Patent Application
20060084017
This invention relates to a flameless thermal oxidizer. More particularly, this invention relates to a gas recuperative flameless thermal oxidizer and a method for oxidizing combustible vapor in a flameless thermal oxidizer.
Many process streams of vapors, such as effluents from chemical processing plants, refineries, etc., utilize oxidizers to destroy the combustible vapor prior to release to the atmosphere. However, with increasing demands on the environmental control of emissions, the use of free flames to oxidize such effluents is in many cases unsatisfactory, since a free flame frequently results in incomplete combustion and uncontrollable production of undesirable side products, including for example carbon monoxide and nitrogen oxides. Thus, methods for destroying combustible streams to a high level of conversion with a minimum of pollutant production and in an energy-efficient manner are in continuing and increasing demand.
One example of a flameless thermal oxidizer is disclosed in U.S. Pat. No. 5,320,518, issued to Stilger et al, which is incorporated herein by reference. While the Stilger system represents an improvement over prior systems, there remains a need for improved flameless thermal oxidizers and methods for oxidizing combustible vapor in a flameless thermal oxidizer.
In one aspect, the invention provides a gas recuperative flameless thermal oxidizer. The oxidizer includes a matrix bed and at least one feed passage extending at least partially within the matrix bed. The feed passage has an inlet configured to receive combustible vapor or an air-combustible vapor mixture and an outlet configured to deliver the combustible vapor or the air-combustible vapor mixture into the matrix bed. The feed passage has a cross-sectional area and a length within the matrix bed, such that the ratio of the length (ft) to the cross-sectional area (in2) is at least about 0.5:1.
In another aspect, the invention provides a method of oxidizing combustible vapor in a gas recuperative flameless thermal oxidizer. The method includes delivering combustible vapor or an air-combustible vapor mixture into an inlet of a feed passage and through an outlet of the feed passage to a matrix bed below the lower flammability limit, while maintaining a length within the matrix bed of the feed passage such that a ratio of the length (ft) to the cross-sectional area (in2) is at least about 0.5:1.
In another aspect, the invention provides a gas recuperative flameless thermal oxidizer having at least one separate fuel inlet configured to introduce fuel into a matrix bed, the fuel inlet being positioned downstream of an outlet of a feed passage through which combustible vapor or an air-combustible vapor mixture is introduced into the matrix bed.
In another aspect, the invention provides a method of oxidizing combustible vapor by introducing fuel into a matrix bed through a separate fuel inlet at a position downstream of an outlet of a feed passage through which combustible vapor or an air-combustible vapor mixture is introduced into the matrix bed.
In another aspect, the invention provides a gas recuperative flameless thermal oxidizer, wherein a feed passage for combustible vapor or an air-combustible vapor mixture defines an interior extending within a matrix, the interior being substantially devoid of matrix.
In another aspect, the invention provides a method of oxidizing combustible vapor while maintaining an interior of a feed passage extending within a matrix substantially devoid of matrix.
In another aspect, the invention provides a gas recuperative flameless thermal oxidizer having a matrix bed positioned to exhaust gaseous oxidation products along an exhaust path, and at least one feed passage extending at least partially within the matrix bed. The feed passage has an inlet configured to receive combustible vapor and an outlet configured to deliver the combustible vapor into the matrix bed, the feed passage defining a combustible vapor path extending within the matrix in a direction substantially opposite that of the exhaust path of the matrix bed. The combustible vapor path of the feed passage and the exhaust path of the matrix bed are configured to provide a ratio between the velocity of combustible vapor in the combustible vapor path and the velocity of exhaust in the exhaust path between about 0.5:1 and about 1.5:1.
In another aspect, the invention provides a method of oxidizing combustible vapor by exhausting gaseous oxidation products along an exhaust path in the matrix bed in a direction that is substantially opposite that of the combustible vapor path of the feed passage. The method also includes maintaining a ratio between the velocity of combustible vapor in the combustible vapor path and the velocity of exhaust in the exhaust path between about 0.5:1 and about 1.5:1.
