prevent formation of soot and cyclic and aromatic hydrocarbons including halogenated and oxygenated compounds which are frequently PICs.
• the use of water is most advantageous when the caloric value of the wastes being incinerated in the primary incineration combustion means is high and/or the ratio of H:C is low.
• the hydrogen formed from water reacts with halogens which are often found in the POHCs forming HC1, HF, etc., thus making halogens mobilized and not available for the formation of halogenated PICs.
• a further modification of the vortex mixing chamber 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.
• 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 recycling 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 equalization of fluctuations of POHC an PIC in the gaseous effluent from the system.
• a reducing atmosphere may be maintained in the first afterburner and/or in recycled gases thus providing N0 X reduction in the flue gases entering the final afterburner.
• An oxidizing atmosphere may be provided in the second afterburner.
• thermo pyrometers such as thermal pyrometers, combustible gas analyzers, oxygen analyzers and UV scanners, may be used to indicate to the control system the existence of prefailure conditions.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Incineration Of Waste (AREA)
• Processing Of Solid Wastes (AREA)
• Solid-Fuel Combustion (AREA)

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• 1988
  • 1988-06-17 EP EP19880906630 patent/EP0419463A4/en not_active Withdrawn
  • 1988-06-17 AU AU21318/88A patent/AU621059B2/en not_active Ceased
  • 1988-06-17 JP JP63506711A patent/JPH03505910A/ja active Pending
  • 1988-06-17 WO PCT/US1988/002116 patent/WO1989012783A1/en not_active Ceased

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