In another aspect, the invention provides a gas recuperative flameless thermal oxidizer having an enclosure, a matrix bed contained within the enclosure, feed tubes extending into the enclosure and at least partially within the matrix bed, and a matrix bed support mounted within the enclosure. The matrix bed support has a surface substantially impervious to the flow of exhaust supporting the matrix bed, the matrix bed support defining apertures each sized to receive a feed tube and exhaust passages proximal to the apertures.
In another aspect, the invention provides a method of oxidizing combustible vapor by directing substantially all gaseous oxidation products in a matrix bed through apertures in a matrix bed support adjacent feed tubes. The method also includes exhausting gaseous oxidation products from the gas recuperative flameless thermal oxidizer through an outlet in the enclosure.
In another aspect, the invention provides a gas recuperative flameless thermal oxidizer having an enclosure extending between opposed end portions, a matrix bed contained within the enclosure, feed tubes extending into the enclosure and at least partially within the matrix bed, and means for adjusting the distance between the opposed end portions of the enclosure to increase or decrease the size of the matrix bed.
The invention will next be illustrated with reference to the Figures, wherein the same numbers indicate the same elements in all Figures. Such Figures are intended to be illustrative rather than limiting and are included herewith to facilitate explanation of the present invention. The Figures are not to scale, and are not intended to serve as engineering drawings. For simplicity, descriptions of the Figures will be based on an orientation of the flameless thermal oxidizer wherein the inlet and outlet nozzles are at the lower end of the unit when it stands upright. However, the unit may be operated in any orientation.
Generally, the present process and apparatus provide a method for controlling and stabilizing a flameless oxidation reaction wave in a heat-resistant solid matrix bed in which the combustible vapor is oxidized within a controlled area of the matrix at substantially uniform and relatively low temperatures, compared with temperatures produced in flames. The uniformity of the reaction wave, and the increased mixing and heat treatment afforded by the matrix, provide for a high conversion of reactants to products with a low level of production of undesired side products, including nitrogen oxides and carbon monoxide.
According to one exemplary embodiment, at least a portion of the bed is initially above the auto-ignition temperature of the mixture (typically a minimum temperature of about 1200° F.), whereby the mixture initiates an exothermic reaction in the bed, forming the reaction wave. This method and apparatus can be functionally applied to processes where the minimization of nitrogen oxides, ammonia, and products of incomplete combustion is desired in conjunction with either (a) destruction of a particular gas or vapor, or (b) combustion of fuel to generate heat.
Within an appropriate range of inlet mixture compositions, the reaction is substantially self-sustaining, i.e., little or no external heat is required to maintain the process temperature. The devices and methods provide unusually good recapture, or recuperation, of heat energy produced by the flameless thermal oxidation, resulting in the ability to efficiently oxidize input streams having relatively low fuel BTU content without the need to supply additional fuel to maintain the reaction, and to oxidize even lower BTU content streams by using only a relatively small amount of supplemental fuel.
More particularly, the present process and apparatus provides a method for flameless combustion in a reaction matrix of gases that have been preheated by an efficient recuperative heat exchange system. This provides a method for reducing the fuel concentration required for oxidation comprising, according to one embodiment, the steps of directing a mixture of the combustible vapor, with air and/or oxygen, into thermally conducting feed tubes embedded in a heat-resistant matrix bed, at least a portion of the bed initially being above approximately 1200° F., whereby the mixture oxidizes exothermally in the bed being premixed prior to entering, creating hot exhaust gases and heating the matrix. The matrix surrounding the feed tubes is heated by forced convection from the exhaust gases, as well as inner body thermal radiation and conduction in the matrix. The feed tubes are heated by thermal radiation from the surrounding matrix, as well as by conduction from the matrix and convection from the exhaust gases. Within an appropriate range of inlet mixture compositions, the reaction is substantially self-sustaining.
Referring generally to the exemplary embodiments selected for illustration in the Figures, the oxidizer 1, 100 includes a matrix bed 50, 150 and at least one feed passage 30, 130 extending at least partially within the matrix bed 50, 150. The feed passage 30, 130 has an inlet 56, 156 configured to receive combustible vapor or an air-combustible vapor mixture and an outlet 8, 108 configured to deliver the combustible vapor or the air-combustible vapor mixture into the matrix bed 50, 150. The feed passage 30, 130 has a cross-sectional area and a length L1 within the matrix bed 50, 150, wherein a ratio of the length L1 (ft) to the cross-sectional area (in2) is at least about 0.5:1. Typically, L1 is about 2 ft. or more. In use, combustible vapor or an air-combustible vapor mixture is delivered into the inlet 56, 156 of the feed passage 30, 130 and through the outlet 8, 108 of the feed passage 30, 130 to a matrix bed 50, 150 below the lower flammability limit, while maintaining a length L1 within the matrix bed 50, 150 of the feed passage 30, 130 such that a ratio of the length L1 (ft) to the cross-sectional area (in2) is at least about 0.5:1.
The gas recuperative flameless thermal oxidizer 1, 100 optionally has at least one separate fuel inlet 24, 124 configured to introduce fuel into the matrix bed 50, 150, the fuel inlet 24, 124 being positioned downstream of the outlet 8, 108 of the feed passage 30, 130 through which combustible vapor or an air-combustible vapor mixture is introduced into the matrix bed 50, 150. In one embodiment, the fuel inlet 24, 124 is proximal to the outlet 8, 108. In use, fuel is introduced into the matrix bed 50, 150 through the separate fuel inlet 24, 124 at a position proximal to the outlet 8, 108 of the feed passage 30, 130 through which combustible vapor or an air-combustible vapor mixture is introduced into the matrix bed 50, 150.
The feed passage 30, 130 of the gas recuperative flameless thermal oxidizer 1, 100 defines an interior extending within a matrix, the interior optionally being substantially devoid of matrix. In use, combustible vapor is oxidized while maintaining the interior of the feed passage 30, 130 substantially devoid of matrix.
The matrix bed 50, 150 of the gas recuperative flameless thermal oxidizer 1, 100 is positioned to exhaust gaseous oxidation products along an exhaust path, and the feed passage 30, 130 defines a combustible vapor path extending within the matrix in a direction substantially opposite that of the exhaust path of the matrix bed 50, 150. The combustible vapor path of the feed passage 30, 130 and the exhaust path of the matrix bed 50, 150 are optionally configured to provide a ratio between the velocity of combustible vapor in the combustible vapor path and the velocity of exhaust in the exhaust path between about 0.5:1 and about 1.5:1. In use, gaseous oxidation products are exhausted along the exhaust path in the matrix bed 50, 150 in a direction that is substantially opposite that of the combustible vapor path of the feed passage 30, 130, while maintaining a ratio between the velocity of combustible vapor in the combustible vapor path and the velocity of exhaust in the exhaust path between about 0.5:1 and about 1.5:1.
The gas recuperative flameless thermal oxidizer 1, 100 has an enclosure 2, 102, a matrix bed 50, 150 contained within the enclosure 2, 102, feed tubes 31, 131 extending into the enclosure 2, 102 and at least partially within the matrix bed 50, 150, and a matrix bed support 117 mounted within the enclosure 2, 102. The matrix bed support 117 optionally has a surface substantially impervious to the flow of exhaust supporting the matrix bed 50, 150, and the matrix bed support 117 defines apertures 127 each sized to receive a feed tube 31, 131 and to define exhaust passages proximal to the apertures 127. In use, substantially all gaseous oxidation products in a matrix bed 50, 150 are directed through apertures 127 in the matrix bed support 117 adjacent feed tubes 31, 131, and gaseous oxidation products are exhausted from the gas recuperative flameless thermal oxidizer through an outlet 20, 120 in the enclosure 2, 102.
The gas recuperative flameless thermal oxidizer 1, 100 has an enclosure 2, 102 extending between opposed end portions 103a, 103b, a matrix bed 50, 150 contained within the enclosure 2, 102, feed tubes 31, 131 extending into the enclosure 2, 102 and at least partially within the matrix bed 50, 150, and optional means for adjusting the distance between the opposed end portions 103a, 103b of the enclosure 2, 102 to increase or decrease the size of the matrix bed 50, 150.
Referring specifically to the several embodiments selected for illustration,
The feed tubes 31 may contain a matrix, which may be the same as or different from that used in matrix bed 50. A description of suitable matrix materials is presented later herein.
In one embodiment, at least the section of feed tube 31 that lies within matrix bed 50 is essentially devoid of matrix. By using such an arrangement, heat transfer between the combustible vapor and the exhaust gases is improved, thereby improving the thermal efficiency of the unit.
More specifically, it has been discovered that the lack of matrix within the feed passages improves performance by enhancing heat transfer rates from the interior walls of the feed tubes that define the feed passages. While it is recognized that matrix material is optionally provided within the feed tubes, a lack of matrix in the feed passages was discovered to increase the gas velocities at the wall and to minimize the stagnant film thickness. In practice, the matrix actually obstructed the path for radiant heat transfer at the tube walls, and repeated heating/cooling cycles caused the matrix to crush. This crushing changes the fluid dynamic properties of the system and can cause the system to become non-uniform resulting in misdistribution of hot gases. When such an imbalance is permitted to progress, performance may suffer because some tubes may have essentially little flow with no effective heat transfer and others may have large flows with reduced heat transfer and short residence times. The lack of matrix may, therefore, in at least some cases, increase gas residence time in the tubes, remove obstructions to radiant heat transfer, and provide a balanced gas flow pattern. It is believed that this will result in improved performance by enhancing heat transfer rates from the interior feed tube walls.
Combustible vapor exits the feed tubes 31 and travels through matrix bed 50, during which time the combustible vapor is oxidized to a high level of completion to form gases constituting an exhaust flow, indicated at arrows 26, the flow of which is in a direction essentially opposite that of combustible vapor flow 25. The exhaust gases enter an exhaust plenum 9 and exit the flameless thermal oxidizer via an outlet nozzle 20.
An optional fuel plenum 12, fed by a fuel supply port 14, is situated at the end of the flameless thermal oxidizer opposite the end where the inlet nozzle 10 is located. Fuel is delivered to fuel supply port 14 from a source (not shown) of supplemental fuel. While a variety of fuels are contemplated, exemplary fuels may comprise natural gas, propane, No. 2 fuel oil, or any combustible petroleum-based fuel. Details of the upper end portion of the oxidizer illustrated in
The feed tubes 131 are connected to a source of combustible vapor (not shown) at inlet nozzle 110, by way of combustible vapor plenum 107, providing combustible vapor flow 125 into the feed tubes 131 and along the feed passages 130 (upwardly in the embodiment illustrated in
An optional fuel plenum 112, fed by a fuel supply port 114 and a fuel source (not shown), is situated at the upper end of the flameless thermal oxidizer. In the embodiment shown in
The fuel plenum 112 is defined by an upper head 103a of the oxidizer 100 as well as a plate 116 that separates the fuel plenum 112 from an interior region of the oxidizer 100 that contains the matrix bed 150. Similarly, the combustible vapor plenum 107 is at least partially defined by a lower head 103b and a tube sheet 106.
As is illustrated in
In the embodiment shown in
Corresponding couplings 132 are used to couple one or more extension sections within feed tubes 131, e.g., to lengthen or shorten feed tubes 131 in a manner corresponding to the lengthening or shortening of the oxidizer 100. In other words, if in a particular application it is desired to increase the length of the feed tubes 131 (i.e., the length between inlet 156 and outlet 108 in the embodiment illustrated in
Optional sampling nozzles are shown at 105. Such nozzles 105 provide access from an exterior of the oxidizer 100 to the matrix bed 150 for sampling the matrix at various locations in the oxidizer or for other purposes.
Feed tubes 131 and matrix bed 150 have diameters D1 and D2, respectively, with feed tubes 131 having a length L1 within the matrix bed 150. The interior of flameless thermal oxidizer 100 has a length L2, defined between the matrix support plate 117 at the bottom portion of the oxidizer 100 and the bottom surface of the insulation 151 at the top portion of the oxidizer 100. The matrix bed 150 is contained within shell 102 at one end by the matrix support plate 117, which may be structurally reinforced with the support bars 118 illustrated in
The feed tubes 131 pass through matrix support plate 117 at the base of the matrix bed 150 and through tube sheet 106, which tube sheet 106 forms a seal against the feed tubes and thereby separates exhaust plenum 109 from combustible vapor plenum 107. Lower head 103b forms the bottom of exhaust plenum 109, which may optionally include a preheat burner mounting nozzle 119. End portions of the feed tubes 131 extend into the combustible vapor plenum 107 to receive combustible vapors.
A pitch P (
Changing the pitch P will change the flow characteristics of exhaust gases through the matrix bed. For example, increasing the pitch P between feed tubes 131 having a particular diameter D1 will increase the size of the spaces in the matrix bed 150 through which exhaust gases will flow. Conversely, decreasing the pitch P between feed tubes 131 having a particular diameter D1 will reduce the size of the spaces in the matrix bed 150 through which exhaust gases will flow. Similarly, increasing or decreasing the pitch P will also impact the heat transfer characteristics of the oxidizer. More specifically, a change in pitch P will change the characteristics of heat transfer from the exhaust gases in the matrix bed 150 to the combustible vapors in the feed tubes 131. Typically the pitch will be between one and eight inches, more typically between five and eight inches.
While a variety of combinations of dimensions can be selected, the embodiment of the oxidizer 100 selected for illustration in the Figures includes feed tubes 131 having a diameter D1 of about 3.5 inches, for example, and a pitch P of about 5 inches, for example. Accordingly, the clearance for exhaust gases flowing between adjacent feed tubes 131 is about 1.5 inches. Other dimensions can be selected based on design considerations, and this invention is not limited to any such dimensions.
The apertures 127 formed in the matrix support plate 117 are substantially open around the perimeter of the feed tubes 131, thereby allowing passage of exhaust gases out of the matrix bed into the exhaust plenum. More specifically, the gap defined between the diameter D4 of the apertures 127 and the outer diameter D1 of the feed tubes 131 provides a passage for the flow of exhaust gases from the matrix bed 150 to the exhaust plenum 109. For example, in an embodiment having feed tubes 131 with a diameter D1 of 3.5 inches and apertures having a diameter D4 of 3.5625 in., an annular gap of 0.03125 in. is provided for the flow of exhaust gases.
While many diameters D1 and D4 can be selected, the resulting gap is preferably small enough to avoid the passage of matrix materials from the matrix bed 150 into the exhaust plenum 109. Also, for reasons explained in greater detail later, the support 117 is optionally substantially impervious to exhaust gas flow in order to direct all exhaust flow toward the annular gap formed between apertures 127 and the outer surfaces of the feed tubes 131. Briefly, such direction of exhaust gases against or adjacent the outer surfaces of the feed tubes 131 helps to equalize the distribution of exhaust gases as it passes from the matrix bed 150 into the exhaust plenum 109 (as opposed to a concentration of exhaust gases exiting the matrix bed 150 into the exhaust plenum 109 at a position proximal to the exhaust outlet 120). This equalization tends to provide a more even and desirable temperature profile throughout the matrix bed. The direction of exhaust gases against or adjacent the outer surfaces of the feed tubes 131 also helps to optimize and equalize the transfer of heat from the exhaust gases to the combustible vapors in the feed tubes 131.
Though the apertures 127 in matrix bed support 117 illustrated in
In the embodiment shown, the tube sheet 106 has a diameter D3 equal to that of the diameter of matrix support plate 117, but this is not required. The diameter of the tube sheet 106 can also be larger or smaller than the diameter of the matrix support plate 117.
Returning again to
The shell of the oxidizer 100 and the feed tubes 131 are typically cylindrical in shape, but they may be of any cross-sectional shape and size. Also, although the feed tubes 131 are shown to be substantially straight and substantially parallel to one another, one or more of the feed tubes 131 can be curved or oriented at an angle with respect to other tubes or the shell of the oxidizer.
The interior or exterior surfaces of the shell may be lined with one or more refractory insulating materials. Typically, the interior surfaces of the shell are lined with one or more refractory materials so that the shell does not have to be constructed of more expensive heat resistant metals. The refractory materials may be for example firebrick, optionally coated with a porosity-reducing compound, ceramic fiber board, or ceramic fiber blanket, or combinations thereof. In one embodiment, the shell is lined with dense castable refractory materials and backed up with insulating refractory materials, such as a ceramic fiber board and a ceramic fiber blanket. The shell surfaces may also optionally be coated with a non-permeable, corrosion-resistant coating, such as is known in the art.
The matrix bed contains heat resistant inert porous media. Typical materials used to construct the matrix bed are ceramic materials, which may be randomly packed or structurally packed. Random packing comprises ceramic balls that may be layered. Generally, for oxidation of organometallic compounds, nitrogen-containing compounds, sulfonated compounds, non-halogenated and halogenated hydrocarbon gases, the ceramic balls are useful if they have a diameter from about 0.0625 to 3 inches (0.159-7.62 cm), typically about 0.75 inch (1.9 cm). Another useful configuration is the use of random ceramic saddles typically from 0.0625 to 3 inches (0.159-7.62 cm) nominal size, typically about 0.5 to 1.5 inches (1.27-3.81 cm) nominal size. Other useful packing materials are pall rings and raschig rings with diameters from about 0.0625 to 3 inches (0.159-7.62 cm), and typically from about 0.5 to 1.5 inches (1.27-3.81 cm). Other ceramic materials may be utilized in the shape of a honeycomb or dogbones.
A ceramic foam material may also be used to construct the matrix bed. Typical foam material that can be utilized has a void fraction of 10 to 99%, typically 65 to 95%, and most typically about 70%. The pore sizes in any preferred ceramic foam material will be about 0.1 to 1,000 pores per inch (about 0.04 to 400 pores per cm), typically about 1 to 100 pores per inch (about 0.4 to 40 pores per cm), and most typically about 10 to 30 pores per inch (about 4 to 12 pores per cm).
Instead of a ceramic, the heat-resistant material used to form the matrix bed may also be a metal, which may be randomly packed or may have a structured packing. A pre-designed, single piece metal structure can also be used to constitute the matrix bed, which structure can be secured to the shell and thereby easily removed for maintenance purposes. Catalytic materials may be used in the matrix bed to promote oxidation or other desired reactions, but typically the materials that constitute the matrix bed are non-catalytic.
Generally, the void fraction of the matrix bed will be between 0.3 and 0.9. In addition, the material in the matrix bed will typically have a specific surface area ranging from 40 m2/m3 to 1040 m2/m3.
Returning again to
Returning again to
In the embodiment shown in
Feed tubes 131 may have any ratio of length to cross sectional passage area. In some exemplary embodiments of the invention, the ratio of length in feet within the matrix bed to the cross sectional area in square inches of each of the feed passages 130 defined by the feed tubes 131 is at least about 0.5:1. A ratio less than about 0.5:1 may compromise the heat transfer benefits achieved according to aspects of this invention. A ratio of at least about 1.2:1 is typical. Also, the ratio of length in feet within the matrix bed to the cross sectional area in square inches of each of the feed passages 130 defined by the feed tubes 131 is typically less than about 2.5:1. A ratio above about 2.5:1 may increase the pressure drop of gas flowing through the feed passages 130. Typically, therefore, a range of the length:area ratio may be maintained between about 0.5:1 and about 2.5:1. More typically, a range of the length:area ratio may be maintained between about 1.2:1 and about 2.1:1. In some embodiments of the invention, the ratio is about 1.6:1.
Flameless thermal oxidizers having length to cross sectional area ratios within these ranges may provide an especially good balance between good thermal transfer from the exhaust gas to the combustible vapor and sufficient flow rate at convenient back-pressure levels. In one embodiment of the invention, the cross sectional area of an individual feed passage 130 is typically about 7.4 in2. In another embodiment, the length of the portion of feed passage within the matrix bed is about 12 feet or more.
The total cross sectional area defined by the one or more feed passages 130, taken together, may be of any percentage relative to the cross sectional area of the matrix bed, calculated from D2. Typically, the percentage will be between about 10% and 50%. More typically, the percentage will be between about 20% and 30%.
In operation, a preheat burner (not shown) may be attached to the flameless thermal oxidizer at mounting nozzle 119, to provide heat to the system during startup. Typically, the burner will be shut off once the flameless thermal oxidizer 100 has reached operating temperature, which is typically substantially or completely self-sustaining. The burner may operate on any type of fuel, and may for example use the same fuel as is supplied to fuel inlets 124, for example natural gas. Alternatively, an electrical heater or other heat source may be used.
Returning again to
Returning again to
Although the diameter D4 of the apertures 127 is shown in
The relationship between tube pitch, tube diameter, and matrix bed diameter controls heat transfer and fluid dynamic characteristics. Overall thermal efficiency and organic destruction efficiency is governed by these parameters. Heat transfer rates are affected by, inter alia, fluid velocities, line of sight radiant heat transfer, turbulence, and thermal conductivity properties of the species making up the entire process.
The matrix support plate 117 may, except for the apertures, be impervious to exhaust gas flow, or it may allow flow through it at other locations as well (e.g., if formed from a screen, mesh, perforated plate, or other structure pervious to flow). Optional support bars 118, or equivalent structures, may be used to help support the weight of the matrix bed 150, especially when the flameless thermal oxidizer 100 is mounted in a vertical orientation.
In operation, combustible vapor enters the flameless thermal oxidizer 100 through the inlet nozzle 110, producing a combustible vapor flow. As used herein, the term “combustible vapor” means a gas (typically air) containing a vapor of an organic compound, or containing a mist or fog of a liquid organic compound. The mixture may be above the lower flammability limit (LFL) thereof, or it may be below the LFL. It may be above the upper flammability limit (UFL), or below it. Typically, the combustible vapor will have a composition below the LFL. Vapors in the combustible vapor flow may originate from a wide variety of sources, nonlimiting examples of which may include capture of volatile organic compounds (VOC's) from any of a variety of processes, for example solvent-based coating operations.
In one embodiment of the invention, the linear flow rate of combustible vapor along the feed passage(s) 130 is close to or equal to that of the exhaust gases moving downward through the matrix bed 150. Such an arrangement may maximize heat transfer between the incoming combustible vapor and the exhaust gases, thereby increasing the fuel efficiency of the flameless thermal oxidizer 100. In one embodiment of the invention, the ratio of combustible vapor flow rate to exhaust flow rate is between about 0.9:1 and about 1.1:1. This range is typical, but it may optionally extend from 0.5:1 to 1.5:1. Typically, the gas velocities should range between about 10 feet per second and about 25 feet per second.
Flameless thermal oxidizer devices according to the invention may be capable of oxidizing combustible vapors at low levels of concentration, due to the high thermal efficiency of the devices. In may cases, no supplemental fuel is needed, and the combustible vapors themselves provide sufficient enthalpy of oxidation to keep the unit running properly. In one embodiment of the invention, the level of combustible material in the combustible vapor entering the flameless thermal oxidizer has a BTU level of less than 20 BTU/scf, and preferably less than 10 BTU/scf. Combustible vapors having a heat content as low as about 4-5 BTU/scf may be efficiently oxidized, using a supplemental fuel such as may be introduced at fuel inlets 124 shown for example in
By keeping the BTU level within the feed tubes low, it may be possible to reduce the absolute amount of oxidation that occurs within the feed tubes, thereby increasing the useful life of the tubes. Fuel such as may be necessary to supplement the heat produced by the flameless oxidation of combustible vapor, in order to maintain a sufficiently high working temperature, is optionally added proximal to the outlets of the feed tubes, for example as indicated at fuel inlets 124 in
In
The map shows lines indicating temperatures T1 to T10 in relation to one side of the feed tube 231, with temperatures outside the tube indicated above the wall of the tube indicated at 231 and temperatures inside the tube 231 indicated below the wall. Mixing region 228 is indicated in the area proximal to the end of feed tube 231.
The simulation illustrated in
wf = weight fraction
As a result of a simulation based on the foregoing parameters, the temperature profiles illustrated in
Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims without departing from the invention.
